DE2537207A1 - Process for the preparation of aqueous wire enamel dispersions - Google Patents

Description

BASP Aktiengesellschaft

Our reference: O.Z. 31 490 Dd / DK 6700 Ludwigshafen, 19-8.1975

Process for the production of aqueous wire enamel dispersions

Me invention relates to aqueous wire enamel dispersions based of polyurethane-forming starting components, as well as processes for their production.

It is known that coatings based on polyurethanes in the Insulation of electrical conductors have advantages: Good moisture resistance and aging resistance are obtained, but above all, the coatings can be soldered.

Such polyurethane coatings are usually produced by applying a paint solution, which is a mixture of one containing hydroxyl-containing polyester and a blocked polyisocyanate, on the wire to be coated and then Baking in the paint, releasing the polyisocyanate and cross-linked the polyester. This method has the disadvantage that in the preparation of the paint and when applied in large quantities organic solvents must be handled, and that the solvents are released into the surrounding air during stoving, so that they represent an environmental burden.

DT-AS 1 729 201 describes aqueous dispersions of polyurethane powders containing salt-like groups. Such Dispersions contain finished polyurethanes, in which the reaction between the starting components with polyurethane formation before Dispersing in water had been made. They are used as a coating agent Not suitable for insulating electrical conductors: If it is a question of cross-linked polyurethanes, then these cannot be applied as a uniform coating on wires j If it is a non-crosslinked linear polyurethane, you can use it to paint wires, but the coatings are used as electrical insulation not suitable because they are too soft to be too

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ORIGINAL INSPECTEC

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low softening range and too low temperature resistance to have.

The invention was based on the object, polyurethane-based wire enamels to develop which can be applied from aqueous dispersion and coatings with good mechanical and electrical properties result.

It has now been found that these requirements are met in the case of aqueous dispersions which contain:

A) 40 to 80 percent by weight water,

B) 60 to 20% by weight of a mixture

% a) 70 to 10 wt. of a polyester or polyether having a hydroxyl number greater than 20 and

b) 30 to 90 percent by weight of at least one blocked Polyisocyanate,

wherein, the mixture in the form of particles with a mean Diameter between 0.05 and 2 µm dispersed in water is,

C) 0.1 to 15% wt. Of a dispersant and

D) 0 to 40 wt.% Of further additives.

A preferred method for preparing such dispersions is that one has a 10 to 80 wt .- # solution of the component B in an inert organic solvent with a solution of the dispersing aid C in water with formation mixed with an emulsion, this emulsion is subjected to a shear movement and at the same time the organic solvent or an azeotrope distilled off from solvent and water.

Another preferred method is that one

1. a solution of component B, and optionally dispersing

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auxiliaries C and additives D in an inert organic solvent with a freezing point between +30 and -5O ⁰ C,

2. this solution solidifies by cooling,

3. the solvent is removed by sublimation under reduced pressure,

² years the resulting solid, solvent-free product mechanically crushed and

5. the powder obtained, possibly together with additives, dispersed in water.

As starting components for the preparation of the dispersions according to the invention Mixtures of hydroxyl-containing polyesters or polyethers and masked polyisocyanates are used. this are the usual starting materials for the production of polyurethanes. Details about substances, production and properties can be found in the chapter "Polyurethane" in Houben-Weyl, Methods of Organic Chemistry, Vol. XIV / 2 (1963), pages 77 to 98.

Preferred polyesters are: reaction products of aliphatic or aromatic dicarboxylic acids, such as adipic acid, terephthalic acid, Isophthalic acid, phthalic acid or azelaic acid or their derivatives with preferably aliphatic diols, such as ethylene glycol, Diethyleneglycol, triethyleneglycol, neopentylglycol, preferably as crosslinkers higher alcohols such as trimethylolpropane, Glycerine, trimethylolbenzene or trishydroxyethyl isocyanurate can also be used. The following polyethers can be used, for example: polyethylene glycol, Polypropylene glycol or polytetrahydrofuran.

The hydroxyl numbers of the polyesters or polyethers are greater than 20, preferably between 25 and MOO, in particular between 60 and 300. They have a molecular weight of preferably 500 to 5000, especially from 1000 to 2000.

-V-

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The other components are blocked polyisocyanates, preferably based on aromatic polyisocyanates with an isocyanate content between 5 and 30 %. Possible polyisocyanates are: hexamethylene isocyanate, 4,4'-diphenylmethanedixocyanate, tolylene diisocyanate, isophorone diisocyanate, naphthalene diisocyanate, and more highly condensed products such as the trimerization product of tolylene diisocyanate or the reaction product of 1 mole of trimethylolpropane and 3 moles of tolylene diisocyanate. Lactams such as caprolactam, phenol, cresols, maleic acid esters, malonic esters, glycols, imidazoles or phthalimide can be used as capping agents.

The weight ratio between polyester or polyether and capped Polyisocyanate is between 10:90 and 70:30, preferably between 20:80 and 6θ: 4θ.

The aqueous dispersions according to the invention contain 0.1 to 15 Percentage by weight of conventional dispersing aids, preferably water-soluble high molecular weight organic compounds with polar groups, such as polyvinylpyrrolidone, copolymers and vinyl propionate and vinyl pyrrolidone, polyacrylic acid, partially saponified copolymers of acrylic esters and acrylonitrile, polyvinyl alcohol, Cellulose ethers, gelatine or mixtures of these substances.

In addition, the usual additives D, such as fillers, Leveling agents, thickening agents, neutralizing agents, antithixotropic agents be contained in amounts up to 40 percent by weight. This also includes substances that increase elasticity and hardness of the finished coatings, such as polyamides, epoxy resins, phenolic resins, melamine resins or polyvinyl formals, preferably in Amounts between 2 and 30 percent by weight. Aliphatic polyamides and acrylic copolymers, such as e.g. a copolymer of acrylic ester, acrylonitrile and acrylic acid.

These additives can be added to the starting solutions or to the finished dispersion.

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In one preferred process, the starting components are dissolved in an inert organic solvent, so that a 10 to 80, preferably 20 to 60, weight solution is formed. The solvent used should preferably have a boiling point below 150 ⁰ C, in particular below 105 ° C. Tetrahydrofuran, dioxane, acetone, methylene chloride, for example, are suitable; also xylenes, benzene, toluene or Ä'thylglykolacetat.

This solution is then mixed with a solution of the dispersing aid C in water. Particularly suitable dispersing aids here are polyvinyl alcohols with a residual acetate content below 35 molar, preferably between 5 and 30 molar 55. The amount of dispersing aid is chosen so that the finished wire enamel contains 0.1 to 15, preferably 0.3 to 3,% by weight.

When the two solutions are mixed, an emulsion is formed, and it depends on the choice of the proportions which solution is the coherent and which represents the disperse phase. The emulsion is subjected to a shear motion. This is done expediently by vigorous stirring, the speed of rotation of the stirrer between 50 and 500 m / min., preferably between 100 and 400 m / min. At the same time the organic solvent or an azeotrope of solvent and water is distilled off. For this purpose, the emulsion is expediently to a temperature above the boiling point of the solvent or the azeotrope heated. However, it is also possible by applying negative pressure remove the solvent. It is important that strong shear forces act on the emulsion during the distillation. only this way a sufficiently finely divided dispersion is obtained. The maximum grain size should preferably be less than 5 μm; the middle one The diameter is between 0.05 and 2 μm, preferably between 0.1 and 1 μm.

In the other preferred production method, a solution of the mixture of polyester or polyether is also first used and the capped polyisocyanate in an inert organic

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Solvent produced. The solvent should have a freezing point between +30 and -50 ⁰ C. For example, xylenes, glacial acetic acid, cyclohexane, ethylene bromide, neopentyl alcohol or tert-butanol come into embossing; dioxane is preferred. In addition to the reaction components for polyurethane formation, the dispersing aids and additives can also be added in whole or in part here. The pesticide content of the solution is again preferably 10 to 80, in particular 20 to 60 percent by weight.

The solution is then brought to a temperature below its freezing point cooled and thereby solidified. This can be dislforrf / useful take place; however, when working on an industrial scale, the continuous mode of operation is preferred, the solution being e.g. applies to an endless belt, where it cools and solidifies and finally detaches the solidified product from the belt. That froze The product is then freed from the solvent under reduced pressure. The pressure is adjusted so that it is less than the vapor pressure of the solvent at the freezing point. He should preferably 3 to 10 torr lower than the vapor pressure of the solvent at the triple point. So in the dry material of even a temperature that is below freezing point. You can also use the solvent from the solidified mixture subliming by passing a gas stream, e.g. air or nitrogen, past the surface of the solid phase, whereby the Adjusts gas flow advantageously to temperatures which are at the freezing point of the solution or moderately above. This operation too can be carried out continuously when working in a vacuum tower with several floors rotating around a longitudinal axis, whereby the dry material is slowly transported to the next floor below. The solvent can be condensed and recycled be returned again.

The dried product is obtained in the form of loose, foam-like aggregates, which, however, above all, even with light touch disintegrate into a loose powder with an average particle size between about 5 and 200 μm by crushing or rubbing. This powder can be further crushed by grinding. Before-

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however, the powder is preferably dispersed in water, if appropriate together with auxiliaries, 40 to 80 parts by weight of water being used for 20 to 60 parts by weight of powder. The powder can be comminuted further in the aqueous phase, for example by dispersing mills, so that a dispersion is produced in which the particles have an average diameter between 0.05 and 2 μm, preferably between 0.1 and 1 μm, in which case more than 99 % of the particles are less than 1 µm in diameter.

In addition to these preferred production methods, the inventive Dispersion also through dry grinding of the solid raw materials, Dispersing in water and then wet milling getting produced. The starting materials can also be dissolved in suitable solvents by adding non-solvents precipitate, wash and then disperse in water. The preferred methods are particularly favorable because they are in in a simple way the desired grain fineness is obtained, which for uniform, smooth coatings are required.

The aqueous wire enamel dispersions of the invention are used for Used to cover electrical conductors.

If necessary, they can also be diluted with water to achieve an optimal concentration. To produce the coatings, the dispersions are applied using conventional coaters and then baked at oven temperatures between 250 and 500 C, preferably between 350 and 45O ⁰ C. The capping agent splits off, the polyisocyanate is released and can crosslink the polyesters or polyethers through reaction with the hydroxyl groups.

example 1

In a stirred flask with a distillation attachment, 375 parts of a • Polyesters made from adipic acid, 1,4-butanediol and trimethylolpropane with a hydroxyl number of 165, as well as 480 parts of one with phenol

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blocked isocyanate from 1 mole of trimethylolpropane and 3 moles of tolylene diisocyanate (with an isocyanate content of 13.4 %) dissolved in 750 parts of tetrahydrofuran. The solution was with 45 parts of ethyl glycol acetate as a leveling agent, and 684 parts of a 5 # aqueous solution of a polyvinyl alcohol with a viscosity of 5 cP (in 2 $ aqueous solution), a hydroxyl number of 653 and a residual acetate content of 27 % and a further 240 parts Water was added with vigorous stirring (stirring speed 450 rpm). An emulsion was formed. The internal temperature of the flask was increased to 99 ° C. within 3 hours. A total of 800 parts of liquid were distilled off. The dispersion was then cooled and 170 parts of a 50 # strength dispersion of a polyamide composed of 39 % hexamethylenediamine adipate, 33 % caprolactam, 24 % 4,4'-diaminodicyclohexylmethane were added. With the dispersion was 0.8 mm copper wires at 38O ⁰ C with a lacquering 8-14 m / min, coated. Properties of the coated wires:

Diameter increase: 50-60 »µm

Heat shock resistance

(DIN 46 453): I85 C

Soldering time at 375 ⁰ C

(DIN 46 416): 2-3 see.

Softening point

(DIN 53 180): 150-210 ^° C.

Pencil hardness (DIN 46 453): 1 H - 2 H.

Example 2

100 parts of a polyester made from phthalic anhydride and trimethylolpropane with a hydroxyl number of 265 and 207 parts of the polyisocyanate according to Example 1 were dissolved in 307 parts of methylene chloride. The solution was then mixed with 21 parts of ethyl glycol acetate and 307 parts of a 5% aqueous solution of the dispersant according to Example 1 with vigorous stirring. The temperature was then increased to 85 ^° C. in the course of 2 hours. 310 parts of solvent distilled off. The dispersion was then cooled and defoamed overnight. With this dispersion

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wires were coated as in Example 1. Their characteristics were:

Diameter increase: 50 - 60,

around

Softening point: Example 3 255 ⁰ C Heat shock resistance: 130 ⁰ C Soldering time at 375 ° C: 3-4 see. Pencil hardness: 7 H.

233.6 g of a polyester (made from phthalic anhydride and trimethylolpropane in a weight ratio of about 1: 1) with a hydroxyl number of 1 * 10 were mixed with 166.4 g of a blocked polyisocyanate (reaction product of trimethylolpropane and 3 mol of toluene diisocyanate, blocked with phenol) in 600 g of dioxane dissolved. The solution was poured into a metal container and cooled with a dry ice / acetone mixture until it forms ice. The mixture was then freeze-dried at a pressure of less than 1 torr for 12 hours without the dioxane melting. The remains of the dioxane to remove, the temperature was raised for 4 hours at 50 ⁰ C. The result was a loose foam, which was pulverized with an ordinary laboratory mill. To produce a dispersion, 350 g of powder were dispersed together with 10.5 g of a copolymer of vinyl pyrrolidone and vinyl propionate and 8.75 g of polyvinyl alcohol in 65O g of water and then dispersed with a Laboratory mill ground at a throughput of 30 1 per hour. With the resulting thixotropic dispersion, after addition of 3.5 g of triethanolamine, 1 mm thick copper wires were coated on a horizontal wire coating machine at 450 ° C. at a coating speed of 6 to 12 m per minute. The resulting coatings had the following properties:

Soldering time at 375 ° C (DIN 46 416): 1 to 2 see Heat shock resistance (DIN 46 453): 130 ⁰ C Thermal pressure (DIN 46 453): 210 to 230 ° C Pencil hardness (DIN 46 453): 1 to 2 H breakdown voltage ( DIN 53 481): 100 to 150 V / / um.

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Claims (12)

- ίο - ο..ζ. 31 claims 1. Aqueous wire enamel dispersions containing A) 40 to 80 percent by weight water, B) 60 to 20 percent by weight of a mixture a) 70 to 10 percent by weight of at least one polyester or polyether with a hydroxyl number above 20 and b) 30 to 90 percent by weight of at least one blocked Polyisocyanate, the mixture being dispersed in water in the form of particles having an average diameter between 0.05 and 2 µm is, C) 0.1 to 15 percent by weight of a dispersing aid and D) 0 to 40 percent by weight of other additives. 2. Aqueous wire enamel dispersion according to claim 1, characterized in that component B a) is a polyester of an aliphatic or aromatic dicarboxylic acid, an aliphatic diol and optionally a trihydric alcohol, with a hydroxyl number between 25 and MOO and a molecular weight between 500 and 5000 is. 3. Aqueous wire enamel dispersion according to claim 1, characterized in that component B a) is an aliphatic polyether with a hydroxyl number between 25 and 400. 4. Aqueous wire enamel dispersion according to claim 1, characterized in that component B b) is an aromatic polyisocyanate, with an isocyanate content between 5 and 30 % _t which is capped with a lactam, a phenol, a glycol, a dicarboxylic acid ester, an imidazole or phthalimide is, - 11 - 709809/0918 - 11 O.Z. 31 5. Aqueous wire enamel dispersion according to claim 1, characterized in that component C is a water-soluble high molecular weight organic compound with polar groups. 6. Aqueous wire enamel dispersions according to claim 1, characterized in that component C is a polyvinyl alcohol with a residual acetate content of less than 35 », preferably between 5 and 30 mol-Si. 7. Aqueous dispersions wire enamel according to claim 1, characterized in that they contain as component D include 2 to 30 wt.% Of an aliphatic polyamide or an acrylic copolymer. 8. A process for the preparation of the aqueous wire enamel dispersions according to claim 1, characterized in that a 10 to 80 wt is subjected to a shear movement and at the same time the organic solvent or an azeotrope of solvent and water is distilled off. 9. A process for the preparation of aqueous wire enamel dispersions according to claim 8, characterized in that an organic solvent with a boiling point below 150 ⁰ C is used. 10. A process for the preparation of aqueous wire enamel dispersions according to claim 8, characterized in that the shear movement is carried out by stirring the emulsion at a speed of rotation of the stirrer between 50 and 500, preferably between 100 and 400 m / min. 11. Process for the preparation of aqueous wire enamel dispersions according to claim 1, characterized in that one 1. a solution of component B, and optionally dispersing aids C and additives D in an organic - 12 - 709809/0918 ο. ζ. 51 490 Produces solvents with a freezing point between +30 and -5O ⁰ C, 2. this solution solidifies by cooling, J>. the solvent is removed by sublimation under reduced pressure, 4. the resulting solid, solvent-free product mechanically crushed and 5. the powder obtained, optionally together with additives, dispersed in water. 12. Use of the aqueous wire enamel dispersions according to claim for coating electrical conductors. BASF Aktiengesellschaft 709809/0918