JPS63196676A - Pressure-sensitive adhesive - Google Patents

Abstract

PURPOSE:To provide the title adhesive which exhibits persistent initial adhesion even upon rough surfaces and curved surfaces and has excellent tack as well as excellent cohesive force, consisting of a graft polymer wherein the main chain is composed of an acrylic polymer and the side chain is composed of a specified side chain-forming compd. CONSTITUTION:An oligomer (a) having an MW of 500-200,000 and COOH groups at its terminals, obtd. by polymerizing an alpha,beta-ethylenically unsaturated monomer having neither oxirane ring nor COOH group in its molecular structure (e.g., 2-ethylhexyl acrylate) in the presence of an azo initiator and a chain transfer agent having a COOH group in an org. solvent, is reacted with a compd. (b) having an oxirane ring and a polymerizable unsaturated group, such as glycidyl acrylate, to obtain a side chain forming compd. (B) having a weight-average MW not lower than 1,000 and a glass transition point lower than 20 deg.C. The component B is grafted onto not less than 50wt.% acrylic polymer (A) having a glass transition point not higher than -10 deg.C and composed of at least 50wt.% ester of acrylic acid with a 1-14C primary or secondary alcohol in the presence of an azo initiator and in an N2 atmosphere.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention is a graft polymer having an acrylic polymer as the main chain and a polymeric compound as the side chain, and has excellent cohesive force and tackiness. Regarding pressure adhesives.

BACKGROUND ART AND PROBLEMS In pressure-sensitive adhesives, the balance between cohesive force and tack regulates the temporal characteristics of adhesive force and is an important factor. For example, if the tack is poor, sufficient initial adhesive strength will not be developed, and if the cohesive strength is poor, hanging objects that are intended to be attached may fall off after a while. Also, due to poor balance, the adhered material may peel off on the curved surface of the adherend.

Conventionally, in the case of acrylic pressure-sensitive adhesives, a method has been adopted in which the balance is adjusted by changing the glass transition point and molecular weight of the acrylic polymer in order to achieve both cohesive force and tack.

However, when adjusting the cohesive force based on the glass transition point, the tack changes significantly, and when increasing the cohesive force based on the molecular weight, the tack decreases and solubility in solvents also decreases, resulting in poor coatability. There was a problem. As described above, the balance adjustment method based on the glass transition point or molecular weight results in adjustment under the contradictory relationship between cohesive force and tack, and it is difficult to achieve a satisfactory balance between them.

Therefore, recently, attempts have been made to convert acrylic polymers into block polymers or graft polymers. However, all of the methods proposed so far have problems such as poor tackiness and poor adhesion to curved or rough surfaces, and are therefore unsatisfactory.

Means for Solving the Problems The inventors of the present invention have conducted intensive research to develop an acrylic pressure-sensitive adhesive that has excellent cohesive force and tackiness, and have developed a new adhesive consisting of a special main chain and side chains. It was discovered that the purpose could be achieved by using a graft polymer, and the present invention was completed.

That is, the present invention uses an acrylic polymer as a main chain containing 50% by weight or more of an acrylic ester using a primary or tertiary alcohol having 14 or less carbon atoms and having a glass transition point of -10°C or less. The present invention provides a pressure-sensitive adhesive characterized by comprising a graft polymer having a side chain of a compound having a weight average molecular weight of 1000 or more and a glass transition point of less than 20°C.

In the present invention, the weight average molecular weight is determined by gel permeation chromatography in terms of polystyrene.

Function: By using the above-mentioned graft polymer, a pressure-sensitive adhesive with high cohesive strength can be obtained based on interactions such as entanglement of side chains (or in any case, without reducing tack).

Exemplification of Components of the Invention The pressure sensitive adhesive of the present invention is comprised of a novel graphite polymer.

The main chain of the graft polymer has a glass transition point of 110°C.
Hereinafter, it is preferably made of an acrylic polymer having a temperature of -20°C or less. If the glass transition point exceeds 110° C., the resulting pressure-sensitive adhesive will have poor tackiness at low temperatures.

The acrylic polymer constituting the main chain is composed of an acrylic ester of acrylic acid or methacrylic acid and a primary or tertiary alcohol having 14 or less carbon atoms. In the case of an ester made using a tertiary alcohol or a primary or tertiary alcohol having 15 or more carbon atoms, the flexibility of the molecular chain is poor, resulting in a pressure-sensitive adhesive having poor tack.

Specific examples of the acrylic esters used include methyl acrylate, ethyl acrylate, butyl acrylate,
Isoamyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, isononyl acrylate, decyl acrylate, dodecyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, isooctyl methacrylate, etc. be able to. These may be used alone or in combination of two or more.

When using two or more types in combination, the average carbon number of the alcohol component in those acrylic esters is 4 to 1.
A combination of 2 is preferable in terms of the flexibility of the resulting acrylic polymer. In addition, when using one type of acrylic acid ester, the number of carbon atoms is 4 to 1 for the same reason.
An ester consisting of two alcohols is preferred.

The acrylic polymer as the main chain in the present invention contains 50% by weight or more, preferably 70% by weight or more of acrylic ester. Its content is 50% by weight
If it is less than that, the molecular chain will have poor flexibility, weather resistance, and heat resistance, resulting in an unsatisfactory pressure-sensitive adhesive.

The acrylic polymer may be composed only of an acrylic ester, but is generally used as a copolymer modified with other monomers in order to satisfy the above-mentioned glass transition point conditions. There are no particular limitations on the vine modifier to be used. Generally, acidic monomers such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, and crotonic acid, hydroxyl group-containing monomers such as 2-hydroxyethyl acrylate and 2-hydroxypropyl acrylate, and N,N-dimethylaminoethyl acrylate , N,N-dimethylaminoethyl methacrylate), amino group-containing monomers such as N-tert-butylaminoethyl acrylate, amide group-containing monomers such as acrylamide, methacrylamide, N-methylolamide, and oxirane rings such as glycidyl methacrylate. Containing monomers and their compounds such as acrylonitrile, vinyl acetate, and vinyl chloride are used.

The weight average molecular weight of the acrylic polymer as the main chain is suitably 50,000 or more, particularly 100,000 to 1,900,000.

The side chain of the graft polymer used in the present invention consists of a compound having a weight average molecular weight of 1000 or more, preferably 3000 or more, and a glass transition point of less than 20°C, preferably 10°C or less. If the weight average molecular weight is less than 1000, it will be difficult to obtain a pressure sensitive adhesive with high cohesive strength due to poor interaction such as entanglement based on side chains, and if the glass transition point is 20°C or higher, it will be difficult to obtain a pressure sensitive adhesive. The pressure-sensitive adhesive becomes less tacky, reducing its versatility and thus its practicality.

The upper limit of the weight average molecular weight of the side chain is not particularly limited (300,000 or less, especially 80,000 or less is common from the viewpoint of controllability of the molecular weight, etc.).

The method for preparing the above-mentioned graft polymer is to separately prepare a side chain-forming compound having a small number of radically polymerizable double bonds (both at one end), and to graft this with the molecular weight of the side chain. This is preferable from the viewpoints of control, suppression of homopolymer formation, and formation of a desired graft polymer.

The side chain-forming compound used in the above preparation method can be synthesized using, for example, esters of acrylic acid or methacrylic acid such as methyl, ethyl, propyl, butyl, hexyl, 2-ethylhexyl, isooctyl, isononyl, acrylamide,
Acid amides such as octylamide and stearylamide, acid nitriles such as acrylonitrile, vinyl esters such as acetate and propionate, styrene, α
- Aromatic monoolefins such as methylstyrene and vinyltoluene (α,β-ethylenically unsaturated monomers that do not have an oxirane ring or a carboxyl group in the molecule)
The species or two or more species are polymerized in an organic solvent in the presence of an azo initiator and a carboxyl group-containing chain transfer agent to form a carboxyl group at the end with a controlled molecular weight of about 500 to 200,000. A system in which this oligomer is reacted with a compound having an oxirane ring and a polymerizable unsaturated group such as glycidyl acrylate or glycidyl methacrylate, or a method in which a styrene-based oligomer such as styrene, α-methylstyrene, or vinyltoluene is reacted. Anionic polymerizable monomers such as diene monomers such as isoprene and butadiene are subjected to living anionic polymerization using an alkali metal initiator such as butyl lithium, and the resulting living polymer and ρ-vinylbenzyl chloride, etc. (The method of reacting with a compound having a halogen and a polymerizable unsaturated group is the same as the method of reacting a living polymer with ethylene oxide and then reacting it with an acid halide such as acrylic acid chloride or methacrylic acid chloride.) It can be cited as a representative example.

The graft polymer used in the present invention has a main chain acrylic polymer content of 50% by weight or more, preferably 70 to 95% by weight, and a weight average molecular weight of 100,000 or more.
Preferably, 200,000 to 2,000,000 is appropriate. If the content of the main chain component is less than 50% by weight, depending on the combination of the main chain component and side chain component, the cohesive force of the pressure-sensitive adhesive obtained may be too high (or it may be difficult to prepare from many directions). There is a disadvantage in that a large amount of the chain-forming compound is used. On the other hand, if the weight average molecular weight is less than 100,000, the resulting pressure-sensitive adhesive will have poor cohesive strength.

In preparing the pressure-sensitive adhesive of the present invention, in addition to the above-mentioned graft polymer, various other materials may be blended as necessary.

Typical optional components include tackifiers made of terpene-based, terpene-phenol-based, coumaron-indene-based, styrene-based, rosin-based, xylene-based, phenol-based, petroleum-based resins, etc., and room temperature A liquid tackifying resin, process oil, polyester plasticizer, polybutene, a softening agent made of liquid rubber, etc., a crosslinking agent made of polyisocyanate, melamine resin, amine-epoxy resin, peroxide, metal chelate compound, etc. I can give it to you. It is appropriate that the total amount of the tackifier and softener is equal to or less than the amount of the graft polymer, and the amount of the crosslinking agent is approximately 10 parts by weight or less per 100 parts by weight of the graft polymer.

Furthermore, various polymers such as acrylic polymers may be blended for the purpose of finely adjusting the adhesive properties.

Other optional ingredients include, for example, additives commonly used in pressure-sensitive adhesives, such as antioxidants, ultraviolet absorbers, fillers, pigments, and extenders. In addition, the compounding amount may be a normal amount.

The pressure-sensitive adhesive of the present invention can be used in a conventional manner, such as by applying it to a support as a solution in a solvent and drying it. Furthermore, it can be applied to common pressure-sensitive adhesive applications such as adhesive tapes attached to base materials such as plastic, paper, cloth, and metal foil. Thickness as pressure sensitive adhesive layer is 3
The amount is generally 500 μl, but it is determined as appropriate depending on the purpose of use.

Effects of the Invention The acrylic pressure-sensitive adhesive of the present invention has excellent tack and high cohesive force, and is excellent in both tackiness and cohesive force.

As a result, it exhibits excellent initial adhesive strength even on rough and curved surfaces, and maintains its initial adhesive state.

Examples Reference Example 1 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), 50 parts of toluene, and 100 parts of 2-ethylhexyl acrylate
1 part of 4,4゛-azobis(4-cyano)valeric acid and 2.3 parts of thioglycolic acid and heated at 60°C under nitrogen atmosphere.
The reaction product was reacted for 3 hours, and the resulting reaction product was purified by precipitation twice with a water-methanol mixed solvent to obtain a terminally carboxylated prepolymer.

The KOH equivalent of this prepolymer was 0.23 mmol/g of polymer.

Next, 100 parts of the prepolymer, 200 parts of xylene, 8.2 parts of glycidyl methacrylate, and 0.0 parts of hydroquinone.
5 parts of triethylamine 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 resulting reaction product was precipitated and purified twice with a water-methanol mixed solvent, and then heated at 50°C under lmHg. The mixture was dried under reduced pressure for 48 hours to obtain a 2-ethylhexyl acrylate side chain forming compound. Based on the KOH equivalent of this compound, the reaction rate of the terminal carboxyl group of the prepolymer was 95%.

Table 1 shows the physical properties of this side chain forming compound.

Reference Examples 2 to 4 Side chain-forming compounds were obtained according to Reference Example 1. Synthesis conditions and physical properties are shown in Table 1.

Table 1 *1 2-ethylhexyl diacrylate *2 Butyl diacrylate *3: Vinyl acetate *4: Methyl methacrylate *5: KOH equivalent of terminal carboxylated prepolymer (mmol/polymer Ig) Example 1 Cooling tube, nitrogen introduction In a reaction vessel equipped with a tube, a thermometer, and a stirring rod, 30 parts of the fecal chain-forming compound obtained in Reference Example 1, 65 parts of butyl acrylate, 5 parts of acrylic acid, 100 parts of vinyl acetate, and 1 part of azobisisobutyronitrile were added. The mixture was reacted at 60° C. for 5 hours and then at 70° C. for 2 hours under nitrogen purge, and the resulting graft polymer was purified by precipitation twice in hexane.

Next, the obtained purified product was dissolved in ethyl acetate to obtain a 30% by weight solution, and 2 parts of a trifunctional isocyanate crosslinking agent was added to this solution to obtain a pressure-sensitive adhesive.

The physical properties of the graft polymer are shown in Table 2.

Examples 2 and 3, Comparative Examples 1 to 3 Pressure-sensitive adhesives were obtained according to Example 1. Table 2 shows the synthesis conditions and the physical properties of the obtained graft polymer.

In addition, as a side chain forming compound, the compound obtained in Reference Example 2 was used in Example 2, the compound obtained in Reference Example 3 was used in Example 3, and the compound obtained in Reference Example 4 was used in Comparative Example 3.

The pressure sensitive adhesive obtained in the evaluation test example and comparative example was applied to one side of a 50 um thick polyester film with a dry thickness of 100 μm.
The adhesive tape was coated uniformly and dried under heat to obtain an adhesive tape, and the following properties were investigated.

[Adhesive force I Measured according to JIS Z 1522.

[Creep] (Displacement distance) Adhesive tape is attached to one end of a phenolic resin plate with a mirror-like surface.
After 30 minutes, this was left at 40° C. for 20 minutes for aging treatment. Next, a uniform load of 500 g was applied to the free end of the adhesive tape to apply shear tensile stress to the adhesive layer, and in this state, the displacement distance per hour was measured using a cleave tester.

[Ball tack 1 (rolling distance) PSTC-6 (US Pressure 5ensiti)
The rolling distance was measured at 0° C. in accordance with VE Tape Council).

The results are shown in Table 2.

Note that the glass transition points in the table are values measured by differential thermal analysis after separately synthesizing main chain-forming compounds with corresponding compositions.

Furthermore, the symbols in the table have the same meanings as in Table 1.

Table 2

Claims (1)

[Claims] 1. Mainly an acrylic polymer containing 50% by weight or more of an acrylic acid ester using a primary or secondary alcohol having 14 or less carbon atoms and having a glass transition point of -10°C or less chain, with a weight average molecular weight of 1000 or more and a glass transition point of 2.
A pressure-sensitive adhesive comprising a graft polymer having a side chain of a compound having a temperature below 0°C. 2. The pressure-sensitive adhesive according to claim 1, wherein the alcohol component in the acrylic ester or acrylic esters constituting the acrylic polymer has a carbon number or an average carbon number of 4 to 12. 3. The pressure-sensitive adhesive according to claim 1, wherein the content of the main chain component in the graft polymer is 50% by weight or more. 4. The pressure-sensitive adhesive according to claim 1, wherein the weight average molecular weight of the graft polymer is 100,000 or more.