JP6641095B2 - Adhesive composition - Google Patents

Description

  The present invention relates to a pressure-sensitive adhesive composition, and more particularly, to a pressure-sensitive adhesive composition that achieves both suppression of foaming when used for a polycarbonate substrate and a pot life of the pressure-sensitive adhesive composition.

  An optical member such as a display of an electronic device is composed of many materials, and an adhesive is frequently used for assembling each material. Pressure-sensitive adhesives used for such applications are required to have various properties in addition to the pressure-sensitive adhesive performance.

For example, when the temperature and humidity are high, the pressure-sensitive adhesive layer is likely to whiten, and when such a whitening phenomenon occurs, the visibility is reduced.
In addition, polycarbonate substrates are widely used for optical members because of their excellent transparency, heat resistance, impact resistance, etc.However, when an adhesive is used for a polycarbonate member, an adhesive layer is formed especially in a high temperature environment. Bubbles are generated in the glass, which adversely affects the visibility. Although the cause is not clear, it is speculated that a low molecular weight compound derived from polycarbonate is a cause of foaming.
Furthermore, when used after long-term storage in the form of a substrate-less pressure-sensitive adhesive sheet protected on both sides of the pressure-sensitive adhesive layer with a release film, there is a problem in film life, such as an increase in foaming derived from the polycarbonate member and a decrease in peel strength. is there. Although the cause is not clear, since the release agent in the release film is mixed into the surface of the adhesive, the adhesion between the base material to be bonded and the adhesive is reduced, causing foaming and a decrease in peel strength. It is speculated that

Patent Literature 1 discloses an adhesive resin composition for an image display device in which generation of bubbles, floating, peeling, and the like on an adherend made of plastic is suppressed. On the other hand, since the adhesive resin composition is an active energy ray-curable type, it is necessary to introduce an expensive device capable of irradiating active energy rays, and there is a problem in versatility.
JP 2013-119604 A

  The problem of the present invention is that even when used on a substrate such as polycarbonate, the foaming is small, the thermosetting is possible, the pot life after mixing each component is long, and the substrate-less pressure-sensitive adhesive sheet can be used for a long time. An object of the present invention is to provide a pressure-sensitive adhesive composition capable of maintaining these properties even after being exposed to high heat.

An object of the present invention is to provide an acrylic polymer (A) having a weight average molecular weight of 500,000 or more obtained by polymerizing an acrylic monomer substantially free of a carboxyl group-containing monomer, an isocyanate compound (B), The acrylic monomer comprising the urethanization catalyst (C) and the active methylene group-containing compound (D), and constituting the (A) is an alkyl (meth) acrylate, a hydroxyl group-containing monomer and an amide group-containing monomer. the amount only including, a blending amount of the (C) is (a) 1 to 3 parts by weight per 100 parts by weight, the amount of the (D) is characterized in that it is a 8-30 parts by weight It is an adhesive composition.

  The pressure-sensitive adhesive composition of the present invention is suitable for use in assembling optical members because bubbles are unlikely to be generated in the pressure-sensitive adhesive layer even when used for a polycarbonate base material that is frequently used for optical members. Further, since the pot life after mixing each component is long, it is unlikely to cause frequent mixing or waste loss. Furthermore, even after the substrate-less pressure-sensitive adhesive sheet is exposed to high heat for a long period of time, these properties can be maintained, so that the film life can be extended.

  The pressure-sensitive adhesive composition of the present invention contains an acrylic polymer (A) having a weight average molecular weight of 500,000 or more obtained by polymerizing an acrylic monomer substantially free of a carboxyl group-containing monomer. . Here, substantially not containing a carboxyl group-containing monomer, when the acrylic polymer contains a carboxyl group, since there is a risk of corrosion when the adherend contains a metal, in order to avoid this It is specified that a carboxyl group-containing monomer such as acrylic acid, methacrylic acid, and itaconic acid is not contained, and there is no such possibility (for example, 0.1% by weight based on the entire acrylic monomer). It does not exclude the use or mixing of the carboxyl group-containing monomer of the following).

  The acrylic monomer constituting the acrylic polymer preferably contains an alkyl (meth) acrylate, a monomer containing a hydroxyl group and a monomer containing an amide group, and further contains another acrylic monomer. Is also good. As the alkyl (meth) acrylate, specifically, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, sec-butyl acrylate, t-butyl acrylate, n-hexyl acrylate, cyclohexyl Acrylate, n-octyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, isodecyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, sec-butyl methacrylate , T-butyl methacrylate, n-hexyl methacrylate, cyclohexyl methacrylate DOO, n- octyl methacrylate, isooctyl methacrylate, 2-ethylhexyl methacrylate, isononyl methacrylate, isodecyl methacrylate, lauryl methacrylate.

From the viewpoint of the adhesive strength of the obtained pressure-sensitive adhesive composition, alkyl (meth) acrylate having 4 to 9 carbon atoms is preferable, and it is particularly preferable to use n-butyl acrylate and / or 2-ethylhexyl acrylate.
The alkyl (meth) acrylate is preferably used in an amount of 40 to 99% by weight based on the entire acrylic monomer from the viewpoint of adhesive strength.

Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate, 2-hydroxy-3-chloropropyl acrylate, 2-hydroxy-3-chloropropyl methacrylate, 2-hydroxy-3-phenoxypropyl acrylate, 2-hydroxy-3-phenoxypropyl methacrylate, and the like.
The hydroxyl group-containing monomer is preferably used in an amount of 1 to 15% by weight based on the entire acrylic monomer from the viewpoint of the crosslinking point and the effect of preventing whitening due to its hydrophilicity.

  Examples of the amide group-containing monomer include acrylamide, methacrylamide, diacetone acrylamide, N, N-dimethylacrylamide, N-vinylpyrrolidone, acryloylmorpholine, N-hydroxyethylamide, and N-methylolacrylamide. The amide group-containing monomer is preferably used in an amount of 1 to 30% by weight based on the entire acrylic monomer, from the viewpoint of securing adhesive strength by cohesion and preventing whitening due to hydrophilicity.

  In addition, a known acrylic monomer or a monomer copolymerizable with the acrylic monomer can be used. Examples of (meth) acrylic acid alkoxy esters include 2-methoxyethyl methacrylate, 2-ethoxyethyl methacrylate, 2-methoxypropyl methacrylate, 3-methoxypropyl methacrylate, 2-methoxybutyl methacrylate, and 4-methoxy methacrylate. Butyl and the like.

  Examples of the alkylene glycol (meth) acrylate include ethylene glycol acrylate, polyethylene glycol acrylate, propylene glycol acrylate, polypropylene glycol acrylate, ethylene glycol methacrylate, polyethylene glycol methacrylate, propylene glycol methacrylate, and polypropylene glycol methacrylate. Is mentioned.

Examples of the aryl (meth) acrylate include benzyl acrylate, phenoxyethyl acrylate, phenyl acrylate, benzyl methacrylate, phenoxyethyl methacrylate, phenyl methacrylate, and the like.

  Furthermore, aromatic vinyl monomers such as styrene, α-methylstyrene, vinyltoluene and ethylvinylbenzene, saturated fatty acid vinyl monomers such as vinyl acetate, vinyl propionate and vinyl versatate, ethylene, propylene, butadiene And polyfunctional monomers such as divinylbenzene, ethylene glycol dimethacrylate, and diallyl phthalate.

An acrylic polymer can be synthesized by, for example, heating the acrylic monomer together with a polymerization initiator in a solvent. In the present invention, the weight average molecular weight of the acrylic polymer needs to be 500,000 or more, which is not preferable because foaming when used for a polycarbonate substrate cannot be sufficiently suppressed.
The weight average molecular weight in the present invention refers to a value measured by GPC (gel permeation chromatography) under the following conditions and calculated in terms of polystyrene. As the sample, a filtrate obtained by dissolving the sample in tetrahydrofuran to prepare a 0.1% by weight solution, leaving the sample in an ultrasonic cleaning device to which water has been added for 10 minutes, and then filtering through a 0.20 μm membrane filter is used.
Analyzer: LC20AD, manufactured by Shimadzu
Column: GPC-80M x 2 manufactured by Shimadzu
Eluent: tetrahydrofuran Flow rate: 1.0 ml / min
Inlet pressure: 10kgf
Detector: Differential refractometer (RI)
Column temperature: 40 ° C
Injection volume: 50 μl
Eluent: Tetrahydrofuran Detector: Differential refractometer Standard sample: Polystyrene

Solvents include methyl acetate, ethyl acetate, butyl acetate, benzene, toluene, xylene, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, n-hexane, isopropyl alcohol, n-butanol, propylene glycol monomethyl ether, propylene glycol dimethyl ether, propylene glycol Organic solvents such as monomethyl ether acetate and propylene carbonate are exemplified. However, other solvents may be used without any problem, and two or more solvents may be used in combination. Particularly preferred solvents are ethyl acetate, butyl acetate, toluene, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, n-hexane and propylene glycol monomethyl ether acetate.
Further, the molecular weight of the produced polymer can be adjusted by selecting the solvent. When methyl ethyl ketone or the like is used, a polymer having a relatively low molecular weight can be obtained. When ethyl acetate or the like is used, a polymer having a relatively high molecular weight can be obtained.

Examples of the polymerization initiator include 2,2′-azobisisobutyronitrile, 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile), and 2,2′-azobis (2,4-dimethyl Valeronitrile), dimethyl-2,2'-azobis (2-methylpropionate), 2,2'-azobis (2-methylbutyronitrile), 1,1'-azobis (cyclohexane-1-carbonitrile) , 2,2'-azobis [N- (2-propenyl) -2-methoxypropionamide], 1-[(1-cyano-1-methylethyl) azo] formamide, 2,2'-azobis (N-butyl) -2-methylpropionamide), 2,2′-azobis (N-cyclohexyl-2-methylpropionamide), [1,1′-azobis (1-acetoxy-1-phenylethane)], etc. Zo compounds, lauroyl peroxide, octanoyl peroxide, benzoyl peroxide, ethyl methyl ketone peroxide, cumene hydroperoxide, dicumyl peroxide, t-butyl hydroperoxide, cumylperoxy neodecanoate, t- Hexyl peroxy neodecanoate, t-butyl peroxy-2-ethylhexanoate, dicumyl peroxide, isobutyl peroxide, di-t-butyl peroxide, t-butyl cumyl peroxide, t-butyl peroxy Benzoate, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, di (2-ethylhexyl) peroxydicarbonate, 1,1-bis (t-butylperoxy) -3,3 5-trimethylcyclohexa , It can be used 3,3,5 organic peroxide compounds such as trimethyl cyclohexanoyl peroxide and the like.
In addition, redox polymerization can be carried out by using a peroxide compound in combination with a reducing agent such as N, N-dimethyltoluidine and N, N-diethyltoluidine.
The polymerization initiator is usually used in an amount of 0.05 to 3 parts by weight based on 100 parts by weight of the acrylic monomer. Increasing the amount of the polymerization initiator tends to decrease the molecular weight of the obtained polymer, and decreasing the amount of the polymerization initiator tends to increase the molecular weight of the obtained polymer.

  The pressure-sensitive adhesive composition of the present invention contains an isocyanate compound (B). As the isocyanate compound, aromatic isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, naphthalene diisocyanate, p-phenylene diisocyanate, aliphatic isocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, nobornene diisocyanate, and dicyclohexylmethane diisocyanate And hydrogenated products of the above aromatic diisocyanates such as isophorone diisocyanate and hydrogenated xylene diisocyanate. In addition, reaction formation of these polyfunctionalized polyisocyanate structures such as adduct type, isocyanurate type, biuret type, polymethylene polyphenyl polyisocyanate, polyester polyisocyanate, polyether polyisocyanate, and trimethylolpropane-modified polyisocyanate. It may be a thing.

The compounding amount of the isocyanate compound (B) is preferably 0.5 to 2.0 parts by weight based on 100 parts by weight of the acrylic polymer (A). When the content is 0.5 parts by weight or more, foaming when used for a polycarbonate substrate is significantly suppressed. When the content is 2.0 parts by weight or less, the pot life after mixing the components can be sufficiently ensured.

  Further, an epoxy compound may be added together with the isocyanate compound. Examples of epoxy compounds include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, bisphenol A / epichlorohydrin type epoxy resin, N, N, N'N'-tetraglycidyl- Examples include m-xylenediamine, 1,3-bis (N, N-diglycidylaminomethyl) cyclohexane, N, N-diglycidylaniline, N, N-diglycidyltoluidine and the like.

The pressure-sensitive adhesive composition of the present invention contains a urethanization catalyst (C). The urethane-forming catalyst promotes the reaction between the active hydrogen groups in the acrylic polymer and the isocyanate compound, and contributes to suppression of foaming when used for a polycarbonate substrate. Known catalysts can be used as the urethanization catalyst, and examples thereof include organometallic compounds and metal chelate compounds. Examples of the organometallic compound include dibutyltin dilaurate and octyltin dilaurate. Examples of the metal chelate compound include bismuth tris (2-ethylhexanoate), tin octoate, zirconium tetraacetylacetonate, zinc neodecanoate, and the like.

The amount of the urethanization catalyst is 1 to 3 with respect to 100 parts by weight of the acrylic polymer (A). It is preferably in parts by weight. When the amount is 1 part by weight or more, foaming when used for a polycarbonate substrate is significantly suppressed. When the amount is 3 parts by weight or less, the transparency of the pressure-sensitive adhesive film is not easily impaired.

The pressure-sensitive adhesive composition of the present invention further contains an active methylene group-containing compound (D). In the present invention, the active methylene group-containing compound is a compound having a methylene group sandwiched between electron-withdrawing groups such as a carbonyl group and an ester group, and specific examples include acetylacetone, ethyl acetoacetate, and malonic ester compounds. Among them, acetylacetone and ethyl acetoacetate are preferred, and acetylacetone is more preferred.
It is considered that the addition of these active methylene group-containing compounds blocks the isocyanate group of the isocyanate compound (B) and contributes to prolonging the pot life after mixing the components.
The compounding amount of the active methylene group-containing compound is preferably 5 to 30 parts by weight based on 100 parts by weight of the acrylic polymer (A). By setting the amount to 5 parts by weight or more, the pot life after mixing each component can be significantly extended. When the content is 30 parts by weight or less, the deprotection reaction of the blocked isocyanate is promptly performed during drying after coating.

Various additives such as an ultraviolet absorber, a near-infrared absorber, an antioxidant, an antiseptic, a fungicide, a tackifier resin, a plasticizer, an antifoaming agent and a wetting agent are added to the pressure-sensitive adhesive composition of the present invention. An agent may be included.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but it shows specific examples and is not particularly limited thereto.

Example 1
86 parts of butyl acrylate (BA), 5 parts of methyl methacrylate (MMA), 1 part of 2-hydroxyethyl acrylate (2-HEA), 8 parts of diacetone acrylamide (DAAM), 0.05 parts of azobisisobutyronitrile, acetic acid 27 parts of ethyl was mixed and dissolved to prepare solution (a). 50 parts of ethyl acetate was placed in a separable flask equipped with a stirrer and a reflux condenser, heated to 75 ° C., and nitrogen gas was introduced for 30 minutes or more to remove oxygen in the polymerization system. Next, the solution (a) was added dropwise over 3 hours while maintaining the temperature at 75 ± 1 ° C., and after completion of the addition, the reaction temperature was raised to 80 ° C., and the reaction was maintained at 80 ± 1 ° C. for 3 hours. After completion of the reaction, the reaction solution was diluted with ethyl acetate to obtain an acrylic polymer of Example 1 which was a pale yellow transparent viscous liquid. The viscosity was 6,000 mPa · s, the solid content was 30%, and the weight average molecular weight was 650,000.

Preparation of Pressure-Sensitive Adhesive Composition With respect to 100 parts by weight of the solid content of the acrylic polymer solution of Example 1, 1.5 parts by weight of coronate HX (manufactured by Nippon Polyurethane Industry Co., Ltd., trade name) as a cross-linking agent, and urethane 2.0 parts by weight of Neostan U-28 (manufactured by Nitto Kasei Co., Ltd., inorganic tin type, trade name) as an activating catalyst and 10 parts by weight of acetylacetone as an active methylene group-containing compound were added to prepare the pressure-sensitive adhesive composition of Example 1. did.

Examples 2 to 8, Comparative Examples 1 to 4
In addition to the materials used in Example 1, as monomers, 2EHA (2-ethylhexyl acrylate), MA (methyl acrylate), 4HBA (4-hydroxybutyl acrylate), DMAAm (N, N-dimethylacrylamide), ACMO (acryloyl) Morpholine), IBMA (isobutoxymethylacrylamide), NVP (N-vinylpyrrolidone), and acrylamide (AAm) in the same manner as in Example 1 except that the polymer was polymerized in the formulation shown in Table 1. A polymer solution was synthesized. Further, only Comparative Example 1 was polymerized by increasing the amount of azobisisobutyronitrile as a polymerization initiator to 0.10 parts to synthesize a polymer solution having a molecular weight of 500,000 or less. Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd., trade name), Coronate HL (manufactured by Nippon Polyurethane Industry Co., trade name) as a polyfunctional isocyanate, and Neostan U- as a urethanization catalyst were used for 100 parts by weight of the solid content of each acrylic polymer solution. 820 (manufactured by Nitto Kasei Co., organic tin, trade name), Neostan U-600 (manufactured by Nitto Kasei Co., bismuth base, trade name), Organix ZC150 (Matsumoto Fine Chemical Co., zirconium base, trade name), BiCAT- Z (manufactured by Shepherd Chemical Company, zinc system, trade name), DABCO (1,4-diazabicyclo [2.2.2] octane), U-CAT SA 102 (manufactured by San Apro Corporation, amine system, trade name), active methylene Each pressure-sensitive adhesive composition was prepared by adding ethyl acetoacetate as a group-containing compound in the composition shown in Table 1. .

Pot life evaluation The following evaluation was carried out using a sample immediately after preparing the pressure-sensitive adhesive composition by stirring each composition until uniform, and a sample left at room temperature for 5 hours after preparation.

Condition after 5 hours of adjustment Viscosity immediately after preparation and viscosity after 5 hours of preparation are measured, respectively, and if the rate of increase in viscosity after 5 hours of adjustment is 1.2 times or less, it is determined as good (）), and the rate of increase in viscosity Was larger than 1.2 times or gelled, it was judged as defective (x).

Immediately after the preparation of the pressure-sensitive adhesive sheet and 5 hours after the preparation, each pressure-sensitive adhesive composition was applied on a release film so that the thickness after drying was 50 μm, and dried by heating at 90 ° C. for 20 minutes. It was bonded to a mold film and further aged at 23 ° C. for 7 days to prepare a substrate-less pressure-sensitive adhesive sheet.

Peel strength Each pressure-sensitive adhesive sheet was bonded to a PET film (trade name: A4100, manufactured by Toyobo Co., Ltd., thickness: 50 μm) to form a film piece having a width of 25 mm and a length of 100 mm. The release film of the film piece was peeled off, adhered to the glass at 23 ° C. and 50% RH using a laminator, and left for 1 day in an atmosphere of 23 ° C. and 50% RH for testing. The pressure-sensitive adhesive tape was pulled in a direction of 180 ° at a pulling speed of 300 mm / min, and the center value was defined as 180 ° peel adhesive strength. If the adhesive strength of the pressure-sensitive adhesive composition left at normal temperature for 5 hours has decreased by 1.5 N / 25 mm or more, the pot life is poor.

Each of the PC foam-resistant pressure-sensitive adhesive sheets was bonded to a PET film (manufactured by Toyobo Co., Ltd., trade name: A4100, thickness: 50 μm) to prepare a film piece having a width of 4 cm and a length of 4 cm. The release film was peeled off from the film piece, bonded to a polycarbonate plate (trade name: Iupilon MR-58, manufactured by Mitsubishi Gas Chemical Company, thickness: 1 mm), and left for 1 day at 23 ° C. and 50% RH atmosphere. A test piece was used.
The test piece was heat-treated in an 85 ° C. oven for 24 hours. After the heat treatment, the test piece was visually observed. If no bubbles were observed at the interface between the polycarbonate plate and the pressure-sensitive adhesive layer, the foaming resistance was determined to be good (良好). When it was observed, it was evaluated as poor foaming resistance (x).

Evaluation of Film Life After heat-treating each PSA sheet at 60 ° C. for 100 hours, the peel strength and the PC foam resistance were similarly evaluated. When the peel strength is reduced by 1.5 N / 25 mm or more as compared with the case where the heat treatment is not performed, or when the foaming resistance is evaluated as x, the film life is determined to be poor.

Each of the pressure-sensitive adhesive sheets was wet and heat-whitened, and was adhered to a PET film (manufactured by Toyobo Co., Ltd., trade name: A4100, thickness: 50 μm) to prepare a film piece having a width of 25 mm and a length of 100 mm. The release film of the film piece was peeled off, and was adhered to the glass at 23 ° C. and 50% RH using a laminator. This was left for 400 hours in an environment of 60 ° C. and 95% RH, cooled at 23 ° C. and 50% RH for 1 hour, and the haze was measured and the presence or absence of foaming was confirmed. The haze was measured using HAZE-GARDII manufactured by Toyo Seiki Seisaku-sho, Ltd. The evaluation criteria are as follows.
：: Haze is less than 1.5 (almost no whitening was observed, and excellent resistance to wet heat whitening)
×: haze 1.5 or more (cannot be used due to poor whitening property)

  The pot life of each of the pressure-sensitive adhesive compositions of Examples was sufficiently ensured, and these pressure-sensitive adhesive sheets had good pot life and film life in terms of PC foam resistance and adhesive strength. On the other hand, none of the pressure-sensitive adhesive sheets using the pressure-sensitive adhesive compositions of Comparative Examples satisfied all the properties. Therefore, only the pressure-sensitive adhesive composition containing an acrylic polymer having a molecular weight of 500,000 or more, an isocyanate compound, a urethanization catalyst, and an active methylene group-containing compound confirmed the effects of the present invention.

Claims (3)

An acrylic polymer (A) having a weight average molecular weight of 500,000 or more, obtained by polymerizing an acrylic monomer substantially free of a carboxyl group-containing monomer, an isocyanate compound (B), a urethanization catalyst (C ), containing an active methylene group-containing compound (D), seen containing an acrylic monomer constituting the (a) is (meth) acrylic acid alkyl esters, hydroxyl group-containing monomers and amide group-containing monomer, The pressure-sensitive adhesive composition , wherein the compounding amount of (C) is 1 to 3 parts by weight with respect to 100 parts by weight of (A), and the compounding amount of (D) is 8 to 30 parts by weight . For the entire acrylic monomer wherein constituting the acrylic polymer (A), the proportion of amide group-containing monomer Ri 6-30 wt% der, the proportion of (meth) acrylic acid alkyl ester monomer The pressure-sensitive adhesive composition according to claim 1 , wherein the content is 84 to 93% by weight . 3. The pressure-sensitive adhesive composition according to claim 1, wherein the amount of the isocyanate compound (B) is 1 to 2 parts by weight based on 100 parts by weight of the acrylic polymer (A). 4.