KR20230093422A - Curved polarizing plate and its manufacturing method - Google Patents

Abstract

According to the present invention, a polarizing plate having excellent optical properties despite being curved and capable of suppressing occurrence of cracks, breakage, and yellowing, and a simple manufacturing method thereof are provided. A polarizing plate according to an embodiment of the present invention includes a polarizer and a protective layer disposed on at least one side of the polarizer, is curved, and has an elongation at break (E) per unit thickness of the polarizer of 0.25 (%/μm) or more. A method for manufacturing a polarizing plate according to an embodiment of the present invention includes preparing a polarizing plate including a polarizer and a protective layer disposed on at least one side of the polarizer; Bonding a polarizing plate to a mold having a predetermined curved surface shape; Heating and processing the polarizing plate bonded to the mold; and humidifying the curved polarizing plate in an environment of 40°C to 65°C and 85%RH to 95%RH for 40 minutes or more.

Description

Curved polarizing plate and its manufacturing method

The present invention relates to a curved polarizing plate and a manufacturing method thereof.

Polarizing plates are widely used in image display devices such as liquid crystal display devices and organic electroluminescence (EL) display devices in order to realize image display and/or improve the performance of the image display. A polarizing plate may require curved surface processing depending on the application. Curve processing typically includes forming a polarizing plate into a predetermined shape in a high-temperature environment. However, the curved polarizing plate has a problem that the optical properties are deteriorated, and cracks, breakage, and/or yellowing are likely to occur.

Japanese Patent Laid-Open No. 8-136731

The present invention has been made to solve the above conventional problems, and its main object is a polarizing plate that has excellent optical properties despite being curved and can suppress cracks, breakage, and yellowing, and simple manufacturing thereof. is to provide a way

A polarizing plate according to an embodiment of the present invention includes a polarizer and a protective layer disposed on at least one side of the polarizer, is curved, and has an elongation at break (E) per unit thickness of the polarizer of 0.25 (%/μm) or more. am.

In one embodiment, the product E×R of the elongation at break (E) (%/μm) and the radius of curvature (R) (mm) of the curved surface processing is 20 or more. In one embodiment, the radius of curvature R is less than or equal to 70 mm.

In one embodiment, the polarizing plate is humidified for 40 minutes or longer in an environment of 40°C to 65°C and 85%RH to 95%RH after being curved.

According to another aspect of the present invention, a method for manufacturing a curved polarizing plate is provided. This manufacturing method includes preparing a polarizing plate including a polarizer and a protective layer disposed on at least one side of the polarizer; processing the polarizing plate by heating it together with a mold having a predetermined curved shape; and humidifying the curved polarizing plate in an environment of 40° C. to 65° C. and 85%RH to 95%RH for 40 minutes or longer.

In one embodiment, the heating temperature in the curved surface processing is 100°C or higher.

According to an embodiment of the present invention, in a curved polarizing plate, by setting the elongation at break per unit thickness of the polarizer to 0.25 (% / μm) or more, it has excellent optical properties and can suppress the occurrence of cracks, breakage, and yellowing. can A polarizer (as a result, a polarizing plate) having such a breaking elongation can be realized by subjecting the polarizing plate after curved surface processing to a predetermined humidification treatment.

1 is a schematic perspective view of a polarizing plate according to one embodiment of the present invention.
FIG. 2 is a schematic cross-sectional view of the polarizing plate of FIG. 1 .
3(a) to 3(c) are schematic diagrams illustrating an example of a method for manufacturing a curved polarizing plate according to an embodiment of the present invention.

EMBODIMENT OF THE INVENTION Hereinafter, although representative embodiment of this invention is described with reference to drawings, this invention is not limited to these embodiment. In addition, the drawing is drawn schematically for ease of viewing, and the shape, thickness, radius of curvature, etc. are different from the actual one, and also different between the drawings.

A. Polarizer

A-1. Overall configuration of polarizer

1 is a schematic perspective view of a polarizing plate according to one embodiment of the present invention; FIG. 2 is a schematic cross-sectional view of the polarizing plate of FIG. 1 . The polarizing plate 100 in the illustrated example is curved. In other words, the polarizing plate is a polarizing plate whose properties (typically, optical properties, chemical properties, and mechanical properties) are once deteriorated by curved surface processing (ie, under a high temperature environment). According to an embodiment of the present invention, by subjecting a polarizing plate whose properties have once deteriorated to a humidification treatment described later, the properties can be restored. As a result, in the polarizing plate after the curved surface, excellent optical properties are maintained, and also cracks, fracture, and yellowing can be suppressed. The curving temperature may be, for example, 100°C or higher, for example, 120°C or higher, or, for example, 140°C or higher, or, for example, 160°C or higher. The upper limit of the curving temperature may be, for example, 200°C. The curved surface processing time may be, for example, 15 seconds to 5 minutes.

As the shape of the curved surface processing, any appropriate shape depending on the purpose can be employed. As a specific example of the shape of curved surface processing, a dome shape like FIG. 1 and a semicircular columnar shape are mentioned. As such a curved polarizing plate, for example, a polarizing plate applied to a curved image display device is exemplified. Examples of the curved image display device include virtual reality (VR) goggles and digital signage installed on a curved wall surface or pillar. In addition, although the polarizing plate in the illustrated examples is convex on the viewer side, the polarizing plate may be convex on the side opposite to the viewer side depending on the purpose.

The polarizing plate 100 typically includes a polarizer 10, a protective layer 20 disposed on one side of the polarizer (visible side in the illustrated example), and a protective layer 30 disposed on the other side. include Depending on the purpose, either the protective layer 20 or the protective layer 30 may be omitted. In addition, in this specification, the protective layer 20 may be called a visual side protective layer, and the protective layer 30 may be called an inner protective layer.

In an embodiment of the present invention, the elongation at break (E) per unit thickness of the polarizer is 0.25 (%/μm) or more, preferably 0.30 (%/μm) or more, more preferably 0.50 (%/μm) or more. , more preferably 0.60 (%/μm) or more, and particularly preferably 0.70 (%/μm) or more. The upper limit of the elongation at break (E) may be, for example, 5.0 (%/μm). The elongation at break (E) in such a range means that the polarizer (as a result, the polarizing plate) hardened by the curved processing is recovered by the humidification treatment described later and becomes soft. As a result, a polarizing plate including a polarizer having such a breaking elongation E has excellent optical properties even after being curved, and cracks, breakage, and yellowing can be suppressed. In addition, breaking elongation (E) can be obtained by dividing the breaking elongation of the light polarizer measured based on JISK7161 by the polarizer thickness. More specifically, a test sample of a predetermined shape is prepared from a polarizer (actually a polarizer) whose properties are restored by further subjecting to a humidification treatment after heating at the same temperature as the curved surface processing, By subjecting the test sample to a tensile test Breaking strength can be measured.

In one embodiment, the product E × R of the elongation at break (E) (% / µm) and the radius of curvature (R) (mm) of curved surface processing is preferably 20 or more, more preferably 25 or more, More preferably, it is 30 or more, Especially preferably, it is 35 or more. The product E×R may be, for example, 50 or more, or, for example, 70 or more, or, for example, 80 or more, or, for example, 90 or more. The upper limit of the product E×R may be 1000, for example. If the product E×R is within this range, even a curved polarizing plate having a small (narrow) radius of curvature can have excellent optical properties, and cracks, breakage, and yellowing can be suppressed. The radius of curvature R may be, for example, 70 mm or less, may be, for example, 60 mm or less, may be, for example, 50 mm or less, may be, for example, 40 mm or less, and may be, for example, 30 mm or less. The lower limit of the radius of curvature R may be, for example, 10 mm.

A polarizing plate is typically subjected to a humidification treatment (substantially, a heating/humidification treatment) after the curved surface processing. By subjecting the curved polarizing plate to heat/humidification treatment, the optical properties of the polarizer can be restored, and cracks, breakage, and yellowing can be suppressed. The effect of such a heating/humidifying treatment is an unexpected and excellent effect. In detail, it is as follows. Heating/humidifying treatment is normally performed as a durability test of a polarizing plate. Subjecting a normal polarizing plate to heating and humidification treatment is a premise that the optical properties of the polarizing plate deteriorate (the degree of deterioration is used as an index of durability). In other words, it is common knowledge in the art that the optical properties of a polarizing plate are deteriorated by heating and humidification treatment. On the other hand, the inventors of the present invention found that the degraded properties can be restored by subjecting a polarizing plate whose properties have once deteriorated under a high temperature environment (by, for example, curved surface processing) to a heating/humidification treatment. That is, the heating and humidification treatment in the embodiment of the present invention is made based on the technical idea in the opposite direction to the common knowledge in the art, and the effect is an unexpected and excellent effect. The heating temperature in the heat/humidification treatment is preferably 40°C to 65°C, more preferably 55°C to 65°C, even more preferably 57°C to 63°C, and particularly preferably 58°C to 62°C. °C, preferably about 60 °C. Even if the heating temperature is too high or too low, there are cases where the properties cannot be sufficiently restored. Humidity in the heating/humidification treatment is preferably 85%RH to 95%RH, more preferably 87%RH to 93%RH, still more preferably 88%RH to 92%RH, particularly preferably is about 90% RH. Even if the humidity is too high or too low, there are cases where the properties cannot be sufficiently restored. The treatment time is preferably 40 minutes or longer, more preferably 50 minutes or longer, still more preferably 1 hour or longer, and particularly preferably 2 hours or longer. The upper limit of the treatment time may be, for example, 5 hours. If the processing time is too short, the properties may not be sufficiently restored. On the other hand, since the obtained effect does not substantially change even if the processing time is excessively long, an excessively long processing time may not be effective.

Hereinafter, a polarizer and a protective layer will be specifically described.

A-2. polarizer

A polarizer is comprised by the resin film containing a dichroic substance (for example, iodine, a dichroic dye) typically. As the resin film, any suitable resin film that can be used as a polarizer can be employed. The resin film is typically a polyvinyl alcohol-based resin (hereinafter referred to as "PVA-based resin") film. The resin film may be a single-layer resin film or a laminate of two or more layers.

As a specific example of the polarizer comprised from the resin film of a single layer, what the dyeing process by iodine and the extending|stretching process (typically uniaxial stretching) were given to the PVA system resin film are mentioned. The dyeing with iodine is performed, for example, by immersing the PVA-based film in an aqueous solution of iodine. The draw ratio of the uniaxial stretching is preferably 3 to 7 times. Stretching may be performed after dyeing treatment or may be performed while dyeing. Moreover, you may dye after extending|stretching. Swelling treatment, crosslinking treatment, washing treatment, drying treatment, etc. are given to the PVA-based resin film as necessary. For example, by immersing the PVA-based resin film in water and washing it with water before dyeing, stains and antiblocking agents on the surface of the PVA-based film can be washed away, and the PVA-based resin film can be swollen to prevent staining and the like.

As a specific example of a polarizer obtained using a laminate, a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a resin substrate and a PVA-based resin layer coated and formed on the resin substrate. A polarizer obtained using a layered product 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 is, for example, coated with a PVA-based resin solution on the resin substrate, dried to form a PVA-based resin layer on the resin substrate, and resin Obtaining a laminated body of a substrate and a PVA-based resin layer; It can be produced by extending|stretching and dyeing the said laminated body, and using a PVA system resin layer as 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 includes immersing the layered product in an aqueous solution of boric acid, followed by stretching. Further, the stretching may further include air-stretching the laminate at a high temperature (eg, 95° C. or higher) before stretching in a boric acid aqueous solution, if necessary. Further, in the present embodiment, the laminate is preferably subjected to a drying shrinkage treatment for shrinking by 2% or more in the width direction by heating while conveying in the longitudinal direction. Typically, the manufacturing method of the present embodiment includes performing an air assisted stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment in this order to the laminate. By introducing auxiliary stretching, even when applying PVA on a thermoplastic resin, it becomes possible to increase the crystallinity of PVA and achieve high optical properties. In addition, by simultaneously increasing the orientation of PVA in advance, it is possible to prevent problems such as deterioration of orientation or dissolution of PVA when immersed in water in a subsequent dyeing step or drawing step, and to achieve high optical properties. It happens. Further, in the case where the PVA-based resin layer is immersed in a liquid, the disorder of the orientation of 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 applied to the purpose. Any suitable protective layer according to the above may be laminated and used. The details of the manufacturing method of such a polarizer are described, for example in Unexamined-Japanese-Patent No. 2012-73580 and Japanese Patent No. 6470455. As for these publications, the entire description is incorporated herein by reference.

As the thickness of the polarizer, any suitable thickness can be employed depending on the purpose. The thickness of the polarizer is, for example, 35 μm or less, preferably 20 μm or less, more preferably 15 μm or less, still more preferably 12 μm or less, particularly preferably 10 μm or less, and still more particularly preferably is 8 μm or less, among which preferably 6 μm or less, and most preferably 5 μm or less. The lower limit of the thickness of the polarizer is preferably 2 μm, more preferably 1 μm.

The initial stage polarization degree (polarization degree before curved surface processing) of the polarizer is preferably 97.0% or more, more preferably 99.0% or more, still more preferably 99.9% or more. The initial single transmittance (single transmittance before curved surface processing) of the polarizer is preferably 40.0% to 46.0%, and more preferably 41.0% to 43.5%. The degree of polarization after the curved surface processing of the polarizer decreases, for example, by 0.005% or more relative to the degree of polarization in the initial stage (the degree of polarization as an optical characteristic decreases). The degree of polarization after the humidification treatment (described later) of the polarizer increases by, for example, 0.005% or more (the degree of polarization as an optical characteristic is restored) with respect to the degree of polarization after the curved surface processing. That is, the humidification treatment can restore the degree of polarization that has been lowered (degraded) by processing the curved surface to the level of the degree of initial polarization.

A-3. protective layer

The visual side protective layer and the inner protective layer are each formed of any suitable film that can be used as a protective layer for a polarizer. Specific examples of the material serving as the main component of the film include cellulose-based resins such as triacetyl cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, and transparent resins such as polysulfone, polystyrene, polynorbornene, polyolefin, (meth)acrylic, and acetate resins. Further, thermosetting resins such as (meth)acrylic, urethane-based, (meth)acrylurethane-based, epoxy-based, and silicone-based resins or ultraviolet curable resins may be used. In addition, glassy type polymers, such as a siloxane type polymer, are also mentioned, for example. Moreover, the polymer film of Unexamined-Japanese-Patent No. 2001-343529 (WO01/37007) can also be used. As the material for this film, a resin composition containing, for example, a thermoplastic resin having a substituted or unsubstituted imide group in its side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in its side chain can be used. For example, isobutene and and a resin composition containing an alternating copolymer containing N-methylmaleimide and an acrylonitrile/styrene copolymer. The polymer film may be, for example, an extrusion molding of the resin composition.

The inner protective layer is preferably optically isotropic. In this specification, 'optically isotropic' means that the in-plane retardation Re (550) is 0 nm to 10 nm and the thickness direction retardation Rth (550) is -10 nm to +10 nm. Here, 'Rth(λ)' is the phase difference in the thickness direction measured with light having a wavelength of λ nm at 23°C. For example, 'Rth (550)' is the phase difference in the thickness direction measured at 23° C. with light having a wavelength of 550 nm. Rth(λ) is obtained by the formula: Rth(λ)=(nx-nz)×d when the thickness of the layer (film) is d(nm). nz is the refractive index in the thickness direction.

When the polarizing plate is disposed on the viewing side of the image display device, the viewing side protective layer may be subjected to surface treatment such as hard coat treatment, antireflection treatment, anti-sticking treatment, antiglare treatment or the like as needed. Further/or, processing for improving visibility when viewing through polarized sunglasses (typically, imparting a (other) circular polarization function or imparting an ultra-high phase difference) is applied to the protective layer on the viewing side as necessary. it may be

Any appropriate thickness may be employed as the thickness of the protective layer. The thickness of the protective layer is, for example, 10 μm to 90 μm, preferably 20 μm to 80 μm, more preferably 20 μm to 60 μm, still more preferably 20 μm to 40 μm. In addition, when the surface treatment is performed, the thickness of the protective layer is the thickness including the thickness of the surface treatment layer.

B. Manufacturing method of polarizer

The polarizing plate described in the above item A is typically a polarizing plate whose properties are restored by humidification treatment after curved surface processing. Accordingly, an embodiment of the present invention includes a method for manufacturing a polarizing plate including curving and humidifying treatment. 3(a) to 3(c) are schematic views illustrating an example of a method for manufacturing a curved polarizing plate according to an embodiment of the present invention.

In the manufacturing method according to the embodiment of the present invention, first, as shown in Fig. 3(a), a polarizing plate 100' including a polarizer and a protective layer disposed on at least one side of the polarizer is prepared. At the same time, as shown in Fig. 3(a), a mold 200 having a predetermined curved surface shape (dome shape in the illustrated example) is also prepared.

Next, in one embodiment, as shown in Fig. 3(b), the polarizing plate 100' is bonded to the mold 200. Bonding of the polarizing plate 100' to the mold 200 may be performed by any appropriate method. In the illustrated example, the polarizing plate 100' is bonded to the mold 200 via, for example, an adhesive. Next, in a state where the polarizing plate 100' is bonded to the mold 200, the polarizing plate is heated, and the polarizing plate is curved (molded). In another embodiment not shown, the polarizing plate 100' is heated in a vacuum state to the curving temperature in a state where it is placed in the mold 200, and after reaching the curving processing temperature, the system is opened to process the curved surface under air pressure (atmospheric pressure). (Forming) The curving processing temperature is as described in A above.

Then, the curved polarizing plate is humidified. The humidification treatment may be performed while the polarizing plate is attached to or placed on the mold, or may be performed after removing the polarizing plate from the mold as shown in FIG. 3(c). The conditions of the humidification treatment are as described in the above section A. In this way, the curved polarizing plate 100 can be obtained.

[Example]

Hereinafter, the present invention will be specifically described by examples, but the present invention is not limited to these examples. Evaluation items in Examples are as follows. In addition, unless otherwise specified, 'part' and '%' in the examples are based on weight.

(1) Modulus of elasticity, strength at break and elongation at break

The polarizing plate before the curved surface was heated under the same conditions (100° C. and 150 seconds) as the curved surface. This was made into the comparative example equivalent polarizing plate. A polarizing plate corresponding to a comparative example was heated and humidified (65°C/95%RH, 2 hours), and this was used as a polarizing plate corresponding to an example. A polarizing plate corresponding to a comparative example or a polarizing plate corresponding to an example was punched into a size of 100 mm × 10 mm to prepare a test sample, and the test sample was subjected to a tensile test of Autograph (manufactured by Shimadzu Corporation). The measurement environment was a temperature of 23° C. and a humidity of 50% RH, and a tensile speed of 300 mm/min. At this tensile rate, the test sample was stretched until it broke, and the breaking strength (breaking stress) and breaking elongation were determined. The breaking strength was automatically measured by an autograph. The elongation at break was obtained from the following formula. In addition, the measurement was independently performed 3 times, and the average value was made into breaking strength and breaking elongation.

Elongation at break (%) = {variation in sample length to breaking point (mm)/initial length (100 mm)} × 100

The modulus of elasticity was calculated from the following formula in the range of tensile stress of 10 N to 20 N.

Elastic modulus = {(20N-10N)/sample cross-sectional area (mm ² )}/{ε(20)-ε(10)}

Here, ε(20) is the amount of deformation per unit length when the stress is 20N (mm/mm: namely, a cotton number), and ε(10) is the amount of deformation per unit length when the stress is 10N.

(2) single transmittance and degree of polarization

For the curved (dome-shaped) polarizers obtained in Examples and Comparative Examples, single transmittance (Ts) and parallel transmittance (Tp) measured using an ultraviolet and visible spectrophotometer ('LPF-200' manufactured by Otsuka Electronics Co., Ltd.) ), and the orthogonal transmittance (Tc) was set as Ts, Tp and Tc of the polarizer, respectively. These Ts, Tp, and Tc are Y values measured with a JIS Z8701 2-degree field of view (C light source) and corrected for visibility.

From the obtained Tp and Tc, the polarization degree (P) was calculated|required by the following formula.

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

The measurement was carried out as follows: excluding the lower end of the dome-shaped polarizer, a 9-division area was defined in a lattice shape (size of one area: 15 mm × 15 mm), each area was measured, and the average value was Single transmittance and polarization degree were used. In addition, the measurement was performed by fixing the dome-shaped polarizing plate to the sample holder and positioning such that each area was accurately measured. In addition, Ts and P of the polarizing plate are substantially dominated by the characteristics of the polarizer.

(3) Appearance

The appearance of the curved polarizing plate obtained in Examples and Comparative Examples was visually observed and evaluated according to the following criteria. In addition, about the polarizing plate of the comparative example, after leaving it to stand in a normal environment for 2 hours (the same time as the humidifying treatment time of the polarizing plate of the example), the external appearance was visually observed.

○: None of cracks, fractures or yellowing was observed

△: Any of cracks, fractures, or yellowing was recognized.

×: Two or more of cracks, fractures, or yellowing were observed

<Example 1>

1. Fabrication of polarizer

As the thermoplastic resin substrate, a long, amorphous isophthalic copolymer polyethylene terephthalate film (thickness: 100 μm) having a Tg of about 75° C. was used, and corona treatment was performed on one side of the resin substrate.

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

A PVA-based resin layer having a thickness of 13 μm was formed by applying the PVA aqueous solution to the corona-treated surface of the resin substrate and drying at 60° C., thereby producing a laminate.

The obtained laminate was uniaxially stretched 2.4 times in the longitudinal direction (longitudinal direction) in an oven at 130°C (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 (100 parts by weight of water, an iodine aqueous solution obtained by blending iodine and potassium iodide at a weight ratio of 1:7) at a solution temperature of 30 ° C., the single transmittance (Ts) of the polarizer finally obtained is a predetermined value. It was immersed for 60 seconds while adjusting the concentration as much as possible (dyeing treatment).

Next, 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 for 30 seconds (crosslinking treatment).

Thereafter, the laminate was immersed in an aqueous solution of boric acid at a liquid temperature of 70°C (boric acid concentration: 4% by weight, potassium iodide concentration: 5% by weight), while the total draw ratio was 5.5 in the machine direction (longitudinal direction) between rolls having different circumferential speeds. Uniaxial stretching was performed so as to double (underwater stretching treatment).

Thereafter, the laminate was immersed in a washing bath (aqueous solution obtained by blending 3 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 about 90°C, it was brought into contact with a heating roll made of SUS whose surface temperature was maintained at about 75°C (dry shrinkage treatment).

In this way, a polarizer was formed on the resin substrate, and a laminate including a configuration of the resin substrate/polarizer was obtained.

2. Fabrication of polarizer

An acrylic resin film (thickness: 40 μm) was bonded to the surface of the polarizer of the laminate obtained above (surface on the opposite side to the resin substrate) as a visual recognition side protective layer through an ultraviolet curable adhesive. Specifically, the coating was applied so that the total thickness of the curable adhesive was about 1.0 μm, and bonding was performed using a roll machine. Thereafter, UV rays were irradiated from the side of the acrylic resin film to cure the adhesive. Then, the resin base material was peeled off to obtain a polarizing plate comprising a configuration of an acrylic resin film (visible side protective layer)/polarizer.

3. Curved processing of polarizer

The obtained polarizing plate was punched into a sheet shape, and curved (molded) into dome shapes with curvature radii of 48 mm, 70 mm, and 105 mm, respectively. Specifically, the punched polarizing plate was heated in a vacuum state to 100 ° C. in a state placed in a dome-shaped mold having each radius of curvature, and after reaching, the system was opened and curved (molded) at air pressure (atmospheric pressure). . The actual processing time (pressing time) was 150 seconds. Next, the curved polarizing plate was put into a chamber set at 65°C/95% RH for 2 hours, and subjected to heating/humidification treatment. In this way, a curved polarizing plate was obtained. The obtained polarizing plate was used for evaluation of the above (2) and (3). The results are shown in Table 1.

<Example 2>

Using a polyvinyl alcohol film (manufactured by Kuraray: VF-PS7500) with a thickness of 75 μm, it was stretched to a draw ratio of 2.5 times while immersed in pure water at 30 ° C. for 60 seconds, and an iodine aqueous solution at 30 ° C. (weight ratio: pure water) / iodine (I) / potassium iodide (KI) = 100 / 0.01 / 1), dyed for 45 seconds, stretched in a 4% by weight boric acid aqueous solution so that the total draw ratio was 5.8 times, immersed in pure water for 10 seconds, and then It dried at 60 degreeC for 3 minutes, maintaining tension, and obtained the polarizer (28 micrometers in thickness).

A triacetyl cellulose (TAC) film (thickness: 47 µm) was bonded to one surface of the obtained polarizer as a visual side protective layer, and an acrylic resin film (thickness: 30 µm) was bonded to the other surface as an inner protective layer to obtain a polarizing plate. got it

The following procedure was carried out similarly to Example 1, and the curved polarizing plate was obtained. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

<Examples 3 and 4>

Except having used the polarizing plate of the structure shown in Table 1, it carried out similarly to Example 1, and obtained the polarizing plate processed into the curved surface. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

<Comparative Example 1>

A curved polarizing plate was obtained in the same manner as in Example 2 except that the heating and humidification treatment was not performed. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

<Comparative Examples 2 and 3>

A curved polarizing plate was obtained in the same manner as in Comparative Example 1 except for using the polarizing plate having the configuration shown in Table 1. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

As is clear from Table 1, according to the embodiment of the present invention, the characteristics of the polarizing plate deteriorated by the curved surface processing can be restored by heating and humidifying treatment. More specifically, as is clear from a comparison of Example 2 and Comparative Example 1, Example 3 and Comparative Example 2, and Example 4 and Comparative Example 3, respectively, the polarizing plates of Examples have a single transmittance deteriorated by curved processing. And the degree of polarization and the elongation at break (E) of the polarizer are recovering dramatically by heating and humidifying treatment. It turns out that the polarizing plate of such an Example suppresses the occurrence of cracks, breakage and yellowing.

A polarizing plate according to an embodiment of the present invention can be suitably used for an image display device having a curved surface (eg, a curved image display device).

10: polarizer
20: protective layer
30: protective layer
100: polarizer

Claims (6)

A polarizer and a protective layer disposed on at least one side of the polarizer,
The curved surface is processed,
The elongation at break (E) per unit thickness of the polarizer is 0.25 (% / μm) or more,
polarizer. The polarizing plate according to claim 1, wherein a product E×R of the elongation at break (E) (%/μm) and the radius of curvature (R) (mm) of the curved surface processing is 20 or more. The polarizing plate according to claim 2, wherein the radius of curvature (R) is 70 mm or less. The polarizing plate according to any one of claims 1 to 3, which is subjected to a humidification treatment for 40 minutes or more in an environment of 40°C to 65°C and 85%RH to 95%RH after the curved surface processing. preparing a polarizing plate including a polarizer and a protective layer disposed on at least one side of the polarizer;
processing the polarizing plate by heating it together with a mold having a predetermined curved shape; and
Including humidifying the curved polarizing plate in an environment of 40 ° C to 65 ° C and 85% RH to 95% RH for 40 minutes or more,
Method for manufacturing a curved polarizing plate. The manufacturing method according to claim 5, wherein the heating temperature in the curved surface processing is 100°C or higher.

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