Thermoformed body and method for producing thermoformed body

Abstract

Provided is a polarizing plate that has sufficient polarization performance and that hardly develops cracks even when the deformation amount during thermoforming is large. This polarizing plate includes a polarizing film containing polyvinyl alcohol as a main component. The thickness of the polarizing film is greater than 20 μm, and the highly oriented amorphous content of the polarizing film is 10.0-18.0%.

Description

Polarizing plate, thermoformed product, and method for manufacturing the thermoformed product

[0001] The present invention relates to a polarizing plate, a thermoformed product, and a method for producing a thermoformed product.

[0002] The polarizing film is a matrix (a stretched film oriented by uniaxial stretching) of polyvinyl alcohol (hereinafter, "polyvinyl alcohol" may be abbreviated as "PVA") film, in which an iodine-based dye (I ３ － Ya I ５ － The mainstream polarizing films are those in which a dichroic dye such as a dichroic organic dye or the like is adsorbed. Such polarizing films are produced by uniaxially stretching a PVA film that has already contained a dichroic dye, by uniaxially stretching the PVA film and simultaneously adsorbing the dichroic dye, or by uniaxially stretching the PVA film and then adsorbing the dichroic dye. Polarizing plates are obtained by laminating protective films such as triacetate cellulose (TAC) film, acrylic film, or polyester film on one or both sides of the resulting polarizing film, and have the function of transmitting and blocking light. Together with liquid crystals that change the polarization state of light, they are fundamental components of liquid crystal displays (LCDs).

[0003] Polarizing plates are also used in optical applications such as sunglasses, goggles, and eyeglasses, taking advantage of their light transmission and blocking properties. For these applications, polarizing plates must be processed into lens shapes such as curved surfaces. Thermoforming is commonly used as a molding method for polarizing plates for these applications.

[0004] Furthermore, in recent years, the introduction of polarizing plates onto automobile instrument panels has been considered as one of the in-vehicle applications. It has been pointed out that with conventional instrument panels, external light reflected from the instrument panel can be reflected onto the windshield, resulting in reduced driver visibility. To solve this problem, a polarizing plate has been proposed that utilizes the polarizing plate's ability to absorb and block light in specific directions, thereby suppressing the reflection of external light on the instrument panel and preventing reflections (Patent Document 1). For this application, a polarizing plate that can be thermoformed to fit the shape of the instrument panel is required, since the anti-reflection effect cannot be fully achieved unless the polarizing plate is in close contact with the instrument panel.

[0005] However, since polarizing plates are required to have high polarization performance, the PVA needs to be sufficiently oriented. As a result, the PVA has little room for stretching in the stretching direction, and if deformation in the stretching direction occurs during thermoforming, the film may crack in a direction perpendicular to the stretching direction.

[0006] As a polarizing film having stretchability that can follow the elongation of the body or clothing, a method has been proposed in which a polyvinyl alcohol-based resin film containing a halide is used, which has a strain of 10% or more when pulled in the absorption axis direction at room temperature at a load change rate of 98.0 mN / min and a shrinkage rate of 5% or less in the absorption axis direction when heated at 85°C for 120 minutes (Patent Document 2). However, Patent Document 2 does not disclose a polarizing film that is suitable for thermoforming at high temperatures.

[0007] Furthermore, as a means for preventing cracking in a direction perpendicular to the stretching direction for in-vehicle applications, a method has been proposed in which a base film is stretched in one direction to impart polarization properties, and while shaping it to the surface shape of a target component, the base film is attached to the surface of the target component, and then the base film is dried (Patent Document 3). However, since durability is required for in-vehicle applications, a protective film needs to be attached to the polarizing layer attached to the surface of the target component, and it is not easy to efficiently attach a protective film to a polarizing film formed by this method.

[0008] JP 2004-130916 A International Publication No. 2020 / 255779 JP 2019-51874 A

[0009] In recent years, polarizing plates that have been thermoformed to a large degree of deformation have become increasingly common in optical applications, such as sunglasses with sophisticated designs. Furthermore, for in-vehicle applications, curved instrument panels with larger deformations are becoming more common to improve design. However, conventional polarizing plates have a problem of being prone to cracking during thermoforming. Furthermore, when a polarizing plate is thermoformed, some parts of the plate deform perpendicular to the stretching direction, which can reduce the polarization performance of the thermoformed product in those parts. This can result in insufficient light-blocking properties in optical applications such as sunglasses and anti-glare properties in in-vehicle applications. Therefore, there is a demand for polarizing plates that combine both polarization performance and thermoformability.

[0010] In other words, the present invention aims to provide a polarizing plate that has sufficient polarizing performance and is less likely to crack even when the amount of deformation during thermoforming is large, a thermoformed product obtained by thermoforming such a polarizing plate, and a method for manufacturing a thermoformed product.

[0011] The present inventors have conducted extensive research to solve the above-mentioned problems and have completed the present invention. Specifically, the present invention relates to the following [1] to [9]. [1] A polarizing plate including a polarizing film containing polyvinyl alcohol as a main component, wherein the polarizing film has a thickness of more than 20 μm and a highly oriented amorphous content of 10.0 to 18.0%. [2] The polarizing plate according to [1], wherein the polarizing film has a boric acid content of 5 to 30% by mass. [3] The polarizing plate according to [1] or [2], wherein the polarizing film has a highly oriented PVA-boric acid aggregate structure content of 4.3% or less. [4] The polarizing plate according to any one of [1] to [3], wherein the polarizing film contains a dichroic organic dye. [5] The polarizing plate according to any one of [1] to [4], wherein the crack rate is 0 to 40% when subjected to heat-vacuum forming at a temperature of 107°C and a vacuum degree of 0.01 MPa using a mold having a spherical depression with a radius of curvature of 5.2 cm and a depth of 3.5 cm. [6] A thermoformed article obtained by thermoforming the polarizing plate according to any one of [1] to [5]. [7] The thermoformed article according to [6], which has a maximum elongation of 35% or less. [8] The thermoformed article according to [6] or [7], which has a polarization degree of 80 to 99.7%. [9] A method for producing a thermoformed article, which comprises a step of thermoforming the polarizing plate according to any one of [1] to [5] at 105°C to 110°C.

[0012] By using the polarizing plate of the present invention, a thermoformed article having sufficient polarizing performance and little or no cracking even when the amount of deformation is large can be obtained. Furthermore, by employing the manufacturing method of the thermoformed article of the present invention, the above-mentioned excellent thermoformed article can be provided.

[0013] FIG. 1 is a schematic diagram of measured data obtained by X-ray profiling of a polarized film. FIG. 2 is a schematic diagram obtained by correction based on the baseline drawn in FIG. 1. FIG. 3 is a schematic diagram obtained by fitting the amorphous portion with a Gaussian function. FIG. 4 is a schematic diagram obtained by fitting the crystalline portion with a Gaussian function. FIG. 5 is a diagram in which a baseline line is drawn on the I(2θ) profile. FIG. 6 is a diagram in which the baseline-corrected I(2θ) profile is separated into "amorphous PVA," "crystalline PVA," and "PVA-boric acid aggregated structure." FIG. 7 is a diagram in which the integrated intensity values ​​(A) of "amorphous PVA," "crystalline PVA," and "PVA-boric acid aggregated structure" obtained by waveform resolution analysis are plotted against the azimuthal angle. FIG. 8 is a diagram in which the integrated intensity values ​​(A) are separated into oriented and non-oriented components. FIG. 9 is a diagram illustrating the maximum deformation length A and the diameter B of the molding die.

[0014] The present invention will be described in detail below. In this specification, the upper and lower limits of numerical ranges (such as the content of each component, values ​​calculated from each component, and physical properties) can be combined as appropriate. In this specification, when a numerical range is described as "XX to YY," it means "XX or more and YY or less." Furthermore, a PVA film generally refers to an unstretched film containing PVA, and a polarizing film refers to a uniaxially stretched PVA film containing a dichroic dye.

[0015] [PVA Film] The polarizing plate of the present invention includes a polarizing film, which is a uniaxially stretched PVA film containing a dichroic dye. PVA, the raw material for the PVA film, can be obtained by saponifying a polyvinyl ester obtained by polymerizing one or more vinyl esters, such as vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl benzoate, and isopropenyl acetate. Among the above vinyl esters, compounds having a vinyloxycarbonyl group in the molecule are preferred, and vinyl acetate is more preferred, in terms of ease of production, availability, cost, and the like of PVA.

[0016] The polyvinyl ester is preferably one obtained by using only one or more vinyl esters as a monomer, more preferably one obtained by using only one vinyl ester as a monomer, but may also be a copolymer of one or more vinyl esters with other monomers copolymerizable therewith, provided that the effects of the present invention are not significantly impaired.

[0017] Examples of other monomers copolymerizable with the vinyl esters include α-olefins having 2 to 30 carbon atoms, such as ethylene, propylene, 1-butene, and isobutene; (meth)acrylic acid or a salt thereof; (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, dodecyl (meth)acrylate, and octadecyl (meth)acrylate; (meth)acrylamide; N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, diacetone(meth)acrylamide, (meth)acrylamidopropanesulfonic acid or a salt thereof, and (meth)acrylamidopropyldimethylamine or a salt thereof. Examples of suitable vinyl esters include (meth)acrylamide derivatives such as N-methylol (meth)acrylamide or derivatives thereof; N-vinylamides such as N-vinylformamide, N-vinylacetamide, and N-vinylpyrrolidone; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, and stearyl vinyl ether; vinyl cyanides such as (meth)acrylonitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid or a salt, ester, or acid anhydride thereof; itaconic acid or a salt, ester, or acid anhydride thereof; vinylsilyl compounds such as vinyltrimethoxysilane; and unsaturated sulfonic acids or salts thereof. The polyvinyl esters may have structural units derived from one or more of the other monomers described above.

[0018] The proportion of the structural units derived from the other monomers in the polyvinyl ester is preferably 15 mol % or less, more preferably 10 mol % or less, and even more preferably 5 mol % or less, based on the number of moles of all structural units constituting the polyvinyl ester.

[0019] PVA that has not been graft-copolymerized can be preferably used. However, as long as the effects of the present invention are not significantly impaired, PVA may be modified with one or more graft-copolymerizable monomers. The graft copolymerization can be carried out on at least one of polyvinyl ester and PVA obtained by saponifying the polyvinyl ester. Examples of the graft-copolymerizable monomer include unsaturated carboxylic acids or derivatives thereof; unsaturated sulfonic acids or derivatives thereof; and α-olefins having 2 to 30 carbon atoms. The proportion of structural units derived from graft-copolymerizable monomers in polyvinyl ester or PVA is preferably 5 mol % or less based on the number of moles of all structural units constituting the polyvinyl ester or PVA.

[0020] The PVA may or may not be crosslinked at some of its hydroxyl groups. In addition, the PVA may have some of its hydroxyl groups reacted with an aldehyde compound such as acetaldehyde or butylaldehyde to form an acetal structure, or may not react with these compounds to form an acetal structure.

[0021] The degree of polymerization of PVA is not particularly limited, but is preferably 1,000 or more. By having a degree of polymerization of PVA of 1,000 or more, the polarization performance of the resulting polarizing film can be further improved. If the degree of polymerization of PVA is too high, it tends to lead to an increase in the production cost of PVA and poor processability during film formation. The degree of polymerization of PVA is more preferably within the range of 1,000 to 10,000, even more preferably within the range of 1,500 to 8,000, and particularly preferably within the range of 1,800 to 4,000. The degree of polymerization of PVA is the viscosity-average degree of polymerization measured by the method described in JIS-K6726-1994.

[0022] The degree of saponification of the PVA is preferably 95 mol% or more, more preferably 98 mol% or more, even more preferably 99 mol% or more, and particularly preferably 99.3 mol% or more, because this improves the durability of the resulting polarized film. The upper limit of the degree of saponification of the PVA may be 100 mol%. The degree of saponification of the PVA is a value measured by the method described in JIS-K6726-1994.

[0023] The PVA film used in the polarizing plate of the present invention will be described below.

[0024] A PVA film is a film containing PVA as a main component. The main component refers to the component with the largest content by mass. The PVA content in the PVA film is preferably within a range of 50 to 100% by mass, more preferably within a range of 80 to 100% by mass, and even more preferably within a range of 85 to 100% by mass.

[0025] The PVA film may contain a plasticizer. By including a plasticizer in the PVA film, the handleability and stretchability of the PVA film can be improved. Polyhydric alcohols are preferably used as the plasticizer, and specific examples include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, and trimethylolpropane. The PVA film can contain one or more of these plasticizers. Among these, glycerin is preferred because it improves the stretchability of the PVA film.

[0026] The content of the plasticizer in the PVA film is preferably 15 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, per 100 parts by mass of PVA. By having the content of the plasticizer in the PVA film be 15 parts by mass or less per 100 parts by mass of PVA, it is possible to prevent the plasticizer from bleeding out onto the surface of the PVA film, which would reduce the handleability of the PVA film. The lower limit of the content of the plasticizer in the PVA film may be 0 parts by mass, 1 part by mass, or 5 parts by mass, per 100 parts by mass of PVA.

[0027] The PVA film preferably contains a surfactant. The inclusion of a surfactant is expected to have the following effects: suppression of unevenness in film thickness when a PVA film is produced using a film-forming solution containing PVA; improved film formability by facilitating release of the PVA film from a metal roll or belt after film formation; and suppression of blocking between the resulting films. The type of surfactant contained in the PVA film is not particularly limited, but from the viewpoint of release from a metal roll or belt, anionic surfactants or nonionic surfactants are preferred, and nonionic surfactants are particularly preferred.

[0028] Preferred examples of the anionic surfactant include carboxylic acid surfactants such as potassium laurate; sulfate ester surfactants such as octyl sulfate; and sulfonic acid surfactants such as dodecylbenzenesulfonate.

[0029] Preferred examples of nonionic surfactants include alkyl ether types such as polyoxyethylene oleyl ether; alkyl phenyl ether types such as polyoxyethylene octylphenyl ether; alkyl ester types such as polyoxyethylene laurate; alkyl amine types such as polyoxyethylene lauryl amino ether; alkyl amide types such as polyoxyethylene lauric acid amide; polypropylene glycol ether types such as polyoxyethylene polyoxypropylene ether; alkanolamide types such as lauric acid diethanolamide and oleic acid diethanolamide; and allyl phenyl ether types such as polyoxyalkylene allyl phenyl ether.

[0030] These surfactants can be used alone or in combination of two or more.

[0031] The surfactant content in the PVA film is preferably in the range of 0.01 to 0.5 parts by mass, more preferably 0.02 to 0.3 parts by mass, per 100 parts by mass of PVA. Having a surfactant content of 0.01 parts by mass or more per 100 parts by mass of PVA can suppress the occurrence of defects and improve releasability from the metal roll. On the other hand, having a surfactant content of 0.5 parts by mass or less per 100 parts by mass of PVA can suppress blocking of the film due to bleed-out of the surfactant, allowing for stable handling.

[0032] The PVA film may consist solely of PVA, or may contain at least one of a plasticizer and a surfactant. The PVA film may further contain other components, such as an antioxidant, an antifreeze agent, a pH adjuster, a masking agent, a color inhibitor, and an oil agent, as needed.

[0033] The PVA film used in producing the polarizing plate of the present invention is not particularly limited, but in order to produce a polarizing plate with sufficient polarizing performance, it preferably has a crystallinity of 31% or more. Furthermore, since a polarizing plate with fewer cracks during thermoforming is more likely to be obtained, it is preferable that the crystallinity be 35% or less. The crystallinity can be determined using the measurement method described below. The crystallinity of the PVA film can be adjusted by the composition of the film-forming solution during film formation, the temperature conditions and atmosphere during drying and heat treatment, etc. The crystallinity of the PVA film can also be controlled by adjusting the type and content of the plasticizer.

[0034] [PVA Film Forming Method] Examples of methods for forming a PVA film include a cast film forming method using a film forming solution containing PVA, an extrusion film forming method, a wet film forming method, and a gel film forming method. These film forming methods may be used alone or in combination of two or more. Among these film forming methods, the cast film forming method or the extrusion film forming method is preferred because it can produce a PVA film with uniform thickness and width and good physical properties. The PVA film can be dried or heat-treated using a drying roll or a heat-treatment roll as needed.

[0035] The membrane-forming solution is usually prepared by dissolving PVA in a liquid solvent. Examples of the liquid medium include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, and diethylenetriamine. One or more of these may be used. Among these, water is preferred from the viewpoints of its environmental friendliness and ease of recovery.

[0036] The volatile content of the membrane-forming solution (the content in the membrane-forming solution of volatile components such as the liquid medium that are removed by volatilization or evaporation during membrane formation) varies depending on the membrane-forming method, membrane-forming conditions, etc., but is preferably in the range of 50 to 95 mass%, more preferably in the range of 55 to 90 mass%, and even more preferably in the range of 60 to 85 mass%. When the membrane-forming solution has a volatile content of 50 mass% or more, the viscosity of the membrane-forming solution does not become too high, which facilitates filtration and degassing during preparation of the membrane-forming solution, facilitating the production of PVA films with few foreign matter and defects. On the other hand, when the membrane-forming solution has a volatile content of 95 mass% or less, the concentration of the membrane-forming solution does not become too low, which facilitates industrial production of PVA films.

[0037] The temperature during drying of the PVA film is not particularly limited, but from the viewpoints of the uniformity of drying of the film, productivity, etc., it is preferably within the range of 80 to 120°C, more preferably within the range of 83 to 105°C, and even more preferably within the range of 85 to 95°C.

[0038] The PVA film is preferably heat-treated for reasons such as improving productivity in the production process of the polarizing film. The heat treatment temperature is preferably 90° C. or higher, more preferably 100° C. or higher, and even more preferably 110° C. or higher. Furthermore, from the viewpoint of improving the stretchability of the resulting PVA film, the surface temperature of the heat treatment roll is preferably 150° C. or lower, more preferably 140° C. or lower, and even more preferably 130° C. or lower.

[0039] There are no particular restrictions on the thickness of the PVA film, but it is preferably 75 μm or more, more preferably 80 μm or more, and even more preferably 85 μm or more. When the PVA film has a thickness of 75 μm or more, breakage is less likely to occur during stretching, allowing for stable production of polarized films. On the other hand, since polarized films can be produced more smoothly, the thickness is preferably 160 μm or less, more preferably 150 μm or less. The "thickness" of the PVA film and the polarized film described below refers to the average value (average thickness) of measurements taken at any five locations.

[0040] The shape of the PVA film is not particularly limited, but a long film is preferred because it allows for continuous production of polarized films with good productivity. The length of the long film is not particularly limited and can be set appropriately depending on the application of the polarized film to be produced, and can be, for example, within a range of 5 to 20,000 m. The width of the long film is not particularly limited and can be, for example, 50 cm or more. However, given the recent demand for wider polarized films, it is preferably 1 m or more, more preferably 2 m or more, and even more preferably 4 m or more. There is no particular upper limit to the width of the long film, but if the width is too wide, uniform stretching tends to be difficult, so the width of the PVA film is preferably 7 m or less.

[0041] [Polarizing Film] Next, a polarizing film using a PVA film will be described.

[0042] The polarizing film contains PVA as a main component. The PVA content in the polarizing film is preferably within a range of 50 to 99% by mass, more preferably within a range of 60 to 90% by mass, and even more preferably within a range of 70 to 85% by mass. The polarizing film may be a monolayer film containing PVA as a main component.

[0043] The cracks that occur when thermoforming a polarizing plate have a strong influence on the solid structure of the polarizing film.

[0044] The solid-state structure of polarizing films can be analyzed by wide-angle X-ray diffraction (WAXD) measurements, which allow for quantitative analysis of three components: "PVA crystals," "amorphous PVA," and "PVA-boric acid aggregate structures." Here, "PVA crystals" refers to a crystalline structure consisting of PVA chains in a crystalline state, and "amorphous PVA" refers to an amorphous structure containing PVA chains that are not crystalline. "Amorphous PVA" may also contain amorphous structures other than PVA chains. In other words, "amorphous PVA" may simply be replaced with "amorphous" (the portion that is not in a crystalline state: amorphous structure). Furthermore, the "PVA-boric acid aggregate structures" are structures derived from peaks known to appear in X-ray profiles when boric acid is contained in polarizing films, and these peaks are thought to be diffraction signals from structures formed by the interaction of PVA and boric acid. The wide-angle X-ray diffraction (WAXD) measurement of the polarizing film used in the present invention is a known method, and is described in, for example, WO 2017 / 138551.

[0045] These three components can be further divided into three components: a non-oriented component, a low-oriented component, and a high-oriented component relative to the stretching direction of the polarizing film, for a total of nine components. In this way, the percentage (%) of each component can be determined when the total of the nine components is taken as 100%. Detailed WAXD measurement and analysis methods will be described later.

[0046] Highly oriented amorphous refers to the highly oriented component of "amorphous PVA." Highly oriented amorphous refers to a structure in which amorphous PVA chains are highly oriented. Based on the WAXD measurement and analysis method described below, highly oriented amorphous can be defined as a structure in which amorphous PVA chains are aligned within a range of ±10° relative to the stretching direction. Highly oriented amorphous is considered to be a region that is less likely to deform when thermoforming a polarizing plate. In other words, it is estimated that the lower the highly oriented amorphous content of the polarizing film contained in the polarizing plate, the greater the elongation margin in the stretching direction of the polarizing film, making it easier to thermoform the polarizing plate. Highly oriented amorphous content refers to the percentage (%) of highly oriented amorphous (highly oriented component of amorphous PVA) relative to the total amount of crystalline PVA, amorphous PVA, and PVA-boric acid aggregated structure.

[0047] The highly oriented amorphous content of the polarizing film contained in the polarizing plate of the present invention is 10.0 to 18.0%. If the highly oriented amorphous content is less than 10.0%, the polarization performance may be significantly reduced. The highly oriented amorphous content is preferably 11.0% or more, more preferably 12.0% or more, and even more preferably 14.0% or more. On the other hand, if the highly oriented amorphous content exceeds 18.0%, cracks are likely to occur during thermoforming. The highly oriented amorphous content is preferably 17.0% or less, and even more preferably 16.0% or less.

[0048] The term "highly oriented PVA-boric acid aggregate structure" refers to a highly oriented component of a "PVA-boric acid aggregate structure." In the present invention, the amount of highly oriented PVA-boric acid aggregate structure in a polarizing film is not particularly limited, but is preferably 4.3% or less because an increase in the crosslinked structure between PVA and boric acid leads to a hardening of the polarizing film. The lower limit of the amount of highly oriented PVA-boric acid aggregate structure may be 0%, 1.0%, 2.0%, or 3.0%. Based on the WAXD measurement and analysis method described below, a highly oriented PVA-boric acid aggregate structure can be defined as a structure in which PVA chains interacting with boric acid (i.e., PVA chains in the PVA-boric acid aggregate structure) are aligned within a ±10° range relative to the stretching direction. The amount of highly oriented PVA-boric acid aggregated structures refers to the ratio (%) of the amount of highly oriented PVA-boric acid aggregated structures (highly oriented components of the amount of PVA-boric acid aggregated structures) to the total amount of crystalline PVA, amorphous PVA, and PVA-boric acid aggregated structures.

[0049] The thickness of the polarizing film contained in the polarizing plate of the present invention is greater than 20 μm. If the thickness of the polarizing film is 20 μm or less, it may be more susceptible to uneven film thickness or the proportion of the skin layer, where stress is likely to concentrate during stretching, may increase, which may result in cracking during thermoforming processing. The thickness of the polarizing film is preferably 21 μm or more, more preferably 30 μm or more, and even more preferably 38 μm or more. On the other hand, there is no particular upper limit to the thickness of the polarizing film, but in order to prevent the film from becoming too rigid and to further improve thermoformability, it is preferably 45 μm or less, more preferably 40 μm or less.

[0050] The amount of highly oriented amorphous structure in a polarizing film can be controlled by adjusting one or more of various factors, such as the degree of polymerization and degree of saponification of PVA, the type and content of plasticizer, the drying temperature during film formation of the PVA film, the content of boric acid in the polarizing film, and the stretching temperature and stretching ratio in the stretching treatment step during production of the polarizing film, as described below. For example, increasing the content of plasticizer tends to decrease the amount of highly oriented amorphous structure. Furthermore, increasing the stretching temperature or decreasing the stretching ratio in the stretching treatment step during production of the polarizing film tends to decrease the amount of highly oriented amorphous structure. The amount of highly oriented PVA-boric acid aggregate structure in a polarizing film can also be controlled by adjusting one or more of the above factors. For example, decreasing the boric acid content or decreasing the stretching ratio tends to decrease the amount of highly oriented PVA-boric acid aggregate structure.

[0051] In the present invention, the polarizing film preferably contains a boron compound as a crosslinking agent. By containing a boron compound, a crosslinked structure can be established, and durability can be exhibited in a humid and hot environment. Examples of boron compounds include boric acid and borate salts such as borax. These boron compounds may be used alone or in combination. Among these boron compounds, boric acid is preferred from the viewpoint of improving durability in a humid and hot environment.

[0052] The boric acid content in the polarizing film is preferably 5 to 30% by mass, based on the mass of the polarizing film. A boric acid content of 5% by mass or more sufficiently improves durability in humid and hot environments. The boric acid content in the polarizing film is more preferably 10% by mass or more, and particularly preferably 18% by mass or more. On the other hand, a boric acid content of 30% by mass or less sufficiently prevents cracks from occurring during thermoforming. The boric acid content in the polarizing film is more preferably 25% by mass or less.

[0053] A dichroic dye is used as a dye for the polarizing film. Examples of the dichroic dye include iodine-based dyes and dichroic organic dyes. From the viewpoint of the heat resistance of the polarizing plate and a thermoformed product made thereof, dichroic organic dyes are particularly preferred. Specific examples of dichroic organic dyes will be described later.

[0054] The polarizing film used in the present invention preferably does not contain halides, since halides cause deterioration of the polarizing plate during thermoforming. The content of halogen compounds in the polarizing film is preferably 1% by mass or less, more preferably 0.1% by mass or less, and particularly preferably 0.001% by mass or less.

[0055] [Method for Producing Polarizing Film] The method for producing the polarizing film contained in the polarizing plate of the present invention is not necessarily limited, and any known method can be used. However, the following method is exemplified as a suitable method.

[0056] A preferred method for producing the polarizing film of the present invention involves a first step of swelling a PVA film (hereinafter sometimes referred to as a "swelling step"), followed by a step of dyeing the PVA film (hereinafter sometimes referred to as a "dyeing step") and a step of stretching the PVA film (hereinafter sometimes referred to as a "stretching step"), as well as a step of crosslinking the PVA film using a crosslinking agent (hereinafter sometimes referred to as a "crosslinking step"). The order of the dyeing, stretching, and crosslinking steps is not limited, but it is preferred that the swelling step be followed by the dyeing, crosslinking, and stretching steps. Each step will be described in detail below.

[0057] The swelling treatment in the swelling step can be carried out by immersing the PVA film in water. The temperature of the water during immersion is preferably within the range of 20 to 55°C, more preferably within the range of 22 to 52°C, and even more preferably within the range of 25 to 50°C. The time for immersion in water is, for example, preferably within the range of 0.1 to 5 minutes, and more preferably within the range of 0.5 to 3 minutes. The water used for immersion in water is not limited to pure water, and may be an aqueous solution in which various components are dissolved, or a mixture of water and an aqueous medium.

[0058] The dyeing process may be carried out before the stretching process, simultaneously with the stretching process, or after the stretching process, but is preferably carried out before the stretching process. Dyeing can be carried out using a dichroic dye. As described above, examples of the dichroic dye include iodine-based dyes and dichroic organic dyes.

[0059] Examples of the iodine-based dye include I ３ － , I ５ － These iodine-based dyes include, for example, iodine (I ２ Therefore, for example, a dyeing treatment can be carried out by immersing a PVA film in a solution (particularly an aqueous solution) containing iodine-potassium iodide as a dye bath.

[0060] Examples of the dichroic organic dyes include Direct Black 17, 19, and 154; Direct Brown 44, 106, 195, 210, and 223; Direct Red 2, 23, 28, 31, 37, 39, 79, 81, 240, 242, and 247; Direct Blue 1, 15, 22, 78, 90, 98, 151, 168, 202, 236, 249, and 270; Direct Violet 9, 12, 51, and 98; Direct Green 1 and 85; Direct Yellow 8, 12, 44, 86, and 87; and Direct Orange 26, 39, 106, and 107. Two or more of these dyes may be used in combination, and the blending ratio is not particularly limited and can be set as desired. Therefore, by combining the above dichroic organic dyes, the hue can be neutral gray.

[0061] The concentration of the dichroic dye in the aqueous solution containing the dichroic dye in the dye bath can be appropriately set depending on the type of dichroic dye, etc. For example, the concentration of the dichroic organic dye is preferably within a range of 0.001 to 0.3% by mass. The temperature of the dye bath is preferably 20 to 55°C, particularly 30 to 50°C.

[0062] The crosslinking treatment in the crosslinking step involves immersing the PVA film in an aqueous solution containing a crosslinking agent. Crosslinking treatment introduces a crosslinked structure into the PVA film, improving the heat resistance of the polarizing film. From this perspective, the crosslinking treatment is preferably performed after the dyeing treatment. The crosslinking agent can be one or more boron compounds, such as boric acid and borax or other borates. The concentration of the crosslinking agent in the aqueous solution is preferably within the range of 1 to 15% by mass, more preferably within the range of 1.5 to 7% by mass. The aqueous solution containing the crosslinking agent may contain an auxiliary agent such as potassium iodide. The temperature of the aqueous solution containing the crosslinking agent is preferably within the range of 20 to 50°C, more preferably within the range of 25 to 45°C.

[0063] The stretching treatment in the stretching step may be performed by either a wet stretching method or a dry stretching method. In the wet stretching method, uniaxial stretching can be performed in an aqueous solution containing boric acid, or in the swelling bath or dyeing bath described above, or in the fixation treatment bath described below. In the dry stretching method, uniaxial stretching can be performed in the atmosphere using a PVA film after water absorption. Among these, the wet stretching method is preferred for the stretching treatment, and a wet stretching method in which uniaxial stretching is performed in an aqueous solution containing boric acid is more preferred. The concentration of boric acid in the aqueous boric acid solution is preferably in the range of 0.5 to 6.0% by mass, more preferably in the range of 1.0 to 5.0% by mass, and particularly preferably in the range of 1.5 to 4.0% by mass.

[0064] The stretching temperature in the stretching treatment is preferably within the range of 45 to 60°C.

[0065] In addition, in terms of polarization performance, the stretching ratio in the stretching treatment is preferably 4 times or more, more preferably 4.5 times or more, and particularly preferably 5 times or more. There is no particular upper limit to the stretching ratio, but the stretching ratio is preferably 8 times or less, and may be 5.5 times or less.

[0066] In the production of a polarizing film, a washing treatment (washing treatment) of the PVA film may be carried out as appropriate between the above steps. Because this can further strengthen the adsorption of the dichroic dye onto the PVA film, it is preferable to carry out the washing treatment before the drying step described below. The washing bath used for washing can be an aqueous solution containing one or more boron compounds, such as boric acid and borax. If necessary, an iodine compound or a metal compound may also be added to the washing bath. In this case, the concentration of the boron compound in the washing bath is preferably 1 to 15% by mass. When potassium iodide is added to the aqueous solution, its concentration is preferably 0.01 to 10% by mass. The temperature of the washing bath is preferably 15 to 60°C, and particularly preferably 20 to 40°C.

[0067] In the method for producing a polarizing film, although not necessarily limited thereto, it is preferable to heat-dry the stretched polarizing film in a drying treatment step for reasons described below. The drying treatment is preferably carried out at 30 to 150°C, particularly preferably 50 to 130°C.

[0068] In the method for producing a polarizing film, one of the above steps may be performed multiple times, or multiple treatments may be performed simultaneously in one step.

[0069] [Polarizing Plate] The polarizing plate of the present invention can be obtained, for example, by laminating a protective film to both sides or one side of the polarizing film. The polarizing plate includes, for example, the polarizing film and a protective film laminated to both sides or one side of the polarizing film directly or via an adhesive or pressure-sensitive adhesive. By including the polarizing film, the polarizing plate of the present invention can achieve both polarization performance and thermoformability. Examples of the protective film include optically transparent and mechanically strong protective films, such as cellulose triacetate (TAC) film, cellulose acetate butyrate (CAB) film, acrylic film, polyester film, and cyclic olefin (COP) film. Examples of adhesives for lamination include PVA-based adhesives, urethane-based adhesives, and ultraviolet-curable adhesives. Furthermore, a pressure-sensitive adhesive can also be used for lamination. An acrylic pressure-sensitive adhesive is typically used as the pressure-sensitive adhesive.

[0070] The polarization degree of the polarizing plate of the present invention is preferably 80% or more. A polarization degree of 80% or more allows the thermoformed article to fully exhibit its light-shielding function and anti-glare effects. The polarization degree of the polarizing plate is more preferably 85% or more, and particularly preferably 90% or more. There is no particular upper limit to the polarization degree, but 99.7% is preferred, more preferably 99.5%, and particularly preferably 99.3%, in order to further suppress the occurrence of cracks during the production of the thermoformed article.

[0071] The single transmittance of the polarizing plate of the present invention is not particularly limited. However, in the case of sunglasses, if the single transmittance of the polarizing plate is less than 20%, the field of view may become too dark, potentially reducing safety. Furthermore, in automotive applications, if the single transmittance of the polarizing plate is less than 20%, the color of the instrument panel may become dark, making it difficult to see the interior color of the instrument panel, potentially impairing the design. For these reasons, the single transmittance of the polarizing plate is preferably 20% or more, more preferably 25% or more. On the other hand, the upper limit of the single transmittance of the polarizing plate is not particularly limited. However, since more sufficient polarization performance can be achieved, the single transmittance of the polarizing plate is preferably 38% or less, more preferably 35% or less. The polarization degree and single transmittance of the polarizing plate are measured as follows. A rectangular film piece measuring 3 cm in the length direction and 1.5 cm in the width direction is taken from the center of the polarizing plate in the width direction. Using a spectrophotometer equipped with an integrating sphere ("V7100" manufactured by JASCO Corporation), the polarization degree and single transmittance of the film piece at the maximum absorption wavelength in the visible light region are measured.

[0072] The method for laminating the protective film to one or both surfaces of the polarizing film is not particularly limited, and the protective film can be laminated by any known method. For example, a method in which the protective film is laminated continuously to the polarizing film is preferred from the viewpoint of production efficiency.

[0073] The polarizing plate thus obtained has sufficient polarizing performance and is not easily broken even when subjected to thermoforming, and is therefore suitable for use as a polarizing plate in the shape of sunglasses or an instrument panel.

[0074] The crack rate when a thermoformed product is formed using the polarizing plate of the present invention is not particularly limited, but it is preferable that the crack rate be 0 to 40% when the polarizing plate is subjected to heat vacuum molding using a mold having a depth of 3.5 cm and a spherical depression with a radius of curvature of 5.2 cm, at a temperature of 107°C and a vacuum degree of 0.01 MPa. If the crack rate measured under the above conditions is 40% or less, it can be determined that cracks are sufficiently unlikely to occur even when heat vacuum molding is performed with a large amount of deformation. The crack rate is more preferably 0 to 30%, and particularly preferably 0 to 20%.

[0075] [Thermoformed Article] The thermoformed article of the present invention can be obtained by thermoforming the polarizing plate described above.

[0076] The maximum elongation of the thermoformed body of the present invention is not particularly limited, but is preferably 35% or less, more preferably 30% or less. A maximum elongation of 35% or less of the thermoformed body suppresses a decrease in the degree of polarization of the thermoformed body due to deformation in a direction perpendicular to the stretching direction, thereby enabling the thermoformed body to exhibit more sufficient polarization performance. Here, the maximum elongation of the thermoformed body refers to the elongation ratio of the deformed length (maximum deformation length) after molding to the length before thermoforming at the position (cutting surface) where the deformation length (peripheral length) of the cut surface is maximum when the thermoformed body is cut along a plane perpendicular to the surface of the polarizing film (polarizing plate) before thermoforming. The length before thermoforming can be determined by the diameter of the molding die used. For example, as shown in FIG. 9, the length before thermoforming is the diameter B of the molding die, and the maximum deformation length A corresponding to the diameter B of the molding die is the length of the inner surface of the molding die along the cross section.

[0077] The degree of polarization of the thermoformed article of the present invention is not particularly limited, but since it can exhibit sufficient polarization performance and suppress a decrease in light-shielding function, the degree of polarization of the thermoformed article is preferably 80% or more, more preferably 86% or more, and particularly preferably 91% or more. Furthermore, the upper limit of the degree of polarization of the thermoformed article is not particularly limited, but if the degree of polarization is too high, the color of the instrument panel may become dark. Therefore, the degree of polarization of the thermoformed article is preferably 99.7% or less, more preferably 99.5% or less, and particularly preferably 99.3% or less. The degree of polarization of the thermoformed article may be 96% or less.

[0078] The single transmittance of the thermoformed product of the present invention is not particularly limited. However, in the case of sunglasses, if the single transmittance of the thermoformed product is less than 20%, the field of view may become too dark, potentially reducing safety. Furthermore, in automotive applications, if the single transmittance of the thermoformed product is less than 20%, the color of the instrument panel may become dark, making it difficult to see the interior color of the instrument panel, potentially impairing the design. For these reasons, the single transmittance of the thermoformed product is preferably 20% or more, more preferably 25% or more. On the other hand, the upper limit of the single transmittance of the thermoformed product is not particularly limited. However, since more sufficient polarization performance can be achieved, the single transmittance of the thermoformed product is preferably 40% or less, more preferably 35% or less, and particularly preferably 30% or less. The method for measuring the polarization degree and single transmittance of the thermoformed product is described below.

[0079] The thickness of the thinnest part of the thermoformed article of the present invention is not particularly limited, but is preferably 1 to 200 μm. If the thickness is less than 1 μm, handling is poor and continuous production may not be possible. Therefore, the thickness is more preferably 3 μm or more. On the other hand, if the thickness exceeds 200 μm, shrinkage of the thermoformed article may be significantly large. The thickness is more preferably 180 μm or less.

[0080] [Method for producing thermoformed article] The method for producing the thermoformed article of the present invention is not particularly limited, but the thermoformed article of the present invention can be produced efficiently by employing the following method for producing a thermoformed article.

[0081] In the method for producing a thermoformed product of the present invention, the thermoforming method is not limited, and the polarizing plate can be thermoformed by, for example, hot vacuum forming, hot pressure forming, hot press forming, etc. to obtain a thermoformed product. The heating temperature is not particularly limited, but if it is too high, the polarizing plate will melt, so the temperature of the polarizing plate is preferably 200°C or less, more preferably 160°C or less, and particularly preferably 110°C or less. On the other hand, the lower limit of the heating temperature is preferably above the glass transition temperature of the PVA or protective film, so the temperature of the polarizing plate is preferably 80°C or more, more preferably 90°C or more, and particularly preferably 105°C or more. The degree of vacuum is not particularly limited, but is preferably 0.001 MPa or more because sufficient molding can be achieved. The upper limit of the degree of vacuum is not particularly limited, but is preferably less than 0.1 MPa because a clean molded product can be obtained.

[0082] The method for producing a thermoformed product may be a production method in which a polarizing plate that has undergone a drying step of heating and drying in the production process of a polarizing film or polarizing plate is thermoformed. By thermoforming a polarizing plate that has undergone a drying step, poor durability and changes in shape over time of the thermoformed product due to excess moisture can be suppressed. Furthermore, if drying is performed before thermoforming, shrinkage of the thermoformed product during drying can be suppressed, which can cause cracks and changes in shape of the thermoformed product.

[0083] The polarizing plate of the present invention can be used to obtain a thermoformed product that has sufficient polarization performance and little cracking even with a large amount of deformation, and is suitable for use in sunglasses with high design quality or polarizing plates in the shape of an instrument panel.

[0084] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The evaluation methods used in the following examples and comparative examples are shown below.

[0085] [Calculation of Crystallinity of PVA Film] (Wide Angle X-ray Diffraction (WAXD) Measurement of PVA Film) Wide angle X-ray diffraction (WAXD) measurement was performed using a D8 Discover manufactured by Bruker AXS. The incident X-ray wavelength was 0.154 nm (Cu target). The detector used was a VANTEC-500, a rare gas-filled micro-gap position-sensitive two-dimensional detector, and the camera distance (distance between the sample and the detector) was set to approximately 170 mm. The X-ray generator filament current was 1 mA, the voltage was 50 kV, and the collimator diameter was 0.5 mm.

[0086] The PVA film was cut into a rectangle with a short side of 5 mm and a long side of 20 mm. The long side was aligned with the length direction of the PVA film. Several cut PVA films were stacked and attached to a sample holder. It was confirmed in advance that the signal from the PVA film was sufficiently strong compared to background scattering and electrical noise from the detector.

[0087] The sample holder was attached to the stage of the X-ray device so that the length direction of the PVA film was aligned with the X-axis direction of the D8 Discover. The normal to the PVA film surface was aligned with the direction of X-ray incidence. The X-, Y-, and Z-axes of the device were adjusted so that the PVA film was irradiated with X-rays from the above-mentioned incident direction.

[0088] WAXD measurements were performed under the following conditions: the ω axis of the sample (the axis set so that the angle between the normal to the PVA film surface and the direction of X-ray incidence is ω; commonly referred to as the θ axis) was set to 11°, the 2θ axis (the axis set so that the angle between the normal to the detector surface and the direction of X-ray incidence is 2θ) representing the detector position was set to 22°, and the ψ axis, corresponding to rotation within the PVA film plane, was set to 90° or 0°. The ψ axis coincides with the azimuthal direction within the PVA film plane. When the stretching direction of the PVA film is the meridian direction and the perpendicular direction within the plane is the equator direction, if the ψ axis is 90°, diffraction information in the equatorial direction can be obtained, and if the ψ axis is 0°, diffraction information in the meridian direction can be obtained. The diffraction or scattering observed by the detector satisfies the Bragg condition. Under these measurement conditions, for example, the 110 diffraction signal detected from the PVA crystals is diffraction from the (110) plane, which roughly coincides with the thickness direction of the PVA film. Measurements were performed with the ψ axis at 90° or 0°, and the X-ray exposure time was 10 minutes for each.

[0089] (Analysis of WAXD Measurement Data of PVA Film) The acquired two-dimensional WAXD photographs were converted into one-dimensional profiles of X-ray intensity I(2θ) versus 2θ using DIFFRAC.EVA software. The 2θ range was 5° to 38°, and the ψ axis range was −135° to −45°. The sampling step was 0.02° intervals. The same operation was also applied to background scattering data (data measured under the same conditions without the PVA film attached).

[0090] The I(2θ) profile was analyzed using the following procedure. First, the I(2θ) profile obtained by background measurement was subtracted from the I(2θ) profile obtained by film measurement. For the I(2θ) profile from which background scattering was subtracted, a baseline line connecting the intensity value I(15) at a 2θ position of 15° and the intensity value I(25) at a 2θ position of 25° was created, as shown in Figure 1, and this baseline line was further subtracted from the I(2θ) profile from which background scattering was subtracted (Figure 2). The baseline line is a linear function passing through the two points (15, I(15)) and (25, I(25)) on the I(2θ)-2θ coordinate system.

[0091] The PVA amorphous peak was fitted to the baseline-corrected I(2θ) profile data (FIG. 2) using the following Gaussian function: f(x)=a·exp(−{(x−b) / c} ２ ) where a: peak height, b: peak top position, c: half-width. Furthermore, fitting was performed using the least squares method to minimize the deviation between 2θ = 15° to 17.6° and 21° to 21.6°. The peak top position 2θ of the Gaussian function was set to the (110) plane, i.e., near 20° (Figure 3). The peak area of ​​this fitting function is taken as the amorphous amount (A).

[0092] Similarly, the peaks in the (110) and (200) planes of the baseline-corrected I(2θ) profile data ( FIG. 2 ) were also fitted with the same functions. The peak tops were adjusted to be near 20° for the (110) plane and near 23° for the (200) plane. Furthermore, fitting was performed by the least squares method to minimize the difference between the sum of all Gaussian functions, including the Gaussian function for amorphous PVA obtained above, and the baseline-corrected data ( FIG. 4 ). The peak areas of these Gaussian functions were defined as the crystalline amounts (B) and (C), respectively. That is, the peak area of ​​the fitting function for the peak in the (110) plane was defined as the crystalline amount (B), and the peak area of ​​the fitting function for the peak in the (200) plane was defined as the crystalline amount (C).

[0093] The degree of crystallinity is defined as the value calculated from the area values ​​of the amorphous and crystalline regions ((A), (B), and (C)) using the following formula: Crystallinity (%) = {(B) + (C)} / {(A) + (B) + (C)} × 100

[0094] [Calculation of the Amount of Highly Oriented Amorphous Crystals and the Amount of Highly Oriented PVA-Boric Acid Aggregated Structures in Polarizing Films] (Wide-Angle X-ray Diffraction (WAXD) Measurement of Polarizing Films) Wide-angle X-ray diffraction (WAXD) measurements were performed using a D8 Discover manufactured by Bruker AXS. The incident X-ray wavelength was 0.154 nm (Cu target). The detector used was a VANTEC-500 rare gas-filled micro-gap position-sensitive two-dimensional detector, and the camera distance (distance between the sample and the detector) was set to approximately 100 mm. The X-ray generator filament current was 1 mA, the voltage was 50 kV, and the collimator diameter was 0.5 mm.

[0095] The polarizing film was cut into a rectangle with a short side of 5 mm and a long side of 20 mm. The long side was aligned with the stretching direction of the polarizing film. Several cut pieces of polarizing film were stacked and fixed on a sample holder. The polarizing films must be fixed so that the stretching direction of each film is completely aligned. It was confirmed in advance that the signal from the polarizing film was sufficiently strong compared to background scattering and electrical noise from the detector.

[0096] The sample holder was attached to the stage of the X-ray apparatus so that the stretching direction of the polarizing film coincided with the X-axis direction of the D8 Discover. The normal to the polarizing film surface was aligned with the direction of X-ray incidence. The X-, Y-, and Z-axes of the apparatus were adjusted so that the polarizing film was irradiated with X-rays from the above-mentioned incident direction.

[0097] The WAXD measurement was performed under the following conditions: the ω axis of the sample (the axis set so that the angle between the normal to the polarizing film surface and the direction of X-ray incidence is ω; commonly referred to as the θ axis) was set to 11°, the 2θ axis (the axis set so that the angle between the normal to the detector surface and the direction of X-ray incidence is 2θ) representing the detector position was set to 22°, and the ψ axis, corresponding to the rotation in the plane of the polarizing film, was set to 50°. The ψ axis coincides with the azimuthal direction in the plane of the polarizing film. The diffraction or scattering observed by the detector satisfies the Bragg condition. Under these measurement conditions, for example, the 110 diffraction signal detected from PVA crystals is diffraction from the (110) plane, which roughly coincides with the thickness direction of the polarizing film. The X-ray exposure time was 30 minutes.

[0098] (Analysis of WAXD Measurement Data of Polarizing Film) The acquired two-dimensional WAXD photograph was converted into a one-dimensional profile of X-ray intensity I(2θ) versus 2θ using DIFFRAC.EVA software. The 2θ range was 5° to 35°, and the stretching direction was set to 0°. I(2θ) profiles were obtained by dividing the azimuthal angle ranges into -5° to 5°, 5° to 15°, 15° to 25°, 25° to 35°, 35° to 45°, 45° to 55°, 55° to 65°, 65° to 75°, 70° to 80°, 75° to 85°, 80° to 90°, 85° to 95°, 90° to 100°, 95° to 105°, 100° to 110°, and 105° to 115°. Sampling intervals were 0.05°. The same procedure was also applied to background scattering data (data measured under the same conditions without a polarizing film attached).

[0099] The I(2θ) profile was analyzed using the following procedure. First, the I(2θ) profile in the same azimuthal angle range obtained in the background measurement was subtracted from the I(2θ) profile obtained in the measurement of the polarizing film. For the I(2θ) profile from which background scattering was subtracted, a baseline line connecting the intensity value I(6.5) at a 2θ position of 6.5° and the intensity value I(30.5) at a 2θ position of 30.5° was created, as shown in Figure 5, and this baseline line was further subtracted from the I(2θ) profile from which background scattering was subtracted. The baseline line is a linear function that passes through the two points (6.5, I(6.5)) and (30.5, I(30.5)) on the I(2θ)-2θ coordinate system.

[0100] Figure 6 shows the baseline-corrected I(2θ) profile. The broad, diffuse scattering component observed in the 2θ range of 10° to 30° is primarily due to amorphous PVA. The peak-like component observed in the 2θ range of 19° to 21° results from diffraction by the (1-10) and (110) planes of PVA crystals. On the other hand, the peak-like component observed in the 2θ range of 21° to 23° is known to appear when boric acid is added to PVA and is thought to be a diffraction signal from a structure formed by the interaction of PVA and boric acid. This structure formed by the interaction of PVA and boric acid is referred to as the "PVA-boric acid aggregate structure." In other words, the corrected I(2θ) profile obtained by measuring a polarized film can be separated into three components: "amorphous PVA," "PVA crystal," and "PVA-boric acid aggregate structure." Therefore, waveform resolution analysis was applied to the corrected I(2θ) profile.

[0101] We assumed that the scattering or diffraction signals from "amorphous PVA," "crystalline PVA," and "PVA-boric acid aggregate structure" could be expressed by Gaussian functions. These functions were designated Gaussian function A, Gaussian function B, and Gaussian function C, respectively. The parameters defining the shape of the Gaussian functions were the peak-top position x, peak height h, and peak width (here, the standard deviation σ of the normal distribution). To ensure that the calculated-I(2θ) profile, which is the sum of the three Gaussian functions representing each component, coincided with the corrected I(2θ) profile, we optimized all parameters by least-squares fitting, using the peak-top position x, peak height h, and peak width of the three Gaussian functions as variable parameters. The results are shown in Figure 6. In this waveform resolution analysis, the calculated-I(2θ) profile must be appropriately expressed by the three Gaussian functions to reflect the polarizing film structure without being affected by variations in the measurement data, analytical errors, or systematic fitting errors. Therefore, in this test, the following constraints (a) to (f) were introduced in the waveform separation analysis.

[0102] (a) Signals in the 2θ ranges of 13° to 16° and 25° to 28° are considered to be scattering caused by "amorphous PVA," so an I(2θ) profile corrected only by Gaussian function A is reproduced in the same 2θ range. (b) Signals in the 2θ range of approximately 17° to 21° are scattering and diffraction caused by "amorphous PVA" and "crystalline PVA," with the contribution of "crystalline PVA" being particularly large. The diffraction peak position due to crystals is known, so the peak top position x of Gaussian function B is fixed. (c) Signals in the 2θ range of approximately 20° to 23° are scattering and diffraction caused by "amorphous PVA" and "PVA-boric acid aggregate structure." The contribution of "PVA-boric acid aggregate structure" is particularly large. Therefore, the peak top position x of Gaussian function C is fixed. (d) To properly separate the "PVA crystals" and the "PVA-boric acid aggregate structure," the peak widths of Gaussian function B and Gaussian function C were set to the same value. This is because, regardless of the polarized film measured, the diffraction intensities between 17° and 21° and between 20° and 23° are approximately equal, and it is expected that there will be no significant difference in the shapes of the diffraction peaks due to the "PVA crystals" and the "PVA-boric acid aggregate structure." (e) Based on (a) to (d) above, optimal values ​​for the peak top position x and peak width σ of each of the three Gaussian functions were searched for so that all corrected I(2θ) profiles could be well reproduced by the calculated-I(2θ) profile, which is the sum of the three Gaussian functions. (f) Least-squares fitting was performed on all corrected I(2θ) profiles, with only the peak height h of the three Gaussian functions as a variable parameter. The fitting range was set to 6.5° to 30.5°.

[0103] In the I(2θ) profile in the equatorial direction, i.e., near an azimuth angle of 90°, a 100 diffraction peak due to PVA crystals oriented in the stretching direction was observed at a 2θ position of approximately 11°. When a 100 diffraction peak was observed, the diffraction peak shape was considered to be expressible by a Gaussian function and was included in the waveform separation analysis of the I(2θ) profile. That is, the peak top position x, peak height h, and peak width σ of the Gaussian function were appropriately adjusted and least-squares fitting was performed.

[0104] After least-squares fitting, the areas of the three Gaussian functions were calculated and considered to be the integrated intensity values ​​(A) of the signals arising from "amorphous PVA," "crystalline PVA," and "PVA-boric acid aggregate structure," respectively. When a 100 diffraction peak was observed, the integrated intensity value of the 100 diffraction peak was included in "crystalline PVA." The waveform separation analysis described above was performed on the corrected I(2θ) profiles for all azimuth angles, and the integrated intensity values ​​(A) of "amorphous PVA," "crystalline PVA," and "PVA-boric acid aggregate structure" were calculated. These analyses were performed using Microsoft Excel software.

[0105] Figure 7 shows the integrated intensity values ​​(A) of "amorphous PVA," "crystalline PVA," and "PVA-boric acid aggregate structure" obtained by waveform resolution analysis plotted against the azimuth angle. The azimuth angle is defined as follows: For example, the analysis results of the corrected I(2θ) profile in the azimuth angle range of -5° to 5° are plotted against an azimuth angle of 0°, and the analysis results of the corrected I(2θ) profile in the azimuth angle range of 85° to 95° are plotted against an azimuth angle of 90°.

[0106] The azimuth angle dispersion plot A(φ) of the integrated intensity values ​​of each component reflects the orientation state of each component relative to the stretching direction of the polarizing film. Assuming that the scattering or diffraction signals observed in the analyzed 2θ range are primarily due to interference between PVA molecular chains, the proportion of signals observed at an azimuth angle of 90° is approximately equal to the proportion of components in which the PVA molecular chains are aligned in the stretching direction. The proportion of signals observed at an azimuth angle of 0° is approximately equal to the proportion of components in which the PVA molecular chains are aligned perpendicular to the stretching direction. In other words, Figure 7 is approximately equal to the distribution function f(φ) of the orientation state of each component. When the PVA is completely unoriented, the distribution function has no azimuth angle dependence. On the other hand, if the PVA is oriented with some distribution in the stretching direction, the distribution function will exhibit a peak shape with maximum intensity at 90°.

[0107] Therefore, the azimuth angle dispersion plot A(φ) of the integrated intensity values ​​was separated into the distribution function f1(φ) of the oriented component and the distribution function f2(φ) of the non-oriented component. Because the distribution function of the non-oriented component is independent of the azimuth angle, f2(φ) = C (C is a constant). As shown in Figure 8, the component that maintains a constant constant C at any azimuth angle is f2(φ), while the component that has a probability distribution at a specific azimuth angle is f1(φ). For any polarizing film, the following data processing procedure was found to be effective for accurately obtaining f1(φ) from the azimuth angle dispersion plot A(φ). The distribution function f1(φ) of the oriented component of the "PVA crystal" and "PVA-boric acid aggregated structure" was assumed to be expressible by a Lorentzian function, with the peak top position set to 90° and the peak height h and half-width of the peak as variable parameters. The distribution function f1(φ) of the orientation component of "amorphous PVA" was assumed to be expressed as the linear sum of two Gaussian functions, with the peak top position set at 90°, and the peak height h and half-width of each function as variable parameters. Least-squares fitting was performed to adequately reproduce A(φ) as the sum of f1(φ) and f2(φ), and optimal solutions for the constant C, peak height h, and half-width of the peak were obtained. Fitting was performed over an azimuth angle range of 0° to 110°. Since the orientation state of the polarizing film is considered symmetrical with respect to the stretching direction, the resulting distribution functions f1(φ) and f2(φ) were applied over an azimuth angle range of 0° to 180° in the calculation of the integral values ​​below.

[0108] Here, the proportion of the oriented component distribution function f1(φ) obtained by the above fitting in the range of azimuth angles φ from 80° to 100°, i.e., the proportion of highly oriented components, was calculated as follows: First, the integral value of the oriented component distribution function f1(φ) was calculated in the azimuth angle range of 0° to 180°. This was designated F1. Next, the integral value of the oriented component distribution function f1(φ) in the range of azimuth angles φ from 80° to 100° was calculated and designated F1a. F1-F1a is the integral value from 0° to 80° and from 100° to 180°, and this is designated F1b. F1b represents an oriented component with a low degree of orientation. In the azimuth angle range from 0° to 180°, the integral value F2 of the non-oriented component distribution function f2(φ) was calculated. The values ​​of F1a, F1b, and F2 were obtained for "amorphous PVA," "crystalline PVA," and "PVA-boric acid aggregated structure," respectively. F1a is an amount proportional to the highly oriented component, F1b is an amount proportional to the low oriented component, and F2 is an amount proportional to the non-oriented component.

[0109] The abundance ratios of the highly oriented, low oriented, and non-oriented components of each of the "amorphous PVA," "crystalline PVA," and "PVA-boric acid aggregated structure," i.e., nine components, were considered to be the ratio of each component to the sum of the integrated values ​​of each component. These were designated F1a-PVA amorphous, F1b-PVA amorphous, F2-PVA amorphous, F1a-PVA crystalline, F1b-PVA crystalline, F2-PVA crystalline, F1a-PVA-boric acid aggregated structure, F1b-PVA-boric acid aggregated structure, and F2-PVA-boric acid aggregated structure.

[0110] Of these, F1a-PVA amorphous, which is a highly oriented component of "amorphous PVA," is the aforementioned highly oriented amorphous, and the ratio of this component to the total of the nine components is referred to as the "highly oriented amorphous amount." Also, F1a-PVA-boric acid aggregate structure, a highly oriented component of "PVA-boric acid aggregate structure," is the aforementioned highly oriented PVA-boric acid aggregate structure, and the ratio of this component to the total of the nine components is referred to as the "highly oriented PVA-boric acid aggregate structure amount."

[0111] [Calculation of boric acid content (% by mass) in polarizing film] The polarizing film obtained in each example or comparative example was conditioned at a temperature of 23°C and a humidity of 50% RH for 16 hours, and then a sample of approximately 1 mg was taken and its mass (J (g)) was measured. Next, the taken sample was dissolved in 20 mL of distilled water to prepare an aqueous solution. This aqueous solution was used as a measurement sample, and its mass (K (g)) was measured. Thereafter, the boron concentration (L (ppm)) of the measurement sample was measured using a Shimadzu Corporation multi-type ICP optical emission analyzer (ICPE-9000). The value was then substituted into the following formula to calculate the value, which was taken as the boric acid content (% by mass) in the polarizing film. Boric acid content (% by mass) in polarizing film = [(L x 10 －６ ×K) / J]×100 / (10.8 / 61.8)

[0112] [Evaluation of Maximum Elongation of Thermoformed Articles] When a thermoformed article is cut along a plane perpendicular to the film surface before thermoforming so that the deformation length (periphery length) of the cut surface is maximized, the deformation length (maximum deformation length) is defined as A, and the diameter of the molding die with a spherical depression used for thermoforming (i.e., the length before thermoforming) is defined as B. The maximum elongation (%) was calculated by the following equation (Figure 9). Maximum elongation (%) = ((A - B) / B) x 100

[0113] [Evaluation of Crack Rate] The polarizing plates obtained in each Example or Comparative Example were subjected to heat vacuum molding using a mold having a depth of 3.5 cm and a spherical depression with a radius of curvature of 5.2 cm at a temperature of 107°C and a vacuum degree of 0.01 MPa. The percentage of samples in which one or more cracks occurred was calculated. The number of samples was 6. Crack rate (%) = (number of samples in which cracks occurred / total number of samples) x 100

[0114] [Evaluation of Polarization Performance of Thermoformed Products] A rectangular film piece measuring 3 cm in the length direction and 1.5 cm in the width direction of the polarizing plate before thermoforming was taken from the thinnest part of the thermoformed product obtained in each Example or Comparative Example. The polarization degree and single transmittance of the film piece at the maximum absorption wavelength in the visible light region were measured using a spectrophotometer equipped with an integrating sphere ("V7100" manufactured by JASCO Corporation).

[0115] [Example 1] A film-forming solution containing 100 parts by mass of PVA (degree of polymerization 2,300, degree of saponification 99.3 mol%), 0 parts by mass of glycerin as a plasticizer, and 0.1 parts by mass of sodium polyoxyethylene lauryl ether sulfate as a surfactant, and containing water as a liquid solvent, with a volatile content of 66% by mass, was continuously formed into a long PVA film with a thickness of 80 μm using a film-forming device equipped with 18 drying rolls whose rotation axes are parallel to each other. The crystallinity of the obtained PVA film was calculated using the method described above and was found to be 33%.

[0116] Specifically, the film-forming solution was extruded from a T-shaped slit die onto a first drying roll (surface temperature 95°C, circumferential speed 10.6 m / min) in the form of a film, and dried on the first drying roll while hot air (temperature 90°C, dew point temperature 10°C) was blown uniformly over the entire non-contact surface of the first drying roll at a wind speed of 5 m / sec until the volatile content of the polyvinyl alcohol film reached 25% by mass. The film was then peeled off from the first drying roll (the volatile content when peeled off from the first drying roll was 25% by mass), and dried with the second and subsequent drying rolls (surface temperature 75 to 95°C, circumferential speed 10.6 m / min) so that the first drying roll contact surface and the first drying roll non-contact surface of the PVA film alternately faced each drying roll. Both widthwise ends (edges) were then cut and removed, and the film was wound into a roll to obtain the PVA film.

[0117] A 40 cm wide x 15 cm long sample was cut from the center of the resulting PVA film widthwise so that a 40 cm wide x 10 cm long region could be uniaxially stretched. This sample was immersed in water at 32°C for 2 minutes, during which it was uniaxially stretched in the longitudinal direction to 2.0 times its original length (first-stage stretching) and swollen (swelling treatment). It was then dyed by immersing it in a Direct Blue 15 solution (dye bath: dichroic organic dye Direct Blue 15 concentration 0.013 wt%, sodium sulfate concentration 0.42 wt%, sodium tripolyphosphate concentration 0.42 wt%) at 32°C for 5 minutes, during which it was uniaxially stretched in the longitudinal direction to 1.3 times its original length (total 2.5 times) (second-stage stretching) (dyeing treatment). Next, the film was immersed in a boric acid aqueous solution (crosslinking bath: boric acid concentration 2.6% by mass) at a liquid temperature of 32°C for 1 minute, during which time it was uniaxially stretched in the longitudinal direction by 1.2 times (total 3.0 times) (third-stage stretching) (crosslinking treatment). Subsequently, while immersed in a boric acid aqueous solution (stretching bath: boric acid concentration 2.8% by mass) at a liquid temperature of 57°C, it was uniaxially stretched in the longitudinal direction by 1.7 times (total 5.0 times) (fourth-stage stretching) (stretching treatment). Subsequently, the film was immersed in a boric acid aqueous solution (washing bath: boric acid concentration 1.5% by mass) at a liquid temperature of 22°C for 1 second without stretching, and washed (washing treatment). Subsequently, the film was dried in a dryer at 60°C for 3 minutes (drying treatment) with both ends fixed to prevent dimensional change in the longitudinal direction, to obtain a polarized film. The thickness of the resulting polarized film was measured, and the highly oriented amorphous content, the amount of highly oriented PVA-boric acid aggregated structure, and the boric acid content were measured using the methods described above. The results are shown in Table 1. The polarizing film obtained contained no halides.

[0118] The central portion of the obtained polarizing film in the width direction was cut to a size of 25 cm wide x 25 cm long, and acrylic films (HI5000, manufactured by Kuraray Co., Ltd., thickness 75 μm) were attached to both sides with an adhesive (MPD62, manufactured by Mitate Imaging Co., Ltd., thickness 25 μm) to produce a polarizing plate of width 25 cm x length 25 cm.

[0119] The resulting polarizing plate was heated to 107°C using a heater set at 250°C in a vacuum pressure molding machine (FVT-400) manufactured by Wakisaka Engineering Co., Ltd., and then subjected to heat vacuum molding at a vacuum of 0.01 MPa for 10 seconds using a 3.5 cm deep mold with a spherical recess with a radius of curvature of 5.2 cm. This produced a thermoformed product with a maximum elongation of 30%. The thermoformed product was cooled for 5 seconds while held in the jig, and then removed from the jig to obtain a thermoformed product. The cracking rate, polarization degree, and single-piece transmittance of the resulting thermoformed product were calculated using the methods described above. The cracking rate and polarization degree are shown in Table 1. The single-piece transmittance was 32%.

[0120] Example 2 A PVA film, a polarizing film, a polarizing plate, and a thermoformed article were produced in the same manner as in Example 1, except that the temperature of the boric acid aqueous solution in the stretching treatment was changed to 49°C. The thickness of the obtained polarizing film was measured, and the highly oriented amorphous content, the amount of highly oriented PVA-boric acid aggregated structure, and the boric acid content were measured using the methods described above. The results are shown in Table 1. Furthermore, the cracking rate, polarization degree, and single-piece transmittance of the obtained thermoformed article were calculated using the methods described above. The cracking rate and polarization degree are shown in Table 1. The single-piece transmittance was 31%.

[0121] Example 3 A PVA film, a polarizing film, a polarizing plate, and a thermoformed article were produced in the same manner as in Example 2, except that the amount of glycerin in the film-forming solution was changed to 12 parts by mass and the thickness of the PVA film to be produced was changed to 75 μm. The crystallinity of the resulting PVA film was calculated using the method described above and was found to be 34%. The thickness of the resulting polarizing film was measured, and the highly oriented amorphous content, the amount of highly oriented PVA-boric acid aggregate structure, and the boric acid content were measured using the methods described above. The results are shown in Table 1. Furthermore, the cracking rate, polarization degree, and single-piece transmittance of the resulting thermoformed article were calculated using the methods described above. The cracking rate and polarization degree are shown in Table 1. The single-piece transmittance was 31%.

[0122] Comparative Example 1 A PVA film, a polarizing film, a polarizing plate, and a thermoformed article were produced in the same manner as in Example 2, except that the stretching ratio was changed to 2.2 times (6.0 times in total). The crystallinity of the resulting PVA film was calculated using the method described above and was found to be 33%. The thickness of the resulting polarizing film was measured, and the highly oriented amorphous content, the amount of highly oriented PVA-boric acid aggregate structures, and the boric acid content were measured using the methods described above. The results are shown in Table 1. Furthermore, the cracking rate, polarization degree, and single-piece transmittance of the resulting thermoformed article were calculated using the methods described above. The cracking rate and polarization degree are shown in Table 1. The single-piece transmittance was 33%.

[0123] Comparative Example 2 A PVA film, a polarizing film, a polarizing plate, and a thermoformed article were produced in the same manner as in Example 3, except that the stretching ratio was changed to 2.2 times (6.0 times in total). The crystallinity of the resulting PVA film was calculated using the method described above and was found to be 34%. The thickness of the resulting polarizing film was measured, and the highly oriented amorphous content, the amount of highly oriented PVA-boric acid aggregated structure, and the boric acid content were measured using the methods described above. The results are shown in Table 1. Furthermore, the cracking rate, polarization degree, and single-piece transmittance of the resulting thermoformed article were calculated using the methods described above. The cracking rate and polarization degree are shown in Table 1. The single-piece transmittance was 31%.

[0124]

[0125] As shown in Table 1, in Examples 1 to 3, thermoformed articles were obtained that had a maximum elongation of 30% and had few cracks and sufficient polarizing properties.

[0126] 1. Maximum deformation length A 2. Diameter of molding die B

Claims

1. A thermoformed product obtained by thermoforming a polarizing plate including a polarizing film mainly composed of polyvinyl alcohol, wherein the polarizing film has a thickness of more than 20 μm and a highly oriented amorphous amount of the polarizing film is 10.0 to 18.0%.

2. The thermoformed product according to claim 1, wherein the polarizing film has a boric acid content of 5 to 30 mass%.

3. 3. The thermoformed product according to claim 1, wherein the polarizing film has a highly oriented PVA-boric acid aggregate structure content of 4.3% or less.

4. 3. The thermoformed article according to claim 1 or 2, wherein the polarizing film comprises a dichroic organic dye.

5. 3. The thermoformed article according to claim 1 or 2, having a maximum elongation of 35% or less.

6. The thermoformed article according to claim 1 or 2, having a polarization degree of 80 to 99.7%.

7. A method for producing a thermoformed body as described in claim 1 or 2, comprising a step of thermoforming the polarizing plate at 105°C to 110°C.