Polarizing film, polarizing film, laminated polarizing film, image display panel, and image display device

Abstract

To provide a polarizing film that can achieve both crack resistance in thermal shock tests and resistance to red degradation in heating reliability tests, while also having a good appearance. [Solution] A polarizing film in which a dichroic substance is adsorbed and oriented on a polyvinyl alcohol-based film and its orientation is fixed by boric acid crosslinking, wherein the thickness is 20 μm or less, and satisfies the condition of the length ratio represented by the general formula: B / A ≥ 2.0 (wherein A represents the length (mm) parallel to the absorption axis of the polarizing film, and B represents the length (mm) perpendicular to the absorption axis of the polarizing film, and is a value of 900 or more), contains 0.05% by weight or more of zinc element, is free of foreign matter larger than 50 μm, has a maximum height (Rz) of less than 5 μm as defined in JIS B 0601-2001, and the difference between the maximum and minimum values ​​of the boron content (by weight) in the direction perpendicular to the absorption axis of the polarizing film is 0.4% by weight or less.

Description

Technical Field

[0001] The present invention relates to a polarizing film, a polarizing film, a laminated polarizing film, an image display panel, and an image display device.

Background Art

[0002] Conventionally, as a polarizing film (also referred to as a "polarizer") used in various image display devices such as liquid crystal display devices and organic EL display devices, a polyvinyl alcohol-based film that has been dyed (containing a dichroic substance such as iodine or a dichroic dye) and has both high transmittance and high polarization degree has been used. The polarizing film is manufactured by subjecting a polyvinyl alcohol-based film to various treatments such as swelling, dyeing, crosslinking, and stretching in a bath, then performing a washing treatment, and then drying. Further, the polarizing film is usually used as a polarizing film (also referred to as a "polarizing plate") in which a protective film such as triacetyl cellulose is adhered to one or both sides thereof using an adhesive.

[0003] The polarizing film is used as a laminated polarizing film (optical laminate) by laminating other optical layers as necessary. The polarizing film or the laminated polarizing film (optical laminate) is bonded between an image display cell such as a liquid crystal cell or an organic EL element and a front transparent member such as a front transparent plate (window layer) or a touch panel on the viewing side via an adhesive layer or an adhesive, and used as the above various image display devices (Patent Document 1).

[0004] In recent years, such various image display devices are used not only in mobile devices such as mobile phones and tablet terminals but also as in-vehicle image display devices such as car navigation devices and rear monitors, and their applications are expanding. In particular, in in-vehicle image display devices, from the viewpoint of design in the vehicle interior space, a polarizing film and a polarizing film (a polarizing film and a polarizing film having a high aspect ratio) in which the ratio of the length parallel to the absorption axis to the length orthogonal to the absorption axis of the polarizing film is a certain value or more are required (Patent Document 2).

[0005] Furthermore, it is known that a specific amount of zinc element can be added to a polarizing film to improve its heat resistance (Patent Document 3). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2014-102353 [Patent Document 2] International Publication No. 2021 / 200390 [Patent Document 3] Japanese Patent Publication No. 2020-71240 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] When manufacturing polarizing films with high aspect ratios as described above, widening the polyvinyl alcohol-based film base material presents a problem: while the resulting polarizing film has a good appearance, it is difficult to achieve both crack resistance in thermal shock tests and resistance to red degradation in heating reliability tests.

[0008] In view of the above circumstances, the present invention aims to provide a polarizing film that can achieve both crack resistance in thermal shock tests and resistance to red degradation in heating reliability tests, and has a good appearance.

[0009] Furthermore, the present invention aims to provide a polarizing film, a laminated polarizing film, an image display panel, and an image display device using the above-described polarizing film. [Means for solving the problem]

[0010] In other words, the present invention relates to a polarizing film in which a dichroic substance is adsorbed and oriented on a polyvinyl alcohol-based film and its orientation is fixed by boric acid crosslinking, characterized in that the film has a thickness of 20 μm or less, satisfies the condition of the length ratio represented by the general formula: B / A ≥ 2.0 (wherein A represents the length (mm) parallel to the absorption axis of the polarizing film, and B represents the length (mm) perpendicular to the absorption axis of the polarizing film, and is a value of 900 or more), contains 0.05% by weight or more of zinc element, is free of foreign matter larger than 50 μm, has a maximum height (Rz) of less than 5 μm as defined in JIS B 0601-2001, and the difference between the maximum and minimum values ​​of the boron content (by weight) in the direction perpendicular to the absorption axis of the polarizing film is 0.4% by weight or less.

[0011] Furthermore, the present invention relates to a polarizing film in which a transparent protective film is laminated to one or both sides of the polarizing film.

[0012] Furthermore, the present invention relates to a laminated polarizing film in which the polarizing film is bonded to an optical layer.

[0013] Furthermore, the present invention relates to an image display panel in which the polarizing film or the laminated polarizing film is bonded to an image display cell.

[0014] Furthermore, the present invention relates to an image display device comprising a front transparent member on the polarizing film or laminated polarizing film side of the image display panel. [Effects of the Invention]

[0015] The present invention relates to a polarizing film in which a dichroic substance is adsorbed and oriented on a polyvinyl alcohol-based film and its orientation is fixed by boric acid crosslinking, wherein the thickness is 20 μm or less, and satisfies the condition of the length ratio represented by the general formula: B / A ≥ 2.0 (wherein A represents the length (mm) parallel to the absorption axis of the polarizing film, and B represents the length (mm) perpendicular to the absorption axis of the polarizing film, and is a value of 900 or more), contains 0.05% by weight or more of zinc element, is free of foreign matter larger than 50 μm, has a maximum height (Rz) of less than 5 μm as defined in JIS B 0601-2001, and the difference between the maximum and minimum values ​​of the boron content (by weight) in the direction perpendicular to the absorption axis of the polarizing film is 0.4% by weight or less. The polarizing film has a good appearance and a high aspect ratio, contains a specific proportion of zinc, and the difference between the maximum and minimum values ​​of the boron content (weight %) in the direction perpendicular to the absorption axis of the polarizing film is less than or equal to a specific amount. Therefore, the variation in the boron content can be reduced, making it possible to achieve both crack resistance in thermal shock tests and resistance to red degradation in heating reliability tests. [Modes for carrying out the invention]

[0016] <Polarizing film> The polarizing film of the present invention is formed by adsorbing and oriented a dichroic substance such as iodine or a dichroic dye onto a polyvinyl alcohol-based film, and then fixing the orientation by boric acid crosslinking. From the viewpoint of the initial polarization performance of the polarizing film, iodine is preferred as the dichroic substance.

[0017] The polyvinyl alcohol (PVA) film described above can be any film that is translucent in the visible light region and disperses and adsorbs dichroic substances such as iodine and dichroic dyes, without any particular limitations. In addition, the PVA film used as the base material is preferably about 1 to 100 μm thick, more preferably about 1 to 50 μm thick, and preferably about 100 to 5000 mm wide.

[0018] Examples of materials for the polyvinyl alcohol-based film include polyvinyl alcohol or its derivatives. Examples of polyvinyl alcohol derivatives include polyvinyl formal, polyvinyl acetal; olefins such as ethylene and propylene; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid, and those modified with their alkyl esters, acrylamide, etc. The average degree of polymerization of the polyvinyl alcohol is preferably about 100 to 10,000, more preferably about 1,000 to 10,000, and even more preferably about 1,500 to 4,500. Furthermore, the degree of saponification of the polyvinyl alcohol is preferably about 80 to 100 mol%, and more preferably about 95 mol% to 99.95 mol. The average degree of polymerization and the degree of saponification can be determined in accordance with JIS K 6726.

[0019] The polyvinyl alcohol-based film may contain additives such as plasticizers and surfactants. Examples of plasticizers include polyols and their condensates, such as glycerin, diglycerin, triglycerin, ethylene glycol, propylene glycol, and polyethylene glycol. There are no particular restrictions on the amount of additives used, but for example, about 20% by weight or less in the polyvinyl alcohol-based film is preferred.

[0020] The polarizing film satisfies the condition of the ratio of lengths represented by the general formula: B / A ≥ 2.0 (in the general formula, A represents the length (mm) parallel to the absorption axis of the polarizing film, B represents the length (mm) perpendicular to the absorption axis of the polarizing film, and it is a value of 900 or more). The above "parallel" includes cases where it is substantially parallel. Here, "substantially parallel" includes cases where it is 0° ± 5.0°, preferably 0° ± 3.0°, more preferably 0° ± 1.0°. Also, the above "orthogonal" includes cases where it is substantially orthogonal. Here, "substantially orthogonal" includes cases where it is 90° ± 5.0°, preferably 90° ± 3.0°, more preferably 90° ± 1.0°. B may be 850 (mm) or more, preferably 900 (mm) or more, from the perspective of the image display size of the display in the vehicle interior space, and may be 2000 (mm) or less, preferably 1500 (mm) or less, from the perspective of the image display size of the display in the vehicle interior space. From the perspective of the design in the vehicle interior space, B / A is preferably 2.8 or more, more preferably 3.3 or more, and from the perspective of the shrinkage amount of the polarizing film during heating, it is preferably 15 or less, more preferably 10 or less.

[0021] The polarizing film has a thickness of 20 μm or less. From the perspective of improving the initial polarization degree of the polarizing film, the thickness is preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 10 μm or more. Also, a polarizing film having a high aspect ratio that satisfies the above general formula: B / A ≥ 2.0 has a problem that when the thickness exceeds 20 μm, the shrinkage amount of the polarizing film during heating becomes large, and cracks in the polarizing film are likely to occur in the thermal shock test.

[0022] The polarizing film contains 0.05% by weight or more of zinc (zinc element). From the viewpoint of resistance to red discoloration in the heat reliability test, the content ratio of zinc (zinc element) in the polarizing film is preferably 0.08% by weight or more, more preferably 0.1% by weight or more, still more preferably 0.12% by weight or more, and from the viewpoint of the appearance of the polarizing film, the content ratio of zinc (zinc element) in the polarizing film is preferably 5% by weight or less, more preferably 1% by weight or less, still more preferably 0.5% by weight or less, and even more preferably 0.25% by weight or less.

[0023] In the direction orthogonal to the absorption axis described above, the difference between the maximum value and the minimum value of the boron content ratio (by weight) of the polarizing film is 0.4% by weight or less. From the viewpoint of suppressing the occurrence of cracks in the polarizing film in the thermal shock test, the difference between the maximum value and the minimum value of the boron content ratio (by weight) described above is preferably 0.38% by weight or less, more preferably 0.35% by weight or less. Further, from the viewpoint of suppressing the deterioration of the optical properties of the polarizing film in a high-temperature environment, the maximum value of the boron content ratio (by weight) described above is preferably 3.5% by weight or more, more preferably 3.8% by weight or more, and from the viewpoint of suppressing the occurrence of cracks in the polarizing film in the thermal shock test, the maximum value of the boron content ratio (by weight) described above is preferably 5.2% by weight or less, more preferably 5.0% by weight or less.

[0024] <Method for manufacturing a polarizing film> The method for manufacturing the polarizing film of the present invention is obtained by subjecting the polyvinyl alcohol-based film to an arbitrary swelling step and washing step, and at least a dyeing step, a crosslinking step, and a stretching step. From the viewpoints of the initial polarization performance and resistance to red discoloration in the heat reliability test, a iodine-based polarizing film containing zinc is preferable for the polarizing film, and the contents of zinc and iodine contained in the polarizing film can be controlled by the concentrations of zinc salts, iodine, potassium iodide, etc. contained in any of the treatment baths in the swelling step, dyeing step, crosslinking step, stretching step, and washing step, the treatment temperature and treatment time by each of the above treatment baths.

[0025] Furthermore, each treatment bath in the swelling step, dyeing step, crosslinking step, stretching step, and washing step may contain additives such as zinc salts, pH adjusters, pH buffers, and other salts. Examples of zinc salts include zinc halides such as zinc chloride and zinc iodide; and inorganic zinc salts such as zinc sulfate and zinc acetate. Examples of pH adjusters include strong acids such as hydrochloric acid, sulfuric acid, and nitric acid, and strong bases such as sodium hydroxide and potassium hydroxide. Examples of pH buffers include carboxylic acids and their salts such as acetic acid, oxalic acid, and citric acid, and inorganic weak acids and their salts such as phosphoric acid and carbonic acid. Examples of other salts include chlorides such as sodium chloride, potassium chloride, and barium chloride; nitrates such as sodium nitrate and potassium nitrate; sulfates such as sodium sulfate and potassium sulfate; and salts of alkali metals and alkaline earth metals.

[0026] The swelling step involves immersing a polyvinyl alcohol-based film in a swelling bath. This step removes dirt and blocking agents from the surface of the polyvinyl alcohol-based film and suppresses uneven dyeing by swelling the film. The swelling bath typically uses a water-based medium such as water, distilled water, or pure water. The swelling bath may also contain surfactants, alcohol, etc., as appropriate, according to conventional methods.

[0027] The temperature of the swelling bath is preferably around 10 to 60°C, more preferably around 15 to 45°C, and even more preferably around 18 to 30°C. The immersion time in the swelling bath cannot be determined definitively because the degree of swelling of the polyvinyl alcohol-based film is affected by the temperature of the swelling bath, but it is preferably around 5 to 300 seconds, more preferably around 10 to 200 seconds, and even more preferably around 20 to 100 seconds. The swelling process may be performed only once, or multiple times as necessary.

[0028] The dyeing step involves immersing a polyvinyl alcohol-based film in a dyeing bath (iodine solution), which allows iodine to be adsorbed and oriented on the polyvinyl alcohol-based film. The iodine solution is preferably an aqueous iodine solution and contains iodine and an iodide as a solubilizing agent. Examples of iodides include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Among these, potassium iodide is preferred from the viewpoint of controlling the potassium content in the polarizing film.

[0029] In the staining bath, the concentration of iodine is preferably about 0.01 to 1% by weight, and more preferably about 0.02 to 0.5% by weight. In the staining bath, the concentration of iodide is preferably about 0.01 to 20% by weight, more preferably about 0.05 to 10% by weight, and even more preferably about 0.1 to 5% by weight.

[0030] The temperature of the dyeing bath is preferably around 10 to 50°C, more preferably around 15 to 45°C, and even more preferably around 18 to 30°C. The immersion time in the dyeing bath cannot be determined definitively because the degree of dyeing of the polyvinyl alcohol-based film is affected by the temperature of the dyeing bath, but it is preferably around 10 to 300 seconds, and more preferably around 20 to 240 seconds. The dyeing process may be performed only once, or multiple times as necessary.

[0031] The crosslinking step involves immersing a polyvinyl alcohol-based film in a treatment bath (crosslinking bath) containing a boron compound. The boron compound crosslinks the polyvinyl alcohol-based film, allowing iodine molecules or dye molecules to be adsorbed onto the crosslinked structure. Examples of the boron compound include boric acid, borate salts, and borax. The crosslinking bath is generally an aqueous solution, but may also be a mixed solution of a water-miscible organic solvent and water. Furthermore, the crosslinking bath may contain potassium iodide to control the potassium content in the polarizing film.

[0032] In the crosslinking bath, the concentration of the boron compound is preferably about 1 to 15% by weight, more preferably about 1.5 to 10% by weight, and even more preferably about 2 to 5% by weight. Furthermore, when potassium iodide is used in the crosslinking bath, the concentration of potassium iodide in the crosslinking bath is preferably about 1 to 15% by weight, more preferably about 1.5 to 10% by weight, and even more preferably about 2 to 5% by weight.

[0033] The temperature of the crosslinking bath is preferably around 20 to 70°C, and more preferably around 30 to 60°C. The immersion time in the crosslinking bath cannot be determined definitively because the degree of crosslinking of the polyvinyl alcohol-based film is affected by the temperature of the crosslinking bath, but it is preferably around 5 to 300 seconds, and more preferably around 10 to 200 seconds. The crosslinking process may be performed only once, or multiple times as necessary.

[0034] The stretching step is a process of stretching a polyvinyl alcohol-based film to a predetermined magnification in at least one direction. Generally, the polyvinyl alcohol-based film is uniaxially stretched in the transport direction (longitudinal direction). The stretching method is not particularly limited, and either wet stretching or dry stretching can be used. The stretching step may be performed only once, or multiple times as necessary. The stretching step may be performed at any stage in the production of a polarizing film.

[0035] The treatment bath (stretching bath) in the wet stretching method can usually be a solvent such as water or a mixed solution of a water-miscible organic solvent and water. The stretching bath may contain potassium iodide from the viewpoint of controlling the potassium content in the polarizing film. When potassium iodide is used in the stretching bath, the concentration of potassium iodide in the stretching bath is preferably about 1 to 15% by weight, more preferably about 2 to 10% by weight, and more preferably about 3 to 6% by weight. In addition, the treatment bath (stretching bath) may contain the boron compound from the viewpoint of suppressing film breakage during stretching, in which case the concentration of the boron compound in the stretching bath is preferably about 1 to 15% by weight, more preferably about 1.5 to 10% by weight, and more preferably about 2 to 5% by weight.

[0036] The temperature of the stretching bath is preferably around 25 to 80°C, more preferably around 40 to 75°C, and even more preferably around 50 to 70°C. The immersion time in the stretching bath cannot be determined definitively because the degree of stretching of the polyvinyl alcohol-based film is affected by the temperature of the stretching bath, but it is preferably around 10 to 800 seconds, and more preferably around 30 to 500 seconds. The stretching treatment in the wet stretching method may be performed together with one or more of the swelling step, the dyeing step, the crosslinking step, and the washing step.

[0037] Examples of the dry stretching method include a roll stretching method, a heated roll stretching method, and a compression stretching method. The dry stretching method may be performed together with the drying process.

[0038] The total stretching ratio (cumulative stretching ratio) applied to the polyvinyl alcohol-based film can be set appropriately depending on the purpose, but is preferably around 2 to 7 times, more preferably around 3 to 6.8 times, and even more preferably around 3.5 to 6.5 times.

[0039] The cleaning step involves immersing the polyvinyl alcohol-based film in a cleaning bath, which removes any foreign matter remaining on the surface of the polyvinyl alcohol-based film. The cleaning bath typically uses a water-based medium such as water, distilled water, or pure water. Furthermore, from the viewpoint of controlling the potassium content in the polarizing film, the cleaning bath may also contain potassium iodide. In this case, the concentration of potassium iodide in the cleaning bath is preferably about 1 to 10% by weight, more preferably about 1.5 to 4% by weight, and even more preferably about 1.8 to 3.8% by weight.

[0040] The temperature of the washing bath is preferably around 5 to 50°C, more preferably around 10 to 40°C, and even more preferably around 15 to 35°C. The immersion time in the washing bath cannot be determined definitively because the degree of washing of the polyvinyl alcohol-based film is affected by the temperature of the washing bath, but it is preferably around 1 to 100 seconds, more preferably around 1 to 50 seconds, even more preferably around 1 to 20 seconds, and in particular, even more preferably around 1 to 5 seconds from the viewpoint of reducing variations in the boron contained in the polarizing film. The washing process may be performed only once, or multiple times as necessary.

[0041] In the aforementioned cleaning process, it is preferable to use a widening roll from the viewpoint of reducing foreign matter and wrinkles in the polarizing film. The widening roll refers to a roll that has a localized curve and has the function of widening the film being conveyed. Examples of the widening roll include expander rolls and crown rolls.

[0042] The method for manufacturing a polarizing film of the present invention may include a drying step. The drying step is a step of drying the polyvinyl alcohol-based film that has been washed in the washing step to obtain a polarizing film, and by drying, a polarizing film having a desired moisture content can be obtained. The drying can be carried out by any suitable method, such as natural drying, forced-air drying, or heat drying.

[0043] The drying temperature is preferably around 20 to 150°C, and more preferably around 25 to 100°C. The drying time cannot be determined definitively because the degree of drying of the polarizing film is affected by the drying temperature, but it is preferably around 10 to 600 seconds, and more preferably around 30 to 300 seconds. The drying process may be performed only once, or multiple times as necessary.

[0044] From the viewpoint of satisfying the length ratio condition expressed by the above general formula: B / A≧2.0 (wherein A represents the length (mm) parallel to the absorption axis of the polarizing film, and B represents the length (mm) perpendicular to the absorption axis of the polarizing film, and is a value of 900 or more), the polarizing film after the above drying process preferably has a width (corresponding to the B direction) of 1270 mm or more, and more preferably 1400 mm or more.

[0045] Furthermore, from the viewpoint of color change after heating reliability testing, the method for manufacturing the polarizing film of the present invention preferably does not include an electromagnetic wave irradiation step, in which electromagnetic waves including infrared rays are irradiated, after the crosslinking step and before the washing step, and more preferably does not include the electromagnetic wave irradiation step, in which electromagnetic waves including infrared rays are irradiated, at all.

[0046] <Polarizing film> The polarizing film of the present invention has a transparent protective film laminated to one or both sides of the polarizing film. Typically, the ratio of the lengths of the polarizing films is the same as the ratio of the lengths of the polarizing films.

[0047] The transparent protective film is not particularly limited, and various transparent protective films used in polarizing films can be used. As the material constituting the transparent protective film, for example, a thermoplastic resin that is excellent in transparency, mechanical strength, thermal stability, moisture barrier properties, isotropy, etc., can be used. Examples of the thermoplastic resin include cellulose ester resins such as triacetylcellulose, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, polyethersulfone resins, polysulfone resins, polycarbonate resins, polyamide resins such as nylon and aromatic polyamides, polyimide resins, polyolefin resins such as polyethylene, polypropylene, and ethylene-propylene copolymers, (meth)acrylic resins, cyclic polyolefin resins having a cyclo or norbornene structure (norbornene resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof. Furthermore, the transparent protective film can be a cured layer formed from thermosetting resins such as (meth)acrylic, urethane, acrylic urethane, epoxy, and silicone resins, or UV-curable resins. Among these, cellulose ester resins, polycarbonate resins, (meth)acrylic resins, cyclic polyolefin resins, and polyester resins are preferred.

[0048] The thickness of the transparent protective film can be determined as appropriate, but generally, from the viewpoint of strength, workability such as handling, and thinness, it is preferably about 1 to 500 μm, more preferably about 1 to 300 μm, and even more preferably about 5 to 100 μm.

[0049] When the transparent protective film is laminated to both sides of the polarizing film, the transparent protective films on both sides may be the same or different.

[0050] The transparent protective film can use a phase difference plate having a front phase difference of 40 nm or more and / or a thickness direction phase difference of 80 nm or more. The front phase difference is usually controlled in the range of 40 to 200 nm, and the thickness direction phase difference is usually controlled in the range of 80 to 300 nm. When a phase difference plate is used as the transparent protective film, the phase difference plate also functions as the transparent protective film, thus enabling a thinner design.

[0051] Examples of the phase difference plate include a birefringent film obtained by uniaxial or biaxial stretching of a polymer material, an orientation film of a liquid crystal polymer, and a liquid crystal polymer orientation layer supported by a film. The thickness of the phase difference plate is not particularly limited, but it is generally around 20 to 150 μm. The phase difference plate may also be used by laminating it to a transparent protective film that does not have a phase difference.

[0052] The transparent protective film may contain any suitable additives such as ultraviolet absorbers, antioxidants, lubricants, plasticizers, mold release agents, color inhibitors, flame retardants, antistatic agents, pigments, and colorants. In particular, if the transparent protective film contains an ultraviolet absorber, the light resistance of the polarizing film can be improved.

[0053] Functional layers such as a hard coat layer, anti-reflective layer, anti-sticking layer, diffusion layer, or anti-glare layer can be provided on the surface of the transparent protective film that does not have a polarizing film bonded to it. These functional layers can be provided on the protective film itself, or they can be provided separately from the protective film.

[0054] The polarizing film and the transparent protective film, or the polarizing film and the functional layer, are usually bonded together via an adhesive layer or bonding agent.

[0055] Various adhesives used in polarizing films can be applied as the adhesive forming the aforementioned adhesive layer. Examples include rubber-based adhesives, acrylic-based adhesives, silicone-based adhesives, urethane-based adhesives, vinyl alkyl ether-based adhesives, polyvinyl alcohol-based adhesives, polyvinyl polyoridone-based adhesives, polyacrylamide-based adhesives, and cellulose-based adhesives. Among these, acrylic-based adhesives are preferred.

[0056] Examples of methods for forming the adhesive layer include applying the adhesive to a peeled separator, drying it to form the adhesive layer, and then transferring it to a polarizing film, or applying the adhesive to a polarizing film and drying it to form the adhesive layer. The thickness of the adhesive layer is not particularly limited, but is preferably about 1 to 100 μm, and preferably about 2 to 50 μm.

[0057] Various adhesives used in polarizing films can be used as the adhesive for forming the adhesive layer, such as isocyanate adhesives, polyvinyl alcohol adhesives, gelatin adhesives, vinyl latex adhesives, and aqueous polyester adhesives. These adhesives are usually used as aqueous solutions (aqueous adhesives) and contain 0.5 to 60% by weight of solids. Among these, polyvinyl alcohol adhesives are preferred, and acetoacetyl group-containing polyvinyl alcohol adhesives are more preferred.

[0058] The water-based adhesive may contain a crosslinking agent. Typically, the crosslinking agent is a compound having at least two functional groups in one molecule that are reactive with the polymer and other components constituting the adhesive. Examples include alkylenediamines; isocyanates; epoxys; aldehydes; amino-formaldehydes such as methylolurea and methylolmelamine. The amount of crosslinking agent in the adhesive is typically about 10 to 60 parts by weight per 100 parts by weight of the polymer and other components constituting the adhesive.

[0059] In addition to the above, other adhesives include active energy ray curing adhesives such as ultraviolet curing adhesives and electron beam curing adhesives. Examples of active energy ray curing adhesives include (meth)acrylate adhesives. Examples of curable components in (meth)acrylate adhesives include compounds having a (meth)acryloyl group and compounds having a vinyl group. Examples of compounds having a (meth)acryloyl group include alkyl (meth)acrylates such as chain-like alkyl (meth)acrylates having 1 to 20 carbon atoms, alicyclic alkyl (meth)acrylates, and polycyclic alkyl (meth)acrylates; hydroxyl group-containing (meth)acrylates; and epoxy group-containing (meth)acrylates such as glycidyl (meth)acrylate. (Meth)acrylate adhesives may contain nitrogen-containing monomers such as hydroxyethyl (meth)acrylamide, N-methylol (meth)acrylamide, N-methoxymethyl (meth)acrylamide, N-ethoxymethyl (meth)acrylamide, (meth)acrylamide, and (meth)acryloylmorpholine. (Meth)acrylate adhesives may also contain polyfunctional monomers as crosslinking components, such as tripropylene glycol diacrylate, 1,9-nonanediol diacrylate, tricyclodecanedimethanol diacrylate, cyclic trimethylolpropaneformal acrylate, dioxane glycol diacrylate, and EO-modified diglycerin tetraacrylate. Compounds having epoxy groups or oxetanyl groups can also be used as cationic polymerization-curable adhesives. Compounds having epoxy groups are not particularly limited as long as they have at least two epoxy groups in the molecule, and various generally known curable epoxy compounds can be used.

[0060] The adhesive may contain appropriate additives as needed. Examples of such additives include coupling agents such as silane coupling agents and titanium coupling agents, adhesion promoters such as ethylene oxide, ultraviolet absorbers, degradation inhibitors, dyes, processing aids, ion trapping agents, antioxidants, tackifiers, fillers, plasticizers, leveling agents, foam inhibitors, antistatic agents, heat stabilizers, hydrolysis stabilizers, and the like.

[0061] The adhesive may be applied to either the transparent protective film side (or the functional layer side), the polarizing film side, or both. After bonding, a drying process is performed to form an adhesive layer consisting of the applied and dried layer. After the drying process, ultraviolet light or electron beams may be irradiated as necessary. The thickness of the adhesive layer is not particularly limited, but when using a water-based adhesive, it is preferably about 10 to 1000 nm, more preferably about 20 to 200 nm, and when using an ultraviolet-curing adhesive, electron beam-curing adhesive, etc., it is preferably about 0.1 to 100 μm, more preferably about 0.5 to 10 μm.

[0062] The transparent protective film and the polarizing film, or the polarizing film and the functional layer, may be laminated with an intervening layer such as a surface modification layer, an easy-adhesion layer, a block layer, or a refractive index adjustment layer.

[0063] Examples of surface modification treatments for forming the aforementioned surface modification layer include corona treatment, plasma treatment, primer treatment, and saponification treatment.

[0064] Examples of easy-to-adhere adhesives for forming the easy-to-adhere layer include forming materials containing various resins having a polyester skeleton, polyether skeleton, polycarbonate skeleton, polyurethane skeleton, silicone-based materials, polyamide skeleton, polyimide skeleton, polyvinyl alcohol skeleton, etc. The easy-to-adhere layer is usually provided in advance on a protective film, and the easy-to-adhere layer side of the protective film and the polarizing film are laminated together with the adhesive layer or the adhesive layer.

[0065] The aforementioned block layer is a layer that functions to prevent impurities such as oligomers and ions eluted from the transparent protective film, etc., from migrating (penetrating) into the polarizing film. The block layer only needs to be transparent and capable of preventing impurities eluted from the transparent protective film, etc. Examples of materials that form the block layer include urethane prepolymer-based forming materials, cyanoacrylate-based forming materials, epoxy-based forming materials, etc.

[0066] The refractive index adjusting layer is provided to suppress the decrease in transmittance due to reflection between layers with different refractive indices, such as the transparent protective film and the polarizing film. Examples of refractive index adjusting materials for forming the refractive index adjusting layer include various resins and additives such as silica-based, acrylic-based, acrylic-styrene-based, and melamine-based resins.

[0067] <Laminated polarizing film> The laminated polarizing film (optical laminate) of the present invention is characterized in that the polarizing film is laminated to an optical layer. The optical layer is not particularly limited, but for example, one or more optical layers that are used in the formation of liquid crystal display devices such as reflectors, semitransparent plates, phase difference plates (including 1 / 2 or 1 / 4 wave plates), and viewing angle compensation films can be used. In particular, examples of the laminated polarizing film include a reflective polarizing film or a semitransparent polarizing film in which a reflector or semitransparent reflector is further laminated on the polarizing film, an elliptical polarizing film or a circular polarizing film in which a phase difference plate is further laminated on the polarizing film, a wide viewing angle polarizing film in which a viewing angle compensation film is further laminated on the polarizing film, or a polarizing film in which a brightness enhancement film is further laminated on the polarizing film.

[0068] An adhesive layer may be provided on one or both sides of the polarizing film, or the laminated polarizing film, for bonding an image display cell such as a liquid crystal cell or an organic EL element to another component such as a transparent front plate or touch panel on the viewing side. A tack layer is preferred as the adhesive layer. The tack forming the tack layer is not particularly limited, but for example, acrylic polymers, silicone polymers, polyesters, polyurethanes, polyamides, polyethers, fluorine-based polymers, rubber-based polymers, etc., can be appropriately selected and used. In particular, tacks containing acrylic polymers are preferred because they have excellent optical transparency, exhibit appropriate wettability, cohesiveness and adhesion, and have excellent weather resistance and heat resistance.

[0069] The adhesive layer can be attached to one or both sides of the polarizing film or the laminated polarizing film by any suitable method. Examples of methods for attaching the adhesive layer include preparing an adhesive solution and directly attaching it to the polarizing film or the laminated polarizing film by any suitable application method such as casting or coating, or forming an adhesive layer on a separator and transferring it to the polarizing film or the laminated polarizing film. The thickness of the adhesive layer can be appropriately determined according to the intended use and adhesive strength, and is generally 1 to 500 μm, preferably 5 to 200 μm, and more preferably 10 to 100 μm. A polarizing film or laminated polarizing film with an adhesive layer on at least one side is called a polarizing film with an adhesive layer or a laminated polarizing film with an adhesive layer.

[0070] It is preferable that a separator be temporarily attached to the exposed surface of the adhesive layer to prevent contamination until it is put into practical use. This prevents contamination of the adhesive layer under normal handling conditions. As the separator, for example, a suitable thin sheet such as a plastic film, rubber sheet, paper, cloth, nonwoven fabric, net, foam sheet, metal foil, or laminate thereof may be used, and may be coated with a suitable release agent such as silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide as needed.

[0071] <Image display panel and image display device> The image display panel of the present invention has the polarizing film or the laminated polarizing film laminated onto an image display cell. Furthermore, the image display device of the present invention is provided with a front transparent member on the polarizing film or laminated polarizing film side (viewing side) of the image display panel.

[0072] Examples of the image display cell include liquid crystal cells and organic EL cells. The liquid crystal cell may be a reflective liquid crystal cell that utilizes ambient light, a transmissive liquid crystal cell that utilizes light from a backlight or other light source, or a semi-transparent, semi-reflective liquid crystal cell that utilizes both ambient light and light from a light source. If the liquid crystal cell utilizes light from a light source, the image display device (liquid crystal display device) also has a polarizing film on the side opposite to the viewing side of the image display cell (liquid crystal cell), and a light source is further positioned therein. Preferably, the polarizing film on the light source side and the liquid crystal cell are bonded together via an appropriate adhesive layer. As for the driving method of the liquid crystal cell, any type may be used, such as VA mode, IPS mode, TN mode, STN mode, or bend orientation (π type).

[0073] As the organic EL cell, for example, one in which a light-emitting body (organic electroluminescent light-emitting body) is formed by sequentially laminating a transparent electrode, an organic light-emitting layer, and a metal electrode on a transparent substrate is preferably used. The organic light-emitting layer is a laminate of various organic thin films, and various layer configurations can be adopted, such as a laminate of a hole injection layer made of a triphenylamine derivative or the like and a light-emitting layer made of a fluorescent organic solid such as anthracene, a laminate of these light-emitting layers and an electron injection layer made of a perylene derivative or the like, or a laminate of a hole injection layer, a light-emitting layer and an electron injection layer.

[0074] Examples of front transparent members positioned on the viewing side of the image display cell include a front transparent plate (window layer) and a touch panel. The front transparent plate is a transparent plate having appropriate mechanical strength and thickness. Examples of such transparent plates include transparent resin plates such as acrylic resin and polycarbonate resin, or glass plates. The touch panel is a variety of touch panels such as resistive, capacitive, optical, and ultrasonic types, or a glass plate or transparent resin plate equipped with a touch sensor function. When a capacitive touch panel is used as the front transparent member, it is preferable to provide a front transparent plate made of glass or a transparent resin plate further on the viewing side than the touch panel. [Examples]

[0075] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0076] <Example 1> <Fabrication of polarizing films> A polyvinyl alcohol film with an average degree of polymerization of 2,400, a degree of saponification of 99.9 mol%, and a thickness of 45 μm was prepared. The polyvinyl alcohol film was immersed in a 24°C swelling bath (water bath) for 110 seconds between rolls with different peripheral speed ratios to swell and stretched to 2.5 times its original size in the conveying direction (swelling process). Subsequently, it was immersed in a 30°C dyeing bath (an iodine aqueous solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with 100 parts by weight of water) for 70 seconds, adjusting the iodine concentration so that the polarizing film had a predetermined transmittance, and dyed while being stretched to 3.8 times its original size in the conveying direction, using the original polyvinyl alcohol film (a polyvinyl alcohol film that had not been stretched at all in the conveying direction) as a reference (dyeing process). Next, the dyed polyvinyl alcohol film was immersed for 30 seconds in a 40°C crosslinking bath (an aqueous solution with boric acid concentration of 3.6 wt%, potassium iodide concentration of 3.0 wt%, and zinc sulfate concentration of 3.6 wt%) to stretch it to 4.2 times its original size in the conveying direction (crosslinking step). Furthermore, the resulting polyvinyl alcohol film was immersed for 60 seconds in a 64°C stretching bath (an aqueous solution with boric acid concentration of 4.4 wt%, potassium iodide concentration of 5.0 wt%, and zinc sulfate concentration of 5.0 wt%) to stretch it to 6.0 times its original size in the conveying direction (stretching step), and then immersed for 2 seconds in an 18°C ​​washing bath (an aqueous solution with potassium iodide concentration of 3.4 wt%) (washing step). In the washing step, an expander roll (arc height 50 mm) was used to immerse the polarizing film. A polarizing film (polarizing film after drying) was prepared by drying a washed polyvinyl alcohol film at 40°C for 30 seconds. The polarizing film had a thickness of 18 μm and a width (length in the TD direction) of 1450 mm.

[0077] <Method for measuring zinc content (weight %) in polarizing films> The zinc content in the polarizing film was measured using a wavelength-dispersive X-ray fluorescence analyzer (ZSX, Rigaku Corporation).

[0078] <Preparation of polarizing film> As an adhesive, an aqueous solution containing polyvinyl alcohol resin containing acetoacetyl groups (average degree of polymerization 1,200, degree of saponification 98.5 mol%, degree of acetoacetylation 5 mol%) and methylolmelamine in a weight ratio of 3:1 was used. Using this adhesive, a 30 μm thick transparent protective film made of (meth)acrylic resin (modified acrylic polymer having a lactone ring structure) (manufactured by Nippon Shokubai, with a moisture permeability of 125 g / m²) was applied to one side (image display device cell side) of the polarizing film obtained above. 2 On the other side (visibility side), a 48μm thick transparent protective film (with moisture permeability of 300g / m²) is formed on a triacetylcellulose film (manufactured by Fujifilm, product name "TJ40UL") with HC formed on it. 2 After laminating the two layers (24h) using a roll laminating machine, the film was subsequently heated and dried in an oven (at 90°C for 10 minutes) to produce a polarizing film with transparent protective films laminated to both sides of the polarizing film.

[0079] <Preparation of acrylic adhesive> A monomer mixture containing 99 parts butyl acrylate and 1 part 4-hydroxybutyl acrylate was charged into a four-necked flask equipped with a stirring blade, thermometer, nitrogen gas inlet tube, and condenser. Furthermore, 0.1 parts 2,2'-azobisisobutyronitrile was added as a polymerization initiator to 100 parts of the monomer mixture (solid content) along with 100 parts ethyl acetate. After introducing nitrogen gas and purging the mixture with nitrogen while gently stirring, the polymerization reaction was carried out for 8 hours while maintaining the liquid temperature in the flask at around 55°C to prepare a solution of an acrylic polymer with a weight-average molecular weight (Mw) of 1.8 million. Subsequently, to 100 parts of the solid content of the obtained acrylic polymer solution, 0.02 parts of an isocyanate crosslinking agent (manufactured by Tosoh Corporation, trade name "Takenate D110N", trimethylolpropane / xylylene diisocyanate adduct) and 0.2 parts of a silane coupling agent (manufactured by Shin-Etsu Chemical Co., Ltd., trade name "X-41-1056") were added to prepare a solution of an acrylic adhesive composition.

[0080] <Fabrication of polarizing film with adhesive> A solution of the acrylic adhesive composition obtained above was applied to one side of a polyethylene terephthalate film (manufactured by Mitsubishi Chemical Polyester Films, trade name "MRF38", release liner) treated with a silicone release agent, so that the thickness of the adhesive layer after drying was 20 μm. The solution was dried at 90°C for 1 minute to form an adhesive layer on the surface of the release liner. Next, the adhesive layer formed on the release liner was transferred to the protective film surface on the image display cell side of the polarizing film prepared above to create a polarizing film with an adhesive layer.

[0081] <Method for measuring the boron content (by weight) in polarizing films calculated by neutralization titration> The polarizing film with adhesive layer obtained above was cut to a size of 1250 × 300 mm so that the absorption axis of the polarizing film was parallel to the short side. Five samples were taken at equal intervals in the direction perpendicular to the absorption axis of the polarizing film, with a size of 20 cm parallel to the absorption axis and a size of 5 cm perpendicular to the absorption axis. The transparent protective film laminated on both sides of the polarizing film was then removed using toluene and dichloromethane. The polarizing film obtained after removing the transparent protective film was dried at 120°C for 2 hours, then dissolved in water. An aqueous solution was added dropwise with a small amount of mannitol and BTB solution, and the solution was titrated with a 0.1 mol / L NaOH aqueous solution to calculate the boron content of the polarizing film based on the following formula. Boron content of polarizing film (weight %) = C × V × Mw / M × 100 C: Concentration of NaOH aqueous solution (mol / L) V: Volume of NaOH aqueous solution added (L) Mw: Molecular weight of boron (g / mol) M: Weight of polarizing film after drying at 120℃ for 2 hours (g)

[0082] <Evaluation of redness resistance in heating reliability tests> The polarizing film with adhesive layer obtained above was cut to a size of 40 × 40 mm so that the absorption axis of the polarizing film was parallel to the edge. After peeling off the release liner, a glass plate (50 × 45 mm, 1.1 mm thick) was bonded to it via the adhesive layer, and the panel was autoclaved at 50°C and 0.5 MPa for 15 minutes to produce a pseudo-image display panel (a laminate with a polarizing film with adhesive layer on one side). The pseudo-image display device obtained above was placed in a hot air oven at 105°C for 500 hours, and the orthogonal hue a values ​​were measured using a spectrophotometer (Otsuka Electronics Co., Ltd., LPF-200). The measurement wavelengths were 380 to 780 nm (in 5 nm increments). [Evaluation Criteria] ○: The orthogonal hue a value is 1 or less after 500 hours at 105℃. ×: The orthogonal hue a value is greater than 1 after 500 hours at 105℃.

[0083] <Evaluation of crack resistance in thermal shock tests> The polarizing film with adhesive layer obtained above was cut to a size of 1250 × 300 mm so that the absorption axis of the polarizing film was parallel to the short side. After peeling off the release liner, a glass plate was bonded to it via the adhesive layer, and the panel was autoclaved at 50°C and 0.5 MPa for 15 minutes to produce a pseudo-image display panel (a laminate having a polarizing film with adhesive layer on one side). The above laminate samples were subjected to a cycle test of -40°C for 30 minutes and 85°C for 30 minutes, 300 times, and then their appearance was visually evaluated according to the following criteria. [Evaluation Criteria] ○: No cracks were found in the polarizing film. ×: Cracks have occurred in the polarizing film.

[0084] <Evaluation of appearance> The polarizing film with an adhesive layer obtained above was evaluated. [Evaluation Criteria] ○: No foreign matter larger than 50 μm is observed on the polarizing film using a magnifying glass, and no wrinkles (streaks) in the MD direction are observed on the polarizing film according to the following evaluation. ×: Foreign matter larger than 50 μm is observed on the polarizing film using a magnifying glass, or wrinkles (streaks) in the MD direction are observed on the polarizing film as determined by the following evaluation. <Evaluation of wrinkles (lines)> After peeling the release liner from the adhesive-coated polarizing film obtained above, the surface shape of the surface opposite to the peeled surface was measured using a 3D optical profiler (NewView9000, ZYGO). From the measured data, the maximum height (surface roughness) Rz was calculated in accordance with JIS B 0601-2001. [Evaluation Criteria] ○: No wrinkles (streaks) in the MD direction with Rz of 5 μm or more have occurred. ×: Wrinkles (streaks) in the MD direction with an Rz of 5 μm or more are present.

[0085] <Example 2> The process for preparing the polarizing film was the same as in Example 1, except that the boric acid concentration in the stretching bath was set to 4.2% by weight.

[0086] <Example 3> The process for preparing the polarizing film was the same as in Example 1, except that the boric acid concentration in the stretching bath was set to 4.0% by weight.

[0087] <Example 4> The process for producing the polarizing film was the same as in Example 1, except that the zinc sulfate concentration in the crosslinking bath was 1.8% by weight and the zinc sulfate concentration in the stretching bath was 2.5% by weight.

[0088] <Comparative Example 1> The process for producing the polarizing film was the same as in Example 1, except that the boric acid concentration in the stretching bath was 4.7% by weight, and the immersion time in the washing bath was 13 seconds.

[0089] <Comparative Example 2> The process for preparing the polarizing film was the same as in Comparative Example 1, except that zinc sulfate was not added to the crosslinking bath and the stretching bath, and that the polarizing film was cut to a size of 1250 × 700 mm so that the absorption axis of the polarizing film was parallel to the short side when evaluating crack formation.

[0090] <Comparative Example 3> The process for preparing the polarizing film was the same as in Example 1, except that zinc sulfate was not added to the crosslinking bath and the stretching bath.

[0091] <Comparative Example 4> The process for preparing the polarizing film is the same as in Example 1, except that the cleaning step was omitted.

[0092] <Comparative Example 5> The process for producing the polarizing film is the same as in Example 1, except that a straight-shaped roll was used for immersion in the washing bath.

[0093] <Comparative Example 6> The procedure was the same as in Example 1, except that polyvinyl alcohol with an average degree of polymerization of 2,400, a degree of saponification of 99.9 mol%, and a thickness of 75 μm was used, the boric acid concentration in the crosslinking bath was set to 3.0% by weight, the boric acid concentration in the stretching bath was set to 4.0% by weight, and the immersion time in the washing bath was set to 5 seconds. The thickness of the obtained polarizing film was 28 μm.

[0094] <Reference example 1> The process for preparing the polarizing film was the same as in Comparative Example 1, except that the film was prepared so that its width after drying was 1300 mm, and that the polarizing film was cut to a size of 850 × 300 mm so that its absorption axis was parallel to its short side, in order to evaluate its crack resistance in the thermal shock test.

[0095] The above evaluation was performed using the samples of the examples and comparative examples obtained above. The results are shown in Table 1.

[0096] [Table 1]

Claims

1. A polarizing film in which a dichroic substance is adsorbed and oriented on a polyvinyl alcohol-based film, and the orientation is fixed by boric acid crosslinking, The thickness is 20 μm or less, and the general formula is: B / A ≥ 2.0 The ratio of lengths expressed by the following formula satisfies the conditions: (In the general formula, A represents the length (mm) of the polarizing film parallel to the absorption axis, and B represents the length (mm) of the polarizing film perpendicular to the absorption axis, and is a value of 900 or greater.) It contains 0.05% by weight or more of zinc element, It is free of foreign matter larger than 50 μm, and the maximum height (Rz) as defined in JIS B 0601-2001 is less than 5 μm. A polarizing film characterized in that, in a direction perpendicular to the absorption axis of the polarizing film, the difference between the maximum and minimum values ​​of the boron content (by weight) is 0.4% by weight or less.

2. A polarizing film characterized in that a transparent protective film is laminated to one or both sides of the polarizing film described in claim 1.

3. A laminated polarizing film characterized in that the polarizing film described in claim 2 is bonded to an optical layer.

4. An image display panel characterized in that an image display cell has a polarizing film according to claim 2 or a laminated polarizing film according to claim 3 laminated to it.

5. An image display device characterized by having a front transparent member on the polarizing film or laminated polarizing film side of the image display panel according to claim 4.

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