TWI842754B - Polarizing plate with phase difference layer and image display device using the same - Google Patents

Abstract

A polarizing plate with a phase difference layer is provided which is thin, has excellent handling properties and excellent optical properties. The polarizing plate with a phase difference layer of the present invention comprises a polarizing plate and a phase difference layer, wherein the polarizing plate comprises a polarizing film and a protective layer located on at least one side of the polarizing film. The polarizing film is made of a polyvinyl alcohol-based resin film containing a dichroic substance, and has a thickness of less than 8 μm, a single body transmittance of more than 44.0%, and a polarization degree of more than 99.50%. The Re(550) of the phase difference layer is 100 nm to 190 nm, and the Re(450)/Re(550) is greater than 0.8 and less than 1. The angle formed by the slow axis of the phase difference layer and the absorption axis of the polarizing film is 40° to 50°.

Description

Polarizing plate with phase difference layer and image display device using the same

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

Background of the invention In recent years, image display devices, typically liquid crystal display devices and electroluminescent (EL) display devices (e.g., organic EL display devices, inorganic EL display devices), have rapidly become popular. Image display devices typically use polarizing plates and phase difference plates. In practical applications, polarizing plates with phase difference layers that are integrated with polarizing plates and phase difference plates are widely used (e.g., Patent Document 1), and recently, as the demand for thinner image display devices has increased, the demand for thinner polarizing plates with phase difference layers has also increased. In addition, in recent years, the demand for curved image display devices and/or bendable or foldable image display devices has increased, and 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 polarizing plates with phase difference layers, the protective layer and phase difference film of the polarizing film, which have a greater impact on the thickness, are being 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 will become relatively large, resulting in problems such as warping of the image display device and reduced operability of the polarizing plate with phase difference layer.

To solve the above problems, the polarizing film must also be thinned. However, if the thickness of the polarizing film is only reduced, the optical properties will be reduced. More specifically, one or both of the polarization degree and the single body transmittance, which have a trade-off relationship, will be reduced to a level that is unacceptable in practical applications. As a result, the optical properties of the polarizing plate with a phase difference layer will also become insufficient.

Prior art documents Patent documents Patent document 1: Japanese Patent No. 3325560

Summary of the invention Problems to be solved by the invention The present invention is made to solve the above-mentioned previous problems, and its main purpose is to provide a polarizing plate with a phase difference layer that is thin, has excellent processing properties and excellent optical properties.

Means for solving the problem The polarizing plate with phase difference layer of the present invention has a polarizing plate and a phase difference layer, and the polarizing plate includes a polarizing film and a protective layer located on at least one side of the polarizing film. The polarizing film is composed of a polyvinyl alcohol-based resin film containing a dichroic substance, and its thickness is less than 8μm, the single body transmittance is greater than 44.0%, and the polarization degree is greater than 99.50%. The Re(550) of the phase difference layer is 100nm~190nm, Re(450)/Re(550) is greater than 0.8 and less than 1, and the angle formed by the slow axis of the phase difference layer and the absorption axis of the polarizing film is 40°~50°. In one embodiment, the above-mentioned protective layer is composed of a substrate with an elastic modulus of more than 3000MPa. In one embodiment, the total thickness of the polarizing plate with a phase difference layer is less than 90 μm, the front reflection hue is less than 3.5, and the protective layer is composed of a resin film having an elastic modulus of more than 3000 MPa. In one embodiment, the protective layer is composed of a cellulose triacetate resin film. In one embodiment, the polarizing plate includes the polarizing film and the protective layer disposed only on one side of the polarizing film, and the phase difference layer is bonded to the polarizing film through an adhesive layer. In one embodiment, the phase difference layer is composed of a polycarbonate resin film. In one embodiment, the phase difference layer is composed of a polycarbonate resin film having a thickness of less than 40 μm. In one embodiment, the difference between the maximum and minimum values of the single transmittance of the above-mentioned polarizing film in an area of 50 ^cm2 is less than 0.2%. In one embodiment, the width of the above-mentioned polarizing plate with a phase difference layer is more than 1000 mm, and the difference between the maximum and minimum values of the single transmittance at a position along the width direction of the above-mentioned polarizing film is less than 0.3%. In one embodiment, the single transmittance of the above-mentioned polarizing film is less than 44.5%, and the degree of polarization is less than 99.95%. In one embodiment, the above-mentioned polarizing plate with a phase difference layer has another phase difference layer outside the above-mentioned 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 outside the phase difference layer. In one embodiment, the polarizing plate with a phase difference layer is in the shape of an elongated strip, the polarizing film has an absorption axis in the direction of the elongated strip, and the phase difference layer is an obliquely stretched film having a slow axis in a direction at an angle of 40° to 50° relative to the direction of the elongated strip. In one embodiment, the polarizing plate with a phase difference layer is wound into a roll. According to another aspect of the present invention, an image display device is provided. The image display device has the polarizing plate with a phase difference layer. In one embodiment, the image display device is an organic electroluminescent display device or an inorganic electroluminescent display device.

Effect of the invention According to the present invention, a polarizing film having excellent optical properties despite being thin can be obtained by combining the following methods: adding 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 with a heating roller. By using the polarizing film, a polarizing plate with a phase difference layer that is thin, has excellent handling properties, and has excellent optical properties can be realized.

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

(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 in-plane refractive index is the largest (i.e., the slow axis direction), “ny” is the refractive index in the direction orthogonal to the slow axis (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. Re(λ) can be obtained by the formula: Re(λ)＝(nx-ny)×d when the thickness of the layer (film) is d(nm). (3) Retardation in the 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. Rth(λ) can be calculated by the formula: Rth(λ)=(nx-nz)×d when the thickness of the layer (film) is d(nm). (4) Nz coefficient The Nz coefficient can be calculated by Nz=Rth/Re. (5) Angle When an angle is mentioned in this manual, the angle includes both clockwise and counterclockwise relative to the reference direction. Therefore, for example, "45°" means ±45°.

A. Overall structure of polarizing plate with phase difference layer Figure 1 is a schematic cross-sectional view of a polarizing plate with phase difference layer in one embodiment of the present invention. The polarizing plate with phase difference layer 100 in this 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 disposed on one side of the polarizing film 11, and a second protective layer 13 disposed on the other side of the polarizing film 11. One of the first protective layer 12 and the second protective layer 13 can also be omitted according to the purpose. For example, when the phase difference layer 20 can function as a protective layer of the polarizing film 11, the second protective layer 13 can also be omitted. In the embodiment of the present invention, the polarizing film is typically composed of a polyvinyl alcohol-based resin film containing a dichroic substance. The thickness of the polarizing film is 8 μm or less, the single body transmittance is 44.0% or more, and the polarization degree is 99.50% or more.

As shown in FIG2 , in another embodiment of the polarizing plate 101 with a phase difference layer, another phase difference layer 50 and/or a conductive layer or an isotropic substrate 60 with a conductive layer may also be provided. The another phase difference layer 50 and the conductive layer or the isotropic substrate 60 with a conductive layer may be provided on the outside of the phase difference layer 20 (the side opposite to the polarizing plate 10). The refractive index characteristic of the another phase difference layer shows the relationship of nz＞nx＝ny. The another phase difference layer 50 and the conductive layer or the isotropic substrate 60 with a conductive layer may be provided in sequence from the side of the phase difference layer 20. The another phase difference layer 50 and the conductive layer or the isotropic substrate 60 with a conductive layer may be provided as required, and either or both of them may be omitted. In addition, for 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. In addition, when a conductive layer or an isotropic substrate with a conductive layer can be provided, a polarizing plate with a phase difference layer can be applied to a so-called internal touch panel type input display device in which a touch sensor is incorporated between an image display unit (e.g., an organic EL unit) and a polarizing plate.

In the embodiment of the present invention, Re(550) of the first phase difference layer 20 is 100nm-190nm, and Re(450)/Re(550) is greater than 0.8 and less than 1. In addition, the angle formed by the slow axis of the first phase difference layer 20 and the absorption axis of the polarizing film 11 is 40°-50°.

The above embodiments can be combined appropriately, and changes that are obvious in the industry can be added to the components of the above embodiments. For example, the structure of the isotropic substrate 60 with a conductive layer provided on the outer side of the second phase difference layer 50 can be replaced with an optically equivalent structure (such as a laminate 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 (such as 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 a phase difference layer of the present invention can be in the form of a thin sheet or in the form of a long strip. The so-called "long strip" in this specification means a long and thin shape that is long enough relative to the width. For example, it includes a long and thin shape that is more than 10 times the width, and preferably more than 20 times the width. The long strip-shaped polarizing plate with a phase difference layer can be rolled into a roll. When the polarizing plate with a phase difference layer is in the form of a long strip, the polarizing plate and the phase difference layer are both in the form of a long strip. At this time, the polarizing film preferably has an absorption axis in the direction of the long strip. The first phase difference layer is preferably an obliquely stretched film having a slow axis in a direction at an angle of 40°~50° relative to the direction of the long strip. As long as the polarizing film and the first phase difference layer have the above-mentioned structure, a polarizing plate with a phase difference layer can be manufactured by roll-to-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, and the polarizing plate with the phase difference layer can be attached to the image display unit. In addition, a peeling film is preferably temporarily attached to the surface of the adhesive layer before the polarizing plate with the phase difference layer is used. By temporarily attaching the peeling film, a roll can be formed while protecting the adhesive layer.

The front reflection hue (√(a ^{* 2} +b ^{* 2} )) of the polarizing plate with a phase difference layer is preferably 3.5 or less, and preferably 3.0 or less. When the front reflection hue is within the above range, undesired coloring can be suppressed, and as a result, a polarizing plate with a phase difference layer having good reflection characteristics can be obtained.

The total thickness of the polarizing plate with a phase difference layer is preferably less than 140 μm, and preferably less than 120 μm, more preferably less than 100 μm, and more preferably less than 90 μm, and more preferably less than 85 μm. The lower limit of the total thickness may be, for example, 30 μm. According to the embodiment of the present invention, an extremely thin polarizing plate with a phase difference layer as described above can be realized. The polarizing plate with a phase difference layer may have extremely excellent flexibility and bending durability. The polarizing plate with a phase difference layer may be particularly suitable for use in a curved image display device and/or a flexible or bendable image display device. In addition, the so-called 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 after deducting the adhesive layer used to make the polarizing plate with a phase difference layer adhere to an external adherend such as a panel or 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 attach the polarizing plate with a phase difference layer to adjacent components such as an image display unit and the peeling film that can be temporarily adhered to its surface).

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

B. Polarizing plate B-1. Polarizing film As described above, the polarizing film 11 has a thickness of less than 8 μm, a single body transmittance of more than 44.0%, and a polarization degree of more than 99.50%. Generally speaking, single body transmittance and polarization degree have a trade-off relationship, so 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, in the past, thin polarizing films that satisfy the optical characteristics of a single body transmittance of more than 44.0% and a polarization degree of more than 99.50% were difficult to be used in practical applications. One of the features of the present invention is to use a thin polarizing film having excellent optical characteristics of a single body transmittance of more than 44.0% and a polarization degree of more than 99.50%, and the optical characteristics The unevenness has been suppressed.

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

The polarizing film preferably shows absorption dichroism at any wavelength between 380nm and 780nm. The single transmittance of the polarizing film should be 44.5% or less. The polarization degree of the polarizing film should be 99.70% or more, and more preferably 99.80% or more. On the other hand, the polarization degree should be 99.95% or less. The above single transmittance is represented by the Y value obtained by measuring and correcting the light performance using an ultraviolet-visible spectrophotometer. The above polarization degree is represented by the parallel transmittance Tp and the orthogonal transmittance Tc obtained by measuring and correcting the light performance using an ultraviolet-visible spectrophotometer, 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 layered product of a polarizing film (refractive index of the surface: 1.53) and a protective film (refractive index: 1.50) as the measurement object using an ultraviolet-visible spectrophotometer. Due to the refractive index of the surface of the polarizing film and/or the refractive index of the surface of the protective film in contact with the air interface, the reflectivity at the interface of each layer will change, resulting in a change in the measured value of the transmittance. Therefore, for example, when using a protective film with a refractive index other than 1.50, the measured value of the transmittance can also be corrected according to the refractive index of the surface of the protective film in contact with the air interface. Specifically, the corrected value C of the transmittance is expressed by the following formula using the reflectivity R ₁ (transmission axis reflectivity) 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) Here, R ₀ is the transmission axis reflectivity when a protective film with a refractive index of 1.50 is used, n ₁ is the refractive index of the protective film used, and T ₁ is the transmittance of the polarizing film. For example, when a substrate (cycloolefin film, film with hard coating, etc.) with a surface refractive index of 1.53 is used as the protective film, the correction amount C is about 0.2%. At this time, the measured transmittance is added with 0.2% to convert it into the transmittance when a protective film with a surface refractive index of 1.50 is used. In addition, according to the above formula, the change in the correction value C after changing the transmittance _T1 of the polarizing film by 2% is less than 0.03%, so the influence of the transmittance of the polarizing film on the correction value C is limited. In addition, when the protective film has absorption other than surface reflection, appropriate correction can be performed according to the absorption amount.

In one embodiment, the width of the polarizing plate with a phase difference layer is more than 1000 mm, so the width of the polarizing film is also more than 1000 mm. At this time, the difference (D1) between the maximum and minimum values of the single transmittance at the position along the width direction of the polarizing film is preferably less than 0.3%, preferably less than 0.29%, and more preferably less than 0.28%. The smaller D1 is, the better, and the lower limit of D1 can be, for example, 0.01%. As long as D1 is within the above range, polarizing plates with phase difference layers having excellent optical properties can be industrially produced. In another embodiment, the difference (D2) between the maximum and minimum values of the single transmittance of the polarizing film in an area of ⁵⁰ cm2 is preferably less than 0.2%, preferably less than 0.15%, and more preferably less than 0.1%. The smaller D2 is, the better, and the lower limit of D2 can be, for example, 0.01%. As long as D2 is within the above range, the brightness variation of the display screen can be suppressed when the polarizing plate with a phase difference layer is used in an image display device.

The polarizing film may be any appropriate polarizing film. The polarizing film may be typically made of a laminate of two or more layers.

A specific example of a polarizing film obtained using a laminate is a polarizing film obtained using a resin substrate and a PVA-based resin layer formed by coating the resin substrate. A polarizing film obtained using a laminate of a resin substrate and a PVA-based resin layer formed by coating the resin substrate can be produced, for example, by coating a PVA-based resin solution on a resin substrate and drying the PVA-based resin layer on the resin substrate to obtain a laminate of the resin substrate and the PVA-based resin layer; and extending and dyeing the laminate to produce a polarizing film from the PVA-based resin layer. In this embodiment, stretching typically includes immersing the laminate in an aqueous boric acid solution and stretching it. And if necessary, stretching may further include stretching the laminate in the air at a high temperature (for example, above 95°C) before stretching it in an aqueous boric acid solution. The resulting laminate of resin substrate/polarizing film can be used directly (that is, the resin substrate can also be used as a protective layer for the polarizing film), or the resin substrate can be peeled off from the laminate of resin substrate/polarizing film and any appropriate protective layer can be laminated on the peeled surface according to the purpose and then used. The details of the method for manufacturing the polarizing film are described, for example, in Japanese Patent Publication No. 2012-73580. The entire description of the publication is cited in this specification as a reference.

The manufacturing method of the polarizing film typically includes the following steps: forming a polyvinyl alcohol resin layer containing a halogenated substance and a polyvinyl alcohol resin on one side of a long thermoplastic resin substrate to form a laminate; and sequentially performing an air-assisted stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying and shrinking treatment on the laminate, wherein the drying and shrinking treatment is to heat the laminate while conveying it along the long side direction, thereby shrinking it by more than 2% in the width direction. Thus, a polarizing film with excellent optical properties and suppressed optical property variation can be provided, and the thickness of the polarizing film is less than 8μm, the single body transmittance is more than 44.0%, and the polarization degree is more than 99.50%. 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 being reduced or dissolved when immersed in water in the subsequent dyeing step or stretching step, and high optical properties can be achieved. Moreover, when the PVA-based 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-based resin layer does not contain halides. Therefore, 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. Furthermore, the optical properties can be improved by shrinking the laminate in width through a drying and shrinking process.

B-2. Protective layer The first protective layer 12 and the second protective layer 13 are each 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), polyester resins, polyvinyl alcohol resins, polycarbonate resins, polyamide resins, polyimide resins, polyether sulfone resins, polysulfone resins, polystyrene resins, polynorbornene resins, polyolefin resins, (meth)acrylic resins, acetate resins, and the like. In addition, thermosetting resins such as (meth)acrylic resins, urethane resins, (meth)acrylic urethane resins, epoxy resins, silicone resins, and the like or ultraviolet curing resins can also be cited. Other examples include glassy polymers such as siloxane polymers. Furthermore, the polymer film described in Japanese Patent Publication No. 2001-343529 (WO01/37007) can also be used. As the material of the film, for example, a resin composition containing 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, for example, a resin composition containing an alternating copolymer composed of 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. In one embodiment, the protective layer (especially the protective layer on the visual side) contains a TAC resin. By using a TAC-based resin film as a protective layer, the bending durability can be improved.

The polarizing plate with phase difference layer of the present invention is typically arranged on the visual side of the image display device as described below, and the first protective layer 12 is typically arranged on its visual side. Therefore, the first protective layer 12 can also be subjected to surface treatments such as hard coating, anti-reflection, anti-adhesion, and anti-glare treatments as needed. And/or, the first protective layer 12 can also be subjected to treatments useful for improving visibility when viewed through polarized sunglasses as needed (typically, providing (elliptical) circular polarization function and providing ultra-high phase difference). By performing the above treatments, excellent visibility can still be achieved even when the displayed image is viewed through polarized lenses such as polarized sunglasses. Therefore, the polarizing plate with a phase difference layer can also be suitably used in image display devices that can be used outdoors.

The thickness of the first protective layer is preferably 5 μm to 80 μm, preferably 10 μm to 40 μm, and more preferably 10 μm to 35 μm. In addition, 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 is a phase difference layer having 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, and preferably 10μm~40μm, and more preferably 10μm~30μm. From the perspective of thinness and weight reduction, it is ideal to omit the second protective layer.

B-3. Manufacturing method of polarizing film The polarizing film can be obtained, for example, by a manufacturing method comprising the following steps: forming a polyvinyl alcohol resin layer (PVA resin layer) on one side of a long thermoplastic resin substrate to form a laminate, wherein the polyvinyl alcohol resin layer contains a halogen and a polyvinyl alcohol resin (PVA resin); and sequentially subjecting the laminate to an air-assisted stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment, wherein the drying shrinkage treatment is to heat the laminate while conveying the laminate in the long side direction so as to shrink the laminate by more than 2% in the width direction. The halogen content 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 in the width direction obtained by the drying and shrinking treatment of the laminate is preferably above 2%. According to the manufacturing method, the polarizing film described in the above item B-1 can be obtained. In particular, a polarizing film having excellent optical properties (represented by single body transmittance and polarization degree) and suppressed optical property variations can be obtained by the following method: after preparing a laminate including a PVA-based resin layer containing a halogenated substance, the above laminate is stretched by a multi-stage stretching including air-assisted stretching and underwater stretching, and the stretched laminate is then heated by a heating roller. Specifically, by using a heated roller in the drying and shrinking step, the laminate 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 variation of the optical properties of the polarizing film (especially the single-unit transmittance).

B-3-1. Preparation of laminate The method of preparing the laminate of the thermoplastic resin substrate and the PVA resin layer can be any appropriate method. It is preferable to apply a coating liquid containing a halogen and a PVA resin on the surface of the thermoplastic resin substrate and dry it, thereby forming a PVA resin layer on the thermoplastic resin substrate. As mentioned above, the content of the halogen in the PVA resin layer is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA resin.

The coating liquid can be applied by any appropriate method, such as roller coating, spin coating, wire rod coating, dip coating, die coating, curtain coating, spray coating, scraper coating (comma coating, etc.), etc. The coating and drying temperature of the coating liquid is preferably above 50°C.

The thickness of the PVA resin layer is preferably 3μm~40μm, 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-adhesion layer may be formed on the thermoplastic resin substrate. By performing the above 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. If it is less than 20μm, it may be difficult to form a PVA resin layer. If it is greater than 300μm, for example, the thermoplastic resin substrate may take a long time to absorb water during the water stretching treatment described later, and there is a risk of excessive load on the stretching.

The water absorption rate of the thermoplastic resin substrate is preferably 0.2% or more, more preferably 0.3% or more. The thermoplastic resin substrate absorbs water, and the water can play the role of a plasticizer to plasticize. As a result, the extension stress can be greatly reduced and a high extension ratio can be achieved. On the other hand, the water absorption rate of the thermoplastic resin substrate is preferably 3.0% or less, more preferably 1.0% or less. By using such a thermoplastic resin substrate, it is possible to prevent the dimensional stability of the thermoplastic resin substrate from being significantly reduced during manufacturing, thereby preventing the appearance of the resulting polarizing film from being deteriorated. It can also prevent the substrate from breaking when stretched in water, or the PVA-based resin layer from peeling off from the thermoplastic resin substrate. In addition, the water absorption rate of the thermoplastic resin substrate can be adjusted by, for example, introducing a modifying base into the constituent material. The water absorption rate is the value obtained according to JIS K 7209.

The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably below 120°C. By using such a thermoplastic resin substrate, the crystallization of the PVA-based resin layer can be suppressed, while the elongation of the laminate is fully ensured. In addition, considering that the thermoplastic resin substrate is plasticized by water and can be well elongated in water, it is preferably below 100°C, and more preferably below 90°C. On the other hand, the glass transition temperature of the thermoplastic resin substrate is preferably above 60°C. By using such a thermoplastic resin substrate, it is possible to prevent the thermoplastic resin substrate from being deformed (such as unevenness, sagging or wrinkling) when applying and drying the coating liquid containing the above-mentioned PVA-based resin, thereby producing a laminate well. Furthermore, the PVA resin layer can be stretched well at an appropriate temperature (e.g., about 60°C). In addition, the glass transition temperature of the thermoplastic resin substrate can be adjusted by heating, for example, using a crystallization material that can introduce a modified group into the constituent material. The glass transition temperature (Tg) is a value obtained in accordance with JIS K 7121.

Any appropriate thermoplastic resin can be used as the constituent material of the thermoplastic resin substrate. Examples of the thermoplastic resin 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 more preferred.

In one embodiment, an amorphous (non-crystallized) polyethylene terephthalate resin is preferably used. Among them, an amorphous (difficult to crystallize) polyethylene terephthalate resin is particularly preferably used. Specific examples of the amorphous polyethylene terephthalate resin include copolymers containing isophthalic acid and/or cyclohexanedicarboxylic acid as dicarboxylic acids, or copolymers containing cyclohexanedimethanol or diethylene glycol as glycols.

In a preferred embodiment, the thermoplastic resin substrate is composed of a polyethylene terephthalate resin having isophthalic acid units. This is because such a thermoplastic resin substrate has extremely excellent extensibility and can suppress crystallization during extension. We speculate that this is due to the introduction of isophthalic acid units to give the main chain a huge twist. Polyethylene terephthalate resins have terephthalic acid units and ethylene glycol units. The content ratio of isophthalic acid units 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 extremely excellent extensibility can be obtained. On the other hand, the content ratio of the isophthalic acid unit 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 the above, the crystallization degree can be well increased in the drying and shrinking treatment described later.

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

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

The thermoplastic resin substrate can be stretched by any appropriate method. Specifically, it can be fixed-end stretching or free-end stretching. The stretching method can be dry or wet. The thermoplastic resin substrate can be stretched in one stage or in multiple stages. When it is stretched in multiple stages, the stretching ratio is the product of the stretching ratios of each stage.

B-3-1-2. Coating liquid The coating liquid contains the halogenated substance and the PVA resin as described above. The coating liquid is typically a solution obtained by dissolving the halogenated substance and the PVA 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. These can be used alone or in combination of two or more. Of these, water is preferred. The PVA resin concentration of the solution is preferably 3 to 20 parts by weight relative to 100 parts by weight of the solvent. As long as the resin concentration is the above, a uniform coating film can be formed that is closely attached to the thermoplastic resin substrate. The halogen content in the coating solution is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA resin.

Additives may also 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 may be used to further enhance the uniformity, dyeability, and elongation of the resulting PVA-based resin layer.

The above-mentioned PVA resin can adopt any appropriate resin. For example, polyvinyl alcohol and ethylene-vinyl alcohol copolymer can be mentioned. 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 is obtained according to JIS K 6726-1994. By using PVA resin with the above-mentioned saponification degree, a polarizing film with excellent durability can be obtained. When the saponification degree is too high, there is a risk of gelling.

The average degree of polymerization of the PVA-based resin can be appropriately selected according to the purpose. The average degree of polymerization is usually 1000 to 10000, preferably 1200 to 4500, and more preferably 1500 to 4300. In addition, the average degree of polymerization can be obtained according to JIS K 6726-1994.

The above-mentioned halides may be any appropriate halides. Examples thereof include iodides and sodium chloride. Examples of iodides include potassium iodide, sodium iodide and lithium iodide. 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. If the amount of halogen is greater than 20 parts by weight relative to 100 parts by weight of the PVA resin, the halogen will overflow and the resulting polarizing film will become cloudy.

Generally speaking, when a PVA resin layer is stretched, the orientation of the polyvinyl alcohol molecules in the PVA resin layer becomes higher. However, if the stretched PVA resin layer is immersed in a water-containing liquid, the orientation of the polyvinyl alcohol molecules will be disordered and the orientation will be 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 of the above orientation to be reduced is very significant. For example, the stretching of a PVA film monomer in boric acid water is generally carried out at 60°C. In contrast, the stretching of a laminate of A-PET (thermoplastic resin substrate) and a PVA-based resin layer is carried out at a relatively high temperature of about 70°C. At this time, the orientation of the PVA at the beginning of the stretching decreases before it rises due to the stretching in water. In contrast, after preparing a laminate of a PVA-based resin layer containing a halogenide and a thermoplastic resin substrate, the laminate is stretched at a high temperature in air (auxiliary stretching) before being stretched in boric acid water, thereby promoting the crystallization of the PVA-based resin in the PVA-based resin layer of the laminate after the auxiliary stretching. 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 halides. 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. Auxiliary stretching in the air In order to obtain high optical properties, a two-stage stretching method combining dry stretching (auxiliary stretching) and stretching in boric acid water is selected. In the two-stage stretching method, by introducing auxiliary stretching, the crystallization of the thermoplastic resin substrate can be suppressed while stretching, solving the problem of reduced stretchability due to excessive crystallization of the thermoplastic resin substrate in the subsequent boric acid water stretching, thereby stretching the laminate at a higher magnification. Furthermore, when coating PVA resin on a thermoplastic resin substrate, in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate, the coating temperature must be lower than when coating PVA resin on a general metal roller, resulting in a problem that the crystallization of PVA resin becomes relatively low and sufficient optical properties cannot be obtained. In contrast, by introducing auxiliary stretching, the crystallization of PVA resin can be improved even when coating PVA resin on a thermoplastic resin, thereby achieving high optical properties. Furthermore, by improving the orientation of the PVA resin in advance, it is possible to prevent the orientation of the PVA resin from being reduced or dissolved when immersed in water in the subsequent dyeing step or stretching step, thereby achieving high optical properties.

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 uniaxially stretching the laminate through rollers with different circumferential speeds). However, in order to obtain high optical properties, free-end stretching can be actively adopted. In one embodiment, the aerial stretching process includes a heating roller stretching step, which is to transport the laminate along its long side and simultaneously stretch it using the circumferential speed difference between the heating rollers. The aerial stretching process typically includes a zone stretching step and a heating roller stretching step. In addition, the order of the zone stretching step and the heating roller stretching step is not limited, and the zone stretching step can be performed first, or the heating roller stretching step can be performed first. The regional stretching step can also be omitted. In one embodiment, the regional stretching step and the heating roller stretching step are performed in sequence. In another embodiment, the film ends are held in a tenter stretching machine, and the distance between the tenters is expanded in the travel direction to stretch (the increase in the distance between the tenters is the stretching ratio). At this time, the distance between the tenters in the width direction (vertical to the travel direction) is set to be arbitrarily close. It is better to set it to the stretching ratio relative to the travel direction to use free end stretching for approach. In the case of free end stretching, the shrinkage rate in the width direction = (1/stretching ratio) ^1/2 is used for calculation.

The air-assisted stretching can be performed in one stage or in multiple stages. When it is performed in multiple stages, the stretching ratio is the product of the stretching ratios of each stage. The stretching direction in the air-assisted stretching is preferably substantially the same as the stretching direction in the underwater stretching.

The stretching ratio of air-assisted stretching is preferably 2.0 to 3.5 times. The maximum stretching ratio when combining air-assisted stretching and underwater stretching is preferably 5.0 times or more, preferably 5.5 times or more, and more preferably 6.0 times or more relative to the original length of the laminate. The "maximum stretching ratio" in this manual means the stretching ratio before the laminate is about to break, which is a value 0.2 lower than the stretching ratio of the laminate after confirming the stretching ratio of the laminate breaking.

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, more 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 the above temperature, the rapid progress of crystallization of the PVA-based resin can be suppressed, thereby suppressing the undesirable conditions caused by the crystallization (for example, the orientation of the PVA-based resin layer is hindered by stretching). The crystallization index of the PVA-based 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 measurement light for measurement, and the crystallization index is calculated according to the following formula using the intensity of 1141cm ^-1 and 1440cm ^-1 of the obtained spectrum. Crystallization index = ( _IC / _IR ) Where, _IC : the intensity of 1141cm ^-1 when the measurement light is incident and the measurement is carried out, _IR : the intensity of 1440cm ^-1 when the measurement light is incident and the measurement is carried out.

B-3-3. Insolubility treatment If necessary, after the air-assisted extension treatment and before the water extension treatment or dyeing treatment, an insolubility treatment is performed. The above-mentioned insolubility treatment is typically performed by immersing the PVA-based resin layer in a boric acid aqueous solution. By performing the insolubility treatment, the PVA-based resin layer can be given water resistance 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 part by weight to 4 parts by weight relative to 100 parts by weight of water. The liquid temperature of the insolubility 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 (laminated body) in a dyeing solution containing iodine, applying the dyeing solution on the PVA resin layer, and spraying the dyeing solution on the PVA resin layer. It is preferred to immerse the laminate in a dyeing solution (dyeing bath). 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 suitable to mix iodide in the iodine aqueous solution. Iodides can be cited as: potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide, etc. Among them, 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 inhibit the dissolution of PVA-based resins, the liquid temperature of the dyeing solution during dyeing is preferably 20°C to 50°C. When the PVA resin layer is immersed in the dye solution, in order to ensure the transmittance of the PVA resin layer, the immersion time is preferably 5 seconds to 5 minutes, and 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 polarizing film obtained finally is 44.0% or more and the polarization degree is 99.50% or more. The dyeing conditions are preferably to use an iodine aqueous solution as the dyeing solution, and set the content ratio of iodine to potassium iodide in the iodine aqueous solution to 1:5 to 1:20. The content ratio of iodine to potassium iodide in the iodine aqueous solution is preferably 1:5 to 1:10. In this way, a polarizing film having the above-mentioned optical characteristics can be obtained.

When the laminate is immersed in a treatment bath containing boric acid (representatively an insolubilization treatment) and then subsequently subjected to a dyeing treatment, the boric acid contained in the treatment bath will be mixed into the dyeing bath and the boric acid concentration of the dyeing bath will change over time, resulting in the situation where the dyeability becomes unstable. In order to suppress the above-mentioned instability of dyeability, the upper limit of the boric acid concentration of the dyeing bath is adjusted to 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 more 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. Thereby, the ratio of boric acid concentration change 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. Crosslinking treatment If necessary, after the dyeing treatment and before the underwater stretching treatment, a crosslinking treatment is performed. The above crosslinking treatment can be performed by immersing the PVA-based resin layer in an aqueous solution of boric acid. By performing the crosslinking treatment, the PVA-based resin layer can be given water resistance, and the orientation of the PVA can be prevented from being reduced when immersed in high-temperature water during the subsequent underwater stretching. The concentration of the aqueous solution of boric acid is preferably 1 part by weight to 5 parts by weight relative to 100 parts by weight of water. In addition, when the crosslinking treatment is performed after the above dyeing treatment, an iodide is further mixed. By mixing an iodide, the dissolution of iodine adsorbed on the PVA-based resin layer can be suppressed. The mixing amount of the iodide is preferably 1 part by weight to 5 parts by weight relative to 100 parts by weight of water. Specific examples of iodide are as described above. The 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. Through the underwater stretching treatment, the laminate can be stretched at a temperature lower than the glass transition temperature of the thermoplastic resin substrate or the PVA resin layer (typically about 80°C), and high-ratio stretching can be performed while suppressing the crystallization of the PVA resin layer. As a result, a polarizing film with excellent optical properties can be produced.

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

It is advisable to immerse the laminate in a boric acid aqueous solution for underwater stretching (boric acid underwater stretching). By using a boric acid aqueous solution as a stretching bath, the PVA resin layer can be given the rigidity to withstand the tension during stretching and the water resistance of being insoluble in water. Specifically, boric acid generates tetrahydroxyboric acid anions in an aqueous solution and can crosslink with the PVA resin through hydrogen bonds. As a result, the PVA resin layer can be given rigidity and water resistance, and good stretching can be performed, thereby producing a polarizing film with excellent optical properties.

The boric acid aqueous solution is preferably obtained by dissolving boric acid and/or boric acid salt in water which is a solvent. The boric acid concentration is preferably 1 to 10 parts by weight, more preferably 2.5 to 6 parts by weight, and particularly preferably 3 to 5 parts by weight relative to 100 parts by weight of water. By setting the boric acid concentration to more than 1 part by weight, the dissolution of the PVA resin layer can be effectively suppressed, and a polarizing film with higher properties can be manufactured. In addition to boric acid or boric acid salt, an aqueous solution obtained by dissolving a boron compound such as borax, glyoxal, glutaraldehyde, etc. in a solvent can also be used.

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

The stretching temperature (liquid temperature of the stretching bath) is preferably 40°C~85°C, more preferably 60°C~75°C. As long as it is the above temperature, the dissolution of the PVA-based resin layer can be suppressed, and at the same time, it can be stretched at a high ratio. Specifically, as mentioned above, if the relationship with the formation of the PVA-based resin layer is taken into consideration, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably above 60°C. At this time, if the stretching temperature is lower than 40°C, even if the thermoplastic resin substrate is plasticized with water, it may not be stretched well. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, and excellent optical properties may not be obtained. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

The stretching ratio of the underwater stretching is preferably 1.5 times or more, preferably 3.0 times or more. The total stretching ratio of the laminate is preferably 5.0 times or more, more preferably 5.5 times or more relative to the original length of the laminate. By achieving the high stretching ratio, a polarizing film with excellent optical properties can be manufactured. The 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 heating the entire area, or by heating the conveying roller (so-called using a heating roller) (heating roller drying method). It is preferred to use both. By using a heating roller to dry it, the heat curling of the laminate can be effectively suppressed, and a polarizing film with excellent appearance can be produced. Specifically, by drying the laminate along the heating roller, the crystallization of the above-mentioned thermoplastic resin substrate can be effectively promoted and the crystallization degree can be increased. Even at a relatively low drying temperature, the crystallization degree of the thermoplastic resin substrate can still be well increased. As a result, the rigidity of the thermoplastic resin substrate increases and becomes a state that can withstand the shrinkage of the PVA-based resin layer due to drying, thereby suppressing curling. In addition, by using a heating roller, the laminate can be dried while maintaining a flat state, so that not only the generation of curling but also the generation of wrinkles can be suppressed. At this time, the laminate can be shrunk in the width direction through a drying and shrinking treatment to improve the optical properties. This is because the orientation of PVA and PVA/iodine complex can be effectively improved. The shrinkage rate in the width direction obtained by the drying and shrinking treatment of the laminate is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using heated rollers, the laminate can be conveyed while being continuously contracted in the width direction, thus achieving high productivity.

FIG3 is a schematic diagram showing an example of a drying and shrinking process. In the drying and shrinking process, the laminate 200 is dried while being transported by using the conveying rollers R1 to R6 and the guide rollers G1 to G4 that have been heated to a predetermined temperature. In the example of the figure, the conveying rollers R1 to R6 are arranged to alternately and continuously heat the surface of the PVA resin layer and the surface of the thermoplastic resin substrate, but, for example, the conveying rollers R1 to R6 may also be arranged to continuously heat only one surface of the laminate 200 (for example, the surface of the thermoplastic resin substrate).

The drying conditions can be controlled by adjusting the heating temperature of the conveyor roller (temperature of the heating roller), the number of heating rollers, and the contact time with the heating roller. The temperature of the heating roller is preferably 60°C~120°C, more preferably 65°C~100°C, and particularly preferably 70°C~80°C. While the crystallization degree of the thermoplastic resin can be increased well and the curling can be suppressed well, an optical laminate with excellent durability can be produced. In addition, the temperature of the heating roller can be measured by a contact thermometer. In the example of the figure, 6 conveyor rollers are provided, but there is no particular limitation as long as there are a plurality of conveyor rollers. The number of conveyor rollers is usually 2~40, and it is preferably 4~30. The contact time (total contact time) between the laminate and the heating roller is preferably 1 second to 300 seconds, more preferably 1 to 20 seconds, and even more 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 best to install it in a heating furnace equipped with an air supply mechanism. By using the heating roller and hot air drying together, 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 should be 30℃~100℃. In addition, the hot air drying time should be 1 second~300 seconds. The wind speed of the hot air should be around 10m/s~30m/s. In addition, the wind speed is the wind speed in the heating furnace, which can be measured by a mini fan-type digital anemometer.

B-3-8. Other treatments It is advisable to perform a cleaning treatment after the water stretching treatment and before the drying shrinkage treatment. The above cleaning treatment can be performed by immersing the PVA resin layer in a potassium iodide aqueous solution.

C. First phase difference layer The first phase difference layer 20 may have any appropriate optical and/or mechanical properties according to the purpose. The first phase difference layer 20 typically has a slow axis. In one embodiment, the angle θ formed by the slow axis of the first phase difference layer 20 and the absorption axis of the polarizing film 11 is 40°~50° as described above, preferably 42°~48°, and more preferably about 45°. As long as the angle θ is within the above range, as described later, by making the first phase difference layer into 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.

The first phase difference layer preferably has a refractive index characteristic showing a relationship of nx>ny≧nz. The first phase difference layer is typically provided to impart anti-reflection characteristics to the polarizing plate, and in one embodiment, can function as a λ/4 plate. At this time, the in-plane phase difference Re(550) of the first phase difference layer is preferably 100nm~190nm, preferably 110nm~170nm, and more preferably 130nm~160nm. In addition, here "ny＝nz" not only includes the case where ny and nz are completely identical, but also includes the case where they are substantially the same. Therefore, there may be a situation where ny>nz without compromising the effect of the present invention.

The Nz coefficient of the first phase difference layer is preferably 0.9-3, preferably 0.9-2.5, more preferably 0.9-1.5, and most preferably 0.9-1.3. By satisfying the above relationship, when the obtained polarizing plate with phase difference layer is used in an image display device, a very excellent reflection hue can be achieved.

The first phase difference layer can exhibit an inverse dispersion wavelength characteristic in which the phase difference value increases with the wavelength of the measured light, a normal wavelength dispersion characteristic in which the phase difference value decreases with 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 exhibits 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 the above configuration, very excellent anti-reflection characteristics can be achieved.

The first phase difference layer includes a resin having an absolute value of a photoelastic coefficient of preferably 2×10 ^-11 m ² /N or less, preferably 2.0×10 ^-13 m ² /N to 1.5×10 ^-11 m ² /N, and more preferably 1.0×10 ^-12 m ^{2 /} N to 1.2× ^{10 -11} m ² /N. When the absolute value of the photoelastic coefficient is within the above range, the phase difference is unlikely to change when shrinkage stress is generated during heating. As a result, thermal unevenness of the obtained image display device can be well prevented.

The first phase difference layer is typically formed of a stretched film of a resin film. In one embodiment, the thickness of the first phase difference layer is preferably 70 μm or less, and preferably 45 μm to 60 μm. As long as the thickness of the first phase difference layer is within the above range, curling during heating can be well suppressed, and curling during bonding can be well adjusted. Moreover, as described later, in an embodiment in which the first phase difference layer is formed of a polycarbonate resin film, the thickness of the first phase difference layer is preferably 40 μm or less, and preferably 10 μm to 40 μm, and more preferably 20 μm to 30 μm. By being formed of a polycarbonate resin film having the above thickness, the first phase difference layer can suppress the occurrence of curling and can help improve bending durability and reflection hue.

The first phase difference layer 20 can be formed of any appropriate resin film that can satisfy the above-mentioned characteristics. Representative examples of the resin include polycarbonate resins, polyester carbonate resins, polyester resins, polyvinyl acetal resins, polyarylate resins, cyclic olefin resins, cellulose resins, polyvinyl alcohol resins, polyamide resins, polyimide resins, polyether resins, polystyrene resins, and acrylic resins. These resins can be used alone or in combination (e.g., blended or copolymerized). When the first phase difference layer is formed of a resin film showing reverse dispersion wavelength characteristics, a polycarbonate resin or a polyester carbonate resin (hereinafter sometimes simply referred to as a polycarbonate resin) can be appropriately used.

As long as the effects of the present invention can be obtained, any appropriate polycarbonate resin can be used as the polycarbonate resin. For example, the polycarbonate resin includes a structural unit derived from a fluorene-based dihydroxy compound, a structural unit derived from an isosorbide-based dihydroxy compound, and a structural unit derived from at least one dihydroxy compound selected from the group consisting of alicyclic diols, alicyclic dimethanols, di-, tri- or polyethylene glycols, and alkylene glycols or spiroglycerol. Preferably, the polycarbonate resin comprises structural units derived from fluorene dihydroxy compounds, structural units derived from isosorbide dihydroxy compounds, structural units derived from alicyclic dimethanol, and/or structural units derived from di, tri or polyethylene glycol; more preferably, it comprises structural units derived from fluorene dihydroxy compounds, structural units derived from isosorbide dihydroxy compounds, and structural units derived from di, tri or polyethylene glycol. The polycarbonate resin may also comprise structural units derived from other dihydroxy compounds as required. In addition, the details of the polycarbonate resin that can be suitably used in the present invention are described in, for example, Japanese Patent Publication No. 2014-10291, Japanese Patent Publication No. 2014-26266, Japanese Patent Publication No. 2015-212816, Japanese Patent Publication No. 2015-212817, and Japanese Patent Publication No. 2015-212818, and this specification cites these descriptions as references.

The glass transition temperature of the polycarbonate resin is preferably 110°C or higher and 150°C or lower, and preferably 120°C or higher and 140°C or lower. If the glass transition temperature is too low, the heat resistance tends to deteriorate, which may cause dimensional changes after film formation or reduce the image quality of the resulting organic EL panel. If the glass transition temperature is too high, the forming stability during film formation may deteriorate or the transparency of the film may be impaired. In addition, the glass transition temperature can be obtained in accordance with JIS K 7121 (1987).

The molecular weight of the aforementioned polycarbonate resin can be expressed as a relative viscosity. The relative viscosity is measured by using methylene chloride as a solvent, after the polycarbonate concentration is precisely adjusted to 0.6 g/dL, using an Oodel viscometer at a temperature of 20.0°C ± 0.1°C. The lower limit of the relative viscosity is usually preferably 0.30 dL/g, and more preferably 0.35 dL/g or more. The upper limit of the relative viscosity is usually preferably 1.20 dL/g, and preferably 1.00 dL/g, and more preferably 0.80 dL/g. If the relative viscosity is less than the aforementioned lower limit, there is a problem that the mechanical strength of the molded product is reduced. On the other hand, if the relative viscosity is greater than the aforementioned upper limit, the fluidity during molding will decrease, and there is a problem of reduced productivity or moldability.

Commercially available polycarbonate resin films may also be used. Specific examples of commercial products include "PURE-ACE WR-S", "PURE-ACE WR-W", and "PURE-ACE WR-M" manufactured by Teijin Co., Ltd. and "NRF" manufactured by Nitto Denko Co., Ltd.

The first phase difference layer 20 can be obtained, for example, by stretching a film formed from the above-mentioned polycarbonate resin. The method of forming a film from a polycarbonate resin can adopt any appropriate molding method. Specific examples include: compression molding, transfer molding, injection molding, extrusion molding, blow molding, powder molding, FRP molding, casting and coating (such as casting), calendering, hot pressing, etc. Extrusion molding or casting and coating is preferred. This is because the smoothness of the obtained film can be improved, thereby obtaining good optical uniformity. The molding conditions can be appropriately set according to the resin composition or type used, the desired properties of the phase difference film, etc. In addition, as mentioned above, many polycarbonate resin films are sold on the market, so the commercially available films can be directly subjected to the stretching treatment.

The thickness of the resin film (unstretched film) can be set to any appropriate value according to the desired thickness of the first phase difference layer, the desired optical properties, the stretching conditions described below, etc. It is preferably 50 μm to 300 μm.

The above-mentioned stretching can adopt any appropriate stretching method and stretching conditions (such as stretching temperature, stretching ratio, stretching direction). Specifically, various stretching methods such as free end stretching, fixed end stretching, free end shrinkage, fixed end shrinkage, etc. can be used alone, or they can be used simultaneously or successively. Regarding the stretching direction, it can also be carried out along various directions or dimensions such as length direction, width direction, thickness direction, oblique direction, etc. The stretching temperature is preferably Tg-30℃~Tg+60℃ relative to the glass transition temperature (Tg) of the resin film, and preferably Tg-10℃~Tg+50℃.

By appropriately selecting the stretching method and stretching conditions, a retardation film having the desired optical properties (such as refractive index properties, in-plane phase difference, Nz coefficient) can be obtained.

In one embodiment, the phase difference film can be produced by uniaxially stretching a resin film or by uniaxially stretching a fixed end. A specific example of uniaxially stretching a fixed end is to move the resin film along the long side and stretch it in the width direction (lateral direction) at the same time. The stretching ratio is preferably 1.1 to 3.5 times.

In another embodiment, the phase difference film can be produced by continuously stretching a long strip of resin film obliquely in the direction of the above-mentioned angle θ relative to the long side direction. By adopting the oblique stretching, a long strip of stretched film having an orientation angle of angle θ relative to the long side direction of the film (having a slow axis in the direction of angle θ) can be obtained. For example, when laminated with a polarizing film, it can be rolled to roll, thereby simplifying the manufacturing steps. In addition, the angle θ can be the angle formed by the absorption axis of the polarizing film in the polarizing plate with a phase difference layer and the slow axis of the phase difference layer. As mentioned above, the angle θ is preferably 40°~50°, preferably 42°~48°, and more preferably about 45°.

The stretching machine used for the oblique stretching may be a tenter-type stretching machine, which is a machine that applies a conveying force or a stretching force or a pulling force at different speeds in the horizontal and/or vertical directions. The tenter-type stretching machine includes a horizontal single-axis stretching machine and a simultaneous double-axis stretching machine. Any appropriate stretching machine can be used as long as it can continuously stretch the long strip of resin film in an oblique direction.

By appropriately controlling the left and right speeds in the stretching machine, a phase difference layer (substantially a long strip phase difference film) having the desired in-plane phase difference and a slow axis in the desired direction can be obtained.

The stretching temperature of the above film will vary depending on the desired in-plane phase difference value and thickness of the phase difference layer, the type of resin used, the thickness of the film used, the stretching ratio, etc. Specifically, the stretching temperature is preferably Tg-30℃~Tg+30℃, more preferably Tg-15℃~Tg+15℃, and most preferably Tg-10℃~Tg+10℃. By stretching at the above temperature, a first phase difference layer having characteristics suitable for the present invention can be obtained. In addition, Tg is the glass transition temperature of the constituent material of the film.

D. Second phase difference layer As mentioned above, the second phase difference layer can 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, oblique reflection can be well prevented, and the anti-reflection function can be widened to a wide viewing angle. At this time, the phase difference Rth(550) in the thickness direction of the second phase difference layer is preferably -50nm~-300nm, and preferably -70nm~-250nm, more preferably -90nm~-200nm, and particularly preferably -100nm~-180nm. Here, "nx=ny" not only includes the case where nx and ny are exactly equal, but also includes 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 of any appropriate material. The second phase difference layer is preferably composed of a film containing a liquid crystal material fixed in a homeotropic orientation. The liquid crystal material (liquid crystal compound) that can be homeotropically oriented can be a liquid crystal monomer or a liquid crystal polymer. Specific examples of the liquid crystal compound and the method for forming the phase difference layer can be cited as the liquid crystal compound and the method for forming the phase difference layer described in paragraphs [0020] to [0028] of Japanese Patent Gazette No. 2002-333642. At this time, the thickness of the second phase difference layer is preferably 0.5μm~10μm, preferably 0.5μm~8μm, and more preferably 0.5μm~5μm.

E. Conductive layer or isotropic substrate with conductive layer attached The conductive layer can be formed by forming a metal oxide film on any suitable substrate using any suitable 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 comprises a metal oxide, the thickness of the conductive layer is preferably 50 nm or less, more preferably 35 nm or less. The lower limit of the thickness of the conductive layer is preferably 10 nm.

The conductive layer can be transferred from the substrate to the first phase difference layer (or the second phase difference layer if there is a 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 laminated on the first phase difference layer (or the second phase difference layer if there is a second phase difference layer) in the form of a laminate of the conductive layer and the substrate (substrate with conductive layer). It is more desirable 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.

The optically isotropic substrate (isotropic substrate) can adopt any appropriate isotropic substrate. The material constituting the isotropic substrate can be, for example, a material having a resin without a conjugated system such as a norbornene resin or an olefin resin as the main skeleton, a material having a cyclic structure such as a lactone ring or a pentylimide ring in the main chain of an acrylic resin, etc. If the above material is used, the phase difference exhibited when the isotropic substrate is formed along with the orientation of the molecular chain can be suppressed to a smaller value. The thickness of the isotropic substrate is preferably less than 50 μm, and more preferably less than 35 μm. The lower limit of the thickness of the isotropic substrate is, for example, 20 μm.

The conductive layer and/or the conductive layer of the isotropic substrate with the conductive layer can be patterned as needed. Conductive portions and insulating portions can be formed by patterning. As a result, electrodes can be formed. The electrodes can function as touch sensing electrodes for sensing contact with the touch panel. Any appropriate method can be used for patterning. Specific examples of patterning methods include wet etching and screen printing.

F. Image display device The polarizing plate with phase difference layer described in items A to E above can be applied to an image display device. Therefore, the present invention includes an image display device using the polarizing plate with phase difference layer. Representative examples of image display devices include liquid crystal display devices and electroluminescent (EL) display devices (e.g., organic EL display devices, inorganic EL display devices). The image display device of the embodiment of the present invention has the polarizing plate with phase difference layer described in items A to E above on its viewing side. The polarizing plate with phase difference layer is laminated in such a manner that the phase difference layer becomes the side of the image display unit (e.g., liquid crystal unit, organic EL unit, inorganic EL unit) (so that the polarizing film becomes the viewing side). In one embodiment, the image display device has a curved shape (essentially a curved display screen) and/or can be bent or folded. In the image display device, the effect of the polarizing plate with a phase difference layer of the present invention is more significant. Embodiment

Hereinafter, the present invention will be specifically described with reference to the embodiments, but the present invention is not limited to the embodiments. The measuring methods of various characteristics are as described below. In addition, unless otherwise specified, the "parts" and "%" in the embodiments and comparative examples are based on weight. (1) The thickness below 10 μm is measured using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name "MCPD-3000"). The thickness greater than 10 μm is measured using a digital micrometer (manufactured by Anritsu Corporation, product name "KC-351C"). (2) Single body transmittance and polarization degree The polarizing film/protective layer laminate (polarizing plate) used in the embodiments and comparative examples was measured using an ultraviolet visible spectrophotometer (V-7100 manufactured by JASCO Corporation), and the measured single body transmittance Ts, parallel transmittance Tp, and orthogonal transmittance Tc were used as Ts, Tp, and Tc of the polarizing film, respectively. These Ts, Tp, and Tc were measured using the 2-degree field of view (C light source) of JIS Z8701 and the Y values obtained by performing a light visual performance calibration. In addition, the refractive index of the protective layer is 1.50, and the refractive index of the surface of the polarizing film on the opposite side of the protective layer is 1.53. The polarization degree P is calculated from the obtained Tp and Tc using the following formula. Polarization degree P (%) = {(Tp-Tc)/(Tp+Tc)} ^1/2 × 100 In addition, the same measurement can be performed using a spectrophotometer such as LPF-200 manufactured by Otsuka Electronics Co., Ltd. As an example, samples 1 to 3 having the same structure as the polarizing plate in the following embodiment were measured using V-7100 and LPF-200, and the measured values of the single transmittance Ts and polarization degree P are listed in Table 1. As shown in Table 1, 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%, which shows that the same measurement results can be obtained regardless of the use of any spectrophotometer. [Table 1] In addition, for example, when a polarizing plate with an anti-glare (AG) surface treatment or an adhesive with diffusion properties is used as the measurement object, different measurement results will be obtained depending on the spectrophotometer. However, in this case, by using the measurement values obtained when measuring the same polarizing plate with each spectrophotometer as the basis for numerical conversion, the difference in the measurement values obtained by the spectrophotometer can be compensated. (3) Optical property variation of long strip polarizing film From the polarizing plate used in the embodiment and the comparative example, measurement samples are cut out at 5 locations at equal intervals along the width direction, and then the single unit transmittance of the central part of each of the 5 measurement samples is measured in the same manner as (2) above. Then, the difference between the maximum and minimum values of the single unit transmittance measured at each measurement position is calculated, and this value is used as the optical property variation of the long strip polarizing film. (4) Optical property variation of thin polarizing film A 100 mm × 100 mm measurement sample was cut from the polarizing plate used in the examples and comparative examples, and the optical property variation of the thin polarizing plate (50 cm ² ) was determined. Specifically, the single transmittance was measured at 5 locations, including the midpoint of each of the 4 sides of the measurement sample, about 1.5 cm to 2.0 cm inward and the center, in the same manner as in (2) above. Then, the difference between the maximum and minimum values of the single transmittance measured at each measurement position was calculated, and the value was taken as the optical property variation of the thin polarizing film. (5) Curvature The polarizing plate with a phase difference layer obtained in the examples and comparative examples was cut into a size of 110 mm × 60 mm. At this time, the cutting was performed in such a way that the absorption axis direction of the polarizing film was the long side direction. The cut polarizing plate with phase difference layer is adhered to a glass plate with a size of 120mm×70mm and a thickness of 0.2mm by an adhesive to prepare a test sample. The test sample is placed in a heating oven maintained at 85°C for 24 hours, and the warp amount is measured after it is taken out. After the test sample is placed on a flat surface with the glass plate at the bottom, the height of the highest part from the flat surface is taken as the warp amount. (6) Bending durability The polarizing plate with phase difference layer obtained in the embodiment and the comparative example is cut into a size of 50mm×100mm. At this time, the cutting is performed with the absorption axis direction of the polarizing film as the short side direction. The cut polarizing plate with phase difference layer was subjected to the bending test using a folding tester with a constant temperature and humidity chamber (manufactured by YUASA, CL09 type-D01) at 20℃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 as the outer side, and the number of bends until cracks, peeling or film rupture that would cause poor image display were measured, and the 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 (7) Front reflection hue The polarizing plate with phase difference layer obtained in the embodiment and the comparative example was bonded to a reflective plate (manufactured by TORAY Film Co., Ltd., trade name "DMS-X42"; reflectivity 86%, reflection hue a ^* =-0.22, b ^* =0.32 without polarizing plate) using an acrylic adhesive without UV absorption function to prepare a measurement sample. At this time, the phase difference plate side of the polarizing plate with phase difference layer is bonded to the reflective plate opposite to the reflective plate. The measurement sample was measured using a spectrophotometer (CM-2600d manufactured by Konica Minolta) by SCE method, and the values of a ^* and b ^* were substituted into √(a ^{* 2} +b ^{* 2} ) to obtain the front reflection hue. (8) Elastic modulus The film to be measured is formed into a tensile test dumbbell-shaped sheet with a parallel width of 10 mm and a length of 40 mm according to JIS K6734:2000, and then subjected to a tensile test according to JIS K7161:1994 to determine the tensile elastic modulus. Here, the length direction is usually consistent with the stretching direction of the polarizing film.

[Example 1] 1. Preparation of polarizing film The thermoplastic resin substrate is 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. One side of the resin substrate is subjected to a corona treatment. 13 parts by weight of potassium iodide is 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") in a ratio of 9:1, and then dissolved in water to prepare a PVA aqueous solution (coating liquid). The PVA aqueous solution was applied to the corona treated surface of the resin substrate and dried at 60°C to form a PVA resin layer with a thickness of 13 μm, thereby producing a laminate. The obtained laminate was subjected to free-end uniaxial stretching 2.4 times in the longitudinal direction (long side direction) between rollers of different peripheral speeds in an oven at 130°C (air-assisted stretching treatment). Then, the laminate was immersed in an insoluble bath (a boric acid aqueous solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (insoluble 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) with a liquid temperature of 30°C for 60 seconds (dyeing treatment) while adjusting the concentration so that the monomer transmittance (Ts) of the polarizing film obtained finally becomes 44.0% or more. Next, the film was immersed in a crosslinking bath (an aqueous boric acid solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid relative to 100 parts by weight of water) with 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 in the longitudinal direction (long side direction) between rollers with different peripheral speeds to achieve a total stretching ratio of 5.5 times (underwater stretching treatment). Afterwards, the laminate was immersed in a cleaning bath (an aqueous solution obtained by mixing 4 parts by weight of potassium iodide with respect to 100 parts by weight of water) at a liquid temperature of 20°C (cleaning treatment). Afterwards, it was dried in an oven maintained at 90°C while contacting a SUS heating roller maintained at a surface temperature of 75°C for about 2 seconds (drying and shrinking treatment). The shrinkage rate in the width direction obtained by the drying and shrinking treatment of the laminate was 5.2%. Through the above process, a polarizing film with a thickness of 5.0 μm was formed on the resin substrate.

2. Preparation of polarizing plate A cycloolefin film (thickness: 28μm, modulus of elasticity 2100MPa) with a hard coating (refractive index 1.53) is bonded to the surface of the polarizing film obtained above (the side opposite to the resin substrate) as a protective layer through a UV-curable adhesive. Specifically, the total thickness of the curable adhesive is applied to 1.0μm, and a roller machine is used for bonding. Thereafter, UV rays are irradiated from the protective layer side to cure the adhesive. Then, after cutting the two ends, the resin substrate is peeled off to obtain a long strip of polarizing plate (width: 1300mm) having a structure of protective layer/adhesive layer/polarizing film. The single transmittance of the polarizing plate (actually a polarizing film) is 44.12%, and the polarization degree is 99.929%. In addition, the optical property variation of the long strip polarizing film is 0.27%, while the optical property variation of the thin sheet polarizing film is 0.10%.

3. Preparation of a phase difference film constituting a phase difference layer 3-1. Polymerization of polyester carbonate resin A batch polymerization apparatus consisting of two vertical reactors equipped with stirring blades and a reflux cooler controlled at 100°C was used for polymerization. 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 spiroglycerol (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 fed. After the reactor is depressurized and replaced with nitrogen, it is heated with a heating medium and agitation is started when the internal temperature reaches 100°C. 40 minutes after the start of the temperature rise, the internal temperature reaches 220°C, and the temperature is controlled and maintained while the pressure is reduced to 13.3 kPa 90 minutes after reaching 220°C. The phenol vapor generated as a by-product of the polymerization reaction is introduced into a 100°C reflux cooler to return a small amount of monomer components contained in the phenol vapor to the reactor, and the uncondensed phenol vapor is introduced into a 45°C condenser for recovery. After nitrogen is introduced into the first reactor to temporarily return it to atmospheric pressure, the oligomerized reaction solution in the first reactor is transferred to the second reactor. Next, the temperature and pressure in the second reactor were raised and reduced, and after 50 minutes, the internal temperature reached 240°C and the pressure reached 0.2 kPa. Thereafter, polymerization was carried out until the predetermined stirring power was reached. At the time when the predetermined power was reached, nitrogen was introduced into the reactor to restore the pressure, and the generated polyester carbonate resin was extruded into water, and the bundle was cut to obtain pellets.

3-2. Preparation of phase difference film The obtained polyester carbonate resin (pellets) was vacuum dried at 80°C for 5 hours, and then a film-making device equipped with a uniaxial extruder (manufactured by Toshiba Machine Co., Ltd., cylinder set temperature: 250°C), a T-die (width 200mm, set temperature: 250°C), a cooling roller (set temperature: 120~130°C) and a winder was used to prepare a long strip of resin film with a thickness of 130μm. The obtained long strip of resin film was stretched while adjusting it to obtain a predetermined phase difference, and a phase difference film with a thickness of 48μm was obtained. The stretching conditions were along the width direction, the stretching temperature was 143°C, and the stretching ratio was 2.8 times. The Re(550) of the obtained retardation film was 141 nm, the Re(450)/Re(550) was 0.86, and the Nz coefficient was 1.12.

4. Preparation of polarizing plate with phase difference layer The phase difference film obtained in 3. is bonded to the surface of the polarizing film of the polarizing plate obtained in 2. above through an acrylic adhesive (thickness 5 μm). At this time, the absorption axis of the polarizing film and the slow axis of the phase difference film are bonded in such a way that the angle of 45° is formed between them. According to the above method, a polarizing plate with phase difference layer having the structure of protective layer/bonding layer/polarizing film/adhesive layer/phase difference layer is obtained. The total thickness of the obtained polarizing plate with phase difference layer is 87 μm. The obtained polarizing plate with phase difference layer is provided for the evaluation of (5) and (6) above. The warp is 3.4 mm. The results are listed in Table 2.

[Example 2] 1. Preparation of polarizing film Except for adjusting the concentration of the dye bath so that the single transmittance (Ts) of the polarizing film becomes 44.0%, a polarizing film with a thickness of 5.0 μm is formed on a resin substrate in the same manner as in Example 1.

2. Preparation of polarizing plate In addition to using the polarizing film obtained in 1. above, a polarizing plate having a protective layer/bonding layer/polarizing film structure was prepared in the same manner as in Example 1. The single body transmittance of the polarizing plate (actually the polarizing film) was 44.0%, and the polarization degree was 99.960%.

3. Preparation of a phase difference film constituting a phase difference layer The phase difference film was prepared in the same manner as in Example 1 except that the phase difference film was stretched so that the Re (550) thereof became 144 nm.

4. Preparation of polarizing plate with phase difference layer The phase difference film obtained in 3. above was bonded to the surface of the polarizing film of the polarizing plate obtained in 2. above in the same manner as in Example 1, thereby preparing a polarizing plate with phase difference layer having a structure of protective layer/bonding layer/polarizer/adhesive layer/phase difference layer. The total thickness of the obtained polarizing plate with phase difference layer was 87 μm. The obtained polarizing plate with phase difference layer was subjected to the evaluations of (5) to (7) above. The results are listed in Table 2.

[Example 3-1] 1. Preparation of polarizing film In the same manner as Example 2, a polarizing film with a thickness of 5.0 μm was formed on a resin substrate.

2. Preparation of polarizing plate A triacetate cellulose (TAC) film with a hard coating (hard coating thickness 7 μm, TAC thickness 25 μm, modulus of elasticity: 3600 MPa) was used as a protective layer. In addition, a polarizing plate having a protective layer/bonding layer/polarizing film structure was prepared in the same manner as in Example 1. The single body transmittance of the polarizing plate was 44.0%, and the polarization degree was 99.960%.

3. Preparation of a phase difference film constituting a phase difference layer Except for melt-kneading 0.7 parts by mass of PMMA, a polyester carbonate resin (pellets) was obtained in the same manner as in Example 1, and after vacuum drying at 80°C for 5 hours, a film-making device equipped with a uniaxial extruder (manufactured by Toshiba Machine Co., Ltd., cylinder set temperature: 250°C), a T-die (width 200mm, set temperature: 250°C), a cooling roller (set temperature: 120~130°C) and a winder was used to prepare a long strip of resin film with a thickness of 105μm. The obtained long strip of resin film was adjusted to obtain a predetermined phase difference and stretched 2.8 times in the width direction at 138°C to obtain a phase difference film with a thickness of 38μm. The Re(550) of the obtained retardation film was 144 nm, and the Re(450)/Re(550) was 0.86.

4. Preparation of polarizing plate with phase difference layer The phase difference film obtained in 3. is bonded to the surface of the polarizing film of the polarizing plate obtained in 2. above through an acrylic adhesive (thickness 5 μm). At this time, the absorption axis of the polarizing film and the slow axis of the phase difference film are bonded in such a way that the angle between them forms 45°. According to the above method, 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 81 μm. The obtained polarizing plate with a phase difference layer is provided for the evaluation of (5) to (7) above. The results are listed in Table 2.

[Example 3-2] A 105μm thick strip of polyester carbonate resin film obtained in the same manner as in Example 3-1 was adjusted to obtain a predetermined phase difference and extended in the width direction to obtain a phase difference film with a thickness of 38μm. The Re(550) of the obtained phase difference film was 140nm. In addition to using the above phase difference film as the phase difference layer, a polarizing plate with a phase difference layer having a structure of a protective layer/bonding layer/polarizing film/adhesive layer/phase difference layer was obtained in the same manner as in Example 3-1. The total thickness of the obtained polarizing plate with a phase difference layer was 81μm. The obtained polarizing plate with a phase difference layer was subjected to the same evaluation as in Example 3-1. The results are listed in Table 2.

[Comparative Example 1] 1. Preparation of polarizer Prepare a polyvinyl alcohol resin film with an average degree of polymerization of 2,400, a saponification degree of 99.9 mol% and a thickness of 30μm. While the polyvinyl alcohol film is immersed in a swelling bath (water bath) at 20°C for 30 seconds between rollers with different peripheral speed ratios to swell it, it is stretched 2.4 times in the conveying direction (swelling step), and then immersed and dyed in a dyeing bath at 30°C (an aqueous solution with an iodine concentration of 0.03 wt% and a potassium iodide concentration of 0.3 wt%) so that the monomer transmittance after the final stretching becomes the desired value, and stretched 3.7 times in the conveying direction based on the original polyvinyl alcohol film (polyvinyl alcohol film that is not stretched in the conveying direction at all) (dyeing step). The immersion time at this time is about 60 seconds. Then, the dyed polyvinyl alcohol film is immersed in a 40°C crosslinking bath (aqueous solution with a boric acid concentration of 3.0% by weight and a potassium iodide concentration of 3.0% by weight) while being stretched to 4.2 times the original polyvinyl alcohol film in the conveying direction (crosslinking step). The obtained polyvinyl alcohol film is immersed in a 64°C stretching bath (aqueous solution with a boric acid concentration of 4.0% by weight and a potassium iodide concentration of 5.0% by weight) for 50 seconds, stretched to 6.0 times the original polyvinyl alcohol film in the conveying direction (stretching step), and then immersed in a 20°C cleaning bath (aqueous solution with a potassium iodide concentration of 3.0% by weight) for 5 seconds (cleaning step). The washed polyvinyl alcohol film was dried at 30° C. for 2 minutes to prepare a polarizer (thickness 12 μm).

2. Making polarizing plates The bonding agent used is an aqueous solution containing acetylacetyl-containing polyvinyl alcohol resin (average degree of polymerization 1,200, saponification degree 98.5 mol%, acetylacetylization degree 5 mol%) and hydroxymethyl melamine. The adhesive is used to form an adhesive layer with a thickness of 0.1 μm, and a triacetate cellulose (TAC) film with a hard coating layer (hard coating thickness 7 μm, TAC thickness 25 μm, modulus of elasticity: 3600 MPa) is bonded to one side of the polarizer obtained above by a roll laminating machine, and a 25 μm thick TAC film is bonded to the other side of the polarizer, and then heated and dried in an oven (temperature of 60°C, time of 5 minutes), thereby producing a polarizing plate having a structure of protective layer 1 (thickness 32 μm)/adhesive layer/polarizer/adhesive layer/protective layer 2.

3. Preparation of polarizing plate with phase difference layer A phase difference film was bonded to the surface of the protective layer 2 of the polarizing plate obtained in 2. above in the same manner as in Example 1, thereby preparing a polarizing plate with phase difference layer having a structure of protective layer 1/bonding layer/polarizer/bonding layer/protective layer 2/adhesive layer/phase difference layer. The total thickness of the obtained polarizing plate with phase difference layer was 122 μm. The obtained polarizing plate with phase difference layer was subjected to the same evaluation as in Example 2. The warp was 5.3 mm.

[Comparative Example 2] 1. Preparation of polarizer A polarizer (thickness 12 μm) was prepared in the same manner as in Comparative Example 1.

2. Preparation of polarizing plate In the same manner as in Comparative Example 1, a polarizing plate having the structure of protective layer 1 (thickness 32 μm)/bonding layer/polarizer/bonding layer/protective layer 2 (thickness 25 μm) was prepared.

3. Preparation of the first oriented solidified layer and the second oriented solidified 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). [Chemical formula 1] The surface of the polyethylene terephthalate (PET) film (thickness 38μm) is wiped with a wiping cloth and an orientation treatment is performed. The direction of the orientation treatment is set to be 15° relative to the absorption axis direction of the polarizer when viewed from the viewing side when attached to the polarizing plate. The above-mentioned liquid crystal coating liquid is applied to the orientation-treated surface using a rod coater, and heat-dried at 90°C for 2 minutes to orient the liquid crystal compound. A metal halogen lamp is used to irradiate the liquid crystal layer formed in the above manner with 1mJ/ ^cm2 of light to harden the liquid crystal layer, thereby forming a liquid crystal orientation solidification layer A on the PET film. The thickness of the liquid crystal orientation solidification layer A is 2.5μm, and the in-plane phase difference Re(550) is 270nm. In addition, the liquid crystal orientation solidification 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 polarizer when viewed from the visual 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 1.5 μm, and the in-plane phase difference Re(550) was 140 nm. In addition, the liquid crystal orientation solidification layer B had a refractive index distribution of nx＞ny＝nz. In addition, the Re(450)/Re(550) of the liquid crystal orientation solidification layers A and B was 1.11.

4. Preparation of polarizing plate with phase difference layer The liquid crystal oriented solidified layer A and liquid crystal oriented solidified layer B obtained in 3. are sequentially transferred to the surface of the protective layer 2 of the polarizing plate obtained in 2. At this time, the transfer (bonding) is performed in such a way that the angle formed by the absorption axis of the polarizer and the slow axis of the oriented solidified layer A is 15° and the angle formed by the absorption axis of the polarizer and the slow axis of the oriented solidified layer B is 75°. In addition, each transfer (bonding) is performed through a UV curable adhesive (thickness 1μm). According to the above method, 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 directional solidification layer/bonding layer/second directional solidification layer) is obtained. The total thickness of the obtained polarizing plate with a phase difference layer is 75 μm. The obtained polarizing plate with a phase difference layer is provided for the same evaluation as in Example 2. The results are listed in Table 2.

[Comparative Example 3] 1. Preparation of polarizing film In addition to making the single transmittance (Ts) of the polarizing film 43.0%, a polarizing film with a thickness of 5.0 μm was formed on a resin substrate in the same manner as in Example 1.

2. Preparation of polarizing plate An acrylic film (surface refractive index 1.50, 20μm) is bonded as a protective layer to the surface of the polarizing film obtained above (the side opposite to the resin substrate) through a UV-curable adhesive. Specifically, the curable adhesive is applied to a total thickness of 1.0μm and bonded using a roller machine. Thereafter, UV light is irradiated from the protective layer side to cure the adhesive. Then, after cutting the two ends, the resin substrate is peeled off to obtain a long strip of polarizing plate (width: 1300mm) having a structure of protective layer/adhesive layer/polarizing film. The single unit transmittance of the polarizing plate (actually a polarizing film) is 43.0%, and the degree of polarization is 99.995%.

3. Preparation of polarizing plate with phase difference layer In the same manner as in comparative example 2, the liquid crystal oriented solidified layer A and the liquid crystal oriented solidified layer B obtained in the same manner as in comparative example 2 are sequentially transferred onto the surface of the polarizing film of the polarizing plate obtained in the above 2. In the above manner, a polarizing plate with phase difference layer having a structure of protective layer/bonding layer/polarizing film/bonding layer/phase difference layer (first oriented solidified layer/bonding layer/second oriented solidified layer) is obtained. The total thickness of the obtained polarizing plate with phase difference layer is 32μm. The obtained polarizing plate with phase difference layer is provided for the same evaluation as in Example 2. The results are listed in Table 2.

[Table 2]

[Comparative Example 4] Potassium iodide was not added to the PVA aqueous solution (coating solution), the stretching ratio of the air-assisted stretching treatment was set to 1.8 times, and no heating roller was used in the dry shrinking treatment. In addition, a polarizing film was attempted to be produced in the same manner as in Example 1. However, the PVA resin layer was dissolved during the dyeing treatment and the underwater stretching treatment, and a polarizing film could not be produced. Therefore, a polarizing plate with a phase difference layer could not be produced.

[Evaluation] Comparing the examples with the comparative examples, it is obvious that the optical properties of the polarizing film of the examples of the present invention are good and the warping after the heating test can be significantly suppressed. In addition, it is known that by combining a phase difference layer composed of a polycarbonate resin (including a polyester carbonate resin) film, an excellent reflection hue can be obtained. In addition, the polycarbonate resin is thinned to less than 40μm, the thickness of the polarizing plate is set to less than 85μm, and a substrate with an elastic modulus of more than 3000MPa is used, preferably a TAC film is used as a protective layer, so that the bending properties can be further improved. On the other hand, the polarizing plate with a phase difference layer of Comparative Example 3 is thin and the warp after the heating test is significantly suppressed, but the reflection hue is large and is not satisfactory from the viewpoint of display characteristics.

Industrial Applicability 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: First protective layer 13: Second protective layer 20: Phase difference layer (first phase difference layer) 50: Another phase difference layer (second phase difference layer) 60: Conductive layer or isotropic substrate with conductive layer 100, 101: Polarizing plate with phase difference layer 200: Laminated body G1~G4: Guide rollers R1~R6: Transport rollers

FIG1 is a schematic cross-sectional view of a polarizing plate with a phase difference layer in one embodiment of the present invention. FIG2 is a schematic cross-sectional view of a polarizing plate with a phase difference layer in another embodiment of the present invention. FIG3 is a schematic view showing an example of a drying and shrinking treatment using a heating roller in a method for manufacturing a polarizing film used in a polarizing plate with a phase difference layer in the present invention.

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 (10)

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 located on at least one side of the polarizing film; the polarizing film is composed of a polyvinyl alcohol-based resin film containing a dichroic substance, and has a thickness of less than 8 μm, a single body transmittance of more than 44.0%, and a polarization degree of more than 99.50%; the Re(550) of the phase difference layer is 100 nm to 190 nm, and the Re(450)/Re(550) is greater than 0.8 and less than 1; the angle formed by the slow axis of the phase difference layer and the absorption axis of the polarizing film is 40°~50°; the manufacturing method comprises the following steps: forming a polyvinyl alcohol resin layer containing iodide or sodium chloride and polyvinyl alcohol resin on one side of a long strip of thermoplastic resin substrate to form a laminate; and sequentially performing air-assisted stretching treatment, dyeing treatment, underwater stretching treatment and drying shrinkage treatment on the laminate to obtain the polarizing film. The drying shrinkage treatment is to heat the laminate while conveying it along the long side direction, thereby shrinking it by 2%~10% in the width direction. The heating is to use a heating roller in a heating furnace and make the total contact time between the laminate and the heating roller be 1~20 seconds. The manufacturing method of the polarizing plate with phase difference layer as claimed in claim 1, wherein the protective layer is composed of a cellulose triacetate resin film. A method for manufacturing a polarizing plate with a phase difference layer as claimed in claim 1 or 2, wherein the phase difference layer is composed of a polycarbonate resin film. A method for manufacturing a polarizing plate with a phase difference layer as claimed in claim 1 or 2, 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%. The manufacturing method of a polarizing plate with a phase difference layer as claimed in claim 1 or 2, 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 at positions along the width direction is less than 0.3%. The manufacturing method of the polarizing plate with phase difference layer as claimed in claim 1 or 2, wherein the monomer transmittance of the aforementioned polarizing film is less than 44.5%, and the polarization degree is less than 99.95%. A method for manufacturing a polarizing plate with a phase difference layer as claimed in claim 1 or 2, wherein the polarizing plate with a phase difference layer 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; the manufacturing method comprises: arranging the other phase difference layer outside the phase difference layer. The manufacturing method of the polarizing plate with phase difference layer as claimed in claim 1 or 2, wherein the polarizing plate with phase difference layer further has a conductive layer or an isotropic substrate with a conductive layer outside the phase difference layer; the manufacturing method comprises: arranging the conductive layer or the isotropic substrate with a conductive layer outside the phase difference layer. A method for manufacturing a polarizing plate with a phase difference layer as claimed in claim 1 or 2, wherein the polarizing plate with a phase difference layer is in a strip shape; The aforementioned manufacturing method comprises: laminating a strip-shaped polarizing film and a strip-shaped phase difference layer by roll-to-roll; the strip-shaped polarizing film has an absorption axis in the strip direction, and the strip-shaped phase difference layer is: an obliquely stretched film having a slow axis in a direction at an angle of 40° to 50° relative to the strip direction. The method for manufacturing a polarizing plate with a phase difference layer as claimed in claim 9 comprises: winding the aforementioned long strip-shaped polarizing plate with a phase difference layer into a roll.