Coating processes – Direct application of electrical – magnetic – wave – or... – Polymerization of coating utilizing direct application of...
Reexamination Certificate
1999-10-27
2001-03-13
Cameron, Erma (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Polymerization of coating utilizing direct application of...
C427S493000, C427S385500
Reexamination Certificate
active
06200645
ABSTRACT:
The invention relates to polyester resin impregnating and coating solutions, to their use for coating shaped articles, and to corresponding processes for the coating of shaped articles.
It is necessary to provide the windings and surfaces of electrical components with electrically insulating coatings for electrical insulation and for protection against external influences such as rain, splashes of water, dust, salts, solvents or mechanical influences. These coatings can be produced by impregnation or coating with electrically insulating resins. At the present time, polyester resin compositions are principally employed for these applications.
In this context it is common to employ unsaturated polyesters as impregnating resin in the form of a solution in a copolymerizable monomer, generally styrene. Following the coating of the shaped articles or components with the polyester resin compositions they are cured by copolymerization with the monomers, especially styrene.
DE-A-31 07 450 describes unsaturated polyesters of this kind containing cyclopentadiene oligomers as end groups. They are composed of maleic acid as unsaturated acid component and are employed in the form of solutions in styrene for the production of shaped articles and coatings.
DE-A-32 30 924 describes processes for preparing unsaturated polyester resins based on maleic anhydride as unsaturated acid component, the resulting polyesters being reacted with dicyclopentadiene, and esterification being carried out in the presence of N-hydroxyalkylimides of monounsaturated cycloaliphatic 1,2-dicarboxylic acids. The polyesters are dissolved in styrene.
EP-B-0 118 786 and EP-B-0 260 688 describe processes for preparing molding materials from unsaturated polyester resins, where esters, based on maleic anhydride as a saturated acid and reacted with dicyclopentadiene, are dissolved in styrene and cured in a two-stage curing process using two different free-radical initiators.
DE-A-1 570 273 and DE-A-1 720 323 describe unsaturated polyesters having cyclic imide groups. These polyesters are also employed as a solution in styrene.
In addition, impregnating varnishes are employed. They comprise dissolved resins, which are frequently based on natural oils and resins and which may also be chemically modified and combined with synthetic polymers, such as alkyd-epoxy resins or phenolic resins. For processing they are dissolved in solvents with typical concentrations of about 50%. The solvents employed here are predominantly aromatic hydrocarbons, such as toluene or xylene, alone or in combination with aliphatic or cycloaliphatic hydrocarbons, such as white spirit. In this case, only low concentrations are obtained in these solutions. Moreover, a high level of safety expenditure is necessary because of the solvents used.
When the above-described polyesters are employed as impregnating resins in the form of solutions in copolymerizable monomers, such as acrylates, allyl phthalate, styrene, methylstyrene or methyltoluene or vinyltoluene, or as impregnating varnishes in the form of solutions in aromatics, some of these monomers or aromatics are released in the course of the use of the mixtures for coating. Known applications of impregnating compositions with these substances are accompanied by losses in mass of about 20 to 30%. These considerable amounts must be removed from the workplace, since the monomers or aromatics are in many cases injurious to health and irritant to the skin, and thus constitute a health hazard to those working with these materials. The amounts of monomer or aromatics drawn off by suction are generally disposed of in waste-air incinerators, possibly giving rise to unwanted emissions. Furthermore, the substances lost in this way represent a considerable economic loss. Furthermore, there is a risk that the monomers will not be completely copolymerized in the course of curing. Residual monomers and aromatics remaining in the cured compositions may escape, especially from electrical insulation compositions, which generally become hot during use, and can cause odor pollution or damage to health. The monomers may also undergo after curing in the compositions, as a result of which they may undesirably alter the service properties of the compositions.
It is an object of the present invention to provide polyester resin impregnating and coating solutions (impregnating varnishes) which avoid these disadvantages and which, in particular, have a high solids content and an acceptable solvent.
We have found that this object is achieved in accordance with the invention by a polyester resin impregnating and coating solution comprising polyesters having structures of the formula (I)
where n is from 0 to 10 and where the solution is essentially free from monomers containing acrylic, vinylic or allylic unsaturation.
It has been found in accordance with the invention that the abovementioned unsaturated polyesters or polyester resins can be cured even without the use of the monomers containing acrylic, allylic or vinylic unsaturation which have hitherto been regarded as absolutely necessary. The compositions are essentially free from these monomers. The term “essentially” means here that there are no amounts of monomers containing acrylic, allylic or vinylic unsaturation that substantially alter the properties of the polyester resin compositions. The amount of monomers containing acrylic, allylic or vinylic unsaturation is preferably not more than 30, particularly preferably not more than 10 and, in particular, not more than 5% by weight based on the overall weight of the polyester resin compositions. With particular preference the polyester resin compositions are free from monomers containing acrylic, allylic or vinylic unsaturation. It has been found that, by using solvents other than compounds containing acrylic, allylic or vinylic unsaturation, it is possible to obtain highly concentrated polyester resin solutions. The content of solvents is preferably from 5 to 60, particularly preferably from 8 to 20, in particular from 10 to 15% by weight, based on the overall weight of the polyester resin solution. The term “solvent” here means those solvents or diluents which are preferably partially or completely free from aromatics which do not enter into any chemical reactions, especially in the course of curing. These are compounds which during or after curing escape from the polyester resin compositions or remain in them without entering into chemical bonds to the polymer structure. Monomeric or oligomeric compounds carrying functional groups which allow them to be reacted in the course of curing of the polyester resin are not embraced by the term “solvent”. As solvents it is preferred to employ aliphatic saturated C
2-6
alcohols, C
3-6
ketones or C
3-6
carboxylic esters or mixtures thereof It is particularly preferred to employ aliphatic saturated C
2-4
alcohols, such as ethanol n-propanol, isopropanol, n-butanol, isobutanol and tert-butanol. The polyester resins employed in accordance with the invention are highly soluble in these solvents, preferably in concentrations of more than 70% by weight, with particular preference more than 75% by weight, and in particular, more than 80% by weight. The solvents dry well so that the polyester resin compositions, after application, can easily be freed from the solvents. The health hazard due to the preferred solvents is low compared to aromatic solvents. The solutions here are of low viscosity, rendering them suitable as impregnating and coating solutions for the coating of shaped articles.
The shaped articles coated by the novel process are preferably electronic or electrical components or carrier materials for electrical insulators, especially flat electrical insulators. Examples of such shaped articles or components are wires, coils, motor windings, transformer windings and other components. Insulators which can be used include carrier materials for sheet-like insulating materials, such as glass fibers, mica tapes and other absorbent materials, and also combinations thereof, and in this
Blum Rainer
Eichhorst Manfred
Lienert Klaus-Wilhelm
Cameron Erma
Keil & Weinkauf
Schnectady International Inc.
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