Adhesive Composition

1. Field of the Invention

The present invention relates to an adhesive composition. In particular, the present invention relates to an .alpha.-cyanoacrylate base adhesive composition having good storage stability.

2. Description of the Related Art

Since an .alpha.-cyanoacrylate base adhesive is a reactive adhesive comprising an .alpha.-cyanoacrylate monomer, it tends to be cured in an adhesive container during storage because of radical or anionic polymerization of said monomer. Therefore, a polymerization inhibitor is added to the adhesive as a stabilizer to improve the storage stability of the adhesive.

As the radical polymerization inhibitor for the .alpha.-cyanoacrylate monomer are used hydroquinone, hydroquinone monomethyl ether, catechol, pyrogallol, bisphenol A and the like. The polymerization inhibitor is added to the adhesive in an amount of 1 to 5000 ppm to inhibit the radical polymerization during room temperature storage.

The anionic polymerization is initiated with a small amount of moisture or a base such as an amine and ammonia. To prevent increase of viscosity and gelation due to anionic polymerization of the monomer are used SO.sub.2, SO.sub.3, SOCl.sub.2, SO.sub.2 Cl.sub.2, HF, BF.sub.3, BF.sub.3 -ether complexes, NO.sub.2, paratholuenesulfonic acid, methanesulfonic acid, propanesultone, phosphoric acid, sulfuric acid and the like.

However, the addition of the anionic polymerization inhibitor increases the setting time of the adhesive and deteriorates instantaneous adhesivity. Since such inhibitors are in a gas state at ambient temperature, their handling and adjustment of their concentration in the adhesive are difficult. Some of them such as SO.sub.3 and BF.sub.3 -ether complexes tend to fume and color the adhesive.

An object of the present invention is to provide a novel anionic polymerization inhibitor which is useful as a stabilizer for an .alpha.-cyanoacrylate base adhesive.

Another object of the present invention is to provide an .alpha.-cyanoacrylate base adhesive composition which does not suffer from the drawbacks of the conventional .alpha.-cyanoacrylate base adhesives.

Accordingly, the present invention provides an .alpha.-cyanoacrylate base adhesive composition comprising 0.0001 to 0.5 part by weight of borofluoric acid (HBF.sub.4) (as 100 %) per 100 parts by weight of an .alpha.-cyanoacrylate monomer.

Specific examples of the .alpha.-cyanoacrylate monomer which is a main component of the adhesive composition are methyl .alpha.-cyanoacrylate, ethyl .alpha.-cyanoacrylate, propyl .alpha.-cyanoacrylate, allyl .alpha.-cyanoacrylate, butyl .alpha.-cyanoacrylate, heptyl .alpha.-cyanoacrylate, hexyl .alpha.-cyanoacrylate, octyl .alpha.-cyanoacrylate, decyl .alpha.-cyanoacrylate, dodecyl .alpha.-cyanoacrylate, (2-chloroethyl) .alpha.-cyanoacrylate, (2-methoxyethyl) .alpha.-cyanoacrylate, (2-ethoxyethyl) .alpha.-cyanoacrylate, (2butoxyethyl) .alpha.-cyanoacrylate, benzyl .alpha.-cyanoacrylate, phenyl .alpha.-cyanoacrylate, trifluoroisopropyl .alpha.-cyanoacrylate, and the like.

Borofluoric acid (HBF.sub.4) may be a commercially available one, for example, a 30 to 40 % aqueous solution thereof.

The amount of borofluoric acid on a100 % basis is from 0.0001 to 0.5 part by weight, preferably 0.0002 to 0.02 part by weight per 100 parts by weight of the .alpha.-cyanoacrylate monomer.

The adhesive composition of the present invention may contain the above described conventional anionic polymerization inhibitor such as SO.sub.2, SO.sub.3, paratoluenesulfonic acid, methanesulfonic acid, propanesultone and the like.

In addition, the adhesive composition of the present invention may contain the above described conventional radical polymerization inhibitor such as hydroquinone, hydroquinone monomethyl ether, catechol, pyrogallol and the like.

To prepare the thickened adhesive composition, a thickening agent such as polymethyl methacrylate (PMMA), polyvinyl acetate, cellulose acetate isobutylate, acrylic elastomer and polyurethane can be added to the adhesive composition in an amount of about 1 to 20 % by weight of the .alpha.-cyanoacrylate monomer.

The adhesive composition of the present invention may contain a quick curing additive for shortening the setting time of the adhesive, an additive for increasing the adhesion strength, a plasticizer which imparts flexibility to the adhesive layer after curing, saturated polyester which improves impact resistance or peeling strength, a modifier for imparting heat resistance, and a dye or pigment for confirming the application of the adhesive composition. For example, methoxypolyethyleneglycol methacrylate, 18-crown-6ether or methoxyethyl gallate can be added to the adhesive composition in an amount of 0.05 to 10 % by weight of the .alpha.-cyanoacrylate monomer.

Since borofluoric acid can be handled in the form of an aqueous solution, its concentration in the adhesive composition is more easily adjusted than the gaseous stabilizers such as SO.sub.2 and HF. In addition, unlike BF.sub.3 complexes, borofluoric acid does not fume or color the composition.

The adhesive composition of the present invention has good storage stability and short setting time when it is used to adhere, in particular, wooden pieces.

The present invention will be illustrated by following Examples, in which "parts" are by weight.

To 100 parts of ethyl .alpha.-cyanoacrylate, 0.05 part of hydroquinone was added. Then, to the mixture, borofluoric acid, SO.sub.2, HF, BF.sub.3 -ether complex (BF.sub.3.O(C.sub.2 H.sub.5).sub.2), methanesulfonic acid, polymethyl methacrylate (PMMA), polyurethane, polyester, acrylic elastomer, methoxypolyethyleneglycol (#1000) methacrylate (MPEGMA), 18-crown-6-ether, pyrogallol and/or gallate was added in an amount (part) shown in Tables 1 and 2 to prepare an adhesive composition.

With the prepared adhesive composition, a pair of Birch pieces or a pair of steel pieces were adhered for measuring the setting time. The adhesive composition was filled in a polyethylene container and the gelation test was carried out at 70.degree. C. The results are shown in Tables 1 and 3.