TWI844561B - Polarizing plate with phase difference layer and image display device using the polarizing plate with phase difference layer - Google Patents

Abstract

The present invention provides a polarizing plate with a phase difference layer that is thin, has excellent handling properties, and has excellent optical properties. The polarizing plate with a phase difference layer of the present invention has a polarizing plate and a phase difference layer, wherein the polarizing plate includes a polarizing film and a protective layer disposed on at least one side of the polarizing film. The polarizing film is composed of a polyvinyl alcohol resin film containing a dichroic substance, and has a thickness of less than 8 μm, a single body transmittance of more than 43.0%, and a polarization degree of more than 99.980%. The phase difference layer is a directional solidification layer of a liquid crystal compound.

Description

Polarizing plate with phase difference layer and image display device using the polarizing plate with phase difference layer Invention Field

The present invention relates to a polarizing plate with a phase difference layer and an image display device using the polarizing plate with a phase difference layer.

Invention background

In recent years, image display devices represented by liquid crystal display devices and electroluminescent (EL) display devices (for example, organic EL display devices, inorganic EL display devices) are rapidly becoming popular. In image display devices, polarizing plates and phase difference plates are typically used. In actual use, polarizing plates with phase difference layers that integrate polarizing plates and phase difference plates are widely used (for example, Patent Document 1). Recently, as the desire for thinner image display devices increases, the desire for thinner polarizing plates with phase difference layers is also increasing. In addition, in recent years, the desire for curved image display devices and/or flexible or bendable image display devices is increasing, and the polarizing plates and polarizing plates with phase difference layers are also required to be further thinned and further flexible. In order to reduce the thickness of the polarizing plate with a phase difference layer, the protective layer and phase difference film of the polarizing film, which contribute greatly to the thickness, are reduced in thickness. However, if the protective layer and phase difference film are reduced in thickness, the impact of the shrinkage of the polarizing film becomes relatively large, causing problems such as warping of the image display device and reduced operability of the polarizing plate with a phase difference layer.

To solve the above problems, the polarizing film must also be thinned. However, if the thickness of the polarizing film is simply reduced, the optical properties will be reduced. More specifically, one or both of the polarization degree and the single body transmittance, which are in a trade-off relationship, will be reduced to a level that is not allowed in practical use. As a result, the optical properties of the polarizing plate with a phase difference layer will also become insufficient.

Existing technical literature Patent Literature

Patent document 1: Japanese Patent No. 3325560

The present invention is made to solve the above existing problems, and its main purpose is to provide a thin polarizing plate with a phase difference layer that has excellent processing properties and excellent optical properties.

The polarizing plate with phase difference layer of the present invention has a polarizing plate and a phase difference layer, wherein the polarizing plate includes a polarizing film and a protective layer disposed on at least one side of the polarizing film. The polarizing film is composed of a polyvinyl alcohol resin film containing a dichroic substance, and has a thickness of less than 8 μm, a single body transmittance of more than 43.0%, and a polarization degree of more than 99.980%. The phase difference layer is a directional solidification layer of a liquid crystal compound.

In one embodiment, the unit weight of the polarizing plate with a phase difference layer is less than 6.5 mg/ ^cm2 .

In one embodiment, the total thickness of the polarizing plate with phase difference layer is less than 60 μm.

In one embodiment, the phase difference layer is a single layer of a directional solidified layer of a liquid crystal compound, the Re (550) of the phase difference layer is 100nm~190nm, and the angle between the slow axis of the phase difference layer and the absorption axis of the polarizing film is 40°~50°.

In one embodiment, the phase difference layer has a stacked structure of an oriented solidified layer of a first liquid crystal compound and an oriented solidified layer of a second liquid crystal compound; the Re(550) of the oriented solidified layer of the first liquid crystal compound is 200nm~300nm, and the angle between its slow axis and the absorption axis of the polarizing film is 10°~20°; the Re(550) of the oriented solidified layer of the second liquid crystal compound is 100nm~190nm, and the angle between its slow axis and the absorption axis of the polarizing film is 70°~80°.

In one embodiment, the difference between the maximum and minimum values of the single transmittance of the polarizing film in an area of 50 ^cm2 is less than 0.2%.

In one embodiment, the width of the polarizing plate with phase difference layer is greater than 1000 mm, and the difference between the maximum and minimum values of the single transmittance of the polarizing film along the width direction is less than 0.3%.

In one embodiment, the single transmittance of the polarizing film is less than 43.5%, and the polarization degree is less than 99.998%.

In one embodiment, the polarizing plate with a phase difference layer further has another phase difference layer outside the phase difference layer, and the refractive index characteristics of the other phase difference layer show the relationship of nz>nx=ny.

In one embodiment, the polarizing plate with a phase difference layer further has a conductive layer or an isotropic substrate with a conductive layer on the outer side of the phase difference layer.

According to other aspects of the present invention, an image display device is provided. The image display device has the above-mentioned polarizing plate with phase difference layer.

In one embodiment, the image display device is an organic electroluminescent display device or an inorganic electroluminescent display device.

According to the present invention, a thin polarizing film with very excellent optical properties can be obtained by combining the addition of a halogen (typically potassium iodide) to a polyvinyl alcohol (PVA) resin, two-stage stretching including air-assisted stretching and underwater stretching, and drying and shrinking using a heated roller. By using such a polarizing film, a thin polarizing plate with a phase difference layer that is excellent in handling and has excellent optical properties can be realized.

10: Polarizing plate

11: Polarizing film

12: 1st protective layer

13: Second protective layer

20: Phase difference layer (first phase difference layer)

21: 1st directional solidification layer

22: Second directional solidification layer

50: Other phase difference layers (second phase difference layer)

60: Isotropic substrate with conductive layer

100: Polarizing plate with phase difference layer

101: Polarizing plate with phase difference layer

102: Polarizing plate with phase difference layer

200:Layered body

G1~G4: Guide roller

R1~R6: Transport rollers

Figure 1 is a schematic cross-sectional view of a polarizing plate with a phase difference layer according to an embodiment of the present invention.

Figure 2 is a schematic cross-sectional view of a polarizing plate with a phase difference layer according to another embodiment of the present invention.

Figure 3 is a schematic cross-sectional view of a polarizing plate with a phase difference layer in another embodiment of the present invention.

FIG4 is a schematic diagram showing an example of a drying and shrinking process using a heating roller in the method for manufacturing a polarizing film of a polarizing plate with a phase difference layer of the present invention.

Detailed description of the preferred embodiment

The following describes the implementation methods of the present invention, but the present invention is not limited to these implementation methods.

(Definition of terms and symbols)

The definitions of terms and symbols in this manual are as follows.

(1) Refractive index (nx, ny, nz)

"nx" is the refractive index in the direction where the refractive index in the plane reaches the maximum (i.e. the slow axis direction), "ny" is the refractive index in the direction orthogonal to the slow axis in the plane (i.e. the fast axis direction), and "nz" is the refractive index in the thickness direction.

(2) In-plane phase difference (Re)

"Re(λ)" is the in-plane phase difference measured at 23°C with light of wavelength λnm. For example, "Re(550)" is the in-plane phase difference measured at 23°C with light of wavelength 550nm. When the thickness of the layer (film) is set to d(nm), Re(λ) can be calculated by the formula: Re(λ)=(nx-ny)×d.

(3) Phase difference in thickness direction (Rth)

"Rth(λ)" is the phase difference in the thickness direction measured at 23°C with light of wavelength λnm. For example, "Rth(550)" is the phase difference in the thickness direction measured at 23°C with light of wavelength 550nm. When the thickness of the layer (film) is set to d(nm), Rth(λ) can be calculated by the formula: Rth(λ)=(nx-nz)×d.

(4) Nz coefficient

The Nz coefficient is calculated by Nz=Rth/Re.

(5) Angle

In this manual, when an angle is mentioned, the angle includes both clockwise and counterclockwise relative to the reference direction. Therefore, for example, "45°" means ± 45°.

A. The overall structure of the polarizing plate with phase difference layer

FIG1 is a schematic cross-sectional view of a polarizing plate with a phase difference layer according to an embodiment of the present invention. The polarizing plate with a phase difference layer 100 according to the present embodiment has a polarizing plate 10 and a phase difference layer 20. The polarizing plate 10 includes: a polarizing film 11, a first protective layer 12 arranged on one side of the polarizing film 11, and a second protective layer 13 arranged on the other side of the polarizing film 11. Depending on the purpose, one of the first protective layer 12 and the second protective layer 13 can be omitted. For example, when the phase difference layer 20 can also function as a protective layer for the polarizing film 11, the second protective layer 13 can be omitted. In an embodiment of the present invention, the polarizing film is composed of a polyvinyl alcohol resin film containing a dichroic substance. The thickness of the polarizing film is less than 8μm, the single body transmittance is more than 43.0%, and the polarization degree is more than 99.980%.

As shown in FIG. 2 , in a polarizing plate 101 with a phase difference layer in another embodiment, another phase difference layer 50 and/or a conductive layer or an isotropic substrate 60 with a conductive layer may be provided. The other phase difference layer 50 and the conductive layer or the isotropic substrate 60 with a conductive layer are typically provided on the outer side of the phase difference layer 20 (the side opposite to the polarizing plate 10). The refractive index characteristics of the other phase difference layer typically show the relationship of nz>nx=ny. Typically, the other phase difference layer 50 and the conductive layer or the isotropic substrate 60 with a conductive layer are provided in order from the phase difference layer 20 side. Representatively, the other phase difference layer 50 and the conductive layer or the isotropic substrate 60 with a conductive layer are arbitrary layers provided as needed, and either or both of them may be omitted. It should be noted that, for the sake of convenience, the phase difference layer 20 is sometimes referred to as the first phase difference layer, and the other phase difference layer 50 is sometimes referred to as the second phase difference layer. It should be noted that, in the case of providing a conductive layer or an isotropic substrate with a conductive layer, the polarizing plate with a phase difference layer can be applied to a so-called embedded touch panel type input display device in which a touch sensor is introduced between an image display unit (e.g., an organic EL unit) and a polarizing plate.

In the embodiment of the present invention, the first phase difference layer 20 is an oriented solidified layer of a liquid crystal compound. The first phase difference layer 20 may be a single oriented solidified layer as shown in FIG. 1 and FIG. 2 , or may have a stacked structure of a first oriented solidified layer 21 and a second oriented solidified layer 22 as shown in FIG. 3 .

The above-mentioned embodiments can be appropriately combined, and the components in the above-mentioned embodiments can also be obviously changed by technicians in this field. For example, the second phase difference layer 50 and/or the conductive layer or the isotropic substrate 60 with the conductive layer can be set on the polarizing plate 102 with the phase difference layer in Figure 3. In addition, for example, the structure of the isotropic substrate 60 with the conductive layer set on the outer side of the second phase difference layer 50 can be replaced with an optically equivalent structure (for example, a stack of the second phase difference layer and the conductive layer).

The polarizing plate with phase difference layer of the embodiment of the present invention may further include other phase difference layers. The optical properties (e.g., refractive index properties, in-plane phase difference, Nz coefficient, photoelastic coefficient), thickness, configuration position, etc. of other phase difference layers can be appropriately set according to the purpose.

The polarizing plate with phase difference layer of the present invention can be in the form of a single sheet or a long strip. In this specification, "long strip" refers to a long and thin shape with a length that is sufficiently long relative to the width, for example, including a long and thin shape with a length that is more than 10 times, preferably more than 20 times, relative to the width. The long strip polarizing plate with phase difference layer can be rolled into a roll.

In actual use, an adhesive layer (not shown) can be provided on the side of the phase difference layer opposite to the polarizing plate, so that the polarizing plate with the phase difference layer can be attached to the image display unit. In addition, it is preferred that a peeling film is temporarily attached to the surface of the adhesive layer until the polarizing plate with the phase difference layer is provided for use. By temporarily attaching the peeling film, the adhesive layer can be protected and a roll can be formed.

The total thickness of the polarizing plate with a phase difference layer is preferably less than 60 μm, more preferably less than 55 μm, further preferably less than 50 μm, and particularly preferably less than 40 μm. The lower limit of the total thickness can be, for example, 28 μm. According to the implementation method of the present invention, a very thin polarizing plate with a phase difference layer can be realized in this way. Such a polarizing plate with a phase difference layer can have very excellent flexibility and bending durability. Such a polarizing plate with a phase difference layer can be particularly suitable for use in a curved image display device and/or a flexible or bendable image display device. It should be noted that the total thickness of the polarizing plate with a phase difference layer refers to the total thickness of all layers constituting the polarizing plate with a phase difference layer, except for the adhesive layer used to adhere the polarizing plate to external adherends such as panels and glass (that is, the total thickness of the polarizing plate with a phase difference layer does not include the thickness of the adhesive layer used to adhere the polarizing plate with a phase difference layer to adjacent components such as image display units and the peeling film that can be temporarily adhered to its surface).

The unit weight of the polarizing plate with a phase difference layer in the embodiment of the present invention is, for example, 6.5 mg/ ^cm2 or less, preferably 2.0 mg/ ^cm2 to 6.0 mg/ ^cm2 , more preferably 3.0 mg/ ^cm2 to 5.5 mg/ ^cm2 , and further preferably 3.5 mg/ ^cm2 to 5.0 mg/ ^cm2 . When the display panel is thin, the panel may be slightly deformed due to the weight of the polarizing plate with a phase difference layer, which may cause poor display. However, the polarizing plate with a phase difference layer having a unit weight of 6.5 mg/ ^cm2 or less can prevent such panel deformation. In addition, the polarizing plate with a phase difference layer having the above unit weight has good handling properties even when it is thinned, and can exhibit very excellent flexibility and bending durability.

The following is a more detailed explanation of the components of the polarizing plate with a phase difference layer.

B. Polarizing plate

B-1. Polarizing film

As described above, the thickness of the polarizing film 11 is less than 8 μm, the single body transmittance is more than 43.0%, and the polarization degree is more than 99.980%. Generally speaking, there is a trade-off relationship between single body transmittance and polarization degree. If the single body transmittance is increased, the polarization degree will decrease, and if the polarization degree is increased, the single body transmittance will decrease. Therefore, it has always been difficult to supply a thin polarizing film that satisfies the optical characteristics of a single body transmittance of more than 43.0% and a polarization degree of more than 99.980% in practical use. One of the characteristics of the present invention is to use a thin polarizing film with excellent optical characteristics of more than 43.0% single body transmittance and more than 99.980% polarization degree, and the deviation of the optical characteristics is suppressed.

The thickness of the polarizing film is preferably 1μm~8μm, more preferably 1μm~7μm, and further preferably 2μm~5μm.

The polarizing film preferably exhibits absorption dichroism at any wavelength of 380nm to 780nm. The single transmittance of the polarizing film is preferably 43.5% or less. The polarization degree of the polarizing film is preferably 99.990% or more, and more preferably 99.998% or less. The single transmittance is typically measured using an ultraviolet-visible spectrophotometer and the Y value obtained by correction for visibility. The polarization degree is typically based on the parallel transmittance Tp and the orthogonal transmittance Tc obtained by measurement using an ultraviolet-visible spectrophotometer and correction for visibility, and is obtained by the following formula.

Polarization degree (%) = {(Tp-Tc)/(Tp+Tc)} ^1/2 × 100

In one embodiment, the transmittance of a thin polarizing film of less than 8 μm is measured using a UV-visible spectrophotometer, typically using a stack of a polarizing film (surface refractive index: 1.53) and a protective film (refractive index: 1.50). Depending on the refractive index of the surface of the polarizing film and/or the refractive index of the surface of the protective film contacting the air interface, the reflectivity of the interface of each layer changes, resulting in a change in the measured value of the transmittance. Therefore, for example, when a protective film having a refractive index other than 1.50 is used, the measured value of the transmittance can be corrected based on the refractive index of the surface of the protective film contacting the air interface. Specifically, the transmittance correction value C is expressed by the following equation using the reflectance R ₁ (transmission axis reflectance) of polarized light parallel to the transmission axis at the interface between the protective film and the air layer.

C=R ₁ -R ₀

R ₀ =((1.50-1) ² /(1.50+1) ² )×(T ₁ /100)

R ₁ =((n ₁ -1) ² /(n ₁ +1) ² )×(T ₁ /100)

Among them, _R0 is the transmission axis reflectivity when a protective film with a refractive index of 1.50 is used, _n1 is the refractive index of the protective film used, and _T1 is the transmittance of the polarizing film. For example, when a substrate with a surface refractive index of 1.53 (cycloolefin film, film with hard coating, etc.) is used as the protective film, the correction amount C becomes about 0.2%. In this case, 0.2% is added to the transmittance obtained by measurement, and it can be converted into the transmittance when a protective film with a surface refractive index of 1.50 is used. It should be noted that according to the calculation based on the above formula, the change in the correction value C when the transmittance _T1 of the polarizing film changes by 2% is less than 0.03%, and the influence of the transmittance of the polarizing film on the value of the correction value C is limited. In addition, if the protective film has absorption other than surface reflection, appropriate correction can be made according to the absorption amount.

In one embodiment, the width of the polarizing plate with a phase difference layer is greater than 1000 mm, and therefore, the width of the polarizing film is also greater than 1000 mm. In this case, the difference (D1) between the maximum and minimum values of the single transmittance in the position along the width direction of the polarizing film is preferably less than 0.3%, more preferably less than 0.25%, further preferably less than 0.2%, and particularly preferably less than 0.17%. The smaller D1 is, the better, and the lower limit of D1 can be, for example, 0.01%. When D1 is within the above range, a polarizing plate with a phase difference layer having excellent optical properties can be manufactured industrially. In another embodiment, the difference (D2) between the maximum and minimum values of the single transmittance of the polarizing film in a ⁵⁰ cm2 area is preferably 0.2% or less, more preferably 0.15% or less, and further preferably 0.1% or less. The smaller D2 is, the better, and the lower limit of D2 can be, for example, 0.01%. When D2 is within the above range, the brightness unevenness in the display screen can be suppressed when the polarizing plate with a phase difference layer is used in an image display device.

As the polarizing film, any appropriate polarizing film can be used. The polarizing film can be typically produced using a stack of two or more layers.

As a specific example of a polarizing film obtained using a laminate, there can be cited a polarizing film obtained using a laminate of a resin substrate and a PVA-type resin layer formed on the resin substrate by coating. A polarizing film obtained using a laminate of a resin substrate and a PVA-type resin layer formed on the resin substrate by coating can be produced by the following method: for example, a PVA-type resin solution is applied to a resin substrate, and the PVA-type resin layer is formed on the resin substrate by drying, thereby obtaining a laminate of the resin substrate and the PVA-type resin layer; the laminate is stretched and dyed to make the PVA-type resin layer into a polarizing film. In this embodiment, stretching typically includes immersing the layer stack in an aqueous boric acid solution for stretching. In addition, stretching may further include stretching the layer stack at a high temperature (for example, above 95°C) in the air before stretching in the aqueous boric acid solution, as needed. The obtained resin substrate/polarizing film layer stack can be used directly (that is, the resin substrate can be used as a protective layer for the polarizing film), or the resin substrate can be peeled off from the resin substrate/polarizing film layer stack and any appropriate protective layer corresponding to the purpose can be stacked on the peeled surface for use. The details of such a method for producing a polarizing film are described in, for example, Japanese Patent Gazette No. 2012-73580. All the contents of the bulletin can be cited as reference in this manual.

The method for manufacturing a polarizing film typically includes: forming a polyvinyl alcohol resin layer containing a halogenated compound and a polyvinyl alcohol resin on one side of a long thermoplastic resin substrate to form a laminate; and sequentially subjecting the laminate to an air-assisted stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment in which the laminate is heated while being transported in the length direction so as to shrink the laminate by more than 2% in the width direction. Thus, a polarizing film having a thickness of less than 8 μm, a single body transmittance of more than 43.0%, a polarization degree of more than 99.980%, excellent optical properties, and suppressed optical property deviation can be provided. That is, by introducing auxiliary stretching, the crystallinity of PVA can be improved even when PVA is coated on a thermoplastic resin, and high 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 and dissolving when immersed in water in the subsequent dyeing and stretching steps, thereby achieving high optical properties. In addition, when the PVA-based resin layer is immersed in a liquid, the orientation disorder 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 polarizing film obtained by the treatment steps of immersing the laminate in a liquid such as dyeing treatment and underwater stretching treatment can be improved. In addition, the optical properties can be improved by shrinking the laminate in the width direction through a drying and shrinking treatment.

B-2. Protective layer

The first protective layer 12 and the second protective layer 13 can be formed of any appropriate film that can be used as a protective layer of a polarizing film. Specific examples of the material that is the main component of the film include cellulose resins such as triacetate cellulose (TAC) and transparent resins such as polyesters, polyvinyl alcohols, polycarbonates, polyamides, polyimides, polyether sulfones, polysulfones, polystyrenes, polynorbornenes, polyolefins, (meth) acrylic acid, and acetates. In addition, thermosetting resins such as (meth) acrylic acid, urethane, (meth) acrylic urethane, epoxy, and polysilicone, or ultraviolet curing resins can also be listed. In addition, glassy polymers such as siloxane polymers can also be cited. In addition, the polymer film described in Japanese Patent Publication No. 2001-343529 (WO01/37007) can also be used. As the material of the film, a resin composition containing, for example, a thermoplastic resin having a substituted or unsubstituted amide group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl and nitrile group in the side chain can be used, and for example: a resin composition having an alternating copolymer formed by isobutylene and N-methylmaleimide and an acrylonitrile-styrene copolymer can be cited. The polymer film can be, for example, an extruded product of the above-mentioned resin composition.

As described later, the polarizing plate with a phase difference layer of the present invention is typically arranged on the visible side of the image display device, and the first protective layer 12 is typically arranged on the visible side thereof. Therefore, the first protective layer 12 may be subjected to surface treatments such as hard coating, anti-reflection, anti-adhesion, and anti-glare treatments as needed. In addition or alternatively, the first protective layer 12 may be subjected to treatments to improve visual recognition when viewing through polarized sunglasses as needed (typically, imparting (elliptical) circular polarization function and imparting ultra-high phase difference). By implementing such processing, excellent visual legibility can be achieved even when viewing the display screen through polarized lenses such as polarized sunglasses. Therefore, polarizing plates with phase difference layers can also be applied to image display devices that can be used outdoors.

The thickness of the first protective layer is preferably 5μm to 80μm, more preferably 10μm to 40μm, and further preferably 10μm to 30μm. It should be noted that when surface treatment is performed, the thickness of the outer protective layer includes the thickness of the surface treatment layer.

In one embodiment, the second protective layer 13 is preferably optically isotropic. In this specification, "optically isotropic" means that the in-plane phase difference Re(550) is 0nm~10nm and the phase difference Rth(550) in the thickness direction is -10nm~+10nm. In one embodiment, the second protective layer 13 can be a phase difference layer with any appropriate phase difference value. In this case, the in-plane phase difference Re(550) of the phase difference layer is, for example, 110nm~150nm. The thickness of the second protective layer is preferably 5μm~80μm, more preferably 10μm~40μm, and further preferably 10μm~30μm. From the perspective of thinning and weight reduction, the second protective layer can be preferably omitted.

B-3. Method for manufacturing polarizing film

The polarizing film can be prepared by a method including the following steps: for example, forming a polyvinyl alcohol resin layer (PVA resin layer) containing a halogenated substance and a polyvinyl alcohol resin (PVA resin) on one side of a long thermoplastic resin substrate to form a laminate; and sequentially subjecting the laminate to an air-assisted stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment in which the laminate is heated while being transported in the length direction so as to shrink the laminate by more than 2% in the width direction. The content of the halogenated substance in the PVA resin layer is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA resin. The drying and shrinking treatment is preferably carried out using a heating roller, and the temperature of the heating roller is preferably 60°C to 120°C. The shrinkage rate of the laminate in the width direction caused by the drying and shrinking treatment is preferably 2% or more. According to such a manufacturing method, the polarizing film described in the above-mentioned item B-1 can be obtained. In particular, a laminate comprising a PVA-type resin layer containing a halogenated substance is prepared, and the stretching of the above-mentioned laminate is performed by multi-stage stretching including air-assisted stretching and underwater stretching, and the stretched laminate is heated by a heating roller, thereby obtaining a polarizing film having excellent optical properties (representatively, single body transmittance and polarization degree) and suppressed deviation in optical properties. Specifically, by using a heated roller in the drying and shrinking treatment step, the stack can be uniformly shrunk while being transported. This not only improves the optical properties of the resulting polarizing film, but also enables stable production of polarizing films with excellent optical properties, and suppresses the deviation of the optical properties of the polarizing film (especially the single body transmittance).

B-3-1. Production of stacked bodies

As a method for producing a laminate of a thermoplastic resin substrate and a PVA-type resin layer, any appropriate method may be adopted. Preferably, a coating liquid containing a halogen and a PVA-type resin is applied to the surface of the thermoplastic resin substrate and dried, thereby forming a PVA-type resin layer on the thermoplastic resin substrate. As described above, the content of the halogen in the PVA-type resin layer is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-type resin.

Any appropriate method can be used as a coating method for the coating liquid. Examples include: roller coating, spin coating, winding rod coating, dip coating, die coating, shower coating, spray coating, scraping coating (corner wheel coating, etc.). The coating/drying temperature of the above coating liquid is preferably above 50°C.

The thickness of the PVA resin layer is preferably 3μm~40μm, and more preferably 3μm~20μm.

Before forming the PVA resin layer, the thermoplastic resin substrate may be subjected to surface treatment (e.g., corona treatment), or an easy-to-adhere layer may be formed on the thermoplastic resin substrate. By performing such treatment, the adhesion between the thermoplastic resin substrate and the PVA resin layer may be improved.

B-3-1-1. Thermoplastic resin substrate

The thickness of the thermoplastic resin substrate is preferably 20μm~300μm, more preferably 50μm~200μm. When it is less than 20μm, it may be difficult to form a PVA-based resin layer. When it exceeds 300μm, for example, in the underwater stretching treatment described later, there is a risk that the thermoplastic resin substrate will take a long time to absorb water and that the stretching will require an excessive load.

The water absorption rate of the thermoplastic resin substrate is preferably 0.2% or more, and more preferably 0.3% or more. The thermoplastic resin substrate absorbs water, and the water acts like a plasticizer to plasticize. As a result, the tensile stress can be greatly reduced, and stretching at a high ratio can be performed. On the other hand, the water absorption rate of the thermoplastic resin substrate is preferably 3.0% or less, and more preferably 1.0% or less. By using such a thermoplastic resin substrate, undesirable situations such as a significant decrease in the dimensional stability of the thermoplastic resin substrate during manufacturing and deterioration in the appearance of the resulting polarizing film can be prevented. In addition, the substrate can be prevented from breaking during underwater stretching and the PVA-type resin layer can be prevented from peeling off from the thermoplastic resin substrate. It should be noted that the water absorption rate of the thermoplastic resin substrate can be adjusted by, for example, introducing a modified group into the constituent material. The water absorption rate is a value calculated in accordance with JIS K 7209.

The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 120°C or less. By using such a thermoplastic resin substrate, the crystallization of the PVA-based resin layer can be suppressed and the stretchability of the laminate can be fully ensured. In addition, considering the plasticization of the thermoplastic resin substrate by water and good underwater stretching, it is more preferably 100°C or less, and further preferably 90°C or less. On the other hand, the glass transition temperature of the thermoplastic resin substrate is preferably 60°C or more. By using such a thermoplastic resin substrate, it is possible to prevent the thermoplastic resin substrate from deforming (e.g., unevenness, sagging, wrinkles, etc.) when applying/drying the coating liquid containing the above-mentioned PVA-based resin, and to produce a laminate well. In addition, the PVA-based resin layer can be stretched well at an appropriate temperature (e.g., around 60°C). It should be noted that the glass transition temperature of the thermoplastic resin substrate can be adjusted by, for example, using a crystallized material that introduces a modified group into the constituent material and heating it. The glass transition temperature (Tg) is a value obtained in accordance with JIS K 7121.

As the constituent material of the thermoplastic resin substrate, any appropriate thermoplastic resin can be used. Examples of thermoplastic resins include ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, polyamide resins, polycarbonate resins, and copolymer resins thereof. Of these, norbornene resins and amorphous polyethylene terephthalate resins are preferred.

In one embodiment, it is preferred to use an amorphous (uncrystallized) polyethylene terephthalate resin. Among them, it is particularly preferred to use an amorphous (not easy to crystallize) polyethylene terephthalate resin. Specific examples of amorphous polyethylene terephthalate resins include copolymers further containing isophthalic acid and/or cyclohexanedicarboxylic acid as dicarboxylic acids, and copolymers further containing cyclohexanedimethanol and diethylene glycol as diols.

In a preferred embodiment, the thermoplastic resin substrate is composed of a polyethylene terephthalate resin having an isophthalic acid unit. This is because such a thermoplastic resin substrate has very excellent stretchability and can suppress crystallization during stretching. This is believed to be due to the large distortion given to the main chain by the introduction of the isophthalic acid unit. Polyethylene terephthalate resins have terephthalic acid units and ethylene glycol units. The content ratio of the isophthalic acid unit relative to the total of all repeating units is preferably 0.1 mol% or more, and more preferably 1.0 mol% or more. This is because a thermoplastic resin substrate with very excellent stretchability can be obtained. On the other hand, the content ratio of isophthalic acid units relative to the total of all repeating units is preferably 20 mol% or less, and more preferably 10 mol% or less. By setting the content ratio to such a level, the crystallinity can be improved well in the drying and shrinking treatment described later.

The thermoplastic resin substrate may be stretched in advance (before forming the PVA resin layer). In one embodiment, the long strip of thermoplastic resin substrate may be stretched in the transverse direction. The transverse direction is preferably a direction orthogonal to the stretching direction of the laminate described later. It should be noted that in this specification, the so-called "orthogonal" also includes substantially orthogonal situations. Here, the so-called "substantially orthogonal" includes 90°±5.0°, preferably 90°±3.0°, and further preferably 90°±1.0°.

Relative to the glass transition temperature (Tg), the stretching temperature of the thermoplastic resin substrate is preferably Tg-10℃~Tg+50℃. The stretching ratio of the thermoplastic resin substrate is preferably 1.5 times~3.0 times.

As a stretching method for a thermoplastic resin substrate, any appropriate method may be adopted. Specifically, it may be fixed-end stretching or free-end stretching. The stretching method may be dry or wet. The stretching of the thermoplastic resin substrate may be performed in one stage or in multiple stages. When the stretching is performed in multiple stages, the above-mentioned stretching ratio is the product of the stretching ratios of each stage.

B-3-1-2. Coating liquid

As described above, the coating liquid contains a halogenated substance and a PVA-based resin. The coating liquid is typically a solution obtained by dissolving the halogenated substance and the PVA-based resin in a solvent. Examples of the solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyols such as trihydroxymethylpropane, and amines such as ethylenediamine and diethylenetriamine. They can be used alone or in combination of two or more. Of these, water is preferred. The PVA-based resin concentration of the solution is preferably 3 to 20 parts by weight relative to 100 parts by weight of the solvent. At such a resin concentration, a uniform coating film that is closely attached to the thermoplastic resin substrate can be formed. The content of halides in the coating liquid is preferably 5 to 20 parts by weight relative to 100 parts by weight of PVA resin.

Additives can be mixed into the coating liquid. Examples of additives include plasticizers and surfactants. Examples of plasticizers include polyols such as ethylene glycol and glycerol. Examples of surfactants include non-ionic surfactants. These additives are used to further improve the uniformity, dyeability, and stretchability of the resulting PVA resin layer.

As the above-mentioned PVA resin, any appropriate resin can be used. For example, polyvinyl alcohol and ethylene-vinyl alcohol copolymer can be listed. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. Ethylene-vinyl alcohol copolymer can be obtained by saponifying ethylene-vinyl acetate copolymer. The saponification degree of PVA resin is usually 85 mol%~100 mol%, preferably 95.0 mol%~99.95 mol%, and more preferably 99.0 mol%~99.93 mol%. The saponification degree can be calculated according to JIS K 6726-1994. By using PVA resin with such a saponification degree, a polarizing film with excellent durability can be obtained. If the saponification degree is too high, there is a risk of gelation.

The average degree of polymerization of PVA-based resins can be appropriately selected according to the purpose. The average degree of polymerization is usually 1000~10000, preferably 1200~4500, and more preferably 1500~4300. It should be noted that the average degree of polymerization can be obtained according to JIS K 6726-1994.

As the above-mentioned halides, any appropriate halides can be used. For example, iodides and sodium chloride can be listed. As iodides, for example, potassium iodide, sodium iodide, and lithium iodide can be listed. Among these, potassium iodide is preferred.

The amount of halogen in the coating liquid is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA resin, and more preferably 10 to 15 parts by weight relative to 100 parts by weight of the PVA resin. When the amount of halogen exceeds 20 parts by weight relative to 100 parts by weight of the PVA resin, the halogen may ooze out and the resulting polarizing film may become cloudy.

Generally speaking, by stretching a PVA resin layer, the orientation of the polyvinyl alcohol molecules in the PVA resin is improved. However, if the stretched PVA resin layer is immersed in a liquid containing water, the orientation of the polyvinyl alcohol molecules is disturbed and the orientation is reduced. In particular, when a laminate of a thermoplastic resin substrate and a PVA resin layer is stretched in boric acid water at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin substrate, the tendency for the above orientation to be reduced is remarkable. For example, the stretching of a PVA film monomer in boric acid water is usually performed at 60°C, whereas the stretching of a laminate of A-PET (thermoplastic resin substrate) and a PVA-based resin layer is performed at a high temperature of about 70°C. In this case, the orientation of the PVA at the initial stage of stretching decreases before it increases by stretching in water. In contrast, by preparing a laminate of a PVA-based resin layer containing a halogenated substance and a thermoplastic resin substrate, and stretching the laminate at a high temperature in air (auxiliary stretching) before stretching the laminate in boric acid water, the crystallization of the PVA-based resin in the PVA-based resin layer of the laminate after auxiliary stretching can be promoted. As a result, when the PVA resin layer is immersed in a liquid, the orientation disorder of the polyvinyl alcohol molecules and the reduction of orientation can be suppressed compared to the case where the PVA resin layer does not contain a halogen. As a result, the optical properties of the polarizing film obtained by immersing the laminate in a liquid through treatment steps such as dyeing and underwater stretching can be improved.

B-3-2. Aerial assisted stretching treatment

In order to obtain high optical properties, a two-stage stretching method combining dry stretching (auxiliary stretching) and boric acid water stretching is particularly selected. By introducing auxiliary stretching as in the two-stage stretching, stretching can be performed while suppressing the crystallization of the thermoplastic resin substrate, which can solve the problem of reduced stretchability due to excessive crystallization of the thermoplastic resin substrate in the subsequent boric acid water stretching, and the laminate can be stretched at a higher magnification. Furthermore, when coating a PVA resin on a thermoplastic resin substrate, the coating temperature needs to be lower than when coating a PVA resin on a metal drum in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate. As a result, the crystallization of the PVA resin is relatively reduced, and sufficient optical properties cannot be obtained. In contrast, by introducing auxiliary stretching, the crystallization of the PVA resin can be improved even when coating the PVA resin on a thermoplastic resin, and high optical properties can be achieved. In addition, by improving the orientation of the PVA resin in advance, when immersed in water in the subsequent dyeing and stretching steps, the orientation of the PVA resin can be prevented from decreasing and dissolving, and high optical properties can be achieved.

The stretching method of aerial assisted stretching can be fixed-end stretching (for example, a method of stretching using a tenter stretching machine) or free-end stretching (for example, a method of unidirectional stretching by passing the laminate through rollers with different circumferential speeds). In order to obtain high optical properties, free-end stretching can be actively adopted. In one embodiment, the aerial stretching treatment includes a heating roller stretching step, which is to transport the above-mentioned laminate in its length direction while stretching it using the circumferential speed difference between the heating rollers. The aerial stretching treatment typically includes a regional stretching step and a heating roller stretching step. It should be noted that the order of the regional stretching step and the heating roller stretching step is not limited, and the regional stretching step can be performed first, or the heating roller stretching step can be performed first. The regional stretching step may also be omitted. In one embodiment, the regional stretching step and the heated roller stretching step are performed sequentially. In addition, in another embodiment, the film ends are held in a tenter stretching machine, and the distance between the tenters is expanded in the conveying direction for stretching (the expansion of the distance between the tenters becomes the stretching ratio). At this time, the distance between the tenters in the width direction (the direction perpendicular to the conveying direction) is set to be arbitrarily close. It is preferably set to be closer to the free end stretching relative to the stretching ratio in the conveying direction. In the case of free end stretching, it is calculated by the shrinkage rate in the width direction = (1/stretching ratio) ^1/2 .

Air-assisted stretching can be performed in one stage or in multiple stages. In the case of multiple stages, the stretching ratio is the product of the stretching ratios of each stage. The stretching direction in air-assisted stretching is preferably roughly the same as the stretching direction in water stretching.

The stretching ratio in air-assisted stretching is preferably 2.0 to 3.5 times. The maximum stretching ratio in the case of combining air-assisted stretching and underwater stretching is preferably 5.0 times or more, more preferably 5.5 times or more, and further preferably 6.0 times or more relative to the original length of the laminate. In this specification, "maximum stretching ratio" refers to the stretching ratio just before the laminate breaks, and also refers to the stretching ratio at which the laminate breaks and is 0.2 less than this value.

The stretching temperature of the air-assisted stretching can be set to any appropriate value according to the forming material of the thermoplastic resin substrate, the stretching method, etc. The stretching temperature is preferably above the glass transition temperature (Tg) of the thermoplastic resin substrate, further preferably above the glass transition temperature (Tg) of the thermoplastic resin substrate + 10°C, and particularly preferably above Tg + 15°C. On the other hand, the upper limit of the stretching temperature is preferably 170°C. By stretching at such a temperature, the rapid crystallization of the PVA-type resin can be suppressed, and the undesirable conditions caused by the crystallization (for example, hindering the orientation of the PVA-type resin layer brought about by stretching) can be suppressed. The crystallization index of the PVA-type resin after air-assisted stretching is preferably 1.3~1.8, and more preferably 1.4~1.7. The crystallization index of PVA resin can be measured by the ATR method using a Fourier transform infrared spectrophotometer. Specifically, polarized light is used as the measuring light, and the crystallization index is calculated by the following formula using the intensity at 1141 cm ^-1 and 1440 cm ^-1 in the obtained spectrum.

Crystallization index = ( _IC / _IR )

in,

I _C : Intensity at 1141 cm ^-1 when measuring light is incident

_IR : Intensity at 1440 cm ^-1 when measuring by incident measuring light.

B-3-3. Insolubilization treatment

If necessary, an insolubilization treatment is performed after the air-assisted stretching treatment and before the underwater stretching treatment and dyeing treatment. The above-mentioned insolubilization treatment is typically performed by immersing the PVA-based resin layer in a boric acid aqueous solution. By performing the insolubilization treatment, water resistance can be imparted to the PVA-based resin layer to prevent the orientation of the PVA from being reduced when immersed in water. The concentration of the boric acid aqueous solution is preferably 1 to 4 parts by weight relative to 100 parts by weight of water. The liquid temperature of the insolubilization bath (boric acid aqueous solution) is preferably 20°C to 50°C.

B-3-4. Dyeing treatment

The dyeing treatment is typically performed by dyeing the PVA resin layer with a dichroic substance (typically iodine). Specifically, it is performed by adsorbing iodine on the PVA resin layer. Examples of the adsorption method include: immersing the PVA resin layer (laminate) in a dyeing solution containing iodine; applying the dyeing solution to the PVA resin layer; spraying the dyeing solution on the PVA resin layer, etc. The method of immersing the laminate in the dyeing solution (dyeing bath) is preferred. This is because iodine can be adsorbed well.

The dyeing solution is preferably an iodine aqueous solution. The amount of iodine mixed is preferably 0.05 to 0.5 parts by weight relative to 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferred to mix iodide in the iodine aqueous solution. As iodide, for example: potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide, etc. can be listed. Among these, potassium iodide is preferred. The amount of iodide mixed is preferably 0.1 to 10 parts by weight relative to 100 parts by weight of water, and more preferably 0.3 to 5 parts by weight. In order to suppress the dissolution of PVA-based resins, the liquid temperature when dyeing with the dyeing solution is preferably 20°C to 50°C. When the PVA resin layer is immersed in the dyeing solution, in order to ensure the transmittance of the PVA resin layer, the immersion time is preferably 5 seconds to 5 minutes, more preferably 30 seconds to 90 seconds.

The dyeing conditions (concentration, liquid temperature, immersion time) can be set so that the monomer transmittance of the final polarizing film is 43.0% or more and the polarization degree is 99.980% or more. As such dyeing conditions, it is preferred to use an iodine aqueous solution as the dyeing solution, and set the ratio of iodine to potassium iodide in the iodine aqueous solution to 1:5~1:20. The ratio of iodine to potassium iodide in the iodine aqueous solution is preferably 1:5~1:10. Thus, a polarizing film having the optical characteristics described above can be obtained.

When dyeing is performed continuously after the laminate is immersed in a treatment bath containing boric acid (typically an insolubilization treatment), the boric acid contained in the treatment bath mixes into the dyeing bath, and the boric acid concentration of the dyeing bath changes over time, resulting in that the dyeing property sometimes becomes unstable. In order to suppress the instability of dyeing property as described above, the upper limit of the boric acid concentration of the dyeing bath is adjusted to preferably 4 parts by weight, more preferably 2 parts by weight, relative to 100 parts by weight of water. On the other hand, the lower limit of the boric acid concentration of the dyeing bath is preferably 0.1 parts by weight, more preferably 0.2 parts by weight, and further preferably 0.5 parts by weight, relative to 100 parts by weight of water. In one embodiment, the dyeing treatment is performed using a dyeing bath pre-mixed with boric acid. Thus, the change ratio of the boric acid concentration when the boric acid in the treatment bath is mixed into the dyeing bath can be reduced. The amount of boric acid pre-mixed into the dyeing bath (i.e., the content of boric acid not from the treatment bath) is preferably 0.1 to 2 parts by weight, more preferably 0.5 to 1.5 parts by weight, relative to 100 parts by weight of water.

B-3-5. Cross-linking treatment

If necessary, a crosslinking treatment is performed after the dyeing treatment and before the underwater stretching treatment. The above-mentioned crosslinking treatment is typically performed by immersing the PVA-type resin layer in an aqueous solution of boric acid. By performing the crosslinking treatment, water resistance can be imparted to the PVA-type resin layer, and in the subsequent underwater stretching, the orientation reduction of the PVA when immersed in high-temperature water can be prevented. The concentration of the aqueous solution of boric acid is preferably 1 to 5 parts by weight relative to 100 parts by weight of water. In addition, when the crosslinking treatment is performed after the above-mentioned dyeing treatment, it is preferred to further mix an iodide. By mixing an iodide, the dissolution of iodine adsorbed on the PVA-type resin layer can be suppressed. The mixing amount of the iodide is preferably 1 to 5 parts by weight relative to 100 parts by weight of water. Specific examples of iodide are as described above. The liquid temperature of the crosslinking bath (boric acid aqueous solution) is preferably 20°C to 50°C.

B-3-6. Underwater stretching treatment

The underwater stretching treatment is performed by immersing the laminate in a stretching bath. According to the underwater stretching treatment, stretching can be performed at a temperature lower than the glass transition temperature (typically around 80°C) of the thermoplastic resin substrate and the PVA resin layer, and stretching can be performed at a high ratio while suppressing the crystallization of the PVA resin layer. As a result, a polarizing film with excellent optical properties can be manufactured.

The stack can be stretched by any appropriate method. Specifically, it can be fixed-end stretching or free-end stretching (for example, a method of unidirectionally stretching the stack by passing it through rollers with different circumferential speeds). Free-end stretching is preferred. The stack can be stretched in one stage or in multiple stages. In the case of multiple stages, the stretching ratio (maximum stretching ratio) of the stack described later is the product of the stretching ratios of each stage.

It is preferred to immerse the laminate in an aqueous solution of boric acid for underwater stretching (boric acid underwater stretching). By using an aqueous solution of boric acid as a stretching bath, the PVA-based resin layer can be given rigidity that can withstand the tension applied during stretching, and water resistance that does not dissolve in water. Specifically, boric acid can generate tetrahydroxyboric acid anions in an aqueous solution and crosslink with the PVA-based resin through hydrogen bonds. As a result, the PVA-based resin layer can be given rigidity and water resistance, and can be stretched well, so that a polarizing film with excellent optical properties can be manufactured.

The above-mentioned boric acid aqueous solution is preferably obtained by dissolving boric acid and/or borate in water as a solvent. The boric acid concentration is preferably 1 to 10 parts by weight relative to 100 parts by weight of water, more preferably 2.5 to 6 parts by weight, and particularly preferably 3 to 5 parts by weight. By setting the boric acid concentration to 1 part by weight or more, the dissolution of the PVA-based resin layer can be effectively suppressed, and a polarizing film with higher properties can be manufactured. It should be noted that an aqueous solution obtained by dissolving boron compounds such as borax, glyoxal, glutaraldehyde, etc. other than boric acid or borate in a solvent can also be used.

It is preferred to mix iodide in the above-mentioned stretching bath (boric acid aqueous solution). By mixing iodide, the dissolution of iodine adsorbed on the PVA resin layer can be suppressed. Specific examples of iodide are as described above. The concentration of iodide is preferably 0.05 to 15 parts by weight, more preferably 0.5 to 8 parts by weight relative to 100 parts by weight of water.

The stretching temperature (liquid temperature of the stretching bath) is preferably 40°C to 85°C, more preferably 60°C to 75°C. At such a temperature, the dissolution of the PVA-type resin layer can be suppressed and the stretching can be performed at a high ratio at the same time. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60°C or above in consideration of the formation of the PVA-type resin layer. In this case, if the stretching temperature is lower than 40°C, it may not be stretched well even considering the plasticization of the thermoplastic resin substrate by water. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-type resin layer, and there is a risk that excellent optical properties cannot be obtained. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

The stretching ratio by underwater stretching is preferably 1.5 times or more, and more preferably 3.0 times or more. The total stretching ratio of the laminate is preferably 5.0 times or more relative to the original length of the laminate, and more preferably 5.5 times or more. By achieving such a high stretching ratio, a polarizing film with excellent optical properties can be manufactured. Such a high stretching ratio can be achieved by adopting an underwater stretching method (boric acid underwater stretching).

B-3-7. Drying and shrinking treatment

The above-mentioned drying and shrinking treatment can be performed by regional heating in which the entire area is heated, or by heating the conveying roller (using the so-called heating roller) (heating roller drying method). It is preferred to use both. By using a heating roller for drying, the heating curling of the laminate can be effectively suppressed, thereby manufacturing a polarizing film with excellent appearance. Specifically, by drying the laminate in a state of relying on a heating roller, the crystallization of the above-mentioned thermoplastic resin substrate can be efficiently promoted and the crystallinity can be increased. Even at a relatively low drying temperature, the crystallinity of the thermoplastic resin substrate can be well increased. As a result, the rigidity of the thermoplastic resin substrate increases, and it becomes a state that can withstand the shrinkage of the PVA-type resin layer caused by drying, and curling can be suppressed. In addition, by using a heating roller, the laminate can be kept in a flat state while drying, so that not only curling but also wrinkles can be suppressed. At this time, the laminate is shrunk in the width direction by the drying and shrinking treatment, thereby improving the optical characteristics. This is because the orientation of PVA and PVA/iodine complex can be effectively improved. The shrinkage rate of the laminate in the width direction caused by the drying and shrinking treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using heated rollers, the stacked body can be continuously shrunk in the width direction while being transported, achieving high productivity.

FIG4 is a schematic diagram showing an example of a drying and shrinking process. In the drying and shrinking process, the stack 200 is dried while being transported by conveying rollers R1 to R6 heated to a predetermined temperature and guide rollers G1 to G4. In the illustrated example, the conveying rollers R1 to R6 are arranged in such a way that the surface of the PVA resin layer and the surface of the thermoplastic resin substrate are continuously heated alternately, but the conveying rollers R1 to R6 may also be arranged in such a way that only one side of the stack 200 (e.g., the surface of the thermoplastic resin substrate) is continuously heated.

Drying conditions can be controlled by adjusting the heating temperature of the conveyor roller (temperature of the heating roller), the number of heating rollers, the contact time with the heating roller, etc. The temperature of the heating roller is preferably 60°C to 120°C, more preferably 65°C to 100°C, and particularly preferably 70°C to 80°C. The crystallinity of the thermoplastic resin can be increased well, curling can be suppressed well, and an optical layer stack with excellent durability can be manufactured. It should be noted that the temperature of the heating roller can be measured by a contact thermometer. In the illustrated example, 6 conveyor rollers are provided, but there is no particular limitation as long as there are multiple conveyor rollers. Conveyor rollers are usually provided in the range of 2 to 40, preferably 4 to 30. The contact time (total contact time) between the stack and the heating roller is preferably 1 second to 300 seconds, more preferably 1 to 20 seconds, and further preferably 1 to 10 seconds.

The heating roller can be installed in a heating furnace (such as an oven) or in a general manufacturing line (at room temperature). It is preferably installed in a heating furnace equipped with an air supply mechanism. By combining drying with the heating roller and hot air drying, the rapid temperature change between the heating rollers can be suppressed, and the shrinkage in the width direction can be easily controlled. The temperature of hot air drying is preferably 30°C to 100°C. In addition, the hot air drying time is preferably 1 second to 300 seconds. The wind speed of the hot air is preferably about 10m/s to 30m/s. It should be noted that this wind speed is the wind speed in the heating furnace, which can be measured by a mini blade type digital anemometer.

B-3-8. Other processing

It is preferred to perform a cleaning treatment after the underwater stretching treatment and before the dry shrinking treatment. The above cleaning treatment is typically performed by immersing the PVA-based resin layer in an aqueous potassium iodide solution.

C. 1st phase difference layer

As described above, the first phase difference layer 20 is an oriented solidified layer of a liquid crystal compound. By using a liquid crystal compound, the difference between nx and ny of the obtained phase difference layer can be greatly increased compared to non-liquid crystal materials, so the thickness of the phase difference layer used to obtain the desired in-plane phase difference can be greatly reduced. As a result, the polarizing plate with a phase difference layer can be further thinned and lightweight. In this specification, "oriented solidified layer" refers to a layer in which the liquid crystal compound is oriented in a predetermined direction within the layer and its oriented state is fixed. It should be noted that the "oriented solidified layer" is a concept including an oriented hardened layer obtained by hardening a liquid crystal monomer as described later. In this embodiment, the representative rod-shaped liquid crystal compound is oriented in a state of being arranged in parallel along the slow axis direction of the first phase difference layer (oriented along the plane).

As a liquid crystal compound, for example, a liquid crystal compound whose liquid crystal phase is a nematic phase (nematic liquid crystal) can be cited. As such a liquid crystal compound, for example, a liquid crystal polymer or a liquid crystal monomer can be used. The manifestation mechanism of the liquid crystal properties of the liquid crystal compound can be lyotropic or thermotropic. The liquid crystal polymer and the liquid crystal monomer can be used alone or in combination.

When the liquid crystal compound is a liquid crystal monomer, it is preferred that the liquid crystal monomer is a polymerizable monomer and a crosslinking monomer. This is because the orientation state of the liquid crystal monomer can be fixed by polymerizing or crosslinking (i.e., curing) the liquid crystal monomer. After the liquid crystal monomer is oriented, for example, if the liquid crystal monomers are polymerized or crosslinked with each other, the above-mentioned orientation state can be fixed. Here, a polymer is formed by polymerization, and a three-dimensional network structure is formed by crosslinking, but they are non-liquid crystal. Therefore, the first phase difference layer formed will not shift to a liquid crystal phase, a glass phase, or a crystalline phase due to, for example, temperature changes unique to liquid crystal compounds. As a result, the first phase difference layer becomes a phase difference layer that is not affected by temperature changes and has excellent stability.

The temperature range in which the liquid crystal monomer exhibits liquid crystallinity varies depending on its type. Specifically, the temperature range is preferably 40°C to 120°C, more preferably 50°C to 100°C, and most preferably 60°C to 90°C.

As the above-mentioned liquid crystal monomer, any appropriate liquid crystal monomer can be used. For example, polymerizable liquid crystal original compounds described in Japanese Patent Publication No. 2002-533742 (WO00/37585), EP358208 (US5211877), EP66137 (US4388453), WO93/22397, EP0261712, DE19504224, DE4408171, and GB2280445 can be used. As specific examples of such polymerizable liquid crystal original compounds, for example, BASF's trade name LC242, Merck's trade name E7, and Wacker-Chem's trade name LC-Sillicon-CC3767 can be cited. As a liquid crystal monomer, for example, a nematic liquid crystal monomer is preferred.

The oriented solidified layer of the liquid crystal compound can be formed by the following method: performing an oriented treatment on the surface of a predetermined substrate, applying a coating liquid containing a liquid crystal compound on the surface, orienting the liquid crystal compound in a direction corresponding to the above-mentioned oriented treatment, and fixing the oriented state. In one embodiment, the substrate is any suitable resin film, and the oriented solidified layer formed on the substrate can be transferred to the surface of the polarizing plate 10. In another embodiment, the substrate can be the second protective layer 13. In this case, the transfer step can be omitted and the oriented solidified layer (first phase difference layer) can be continuously stacked by rollers after forming the oriented solidified layer, thereby further improving productivity.

As the above-mentioned orientation treatment, any suitable orientation treatment can be adopted. Specifically, mechanical orientation treatment, physical orientation treatment, and chemical orientation treatment can be cited. Specific examples of mechanical orientation treatment include friction treatment and stretching treatment. Specific examples of physical orientation treatment include magnetic field orientation treatment and electric field orientation treatment. Specific examples of chemical orientation treatment include tilted evaporation method and light orientation treatment. The treatment conditions of various orientation treatments can adopt any suitable conditions according to the purpose.

The liquid crystal compound can be oriented as follows: the liquid crystal compound is treated at a temperature that exhibits a liquid crystal phase according to the type of the liquid crystal compound. By performing such a temperature treatment, the liquid crystal compound becomes a liquid crystal state, and the liquid crystal compound is oriented in accordance with the orientation treatment direction of the substrate surface.

In one embodiment, the fixation of the orientation state is performed by cooling the liquid crystal compound that has been aligned as described above. In the case where the liquid crystal compound is a polymerizable monomer or a crosslinking monomer, the fixation of the orientation state can be performed by subjecting the liquid crystal compound that has been aligned as described above to a polymerization treatment or a crosslinking treatment.

Specific examples of liquid crystal compounds and details of the method for forming an oriented solidified layer are described in Japanese Patent Publication No. 2006-163343. The contents of the publication are incorporated into this specification as a reference.

、杯芳烴等這樣的環狀母核配置於分子的中心，並將直鏈的烷基、烷氧基、取代苯甲醯氧基等作為其側鏈放射狀地取代而成的結構。作為盤狀液晶的代表例，可列舉在C.Destrade等的研究報告、Mol.Cryst.Liq.Cryst.71卷、111頁(1981年)中記載的苯衍生物、聯伸三苯衍生物、參茚并苯衍生物、酞 菁衍生物、B.Kohne等的研究報告、Angew.Chem.96卷、70頁(1984年)中記載的環己烷衍生物、以及J.M.Lehn等的研究報告、J.Chem.Soc.Chem.Commun.，1794頁(1985年)、J.Zhang等的研究報告、J.Am.Chem.Soc.116卷、2655頁(1994年)中記載的氮冠類、苯基乙炔類的大環。作為盤狀液晶化合物的其它具體例，可列舉例如：日本特開2006-133652號公報、日本特開2007-108732號公報、日本特開2010-244038號公報中記載的化合物。將上述文獻及公報的記載作為參考引用至本說明書。 As other examples of oriented solidified layers, discotic liquid crystal compounds can be listed as being oriented in any of the states of vertical orientation, mixed orientation, and tilted orientation. For discotic liquid crystal compounds, typically, the disc plane of the discotic liquid crystal compound is oriented substantially perpendicular to the film plane of the first phase difference layer. The discotic liquid crystal compound being substantially perpendicular means that the average value of the angle between the film plane and the disc plane of the discotic liquid crystal compound is preferably 70°~90°, more preferably 80°~90°, and further preferably 85°~90°. Discotic liquid crystal compounds generally refer to liquid crystal compounds having a discotic molecular structure, wherein the discotic molecular structure is a combination of benzene, 1,3,5-triazine, and 1,4-dole-2-nitropropene.

A structure in which a cyclic mother core such as calixarene is placed at the center of the molecule, and a straight chain alkyl, alkoxy, substituted benzoyloxy, etc. is radially substituted as its side chains. Representative examples of discotic liquid crystals include benzene derivatives, triphenylene derivatives, indenylene derivatives, and phthalocyanine derivatives described in the research report of C. Destrade et al., Mol. Cryst. Liq. Cryst., Vol. 71, p. 111 (1981); cyclohexane derivatives described in the research report of B. Kohne et al., Angew. Chem., Vol. 96, p. 70 (1984); and nitrogen crown-type and phenylacetylene-type macrocycles described in the research report of J. M. Lehn et al., J. Chem. Soc. Chem. Commun., p. 1794 (1985); and in the research report of J. Zhang et al., J. Am. Chem. Soc., Vol. 116, p. 2655 (1994). Other specific examples of discotic liquid crystal compounds include compounds described in Japanese Patent Application Publication No. 2006-133652, Japanese Patent Application Publication No. 2007-108732, and Japanese Patent Application Publication No. 2010-244038. The contents of the above documents and publications are incorporated herein by reference.

In one embodiment, the first phase difference layer 20 is a single layer of an oriented solidified layer of a liquid crystal compound as shown in FIG1 and FIG2. When the first phase difference layer 20 is composed of a single layer of an oriented solidified layer of a liquid crystal compound, its thickness is preferably 0.5 μm to 7 μm, and more preferably 1 μm to 5 μm. By using a liquid crystal compound, an in-plane phase difference equivalent to that of a resin film can be achieved with a thickness significantly thinner than that of a resin film.

Typically, the refractive index characteristics of the first phase difference layer show a relationship of nx>ny=nz. The first phase difference layer is typically provided to impart anti-reflection characteristics to the polarizing plate, and when the first phase difference layer is a single layer of a directional solidification layer, it can function as a λ/4 plate. In this case, the in-plane phase difference Re(550) of the first phase difference layer is preferably 100nm~190nm, more preferably 110nm~170nm, and further preferably 130nm~160nm. It should be noted that, here, "ny=nz" includes not only the case where ny and nz are completely equal, but also the case where they are substantially equal. Therefore, within the range that does not impair the effect of the present invention, it may be ny>nz or ny< nz.

The Nz coefficient of the first phase difference layer is preferably 0.9 to 1.5, and more preferably 0.9 to 1.3. By satisfying this relationship, when the obtained polarizing plate with a phase difference layer is used in an image display device, a very excellent reflection hue can be achieved.

The first phase difference layer can show an inverse dispersion wavelength characteristic in which the phase difference value increases in response to the wavelength of the measured light, a positive wavelength dispersion characteristic in which the phase difference value decreases in response to the wavelength of the measured light, or a flat wavelength dispersion characteristic in which the phase difference value hardly changes with the wavelength of the measured light. In one embodiment, the first phase difference layer shows an inverse dispersion wavelength characteristic. In this case, Re(450)/Re(550) of the phase difference layer is preferably greater than 0.8 and less than 1, and more preferably greater than 0.8 and less than 0.95. With such a structure, very excellent anti-reflection characteristics can be achieved.

The angle θ between the slow axis of the first phase difference layer 20 and the absorption axis of the polarizing film 11 is preferably 40°~50°, more preferably 42°~48°, and further preferably about 45°. When the angle θ is in such a range, as described above, by setting the first phase difference layer to a λ/4 plate, a polarizing plate with a phase difference layer having very excellent circular polarization characteristics (resulting in very excellent anti-reflection characteristics) can be obtained.

In another embodiment, the first retardation layer 20 may have a stacked structure of a first oriented solidified layer 21 and a second oriented solidified layer 22 as shown in FIG3 . In this case, one of the first oriented solidified layer 21 and the second oriented solidified layer 22 may function as a λ/4 plate, and the other may function as a λ/2 plate. Therefore, the thickness of the first oriented solidified layer 21 and the second oriented solidified layer 22 may be adjusted so as to obtain a desired in-plane retardation of a λ/4 plate or a λ/2 plate. For example, when the first oriented solidified layer 21 functions as a λ/2 plate and the second oriented solidified layer 22 functions as a λ/4 plate, the thickness of the first oriented solidified layer 21 is, for example, 2.0 μm to 3.0 μm, and the thickness of the second oriented solidified layer 22 is, for example, 1.0 μm to 2.0 μm. In this case, the in-plane phase difference Re(550) of the first oriented solidified layer is preferably 200 nm to 300 nm, more preferably 230 nm to 290 nm, and further preferably 250 nm to 280 nm. The in-plane phase difference Re(550) of the second oriented solidified layer is as described above with respect to the single-layer oriented solidified layer. The angle between the slow axis of the first oriented solidified layer and the absorption axis of the polarizing film is preferably 10°~20°, more preferably 12°~18°, and further preferably about 15°. The angle between the slow axis of the second oriented solidified layer and the absorption axis of the polarizing film is preferably 70°~80°, more preferably 72°~78°, and further preferably about 75°. With such a structure, characteristics close to the ideal reverse wavelength dispersion characteristics can be obtained, and as a result, very excellent anti-reflection characteristics can be achieved. The liquid crystal compounds constituting the first oriented solidified layer and the second oriented solidified layer, the formation methods of the first oriented solidified layer and the second oriented solidified layer, the optical characteristics, etc. are as described above for the single-layer oriented solidified layer.

D. Second phase difference layer

As described above, the second phase difference layer may be a so-called positive C plate whose refractive index characteristics show the relationship of nz>nx=ny. By using a positive C plate as the second phase difference layer, reflection in the tilt direction can be well prevented, and a wide viewing angle of the anti-reflection function can be achieved. In this case, the phase difference Rth(550) in the thickness direction of the second phase difference layer is preferably -50nm~-300nm, more preferably -70nm~-250nm, further preferably -90nm~-200nm, and particularly preferably -100nm~-180nm. Here, "nx=ny" includes not only the case where nx and ny are strictly equal, but also the case where nx and ny are substantially equal. That is, the in-plane phase difference Re(550) of the second phase difference layer can be less than 10nm.

The second phase difference layer having the refractive index characteristic of nz>nx=ny can be formed by any appropriate material. The second phase difference layer is preferably formed by a film containing a liquid crystal material fixed to a homeotropic alignment. The liquid crystal material (liquid crystal compound) that can be homeotropically aligned can be a liquid crystal monomer or a liquid crystal polymer. As a specific example of the method for forming the liquid crystal compound and the phase difference layer, the liquid crystal compound and the method for forming the phase difference layer described in [0020] to [0028] of Japanese Patent Publication No. 2002-333642 can be cited. In this case, the thickness of the second phase difference layer is preferably 0.5μm~10μm, more preferably 0.5μm~8μm, and further preferably 0.5μm~5μm.

E. Conductive layer or isotropic substrate with conductive layer

The conductive layer can be formed by forming a metal oxide film on any appropriate substrate using any appropriate film forming method (e.g., vacuum evaporation, sputtering, CVD, ion plating, spraying, etc.). Examples of metal oxides include: indium oxide, tin oxide, zinc oxide, indium-tin composite oxide, tin-antimony composite oxide, zinc-aluminum composite oxide, and indium-zinc composite oxide. Among them, indium-tin composite oxide (ITO) is preferred.

When the conductive layer contains metal oxide, the thickness of the conductive layer is preferably less than 50nm, and more preferably less than 35nm. The lower limit of the thickness of the conductive layer is preferably 10nm.

The conductive layer can be transferred from the substrate to the first phase difference layer (or, if there is a second phase difference layer, the second phase difference layer), and the conductive layer can be used alone as a constituent layer of the polarizing plate with a phase difference layer, or can be made into a layer stack with the substrate (substrate with a conductive layer) and stacked on the first phase difference layer (or, if there is a second phase difference layer, the second phase difference layer). It is preferred that the substrate is optically isotropic, so the conductive layer can be used as an isotropic substrate with a conductive layer for the polarizing plate with a phase difference layer.

As an optically isotropic substrate (isotropic substrate), any appropriate isotropic substrate can be used. As materials constituting the isotropic substrate, for example, materials having a main skeleton of resins without a conjugated system such as norbornene resins and olefin resins; materials having cyclic structures such as lactone rings and pentylimide rings in the main chain of acrylic resins, etc. If such materials are used, when forming an isotropic substrate, the phenomenon of phase difference accompanying the orientation of the molecular chain can be suppressed to a relatively small level. The thickness of the isotropic substrate is preferably less than 50μm, and more preferably less than 35μm. The lower limit of the thickness of the isotropic substrate is, for example, 20μm.

The conductive layer and/or the conductive layer of the isotropic substrate with the conductive layer can be patterned as needed. Through patterning, a conductive portion and an insulating portion can be formed. As a result, an electrode can be formed. The electrode can function as a touch sensor electrode that senses contact with the touch panel. As a patterning method, any appropriate method can be adopted. As specific examples of patterning methods, wet etching and screen printing can be listed.

F. Image display device

The polarizing plate with a phase difference layer described in the above items A to E can be applied to an image display device. Therefore, the present invention includes an image display device using such a polarizing plate with a phase difference layer. As representative examples of image display devices, there can be cited a liquid crystal display device and an electroluminescent (EL) display device (for example, an organic EL display device, an inorganic EL display device). The image display device of the embodiment of the present invention has a polarizing plate with a phase difference layer described in the above items A to E on its visible side. The polarizing plate with a phase difference layer is stacked in a manner that the phase difference layer becomes the side of the image display unit (for example, a liquid crystal unit, an organic EL unit, an inorganic EL unit) (in a manner that the polarizing film becomes the visible side). In one embodiment, the image display device may have a curved shape (essentially a curved display screen), and/or bendable or foldable. In such an image display device, the effect of the polarizing plate with a phase difference layer of the present invention becomes significant.

Implementation example

The present invention is described in detail below through examples, but the present invention is not limited to these examples. The measurement methods of various properties are as follows. It should be noted that, unless otherwise specified, the "parts" and "%" in the examples and comparative examples are based on weight.

(1)Thickness

Thickness below 10μm is measured using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name "MCPD-3000"). Thickness greater than 10μm is measured using a digital micrometer (manufactured by Anritsu Co., Ltd., product name "KC-351C").

(2) Single body transmittance and polarization degree

For the polarizing film/protective layer stack (polarizing plate) used in the examples and comparative examples, the single transmittance Ts, parallel transmittance Tp, and orthogonal transmittance Tc measured using an ultraviolet-visible spectrophotometer (V-7100 manufactured by JASCO Corporation) are used as the Ts, Tp, and Tc of the polarizing film. These Ts, Tp, and Tc are Y values obtained by measuring the 2-degree field of view (C light source) of JIS Z8701 and correcting for visibility. It should be noted that the refractive index of the protective layer is 1.50, and the refractive index of the surface of the polarizing film opposite to the protective layer is 1.53.

Based on the obtained Tp and Tc, the polarization degree P is calculated using the following formula.

Polarization degree P(%) = {(Tp-Tc)/(Tp+Tc)} ^1/2 ×100

It should be noted that the spectrophotometer can be used for equivalent measurements using LPF-200 manufactured by Otsuka Electronics Co., Ltd. For example, for samples 1 to 3 of polarizing plates having the same structure as the following embodiment, the single transmittance Ts and polarization degree P were obtained by using V-7100 and LPF-200, and their measured values are shown in Table 1. As shown in Table 1, it can be seen that the difference between the measured value of the single transmittance of V-7100 and the measured value of the single transmittance of LPF-200 is less than 0.1%, and the same measurement results can be obtained using any spectrophotometer.

It should be noted that, for example, when a polarizing plate with an adhesive having an anti-glare (AG) surface treatment and diffusion properties is used as a measurement object, different measurement results may be obtained depending on the spectrophotometer. In this case, numerical conversion is performed based on the measurement values when the same polarizing plate is measured by each spectrophotometer, thereby compensating for the difference in the measurement values depending on the spectrophotometer.

(3) Deviation of the optical properties of long strip polarizing films

From the polarizing plate used in the embodiment and the comparative example, measurement samples were cut out at five locations at equal intervals along the width direction, and the single body transmittance of the central portion of each of the five measurement samples was measured in the same manner as in (2) above. Then, the difference between the maximum and minimum values of the single body transmittance measured at each measurement position was calculated, and this value was set as the deviation of the optical characteristics of the long strip polarizing film.

(4) Deviation of optical properties of single-sheet polarizing film

A 100 mm × 100 mm measurement sample was cut out from the polarizing plate used in the embodiment and the comparative example, and the deviation of the optical characteristics of the single polarizing plate (50 cm ² ) was obtained. Specifically, the single transmittance was measured at a total of 5 positions, including a position about 1.5 cm to 2.0 cm inward from the midpoint of each of the 4 sides of the measurement sample and the central part, in the same manner as in (2) above. Next, the difference between the maximum and minimum values of the single transmittance measured at each measurement position was calculated, and this value was set as the deviation of the optical characteristics of the single polarizing film.

(5) Curve

The polarizing plate with phase difference layer obtained in the embodiment and comparative example was cut into a size of 110mm×60mm. At this time, it was cut in such a way that the absorption axis direction of the polarizing film became the long side direction. The cut polarizing plate with phase difference layer was adhered to a glass plate with a size of 120mm×70mm and a thickness of 0.2mm through an adhesive as a test sample. The test sample was placed in a heating oven maintained at 85°C for 24 hours, and the warp amount after being taken out was measured. When the test sample was placed on a plane with the glass plate facing down, the height of the highest part from the plane was taken as the warp amount.

(6) Unit weight

The polarizing plates with retardation layers obtained in Examples and Comparative Examples were cut into predetermined sizes, and the weight (mg) was divided by the area (cm ² ) to calculate the weight per unit area of the polarizing plates with retardation layers (unit weight).

(7) Bending resistance

The polarizing plate with phase difference layer obtained in the examples and comparative examples was cut into a size of 50mm×100mm. At this time, it was cut in such a way that the absorption axis direction of the polarizing film became the short side direction. Using a folding tester with a constant temperature and humidity chamber (manufactured by YUASA, CL09 type-D01), the cut polarizing plate with phase difference layer was subjected to a bending test at 20°C and 50%RH. Specifically, the polarizing plate with phase difference layer was repeatedly bent in a direction parallel to the absorption axis direction with the phase difference layer side becoming the outer side, and the number of bends until cracks, peeling, film breakage, etc. that caused display defects were generated was measured, and evaluation was performed according to the following criteria (bending diameter: 2mmφ).

<Evaluation criteria>

Less than 10,000 times: defective

More than 10,000 times and less than 30,000 times: Good

More than 30,000 times: Excellent

[Implementation Example 1]

1. Production of polarizing film

As the thermoplastic resin substrate, a long strip of amorphous isophthalic acid copolymer polyethylene terephthalate film (thickness: 100μm) with a water absorption rate of 0.75% and a Tg of about 75°C was used. One side of the resin substrate was subjected to 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 acetyl acetyl modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER Z410") at a ratio of 9:1, and the resulting mixture was dissolved in water to prepare a PVA aqueous solution (coating solution).

The above-mentioned PVA aqueous solution was applied to the corona-treated surface of the resin substrate and dried at 60°C to form a PVA-based resin layer with a thickness of 13 μm, thereby producing a laminate.

In an oven at 130°C, the obtained laminate is uniaxially stretched to 2.4 times in the longitudinal direction (length direction) between rollers with different circumferential speeds (air-assisted stretching treatment).

Next, the laminate was immersed in an insolubilization bath (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 relative to 100 parts by weight of water) at a liquid temperature of 30°C for 60 seconds while adjusting the concentration so that the single transmittance (Ts) of the final polarizing film would be 43.0% or more (dyeing treatment).

Then, it was immersed in a crosslinking bath (boric acid aqueous solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (crosslinking treatment).

Then, the laminate was immersed in a boric acid aqueous solution (boric acid concentration 4.0 wt%) at a liquid temperature of 70°C, and uniaxially stretched (underwater stretching treatment) between rollers of different circumferential speeds in a manner such that the total stretching ratio in the longitudinal direction (length direction) was 5.5 times.

Then, the laminate is immersed in a cleaning bath (aqueous solution obtained by mixing 4 parts by weight of potassium iodide with 100 parts by weight of water) at a liquid temperature of 20°C (cleaning treatment).

Then, while drying in an oven maintained at 90°C, it was placed in contact with a SUS heating roller maintained at 75°C for about 2 seconds (drying and shrinking treatment). The shrinkage rate of the laminate in the width direction due to the drying and shrinking treatment was 5.2%.

In this way, a polarizing film with a thickness of 5μm is formed on the resin substrate.

2. Production of polarizing plate

On the surface of the polarizing film obtained above (the surface opposite to the resin substrate), an acrylic film (surface refractive index 1.50, 40μm) is bonded as a protective layer through a UV-curable adhesive. Specifically, the curable adhesive is applied in such a way that the total thickness becomes 1.0μm, and the bonding is performed using a roller. Then, UV light is irradiated from the protective layer side to cure the adhesive. Next, after cutting the two ends, the resin substrate is peeled off to obtain a long strip of polarizing plate (width: 1300mm) having a protective layer/polarizing film structure. The single transmittance of the polarizing plate (actually a polarizing film) is 43.15%, and the degree of polarization is 99.995%. In addition, the deviation of the optical properties of the long strip polarizing film is 0.14%, and the deviation of the optical properties of the single sheet polarizing film is 0.09%.

3. Preparation of the first directional solidification layer and the second directional solidification layer constituting the phase difference layer

10 g of polymerizable liquid crystal (manufactured by BASF: trade name "Paliocolor LC242", represented by the following formula) showing a nematic liquid crystal phase and 3 g of a photopolymerization initiator for the polymerizable liquid crystal compound (manufactured by BASF: trade name "IRGACURE 907") were dissolved in 40 g of toluene to prepare a liquid crystal composition (coating liquid).

The surface of a polyethylene terephthalate (PET) film (38 μm thick) was rubbed with a rubbing cloth to perform an orientation treatment. The orientation treatment direction was set to be 15° relative to the absorption axis direction of the polarizing film when attached to a polarizing plate when observed from the visible side. The above-mentioned liquid crystal coating liquid was applied to the orientation-treated surface using a rod coater, and heated and dried at 90°C for 2 minutes to orient the liquid crystal compound. Using a metal halide lamp, the liquid crystal layer thus formed was irradiated with 1 mJ/ ^cm2 of light to harden the liquid crystal layer, thereby forming a liquid crystal orientation solidified layer A on the PET film. The thickness of the liquid crystal orientation solidified layer A is 2.5 μm, and the in-plane phase difference Re (550) is 270 nm. In addition, the liquid crystal orientation solidified layer A has a refractive index distribution of nx>ny=nz.

The coating thickness was changed, and the orientation treatment direction was set to be 75° relative to the absorption axis direction of the polarizing film when viewed from the visible side. In addition, a liquid crystal orientation solidification layer B was formed on the PET film in the same manner as above. The thickness of the liquid crystal orientation solidification layer B was 1.5μm, and the in-plane phase difference Re(550) was 140nm. In addition, the liquid crystal orientation solidification layer B had a refractive index distribution of nx>ny=nz.

4. Production of polarizing plate with phase difference layer

The liquid crystal oriented solidified layer A and the liquid crystal oriented solidified layer B obtained in 3. above are sequentially transferred to the surface of the polarizing film of the polarizing plate obtained in 2. above. At this time, the transfer (lamination) is performed in such a way that the angle formed by the absorption axis of the polarizing film and the slow axis of the oriented solidified layer A is 15°, and the angle formed by the absorption axis of the polarizing film and the slow axis of the oriented solidified layer B is 75°. It should be noted that each transfer (lamination) is performed through the ultraviolet curing adhesive (thickness 1.0μm) used in 2. above. In this way, a polarizing plate with a phase difference layer having a structure of protective layer/adhesive layer/polarizing film/adhesive layer/phase difference layer (first oriented solidified layer/adhesive layer/second oriented solidified layer) is obtained. The total thickness of the obtained polarizing plate with phase difference layer is 52μm. The obtained polarizing plate with phase difference layer is subjected to the evaluations of (5) to (7) above. The warp amount is 1.8mm.

[Example 2]

A polarizing plate with a phase difference layer was prepared in the same manner as in Example 1 except that an acrylic film with a thickness of 20 μm was used as a protective layer. The total thickness of the obtained polarizing plate with a phase difference layer was 32 μm. The obtained polarizing plate with a phase difference layer was subjected to the same evaluation as in Example 1. The warp amount was 1.5 mm.

[Implementation Example 3]

A polarizing plate with a phase difference layer was prepared in the same manner as in Example 1 except that a 25 μm thick triacetate cellulose (TAC) film was used as a protective layer. The total thickness of the obtained polarizing plate with a phase difference layer was 37 μm. The obtained polarizing plate with a phase difference layer was evaluated in the same manner as in Example 1. The warp amount was 1.3 mm.

[Comparison Example 1]

1. Production of polarizers

A polyvinyl alcohol resin film having an average degree of polymerization of 2,400, a saponification degree of 99.9 mol%, and a thickness of 30 μm was prepared. The polyvinyl alcohol film was immersed in a 20°C swelling bath (water bath) for 30 seconds to be swelled, and stretched to 2.4 times in the transport direction between rollers with different peripheral speed ratios (swelling step). Then, the film was immersed in a 30°C dyeing bath (an aqueous solution having an iodine concentration of 0.03 wt% and a potassium iodide concentration of 0.3 wt%) and dyed so that the final monomer transmittance after stretching would be a desired value, and stretched to 3.7 times in the transport direction based on the original polyvinyl alcohol film (polyvinyl alcohol film that was not stretched in the transport direction at all) (dyeing step). The immersion time at this time was about 60 seconds. Next, the dyed polyvinyl alcohol film was immersed in a crosslinking bath (aqueous solution with a boric acid concentration of 3.0% by weight and a potassium iodide concentration of 3.0% by weight) at 40°C, and stretched to 4.2 times the original polyvinyl alcohol film in the transport direction (crosslinking step). Furthermore, the obtained polyvinyl alcohol film was immersed in a stretching bath (aqueous solution with a boric acid concentration of 4.0% by weight and a potassium iodide concentration of 5.0% by weight) at 64°C for 50 seconds, stretched to 6.0 times the original polyvinyl alcohol film in the transport direction (stretching step), and then immersed in a cleaning bath (aqueous solution with a potassium iodide concentration of 3.0% by weight) at 20°C for 5 seconds (cleaning step). The washed polyvinyl alcohol film was dried at 30°C for 2 minutes to produce a polarizer (thickness 12μm).

2. Production of polarizing plate

As an adhesive, an aqueous solution containing a polyvinyl alcohol resin having an acetylacetyl group (average degree of polymerization of 1,200, saponification degree of 98.5 mol%, acetylacetylization rate of 5 mol%) and hydroxymethyl melamine in a weight ratio of 3:1 was used. Using the adhesive, a 25μm thick triacetyl cellulose (TAC) film with a hard coating layer was laminated to one side of the polarizer obtained above using a roll laminator, and a 25μm thick TAC film was laminated to the other side of the polarizer, and then heated and dried in an oven (temperature of 60°C, time of 5 minutes), and a polarizing plate having a structure of protective layer 1 (thickness 25μm)/adhesive layer/polarizer/adhesive layer/protective layer 2 (thickness 25μm) was produced.

3. Production of polarizing plate with phase difference layer

The surface of the protective layer 2 of the polarizing plate obtained in 2. above was transferred with the liquid crystal oriented solidification layer A and the liquid crystal oriented solidification layer B in the same manner as in Example 1, and a polarizing plate with a phase difference layer having a structure of protective layer 1/bonding layer/polarizer/bonding layer/protective layer 2/bonding layer/phase difference layer (first oriented solidification layer/bonding layer/second oriented solidification layer) was prepared. The total thickness of the obtained polarizing plate with a phase difference layer was 68μm. The obtained polarizing plate with a phase difference layer was subjected to the same evaluation as in Example 1. The warpage was 4.2mm.

[Comparison Example 2]

A polarizing film and a polarizing plate were prepared in the same manner as in Example 1 except that potassium iodide was not added to the PVA aqueous solution (coating solution), the stretching ratio in the air-assisted stretching treatment was set to 1.8 times, and no heating roller was used in the dry shrinking treatment. The single transmittance of the polarizing plate (actually a polarizing film) was 42.34%, and the polarization degree was 99.988%. A polarizing plate with a phase difference layer was prepared in the same manner as in Example 1 except that the polarizing plate was used.

[Comparison Example 3]

1. Production of polarizing plate

A TAC film with a thickness of 25 μm was used as the protective layer. In addition, a long polarizing plate (width: 1300 mm) having a protective layer/polarizing film structure was obtained in the same manner as in Example 1.

2. Preparation of phase difference film constituting the phase difference layer

2-1. Polymerization of polyester carbonate resins

The polymerization was carried out using a batch polymerization apparatus consisting of two vertical reactors equipped with stirring blades and a reflux cooler controlled at 100°C. 29.60 parts by mass (0.046 mol) of bis[9-(2-phenoxycarbonylethyl)fluoren-9-yl]methane, 29.21 parts by mass (0.200 mol) of isosorbide (ISB), 42.28 parts by mass (0.139 mol) of spiroglycol (SPG), 63.77 parts by mass (0.298 mol) of diphenyl carbonate (DPC), and 1.19×10 ^-2 parts by mass (6.78×10 ^-5 mol) of calcium acetate monohydrate as a catalyst were added. After the reactor was depressurized and replaced with nitrogen, it was heated with a heating medium and agitation was started when the internal temperature reached 100°C. 40 minutes after the start of the temperature rise, the internal temperature reached 220°C, and the pressure was reduced while controlling and maintaining the temperature. It reached 13.3 kPa 90 minutes after reaching 220°C. The phenol vapor produced as a by-product during the polymerization reaction was introduced into a 100°C reflux cooler, and a certain amount of monomer components contained in the phenol vapor was returned to the reactor, while the uncondensed phenol vapor was introduced into a 45°C condenser for recovery. After nitrogen was introduced into the first reactor to temporarily restore it to atmospheric pressure, the oligomerized reaction liquid in the first reactor was transferred to the second reactor. Next, the temperature in the second reactor was raised and the pressure was reduced, and the internal temperature reached 240°C and the pressure reached 0.2 kPa in 50 minutes. Then, polymerization was carried out until the predetermined stirring power was reached. When the predetermined power was reached, nitrogen was introduced into the reactor, the pressure was restored, and the generated polyester carbonate resin was extruded into water, and the strands were cut to obtain pellets.

2-2. Preparation of phase difference film

The obtained polyester carbonate resin (particles) was vacuum dried at 80°C for 5 hours, and then a 135μm thick long resin film was produced using a film-making device equipped with a single screw extruder (manufactured by Toshiba Machinery Co., Ltd., cylinder setting temperature: 250°C), a T-die (width 200mm, setting temperature: 250°C), a chill roll (setting temperature: 120~130°C) and a winder. The obtained long resin film was stretched in the width direction at a stretching temperature of 133°C and a stretching ratio of 2.8 times to obtain a 53μm thick phase difference film. The obtained phase difference film had a Re(550) of 141nm, a Re(450)/Re(550) of 0.82, and an Nz coefficient of 1.12.

3. Production of polarizing plate with phase difference layer

The phase difference film obtained in 2. is bonded to the surface of the polarizing film of the polarizing plate obtained in 1. above through an acrylic adhesive (thickness 5 μm). At this time, bonding is performed in a manner that the absorption axis of the polarizing film and the slow axis of the phase difference film form an angle of 45°. In this way, a polarizing plate with a phase difference layer having a structure of protective layer/bonding layer/polarizing film/adhesive layer/phase difference layer is obtained. The total thickness of the obtained polarizing plate with a phase difference layer is 89 μm. The obtained polarizing plate with a phase difference layer is provided for the evaluation of (6) and (7) above.

The structures and evaluation results of the polarizing plates with phase difference layers obtained in Examples 1 to 3 and Comparative Examples 1 and 3 are shown in Table 2.

[Table 2]

[Evaluation]

According to Table 2 and the comparison between Example 1 and Comparative Example 2, it can be seen that the polarizing plate with a phase difference layer of the embodiment of the present invention is thin, which can suppress the warp after the heating test and has excellent optical properties. In addition, by making the weight per unit area of the polarizing plate with a phase difference layer below a predetermined value, the bending resistance is improved.

Industrial practicality

The polarizing plate with phase difference layer of the present invention can be suitably used as a circular polarizing plate for liquid crystal display devices, organic EL display devices and inorganic EL display devices.

10: Polarizing plate

11: Polarizing film

12: 1st protective layer

13: Second protective layer

20: Phase difference layer (first phase difference layer)

100: Polarizing plate with phase difference layer

Claims (9)

A method for manufacturing a polarizing plate with a phase difference layer, wherein the polarizing plate with a phase difference layer comprises a polarizing plate and a phase difference layer, wherein the polarizing plate comprises a polarizing film and a protective layer disposed on at least one side of the polarizing film, wherein the polarizing film is composed of a polyvinyl alcohol resin film containing a dichroic substance, wherein the thickness is less than 8 μm, the single body transmittance is greater than 43.0%, and the polarization degree is greater than 99.980%, and the phase difference layer is a directional solidification layer of a liquid crystal compound. The manufacturing method comprises: manufacturing the polarizing film by the following manufacturing method, wherein: A laminate is formed by forming a polyvinyl alcohol resin layer on one side of a shaped thermoplastic resin substrate, wherein the polyvinyl alcohol resin layer contains iodide or sodium chloride and polyvinyl alcohol resin; and the laminate is subjected to an air-assisted stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment in sequence, wherein the drying shrinkage treatment is to heat the laminate while conveying it in the length direction so that the laminate shrinks by 2% to 10% in the width direction, and the heating is to use a heating roller in a heating furnace and the total contact time between the laminate and the heating roller is 1 to 20 seconds. A method for manufacturing a polarizing plate with a phase difference layer as claimed in claim 1, wherein the total thickness of the polarizing plate with a phase difference layer is less than 60 μm. The manufacturing method of a polarizing plate with a phase difference layer as claimed in claim 1, wherein the phase difference layer is a single layer of a directional solidified layer of a liquid crystal compound, the Re (550) of the phase difference layer is 100nm~190nm, and the angle between the slow axis of the phase difference layer and the absorption axis of the polarizing film is 40°~50°. The manufacturing method of a polarizing plate with a phase difference layer as claimed in claim 1, wherein the phase difference layer has a stacked structure of an oriented solidified layer of a first liquid crystal compound and an oriented solidified layer of a second liquid crystal compound, the Re(550) of the oriented solidified layer of the first liquid crystal compound is 200nm~300nm, and the angle between its slow axis and the absorption axis of the polarizing film is 10°~20°, and the Re(550) of the oriented solidified layer of the second liquid crystal compound is 100nm~190nm, and the angle between its slow axis and the absorption axis of the polarizing film is 70°~80°. A method for manufacturing a polarizing plate with a phase difference layer as claimed in claim 1, wherein the difference between the maximum and minimum values of the single transmittance of the polarizing film in an area of 50 ^cm2 is less than 0.2%. A method for manufacturing a polarizing plate with a phase difference layer as claimed in claim 1, wherein the width of the polarizing film is greater than 1000 mm, and the difference between the maximum and minimum values of the single transmittance in the position along the width direction is less than 0.3%. The method for manufacturing a polarizing plate with a phase difference layer as claimed in claim 1, wherein the single transmittance of the polarizing film is less than 43.5% and the polarization degree is less than 99.998%. A method for manufacturing a polarizing plate with a phase difference layer as claimed in claim 1, wherein the polarizing plate with a phase difference layer further has another phase difference layer outside the phase difference layer; the manufacturing method comprises: arranging the other phase difference layer outside the phase difference layer; the refractive index characteristics of the other phase difference layer show the relationship of nz>nx=ny. A method for manufacturing a polarizing plate with a phase difference layer as claimed in claim 1, wherein the polarizing plate with a phase difference layer further has a conductive layer or an isotropic substrate with a conductive layer on the outer side of the phase difference layer; the manufacturing method comprises: arranging the conductive layer or the isotropic substrate with a conductive layer on the outer side of the phase difference layer.