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Thermoset imidazole cured epoxy-polysulfide rubber automotive body solder
| Details |
Inventors: Dearlove, Thomas J.; Gray, Richard K.; Atkins, Richard P.;
Assignee: General Motors Corporation (Detroit, MI)
Primary Examiner: Jacobs; Lewis T.
Assistant Examiner:
Attorney, Agent or Firm: Goldberg; Elizabeth F.
In a preferred embodiment, a spreadable, thermosetting automotive body solder is comprised of 100 parts of an epoxy resin adduct of epichlorohydrin and bisphenol A, 25 to 40 parts liquid polysulfide rubber, 0.02 to 0.06 moles of an imidazole curing agent substituted in the 2-position with a hydrocarbon group, and a filler system consisting of 5 to 20 parts aluminum powder, 10 to 20 parts ion-exchanged clay, 3 to 6 parts wetting agent for the clay, and 70 to 130 parts fibrous or plate talc average particle size 3 microns or less. The composition is workable for several hours at room temperatures but cures in a few minutes at temperatures over 100.degree. C. The filler system provides the body solder with thixotropic properties at room temperatures, and sag resistance in both the cured and uncured states at temperatures up to 200.degree. C. The solder is corrosion resistant without other additives. |
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DETAILED DESCRIPTION OF THE INVENTION Our invention may be more clearly understood in view of the detailed description which follows: In the drawings, FIG.
1 is a photomicrograph at 1000X magnification of Nytal.
RTM.
400 talc showing the generally fibrous nature of individual talc particles; FIG.
2 is a photomicrograph at 1000X magnification of Nytal.
RTM.
200 talc showing fibrous particles of substantially larger size than Nytal.
RTM.
400; FIG.
3 is a photomicrograph at 1000X magnification of Emtal.
RTM.
599 talc showing the plate-like nature of individual talc particles; FIG.
4 is a graph of viscosity versus Brookfield Viscometer spindle shear rates for each component of a two-part solder system.
The curves indicate their thixotropic natures; and FIG.
5 is a plot of lap shear strength of a solder composition plotted against time spent in crack and corrosion test cycles.
The curve is indicative of the durability of our solders under adverse environmental conditions.
In accordance with the practice of our invention, preferred solder constituents may be described as follows.
By epoxy resins, herein are meant adducts of epichlorohydrin and bisphenol A having epoxy equivalent weights in the range of from about 180 to 200.
These resins may also be referred to as diglycidyl ethers of bisphenol A (DGEBA).
Preferably, the epoxy resins are liquid to facilitate mixing with the other ingredients and promote mixtures with spreadable viscosities.
Cured bisphenol A-epichlorohydrin resins are fairly rigid.
Thus, a flexibilizer is required for our solder systems.
A number of different types were tried including flexible epoxy resins as well as carboxylic acids and amino terminated polybutadienes.
Surprisingly, none of these flexibilizers provided the epoxy resin with adequate shear strength or tensile elongation.
Higher flexibilizer loading levels did not improve the properties.
Polysulfide rubbers were found to be suitable flexibilizers for our body solder compositions.
Liquid mercaptan terminated polysulfides, number average molecular weight about 1,000, are particularly useful
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Manufacturing Materials 
