JPH01271471A - Pressure-sensitive adhesive - Google Patents

Abstract

PURPOSE:To obtain a pressure-sensitive adhesive having improved adhesiveness to both a rough surface and a curved surface by using a specified acrylic copolymer as a base. CONSTITUTION:A polymerizable unsaturated group-terminated, carboxylic monomer (a) is polymerized with an alkyl acrylate (b) and, optionally, other copolymerizable monomers (c) to obtain an acrylic copolymer (A) composed of a main chain containing at least 50mol% units of an alkyl acrylate (wherein the alkyl is 14C or lower) and side chains each having a carboxyl group which is distant from the carbon atom of the main chain by at least three carbon atoms, and having a carboxyl group content of 4-50mol%, a weight-average MW>=200000, a shear storage modulus (at 20 deg.C and a frequency of 1Hz) of 200-1000kdyn/cm<2>. Component A is optionally mixed with a tackifier, a softener, a crosslinking agent, etc., (B).

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a pressure-sensitive adhesive that is made of a low modulus acrylic copolymer having a carboxyl group in its side chain and has excellent adhesion performance to rough and curved surfaces. .

BACKGROUND OF THE INVENTION There is a need for an acrylic pressure-sensitive adhesive that exhibits excellent adhesive performance even on rough and curved surfaces and that can be crosslinked.

Conventionally, acrylic pressure-sensitive adhesives that can be crosslinked are acrylic adhesives that are made by copolymerizing acrylic acid or methacrylic acid and introducing carboxyl groups into the main chain of a polymer whose main component is an acrylic acid alkyl ester. Those made of polymers were known.

However, although the cohesive force and adhesive force are improved by introducing acrylic acid or the like, there is a problem in that the adhesion performance to rough or curved surfaces is rather deteriorated.

Attempts have been made to introduce a hydroxyl group into the crosslinkable functional group, but the adhesion performance to curved surfaces is poor, and so far no product has been obtained that exhibits adhesion properties comparable to those introduced with a carboxyl group.

Means for Solving the Problems ′ As a result of extensive research in order to overcome the above problems, the present inventors have developed an acrylic copolymer with a low elastic modulus in which carboxyl groups have been introduced into the side chain moieties. The present invention has been made based on the discovery that this can be achieved.

That is, the present invention provides that a side chain having a carboxyl group branches from a main chain containing 50 mol% or more of acrylic acid alkyl ester units having an alkyl group having 14 or less carbon atoms, and the side chain has a carboxyl group in the side chain. is present through 3 or more carbons between it and the main chain carbon, the weight average molecular weight is 200,000 or more, and the content of carboxyl group units is 4 to 4.
50 mol% and a frequency of 1 Hz at 20°C
Shear storage modulus at 200-1000 K dy
The present invention provides a pressure-sensitive adhesive characterized by being made of an acrylic copolymer with ne/cd.

The desired purpose can be achieved by using an acrylic copolymer having the above structure in which a functional carboxyl group is introduced into the side chain portion and the modulus of elasticity is low. In other words, it is a pressure-sensitive adhesive that has improved cohesive strength and adhesive strength, has excellent adhesion performance on rough and curved surfaces, and is easy to cross-link, without impairing the properties unique to acrylic pressure-sensitive adhesives such as weather resistance. It was unexpected that, while exhibiting the same improvement in cohesive force and adhesive strength due to the introduction of carboxyl groups, there was no decrease in adhesive performance on rough and curved surfaces.

Examples of Constituent Elements of the Invention The acrylic copolymer used in the present invention has a main chain mainly composed of an acrylic alkyl ester having an alkyl group having 14 or less carbon atoms. The content of acrylic acid alkyl ester units in the main chain is 50
It is necessary that the amount is mol% or more. Its content is 50
If the amount is less than mol%, the resulting acrylic copolymer will have poor flexibility. In addition, the acrylic copolymer as a whole is 50 to 9
A content of 6 mol %, particularly 70 to 80 mol %, is suitable.

Further, the acrylic copolymer used in the present invention has a side chain containing a carboxyl group via three or more carbons between it and the main chain forming carbon. The side chain may have a molecular weight high enough to be called a graft polymer.

The content of carboxyl group units in the side chains needs to be 4 mol % or more in total in all side chains, based on the introduced units of the monomer having a carboxyl group. If the content is less than 4 mol %, the resulting pressure-sensitive adhesive will have poor adhesion performance to curved surfaces. The content of the acrylic copolymer as a whole is preferably 4 to 50 mol%, particularly 6 to 20 mol%.

The acrylic copolymer may contain 0 to 46 mol% of copolymerizable monomer units other than the above-mentioned components.

This copolymerizable monomer unit is introduced as necessary to make the adhesive properties of the acrylic copolymer more suitable for the adherend. If the amount exceeds mol%, the resulting acrylic copolymer may have poor flexibility and weather resistance.

As a method for preparing the acrylic copolymer that can be used in the present invention, for example, an acrylic acid alkyl ester, a monomer having a carboxyl group, and other copolymerizable monomers as necessary are prepared by a radical polymerization method or an anionic polymerization method. or a method of polymerizing a carboxyl group-containing monomer having a polymerizable unsaturated group at the terminal, an acrylic acid alkyl ester, and other copolymerizable monomers as necessary. It will be done.

In the latter case, the carboxyl group-containing monomer is introduced into the main chain via the terminal polymerizable unsaturated group, and as a result, the remainder of the carboxyl group-containing monomer forms a side chain.

As the acrylic acid alkyl ester, those having an argyl group having 14 or less carbon atoms are used in view of the flexibility of the resulting acrylic copolymer and the tack of the pressure-sensitive adhesive. Examples include alkyl esters of acrylic acid or methacrylic acid in which the alkyl group is a methyl group, ethyl group, butyl group, isoamyl group, 2-ethylhexyl group, isooctyl group, isononyl group, decyl group, dodecyl group, etc. It will be done. When only one type of acrylic acid alkyl ester is used, it is preferable that the alkyl group has a carbon number of 4 to 12, and when two or more types are used together, the average value of the alkyl groups is 4 to 12. A combination of these is preferred.

Examples of monomers having a carboxyl group that are mainly used when the above graft polymerization method is applied include acrylic acid, methacrylic acid, maleic acid, itaconic acid, and crotonic acid.

On the other hand, in the case of polymerization using a carboxyl group-containing monomer having a polymerizable unsaturated group at the terminal, examples of the carboxyl group-containing monomer include the general formula 2CH2=C(R)C
oo→(CH2,+; lCo0+; 1-H (however, R
is hydrogen or a methyl group, m is an integer of 2 to 1O, and n is an integer of 1 to 5. ) can be mentioned. The above carboxyl group-containing monomer can be obtained, for example, by reacting acrylic acid or methacrylic acid with a hydroxy acid or lactone.

Other carboxyl group-containing monomers having polymerizable unsaturated groups at their terminals include terminal carboxylated prepolymers with tertiary alcohol ester units of acrylic acid or methacrylic acid introduced, and epoxy compounds having polymerizable unsaturated groups. and the like in the presence of a catalyst such as a tertiary amine or a quaternary ammonium salt, and the product is hydrolyzed in the presence of an acid catalyst. in this case,
The tertiary alcohol ester unit is selectively hydrolyzed to introduce a carboxyl group. Note that the above hydrolysis can also be performed after the copolymerization treatment. Therefore, after the reaction product of the terminal carboxylated prepolymer and the epoxy compound having a polymerizable unsaturated group is copolymerized with an acrylic acid alkyl ester and other copolymerizable monomers as necessary, The acrylic copolymer that can be used in the present invention can also be prepared by a method of hydrolysis in the presence of an acid catalyst.

Copolymerizable monomers used as necessary include hydroxyl group-containing materials such as hydroxyethyl methacrylate and hydroxypropyl methacrylate; amide group-containing materials such as acrylamide, methacrylamide, diacetone acrylamide, and diacetone methacrylamide; acrylonitrile; nitrile group-containing materials such as methacrylate trile;
Glycidyl acrylate, glycidyl methacrylate, α-
Examples include vinyl monomers such as glycidyl group-containing substances such as glycidyl ethyl acrylate, aromatic compounds such as styrene and vinyltoluene, and ester compounds such as vinyl acetate and vinyl propionate.

The tertiary alcohol esters of acrylic acid and methacrylic acid that can be used to prepare the carboxyl group-containing monomer having a polymerizable unsaturated group at the terminal mentioned above include t-butyl acrylate, t-butyl methacrylate, 1,1
-dimethylpropyl acrylate, 1,1-dimethylpropyl methacrylate, 1,1-dimethylbutyl acrylate, 1,1-dimethylbutyl methacrylate, 1,
Examples include 1-diethylpropyl acrylate and 1.1-diethylbutyl methacrylate. In addition to the tertiary alcohol ester unit, the terminally carboxylated prepolymer may contain the above-mentioned acrylic acid alkyl ester unit and other copolymerizable monomer units. Further, as the epoxy compound having a polymerizable unsaturated group, the above-mentioned acrylic acid glycidyl ester and the like are used.

In addition to the above, the χ acrylic copolymer used in the present invention has a weight average molecular weight of 200,000 or more, preferably 30,000 or more.
10,000 to 2,000,000, and the shear storage modulus at a frequency of 1 Hz at 20°C is 200 to 1,000 Kdyne/c+j,
Preferably it is 300 to 900 K dyne/cj. If the weight average molecular weight is less than 200,000, the resulting pressure-sensitive adhesive will have poor cohesive force and poor adhesion performance to curved surfaces. In addition, its shear storage modulus is 200 K
Even if the pressure-sensitive adhesive is less than d y n e / cd, the resulting pressure-sensitive adhesive has poor cohesive force and poor adhesion performance to curved surfaces;
If it exceeds 00 Kdyne/cd, the adhesion performance to rough surfaces will be poor. In addition, the shear storage modulus is 1000Kdyne
The acrylic copolymer may contain a monomer unit having a carboxyl group in its main chain within a range not exceeding /cj.

When preparing the pressure-sensitive adhesive of the present invention, various materials may be blended as necessary. Typical examples of combination drugs include:
Tackifiers such as terpene-based, terpene-phenol-based, coumaron-indene-based, styrene-based, rosin-based, xylene-based, phenol-based, petroleum-based resins, adhesive resins that are liquid at room temperature, process oils, and polyesters. Examples include softeners made of plasticizers, polybutene, liquid rubber, etc., and crosslinking agents made of polyisocyanates, melamine resins, amine-epoxy resins, peroxides, metal chelate compounds, etc. The total amount of the tackifier and softener is preferably equal to or less than the amount of the acrylic copolymer, and the appropriate amount of the crosslinking agent is approximately 10 parts by weight or less per 100 parts by weight of the acrylic copolymer. It is. Various polymers such as acrylic polymers may be blended for the purpose of finely adjusting the adhesive properties. Other optional ingredients include, for example, antioxidants,
Common additives that are sometimes incorporated into pressure-sensitive adhesives include ultraviolet absorbers, fillers, pigments, extenders, and the like, and their usual amounts are sufficient.

The pressure-sensitive adhesive of the present invention can be used in common applications such as adhesive tapes and adhesive sheets. For coating treatment, etc., normal application methods such as a solution type using a solvent or a water dispersion type can be used as required. The thickness of the pressure-sensitive adhesive provided may be appropriately determined depending on the purpose of use, and is generally 1 to 500 μm.

Effects of the Invention The pressure-sensitive adhesive of the present invention is made of an acrylic copolymer with a low elastic modulus that has a carboxyl group in the side chain portion, so it is easy to crosslink and has excellent adhesion performance to rough and curved surfaces. It also has excellent cohesive strength and adhesive strength.

Examples Reference Examples In a reaction vessel equipped with a cooling tube, a nitrogen introduction tube, a thermometer, and a stirring bar, 50 parts of methyl ethyl ketone (parts by weight, the same applies hereinafter),
Add 50 parts of toluene, 20 parts of n-butyl acrylate, 80 parts of t-butyl acrylate, 1.2 parts of thioglycolic acid and 1 part of 4,4'-azobis(4-cyano)valeric acid,
The reaction was carried out at 60° C. for 3 hours under nitrogen substitution, and the product was purified by precipitation with a mixed solvent of water and methanol to obtain a terminally carboxylated prepolymer.

Next, 100 parts of the terminal carboxylated prepolymer,
200 parts of xylene, 3.7 parts of glycidyl methacrylate,
0.5 parts of hydroquinone and 0.5 parts of triethylamine were placed in the same reaction vessel as above and reacted at 140°C for 5 hours, and the product was purified by precipitation with a mixed solvent of water and methanol. The mixture was dried under reduced pressure for hours to obtain a terminal methacrylate type monomer consisting of a copolymer of n-butyl acrylate and t-butyl acrylate.

The number average molecular weight of the terminal methacrylate type monomer measured by GPC (gel permeation chromatography) in terms of polystyrene was s, 600, and the weight average molecular weight was 11,900.

Example 1 15 parts of the terminal methacrylate type monomer obtained in Reference Example, 85 parts of n-butyl acrylate, 100 parts of ethyl acetate, and 1 part of azobisisobutyronitrile were added to the same reaction vessel as above, and the mixture was heated for 60 minutes under a nitrogen stream. C. for 5 hours and then at 70.degree. C. for 2 hours to obtain a butyl acrylate graft polymer into which the terminal methacrylate monomer was introduced as a side chain forming component.

The graft polymer was precipitated and purified using methanol, and 28.
2ppm? -CH group in the t-butyl group seen in this,
-CH in the n-butyl group found at 30.8 pp-.

The reaction rate of the terminal methacrylate type monomer calculated from the area ratio with the group was 70%, and the molar percentage ratio of t-butyl group/n-butyl group in the graft polymer was 8.7/91.3. .

Next, 15 parts of ethyl acetate was added to 100 parts of the graft polymer.
0 parts of water, 50 parts of water, and 10 parts of sulfuric acid were added and hydrolyzed at 70° C. for 2 hours to obtain a graft polymer having a carboxyl group. To this was added 1 part of benzoyl peroxide to obtain a pressure-sensitive adhesive.

The weight average molecular weight of the carboxylated graft polymer as determined by GPC in terms of polystyrene was 540,000. Furthermore, as a result of analysis using 400MHz 'C-NMR, the molar percentage ratio of acrylic acid/butyl acrylate was 8/92.
It was confirmed that the t-butyl group in the side chain was almost selectively hydrolyzed.

Example 2 CH = CHCOO* Cr H/6 COO+
- Contains compounds with Hn of 1 to 5, and the average value of n is 1.82
Polycaprolactone acrylate 16 having the above structure
part (8 mol%), butyl acrylate 84 parts (92 mol%)
), 150 parts of ethyl acetate, and 1 part of azobisisobutyronitrile were placed in a reaction vessel equipped with a cooling tube, a nitrogen introduction tube, and a stirring bar, and reacted under nitrogen at 60°C for 5 hours and then at 70°C for 2 hours. A butyl acrylate copolymer containing the aforementioned polycaprolactone acrylate as a side chain-forming component was obtained, and 1 part of benzoyl peroxide was added thereto to prepare a pressure-sensitive adhesive. The weight average molecular weight of the copolymer was 650,000.

Comparative Example 4.7 parts (8 mol%) of acrylic acid and 9 butyl acrylate
An acrylic copolymer having an acrylic acid unit in the main chain was synthesized according to Example 2 using 5.3 parts (92 mol%), and a pressure-sensitive adhesive containing 1 part of benzoyl peroxide was prepared using this copolymer. I got it. Note that the weight average molecular weight of the copolymer was 620,000.

The thickness of the pressure sensitive adhesive obtained in the evaluation test example and comparative example after drying was 50
The adhesive tape was applied onto a polyester film (thickness: 50 mm) and heated and dried at 100° C. for 5 minutes to prepare an adhesive tape, which was subjected to the following test.

[Adhesive strength] Measured according to JIS ZZ1522.

[Curved surface adhesion J (repulsion resistance) Samples made of double-sided adhesive tape, thickness 0, 4 m, width 1
0-1 has a length of 1100n+ and is attached to an aluminum plate with a mirror-like surface, and then this is attached to an aluminum plate made of ABS resin with a diameter of 20n+.
The aluminum plate was crimped at 20° C. using the adhesive surface remaining on the 0ow cylinder by moving a rubber roll back and forth once, and the floating height at the end of the aluminum plate was measured 24 hours later.

[Adhesion to rough surface] As shown in the figure, the longest side of the isosceles rectangular prism 2 was roughened to a center line average roughness of 3.5 us), and the adhesive tape 1 was applied to the surface at 20° C. for two coats. The rubber roll is crimped by moving it back and forth once, and a light beam is incident on one isosceles side of a right-angled prism using a lamp 3, and the sensor 4 detects the reflected light from the side to which the adhesive tape is attached to bond the adhesive part. The effective adhesion area ratio was calculated using the following formula.

Effective adhesive area ratio = (adhesive area/apparent adhesive area) X1
00 Note that the incident light has a wavelength of 300 to 700 ns+ (beak 380 ns+).

The above results are shown in the table.

The table also shows the shear storage modulus of the acrylic copolymer on each side.

From the table, it can be seen that the pressure sensitive adhesive of the present invention has excellent adhesion performance to curved surfaces and rough surfaces.

[Brief explanation of the drawing]

The attached figure is an explanatory diagram of the adhesive area measuring method. 1: Adhesive tape 2: Isosceles right angle prism 3: Lamp 4: Sensor patent applicant Nitto Electric Industry Co., Ltd.

Claims (1)

[Claims] 1. A side chain having a carboxyl group branches to a main chain containing 50 mol% or more of acrylic acid alkyl ester units in which the alkyl group has 14 or less carbon atoms, and in that side chain, the carboxyl group is connected to the main chain carbon. exists through 3 or more carbon atoms, has a weight average molecular weight of 200,000 or more, has a carboxyl group unit content of 4 to 50 mol%, and has a shear storage modulus at a frequency of 1 Hz at 20 ° C. A pressure-sensitive adhesive comprising an acrylic copolymer having a kdyne/cm^2 of 200 to 1000 Kdyne/cm^2.