WO2019167420A1 - Polarization plate and manufacturing method therefor - Google Patents

Abstract

A sheet polarization plate (10) is provided with a transparent film (31, 32) on at least one surface of a polyvinyl alcohol-based polarizer (21). The polarizer is preferably denatured by irradiating an end surface of the polarization plate obtained by being cut into a sheet, with a light beam having a wavelength in which the light beam can be absorbed by the polarizer. A ratio A3300/A1089 of an absorbance A3300 of a peak around 3300 cm-1 to an absorbance A1089 of a peak around 1089 cm-1 in an infrared absorption spectrum at an end part in a surface of the polarizer having been subjected to the denaturation is preferably less than A3300/A1089 in the infrared absorption spectrum at the center part in the surface.

Description

Polarizing plate and manufacturing method thereof

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

Liquid crystal display devices and organic EL display devices are widely used as various image display devices such as mobile devices, car navigation devices, personal computer monitors, and televisions. In the liquid crystal display device, a polarizing plate is disposed on the viewing side surface of the liquid crystal cell because of its display principle. In the transmissive liquid crystal display device, polarizing plates are arranged on both surfaces of the liquid crystal cell. In an organic EL display device, in order to prevent external light from being reflected by a metal electrode (cathode) and viewed like a mirror surface, a circularly polarizing plate (typically, a polarizing plate and 1 / There are cases where a laminate of four-wave plates is disposed.

As a polarizer constituting a polarizing plate, a polarizer in which iodine is adsorbed on a polyvinyl alcohol (PVA) film and molecules are oriented by stretching or the like is widely used. Since polyvinyl alcohol has high hydrophilicity, the polyvinyl alcohol polarizer is easily deteriorated by moisture absorption. Therefore, in general, a polarizer protective film is bonded to one or both main surfaces of a polyvinyl alcohol polarizer.

Even when a polarizer protective film is bonded to the main surface of the polarizer, the end face of the polarizer is exposed, so that moisture intrusion from the end face causes deterioration of the polarizer around the polarizing plate, resulting in color loss. Cheap. In order to prevent the deterioration of the polarizer on the end face of the polarizing plate, Patent Document 1 discloses a method in which the end face of the polarizing plate is sealed with an ultraviolet curable resin or a thermosetting resin to suppress moisture from entering from the end face. Proposed. In Patent Document 2, laser light is irradiated from the main surface to the periphery of the polarizing plate, and the polarizer protective film provided on the main surface of the polarizer is melted to form a thick portion covering the end surface of the polarizer. It is described that the crack resistance of the end face can be improved.

JP 2011-22202 A JP 2012-173588 A

In recent years, display devices have become narrower and bezelless, mainly for mobile devices such as smartphones. Conventionally, the peripheral portion of the polarizing plate (for example, an area of about 1 mm from the end face) is accommodated in the housing of the image display device and has not been visually recognized from the outside, but with the narrowing of the frame and the bezellessness, The peripheral part of the polarizing plate is also used as a display area. In the processing methods described in Patent Literature 1 and Patent Literature 2, a resin layer for sealing and a thick portion by laser processing are formed on the peripheral portion of the polarizing plate, so that the frame is narrowed or the bezelless is narrowed. Not suitable for.

When chemicals or cosmetics adhering to the human body enter the polarizer from the end face of the polarizing plate, the end face of the polarizer tends to deteriorate significantly. Therefore, not only the durability against moisture but also the durability against chemicals is required for the polarizing plate.

The present invention relates to a single-wafer polarizing plate provided with a transparent film on at least one surface of a polyvinyl alcohol polarizer and a method for producing the same.

The polarizer in the polarizing plate of the present invention has a ratio A ₃₃₀₀ / A ₁₀₈₉ of the absorbance A ₁₀₈₉ at the peak near ₁₀₈₉ cm ⁻¹ and the absorbance A _{3300 at} the peak near ₃₃₀₀ cm ⁻¹ in the infra-red absorption spectrum at the end of the plane. However, it is preferable that it is smaller than _A3300 / _A1089 in the infrared absorption spectrum of the center part in a surface. The A ₃₃₀₀ / A ₁₀₈₉ at the end in the plane of the polarizer is preferably 0.97 times or less the A ₃₃₀₀ / A _{1089 at} the center in the plane.

In producing a polarizing plate, first, a polarizing plate having a relatively large size is cut to cut out a single-wafer polarizing plate. A relatively large polarizing plate is, for example, a long polarizing plate manufactured by a roll-to-roll method. In the manufacturing method of this invention, the polarizer of the end surface of a polarizing plate is modified | denatured by irradiating the light beam of the wavelength which a polarizer can absorb to the end surface of the polarizing plate after cutting out. The light irradiation to the polarizing plate cut out in a sheet may be performed in a state where a plurality of polarizing plates are laminated.

The light beam applied to the end face of the polarizer is preferably incoherent light. Pulse irradiation may be sufficient as the light irradiation to the end surface of a polarizer. The pulse time width in the pulse irradiation is preferably 10 microseconds to 100 milliseconds.

According to the present invention, even when exposed to a high temperature and high humidity environment with chemicals attached, a polarizing plate that is less likely to fade at the end and has excellent durability can be obtained.

FIG. 1A is a plan view schematically illustrating an embodiment of a single-wafer polarizing plate, and FIG. 1B is a schematic cross-sectional view illustrating a cross section taken along line B1-B2 of FIG. 1A. It is a conceptual diagram showing a mode that the light irradiation to the end surface of a polarizing plate in the state which laminated | stacked the several polarizing plate is performed.

The present invention relates to a single-wafer polarizing plate having a transparent film as a polarizer protective film on at least one surface of a polyvinyl alcohol-based polarizer, wherein the polarizer is denatured at the end surface.

[Configuration of polarizing plate]
1A is a plan view of the polarizing plate 10, and FIG. 1B is a cross-sectional view taken along line B1-B2 of FIG. 1A. The polarizing plate shown in FIG. 1B includes a first polarizer protective film 31 on one surface of a polyvinyl alcohol (PVA) polarizer 21 and a second polarizer protective film 32 on the other surface of the polarizer 21.

<Polarizer>
The polarizer 21 is a polyvinyl alcohol (PVA) film containing iodine. Polyvinyl alcohol or a derivative thereof is used as a material for the PVA film applied to the polarizer. Derivatives of polyvinyl alcohol include polyvinyl formal, polyvinyl acetal and the like, olefins such as ethylene and propylene, unsaturated carboxylic acids such as acrylic acid, methacrylic acid and crotonic acid, alkyl esters thereof, acrylamide and the like. Can be mentioned. Polyvinyl alcohol having a polymerization degree of about 1000 to 10,000 and a saponification degree of about 80 to 100 mol% is generally used.

A polarizer is obtained by subjecting a PVA film to iodine staining and stretching. In the production process of the polarizer, treatments such as washing with water, swelling, and crosslinking may be performed as necessary. Stretching may be performed before or after iodine dyeing, or may be performed while dyeing. Stretching may be either stretching in the air (dry stretching) or stretching in water or an aqueous solution containing boric acid, potassium iodide, etc. (wet stretching), and these may be used in combination.

As the PVA polarizer, a thin polarizer having a thickness of 10 μm or less can be used. Thin polarizers are described in, for example, JP-A-51-069644, JP-A-2000-338329, WO2010 / 100917, Patent No. 4691205, Patent No. 4751481, and the like. A thin polarizer may be mentioned. These thin polarizers are obtained by a production method including a step of stretching a PVA-based resin layer and a stretching resin base material in the state of a laminate, and a step of iodine staining.

<Polarizer protective film>
In the polarizing plate 10, transparent films are bonded to both main surfaces of the polarizer 21 as the polarizer protective films 31 and 32. 1B shows a form in which the transparent protective films 31 and 32 are provided on both surfaces of the polarizer 21, but the polarizer protective film may be provided on only one surface of the polarizer 21. Good.

As a material constituting the polarizer protective films 31 and 32, a thermoplastic resin excellent in transparency, mechanical strength, and thermal stability is preferable. Specific examples of the thermoplastic resin include cellulose resins such as triacetyl cellulose, polyester resins, polyether sulfone resins, polysulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meta ) Acrylic resins, cyclic polyolefin resins (norbornene resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof.

When the polarizer protective films 31 and 32 are provided on both surfaces of the polarizer 21, films made of the same resin material may be used on the front and back sides, or films made of different resin materials may be used. In addition, for the purpose of optical compensation of the liquid crystal cell, expansion of the viewing angle, and the like, an optical anisotropic film such as a retardation plate (stretched film) can also be used as a polarizer protective film. The polarizer protective film may be a λ / 4 plate, and the polarizer and the polarizer protective film may constitute a circularly polarizing plate. For example, by disposing a circularly polarizing plate on the viewing side surface of the organic EL element, it is possible to improve the visibility of display by shielding the reflection of external light by a metal electrode or the like.

The thickness of the polarizer protective film is not particularly limited, but is preferably about 5 to 100 μm, more preferably 10 to 80 μm from the viewpoints of workability such as strength and handleability, and thin film properties.

<Adhesive>
It is preferable that the polarizer 21 and the polarizer protective films 31 and 32 are bonded through an appropriate adhesive layer (not shown). The adhesive used for bonding the PVA polarizer and the polarizer protective film is not particularly limited as long as it is optically transparent. Epoxy resin, silicone resin, acrylic resin, polyurethane, polyamide , Polyether, polyvinyl alcohol and the like. The thickness of the adhesive is preferably 5 μm or less, more preferably 0.01 to 3 μm, and even more preferably 0.05 to 2 μm.

As the adhesive, various forms such as a water-based adhesive, a solvent-based adhesive, a hot-melt adhesive, and an active energy ray-curable adhesive are used. Among these, a water-based adhesive or an active energy ray-curable adhesive is preferable because the thickness of the adhesive layer can be reduced.

Examples of the water-based adhesive include those containing a water-soluble or water-dispersible polymer such as vinyl polymer, gelatin, vinyl latex, polyurethane, isocyanate, polyester, and epoxy. An adhesive layer made of such an aqueous adhesive is formed by applying an aqueous solution on a film and drying it. In preparing the aqueous solution, a catalyst such as a crosslinking agent, other additives, and an acid can be blended as necessary.

As the polymer of the water-based adhesive, a polyvinyl alcohol-based resin is preferable because it is excellent in adhesiveness with a PVA-based polarizer, and a polymer containing a polyvinyl alcohol-based resin having an acetoacetyl group is preferable in terms of improving adhesion durability. Particularly preferred. In the water-based adhesive, a compound having at least two functional groups having reactivity with the polyvinyl alcohol-based resin can be blended as a crosslinking agent. Such cross-linking agents include boric acid and borax; carboxylic acid compounds; alkyl diamines; isocyanates; epoxies; monoaldehydes; dialdehydes; amino-formaldehyde resins; And oxides thereof.

The active energy ray-curable adhesive is an adhesive capable of radical polymerization, cationic polymerization, or anion polymerization by irradiation with active energy rays such as electron beams and ultraviolet rays. Among these, a photo-radical polymerizable adhesive that initiates radical polymerization upon irradiation with ultraviolet rays is preferable because it can be cured with low energy.

Examples of the monomer for the radical polymerizable adhesive include a compound having a (meth) acryloyl group and a compound having a vinyl group. Among these, a compound having a (meth) acryloyl group is preferable. Examples of the compound having a (meth) acryloyl group include a C _1-20 chain alkyl (meth) acrylate, an alicyclic alkyl (meth) acrylate, an alkyl (meth) acrylate such as a polycyclic alkyl (meth) acrylate; a hydroxyl group Containing (meth) acrylate; Epoxy group-containing (meth) acrylate such as glycidyl (meth) acrylate and the like. Radical polymerizable adhesives are hydroxyethyl (meth) acrylamide, N-methylol (meth) acrylamide, N-methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, (meth) acrylamide, (meth) acryloylmorpholine Nitrogen-containing monomers such as The radical polymerizable adhesive is composed of tripropylene glycol diacrylate, 1,9-nonanediol diacrylate, tricyclodecane dimethanol diacrylate, cyclic trimethylolpropane formal acrylate, dioxane glycol diacrylate, EO modified diester as a crosslinking component. A polyfunctional monomer such as glycerin tetraacrylate may be included.

The photo radical polymerizable adhesive preferably contains a photo radical polymerization initiator. The content of the radical polymerization initiator is usually about 0.1 to 10 parts by weight, preferably 0.5 to 3 parts by weight with respect to 100 parts by weight of the monomer. In addition, when using a radically polymerizable adhesive as an electron beam curable type, a polymerization initiator is not particularly required. If necessary, a photosensitizer represented by a carbonyl compound or the like can be added to the radical polymerizable adhesive. The photosensitizer is used for increasing the curing rate and sensitivity of the electron beam. The amount of the photosensitizer used is usually about 0.001 to 10 parts by weight, preferably 0.01 to 3 parts by weight with respect to 100 parts by weight of the monomer.

The adhesive may contain an appropriate additive as necessary. Examples of additives include coupling agents such as silane coupling agents and titanium coupling agents, adhesion promoters such as ethylene oxide, ultraviolet absorbers, deterioration inhibitors, dyes, processing aids, ion trap agents, and antioxidants. , Tackifiers, fillers, plasticizers, leveling agents, foam inhibitors, antistatic agents, heat stabilizers, hydrolysis stabilizers, and the like.

<Additional layer>
The polarizing plate may have various additional layers in addition to the polarizer and the polarizer protective film. As an additional layer, various functional optical films used for forming image display devices such as retardation plates, viewing angle widening films, viewing angle limiting (preventing peeping) films, brightness enhancement films, polarizing plates and image display cells Examples thereof include a pressure-sensitive adhesive for bonding to the surface, a surface protective film for protecting the surface of a polarizing plate, a functional optical film, and the like.

The pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer is not particularly limited, and an adhesive based on acrylic polymers, silicone polymers, polyesters, polyurethanes, polyamides, polyethers, fluoropolymers, rubber polymers, etc. is appropriately selected. Can be used. In particular, a pressure-sensitive adhesive such as an acrylic pressure-sensitive adhesive that is excellent in transparency, exhibits appropriate wettability, cohesiveness, and adhesion, and is excellent in weather resistance, heat resistance, and the like. The thickness of the pressure-sensitive adhesive layer is appropriately set according to the type of adherend and the like, and is generally about 5 to 500 μm.

It is preferable that a separator is temporarily attached to the surface of the pressure-sensitive adhesive layer. The separator protects the surface of the pressure-sensitive adhesive layer until the polarizing plate is bonded to the image display cell or the like. As a constituent material of the separator, plastic films such as acrylic, polyolefin, cyclic polyolefin, and polyester are preferably used. The thickness of the separator is usually about 5 to 200 μm. It is preferable that a release treatment is performed on the surface of the separator. Examples of the release agent include silicone materials, fluorine materials, long chain alkyl materials, fatty acid amide materials, and the like.

As the material for the surface protective film, the same plastic material as that for the above separator is preferably used. The thickness of the surface protective film is, for example, about 20 to 1000 μm.

Even if the surface of the polarizer protective film or functional optical film constituting the polarizing plate is provided with a function-imparting layer such as an antireflection layer, an antifouling layer, a light diffusion layer, an easy adhesion layer, an antistatic layer, etc. Good.

Examples of the antireflection layer include a thin layer type that prevents reflection by using a cancellation effect of reflected light due to the multiple interference action of light, and a type that reduces reflectance by providing a fine structure on the surface. . As a specific example of the antireflection layer using multiple interference of light, there is an alternate laminate of a high refractive index layer such as titanium oxide, zirconium oxide, niobium oxide, and a low refractive index layer such as silicon oxide or magnesium fluoride. Can be mentioned. The thickness of the antireflection layer is, for example, about 0.01 to 2 μm, preferably 0.05 to 1.5 μm.

Examples of the material for the antifouling layer include fluorine group-containing silane compounds and fluorine group-containing organic compounds. Diamond-like carbon or the like can also be used as a material for the antifouling layer. The thickness of the antifouling layer is, for example, about 0.01 to 2 μm, preferably 0.05 to 1.5 μm.

As the light diffusion layer, a layer having small backscattering is preferable. The haze of the light diffusion layer is preferably 20 to 88%, more preferably 30 to 75%. For example, a diffusion adhesive layer is used as the light diffusion layer. As the diffusion pressure-sensitive adhesive layer, a mixture of particles having different refractive indexes in a polymer constituting the pressure-sensitive adhesive is used. A diffusion adhesive layer may be used as the above-mentioned adhesive layer.

Instead of providing the light diffusion layer, or in addition to the light diffusion layer, the surface of the polarizer protective film or the functional optical film may be subjected to an antiglare treatment. Examples of the antiglare treatment include a method of imparting a fine concavo-convex structure to the surface by roughening by sandblasting or embossing, blending of transparent fine particles, and the like.

An easy-adhesion layer may be provided on the surfaces of the polarizer, the polarizer protective film and the functional optical film for the purpose of improving wettability and adhesion to an adhesive or the like. Examples of the material for the easy adhesion layer include epoxy resins, isocyanate resins, polyurethane resins, polyester resins, polymers having amino groups in the molecule, ester urethane resins, acrylic resins having an oxazoline group, and the like. . The thickness of the easy adhesion layer is, for example, 0.05 to 3 μm, preferably 0.1 to 1 μm.

As the antistatic layer, a binder resin added with an antistatic agent is preferably used. Examples of the antistatic agent include ionic surfactants, conductive polymers such as polyaniline, polythiophene, polypyrrole, and polyquinoxaline; metal oxides such as tin oxide, antimony oxide, and indium oxide. In particular, a conductive polymer is preferably used from the viewpoint of optical characteristics, appearance, antistatic effect, and the like. Among these, water-soluble or water-dispersible conductive polymers such as polyaniline and polythiophene are preferable. The thickness of the antistatic layer is, for example, 0.01 to 2 μm, preferably 0.05 to 1 μm. By including an antistatic agent in the binder resin of the easy adhesion layer, an easy adhesion layer having antistatic properties may be formed.

[Processing of polarizing plate]
<Cutting of polarizing plate>
A sheet-shaped polarizing plate is cut out from a polarizing plate having a relatively large area. The attachment of the polarizer and the polarizer protective film, and the addition of an additional layer such as an adhesive layer, a surface protective film, and a functional optical film are preferably performed by a roll-to-roll process. A large area polarizing plate is obtained by a roll-to-roll process. A large-area polarizing plate is cut into a product size that matches the size (screen size) of the image display device. Examples of the cutting method include a method of punching with a Thomson blade or the like, a method of using a cutter such as a round blade or a countersink, a method of using laser light or water pressure, and the like. In FIG. 1A, a rectangular polarizing plate is illustrated, but the shape of the polarizing plate is not limited to a rectangular shape, and may be a polygon such as a triangle, a rhombus, a pentagon, or a hexagon. The shape of the polarizing plate may be a circle, an ellipse, or the like, and may have a straight portion and a curved portion, such as a shape in which a polygonal apex portion is chamfered.

When the polarizing plate is cut, microcracks are likely to occur in the polarizer on the cut end surface perpendicular to the stretching direction during the production of the polarizer. The cut end face of the polarizing plate may be cut for the purpose of removing micro cracks on the cut end face. Examples of the cutting method include the methods described in JP-A Nos. 2004-167673 and 2004-148419.

The cutting process of the cut end face may be performed on the entire outer periphery of the polarizing plate, or only a specific cut end face may be cut. The cutting width only needs to be able to remove microcracks generated during cutting. The cutting width is usually 10 mm or less, preferably about 0.1 to 5 mm. Cutting may be performed by laminating a plurality of cut polarizing plates. Processing efficiency can be improved by laminating a plurality of polarizing plates and carrying out cutting.

<End face modification of polarizer>
After cutting into a sheet and performing cutting as needed, the end surface modification | denaturation process of a polarizer is performed. By applying heat and light energy to the polarizer exposed on the end face and modifying it, durability against moisture and chemicals is improved, and deterioration of the polarizer at the periphery of the polarizing plate tends to be suppressed. .

In order to selectively modify the peripheral portion of the polarizing plate, light irradiation to the end face of the polarizing plate is preferable. A modified region 21 e is formed in the polarizer 21 at the peripheral edge of the polarizing plate 10 by light irradiation from the end face. For example, in order to modify the polarizer at the peripheral portion of the polarizing plate 10 shown in FIG. 1, it is preferable to irradiate light from the end faces 11, 12, 13, and 14 of the polarizing plate. As shown in FIG. 2, in a state where a plurality of polarizing plates are laminated, light is irradiated to each of the four end faces 101, 102, 103, and 104 of the laminate 100, and a plurality of polarizing plates are subjected to modification treatment simultaneously. Also good. By laminating a plurality of polarizing plates and carrying out the end face modification treatment, the treatment efficiency can be improved.

When the modification treatment is performed by light irradiation, it is preferable to irradiate light having a wavelength that can be absorbed by the polarizer. The light energy absorbed by the polarizer is converted into thermal energy, and the polarizer is denatured by the temperature rise.

A PVA polarizer containing iodine as a dichroic substance has an absorptivity mainly in a visible light region of about 380 to 800 nm, and particularly has a high absorption rate of 400 to 700 nm. Therefore, it is preferable to modify the polarizer by irradiating with light having a wavelength of 400 to 700 nm. Moreover, since the polarizer protective film provided adjacent to the polarizer has small absorption of visible light, it is possible to selectively denature the polarizer by irradiation with visible light. The light beam applied to the polarizing plate may be coherent light or incoherent light.

Coherent light such as laser has high energy per unit time unit space density, and easily causes evaporation and dissolution of the polarizer and the polarizer protective film constituting the polarizing plate. Further, since the irradiation area of coherent light is small, in order to modify the entire end face of the polarizing plate, it is necessary to perform processing while moving the position of the light source or the polarizing plate. On the other hand, incoherent light is not excessively intensified due to multiphoton processes or interference, and energy is not supplied more than necessary. It is possible to denature. Further, since incoherent light can be irradiated in a larger area than coherent light, a plurality of polarizing plates can be stacked and end face modification treatment can be performed simultaneously. Therefore, incoherent light is preferable as the light beam applied to the polarizing plate.

The light irradiation to the end face of the polarizing plate may be carried out continuously or intermittently. The light irradiation may be pulse irradiation. Pulse irradiation is an irradiation method in which light irradiation (on) and non-irradiation (off) with a predetermined pulse time width are continuously repeated. Pulsed irradiation is preferred because it is possible to locally denature the irradiated surface and its vicinity while suppressing melting of the polarizer due to excessive heating.

The pulse irradiation width of the light beam is generally about 1 nanosecond to 1 second. From the viewpoint of accelerating the heat denaturation by light absorption of the polarizer and suppressing the melting and the expansion of the denatured region due to excessive heating, the pulse time width is preferably 10 microseconds to 100 milliseconds, and 50 microseconds to 50 milliseconds. Is more preferable, and 100 microseconds to 10 milliseconds is even more preferable. Pulse irradiation may be performed only once or may be repeated twice or more. In order to sufficiently progress the modification of the polarizer, it is preferable to perform pulse irradiation a plurality of times. The irradiation time (the product of the pulse width and the number of irradiation times) is preferably about 1 millisecond to 1 second, and more preferably 5 milliseconds to 500 milliseconds.

It is preferable to use a flash light source for irradiation of incoherent pulsed light. The flash lamp can adjust the heating depth by controlling the pulse width, and the shorter the pulse width, the smaller the heating depth. Therefore, it is possible to locally denature the vicinity of the irradiated surface. Examples of the flash light source include a xenon flash lamp, an argon flash lamp, and a krypton flash lamp. Among these, a xenon flash lamp is preferable because it has a strong emission spectrum in the visible region that can be absorbed by the polarizer.

It is preferable to use a high-intensity flash lamp in order to selectively heat and denature the vicinity of the irradiated surface with short-time pulse irradiation on the order of microseconds to milliseconds. For example, a flash lamp used for semiconductor flash lamp annealing is preferably used. What is necessary is just to adjust the distance to a light source and the end surface (irradiation surface) of a polarizing plate so that light may be irradiated to the whole modification | denaturation object area | region. Since the intensity of the incoherent light is inversely proportional to the square of the distance, if the distance from the light source to the end face of the polarizing plate is excessively large, modification by light irradiation may be insufficient. The distance between the light source and the end face of the polarizing plate is preferably about 1 to 500 mm, more preferably about 2 to 100 mm.

By performing light irradiation with a xenon flash lamp or the like from the end face of the polarizing plate, the polarizer 21 at the peripheral edge of the polarizing plate 10 is modified to form a modified region 21e. Since the polarizer is modified in the modified region 21e, the characteristics of the polarizer are different from those of the central portion 21c. A characteristic change when the PVA polarizer is locally heated by light irradiation from the end face is an increase in absorbance around 1089 cm ⁻¹ in the infrared absorption spectrum.

Absorption near 1089 cm ⁻¹ originates from the C—O stretching of the ether bond (C—O—C). Thus, an increase in absorbance near 1089 cm ⁻¹ means the formation of an ether bond due to denaturation. The formation of the ether bond is considered to be due to dehydration condensation of the hydroxyl group of polyvinyl alcohol. That is, the modification introduces a cross-linked structure into the molecular chain of polyvinyl alcohol, resulting in a denser molecular structure. Therefore, entry of moisture, oil, etc. into the polarizer from the end face of the polarizing plate is suppressed, and the polarizing plate It is thought that durability is improved. Moreover, since the mechanical strength is improved by the introduction of the crosslinked structure, effects such as crack suppression can be expected.

The local modification of the polarizer in the vicinity of the end surface can be confirmed by comparing the in-plane central portion and the end portion of the infrared absorption spectrum of the polarizer. When an ether bond is generated due to the modification of the PVA polarizer, the ratio A ₃₃₀₀ / A ₁₀₈₉ between the absorbance A ₁₀₈₉ of the peak near ₁₀₈₉ cm ⁻¹ and the absorbance A ₃₃₀₀ of the peak near ₃₃₀₀ cm ⁻¹ in the infrared absorption spectrum is small. Become. Absorption near 3300 cm ⁻¹ originates from the OH stretching of the hydroxyl group. As described above, the absorption around 1089 cm ⁻¹ originates from the C—O stretching of the ether bond. In this specification, the peak at a specific wave number “near” refers to the peak of the wave number closest to the wave number among the peaks existing at the wave number ± 15 cm ⁻¹ .

When the PVA polarizer is modified by light irradiation, the absorbance A ₃₃₀₀ of the peak near ₃₃₀₀ cm ⁻¹ derived from the hydroxyl group decreases, and the absorbance A ₁₀₈₉ of the peak near ₁₀₈₉ cm ⁻¹ derived from the ether bond increases. When the polarizer in the vicinity of the end face is locally modified, A ₃₃₀₀ / A ₁₀₈₉ in the infrared absorption spectrum of the end portion 21e (modified portion) in the plane of the polarizer is the infrared absorption spectrum of the central portion 21c. It is smaller than _A3300 / _A1089 . In other words, the polarizing plate in which A ₃₃₀₀ / A ₁₀₈₉ in the infrared absorption spectrum of the end portion 21e in the plane of the polarizer is smaller than A ₃₃₀₀ / A ₁₀₈₉ in the infrared absorption spectrum of the central portion 21c is The polarizer has good optical properties without being modified, and the polarizer is modified at the in-plane end. Due to the modification of the in-plane end polarizer, the durability of the polarizing plate tends to be improved. In particular, the polarizing plate of the present invention is excellent in chemical resistance, and even when exposed to a high-temperature and high-humidity environment with chemicals attached thereto, the fading deterioration of the end portion hardly occurs.

Polarizer 21, _A 3300 _{/ A 1089} of the end portion 21e of the plane is preferably not more than 0.97 times the _A 3300 _{/ A 1089} in the in-plane central portion 21c. As A ₃₃₀₀ / A ₁₀₈₉ at the end 21e in the surface is smaller, the chemical resistance tends to be improved. _A 3300 _{/ A 1089} of the end portion 21e is more preferably 0.95 times or less of the _A 3300 _{/ A 1089} of the central portion 21c, more preferably 0.9 times or less, particularly preferably 0.85 times or less.

From the viewpoint of improving the durability of the polarizing plate, the smaller A ₃₃₀₀ / A ₁₀₈₉ of the in-plane end 21e of the polarizer is, the better. On the other hand, in order to significantly reduce A ₃₃₀₀ / A ₁₀₈₉ , a long time is required for the modification treatment, which may lead to a decrease in productivity. Further, if A ₃₃₀₀ / A ₁₀₈₉ of the polarizer at the end portion is reduced, the width W ₁ of the modified region 21e is increased and the effective area of the polarizing plate is reduced. Therefore, it is difficult to adapt the image display device to a narrow frame. It may become. Therefore, _A 3300 _{/ A 1089} of the end portion 21e is preferably 0.05 times or more of the _A 3300 _{/ A 1089} of the central portion 21c, more preferably at least 0.1 times, more preferably not less than 0.2 times.

The infrared absorption spectrum of the polarizer is measured by a total reflection method (ATR method) using a microinfrared spectrometer with the polarizer protective film and the like peeled off from the polarizing plate to expose the polarizer. The infrared absorption spectrum of the polarizer at the in-plane end is measured by irradiating measurement light onto a region 100 μm from the end surface (outer periphery).

A ₃₃₀₀ / _{A 1089} is, in the case where the area is 0.95 times or less of the _A 3300 _{/ A 1089} in the in-plane central portion and the modified region, the width _{W 1} of the modified region is preferably at least 10 [mu] m, more than 30μm More preferably, it is more preferably 50 μm or more. The width of the denatured region is such that the diameter of the measurement light (incident light) of micro infrared spectroscopy is set to about 10 μm, the infrared absorption spectrum is measured at a plurality of points from the end surface side to the center portion, It is obtained by plotting the distance and the value of A ₃₃₀₀ / A ₁₀₈₉ . As the width W _{1 of the} modified region is larger, the durability of the polarizing plate tends to be improved. On the other hand, if the width W _{1 of the} denatured region is excessively large, it is difficult to adapt to the narrowing of the image display device due to a decrease in the effective area. Therefore, W ₁ is preferably 3 mm or less, more preferably 2 mm or less. It is more preferably 5 mm or less, and particularly preferably 1 mm or less. As described above, W ₁ can be reduced by locally modifying the vicinity of the end face using a flash lamp or the like. In addition, when a flash lamp is used, the heating depth can be controlled by adjusting the pulse time width, so that the width of the denatured region can be set to a desired range.

[Use of polarizing plate]
The polarizing plate of the present invention can be used for forming various optical devices such as liquid crystal display devices, organic EL display devices, and organic EL lighting.

The liquid crystal display device can be manufactured, for example, by appropriately assembling a polarizing plate and an optical member such as a liquid crystal cell and a backlight and incorporating a drive circuit. In organic EL display devices and organic EL lighting, by arranging a circularly polarizing plate in which a polarizing plate and a quarter-wave plate are laminated on the surface of an organic EL panel, external light is reflected by a metal electrode layer and looks like a mirror surface. Can be prevented from being visually recognized.

The polarizing plate of the present invention is less susceptible to fading deterioration at the end even when exposed to a high temperature and high humidity environment with chemicals attached. Therefore, even if the polarizing plate is arranged in a state where it can be contacted from the outside and chemicals or cosmetics attached to the human body are transferred to the polarizing plate, the polarization characteristics in the vicinity of the end portion of the device are hardly deteriorated. Therefore, the polarizing plate of the present invention can be suitably used for an image display device having a narrow frame width and a large display area.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

[Production of pressure-sensitive adhesive polarizing plate]
<Polarizer>
One side of an amorphous polyester film (polyethylene-terephthalate / isophthalate; glass transition temperature 75 ° C.) having a thickness of 100 μm is subjected to corona treatment, and polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) is applied to the corona treatment surface. ) And acetoacetyl-modified polyvinyl alcohol (Nippon Synthetic Chemical Industry "Goseifamer Z200"; polymerization degree 1200, acetoacetyl modification degree 4.6%, saponification degree 99.0 mol% or more) in a weight ratio of 9: 1 The aqueous solution containing this was applied and dried at 25 ° C. to produce a laminate in which a PVA resin layer having a thickness of 11 μm was provided on an amorphous polyester film substrate.

The laminate was uniaxially stretched 2.0 times in the longitudinal direction by air-assisted stretching in an oven at 120 ° C., and then conveyed to a 4% boric acid aqueous solution at 30 ° C. for 30 seconds at 30 ° C. while being rolled. Were sequentially immersed in a dyeing solution (0.2% iodine, 1.0% potassium iodide aqueous solution) for 60 seconds. Next, while roll transporting the laminate, it was immersed in a crosslinking solution at 30 ° C. (3% potassium iodide, 3% boric acid aqueous solution) for 30 seconds to perform crosslinking treatment, 4% boric acid at 70 ° C., iodinated While immersed in a 5% aqueous solution of potassium, free end uniaxial stretching was performed in the longitudinal direction so that the total stretching ratio was 5.5 times. Thereafter, the laminate was immersed in a cleaning solution (4% potassium iodide aqueous solution) at 30 ° C. to obtain a laminate in which a PVA polarizer having a thickness of 5 μm was provided on an amorphous polyester film substrate.

<Lamination of polarizer protective film>
It contains 40 parts by weight of N-hydroxyethylacrylamide and 60 parts by weight of acryloylmorpholine as a curable component, and further contains 2-methyl-1- (4-methylthiophenyl) -2-morpholinopropan-1-one (BASF) as a polymerization initiator. An ultraviolet curable adhesive containing 3 parts by weight of “Irgacure 819” (manufactured “Irgacure 819”) was prepared. This adhesive is applied to the surface of the polarizer of the above laminate with a thickness of about 1 μm, and a cyclic olefin film (“Zeonor film ZF14” manufactured by Nippon Zeon Co., Ltd., thickness 40 μm) is bonded to the adhesive. The adhesive was cured by irradiating with 1000 / mJ / cm ² ultraviolet rays.

After peeling the amorphous polyester film substrate from the laminate, applying the above active energy ray-curable adhesive solution to the surface of the PVA resin layer from which the film substrate was peeled, and laminating the cyclic olefin film Then, the adhesive was cured by irradiating ultraviolet rays to obtain a polarizing plate having a cyclic olefin-based film as a polarizer protective film on both surfaces of a 5 μm thick polarizer.

<Attachment of protective film and adhesive sheet>
On one surface of the polarizing plate, a polyester film having a surface provided with a slightly adhesive layer was bonded as a protective film.

A release film on one side is peeled off from an acrylic adhesive sheet having a thickness of 20 μm and a polyethylene terephthalate film (release film) having a release layer bonded on both sides, and the exposed surface of the adhesive sheet is placed on the other side of the polarizing plate. It was pasted on the surface. Bonding of the protective film to the polarizing plate and bonding of the adhesive sheet were both performed using a roll laminator.

Through the above steps, a protective film was bonded to one surface of a polarizing plate provided with a polarizer protective film on both sides of the PVA polarizer, and a pressure-sensitive adhesive polarizing plate provided with an adhesive layer on the other surface was obtained.

<Cutting of polarizing plate>
A polarizing plate with an adhesive was punched into a rectangular size of 255 mm × 195 mm. Laminate 100 polarizing plates with adhesive punched to the same size, and cut and polish 2.5mm each end face of the four sides of the rectangle with a full back cutter to obtain a polarizing plate with adhesive of 250mm x 190mm It was.

[Flash lamp processing of polarizing plate edge]
Pulse light (pulse width 1 millisecond, pulse width) of xenon flash lamp (manufactured by USHIO INC., Light source voltage 1.5 kV) from a distance of 10 mm from the end face in a state where 100 polarizing plates with adhesive of 250 mm × 190 mm are laminated. In Example 1, which was irradiated with a frequency of 3 Hz, 20 shots were irradiated on the end faces of the four sides of the rectangle. In Example 2 and Example 3, the number of irradiation shots was changed to 30 times and 50 times, respectively. In the comparative example, the flash lamp was not irradiated.

[Evaluation]
<Infrared spectrum>
A sample of 3 mm x 3 mm size is cut out from the edge and the center of the polarizing plate of the single wafer, cut into the interface between the polarizer and the cyclic olefin film with a cutter knife, and the cyclic olefin film is peeled off from the cut portion. Then, the polarizer was exposed. Using this sample, the infrared absorption spectrum of the polarizer was measured by microscopic FTIR (“UMA600” and “FTS3000” manufactured by Agilent) under the following conditions.
Measurement method: ATR method Incident light diameter: 100 μm
Prism: Ge (incident angle 45 °)
Detector: MCT-A
Resolution: 4.0cm ^-1
Integration: 64 times Note that the position of the sample at the end of the polarizing plate was adjusted so that the region of 100 μm from the end face would be the measurement range.

From the obtained spectra, we determined absorbance _{A 1089} peak around absorbance _{A 3300} and 1089cm ^-1 peak around 3300 cm ^-1, and calculating the ratio _A 3300 _{/ A 1089} therebetween.

<Chemical adhesion durability test>
The release film bonded to the surface of the pressure-sensitive adhesive layer of the polarizing plate with pressure-sensitive adhesive was peeled off, and the pressure-sensitive adhesive layer was bonded onto the glass plate. The protective sheet on the surface of the polarizing plate bonded to the glass plate was peeled off, and glycerin was applied to the periphery of the polarizing plate using a dispenser. This sample was placed in a constant temperature and humidity chamber at a temperature of 65 ° C. and a relative humidity of 90%, and held for 240 hours to perform a wet heat durability test. Another polarizing plate is placed in crossed Nicols on the polarizing plate after the test, and the peripheral edge of the polarizing plate is observed with an optical microscope (“MX61L” manufactured by Olympus, magnification 10 ×). (Distance from the end of the polarizing plate) was measured.

<Humidity heat durability test>
Except that glycerin was not applied, a wet heat test was performed in the same manner as described above, and the width of the color loss region at the end of the polarizing plate after the test was measured.

[Evaluation results]
Table 1 shows the flash lamp processing conditions of the end faces of the polarizing plates of Examples 1 to 3 and the comparative example, and the evaluation results.

In Comparative Example 1 in which the light irradiation by the flash lamp was not performed, A ₃₃₀₀ / A ₁₀₈₉ at the end portion of the polarizing plate and the central portion were equal, whereas in Example 1 in which the 20-shot flash lamp irradiation was performed, The ratio of A ₃₃₀₀ / A ₁₀₈₉ at the end and the end was reduced to 0.94. In Examples 1 to 3, as the number of irradiation shots increased, A ₃₃₀₀ / A ₁₀₈₉ at the end decreased, and the ratio of A ₃₃₀₀ / A ₁₀₈₉ at the center and end decreased accordingly. . On the other hand, even if the number of irradiation shots was increased, no clear change was observed in the A ₃₃₀₀ / A ₁₀₈₉ of the polarizer in the center. From these results, it can be seen that the end polarizer is selectively denatured by the irradiation of the flash lamp.

In the wet heat test conducted without applying a chemical, no clear difference in durability was found between Comparative Example 1 and Examples 1 to 3. On the other hand, in the chemical adhesion test, in the polarizing plate of Comparative Example 1, the color loss width at the end exceeded 500 μm, whereas in Examples 1 to 3, the color loss width was small, and the center portion and the edge As the ratio of A ₃₃₀₀ / A _{1089 in} the part was smaller, the durability tended to improve.

From the above results, it is possible to denature the polarizer exposed to the end face by light irradiation from the end face of the polarizing plate, and by decoloring the end face polarizer, even if chemicals adhere, the peripheral edge fading It can be seen that there can be obtained a polarizing plate with little deterioration in properties and excellent durability.

DESCRIPTION OF SYMBOLS 10 Polarizing plate 21 Polarizer 21e Modification | denaturation area | region 31, 32 Polarizer protective film 100 Polarizing plate laminated body

Claims (7)

1. A single-wafer polarizing plate comprising a transparent film on at least one surface of a polyvinyl alcohol-based polarizer,
   The polarizer has an in-plane ratio A ₃₃₀₀ / A ₁₀₈₉ between the absorbance A ₁₀₈₉ at the peak near ₁₀₈₉ cm ⁻¹ and the absorbance A _{3300 at} the peak near ₃₃₀₀ cm ⁻¹ in the infrared absorption spectrum at the end of the plane. A polarizing plate that is smaller than A ₃₃₀₀ / A ₁₀₈₉ in the infrared absorption spectrum at the center.
2. The polarizer, _A 3300 _{/ A 1089} of the end portion of the plane is not more than 0.97 times the _A 3300 _{/ A 1089} in the in-plane central portion, polarizing plate according to claim 1.
3. A method for producing a single-wafer polarizing plate comprising a transparent film on at least one surface of a polyvinyl alcohol polarizer,
   Cut a relatively large polarizing plate to cut out a sheet polarizing plate,
   The manufacturing method of a polarizing plate which irradiates the light beam of the wavelength which the said polarizer can absorb to the end surface of the polarizing plate after cut out, and denatures the polarizer of the end surface of a polarizing plate.
4. The method for producing a polarizing plate according to claim 3, wherein the light beam is incoherent light.
5. The method for producing a polarizing plate according to claim 3 or 4, wherein the light beam is pulse-irradiated.
6. 6. The method for producing a polarizing plate according to claim 5, wherein a pulse time width of the light beam is 10 microseconds to 100 milliseconds.
7. The method for producing a polarizing plate according to any one of claims 3 to 6, wherein the irradiation with the light beam is performed in a state where a plurality of polarizing plates cut out on a sheet are laminated.

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