Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2000-07-26
2001-08-14
Berman, Susan W. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S113000, C522S100000, C522S102000, C522S134000, C522S143000, C522S083000, C522S066000, C522S064000, C522S071000, C522S122000
Reexamination Certificate
active
06274643
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to adhesive compositions. More specifically, this invention relates to adhesive compositions comprising thermoplastic resins and epoxy resins. The invention also provides a method of preparing adhesive compositions and adhesive articles and uses thereof.
BACKGROUND OF THE INVENTION
Adhesive composition blends of curable epoxy resins with various thermoplastic polymers are known. For example, adhesive compositions comprising epoxy and polyester thermoplastic resins have been used as hot melt adhesives and in the manufacture of structural bonding and sealing tapes.
However, adhesive compositions consisting of epoxy resins and thermoplastic polyesters have several deficiencies. For example, they can be prone to excessive flow prior to or during cure, unless flow control additives are incorporated. This excessive flow may result in a messy adhesive bond line that must be smoothed out in a subsequent step in cases where appearance is important (for example, exterior automotive applications such as trim adhesion, body panel and door skin replacement). Additionally, excessive flow can form gaps in the bond line which may lead to bond failure due to moisture penetration or corrosion. Also, those epoxy-polyester adhesive compositions that have been formulated not to undergo excessive flow typically lack sufficient tack to be used in the form of a thermosettable pressure-sensitive tape without incorporation of additional ingredients or a separate adhesive layer. Further, in order to obtain tack and good adhesion to painted metal substrates it is often necessary to increase the epoxy content of the adhesive composition above that level which otherwise achieves optimal properties.
Thermally curable compositions of epoxy resins having ethylene-vinyl acetate (also called “EVA” herein) copolymer particles dispersed therein have also been disclosed as toughened epoxy resins containing a dispersed phase of EVA polymerized in situ.
Epoxy material containing compositions having thermal curatives or hardeners such as those described above are difficult to melt process into articles (for example, tapes, films, or rods) without causing premature curing of the composition. Use of high temperature curatives that do not cause curing during such processing steps requires a high cure temperature during formation of the adhesive bond, which can cause excessive flow of the adhesive during cure thereby resulting in an aesthetically unpleasant or structurally defective bond or thermal damage on the case of thermally sensitive substrates.
SUMMARY OF THE INVENTION
The invention provides curable compositions formed by mixing components comprising:
a) from about 20 to about 80 weight percent of a curable epoxy resin;
b) from about 20 to about 80 weight percent of a thermoplastic ethylene-vinyl acetate copolymer resin; and
c) an effective amount of a photocatalyst for the curable epoxy resin such that the total of components a) and b) is 100 percent and, wherein the compositions are free from hydrocarbon polyolefins and are homogeneous mixtures.
The compositions of the invention, exclusive of additives, form homogeneous and single phased molten mixtures and resulting uncured solids, for example, unsupported films.
The compositions of the invention may also contain up to 50 percent by volume, preferably up to 30 percent by volume, of the total composition of various additives such as fillers, tackifiers, and the like.
In another aspect, the invention describes a method comprising the steps of:
a) providing a homogeneous molten mixture comprising a curable epoxy resin, a thermoplastic ethylene-vinyl acetate copolymer resin; and an effective amount of a photocatalyst for the curable epoxy resin, wherein the composition is free from hydrocarbon polyolefins;
b) applying the mixture to a substrate or processing into an unsupported film; and
c) at any subsequent time, activating the photocatalyst to cure the epoxy containing material.
If necessary, the compositions may be heated to accelerate cure or to ensure complete cure.
The present invention overcomes the deficiencies of polyester-epoxy and thermally cured EVA-epoxy adhesives by providing compositions having significant tack in the uncured state, good cured adhesion to surface treated (for example, E-coated) metals, low controlled flow during curing and desirable physical properties of the cured resin (structural adhesive and cohesive strength, and paintability). The improved tack of the adhesive in the uncured state keeps the adhesive in place during assembly and minimizes the need for the use of clamps during the cure step. Further, the present invention provides bonding tapes characterized by good tack, limited mass flow and structural bond strength (that is, >1000 psi (6.9 mega Pascals (Mpa)) overlap shear strength) and can be processed on a 100 percent solids basis without the use of solvents typically used in the art.
The adhesive compositions of the invention are free from, that is, do not contain, hydrocarbon polyolefin resins. “Hydrocarbon polyolefin resin” refers to a fully prepolymerized uncrosslinked polymeric hydrocarbon bearing essentially no organic functional groups, prepared from homopolymerization and/or copolymerization of an olefinic monomer(s). Such resins are typically incompatible with epoxy resins and will cause phase separation of compositions containing an appreciable amount of epoxy resin. Examples of such resins include polyethylene, polypropylene, and the like, and poly(ethylene-co-propylene), poly(propylene-co-1-butene), and the like.
A “tape” is defined as an uncured adhesive film attached to either a release liner or a backing that can be formed into a roll or cut into pieces and having a length greater than its width.
An “unsupported film” is defined as an uncured adhesive film having adhesive characteristics that may be tacky or not tacky at ambient temperature.
A “curable” or “uncured” composition is a composition that remains thermoplastic and melt processable and substantially uncrosslinked until subjected to either heat, light, or a combination of both at which time the composition polymerizes and/or crosslinks to form a thermoset material.
A “protected film” is an uncured adhesive film having a release liner or backing attached that can be formed into a roll or cut into pieces and having a length that is substantially the same as its width.
DETAILED DESCRIPTION
The adhesive compositions of the invention comprise from about 20 to about 80, preferably 30 to 70, more preferably 40 to 60 weight percent of an epoxy containing material, from about 20 to about 80, preferably from about 30 to about 70, more preferably from about 40 to about 60, weight percent ethylene-vinyl acetate copolymer, and an effective amount of a photocatalyst for the curable epoxy containing material, the weight percent being based on the total weight of epoxy resin and ethylene-vinyl acetate copolymer, and the compositions are free of hydrocarbon polyolefin resins.
Epoxy resins useful in the adhesive compositions of the invention are any organic compounds having at least one oxirane ring, that is,
polymerizable by a ring opening reaction. Such materials, broadly called epoxides, include both monomeric and polymeric epoxides and can be aliphatic, alicyclic, heterocyclic, cycloaliphatic, or aromatic and can be combinations thereof. They can be liquid or solid or blends thereof, blends being useful in providing tacky adhesive films. These materials generally have, on the average, at least two epoxy groups per molecule and are also called “polyepoxides.” The polymeric epoxides include linear polymers having terminal epoxy groups (for example, a diglycidyl ether of a polyoxyalkylene glycol), polymers having skeletal oxirane units (for example, polybutadiene polyepoxide), and polymers having pendent epoxy groups (for example, a glycidyl methacrylate polymer or copolymer). The molecular weight of the epoxy resin may vary from about 74 to about 100,000 or more. Mixtures of various epoxy resins can also be used in t
George Clayton A.
Karim Naimul
Meyer Christopher M.
3M Innovative Properties Company
Bardell Scott A.
Berman Susan W.
McClendon Sanza
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