Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2001-06-05
2003-07-01
Dixon, Merrick (Department: 1774)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S040200, C428S068000, C428S200000, C428S433000, C156S273500, C156S275500, C156S307300, C156S320000, C156S329000
Reexamination Certificate
active
06586089
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to reinforcing sheets such as those adapted for applying localized reinforcement to sheet metal or sheet plastic structures.
It is common practice in the automotive industry to apply reinforcing sheets to sheet metal and other parts for localized, lightweight reinforcement. Examples of such reinforcing sheets are described, for example, in U.S. Pat. No. 4,444,818 to Tominaga, U.S. Pat. No. 4,766,183 and U.S. Pat. No. 4,842,938 to Rizk et al., U.S. Pat. No. 4,803,105 to Kretow et al., U.S. Pat. No. 4,803,108 to Leuchten et al., and U.S. Pat. Nos. 4,900,601, 4,929,483 and 5,092,947 to Hälg et al. Generally, these reinforcing sheets include one or more layers of a stiffening material and one or more layers of a polymeric material that acts as a binder for the stiffening material as well as an adhesive for securing the reinforcing sheet to a substrate. Often, protective foils, moisture barriers and other layers may be included in the reinforcing sheet.
A common adhesive for these reinforcing sheets is described in U.S. Pat. No. 4,803,105. That adhesive includes a mixture of an epoxy resin, a curing agent and a carboxy-terminated butadiene-acrylonitrile rubber. The butadiene-acrylonitrile rubber commonly used contains about 18 weight % or more polymerized acrylonitrile, has a glass transition temperature of about −52° C. or higher and has a solubility parameter, as reported by its manufacturer, of about 8.82 or above. The amount of the butadiene-acrylonitrile rubber is such that the adhesive as a whole contains about 4% or more by weight polymerized acrylonitrile. The rubber is typically pre-reacted with a portion of the epoxy resin before being formulated into the adhesive mixture. The rubber imparts a certain amount of toughness to the adhesive once it is cured.
In the automotive industry, these reinforcing sheets are typically applied to exterior body panels. Because the epoxy resin in these reinforcing sheets must be cured, the reinforcing sheets are usually applied before the body panel is painted, so that the epoxy resin and paint can be cured simultaneously. Often, the unpainted body panel (or other substrate) is contaminated with oily materials. In other cases, the substrate is cold for one reason or another when the reinforcing sheet is applied.
The epoxy adhesive commonly used in the reinforcing sheets does not adhere well to oily or cold surfaces. When these conditions are present, the manufacturer either accepts that a certain amount of reinforcing sheets will be poorly adhered, or else the substrate parts must be warmed and/or cleaned before applying the reinforcing sheet. Neither of these options is attractive. Warming and cleaning the substrate introduce extra steps into the process of assembling a vehicle. This in turn imposes extra costs for time, energy and handling. It would be desirable to provide a reinforcing sheet that adheres better to oily or cold substrates.
SUMMARY OF THE INVENTION
This invention is a reinforcing sheet comprising at least one layer of a reinforcing material and a layer of a solid thermosetting adhesive, wherein the thermosetting adhesive includes (a) a curing agent and (b) an epoxy-terminated adduct of an epoxy resin and a conjugated diene or conjugated diene
itrile rubber containing not more than about 15% by weight polymerized nitrile monomer, and wherein said thermosetting adhesive contains no more than about 3.5% by weight polymerized nitrile monomer.
Surprisingly, the reinforcing sheet of the invention adheres well to oily substrates as well as to colder substrates, compared to otherwise similar reinforcing sheets in which the nitrile monomer content in the thermosetting adhesive layer is somewhat higher.
In a second aspect, this invention is a method of reinforcing a substrate, comprising
(A) applying to the substrate a reinforcing sheet comprising at least one layer of a reinforcing material and a layer of a solid thermosetting adhesive, wherein the thermosetting adhesive includes (a) a curing agent and (b) an epoxy-terminated adduct of an epoxy resin and a conjugated diene or conjugated diene
itrile rubber containing not more than about 15% by weight polymerized nitrile monomer, and wherein said thermosetting adhesive contains no more than about 3.5% by weight polymerized nitrile monomer, and then
(B) curing said thermosetting adhesive.
DETAILED DESCRIPTION OF THE INVENTION
The thermosetting adhesive layer of the invention includes an epoxy-terminated adduct of an epoxy resin and a diene rubber or a conjugated diene
itrile rubber having containing not more than about 15% by weight polymerized nitrile monomer. This adduct is suitably prepared in the reaction of a polyepoxide with a carboxy-functional conjugated diene rubber or a conjugated diene
itrile rubber.
The diene rubber is a polymer of a conjugated diene monomer such as butadiene, isoprene, and the like. Butadiene rubbers are preferred. Conjugated diene
itrile rubbers are copolymers of a conjugated diene and an ethylenically unsaturated nitrile monomer, of which acrylonitrile is the most preferred one. When a conjugated diene
itrile rubber is used, at least one such rubber present in the composition contains less than about 15 weight percent polymerized unsaturated nitrile, and preferably no more than about 12 weight percent polymerized unsaturated nitrile. The rubber also contains terminal groups that will react with an epoxide to form a covalent bond thereto. Preferably, the rubber contains from about 1.5, more preferably from about 1.8, to about 2.5, more preferably to about 2.2, of such terminal groups per molecule, on average. Carboxyl-terminated rubbers are preferred.
The rubber is preferably a liquid at room temperature, and preferably has a glass transition temperature of less than about −55° C., preferably from about −60 to about −90° C. The molecular weight (M
n
) of the rubber is suitably about 2000 to about 6000, more preferably from about 3000 to about 5000.
Suitable carboxyl-functional butadiene and butadiene/acrylonitrile rubbers are commercially available from B. F. Goodrich under the trade names Hycar® 2000X162 carboxyl-terminated butadiene homopolymer and Hycar® 1300X31 carboxyl-terminated butadiene/acrylonitrile copolymer. A suitable amine-terminated butadiene/acrylonitrile copolymer is sold under the tradename Hycar® 1300X21.
In addition, a conjugated diene or conjugated diene
itrile rubber having a somewhat higher polymerized nitrile content (“high nitrile rubber”) can be used in addition to the rubber described above. Higher acrylonitrile content provides better adhesion between the polymer and some substrates such as glass, and tends to increase flexural strength somewhat. The high nitrile rubber also preferably contains terminal epoxy-reactive groups. The high nitrile rubber advantageously contains from above 15%, more preferably at least about 18% to about 40%, more preferably to about 32% polymerized nitrile monomer. The high nitrile rubber suitably has a molecular weight of about 3000 to about 6000, and contains from about 1.5 more preferably from about 1.8, to about 2.5, more preferably to about 2.2, epoxy-reactive terminal groups per molecule, on average. Examples of such high nitrile rubbers are Hycar® 1300X8, Hycar® 1300X13®, Hycar® 1300X9 and Hycar® 1300X18 carboxyl-terminated butadiene acrylonitrile copolymers, all commercially available from B. F. Goodrich.
The rubbers (i.e., the conjugated diene or conjugated diene
itrile rubber, plus the high nitrile rubber, if used) are present in an amount such that the thermosetting composition contains no more than about 3.5% polymerized nitrile monomer. It is more preferred that the thermosetting adhesive contains from about 1 to about 3.25% by weight polymerized nitrile monomer. Preferably, the rubbers constitute from about 5, more preferably from about 10, to about 40, more preferably to about 25% of the total weight of the thermosetting adhesive. The high nitrile rubber preferably constitutes no more than 50, prefer
Dixon Merrick
Dow Global Technologies Inc.
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