Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-06-03
2001-03-20
Yoon, Tae (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S539000, C528S220000, C524S401000, C524S425000, C524S443000, C524S451000, C524S492000
Reexamination Certificate
active
06204343
ABSTRACT:
DESCRIPTION
1. Field of the Invention
This invention relates to room temperature curable resin systems that are obtainable by a Michael reaction of a compound having two or more (&agr;,&bgr;-unsaturated groups and a Michael donor in the presence of a suitable catalyst. The obtained cured compositions are suitable for use in electrical applications and in particular for insulation of electrical splices.
2. Background of the Invention
Pourable resins which cure quickly to hard, tough masses have been used for years to protect and insulate electronic parts and electrical cables at points where they have been spliced together. Resins developed for protecting large cable splices have had great demands placed upon them because they are required to function under such adverse conditions. Electrical cables, in particular underground cables, and splices associated with them are routinely exposed to fluctuating temperatures as well as humidity and standing water. The elevated temperatures which the splice must withstand are caused not only by the environment, but also because of the heat generated by the passage of current through the electrical splice. The curable compositions according to the present invention and the splices made using them are suitable for, but not restricted to, low to medium voltage applications, typically those carrying a voltage in the range of up to 10K Volt.
Increasing awareness of environmental issues and pressure from regulatory authorities have made it necessary to develop new resin formulations for this purpose which have a reduced amount of toxic components or are essentially free of materials which are environmental or health hazards. In particular, curable resin systems where the crosslinking mechanism is based on polyurethane chemistry have been used. In such resins, hydroxyl-bearing oligomers such as polyether polyols are crosslinked using low molecular weight polyfunctional isocyanate compounds. Epoxy resins, also commonly used for splices, require the use of stoichiometric amounts of amine-containing hardeners. Replacement of isocyanate-containing and amine-containing systems with less objectionable systems is a long-standing need.
Recently, the use of curable compositions based on a Michael reaction of acetoacetylated resins as a replacement for isocyanate based cross-linking systems has been described as examplified by the publications discussed below. The Michael reaction is a well-known reaction for the formation of carbon-carbon bonds and involves the 1,4-addition of a stabilized carbanion to a &agr;,&bgr;-unsaturated carbonyl compound. This reaction is described in, for example, Mechanism and Structure in Organic Chemistry (E. S. Gould, p. 392-394; Holdt Rinehard and Winston, New York, 1959).
However when replacing the chemistry based on isocyanate cross-linking, it is desirable to have a curing system that meets the requirements generally imposed in electrical applications and in particular in insulation of electrical splice in low (up to 1K Volt) or medium (up to 10K Volt) voltage applications. Such requirements typically include, setting capability at room temperature, appropriate viscosity, good adhesion to cable jacket, high volume resistivity, high electrical resistance, an appropriate pot life, a high hardness and non-foaming behavior in the presence of water, low moisture pickup etc.
U.S. Pat. No. 5,132,367 describes NCO-free resins and cured products thereof. The cured products are obtained by a Michael reaction of an acetoacetylated (meth)acrylic resin or an acetoacetylated polyester and an NCO-free polyurethane having at least two (meth)acrylic end groups. U.S. Pat. No. 5,132,367 however does not teach the use of these products in electrical applications.
EP 227454 discloses a process for preparing a cured polymer involving the Michael reaction of an acetoacetylated polyol and a poly &agr;,&bgr;-unsaturated ester. The obtained cured products are said to exhibit excellent adhesion, excellent solvent resistance, excellent gloss retention, good flexibility and hardness.
U.S. Pat. No. 5,459,178 describes foundry mixtures comprising an acetoacetate ester, an &agr;,&bgr;-ethylenically unsaturated monomer and a liquid tertiary amine catalyst. A cured system is obtained by reacting these components. The acetoacetate ester used is prepared by transesterification of polyhydroxyl compound having an average of at least two hydroxy groups with an alkylacetoacetate.
DE 3508399 corresponding to U.S. Pat. No. 4,871,822 discloses a Michael reaction of olefinically unsaturated compounds with compounds containing at least two active hydrogens for 2 component lacquers. As olefinically unsaturated compounds there are considered compounds having at least two &agr;,&bgr;-unsaturated carbonyl groups. As Michael donors there are considered a large number of compounds amongst which are acetoacetylated polyols or polyamines and such compounds as e.g. acetylacetone or benzoylacetone.
David L. Trumbo in Polymer Bulletin 26, pages 265-270 (1991) discloses Michael addition polymers obtained from 1,4 and 1,3 benzenedimethanol diacetoacetates and tripropylene glycol diacrylate. He further describes that in case the reactants are used in stoichometric amounts of the reactive groups, gelation of the system is observed. In another paper (Polymer Bulletin 26, pages 481-485 (1991)) the same author described Michael addition polymers obtained from the reaction of a bis(acetoacetyl) amide or an aliphatic acetoacetate and a di-acrylate comonomer. However, no utilisation or properties of the polymers are described in these articles.
WO 95/16749 describes a water-borne curable composition that comprises an acetoacetylated polymer in the form of an aqueous solution, dispersion or emulsion and a polyacrylate that has at least two (meth)acrylate end groups. According to this publication, such composition is stable even in the presence of a catalyst until the water is evaporated from the system.
The use of acetoacetyl chemistry, in particular the use of acetoacetylated resin, in thermosetting systems is further described in Journal of Coatings Technology Vol. 61 no. 771 page 31 to 37; Journal of Coatings Technology Vol. 65 no. 821 page 63 to 69; Surface Coatings Australia, September 1989 page 6 to 15; and Journal of Coatings Technology Vol. 61 no. 770 page 83 to 91.
It is now an object of the present invention to provide a pourable, preferably solvent free, room temperature, curable low toxicity composition (isocyanate free) having appropriate electrical properties when cured, in particular insulating characteristics making it suitable for use in electrical applications and in particular for insulation of low- or medium-voltage electrical splices. By room temperature is meant a temperature of about 5° C. to about 30° C., in particular from about 10° C. to about 25° C.
Further objects of the present invention will become clear from the description hereinafter.
SUMMARY OF INVENTION
The present invention provides the use of a curable composition for electrical applications, said curable composition comprising (i) a compound having at least two &agr;,&bgr;-unsaturated groups and an equivalent weight of less than 250 g/mol, (ii) a catalyst capable of initiating a Michael reaction and (iii) a Michael donor having an equivalent weight of less than 250 g/mol.
This invention also provides a package containing constituents of a curable composition, said package comprising two compartments, one of said compartments comprising a Michael donor having an equivalent weight of less than 250 g/mol and a compound having at least two &agr;,&bgr;-unsaturated groups and an equivalent weight of less than 250 g/mol and the other compartment comprising a catalyst capable of initiating a Michael reaction.
The invention also provides the use of the above package for electrical applications, in particular for insulation of electrical splices.
Further, the present invention provides curable compositions.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with the present invention it was found that a cur
Barucha Dieter
Moren Dean M.
Stepputtis Manfred
Xu Frank Y.
3M Innovative Properties Company
Fonseca Darla P.
Yoon Tae
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