US1980413A - Insulating materials and method of preparing insulating materials - Google Patents

Description

Nov. 13, 1934- M, c. LEWIS ET AL 1,980,413

INSULATING MATERIALS AND METHOD OF* PREPARNG INSULATING MATERIALS Filed Aug. 24, 1930 2 Sheets-Sheet l Nov. 13, 1934. M. c LEWIS ET AL INSULATING MATERIALS AND METHOD OF PREPARING INSULATING MATERIALS Filed Aug. 24, 1930 2 Sheets-Sheet 2 fil. ////7 GUN w Patented Nov. 13, i934 1,980,413

UNITED STATES PATENT OFFICE INSULATING MATERIALS AND MIETHOD F PREPARING INSULATING MATERIALS Mark C. Lewis, Cranford, N. J., and Alger M.

Lynn, Oak Park, Ill., assignors to Western Electric Company, Incorporated, New York, N. Y., 'a corporation of New York Application August 24, 1929, Serial No. 388,251

24 Claims. (Cl. 8 2) This invention relates generally to insulating ments spun into a strand, such as is known as materials and methods of preparing insulating tussah spun silk. materials and more particularly to iibrous in- In the degumming of silk by one commercial sulating materials, such as silks, and methods of method the usual steps employed are to subject preparing them, Y the silk to a hot solution containing an alkaline 60 The characteristics of many insulating masubstance, such as soap, caustic soda, soda ash, terials vary with the conditions under which sodium phosphate or the potassium compounds they are used and it is sometimes necessary to corresponding to these sodium compounds. then employ an excess of certain insulating materials to wash the thus treated silk with water, then over the amount required for normal conditions with a dilute solution oi sulphuric acid, and 65 in order to provide adequate insulation under finally to wash the silk several more times with unusual conditions. For example, the electrical water. characteristics of the usual commercial insulat- Another commercial method of degumming ing silks, such as are employed to insulate elecspun silk is to treat the silk with hydrochloric n trical conductors, vary noticeably with variations acid to remove soluble impurities, then to treat 70 in humidity, and in order to insure the desired the silk with a degumming agent, such as one of electrical characteristics under all conditions, it those enumerated hereinabove, and finally to is necessary when using such insulating silks to wash the silk a number of times with water.

provide not only the amount oi silk required for Experiments have shown that when silk is deordinary conditions, but also an additional gummed by the usual commercial methods the 76 quantity of the silk which is suiilcient to give silk may contain small quantities of impurities the required characteristics under conditions of introduced in the degumming process which may high humidity. comprise compounds having either acid or alka The economic losses, such as increased costs line reactions, The usual impurities present in 26 of materials, additional labor, loss of time., wear degummed silk are sulphuric acid in the case of 80 on machinery, investments in additional macontinuous filament silk and alkaline compounds chinery; etc., resulting from using such insulating in the case of spun silk. Since all of these mamaterials are readily apparent, and furthermore terials are readily ionizable in water, insulating the electrical characteristics oi conductors insilks which contain them vary in electrical char- 30 sulated with such materials are also likely to be acteristics in accordance with the amount of mois- 85 irregular. ture present therein, and the electrical charac- This invention has for its objects the provision teristics of such insulating silks are likely to be of insulating material having substantially uniseriously affected under conditions oi high huiorm characteristics under varying conditions of midity.

service, and the provision of simple, expeditious, insulating silk embodying the invention, from 90 and economical methods of preparing such mawhich such ionizable substances have been reterials. moved and which in consequence has substan- Insulating materials embodying the invention tially constant electrical characteristics under may be prepared in accordance with the invenvarying conditions oi service, may be produced tion by subjecting a fibrous material, such `as inin accordance with the methods embodying the 95 sulating silk, to a plurality oi' hot washing fluids invention which will now be described. under pressure, at least one oi the fluids includ- The methods embodying the invention may be ing a reagent capable of neutralizing impurities most effectively practiced by means of apparatus in the insulating material, and the remaining of the type o1' the so-called Franklin dyeing fluids comprising water. machine disclosed in the accompanying draw- 100 In the preparation oi' insulating silks by the ings, in which usual methods one of the steps employed is that Fig. 1 is an elevational. view partly broken away of degumming the silk in order to remove the of a. material treating apparatus; gum (serecin) and other extraneous materials Fig. 2 is a plan view thereof, and

which may be present, from the'silk'bre itself. Fig. 3 is a graph showing the electric charac- 105 The degumming proces's varies with the diiierent teristics of treated and untreated insulating silks. kinds of silk treated, and depends upon'whether Referring now to the drawings, in which like the silk treated is a continuous filament silk, such numerals designate like parts throughout the as is known as tussah tram silk, or whether the several views, the numeral 10 designates a cylin- Silk iS made 0f a Dumber 0f discontinuous 111%- drical vessel having a removable cover 11 which 110 Vwhich permit the ow of uid from the chamber 17 into the chamber 18, and-the' partition 15 is provided with a larger central opening 21, which leads into a pipe k23, extending through the chamber19 and through the bottom o! the vessel 10 where it'connects with a pipe 24. The partition 15A is provided with a plurality or openings 26.-26, which are in alignmentnwith corresponding openings in the'partition 14".through which openings hollow, perforated spires 27-27 extend, so as to permit the H ow of a fluid to and from the chambers 17 and 19 without the "fluid owing into the chamber 18.

'I'he cover 11 is provided with a plurality of spring pressed plungers 29-29, one for each of the spindles 27-27 and in alignment with these spindles, lso as to exert pressure upon packages of insulating silk 30-30 wound upon springs 31-31 and positioned upon the spindles 27-27 in the mannerclearly illustrated in Fig. 1. The plungers 29--29 also prevent thefluid which flows through the openings inthe spindles 27 27 from passing out of the top of the channel surrounding the spindles formed by the springs 31-31 and the silk wound thereon, and the plungers thereby cause the liquidto iiow through the silk under pressure so. as to wash the silk.

The bottom of the vessel 10 has an openingl33 therein, at which point a pipe 34 is connected so as to convey fluid to and from the chamber 19.

`The pipes 24 and 34 lead from the vessel 10 to a reversing valve 36 from which pipes 37 and 38 lead to the inlet and outlet ports respectively of a centrifugal pump 40 driven by an electric motor 41. An expansion tank 43 is positioned .abovethe pump 40 and a drain pipe 44 leads from the bottom of the tank 43 to the pipe 37 so as to discharge the contentsof the expansion tank into the-,centrifugal pump 40. The expansion tank 43 is also provided with an overflow pipe 46 leading to a waste discharge system, of any suitable type (not shown), -to prevent the contents of the expansion tank from overflowing into the room'.

lSteam inlet pipes 51 and 52 are provided below the vessel 10 to permit the introductionof steam into the pipes 24 and 34, respectively, and the vessel 10 is provided with pressure gauges 47 and 48 which indicate the pressure within the chambers 17 and 19, respectively. The vessel 10 is also 'provided with an overflow pipe 49 leading into the expansion tank 43, in which pipe is positioned athermometer 50, by means of which the temperature within the chamber 17 may be ascertained and a valve 54 is provided to permit the iiow of uid through the pipe 49 when desired. A drain valve 53 is also provided adjacent the reversing valve 36 to drain the fluid from the apparatus into a Waste discharge system (not shown) whenever it is desirable.

The operationv oi the apparatus is as follows:

The cover 11 is removed from the vessel 10 and a plurality of packages of silk 30-30 are -will enter 'the vessel 10 through the pipe 24 and The pump 40 is then started, whereupon the washing fluid is pumped from the tank 43 through the pipe 38 through the reversing valve 36, through the pipe 34 and into the chamber 19 in the bottom of the vessel 10. The uid passes from the chamber 19 up through the spindles 27--27, out through the packages oi silk 30,-30, down through the spaces between the packages, through the openings 20-20 in the false bottom 14 and through the opening 21 in the false bot- 85 ,tom 15, then `through the pipes 23 and 24-back through the reversing valve 36, through the pipe 37 and to the centrifugal pump 40, whichthen recirculates the fluid through the apparatus. Whenever it is desired Ato change the direction of the flow of the washing uid the reversing valve 36 is actuatedto connect the pipe 24 to theoutlet port of the pump 40 and to connect the pipe 34 to the inlet port of the pump so that the liquid leave the vessel through the pipe y34 in a path which is directly opposite that described hereinabove. When it is desired to heat the iluid being circulated through the apparatus, steam may be introduced into the fluid through the pipes 51 and 52 for that purpose. l l f The above described apparatus may be employed to practice a number of methods embodying the invention, and in order that the invention may be clearly understood one specic method embodying the invention will now be described. Y.

In practicing this method, silk spun into strands is wound upon the springs 31-31, each spring carrying about .75 pound of silk, and the resulting packages `are positioned in the vessel 10l over the'spindl 27-27 in the manner dey scribed hereinbefore. Water at a temperature of about 130 F. is then introduced into the expanson tank 43 until about 1.7 gallons of water 115 per poundof silk has been introduced therein; and the circulating pump 40 is then started, whereupon the water is caused to circulate under pressure through the .silk in thel manner which' has already been described. A quantity of acetic 120 acid equivalent to about, .'13- pound of 100% acetic acid per pound of silk is then introduced into the expansion tank 43 and forms a solution with the water therein, which is capable of neutralizing the alkaline impurities, such as degumming agents, which are present in the silk. Steam is then admitted through the pipes 51 and 52 into the streams of washing uid passing to and from the vessel 10, which rapidly heats the solution to a temperatureof about 200 F. The 130 hot solution is circulated through the silk for about twenty minutes, during whichttlme the direction of ow of the iiuid is changed twice by v.

actuating the reversing valve 36; thenzthe-upump f Y 40 is stopped and the washing iluid' is drained 135 from the apparatus through the drainfvalye/SS.'

Water at a temperature of about v F, is thenagain introduced into the expansion-tank 40.; `and the above steps, except the addition v of, acetic l acid, are repeated. The silk is washed a'- num1140 ber of times with hot water under pressure-` the manner just described, in order to washthesilk free of ionizable-materials, the numl'aeijv oi?v washes depending upon the amount of impuri-A ties in the silk. Experiments have shown that a process including one washing with a hot acetic 1 1 acid solution followed by four Vwashingsfvvith hot water gives very satisfactory results.v

After the silk has been'subjected tog-the i1$ribed washing steps, it is then dredfbyiirst {15(1- centrifuging it and then heating it in a hot air drier at a temperature sufllciently high to evaporate the water retained by the silk and to volatilize the acetic acid retained therein. Any acetic acid which remains on the silk after the -drying operation gradually volatilizes until substantially all of the acetic acid disappears, and in' any event the quantity of acetc acid retained on the silk is so small and the acetic acid is such a weakly ionizable substance that it does not materially alter the electrical characteristics of the silk under conditions of high humidity.

It is, of course, to be understood that the method just described is merely an example of numerous methods embodying the invention which may be employed and various modications may be made without departing from the spirit'and scope of the invention. For example, when the silk has been degummed with soap it is sometimes desirable to first subject the slk to hot water under pressure, then to employ a hot washing uid containing acetic acid, and nally to 'wash the silk several times with hot jwater. Furthermore, the number of washing steps employing either` acetic acid or water may be varied in accordance with the amount of impurities present in thefsilk.4 If the silk contains a large amount of alkaline materials, the step "of washing the .silk with yan acetic acid solution may be ref-'- heated; or if the silk contains only asmall quantity of' impurities, the acetic acid washing stepv may be omitted entirely; or one acetic acid wash maybe employed and followed by less than four water washes. The quantity of acetic used in any one washing step may also be variedinaccordance with the amount of alkaline materials in the'silk-being treated.

Nor-is it necessary to use only acetic acid as a reagent for neutralizing the alkaline impurities in the silk, for any 'weakly ionizable acid or mixture of acids may be employed Ior'this purpose. The volatile fatty acids are preferred, however, because they do not ionize strongly and because they either decompose or vaporize during the drying of the silk, or on standing after the silk is d'ied, without leaving residues which act as electrical conductors. Among the `acids whichl may be used either alone or in combinations are formic, acetic, propionic, lactic, oxalic, tartaric, citric, carbonio and malic.

It is, of course, not essential in all cases to employ an 'acid solution to neutralize impuritiesA in the silk, for if the silk should happen to contain impurities having acid reactions, an alkaline neutralizing agent, such as sodium phosphate, or other weakly ionizable alkaline material, or ammonium` hydroxide, may be employed for this purpose.

The methods embodying the invention are also not limited to their use with the particular type o! apparatus described hereinabove, for other apparatus may be used with comparable results. For instance, instead of employing a Franklin dyeing machine to practice the invention, the apparatus known as the "Theis dyeing machine and "Obermaier ldyeing machine, which work on a similar principle, may be employed.

As examples of the improvements which result from practicing the methods embodying the invention, strands of No. 62 spun silk three quarters of an-inch in length, which have been treated in accordance with the invention, have a direct curf rent resistance of from 2000 to 3000 kilomegohms at a relative humidity of 87.5% and a temperature commercial silk have a direct current resistance of from 5 to '7 kilomegohms under similar conditions. Silk which has been treated with water alone in accordance with the invention has a resistance of about 1000 kilomegohms.

The curves' shown in Fig. 3 of the drawing also clearly illustrate the improvements which result tained by employing a conductor 'which was identical in every respect with that employed in obtaining curve A, except that spun silk treated in accordance with the invention was employed to insulate the conductor. Curve D shows them. C. conductance of the insulation in milimhos of a conductor at 1000 cyclesV per second when insulated with commercial spun silk, while curve E shows the A. C. conductance of the insulation f of alike conductor insulated with spun silk which vention.

The marked differences in the characteristics ot'silk which has been treated in accordance with thev invention and silk which has not been so treated are readily apparent from these curves. Itmayk be seen that as the relative humidity increases the' A. C. capacity of a conductor insulated with commercial spun silk increases rapidly, while the A. C. capacity of a similar conductor insulated with spun silk which has been treated in accordance with the invention rises only a comparatively small amount and remains substantially constant. Similarly the A. C. conductance of the insulation of a conductor insulated with commercial silk increases materially has been treated by methods embodying the inas the relative humidity increases, but the A. C.

conductance of a similar'conductor insulated with treated silk remains substantially unchanged.

The comparative stability of the'v electrical characteristics of insulating silk which has been produced in accordance with the invention renders such silk especially useful in insulating conductors for use in various types of electrical apparatus, particularly telephone apparatus. Since the currents employed in telephone circuits are alternative currents of audiofrequencies, and as the quality of transmission in these circuits is inversely proportional to the A. C. conductance between adjacent insulated conductors, it may be readily seen that transmisson of good quality may be obtained by employing a relatively small quantity of insulating silk embodying the invention; whereas, if ordinary commercial silk is employed a comparatively large quantity of the silk must be used in order to obtain comparable results.

For example, it has been found that. due to the improved properties of insulating silk embodying the invention, one type of insulated conductor employed in telephone apparatus may be insulated with two servings of the improved silk, Whereas three servings are usually required when the ordinary commercal silk is used, and in addition the conductors possess satisfactory insulating properties with equal or better transmission characteristics than heretofore obtained. In

vsome cases', it is possible to substitute silk mixed with cheaper materials, such as cotton, for pure nil) , which comprises repeatedly subjecting degummed silk to washing baths under pressure to remove ionizable impurities from the silk, at least one of the baths including a reagent capable of neutralizing impurities in the silk and the remaining baths comprising water.

2; The method of preparing insulating silk, which comprises repeatedly subjecting degummed silkyto circulating washing baths under pressure Vto remove ionizable impurities from the silk, at

least one ofwhich baths includes a volatile reagent capable of neutralizing impurities in the silk and the remaining baths consisting of water.

3. The method of improving degummed insulating silk which comprises repeatedly washing the silk under pressure with a plurality of circulating washing baths toremove ionizable irnpurities from the silk, at least one'of which baths contains a fatty organic acid and the remaining baths consisting of water.

'4. The method of improving degammed insulating silk having an alkaline reaction, which comprises in circulating a dilute solution of' acetic acid through a mass of silk under pressure, and then circulating water under pressure through the silk until substantially all ionizable materials are removed from the silk.

5. The method of Y preparing insulating silk, which consists in washing degummed silk under pressure with a plurality of circulating washing baths to remove the ionizable materials from the silk, at least one of which baths other than the last one includes a reagent capable of neutralizing impurities in the silk and the' remaining baths consisting of water, and drying the silk to remove substantially all of the washing iiuids therefrom.

6. As a new article of manufacture, electrical insulating material comprising-silk which is substantially free from ionizable impurities.

J7. The method of preparing insulating silk, which comprises repeatedly washing degummed silk under pressure with a plurality of circulating washing baths to remove ionizable impurities from the silk, at least one of which baths contains a weakly ionizable reagent capable oi.'V neutralizing impurities in the silk and the remaining baths ,lating silk, which comprises circulating through f,

a mass of the silk a reagent capable of neutralizing reagents employed in producing the degummed silk, and then circulating Water under pressure through the silk until substantially all ionizable substances are removed from the silk.

9. As a new article of manufacture, insulating silkwhich isA substantially free from ionizable impurities and which has substantially constant electrical characteristics under varying conditions of service. 10. As a new article of manufacture, insulating silk Vcharacterized by being substantially free from ionizable impurities and by having a direct current resistance ofA at least 1000 kilomegohms per length of three-quarters of an inch at ST1/2% relative humidity and F.

11. The process of improving commercial degummed insulating silk, which consists in cirprises circulating a sodium phosphate solution culating a volatile reagent capable of neutralizing impurities in theA silk under pressure through a mass of the silk, washing the silk with water to' remove ionizable impurities therefrom, and heating the silk to remove the water and any remaining neutralizing reagent from the silk. Y

12. The process of improving commercial spun silk, which consists in circulating a hot solution of acetic acid through a mass ofthe silk under pressure, circulating water under pressure through the silk to remove ionizable impurities therefrom, and heating the silk to remove Vthe water and any remaining acid from the silk.

13. The method of improving commercial degummed tram silk. which comprises circulating an ammonia solution through a massof the silk, and Washing the silk with water to remove the ionizable materials therefrom. x

14 The method of improving commercial degummed tram silk, which consists in circulating an ammonia solution through a mass of the silk, washing the silk with water to remove the ionizable materials therefrom, and heating the silk to remove the water and any remaining ammonia from the silk.

15. The method of improving commercial degummed insulating silk, which comprises circulating a neutralizing solution through a mass of the silk, and circulatingwater through the silk to remove the ionizable materialstherefrom.

16. The method of improving degummed insulating silk' having an alkaline reaction, which .comprises circulating a solution of a volatile acid through a mass of the silk, and washing the siik with water to remove the ionizable materials'no therefrom.l

1'7. The method of improving degummed insulating silk having an alkaline reaction, which comprises circulating a solution of a weakly ionizable acid through a mass of the silk, and washing the silk with water to remove the ionizable materials therefrom.

18. The method of improving degummed insulating silk having an alkaline reaction, which comprises circulating through a mass of the silk a solution of a compound falling within the empiricalv class of foi-mic, acetic, propionic, lactic, oxalic, tartaric, citric, carbonic and malic acids, and washing the silk with water to remove the ionizable materials therefrom.

19. The method of improving degummedinsulating silk having an acid reaction, which. comprises circulating a solution of a volatile basic reagent through a mass of the silk, and washing the silk with water to remove the ionizable materials therefrom. v

20. The method of improving degummed insulating silk having an acid reaction, which comprises circulating a solution of a weakly ionizable basic reagent through a mass of the silk, and

washingthe silk with water to remove the ionizable materials therefrom.

21. The method of improving degummed insulating silk having an acid reaction, which comthrough a mass of the silk, and washing the silk with water to remove the ionizable materials therefrom.

22. The method of improvingtne. insulating lating silk having an alkaline reaction which comprises neutralizing the free alkali in the silk with a volatile organic acid and then circulating water through the silk until substantially all the products of the neutralizing reaction and other ionizable materials are removed from the silk.

MARK C. LEWIS. ALGER M. LYNN.

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