US1924573A - Fibrous web for artificial leathers or the like - Google Patents

Description

M, O, SCHUR Aug. 29, 1933.

FIBROUS WEB FOR ARTIFICIAL LEATHERS OR THE LIKE Filed Jan. 19, 1932 Jaw? 7 744%72 d (12% 4 m1 Patented Aug. 29, 1933 UNITED STATES FIBROUS WEB FOR ARTIFICIAL LEATHERS OR THE LIKE Milton 0. Schur, Berlin, N. 11., assignor to Brown Company, Berlin, N. H., a corporation of Maine Application January 19, 1932. Serial No. 587,543

8 Claims.

This invention relates to fibrous webs of the class sometimes known as waterlaid, on account of the fact that they are deposited from aqueous fiber suspensions on machinery of the papermaking type. While not restricted thereto, the waterlaid webs of the present invention are intended more particularly for use as bases or foundations in the manufacture of artificial leathers.

In manufacturing artificial leather by impregnating waterlaid webs with liquid rubber, as in the form of latex, and then drying the impregnated webs, it is found that if fibers sufliciently long and coarse to yield leathers of high tear resistance and good stitch-holding ability are employed, it is difficult, if not impossible, to obtain a surface which can be finished so as to be free from pit marks, ripples, fiber bunches, or the like, which give the artificial leather a cheap appearance recalling to mind a split skin rather than a first grade natural leather with a smooth grain side like that possessed by calfskin and kidskin. If it be attempted to scour the surface of the artificial leather as with fine emery cloth, it is found that although the scoured surface may feel quite smooth, nevertheless, when the leather finish is applied, pit marks are readily observable to an annoying extent; These pit marks are undoubtedly caused by the breaking away of the bundles of fibers and/or by the poor texture ensuing from the use of coarse, long-fibered pulps in making the web. By long-fibered pulps, I mean those of an average fiber length of about 0.75 mm. or greater and containing a relatively small proportion of fibers of less than, say, 0.50 mm. in length. Such long-fibered pulps are prepared, for example, by cooking spruce wood in the usual way with chemical pulping liquors I of the character of the usual sulphite or kraft liquors. They may also be derived from raw cellulosic materials, such as, hemp, jute, manila, sisal, and cotton. In those instances where the pulp employed as raw material is of an average fiber length of about 0.75 mm. or greater, it is found exceedingly difficult, if not impossible, to realize the web texture necessary for the best grade of artificial leather. As the average fiber length of the pulp used as raw material falls below about 0.75 mm., it is found that the web texture desired for finishing rapidly improves, but at the expense of other important qualities sought in the artificial leather, such as, tear resistance, stitch-holding ability, etc.

In accordance with the present invention I prepare a waterlaid web of interfelted fibers whose surface portion is rich in much shorter fibers than those constituting its main body portion. Indeed, either or both surface portions of the web may so be made, with the shorter fibers gradually diminishing in density toward the interior of the web and being interfelted with the longer fibers constituting the interior. The

surface portion may be composed essentially of the shorter fibers, which can consist of chemi cally pulped birch or other similar short-fibered wood and/or so-called gelatinized pulps whose fiber lengths have been sufilciently reduced by mechanical and/ or chemical action. In some instances, the fibers may be shortened in a dry way and substantially without hydration in a hammer mill, ball mill, or other suitable instrumentality. The main body portion, on the other hand, should be composed essentially of cellulose fiber having at least about the average fiber length of substantially unbeaten chemical wood pulps derived from spruce. When spruce fibers are em- .ployed, the chemically pulped spruce is preferably usedin substantially unbeaten condition so as to secure the benefit of the spruce fiber at their maximum average length, since heating or hydration in a hollander or beater engine causes a reduction in average fiber length. I have found that a web prepared in accordance with the present invention lends itself to conversion into a high grade artificial leather, for, after the web has gone through the'steps of impregnation with latex or other suitable kind of liquid rubber and of drying, it has both the requisite mechanical properties, including tear resistance and stich-holding ability, and a surface which can properly be finished.

With the foregoing and other features and objects in view, the present invention will now be described in greater detail in conjunction with the accompanying drawing, wherein Figure 1 illustrates diagrammatically and conventionally a machine forv preparing the web of the present invention.

Figure 2 represents an enlarged section through an artificial leather whose base is such a web.

The machine shown in Figure 1 is designed to produce a waterlaid web of low compactness and high absorbency, as this kind of web is best suited as a base for artificial leathers which simulate most closely real leathers. Since artificial leathers are ordinarily finished only at one face, the machine illustrated is one which delivers a web only one surface portion of which contains short fibers, the remainder of the web being composed .of comparatively long, coarse fibers. The machine includes an endless wire cloth or screen 1 of the type ordinarily used on a Fourdrinier machine but travelling about a cylinder mold 2 rotating partially submerged in a vat of aqueous pulp suspension. The vat shown is made up of three compartments, namely, a central compartment 3, in which the mold 2 rotates, and two end compartments 4 and 5'separated from the central compartment by a partition 6 and a vertically adjustable gate 7, respectively. he compartment 4 can-be supplied by a pipe with an aqueous suspension of long, coarse pulp fibers of the nature already described and preferably in substantially unbeaten condition. This supension overflows the partition 6 and its fibers deposit progressively as a layer of interfelted structure on the wire cloth as the water of the suspension flows through the cloth and mold periphery into the interior of the mold, whence it leaves through the usual drain pipe 9 entering through the side of the mold into the mold interior. The compartment 5 can be supplied by a pipe 10 with an aqueous suspension of the much shorter pulp fibers, which suspension overflows the gate 7 and deposits its fibers on.

the layer of longer pulp fibers already deposited on the wire cloth. Thereis, of course, more or less commingling of the two kinds of pulp suspension in the compartment 3, but this simply means that there will be no sharp plane of demarcation between the long-fibered-layer on the cloth and the short-fibered layer deposited thereover. The fact is that the fibers of both layers become interfelted as 'a unitary structure, with the shorter fibers gradually diminishing in density toward the under face, i. e., the one lying next to the wire cloth. The wet, waterlaid web or base of fibers is carried out of the vat by the wire cloth over one or more suction boxes 11 which partially dewaterit, whereupon it can be completely dewatered or dried while still supported exteriorly on the wire cloth, as by passing over a large drier drum 12. The dry web can be removed from the wire cloth and accumulated as a roll on a mandrel 13, shown adjacent to the drum 12. The wire can complete its journey from the drier drumto the mold over appropriately located guide rolls 14. The web thus prepared can be impregnated throughout with suitable latex compositions or other liquid rubbers and then dried so as to set the rubber and thereby bond together the fibers into a sheet of artificial leather.

The artificial leather sheet thus produced is preferably scoured as with fine emery cloth at the surface containing the short fibers before the leather finish is applied. The usual so-called of the sheet thickness, whereas the rest of the sheet is composed of spruce pulp fibers. The surface portion can be secured until it is reduced to, say, about one-half its original thickness. Such a product is illustrated in Figure 2, wherein the surface portion a is about oneseventh of the thickness of the remaining portion 12 containing the longer fibers. Ordinarily, it is desired that the sheet be rich in short fibers on only the one face to be finished, as this means that the sheet can contain in larger measure. the long, coarse fibers lending the best mechanical qualities thereto. It is, however, within the purviewtof the present invention to prepare a sheet both of whose facial portions are rich in short fibers. The best relationship between the thickness of the-layer containing the short fibers and the rest of the sheet is subject to variation depending upon the particular fibers used. This relationship can be controlled in forming the web on the machine illustrated in Figure 1 by adjusting the gate 7, which governs the volume of overflow of short fibers into the compartment 3 in which the web is formed. It may atthis point be mentioned that the machine could be operated in a manner to deliver the short fibers directly on the wire and the longer fibers over the layer of shorter fibers. So, too, onemight use machines of the straight Fourdrinier type wherein two streams of pulp suspension are'delivered successively on to the wire from different ponds, one pond containing the long fibers and the other pond the short fibers.

As already indicated, I can use chemical wood pulps of both long-fibered and short-fibered variety in making waterlaid web or base. The longfibered pulp should, however, have at least about the average fiber length of substantially unbeaten chemical wood pulp derived from, spruce or similar long-fibered raw cellulosic material, whereas, the short-fibered pulp should possess no greater than about the average fiber length of chemical wood pulps such as secured from birch, maple, beech, poplar or similar shortfibered raw cellulosic materials. It is preferable to employ pulps of high alpha cellulose content as the raw material in making the web, as they are soft and contribute pliancy and mellowness to the finished artificial leather. For instance, the pulps may be liberated from raw wood in sulphite cooking liquors and the resulting pulps then purified in alkaline liquors, e. g., a caustic soda solution, to an alpha cellulose content of about 93% to 96%. The purified pulp is soft and highly absorbent and so imparts these prop erties to the webs made, therefrom.

What I claim is:

1. A waterlaid web of interfelted cellulose fibers' whose main body portion is composed essentially of chemically pulped spruce and whose surface is composed essentially of chemically pulped birch no and gelatinized cellulose.

2. A waterlaid web of interfelted cellulose fibers whose main body portion is of chemically pulped spruce and whose surface is composed essentially of chemically pulped birch.

3. A waterlaid web of interfelted cellulose fibers whose main body portion is essentially of chemically pulped spruce and whose surface portion is composed essentially of gelatinized celulose.

4. A waterlaid web of cellulose fibers whose interior fibers exist in substantially unbeaten condition but whose surface fibers have been well beaten.

5. A waterlaid web of interfelted cellulose fibers whose interior fibers exist in substantially ungelatinized condition but whose surface fibers have been gelatinized.

'6. In an artificial leather, a waterlaid base of interfelted fibers whose surface portion is composed essentiallyof much shorter fibers thanits main body portion, said base being impregnated 'base being of 'low compactness and high absorbency and carrying rubber distributed therethrough as an added element bonding together artificial leather, a waterlaid base its fibers and imparting leather like qualities thereto.

8. An artificial leather comprising a rubberimpregnated waterlaid base of interfelted fibers whose surface portion is composed essentially of much shorter fibers than its main body portion,

said surface portion being scoured smooth and carrying a leather finish.

MILTON O. SCHUR.

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