EP0066194B1 - Process for preparing an electrically insulating aqueous and thermosetting enamel, and its use - Google Patents

Abstract

Aqueous thermosetting electrical insulating varnishes are prepared by a process wherein hydroxyl-containing polyester-imides which have kinematic viscosities of from 16 to 30 mm2 x s-1 and acid numbers of <10, and which have been obtained by condensing aromatic tricarboxylic acid monoanhydrides, aromatic dicarboxylic acids or their esterifiable or transesterifiable derivatives, diamines, diols, and triols containing an isocyanurate ring, are treated, at from 80 DEG to 130 DEG C., in the presence or absence of up to 5% by weight, based on polyester-imide, of an organic solvent, with from 5 to 15% by weight, based on polyester-imide, of ammonia in the form of an aqueous solution, thereby producing aminolysis and hydrolysis so that a neutral or slightly acidic solution results, which is diluted to a viscosity of from 100 to 10,000 mPa.s by adding demineralized water, from 0.1 to 5% by weight, based on polyester-imide, of a water-soluble curing catalyst being added, if desired, after the treatment with ammonia. The electrical insulating varnishes are used as wire enamels or as impregnating varnishes.

Description

The invention relates to a process for the preparation of aqueous thermosetting electrical insulating lacquers based on polyesterimides and their use as wire enamels or as impregnating lacquers, for. B. for the impregnation of enamelled wire windings.

The production of polyesterimides (= PEI) and their use for electrical insulation has long been known and is described, for example, in DE-B-14 45 263, 14 95 100, 14 95 152 and 16 45 435.

In order to process polyesterimide solutions well, relatively low solids contents have to be produced. Due to the specific solubility properties of PEI, phenols, cresols, xylenols, N-methylpyrrolidone, etc. must be used as solvents or as solvent mixtures. These solvents are mostly non-volatile, expensive and sometimes have a very unpleasant smell. In order to avoid unpleasant smells and environmental pollution from such solvents, very complex post-combustion systems are necessary.

In addition to coating electrical conductors with solvent-free resins from the melt, aqueous systems have also been proposed as environmentally friendly and economical alternatives. DE-A-23 51 077 and 23 51 078 describe aqueous PEI secondary dispersions. However, these secondary dispersions have a solids content that is too low and also require special application devices. FR-A-23 01 579, which corresponds to the content of DE-A-26 05 790, describes water-thinnable PEI electrical insulating lacquers which are tertiary with the aid of considerable amounts (5 to 30% by weight, preferably 20 to 30%) Amine and with the use of 5 to 20 wt.% Auxiliary solvent are converted into an aqueous form. The paintwork thus obtained has softening points between 290 and 315 ° C.

DE-A-17 20 321 describes a process for the preparation of water-dilutable polyester imide resins with the aid of ammonia. According to this DE-OS, aromatic tricarboxylic anhydrides are first reacted with up to 80% of the stoichiometric amount of primary diamines which are necessary for imide formation and condensed with an excess of di- and / or trial alcohols. The excess alcohol is then distilled off and the condensation product is heated to a temperature of above 80 ° C. with a small amount of aqueous ammonia, if appropriate with the addition of dialcohols, and the condensation product is then diluted with water.

However, the lacquers produced in this way do not meet the properties required today for conventional polyesterimide wire lacquers.

FR-A-23 54 371, which corresponds to the content of DE-A-27 24 913, also shows water-soluble polyesterimide resins and processes for their preparation. However, the products and manufacturing processes described herein result in products that have to be adjusted to a pH> 7 with amines, i. H. these products smell strongly of amines, which has an adverse effect on workplace hygiene. In addition, as in DE-OS 26 05 790, larger amounts of auxiliary solvents are used (> 10%, as can be seen from the examples).

The object of the present invention is to provide a process for the production of aqueous thermosetting electrical insulating lacquers based on polyesterimides which makes it possible to easily obtain aqueous electrical insulating lacquers which do not have the disadvantages described above.

The present invention relates to a process for the preparation of aqueous thermosetting electrical insulating lacquers based on polyesterimides which have been obtained by condensation of aromatic tricarboxylic acid monoanhydrides, aromatic dicarboxylic acids or their esterifiable derivatives, diamines, diols and a triols containing an isocyanurate ring, which is characterized in that hydroxyl group-containing Polyesterimides with kinematic viscosities of 16 to 30 _MM ^{2 -} _S - ¹ (measured in a solution of 1 part of polyesterimide in 2 parts of N-methylpyrrolidone at 30 ° C) and acid numbers <10 at temperatures between 80 and 130 ° C, optionally with use of up to 5% by weight, based on polyesterimide, of an organic solvent, with 5 to 15% by weight, based on polyesterimide, of ammonia in the form of an aqueous ammonia solution with aminolysis and hydrolysis, so that a solution with pH values between 6 and 6.9 results, and by the addition of demineralized tem water are diluted to a viscosity between 100 and 10000 mPa - s, 0.1 to 5% by weight, based on polyesterimide, of a water-soluble curing catalyst optionally being added after the treatment with ammonia.

The present invention also relates to the use of these aqueous electrical insulating lacquers as wire lacquers or impregnating lacquers.

Surprisingly, completely clear, water-thinnable lacquers are obtained by the process according to the invention, which show improved values in heat level compared to the water-thinnable lacquers obtained with tertiary amines. In addition, the electrical insulating lacquers according to the invention are more economical and considerably more environmentally friendly due to the use of cheap ammonia instead of ethanolamines. They can be applied to the substrates to be coated using customary application systems and, after baking, show that the technical properties of the conventional polyesterimide lacquers dissolved in the above-mentioned organic solvents and thus problematic with regard to their environmental impact are at least equivalent.

With regard to the polyesterimides to be used for the process according to the invention and their structural components, it should be stated that the basic structure of suitable polyesterimides can be found in DE-AS 14 45 263 and DE-AS 14 55 100. The hydroxyl-containing polyester imide to be used according to the invention can preferably be prepared by the process described in DE-OS 14 55 182.

The PEI are condensation products from aromatic tricarboxylic acid monoanhydrides, aromatic dicarboxylic acids or their derivatives, diamines, diols and triols with an isocyanurate ring.

As aromatic tricarboxylic acid monoanhydrides such. B. consider trimellitic anhydride, 3,4,3'-benzophenone tricarboxylic anhydride and hemimellitic anhydride, with trimellitic anhydride being preferred.

Suitable aromatic dicarboxylic acids and their esterifiable derivatives are e.g. B. terephthalic acid, isophthalic acid, benzophenone-4,4'-dicarboxylic acid; Esters of aromatic dicarboxylic acids, such as. B. the esters of terephthalic acid with lower alcohols containing 1 to 3 carbon atoms, e.g. B. dimethyl terephthalate, dimethyl isophthalate, diethyl terephthalate.

wobei X für einen zweiwertigen Rest, z. B. -CH2-, -0-. -CO-, ―S― oder ―SO₂― steht. Beispiele für derartige Diamine sind Diaminodiphenylmethan, Diaminodiphenyloxid und Benzophenondiamin.As diamines are preferably those with primary amino groups, which are bound to aromatic groups, for. B. those of the general formula

where X for a divalent residue, e.g. B. -CH2-, -0-. -CO-, ―S― or ―SO ₂ - stands. Examples of such diamines are diaminodiphenylmethane, diaminodiphenyloxide and benzophenonediamine.

Suitable diols are customary dihydric aliphatic alcohols, such as: 1,4-butanediol, trimethylene glycol, preferably ethylene glycol.

Suitable triols with an isocyanurate ring are trishydroxyethyl isocyanate, trishydroxypropyl isocyanurate, in particular trishydroxy ethyl isocyanurate (= THEIC). If necessary, other triols, such as e.g. B. Glycerin can also be used.

Tricarboxylic acid monoanhydride, dicarboxylic acid (derivative), diamine, diol and triol are generally in a molar ratio of 1.7-2.8 / 0.5-1.2 / 0.7-1.4 / 0.4-1.2 / 0.8-1.4, preferably 1.9-2.110.7-1.0 / 0.9-1.1 / 0.5-0.8 / 1.0-1.3.

As already mentioned above, the hydroxyl-containing polyesterimides can be prepared, for example, by the process described in DE-OS 14 55 182. The condensation is carried out here in ethylene glycol, polyesterimides being obtained which no longer contain carboxyl groups and thus have no acid number.

The hydroxyl group-containing polyesterimides to be used for the process according to the invention have acid numbers <10, preferably <5 and kinematic viscosities of 16 to 30, preferably 18 to 28 mm ² . S ^―1 (measured in a solution of 1 part by weight of polyesterimide in 2 parts by weight of N-methylpyrrolidone at 30 ° C).

The usual principle of producing water-soluble resins by neutralizing free carboxyl groups with amines to form the salts cannot therefore be applied to these PEI.

According to the invention, the hydroxyl-containing polyesterimides are at temperatures between 80 and 130 ° C, preferably 90 and 110 ° C, optionally with the use of up to 5% by weight, based on PEI, of an organic solvent, with 5 to 15, preferably 7.5 to 10% by weight, based on PEI, of ammonia in the form of an aqueous ammonia solution, which can contain, for example, 5 to 25% by weight of ammonia, treated with aminolysis and hydrolysis. The result is a weakly acidic aqueous solution with pH values between 6 and 6.9, preferably 6.5 and 6.9.

Suitable organic solvents, optionally in amounts of up to 5% by weight, based on PEI, are water-miscible solvents, such as. B. N-methylpyrrolidone, glycols, such as ethylene glycol, glycol ethers, such as butyl glycol, methyl diglycol, ethyl diglycol, butyl diglycol or other polar solvents, such as dimethylformamide or dimethylacetamide.

After the PEI has been treated with aqueous ammonia, the PEI solution, which is expediently cooled to 20 to 50 ° C., can also be mixed with 0.1 to 5, preferably 2 to 4,% by weight, based on PEI, of a water-soluble curing catalyst . As such water-soluble curing catalysts are preferably water-soluble titanates, such as. B. Titanium tetralactate.

The dilution of the polyesterimide solutions to viscosities between 100 and 10000 mPa. s is done by adding deionized water.

In this form, the polyesterimide solutions prepared according to the invention can be used directly for coating wires, e.g. B. of copper wires or as impregnating varnish for impregnating enamelled wire windings. The application methods and devices which are customary for this purpose come into question.

The coatings are generally baked at temperatures of 200 to 550, preferably 400 to 520 ° C.

The aqueous thermosetting polyesterimide lacquers produced according to the invention have good storage stability, are completely clear and have no ammonia smell. The paintwork thus obtained also shows excellent properties with regard to the softening temperature, the thermal shock and the thermal aging behavior.

The parts and percentages given in the following examples are, unless stated otherwise. Parts by weight and% by weight e.

example 1

werden nach Zugabe von 2,6 Teilen Bleiacetat bei Temperaturen bis 220 °C bis zum Klarpunkt verestert. Dann wird bei 150 bis 200 °C das überschüssige Ethylenglykol in Vakuum (5,33 KPd (40 Torr)) abdestilliert, bis das Harz, im Verhältnis 1 : 2 in N-Methylpyrrolidon gelöst, eine Viskosität von 19 mm^{2 .} S^―1 (Ubelohde 3) bei 30 °C aufweist. Bei 95 °C werden dann 87.8 Teile N-Methylpyrrolidon zugefügt und 851,4 Teile Ammoniak (25%ig) langsam hinzugegeben. Nach 1 Stunde bei dieser Temperatur werden 991 Teile vollentsalztes Wasser zugegeben und erneut 3 Stunden bei 100 °C gehalten. Nach dem Abkühlen werden 95 teile Titantetralactat hinzugegeben. Der so erhaltene wäßrige Drahtlack hat einen Feststoffgehalt von 52,3 % mit einer Durchlaufviskosität im Ford-Becher (4 mm) nach DIN 53 211 von 41 sek.

are esterified after the addition of 2.6 parts of lead acetate at temperatures up to 220 ° C to the clear point. The excess ethylene glycol is then distilled off in vacuo (5.33 KPd (40 Torr)) at 150 to 200 ° C. until the resin, dissolved in a ratio of 1: 2 in N-methylpyrrolidone, has a viscosity of 19 mm ^2. S ^―1 (Ubelohde 3) at 30 ° C. 87.8 parts of N-methylpyrrolidone are then added at 95 ° C., and 851.4 parts of ammonia (25% strength) are added slowly. After 1 hour at this temperature, 991 parts of demineralized water are added and the mixture is again held at 100 ° C. for 3 hours. After cooling, 95 parts of titanium tetralactate are added. The aqueous wire enamel thus obtained has a solids content of 52.3% with a continuous viscosity in the Ford cup (4 mm) according to DIN 53 211 of 41 seconds.

The varnish is applied to a copper wire of 0.5 mm 0 in 8 passes using a conventional wire varnishing furnace 2.50 m long and baked at 460 ° C. The take-off speed was 22 m / min.

Vergleichsbeispiel (nach DE-AS 17 20 321)The enamelled wire had the following properties when tested according to DIN 46453:

Comparative example (according to DE-AS 17 20 321)

Example 1 of DE-AS 1720321 was reworked. The solution thus obtained was coated (baking temperature 460 ° C., take-off speed 22 m / min).

Claims (4)

1. A process for the preparation of aqueous thermosetting electrical insulating varnishes based on polyester-imides which have been obtained by condensing aromatic tricarboxylic acid monoanhydrides, aromatic dicarboxylic acids or their esterifiable derivatives, diamines, diols, and triols containing an isocyanurate ring, wherein hydroxylcontaining polyester-imides which have kinematic viscosities of from 16 to 30 mm². _S-¹ (measured in a solution of 1 part of polyester-imide in 2 parts of N-methyl-pyrrolidone at 30 °C) and acid numbers of < 10 are treated, at from 80 to 130 °C, in the presence or absence of up to 5 % by weight, based on polyester-imide, of an organic solvent, with from 5 to 15 % by weight, based on polyester-imide, of ammonia in the from of an aqueous solution, thereby producing aminolysis and hydrolysis so that a solution having a pH of from 6 to 6.9 results, which is diluted to a viscosity of from 100 to 10 000 mPa - s by adding demineralized water, from 0.1 to 5 % by weight, based on polyester-imide, of a water-soluble curing catalyst being added, if desired, after the treatment with ammonia.

2. A process as claimed in claim 1, wherein tris-hydroxyethyl isocyanurate is used as the triol containing an isocyanurate ring.

3. A process as claimed in claim 1 or 2, wherein dimethyl terephthalate is used as the esterifiable derivative of an aromatic dicarboxylic acid.

4. The use of the aqueous electrical insulating varnishes prepared by a process as claimed in any of the preceding claims, as wire enamels or impregnating varnishes.