US2237235A - Process for making leather sheets - Google Patents

Description

Patented Apr. 1, 1941 TENT QFFICE PROCESS FOR '1 I G LEATHER SHEETS Thornton L. Lynam, New Bediord,

No Drawing. Application November 11, 1936, Serial No. 110,388

6 Claims. (CI; 92-21) My invention'relates generally to products containing leather and to process of making the same, and particularly to products of this type the principal ingredient of which is ground, torn, shredded or comminuted leather, and to a proces of manufacturing these products in part on an ordinary paper making machine. This application is a. continuation in part of my copending application "Leather products and processes of making the same," Serial No. 724,618, filed May 8, 1934.

An important object of my invention is to provide sheet material hi the character indicated having leather as its principal ingredient, the said sheet being highly absorbent and at the same time relatively dense and opaque in comparison to similar sheets of common absorbent paper being manufactured at the present time for imitation leather purposes.

It is also an important object of my invention to provide a process of making products of the character indicated consisting in forming the same on an ordinary paper making machine and subsequently impregnating the products to give the products the desired finish and texture.

It is also an important object of my invention to provide products of the character indicated by the method of manufacture stated, which have the feel, odor, appearance and other characteristics of genuine leather and are capable of being subsequently impregnated with vulcanizable and unvulcanizable binders and body forming materials.

free from lumps, in any suitable proportions on an ordinary paper making machine, whereby to produce an absorbent sheet or body having a smooth surface, a long fibre, and having the odor, appearance, and feel of leather, and adapted to be subsequently impregnated with binding machine is susceptible to treatment with rubber cements (having inflammable solvents) as subsequently described herein.

Absorbent papers mad from alpha, kraft and rope, and of other related substances have heretofore been made for-conversion into imitation leather bases by impregnation with difierent Another important object of my, invention is to provide leather-containing or all-leather sheets of the character indicated above which are not subject to air-size.

It is also an important object of my invention to provide in a process of the character indicated above, steps producing vulcanization of the products subsequent to impregnation with vulcanizable material, the said steps applying eq ly well to products containing only leather'as well as products containing other substances as well.

Other objects and advantages of my invention will be apparent from a. reading of the following description and explanation wherein for purposes of illustration I have set forth preferred embodiments of my invention.

The present invention contemplates the formation of material of the character indicated in sheet form having an all-leather content of tanned ground leather or a combination of paper types of compounds and compositions. These papers were usually coated with cellulose com-l pounds, embossed and sold to the trade as a leather substitute. There is now a great demand for leather substitutes in certain industries, notably 'in the shoe industry, but the presently available substitutes lack certain qualities which are inherent in genuine leather, such as flumness, softness, leather odor, feel, appearance and strength. With the exception of certain rope reinforced stocks, the presently available leather substitutes lack useful strength.

Leather substitutes made from paper are objectionably ununiform and are translucent and when held up to the light disclose a blotchy web.

The products of the present invention in contrast to those alluded to above, have all of the desirable leather qualities, and when held up to the light, no transparency whatever is observable, the formation of the web being very dense. Despite this dense character the products are highly'absorbent, and this highly absorbent yet dense character is due to the type of fibres and treatment used.

It is obvious that the availability of leather substitutes made 01' all-leather fibres or a combination of leather and paper fibres having the advantages and desirable characteristics indicated should create anenormous demand for the same, in view of the present lack of any capable or of any attractive substitute for leather.

The coarse or long fibres used in my process making fibres and tanned ground leather fibres, are obtained by selecting the finest of bark tannages of shoe sole scrap and, by means of a very intricate mechanical device, so shredding or tearing these fibres that they retain a long, soft, fibrous construction of fibre.

The fine or short fibres used in the present invention are obtained by selecting a different grade of leather from that used in obtaining the long fibres, such as that used for upper stock and grinding it through a different type of intricate mechanical device to produce a uniform length of soft, absorbent powdery fibre.

It will be understood that the grinding, shredding or tearing of this leather is no simple matter and must be carried out along definite scientific and mechanical lines with due regard being given to the chemical and physical constitution of these fibres so that they will not be burned or suffer other injury rendering them unsuitable for the purpose intended. The actual fact that the long fibres and short fibres cannot be produced on the same machine proves the delicacy of this operation and the accuracy necessary for proper results.

It is not possible to use ordinary scrap for the purposes of the present invention because such scrap contains large quantities of impurities such as sand and emery dust, and leather dust from a variety of different tannages and different c01- ored leathers, so it is obvious that very special attention must be given to selecting and producing the proper kinds of disintegrated leather to be used if a satisfactory sheet is to be produced.

- Ordinary scrap could be made into a sheet by screening out the undesirable parts but this would produce only an unsatisfactory sheet lacking uniformity, because of the different varieties of tannages used, and the other impurities referred to which it contains. Ordinary scrap consists principally of leather dust secured by sanding or buifing various kinds of leather.

The available physical characteristics and dimensions of the coarse and of the fine leather fibres are as follows:

The results of an analysis of a sample of the fine short fibres were as follows:

Per cent Material passed through a 20 mesh screen;

that is, a wire screen having 20 openings per inch By weight failed to pass a 28 mesh screen Passed the 28 mesh screen but was retained on the 40 mesh 3.4 Passed the 40 mesh screen; retained on the 50 mesh 5.1 Passed the 50 mesh; retained on 80 mesh 7.3 Passed the 80 mesh; retained on 200 mesh- 8.8 Passed through the 200 mesh screen 44.7

The various fractions separated in this way were found to diifer considerably in their appearance under the microscope.

The material which was retained on the 28 mesh screen consisted practically entirely of fibers of fairly uniform diameter, namely, about 0.004 to 0.008 millimeter. These fibers varied somewhat in length, but were mostly 0.8 and 1.6 millimeters in length. There were also in this fraction a number of loose aggregates or bundles of fibers, as well as a number of very fine fibers or fibrils.

The fraction passing the 50 mesh screen and left on the so mesh-screen consisted c efly of clumps of very short fibers of about the same diameter as above, but having an average approximate length between.0.2 and 0.6 millimeter as nearly as'they'could be measured.

The fraction passing the 80 mesh screen and retained on the 100 mesh consisted of fibers together with a considerable proportion of small pieces of skin tissue of widely varying shape and size, but mostly, roughly two or three times longer than the width. the largest diameter averaging between 0.2 and 0.4 millimeter.

The fraction passing through the 200 mesh screen, which constituted almost one-half of the material by weight is chiefly fine dust, which is apparently composed of bits of skin tissue, very short fiber fragments, etc. They are mostly, approximately round or oval in shape. The largest particles may be about 0.1 millimeter in their largest dimension, while the great majority of the particles appear to be between 0.03 and 0.05

- millimeter in their largest diameter.

Turning to the coarse material, it was found impossible to subject this to a screen analysis owing to the readiness with which this material forms into flocks or balls of fiber.-

As far as could be judged this sample consists almost entirely of fibers, although there appears to be a small amount of very short fibers and dust. The length of fibers varies over a very wire range, but apparently most of them are of the order of several millimeters in length. If

the fiber is opened or picked apart by hand it is possible to shake out a number of short fibers,

and we have found some material which will pass even a 200 mesh screen. A determination of the verage fiber length or the distribution of paricle size in this sample would be extremely difilcult.

The two samples differ also in their bulk density, by which we mean the volume occupied by a given weightof the material. The fine sample when loosely packed has a bulk density of 12.3 pounds per. cubic foot, while the coarse sample under the same conditions weighs 6.1 lbs. per cubic foot. It is, therefore, evident that the fine sample is almost exactly twice as dense as the coarse. Other experiments in which the materials were packed under. higher pressure indicated almost exactly the same relation between the two samples.

The dry bark: tanned shoe sole scrap is selected and put into the disintegrating machine which is equipped with a special shredding roll and tearing device which both shreds and tears, leaving the fibres long and silky and of a very uniform length. It is, of course, impossible to disintegrate leather without some useless matter being present so the stodk is first screened to take out the coarse untouched hubs and is then put through a metal shaft consisting of baiiles with a forced draft, which takes out even the finest unshredded particles and leaves the. re-

sultant fibres perfectly clean and ready to be used as a constituent of a leather sheet in accordance with the present invention.

The upper stock leather is selected for proper tannage color andcondition and is then ground 7 in dry form througha special grinding apparatus, which grinds .without burning the tender leather fibres, and is then screened and put through the baiifes for cleaning out the fine nubs. After going-through these-baiiles, it is then ready to be used as a constituent of leather sheet in accordance with the present invention.

Beaten fibres utilized prior to the present inwhere it becomes non-absorbent, so that where it the leather fibres -is only approximately three-quarters of an hour vention are those fibres that are beaten in wet form in a mechanical beater. Veryflittle atten tion is given to what type of leather fibres is used and' they are seldom selected. But. assuming thatthe same stock as used in the present invention was selected for beating purposes it is evident that the fibres must be disintegrated in the wet form before they could be run into a sheet v with or without a mixture of other fibres. The beating of these wet fibres to a point where'they would be suitable to run on a paper making ma chine would, undoubtedly, take about 12 hours if everything wentv well, but in order to thoroughly eliminate the nubs that. resist disintegration it might take 24 hours to eliminate them sufilciei'itly so that a run could be made. Even then this -beaten stock would still contain imperfectly beaten nubs that could cause lumps and specks in the sheet to the extent that it might become necessary to sand the surface to eliminatethe'se nubs. The beaten fibres being wet they could not be screened or put through forced draft to remove nubs and other impurities. Considering the above description of the beater methodand the difilculties surrounding this method including the time required for disintegration by beating and the fact that only an imperfect result is possible by the beaten method, it is evident that a lot of work must be done to secure an imperfect job.

Beating a lot .of leather for 12 hours has a tendency to hydrate the leather to the point is necessary to beat it for 24 hours the result is obvious; so that as a matter of fact, an absorbent sheet cannot be obtained where the fibres are beaten in a mechanical heater for such periods of time.

The properly ground, torn or shredded fibres of the present invention do not require any beating, 40 so that they retain their absorbency and all that is necessary to produce an absorbent sheet from these all-leather fibres orfrom a combination of these leather fibresand paper making fibres is to simply mix the fibres together in a mixer with water. so as to get a uniform distribution of leather fibres throughout the slurry or mix, Jorden, and then to run the sheet on the paper making machine. The time required for mixing with the paper making fibres as against twelve hours upwards in the case of processes involving beating the leather.

The torn, ground, or shredded fibres, of the present invention contain no bothersome or unground nubs, the whole fibre structure-being uniform. Therefore, whether run'as 100%.leather fibres or as a combination of leather fibres and paper making fibres, the sheet is absolutely free from lumps. The beating referred'to above is a mo long drawn out process besides destroying'the absorbency, and is unreliable at best, whereas the previously ground, shredded or torn fibres of the present invention are ready for instant use, andv they have full saturating qualities and produce a very reliable and uniform sheet. Experience in the manufacture of these leather sheets, shows that the best'coarse tanned leather 1 fibres forproducing asheet-isbbtalned by tearing and shredding selected bark tanned shoe sole scrap. In manufacturing a. sheet where the finely ground or coinminuted leather is used, certain types of tanned upper stock are found best.

In both cases, the. shredding, tearing or grinding methods describedabove produce fibres entirely leather fibres are beat-en or disintegrated inthe beater wet and a leather sheet whose dry fibres are previously ground, torn, shredded or comminuted and required no beating or further disintegration to produce the sheet.

Heretofore, no ground,'torn, shredded or comminuted leather has been available for manufacturing. a sheet of the type as disclosed in this application. Not only are the ground, torn, shredded or comminuted leather fibres distinctly advantageous in the manufacture ofa sheet, but the fibres, taken together with the method of manufacture. produce a sheet far superior and without parallel for saturating purposes.

No leather sheet, no matter how well made or by the method of heating it in the beater while wet from the raw stock unground could possibly produce a sheet that would in any way compare with my idea because it would not be capable of being saturated, and without having saturating qualities it is absolutely worthless as a substitute for leather.

It shouldalso be noted that the sheet is made without any type of binding material whatsoever. It contains nothing but the leather fibres themselves, and because of the fact that no binding material of any description is used during the actual manufacture of the sheet itself, it is apparent that there is nothing contained in the sheet at this stage to prevent saturation thereof and that a sheet made in accordance with the -follo "ingrdescribed methods, is quite absorbent and capable of being impregnated with numerous kinds of materials. To put it plainly, this sheet is made without binder and is subsequently impregnated with'binders.

Following the disintegration operation, the tanned leather fibres whether of coarse texture or of finely ground texture are ready to use in the formation of either a leather fibre sheet or in conjunction with paper making fibres.

For instance, if it is desired to' produce a sheet consisting of 100% leather fibres, 500 gallons (4250 1bs.) of water is run into a mixer, to which is added an alkaline solution which has been previously dissolved in some warm water. The object of adding this alkaline solution is to elimihate the natural oils and greases which the leather contains. The alkaline solution having been added to the 500 gallons of water, I then add 600 lbs (dry weight) of the previously ground,

torn, shredded or comminuted tanned leather fibres which have been previously soaked in water while in the bags. As soon as these 600 lbs. (dry weight) of the previously soaked leather fibres are put into the mixer containing the 500 gallons.

of water, and mixed, a test is made to determine the pH reading. This should not exceed 5.5 because the leather paper will ot permit of saturation if it is on or near the pH is over 5.5, an acid is added, for instance, vitriol to bring the pH to between 4.5 and 5.5. About one quartof the above acid in ten quarts of water is required to be added to the above described quantity of leather fibres if the pH should happen to read over 6 to 6.5.

Now having established the pH reading, su'fil-.

cient water is added to-bring this slurry toss,

workable condition-for example, 96 water alkaline side. If the v and ti of tanned leather fibres. The proportion of alkaline solution depends upon the type and condition of the ground, torn, shredded or comminuted leather used, but for general purposes fi; of 1% to 1% of the alkaline solution is used based upon the pounds of water and pounds of leather involved. It has been found under actual manufacturing conditions that an alkaline solution of material known as Alkanol B which is the sodium salt of naphthalene sulphonic acid derivative, can be used to the best advantage. It is a cream colored powder which is readily soluble in warm or hot water. It is very soluble in alcohol and acetone but is'insoluble in most other organic solvents. It is an extremely em-.

cient wetting agent in concentrations as low as 1 6% and as high as 1% and will wet all fibres and surfaces practically instantaneously. Alkanol B has no detergent eifect except as it acts as an emulsifying agent for solvents and detergents. Such alkaline solutions as caustic soda, soda ash or other alkalies can be used but the use of "Alkanol B works out considerably cheaper and more effectiveb'.

While the alkaline solution is necessary for the removal of oils and greases contained in the leather, it has been found that the leather paper must be on the acid side to afford proper absorption. Therefore, it is very important that the pulp or slurry should have the proper pH reading .before it is run on the paper making machine.

The theory of the action of alkaline wetting-out I but furthermore they allow the production of a leather paper that does not subsequently air size. In other words, they permit of the manufacture of a leather product which will retain its absorbent properties over a long period of time which is really the most important point of all.

The leather fibres having been wet and having had the oils and grease removed through the use of the alkaline solution and having been acidified to the proper pH reading of 5.5 and water havin been added so that the slurry contains about 96 of water and il of tanned leather fibres, the slurry is thoroughly and continuously mixed until a homogeneous mass is obtained. This takes approximately a half hour, after which the slurry is pumped through a Jordan or refiner for the specific purpose of refining the fibres so as to obtain a better formation on the paper making machine. making machine through screens to remove impurities such as dirt and strings which may have become mixed with the fibres during the preparation of the same.

The stock then fiows onto the endless wire of the regular paper making machine (whether Fourdrinier or cylinder). Here a large proportion of the water is drained ofi by gravity and suction and the web then formed as it leaves the-endless wire of the regular paper making machine but is not "wet pressed as is a regular paper but allowed to pass directly to the paper making dryers. The elimination of "wet pressing insures a softer, more absorbent, bulkier type ofsheet.

It should be observed that when making a sheet consisting of 100% tanned leather fibres that the heat of the drying cans should not exceed 150 They are .then pumped to the paper of the mixed paper making fibres.

burning the tender leather fibres while they are being dried around the cans. After being dried around the cans, the sheet goes to the calender where it is run through a sumcient number of rolls to soften and smooth up the surface and give it the proper thickness, after which it is slit and wound on a' core in whatever width may be required.

There has been no mention of binder because here no binder is used in the formation of the slurry nor is there any spraying of rubber or use of coagulant during the manufacture of the sheet. The slurry is run exactly like paper with the exceptions noted.

Leather and paper making fibre sheet The manufacture of a sheet consisting of previously ground, torn, shredded or comminuted tanned leather fibres and paper making fibres is quite simple.

Assuming the manufacture of a sheet consisting of 80% paper making fibres (10% Manila rope fibres and 50% wood pulp "sulphate fibres) and 40% previously tannedieather fibres, I proceed as follows: I

Both fibres are cookedseparately, the rope fibres requiring a different treatment from the wood pulp fibres. After being cooked these fibres are mixed together in the proportion of 600 gallons of water and approximating 720 lbs. (dry weight) The or 720 lbs. (dry weight) of. mixed paper making fibres are strongly alkaline. The object of mixing them together isto determine their pH reading and to thoroughly commingle them. These paper making fibres are now washed in clear water until the pH reading is 10 and-the mixer is then stopped.

In the meantime, 40% or 480 lbs. (dry weight) of the previously ground, torn, shredded or come minuted tanned leather fibres which have been previously soaked in water overnight in the bags are prepared as follows:

400 gallons of water are runinto a mixer to which is added 1% of 1% and as high as s of 1% of the alkaline solution (in this instance Alkanol B) which has been previously dissolved in a small amount of warm water. The mixer is then run continuously-for about ten minutes to thor- .oughly mingle the water and the alkaline substance. Now the 480 lbs. (dry weight) of ground,

torn, shredded or comminuted tanned leather oughly mixed as described above, are added to 60 the tanned leather fibres in the mixer and the mixer is run again for a period of approximately twenty minutes to thoroughly amalgamate the paper making fibres with the tanned leather fibres. At this time a test is made to determine the pH reading. If the pH reading is over 5.5, an acid is added, for example, vitriol to bring the pH reading between 4.5 and 5.5. Different amounts of acids are necessary for each batch because leathers difier. However, about one quart of acid in ten quarts of water will sufilce as an illustration. No'w having established the pH readins, sufiicient water is added to bring this pulp or slurry to a workable condition, such as 96%% water and 355% mixed tanned leather and paper degrees Fahrenheit because of the liability of making fibres.

- up the surface and give it the after which it is slit and wound on a core of 'with the exceptions noted.

While the alkaline treatment as applied to the tanned leather fibres and the paper making fibres is necessary to remove oils, greases, lignins and the like, it has been found that this combination of paper making-and tanned leather fibres must be on the acid side to produce proper absorption, therefore, the addition of vitriol above referred to. It isvery important that the pulp or slurry should have the proper pH- reading, namely, approximately from 4.5 to 5.5 in order that it may be run successfully on the paper making machine and have proper absorption qualities.

The alkaline solution acts also as a wetting-- out agent and serves to break down surface tension as well as dissolve the oils, greases, llgnins and the like and permits better penetration of liquids and furthermore, it permit the production 01' a sheet consisting of previously ground, shredded, torn or comminuted leather fibres and paper making fibres which does not subsequently refining the fibres so as to obtain a better formation on the paper making machine, and it is then pumped to the paper making machine through screens acting to remove impurities such as dirt and strings which may have become mixed with the fibres during the preparation of the same.

The stock fiows onto an endless wire of the regular paper making machine (whether Fourdrinier or cylinder). Here a large proportion of the water is drained oil by gravity and suction but the web thus formed as it leaves the "endless wire of the regular paper making machine is not "wet pressed as is ordinary paper but it isallowed to pass directly to the paper making dryers. The elimination of; wet pressing" insures a softer, more absorbent and bulkier type of sheet. It is not necessary to observe the same conditions as to heat as when making a sheet of 100% tanned leather fibres because the paper making fibres do not char as do the tender leather fibres and these paper making fibres act as an insulator and prevent the heat in the cans from burning the tender leather fibres.

After being dried around the cans, the sheet goes to the calender where it is run through a sufiicient number 01' rolls to soften it and smooth proper thickness,

whatever width may be required.

7 It is to be noted that here as in the case of 100% tanned leather fibre sheet no binder'is used in the formation of the slurry and no spraying of rubber or any other binder takes place and that no use of coagulant or fillers attends the manu-' facture of the sheet. It is run exactly like paper It'should also tie noted that .when a sheet is made in accordance with the above processes described herein whether of 100% previously ground tanned leather fibres or of a combination of. preyiously ground. tanned leather fibres and paper making fibres, it can be kept in storage indefinitely and will still be capable of being impregnated as easily and perfectly as when freshly made. The method of making either or both of these sheets provides for the removal and elimination of oils, greases, lignins and other resinous substances whose tendency it is to prevent saturation, but this is not necessary in all cases.

Having succeeded in making the two types of sheets commercially in accordance with the above descriptions, 'each of these sheets is ready for impregnation, neither having been up to this point in any way altered by any impregnation, spraying or containing any binder or filling materials whatsoever.

To make an absorbent sheet is one thing and to impregnate it is another. The above described sheet made without binder is very absorbent and can be made in any desired width of roll or thickness of sheet from .010 to .070 of an inch thick, any thickness of which can be impregnated at any time. The difference between this sheet and sheets covered by prior-processes is that the end achieved here is to make an absorbent sheet from previously ground, torn, shredded, or comminuted unbeaten tanned leather fibres or previously ground, torn, shredded, orcomminuted unbeaten tanned leather fibres in combination with paper making fibres that can be carried in stock as long as required and can be impregnated at any time, due to the fact that it does not air size. When it comes off the machine it is not impreghated but can be impregnated at any time to such paper making fibres as cotton,

meet current needs with any impregnating com-- pound to make different types of products. The non-impregnated material is. not cut up. into sheets. It is carried in rolls of various yardages up to 2000- yards according to thickness, so that when it needs to be impregnated for some particular purpose it can be very effectively handled.

If, however, it is desired to make a leather paper containing other substances besides leather,

in addition to the hemp rope and wood pulp (sulphate) paper making fibres before mentioned,

rayon, rags,

' jute, sisal, long wood, Chinese or Oriental grass,

, is added to them in whatever or asbestos fibres may be employed. These paper making fibres are cooked and otherwise treated to procure maximum absorbency and are either added to the disintegrated leather or the leather proportions areconsidered proper to produce sheets 01' a given character.

Having made the above mentioned sheet free from binder with 40% leather fibres and 60% of paper making fibres, the

done as follows:

impregnation of same is Without regard to the kind of impregnating materials used, the manner of impregnating and drying is substantially as follows:

A saturating machine being provided, a roll 01' all leather or combined leather and paper stock it moves along and the surplus is squeezed out sheeting is placed upon the unwind stand and is then unrolled and immersed in the impregnating material in the tankand the surplus squeezed out between squeeze rolls or it is allowed to float upon the surface of the impregnating material as with squeeze rolls or it is passed between two rollers containing a. puddle of the impregnating material, which not only impregnate but squeeze out -the surplus impregnating material. The sheeting then goes through the drying system containing usually a festoon, straight pass dryer, can dryer, steam coils or combination of same,

in continuously circulated hot air wherein the moisture is entirely dried out of the stock, which has just been impregnated. After it is dry, the impregnated sheeting is rolled into a bundle on an ordinary reeling machine and is then ready for the next step, whether it be combining, finishing, embossing or any handling which may be dictate'd by the purpose for which it is to be used.

The impregnating compound usually consists of some combination of either latex, Vultex," rubber cement, dispersed rubber, or vulcanizable latex with some gum adhesive element such as one or more of those described above. It is the amount of solids which is left in the impregnated products which determine the quality thereof. It is possible to use as little as 2% of rubber and 98% of adhesive substance, and it is possible to obtain sheeting containing as much as 70% of solids.

The amounts of rubber and adhesive substance to be used will vary according to the results desired.

For instance, if a very firm rigid material is desired I impregnate the sheeting with a solution consisting of 14 gallons of rubber and 20 -ard rubber millers, for softeners, and the resultants are then'dissolved with the aid of gasoline, benzol or similar solvents in an agitator until a smooth heavy solution is obtained having the desired rubber content.

The method of impregnating the sheeting with such a rubber impregnating solution is as follows:

The roll of sheeting to be so impregnated is placed on the unwinding frame of the saturating machine'and passedeither through the solution in a tank or floated 'on the surface of the solution until thoroughly saturated and is then squeezed between rolls to remove the surplus solution; or passed through squeeze rolls where a heavy solution is thrown on the top side of the sheeting just before it goes through the rolls.

The passage of the sheeting through the squeeze canizing elements, the excess squeezed out and then passed through a dryer to dry out or evaporate the solvents after which it is passed through another enclosed compartment at slow speed where the temperature may run from 220 to 250 degrees Fahrenheit and there remain in the compartment exposed to the above heat for a period of from one'to two hours. It is advantageous to have a current of air in the compartment and to have the stock pass through in continuous movement. An enclosed festoon is preferred, but other types of dryers can be utilized, for this work because the heats and speeds can be regulated to meet variable conditions.

It is to be understood that reference herein to combination of leather and paper fibres in the form of sheets is not intended to apply to wovenfabrics and the like, but to include only either the be definitely understood that I do not desire to rolls causes the solution to be squeezed into the sheeting and the surplus solution to be squeezed out.

The thus impregnated sheeting is then passed through the festoon dryer or passed through a straight pass or other type of dryer to pass off the vapors. The resultant sheeting is then vulcanized on both sides by exposing both sides of theimpregnated sheet to the action of vapors of sulphur monochloride in a vulcanizing chamber ac- .companied by air circulation and heat operating limit the application of the invention thereto, and any change or changes may be made in the materials and in the manner of assembling the same,

within the spirit of the invention. and the scope of the subjoined claims.

What is claimed is:

1. A method of making an unsized binder-free permanently absorbent leather-containing sheet capable of subsequent impregnation, said method comprising providing a quantity of fibres, a portion of said fibres being short, fine unhydrated leather fibres obtained by dry grinding tanned, scrap leather and another portion of said fibres being long, coarse unhydrated leather fibres obtained by dry shredding tanned scrap leather, then mixing said fibres with water to obtain a uniform'distribution of the fibres in the resulting slurry, then adjusting the pH of the slurry to between 4.5 and 5.5, and then running said slurry on a paper making machine to form a sheet,

2. A method of making an unsized binder-free permanently absorbent leather-containing sheet capable of subsequent impregnation, said method comprising providing a quantity of fibres, a portion of said fibres being short, fine unhydrated leather fibres' obtained by dry' rinding tanned scrap leather and another portion of said fibres being long, coarse unhydrated leather fibres obtained by dry shredding tanned scrap leather and another portion of said fibres bei g P per making fibres, then mixing said fibres with water to obtain a uniform distribution of'the fibres in the resultingslurry, then adjusting the pH of the slurry to between 4.5 and 5.5, and then running said slurry on a paper making machine to form a sheet.

3. A method of making an unsized binder-free permanently absorbent leather-containing sheet capable of subsequent impregnation, said method comprising providing a quantity of fibres, all of said fibres being unhydrated leather fibres obtained by dry grinding tanned scrap leather, then mixing said fibres with water containing an alkaline wetting agent for approximately three-- quarters of an hour assuring definite subsequent absorptiveness while obtaining a uniform distribution of the fibres in the resulting slurry, then consistency, and then running said slurry on a paper making machine to'fonn a sheet.

4. A method of making an imitation leather sheet, said method comprising providing a quantity of fibres, a portion of said fibres being short, fine unhydrated leather fibres obtained by dry grinding tanned scrap leather, another portion of said fibres being long, coarse unhydrated leather fibres obtained by dry shredding tanned scrap leather, then mixing said fibres with water to obtain a uniform distribution of the fibres in the resulting slurry, then adjusting the pH of the slurry to between 4.5 and 5.5, then running the slurry on a paper making machine to form a sheet, and thereafter impregnating said sheet with at least one of a group consisting of dispersed rubber, dispersed rubber with water soluble gum, dispersed rubber with natural resinous emulsions, dispersed rubber with synthetic resinous emulsions produced by the action of ammonia upon resinous bases.

5. A method of making an imitation leather sheet, said method comprising providing a quantity of fibres, a portion of said fibres being short, fine unhydrated leather fibres obtained by dry grinding tanned scrap leather, another portion of said fibres being long, coarse unhydrated.

leather fibres obtained by dry shredding tanned scrap leather, and another portion of said fibres being cooked paper making fibres mixed with water and having a pH approximating 10; mixing the leather fibres with water containing an alkaline wetting agent to obtain a uniform distribution of the leather fibres in the resulting slurry; then to this slurry adding the batch of paper making fibres with mixing to obtain amalgamation of the leather fibres and the paper making fibres; then adjusting the pH of resultant slurry to between 4.5 and 5.5, then diluting the slurry to a paper making consistency, and then running the slurry on a paper making machine to form'a sheet.

6. A method of making an imitation leather sheet, said methodcomprising providing a quantity of fibres, a portion of said fibres being short,

slurry adding the batch of paper making fibres with mixing to obtain amalgamation of the leather fibres and the paper making fibres; then adjusting the pH of the resultant slurry to between 4.5 and 5.5, then diluting the slurry to a paper making consistency, and then running the slurry on a paper making machine to form a sheet, then subsequently impregnating the sheet with rubber.

THORNTON L. LYNAIVL-