Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1997-02-06
2002-02-19
Gallagher, John J. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S273500, C156S246000, C156S064000, C248S205300, C248S467000, C522S071000, C522S103000, C522S170000
Reexamination Certificate
active
06348118
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a thermosettable pressure sensitive adhesive, a sheet material comprising the adhesive, and a method for bonding components to glass.
BACKGROUND
In the automotive industry, mirrors bases have been attached to windshields and the automobile body by means of paste-like urethane or silicone adhesives, as well as polyvinyl butyral films. There have been some shortcomings of using the paste-like adhesives, including a lack of strength prior to curing which can cause the mirror base to slip and become misaligned. There is also a tendency to flow out under the weight of the mirror base, which may require an additional finishing step to remove the material that has flowed out. Polyvinyl butyral films, on the other hand, suffer from having poor moisture and heat resistance which can result in the mirror base falling off of the glass plate to which it is adhered.
U.S. Pat. No. 5,160,780 (Ono) describes the use of an organopolysiloxane material (also referred to in the industry as silicone rubbers) useful for bonding a mirror base to glass plate. The organopolysiloxane becomes cross-linked after autoclaving at elevated temperatures. However, the silicone rubbers are elastomeric and can be subject to creep during sustained loads.
Thermosetting pressure sensitive adhesive materials have been described in U.S. Pat. No. 5,086,088 (Kitano et al.). Viscoelastic materials useful in damping constructions are described in U.S. Pat. No. 5,262,232 (Wilfong et al.).
SUMMARY OF THE INVENTION
A method of bonding a component to glass comprising disposing a pressure-sensitive adhesive sheet material between said component and said glass so that said adhesive sheet material is adhered to said component and said glass. The adhesive sheet material comprises the photopolymerization reaction product of starting materials comprising:
(a) a monomeric mixture or partially prepolymerized syrup comprising at least one acrylic acid ester of an alkyl alcohol and at least one copolymerizable monomer;
(b) an epoxy resin or a mixture of epoxy resins;
(c) a heat-activatable hardener for the epoxy resin or mixture of epoxy resins;
(d) a photoinitiator; and
(e) a pigment.
In another embodiment, the starting materials further comprise a silane. The invention also provides a pressure-sensitive adhesive sheet material comprising the photopolymerization reaction product of starting materials comprising components (a) to (e) above and further comprising a silane.
DETAILED DESCRIPTION
The present invention provides colored thermosettable pressure sensitive adhesive sheet materials which change in the shade of color on curing. The preferred adhesives, after thermal curing, have a relatively low elasticity and are characterized by having an elongation at break of less than 100%, and preferably less than 75%. The cured adhesives have good vibration damping properties and exhibit a tan delta greater than 0.1 between a range of between about 0 C. and 170 C. The adhesive sheet materials are pressure sensitive in nature, i.e., tacky, and have a storage modulus between about 5×10
4
to about 10
7
dynes per square centimeter at room temperature before thermal curing. Alternatively, instead of thermal curing, the adhesive may be cured by radiation. After thermally curing of the sheet materials, the adhesives are thermoset and have a storage modulus greater than 2×10
7
between temperatures of−40 C. and 100 C. Preferably, the sheet material is initially prepared by coating a photopolymerizable, thermosettable pressure sensitive adhesive composition onto a film treated with a release coating and exposing to ultraviolet radiation to form the sheet material. The sheet material is subsequently adhesively adhered between two objects to be bonded, and thermally cured at temperatures from about 100 C. to 200 C. for about 5 to 60 minutes. As the pressure sensitive adhesive is cured to form a thermoset resin the adhesive becomes lighter in color as measured by a HunterLab colorimeter, and indicates when sufficient curing has occurred. In a preferred embodiment, the adhesive comprises an acrylic moiety, an epoxy moiety, and a pigment. In a more preferred embodiment, the adhesive comprises an acrylic moiety, an epoxy moiety, a coloring agent, and an organofunctional silane.
In the practice of the invention, the epoxy moiety comprises from about 20 to 150 parts by weight per one hundred parts of acrylate, i.e., the acrylate and the co-polymerizable monomers, and preferably from 40 to 120 parts epoxy per one hundred parts of acrylate, and more preferably 60 to 100 parts of epoxy per one hundred parts of acrylate. .In a highly preferred composition, the pigment comprises a carbon black or graphite pigment.
Preferred acrylic materials include photopolymerizable prepolymeric or monomeric acrylate mixtures. Useful acrylic materials include monoethyleneically unsaturated monomers that have a homopolymer glass transition temperature less than 0 C. Preferred monomers are monofunctional acrylic or methacrylic esters of non-tertiary alkyl alcohols having from 2 to 20 carbon atoms, and preferably from 4 to 12 carbon atoms in the alkyl moiety. Useful esters include n-butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, dodecyl acrylate, lauryl acrylate, octadecyl acrylate, and mixtures thereof.
The acrylate moiety may optionally include a co-polymerizable reinforcing monomer. The reinforcing monomer is selected to have a higher homopolymer glass transition temperature than a homopolymer of only the acrylate monomer. Useful reinforcing monomers include isobornyl acrylate, N-vinyl pyrrolidone, N-vinyl caprolactam, N-vinyl piperidine, N,N-dimethylacrylamide, and acrylonitrile.
A small amount of an acidic monomer, such as acrylic acid, may also be included in the acrylic moiety as long as it does not negatively affect the curing of the epoxy moiety or the desired overall performance of the adhesive. If used, the amount of acid is preferably less than about 2 percent by weight of the acrylic moiety, i.e., the total weight of the acrylate, the co-polymerizable reinforcing monomer, and the acidic monomer.
When the prepolymeric or monomeric mixture includes both an acrylate and a reinforcing monomer, the acrylate will generally be present in an amount of about 50 to 95 parts by and the reinforcing monomer will be present in a corresponding amount of 50 to 5 parts by weight.
The adhesive compositions also preferably include a free radical photoinitiator that is activatable by ultraviolet radiation. An example of useful photoinitiator is benzil dimethyl ketall (Irgacure™651 available from Ciba Geigy). The photoinitiator is typically used in amounts from about 0.01 to 5 parts by weight per 100 parts of the acrylate monomers.
The adhesives of the invention also preferably include an acrylate cross-linking agent. The cross-lking agent increases the modulus of the adhesive in the pressure-sensitive state so that when it is used to bond an object to a surface with pressure either from the weight of the object or from an external source it resists flowing out and around the object during thermal curing. Useful cross-linking agents are those that are free-radically polymerizable from acrylate monomers such as divinyl ethers and multi-functional acrylates that do not interfere with the curing of the epoxy resin. Examples of multi-functional acrylates include, but are not limited to, 1,6-hexanediol diacrylate, tri-methylol-propane triacrylate, pentaerythritol tetraacrylate, and 1,2-ethylene glycol diacrylate. Amounts up to about 1 part per 100 parts acrylate monomers are preferred, and amounts of 0.01 to 0.2 part are preferred.
Useful epoxy resins are selected from the group of compounds that contain an average of more than one, and preferably at least two epoxy groups per molecule. The epoxy resin can be either solid, semi-solid, or liquid at room temperature. Combinations of different types of epoxy resins can be used. Representative epoxy resins include, but are not limited to phenolic epoxy
Johnson Michael A.
Pennycook Jon M.
3M Innovative Properties Company
Gallagher John J.
O'Connell Patrick J.
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