JPS63260973A - Production of microspherical pressure-sensitive adhesive - Google Patents

Abstract

PURPOSE:To obtain a restrippable pressure-sensitive adhesive having excellent properties with good reproducibility under stable reaction conditions, by suspension-polymerizing a (meth)acrylate with a water-soluble monomer and a polyfunctional monomer in the presence of a polymn. initiator and a surfactant. CONSTITUTION:A compsn. contg. a (meth)acrylate, a water-soluble monomer copolymerizable with said (meth)acrylate and an oil-soluble polyfunctional monomer having at least two polymerizable unsaturated groups per molecule is suspension-polymerized in the presence of an oil-soluble polymn. initiator and a surfactant in an aq. medium. The raw compsn. for the adhesive contains 100pts.wt. (meth)acrylate, 1.0-10.0pts.wt. water-soluble monomer and 0.01-0.5pts. wt. polyfunctional monomer. A microspherical polymer having an average particle size of 10-150mu can be obtd. by said polymn. reaction.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for producing removable pressure-sensitive adhesives with excellent properties in a short period of time and with good reproducibility.

(Prior Art) Removable memo pads and resealable envelopes, which have a pressure-sensitive adhesive layer formed on a portion of a base material such as high-quality paper, are used in offices and the like. For example, the memo paper having a pressure-sensitive adhesive layer has good removability, and after being peeled off from an object to be bonded, it can be reattached to another object to be bonded. Adhesives used for such applications have excellent initial adhesion.

In addition, it is necessary to have good removability. In other words,
The adhesive strength is relatively high when the sheet with the adhesive layer formed on the base material is lightly pressed against the object to be adhered.
Furthermore, it is desirable that the adhesive strength does not increase significantly even when the adhesive is strongly pressed and that the adhesive can be peeled off with a relatively small force. Furthermore, it is desired that there is no so-called adhesive residue, and that it can be bonded to other objects to be bonded again with good adhesion.

An adhesive having such removable and readhesive properties (hereinafter referred to as a removable adhesive) and a sheet on which a layer of this adhesive is formed are used, for example, in U.S. Pat. No. 3,691,140 and U.S. Pat. , 857,731, U.S. Patent No. 4.166
, No. 152, JP-A-50-2736, and JP-A-60-11569. The adhesives described herein are all microspherical adhesives obtained by aqueous suspension polymerization of alkyl acrylate monomers and polar polymers. Since the adhesive has a microspherical shape, it can be re-peeled relatively well. However, 1 For example, JP-A-1989
When the monomer composition described in JP-A-2736 is subjected to aqueous suspension polymerization, the temperature during one polymerization reaction.

The quality of the microspherical adhesive obtained is inconsistent depending on the time and stirring conditions. When, for example, a pressure-sensitive adhesive sheet is prepared using such an adhesive, the adhesive strength of the resulting sheet varies, making it impossible to obtain a sheet of consistent quality. the above:
T! ? ';'I During polymerization, the radicals generated (
It is thought that at the same time as the meth)acrylate monomer polymerizes to form a main chain, a crosslinking reaction occurs due to a radical chain transfer reaction between the resulting (meth)acrylate polymer and radicals. However, this radical chain transfer reaction.

There are large uncertainties, and it is not possible to obtain a polymer of stable quality with a constant crosslinking state as a result of the radical reaction. As a result, it is thought that the above-mentioned variations in quality are brought about. in this way.

At present, no method has been developed for producing removable pressure-sensitive adhesives with excellent properties under stable reaction conditions with good reproducibility.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned conventional drawbacks, and its purpose is to produce a pressure-sensitive adhesive with excellent initial adhesion and removability under stable reaction conditions. The objective is to provide a method for manufacturing with good reproducibility.

Another object of the present invention is to provide a method for producing a microspherical removable adhesive of stable quality through a polymerization reaction of acrylic monomers.

(Means and effects for solving the problems) The method for producing a microspherical pressure-sensitive adhesive of the present invention comprises (meth)acrylate, a water-soluble monomer copolymerizable with the (meth)acrylate, and A composition containing an oil-soluble polyfunctional monomer having two or more polymerizable unsaturated groups is subjected to aqueous suspension polymerization in the presence of an oil-soluble polymerization initiator and a surfactant, thereby achieving the above purpose. achieved.

(meth)acrylate (acrylate and/or R2) used in the microspherical pressure-sensitive adhesive of the present invention, R1 is a saturated hydrocarbon group having 4 to 9 carbon atoms, and R2
represents 11 or C113. Such (meth)acrylates include n-butyl (meth)acrylate,
2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, and the like.

Examples of water-soluble monomers copolymerizable with the above (meth)acrylates include (meth)acrylic acid, fumaric acid, maleic acid, itaconic acid, and salts thereof.

The oil-soluble polyfunctional monomer having two or more polymerizable unsaturated groups in the molecule is preferably a compound that is substantially insoluble in water and compatible with the above (meth)acrylate. Divinylbenzene is an example of such a polyfunctional polymer.

Examples include triallylisocyanurate.

The raw material composition of the adhesive of the present invention contains 100 parts by weight of the (meth)acrylate and 100 parts by weight of the water-soluble monomer.
．． 0 to 1000 parts by weight, and the polyfunctional monomer is 0. It is contained in a proportion of 1 to 0.5 parts by weight. If the amount of the water-soluble monomer in the above composition is too small, the microspheres will tend to aggregate, while if it is too large, appropriate tackiness and flexibility will not be obtained. If the amount of the polyfunctional monomer is too small, the crosslinking reaction during production will not occur stably, resulting in poor reproducibility and variations in quality. On the other hand, if the amount is too low, the degree of crosslinking will be high and no adhesiveness will be developed.

The initiator (polymerization reaction initiator) has the property of generating radicals when decomposed by heat or the like. In the present invention, the initiator is substantially water-insoluble (oil-soluble);
A material that is soluble in the acrylic thread is used. For example, azo compounds such as azobisisobuty70nitrile and peroxides such as benzoyl peroxide are preferably used. The oil-soluble initiator is used in an amount of 0.05 to 0.5 parts by weight based on 100 parts by weight of all monomer components.

As the surfactant, ionic surfactants such as sodium dodecylbenzenesulfonate and nonionic surfactants such as polyoxyethylene lauryl alcohol ether can be used. Surfactants are used above the critical micelle concentration.

In order to obtain the microspherical pressure-sensitive adhesive of the present invention, the above (meth)
1 Polymerization conditions in which an acrylate, a polyfunctional monomer, a surfactant, and an oil-soluble initiator are added to water or an aqueous solvent and the polymerization reaction is carried out with stirring are similar to those for a typical aqueous suspension polymerization reaction. For example, stirring is performed at around 75° C. for about 1 hour. Since the composition used in the method of the present invention contains (meth)acrylate, a water-soluble monomer, and an oil-soluble polyfunctional monomer in appropriate proportions, the polymerization reaction proceeds under stable reaction conditions. In particular, since the polyfunctional monomer is oil-soluble, it is sufficiently compatible with (meth)acrylate.

As a result, there is no variation in crosslinking rate and the reaction proceeds stably. Due to such a reaction, the polymerization/crosslinking reaction is completed in a relatively short time. The average particle size is 10-15 due to polymerization reaction.
A microspherical polymer with a uniform particle size of 0 μm is obtained. The obtained microspherical polymer exhibits good adhesion and has an appropriate degree of crosslinking, so it has excellent removability. For example, to prepare a pressure-sensitive adhesive sheet using this adhesive, e.g.
A base material such as paper or plastic film is undercoated with a binder such as nitrocellulose, and an organic solvent dispersion of the adhesive described above is coated thereon and dried.

The adhesive and binder may be mixed and coated onto the substrate.

As an adhesive composition having a crosslinked structure, JP-A-57-
No. 111368 discloses a composition in which 100 parts by weight of an emulsion polymer is blended with a crosslinking agent at a ratio of 2 parts by weight or less. As the crosslinking agent, a polyfunctional epoxy compound, a melamine compound, an isocyanate compound, etc. are used. However, it differs from the adhesive of the present invention in that a crosslinking reaction occurs by heating after coating on a substrate. moreover.

When this adhesive is applied onto a substrate and heated to cause a crosslinking reaction, the spherical polymer loses its shape and becomes a film, making it unsuitable as a removable adhesive as in the present invention. In addition, as a microspherical polymer having a crosslinked structure, styrene-based microparticles are manufactured for chromatography, but these have a high Tg and do not have adhesive properties. It's completely different.

(Example) The invention will be explained below with reference to examples.

291 g of 2-ethylhexyl acrylate, 9 g of acrylic acid, 0.09 g of divinylbenzene (0,0
43 mol%) and 0.9 g of benzoyl peroxide in a 2β separable flask.
0 g of sodium dodecylbenzenesulfonate as a surfactant, and 5.4 g of sodium hydroxide for pHMfR adjustment. This suspension was stirred at 40° C. for 1 hour at a rotational speed of 27 rpm, and then the temperature of the suspension was raised to 75° C. to initiate the reaction. After the liquid temperature rose to 75°C, a portion of the reaction liquid was taken out at 1 hour, 3 hours, 6 hours, and 12 hours, and methanol was added to each part. Each solid component was separated and dried. The average particle diameter was about 30 μm in all cases.

This polymer was added to toluene to a concentration of 8%, and the toluene dispersion was applied to high-quality paper primed with nitrocellulose at a rate of 10 g/rrl and dried, thereby adjusting the reaction time. Four types of corresponding paper adhesive sheets were obtained.

The adhesive and paper adhesive sheet obtained in the above steps were evaluated by the following method. The results are shown in the table below. The results of Example 2 and Comparative Examples 1 and 2 are also shown in the table below.

(1) Gel fraction.

The solid content obtained by the reaction is mixed with toluene at a ratio of 8%, the toluene dispersion is centrifuged, and the weight is calculated from the weight of the precipitated toluene-insoluble content.

(2) Adhesive strength The obtained paper adhesive sheet was attached to a stainless steel plate for 2k.
Determine the 180° peel adhesive strength at 20° C. when pressed with an adhesive roll. Separately, a similar test is conducted using a 200g adhesive roll.

Implementation M1 The process of Example 1 was repeated and the reproducibility was evaluated.

Le comparison soil Except that divinylbenzene was not used.

This is the same as in Example 1.

Comparison ■1 The process of Comparative Example 1 was repeated and the reproducibility was evaluated.

(The following is a blank space) As is clear from the table, the method of the present invention using an oil-soluble polyfunctional hexamer as a radical copolymerizable crosslinking agent
A microspherical adhesive having a crosslinked structure suitable as a removable adhesive can be obtained in a short time. It can be seen that the adhesive properties of such pressure-sensitive adhesives do not vary greatly depending on the double polymerization reaction time, and that polymers obtained by reaction for one hour or more have stable adhesive strength because the degree of crosslinking is constant.

It can be seen from the adhesive strength that this adhesive has properties suitable as a removable adhesive. It can be seen that the reproducibility of the polymerization reaction is good and that a removable adhesive of consistently stable quality can be obtained.

On the other hand, when a polymerization reaction is carried out without using an oil-soluble polyfunctional monomer, the rate of one polymerization is slow, and an adhesive of stable quality cannot be obtained, resulting in poor reproducibility of one reaction. In particular, even if the reaction is carried out under similar conditions, the degree of crosslinking is not constant depending on the reaction time, making it impossible to obtain an adhesive of a predetermined quality.

(Effects of the Invention) According to the method of the present invention, a pressure-sensitive adhesive with excellent initial adhesion and removability is obtained by using a specific composition containing an acrylic monomer and an oil-soluble polyfunctional monomer. Provided is a method for producing reproducible agents in a short time under stable reaction conditions.

The obtained pressure-sensitive adhesive can be suitably used for memo pads having an adhesive layer, openable envelopes, and the like.

that's all

Claims (1)

[Claims] 1. (meth)acrylate, a water-soluble monomer copolymerizable with the (meth)acrylate, and an oil-soluble polyfunctional monomer having two or more polymerizable unsaturated groups in the molecule. A method for producing a microspherical pressure-sensitive adhesive comprising the step of aqueous suspension polymerization of a composition containing the following in the presence of an oil-soluble polymerization initiator and a surfactant. 2. The ratio of the water-soluble monomer to 100 parts by weight of the (meth)acrylate is 10.0 to 1.0 parts by weight,
The manufacturing method according to claim 1, wherein the polyfunctional monomer is contained in a proportion of 0.01 to 0.5 parts by weight. 3. The particle size of the microspherical pressure-sensitive adhesive is 10 to 150 μm.
The manufacturing method according to claim 1.