JPS63260977A - Radiation-curable pressure sensitive adhesive composition - Google Patents

Abstract

PURPOSE:To provide the title compsn. which has a low viscosity and high adhesion and is excellent in temp. characteristics and dependence on peeling velocity, consisting of an adhesive compsn. mainly composed of a specific liquid polyether urethane oligomer and a thiol compd. CONSTITUTION:100pts.wt. adhesive compsn. (A) consisting of a liquid polyether urethane oligomer having a viscosity not higher than 20,000cps at 50<=, a weight- average MW of 1,000-50,000, electron-attractive substituents at both terminals and unsaturated bonds, a tackifier, a modifier, a stabilizer, a diluent, etc. is blended with 0.1-30pts.wt. thiol compd. (B) having at least three functional groups per molecule [e.g., trimethylolpropanetris (beta-thiopropionate)].

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a radiation-curable pressure-sensitive adhesive composition used for pressure-sensitive adhesive tapes, etc., and in particular to a radiation-curable pressure-sensitive adhesive composition suitable for surface protection films. The present invention relates to pressure sensitive adhesive compositions.

(Prior art) Pressure-sensitive adhesive tapes have traditionally been produced by dissolving high molecular weight polymers such as natural rubber or synthetic rubber in a suitable organic solvent, applying this solution onto a base material such as a plastic film, and drying it. It has been manufactured by However, due to coating constraints, it was necessary to lower the viscosity of the solution, which required a large amount of diluting solvent.

In recent years, the use of solvents has been considered from the viewpoints of resource saving, energy saving, pollution-free and safety.

One of the measures to eliminate solvents is radiation-curable adhesives that use liquid oligomers. Such adhesives have a relatively low molecular weight liquid oligomer coated on a base material and are irradiated with ionizing radiation to increase the molecular weight on the base material.

However, since this method uses low molecular weight oligomers with random functional groups as the main component, the elongation at break and tensile modulus are small compared to polymers with a high degree of polymerization, resulting in poor adhesion. Only adhesive tapes with poor adhesive properties were obtained. Furthermore, attempts have been made to add a chain transfer agent having a mercapto group or the like to such oligomers (Japanese Patent No. 1307060). Also, polymer? Attempts have also been made to add aR (Japanese Patent Application No. 59-112071) and to add polar substances (Japanese Patent Publication No. 60-25070).

(Problem to be solved by the invention) However, when using a low molecular weight oligomer having functional groups randomly in the molecule, even if a chain transfer agent or a polarizer is added, the adhesive strength and temperature Characteristic,
In terms of properties such as peel rate dependence, it was far behind polymers with a high degree of polymerization.

In addition, the method of adding a small amount of polymer cannot essentially solve these problems, and the viscosity becomes extremely high, which is a major hindrance to solvent-free coating.

Therefore, it is an object of the present invention to solve the above-mentioned problems and provide a radiation-curable sensitive adhesive with low viscosity, high adhesive strength, and excellent temperature characteristics and peel rate dependence. .

(Means for Solving the Problems) The present invention solves the above problems by blending a specific chain transfer agent in a specific ratio into an adhesive composition containing a liquid oligomer having a specific structure as a main component. .

That is, the present invention provides a method for adding a functional group in one molecule to 100 parts by weight of an adhesive composition whose main component is a liquid polyether urethane oligomer having unsaturated double bonds with electron-withdrawing substituents at both ends of the molecule. The present invention relates to a radiation-curable pressure-sensitive adhesive composition containing 0.1 to 30 parts by weight of a thiol compound having three or more groups.

Next, the components used in the adhesive composition of the present invention will be explained in detail.

The liquid polyether urethane oligomer having unsaturated double bonds with electron-withdrawing substituents at both ends of the molecule used in the present invention is a polyether whose oligomer base is a polyether obtained by ordinary condensation polymerization, etc. It is obtained by reacting the hydroxyl groups present at both ends of with a compound having an unsaturated double bond having an electron-withdrawing substituent, such as acrylic acid hydroxyethyl ester, via a diisocyanate.

Examples of unsaturated double bonds with electron-withdrawing substituents include acrylic acid alkyl ester-based carbon-carbon double bonds, methacrylic acid alkyl ester-based carbon-carbon double bonds, and epoxy resin acrylate-based carbon-carbon double bonds. Examples include acrylic unsaturated bonds and corresponding methacrylic unsaturated bonds.

Among these oligomers with unsaturated double bonds,
Particularly good results can be obtained by using oligomers containing highly reactive acrylic double bonds, and by introducing acrylic double bonds using acrylic acid hydroxyalkyl esters, such as acrylic acid hydroxyethyl ester. Can be done.

In addition, as diisocyanates used for chain extension,
Trimethylhexamethylene diisocyanate, which has a glass transition temperature suitable for use as an adhesive and is flexible, is particularly excellent. As a substitute for this, for example, when hexamethylene diisocyanate is used, the adhesive strength at high temperatures becomes low, and when tolylene diisocyanate or the like is used, low-temperature adhesion properties are extremely deteriorated.

Note that these oligomers may be used alone or in combination of two or more.

These oligomers must be liquid at temperatures between room temperature and 80° C. in order to be applied to a substrate without a solvent and to be radiation-cured. And its viscosity is 200 at 50℃
00 cps or less is more suitable for coating. Moreover, the weight average molecular weight of the oligomer is 1000 to 500.
Preferably it is 00. If the weight average molecular weight of the oligomer exceeds 50,000, the upper limit of the coating temperature is 80.
It is difficult to become liquid at a temperature of less than 1,000°C, and its adhesive strength is lower than that of a polymer.

The adhesive composition of the present invention includes the above-mentioned oligomer or additives such as a tackifier, a regulator, a stabilizer, a diluent, etc., which are used in combination with the oligomer and a normal adhesive composition;
It is a composition consisting of a compounding agent. Examples of such additives include, for example, acidic group-containing monomers, diluting monomers, tackifiers, and other additives for the purpose of improving interfacial properties. Examples include stabilizers such as antioxidants, radiation curing accelerators, ultraviolet absorbers, and solvents. These can be used by appropriately selecting and adjusting their types, combinations, usage amounts, etc., as necessary.

The chain transfer agent used in the present invention has a chain transfer agent in one molecule.

It is a thiol compound having three or more functional groups, such as trimethylolpropane tris (β-thiopropionate) and pentaerythritoltetrakis (β-thiopropionate). These may be used alone or in combination of two or more.

These chain transfer agents are added to disperse crosslinking during radiation curing. For that purpose, the amount usually added is 0.1 to 30 parts by weight per 100 parts of the adhesive composition.
Preferably, it is selected within the range of 1 to 15 parts by weight. If this amount is less than 0.1 parts by weight, the effect of crosslinking and dispersion will be insufficient, and if it exceeds 30 parts by weight, curing will be insufficient and cohesive strength will be insufficient, which may adversely affect adhesive properties. be.

The adhesive composition of the present invention is obtained by blending the various components described above. This adhesive composition can be applied to a base film such as a polyethylene film to an appropriate coating thickness, and then cured by irradiation with radiation to form an adhesive tape.

The radiation referred to in the present invention refers to active energy rays, α
refers to ionizing radiation such as rays, beta rays, gamma rays, neutron beams, and accelerated electron beams. This ionizing radiation! T! Affi is
Usually it can be used in the range of 0.5 to 50 Mrad, but 1
~10 Mrad is desirable. In addition, when irradiating,
Care may be required regarding the irradiation atmosphere. That is, since the generated radicals are normally inhibited by oxygen in the air, it may be necessary to use an inert gas such as nitrogen to maintain an appropriate oxygen concentration.

(Function) The adhesive tape obtained using the adhesive composition of the present invention is
It has high adhesive strength, and its temperature dependence and peeling rate dependence are extremely small. The reason for this phenomenon is not necessarily clear, but because the functional groups of the oligomer are located at both ends of the molecule, when polymerized by a chain reaction with radiation, the growth reaction occurs more linearly than when the functional groups are located at the side chains. It is presumed that the structure will approach that of a polymer with a high degree of polymerization.

At this time, if a trifunctional or higher thiol compound is present,
1. Because it has the effect of crosslinking dispersion. ! It is estimated that the tiA-like growth reaction is further promoted.

(Example) Next, the present invention will be described in detail based on Examples, but the present invention is not limited thereto.

Tear-resistant Oligomer A Polypropylene Glycol-1000 (Asahi Denka Co., Ltd.
Trimethylhexamethylene diisocyanate (hereinafter abbreviated as TMDI) per mole (molecular weight approximately 1000)
After mixing 2 moles and heating at 80°C for 5 hours, add 2 moles of acrylic acid hydroxyethyl ester and heat again at 80°C.
It was heated for 4 hours. The obtained oligomer (hereinafter referred to as oligomer A) had a viscosity of 4000 cps at 50°C, and a molecular weight of Mn#2000 and Mw=4500.

Oligomer B To 10,001 mol of polypropylene glycol, add 2 mol of TMD + and 2 mol of hydroxyethyl acrylate in the same manner as above to prepare a radiation-curable oligomer (
Oligomer B) was obtained. This oligomer has 11,000
Viscosity in cps (50°C), Mn #6000, MW=1
It had a molecular weight of 3000.

Oligomer C hydroxyethyl acrylate from 2 moles to 1 mole 41
An oligomer (oligomer C) was obtained in the same manner as in the case of oligomer B except for the following steps.

This oligomer has a viscosity of 7400 cps (50°C),
It had a molecular weight of Mn#5400 and Mw'=11000.

Oligomer D 1,6-hexanediol (manufactured by Wako Pure Chemical Industries, Ltd., Molecule f
t120) 2 moles of isocyanatoethyl acrylate were mixed with 1 mole of the mixture and heated at 80°C for 3 hours. The resulting oligomer (oligomer D) was obtained. This oligomer has a viscosity of 300 cps (50°C), Mn=450, M
It had a molecular weight of w=700°.

Oligomer E 10 parts of ethyl acrylate, 70 parts of butyl acrylate and 20 parts of metaglycidyl acrylate were solution polymerized in a 30% solution, and after removing the solvent, the viscosity was 1×10'c at 50°C.
A solvent-free copolymer of ps was synthesized. Next, this copolymerized pre-oligomer was subjected to an addition reaction with 5 parts of acrylic acid to impart a double bond to the side chain.

Example 1 An adhesive composition was prepared by adding 5 parts of trimethylolpropane tris (β-thiopropionate) to 100 parts of oligomer A.

Example 2 An adhesive composition was obtained in the same manner as in Example 1, except that 20 parts of trimethylolpropane tris (β-thiopropionate) was used.

Example 3 An adhesive composition was obtained by adding 10 parts of pentaerythritoltetrakis (β-thiopropionate) to 100 parts of oligomer A.

Example 4 10 parts of trimethylolpropane tris (β-thiopropionate) was added to 100 parts of oligomer B to obtain an adhesive composition.

Comparative example 1 Oligomer 8 alone was used as an adhesive composition.

Comparative Example 2 Trimethylolpropane tris (β-thiopropione)
An adhesive composition was obtained in the same manner as in Example 1 except that 1.) was changed to 40 parts.

Comparative Examples 3 to 5 10 parts by weight of each of oligomers C, D, or E were blended with 10 parts of trimethylolpropane tris (β-thiopropionate).

Comparative Example 6 An adhesive composition was obtained in the same manner as in Example 4, except that 5 parts of carbon tetrabromide was used instead of trimethylolpropane tris (β-thiopropionate).

Application example These compositions were applied to a polyethylene film (thickness 60 μm)
) to a coating thickness of 10 μm without using any solvent, and then using an electron beam irradiation device (linear filament type, Energy 5ci) with an accelerating voltage of 200 kV and a beam current of 10 mA.
6Mra under a nitrogen gas atmosphere (02 part concentration 500 ppm) using ence Inc., product name Electro Curtain).
d irradiation to produce an adhesive film. This adhesive film was attached to a 5US-430BA board, and an adhesive strength test was conducted using a Tensilon type tensile tester.

At measurement temperatures of 0°C and 40°C, the tensile speed was 200/min.
At a measurement temperature of 20°C, a tensile speed of 501 m/min, 200 m
Measurements were taken at m/min and 1000 mm/min and the results were
Shown in the table.

Note that cloudiness, migration, etc. of the adhesive were visually determined.

(Margins below) Table 1 (Units: g/25 cranes, 10μ) (Effects of the invention) The radiation-curable anger pressure adhesive composition of the present invention has a viscosity low enough to be applied without solvent. It also has excellent adhesive properties such as adhesiveness.

Claims (1)

[Scope of Claims] 1. In 1 molecule per 100 parts by weight of an adhesive composition containing as a main component a liquid polyether urethane oligomer having unsaturated double bonds with electron-withdrawing substituents at both ends of the molecule. 0.1 to 3 thiol compounds having 3 or more functional groups in
A radiation-curable pressure-sensitive adhesive composition comprising 0 parts by weight. 2. Claim 1 in which the unsaturated double bond having an electron-withdrawing substituent is an acryloyl group or a methacryloyl group
Compositions as described in Section. 3. The composition according to claim 1 or 2, wherein the liquid polyether urethane oligomer has a viscosity of 20,000 cps or less at 50°C. 4. The composition according to any one of claims 1 to 3, wherein the liquid polyether urethane oligomer has a weight average molecular weight of 1,000 to 50,000. 5. The composition according to any one of claims 1 to 5, wherein the liquid polyether urethane oligomer is an oligomer using trimethylhexamethylene diisocyanate as a chain extender.