FI61365C - ELEKTRISKT ISOLERINGSMATERIAL PAO CELLULOSA-BASIS OCH PROCESS FOER FRAMSTAELLNING DAERAV - Google Patents

Description

• · jJMter! ΓΒ1 m> ADVERTISEMENT, Λ 7, c ^ SSTa lJ '^ utlAggningsskrift ^ Iooo • 53S c (4S) Patent granted on 12 07 1932 utt #? / Patent raoddelat * (51) Kv.ik? /Int.ct.3 H 01 B 3/52, D 21 H 5/00 ENGLISH I — FI N LAN D <*) Pn * nttlhak «iMit— Pat« ntans6knlng 791 ^ + 55 (22) H »k« ml * ptlvl - Arafiknlngadag 07.05.79 " (23) Alkuptlvi — Glltlghattdtg 07.05.79 (41) Tullut lulklMlul - Bllvlt offwttllg 27.OL.80

National Board of Patents and Registration u ... ......

rWO OCt, <♦ ·> 31-03.82 (32) (33) (31) Privilege claimed —Begird prlorltet 26.10.70 26.10.78 USSR (SU) 2671 + 052, 267 ^ 053 (71) Malinskaya Bumazhnaya Fabrika imeni 50- -Letia Velikoi Oktyabrskoi Sotsialisticheskoi Revoljutsii, ulitsa Gagarina, 2, Malin Zhitomirskaya oblast, USSR (SU) (72) Lev Nikolaevich Tkach, Malin Zhitomirskoi oblast, Jury Nikolaevich Prikhodko, Malin Zhitomiridise oblasti,

Kiev, Vladimir Ilich Soldatenko, Malin Zhitomirskoi oblast,

Vasily Vasilievich Kostyuchenko, Malin Zhitomirskoi oblast, USSR (SU) (7 ^) Oy Kolster Ab (5M Cellulose-based electrical insulator and method for its preparation -Electric insulating material pH Cellulose-basis and process for framställning därav

The invention relates to electrical insulating agents and methods for their preparation, and in particular to a cellulose-based electrical insulating agent and a method for its preparation.

There is a growing need for such materials (electrical insulating paper and board) despite the increasing use of electrical insulating materials based on artificial polymers, ceramics, etc.

Nevertheless, in terms of main insulation properties and extended durability over a wide range of operating temperatures, cellulose-based electrical insulation materials do not meet the growing quality requirements of the electrical and radio engineering industry.

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One of the main dielectric properties is the power dissipation of the insulator in insulators that operate in AC circuits, such as as interlayers in paper capacitors or cables. Qualitatively, these losses are estimated as the insulation loss factor, which is hereinafter referred to as tg £. The lower this parameter, the lower the amount of electrical energy consumed in heat loss and the safer and longer lasting the product in which the electrical insulator is used.

Another important property of electrical insulators is their resistivity, usually measured in ohms * cm.

The above-mentioned dielectric properties affect a third important parameter, namely electrical strength. This effect is stronger the less stable tg £ and resistivity are in the operating temperature range and the more pronounced their change during use. Thus, for example, it has been shown that an increase in tg uva due to cellulose aging results in a rise in temperature inside the capacitor, which in turn accelerates cellulose aging and further causes an increase in tg ja and temperature until thermal breakthrough occurs and the capacitor or cable ceases to operate. The decrease in resistivity occurs as the operating temperature increases for some other reason.

Some cellulose-based electrical insulators are still known in the art, as well as methods for their preparation with the aim of improving the stability and resistivity of tg &. Known methods comprise the steps of making pulp, forming, pressing and drying the web. Reduction of ionic insulation losses is achieved by adding chemical reagents to the pulp, for example zinc salts (inventor's certificate, USSR No. 540,003) and magnesium salts (inventor's certificate, USSR No. 300562).

However, the decrease in tg £ of the electrical insulator is only observed at elevated temperatures (80-140 ° C) and is very small at lower temperatures (30-80 ° C).

An electrical crosslinking agent based on modified cellulose and a process for its preparation are also known in the art.

The modified cellulose used is boronized cellulose obtained by treating the cellulose with a melt of a mixture of boric acid, urea and borax at 180-260 ° C and then washing off 3,61365 of the water-unreacted boric acid (inventors' certificates SSSR not 303390 and 536275). The electrically insulating material obtained by this known method has reduced dipole insulation losses, while the ionic insulation losses remain unchanged. In addition, this method is technologically complex and not practical.

The object of the present invention is to eliminate the above-mentioned disadvantages.

The main object of the invention is, by selecting a new chemical reagent for treating the pulp or paper web, to provide a cellulose-based electrical insulating agent which improves the values of tg £ and specific electrical resistance.

The object of the invention is achieved by preparing a cellulose-based electrical insulating material containing 0.02-1.1% by weight of boron, calculated on the absolute dry matter.

The method of making a cellulose-based electrical insulating material comprises the steps of making and forming a cellulose-based pulp into a web, pressing, treating with a chemical reagent, drying, and preparing the final material; According to the invention, the chemical reagent used is boric acid or a boron compound which forms boric acid when it reacts with water, these reagents being used either separately or together and in amounts which guarantee a boron content in the final product of between 0.02 and 1.1% by weight of absolute dry matter.

To simplify the treatment of the pulp or paper web with a chemical reagent, it is suitable to use boric acid in the form of its aqueous solution or water / alcohol solution. The use of boric acid in the form of an aqueous / alcoholic solution makes it possible to obtain paper with a virtually constant density without considerable deformation, which precludes the subsequent shrinkage of the sheets of paper in special equipment.

As the boron compound forming the boric acid when reacting with water, it is preferable to use boric anhydride, metaboric acid or triethylborate, and it is appropriate to use the boron compound in the form of its alcoholic solution for better handling of the pulp or paper web.

Compounds used as a chemical reagent, namely boric acid tsy. boron compounds which react with boric acid to react with water, which reagents may be used alone or in combination, may be added both during the pulp production step and before the pressing or drying step.

The proposed method is implemented as follows.

The pulp, which contains wood or cotton pulp as the main ingredient, is prepared by any of the methods known in the art.

Already at the pulping stage, boric acid or boron compounds such as boric anhydride, metaboric acid, triethylborate or mixtures thereof can be added to the pulp. Boric acid dissolves in water into the composition of the pulp, while boric anhydride, metaboric acid or triethyl borate reacts with water to give a boric acid solution. The amount of boric acid or a boron compound or a mixture thereof is calculated in such a way as to guarantee a boron content of 0.02 to 1.1% by weight, based on the absolute dry matter, of the final product.

Boric acid and boron compounds can be used both in their crystalline state and in the form of solutions.

It is convenient to use boric acid as an aqueous or water / alcohol solution and the boron compound as an alcoholic solution.

The resulting pulp is felted for web formation by any of the conventional methods; the formed web is compressed and dried using equipment commonly used in paper mills. When an electrically insulating material having an increased density is desired, the paper web is calendered.

The introduction of boric acid, a boron compound or a mixture thereof is possible in other stages of the process following the production of the pulp and the formation of the web, namely before compression or drying.

The introduction of boric acid or boron compounds into the pulp or Taino not only reduces the ionic insulation losses in the electrical insulating material, but also the dipole insulating losses and stabilizes the tg ^ value of the absolute dry electrical insulating material over a wide temperature range. Thus, for example, between 60 and 120 ° C, when the boron content of the electrical insulating paper is 0.27 to 0.45% by weight, the tg £ is practically constant.

As the boron content in the absolutely dry electrical insulating material increases to 1.1% by weight, the tg & at different temperatures changes only slightly.

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The cellulose-based electrical insulating material obtained by the described method has the following technical parameters: thickness, mm 5-500 3 bulk density, g / cm 0.6-1.35

Boron content in% by weight, calculated on the absolute dry matter 0,02 to 1,1, tg £ of dry electrical insulating paper made of electrical insulating wood with a density of 0,7 g / cm: Temperature For paper made for Paper made using industrial water , with deionized water having an electrical conductivity of about 250 uS / cm and containing about 0.5 mg-equivalents / l of sodium salts_0 0.00040 0.00040 60 0.00035 0.00035 100 0.00030 0, 00040 120 0,00035 0,00050 Dry paper made of electrically insulating pulp with a density of 1,2 g / cm3 tgi>: Temperature For paper made on Paper made using industrial water with deionized water of electrical conductivity of about 250, uS / cm and containing about 0.5 mg - equivalents / l of sodium salts - 60 0.0008 0.0008 100 0.0008 0.0010 120 0.0008 0.0013 illuminating but not in any way limiting the scope of the invention, such as it is clear to a person skilled in the art.

Example 1 Electrical insulating paper is prepared under laboratory conditions from pure electrical insulating cellulose obtained from softwood silk paper using desalinated water.

The pulp is prepared by crushing in a laboratory mixer, 10 g of electricity insulation cellulose, on top of which is poured into 0.1% 6 61 365 aqueous boric acid solution for half an hour kierrosnopeudel-la of 1000 r / min, and the product obtained by milling the suspension laboratoriojauhimes-SA 12 hours at 95 ° Schopper-Riegler degree.

The pulp is then diluted with 1000 ml of desalinated water, after which the paper is prepared in a laboratory apparatus by felting, pressing and drying the paper sheets. The paper produced has a density of 0.7 g / cm, a thickness of 50 and contains 0.02% by weight of boron, calculated on the absolute dry matter.

The same substance, the same method and the same equipment are used, but using desalinated water, to produce reference samples of electrical insulating paper having the same density and thickness as the paper containing boric acid.

The value of Tgi is determined for samples of both paper types as follows.

Paper samples are assembled into a pack of 280-320 μm thick.

The pack is compressed between 46 mm diameter planar electrodes at a pressure of 0.2 kgf / cm and dried under vacuum at a residual pressure of 5.10 mm Hg at 125 ° C for 2 hours. The packages are then cooled in vacuo at the same residual pressure to a test temperature of 30, 60, 100 or 120 ° C and thermostatically controlled to one of these temperatures. After the electrodes are connected to the measuring branch of the Schering bridge, the tests are performed using an industrial alternating current with a frequency of 50 Hz at a voltage of 5 V / ^ im. Tg values are read directly from the Schering bridge after this has been balanced.

Table 1 shows the values of tg ^ determined for paper samples obtained according to the described method.

Table 1 Temperature, ° C Comparison of samples tg <$ containing boron 30 0.00105 0.00105 60 0.00085 0.00085 100 0.00085 0.00085 120 0.0010 0.0012 61365

Example 2 Electrical insulating paper is prepared under laboratory conditions from pure electrical insulating cellulose obtained from softwood silk paper using deionized water.

The pulp is prepared by grinding 10 g of electrically insulating pulp over which 1000 ml of a 1.2% aqueous solution of boric acid has been poured, in a laboratory mixer for half an hour at 1000 rpm and grinding the resulting pulp in a laboratory grinder for 16 hours at 96 ° SR (Schopper-Rieg) .

The pulp is then diluted with 3000 ml of desalted water, after which the paper is prepared in a laboratory apparatus by felting, pressing and drying the paper sheets. The paper produced has a density of 0.7 g / cm 3, a thickness of 50 μm and contains 0.11% by weight of boron based on absolute dry matter.

Reference samples of electrical insulating paper are obtained from the same material by the same method and with the same equipment, but using deionized water. The density and thickness of the reference paper are the same as for paper containing boric acid.

The tg & value is determined for both types of paper samples following the procedure described in Example 1.

The determined values of Tg & are given in Table 2.

Table 2 Temperature, ° C Tg of samples <£

Comparison containing boron 30 0.0009 0.00105 60 0.0007 0.00085 100 0.0007 0.00090 120 0.0007 0.0012

Example 3 Electrical insulating paper is prepared under laboratory conditions from pure electrical insulating cellulose obtained from softwood silk paper using deionized water.

The pulp is obtained by grinding 10 g of electrically insulating cellulose on top of which 100 ml of a 28% aqueous solution of boric acid and 900 ml of deionized water have been poured in a laboratory mixer for half an hour at 1000 rpm.

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Dilution and preparation of paper samples as well as preparation of reference samples of boron-free electrical insulating paper are performed following the procedure described in Example 2. The samples have a thickness of 50 μm, a density of 0.7 g / cm 2 and a boron content of 0.25% by weight, calculated on the absolute dry matter.

Samples of both paper types are tested following the procedure described in Example 1.

The values determined for Tg & are given in Table 3.

Table 3 Temperature, ° C Samples tg £

Comparison containing boron 30 0.0006 0.00105 60 0.0005 0.00085 100 0.0005 0.00090 120 0.0005 0.0012

Example 4 Electrical insulating paper is prepared under laboratory conditions from pure electrical insulating cellulose obtained from softwood silk paper using deionized water.

Laboratory paper samples are prepared using paper pulp containing 2% cellulose and prepared under industrial conditions. 100 g of paper pulp are ground in a laboratory coater to 96.5 ° SR. 30 g of boric acid are then added to the pulp and the volume of the mixture is made up to 1000 by adding deionized water. After mixing the diluted pulp for 3 minutes, samples of the electrical insulating paper are prepared by felting, pressing, and drying the paper sheets with a laboratory papermaking machine. The samples have a thickness of 50 μm, a density of 0.7 g / cm 2 and contain 1.1% by weight of boron, calculated on the absolute dry matter.

Control samples of electrical insulating paper that do not contain boron are obtained in the same way, but using deionized water only. Tg ^ is measured following the procedure described in Example 1.

The tg & values determined for these paper samples are given in Table 4.

Table 61365 Temperature, ° C Tg of samples <$

Comparison containing boron 30 0.00050 0.00105 60 0.00040 0.00085 100 0.00035 0.00090 120 0.00040 0.00120

Example 5

Capacitor paper prepared under industrial conditions using deionized water at all stages of the process and having a basis weight of 13 g / m 2, a moisture content of 8% and a density of 0.8 g / cm 2 is moistened with an 8% aqueous solution of boric acid to a moisture content of 26%.

The wetted paper is calendered to a density of 1.2 g / cm 2 and dried. Control samples are prepared from the same paper moistened with deposited water only.

The samples obtained are submitted for testing. Tg 1 values are determined following the procedure described in Example 1. The other technical parameters presented below are obtained by known methods.

The parameters of the electrical insulation paper test and control samples are given in Table 5.

Table 5 n Parameter Samples containing boron for comparison 12 3 4 1 2 3 4 5 6 7 thickness, μm 10.6 10.4 2 density, g / cm3 1.20 1.19 3 breaking length, km 9.6 9 .7 4 specific conductivity of the aqueous extract ^ uS / cm with a modulus of 1:50 11 10 5 pH of the aqueous extract pH 6.8 7.0 6 breakdown voltage for one layer of paper, V 490 490 7

insulation loss factor for dry paper at ° C

10 61 365 12 3 4 30 0.0012 0.0020 60 0.00095 0.00165 100 0.00095 0.018 120 0.0010 0.0023 8. Specific resistance of paper, ohm, cm at 120 C 3 , 9χ10Χ 2.8x1ο · 1 9. insulation constant 2.9 3.1

10. Insulation loss factor of paper impregnated with trichlorophenyl (in small capacitors at temperature) ° C

20 0.0021 0.0035 60 0.0018 0.0030 100 0.0017 0.0032 120 0.0020 0.0040 11. Boron content calculated on the absolute dry matter,% by weight 0.27 0

Example 6

Capacitor paper prepared under industrial conditions using, at all stages, water with an electrical conductivity of about 250 / US / cm and containing 0.5 mg -equiv./l of sodium salts and a paper density of 0.76 g / cm is moistened with an 8% aqueous solution of boric acid to a moisture content of 25%, calendered to a density of 1.2 g / cm2 and dried.

The same paper, moistened only with industrial water, is treated in the same way and used for the preparation of reference samples.

The samples obtained are placed in a series of tests and the results are given in Table 6.

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Table 6 No. Parameter Samples containing boron Comparison 12 3 4 1. thickness, ^ 8.2 8.2 8.2 density, g / cm3 1.20 1.20 3. breaking length, km 9.7 9.5 4 specific conductivity of aqueous extract, yUS / cm, with modulus 1.50 33 26 5. aqueous extract pH 7.3 7.6 6. breakthrough voltage of one paper layer, V 400 400

7. dry paper insulation efficiency at temperature, ° C

30 0.0010 0.0023 60 0.0008 0.0019 100 0.0010 0.0032 120 0.00135 0.0068 8. Specific resistance of dry paper at 120 ° C, ohm · cm 6.1 * 1015 2.8 -1014 9. Insulation constant of dry paper 2.7 3.1

10. Coefficient of loss of insulation (for small condensers) of paper impregnated with trichlorodiphenyl at a temperature of C

20 0.0021 0.0035 60 0.0018 0.0032 100 0.0018 0.0046 120 0.0025 0.0081 11. Boron content,% by weight, calculated on the absolute dry matter 0.45 0

Example 7 Electrical insulating paper based on pure electrical insulating cellulose obtained from softwood tissue paper using deionized water is prepared as follows.

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Pulp produced under industrial conditions with 0.23% by weight of pulp and ground to 96 ° SR is taken from the pressure box of a paper machine. 14 g of boric anhydride are added to 1000 ml of this pulp and the mixture is stirred for 3 minutes.

Boric anhydride added to the pulp reacts with the water in the pulp according to the following reaction: B203 + 3H2O -> 2 H3BO3.

From your pulp treated as described, electrical insulating paper samples are prepared on a laboratory paper-forming machine by felting, pressing and drying the paper sheets.

The resulting paper had a thickness of 50, a density of 0.7 g / cm 2 and a boron content of 0.9% by weight, based on the absolute dry matter.

Control samples of electrical insulating paper which do not contain boron are prepared by the same method but without the addition of boric anhydride, and with the same equipment.

The Tg E is determined for the prepared samples following the procedure described in Example 1; its values are listed in Table 7.

Table 7 Temperature, ° C Comparison of samples containing tg £ of boron 30 0.0005 0.00105 60 0.0004 0.0085 100 0.0004 0.00090 120 0.0004 0.0012

Example 8 Samples of electrical insulating paper containing 0.9% by weight of boron, calculated on the absolute dry matter, and control samples without boron are prepared following the procedure described in Example 7, using metaboric acid as the boron compound.

Metaboric acid reacts with the water contained in the paper stock to form boric acid according to the following formula: hbo2 + h2o- ^ h3bo3.

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The tgE values given in Table 8 for the samples are then determined following the procedure described in Example 1.

Table 8 Temperature, ° C Comparison of tg £ boron in samples 30 0 T 0005 0.00105 60 0.0004 0.00085 100 0.0004 0.0009 120 0.0004 0.0012

Example 9 Electrical insulating paper is prepared under laboratory conditions from pure electrical insulating cellulose obtained from softwood silk paper using deionized water.

The pulp is prepared by grinding 20 g of electrically insulating cellulose over which 1000 ml of deionized water has been poured, in a laboratory mixer for half an hour at 1000 rpm and grinding the resulting pulp in a laboratory grinder for 12 hours at 95 ° SR.

The paper stock thus prepared is diluted with 1000 ml of deionized water, after which the paper sheet is obtained by felting and pressing with a laboratory device.

Half of the paper sheet is treated with 10 ml of a 0.1% aqueous solution of comminuted boric acid, whereby the boric acid is spread evenly over the entire surface of the paper sheet. After repeated pressing and drying, an electrical insulating paper with a thickness of 50 μm, a density of 0.7 g / cm 3 and containing 0.04% by weight of boron, calculated on the absolute dry matter, is produced.

The remaining half of the sheet of paper is dried and used to make reference samples of electrical insulating paper which do not contain boron and have the same thickness and density.

The tg <f values given in Table 9 have been determined for samples of both paper types following the procedure described in Example 1.

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Table 9 Temperature, ° C Comparison of samples containing tg <i boron 30 0.0010 0r0011 60 0 j0008 0, 00085 100 0.0010 0.0012 120 0.0010 0.0012

Example 10 Samples of electrical insulating paper treated with boric acid and control samples of electrical insulating paper which do not contain boron are prepared following the procedure described in Example 9. The samples have a thickness of 50 μm and a density of 0.7 g / cm 2.

The paper sheet is treated with a 6% aqueous solution of boric acid to prepare samples of electrical insulating paper. The samples obtained contain 0.91% by weight of boron, calculated on the absolute dry matter.

The tg $ values given in Table 10 are determined for samples of both paper types.

Table 10 Temperature, ° C Comparison of samples containing tg & boron 60 0.0004 0.00085 100 0.00035 0.0009 120 0.0004 0.0012

Example 11

Samples of cable electrical insulation paper are prepared under industrial conditions from pure electrical insulation cellulose obtained from softwood tissue paper using deionized water. The pulp used in the sample preparation process has also been obtained using deionized water. The samples have a thickness of 120 μm and a density of 0.80 g / cm 2.

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The resulting samples are immersed in a 6% aqueous solution of boric acid for 5 seconds and dried. The dried samples have a density of 0.7 g / cm and a boron content of 1.1% by weight, calculated on the absolute dry matter.

The tg & values given in Table 11 have been determined in accordance with the invention for samples of boric acid-treated cable paper and for samples of original boron-free cable paper. The Tg £ is determined following the procedure described in Example 1.

Table 11 Temperature, ° C Comparison of samples containing tg§ of boron 60 0.0008 0.0018 100 0.0009 0.0025 120 0.001 0.0049

Example 12

A pulp containing 2.0% by weight of electrical insulating cellulose is prepared under industrial conditions, using deionized water, from pure electrical insulating cellulose, the cellulose also being obtained from softwood tissue paper also using deionized water. batch. 100 ml of a 0.08% aqueous suspension of active Aluminum oxide and 50 ml of a 28% boronic acid solution are added only 100 ml of a 0.08% aqueous suspension of active Aluminum oxide.

After adding the above ingredients to 1000 ml, make up to 1000 ml with deionized water, mix for 5 minutes at 1000 rpm and use the pulp thus obtained to make electrical insulating paper samples containing 0,55% by weight of boron by felting, pressing and drying the paper sheets in a laboratory apparatus and also for making samples from paper that does not contain boron. All samples have a thickness of 50 and a density of 0.7 g / cm.

The tg <f values given in Table 12 are determined for all samples following the procedure described in Example 1.

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Table 12 Temperature, ° C Comparison of samples containing tg £ boron 60 0.00045 0.0009 100 0.00040 0.0010 120 0.00045 0.00115

Example 13 Electrical insulating paper is prepared under laboratory conditions from pure electrical insulating cellulose obtained from softwood silk paper using deionized water.

The pulp is prepared by grinding 10 g of electrically insulating pulp to which 1000 ml of desalted water has been poured, in a laboratory mixer for half an hour at 1000 rpm and grinding the obtained pulp in a laboratory grinder for 16 hours at 96 ° SR. The pulp thus obtained is diluted with 3000 ml of desalted water, then 75 g of triethylborate are added to the pulp and the mixture is stirred for 5 minutes.

Triethylborate reacts with water in the pulp to give boric acid according to the following reaction: (C2H50) 3B + 3 H2O -> 3 C2H50H + H3BC> 3.

The pulp is then used to sample electrical insulating paper.

O

for the preparation of teas having a density of 0.7 g / cm 3, a thickness of 50 μm and a boron content of 0.37% by weight, calculated on the absolute dry matter.

Electrical insulation paper reference samples are made of the same material with the same equipment and the same method. The thickness and density of the control samples are the same as those of the boric acid-containing samples.

Tg E values were determined for samples of both paper types following the procedure described in Example 1. The values obtained are shown in Table 13.

Table 13 61365 Temperature, ° C Comparison of samples containing tg ^ boron 30 0.00050 0.00105 60 0.00040 0.00085 100 0.00035 0.00090

Example 14 Electrical insulating paper based on pure electrical insulating cellulose obtained from softwood tissue paper using deposited water is prepared as follows.

The pulp, produced under industrial conditions and containing 0.23% by weight of cellulose and ground to 96 ° SR, is taken from the pressure box of a paper machine. A mixture of 5 g of boric acid and 1.4 g of boric anhydride is added to 1000 ml of this pulp with stirring and stirring is continued for 3 minutes.

The above-mentioned boric anhydride, which was added to the pulp, reacted with the water it contained to form boric acid according to the following formula: B 2 O 3 + 3 H 2 O -> 2 H 3 BO 3.

Samples of electrical insulating paper are prepared from pulp treated as described above by a laboratory paper forming apparatus by felting, pressing, and drying a sheet of paper. The samples have a thickness of 50, a density of 0.7 g / cm and a boron content of 0.27% by weight, calculated on the absolute dry matter.

Reference samples of electrical insulating paper having the same thickness and density but not containing boron are obtained by the same apparatus by the same method except for the step of adding boric acid and boric anhydride.

The tg ^ values given in Table 14 are determined for samples of these papers.

Table 14 18 61 365 Temperature, ° C Comparison of samples containing tg ^ boron 30 0.00070 0.00105 60 0.00060 0.00085 100 0.00055 0.00090 120 0.00055 0.00120

Example 15 Samples of electrical insulating paper containing 0.45% by weight of boron, calculated on the absolute dry matter, and control samples without boron are prepared following the procedure described in Example 14, but using a mixture of boric acid 7.5 as the boron compound. g and metaboric acid 3.5 g.

Metaboric acid reacts in the water flake contained in the paper stock to form boric acid according to the following formula: HBO 2 + H 2 O -> H 3 BO 3.

The tg & values shown in Table 15 are determined for all papers following the procedure described in Example 1.

Table 15 Temperature, ° C Comparison of samples containing tg ^ boron 30 0.00050 0.00105 60 0.00040 0.00085 100 0.00040 0.00090 120 0.00040 0.0012 19 61365

Example 16 Samples of electrical insulating paper containing 0.35% by weight of boron, calculated on the absolute dry matter, and control samples not containing boron were prepared following the procedure described in Example 14 using a mixture of 5 g of boric acid and triethylborate as the boron compound. 12 g.

Triethylborate reacts with the tens of water contained in the pulp to form boric acid according to the following formula: (C2H50) 3B + 3 H2O -> 3 C2H50H + H3BC> 3.

The tg £ values shown in Table 16 have been determined for samples of both paper types following the procedure described in Example 1.

Table 16 Temperature, ° C Comparison of samples containing tg & boron 30 0.00055 0.00105 60 0.00045 0.00085 100 0.00045 0.00090 120 0.00045 0.00120

Example 17 Electrical insulating paper is prepared under laboratory conditions following the procedure described in Example 1 from pure electrical insulating cellulose obtained from softwood tissue papers using desalinated water.

Some of the samples are then finely ground with a 40% boric acid water / alcohol solution (water / alcohol weight ratio 6: 4) in an amount of 0.5 g solution / g absolutely dry paper. The samples are then dried. The boron content is 0.36% by weight, calculated on absolutely dry paper; the paper has a density of 0.7 g / cm 2 and a thickness of 50 μm.

The tg £ values shown in Table 17 are determined for treated and untreated samples following the procedure described in Example 1.

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Table 17 Temperature, ° C Comparison of samples containing tg ^ j of boron 30 0.0006 0.00105 60 0.0005 0.00085 100 0.0005 0.0009 120 0.0005 0.0012

Example 18 Electrical insulating paper is prepared under laboratory conditions following the procedure described in Example 1 from pure electrical insulating cellulose obtained from softwood tissue paper.

Some of the samples are then treated with a 3% boric acid water / alcohol solution (alcohol / water weight ratio 14: 1) at 1 ml of solution / g of absolute dry paper. The boron content of the paper is 0.54% by weight, calculated on absolutely dry paper.

The tgfc, values listed in Table 18 are determined for samples of treated and untreated paper following the procedure described in Example 1. The paper has a density of 0.7 g / cm 3 and a thickness of 50 μm.

Table 18 Temperature, ° C Comparison of samples containing tg & boron 30 0.0005 0.00105 60 0.0004 0.00085 100 0.0004 0.0009 120 0.0004 0.0012

Claims (8)

61 365 21 Cellulose-based electrical insulating agent, characterized in that it contains 0.02 to 1.1% by weight of boron, calculated on the absolute dry matter. A process for preparing a cellulose-based electrical insulating material according to claim 1, which comprises the steps of preparing a cellulose-based pulp, felting the web to form a web, pressing, drying and obtaining a final product, characterized in that boric acid or a boron acid by reacting with water, these reagents being used either separately or in combination and in amounts which guarantee a boron content of 0.02 to 1.1% by weight, based on the absolute dry matter, of the final product. Process according to Claim 2, characterized in that the boric acid is used in the form of its aqueous or aqueous / alcoholic solution. Process according to Claim 2, characterized in that boric anhydride, metabolic acid or triethylborate is used as the boron compound. Process according to Claims 2 and 4, characterized in that the boron compound is used in the form of its alcoholic solution. Process according to one of Claims 2 to 5, characterized in that the compounds used as chemical reagents are added in the pulping process. Process according to one of Claims 2 to 5, characterized in that the compounds selected as chemical reagents are added before the pressing step. Process according to one of Claims 2 to 5, characterized in that the compounds used as chemical reagents are added before the drying step.