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

Abstract

This polarizing membrane that is obtained by adsorbing and aligning a dichroic substance in a polyvinyl alcohol film, and fixing the alignment of same by borate crosslinking. In the polarizing membrane, the ratio ((A) / (B)) of (A) a borate index calculated by an ATR method using FT-IR and (B) a borate content (wt%) calculated by an acid-base titration method is less than 0.13. The polarizing membrane has excellent durability in environments of high temperature and high humidity, and can form a polarizing film capable of preventing the occurrence of pattern marks.

Description

[Technical Field]

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

[0002] Conventionally, dyed polyvinyl alcohol films (containing dichroic substances such as iodine and dichroic dyes) have been used as polarizing films (polarizers) for use in various image display devices such as liquid crystal display devices and organic EL display devices, because they have both high transmittance and high polarization. The polarizing films are produced by subjecting a polyvinyl alcohol film to treatments such as swelling, dyeing, crosslinking, and stretching in a bath, followed by washing and drying.

[0003] The polarizing film is used as a polarizing film by being laminated via a transparent protective film adhesive layer, and the polarizing film is further laminated with other optical layers as needed to be used as a laminated polarizing film (optical laminate). The polarizing film or the laminated polarizing film (optical laminate) is used as an image display panel by being laminated to an image display cell such as a liquid crystal cell or an organic EL element. The image display panel is further laminated via a pressure-sensitive adhesive layer or adhesive layer to a front transparent plate (window layer) on the viewing side, a front transparent member such as a touch panel, and used as the various image display devices mentioned above (Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-102353 [Patent Document 2] International Publication No. 2019 / 188779 [Patent Document 3] Special Publication No. 2018-44992 Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Document 2 describes that increasing the boron content in a polarizing film is effective in improving the durability of the optical properties of the polarizing film in high-temperature environments. However, in a polarizing film in which a low-moisture-permeable transparent protective film and a polarizing film are bonded via a water-based adhesive layer, as in Patent Document 3, simply increasing the boric acid content of the polarizing film may cause the polarizing film to re-swell as it becomes more likely to absorb moisture contained in the water-based adhesive layer. This re-swelling of the polarizing film can cause defects in the appearance of an uneven pattern (pattern marks) that can be seen by reflecting light from a fluorescent lamp, resulting in a problem of poor appearance of the polarizing film.

[0006] Furthermore, in a polarizing film such as that disclosed in Patent Document 3, in which a low-moisture-permeable transparent protective film and a polarizing film are bonded together via a water-based adhesive layer, durability under high temperature and high humidity conditions is also required.

[0007] In view of the above circumstances, an object of the present invention is to provide a polarizing film that can be used to form a polarizing film that has excellent durability in a high-temperature and high-humidity environment and is capable of preventing the occurrence of pattern marks. [Means for solving the problem]

[0008] Specifically, the present invention relates to a polarizing film in which a dichroic substance is adsorbed and aligned on a polyvinyl alcohol-based film and the alignment is fixed by boric acid crosslinking, wherein the ratio ((A) / (B)) of (A) the boric acid index calculated by the ATR method in FT-IR and (B) the boric acid content (wt%) calculated by the neutralization titration method is less than 0.13.

[0009] The present invention also relates to a polarizing film in which a first transparent protective film and the polarizing film are bonded via a water-based adhesive layer. The present invention also relates to an image display panel in which the polarizing film is bonded to an image display cell. The present invention also relates to an image display device having the image display panel and a front transparent member. [Effects of the Invention]

[0010] The mechanism of action of the polarizing film of the present invention is presumed to be as follows: However, the present invention is not limited to this mechanism.

[0011] The polarizing film of the present invention is a polarizing film in which a dichroic material is adsorbed and aligned on a polyvinyl alcohol-based film and the alignment is fixed by boric acid crosslinking, and the ratio ((A) / (B)) of (A) the boric acid index calculated by the ATR method in FT-IR and (B) the boric acid content (wt%) calculated by the neutralization titration method is less than 0.13. The boric acid index (A) calculated by the ATR method in FT-IR indicates the amount of boric acid on the surface of the polarizing film (surface boric acid amount), and the boric acid content (wt%) calculated by the neutralization titration method (B) indicates the boric acid concentration throughout the polarizing film (bulk boric acid concentration). Since the ratio ((A) / (B)) of (A) to (B) is less than 0.13, the polarizing film of the present invention is less susceptible to re-swelling due to moisture in the aqueous adhesive layer, and therefore a polarizing film can be formed that exhibits excellent durability in high-temperature, high-humidity environments while preventing the formation of pattern marks. DETAILED DESCRIPTION OF THE INVENTION

[0012] <Polarizing film> In the polarizing film of the present invention, a dichroic substance is adsorbed and aligned on a polyvinyl alcohol-based film, and the alignment is fixed by boric acid crosslinking. The ratio ((A) / (B)) of (A) the boric acid index calculated by the ATR method in FT-IR and (B) the boric acid content (wt%) calculated by the neutralization titration method is less than 0.13.

[0013] The polarizing film is formed by adsorbing and aligning a dichroic material such as iodine or a dichroic dye on a polyvinyl alcohol film. Examples of the dichroic dye include acridine dyes, oxazine dyes, cyanine dyes, naphthalene dyes, azo dyes, and anthraquinone dyes. From the viewpoint of the initial polarization performance of the polarizing film, an iodine-based polarizing film containing iodine as the dichroic material is preferred.

[0014] The polyvinyl alcohol (PVA) film is transparent in the visible light region and can be used without any particular limitation as long as it disperses and adsorbs dichroic substances such as iodine and dichroic dyes. Examples of materials for the polyvinyl alcohol film include polyvinyl alcohol and 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 their alkyl esters, modified with acrylamide, etc. The polyvinyl alcohol preferably has an average degree of polymerization of approximately 100 to 10,000, more preferably approximately 1,000 to 10,000, and even more preferably approximately 1,500 to 4,500. The polyvinyl alcohol preferably has a saponification degree of approximately 80 to 100 mol%, more preferably approximately 95 mol% to 99.95 mol%. The average degree of polymerization and the saponification degree can be determined in accordance with JIS K 6726.

[0015] The polarizing film has a ratio ((A) / (B)) of (A) the boric acid index calculated by the ATR method in FT-IR to (B) the boric acid content (wt%) calculated by the neutralization titration method of less than 0.13.

[0016] The boric acid index (A) calculated by the ATR method in FT-IR is calculated by attenuated total reflection spectroscopy (ATR) using a Fourier transform infrared spectrophotometer (FT-IR) and indicates the amount of boric acid (surface boric acid amount) on the surface of the polarizing film. For example, International Publication No. 2017 / 145607 is a useful reference for measuring the amount of boric acid on the surface of such a polarizing film. From the viewpoint of improving durability, the boric acid index (A) calculated by the ATR method in FT-IR is preferably 2.00 or more, more preferably 2.22 or more, and even more preferably 2.91 or more. From the viewpoint of preventing the formation of pattern marks, it is preferably 3.46 or less.

[0017] The boric acid content (wt%) calculated by (B) neutralization titration method indicates the boric acid concentration (bulk boric acid concentration) of the entire polarizing film. For example, International Publication No. 2019 / 188779 is a useful reference for measuring the boric acid concentration of the entire polarizing film. From the viewpoint of improving durability, the boric acid content (wt%) calculated by (B) neutralization titration method is preferably 20 wt% or more, more preferably 22 wt% or more, and even more preferably 24 wt% or more. From the viewpoint of dimensional change rate (shrinkage rate), the boric acid content (wt%) is preferably 35 wt% or less, more preferably 32 wt% or less, and even more preferably 30 wt% or less.

[0018] The polarizing film has a ratio ((A) / (B)) of (A) the boric acid index calculated by the ATR method in FT-IR to (B) the boric acid content (wt%) calculated by the neutralization titration method, which is preferably 0.06 or more, more preferably 0.074 or more, from the viewpoint of improving transportability (preventing breakage in the bath), and more preferably 0.122 or less, from the viewpoint of preventing pattern marks.

[0019] <Method of manufacturing polarizing film> The polarizing film is obtained by subjecting the polyvinyl alcohol-based film to a dyeing process, a crosslinking process, and a stretching process, and optionally to at least one of a swelling process, a washing process, and a drying process. The boron content in the polarizing film can be controlled by the concentration of a boron component donor, such as boric acid, a borate salt, or a boron compound such as borax, contained in any of the treatment baths in the swelling process, dyeing process, crosslinking process, stretching process, and washing process, as well as the treatment temperature and treatment time in each of the treatment baths. In particular, the crosslinking process and stretching process facilitate adjustment of the boron content within a desired range by adjusting the treatment conditions, such as the concentration of the boron component donor. Furthermore, the washing process facilitates adjustment of the boron content within a desired range, considering the treatment conditions, such as the boron component donor, used in the dyeing process, crosslinking process, or stretching process.

[0020] The swelling step is a treatment step in which the polyvinyl alcohol film is immersed in a swelling bath, which can remove stains and blocking agents from the surface of the polyvinyl alcohol film and suppress uneven dyeing by swelling the polyvinyl alcohol film. The swelling bath typically uses a medium whose main component is water, distilled water, pure water, or the like. The swelling bath may contain surfactants, alcohol, or the like, as appropriate, according to conventional methods. Potassium iodide may also be used in the swelling bath. In this case, the concentration of potassium iodide in the swelling bath is preferably 1.5 wt % or less, more preferably 1.0 wt % or less, and even more preferably 0.5 wt % or less.

[0021] The temperature of the swelling bath is preferably about 10 to 60°C, more preferably about 15 to 45°C, and even more preferably about 18 to 30°C. The immersion time in the swelling bath cannot be determined in general because the degree of swelling of the polyvinyl alcohol film is affected by the temperature of the swelling bath, but is preferably about 5 to 300 seconds, more preferably about 10 to 200 seconds, and even more preferably about 20 to 100 seconds. The swelling step may be carried out only once, or may be carried out multiple times as necessary.

[0022] The dyeing step is a treatment step in which a polyvinyl alcohol film is immersed in a dye bath (iodine solution), and iodine or a dichroic substance such as a dichroic dye can be adsorbed and oriented in the polyvinyl alcohol film. The iodine solution is usually preferably an aqueous iodine solution, and contains iodine and an iodide as a solubilizing agent. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide.

[0023] The concentration of iodine in the dye bath is preferably about 0.01 to 1% by weight, more preferably about 0.02 to 0.5% by weight, and the concentration of iodide in the dye bath is preferably about 0.01 to 10% by weight, more preferably about 0.05 to 5% by weight, and even more preferably about 0.1 to 3% by weight.

[0024] The temperature of the dye bath is preferably about 10 to 50° C., more preferably about 15 to 45° C., and even more preferably about 18 to 30° C. The immersion time in the dye bath cannot be determined in general because the degree of dyeing of the polyvinyl alcohol film is affected by the temperature of the dye bath, but is preferably about 10 to 300 seconds, and more preferably about 20 to 240 seconds. The dyeing step may be carried out only once, or may be carried out multiple times as necessary.

[0025] The crosslinking step is a treatment step in which the polyvinyl alcohol-based film dyed in the dyeing step is immersed 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 to 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, for example, a mixed solution of water and an organic solvent miscible with water. The crosslinking bath preferably contains potassium iodide.

[0026] The concentration of the boron compound 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. 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.

[0027] The temperature of the crosslinking bath is preferably about 20 to 70° C., more preferably about 30 to 60° C. The immersion time in the crosslinking bath cannot be determined in general because the degree of crosslinking of the polyvinyl alcohol film is affected by the temperature of the crosslinking bath, but is preferably about 5 to 300 seconds, more preferably about 10 to 200 seconds. The crosslinking step may be carried out only once, or may be carried out multiple times as necessary.

[0028] The stretching step is a treatment step in which a polyvinyl alcohol-based film is stretched at least in one direction to a predetermined stretching ratio. Generally, the polyvinyl alcohol-based film is uniaxially stretched in the conveying direction (longitudinal direction). The stretching method is not particularly limited, and either a wet stretching method or a dry stretching method can be used. The stretching step may be carried out only once, or may be carried out multiple times as necessary. The stretching step may be carried out at any stage in the production of a polarizing film.

[0029] The treatment bath (stretching bath) in the wet stretching method can typically be water or a solvent such as a mixed solution of water and a water-miscible organic solvent. The stretching bath preferably contains potassium iodide. When potassium iodide is used in the stretching bath, the concentration of potassium iodide in the stretching bath is preferably about 1 to 15 wt%, more preferably about 2 to 10 wt%, and even more preferably about 3 to 6 wt%. Furthermore, the treatment bath (stretching bath) can contain the boron compound to prevent film breakage during stretching. In this case, the concentration of the boron compound in the stretching bath is preferably about 1 to 15 wt%, more preferably about 1.5 to 10 wt%, and even more preferably about 2 to 5 wt%.

[0030] The temperature of the stretching bath is preferably about 25 to 80°C, more preferably about 40 to 75°C, and even more preferably about 50 to 70°C. The immersion time in the stretching bath cannot be determined in general because the degree of stretching of the polyvinyl alcohol film is affected by the temperature of the stretching bath, but is preferably about 10 to 800 seconds, and more preferably about 30 to 500 seconds. The stretching treatment in the wet stretching method may be carried out together with one or more of the swelling step, the dyeing step, the crosslinking step, and the washing step.

[0031] Examples of the dry stretching method include a roll-to-roll stretching method, a heated roll stretching method, a compression stretching method, etc. The dry stretching method may be carried out together with the drying step.

[0032] The total stretching ratio (cumulative stretching ratio) applied to the polyvinyl alcohol film can be appropriately set depending on the purpose, but is preferably about 2 to 7 times, more preferably about 3 to 6.8 times, and even more preferably about 3.5 to 6.5 times.

[0033] The washing step is a treatment step in which the polyvinyl alcohol film is immersed in a washing bath, and foreign matter remaining on the surface of the polyvinyl alcohol film can be removed. The washing bath typically uses a medium whose main component is water, such as water, distilled water, or pure water. It is also preferable to use potassium iodide in the washing bath. In this case, the concentration of potassium iodide in the washing bath is preferably about 1 to 10 wt %, more preferably about 1.5 to 4 wt %, and even more preferably about 1.8 to 3.8 wt %.

[0034] The temperature of the cleaning bath is preferably about 5 to 50°C, more preferably about 10 to 40°C, and even more preferably about 20 to 36°C. The immersion time in the cleaning bath cannot be determined in general because the degree of cleaning of the polyvinyl alcohol film is affected by the temperature of the cleaning bath, but is preferably about 1 to 100 seconds, more preferably about 2 to 50 seconds, and even more preferably about 3 to 20 seconds. The swelling step may be carried out only once, or may be carried out multiple times as necessary.

[0035] The cleaning step is not particularly limited as long as it can remove foreign matter remaining on the surface of the polyvinyl alcohol film, and cleaning may be performed by applying (coating) the above-mentioned medium. Examples of the application (coating) method include coating methods such as roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, and knife coating (comma coating, etc.). The cleaning step may be performed only once, or multiple times as necessary.

[0036] The drying step is a step of drying the polyvinyl alcohol film washed in the washing step to obtain a polarizing film, and a polarizing film having a desired moisture content can be obtained by drying. The drying can be performed by any appropriate method, for example, natural drying, air drying, or heat drying. The moisture content of the polarizing film is preferably about 8 to 25 wt %, more preferably about 12 to 20 wt %.

[0037] The drying temperature is preferably about 20 to 150° C., more preferably about 25 to 100° C. The drying time cannot be determined in general because the degree of drying of the polarizing film is affected by the drying temperature, but is preferably about 30 to 600 seconds, more preferably about 60 to 300 seconds. The drying step may be carried out only once, or may be carried out multiple times as necessary.

[0038] The polarizing film preferably has a thickness of 1 μm or more, more preferably 2 μm or more, from the viewpoint of improving the initial polarization degree of the polarizing film, and preferably has a thickness of 20 μm or less, from the viewpoint of preventing warping of the panel. In particular, to obtain a polarizing film having a thickness of about 8 μm or less, the following method for producing a thin polarizing film can be applied, in which the polyvinyl alcohol-based film is a laminate including a polyvinyl alcohol-based resin layer formed on a thermoplastic resin substrate.

[0039] A polarizing film (thin polarizing film) can be obtained by a conventional polarizing film manufacturing method, for example, by the following steps: forming a polyvinyl alcohol-based resin layer (PVA-based resin layer) containing a polyvinyl alcohol-based resin (PVA-based resin) on one side of a long thermoplastic resin substrate to prepare a laminate; and subjecting the obtained laminate to optional insolubilization, crosslinking, and washing steps, and at least an auxiliary in-air stretching step, a dyeing step, and an underwater stretching step while conveying the laminate in the longitudinal direction. The boron content in the thin polarizing film can be controlled by the concentration of a boron component-donating substance (e.g., boric acid, borate, or a boron compound such as borax) contained in any of the treatment baths in the insolubilization, crosslinking, washing, dyeing, and underwater stretching steps, and by the treatment temperature and treatment time in each of the treatment baths.

[0040] <Polarizing film> In the polarizing film of the present invention, the first transparent protective film and the polarizing membrane are bonded together via a water-based adhesive layer.

[0041] <First transparent protective film> The first transparent protective film is not particularly limited as long as it is a transparent protective film used in a polarizing film. However, when the first transparent protective film side of the polarizing film is attached to an image display cell, it is preferable that the first transparent protective film has a moisture permeability of 50 g / (m 2 24h) or less, and the moisture permeability is 30g / (m 2 24h) or less is more preferable, and 15g / (m 224h) or less. A second transparent protective film may be attached to the surface of the polarizing film opposite to the first transparent protective film. In this case, the second transparent protective film should have a moisture permeability of 1000 g / (m 2 24h) or less, and 800g / (m 2 24h) or less is more preferable, and 600g / (m 2 The moisture permeability can be calculated according to the moisture permeability test (cup method) of JIS Z0208 by cutting a sample to a diameter of 60 mm, placing it in a moisture permeability cup containing approximately 15 g of calcium chloride, placing it in an incubator at a temperature of 40°C and a humidity of 90% RH, and measuring the increase in weight of the calcium chloride before and after leaving it for 24 hours.

[0042] The material of the first and second transparent protective films is not particularly limited, and for example, organic base materials such as transparent protective films used in polarizing films and retardation films can be used.

[0043] Examples of materials constituting the first and second transparent protective films include cellulose ester resins, polycarbonate resins, (meth)acrylic resins, cyclic polyolefin resins, polyester resins, etc. Examples of the retardation film include birefringent films obtained by uniaxially or biaxially stretching a polymer material, oriented films of liquid crystal polymers, and films in which an oriented layer of liquid crystal polymer is supported by a film.

[0044] In the polarizing film, other layers such as a hard coat layer, an anti-sticking layer, a diffusion layer, or an anti-glare layer may be provided on the surfaces of the first and second transparent protective films that are not bonded to the polarizing film. The other layers may be provided on the protective film itself, or may be provided separately from the protective film.

[0045] The thickness of the first and second transparent protective films can be determined as appropriate, but generally, from the standpoint of workability such as strength and handling, thinness, etc., it is preferably about 1 to 500 μm, more preferably about 1 to 300 μm, and even more preferably about 5 to 100 μm.

[0046] The first and second transparent protective films may contain any suitable additives such as ultraviolet absorbers, antioxidants, lubricants, plasticizers, release agents, coloring inhibitors, flame retardants, antistatic agents, pigments, and colorants.

[0047] <Water-based adhesive layer> The adhesive for forming the aqueous adhesive layer can be any of various aqueous adhesives used in polarizing films, including, for example, isocyanate-based adhesives, polyvinyl alcohol-based adhesives, gelatin-based adhesives, vinyl latex-based adhesives, aqueous polyester adhesives, etc. Among these, polyvinyl alcohol-based adhesives are preferred, and acetoacetyl group-containing polyvinyl alcohol-based adhesives are more preferred.

[0048] The aqueous adhesive may contain a crosslinking agent. The crosslinking agent is typically a compound having at least two functional groups per molecule that are reactive with the polymer or other components that make up the adhesive, such as alkylenediamines, isocyanates, epoxies, aldehydes, and amino-formaldehydes such as methylol urea and methylol melamine. 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 or other components that make up the adhesive.

[0049] When the second transparent protective film is attached to the polarizing film, an adhesive is usually used. Examples of the adhesive include the above-mentioned aqueous adhesives, ultraviolet-curable adhesives, and electron beam-curable adhesives. The adhesive may also contain a metal compound filler.

[0050] The adhesive, such as the aqueous adhesive, may be applied to either the first and second transparent protective films or the polarizing film, or to both. After lamination, a drying step is performed to form an adhesive layer consisting of a dried coated layer. The polarizing film and the transparent protective film can be laminated using a roll laminator or the like. After the drying step, ultraviolet light or electron beams can be irradiated as needed. The thickness of the adhesive layer is not particularly limited, but is preferably about 30 to 5,000 nm, and more preferably about 100 to 1,000 nm.

[0051] The first and second transparent protective films and the polarizing film may be laminated via an intervening layer such as a surface modification treatment layer, an easy-adhesive layer, a blocking layer, or a refractive index adjustment layer.

[0052] Examples of the surface modification treatment for forming the surface modification layer include corona treatment, plasma treatment, primer treatment, and saponification treatment.

[0053] Examples of the easy-adhesion adhesive that forms the easy-adhesion layer include forming materials containing various resins having a polyester skeleton, a polyether skeleton, a polycarbonate skeleton, a polyurethane skeleton, a silicone skeleton, a polyamide skeleton, a polyimide skeleton, a polyvinyl alcohol skeleton, etc. The easy-adhesion layer is usually provided in advance on the protective film, and the easy-adhesion layer side of the protective film and the polarizing film are laminated with the pressure-sensitive adhesive layer or the adhesive layer.

[0054] The blocking layer has the function of preventing impurities such as oligomers and ions eluted from a transparent protective film, etc., from migrating (penetrating) into the polarizing film. The blocking layer may be any layer as long as it is transparent and can prevent impurities from eluting from a transparent protective film, etc. Examples of materials for forming the blocking layer include urethane prepolymer-based forming materials, cyanoacrylate-based forming materials, and epoxy-based forming materials.

[0055] The refractive index adjusting layer is a layer provided to suppress a decrease in transmittance due to reflection between layers having different refractive indices, such as the transparent protective film and a polarizing film, etc. Examples of refractive index adjusting materials that form the refractive index adjusting layer include forming agents containing various resins such as silica-based, acrylic-based, acrylic-styrene-based, and melamine-based resins and additives.

[0056] The polarizing film may be a laminated polarizing film (optical laminate) in which the polarizing film is bonded to an optical layer. The optical layer is not particularly limited, and may be, for example, one or more optical layers that are sometimes used in forming liquid crystal displays, such as a reflector, a semi-transmitting plate, a retardation plate (including half-wave or quarter-wave plates), or a viewing angle compensation film. Examples of the laminated polarizing film include a reflective polarizing film or a semi-transmitting polarizing film in which a reflector or semi-transmitting reflector is laminated on the polarizing film; an elliptical polarizing film or a circular polarizing film in which a retardation plate is laminated on the polarizing film; a wide-viewing-angle polarizing film in which a viewing angle compensation film is laminated on the polarizing film; and a polarizing film in which a brightness-enhancing film is laminated on the polarizing film.

[0057] An adhesive layer may be provided on one or both surfaces 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 other components, such as a front transparent plate or a front transparent member such as a touch panel on the viewing side. A pressure-sensitive adhesive layer is suitable as the adhesive layer. The pressure-sensitive adhesive forming the pressure-sensitive adhesive layer is not particularly limited, and may be appropriately selected from those having a base polymer such as an acrylic polymer, a silicone polymer, polyester, polyurethane, polyamide, polyether, a fluorine-based polymer, or a rubber-based polymer. In particular, pressure-sensitive adhesives that have excellent optical transparency, moderate wettability, cohesion, and adhesion, and excellent weather resistance, heat resistance, etc., such as pressure-sensitive adhesives containing acrylic polymers, are preferably used.

[0058] The application of a pressure-sensitive adhesive layer to one or both surfaces of the polarizing film or the laminated polarizing film can be carried out by any suitable method. Examples of application of a pressure-sensitive adhesive layer include preparing a pressure-sensitive adhesive solution and applying it directly to the polarizing film or the laminated polarizing film by a suitable application method such as a casting method or a coating method, or forming a pressure-sensitive adhesive layer on a separator and then transferring it onto the polarizing film or the laminated polarizing film. The thickness of the pressure-sensitive adhesive layer can be determined appropriately depending on the intended use, adhesive strength, etc., and is generally 1 to 500 μm, preferably 5 to 200 μm, and more preferably 10 to 100 μm. The polarizing film or the laminated polarizing film having a pressure-sensitive adhesive layer on at least one surface thereof is referred to as a pressure-sensitive adhesive layer-attached polarizing film or a pressure-sensitive adhesive layer-attached laminated polarizing film.

[0059] It is preferable that a separator be temporarily attached to cover the exposed surface of the pressure-sensitive adhesive layer to prevent contamination, etc., until the product is put into practical use. This prevents contamination, etc., of the pressure-sensitive adhesive layer under normal handling conditions. Examples of the separator include suitable thin sheets such as plastic films, rubber sheets, paper, cloth, nonwoven fabrics, nets, foam sheets, metal foils, and laminates thereof, which are coated with a suitable release agent, such as a silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide-based release agent, as needed.

[0060] <Image display panel> In the image display panel of the present invention, the first transparent protective film side of the polarizing film is bonded to an image display cell. Examples of the image display cell include a liquid crystal cell and an organic EL cell. The liquid crystal cell may be, for example, a reflective liquid crystal cell that uses external light, a transmissive liquid crystal cell that uses light from a light source such as a backlight, or a semi-transmissive semi-reflective liquid crystal cell that uses both external light and light from the light source. When the liquid crystal cell uses light from a light source, the image display device (liquid crystal display device) has a polarizing film disposed on the opposite side of the image display cell (liquid crystal cell) from the viewing side, and further has a light source disposed thereon. The polarizing film on the light source side and the liquid crystal cell are preferably bonded together via an appropriate adhesive layer. The liquid crystal cell may be driven in any mode, such as VA mode, IPS mode, TN mode, STN mode, or bend alignment (π type).

[0061] The organic EL cell preferably has a light-emitting body (organic electroluminescence light-emitting body) formed by sequentially laminating a transparent electrode, an organic light-emitting layer, and a metal electrode on a transparent substrate. 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 such a light-emitting layer 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.

[0062] <Image display device> The image display device of the present invention includes the image display panel and a front transparent member. The image display panel typically includes a front transparent member on the second transparent protective film side of the image display panel.

[0063] Examples of the front transparent member disposed on the viewing side of the image display cell include a front transparent plate (window layer) and a touch panel. A transparent plate having appropriate mechanical strength and thickness is used as the front transparent plate. Examples of such transparent plates include transparent resin plates such as acrylic resins and polycarbonate resins, and glass plates. Examples of the touch panel include various touch panels such as resistive, capacitive, optical, and ultrasonic touch panels, as well as glass or transparent resin plates equipped with touch sensor functions. 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 on the viewing side of the touch panel.

[0064] The polarizing film of the present invention has excellent durability in high-temperature and high-humidity environments, and therefore can be preferably used not only for flat panel display applications and mobile applications, but also for in-vehicle display applications and display applications intended for outdoor use, such as signage. [Example]

[0065] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0066] Example 1 <Preparation of polarizing film> 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 30°C swelling bath (water bath) for 30 seconds between rolls with different peripheral speed ratios, where it was stretched 2.2 times in the conveying direction while swelling (swelling step). Subsequently, the film was immersed in a 30°C dye bath (iodine solution obtained by blending iodine and potassium iodide in a weight ratio of 1:7 with 100 parts by weight of water) for 30 seconds, with the iodine concentration adjusted so that the polarizing film had the desired transmittance. The film was then stretched 3.3 times in the conveying direction relative to the original polyvinyl alcohol film (polyvinyl alcohol film that was not stretched in the conveying direction at all) while dyeing (dyeing step). The dyed polyvinyl alcohol film was then immersed in a 40°C crosslinking bath (aqueous solution containing 3.5 wt% boric acid, 3.0 wt% potassium iodide, and 3.6 wt% zinc sulfate) for 28 seconds and stretched in the machine direction to 3.6 times its original size (crosslinking step). The resulting polyvinyl alcohol film was then immersed in a 64°C stretching bath (aqueous solution containing 4.8 wt% boric acid, 5.0 wt% potassium iodide, and 5.0 wt% zinc sulfate) for 60 seconds and stretched in the machine direction to 6.0 times its original size (stretching step). The resulting polyvinyl alcohol film was then immersed in a 29°C washing bath (potassium iodide concentration: 2.3 wt%) for 10 seconds (washing step). The washed polyvinyl alcohol film was dried at 40°C for 30 seconds to produce a polarizing film. The boric acid index calculated by the ATR method in FT-IR was 3.20, and the boric acid content (wt%) calculated by the neutralization titration method was 27.5 wt%. The thickness of the polarizing film was 18 μm.

[0067] <(A) Measurement method of boric acid index calculated by ATR method in FT-IR> Using the polarizing film obtained above, a boric acid peak (665 cm ) was detected by attenuated total reflection spectroscopy (ATR) measurement using a Fourier transform infrared spectrophotometer (FT-IR) (manufactured by Perkin Elmer, trade name “SPECTRUM2000”). -1 ) and the intensity of the reference peak (2940 cm -1The boric acid index was calculated from the obtained boric acid peak intensity and reference peak intensity using the following formula. (Boric acid index) = (boric acid peak 665 cm -1 Intensity of the reference peak at 2940 cm -1 (Intensity of

[0068] <(B) Method for measuring boric acid content (wt%) calculated by neutralization titration method> A polarizing film (approximately 0.2 g) dried at 120°C for 2 hours was dissolved in water, and a small amount of mannitol and BTB solution was added dropwise to the resulting solution. The solution was then neutralized with a 0.1 mol / L NaOH solution using a burette, and the boron content of the polarizing film was calculated using the following formula. Boron content of polarizing film (wt%) = C × V × Mw / M × 100 C: Concentration of NaOH solution (mol / L) V: Amount of NaOH solution dropped (L) Mw: Molecular weight of boron (g / mol) M: Weight of polarizing film after drying at 120°C for 2 hours (g)

[0069] <Preparation of polarizing film> The adhesive used was an aqueous solution containing an acetoacetyl group-containing polyvinyl alcohol resin (average polymerization degree 1,200, saponification degree 98.5 mol%, acetoacetylation degree 5 mol%) and methylolmelamine in a weight ratio of 3:1. Using this adhesive, a cycloolefin film (moisture permeability 10 g / (m)) was attached to one side of the polarizing film obtained above (the surface on the image display cell side) as a first transparent protective film. 2 24h), manufactured by Nippon Shokubai, product name "ZT Film" (hereinafter, this film will be referred to as "Transparent Film A"). Also, as a second transparent protective film, a 48 μm-thick transparent protective film (moisture permeability 300 g / (m)) was used on the other side (viewing side) of the film, which was made of triacetyl cellulose film (manufactured by Fuji Film, product name "TJ40UL") with HC formed thereon. 2After laminating the transparent film B with a roll laminator, the film was subsequently dried by heating in an oven (at 90°C for 10 minutes) to produce a polarizing film with transparent protective films laminated on both sides of the polarizing film.

[0070] <Evaluation of pattern marks> The levels were determined by visual appearance inspection (relative evaluation using level samples, sensory evaluation). Levels 1 and 2 were considered to be suitable for practical use, with level 1 being more preferable. Level 1: No irregularities are visible when the polarized film is on. Level 2: Unnoticeable when attached to a pseudo panel (glass), but visible when attached to a polarized film. Level 3: Irregularities are visible when the pseudo panel (glass) is attached.

[0071] <Preparation of acrylic adhesive> A four-neck flask equipped with a stirring blade, a thermometer, a nitrogen gas inlet tube, and a condenser was charged with a monomer mixture containing 99 parts of butyl acrylate and 1 part of 4-hydroxybutyl acrylate. Furthermore, 0.1 parts of 2,2'-azobisisobutyronitrile as a polymerization initiator and 100 parts of ethyl acetate were charged to 100 parts of the monomer mixture (solid content). Nitrogen gas was introduced with gentle stirring to replace the atmosphere, and the temperature in the flask was maintained at around 55°C to carry out a polymerization reaction for 8 hours, producing an acrylic polymer solution with a weight-average molecular weight (Mw) of 1,800,000. Thereafter, 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 blended with 100 parts of the solid content of the obtained acrylic polymer solution to prepare a solution of an acrylic pressure-sensitive adhesive composition.

[0072] <Preparation of polarizing film with adhesive> The solution of the acrylic pressure-sensitive adhesive composition obtained above was applied to one side of a polyethylene terephthalate film (Mitsubishi Chemical Polyester Film Co., Ltd., product name "MRF38", separator film) treated with a silicone-based release agent so that the thickness of the pressure-sensitive adhesive layer after drying would be 20 μm, and the film was dried at 90° C. for 1 minute to form a pressure-sensitive adhesive layer on the surface of the separator film. Next, the pressure-sensitive adhesive layer formed on the separator film was transferred to the protective film surface on the image display cell side of the polarized film prepared above, to prepare a polarized film with a pressure-sensitive adhesive layer.

[0073] <Fabrication of pseudo image display panel> The polarizing film with adhesive layer obtained above was cut to a size of 40 x 40 mm so that the absorption axis of the polarizing film was parallel to the long side, and a glass plate (50 x 45 mm, thickness 1.1 mm) was attached to it via the adhesive layer. The resulting sheet 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 an adhesive layer on one side).

[0074] <Evaluation of durability under high temperature and humidity conditions> The pseudo image display panel obtained above was subjected to a durability test for 240 hours at a temperature of 85°C and a relative humidity of 85%. The polarization degree (ΔP) was measured before and after the test (humidification). The polarization degree was measured using a spectrophotometer (LPF-200, manufactured by Otsuka Electronics Co., Ltd.). The polarization degree (ΔP) was 0 The refractive index is preferably within a range of 0 to -0.03, and more preferably within a range of 0 to -0.01. The measurement wavelength is 380 to 780 nm (at intervals of 5 nm). The results are shown in Table 1.

[0075] <Examples 2-7 and 9> A pseudo image display panel was produced in the same manner as in Example 1, except that in producing the polarizing film, the boric acid concentration in the stretching bath and the temperature of the washing bath were changed as shown in Table 1.

[0076] Example 8 A pseudo-image display panel was produced in the same manner as in Example 1, except that in the production of the polarizing film, a second cleaning step was added between the cleaning bath step and the polarizer drying step, in which the polarizer was brought into contact with a gravure roll to which warm water of approximately 40°C had been supplied, and the boric acid concentration in the stretching bath and the temperature of the cleaning bath were changed as shown in Table 1.

[0077] <Comparative Example 1-2> A pseudo image display panel was produced in the same manner as in Example 1, except that in producing the polarizing film, the boric acid concentration in the stretching bath and the temperature of the washing bath were changed as shown in Table 1.

[0078] The pseudo image display panels of the examples and comparative examples obtained above were used to carry out the evaluation of the pattern marks and the evaluation of durability under high temperature and humidity conditions. The results are shown in Table 1.

[0079] [Table 1]

Claims

1. A polarizing film in which a first transparent protective film and a polarizing film are bonded together via a water-based adhesive layer, the first transparent protective film has a moisture permeability of 50 g / (m 2 ·24 h) or less; The polarizing film is a polarizing film in which a dichroic substance is adsorbed and aligned on a polyvinyl alcohol-based film, and the alignment is fixed by boric acid crosslinking, and the polarizing film is characterized in that the ratio ((A) / (B)) of (A) a boric acid index calculated by an ATR method in FT-IR and (B) a boric acid content (wt%) calculated by a neutralization titration method is less than 0.

13.

2. 2. The polarizing film according to claim 1, wherein the ratio ((A) / (B)) of the (A) boric acid index calculated by the ATR method in FT-IR and the (B) boric acid content (% by weight) calculated by the neutralization titration method is 0.06 or more.

3. 3. The polarizing film according to claim 1, wherein the boric acid index (A) calculated by the ATR method in FT-IR is 3.46 or less.

4. 3. The polarizing film according to claim 1, wherein the content (% by weight) of boric acid (B) calculated by neutralization titration method is 20% by weight or more.

5. 3. The polarizing film according to claim 1, wherein the polarizing film is an iodine-based polarizing film in which iodine is adsorbed and aligned.

6. 3. An image display panel comprising the polarizing film according to claim 1 or 2, with the first transparent protective film side attached to an image display cell.

7. An image display device characterized by having the image display panel described in claim 6 and a front transparent member.

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