TWI885575B - Optical laminate, optical laminate roll and method for manufacturing polarizing plate - Google Patents

Abstract

The subject of this case is to provide an optical laminate, which suppresses the peeling failure of the surface protective film during the manufacturing step despite containing a polarizer with a high degree of orientation. The solution is as follows: the optical laminate of the embodiment of the present invention is in the shape of a long strip, and the optical laminate has a polarizer, a protective layer arranged on one side of the polarizer, and a surface protective film temporarily attached to the other side of the polarizer in a removable manner. The indentation hardness of the polarizer is above 0.65GPa, and the optical laminate has a crack of 50μm~5000μm formed at the end of the width direction of the polarizer, and the extension direction of the crack is 30°~150° relative to the strip direction.

Description

Optical laminate, optical laminate roll and method for manufacturing polarizing plate

The present invention relates to a method for manufacturing an optical laminate, an optical laminate roll and a polarizing plate.

In image display devices (such as liquid crystal display devices, organic EL display devices, and quantum dot display devices), a polarizing plate is often disposed on at least one side of a display panel due to the image forming method. In recent years, there has been an increasing demand for narrow frame (or so-called frameless display depending on the situation) image display devices, and the need to prevent fading (end discoloration) of the ends of the polarizing plate is increasing. In order to suppress or prevent end discoloration of the polarizing plate, a technology has been proposed to improve the durability of the polarizer, which substantially controls the optical properties of the polarizing plate, in a high temperature and high humidity environment. As such a technology, for example, a polarizer with a high degree of orientation is being studied.

In addition, a polarizing plate (or an optical film including a polarizing plate) is typically produced by laminating polarizers and various optical functional layers that meet the purpose. For at least a portion of the lamination, a so-called roll-to-roll operation is often used. In addition, when lamination is performed in multiple stages, the widthwise ends of the laminate are sometimes slit at predetermined stages. Furthermore, when lamination is performed in multiple stages, a surface protection film called step SPV is often temporarily attached to the laminate in a removable manner to protect the laminate, which is a precursor of the polarizing plate (or an optical film including a polarizing plate), from damage and contamination.

When a polarizer with a high degree of orientation as described above is subjected to lamination and slitting, cracks may be formed at the ends of the polarizer in the width direction due to the slitting. If the surface protection film is peeled off from such a polarizer with a high degree of orientation and cracks, at least a portion of the polarizer may be peeled off from the laminated body including the polarizer. Prior Art Literature Patent Literature

Patent document 1: Japanese Patent Publication No. 2020-160231 Patent document 2: Japanese Patent Publication No. 2020-001382

Problem to be solved by the invention The present invention is made to solve the above-mentioned previous problems, and its main purpose is to provide an optical laminate that suppresses poor peeling when peeling off the surface protection film in the manufacturing step despite including a polarizer with a high degree of orientation.

Means for solving the problem [1] The embodiment of the present invention provides an optical laminate, which is in the shape of an elongated strip, and the optical laminate has a polarizer, a protective layer provided on one side of the polarizer, and a surface protective film temporarily attached to the other side of the polarizer in a removable manner. The indentation hardness of the polarizer is greater than 0.65 GPa, and the optical laminate has a crack of 50 μm to 5000 μm formed at the end of the width direction of the polarizer, and the extension direction of the crack is 30° to 150° relative to the strip direction. [2] In the above [1], the indentation elastic modulus of the above polarizer is less than 9.5 GPa. [3] In the above [1] or [2], the orientation function of the above polarizer is greater than 0.30. [4] According to another embodiment of the present invention, an optical laminate roll is provided. The optical laminate roll is formed by winding the optical laminate of any one of the above [1] to [3]. [5] According to another embodiment of the present invention, a method for manufacturing a polarizing plate is provided. The manufacturing method comprises the following steps: a step of conveying the optical laminate of any one of [1] to [3] or the optical laminate roll of [4] along the longitudinal direction of the optical laminate; and a step of peeling off the surface protection film while conveying the optical laminate; the manufacturing method peels off the surface protection film when the extension direction of the crack is at an angle of 30° or more and less than 180° relative to the conveying direction. [6] In the above [5], the extension direction of the crack is greater than 0° and less than 30° relative to the transport direction of the optical laminate, and the manufacturing method includes the step of rewinding the optical laminate so that the extension direction of the crack becomes an angle of greater than 30° and less than 180° relative to the transport direction.

Effect of the invention According to the implementation method of the present invention, an optical laminate can be realized which suppresses poor peeling when peeling off the surface protection film in the manufacturing step despite including a polarizer with a high degree of orientation.

Hereinafter, representative embodiments of the present invention will be described with reference to the accompanying drawings, but the present invention is not limited to these embodiments. In addition, for the convenience of viewing, the accompanying drawings are schematically depicted and do not accurately reflect actual lengths, widths, thicknesses, angles, ratios, etc.

A. Overall structure of optical laminate Fig. 1(a) is a schematic top view of an optical laminate of an embodiment of the present invention; Fig. 1(b) is a schematic cross-sectional view of the optical laminate of Fig. 1(a) along line B-B. Fig. 2(a) is a schematic top view of an example of the relationship between the direction of extension of the end crack of the polarizer and the long strip direction and the transport direction of the optical laminate in an embodiment of the present invention; Fig. 2(b) is a schematic top view of another example of the relationship. The optical laminate 100 shown in the figure is in the shape of a long strip extending in the vertical direction of the attached figure. Such a long strip optical laminate can be rolled into a roll. Therefore, the optical laminate can be rolled into a roll to form an optical laminate roll. The optical laminate 100 has a polarizer 11, a protective layer 12 provided on one side of the polarizer 11, and a surface protection film 20 temporarily and releasably attached to the other side of the polarizer 11. In one embodiment, as shown in the figure, the optical laminate 100 has a protective layer 12, a polarizer 11, and a surface protection film 20 in order from the top. In another embodiment, the optical laminate may also have a surface protection film, a polarizer, and a protective layer in order from the top. A crack 50 is formed at the end of the polarizer 11 in the width direction. The cracks can typically be formed by the opening in the previous step. In other words, the ends of the optical laminate in the embodiment of the present invention are opened in the width direction. The size (length) of the crack is 50μm~5000μm, and the extension direction of the crack is 30°~150° relative to the longitudinal direction. According to the embodiment of the present invention, even if cracks are formed at the ends of a polarizer with a higher degree of orientation as described later, it is possible to significantly suppress poor peeling by controlling the direction in which the cracks extend. In this specification, "poor peeling" refers to the phenomenon that when peeling a surface protection film from an optical laminate, not only the surface protection film is peeled off, but also at least a portion of the polarizer is peeled off. Since the cracks in the embodiment of the present invention can be formed by the slitting in the previous step as described above, the direction of crack extension is maintained within a predetermined range. For example, more than 90% of the cracks extend in a direction within a range of ±20°, preferably ±10°, and more preferably ±5° relative to the center value of the direction (the average value of the angle between the extension direction of all cracks and the strip direction). Therefore, by adjusting the slitting conditions, the direction of crack extension can be controlled. In addition, as long as the extension direction of the crack does not deviate from the range of 30° to 150° relative to the strip direction, the deviation within this range is not a problem in the embodiment of the present invention. For example, when randomly inspecting the end face of an optical laminate cut out to a length of 10 cm, if the extension direction of all identified cracks is within the range of 30° to 150° relative to the strip direction, even if the extension direction of the crack deviates significantly (for example, more than ±20°) from the center value of the above direction, peeling defects can be suppressed. In this manual, unless otherwise specified, the direction of crack extension is the direction when the optical laminate is observed from the top.

The size (length) of the crack is preferably 50 μm to 3500 μm, more preferably 50 μm to 2000 μm. When the size of the crack is relatively small (for example, less than 50 μm), the problem of poor peeling does not usually occur. Since the upper limit of the size of the crack formed by the slitting in the previous step is sufficiently smaller than the remaining amount required for the subsequent step (the portion ultimately removed by the slitting), the specific upper limit has no technical significance in essence. If the extension direction of the crack is within the above range (30° to 150° relative to the strip direction), the effect of the implementation method of the present invention can be reflected. The extension direction of the crack may be, for example, 35° or more, 40° or more, 45° or more, 50° or more, 60° or more, or 70° or more. On the other hand, the extension direction of the crack may be, for example, 145° or less, 140° or less, 135° or less, 130° or less, 120° or less, or 110° or less.

Referring to FIG. 2(a) and FIG. 2(b), the relationship between the direction of crack extension and the long strip direction and the transport direction of the optical laminate is specifically described. As described above, the extension direction (angle θ) of the crack 50 is 30° to 150° relative to the long strip direction of the optical laminate. The long strip direction of the optical laminate substantially corresponds to the transport direction of the optical laminate (arrow 30 in the figure). As shown in FIG. 2(a), when the angle θ is a sharp angle, the direction of crack 50 extension is positive relative to the transport direction 30; as shown in FIG. 2(b), when the angle θ is a blunt angle, the direction of crack 50 extension is opposite to the transport direction 30. When the angle θ is 90° (right angle), the direction in which the crack 50 extends is a direction (width direction) perpendicular to the conveying direction.

In an embodiment of the present invention, the indentation hardness of the polarizer 11 is greater than 0.65 GPa. Furthermore, the indentation elastic modulus of the polarizer 11 is typically less than 9.5 GPa, and the orientation function is typically greater than 0.30. When such a harder and more highly oriented polarizer is used, the effect of the embodiment of the present invention is remarkable. Specifically, even when cracks are formed in such a more highly oriented polarizer, peeling defects when peeling the surface protection film from the optical laminate can be significantly suppressed.

The following describes a method for forming a crack at the end of a polarizer. As described above, the crack can be formed by the slitting in the previous step (by cutting and removing the end in the width direction). As described above, by adjusting the slitting conditions, the direction in which the crack extends can be controlled. As slitting conditions, for example, the taper angle of the cutting blade of the slitting knife, the conveying tension during slitting, the pulling tension of the end of the slit film, the state of the slitting knife, and the overlapping length of the slitting knife can be cited. The following describes an example of a specific step of slitting.

FIG3(a) is a diagram obtained by observing the cutting knife and the receiving knife of the slitting knife that can be used in the embodiment of the present invention from the side; FIG3(b) is an explanatory diagram showing the situation of cutting the optical laminate using the slitting knife. As shown in FIG3(a) and FIG3(b), the optical laminate 100 is cut using the cutting knife 1 and the receiving knife 2 for supporting the optical laminate 100. The cutting knife 1 and the receiving knife 2 are supported in a manner such that the tips of the cutting knife partially overlap each other. The overlapping length L is set, for example, according to the thickness of the optical laminate to be cut. The overlapping length L preferably satisfies the relationship of d≤L≤d+0.15mm relative to the thickness d (mm) of the optical laminate. The overlap length L is, for example, 0.2 mm to 2.0 mm. The cutting blade shaft 1a and the receiving blade shaft 2a are arranged in parallel with the optical laminate 100. By passing the optical laminate 100 between the cutting blade 1 and the receiving blade 2, the ends of the optical laminate 100 in the width direction are slit (cut) in a strip shape. The conveying speed of the optical laminate 100 can be set, for example, in the range of 10 m/min to 50 m/min.

The receiving knife 2 is not fixed to the receiving knife shaft 2a, but rotates freely (for example, in the counterclockwise direction). The cutting knife 1 is mounted on the cutting knife shaft 1a by a spring force in a manner that it can contact the receiving knife 2 through any appropriate supporting mechanism, and rotates integrally with the cutting knife shaft 1a (for example, in the clockwise direction). The contact pressure between the cutting knife and the receiving knife is set, for example, according to the shape of the knife described later. The contact pressure between the cutting knife and the receiving knife is, for example, 2.0N~10.0N. The rotation speed of the cutting knife should be the same as the conveying speed of the optical laminate or faster than the conveying speed of the optical laminate. Specifically, the rotation speed of the cutting blade is set to, for example, 90% to 130% of the conveying speed of the polarizing film laminate, preferably 95% to 130%, and further preferably 98% to 130%.

The outer diameter of the cutting knife and the receiving knife is, for example, 90.0 mm to 110.0 mm. Since the receiving knife 2 supports the optical multilayer body 100 at the cutting position, as shown in the figure, the wider blade tip is used. In the illustrated example, one side surface 1b of the cutting knife 1 is set as a vertical surface, and the other side surface 1c is set as a conical surface. The taper angle of the conical surface can be, for example, 35° to 85°, and can also be, for example, 40° to 60°, and can also be, for example, 60° to 85°. By adjusting the taper angle, the extension direction of the crack can be controlled. In addition, the cut pieces are removed, for example, by rolling or suction.

In the illustrated example, the relatively thicker portion of the tapered dicing blade 1 that gradually narrows toward the blade tip is located on the protective layer 12 side, the relatively thinner portion of the dicing blade 1 is located on the surface protection film 20 side, and the blade tip of the dicing blade 1 is in contact with the optical laminate 100, but the optical laminate may be reversed upside down. In other words, the relatively thicker portion of the dicing blade 1 may be located on the surface protection film 20 side, the relatively thinner portion of the dicing blade 1 may be located on the protective layer 12 side, and the blade tip of the dicing blade 1 may be in contact with the optical laminate 100.

The transport tension of the optical laminate during slitting is preferably 220 N or more, more preferably 270 N or more, further preferably 300 N or more, and particularly preferably 320 N or more. If the transport tension is within such a range, the extension direction of the crack can be adjusted to the desired direction by adjusting the taper angle of the cutting knife combined with the slitting knife. In addition, the upper limit of the transport tension can be, for example, 400 N.

B. Polarizer As described above, the indentation hardness of the polarizer 11 is 0.65 GPa or more. The indentation hardness of the polarizer is preferably 0.65 GPa to 0.80 GPa, more preferably 0.66 GPa to 0.76 GPa, further preferably 0.67 GPa to 0.74 GPa, and particularly preferably 0.68 GPa to 0.72 GPa. That is, the polarizer used in the embodiment of the present invention is very hard. Such a polarizer can significantly suppress end discoloration in a high temperature and high humidity environment. As a result, such a polarizer can be applied to image display devices with narrow frames (so-called frameless depending on the situation). As described above, when such a harder polarizer is used, the effect of the embodiment of the present invention is remarkable.

The compression modulus of elasticity of the polarizer is typically below 9.5 GPa, preferably 7.5 GPa to 9.4 GPa, more preferably 8.0 GPa to 9.3 GPa, further preferably 8.2 GPa to 9.2 GPa, and particularly preferably 8.5 GPa to 9.2 GPa. Although the polarizer used in the embodiment of the present invention is very hard as described above, the compression modulus of elasticity is relatively low. Such a polarizer is easy to stretch while maintaining the advantages of hardness (suppressing end discoloration), so it is easy to be thinned.

The indentation hardness and indentation elastic modulus can be measured by the nanoindentation method using an indentation tester (typically a nanoindenter). More specifically, the indentation hardness is calculated by the following formula based on the maximum load Pmax obtained by pressing the probe (indenter) on the surface of the polarizer to be measured from the displacement-load hysteresis curve and the contact projection area A between the indenter and the polarizer. Indentation hardness (GPa) = Pmax/A In addition, the indentation elastic modulus is calculated by the following formula based on the contact projection area A, the slope of the tangent to the unloading curve of the displacement-load hysteresis curve (contact rigidity) S, and pi. Indentation elastic modulus (GPa) = ( /2)×(S/ )

The orientation function of the polarizer is preferably greater than 0.30, more preferably greater than 0.35, further preferably greater than 0.37, and particularly preferably greater than 0.40. If the orientation function of the polarizer is within such a range, it is possible to easily make the indentation elastic modulus and indentation hardness within the above-mentioned desired range. The upper limit of the orientation function of the polarizer may be, for example, 0.50. For the orientation function (y), for example, a Fourier transform infrared spectrometer (FT-IR) is used, and polarized light is used as the measurement light, and the orientation function (y) is obtained by attenuated total reflection spectroscopy (ATR). Specifically, the measurement is carried out in a state where the extension direction of the polarizer is parallel and perpendicular to the polarization direction of the measurement light, and the intensity of 2941 cm ^-1 of the obtained absorbance spectrum is used to calculate the orientation function (y) by the following formula. Here, the intensity I is the value of 2941cm ^-1 /3330cm ^-1 with 3330cm ^-1 as the reference peak. In addition, y = 1 is completely oriented, and y = 0 is random. In addition, the peak at 2941cm ^-1 is considered to be the absorption caused by the vibration of the main chain (-CH ₂ -) of PVA in the polarizer. y = (3 < cos ² θ > -1) / 2 = (1-D) / [c (2D + 1)] = -2 × (1-D) / (2D + 1) Where, c = (3cos ² β-1) / 2, in the case of the vibration of 2941cm ^-1 , β = 90°. θ: Angle of the molecular chain relative to the stretching direction β: Angle of the transition dipole moment relative to the molecular chain axis D = (I _⊥ ) / (I _// ) (In this case, the more oriented the PVA molecules are, the larger D becomes) I _⊥ : Absorption intensity when the polarization direction of the measured light is perpendicular to the stretching direction of the polarizer I _// : Absorption intensity when the polarization direction of the measured light is parallel to the stretching direction of the polarizer

As a polarizer, any appropriate structure can be adopted as long as it has the above-mentioned characteristics. Typically, the polarizer is composed of a polyvinyl alcohol (PVA) resin film containing a dichroic substance (such as iodine). Examples of PVA resins include polyvinyl alcohol, partially formalized polyvinyl alcohol, ethylene-vinyl alcohol copolymer, and ethylene-vinyl acetate copolymer partially saponified products.

The PVA resin preferably includes an acetyl-modified PVA resin. With such a structure, a polarizer having a desired mechanical strength can be obtained. When the entire PVA resin is set to 100 wt %, the blending amount of the acetyl-modified PVA resin is preferably 5 wt % to 20 wt %, and more preferably 8 wt % to 12 wt %. If the blending amount is within such a range, a polarizer having a more excellent mechanical strength can be obtained.

The polarizer preferably contains iodide or sodium chloride (sometimes collectively referred to as halides). As iodides, for example, potassium iodide, sodium iodide, and lithium iodide can be cited. The content of halides in the polarizer is preferably 5 to 20 parts by weight, and more preferably 10 to 15 parts by weight, relative to 100 parts by weight of the PVA-based resin. In the manufacturing method described below, the halides are compounded in a coating liquid that forms a PVA-based resin layer as a precursor of the polarizer, and can ultimately be introduced into the polarizer. By introducing the halides into the polarizer, the orientation of the PVA molecules in the polarizer can be improved, thereby achieving the desired orientation function and indentation hardness. Furthermore, it is possible to realize a polarizer having excellent optical properties (typically, having both a high degree of polarization and a high single-body transmittance).

The iodine concentration of the polarizer is preferably 4 wt% to 10 wt%, more preferably 5.5 wt% to 8 wt%. In this specification, "iodine concentration" refers to the total amount of iodine contained in the polarizer. More specifically, in the polarizer, iodine exists in the form of ^I- , _I2 , _I3- , ^{I5- ,} etc., _and the iodine concentration in this specification refers to the concentration of iodine including all these forms. The iodine concentration is calculated, for example, from the intensity of fluorescent X-rays based on fluorescent X-ray analysis and the thickness of the film (polarizer).

The thickness of the polarizer is preferably 1 μm to 8 μm, more preferably 2 μm to 7 μm, and further preferably 3 μm to 6 μm. If the thickness of the polarizer is within this range, curling during heating can be well suppressed, and good appearance durability during heating can be obtained.

The polarizer preferably shows absorption dichroism at any wavelength between 380nm and 780nm. The single transmittance of the polarizer is, for example, 41.0% to 45.0%, preferably 41.5% to 43.5%, and more preferably 42.0% to 43.0%. The polarization degree of the polarizer is preferably above 97.0%, more preferably above 99.0%, and further preferably above 99.9%. According to the implementation mode of the present invention, even if the single transmittance is in the above range, the polarization degree can be maintained within such a range.

A polarizer can be typically obtained using a laminate of a resin substrate and a PVA-based resin layer. Specific examples of polarizers obtained using a laminate include a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate. A polarizer obtained by using a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate is produced, for example, by applying a PVA-based resin solution to the resin substrate, drying it, and forming a PVA-based resin layer on the resin substrate to obtain a laminate of the resin substrate and the PVA-based resin layer; and stretching and dyeing the laminate to make the PVA-based resin layer into a polarizer. In this embodiment, it is ideal to form a polyvinyl alcohol-based resin layer containing a halogenated compound and a polyvinyl alcohol-based resin on one side of the resin substrate. The stretching typically includes immersing the laminate in an aqueous solution of boric acid for stretching. Furthermore, the stretching may include, as required, stretching the laminate in the air at a high temperature (for example, above 95°C) before stretching in an aqueous boric acid solution. In addition, in the present embodiment, the laminate is preferably subjected to a dry shrinking treatment, wherein the laminate is heated while being transported in the length direction, thereby shrinking the laminate in the width direction by more than 2%. Typically, the manufacturing method of the present embodiment includes sequentially subjecting the laminate to an air-assisted stretching treatment, a dyeing treatment, an underwater stretching treatment, and a dry shrinking treatment. By introducing the auxiliary stretching, the crystallinity of the PVA can be improved even when the PVA is coated on a thermoplastic resin, and higher optical properties can be achieved. In addition, by improving the orientation of PVA in advance, it is possible to prevent the orientation of PVA from decreasing or dissolving when immersed in water in the subsequent dyeing and stretching steps, and to achieve higher optical properties. Moreover, when the PVA-based resin layer is immersed in a liquid, the disorder of the orientation of the polyvinyl alcohol molecules and the decrease in orientation can be suppressed compared to the case where the PVA-based resin layer does not contain halides. As a result, the optical properties of the polarizer obtained by the treatment steps of immersing the laminate in a liquid such as dyeing treatment and underwater stretching treatment can be improved. Furthermore, the laminate is shrunk in the width direction by a drying and shrinking treatment, thereby improving the optical properties. The obtained resin substrate/polarizer laminate can be used directly (i.e., the resin substrate can be used as a protective layer of the polarizer), or it can be used as any appropriate protective layer that meets the purpose on the peeling surface after the resin substrate is peeled off from the resin substrate/polarizer laminate or on the surface opposite to the peeling surface. The details of the manufacturing method of such a polarizer are described in, for example, Japanese Patent Publication No. 2012-73580 and Japanese Patent No. 6470455. The entire description of these publications is cited in this specification as a reference.

The above-mentioned harder and more oriented polarizer can be obtained by stretching at a higher temperature and a higher stretching ratio than before in an air-assisted stretching process. Ideally, the stretching temperature in the air-assisted stretching process is above 140°C and the stretching ratio is above 2.5 times. The stretching temperature is more preferably above 145°C, further preferably above 150°C, and particularly preferably above 155°C. The upper limit of the stretching temperature can be, for example, 170°C. The stretching ratio is more preferably 2.5 times to 3.2 times, further preferably 2.6 times to 3.1 times, and particularly preferably 2.7 times to 3.0 times. In the conventional method for manufacturing thin polarizers, typically, an air-assisted stretching treatment is performed at a temperature above the glass transition temperature (Tg) of the thermoplastic resin substrate (typically polyethylene terephthalate (PET)) + 15°C and at a temperature that can suppress the rapid crystallization of the PVA-based resin. Such a stretching temperature is specifically around 130°C. In addition, the stretching ratio of the air-assisted stretching treatment in the conventional method for manufacturing thin polarizers is usually set to 2.0 times to 2.4 times. Since the total stretching ratio of the air-assisted stretching treatment and the underwater stretching treatment is preferably constant (for example, 5.5 times to 6.0 times), when stretching is performed at around 130°C, when the stretching ratio is greater than 2.5 times, the stretching ratio of the underwater stretching treatment needs to be reduced. This is because sometimes the reduced orientation of iodine leads to reduced optical properties. In addition, at a temperature greater than 130°C, as mentioned above, it is difficult to suppress the rapid crystallization of the PVA resin and to control the elongation. The inventors have found that by performing an in-flight auxiliary stretching treatment at a high temperature and a high stretching ratio that has not been implemented before, a relatively hard and thin polarizer can be realized while maintaining the desired optical properties (having both high monomer transmittance and high polarization degree).

C. Protective layer The protective layer 12 is composed of any appropriate resin film that can be used as a protective film for the polarizer. Representative materials constituting the resin film include cellulose resins such as triacetylcellulose (TAC), cycloolefin resins such as polynorthene, (meth)acrylic resins, polyester resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polyolefin resins such as polyethylene, and polycarbonate resins. As a representative example of a (meth)acrylic resin, a (meth)acrylic resin having a lactone ring structure can be cited. (Meth) acrylic resins having a lactone ring structure are described in, for example, Japanese Patent Publication No. 2000-230016, Japanese Patent Publication No. 2001-151814, Japanese Patent Publication No. 2002-120326, Japanese Patent Publication No. 2002-254544, and Japanese Patent Publication No. 2005-146084. These publications are cited in this specification as references. From the perspective of ease of special-shaped processing, cellulose resins are preferred, and TAC is more preferred. From the perspective of obtaining a polarizing plate with low moisture permeability and excellent durability, cycloolefin resins and (meth) acrylic resins are preferred.

The protective layer 12 may be subjected to surface treatment as required. Examples of surface treatment include hard coating, anti-reflection, anti-sticking, and anti-glare. Furthermore, or alternatively, the protective layer 12 may be subjected to treatment to improve visibility when viewed through polarized sunglasses (representatively, providing (elliptical) circular polarization function and providing ultra-high phase difference) as required. By performing such treatment, excellent visibility can be achieved even when the display screen is viewed through a polarized lens such as polarized sunglasses. Therefore, the optical multilayer body can also be preferably used in image display devices that can be used outdoors.

The thickness of the protective layer 12 is preferably 10 μm to 80 μm, more preferably 12 μm to 40 μm, and further preferably 15 μm to 35 μm. In addition, when the surface treatment is applied, the thickness of the protective layer includes the thickness of the surface treatment layer.

D. Surface protection film The surface protection film 20 typically has a substrate and an adhesive layer, and is temporarily attached to the polarizer in a removable manner by means of the adhesive layer. The substrate can be composed of any appropriate material. As a constituent material, from the viewpoints of inspection and management, a material having isotropy or nearly isotropy can be used. As specific examples of constituent materials, transparent polymers such as polyester resins such as polyethylene terephthalate film, cellulose resins, acetate resins, polyether sulfide resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, and acrylic resins can be cited. Among these, polyolefin resins are preferred. The substrate can be a laminate of one or more constituent materials, or a stretched film.

As polyolefin resins, for example, homopolymers of olefin monomers and copolymers of olefin monomers can be cited. Specific examples of polyolefin resins include polyethylene resins such as high-density polyethylene (HDPE), medium-density polyethylene, low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE); polypropylene; propylene copolymers such as block, random, and graft copolymers with ethylene as a copolymer component; reactor-type TPO; ethylene copolymers such as ethylene-vinyl acetate copolymers, ethylene-methyl acrylate copolymers, ethylene-ethyl acrylate copolymers, ethylene-butyl acrylate copolymers, ethylene-methacrylic acid copolymers, and ethylene-methyl methacrylate copolymers, and the like. Among these, polyethylene resins are preferred.

The thickness of the substrate can be appropriately set according to the purpose. The thickness of the substrate is, for example, 200 μm or less, preferably 10 to 150 μm.

Any appropriate adhesive can be used as the adhesive constituting the adhesive layer. The thickness (dry film thickness) of the adhesive layer is preferably 1 μm to 100 μm, more preferably 5 μm to 50 μm. If the thickness is within this range, the desired peeling force can be achieved for the polarizer.

If necessary, a release treatment layer may be provided on the surface of the substrate opposite to the adhesive layer. The release treatment layer may be, for example, a surface treatment layer based on a low adhesion material such as polysilicon, long chain alkyl, or fluorine.

A commercially available product can be used as the surface protection film. As a commercially available product, TORETEC 7832C #30 manufactured by TORAY ADVANCED FILM CO., LTD. can be preferably used.

The peeling force between the polarizer and the surface protection film is preferably 0.01 N/10 mm to 5.0 N/10 mm, more preferably 0.01 to 0.5 N/10 mm, and further preferably 0.035 to 0.1 N/10 mm. The peeling force can be measured based on JIS Z 0237, for example.

The initial peeling force when peeling the surface protection film may be, for example, 2.0 N or less, 1.5 N or less, 1.2 N or less, 1.0 N or less, 0.8 N or less, 0.7 N or less, 0.6 N or less, or 0.5 N or less. The lower limit of the initial peeling force may be, for example, 0.05 N. If the initial peeling force is within such a range, the surface protection film can be easily peeled off, and peeling defects can be significantly suppressed. The initial peeling force can be measured, for example, based on JIS Z 0237. Specifically, a pick-up tape is attached to the surface of the surface protection film of the test sample (optical laminate) along the peeling direction, and the peeling force when the pick-up tape is used to pull the film in a 90° direction can be measured as the initial peeling force. The width of the pick-up tape can be, for example, 10 mm, and the pulling speed can be, for example, 300 mm/minute.

E. Method for manufacturing polarizing plate The optical laminate of the embodiment of the present invention described in the above items A to D is an intermediate of a polarizing plate or an intermediate of an optical film including a polarizing plate. In other words, a polarizing plate or an optical film including a polarizing plate can be manufactured using the optical laminate of the embodiment of the present invention. Therefore, the method for manufacturing a polarizing plate using the optical laminate of the embodiment of the present invention is also included in the embodiment of the present invention.

The manufacturing method of the polarizing plate of the embodiment of the present invention comprises: a step of transporting the optical laminate of the embodiment of the present invention described in the above items A to D along the longitudinal direction of the optical laminate; and a step of peeling off the surface protection film temporarily attached to the polarizer while transporting the optical laminate. In the embodiment of the present invention, the surface protection film is peeled off when the extension direction of the crack of the polarizer is at an angle of 30° or more and less than 180° relative to the transport direction.

For example, when the optical laminate is transported with the protective layer as the upper side and the extension direction of the crack when observed from the upper side (protective layer side) is an angle of 30° or more and less than 180° relative to the transport direction, the surface protective film can be peeled off while the optical laminate is transported in this state. When the optical laminate is the optical laminate described in the above items A to D, the extension direction of the crack is an angle of 30° to 150° relative to the transport direction regardless of which side (protective layer side or surface protective film side) is observed from. Therefore, for such optical laminates, the surface protection film can be well peeled off regardless of the state (layering order) during transportation.

In addition, for example, when the optical laminate is transported with the protective layer as the upper side and the extension direction of the crack when observed from the upper side (protective layer side) is an angle greater than 0° and less than 30° relative to the transport direction, if the surface protective film is peeled off while the optical laminate is transported in this state, peeling failure often occurs. In this case, peeling failure can be suppressed by rewinding the optical laminate. Specifically, the optical laminate can be temporarily rolled up and then unwound again and transported in the reverse direction. Thus, the surface protection film can be peeled off in a state where the extension direction of the crack is at an angle of 30° or more and less than 180° relative to the conveying direction. For example, when the extension direction of the crack when observed from the upper side (protective layer side) is 15° relative to the conveying direction, the extension direction of the crack when observed from the upper side (protective layer side) is 165° relative to the conveying direction by rewinding. That is, even an optical laminate that does not meet the requirements of the embodiment of the present invention can suppress peeling defects by rewinding.

Furthermore, when peeling off the surface protection film, it is sufficient to control the extension direction of the cracks and the transport direction. The surface protection film can be peeled off on the upper side (the optical laminate is transported with the surface protection film on the upper side) or on the lower side (the optical laminate is transported with the surface protection film on the lower side).

After peeling off the surface protective film, various optical functional layers that meet the purpose are laminated on the polarizer surface of the protective layer/polarizer laminate and/or the protective layer surface, and cut to a predetermined size (typically, a size corresponding to the image display device) at an appropriate time to obtain a polarizing plate or an optical film containing a polarizing plate as a final product. The optical functional layer can be laminated by roll-to-roll or can be bonded after cutting to a predetermined size. When multiple optical functional layers are laminated, a part of the optical functional layers can be laminated by roll-to-roll, and the remaining optical functional layers can be bonded after cutting to a predetermined size.

Examples The present invention is specifically described below through examples, but the present invention is not limited to these examples. In addition, various measurement methods in the examples and comparative examples are described below. In addition, unless otherwise specified, "parts" and "%" are based on weight.

(1) Indentation hardness A nanoindenter ("Triboindenter" manufactured by Hysitron Inc.) was used to perform the measurement using the nanoindentation method under the following measurement conditions. Specifically, the probe (indenter) of the nanoindenter was pressed into the surface of the polarizer of the polarizing plate obtained in the embodiment and the comparative example, and the indentation hardness was calculated by the following formula based on the displacement-load hysteresis curve. Indentation hardness (GPa) = Pmax/A Here, Pmax is the maximum load obtained from the displacement-load hysteresis curve, and A is the contact projection area between the indenter and the polarizer. (Measurement conditions) ・Measurement method: Single indentation method ・Measurement temperature: 25°C ・Indentation speed: Approximately 2nm/sec ・Indentation depth: Approximately 300nm ・Indenter used: Diamond, Berkovich type (triangular pyramid type)

(2) Peeling of surface protection film The surface protection film was peeled off from the optical laminate while the slit strips obtained in the embodiment and the comparative example were transported. The state at this time was visually observed and evaluated according to the following criteria. ○ (good): The surface protection film was peeled off well × (bad): At least a portion of the polarizer was peeled off together with the surface protection film

(3) End discoloration A test piece (50 mm × 50 mm) was cut out from the optical laminate (polarizer) obtained in the embodiment and the comparative example, with the polarizer extending in the direction opposite to the extending direction and the direction perpendicular to the extending direction as two opposite sides, and the test piece was adhered to an alkali-free glass plate using an adhesive to prepare a test sample. After the test sample was heated and humidified in an oven at 65°C and 95% RH for 240 hours, the end discoloration of the polarizer was investigated under a microscope when the sample was configured as a cross prism with a standard polarizer. Specifically, the amount of discoloration from the end of the polarizer was measured (end discoloration amount: μm). As a microscope, MX61L manufactured by Olympus was used, and the end discoloration amount was measured based on the image taken at 10 times magnification. The end discoloration amount a in the stretching direction and the end discoloration amount b in the direction perpendicular to the stretching direction were taken as the end discoloration amount. The evaluation criteria for the end discoloration amount are as follows. The evaluation results are shown in Table 1. ○ (good): The end discoloration amount is less than 400μm × (bad): The end discoloration amount is greater than 400μm

[Production Example 1] 1. Preparation of polarizer As a thermoplastic resin substrate, a long, amorphous isophthalic acid copolymer polyethylene terephthalate film (thickness: 100 μm) with a Tg of about 75°C was used, and one side of the resin substrate was subjected to a corona treatment. 13 parts by weight of potassium iodide was added to 100 parts by weight of a PVA-based resin prepared by mixing polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER") in a ratio of 9:1, and the resulting product was dissolved in water to prepare a PVA aqueous solution (coating liquid). The PVA aqueous solution was applied to the corona treated surface of the resin substrate and dried at 60°C to form a PVA resin layer with a thickness of 13 μm to produce a laminate. The obtained laminate was uniaxially stretched to 3.0 times in the longitudinal direction (length direction) in an oven at 140°C (in-air assisted stretching treatment). Next, the laminate was immersed in an insolubilization bath (a boric acid aqueous solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (insolubilization treatment). Next, the film was immersed in a dyeing bath (an iodine aqueous solution obtained by mixing iodine and potassium iodide at a weight ratio of 1:7 with respect to 100 parts by weight of water) at a liquid temperature of 30°C for 60 seconds (dyeing treatment). Next, the film was immersed in a crosslinking bath (an aqueous boric acid solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with respect to 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (crosslinking treatment). Thereafter, the laminate was immersed in a boric acid aqueous solution (boric acid concentration 4 wt%, potassium iodide concentration 5 wt%) at a liquid temperature of 64°C, and uniaxially stretched in the longitudinal direction (length direction) between rollers of different circumferential speeds at a total stretching ratio of 5.5 times (underwater stretching treatment). Thereafter, the laminate was immersed in a cleaning bath (aqueous solution obtained by mixing 3 parts by weight of potassium iodide with respect to 100 parts by weight of water) at a liquid temperature of 20°C (cleaning treatment). Thereafter, it was dried in an oven maintained at approximately 90°C, and contacted with a SUS heating roller maintained at a surface temperature of approximately 75°C (drying shrinkage treatment). In this way, a polarizer P1 with a thickness of 5.5 μm is formed on the resin substrate, and a long strip of polarizing plate having a structure of resin substrate/polarizer P1 is obtained. The single transmittance Ts of the polarizer P1 is 43.0%, and the indentation hardness is 0.688 GPa.

[Manufacturing Example 2] The same procedures as in Example 1 were followed except that the stretching temperature in the air-assisted stretching treatment was set to 130°C, the stretching ratio was set to 2.4 times, and the temperature of the boric acid aqueous solution in the water stretching treatment was set to 70°C. A long strip of polarizing plate having a structure of resin substrate/polarizer P2 was obtained. The single transmittance Ts of the polarizer P2 was 43.0%, and the indentation hardness was 0.646 GPa.

[Example 1] 1. Preparation of optical laminate The surface of the polarizer P1 of the polarizing plate obtained in Example 1 (the surface opposite to the resin substrate) is bonded with an HC-TAC film by roll-to-roll bonding with the aid of a UV-curable adhesive. The HC-TAC film is a film in which an HC layer (7 μm thick) is formed on a triacetylcellulose (TAC) film (25 μm thick), and the film is bonded in such a way that the TAC film becomes the polarizer side. Then, the resin substrate is peeled off to obtain a long strip of polarizing plate having a structure of HC layer/TAC film (protective layer)/polarizer P1. On the surface of the polarizer P1 of the obtained polarizing plate, a surface protection film having a structure of PET substrate (50μm)/adhesive layer (10μm) was laminated roll to roll, and a long optical laminate having a structure of HC layer/TAC film (protective layer)/polarizer P1/surface protection film was obtained.

2. Slitting of optical laminates While the optical laminate obtained above is transported by a roller, the slitting knife shown in Figure 3 is set and slit (cut) at the positions 30mm away from the end edge of the polarizer at both ends in the width direction of the optical laminate. The taper angle of the slitting knife is 40°, and the transport tension of the optical laminate during slitting is 350N. In addition, the contact pressure between the cutting knife and the receiving knife during slitting is 5N, the overlapping length L between the cutting knife and the receiving knife is 0.24mm, and the rotation speed of the cutting knife is 102% relative to the transport speed of the optical laminate.

As described above, a slit long strip optical laminate was obtained. In the obtained optical laminate, cracks were formed at the ends of the polarizer. When the optical laminate was observed from the protective layer (HC layer) side, the direction of the crack extension was 80° relative to the transport direction of the optical laminate, and the average length of the crack was 825 μm. The obtained optical laminate was subjected to the evaluations of (2) and (3) above. The results are shown in Table 1.

[Example 2~Example 3 and Comparative Example 1~Comparative Example 3] Using the polarizer shown in Table 1, and changing the taper angle of the cutting knife of the slitting knife and the conveying tension of the optical laminate during slitting as shown in Table 1, the same settings as in Example 1 were made to obtain a slit long strip optical laminate. The obtained optical laminate was subjected to the same evaluation as in Example 1. The results are shown in Table 1. In the item "Peeling of surface protection film" in Table 1, "directly" means peeling off the surface protection film while conveying the optical laminate in its original state, and "rewinding" means peeling off the surface protection film after rewinding the optical laminate so that the conveying direction is reversed.

[Table 1]

[Evaluation] As can be seen from Table 1, according to the embodiment of the present invention, even when the optical laminate includes a polarizer with a high degree of orientation, it is possible to suppress the peeling failure when peeling the surface protection film. Moreover, by comparing Comparative Example 1 and Comparative Example 2, it can be seen that when the optical laminate includes a polarizer with a low degree of orientation, the problem of peeling failure depending on the direction of crack extension does not occur. However, such a polarizer has the disadvantage that the end portion discolors greatly in a high temperature and high humidity environment.

Industrial Applicability The optical laminate of the embodiment of the present invention can be used as an intermediate of a polarizing plate or an optical film including a polarizing plate. The polarizing plate and optical film obtained from the optical laminate of the embodiment of the present invention are suitable for image display devices (representatively, liquid crystal display devices and organic EL display devices).

1: Cutter 1a: Cutter shaft 1b: One side of the cutter 1c: The other side of the cutter 2: Receiver 2a: Receiver shaft 11: Polarizer 12: Protective layer 20: Surface protection film 30: Arrow 50: Crack 100: Optical laminate B-B: Line L: Overlap length θ: Angle

FIG. 1(a) is a schematic top view of an optical laminate of one embodiment of the present invention; FIG. 1(b) is a schematic cross-sectional view of the optical laminate of FIG. 1(a) along the B-B line. FIG. 2(a) is a schematic top view showing an example of the relationship between the direction in which the end crack of the polarizer extends and the strip direction and the transport direction of the optical laminate in the embodiment of the present invention; FIG. 2(b) is a schematic top view showing another example of the relationship. FIG. 3(a) is a side view of a cutting knife and a receiving knife of a slitting knife that can be used in the embodiment of the present invention; FIG. 3(b) is an explanatory view showing the situation of cutting the optical laminate using the slitting knife.

11:Polarizer

12: Protective layer

20: Surface protection film

30: Arrow

100: Optical multilayers

B-B: line

Claims (6)

An optical laminate is a strip-shaped optical laminate; The optical laminate has a polarizer, a protective layer disposed on one side of the polarizer, and a surface protective film temporarily attached to the other side of the polarizer in a removable manner; The indentation hardness of the polarizer is above 0.65 GPa; The optical laminate has a crack of 50 μm to 5000 μm formed at the end of the polarizer in the width direction; The extension direction of the crack is 30° to 150° relative to the strip direction. The optical laminate of claim 1, wherein the compression elastic modulus of the polarizer is less than 9.5 GPa. An optical multilayer as claimed in claim 2, wherein the orientation function of the polarizer is greater than 0.30. An optical laminate roll is obtained by winding the optical laminate according to any one of claims 1 to 3. A method for manufacturing a polarizing plate comprises the following steps: A step of transporting an optical laminate as described in any one of claims 1 to 3 along the longitudinal direction of the optical laminate; and A step of peeling off the surface protection film while transporting the optical laminate; Peeling off the surface protection film when the extension direction of the crack is at an angle of 30° or more and less than 180° relative to the transport direction. A method for manufacturing a polarizing plate comprises the following steps: A step of transporting an optical laminate along the longitudinal direction of the optical laminate, wherein the optical laminate is a long strip optical laminate and has: a polarizer, a protective layer disposed on one side of the polarizer, and a surface protective film temporarily attached to the other side of the polarizer in a removable manner; and A step of peeling off the surface protective film while transporting the optical laminate; The indentation hardness of the polarizer is above 0.65 GPa; A crack of 50 μm to 5000 μm is formed at the end of the polarizer in the width direction, The extension direction of the crack is greater than 0° and less than 30° relative to the transport direction of the optical laminate; The peeling of the surface protection film includes peeling in the following state: after rewinding the optical laminate so that the transport direction of the optical laminate is in the opposite direction, the extension direction of the crack is made to be greater than 30° and less than 180° relative to the transport direction, and peeling is performed in this state.

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