JP7552009B2 - Resin composition for active energy ray-curable adhesive and adhesive sheet - Google Patents

Description

The present invention relates to a resin composition for adhesives and an adhesive sheet that are cured to form a film by active energy rays.

Activation energy ray curing technology has the advantages of energy saving, space saving, and short curing time, and its range of use has expanded in recent years. In particular, solventless activation energy ray curable resin compositions containing polymerizable monomers have attracted attention. Solventless activation energy ray curable resin compositions consist of polymerizable oligomers, polymerizable monomers, polymerization initiators (not required for electron beam curing), and other additives.

As polymerizable oligomers, unsaturated polyesters, urethane (meth)acrylates, epoxy (meth)acrylates, polyester (meth)acrylates, etc. are used, and among these, urethane (meth)acrylate resins are often used in woodworking coatings because they are fast curing and allow a large degree of freedom in resin design. For example, curable resin compositions containing urethane (meth)acrylate resins are disclosed in Patent Documents 1 and 2.

JP 2000-281935 A JP 2001-2744 A

For pressure-sensitive adhesives, which have so far been mainly heat-cured or two-component-cured, active energy ray-curable properties have been actively investigated for the purpose of saving energy and shortening the process.
However, unlike urethanes, etc., in which functional groups react linearly to grow one-to-one, radical polymerization type active energy ray curable resins form a film by three-dimensional crosslinking with acryloyl groups, so the coating film tends to harden and is disadvantageous in terms of flexibility required for mitigating external stress for adhesives. This can be solved by increasing the molecular weight of the resin and decreasing the concentration of acryloyl groups, but on the other hand, the viscosity increases with increasing molecular weight, and deterioration of handleability is unavoidable.
An object of the present invention is to provide an active energy ray-curable resin composition for adhesives which has a relatively low molecular weight and provides good adhesive properties.

As a result of extensive investigation into the above-mentioned techniques, the inventors have discovered that by replacing the hydroxyl-containing acrylate, which is a constituent material of typical polyol-based urethane acrylates, with an alcohol, sufficient adhesive strength can be achieved even with a relatively low molecular weight composition.
The present invention relates to [1] a resin composition for active energy ray-curable pressure-sensitive adhesives, comprising as its constituent a urethane (meth)acrylate resin obtained by reacting a polyisocyanate compound (a) having two or more isocyanate groups per molecule, at least one polyol (b) selected from polyester polyols, polycaprolactone polyols, polyether polyols, and polycarbonate polyols, a hydroxyl group-containing (meth)acrylate (c), and an aliphatic alcohol (d) having 4 to 12 carbon atoms, such that the sum of the isocyanate groups of the isocyanate compound (a) and the hydroxyl groups of the polyol (b), the hydroxyl group-containing (meth)acrylate (c), and the aliphatic alcohol (d) is equal, and the molar ratio of the hydroxyl group-containing (meth)acrylate (c) to the aliphatic alcohol (d) is 1/9 to 2/8.

The present invention also relates to [2] the active energy ray-curable resin composition for pressure-sensitive adhesives according to [1], wherein the polyol (b) has a molecular weight of 1,000 to 3,000.
The present invention also relates to [3] the active energy ray-curable resin composition for adhesives according to [1] or [2], wherein the hydroxyl group-containing (meth)acrylate (c) is 2-hydroxyethyl acrylate.
The present invention also relates to [4] a pressure-sensitive adhesive sheet obtained by coating the active energy ray-curable resin composition for pressure-sensitive adhesives according to any one of [1] to [3] above on a paper or film substrate.

The present invention makes it possible to obtain a resin composition for active energy ray-curable adhesives that has a relatively low molecular weight and good adhesive properties without leaving any adhesive residue.

Representative compounds of the isocyanate compound (a), the polyol (b), the hydroxyl group-containing (meth)acrylate (c), and the aliphatic alcohol (d) are listed below.
In the present invention, the polyisocyanate compound (a) may be a diisocyanate compound such as tolylene diisocyanate, hydrogenated tolylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, lysine diisocyanate, naphthalene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, or hydrogenated xylylene diisocyanate.

Furthermore, biuret-type polyisocyanate compounds obtained by reacting the above-mentioned various diisocyanate compounds with water, or adduct-type polyisocyanate compounds obtained by reacting the above-mentioned various diisocyanate compounds with polyhydric alcohols such as trimethylolpropane, or polymers obtained by isocyanurating the above-mentioned various diisocyanate compounds can be used.

In the present invention, the polyester polyol of the component (b) is obtained by subjecting a polyvalent carboxylic acid and a polyhydric alcohol to an esterification reaction.
Examples of polyvalent carboxylic acids include known and commonly used polyvalent carboxylic acids such as adipic acid, azelaic acid, sebacic acid, succinic acid, dimer acid, phthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, tetrahydrophthalic anhydride, fumaric acid, maleic acid, maleic anhydride, itaconic acid, trimellitic acid, trimellitic anhydride, pyromellitic acid, and pyromellitic anhydride.

Examples of polyhydric alcohols include well-known and commonly used ones such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, neopentyl glycol, 1,4-butanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, ethylene oxide or propylene oxide adducts of bisphenol A, glycerin, trimethylolpropane, trimethylolethane, pentaerythritol, dimethylolpropionic acid, and dimethylolbutanoic acid.

In the present invention, examples of the polycaprolactone polyol of component (b) include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, neopentyl glycol, 1,4-butanediol, 1,6-hexanediol, ethylene oxide or propylene oxide adducts of bisphenol A, glycerin, trimethylolpropane, trimethylolethane, pentaerythritol, and other commonly known and commonly used polyhydric alcohols such as ε-caprolactone adducts.

In the present invention, the polyether polyol of component (b) may be a known, commonly used polyether polyol obtained by cationic polymerization of ethylene oxide, propylene oxide, or tetrahydrofuran.

In the present invention, the polycarbonate polyol of component (b) may be any of the known and commonly used polycarbonate polyols obtained by reacting glycols such as 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, and diethylene glycol with dimethyl carbonate, diethyl carbonate, ethylene carbonate, diphenyl carbonate, and phosgene.

In the present invention, the molecular weight of polyol (b) is preferably within the range of 1,000 to 4,000. If it is smaller than this, good adhesion cannot be obtained, and if it is larger, the viscosity becomes high and handling properties are significantly deteriorated.

In the present invention, the hydroxyl group-containing (meth)acrylate of component (c) may be any of the commonly known and commonly used compounds such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, butanediol mono(meth)acrylate, caprolactone-modified 2-hydroxyethyl (meth)acrylate, glycidol di(meth)acrylate, and pentaerythritol tri(meth)acrylate. Here, (meth)acrylate refers to acrylate and/or methacrylate.

Examples of the aliphatic alcohols having 4 to 12 carbon atoms include butyl alcohol, hexyl alcohol, octyl alcohol, decyl alcohol, lauryl alcohol, and isomers thereof. Commercially available products can be used. For example, examples of linear saturated aliphatic alcohols include Conol 10WS, Conol 1098, Conol 1275 (trade names, manufactured by New Japan Chemical Co., Ltd.), Kalcol 0898, Kalcol 0880, Kalcol 1098, and Kalcol 2098 (trade names, manufactured by Kao Corporation).

The aliphatic alcohol used in the present invention preferably has 4 to 12 carbon atoms. If the carbon number is less than 4, the viscosity will be high, and if the carbon number is more than 12, the adhesive strength will be lost due to the crystallinity of the material.

In the present invention, the molar ratio of the hydroxyl group-containing (meth)acrylate (c) to the aliphatic alcohol (d) is preferably within the range of 1/9 to 2/8. If the ratio of the aliphatic alcohol (d) is greater than this, adhesive residue will occur on the substrate, and conversely, if it is smaller, the coating film after curing will be too hard and will not exhibit good adhesion.

In the present invention, it is preferable to adjust the isocyanate group of the isocyanate compound (a) to be equal to the sum of the hydroxyl groups of the polyol (b), the hydroxyl group-containing (meth)acrylate (c), and the aliphatic alcohol (d). If there is too much isocyanate compound (a), the remaining isocyanate group reacts with moisture to form a urea bond, which causes high viscosity and cloudiness. Conversely, if there is too little, the aliphatic alcohol remains unreacted, which causes glue residue.

The active energy rays in the present invention include electron beams, α rays, β rays, γ rays, infrared rays, visible light, ultraviolet rays, etc. Among them, electron beams and ultraviolet rays have been relatively well researched, and ultraviolet rays in particular have the advantage that irradiation equipment for them is inexpensive.

When the active energy ray-curable pressure-sensitive adhesive resin composition of the present invention is cured with active energy rays, if the above-mentioned electron beam is used, it is not necessary to mix a photopolymerization initiator. When the active energy ray-curable pressure-sensitive adhesive resin composition is cured with ultraviolet rays, it is necessary to mix a photopolymerization initiator with the active energy ray-curable pressure-sensitive adhesive resin composition.
Examples of photopolymerization initiators include 2,2-dimethoxy-1,2-diphenylethan-1-one, benzophenone, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, oxy-phenyl-acetic acid 2-[2-oxo-2-phenyl-acetoxy-ethoxy]ethyl ester, oxy-phenyl-acetic acid 2-[2-hydroxy-ethoxy]-ethyl ester, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, 2-dimethylamino-2-(4-methylbenzyl)-(4-1-morpholin-4-yl-phenyl)-butan-1-one, bis(2,4,6-trimethylbenzoyl) From among known and commonly used ones such as bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, 1,2-octanedione, 1-[4-(phenylthio)-, 2-(o-benzoyloxime)], ethanone, 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-, 1-(o-acetyloxime), 2-chlorothioxanthone, 2,4-diethylthioxanthone, benzophenone, [4-(methylphenylthio)phenyl]phenylmethanone, and ethylanthraquinone, a single one or a mixture of two or more kinds can be used. The amount of the photopolymerization initiator to be blended is preferably 1 to 5% by mass based on the resin solid content of the resin composition for active energy ray-curable adhesives in terms of adhesion, curability, cost, etc.

In addition, to enhance the effect of the photopolymerization initiator, initiator assistants such as p-dimethylaminobenzoic acid isoamyl ester, p-dimethylamino-benzoic acid ethyl ester, N-methyldiethanolamine, bisethylaminobenzophenone, ethyl-4-dimethylaminobenzoate, and 2-ethylhexyl-4-dimethylaminobenzoate can also be used.

The active energy ray-curable adhesive resin composition of the present invention can be applied (painted) to a substrate, and then irradiated with active energy rays to cure it to form a coating film (adhesive layer), which can be used as an adhesive sheet. When applying to a substrate, it is preferable to adjust the film thickness to 5 to 50 μm in terms of resin solid content.

Specific examples of substrates for adhesive sheets include film substrates such as polyethylene film, polypropylene film, polyethylene terephthalate film, and polyethylene naphthalate film, as well as paper substrates such as fine paper, medium quality paper, art paper, cast coated paper, and coated paper.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these. Furthermore, "parts" and "%" shown in the examples and comparative examples indicate parts by mass and % by mass unless otherwise specified. The performance evaluation of the adhesive tape was performed according to the following method.

1) Preparation of adhesive sheet: 3% of 2,2-dimethoxy-1,2-diphenylethan-1-one was mixed with the resin compositions prepared in the Examples and Comparative Examples, and the mixture was applied to untreated PET (polyethylene terephthalate material whose surface had not been subjected to plasma treatment or the like) to a thickness of 25 μm. The mixture was then irradiated with ultraviolet light from a high-pressure mercury lamp at an integrated light dose of 500 mJ/ ^cm2 to form a cured film.
2) Adhesive strength: The prepared adhesive sheet was pressed against a stainless steel plate by a 2 kg roller in one reciprocating motion, cut into a width of 25 mm, and measured by pulling at 180° at room temperature (23° C.) and at a speed of 200 mm/min.
3) Adhesive residue: The stainless steel plate used in the measurement in 2) was visually inspected and touched to confirm whether any adhesive remained.

[Example 1]
In a flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen inlet tube, 336 parts of HDI (manufactured by Tosoh Corporation, trade name hexamethylene diisocyanate) as the isocyanate compound (a), 1000 parts of Exenol 1020 (manufactured by AGC Corporation, trade name polypropylene glycol with a molecular weight of 1000) as the polyol (b) were charged, and the temperature was raised to 90 ° C., and the reaction was allowed to proceed for 8 hours while keeping the temperature. After confirming that the NCO% was saturated, 23.2 parts of BHEA (manufactured by Nippon Shokubai Co., Ltd., trade name 2-hydroxyethyl acrylate) as the hydroxyl group-containing (meth)acrylate (c) and 66.6 parts of butyl alcohol as the aliphatic alcohol (d) were charged, and the reaction was allowed to proceed for 7 hours while keeping the temperature, and IR was measured to confirm that the isocyanate group had disappeared, to obtain an active energy ray-curable resin composition. The molar ratio of the hydroxyl group-containing (meth)acrylate to the aliphatic alcohol (d) was 1/9, and the aliphatic alcohol had 4 carbon atoms.

[Example 2]
In a flask similar to that of Example 1, 500 parts of MDI (manufactured by Tosoh Corporation, trade name diphenylmethane diisocyanate) as the isocyanate compound (a), 2000 parts of Exenol 2020 (manufactured by AGC Corporation, trade name polypropylene glycol with a molecular weight of 2000) as the polyol (b) were charged, and the temperature was raised to 90 ° C., and the reaction was allowed to proceed for 8 hours while keeping the temperature. After confirming that the NCO% was saturated, 46.4 parts of BHEA (manufactured by Nippon Shokubai Co., Ltd., trade name 2-hydroxyethyl acrylate) as the hydroxyl group-containing (meth)acrylate (c) and 297.6 parts of Conol 1275 (manufactured by New Japan Chemical Co., Ltd., trade name lauryl alcohol) as the aliphatic alcohol (d) were charged, and the reaction was allowed to proceed for 7 hours while keeping the temperature, and IR was measured to confirm that the isocyanate group had disappeared, to obtain an active energy ray-curable resin composition. The molar ratio of the hydroxyl group-containing (meth)acrylate to the aliphatic alcohol (d) was 2/8, and the aliphatic alcohol had 12 carbon atoms.

[Comparative Example 1]
In a flask similar to that of Example 1, 444 parts of Desmodur I (manufactured by Sumika Covestro Urethane Co., Ltd., trade name isophorone diisocyanate) as the isocyanate compound (a), 1000 parts of Exenol 1020 (manufactured by AGC Corporation, trade name polypropylene glycol with a molecular weight of 1000) as the polyol (b) were charged, and the temperature was raised to 90 ° C., and the mixture was allowed to react for 8 hours. After confirming that the NCO% was saturated, 232 parts of BHEA (manufactured by Nippon Shokubai Co., Ltd., trade name 2-hydroxyethyl acrylate) as the hydroxyl group-containing (meth)acrylate (c) were charged, and the mixture was allowed to react for 7 hours while keeping the temperature, and the IR was measured to confirm that the isocyanate group had disappeared, to obtain an active energy ray-curable resin composition. The molar ratio of the hydroxyl group-containing (meth)acrylate and the aliphatic alcohol (d) was 10/0.

[Comparative Example 2]
In a flask similar to that of Example 1, 336 parts of HDI (manufactured by Tosoh Corporation, trade name hexamethylene diisocyanate) as the isocyanate compound (a) and 1000 parts of Exenol 1020 (manufactured by AGC Corporation, trade name polypropylene glycol with a molecular weight of 1000) as the polyol (b) were charged, and the temperature was raised to 90°C and the reaction was allowed to proceed for 8 hours. After confirming that the NCO% was saturated, 46.4 parts of BHEA Corporation (manufactured by Nippon Shokubai Co., Ltd., trade name 2-hydroxyethyl acrylate) as the hydroxyl group-containing (meth)acrylate (c) and 432 parts of Conol 30SS (manufactured by New Japan Chemical Co., Ltd., trade name stearyl alcohol) as the aliphatic alcohol (d) were charged, and the reaction was allowed to proceed for 7 hours by keeping the temperature, and IR was measured to confirm that the isocyanate group had disappeared, to obtain an active energy ray-curable resin composition. The molar ratio of the hydroxyl group-containing (meth)acrylate to the aliphatic alcohol (d) was 2/8, and the aliphatic alcohol had 18 carbon atoms.

The evaluation results for Examples 1-2 and Comparative Examples 1-2 are shown in Table 1.

From Table 1, we can see that good adhesive strength can be obtained by reacting aliphatic alcohols with 4 to 12 carbon atoms with a ratio of (c)/(d) = 1/9 to 2/8 using a general urethane acrylate that does not exhibit adhesive strength.

Claims (4)

The resin composition for active energy ray-curable pressure-sensitive adhesives comprises as its constituent a urethane (meth)acrylate resin obtained by reacting a polyisocyanate compound (a) having two or more isocyanate groups per molecule, at least one polyol (b) selected from polyester polyols, polycaprolactone polyols, polyether polyols, and polycarbonate polyols, a hydroxyl group-containing (meth)acrylate (c), and an aliphatic alcohol (d) which is butyl alcohol, such that the sum of the isocyanate groups of the isocyanate compound (a) and the hydroxyl groups of the polyol (b), the hydroxyl group-containing (meth)acrylate (c), and the aliphatic alcohol (d) is equal, and the molar ratio of the hydroxyl group-containing (meth)acrylate (c) to the aliphatic alcohol (d) is 1/9 to 2/8. The resin composition for active energy ray-curable adhesives according to claim 1, characterized in that the polyol (b) has a molecular weight of 1,000 to 3,000. The active energy ray-curable adhesive resin composition according to claim 1 or 2, characterized in that the hydroxyl group-containing (meth)acrylate (c) is 2-hydroxyethyl acrylate. An adhesive sheet obtained by coating a paper or film substrate with the active energy ray-curable adhesive resin composition according to any one of claims 1 to 3.