CA1126500A - Cellulose-based electric insulation material and process for producing thereof - Google Patents

Abstract

Abstract of the Disclosure The present invention relates to a cellulose-based electric insulation material and to a process for producing thereof.
The cellulose-based electric insulation material contains from 0.02 to 1.1 weight % of boron with respect to absolu-tely dry material. The process for preparing said cellu-lose-based electric insulation material resides in that a cellulose-bused paper pulp is prepared and cast for sheet making, the obtained paper sheets being pressed and dried. One of said intermediate products, namoly paper pulp or paper sheets is treated with a chemical reagent which is boric acid or a boron compound forming boric acid when reacting with water or mixtures thereof, said chemical reagents being taken in amounts ensuring the boron content in the end product from 0.02 to 1.1 weight %
with respect to absolutely dry material.

Description

11~65VO

1. Title of the Inventio~
C~L~ULO~ A~ED ELECTRIC I~SUI~TIO~ MATERIAL AND
P~OCESS FOR ~RODUCI~G '~`~R~O~

2. Field of Applicatio~ of the Inve~tion rl'he prese~t i~ve~tion relates to electric i~sulation materials ~nd ~rocesses ~or produci~g thereof, and more particularly to a collulose-b~sed electric insalation material and to a process of produci~g thereo~.
There is a~ ever gI'OWi~g demand for usuch mater1als (electric insul~tion paper and cardboard) i~ spite of -~he fact that more and more electric insulation materials based o~ ~y~the~ic polymers, ceramics, etc find wide application .
I~evertheless, as ~ar as the mai~ dielectric properties and prolon~ed stability i~ a wide ran~e o~ operating tem-peratures are co~cerned, cellulose-based electric insula-tion materials do not meet growing requireme~ts imposed on their quality by the electrical and radio engi~eeri~g i~dustries.
One o~ the main dielectric properties are dielectric power los~e~ i~ insulators op~rating in alter~ati~g curre~t curcuits a3, ~or e~ample, intermediate layer i~ paper c~pacitors or cable wi~di~s. Qualitatively these losses are evaluated by dielec~ric lo~s ta~gent de~oted further as ta~ ~ . The smaller this parameter, the lesser part ,,,. ~ , ~
- 2 - ~

65~0 of electric ~nergy is co~sumed for heat losses ar~d the more reliable and long-lived is an article in which an electric insulation material is used.
Another important property of electric insulation ma-terials is their resistiYit~ measured usually in Ohm.cm.
'~he above-mentioned dielectric properties affect the third importarlt parameter, ~amely, electric stre~gth.
This ef~ect is the stror~er, the less stable are tan and resistivity within the operating temperature range and the more pronounced i8 their change during operation.
Thus, for example, it has been shown that an ancre~se in tan ~ due to cellulose ageing leads to a temperature rise i~side the condenser which, in its tur~, accelerates cellulose ageing and causes a further increase of tan a~d temperature u~til a therm~lbreak-dow~ takes place and the condenser or cable fail to operate. A decrease of resistivity due to a rise irl operating temperature because o~ some other reasons. -

3. Background of the Inve~tio~
~ ow~ i~ the art are some electric insulation materials based o~ cellulose a~d processes for producing thereof aimed at impro~in~ stabilization of tan ~ a~d resistivit~
Enown processe~ comprise the ~tages of paper pulp prepara-tio~, ~heet-maki~g, pressiDg, and dryiDg, A decrease in , .. . . . . . . .
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~651)0 io~ic dielectric los~es is attained by introducing of chemlcal reagents in~o a paper pulp, (for instance, zinc salts (InYentor'~ Certificate of the USS~ ~o.540,003) and magnesium salts (I~ven~or's Certificate of the USSl~
I~o.~00562).
~ owever, a decrease i~ tan ~ o~ electric in~ulation material is observed o~ly at elevated temperatures (80-140~C) and is very small at lowered temperatu~e (30-80C).
Also knoYJn in the art is electric insulation material based on a ~odified cellulo~e and process for preparing thereof.
As ~ modified cellulose use is made of boryla~ed cellulose obtained by .treating cellulo~e with a melt of a boric acid mixture with urea.or borax at 180-260C
with subsequent water - washing o~ an unreacted boric acid (Inve~tor's Certificate~ of the USSR Nos ~03390 and 536275)~ The eleccric insulation material obbained by know~ method has decreased dipole dielectric los~es, ~hereas ionic dielectric lo~es remal~ unchanged. In addi-tion, thi~ method is tech~ologically complicated and does not ~ind practical application.

4. Brief Description of the I~vention It i~ an object of the invention to eliminate the above--cited disadva~tages.
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. _ 4 _ ~;26500 ~ 'he principal object of the inventio~ is, by selecting a new chemical reagent for treating paper pulp or paper sheet, to provide a cellulose-ba~ed electric i~sulation material which will improve the value~ of tan ~ and electric resistivity.
I~he principal ob~ect of the iL~ention is to decrease tan ~ , increase electric resistivity of cel}ulose-ba-sed electric insulation materials and to stabilizea said parameters during operation.
Said principal ob3ect i8 aocomplished by the provision of a cellulose-based electric~insulation material contai- -ni~g ~rom 0.02 to ~.1 weight ~ of boron with respect to absolutely dry material. ~ ~' 'l'he process ~or preparlng a cellulose-based electric insulation mat~rial comprises bhe~staees o~ cellulose-based p~aper pulp prepara~ion, sheet-making,; pressing, ~ ~'",','', '-"~,~reating with~a,chemical reagent, drying, and prepara~
tion of the final material;~ according to the i~ve~tion, as a chemical reagent use ie made or boric acid or a bo- ~ ' ron compound~forming boric acid when reacting with water, aid reagents being used either se~arately or in combi-nation and taken in amounts ensuraug the boron content in the fi~al product of ~rom 0.0~ to ~.1 w~ight % with ~, ~
re~ect to ~b~olu~iy dry material.

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; ~ ~ Z 6 S~ 0 ~ o simplify the treatment of paper pulp or paper sheet with a chemical reage~t, it is expedient to use boric acid in the form of its aqueous or water-alcohol solution. '~he us~ of boric acid i3 the ~orm of water-al-cohol solution makes it possible to obtain paper with practically constant den~ity without co~siderable deforma-~ion, which excludes subse~uent shrinkage of the paper sheets on special eguipme~t, It is pre~erable to use ~s the boron compound formi~g boric acid w~en reacti~g with water, boric a~hydride, meta-boric acid, or trie~hylborate; it iB expedient to use the boron compouna in the form of its alcohol solution for a better treatment o~ paper pulp or paper sheets.
The compounds used as the chemical reagent, namely, boric acid or boron compou~ds forming boric acid when reac~ing with water, said reage~ts bei~g used either se-parately or in combinatio~, can be introduced both at the stage of paper pulp preparation and ~efore the pressing or drying Rtage.

5. Detailed Description of the Invention The propo~ed process i~ accomplished in the ~ollowi~g way.
Paper pulp containing wood or cotton cellulo~e as the mai~ ingredient is prepared by one o~ the method~ ~own i~ the alt.

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~L~;Z6500 Alreaoy at the stage o~ paper pulp preparation, boric acid or such boron compounds as boric anhydride~ metaboric acid, triethylborate, or mixtures thereo~, can be introduced into the pulp. Boric ~cid dissolves in water enteri~g the pap~r pulp composition, whereas boric anhydride, metaboric acid, or triethylborate react with water yielding boric acid solu~ion. The amount OI` boric acid or one of the boron compound~, or the mix~ure thereof lS calculated so ~s to ensure the boro~ co~tent in the final product from 0.02 to 1.~ weight % with respect to absolutely dry material. ` ~
Boric acid and boron compou~s can be used both in :~ -their crystalline state and in the ~orm of solutions.
It is expedient to use boric acid ~8 an aqueous or water-alcohol solution and the boro~ compound as an alcohol solution.
The paper pulp obtained is cast for sheet making by one of co~ventional processes; the sheet prepared is pressed and dried with the use o~ e~uipment commonly employed in paper-making plant~. When electric insulatio~ material with a~ i~creased de~sity is required, the paper sheet is ~ub~ected to calendering.
~; - The introductio~ of borio acid, the boron compound, - or a mixture thereof i~ po~8ible at other Atages of the , ' .

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~', . ' ~ ' . -process which follow after ~aper ~ulp prep~ration andsheet making, nam~ly, before pressing or drying.
The introduction of boric acid or boron compounds into paper pulp or sheet~ decreases not only ionic dielectric losses in electric i~sulation material but dipole dielectric losses as well and stabilize tan S
value of absolutely dry electric i~sulation material within a wide temperature range. Thus, for example, at 60-120C, when the boron content in electric insulation can ~
paper i8 0.27-0.45 weight %, ~ i8 practically constant.
7Jith i~creasing boron content in absolutely dry electric insulation material up to 1.1 weight ~o, tan at different temperatures changes only slightly.
Cellulose-b~sed electric insulation materials obtai-ned by the described proce~s has the followiDg technical parameters:
thickness, mm 5-500 volume mass, g/cm 0.6-1.35 boron content in weight %
with respect to absolu~ely dry material 0.02-1.~
~a~ S of dry electric insulatio~ papér made ~rom electric insulation wood cellulose and having a density of .7 g/cm3:

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~Z65~

-- _ _ _ . . . A . _ _ _ l`empera- For paper prep~red For paper prepared with ture C with the use of the u~e of inaustrial deionized water water with conductivity about 250~ ~/cm and containing about 0.5 mg-equiv/l of sodium salts ~:
0.00040 0.00040 0.00035 o.ooo~5 100 o.ooQ30 0.00040 120 0.000~5 0-00050 . __ tan ~ of dry paper prepared from electric insulation cellulose and havi~g a den~ity of 1.2 g/cm3:

~empera- For papex prepared P~or paper prepared with tuxe & with the use of the u~e of industrial deio~ized Y~ater . water with co~ductivity . about 250 ~ S/cm a~d containing about 0.5 mg-eguiv/l of ~odium ~alts 0.0008 ~.0008 100 0.0008 . 0.0010 1Z0 0.0008 0,0013 9 _ ,..... ......

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~ or a better u~derstanding of the present invention specific examples of realizi~ thereo~` are give~ herein-below by way of illustratio~ which i~ no way limit the scope of the i~vention as it i8 to be u~derstood by ~hose skillad i~ the art.
Example Electric i~sulatio~ paper is prepared u~der labora~o~
co~ditions on the basis of pure electric i~sulation cellu-lose obtained ~rom tissue of cunifers with the use of desalted water.
Paper pulp is prepared by breaking i~ a laboratory stir-rer 10 g of electric insulation cellulose poured over ~ith 0.~ % o~ aqueous solution of boric acid àuring half of a~
hou at 1000 rpm, a~d by grinding the obtai~ed suspensio~
in a la~oratory beater ~or 12 hours to 95Schotter-i~iegler.
~ 'he paper pulp i~ the~ diluted with 1000 ml o~ desal-ted ~iater a~ter which paper is ma~ufactures o~ a laboratory i~sballation by easti~g, pressi~g, a~d dr~i~g of the paper sheets. ~he paper prepared has a density of 0.7 g/cm3, thickness 50 ~ , and co~tai~ 0.02 weight % o~ boron with respect to absolutely dry material.
The same material i8 used ~or prepari~g b~ the same proces~ a~d o~ the same equipment but with the use o~
desalted water control ~amples o~ electric insulation paper, the density and thick~e~s o~ which equal those of the paper conbai~ing boric acid.
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1~;265(~0 The value o~ ta~ ~ is determined ~or the samples of paper o~ both types in the ~ollowing way.
Paper samples are collected into a pack 280-3~0~( thick. The pack is pressed between flat electrodes 46 mm in diameter u~der a pressure o~ 0.2 kg~/cm2 an~ dxied in vacuum under a residual pressure of 5.10-4 mm Hg at 125C for 2 hours. Then the packs are cooled i~ v~uum under the same residual pressure down to experimental tem-perature ~7hich is 30,~,100, or 120C and thermostat~ea at o~e of the~e temperature value. After the electrodes are co~nected to the measuri~g arm of the Schering bridge, the tests are conducted with ~he use o~ i~dustri-al alt~rnating current with a frequency of 50 Hz at a volta~e of 5 V~ . ~he ta~ ~ values are bei~g read directly off the Scheri~g bridge aYter bhe latter has be~ bala~ced.
Table 1 presents the values oY ta~ ~ determi~ed ~or the paper samples obtained accordi~g to the described process.
Table 1 'i'empera- ta~ S of the samples o ture, C co~tai~i~g co~trol boro~
0.00105 0.00105 0.00085 0.00085 100 0 .00085 o .00085 120 0.0010 0.0012 ,............ .
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11265~0 ~xample 2 ~ lectric i~sulatio~ paper is prep~red under laboratory condi~ions o~ the basis of pure electric insulation cellu-lose obtai~d from fissu~ of coni~ers with the use of deionized water.
Paper pulp is prepared b~ breaki~g ~0 g of electric insulation cellulose poured over with 1000 ml of 1,Z~o aqueous solution of boric acid in a la~oratory stirrer for half an hour at 1000 rpm and by grinding the obtained suspe~sion i~ a laborabory beater for 16 hour~ to 96 Schotter-Riegler.
The paper pulp i~ then diluted with 3000 ml of desalted water after which paper is manuYactured on a laboratory i~stallation by c~sti~g, pressi~g, a~d drying of the paper sheets. l'he paper prepared has a density of 0.7 g/cm3t thickness 50~ , and contai~s 0.11 weight % of boron with respect to absolutely dry material.
The co~trol samples o~ electric i~sulatio~ paper are obtained from the same material by the same process and o~
the same equipme~t but with the use of deionized water. The density and thickness of control paper equal those of the paper containin~ boric acid.
The value of tan ~ i~ determined for the samples of paper of both t~pes by following the proceaure described ,~ ~xample 1.
The determi~ed values of tan S are give~ in ~able 2.

, , _ 12 -~Z65~0 Table 2 .
Tempera- ta~ S o~ the samPles __ ture, C co~taini~g control boron _. ... . _ . . . .
0~0009 0.00105 0 .0007 0 .00085 100 0 . 000 7 0 . 00090 120 0.0007 0.0012 Example 3 Electric insulation paper is prepared under laboratory co~ditio~s on the basis o~ pure electric insulation cellu-lose obtained from fissue o~ conifers with the use of deionized water.
Paper pulp is obtai~ed by breaking 10 g of electric insulation cellulose, poured over Yiith 100 ml of Z~
aqueous solutio~ of boric acid a~d 900 ml of deionized water, in a laboratory stirrer ~or half an hour at 1000 rpm.
Dilution and preparatio~ of paper samples as ~ell as preparation of control samples of electric insulation paper not contai~i~g boro~ is performed by following the ljrocedure described in Example 2. The thickness of the salllples is 50 ~ , de~sity 0.7 g/cm3, and boro~
co~te~t 0,2~ weight % with respect to absolutely dry ma-terial.

~'1265VO

'l`he sa~ples o~ the paper of both types are tested by ~ollowing the procedure described in ~xa~lple 1.
The determi~ed values of tan ~ are given i~ ~able 3 ~able 3 .
~empera-ture, C co~tai~ing co~trol boro~
.
0.0006 0.00105 0.000~ 0.00085 ~00 0.0005 0,00090 120 0.0005 0.00~2 .
Example 4 31ectric i~sulation paper i~ prepared u~der l~boratory co~ditions on the basis o~ pure ele ctric i~sulation cellulo-se obtained from tissue o~ co~i~ers with the use of ::
deionozed water~
~ or preparatio~ of the laboratory paper samples use ismade of ~he paper pulp co~taini~g 2~o cellulose and manu~ac-~ured u~der industrial conditions. ~00 g o~ said paper pulp are ground i~ a laboratory breaker to ~6,5 Schovter-Riegler. Th~ ~0 g of boric aci~ are lntroduced into the pulp a~d the volume o~ the mixture i8 brought ul~ to 'lO00 by adding deio~ized water. After stirri~g the diluted paper pulp for three mi~utes, the s~mples _ 14 --of electric insulation paper are prepared by casting, pressing, and drying paper shee~s on a laboratory paper-maki~ installation. qlhe samples are 50 ~ thick, have a density o~ 0.7 g/cm3 and contain 1.1 weight ~o of boron with respect to absolutely dry material.
Control samples of electrla insulation paper not con-taining boron are obtained in a similar way but with the use of deio~ized water onl~. Tan ~ iR measured by follo-wi~g t~e pLocedure described in Example 1.
~ T'he Yalu~s of tan S determined for the paper samples .
are given in T~able 4.
Table 4 , ~empe- tan g of the-:samples ~: :: rature, ~-~- & ~ ; obntaining ~ control , ~ .. . - . ~.. ..
:: ~ ~ 0.00050 ~ 0.00105 ~ ~ 0.00040~ 0.00085 100 ~ -35 ~ -9 120 0,00040 : 0,00120 E~ample 5 hé~capacitor paper manufaotured under industrial condi-tio~s with the use of deionized waber at all stages of the proae~s~ ~aid paper having a maBs of 13 g per ~ , humidity 8~, dénsiity 0.8 g/cm3, i~ wetted;with 8% aqueous solution ,~"",,, ~, , ,, , , :
~ ol bario acid~up eO~ a moi8ture~aonte~t o~ 26~o~

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i~26500 The wetted paper is calendered up to a density of 1.2 g/cm3 and dried. Co~trol samples are prepared from th~ ~ame paper wetted with deio~ized water o~ly.
~ lhe ~amples obtained are subjected to complex testing.
Tan ~ values are determi~ed by ~ollowing the procedure described in ¢xample 1. Other technical palameters show~
below are ~ound by k~ow~ procedures~
The parameters o~ experimental a~d &ontrol samples o~
electric insulation paper aré give~ i~ Table 5.
~able 5 .
~OB Parameter ~ a m p 1 e co~taini~g co~trol boron 1 2 ~ 4 1. ~hick~es~, ~ 10.6 10.4 2. Density, g/cm3 1.20 1.19 ~. ~ength o~ fracture, km 9.6 9~7 4, ~peci~ic conductivity of water extract ~ S/cm at a ~odulu~ o~ 1;50 11 10 5, p~ of water extract 6.8 7.

6. Breakaow~ voltage ~or one paper layer, V 490 490

7. Dielectric los~ tange~t for dry paper at temp~ratu~e, C
30 Q,0012 0.0020 ~0 0.00095 0.00165 ~ 16 -' .... ..

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~ 2 ~ 4 100 0.00095 0.018 120 0.0010 0.0023

8. ReqistiYity of dry paper, Ohm,cm, at 120C 3.9.1016 2.8.~o15

9. Dielectric constant 2.9 ~1

10. Dielectric loss tanæent of the paper impreg~ated with trich-lorophenyl (in small-size capa-citors at tempera~ure, C
0.0021 o.oo35 0.0018 0.0030 100 0.0017 0.00~2 120 0.0020 0.0040

11. ~oron conte~t with respect toabsolutely dry material, weight % 0.27 : :

Ex~mple ~
Ca~acitor paper manufactured under industrial conditio~s with the use at all stages of water with conductivity about ~50 ~ s/cm, containing 0.5 mg-equiY/l o~ ~odium s~lts a~d havi~g a density of 0.76 g/cm3, i~ wetted with 8% aqu~ou~ ~olution of boric acid up to a ~ moisture co~te~ 2~%~ cale~dered to a de~sity o~ 1.2 g/cm3, :~ a~d dried.

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The same paper wetted o~ly with i~u~trial water is treated i~ a similar way a~d used f'or preparin~ control samples.
The samples obtained are sub3ected to complex testing th~ results of which are given in Table 6.
Table 6 .
~os Parameter S a m ~ l e s co~tai~ing co~trol boron .. . .. ~
1 2 . 3 4 , . , , , ~ , , , 1. Thicknes~, ~ 8.2 8.2 2. Density, g/cm3 1.20 . 1,Z0 3. Length of fracture, km 9.7 9.5 4. Specific conductivity of water extract,~ S/cm, at a modulu~ of 1.50 33 26 5. pH o~ water extract 7.3 7.6 6. .Breakdow~ voltage of one paper layer, V 400 400 7. Dielectric lo~s tange~t of dry paper at tempera-ture, C
30 0.0010 0.0023 60 0.0008 0.0019 100 0.0010 0.0032 120 0.00135 0.0068 ; - 18 -65()0 .. _ . ........... . .... ..U . . . ~ . ~

. , . ................. _ . . . . . . . _ .. . . .
8. ~esistivity o~ dry paper at 120, Ohm.cm 6.1.10~5 2.8.1014 9. Diel~ctric consta~t of dry paper 2.7 3.1 10. Dielectric loss tangent of the paper impre~nated with trichlorodiphenyl (i~ small-.
-size capacitors) at tempe-rature,C
0.0021 0.0035 0.0018 0.00~2 100 0.0018 0.0046 120 0.0025 0.0081 11. Boron content, weig~t %
with respect to absolutely dr~ material 0.45 0 .. . ...................... .
Exam~le 7 El0ctric i~sulation paper on the basis of pure electric insulatio~ cellulose obtai~ed ~rom tissue o~ coni~ers with the use of deio~iæed water i~ prepared in the followi~g vJay .

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Paper pulp manufactured under industrial co~ditions with 0.23 weight ~o o~ cel~ulose and ground to 96 Schotter--~iegler i~ taken from a pre6sure box of a paper-making machine. 14 g o~ boric an~ydride are added to 1000 ml of said ~aper pulp and the mixture i~ stirred ~or 3 mi~utes.
Boric an~ydride introduced into the paper pulp reacts ~itn water co~taining i~ the pulp accordi~ to the reaction:

B20~ + 3X20 ~ 2 H3B0~
~ rom the paper pulp treated i~ the described way the sample~ of electric insulation paper are prepared on a labora~ory paper-making machine by casting, pressing, and dL~in~r 0~ paper sheets.
l'he paper obtained a thick~ess of 50 ~ , density 0.7 g/cm3, and boron content 0.9 weight % with respect to absolutely dr7 msterial.
~ Control samples o~ eIectric insulation paper not co~-taining boron are prepared by the same proces~ but without i~troduction o~ boro~ a~hydride a~d on the same equipment.
'g S is determi~ed ~or the prepared samples by fol-lowing the procedure de~cribed i~ example ~; its value are listed i~ r~able 7.

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~z~ss~o Table 7 'i~empera- tan (~ __ o~ the samples ture, C con~aining control boron ~0 0.0005 0.00~05 0.0004 0.0085 100 0.0004 0.00090 ~20 0,0004 0.0012 ~xample 8 Samples of electric insulation paper containi~g 0.9 wei~ht % o~ boron with respect to absolu~ely dry ~aterial and control samples without boron are prepared by follo-~ing the procedure described in ~xàmple 7, as the boron compound use being made o~ metaboric acid.
~ etaboric acid reacts with water cortai~ed i~ the paper pulp with the ~ormation of boric acid according to the scheme:

~2 + ~2 ~~~ ~I3B03 ~ he tan ~ values given i~ Table 8 are de~ermined for the ~amples b~ ~ollowing the procedure described in ~xample 1.
l~able 8 '~empera- tan c~ o~ the samples ture,oa containing boron control .
~0 0~0005 0.00105 0.0004 0.00085 100 0.0004 0.0009 120 0.000~ 0.0012 ~ r,~ ~ _ .
. . . .

11265~0 ~xal~ple 9 ~ lectric insulation pap~r is prepared u~der labora-co~J
conditions o~ the basis of pure electric insulation cellulose obtained from tissue of conifers with the use of deionized water.
~ a~r pulp is prepared b~ breaking 20 g o~ electric insulation cellulose poured over with 1000 ml of deionized water in a laboratory stirrer for half an hour at 1000 rpm and by grinding the obtained suspension in a laboratory breaker ~or 12 hours to 95 Schotter-Riegler.
The paper pulp thus prepared is diluted with 1000 ml o~ deionized water after which paper sheet is obtai~ed on a laboratory installat~on by cas~ing a~d pressing.
Half amou~t of the paper ~heet is treated with the aid of a pulverized by 10 ml of 0.1% a~ueous solution of boric acid, said boric acid being applied evenly to the whole surface area of the paper sheet. After repeated pressing and dr~ing, electric insulation paper is pre-pared with a thickness of 50 mkm, density 0.7 g/cm3, and 0.04 weight % of boron with respect to absolutely dry material.
The remaining half of the paper sheet is dried and u~ed for prepar mg control samples of electric i~sulation paper which doeA not co~tain boron and has the ~ame thick~e~s a~d density.

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The values o~ ta~ ~ ~ive~ in 'l'able ~ are dQter-mi~ed for the samples of paper of both types by followi~g the ~rocedure de~cribed in Example 1.
Table 9 . . , , _ _ Temper~- ta~ ~ of samples ture, ~C containing co~trol boro~
- 30 0.0010 0.0011 0.0008 0~00085 ~00 0.0008 0.0009 120 0.0010 0.0012 Example 10 The samples of electric insulatio~ paper traated ~vith boric acid a~d co~trol samples of electric insulation paper ~ot containi~g boro~ are prepared by following the procedure described in ~ample 9. The samples are 50 mkm thick and have a density o~ 0.7 g/cm3 ~ he paper sheet i8 treated with 6~o aqueous solutio~
of boric acid to produce the samples of electric insula-tio~ paper. The sarnples obtained co~tai~ 0.91 weight %
o~ poro~ with respect to absolutely dry material.
The values o~ ta~ ~ given i~ 'l'able 10 are determi~ed for the ~amples o~ paper ot` both types.

1126S/~0 Table 10 __ ,_ . . , . . . . __ .. ,. . _ _ . . _ _ ~
'i`emperature, tan ~o~ the sam~les .. _ _ ~
C contai~i~g control boro~

~0 0.0004 0.00085 100 o . 00035 o . ooog 120 0.0004 0.0012 .
Example 11 The samples of cable electric insulatio~ paper are prepared under industxial co~ditio~s ~rom pure electric i~sulation cellulose obtained from tissue of conifers with the use of deionized wa~er. In the process o~
sample pxeparatio~ the paper pulp is used also obtained with deio~ized water. The samples are 120 mkm thick and have a density of 0,80 g/cm~.
'l'he obtained samples are im~ersed ~or 5 s~cond6 i~to ~0 aqueous solution of boric acid and aried. The density of dried samples i8 0.7 g/cm3, boron content 1~1 weight %
with respect to absolutely dry material.
The values o~ tan S give~ i~ Table 11 have been determined for the samples of cable paper treated with boric acid accol~ding to t~é invention a~d ~or the samples of the initial cabel paper not containing boro~. ~an S
is determined by follo~Jing the procedure described in ~xample 1.

.

, 1126S~30 Table 11 . . ~ . . _ .. _ . _ Tempera- tan ~ o~ the samples -ture~C containing co~trol boron .
0.0008 0~0018 100 0,0009 0.0025 120 0.0011 0.0049 .
Example 12 Suspension containing 2.0 weight % oX electric insula-~ion cellulose is prepared under industrial conditions with the use of deionized ~ater from pure electric insu-lation cellulose, said cellulose being obtained fro~ the tissue of coni~ers also with the use of deionized ~ater.
After grinding the above-cited suspension to 96Schotter--Xiegler, two portions are withdrawn 150 g each. 100 ml of 0.08% aqueous suspe~sion of active aluminium \6-oxide a~d 50 ml of 28% boric acid solution are succes-sive~r added to one portion whereas to the other portio:~
only 100 ml of 0.08~o aqueous suspe~sion of active alumi-nium y -oxide are added.
rl'he volume of each portion a~ter a~ding the above-ci-ted in~redients is brought to 1000 ml with deionized water, ~tirred for 5 minutes at 1000 rpm and the paper ,..

1126S~O
pulp thus obtained is used for prepari~ the sa~ples of electric insulation paper with 0.55 weight % of boron by casting~ pressing, and dryi~g of paper sheets o~ a laboratory installatio~ as well as for preparin6r co~trol ~amples ~rom paper ~ot containin~ boro~. The thickness of all the samples is 50~ , density 0.7 g/cm3.
~ l'he values of tan S given i~ Table 12 are deter~ined ~or all samples by ~ollowi~g the procedure described in Example 1.
Table 12 'i'empera- tan ~ of the samPles ture,C containi~g control boron .
0.00045 0.0009 100 0.00040 0.0010 120 0.00045 0,00115 :

Example 13 Electric insulatio~ paper is prepared under laboratory conditions from pure electric insulatio~ cellulose ob~ai~ed ~rom ti~sue of conifers with ~he use of deio~ized water.
Paper pulp is prepared by breaki~g 10 6~ of electric i~sulatio~ cellulos~ poured over with 1000 ml of desaltled water i~ a laboratory ~irrer for half an hour at 1000 :rpm a~d by grinding the obtai~ed suspension in a laborator~

.

.. .............. .

.' , . . .
- . -', ~
' l~Z65~0 braaker for 16 hours to 96 ~chotter-Riegler. The paper pulp thus prepared is diluted with 3000 ml of desalteà
water then 75 g o~ triethylborate are ad~ed into the pulp alld the mixture is stirred for 5 mi~utes.
Triet~ylborate reacts with water contai~ed in the pape ~ ulp giving boric aci~ accor~in~ to the reaction:

(C2~5o)3B~ ~ H20 3 C2M50H + ~3B03.
After this the paper pulp i6 used for prepari~g the ~amples of electric insulatio~ paper ~vibh a density of 0.7 g/cm3, thick~ess 50~ , and a boron co~tant of 0.~7 weight % with respect to absolutely dry material.
The control samples of electric insulation paper are prepared from the same material, on the same equipme~t r and by the same process. The co~trol samples are of th~
same thick~ess and density as those containing boric acid.
The values of tan S were determined for the samples of both ~ypes of the paper by ~ollowing the ~rocedure described in Example 1. The values obtained are prese~ted in Table 13.
$~able 13 . . .
TempeOra- , tan ~ o~ the samples ture, C containing control _boron _ _ 0.00050 0.00105 0.00040 0.00085 100 0.00035 0.00090 .

li265~)0 ~xample 1 Electric insul~tion paper ba~ed on pure electric insulation cellulose obtained from tissues of coni~ars with the use of deionized water is prepared in the following way.
Paper pulp prepared under industrial conditions, con-taining 0.2~ weight % of cellulose, and grinding to 96 ~ -Schotter-Riegler is withdrawn from a pressure box of a paper-making machine. A~mixture of boric aci~ and boric anhydrice in amounts 5 and ~.4 g~ respectively is aaded ;
upon stirrin~ to ~OOO ml of Raid paper pulp and stirring --i8 continued for 3 minutes.
he above-clted boric anbydride, being introduced -~ -into the paper pulp, intoracts with water conGainad in it with the formation of boric acid~according to the scheme: ;

The samples of electric insulation paper~are prepared from the~paper pulp treated in the above way on a labora-tory paper-making machine by casting, pressing~and drying paper shoet. ~he ~amples are 50 ~ /thick, has a density o~ 0.7 g~cm3 and boron content 0.27 weight % with respect ~;r~ m" ~: to absolutely~dry~material.
he co~trol 8amples 0f electric insulation paper of he~ame ~hiGkness and densit~ but not containing boron . , , ~ . ~ , . , ~ 28 -~'' ~ , ', .
,. ~ , , .
, ' . . ' ' . . l :' ''.~ '', ' ' ,' ~ "' . . ' ,': ', ,: ' '. ' ' ' '' '' ' '' , ' ' ' ' ' . ' ' ' :

', . : ' ' ' " . ' : ' '.
; :~' ' . .. .
. ' " -~ :

, ' :-:` : ' .. ..

11265~0 are obtained o~ the same equipment by the sam~ process with the exception o~ the stage o~ boric acid and boron anhydride introductlon.
The ~alues of ta~ ~ given in Table 14 are determined for the samples of said papers.
Table ~.4 'l~emper~- tan S of the samples ure, C contaiLing control boron .
0.00070 0.00105 0.00060 0.00085 100 0.00055 - 0.00090 120 0.00055 0.00~20 .
~xample ~5 The samples of electric insulation paper co~taini~g 0.45 weight % of boron with respect to absolu~ely dry material and control samples without boron are prepared b~ followi~g the procedure described in ~xample 14 but with the u~e as the boro~ compound o~ a mixtuxe o~
boric and metaboric acids in amou~ts 7.5 and 3.5 g, res~ectivelY.
Metaboric acid interact~ with water contained in the pa~er pulp with the ~ormation o~ boric acid according ~o the scheme:
. HB02 + H20 ~ H3B03.
' fS.. ' ~ , - Z~ _ : .. ~ - .

' ~ :

.
.
.

~lZ65~0 ll~he values of ta~ ~ presented in rl`able ~5 are determined for all the ~apers by following the procedure described in Example 1.
Table 15 .
Tempe~a- tan_c~ of the samples ture,C containi~g co~trol boron , 0.00050 0.00'105 ~ -0.00040 0.00085 100 0.00040 0.00090 120 0.00040 0.0012 .
Example 16 'l'he samples of electric insulation paper containing 0.35 weight % of boron with respect to absolutely dry material and control sample~ not contai~in~ boro~ have been prepared by followi~g ~he procedure de~cribed i~ ~
~xample 1~ with the use as the boxon compound of a mixture of boric acid and triethylborate in amou~ts 5 and 12 g, respectively.
l'rie~bylborate react~ with water co~tai~ed i~ the paper ~ulp with the ~ormatio~ of boric acid according to the ~cheme:
~C2H50)~B ~ 3 ~2 3 C2H50H ~ H3B03 , ,,,, . ~ , .. .... .. .

, .

' -l~Z6~0 'l'he values o~ pre~sented in '~able 1~ are deter-mined ~or the samples of the paper of both types by followi~g the procedure deæcribea in ~xample 1.
'l'able 16 ~em~era- ton ~ o~ the sarnples ture,C --containing co~trol boron 0~00055 0.00105 0.00045 0.00085 '100 0.00045 0.00090 120 o . 00045 o .00120 _ : .

Example 17 Electric i~sulation p~per is prepared under laboratory co~ditions~y ~ollowi~g the procedure described in ~ample 1 on the basis of pure electric insulation cellulose obtained from tissues of coni~ers with the use of desalted water.
Then the part o~ the samples is u~iformly pulverized with 4% water-alcohol solution of boric acid (weight ratio water: alcohol is 6:4) in amou~t 0.5 g o~ solutio~
per g o~ absolutely dry paper. Then the samples are dried. 'l'he boro~ content is 0.~6 wt.% with re~pect to ~b~olutely dry paper; dcnsity o~ the paper is 0.7 g/cm3, thickness 50~ .

_ 31 _ , .
:` , . , ~
.

~Z65~;)0 ~he value~ o~ ta,~ 0 prese~ted in Table 17 are de-termined for treated and untreated samples by following -:
the procedure described in Example 1.
Table 17 -- , ~empe~a- _ tan ~ of the samPles ture, C co~taining co~trol boron .
0.0006 0.00105 0.0005 0.00085 100 0.0005 0.0009 120 0.0005~ 0.0012 ~xample 18 Electric i~sulation paper is prepared u~der labora-tor7 conditions by following the procedure deacribed in ~xample 1 on the ba~ie of pure electric insulation : cellulo~e obtained from tissue of coni~ers.
. '1'he~:the part o~ the samples is treated with 3%
: ~ ~water-alcohol ~olution of boric acid (weight ratio , alcohol:water is 14:1) in amount 1 ml of the solution per g of absolutely dry paper. The boron conte~t i~
t~ paper i~ 0.54 weight Yo with respect to absolutely dry paper.
~ ` ~ The ~alues o~ tan ~ listed i~ table 18 are determi-: ned ~or the samples of treated and untreated paper by ~ollowi~g the procedure described in Example 1. The den-siby of ~he paper is 0.7 g/cm3, thickness 50 ~ .
~ ., ~ ~r ; ~: ~

.
' '' ' ' ' ' ' ' ' I
' ' ' ~' ' ' .

''. '''' ' '' ' ' ~ ~ , .
, 1~65~0 Table 1 ~

.
Tempera- tan ~,g OI the samples ture, C -- -containing co:~trol boron ~0 0.0005 0 .00'105 ~0 0.0004 0.00085 100 0.0004 0.0039 120 0.0004 0~0012 .

Claims (11)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A cellulose-based electric insulation material selected from paper and cardboard containing from 0.02 to 1.1%
by weight of boron relative to the absolutely dry material obtained by preparing a cellulose-based paper pulp, casting the pulp to produce a paper web, and pressing and drying the resulting web, one of the intermediate products, selected from the paper pulp and the paper web, being treated with at least one chemical reagent selected from boric acid and boron compounds producing boric acid on reaction with water, said reagents being applied separately or in combination and in amounts ensuring a boron con-tent in the end product between 0.02 to 1.1% by weight relative to the absolutely dry material.

2. An electric insulation material as claimed in claim 1, which is produced with an aqueous or water-alcohol solution of boric acid.

3. An electric insulation material as claimed in claim 1, which is produced with a boron compound selected from boric anhydride,metaboric acid and triethyl borate.

4. An electric insulation material as claimed in claim 1 in which the chemical reagent is introduced at the stage of paper pulp preparation.

5. An electric insulation material as claimed in claim 1 which is produced in which the chemical reagent is introduced before the pressing stage.

6. An electric insulation material as claimed in claim 1, in which the chemical reagent is introduced before the drying stage.

7. An electric insulation material as claimed in claim 1, 2 or 3 in which an alcohol solution of the boron compound is applied.

8. An electric insulation material as claimed in claim 4 which an alcohol solution of the boron compound is applied.

9. An electric insulation material as claimed in claim 5 in which an alcohol solution of the boron compound is applied.

10. An electric insulation material as claimed in claim 6, in which an alcohol solution of the boron compound is applied.

11. An electric insulation material as claimed in claim 1, 2 or 3 in a capacitor.