Coating processes – Direct application of electrical – magnetic – wave – or... – Polymerization of coating utilizing direct application of...
Reexamination Certificate
2000-02-02
2002-09-24
Berman, Susan W. (Department: 1711)
Coating processes
Direct application of electrical, magnetic, wave, or...
Polymerization of coating utilizing direct application of...
C522S179000, C522S181000, C522S107000, C427S501000, C427S512000, C427S513000, C427S058000, C427S096400, C427S116000
Reexamination Certificate
active
06455111
ABSTRACT:
The present invention relates to the use of unsaturated polyester resins as impregnating, casting and coating compositions for electrical and/or electronic components and for carrier materials for sheetlike insulating materials.
The present invention also relates to coating compositions suitable for this purpose which can be cured with low levels of emissions.
By impregnating, casting and coating compositions are meant, according to the present application, resin compositions that are employed in electrical engineering by the commonly known methods of dip impregnation, the trickle technique, the dip-rolling technique, the flooding technique and the process of casting for the impregnation of windings or the like, these methods possibly being assisted by the application of reduced and/or superatmospheric pressure. This term also embraces the impregnation of carrier materials for sheetlike insulating materials, such as glass fibres, 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.
The windings of electrical machines are customarily impregnated by saturation. The function of this impregnation is to induce a mechanical strengthening of the winding, so that the winding is able to absorb mechanical and electromechanical forces, so that the winding is protected against harmful external influences, such as, for example, the deposition of dust particles, collector abrasion, humidity, salts and solvents, so that mechanical damage due to particles sucked in, for example, by the fan is prevented and so that the heat which develops when the electrical machines are operated can be dissipated by ohmic and dielectric losses from the winding to the surrounding cooling devices, which contributes to prolonging the service life of the electrical device.
The impregnation of these windings, or the coating/impregnation of other electrical and/or electronic components, is usually carried out by means of resins or lacquers which cure to form thermosets. Since firstly the requirements on the long-term thermal stability of these thermosets are very high and secondly the properties set out above, especially the electrical insulation capacity, must be provided, there are a range of lacquers and resins that are tailored to the specific fields of use.
In the case of the solvent-containing lacquers, whose solvent fraction must be removed prior to the curing operation, the penetrative extent of impregnation of the electrical windings is generally poor in the case of a single application. This hinders the dissipation, already referred to above, of ohmic and dielectric heat losses from the interior of the windings. In addition, the removal of the solvent often necessitates long preheating periods and complex temperature regimes for the curing of the lacquer. With the solvent-containing lacquers, moreover, expensive apparatus is required for cleaning the waste air, since otherwise there is considerable pollution of the environment as a result of solvent vapours.
For this reason the lacquers in the electrical industry, aside from special cases, have been replaced by solvent-free resins. Here, the unsaturated polyester resins in particular have come to occupy a broad area, since they have considerable advantages over other thermosetting resin systems. For example, the properties required can to a large extent be met by molecular tailoring of the unsaturated polyester resins: for example, the selection of specific monomer building blocks or the establishment of specific molecular weights. In addition, the reactivity of the unsaturated polyester resins can be influenced in such a way as to permit short and hence cost-effective production processes for windings of electrical machines.
The unsaturated polyester resins, and especially the unsaturated polyesterimide resins, have particularly outstanding properties with respect to the requirement of long-term heat resistance in particular.
In general, the unsaturated polyester resins are constructed on the one hand from base resins consisting, for example, of alpha,beta-unsaturated dicarboxylic acids, further, modifying mono-, di- and/or polycarboxylic acids, di- and/or polyols and, in the case of polyesterimides, from imide-functional hydroxyl- and carboxyl-containing building blocks, and on the other hand from comonomers which react with the alpha,beta-unsaturated dicarboxylic acid units of the base resin and are able to lead to thermosets. A preferred comonomer is styrene, which owing to its good dissolution properties is also used to establish the processing viscosity. Under appropriate conditions in the course of curing, the comonomers are fully copolymerized. A solvent-free system of this kind is dubbed an impregnating resin. As with the impregnating lacquers, the vapour pressures of the comonomers give rise at application temperature to evaporation losses, although generally lower than those in solvent-containing systems (50%, based on amount of solvent employed, evaporation loss with solvent-containing impregnating lacquers, from 10 to 30% evaporation loss with impregnating resins).
Nevertheless, even when using impregnating resins based on unsaturated polyesters there is still a need for the waste air to be cleaned, although such waste-air units can be given a lower design cleaning capacity than when impregnating lacquers are used, since by suitable resin formulations and process adaptations it is possible to reduce the monomer losses.
The use of other resin systems, such as epoxy resins, for example, has the disadvantages that long curing times are necessary, that the possibilities for adapting the processing properties to the production processes are small without seriously impairing the dielectric properties, and that some resin constituents, such as, in the case of epoxy resins, for example, the highly heat-resistant cycloaliphatic types and, in the case of the curing agents, the amines, may have a high toxicity.
German Patent Application P 195 425 64.2, then, which is not a prior publication, describes a process for impregnating electrically conducting substrates which uses free-radically curing resin systems which in addition to a resin that can be cured free-radically to form a thermoset, a hardener and, if desired, an accelerator may also include, if desired, comonomer-free vinyl ethers. Details of suitable vinyl ethers, however, are not given in this document. German Patent Applications P 196 00 136.6 and P 196 00 137.4, likewise not prior publications, disclose solvent-free coating compositions comprising polyesters having dihydrodicyclopentadienyl end groups. These coating compositions in accordance with German Patent Application P 196 00 136.6 are used for coating or for printing metal containers, and the coating compositions in accordance with German Patent Application P 196 00 137.4 are employed, in particular, as printing inks.
Furthermore, German Patent Applications P 196 00 149.8 and P 197 07 492.8, both not prior publications, disclose the use of polyester resins having dihydrodicyclopentadiene end groups as impregnating, casting and coating compositions for electrical and electronic components. The additional use of vinyl ethers in the resin compositions is not described in these applications.
DE-A-31 07 450 describes unsaturated polyester with oligomers of dicyclopentadiene as end groups, which are used as solutions in ethylenically unsaturated monomers to produce mouldings and coatings. The ethylenically unsaturated monomers employed as reactive diluents are, in general, problematic owing to their high vapour pressure at room temperature and at processing temperature, and to the emission problems which this entails.
EP-A-0 101 585 describes unsaturated polyester resins which are modified by the addition of cyclopentadiene onto the double bonds of the unsaturated units of the polyester and are then dissolved in vinyl monomers as reactive diluents. Again a problem is the use of vinyl monomers as reactive diluents, from a
Blum Rainer
Eichhorst Manfred
Hegemann Gunther
Lienert Klaus-Wilhelm
Berman Susan W.
Pillsbury & Winthrop LLP
Schenectady International Inc.
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