JPH0841434A - Acrylic adhesive composition - Google Patents

Abstract

PURPOSE:To obtain the solution type acrylic adhesive composition capable of being cured at low temperatures in a short time and excellent in the balance of physical properties. CONSTITUTION:The acrylic adhesive composition comprises 100 pts.wt. of an acrylic copolymer comprising 60-99.9wt.% (based on the whole amount of monomers) of one or more (meth)acrylate esters of a formula: CH2=CR<1>= COOR<2> (R<1> is hydrogen or methyl group; R<2> is 4-14C alkyl group), 1-20 pts.wt. of a 2-12C low molecular compound having one or more carboxyl groups in the molecule or 5-20 pts.wt. of a tackifying resin having one or more carboxyl groups and one or more abietine skeletons in the molecule, and 0.05-3 pts.wt. of a multifunctional carbodiimide compound.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acrylic pressure-sensitive adhesive composition used for pressure-sensitive adhesive layers such as pressure-sensitive adhesive tapes, sheets and labels.

[0002]

2. Description of the Related Art In recent years, acrylic pressure-sensitive adhesives have been widely used in place of natural rubber-based or synthetic rubber-based pressure-sensitive adhesives because of their excellent balance of physical properties and good durability. Further, in order to improve the creep resistance of the acrylic pressure-sensitive adhesive, it is well known that the base polymer of the acrylic pressure-sensitive adhesive is made into a three-dimensional stitch structure by using a crosslinking agent or the like. And as this crosslinking agent, Japanese Patent Publication No. 5-6
It is common to use an isocyanate compound as described in Japanese Patent No. 0511, but in this case, since the curing rate is slow, it must be cured for 3 days to 1 week after coating the adhesive. For example, there is a problem that adhesive tapes cannot be shipped.

[0003]

In order to solve the above problems, instead of isocyanate as a cross-linking agent, as described in JP-A-63-91356 and JP-A-63-233965. It is possible to increase the curing rate by using a polyfunctional carbodiimide compound. By the way, when a polyfunctional carbodiimide compound is used, the curing is extremely fast, there is a problem that the pot life is too short, such as coating on the article to be coated due to gelation immediately after stirring, and the water-dispersed pressure-sensitive adhesive composition. Only applicable.

In view of the above-mentioned drawbacks of the prior art, it is an object of the present invention to provide a solvent-type acrylic pressure-sensitive adhesive composition which can be cured at low temperature in a short time and has an excellent physical property balance.

[0005]

The acrylic pressure-sensitive adhesive composition of the present invention has a general formula CH ₂ = CR ¹ = COOR ² (wherein R is
¹ is hydrogen or a methyl group, and R ² is an alkyl group having 4 to 14 carbon atoms, respectively)
Acrylic copolymer (A) containing 60 to 99.9% by weight of acrylic acid ester and 0.1 to 5% by weight of carboxyl group-containing monomer as essential components in the total amount of monomers, 1 in the molecule
A low molecular weight compound having 2 to 12 carbon atoms (B) or a tackifying resin (C) having at least one carboxyl group and an abietin skeleton in the molecule, and a polyfunctional carbodiimide compound (D). Contains.

The above general formula CH ₂ = CR ¹ = COOR ² (wherein R ¹ is hydrogen or a methyl group, R ² is a carbon number of 4 to 14)
Examples of the (meth) acrylic acid ester represented by (indicating each alkyl group of) are butyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, and lauryl methacrylate. When the content of this (meth) acrylic acid ester is less than 60% by weight in the total amount of the monomers, the cohesive force of the obtained pressure-sensitive adhesive is large and the adhesiveness at low temperature is poor, and when it exceeds 99.9% by weight, conversely Since the cohesive force becomes low and the creep resistance becomes poor, it is necessary to be in the range of 60 to 99.9% by weight as described above.

Further, as the carboxyl group-containing monomer, (meth) acrylic acid, maleic acid, fumaric acid,
Itaconic acid / comb, monoesters of these dicarboxylic monomers, or their acid anhydrides, carboxyethyl acrylate, 2-hydroxyethyl (meth)
Examples thereof include acrylates to which a dicarboxylic acid such as succinic acid or o-phthalic acid is added. If the carboxyl group-containing monomer is less than 0.1% by weight in the total amount of the monomers, the curing rate will be too slow, and if it exceeds 5% by weight, the curing rate will be too fast.
It is necessary to be in the range of 5 wt%.

The acrylic copolymer (A) contains, in addition to the above-mentioned monomers, styrene, vinyl acetate and ethyl (meth).
Acrylics, Methyl (meth) acrylates and other moderately polar monomers, (meth) acrylamides, N-
Substituted acrylamides such as isopropyl acrylamide, cyclic amides such as N-vinylpyrrolidone and acryloylmorpholine, and highly polar monomers having a hydroxyl group such as 2-hydroxyethyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate are used together. It may be polymerized. It should be noted that such a copolymerizable monomer should be 40% by weight or less based on all monomers. This is because if it exceeds 40% by weight, the cohesive force of the obtained pressure-sensitive adhesive becomes too high.

The acrylic copolymer (A) is required to have a weight average molecular weight of 200,000 to 1,500,000. If the weight average molecular weight is less than 200,000, the curing rate will be slow, and the required physical properties as an adhesive will not be obtained. If it exceeds 1.5 million, the curing rate will be fast and the solution viscosity will be too high, resulting in poor productivity. Because it will be. The preferred weight average molecular weight range is 300,000 to 700,000.

The low molecular weight compound (B) having 2 to 12 carbon atoms having at least one carboxyl group in the molecule is
Monofunctional carboxy group-containing compounds such as acetic acid, propionic acid, 2-ethylhexanoic acid, lauric acid, (meth) acrylic acid, benzoic acid, maleic acid, fumaric acid, phthalic acid,
Alternatively, a bifunctional carboxy group-containing compound such as an anhydride thereof may be used.

The content of the low molecular weight compound (B) must be 1 to 20 parts by weight based on 100 parts by weight of the acrylic copolymer (A). This is because if it is less than 1 part by weight, the effect of suppressing the curing rate is not sufficient, and if it exceeds 20 parts by weight, the curing inhibitory property becomes too strong, and there is a possibility that satisfactory physical properties as an adhesive cannot be obtained.

The tackifying resin (C) having at least one carboxyl group and an abietin skeleton in the molecule is
For example, abietic acid, dehydroabietic acid, tetrahydroabietic acid, a mixture of these, so-called disproportionated rosin, hydrogenated rosin, polymerized rosin, and the like. It may be an esterified product with alcohol having an acid value.

The content of the tackifier (C) must be 5 to 20 parts by weight based on 100 parts by weight of the acrylic copolymer (A). This is because if it is less than 5 parts by weight, the effect of suppressing the curing rate is not sufficient, and if it exceeds 20 parts by weight, the curing inhibitory property becomes too strong, and there is a possibility that satisfactory physical properties as an adhesive cannot be obtained.

The polyfunctional carbodiimide compound (D) is, for example, a compound represented by the following formula: -N =
Examples thereof include compounds having two or more C = N- groups in the molecule.

[0015]

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In the formula, R ¹ , R ² and R ³ may be the same or different, and represent an alkyl group having 1 to 12 carbon atoms, and R ⁴ and R ⁵ are the same or different. And hydrogen, alkyl (including cycloalkyl) aryl, aralkyl, alkaryl,
Heterocyclic, cyano, nitro, halo, alkyl sulfide, dialkylaminoalkyl, silane, alkoxy and aryloxy groups and substituted groups thereof, Z is a compound suitable for functioning as a branching site. Represents a residue, and a, b and c represent 0 or an integer of 1 to 12.

The content of the polyfunctional carbodiimide compound (D) must be 0.05 to 3 parts by weight with respect to 100 parts by weight of the acrylic copolymer (A). 0.
This is because if it is less than 05 parts by weight, the expected effect of improving cohesive force cannot be obtained, and if it exceeds 3 parts by weight, the cohesive force becomes too strong and the peeling force decreases.

The acrylic adhesive composition of the present invention may contain an adhesive resin of C5 petroleum resin, C9 petroleum resin, rosin ester and terpene phenol.

[0019]

In the acrylic pressure-sensitive adhesive composition of the present invention,
The polyfunctional carbodiimide compound (D) not only reacts between the carboxyl groups of the polymer, but also has a low molecular weight compound (B) having 2 to 12 carbon atoms and one or more carboxyl groups in the molecule or one in the molecule. Since it reacts with the above-mentioned tackifying resin (C) having a carboxyl group and an abietin skeleton, the proportion of the reaction directly involved in the cross-linking is relatively small, the reaction rate is suppressed, and the obtained acrylic pressure-sensitive adhesive composition The pot life of goods becomes moderate.

[0020]

EXAMPLES Examples of the present invention will be described in detail below. The parts by weight are simply referred to as parts.

Examples 1 to 16 and Comparative Examples 1 to 15 (Acrylic Copolymer) Monomers and the like as shown in Table 1 and 80 parts of ethyl acetate as a solvent, a stirrer, a reflux condenser and a thermometer. A five-necked flask equipped with a dropping funnel and a nitrogen gas inlet was charged, stirred and dissolved, and then purged with nitrogen gas for about 30 minutes to eliminate oxygen dissolved in the monomer solution. Then, the air in the flask is replaced with nitrogen gas, and the temperature is maintained at 70 ° C., 0.03 parts of benzoyl peroxide as a thermal polymerization initiator is dissolved in a part of ethyl acetate, and the mixture is added dropwise by a dropping funnel. After the reaction started, the reaction was carried out at the same temperature for 10 hours to obtain acrylic copolymer solutions A to H.

The weight average molecular weight (Mw) of the obtained acrylic copolymer solutions A to H was detected by gel permeation chromatography (GPC) using standard crosslinked polystyrene as a standard and tetrahydrofuran as a separating agent. Was measured using a refractometer. The results are shown in Table 1.

[0023]

[Table 1]

(Preparation of Acrylic Pressure-Sensitive Adhesive Composition) The above acrylic copolymer solution was diluted with toluene so that the solid content was 50% by weight, and then a cross-linking agent was prepared according to the composition shown in Tables 2-5. As a polyfunctional carbodiimide compound (manufactured by Union Carbide Co., Ukerling XL-29S
E and a solid content of 50%) were mixed to obtain an acrylic pressure-sensitive adhesive composition.

(Preparation of Test Pieces for Measuring Physical Properties) The obtained solutions of each acrylic pressure-sensitive adhesive composition were coated on a silicone-treated release paper (polyethylene terephthalate film having a thickness of 38 μm) with an applicator, and 110 It was dried at 5 ° C. for 5 minutes to form a pressure-sensitive adhesive layer having a thickness of 65 μm.

Next, the adhesive on the release paper was applied to a basis weight of 1
It was transferred to both sides of 4 g of non-woven fabric and cured at 40 ° C. for 24 hours to obtain a double-sided tape, which was used as a sample for measurement of adhesive physical properties. In addition,
At the time of measuring the adhesive physical properties, a polyethylene terephthalate film having a thickness of 38 μm was lined on one surface to form a single-sided adhesive tape.

(Measurement of Adhesive Physical Properties) Adhesive physical properties of each of the above sample pieces were measured as follows. SP adhesive strength: According to JIS Z0237, the adhesive tape of the above sample is 20 m on a stainless plate (SUS304).
18 m width after bonding and leaving at 23 ℃ for 20 minutes
The 0 ° peel strength was measured. The tensile speed is 300 mm
/ Min. PP adhesive strength: In accordance with JIS Z0237, a PP (polypropylene) plate is coated with the adhesive tape of the above sample of 20 mm.
Width, and leave at 23 ℃ for 20 minutes, then 180
The peel strength was measured. The pulling speed is 300 mm /
Minutes Holding power (80 ℃): At room temperature, stainless steel plate (SUS3
The adhesive tape of the above sample was adhered to 04) in a size of 20 × 20 mm, left at 23 ° C. for 20 minutes, and then placed in an area of 80 ° C.
It was left for 0 minutes, a load of 1 kg was applied, and the shift length (mm) after 1 hour was measured. When the adhesive tape dropped within 1 hour, the time was measured. The above measurement results are shown in Tables 2-5.

[0028]

[Table 2]

[0029]

[Table 3]

[0030]

[Table 4]

[0031]

[Table 5]

[0032]

As described above, the acrylic pressure-sensitive adhesive composition of the present invention comprises 100 parts by weight of an acrylic copolymer and 2 to 1 carbon atoms having at least one carboxyl group in the molecule.
1 to 20 parts by weight of the low molecular weight compound 2 or 5 to 20 parts by weight of a tackifying resin having one or more carboxyl groups and an abietin skeleton in the molecule, and 0.05 to 3 parts by weight of a polyfunctional carbodiimide compound. Therefore, the crosslinking reaction rate by the polyfunctional carbodiimide compound is suppressed, the pot life becomes appropriate, it can be used as a solvent-type pressure-sensitive adhesive, and various adhesive properties are excellent.

Claims (2)

[Claims] 1. A general formula CH ₂ = CR ¹ = COOR ² (wherein
R ¹ represents hydrogen or a methyl group, and R ² represents an alkyl group having 4 to 14 carbon atoms), and 60 to 99.
100 parts by weight of an acrylic copolymer having 9% by weight and 0.1 to 5% by weight of a carboxyl group-containing monomer as an essential component and having a weight average molecular weight of 200,000 to 1,500,000, and having one or more carboxyl groups in the molecule An acrylic pressure-sensitive adhesive composition comprising 1 to 20 parts by weight of a low molecular weight compound having 2 to 12 carbon atoms and 0.05 to 3 parts by weight of a polyfunctional carbodiimide compound. 2. The general formula CH ₂ = CR ¹ = COOR ² (wherein
R ¹ represents hydrogen or a methyl group, and R ² represents an alkyl group having a carbon number of 4 to 14), and one or more (meth) acrylic acid ester represented by 60 to 99.
100 parts by weight of an acrylic copolymer having 9% by weight and 0.1 to 5% by weight of a carboxyl group-containing monomer as an essential component and having a weight average molecular weight of 200,000 to 1,500,000, one or more carboxyl groups and abietin in the molecule An acrylic pressure-sensitive adhesive composition comprising 5 to 20 parts by weight of a tackifying resin having a skeleton and 0.05 to 3 parts by weight of a polyfunctional carbodiimide compound.