TWI872103B - Polarizing plate, polarizing plate assembly and image display device - Google Patents

Abstract

The present invention provides a polarizing plate having a through hole formed near an end portion, and cracks around the through hole are significantly suppressed. The polarizing plate of the present invention has a polarizer, a protective layer disposed on at least one side of the polarizer, and an adhesive layer. The polarizing plate has a rectangular shape and is formed with a through hole. The thickness of the polarizer is less than 10 μm. The diameter of the through hole is less than 5 mm, and the through hole is formed at a position within 11 mm from the long side and within 11 mm from the short side.

Description

Polarizing plate, polarizing plate assembly and image display device

The present invention relates to a polarizing plate, an assembly of polarizing plates and an image display device.

Polarizing plates are widely used in image display devices such as mobile phones and notebook personal computers to realize image display and/or improve the image display performance. In recent years, due to the rapid popularization of smart phones and touch panel information processing devices, image display devices equipped with cameras are becoming more and more widely used. In response to this, polarizing plates having through holes at positions corresponding to camera parts are also becoming more and more widely used. Regarding polarizing plates having such through holes, there are various review issues regarding the through holes or their vicinity. Prior Art Literature Patent Literature

Patent Document 1: International Publication No. 2017/047510

Problem to be solved by the invention The present invention is made to solve the above-mentioned previous problems, and its main purpose is to provide a polarizing plate having through holes formed near the end and cracks around the through holes are significantly suppressed.

Means for solving the problem The polarizing plate of the embodiment of the present invention has a polarizing element, a protective layer disposed on at least one side of the polarizing element, and an adhesive layer. The polarizing plate has a rectangular shape and is formed with a through hole. The thickness of the polarizing element is less than 10 μm. The diameter of the through hole is less than 5 mm, and the through hole is formed at a position within 11 mm from the long side and within 11 mm from the short side. In one embodiment, the thickness of the polarizing element is less than 8 μm. In one embodiment, the thickness of the polarizing element is less than 6 μm. In one embodiment, after the polarizing plate is subjected to a thermal shock test in a state where the polarizing plate is bonded to a glass plate through the adhesive layer, the offset of the polarizing plate at the through hole portion is less than 120 μm, and the thermal shock test is repeated 100 times at -40°C for 30 minutes and then at 85°C for 30 minutes. In one embodiment, two through holes are formed, and the through holes are both formed at positions within 11 mm from the long side and within 11 mm from the short side. In one embodiment, the absorption axis of the polarizer extends in the short side direction. In another embodiment, the absorption axis of the polarizer extends in the long side direction. According to another aspect of the present invention, a polarizing plate assembly is provided. The assembly of polarizing plates is composed of a polarizing plate whose absorption axis of the above-mentioned polarizing element extends along the short side direction and a polarizing plate whose absorption axis of the above-mentioned polarizing element extends along the long side direction, and the through holes of each polarizing plate are formed at corresponding positions. According to another aspect of the present invention, an image display device is provided. The image display device includes an image display unit and the above-mentioned polarizing plate. Another image display device of the present invention includes an assembly of an image display unit and the above-mentioned polarizing plate. One of the polarizing plates of the assembly of polarizing plates is arranged on the visual side of the image display unit, and the other polarizing plate is arranged on the back side of the image display unit.

Effect of the invention According to the implementation form of the present invention, for a polarizing plate having a through hole formed near the end, the diameter of the through hole, the formation position of the through hole and the thickness of the polarizing element are optimized, thereby realizing a polarizing plate in which cracks around the through hole are significantly suppressed.

The following is a description of specific embodiments of the present invention with reference to the drawings, but the present invention is not limited to the embodiments. In addition, the drawings are shown schematically for ease of viewing, and the ratios of length, width, thickness, etc., and angles in the drawings are different from the actual ones.

A. Polarizing plate A-1. Overall structure of polarizing plate Figure 1A is a schematic top view of a polarizing plate of one embodiment of the present invention; Figure 2 is a schematic cross-sectional view of the polarizing plate of Figure 1A along line II-II. The polarizing plate 100 of the illustrated example comprises: a polarizing element 11, a protective layer (hereinafter sometimes referred to as an outer protective layer) 12 disposed on one side of the polarizing element 11, a protective layer (hereinafter sometimes referred to as an inner protective layer) 13 disposed on the other side of the polarizing element 11, and an adhesive layer 20. Depending on the purpose and the desired structure, one of the outer protective layer 12 and the inner protective layer 13 may be omitted.

In the embodiment of the present invention, the thickness of the polarizer 11 is less than 10 μm, and preferably less than 8 μm, more preferably less than 6 μm, and even more preferably less than 5 μm. The thickness of the polarizer is, for example, greater than 1 μm, and for example, greater than 2 μm. As long as the thickness of the polarizer is within the above range, the cracks around the through hole can be significantly suppressed by the multiplication effect of the effects brought about by the optimization of the diameter of the through hole and the optimization of the formation position of the through hole. The absorption axis of the polarizer 11 can extend along the long side direction or along the short side direction.

The polarizing plate 100 is typically in a rectangular shape as shown in FIG1A. When the term "rectangular shape" is mentioned in this specification, it also includes a shape including an R-shaped portion obtained by chamfering each vertex as shown in FIG1A.

In the embodiment of the present invention, a through hole 30 is formed in the polarizing plate 100. By forming the through hole, for example, when a camera is embedded in an image display device, it is possible to prevent the performance of the camera from being adversely affected. The through hole 30 is typically formed at the end of the polarizing plate or in its vicinity, and is preferably formed at a corner as shown in the figure. By forming the through hole at the end of the polarizing plate or in its vicinity, the effect of the polarizing plate on the image display can be minimized when the polarizing plate is used in the image display device. The top view shape of the through hole 30 can adopt any appropriate shape according to the purpose and the desired structure of the image display device. A representative example can be a roughly circular shape as shown in the figure. The through hole can be formed by various methods such as laser processing, cutting using an end milling cutter, and punching using a Thompson cutter or a PINNACLE (registered trademark) cutter.

In the embodiment of the present invention, the diameter of the through hole is typically less than 5 mm, preferably 1 mm to 5 mm, and more preferably 2 mm to 4 mm. That is, as long as the diameter of the through hole is within the above range, the cracks around the through hole can be significantly suppressed by the multiplication effect brought about by the optimization of the thickness of the polarizer and the optimization of the formation position of the through hole.

In the embodiment of the present invention, the through hole 30 is formed at a position within 11 mm from the long side and within 11 mm from the short side. The through hole is preferably formed at a position within 11 mm from the long side and within 3 mm from the short side, within 3 mm from the long side and within 11 mm from the short side, within 9 mm from the long side and within 7 mm from the short side, or within 7 mm from the long side and within 9 mm from the short side; preferably, it is formed at a position within 5 mm from the long side and within 3 mm from the short side, or within 3 mm from the long side and within 5 mm from the short side; more preferably, it is formed at a position within 3 mm from the long side and within 3 mm from the short side. According to the embodiment of the present invention, it can still be applied even when a through hole is formed near the end, and cracks around the through hole can be significantly suppressed. As a result, even if the camera unit is set very close to the end in the image display device due to design requirements, a polarizing plate with excellent durability can still be achieved. Therefore, the polarizing plate of the embodiment of the present invention has a very high industrial and commercial value. In addition, in this specification, the so-called distance from the long side to the through hole is the distance from the long side (that is, the outer periphery of the polarizing plate) to the end of the outer periphery of the polarizing plate of the through hole on the straight line connecting the long side and the center of the through hole in the direction orthogonal to the long side (that is, the direction in which the short side extends), as shown in Figure 1B. Similarly, the distance from the short side to the through hole is the distance from the short side (i.e., the outer periphery of the polarizing plate) to the end of the outer periphery of the polarizing plate of the through hole on the straight line connecting the short side and the center of the through hole in a direction orthogonal to the short side (i.e., the direction in which the long side extends), as shown in FIG. 1B.

A plurality of through holes may be formed as shown in FIG1C. In the example of the figure, two through holes are formed, but the number of through holes may be three or more than four. For example, when two through holes are formed as shown in FIG1C, the two through holes are formed at positions within 11 mm from the long side and within 11 mm from the short side. The through hole is preferably formed within 11 mm from the long side and within 3 mm from the short side, within 3 mm from the long side and within 11 mm from the short side, within 9 mm from the long side and within 7 mm from the short side, or within 7 mm from the long side and within 9 mm from the short side; preferably, it is formed within 5 mm from the long side and within 3 mm from the short side, or within 3 mm from the long side and within 5 mm from the short side; more preferably, it is formed within 3 mm from the long side and within 3 mm from the short side. In addition, when two through holes are formed, for example as shown in FIG. 1C, one of them can be replaced by a thin and long elliptical through hole.

In one embodiment, as shown in FIG3 , after the polarizing plate 100 is bonded to a glass plate (which may correspond to a substrate of an image display unit) 120 through an adhesive layer 20 and subjected to a thermal shock test, the offset D of the polarizing plate at the through hole portion is preferably less than 120 μm, more preferably less than 100 μm, more preferably less than 80 μm, and particularly preferably less than 60 μm. The thermal shock test is repeated 100 times at -40°C for 30 minutes and then at 85°C for 30 minutes. The smaller the offset D, the better. The lower limit of the offset D may be, for example, 10 μm. The offset D refers to the largest portion of the polarizing plate that is away from the through hole portion when viewed in cross section. The base representative of the through hole portion can be the lower end of the adhesive layer. That is, when the polarizing plate is displaced mainly due to the contraction of the polarizer 11 (to the right in the example of the figure), the adhesive layer 20 will stay on the glass plate 120 to which it is adhered, so the displacement will be recognized in the through hole portion. In addition, as shown in FIG3, the polarizing plate is representatively displaced away from the through hole side in the through hole portion (the right side of FIG3), and at the same time, the portion opposite thereto is displaced in a manner of protruding from the through hole (the left side of FIG3). As described above, the displacement of the polarizing plate in the through hole portion is essentially the displacement of the adhesive layer. As long as the offset D is within the above range, not only can cracks around the through hole be significantly suppressed, but also light leakage caused by the offset in the image display device can be reduced.

The ratio D/R of the offset D to the diameter R of the through hole is preferably 5% to 30%, more preferably 10% to 30%. If D/R is within the above range, cracks and light leakage around the through hole can be significantly suppressed.

In the embodiment of the present invention, the ratio (%) of the residual stress in the through hole portion to the residual stress in the center of the polarizing plate is preferably 77% or less. The ratio varies depending on the diameter of the through hole. When the diameter of the through hole is 3 mm to 5 mm (for example, 4 mm), the ratio is preferably 70% or less, more preferably 68% or less, and particularly preferably 65% or less. When the diameter of the through hole is less than 3 mm (for example, 2 mm), the ratio is preferably 76% or less, more preferably 74% or less, and particularly preferably 72% or less. Regardless of the diameter of the through hole, the lower limit of the ratio may be, for example, 50%. As long as the ratio of residual stress is within the above range, cracks around the through hole can be significantly suppressed. The residual stress ratio can be achieved by adjusting the position of the through hole formation and the offset D. In addition, the "residual stress of the through hole portion" in this specification refers to the residual stress of the portion where the residual stress becomes the largest at the periphery of the through hole.

The polarizing plate of the embodiment of the present invention may have any appropriate optical functional layer according to the purpose. The optical functional layer may be, for example, a phase difference layer, a conductive layer for a touch panel, or a reflective polarizer. The type, quantity, combination, and configuration position of the optical functional layer incorporated into the polarizing plate may be appropriately set according to the purpose.

The aspect ratio of the polarizing plate of the embodiment of the present invention is preferably 1.3 to 2.5. In this case, the size of the polarizing plate is, for example, 145 mm to 155 mm long and 65 mm to 75 mm wide, or 230 mm to 240 mm long and 140 mm to 150 mm wide. That is, the polarizing plate of the embodiment of the present invention can be suitably used in a smartphone or a tablet PC. The size of a smartphone can be, for example, 120 mm to 200 mm long and 30 mm to 120 mm wide.

The following is a detailed description of the polarizer, protective layer, and adhesive layer that make up the polarizing plate.

A-2. Polarizer The polarizer is typically composed of a resin film containing a dichroic substance. As for the resin film, any appropriate resin film that can be used as a polarizer can be used. The resin film is typically a polyvinyl alcohol resin (hereinafter referred to as "PVA resin") film. The resin film can be a single-layer resin film or a laminate of two or more layers.

A specific example of a polarizer composed of a single-layer resin film is a PVA-based resin film that has been subjected to a dyeing treatment using iodine and a stretching treatment (typically uniaxial stretching). The dyeing using iodine can be performed, for example, by immersing the PVA-based resin film in an iodine aqueous solution. The stretching ratio of the uniaxial stretching is preferably 3 to 7 times. The stretching can be performed after the dyeing treatment or while the dyeing is being performed. In addition, the dyeing can be performed after the stretching. The PVA-based resin film can be subjected to a swelling treatment, a crosslinking treatment, a washing treatment, a drying treatment, etc. as required. For example, before dyeing, the PVA resin film is immersed in water and washed, which can not only clean the dirt or anti-adhesive agent on the surface of the PVA resin film, but also make the PVA resin film swell, thereby preventing uneven dyeing.

Specific examples of polarizers using laminates include a laminate using a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a laminate using a resin substrate and a PVA-based resin layer coated on the resin substrate. A polarizer obtained by using a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate can be produced, for example, by the following method: a PVA-based resin solution is coated on the resin substrate and dried 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; and the laminate is stretched and dyed to make the PVA-based resin layer into a polarizer. In this embodiment, stretching typically includes immersing the laminate in a boric acid aqueous solution and stretching it. And, if necessary, stretching can further include stretching the laminate in the air at a high temperature (e.g., above 95° C.) before stretching in the boric acid aqueous solution. The obtained resin substrate/polarizer laminate can be used directly (i.e., the resin substrate can be used as a protective layer of the polarizer), or the resin substrate can be peeled off from the resin substrate/polarizer laminate and any appropriate protective layer can be laminated on the peeled surface before use. The details of the manufacturing method of the polarizer are described in, for example, Japanese Patent Publication No. 2012-73580 and Japanese Patent No. 6470455. The description of these patent documents is cited in this specification as a reference.

The thickness of the polarizer is as described in the above item A-1.

The polarizer preferably exhibits absorption dichroism at any wavelength of 380nm to 780nm. The single body transmittance of the polarizer is, for example, 41.5% to 46.0%, preferably 43.0% to 46.0%, more preferably 44.5% to 46.0%. The polarization degree of the polarizer is preferably 97.0% or more, preferably 99.0% or more, and even more preferably 99.9% or more.

A-3. Protective layer The protective layer is formed of any suitable film that can be used as a protective layer for a polarizer. Specific examples of the material that is the main component of the film include cellulose resins such as triacetate cellulose (TAC), polyester resins, polyvinyl alcohol resins, polycarbonate resins, polyamide resins, polyimide resins, polyether sulfone resins, polysulfone resins, polystyrene resins, polynorbornene resins, polyolefin resins, (meth)acrylic acid resins, acetate resins, and other transparent resins. In addition, thermosetting resins or ultraviolet curing resins such as (meth)acrylic acid resins, urethane resins, (meth)acrylic acid urethane resins, epoxy resins, and polysilicone resins can also be cited. Other examples include glassy polymers such as silicone polymers. Furthermore, the polymer film described in Japanese Patent Publication No. 2001-343529 (WO01/37007) can also be used. As the material of the film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted amide group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in the side chain can be used, for example, a resin composition containing an alternating copolymer composed of isobutylene and N-methylmaleimide and an acrylonitrile-styrene copolymer can be used. The polymer film can be, for example, an extruded product of the above resin composition.

The outer protective layer 12 (especially when the polarizing plate is a viewing side polarizing plate) can also be subjected to surface treatments such as hard coating, anti-reflection, anti-adhesion, and anti-glare treatments as needed. And/or, the outer protective layer 12 can also be subjected to treatments to improve visibility when viewed through polarized sunglasses (typically, providing (elliptical) circular polarization function and providing ultra-high phase difference) as needed. By performing the above treatments, even when viewing the display screen through polarized lenses such as polarized sunglasses, excellent visibility can still be achieved. Therefore, the polarizing plate can also be suitably used in image display devices that can be used outdoors.

The inner protective layer is preferably optically isotropic. In this specification, "optically isotropic" means that the in-plane phase difference Re(550) is 0nm~10nm, and the phase difference in the thickness direction Rth(550) is -10nm~+10nm. Here, "Re(λ)" is the in-plane phase difference measured at 23°C with light of wavelength λnm. For example, "Re(550)" is the phase difference in the thickness direction measured at 23°C with light of wavelength 550nm. Re(λ) can be calculated by the formula: Re(λ)=(nx-ny)×d when the thickness of the layer (film) is d(nm). In addition, "Rth(λ)" is the phase difference in the thickness direction measured at 23°C with light of wavelength λnm. For example, "Rth(550)" is the phase difference in the thickness direction measured at 23°C with light of a wavelength of 550nm. Rth(λ) can be obtained by the formula: Rth(λ)=(nx-nz)×d when the thickness of the layer (film) is d(nm). In addition, nx is the refractive index in the direction where the refractive index in the plane is the largest (i.e., the slow axis direction), ny is the refractive index in the direction orthogonal to the slow axis in the plane (i.e., the fast axis direction), and nz is the refractive index in the thickness direction.

The thickness of the protective layer can be any appropriate thickness. The thickness of the protective layer is, for example, 10 μm to 50 μm, and preferably 20 μm to 40 μm. In addition, when surface treatment is applied, the thickness of the protective layer includes the thickness of the surface treatment layer.

A-4. Adhesive layer The adhesive layer 20 is typically used to attach the polarizing plate to the image display unit. The adhesive layer is typically composed of an acrylic adhesive (acrylic adhesive composition). The acrylic adhesive composition typically includes a (meth)acrylic polymer as a main component. The (meth)acrylic polymer can be contained in the adhesive composition at a ratio of, for example, 50% by weight or more, preferably 70% by weight or more, and more preferably 90% by weight or more in the solid component of the adhesive composition. The (meth)acrylic polymer contains an alkyl (meth)acrylate as a main component as a monomer unit. In addition, (meth)acrylate refers to acrylate and/or methacrylate. The alkyl (meth)acrylate is preferably contained in the monomer component forming the (meth)acrylic polymer at a ratio of 80% by weight or more, preferably 90% by weight or more. The alkyl group of the (meth)acrylic acid alkyl ester may be, for example, a straight or branched chain alkyl group having 1 to 18 carbon atoms. The average carbon number of the alkyl group is preferably 3 to 9, more preferably 3 to 6. A preferred (meth)acrylic acid alkyl ester is butyl acrylate. In addition to the (meth)acrylic acid alkyl ester, the monomers (co-monomers) constituting the (meth)acrylic acid polymer may include carboxyl-containing monomers, hydroxyl-containing monomers, amide-containing monomers, aromatic ring-containing (meth)acrylic acid esters, heterocyclic vinyl-containing monomers, etc. Representative examples of copolymers include acrylic acid, 4-hydroxybutyl acrylate, phenoxyethyl acrylate, and N-vinyl-2-pyrrolidone. The acrylic adhesive composition preferably contains a silane coupling agent and/or a crosslinking agent. Examples of silane coupling agents include epoxy-containing silane coupling agents. Examples of crosslinking agents include isocyanate crosslinking agents and peroxide crosslinking agents. In addition, the acrylic adhesive composition may also contain an antioxidant and/or a conductive agent. By adjusting the type, amount, combination and copolymerization ratio of the monomer units, the type, amount, combination and blending ratio of the silane coupling agent, and the type, amount, combination and blending ratio of the crosslinking agent, an acrylic adhesive composition (in terms of the result, an adhesive layer) having the desired properties corresponding to the purpose can be obtained. As a result, the above-mentioned desired offset D can be achieved in the embodiment of the present invention. The details of the adhesive layer or the acrylic adhesive composition are described in, for example, Japanese Patent Publication No. 2006-183022, Japanese Patent Publication No. 2015-199942, Japanese Patent Publication No. 2018-053114, Japanese Patent Publication No. 2016-190996, and International Publication No. 2018/008712, and this specification refers to the descriptions of these publications as references.

The thickness of the adhesive layer is preferably 5 μm to 50 μm, more preferably 10 μm to 30 μm. As long as the thickness of the adhesive layer is within the above range, the above-mentioned desired offset D can be achieved.

The storage elastic modulus G' of the adhesive layer at -40°C is preferably 1.0×10 ⁵ (Pa) or more, more preferably 1.0×10 ⁶ (Pa) or more, more preferably 1.0×10 ⁷ (Pa) or more, and particularly preferably 1.0×10 ⁸ (Pa) or more. The storage elastic modulus G' may be, for example, 1.0×10 ⁹ (Pa) or less. As long as the storage elastic modulus of the adhesive layer at -40°C is within the above range, the above-mentioned desired deflection amount D can be achieved.

B. Assembly of polarizing plates The polarizing plate described in item A above can be used as a viewing side polarizing plate or as a back side polarizing plate. By combining two specific implementation forms of the polarizing plates described in item A above, an assembly of polarizing plates can be provided. Therefore, the implementation form of the present invention also includes the assembly of polarizing plates. In the assembly of polarizing plates, each through hole of the two polarizing plates constituting the assembly is formed at a position corresponding to each other. In this specification, "formed at a position corresponding to each other" means that the through holes will overlap when the two polarizing plates are stacked.

In one embodiment, the polarizing plate assembly is composed of a polarizing plate whose absorption axis extends along the short side direction and a polarizing plate whose absorption axis extends along the long side direction. At this time, the through holes of the two polarizing plates are typically formed at a position within 11 mm from the long side and within 11 mm from the short side; preferably, they are formed at a position within 11 mm from the long side and within 3 mm from the short side, within 3 mm from the long side and within 11 mm from the short side, within 9 mm from the long side and within 7 mm from the short side, or within 7 mm from the long side and within 9 mm from the short side; more preferably, they are formed at a position within 5 mm from the long side and within 3 mm from the short side, or within 3 mm from the long side and within 5 mm from the short side; more preferably, they are formed at a position within 3 mm from the long side and within 3 mm from the short side; and they are formed at positions corresponding to each other.

C. Image display device The polarizing plate and the assembly of polarizing plates of the embodiment of the present invention can be applied to an image display device. Therefore, the image display device is also included in the embodiment of the present invention. In one embodiment, the image display device includes an image display unit and a polarizing plate. The polarizing plate is the polarizing plate of the embodiment of the present invention described in item A above. The polarizing plate is attached to the image display unit through an adhesive layer. In another embodiment, the image display device includes an image display unit and an assembly of polarizing plates. The assembly of polarizing plates is the assembly of polarizing plates of the embodiment of the present invention described in item B above. At this time, one of the polarizing plates of the assembly of polarizing plates is arranged on the visual side of the image display unit, and the other polarizing plate is arranged on the back side of the image display unit. The image display device may be, for example, a liquid crystal display device, an organic electroluminescent (EL) display device, or a quantum dot display device. Implementation Example

The present invention is specifically described below with reference to the examples, but the present invention is not limited to the examples. The evaluation items of the examples are as follows. In addition, unless otherwise specified, the "parts" and "%" in the examples are by weight.

(1) Offset The polarizing plates obtained in the examples and comparative examples were attached to a glass plate (Matsunami Glass Ind., Ltd., length 350 mm × width 250 mm × thickness 1.1 mm) through an adhesive layer to prepare a test sample. The test sample was subjected to the following thermal shock test: 100 cycles of maintaining at -40°C for 30 minutes and then maintaining at 85°C for 30 minutes. The heating and cooling rate of the thermal shock test was 10°C/minute. After the test, the offset of the polarizing plate in the through hole portion (essentially the adhesive layer) was measured using an optical microscope (MX61L) manufactured by OLYMPUS. In addition, the measurement was performed on three test samples, and the maximum value of the three measured values was taken as the offset. (2) Cracks The polarizing plates obtained in the examples and comparative examples were subjected to a thermal shock test in the same manner as the "offset" in (1) above. The cracks in the through-holes after the test were observed using an optical microscope (MX61L) manufactured by OLYMPUS Corporation and evaluated according to the following criteria. AA: No cracks were observed A: Only small cracks less than 300μm in length were observed B: Although cracks with a length of 300μm to 1mm were observed, no light leakage occurred C: Significant cracks and light leakage occurred

<Production Example 1> A monomer mixture containing 80.3 parts of butyl acrylate, 16 parts of phenoxyethyl acrylate, 3 parts of N-vinyl-2-pyrrolidone, 0.3 parts of acrylic acid and 0.4 parts of 4-hydroxybutyl acrylate was added to a 4-necked flask equipped with a stirring blade, a thermometer, a nitrogen inlet tube and a cooler. And 0.1 parts of 2,2'-azobisisobutyronitrile as a polymerization initiator and 100 parts by weight of ethyl acetate were added to 100 parts of the monomer mixture (solid component). After nitrogen was introduced while slowly stirring to replace the nitrogen, the liquid temperature in the flask was maintained at about 55°C, and a polymerization reaction was carried out for 8 hours to prepare a solution of an acrylic polymer with a weight average molecular weight (Mw) of 1.5 million. With respect to 100 parts of the solid content of the obtained acrylic polymer solution, 0.1 parts of an isocyanate crosslinking agent (trade name: TAKENATE D160N, trihydroxymethyl propane hexamethylene diisocyanate, manufactured by Mitsui Chemicals Co., Ltd.), 0.3 parts of benzoyl peroxide (trade name: NYPER BMT 40SV, manufactured by NOF Corporation), 0.1 parts of a thiol-containing silane coupling agent (trade name: X-41-1810, manufactured by Shin-Etsu Chemical Co., Ltd., alkoxy content: 30%, thiol equivalent: 450 g/mol), and 0.1 parts of an antioxidant (trade name: Irganox 1010, hindered phenol, manufactured by BASF Japan Co., Ltd.) and 5 parts of a conductive agent (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, an ionic liquid manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) to obtain an adhesive composition.

<Example 1> The thermoplastic resin substrate is a long amorphous isophthalic acid copolymer polyethylene terephthalate film (thickness: 100μm) with a Tg of about 75°C, and a corona treatment is applied to one side of the resin substrate. 13 parts by weight of potassium iodide is added to 100 parts by weight of a PVA-based resin prepared by mixing polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER") in a ratio of 9:1, and the resulting mixture is dissolved in water to prepare a PVA aqueous solution (coating liquid). The PVA aqueous solution was applied to the corona treated surface of the resin substrate and dried at 60°C to form a PVA resin layer with a thickness of 13 μm, thereby producing a laminate. The obtained laminate was uniaxially stretched to 2.4 times in the longitudinal direction (long side direction) in an oven at 130°C (air-assisted stretching treatment). Then, the laminate was immersed in an insolubilizing bath (a boric acid aqueous solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (insolubilizing treatment). Then, the film was immersed in a dyeing bath (an iodine aqueous solution obtained by mixing iodine and potassium iodide at a weight ratio of 1:7 relative to 100 parts by weight of water) with a liquid temperature of 30°C for 60 seconds to adjust the concentration so that the monomer transmittance (Ts) of the polarizer obtained finally becomes the desired value (dyeing treatment). Then, it was immersed in a crosslinking bath (an aqueous boric acid solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid relative to 100 parts by weight of water) with a liquid temperature of 40°C for 30 seconds (crosslinking treatment). Then, the laminate was immersed in a boric acid aqueous solution (boric acid concentration 4 weight%, potassium iodide concentration 5 weight%) at a liquid temperature of 70°C, and simultaneously uniaxially stretched in the longitudinal direction (long side direction) between rollers of different circumferential speeds to achieve a total stretching ratio of 5.5 times (underwater stretching treatment). Afterwards, the laminate was immersed in a cleaning bath (aqueous solution obtained by mixing 4 weight parts of potassium iodide with 100 weight parts of water) at a liquid temperature of 20°C (cleaning treatment). Afterwards, it was dried in an oven maintained at about 90°C while contacting a SUS heating roller maintained at a surface temperature of about 75°C (drying shrinkage treatment). According to the above method, a polarizer with a thickness of about 5 μm is formed on the resin substrate, and a laminate having a structure of resin substrate/polarizer is obtained.

The HC-TAC film is bonded to the surface of the polarizer of the above-mentioned laminate. In addition, the HC-TAC film is a film having a hard coating (HC) layer (thickness 7μm) formed on a cellulose triacetate (TAC) film (thickness 25μm), and the TAC film is bonded to form the side of the polarizer. Next, the resin substrate is peeled off, and an adhesive layer (thickness 20μm) is formed on the peeled surface using the adhesive composition of Manufacturing Example 1 to obtain a long strip of polarizing plate having the structure of HC layer/outer protective layer/polarizer/adhesive layer. The polarizing plate is punched into a shape with a length of 142.0mm and a width of 66.8mm and an R portion of R 7.0mm is set at the four corners. At this time, punching is performed in a manner that the absorption axis direction of the polarizer is the short side direction. A through hole with a diameter of 4 mm is formed at a position 2 mm away from the long side and 2 mm away from the short side. The through hole can be formed by end milling. The feed speed of the end mill is 500 mm/min, the number of rotations is 2500 rpm, and the cutting amount is 0.1 mm. A polarizing plate with a through hole is produced in the above manner. The obtained polarizing plate is provided for the evaluation of (2) above. The results are shown in Table 1 together with the detailed structure of the polarizing plate. In addition, in Table 1, "0°" refers to the long side direction, and "90°" refers to the short side direction.

<Example 2> A polarizing plate was produced in the same manner as in Example 1 except that the through-holes were formed at positions 6 mm from the long side and 4 mm from the short side. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1 together with the detailed structure of the polarizing plate.

<Examples 3 to 6> Except that the through-hole formation positions are set to the positions shown in Table 1, polarizing plates are produced in the same manner as in Example 1. The obtained polarizing plates are subjected to the same evaluation as in Example 1. The results are shown in Table 1 together with the detailed structure of the polarizing plates.

<Example 7> A long strip polarizing plate was obtained in the same manner as in Example 1. The polarizing plate was punched into a shape with a length of 142.0 mm and a width of 66.8 mm and an R portion of 7.0 mm was set at the four corners. At this time, the punching was performed in a manner that the absorption axis direction of the polarizer was the long side direction. The following procedure was performed in the same manner as in Example 1 to produce a polarizing plate having through holes with a diameter of 4 mm at a distance of 2 mm from the long side and 2 mm from the short side. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1 together with the detailed structure of the polarizing plate.

<Example 8> A polarizing plate was produced in the same manner as Example 7 except that the through-holes were formed at 6 mm from the long side and 4 mm from the short side. The obtained polarizing plate was subjected to the same evaluation as Example 1. The results are shown in Table 1 together with the detailed structure of the polarizing plate.

<Examples 9 to 12> Except that the through-hole formation positions are set to the positions shown in Table 1, polarizing plates are produced in the same manner as in Example 7. The obtained polarizing plates are subjected to the same evaluation as in Example 1. The results are shown in Table 1 together with the detailed structure of the polarizing plates.

<Example 13> A polarizing plate was produced in the same manner as in Example 1 except that a through hole with a diameter of 2 mm was formed. In addition, the through hole was formed by CO ₂ laser. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1 together with the detailed structure of the polarizing plate.

<Example 14> A polarizing plate was produced in the same manner as in Example 13 except that the through-holes were formed at 6 mm from the long side and 4 mm from the short side. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1 together with the detailed structure of the polarizing plate.

<Examples 15 to 18> Except that the through-hole formation positions are set to the positions shown in Table 1, polarizing plates are produced in the same manner as in Example 13. The obtained polarizing plates are subjected to the same evaluation as in Example 1. The results are shown in Table 1 together with the detailed structure of the polarizing plates.

<Example 19> Except for forming a through hole with a diameter of 2 mm, a polarizing plate was produced in the same manner as in Example 7. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1 together with the detailed structure of the polarizing plate.

<Example 20> A polarizing plate was produced in the same manner as in Example 19 except that the through-holes were formed at positions 6 mm from the long side and 4 mm from the short side. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1 together with the detailed structure of the polarizing plate.

<Examples 21 to 24> Except that the through-hole formation positions were set to the positions shown in Table 1, polarizing plates were produced in the same manner as in Example 19. The obtained polarizing plates were subjected to the same evaluation as in Example 1. The results are shown in Table 1 together with the detailed structure of the polarizing plates.

<Comparative Example 1> The polarizer is a film (thickness 12μm) obtained by adding iodine to a long strip of polyvinyl alcohol (PVA) resin film and uniaxially stretching it along the long side direction (MD direction). On both sides of the polarizer, a long strip of HC-TAC film to be used as an outer protective layer and a long strip of acrylic resin film (thickness 20μm) to be used as an inner protective layer are respectively bonded in a manner that the long sides of both sides are aligned. In addition, the HC-TAC film is a TAC film bonded to form the polarizer side. An adhesive layer (thickness 20μm) is formed on the surface of the inner protective layer using the adhesive composition of Manufacturing Example 1 to obtain a long strip of polarizing plate. The polarizing plate was punched into a shape with a length of 142.0 mm and a width of 66.8 mm and an R portion of 7.0 mm was set at the four corners. At this time, the punching was performed in a manner that the absorption axis direction of the polarizer was the short side direction. A through hole with a diameter of 4 mm was formed at a position 8 mm away from the long side and 6 mm away from the short side in the same manner as in Example 1. A polarizing plate with a through hole was produced in the above manner. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1 together with the detailed structure of the polarizing plate.

<Comparative Example 2> A polarizing plate was produced in the same manner as in Comparative Example 1 except that the through-holes were formed at positions 10 mm from the long side and 8 mm from the short side. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1 together with the detailed structure of the polarizing plate.

<Comparative Example 3> A long strip polarizing plate was obtained in the same manner as in Comparative Example 1. The polarizing plate was punched into a shape with a length of 142.0 mm and a width of 66.8 mm and an R portion of 7.0 mm was set at the four corners. At this time, the punching was performed in a manner that the absorption axis direction of the polarizer was the long side direction. The following procedure was performed in the same manner as in Comparative Example 1 to produce a polarizing plate having a through hole of 4 mm in diameter at a distance of 8 mm from the long side and 6 mm from the short side. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1 together with the detailed structure of the polarizing plate.

<Comparative Example 4> A polarizing plate was produced in the same manner as in Comparative Example 3 except that the through-holes were formed at positions 10 mm from the long side and 8 mm from the short side. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1 together with the detailed structure of the polarizing plate.

<Comparative Example 5> A polarizing plate was produced in the same manner as in Comparative Example 1 except that the through hole was formed at a position 6 mm from the long side and 4 mm from the short side, and the diameter of the through hole was set to 2 mm. In addition, the through hole was formed by CO ₂ laser. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1 together with the detailed structure of the polarizing plate.

<Comparative Examples 6-7> Except that the through-hole formation positions are set to the positions shown in Table 1, polarizing plates are produced in the same manner as in Comparative Example 5. The obtained polarizing plates are subjected to the same evaluation as in Example 1. The results are shown in Table 1 together with the detailed structure of the polarizing plates.

<Comparative Example 8> A polarizing plate was produced in the same manner as in Comparative Example 3 except that the through hole was formed at a position 6 mm from the long side and 4 mm from the short side, and the diameter of the through hole was set to 2 mm. In addition, the through hole was formed by CO ₂ laser. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1 together with the detailed structure of the polarizing plate.

<Comparative Examples 9-10> Except that the through-hole formation positions are set to the positions shown in Table 1, polarizing plates are produced in the same manner as in Comparative Example 8. The obtained polarizing plates are subjected to the same evaluation as in Example 1. The results are shown in Table 1 together with the detailed structure of the polarizing plates.

<Example 25> A resin substrate/polarizer laminate is obtained in the same manner as in Example 1. A HC-COP film is bonded to the polarizer surface of the laminate. The HC-COP film is a film having an HC layer (thickness 2μm) formed on a cycloolefin resin (COP) film (thickness 25μm), and the COP film is bonded to form the polarizer side. Next, the resin substrate is peeled off, and after a COP film is attached to the peeled surface, an adhesive layer (thickness 20 μm) is formed on the surface of the COP film using the adhesive composition of Manufacturing Example 1, and a long strip of polarizing plate having the structure of HC layer/outer protective layer/polarizer/inner protective layer/adhesive layer is obtained. The polarizing plate is punched into a shape with a length of 142.0 mm and a width of 66.8 mm and an R portion of R 7.0 mm is set at the four corners. At this time, the punching is performed in a manner that the absorption axis direction of the polarizer is the short side direction. A through hole with a diameter of 3.9 mm is formed at a position 2.6 mm away from the long side and 4.3 mm away from the short side. A polarizing plate with through holes was prepared in the above manner and the obtained polarizing plate was subjected to the same evaluation as in Example 1.

<Example 26> A long strip polarizing plate was obtained in the same manner as in Example 25. The polarizing plate was punched into a shape with a length of 142.0 mm and a width of 66.8 mm and an R portion of 7.0 mm was provided at the four corners. At this time, the punching was performed in such a way that the absorption axis direction of the polarizer was the long side direction. The following procedure was performed in the same manner as in Example 25 to produce a polarizing plate having a through hole of 3.9 mm in diameter at a distance of 2.6 mm from the long side and 4.3 mm from the short side. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1 together with the detailed structure of the polarizing plate.

[Table 1]

It is obvious from Table 1 that the polarizing plate of the embodiment of the present invention has significantly suppressed the generation of cracks in the through-hole portion after the thermal shock test by reducing the thickness of the polarizer.

Industrial Applicability The polarizing plate of the present invention can be suitably used in image display devices, and in particular, can be suitably used in image display devices with camera parts, such as smart phones, tablet PCs or smart watches.

11: Polarizer 12: Outer protective layer 13: Inner protective layer 20: Adhesive layer 30: Through hole 100: Polarizer 120: Glass plate R: Through hole diameter D: Offset II-II: Line

FIG. 1A is a schematic top view of a polarizing plate according to one embodiment of the present invention. FIG. 1B is a schematic view of the formation position of a through hole in a polarizing plate according to an embodiment of the present invention. FIG. 1C is a schematic top view of a polarizing plate according to an embodiment of the present invention in which a plurality of through holes are formed. FIG. 2 is a schematic cross-sectional view of the polarizing plate according to FIG. 1 along the II-II line. FIG. 3 is an enlarged cross-sectional view of a key portion of the polarizing plate according to an embodiment of the present invention showing the offset of the through hole portion.

30:Through hole

II-II: Line

Claims (9)

A polarizing plate is a rectangular polarizing plate with a through hole formed therein, and comprises: a polarizer, a protective layer disposed on at least one side of the polarizer, and an adhesive layer; the thickness of the polarizer is less than 10 μm; the diameter of the through hole is less than 5 mm; and the through hole is formed at a position within 11 mm from the long side and within 11 mm from the short side; after the polarizing plate is subjected to a thermal shock test in a state where it is bonded to a glass plate through the adhesive layer, the displacement of the polarizing plate at the through hole portion is less than 120 μm, and the thermal shock test is repeated 100 cycles of maintaining at -40°C for 30 minutes and then maintaining at 85°C for 30 minutes. As in claim 1, the polarizing plate, wherein the thickness of the aforementioned polarizing element is less than 8μm. As in claim 2, the polarizing plate, wherein the thickness of the aforementioned polarizing element is less than 6 μm. A polarizing plate as claimed in any one of claims 1 to 3, wherein the through holes are formed in two numbers, and the through holes are formed at positions within 11 mm from the long side and within 11 mm from the short side. A polarizing plate as claimed in any one of claims 1 to 3, wherein the absorption axis of the polarizer extends along the short side direction. A polarizing plate as claimed in any one of claims 1 to 3, wherein the absorption axis of the polarizer extends along the long side direction. A polarizing plate assembly is composed of a polarizing plate as in claim 5 and a polarizing plate as in claim 6, and the through holes of each polarizing plate are formed at positions corresponding to each other. An image display device, comprising an image display unit and a polarizing plate as described in any one of claims 1 to 3. An image display device comprises an image display unit and a polarizing plate assembly as in claim 7; one polarizing plate of the polarizing plate assembly is disposed on the visual side of the image display unit, and the other polarizing plate is disposed on the back side of the image display unit.

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