Stacked body and method for manufacturing stacked body

Abstract

The present invention provides a laminate having both excellent adhesion and excellent appearance. The laminate of the present invention has a resin base material and a polyvinyl alcohol-based resin layer formed on one side of the resin base material. The resin base material side of the polyvinyl alcohol-based resin layer is provided with an intermediate region in which a polyolefin-based component is present.

Description

[0001] This application is a divisional application of the application with the application number 201680076115.6, the application date of December 19, 2016, and the title of "Laminate and method for manufacturing laminate". TECHNICAL FIELD

[0002] The present application relates to a laminate having a polyvinyl alcohol-based resin layer. BACKGROUND

[0003] A method of forming a polyvinyl alcohol-based resin layer on a resin base material, and stretching and dyeing the laminate to obtain a polarizing film has been proposed (for example, Patent Literature 1). By such a method, a polarizing film having a thin thickness can be obtained, and therefore, for example, it is expected to contribute to the thinness of an image display device, and is attracting attention.

[0004] The above-described polarizing film can be used as it is in a state of being laminated to the above-described resin base material. In this embodiment, sufficient adhesion of the polyvinyl alcohol-based resin layer (polarizing film) to the resin base material is required. Specifically, it is required that the polyvinyl alcohol-based resin layer does not peel from the resin base material in the production of the polarizing film (for example, in stretching, conveyance), does not peel from the resin base material at the time of rework, or does not float or the like of the polarizing film or the resin base material due to impact at the time of processing (for example, punching) or use.

[0005] In order to improve the above-described adhesion, a primer layer containing a polyvinyl alcohol-based material is provided between the resin base material and the polyvinyl alcohol-based resin layer (Patent Literature 2). However, in the case where the primer layer is provided, there is a problem that it is difficult to obtain a good appearance.

[0006] PRIOR ART DOCUMENTS

[0007] PATENT LITERATURE

[0008] Patent Literature 1: Japanese Patent Application Laid-Open No. 2000-338329

[0009] Patent Literature 2: Japanese Patent No. 4950357 SUMMARY

[0010] PROBLEMS TO BE SOLVED BY THE INVENTION

[0011] The present application has been achieved in order to solve the above-described problems, and a main object thereof is to provide a laminate having both excellent adhesion and excellent appearance.

[0012] METHOD FOR SOLVING PROBLEMS

[0013] A laminate can be provided according to the present application. The laminate of the present application has a resin substrate and a polyvinyl alcohol-based resin layer formed on one side of the resin substrate. The resin substrate side of the polyvinyl alcohol-based resin layer is provided with an intermediate region in which a polyolefin-based component is present.

[0014] In one embodiment, the intermediate region contains a polyvinyl alcohol-based component and a polyolefin-based component.

[0015] In one embodiment, the polyvinyl alcohol-based component contains an acetoacetyl-modified polyvinyl alcohol.

[0016] In one embodiment, the mixing ratio of the polyvinyl alcohol-based component to the polyolefin-based component is 5:95 to 60:40.

[0017] In one embodiment, the thickness of the intermediate region is 100 nm to 1000 nm.

[0018] According to another aspect of the present application, a method for manufacturing a laminate can be provided. The method for manufacturing a laminate includes a step of forming a primer layer on one side of a resin substrate by applying a primer layer-forming composition containing a polyolefin-based component, and a step of forming a polyvinyl alcohol-based resin coating layer on the surface of the primer layer by applying a coating liquid containing a polyvinyl alcohol-based resin.

[0019] In one embodiment, the primer layer-forming composition contains a polyvinyl alcohol-based component and a polyolefin-based component.

[0020] In one embodiment, the polyvinyl alcohol-based component contains an acetoacetyl-modified polyvinyl alcohol.

[0021] In one embodiment, the mixing ratio of the solid content of the polyvinyl alcohol-based component to the polyolefin-based component is 5:95 to 60:40.

[0022] In one embodiment, the thickness of the primer layer is 500 nm to 3000 nm.

[0023] According to another aspect of the present application, a method for manufacturing a polarizing plate can be provided. The method for manufacturing a polarizing plate includes a step of stretching and dyeing the laminate obtained by the above manufacturing method.

[0024] According to another aspect of the present application, a polarizing plate can be provided. The polarizing plate has a resin substrate and a polyvinyl alcohol-based resin layer formed on one side of the resin substrate. The resin substrate side of the polyvinyl alcohol-based resin layer is provided with an intermediate region in which a polyolefin-based component is present, and the polyvinyl alcohol-based resin layer is a polarizing film obtained by adsorption orientation of a dichroic substance.

[0025] In one embodiment, the intermediate region contains a polyvinyl alcohol-based component and a polyolefin-based component.

[0026] In one embodiment, the polyvinyl alcohol-based component contains an acetoacetyl-modified polyvinyl alcohol.

[0027] In one embodiment, the mixing ratio of the polyvinyl alcohol-based component to the polyolefin-based component is 5:95 to 60:40.

[0028] In one embodiment, the thickness of the intermediate region is 100 nm to 1000 nm.

[0029] Effects of the Invention

[0030] According to the present application, by providing the resin substrate side of the polyvinyl alcohol-based resin layer with an intermediate region containing a polyolefin-based component, a laminate having both excellent adhesion and excellent appearance can be obtained. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 SEM observation photographs of the cross sections of the laminates of Examples and Comparative Examples. EMBODIMENTS

[0032] Hereinafter, embodiments of the present application will be described, but the present application is not limited to these embodiments.

[0033] A. LAMINATE

[0034] The laminate of the present application has a resin substrate and a polyvinyl alcohol-based resin (hereinafter referred to as "PVA-based resin") layer formed on one side of the resin substrate, and at least the resin substrate side of the PVA-based resin layer is provided with an intermediate region containing a polyolefin-based component. In one embodiment, the intermediate region substantially corresponds to a primer layer described later, and the PVA-based resin layer contains the primer layer and a PVA-based resin coating layer described later. In another embodiment, the PVA-based resin layer substantially forms a single layer, and the intermediate region is provided as, for example, a compatible region of the PVA-based resin coating layer and the primer layer. Note that the PVA-based resin layer is processed into a polarizing film by various processes, and the laminate can be made into a polarizing sheet.

[0035] A-1. RESIN SUBSTRATE

[0036] As the material constituting the resin substrate, any appropriate material can be used. Examples include ester resins such as polyethylene terephthalate resins, cyclic olefin resins, olefin resins such as polypropylene, (meth)acrylic resins, polyamide resins, polycarbonate resins, and copolymer resins of these resins. It is preferable to use a polyethylene terephthalate resin. Of these, it is preferable to use an amorphous polyethylene terephthalate resin. Specific examples of the amorphous polyethylene terephthalate resin include copolymers further containing isophthalic acid as a dicarboxylic acid and copolymers further containing cyclohexane dimethanol as a diol.

[0037] The glass transition temperature (Tg) of the resin substrate is preferably 170°C or lower. By using such a resin substrate, crystallization of the PVA-based resin layer can be suppressed, and stretchability can be sufficiently ensured. In view of plasticization of the resin substrate with water and good stretching in water, 120°C or lower is more preferable. In one embodiment, the glass transition temperature of the resin substrate is preferably 60°C or higher. By using such a resin substrate, deformation (e.g., generation of unevenness, sagging, wrinkles, etc.) of the resin substrate and the like can be prevented when the coating liquid containing the PVA-based resin is coated and dried as described later. In addition, stretching of the laminate can be performed at an appropriate temperature (e.g., around 60°C to 70°C). In another embodiment, the glass transition temperature can be lower than 60°C as long as the resin substrate does not deform when the coating liquid containing the PVA-based resin is coated and dried. Note that the glass transition temperature (Tg) is a value obtained in accordance with JIS K 7121.

[0038] In one embodiment, the water absorption of the resin substrate is preferably 0.2% or more, and more preferably 0.3% or more. Such a resin substrate absorbs water, and the water functions as a plasticizer to perform plasticization. As a result, in stretching in water, the stretching stress can be greatly reduced, and excellent stretchability can be achieved. On the other hand, the water absorption of the resin substrate is preferably 3.0% or less, and more preferably 1.0% or less. By using such a resin substrate, a significant decrease in the dimensional stability of the resin substrate at the time of manufacture can be prevented, and the appearance of the obtained laminate can be deteriorated, and the like. In addition, breakage at the time of stretching in water and peeling of the PVA-based resin film from the resin substrate can be prevented. Note that the water absorption is a value obtained in accordance with JIS K 7209.

[0039] The thickness of the resin substrate is preferably 20 μm to 300 μm, and more preferably 30 μm to 200 μm.

[0040] The surface of the resin substrate can be subjected to a surface modification treatment (e.g., corona treatment) in advance, or an easy-adhesion layer can be formed. By these treatments, the adhesion can be further improved.

[0041] A-2. PVA-based resin layer

[0042] As the PVA-based resin forming the PVA-based resin layer, any appropriate resin can be used. Examples include polyvinyl alcohol and ethylene-vinyl alcohol copolymer. The polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer can be obtained by saponifying ethylene-vinyl acetate copolymer. The saponification degree of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, and more preferably 99.0 mol% to 99.93 mol%. The saponification degree can be determined according to JIS K6726-1994. By using a PVA-based resin having such a saponification degree, a polarizing film having excellent durability can be obtained. When the saponification degree is too high, there is a risk of gelation.

[0043] The average polymerization degree of the PVA-based resin can be appropriately selected according to the purpose. The average polymerization degree is usually 1000 to 10000, preferably 1200 to 4500, and more preferably 1500 to 4300. Note that the average polymerization degree can be determined according to JIS K6726-1994.

[0044] The representative thickness of the PVA-based resin layer is 20 μm or less, and preferably 15 μm or less. When the PVA-based resin layer is used as a polarizing film, the thickness thereof is preferably 10 μm or less, more preferably 8 μm or less, further preferably 7 μm or less, and particularly preferably 6 μm or less. On the other hand, the thickness of the PVA-based resin layer is preferably 1.0 μm or more, and more preferably 2.0 μm or more.

[0045] When the PVA-based resin layer is used as a polarizing film, the PVA-based resin layer is in a state in which a dichroic substance is adsorbed and oriented, and preferably exhibits absorption dichroism at any wavelength in the wavelength range of 380 nm to 780 nm. In this case, the monomer transmittance of the PVA-based resin layer is preferably 40.0% or more, more preferably 41.0% or more, further preferably 42.0% or more, and particularly preferably 43.0% or more. The polarization degree of the PVA-based resin layer is preferably 99.8% or more, more preferably 99.9% or more, and further preferably 99.95% or more.

[0046] As described above, the resin substrate side of the PVA-based resin layer is provided with an intermediate region in which the polyolefin-based component is present. By forming such a region, excellent adhesion and excellent appearance can be achieved. The thickness of the intermediate region is, for example, 100 nm to 1000 nm. The intermediate region can be confirmed, for example, by observing the cross section of the laminate using a scanning electron microscope (SEM). In addition, the presence or absence of the polyolefin-based component can be confirmed, for example, by time-of-flight secondary ion mass spectrometry (TOF-SIMS), infrared spectroscopy (IR). In one embodiment, the intermediate region contains a polyvinyl alcohol-based component and a polyolefin-based component. Note that the details of the polyolefin-based component and the polyvinyl alcohol-based component are described later.

[0047] B. Manufacturing method

[0048] The laminate of the present application can be manufactured by any appropriate method as long as the above-described structure is obtained. In one embodiment, the laminate is manufactured by a method including a step of forming a primer layer by applying a primer layer-forming composition containing a polyolefin-based component to one side of a resin substrate; and a step of forming a PVA-based resin coating layer by applying a coating liquid containing a PVA-based resin to the surface of the primer layer.

[0049] B-1. Formation of primer layer

[0050] The above-described primer layer-forming composition preferably contains a polyvinyl alcohol-based component and a polyolefin-based component. By being composed as such, a laminate having both excellent adhesion and excellent appearance can be obtained. As the polyvinyl alcohol-based component, any appropriate PVA-based resin can be used. Specifically, polyvinyl alcohol, modified polyvinyl alcohol can be mentioned. As the modified polyvinyl alcohol, for example, polyvinyl alcohol modified with acetoacetyl group, carboxyl group, acryl group, and / or urethane group can be mentioned. Among them, acetoacetyl group-modified PVA is preferably used. As the acetoacetyl group-modified PVA, a polymer having at least a repeating unit represented by the following general formula (I) is preferably used.

[0051] [Chemical Formula 1]

[0052]

[0053] In the above-described formula (I), the ratio of n with respect to l+m+n is preferably 1% to 10%.

[0054] The average polymerization degree of the acetoacetyl group-modified PVA is preferably 1000 to 10000, and preferably 1200 to 5000. The saponification degree of the acetoacetyl group-modified PVA is preferably 97 mol% or more. The pH of a 4 wt% aqueous solution of the acetoacetyl group-modified PVA is preferably 3.5 to 5.5. Note that the average polymerization degree and the saponification degree can be found in accordance with JIS K 6726-1994.

[0055] As the above polyolefin-based component, any appropriate polyolefin-based resin can be used. As the olefin component of the main component of the polyolefin-based resin, for example, an olefin-based hydrocarbon having 2 to 6 carbon atoms such as ethylene, propylene, isobutylene, 1-butene, 1-pentene, 1-hexene, and the like can be listed. These components can be used alone or in combination of two or more. Among them, an olefin-based hydrocarbon having 2 to 4 carbon atoms such as ethylene, propylene, isobutylene, 1-butene, and the like is preferred, and ethylene is more preferred to be used.

[0056] In the monomer component constituting the above polyolefin-based resin, the ratio of the olefin component is preferably 50 to 95% by weight.

[0057] The above polyolefin-based resin preferably has a carboxyl group and / or an anhydride group thereof. Such a polyolefin-based resin can be dispersed in water and can form a primer layer well. As the monomer component having such a functional group, for example, an unsaturated carboxylic acid and an anhydride thereof, a half ester of an unsaturated dicarboxylic acid, a half amide can be listed. As specific examples of these, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, fumaric acid, crotonic acid can be listed.

[0058] The molecular weight of the polyolefin-based resin is, for example, 5,000 to 80,000.

[0059] In the above primer layer-forming composition, the blending ratio (solid component) of the polyvinyl alcohol-based component to the polyolefin-based component is preferably 5:95 to 60:40, and more preferably 20:80 to 50:50. If the polyvinyl alcohol-based component is too much, there is a risk that adhesion cannot be sufficiently obtained. Specifically, there is a risk that the peeling force required when peeling the PVA-based resin layer from the resin base material decreases and sufficient adhesion cannot be obtained. On the other hand, if the polyvinyl alcohol-based component is too little, there is a risk that the appearance of the obtained laminate is impaired. Specifically, there is a risk that the coating film becomes white turbid and the like when forming the primer layer as described later, and it is difficult to obtain a laminate excellent in appearance.

[0060] The primer layer-forming composition is preferably aqueous. The primer layer-forming composition can contain an organic solvent. As the organic solvent, for example, ethanol, isopropanol, and the like can be listed. The solid component concentration of the primer layer-forming composition is preferably 1.0 to 10% by weight.

[0061] An additive can also be blended in the primer layer-forming composition. As the additive, for example, a crosslinking agent and the like can be listed. As the crosslinking agent, for example, a compound having two or more functional groups such as an amino group, a hydroxyl group, and the like can be listed. oxazoline, boric acid, a methylol compound such as a methylolated compound, a carbodiimide, an isocyanate compound, an epoxy compound, and the like. The blending amount of the additive in the composition for forming a primer layer can be appropriately set according to the purpose or the like. For example, the blending amount of the crosslinking agent is preferably 10 parts by weight or less, more preferably 0.01 parts by weight to 10 parts by weight, and further preferably 0.1 parts by weight to 5 parts by weight, with respect to 100 parts by weight of the total of the polyvinyl alcohol-based component and the polyolefin-based component.

[0062] As the coating method of the composition for forming a primer layer, any appropriate method can be employed. Examples that can be cited include: roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, doctor blade coating (notched wheel coating and the like), and the like.

[0063] The composition for forming a primer layer is preferably coated in such a manner that the thickness of the resulting primer layer is 500 nm to 3000 nm, and more preferably 800 nm to 2000 nm. When the primer layer is too thin, there is a risk that sufficient adhesion cannot be obtained. On the other hand, when the primer layer is too thick, there is a risk that, at the time of formation of the PVA-based resin coating layer described later, coating becomes difficult, unevenness occurs in the resulting coating film, and a problem occurs, making it difficult to obtain a laminate with an excellent appearance.

[0064] After the composition for forming a primer layer is coated, the coating film can be dried. The drying temperature is, for example, 50°C or higher.

[0065] B-2. Formation of a PVA-based resin coating layer

[0066] The surface of the primer layer to which the coating liquid containing the PVA-based resin described above is applied can be subjected to a surface modification treatment (for example, corona treatment or the like) in advance. By such a treatment, adhesion can be further improved.

[0067] As the coating liquid containing the PVA-based resin described above, a solution obtained by dissolving the PVA-based resin described above in a solvent can generally be used. As the solvent, examples that can be cited include: water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, a polyol such as trimethylolpropane, ethylenediamine, diethylenetriamine, and the like. These solvents can be used alone or in combination with two or more. Among them, water is preferred. The PVA-based resin concentration of the coating liquid is preferably 3 parts by weight to 20 parts by weight with respect to 100 parts by weight of the solvent. As long as the resin concentration is such, a uniform coating film can be formed.

[0068] An additive can be incorporated in the coating liquid. As the additive, for example, a plasticizer, a surfactant, or the like can be exemplified. As the plasticizer, for example, a polyhydric alcohol such as ethylene glycol or glycerol can be exemplified. As the surfactant, for example, a nonionic surfactant can be exemplified. These additives can be used in order to further improve the uniformity, dyeability, and stretchability of the obtained PVA-based resin layer. In addition, as the additive, for example, an easy-adhesion component can be exemplified. By using the easy-adhesion component, the adhesion can be further improved. As the easy-adhesion component, for example, a modified PVA such as acetyl acetyl-modified PVA can be used.

[0069] The coating method of the coating liquid can be the same as the coating method of the above-mentioned undercoat layer-forming composition. The coating film can be dried after the coating. The drying temperature is, for example, 50°C or higher.

[0070] B-3. Production of Polarizing Film

[0071] As described above, the laminate can be subjected to various treatments. As specific examples of the various treatments, for example, a dyeing treatment, a stretching treatment, an insolubilization treatment, a crosslinking treatment, a cleaning treatment, a drying treatment, or the like can be exemplified. These treatments can be appropriately selected depending on the purpose. In addition, the order of the treatments, the timing of the treatments, the number of times of the treatments, or the like can be appropriately set. Hereinafter, each treatment will be described.

[0072] (Dyeing Treatment)

[0073] The above-mentioned dyeing treatment is generally performed by dyeing the PVA-based resin layer with a dichroic substance. It is preferable to perform by adsorbing the dichroic substance to the PVA-based resin layer. As the adsorption method, for example, a method in which the PVA-based resin layer (laminate) is immersed in a dyeing liquid containing a dichroic substance, a method in which the dyeing liquid is applied to the PVA-based resin layer, and a method in which the dyeing liquid is sprayed to the PVA-based resin layer, or the like can be exemplified. It is preferable to be the method in which the PVA-based resin layer is immersed in the dyeing liquid. This is because the dichroic substance can be adsorbed well.

[0074] As the above-mentioned dichroic substance, for example, iodine, an organic dye can be exemplified. These dichroic substances can be used alone, or two or more kinds can be used in combination. The dichroic substance is preferably iodine. In the case where iodine is used as the dichroic substance, the above-mentioned dyeing liquid is preferably an aqueous iodine solution. The incorporation amount of iodine with respect to 100 parts by weight of water is preferably 0.1 part by weight to 0.5 part by weight. In order to improve the solubility of iodine in water, it is preferable to incorporate an iodide in the aqueous iodine solution. As the iodide, for example, potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide, or the like can be exemplified. Among them, potassium iodide is preferable. The incorporation amount of the iodide with respect to 100 parts by weight of water is preferably 0.02 part by weight to 20 parts by weight, more preferably 0.1 part by weight to 10 parts by weight.

[0075] In order to suppress the dissolution of the PVA-based resin, the liquid temperature of the dyeing solution at the time of dyeing is preferably 20°C to 50°C. In order to ensure the transmittance of the PVA-based resin layer when the PVA-based resin layer is immersed in the dyeing solution, the immersion time is preferably 5 seconds to 5 minutes. In addition, the dyeing conditions (concentration, liquid temperature, immersion time) can be set so that the degree of polarization or the monomer transmittance of the polarizing film finally obtained is within a given range. In one embodiment, the immersion time is set so that the degree of polarization of the obtained polarizing film is 99.98% or more. In another embodiment, the immersion time is set so that the monomer transmittance of the obtained polarizing film is 40% to 44%.

[0076] (Stretching treatment)

[0077] The stretching method of the laminate can be any appropriate method. Specifically, it can be a fixed-end stretching (for example, a method using a tenter stretching machine), or a free-end stretching (for example, a method in which the laminate is passed between rollers having different circumferential speeds to perform uniaxial stretching). In addition, it can be a simultaneous biaxial stretching (for example, a method using a simultaneous biaxial stretching machine), or a stepwise biaxial stretching. The stretching of the laminate can be performed in one step, or in multiple steps. In the case of multiple steps, the stretching ratio (maximum stretching ratio) of the laminate described later is the product of the stretching ratios of the respective steps.

[0078] The stretching treatment can be a water stretching method in which the laminate is immersed in a stretching bath, or a stretching method in a gas atmosphere. In one embodiment, at least one water stretching treatment is performed, and preferably the water stretching treatment is combined with a stretching treatment in a gas atmosphere. By water stretching, the laminate can be stretched at a lower temperature than the glass transition temperature of the above-described resin substrate and the PVA-based resin layer (typically, about 80°C), and the crystallization of the PVA-based resin layer can be suppressed, and the laminate can be stretched at a high ratio. As a result, a polarizing film having excellent polarizing properties can be produced.

[0079] The stretching direction of the laminate can be any appropriate direction. In one embodiment, the stretching is performed in the length direction of the long-streak-shaped laminate. Specifically, the laminate is transported in the length direction, and the transport direction (MD) thereof. In another embodiment, the stretching is performed in the width direction of the long-streak-shaped laminate. Specifically, the laminate is transported in the length direction, and the direction perpendicular to the transport direction (MD) thereof.

[0080] The stretching temperature of the laminate can be set to any appropriate value depending on the forming material of the resin substrate, the stretching method, and the like. In the case of using a gas atmosphere stretching method, the stretching temperature is preferably equal to or higher than the glass transition temperature (Tg) of the resin substrate, more preferably equal to or higher than the glass transition temperature (Tg) of the resin substrate + 10°C, and particularly preferably equal to or higher than Tg + 15°C. On the other hand, the stretching temperature of the laminate is preferably equal to or lower than 170°C. By stretching at such a temperature, the rapid development of crystallization of the PVA-based resin can be suppressed, and adverse effects caused by the crystallization (for example, hindering the orientation of the PVA-based resin layer due to stretching) can be suppressed.

[0081] In the case of using a water stretching method as the stretching method, the liquid temperature of the stretching bath is preferably 40°C to 85°C, and more preferably 50°C to 85°C. As long as the temperature is such, the PVA-based resin layer can be suppressed from dissolving, and stretching can be performed at a high magnification. Specifically, as described above, the glass transition temperature (Tg) of the resin substrate is preferably equal to or higher than 60°C in relation to the formation of the PVA-based resin layer. In this case, if the stretching temperature is lower than 40°C, even if the plasticization of the resin substrate by water is taken into account, there is a risk that the stretching cannot be performed well. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, and there is a risk that excellent polarization characteristics cannot be obtained.

[0082] In the case of using a water stretching method, the laminate is preferably stretched by being immersed in an aqueous boric acid solution (boric acid water stretching). By using an aqueous boric acid solution as the stretching bath, the PVA-based resin layer can be given rigidity against the tension applied at the time of stretching and water resistance against dissolving in water. Specifically, boric acid can generate tetraborate anions in an aqueous solution and crosslink with the PVA-based resin through hydrogen bonds. As a result, the PVA-based resin layer can be given rigidity and water resistance, stretching can be performed well, and a polarizing film having excellent polarization characteristics can be produced.

[0083] The above-described aqueous boric acid solution can be preferably obtained by dissolving boric acid and / or a boric acid salt in water as a solvent. The boric acid concentration is preferably 1 part by weight to 10 parts by weight with respect to 100 parts by weight of water. By making the boric acid concentration equal to or higher than 1 part by weight, the dissolution of the PVA-based resin layer can be effectively suppressed, and a polarizing film having higher characteristics can be produced. Note that, in addition to boric acid or a boric acid salt, an aqueous solution obtained by dissolving a boron compound such as borax, glyoxal, glutaraldehyde, or the like in a solvent can also be used.

[0084] The above-described stretching bath (boric acid aqueous solution) preferably contains an iodide. By containing an iodide, the elution of iodine adsorbed to the PVA-based resin layer can be suppressed. Specific examples of the iodide are as described above. The concentration of the iodide with respect to 100 parts by weight of water is preferably 0.05 parts by weight to 15 parts by weight, and more preferably 0.5 parts by weight to 8 parts by weight.

[0085] The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes. The water stretching treatment is preferably performed after the dyeing treatment.

[0086] The stretching ratio (maximum stretching ratio) of the laminate with respect to the original length of the laminate is preferably 4.0 times or more, and more preferably 5.0 times or more. Such a high stretching ratio can be achieved, for example, by using a water stretching method (boric acid water stretching). Note that, in the present specification, the "maximum stretching ratio" refers to the stretching ratio just before the laminate breaks, and is a value lower than the stretching ratio at which the laminate breaks by 0.2.

[0087] (Nonsolubilization treatment)

[0088] The above-described nonsolubilization treatment can be generally performed by immersing the PVA-based resin layer in a boric acid aqueous solution. In particular, when a water stretching method is used, by performing the nonsolubilization treatment, water resistance can be imparted to the PVA-based resin layer. The concentration of the boric acid aqueous solution with respect to 100 parts by weight of water is preferably 1 part by weight to 4 parts by weight. The liquid temperature of the nonsolubilization bath (boric acid aqueous solution) is preferably 20°C to 40°C. The nonsolubilization treatment is preferably performed after the laminate is produced, and before the dyeing treatment and the water stretching treatment.

[0089] (Crosslinking treatment)

[0090] The above-described crosslinking treatment can be generally performed by immersing the PVA-based resin layer in a boric acid aqueous solution. By performing the crosslinking treatment, water resistance can be imparted to the PVA-based resin layer. The concentration of the boric acid aqueous solution with respect to 100 parts by weight of water is preferably 1 part by weight to 4 parts by weight. In addition, when the crosslinking treatment is performed after the above-described dyeing treatment, it is preferable to further contain an iodide. By containing an iodide, the elution of iodine adsorbed to the PVA-based resin layer can be suppressed. The amount of the iodide with respect to 100 parts by weight of water is preferably 1 part by weight to 5 parts by weight. Specific examples of the iodide are as described above. The liquid temperature of the crosslinking bath (boric acid aqueous solution) is preferably 20°C to 50°C. The crosslinking treatment is preferably performed before the water stretching treatment. In the preferable embodiment, the dyeing treatment, the crosslinking treatment, and the water stretching treatment are performed in this order.

[0091] (Cleaning treatment)

[0092] The above-described cleaning treatment can be generally performed by immersing the PVA-based resin layer in a potassium iodide aqueous solution.

[0093] (drying treatment)

[0094] The drying temperature in the drying treatment is preferably from 30°C to 100°C.

[0095] B-4. Others

[0096] The above polarizing plate can have a protective film disposed on the side opposite to the side on which the resin base material is disposed. As a forming material for the protective film, for example, a (meth)acrylic resin, a cellulose resin such as diacetyl cellulose, triacetyl cellulose, a cyclic olefin resin, an olefin resin such as polypropylene, an ester resin such as polyethylene terephthalate resin, a polyamide resin, a polycarbonate resin, a copolymer resin thereof, and the like can be cited. The thickness of the protective film is preferably from 10 μm to 100 μm. The protective film can be laminated to the polarizing film with an adhesive layer interposed therebetween, or can be laminated with the protective film being in close contact (without an adhesive layer interposed therebetween). The adhesive layer is usually formed of an adhesive or a binder.

[0097] The polarizing plate can be mounted, for example, on a liquid crystal display device. In this case, the polarizing film is preferably mounted in a manner disposed closer to the liquid crystal cell side than the resin base material. With such a structure, the influence of the phase difference that the resin base material can have on the image characteristics of the resulting liquid crystal display device can be eliminated. Examples

[0098] Hereinafter, the present application will be specifically described by way of examples, but the present application is not limited by these examples. Note that the method for measuring the thickness is described below. Further, "parts" and "%" in the following examples and comparative examples represent "parts by weight" and "% by weight", respectively.

[0099] (thickness)

[0100] A digital micrometer (manufactured by Anritsu Corporation, product name "KC-351C") was used for the measurement.

[0101] [Example 1]

[0102] As the resin base material, a long, amorphous isophthalic acid copolymerized polyethylene terephthalate (IPA copolymerized PET) film (thickness: 100 μm) having a water absorption of 0.75% and a Tg of 75°C was used.

[0103] One side of the resin substrate was subjected to corona treatment. A mixture of 4.0% aqueous solution of acetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMERTM Z200", degree of polymerization 1200, degree of saponification ≥99.0 mol%, acetyl-modification degree 4.6%), an aqueous dispersion of modified polyolefin resin (manufactured by Unitika Ltd., trade name "ARROWBASE SE1030N", solids concentration 22%), and pure water (solids concentration 4.0%) was applied to this corona-treated surface. The resulting layer had a thickness of 2000 nm after drying and was dried at 60°C for 3 minutes to form a base coating. Here, the solids ratio of acetyl-modified PVA to modified polyolefin in the mixture was 30:70.

[0104] Next, the surface of the base coating was subjected to corona treatment. An aqueous solution containing polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetyl-modified PVA (degree of polymerization 1200, degree of acetyl-modification 4.6%, degree of saponification ≥ 99.0 mol%, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMERTM Z200") in a 9:1 ratio was applied to the corona-treated surface at 25°C and dried, forming a PVA resin layer with a thickness of 11 μm. Thus, a laminate was fabricated.

[0105] The resulting laminate was stretched unidirectionally by 2.0 times along the longitudinal (length direction) free end between rollers with different circumferential speeds in an oven at 120°C (assisted stretching in a gas atmosphere).

[0106] Next, the laminate was immersed in an insoluble bath (an aqueous solution of boric acid prepared by adding 4 parts by weight of boric acid to 100 parts by weight of water) at a liquid temperature of 30°C for 30 seconds (insoluble treatment).

[0107] Next, the iodine concentration and immersion time were adjusted in a staining bath at a liquid temperature of 30°C, and the sample was immersed in the bath to obtain a polarizer with a given transmittance. In this embodiment, the sample was immersed in an iodine aqueous solution for 60 seconds (staining treatment). The iodine aqueous solution was prepared by adding 0.2 parts by weight of iodine and 1.0 parts by weight of potassium iodide to 100 parts by weight of water.

[0108] Next, it is immersed in a crosslinking bath (an aqueous solution of boric acid prepared relative to 100 parts by weight of water, 3 parts by weight of potassium iodide, and 3 parts by weight of boric acid) at a liquid temperature of 30°C for 30 seconds (crosslinking treatment).

[0109] Then, the laminate was immersed in a liquid temperature 70°C boric acid aqueous solution (an aqueous solution obtained by mixing 4 parts by weight of boric acid and 5 parts by weight of potassium iodide with respect to 100 parts by weight of water) and uniaxially stretched (water stretching) in the longitudinal direction (lengthwise direction) between rollers having different circumferential speeds so that the total stretch ratio was 5.5 times.

[0110] Then, the laminate was immersed in a liquid temperature 30°C cleaning bath (an aqueous solution obtained by mixing 4 parts by weight of potassium iodide with respect to 100 parts by weight of water) (cleaning treatment).

[0111] Thus, a laminate (polarizing plate) in which a polarizing film having a thickness of 5 μm was formed on one side of a resin substrate having a thickness of 30 μm was obtained.

[0112] [Example 2]

[0113] A polarizing plate was obtained in the same manner as in Example 1, except that the above-mentioned mixed solution was applied so as to have a dried thickness of 1000 nm.

[0114] [Example 3]

[0115] A polarizing plate was obtained in the same manner as in Example 1, except that the above-mentioned mixed solution was applied so as to have a dried thickness of 500 nm.

[0116] [Example 4]

[0117] A polarizing plate was obtained in the same manner as in Example 1, except that the mixing ratio of the acetoacetyl-modified PVA to the solid content of the modified polyolefin in the mixed solution was set to 50:50.

[0118] [Example 5]

[0119] A polarizing plate was obtained in the same manner as in Example 1, except that a mixed solution (solid content concentration 4.0%) obtained by mixing a 4.0% aqueous solution of acetoacetyl-modified PVA (GOHSEFIMER™ Z200), a modified polyolefin resin aqueous dispersion (manufactured by Unitika Ltd., trade name "ARROW BASE SD1030N", solid content concentration 22%), and pure water was used when forming the primer layer.

[0120] [Example 6]

[0121] A mixed solution (solid content concentration 4.0%) of a 4.0% aqueous solution of acetoacetyl-modified PVA (manufactured by Nippon Shokubai Co., Ltd., trade name "GOHSEFIMER™ Z200", degree of polymerization 2200, saponification degree 97.5 to 98.5%, acetoacetyl modification degree 4.6%), a modified polyolefin resin aqueous dispersion (manufactured by Unitika Ltd., trade name "ARROWBASE SE1035NJ2", solid content concentration 22%), and pure water was used when forming the primer layer, and otherwise, a polarizing plate was obtained in the same manner as in Example 4.

[0122] [Example 7]

[0123] A mixed solution (solid content concentration 4.0%) of a 4.0% aqueous solution of acetoacetyl-modified PVA (manufactured by Nippon Shokubai Co., Ltd., trade name "GOHSEFIMER™ Z410", degree of polymerization 2200, saponification degree 97.5 to 98.5%, acetoacetyl modification degree 4.6%), a modified polyolefin resin aqueous dispersion (manufactured by Unitika Ltd., trade name "ARROWBASE SE1030N", solid content concentration 22%), and pure water was used when forming the primer layer, and otherwise, a polarizing plate was obtained in the same manner as in Example 1.

[0124] [Example 8]

[0125] The stretching ratio of the auxiliary stretching in a gaseous atmosphere was set to 4.0 times, and the insolubilization treatment and the stretching in water were not performed, and otherwise, a polarizing plate in which a polarizing film having a thickness of 6 μm was formed on one side of a resin substrate having a thickness of 37 μm was obtained in the same manner as in Example 1.

[0126] [Comparative Example 1]

[0127] A polarizing plate was obtained in the same manner as in Example 1, except that the primer layer was not formed and a PVA-based resin coating layer was directly formed on the resin substrate.

[0128] [Comparative Example 2]

[0129] A polarizing plate was obtained in the same manner as in Example 8, except that the primer layer was not formed and a PVA-based resin coating layer was directly formed on the resin substrate.

[0130] [Comparative Example 3]

[0131] A mixed solution (solid content concentration 4.0%) of a 4.0% aqueous solution of acetoacetyl-modified PVA (manufactured by Nippon Shokubai Co., Ltd., trade name "GOHSEFIMER™ Z200", degree of polymerization 2200, saponification degree 97.5 to 98.5%, acetoacetyl modification degree 4.6%) was used when forming the primer layer, and otherwise, a polarizing plate was obtained in the same manner as in Example 3.

[0132] [Comparative Example 4]

[0133] A polarizing plate was obtained in the same manner as in Example 1, except that a 4.0% aqueous solution of acetoacetyl-modified PVA (GOHSEFIMER™ Z200) was used in forming the primer layer.

[0134] [Comparative Example 5]

[0135] A polarizing plate was obtained in the same manner as in Example 1, except that a 4.0% aqueous solution of acetoacetyl-modified PVA (GOHSEFIMER™ Z200) was used in forming the primer layer.

[0136] [Comparative Example 6]

[0137] A polarizing plate was obtained in the same manner as in Example 8, except that a 4.0% aqueous solution of acetoacetyl-modified PVA (GOHSEFIMER™ Z200) was used in forming the primer layer, and the mixed solution was applied in a manner such that the dried thickness was 1000 nm.

[0138] [Comparative Example 7]

[0139] A polarizing plate was obtained in the same manner as in Example 3, except that a polyester water-based emulsion resin (manufactured by Unitika Ltd., trade name "Elitel KT0507E6") was used in forming the primer layer.

[0140] [Comparative Example 8]

[0141] A polarizing plate was obtained in the same manner as in Example 2, except that a polyester water-based emulsion resin (manufactured by Unitika Ltd., trade name "Elitel KT0507E6") was used in forming the primer layer.

[0142] [Comparative Example 9]

[0143] A polarizing plate was obtained in the same manner as in Example 2, except that a modified polyolefin resin water-based dispersion (ARROWBASE SB1035NJ2) was used in forming the primer layer.

[0144] [Comparative Example 10]

[0145] A polarizing plate was obtained in the same manner as in Example 3, except that a mixed solution prepared by mixing 10 g of a 4.0% aqueous solution of acetoacetyl-modified PVA (GOHSEFIMER™ Z200) and 62.5 g of a polyester water-based emulsion resin (Elitel KT0507E6) was used in forming the primer layer. Here, the solid content mixing ratio of the acetoacetyl-modified PVA to the polyester in the mixed solution was 50:50.

[0146] [Comparative Example 11]

[0147] A mixed solution prepared by mixing 10 g of a 4.0% aqueous solution of acetoacetyl-modified PVA (GOHSEFIMER™ Z200) and 62.5 g of a polyester water-based emulsion resin (Elitel KT0507E6) was used to form the primer layer, and otherwise, a polarizing plate was obtained in the same manner as in Example 1. Here, the solid content mixing ratio of the acetoacetyl-modified PVA to the polyester in the mixed solution was 50:50.

[0148] (Evaluation)

[0149] The above examples and comparative examples were evaluated as follows. The evaluation results are summarized in Table 1. In addition, the results of SEM observation (6500x) of the cross section of the stretched laminate in Example 1, Example 2, Example 8, Comparative Example 1, and Comparative Example 11 are shown in Figs. 1 to 5, respectively. Figure 1 .

[0150] 1. Adhesion

[0151] The adhesion was evaluated by measuring the PVA peel strength and the substrate peel strength. The measurement methods of the PVA peel strength and the substrate peel strength are described below.

[0152] (PVA peel strength)

[0153] A measurement sample was prepared by applying an adhesive to the resin substrate side of the obtained polarizing plate and adhering it to a glass plate, and by adhering a reinforcing polyimide tape (manufactured by Nitto Electric Industrial Co., Ltd., polyimide adhesive tape No. 360A) to the polarizing film side. A cut was made between the polarizing film and the resin substrate of the measurement sample with a cutter, the resin substrate was made to stand at a 90° angle with respect to the polarizing film side, and the force (N / 15 mm) required when peeling at a peeling speed of 3000 mm / min was measured with an angle-free type adhesive / film peeling analysis device "VPA-2" (manufactured by Republic Seiho Kogyo Co., Ltd.).

[0154] (Substrate peel strength)

[0155] A measurement sample was prepared by applying an adhesive to the resin substrate side of the obtained polarizing plate and adhering it to a glass plate, and by adhering a reinforcing polyimide tape (manufactured by Nitto Electric Industrial Co., Ltd., polyimide adhesive tape No. 360A) to the polarizing film side. A cut was made between the polarizing film and the resin substrate of the measurement sample with a cutter, the resin substrate was made to stand at a 90° angle with respect to the polarizing film side, and the force (N / 15 mm) required when peeling at a peeling speed of 3000 mm / min was measured with an angle-free type adhesive / film peeling analysis device "VPA-2" (manufactured by Republic Seiho Kogyo Co., Ltd.).

[0156] 2. Appearance

[0157] When forming the primer layer and applying the polyvinyl alcohol solution, the appearance of the applied film was observed with the naked eye.

[0158] [Table 1]

[0159]

[0160] As shown in Table 1, the adhesion and appearance of the laminates of the examples were both excellent. Even if underwater stretching was performed, sufficient adhesion was maintained. On the other hand, in Comparative Examples 1 and 2 in which the primer layer was not formed, sufficient adhesion was not obtained. In Comparative Examples 3 to 6 in which the primer layer was formed without using the polyolefin component, not only was sufficient adhesion not obtained, but as the primer layer thickened, brushability at the time of forming the primer layer (at the time of coating) became difficult, bubbles were formed in the brushability-difficult portion, and the appearance deteriorated. In Comparative Examples 7 to 9 in which the primer layer was formed without using the polyvinyl alcohol component, the coated film became hazy at the time of forming the primer layer, and excellent appearance was not obtained. In Comparative Examples 10 and 11 in which the primer layer was formed using the polyvinyl alcohol component and the polyester component, agglomerates (protrusions) were formed in the primer layer, and excellent appearance was not obtained.

[0161] Industrial applicability

[0162] The laminate of the present application is suitable for use in, for example, image display devices. It is particularly suitable for use as an antireflection plate for liquid crystal televisions, liquid crystal displays, mobile phones, digital cameras, video cameras, portable game machines, car navigation systems, copiers, printers, facsimile machines, clocks, microwave ovens, and the like, liquid crystal panels, organic EL devices, and the like.

Claims

1. A method for producing a polarizing plate, the method comprising: a step of forming a primer layer by applying a primer layer-forming composition to one side of a resin substrate and drying; a step of forming a polyvinyl alcohol-based coating layer by applying a polyvinyl alcohol-based coating liquid to the surface of the primer layer and drying, to obtain a laminate; a step of stretching and dyeing the laminate, wherein the primer layer-forming composition contains a polyvinyl alcohol-based component and a polyolefin-based component, but does not contain a crosslinking agent, the mixing ratio of the polyvinyl alcohol-based component to the polyolefin-based component is 20:80 to 50:50, the stretching includes a water stretching treatment in which the laminate is immersed in a stretching bath, and the water stretching treatment is performed in a stretching bath having a liquid temperature of 50°C to 85°C, and the dyeing includes immersing the laminate in a dyeing liquid containing a dichroic substance.

2. The method for producing a polarizing plate according to claim 1, wherein the polyolefin-based component is a polyolefin-based resin containing ethylene as a monomer component.

3. The method for producing a polarizing plate according to claim 1, wherein the polyvinyl alcohol-based component contains acetoacetyl-modified polyvinyl alcohol.

4. The method for producing a polarizing plate according to claim 1, wherein the proportion of an olefin component in the monomer component constituting the polyolefin-based component is 50 to 95% by weight.

5. The method for producing a polarizing plate according to claim 1, wherein the thickness of the primer layer is 500 nm to 3000 nm.

6. A polarizing plate obtained by the method for producing a polarizing plate according to any one of claims 1 to 5. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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