TWI900831B - Film roll, manufacturing method thereof, polarizing plate and display device - Google Patents

Abstract

The present invention is to provide a film roll that does not leave any tape transfer marks and does not cause chain-like film deformation due to air leakage during long-term storage, as well as a method for manufacturing the same, a polarizing plate, and a display device. The film roll of the present invention is a film roll that does not have a knurled portion. Its characteristic is that when the thickness of the gap layer between adjacent films at the peripheral portion of the roll core measured in the width direction of the film roll is set to X [μm] and the thickness of the gap layer between adjacent films at the peripheral portion of the roll core is set to Y [μm], the aforementioned X and the aforementioned Y satisfy the relationship of the following formula (1). Formula (1): Y < X

Description

Film roll, manufacturing method thereof, polarizing plate and display device

The present invention relates to a film roll, a method for manufacturing the same, a polarizing plate, and a display device. More specifically, the present invention relates to a film roll that does not leave any transfer marks from the tape and does not deform the chain film due to air leakage during long-term storage.

In recent years, with fierce price competition in LCD TVs, polarizer manufacturers have been reviewing cost-cutting measures to reduce switching losses. Accordingly, progress has been made in making the films used in polarizers longer.

By making the film longer, costs can be expected to be reduced from various perspectives, such as connection loss, inspection labor, transportation, and auxiliary materials. Typically, the film is rolled into a roll after production for ease of storage and transportation.

However, when long-term storage is performed on a film roll wound in long strips, the film may become loosened, causing problems such as residual tape transfer marks (hereinafter referred to as "tape transfer") due to the films adhering to each other, and chain-like film deformation (hereinafter referred to as "chain deformation") due to air leakage between the films.

Here, the "chain deformation" mentioned above refers to the deformation (chain defect) of the film caused by the stress caused by the weight of the film after being rolled up and the stress that attempts to stretch the film in the width direction.

As a means of solving the above problem, although a method of winding the film together with the protective film is considered, there is a problem that the protective film will become waste.

To address this issue and prevent waste, one approach is to pre-roll the film ends with a knurling process. This creates a suitable air layer (also known as an "air layer") by entraining air between the films during winding, thereby preventing the films from sticking together. However, this knurling process is less effective in preventing sticking than rolling the film together with the protective film.

Furthermore, by using the above-mentioned means, the closer the core is to the film roll, the greater the pressure applied to the film surface. Since the air between the films is released more easily, the gap layer becomes thinner, which may cause the following problems: tape transfer marks are produced in the part close to the core due to the adhesion of the wound films to each other, or chain-like deformation is caused by air leakage between the films when the film roll is stored for a long time.

Although Patent Document 1 discloses a method for maintaining a constant amount of air between the films and forming an air layer of appropriate thickness by varying the winding tension and the height of the rollers at the film ends in accordance with the winding diameter of the film roll when winding the film, there is still room for improvement in order to resolve the above-mentioned problem.

The "gap layer" referred to in this specification is a layer formed by the gap between the opposing surfaces of adjacent films in a film roll. This layer may contain air or other substances other than air (e.g., inert gases). Strictly speaking, the portion of the "gap layer" consisting of air is referred to as the "air layer." Where a distinction between the two does not significantly impact the present invention, the "air layer" will be referred to as the "gap layer." Another form of the gap layer occurs when fine, concave-convex ridges inherent to the surface of one of the adjacent films contact the opposing surface of the other film. Furthermore, the present invention does not include void layers formed by artificially imparting knurling (concave and convex shapes) to the film through knurling. [Previous Patent Document] [Patent Document]

[Patent Document 1] Japanese Patent Application Laid-Open No. 2013-46966

The present invention was developed in light of the aforementioned problems. Its solution is to provide a film roll that leaves no tape transfer marks and does not cause chain-like film deformation due to air leakage during long-term storage, as well as a manufacturing method, polarizing plate, and display device.

To address the above-mentioned issues, the inventors investigated the causes of these problems and discovered that the problem can be solved by not knurling the film roll and instead making the interstitial layer between the films thicker at the periphery of the roll core than at the outer periphery. This led to the completion of the present invention. That is, the above-mentioned issues of the present invention can be addressed by the following means.

1. A film roll having no knurled portion, wherein, when the thickness of the interstitial layer between adjacent films at the peripheral portion of the roll core measured along the widthwise side of the film roll is X [μm], and the thickness of the interstitial layer between adjacent films at the peripheral portion of the roll core is Y [μm], X and Y satisfy the relationship of the following formula (1).

Formula (1): Y＜X

2. The film roll according to item 1, wherein the aforementioned X [μm] and the aforementioned Y [μm] satisfy the relationship of the following formula (2) and the following formula (3).

Formula (2): 0.05＜Y＜0.50 Formula (3): 1＜(X/Y)＜3

3. A method for manufacturing a film roll, which is a method for manufacturing a film roll without a knurled portion, wherein the thickness of the gap layer between adjacent films at the peripheral portion of the aforementioned roll core, as measured on the widthwise side portion of the aforementioned film roll, is set to X [μm], and the thickness of the gap layer between adjacent films at the peripheral portion of the aforementioned roll is set to Y [μm], and the aforementioned X and the aforementioned Y are adjusted to satisfy the relationship of the following formula (1).

Formula (1): Y＜X

4. The method for manufacturing a thin film roll as described in item 3, wherein the aforementioned X [μm] and the aforementioned Y [μm] are adjusted to satisfy the relationship of the following equations (2) and (3).

Formula (2): 0.05＜Y＜0.50 Formula (3): 1＜(X/Y)＜3

5. A method for manufacturing a film roll according to item 3 or 4, wherein the film contact pressure at the periphery of the core is adjusted to within a range of 2-30 [N/m], the film contact pressure at the center of the roll is adjusted to within a range of 3-40 [N/m], and the film contact pressure at the outer periphery of the roll is adjusted to within a range of 5-55 [N/m]. 6. A polarizing plate characterized by comprising a portion of the film of the film roll according to item 1 or 2.

7. A display device, characterized by comprising a portion of the film of the film roll as described in item 1 or 2.

The above-described means of the present invention provide a film roll that leaves no residual tape transfer marks and exhibits no chain-like film deformation due to air leakage during long-term storage, as well as a method for manufacturing the roll, a polarizing plate, and a display device. While the mechanism by which the effects of the present invention are achieved or how they function is not yet clearly understood, the following is a hypothesis.

The film roll of the present invention is not subjected to a knurling treatment. By making the interstitial layer thickness between the films at the periphery of the core thicker than the interstitial layer thickness at the periphery of the roll, no tape transfer marks resulting from the adhesion of the films remain, thereby preventing chain-like film deformation (hereinafter also referred to as "chain-like deformation") caused by air leakage between the films.

As mentioned above, the "chain deformation" refers to the film deformation (chain defect) caused by the stress caused by the weight of the film after winding and the stress that attempts to stretch the film in the width direction.

Conventional knurling increases the amount of air trapped between the films, thickening the gaps between the films compared to unprocessed films. When a film roll is stored for extended periods, its own weight exerts greater radial stress on the film closer to the core, and this stress is particularly pronounced when the roll is subjected to minor impacts.

Therefore, since the air between the films is released when radial stress is applied to the films, the thickness variation of the interstitial layer near the core of the film roll that has undergone knurling becomes larger than that of a conventional film roll. In particular, the core portion is prone to causing the films to stick to each other, and more tape transfer marks caused by the adhesion of the films to each other remain on the core portion.

Furthermore, since the knurled film roll only supports the film at the knurled portion, a restraining force is applied to the knurled portion to prevent winding and misalignment. Furthermore, the biased stress applied to the film causes an offset in the amount of air leakage between the films. As the thickness of the interstitial layer becomes uneven, chain-like deformation easily occurs during long-term storage.

In contrast, the film roll of the present invention has no knurled portion, and the film is entirely supported by the gas (e.g., air) in the micro-contact surface or gap layer between the films. Therefore, the limiting force to prevent winding misalignment is not biased, making the stress applied to the film uniform.

To explain in more detail, although the film roll of the present invention is not knurled, it typically has gaps on its surface formed by the film's inherent nanoscale micro-concave and convex shapes. When the multiple protrusions on the opposing surfaces of adjacent films come into contact with each other, the microscopic contact surfaces of these protrusions may support the entire film.

That is, for example, in order to make a portion of the protrusions contact, the films are not only supported by a void layer such as an air layer, but are also supported by multiple contact points of the tiny protrusions and recesses.

It is also speculated that by increasing the thickness of the interstitial layer, which is used to take in an appropriate amount of air, at the core portion during long-term storage of the film roll, even if more air is released, particularly at the core portion, the thickness deviation of the interstitial layer throughout the film roll is suppressed to a minimum. This allows for the formation of an interstitial layer of uniform thickness between the films, ensuring that when the film roll is wound and unwound, no tape transfer marks remain and no chain-like deformation occurs.

The film roll of the present invention is characterized in that it does not have a knurled portion. When the thickness of the gap layer between adjacent films at the periphery of the core, measured on the widthwise side of the film roll, is X [μm], and the thickness of the gap layer between adjacent films at the periphery of the roll is Y [μm], X and Y satisfy the relationship of the aforementioned formula (1). Based on the above-mentioned characteristics, the problem of the present invention is solved.

Furthermore, the film roll manufacturing method of the present invention is a method for manufacturing a film roll without a knurled portion, characterized in that the thickness of the gap layer between adjacent films at the peripheral portion of the aforementioned core, as measured on the widthwise side of the aforementioned film roll, is set to X [μm], and the thickness of the gap layer between adjacent films at the peripheral portion of the aforementioned roll is set to Y [μm], and the aforementioned X and Y are adjusted to satisfy the relationship of the aforementioned formula (1). The above two features are common or corresponding technical features in each of the following embodiments (modes).

In an embodiment of the present invention, from the perspective of forming a uniform void layer during long-term storage, the aforementioned X [μm] and the aforementioned Y [μm] satisfy the aforementioned formula (2) and the aforementioned formula (3).

From the perspective of forming a uniform void layer during long-term storage, it is preferred to adjust the aforementioned X [μm] and the aforementioned Y [μm] to satisfy the aforementioned formula (2) and the aforementioned formula (3).

From the perspective of forming a uniform void layer during long-term storage, it is further preferred to adjust the film contact pressure at the periphery of the roll core to within the range of 2-30 [N/m], the film contact pressure at the center of the roll to within the range of 3-40 [N/m], and the film contact pressure at the outer periphery of the roll to within the range of 5-55 [N/m].

A portion of the film roll of the present invention is preferably used by being included in a polarizing plate.

A portion of the film of the film roll of the present invention is preferably used by being incorporated into a display device.

The present invention, its components, and the forms and aspects for implementing the present invention are described in detail below. In this application, "~" is used to include the lower and upper limits of the numerical values before and after it.

1. Film Roll (1.1) Overview of Film Roll The film roll of the present invention is a film roll without a knurled portion, and is characterized in that, when the thickness of the gap layer between adjacent films at the peripheral portion of the roll core measured on the side portion in the width direction of the film roll is set to X [μm], and the thickness of the gap layer between adjacent films at the peripheral portion of the roll is set to Y [μm], the aforementioned X and the aforementioned Y satisfy the relationship of the following formula (1):

Formula (1): Y＜X

The film roll of the present invention (the so-called "film roll" refers to a film wound into a roll) has no knurled (also called "knurled") portion. The film is entirely supported by the gas (e.g., air) in the gaps between adjacent films or the tiny contact surfaces between the films, as described above. Therefore, the limiting force to prevent rolling misalignment is not biased, and the stress applied to the film becomes uniform.

Furthermore, by using a gap layer that introduces an appropriate amount of air through a clamp and making it thicker in the core portion, the gap layer thickness deviation of the entire film roll can be suppressed to a smaller value during long-term storage of the film roll, especially even if more gas is released in the core portion. This is because a uniform air layer can be formed between the films, and even when the film roll of the film roll is relaxed, no tape transfer marks remain, and there is no chain deformation.

As an embodiment of the present invention, from the perspective of forming a uniform void layer during long-term storage, the aforementioned X [μm] and the aforementioned Y [μm] preferably satisfy the aforementioned formula (2) and the aforementioned formula (3).

(1.2) Gap Layer Between Films (1.2.1) Gap Layer Thickness Control Method The film roll of the present invention utilizes a gap layer that introduces an appropriate amount of air through a clamp, and is thicker at the core. During long-term storage of the film roll, even when more air is released from the core, the gap layer thickness deviation throughout the entire film roll can be minimized, thereby forming a uniform gap layer between the films.

Examples of such methods include varying the film contact pressure using a contact roller, or varying the winding tension, winding speed, and roll wrap angle. The contact rollers may be multiple, and may be chromium-plated as a surface treatment. Alternatively, the contact rollers may be elastic rollers.

(1.2.2) Method for calculating the thickness of the gap layer Figure 1 shows a schematic diagram of the positional relationship between the widthwise side of the film roll and the imaging device. As shown in Figure 1, the imaging device (E) is installed on the widthwise side of the film roll (30) wound on the core (R). In addition, TD in Figure 1 is the widthwise direction of the film roll.

The following describes an example of a method for photographing the side face of a film roll along its width using the aforementioned imaging device and a method for calculating the thickness of the interstitial layer.

A photographing unit (U) which is part of the photographing device photographs the widthwise side of the film roll with an arbitrary point (P) on the widthwise side of the film roll as the center, and obtains image data for calculating the gap between the films.

FIG2 is a schematic diagram of the side surface of the film roll when viewed from a plane perpendicular to the side surface in the width direction.

Here, as shown in FIG2 , when the diameter from the core surface (S ₀ ) to the outermost film layer (S ₄ ) of the film roll is expressed as a percentage, the diameter of the core surface (S ₀ ) is 0% and the diameter of the outermost film layer (S ₄ ) of the film roll is 100%.

When photographing the periphery of the roll core, take the position where the roll diameter becomes 20% (P ₂₀ ) as the center and photograph that side of the face to obtain the aforementioned image data.

Furthermore, when shooting the center of the roll, the side of the face is shot with the position ( _P50 ) where the roll diameter becomes 50% as the center, and when shooting the outer periphery of the roll, the side of the face is shot with the position ( _P80 ) where the roll diameter becomes 80% as the center, to obtain the aforementioned image data.

Subsequently, the acquired image data is subjected to edge emphasis processing to obtain a processed image for calculating the gap layer thickness as shown in Figure 3. The thickness of the gap layer between the adjacent films at the core periphery, the roll center, and the roll outer periphery on the width direction of the film roll is calculated.

Since the thickness of the interstitial layer between films is calculated in three regions: the core periphery, the center, and the outer periphery, before providing a specific example of calculating the interstitial layer thickness, let's first explain the concepts of the three regions: the core periphery, the center, and the outer periphery.

Figure 4 is a simplified conceptual diagram of a portion of the widthwise side of a film roll, illustrating the core periphery, roll center, and roll outer periphery.

In Figure 4 , the film layer directly wound around the core (R) and attached to the core surface (S ₀ ) (not shown) is designated as S ₁ , and the outermost layer of the film roll is designated as S ₄ . When the region from S ₁ to S ₄ is equally divided into three regions, the region on the core side is designated as the core peripheral portion (A), the region on the outer side of the roll is designated as the roll outer peripheral portion (C), and the region between the core peripheral portion (A) and the roll outer peripheral portion (C) of the roll is designated as the roll center portion (B).

The film layer forming the boundary between the core peripheral portion (A) and the roll center portion (B) is designated as S ₂ , and the film layer forming the boundary between the roll center portion (B) and the roll outer peripheral portion (C) is designated as S ₃ .

The following calculation method is used as a specific example to calculate the thickness of the gap layer at the periphery of the roll.

(Specific example of void layer thickness calculation method)

For example, to calculate the thickness of the interstitial layer at the periphery of a roll core, the film roll's widthwise side is photographed with the aforementioned position ( _P20 ) as the center. This image data is then processed with edge emphasis to produce the processed image shown in Figure 3. The radial length is measured starting from the center of this processed image ( _P20 ) and ending at the 100th layer on the outer side of the roll perpendicular to the film surface. The thickness of the interstitial layer X (μm) is calculated using the following formula (A).

Formula (A) Void layer thickness X [μm] = [Radial length [μm] - (Average thickness of each film layer measured with a film thickness gauge [μm]) × (Number of layers)] ÷ (Number of layers)

Furthermore, the (number of layers) in the above formula depends on the layer perpendicular to the film surface and facing the outside of the roll at which the endpoint is located. For example, if it is located at the 100th layer, (number of layers) = 100.

When calculating the gap layer thickness at the center of the roll, the calculation is the same as above, except that the aforementioned position ( _P20 ) is changed to position ( _P50 ). Regarding the gap layer thickness at the outer periphery of the roll, the calculation is the same as above, except that the aforementioned position ( _P20 ) is changed to position ( _P80 ).

Since the total length of the film roll is relatively short, if the widthwise side of the film roll is photographed with the arbitrary point (P) as the center, and if there are not 100 layers perpendicular to the film surface and facing outward from the roll, for example, only 70 layers at most, the radial length can be measured with the point at the 70th layer as the end point, and the thickness X [μm] of the interstitial layer can be calculated using the above formula (A).

As the film thickness meter in the above formula (A), for example, the online delay/film thickness measuring device RE-200L2T-Rth+Film Thickness (manufactured by Otsuka Electronics Co., Ltd.) can be used.

(System structure of imaging unit and imaging device)

The following components are used as imaging units.

Figure 5 is a schematic diagram of the internal structure of the imaging unit (U). In Figure 5, S represents the measured surface (lateral surface in the width direction) of the film roll. The main components in Figure 5 are as follows.

(Components) ・Total reflection mirror (60) ・Half mirror (61) ・Telecentric lens (62) (MML1-HR130VI-35F: made by Moritex, magnification ×1, WD130mm) ・High-brightness line lighting (63) (LNSP2-100SW: made by CCS) ・Monochromatic line sensor camera (64) (RMSL8K39CL: made by JEC, 8000 pixels at 3.5μm/pixel)

The system configuration of the imaging device is as shown in the schematic diagram of FIG6 .

2. Film Roll Manufacturing Method The film roll manufacturing method of the present invention is a method for manufacturing a film roll without a knurled portion. The method is characterized in that, when the thickness of the gap layer between adjacent films at the peripheral portion of the core, as measured on the widthwise side of the film roll, is set to X [μm], and the thickness of the gap layer between adjacent films at the peripheral portion of the roll is set to Y [μm], X and Y are adjusted to satisfy the relationship of the aforementioned formula (1).

In the above-mentioned method for manufacturing the thin film roll, from the perspective of forming a uniform void layer during long-term storage, it is preferred to adjust the aforementioned X [μm] and the aforementioned Y [μm] to satisfy the relationship of the aforementioned formula (2) and the aforementioned formula (3).

Furthermore, from the perspective of forming a uniform air layer during long-term storage, it is preferred to adjust the film contact pressure at the periphery of the aforementioned roll core to within the range of 2-30 [N/m], the film contact pressure at the center of the roll to within the range of 3-40 [N/m], and the film contact pressure at the outer periphery of the aforementioned roll to within the range of 5-55 [N/m].

The film roll of the present invention can be manufactured using conventional methods such as inflation, T-die, rolling, cutting, casting, emulsion, and hot pressing. However, from the perspective of suppressing coloration, foreign matter defects, and optical defects such as die lines, solution casting and melt casting are preferred. Solution casting is particularly preferred because it can achieve a uniform film surface.

(2.1) Solution Casting Method Figure 7 is a flow chart showing the manufacturing steps of the solution casting method. Figure 8 is a schematic diagram of the apparatus for thin film production using the solution casting method.

The following solution casting method is described with reference to Figures 7 and 8. The method for producing a thin film using the solution casting method includes a dope preparation step [S1], a casting step [S2], a peeling step [S3], a shrinking step [S4], a first drying step [S5], a first stretching step [S6], a first cutting step [S7], a second stretching step [S8], a second cutting step [S9], a second drying step [S10], a third cutting step [S11], and a winding step [S12].

Furthermore, the above-mentioned production method does not necessarily need to include both the first drying step [S5] and the second drying step [S10]; it is sufficient to include at least one of these steps. Furthermore, it is sufficient to include any of the first stretching step [S6], the second stretching step [S8], and the first cutting step [S7], the second cutting step [S9], and the third cutting step [S11].

(2.1.1) Concentrate Preparation (Stirring) Step [S1] The following describes the concentrate preparation step using a cycloolefin resin (hereinafter also referred to as "COP") as a thermoplastic resin as an example of one embodiment of the present invention. However, the present invention is not limited thereto.

The concentrated solution preparation (stirring preparation) step [S1] of FIG. 7 is to stir at least the resin and the solvent in the stirring tank (1a) of the stirring device (1) of FIG. 8 to prepare the concentrated solution to be cast on the support (3) (annular belt).

(Solvent) A mixture of a good solvent and a weak solvent is used as the solvent. This step involves dissolving the COP and, if necessary, other compounds in a solvent primarily composed of a good solvent for the COP, while stirring in a dissolution vessel to form a concentrated solution. Alternatively, the COP solution may be mixed with other compound solutions to form a concentrated solution of the main solution.

To reduce the drying load after casting the concentrate onto the support, the COP concentration in the concentrate is preferably as high as possible. However, if the concentration is too high, the load during filtration increases, resulting in reduced accuracy. Therefore, both reducing the drying load and suppressing the load during filtration are necessary. To achieve this balance, the COP concentration in the concentrate is preferably within the range of 10-35 mass%, more preferably 15-30 mass%. Furthermore, the water content in the concentrate is preferably within the range of 0.01-2 mass%.

The solvents used in the concentrated solution can be used alone or in combination of two or more. However, from the perspective of production efficiency, it is better to mix a good solvent for COP with a weak solvent. The better the solubility of COP, the better the solvent.

The optimal mixing ratio of good solvent to weak solvent is 70-98 mass% of good solvent and 2-30 mass% of weak solvent.

In this specification, a "good solvent" for COP is defined as one that can dissolve COP on its own, while a "weak solvent" for COP is defined as one that can swell COP or not dissolve it on its own. Therefore, the good and weak solvents are varied based on the average degree of substitution of COP as described above.

The good solvent used in the present invention is not particularly limited, but examples thereof include organic halogen compounds such as dichloromethane and dioxolanes, acetone, methyl acetate, methyl acetylacetate, etc., with dichloromethane or methyl acetate being particularly preferred.

The weak solvent used in the present invention is not particularly limited, but preferably used are methanol, ethanol, n-butanol, cyclohexane, cyclohexanone, etc.

Furthermore, the solvent used to dissolve the COP is recovered and reused by removing the solvent from the thin film by drying in each step.

Recycled solvents sometimes contain trace amounts of additives added to COP, such as plasticizers, UV absorbers, resins, monomer components, etc. However, even if they contain these, they can be preferably reused or, if necessary, purified for reuse.

(Dissolution Method) General methods can be used to dissolve the COP when preparing the concentrate described above. Specifically, methods performed under normal pressure, below the boiling point of the main solvent, or under pressure above the boiling point of the main solvent are preferred. If heating and pressure are combined, heating above the boiling point at normal pressure is acceptable.

Furthermore, a method of heating and stirring the solvent at a temperature above the boiling point of the solvent at normal pressure but within a range that does not cause the solvent to boil under pressure is also preferred because it prevents the formation of lumps of undissolved matter called gel or lumps.

Alternatively, it is preferable to mix COP with a weak solvent to wet or swell it, and then add a good solvent to dissolve it.

Pressurization can be achieved by injecting an inert gas such as nitrogen or by heating the solvent to increase its vapor pressure. Heating is preferably performed externally, such as with a jacketed type, as this allows for temperature control of the solution.

The higher the heating temperature for adding the solvent, the better it is from the perspective of COP solubility. If the nitrogen heating temperature is too high, the necessary pressure will increase, which will reduce productivity.

The heating temperature is preferably within the range of 30-120°C, more preferably within the range of 60-110°C, and even more preferably within the range of 70-105°C. In addition, the pressure is adjusted so that the solvent does not boil at the specified temperature.

Alternatively, a cold dissolution method is also preferably used, whereby COP is dissolved in a solvent such as methyl acetate.

(Filtration) Secondly, it is best to filter the COP solution (either in the dissolving phase or in the concentrated form) using an appropriate filter medium such as filter paper.

To remove insoluble matter, a filter medium with a low absolute filtration precision is preferred. However, if the absolute filtration precision is too low, clogging of the filter medium is more likely to occur. Therefore, a filter medium with an absolute filtration precision of 0.008mm or less is preferred, with a range of 0.001-0.008mm being even more preferred, and a range of 0.003-0.006mm being even more preferred.

The material of the filter is not particularly limited, and conventional filter materials can be used. However, plastic filter materials such as polypropylene and Teflon (registered trademark), or metal filter materials such as stainless steel are preferred because they do not shed fibers.

It is best to remove and reduce impurities, especially bright spots and foreign matter, contained in the raw material COP by filtering.

Bright spot foreign matter refers to foreign matter that is visible when light is irradiated from one polarizing plate and observed from the other polarizing plate when light is irradiated from one polarizing plate. The number of bright spots with a diameter of 0.01 mm or larger is preferably 200 ^{or fewer} per cm², more preferably 100 or ^fewer per cm², even more preferably 50 or ^fewer per ^cm² , and even more preferably 0-10 or fewer per cm². The fewer bright spots smaller than 0.01 mm, the better.

Concentrated solutions can be filtered by conventional methods, but filtering while heating the solvent at a temperature above its boiling point at normal pressure but below boiling point under pressure is preferred because the increase in the filtration pressure difference (called differential pressure) before and after filtration is small.

The optimal temperature is 30-120°C, more preferably 45-70°C, and even more preferably 45-55°C.

The lower the filtration pressure, the better. Specifically, it is preferably 1.6 MPa or less, more preferably 1.2 MPa or less, and even more preferably 1.0 MPa or less.

(2.1.2) Casting step [S2] In the casting step [S2] of Figure 7, the concentrated liquid prepared in the concentrated liquid preparation step [S1] is transported through a pressure-type quantitative gear pump, etc., to the casting die (2) of Figure 8 through a conduit. The concentrated liquid is cast from the casting die (2) at a casting position on a support body (3) formed by a rotating stainless steel annular belt for annular transport, forming a casting film (5).

At this time, the inclination of the casting die nozzle (2), that is, the direction of the concentrated liquid ejected from the casting die nozzle (2) toward the support body (3), can be appropriately set in a manner such that the angle formed by the normal line relative to the surface of the support body (3) (the surface on which the concentrated liquid is cast) is within the range of 0 to 90 degrees.

Subsequently, the cast film (5) is heated and dried on the support (3) to evaporate the solvent until the cast film (5) can be peeled off from the support (3) by a peeling roller (4). In the present invention, the cast film refers to the concentrated liquid film cast from the lip portion.

The above evaporation is preferably carried out in an environment within the range of 5-75°C. In order to evaporate the solvent, there are methods of blowing warm air onto the casting film (5) and/or transferring heat from the back of the support (3) by the liquid, and methods of transferring heat from the front to the back by radiant heat, etc. However, the method of transferring heat from the front to the back by radiant heat has a better drying efficiency. It is also preferable to use a combination of these methods.

From a productivity perspective, the cast width is preferably at least 1.3m. More preferably, it is within the range of 1.3-4.0m. A cast width of 4.0m or less prevents streaking during the manufacturing process and improves stability during the subsequent transport step. From the perspectives of transportability and productivity, the cast width is more preferably within the range of 1.3-3.0m.

(Casting Die Nozzle) Casting die nozzles come in two types: coat hanger nozzles and T-die nozzles. Either type can be used effectively.

In order to improve the uniformity of film thickness during the casting process, technicians in this field have used methods such as controlling the slit gap (the front opening of the liquid outlet of the slit nozzle) of the lip portion of the casting die (the part of the slit of the casting die where the concentrated liquid flows out) in both solution casting and melt casting methods.

For example, when extruding a high-viscosity concentrated liquid (including melt), the above-mentioned slit width deviation will occur. However, in order to prevent this situation, a method of controlling the slit width is used by configuring multiple hot bolts.

However, this method has a physical limitation on the number of hot bolts. Furthermore, to suppress the pressure fluctuations in width that cause the aforementioned slit gap width variations, there are methods that vary the width of the die. However, this requires switching the die for each product type, which is time-consuming and costly.

The casting die is equipped with a mechanism for adjusting the width of the narrow slit used to eject the concentrated liquid (used for resin extrusion when molten). Preferably, the casting die's heat bolt adjusts the width of the narrow slit used to eject the concentrated liquid to a thickness within a range of 1.0-5.0% relative to the overall thickness of the casting die immediately after ejection, thereby controlling the initial thickness of the casting die.

To increase the film production speed of the film of the present invention, two or more of the aforementioned casting dies may be installed on the support to divide the concentrate into layers. Alternatively, a co-casting method, in which multiple concentrates are cast simultaneously, is preferably used to produce a film roll with a layered structure. To increase the film production speed, two or more of the aforementioned casting dies may be installed on the support to divide the concentrate into layers.

(Supporting body) The supporting body (3) is preferably a roller coated with a stainless steel belt or a casting, and is supported by a pair of rollers (3a), a roller (3b), and a plurality of rollers located therebetween. In this case, the surface of the supporting body is preferably a mirror surface.

One or both of the rollers (3a) and (3b) are provided with a driving device for applying tension to the support body (3), thereby allowing the support body (3) to be used in an expanded state with tension applied.

The surface temperature of the support (3) in the casting step [S2] is within the range of -50°C to the boiling point of the solvent. The higher the temperature, the faster the drying speed of the cast film.

The optimal support body temperature is in the range of 0~55℃, and more preferably in the range of 22~50℃.

Furthermore, the temperature of the support body can be the same throughout or vary according to location.

The method for controlling the temperature of the support body (3) is not particularly limited, but there are methods of blowing warm air or cold air and methods of bringing hot water into contact with the back of the support body. When using warm water, heat transfer can be carried out efficiently, so the time required to keep the temperature of the support body constant is short and preferable. When using warm air, it is sometimes possible to use air with a temperature higher than the target temperature.

(2.1.3) Peeling step [S3] In this step, the solvent is evaporated in the casting step [S2] until the cast film (5) on the support (3) has a peelable film strength. After drying and solidifying or cooling and solidifying, the film is peeled off from the support (3) before the film wraps around the support (3) for one week. In other words, this step is to peel off the film from the support (3) at the peeling position. At this time, based on the viewpoints of surface quality, moisture permeability, and peelability, it is preferably peeled off from the support within a range of 30 to 600 seconds.

In the peeling step [S3], the film is peeled by a self-supporting peeling roller (4) (a roller that helps peel the film). The temperature of the peeling position on the support is preferably in the range of -50 to 40°C, more preferably in the range of 10 to 40°C, and most preferably in the range of 15 to 30°C.

(Residual Solvent Amount) The residual solvent amount of the film on the support (3) during the peeling step [S3] can be appropriately adjusted according to the intensity of the drying conditions, the length of the support (3), etc. The residual solvent amount in the shrinking step [S4] is greatly affected by the film thickness, resin, etc. Therefore, there is an overlap in the optimal range of the residual solvent amount in the peeling step [S3] and the shrinking step [S4].

While the amount of residual solvent in a film varies depending on film thickness, if the residual solvent level at the peeling point (where the film separates from the support) is too high, the film may become too soft and difficult to peel, affecting its flatness and causing horizontal fragments, wrinkles, or vertical streaks due to peeling tension. Conversely, if the residual solvent level is too low, portions of the film may fall off during the peeling process.

Based on the above viewpoints, in order to make the film show good planarity, based on the viewpoint of both economic speed and quality, the residual solvent amount is expected to be in the range of 10~50% by weight.

Methods for increasing film production speed (because stripping is performed while the amount of residual solvent is as low as possible), for example, gel casting, which allows stripping even when the amount of residual solvent is high.

Among these methods, there are those that add a weak solvent for COP to the concentrate, cast the concentrate, and then gel the cast film. Other methods involve cooling the support to gel the cast film and then peeling it off while it still contains a large amount of residual solvent. Another method involves adding a metal salt to the concentrate.

As described above, by gelling the cast film on the support, the film is strengthened and the film is quickly peeled off from the support, thereby increasing the film production speed.

The amount of residual solvent is defined by the following formula.

Formula: Residual solvent amount [mass %] = {(M-N)/N} × 100

In the above formula, M is the mass of the sample collected at any time during or after the production of the cast film or thin film, and N is the mass of M after heating at 115°C for 1 hour.

(Peeling Tension) The peeling tension for peeling the support and film is preferably 300 N/m or less. A range of 196-245 N/m is more preferred. However, if wrinkles are likely to form during peeling, a peeling tension of 190 N/m or less is preferred.

(2.1.4) Shrinking Step [S4] The shrinking step [S4] is a step of shrinking the film (F) in the in-plane width direction. Methods for shrinking the film (F) include, for example, increasing the film density by subjecting it to a high-temperature treatment while it is not wide, applying tension to the film after it has been peeled off the support in the conveying direction (machine direction, hereinafter referred to as "MD") to stretch and shrink the film in the in-plane width direction (TD) perpendicular to the MD, and rapidly reducing the amount of residual solvent in the film. In this case, the film shrinks in the width direction (transverse direction, hereinafter also referred to as "TD") perpendicular to the MD direction within the film plane.

The shrinking step promotes entanglement between resin molecules (matrix molecules) throughout the film's thickness. Therefore, when bonding the film to a polarizer through adhesive, for example, the adhesive easily penetrates the film's interior through the entangled (crosslinked) regions between the matrix molecules. As a result, the film is securely fixed to the polarizer via the adhesive, and the film's peel strength from the polarizer is enhanced. This ensures excellent adhesion between the film and the polarizer.

(Definition of Shrinkage) In the present invention, shrinkage is defined by the following formula.

Formula: Shrinkage rate [%] = Film width at the end of the shrinkage step [mm] / Film width at the beginning of the shrinkage step [mm] × 100

In the shrinking step [S4], if the shrinkage rate of the film is too low, the effect of promoting entanglement between matrix molecules will be insufficient. If it is too high, there is a concern that the production efficiency of the film (stretched film) will be reduced. Therefore, the shrinkage rate of the film in the shrinking step [S4] is preferably within the range of 1-40%, and more preferably within the range of 5-20%.

(Shrinkage Measurement and Calculation Method) Film width can be measured using the LS-9000 manufactured by KEYENCE. The shrinkage of the film of the present invention is determined by substituting the average of the values measured by the measuring instrument at 1-second intervals for 5 minutes (300 seconds) into the above formula. However, this method is not necessarily limited to the above one; for example, the film width can be measured using a ruler and substituted into the above formula.

(2.1.5) First Drying Step [S5] The first drying step [S5] is a step in which the solvent is evaporated and dried by heating the film (F) on the support using a drying device (6).

In the drying device (6) of FIG8 , a film (F) is transported by a plurality of transport rollers arranged in a staggered manner as viewed from the side, and the film (F) is dried during the transport.

The drying method in the drying device (6) is not particularly limited. Generally, hot air, infrared rays, heated rollers, microwaves, etc. are used to dry the film (F). However, from the perspective of simplicity, the method of drying the film (F) with hot air is preferred. In addition, a combination of these methods is also preferred. The first drying step [S5] can be performed as needed.

Thin films dry quickly, but rapid drying can damage the flatness of the finished film. When drying films at high temperatures, the amount of residual solvent before drying must be considered. By limiting the amount of residual solvent to an excessive level, failures caused by foaming can be prevented.

The residual solvent content before the first drying step [S5] is preferably less than 30% by mass. The entire drying step is carried out at a drying temperature of approximately 30-250°C. Drying is particularly preferably performed in the range of 35-200°C, with the drying temperature preferably increasing in stages.

Film drying is generally done by roller drying (a method in which the film is dried by passing it alternately over a plurality of rollers arranged above and below) or by conveying the film in a tentering manner while drying it simultaneously.

When using a tenter stretching device during film drying, it is preferred that the tenter stretching device independently control the film's grip length (the distance from the start of gripping to the end of gripping) during the stretching step described below. Furthermore, during the stretching step, it is preferred to intentionally create zones with different temperatures to improve flatness.

Furthermore, it is also preferable to set a neutral zone so that different temperature zones do not interfere with each other.

(2.1.6) First stretching step [S6] The first stretching step [S6] may be a step of stretching the film (F) only in the MD direction within the film surface, a step of stretching only in the TD direction, a step of stretching in both the MD and TD directions, or a step of stretching in an oblique direction. Furthermore, the stretching direction is not limited, but from the perspective of obtaining a wide film, it is preferred to include at least a step of stretching in the width direction. These stretching steps are performed by a stretching device (7).

(Stretching Method) Examples of stretching methods include stretching in the direction of transport (lengthwise direction of the film; film forming direction; casting direction; longitudinal direction; MD direction) with a roller having a circumferential speed different from that of the roller; or stretching in the widthwise direction (orthogonal to the film plane; film width direction; transverse direction; TD direction) by securing the two side edges of the film (F) with a clamp or the like; or stretching in the longitudinal and transverse directions sequentially (sequential biaxial stretching); or simultaneously (simultaneous biaxial stretching). However, in these methods, transverse stretching or simultaneous biaxial stretching (including diagonal stretching) is performed using a tenter stretching apparatus. The tenter stretching device uses clamps to hold the film in its width direction and stretches the film by extending the gap as the clamps and film move together.

Among the above methods, the so-called tentering method using a tenter stretching device is preferred because it improves the performance/productivity, flatness and dimensional stability of the film.

Furthermore, in the case of the so-called tentering method, if the clamping part is driven by a linear drive method, it can be extended smoothly and the risk of breakage can be reduced, so it is better.

The width maintenance or transverse stretching in the film-making step is preferably performed by a tentering stretching device, which can be a pin tenter or a clamp tenter. In addition to stretching, drying can also be performed in the stretching device (7).

(Stretching Ratio) To ensure a high retardation, wide width, and promote adhesive penetration during bonding with a polarizer, it is best to stretch the film at a high ratio during the stretching step. However, if the stretching ratio is too high, the stretching stress may cause cracks in the film, disentangling the matrix molecules that provide film strength, and weakening the film.

Therefore, the stretching ratio in the stretching step is preferably in the range of 1.1 to 5.0 times, more preferably in the range of 1.3 to 3.0 times.

Furthermore, the term "stretching ratio" as used herein refers to the ratio [%] of the film area after stretching to the film area before stretching. That is, the "stretching ratio" in the stretching step is the total stretching ratio achieved by stretching the film in the longitudinal (length) and transverse (width) directions, preferably in the range of 1.1 to 5.0 times, more preferably 1.3 to 3.0 times, as an area ratio.

When multiple extensions are performed, the highest-rate extension, where the risk of matrix molecule dissociation is highest, is preferably performed as the last extension. For example, in Figure 7, the highest-rate extension is preferably performed in the second extension step. In this case, the matrix molecules are entangled until the highest-rate extension. Therefore, even during the highest-rate extension, dissociation of the matrix molecules is suppressed, thereby preventing aggregation disruption.

(Tenter stretching device) Below, the description will be given using a tenter stretching device as the stretching device (7) as an example with reference to Figures 9, 10, 11, and 12.

Figure 9 is a top view schematically showing the internal structure of the tenter stretching apparatus, a cross-sectional view taken from above, taken perpendicular to the plane of the film. Figure 10 shows the tenter stretching apparatus with its cover removed, with the cover represented by a two-point chain.

Figure 11 is a schematic diagram of the nozzle and heater arrangement, viewed from the front, in the three zones within the tenter stretching apparatus. As shown in Figure 11, the IR heater is located only above the nozzle, preventing contact with the film during film breakage. However, placing the IR heater closer to the film concentrates its radiation energy into a narrower area. Therefore, the IR heater should be placed as close to the film as possible without interfering with the widthwise movement of the clamps.

FIG11 mainly shows the heat treatment from the central nozzle (105). In this embodiment, although the heat treatment by the end nozzle (104) is not performed, it can be used in combination in this embodiment.

During heat treatment, the radiation energy emitted from the infrared (IR) heater in the nozzle gap can be transferred to the film without waste, as shown in Figure 12.

As shown in Figure 9, infrared (IR) heaters are arranged in a row, allowing the entire width of the film to be heated even before stretching. The heaters can also be arranged in a staggered pattern along the length of the film.

The tenter stretching device (40) includes a plurality of clamps (42) that grip the two ends of the film (F) in the width direction. The clamps (42) are mounted on an endless chain (48) at regular intervals. The endless chain (48) is arranged on both sides of the film (F) and is suspended between a driving sprocket (50) on the inlet side and a driven sprocket (52) on the outlet side. The driving sprocket (50) is connected to a motor (not shown) that is driven to rotate the driving sprocket (50). As a result, since the endless chain (48) moves in a circular motion between the driving sprocket (50) and the driven sprocket (52), the clamp (42) mounted on the endless chain (48) also moves in a circular motion.

A guide rail (54) for guiding the circular chain (48) (or the clamp (42)) is provided between the driving sprocket (50) and the driven sprocket (52). The guide rails (54) are arranged on both sides of the film (F), and the distance between the guide rails (54) is configured so that the downstream side is wider than the upstream side in the conveying direction of the film (F). As a result, when the clamp (42) moves in a circular motion, the distance between the clamps (42) increases, so that the film (F) held by the clamp (42) can extend laterally in the width direction.

An opening member (56) is installed between the driving sprocket (50) and the driven sprocket (52). The opening member (56) is a device that shifts the fastener (not shown) of the clamp (42) described later from the holding position to the opening position. The film (F) is automatically held and opened by the opening member (56).

Therefore, as shown in Figures 9, 10, and 12, a preheating zone, a (transverse) stretching zone, and a heat fixing zone are provided within the tenter stretching device (40). The zones are separated from each other by wind screens (not shown). Furthermore, hot air is supplied to each zone from above, below, or both relative to the film (F).

Hot air is blown evenly across the width of the film (F) to maintain a specific temperature in each zone. This ensures the desired temperature is maintained within each zone. Each zone is explained below.

The preheating zone is an area for preheating the film (F) so as to heat the film (F) without expanding the gap of the clamp (42).

The film (F) preheated in the preheating zone is moved to the (transverse) stretching zone. The (transverse) stretching zone is a zone where the film (F) is stretched in the width direction (transversely) by expanding the spacing of the clamps (42). The stretching ratio in the (transverse) stretching process is preferably in the range of 1.0 to 2.5 times, more preferably in the range of 1.05 to 2.3 times, and even more preferably in the range of 1.1 to 2 times.

The film (F) stretched transversely in the transverse stretching zone is moved to a heat fixing zone.

In the embodiment of the present invention, the interior of the tenter stretching device (40) is divided into a preheating zone, a (transverse) stretching zone, and a heat setting zone. However, the types and configurations of the zones are not limited thereto. For example, a cooling zone for cooling the film (F) may be provided after the (transverse) stretching zone. Furthermore, a heat buffering zone may be provided within the heat setting zone.

In the embodiment of the present invention, although the tenter stretching device (40) is used only for (horizontal) stretching, it can also be stretched in the vertical direction at the same time. In this case, when the clamps (42) are moved, it is sufficient to change the distance between the clamps (42) (the distance between the clamps (42) in the conveying direction). As a mechanism for changing the distance between the clamps (42), a pantograph mechanism or a linear guide mechanism can be used.

(Heat Treatment) A tenter stretching system is typically divided into multiple zones. For example, as shown in Figures 9, 10, and 12, these zones include a preheating zone for heating the film, a transverse stretching zone for stretching the film laterally, a thermal fixation zone for crystallization, and a relaxation zone for relieving thermal stress on the film.

(Furnace Temperature) Generally, the furnace temperature is preferably within the range of 120-200°C, more preferably within the range of 120-180°C. Here, "furnace temperature" refers to the temperature measured 100 mm above the center of the film immediately before stretching ( _HA = 100 mm) in the stretching zone of the tenter stretching apparatus described below. This is defined as the average of the temperatures measured every minute for one hour.

Typically, the furnace temperature is preferably within the range of 120-200°C, more preferably within the range of 120-180°C. Here, when multiple segments have a temperature gradient along the length, the segments being heat treated are considered.

In addition, the furnace temperature is different when heat treatment is performed in the stretching zone and when heat treatment is not performed. However, when heat treatment is performed in the stretching zone, the furnace temperature refers to the furnace temperature of the stretching zone before the heat treatment is performed.

(Residual Solvent Amount) The residual solvent amount in the film during stretching is preferably 20% by mass or less, more preferably 15% by mass or less.

(2.1.7) First Cutting Step [S7] In the first cutting step [S7], the cutting portion (8) formed by the slitter cuts the film (F) stretched in the first stretching step [S6] at both ends in the width direction. The remaining portion of the film (F) after the two ends are cut constitutes the product portion of the film product. On the other hand, the portion cut from the film (F) can be recovered and reused as part of the raw material for film production.

(2.1.8) Second stretching step [S8] In the second stretching step [S8], the film (F) is stretched by the stretching device (9) in the same manner as in the first stretching step [S6]. As the stretching method at this time, a stretching method in which a roller speed difference is provided and the film (F) is stretched in the conveying direction (MD direction), or a tentering method in which the film (F) is fixed at both side edges with a clamp or the like and stretched in the width direction (TD direction) is preferably used because it can improve the performance/productivity, flatness, and dimensional stability of the film. In addition, in addition to stretching, drying can also be performed in the stretching device (9).

(2.1.9) Second Cutting Step [S9] In the second cutting step [S9], similar to the first cutting step [S7], the cutting portion (10) formed by the slitter cuts the two ends of the film (F) in the width direction. Furthermore, the gripping portions of the clamps at the two ends of the film usually deform the film, making it unusable as a product, so they are cut off. If the material does not deteriorate due to heat, it is recycled and reused.

The remaining portion of the film (F) after the ends are cut constitutes the finished film portion. On the other hand, the cut portion of the film (F) is recovered and reused as a raw material for the film production process.

(2.1.10) Second Drying Step [S10] In the second drying step [S10], the film (F) is dried using the drying device (11) in the same manner as in the first drying step [S5]. In the drying device (11), the film (F) is dried while being transported by a plurality of transport rollers arranged in a staggered pattern as viewed from the side.

The drying method used in the drying device (6) is not particularly limited, and common examples include hot air, infrared rays, heated rollers, and microwaves. Among the above drying methods, the method of drying the film (F) with hot air is preferred from the perspective of simplicity. In addition, a second drying step [S10] may be performed as needed.

(2.1.11) Third Cutting Step [S11] In the third cutting step [S11], similar to the first cutting step [S7] and the second cutting step [S9], the cutting portion (12) formed by the slitter cuts the film (F) at both ends in the width direction. The remaining portion of the film (F) after the ends are cut constitutes the product portion of the film product. On the other hand, the portion cut from the film (F) is recovered and reused as part of the raw material for film production.

(2.1.12) Winding Step [S12] Finally, in the winding step [S12], the film (F) is wound by the winding device (13) to obtain a film roll. That is, in the winding step, the film (F) is transported while being wound onto the winding core to produce a film roll. The preferred range of the initial tension when winding the film in the winding step is 20 to 300 N/m.

FIG13 is a schematic diagram showing the steps of winding a film and a cross-section of the film roll of the present invention after winding.

When rolling up the film (F), a contact roller (33) is set as shown in Figure 13, and the film contact pressure is appropriately changed to meet the gap required for the stroke.

In Figure 13, the film (31) is wound by the roll (32) and the contact roll (33) to form a film roll (30).

(Residual solvent amount)

More specifically, after reducing the residual solvent content in the film to less than 2% by mass, the film is wound into a film by a winding device (13). By reducing the residual solvent content to less than 0.4% by mass, a film with good dimensional stability can be obtained.

It is particularly suitable to carry out coiling within the residual solvent range of 0.00-0.20 mass%.

(Rolling method)

The film (F) can be wound using a commonly used winding machine. There are various tension control methods, including the constant torque method, the constant tension method, the taper tension method, and the programmed tension control method with constant internal stress. These methods can be used appropriately.

Before rolling, the ends of the film are cut to the width of the finished product. To prevent sticking and scratching during rolling, the film ends can be surface-modified.

[After rolling]

The film roll of the present invention is preferably a long film, specifically, one with a length of approximately 100 to 10,000 μm, and is typically provided in a roll form.

(2.2) Manufacturing steps of film roll using melt casting method

The film of the present invention can also be produced by melt casting.

The so-called "melt film casting method" refers to a method in which a composition containing a thermoplastic resin and the above-mentioned additives is heated and melted to a temperature at which it exhibits fluidity, and the melt containing the fluid thermoplastic resin is then cast.

Molding methods involving heating and melting can be further categorized into melt extrusion, compression molding, inflation molding, injection molding, blow molding, and stretch molding.

Among these forming methods, melt extrusion is preferred from the perspectives of mechanical strength and surface accuracy.

Figure 14 is a flow chart showing the manufacturing steps of the melt casting method.

Figure 15 is a schematic diagram of a device for producing thin films using the melt casting method.

The following solution casting method will be explained with reference to Figures 14 and 15.

The method for manufacturing a film roll by melt casting includes an extrusion step [M1], a casting/forming step [M2], a first stretching step [M3], a first cutting step [M4], a second stretching step [M5], a second cutting step [M6], and a rolling step [M7].

Furthermore, the above-mentioned manufacturing method does not necessarily need to include both the first stretching step [M3] and the second stretching step [M5]; it is sufficient to include at least one of the steps.

Furthermore, the first cutting step [M4] and the second cutting step [M6] also need only include at least one of the steps.

(2.2.1) Extrusion step [M1]

In the extrusion step [M1], the resin is at least melted and extruded by an extruder (14) and formed on a casting roller (16).

The above-mentioned resins that can be used in the present invention will be described later.

In addition, it is better to pre-mix the resin and granulate it.

Granulation can be carried out by known methods.

For example, dry resin or plasticizer and other additives are fed to the extruder through a feeder, mixed using a single-shaft or double-shaft extruder, extruded into strands through a self-watering die (15), water-cooled or air-cooled, and cut to form pellets.

The additive can be mixed with the resin before being supplied to the extruder, or the additive and resin can be supplied to the extruder separately using feeders.

In addition, in order to ensure that the particles and small amounts of additives such as antioxidants are mixed evenly, it is best to mix them with the resin in advance.

When introducing granules from the feed hopper into the extruder, it is best to set it up dry, under vacuum or reduced pressure, or in an inert gas environment to prevent oxidative decomposition, etc.

The extruder is preferably operated at the lowest possible temperature to suppress shear forces and prevent resin degradation (molecular weight reduction, coloration, gel formation, etc.) while pelletizing.

For example, in a twin-spindle extruder, it is best to use deep-groove screws rotating in the same direction.

Based on the uniformity of mixing, the blending type is preferred.

When the resin/particles are melted, it is best to filter them using a blade filter or other filter to remove foreign matter.

Use the particles obtained above to form thin films.

Of course, it is also possible to skip granulation and directly feed the raw resin (powder, etc.) to the extruder via a feeder to directly produce the film.

(2.2.2) Casting step [M2]

In the casting/forming step [M2], the resin/particles melted in the extrusion step are cast into a film form from the casting die (15) through a pressure-type metering gear pump or the like through a conduit, and the melted resin/particles are cast from the casting die (15) at a casting position on the circularly conveyed rotating driven stainless steel annular casting roller (16).

Next, the molten resin/particles are formed on a casting roller (16) to form a casting film (18).

The inclination of the casting die nozzle (15), that is, the ejection direction of the molten resin/particles from the casting die nozzle (15) to the casting drum (16), can be appropriately set so that the angle relative to the normal line of the casting drum (16) surface (the surface on which the molten resin/particles are cast) is within the range of 0 to 90 degrees.

The auxiliary contact roller (16a) and the cooling roller (17) of the casting roller (16) can also be used alone or in combination to form the film (F).

(2.2.3) First stretching step [M3] In the first stretching step [M3], the film (F) is stretched by the stretching device (19). As the stretching method at this time, a stretching method in which a roller is provided with a circumferential speed difference and the film (F) is stretched in the MD direction, or a tentering method in which the film (F) is fixed at both side edges with a clamp or the like and the film (F) is stretched in the TD direction is preferably used because the film's performance/productivity, flatness, and dimensional stability can be improved. In addition, in the stretching device (19), drying can also be performed in addition to stretching.

The description of the tenter stretching device, heat treatment timing, furnace temperature, stretching temperature, temperature in the stretching furnace, and residual solvent amount is omitted because it is repeated in the first stretching step [S6] in the film roll manufacturing step by the solution casting method.

(2.2.4) First Cutting Step [M4] In the first cutting step [M4], the cutting portion (20) formed by the slitter cuts both ends of the film (F) in the width direction. The remaining portion of the film (F) after the both ends are cut constitutes the product portion of the film product. On the other hand, the portion cut from the film (F) can be recycled and reused as part of the raw material for film production.

(2.2.5) Second stretching step [M5] In the second stretching step [M5], the film (F) is stretched by the stretching device (21) in the same manner as in the first stretching step [M3]. As the stretching method at this time, a stretching method in which a roller speed difference is provided and the film (F) is stretched in the MD direction, or a tentering method in which the film (F) is fixed at both side edges with a clamp or the like and stretched in the TD direction is preferably used because it can improve the performance/productivity, flatness, and dimensional stability of the film. In addition, in addition to stretching, drying can also be performed in the stretching device (21).

(2.2.6) Second Cutting Step [M6] In the second cutting step [M6], similarly to the first cutting step [M4], the cutting portion (22) formed by the slitter cuts both ends of the film (F) in the width direction. The remaining portion of the film (F) after the cut ends constitutes the product portion of the film product. On the other hand, the portion cut from the film (F) is recovered and reused as part of the raw material for film production.

(2.2.7) Winding Step [M7] Finally, in the winding step [M7], the film (F) is wound by the winding device (23) to obtain a film roll. That is, in the winding step [M7], the film (F) is wound around the winding core while being transported to produce a film roll.

As a method for winding the film (F), a generally used winding machine may be used. There are various tension control methods such as a constant torque method, a constant tension method, a taper tension method, and a program tension control method with constant internal stress, and any of these methods may be used appropriately.

3. Film-Constructing Resins (3.1) Thermoplastic Resins Thermoplastic resin materials used in the films of the present invention are not particularly limited as long as they can be processed as film rolls after film formation.

Suitable thermoplastic resins for use in polarizing plates include cellulose ester resins such as triacetyl cellulose (TAC), cellulose acetate propionate (CAP), and diacetyl cellulose (DAC); cyclic olefin resins such as cycloolefin resin (hereinafter also referred to as "COP"); polypropylene resins such as polypropylene (PP); acrylic resins such as polymethyl methacrylate (PMMA); and polyester resins such as polyethylene terephthalate (PET).

However, COP is desirable due to its ease of controlling elongation and crystallinity, as well as its ease of adhesive penetration and ability to ensure better adhesion to the polarizer. Furthermore, the above-mentioned films can also undergo surface modification after production.

Furthermore, the effects of this invention are highly valuable in the thin film field. The film thickness is preferably in the range of 5-80 μm, more preferably in the range of 10-65 μm, and even more preferably in the range of 10-45 μm.

A film thickness of 5μm or greater provides high roll rigidity, making it easier to maintain the roll's shape. A film thickness of 80μm or less minimizes weight loss, making it easier to manufacture long rolls.

(3.1.1) Cycloolefin Resin The cycloolefin resin contained in the film roll of the present invention is preferably a polymer of a cycloolefin monomer or a copolymer of a cycloolefin monomer and a non-copolymerizable monomer.

The cycloolefin monomer is preferably a cycloolefin monomer having a norbornene skeleton, and more preferably a cycloolefin monomer having a structure represented by the following general formula (A-1) or (A-2).

In general formula (A-1), R ¹ to R ⁴ each independently represent a hydrogen atom, a alkyl group having 1 to 30 carbon atoms, or a polar group. p represents an integer from 0 to 2. However, R ¹ to R ⁴ do not all represent hydrogen atoms, R ¹ and R ² do not both represent hydrogen atoms, and R ³ and R ⁴ do not both represent hydrogen atoms.

In general formula (A-1), the alkyl group having 1 to 30 carbon atoms represented by R ¹ to R ⁴ is preferably a alkyl group having 1 to 10 carbon atoms, and more preferably a alkyl group having 1 to 5 carbon atoms.

A alkyl group having 1 to 30 carbon atoms may further have a linking group comprising, for example, a halogen atom, an oxygen atom, a nitrogen atom, a sulfur atom, or a silicon atom. Examples of such linking groups include divalent polar groups such as carbonyl groups, imino groups, ether bonds, silane ether bonds, and sulfide bonds. Examples of alkyl groups having 1 to 30 carbon atoms include methyl, ethyl, propyl, and butyl groups.

Examples of the polar group represented by R ¹ to R ⁴ in general formula (A-1) include a carboxyl group, a hydroxyl group, an alkoxy group, an alkoxycarbonyl group, an aryloxycarbonyl group, an amino group, an amide group, and a cyano group.

Among them, carboxyl, hydroxyl, alkoxycarbonyl and aryloxycarbonyl are preferred. From the viewpoint of ensuring solubility during film formation from a solution, alkoxycarbonyl and aryloxycarbonyl are preferred.

In general formula (A-1), p is preferably 1 or 2 to improve the heat resistance of the film. This is because when p is 1 or 2, the resulting polymer has a higher volume and tends to have a higher glass transition temperature.

In general formula (A-2), ^R₅ represents a hydrogen atom, a alkyl group having 1 to 5 carbon atoms, or an alkylsilyl group having an alkyl group having 1 to 5 carbon atoms. ^R₆ represents a carboxyl group, a hydroxyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, an amino group, an amide group, a cyano group, or a halogen atom (fluorine atom, chlorine atom, bromine atom, or iodine atom). p represents an integer from 0 to 2.

In general formula (A-2), R ⁵ preferably represents a alkyl group having 1 to 5 carbon atoms, and more preferably represents a alkyl group having 1 to 3 carbon atoms.

^R6 in general formula (A-2) preferably represents a carboxyl group, a hydroxyl group, an alkoxycarbonyl group, or an aryloxycarbonyl group. In order to ensure solubility during film formation from a solution, an alkoxycarbonyl group or an aryloxycarbonyl group is more preferred.

In general formula (A-2), p is preferably 1 or 2 to improve the heat resistance of the film. This is because when p is 1 or 2, the resulting polymer has a higher volume and tends to have a higher glass transition temperature.

A cycloolefin monomer having a structure represented by the general formula (A-2) is preferred from the viewpoint of improving solubility in organic solvents.

Generally, organic compounds reduce their crystallinity by destroying their symmetry, thus increasing their solubility in organic solvents.

Because ^R5 and ^R6 in general formula (A-2) are substituted only on one side of the ring-constituting carbon atom relative to the molecular axis of symmetry, the molecule has low symmetry. This means that the cycloolefin monomer having the structure represented by general formula (A-2) has high solubility, making it suitable for thin film production by solution casting.

The content ratio of the cycloolefin monomer having the structure represented by the general formula (A-2) in the polymer of the cycloolefin monomer is, for example, 70 mol% or more, preferably 80 mol% or more, and more preferably 100 mol% relative to the total of all cycloolefin monomers constituting the cycloolefin resin.

When a certain amount or more of a cycloolefin monomer having a structure represented by the general formula (A-2) is contained, the phase difference (retardation) value tends to increase because the orientation of the resin is improved.

Hereinafter, specific examples of cycloalkene monomers having a structure represented by general formula (A-1) are shown in Exemplary Compounds 1 to 14, and specific examples of cycloalkene monomers having a structure represented by general formula (A-2) are shown in Exemplary Compounds 15 to 34.

Examples of the copolymerizable monomers copolymerizable with the cycloolefin monomers include copolymerizable monomers capable of ring-opening copolymerization with the cycloolefin monomers and copolymerizable monomers capable of addition copolymerization with the cycloolefin monomers.

Examples of the ring-opening copolymerizable copolymerizable monomers include cycloalkenes such as cyclobutene, cyclopentene, cycloheptene, cyclooctene, and dicyclopentadiene.

Examples of addition copolymerizable copolymerizable monomers include compounds containing unsaturated double bonds, vinyl cyclic hydrocarbon monomers, and (meth)acrylates.

Examples of compounds containing unsaturated double bonds include olefinic compounds having 2 to 12 carbon atoms (preferably 2 to 8 carbon atoms), including ethylene, propylene, and butene.

Examples of vinyl cyclopentene monomers include vinyl cyclopentene monomers such as 4-vinylcyclopentene and 2-methyl-4-isopropenylcyclopentene.

Examples of (meth)acrylates include (meth)acrylic acid alkyl esters having 1 to 20 carbon atoms, such as methyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate.

The content ratio of the cycloolefin monomer in the copolymer of the cycloolefin monomer and the copolymerizable monomer is, for example, in the range of 20 to 80 mol %, preferably in the range of 30 to 70 mol %, relative to the total of all monomers constituting the copolymer.

The cycloolefin resin is a polymer obtained by polymerizing or copolymerizing a cycloolefin monomer having a norbornene skeleton, preferably a cycloolefin monomer having a structure represented by the general formula (A-1) or (A-2), as described above. Examples thereof include the following polymers (1) to (7).

(1) Ring-opening polymers of cycloolefin monomers (2) Ring-opening copolymers of cycloolefin monomers and copolymerizable monomers capable of ring-opening copolymerization with the cycloolefin monomers (3) Hydrogenates of the ring-opening (co)polymers of (1) or (2) above (4) (Co)polymers obtained by cyclization of the ring-opening (co)polymers of (1) or (2) above by Friedel–Crafts reaction (5) Saturated copolymers of cycloolefin monomers and compounds containing unsaturated double bonds (6) Addition copolymers of cycloolefin monomers with vinyl cyclic monomers and their hydrogenates (7) Alternating copolymers of cycloolefin monomers and (meth)acrylates

The polymers (1) to (7) above can be obtained by known methods, such as the method described in Japanese Patent Application Publication No. 2008-107534 or Japanese Patent Application Publication No. 2005-227606.

For example, the catalyst and solvent used in the ring-opening copolymerization (2) described in paragraphs 0019 to 0024 of Japanese Patent Application Laid-Open No. 2008-107534 can be used.

The catalyst used for the hydride of (3) and (6) above may be, for example, the catalyst described in paragraphs 0025 to 0028 of Japanese Patent Application Laid-Open No. 2008-107534.

As the acidic compound used in the Friedel-Crafts reaction of (4) above, for example, the one described in paragraph 0029 of JP-A-2008-107534 can be used.

The catalyst used in the addition polymerization of (5) to (7) above can be, for example, the catalyst described in paragraphs 0058 to 0063 of Japanese Patent Application Laid-Open No. 2005-227606.

The alternating copolymerization reaction (7) can be carried out by the method described in paragraphs 0071 and 0072 of JP-A-2005-227606, for example.

Among them, the polymers of (1) to (3) and (5) are preferred, and the polymers of (3) and (5) are more preferred.

That is, from the viewpoint of increasing the glass transition temperature of the resulting cycloolefin resin and improving the light transmittance, the cycloolefin resin preferably includes at least one of the structural units represented by the following general formula (B-1) and the structural units represented by the following general formula (B-2), more preferably includes only the structural units represented by the general formula (B-2), or includes both the structural units represented by the general formula (B-1) and the structural units represented by the general formula (B-2).

The structural units represented by the general formula (B-1) are derived from the structural units of the cycloalkene monomer represented by the aforementioned general formula (A-1), and the structural units represented by the general formula (B-2) are derived from the structural units of the cycloalkene monomer represented by the aforementioned general formula (A-2).

In general formula (B-1), X represents -CH=CH- or -CH ₂ CH ₂ -. R ¹ to R ⁴ and p are the same as R ¹ to R ⁴ and p in general formula (A-1), respectively.

In general formula (B-2), X represents -CH=CH- or -CH ₂ CH ₂ -. R ⁵ to R ⁶ and p are the same as R ⁵ to R ⁶ and p in general formula (A-2), respectively.

The cycloolefin resin of the present invention may be a commercially available product. Examples of commercially available cycloolefin resins include Arton G (e.g., G7810), Arton F, Arton R (e.g., R4500, R4900, and R5000), and Arton RX manufactured by JSR Corporation.

The intrinsic viscosity [η]inh of the cycloolefin resin, measured at 30°C, is preferably in the range of 0.2 to 5 cm ³ /g, more preferably in the range of 0.3 to 3 cm ³ /g, and even more preferably in the range of 0.4 to 1.5 cm ³ /g.

The number average molecular weight (Mn) of the cycloolefin resin is preferably in the range of 8,000 to 100,000, more preferably in the range of 10,000 to 80,000, and even more preferably in the range of 12,000 to 50,000.

The weight average molecular weight (Mw) of the cycloolefin resin is preferably in the range of 20,000 to 300,000, more preferably in the range of 30,000 to 250,000, and even more preferably in the range of 40,000 to 200,000.

The number average molecular weight and weight average molecular weight of cycloolefin resins can be determined by gel permeation chromatography (GPC) in terms of polystyrene.

(Gel Permeation Chromatography) Solvent: Methylene Chloroform Columns: Shodex K806, K805, K803G (Showa Denko Co., Ltd., three columns connected) Column Temperature: 25°C Sample Concentration: 0.1% by mass Detector: RI Model 504 (GL Scientific Co., Ltd.) Pump: L6000 (Hitachi, Ltd.) Flow Rate: 1.0 mL/min Calibration Curve: 13 samples with STK polystyrene standards (Tosoh Co., Ltd.) ranging in Mw from 500 to 2,800,000 were used. It is best to use these 13 samples at approximately equal intervals.

If the intrinsic viscosity [η]inh, number average molecular weight, and weight average molecular weight are within the above ranges, the cycloolefin resin can have good heat resistance, water resistance, chemical resistance, mechanical properties, and film forming processability.

The glass transition temperature (Tg) [°C] of cycloolefin resins is generally above 110°C, preferably within the range of 110-350°C, more preferably within the range of 120-250°C, and even more preferably within the range of 120-220°C.

A glass transition temperature (Tg) of 110°C or higher can easily suppress deformation under high-temperature conditions. On the other hand, a glass transition temperature (Tg) of 350°C or lower can facilitate molding and prevent resin degradation due to heat during molding.

The content of the cycloolefin resin is preferably 70% by mass or more, more preferably 80% by mass or more, relative to the film.

(3.1.2) Acrylic Resins The acrylic resins of the present invention are polymers of acrylic acid esters or methacrylic acid esters, and include copolymers with other monomers. Therefore, the acrylic resins of the present invention also include methacrylic acid resins.

Although the resin is not particularly limited, it is preferred that the methyl methacrylate unit be in the range of 50-99 mass % and the other monomer units copolymerizable therewith be in the range of 1-50 mass %.

Examples of other units constituting the acrylic resin formed by copolymerization include alkyl methacrylates having an alkyl group with 2 to 18 carbon atoms, alkyl acrylates having an alkyl group with 1 to 18 carbon atoms, hydroxyalkyl acrylates such as isobornyl methacrylate and 2-hydroxyethyl acrylate, α,β-unsaturated acids such as acrylic acid and methacrylic acid, acrylamides such as acrylamide morpholine and N-hydroxyphenylmethacrylamide, N-vinyl pyrrolidone, divalent carboxylic acids containing an unsaturated group such as maleic acid, fumaric acid, and itaconic acid, aromatic vinyl compounds such as styrene and α-methylstyrene, α,β-unsaturated nitriles such as acrylonitrile and methacrylonitrile, maleic anhydride, maleimide, N-substituted maleimide, glutarimide, and glutaric anhydride.

Examples of copolymerizable monomers for forming the units other than glutarimide and glutaric anhydride from the above units include monomers corresponding to the above units.

Examples include alkyl methacrylates having an alkyl group with 2 to 18 carbon atoms, alkyl acrylates having an alkyl group with 1 to 18 carbon atoms, hydroxyalkyl acrylates such as isobornyl methacrylate and 2-hydroxyethyl acrylate, α,β-unsaturated acids such as acrylic acid and methacrylic acid, acrylamides such as acrylamide morpholine and N-hydroxyphenylmethacrylamide, N-vinylpyrrolidone, divalent carboxylic acids containing an unsaturated group such as maleic acid, fumaric acid, and itaconic acid, aromatic vinyl compounds such as styrene and α-methylstyrene, α,β-unsaturated nitriles such as acrylonitrile and methacrylonitrile, maleic anhydride, maleimide, and N-substituted maleimide.

The glutarimide unit can be formed, for example, by reacting an intermediate resin having a (meth)acrylate unit with a primary amine (imidizing agent) to imidize the resin (see JP-A-2011-26563).

Glutaric anhydride units can be formed, for example, by heating an intermediate resin having (meth)acrylate units (see Japanese Patent No. 4961164).

In the acrylic resin of the present invention, the aforementioned constituent units particularly preferably include isobornyl methacrylate, acrylamide, N-hydroxyphenylmethacrylamide, N-vinylpyrrolidone, styrene, hydroxyethyl methacrylate, maleic anhydride, maleimide, N-substituted maleimide, glutaric anhydride, or glutarimide, from the viewpoint of mechanical strength.

The acrylic resin of the present invention preferably has a weight-average molecular weight (Mw) in the range of 50,000 to 1,000,000, more preferably 100,000 to 1,000,000, and particularly preferably 200,000 to 800,000, from the viewpoint of controlling dimensional changes due to changes in ambient temperature and humidity, or improving releasability from metal supports during film production, drying properties from organic solvents, heat resistance, and mechanical strength.

If it is 50,000 or more, the heat resistance and mechanical strength are excellent, and if it is 1,000,000 or less, the peeling property from the metal support and the drying property of organic solvents are excellent.

The method for producing the acrylic resin of the present invention is not particularly limited, and any known method such as suspension polymerization, emulsion polymerization, bulk polymerization, or solution polymerization may be used.

Here, as the polymerization initiator, conventional peroxide-based and azo-based initiators can be used, and redox-based initiators may also be used.

Regarding the polymerization temperature, suspension or emulsion polymerization can be carried out in the range of 30-100°C, and bulk or solution polymerization can be carried out in the range of 80-160°C.

In order to control the reduced viscosity of the resulting copolymer, alkyl mercaptan or the like can be used as a chain transfer agent during polymerization.

The glass transition temperature (Tg) of acrylic resin is preferably in the range of 80~120℃ in order to maintain the mechanical strength of the film.

Commercially available acrylic resins may also be used as the acrylic resins of the present invention. Examples include DELPET 60N, 80N, 980N, and SR8200 (all manufactured by Asahi Kasei Chemicals Co., Ltd.), DIANALS BR52, BR80, BR83, BR85, BR88, EMB-143, EMB-159, EMB-160, EMB-161, EMB-218, EMB-229, EMB-270, and EMB-273 (all manufactured by Mitsubishi Tissue Co., Ltd.), and KT75, TX400S, and IPX012 (all manufactured by Denki Kagaku Kogyo Co., Ltd.). Two or more acrylic resins may also be used in combination.

The acrylic resin of the present invention preferably contains an additive. As an example of the additive, it preferably contains acrylic particles (rubber elastomer particles) described in International Publication No. 2010/001668 to improve the mechanical strength of the film and adjust the dimensional change rate.

Examples of commercially available products of such multi-layer acrylic granular composites include "METABLEN W-341" manufactured by Mitsubishi Twisting Corporation, "KANEACE" manufactured by Kaneka Corporation, "PARALOID" manufactured by KUREHA, "ACRYLOID" manufactured by Rohm and Haas Company, "STAFYROID" manufactured by AICA, CHEMISNOW MR-2G, MS-300X (all manufactured by Soken Chemical Co., Ltd.), and "PARAPET SA" manufactured by KURARAY Co., Ltd. These can be used alone or in combination of two or more.

The volume average particle size of the acrylic particles is 0.35 μm or less, preferably 0.01 to 0.35 μm, and even more preferably 0.05 to 0.30 μm. A particle size above a certain value facilitates film stretching under heating, while a particle size below a certain value minimizes degradation of the resulting film's transparency.

From the perspective of flexibility, the film of the present invention preferably has a flexural modulus (JIS K7171) of 10.5 GPa or less, more preferably 1.3 GPa or less, and even more preferably 1.2 GPa or less.

The above-mentioned flexural modulus varies with the type and amount of acrylic resin and rubber elastomer particles in the film. For example, the higher the content of rubber elastomer particles, the lower the flexural modulus generally is.

Furthermore, as acrylic resins, when copolymers of alkyl methacrylates and alkyl acrylates are used, the flexural modulus is generally smaller than when homopolymers of alkyl methacrylates are used.

(3.1.3) Cellulose Ester Resins Cellulose ester resins are also preferably used in the film rolls of the present invention.

The cellulose ester resin used in the present invention refers to a cellulose acylate resin in which some or all of the hydrogen atoms of the hydroxyl groups (-OH) at the 2nd, 3rd, and 6th positions in the β-1,4-linked glucose units constituting cellulose are substituted with acyl groups.

The cellulose ester is not particularly limited, but preferably is a linear or branched carboxylic acid ester with approximately 2 to 22 carbon atoms. The carboxylic acid constituting the ester may be aliphatic, cyclic, or aromatic.

As an example of the above, for example, a cellulose ester in which the hydrogen atom of the hydroxyl portion of cellulose is substituted with an acyl group having 2 to 22 carbon atoms, such as acetyl, propionyl, butyryl, isobutyryl, pentyl, t-pentyl, hexyl, octyl, lauryl, or stearyl.

The carboxylic acid (acyl group) constituting the ester may have a substituent. The carboxylic acid constituting the ester is particularly preferably a lower fatty acid having 6 or fewer carbon atoms, and more preferably a lower fatty acid having 3 or fewer carbon atoms.

Furthermore, the acyl group in the cellulose ester may be a single type or a combination of multiple types of acyl groups.

Specific examples of preferred cellulose esters include cellulose acetate esters such as diacetylcellulose (DAC) and triacetylcellulose (TAC). Other examples include mixed fatty acid esters of cellulose in which acrylate or butyrate groups are bonded in addition to acetyl groups, such as cellulose acetate propionate (CAP), cellulose acetate butyrate, and cellulose acetate propionate butyrate. These cellulose esters may be used alone or in combination.

(Acyl Group Type and Degree of Substitution) By adjusting the acyl group type and degree of substitution of the cellulose ester, the humidity variation of the phase difference can be controlled within the desired range and the uniformity of the film thickness can be improved.

A lower degree of acyl substitution in cellulose esters improves retardation, allowing for thinner films. On the other hand, too low a degree of acyl substitution may reduce durability, making it less desirable.

On the other hand, since the greater the degree of acyl substitution of cellulose ester, the less phase difference is exhibited, the stretching ratio must be increased during film formation. However, uniform stretching is difficult at a high stretching ratio, and thus the deviation in film thickness becomes larger (deterioration).

Furthermore, since the Rt humidity variation of the retardation (phase difference) in the thickness direction is caused by the coordination of water molecules to the carbonyl groups of cellulose, the higher the degree of acyl substitution, that is, the more carbonyl groups in the cellulose, the lower the Rt humidity variation tends to be.

The optimal total degree of substitution for cellulose ester is between 2.1 and 2.5. This range suppresses environmental fluctuations (particularly Rt fluctuations caused by humidity) while also improving film thickness uniformity.

More preferably, from the perspective of improving castability and elongation during film formation and further improving the uniformity of film thickness, it is in the range of 2.2 to 2.45.

More specifically, the cellulose ester satisfies both the following formulas (a) and (b). In the following formulas (a) and (b), X is the degree of substitution of acetyl groups, and Y is the degree of substitution of propionyl groups or butyryl groups, or a mixture thereof.

Formula (a): 2.1 ≤ X + Y ≤ 2.5 Formula (b): 0 ≤ Y ≤ 1.5

The cellulose ester is more preferably cellulose acetate (Y=0) and cellulose acetate propionate (CAP) (Y: propionyl, Y>0). From the perspective of reducing film thickness deviation, cellulose acetate with Y=0 is even more preferred.

The most preferred cellulose acetate is cellulose acetate (DAC) with a ratio of 2.1≦X≦2.5 (more preferably 2.15≦X≦2.45) based on the viewpoint of keeping the phase difference display, Rt humidity variation, and film thickness deviation within the desired range.

When Y>0, the cellulose acetate propionate (CAP) preferably used is 0.95≦X≦2.25, 0.1≦Y≦1.2, and 2.15≦X+Y≦2.45.

By using the above-mentioned cellulose acetate or cellulose acetate propionate, a film roll having excellent delay, mechanical strength, and environmental change resistance can be obtained.

The degree of acyl substitution represents the average number of acyl groups per glucose unit, indicating how many hydrogen atoms at the 2-, 3-, and 6-hydroxyl groups per glucose unit have been replaced by acyl groups. Thus, a maximum degree of substitution of 3.0 means that all hydrogen atoms at the 2-, 3-, and 6-hydroxyl groups have been replaced by acyl groups.

These acyl groups may be substituted evenly at the 2-, 3-, and 6-positions of the glucose unit, or they may be substituted in a distributed pattern. The degree of substitution is determined according to the method specified in ASTM-D817-96.

To achieve desired optical properties, cellulose acetates with different degrees of substitution can be mixed. In this case, the mixing ratio of the different cellulose acetates is not particularly limited.

The number average molecular weight (Mn) of the cellulose ester is preferably within the range of 2×10 ⁴ to 3×10 ⁵ , further within the range of 2×10 ⁴ to 1.2×10 ⁵ , and further within the range of 4×10 ⁴ to 8×10 ⁴ , from the perspective of increasing the mechanical strength of the resulting film roll.

The number average molecular weight (Mn) of cellulose ester was calculated using gel permeation chromatography (GPC) under the aforementioned conditions.

The weight average molecular weight (Mw) of the cellulose ester is preferably within the range of 2×10 ⁴ to 1×10 ⁶ , further within the range of 2×10 ⁴ to 1.2×10 ⁵ , and further within the range of 4×10 ⁴ to 8×10 ⁴ , from the viewpoint of increasing the mechanical strength of the resulting film roll.

The cellulose ester raw material is not particularly limited, but examples thereof include cotton linter, wood pulp, and hemp. Cellulose esters obtained from these sources can also be mixed in any proportion.

Cellulose esters such as cellulose acetate and cellulose acetate propionate can be produced by conventional methods.

Generally, the raw material cellulose is mixed with a specific organic acid (acetic acid, propionic acid, etc.), an acid anhydride (acetic anhydride, propionic anhydride, etc.), and a catalyst (sulfuric acid, etc.) to esterify the cellulose and react until a cellulose triester is formed.

In triesters, the three hydroxyl groups of the glucose unit are replaced by acyl groups of an organic acid.

If two organic acids are used simultaneously, mixed esters of cellulose esters can be produced, such as cellulose acetate propionate or cellulose acetate butyrate.

Next, the cellulose triester is hydrolyzed to synthesize a cellulose ester resin with the desired degree of acyl substitution. Subsequently, filtration, precipitation, washing, dehydration, and drying are performed to produce the cellulose ester resin. The specific synthesis method described in Japanese Patent Application Laid-Open No. 10-45804 can be found here.

(3.2) Other Additives In addition to the aforementioned thermoplastic resin, the film roll of the present invention may contain the following other additives.

(3.2.1) Plasticizer The film roll of the present invention preferably contains at least one plasticizer for the purpose of enhancing processability, such as in a polarizing plate protective film. Plasticizers are preferably used singly or as a mixture of two or more.

From the perspective of achieving both effective control of moisture permeability and compatibility with base resins such as cellulose esters, the plasticizer preferably includes at least one plasticizer selected from the group consisting of sugar esters, polyesters, and styrene-based compounds.

From the perspective of improving moisture and heat resistance and compatibility with base resins such as cellulose ester, the molecular weight of the plasticizer is preferably 15,000 or less, more preferably 10,000 or less.

When the compound having a molecular weight of 10,000 or less is a polymer, the weight-average molecular weight (Mw) is preferably 10,000 or less. The preferred weight-average molecular weight (Mw) range is 100-10,000, and more preferably 400-8,000.

In particular, to achieve the effects of the present invention, the compound having a molecular weight of 1500 or less is preferably contained in an amount of 6 to 40 parts by mass, and more preferably 10 to 20 parts by mass, per 100 parts by mass of the base resin. This content within these ranges allows for effective control of moisture permeability and improved compatibility with the base resin.

(Sugar Ester) The film roll of the present invention may contain a sugar ester compound for the purpose of preventing hydrolysis.

Specifically, as the sugar ester compound, there can be used a sugar ester having at least one of 1 to 12 pyranose structures or furanose structures, in which all or part of the OH groups of the structure are esterified.

(Polyester) The film roll of the present invention may also contain polyester.

The polyester is not particularly limited, but for example, a polymer having a hydroxyl group at the end (polyester polyol) obtained by a condensation reaction between a dicarboxylic acid or an ester-forming derivative thereof and a diol, or a polymer in which the terminal hydroxyl group of the polyester polyol is capped with a monocarboxylic acid (terminal-capped polyester) can be used.

Here, the ester-forming derivatives include esters of dicarboxylic acids, dicarboxylic acid chlorides, and anhydrides of dicarboxylic acids.

(Styrene-Based Compounds) In the film roll of the present invention, styrene-based compounds may be used in addition to or in place of the aforementioned sugar esters and polyesters to improve the water resistance of the film.

The styrene compound may be a homopolymer of a styrene monomer or a copolymer of a styrene monomer and a comonomer other than the styrene monomer.

The content ratio of the structural units derived from the styrene monomer in the styrene compound is preferably in the range of 30 to 100 mol %, more preferably in the range of 50 to 100 mol %, so that the molecular structure has a certain volume or above.

Examples of styrene monomers include styrene; alkyl-substituted styrenes such as α-methylstyrene, β-methylstyrene, and p-methylstyrene; halogen-substituted styrenes such as 4-chlorostyrene and 4-bromostyrene; hydroxystyrenes such as p-hydroxystyrene, α-methyl-p-hydroxystyrene, 2-methyl-4-hydroxystyrene, and 3,4-dihydroxystyrene; vinylbenzyl alcohol; alkoxy-substituted styrenes such as p-methoxystyrene, p-tert-butoxystyrene, and m-tert-butoxystyrene; 3-vinylbenzoic acid, 4- Vinylbenzoic acids such as vinylbenzoic acid; 4-vinylbenzyl acetate; 4-acetoxystyrene; amide styrenes such as 2-butylamidostyrene, 4-formamidostyrene, and p-sulfonamidostyrene; aminostyrenes such as 3-aminostyrene, 4-aminostyrene, 2-isopropenylaniline, and vinylbenzyldimethylamine; nitrostyrenes such as 3-nitrostyrene and 4-nitrostyrene; cyanostyrenes such as 3-cyanostyrene and 4-cyanostyrene; vinylphenylacetonitrile; arylstyrenes such as phenylstyrene, and indenes. The styrene-based monomer may be one type or a combination of two or more.

(3.2.2) Optional Ingredients The film roll of the present invention may contain other optional ingredients, such as antioxidants, colorants, UV absorbers, matting agents, acrylic particles, hydrogen bonding solvents, and ionic surfactants. These ingredients may be added in an amount ranging from 0.01 to 20 parts by weight per 100 parts by weight of the base resin.

(Antioxidant) Commonly known antioxidants can be used as antioxidants in the film rolls of the present invention. In particular, lactone-based, sulfur-based, phenol-based, double-bond-based, hindered amine-based, and phosphorus-based compounds are particularly preferred.

These antioxidants should be added at a rate of 0.05-20% by mass, preferably 0.1-1% by mass, relative to the main resin of the film. Compared to using only one type of antioxidant, combining several different types of compounds can achieve a synergistic effect. For example, lactone-based, phosphine-based, phenol-based, and double-bond-based compounds are preferred.

(Colorant) The film roll of the present invention preferably contains a colorant for color adjustment, without impairing the effectiveness of the present invention.

The so-called colorant refers to a dye or pigment. In the present invention, it refers to a colorant that has the effect of changing the color tone of the liquid crystal screen to a blue hue, adjusting the yellow index, or reducing the haze.

As coloring agents, various dyes and pigments can be used, but anthraquinone dyes, azo dyes, and phthalocyanine pigments are particularly effective.

(UV Absorber) Since the film roll of this invention can also be used on the viewing side or backlight side of a polarizing plate, it may contain a UV absorber for the purpose of imparting UV absorption.

The ultraviolet absorber is not particularly limited, but examples thereof include benzotriazole-based, 2-hydroxybenzophenone-based, or phenyl salicylate-based ultraviolet absorbers.

Examples include triazoles such as 2-(5-methyl-2-hydroxyphenyl)benzotriazole, 2-[2-hydroxy-3,5-bis(α,α-dimethylbenzyl)phenyl]-2H-benzotriazole, and 2-(3,5-di-tert-butyl-2-hydroxyphenyl)benzotriazole; and benzophenones such as 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octyloxybenzophenone, and 2,2'-dihydroxy-4-methoxybenzophenone. These UV absorbers may be used alone or in combination of two or more.

The amount of UV absorber used varies depending on the type of UV absorber, usage conditions, etc., but is generally added in the range of 0.05-10% by mass relative to the base resin, preferably in the range of 0.1-5% by mass.

(Fine Particles) The film roll of the present invention preferably contains fine particles that impart smoothness to the film roll. Adding fine particles is particularly effective from the perspective of enhancing the surface smoothness of the film of the present invention, improving smoothness during winding, and preventing scratches and sticking.

As fine particles, either inorganic or organic fine particles can be used, as long as they do not impair the transparency of the resulting film roll and are heat-resistant during melting. Inorganic fine particles are preferred. These fine particles may be used alone or in combination of two or more.

By combining particles of different sizes or shapes (e.g., needle-shaped and spherical), both high transparency and smoothness can be achieved.

Among the compounds constituting the above-mentioned microparticles, silica is particularly preferably used because it has a refractive index close to that of the aforementioned cycloolefin resins, acrylic resins, or cellulose ester resins and therefore has excellent transparency (turbidity).

As specific examples of silicon dioxide, preferably used are AEROSIL (registered trademark) 200V, AEROSIL (registered trademark) R972V, AEROSIL (registered trademark) R972, R974, R812, 200, 300, R202, OX50, TT600, NAX50 (all manufactured by Japan AEROSIL Co., Ltd.), Seahoster (registered trademark) KEP-10, Seahoster (registered trademark) KEP-30, Seahoster (registered trademark) KEP-50 (all manufactured by Japan Catalyst Co., Ltd.), Silohovic (registered trademark) 100 (manufactured by Fuji Silysia Co., Ltd.), Nip Commercially available products under trade names such as Seal (registered trademark) E220A (manufactured by Nippon Silica Industries Co., Ltd.) and AdmaFine (registered trademark) SO (manufactured by Admatex Co., Ltd.).

The particle shape may be amorphous, needle-shaped, flat, or spherical without particular limitation, but spherical particles are particularly preferred because the transparency of the resulting film roll can be improved.

If the particle size is close to the wavelength of visible light, the light will be scattered and the transparency will be reduced. Therefore, it is better to be smaller than the wavelength of visible light, and more preferably less than 1/2 of the wavelength of visible light.

If the particle size is too small, smoothness may not be improved, so it is particularly preferably within the range of 80-180 nm. When the particle is an agglomerate of primary particles, the particle size refers to the size of the agglomerate. When the particle is non-spherical, the particle size refers to the diameter of a circle equal to its projected area.

The microparticles are preferably added in an amount of 0.05-10% by mass relative to the base resin, more preferably in an amount of 0.1-5% by mass.

4. Polarizing Plate A portion of the film roll of the present invention can be suitably used by being incorporated into a polarizing plate. A polarizing plate is typically composed of a polarizer (also called a "polarizing film" or "polarizer film") and transparent resin films laminated on both sides. For example, a portion of the film roll of the present invention can be incorporated into a polarizing plate as this resin film.

For example, a polarizing plate includes a polarizer layer made of a polarizer film, a polarizing plate protective film made of a resin film, and an adhesive layer provided therebetween.

(4.1) Polarizer Layer The polarizer layer is composed of at least one polarizer film. Herein, "polarizer" refers to a device that only transmits light with a specific polarization direction.

Examples of polarizing films include polyvinyl alcohol-based polarizing films and cellulose ester-based polarizing films. Polyvinyl alcohol-based resins are superior to cellulose ester-based resins in terms of transparency, optical properties, durability, etc.

Polyvinyl alcohol-based polarizing films can be dyed with iodine or with dichroic dyes.

Polyvinyl alcohol-based polarizing films can be obtained by uniaxially stretching a polyvinyl alcohol film and then dyeing it with iodine or a dichroic dye (preferably further treated with a boron compound for durability), or by dyeing a polyvinyl alcohol film with iodine or a dichroic dye and then uniaxially stretching it (preferably further treated with a boron compound for durability). The absorption axis of the polarizer layer is typically parallel to the direction of maximum stretching.

For example, ethylene-modified polyvinyl alcohol having an ethylene unit content of 1 to 4 mol %, a degree of polymerization of 2000 to 4000, and a saponification degree of 99.0 to 99.99 mol % as described in Japanese Patent Application Laid-Open Nos. 2003-248123 and 2003-342322 can be used.

The thickness of the polarizer layer is preferably 5-30 μm, and more preferably 5-20 μm to reduce the thickness of the polarizer.

(4.2) Polarizing Plate Protective Film A portion of the film roll of the present invention can be placed on at least one side of the polarizer layer (at least the side facing the liquid crystal cell), and can be used as a polarizing plate protective film or a retardation film. The surface of the polarizer layer of the polarizing plate protective film can also be subjected to the activation treatment described below.

When a portion of the film roll of the present invention is configured as a polarizing plate protective film on only one side of the polarizer layer, other optical films such as a phase difference film can be configured on the other side of the polarizer layer.

Examples of other optical films include commercially available cellulose ester films (e.g., KONICA MINOLTA TAC KC8UX, KC5UX, KC4UX, KC8UCR3, KC4SR, KC4BR, KC4CR, KC4DR, KC4FR, KC4KR, KC8UY, KC6UY, KC4UY, KC4UE, KC8UE, KC8UY-HA, KC2UA, KC4UA, KC6UA, KC8UA, KC2UAH, KC4UAH, KC6UAH, all manufactured by KONICA MINOLTA Co., Ltd.), FUJITAC T40UZ, FUJITAC T60UZ, FUJITAC T80UZ, FUJITAC TD80UL, FUJITAC TD60UL, FUJITAC TD40UL, FUJITAC R02, FUJITAC R06, the above are made by Fujisoft Co., Ltd.) etc.

The thickness of other optical films can be, for example, 5-100 μm, preferably 40-80 μm.

(4.3) Adhesive Layer The adhesive layer is a dried aqueous adhesive or UV-curable adhesive placed between a portion of the film roll (or other optical film) and the polarizer layer.

The thickness of the bonding layer may be, for example, 0.01 to 10 μm, preferably about 0.03 to 5 μm.

(Water-Based Adhesives) Examples of water-based adhesives include vinyl-based, gelatin-based, vinyl latex-based, polyurethane-based, isocyanate-based, polyester-based, and epoxy-based adhesives.

When a polyvinyl alcohol-based polarizing film is used as the polarizer layer, a water-based adhesive containing a vinyl resin is preferred from the perspective of easy adhesion, and a water-based adhesive containing a polyvinyl alcohol resin (such as a fully saponified polyvinyl alcohol aqueous solution) is more preferred.

Water-based adhesives containing polyvinyl alcohol resins may also contain water-soluble crosslinking agents such as boric acid or borax, glutaraldehyde or melamine, oxalic acid, etc.

(UV-curable adhesive) UV-curable adhesives can be either photo-radical polymerizable or photo-cationic polymerizable. Of these, photo-cationic polymerizable compositions are preferred.

The photocatalytic polymerizable composition includes an epoxy compound and a photocatalytic polymerization initiator.

Epoxy compounds are compounds having one or more, preferably two or more, epoxy groups in a molecule.

Examples of epoxy compounds include hydroepoxides (glycidyl ethers of polyols having an alicyclic ring) obtained by reacting alicyclic polyols with epichlorohydrin; aliphatic epoxy compounds such as polyglycidyl ethers of aliphatic polyols or their alkylene oxide adducts; and alicyclic epoxy compounds having one or more alicyclic epoxy groups bonded to an alicyclic epoxy group in the molecule. Epioxide compounds may be used alone or in combination of two or more.

Examples of photocatalytic polymerization initiators include aromatic diazonium salts, aromatic iodine salts, aromatic onium salts, and iron-aromatic hydrocarbon complexes.

The photocatalytic polymerization initiator may further contain additives such as cationic polymerization accelerators such as cyclobutane oxide and polyols, photosensitizers, and solvents as needed.

(4.4) Polarizing Plate Manufacturing Method The polarizing plate manufacturing method of the present invention comprises the following steps: 1) activating the surface of a polarizing plate protective film, 2) laminating a polarizer layer (polarizing film) on the activated surface of the polarizing plate protective film using a water-based adhesive or a UV-curable adhesive, and 3) drying the resulting laminate.

Regarding step 1), the surface of the polarizing plate protective film (the side that contacts the polarizer layer) is activated. This facilitates adhesion to the polarizer layer.

Specifically, through activation treatment, the siloxane bonds or ether bonds, tertiary carbon atoms, etc. of the side chains of the specific grafted polymer contained in the polarizing plate protective film are hydrophilized, thereby improving the affinity with the water-based adhesive, facilitating interaction, and facilitating the bonding of the polarizing plate protective film and the polarizer layer.

Examples of activation treatment include coma treatment, plasma treatment, and alkalization treatment, with coma treatment and plasma treatment being preferred, and coma treatment being more preferred.

The activation treatment conditions are sufficient to fully activate the siloxane bonds, ether bonds, and tertiary carbon atoms contained in the side chains of the specific grafted polymer. When the activation treatment is a corona treatment, the irradiation dose is preferably in the range of 100-1000 [W·min/m ² ], more preferably in the range of 150-900 [W·min/m ² ].

Regarding step 2) Next, a polarizer layer is deposited on the activated surface of the polarizer protective film using a water-based adhesive or a UV-curable adhesive.

Regarding step 3) Next, the resulting laminate is dried to obtain a polarizing plate.

Drying can be performed by heat drying. The drying temperature can be any temperature that fully dries the water-based adhesive or UV-curable adhesive, for example, within the range of 60-100°C.

5. Display Devices A portion of the film roll of the present invention can be suitably incorporated into a display device. Examples of such display devices include various image display devices such as liquid crystal display devices and organic EL display devices.

The following describes an example of the use of a portion of the film roll of the present invention, specifically its use as a polarizing plate protective film in polarizers and liquid crystal display devices.

(5.1) Liquid crystal display device

A specific example of the display device of the present invention is a liquid crystal display device including a liquid crystal cell and a pair of polarizing plates sandwiching the liquid crystal cell.

Figure 16 is a schematic diagram showing an example of the structure of the liquid crystal display device of the present invention.

As shown in FIG16 , the liquid crystal display device (200) includes a liquid crystal unit (220), a first polarizing plate (210) and a second polarizing plate (230) sandwiching the liquid crystal unit, and a backlight source (240).

The display mode of the liquid crystal unit (220) can be various display modes such as STN, TN, OCB, HAN, VA (MVA, PVA), IPS, etc. In order to obtain a high contrast, the VA (MVA, PVA) mode is preferred.

The first polarizing plate (210) includes a first polarizer (212), a polarizing plate protective film (211) disposed on the side of the first polarizer (212) opposite to the liquid crystal unit, and a polarizing plate protective film (213) disposed on the side of the first polarizer (212) on the liquid crystal unit side.

The second polarizing plate (230) includes a second polarizer (232), a polarizing plate protective film (231) disposed on the liquid crystal unit side of the second polarizer (232), and a polarizing plate protective film (233) disposed on the side of the second polarizer (232) opposite to the liquid crystal unit. Either the polarizing plate protective film (213) or (231) may be omitted as needed.

Therefore, at least one of the polarizing plate protective films (211) and (233) can be the resin film of the present invention.

(5.2) Other Uses

A portion of the film roll of the present invention can be used not only as a protective film for polarizing plates in liquid crystal display devices, but can also be preferably used as a protective film for image display devices with touch panels, or image display devices such as organic EL displays or plasma displays.

Furthermore, the applicable embodiments of the present invention are not limited to the above-mentioned embodiments and can be appropriately modified without departing from the spirit of the present invention.

[Example]

The present invention is further described below with reference to the following examples, but the present invention is not limited thereto. In the examples, when "parts" or "%" are used, they represent "parts by mass" or "mass %" unless otherwise specified.

[A. Production of film rolls] [A.1 Production of Film Roll No. 1]

The film is produced using the solution casting method.

(Concentrated solution preparation step [S1]) <Synthesis of Cyclic Polyolefin Polymer [P-1]>

Place 100 parts by mass of purified toluene and 100 parts by mass of methyl norbornene carboxylate into a stirring device.

Next, 25 mmol% (relative to monomer mass) of ethyl acetate-Ni dissolved in toluene, 0.225 mol% (relative to monomer mass) of tris(pentafluorophenyl)boron, and 0.25 mol% (relative to monomer mass) of triethylaluminum dissolved in toluene were placed in a stirring apparatus. The reaction was allowed to proceed at room temperature with stirring for 18 hours.

After the reaction was complete, the reaction mixture was added to an excess of ethanol to form a polymer precipitate. The polymer obtained by precipitation was purified and dried in a vacuum dryer at 65°C for 24 hours to synthesize a cyclic polyolefin polymer [P-1].

<Preparation of cyclic polyolefin solution (concentrated solution [D-1])> Place the following composition [1] in a mixing tank, stir to dissolve the components, and filter through a filter paper with an average pore size of 34 μm and a sintered metal filter with an average pore size of 10 μm to prepare a cyclic polyolefin solution (concentrated solution [D-1]).

《Composition [1]》 ・Cyclic polyolefin polymer [P-1] 25 parts by mass ・Dichloromethane 65 parts by mass ・Ethanol 10 parts by weight

<Preparation of microparticle dispersion [1]> Next, place the following composition [2] into a disperser to prepare a microparticle dispersion [1] as an additive.

《Composition [2]》 ・Microparticles (Aerosil R812: manufactured by Japan Aerosil Co., Ltd., primary average particle size: 7 nm, apparent specific gravity 50 g/L)             4 parts by mass ・Dichloromethane                                         76 parts by mass ・Ethanol                                             20 parts by mass

<Preparation of the film-forming concentrated solution [1]> 100 parts by mass of the above-mentioned cyclic polyolefin solution (concentrated solution [D-1]) and 0.75 parts by mass of the microparticle dispersion [1] were mixed to prepare the film-forming concentrated solution [1] (resin composition: cycloolefin resin: COP).

(Casting step [S2]) The film-forming concentrated solution [1] (resin composition cycloolefin resin: COP) prepared in the concentrated solution preparation step [S1] is fed to the casting die through a pressure-type quantitative gear pump through a conduit. The concentrated solution is cast from the casting die through a casting line of 1800 mm wide to a casting position on a support body formed by a rotating stainless steel endless belt driven by an endless conveyor. The concentrated solution is heated on the support body until it has self-supporting properties. The solvent is evaporated and dried until the cast film can be peeled off from the support body by a peeling roller to form a cast film.

(Peeling Step [S3]) In the casting step [S2], after the casting film is formed, the casting film is peeled off from the support in a self-supporting state by a peeling roller.

(Shrinkage Step [S4]) The film is subjected to a high-temperature treatment without maintaining its width. This increases the film density and shrinks it in the width direction by 7%.

(First Drying Step [S5]) The film was then heated on a support to evaporate the solvent. The residual solvent content in the film was measured using the following method and was found to be less than 5% by mass.

<Residual Solvent Amount Determination> Residual solvent amount was determined by mass analysis using gas chromatography as follows. Specifically, a film piece was sampled from an arbitrary area and immediately placed in a vial with a stopper to prevent evaporation of residual solvent. Next, a needle was inserted into the vial, and mass analysis was performed using a gas chromatograph (Agilent Technologies).

The residual solvent content is defined by the following formula: Residual solvent content [mass %] = {(M-N)/N} × 100 In the above formula, M is the mass [g] of the sample taken at any point during or after the production of the cast film or thin film, and N is the mass [g] of the sample after heating at 115°C for one hour.

(First Stretching Step [S6]) The film is then conveyed in a tenter stretching device and stretched in the transverse direction.

(First Cutting Step [S7]) The stretched film is cut at both ends in the width direction.

(Second Stretching Step [S8]) Similar to the first stretching step, the film is stretched using a tenter stretching device. The residual solvent content of the film, measured using the above method, is 1-5% by mass.

(Second Cutting Step [S9]) Similar to the first cutting step, the stretched film is cut at both ends in the width direction.

(First Drying Step [S10]) Similar to the first drying step, the film is heated on a support to evaporate the solvent. The residual solvent content in the film, measured using the above method, was 0.1-2% by mass.

(Third Cutting Step [S11]) Similar to the first and second cutting steps, the stretched film is cut along its width at both ends.

(Reeling Step [S12]) The film was reeled to a length of 10,000 m at a reeling speed (the linear speed of the film) of 60 m/min, with a film roll width of 2,000 mm. The film thickness during reeling was measured and found to be 40 μm.

In addition, using a winding device and TR (contact roller), the contact pressure at the periphery of the roll core during winding was adjusted to 15.2 N/m and the tension was adjusted to 40 N/m. The contact pressure at the center of the roll was adjusted to 16.0 N/m and the tension was adjusted to 40 N/m. The contact pressure at the outer periphery of the roll was adjusted to 16.0 N/m and the tension was adjusted to 40 N/m. This was implemented with a taper of 70% and a corner of 25%.

The film thickness was measured at 1612 locations using a linear delay/film thickness measurement device, RE-200L2T-Rth+Film Thickness (manufactured by Otsuka Electronics Co., Ltd.). The average height difference between the highest and lowest points of the uneven structure formed on the film surface was calculated. The measurement was performed at a lateral motion speed of 100 mm/sec.

Through the above steps, the film roll No. 1 is manufactured.

[A.2 Preparation of Film Rolls No. 2-13] In the concentrate preparation step [S1], film rolls No. 2-13 were prepared in the same manner as for film roll No. 1, except that the type of film-forming concentrate (resin composition), the roll length [m], the roll speed [m/min], the film thickness [μm], the core periphery contact pressure [N/m] and tension [N/m], the center contact pressure [N/m] and tension [N/m], and the outer periphery contact pressure [N/m] and tension [N/m] during roll preparation were changed as shown in Table 1.

[B. Calculation of the Void Layer Thickness at the Core Periphery, Center, and Outer Periphery] After storing each film roll at 40°C and 80% RH for one week, the thickness of the void layer at the core periphery, center, and outer periphery was calculated using the method described above (Example of Void Layer Calculation Method).

The following shows a specific method for calculating the thickness of the void layer at the periphery of the core using film roll No. 1.

After one week of storage, the widthwise side of film roll No. 1, centered at the position (P ₂₀ ) where the roll diameter is 20%, was photographed to obtain the aforementioned image data. This image data was then subjected to edge emphasis processing to produce the processed image used to calculate the gap layer thickness (Figure 3).

Then, starting from the center of the processed image ( _P20 ) and ending at the point at the 100th layer perpendicular to the film surface toward the outside of the roll, the radial length is measured, and the thickness of the void layer X [μm] at the periphery of the roll core is calculated using the following formula (A).

Formula (A) Void layer thickness X [μm] = [radial length [μm] - (average thickness of each thin film layer measured by a film thickness gauge [μm]) × (number of layers)] ÷ (number of layers)

Substituting the measured value, the gap layer thickness of film roll No. 1 becomes X [μm] = [4021μm - 40.00μm × 100] ÷ 100 = 0.21μm.

The thickness of the interstitial layer in the center of the roll is calculated in the same way as the thickness of the interstitial layer at the periphery of the roll core, except that the side surface is photographed with the position ( _P50 ) that constitutes 50% of the roll diameter in the width direction as the center, and the center of the processed image ( _P50 ) is used as the starting point.

The thickness of the void layer at the outer periphery of the roll is calculated in the same way as the thickness of the void layer at the outer periphery of the core, except that the side surface is photographed with the position ( _P80 ) of the processed image as the center, which is ₈₀ % of the roll diameter in the width direction, as the starting point.

[C. Evaluation] [C.1 Evaluation Based on Tape Transfer] (Evaluation Method) After one week of storage, the film rolls were allowed to slacken. A tachometer was used to measure the length of the film displayed on the take-up device from the core to the film's core. Based on the following evaluation criteria, tape transfer was evaluated for visible tape deformation in the width direction. The results are shown in Table 1.

(Evaluation Criteria) ○: Tape transfer occurs only on the portion of the tape that is less than 20 meters from the core. △: Tape transfer occurs on the portion of the tape that is more than 20 meters but less than 50 meters from the core. ×: Tape transfer occurs only on the portion of the tape that is more than 50 meters from the core.

[C.2 Evaluation of Chain Deformation] (Evaluation Method) After one week of storage, the film rolls were allowed to slacken. The position displayed on each take-up device in the longitudinal direction of the film was measured using a tachometer. The length of the film at which chain deformation occurred was evaluated based on the following evaluation criteria. A value of △ or higher on the following evaluation criteria was considered to be non-problematic. The results are shown in Table I.

(Evaluation Criteria) ◎: The film length at which chain deformation occurred was less than 10 m. ○: The film length at which chain deformation occurred was 10 m or more and less than 50 m. △: The film length at which chain deformation occurred was 50 m or more and less than 200 m. ×: The film length at which chain deformation occurred was 200 m or more.

[D. Summary] As can be seen from the conditions and evaluation results shown in Table I, the embodiment of the present invention scored higher in terms of tape transfer and chain deformation compared to the comparative example, and was generally superior.

1,1a: Stirring device (stirring tank)

2: Casting die nozzle

3: Support body (ring belt, roller)

3a,3b: Roll

4: Peeling Roller

5: Casting film

6: Drying device

7: Stretching device (tenter stretching device, oblique stretching device)

8: Cutting part

9: Extension device (tenter extension device)

10: Cutting part

11: Drying device

12: Cutting part

13: Rolling device

14: Extruder

15: Casting die nozzle

16: Casting drum, support body

16a: Contact Roller

17: Cooling drum

19: Extension device (tenter extension device)

20: Cutting part

21: Extension device (tenter extension device)

22: Cutting part

23: Rolling device

30: Film Roll

31:Film

32: Roll

33: Contact Roller

40: Extension device (tenter extension device)

42: Clamps

46: Cover

48: Ring Chain

50: Drive sprocket

52: Driven sprocket

54:Guide rails

56: Open component

60: Total Reflection Mirror

61: Semi-mirror

62: Telecentric lens

63: High-brightness line lighting

64: Monochrome Line Sensor Camera

80: Temperature distribution sensor

101: Nozzle fixing part

102: Spray nozzle

103: Casting film

104: End nozzle

105: Central nozzle

106: Clamp cover

200: LCD display device

210: 1st polarizing plate

211: Polarizing plate protective film disposed on the surface of the first polarizer opposite to the liquid crystal cell side

212: 1st polarizer

213: Polarizer protective film disposed on the liquid crystal cell side of the first polarizer

220: Liquid crystal unit

230: 2nd polarizing plate

231: Polarizer protective film placed on the liquid crystal cell side of the second polarizer

232: Second polarizer

233: Polarizing plate protective film disposed on the side of the second polarizer opposite to the liquid crystal cell side

240: Backlight

A: The periphery of the winding core

B: Center of the roll

C: Roll outer edge

F: Film

H _A ,H _B : width

Q: Thermocouple, infrared (IR) heater

E: Camera equipment

R: Rolling core

TD: width direction of the film roll

U: Imaging unit

P: Any point on the longitudinal side of the film roll

S: Surface of the film roll being measured (lateral surface in the width direction)

S ₀ : core surface

_S1 : Film layer attached to the surface of the roll core

_S2 : The film layer that forms the boundary between the periphery of the core and the center of the roll

_S3 : The film layer that forms the boundary between the center of the roll and the outer periphery of the roll

_S4 : The outermost film layer of the film roll

P ₂₀ : 20% of the roll diameter

P ₅₀ : 50% of the roll diameter

P ₈₀ : 80% of the roll diameter

Figure 1 is a schematic diagram showing the positional relationship between the widthwise side of the film roll and the imaging device.

Figure 2 is a schematic diagram of the film roll when viewed from a plane perpendicular to the width of the film roll.

[Figure 3] is a processed image used to calculate the thickness of the void layer.

Figure 4 is a simplified conceptual diagram of a portion of the widthwise side of a film roll, used to illustrate the core periphery, roll center, and roll outer periphery.

[Figure 5] is a schematic diagram of the internal structure of the camera unit.

[Figure 6] is a schematic diagram of the system structure of the imaging device.

[Figure 7] is a flow chart showing the manufacturing steps of the solution casting method.

[Figure 8 is a schematic diagram of a device for producing thin films using solution casting.]

Figure 9 is a top view schematically showing the internal structure of the tenter stretching device.

Figure 10 is a top view of the tenter extension device with the cover removed.

Figure 11 is a schematic diagram showing the nozzle and heater installation in the three zones of the stenter stretching device, viewed from the front.

[Figure 12] is a side view of the three areas within the stenter stretching device.

Figure 13 is a schematic diagram showing the film rolling process and a cross-section of the film roll of the present invention after rolling.

Figure 14 is a flow chart showing the manufacturing steps of the melt casting method.

[Figure 15] is a schematic diagram of a device for producing thin films using the melt casting method.

[Figure 16] is a schematic diagram showing an example of the structure of the liquid crystal display device of the present invention.

No. 30: Film roll E: Imaging device R: Core TD: Width direction of film roll U: Imaging unit P: Any point on the side of the length direction of film roll S ₀ : Core surface S ₄ : Outermost film layer of film roll

Claims (7)

A film roll having no knurled portion, characterized in that when the thickness of the gap layer between adjacent films at the peripheral portion of the roll core measured on the side portion in the width direction of the film roll is set to X [μm] and the thickness of the gap layer between adjacent films at the peripheral portion of the roll core is set to Y [μm], the aforementioned X and the aforementioned Y satisfy the relationship of the following formula (1): Formula (1): Y < X. The film roll of claim 1, wherein the aforementioned X [μm] and the aforementioned Y [μm] satisfy the relationship of the following formula (2) and the following formula (3), formula (2): 0.05 < Y < 0.50, formula (3): 1 < (X/Y) < 3. A method for manufacturing a film roll, which is a method for manufacturing a film roll without a knurled portion, is characterized in that the thickness of the gap layer between adjacent films at the peripheral portion of the roll core measured on the side portion in the width direction of the film roll is set to X [μm], and the thickness of the gap layer between adjacent films at the peripheral portion of the roll is set to Y [μm], and the above-mentioned X and the above-mentioned Y are adjusted to satisfy the relationship of the following formula (1): Formula (1): Y < X. As in claim 3, the method for manufacturing a thin film roll, wherein the aforementioned X [μm] and the aforementioned Y [μm] are adjusted to satisfy the relationship of the following formula (2) and the following formula (3), Formula (2): 0.05 < Y < 0.50, Formula (3): 1 < (X/Y) < 3. The method for manufacturing a film roll according to claim 3 or 4, wherein the film contact pressure at the peripheral portion of the roll core is adjusted to within a range of 2 to 30 [N/m], the film contact pressure at the central portion of the roll is adjusted to within a range of 3 to 40 [N/m], and the film contact pressure at the outer peripheral portion of the roll is adjusted to within a range of 5 to 55 [N/m]. A polarizing plate characterized by comprising a portion of the film roll as claimed in claim 1 or 2. A display device is characterized by comprising a portion of a film of the film roll as claimed in claim 1 or 2.