JPH09324163A - Tacky agent for optical use - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a tacky agent for optical use, comprising a specific acrylic resin copolymer without deteriorating triacetylcellulose under high-temperature and high-humidity conditions, excellent in durability and suitable for bonding a member for the optical use such as a sheet for the optical use, e.g. a polarizing plate or a phase difference plate. SOLUTION: This tacky agent for optical use comprises an acrylic resin copolymer at pH >=7 of extraction water at 105 deg.C for 100hr in s pressure cooker test [e.g. the one consisting essentially of an acrylic acid-based alkyl ester, an amide group-containing monomer and a monomer containing a functional group other than the amide group (e.g. a carboxyl-containing and an OH- containing monomer) having 1:(3-5) ratio Z1 :Z2 of the number of the carboxyl groups (Z1 ) to that of the amide groups (Z2 ) in the copolymer and 1000000-2000000 weight-average molecular weight].

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pressure-sensitive adhesive suitable for bonding optical members such as optical sheets such as polarizing plates and retardation plates. More specifically, it relates to a pressure-sensitive adhesive type pressure-sensitive adhesive for a pressure-sensitive adhesive type optical sheet such as a pressure-sensitive adhesive type polarizing plate and a pressure sensitive adhesive type retardation plate which have excellent durability under high temperature and high humidity conditions.

[0002]

2. Description of the Related Art Polarizing plates have been industrially produced and used in large quantities due to the spread of liquid crystal displays. Liquid crystal displays starting from small displays such as watches and calculators can also be used for personal computers, office automation equipment such as word processors, liquid crystal televisions, liquid crystal projectors, in-vehicle instrument panels, in-vehicle navigation systems, etc. As it has been applied to high-priced equipment and highly durable equipment, its high reliability has been required more and more. Among the reliability of the liquid crystal display, one of the components most desired to be improved is a polarizing plate. Most of the product forms of this polarizing plate for liquid crystal are pressure-sensitive adhesive type polarizing plates having a pressure-sensitive adhesive layer in order to simplify assembly and reduce reflection loss on the surface. Besides the improvement of durability, the most important point for practical use is the improvement of the durability of the pressure-sensitive adhesive layer used for the polarizing plate.

In general, a pressure-sensitive adhesive type polarizing plate has a triacetyl cellulose (hereinafter abbreviated as TAC) on both sides of a stretched polyvinyl alcohol (hereinafter abbreviated as PVA) film in which iodine or a dichroic dye is used as a polarizer. ) A film is laminated and adhered, and a pressure-sensitive adhesive layer is further provided on the surface of the TAC to manufacture. In the actual production, the pressure-sensitive adhesive type polarizing plate is attached to the surface of the glass plate of the liquid crystal cell via a pressure-sensitive adhesive layer. If a general liquid crystal cell with a polarizing plate made in this way is exposed to high temperature and high humidity conditions for a long time, the TAC of the polarizing plate deteriorates to white turbidity, discoloration, and physical destruction, and finally In some cases, the function as a polarizing plate may be lost.

On the other hand, a method of providing a retardation plate between a liquid crystal cell and a polarizing plate has become widespread as one of black and white display methods by an STN type liquid crystal display. One type of retardation plate PVA retardation plate is produced by supporting one or both sides of a stretched PVA film with a TAC film and providing a pressure-sensitive adhesive layer on the surface. In this case, a liquid crystal display is constructed by laminating this one-layer or a plurality of layers of retardation films to an STN cell via a pressure-sensitive adhesive layer and laminating a polarizing plate to the outermost layer. Similar to the case where the polarizing plates alone are bonded together, if they are exposed to high temperature and high humidity for a long time, they may become cloudy and physically destroyed, and the function may be completely lost in a time not so long.

As a means for preventing the deterioration of the TAC,
Japanese Patent Laid-Open No. 59-111114 discloses a method of reducing the acrylic acid content of a pressure-sensitive adhesive.
3 proposes a method of adding a tertiary amine. However, although the above-mentioned means is effective in preventing the deterioration of TAC, the adhesion with the glass tends to deteriorate, so that peeling or the like occurs under high temperature and high humidity and the durability tends to decrease.

[0006]

DISCLOSURE OF THE INVENTION The present invention relates to a pressure-sensitive adhesive type polarizing plate, a pressure-sensitive adhesive type retardation plate or the like having high durability, which does not deteriorate TAC even when exposed to a high temperature and high humidity for a long time. The present invention provides a pressure-sensitive adhesive for a pressure-adhesive optical sheet.

[0007]

[Means for Solving the Problems] The inventors of the present invention have made extensive studies to solve the above problems, and have made thorough investigations into their causes. As a result, the acidity of acrylic acid, which is one of the copolymerization components of pressure-sensitive adhesives, has been investigated. It was found that the acetyl group of TAC contacted under high temperature and high humidity conditions is hydrolyzed, and the acetic acid hydrolyzes other acetyl groups one after another, causing rapid destruction and deterioration. Then, as a countermeasure, in the resin copolymer-based pressure-sensitive adhesive forming the pressure-sensitive adhesive layer provided on the optical element such as the polarizing plate and the retardation plate, the pH of the extracted water after 105 ° C./100 hours in the pressure cooker test. It was found that the conventional drawbacks are improved by using an acrylic resin copolymer-based pressure-sensitive adhesive having a value of 7 or more. That is, the present invention provides (1) an acrylic resin copolymer-based pressure-sensitive adhesive for optics, wherein the acrylic resin copolymer is 10 in a pressure cooker test.
An optical pressure-sensitive adhesive characterized in that the pH of the extracted water after 5 ° C./100 hours is an acrylic resin copolymer having a pH of 7 or more,
(2) The optical pressure-sensitive adhesive according to (1), wherein the acrylic resin copolymer is a copolymer containing acrylic acid alkyl ester, amide group-containing monomer, and functional group-containing monomer other than amide group as essential components as polymerization components. And (3) the acrylic resin copolymer is an acrylic acid-based alkyl ester as a polymerization component, a polymerizable monomer having a carboxyl group in the molecule,
(1) an optical pressure-sensitive adhesive, which is a copolymer containing a polymerizable monomer having a hydroxyl group in the molecule and a polymerizable monomer having an amide group in the molecule as essential components, and (4) an acrylic resin copolymer The optical pressure-sensitive adhesive of (1) or (3), wherein the ratio of the carboxyl group to the amide group is 3 to 5 amide groups per one carboxyl group, and (5) the acrylic resin copolymer has a weight average molecular weight of 1 ,, 000,000-2,000
(1) to (4) optical adhesive, which is 10,000,
(6) An optical sheet having the pressure-sensitive adhesive layer according to any one of (1) to (5) above, and (7) an optical sheet according to (6), wherein the optical film sheet is a polarizing plate or a retardation plate. .

The monomer component of the acrylic resin copolymer used in the present invention is not particularly limited as long as it is a polymerizable monomer, but it is mainly composed of an acrylic acid type alkyl ester and contains an amide group-containing monomer and a functional group other than the amide group. Other monomers such as group-containing monomers and, if necessary, comonomers are used. Examples of the acrylic acid-based alkyl ester include methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-propyl (meth) acrylate, isobutyl (meth) acrylate, and (meth) acrylate. Examples thereof include (meth) acrylic acid (having 1 to 12 carbon atoms) alkyl esters such as n-butyl acrylate, t-butyl (meth) acrylate, and dodecyl (meth) acrylate.

Examples of the amide group-containing monomer (polymerizable monomer having an amide group in the molecule) include N, N-dimethylaminopropylacrylamide, N, N-dimethylacrylamide, N, N-diethylacrylamide,
Examples of acrylamide monomers such as acryloylmorpholine, N-isopropylacrylamide, N-methylolacrylamide, and acrylamide. Examples of the functional group-containing monomer other than the amide group include a polymerizable monomer having a carboxyl group in the molecule and a polymerizable monomer having a hydroxyl group in the molecule, but it is preferable to use both in combination. Examples of the polymerizable monomer having a carboxyl group in the molecule include acrylic acid, methacrylic acid, maleic acid, itaconic acid and the like. As a polymerizable monomer having a hydroxyl group in the molecule, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-chloro-2-hydroxypropyl acrylate, 3-chloro-2 -Hydroxy such as hydroxypropyl methacrylate (1 carbon atom
~ 5) Diethylene glycol (meth) acrylates such as alkyl (meth) acrylate, diethylene glycol monoacrylate, and diethylene glycol monomethacrylate. Examples of other monomers such as comonomers include vinyl acetate, acrylonitrile,
Examples include styrene.

The use ratio of these monomers is 50 to 98% by weight, preferably 70 to 95% by weight of acrylic acid type alkyl ester, and 0.1 to 20% by weight of the functional group-containing polymerizable monomer other than the amide group. 1 to 10% by weight, preferably 1 to 20% by weight of the amide group-containing polymerizable monomer,
It is preferably 3 to 15% by weight, and the functional group-free polymerizable monomer is 0 to 20% by weight, preferably 0 to 10% by weight. As a functional group-containing polymerizable monomer other than an amide group,
When the polymerizable monomer having a carboxyl group in the molecule and the polymerizable monomer having a hydroxyl group in the molecule are used in combination, the proportion of the polymerizable monomer having a carboxyl group in the molecule is 0.5 to 10% by weight, preferably Is 1 to 7% by weight, and the polymerizable monomer having a hydroxyl group in the molecule is 0.1 to
It is about 10% by weight, preferably about 0.5 to 5% by weight.
Further, the number of amide groups of the polymerizable monomer component having an amide group in the molecule is not particularly limited, but when a polymerizable monomer having a carboxyl group in the molecule is used as a monomer, the durability at high temperature and high humidity is high. Considering the adhesive strength and the adhesive strength, it is preferably 3 to 5 times the number of carboxyl groups in the entire acrylic resin copolymer.

The acrylic resin copolymer used in the present invention can be easily produced by dissolving the monomer to be used in an organic solvent and radical-copolymerizing in the organic solvent by a general method. As the organic solvent used in the polymerization, aromatic hydrocarbons such as toluene and xylene, esters such as ethyl acetate and butyl acetate, aliphatic alcohols such as n-propyl alcohol and iso-propyl alcohol, methyl ethyl ketone and methyl. Examples thereof include ketones such as isobutyl ketone. Examples of the polymerization catalyst used for the radical polymerization include azobisisobutyronitrile, benzoyl peroxide, di-t-butyl peroxide, cumene hydroperoxide and the like which are common polymerization catalysts.

The thus obtained acrylic resin copolymer is colorless and transparent, has a glass transition temperature (hereinafter abbreviated as Tg) of -20 ° C or lower, preferably -30 ° C to -60 ° C, and has a weight average. The molecular weight is 500,000 or more, preferably 700,000 to 2,500,000, and more preferably about 1,000,000 to 2,000,000. If the Tg exceeds -20 ° C, the adhesive strength is poor and the durability is poor. If the average molecular weight is 500,000 or less, heat resistance may be insufficient,
If it exceeds, the adhesiveness tends to be insufficient and peeling or the like is likely to occur. The acrylic resin copolymer preferably has a pH of the extracted water after 105 ° C./100 hours in the pressure cooker test of 7 or more, more preferably 7 to 10, still more preferably 7 to 9.
Are preferred. Furthermore, in the case of a copolymer in which a polymerizable monomer having a carboxyl group in the molecule and a polymerizable monomer having a hydroxyl group in the molecule are used in combination as the functional group-containing polymerizable monomer other than the amide group, The ratio of carboxyl group to amide group is preferably 3 to 5 amide groups per one carboxyl group.

The acrylic resin copolymer used in the present invention can of course be used alone as an optical pressure-sensitive adhesive, but if necessary, it may be used as an optical pressure-sensitive adhesive in a composition which can be crosslinked by incorporating a crosslinking agent. May be. A suitable crosslinking agent may be used. Generally, for example, aliphatic diisocyanates, polyisocyanate compounds such as aromatic diisocyanates, butyl etherified styrene melamine, melamine compounds such as trimethylol melamine, diamine compounds, epoxy resin compounds, urea resin compounds, metal salts and the like are used. . When the cross-linking agent is blended, the blending amount is 0.001 per 100 parts by weight of the acrylic resin copolymer.
10 to 10 parts by weight, preferably 0.005 to 5 parts by weight, and more preferably 0.01 to 5 parts by weight. Moreover, you may mix | blend a silane coupling agent. When the silane coupling agent is blended, the blending amount is the acrylic resin copolymer 1
0.001 to 10 parts by weight, preferably 0.005 to 5 parts by weight, and more preferably 0.01 to 5 parts by weight per 00 parts by weight.
Parts by weight.

To produce the pressure-sensitive adhesive of the present invention, for example, the above-mentioned components may be uniformly mixed. Further, the pressure-sensitive adhesive of the present invention contains the above-mentioned components in the form of methyl ethyl ketone, toluene,
It is dissolved in an organic solvent such as ethyl acetate to obtain a pressure-sensitive adhesive solution, which is then diluted to a concentration of the acrylic resin copolymer of 10 to 30% by weight before use. Incidentally, the adhesive of the present invention,
105 ° C / 100 in pressure cooker test
It is preferable that the pH of the extracted water after 7 hours is 7 or more,
More preferably pH 7 to 10, still more preferably pH 7 to
It is preferably about 9.

Examples of the optical sheet of the present invention include a polarizing plate and a retardation plate. The polarizing plate and the retardation plate are usually obtained by coating one side or both sides of the polarizing film or the retardation film with a cellulosic protective layer. The above-mentioned polarizing film is usually polyvinyl alcohol, polyvinyl formal, polyvinyl acetal, ethylene-
A film made of a polyvinyl alcohol-based resin such as a saponified product of vinyl acetate copolymer is preferably impregnated with a polarizing element such as iodine or a dichroic dye to give a polarizing property by stretching the film. However, other types may be used. Further, the retardation film is usually retarded by stretching a film made of polyvinyl alcohol, polyvinyl formal, polyvinyl acetal, polyvinyl alcohol resin such as saponified ethylene-vinyl acetate copolymer. However, other types may be used. As the cellulose-based protective layer that covers the polarizing film and the retardation film, for example, triacetate cellulose or other transparent cellulose-based film is used.

The above-mentioned pressure-sensitive adhesive of the present invention is applied to one side or both sides of an optical sheet, especially to a cellulose-based protective layer of a polarizing plate or a retardation plate. The coating method is generally after drying a release film with a coater. Is applied and dried to a film thickness of 20 to 30 μm, and then transferred onto one side or both sides of the optical sheet.

The pressure-sensitive adhesive of the present invention is useful as an optical pressure-sensitive adhesive, particularly as a pressure-sensitive adhesive for adhering a polarizing film or a retardation film coated with a cellulosic protective layer and a glass substrate of a liquid crystal cell. Such a pressure-sensitive adhesive does not cause abnormal appearance such as foaming, peeling or deterioration even if it is left in a high temperature and high humidity state for a long time. Utilizing such characteristics, it is used for a liquid crystal display, and is particularly useful for a vehicle, various industrial instruments, display of household electric appliances, and the like.

[0018]

EXAMPLES The present invention will be described more specifically below with reference to examples and comparative examples. Example 1 Monomer composition (parts by weight) is n-butyl acrylate / 2-
Hydroxyethyl acrylate / acrylic acid / N, N-
100% by weight of a 20% by weight ethyl acetate solution (viscosity 2,000 cps / 25 ° C.) of an acrylic resin copolymer (average molecular weight 1,200,000) obtained by polymerizing a mixture of dimethylacrylamide = 81/1/2/11. In the present invention, 0.5 part by weight of a trimethylolpropane (1 mol) adduct of tolylene diisocyanate (3 mol) and 0.5 part by weight of γ-glycidoxypropyl methoxysilane were added to 10 parts by weight and uniformly dissolved. To obtain a solution of adhesive. A film thickness after drying this adhesive solution on a release film is 20 to 30 μm.
And then dried, and laminated on the side of the cellulose triacetate film of a polyvinyl alcohol polarizing film (average degree of polymerization 1700, average degree of saponification 99.5 mol%, 5 times stretched) having a cellulose triacetate film as a protective layer. Then, it was pressed with a roller to prepare a polarizing plate. A durability test (80 ° C / 90% RH, 10%
It was left standing for 00 hours), and the foaming state of the pressure-sensitive adhesive, the peeling state of the polarizing plate, and the deterioration state were observed. The results are shown in Table 1. On the other hand, 5 g of the above acrylic resin copolymer and 50 g of pure water were placed in a Teflon hermetically sealed pressure vessel and subjected to a pressure cooker test in which a 100 ° C. constant temperature tester was left for 100 hours. PH of the extracted water of the pH meter (HM-10K: manufactured by Toa Denpa Kogyo Co., Ltd.)
It was measured at. As the pure water, distilled water was passed through an ion exchange resin, and a pure water having a resistance value of 10 M ohm or more was used. The results are shown in Table 1.

Comparative Example 1 Monomer composition (parts by weight) was changed to n-butyl acrylate / 2-
Hydroxyethyl acrylate / acrylic acid = 95/1
An experiment was performed according to Example 1 except that the value was changed to / 4, and a durability test and a pressure cooker test were performed. The results are shown in Table 1.

[0020]

[Table 1] Table 1 Example 1 Comparative Example 1 Foamed state ◎ The TAC of the polarizing plate is broken and cannot be observed and peeled off ◎ The TAC of the polarizing plate is broken and cannot be observed and deteriorated ◎ The polarizing plate TAC breaks down to pH 7.82 3.75

Foaming state ◎: No foaming is observed between the polarizing plate and the glass plate Peeling state ◎: No peeling is observed between the polarizing plate and the glass plate ◎: No change is observed in the polarizing plate

[0021]

EFFECTS OF THE INVENTION By using a pressure-sensitive adhesive containing an acrylic resin copolymer having a pH of 7 or more of extracted water after a pressure cooker test, the pressure-sensitive adhesive type is excellent in durability under high temperature and high humidity conditions. A pressure-sensitive adhesive type optical sheet such as a polarizing plate or a pressure-sensitive adhesive type retardation plate can be obtained.

Claims (7)

[Claims] 1. An optical acrylic resin copolymer-based pressure-sensitive adhesive, wherein the acrylic resin copolymer is an acrylic resin copolymer having a pH of 7 or more in extracted water after 105 ° C./100 hours in a pressure cooker test. An optical pressure-sensitive adhesive characterized by being present. 2. An optical resin according to claim 1, wherein the acrylic resin copolymer is a copolymer containing as a polymerization component an acrylic acid alkyl ester, an amide group-containing monomer, and a functional group-containing monomer other than an amide group as essential components. Adhesive. 3. An acrylic resin copolymer having an acrylic acid alkyl ester as a polymerization component, a polymerizable monomer having a carboxyl group in the molecule, a polymerizable monomer having a hydroxyl group in the molecule, and an amide group in the molecule. The optical pressure-sensitive adhesive according to claim 1, which is a copolymer containing a polymerizable monomer as an essential component. 4. The optical pressure-sensitive adhesive according to claim 3, wherein the ratio of carboxyl groups to amide groups in the acrylic resin copolymer is 3 to 5 amide groups per one carboxyl group. 5. The optical pressure-sensitive adhesive according to any one of claims 1 to 4, wherein the acrylic resin copolymer has a weight average molecular weight of 1,000,000 to 2,000,000. 6. An optical sheet having a layer of the pressure-sensitive adhesive according to any one of claims 1 to 5. 7. The optical sheet according to claim 6, which is a polarizing plate or a retardation plate.