DE1490285C - Multi-layer insulation of electrical conductors - Google Patents

Description

The invention relates to multilayer insulation of electrical conductors.

As is well known, magnet wires of "Class B" or "Class F", ie wires that ^{are suitable for working at temperatures of up to 130 or 150 0} C, can be produced by using polyester resins made from terephthalic acid and simple polyhydric alcohol mixtures, such as glycol-glycerin, glycol-glycerin-phentaerythritol and 1,3-butylene glycol-glycerin. Their short service life at temperatures of 300 ^° C. must be regarded as a major disadvantage of these wires.

Another type of known magnet wire made with defined-compound aromatic polyamides are coated, which are converted to polyimides in situ when cured in a wire coating oven a longer service life than the polyester-coatedeix wires in the event of thermal stress. However, these polyimide coatings lack the desired abrasion resistance, which is a serious problem Disadvantage with regard to the rough mechanical treatment means that the magnet wires pass through exposed to high speed rotating coil winding machines. Another disadvantage The reason for these wires is that their coating tends to show hairline cracks if they are not appropriately have been heated. If such crazing occurs once, it can occur later Heating cannot be reversed. Finally, those are coated with polyimide resins Wires have the further disadvantage that the application of a layer of lacquer is a rather expensive one Solvent system compared to the system used in more common paints.

The object of the invention is to produce an improved magnet wire that has good abrasion resistance, excellent electrical stability at high temperatures, good elasticity and good Has adhesive strength of the lacquer coating on the wire.

A multilayer insulation for electrical conductors with these properties is according to the invention achieved by the fact that the insulation is composed of one or more layers of polyester resin varnish, which is the polymeric product of terephthalic acid, isophthalic acid, and mixtures thereof with a dihydric a, w-alcohol and a polyhydric alcohol with at least three hydroxyl groups represents, and from one or more layers of a polyamide, which by heating in situ in a Polyimide is converted from the polymeric condensation product of an aromatic tetracarboxylic acid with a diamine compound such as an aromatic diamine with 6 to 16 carbon atoms and saturated aliphatic amines with up to 6 carbon atoms. It has been found that the life of such Multi-layer insulation at high temperatures is significantly greater than when using only one of the combination paints. A synergetic effect is apparently achieved by this combination, i. H., A protective effect is created that far exceeds that of the pure addition of the individual layers of paint achievable protective effects. In terms of abrasion resistance, it was very good Results noted when polyester varnish is applied over the polyimide varnish layer. When the shift is reversed of the two types of resin one obtains an abrasion resistance of the overall coating which is worse than the of the polyester alone, but still over that of a polyimide coating located.

The compositions of the polyester resin lacquers are shown in the table below, in which all of them Figures-parts by weight mean:

Table I. IO Varnish A . Lacquer B Terephthalic acid polyester resin.
Polyurethane
Cresolic acid, ml
* 5 hydrocarbon solvents,
ml 100.0
29.2
242
60 100.0
240
60

All components and lacquers are well-known commercially available products. The terephthalic acid polyester resin is the product of terephthalic acid with a mixture of ethylene glycol and glycerine. The. The polyurethane used is a phenol adduct of a trimer of tolylene diisocyanate. The two others Components are commercially available cresolic acid and naphtha. In addition, each resin contains a metallic one Catalyst, such as zinc.

One of the polyamides used in the examples is the condensation product of pyromellitic dianhydride with aromatic amines (LackC).

The other polyimide used in the examples

paint (varnish D) represents a commercially available product, which mainly consists of a polyamide which is chemically ähnhch the polyamide contained in the coating material C and is dissolved as 15gewichtsprozentige solution in a mixture of N-methylpyrrolidone and dimethylacetamide and at 25 ⁰ C a viscosity of 4800 cP.

Examples 1 to 3

The lacquers were applied to copper wire 1.023 mm thick by means of a known coating process and each layer of lacquer was applied by passing the dip-coated wire through a vertical oven about 4 m long at a temperature of 350 or 390 ° C at a constant flow rate between 3.20 and 4.27 m / min, dried. By using a subdivided application device for the paint, the desired number of different top layers could be produced in one continuous operation.
Comparison wires were coated with the known lacquers A and B by applying six successive layers of lacquer to the bare wire. Since each cover layer has an approximate thickness of 0.00635 mm, a "strong layer structure" was obtained on the wires treated in this way, ie the diameter of the treated wires was about 0.0762 mm larger than that of the bare starting wire.

If, however, polyamides are used, a test wire coated with two outer layers was combined with one Layer thickness of about 0.0254 mm is considered sufficient. The examination of the enamel-coated wires was carried out according to a standard procedure. Although different chemical, physical and

electrical properties of the test wires and the with As the new wires coated with facings have been examined, the description is intended to refer to those Test procedures are restricted, which are restricted to the investigation of those test procedures, which were used to investigate those properties in which significant changes were observed namely, the 1 kV life test and the scratch abrasion resistance test.

1 kV life test: The 1 kV life test was carried out in accordance with the regulations of Leaflet No. 57 of October 1955 issued by the American Institute for Electrical Engineers accomplished. The experiment allows the determination of the length of time that a coating for a certain, specified temperature can be exposed before its electrical insulation when applying a Voltage of 1000 V to the sample for one second. In each experiment 10 parallel measurements were made accomplished.

Scratch Resistance Test: This test consists in repeating the insulated wire sample with a steel needle that is loaded with a set of weights corresponding to the structure of the outer layers of the wire is variable. The number of stitches is registered and you switch off when Contact between the needle and the bare wire core is established.

In Table II are the characteristic properties of those with standard paints at optimal cure coated comparison wires. These values serve as a basis for estimating the with the values obtained from new isolations of the later examples.

Table HI
Polyester over polyimide varnishes

Table II
Comparative paints

layer Abrasion 1 kV service life (Hours) 250 ° C 300 ° C 2 paint strength strength 225 ° C 63 7th (mm) (Stitches) 200 ° C 2700 ⁷ 125 27 A. 0.0762 45 2400 ⁹ 1287 50 B. 0.0762 50 2400 ¹⁰ 544 D. 0.0254 1 880 ⁴

Curing
conditions Speed Abrasion 1 kV service life 250 ° C 300 ° C 134 42 Lacquers Tempe age firm
speed (Hours) - 95 76 55 rature (m / min.) 1452 71 ( ⁰ Q 3.20 (Stitches) 200 ° C - j 42 AaufD 350 3.96 222 _ ■ _ 3.35 74 2000 ¹⁰ - A onD 390 4.27 395 . 3.35 89 -. AaufC 390 3.35 95 - B onD 390 4.27 135 89 • - ■

35

40

45

The values with superscript additional digits do not represent final values because, for example, with the ^{specified service life of 880 hours for paint D at 200 °} C., a number of samples, namely that of the superscript digit, in this example 4, still withstood the test conditions. From what follows it will be seen that these incomplete values do not impair the understanding of the invention. The poor abrasion resistance of the polyimide varnish D and the relatively low thermal stability of all three varnishes at 300 ° C. should be given particular attention in view of the later explanations.

60

B e i s ρ i el e 4 to i s 7

Then wires with an insulation of four layers of a polyester resin varnish over two Coated layers of a polyimide varnish. The characteristic properties of these new wires are compiled in Table III.

Comparison of these results with the data in Table II clearly shows that the introduction of two top coats of polyimide varnish between the wire and the four top coats on polyester varnish wires allows to produce, which has an abrasion resistance and a lifetime under thermal stress at 300 ° C, which is far superior to the values obtained when using one or the other Let Lacks reach it alone. In addition, a so-called synergetic effect could be observed, since the above widths for the properties discussed are much larger than they are according to a calculation with an additive composition of the properties of the two types of paint would have predicted can be.

Examples 8 and 9

The order of application of the two paints was then reversed, i.e. H. two layers Polyimide varnish was applied to four layers of polyester varnish. When comparing the properties of the obtained wires with those of the comparison wires can also be a remarkable improvement Observe the service life under thermal stress at 300 ° C. The results are in Table IV contain.

Table IV

Polyimide over polyester lacquers

onA Curing
conditions Speed Abrasion 1 kV service life 1485 300 ° C onB Tempe age speed (Hours) - 192 Lacquers rature (m / min.) 38 ° C 3.96 (Stitches) 200 ° C j 250 ° C 350 4.27 14th 2000 ⁹ D. 390 19th - D.

However, it can be seen from Table IV that, for the reasons mentioned, the abrasion resistance is not in the Dimensions could be improved than when the polyimide layer was arranged under the polyester layer Is the case (see Table III).

In summary, it can be concluded from the examples that wires with a better thermal Lifespan at 300 ° C by coating the same with both types of resin one after the other in any Sequence can be produced and that this service life is superior to that of wires that either with terephthalic acid polyester resins only or

are only coated with polyimide resins. It can also be seen that this improvement is over the assumption a purely additive effect of the two types of coating goes beyond the improvement expected. A A similar synergetic effect could also be found in the abrasion resistance when the polyimide layers placed under the polyester layers.

The polyamides suitable for the invention are condensation products of aromatic tetracarboxylic acids with diamines and can be represented by the following repeating structural unit:

HO

-N-C

HOOC

C —N —R '·
COOH

These polymers are soluble and can be removed in place, as mentioned earlier, by further means Heating converts them into polyimide structures of the following formula, which are very resistant to solvents are:

NO'-

The pyromellitic acid residue built into this formula can also be replaced by tetracarboxylic acids containing two rings, provided that that the carboxyl groups of the latter compounds are arranged in two o-phthalic acid configurations are. These requirements are, for example, of the naphthalene-diphenylmethane, 2,2'-diphenylpropane-diphenylether, Diphenyl sulfide and diphenyl sulfone met the corresponding tetracarboxylic acids. The R 'of the formula stands for a divalent radical of either benzene, naphthalene, diphenyl, diphenyl ether, Ditolyl ether, diphenyl sulfide, diphenyl sulfone, diphenyl methane, 2,2'-diphenyl propane, benzophenone or for a saturated aliphatic hydrocarbon of low molecular weight and at most 6 carbon atoms.

Usable polyamides are e.g. B. Condensation products of pyromellitic dianhydride with a Diamine, which by the lack of aliphatic hydrogen atoms and by the possession of an elastic one Bond, as the ether group of 4,4'-oxydianiline is excellent. These polyamides are supposed to expediently a viscosity of about 1300 to 5000 cP for a 15 weight percent solution in 1: 1 dimethylacetamide and N-methylpyrrolidone at 25 ° C.

In cases in which a particularly good abrasion resistance is important, the polyester resin layer is expediently applied over the polyimide lacquer layer; higher curing temperatures give a stronger abrasion resistance. Greater care must be taken when making wires with a polyimide topcoat. By adding a polyurethane to the polyester resin, excellent thermal lifetimes at 300 ^° C. can be achieved. In such cases, however, higher curing temperatures, for example 39O ⁰ C, must be avoided if satisfactory mechanical properties, such as the adhesion to the bare metal, are to be maintained.

A suitable number of layers of lacquer has been found to be four, two for the polyester and two two for the polyimide varnish. These numbers apply to a magnet wire with a strong layer structure. In Depending on the diameter of the wire to be coated, the viscosity of the wire to be used Lacquer solutions and the conditions under which the finished wire will be used can be used to create insulation Apply any thickness between 0.00254 and 0.1016 mm in 2 to 14 layers.

Various other materials such as fillers, plasticizers, dyes, etc., as well as lesser ones Amounts of other resins, such as epoxy resins, can be incorporated into these paints, as is often the case with known ones Paint manufacturing process is the case.

25th

Claims (5)

Patent claims: 1. Multi-layer insulation of electrical conductors, characterized in that the insulation is composed of one or more layers of a polyester resin varnish that makes the polymeric product of terephthalic acid, isophthalic acid, and mixtures thereof with one dihydric a, cu-alcohol and a polyhydric alcohol with at least three hydroxyl groups represents, and from one or more layers of a polyamide, which by heating has been converted in situ into a polyimide, from the polymeric condensation product of a aromatic tetracarboxylic acid with a diamine compound such as an aromatic diamine with 6 to 16 carbon atoms and saturated aliphatic amines with up to 6 carbon atoms. 2. Multi-layer insulation according to claim 1, characterized in that the insulating layer has a thickness of 0.00254 to 0.01016 mm and of 2 to 14 layers of the resin lacquer compounds mentioned consists. 3. Multi-layer insulation according to claim 1 or 2, characterized in that the polyester resin lacquer layers consist of 100 parts of a polyester resin with free hydroxyl groups, which are the product of isophthalic acid, terephthalic acid and mixtures thereof with a divalent a, a> -alcohol and a polyhydric alcohol with at least three hydroxyl groups and 5 to 60 parts of a blocked organic polyisocyanate, where the blocked polyisocyanate adduct can be an aromatic hydrocarbon radical with up to 13 carbon atoms or an alkyl-aryl substitute thereof and the blocking compound can be a phenol. 4. Multi-layer insulation according to claim 3, characterized in that the blocked organic Polyisocyanate is the phenol adduct of a tolylene diisocyanate trimer. 5. A method for producing a multilayer insulation according to any one of the preceding claims, characterized in that the insulating layers are applied one after the other by continuously pulling the electrical conductor through the various liquid coating resins, each dried and cured ^{between 250 and 500 ° C.}