Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From reactant having at least one -n=c=x group as well as...
Reexamination Certificate
2001-10-15
2003-01-28
Sergent, Rabon (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From reactant having at least one -n=c=x group as well as...
C528S073000, C427S385500, C525S454000, C525S455000, C525S457000, C525S458000, C525S459000, C525S460000
Reexamination Certificate
active
06512073
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to novel binders for electrical insulating enamels, the resulting enamels being distinguished by high temperature stability and good solderability.
The electrical and electronics industry today requires large amounts of coated wires for the production of motors, transformers, picture tubes and other products. Since the design of modern machines increasingly demands smaller motors, coils, transformers etc., and they work at a higher temperature than their larger equivalent, increased demands are being made of the temperature stability of the wire coatings. In the present application, the temperature stability is defined by the softening temperature of the coating. In many applications, the products are also required to be quickly solderable in order to connect the ends of the coated wires rapidly and simply to other components in an electrically conducting manner.
The electrical insulating enamel coating compositions conventionally used today include conventional coatings having high temperature stability in which polyhydantoins (e.g. FR-A 1 484 694, DE-A 246020), polyimides, polyamide imides (e.g. DE-A 3 544 548, DE-A 3 714 033, DE-A 3 817 614) or polyester amide imides (e.g. U.S. Pat. Nos. 3,652,471, 4,997,891, DE-A 3 249 497) form the main binder component. Wires coated with such products cannot be soldered below a temperature of from 400 to 450° C.
By contrast, electrical insulating enamels based on polyurethane permit rapid solder-ability at comparatively low temperatures. The binders in the wire enamels used in such cases are based on combinations of polyester polyols and phenol or alkanol-blocked polyisocyanates (DE-A 1 170 096 or DE-A 2 626 175). An improvement in the solderability can be achieved by combining blocked polyisocyanates with hydroxy-functional oligourethanes, e.g., DE-A-1 644 794.
In S. Darling, “International Wire Standards-Progress Towards Harmonization” in Proceedings 19th EEI Conference, Chicago 25th to 28th Sep. 1989, p. 56, polyester imides having a temperature index of 180° C. are described as being solderable, but solderability is likewise only present at temperatures above 400° C.
Polyester imides having a high hydroxyl group content, in combination with heat-resistant blocked polyisocyanates, are solderable at 370° C., but they exhibit markedly deteriorating properties in respect of the tan &dgr; break point and the softening temperature as compared with conventional polyester imides. Amide-imide-polyurethane combinations, which are described in EP-A 365 877, also have similar disadvantages. EP-A 752 434 describes raising the softening temperature of solderable wires by introduction of amide/imide-group containing blocked polyisocyanates. Although a marked improvement in solderability is achieved thereby as compared with U.S. Pat. No. 4,997,891, the softening temperature is not improved.
From EP-A 231 509 there are known polyisocyanates containing carbodiimide and/or uretonimine groups and their use in wire enamelling. Depending on the reaction partner, such polyisocyanates are suitable for the production of solderable (Example 1 of EP-A 231 509) or, alternatively, heat-resistant enamelled wires (Example 3 of EP-A 231 509).
According to the teaching of EP-A 287 947, heat-resistant electrical insulating enamels are obtained using unsaturated carboxylic acids in combination with polyisocyanates containing carbodiimide and/or uretonimine groups. If in the production of the wire enamel having hydantoin structures there is used an isocyanurate-containing compound (EP-A 287 947 Example 3), then there is obtained a wire enamel that is solderable at 420° C. and has a softening temperature of 250° C.; if the mixture contains no further OH components other than the OH-containing blocking agents, then non-solderable products having softening temperatures >300° C. are obtained (EP-A 287 947 Example 2).
The use of N,N′,N″-tris-(2-hydroxyethyl)-isocyanurate as an additive for polyurethane-based wire enamels also leads to heat-resistant enamelled wires (DE-A 3 133 571).
U.S. Pat. No. 5,254,659 describes the production of heat-resistant, solderable wire enamels from polyimides and imide-modified polyurethanes. Owing to the low solids content of the binders and to the solvents, which are unconventional in the wire enamels industry and, moreover, are comparatively expensive, such products are definitely used only in exceptional cases and for the coating of thin wires.
It may be stated in summary that the teaching of the prior-known prior art amounts either to the production of electrical insulating enamels having a high level of heat resistance (>270° C.) that are not solderable or can be soldered only very slowly at 390° C., or to the production of electrical insulating enamels that are rapidly solderable at 390° C. but have a level of heat resistance of only ≦270° C.
It was an object of the invention to provide a coating composition for heat-resistant substrates, especially for the wire-enamelling of wires, that combines both advantages—heat resistance >270° C. and improved solderability at a temperature of 390° C.
It has been possible to achieve that object by means of the electrical insulating enamel binders according to the invention that are described in greater detail below. The invention is based on the surprising finding that, by using hydroxy-functional compounds containing particular urea and/or hydantoin groups, it is possible to produce electrical insulating enamels that are solderable at temperatures of <400° C. in spite of their excellent temperature stability.
SUMMARY OF THE INVENTION
The invention relates to a binder containing:
A) at least one hydroxy- and/or amino-functional polyurethane containing urea and/or hydantoin groups, prepared by reacting
a) from 15 to 40 wt. % of an organic polyisocyanate or of a mixture of organic polyisocyanates,
b) from 5 to 20 wt. % of at least one aspartic acid ester, and
c) from 5 to 50 wt. % of a polyhydroxy compound having a molar weight from 62 to 3000 g/mol in
d) from 25 to 50 wt. % of a solvent or of a solvent mixture.
B) at least one blocked isocyanate component containing ester, imide, amide, and/or urethane groups, and
C) organic solvents.
DETAILED DESCRIPTION OF THE INVENTION
Suitable hydroxy-functional polyurethane prepolymers having a hydantoin or urea structure useful as component A) are known from EP-A 743 333. According to that teaching, those compounds are distinguished by improved thermal stability and are suitable especially as binders for the coating of sheet steel. U.S. Pat. No. 3,549,599 describes the preparation of polyhydantoins from aspartic acid esters, as well as the high temperature stability of the products obtained therewith. Even in conjunction with other publications, the person skilled in the art will find in that teaching no indication as regards either the production of solderable wire enamel binders having high temperature stability, or the use of those substances in the production of solderable wire enamel binders.
Suitable starting polyisocyanates a) for the preparation of the hydroxy- and/or amino-functional polyurethanes A) include aromatic, aliphatic or cycloaliphatic polyisocyanates, preferably polyisocyanates having a uniform molecular weight or an average molecular weight in the mean of from 140 to 500 with an average NCO functionality in the statistical mean of not more than 2.6.
Such polyisocyanates include 1,4-phenylene diisocyanate, 2,4- and 2,6-diisocyanatotoluene (TDI) as well as any desired mixtures of those isomers, 4,4′-, 2,4′- and 2,2′-diisocyanatodiphenylmethane (MDI) or any desired mixtures of those isomers or mixtures of those isomers with their higher homologues, as are obtained in a known manner by phosgenation of aniline/formaldehyde condensation products, 1,5-naphthylene diisocyanate, 1,4-butane diisocyanate, 2-methylpentane 1,5-diisocyanate, 1,5-hexane diisocyanate, 1,6-hexane diisocyanate (HDI), 1,3- and 1,4-cyclohexane diisocyanate and any desired m
Gertzmann Rolf
Hausstätter Bernd
Mazanek Jan
Schmalstieg Lutz
Bayer Aktiengesellschaft
Roy Thomas W.
Sergent Rabon
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