Method for manufacturing a polarizing plate

Abstract

The object of this invention is to provide a method for manufacturing a polarizing plate that can improve the water resistance of the adhesive layer between the polarizing element and the protective film. This invention provides a method for manufacturing a polarizing plate, comprising: an adhesive preparation step of preparing an adhesive for forming an adhesive layer; and a bonding step of applying the adhesive to the surface of at least one of a polarizing element and a transparent protective film and bonding the polarizing element to the transparent protective film. The adhesive preparation step includes: a preparation step of obtaining an aqueous solution A containing a polyvinyl alcohol-based resin; a first addition step of adding a urea-based compound to the aqueous solution A to obtain an aqueous solution B; and a second addition step of adding a dialdehyde to the aqueous solution B to obtain an adhesive. The bonding step is performed such that the time elapsed after adding the dialdehyde to the aqueous solution B is 100 hours or less.

Description

Technical Field

[0001] This invention relates to a method for manufacturing a polarizing plate. Background Technology

[0002] Liquid crystal displays (LCDs) are not only used in LCD televisions, but also widely used in personal computers, mobile devices such as mobile phones, and automotive applications such as car navigation systems. Typically, an LCD has a liquid crystal panel with polarizing plates bonded to both sides of the liquid crystal cells using adhesive. The display is achieved by controlling the light from the backlight using the liquid crystal panel. In recent years, organic EL displays have also been widely used, similarly to LCDs, in televisions, mobile devices such as mobile phones, and automotive applications such as car navigation systems. In organic EL displays, to suppress the reflection of external light by the metal electrodes (cathodes) and thus prevent it from appearing as a mirror, a circular polarizing plate (a laminate containing polarizing elements and a λ / 4 plate) is sometimes placed on the viewing side surface of the image display panel.

[0003] In polarizing plates, polyvinyl alcohol-based resin adhesives are used to achieve good adhesion in the bonding of polarizing elements and protective films. Patent Document 1 (Japanese Patent Application Publication No. 2009-42383) discloses an adhesive in which the weight ratio of polyvinyl alcohol-based resin to zirconium oxide salt is adjusted to a specific range, thereby improving the adhesion and water resistance between the polarizing element and the protective film.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2009-42383 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] The purpose of this invention is to provide a method for manufacturing a polarizing plate using an adhesive comprising a polyvinyl alcohol resin in the bonding of a polarizing element and a protective film, wherein the water resistance of the adhesive layer between the polarizing element and the protective film can be improved.

[0009] Methods for solving problems

[0010] The present invention provides a method for manufacturing a polarizing plate as illustrated below.

[0011] [1] A method for manufacturing a polarizing plate, the polarizing plate having a polarizing element and a transparent protective film, the polarizing element being formed by adsorbing and oriented a dichroic pigment on a polyvinyl alcohol-based resin layer, and the transparent protective film being laminated onto at least one side of the polarizing element via an adhesive layer.

[0012] The method for manufacturing the polarizing plate includes:

[0013] The adhesive preparation process includes preparing an adhesive for forming the aforementioned adhesive layer; and

[0014] In the bonding process, the adhesive is applied to the surface of at least one of the polarizing element and the transparent protective film, and the polarizing element is bonded to the transparent protective film.

[0015] The above adhesive preparation process includes:

[0016] The preparation process yields an aqueous solution A containing polyvinyl alcohol resin.

[0017] The first addition step involves adding the first compound to the aforementioned aqueous solution A to obtain aqueous solution B; and

[0018] In the second addition step, the second compound is added to the above aqueous solution B to obtain the adhesive.

[0019] The first compound mentioned above is selected from at least one of urea, urea derivatives, thiourea, and thiourea derivatives; the second compound mentioned above is a dialdehyde.

[0020] The bonding process described above is carried out such that the time elapsed after adding the second compound to the aqueous solution B is less than 100 hours.

[0021] [2] A method for manufacturing a polarizing plate, the polarizing plate having a polarizing element and a transparent protective film, the polarizing element being formed by adsorbing and oriented a dichroic pigment on a polyvinyl alcohol-based resin layer, and the transparent protective film being laminated on at least one side of the polarizing element via an adhesive layer.

[0022] The method for manufacturing the polarizing plate includes:

[0023] The adhesive preparation process includes preparing an adhesive for forming the aforementioned adhesive layer; and

[0024] In the bonding process, the adhesive is applied to the surface of at least one of the polarizing element and the transparent protective film, and the polarizing element is bonded to the transparent protective film.

[0025] The above adhesive preparation process includes:

[0026] The preparation process yields an aqueous solution A containing polyvinyl alcohol resin.

[0027] The first addition step involves adding the first compound to the aforementioned aqueous solution A to obtain aqueous solution B; and

[0028] In the second addition step, the second compound is added to the above aqueous solution B to obtain the adhesive.

[0029] A third compound is further added in at least one of the first and second addition steps described above.

[0030] The first compound is selected from at least one of urea, urea derivatives, thiourea, and thiourea derivatives; the second compound is a dialdehyde; and the third compound is a dicarboxylic acid.

[0031] The bonding process described above is carried out in such a way that the time elapsed after adding the second compound to the aqueous solution B is less than 200 hours.

[0032] [3] The method for manufacturing a polarizing plate as described in [1] or [2], wherein, in the adhesive, the content of the first compound is 0.1 parts by mass or more and 400 parts by mass or less relative to 100 parts by mass of the polyvinyl alcohol resin.

[0033] [4] The method for manufacturing a polarizing plate according to any one of [1] to [3], wherein, in the adhesive, the content of the second compound is 0.03 parts by mass or more and 20 parts by mass or less relative to 1 part by mass of the first compound.

[0034] [5] The method for manufacturing a polarizing plate according to any one of [1] to [4], wherein the dialdehyde is glyoxal.

[0035] [6] According to the method for manufacturing a polarizing plate described in [2], in the adhesive, the content of the third compound is 0.01 parts by mass or more and 400 parts by mass or less relative to 100 parts by mass of the polyvinyl alcohol resin.

[0036] [7] The method for manufacturing a polarizing plate according to any one of [1] to [6], wherein the thickness of the adhesive layer is 0.01 μm or more and 7 μm or less.

[0037] Invention Effects

[0038] According to the method for manufacturing a polarizing plate of the present invention, the water resistance of the adhesive layer between the polarizing element and the protective film can be improved. Detailed Implementation

[0039] The embodiments of the present invention will be described below. The present invention is not limited to the following embodiments.

[0040] [Manufacturing method of polarizing plate]

[0041] The manufacturing method of this embodiment is a method for manufacturing a polarizing plate having a polarizing element and a transparent protective film. The polarizing element is formed by adsorbing and oriented a dichroic pigment onto a layer containing a polyvinyl alcohol-based resin (hereinafter also referred to as "PVA-based resin"). The transparent protective film is laminated on at least one side of the polarizing element via an adhesive layer. The manufacturing method of the polarizing plate includes: an adhesive preparation step, in which an adhesive for forming the adhesive layer is prepared; and a bonding step, in which the adhesive is applied to the surface of at least one of the polarizing element and the transparent protective film, and the polarizing element is bonded to the transparent protective film. In the method for manufacturing a polarizing plate in which a transparent protective film is bonded to both sides of the polarizing element via an adhesive layer, at least the adhesive layer on one side of the polarizing element, and preferably the adhesive layers on both sides of the polarizing element, are formed using the adhesive prepared in the adhesive layer preparation step.

[0042] <Method 1>

[0043] In a first embodiment of the method for manufacturing a polarizing plate according to the present invention, the adhesive preparation step includes: a preparation step to obtain an aqueous solution A containing a PVA-based resin; a first addition step to add a first compound to the aqueous solution A to obtain an aqueous solution B; and a second addition step to add a second compound to the aqueous solution B to obtain an adhesive, wherein the bonding step is performed such that the elapsed time (hereinafter also referred to as "elapsed time T1") after adding the second compound to the aqueous solution B is 100 hours or less. By setting the elapsed time T1 to 100 hours or less, it is possible to manufacture a polarizing plate with an adhesive layer having high water resistance.

[0044] (Compound 1)

[0045] The first compound is selected from at least one of urea, urea derivatives, thiourea, and thiourea derivatives. One first compound may be used alone or in combination of two or more. The first compound may include water-soluble and water-poorly soluble compounds; any one of the first compounds may be used. When using a water-poorly soluble first compound in a water-soluble adhesive, it is preferable to design a dispersion method that does not cause an increase in haze after the adhesive layer is formed. By including the first compound, the decrease in the transmittance of the polarizing element can be suppressed. It is speculated that one reason for the decrease in the transmittance of the polarizing element is the polyolefination of the PVA-based resin constituting the polarizing element through dehydration. It is speculated that the first compound contained in the adhesive layer transfers to the polarizing element, thereby suppressing polyolefination.

[0046] (Urea derivatives)

[0047] Urea derivatives are compounds in which at least one of the four hydrogen atoms of a urea molecule has been substituted with a substituent. In this case, there are no particular limitations on the substituent, but substituents containing carbon, hydrogen, and oxygen atoms are preferred.

[0048] Specific examples of urea derivatives, as 1-substituted ureas, include methylurea, ethylurea, propylurea, butylurea, isobutylurea, N-octadecylurea, 2-hydroxyethylurea, hydroxyurea, acetylurea, allylurea, 2-propynylurea, cyclohexylurea, phenylurea, 3-hydroxyphenylurea, (4-methoxyphenyl)urea, benzylurea, benzoylurea, o-tolylurea, and p-tolylurea.

[0049] Examples of disubstituted ureas include 1,1-dimethylurea, 1,3-dimethylurea, 1,1-diethylurea, 1,3-diethylurea, 1,3-di(hydroxymethyl)urea, 1,3-tert-butylurea, 1,3-dicyclohexylurea, 1,3-diphenylurea, 1,3-di(4-methoxyphenyl)urea, 1-acetyl-3-methylurea, 2-imidazolidineone (vinylurea), and tetrahydro-2-pyrimidinone (acrylurea).

[0050] Examples of 4-substituted ureas include tetramethylurea, 1,1,3,3-tetraethylurea, 1,1,3,3-tetrabutylurea, 1,3-dimethoxy-1,3-dimethylurea, 1,3-dimethyl-2-imidazolidineone, and 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone.

[0051] (Thiocarbamide derivatives)

[0052] Thiourea derivatives are compounds in which at least one of the four hydrogen atoms of a thiourea molecule is substituted with a substituent. In this case, there are no particular restrictions on the substituent, but substituents containing carbon, hydrogen, and oxygen atoms are preferred.

[0053] Specific examples of thiourea derivatives, as 1-substituted thioureas, include N-methylthiourea, ethylthiourea, propylthiourea, isopropylthiourea, 1-butylthiourea, cyclohexylthiourea, N-acetylthiourea, N-allylthiourea, (2-methoxyethyl)thiourea, N-phenylthiourea, (4-methoxyphenyl)thiourea, N-(2-methoxyphenyl)thiourea, N-(1-naphthyl)thiourea, (2-pyridyl)thiourea, o-tolylthiourea, and p-tolylthiourea.

[0054] Examples of disubstituted thioureas include 1,1-dimethylthiourea, 1,3-dimethylthiourea, 1,1-diethylthiourea, 1,3-diethylthiourea, 1,3-dibutylthiourea, 1,3-diisopropylthiourea, 1,3-dicyclohexylthiourea, N,N-diphenylthiourea, N,N'-diphenylthiourea, 1,3-di(o-tolyl)thiourea, 1,3-di(p-tolyl)thiourea, 1-benzyl-3-phenylthiourea, 1-methyl-3-phenylthiourea, N-allyl-N'-(2-hydroxyethyl)thiourea, and ethylenethiourea.

[0055] Examples of 3-substituted thioureas include trimethylthiourea, and examples of 4-substituted thioureas include tetramethylthiourea and 1,1,3,3-tetraethylthiourea.

[0056] In the first compound, when used in an image display device with interlayer filling, considering the aspects of suppressing the decrease in transmittance under high-temperature environments and minimizing the decrease in polarization degree (suppressing orthogonal light leakage), urea derivatives or thiourea derivatives are preferred, and urea derivatives are more preferred. Among the urea derivatives, 1-substituted urea or 2-substituted urea are preferred, and 1-substituted urea is more preferred. Among the 2-substituted urea, there are 1,1-substituted urea and 1,3-substituted urea, and 1,3-substituted urea is more preferred.

[0057] (Compound 2)

[0058] The second compound is a dialdehyde. The dialdehyde, as the second compound, can be used as a cross-linking agent. Examples of dialdehydes include glyoxal, malondialdehyde, and succinaldehyde. Glyoxal, which has a simple structure and is highly reactive, is particularly preferred. Hereinafter, glyoxal will sometimes be described, but as mentioned above, conventionally known dialdehydes can be used, and it is not limited to glyoxal.

[0059] <Adhesive Preparation Process>

[0060] The adhesive preparation process includes: a preparation step to obtain an aqueous solution A containing a PVA-based resin; a first addition step to add a first compound to the aqueous solution A to obtain an aqueous solution B; and a second addition step to add a second compound to the aqueous solution B to obtain an adhesive.

[0061] <Preparation Process>

[0062] In the preparation step, PVA-based resin is added to water and stirred to obtain aqueous solution A. From the viewpoint of adhesion, the average degree of polymerization of the PVA-based resin is preferably 100 or more and about 5500 or less, more preferably 1000 or more and about 4500 or less. From the viewpoint of adhesion, the average degree of saponification is preferably 85 mol% or more and about 100 mol% or less, more preferably 90 mol% or more and about 100 mol% or less.

[0063] As a PVA-based resin, it is preferable to contain acetyl groups because the PVA-based resin layer exhibits excellent adhesion and durability to the protective film. Acetyl-acetyl-containing PVA-based resins can be obtained, for example, by reacting a PVA-based resin with a diene using any method. The degree of acetyl-acetyl modification in the acetyl-acetyl-containing PVA-based resin is typically 0.1 mol% or more, preferably 0.1 mol% or more and about 20 mol% or less. The resin concentration in aqueous solution A is preferably 0.1 wt% or more and 15 wt% or less, more preferably 0.5 wt% or more and 10 wt% or less.

[0064] The water used to prepare aqueous solution A can be pure water, ultrapure water, well water, tap water, etc., without particular restrictions. From the viewpoint of maintaining the uniformity and transparency of the formed adhesive layer, pure water or ultrapure water is preferred. Aqueous solution A is supplied to the first addition step. Aqueous solution A can be supplied to the first addition step immediately after preparation, or it can be supplied to the first addition step after being stored for a period of time. When storing aqueous solution A, the storage environment is preferably a temperature of 10°C or higher and 40°C or lower, and a relative humidity of 30%RH% or higher and 90%RH% or lower. There are no particular limitations on the storage period; for example, it can be stored for more than 10 minutes, or for less than 60 days, preferably for less than 30 days, and more preferably for less than 10 days.

[0065] <First Addition Step>

[0066] In the first addition step, the first compound is added to aqueous solution A to obtain aqueous solution B. The content of the first compound relative to 100 parts by mass of PVA-based resin is preferably 0.1 parts by mass or more and 400 parts by mass or less, more preferably 1 part by mass or more and 200 parts by mass or less, and even more preferably 3 parts by mass or more and 100 parts by mass or less. If it is less than 0.1 parts by mass, the inhibition effect on polyene formation of the polarizing element under high-temperature conditions may be insufficient. On the other hand, if it exceeds 400 parts by mass, the first compound may precipitate after the polarizing plate is fabricated, resulting in increased haze. After adding the first compound to aqueous solution A, it is preferable to stir thoroughly to obtain aqueous solution B.

[0067] <Second Addition Step>

[0068] In the second addition step, the second compound is added to the aqueous solution B to obtain the adhesive. The content of the second compound is preferably 1 part by mass or more and 60 parts by mass or less, more preferably 1.5 parts by mass or more and 50 parts by mass or less, and even more preferably 2 parts by mass or more and 45 parts by mass or less, relative to 100 parts by mass of the PVA-based resin. If it is less than 1 part by mass, the improvement in water resistance may be insufficient. On the other hand, if it exceeds 60 parts by mass, the solution stability of the adhesive may decrease.

[0069] In the adhesive, the content of the second compound, dialdehyde, is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less, relative to 1 part by mass of the urea compound as the first compound. The lower limit is not limited, for example, it is 0.03 parts by mass or more. By keeping the ratio of the urea compound to dialdehyde in the adhesive within the above-mentioned range, it is easy to achieve both the improved water resistance effect brought by the urea compound and the improved adhesiveness effect brought by the dialdehyde. It can be understood that the improved adhesiveness effect brought by the dialdehyde can lead to an improved water resistance effect. When the dialdehyde content exceeds 20 parts by mass relative to 1 part by mass of the urea compound, the improved high-temperature durability effect brought by the urea compound may not be fully realized. The ratio of the urea compound to dialdehyde in the adhesive and the ratio of the urea compound to dialdehyde in the adhesive layer can be considered the same.

[0070] In addition to PVA-based resin, Compound 1, and Compound 2, the adhesive may also contain other additives. These other additives may include crosslinking agents other than dialdehyde, plasticizers, silane coupling agents, antistatic agents, microparticles, and other suitable additives known to the public. There are no restrictions on the timing of adding these other additives; they can be added during the preparation process, the first addition process, the second addition process, etc.

[0071] Adhesives may contain water. There are no restrictions on when water is added; it can be added during the preparation process, the first addition process, the second addition process, etc.

[0072] The adhesive may also contain an organic solvent. From the viewpoint of being miscible with water, alcohols are preferred organic solvents, and methanol or ethanol are more preferred among alcohols. When the adhesive contains methanol, the concentration of methanol in the adhesive is preferably 10% by mass or more and 70% by mass or less, more preferably 15% by mass or more and 60% by mass or less, and even more preferably 20% by mass or more and 60% by mass or less. By keeping the concentration of methanol at 10% by mass or more, it is easier to suppress the polyolefination of PVA-based resins under high-temperature conditions. In addition, by keeping the methanol content at 70% by mass or less, it is possible to suppress the deterioration of the color tone. Some urea derivatives have low solubility in water, but on the other hand, they have sufficient solubility in alcohols. In this case, it is also a preferred method to prepare an alcoholic solution of the urea compound by dissolving it in an alcohol, and then adding the alcoholic solution of the urea compound to an aqueous PVA solution to prepare the adhesive.

[0073] <Lamination Process>

[0074] In the bonding process, the adhesive prepared in the adhesive preparation process is applied to the surface of at least one of the polarizing element and the transparent protective film, and the polarizing element is bonded to the transparent protective film. The bonding process is carried out such that the elapsed time (hereinafter also referred to as "elapsed time T1") after the addition of the second compound to the aqueous solution B in the second addition step of the adhesive preparation process is 100 hours or less. In the bonding process, more specifically, the adhesive is applied to the surface of at least one of the polarizing element and the transparent protective film, the polarizing element is bonded to the transparent protective film via the adhesive layer, and then the adhesive layer is cured or dried. Elapsed time T1 refers to the time elapsed from the addition of the second compound to the aqueous solution B in the second addition step to the bonding process of bonding the polarizing element to the transparent protective film via the adhesive layer, excluding the time required for the adhesive layer to dry. By making the elapsed time T1 100 hours or less, an adhesive layer with excellent water resistance can be obtained.

[0075] The elapsed time T1 is preferably 90 hours or less, more preferably 80 hours or less. As for the elapsed time T1, since it is desirable to stir sufficiently after adding the second compound to the aqueous solution B, it can be, for example, 1 minute or more, 5 minutes or more, or 10 minutes or more.

[0076] The thickness of the adhesive coating can be set to any value, for example, it can be set in such a way that an adhesive layer with a desired thickness can be obtained after drying. The thickness of the adhesive layer is preferably 0.01 μm or more and 7 μm or less, more preferably 0.01 μm or more and 5 μm or less, further preferably 0.01 μm or more and 2 μm or less, and most preferably 0.01 μm or more and 1 μm or less. The coating method is not particularly limited, and various methods such as roller coating, spray coating, and immersion coating can be used.

[0077] After applying the adhesive, the polarizing element is bonded to the transparent protective film using a roller laminator or similar machine. After bonding, the film is dried to form a dry adhesive layer. The drying temperature is, for example, 5–150°C, preferably 30–120°C, and the drying time is, for example, 120 seconds or more, preferably 300 seconds or more.

[0078] In the processes of adhesive preparation, adhesive coating, and bonding the polarizing element to the transparent protective film, temperature control is preferably implemented, for example, within the range of 20–50°C. Temperature control further improves the water resistance of the adhesive layer.

[0079] In a configuration where a transparent protective film is bonded to both sides of a polarizing element via an adhesive layer, the adhesive layer on one side of the polarizing element can be formed using an adhesive different from the adhesive prepared through the aforementioned adhesive preparation process. Examples of such adhesives include active energy ray-curable adhesives.

[0080] (Active energy radiation curing adhesive)

[0081] Reactive energy radiation-cured adhesives are adhesives that cure upon exposure to reactive energy radiation such as ultraviolet light. Examples include adhesives containing polymerizable compounds and photopolymerizable initiators, adhesives containing photoreactive resins, and adhesive resins containing photoreactive crosslinking agents. Examples of polymerizable compounds include photopolymerizable monomers such as photocurable epoxy monomers, photocurable acrylic monomers, and photocurable urethane monomers, as well as oligomers derived from these monomers. Examples of photopolymerizable initiators include compounds containing substances that generate reactive species such as neutral free radicals, anionic free radicals, and cationic free radicals upon exposure to reactive energy radiation such as ultraviolet light.

[0082] <Polarizing plate>

[0083] The polarizing plate has a polarizing element and a transparent protective film. The polarizing element is formed by adsorbing and oriented dichroic pigments onto a polyvinyl alcohol-based resin layer. The transparent protective film is laminated onto at least one side of the polarizing element via an adhesive layer. The polarizing plate may be a polarizing plate with adjusted moisture content, and preferably has at least one of the features described in (a) and (b) below.

[0084] (a) The moisture content of the polarization element is above the equilibrium moisture content at 20°C and 30% relative humidity and below the equilibrium moisture content at 20°C and 70% relative humidity.

[0085] (b) The moisture content of the polarizing plate is above the equilibrium moisture content at 20°C and 30% relative humidity and below the equilibrium moisture content at 20°C and 70% relative humidity.

[0086] <Polarization element>

[0087] As a polarizing element formed by adsorbing and oriented a dichroic dye onto a layer containing a PVA-based resin (hereinafter also referred to as "PVA-based resin layer"), a known polarizing element can be used. Examples of polarizing elements include a stretched film obtained by dyeing a PVA-based resin film with a dichroic dye and then uniaxially stretching it; and a stretched layer obtained by dyeing a coating layer formed by coating a substrate film with a coating liquid containing a PVA-based resin, and then uniaxially stretching the stretched film. Stretching can be performed after dyeing with the dichroic dye, or while dyeing, or after stretching.

[0088] PVA-based resins are obtained by saponifying polyvinyl acetate-based resins. Besides polyvinyl acetate as a homopolymer of vinyl acetate, copolymers of vinyl acetate and other monomers that can be copolymerized with it can also be cited as polyvinyl acetate-based resins. Examples of other monomers that can be copolymerized include unsaturated carboxylic acids, olefins such as ethylene, vinyl ethers, and unsaturated sulfonic acids.

[0089] The PVA-based resin layer is preferably formed from a PVA-based resin with a boron adsorption rate of 5.70% by mass or more. That is, the boron adsorption rate of the PVA-based resin in the raw material stage before dyeing and stretching is 5.70% by mass or more. By using such a PVA-based resin, the transmittance is less likely to decrease, even when exposed to a high-temperature environment of 105°C. Furthermore, the boron adsorption rate of the PVA-based resin is preferably 10% by mass or less. By using such a PVA-based resin to manufacture polarizing elements, the boric acid concentration in the boric acid treatment bath is not high, the boric acid treatment time is shortened, the desired polarizing element is easily obtained, and the productivity of polarizing elements is improved. If the boron adsorption rate of the PVA-based resin is 10% by mass or less, boron enters the PVA-based resin layer in an appropriate amount, easily reducing the shrinkage force of the polarizing element. As a result, when assembled into an image display device, defects such as peeling between the front panel and other components and the polarizing plate are less likely to occur. The boron adsorption rate of the PVA-based resin can be measured using the method described in the examples below.

[0090] The boron adsorption rate of PVA-based resins reflects the spacing between molecular chains and the characteristics of the crystal structure. It is believed that PVA-based resins with a boron adsorption rate of 5.70% by mass or higher have wider molecular chain spacing and fewer crystals compared to those with a boron adsorption rate of less than 5.70% by mass. Therefore, it is speculated that boron, the first metal ion, and the second metal ion can easily enter the PVA-based resin layer, thus better preventing polyolefin formation under high-temperature environments.

[0091] The boron adsorption rate of PVA-based resins can be adjusted, for example, by pretreatment of the PVA-based resins before manufacturing polarizing elements, such as hot water treatment, acidic solution treatment, ultrasonic irradiation treatment, or radiation irradiation treatment. These treatments can increase the spacing between the molecular chains in the PVA-based resin or disrupt the crystal structure. Examples of hot water treatment include immersion in pure water at 30°C to 100°C for 1 to 90 seconds followed by drying. Examples of acidic solution treatment include immersion in an aqueous solution of boric acid with a concentration of 10% to 20% by mass for 1 to 90 seconds followed by drying. Examples of ultrasonic treatment include irradiation with ultrasound at a frequency of 20 to 29 kC at an output power of 200 W to 500 W for 30 seconds to 10 minutes. Ultrasonic treatment can be performed in solvents such as water.

[0092] The degree of saponification of the PVA-based resin is preferably 85 mol% or more, more preferably 90 mol% or more, and even more preferably 99 mol% or more and 100 mol% or less. The degree of polymerization of the PVA-based resin is, for example, 1000 or more and 10000 or less, preferably 1500 or more and 5000 or less. The PVA-based resin can be modified, for example, it can be aldehyde-modified polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc.

[0093] The thickness of the polarizing element is preferably 3 μm or more and 35 μm or less, more preferably 4 μm or more and 30 μm or less, and even more preferably 5 μm or more and 25 μm or less. By making the thickness of the polarizing element 35 μm or less, the effect of polyolefination of PVA-based resin on the reduction of optical properties under high-temperature conditions can be suppressed. By making the thickness of the polarizing element 3 μm or more, it is easy to manufacture a configuration that achieves the desired optical properties.

[0094] The polarizing element preferably comprises a first compound and a second compound. In this embodiment, since the polarizing element and the transparent protective film are bonded together by an adhesive layer formed from an adhesive containing the first and second compounds, a portion of the first compound and a portion of the second compound transferred from the adhesive layer may be included in the polarizing element. The first and second compounds in the polarizing element may include compounds added during the manufacturing process of the polarizing element. By having an adhesive layer containing the first and second compounds, the transmittance is not easily reduced even when the polarizing plate is exposed to a high-temperature environment. In addition, by having an adhesive layer containing the first and second compounds, the reduction in polarization degree can be suppressed even when the polarizing plate is exposed to a high-temperature environment. When two polarizing plates are arranged in an orthogonal Nicol relationship, light leakage (hereinafter also referred to as "orthogonal light leakage") is likely to occur if the polarization degree of the polarizing plate is reduced, but according to the present invention, the polarization degree is not easily reduced even when exposed to a high-temperature environment, and therefore orthogonal light leakage is easily suppressed. It is speculated that this is because the polyolefination of PVA-based resins is suppressed by the synergistic effect of the first and second compounds contained in the polarization element.

[0095] In manufacturing polarizing elements, methods containing the first compound and the second compound include impregnating a PVA-based resin layer in a processing solvent containing the first compound and / or the second compound, or spraying, dripping, or adding the processing solvent to the PVA-based resin layer. Preferably, the method of impregnating the PVA-based resin layer in a processing solvent containing both the first compound and the second compound is used. Specific examples of the first compound and the second compound include compounds exemplified as contained in the aforementioned adhesive.

[0096] The process of immersing the PVA-based resin layer in a processing solvent containing the first and second compounds can be performed simultaneously with the swelling, stretching, dyeing, crosslinking, and cleaning processes in the polarization element manufacturing method described later, or it can be performed separately from these processes. The process of incorporating the first and second compounds into the PVA-based resin layer is preferably performed after dyeing the PVA-based resin layer with iodine, and more preferably simultaneously with the crosslinking process after dyeing. According to this method, the color tone variation is small, and the impact on the optical properties of the polarization element can be reduced.

[0097] To make the polarizing element contain the first compound and the second compound, both addition during the manufacturing of the polarizing element and addition to the adhesive can be performed. For example, an adhesive containing the first compound and the second compound can be used as the adhesive, and at least one of the first compound and the second compound can also be added during the manufacturing of the polarizing element.

[0098] Polarizing elements typically contain potassium ions (also referred to as "first metal ions"), and preferably also contain other metal ions besides potassium ions (also referred to as "second metal ions"). The content of the second metal ions in the polarizing element is preferably 0.05% by mass or more and 10.0% by mass or less, more preferably 0.05% by mass or more and 8.0% by mass or less, and even more preferably 0.1% by mass or more and 6.0% by mass or less. When the content of the second metal ions in the polarizing element exceeds 10.0% by mass, the degree of polarization may sometimes decrease under high temperature and high humidity conditions. Furthermore, when the content of the second metal ions is less than 0.05% by mass, the improvement in durability under high temperature conditions may sometimes be insufficient. It should be noted that the content of the second metal ions in the polarizing element can be calculated, for example, by high-frequency inductively coupled plasma (ICP) emission spectrophotometry as a mass fraction (mass%) of the metal element relative to the mass of the polarizing element. It is believed that metal elements exist in polarization elements as metal ions or as cross-linked structures formed with the constituent elements of polyvinyl alcohol resins. The content of the second metal ion mentioned here is a value based on metal atoms.

[0099] The second metal ion is not limited to any metal ion other than potassium ions, but is preferably an ion of a metal other than an alkali metal. In particular, from the viewpoint of adjusting the color tone and imparting durability, at least one metal ion from the group consisting of transition metals such as cobalt, nickel, zinc, chromium, aluminum, copper, manganese, and iron is preferred. Among these metal ions, zinc ions are preferred from the viewpoint of adjusting the color tone and imparting heat resistance.

[0100] The boron content of the polarizing element is preferably 2.4% by mass or more. Furthermore, the boron content is preferably 3.9% by mass or more and 8.0% by mass or less, more preferably 4.2% by mass or more and 7.0% by mass or less, and even more preferably 4.4% by mass or more and 6.0% by mass or less. When the boron content of the polarizing element exceeds 8.0% by mass, the shrinkage force of the polarizing element increases, sometimes resulting in defects such as peeling from the front panel or other components that are bonded to the image display device. Additionally, when the boron content is less than 2.4% by mass, the desired optical properties may not be achieved. It should be noted that the boron content in the polarizing element can be calculated, for example, by high-frequency inductively coupled plasma (ICP) emission spectrophotometry as a mass fraction (mass %) of boron relative to the mass of the polarizing element. It is assumed that boron exists in the polarizing element in the form of boric acid or a cross-linked structure formed with a component of polyvinyl alcohol resin; the boron content mentioned here is a value based on boron atoms (B).

[0101] By ensuring that the boron content of the polarization element is 2.4% by mass or more and 8.0% by mass or less, the decrease in transmittance is further suppressed even when the element, as a component of an image display device consisting of interlayer filler, is exposed to a high-temperature environment. This is presumably because, when the boron content of the polarization element is 2.4% by mass or more and 8.0% by mass or less, polyolefin formation is less likely to occur even at high temperatures, thus suppressing the decrease in transmittance.

[0102] From the viewpoint of suppressing the degradation of the optical properties of the polarization element under high-temperature conditions, the potassium ion content in the polarization element is preferably 0.28% by mass or more, more preferably 0.32% by mass or more, and even more preferably 0.34% by mass or more. Furthermore, from the viewpoint of suppressing color tone changes under high-temperature conditions, it is preferably 0.60% by mass or less, more preferably 0.55% by mass or less, and even more preferably 0.50% by mass or less. The potassium ion content can be determined using the same method as the content of the second metal ion, and the potassium ion content mentioned here is a value calculated on a potassium atomic basis.

[0103] (Manufacturing method of polarization element)

[0104] There is no particular limitation on the manufacturing method of polarization elements. A typical method is to produce them by feeding out a pre-wound PVA-based resin film and stretching, dyeing, cross-linking, etc. (hereinafter referred to as "manufacturing method 1"). Another method includes coating a coating liquid containing PVA-based resin onto a substrate film to form a PVA-based resin layer as a coating layer, and stretching the resulting laminate (hereinafter referred to as "manufacturing method 2").

[0105] Manufacturing method 1 can be carried out through the following steps: a step of uniaxially stretching a PVA-based resin film, a step of dyeing the PVA-based resin film with dichroic pigments such as iodine to adsorb the dichroic pigments, a step of treating the PVA-based resin film with adsorbed dichroic pigments with a boric acid aqueous solution, and a step of washing with water after treatment with boric acid aqueous solution.

[0106] The swelling process involves immersing a PVA-based resin film in a swelling bath. This process removes surface contaminants and sealing agents from the PVA-based resin film and also suppresses uneven dyeing by causing the film to swell. The swelling bath typically uses a water-based medium, such as water, distilled water, or pure water. Surfactants, alcohols, etc., can be added to the swelling bath using conventional methods. From the viewpoint of controlling the potassium content of the polarizing element, potassium iodide can be used in the swelling bath. In this case, the concentration of potassium iodide in the swelling bath is preferably 1.5% by mass or less, more preferably 1.0% by mass or less, and even more preferably 0.5% by mass or less.

[0107] The temperature of the swelling bath is preferably above 10°C and below 60°C, more preferably above 15°C and below 45°C, and even more preferably above 18°C ​​and below 30°C. Since the degree of swelling of the PVA resin film is affected by the temperature of the swelling bath, the immersion time in the swelling bath cannot be fixed. It is preferably above 5 seconds and below 300 seconds, more preferably above 10 seconds and below 200 seconds, and even more preferably above 20 seconds and below 100 seconds. The swelling process can be performed only once or multiple times as needed.

[0108] The dyeing process involves immersing a PVA-based resin film in a dyeing bath (iodine solution), which allows dichroic pigments such as iodine to be adsorbed and oriented on the PVA-based resin film. The iodine solution is typically an aqueous iodine solution containing iodine and an iodide as a dissolving agent. Examples of iodides include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. From the viewpoint of controlling the potassium content in the polarization element, potassium iodide is suitable.

[0109] The concentration of iodine in the staining bath is preferably 0.01% by mass or more and about 1% by mass, more preferably 0.02% by mass or more and about 0.5% by mass or less. The concentration of iodide in the staining bath is preferably 0.01% by mass or more and about 10% by mass, more preferably 0.05% by mass or more and about 5% by mass, and even more preferably 0.1% by mass or more and about 3% by mass or less.

[0110] The temperature of the dyeing bath is preferably above 10°C and below 50°C, more preferably above 15°C and below 45°C, and even more preferably above 18°C ​​and below 30°C. Since the degree of dyeing of the PVA-based resin film is affected by the temperature of the dyeing bath, the immersion time in the dyeing bath cannot be fixed. It is preferably above 10 seconds and below 300 seconds, more preferably above 20 seconds and below 240 seconds. The dyeing process can be performed only once or multiple times as needed.

[0111] The crosslinking process involves immersing a dyed PVA-based resin film in a treatment bath (crosslinking bath) containing a boron compound. The polyvinyl alcohol-based resin film is crosslinked by the boron compound, and iodine molecules or dye molecules can be adsorbed onto this crosslinked structure. Examples of boron compounds include boric acid, borates, and borax. The crosslinking bath is typically an aqueous solution, but it can also be a mixture of an organic solvent miscible with water and water. From the viewpoint of controlling the potassium content in the polarizing element, the crosslinking bath preferably contains potassium iodide.

[0112] In the crosslinking bath, the concentration of the boron compound is preferably 1% by mass or more and about 15% by mass or less, more preferably 1.5% by mass or more and about 10% by mass or less, and even more preferably 2% by mass or more and about 5% by mass or less. When potassium iodide is used in the crosslinking bath, the concentration of potassium iodide in the crosslinking bath is preferably 1% by mass or more and about 15% by mass or less, more preferably 1.5% by mass or more and about 10% by mass or less, and even more preferably 2% by mass or more and about 5% by mass or less.

[0113] The temperature of the crosslinking bath is preferably above 20°C and below 70°C, more preferably above 30°C and below 60°C. Since the degree of crosslinking of the PVA resin film is affected by the temperature of the crosslinking bath, the immersion time in the crosslinking bath cannot be fixed in general. It is preferably above 5 seconds and below 300 seconds, more preferably above 10 seconds and below 200 seconds.

[0114] The crosslinking process can be performed only once, or it can be performed multiple times as needed.

[0115] The stretching process is a procedure in which a PVA-based resin film is stretched to a specified ratio along at least one direction. Typically, the PVA-based resin film is uniaxially stretched along the conveying direction (length direction). There are no particular limitations on the stretching method; both wet stretching and dry stretching methods can be used. The stretching process can be performed once or multiple times as needed. The stretching process can be performed at any stage in the manufacturing of polarization elements.

[0116] The treatment bath (stretching bath) in the wet stretching method can typically be water or a mixture of water and an organic solvent miscible with water. From the viewpoint of controlling the potassium content in the polarization element, the stretching bath preferably contains potassium iodide. When potassium iodide is used in the stretching bath, the concentration of potassium iodide in the stretching bath is preferably about 1% by mass and 15% by mass, more preferably about 2% by mass and 10% by mass, and even more preferably about 3% by mass and 6% by mass. From the viewpoint of suppressing film breakage during stretching, the treatment bath (stretching bath) may contain a boron compound. When a boron compound is included, the concentration of the boron compound in the stretching bath is preferably about 1% by mass and 15% by mass, more preferably about 1.5% by mass and 10% by mass, and even more preferably about 2% by mass and 5% by mass.

[0117] The temperature of the stretching bath is preferably 25–80°C, more preferably 40–80°C, further preferably 50–75°C, and particularly preferably 65–75°C. Since the degree of stretching of the PVA-based resin film is affected by the temperature of the stretching bath, the immersion time in the stretching bath cannot be fixed in a fixed amount; it is preferably 10 seconds or more and about 800 seconds or less, more preferably 30 seconds or more and about 500 seconds or less. The stretching treatment in the wet stretching method can be carried out together with any one or more of the following processing steps: swelling, dyeing, crosslinking, and cleaning.

[0118] Examples of dry stretching methods include inter-roll stretching, heated roll stretching, and compression stretching. It should be noted that dry stretching can be performed concurrently with the drying process.

[0119] The total stretch ratio (cumulative stretch ratio) applied to the polyvinyl alcohol-based resin film can be appropriately set according to the purpose, preferably about 2 times or more and about 7 times or less, more preferably about 3 times or more and about 6.8 times or less, and even more preferably about 3.5 times or more and about 6.5 times or less.

[0120] The cleaning process involves immersing the polyvinyl alcohol (PVA) resin film in a cleaning bath to remove foreign matter remaining on the surface of the PVA resin film. The cleaning bath typically uses a water-based medium such as water, distilled water, or pure water. Furthermore, from the viewpoint of controlling the potassium content in the polarization element, potassium iodide is preferably used in the cleaning bath. In this case, the concentration of potassium iodide in the cleaning bath is preferably about 1% by mass and 10% by mass, more preferably about 1.5% by mass and 4% by mass, and even more preferably about 1.8% by mass and 3.8% by mass.

[0121] The temperature of the cleaning bath is preferably above 5°C and below 50°C, more preferably above 10°C and below 40°C, and even more preferably above 15°C and below 30°C. Since the degree of cleaning of the PVA resin film is affected by the temperature of the cleaning bath, the immersion time in the cleaning bath cannot be fixed. It is preferably above 1 second and below 100 seconds, more preferably above 2 seconds and below 50 seconds, and even more preferably above 3 seconds and below 20 seconds. The cleaning process can be performed only once or multiple times as needed.

[0122] Furthermore, a metal ion treatment step is preferably included in the above-described process, or as a step different from the above-described process. The metal ion treatment step is performed by impregnating the polyvinyl alcohol-based resin film in a solution containing a metal salt of a second metal ion. Through the metal ion treatment step, the polyvinyl alcohol-based resin film contains the second metal ion.

[0123] The second metal ion is not limited to any metal ion other than potassium ions, but is preferably an ion of a metal other than an alkali metal. In particular, from the viewpoint of adjusting the color and imparting durability, at least one metal ion from the group consisting of transition metals such as cobalt, nickel, zinc, chromium, aluminum, copper, manganese, and iron is preferred. Among these metal ions, zinc ions are preferred from the viewpoint of adjusting the color and imparting heat resistance. Examples of zinc salts include zinc chloride, zinc halides such as zinc iodide, zinc sulfate, and zinc acetate.

[0124] Metal salt solutions can be used in metal ion treatment processes. The following describes an immersion treatment in a zinc-containing solution, using a zinc salt aqueous solution as a representative example in the metal ion treatment process.

[0125] The concentration of zinc ions in the zinc salt aqueous solution is approximately 0.1–10% by mass, preferably in the range of 0.3–7% by mass. Furthermore, it is preferable that the zinc salt solution readily impregnates zinc ions when using an aqueous solution containing potassium and iodide ions, such as potassium iodide. The concentration of potassium iodide in the zinc salt solution is preferably set to approximately 0.1–10% by mass, more preferably 0.2–5% by mass.

[0126] When performing immersion treatment in a zinc-containing solution, the temperature of the zinc salt solution is typically around 15–85°C, preferably 25–70°C. The immersion time is typically around 1–120 seconds, preferably in the range of 3–90 seconds. During immersion treatment in the zinc-containing solution, the zinc content in the polyvinyl alcohol (PVA) resin film is adjusted to fall within the aforementioned range by modifying the concentration of the zinc salt solution, the immersion temperature of the PVA resin film in the zinc salt solution, and the immersion time. There are no particular restrictions on when to perform the immersion treatment in the zinc-containing solution. Immersion treatment in the zinc-containing liquid can be performed alone, or the zinc salt can be co-present in a dyeing bath, crosslinking bath, or stretching bath, and performed simultaneously with at least one of the dyeing, crosslinking, or stretching processes.

[0127] The drying process is the process of drying the PVA-based resin film that has been cleaned in the cleaning process to obtain the polarizing element. Drying can be carried out by any suitable method, such as natural drying, air drying, or heat drying.

[0128] Manufacturing method 2 can be performed through the following steps: applying a coating solution containing PVA-based resin onto a substrate film; uniaxially stretching the resulting laminated film; dyeing the PVA-based resin layer of the uniaxially stretched laminated film with a dichroic dye to adsorb the dye and thus form a polarizing element; treating the film with the adsorbed dichroic dye with a boric acid aqueous solution; and washing with water after treatment with the boric acid aqueous solution. The substrate film used to form the polarizing element can also be used as a protective layer for the polarizing element. The substrate film can be peeled off from the polarizing element as needed.

[0129] <Transparent protective film>

[0130] The transparent protective film used in this embodiment (hereinafter also simply referred to as "protective film") is adhered to at least one side of the polarization element via an adhesive layer. This transparent protective film is adhered to one or both sides of the polarization element, preferably to both sides.

[0131] The protective film may also have other optical functions or may be formed into a laminated structure with multiple layers laminated. From the viewpoint of optical characteristics, the film thickness of the protective film is preferably thin, but if it is too thin, the strength decreases and the workability is poor. As an appropriate film thickness, it is 5 μm or more and 100 μm or less, preferably 10 μm or more and 80 μm or less, and more preferably 15 μm or more and 70 μm or less.

[0132] As the protective film, a film such as an acylated cellulose (Japanese: cellulose acylate) - based film, a film containing a polycarbonate - based resin, a film containing a cycloolefin - based resin such as norbornene, a (meth) acrylic - based polymer film, a polyester resin - based film such as polyethylene terephthalate, etc. can be used. When adhering protective films to both sides of the polarization element using an aqueous adhesive such as a PVA adhesive, from the viewpoint of moisture permeability, it is preferable that at least one side of the protective film is either an acylated cellulose - based film or a (meth) acrylic - based polymer film, and among them, an acylated cellulose film is preferred.

[0133] At least one protective film may have a retardation function for purposes such as viewing angle compensation. In this case, the protective film itself may have a retardation function, may additionally have a retardation layer, or may be a combination of both. The film having a retardation function can be adhered directly to the polarization element via an adhesive, or can be configured to be adhered via an adhesive or an adhesive隔着贴合于偏振元件的其他保护膜并经由粘合剂或粘接剂贴合的构成。 (This part seems a bit unclear in the original Chinese. The translation attempts to make sense based on the context, but it might need further clarification in the original text.)

[0134] <Second method>

[0135] In the second method of the method for manufacturing a polarizing plate of the present invention, the above - mentioned adhesive preparation process includes: a preparation process of obtaining an aqueous solution A containing a PVA - based resin; a first addition process of adding a first compound to the aqueous solution A to obtain an aqueous solution B; and a second addition process of adding a second compound to the aqueous solution B to obtain an adhesive, and the above - mentioned adhering process is carried out such that the elapsed time (hereinafter also referred to as "elapsed time T2") after adding the second compound to the aqueous solution B is 200 hours or less. The difference between the second method and the first method lies in adding a third compound in at least one of the above - mentioned first addition process and the above - mentioned second addition process, and the range of the elapsed time T2. Hereinafter, in the second method, only the differences from the first method will be described.

[0136] When adding the third compound in the first addition step, the third compound can be added to aqueous solution A before, after, or simultaneously with the addition of the first compound. When adding the third compound in the second addition step, the third compound can be added to aqueous solution B before, after, or simultaneously with the addition of the second compound.

[0137] In the second method, by including a third compound in the adhesive, the elapsed time T2 until the aforementioned bonding process is performed can be set to be longer than the elapsed time T1 in the first method. In the second method, if the elapsed time T2 is 200 hours or less, an adhesive layer with excellent water resistance can be obtained. This is presumably because including the third compound in the adhesive can suppress the decomposition of the second compound in the adhesive, thereby improving the adhesive's pot life.

[0138] Time T2 refers to the time elapsed from the addition of the second compound to aqueous solution B in the second addition step until the polarizing element is bonded to the transparent protective film via the adhesive layer in the bonding step, excluding the time required for the adhesive layer to dry.

[0139] The elapsed time T2 is preferably 190 hours or less, more preferably 180 hours or less. As for the elapsed time T2, since it is desirable to stir thoroughly after adding the second compound to the aqueous solution B, it can be, for example, 1 minute or more, 5 minutes or more, or 10 minutes or more.

[0140] (Compound 3)

[0141] The third compound is a dicarboxylic acid. Examples of dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, tartaric acid, glutamic acid, malic acid, maleic acid, fumaric acid, itaconic acid, mucoaconic acid, 1,4-cyclohexanedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, 2,5-pyridinedicarboxylic acid, 3,5-pyridinedicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenylmethanedicarboxylic acid, oxaloacetic acid, methyl fumaric acid, and 2,6-pyridinedicarboxylic acid. Citric acid, malic acid, maleic acid, or tartaric acid are preferred. These dicarboxylic acids can be used alone or in combination of two or more.

[0142] In the adhesive, the content of the third compound relative to 100 parts by weight of PVA-based resin is, for example, 0.01 parts by weight or more and 400 parts by weight or less, preferably 0.05 parts by weight or more and 50 parts by weight or less, and more preferably 0.1 parts by weight or more and 10 parts by weight or less. If it is less than 0.01 parts by weight, the effect of improving the pot life is sometimes insufficient, and the effect of suppressing polyene formation of polarizing elements under high temperature environments is sometimes insufficient. On the other hand, if it exceeds 400 parts by weight, the third compound sometimes precipitates after the polarizing plate is manufactured.

[0143] In the adhesive, the content of the third compound is preferably 0.001 parts by mass or more and 100 parts by mass or less, more preferably 0.01 parts by mass or more and 80 parts by mass or less, relative to 1 part by mass of the dialdehyde as the second compound. If it is less than 0.001 parts by mass, the improvement in pot life may sometimes be insufficient. On the other hand, if it is more than 100 parts by mass, the third compound may sometimes precipitate out after the polarizing plate is manufactured.

[0144] The third compound can be included in the polarization element in the same way as the first and second compounds described in the first embodiment. The method for including the third compound in the polarization element can be the same as the method for including the first and second compounds described in the first embodiment.

[0145] [Composition of an image display device]

[0146] The polarizing plate manufactured as described above is used in various image display devices such as liquid crystal display devices and organic EL display devices. In image display devices, when an interlayer filling configuration is used, where both sides of the polarizing plate are in contact with a solid layer other than an air layer, specifically an adhesive layer, the transmittance tends to decrease at high temperatures. In image display devices using the polarizing plate of this embodiment, even with an interlayer filling configuration, the decrease in the transmittance of the polarizing plate at high temperatures can be suppressed. An example of an image display device is a configuration having an image display unit, a first adhesive layer laminated to the viewing-side surface of the image display unit, and a polarizing plate laminated to the viewing-side surface of the first adhesive layer. This image display device may further include a second adhesive layer laminated to the viewing-side surface of the polarizing plate and a transparent member laminated to the viewing-side surface of the second adhesive layer. In particular, the polarizing plate of this embodiment is suitable for image display devices where a transparent member is disposed on the viewing side of the image display device, the polarizing plate is bonded to the image display unit via a first adhesive layer, and the polarizing plate and the transparent member are bonded via a second adhesive layer, forming an interlayer filling configuration. In this specification, either or both of the first adhesive layer and the second adhesive layer are sometimes referred to simply as "adhesive layer". It should be noted that the component used for bonding the polarizing plate to the image display unit, and the component used for bonding the polarizing plate to the transparent component, is not limited to an adhesive layer and may also be an adhesive layer.

[0147] <Image Display Unit>

[0148] Examples of image display units include liquid crystal units (LCDs) and organic EL units (OLEDs). As a liquid crystal unit, one can use a reflective liquid crystal unit that utilizes external light, a transmissive liquid crystal unit that utilizes light from a light source such as a backlight, or a semi-transmissive / semi-reflective liquid crystal unit that utilizes both external light and light from a light source. When the liquid crystal unit utilizes light from a light source, the image display device (liquid crystal display device) also provides a polarizing plate on the side opposite to the viewing side of the image display unit (liquid crystal unit), and further provides a light source. The polarizing plate on the light source side is preferably bonded to the liquid crystal unit via a suitable adhesive layer. As for the driving method of the liquid crystal unit, any type can be used, such as VA mode, IPS mode, TN mode, STN mode, or π-type bending orientation.

[0149] As an organic EL unit, it is suitable to use units in which a light emitter (organic electroluminescent body) is formed by sequentially stacking a transparent electrode, an organic light-emitting layer, and a metal electrode on a transparent substrate. The organic light-emitting layer is a stack of various organic thin films, such as a stack of a hole injection layer containing a triphenylamine derivative and a light-emitting layer containing a fluorescent organic solid such as anthracene, a stack of these light-emitting layers and an electron injection layer containing a perylene derivative, or a stack of a hole injection layer, a light-emitting layer, and an electron injection layer, etc.

[0150] <Attachment of image display unit to polarizing plate>

[0151] In the bonding of the image display unit and the polarizing plate, an adhesive layer (adhesive sheet) is suitable. From an operational perspective, it is preferable to bond the image display unit to the polarizing plate having an adhesive layer attached to one side of the polarizing plate. The attachment of the adhesive layer to the polarizing plate can be performed in a suitable manner. Examples include preparing an adhesive solution of 10% to 40% by mass, obtained by dissolving or dispersing a base polymer or a composition thereof in a solvent containing a single substance or mixture of suitable solvents such as toluene or ethyl acetate, and directly attaching it to the polarizing plate using a suitable spreading method such as casting or coating; or forming the adhesive layer on a spacer and transferring it to the polarizing plate.

[0152] <Adhesive layer>

[0153] The adhesive layer can consist of one or more layers, preferably one layer. The adhesive layer can be composed of an adhesive composition with (meth)acrylic resin, rubber resin, urethane resin, ester resin, silicone resin, or polyvinyl ether resin as the main component. Among these, adhesive compositions using (meth)acrylic resin as the base polymer, which exhibits excellent transparency, weather resistance, and heat resistance, are suitable. The adhesive composition can be either an active energy radiation-cured or thermosetting type.

[0154] The (meth)acrylic resin (base polymer) used in the adhesive composition is preferably a polymer or copolymer with one or more of the following (meth)acrylate monomers: butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, etc. It is preferable to copolymerize the polar monomer with the base polymer. Examples of polar monomers include (meth)acrylic acid compounds, 2-hydroxypropyl (meth)acrylate compounds, hydroxyethyl (meth)acrylate compounds, (meth)acrylamide compounds, N,N-dimethylaminoethyl (meth)acrylate compounds, glycidyl (meth)acrylate compounds, etc., monomers having carboxyl, hydroxyl, amide, amino, epoxy, etc.

[0155] The adhesive composition may contain only the aforementioned base polymer, but typically also contains a crosslinking agent. Examples of crosslinking agents include metal ions with a valence of divalent or higher that form a carboxylic acid metal salt with a carboxyl group, polyamine compounds that form an amide bond with a carboxyl group, polyepoxide compounds or polyols that form an ester bond with a carboxyl group, and polyisocyanate compounds that form an amide bond with a carboxyl group. Among these, polyisocyanate compounds are preferred.

[0156] The active energy radiation-curing adhesive composition possesses the property of curing upon irradiation with active energy radiation such as ultraviolet rays or electron beams. It exhibits adhesiveness even before irradiation, enabling it to adhere tightly to substrates such as films, and its curing upon irradiation allows for adjustment of the adhesion strength. The active energy radiation-curing adhesive composition is preferably ultraviolet-curing. In addition to the base polymer and crosslinking agent, the active energy radiation-curing adhesive composition also contains an active energy radiation-polymerizable compound. Depending on the requirements, it may contain photopolymerization initiators, photosensitizers, etc.

[0157] The adhesive composition may contain additives such as microparticles, beads (resin beads, glass beads, etc.) for imparting light scattering properties, glass fibers, resins other than the base polymer, tackifiers, fillers (metal powders, other inorganic powders, etc.), antioxidants, ultraviolet absorbers, dyes, pigments, colorants, defoamers, corrosion inhibitors, and photopolymerization initiators.

[0158] The adhesive layer can be formed by applying an organic solvent dilution of the adhesive composition described above to the surface of a substrate film, image display unit, or polarizer and then drying it. The substrate film is typically a thermoplastic resin film; a typical example is a separator that has undergone a release treatment. The separator can be, for example, a film obtained by performing a release treatment, such as silicone treatment, on the surface of a film containing resins such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, or polyarylate, where the adhesive layer is formed.

[0159] An adhesive composition can be directly applied to the release surface of the diaphragm to form an adhesive layer, and this adhesive layer with the diaphragm is then laminated onto the surface of the polarizing plate. Alternatively, an adhesive composition can be directly applied to the surface of the polarizing plate to form an adhesive layer, and the diaphragm can be laminated onto the outer surface of the adhesive layer.

[0160] When the adhesive layer is applied to the surface of the polarizing plate, it is preferable to perform surface activation treatments such as plasma treatment or corona treatment on the bonding surface of the polarizing plate and / or the bonding surface of the adhesive layer, and more preferably to perform corona treatment.

[0161] Alternatively, it is also possible to prepare an adhesive sheet in which an adhesive layer is formed by coating an adhesive composition on a second separator, and a separator is laminated on the formed adhesive layer, and laminate the separator-attached adhesive layer after peeling the second separator from the adhesive sheet on the polarizing plate. The second separator is a separator that has a weaker adhesion force to the adhesive layer than the separator and is easily peeled off.

[0162] The thickness of the adhesive layer is not particularly limited. For example, it is preferably 1 μm or more and 100 μm or less, more preferably 3 μm or more and 50 μm or less, and may be 20 μm or more.

[0163] <Transparent member>

[0164] Examples of the transparent member disposed on the viewing side of the image display device include a transparent plate (window layer), a touch panel, etc. As the transparent plate, a transparent plate having appropriate mechanical strength and thickness can be used. Examples of such a transparent plate include a transparent resin plate such as a polyimide-based resin, an acrylic-based resin, a polycarbonate-based resin, or a glass plate. Functional layers such as an antireflection layer can be laminated on the viewing side of the transparent plate. In addition, when the transparent plate is a transparent resin plate, a hard coat can be laminated to improve physical strength, and a low moisture permeability layer can be laminated to reduce the moisture permeability. As the touch panel, various touch panels such as a resistive film method, a capacitive method, an optical method, an ultrasonic method, etc., a glass plate or a transparent resin plate having a touch sensor function can be used. When using a capacitive touch panel as the transparent member, it is preferable to provide a transparent plate formed of glass or a transparent resin plate at a position closer to the viewing side than the touch panel.

[0165] <Lamination of polarizing plate and transparent member>

[0166] The lamination of the polarizing plate and the transparent member is preferably performed using an adhesive or an active energy ray-curable adhesive. When using an adhesive, the adhesive can be attached by an appropriate method. As a specific attachment method, for example, the attachment method of the adhesive layer used in the lamination of the above-described image display unit and the polarizing plate can be cited.

[0167] When using an active energy ray-curable adhesive, for the purpose of preventing the spread of the adhesive solution before curing, the following method is preferably used: a dam material is provided so as to surround the peripheral portion on the image display panel, the transparent member is placed on the dam material, and the adhesive solution is injected. After injecting the adhesive solution, alignment and defoaming are performed as needed, and then the active energy ray is irradiated for curing. ​​​​The present invention will now be described in detail based on specific embodiments. The materials, reagents, quantities, proportions, and operations shown in the following embodiments can be appropriately modified without departing from the spirit of the invention. Therefore, the present invention is not limited to the following embodiments.

[0170] (1) Measurement of the thickness of the polarization element:

[0171] Measurements were performed using a digital micrometer "MH-15M" manufactured by Nikon Corporation.

[0172] (2) Measurement of the polarization degree of the polarizer with visibility correction, the transmittance of the visible-corrected monomer, and the hue:

[0173] Measurements were performed using a spectrophotometer with an integrating sphere (V7100 manufactured by Nippon Spectrophotometer Co., Ltd., 2-degree field of view; C light source).

[0174] (3) Determination of boron content:

[0175] Dissolve 0.2 g of the polarizing element in 200 g of a 1.9% (w / w) mannitol aqueous solution. Next, titrate the resulting aqueous solution with a 1 mol / L sodium hydroxide aqueous solution. Calculate the boron content of the polarizing element by comparing the amount of sodium hydroxide solution required for neutralization with a standard curve.

[0176] (4) Determination of zinc ion content:

[0177] Nitric acid was added to a precisely weighed polarization element, and acid decomposition was performed using a Milestone General microwave sample pretreatment device (ETHOSD). The resulting solution was used as the assay solution. The zinc ion content was quantified using an Agilent Technologies ICP-OES system (5110 ICP-OES) to determine the zinc concentration in the assay solution, calculated as the mass of zinc relative to the mass of the polarization element.

[0178] (5) Determination of boron adsorption rate of PVA-based resin membrane:

[0179] PVA-based resin membranes cut into 100 mm squares were immersed in pure water at 30°C for 60 seconds, and then immersed in an aqueous solution containing 5 parts boric acid at 60°C for 120 seconds. The PVA-based resin membranes removed from the boric acid aqueous solution were dried in an oven at 80°C for 11 minutes. After conditioning at 23°C and 55% RH for 24 hours, boron-containing PVA membranes were obtained. 0.2 g of the thus obtained boron-containing PVA-based resin membrane was dissolved in 200 g of a 1.9% (w / w) mannitol aqueous solution. Next, the resulting aqueous solution was titrated with a 1 mol / L sodium hydroxide aqueous solution. The boron content of the PVA-based resin membrane was calculated by comparing the amount of sodium hydroxide solution required for neutralization with a standard curve. The boron content of the thus obtained PVA-based resin membrane was used as the boron adsorption rate of the PVA-based resin membrane.

[0180] (Fabrication of polarization element 1)

[0181] A 30 μm thick polyvinyl alcohol (PVA) resin film with a boron adsorption rate of 5.71% by mass was immersed in pure water at 21.5 °C for 79 seconds (swelling treatment), followed by immersion in an aqueous solution at 23 °C containing 1.0 mM iodine in a potassium iodide / boric acid / water mass ratio of 2 / 2 / 100 for 151 seconds (dyeing process). Then, it was immersed in an aqueous solution at 68.5 °C in a potassium iodide / boric acid / water mass ratio of 2.5 / 4 / 100 for 76 seconds (first crosslinking process). Next, it was immersed in an aqueous solution at 45 °C in a potassium iodide / boric acid / zinc chloride / water mass ratio of 3 / 5.5 / 0.6 / 100 for 11 seconds (second crosslinking process, metal ion treatment process). Finally, it was cleaned in a cleaning bath (cleaning process) and dried at 38 °C (drying process) to obtain a 12 μm thick polarizing element formed by iodine adsorption and orientation in PVA. The stretching was mainly carried out during the dyeing and first cross-linking processes, with a total stretching ratio of 5.85 times. The resulting polarizing element contained 0.17% zinc ions by mass and 4.62% boron by mass.

[0182] (Preparation of PVA solution for adhesives)

[0183] 50g of a modified PVA resin containing acetyl groups (manufactured by Mitsubishi Chemical Corporation: GOHSENX Z-410) was dissolved in 950g of pure water. The solution was heated at 90°C for 2 hours and then cooled to room temperature to obtain a PVA solution for adhesives (preparation step).

[0184] (Preparation of adhesive 1 for polarizing plates)

[0185] Urea and pure water were added to the PVA solution obtained in the preparation step and stirred (first addition step). 96 hours after the addition of urea, commercially available glyoxal solution (glyoxal concentration 40% by mass) and pure water were added and stirred to obtain adhesive 1 (second addition step). The composition of adhesive 1 is shown in Table 1.

[0186] (Preparation of adhesive 2 for polarizing plates)

[0187] Urea, maleic acid, and purified water were added to the PVA solution (PVA concentration 3.0% by mass) obtained in the preparation step and stirred (first addition step). 96 hours after the addition of urea, commercially available glyoxal solution (glyoxal concentration 40% by mass) and purified water were added and stirred to obtain adhesive 2 (second addition step). The composition of adhesive 2 is shown in Table 1.

[0188] [Table 1]

[0189]

[0190] (Saponification of acylated cellulose membranes)

[0191] A commercially available acylated cellulose membrane TJ40UL (manufactured by Fujifilm Corporation: 40 μm thickness) was immersed in a 1.5 mol / L NaOH aqueous solution (saponification solution) maintained at 55°C for 2 minutes, followed by washing with water. Then, the membrane was immersed in a 0.05 mol / L sulfuric acid aqueous solution at 25°C for 30 seconds, and further washed under running water for 30 seconds to neutralize the membrane. This process was then repeated three times using an air knife to remove water. After water removal, the membrane was dried in a drying zone at 70°C for 15 seconds, thus producing a saponified membrane.

[0192] (Fabrication of polarizing plates 1a, 1b, and 1c)

[0193] Using adhesive 1 prepared as described above and then stored for a specified time, saponified acylated cellulose films were laminated onto both sides of polarizing element 1 using a roller laminator. After lamination, the films were dried at 80°C for 5 minutes to obtain polarizing plates 1a, 1b, and 1c, respectively. The elapsed time T1 is the time from the addition of glyoxal during the preparation of adhesive 1 to the removal of the polarizing plates 1a, 1b, and 1c from the roller laminator before drying. Adhesive 1 was stored and used with elapsed time T1 as specified in Table 2.

[0194] (Fabrication of polarizing plates 2a, 2b, and 2c)

[0195] Using adhesive 2 prepared as described above and then stored for a specified time, a saponified acylated cellulose membrane was laminated onto both sides of polarizing element 1 using a roller laminator. After lamination, the membranes were dried at 80°C for 5 minutes to obtain polarizing plates 2a, 2b, and 2c, respectively. The elapsed time T2 is the time from the addition of glyoxal during the preparation of adhesive 2 until the polarizing plates 2a, 2b, and 2c were removed from the roller laminator before drying. Adhesive 1 was stored and used with elapsed time T2 as specified in Table 3.

[0196] (Adjustment of moisture content in polarizing plate (polarizing element))

[0197] The polarizing plates 1a, 1b, 1c, 2a, 2b, and 2c obtained above were stored for 72 hours at a temperature of 20°C and relative humidity of 30%, 35%, 40%, 45%, 50%, or 55%. The moisture content was measured using the Karl Fischer method at 66, 69, and 72 hours of storage. Under any humidity condition, the moisture content remained unchanged at 66, 69, and 72 hours of storage. Therefore, the moisture content of each polarizing plate can be considered to be the same as the equilibrium moisture content of the 72-hour storage environment used in this experimental example. When the moisture content of a polarizing plate reaches equilibrium in a certain storage environment, it can be assumed that the moisture content of the polarizing element in the polarizing plate also reaches equilibrium in that storage environment. Furthermore, when the moisture content of the polarizing element in a polarizing plate reaches equilibrium in a certain storage environment, it can be assumed that the moisture content of the polarizing plate also reaches equilibrium in that storage environment.

[0198] (Adjustment of moisture content of polarizing plates 1a, 1b, 1c, 2a, 2b, and 2c)

[0199] The moisture content of polarizing plates 1a, 1b, 1c, 2a, 2b, and 2c was adjusted by storing them at 20°C and 55% relative humidity for 72 hours to achieve the equilibrium moisture content in an environment with a temperature of 20°C and a relative humidity of 55%.

[0200] <Water Resistance Evaluation (Warm Water Immersion Test)>

[0201] The water resistance test in this embodiment was conducted according to the water resistance test described in Japanese Patent Application Publication No. 2009-025728

[0060] .

[0202] An acrylic adhesive (manufactured by Lintec Corporation, product number: #7) is formed on one side of the polarizing plate prepared above. The plate is then cut into strips measuring 50mm × 20mm, with the absorption axis (tension direction) of the polarizing plate as the long side, and the dimensions along the long side are accurately measured. Here, the sample is evaluated for its unique color uniformly across the entire surface due to the iodine adsorbed on the polarizing element.

[0203] Holding the sample by one short side with a gripper, approximately 80% of its length was immersed in a water bath at 60°C for 4 hours. Then, the sample was removed from the water bath and the moisture was wiped off. Immersion in warm water causes the polarizing element of the polarizing plate to shrink. The degree of shrinkage of the polarizing element was evaluated in three stages according to the following criteria by measuring the distance from the center of the short side of the sample (the end of the protective film) to the end of the shrunken polarizing element. The results are shown in Tables 2 and 3.

[0204] When the distance from the end of the sample to the end of the polarizing element is less than 1 mm: A

[0205] Case B: The distance from the end of the sample to the end of the polarizing element is more than 1 mm but less than 3 mm.

[0206] When the distance from the end of the sample to the end of the polarizing element is greater than 3 mm: C

[0207] [Table 2]

[0208]

[0209] It is known that for polarizing plates containing compound 1 (urea) and compound 2 (glyoxal) in the adhesive, excellent water resistance is achieved by passing a time T1 of less than 100 hours.

[0210] [Table 3]

[0211]

[0212] It can be seen that for polarizing plates containing compound 1 (urea), compound 2 (glyoxal), and compound 3 (maleic acid) in the adhesive, excellent water resistance is achieved with an elapsed time T2 of less than 200 hours. Furthermore, comparing the results shown in Tables 1 and 2, it can be seen that by including compound 3 (maleic acid) in the adhesive in addition to compound 1 (urea) and compound 2 (glyoxal), the permissible elapsed time for providing polarizing plates with excellent water resistance can be extended.

Claims

1. A method for manufacturing a polarizing plate, the polarizing plate having a polarizing element and a transparent protective film, the polarizing element being formed by adsorbing and oriented dichroic pigments on a polyvinyl alcohol-based resin layer, and the transparent protective film being laminated onto at least one side of the polarizing element via an adhesive layer. The method for manufacturing the polarizing plate includes: an adhesive preparation step of preparing an adhesive for forming the adhesive layer; as well as In the bonding process, the adhesive is applied to the surface of at least one of the polarizing element and the transparent protective film, and the polarizing element is bonded to the transparent protective film. The adhesive preparation process includes: The preparation process yields an aqueous solution A containing polyvinyl alcohol resin. The first addition step involves adding the first compound to the aqueous solution A to obtain aqueous solution B; and In the second addition step, a second compound is added to the aqueous solution B to obtain an adhesive. The first compound is selected from at least one of urea, urea derivatives, thiourea, and thiourea derivatives, and the second compound is a dialdehyde. The urea derivative is selected from methylurea, ethylurea, propylurea, butylurea, isobutylurea, N-octadecylurea, 2-hydroxyethylurea, hydroxyurea, acetylurea, allylurea, 2-propynylurea, cyclohexylurea, phenylurea, 3-hydroxyphenylurea, (4-methoxyphenyl)urea, benzylurea, benzoylurea, o-tolylurea, p-tolylurea, 1,1-dimethylurea, 1,3-dimethylurea, 1,1-diethylurea, 1,3-diethylurea, 1,3-di(hydroxymethyl)urea, 1,3-tert-butylurea. The following are at least one of the following: 1,3-dicyclohexylurea, 1,3-diphenylurea, 1,3-bis(4-methoxyphenyl)urea, 1-acetyl-3-methylurea, 2-imidazolium ketone (i.e., ethyleneurea), tetrahydro-2-pyrimidinium ketone (i.e., propenilium urea), tetramethylurea, 1,1,3,3-tetraethylurea, 1,1,3,3-tetrabutylurea, 1,3-dimethoxy-1,3-dimethylurea, 1,3-dimethyl-2-imidazolium ketone, and 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinium ketone. The bonding process is carried out such that the time elapsed after adding the second compound to the aqueous solution B is less than 100 hours.

2. A method for manufacturing a polarizing plate, the polarizing plate having a polarizing element and a transparent protective film, the polarizing element being formed by adsorbing and oriented dichroic pigments on a polyvinyl alcohol-based resin layer, and the transparent protective film being laminated onto at least one side of the polarizing element via an adhesive layer. The method for manufacturing the polarizing plate includes: an adhesive preparation step of preparing an adhesive for forming the adhesive layer; as well as In the bonding process, the adhesive is applied to the surface of at least one of the polarizing element and the transparent protective film, and the polarizing element is bonded to the transparent protective film. The adhesive preparation process includes: The preparation process yields an aqueous solution A containing polyvinyl alcohol resin. The first addition step involves adding the first compound to the aqueous solution A to obtain aqueous solution B; and In the second addition step, a second compound is added to the aqueous solution B to obtain an adhesive. A third compound is further added in at least one of the first and second addition steps. The first compound is selected from at least one of urea, urea derivatives, thiourea, and thiourea derivatives; the second compound is a dialdehyde; and the third compound is a dicarboxylic acid. The urea derivative is selected from methylurea, ethylurea, propylurea, butylurea, isobutylurea, N-octadecylurea, 2-hydroxyethylurea, hydroxyurea, acetylurea, allylurea, 2-propynylurea, cyclohexylurea, phenylurea, 3-hydroxyphenylurea, (4-methoxyphenyl)urea, benzylurea, benzoylurea, o-tolylurea, p-tolylurea, 1,1-dimethylurea, 1,3-dimethylurea, 1,1-diethylurea, 1,3-diethylurea, 1,3-di(hydroxymethyl)urea, 1,3-tert-butylurea. The following are at least one of the following: 1,3-dicyclohexylurea, 1,3-diphenylurea, 1,3-bis(4-methoxyphenyl)urea, 1-acetyl-3-methylurea, 2-imidazolium ketone (i.e., ethyleneurea), tetrahydro-2-pyrimidinium ketone (i.e., propenilium urea), tetramethylurea, 1,1,3,3-tetraethylurea, 1,1,3,3-tetrabutylurea, 1,3-dimethoxy-1,3-dimethylurea, 1,3-dimethyl-2-imidazolium ketone, and 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinium ketone. The bonding process is carried out such that the time elapsed after adding the second compound to the aqueous solution B is less than 200 hours.

3. The method of producing a polarizing plate according to claim 1 or 2, wherein In the adhesive, the content of the first compound is 0.1 parts by mass or more and 400 parts by mass or less relative to 100 parts by mass of the polyvinyl alcohol resin.

4. The method for manufacturing a polarizing plate according to claim 1 or 2, wherein, In the adhesive, the content of the second compound is 0.03 parts by mass or more and 20 parts by mass or less relative to 1 part by mass of the first compound.

5. The method for manufacturing a polarizing plate according to claim 1 or 2, wherein, The dialdehyde is glyoxal.

6. The method for manufacturing a polarizing plate according to claim 2, wherein, In the adhesive, the content of the third compound is 0.01 parts by weight or more and 400 parts by weight or less, relative to 100 parts by weight of the polyvinyl alcohol resin.

7. The method for manufacturing a polarizing plate according to claim 1 or 2, wherein, The thickness of the adhesive layer is greater than 0.01 μm and less than 7 μm.

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