Adhesive compositions for bonding and filling large assemblies

Abstract

Adhesive composition for bonding and filling large assemblies, including a mixture of about 5 percent to about 75 percent by weight of a thermoplastic polymer, about 0.5 percent to about 35 percent by weight of a polyester resin or vinyl ester resin, and about 20 percent to about 80 percent by weight of an alkyl acrylate or methacrylate monomer.

Description

BACKGROUND OF INVENTION 1. Field of Invention This invention relates to polymerizable vinyl adhesive or filling compositions that are useful for a variety of adhesive, coating, filling, repair and related applications. More particularly, this invention relates to two-part room-temperature curing polymerizable vinyl adhesive compositions comprising mixtures of free-radical polymerizable monomers and additives that generate heat and undergo expansion and contraction during the polymerization process. The improved compositions comprise mixtures of elastomers, thermoplastic resins, acrylate, methacrylate and styrenic monomers, and polyester or vinyl ester resins that can be applied in large masses or thick cross sections without gassing and void formation from the exothermic cure reaction. It also relates to improvements in the ability of adhesives based on the compositions to bond thermoplastic and thermoset materials, and to bond such materials with a reduced tendency to cause “read...

AI Technical Summary

Benefits of technology

This invention provides compositions that include about 5 percent to about 75 percent of a thermoplastic or partially thermoplastic polymer or elastomer, about 0.5 percent to about 35 percent of an unsaturated polyester resin or vinyl ester resin, and about 20 percent to about 80 percent of an acrylate or methacrylate monomer. The inventive compositions exhibit better control of the exothermic curing and dimensional changes associated with adhesives and filling compositions. As a result, they can be applied in thicker masses and can be used to bond and fill large areas and gaps with greatly reduced tendency to gas or boil, exhibit read-through or print-through or other effects of reaction exotherm, with freedom from the negative effects of under-curing at the surface or in thin cross-sections or films.

Problems solved by technology

However, adhesive applications are among the most demanding of those anticipated for such compositions.

The growing acceptance of methacrylate adhesives has extended their use to larger and larger assemblies and applications, which has resulted in more demanding application requirements.

Conventional and prior art techniques for increasing the open working time of adhesives by retarding the onset of cure or cure rate of the composition with chemical inhibitors or retarders often introduce unwanted negative factors or compromises in the application or performance characteristics of the compositions.

This can be a particular problem with open molded fiberglass structures, which are prevalent in the construction of boats, large vehicular assemblies, architectural structures, bridge decks, and other large structures.

When traditional polymerizable methacrylate adhesives are applied in such thick gaps, the exothermic reaction of curing and the volatility of the monomer generally cause gassing and the formation of voids in the adhesive bond which lead to unacceptable bond integrity and part performance.

The additive techniques described above for increasing open working time can also be used to reduce the exotherm and gassing problem, but the same negative application and performance characteristics generally result.

However, such fillers often have a negative effect on the strength and durability of the compositions in adhesive applications.

This is an appearance problem that can result when an adhesive is used to bond an inner reinforcement, stiffener, bracket or other component to an outer panel or “skin” that has a smooth or glossy finish.

The irregularity is generally a depression, outline, distortion or other disturbance of the surface that is visible to the eye and which is aesthetically objectionable.

The occurrence and severity of the problem generally increases with the thickness of the bond and the overall mass of adhesive involved.

The causes of such appearance problems can be complex, including contributions from the specific nature of the bonded substrates.

However, as in the case of the gassing problem noted above, the exclusive addition of these inert components in quantities that are sufficient to effectively reduce read through are generally detrimental to the performance of the adhesives.

However, as pointed out in U.S. Pat. No. 5,859,160 referenced below, these techniques can allow other, undesirable competing side reactions such as oxygen inhibition to interfere with effective polymerization and bond formation.

The disadvantages of such air inhibition, as noted in U.S. Pat. No. 5,932,638 also referenced below, include weakening of the adhesive bond, increased odor resulting from escaping, unreacted monomer, and problems related to tackiness of the surface of the adhesive.

The problem is especially acute when low levels of catalytic species and added retarding agents are used to extend the open working time of methacrylate based adhesive compositions to periods of about 45 minutes to one hour or more.

The problem is further exacerbated by low ambient application temperatures that further reduce the cure rate, and may prevent completion of the free-radical curing process.

It is well known to those skilled in the art that the addition of styrenic monomers to certain methacrylate compositions, especially when combined with low levels of catalytic species to extend open time and reduce exothermic gassing, can have a negative effect on the cure behavior of adhesives.

However, actual commercial experience has shown that even the lesser amounts of uncured adhesive cited can be sufficient to cause serious lingering odor problems.

Such problems can occur when, for example, the incompletely cured surface of a squeezed out bead or “fillet” of adhesive is in a confined area such the stringer grid of a boat.

The problem can be further exacerbated when the fillet or other uncured adhesive bond area is trimmed or smoothed with a spatula or other device that smears a thin film of the adhesive against an exposed surface such as the boat hull.

The resulting thin film of adhesive is especially susceptible to the effects of air inhibition.

Trapped vapors can eventually migrate to the enclosed cabin area of the boat and create an objectionable or unacceptable level of odor in spite of the very low levels that are present.