NO123872B - - Google Patents

Description

Process for the production of insulating

covering of electrical conductors.

The invention relates to a method for producing insulating covers on electrical conductors by coating conductors with a solution of ester imide condensation products and heating the coated conductor at elevated temperatures.

Electrical conductors which are provided with an insulating coating based on carboxylic acids, especially terephthalic acid, glycols and glyceryl, have a number of advantageous properties, and have therefore gained considerable technical importance. However, such insulation covers did not meet the high overload requirements that are set today in electromechanical engineering." to the insulated conductors.

It has been proposed to supply electrical conductors with insulating coatings of linear polyimides, produced by condensation of diamines and tetracarboxylic anhydrides. These covers are characterized by extremely high temperature resistance and resistance to heat stress. This high temperature resistance is obviously caused primarily by the five-membered ring in the molecule.

It was therefore obvious to try to modify the molecules in the first-mentioned known polyester insulation cover in such a way that five-membered imide rings of the type found in large numbers in linear polyimide resins are incorporated into the polyester resins, thereby increasing the heat resistance. The implementation of this experiment showed that there really was an effect in the expected direction, i.e. in particular an improvement of the thermal resistance. For this reason, such so-called ester imide condensation products have recently gained importance in the production of insulating coatings on electrical conductors.

In the case of ester imide condensation products according to

French patent no. 1,368,741, it was not possible to fulfill the demands made by the electrical industry for heat loadability, i.e. according to the lasting insulating ability of the covers at relatively high temperatures produced by electric heating. This important characteristic of •lacquered wires is termed char resistance and is determined in practice according to Herberts-Werksnorm 2010. The investigation is carried out in such a way that a four-layer coil of a lacquered wire is wound on a porcelain armature and then charged with 165 watts to short-circuit. The time duration in minutes to short circuit is a measure of the charring resistance of the insulating varnish layer.

Moreover, varnished threads of ester imide condensation products (French patent no. 1,368,741) do not satisfy the electrical industry's requirements with regard to so-called residual distance. Now, the residual distance is a particularly important property for lacquered wires used in electric motor construction, as they relate to the electrical insulation coating's dimensional stability in heat. The dimensional stability is of course of the greatest importance, e.g. in the event of overloading a blocked armature in a motor, the insulating layers of the varnished wire windings produced with strong winding tension should not press in at the resulting high temperatures. The dimensional stability in the heat is determined in practice according to Herberts-Werknorm 2008, by determining the thickness reduction of ten right-angled, crossing varnish wires under a fixed, blank wire diameter-dependent weight load at temperatures from 20 - 300°C. The remaining at the relevant temperature

thickness of the insulation layer in percent is referred to as the residual distance.

According to French patent no. 1,368,741, the relevant aromatic compounds with symmetrical groups are exclusively incorporated in the polycondensate in such a way that a linear condensation takes place. When, for example, according to the French patent, pyromellitic acid is incorporated, this must take place in accordance with the instructions in this patent by each time two carboxyl groups placed in the ortho position form a five-membered imide ring with an amino group. This is achieved by corresponding selection of quantity ratios. According to this French patent, it is thus excluded that aromatic compounds with at least three similar groups present in a symmetrical arrangement and leading to a symmetrical net formation are condensed. Such a symmetrical net formation does not take place according to this French patent.

Surprisingly, it was found that the properties of the

Insulating coatings on electrical conductors produced on the basis of the ester imide condensation products, in any case with regard to char resistance and possibly at the same time with regard to residual distance, can be considerably improved when the previously known ester imide condensation products are modified in their chemical structure, by condensing certain phenols or phenolic derivatives and/or symmetrical network-forming components in the polycondensate. As the following examples and comparison examples show, the surprising improvement in carburization resistance and residual distance is clearly a consequence of this change in molecular structure, improvement in carburization resistance is effected both by the incorporation of phenols and phenol derivatives as well as by incorporation of symmetric network-forming components, while higher residual distances are exclusively achieved by condensation of the symmetric network-formed compounds.

Curable ester imide condensation products containing built-in phenols or phenol derivatives were not previously known. The network formation of the previously known ester imide condensation products is effected mainly by polyhydric alcohols, such as glycerol for example, or also by using the reaction product of trimellitic acid (anhydride) and 4,4'-diaminodiphenylmethane used mostly for imide formation in excess amounts of trimellitic acid (anhydride), however, this has carboxyl groups in an unsymmetrical arrangement. The use of carboxylic acid with at least three carboxyl groups present in a symmetrical arrangement is not previously known for network formation of polyester imides.

The invention relates to a method for producing insulating coatings on electrical conductors based on ester imide condensation products which contain five-membered imide groups and which have an imide nitrogen content of 1 - 8 percent by weight of 3~ or polybasic aromatic dicarboxylic acids or their anhydrides and optionally dibasic carboxylic acids, polyhydric alcohols and imide-forming, multifunctional nitrogen compounds by applying solutions of these condensates in organic solvents, possibly with the addition of curing catalysts and network formation at an elevated temperature, the method being characterized by the use of solutions of ester, imide condensation products that have been modified by means of a) 0 .2 - 2.0 equivalents, referred to each mole of imide nitrogen in the condensate of:

aa) mononuclear diphenols, preferably dioxybenzenes,

ab) polynuclear diphenols, preferably those with structure

where R means an alkylene, cycloalkylene or arylene residue,

ac) monophenols which, in addition to the phenolic OH group, have at least one functional group suitable for esterification or imide formation, preferably p-aminophenol and/or p-hydroxybenzoic acid,

ad) diphenol ethers of the compounds in åa) and ab), provided that these phenol ethers have at least tb functional groups suitable for esterification or imide formation, or mixtures of these compounds, and

b) up to 2 equivalents referred to each mole of imide nitrogen in the condensate of one or more aromatic compounds

with at least three similar groups present in a symmetrical arrangement and leading to a symmetrical net formation, preferably tris-(2-hydroxyethyl)-isocyanurate, trimesic acid

and/or pyromellitic acid, or one or more compounds which have only feature a) or only feature b).

Aromatic compounds which have been condensed with at least three similar groups present in a symmetrical arrangement and leading to a symmetrical net formation are, for example, trimesic acid, pyromellitic acid, tris-(2-hydroxylethyl)-isocyanurate, 1,3,5-triaminobenzene and 1,2, 4,5-tetrahydroxylethyl-benzene.

Surprisingly, with the method according to the invention, coatings are obtained whose char resistance, examined according to Herberts-Werksnorm 2010, is improved to approx. 40 - 100 minutes, while with the known esterimide wire varnishes they are at a level of approx. 15 - 20 minutes.

The residual distances achievable with the previously known ester imide condensation products at 300°C are, depending on the type and quantity of the starting compounds used, between 10 and 30%. Condensation of symmetrical aromatic network formation components also leads to an increase in charring strength to approx. 40 - 100 minutes, to improve the residual distance at 300°C to 30 - 50%.

The preparation of the ester imide condensation products takes place in the manner known per se by polycondensation, whereby, as in the case of previously known ester imide condensation products, the following starting compounds are first used: 1) Polybasic carboxylic acids, their esters and/or anhydrides, preferably trimellitic anhydride, possibly in admixture with divalent carboxylic acids , preferably terephthalic acid, 2) polyhydric alcohols, preferably ethylene glycol and/or glycerol, 3) multifunctional nitrogen compounds capable of imide formation, for example p,p'-diaminodiphenylmethane, o-amino-benzoic acid, ethanolamine and aminoacetic acid.

In addition, in the method according to the invention, phenols or phenolic derivatives and/or symmetrical network-forming compounds. As phenols or phenol derivatives within the scope of the invention; the following compounds can be used:

1. Mononuclear diphenols such as hydroquinone and resorcinol. 2. Polynuclear diphenols, preferably phenols where the OH groups are in the p,p' position, with the general formula

where R is alkylene, cycloalkylene or arylene residue, for example p,p'-dihydroxydiphenyldimethylmethane (Bisphenol A) and phenolphthalein. 3. Monophenols, when in addition to the phenolic OH group, these have at least one reactive ester- or imide-forming group, for example p-aminophenol and p-hydroxybenzoic acid. 4. Diphenol ethers of the compounds in 1) and 2) with partially or completely etherified phenolic OH groups, and which have at least as many reactive ester- or imide-forming groups as the number of etherified phenolic OH groups, for example p,p'-bis-Chydroxy -ethoxy)-diphenyldimethylmethane.

It is assumed that the diphenols and phenol derivatives are incorporated into the polyester imide molecule at the temperatures, 220 - 280°C, which are required in the production of such resins. This assumption is justified in that, in contrast to the monophenols listed under 3, whose incorporation takes place via ester or imide-forming groups, the monophenols (cresols) used as solvents do not have any charring time-improving effect, i.e. obviously do not condense .

In order to achieve a higher char resistance of the order of 40 - 100 minutes, the starting point is the known starting products for the production of the previously known ester imide condensation products, which are mentioned above, and when carrying out the condensation uses not only polyhydric alcohols, preferably ethylene glycol and/or glycerol, but a mixture of these alcohols with the above-mentioned phenolic compounds. It is also possible to first precondense the alcohols with polycarboxylic acids and/or imide carboxylic acids and at a later stage add the phenol or phenol derivative in order to achieve co-condensation of the phenol or phenol derivative in a secondary step. The quantity ratios with which the effect of the phenol derivatives or phenols is achieved vary and depend on the particular structure of the phenol or phenol derivative and on the degree of branching of the condensation resin, i.e. the proportion of tri- or higher-functional network-forming molecules. Thus, phenolphthalein is already very effective in small quantities. For example, with 0.3 mol of phenolphthalein on 2.8 mol of trimellitic anhydride, a charring resistance of 88 minutes was achieved, while when using bisphenol A, 1 mol per 4 moles of trimellitic anhydride, half of this quantity producing no appreciable effect. Referred to the formed five-membered imide rings from trimellitic anhydride and p,p'-diaminodiphenylmethane, this means that phenolphthalein already in an amount of about 0.3 equivalents per moles of imide nitrogen triggers a noticeable increase in char resistance. For p,p'-^bis^hydroxy-ethoxy)-diphenyldimethylmethane, it was found during the research series that the smallest amount needed to improve the charring resistance was approx. 0.24 equivalents per moles of imide nitrogen.

Besides when incorporating phenols or phenol derivatives, the char resistance is improved when the quantities mentioned in the introduction are contained in the molecule by at least three similar bonds of symmetrically condensed aromatic compounds. Symmetric compounds of this type, which residues are therefore built into the molecule, are preferably trimesic acid and/or pyromellitic acid. The effect" on fprcurling resistance is obviously due to a sterically more favorable network formation (branching)

due to the symmetric and at least trifunctional compounds. It is thus in principle also possible to achieve this effect with the help of other similarly structured compounds, for example 1,3,5-triaminobenzene and/or 1,2,4,5-tetrahydroxyethylbenzene.

The aforementioned symmetrical compounds must be condensed in such a way that they do not lose their symmetrical structure in the condensation product. In particular, compounds which have 2-ortho-positioned carboxyl groups, especially in the form of reactive anhydrides, should not be reacted with an amino group, because a five-membered imide ring is then formed and no symmetrical branching of the molecule. On the other hand, the symmetrically branched compounds include compounds containing at least 3 five-membered imide rings, in which the imide nitrogen atoms have equivalent substituents, such as e.g. N-Trihydroxyethyl mellitol triimide.

The condensation of the diphenols or phenol derivatives on the one hand and said symmetrical aromatic compounds on the other hand provides two independent methods of increasing the char resistance from about 15 to 20 minutes and to 40 to 100 minutes. If both diphenols or phenol derivatives and said symmetrical-aromatic compounds are used in the esterimide condensation product, high charring times of HO of up to 100 minutes are likewise achieved, whereby the quantity of the charring resistance-increasing compounds is reduced. In this way, economic combinations of these substances can be chosen, while achieving high carbonization resistance and at the same time good residual distance at high temperatures, so that all in all an extended lifetime of the insulation layer is achieved under thermal and mechanical stress.

Admittedly, using esterimide resins, it is possible to achieve carburization resistances or times of more than 15 to 20 minutes and residual distances of 30% and more at 300°C also without condensation of the invention's carburizing resistance-seeking compounds. You then have to let the net formation go so far, for example with very large amounts of trimellitic anhydride, that with regard to the elasticity of the paint film, you get wire varnishes that are unusable in practice. For use within today's electrical insulation technology, wire thicknesses of 0.8 mm diameter are required a winding resistance that can withstand winding around its own diameter under 10% pre-stretch, and that no cracks occur or possibly one or at most two cracks occur when winding around a bend corresponding to the single or double wire diameter after the wire has been exposed to a thermal shock duration 15 minutes at 200° C. However, esterimide resins which are super-cured by means of unsymmetrical polycarboxylic acids do not meet these requirements.

However, the requirements are surprisingly met without the necessary elasticity being lost when, in accordance with the invention, phenol (derivatives) and/or said symmetrical, aromatic compounds are incorporated into the ester imide condensation products.

According to the invention, the ester imide condensation products contain five-membered imide rings which are largely formed in advance. However, it is possible that at least part of the five-membered imide rings are first formed by burning the varnish onto the electrical conductor, i.e. that in the ester imide condensation product there are groups such as below: the.

Otherwise, it is in principle • possible, and to a certain extent even probable, that not all • starting substances are reacted with all their functional groups in the ester imide condensation product. v

On the contrary, it must be assumed that only at the elevated temperatures of the firing process will a part of the functional groups react during advanced branching, as the good properties of the lacquer coating are only achieved after the firing process. Essentially, the burn-in process consists, as is known, in that low-molecular* compounds are split off to form larger molecules of ester imide resin.

The varnish solutions can also contain known additives, curing catalysts and the like. The condensation products can also, in a known manner, contain polyvalent metals in the form of salt-forming components, e.g. zinc and/or magnesium.

As solvents, the known terephthalic acid polyester condensation products are preferably used to dissolve the aforementioned compounds. Trimellitic acid bg pyromellitic acid is particularly suitable for building up the acid components, possibly with the addition of terephthalic acid, respectively its derivatives such as anhydrides, esters and half-esters.

Ethylene glycol, propylene glycol, glycerol, neopentyl glycol, trimethylolmethane and/or dimethylol-cyclohexane are particularly suitable as alcohols for forming the condensation products. The temperatures during the production of the condensation products are, as is otherwise known, between 150 and 280°C, while the firing oven temperatures, which are also known, are between 300 and 500°C.

Example 1

Compounds used in the production of condensate

tion product:

7.5 mol ethylene glycol = 465 g^, 4.93 mol of this is condensed

and the remainder is distilled off,

1.0 mol bisphenol A = 230 g

Altogether 4>° moles of trimellitic anhydride = 768 g

and 1.5 mol of p,p'-diaminodiphenylmethane = 297 g

distributed in the following portion-wise additions:

1st portion 114 g trimellitic anhydride mixed with

45 g of p,p'-diaminodiphenylmethane

2. - 7. " n-^no- 1^9 g trimellitic anhydride mixed with time

42 g of p,p'-diaminodiphenylmetaa,

1 g zincace.tat.

After achieving the below specified viscosity for the ester imide condensate, add:

6 g polymer butyl titanate, dissolved in

94 g of crude cresol at 120°C.

Method of production:

Ethylene glycol and bisphenol A are filled into a flask and heated to approx. 60 - 80°C, below which bisphenol A completely dissolves. The first portion of the mixture with the immediately reacting components trimellitic anhydride and p,p'-diaminodiphenylmethane is added at around 120°C. It is heated further, until approx. 5 ~ 10 ml of water is distilled off. Before the second portion is added, the temperature is lowered to below 140°C, and the above-mentioned mixture for the 2nd portion is added. The temperature is then raised again until a further 10 - 20 ml of water has been distilled off. This portionwise addition is repeated until the Jth portion has been added, lowering the temperature before each addition to below 140°C, and after addition the temperature increases to complete the reaction. When adding each portion, wait until 20 - 30 ml of water has been distilled, which amount of water collects in the pre-layer. After a total of 110 ml of distillate, the 6th portion is added at 140°C, and the 7th portion after approx. 130 - 140 ml of distilled water. At around 140 - 150 ml of distillate, the resin becomes clear, and after 150 ml of water has been distilled off, the resin is fully condensed. The resin is further condensed for about 1 hour in the 2-litre flask used for this trial. With larger quantities, the reaction time must be extended, for a 100 kg portion the reaction time is an appropriate 3 hours. The mixture is run over a tall column to keep the ethylene glycol loss as low as possible. The boiler temperature is around 230 to 240°C. When no more water passes over, it is cooled to around 200°C and the excess ethylene glycol is distilled off directly. It is then further condensed while measuring the viscosity, during which the resin melt is heated to around 260 - 280°C. When the viscosity of the solution, measured with one part resin and two parts m-cresol at 25°C in a Høppler viscometer (Høppler Visko-Waage) is between 1600 - 2500 cP, the resin is cooled to around 200°C and diluted with 100 - 200 green cresol, whereby the mixture reaches a temperature of around 180°C. At this temperature, the above-mentioned solution of 6 g of polymeric butyl titanate in 94 g of crude cresol is added, and the temperature is maintained for 10 - 15 minutes at 180°C, after which the solution is finally diluted with crude cresol to a 50% resin solution.

Where not otherwise stated, the above method is used in the following examples of the ester imide condensation product.

Production of wire varnish:

560 g of the 50% resin solution is added to 200 g of crude cresol and 140 g of solvent naphtha, 40 g of xylene, .40 g of tetralin and 20 g of propylene glycol-1,2. The viscosity or flow rate of this varnish solution measured in a DIN cup at 20°C, depending on the degree of condensation, is between 60 and 125 seconds.

Wire coating:

With the varnish thus prepared, a copper wire with a diameter of 0.8 mm is varnished in a varnishing machine with an oven length of 2.7 m at shaft temperature as measured inside the oven, at distances ^ O, 90°g 200 cm from the oven inlet, which is about 220 , 320 and 45°°C. respectively, as the thread is passed 8 times through this process. The above conditions for wire coating apply to all examples. Sample values:

The special advantage of the composition described in example 1 lies in the test value for char resistance, which is evident from a comparison between example and the composition in example la, which does not contain bisphenol A. Comparative example la.

7.0 mol ethylene glycol = 435 g>of which 5>47 m°l condensed in 4.0 mol trimellitic anhydride = 7^8 g,

1.5 mol p,p'-diaminodiphenylmethane = 297 g

1 g zinc acetate

6 g polymeric butyl titanate, dissolved in 94 g crude cresol.

The addition of trimellitic anhydride and p,p'-diamino-diphenylmethane is carried out as described in example 1 in 7 portions.

In the comparative experiments, and it also applies - in the following examples, the method of preparation for the esterimide condensation ion product and the lacquer composition, if nothing else is stated, corresponds to the corresponding example.

Sample values:

In this example, the charring resistance without bisphenol A is only about 1/5 of the charring time for resin with bisphenol A.

Comparative example lb, to - example . 1-.- - ,, ....

With the following composition with 0.5 mol of bisphenol A, only 18.3 minutes of charring time was obtained. 8.0 mol of ethyl englycol = 496 g of which ' 5'T4= mol' ihhkbirdéhsert 0.5 mol bisphenol Å ' = 115 g,"1 : ''"''• '"" '"'•"':"•: •

4.0. mol trimellitic anhydride 768 g"V' • —-'-' 1.5. mol p,p'-diaminephenylmethane=297'g'

1g zinc acetate,

- 6 g polymeric butyl titanate, dissolved: ■ in 94 g crude cresol-Test values:' ''

From comparison experiments lb, it is found that the char resistance-increasing effect of a composition with 0.5 mol of bisphenol A per 4 moles of trimellitic anhydride and 1., 5 moles of aromatic diamine do not yet appear.

Instead of zinc acetate, other esterification catalysts can also be used, e.g. Mg-acetate, Pb.O, -Pb-acetate, Al-acetate, Cu-acetate, Cd-acetate, Sb(III) -fluoride. In all cases, the carburization resistance-improving effect of the diphenols or phenol derivatives is retained....

Example 2 •

Compounds used in the preparation of the condensation product: 6y0:-- molj- jetyie.ngly.kql-, ==,• .372 gj of which condensed 5.0 mol',-"-■'— 1.0 m" ol ctBref-talsyr^dwimejt.ydester...=..192 g,

1.0 mol bisphenol A = 230 g,

3.0 mol trimellitic anhydride=57^ g»

1.0 mol p,p'-diaminodiphenylmethane = 198 g

1 g of magnesium acetate.

Manufacturing method:

Ethylene glycol, terephthalic acid dimethyl ester and magnesium acetate are mixed together and heated, whereby the transesterification of the terephthalic acid dimethyl ester takes place during methanol separation. After almost complete distillation of the theoretical amount of methanol, whereby a reaction temperature of 220°C is finally obtained, the whole is allowed to cool. At 120°C, bisphenol A is added, and the process continues as indicated in example 1. The addition of the mixture of trimellitic anhydride and p,p'-diaminodiphenylmethane takes place in five equal portions.

Production of the wire varnish:

Based on the approx. A varnish is prepared from 50 mg of a cresol-containing solution of the resin. with the following composition:

50% cresol-containing resin solution (50%ig)

21% cresol

2% propylene glycol-1,2

4% tetralin

4% diacetone alcohol

l6% xylene

3% of a 33% strength solution of polymeric butyl titanate in cresol. Sample values:

A comparison mixture without bisphenol A gave a char resistance of only 15 minutes.

Example 3

In this example, in addition to ethylene glycol, glycerol is also added to the esterification. The glycerol causes together with the excess trimellitic anhydride, i.e. the amount of trimellitic anhydride that is not used for the imide formation, • d-a desired branching - in the polymer moleculec. "" • 1.60 mol ethylene glycol 100 g, of which condensed 0.86 mol 1.60 mol --lye is Ln = 148 g,

1.00 mol bisphenol A 228 g,

3.35 m°l trimellitic anhydride 642 g,

,1.44 mol p,p'-diamiriodiphenylmethane = 288 g,

1 g zinc acetate

6 g polymeric butyl titanate

Composition of the wire varnish:

60% cresol resin solution (50 $ig

17% crude cresol

17% solvent naphtha

4% xylene

2% propylene glycol-1,2

Sample values:

As comparative experiments show, the reduction of the amount of bisphenol A in example 3 from 1 mol t5-l 0.64 mol resulted in a reduction of the "carburization time from'92 minutes to 41 minutes. When bisphenol A was completely omitted, the char resistance was still only 14 minutes.

Example 4

In this example, a bisphenol ether alcohol was condensed in as a char resistance-increasing component. Ethylene glycol and p,p'-bis-(oxyethoxy~)-diphenyldimethylmethane were esterified with diimidedicarbonic acid from trimellitic anhydride and p,p'-diaminodiphenylmethane, as well as excess trimellitic anhydride.

3.256 mol ethylene glycol = 202 g, of which 2.93 mol condensed in 0.308 mol p,p'-bis-(hydroxyethoxy)-diphenyldimethylmethane = 97 g 3.300 mol trimellitic anhydride = 643 g

1.320 mol p,p'-diaminodiphenylmethane = 26l g.

0.5 g zinc acetate

8.0 g of monomeric butyl titanate dissolved in 92 g of crude cresol.

The resin was prepared as indicated in example 1. Composition of the wire varnish:

60% cresol-containing resin solution (50%)

16% cresol (crude)

2% isocyanate remover CT, stable type (manufacturer: Farbenfabriken Bayer AG, Leverkusen), 50 folg dissolved in a mixture of 50% crude cresol and 5% solvent naphtha

l6% solvent naphtha,

4% xylene,

2% propylene glycol-1,2.

Sample values:

Comparative example 4a to example 4:

2.93 m°l ethylene glycol = 182 g, of which condensed 2.64 mol 0.27 mol p,p'-bis-(hydroxyethoxy)-diphenyldimethylmethane = 85 g 3.05 mol trimellitic anhydride = 586 g

1.25 mol p,p^_-diaminodiphenylmethane = 247 g

0.5 g zinc acetate

8.0 g of monomeric butyl titanate, dissolved in 92 g of crude cresol. Sample values:

Based on examples 4»4a and other systematic investigations that have been carried out, it appears that in order to achieve a charring resistance of more than 15 - 20 minutes, a composition must be provided as follows: The content of p.,.p'-bis -(hydroxyethoxy)-diphenyldimethyl- methane must be at least 23 f°> calculated on the molar amount of the formed diimide-dicarboxylic acid as the main component in the polycondensate.

Furthermore, there must be an excess of the branched tricarboxylic acid of at least 50%., calculated on the diimide-carboxylic acid..If. the content of p,p' -bis--{hydroxyethoxy)-diphenyldimethylmethane, calculated on the amount of diimide-dicarboxylic acid, is high, in the order of &5%, then the excess of the branching tricarboxylic acid, likewise calculated on the amount of diimide-dicarboxylic acid, can lie between - 5O and 80 With higher amounts of excess branching tricarboxylic acid, the branching obviously becomes too strong, so that the varnish film becomes too brittle, so that the carbonization times are again reduced; With only a low content of PjP^bis-ihydroxyethpxyl-diphenyl-dimethylmethane, of approx. 25%, calculated on the diimide-dicarboxylic acid-, a reduction of f orcul- the ling times. This means that an earlier brittleness of the lacquer film occurs. The lack of elastifying influence of the phenol ether alcohol shows itself in this way.

Example 5

In this example - the smallest amount of imide-forming p,.p'-diaminodiphenylmethane is used, -i.e.-. the mixture has the lowest nitrogen content. To improve the charring resistance, phenolphthalein was condensed in.

3,500 mol ethylene glycol 218 g, of which 3>16 m°l condensed in 2,000 mol glycerol = 184 g

3.350 mol terephthalic acid = 55 g 0.3.00 mol phenolphthalein = 96 g

1.125 m°l trimellitic anhydride - 216 g

.0.500 mol p,p<v->dlaminodiphenylmethane 99 g

1 g zinc acetate.

Method of production:

Ethylene glycol, glycerol, phenolphthalein and zinc acetate were filled into a flask. It then started at 140°C while increasing to 160°C, with the addition of the following compounds:

Between each portion addition, the water is distilled off. Towards the end of the condensation, whereby the reaction temperature is increased to between 220 and 240°C, approx. 20 ml of ethylene glycol over. The mixture is diluted with crude cresol to a 50% ± g solution. Varnish composition:

58.8 fo cresol resin solution (50% ±g)

5.5% cresol

9.8% xylene

20.4% solvent naphtha

1.8% propylene glycol-i.2"

1.8% isocyanate remover CT, stable type

(manufacturer: Bayer, Leverkusen)

50% dissolved in a. mixture of. 50% crude cresol and

50 f° solvent-naphtho.

0>9 ■% 25% solution of zinc resin in xylene 0)9 i° 33% solution of polymeric butyl titanate in crude cresol 0.1% 1% solution of silicone resin in xylene

(manufacturer: Bayer, Leverkusen).'

Sample values:

Example 6 5.2 mol ethylene glycol = 322 g, of which condensed '3.23 mol 0.3 mol phenolphthalein = 95. g

2.8 mol trimellitic anhydride = 53^ g

1.0 mol p,pj_-diaminodif enylmethane ..."

0.5 g zinc acetate.. -v.

- -6.0 g polymeric butyl titanate,.: dissolved in 94 g crude cresol. Lacquer composition as ■irexample 3- - Sample values: ■

Example 7

7) 5 m°l ethylene glycol = 4b~5 §> of which 4» 4 mol condensed in 1.0 mol hydroquinone = -110 g,

4.0 mol trimellitic anhydride = 768 g,,

1.5 mol p,p1-diaminodiphenylmethane = .297 g

1 g zinc acetate 6 g polymeric butyl titanate., dissolved in 94 g crude cresol. Etching of the varnish:

56 cresol resin solution {50% ±g)

20% crude cresol'

4% xylene

2% propyl engl ycol-1,2 8% tetralin

$10 solvent naphtha

Sample values:

Example 8

7.5 mol ethylene glycol = 465 g>of which condensed 4.7 mol 1.0 mol resorcinol = 110 g 4.0 mol trimellitic anhydride = 768 g

1.5 mol p,p'-diaminodiphenylmethane = 297 g

1 g zinc acetate

6 g of polymeric butyl titanate, dissolved in 94 g of crude cresol - '•' Lacquer composition as stated in elcsample 7« Test values r

Example

6.0 mol ethylene glycol = 370 g, of which condensed 3»-5--m°l 0.6 mol p-aminophenol = 66 g

1.0 mol trimellitic anhydride = 19.2 g

2.4 mol trimellitic anhydride = 4&0 g

1.0 mol p,p'-diaminodiphenylmethane = 198 g

0.5 g zinc acetate

6.0 g polymeric butyl titanate, dissolved in 94 g crude cresol. Procedure: Ethylene glycol, p-aminophenol, 192 g of trimellitic anhydride and zinc acetate are mixed together and heated. First, the imide-phenol carboxylic acid is formed from p-aminophenol and trimellitic anhydride, and during the further reaction the carboxylic acid is esterified with 1 ethylene glycol. At the same time, the excess trimellitic anhydride (0.4 mol) is condensed. The procedure corresponds to the previous examples. After distilling off the calculated amount of water for the imide formation, a mixture of 2.4 mol of trimellitic anhydride and 1.0 mol of p',p'-diaminodiphenylmethane is added gradually in 4 portions, and the water formed after each addition is distilled off. The further condensation takes place as indicated in Example 1.

The varnish composition is as indicated in example ■3*

Sample values:

That part. ouch. The p.-aminophenol which increases char resistance is 60 mol-% calculated on the diimide-dicarboxylic acid which

main component of the polycondensate.

Example 10

8.0 mol ethylene glycol = 497 g>of which condensed in 4>5m°l 1.0 mol p-hydroxybenzoic acid = 138 g

4) 0 mol trimellitic anhydride = 768 g

1.5 mol p,p'-diaminodiphenylmethane = 297 g

1 g zinc acetate

6 g polymeric butyl titanate, dissolved in 94 g crude cresol.

Varnish composition as in example 7>"

Sample values:

Example 11

This example shows that you also get high cooling times when you condense different phenols, in this case a diphenol and monophenol derivative, together in the polyesterimide resin. 6.0 mol ethylene glycol = 370 g, of which condensed 3> l6 mol

0.8 mol bisphenol A = 182 g 0.6 mol p-aminophenol" = 66 g

1.0 mol trimellitic anhydride = 192 g 2.4 mol trimellitic anhydride = 4&0 g

1.0 mol'' p,p'-diaminodiphenylmethane = 198 g

0.5 g zinc acetate

6.0 polymeric butyl titanate.

The resin was prepared as in example 9>: Our lacquer composition as in example 7• Sample values*:

While in the above examples it exclusively has

imide-free alcohols have been used, the di-imide-alcohol of pyromellitic anhydride and ethanolamine - partly together with imide-free alcohols - will be esterified in a molar ratio of 2:1 with di-imide-dicarboxylic acid from trimellitic anhydride and p, p'-diaminodiphenylmethane. in the presence of. excess of trimellitic anhydride, as well as a dipheriol or phenol derivative. "In these examples, a complete conversion of pyromellitic anhydride and ethanolamine to di-imidalcohbl is first carried out, in a pre-reaction, before the necessary compounds for the formation of di-imide-dicarboxylic acid are added, so that the esterification of both imide components together with the possibly present imide-free alcohols can occur.

Example 12

4.0 mol ethylene glycol = 247. gj of which condensed 0.5 mol 2.0 mol ethanolamine = 122 g

1.0 mol pyromellitic anhydride = 218 g

0.75 mol p>p'-bis-{hydroxyethoxy)-diphenyldimethylmethane = 237 g 2.0 mol trimellitic anhydride.= 3^4 g

0.75 m°l p.p'-diaminodiphenylmethane = 148 g

0.5 g zinc acetate

8.0 g of monomeric butyl titanate, dissolved in 92 g of crude cresol. Method of production..

Ethylene glycol, ethanolamine, p,p'-bis-(hydroxyethoxy')-diphenyldimethylmethane, zinc acetate and 30 g of crude cresol as a reaction promoter are filled into a "flask and heated to K)0<Q>C. The pyromellitic anhydride is added in four-portions 1 in rapid succession, whereby an exothermic reaction with ethanolamine occurs. • The temperature during the portion additions must not rise above 180°C. The - rapidly formed water is distilled off as quickly as possible. The mixture must be stirred carefully. Di—imide - the alcohol of 1 mol pyrmellitic anhydride and 2 moles of ethanolamine falls out in the form of gold-guy needles which, on raising the temperature to 200 - 220°C and distilling off the resulting water, largely dissolve.

After this pre-condensation to produce

-di-imide alcohol is added to the mixture of trimellitic anhydride and

p,p'-diaminodiphenylmethane, whereby the diimide-dicarboxylic acid is formed, which is gradually esterified with the alcohols present. Addition of the mixture takes place in 4 portions at 180°C. The water formed is distilled off between each addition, and the reaction temperature is subsequently raised to 200-220°C. Further processing takes place as indicated in example 1.

Varnish composition as stated in example 3* Sample values:

A comparative mixture which, except for the lack of p,p'-bis-(hydroxyethoxy)-diphenyldimethylmethane, has a composition very similar to that of Example 12, gave a charring resistance. complete in just 16 minutes.

As regards the correlation between the char resistance and the amount of condensed-p,p'.-bis-(hydroxyethoxy)-diphenyldimethylmethane, this is found, in table 1. -. • • - ........

The table is built on the basis of 6 mixtures with the following composition:

250 to 0 moles of ethylene glycol

0.25 to 2.75 mol p,p'-bis-(hydroxyethoxy)-diphenyldimethylmethane

2.0 mol -ethanolamine

1.0 mole of pyromellitic dianhydride

3.5 mol of trimellitic anhydride

1.5 mol of p,p'-diaminodiphenylmethane

0.4 g zinc acetate

8.0 g of monomeric butyl titanate

...... Wood. smaller amounts of ethylene glycol were added, to yield more p,p'-bis-(hydroxyethoxy)-diphenyldimethylmethane, so that each portion contained a total of 2.75 mol of these two alcohols'.

Method of manufacture.

Ethylene glycol, p\p'-bis-(hydroxyethoxy)-diphenyldimethylmethane, ethanolamine, zinc acetate and 100 g of crude cresol as carrier were mixed together in a flask. After heating to 70°C, pyromellitic dianhydride is added in 2 portions and, over the course of 4 - 5 hours, the quantity of water originating from the formation of the imidalk-ohol is quantitatively distilled off, during which the reaction mixture reaches a temperature of around 200°C. The mixture of trimellitic anhydride and p,p'-diaminodiphenylmethane is then added in 6 portions, with the water formed being distilled off between each new addition and condensed as indicated in example 1,

With all added amounts being equal, the proportion of the trimellitic anhydride included as a branching agent is equal to 33 > 3 mol%, calculated on the amount of diimide-dicarboxylic acid which is formed from trimellitic anhydride and p,p'-diaminodiphenylmethane.

Due to the large molecular weight of p,p<J->bis-{hydroxy-ethoxy)-diphenyldimethylmethane in relation to ethylene glycol, the amount of branching trimellitic acid, calculated on the amount of resin, decreases to the same extent as the amount of p,p<*- >bis-(hydroxyethoxy}-diphenyldimethylmethane rises. This explains the negligible reduction in the charring values with increasing content of diphenol ethers. At the same time, it appears from the table that the charring time-improving effect of p,p'-bis-(hydroxyethoxy )-diphenyldimethylmethane sets in at a content between 16.7 and 50 mol-^, calculated on the amount of diimide-dicarboxylic acid.

Example 13

In this example, only diimide alcohol is used as alcohol.

1.25 mol bisphenol A = 285 g

3.5° mol ethanolamine = 214 g

1.75 mol pyromellitic dianhydride = 381 g

2.25 mol trimellitic anhydride = 432 g

0. 75 mol p,p'-diaminodiphenylmethane = 148 g

0.5 g zinc acetate

3.0 g polymeric butyl titanate

Method of production:

Bisphenol A, ethanolamine, zinc acetate<p>g and 150 g of crude cresol were mixed as reaction promoter and solvent in a flask. After heating to 100°C, pyromellitic acid dianhydride is added in 4 portions. The exothermic reaction with the ethanolamine causes a further increase in temperature. Initially, the temperature should not exceed 180°C. The amount of water corresponding to the formation of diimide alcohol from pyromellitic acid dianhydride and ethanolamine is then distilled off, whereby the temperature of the reaction mixture rises to 200°C. Addition of the mixture consisting of trimellitic anhydride and p,p'-diaminodiphenylmethane takes place in 5 portions:

1st portion = 80 g, 2nd - 5th portion: 125 g

The water formed is distilled off between each addition. The condensation and addition of the polymeric butyl titanate takes place as indicated in example 1.

Varnish was produced as indicated in example 3 - Test results:

In a comparison experiment, the amount of trimellitic anhydride was compared to example 13 reduced by approx. 10% and the amount of bisphenol A completely replaced with equimolar amounts of pyromellitic dianhydride. The charring resistance amounted to only 21 minutes.

Example 14

In this example, another diimide dicarboxylic acid was esterified with ethylene glycol and diimide alcohol in the presence of bisphenol A.

It concerns diimide-dicarboxylic acid and pyromellitic acid dianhydride and aminoacetic acid in the molar ratio 1:2.

By the fact that the addition of the pyromellitic acid dianhydride takes place before, respectively simultaneously with the addition of the mino compounds ethanolamine, respectively aminoacetic acid, and not after this addition, it can be assumed that the excess of pyromellitic acid dianhydride predominantly leads to the formation of diimide alcohol and imidoxydicarboxylic acid upon addition of ethanblamine, and to diimide-dicarboxylic acid and imide-tricarboxylic acid by addition of aminoacetic acid, so that the branching mainly takes place by trifunctional and unsymmetrical compounds.

5,000 mol ethylene glycol = 310 g>of which condensed 2.4 mol 1,000 mol bisphenol A = 228 g

2,000 mol -ethanolamine = 120 g

1.375 ra°l pyromellitic dianhydride = 300 g

1.375 mol of pyromellitic acid redi-anhydride = ^ 00 g

2,000 mol aminoacetic acid (Glycine) = 150 g

0.5 g zinc acetate

6.0 g polymeric butyl titanate

Manufacturing method:

Bisphenol A, ethylene glycol and zinc acetate are mixed together

and 50 g of crude cresol as reaction agent in a flask. After heating to 120°C, 100 g of pyromellitic acid dianhydride is added and then

little by little 1/3 of the amount of ethanolamine, so that a temperature of 200°C is not exceeded. You have to stir vigorously during the reaction. Then practically the entire theoretical amount of separated water from the imide alcohol formation is distilled off. This procedure is repeated twice. After that. third addition of ethanolamine ensures as complete removal of the formed water from the reaction mixture as possible. The addition of the mixture of pyromellitic dianhydride

(3OO g) and aminoacetic acid (150 g) occur in three portions of each

150 g. In between the additions, the water that splits off during the formation of diimidic acid from pyromellitic acid dianhydride and aminoacetic acid is quantitatively distilled off, whereby the temperature of the reaction mixture rises to 230°C. Finally, 160 g of ethylene glycol is distilled off, and after diluting the mixture with crude cresol, 6 g of polymeric butyl titanate is added during 15 minutes at 170°C.

The varnish is worked up as described in example 3-Test values:

In a comparative test where the composition of the resin was very similar to that of example 14, however bisphenol A was not used, the char resistance was 25 minutes.

In the following examples, the char resistance-improving effect of symmetrical, aromatic compounds with at least 3 similar functional groups shall be demonstrated, without diphenols or phenol derivatives being condensed. Apart from an increase in the charring time, an improvement in the residual distance is achieved.

The polycarboxylic acids used are esterified as completely as possible with the added polyhydric alcohols to ensure the symmetrical incorporation of the polycarboxylic acids, before the imide-forming components are added.

Example 15

6.0 mol ethylene glycol = 372 g, of which 5.5 ml condensed 1.2 mol trimesic acid = 252 g,

2.4 mol trimellitic anhydride = 462 g>

1.2 mol p,p'-diaminodiphenylmethane = 237 g»

0.5 g zinc acetate

8.0 g of monomeric butyl titanate.

The varnish is composed as indicated in example 3*

In a comparison experiment, the trimesic acid was completely replaced with the unsymmetrically built trimellitic anhydride. ' The varnish film shows a .carburization resistance of 18.5 minutes with a residual distance at ^ 00°G of 34%°g and a wrap resistance of only 5

A corresponding mixture in which the trimellitic anhydride was not pre-condensed, but added together with the imide-forming compounds, gave, under otherwise identical conditions, a charring time of just 1(5.2 minutes.

When the amount of trimesic acid of 1.2 mol in Example 15 was reduced to 0.8 mol, char resistance was 17 minutes and the residual distance at 100°C was only 25

A further mixture with 0.8 mol trimellitic acid and 2.8 mol trimellitic anhydride as an example of a network formation, both with regard to the imide formation -excess trimellitic anhydride as also with trimellitic acid, gave a charring resistance of 42 minutes -and a residual distance at 3° 0°c Pa 44%•

Example 16

In this example, pyromellitic dianhydride is used as a symmetrically branching aromatic compound, without diphenols or phenol derivatives being condensed. The comparison tests of examples 1 and 15 show the charring time-improving effect of the pyromellitic dianhydride condensed as an ester . 8.00 mol ethylene glycol = 497 g> -thereof, A, 71 ..mol condensed in 0.45 m°l pyromellitic acid dianhydride._=. 93. g -2.80 mol trimellitic anhydride = 537 g 1.20 mol p,p'-diaminodiphenylmethane = 23.8., g _ _

1 g zinc acetate.-.... - - ......... : -

6 g polymeric butyl titanate.

The pyromellitic dianhydride is completely esterified with ethylene glycol before the mixture of trimellitic anhydride and p,p'-diamino-diphenylmethane is added in portions. The varnish is composed and worked up as indicated in example 7«

Sample values:

In the following examples, both diphenols or phenol derivatives and symmetrically branching aromatic compounds are incorporated into the esterimide condensate. This shows that the carburizing resistance-increasing minimum amount of the individual carburizing time-improving components can be reduced. Also in these examples, good residual distances are generally achieved at ^ 00°C in the range between 25% and 50%.

Example 17

3.90 mol ethylene glycol = 242 g, of which condensed 3>35 m°l 0.40 mol p,p'-bis-(hydroxyethoxy)-diphenyldimethylmethane = 126 g 0.80 mol trimesic acid = 168 g

2.50 mol trimellitic anhydride = 480 g

1.15 mol p,p'-diaminodiphenylmethane = 228 g

0.5 g zinc acetate

8.0 g of monomeric butyl titanate

The varnish is composed as in example 3*

Sample values:

In this example, the amount of branching polycarboxylic acid is 87.0 mol% calculated from the total amount of diimide-dicarboxylic acid, whereby 69.6 mol% is added through the symmetrical trimesic acid and 17.4 mol% through trimellitic anhydride. It contains approx. 39 mol% diphenol ether alcohol, calculated on the amount of diimide-dicarboxylic acid.

Example 18

8.00 mol ethylene glycol = 49^ give 5>25 mol condensed 1.00 mol bisphenol A = 228 g

0.25 mol pyromellitic dianhydride = 55 g

4.00 mol trimellitic anhydride = 768 g

1.50 mol p,p"*-diaminodiphenylmethane = 297 g

1 g zinc acetate

6 g polymeric butyl titanate dissolved in 94 g crude cresol. " Preparation method: Ethylene glycol, bisphenol A-, pyromellitic acid dianhydride and zinc acetate are weighed into a 2.1/- wooden-necked flask equipped with a stirrer, thermometer and a 50 cm high column with an attached distillation apparatus, cooler and publisher. The pyromellitic acid dianhydride is esterified as long at l60 - 1- 80°C that the column head temperature falls below 100°C. Then the temperature of the reaction mixture is lowered to 160<G>C-. The two reaction partners trimellitic anhydride and p,p'-diaminodiphenylmethane are added in 7 portions. After each addition the temperature is raised to about 180 - 200°C, until the reaction mixture becomes thin. After complete addition of this mixture, water is distilled off at a column temperature of 100°C until it has distilled down to a temperature of about 60°C, -and a clear resin. After the column has been removed, enough ethylene glycol is distilled off through a still so that the resin has a viscosity of 1800 to 2000 cP (oppl east in the ratio-1 : 2 in m-cresol). The resin is then cooled to 200°C and about 200 g of cresol is added, whereby the temperature drops to 180°C. At this temperature, 100 g of a €% lg solution of polymeric butyl titanate in cresol are added. The temperature is kept at 180°C for 15 minutes, and the mixture is further diluted with cresol until a 50-g

resin solution.

Varnish composition:

56% cresol resin solution (50%ig)

21 fo crude cresol

13% solvent naphtha

4% tar oil

4% tetralin

2% propylene glycol-1,2

At a dry matter content of 28 fo, the consistency of the varnish measured in a DIN cup at 20°C is around 100 seconds. Sample values:

The amount of branching polycarboxylic acid in this example is 83.4 mol% calculated on the total amount of diimide-dicarboxylic acid, of which 16.7 mol% consists of symmetrically branched tetracarboxylic acids and 66.7 mol% consists of trimellitic anhydride. It contains about 67 mol% diphenol, calculated on the amount of diimide-dicarboxylic acid.

Further experiments, in which the quantity ratio of bisphenol A, pyromellitic dianhydride and trimellitic anhydride excess with respect to imide formation were modified in relation to example l8, have shown that the amount of pyromellitic dianhydride has a significantly stronger effect on charring time and residual distance than the amount of trimellitic anhydride and that furthermore the charring resistance is determined under taking into account the present amount of network-forming polycarboxylic acid of the amount of bisphenol A.

The correlation between charring time, residual distance and contained amount of branching pyromellitic dianhydride at a constant content of 33.3 mol-% trimellitic anhydride and 83.3 mol-% bisphenol A, calculated on the amount of diimide-dicarboxylic acid, appears in table 2. Basis for the table there are three composition mixtures, with weighed amounts:

6.5 mol ethylene glycol

1.0 mol bisphenol A

0.3>0>4 0>'5 moles of pyromellitic dianhydride

2.8 mol of trimellitic anhydride

1.2 mol of p,p'-diaminodiphenylmethane

Example 19

7.50 mol ethylene glycol = 465 g>of which condensed in 4>2 mol 0.10 mol phenolphthalein = 32 g

0.45 mol pyromellitic dianhydride = 98 g

3.00 mol trimellitic anhydride = 57& g

1.50 mol p,p'-diaminodiphenylmethane = 297 g

1.0 g zinc acetate

6.0 g polymeric butyl titanate

The varnish is produced in the same way as in example 3-Test values:

In this example, the amount of symmetrically branching tetracarboxylic acid is 30 mol% calculated on the amount of diimide-dicarboxylic acid. The trifunctional carboxylic acid does not act as a branching partner. The amount of phenolphthalein, namely 6.67 mol% calculated on the diimide-dicarboxylic acid, is the smallest amount of diphenols and phenol derivatives listed in the examples as a char resistance-enhancing component. Comparison with example 18 shows that 6.67 mol% phenolphthalein causes a slightly higher charring time at the same branching through pyromellitic acid dianhydride, than 40 mol% bisphenol A, calculated on the amount of diimide-dicarboxylic acid.

Example 20

8.00 mol ethylene glycol = 49^ g>of which condensed in 0.5 mol 1.00 mol hydroquinone = 110 g

0.25 mol pyromellitic dianhydride = 55 g

3.80 mol trimellitic anhydride = 728 g

1.50 mol p,p'-diaminodiphenylmethane = 297 g

1.0 g zinc acetate

6.0 g polymeric butyl titanate

Composition of varnish as stated in example 7-Test values:

Example 21

8.00 mol ethylene glycol = 49& g>of which condensed in 4.7 mol 1.00 mol resorcinol = .110 g

0.25 mol pyromellitic dianhydride = 55 g

3.80 mol trimellitic anhydride = 728 g

1.50 mol p,p'-diaminodiphenylmethane = 297 g

1.0 g zinc acetate

6.0 g polymeric butyl titanate

Lacquer composition as indicated in example 7-Test values:

Example 22

In this example, ethylene glycol is added next to it

and p,p'-bis-(hydroxyethoxy)-diphenyldimethylmethane also the diimide alcohol from pyromellitic dianhydride and ethanolamine. Only symmetrically branching trimesic acid (66 mol%, calculated on the amount of diimide-dicarboxylic acid from trimellitic acid anhydride and p,p'-diaminodiphenylmethane) is added as a branching partner. The added amount of phenol ethers, which also improve charring time, is 80 mol% calculated on the amount of diimide-dicarboxylic acid.

1.82 mol ethylene glycol = 113 g of which condensed in approx. 1.48 mol 0.84 mol p,p'-(hydroxyethoxy)-diphenyldimethylmethane = 265 g 0.70 mol trimesic acid = 147 g

1.40 mol ethanolamine = 86 g

0.70 mol pyromellitic dianhydride = 153 g

2.10 mol trimellitic anhydride = 402 g

1.05 mol p,p'-diaminodiphenylmethane = 208 g

0.4 g zinc acetate.

Method of production:

Ethylene glycol, p,p'-bis-(hydroxyethoxy)-diphenyl-dimethylmethane, trimesic acid and zinc acetate are mixed in a container. First, trimesic acid is esterified as completely as possible, whereby 39 40 ml of distillate passes over and a temperature of 230°C is obtained. 100 g of crude cresol are then added as a carrier and at the same time as a solvent. After cooling to 140°C, ethanolamine is added, and immediately thereafter pyromellitic dianhydride in portions, so that a temperature of 180°C is not exceeded during the exothermic reaction. The water that splits off during the formation of the diimide alcohol is distilled off as carefully as possible. Go. 27 ml of distillate, mainly water, must pass through this operation. This is achieved by heating to around 200°C. The addition of trimellitic anhydride and p,p'-diaminodiphenylmethane takes place in 5 portions of 122 g each at the temperatures 155°C, 160°C, 165°C, 170°C o-. l80°C. The water which is split off during the formation of diimide-dicarboxylic acid and during the esterification is distilled off at temperatures of 210, 215»225»23O and 240°C, respectively. After the 4th portion, 50 g of crude cresol is added, and after the 5th portion 100 g of crude cresol to reduce the viscosity. After distilling off a total of 160 mm of water (containing some crude cresol and ethylene glycol), dilute with crude cresol to 50

Varnish composition:

60.0% resin solution (50 fig solution in cresol)

3.8 f crude cresol

2.0 µg of isocyanate separator CT stable type (manufacturer: Farbenfabriken Bayer, Leverkusen) 50 µg of mixture dissolved in a mixture of 50 µg of crude cresol and 50 µg of solvent naphtha

3.0% benzyl alcohol

3.0 fo tetralin

7.0 fo xylene

l8.2 fo solvent-naphtha

0.7% of a 25% solution of zinc resinate in xylene 2.3% of a 33% solution of polymeric butyl titanate dissolved in crude cresol.

The outlet speed for this varnish solution measured in a DIN cup at 20°C is, depending on the degree of condensation of the resin, between 80 and 140 seconds.

Sample values:

Example 23

0.8 mol bisphenol A = 182 g

3.0 mol ethanolamine = 183 g

1.6 mol pyromellitic dianhydride = 350 g 1.8 mol trimellitic anhydride = 346 g 0.6 mol p,p'-diaminodiphenylmethane = 119 g 0.5 g zinc acetate

6.0 g polymeric butyl titanate

175>0 g crude cresol as carrier and solvent.

Production takes place as indicated in example 13.

Varnish composition: 56.0% cresol resin solution (50% strength) 15.9% raw cresol

22.4% solvent naphtha

3.7% xylene

2.0% propylene glycol-1,2

Sample values:

Example 24

5.60 mol ethylene glycol, of which condensed 1.90 mol 0.80 mol bisphenol A

0.96 mol of ethanolamine

0.32 mol of trimellitic anhydride

1.20 mol of 4,4'-diaminodiphenylmethane

1 g zinc acetate

6 g polymeric butyl titanate, dissolved in 94 g crude cresol. Production method: Ethylene glycol, ethanolamine, bisphenol A and zinc acetate are filled into a flask and heated to 100°C. The mellitic acid is added in 4 portions in quick succession. By increasing the temperature to around 200°C, the separated water is distilled off little by little. After pre-condensation to produce triimide triol from mellitic acid and ethanolamine, a mixture consisting of trimellitic anhydride and 4,4'-diaminodiphenylmethane is added in 6 portions, . during which diimide-dicarboxylic acid is formed and is then esterified with the added ethylene glycol, bisphenol A and the previously formed triimide triol. After distilling off the theoretical amount of water and excess ethylene glycol, a temperature of around 270°C is achieved. The further processing of wire varnish with J>2% dry substance f content, and the actual wire varnishing takes place as indicated in example 1.

Sample values:

Example 25.

1.6 mol = 100 g ethylene glycol

1.6 mol = 418 g of tris-2-hydroxyethyl isocyanurate

1.0 mol = 228 g bisphenol A

3.25 mol = 642 g of trimellitic anhydride

1.44 mol = 288 g of p,p'-daninodiphenylmethane

1 g zinc acetate

6 g polymeric butyl titanate.

Work is carried out as indicated in example 3. From the above-mentioned listing of the starting products, it appears that tris-2-hydroxyethyl isocyanurate is used instead of glycerin. Otherwise, reac-

Table 3:

Overview of the composition of the esterimide condensation products listed in the examples and comparison experiments, compared to the obtained char resistance times for lacquered conductors produced with these lacquers.

The specified equivalents are calculated for 1 mol of imide nitrogen in the ester imide condensate.

Claims (2)

1. Method for producing insulating coatings on electrical conductors based on ester-imide condensation products which contain five-membered imide groups and which have an imide nitrogen content of 1 - 8% by weight, of 3~ or more basic, aromatic carboxylic acids or their anhydrides and possibly dibasic carboxylic acids, polyhydric alcohols and imide-forming multifunctional nitrogen compounds, by applying solutions of these condensates in organic solvents , optionally with the addition of curing catalysts and network formation at an elevated temperature, characterized by using solutions of ester-imide condensation products that have been modified with the help of a) 0.2 - 2.0 equivalents, referred to each mole of imide nitrogen in the condensate of: aa) mononuclear diphenols, preferably dioxybenzenes, ab) polynuclear diphenols, preferably those with structure where R means an alkylene, cycloalkylene or arylene residue, ac) monophenols which, in addition to the phenolic OH group, have at least one functional group suitable for esterification or imide formation, preferably p-aminophenol and/or p-hydroxybenzoic acid, ad) diphenol ethers of the compounds in aa) and ab), provided that these phenol ethers have at least two functional groups suitable for esterification or imide formation, or mixtures of these compounds, and b) up to 2 equivalents, referred to each mole of imide nitrogen in the condensate of one or more aromatic compounds with at least three similar groups present in a symmetrical arrangement and leading to a symmetrical net formation, preferably tris-(2-hydroxyethyl) —isocyanurate, trimesic acid and/or pyromellitic acid, or one or more compounds having only feature a) or only feature b). 2. Process according to claim 1, characterized in that solutions of ester-imide condensation products are used which have been modified with a) hydroquinone, resorcinol, p,p*-dihydroxydiphenyl-dimethylmethane, phenolphthalein, and p.»p'-bis-( hydroxyethoxy)-diphenyldimethylmethane, -b) 1,3,5-triaminobenzene or 1,2,4,5-tetrahydroxyethylbenzene, or several of the above compounds.