Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Patent
1989-10-10
1992-02-11
Marquis, Melvyn I.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
525455, 525502, 525532, C08F29900, C08G 5914
Patent
active
050876430
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a single-component anaerobic acrylic adhesive formulation which is chemically stable and which is capable of producing a cured adhesive joint exhibiting improved impact and shear strengths or/and a good thermal behaviour.
BACKGROUND OF THE INVENTION
Anaerobic acrylic adhesive formulations are mixtures based on acrylic esters capable of being polymerized by a radical route and consisting predominantly of multiacrylic esters and chemical generators of free radicals chosen from peroxy compounds, the said mixtures having a cure which is inhibited by oxygen.
These anaerobic formulations remain in the uncured state as long as they are in contact with atmospheric oxygen. On the other hand, when they are placed between metal surfaces or other surfaces which are impervious to atmospheric oxygen, the absence of contact with oxygen leads rapidly to their curing.
Anaerobic adhesive formulations of this kind are employed in various fields of industry, for producing seals or assemblies and especially for locking nuts.
Despite their growing use, anaerobic acrylic adhesive formulations still exhibit certain disadvantages. First of all, their chemical stability still remains insufficient because of the fact that, in the majority of cases it is necessary to incorporate latent accelerators of radical polymerization in these formulations in order to increase the rate of polymerization of the acrylic monomers once the said polymerization has been initiated by the free-radical generator. The presence of these ingredients in the anaerobic formulation can result in an undesirable curing of the said formulation before its use and, for example, during its storage. The incorporation of polymerization inhibitors, for example of compounds of the hydroquinone type, in the formulation reduces this risk of premature curing, but does not enable it to be eliminated altogether.
In addition, since the acrylic monomers present in the anaerobic formulations are predominantly multiacrylic esters whose polymerization produces a very compact polymeric network, the adhesive joints obtained after curing the said formulations exhibit an excessive mechanical rigidity and hence an inadequate resistance to impact and to peeling forces. Furthermore, anaerobic adhesive formulations have a thermal stability which is not satisfactory in most cases. Finally, the said formulations are highly fluid and this rules out the possibility of employing them for applications requiring the use of highly thickened adhesive formulations, especially adhesive bonding of large flat metal surfaces.
The objective of the invention is to provide a single-component anaerobic acrylic adhesive formulation which makes it possible to overcome the disadvantages of the corresponding earlier formulations.
SUMMARY OF THE INVENTION
The formulation according to the invention is of the type comprising a monomeric acrylic phase consisting, by weight, of 50 to 100 % of one or more multiacrylic esters and of 50 to 0 % of at least one unsaturated monomer chosen from monoacrylic monomers and nonacrylic unsaturated monomers capable of being polymerized by a radical route and a free-radical generating system which is soluble in the monomeric acrylic phase and whose action generating free radicals is inhibited in the presence of oxygen, and it is characterized in that it additionally contains, in solution in the monomeric acrylic phase, an adjuvant for improving the impact and shear strength of the cured formulation, chosen from unreactive linear polyurethanes and crosslinked or uncrosslinked polyurethane networks formed in situ within the monomeric acrylic phase from a polyurethane precursor system dissolved in the said acrylic phase and comprising one or more polyfunctional isocyanates and one or more polyols, or/and a thermally stabilizing adjuvant consisting of at least one epoxy resin used in combination with a latent hardener for the said resin.
The presence, in the adhesive formulation, of the crosslinked or uncrosslinked polyurethane
REFERENCES:
patent: 4408023 (1983-10-01), Gould et al.
patent: 4533446 (1985-08-01), Conway et al.
patent: 4755571 (1988-07-01), Irving et al.
patent: 4929660 (1990-05-01), Chen
Hamilton, III Thomas
Marquis Melvyn I.
Societe Nationale Elf Aquitaine
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