EP0365380B1 - Composition, its use as an electric insulator and process for manufacturing same - Google Patents

Abstract

The invention relates to a composition comprising at least one electrically insulating oil (A) and at least one product (B) containing at least six carbon atoms and carrying an aldehyde functional group. The Applicant has thus greatly increased the dielectric properties of benzyltoluene and its oligomers (A) by incorporating 3-ethoxy-4-hydroxybenzaldehyde therein. Application of this composition as a dielectric liquid in electrical transformers or capacitors and as a solvent for carbonless copying paper.

Description

The present invention relates to a new composition, its application as an electrical insulator and as a solvent for carbonless copying paper. The invention relates more particularly to insulating oils which are used in transformers and electric capacitors. Such oils are described, for example, in European patent EP 8251 and in US patent 4,523,044.

The Applicant has unexpectedly discovered that the dielectric properties of these insulating oils can be greatly improved when certain products are added in small proportion. The present invention is a composition comprising at least one electrical insulating oil (A) and at least one product (B) having at least 6 carbon atoms, carrying an aldehyde function and having at most two OH groups.

Electrical insulating oil (A) designates all products which can be used in electrical transformers and capacitors. These are liquid products at operating temperatures, i.e. between -40 and 100 ° C or as soon as the temperature exceeds a value between ambient and 100 ° C. These products have a resistivity at least equal to 10¹⁰Ωcm and preferably greater than 10¹²Ωcm.

• les huiles minérales,
• les polychlorobenzènes, par exemple le trichlorobenzène,
• les polychlorotoluènes,
• les phtalates, et alkylphtalates, par exemple le di-2-éthylhexylphtalate,
• les silicones, par exemple le polydiméthylsiloxane,
• les arylalcanes et polyarylalcanes tels que par exemple les oligomères du benzyltoluène décrits dans le brevet US 4 523 044,
• des arylalcanes et polyarylalcanes chlorés, par exemple le produit décrit dans le brevet européen EP 8251,
• des alcanes ou des alcènes substitués par au moins un phényl, ledit phényl étant lui-même substitué par des groupements alkyls. Par exemple les alkylbenzène ramifiés ou non, en particulier le dodécylbenzène,
• les composés à base de phényl xylyléthane (PXE) et en particulier à base de phényl-1 xylyl-1 éthane,
• les alkylnaphtalène par exemple le diisopropylnaphtalène
• l'isopropylbiphényl.

The invention is particularly applicable to the following products:

• mineral oils,
• polychlorobenzenes, for example trichlorobenzene,
• polychlorotoluenes,
• phthalates, and alkylphthalates, for example di-2-ethylhexylphthalate,
• silicones, for example polydimethylsiloxane,
• arylalkanes and polyarylalkanes such as, for example, the benzyltoluene oligomers described in US Pat. No. 4,523,044,
• chlorinated arylalkanes and polyarylalkanes, for example the product described in European patent EP 8251,
• alkanes or alkenes substituted by at least one phenyl, said phenyl itself being substituted by alkyl groups. For example branched or unbranched alkylbenzene, in particular dodecylbenzene,
• compounds based on phenyl xylylethane (PXE) and in particular based on 1-phenyl xylyl-1 ethane,
• alkylnaphthalene for example diisopropylnaphthalene
• isopropylbiphenyl.

The product (A) can also be a mixture of at least any two of the products mentioned above. All these products are purified for example on absorbers or on land, and optionally degassed to obtain sufficient resistivity.

The invention is particularly useful for the products described in US Pat. No. 4,523,044 which are compositions of polyarylalkane oligomers consisting of the mixture of two oligomers A and B.

avec n₁ et n₂ = 0, 1 et 2, sachant que n₁ + n₂ ≦ 3 et l'oligomère B est un mélange d'isomères de formule :

avec n′₁, n˝₁ et n₄ = 0, 1 et 2
et n′₂, n˝₂, n₃, n′₃ et n₅ = 0 et 1,
sachant que n′₁ + n˝₁ + n′₂ + n˝₂ + n₃ + n′₃ + n₄ + n₅ ≦ 2.The oligomer A is a mixture of isomers of formula:

with n₁ and n₂ = 0, 1 and 2, knowing that n₁ + n₂ ≦ 3 and oligomer B is a mixture of isomers of formula:

with n′₁, n˝₁ and n₄ = 0, 1 and 2
and n′₂, n˝₂, n₃, n′₃ and n₅ = 0 and 1,
knowing that n′₁ + n˝₁ + n′₂ + n˝₂ + n₃ + n′₃ + n₄ + n₅ ≦ 2.

où n et y ont la valeur 1 ou 2 qui peuvent être en mélange avec un ou plusieurs produits de formule générale :

où a varie de 2 à 4, b varie de 0 à 2, et R est un radical hydrocarboné aliphatique comportant de 1 à 3 atomes de carbone, ce mélange étant additionné d'un accepteur d'acide du type huile époxydée ou tétraphénylétain en quantité comprise entre 0,001 et 10 % et de préférence de 0,01 à 0,3 %.The invention also applies in particular to the liquid dielectrics described in EP 8251 of formula:

where n and y have the value 1 or 2 which can be mixed with one or more products of general formula:

where a varies from 2 to 4, b varies from 0 to 2, and R is an aliphatic hydrocarbon radical containing from 1 to 3 carbon atoms, this mixture being added with an acid acceptor of the epoxidized oil or tetraphenyltin type in quantity between 0.001 and 10% and preferably from 0.01 to 0.3%.

The product (B) can be chosen from products having at least 6 carbon atoms and carrying an aldehyde function. It can also carry other functions but not more than two OH groups. We use for example:

Advantageously, the product (B) contains at least one phenyl, for example:

These last three products are advantageously used and preferably 3-hydroxy-4-benzaldehyde ethoxy.

The proportion of (B) can be included within wide limits. Advantageously, the amount of (B) is such that it can represent up to 1 to 5% by weight of the mixture of (A) and (B). Preferably the amount of (B), expressed on the same basis is between 50 and 1000 ppm.

The product (B) can also be a mixture of at least two products having 6 carbon atoms and carrying an aldehyde function, one of these products may or may not contain a phenyl.

The composition according to the invention may contain antioxidants, epoxides and other additives customary in dielectric liquids.

The present invention also relates to the process for the preparation of these compositions.

It can be done by simple mixing. it is advantageous to prepare a stock solution of products (A) containing 10 to 20% by weight of product (B) and then to purify it by absorption on an absorbent earth such as a bleaching earth, a bentonite, etc. It is purified until a sufficiently high resistivity is obtained. Then this stock solution is used to obtain, after mixing with (A) in the desired proportions, the composition of the invention.

The present invention also relates to the application of this composition in transformers and electrical capacitors.

The composition according to the invention can be used as a solvent for manufacturing pressure-sensitive recording materials such as carbonless copying paper. Such techniques are described for example in the patents FR 2 257 432 (NCR), GB 1 346 364 (FUJI) and FR 2 157 587 (Monsanto).

EXAMPLE

The evolution over the residence time at 100 ° C. of the angle of loss of different liquids is followed.

The angle of loss (tan-delta) is one of the important characteristics of a dielectric liquid. It characterizes the electrical conduction of the liquid and must be as low as possible.

Maintaining the temperature of 100 ° C., in the presence of air, of the liquids results in a gradual, more or less rapid rise in the tan-delta. The lower the evolution, the better the result.

The increase in the tan-delta during this test is generally due to the appearance of ionic products of oxidation of the liquid (or its impurities).

Test results

• liquide de référence : un produit à base de dibenzyltoluène décrit dans l'exemple 2 du brevet US 4 523 044 et stabilisé par 1 % en poids d'éther diglycidique du bisphénol A. Ce diélectrique est désigné dans la suite par A1.
• deux compositions selon l'invention :

• (i) A1 + 200 ppm de B1 (B1 dans la suite du texte désigne l'éthoxy-3 hydroxy-4 benzaldéhyde)
• (ii) A1 + 200 ppm de B1 + 1000 ppm de ditertiobutylparacrésol (antioxydant)

Have been studied:

• reference liquid: a product based on dibenzyltoluene described in Example 2 of US Pat. No. 4,523,044 and stabilized with 1% by weight of diglycidyl ether of bisphenol A. This dielectric is designated in the following by A1.
• two compositions according to the invention:

• (i) A1 + 200 ppm of B1 (B1 in the remainder of the text denotes 3-ethoxy-4-hydroxy benzaldehyde)
• (ii) A1 + 200 ppm of B1 + 1000 ppm of ditertiobutylparacresol (antioxidant)

The table below shows tan-delta values during the residence time of liquids at 100 ° C.

The addition of 200 ppm of B1 does not deteriorate the angle of loss of the liquid even after prolonged stay at 100 ° C.

CAPACITOR TESTS

The tests consist in manufacturing and impregnating models of capacitors and in subjecting these models to accelerated aging (high voltages and temperatures).

The main sanction of the test is the number of capacitors which are deteriorated (breakdowns) during the test.

To study the effect of the presence of B1 in A1, two series of 10 capacitors were made, comprising 2 films of smooth polypropylene 12 µm thick (24 µm in total) and a layer of kraft paper, 12 µm thick, located between the two films. The paper has a density of 1.0.

The two series of 10 capacitors were impregnated using A1 and A1 + 200 ppm of B1 respectively.

After impregnation and thermal formation for 80 hours at 100 ° C., the capacitance and tan-delta values of the capacitors at the temperature of 85 ° C. were measured, under the voltage of 1000 AC.

The following results were obtained:

The capacitors were then subjected to aging at 85 ° C at 2700 V (75.0 V / µm) for 535 hours.

After this first aging, the values of the capacity and of tan-delta were measured at 85 ° C. under 1000 V. The following results were obtained:

No capacitor was damaged during the test at 2700 V. The test was continued by raising the voltage to 3000 Volts (83.3 V / µm) in order to further increase the severity of the test. The results of this 3000 V aging test are as follows:

The results obtained are in favor of the group comprising 3-ethoxy-4-hydroxy benzaldehyde (B1).

Evolution of the tan-delta

After 925 hours of aging at 85 ° C at 3000 Volts, the tan-delta of all the remaining capacitors was measured as a function of the voltage at the temperature of 85 ° C.

The following results were obtained:

The Tan-delta of the group of A1 capacitors comprising aldehyde B1 is significantly lower than that of the reference group A1 without this additive. (Reminder: the result is all the more favorable the lower the tan-delta).

Claims (5)

1. Composition comprising:

- at least one electrical insulating oil (A) which has a resistivity of at least 10⁸ m³ · kg · s⁻³ · A⁻² (10¹⁰ Ω cm),

- and at least one compound (B) containing at least 6 carbon atoms, bearing an aldehyde functional group and containing not more than two OH groups.

2. Composition according to Claim 1, characterised in that (B) contains a phenyl group.

3. Composition according to Claim 2, characterised in that (B) is chosen from 3-methoxy-4-hydroxybenzaldehyde, 4-methoxy-3-hydroxybenzaldehyde and 3-ethoxy-4-hydroxybenzaldehyde, or a mixture of any two of these.

4. Application of the compositions according to one of Claims 1 to 3 as a dielectric liquid in electrical transformers or capacitors.

5. Application of the compositions according to one of Claims 1 to 3 as a solvent for carbonless copying paper.