1. Field of the Invention
This invention relates to cyanoacrylate adhesive compositions which are improved in toughness by incorporation of certain organic fillers or thickeners.
2. Description of the Prior Art
Liquid cyanoacrylate compositions have long been known in the art as excellent adhesives. One of their primary shortcomings, however, has been their brittleness after cure.
A variety of fillers has been incorporated into cyanoacrylate adhesive compositions to bring about certain changes in properties. U.S. Pat. No. 2,794,788 teaches thickening of cyanoacrylate adhesives by dissolving therein quantities of polymeric alkyl cyanoacrylates, as well as other compounds including polyacrylates, methacrylates and cellulose esters such as acetate, propionate and butyrate.
U.S. Pat. No. 3,836,377 notes among the additional known thickeners polyvinyl ethers such as polyvinyl-methyl ether. U.S. Pat. No. 3,692,752 discloses thickened cyanoacrylate solutions containing certain polyether acrylates/methacrylates, acrylic/methacrylic esters of bis(hydroxyalkyl) phosphonic acid derivatives, and acrylic/methacrylic esters of tris(hydroxyalkyl) cyanuric acid derivatives.
The preceding references relate to thickened homogeneous solutions containing organic compounds as thickeners. Various inorganic materials have also been proposed as fillers, which also have the effect of thickening the composition. Thus, U.S. Pat. No. 3,663,501 teaches preparation of a dental cement containing inert, finely-divided solids such as fused silica, quartz and alumina. Similarly, U.S. Pat. No. 3,607,542 teaches the preparation of a water-resistant cyanoacrylate paste containing insoluble, inert fillers such as salts of calcium, titanium, zinc, tin, aluminum, iron and copper, among others. Non-soluble organic fillers are disclosed by U.S. Pat. No. 4,105,715.
U.S. Pat. No. 4,102,945 discloses a cyanoacrylate adhesive composition thickened by a copolymer or terpolymer resin capable of being dissolved or solvated by the cyanoacrylate monomer, resulting in significantly improved peel strength. Preferred thickeners are acrylonitrilebutadiene-styrene terpolymers, methacrylate-butadiene-styrene terpolymers, and vinylidene chlorideacrylonitrile copolymers.
It has now been found that use of elastomeric polymers as fillers in cyanoacrylate systems results in suprisingly beneficial properties.