CN116158205A

CN116158205A - Polarizing element, polarizing plate comprising same and image display device

Info

Publication number: CN116158205A
Application number: CN202180059340.XA
Authority: CN
Inventors: 高永幸佑; 上条卓史; 近野洋
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2020-07-29
Filing date: 2021-07-16
Publication date: 2023-05-23
Also published as: TW202212870A; WO2022024796A1; JPWO2022024796A1; KR20230042466A

Abstract

The invention provides a polarizing material which is extremely thin and can inhibit cracks from occurring in a special-shaped processing part. The polarizing material of the present invention is composed of a PVA-based resin film containing a dichroic material, and has a special shape other than a rectangular shape. In one embodiment, the polarizer satisfies the following formula (1) when the transmittance of the monomer 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 set to x% and the in-plane retardation of the PVA-based resin film is set to znm. In still another embodiment, the polarizer satisfies the following formula (3) when the monomer transmittance is x% and the orientation function of the PVA-based resin is f. In yet another embodiment, the puncture strength of the polarizer is 30gf/μm or more. y < -0.0111 x+0.525 (1) z < -60x+2875 (2) f < -0.018x+1.11 (3).

Description

Polarizing element, polarizing plate comprising same and image display device

Technical Field

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

Background

In recent years, image display devices typified by liquid crystal display devices and Electroluminescent (EL) display devices (for example, organic EL display devices and inorganic EL display devices) have been rapidly popularized. In accordance with an image forming method of the image display device, a polarizing material is disposed on at least one side of the image display device. In recent years, as the demand for thinning of image display devices increases, the demand for thinning of polarizers also increases. However, in recent years, it is sometimes desired to process the polarizing material into a shape other than a rectangle (a special-shaped process: for example, forming a notch and/or a through hole). However, there is a problem in that cracks are likely to occur in the deformed portion of the thin polarizing material.

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open No. 2001-343521

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made to solve the above-described conventional problems, and a main object of the present invention is to provide a polarizing element which is extremely thin and can suppress the occurrence of cracks in a deformed portion.

Solution for solving the problem

The polarizing material according to one embodiment of the present invention is composed of a polyvinyl alcohol resin film containing a dichroic material, has a special shape other than a rectangle, and satisfies the following formula (1) when the transmittance of a monomer is x% and the birefringence of the polyvinyl alcohol resin is y:

y＜-0.011x+0.525 (1)。

another embodiment of the present invention provides a polarizing material comprising a polyvinyl alcohol resin film containing a dichroic material, wherein the polarizing material has a special shape other than a rectangle, and satisfies the following formula (2) when the transmittance of a monomer is x% and the in-plane retardation of the polyvinyl alcohol resin film is znm:

z＜-60x+2875 (2)。

a polarizing material according to still another embodiment of the present invention is composed of a polyvinyl alcohol resin film containing a dichroic material, and has a special shape other than a rectangle, and satisfies the following formula (3) when the monomer transmittance is x% and the orientation function of the polyvinyl alcohol resin is f:

f＜-0.018x+1.11 (3)。

In still another embodiment of the present invention, the polarizing material is composed of a polyvinyl alcohol resin film containing a dichroic material, has a special shape other than a rectangular shape, and has a puncture strength of 30gf/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 special-shaped member is selected from the group consisting of a through hole, a V-notch, a U-notch, a recess having a shape similar to a boat shape in plan view, a recess having a rectangular shape in plan view, a recess having an R shape similar to a bathtub shape in plan view, and a combination thereof.

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

According to another aspect of the present invention, a polarizing plate may be provided. The polarizing plate comprises the polarizing element.

According to another aspect of the present invention, an image display apparatus may be provided. The image display device comprises the polarizer or the polarizing plate.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the embodiment of the present invention, by controlling the orientation state of the polyvinyl alcohol (PVA) based resin with respect to the polarizing material having a deformed portion (deformed portion), it is possible to realize a polarizing material which is extremely thin and can suppress the occurrence of cracks in the deformed portion. Further, such a polarizer can exhibit practically acceptable optical characteristics.

Drawings

Fig. 1 is a schematic plan view illustrating an example of a deformed or deformed portion in a polarizer according to an embodiment of the present invention.

Fig. 2 is a schematic plan view illustrating a modified example of a deformed or deformed portion in the polarizing plate according to the embodiment of the present invention.

Fig. 3 is a schematic plan view illustrating still another modification of the deformed or deformed portion in the polarizer according to the embodiment of the present invention.

Fig. 4 is a schematic plan view illustrating still another modification of the deformed or deformed portion in the polarizer according to the embodiment of the present invention.

Fig. 5 is a schematic diagram showing an example of a drying shrinkage process using a heating roller in the method for manufacturing a polarizing material according to the embodiment of the present invention.

Fig. 6 is a graph showing the relationship between the single transmittance of the polarizers produced in examples and comparative examples and the birefringence of the PVA-based resin.

Fig. 7 is a graph showing the relationship between the single transmittance and the in-plane retardation of the PVA-based resin film for the polarizers produced in examples and comparative examples.

Fig. 8 is a graph showing the relationship between the individual transmittance of the polarizers produced in examples and comparative examples and the orientation function of the PVA-based resin.

Detailed Description

Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.

A. Overall construction and characteristics of polarizer

The polarizing material according to the embodiment of the present invention is composed of a PVA-based resin film containing a dichroic material. Further, the polarizer has a special shape other than a rectangle. In the present specification, "having a special shape other than a rectangle" means that the planar shape of the polarizer has a shape other than a rectangle. The profile is typically a profiled portion profiled. Accordingly, the term "polarizing material having a special shape other than a rectangle" (hereinafter, sometimes referred to as "special-shaped polarizing material") includes not only a case where the whole of the special-shaped polarizing material (that is, an outer edge defining a planar shape of the polarizing material) is other than a rectangle, but also a case where a special-shaped processed portion is formed at a portion apart from the outer edge of the rectangular polarizing material inward. The polarizing material is likely to generate cracks in such a deformed portion, but according to the embodiment of the present invention, such cracks can be significantly suppressed. In more detail, the following is described. In general (i.e., non-profiled) polarizers, in most cases, the cracks occur along the absorption axis (stretching direction). On the other hand, an L-shaped fracture (a fracture inclined to the absorption axis) may occur in the deformed portion. According to the embodiment of the present invention, as described later, by making the molecular chain orientation of the PVA-based resin in the absorption axis direction gentler than that of the conventional polarizer, not only the normal crack but also such an L-shaped crack can be significantly suppressed.

As the special-shaped portion (special-shaped portion), for example, as shown in fig. 1 and 2, a cutting portion in which a corner portion is chamfered into an R-shape, a through hole, and a concave portion in a plan view is exemplified. Typical examples of the concave portion include a substantially boat-shaped, rectangular, and substantially bathtub-shaped R-shaped, V-shaped, and U-shaped. Another example of the special-shaped portion (special-shaped portion) is a shape corresponding to an instrument panel of an automobile as shown in fig. 3 and 4. The shape includes a region in which the outer edge is formed in an arc shape along the rotation direction of the instrument needle, and the outer edge is formed in a V-shape (including an R-shape) protruding inward in the plane direction. Of course, the shape of the special shape (special-shaped processed portion) is not limited to the example of the drawing. For example, the shape of the through hole may be any suitable shape (for example, elliptical, triangular, quadrangular, pentagonal, hexagonal, octagonal) in addition to the substantially circular shape of the illustrated example. The through hole may be provided at any appropriate position according to the purpose. The through hole may be provided in a substantially central portion of the longitudinal end portion of the rectangular polarizing material as shown in fig. 2, may be provided at a predetermined position of the longitudinal end portion, or may be provided at a corner portion of the polarizing material; although not shown, the polarizing plate may be provided at the end in the short side direction of the rectangular polarizing plate; as shown in fig. 3 or 4, the polarizing plate may be provided in the center of the shaped polarizer. As shown in fig. 2, a plurality of through holes may be provided. Further, the shapes of the drawing examples may be appropriately combined according to the purpose. For example, a through hole may be formed at an arbitrary position of the shaped polarizer of fig. 1; v-shaped notches and/or U-shaped notches may also be formed at any suitable location on the outer edge of the shaped polarizer of FIG. 3 or FIG. 4. The special-shaped polarizing piece can be suitable for image display devices such as automobile dashboards, smart phones, tablet PCs or smart watches. For example, when the shaped portion includes an R shape, the radius of curvature is, for example, 0.2mm or more, for example, 1mm or more, and for example, 2mm or more. On the other hand, the radius of curvature is, for example, 10mm or less, and is, for example, 5mm or less. For example, when the special-shaped is a U-shaped notch, the radius of curvature (radius of curvature of the U-shaped portion) is, for example, 5mm or less, for example, 1mm to 4mm, and for example, 2mm to 3mm.

The profile (profile processed portion) may be formed by any suitable method. Specific examples of the forming method include cutting by an end mill, punching by a punching blade such as a thomson blade, and cutting by laser irradiation. These methods may also be combined.

In one embodiment, the polarizer satisfies the following formula (1) when the transmittance of the monomer is x% and the birefringence of the polyvinyl alcohol resin constituting the polarizer is y. In one embodiment, the polarizer satisfies the following formula (2) when the single transmittance is set to x% and the in-plane retardation of the polyvinyl alcohol resin film constituting the polarizer is set to znm. In one embodiment, the polarizer satisfies the following formula (3) when the single transmittance is x% and the orientation function of the polyvinyl alcohol resin constituting the polarizer is f. In one embodiment, the puncture strength of the polarizer is 30gf/μm or more.

y＜-0.011x+0.525 (1)

z＜-60x+2875 (2)

f＜-0.018x+1.11 (3)

The birefringence of the PVA-based resin of the polarizer (hereinafter referred to as birefringence of PVA or Δn of PVA), the in-plane retardation of the PVA-based resin film (hereinafter referred to as "in-plane retardation of PVA"), the orientation function of the PVA-based resin (hereinafter referred to as "orientation function of PVA"), and the puncture strength of the polarizer are values related to the degree of orientation of molecular chains of the PVA-based resin constituting the polarizer. Specifically, the birefringence, in-plane retardation, and alignment function of PVA may become large as the degree of alignment increases, and the puncture strength may decrease as the degree of alignment increases. The polarizing material according to the embodiment of the present invention (that is, the polarizing material satisfying the above-described formulae (1) to (3) or puncture strength) is suppressed in heat shrinkage in the absorption axis direction because the molecular chain orientation of the PVA-based resin in the absorption axis direction is more gentle than that of the conventional polarizing material. As a result, even though the thickness is extremely thin, the occurrence of cracks in the deformed portion can be suppressed. Further, such a polarizing material is also excellent in flexibility and bending durability, and therefore, is preferably applicable to a curved image display device, more preferably to a bendable image display device, and even more preferably to a foldable image display device. While it has been difficult to obtain acceptable optical properties (typically, monomer transmittance and polarization degree) for a polarizer with a low degree of orientation, the polarizer of the embodiment of the present invention can achieve both a lower degree of orientation of the PVA-based resin than before and acceptable optical properties.

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

-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 23℃and the in-plane retardation of the PVA based resin film at a wavelength of 1000 nm. By setting the near infrared region to the measurement wavelength, the influence of the absorption of iodine in the polarizer can be eliminated, and the phase difference can be measured. 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 polarizing material.

The in-plane retardation of PVA was evaluated as follows. First, phase difference values are measured at a plurality of wavelengths of 850nm or more, and the measured phase difference values are performed: r (λ) and wavelength: lambda points were fitted to the following selmeyer equation using the least squares method. Wherein A and B are fitting parameters, and are coefficients determined by a least square method.

R(λ)＝A+B/(λ ² -600 ² )

At this time, the phase difference value R (λ) can be separated into an in-plane phase difference (Rpva) of the PVA having no wavelength dependence and an in-plane phase difference value (Ri) of iodine having strong wavelength dependence as described below.

Rpva＝A

Ri＝B/(λ ² -600 ² )

From this separation formula, the in-plane retardation (i.e., rpva) of PVA at wavelength λ=1000 nm can be calculated. The method for evaluating the in-plane retardation of the PVA is also described in japanese patent No. 5932760, and can be referred to as needed.

Further, the phase difference is divided by the thickness, whereby the birefringence (Δn) of PVA can be calculated.

As a commercially available device for measuring the in-plane retardation of PVA at the above wavelength of 1000nm, KOBA-WR/IR series, KOBA-31X/IR series, etc. manufactured by prince measurement Co.

The orientation function (f) of the polarizer preferably satisfies the following formula (3 a), more preferably the following formula (3 b). If the orientation function is too small, acceptable monomer 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) is measured by attenuated total reflection spectroscopy (ATR: attenuated total reflection) using, for example, a Fourier transform infrared spectrometer (FT-IR) and polarized light as measurement lightAnd (5) determining. Specifically, germanium was used as the microcrystal for adhering the polarizing material, the incident angle of the measurement light was set to 45 ° incidence, the incident polarized infrared ray (measurement light) was set to polarized light (s-polarized light) vibrating parallel to the specimen adhering surface of germanium crystal, measurement was performed in a state in which the stretching direction of the polarizing material was arranged parallel and perpendicular to the polarizing direction of the measurement light, and 2941cm of the absorbance spectrum obtained was used ^-1 The strength of (2) is calculated according to the following formula. Here, the intensity I is 3330cm ^-1 As a reference peak, 2941cm ^-1 /3330cm ^-1 Is a value of (2). The alignment was complete when f=1, and random when f=0. Furthermore, we consider 2941cm ^-1 The peak of (C) is represented by the main chain (-CH) of PVA in the polarizer ₂ (-) absorption by vibration.

f＝(3<cos ² θ>-1)/2

＝(1-D)/[c(2D+1)]

＝-2×(1-D)/(2D+1)

Wherein, the liquid crystal display device comprises a liquid crystal display device,

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

θ: angle of molecular chain with respect to stretching direction

Beta: angle of transition dipole moment relative to molecular chain axis

D＝(I _⊥ )/(I _// ) (in this case, the more oriented the PVA molecules are, the greater the D is)

I _⊥ : measuring absorption intensity when the polarization direction of light is perpendicular to the stretching direction of the polarizer

I _// : measuring absorption intensity when polarization direction of light is parallel to stretching direction of polarizer

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 may be 2 μm to 8 μm in another embodiment. By making the thickness of the polarizing element so thin, the heat shrinkage can be made very small. It is presumed that such a configuration also contributes to suppression of occurrence of cracks in the deformed portion.

The polarizer preferably exhibits absorption dichroism at any one of wavelengths 380nm to 780 nm. The monomer transmittance of the polarizer is preferably 40.0% or more, more preferably 41.0% or more. The upper limit of the transmittance of the monomer may be 49.0%, for example. The monomer transmittance of the polarizer is in one embodiment 40.0% to 45.0%. The polarization degree 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 in one embodiment 99.0% to 99.9%. One feature of the polarizing material according to the embodiment of the present invention is that: even if the PVA-based resin constituting the polarizer has a lower degree of orientation than before and has the in-plane retardation, birefringence and/or orientation function as described above, such practically acceptable monomer transmittance and polarization degree can be achieved. We speculate that this is caused by the manufacturing method described later. The monomer transmittance is typically a Y value obtained by measuring with an ultraviolet-visible spectrophotometer and correcting for visibility. The polarization degree is typically obtained by the following equation based on the parallel transmittance Tp and the orthogonal transmittance Tc obtained by measurement using an ultraviolet-visible spectrophotometer and performing sensitivity correction.

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

The puncture strength of the polarizing material is, for example, 30gf/μm or more, preferably 35gf/μm or more, more preferably 40gf/μm or more, still more preferably 45gf/μm or more, and particularly preferably 50gf/μm or more. The upper limit of the puncture strength may be, for example, 80 gf/. Mu.m. By setting the puncture strength of the polarizing material to such a range, occurrence of cracks in the deformed portion and cracking of the polarizing material in the absorption axis direction can be significantly suppressed. As a result, a polarizing material (as a result, a polarizing plate) having very excellent flexibility can be obtained. The puncture strength is the resistance to breakage of the polarizer when the polarizer is punctured with a predetermined strength. The puncture strength can be expressed, for example, as the following strength (breaking strength): a predetermined needle was attached to a compression tester, and the strength of the polarizing element was such that the polarizing element was broken when the polarizing element was pierced with the needle at a predetermined speed. The puncture strength means the puncture strength per unit thickness (1 μm) of the polarizer, as can be seen from the unit.

The polarizer is constituted by the PVA-based resin film containing the dichroic material as described above. The PVA-based resin constituting the PVA-based resin film (substantially, polarizing element) preferably contains an acetoacetyl-modified PVA-based resin. With such a constitution, a polarizing material having a desired puncture strength can be obtained. The amount of the acetoacetyl-modified PVA resin to be blended is preferably 5 to 20 wt%, more preferably 8 to 12 wt%, based on 100 wt% of the entire PVA resin. When the blending amount is in such a range, the puncture strength can be set to a more appropriate range.

The polarizing element can be typically manufactured using a laminate of two or more layers. Specific examples of the polarizing material obtained by using the laminate include a polarizing material obtained by using a laminate of a resin base material and a PVA-based resin layer formed on the resin base material. A polarizing material obtained by using a laminate of a resin substrate and a PVA-based resin layer formed on the resin substrate can be produced, for example, as follows: coating a PVA-based resin solution on a resin substrate and drying the same to form a PVA-based resin layer on the resin substrate, thereby obtaining a laminate of the resin substrate and the PVA-based resin layer; the laminate was stretched and dyed to prepare a polarizing element from the PVA-based resin layer. In the present embodiment, it is preferable to form a polyvinyl alcohol resin layer containing a halide and a polyvinyl alcohol resin on one side of the resin base material. Stretching typically involves immersing the laminate in an aqueous boric acid solution and stretching. Further, stretching preferably further includes subjecting the laminate to air stretching at a high temperature (for example, 95 ℃ or higher) before stretching in the aqueous boric acid solution. 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 with such a total magnification of stretching, a polarizer having acceptable optical characteristics can be obtained by a combination of addition of a halide and a drying shrinkage treatment. Further, in the embodiment of the present invention, the stretching ratio of the air-assisted stretching is preferably larger than that of the stretching in boric acid water. By adopting such a configuration, a polarizing element having acceptable optical characteristics can be obtained even if the total magnification of stretching is small. The laminate is preferably subjected to a drying shrinkage treatment in which the laminate is heated while being conveyed in the longitudinal direction and is shrunk by 2% or more in the width direction. In one embodiment, the method for producing the polarizing element includes sequentially subjecting the laminate to an air-assisted stretching treatment, a dyeing treatment, an in-water stretching treatment, and a drying shrinkage treatment. By introducing the auxiliary stretching, crystallinity of the PVA-based resin can be improved and high optical characteristics can be achieved even when the PVA-based resin is coated on the thermoplastic resin. In addition, by simultaneously improving the orientation of the PVA-based resin in advance, it is possible to prevent problems such as a decrease in orientation and dissolution of the PVA-based resin when immersed in water in a subsequent dyeing step and stretching step, and to realize high optical characteristics. Further, when the PVA-based resin layer is immersed in a liquid, disturbance of orientation and decrease of orientation of polyvinyl alcohol molecules can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. This improves the optical characteristics of the polarizing material obtained by the treatment step of immersing the laminate in a liquid, such as dyeing treatment and stretching in water. Further, the laminate is shrunk in the width direction by the drying shrinkage treatment, whereby the optical characteristics can be improved. The obtained laminate of the resin substrate and the polarizer may be used as it is (that is, the resin substrate may be used as a protective layer for the polarizer), or the resin substrate may be peeled from the laminate of the resin substrate and the polarizer and any appropriate protective layer may be laminated on the peeled surface according to the purpose. Details of the method for manufacturing the polarizing element will be described in item B.

B. Method for manufacturing polarizing element

The method for manufacturing the polarizing element preferably includes: forming a polyvinyl alcohol resin layer (PVA resin layer) containing a halide and a polyvinyl alcohol resin (PVA resin) on one side of a long thermoplastic resin substrate to form a laminate; and sequentially performing an air-assisted stretching process, a dyeing process, an in-water stretching process, and a drying shrinkage process in which the laminate is heated while being conveyed in the longitudinal direction, thereby shrinking the laminate by 2% or more in the width direction. The content of the halide in the PVA-based resin layer is preferably 5 parts by weight to 20 parts by weight relative to 100 parts by weight of the PVA-based resin. For the drying shrinkage treatment, the treatment is preferably performed using a heating roller, and the temperature of the heating roller is preferably 60 to 120 ℃. The shrinkage in the width direction of the laminate due to the drying shrinkage treatment is preferably 2% or more. Further, the stretching ratio of the air-assisted stretching is preferably larger than that of the stretching in water. According to the above manufacturing method, the polarizing material described in item a above can be obtained. In particular, by producing a laminate having a PVA-based resin layer containing a halide, stretching the laminate in multiple stages including air-assisted stretching and in-water stretching, and heating the stretched laminate with a heating roller to shrink the laminate by 2% or more in the width direction, a polarizing element having excellent optical characteristics (typically, monomer transmittance and polarization degree) can be obtained.

B-1, laminate was produced

As a method for producing the laminate of the thermoplastic resin base material and the PVA-based resin layer, any suitable method can be used. The PVA-based resin layer is preferably formed on the thermoplastic resin substrate by coating a coating liquid containing a halide and a PVA-based resin on the surface of the thermoplastic resin substrate and drying. 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 coating method of the coating liquid, any suitable method can be employed. Examples thereof include roll coating, spin coating, bar coating, dip coating, die coating, curtain coating, spray coating, knife coating (comma coating, etc.), and the like. The coating/drying temperature of the coating liquid is preferably 50℃or higher.

The thickness of the PVA based resin layer is preferably 2 μm to 30 μm, more preferably 2 μm to 20 μm. By making the thickness of the PVA-based resin layer before stretching extremely thin as described above and reducing the total magnification of stretching as described below, a polarizing element having acceptable monomer transmittance and polarization degree can be obtained even if the degree of orientation of the PVA-based resin is lower than before.

The thermoplastic resin substrate may be subjected to a surface treatment (for example, corona treatment or the like) before the PVA-based resin layer is formed, or an easy-to-adhere layer may be formed on the thermoplastic resin substrate. By performing such a treatment, the adhesion between the thermoplastic resin base material and the PVA-based resin layer can be improved.

B-1-1. Thermoplastic resin substrate

As the thermoplastic resin base material, any suitable thermoplastic resin film can be used. Details of the thermoplastic resin base material are described in, for example, japanese patent application laid-open No. 2012-73580. The entire disclosure of this publication is incorporated by reference into this specification.

B-1-2. Coating solution

The coating liquid contains a halide and a PVA-based resin as described above. 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, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, polyols such as various diols and trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. These may be used singly or in combination of two or more. Among these, water is preferable. 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. When the resin concentration is such, a uniform coating film can be formed to be adhered to the thermoplastic resin base material. The halide content in the coating liquid is preferably 5 parts by weight to 20 parts by weight relative to 100 parts by weight of the PVA-based resin.

Additives may be compounded in the coating liquid. Examples of the additive include a plasticizer and a surfactant. Examples of the plasticizer include polyols such as ethylene glycol and glycerin. Examples of the surfactant include nonionic surfactants. These may be used for the purpose of further improving the uniformity, dyeing property, and stretchability of the resulting PVA-based resin layer.

As the PVA-based resin, any suitable resin may be used. For example, polyvinyl alcohol and an ethylene-vinyl alcohol copolymer are mentioned. The polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer can be obtained by saponifying an 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 saponification degree can be determined according to JIS K6726-1994. By using the PVA-based resin having such a saponification degree, a polarizing element excellent in durability can be obtained. If the saponification degree is too high, gelation may occur. As described above, the PVA-based resin preferably contains an acetoacetyl-modified PVA-based resin.

The average polymerization degree of the PVA-based resin may be appropriately selected according to purposes. The average polymerization degree is usually 1000 to 10000, preferably 1200 to 4500, more preferably 1500 to 4300. The average polymerization degree can be determined according to JIS K6726-1994.

As the above-mentioned halide, any suitable halide may be used. For example, iodide and sodium chloride may be mentioned. Examples of the iodide include potassium iodide, sodium iodide, and lithium iodide. Among these, potassium iodide is preferable.

The amount of the halide in the coating liquid is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin, and more preferably 10 to 15 parts by weight relative to 100 parts by weight of the PVA-based resin. If the amount of the halide is more than 20 parts by weight based on 100 parts by weight of the PVA-based resin, the halide may ooze out and the finally obtained polarizing element may be clouded.

In general, the orientation of the polyvinyl alcohol molecules in the PVA-based resin layer is increased by stretching the PVA-based resin layer, but when the PVA-based resin layer after stretching is immersed in a liquid containing water, the orientation of the polyvinyl alcohol molecules may be disturbed and the orientation may be reduced. In particular, when the laminate of the thermoplastic resin base material and the PVA-based resin layer is stretched in boric acid water at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin base material, the degree of orientation tends to be significantly reduced. For example, in general, stretching in boric acid water of a PVA film itself is performed at 60 ℃, and stretching of a laminate of a-PET (thermoplastic resin base material) and a PVA-based resin layer is performed at a temperature as high as about 70 ℃, and in this case, there is a possibility that the orientation of PVA at the initial stage of stretching is lowered at a stage before it is raised by stretching in water. In contrast, by producing a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin substrate and stretching the laminate in air at a high temperature (auxiliary stretching) before stretching the laminate in boric acid water, crystallization of the PVA-based resin in the PVA-based resin layer of the laminate after the auxiliary stretching can be promoted. As a result, when the PVA-based resin layer is immersed in a liquid, disturbance of orientation of polyvinyl alcohol molecules and reduction of orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. This improves the optical characteristics of the polarizing material obtained by the treatment step of immersing the laminate in a liquid, such as dyeing treatment and stretching in water.

B-2, auxiliary stretching treatment in the air

In particular, in order to obtain high optical characteristics, a method of 2-stage stretching in which dry stretching (auxiliary stretching) and boric acid in-water stretching are combined is selected. By introducing the auxiliary stretching as in the 2-stage stretching, the stretching can be performed while suppressing crystallization of the thermoplastic resin base material. Further, when the PVA-based resin is coated on the 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 coating temperature than when the PVA-based resin is usually coated on a metal drum, and as a result, there is a problem that crystallization of the PVA-based resin is relatively low and sufficient optical characteristics are not obtained. In contrast, even when the PVA-based resin is coated on the thermoplastic resin by introducing the auxiliary stretching, crystallinity of the PVA-based resin can be improved, and high optical characteristics can be achieved. Further, by increasing the orientation of the PVA-based resin in advance, problems such as a decrease in orientation and dissolution of the PVA-based resin can be prevented when immersed in water in a subsequent dyeing step and stretching step, and high optical characteristics can be achieved.

The stretching method of the air-assisted stretching may be either fixed-end stretching (for example, stretching using a tenter stretcher) or free-end stretching (for example, unidirectional stretching by passing the laminate between rolls having different circumferential speeds), and can be integrated to obtain high optical characteristics The poles are stretched with free ends. In one embodiment, the air stretching process includes a heated roll stretching step of stretching the laminate by a circumferential speed difference between heated rolls while conveying the laminate in the longitudinal direction thereof. The air stretching treatment typically includes a zone stretching process and a heated roll stretching process. The order of the region stretching step and the heat roller stretching step is not limited, and the region stretching step may be performed first, or the heat roller stretching step may be performed first. The zone stretching process may be omitted. In 1 embodiment, the zone stretching step and the heat roller stretching step are sequentially performed. In still another embodiment, stretching is performed by holding the end of the film in a tenter and expanding the distance between tenters in the moving direction (the expansion of the distance between tenters is the stretching ratio). In this case, the distance of the tenter in the width direction (the direction perpendicular to the moving direction) may be set to be arbitrarily close. The stretch ratio in the moving direction can be preferably set so as to be closer to the free end stretch. In the case of free end stretching, the shrinkage in the width direction= (1/stretch ratio) ^1/2 To calculate.

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

The stretching ratio of the air-assisted stretching is preferably 1.0 to 4.0 times, more preferably 1.5 to 3.5 times, and even more preferably 2.0 to 3.0 times. When the stretching magnification of the air-assist stretching is within such a range, the total stretching magnification can be set to a desired range when combined with the in-water stretching, and a desired birefringence, in-plane retardation, and/or orientation function can be achieved. As a result, a polarizing material that can suppress the occurrence of cracks in the deformed portion can be obtained. Further, as described above, the stretching ratio of the air-assisted stretching is preferably larger than that of the stretching in water. By such a constitution, a polarizing element having acceptable optical characteristics can be obtained even if the total magnification of stretching is small. More specifically, the ratio of the stretching ratio of the air-assist stretching to the stretching ratio of the in-water stretching (in-water stretching/air-assist stretching) is preferably 0.4 to 0.9, and more preferably 0.5 to 0.8.

The stretching temperature of the air-assisted stretching may be set to any appropriate value depending on the material forming 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 substrate, more preferably not less than the glass transition temperature (Tg) +10 ℃ of the thermoplastic resin substrate, particularly preferably not less than tg+15 ℃. On the other hand, the upper limit of the stretching temperature is preferably 170 ℃. By stretching at such a temperature, crystallization of the PVA-based resin can be suppressed from proceeding rapidly, and thus, defects caused by the crystallization (e.g., inhibition of orientation of the PVA-based resin layer caused by stretching) can be suppressed.

B-3 insolubilization treatment, dyeing treatment and crosslinking treatment

The insolubilization treatment is performed after the air-assisted stretching treatment and before the underwater stretching treatment and dyeing treatment, as required. The insolubilization treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. The dyeing treatment is typically performed by dyeing the PVA-based resin layer with a dichroic substance (typically iodine). If necessary, the crosslinking treatment is performed after the dyeing treatment and before the stretching treatment in water. The crosslinking treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. Details of the insolubilization treatment, dyeing treatment, and crosslinking treatment are described in, for example, japanese patent application laid-open No. 2012-73580.

B-4 stretching treatment in water

The stretching treatment in water is performed by immersing the laminate in a stretching bath. The stretching treatment in water can be performed at a temperature lower than the glass transition temperature (typically about 80 ℃) of the thermoplastic resin base material and the PVA-based resin layer, and can be performed while suppressing crystallization of the PVA-based resin layer. As a result, a polarizing element having excellent optical characteristics can be manufactured.

Any suitable method may be used for stretching the laminate. Specifically, the stretching may be performed at a fixed end or at a free end (for example, a method of stretching a laminate unidirectionally by passing the laminate between rolls having different peripheral speeds). The free end stretch is preferably selected. Stretching of the laminate may be performed in one stage or may be performed in multiple stages. When the stretching is performed in multiple stages, the total stretching ratio is the product of the stretching ratios in the respective stages.

The stretching in water is preferably performed by immersing the laminate in an aqueous boric acid solution (stretching in boric acid water). By using an aqueous boric acid solution as the stretching bath, rigidity against tensile force applied at the time of stretching and water resistance insoluble in water can be imparted to the PVA-based resin layer. Specifically, boric acid generates tetrahydroxyboric acid anions in an aqueous solution so as to be crosslinkable with the PVA-based resin through hydrogen bonds. As a result, the PVA-based resin layer can be provided with rigidity and water resistance, and can be stretched well, and a polarizing element having excellent optical characteristics can be produced.

The aqueous boric acid solution is preferably obtained by dissolving boric acid and/or a borate in water as a solvent. The boric acid concentration is preferably 1 to 10 parts by weight, more preferably 2.5 to 6 parts by weight, particularly preferably 3 to 5 parts by weight, relative to 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 polarizing element having higher characteristics can be produced. In addition to boric acid or borate, an aqueous solution obtained by dissolving a boron compound such as borax, glyoxal, glutaraldehyde, or the like in a solvent may be used.

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

The stretching temperature (liquid temperature of the stretching bath) is preferably 40 to 85 ℃, more preferably 60 to 75 ℃. At such a temperature, the PVA-based resin layer can be stretched at a high rate while suppressing dissolution. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60 ℃ or higher due to the relationship with the formation of the PVA-based resin layer. In this case, if the stretching temperature is lower than 40 ℃, there is a concern that the thermoplastic resin base material cannot be stretched well even if plasticization of the thermoplastic resin base material by water is considered. On the other hand, if the temperature of the stretching bath is high, there is a concern that the PVA-based resin layer becomes high in solubility and excellent optical characteristics cannot be obtained. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

The stretching ratio based on stretching in water is preferably 1.0 to 2.2 times, more preferably 1.1 to 2.0 times, further preferably 1.1 to 1.8 times, still further preferably 1.2 to 1.6 times. When the stretching magnification in water is within such a range, the total magnification of stretching can be set to a desired range, and a desired birefringence, in-plane retardation, and/or orientation function can be achieved. As a result, a polarizing material that can suppress the occurrence of cracks in the deformed portion can be obtained. The total draw ratio (total of the draw ratio in combination of the air-assisted draw and the underwater draw) is preferably 3.0 to 4.5 times, more preferably 3.0 to 4.3 times, and even more preferably 3.0 to 4.0 times, the original length of the laminate as described above. By properly combining the addition of a halide to the coating liquid, adjustment of the stretching ratio of the air-assisted stretching and the in-water stretching, and the drying shrinkage treatment, a polarizing element having acceptable optical characteristics can be obtained even at the total ratio of such stretching.

B-5 drying shrinkage treatment

The drying shrinkage treatment may be performed by zone heating in which the entire zone is heated, or may be performed by heating a conveying roller (using a so-called heating roller) (heating roller drying method). Both are preferably used. By drying with the heating roller, the laminate can be effectively restrained from curling by heating, and a polarizing element excellent in appearance can be produced. Specifically, by drying the laminate in a state of being brought along the heated roller, crystallization of the thermoplastic resin base material can be effectively promoted to increase the crystallinity, and even at a relatively low drying temperature, the crystallinity of the thermoplastic resin base material can be satisfactorily increased. As a result, the rigidity of the thermoplastic resin base material increases, and the PVA-based resin layer is allowed to shrink due to drying, so that curling can be suppressed. Further, since the laminate can be dried while being kept flat by using the heating roller, not only curling but also the generation of wrinkles can be suppressed. At this time, the laminate is shrunk in the width direction by the drying shrinkage treatment, and the optical characteristics can be improved. This is because the orientation of PVA and PVA/iodine complex can be effectively improved. The shrinkage in the width direction of the laminate due to the drying shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 2% to 6%.

Fig. 5 is a schematic diagram showing an example of the drying shrinkage treatment. In the drying shrinkage process, the laminate 200 is dried while being conveyed by the conveying rollers R1 to R6 and the guide rollers G1 to G4 heated to predetermined temperatures. In the example shown in the figure, the conveying rollers R1 to R6 are arranged so as to continuously heat alternately the surface of the PVA resin layer and the surface of the thermoplastic resin substrate, but for example, the conveying rollers R1 to R6 may be arranged so as to continuously heat only one surface of the laminate 200 (for example, the surface of the thermoplastic resin substrate).

The drying condition can be controlled by adjusting the heating temperature of the conveying 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 to 120 ℃, more preferably 65 to 100 ℃, particularly preferably 70 to 80 ℃. The crystallinity of the thermoplastic resin can be increased well to suppress curling well, and an optical laminate extremely excellent in durability can be produced. The temperature of the heating roller may be measured by a contact thermometer. In the example of the figure, 6 conveying rollers are provided, but there is no particular limitation as long as the conveying rollers are plural. The number of the conveying rollers is usually 2 to 40, preferably 4 to 30. The contact time (total contact time) of the laminate with 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 may be provided in a heating furnace (for example, an oven) or may be provided in a general production line (in a room temperature environment). Preferably, the air supply device is installed in a heating furnace provided with an air supply means. By using a combination of drying by the heating rollers and hot air drying, rapid temperature changes between the heating rollers can be suppressed, and shrinkage in the width direction can be easily controlled. The temperature of the hot air drying is preferably 30 to 100 ℃. The hot air drying time is preferably 1 to 300 seconds. The wind speed of the hot air is preferably about 10m/s to 30 m/s. The wind speed is the wind speed in the heating furnace, and can be measured by a mini-vane type digital anemometer.

B-6 other treatments

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

C. Polarizing plate

The polarizing material can be practically provided as a polarizing plate. Accordingly, embodiments of the present invention also include a polarizing plate. The polarizing plate includes the polarizing material described in item A and item B above, and a protective layer disposed on at least one surface of the polarizing material. The protective layer may be formed by a known method in the art, and thus a detailed description thereof will be omitted.

D. Image display device

The polarizer and the polarizing plate can be applied to an image display device. Accordingly, embodiments of the present invention include an image display device using such a polarizing material or polarizing plate. Typical examples of the image display device include a liquid crystal display device and an Electroluminescence (EL) display device (for example, an organic EL display device and an inorganic EL display device). The image display device preferably has a special shape other than a rectangle. In such an image display device, the effects of the embodiments of the present invention are remarkable. Specific examples of the image display device having a special shape include a dashboard of an automobile, a smart phone, a tablet PC, and a smart watch.

Examples

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. The measurement method of each characteristic is as follows. Unless otherwise specified, "parts" and "%" in examples are based on weight.

(1) Thickness of (L)

The measurement was performed using an interferometric film thickness meter (manufactured by tsukamu electronics corporation under the product name "MCPD-3000"). The calculation wavelength used in the thickness calculation was 400nm to 500nm, and the refractive index was 1.53.

(2) In-plane phase difference (Re) of PVA

The polarizer (polarizer itself) from which the resin substrate was removed was peeled off from the laminate of polarizer/thermoplastic resin substrate obtained in examples and comparative examples, and the in-plane retardation (Rpva) of PVA at a wavelength of 1000nm (a value obtained by subtracting the in-plane retardation (Ri) of iodine from the total in-plane retardation at a wavelength of 1000nm according to the principle described) was evaluated using a retardation measuring apparatus (product name "KOBRA-31X100/IR" manufactured by prince measuring machine). The absorption end wavelength is 600nm.

(3) Birefringence of PVA (Δn)

The birefringence (Δn) of PVA was calculated by dividing the in-plane retardation of PVA measured in the above (2) by the thickness of the polarizing element.

(4) Monomer transmittance and polarization degree

The polarizers (polarizers themselves) from which the resin base material was removed were peeled off from the laminate of polarizers/thermoplastic resin base materials obtained in examples and comparative examples, and the single transmittance Ts, the parallel transmittance Tp, and the orthogonal transmittance Tc were measured using an ultraviolet-visible spectrophotometer (japan spectroscopic corporation "V-7100"). These Ts, tp, and Tc are Y values obtained by measuring a 2-degree field of view (C light source) according to JIS Z8701 and performing sensitivity correction. The polarization degree P was obtained from Tp and Tc by the following equation.

The polarization degree P (%) = { (Tp-Tc)/(tp+tc) } ^1/2 ×100

In the spectrophotometer, it was confirmed that: equivalent measurement can be performed by LPF-200 manufactured by tsukamureluctor electronics, and equivalent measurement results can be obtained by using any spectrophotometer.

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

Layer of polarizer/thermoplastic resin substrate obtained from examples and comparative examplesThe laminate was peeled off, and the laminate was placed on a compression tester (KATO TECH co., ltd. Manufactured under the product name "NDG5" needle penetration force measurement standard) equipped with a needle, and the laminate was subjected to piercing at a piercing speed of 0.33 cm/sec under room temperature (23 ℃ ±3 ℃) environment, whereby the strength at the time of breakage of the laminate was regarded as breaking strength. Evaluation value the breaking strength of 10 test pieces was measured and the average value thereof was used. The diameter of the needle tip

0.5R needle. For the polarizer to be measured, a jig having a circular opening with a diameter of about 11mm was clamped and fixed from both sides of the polarizer, and then a center puncture needle of the opening was tested.

(6) Orientation function of PVA

The polarizing material (polarizing material itself) obtained by peeling off the resin substrate from the polarizing material/thermoplastic resin substrate laminate obtained in examples and comparative examples was subjected to attenuated total reflection spectroscopy (ATR: attenuated total reflection) on the surface of the polarizing material, which was opposite to the surface from which the resin substrate was peeled off, using a fourier transform infrared spectrometer (FT-IR) (trade name: "front tier" manufactured by Perkin Elmer corporation) and using polarized infrared light as measurement light. The crystallites used to seal the polarizers were germanium, and the incident angle of the measured light was 45 °. The orientation function was calculated as follows. The incident polarized infrared light (measurement light) was polarized light (s-polarized light) vibrating parallel to the sample adhesion surface of germanium crystals, and absorbance spectra were measured in a state in which the stretching directions of the polarizers were arranged perpendicular (∈) and parallel (/ /) with respect to the polarization direction of the measurement light. From the absorbance spectrum obtained, the absorbance was calculated as (3330 cm ^-1 Intensity) as reference (2941 cm ^-1 Intensity) I. I _⊥ Is obtained from absorbance spectrum obtained when the stretching direction of the polarizer was perpendicular (∈) to the polarizing direction of the measurement light (2941 cm) ^-1 Intensity)/(3330 cm ^-1 Intensity). Furthermore, I _// Is obtained from absorbance spectra obtained when the stretching direction of the polarizer was arranged in parallel (///) with respect to the polarizing direction of the measurement light (2941 c)m ^-1 Intensity)/(3330 cm ^-1 Intensity). Here, (2941 cm) ^-1 Intensity) is 2770cm which will be the bottom of the absorbance spectrum ^-1 And 2990cm ^-1 2941cm at baseline ^-1 Absorbance of (3330 cm) ^-1 Intensity) of 2990cm ^-1 And 3650cm ^-1 3330cm at baseline ^-1 Is a solid phase, and is a liquid phase. Using the obtained I _⊥ I _// The orientation function f is calculated according to equation 1. The alignment was complete when f=1, and random when f=0. Furthermore, 2941cm ^-1 The peak of (C) is called as the peak of the PVA backbone (-CH) in the polarizer ₂ (-) absorption by vibration. Furthermore, 3330cm ^-1 The peak of (2) is absorption caused by vibration of the hydroxyl group of PVA.

(1) f= (3)<cos ² θ>-1)/2

＝(1-D)/[c(2D+1)]

c＝(3cos ² beta-1)/2, 2941cm was used as described above ^-1 In the time-course of which the first and second contact surfaces,

θ: angle of molecular chain with respect to stretching direction

Beta: angle of transition dipole moment relative to molecular chain axis

D＝(I _⊥ )/(I _// )

(7) Fracture generation rate

The surface protective films were temporarily adhered to the polarizer surfaces of the resin base material/polarizer laminates obtained in examples and comparative examples. Then, the resin base material was peeled off, an acrylic pressure-sensitive adhesive layer (thickness: 20 μm) was provided on the peeled off surface, and the separator was temporarily bonded to the pressure-sensitive adhesive layer. The laminate was cut to about 130mm by about 70mm. At this time, the polarizing element is cut so that the absorption axis thereof is in the short side direction. A U-shaped notch having a width of 5mm, a depth (recess length) of 6.85mm, and a radius of curvature of 2.5mm was formed in the center of the short side of the cut laminate. The U-shaped notch is formed by processing an end mill. The end mill had an outer diameter of 4mm, a feed rate of 500 mm/min, a rotational speed of 35000rpm, a cutting amount and a cutting number of times of 0.2 mm/time for rough cutting and 0.1 mm/time for finish cutting 2 times in total. The separator was peeled from the laminate having the U-shaped notch formed therein, and attached to a glass plate (thickness 1.1 mm) via an acrylic pressure-sensitive adhesive layer. Finally, the surface protective film was peeled off to obtain a test specimen having a constitution of a polarizer/an adhesive layer/a glass plate. After the test specimen was placed in an oven at 85℃for 120 hours, the presence or absence of occurrence of an L-shaped crack was visually confirmed. The evaluation was performed using 3 sheets of polarizers, and the number of polarizers in which cracks (substantially L-shaped cracks) were generated was evaluated.

Example 1

As the thermoplastic resin base material, an amorphous isophthalic acid-copolymerized polyethylene terephthalate film (thickness: 100 μm) having a long water absorption of 0.75% and a Tg of about 75℃was used. Corona treatment of one side of the resin substrate (treatment conditions: 55 W.min/m) ² )。

At 9:1 to 100 parts by weight of a PVA based resin obtained by mixing polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (trade name "GOHSEFIMER Z410" manufactured by Nippon chemical industry Co., ltd.), 13 parts by weight of potassium iodide was added to prepare a PVA aqueous solution (coating liquid).

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

The resulting laminate was uniaxially stretched to 2.4 times in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds in an oven at 130 ℃.

Subsequently, the laminate was immersed in an insolubilization bath (an aqueous boric acid solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40 ℃ for 30 seconds (insolubilization treatment).

Next, the resultant polarizing material was immersed in a dyeing bath (aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with respect to 100 parts by weight of water) at a liquid temperature of 30 ℃ for 60 seconds (dyeing treatment) while adjusting the concentration so that the monomer transmittance (Ts) of the resultant polarizing material became 40.5%.

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

Then, the laminate was immersed in an aqueous boric acid solution (boric acid concentration: 4.0 wt% and potassium iodide: 5.0 wt%) at a liquid temperature of 62 ℃ and uniaxially stretched (in the longitudinal direction) between rolls having different peripheral speeds so that the total stretching magnification became 3.0 times (stretching magnification in the underwater stretching treatment: 1.25 times).

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

After that, the surface was kept at 75℃for about 2 seconds while being dried in an oven kept at 90℃by a SUS-made heating roller (drying shrinkage treatment). The shrinkage in the width direction of the laminate based on the drying shrinkage treatment was 2%.

Thus, a polarizer having a thickness of 7.4 μm was formed on the resin substrate.

Examples 2 to 4

A polarizing element (thickness: 7.4 μm) was formed on a resin substrate in the same manner as in example 1, except that a dyeing bath having a different iodine concentration (weight ratio of iodine to potassium iodide=1:7) was used.

Examples 5 to 8

A polarizing element (thickness: 6.7 μm) was formed on a resin substrate in the same manner as in example 1, except that the stretching magnification in water was set to 1.46 times (as a result, the total stretching magnification was set to 3.5 times), and a dyeing bath having a different iodine concentration (weight ratio of iodine to potassium iodide=1:7) was used.

Examples 9 to 12

A polarizing element (thickness: 6.2 μm) was formed on a resin substrate in the same manner as in example 1, except that the stretching magnification in water was set to 1.67 times (as a result, the total stretching magnification was set to 4.0 times), and a dyeing bath having a different iodine concentration was used (weight ratio of iodine to potassium iodide=1:7).

Examples 13 to 16

A polarizing element (thickness: 6.0 μm) was formed on a resin substrate in the same manner as in example 1, except that the stretching magnification in water was 1.88 times (as a result, the total stretching magnification was 4.5 times), and a dyeing bath having a different iodine concentration was used (weight ratio of iodine to potassium iodide=1:7).

Comparative examples 1 to 4

A polarizing element (thickness: 5.5 μm) was formed on a resin substrate in the same manner as in example 1, except that the stretching magnification in water was set to 2.29 times (as a result, the total magnification in stretching was set to 5.5 times), and a dyeing bath having a different iodine concentration (weight ratio of iodine to potassium iodide=1:7) was used.

The polarizers obtained in examples and comparative examples were subjected to the evaluations of (2) to (7) above. The results are shown in Table 1.

TABLE 1

As is clear from table 1, the polarizing plate of the example can suppress the occurrence of cracks in the deformed portion (U-notched portion).

Fig. 6 to 8 show the relationship between the transmittance of the polarizing material alone and the PVA Δn, in-plane retardation, or orientation function of the polarizing material obtained in the examples and comparative examples, respectively. As shown in fig. 6 to 8, even if the birefringence, in-plane retardation, or orientation function is the same (as a result, the degree of orientation is the same), cracks are likely to occur in the deformed portion when the transmittance of the monomer is high. For example, as seen in FIG. 6, Δn is 35 (. Times.10) ^-3 ) When the monomer transmittance is more than about 44.2%, the formula (1) is not satisfied, and as a result, cracks are generated as shown in comparative example 4. Therefore, it was found that in order to effectively suppress the occurrence of cracks in the deformed portion, not only the degree of orientation of the PVA based resin but also the transmittance of the monomer(as a result, the adsorption amount of the dichroic material) is also important. It is also known that the polarizing materials satisfying the formulas (1), (2) and/or (3) are suitably adjusted, and the occurrence of cracks in the deformed portion can be suitably suppressed.

Industrial applicability

The polarizing element can be used for an image display device, and is particularly suitable for the image display devices with special shapes such as instrument panels, smart phones, tablet Personal Computers (PC), smart watches and the like of automobiles.

Claims

1. A polarizing material comprising a polyvinyl alcohol resin film containing a dichroic material, and

has a special-shaped form other than a rectangle,

when the monomer transmittance is x% and the birefringence of the polyvinyl alcohol resin is y, the following formula (1) is satisfied:

y＜-0.011x+0.525 (1)。

2. a polarizing material comprising a polyvinyl alcohol resin film containing a dichroic material, and

has a special-shaped form other than a rectangle,

when the monomer transmittance is x% and the in-plane retardation of the polyvinyl alcohol resin film is znm, the following formula (2) is satisfied:

z＜-60x+2875 (2)。

3. a polarizing material comprising a polyvinyl alcohol resin film containing a dichroic material, and

has a special-shaped form other than a rectangle,

when the monomer transmittance is x% and the orientation function of the polyvinyl alcohol resin is f, the following formula (3) is satisfied:

f＜-0.018x+1.11 (3)。

4. a polarizing material comprising a polyvinyl alcohol resin film containing a dichroic material, and

has a special-shaped form other than a rectangle,

the puncture strength is 30gf/μm or more.

5. The polarizing element according to any one of claims 1 to 4, which has a thickness of 10 μm or less.

6. The polarizing element according to any one of claims 1 to 5, which has a monomer transmittance of 40.0% or more and a polarization degree of 99.0% or more.

7. The polarizer of any of claims 1-6, wherein the profile is selected from the group consisting of a through hole, a V-notch, a U-notch, a recess that approximates a boat shape in plan view, a rectangular recess in plan view, an R-shaped recess that approximates a bathtub shape in plan view, and combinations thereof.

8. The polarizer of claim 7, wherein the U-notch has a radius of curvature of 5mm or less.

9. A polarizing plate comprising the polarizing element according to any one of claims 1 to 8.

10. An image display device comprising the polarizing element according to any one of claims 1 to 8 or the polarizing plate according to claim 9.