Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-12-16
2003-04-29
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S443000, C523S466000, C525S523000, C525S524000, C525S525000, C525S532000, C525S533000
Reexamination Certificate
active
06555601
ABSTRACT:
The present invention relates to a process for impregnating an electrical coil, comprising a winding of two or more layers each of which consists of more than one turn of an electrically conducting material in wire form, with a polymer material which electrically insulates the individual turns of the wire-form material from one another, wherein the individual windings of the coil are enveloped with the aid of a curable epoxy resin composition and this composition is thermally cured, and to particularly preferred curable compositions for carrying out the impregnation.
From WO-A-96/01481 it is known to use curable epoxy resin compositions which are liquid at room temperature and comprise (a) a liquid bisphenol A diglycidyl ether, (b) a crosslinking agent for it, (c) a suitable accelerator for the reaction of the liquid diglycidyl ether (a) with the crosslinking agent (b), and (d) a filler material which, based on component (a) and (b), comprises from 40 to 60 percent by weight of calcite and acicular, synthetic wollastonite for the impregnation and, if desired, for the coating of electrical coils comprising windings which in turn comprise a multiplicity of layers each of which consists of a large number of turns of a thin, wire-form conductor material, examples being the secondary windings of transformers or ignition coils. The use of liquid epoxy resin systems such as those mentioned, although it enables such windings to be impregnated sufficiently, i.e. enables the epoxy material to penetrate between all of the turns of a winding, nevertheless still has some disadvantages. For instance, the liquid epoxy resin systems can only be formulated in two-pack form, which as far as the user is concerned constitutes a not inconsiderable increase in processing complexity. In addition, the liquid impregnating systems referred to require the use of a sacrificial mould having the external contours desired for the finished coil. The coil to be potted has to be introduced into this mould. Subsequently it is necessary, generally following its evacuation, to fill the mould with the liquid curable epoxy resin composition and to cure the composition in the mould. After curing, the mould can no longer be removed and must therefore remain permanently around the coil, as a sacrificial mould. A further highly significant disadvantage of the abovementioned liquid epoxy resin compositions, moreover, is their extremely long curing time, which in general amounts to several hours and which, for the mass production of coils, necessitates the use of huge curing ovens.
The object of the present invention is inter alia to avoid the abovementioned disadvantages associated with the impregnation of coils, especially ignition coils, print transformers and flyback transformers.
It has now been found that such coils can be impregnated even at room temperature, i.e. at a temperature from about 15 to 25° C., using solid, preferably fibre-reinforced, curable epoxy resin compositions having the specific composition defined below. A particular surprise in this context is that such compositions are also able to penetrate sufficiently the secondary windings of customary ignition coils and transformers even if they comprise relatively large amounts of a reinforcing material which consists of inorganic fibres with a length of up to about 2.5 mm. The use of these solid epoxy resin compositions does away with the need to use a housing (sometimes referred to as “lost housing”) and reduces by a multiple the curing time required for completing the coating of the coils, reducing it to the region of a few minutes, generally not more than 15 minutes.
The present invention therefore provides in its widest sense a process for impregnating an electrical coil which comprises a winding comprising two or more layers consisting of more than one turn of an electrically conducting wire-form material with a polymer material which electrically insulates the individual turns of the wire-form material from one another with the aid of a thermally curable epoxy resin composition, which composition is solid at room temperature and comprises the following constituents:
(a) an epoxy resin which is solid at room temperature, selected from
(a1) polyglycidyl ethers based on novolaks;
(a2) diglycidyl ethers based on bisphenols, and
(a3) mixtures of more than one of components (a1) and (a2);
(b) a crosslinking agent for component (a);
(c) a suitable accelerator for the reaction of component (a) and component (b);
(d) from 15 to 70 percent by weight, based on the overall weight of the composition, of filler selected from
(d1) calcium carbonate,
(d2) quartz flour,
(d3) wollastonite whose particles have an average ratio of length to cross-section which is less than 5:1;
(d4) mixtures of components (d1), (d2) and (d3) and
(d5) mixtures of components (d1), (d2), (d3) and (d4) with other inorganic fillers.
By impregnation is meant in this application a treatment of the electrical coil whereby the individual turns of at least one coil winding are enveloped with the aid of the curable epoxy resin composition and the composition is thermally cured. This treatment may, however, comprise the total encapsulation of parts of the coil or else of the whole coil, including the coil former, with the curable epoxy resin composition.
In addition, the composition employed in the process of the invention preferably comprises:
(e) from 10 to 60 percent by weight, based on the overall weight of the composition, of inorganic reinforcements in the form of acicular or fibrillar particles with a length of from 0.05 to 2.5 mm which have an average ratio of length to cross-section of 5:1 or more,
the overall amount of component (d) and (e) being not more than 80 percent by weight, based on the overall weight of the composition.
It is preferred to employ specially selected compositions in which the reinforcement (e) consists of acicular or fibrillar particles having a length of from 0.15 to 2.5 mm. The present invention additionally provides these compositions.
With particular preference, the reinforcement (e) comprises a glass fibre material, especially milled or chopped glass fibres having a length of from 0.05 to 2.5 mm and a diameter of preferably from 10 to 30 &mgr;m, which are available in various forms and commercially. A reinforcing material which has proven particularly suitable, for example, comprises glass fibres with a length from 0.05 mm, in particular from 0.15 mm, to 2 mm, in particular to 1 mm: for example, approximately 0.2 to 0.25 mm.
The novolak-based polyglycidyl ethers which are employed in the process of the invention and in the compositions of the invention as component (a1) are in particular:
(a1.1) polyglycidyl ethers based on epoxy-phenol novolaks,
(a1.2) polyglycidyl ethers based on epoxy-cresol novolaks, or
(a1.3) mixtures of epoxy novolaks of type (a1.1) and/or (a1.2).
Component (a2) preferably comprises diglycidyl ethers based on bisphenol A. These may, for example, be pre-extended (advanced) resins obtainable by reacting bisphenol A diglycidyl ether with a stoichiometric deficit of substances having two functional groups which are reactive with epoxide groups, in particular by reacting from 1.1 to 2 mol of bisphenol A diglycidyl ether with 1 mol of bisphenol A.
The crosslinking agent (b) is judiciously selected from:
(b1) dicyandiamide,
(b2) polycarboxylic anhydrides and
(b3) mixtures of more than one of components (b1) and/or (b2) and/or one or more polyphenols.
If an organic carboxylic anhydride is employed as crosslinking agent it is preferably an aromatic or cycloaliphatic polycarboxylic anhydride, especially a corresponding dicarboxylic anhydride, such as phthalic, hexahydrophthalic or methyltetrahydrophthalic anhydride. Preference is given in particular to carboxylic anhydrides which are solid at room temperature.
If the crosslinking agent includes a certain proportion of polyphenols, this may be advantageous in terms of the processing of the impregnating compositions. Since, however,. the presence of relatively large amounts of polyphenols may h
Behm Dean Tallak
Bleuel Felix
Buchmann Hans-Fred
Glauch Dieter
Weidmann Ulrich
Aylward D.
Esq. Kristin Neuman
Moore Margaret G.
Proskauer Rose LLP
Vantico Inc.
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