The present invention relates to an electroinsulating polyesterimide enamel,, particularly used for wires.

There are known electroinsulating polyesterimide enamel which are composed of polyesteimide resin, solvents, dilut- ents, catalysts and/or phenolic and/or hydantoine resins. Thermal properties and flexibility of the enamel coating on wires depend mainly on chemical structure of the polyester¬ imide resin used for enamel formulation.

According to Polish Patent No. 125 456 there is known a method of manufacture a polyesterimide resin for enamels by means of one-stage catalytic polycondensation and imidization trimellitic anhydride, dimethyl terephthalate, ethylene gly¬ col, 4,4'-diaminodiphenylmethane, tris(2-hydroxyethyl)-isocy- anurate and/or glycerol with simultaneous distilling of by¬ products. Enamels formulated on the basis of polyesterimide resins manufactured in that way give coatings of good thermal resistance but unsatisfactory flexibility so that application of the enamels is limited to wires of diameter up to 1 mm.

There is also known (according to Polish Patent No. 139 706) a method of manufacturing polyesterimide enamels in which polyesterimide resin is manufactured by additional hea¬ ting at temperature 160°C in one-stage process. Coatings ob¬ tained by enamelling copper wires with these enamels have un¬ satisfactory flexibility, even if polyhydantoine resin has been added.

In order to improve thermal resistance, polyesterimide resins with built-up aromatic fragments or with reduced amo¬ unt of aliphatic chains or ether bonds in the molecule, and also polyesterimide resins modified by means of polyhydanto¬ ine resins are used. Improvement of thermal resistance of the enamel coatings is accompanied, unfortunately, reduction of flexibility.

It turns out, that there is possible to obtain electro¬ insulating polyesterimide coatings of high thermal resistance and simultaneously of very good flexibility, if diphenols with alkylene carbonate or mixture of alkylene carbonates are used for manufacturing the polyesterimide resin.

The enamel according to the invention is composed of.25- 75 mass % thermoresistant polyesterimide . resin manufactured by catalytic polycondensation, profitably at the presence of zinc acetate, dicarboxylic acids or esters, diols, triols, diphenols and alkylene carbonates with addition of diamines, polyamines, aminoacids, if nescessary, and also with addition of anhydrides or anhydrides having free carboxy groups with removing low-molecular-weight products: methanol, water and dioxide in the process of distillation under atmospheric pre¬ ssure.

To the initial reaction mixture, at the beginning or when heated, 0.01-1.0 mole diphenol and 0.02-2.0 moles alky¬ lene carbonate or an alkylene carbonates mixture to every 10 moles all the raw materials used in the synthesis are intro¬ duced. In the polycondensation process for manufacturing polyesterimide resin resorcine, hydrochinon, di(4-hydroxy- phenyl) ethane, low-molecular-weight polycarbonates and par¬ ticularly 2,2-di(4-hydroxyphenyl)propane as diphenols, and predominantly ethylene carbonate and/or propylene carbonate as alkylene carbonates are used. The enamel according to the invention contains 20-70 mass % m-cresol, o-cresol, p-cresol separately or as a mixture, 2.5-45 mass % aromatic, aliphatic and, if necessary, cycloaliphatic hydrocarbons having 6-20 carbon atoms, separately or as a mixture, 0.5-5.0 mass % bu¬ tyl and/or cresyl titanate with the addition 1.0-6.0 mass % phenolic resins and/or polyisocyanurate resins and/or polyhy- dantoine resins.

Polyesterimide resin used to formulate the enamel accor¬ ding to the invention has hydroxy value 150-250 mg KOH/g, number-average molecular mass 650-4500, softening point (Boe- tius method) 85-120°C.

The following examples illustrate the manner in which the enamel according to the invention may be obtained.

EXAMPLE 1

55 kg 2,2-bis(4-hydroxyphenyl)propane, 43 kg ethylene carbonate, 215 kg dimethyl terephthaiate, 81 kg tris(2-hydro- xyethyl) isocyanurate, 37 kg glycerol, 40 kg 4,4'-diaminodi- phenylmethane, 77 kg trimellitic anhydride, 38 kg ethylene

glycol and l kg zinc acetate were loaded to a reactor 1 m ³ capacity. The mixture of the components was heated slowly up to temperature 225-230°C and 70 kg water-methanol mixture was distilled off and 24 kg carbon dioxide was evolved. The rea¬ ction mixture was maintained at above temperature as far as softening point of the obtained polyesterimide resin incre¬ ased to 100-115°C (Boqtius method) . Then the reaction was ra¬ pidly stopped by addition 300 kg tricresol and reduction tem¬ perature down to 160-165°C. Stirring, next portion 340 kg tricresol and, after cooling the solution to 100°C, 350 kg solventnaphta, 10 kg tetraϊine and 15 kg cresol-formaldehyde resin were added. When temperature was decreased to 40°C, 25 kg poly(butyl titane) as a catalyst was added and the con¬ tents was thoroughly mixed. The product was diluted with the mixture of tricresol and solventnaphta in mass ratio 4:1- so that viscosity of the product was 120-150 seconds at tempera¬ ture 25°C according to Ford Cup No. 4, and non-volatile mat¬ ter was 34+1 mass % (30 min. at 180°C) and the enamel was filtered. The enamel was used for enamelling copper wires in horizontal or vertical machines of all coating systems.. The enamel accrding to the invention gave on copper wires elec¬ troinsulating coatings having very good high temperature re¬ sistance and very good flexibility simultaneously. Enamelling parameters and coating properties of the enamel according to the invention in the Table 1 column A are given.

EXAMPLE 2 The process of Example 1 was repeated employing 50 kg propylene carbonate instead of 43 kg ethylene carbonate as

mentioned in Example 1. The other components were unchanged. The electroinsulating enamel of the coating properties given in the Table 1 column B was obtained.

EXAMPLE 3 - comparative 215 kg dimethyl terephthalate, 8 kg tris(2-hydroxy- ethyl)isocyanurate, 37 kg glycerol, 40 kg 4,4'-diaminodiphe- nylmethane, 77 kg trimellitic anhydride, 52 kg ethylene gly¬ col and 1 kg zinc acetate were loaded to a reactor 1 m ³ capa¬ city. The mixture of the components was heated slowly up to temperature 225°C and 74 kg mixture of water-methanol was di¬ stilled off simultaneously. The reaction mixture was main¬ tained at 225°C until the polyesterimide resin had softening point 95-110°C (Boqtius method) . Then temperature of the re- acton mixture was reduced to 160-165°C by adding 300 kg tri¬ cresol and the polycondensation was rapidly stopped, next the reaction mixture was thoroughly stirred and filtered and the enamel having viscosity 120-140 seconds at 25°C (Ford Cup No. 4) and non-volatile matter 34+1 mass % (30 minutes at 180°) was obtained. Copper wire coating of the enamel obtained acc¬ ording th hitherto existing knowledge had properties given in the Table 1 column C.

o Table 1. Properties of the copper wire coatings from the electroinsulating enamels.

Enamel mark According to According the invention to the hit- hertoexist-

Property ting know- lege

B

Wire diameter [mm] 1. 1.0 1.0

Coating thickness [mm] 59. 59.0 58.0

Flexibility* ¹ , with pre-stretch 0 1 d 0 0 0 15 1 d 0 0 0 20 1 d 0 0 0 25 1 d 0 0 7

30 % 1 d 0 5 30

Heat shock ³⁾ 175-180°C, 0.5 hr 2 d 0 0 0

1 d 0 0 2

200-205°C, 0.5 hr 2 d 0 0 6 1 d 3 4 18

Thermoplastic flow [°C] 380 360 350

Resistance to abrasion average [N] 11.2 10.6 9.7 min [N] 10.0 9.4 8.9

Breakdown voltage [kV] 9.6 9.8 7.3

Tangent Delt Temperature[°C] 165 165 155

Enameling parameters

Type of oven (horizontal) MAG MAG MAG Oven temperature [°C] 380 380 380 Enamelling speed [m/min] - 14 14 12

^a) Number of cracks /60 coils