Sealants and adhesives and the use thereof

Details Sealants and adhesives and the use thereof Sealants and adhesives and the use thereof

1988-12-16

1990-08-21

Welsh, Maurice J.

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

20415777, 528 58, 528 59, 528 64, C08L 7504

Patent

active

049507150

DESCRIPTION:

BRIEF SUMMARY
Numerous formulations for sealants and adhesives are known, which contain prepolymers with telechelic isocyanate groups (produced from diisocyanates in stoichiometric excess with polyols) and which harden or set under the influence of moisture. When using aromatic isocyanates catalysts, such as in particular tin compounds, are added to these systems for speeding up hardening.
Such one-component PU systems are inter alia used in automobile manufacture for the direct glazing of motor vehicles. However, problems can occur if the atmospheric humidity is low, particularly in the case of lower temperatures in winter. The sealant then hardens so slowly, that the inserted panes or plates must be secured for a long period with the aid of suitable fixing devices. It is not possible to carry out further fitting work, e.g. the fastening of doors or working accompanied by the tilting of the body until the sealant has adequately hardened.
Although two-component PU systems are able to harden or set rapidly, they are much more difficult to handle and are much more complicated from the apparatus standpoint.
There is consequently a need for a one-component polyurethane based sealant and adhesive, which rapidly hardens to such an extent that adequate mechanical stability is achieved. However, complete curing, e.g. under the influence of moisture could take much longer without it impairing the fitting and assembly work.
For solving the aforementioned problems, the invention proposes a sealant and adhesive, which is both thermosetting and moisture-setting or initiating, so that it can be set by brief heating and then subsequently cured by moisture.
The known moisture-hardening PU-systems are only slightly accelerated by heat. However, it is known that prepolymers with terminal isocyanate groups can be crosslinked at elevated temperature, if a complex compound of methylene dianiline and sodium chloride is added thereto. At higher temperatures the methylene dianiline is decomplexed and reacts in a crosslinking reaction with the prepolymer. The mixture is stable in storage and is scarcely initiated by moisture at below the decomplexing temperature. It is also known that such PU systems can be heated and consequently hardened with the aid of microwaves (US patents 37 55 261 and 40 83 901).
The present invention therefore relates to thermosetting and moisture-setting one-component polyurethane sealants and adhesives based on telechelic isocyanate prepolymers of aromatic diisocyanates in stoichiometric excess and polyols, which are characterized in that they contain
(a) a catalyst for moisture-setting and
(b) a blocked crosslinking agent, which can be activated by heating.
The inventive sealants and adhesives can be hardened by brief heating and the subsequent curing is brought about by moisture action. Such a system in particular makes it possible to solve the above-described problems linked with the direct glazing of motor vehicles on assembly lines.
The polyurethane prepolymers are produced in per se known manner from excess aromatic diisocyanate and a polyol. Suitable aromatic diisocyanates are e.g. diphenyl methane diisocyanate (MDI), toluylene diisocyanate (TDI), naphthalene diisocyanate, p-phenylene diisocyanate and 1,3-bis(isocyanatomethyl)-benzene and m or p-tetramethyl xylene diisocyanate (m-TMXDI or p-TMXDI).
The polyol component can be in the form of polyether polyols, such as polyethylene oxide, polypropylene oxide and their copolymers, as well as polyester polyols.
The preferred catalysts for moisture setting of the aromatic isocyanate prepolymers are tin compounds, such as tin(II)-octoate, dibutyl tin laurate and dibutyl tin maleate. It is also possible to use organo-mercury, lead and bismuth compounds, such as e.g. phenyl mercury acetate or lead naphthenate.
Examples of blocked crosslinking agents which can be activated by heating are complexed amines, particularly the complex compound of methyl dianiline (MDA) and NaCl. The formula for said complex compound is generally given as (DA).sub.3.NaCl. The compound can be

REFERENCES:
patent: 3755261 (1973-08-01), VanGullck
patent: 4481345 (1918-11-01), Nachtkamp et al.

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