JPH0466322B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a polarizing plate. [Prior Art] A polarizing film is formed by laminating a protective film such as a cellulose triacetate film on both sides of a polyvinyl alcohol film that has been imparted with polarizing properties using, for example, iodine or a dichroic dye. A liquid crystal display plate is manufactured by providing a pressure-sensitive adhesive layer on the polarizing film and press-bonding it to a liquid crystal cell. The above-mentioned pressure-sensitive adhesive has adhesive properties, transparency,
Acrylic pressure-sensitive adhesives are often used due to their weather resistance, but when the temperature rises, fine bubbles form in the adhesive layer and interfacial peeling occurs; There were drawbacks such as the cellulose acetate film decomposing and deteriorating, and the reflective metal foil of reflective liquid crystal display elements rotting and deteriorating. As a means to compensate for the above drawbacks, compositions having a crosslinked structure have been studied, and various crosslinked acrylic pressure sensitive adhesives have been proposed. For example, JP-A-56-95965 discloses copolymer A of alkyl (meth)acrylate and hydroxyalkyl (meth)acrylate, copolymer B of alkyl (meth)acrylate and (meth)acrylic acid, and polyfunctional isocyanate. Pressure sensitive adhesives consisting of compounds are described. However, in this pressure-sensitive adhesive, copolymers A and B are both crosslinked by an isocyanate compound, so the storage stability is poor, and after lamination on a polarizing film, the crosslinking density varies depending on the curing conditions, and over time. The disadvantage was that the quality was unstable because crosslinking progressed due to the oxidation process. [Object of the Invention] In view of the above-mentioned drawbacks, the object of the present invention is to provide a material with excellent cohesive force, adhesive force, and viscoelasticity, which are well-balanced;
A pressure-sensitive adhesive layer with stable quality is formed, and when attached to a liquid crystal cell, etc., it will not cause bubbles or interfacial peeling under high temperature conditions, or the cellulose triacetate film will decompose and deteriorate. To provide a polarizing plate whose reflective metal foil does not deteriorate due to rot. [Structure of the Invention] The gist of the present invention is that (A) the content of alkyl (meth)acrylate is 70
~99.9 mol%, and the content of the polymerizable monomer having reactive functional group X is 0.1 to 10 mol%, (B) a copolymer mainly composed of alkyl (meth)acrylate,
A polymer or copolymer that does not have a reactive functional group X and other functional groups that can react with the functional group
and (C) a polyfunctional compound having at least two functional groups Y that can react with the reactive functional group X, and the mixing ratio of copolymer A and polymer or copolymer B is 1:4 to 4. :1, and a pressure-sensitive adhesive layer in which copolymer A is crosslinked with polyfunctional compound C is laminated on at least one surface of a polarizing film. The alkyl (meth)acrylates used in the present invention are alkyl acrylates and alkyl methacrylates, and the alkyl group has 4 to 4 carbon atoms.
18, such as n-butyl acrylate, iso-butyl acrylate, ter-butyl acrylate, iso-amyl acrylate, 2
Examples include ethylhexyl acrylate, n-octyl acrylate, lauryl acrylate or n-butyl methacrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate, and lauryl methacrylate. Of these, n-
butyl acrylate, iso-amyl acrylate,
One or two selected from the group of 2-ethylhexyl acrylate, n-octyl acrylate, n-octyl methacrylate, and lauryl methacrylate.
More than one species of monomer is more preferably used. The polymerizable monomer used in the present invention is a monomer having a reactive functional group It is preferably a group such as acrylic acid, methacrylic acid, β-hydroxyethyl acrylate, β-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, polyethylene glycol acrylate, polyethylene glycol methacrylate, polypropylene glycol acrylate, polypropylene glycol methacrylate, glycidyl acrylate, maleic anhydride,
Examples include acrylamide and methacrylamide, and monomers having a hydroxyl group are more preferably used. Copolymer A in the present invention is a copolymer of the above-mentioned alkyl (meth)acrylate and the above-mentioned polymerizable monomer, and since the alkyl (meth)acrylate in copolymer A imparts tackiness, the content is 70%. ~99.9 mol%, and if the content of the polymerizable monomer is too small, sufficient cohesive force cannot be expressed when crosslinked, and on the other hand, if the content is too large, the crosslinking density increases and the adhesiveness decreases, so 0.1 -20 mol%, preferably 0.5-5 mol%. In addition, the above-mentioned copolymer A may be copolymerized with a polymerizable monomer that does not have the reactive functional group X and other functional groups that can react with the functional group Examples of monomers include benzyl acrylate, benzyl methacrylate,
Examples include aromatic acrylates such as phenoxyethyl acrylate, styrene, and vinyl acetate. The polymer or copolymer B in the present invention is mainly composed of alkyl (meth)acrylate, does not have a reactive functional group X and other functional groups that can react with the functional group ) As the content of acrylate decreases, the tackiness decreases, so the content of alkyl (meth)acrylate
The amount is preferably 70 mol % or more, and the polymerizable monomer that does not have the reactive functional group X and other functional groups that can react with the functional group X may be copolymerized in a range of 30 mol % or less. The above copolymer A and polymer or copolymer B
Any known method may be adopted as the polymerization method, and solution polymerization using an organic peroxide, an azo polymerization initiator, etc. in an organic solvent such as ethyl acetate, toluene, acetone, methyl ethyl ketone, or cyclohexane is preferred. preferable. The polyfunctional compound C used in the present invention has at least two functional groups Y capable of reacting with the reactive functional group X.
Examples of functional groups Y include isocyanate groups, amino groups, metal ions, etc., and examples of polyfunctional compounds include compounds selected from the group consisting of isocyanate compounds, amine compounds, and alkali metals. For example, 2,4 tolylene diisocyanate, methylene bisphenyl isocyanate, trimethylolpropane tolylene diisocyanate,
Examples include trimethylolpropane triisocyanate, hexamethylene diamine, calcium, magnesium, zinc, etc., and isocyanate compounds are more preferably used. The pressure-sensitive adhesive used in the present invention is composed of the above-mentioned copolymer A, polymer or copolymer B, and polyfunctional compound C, and the ratio of copolymer A to polymer or copolymer B is , As the ratio of A increases, the ratio of crosslinkable copolymer increases, making it difficult to control the crosslinking rate and decreasing storage stability.
On the other hand, if the ratio of B becomes too large, sufficient cohesive force cannot be obtained even if crosslinked, so it is used in the range of 1:4 to 4:1. Also, if the amount of polyfunctional compound C added is too large, free polyfunctional compound C will be present, resulting in a decrease in adhesive properties, and if it is too small, the crosslinking density will become small, making it impossible to obtain sufficient cohesive force. Therefore, it is preferable that the amount is added to such an extent that all of the functional groups X are crosslinked, that is, in an approximately equivalent amount to the functional groups X. The polarizing film used in the present invention is not particularly limited, and any conventionally known film can be used. For example, polyvinyl alcohol, polyvinyl formal, polyvinyl acetal, saponified products of ethylene/vinyl acetate copolymer, etc. Films made of resins are impregnated with polarizing elements such as iodine and dichroic dyes, and then stretched to impart polarizing properties, such as cellulose-based films such as cellulose triacetate, polycarbonate-based films, polyethersulfone-based films, etc. Examples include those with a protective film laminated. The polarizing plate of the present invention has a pressure-sensitive adhesive layer laminated on at least one surface of the polarizing film,
The pressure-sensitive adhesive layer is cross-linked by the polyfunctional compound C, and any method may be used for laminating the pressure-sensitive adhesive layer. For example, by using a solution-polymerized pressure-sensitive adhesive, Apply to release paper such as polyester film that has been subjected to silicone release treatment using a roll coater, knife coater, etc. so that the solid content is several tens of microns to several hundred microns, evaporate the solvent with hot air, and then apply polarized light. An example is a method of transferring the image to a sex film. Further, crosslinking of the pressure sensitive adhesive layer is carried out when the pressure sensitive adhesive is laminated on a release paper and the solvent etc. are volatilized, but in order to ensure crosslinking, heat curing may be performed. In addition, when the crosslinking density decreases, the cohesive force becomes insufficient, the adhesive strength decreases, and the creep properties deteriorate.
On the other hand, if it becomes too large, it becomes hard and the wettability decreases, leading to a decrease in adhesive strength, so it is preferable that the gel fraction is 15 to 60%. The gel fraction here is the weight fraction of the insoluble portion after immersion in ethyl acetate at 20°C and extraction for 72 hours. [Effects of the Invention] The structure of the polarizing plate of the present invention is as described above, and the adhesive layer after crosslinking is made of crosslinked gel-like copolymer A.
and a non-crosslinked sol-like polymer or copolymer B coexist, and the cohesive force, adhesive force, and viscoelasticity are excellent and well-balanced. , since no free functional groups remain, the quality is stable,
Even under high temperature and high humidity conditions, bubbles will not form, interfacial peeling will not occur, protective films such as cellulose triacetate will not decompose and deteriorate, and reflective metal foil will not deteriorate due to rot. Therefore, the polarizing plate of the present invention can be suitably used even under high temperature and high humidity conditions. [Example] Next, an example of the present invention will be described. Examples 1 to 6, Comparative Examples 1 to 4 The compositions shown in Table 1 were charged into a reactor equipped with a stirrer, a cooler, a thermometer, and a nitrogen introduction device, and the inside of the reactor was heated by a nitrogen stream. After expelling the oxygen, the reactor was heated to 60°C and polymerization was carried out under a nitrogen stream for 15 hours to obtain a copolymer solution. In addition, ethyl acetate was added 3 hours and 6 hours after the start of polymerization, respectively.
500g was added, and at 10 hours, 1000g of ethyl acetate and 3g of azobisisobutyronitrile (A-1 to 3, A-
5,6,B-1) or benzoyl peroxide
3 g (A-4, B-2) was added, and then the temperature was raised until ethyl acetate refluxed. Furthermore, ethyl acetate was added to the obtained copolymer solution to obtain adhesives A and B having a solid content of 15%.

[Table] Next, take Adhesives A and B in the ratio shown in Tables 2 and 3 so that the solid content is 100g, mix them evenly, and add 0.02% of trimethylolpropane triisocyanate as a crosslinking agent. g to obtain a pressure sensitive adhesive solution. Next, the above pressure-sensitive adhesive composition solution was applied to one side of a 25μ thick polyester film that had been subjected to a silicone mold release treatment so that the adhesive thickness was 25μ, and the mixture was heated at 80°C.
After drying and crosslinking for 20 minutes, a polarizing plate was obtained by pasting it on one side of a polarizing film in which 80 μm thick cellulose triacetate film was laminated on both sides of a 25 μm thick polyvinyl alcohol polarizing film. The obtained polarizing plate was cut into a size of 40 x 50 mm, the polyester film was gradually removed, and it was pasted on a glass plate for a liquid crystal cell to prepare a test piece, which was subjected to heat resistance test and moisture resistance test under the following conditions. The observation results are shown in Tables 2 and 3. Heat resistance test: 100℃, 500 hours Humidity resistance test: 80℃, 95%RH, 500 hours

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Claims (1)

[Claims] 1 (A) The content of alkyl (meth)acrylate is 70 to 99.9 mol%, and the content of the polymerizable monomer having a reactive functional group X is 0.1 to 20 mol%.
(B) a copolymer mainly composed of alkyl (meth)acrylate,
A polymer or copolymer that does not have a reactive functional group X and other functional groups that can react with the functional group
and (C) a polyfunctional compound having at least two functional groups Y that can react with the reactive functional group X, and the mixing ratio of copolymer A and polymer or copolymer B is 1:4 to 4. :1, and a pressure-sensitive adhesive layer in which copolymer A is crosslinked with polyfunctional compound C is laminated on at least one surface of a polarizing film. 2. The polarizing plate according to claim 1, wherein the reactive functional group X is a functional group selected from the group consisting of a carboxyl group, a hydroxyl group, an epoxy group, an acid anhydride group, and an amide group. 3. The polarizing plate according to claim 1 or 2, wherein the polyfunctional compound C is a compound selected from the group consisting of isocyanate compounds, amine compounds, and alkali metals.