EP1786874A1

EP1786874A1 - Enamelling varnish composition, such as for a magnet wire

Info

Publication number: EP1786874A1
Application number: EP05797537A
Authority: EP
Inventors: Jérome Fournier; Arnaud Piechaczyk; Laurent Schildknecht; Olivier Pinto
Original assignee: Nexans SA
Current assignee: Nexans SA
Priority date: 2004-08-30
Filing date: 2005-08-30
Publication date: 2007-05-23
Also published as: FR2874615B1; US20070248821A1; CN101010389A; WO2006027524A1; FR2874615A1

Abstract

The invention relates to an enamelling varnish composition which is intended, for example, for a magnet wire. The invention is characterised in that the enamelling varnish composition comprises a polymer resin and an alkyl lactate and in that the polymer resin is selected from the group containing polyesters, polyesteramides, THEIC-modified polyesteramides, polyurethanes, polyamides, polyamideimides, polyvinyl aceto-formals or any mixture of said compounds.

Description

COMPOSITION OF ENAMELLED VARNISH IN PARTICULAR FOR WINDING WIRE

The present invention relates to a composition intended to constitute an electrically insulating enameling varnish.

The invention finds a particularly advantageous, but not exclusive, application in the field of winding wires. The vast majority of varnishes used for the insulation of enamelled wires are produced in the form of a solution of polymer in a mixture of cresylic solvents and aromatic hydrocarbons, or in a mixture of N-methyl pyrollidone and aromatic hydrocarbons. The effectiveness of these solvents is indeed quite obvious in practice, either during the synthesis of the varnish, in terms of solubility or at the time of application on the wire. However, cresylic solvents are also known to be highly toxic products, which, moreover, have very unpleasant odors. N-methyl pyrollidone, commonly referred to by the abbreviation NMP, is suspected of toxicity. Today, the entire enamelled wire industry is under increasing pressure to reduce the use of these conventional solvents.

Glazing varnishes devoid of cresylic solvents have of course been developed.

In this respect, benzyl alcohol is known to be a good solvent for replacing cresol and phenol in particular, but its toxicity still remains too important and its cost price is disadvantageously higher.

It is also possible to use methoxy propyl acetate, better known under the trademark Dowanol PMA. Unfortunately, this product is expensive and has low heat yields during enameling. The surface appearance of the varnish is otherwise insufficiently good in most cases. If water can be used a priori instead of the solvents cresyl, it is absolutely not suitable for standard enamelling machines. These last require indeed a solvent capable of providing energy by combustion, that is to say an organic solvent. Apart from the additional cost that a new manufacturing process would imply, the performances of the final product are in any case inferior to those of the cresylic solvents based varnishes.

Therefore, the technical problem to be solved, by the object of the present invention, is to propose an enameling varnish composition especially for winding wire, a composition which would make it possible to avoid the problems of the state of the art by offering a significantly reduced toxic solvent content, while preserving the performance of the final product and not restoring the standard enameling processes currently used.

According to the present invention, the solution to the technical problem consists in that the enameling varnish composition comprises a polymer resin and an alkyl lactate, and in that the polymeric resin is selected from the group of polyesters, polyesters imides, THEIC modified polyesters imides, polyurethanes, polyamides, imide polyamides, polyvinyl acetoformals, or any mixture of these compounds.

The invention as defined thus therefore consists in substituting at least a portion of the toxic solvents commonly used in the prior art, and in particular the cresylic solvents, with a solvent which is known to it and recognized as being completely harmless, the occurrence a lactate. This ultimately allows to reduce in more or less significant proportions the toxicity of the enameling varnish.

Lactate type solvents have the advantage of not altering the mechanical and insulating properties of the enamelling varnishes in which they are integrated. As application examples, enamelled son prepared from lacquer based on lactates offer the same performance as their counterparts developed using varnishes of conventional formulations.

Lactate-type solvents furthermore give the enameling varnish excellent stability, good application capacity and a satisfactory surface finish.

The price level of lactates, and especially that of ethyl lactate, is also of the same order of magnitude as that of cresol and NMP, so that their use does not generate any increase in the particular cost. According to one particularity of the invention, the alkyl lactate is chosen from methyl lactate, ethyl lactate, propyl lactate, butyl lactate or any mixture of these compounds.

A first embodiment of the invention is related to the fact that the polymer resin is chosen from the group of polyesters, polyesters imides, THEIC modified polyesters imides, polyurethanes, polyvinyl acetoformals, or any mixture of these compounds. Under these conditions, the proportion by weight of alkyl lactate relative to the total amount of solvents may advantageously be between 5 and 100%, and preferably between 10 and 70%. This means in other words that when the polymer resin is as previously defined, the enameling varnish composition may comprise 5 to 100% by weight of alkyl lactate, and preferably 10 to 70% by weight, all this in relation to the total amount of solvents.

Particularly advantageously, a composition according to this first embodiment may further comprise at least one cresylic solvent. In this respect, it should be noted that the concept of cresylic solvent denotes phenol, cresol, xylenol and their derivatives.

This characteristic is essentially intended to obtain in the end a varnish whose mechanical and insulating properties are equivalent to those of varnishes based on cresylic solvents, all this in order not to have to question the standard manufacturing processes currently used.

A second embodiment of the invention relates to demisting varnish compositions whose polymer resin is chosen from polyamides, polyamide imides, or any mixture of these compounds. In this case, the proportion by weight of alkyl lactate may advantageously be between 5 and 70% relative to the total amount of solvents, and preferably between 10 and 40% by weight.

According to an advantageous characteristic of this second embodiment, the enameling varnish composition may also comprise N-methyl pyrollidone.

Whether the enameling varnish composition meets the conditions of the first or second embodiment of the invention, it may further comprise at least one aromatic hydrocarbon. In this regard, it should be noted that the concept of aromatic hydrocarbon very generally designates all isomers of xylenes, but also of petroleum fractions, and more particularly of hydrocarbon cuts having a boiling point between 160 and 21O ⁰ C .

The presence of aromatics in the enameling varnish composition makes it possible to reduce the cost price, to adjust the viscosity if necessary, but also to raise the boiling point of the solvent mixture. With regard more particularly to this latter aspect, the aim is not to be penalized by the relatively low boiling point of lactates, which is generally between 145 and 170 ^° C., and thus to avoid any risk of drying in the applicators. Such a phenomenon could indeed compromise the manufacturing process as a whole.

In any event, the proportion by weight of aromatic hydrocarbon will advantageously be between 10 and 50% relative to the total amount of solvents.

Of course, an enameling varnish composition according to the invention may further comprise any kind of additive known from the state of the art.

Of course, the invention also relates to any winding wire comprising a conductive element covered with an insulating layer made from an enameling varnish composition as previously described.

Other features and advantages of the present invention will become apparent during the description of the examples which follow; these latter being given for illustrative purposes and in no way limiting.

Examples I to V relate to enameling varnish compositions which are all intended to form electrically insulating layers for winding wires. More specifically, each example relates to compositions consisting of the same polymer resin but with different solvent mixtures, namely in each case a composition according to the invention and a reference composition comprising a solvent mixture typical of the prior art.

Example I Samples 1 and 2 both relate to polyester imide (PEI) compositions. They relate respectively to a composition according to the invention, that is to say whose solvent mixture is provided with lactate, and to a reference composition, that is to say whose solvent mixture is based only conventional solvents.

The preparation of sample 1 begins with the addition of 437 g of trimellitic anhydride to 285 g of diphenyl methane diisocyanate in 590 g of cresol. The mixture is then heated to 200 ⁰ C, resulting in a release of carbon dioxide of 105 g. 430 g of ethylene glycol, 328 g of trimellitic anhydride and 51 g of isophthalic acid are then introduced into the reactor at 120 ^° C. The whole is heated with vigorous stirring up to about 215 ^° C. 110 g of distillate are then collected. 385 g of ethyl lactate, 20 g of titanate and then 680 g of aromatic solvent in the form of Solvesso 100 (trademark of Exxon) are added in order to obtain an enameling varnish of dry extract 44% and viscosity at 20 ^° C. C of 1205 mPa.s.

Sample 2 is prepared by adding 437 g of trimellitic anhydride to 285 g of diphenyl methane diisocyanate in 590 g of cresol. The mixture is heated to 200 ⁰ C, resulting in a release of carbon dioxide of 105g. 430 g of ethylene glycol, 328 g of trimellitic anhydride and 51 g of isophthalic acid are then introduced into the reactor at 120 ^° C. The whole is heated with vigorous stirring up to about 215 ^° C. 110 g of distillate are then collected. 150 g of cresol, 235 g of phenol, 20 g of titanate and then 680 g of aromatic solvent in the form of Solvesso 100 are added in order to obtain an enameling varnish of dry extract 44% and viscosity at 20 ^° C. of 2600 mPa. s.

It should be noted that the titanate introduced is generally tetra n-butyl titanate. This compound acts as a catalyst for the esterification and transesterification reaction. It is also a crosslinking agent.

For clarity, Table 1 summarizes the differences in compositions between the solvent mixtures of samples 1 and 2.

Table 1

Measurements of the concentration of dry extract after drying of 1 g of product for 1 hour at 18O ⁰ C, as well as the viscosity at 20 ^° C., are carried out on each sample in order to be able to compare the characteristic properties of the enamel varnishes. previously prepared. Table 2 summarizes the results of the measures in question.

Table 2

Ech. 1 Ech. 2

Dry extract (Ih, Ig, 44% 44% 18O ⁰ C)

Viscosity at 20 ^° C. 1,205 mPa. s 2,600 mPa. s It is observed that the characteristic properties of the two types of enamel varnish are directly comparable. However, it is noted that the presence of lactate advantageously reduces the viscosity in the case of the composition according to the invention (Sample 1). This characteristic makes it possible to work with much more concentrated compositions. Winding son are then made using as enameling varnish the compositions corresponding to samples 1 and 2. Concretely, layers of varnish are applied in a predetermined number, in successive passes and at a given speed, on conductors son of identical diameters . The extra thickness of the varnish, as well as its appearance on the surface, are then evaluated for each enamelled wire.

Standard characterization tests are then conducted to determine the essential properties of both types of winding wires (in accordance with the international standard IEC 60317). These are conventionally tests of flexibility, thermal shock at 200 ⁰ C, and solderability at 475 ⁰ C. With the aid of Dansk brand apparatus and type TD300, a well-known value is also determined. in the field of enameling, namely the delta tangent.

Table 3 combines both the structural characteristics of the two types of enamelled wires, and their specific properties.

Table 3

It is observed that the enameling results are quite equivalent. This means that, compared with a solvent mixture of the state of the art, a lactate-based solvent mixture in no way affects the performance of an enameling varnish based on polyester imide.

Example II

Samples 3 and 4 both relate to THEIC-modified imide polyester compositions. They are respectively relative to a composition according to the invention, that is to say whose solvent mixture is provided with lactate, and a reference composition, that is to say whose solvent mixture is based only conventional solvents. The preparation of sample 3 begins with the introduction of 190 g of ethylene glycol and 435 g of trishydroxyethyl isocyanurate (THEIC) into a reactor at room temperature. The mixture is then heated to 120 ^° C. at this temperature, 122 g of diphenyl methane (MDA) diamine, 270 g of dimethoxy terephthalate, 277 g of trimellitic anhydride, and 13 g of Xylene are introduced into the reactor. 2 g of Titanate are then added before heating the mixture with vigorous stirring up to 240 ^° C. 140 g of distillate are then collected. 927 g of ethyl lactate, 82 g of benzyl alcohol, 44 g of ethylene glycol and 326 g of Solvesso 150 (trademark of Exxon) are then added to the varnish. At 60 ^° C., 46 g of titanate and 80 g of phenolic resin are added to the varnish. The varnish obtained is of dry extract 44% and viscosity at 20 ^° C. of 860 mPa.s- ¹ . Sample 4 is prepared by introducing 190 g of ethylene glycol and 435 g of trishydroxyethyl isocyanurate (THEIC) into The mixture is then heated to 120 ^° C. At this temperature, 122 g of diphenyl methane diamine, 270 g of dimethoxy terephthalate, 277 g of trimellitic anhydride, and 13 g of Xylene are introduced into the reactor. 2 g of Titanate are in turn added before heating the mixture with vigorous stirring to 22O ⁰ C. 140 g of distillate are then collected: 463 g of cresol, 463 g of phenol, 82 g of benzyl alcohol, 44 g of ethylene glycol and 326 g of Solvesso 150 are then added to the lacquer At 60 ^° C., 46 g of titanate and 80 g of phenolic resin are added to the lacquer The varnish obtained is 44% solids and has a viscosity at 20 ^° C. of 1300 mPa. s ^"1 .

It should be noted that the phenolic resin makes it possible to improve the applicability of the varnish and especially to increase its chemical and thermal resistance. For clarity, Table 4 summarizes the differences in compositions between the solvent mixtures of samples 3 and 4.

Table 4

Measurements of the concentration of dry extract after drying of 1 g of product for 1 hour at 18O ⁰ C, as well as the viscosity at 20 ^° C., are carried out on each sample in order to be able to compare the characteristic properties of the enamel varnishes. previously prepared. Table 5 summarizes the results of the measures in question.

Table 5

Ech.3 Ech.4

Dry extract (Ih, Ig, 44% 44% 18O ⁰ C)

Viscosity at 20 ^° C 860 mPa.s 1300 mPa.s

It is also observed in this example that the characteristic properties of the two types of enamel varnish are directly comparable. It is also noted that the presence of lactate causes the viscosity in the case of the composition according to the invention (Sample 3), thus advantageously allowing to work with much more concentrated compositions.

The winding wires are then made using, as enameling varnish, the compositions corresponding to the samples 3 and 4. Concretely, layers of varnish are applied in a predetermined number, in successive passes and at a given speed, on conducting wires of identical diameters. . The extra thickness of the varnish, as well as its appearance on the surface, are then evaluated for each enamelled wire.

Standard characterization tests are then conducted to determine the essential properties of both types of winding wires. This is conventionally tests of flexibility and thermal shock at 200 ^° C. As in Example I, the delta tangent is determined using a Dansk TD300 type device.

Table 6 combines both the structural characteristics of the two types of enamelled wires, as well as their specific properties.

Table 6

It is observed that the enameling results are quite equivalent. This means that, compared with a solvent mixture of the state of the art, a lactate-based solvent mixture in no way affects the performance of an enamel-based imide-based enameling varnish modified with THEIC.

Example III

Samples 5 and 6 both relate to polyurethane compositions. They are respectively relative to a composition according to the invention, that is to say whose solvent mixture is provided with lactate, and a reference composition, that is to say whose solvent mixture is based only conventional solvents.

Preparation of sample 5 begins with the introduction of 416.5g of Cresol, 544g of ethyl lactate and 55.4g of Xylene into the reactor. At 60 ^° C., 120 g of trimethylolpropane (TMP) and 26 g of trishydroxyethyl isocyanurate (THEIC) are added. The mixture is heated until the total distillation of Xylene. After cooling, 835 g of diphenyl methane diisocyanate and 1.5 g of catalyst are introduced. The varnish is then heated with vigorous stirring up to 140 ^° C. At this temperature 412 g of aromatic solvent (Solvesso 100 - Exxon), 388.7 g of Xylene and 256 g of ethyl lactate are added in order to obtain a blocked isocyanate polyisocyanate. in solution. In a second step, 3000 g of blocked isocyanate polyisocyanate in solution and 5858 g of polyester imide containing ethyl lactate (Sample 1) are introduced into a reactor. At 50 ^° C., 7 g of catalyst are added to the mixture. To reach a dry extract of 40%, 100g of Cresol then 68g of aromatic solvent (Solvesso 100 - Exxon) are added to the varnish.

Sample 6 is prepared by introducing 960.5 g of cresol and 55.4 g of Xylene into the reactor. At 60 ^° C., 120 g of trimethylolpropane (TMP) and 26 g of trishydroxyethyl isocyanurate (THEIC) are added. The mixture is heated until total distillation of Xylene. After cooling, 835 g of diphenyl methane diisocyanate and 1.5 g of catalyst are introduced. The varnish is then heated with vigorous stirring up to 140 ^° C. At this temperature, 412 g of aromatic solvent, in this case Solvesso 100 from Exxon, 388.7 g of Xylene and 256 g of phenol are added in order to obtain a blocked isocyanate polyisocyanate in solution.

In a second step, 3000 g of isocyanate polyisocyanate blocked in solution and 5858 g of polyester imide (Sample 2) are introduced into a reactor. At 50 ^° C., 7 g of catalyst are added to the mixture. To reach a dry extract of 40%, 100g of Cresol then 68g of aromatic solvent (Solvesso 100 - Exxon) are added to the varnish. For clarity, Table 7 summarizes the differences in compositions between the solvent mixtures of samples 5 and 6.

Table 7

Measurements of the concentration of dry extract after drying of 1 g of product for 1 hour at 18O ⁰ C, as well as the viscosity at 20 ^° C., are carried out on each sample in order to be able to compare the characteristic properties of the enamel varnishes. previously prepared. Table 8 summarizes the results of the measures in question.

Table 8

Ech.5 Ech.6

Dry extract (Ih, Ig, 40% 40% 18O ⁰ C)

Viscosity at 20 ⁰ C 1050 mPa. s 1820 mPa.s

It is also observed in this example that the characteristic properties of the two types of enamel varnish are directly comparable. It is also noted that the presence of lactate advantageously reduces the viscosity in the case of the composition according to the invention (Sample 5), thus offering the possibility of being able to work with much more concentrated compositions.

Winding son are then made using as enameling varnish the compositions corresponding to samples 5 and 6. Concretely, layers of varnish are applied in a predetermined number, in successive passes and at a given speed, on conductors son of identical diameters. The extra thickness of the varnish, as well as its appearance on the surface, are then evaluated for each enamelled wire.

Standard characterization tests are then conducted to determine the essential properties of both types of winding wires. These are conventionally tests of flexibility, thermal shock at 200 ^° C., and weldability at 39 ^° C. Using a Dansk-branded apparatus and of the TD300 type, the value of the tangent delta.

Table 9 combines both the structural characteristics of the two types of enamelled wires, as well as their characteristic properties.

Table 9

In a similar manner to the previous examples, it is observed that the enameling results are quite equivalent. This means that, compared to a solvent mixture of the state of the art, a lactate-based solvent mixture does not affect the performance of a polyurethane-based enameling varnish.

Example IV

Samples 7 and 8 both relate to polyvinyl acetoformal (PVF) compositions. They are respectively relative to a composition according to the invention, that is to say whose solvent mixture is provided with lactate, and a reference composition, that is to say whose solvent mixture is based only conventional solvents. The preparation of sample 7 begins with the cold loading of 755 g of ethyl lactate, 799 g of aromatic solvent (Solvesso 100), and 278.5 g of Xylene. At 90 ^° C., 429 g of polyvinyl acetoformal powder are in turn charged. The mixture is maintained at 90 ^° C. for 1 hour and then cooled. 61.2 g of blocked polyisocyanate Desmodur AP (trademark of Bayer) are introduced at 80 ^° C. and the varnish is maintained at this temperature for 1 hour and until perfect clarity. The mixture is then cooled to 50 ^° C. by adding 255 g of Xylene. After good stirring 306g of phenolic resin, 37g of melamine resin are added to the varnish. The polish is finally diluted with 2.5 g of aromatic solvent (Solvesso 100) and 69 g of ethyl lactate to reach a solids content of 19.5% and a viscosity of 5200 mPa.s.

Sample 8 is prepared by cold loading 528.5g of Cresol, 226.5g of Phenol, 799g of aromatic solvent (Solvesso 100 - Exxon), and 278.5g of Xylene. At 90 ^° C., 429 g of polyvinyl acetoformal powder are in turn charged. The mixture is maintained at 90 ^° C. for 1 hour and then cooled. 61.2 g of Desmodur AP are introduced at 80 ^° C. and the varnish is maintained at this temperature for 1 hour and until perfect clarity. The mixture is then cooled to 50 ^° C. by adding 255 g of Xylene. After good stirring 306g of phenolic resin, 37g of melamine resin are added to the varnish. The varnish is finally diluted with 2.5 g of aromatic solvent (Solvesso 100 from Exxon) and 69 g of Cresol to reach a solids content of 19.7% and a viscosity of 6450 mPa. s.

It should be noted that the phenolic resin here makes it possible to provide good resistance to hydrolysis, and that the melamine resin allows an improvement in the chemical resistance. For clarity, Table 10 summarizes the differences in compositions between the solvent mixtures of samples 7 and 8.

Table 10

Measurements of the concentration of dry extract after drying of 1 g of product for 1 hour at

18O ⁰ C, as well as the viscosity 20 ^° C., are made on each sample in order to be able to compare the characteristic properties of the previously prepared enamel varnishes. Table 11 summarizes the results of the measures in question.

Table 11

Ech.7 Ech.8

Dry extract (Ih, Ig, Ii 30 ⁰ C) 19.5% 19.7%

Viscosity at 20 ^° C 5200 mPa. s 64 50 mPa. s

Again, it is observed that the characteristic properties of the two types of enamel varnish are directly comparable and that the presence of lactate advantageously drops the viscosity in the case of the composition according to the invention (Sample 7).

Winding wires are then produced by using, as enameling varnish, the compositions corresponding to samples 7 and 8. Concretely, layers of varnish are applied in a predetermined number, in successive passes and at a given speed, on conducting wires of identical diameters. . The extra thickness of the varnish, as well as its appearance on the surface, are then evaluated for each enamelled wire.

Standard characterization tests are then conducted to determine the properties essential of both types of winding wires. These are typically flexibility tests, thermal shock at 160 ^° C. for 30 minutes, unidirectional abrasion and breakdown voltage.

Table 3 combines both the structural characteristics of the two types of enamelled wires, as well as their characteristic properties.

Table 12

It is still observed that the enameling results are quite equivalent. For this example, this means that, compared to a solvent mixture of the state of the art, a lactate-based solvent mixture in no way affects the performance of an enameling varnish based on polyvinyl acetoformal.

Example V Samples 9 and 10 both relate to polyamide imide (PAI) based compositions. They are respectively relative to a composition according to the invention, that is to say whose solvent mixture is provided with lactate, and a reference composition, that is to say whose solvent mixture is based only conventional solvents.

The preparation of sample 9 begins with the introduction at 60 ^° C. of 2420 g of N-methylpyrrolidone, 30.4 g of blocking agent, 836 g of trimellitic anhydride, 81 g of terephthalic acid and 580 g of solvent. aromatic

(Solvesso 100 from Exxon) and 1258 g of diphenyl methane diisocyanate. The reaction mixture is heated at 140 ^° C. in 5 hours and the evolution of the reaction is monitored by measuring the viscosity and observing the evolution of CO ₂ . When the target viscosity is reached, the reactor is cooled by adding 712 g of N-methyl pyrrolidone and 1200 g of ethyl lactate. An enameling varnish of dry extract 30% and viscosity at 20 ^° C. of 2080 mPa.s is then obtained.

Sample 10 is prepared by introducing at 60 ^° C., 2420 g of N-methyl pyrrolidone, 30.4 g of blocking agent, 836 g of trimellitic anhydride, 81 g of terephthalic acid and 580 g of aromatic solvent (Solvesso 100). ) and 1258g of diphenyl methane diisocyanate. The reaction mixture is heated at 140 ^° C. in 5 hours and the evolution of the reaction is monitored by measuring the viscosity and observing the evolution of CO ₂ . When the target viscosity is reached, the reactor is cooled by adding 1212 g of N-methyl pyrrolidone and 700 g of aromatic solvent (Solvesso 100). An enameling varnish of dry extract 30% and viscosity at 20 ^° C. of 2820 mPa.s is then obtained.

For clarity, Table 13 summarizes the differences in compositions between the solvent mixtures of samples 9 and 10.

Table 13

Solvent Mix Sample 9 Sample 10

NMP 63.8% 74%

Ethyl lactate 24.4% 0

Solvesso 100 11.8% 26%

Measurements of the concentration of dry extract after drying of 1 g of product for 1 hour at 18O ⁰ C, as well as the viscosity at 20 ^° C., are carried out on each sample in order to be able to compare the characteristic properties of the enamel varnishes. previously prepared. Table 14 summarizes the results of the measures in question.

Table 14

It is once again observed that the characteristic properties of the two types of enamelling varnish are directly comparable and that the presence of lactate causes the viscosity to drop again in the case of the composition according to the invention (Sample 9). Winding son are then made using as enameling varnish the compositions corresponding to samples 9 and 10. Concretely, layers of varnish are applied in a predetermined number, in successive passes and at a given speed, on conductors son of identical diameters . The extra thickness of the varnish, as well as its appearance on the surface, are then evaluated for each enamelled wire. Standard characterization tests are then conducted to determine the essential properties of both types of winding wires. This is classically tests of flexibility and thermal shock at 22O ⁰ C. Using a Dansk TD300 device, the delta tangent is also determined.

Table 15 gathers both the structural characteristics of the two types of enamelled wires, as well as their specific properties.

Table 15

It is observed once again that the enameling results are quite equivalent. This means that, compared with a solvent mixture of the state of the art, a lactate-based solvent mixture in no way affects the performance of an enameling varnish based on polyamide imide.

Claims

1. enameling varnish composition especially for winding wire, characterized in that it comprises a polymer resin and an alkyl lactate, and in that the polymer resin is chosen from the group of polyesters, imide polyesters, OHIC modified polyesters, polyurethanes, polyamides, imide polyamides, polyvinyl acetoformals, or any mixture of these compounds.

2. Composition according to claim 1, characterized in that the alkyl lactate is selected from methyl lactate, ethyl lactate, propyl lactate, butyl lactate, or any mixture of these compounds.

3. Composition according to one of claims 1 or 2, characterized in that the polymer resin is selected from the group of polyesters, polyesters imides, polyesters imides modified with THEIC, polyurethanes, polyvinyl acetoformals, or a any mixture of these compounds, said composition comprises 5 to 100% by weight of alkyl lactate relative to the total amount of solvents, and preferably 10 to 70%.

4. Composition according to claim 3, characterized in that it further comprises at least one cresylic solvent.

5. Composition according to one of claims 1 or 2, characterized in that the polymer resin being chosen from the group of polyamides, polyamide imides, or any mixture of these compounds, said composition comprises 5 to 70% by weight of alkyl lactate relative to the total amount of solvents, and preferably 10 to 40%.

6. Composition according to claim 5, characterized in that it further comprises N-methyl pyrollidone.

7. Composition according to any one of claims 1 to 6, characterized in that it further comprises at least one aromatic hydrocarbon.

8. Composition according to claim 7, characterized in that it comprises 10 to 50% by weight of aromatic hydrocarbon, relative to the total amount of solvents.

9. A winding wire comprising a conductive element covered with an insulating layer, characterized in that the insulating layer is made from an enameling varnish composition according to any one of the preceding claims.