DE2452213A1 - DIELECTRIC IMPRAEGNATION PREPARATION FOR CAPACITORS - Google Patents

Description

Attorney's file 25 482 ^ ^ QV. 1974

Be / Ro

Monsanto Company St. Louis / USA

"Dielectric Impregnation Composition for

Capacitors "

The present invention relates to capacitors of the
Type that contain wound or stacked, alternately arranged, conductive and dielectric layers in a closed container and a liquid, dielectric preparation suitable for impregnating such capacitors "

43-4116A GW -2-

509819/0838

(DM) MKtTl »Λ43 M3310 T« tagr <MMMi KKGSTAPPPATEHT Mt «diM THlX OS M MO IEKO d ki loyfitd "iibtncfc" 8 K "Pcihdmfci Mlnümi" 5343

Common type electrical capacitors contain a combination of spaced apart metal foil conductors and an interposed dielectric sheet, the paper, polymeric film or can be a combination of paper and polymer em film. The dielectric sheet and spaces between the dielectric sheet and between the dielectric sheet and the conductors impregnated with a liquid dielectric preparation. Such impregnation is essential to the greatest to achieve dielectric resistance or dielectric strength.

The preferred dielectric preparation for impregnation of capacitors was previously polychlorinated biphenyl, that has a relatively high dielectric constant and good low temperature properties having. It has now been found, however, that 'certain polychlorinated biphenyls are resistant to natural degradation and that, when released into the environment, they enter the life cycle and therefore potentially in an ecological sense are harmful. Although capacitors are usually closed units and the leakage of the impregnant to a large extent to be avoided in the environment can, it still seems desirable / to create another preparation for impregnating capacitors that does not

509819/0838

which contains potentially harmful polychlorinated biphenyls.

It is accordingly an object of the present invention to provide a dielectric liquid preparation for impregnation of electrical capacitors that are free from polychlorinated biphenylene. Another The subject of this invention is a capacitor containing this other dielectric liquid preparation.

The formulations of the present invention are useful impregnating agents for capacitors of the type comprising alternating layers of metal foil conductor and a sheet of solid dielectric material. These formulations contain at least one ketone having a boiling point under atmospheric conditions greater than about 15O ⁰ C and have the following formula

R,

wherein the radicals R. and Rp have a combined carbon atom content of less than 20 and independently of one another alkyl, alkenyl, phenyl, tolyl, naphthyl,

509819/0838

Substituted phenyl, substituted tolyl or substituted naphthyl groups, in which the substituted aromatic radicals, independently of one another, contain no more than 18 carbon atoms and the radicals R. and Rp further form part of the same proportion that a cyclic ketone has, in which the radicals R. and Rp together have 4 or more contiguous carbon atoms to form a chain and the radicals R- and R., independently of one another, are hydrogen atoms or C ₁ - to Co-alkyl groups, η = 0 or 1 and m e-an integer is from 0 to 6, with the proviso that ₉ when η and m are both 1, neither R ^ nor R. can be a hydrogen atom.

The ketone can be mixed with other ketones of the same class or with certain non-ketonic organic compounds, as described below, be mixed.

Epoxy stabilizers are preferably used in dielectric Preparations of this invention used «

Capacitors containing such preparations can be manufactured and impregnated using standard methods will. The dielectric sheet j that between The metal foil conductors can be paper, a polymeric film such as polypropylene, or a combination

BQ9B19 / 083S

of paper and film. Such ige, with the preparations The capacitors impregnated according to the present invention have a low dissipation factor and a high dielectric constant and good low temperature behavior.

The invention is illustrated by the accompanying drawings, wherein Fig. 1 is a perspective view of a partially wound capacitor wound in turns and own. Figure 2 shows a fully completed capacitor having a coil wound capacitor des in Pig. 1 and contains a dielectric liquid impregnant.

The useful in the present invention ketones have a boiling point at atmospheric pressure that is great than 15O ⁰ C. To illustrate, the ketones can be aliphatic ketones, for example methyl isobutyl ketone, aliphatic ^ diketones, for example 2-3-hexadione, cyclic ketones, for example cyclohexanone, aromatic ketones and diketones, for example acetophenone, benzophenone and diphenyl ketone.

Typical examples of ketones in the context of the present

Invention are:

Cyclohexanone 2,3-hexanedione 3,4-imethyl-2-hexanone 2,2,4-trimethyl-3-hexanone

—6—

509819/0833

1-methoxy-2,3-clime thy! Butan on 1-l3opropoxy-3-methyl-2-butanone 2-methyl-3-oyolopentanone 1-ethyloyolopentanone 3-methyl-2-jieptanoii 3 1 5-dimethyl-4-heptanone

2-methoxy-3-jaethyl ~ 2-pentanone 1-Metnoxy - ^ - methyl - ^ - pentanone 2-methylcycloliexanone 2,2-dimethyl ~ 3-3aeptanone 2,6-dimethyl-4-lieptanone 2-methyl-4-octanone 2,5-dimethyl-4-heptanone 3-methylcyclohexanone 6-methyl-2-heptanone

1-methoxy-2-hexanone. 4-octanone

2,2-dimethylcyolohexanone

2 _f 4-Dimethylcyclohexanone 4-Methyloyclohexanone 2,5-Dimethylcyclohexanone 2-Octanone

5 -S.thyl-3-heptanone 2,5-dimethyloycloiiexanone 2-methyl-3-ethylenecyclopentanone 2,6-dimethyloyclohexanone

509819/0838 " ⁷ "

2-Isopropylcyelopentanone 2,4 - ime t hy 1 cy c 1 oil e xanone 2,3-dimethylcyclohexanone 2,2, δ-trimethylcyclohexanone 3,3-dimethylcyololiexanone ^ -Mettiyl ^ -ätliylcyclopeirtarLon.

Cy cloliexylmetliylketon 3,5-dimethylcycloliexanone Gyclot Leptanone

3,5-dimethylcycloliexanone 2-Atky.l-5-methyloyclohexan.one 2-propylcyolopentanone 2,2,6,6-tetramethyl / cyclohexanone 3 -Met hy 1 -2,4 -hexanedion 5-nonanone

3,4-diniethylcyclohexanone 3-nonanone

3-propylcyclopentanone 3-ethylcyclohexanone 2,5-hexanedione

fenchon

2-nonanone

2-propylcyclohexanone acetophenone

3-methyl-5-ethylcyclohexanone 4-decanone

Ment hon

509 819/083 8 ~ ⁸

2-decanone

4-n-Propyl cy c 1 ohexanone 2-methyl acetophenone Propiophenone phenyl-n-propyl ketone 3-methylacetophenone Isobutyrophenone Pivalophenone 1-phenyl-2 »butanone 6-CJnd canon

1-thienyl ethyl ketone 2-undecanone

2,4-dimethyl acetophenone 1-phenoxy-2-propanone n-butyrophenone Carvone

2,5-dimethylacetophenon Phenyl isobutyl ketone 4-phenyl- = 2-butanone 1-phenyl-3-methyl-1-butanone 3 j 5 - Dime thy lac et ophenon 2-methoxyacetophenone 3-methoxyacetophenone 5-phenyl-3-pentanone 5 ™ isopropyl-2-methyl acetophenone 3 ρ 4-kiniethylacetophenon 2 j, 4 s 5 ~ trimethylacetophenone

50-9 819/0831 '. - -9-

1-phenyl-1-pentanone 4-isopropylacetophenone 1-phenylheptanone 3-phenylcyclohexanone 1-ac et onaphthon 1-naphthylethylketon 2-benzolpyridine 2,4 $ 5-trimethylbenzophenone 2,4,4'-trimethylbenzophenone 1,5- I> ip: henyl-3-pentanone

Ketones of the present invention can be classified according to various Methods which are entirely known to the person skilled in the art can be produced. Cyclohexanone can, for example, in high yield obtained by oxidation of cyclohexanol with a solution of sodium dichromate in acetic acid solution will.

It should be noted that if a ketone described and claimed here is a pesticide at room temperature or semi-solid, it may be convenient and desirable to use the ketone in admixture with one or more to use liquid ketones of the defined class to facilitate the impregnation of the capacitor.

To typical, non-ketonic organic compounds,

which are suitable for mixing with the ketones belong

-10-

509819/0838

aromatic hydrocarbons such as alkylbenzene, alkylnaphthalene, Alkylbiphenyl, alkylpolyplienyl, alkylaryl ethers and alkyl substituted derivatives thereof, diarylalkanes and alkyl substituted derivatives thereof and diaryl ethers and alkyl substituted derivatives thereof, wherein the alkyl groups and alkanes have 1 to about 20 carbon atoms, the aryl radicals benzene, naphthalene, Are biphenyl or polyphenyl radicals and the polyphenyls 3 contain up to about 5 phenyl groups.

For specific examples of halogen-free aromatic Hydrocarbons include C ~ _, - alkylbenzene, cyclohexylethylbenzene, C,.-Alky! Naphthalene, C,, -Alkyltetralin, Isopropylbiphenyl, cyclohexylbiphenyl, C. g-alkylphenyl ether, Diphenylmethylpentane, benzylethylbenzene, diphenylether and phenoxybiphenyl.

To other non-ketonic organic compounds, those suitable for mixing with the ketone include the esters of carboxylic acid. The eter can be saturated or unsaturated, monoester, diester or polyester and their nature aliphatic, aromatic or mixed aliphatic / aromatic be.

The carboxylic acid reactant to make the ester can be any organic carboxylic acid _o Non-limiting examples include acids such as acetic acid, pro

509819/0838

pionic acid, butyric acid, caproic acid, caprylic acid, capric acid, lauric acid, tridecanoic acid, myristic acid, oleic acid, Palmitic acid, stearic acid, acrylic acid, methacrylic acid, Crotonic acid, isocrotonic acid, 3-butanoic acid, sorbic acid, Malonic acid, succinic acid, adipic acid, suberic acid, sebacic acid, dodecanoic acid, maleic acid, fumaric acid, benzoic acid, Naphthoic acid, phthalic acid, isophthalic acid, terephthalic acid, Ufa pht hai ins äur e, pyromelitic acid, salicylic acid, Azelaic acid, yaleric acid, hexanoic acid, heptanoic acid, Octanoic acid, nonanoic acid, decanoic acid, glutaric acid and the toluic acids. It should be noted that the appropriate anhydrides can be used in place of the acid, such as phthalic anhydride.

Thus, typical carboxylic acids that can be used to prepare the esters of this invention include aliphatic ^ dicarboxylic acids with 4-10 carbon atoms and aromatic dicarboxylic acids having 8-16 carbon atoms.

Alkyl esters of carboxylic acids are for use with ketones in capacitor impregnation formulations of the present invention Invention suitable. Such alkyl esters can be esters of mono-, di- or polycarboxylic acids.

Preferred esters for the purposes of the present invention are the dialkyl esters of dicarboxylic acids, viz

-12-509819 / 0838

of adipic, azelaic, sebacic, phthalic, isophthalic and / or mixtures of isomeric phthalic acids. Dialkyl esters of phthalic acid in which the esterification _{alcohol is a mixture of O 7} -C ... aliphatic alcohols, for example dialkyl _{phthalate esters of C 7} -C _{11 alcohols, are particularly preferred.}

Other non-ketonic organic materials that mix with the ketones are the well-known "transformer oils" and similar hydrocarbons.

Weaving the ketone and non-ketone organic compounds (if the latter are present) can make the dielectric liquid formulations of this invention contain minor amounts of numerous other components. In particular it is often desirable to incorporate a component that acts as a stabilizer in the impregnated dielectric System works. In general, the purpose of such a stabilizer is to make certain ionizable ones in the system To neutralize impurities or foreign materials that may be present or may be formed in the system. Residual catalysts or catalyst activators that are used by the Resin formation reactions remain, belong. To impurities may also include degradation products caused by environmental or voltage-induced chemical reactions are caused in the system, such-undesirable

»13-

B09819 / 0838

Cleaning and third-party products have an adverse effect on the loss factor or power factor of the impregnated dielectric system and it has been found that stabilizers are particularly effective are, a low conductivity of the impregnated dielectric System.

Particularly preferred stabilizing agents are epoxides, which are generally recognized by the group

-CH y CH-

may be characterized, examples of such epoxides being the glycidyl ethers and derivatives of ethylene oxide are. Other examples are 1-epoxyethyl-3,4-epoxycyclohexane, 3 ^ -epoxycyclohexylmethyl ^, 4-epoxycyclohexanecarboxylate, -3 ^ -Epoxy-e-methylcyclohexylmethyl ^, 4-epoxy-6-methylcyclohexane carboxylate and the same. These stabilizers are preferably used in the liquid dielectric Preparations of this invention in amounts generally range from 0.001 to about 8, and preferably from about 0.1 to 3 wt. ^ used.

The. non-ketone organic invention is not always found in the liquid dielectric compositions of this invention. It can therefore affect the liquid dielectric

-H-509819/0838

trisohe preparation essentially of one or more Ketones of the defined class together with an epoxy stabilizer exist. In many cases, however, the essential properties of liquid dielectric Preparation by the presence of a non-ketonic organic compound, as described above, 'preferably with the additional presence of an epoxy stabilizer, materially improved.

When the non-ketone component is used, it usually constitutes from about 50 to about 80 percent by weight. dielectric liquid, d _e h _a capacitor impregnation preparation of this invention. The non-ketonic component is more advantageously present in amounts of about 45 to about 70 wt. These ranges can of course be adjusted to compensate for the presence of stabilizers.

A particularly preferred liquid dielectric composition of this invention contains a mixture of 52.8 wt. $ Dimethylbenzophenong, 46.9 wt. Fo monoisopropylbiphenyl and 0.3 wt. Fo ^ j -Epoxycyclohexylmethyl-Js ^ -epoxyeyclohexancarboxylat.

The dielectric sheet materials between the Conductors arranged in the capacitor and connected to the dielectric

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impregnated tric liquid formulations of this invention Can be made of strong, flexible, porous materials, such as a highly refined cellulose paper or of a substantially non-porous, polymeric Film material, such as a polyolefin or a Combination of τοη paper and polymeric JiIm exist. That Paper material is preferably a two- or multi-sheet Kraft condensate Or paper having a single sheet thickness no greater than about 0.025 and preferably about 0.0075mm is the total combined thickness for the intended voltage of the capacitor is designed. Such paper has a dielectric strength that is relative is good compared to other dielectric materials and it has a relatively high dielectric constant. The polymeric material is preferably a biaxially oriented polypropylene film, although other members as well of the polyolefin family, in particular polyethylene and 4-methylpentene-1, have been used for condenser purposes to have. Other useful polymeric materials include polyesters, polycarbonates, polyvinylidene fluoride and polysulfone. Although both paper and polymeric films can be used alone, however often combinations of the two are used. The paper is placed in the vicinity of the polymeric film in such a way that that it acts as a wick to keep the liquid dielectric impregnant in the area to lead, which is of the same scope as the consortium

509819/0833 ~ ¹⁶ ~

a ».

contact surface between the porous paper and the essentially non-porous polymeric material.

The capacitor elements made according to the present invention Find use have the general shape shown in Fig. 1, this figure being one in turns shows wound capacitor 10, the separate electrode foils or fittings 11 and 12 and arranged therebetween dielectric spacers 13 and 14. The end joints 15 and 16 have enlarged surface areas (not shown) which are connected to the electrode foils 11 and 12. Electrode foils 11 and 12 can be one or more different materials, generally metals, ζ „Bo aluminum, copper and stainless Stahlt, contain »The dielectric spacers 15 and 14 generally contain paper and / or polymeric films, as previously discussed. Form in the given case the dielectric spacer 13 and the metal electrode foils 11 and 12 together form a capacitor element. the dielectric spacer and the spaces within and between the materials and the electrode foils are impregnated or "filled" with a liquid dielectric preparation,

Fig. 2 shows a finished capacitor 18, u.m its Housing a wound capacitor of the type shown in Fig. 1 is housed. The unity shows

-17- 509819/0 838

a container 19, a hermetically sealed cover 20, which has a small filling hole for the dielectric liquid 21 and a pair of connection points 22 and 23 which pass through the cover 20 and are isolated from this. Inside the container 19 are the connection points 22 and 23 are connected to the end connection points 15 and 16, as shown in FIG. Although this is not shown, the unit 18 shown in FIG. 2 furthermore contains the liquid dielectric preparation, which fills the space not occupied by the capacitor element in the container 19 and continues the dielectric spacers 13 and 14 are impregnated.

Impregnation of the capacitor is achieved using conventional methods. For example, after a generally customary impregnation process, the condenser units contained in containers, such as the condenser 18 of Fig. 2, dried under vacuum to remove residual moisture. The drying temperature will depend on the length of the drying time but generally in the range of about 60-150 C. If the temperatures are too low, the drying process takes an excessive amount of time

to
long, while at / high temperatures, degradation of the paper or shrinkage of the polymeric film used as dielectric spacers can occur. That

5 0.9 819/0838

Looli 21 allows the moisture and gases out of the Leak inside the container during the drying process.

The dielectric impregnation liquid becomes the condensate It is then preferably supplied through the hole 21 while the dried condenser body is in place is still under vacuum in a suitable ventilated space ". The impregnation liquid must be above the capacitor element stand in the container and usually enough impregnation liquid is introduced to completely fill the container and displace the air it contains. The pressure of the Heratellan Chamber is then on atmospheric pressure is increased and the capacitor body produced is left to stand for hours to ensure a thorough Ensure penetration of the liquid impregnation agent. After impregnation, the condenser unit by applying a suitable sealing compound to the hole 21 or by any other suitable means. Procedure locked. Subjects the condensate container one then elevated temperatures to increase the pressure in the container and the impregnation process to support. Heat and pressure can reduce the impregnability by changing the relative usability, Improve the viscosity and solubility of the materials. It can also allow expansion and contraction of the individual Components of the system as a result of heat and

509819/0838 ~ ¹⁹ ~

Pressure act as a driving force to cause migration of the liquid into the interstices of the dielectric spacer material to evoke or improve.

Numerous capacitors of the · in the! Ig. 1 and 2 were made from aluminum foil and paper separations and they were impregnated as described above with a dielectric preparation containing 52.8 $ dimethylbenzophenol, 46.9 $> monoisopropylbiphenyl and 0.3 $> 3 »4-epoxycyclohexylmethyl -3,4-epoxycyclohexane carboxylate. A group of eight of these capacitors, referred to as "test capacitors", were subjected to stress and service life studies. The results of these tests were compared with those obtained with a similar set of identical capacitors impregnated in the same manner but with an electrical grade polychlorinated biphenyl containing about 42% chlorine and referred to herein as the "control capacitor". The impregnant for the control capacitor contained 0.3 wt. $ 3 »4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate. The test results are given in Table I.

Table II

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Tabel

Investigations temp. C with regard to the service voltage permanent conditions ge it

hours

Paper ice oled Condensers X 70 ° 70 ° 70 ° 70 ° 70 ° 1000 870 900 930 960 168 744 168 168 168

80 ^υ
1000

168

90 ^υ 1000

168

Investigation Yerlust

Capacitors factor 0.00378 0 ^ 00309 0.00309 0.00308 0.00308 0.00308 0.00314 0.00321 0.00539

8 units

Load capacity 1o988 1a899 1,899 1,898 1,897 1,896 1,884 1,871 1,360 Microfarads

Number of failures

Control condens = - yloss-

factors factor O _s OO351 0.00315 0.003H 0.00316 0.00319 0.00320 0.00336 0.00378

- 8 units - _Belas t-

availability 1,974 1,885 1,884 1,883 1,883 1,883 1,873 1,864 Microfarads

Number of failures

^: Two sheets of kraft paper, 0.0165 thickness

cn

NJ

NJ

The values in the table show the excellent performance and operational safety of the capacitors impregnated with a liquid dielectric preparation of this invention in comparison to similar capacitors according to the prior art. The table shows in detail that no failures occurred in the test capacitors, although these ^{were subjected to extreme test conditions at 100 °} C. and 1000 V. On the other hand, although the control capacitors held up to the final test conditions, 100% failure occurred under these conditions.

The preceding examples and values in the table serve only to explain a preferred embodiment of the invention, without, however, the invention on the preparations or described in these examples Capacitors should be restricted. The invention includes, by definition, liquid, dielectric Preparations as described above, as well as capacitors containing these preparations. Furthermore is point out that although the examples and discussions referred only to capacitors made up of individual surface materials for conductors and insulators are also a metallized PiIm along with the Here -defined liquid, dielectric preparations can be used, and that produced in this way Capacitors also fall within the scope of the invention.

Claims: 509819/083 8 _ ₂₂ _

Claims (13)

Patent claims: 1J Electrical capacitor with at least two electrodes and a dielectric sheet material arranged between them, the dielectric sheet material and the spaces between the dielectric sheet material and the electrodes being impregnated with a liquid dielectric preparation, characterized in that this is at least contains a ketone which has a boiling point at atmospheric conditions which is higher than about 150 ⁰ C, and that the ketone has the following general formula It R <- C C t 0 ti wherein the radicals R. and Rp have a combined carbon atom content of less than 20 and independently of one another alkyl, alkenyl, phenyl, tolyl, naphthyl, substituted phenyl, substituted tolyl or substituted Laphthyl groups are in which the substituted aromatic radicals, independently of one another, no more than can continue to form part of the same proportion as the one -23-509819 / 0838 Contains 18 carbon atoms and the radicals R. and contains cyclic ketone, in which the best R and Rp together form 4 or more contiguous carbon atoms to form a chain and the radicals R and R, independently of one another, are hydrogen atoms or C ₁ - to C _ft -alkyl groups, η = 0 or 1 and m is an integer from 0 to 6, with the proviso that if η and m are both 1, neither R nor R. can be a hydrogen atom * 2. Capacitor according to claim 1, characterized in that the preparation of about 0.001 to 8 wt. ^ Contains epoxy stabilizer. 3. Capacitor according to claim 2, characterized in that the preparation contains about 0.1 to 3 G-ew. $ 3,4-Epo: xycyclohexyl-methyl-3 _i 4-epoxycyclohexanecarboxylate. 4. capacitor according to claim 2, characterized in that the ketone dimethylbenzophenone, Is cyclohexanone and / or acetophenone. 5. Capacitor according to claim 2, characterized that the preparation further contains a non-ketone organic compound, namely an ester of a carboxylic acid, an alkylbenzene, alkylnaphthalene, Alkylbiphenyl, alkylpolyphenyl, alkylaryl ethers and alkyl-substituted derivatives thereof, diarylalkanes and alkyl-substituted derivatives thereof and / or diaryl 509819/0838 -24- ethers and alkyl substituted derivatives thereof, wherein the alkyl groups and alkanes have 1 to about 20 carbon atoms contain, the aryl radicals being benzene, naphthalene, biphenyl or polyphenyl radicals and the polyphenyls Have 3 to about 5 phenyl groups. 6. capacitor according to claim 5, characterized that the ester is one of aliphatic dicarboxylic acids having 4-10 carbon atoms and aromatic dicarboxylic acids having 8-16 carbon atoms is. 7. Capacitor according to claim ^ _i, characterized in that the dielectric sheet material is paper, polyolefin film and their combinations ο 8. composition suitable as a capacitor impregnating agent, characterized in that it contains at least one ketone having a boiling point at atmospheric conditions of greater than about 15O ⁰ C the following formula C -I .25- 5098 19/083 wherein the radicals R. and Rp have a combined carbon atom content of less than 20 and are independently alkyl, alkenyl, phenyl, tolyl, naphthyl, substituted phenyl, substituted tolyl or substituted naphthyl groups, wherein the substituted aromatic radicals , independently of one another, do not contain more than 18 carbon atoms and the radicals R. and Rp can continue to form part of the same proportion that a cyclic ketone contains, in which the radicals R. and R »together have 4 or more contiguous carbon atoms to form one Form a chain and the radicals R ₇ and R., independently of one another, are hydrogen atoms or C ₁ - to C ₀ -alkyl groups, η = 0 or 1 and m is an integer from 0 to β, with the proviso that, if η and m are both 1, neither R ~ nor R. can be a hydrogen atom. 9. Preparation according to claim 8, characterized in that 3ie about 0.001 to 8 wt. ^ Contains epoxy stabilizer. 10. Preparation according to claim 9, characterized in that it contains about 0.1 to 3 wt. ^ 3, / J.-Epoxycyclohexyl-methyl ^, 4-epoxycyclohexane carboxylate contains. . . 11. Preparation according to claim 9, dadur. ch marked that the ketone dimethylbenzo 5 0.9-81 9/0 8 38 phenone, cyclohexanone and / or acetophenone is » 12. Preparation according to claim 9, characterized that it continues to be a non-ketonic contains organic compound, namely an ester of a carboxylic acid "an alkylbenzene, alky! naphthalene, Alkyl biphenyl, alkyl polyphenyl, alkyl aryl ethers and alkyl substituted Derivatives thereof, diarylakanes and alkyl-substituted ones Derivatives thereof and / or diaryl ethers and Alkyl substituted derivatives thereof, wherein the alkyl groups and alkanes contain 1 to about 20 carbon atoms, wherein the aryl radicals are benzene, naphthalene, biphenyl or polyphenyl radicals and the polyphenyls are 3 to about Have 5 phenyl groups » 13. Preparation according to claim 12, characterized in that the ester is one of aliphatic dicarboxylic acids with 4-10 carbon atoms and aromatic dicarboxylic acids having 8-16 carbon atoms. 509819/0838