JPH01261479A - Pressure-sensitive adhesive - Google Patents

Abstract

PURPOSE:To improve the adhesive power to an adherend of a low energy surface, by incorporating a tackifier resin, as required, into a specified acrylic copolymer having units of an acrylic ester of a long-chain alkyl. CONSTITUTION:A (meth)acrylic ester of 15-20C alkyl and a (meth)acrylic ester of 2-14C alkyl in a prescribed ratio, and if necessary, a modifier monomer comprising a monoethylenically unsaturated compound (e.g., acrylic acid) copolymerizable with these acrylic alkyl esters are copolymerized to give an acrylic copolymer which has a glass transition point of -23 deg.C or lower and consists mainly of 5-25wt.% units of an acrylic ester of a long-chain alkyl, i.e., a 15-20C alkyl, and 95-75wt.% units of an acrylic ester of a 2-14C alkyl, wherein 1/3 or loss of the latter units are replaced by said mondifier monomer if required. 100 pts.wt. this copolymer is mixed with 100 pts.wt. or less tackifier resin (e.g., terpene resin) as required.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention consists of an acrylic copolymer containing an acrylic ester having a long-chain alkyl group as a copolymerization component, and is suitable for use on adherends with low energy surfaces. This invention relates to pressure-sensitive adhesives that exhibit adhesive strength.

Conventional technology Conventionally, low-molecular-weight acrylic alkyl ester copolymers without crosslinkable functional groups have been used as pressure-sensitive adhesives that exhibit good adhesion to adherends with low-energy surfaces made of polyolefins such as polyethylene and polypropylene. A mixture of acrylic alkyl ester copolymer and an acrylic alkyl ester copolymer into which a crosslinkable functional group has been introduced has been proposed (Japanese Patent Publication No. 61
-21980 Publication).

Problems to be Solved by the Invention The pressure-sensitive adhesive described above is made by blending a crosslinking agent with it to form a crosslinked structure to make it stick. There is a problem in that the ester copolymer bleeds into the adhesive interface, resulting in a decrease in adhesive strength. Further, there was a problem that the copolymer caused a decrease in cohesive force.

Means for Solving the Problems The present inventors have overcome the above-mentioned problems and have developed an adhesive that has excellent adhesive strength even on adherends with low-energy surfaces made of polyolefins, fluororesins, etc., and adherends made of various other materials. As a result of intensive research to develop a pressure-sensitive adhesive that exhibits
Surprisingly, the inventors have discovered that the object can be achieved by using a copolymer using an acrylic ester having a long-chain alkyl group, and have completed the present invention.

That is, in the present invention, the alkyl group has 15 to 20 carbon atoms.
The main component is an acrylic alkyl ester that contains 5 to 25% by weight of acrylic long-chain alkyl ester units, the alkyl group has 2 to 14 carbon atoms, and has a glass transition point of 123°C or less. 100 parts by weight of polymer,
The present invention provides a pressure-sensitive adhesive containing 0 to 100 parts by weight of a tackifying resin.

By copolymerizing an acrylic long-chain alkyl ester with a working alkyl group having 15 to 20 carbon atoms at a predetermined ratio,
The adhesion of low energy surfaces to adherends can be improved without the usual reduction in adhesion to adherends, and the bleed problem is eliminated. Also,
It is possible to avoid the introduction of the long-chain alkyl component from causing a decrease in cohesive force. On the other hand, the glass transition point is 12
By using an acrylic copolymer with a temperature of 3°C (250°K) or less, a polymer exhibiting good adhesive strength can be obtained.

As mentioned above, even when copolymerizing an acrylic ester with a long-chain alkyl group, a polymer with excellent adhesive properties can be obtained, which is contrary to the adhesive properties of such long-chain alkyl compounds. This was unexpected since it has been used as a related agent for imparting peelability or mold release properties.

In addition, the acrylic copolymer can be modified to have a functional group such as a carboxyl group using a modifying monomer if necessary.
It is also possible to make it crosslinkable, to improve its affinity for adherends made of polar materials such as glass and metals, or to improve its cohesive force. Also,
If necessary, a tackifying resin may be added to improve cohesive force, holding power or adhesion persistence, and wettability to adherends.

Examples of Constituent Elements of the Invention The acrylic copolymer used in the present invention is an acrylic long-chain alkyl ester in which the alkyl group has 15 to 20 carbon atoms, and an acrylic alkyl ester in which the alkyl group has 2 to 14 carbon atoms. is the component.

Examples of acrylic long-chain alkyl esters in which the alkyl group has 15 to 20 carbon atoms include n-pentadecyl group, n-hexadecyl group, n-heptadecyl group, n-octadecyl group, n-nonadecyl group, and n-eicosyl group. Examples include long-chain alkyl esters of acrylic acid or methacrylic acid consisting of groups, etc. Note that the long-chain alkyl group may be a branched one.

Examples of the acrylic alkyl ester having an alkyl group having 2 to 14 carbon atoms include those known in the art and used in conventional acrylic pressure sensitive adhesives.

Typical examples include alkyl acrylic or methacrylic acids in which the alkyl group is ethyl, propyl, butyl, 2-ethylhexyl, isooctyl, isononyl, isodecyl, dodecyl, lauryl, tridecyl, etc. I can give you ester.

The acrylic copolymer may be one obtained by copolymerizing one fI or two or more of the above-mentioned components.

The content of the acrylic long-chain alkyl ester unit in the acrylic copolymer needs to be 5 to 25% by weight, and preferably 10 to 20% by weight. If its content is less than 5% by weight, it will have poor adhesion to adherends on low-energy surfaces, and if it exceeds 25% by weight, it will have poor adhesion to adherends other than low-energy surfaces. The remaining 95 to 75% by weight of the acrylic copolymer may consist only of acrylic alkyl ester units whose alkyl groups have 2 to 14 carbon atoms, or may contain modifying monomer units in addition to that. good. However, from the viewpoint of adhesive properties, the content of the modifying monomer unit is suitably 1/3 or less of the acrylic alkyl ester unit in which the alkyl group has 2 to 14 carbon atoms based on the weight.

As the modifying monomer, a monoethylenically unsaturated compound that can be copolymerized with the above-mentioned acrylic (long chain) alkyl ester is used. Typical examples include acrylic acid, methacrylic acid, itaconic acid, methyl acrylate, methyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, and 2-hydroxypropyl methacrylate. , N-
Examples include methylol acrylamide, acrylonitrile, methacrylonitrile, glycidyl acrylate, glycidyl methacrylate, vinyl acetate, and styrene. The modifying monomer to be used is appropriately determined depending on the purpose of modification, such as imparting crosslinking properties, improving cohesive force, or improving wettability and adhesive strength with an adherend.

The acrylic copolymer of the present invention may be prepared by a known method such as a solution polymerization method, a bulk polymerization method, an emulsion polymerization method, or a pearl polymerization method. When the components used have poor compatibility, a solution polymerization method or a bulk polymerization method is preferable because it is easy to obtain a uniform copolymer.

The solution polymerization method is one or two of hydrocarbon systems such as heptane, hexane, benzene, toluene, acetone, methyl ethyl ketone, ethyl acetate, methanol, and ethanol, aromatic systems, ketone systems, ester systems, alcohol systems, etc. A conventional method of copolymerization using a polymerization initiator such as azobisisobutyronitrile or benzoyl peroxide in the presence of more than one type of solvent may be used.

The acrylic copolymer used in the present invention has a glass transition point of 123°C or lower. If the glass transition point is higher than this, adhesive strength may be poor.

In addition, when obtaining an adhesive tape, one having a weight average molecular weight of 100,000 or more is preferably used from the viewpoint of physical properties such as cohesive force and strength.

A tackifying resin may be added to the pressure-sensitive adhesive of the present invention, if necessary. The tackifying resin is blended for the purpose of improving adhesive strength, cohesive strength, etc., and the blending amount is suitably 100 parts by weight or less per 100 parts by weight of the acrylic copolymer.

As the tackifier resin, known ones can be used. Typical examples include rosin resins, terpene resins, petroleum resins usually having 5 to 9 carbon atoms, xylene resins, phenol resins, coumaron resins, etc.
Among them, rosin-based resins and terpene-based resins are preferably used.

The pressure-sensitive adhesive of the present invention may include fillers, softeners,
Additives such as plasticizers and colorants may be added. Further, in order to further increase the cohesive force, it may be possible to perform crosslinking treatment. Crosslinking methods include thermal crosslinking methods that use crosslinking agents such as peroxides, polyfunctional isocyanates, epoxy compounds, melamine compounds, and metal compounds, as well as heat crosslinking methods that use ultraviolet rays, electron beams, gamma rays, etc. A known crosslinking method for acrylic pressure-sensitive adhesives can be used, such as a crosslinking method using radiation irradiation. In addition, when using a crosslinking method using ultraviolet irradiation or the like, a method of copolymerizing a modifying monomer component having a photosensitive functional group such as an acryloyl group or an epoxy group in an acrylic copolymer can also be adopted.

The pressure-sensitive adhesive of the present invention can be used in known pressure-sensitive adhesive applications such as adhesive tapes and adhesive sheets as packaging materials, masking materials, electrical insulation materials, surface protection materials, anti-corrosion materials, bonding materials, etc. It can be preferably used for.

Effects of the Invention Since the pressure-sensitive adhesive of the present invention is composed of an acrylic copolymer containing long-chain acrylic alkyl ester units, it can be applied to adherends made of various materials including adhesive bonds on low-energy surfaces. Excellent adhesive strength. Moreover, since the long-chain alkyl component is chemically bonded in the polymer, it does not bleed, does not contaminate the adherend, and does not reduce adhesive strength. Therefore, the pressure sensitive adhesive of the present invention has excellent stability in adhesive properties.

Examples Example 1 72 parts of isononyl acrylate (parts by weight, the same applies hereinafter),
36 parts of ethyl acrylate, 3 parts of acrylic acid, and 12 parts of octadecyl acrylate were placed in a reaction vessel equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser, and 0.48 parts of benzoyl peroxide was added. Obtained by solution polymerization at 60 to 70°C in a solvent of 216 parts of ethyl acetate while substituting with nitrogen, weight average molecular weight 1.2 million, glass transition point -56°C
In a 35% by weight ethyl acetate solution containing an acrylic copolymer, 45 parts of an aromatic modified terpene hydrocarbon resin (softening point 110°C) and 1.2 parts of a trifunctional isocyanate (per 100 parts of the copolymer) were added. Add crosslinking agent) and mix uniformly.
A solution of the pressure sensitive adhesive of the invention was obtained.

Example 2 A solution of the pressure-sensitive adhesive of the present invention was obtained in accordance with Example 1, except that the aromatic modified terpene hydrocarbon resin was not blended.

Example 3 A solution of the pressure-sensitive adhesive of the present invention was obtained in the same manner as in Example 11' except that the aromatic modified terpene hydrocarbon resin and the trifunctional 11-isocyanate were not blended.

Example 4 A portion of a mixture consisting of 77 parts of butyl acrylate, 4 parts of acrylic acid, 20 parts of octadecyl methacrylate, 0.2 parts of azobisui, tributyronitrile, and 0.05 parts of lauryl mercaptan was poured into lO% ) was placed in a reaction vessel equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser, and the mixture was replaced with nitrogen for 40 minutes while stirring, and then the remainder of the mixture was added dropwise to the reaction system using a dropping funnel. 20 parts by weight of 100 parts of an acrylic copolymer with a weight average molecular weight of 650,000 and a glass transition point of -42°C obtained by bulk polymerization at 83°C for 4 hours. 6 Pentaerythritol ester of disproportionated rosin (softening point 120°C) 3 in ethyl acetate solution
0 parts and 0.08 parts of a tetrafunctional epoxy crosslinking agent were added and mixed uniformly to obtain a solution of the pressure sensitive adhesive of the present invention.

Example 5 A solution of the pressure-sensitive adhesive of the present invention was obtained in accordance with Example 4, except that pentaerythritol ester of disproportionated rosin was not blended.

Example 6 85 parts of 2-ethylhexyl acrylate, 5 parts of methyl acrylate, 10 parts of vinyl acetate, 8 parts of hexadecyl methacrylate, 0.1 part of azobisisobutyronitrile, and 180 parts of ethyl acetate. Per 100 parts of the copolymer was added to a 37% by weight ethyl acetate solution containing an acrylic copolymer with a weight average molecular weight of 11.32 million and a glass transition point of -50°C obtained by solution polymerization according to Example 1. 25 parts of polymerized rosin (softening point: 95° C.) was added and mixed uniformly to obtain a solution of the pressure sensitive adhesive of the present invention.

Comparative Example 1 A pressure-sensitive adhesive solution was obtained according to Example 1 using an acrylic copolymer containing no acrylic long-chain alkyl ester, having a weight average molecular weight of 11,310,000 ff, and a glass transition point of -48°C. The above acrylic copolymer was prepared in the same manner as in Example 1 except that octadecyl acrylate was not used.

Comparative Example 2 A pressure-sensitive adhesive solution was obtained in accordance with Comparative Example 1, except that the aromatic modified terpene hydrocarbon resin was not blended.

Comparative Example 3 A pressure-sensitive adhesive solution was obtained according to Example 4 using an acrylic copolymer containing no acrylic long-chain alkyl ester, having a weight average molecular weight of 690,000, and a glass transition point of -50°C. The above acrylic copolymer was prepared in the same manner as in Example 4 except that octadecyl methacrylate was not used.

Comparative Example 4 A pressure-sensitive adhesive solution was obtained in accordance with Comparative Example 3, except that pentaerythritol ester of disproportionated rosin was not blended.

Comparative Example 5 An acrylic copolymer with a weight average molecular weight of 710,000 and a glass transition point of -35°C obtained by using 30 parts of octadecyl methacrylate was used (the pressure sensitive adhesive was used in accordance with Example 4). The solution was recorded.

Comparative Example 6 A pressure-sensitive adhesive solution was obtained in accordance with Comparative Example 5, except that pentaerythritol ester of disproportionated rosin was not blended.

Comparative Example 7 (i) 72 parts of isononyl acrylate, 36 parts of ethyl acrylate, and 3 parts of acrylic acid were mixed in a solvent of 200 parts of ethyl acetate containing 0.4 part of hensyl peroxide, while substituting with nitrogen for 60 to 70% A 35.6% by weight ethyl acetate solution containing an acrylic copolymer (viscosity 13
0 voices) was obtained. The intrinsic viscosity of this acrylic copolymer at 30°C using acetone as a solvent was 92.

(ii) 72 parts of isononyl acrylate and 36 parts of ethyl acrylate were dissolved in a solvent of 200 parts of ethyl acetate containing 0.4 parts of benzoyl peroxide and 0.4 parts of lauryl mercaptan at 60 to 70°C while purging with nitrogen. A 35% by weight ethyl acetate solution (viscosity: 16 voices) containing an acrylic copolymer was obtained by polymerization. This acrylic copolymer has an intrinsic viscosity of 0.5 at 30°C using acetone as a solvent.
2 and had a low molecular weight.

100 parts of the acrylic copolymer solution of (1) above,
50 parts of the acrylic copolymer solution of (ii), 16 parts of aromatic modified terpene hydrocarbon resin (softening point 110°C),
0.43 part of trifunctional isocyanate was mixed uniformly to obtain a pressure sensitive adhesive solution.

The pressure-sensitive adhesive solutions obtained in the evaluation test examples and comparative examples were placed on a polyester film (thickness 25 μm) so that the thickness after drying was 50 μm.
μ111) and heat-dried at 130° C. for 5 minutes to prepare an adhesive tape, which was subjected to the following test.

[Adhesive strength J 20 + 1℃, 65% Fl, II, length 150mm, cut piece of lf1M20 adhesive tape was placed on an adherend with a smooth and clear surface once with a rubber roller weighing 2 kg. The adhesive force (180 degrees beer, tensile speed 300 rIn/min) was measured after being left for 30 minutes.

A stainless steel plate (S plate) and a polypropylene plate (P plate) were used as adherends.

[Cohesive force 1] Cut a piece of adhesive tape with a weight of 2 on the same stainless steel plate as above so that the adhesion area has a length of 2On++a and a width of 10mm.
1 kg of rubber roller back and forth once, and after leaving it for 30 minutes, one end of the stainless steel plate was fixed, and a load of 500 g was applied to the free end of the piece of adhesive tape.
The time required for the adhesive tape piece to peel off was measured. The test was conducted in an atmosphere of 30°C or 80°C.

The above test results are shown in the table.

*: When adhesive remains on the adherend after crosslinking It can be seen that it exhibits great strength and has excellent cohesive force.

In particular, as is clear from the comparison with Comparative Example 7, when it is crosslinked, it is possible to impart better cohesive force,
It can be seen that no adhesive remains at room temperature.

Patent applicant: Nitto Electric Industry Co., Ltd.

Claims (1)

[Claims] 1. Contains 5 to 25% by weight of acrylic long-chain alkyl ester units in which the alkyl group has 15 to 20 carbon atoms, and is mainly composed of acrylic alkyl ester units in which the alkyl group has 2 to 14 carbon atoms; Add 0 tackifying resin to 100 parts by weight of an acrylic copolymer with a transition point of -23°C or less.
A pressure-sensitive adhesive containing ~100 parts by weight.