JP5530477B2 - Adhesive composition for polarizing plate and polarizing plate using the same - Google Patents

Description

  The present invention relates to an adhesive composition for bonding a polarizer and a protective film, which is used when manufacturing a polarizing plate, and a polarizing plate manufactured using the same. In more detail, this invention relates to the adhesive composition which can provide the polarizing plate excellent in heat-and-moisture resistance, and such a polarizing plate.

  In recent years, flat displays such as liquid crystal displays and plasma displays have been widely used as display devices because they are space-saving and have high definition. Among these, liquid crystal displays are attracting attention and are being developed because they are more power-saving and have higher definition.

  In a liquid crystal display panel, a polarizing plate that functions as an optical shutter is used in combination with liquid crystal in order to perform its function. A polarizing plate is an essential component for a liquid crystal display panel including a polarizer. Usually, a polarizer is produced by uniaxially stretching a polyvinyl alcohol-based resin to a length of 5 to 6 times, so that it has a drawback that it is easily broken in the stretching direction and is brittle. Therefore, the polarizer is used by forming a polarizing plate by adhering a protective film to the front surface and / or back surface thereof. At that time, the adhesive for bonding the protective film to the polarizer is also required to satisfy the characteristics required when using a polarizing plate.

  As a technique relating to such an adhesive for polarizing plates, Patent Document 1 below describes a polarizing solution in which a polyvinyl alcohol resin and a resin solution containing a water-soluble silicate are used to provide a transparent protective film on at least one surface of a polarizer. It is disclosed to be used as an adhesive for plates. In Patent Document 1, since the resin solution is used in the form of an aqueous solution (paragraph “0036”), the water-soluble silicate can be uniformly dispersed in the resin solution. By using such a resin solution, the adhesive has excellent adhesive strength, can prevent a decrease in light transmittance of the polarizing plate, and has a local unevenness defect (knick) that occurs at the interface between the polarizer and the transparent protective film. (Defect) can be suppressed (paragraph “0010”).

JP 2011-203709 A

  However, since the adhesive disclosed in Patent Document 1 is water-soluble, a polarizing plate formed by laminating a transparent protective film and a polarizer using the adhesive described in Patent Document 1 has poor moisture and heat resistance. There was a problem with durability.

  This invention is made | formed in view of the said situation, and it aims at providing the adhesive composition for polarizing plates which can form the contact bonding layer which has high heat-and-moisture resistance.

  Moreover, the other objective of this invention is to provide the polarizing plate which is excellent in heat-and-moisture resistance by using such an adhesive composition.

  The present inventors have intensively studied to solve the above problems. As a result, a polarizing plate produced by laminating a protective film and a polarizer using an adhesive composition containing a specific amount of polysilicate and a curing agent with respect to a polyvinyl alcohol resin is excellent in heat and moisture resistance. The present invention has been completed.

  That is, the said objective is achieved by the adhesive composition for polarizing plates containing 100 mass parts of polyvinyl alcohol-type resin, 3-50 mass parts of hardening | curing agents, and 2-100 mass parts of polysilicate.

  According to the adhesive composition of the present invention, it is possible to form an adhesive layer having excellent heat and moisture resistance. Therefore, the polarizing plate produced by laminating the protective film and the polarizer using the adhesive composition of the present invention has high wet heat resistance and excellent durability in an environment exposed to high humidity and high temperature. Therefore, the polarizing plate of this invention can be used conveniently for a liquid crystal display.

It is the schematic for demonstrating the manufacturing process of the polarizing plate in an Example.

  Hereinafter, the present invention will be described in detail for each element.

(1) Adhesive composition for polarizing plate The 1st aspect of this invention is a polarizing plate containing 100 mass parts of polyvinyl alcohol-type resin, 3-50 mass parts of hardening | curing agents, and 2-100 mass parts of polysilicate. Adhesive composition for use.

(A) Polysilicate The adhesive composition of this invention contains 2-100 mass parts of polysilicate with respect to 100 mass parts of polyvinyl alcohol-type resin. The polysilicate is uniformly dispersed in the adhesive layer formed by applying and drying an adhesive solution in which the polysilicate is uniformly distributed. Polysilicate exhibits a water-insoluble glassy state upon drying. Therefore, since the adhesive layer containing polysilicate is impermeable to water (water vapor), the obtained adhesive layer is excellent in heat and moisture resistance. Therefore, the polarizing plate produced by laminating the protective film and the polarizer using the adhesive composition of the present invention has high wet heat resistance and is excellent in durability in an environment exposed to high humidity and high temperature. The above is speculation, and the present invention is not limited to such a mechanism.

  As described above, the adhesive layer formed with the adhesive composition of the present invention is excellent in moisture and heat resistance. Here, “excellent in heat and humidity resistance” means that the polarizer does not shrink much even in an atmosphere of high temperature (60 ° C.) and high humidity (100% RH). Specifically, in the heat-and-moisture resistance test (humidification test) described in the following examples, the ideal value of the shrinkage width is 0 mm, but even if it shrinks by about 0.5 mm, it is within an allowable range in actual use. For this reason, when the shrinkage width is 0.5 mm or less, it is referred to as “the adhesive layer or the polarizing plate using the adhesive layer is excellent in moisture and heat resistance”. Preferably, in the heat and humidity resistance test (humidification test) described in the examples below, the shrinkage width is preferably 0.5 mm or less, more preferably 0.4 mm or less, and even more preferably 0.3 mm or less. And particularly preferably 0.2 mm or less.

  The compounding quantity of a polysilicate is 2-100 mass parts with respect to 100 mass parts of polyvinyl alcohol-type resin in an adhesive composition. By including the polysilicate in the above-described blending amount, the adhesive layer formed using the adhesive composition of the present invention has improved moist heat resistance. Therefore, when a polarizing plate is formed by laminating a protective film and a polarizer through the adhesive layer, the adhesive layer effectively suppresses the movement of the polarizer even when the polarizer expands and contracts due to thermal shock. Can do. Therefore, the adhesive layer of the adhesive composition of the present invention can effectively prevent the polarizer from cracking even in such a case. Here, the film obtained is inferior in heat-and-moisture resistance as the compounding quantity of a polysilicate is less than 2 mass parts. On the other hand, when the amount exceeds 100 parts by mass, the resulting film becomes too hard, causing peeling or cracking at the end against impact (for example, during cutting), and insufficient adhesion between the protective film and the polarizer. Become. In the present invention, the blending amount of polysilicate is more preferably 10 to 99 parts by mass, still more preferably 20 to 95 parts by mass, and particularly preferably 30 to 90 parts by mass. If it is this range, the obtained film is excellent in wet heat resistance and adhesiveness, and is suitable for actual use.

  In the present invention, “polysilicate” is a condensate of alkyl silicate which is an alkoxysilane oligomer starting from tetraalkoxysilane. Specifically, it is presumed that the polysilicate has a structure of the following formula (1).

  In the above formula (1), R represents an alkyl group having 1 to 8 carbon atoms, a fluorinated alkyl group having 1 to 8 carbon atoms, or an alkoxyalkyl group having 2 to 8 carbon atoms. R ′ each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, a fluorinated alkyl group having 1 to 8 carbon atoms, or an alkoxyalkyl group having 2 to 8 carbon atoms. Here, the alkyl group is not particularly limited, and specifically, methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, pentyl. And linear or branched alkyl groups such as a group, isopentyl group, neopentyl group, hexyl group, heptyl group, octyl group and 2-ethylhexyl group. Although there is no restriction | limiting in particular as a fluorinated alkyl group, For example, the group by which at least 1 of the hydrogen atom contained in the alkyl group illustrated above was substituted by the fluorine atom is mentioned. Specific examples include a fluoromethyl group, a 1-fluoroethyl group, a 1-fluoropropyl group, a 1-fluorobutyl group, and a 1-fluorooctyl group. Although there is no restriction | limiting in particular as an alkoxyalkyl group, Specifically, a methoxymethyl group, 1-methoxyethyl group, 2-methoxyethyl group, 3-methoxybutyl group, 1-ethoxyethyl group, 2-ethoxyethyl group 2-propoxymethyl group, 1-iso-propoxyethyl group, 2-propoxyethyl group, 1-n-butoxyethyl group, 2-butoxyethyl group, 1-tert-butoxyethyl group, methoxymethyl group, ethoxymethyl group , Iso-propoxymethyl group, n-butoxymethyl group, tert-butoxymethyl group, propoxypropyl group and the like. Among these, from the viewpoint of reactivity, R preferably represents an alkyl group having 1 to 4 carbon atoms, a fluorinated alkyl group having 1 to 4 carbon atoms, or an alkoxyalkyl group having 3 to 6 carbon atoms. And more preferably an alkyl group having 1 to 4 carbon atoms, and particularly preferably a methyl group or an ethyl group. R ′ preferably represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a fluorinated alkyl group having 1 to 4 carbon atoms, or an alkoxyalkyl group having 3 to 6 carbon atoms. More preferably, it represents an alkyl group having 1 to 4 carbon atoms, and particularly preferably a hydrogen atom, a methyl group, or an ethyl group.

In the above formula (1), p represents the number of repeating units of the formula: —Si (OR) ₂ —O—, and q represents the number of repeating units of the formula: —Si (O—) ₂ —O—. Where r represents the number of repeating units of the formula: —Si (OR) (O —) — O—.

In the above formula (1), when p, q and r are 2 or more, each repeating unit may be the same or different from each other, and in the latter case, p, q and r are respectively a repeating unit of the formula: —Si (OR) ₂ —O—, a repeating unit of the formula: —Si (O—) ₂ —O—, and a formula: —Si (OR) (O —) —. Represents the average number of repeating units of O-. Similarly, R ′ representing the end of the polysilicate of the above formula (1) may be the same or different from each other. The polysilicate may have a single structure or may be in the form of a mixture.

  The method for producing the polysilicate is not particularly limited, but it is preferably synthesized by mixing an alkyl silicate, water and an alcohol. Specifically, the following reaction occurs. In addition, the following reaction is estimation and the polysilicate which concerns on this invention is not limited by the following reaction.

  In the above reaction, the alkyl silicate is represented by the following formula (2):

It is represented by In said formula (2), R represents a C1-C8 alkyl group, a C1-C8 fluorinated alkyl group, and a C2-C8 alkoxyalkyl group. Here, the definitions of the alkyl group, the fluorinated alkyl group, and the alkoxyalkyl group having 2 to 8 carbon atoms are the same as those in the above formula (1), and thus the description thereof is omitted here. From the viewpoint of reactivity, R preferably represents an alkyl group having 1 to 4 carbon atoms, a fluorinated alkyl group having 1 to 4 carbon atoms, or an alkoxyalkyl group having 3 to 6 carbon atoms. It is more preferable that the alkyl group is 1-4, and a methyl group or an ethyl group is particularly preferable. N represents the number of repeating units of the formula: —Si (OR) ₂ —O—, and can be appropriately selected according to the desired polysilicate structure. The alkyl silicate may be a single compound or a mixture.

  Alkyl silicates may be prepared synthetically or commercially available. The synthesis method in the former case is not particularly limited, and MG Voronkov, VP Mileshkevich, Yu. A. Yuzhelevskii, “THE SILOXANE BOND”, p.323-340, 365-380, Consultants Bureau, New York (1978 ); Satoshi Hamada, Satoshi Urano, J. Jpn. Soc. Color Mater. (Color material), 73, 336-338 (2000); Satoshi Urano, Satoshi Hamada, TECHNO-COSMOS, 14, 14-20 (2001) Known methods such as those described can be applied in the same manner or appropriately modified. Commercially available products include methyl silicate 51, methyl silicate 53A, ethyl silicate 40, ethyl silicate 48, and EMS-485 in which equimolar amounts of methoxy and ethoxy groups are introduced (all are trade names manufactured by Colcoat Co., Ltd.). , MKC silicates 51, 56, 56S (all manufactured by Mitsubishi Chemical Corporation).

  In the above reaction, the alcohol is not particularly limited as long as it can dissolve the alkyl silicate, and can be appropriately selected depending on the type of alkyl silicate to be used. Specifically, alcohol having 1 to 3 carbon atoms is preferably used, and more specifically, methanol, ethanol, propyl alcohol, isopropyl alcohol, butanol and the like can be mentioned. Of these, ethanol and isopropyl alcohol are preferred. The alcohol may be used alone or in the form of a mixture of two or more.

  Further, the mixing ratio of the alkyl silicate, water and alcohol is not particularly limited. Considering the hydrolysis rate of the alkyl silicate (conversion efficiency of alkoxy group to hydroxyl group) and the condensation rate, that is, the structure of the desired polysilicate, water is preferably added to 100 parts by mass of the alkyl silicate added. It is 10-150 mass parts, More preferably, it is 30-100 mass parts. Similarly, in consideration of the hydrolysis rate (conversion efficiency of alkoxy group to hydroxyl group) and condensation rate of the above alkyl silicate, that is, the desired polysilicate structure, the alcohol is added to 100 parts by mass of the alkyl silicate added. And preferably 500 to 1500 parts by mass, more preferably 700 to 1400 parts by mass. The hydrolysis rate and condensation rate of alkyl silicate can be analyzed by X-ray photoelectron spectroscopy (XPS) analysis. Specifically, the hydrolysis rate and condensation rate of alkyl silicates are described in TECHNO-COSMOS 2007 March, Vol. 20, page 9-15.

  The mixing order of the alkyl silicate, water and alcohol is not particularly limited. (A) After mixing the alkyl silicate and alcohol, add and mix water; (b) Add the alcohol after mixing the alkyl silicate and water.・ Mix; (c) Alkyl silicate, water and alcohol are mixed together; (d) After mixing alcohol and water, add and mix alkyl silicate; (e) Any of alkyl silicate, water and alcohol In this order, add and mix sequentially. Of these, (a) is preferred.

  The mixture thus obtained is mixed at a predetermined temperature and time to perform hydrolysis / dehydration reaction. Here, the mixing temperature is not particularly limited as long as the hydrolysis / dehydration reaction proceeds, but it is preferably 10 to 60 ° C, more preferably 20 to 40 ° C. Also, the mixing time is not particularly limited as long as the hydrolysis / dehydration reaction proceeds, but it is preferably 1 to 6 hours, more preferably 2 to 4 hours. Under such conditions, the hydrolysis / dehydration reaction proceeds sufficiently. The mixing may be performed in a stationary state or under stirring. The mixing may be performed under normal pressure, under reduced pressure or under pressure, but is usually performed under normal pressure.

  The hydrolysis / dehydration reaction is preferably performed in the presence of an acid. The presence of the acid can promote the hydrolysis / dehydration reaction. Here, the acid is not particularly limited, but concentrated sulfuric acid, trichloroacetic acid, sulfuric acid, pyrophosphoric acid, triphosphoric acid, polymetaphosphoric acid such as trimetaphosphoric acid and tetrametaphosphoric acid, trifluoroacetic acid, trifluoroacetic anhydride, hydrochloric acid, fuming sulfuric acid, Concentrated hydrochloric acid, hydrobromic acid, propionic acid, formic acid, nitric acid and acetic acid; and mixtures thereof such as trifluoroacetic acid-trifluoroacetic anhydride (mixing ratio is 1: 9 to 9: 1 by mass, preferably 3: 7 to 7: 3) and a mixed solution of trichloroacetic acid and sulfuric acid (mixing ratio is 1: 9 to 9: 1 by mass ratio, preferably 3: 7 to 7: 3). The acid may be used alone or in the form of a mixture of two or more. These acids may be used as they are or in the form of an aqueous solution, and the concentration in the latter case is not particularly limited as long as it can sufficiently promote hydrolysis / dehydration reaction, and the reaction temperature For example, it is 0.01 to 0.5 mol / L, although it varies depending on the type of acid. Further, the amount of acid added when the hydrolysis / dehydration reaction is carried out in the presence of an acid is not particularly limited as long as the hydrolysis / dehydration reaction can be promoted, but is preferably based on 100 parts by mass of the alkyl silicate. It is 0-5 mass parts, More preferably, it is 0.5-3 mass parts.

  Here, the acid may be added during the mixing or at any stage after the mixing, but it is preferable to add and mix the reactants after the mixing. The mixing conditions at this time are not particularly limited. For example, the mixing temperature is not particularly limited as long as the hydrolysis / dehydration reaction can be promoted, but is preferably 10 to 60 ° C, more preferably 20 to 40 ° C. Also, the mixing time is not particularly limited as long as the hydrolysis / dehydration reaction can be promoted, but it is preferably 1 to 6 hours, more preferably 2 to 4 hours. Under such conditions, the hydrolysis / dehydration reaction can be sufficiently accelerated. The mixing may be performed in a stationary state or under stirring. The mixing may be performed under normal pressure, under reduced pressure or under pressure, but is usually performed under normal pressure.

(B) Curing agent The adhesive composition of the present invention contains 3 to 50 parts by mass of a curing agent with respect to 100 parts by mass of the polyvinyl alcohol resin. The curing agent has a role of preventing the phenomenon in which the cohesive force is lowered by heat because the polyvinyl alcohol-based resin that mainly exhibits adhesiveness is thermoplastic, by forming a crosslink in the adhesive layer.

  Here, if the usage-amount of a hardening | curing agent is less than 3 mass parts, adhesiveness (for example, adhesiveness of a polarizer and a protective film) will fall, and, as a result, heat-and-moisture resistance (for example, moisture-heat resistance of a polarizing plate) will fall. To do. On the other hand, if it exceeds 50 parts by mass, the degree of cross-linking of the polyvinyl alcohol resin increases, so that the shear strength increases, but the pot life after mixing as an adhesive composition is shortened, which is not practical. The usage-amount of a hardening | curing agent becomes like this. Preferably it is 5-40 mass parts with respect to 100 mass parts of polyvinyl alcohol-type resin in an adhesive composition, More preferably, it is 7-20 mass parts. If it is such a range, adhesive composition will show favorable adhesiveness (for example, adhesiveness of a polarizer and a protective film), wet heat resistance (for example, wet heat resistance of a polarizing plate), and long enough The pot life can be secured.

  There is no restriction | limiting in particular as a hardening | curing agent, What is necessary is just a compound which has a functional group which has reactivity with respect to polyvinyl alcohol-type resin, The hardening | curing agent conventionally used with the polyvinyl alcohol-type resin can be used. For example, dialdehydes such as glyoxal, malondialdehyde, succindialdehyde, glutardialdehyde, maleidialdehyde, phthaldialdehyde; metal glyoxylic acid such as sodium glyoxylate, potassium glyoxylate; ethylenediamine, triethylenediamine, hexa Alkylenediamines such as methylenediamine; isocyanates such as tolylene diisocyanate, hydrogenated tolylene diisocyanate, trimethylolpropane tolylene diisocyanate adduct, triphenylmethane triisocyanate, methylenebis (4-phenylmethane triisocyanate, isophorone diisocyanate; ethylene glycol Diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin di or Epoxys such as triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, diglycidylaniline, diglycidylamine; monoaldehydes such as formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde; methylol urea Aminoformaldehyde resins such as condensates of methylol melamine, alkylated methylol urea, alkylated methylolated melamine, acetoguanamine, benzoguanamine and formaldehyde; and sodium, potassium, magnesium, calcium, aluminum, iron, nickel, zirconium, etc. Examples include salts of divalent to tetravalent metals and oxides thereof, and these curing agents may be used alone or in the form of a mixture of two or more. Among them, dialdehydes and metal salts of glyoxylic acid are more preferable from the viewpoints of stability of polysilicate in a solution state, heat resistance and adhesiveness, and glyoxal and sodium glyoxylate are more preferable. Particularly preferred.

(C) Polyvinyl alcohol-type resin Polyvinyl alcohol-type resin is a main component which shows adhesiveness as an adhesive agent for polarizing plates. The polyvinyl alcohol-based resin has a large number of hydroxyl groups in the molecule, and these hydroxyl groups express adhesiveness.

  There is no restriction | limiting in particular as a polyvinyl alcohol-type resin, Any may be used. More specifically, the polyvinyl alcohol-based resin that can be used in the present invention is a polyvinyl alcohol obtained by saponifying polyvinyl acetate; a derivative thereof; and a copolymer of vinyl acetate and a copolymerizable monomer. Saponified product of: modified polyvinyl alcohol obtained by acetalizing, urethanizing, etherifying, grafting, phosphate esterifying, etc. polyvinyl alcohol. Examples of the monomer include unsaturated carboxylic acids such as (anhydrous) maleic acid, fumaric acid, crotonic acid, itaconic acid, (meth) acrylic acid, and esters thereof; α-olefins such as ethylene and propylene; Examples include sulfonic acid (soda), sulfonic acid soda (monoalkylmalate), disulfonic acid soda alkylmalate, N-methylolacrylamide, acrylamide alkylsulfonic acid alkali salt, N-vinylpyrrolidone, and N-vinylpyrrolidone derivatives. These polyvinyl alcohol resins can be used singly or in combination of two or more.

  Among the above, the polyvinyl alcohol resin is particularly preferably a polyvinyl alcohol resin having an acetoacetyl group. This is because the acetoacetyl group has high reactivity and exhibits high durability due to crosslinking when used in an adhesive for polarizing plates. A polyvinyl alcohol-based resin containing an acetoacetyl group is obtained by reacting a polyvinyl alcohol-based resin with diketene by a known method. For example, a method of dispersing a polyvinyl alcohol resin in a solvent such as acetic acid and adding diketene thereto, a method of dissolving a polyvinyl alcohol resin in a solvent such as dimethylformamide or dioxane, and adding diketene thereto. Can be mentioned. Moreover, the method of making diketene gas or liquid diketene contact directly to polyvinyl alcohol is mentioned.

  The polyvinyl alcohol resin as described above may be synthesized by itself, but a commercially available product may be used. Examples of the polyvinyl alcohol-based resin that can be used in the present invention include Goseifamer (registered trademark) Z Z-100, Z-200, Z-205, Z-210, Z-300, Z manufactured by Nippon Synthetic Chemical Industry Co., Ltd. -320, Z-410, Kuraray Kuraray Poval PVA-117, PVA-217, Denka Poval (registered trademark) K-05, K17-E, K-17C, H-12, H -17, PC-1000 and the like. Of these, Goseifamer (registered trademark) Z Z-200 and Z-410 manufactured by Nippon Synthetic Chemical Industry Co., Ltd. are particularly preferable.

  As for the polymerization degree of the polyvinyl alcohol-type resin used for this invention, 1000-2500 are preferable. Since durability and heat resistance are required for use as an adhesive for polarizing plates, a higher degree of polymerization is preferable from such a viewpoint. On the other hand, when the degree of polymerization is high, the viscosity of the solution is high and the coating property is inferior, so that the coating film is thick, and thus the waviness is generated in the polarizing plate. The above range is preferred because of fear. Moreover, 90-100 mol% is preferable and, as for the saponification degree of the polyvinyl alcohol-type resin used for this invention, 96-99 mol% is more preferable. When the degree of saponification is within this range, sufficient durability and heat resistance can be exhibited when a polyvinyl alcohol resin having a polymerization degree within the above range is used.

(D) Manufacturing method of adhesive composition for polarizing plate There is no restriction | limiting in particular in manufacturing the adhesive composition of this invention, Usually, polyvinyl alcohol-type resin and a hardening | curing agent are mixed by predetermined amount, and a density | concentration is appropriate. After adjusting to make an aqueous solution, a predetermined amount of polysilicate is mixed to obtain an adhesive composition. The order of mixing the polyvinyl alcohol resin, the curing agent and the polysilicate is not limited to the above, and the polyvinyl alcohol resin, the curing agent and the polysilicate are mixed together; the polyvinyl alcohol resin and the polysilicate are mixed. Then, add and mix the curing agent; mix the curing agent and polysilicate, then add and mix the polyvinyl alcohol resin; sequentially add the polyvinyl alcohol resin, curing agent and polysilicate in any order. The method of mixing; etc. may be used. The mixing method is not particularly limited, and may be sufficiently stirred and mixed at room temperature (25 ° C.) until the inside of the liquid becomes uniform. These polyvinyl alcohol resins, curing agents and polysilicates may be mixed in the form as they are, or may be mixed in the form of a solution dissolved in an appropriate solvent. The polyvinyl alcohol resin is preferably mixed in the form of a solution dissolved in a solvent. Here, the solvent is not particularly limited as long as desired components (polyvinyl alcohol resin, curing agent and polysilicate) can be dissolved. For example, when a polyvinyl alcohol-based resin is used in the form of a solution, the solvent is not particularly limited, and examples thereof include water. Moreover, the density | concentration of the polyvinyl alcohol-type resin in this case is although it does not restrict | limit in particular, It is preferable to adjust so that solid content may be about 1-10 mass%. In addition, in this specification, "solid content" means the value measured by the method described in the following Example.

  Here, the pH of the adhesive composition of the present invention is not particularly limited, but considering that the adhesive composition is obtained in a stable state, it is preferable that the adhesive composition stably disperses the polysilicate. Considering that the aqueous polysilicate solution is acidic, the pH of the adhesive composition is preferably adjusted to 2.0 to 7.0, more preferably 3.0 to 6.5. The pH may be adjusted using a known pH adjusting agent such as hydrochloric acid or sodium hydroxide, but may also use a crosslinking agent. For example, since glyoxal has a pH of 3.3 in a 10% by mass aqueous solution, the pH of the adhesive composition can be adjusted to the acidic side by using glyoxal as a crosslinking agent. Moreover, since pH of sodium glyoxylate is 6.3 in 10 mass% aqueous solution, pH of an acidic side can be adjusted to a neutral side.

  Although there is no restriction | limiting in particular in the viscosity of the adhesive composition of this invention, when the ease of coating is considered, 1-50 mPa * s is preferable.

  Moreover, the adhesive composition for polarizing plates of the present invention includes, as necessary, silane compounds such as pressure-sensitive adhesives, ultraviolet absorbers, antioxidants, heat stabilizers, hydrolysis resistance stabilizers, silane coupling agents, and the like. May be added.

(2) Polarizing plate According to the 2nd aspect of this invention, the polarizing plate provided with the protective film and polarizer which were adhere | attached using the adhesive composition of this invention is provided. The polarizing plate of the present invention has sufficient durability against thermal shock.

(A) Polarizer There is no restriction | limiting in particular as a polarizer, A conventionally well-known thing can be used. For example, dichroic materials such as iodine and dichroic dyes are adsorbed on hydrophilic polymer films such as polyvinyl alcohol films, partially formalized polyvinyl alcohol films, and ethylene / vinyl acetate copolymer partially saponified films. And polyene-based oriented films such as a uniaxially stretched product, a polyvinyl alcohol dehydrated product and a polyvinyl chloride dehydrochlorinated product. Here, the thickness in particular of the said film (before swelling) is not restrict | limited, The thickness similar to the film used for a general polarizer is applicable. Specifically, the thickness of the film (before swelling) is preferably about 20 to 100 μm.

  Among these, a polarizer produced by dyeing a polyvinyl alcohol film having an average polymerization degree of 2000 to 2800 and a saponification degree of 90 to 100 mol% with iodine and uniaxially stretching it 5 to 6 times is particularly preferable. More specifically, such a polarizer is obtained by, for example, immersing and stretching a polyvinyl alcohol film by immersing it in an aqueous solution of iodine. As an aqueous solution of iodine, for example, it is preferable to immerse in an aqueous solution of 0.1 to 1.0% by mass of iodine / potassium iodide. If necessary, it may be immersed in an aqueous solution such as boric acid or potassium iodide at 50 to 70 ° C., or may be immersed in water at 25 to 35 ° C. in order to prevent washing or uneven dyeing. Stretching may be performed after dyeing with iodine, may be stretched while dyeing, or may be dyed with iodine after stretching. After dyeing and stretching, it may be washed with water and dried at 35 to 55 ° C. for about 1 to 10 minutes.

(B) Protective film As the protective film, a material excellent in transparency, mechanical strength, thermal stability, moisture barrier property, isotropy and the like is preferable. For example, cellulose resins such as cellulose diacetate and cellulose triacetate, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, acrylic resins such as polymethyl methacrylate, styrene such as polystyrene and acrylonitrile / styrene copolymer (AS resin) Resin, polycarbonate resin, polyethylene, polypropylene, polyolefin having cyclo or norbornene structure, polyolefin resin such as ethylene / propylene copolymer, vinyl chloride resin, amide resin such as nylon and aromatic polyamide, imide resin Resin, sulfone resin, polyether sulfone resin, polyether ether ketone resin, polyphenylene sulfide resin, vinyl alcohol resin, vinylidene chloride Resins, vinyl butyral resins, arylate resins, polyoxymethylene resins, such as blends of epoxy resin or the resin, and the like.

  Of the above, the polarizing plate is preferably a cellulose resin that is an ester of cellulose and a fatty acid. Examples of the cellulose resin include cellulose triacetate, cellulose diacetate, cellulose tripropionate, and cellulose dipropionate. Among these, cellulose triacetate is particularly preferable from the viewpoint of availability and cost. Examples of commercially available products include UV-50, UV-80, SH-80, TD-80U, TD-TAC, UZ-TAC, and Kika series manufactured by Konica Minolta Opto, manufactured by Fujifilm Corporation.

  The thickness in particular of a protective film is not restrict | limited, The same thickness as a general protective film is applicable. Specifically, the thickness of the protective film is preferably about 15 to 100 μm.

(C) Manufacturing method There is no restriction | limiting in particular as a manufacturing method of a polarizing plate, It manufactures by bonding together a protective film and a polarizer using the adhesive composition of this invention by a conventionally well-known method, and heat-drying. Can do. The applied adhesive composition expresses adhesiveness by drying to constitute an adhesive layer.

  When apply | coating an adhesive composition, you may apply | coat to any of a protective film and a polarizer, and may apply | coat to both. The adhesive composition is preferably applied so that the thickness of the adhesive layer after drying is 10 to 300 nm. The thickness of the adhesive layer is more preferably 10 to 200 nm in order to obtain a uniform in-plane thickness and sufficient adhesive strength. The thickness of the adhesive layer can be adjusted by the solid content concentration in the solution of the adhesive composition or the application device for the adhesive composition. The thickness of the adhesive layer can be confirmed by observing the cross section with a scanning electron microscope (SEM). There is no restriction | limiting in particular also in the method of apply | coating an adhesive composition, Various means, such as the method of dripping an adhesive composition directly, the roll coat method, the spraying method, the immersion method, are employable.

  After apply | coating an adhesive composition, a polarizer and a protective film are bonded together by a roll laminator etc. After bonding, a drying process is implemented. The layer of the adhesive composition constitutes an adhesive layer by drying, and the polarizing plate is completed. The drying temperature is preferably 30 to 100 ° C, more preferably 40 to 85 ° C, and the drying time is preferably 1 to 10 minutes, more preferably 3 to 7 minutes.

  Hereinafter, the present invention will be described using examples and comparative examples. However, the technical scope of the present invention is not limited only to the following examples.

<Solid content>
The solid content of the solution in which the polyvinyl alcohol-based resin is dissolved was measured by the following method. About 1 g of the polyvinyl alcohol-based resin solution is precisely weighed in a precisely weighed glass dish. After drying at 105 ° C. for 1 hour, the temperature is returned to room temperature (25 ° C.), and the total mass of the glass dish and the remaining solid is precisely weighed. The solid content was calculated by the following formula 1, where X is the mass of the glass plate, Y is the total mass of the glass plate before drying and the resin solution, Y is the total mass Z of the glass plate and the remaining solid content.

Synthesis Example 1: Preparation of polysilicate Methyl silicate 51 (manufactured by Colcoat Co., Ltd.) 10 parts by mass, isopropyl alcohol 84 parts by mass and water 5 parts by mass were mixed at 30 ° C. for 2 hours. After mixing for a predetermined time, 1 part by mass of 0.1N HCl was added to the mixture, and the mixture was further mixed at 30 ° C. for 2 hours.

Example 1
[Preparation of adhesive composition]
A polyvinyl alcohol-based resin (Goseifamer (registered trademark) ZZ-200 manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was adjusted to a solid content of 2% by mass to obtain an aqueous solution. Glyoxal (pH 3.3) prepared with 10% by mass of an active ingredient (10 parts by mass with respect to 100 parts by mass of the polyvinyl alcohol resin) was mixed with this aqueous solution as a curing agent. Next, the polysilicate prepared in Synthesis Example 1 is uniformly added to this mixed solution visually at room temperature (25 ° C.) in an amount of 30% by mass of the active ingredient (30 parts by mass with respect to 100 parts by mass of the polyvinyl alcohol resin). To obtain an adhesive composition as a solution. The blending ratio (effective component ratio) of each material is as shown in Table 1 below.

[Production of polarizing plate]
The polarizer was produced by the following method. A polyvinyl alcohol film having a mean polymerization degree of 2400 and a saponification degree of 99.9% and a thickness of 75 μm is immersed in warm water at 28 ° C. for 90 seconds to swell, then iodine / potassium iodide (weight ratio 2/3) concentration 0 A polyvinyl alcohol film was dyed while being immersed in a 6% by weight aqueous solution and stretched 2.1 times. Then, it extended | stretched so that a total draw ratio might be set to 5.8 times in 60 degreeC boric-acid-ester aqueous solution, and it washed with water and dried for 3 minutes at 45 degreeC, and produced the polarizer (25 micrometers in thickness).

  As shown in FIG. 1, the polarizer (thickness: 25 μm) prepared above is sandwiched between two sheets of cellulose triacetate film (TAC film, Fuji Film Co., Ltd., thickness 80 μm, abbreviated as TAC). An appropriate amount of the obtained adhesive composition was dropped between the TAC and the polarizer with a dropper, and bonded by a roll press. The thus-bonded polarizing plate before drying was dried at 70 ° C. for 5 minutes to obtain a polarizing plate bonded through an adhesive layer.

  The obtained polarizing plate was evaluated by performing a cutting test, an optical property measurement, and a moist heat resistance test as follows. The evaluation results are shown in Table 1 below together with the composition of the adhesive composition. In Table 1 below, the composition of the adhesive composition is expressed in parts by mass.

<Cutting test>
The obtained polarizing plate was cut into 5 cm × 5 cm with a Thonsom blade, and the state of peeling at the end during the cutting was visually observed. If the length of peeling was 0.5 mm or less from the end, the adhesiveness was considered sufficient.

<Optical characteristics>
The obtained polarizing plate measured the transmittance | permeability and haze using the haze meter (Nippon Denshoku Industries Co., Ltd. HazeMeter NDH5000W). If the transmittance was 43% or more and the haze was 0.5% or less, it was considered suitable for practical use as a polarizing plate.

<Moisture and heat resistance test>
The obtained polarizing plate was cut into 5 cm × 5 cm with a Thonsom blade to obtain a test piece. This specimen was stored for 2 hours in an atmosphere of 60 ° C. and 100% RH, and then the shrinkage width (total shrinkage width in the longitudinal direction) of the polarizer was measured. If the shrinkage width is 0.5 mm or less, the heat and humidity resistance is sufficient.

Example 2
In Example 1 above, a polarizing plate was produced in the same manner as Example 1 except that the polysilicate was mixed in an amount of 60% by mass of the active ingredient (60 parts by mass with respect to 100 parts by mass of the polyvinyl alcohol resin). .

  The obtained polarizing plate was evaluated in the same manner as in Example 1 by performing a cutting test, an optical property measurement, and a wet heat resistance test. The evaluation results are shown in Table 1 below together with the composition of the adhesive composition.

Example 3
In Example 1 above, a polarizing plate was produced in the same manner as Example 1 except that the polysilicate was mixed in an amount of 90% by mass of the active ingredient (90 parts by mass with respect to 100 parts by mass of the polyvinyl alcohol resin). .

  The obtained polarizing plate was evaluated in the same manner as in Example 1 by performing a cutting test, an optical property measurement, and a wet heat resistance test. The evaluation results are shown in Table 1 below together with the composition of the adhesive composition.

Comparative Example 1
A polarizing plate was produced in the same manner as in Example 1 except that no polysilicate was added in Example 1.

  The obtained polarizing plate was evaluated in the same manner as in Example 1 by performing a cutting test, an optical property measurement, and a wet heat resistance test. The evaluation results are shown in Table 1 below together with the composition of the adhesive composition.

Comparative Example 2
In Example 1 above, a polarizing plate was produced in the same manner as in Example 1 except that the polysilicate was mixed in an amount of 150% by mass of the active ingredient (150 parts by mass with respect to 100 parts by mass of the polyvinyl alcohol resin). .

  The obtained polarizing plate was evaluated in the same manner as in Example 1 by performing a cutting test, an optical property measurement, and a wet heat resistance test. The evaluation results are shown in Table 1 below together with the composition of the adhesive composition.

  As shown in Table 1 above, the polarizing plates of Examples 1 to 3 were excellent in optical properties, adhesiveness, and wet heat resistance. On the other hand, the polarizing plate of Comparative Example 1 to which no polysilicate is added is significantly inferior in heat and moisture resistance as compared with the polarizing plate of the present invention. Moreover, although the polarizing plate of the comparative example 2 which mix | blended many polysilicates is excellent in heat-and-moisture resistance, peeling is observed in a cutting test and it turns out that it is inferior to the adhesive strength of the polarizing plate of this invention.

  Thus, since the adhesive layer using the adhesive composition of the present invention is excellent in adhesiveness, optical properties, and heat and humidity resistance, it is considered that it can be suitably applied to a polarizing plate.

Claims (3)

100 parts by weight of polyvinyl alcohol resin,
3 to 50 parts by weight of a curing agent,
2 to 100 parts by mass of polysilicate,
A polarizing plate adhesive composition comprising:   The adhesive composition according to claim 1, wherein the polysilicate is synthesized by mixing an alkyl silicate, water, and alcohol.   A polarizing plate comprising a protective film and a polarizer, which are bonded using the adhesive composition according to claim 1.

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