US2008141A - Insulating or "fish" paper and method of making - Google Patents

Description

y 6, 1935- J. L. M CLELLAN 2,008,141

INSULATING OR "FISH" PAPER AND METHOD OF MAKING V Filed'March 24, 1931 w y W Mv9/M4M Patented Jul 1c, 1935 2,008,141

UNITED STATES PATENT orrice INSULATING R FISH PAPER AND v METHOD 0]? MAKING James L. McClellan, Littleton, Mass, assignor to Hollingsworth & Vose Company, Boston, Mass, a corporation of Massachusetts Application March 24, 1931, Serial N 0. 524,851 15 Claims. (Cl. 154-34) This invention relates to papers which are escontrol of the paper-making operation, in ways pecially suitable for electrical insulating purposes well known by those skilled in the art) that it preand the like and to a method of'making the sents a relatively open, absorbent structure. same. Thus, for purposes of the present invention, the

5 Papers heretofore made for use in electrical open structure of the sheet is so controlled that 5 insulations have been prepared with respect to subsequent impregnation, even by active reagents the improvement of their electrical resistance or which tend to swell the cellulosic compounds of dielectric strength but such improvements have the paper and thus close the interstices, may be usually been effected at the expense of their effected to the desired degree throughout the physical properties, such as mechanical strength, sheet. Other things being equal, it may be de- 10 toughness, flexibility, etc. Consequently, the insirable to employ a relatively more porous sheet sulating or fish papers, so-called, which are when thick, and a less porous sheet when thin. now available, are either of low dielectric strength In any event, the paper is especially charor of a weak, brittle, mechanical structure. acterized by a tough fibrous structure in which It is therefore an object of the present inventhe original fibers have not been materially 15 tion to provide an electrical insulating paper weakened and compose a considerable proporwhich shall have both a high dielectric or intion of the stock. In some instances, cellulosic sulating value and also a high degree of mechanimaterials, which are subject to parchmentizing,

. cal strength or toughness, and which shall be may be added to provide an additional matrix adapted to resist the strains of folding and shapbond g material for the tough fi s. but 20 ing as well as the wear incident to its subsequent the amounts of such materials should be limited use, without interruption of its structural conin order to avoid loss of strength in the finished tinuity. Other objects will appear from the folproduct. lowing disclosure. I It is further found that the paper sheet thus It is found as a part ofthis invention that obtained may be subjected to a parchmentizing 25 fibers,-typicallythose derived from long fiber a n as y pass the S through a leaves namely the true hemps,.such as manila parchmentizing solution of sulfuric acid, zinc and sisal hemps, in contradistinction to jute'or chloride, or the Ilka-preferably at such tembast fibers, and cotton, as well as straw and the perature and for such time, in connection with like,--are not only strong and tough but may be the weight or thickness of the sheet, as to per- 30 formed into sheets of paper and so treated that mit thorough penetration of the sheet by the they shall preserve substantially the original parchmentizing solutio'n,-the rate and degree strength of the individual fibers and also acquire of the parchmentizing efiect being controlled in a high dielectric strength or resistance to the part by the concentration of the solution used.

passage of the electric current. 1 The treated sheet is then washed free from the 35 The fibers which are thus suitable belong geparchmentizing reagents, dried, and calendered nerically to the musaceee or banana family and to provide the desired thickness, density and fininclude more specifically the fibers which are ish, according to known methods of the 'paper known as manila and sisal hemps. These fibers making art. 40 are available in the form of the freshly pre- 'A typical instance of carrying out the inven- 40 pared material but are more commonly obtained tion will be described with reference to the acas old rope which has been made from these companying drawing, in which fibers. Common hemp and jute, however, which Fig. 1 is a diagrammatic side elevation of v are bast fibers, are not suitable. suitable apparatus therefor; and 425 The process of the present invention includes, Fig. 2 illustrates drying and calendering equip generally, the reduction of the fiber or rope to ment.

short lengths (e. g., two inches. more or less) For example, paper, which has been prepared which-are then beaten out to separate the fibers from sisal or manila hemp fibers, or both, as and may be subjected to an alkaline cooking above described and which is ofarelatively open treatment in a digester and underpressure for structure, is shown in the form of one or more a. sufiicient time to produce a pulp. This pulp rolls,e. g., as indicated at l, 2, 3 and 4, respecmay then be formed into an absorbent sheet of tively. These sheets may also contain additions paper in any of the customary ways for making of more parchmentizable material, if desired, .manila fiber papers. Preferably, however, the such as cotton or other forms of cellulosic masheet is so made (by adjustments of the stock and terial, which has been incorporated with the 5.

sisal or manila fiber in the beater. All four sheets may be composed of sisal or manila fibers, for maximum strength in the finished sheet or one or more sheets may be composed of alpha cellulose or cotton fiber, if desired, for special purposes, such as to provide anjntervening layer or matrix of readily parchmentized cellulose. other numbers and arrangements of such sheets may also be provided for and integrated together, in like manner. r

The sheets are drawn, in parallel, into and through a tank 5 containing a parchmentizing solution,--e. g., a Baum solution ZIiClz in water, which is maintained at about F. The degree of penetration and parchmentizing effect of the solution upon the sheet may also be controlled by the rate at which the sheets travel and the length of the tank. It may be still further regulated by passing each sheet through a separate tank (not shown) having correspondingly prepared and regulated parchmentizing solutions therein to effect the desired parchmentizing action upon each sheet severally.

In passing through the tank (or tanks) 5% the sheets I, 2, 3 and 4, are guided by rolls 6, I, 8, 9 and H, l2, l3, l4,-and upon leaving the parchmentizing solution they are associated in intimate face contact. The composite sheet is then passed over a heated calender roll l5 (preferably heatede. g., to 100 F.) and then between the upper roll l5 and. the lower calender roll I6, which may also be heated, (e. g., to F.) In thus passing between the calender rolls, the

' sheets are integrated into a single sheet of substant-ially uniform, continuous structure. The

thus integrated sheet I! may be passed over spaced guide rolls [8,

19, 2|, while they are freely exposed to the air, thus permitting the parchmentizing action to become more completely effective throughout the sheet. By suitably spacing the rolls I8, l9 and 2|, the length of time, etc., of such aerating treatment" may be adjusted to the desired degree.

The sheet is then. subjected to a thorough washing treatment, which is efiected by passin through a long series of washing tanks 22,- 22, or

other appropriate apparatus. As shown, the sheet is conveyed, alternately over upper rollers 23, which may be connected to a suitable source of power (not shown) to drive the same, and

under lower rollers 24, which are mounted near the bottom of the successive tanks 22 of the series. These rollers are customarily mounted in frames (not shown) which may be raised from and lowered into the tanks, as desired, in order to thread and rethread the paper sheet therethrough. In operation, the tanks are periodically emptied-the contents of the'first tank being withdrawn and the waste water from each succeeding tank being advanced. the last tank of the series being filled with fresh water.

At the end of the series of washing tanks, the washed sheet may be passed over a series of drying drums 26, 21, and thence through calendar rolls 28, if desired, and finally wound up in a roll, 29. which constitutes the finished product.

It is found that the parchmentizing treatment.

while substantially ineffective to soften or weaken the hard fibers of the type indicated, is never- 'lil theless sufficiently reactive upon a portion of the paper stock to provide a. bond between the tough fibers and also to fill the interstices, thus forming a 'relatively dense, impervious sheet. Moreover, this interfibrile parchmentized material or matrix is characterized by high dielectric strength. At the same time, it is relatively soft and flexible, so that it preserves its continuity and bonding adhesion to the fibers in spite of repeated and drastic folding.

If for any reason, the particular fiber emp yed does not contain a sufficient amount of such bonding material or if it is not rendered available by the desired parchmentizing treatment, additions of cellulosic materials which are especially susceptible to the parchmentizing treatment (preferably cotton pulp) may be made advantageously as pointed out above.

In either case, the strong and tough, undegenerated fibers form an interlacing network throughout the paper sheet, imparting both strength and toughness thereto which permit the finished sheet to be sharply bent or folded, without rupture on the stretched side of thefold nor buckling or delamination in the compressed side of the fold. Consequently the continuity and structure of the sheet is preserved and its dielectric strength as well as its mechanical strength remains unimpaired. That the paper has an intrinsically high value in respect of these properties, as compared with "fish paper heretofore produced is indicated by the data obtained in tests upon paper made as above described in which it was found that:

(1) The dielectric strength (volts per mm. of thickness) is more than doubled.

(2) The tearing strength (grams per millimeter of thickness) is approximately doubled; and

(3) The folding strength (number of folds before rupture) is greatly improved.

Not onlyis the paper thusprepared stronger than the unparchmentized sheet, but it is more resistant to abrasion and will not delaminate or separate into the layers of which itis initially composed. If split, by cutting at the edge for example, and torn apart, it not only presents high resistance to such separation but does not tear continuously in this plane. On the contrary the torn section tapers oil to the outer surface'of the sheet, and no evidence of an irregular or delaminated structure is observable.

Another feature of the product is a characteristic increase of tensile strength upon wetting of the sheet with water, which continues with increasing amounts of water up to such degree of saturation as it is capable of.

While the resulting product is thus particularly advantageous for use as an insulating paper, it is clear. that its properties of strength, toughness, etc., and the preservation of these properties in spite of repeated folding or wear, make it especially applicable for many other applications and uses in which its dielectric properties may not be of importance.

Other modifications and adaptations of the method and applications of the product are therefore contemplated and are to-be considered as included by the following claims.

' I claim:

1. Method of treating paper, comprising as a step subjecting paper containing true hemp fibers to a parchmentlzing treatment.

2. Method of making paper, comprising as steps preparing an absorbent sheet of paper from sisal and/or manila hemp fiber and subjecting the same to a parchmentizing treatment.

3. Method of treating paper, comprising as a step subjecting paper containing sisal and/or manila hemp fibers and additional cellulosic material, to a parchmentizing treatment.

' 4. Method of making paper, comprising as steps fibers and characterized-by being parchmentized.

6. Paper, consisting substantially of sisal fibers and characterized by being parchmentized.

7. Paper, consisting substantially of manila fibers and characterized by being parchmentized,

8. Paper, containing true hemp fibers and other cellulosic material, and characterized by being parchmentized.

9. Paper, containing sisal fibers and other cel lulosic material, and characterized by being parchmentized.

10. Paper, containing manila fibers and other cellulosic, material, andcharacterized by being parchmentized.

11. Paper, characterized by containing true hemp fibers and a bonding matrix of parchmentized cellulosic material.

12. Paper, containing true hemp fibers and a layer of cellulosic material, the whole characterized by being parchmentized.

13. Paper, characterized by containing true hemp fibers and a layer of other celluloslc material, said cellulosic layer being parchmentizecl.

14. Paper characterized by high dielectric capacity and flexibility, and containing sisal or manila hemp fibers and a bonding matrix of parchmentized cellulosic material.

15. Paper characterized by high dielectric capacity and flexibility, and containing sisal or' manila hemp fibers and a layer of parchmentized cellulosic material integrated therewith.

JAMES L. Mccnmmn.

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