Thermally crosslinkable heat-sealing adhesive

Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...

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Details

525453, 525456, 525458, 525528, 525532, 525533, C08F 2000, C08F28304

Patent

active

058046720

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to a thermally crosslinkable heat-sealing adhesive based on polyurethane and to its use in electrical articles.
2. Discussion of Related Art
A heat-sealing adhesive is a heat-activatable adhesive which is applied to one or both substrates to be joined and forms a film thereon. When the substrates are heated and pressed together, the adhesive is activated so that both parts are joined to one another after cooling. Heat-sealing adhesives are based inter alia on polymers of ethylene, vinyl chloride, vinylidene chloride, vinyl acetate and (meth)acrylates and also polyamides, polyesters and polyurethanes. If it is intended to establish heat-resistant bonds, thermoplastic polymers, such as polyesters, polyamide and polyolefin, are replaced by systems which crosslink on heating--generally to 150.degree. to 250.degree. C.--to form thermosets, such as for example polyurethanes, copolymethacrylates, epoxy resins and phenolic resins. The heat-sealing adhesives are applied to the substrate(s) by dip coating, impregnation, spray coating or by roll coating and screen printing. The substrates in question are, above all, web-form materials of metals and plastics in the form of films/foils, textiles and papers. In this way, two or more layers of the same kind or of different kinds may generally be joined readily to one another (laminated) by calendering.
A polyurethane-based thermally crosslinkable heat-sealing adhesive is described in DE-A-25 13 378. It consists of a polyurethane or polyisocyanates, a solvent and an adduct prepared from a polyfunctional epoxy compound and novolak (see claim 1). The epoxy resins are based, for example, on diphenylol propane or epoxidized cycloaliphatic dienes. However, they may also be diazine epoxy resins. Adducts of crystallized triglycidyl isocyanurate with novolak in a ratio by weight of 30:70 to 60:40, in which the epoxy content should be from 3 to 6%, are preferred. The bonding process requires only a light pressure of 1 to 10 kp/cm.sup.2 and, more particularly, 2 to 5 kp/cm.sup.2, temperatures in the range from about 120.degree. to 180.degree. C. and times of about 2 to 30 minutes. Copper/polyimide laminates produced in this way have a solder bath resistance of at least 10 seconds at 260.degree. C. Tensile strengths of 80 and 120 kg/cm.sup.2 and peel strengths of 11 and 20 kg/cm.sup.2 were measured on steel plates.
Unfortunately, this known adhesive no longer satisfies modern-day requirements. New technologies in the manufacture of printed circuits (surface assembly of components, rigid/flex circuits, remelting processes) require short-term heat resistances of 350.degree.C. In addition, new exterior applications for laminates require improved hydrolysis stability coupled with firm adhesion to critical materials (for example fluorine-containing polymers).
Accordingly, the problem addressed by the present invention was to provide heat-sealing adhesives of which the film would be tacky or blocking-resistant, depending on the particular requirements and formulation, and which would combine high heat resistance with high stability to hydrolysis. In more general terms, the adhesive would be easy to produce and more universal in its use and would show better performance properties.


SUMMARY OF THE INVENTION

The solution provided by the invention is defined in the claims. It lies in a thermally crosslinkable heat-sealing adhesive of a mixture of a polyacrylate, a modified bisphenol A or a polyol on the one hand and an epoxy resin
ovolak adduct on the other hand (component A) as reaction component for a polyisocyanate (component B) or a polyol (component C) of an OH-terminated polyurethane or polyester. The adduct consists of an epoxy resin based on bisphenol A, heterocyclic or aliphatic epoxy compounds and of novolak or bisphenol A novolak.
Component A contains a crosslinking adduct based on novolak and epoxy resin to which an acrylate polymer, a modified bisphenol A or a polyol is added.


DETAILED DESCRIPTION

REFERENCES:
patent: 4080401 (1978-03-01), Kassner
patent: 4560579 (1985-12-01), Siadat et al.
patent: 4836878 (1989-06-01), Irving et al.
patent: 5223106 (1993-06-01), Gerace et al.

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