TWI832889B - Polarizing plate with retardation layer and image display device using the polarizing plate with retardation layer - Google Patents

Abstract

The present invention provides a polarizing plate with a retardation layer that is thin, has excellent handleability, and has excellent optical properties. The polarizing plate with a retardation layer of the present invention has a polarizing plate and a retardation layer. The polarizing plate includes a polarizing film and a protective layer provided 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. Its thickness is 8 μm or less, its single transmittance is 46% or more, and its polarization degree is 92% or more. The retardation layer is a directionally solidified layer of liquid crystal compound.

Description

Polarizing plate with retardation layer and image display device using the polarizing plate with retardation layer

Field of invention

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

Background of the invention

In recent years, image display devices represented by liquid crystal display devices and electroluminescence (EL) display devices (eg, organic EL display devices, inorganic EL display devices) have been rapidly popularized. In image display devices, polarizing plates and phase difference plates are typically used. In actual use, a polarizing plate with a retardation layer in which a polarizing plate and a retardation plate are integrated is widely used (for example, Patent Document 1). Recently, as expectations for thinner image display devices have increased, the need for attached retardation layers has increased. There is also an increasing demand for thinning of polarizing plates with retardation layers. In addition, in recent years, expectations for curved image display devices and/or bendable or bendable image display devices are increasing, and polarizing plates and polarizing plates with retardation layers are also required to be further thinned and further softened. In order to make the polarizing plate with the retardation layer thinner, the protective layer of the polarizing film and the retardation film, which contribute greatly to the thickness, are made thinner. However, if the protective layer and the retardation film are made thinner, the shrinkage of the polarizing film will have a relatively greater impact, causing the image display device to warp and the operability of the polarizing plate with the retardation layer to deteriorate. low such problem.

In order to solve the above-mentioned problems, the polarizing film also needs to be thinned. However, if the thickness of the polarizing film is simply reduced, the optical properties will be reduced. More specifically, one or both of the polarization degree and the monomer transmittance, which have a trade-off relationship, are reduced to an extent that is not allowed for practical use. As a result, the optical characteristics of the polarizing plate with the retardation layer also become insufficient.

existing technical documents

patent documents

Patent Document 1: Japanese Patent No. 3325560

The present invention was made in order to solve the above-mentioned conventional problems, and its main purpose is to provide a polarizing plate with a retardation layer that is thin, has excellent handleability, and has excellent optical properties.

The polarizing plate with a retardation layer of the present invention has a polarizing plate and a retardation layer. The polarizing plate includes a polarizing film and a protective layer provided 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. Its thickness is 8 μm or less, its monomer transmittance is more than 46%, and its polarization degree is more than 92%. The retardation layer is a liquid crystal compound orientationally solidified layer.

In one embodiment, the unit weight of the polarizing plate with a retardation layer is 6.5 mg/cm ² or less.

In one embodiment, the total thickness of the polarizing plate with the retardation layer is 60 μm or less.

In one embodiment, the above-mentioned retardation layer is a single layer of a liquid crystal compound orientationally solidified layer, the Re(550) of the retardation layer is 100nm~190nm, and the slow axis of the retardation layer is formed by the absorption axis of the above-mentioned polarizing film. The angle is 40°~50°.

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

In one embodiment, the difference between the maximum value and the minimum value of the single transmittance of the above-mentioned polarizing film in a 50 cm ² area is less than 0.3%.

In one embodiment, the width of the polarizing plate with the retardation layer is 1000 mm or more, and the difference between the maximum value and the minimum value of the single transmittance of the polarizing film at a position along the width direction is 0.7% or less.

In one embodiment, the polarizing film has a single transmittance of 48% or less and a polarization degree of 97% or less.

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

In one embodiment, the above-mentioned polarizing plate with a retardation layer is The outside of the retardation layer further has a conductive layer or an isotropic base material with a conductive layer.

According to another aspect of the present invention, there is provided an image display device including the above-mentioned polarizing plate with a retardation layer.

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

According to the present invention, adding a halide (typically potassium iodide) to a polyvinyl alcohol (PVA)-based resin, two-stage stretching including in-air auxiliary stretching and underwater stretching, and drying and shrinkage using a heated roller are employed. , a polarizing film that is thin and has very excellent optical properties can be obtained. By using such a polarizing film, a polarizing plate with a retardation layer that is thin, has excellent handleability, and has excellent optical properties can be realized.

10:Polarizing plate

11:Polarizing film

12: 1st protective layer

13: 2nd protective layer

20: Phase difference layer

21: The first directional solidification layer

22: The second directional solidification layer

50: 2nd phase difference layer

60: Isotropic substrate

100: Polarizing plate with phase difference layer

101: Polarizing plate with phase difference layer

102: Polarizing plate with phase difference layer

200: stacked body

G1~G4: guide roller

R1~R6: conveying roller

FIG. 1 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to one embodiment of the present invention.

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

3 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to another embodiment of the present invention.

4 is a schematic diagram showing an example of drying and shrinkage treatment using a heating roller in the manufacturing method of the polarizing film used in the polarizing plate with a retardation layer of the present invention.

Detailed description of preferred embodiments

Hereinafter, embodiments of the present invention will be described, 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 reaches the maximum (i.e., the slow axis direction), "ny" is the refractive index in the direction orthogonal to the slow axis in the plane (i.e., the fast axis direction), and "nz" is The refractive index in the thickness direction.

(2) In-plane phase difference (Re)

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

(3) Thickness direction phase difference (Rth)

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

(4)Nz coefficient

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

(5)Angle

In this specification, when referring to an angle, the angle includes both clockwise and counterclockwise relative to the reference direction. So, for example, "45°" means ± 45°.

A. The overall composition of a polarizing plate with a retardation layer

FIG. 1 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to one embodiment of the present invention. The polarizing plate with retardation layer 100 of this embodiment has the polarizing plate 10 and the retardation 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 . Depending on the purpose, one of the first protective layer 12 and the second protective layer 13 may be omitted. For example, when the retardation layer 20 can also function as a protective layer for the polarizing film 11, the second protective layer 13 may be omitted. In an embodiment of the present invention, the polarizing film is composed of a polyvinyl alcohol-based resin film containing a dichroic substance. The thickness of the polarizing film is less than 8 μm, the single transmittance is more than 46%, and the polarization degree is more than 92%.

As shown in FIG. 2 , in another embodiment of the polarizing plate 101 with a retardation layer, other retardation layers 50 and/or a conductive layer or an isotropic base material 60 with a conductive layer may be provided. The other retardation layers 50 and the conductive layer or the isotropic base material 60 with the conductive layer are typically provided on the outside of the retardation layer 20 (the side opposite to the polarizing plate 10 ). The refractive index characteristics of other retardation layers typically show the relationship nz>nx=ny. Typically, other retardation layers 50 and a conductive layer or an isotropic base material 60 with a conductive layer are provided in order from the retardation layer 20 side. Representatively, the other phase difference layers 50 and the conductive layer or the isotropic base material 60 with the conductive layer are any layers provided as needed, and any one or both of them may be omitted. For convenience, the retardation layer 20 may be called a first retardation layer, and the other retardation layers 50 may be called a second retardation layer. Furthermore, when a conductive layer is provided or attached to a conductive In the case of an isotropic base material, a polarizing plate with a retardation layer can be applied to a so-called in-cell touch system with a touch sensor introduced between the image display unit (such as an organic EL unit) and the polarizing plate. Panel type input display device.

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

The above-described embodiments may be combined appropriately, and obvious changes in the technical field may be added to the constituent elements in the above-described embodiments. For example, the second retardation layer 50 and/or the conductive layer or the isotropic base material 60 with the conductive layer can be provided on the polarizing plate 102 with a retardation layer in FIG. 3 . For example, the structure in which the isotropic base material 60 with a conductive layer is provided outside the second retardation layer 50 may be replaced by an optically equivalent structure (for example, a laminate of a second retardation layer and a conductive layer).

The polarizing plate with a retardation layer obtained by embodiments of the present invention may further include other retardation layers. The optical properties (for example, refractive index characteristics, in-plane phase difference, Nz coefficient, photoelastic coefficient), thickness, arrangement position, etc. of other retardation layers can be appropriately set according to the purpose.

The polarizing plate with a retardation layer of the present invention may be in the shape of a single piece or in the shape of a strip. In this specification, "elongated shape" refers to an elongated shape with a length that is sufficiently long relative to the width, and includes, for example, an elongated shape with a length that is 10 times or more, preferably 20 times or more, with respect to the width. The long polarizing plate with retardation layer can be rolled into a roll.

In actual use, it can be set to be the same as the polarized light in the phase difference layer. An adhesive layer (not shown) is provided on the opposite side of the plate, and the polarizing plate with a retardation layer can be adhered to the image display unit. In addition, it is preferable that a release film is temporarily adhered to the surface of the adhesive layer until the polarizing plate with the retardation layer is used. By temporarily attaching the release film, the adhesive layer can be protected and rolled.

The total thickness of the polarizing plate with the retardation layer is preferably 60 μm or less, more preferably 55 μm or less, further preferably 50 μm or less, particularly preferably 40 μm or less. The lower limit of the total thickness may be, for example, 28 μm. According to the embodiment of the present invention, a very thin polarizing plate with a retardation layer can be realized in this way. Such a polarizing plate with a retardation layer can have very excellent flexibility and bending durability. Such a polarizing plate with a retardation layer can be particularly suitably used for a curved image display device and/or a bendable or bendable image display device. Furthermore, the total thickness of the polarizing plate with a retardation layer refers to all the layers that make up the polarizing plate with a retardation layer, except for the adhesive layer used to adhere the polarizing plate to external adherends such as panels and glass. The total thickness of the polarizing plate with a retardation layer does not include the adhesive layer used to adhere the polarizing plate with the retardation layer to adjacent components such as the image display unit and the peeling layer that can be temporarily adhered to its surface. film thickness).

The unit weight of the polarizing plate with a retardation layer according to the embodiment of the present invention is, for example, 6.5 mg/cm ² or less, preferably 2.0 mg/cm ² to 6.0 mg/cm ² , and more preferably 3.0 mg/cm ² to 5.5 mg. /cm ² , more preferably 3.5 mg/cm ² to 5.0 mg/cm ² . When the display panel is thin, there is a concern that the panel may be slightly deformed due to the weight of the polarizing plate with a retardation layer, causing display defects. However, according to the polarizing plate with a retardation layer having a unit weight of 6.5 mg/cm ² or less, , which prevents such panel deformation. In addition, the polarizing plate with the retardation layer having the above-mentioned unit weight has good handleability even when the thickness is reduced, and can exhibit very excellent flexibility and bending durability.

Hereinafter, the components of the polarizing plate with a retardation layer will be described in more detail.

B.Polarizing plate

B-1.Polarizing film

As mentioned above, the polarizing film 11 has a thickness of 8 μm or less, a single transmittance of 46% or more, and a polarization degree of 92% or more. Generally speaking, there is a trade-off relationship between monomer transmittance and absorbance. If the monomer transmittance is increased, the polarization degree will decrease. If the polarization degree is increased, the monomer transmittance will decrease. Therefore, in the past, it has been difficult to put into practical use a thin polarizing film that satisfies the optical characteristics of a single transmittance of 46% or more and a polarization degree of 92% or more. It is one of the features of the present invention to use a thin polarizing film that has excellent optical properties such as a single transmittance of 46% or more and a polarization degree of 92% or more, and in which variation in optical properties is suppressed.

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

The polarizing film preferably exhibits absorption dichroism at any wavelength from 380 nm to 780 nm. The single transmittance of the polarizing film is preferably 48% or less. The degree of polarization of the polarizing film is preferably 92.5% or more, more preferably 93% or more. On the other hand, the degree of polarization is preferably 97% or less. The above-mentioned monomer transmittance is typically measured using a UV-visible spectrophotometer, and The Y value obtained with visibility correction. The above-mentioned degree of polarization is typically determined by the following equation based on the parallel transmittance Tp and the orthogonal transmittance Tc measured using a UV-visible spectrophotometer and corrected for visibility.

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

In one embodiment, the transmittance of a thin polarizing film of 8 μm or less is typically measured using a laminate of a polarizing film (surface refractive index: 1.53) and a protective film (refractive index: 1.50) using an ultraviolet-visible spectrophotometer. And measure. Depending on the surface refractive index of the polarizing film and/or the refractive index of the surface of the protective film that is in contact with the air interface, the reflectance of the interface between each layer changes, and as a result, the measured value of the transmittance may change. Therefore, for example, when a protective film with a refractive index other than 1.50 is used, the measured value of the transmittance can be corrected based on the refractive index of the surface of the protective film that is in contact with the air interface. Specifically, the correction value C of the transmittance uses the reflectance R ₁ (transmission axis reflectance) of polarized light parallel to the transmission axis in the interface between the protective film and the air layer, and is expressed by the following formula.

C=R ₁ -R ₀

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

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

Among them, R ₀ is the transmission axis reflectance 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 base material with a surface refractive index of 1.53 (cycloolefin-based film, hard-coated film, etc.) is used as a protective film, the correction amount C becomes approximately 0.2%. In this case, adding 0.2% to the measured transmittance can be converted to the transmittance when a protective film with a surface refractive index of 1.50 is used. Furthermore, according to the calculation based on the above formula, the change in the correction value C when the transmittance T ₁ of the polarizing film is changed by 2% is 0.03% or less. The impact of the transmittance of the polarizing film on the value of the correction value C is limited. In addition, when the protective film has absorption other than surface reflection, appropriate correction can be performed based on the amount of absorption.

In one embodiment, the width of the polarizing plate with the retardation layer is 1000 mm or more. Therefore, the width of the polarizing film is also 1000 mm or more. In this case, the difference (D1) between the maximum value and the minimum value of the single transmittance of the polarizing film at a position along the width direction is preferably 0.7% or less, more preferably 0.6% or less, still more preferably 0.5% or less. Particularly preferably, it is 0.44% or less. The smaller D1 is, the more preferred it is, and the lower limit of D1 may be, for example, 0.01%. When D1 is within the above range, a polarizing plate with a retardation layer having excellent optical properties can be produced industrially. In another embodiment, the difference (D2) between the maximum value and the minimum value of the single transmittance of the polarizing film in an area of 50 ^cm is preferably 0.3% or less, more preferably 0.2% or less, and still more preferably 0.15% or less. . The smaller D2 is, the more preferred it is, and the lower limit of D2 may be, for example, 0.01%. When D2 is within the above range, when the polarizing plate with the retardation layer is used in an image display device, uneven brightness in the display screen can be suppressed.

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

Specific examples of the polarizing film obtained using a laminate include a polarizing film obtained using a laminate of a resin base material and a PVA-based resin layer coated on the resin base material. A polarizing film obtained by using a laminate of a resin base material and a PVA-based resin layer coated on the resin base material is, for example, It can be produced by the following method: applying a PVA-based resin solution to a resin base material, drying it, forming a PVA-based resin layer on the resin base material, and obtaining a laminate of the resin base material and the PVA-based resin layer; The body is stretched and dyed to make the PVA resin layer into a polarizing film. In this embodiment, stretching typically includes immersing the laminate in a boric acid aqueous solution and stretching. In addition, stretching may further include stretching the laminate in the air at a high temperature (for example, 95° C. or higher) before stretching in a boric acid aqueous solution, if necessary. The obtained laminated body of the resin base material/polarizing film can be used as it is (that is, the resin base material can be used as a protective layer of the polarizing film), or the resin base material can be peeled off from the laminated body of the resin base material/polarizing film. The overlay on the peeling surface may be any suitable protective layer depending on the purpose. Details of the manufacturing method of such a polarizing film are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580. The entire description of this publication can be incorporated into this specification as a reference.

The manufacturing method of the polarizing film typically includes: forming a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin on one side of a long thermoplastic resin base material to prepare a laminated body; and sequentially processing the laminated body. An in-air auxiliary stretching process, a dyeing process, an underwater stretching process, and a drying shrinkage process in which the film is heated while being transported in the length direction to shrink it by 2% or more in the width direction are performed. This makes it possible to provide a polarizing film with a thickness of 8 μm or less, a single transmittance of 46% or more, a polarization degree of 92% or more, excellent optical properties, and suppressed variation in optical properties. That is, by introducing auxiliary stretching, even when PVA is coated on a thermoplastic resin, the crystallinity of PVA can be improved and high optical properties can be achieved. In addition, by simultaneously improving the orientation of PVA in advance, it can be used in subsequent dyeing steps and When immersed in water during the stretching step, problems such as reduced orientation and dissolution of PVA can be prevented and high optical properties can be achieved. Furthermore, when the PVA-based resin layer is immersed in a liquid, compared with the case where the PVA-based resin layer does not contain a halide, it is possible to suppress the disorder of the orientation of the polyvinyl alcohol molecules and the decrease in orientation. This can improve the optical properties of a polarizing film obtained through a treatment step of immersing the laminate in a liquid, such as dyeing treatment and water stretching treatment. Furthermore, the optical properties can be improved by shrinking the laminated body in the width direction through drying and shrinkage treatment.

B-2.Protective layer

烯系、聚烯烴系、(甲基)丙烯酸系、乙酸酯系等的透明樹脂等。另外，還可列舉(甲基)丙烯酸系、胺基甲酸酯系、(甲基)丙烯酸胺基甲酸酯系、環氧系、矽酮系等熱硬化型樹脂或紫外線硬化型樹脂等。除此以外，還可列舉例如矽氧烷系聚合物等玻璃質系聚合物。另外，也可以使用日本特開2001-343529號公報(WO01/37007)中記載的聚合物薄膜。作為該薄膜的材料，可使用例如含有下述熱塑性樹脂的樹脂組成物：在側鏈具有取代或非取代之醯亞胺基的熱塑性樹脂、和在側鏈具有取代或非取代之苯基及腈基的熱塑性樹脂，可列舉例如：具有由異丁烯和N-甲基馬來醯 亞胺形成的交替共聚物、和丙烯腈-苯乙烯共聚物的樹脂組成物。該聚合物薄膜可以是例如上述樹脂組成物的擠出成形物。 The first protective layer 12 and the second protective layer 13 can each be formed of any appropriate film that can be used as a protective layer of the polarizing film. Specific examples of the material that is the main component of the film include cellulose-based resins such as triacetyl cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, and polyamide-based resins. Amine series, polyether series, polystyrene series, polystyrene series, polypropylene series

Transparent resins such as olefin-based, polyolefin-based, (meth)acrylic-based, acetate-based, etc. In addition, thermosetting resins such as (meth)acrylic, urethane, (meth)acrylic urethane, epoxy, and silicone resins, or ultraviolet curing resins can be used. Other examples include glassy polymers such as siloxane polymers. In addition, the polymer film described in Japanese Patent Application Laid-Open No. 2001-343529 (WO01/37007) can also be used. As a material for this film, a resin composition containing, for example, a thermoplastic resin having a substituted or unsubstituted acyl imine group in the side chain, and a substituted or unsubstituted phenyl group or nitrile in the side chain can be used. Examples of base thermoplastic resins include resin compositions having an alternating copolymer of isobutylene and N-methylmaleimide and an acrylonitrile-styrene copolymer. The polymer film may be, for example, an extrusion molded product of the above-mentioned resin composition.

As will be described later, the polarizing plate with a retardation layer of the present invention is typically disposed on the viewable side of the image display device, and the first protective layer 12 is typically disposed on the viewable side. Therefore, if necessary, the first protective layer 12 may be subjected to surface treatment such as hard coating treatment, anti-reflection treatment, anti-adhesion treatment, and anti-glare treatment. In addition/or when viewing through polarized sunglasses, the first protective layer 12 may be subjected to processing to improve visibility (typically, imparting (elliptic) circular polarization function and imparting ultra-high phase difference) to the first protective layer 12 as needed. By performing such processing, excellent visibility can be achieved even when the display screen is viewed through polarized lenses such as polarized sunglasses. Therefore, the polarizing plate with the retardation layer can also be applied to an image display device that can be used outdoors.

The thickness of the first protective layer is preferably 5 μm to 80 μm, more preferably 10 μm to 40 μm, and even more preferably 10 μm to 30 μm. In addition, when surface treatment is performed, the thickness of the outer protective layer is the thickness including the thickness of the surface treatment layer.

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

B-3. Manufacturing method of polarizing film

The polarizing film can be produced, for example, by a method including forming a polyvinyl alcohol-based resin layer (PVA-based resin) containing a halide and a polyvinyl alcohol-based resin (PVA-based resin) on one side of a long thermoplastic resin base material. resin layer) to form a laminated body; and the laminated body is sequentially subjected to air-assisted stretching treatment, dyeing treatment, water stretching treatment, and drying by heating while being transported in the length direction to shrink it by more than 2% in the width direction. Shrink processing. The halide content in the PVA-based resin layer is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin. The drying shrinkage treatment is preferably performed 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 of the laminate obtained by the drying shrinkage treatment is preferably 2% or more. According to such a manufacturing method, the polarizing film described in the above item B-1 can be obtained. In particular, a laminated body containing a halide-containing PVA-based resin layer is produced, and the stretching of the laminated body is a multi-stage stretching including auxiliary stretching in the air and stretching in water, and the heated roller is used to stretch the laminated body. By heating the laminate, a polarizing film can be obtained that has excellent optical properties (typically single transmittance and degree of polarization) and in which variation in optical properties is suppressed. Specifically, by using a heating roller in the drying and shrinkage treatment step, the entire laminated body can be uniformly shrunk while conveying the laminated body. This not only improves the optical properties of the polarizing film obtained, but also stably produces a polarizing film with excellent optical properties, and suppresses the optical properties of the polarizing film (especially is the deviation of the monomer transmittance).

B-3-1. Production of laminated body

As a method of producing a laminate of a thermoplastic resin base material and a PVA-based resin layer, any appropriate method can be adopted. Preferably, a coating liquid containing a halide and a PVA-based resin is applied to the surface of the thermoplastic resin base material and dried to form a PVA-based resin layer on the thermoplastic resin base material. As mentioned above, the halide content in the PVA-based resin layer is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin.

As a method of applying the coating liquid, any appropriate method can be adopted. Examples include roll coating, spin coating, wire-wound bar coating, dip coating, die coating, shower coating, spray coating, blade coating (blade coating, etc.). The coating/drying temperature of the coating liquid is preferably 50°C or higher.

The thickness of the PVA-based resin layer is preferably 3 μm to 40 μm, more preferably 3 μm to 20 μm.

Before forming the PVA-based resin layer, the thermoplastic resin base material may be subjected to surface treatment (for example, corona treatment, etc.), and an easy-adhesion layer may be formed on the thermoplastic resin base material. By performing such treatment, the adhesion between the thermoplastic resin base material and the PVA-based resin layer can be improved.

B-3-1-1. Thermoplastic resin base material

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

The water absorption rate of the thermoplastic resin base material is preferably 0.2% or more, more preferably 0.3% or more. The thermoplastic resin base material absorbs water, and the water acts like a plasticizer and is plasticized. As a result, the tensile stress can be significantly reduced and stretching can be performed at a high magnification ratio. On the other hand, the water absorption rate of the thermoplastic resin base material is preferably 3.0% or less, and more preferably 1.0% or less. By using such a thermoplastic resin base material, it is possible to prevent disadvantages such as significant reduction in the dimensional stability of the thermoplastic resin base material during production and deterioration in the appearance of the obtained polarizing film. In addition, it can prevent the base material from breaking and the PVA-based resin layer from peeling off the thermoplastic resin base material during stretching in water. Furthermore, the water absorption rate of the thermoplastic resin base material can be adjusted, for example, by introducing a modifying group into the constituent material. The water absorption rate is a value calculated in accordance with JIS K 7209.

The glass transition temperature (Tg) of the thermoplastic resin base material is preferably 120°C or lower. By using such a thermoplastic resin base material, it is possible to suppress crystallization of the PVA-based resin layer while ensuring sufficient stretchability of the laminate. In addition, in consideration of plasticization of the thermoplastic resin base material by water and satisfactory stretching in water, the temperature is more preferably 100°C or lower, and further preferably 90°C or lower. On the other hand, the glass transition temperature of the thermoplastic resin base material is preferably 60° C. or higher. By using such a thermoplastic resin base material, it is possible to prevent defects such as deformation of the thermoplastic resin base material (for example, occurrence of unevenness, sagging, wrinkles, etc.) when applying/drying the PVA-based resin-containing coating liquid. Make the laminated body well. In addition, the PVA-based resin layer can be stretched satisfactorily at a suitable temperature (for example, about 60° C.). Furthermore, the glass transition temperature of the thermoplastic resin base material can be adjusted, for example, by using a crystallized material in which a modifying group is introduced into the constituent material and heating the material. glass turn The transfer temperature (Tg) is a value calculated in accordance with JIS K 7121.

烯系樹脂等環烯烴系樹脂、聚丙烯等烯烴系樹脂、聚醯胺系樹脂、聚碳酸酯系樹脂、它們的共聚物樹脂等。這些中，優選降

烯系樹脂、非晶質的聚對苯二甲酸乙二醇酯系樹脂。 As the constituent material of the thermoplastic resin base material, any appropriate thermoplastic resin can be used. Examples of the thermoplastic resin include ester-based resins such as polyethylene terephthalate-based resin,

Cycloolefin resins such as olefin resins, olefin resins such as polypropylene, polyamide resins, polycarbonate resins, copolymer resins thereof, etc. Among these, it is preferable to reduce

Vinyl resin and amorphous polyethylene terephthalate resin.

In one embodiment, it is preferable to use amorphous (non-crystallized) polyethylene terephthalate-based resin. Among them, amorphous (hard to crystallize) polyethylene terephthalate-based resin is particularly preferably used. Specific examples of the amorphous polyethylene terephthalate resin include a copolymer further containing isophthalic acid and/or cyclohexanedicarboxylic acid as a dicarboxylic acid, or a copolymer further containing cyclohexanedicarboxylic acid. Alkanedimethanol and diethylene glycol are copolymers of diols.

In a preferred embodiment, the thermoplastic resin base material is composed of polyethylene terephthalate-based resin having an isophthalic acid unit. This is because such a thermoplastic resin base material has extremely excellent stretchability and can suppress crystallization during stretching. This is thought to be because introduction of an isophthalic acid unit gives a large bend to the main chain. The polyethylene terephthalate resin has a terephthalic acid unit and an ethylene glycol unit. The content ratio of isophthalic acid units is preferably 0.1 mol% or more, more preferably 1.0 mol% or more, based on the total of all repeating units. This is because a thermoplastic resin base material with extremely excellent stretchability can be obtained. On the other hand, the content ratio of isophthalic acid units is preferably 20 mol relative to the total of all repeating units. mol% or less, more preferably 10 mol% or less. By setting the content ratio to such a content ratio, the crystallinity can be favorably increased in the drying shrinkage treatment described below.

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

Relative to the glass transition temperature (Tg), the stretching temperature of the thermoplastic resin base material is preferably Tg-10°C to Tg+50°C. The stretching ratio of the thermoplastic resin base material is preferably 1.5 times to 3.0 times.

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

B-3-1-2. Coating liquid

As mentioned above, the coating liquid contains a halide and a PVA-based resin. The coating liquid may typically be a solution obtained by dissolving the halide and the PVA-based resin in a solvent. Examples of the solvent include water, dimethylstyrene, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, Various glycols, polyols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. They can be used individually or in combination of 2 or more types. Among these, water is preferred. The PVA-based resin concentration of the solution is preferably 3 to 20 parts by weight relative to 100 parts by weight of the solvent. If the resin concentration is such, a uniform coating film that closely adheres to the thermoplastic resin base material can be formed. The halide content in the coating liquid is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin.

Additives may be blended into the coating liquid. Examples of additives include plasticizers, surfactants, and the like. Examples of plasticizers include polyhydric alcohols such as ethylene glycol and glycerin. Examples of the surfactant include nonionic surfactants. These additives are used for the purpose of further improving the uniformity, dyeability, and stretchability of the obtained PVA-based resin layer.

As the PVA-based resin, any appropriate resin can be used. Examples include polyvinyl alcohol and ethylene-vinyl alcohol copolymer. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. Ethylene-vinyl alcohol copolymer is obtained by saponifying ethylene-vinyl acetate copolymer. The saponification degree of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, and more preferably 99.0 mol% to 99.93 mol%. The degree of saponification can be determined in accordance with JIS K 6726-1994. By using a PVA-based resin with such a degree of saponification, a polarizing film excellent in durability can be obtained. When saponification is too high, gelation may occur.

The average degree of polymerization of the PVA-based resin can be appropriately selected depending on the purpose. The average degree of polymerization is usually 1000~10000, preferably 1200~4500, more preferably 1500~4300. In addition, the average degree of polymerization can be determined in accordance with JIS K 6726-1994.

As the above-mentioned halide, any appropriate halide can be used. Examples include iodide and sodium chloride. Examples of the iodide include potassium iodide, sodium iodide, and lithium iodide. Among these, potassium iodide is preferred.

The amount of the halide in the coating liquid is preferably 5 to 20 parts by weight based on 100 parts by weight of the PVA resin, and more preferably 10 to 15 parts by weight based on 100 parts by weight of the PVA resin. When the amount of the halide exceeds 20 parts by weight relative to 100 parts by weight of the PVA-based resin, the halide may bleed out and the polarizing film finally obtained may become cloudy.

Generally speaking, by stretching the PVA-based resin layer, the orientation of the polyvinyl alcohol molecules in the PVA-based resin is improved. However, if the stretched PVA-based resin layer is immersed in a liquid containing water, there will be The orientation of vinyl alcohol molecules is disordered and the orientation is reduced. Especially when the laminate of a thermoplastic resin base material and a PVA-based resin layer is stretched in a boric acid aqueous solution, the laminate is immersed in a boric acid aqueous solution at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin base material. During stretching, the above orientation degree tends to decrease significantly. For example, stretching of a PVA film monomer in a boric acid aqueous solution is usually performed at 60°C. On the other hand, a laminate of A-PET (thermoplastic resin base material) and a PVA-based resin layer is stretched at a temperature of about 70°C. It is carried out at a high temperature. In this case, the orientation of PVA at the beginning of stretching will decrease in the stage before it rises by stretching in water. In contrast, a laminate of a halide-containing PVA-based resin layer and a thermoplastic resin base material is produced, and the laminate is stretched in the air in a boric acid aqueous solution. By performing high-temperature stretching (auxiliary stretching) during the stretching, the crystallization of the PVA-based resin in the PVA-based resin layer of the laminated body after auxiliary stretching can be promoted. As a result, when the PVA-based resin layer is immersed in a liquid, compared with the case where the PVA-based resin layer does not contain a halide, the orientation disorder of the polyvinyl alcohol molecules and the decrease in orientation can be suppressed. This can improve the optical properties of a polarizing film obtained through a process step of immersing the laminate in a liquid, such as dyeing treatment and water stretching treatment.

B-3-2. Aerial auxiliary stretching processing

In particular, in order to obtain high optical properties, a two-stage stretching method that combines dry stretching (auxiliary stretching) and stretching in a boric acid aqueous solution can be selected. By introducing auxiliary stretching like two-stage stretching, the thermoplastic resin base material can be stretched while suppressing crystallization. This can solve the problem of excessive crystallization of the thermoplastic resin base material during subsequent stretching in a boric acid aqueous solution. By eliminating the problem of reduced stretchability, the laminate can be stretched at a higher rate. In addition, when coating PVA-based resin on a thermoplastic resin base material, in order to suppress the influence of the glass transition temperature of the thermoplastic resin base material, it is necessary to lower the coating temperature compared with the case where PVA-based resin is generally coated on a metal drum. As a result, there is a problem that the crystallization of the PVA-based resin is relatively reduced and sufficient optical properties cannot be obtained. In contrast, by introducing auxiliary stretching, even when a PVA-based resin is coated on a thermoplastic resin, the crystallinity of the PVA-based resin can be improved and high optical properties can be achieved. In addition, by simultaneously improving the orientation of the PVA-based resin in advance, problems such as reduction in orientation and dissolution of the PVA-based resin can be prevented when immersed in water in the subsequent dyeing step and stretching step, and high optical properties can be achieved.

The stretching method of in-air auxiliary stretching may be fixed-end stretching (for example, stretching using a tenter stretching machine) or free-end stretching (for example, passing the laminated body between rollers with different peripheral speeds). As for the method of uniaxial stretching), in order to obtain high optical properties, free-end stretching can be actively used. In one embodiment, the in-air stretching treatment includes a heating roller stretching step of utilizing a circumferential speed difference between the heating rollers to stretch the laminated body while transporting the layered body in its longitudinal direction. The in-air stretching process typically includes a zone stretching step and a heated roller stretching step. Furthermore, the order of the zone stretching step and the heating roller stretching step is not limited. The zone stretching step may be performed first, or the heating roll stretching step may be performed first. The region stretching step can be omitted. In one embodiment, the zone stretching step and the heated roller stretching step are performed sequentially. In another embodiment, in a tenter stretching machine, the ends of the film are held, and the distance between the tenters is expanded in the conveyance direction (the expansion of the distance between the tenters is referred to as the stretch ratio). . At this time, the distance of the tenter in the width direction (the direction perpendicular to the conveyance direction) is set to be arbitrarily close. It is preferable to set it so that it may be closer to the free-end stretch with respect to the stretch ratio in the conveyance direction. In the case of free end stretching, the shrinkage rate in the width direction = (1/stretch ratio) ^1/2 is calculated.

Aerial assisted stretching can be performed in one stage or in multiple stages. When the process is performed in multiple stages, the draw ratio is the product of the draw ratios in 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 in the air-assisted stretching is preferably 2.0 times ~3.5 times. The maximum stretching ratio when combining in-air auxiliary stretching and underwater stretching is preferably 5.0 times or more, more preferably 5.5 times or more, and even more preferably 6.0 times or more relative to the original length of the laminated body. In this specification, the "maximum stretch ratio" refers to the stretch ratio immediately before the laminated body breaks, and refers to the stretch ratio at which rupture of the laminated body is separately confirmed and is 0.2 smaller than this value.

The stretching temperature of the in-air auxiliary stretching can be set to any appropriate value depending on the forming material of the thermoplastic resin base material, the stretching method, and the like. The stretching temperature is preferably not less than the glass transition temperature (Tg) of the thermoplastic resin base material, more preferably not less than the glass transition temperature (Tg) of the thermoplastic resin base material + 10°C, and particularly preferably not less than Tg + 15°C. On the other hand, the upper limit of the stretching temperature is preferably 170°C. By stretching at such a temperature, rapid crystallization of the PVA-based resin can be suppressed, and problems caused by the crystallization (for example, obstruction of the orientation of the PVA-based resin layer caused by stretching) can be suppressed. The crystallization index of the PVA-based resin after in-air auxiliary stretching is preferably 1.3 to 1.8, and more preferably 1.4 to 1.7. The crystallization index of PVA-based resin can be measured by the ATR method using a Fourier transform infrared spectrophotometer. Specifically, polarized light was measured as measurement light, and the intensity at 1141 cm ^-1 and 1440 cm ^-1 in the obtained spectrum was used to calculate the crystallization index according to the following formula.

Crystallization index = (I _C /I _R )

Among them, I _C : The intensity at 1141 cm ^-1 when measuring light is incident on it

_IR : Intensity at 1440 cm ^-1 when measuring light is incident on it.

B-3-3.Insolubilization treatment

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

B-3-4. Dyeing treatment

The above dyeing treatment is typically performed by dyeing the PVA-based resin layer with a dichroic substance (typically iodine). Specifically, it is performed by adsorbing iodine on the PVA-based resin layer. Examples of the adsorption method include: a method of immersing a PVA-based resin layer (laminated body) in a dyeing liquid containing iodine; a method of applying the dyeing liquid to the PVA-based resin layer; and spraying the dyeing liquid to the PVA-based resin layer. liquid method, etc. The method of immersing the laminated body in a dyeing liquid (dyeing bath) is preferable. This is because iodine adsorbs well.

The above-mentioned dyeing liquid is preferably an iodine aqueous solution. The blending amount of iodine 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 preferable to blend iodide into the aqueous iodine solution. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide, etc. . Among these, potassium iodide is preferred. The blending amount of iodide is preferably 0.1 to 10 parts by weight, and more preferably 0.3 to 5 parts by weight relative to 100 parts by weight of water. In order to suppress the dissolution of the PVA-based resin, the liquid temperature when dyeing with the dyeing liquid is preferably 20°C to 50°C. After impregnating the PVA resin layer In the case of dyeing liquid, in order to ensure the transmittance of the PVA-based 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 single transmittance of the finally obtained polarizing film is 46% or more and the degree of polarization is 92% or more. As such dyeing conditions, it is preferable to use an iodine aqueous solution as the dyeing liquid, and set the ratio of the content 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. Thus, a polarizing film having the above-mentioned optical characteristics can be obtained.

When the laminate is immersed in a treatment bath containing boric acid (typically an insolubilization treatment) and then dyed continuously, the boric acid concentration in the dyeing bath changes due to the boric acid contained in the treatment bath being mixed into the dyeing bath. It changes with time, and as a result, the dyeability may become unstable. In order to suppress the instability of the dyeability as described above, the upper limit of the boric acid concentration in the dyeing bath is adjusted so that it is preferably 4 parts by weight, and 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 in the dyeing bath is preferably 0.1 parts by weight, more preferably 0.2 parts by weight, and even more preferably 0.5 parts by weight based on 100 parts by weight of water. In one embodiment, the dyeing process is performed using a dye bath pre-mixed with boric acid. This can reduce the change ratio of the boric acid concentration when the boric acid in the treatment bath is mixed into the dyeing bath. The blending amount of boric acid previously blended in the dyeing bath (that is, the content of boric acid not derived from the above-mentioned treatment bath) is preferably 0.1 to 2 parts by weight, and more preferably 0.5 to 2 parts by weight relative to 100 parts by weight of water. 1.5 parts by weight.

B-3-5. Cross-linking treatment

If necessary, cross-linking treatment is performed after the dyeing treatment and before the water stretching treatment. The cross-linking treatment is typically performed by immersing the PVA-based resin layer in a boric acid aqueous solution. By performing cross-linking treatment, water resistance can be imparted to the PVA-based resin layer, and during subsequent stretching in water, the orientation of the PVA can be prevented from being reduced when immersed in high-temperature water. The concentration of the boric acid aqueous solution is preferably 1 to 5 parts by weight relative to 100 parts by weight of water. In addition, when performing cross-linking treatment after the above-mentioned dyeing treatment, it is preferable to further blend iodide. By blending iodide, elution of iodine adsorbed on the PVA-based resin layer can be suppressed. The blending amount of iodide is preferably 1 to 5 parts by weight relative to 100 parts by weight of water. Specific examples of iodide are as described above. The liquid temperature of the cross-linking bath (boric acid aqueous solution) is preferably 20°C to 50°C.

B-3-6. Stretching in water

The underwater stretching treatment is performed by immersing the laminate in a stretching bath. According to the underwater stretching treatment, stretching can be performed at a temperature lower than the glass transition temperature (typically about 80°C) of the thermoplastic resin base material or PVA-based resin layer, and the crystallization of the PVA-based resin layer can be suppressed. Stretching is performed at high magnification simultaneously. As a result, a polarizing film having excellent optical properties can be produced.

The laminate may be stretched by any appropriate method. Specifically, it may be fixed end stretching or free end stretching (for example, a method of uniaxial stretching by passing the laminate between rollers having different peripheral speeds). Free end stretching is preferred. The laminate may be stretched in one stage or in multiple stages. When the process is performed in multiple stages, the draw ratio (maximum draw ratio) of the laminate described below is the draw ratio of each stage. The accumulation.

Stretching in water is preferably performed by immersing the laminate in a boric acid aqueous solution (stretching in a boric acid aqueous solution). By using a boric acid aqueous solution as a stretching bath, the PVA-based resin layer can be provided with rigidity that can withstand the tension applied during stretching and water resistance that is insoluble in water. Specifically, boric acid can generate tetrahydroxyborate anions in an aqueous solution, and cross-link with PVA-based resin through hydrogen bonds. As a result, the PVA-based resin layer can be provided with rigidity and water resistance, can be stretched favorably, and can produce a polarizing film having excellent optical properties.

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

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

The stretching temperature (liquid temperature of the stretching bath) is preferably 40°C to 85°C, more preferably 60°C to 75°C. If it is such a temperature, it can be suppressed The PVA resin layer is dissolved and stretched at a high magnification at the same time. Specifically, as mentioned above, in relation to the formation of the PVA-based resin layer, the glass transition temperature (Tg) of the thermoplastic resin base material is preferably 60° C. or higher. In this case, when the stretching temperature is lower than 40° C., there is a concern that the thermoplastic resin base material may not be stretched satisfactorily even if plasticization of the thermoplastic resin base material by water is taken into consideration. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, and there is a concern that excellent optical properties cannot be obtained. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

The stretching ratio by stretching in water is preferably 1.5 times or more, and more preferably 3.0 times or more. The total stretch ratio of the laminated body is preferably 5.0 times or more, and more preferably 5.5 times or more relative to the original length of the laminated body. By achieving such a high stretching ratio, a polarizing film with extremely excellent optical properties can be produced. Such a high stretching ratio can be achieved by using water stretching (stretching in boric acid aqueous solution).

B-3-7. Drying and shrinkage treatment

The above-mentioned drying shrinkage treatment may be performed by regional heating by heating the entire area, or may be performed by heating a transport roller (using a so-called heating roller) (heated roller drying method). It is preferred to utilize both. By using a heating roller for drying, heating curling of the laminate can be effectively suppressed and a polarizing film with excellent appearance can be produced. Specifically, by drying the laminated body along the heating roller, the crystallization of the thermoplastic resin base material can be efficiently promoted to increase the crystallinity, and the thermoplasticity can be favorably increased even at a relatively low drying temperature. Crystallinity of the resin substrate. As a result, the rigidity of the thermoplastic resin base material increases, making it resistant to drying. The shrinkage state of the PVA-based resin layer can suppress curling. In addition, by using a heating roller, the laminated body can be dried while being kept in a flat state. Therefore, not only curling but also the occurrence of wrinkles can be suppressed. At this time, the optical properties can be improved by shrinking the laminated body in the width direction through drying and shrinkage treatment. This is because the orientation of PVA and PVA/iodine complex can be effectively improved. The shrinkage rate in the width direction of the laminate subjected to drying shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using a heating roller, the laminated body can be continuously shrunk in the width direction while being conveyed, thereby achieving high productivity.

FIG. 4 is a schematic diagram showing an example of drying shrinkage treatment. In the drying shrinkage process, the laminated body 200 is dried while being transported using the transport rollers R1 to R6 heated to a predetermined temperature and the guide rollers G1 to G4. In the illustrated example, the transport rollers R1 to R6 are arranged so as to alternately and continuously heat the PVA resin layer and the thermoplastic resin base material surface. However, they may also be used to heat only one side of the laminated body 200 (for example, the thermoplastic resin base material side). Conveyor rollers R1~R6 are configured in continuous heating mode.

Drying conditions can be controlled by adjusting the heating temperature of the transport roller (temperature of the heating roller), the number of heating rollers, the contact time with the heating roller, and the like. The temperature of the heating roller is preferably 60°C to 120°C, more preferably 65°C to 100°C, and particularly preferably 70°C to 80°C. The crystallinity of the thermoplastic resin can be effectively increased, curling can be effectively suppressed, and an optical laminate with extremely excellent durability can be produced. Furthermore, the temperature of the heating roller can be measured with a contact thermometer. In the illustrated example, six conveyance rollers are provided, but there is no particular limitation as long as there are a plurality of conveyance rollers. There are usually 2 transport rollers ~40, preferably 4~30. The contact time (total contact time) between the laminated body and the heating roller is preferably 1 to 300 seconds, more preferably 1 to 20 seconds, and still more preferably 1 to 10 seconds.

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

B-3-8.Other processing

It is preferable to perform a cleaning process after the water stretching process and before the dry shrinkage process. The above-described cleaning treatment is typically performed by immersing the PVA-based resin layer in a potassium iodide aqueous solution.

C. 1st phase difference layer

As mentioned above, the first retardation layer 20 is an orientationally solidified liquid crystal compound layer. By using a liquid crystal compound, the difference between nx and ny of the resulting retardation layer can be greatly increased compared to a non-liquid crystal material. Therefore, the thickness of the retardation layer for obtaining a desired in-plane retardation can be significantly reduced. As a result, the polarizing plate with the retardation layer can be further reduced in thickness and weight. In this specification, the "orientation solidified layer" refers to a layer in which a liquid crystal compound is oriented in a predetermined direction within the layer and the orientation state is fixed. Furthermore, as described later, the "directionally solidified layer" includes a fixed layer obtained by hardening the liquid crystal monomer. Toward the concept of hardened layer. In this embodiment, the rod-shaped liquid crystal compounds are typically aligned (uniformly aligned) in a state of being juxtaposed toward the slow axis direction of the first retardation layer.

Examples of the liquid crystal compound include a liquid crystal compound whose liquid crystal phase is a nematic phase (nematic liquid crystal). As such a liquid crystal compound, for example, a liquid crystal polymer or a liquid crystal monomer can be used. The liquid crystallinity development mechanism of the liquid crystal compound may be either lyotropic or thermal. The liquid crystal polymer and the liquid crystal monomer can be used individually or in combination.

When the liquid crystal compound is a liquid crystal monomer, it is preferable that the liquid crystal monomer is a polymerizable monomer and a crosslinkable monomer. This is because the alignment state of the liquid crystal monomer can be fixed by polymerizing or crosslinking the liquid crystal monomer (ie, hardening). After aligning the liquid crystal monomers, for example, if the liquid crystal monomers are polymerized or cross-linked with each other, the above-described alignment state can thereby be fixed. Here, the polymer is formed by polymerization and the three-dimensional network structure is formed by cross-linking, but they are non-liquid crystalline. Therefore, the formed first retardation layer does not undergo transition to a liquid crystal phase, a glass phase, or a crystal phase due to temperature changes specific to liquid crystalline compounds, for example. As a result, the first retardation layer becomes a retardation layer that is not affected by temperature changes and has extremely excellent stability.

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

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

The liquid crystal compound orientation-hardened layer can be formed by subjecting the surface of a predetermined base material to orientation treatment, applying a coating liquid containing a liquid crystal compound to the surface, orienting the liquid crystal compound in a direction corresponding to the above-mentioned orientation treatment, and fixing it. the orientation status. In one embodiment, the substrate is any suitable resin film, and the directionally solidified layer formed on the substrate can be transferred to the surface of the polarizing plate 10 . In another embodiment, the base material may be the second protective layer 13 . In this case, the transfer step can be omitted and the directionally solidified layer (first retardation layer) can be formed and then continuously laminated from roll to roll. Therefore, productivity can be further improved.

As the above-mentioned orientation processing, any suitable orientation processing can be adopted. Specifically, they can be enumerated: mechanical orientation treatment, physical orientation treatment, and chemical orientation treatment. Specific examples of mechanical orientation treatment include rubbing treatment and stretching treatment. Specific examples of physical orientation processing include magnetic field orientation processing and electric field orientation processing. Specific examples of chemical alignment treatment include tilt evaporation and photo-alignment treatment. The processing conditions of various orientation treatments can adopt any appropriate conditions depending on the purpose.

Orientation of the liquid crystal compound can be carried out by performing treatment at a temperature that exhibits a liquid crystal phase according to the type of the liquid crystal compound. by doing Such temperature treatment causes the liquid crystal compound to enter a liquid crystal state, and the liquid crystal compound is oriented in accordance with the orientation treatment direction of the substrate surface.

In one embodiment, the alignment state is fixed by cooling the liquid crystal compound that has been aligned as described above. When the liquid crystal compound is a polymerizable monomer or a crosslinkable monomer, the alignment state can be fixed by subjecting the aligned liquid crystal compound to a polymerization treatment or a crosslinking treatment as described above.

Specific examples of the liquid crystal compound and details of the formation method of the orientationally solidified layer are described in Japanese Patent Application Laid-Open No. 2006-163343. The description of this publication is incorporated into this specification as a reference.

Other examples of the orientation-hardened layer include a form in which a discotic liquid crystal compound is oriented in any state among vertical alignment, mixed alignment, and oblique alignment. In the case of a discotic liquid crystal compound, typically, the disk surface of the discotic liquid crystal compound is oriented substantially perpendicularly to the film surface of the first retardation layer. The term "the discotic liquid crystal compound is substantially vertical" means that the average angle between the film surface and the disc surface of the discotic liquid crystal compound is preferably 70° to 90°, more preferably 80° to 90°, and still more preferably 85°. °~90°. A discoidal liquid crystal compound generally refers to a liquid crystal compound having a discoidal molecular structure in which a cyclic core such as benzene, 1,3,5-triazine, calixarene, etc. is arranged in the center of the molecule , and a structure in which straight-chain alkyl groups, alkoxy groups, substituted benzyloxy groups, etc. are substituted radially as the side chains. Representative examples of discotic liquid crystals include benzene derivatives, triphenylene derivatives, and triphenylene derivatives described in the research report of C. Destrade et al., Mol. Cryst. Liq. Cryst. Vol. 71, page 111 (1981). Polyindene derivatives, phthalocyanine derivatives, Cyclohexane derivatives described in the research report of B. Kohne et al., Angew. Chem. Vol. 96, page 70 (1984), and the research report of J.M. Lehn et al., J. Chem. Soc. Chem. Commun., 1794 Page (1985), the research report of J. Zhang et al., J. Am. Chem. Soc. Volume 116, Page 2655 (1994), macrocycles such as nitrogen crown series and phenylethyne series. Other specific examples of discotic liquid crystal compounds include compounds described in Japanese Patent Application Laid-Open Nos. 2006-133652, 2007-108732, and 2010-244038. The descriptions in the above-mentioned documents and gazettes are incorporated into this specification by reference.

In one embodiment, the first retardation layer 20 is a single layer of a liquid crystal compound orientationally solidified layer as shown in FIGS. 1 and 2 . When the first retardation layer 20 is composed of a single layer of the liquid crystal compound orientationally solidified layer, the thickness is preferably 0.5 μm to 7 μm, and more preferably 1 μm to 5 μm. By using a liquid crystal compound, it is possible to achieve an in-plane phase difference equivalent to that of a resin film at a thickness that is significantly thinner than that of a resin film.

Typically, the refractive index characteristics of the first retardation layer show the relationship nx>ny=nz. The first retardation layer is typically provided to impart antireflection properties to the polarizing plate. When the first retardation layer is a single layer of an orientationally solidified layer, it can function as a λ/4 plate. In this case, the in-plane retardation Re (550) of the first retardation layer is preferably 100 nm to 190 nm, more preferably 110 nm to 170 nm, and even more preferably 130 nm to 160 nm. Furthermore, here, "ny=nz" includes not only the case where ny and nz are completely equal, but also the case where they are substantially equal. Therefore, within the range that does not impair the effect of the present invention, it may be ny>nz or ny<nz.

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

The first phase difference layer may exhibit inverse wavelength dispersion characteristics in which the phase difference value becomes larger depending on the wavelength of the measurement light, or may exhibit positive wavelength dispersion characteristics in which the phase difference value becomes smaller in accordance with the wavelength of the measurement light. It may also exhibit It produces flat wavelength dispersion characteristics in which the phase difference value hardly changes with the wavelength of the measurement light. In one embodiment, the first retardation layer exhibits reverse dispersion wavelength characteristics. In this case, Re(450)/Re(550) of the retardation layer is preferably 0.8 or more and less than 1, and more preferably 0.8 or more and 0.95 or less. With such a configuration, very excellent anti-reflection properties can be achieved.

The angle θ formed by the slow axis of the first retardation layer 20 and the absorption axis of the polarizing film 11 is preferably 40° to 50°, more preferably 42° to 48°, and even more preferably about 45°. When the angle θ is in such a range, as mentioned above, by using the first retardation layer as a λ/4 plate, a retardation having very excellent circular polarization properties (and as a result, very excellent antireflection properties) can be obtained. layer of polarizing plate.

In another embodiment, as shown in FIG. 3 , the first retardation layer 20 may have a laminated structure of a first orientationally solidified layer 21 and a second orientationally solidified layer 22 . In this case, either one of the first directionally solidified layer 21 and the second directionally solidified layer 22 can function as a λ/4 plate, and the other can function as a λ/2 plate. Therefore, the thickness of the first directionally solidified layer 21 and the second directionally solidified layer 22 can be adjusted to obtain the desired in-plane phase difference of the λ/4 plate or the λ/2 plate. For example, when the first directionally solidified layer 21 functions as a λ/2 plate and the second directionally solidified layer 22 functions as a λ/4 plate, the thickness of the first directionally solidified layer 21 is, for example, 2.0 μm to 3.0 μm, and the second directionally solidified layer 22 functions as a λ/4 plate. The thickness of the solidified layer 22 is, for example, 1.0 μm to 2.0 μm. In this case, the in-plane phase difference Re(550) of the first directionally solidified layer is preferably 200 nm to 300 nm, more preferably 230 nm to 290 nm, and still more preferably 250 nm to 280 nm. Regarding the single-layer orientationally solidified layer, the in-plane phase difference Re (550) of the second orientationally solidified layer is as described above. The angle between the slow axis of the first directionally solidified layer and the absorption axis of the polarizing film is preferably 10° to 20°, more preferably 12° to 18°, and even more preferably about 15°. The angle between the slow axis of the second directionally solidified layer and the absorption axis of the polarizing film is preferably 70° to 80°, more preferably 72° to 78°, and even more preferably about 75°. With such a configuration, characteristics close to ideal reverse wavelength dispersion characteristics can be obtained, and as a result, very excellent anti-reflection characteristics can be achieved. The liquid crystal compound constituting the first directionally solidified layer and the second directionally solidified layer, the formation method of the first directionally solidified layer and the second directionally solidified layer, optical properties, etc. are as described above for the single-layer directionally solidified layer.

D. 2nd phase difference layer

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

The second retardation layer having refractive index characteristics of nz>nx=ny can be formed of any appropriate material. The second retardation layer is preferably formed of a thin film containing a liquid crystal material fixed in a homeotropic alignment orientation. The liquid crystal material (liquid crystal compound) that can be aligned vertically can be a liquid crystal monomer or a liquid crystal polymer. Specific examples of the liquid crystal compound and the method of forming the retardation layer include the liquid crystal compound and the method of forming the retardation layer described in [0020] to [0028] of Japanese Patent Application Laid-Open No. 2002-333642. In this case, the thickness of the second retardation layer is preferably 0.5 μm to 10 μm, more preferably 0.5 μm to 8 μm, and even more preferably 0.5 μm to 5 μm.

E. Conductive layer or isotropic substrate with conductive layer

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

When the conductive layer contains a metal oxide, the thickness of the conductive layer is preferably 50 nm or less, and 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 above-mentioned base material to the first retardation layer (or, when the second retardation layer exists, the second retardation layer), The conductive layer alone can be used as a constituent layer of the polarizing plate with a retardation layer, or it can be formed into a laminate with a base material (a base material with a conductive layer), and can be laminated on the first retardation layer (or as the second retardation layer). If the layer exists, it is the second phase difference layer). It is preferable that the base material is optically isotropic. Therefore, the conductive layer can be used as an isotropic base material with a conductive layer and used in a polarizing plate with a retardation layer.

烯系樹脂、烯烴系樹脂等不具有共軛系的樹脂為主骨架的材料；在丙烯酸系樹脂的主鏈中具有內酯環、戊二醯亞胺環等環狀結構的材料等。如果使用這樣的材料，則形成各向同性基材時，可將伴隨著分子鏈定向而表現出的相位差抑制為較小水平。各向同性基材的厚度優選為50μm以下，更優選為35μm以下。各向同性基材的厚度的下限例如為20μm。 As the optically isotropic base material (isotropic base material), any appropriate isotropic base material can be used. Examples of materials constituting the isotropic base material include:

Materials having a non-conjugated resin as the main skeleton, such as vinyl resins and olefin-based resins; materials having cyclic structures such as lactone rings and glutadiimide rings in the main chain of acrylic resins, etc. If such a material is used, when the isotropic base material is formed, the phase difference caused by the orientation of the molecular chain can be suppressed to a small level. The thickness of the isotropic base material is preferably 50 μm or less, and more preferably 35 μm or less. The lower limit of the thickness of the isotropic base material 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. Through patterning, conductive portions and insulating portions can be formed. As a result, an electrode can be formed. The electrodes may function as touch sensor electrodes that sense contact with the touch panel. As the pattern forming method, any appropriate method can be adopted. Specific examples of the pattern forming method include wet etching and screen printing.

F.Image display device

The polarizing plate with a retardation layer described in the above items A to E can be applied to an image display device. Therefore, the present invention includes an image display device using such a polarizing plate with a retardation layer. As a representative example of an image display device, Examples include liquid crystal display devices and electroluminescence (EL) display devices (for example, organic EL display devices and inorganic EL display devices). The image display device according to the embodiment of the present invention includes the polarizing plate with a retardation layer described in the above items A to E on the viewing side thereof. The polarizing plate with a retardation layer is laminated so that the retardation layer becomes the image display unit (for example, a liquid crystal unit, an organic EL unit, an inorganic EL unit) side (the polarizing film becomes a visible side). In one embodiment, the image display device may have a curved shape (substantially a curved display screen), and/or may be bendable or bendable. In such an image display device, the effect of the polarizing plate with a retardation layer of the present invention becomes remarkable.

Example

Hereinafter, the present invention will be specifically described using examples, but the present invention is not limited to these examples. The measurement method of each characteristic is as follows. In addition, unless otherwise stated, "part" and "%" in Examples and Comparative Examples are based on weight.

(1)Thickness

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

(2)Monomer transmittance and polarization degree

For the polarizing film/protective layer laminate (polarizing plate) used in the Examples and Comparative Examples, the single transmittance Ts and parallel measured using a UV-visible spectrophotometer (V-7100 manufactured by JASCO Corporation) were measured. The transmittance Tp and the cross transmittance Tc are Ts, Tp and Tc of the polarizing film. These Ts, Tp, and Tc were measured using the 2-degree field of view (C light source) of JIS Z8701 and visibility correction was performed. And get the Y value. Furthermore, the refractive index of the protective layer is 1.50, and the refractive index of the surface of the polarizing film opposite to the protective layer is 1.53.

From the obtained Tp and Tc, the degree of polarization P is determined by the following equation.

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

In addition, a spectrophotometer such as LPF-200 manufactured by Otsuka Electronics Co., Ltd. can be used to perform equivalent measurements. As an example, for Samples 1 to 3 of polarizing plates having the same structure as the following examples, the single transmittance Ts and polarization P were obtained by measurement using V-7100 and LPF-200, and their values were The measured values are shown in Table 1. As shown in Table 1, it can be seen that the difference between the measured value of the single-unit transmittance of V-7100 and the measured value of the single-unit transmittance of LPF-200 is 0.1% or less. When either spectrophotometer is used, the difference is obtained. Equivalent measurement results.

Furthermore, for example, when a polarizing plate with an adhesive that has anti-glare (AG) surface treatment and diffusion properties is used as the measurement object, different measurement results will be obtained depending on the spectrophotometer. In this case, based on By numerically converting the measured values of the same polarizing plate measured with each spectrophotometer, differences in measured values depending on the spectrophotometer can be compensated.

(3) Deviation in the optical properties of the long polarizing film

From the polarizing plates used in Examples and Comparative Examples, measurement samples were cut out at five positions at equal intervals in the width direction, and the monomers in the center portions of each of the five measurement samples were measured in the same manner as in (2) above. Transmittance. Next, plan The difference between the maximum value and the minimum value of the single transmittance measured at each measurement position was calculated, and this value was regarded as the variation in the optical characteristics of the long polarizing film.

(4) Deviation in optical properties of single-piece polarizing film

From the polarizing plates used in Examples and Comparative Examples, a measurement sample of 100 mm×100 mm was cut out, and the variation in optical characteristics of a single polarizing plate (50 cm ² ) was determined. Specifically, in the same manner as in (2) above, the single transmittance was measured at a total of five positions at positions approximately 1.5 cm to 2.0 cm inward from the midpoint of each of the four sides of the measurement sample and the central portion. Next, the difference between the maximum value and the minimum value of the single transmittance measured at each measurement position was calculated, and this value was regarded as the variation in the optical characteristics of the monolithic polarizing film.

(5)Warpage

The polarizing plate with a retardation layer obtained in the Example and the Comparative Example was cut into a size of 110 mm×60 mm. At this time, the polarizing film is cut out so that the absorption axis direction becomes the long side direction. The cut out polarizing plate with a retardation layer was bonded to a glass plate with a size of 120mm×70mm and a thickness of 0.2mm using an adhesive to serve as a test sample. The test sample was put into a heating oven maintained at 85°C for 24 hours, and the amount of warpage after taking it out was measured. When the test sample is placed on a flat surface with the glass plate facing down, the height of the highest part from the flat surface is taken as the amount of warpage.

(6)Unit weight

The polarizing plate with a retardation layer obtained in the Examples and Comparative Examples was cut into a predetermined size, and the weight (mg) was divided by the area (cm ² ) to calculate the weight per unit area of the polarizing plate with a retardation layer. (unit weight).

(7)Bending resistance

The polarizing plate with a retardation layer obtained in the Example and the Comparative Example was cut into a size of 50 mm×100 mm. At this time, the polarizing film is cut out so that the absorption axis direction becomes the short side direction. Using a folding endurance testing machine (manufactured by YUASA, CL09 type-D01) equipped with a constant temperature and humidity chamber, the cut polarizing plate with a retardation layer was subjected to a bending test under conditions of 20°C and 50% RH. . Specifically, the polarizing plate with the retardation layer is repeatedly bent in a direction parallel to the absorption axis direction so that the retardation layer side becomes the outside, and the measurement is performed until cracks, peeling, film breakage, etc. resulting in display failure occur. The number of bends was evaluated based on the following criteria (bending diameter: 2mm φ).

<Evaluation Criteria>

Less than 10,000 times: bad

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

More than 30,000 times: Excellent

[Example 1]

1. Production of polarizing film

As the thermoplastic resin base material, a long amorphous isophthalic acid copolymerized polyethylene terephthalate film (thickness: 100 μm) with a water absorption rate of 0.75% and a Tg of approximately 75°C was used. Corona treatment was performed on one side of the resin base material.

It is made by mixing polyvinyl alcohol (degree of polymerization 4200, saponification degree 99.2 mol%) and acetyl-acetyl modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER Z410") at a ratio of 9:1 To 100 parts by weight of the PVA-based resin, 13 parts by weight of potassium iodide was added, and the resulting mixture was dissolved in water to prepare a PVA aqueous solution (coating liquid).

The above-mentioned PVA aqueous solution was applied to the corona-treated surface of the resin base material and dried at 60° C. to form a PVA-based resin layer with a thickness of 13 μm, and a laminated body was produced.

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

Next, the laminated body was immersed in an insolubilization bath (a boric acid aqueous solution in which 4 parts by weight of boric acid was mixed with 100 parts by weight of water) having a liquid temperature of 40° C. for 30 seconds (insolubilization treatment).

Next, in a dyeing bath with a liquid temperature of 30° C. (an iodine aqueous solution obtained by mixing iodine and potassium iodide at a weight ratio of 1:7 with respect to 100 parts by weight of water), the single transmittance of the finally obtained polarizing film was determined. (Ts) was immersed for 60 seconds (dyeing process) while adjusting the concentration to reach 46% or more.

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

Then, while immersing the laminated body in a boric acid aqueous solution with a liquid temperature of 70° C. (boric acid concentration 4.0% by weight), the laminate was stretched between rollers with different circumferential speeds so that the total stretching ratio in the longitudinal direction (longitudinal direction) became 5.5 times. One-way stretching (stretching in water).

Then, the laminated body was immersed in a cleaning bath (an aqueous solution in which 4 parts by weight of potassium iodide was mixed with 100 parts by weight of water) having a liquid temperature of 20° C. (cleaning treatment).

Then, while drying in an oven maintained at 90°C, The SUS heated roller maintained at a surface temperature of 75° C. was contacted for about 2 seconds (drying shrinkage treatment). The shrinkage rate of the laminate in the width direction after drying and shrinkage treatment was 5.2%.

In this way, a polarizing film with a thickness of 5 μm was formed on the resin base material.

2. Production of polarizing plates

On the surface of the polarizing film obtained above (the surface opposite to the resin base material), an acrylic film (surface refractive index 1.50, 40 μm) was bonded as a protective layer via an ultraviolet curable adhesive. Specifically, the curable adhesive was applied so that the total thickness became 1.0 μm, and bonded using a roller machine. Then, UV light is irradiated from the protective layer side to harden the adhesive. Next, after cutting both ends, the resin base material was peeled off, and a long polarizing plate (width: 1300 mm) having a protective layer/polarizing film structure was obtained. The single transmittance of the polarizing plate (essentially a polarizing film) is 46.82%, and the degree of polarization is 93.238%. In addition, the variation in the optical properties of the strip-shaped polarizing film was 0.44%, and the variation in the optical properties of the single-piece polarizing film was 0.14%.

3. Preparation of the first directionally solidified layer and the second directionally solidified layer constituting the retardation layer

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

[Chemical formula 1]

The surface of a polyethylene terephthalate (PET) film (thickness: 38 μm) was rubbed with a rubbing cloth to perform orientation treatment. When bonding to a polarizing plate, the direction of the orientation treatment is 15° with respect to the direction of the absorption axis of the polarizing film when viewed from the viewing side. The above-mentioned liquid crystal coating liquid was applied to the alignment-treated surface using a bar coater, and the liquid crystal compound was oriented by heating and drying at 90° C. for 2 minutes. The thus formed liquid crystal layer was irradiated with light of 1 mJ/cm ² using a metal halide lamp to solidify the liquid crystal layer, thereby forming the liquid crystal orientation solidified layer A on the PET film. The thickness of the liquid crystal orientation solidified layer A is 2.5 μm, and the in-plane phase difference Re (550) is 270 nm. In addition, the liquid crystal alignment solidified layer A has a refractive index distribution of nx>ny=nz.

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

4. Production of polarizing plate with phase difference layer

The liquid crystal orientation solidified layer A and the liquid crystal orientation solidified layer B obtained in the above 3. are sequentially transferred to the surface of the polarizing film of the polarizing plate obtained in the above 2.. At this time, the angle between the absorption axis of the polarizing film and the slow axis of the orientationally solidified layer A is 15°, and the angle between the absorption axis of the polarizing film and the slow axis of the orientationally solidified layer B is 15°. It is transferred (laminated) at 75°. In addition, each transfer (bonding) was performed using the ultraviolet curable adhesive (thickness: 1.0 μm) used in 2. above. In this way, a polarizing plate with a retardation layer having a structure of protective layer/adhesive layer/polarizing film/adhesive layer/retardation layer (first orientationally solidified layer/adhesion layer/second orientationally solidified layer) is obtained. The total thickness of the obtained polarizing plate with a retardation layer was 52 μm. The obtained polarizing plate with a retardation layer was used for the evaluation of the above (5) to (7). The amount of warpage is 1.8mm.

[Example 2]

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

[Example 3]

A polarizing plate with a retardation layer was produced in the same manner as in Example 1, except that a triacetylcellulose (TAC) film with a thickness of 25 μm was used as a protective layer. The total thickness of the obtained polarizing plate with a retardation layer was 37 μm. The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in Example 1. The amount of warpage is 1.3mm.

[Comparative example 1]

1. Production of polarizers

A polyvinyl alcohol-based resin film with an average polymerization degree of 2,400, a saponification degree of 99.9 mol%, and a thickness of 30 μm was prepared. While the polyvinyl alcohol film was immersed in a swelling bath (water bath) at 20°C for 30 seconds to swell, it was stretched to 2.4 times in the conveying direction between rollers with different peripheral speed ratios (swelling step), and then Next, it was immersed and dyed in a dyeing bath (an aqueous solution with an iodine concentration of 0.03% by weight and a potassium iodide concentration of 0.3% by weight) at 30°C so that the monomer transmittance after final stretching becomes the desired value, while being dyed in the original color. The polyvinyl alcohol film (polyvinyl alcohol film that is completely unstretched in the conveyance direction) is stretched to 3.7 times in the conveyance direction (dyeing step). The soaking time at this point is approximately 60 seconds. Next, the dyed polyvinyl alcohol film was immersed in a 40° C. cross-linking bath (an aqueous solution with a boric acid concentration of 3.0% by weight and a potassium iodide concentration of 3.0% by weight), while facing the original polyvinyl alcohol film as a reference. Stretch to 4.2 times in transport direction (cross-linking step). Furthermore, the obtained polyvinyl alcohol film was immersed in a 64°C stretching bath (an 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, and was transported to direction to 6.0 times (stretching step), and then immersed in a cleaning bath (aqueous solution with potassium iodide concentration of 3.0% by weight) at 20° C. for 5 seconds (cleaning step). The washed polyvinyl alcohol film was dried at 30° C. for 2 minutes to produce a polarizer (thickness: 12 μm).

2. Production of polarizing plates

As an adhesive, a polyvinyl alcohol resin containing an acetyl acetyl group was used at a weight ratio of 3:1 (average degree of polymerization: 1,200, degree of saponification: 98.5 mole%, acetyl acetylation rate: 5 mole). %) and an aqueous solution of hydroxymethylmelamine. Using this adhesive, a 25-μm-thick triacetylcellulose (TAC) film with a hard coating layer was bonded to one side of the polarizer obtained above using a roller laminating machine, and a 25-μm-thick triacetate cellulose (TAC) film was bonded to the other side of the polarizer. After the TAC film was heated and dried in an oven (temperature: 60°C, time: 5 minutes), a protective layer 1 (thickness: 25 μm)/adhesive layer/polarizer/adhesive layer/protection was produced. Polarizing plate composed of layer 2 (thickness 25 μm).

3. Production of polarizing plate with phase difference layer

On the surface of the protective layer 2 of the polarizing plate obtained in 2. above, the liquid crystal orientation solidified layer A and the liquid crystal orientation solidified layer B were sequentially transferred in the same manner as in Example 1, and a protective layer 1/adhesive layer/polarizer/ A polarizing plate with a retardation layer composed of an adhesive layer/protective layer 2/adhesive layer/retardation layer (first orientationally solidified layer/adhesion layer/second orientationally solidified layer). The total thickness of the obtained polarizing plate with a retardation layer was 68 μm. The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in Example 1. The amount of warpage is 4.2mm.

[Comparative example 2]

The same procedure as in Example 1 was performed except that potassium iodide was not added to the PVA aqueous solution (coating liquid), the stretching ratio in the air-assisted stretching process was set to 1.8 times, and a heating roller was not used in the drying shrinkage process. An attempt was made to produce a polarizing film, but the PVA-based resin layer dissolved during the dyeing process and water stretching process, making it impossible to produce a polarizing film. Therefore, it is also impossible to produce a polarizing plate with a retardation layer.

[Comparative example 3]

1. Production of polarizing plates

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

2. Preparation of retardation film constituting the retardation layer

2-1. Polymerization of polyester carbonate resin

Polymerization was performed using a batch polymerization apparatus consisting of two vertical reactors equipped with stirring blades and a reflux cooler controlled to 100°C. Add 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), and spiroglycol (SPG). 42.28 parts by mass (0.139 mol), 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. After replacing the pressure-reduced nitrogen in the reactor, the reactor was heated with a heat medium, and stirring was started when the internal temperature reached 100°C. 40 minutes after the temperature rise starts, the internal temperature reaches 220°C, and the pressure is maintained at this temperature while starting to reduce the pressure. It takes 90 minutes to reach 13.3kPa after reaching 220°C. The phenol vapor produced by the polymerization reaction is introduced into a reflux cooler at 100°C, a certain amount of monomer components contained in the phenol vapor is returned to the reactor, and the uncondensed phenol vapor is introduced to 45°C. recycled in the condenser. After introducing nitrogen gas into the first reactor and temporarily returning it to atmospheric pressure, the oligomerized reaction liquid in the first reactor is transferred to the second reactor. Next, the temperature rise and pressure reduction in the second reactor were started, and it took 50 minutes to reach the internal temperature of 240° C. and the pressure of 0.2 kPa. Then, polymerization is performed until a predetermined stirring power is achieved. When the predetermined power is reached, nitrogen gas is introduced into the reactor, the pressure is restored, the generated polyester carbonate resin is extruded into water, and the strands are cut to obtain pellets.

2-2. Production of retardation film

The obtained polyester carbonate resin (pellets) was vacuum dried at 80°C for 5 hours, and then dried using a single-screw extruder (manufactured by Toshiba Machine Co., Ltd., cylinder setting temperature: 250°C), a T-die (width 200mm, set temperature: 250℃), chilled roll (set temperature: 120~130℃) and film forming device of the coiler A long resin film with a thickness of 135 μm was produced. The obtained long resin film was stretched in the width direction at a stretching temperature of 133° C. and a stretching ratio of 2.8 times to obtain a retardation film with a thickness of 53 μm. The Re(550) of the obtained retardation film was 141 nm, Re(450)/Re(550) was 0.82, and the Nz coefficient was 1.12.

3. Production of polarizing plate with phase difference layer

The retardation film obtained in 2. above was bonded to the surface of the polarizing film of the polarizing plate obtained in 1. above using an acrylic adhesive (thickness: 5 μm). At this time, they were bonded so that the absorption axis of the polarizing film and the slow axis of the retardation film formed an angle of 45°. In this way, a polarizing plate with a retardation layer having a structure of a protective layer/adhesive layer/polarizing film/adhesive layer/retardation layer was obtained. The total thickness of the obtained polarizing plate with a retardation layer was 89 μm. The obtained polarizing plate with a retardation layer was used for the evaluation of the above (6) and (7).

Table 2 shows the structure and respective evaluation results of the polarizing plates with retardation layers obtained in Examples 1 to 3 and Comparative Examples 1 and 3.

[Table 2]

[evaluation]

From Table 2 and comparison between Example 1 and Comparative Example 2, it can be clearly understood that the polarizing plate with a retardation layer according to the embodiment of the present invention is thin, its warpage after the heating test can be suppressed, and it has excellent optical properties. . In addition, by setting the weight per unit area of the polarizing plate with a retardation layer to a predetermined value or less, the bending resistance is improved.

Industrial availability

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

10:Polarizing plate

11:Polarizing film

12: 1st protective layer

13: 2nd protective layer

20: 1st phase difference layer

100: Polarizing plate with phase difference layer

Claims (10)

A method of manufacturing a polarizing plate with a retardation layer. The polarizing plate with a retardation layer has a polarizing plate and a retardation layer. The polarizing plate includes a polarizing film and a protective layer provided on at least one side of the polarizing film. The polarizing film It is composed of a polyvinyl alcohol-based resin film containing a dichroic substance. Its thickness is 8 μm or less, its monomer transmittance is more than 46%, and its polarization degree is more than 92%. The retardation layer is a liquid crystal compound orientationally solidified layer. The manufacturing The method includes: producing the polarizing film by the following production method, which includes: forming a polyvinyl alcohol-based resin layer on one side of a long thermoplastic resin base material to form a laminate, the polyvinyl alcohol-based resin The layer contains iodide or sodium chloride, and a polyvinyl alcohol-based resin; and the laminated body is sequentially subjected to an air-assisted stretching process, a dyeing process, an underwater stretching process, and a drying shrinkage process, and the drying shrinkage process is directed toward the length of one side. The laminate is heated while being transported in the direction to shrink the laminate by 2% to 10% in the width direction. The heating system uses a heating roller in a heating furnace and the total contact time between the laminate and the heating roller is 1 to 20 seconds. . The method for manufacturing a polarizing plate with a retardation layer according to claim 1, wherein the unit weight of the polarizing plate with a retardation layer is 6.5 mg/cm ² or less. The method for manufacturing a polarizing plate with a retardation layer as claimed in claim 1, wherein the total thickness of the polarizing plate with a retardation layer is less than 60 μm. Down. The manufacturing method of a polarizing plate with a retardation layer as claimed in claim 1, wherein the retardation layer is a single layer of a liquid crystal compound orientationally solidified layer, Re(550) of the retardation layer is 100nm~190nm, and the retardation layer The angle between the slow axis of the polarizing film and the absorption axis of the polarizing film is 40°~50°. The method for manufacturing a polarizing plate with a retardation layer according to claim 1, wherein the retardation layer has a laminated structure of a first orientationally solidified liquid crystal compound layer and a second orientationally solidified liquid crystal compound layer, and the first orientationally solidified liquid crystal compound layer The Re(550) of the second liquid crystal compound orientationally solidified layer is 200nm~300nm, and the angle between the slow axis and the absorption axis of the polarizing film is 10°~20°. The Re(550) of the second liquid crystal compound orientationally solidified layer is 100nm~190nm. The angle between the slow axis and the absorption axis of the polarizing film is 70°~80°. The method for manufacturing a polarizing plate with a retardation layer as claimed in claim 1, wherein the difference between the maximum value and the minimum value of the single transmittance of the polarizing film in a 50 cm ² area is less than 0.3%. The manufacturing method of a polarizing plate with a phase difference layer as claimed in claim 1, wherein the width of the polarizing film is 1000 mm or more, and the difference between the maximum value and the minimum value of the single transmittance at a position along the width direction is 0.7%. the following. The method for manufacturing a polarizing plate with a retardation layer according to claim 1, wherein the single transmittance of the polarizing film is 48% or less, and the polarization degree is 97% or less. The manufacturing method of a polarizing plate with a retardation layer as claimed in claim 1, wherein the polarizing plate with a retardation layer further has other retardation layers outside the retardation layer; the manufacturing method includes: The other phase difference layer is provided on the outside; the refractive index characteristics of the other phase difference layer show the relationship nz>nx=ny. The manufacturing method of a polarizing plate with a retardation layer as claimed in claim 1, wherein the polarizing plate with a retardation layer further has a conductive layer or an isotropic substrate with a conductive layer outside the retardation layer; the manufacturing method It includes: arranging the conductive layer or the isotropic base material with the conductive layer outside the aforementioned phase difference layer.

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