KR20230038718A - A polarizing plate and an image display device including the polarizing plate - Google Patents

Abstract

The present invention provides a polarizing plate that is extremely thin and suppresses cracking in a release processing part. The polarizing plate of the present invention includes a polarizer and a protective layer disposed on at least one side of the polarizer, and has a shape other than rectangular. The protective layer is composed of a resin film. The polarizer is composed of a PVA-based resin film containing a dichroic substance. In one embodiment, the polarizer satisfies the following formula (1) when the single transmittance is x% and the birefringence of the PVA-based resin is y. In another embodiment, the polarizer satisfies the following formula (2) when the single transmittance is x% and the in-plane retardation of the PVA-based resin film is znm. In another embodiment, the polarizer satisfies the following formula (3) when the single transmittance is x% and the orientation function of the PVA-based resin is f. In another embodiment, the polarizer has a puncture strength of 30 gf/μm or more.
y<-0.011x+0.525 (1)
z<-60x+2875 (2)
f<-0.018x+1.11 (3)

Description

A polarizing plate and an image display device including the polarizing plate

The present invention relates to a polarizing plate and an image display device including the polarizing plate.

In recent years, image display devices typified by liquid crystal display devices and electroluminescence (EL) display devices (eg, organic EL display devices and inorganic EL display devices) are rapidly spreading. Due to the image forming method of the image display device, a polarizing plate is disposed on at least one side of the image display device. In recent years, as the demand for thinning of image display devices has increased, the demand for thinning has also increased for polarizing plates. By the way, in recent years, processing of a polarizing plate into a shape other than a rectangular shape (special shape processing: formation of notches and/or through holes, for example) is sometimes required. However, there is a problem that cracks tend to occur in the release processing part of the thin polarizing plate.

Japanese Unexamined Patent Publication No. 2001-343521

The present invention has been made in order to solve the above conventional problems, and its main object is to provide a polarizing plate that is extremely thin and suppresses cracking in a release processing part.

A polarizing plate according to one embodiment of the present invention includes a polarizer and a protective layer disposed on at least one side of the polarizer, and has a shape other than rectangular. The protective layer is composed of a resin film. The polarizer is composed of a polyvinyl alcohol-based resin film containing a dichroic substance, and when the single transmittance is x% and the birefringence of the polyvinyl alcohol-based resin is y, the following formula (1) is satisfied:

y<-0.011x+0.525 (1).

A polarizing plate according to another embodiment of the present invention includes a polarizer and a protective layer disposed on at least one side of the polarizer, and has a shape other than rectangular. The protective layer is composed of a resin film. The polarizer is composed of a polyvinyl alcohol-based resin film containing a dichroic substance, and when the single transmittance is x% and the in-plane retardation of the polyvinyl alcohol-based resin film is znm, the following formula (2) satisfies:

z<-60x+2875 (2).

A polarizing plate according to another embodiment of the present invention includes a polarizer and a protective layer disposed on at least one side of the polarizer, and has a shape other than rectangular. The protective layer is composed of a resin film. When the polarizer is composed of a polyvinyl alcohol-based resin film containing a dichroic substance, the single transmittance is x%, and the orientation function of the polyvinyl alcohol-based resin is f, the following formula (3) is Satisfies:

f<-0.018x+1.11 (3).

A polarizing plate according to another embodiment of the present invention includes a polarizer and a protective layer disposed on at least one side of the polarizer, and has a shape other than rectangular. The protective layer is composed of a resin film. The polarizer is composed of a polyvinyl alcohol-based resin film containing a dichroic substance, and has a puncture strength of 30 gf/μm or more.

In one embodiment, the thickness of the polarizer is 10 μm or less.

In one embodiment, the polarizer has a single transmittance of 40.0% or more, and a polarization degree of 99.0% or more.

In one embodiment, the irregular shape is a through hole, a V-shaped notch, a U-shaped notch, a concave portion having a shape approximate to a ship shape when viewed in plan view, a rectangular concave portion when viewed in plan view, and a concave portion having a shape approximated to a ship shape when viewed in plan view. It is selected from the group consisting of an R-shaped concave portion approximate to a bathtub shape, and a combination thereof.

In one embodiment, the radius of curvature of the U-shaped notch is 5 mm or less.

In one embodiment, the polarizing plate further includes a reflective polarizer on a side opposite to the polarizer of the protective layer.

According to another aspect of the present invention, an image display device is provided. The said image display device contains said polarizing plate.

According to an embodiment of the present invention, in a polarizing plate having a mold release (release processing part), by controlling the alignment state of the polyvinyl alcohol (PVA)-based resin of the polarizer, while being extremely thin, cracking in the release processing part is suppressed A polarizing plate can be realized. Further, such a polarizer (as a result, a polarizing plate) can exhibit practically acceptable optical properties.

1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention.
2 is a schematic plan view illustrating an example of a release or release processing part in a polarizing plate according to an embodiment of the present invention.
3 is a schematic plan view illustrating a modified example of a release or release processing unit in a polarizing plate according to an embodiment of the present invention.
4 is a schematic plan view illustrating another modified example of a release or release processing unit in a polarizing plate according to an embodiment of the present invention.
5 is a schematic plan view illustrating an example of further modification of a mold release or mold release processing part in a polarizing plate according to an embodiment of the present invention.
6 is a schematic view showing an example of drying shrinkage treatment using a heating roll in the manufacturing method of a polarizer that can be used for a polarizing plate according to an embodiment of the present invention.
7 is a schematic perspective view of an example of a reflective polarizer that can be used in a polarizing plate according to an embodiment of the present invention.
8 is a graph showing the relationship between the single transmittance of polarizers produced in Examples and Comparative Examples and the birefringence of PVA-based resin.
9 is a graph showing the relationship between the single transmittance of light polarizers produced in Examples and Comparative Examples and the in-plane retardation of the PVA-based resin film.
10 is a graph showing the relationship between the single transmittance of light polarizers produced in Examples and Comparative Examples and the orientation function of PVA-based resin.

EMBODIMENT OF THE INVENTION Hereinafter, although embodiment of this invention is described, this invention is not limited to these embodiment.

A. Overall composition of the polarizer

1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. The polarizing plate 100 of the illustrated example includes a polarizer 10 and a protective layer 20 disposed on one side of the polarizer 10 . Depending on the purpose, a separate protective layer (not shown) may be provided on the side opposite to the protective layer 20 of the polarizer 10 . The protective layer 20 is composed of a resin film, and is typically bonded to a polarizer via an adhesive layer (not shown). In one embodiment, the polarizing plate 100 may further include a reflection type polarizer (not shown) on the side opposite to the polarizer 10 of the protective layer 20 . The polarizing plate may be used as a viewing-side polarizing plate of an image display device or as a rear-side polarizing plate. When the polarizing plate contains a reflective polarizer, the polarizing plate is typically used as a back-side polarizing plate. In this case, the reflective polarizer may be disposed on the outer side (on the side opposite to the image display cell).

A polarizing plate according to an embodiment of the present invention has a shape other than rectangular. In this specification, 'having a non-rectangular shape' means that the planar view shape of the polarizing plate has a shape other than rectangular. The mold release is typically a mold release processed part. Therefore, 'a polarizing plate having a non-rectangular shape' (hereinafter sometimes referred to as 'a different type polarizing plate') is not only a case where the entire hetero-shaped polarizing plate (ie, the outer edge defining the planar view shape of the polarizing plate) is other than a rectangular shape, The case where a mold release process part is formed in the part separated inward from the outer edge of a rectangular polarizing plate is also included. In a polarizing plate, cracks tend to occur in such a mold release part, but according to the embodiment of the present invention, such cracks can be remarkably suppressed. More specifically, it is as follows. In a normal (ie, non-release) polarizer (substantially a polarizer), cracks occur along the absorption axis (stretching direction) of the polarizer in many cases. On the other hand, L-shaped cracks (cracks in an oblique direction with respect to the absorption axis) may occur in the molded part. According to the embodiment of the present invention, as will be described later, by making the orientation in the direction of the absorption axis of the molecular chain of the PVA-based resin of the polarizer gentler than that of the conventional polarizer, not only ordinary cracks but also such L-shaped cracks are remarkable. can be suppressed.

As the release (release processing part), for example, as shown in Figs. 2 and 3, those obtained by chamfering corners into R shapes, through holes, and cutting parts that become concave parts in the case of planar view are exemplified. Representative examples of the concave portion include a shape approximating a linear shape, a rectangle, an R shape approximating a bathtub shape, a V-shaped notch, and a U-shaped notch. As another example of the release (release processing part), as shown in Figs. 4 and 5, a shape corresponding to the meter panel of an automobile can be given. The shape includes a portion where the outer edge is formed in an arc shape along the rotational direction of the meter needle and the outer edge forms a V-shape (including an R shape) convex inward in the plane direction. Needless to say, the shape of the release (release processing part) is not limited to the illustrated example. For example, the shape of the through hole may be any suitable shape (eg, elliptical, triangular, quadrangular, pentagonal, hexagonal, octagonal) depending on the purpose other than the approximate circular shape shown in the illustrated example. Further, the through hole is provided at any suitable position depending on the purpose. As shown in Fig. 3, the through hole may be provided at a substantially central portion of the longitudinal end of the rectangular polarizing plate, may be provided at a predetermined position at the longitudinal end, or may be provided at a corner portion of the polarizing plate; Although not shown, it may be provided at the short end of the rectangular polarizing plate; As shown in Fig. 4 or Fig. 5, it may be provided in the central portion of the release polarizing plate. As shown in Fig. 3, a plurality of through holes may be provided. Moreover, you may combine the shapes of an illustration suitably according to a purpose. For example, a through hole may be formed at an arbitrary position of the heterogeneous polarizing plate of FIG. 2, or a V-shaped notch and/or a U-shaped notch may be formed at an arbitrary appropriate position on the outer edge of the heteromorphic polarizing plate of FIG. 4 or 5. . Such a release polarizer can be suitably used for image display devices such as meter panels of automobiles, smart phones, tablet PCs, or smart watches. Further, for example, when the irregular shape includes an R shape, the radius of curvature thereof is, for example, 0.2 mm or more, and is, for example, 1 mm or more, and is, for example, 2 mm or more. On the other hand, the radius of curvature is, for example, 10 mm or less, and for example, 5 mm or less. Further, for example, when the irregular shape is a U-shaped notch, its radius of curvature (the radius of curvature of the U-shaped portion) is, for example, 5 mm or less, and is, for example, 1 mm to 4 mm, and, for example, 2 mm to 3 mm.

The mold release (release processing part) can be formed by any suitable method. Specific examples of the forming method include cutting with an end mill, punching with a punching blade such as a Thomson blade, and cutting with laser light irradiation. These methods may be combined.

Hereinafter, a polarizer, a protective layer, and a reflective polarizer, which are components of the polarizing plate, will be described.

B. Polarizer

The polarizer is composed of a PVA-based resin film containing a dichroic material. In one embodiment, the polarizer satisfies the following formula (1) when x% is the single transmittance and birefringence of the polyvinyl alcohol-based resin constituting the polarizer is y. In one embodiment, the polarizer satisfies the following formula (2), when the single transmittance is x% and the in-plane retardation of the polyvinyl alcohol-based resin film constituting the polarizer is znm. In one embodiment, a polarizer satisfies the following formula (3), when x% is the single transmittance and the orientation function of the polyvinyl alcohol-based resin constituting the polarizer is f. In one embodiment, the polarizer has a puncture strength of 30 gf/μm or more.

y<-0.011x+0.525 　(1)

z<-60x+2875 (2)

f<-0.018x+1.11 (3)

Birefringence of the PVA-based resin in the polarizer (hereinafter referred to as birefringence of PVA or Δn of PVA), in-plane retardation of the PVA-based resin film (hereinafter referred to as 'in-plane retardation of PVA'), orientation of the PVA-based resin Both the function (hereinafter referred to as 'PVA orientation function') and the piercing strength of the polarizer are values related to the degree of orientation of the molecular chains of the PVA-based resin constituting the polarizer. Specifically, the birefringence, in-plane retardation, and orientation function of PVA may become large values as the degree of orientation increases, and the puncture strength may decrease as the degree of orientation increases. A polarizer according to an embodiment of the present invention (that is, a polarizer satisfying the above equations (1) to (3) or the stabbing strength) has a more gentle orientation of the molecular chain of the PVA-based resin in the direction of the absorption axis than a conventional polarizer. Due to this, heating shrinkage in the direction of the absorption axis is suppressed. As a result, such a polarizer (as a result, a polarizing plate) can suppress crack generation in a mold release processing part while being extremely thin. In addition, such a polarizer (as a result, a polarizing plate) is also excellent in flexibility and bending durability, so it is preferably a curved image display device, more preferably a bendable image display device, and still more preferably a foldable image display device. can be applied Conventionally, it has been difficult to obtain acceptable optical characteristics (typically single transmittance and polarization degree) with a polarizer having a low degree of orientation. Optical properties are compatible.

The polarizer preferably satisfies the following formula (1a) and/or formula (2a), and more preferably satisfies the following formula (1b) and/or formula (2b).

-0.004x+0.18<y<-0.011x+0.525 (1a)

-0.003x+0.145<y<-0.011x+0.520 (1b)

-40x+1800<z<-60x+2875 (2a)

-30x+1450<z<-60x+2850 (2b)

In the present specification, the in-plane retardation of the PVA is the in-plane retardation value of the PVA-based resin film at 23° C. and a wavelength of 1000 nm. By setting the near-infrared region as the measurement wavelength, the influence of iodine absorption in the polarizer can be eliminated, and it becomes possible to measure the phase difference. In addition, the birefringence (in-plane birefringence) of the PVA is a value obtained by dividing the in-plane retardation of the PVA by the thickness of the polarizer.

The in-plane retardation of PVA was evaluated as follows. First, phase difference values are measured at a plurality of wavelengths with a wavelength of 850 nm or more, and a plot of the measured phase difference values: R(λ) and wavelength: λ is performed, and these are fit to the following Selmeier equation by the least square method. Here, A and B are fitting parameters and are coefficients determined by the least squares method.

R(λ)=A+B/(λ ^2- 600 ² )

At this time, this retardation value R(λ) can be separated into an in-plane retardation value (Rpva) of PVA having no wavelength dependence and an in-plane retardation value (Ri) of iodine having a strong wavelength dependence as follows.

Rpva=A

Ri=B/(λ ² -600 ² )

Based on this separation equation, the in-plane retardation of PVA at a wavelength of λ = 1000 nm (ie, Rpva) can be calculated. In addition, the evaluation method of the in-plane retardation of the said PVA is also described in Japanese Patent Publication No. 5932760, and can be referred as needed.

In addition, birefringence (Δn) of PVA can be calculated by dividing this retardation by the thickness.

Examples of commercially available devices for measuring the in-plane retardation of PVA at the wavelength of 1000 nm include the KOBRA-WR/IR series and KOBRA-31X/IR series manufactured by Oji Instruments Co., Ltd.

The orientation function (f) of the polarizer preferably satisfies the following formula (3a), and more preferably satisfies the following formula (3b). When the orientation function is too small, acceptable single transmittance and/or polarization degree may not be obtained.

-0.01x+0.50<f<-0.018x+1.11 (3a)

-0.01x+0.57<f<-0.018x+1.1 (3b)

The orientation function f can be obtained by attenuated total reflection (ATR) measurement using, for example, a Fourier transform infrared spectrophotometer (FT-IR) and using polarized light as measurement light. Specifically, germanium is used as the crystallizer for adhering the polarizer, the incident angle of the measurement light is 45° incident, and the incident polarized infrared light (measurement light) is polarized light that oscillates parallel to the surface of the germanium crystal that adheres the sample. (s-polarized light), and the measurement was performed in a state in which the stretching direction of the polarizer was arranged parallel and perpendicular to the polarization direction of the measurement light, and the absorbance spectrum obtained at 2941 cm ^-1 was calculated according to the following formula using the intensity do. Here, intensity I is a value of 2941 cm ^{-1 /} 3330 cm ^{-1 with 3330 cm -1} as a reference peak. Also, when f = 1, the orientation is perfect, and when f = 0, it becomes random. In addition, it is considered that the peak at 2941 cm ^-1 is absorption due to vibration of the main chain (-CH ₂ -) of PVA in the polarizer.

f=(3<cos ² θ>-1)/2

=(1-D)/[c(2D+1)]

=-2×(1-D)/(2D+1)

step,

c=(3cos ² β-1)/2, and in case of vibration of 2941cm ^-1, β=90°.

θ: angle of the molecular chain with respect to the stretching direction

β: angle of the transition dipole moment with respect to the molecular chain axis

D=(I _⊥ )/(I _// ) (in this case, D increases as the PVA molecules are oriented)

I _⊥ : Absorption intensity when the polarization direction of the measurement light and the stretching direction of the polarizer are perpendicular to each other

I _// : Absorption intensity when the polarization direction of the measurement light and the stretching direction of the polarizer are parallel

The thickness of the polarizer is preferably 10 μm or less, more preferably 8 μm or less. The lower limit of the thickness of the polarizer may be, for example, 1 μm. The thickness of the polarizer may be 2 μm to 10 μm in one embodiment, and 2 μm to 8 μm in another embodiment. By making the thickness of the polarizer very thin in this way, heat shrinkage can be made very small. It is inferred that such a configuration can also contribute to suppression of crack generation in the release processing part of the polarizing plate.

The polarizer preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm. The single transmittance of the polarizer is preferably 40.0% or more, more preferably 41.0% or more. The upper limit of single transmittance may be, for example, 49.0%. The single transmittance of the polarizer is 40.0% to 45.0% in one embodiment. The degree of polarization of the polarizer is preferably 99.0% or more, more preferably 99.4% or more. The upper limit of the degree of polarization may be, for example, 99.999%. The degree of polarization of the polarizer is 99.0% to 99.9% in one embodiment. Although the polarizer according to the embodiment of the present invention has a lower degree of orientation of the PVA-based resin constituting the polarizer than before, and has the above in-plane retardation, birefringence and / or orientation function, such a practically acceptable single transmittance and a degree of polarization can be realized. It is guessed that this originates in the manufacturing method mentioned later. Incidentally, the single transmittance is typically a Y value measured using an ultraviolet/visible ray spectrophotometer and corrected for visibility. The degree of polarization can be obtained by the following formula, typically based on the parallel transmittance Tp and the orthogonal transmittance Tc measured using an ultraviolet/visible spectrophotometer and corrected for visibility.

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

The puncture strength of the polarizer is, for example, 30 gf/μm or more, preferably 35 gf/μm or more, more preferably 40 gf/μm or more, still more preferably 45 gf/μm or more, and particularly preferably 50 gf/μm or more. am. The upper limit of the piercing strength may be, for example, 80 gf/μm. By making the puncture strength of a polarizer into such a range, it can suppress remarkably that a crack arises in a mold release process part, and that a polarizer is torn along an absorption axis direction. As a result, a polarizer (as a result, a polarizing plate) having very excellent flexibility can be obtained. The puncture strength represents the crack resistance of the polarizer when the polarizer is pierced with a predetermined strength. The puncture strength can be expressed as, for example, the strength at which the polarizer cracks (breaking strength) when a predetermined needle is attached to a compression tester and the needle is pierced into the polarizer at a predetermined speed. In addition, as is clear from the unit, the piercing strength means the piercing strength per unit thickness (1 μm) of the polarizer.

As described above, the polarizer is composed of a PVA-based resin film containing a dichroic substance. Preferably, the PVA-based resin constituting the PVA-based resin film (substantially the polarizer) contains an acetoacetyl-modified PVA-based resin. With such a structure, a polarizer having a desired piercing strength can be obtained. The blending amount of the acetoacetyl-modified PVA-based resin is preferably from 5% by weight to 20% by weight, more preferably from 8% by weight to 12% by weight, based on 100% by weight of the entire PVA-based resin. If the blending amount is in such a range, the piercing strength can be made into a more suitable range.

A polarizer can be typically manufactured using a laminate of two or more layers. As a specific example of the light polarizer obtained using a laminated body, the polarizer obtained using the laminated body of the resin base material and the PVA system resin layer applied and formed on the said resin base material is mentioned. A polarizer obtained by using a laminate of a resin substrate and a PVA-based resin layer coated and formed on the resin substrate, for example, by applying a PVA-based resin solution to the resin substrate, drying it, forming a PVA-based resin layer on the resin substrate, Obtaining a laminated body of a resin substrate and a PVA-based resin layer; It can be produced by: stretching and dyeing the layered product to make the PVA-based resin layer a polarizer. In this embodiment, preferably, a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin is formed on one side of the resin substrate. Stretching typically involves immersing the layered product in an aqueous solution of boric acid and extending the laminate. Further, the stretching preferably further includes air stretching the laminate at a high temperature (eg, 95° C. or higher) prior to stretching in an aqueous solution of boric acid. In the embodiment of the present invention, the total magnification of stretching is preferably 3.0 to 4.5 times, which is significantly smaller than usual. Even at such a total magnification of stretching, a polarizer having acceptable optical characteristics can be obtained by a combination of halide addition and drying shrinkage treatment. Further, in the embodiment of the present invention, the draw ratio of air assisted stretching is preferably greater than the draw ratio of stretching in boric acid water. By setting it as such a structure, even if the total magnification of extending|stretching is small, the polarizer which has acceptable optical characteristics can be obtained. Further, the laminate is preferably subjected to a drying shrinkage treatment in which it shrinks by 2% or more in the width direction by heating while conveying in the longitudinal direction. In one embodiment, the manufacturing method of a light polarizer includes giving a laminated body an air assisted stretching process, a dyeing process, an underwater stretching process, and a drying shrinkage process in this order. By introducing auxiliary stretching, even when the PVA-based resin is applied on a thermoplastic resin, it becomes possible to increase the crystallinity of the PVA-based resin and achieve high optical properties. In addition, by simultaneously increasing the orientation of the PVA-based resin in advance, problems such as deterioration in orientation and dissolution of the PVA-based resin when immersed in water in a subsequent dyeing step or stretching step can be prevented, and high optical properties can be obtained. it becomes possible to achieve Further, in the case where the PVA-based resin layer is immersed in a liquid, the disorder of the orientation of the polyvinyl alcohol molecules and the decrease in orientation can be suppressed compared to the case where the PVA-based resin layer does not contain a halide. Thereby, the optical characteristics of the polarizer obtained through the processing process performed by immersing a layered product in liquid, such as a dyeing process and an underwater extension process, can be improved. In addition, optical properties can be improved by shrinking the laminate in the width direction by drying shrinkage treatment. The obtained laminate of the resin substrate/polarizer may be used as it is (that is, the resin substrate may be used as a protective layer for the polarizer), and the resin substrate is peeled from the laminate of the resin substrate/polarizer, and the peel surface is used for the purpose. Any suitable protective layer according to the above may be laminated and used. The detail of the manufacturing method of a polarizer is demonstrated in section C.

C. Manufacturing method of polarizer

The method for producing the polarizer is preferably to form a polyvinyl alcohol-based resin layer (PVA-based resin layer) containing a halide and a polyvinyl alcohol-based resin (PVA-based resin) on one side of a long thermoplastic resin substrate, Forming a laminate, and subjecting the laminate to an air-assisted stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment for shrinking by 2% or more in the width direction by heating while conveying in the longitudinal direction in this order. include The content of the halide in the PVA-based resin layer is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin. The drying shrinkage treatment is preferably performed using a heating roll, and the temperature of the heating roll is preferably 60°C to 120°C. The shrinkage rate in the width direction of the layered product by the drying shrinkage treatment is preferably 2% or more. In addition, the draw ratio of air assisted stretching is preferably larger than that of underwater stretching. According to such a manufacturing method, the light polarizer demonstrated in the said item B can be obtained. In particular, a laminate comprising a PVA-based resin layer containing a halide is produced, and stretching of the laminate is multi-step stretching including air-assisted stretching and underwater stretching, and the laminate after stretching is heated with a heating roll to obtain a width By shrinking by 2% or more in the direction, a polarizer having excellent optical properties (typically single transmittance and polarization degree) can be obtained.

C-1. Fabrication of the laminate

Arbitrary suitable methods can be adopted as a method of producing the laminated body of a thermoplastic resin base material and a PVA system resin layer. Preferably, a PVA-based resin layer is formed on the thermoplastic resin substrate by applying a coating liquid containing a halide and a PVA-based resin to the surface of the thermoplastic resin substrate and drying it. As described above, the content of the halide in the PVA-based resin layer is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.

As a method of applying the coating liquid, any suitable method can be employed. For example, roll coating method, spin coating method, wire bar coating method, dip coating method, die coating method, curtain coating method, spray coating method, knife coating method (comma coating method etc.), etc. are mentioned. The coating/drying temperature of the coating liquid is preferably 50°C or higher.

The thickness of the PVA-based resin layer is preferably 2 μm to 30 μm, more preferably 2 μm to 20 μm. A polarizer having allowable single transmittance and polarization degree despite a lower degree of orientation of the PVA-based resin than before by making the thickness of the PVA-based resin layer before stretching extremely thin in this way and reducing the total magnification of the stretching as described below. can be obtained.

Before forming the PVA-based resin layer, surface treatment (for example, corona treatment, etc.) may be performed on the thermoplastic resin substrate, or an easily bonding layer may be formed on the thermoplastic resin substrate. By performing such a process, the adhesiveness of a thermoplastic resin base material and a PVA system resin layer can be improved.

C-1-1. Thermoplastic resin substrate

As the thermoplastic resin substrate, any suitable thermoplastic resin film can be employed. About the detail of a thermoplastic resin base material, it describes, for example in Unexamined-Japanese-Patent No. 2012-73580. The entire description of the publication is incorporated herein by reference.

C-1-2. coating liquid

As described above, the coating liquid contains a halide and a PVA-based resin. The coating liquid is typically a solution obtained by dissolving the halide and the PVA-based resin in a solvent. Examples of the solvent include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. can These can be used individually or in combination of 2 or more types. Among these, water is preferable. The concentration of the PVA-based resin in the solution is preferably 3 to 20 parts by weight based on 100 parts by weight of the solvent. With such a resin concentration, a uniform coating film adhering to the thermoplastic resin substrate can be formed. The content of the halide in the coating liquid is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.

You may mix|blend additives with a coating liquid. Examples of additives include plasticizers and surfactants. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol and glycerin. As surfactant, a nonionic surfactant is mentioned, for example. These can be 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 suitable resin can be employed. Examples include polyvinyl alcohol and ethylene-vinyl alcohol copolymers. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. An ethylene-vinyl alcohol copolymer can be obtained by saponifying an ethylene-vinyl acetate copolymer. The degree of saponification 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 according to JIS K 6726-1994. A light polarizer excellent in durability can be obtained by using PVA-type resin of such a degree of saponification. When the saponification degree is too high, there exists a possibility of saponification. As described above, the PVA-based resin preferably includes an acetoacetyl-modified PVA-based resin.

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 to 10000, preferably 1200 to 4500, more preferably 1500 to 4300. In addition, the average degree of polymerization can be obtained according to JIS K 6726-1994.

As the halide, any suitable halide can be employed. Examples include iodide and sodium chloride. As iodide, potassium iodide, sodium iodide, and lithium iodide are mentioned, for example. Among these, potassium iodide is preferable.

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

In general, when the PVA-based resin layer is stretched, the orientation of the polyvinyl alcohol molecules in the PVA-based resin layer increases, but when the stretched PVA-based resin layer is immersed in a liquid containing water, the orientation of the polyvinyl alcohol molecules is disturbed. , the orientation may decrease. In particular, in the case of stretching the laminate of the thermoplastic resin substrate and the PVA-based resin layer in boric acid water, in the case of stretching the laminate in boric acid water at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin substrate, the lowering of the orientation The trend is remarkable. For example, while it is common for stretching of a PVA film alone in boric acid to be carried out at 60°C, the stretching of a laminate of A-PET (thermoplastic resin substrate) and a PVA-based resin layer is performed at a high temperature of around 70°C. In this case, the orientation of PVA in the initial stage of stretching may be lowered in the stage before rising by underwater stretching. In contrast, by preparing a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin substrate, and stretching the laminate in air at high temperature (auxiliary stretching) before stretching the laminate in boric acid, the PVA of the laminate after auxiliary stretching Crystallization of the PVA-based resin in the resin-based layer can be promoted. As a result, in the case where the PVA-based resin layer is immersed in the liquid, the disorder of the orientation of the polyvinyl alcohol molecules and the decrease in the orientation can be suppressed compared to the case where the PVA-based resin layer does not contain a halide. Thereby, the optical characteristics of the polarizer obtained through the processing process performed by immersing a layered product in liquid, such as a dyeing process and an underwater extension process, can be improved.

C-2. Air Assisted Stretching Treatment

In particular, in order to obtain high optical properties, a method of two-step stretching is selected in which dry stretching (auxiliary stretching) and stretching in boric acid are combined. Like the two-stage stretching, by introducing auxiliary stretching, the thermoplastic resin substrate can be stretched while suppressing crystallization. Furthermore, in the case of applying the PVA-based resin on a thermoplastic resin substrate, in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate, it is necessary to lower the application temperature compared to the case of applying the PVA-based resin on a normal metal drum. As a result, the crystallization of the PVA-based resin is relatively low, resulting in a problem that sufficient optical properties cannot be obtained. In contrast, by introducing auxiliary stretching, the crystallinity of the PVA-based resin can be increased even when the PVA-based resin is applied on the thermoplastic resin, and high optical properties can be achieved. In addition, by simultaneously increasing the orientation of the PVA-based resin in advance, it is possible to prevent problems such as deterioration in the orientation of the PVA-based resin and dissolution when immersed in water in a subsequent dyeing step or drawing step, thereby achieving high optical properties. it becomes possible to do

The stretching method of air assisted stretching may be fixed end stretching (eg, stretching using a tenter stretching machine) or free end stretching (eg, uniaxial stretching by passing a laminate between rolls having different circumferential speeds). However, in order to obtain high optical properties, free end stretching may be actively employed. In one embodiment, the air stretching treatment includes a heating roll stretching step of stretching the laminate by a circumferential speed difference between heating rolls while conveying the laminate in its longitudinal direction. The aerial stretching treatment typically includes a zone stretching process and a heated roll stretching process. In addition, the order of the zone stretching process and the hot roll stretching process is not limited, and the zone stretching process may be performed first, or the hot roll stretching process may be performed first. The zone stretching step may be omitted. In one embodiment, the zone stretching process and the hot roll stretching process are performed in this order. Further, in another embodiment, the film is stretched by gripping an end portion of the film in a tenter stretching machine and extending the distance between tenters in the flow direction (expansion of the distance between tenters becomes a stretching ratio). At this time, the distance of the tenter in the width direction (direction perpendicular to the flow direction) is set to be arbitrarily close. Preferably, with respect to the stretching ratio in the flow direction, it can be set to be approached by free end stretching. In the case of free end drawing, the shrinkage rate in the width direction = (1/stretching ratio) is calculated as ^1/2 .

Air assisted stretching may be performed in one step or may be performed in multiple steps. When performing in multiple steps, the draw ratio is the product of the draw ratios of each step. The stretching direction in air assisted stretching is preferably approximately the same as that in underwater stretching.

The draw ratio in air assisted stretching is preferably 1.0 to 4.0 times, more preferably 1.5 to 3.5 times, still more preferably 2.0 to 3.0 times. If the draw ratio of air-assisted stretching is within this range, when combined with underwater stretching, the total stretching magnification can be set within a desired range, and desired birefringence, in-plane retardation, and/or orientation function can be realized. As a result, it is possible to obtain a polarizer (as a result, a polarizing plate) in which the generation of cracks in the release processing part is suppressed. Moreover, as mentioned above, it is preferable that the draw ratio of air assisted stretching is larger than the draw ratio of stretching in boric acid water. By setting it as such a structure, even if the total magnification of extending|stretching is small, the polarizer which has acceptable optical characteristics can be obtained. More specifically, the ratio of the draw ratio in air-assisted stretching to the draw ratio in underwater stretching (underwater stretching/air-assisted stretching) is preferably 0.4 to 0.9, more preferably 0.5 to 0.8.

The stretching temperature of the air-assisted stretching can be set to any suitable value depending on the forming material of the thermoplastic resin substrate, the stretching method, and the like. The stretching temperature is preferably equal to or higher than the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably equal to or higher than the glass transition temperature (Tg) of the thermoplastic resin substrate (Tg) + 10°C, particularly preferably equal to or higher 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 orientation of the PVA-based resin layer by stretching) can be suppressed.

C-3. Insolubilization treatment, dyeing treatment and cross-linking treatment

If necessary, insolubilization treatment is performed after the air-assisted stretching treatment and before the underwater stretching treatment or the dyeing treatment. The insolubilization treatment is typically performed by immersing the PVA-based resin layer in an aqueous solution of boric acid. The dyeing treatment is typically performed by dyeing the PVA-based resin layer with a dichroic substance (typically iodine). If necessary, a crosslinking treatment is performed after the dyeing treatment and before the underwater stretching treatment. The crosslinking treatment is typically performed by immersing the PVA-based resin layer in an aqueous solution of boric acid. Details of the insolubilization treatment, dyeing treatment, and crosslinking treatment are described, for example, in Japanese Unexamined Patent Publication No. 2012-73580.

C-4. Underwater stretching treatment

The underwater stretching treatment is performed by immersing the laminate in a stretching bath. According to the underwater stretching treatment, stretching can be performed at a temperature lower than the glass transition temperature (typically about 80° C.) of the thermoplastic resin substrate or the PVA-based resin layer, and the PVA-based resin layer can be stretched while suppressing its crystallization. . As a result, a polarizer having excellent optical properties can be manufactured.

Arbitrary suitable methods can be employed for the stretching method of the laminate. Specifically, fixed-end stretching or free-end stretching (for example, a method of uniaxially stretching a laminate by passing it between rolls having different circumferential speeds) may be used. Preferably, free end stretching is selected. Stretching of the laminate may be performed in one step or in multiple steps. When carried out in multiple stages, the total stretching ratio is the product of the stretching ratios of each stage.

Stretching in water is preferably performed by immersing the layered product in an aqueous boric acid solution (stretching in boric acid water). By using a boric acid aqueous solution as a stretching bath, rigidity that can withstand the tension applied during stretching and water resistance that does not dissolve in water can be imparted to the PVA-based resin layer. Specifically, boric acid generates tetrahydroxyboric acid anions in an aqueous solution and can be crosslinked with PVA-based resins by hydrogen bonding. As a result, rigidity and water resistance can be imparted to the PVA-based resin layer so that it can be stretched satisfactorily, and a polarizer having excellent optical properties can be manufactured.

The aqueous solution of boric acid is preferably obtained by dissolving boric acid and/or a borate salt in water as a solvent. The boric acid concentration is preferably 1 part by weight to 10 parts by weight, more preferably 2.5 parts by weight to 6 parts by weight, and particularly preferably 3 parts by weight to 5 parts by weight, based on 100 parts by weight of water. By setting the boric acid concentration to 1 part by weight or more, dissolution of the PVA-based resin layer can be effectively suppressed, and a polarizer with higher characteristics can be manufactured. In addition to boric acid or borate salts, an aqueous solution obtained by dissolving boron compounds such as borax, glyoxal, glutaraldehyde, and the like in a solvent can also be used.

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

The stretching temperature (liquid temperature of the stretching bath) is preferably 40°C to 85°C, more preferably 60°C to 75°C. At such a temperature, it can be extended at a high magnification while suppressing dissolution of the PVA-based resin layer. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60°C or higher in relation to the formation of the PVA-based resin layer. In this case, if the stretching temperature is lower than 40°C, there is a risk that satisfactory stretching may not be possible even if plasticization of the thermoplastic resin substrate by water is taken into consideration. On the other hand, as the temperature of the stretching bath becomes higher, the solubility of the PVA-based resin layer increases, and there is a possibility that excellent optical properties may not be obtained. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

The draw ratio by underwater stretching is preferably 1.0 to 2.2 times, more preferably 1.1 to 2.0 times, even more preferably 1.1 to 1.8 times, still more preferably 1.2 to 1.6 times. If the stretching magnification in the underwater stretching is within such a range, the total stretching magnification can be set within a desired range, and desired birefringence, in-plane retardation and/or orientation function can be realized. As a result, it is possible to obtain a polarizer (as a result, a polarizing plate) in which the generation of cracks in the release processing part is suppressed. The total stretching ratio (total stretching ratio when air assisted stretching and underwater stretching are combined) is, as described above, preferably 3.0 to 4.5 times, more preferably 3.0 times the original length of the laminate. times to 4.3 times, more preferably 3.0 times to 4.0 times. By appropriately combining the addition of a halide to the coating liquid, adjustment of the draw ratio of air assisted extension and underwater extension, and drying shrinkage treatment, a polarizer having acceptable optical properties can be obtained even at the total magnification of such extension.

C-5. dry shrink treatment

The drying shrinkage treatment may be performed by zone heating performed by heating the entire zone, or may be performed by heating the conveying roll (using a so-called heating roll) (heating roll drying method). Preferably, both of them are used. By drying using a heating roll, heating curl of a layered product can be suppressed efficiently and a light polarizer excellent in external appearance can be manufactured. Specifically, by drying in a state where the laminate is attached to a heating roll, the crystallization of the thermoplastic resin substrate can be efficiently promoted to increase the crystallinity, and even at a relatively low drying temperature, the crystallinity of the thermoplastic resin substrate can be increased satisfactorily. can As a result, the rigidity of the thermoplastic resin base material is increased, and curling is suppressed in a state capable of withstanding shrinkage of the PVA-based resin layer due to drying. In addition, since it is possible to dry the layered product while maintaining it in a flat state by using a heating roll, not only curling but also occurrence of wrinkles can be suppressed. At this time, the optical properties can be improved by shrinking the laminate in the width direction by drying shrinkage treatment. This is because the orientation properties of PVA and PVA/iodine complexes can be effectively increased. The shrinkage in the width direction of the laminate by the drying shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 2% to 6%.

6 is a schematic diagram showing an example of drying shrinkage treatment. In the drying shrinkage treatment, the laminate 200 is dried while being conveyed by conveyance rolls R1 to R6 and guide rolls G1 to G4 heated to a predetermined temperature. In the illustrated example, the transport rolls R1 to R6 are arranged so that the PVA resin layer surface and the thermoplastic resin substrate surface are alternately and continuously heated. You may arrange conveyance rolls R1-R6 so that only may be heated continuously.

Drying conditions can be controlled by adjusting the heating temperature of the conveying rolls (temperature of the heating rolls), the number of heating rolls, and the contact time with the heating rolls. The temperature of the heating roll is preferably 60°C to 120°C, more preferably 65°C to 100°C, and particularly preferably 70°C to 80°C. While the crystallinity of the thermoplastic resin can be increased satisfactorily and curling can be suppressed satisfactorily, an optical laminate having extremely excellent durability can be manufactured. In addition, the temperature of a heating roll can be measured with a contact thermometer. Although six conveyance rolls are provided in the illustrated example, there is no particular restriction as long as there are a plurality of conveyance rolls. The conveyance rolls are usually provided in 2 to 40 pieces, preferably 4 to 30 pieces. The contact time (total contact time) between the laminate and the heating roll is preferably 1 second to 300 seconds, more preferably 1 to 20 seconds, still more preferably 1 to 10 seconds.

The heating roll may be provided in a heating furnace (for example, an oven) or may be provided in a normal production line (in a room temperature environment). Preferably, it is provided in a heating furnace equipped with a blowing means. By using both heating roll drying and hot air drying, rapid temperature change between the heating rolls 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 10 m/s to 30 m/s. In addition, the said wind speed is the wind speed in a heating furnace, and can be measured with a mini-vane type digital anemometer.

C-6. other processing

Preferably, washing treatment is performed after the underwater stretching treatment and before the drying shrinkage treatment. The washing treatment is typically performed by immersing the PVA-based resin layer in an aqueous solution of potassium iodide.

D. protective layer

The protective layer is composed of a resin film. The resin film (protective layer) may be formed of any suitable material depending on the purpose. Specific examples of the material for forming the protective layer include cellulose-based resins such as triacetyl cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, and polysulfone-based transparent resins such as polystyrene-based, polynorbornene-based, polyolefin-based, (meth)acrylic-based, and acetate-based; (meth)acrylic, urethane-based, (meth)acrylurethane-based, epoxy-based, silicone-based thermosetting resins or ultraviolet curable resins; Glassy type polymers, such as a siloxane type polymer, are mentioned. Preferably, the protective layer is composed of TAC or a (meth)acrylic resin film.

The thickness of the protective layer is preferably 5 μm to 80 μm, more preferably 10 μm to 40 μm, still more preferably 10 μm to 30 μm.

E. Reflective polarizer

As described above, the reflective polarizer may be provided on the opposite side of the protective layer 20 to the polarizer 10 . A reflective polarizer has a function of transmitting polarized light of a specific polarization state (polarization direction) and reflecting light of other polarization states. The reflective polarizer may be of a linear polarization splitting type or a circular polarization splitting type. Hereinafter, as an example, a linear polarization separation type reflective polarizer will be described. Further, examples of the reflective polarizer of the circular polarization separation type include, for example, a laminate of a film immobilized with cholesteric liquid crystal and a λ/4 plate.

7 is a schematic perspective view of an example of a reflective polarizer. A reflective polarizer is a multilayer laminate in which a layer A having birefringence and a layer B having substantially no birefringence are alternately laminated. For example, the total number of layers of such a multilayer laminate may be 50 to 1000. In the illustrated example, the refractive index nx of the A layer in the x-axis direction is greater than the refractive index ny of the y-axis direction, and the refractive index nx of the B layer in the x-axis direction is substantially equal to the refractive index ny of the y-axis direction. Therefore, the refractive index difference between the A layer and the B layer is large in the x-axis direction and substantially zero in the y-axis direction. As a result, the x-axis direction becomes the reflection axis and the y-axis direction becomes the transmission axis. The refractive index difference between the A layer and the B layer in the x-axis direction is preferably 0.2 to 0.3. In addition, the x-axis direction corresponds to the stretching direction of the reflective polarizer in the manufacturing method of the reflective polarizer.

The A layer is preferably composed of a material that exhibits birefringence when stretched. Representative examples of such a material include naphthalenedicarboxylic acid polyester (eg, polyethylene naphthalate), polycarbonate, and (meth)acrylic resin (eg, polymethyl methacrylate). Polyethylene naphthalate is preferred. The layer B is preferably made of a material that does not substantially exhibit birefringence even when stretched. A representative example of such a material is a copolyester of naphthalene dicarboxylic acid and terephthalic acid.

The reflective polarizer transmits light (eg, p-wave) having a first polarization direction at the interface between the A layer and the B layer, and transmits light (eg, s wave) having a second polarization direction orthogonal to the first polarization direction. wave) is reflected. Part of the reflected light is transmitted as light having the first polarization direction and part of the reflected light is reflected as light having the second polarization direction at the interface between the A layer and the B layer. By repeating many such reflections and transmissions inside the reflective polarizer, the efficiency of using light can be increased.

In one embodiment, the reflective polarizer may include a reflective layer R as an outermost layer opposite to the image display cell, as shown in FIG. 7 . By providing the reflective layer R, the light returned to the outermost portion of the reflective polarizer without being finally used can be further utilized, so the light utilization efficiency can be further increased. The reflective layer R typically exhibits a reflective function by a multilayer structure of a polyester resin layer.

The total thickness of the reflective polarizer can be appropriately set depending on the purpose, the total number of layers included in the reflective polarizer, and the like. The total thickness of the reflective polarizer is preferably 10 μm to 150 μm.

As the reflective polarizer, those described in, for example, Japanese Patent Application Publication No. 9-507308 and Japanese Unexamined Patent Publication No. 2013-235259 can be used. A commercial product may be used as it is, or a commercial product may be used after secondary processing (eg, stretching) of the reflection type polarizer. As a commercial item, the brand name DBEF by the 3M company, and the brand name APF by the 3M company are mentioned, for example.

F. Image display device

The polarizing plate may be applied to an image display device. Accordingly, embodiments of the present invention include an image display device using such a polarizing plate. Representative examples of the image display device include a liquid crystal display device and an electroluminescence (EL) display device (eg, an organic EL display device and an inorganic EL display device). The image display device preferably has a shape other than rectangular. In such an image display device, the effect of the embodiment of the present invention is remarkable. Specific examples of the image display device having a mold release include an automobile meter panel, a smartphone, a tablet PC, and a smart watch.

[Example]

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

(1) Thickness

It was measured using an interference film thickness meter (manufactured by Otsuka Electronics, product name 'MCPD-3000'). The calculated wavelength range used for thickness calculation was 400 nm to 500 nm, and the refractive index was 1.53.

(2) In-plane retardation of PVA (Re)

With respect to the polarizer (polarizer alone) obtained by peeling and removing the resin substrate from the laminate of the polarizer / thermoplastic resin substrate obtained in Examples and Comparative Examples, using a retardation measuring device (product name 'KOBRA-31X100 / IR' manufactured by Oji Instruments Co., Ltd.), The in-plane retardation (Rpva) of PVA at a wavelength of 1000 nm was evaluated (a value obtained by subtracting the in-plane retardation (Ri) of iodine from the total in-plane retardation at a wavelength of 1000 nm, according to the principle described). The absorption edge wavelength was 600 nm.

(3) Birefringence of PVA (Δn)

Birefringence (Δn) of PVA was calculated by dividing the in-plane retardation of PVA measured in (2) by the thickness of the polarizer.

(4) single transmittance and degree of polarization

With respect to the polarizer (polarizer alone) obtained by peeling and removing the resin substrate from the laminate of the polarizer/thermoplastic resin substrate obtained in Examples and Comparative Examples, using an ultraviolet / visible ray spectrophotometer ("V-7100" manufactured by Nippon Bunko Co., Ltd.) Transmittance Ts, parallel transmittance Tp, and orthogonal transmittance Tc were measured. These Ts, Tp, and Tc are Y values measured with a 2-degree field of view (C light source) of JIS Z8701 and corrected for visibility. From the obtained Tp and Tc, the polarization degree P was calculated|required by the following formula.

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

In addition, as for the spectrophotometer, "LPF-200" manufactured by Otsuka Electronics Co., Ltd. can perform equivalent measurements, and it has been confirmed that equivalent measurement results can be obtained even when any spectrophotometer is used.

(5) Puncture strength (breaking strength per unit thickness)

The polarizer was peeled off from the laminate of the polarizer/thermoplastic resin base material obtained in Examples and Comparative Examples, and placed in a compression tester equipped with a needle (manufactured by Katotech, product name 'NDG5' needle penetration measurement specification), In a room temperature (23°C ± 3°C) environment, it was stabbed at a stabbing speed of 0.33 cm/sec, and the strength when the polarizer was cracked was defined as the breaking strength. The evaluation value measured the breaking strength of 10 sample pieces, and used the average value. In addition, a needle having a tip diameter of 1 mmφ and a diameter of 0.5R was used. For the polarizer to be measured, a jig having a circular opening with a diameter of about 11 mm was clamped and fixed from both sides of the polarizer, and a needle was pierced into the center of the opening to conduct a test.

(6) Orientation function of PVA

Regarding the polarizer (polarizer alone) obtained by peeling and removing the resin substrate from the polarizer / thermoplastic resin substrate laminate obtained in Examples and Comparative Examples, with respect to the surface opposite to the surface from which the resin substrate was peeled, a Fourier transform infrared spectrophotometer (FT -IR) (manufactured by Perkin Elmer, trade name: 'Frontier') was used, and polarized infrared light was used as measurement light to measure attenuated total reflection (ATR) on the surface of the polarizer. . Germanium was used as a crystallite for adhering the polarizer, and the incident angle of the measurement light was 45° incident. The orientation function was calculated in the following procedure. Incident polarized infrared light (measurement light) is polarized light (s-polarized light) that oscillates parallel to the surface of the germanium crystal on which the sample is brought into close contact. Each absorbance spectrum was measured in a state of being arranged in parallel (//). From the obtained absorbance spectrum, (2941 cm ^-1 intensity) I was calculated with reference to (3330 cm ^-1 intensity). I _⊥ is It is (2941 cm ^-1 intensity) / (3330 cm ^-1 intensity) obtained from the absorbance spectrum obtained when the polarizer is stretched perpendicularly (⊥) to the polarization direction of the measurement light. In addition, I _// is (2941 cm ^-1 intensity) / (3330 cm ^-1 intensity) obtained from the absorbance spectrum obtained when the polarizer is arranged parallel to the polarization direction of the measurement light (//). Here, (2941 cm ^-1 intensity) is the bottom of the absorbance spectrum. Absorbance ^at 2941 cm -1 when 2770 cm ^-1 and 2990 cm ^-1 are used as baselines, (3330 cm ^-1 intensity) is 2990 cm ^-1 and It is the absorbance at 3330 cm ^-1 when 3650 cm ^-1 is taken as the baseline. An orientation function f was calculated according to Equation 1 using the obtained I _⊥ and I _// . In addition, when f = 1, it becomes perfect orientation, and when f = 0, it becomes random. The peak at 2941 cm ^-1 is said to be absorption due to vibration of the PVA main chain (-CH ₂ -) in the polarizer. In addition, the peak at 3330 cm ^-1 is said to be absorption due to vibration of the hydroxyl group of PVA.

(Equation 1) f=(3<cos ² θ>-1)/2

=(1-D)/[c(2D+1)]

step,

c=(3cos ² β-1)/2

Therefore, when 2941 cm ^-1 is used as described above, β = 90 ° ⇒ y = -2 × (1-D) / (2D + 1).

θ: angle of the molecular chain with respect to the stretching direction

β: angle of the transition dipole moment with respect to the molecular chain axis

D=(I _⊥ )/(I _// )

I _⊥ : Absorption intensity when the polarization direction of the measurement light and the stretching direction of the polarizer are perpendicular to each other

I _// : Absorption intensity when the polarization direction of the measurement light and the stretching direction of the polarizer are parallel

(7) Crack occurrence rate

A surface protection film was temporarily attached to the surface of the reflective polarizer of the polarizing plate obtained in Examples and Comparative Examples. Next, a separator was temporarily attached to the pressure-sensitive adhesive layer. This laminate was cut into about 130 mm x about 70 mm. At this time, the polarizer was cut so that the absorption axis was in the short direction. A U-shaped notch having a width of 5 mm, a depth (length of the concave portion) of 6.85 mm, and a radius of curvature of 2.5 mm was formed in the central portion of the short side of the cut laminate. The U-shaped notch was formed by end milling. The outer diameter of the end mill was 4 mm, the feed speed was 500 mm/min, the rotation speed was 35000 rpm, and the cutting amount and number of cuts were 0.2 mm/time for rough cutting and 0.1 mm/time for finishing cutting, total of 2 times. The separator was peeled off from the laminate in which the U-shaped notch was formed, and it was affixed to a glass plate (thickness: 1.1 mm) through an acrylic pressure-sensitive adhesive layer. Finally, the surface protection film was peeled off to obtain a test sample having a configuration of reflection type polarizer/adhesive layer/protective layer/polarizer/adhesive layer/glass plate. This test sample was subjected to a heat shock test in which holding at -40°C for 30 minutes and then holding at 85°C for 30 minutes was repeated 300 cycles, and the presence or absence of L-shaped cracks after the test was visually confirmed. This evaluation was performed using three polarizing plates, and the number of polarizing plates with cracks (substantially L-shaped cracks) was evaluated.

[Example 1]

1. Fabrication of polarizer

As the thermoplastic resin substrate, an amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) having a long shape, water absorption of 0.75%, and Tg of about 75° C. was used. Corona treatment (treatment conditions: 55 W·min/m 2 ) was performed on one side of the resin substrate.

Polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name 'Gosefimer Z410') were mixed in a ratio of 9:1 to 100 parts by weight of a PVA-based resin, potassium iodide 13 weight parts were added and the PVA aqueous solution (coating liquid) was prepared.

A PVA-based resin layer having a thickness of 13.5 μm was formed by applying the PVA aqueous solution to the corona-treated surface of the resin substrate and drying at 60° C. to prepare a laminate.

The obtained layered product was uniaxially stretched at the free end by 2.4 times in the machine direction (longitudinal direction) between rolls having different circumferential speeds in a 130°C oven (air assisted stretching treatment).

Next, the laminate was immersed in an insolubilization bath (boric acid aqueous solution obtained by blending 4 parts by weight of boric acid with respect to 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (insolubilization treatment).

Next, in a dyeing bath (water = 100 parts by weight, iodine and potassium iodide obtained by blending iodine and potassium iodide at a weight ratio of 1:7) at a liquid temperature of 30 ° C., the single transmittance (Ts) of the finally obtained polarizer is 40.5% or more. It was immersed for 60 seconds while adjusting the concentration so as to be (dyeing treatment).

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

Thereafter, the laminate was immersed in an aqueous boric acid solution (boric acid concentration = 4.0% by weight, potassium iodide 5.0% by weight) at a liquid temperature of 62°C, while the total stretching ratio in the machine direction (longitudinal direction) was 3.0 between rolls having different circumferential speeds. Uniaxial stretching was performed so as to double (underwater stretching treatment: the stretching ratio in the underwater stretching treatment is 1.25 times).

Thereafter, the laminate was immersed in a washing bath (aqueous solution obtained by blending 4 parts by weight of potassium iodide with respect to 100 parts by weight of water) at a liquid temperature of 20°C (washing treatment).

Thereafter, while drying in an oven maintained at 90°C, it was brought into contact with a heating roll made of SUS whose surface temperature was maintained at 75°C for about 2 seconds (dry shrinkage treatment). The shrinkage rate in the width direction of the layered product by the drying shrinkage treatment was 2%.

In this way, a polarizer having a thickness of 7.4 μm was formed on the resin substrate.

2. Fabrication of polarizer

A TAC film (20 μm in thickness) was bonded to the surface of the polarizer of the laminate of the resin substrate/polarizer through an ultraviolet curing adhesive (1.0 μm in thickness). Further, a reflection type polarizer was bonded to the surface of the TAC film through an acrylic pressure-sensitive adhesive (thickness: 5 µm). Then, the resin substrate was peeled off, and an acrylic pressure-sensitive adhesive layer (thickness: 15 µm) was provided on the peeled surface. In this way, a polarizing plate having a structure of reflection type polarizer/pressure-sensitive adhesive layer/protective layer/polarizer/pressure-sensitive adhesive layer was obtained.

[Examples 2 to 4]

A polarizer (thickness: 7.4 μm) was formed on a resin substrate in the same manner as in Example 1 except that dye baths having different iodine concentrations (weight ratio of iodine and potassium iodide = 1:7) were used. The following procedure was carried out similarly to Example 1, and the polarizing plate which had the structure of a reflective polarizer/adhesive layer/protective layer/polarizer/adhesive layer was obtained.

[Examples 5 to 8]

Example 1 except that the draw ratio of the underwater stretching was increased to 1.46 times (as a result, the total stretching ratio was increased to 3.5 times) and dyeing baths having different iodine concentrations (weight ratio of iodine and potassium iodide = 1:7) were used. Similarly, a polarizer (thickness: 6.7 µm) was formed on the resin substrate. The following procedure was carried out similarly to Example 1, and the polarizing plate which had the structure of a reflective polarizer/adhesive layer/protective layer/polarizer/adhesive layer was obtained.

[Examples 9 to 12]

EXAMPLES EXCEPT EXAMPLES Except for using a dyeing bath having a different iodine concentration (weight ratio of iodine and potassium iodide = 1:7), the draw ratio of the underwater drawing was increased to 1.67 times (as a result, the total stretching ratio was increased to 4.0 times). It carried out similarly to 1, and formed the polarizer (thickness: 6.2 micrometer) on the resin substrate. The following procedure was carried out similarly to Example 1, and the polarizing plate which had the structure of a reflective polarizer/adhesive layer/protective layer/polarizer/adhesive layer was obtained.

[Examples 13 to 16]

Example except that the draw ratio of the underwater drawing was increased to 1.88 times (as a result, the total extension ratio of the drawing was increased to 4.5 times), and dyeing baths having different iodine concentrations (weight ratio of iodine and potassium iodide = 1:7) were used. It carried out similarly to 1, and formed the polarizer (thickness: 6.0 micrometer) on the resin substrate. The following procedure was carried out similarly to Example 1, and the polarizing plate which had the structure of a reflective polarizer/adhesive layer/protective layer/polarizer/adhesive layer was obtained.

[Comparative Examples 1 to 4]

EXAMPLES EXCEPT EXAMPLES Except for using a dyeing bath having a different iodine concentration (weight ratio of iodine and potassium iodide = 1:7) with a draw ratio of 2.29 times the stretching in water (as a result, a total stretching ratio of 5.5 times). It carried out similarly to 1, and formed the polarizer (thickness: 5.5 micrometers) on the resin substrate. The following procedure was carried out similarly to Example 1, and the polarizing plate which had the structure of a reflective polarizer/adhesive layer/protective layer/polarizer/adhesive layer was obtained.

The polarizing plate obtained in Examples and Comparative Examples was used for evaluation of the above (2) to (7). The results are shown in Table 1.

[Table 1]

As is clear from Table 1, in the polarizing plate of the examples, cracking of the mold release portion (U-shaped notch portion) is suppressed.

8 to 10, respectively, the relationship between the single transmittance of the polarizer obtained in Examples and Comparative Examples and Δn of PVA, in-plane retardation or orientation function is shown. As shown in FIGS. 8 to 10, even if the birefringence, in-plane retardation, or orientation function is about the same (as a result, the degree of orientation is about the same), when the single transmittance is high, it can be seen that cracks tend to occur in the release processing part. there is. For example, when Δn is around 35 (×10 ^-3 ) in FIG. 8 , when the single transmittance is greater than about 44.2%, equation (1) is not satisfied, and cracks occur as in Comparative Example 4 as a result. Therefore, it can be seen that, in addition to the degree of orientation of the PVA-based resin, it is also important to adjust the single transmittance (resulting in the adsorption amount of the dichroic substance) in order to effectively suppress the occurrence of cracks in the mold release processing part. In addition, it can be seen that the polarizer satisfying Expression (1), Expression (2) and/or Expression (3) is one in which these adjustments have been suitably performed, and generation of cracks in the release processing part can be suitably suppressed. can

The polarizing plate of the present invention is used in an image display device, and is particularly suitably used in an image display device having a different shape such as a meter panel of an automobile, a smartphone, a tablet type PC, and a smart watch.

Claims (10)

A polarizing plate comprising a polarizer and a protective layer disposed on at least one side of the polarizer,
The polarizing plate has a shape other than a rectangle,
The protective layer is composed of a resin film,
When the polarizer is composed of a polyvinyl alcohol-based resin film containing a dichroic substance, and the single transmittance is x%, and the birefringence of the polyvinyl alcohol-based resin is y, A polarizing plate that satisfies the following formula (1):
y<-0.011x+0.525 (1). A polarizing plate comprising a polarizer and a protective layer disposed on at least one side of the polarizer,
The polarizing plate has a release shape other than rectangular,
The protective layer is composed of a resin film,
The polarizer is composed of a polyvinyl alcohol-based resin film containing a dichroic substance, and when the single transmittance is x% and the in-plane retardation of the polyvinyl alcohol-based resin film is z nm, the following formula ( 2), a polarizer that satisfies:
z<-60x+2875 (2). A polarizing plate comprising a polarizer and a protective layer disposed on at least one side of the polarizer,
The polarizing plate has a release shape other than rectangular,
The protective layer is composed of a resin film,
The polarizer is composed of a polyvinyl alcohol-based resin film containing a dichroic substance, and when the single transmittance is x% and the orientation function of the polyvinyl alcohol-based resin is f, the following formula (3 ), a polarizer that satisfies:
f<-0.018x+1.11 (3). A polarizing plate comprising a polarizer and a protective layer disposed on at least one side of the polarizer,
The polarizing plate has a release shape other than rectangular,
The protective layer is composed of a resin film,
The polarizer is composed of a polyvinyl alcohol-based resin film containing a dichroic substance, and has a puncture strength of 30 gf/μm or more. According to any one of claims 1 to 4,
A polarizing plate having a thickness of the polarizer of 10 μm or less. According to any one of claims 1 to 5,
A polarizing plate having a single transmittance of the polarizer of 40.0% or more and a polarization degree of 99.0% or more. According to any one of claims 1 to 6,
The deformation is a through hole, a V-shaped notch, a U-shaped notch, a concave portion having a shape approximate to a ship shape when viewed in plan view, a rectangular concave portion when viewed in plan view, and a bathtub shape when viewed in plan view. A polarizing plate selected from the group consisting of R-shaped concave portions approximate to , and combinations thereof. According to claim 7,
A polarizing plate in which the radius of curvature of the U-shaped notch is 5 mm or less. According to any one of claims 1 to 8,
Further comprising a reflective polarizer on a side opposite to the polarizer of the protective layer, the polarizing plate. An image display device comprising the polarizing plate according to any one of claims 1 to 9.

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