JP2016190992A - Adhesive composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an adhesive composition which causes little foaming even when used for a substrate such as polycarbonate, is thermally curable, has a long pot life even after each component is mixed and can maintain these properties even after exposed to high temperature for a long time.SOLUTION: There is provided an adhesive composition which comprises an acrylic polymer (A) having a weight average molecular weight of 500000 or more obtained by polymerization of an acrylic monomer containing substantially no carboxyl group-containing monomer, an isocyanate compound (B), a urethanization catalyst (C) and an active methylene group-containing compound (D).SELECTED DRAWING: None

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 in a polycarbonate substrate and pot life of an adhesive composition.

  An optical member such as a display of an electronic device is composed of many materials, and an adhesive is often used for assembling each material. In addition to the adhesive performance, various properties are required for the adhesive used in such applications.

For example, when the temperature and humidity are increased, the pressure-sensitive adhesive layer is likely to be whitened, and when such a whitening phenomenon occurs, the visibility is lowered, so that moisture and heat whitening resistance is required.
In addition, since polycarbonate substrates are excellent in transparency, heat resistance, impact resistance, etc., they are also actively used in optical members. However, when a pressure-sensitive adhesive is used for a polycarbonate member, the pressure-sensitive adhesive layer particularly in a high-temperature environment. Air bubbles are generated in the surface, which adversely affects the visibility. Although the cause of this is not clear, a low molecular weight compound derived from polycarbonate is presumed to be the cause of foaming.
In addition, 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, there is a problem in film life, such as increased foaming from the polycarbonate member and reduced peel strength. is there. Although the cause of this is not clear, the release agent in the release film is mixed into the adhesive surface, which reduces the adhesion between the base material and the adhesive to be bonded, causing foaming and reduced peel strength. I guess that.

Patent Document 1 discloses an adhesive resin composition for an image display device in which generation of bubbles, floats, peeling, and the like is suppressed with respect to an adherend made of plastic. On the other hand, since the adhesive resin composition is an active energy ray curable type, it is necessary to introduce an expensive apparatus 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 if it is used on a substrate such as polycarbonate, it has little foaming and can be cured by heat, and the usable time after mixing each component is long. It is to provide a pressure-sensitive adhesive composition that can maintain these performances even after being exposed to high heat.

    In the present invention, an acrylic polymer (A), an isocyanate compound (B), and a urethanization 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 A pressure-sensitive adhesive composition comprising a catalyst (C) and an active methylene group-containing compound (D).

  The pressure-sensitive adhesive composition of the present invention is suitable for assembling an optical member because bubbles are hardly generated in the pressure-sensitive adhesive layer even when used on a polycarbonate base material that is also actively used for optical members. Moreover, since the pot life after mixing each component is long, it is difficult to mix frequently and to cause a loss of disposal. Furthermore, since these performances can be maintained even after the substrate-less pressure-sensitive adhesive sheet is exposed to high heat for a long period of time, the film life can be lengthened.

  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 that does not substantially contain a carboxyl group-containing monomer. . Here, substantially not containing a carboxyl group-containing monomer means that when the acrylic polymer contains a carboxyl group, the adherend may corrode if a metal is contained. It stipulates that it does not contain a carboxyl group-containing monomer such as acrylic acid, methacrylic acid, and itaconic acid. This does not exclude the use or contamination of the following carboxyl group-containing monomers.

  The acrylic monomer constituting the acrylic polymer preferably contains a (meth) acrylic acid alkyl ester, a hydroxyl group-containing monomer and an amide group-containing monomer, and further uses other acrylic monomers. Also good. Specific examples of (meth) acrylic acid alkyl esters include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, sec-butyl acrylate, t-butyl acrylate, n-hexyl acrylate, and 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 point of the adhesive strength of the obtained adhesive composition, a C4-C9 (meth) acrylic-acid alkylester is preferable, and it is especially preferable to use n-butyl acrylate and / or 2-ethylhexyl acrylate.
The (meth) acrylic acid alkyl ester 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, Examples include 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate, 2-hydroxy-3-chloropropyl acrylate, 2-hydroxy-3-chloropropyl methacrylate, 2-hydroxy-3-phenoxypropyl acrylate, and 2-hydroxy-3-phenoxypropyl methacrylate.
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, N-methylolacrylamide and the like. The amide group-containing monomer is preferably used in an amount of 1 to 30% by weight based on the whole acrylic monomer from the viewpoint of securing adhesive force due to cohesive force and preventing whitening due to hydrophilicity.

  In addition, a known acrylic monomer or a monomer copolymerizable with an acrylic monomer can be used. Examples of (meth) acrylic acid alkoxyesters include 2-methoxyethyl methacrylate, 2-ethoxyethyl methacrylate, 2-methoxypropyl methacrylate, 3-methoxypropyl methacrylate, 2-methoxybutyl methacrylate, 4-methoxy methacrylate. Examples include butyl.

  As (meth) acrylic acid alkylene glycol, ethylene glycol acrylate, polyethylene glycol acrylate, propylene glycol acrylate, polypropylene glycol acrylate, ethylene glycol methacrylate, polyethylene glycol methacrylate, propylene glycol methacrylate, polypropylene glycol methacrylate, etc. Is mentioned.

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

  In addition, aromatic vinyl monomers such as styrene, α-methylstyrene, vinyl toluene, ethyl vinyl benzene, saturated fatty acid vinyl monomers such as vinyl acetate, vinyl propionate, vinyl versatate, ethylene, propylene, butadiene And other polyfunctional monomers such as divinylbenzene, ethylene glycol dimethacrylate, and diallyl phthalate.

An acrylic polymer can be synthesized by heating the acrylic monomer together with a polymerization initiator in a solvent, for example. In the present invention, the acrylic polymer needs to have a weight average molecular weight of 500,000 or more, which is not preferable because foaming when used on a polycarbonate substrate cannot be sufficiently suppressed.
In addition, the weight average molecular weight in this invention means the value calculated by GPC (gel permeation chromatography) by the following conditions, and computed by polystyrene conversion. The sample is dissolved in tetrahydrofuran to give a 0.1% by weight solution, left in an ultrasonic cleaning apparatus to which water has been added for 10 minutes, and then filtrated through a 0.20 μm membrane filter is used.
Analyzer: SHIMADZU, LC20AD
Column: GPC-80M x2 made 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 Examples thereof include organic solvents such as monomethyl ether acetate and propylene carbonate. However, any other solvent may be used, 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.
Moreover, the molecular weight of the polymer produced | generated can be adjusted by selection of a solvent. When methyl ethyl ketone or the like is used, a relatively low molecular weight polymer can be obtained. When ethyl acetate or the like is used, a relatively high molecular weight polymer can be obtained.

Examples of the polymerization initiator include 2,2′-azobisisobutyronitrile, 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile), 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)], and the like Zo compounds, lauroyl peroxide, octanoyl peroxide, benzoyl peroxide, ethyl methyl ketone peroxide, cumene hydroperoxide, dicumyl peroxide, t-butyl hydroperoxide, cumyl peroxyneodecanoate, t- Hexylperoxyneodecanoate, t-butylperoxy-2-ethylhexanoate, dicumyl peroxide, isobutyl peroxide, di-t-butyl peroxide, t-butylcumyl peroxide, t-butylperoxy 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, the peroxide compound can be subjected to redox polymerization by using a reducing agent such as N, N-dimethyltoluidine, N, N-diethyltoluidine or the like in combination.
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 polymerization initiator used tends to decrease the molecular weight of the polymer obtained, and decreasing the amount of polymerization initiator used tends to increase the molecular weight of the polymer obtained.

  The pressure-sensitive adhesive composition of the present invention contains an isocyanate compound (B). Isocyanate compounds include aromatic isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, naphthalene diisocyanate, and p-phenylene diisocyanate, and 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. Also, reaction products of polyfunctionalized polyisocyanate structures such as adduct type, isocyanurate type, biuret type, polymethylene polyphenyl polyisocyanate, polyester polyisocyanate, polyether polyisocyanate, trimethylolpropane modified polyisocyanate, etc. It may be a thing.

As for the compounding quantity of an isocyanate compound (B), 0.5-2.0 weight part is preferable with respect to 100 weight part of said acrylic polymers (A). By setting it as 0.5 weight part or more, foaming at the time of using for a polycarbonate base material is suppressed notably. Moreover, the pot life after mixing each component is fully securable by setting it as 2.0 weight part or less.

  Moreover, you may add an epoxy compound with an isocyanate compound. Examples of the epoxy compound 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 thereof 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 urethanization catalyst promotes the reaction between the active hydrogen group in the acrylic polymer and the isocyanate compound, and contributes to the suppression of foaming when used for a polycarbonate substrate. A known catalyst can be used as the urethanization catalyst, and examples thereof include organic metal 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, and zinc neodecanoate.

The compounding amount of the urethanization catalyst is 1 to 3 with respect to 100 parts by weight of the acrylic polymer (A). It is preferable that it is a weight part. By setting it as 1 weight part or more, foaming at the time of using for a polycarbonate base material is suppressed notably. Moreover, the transparency of an adhesive film | membrane is hard to be impaired by setting it as 3 weight part or less.

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 a malonic ester compound. Among them, acetylacetone and ethyl acetoacetate are preferable, and acetylacetone is more preferable.
By adding these active methylene group-containing compounds, it is considered that the isocyanate group of the isocyanate compound (B) is blocked and contributes to the extension of the pot life after mixing the respective components.
It is preferable that the compounding quantity of an active methylene group containing compound is 5-30 weight part with respect to 100 weight part of said acrylic polymers (A). By setting it as 5 weight part or more, the pot life after mixing each component can be extended significantly. Moreover, by setting it as 30 weight part or less, the deprotection reaction of the blocked isocyanate at the time of the drying after coating is performed rapidly.

Various additions such as ultraviolet absorbers, near infrared absorbers, antioxidants, antiseptics, antifungal agents, tackifying resins, plasticizers, antifoaming agents, and wettability adjusting agents are added to the adhesive composition of the present invention. An agent may be included.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and demonstrated in detail about this invention, a specific example is shown and it does not specifically limit to these.

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 part of azobisisobutyronitrile, acetic acid A solution (a) was prepared by mixing and dissolving 27 parts of ethyl. In a separable flask equipped with a stirrer and a reflux condenser, 50 parts of ethyl acetate was added, the temperature was raised to 75 ° C., nitrogen gas was introduced for 30 minutes or more, and oxygen in the polymerization system was removed. Subsequently, the liquid (a) was added dropwise over 3 hours while maintaining at 75 ± 1 ° C., and after completion of the addition, the reaction temperature was raised to 80 ° C. and the reaction was continued for 3 hours at 80 ± 1 ° C. 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 6000 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 (trade name, manufactured by Nippon Polyurethane Industry Co., Ltd.), which is a polyfunctional isocyanate compound, is used as a crosslinking agent. The pressure-sensitive adhesive composition of Example 1 was prepared by adding 2.0 parts by weight of Neostan U-28 (manufactured by Nitto Kasei Co., Ltd., trade name), and 10 parts by weight of acetylacetone as an active methylene group-containing compound. did.

Examples 2-8, Comparative Examples 1-4
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) were used in the same manner as in Example 1 except that the polymer was polymerized according to the formulation shown in Table 1. A polymer solution was synthesized. Further, only in Comparative Example 1, azobisisobutyronitrile as a polymerization initiator was increased to 0.10 parts for polymerization to synthesize a polymer solution having a molecular weight of 500,000 or less. Coronate L (trade name, manufactured by Nippon Polyurethane Industry Co., Ltd.), Coronate HL (product name, manufactured by Nippon Polyurethane Industry Co., Ltd.) as a polyfunctional isocyanate, Neostan U- as a urethanization catalyst, based on 100 parts by weight of the solid content of each acrylic polymer solution 820 (manufactured by Nitto Kasei Co., Ltd., organic tin, trade name), Neostan U-600 (manufactured by Nitto Kasei Co., Ltd., bismuth, trade name), ORGATIZ ZC150 (manufactured by Matsumoto Fine Chemical Co., zirconium, trade name), BiCAT- Z (manufactured by Shepherd Chemical, zinc-based, trade name), DABCO (1,4-diazabicyclo [2.2.2] octane), U-CAT SA 102 (manufactured by San Apro, amine-based, trade name), active methylene Each pressure-sensitive adhesive composition was prepared by adding ethyl acetoacetate as a group-containing compound in the formulation shown in Table 1. .

Pot Life Evaluation Each formulation was stirred until it became uniform, and the following evaluation was performed using a sample immediately after preparing an adhesive composition and a sample left at room temperature for 5 hours after preparation.

The viscosity immediately after preparation of the condition after 5 hours of adjustment and the viscosity after 5 hours of preparation were measured, respectively, and if the rate of increase in viscosity after 5 hours of adjustment was 1.2 times or less, it was judged as good (◯). Is larger than 1.2 times or gelled, it was judged as bad (x).

Each pressure-sensitive adhesive composition immediately after the preparation of the pressure-sensitive adhesive sheet and 5 hours after the preparation was coated on the release film so that the thickness after drying was 50 μm, dried at 90 ° C. for 20 minutes, and then another release. The film was bonded to a mold film, and further aged at 23 ° C. for 7 days to prepare a base material-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 is peeled off, and pasted on glass at 23 ° C. and 50% RH atmosphere using a laminator, and left in an atmosphere of 23 ° C. and relative humidity 50% RH for 1 day, then for testing The pressure-sensitive adhesive tape was pulled in a 180 ° direction at a pulling speed of 300 mm / min, and the center value was defined as a 180 ° peel adhesive strength. When the adhesive strength of the pressure-sensitive adhesive composition left at room temperature for 5 hours has decreased by 1.5 N / 25 mm or more, the pot life is poor.

Each PC foam-resistant 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 4 cm and a length of 4 cm. The release film was peeled off from this film piece, bonded to a polycarbonate plate (Mitsubishi Gas Chemical Co., Ltd., trade name Iupilon MR-58, thickness 1 mm), and left for 1 day in an atmosphere of 23 ° C. and 50% RH. A test piece was obtained.
The test piece is heat-treated in an oven at 85 ° C. for 24 hours. After the heat treatment, the test piece is visually observed. If no bubbles are observed at the polycarbonate plate / adhesive layer interface, the foam resistance is good (O). When it was seen, it was regarded as poor foam resistance (x).

Film Life Evaluation After heat-treating each pressure-sensitive adhesive sheet at 60 ° C. for 100 hours, the peel strength and 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 heat treatment is not performed, or the foam resistance is evaluated as x, the film life is determined to be poor.

Moisture and heat whitening-resistant pressure-sensitive adhesive sheets were bonded to a PET film (trade name A4100, manufactured by Toyobo Co., Ltd., 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 stuck on glass at 23 ° C. and 50% RH atmosphere using a laminator. This was allowed to stand in an environment of 60 ° C. and 95% RH for 400 hours, and after cooling at 23 ° C. and 50% RH for 1 hour, the haze measurement and the presence or absence of foaming were confirmed. In addition, haze was measured using Toyo Seiki Seisakusho Co., Ltd. HAZE-GARDII. The evaluation criteria are as follows.
◯: Haze is less than 1.5 (almost no whitening is confirmed and moisture and heat whitening resistance is good)
X: Haze is 1.5 or more (cannot be used due to poor whitening property)

  The pot life of each pressure-sensitive adhesive composition in the examples was sufficiently secured, and these pressure-sensitive adhesive sheets were both good in pot life and film life from the viewpoint of PC foam resistance and adhesive strength. On the other hand, none of the pressure-sensitive adhesive sheets using the respective pressure-sensitive adhesive compositions of Comparative Examples satisfied all the performances. 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 was confirmed.

Claims (6)

  Acrylic polymer (A), isocyanate compound (B), urethanization catalyst (C) 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 active methylene group-containing compound (D).   The pressure-sensitive adhesive composition according to claim 1, wherein the ratio of the amide group-containing monomer is 0.1 to 30 wt% with respect to the entire acrylic monomer constituting the acrylic polymer (A). object.   The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the urethanization catalyst (C) contains one or more selected from the group consisting of an organometallic compound and a metal chelate compound. The pressure-sensitive adhesive composition according to any one of claims 1 to 3, wherein the amount of the urethanization catalyst (C) is 1 to 3 parts by weight with respect to 100 parts by weight of the acrylic polymer (A). .   The pressure-sensitive adhesive composition according to claim 1, wherein the active methylene group-containing compound (D) contains acetylacetone or ethyl acetoacetate. The pressure-sensitive adhesive according to any one of claims 1 to 5, wherein the amount of the active methylene group-containing compound (D) is 5 to 30 parts by weight with respect to 100 parts by weight of the acrylic polymer (A). Composition.