Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Patent
1998-07-06
2000-12-19
Berman, Susan
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
522 13, 522 35, 522104, 522107, 522179, 522904, 522905, 528289, 528291, 528292, 528300, 528302, 528303, 528306, 528307, C08F 250, C08F 63199, C08F 6352, C08L 3106, C08G 63137
Patent
active
061628409
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the use of monomer-free polyester resins as impregnating, casting and coating compositions for electrical and electronic components and for carrier materials for sheet-form insulating materials.
The polymer matrix of known impregnating, casting and coating compositions for electrical components, such as motor windings, transformer windings and the like, is composed of unsaturated polyesters dissolved in compounds containing vinylic unsaturation, such as styrene, vinyltoluene, allyl phthalate and monomeric or oligomeric acrylic or vinylesters by means of free-radically initiated copolymerization. The term impregnating, casting and coating compositions refers to resin compositions which are employed in electrical engineering by the generally known processes of dip impregnation, the trickle technique, the dip-rolling technique, the flooding technique and the process of casting for the impregnation of windings, these processes possibly being assisted by the application of reduced pressure, superatmospheric pressure or a combination of both. The term also embraces the impregnation of carrier materials for sheet-form insulating materials such as glass fibers, mica tapes and other absorbent materials, and combinations thereof, and in this context one option is to terminate curing at the B-stage in order to obtain curable prepregs.
Disadvantages of this prior art process result from the unsaturated monomers which are absolutely necessary for rapid and complete curing of the compositions. Examples of such substances are acrylates, allyl phthalate, styrene, .alpha.-methylstyrene and vinyltoluene, either in monomeric form or as low molecular mass oligomers. These substances are injurious to health and are skin irritants. Known applications of impregnating compositions using these substances are accompanied by losses in mass of 20-30%. These considerable amounts must be removed from the workplace in order to avoid a health hazard to employees. The evaporated materials, drawn off by suction, are generally disposed of in waste-air incinerators, giving rise to unwanted emissions. The incinerated substances are also associated with considerable economic losses. Furthermore, there is a risk of these monomeric substances not being incorporated completely in the course of curing. Residual monomers remaining in the cured compositions may escape, especially from electrical-insulation compositions, which generally become hot during use, and can cause odor pollution or health damage, or else they gradually undergo aftercuring in the compositions, thereby undesirably altering the service properties of such compositions.
Unsaturated polyester resins containing structural units of dihydrodicyclopentadiene (=DCPD) are the subject of numerous patents.
DE-A-31 07 450 describes unsaturated polyesters containing cyclopentadiene oligomers as end groups, which in the form of solutions in ethylenically unsaturated monomers are used to produce moldings and coatings.
EP-A-101 585 relates to unsaturated polyester resins which are modified by the addition of cyclopentadiene onto the double bond of the polyester and are then dissolved in vinyl monomers.
EP-A-118 786 relates to unsaturated polyester resins which are modified with dicyclopentadiene and, as solutions in vinyl or allyl monomers, are cured in a two-stage process in order to form molding compounds with high temperature resistance. The second stage of this process requires the use of temperatures of above 200.degree. C. for at least one hour, preferably 250.degree. C. for 24 hours, or irradiation with accelerated electrons with an acceleration voltage of 300-1000 kV. The good properties of such compositions is said to make them suitable for use in the electrical sector. However, the aftercuring conditions required rule out use as a casting composition for the majority of applications, since more modern electrical assemblies, comprising a combination of electrical and electronic components, are destroyed by such high temperatures. Furthermore, the long
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Blum Rainer
Eichhorst Manfred
Hegemann Gunther
Loerzer Thomas
Berman Susan
Dr. Beck + CO.AG
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