JPS6320381A - Pressure sensitive adhesive sheet - Google Patents

Abstract

PURPOSE:To obtain a pressure sensitive adhesive sheet which has excellent adhesiveness and suffers neither the reduction of tack nor the contamination of the adhesive sheet after sticking to an adherend, by applying a specified radiation-curable adhesive composition to a base sheet and irradiating with electron beams and ultraviolet rays. CONSTITUTION:A radiation-curable pressure sensitive adhesive composition (B) is obtained by mixing a thermoplastic resin (a) preferably comprising an acrylic polymer, a compound (b) having one ethylenically unsaturated double bond in a molecule, preferably comprising a monomer having one (meth)acryloyl group in a molecule [e.g., an N-alkylcarbamoyloxyalkyl (meth)acrylate], a compound (c) having at least two ethylenically unsaturated double bonds in a molecule, preferably comprising a polyfunctional monomer having at least two (meth)acryloyl groups in a molecule [e.g., ethylene glycol di(meth)acrylate], and a photopolymerization initiator (d). Component B is applied to a base sheet (A), which is irradiated with electron beams and ultraviolet rays, preferably in an inert atmosphere.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial use ￥P) The present invention relates to an adhesive sheet. More details.

The present invention relates to a pressure-sensitive adhesive sheet formed by curing a radiation-curable pressure-sensitive adhesive composition coated on a base sheet by electron beam irradiation and ultraviolet irradiation.

(Prior Art) Conventionally, radiation-curable adhesive sheets have been produced by applying an ultraviolet-curable adhesive composition onto a base sheet such as plastic film, paper, textile fabric, non-woven fabric, metal foil, etc., and then irradiating it with ultraviolet rays. Alternatively, after applying an electron beam curable adhesive composition, the adhesive composition is cured by electron beam irradiation.

Examples of the above-mentioned ultraviolet curable pressure-sensitive adhesive composition include 1.

A thermoplastic resin such as an acrylic polymer, a monomer having one (meth)acryloyl group, a polyfunctional monomer having two or more (meth)acryloyl groups, and a photoinitiator are being considered. It was done. However, although the use of these adhesive compositions improves the adhesion with the base sheet after curing by ultraviolet irradiation, the thermoplastic resin of the adhesive composition does not participate in the curing reaction, so the retention after curing is poor. Low strength (during storage of the adhesive sheet after curing or after pasting the adhesive sheet to an adherend, the thermoplastic resin may migrate, causing problems such as a decrease in adhesive strength and staining of the adhesive sheet) It had become.

On the other hand, the electron beam curable adhesive composition may include a thermoplastic resin such as an acrylic polymer, a monomer having one (meth)acryloyl group, and a polyfunctional monomer having two or more (meth)acryloyl groups. A solvent-free material is used. These pressure-sensitive adhesive compositions contain a large amount of a monomer having one (meth)acryloyl group with a relatively large molecular weight and a high boiling point, in order to have a low viscosity that allows it to be applied and a low odor. Contains. Therefore, it is necessary to cure these pressure-sensitive adhesive compositions sufficiently so that no unreacted monomer remains, and there is no odor or hygiene problem.

A high dose of electron beam irradiation is required, but when irradiated with such a high dose of electron beam, crosslinking of thermoplastic resins such as acrylic polymers contained in the adhesive composition progresses excessively, resulting in electron beam curing. This method has disadvantages in that the adhesion and tack of the subsequent pressure-sensitive adhesive composition decreases, and depending on the type of base sheet, such as paper or certain plastic films, the base sheet deteriorates.

(Problems to be Solved by the Invention) The present invention improves the various drawbacks mentioned above, and (i) Since no unreacted monomer remains after the adhesive composition is cured,
(ii) The adhesive composition has sufficient adhesive properties such as adhesive strength, tank strength, and holding power after curing. (iii) Radiation-curable adhesive that does not cause the thermoplastic resin to migrate and reduce adhesive strength or stain the adhesive sheet during storage or after the adhesive sheet is attached to an adherend. It provides sheets.

(Means for Solving the Problems) The present invention provides an adhesive formed by applying a radiation-curable adhesive composition onto a base sheet and then curing the adhesive composition by electron beam irradiation and ultraviolet irradiation. It is a sheet.

In the present invention, as the base sheet, conventionally known base sheets for pressure-sensitive adhesive sheets can be used, and examples of such base sheets include paper, plastic film, fiber fabric, nonwoven fabric, metal foil, etc. .

In the present invention, the radiation-curable adhesive composition may be any composition that has properties as an adhesive after curing by electron beam irradiation and ultraviolet irradiation, such as thermoplastic resins and compounds having one ethylenically unsaturated double bond. , a compound having two or more ethylenically unsaturated double bonds, and a photopolymerization initiator are used, but among these, acrylic A monomer having one (meth)acryloyl group.

It is preferable to use a polyfunctional monomer having two or more (meth)acryloyl groups and a photopolymerization initiator.

Examples of the thermoplastic resin include acrylic polymer, polyurethane, silicone, ethylene-vinyl acetate copolymer,
Examples include polybutadiene, isobutylene rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber, and it is preferable to use an acrylic polymer. Examples of the acrylic polymer include homopolymers or copolymers of acrylic acid alkyl esters, copolymers of acrylic acid alkyl esters and other monomers copolymerizable therewith, or mixtures thereof. Other 13 copolymerizable with acrylic acid alkyl esters? Its body is styrene and vinyl acetate.

(meth)acrylic acid, methacrylic acid alkyl ester, (meth)acrylonitrile, (meth)acrylic acid amide, (meth)acrylic acid 2-hydroxyethyl,
Examples include glycidyl (meth)acrylate.

Examples of compounds having one ethylenically unsaturated double bond include monomers having one (meth)acryloyl group, styrene monomers such as styrene and α-styrene, vinyl acetate, and (meth)acrylonitrile. etc., but
It is preferable to use a monomer having one (meth)acryloyl group. Monomers having one (meth)acryloyl group include (meth)acrylic acid, methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. (meth)acrylic acid alkyl esters, (meth)acrylic acid hydroxyethyl esters, (meth)acrylic acid alkyl esters, etc.
Hydroxypropyl acrylate, (meth)acrylic acid amide, (meth)glycidyl acrylate, (meth)
Phenoxyethyl acrylate, isocyanatoalkyl (
meth)acrylate), N-alkylcarbamoyloxyalkyl(meth)acrylate, and N-alkylcarbamoyloxyalkoxyalkyl(meth)acrylate.

In addition, the above-mentioned compounds having two or more ethylenically unsaturated double bonds include ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, Methylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, epoxy poly(meth)acrylate.

In addition to polyfunctional monomers having two or more (meth)acryloyl groups such as polyurethane (meth)acrylate.

Examples include unsaturated polyester and diallyl phthalate, but it is preferable to use a polyfunctional monomer having two or more (meth)acryloyl groups.

Examples of the photopolymerization initiator include benzophenone, methylbenzophenone, and methyl p-benzoin ethyl 0-benzoylbenzoate. These photoinitiators include 4,4-bis(diethylamino)benzophenone,
It can also be used in combination with photopolymerization accelerators such as ethyl N-dimethylaminobenzoate, dimethylethanolamine, and glycine.

The radiation-curable adhesive composition in the present invention includes:

These compounds 1. In addition to dyes and pigments, fillers, tackifiers, plasticizers, solvents, antioxidants, etc., to the extent that they do not impede the effects of the present invention, to suppress dark reactions and increase stability during storage. A polymerization inhibitor such as hydroquinone, hydroquinone methyl ether, or benzoquinone can also be added to the polymerization agent.

In the present invention, the radiation-curable adhesive composition is applied onto a base sheet by a conventionally known method such as roll coating, knife coating, or spray coating, and the adhesive composition is cured by electron beam irradiation and ultraviolet irradiation. It is made into an adhesive sheet.

Electron beam irradiation and ultraviolet irradiation are preferably carried out in an inert atmosphere such as nitrogen or carbon dioxide in order to prevent oxygen inhibition, and the electron beam irradiation amount is usually 0.5 to 0.
It is about 20 Mrad.

The order of electron beam irradiation and ultraviolet ray irradiation is selected depending on the purpose. For example, there are (i) a method of irradiating ultraviolet rays after irradiating electron beams, (ii) a method of irradiating electron beams after irradiating ultraviolet rays, and (iii) a method of irradiating electron beams after irradiating ultraviolet rays, and then irradiating ultraviolet rays.

(i) A method in which ultraviolet rays are irradiated after electron beam irradiation.

Thermoplastic resin in adhesive composition by electron beam irradiation.

A compound having one ethylenically unsaturated double bond and a compound having two (1! or more) ethylenically unsaturated double bonds react simultaneously, but a compound having one ethylenically unsaturated double bond in the adhesive composition reacts at the same time. Much of it remains unreacted.

By the subsequent ultraviolet irradiation, all of these remaining unreacted compounds having one ethylenically unsaturated double bond are reacted, and no unreacted compounds remain in the pressure-sensitive adhesive composition. Furthermore, since the thermoplastic resin does not react when irradiated with ultraviolet rays, the properties of the adhesive composition do not deteriorate.

(ii) In the method of irradiating an electron beam after irradiating ultraviolet rays.

The ultraviolet irradiation causes the compound having ethylenically unsaturated double bonds in the adhesive composition to react, and the thermoplastic resin is trapped in the crosslinked copolymer produced by this reaction without reacting, causing the adhesive composition to react. Although the adhesion of the composition is good, the holding power is reduced and the thermoplastic resin migrates over time, causing various troubles.

However, subsequent electron beam irradiation causes the crosslinked copolymer and thermoplastic resin to react, increasing the holding power of the adhesive composition (as well as causing migration of the thermoplastic resin over time). It will no longer occur.

(iii) In the method of irradiating with an electron beam after irradiating ultraviolet rays, and then irradiating with ultraviolet rays, by the first irradiation of ultraviolet rays.

A part of the compound having an ethylenically unsaturated double bond in the adhesive composition reacts to form a crosslinked copolymer, and then by electron beam irradiation, a part of the compound having an unreacted ethylenically unsaturated double bond is removed. , the crosslinked copolymer and thermoplastic resin react, followed by ultraviolet irradiation.

All remaining unreacted compounds with ethylenically unsaturated double bonds are reacted. In this method, by appropriately adjusting the doses of two UV irradiations and one electron beam irradiation, (i) UV irradiation after electron beam irradiation, and (ii) Electron beam irradiation after UV irradiation. Take advantage of the characteristics of each method.

The crosslinking density of the adhesive composition after curing can be freely controlled, and a pressure-sensitive adhesive sheet that can be used in a wide range of applications can be obtained.

(Example) The present invention will be explained below with reference to Examples. In the examples, 5 parts means parts by weight, and 9% means % by weight.

Examples 1 to 3 and Comparative Examples 1 to 3 41 parts of n-butyl acrylate, 41 parts of 2-ethylhexyl acrylate, 10 parts of vinyl acetate, and 8 parts of acrylic acid were copolymerized in toluene, and the solvent was removed to obtain acrylic A system polymer was obtained.

60 parts of N-butylcarbamoyloxyethyl acrylate was added to 100 parts of the obtained acrylic polymer.

3 parts of polyethylene glycol (molecular weight approximately 400) diacrylate, and photopolymerization initiator "Glocure 1173J"
(trade name, manufactured by Merck & Co., Ltd.). Two parts were mixed to obtain a radiation-curable adhesive composition.

The obtained radiation-curable adhesive composition was applied to a polyester film with a thickness of 25 μm so that the film thickness was 25 μm, and then exposed to electron beams from the coated side under the irradiation conditions shown in Table 1 in a small atmosphere. and/or irradiated with ultraviolet rays to cure the adhesive composition to obtain an adhesive sheet. The ultraviolet irradiation at this time was carried out at a position of 150 below one 80 W/Cal high pressure mercury lamp.

Table 1 shows the results of measuring the adhesive strength, tank and holding power of the obtained adhesive sheet, and the amount of unreacted monomer in the cured adhesive composition.

In addition, the adhesive strength, tack and holding power of the adhesive sheet.

The method for measuring the amount of unreacted monomer in the adhesive composition after curing is as follows.

(i) Adhesive force measurement JIS Z0237 except that the width of the test piece was 12 mm.
30 minutes after adhesion to a stainless steel plate, it was peeled off at 180° and measured. The measurement results were expressed in units of g/12mm. Although it varies depending on the application, it is considered to be within the practical range if it is 400 g/12 dragons or more.

(ii) JIS 20237 except that the width of the tank measurement test piece was 120 mm.
The number of the largest steel ball that stopped at an inclination angle of 30' was measured using the 5-ball rolling method in accordance with the above. Although it differs depending on the application, if it is 7 or more, it is considered to be within the practical range.

(iii) Measurement of holding force JIs except that the size of the test piece was 12 mm x 25 m.
20237, 30 minutes after being attached to a stainless steel plate, a load of 1 kg is applied at 40°C, and the time (seconds) it takes for the test piece to fall off the stainless steel plate, or if it does not fall off within 3 hours. The distance (value) of deviation from the original position was measured. It varies depending on the purpose.

If the tax does not drop for more than one hour, it is considered to be in the practical range.

(iv) Measurement of the amount of unreacted monomer Apply a certain amount of the cured adhesive composition to the adhesive sheet.

Collect it and add it to 50+1 tetrahydrofuran.
It was left as it is for 124 hours. After standing, strain and remove the filtrate.
□ A sample was measured by gel permini-silane chromatography to determine the amount (%) of the unreacted monomer N-butylcarbamoyloxyethyl acrylate in the cured adhesive composition. In determining the concentration, a calibration curve between concentration and area was used, which was prepared using a tetrahydrofuran solution of N-butylcarbamoylethyl acrylate with a known concentration.

The amount of unreacted monomer in the adhesive composition after curing.

If it was less than 1.0%, it was considered to be within the practical range.

(The following is the margin) Table 1 □ EB: Electron beam. Irradiation dose in parentheses (Mrad) Uv: ultraviolet light. Comparison time (seconds) in parentheses Since no reaction monomer remains, there is no odor or hygiene problem. <ii) Adhesive strength of the adhesive composition after curing.

Adhesive performance such as tank and holding power is sufficient. (i
ii) The thermoplastic resin will not migrate during storage of the adhesive sheet or after it is attached to an adherend, resulting in no decrease in adhesive strength or staining of the adhesive sheet.
Radiation-curable adhesive sheets can now be obtained.

Claims (1)

[Scope of Claims] 1. A pressure-sensitive adhesive sheet obtained by coating a radiation-curable pressure-sensitive adhesive composition on a base sheet and then curing the pressure-sensitive adhesive composition by electron beam irradiation and ultraviolet irradiation. 2. The radiation-curable adhesive composition is an acrylic polymer,
(meth)monomer having one acryloyl group, (meth)
The pressure-sensitive adhesive sheet according to claim 1, comprising a polyfunctional monomer having two or more acryloyl groups and a photopolymerization initiator.