TW201817837A - Adhesive composition, polarizing plate and image display device containing the same - Google Patents

Abstract

The present invention relates to an adhesive composition, a polarizing plate including the same, and an image display device. More specifically, the present invention relates to an adhesive composition consisting of an acetoacetyl group-modified polyvinyl alcohol-based resin, a glyoxal-based cross-linking agent, and a water-soluble salt of at least two types of polyvalent metal ions.

Description

Adhesive composition, polarizing plate, and image display device including the same

The present invention relates to an adhesive composition with improved water resistance, a polarizing plate including the same, and an image display device.

The polarizing plate can be used as one of optical components constituting a liquid crystal display device. A polarizing plate generally has a structure in which protective films are laminated on both sides of a polarizer, and is inserted into a liquid crystal display device. It is known that a protective film is also provided only on one side of the polarizer, but in many cases, a simple protective film is not bonded on the other side, but a layer having another function such as an optical function is also used as a protective film. Generally, a polarizing plate having the following structure is used: an iodine-based film in which iodine is adsorbed and oriented in polyvinyl alcohol, and a dye-based film in which dichroic dye is adsorbed and oriented in polyvinyl alcohol as a polarizer, at least on one side of the film. Adhesive layers formed using an aqueous solution of polyvinyl alcohol resin (polyvinyl alcohol adhesive) are used to join protective films such as triethyl cellulose (TAC). The polarizing plate thus constituted exists under long-term use under moist heat. The problem that the protective film and the end face of the polarizer are easily peeled off. Thus, a polarizing plate has been proposed in which a polarizer (polarizing film) is bonded to a protective film using a polyvinyl alcohol-based adhesive, and then heated and dried at a temperature of 80 to 100 ° C, thereby improving the humidity and heat resistance. In the case of long-term use under moist heat, the problem that the end faces of the protective film and the polarizer are easily peeled off remains unsolved. In order to solve such problems, Patent Document 1 discloses an acetonitrile-modified polyvinyl alcohol-based resin, a polyvinyl alcohol-based resin (crosslinking regulator), a glyoxal (crosslinking agent), and chlorination. Adhesive composition of zinc (crosslinking catalyst). However, in the case of the above-mentioned composition, there is a problem in that a curing rate is slow due to the inclusion of a cross-linking regulator, and the degree of polarization due to the damp heat degradation is reduced. Therefore, in order to prevent the protective film from being separated from the short side of the polarizer even under hot and humid conditions, it is currently required to develop an adhesive composition that is excellent in water resistance and capable of preventing a reduction in the degree of polarization caused by it. Prior Art Literature Patent Literature Patent Literature 1: Japanese Patent Laid-Open No. 1995-134212

Problem to be Solved by the Invention In order to solve the above-mentioned problems, an object of the present invention is to provide an adhesive composition excellent in water resistance and capable of preventing a reduction in polarization, a polarizing plate including the same, and an image display device. Means for Solving the Problem In order to achieve the above-mentioned object, the adhesive composition according to the present invention is characterized by including an acetamidine-modified polyvinyl alcohol-based resin, a glyoxal-based crosslinking agent, and two or more kinds of Water-soluble salts of polyvalent metal ions. The polarizing plate and the image display device according to the present invention for achieving the above-mentioned objects include an adhesive layer formed of the above-mentioned adhesive composition. Effects of the Invention The adhesive composition according to the present invention has an effect of improving water resistance without reducing the degree of polarization by including a water-soluble salt of two or more polyvalent metal ions.

When a certain part of the present invention “contains” a certain constituent element, as long as there is no particularly contrary description, it does not exclude other constituent elements, which means that other constituent elements can be further included. The preferred embodiments of the present invention will be described in detail below. < Adhesive composition > The adhesive composition according to one embodiment of the present invention includes an ethylene vinylacetate-modified polyvinyl alcohol-based resin (A), a glyoxal-based crosslinking agent (B), and two The water-soluble salt (C) of more than two kinds of polyvalent metal ions prevents the protective film from being separated from the short side of the polarizer even under humid and hot conditions, and thus has the effect of improving water resistance. Specifically, according to one implementation of the present invention, the above-mentioned adhesive composition includes: liquid A containing acetoacetate-modified polyvinyl alcohol resin (A) and glyoxal-based crosslinking agent (B), and A liquid B containing acetofluorene-modified polyvinyl alcohol-based resin (A) and two or more water-soluble salts (C) of polyvalent metal ions can be produced by mixing the liquids A and B described above. When the two-liquid-type adhesive composition is produced in this manner, there is an advantage that the pot life of the produced adhesive composition is improved, and gelation of the adhesive composition can be prevented. Acetylacetamyl-modified polyvinyl alcohol-based resin (A) The adhesive composition of the present invention contains an ethylacetamyl-based polyvinyl alcohol-based resin (A), and has a protective film and a polarizer. Improved adhesion. Compared with the modified polyvinyl alcohol resins such as carboxyl group modification, hydroxymethyl group modification, and amino group modification, the aforementioned ethyl alcohol ethyl acetate-modified polyvinyl alcohol resin (A) contains a highly reactive function It is excellent in durability improvement. The acetamidine-modified vinyl alcohol-based resin (A) is obtained by reacting the polyvinyl alcohol-based resin with diketene by a known method. Specifically, a method is used in which polyvinyl alcohol-based resin is dispersed in a solvent such as acetic acid, and dienone is added thereto; the polyvinyl alcohol-based resin is previously dissolved in a solvent such as dimethylformamide or dioxane, and then A method of adding diketene; or a method of directly contacting a polyvinyl alcohol resin with a diketene gas or a liquid diketene. The above-mentioned ethyl acetoacetate-modified polyvinyl alcohol-based resin (A) is not particularly limited as long as the degree of modification of the ethyl acetoacetate group is greater than 0.1 mol%, preferably 0.1 to 40 mol%, more It is preferably 1 to 20 mole%, and most preferably 2 to 7 mole%. In the case where the degree of modification of the above ethyl acetofluorene group is less than 0.1 mol%, because the water resistance of the adhesive layer is insufficient, it is not suitable. The effect of improving water resistance is extremely low. In addition, the degree of saponification of the above-mentioned ethyl acetoacetate-modified polyvinyl alcohol-based resin (A) is not particularly limited, but is preferably more than 80 mol%, and more preferably more than 85 mol%. When the degree of saponification of the modified polyvinyl alcohol-based resin (A) is less than the above range, it is difficult to exhibit sufficient water solubility, and thus a problem of reduced adhesion may occur. The degree of polymerization of the above-mentioned acetofluorene-modified polyvinyl alcohol-based resin (A) is preferably within a range of 100 to 1500. When the degree of polymerization of the ethyl acetoacetate-modified polyvinyl alcohol-based resin (A) is within the above range, there is an effect of improving the adhesion between the polarizer and the protective film in the polarizing plate. Specific examples of the acetoacetic acid-modified polyvinyl alcohol resin (A) include Z-100, Z-200, Z-200H, Z-210, Z-220, and Z-320 (Nippon Synthetic Chemical Gohsefimer Co., Ltd. Society), etc., but not limited to this. Glyoxal-based crosslinking agent (B) The adhesive composition of the present invention contains a glyoxal-based crosslinking agent (B). When the glyoxal-based cross-linking agent (B) is contained, the aldehyde group in the glyoxal-based cross-linking agent (B) is not limited to the above-mentioned acetoacetaldehyde-modified polyvinyl alcohol-based resin (A ) It also undergoes a condensation reaction with the hydroxyl groups contained in the polarizer and the protective film, so that the degree of cross-linking of the adhesive composition is improved, and the adhesive force and water resistance between the polarizer and the protective film that are joined by it are improved. effect. The content of the glyoxal-based cross-linking agent (B) can be 100 parts by weight based on 100 parts by weight of the solid content of the acetoacetic acid-modified polyvinyl alcohol-based resin (A) contained in the A liquid. The glyoxal-based crosslinking agent (B) is contained in an amount of 30 to 70 parts by weight. When the content of the glyoxal-based crosslinking agent (B) is less than the above range, water resistance of the adhesive layer formed from the adhesive composition containing the glyoxal-based crosslinking agent (B) may occur. If the property is lower than the above range, there may be a problem that the stability of the liquid-regulation is lowered. Water-soluble salt (C) of polyvalent metal ion The adhesive composition of the present invention promotes not only the above-mentioned glyoxal-based cross-linking agent (C) by including two or more water-soluble salts (C) of polyvalent metal ion. The effect of B) is to increase the degree of cross-linking of the adhesive composition containing the same, and to have the effect of increasing the degree of cross-linking between the polarizer and the protective film to which it is adhered. This has the effect that it is possible to improve the adhesive force and water resistance of the adhesive layer, and it is also possible to prevent a decrease in the optical durability accompanying it. The water-soluble salt (C) of the above-mentioned polyvalent metal ion can be specifically selected from zinc chloride, cobalt chloride, magnesium chloride, magnesium acetate, aluminum nitrate, zinc nitrate, and zinc sulfate, and the effect of the self-crosslinking catalyst is better. Choose from zinc chloride, zinc nitrate and aluminum nitrate. In the case where the water-soluble salt (C) of the polyvalent metal ion contains zinc chloride, the content thereof is relative to the ethyl acetamidine modified polyvinyl alcohol resin (A) contained in the B liquid. 100 parts by weight of solid content can be contained in 2 to 10 parts by weight. When the content of the zinc chloride is less than the above range, the problem of insufficient water resistance of the adhesive layer formed from the adhesive composition containing the zinc chloride may occur. When the content exceeds the above range, A problem may arise in that the stability of liquid adjustment is reduced. When the water-soluble salt (C) of the polyvalent metal ion includes zinc nitrate or aluminum nitrate, the solid content of the ethyl acetate-modified vinyl alcohol resin (A) contained in the B liquid is 100. The content can be 30 to 90 parts by weight. When the content of the zinc nitrate or aluminum nitrate is less than the above range, the problem of insufficient water resistance of the adhesive layer formed from the adhesive composition containing the zinc nitrate or aluminum nitrate may occur. In this case, a problem that the stability of the liquid adjustment may decrease may occur. The viscosity at 20 ° C of the adhesive composition of the present invention is preferably in the range of 3 to 25 mPa · sec. When the viscosity of the adhesive composition is less than 3 mPa · sec, the water resistance of the adhesive layer formed by the above-mentioned adhesive composition cannot be sufficiently exhibited. When the viscosity exceeds 25 mPa · sec, it may contain The problem that the optical characteristics of the polarizing plate of the adhesive layer is reduced. The said adhesive composition can further contain additives, such as a plasticizer, a silane coupling agent, an antistatic agent, a fine particle, alcohol, a leveling agent, etc. which are good in the range which does not inhibit the effect of this invention. The form of the above-mentioned adhesive composition is not particularly limited. In order to form a uniform adhesive layer on the surface of the polarizer or the protective film as an adherend, it is preferably a liquid type. As such a liquid type adhesive, a solution type or a dispersion liquid type of various solvents can be used. If the coating property of the substrate is considered, the solution type is preferred, and if the stability is considered, water is preferred. Solution type or dispersion type as a solvent. Another aspect of the present invention is a polarizing plate including the above-mentioned adhesive composition and an image display device including the same. < Polarizing Plate > The polarizing plate of the present invention can be a polarizing plate in which a protective film is laminated on at least one side of a polarizer (polarizing film) together with an adhesive layer formed of the adhesive composition of the present invention. Polarizer ( Polarizing Film ) A polyvinyl alcohol-based resin used to form a polarizer is obtained by saponifying a polyvinyl acetate-based resin. Examples of the polyvinyl acetate-based resin include, in addition to polyvinyl acetate, which is a homopolymer of vinyl acetate, copolymers of vinyl acetate and other monomers copolymerizable therewith. Examples of other monomers copolymerized with vinyl acetate include unsaturated carboxylic acids, unsaturated sulfonic acids, olefins, vinyl ethers, and acrylamides having an ammonium group. The saponification degree of the polyvinyl alcohol-based resin is usually 85 to 100 mol%, preferably more than 98 mol%. The polyvinyl alcohol-based resin can be further modified, and for example, an aldehyde-modified polyvinyl alcohol polymer, a polyvinyl acetal, or the like can be used. The average degree of polymerization of the polyvinyl alcohol-based resin constituting the polarizer is usually 1,000 to 10,000, preferably 1500 to 5000. A product obtained by forming such a polyvinyl alcohol-based resin on a film (polyvinyl alcohol-based resin film) is used as an original film of a polarizer. The method of forming a polyvinyl alcohol-type resin into a film is not specifically limited, A well-known film-forming method can be used. The film thickness of the original polyvinyl alcohol-based resin film is not particularly limited, and it can be, for example, 10 to 150 μm. A polarizer can be generally manufactured by a method including a process of uniaxially stretching such an original polyvinyl alcohol-based resin film, dyeing the polyvinyl alcohol-based resin film with a dichroic dye, and Procedures for dichroic pigment adsorption, procedures for treating a polyvinyl alcohol-based resin film having adsorbed dichroic pigments with an aqueous boric acid solution, and procedures for washing with water after treatment with the aqueous boric acid solution. Uniaxial stretching may be performed before dyeing, simultaneously with dyeing, or after dyeing. When uniaxial stretching is performed after dyeing, uniaxial stretching may be performed before the boric acid treatment, or may be performed during the boric acid treatment, or may be performed after the boric acid treatment. Of course, uniaxial stretching can also be performed by multiple steps. In uniaxial stretching, the original film can be uniaxially stretched between different rolls, and it can also be uniaxially stretched using hot rolls. In addition, it may be dry stretching, such as stretching in the air, or wet stretching, which is performed while being swollen with a solvent. The stretching ratio is usually 3 to 8 times. In order to dye a polyvinyl alcohol-type resin film with a dichroic dye, for example, a polyvinyl alcohol-type resin film can be immersed in the aqueous solution containing a dichroic dye. As the dichroic dye, specifically, iodine or a dichroic dye can be used. The polyvinyl alcohol-based resin film is preferably subjected to a dipping treatment in water before the dyeing treatment. When iodine is used as a dichroic dye, a method of dyeing a polyvinyl alcohol-based resin film in an aqueous solution containing iodine and potassium iodide is generally adopted. The content of iodine in the aqueous solution is usually 0.01 to 1 part by weight per 100 parts by weight of water, and the content of potassium iodide is usually 0.5 to 20 parts by weight per 100 parts by weight of water. The temperature of the aqueous solution used for dyeing is usually 20 to 40 ° C, and the immersion time in the aqueous solution is usually 20 to 1800 seconds. When a dichroic dye is used as the dichroic dye, a method of dyeing a polyvinyl alcohol-based resin film in an aqueous solution containing a water-soluble dichroic dye is generally adopted. The content of the dichroic dye in the aqueous solution is usually 1 × 10 ^-4 to 10 parts by weight, and preferably 1 × 10 ^-3 to 1 part by weight relative to 100 parts by weight of water. This aqueous solution can also contain inorganic salts, such as sodium sulfate, as a dyeing adjuvant. The temperature of the aqueous dye solution used in the dyeing is usually 20 to 80 ° C, and the immersion time for the aqueous solution is usually 10 to 1800 seconds. The boric acid treatment after dyeing with a dichroic dye is performed by immersing the dyed polyvinyl alcohol-based resin film in an aqueous solution containing boric acid. The amount of boric acid in the aqueous solution containing boric acid is usually 2 to 15 parts by weight, and preferably 5 to 12 parts by weight with respect to 100 parts by weight of water. When iodine is used as the dichroic dye, the boric acid-containing aqueous solution preferably contains potassium iodide. The amount of potassium iodide in the boric acid-containing aqueous solution is usually 0.1 to 15 parts by weight, and preferably 5 to 12 parts by weight with respect to 100 parts by weight of water. The immersion time in an aqueous solution containing boric acid is usually 60 to 1200 seconds, preferably 150 to 600 seconds, and more preferably 200 to 400 seconds. The temperature of the boric acid-containing aqueous solution is usually more than 50 ° C, preferably 50 to 85 ° C, and more preferably 60 to 80 ° C. The polyvinyl alcohol-based resin film after the boric acid treatment is usually subjected to a water washing treatment. The water washing treatment is performed, for example, by immersing a boric acid-treated polyvinyl alcohol-based resin film in water. The temperature of the water in the water washing treatment is usually 5 to 40 ° C, and the immersion time is usually 1 to 120 seconds. After washing with water, a drying process was performed to obtain a polarizer. The drying process is usually performed using a hot-air dryer and a far-infrared heater. The temperature of the drying treatment is usually 30 to 100 ° C, preferably 50 to 80 ° C. The drying time is usually 60 to 600 seconds, preferably 120 to 600 seconds. In this manner, the polyvinyl alcohol-based resin film was uniaxially stretched, dyed with a dichroic dye, and treated with boric acid to obtain a polarizer. The thickness of the polarizer is usually in a range of 5 to 40 μm, and preferably in a range of 10 to 35 μm. Protective film As the protective film, various transparent resin films such as a cellulose resin film, a cycloolefin resin film, an acrylic resin film, and a polyester resin film can be used. When a cellulose-based resin film is used as the protective film, a cellulose acetate-based resin in which at least a part of cellulose is esterified is preferred. For example, triethylammonium cellulose, diethylammonium cellulose, cellulose acetate propionate, and the like are mentioned. The cyclic olefin-based resin is, for example, a thermoplastic resin having a monomer unit of a cyclic olefin of a norbornene and a polycyclic norbornene-based monomer. The hydrogenated product of the olefin ring-opening copolymer may be an addition copolymer of a cyclic olefin, a chain olefin, or an aromatic compound having a vinyl group. In addition, a polar group may be introduced into a cycloolefin-based resin. The method of bonding the polarizer and the protective film using the adhesive composition is not particularly limited, and examples thereof include a method using a casting method, a wire rod coating method, a gravure coating method, and a die coating method. , Dip coating method, spray method, etc. apply the adhesive composition to the polarizer and / or the adhesive surface of the protective film so that the two overlap. The casting method described above is a method of applying an adhesive composition to the surface of a polarizer or a protective film that is an object to be coated while moving in a substantially vertical direction, a substantially horizontal direction, or an inclined direction therebetween. . After the above-mentioned adhesive composition is applied, the polarizer and the protective film are held by a nip roll and bonded to each other. In addition, in order to improve the adhesion, the surface of the polarizer and / or the protective film may be appropriately subjected to surface treatments such as plasma treatment, corona treatment, ultraviolet irradiation treatment, flame treatment, saponification treatment, and the like. Examples of the saponification treatment include a method of immersing in an aqueous alkali solution such as sodium hydroxide and potassium hydroxide. After the polarizer and the protective film are laminated, a drying process is performed. The drying treatment is performed, for example, by spraying hot air, and the temperature at this time is appropriately selected from the range of 50 to 100 ° C. The drying time is usually 30 to 1000 seconds. < Image display device > Another aspect of the present invention is an image display device including the above-mentioned polarizing plate. The image display device of the present invention includes the above-mentioned polarizing plate. Specific examples include a liquid crystal display, an OLED, and a flexible display, but the invention is not limited to this. In order to help the understanding of the present invention, a preferred embodiment is provided below. The following embodiments merely illustrate the present invention. Various changes and modifications can be made within the scope of the present invention and the technical idea. It is clear that such deformations and amendments belong to the scope of the attached patent application, and of course. In the following examples and comparative examples, "%" and "parts" indicating content are based on weight unless otherwise specified. Manufacturing example Manufacturing example 1. Manufacturing of polarizer A 75 μm-thick polyvinyl alcohol film having an average degree of polymerization of 2400 and a degree of saponification of more than 99.9 mol% was uniaxially stretched about 5 times in a dry manner, and the stretched state was maintained. After being immersed in water (distilled water) at 60 ° C for 1 minute, it was immersed in a 28 ° C aqueous solution having a weight ratio of iodine / potassium iodide / distilled water at 0.05 / 5/100 for 60 seconds. Then, it was immersed in a 72 ° C aqueous solution having a weight ratio of potassium iodide / boric acid / distilled water of 8.5 / 8.5 / 100 for 300 seconds, washed with distilled water at 26 ° C for 20 seconds, and then dried at 65 ° C to produce a film of iodine in a PVA system. Polarizer with adsorption orientation. Production Example 2. Production of Protective Film KC8UX (Konica, T), which is a triethyl cellulose based film, was saponified and used. Manufacture example 3. Manufacture of adhesive composition Manufacture of liquid A composition: dissolving acetamethylene modified polyvinyl alcohol-based resin (セ ノ ー セ ノ ー ル Z200, Japan) with a degree of saponification of 99.2 mol% in water (distilled water) Synthetic Chemical Industry Co., Ltd.) to produce an aqueous solution with a solid content of 3.8%. A 40% aqueous solution of glyoxal cross-linking agent (Oai Kagaku) was added to the above-mentioned aqueous solution at the content described in Table 1, and then mixed to produce an adhesive agent A liquid composition. Production of liquid B composition: dissolved in water (distilled water) with 99.2 mol% of acetoacetic acid modified polyvinyl alcohol resin (树脂 ー セ ノ ル 200200, Nippon Synthetic Chemical Industry Co., Ltd.), and produced a solid component Its content is an aqueous solution of 3.8% by weight. To the above-mentioned aqueous solution, zinc chloride (Oi Kagaku) and zinc nitrate (Oi Kagaku) were added as water-soluble salts of polyvalent metal ions at the contents described in Table 1, and mixed to prepare an adhesive B liquid composition. . The A liquid composition and the B liquid composition prepared above were mixed at normal temperature and stirred for about 30 minutes to produce an adhesive composition. Examples 1 to 10 and Comparative Examples 1 to 18 : Production of Polarizing Plates Examples 1 to 9 Both sides of the polarizer manufactured in Manufacturing Example 1 described above were coated with the content described in Table 1 by the method using Manufacturing Example 3 above After the produced adhesive composition, the protective film of Production Example 2 was bonded by a nip roll. The bonded polarizing plate was dried with a hot air drier at 80 ° C. for 5 minutes to produce a polarizing plate. Example 10 A polarizing plate was manufactured in the same manner as in Examples 1 to 9 except that the zinc nitrate or aluminum nitrate (Aldrich) contained in the liquid B of Production Example 3 was used. Comparative Examples 1 to 5 are as described in Table 2. In the above Production Example 3, instead of the acetoacetamidine-modified polyvinyl alcohol resin used in the B liquid, a polyvinyl alcohol resin (PVA-117H, Cola Lai Co., Ltd.), except that only one water-soluble salt (zinc chloride) of a polyvalent metal ion was used, a polarizing plate was produced in the same manner as in Examples 1 to 9 above. In Comparative Examples 6 to 18, as described in Table 2, a polarizing plate was produced in the same manner as in Examples 1 to 9 except that only one water-soluble salt of a polyvalent metal ion was used. [Table 1] [Table 2] Experimental Example 1. Evaluation of Adhesion ( Cutting Tool Evaluation ) The evaluation of adhesion was performed for the above-mentioned Examples 1 to 10 and Comparative Examples 1 to 8. After the polarizing plate manufactured above was left at room temperature for 1 hour, the blade of the cutting tool was placed between the films of the polarizing plate (between the polarizer and the polarizer protective film), and the time when the blade was advanced according to the following criteria was evaluated. Table 2 shows the manner of blade entry. ：: The blade of the cutting tool did not enter all the films. ○: When the blade is advanced, the blade stops when it enters 1 to 2 mm between at least one of the membranes. △: When the blade is advanced, the blade stops when it enters 3 to 5 mm between at least one of the membranes. ×: When the blade is advanced, the blade can easily enter between at least one of the membranes. Experimental example 2. Evaluation of water resistance The evaluation of water resistance for the above-mentioned Examples 1 to 10 and Comparative Examples 1 to 18 was performed. Each polarizing plate which was left in an environment of 23 ° C. and a relative humidity of 55% for 24 hours was subjected to a temperature and water resistance test by the method described below to evaluate water resistance. The long axis of the polarizing plate was used as the long side, and the polarizing plate was cut to a size of 5 cm × 2 cm to prepare a sample, and the dimension in the long side direction was accurately measured. At this time, the iodine adsorbed on the polarizing film of the above sample exhibited a unique color uniformly and comprehensively. FIG. 1 is a view schematically showing a method for evaluating water resistance. (A) shows sample 1 before warm water immersion, and (B) shows sample 1 after warm water immersion. As shown in FIG. 1 (A), the short side of the sample was held by the holding tool 5, and about 80% of the length was immersed in a water bath at 60 ° C for 8 hours. Then, the sample 1 was taken out of the water tank, and the water was wiped off. By the above-mentioned warm water immersion, the polarizer 4 of the polarizing plate contracts. The degree of contraction of the polarizer 4 was evaluated by measuring the distance from the end portion 1a (the end of the protective film) at the center of the short side of the sample 1 to the end of the contracted polarizer 4, and the contracted length was set. In addition, as shown in FIG. 1 (B), the polarizer 4 located in the center of the polarizing plate was shrunk by immersion in warm water to dissolve iodine from the peripheral portion of the polarizer 4 between the protective films. Discolored portion 3 is generated at the peripheral edge portion. The degree of discoloration was evaluated by measuring the distance from the end of the contracted polarizer 4 at the center of the short side of the sample 1 to the area where the color peculiar to the polarizing plate remained, and it was set as the length of iodine discoloration. The sum of the contracted length and the length of iodine discoloration is defined as the total etching length x. The total etching length x is the distance from the end portion 1a of the sample 1 at the center of the short side of the sample 1 to the region where the color of the polarizing plate is unique. The smaller the shrinkage length, the discoloration length of iodine, and the total erosion length x, the higher the adhesion can be determined in the presence of water. Based on the total etch length x, the following four grades were evaluated, and the results are shown in Table 3. ◎: Total etch length x less than 0.1 mm ○: Total etch length x is more than 0.1 mm and less than 0.5 mm △: Total etch length x is more than 0.5 mm and less than 2 mm ×: Total etch length x is more than 2 mm Experimental Example 3. Transmittance and polarization (%) The polarizations were measured for the above-mentioned Examples 1 to 10 and Comparative Examples 1 to 18. The manufactured polarizing plate was cut to a size of 4 cm × 4 cm, and a test piece was produced. The test piece was attached to a measurement stand, and then measured with a UV-visible spectrometer (V-7100, manufactured by JASCO Corporation). The results were measured. It is described in Table 3. [table 3] With reference to Table 3, it can be confirmed that the polarizing plate of the adhesive composition of the present invention containing the water-soluble salt of two or more kinds of polyvalent metal ions (Examples 1 to 10) and the case of using the polarizing plate containing one kind of polyvalent metal ion Compared with the case of the polarizing plate of the conventional adhesive composition of a water-soluble salt (comparative examples 1 to 18), both the water resistance and the light characteristics were superior.

1‧‧‧ sample

1a‧‧‧end

Section ‧‧‧

4‧‧‧ polarizer

5‧‧‧Grip

FIG. 1 is a view schematically showing a test method for evaluating water resistance according to an experimental example.

Claims (9)

An adhesive composition is characterized in that it includes: acetofluorene-modified polyvinyl alcohol-based resin, glyoxal-based cross-linking agent, and two or more water-soluble salts of polyvalent metal ions. The adhesive composition according to claim 1, wherein the adhesive composition comprises: liquid A containing acetoacetate-modified polyvinyl alcohol resin and glyoxal-based cross-linking agent, and acetoacetate Liquid B of fluorenyl-modified polyvinyl alcohol resin and water-soluble salts of two or more polyvalent metal ions. The adhesive composition according to claim 1, wherein the water-soluble salt of the polyvalent metal ion comprises two or more kinds selected from zinc chloride, zinc nitrate, and aluminum nitrate. The adhesive composition according to claim 1, wherein the average degree of polymerization of the acetamidine modified polyvinyl alcohol resin is 100 to 1500. For example, the adhesive composition of claim 2, wherein a total of 100 parts by weight of the solid content of the acetoacetamidine-modified polyvinyl alcohol-based resin contained in the A solution, and the ethylene glycol contained in the A solution The content of the aldehyde-based crosslinking agent is 30 to 70 parts by weight. The adhesive composition according to claim 2, wherein the water-soluble salt of the polyvalent metal ion comprises two or more kinds selected from the group consisting of zinc chloride, zinc nitrate, and aluminum nitrate, relative to the acetamidine contained in the B liquid. The solid content of the ethyl acetate-modified polyvinyl alcohol resin is 100 parts by weight in total, and the content of the zinc chloride is 2 to 10 parts by weight. The adhesive composition according to claim 2, wherein the water-soluble salt of the polyvalent metal ion comprises two or more kinds selected from the group consisting of zinc chloride, zinc nitrate, and aluminum nitrate, relative to the acetamidine contained in the B liquid. The solid content of the ethyl acetate-modified polyvinyl alcohol resin is 100 parts by weight in total, and the content of the zinc nitrate or aluminum nitrate is 30 to 90 parts by weight. A polarizing plate including an adhesive layer formed of the adhesive composition according to any one of claims 1 to 7. An image display device includes a polarizing plate as claimed in claim 8.