US1889643A - Fibrous sheet material, composition therefor, and process of making - Google Patents

Description

H Patented Nov. 29, 1932' GEORGE IE. DAVIS, 01 WALTHAM, MASSlLCHUSETTS FIBROUS SHEET MATERIAL, COMIOSITION THEREFOR, AND PROCESS OF MAKII IG No Drawing.

The subject of this invention is fibrous sheet material, compositions therefor, and a process of making the same. It is more particularly concerned with a sheet made of interfelted fibers on machinery of the papermaking type and serviceable in producing shoe counters or other articleswhere a tough, waterproof sheet having good strength and tear-resisting qualities coupled with flexibil- Q ity or mellowness is desired.

In the manufacture of commercial counterboard, it has been the practice to use Waste fibrous material, such as old ropes, strings, bagging, etc., for not only is such material inexpensive, but it consists largely of strong vegetable fibers, such as manila, hemp and jute, which impart to the resulting sheet the toughness essential for resisting the stresses 2 trouble with such raw-material is that, of

may to some extent be offset by cooking in al-- kaline liquors, such as a solution of sodium carbonate or a lime suspension, which serve as cleansing or purifying agents, and by blending strength-giving fibrous material 'thereinto when the waste raw material is of an inferior nature. These expedients, however, fall short of being completely satisfactory cures for the uncontrollable variability in the scrap or waste fibrous material used.

Because of the low price at which counters must be sold, the manufacturer of counterboard is limited to the use of relatively inexpensive raw materials. On'the other hand, he is obliged to select raw materials and so process'them as to produce a counterboard having the desiderata hereinbefore enumerated. New rag stock is a desirable raw material, but it, alone, is too expensive. Wood pulps, such as kraft and groundwood, are in the desired low-price field, but a counterboard made therefrom is likely to become hard, brittle and otherwise defective under the stresses of use.

I have found that if a substantial proportion of sized or waterproofedleather fibers in substantially unbeaten condition is incorporated into a beaten stock prepaied from celluto which counters are subjected in use. The

Application filed February 19, 1931. Serial No. 517,115.

lose fibers, and more especially wood pulp, and sized as usual, it becomes possible to produce counterboards having enduring flexibility or. mellowness and other qualities desired in counters. Such sized or Waterproofed 5 ly-tanned leather in water is not only accompa'nied by the leaching out of considerable valuable Water-soluble constituent, including water-soluble tanning agent, from the leather, but further by the generation of a distinctly acid condition in the beater water.

This acid condition in the beater Water precludes the application of the usual acid-precipitable sizing agents to the leather fibers. Thus,the addition to the beaten leather stock of rosin size or of aqueous dispersions of sizing agents, such as waxes, asphalt, resins, and rubber, stabilized by soap or other acid-precipitab'le protective colloid, is attended by the precipitation of the sizing agent immediately upon contact with the acid beater water, with the result that the sizing agent, rather than becoming attached to the leather fibers, is liberated in the beater water and is lost along with the water removed during formation into sheets on a paper machine. This'difliculty is overcome, as taught in that application, by finely shredding the leather scrap into a fiuify mass of fibers capable of being suspended in water to form a pulp which needs little, if any, beating for 'interfelting on a paper machine; The usual sizing agents carried in an aqueous vehicle from which they are precipitable by acid substances are .then applied to the dry fibers as a fine spray or mist while the fibers are suspended in a gaseous medium, such as air. The sizing agents are thus precipitated in situ on the acid fibers to form waterproof envelopes or coatings which shield the fibers against loss of appreciable water-soluble constituent when they are subsequently suspended in water to form a pulp. Such sized or waterproofed leather fibers may be used in admixture with adopted in practice with eminently satisfactory results may be substantially as follows. A beater is furnished with 100 parts by weight of kraft pulp and 100 parts of mechanical wood pulp together with sufficient water to produce a stock consistency of about 5%. The stock is beaten hard for about 8 to 12 hours to develop the desired hydration or gelatinization of its fibers. To the beaten stock is then added about 5% of dry size, based on the weight of fiber, for instance rosin size or an aqueous dispersion of paraffin wax stabilized by soap. If desired coloring ingredients may also be added. About 5% of alum or other acid substance is then added to precipitate the sizing and coloring ingredients on the fibers.

The beater roll is then raised; about 100 parts of waterproofed leather fibers prepared as hereinbefore described is then added to the sized, well-beaten, wood pulp; and the engine is operated with the roll raised so as to efi'ect merely a homogeneous mixture of the sized fiber components. The sized leather fibers may be added in a thickened condition, e. g. in the form of a thick mass containing only about 40% water, or in the form of laps of about similar Water content produced on a wet machine, to avoid the addition of much water to the stock in the engine. The sized leather fibers may contain, say about 2% to 2Z0 sizing agent, based on the weight of dry The addition of sized leather fibers is made to the already beaten and sized wood pulp for the reason that the beating of such fibers is unnecessary and undesirable. Were such fibers subjected to severe beating, much of their desirable water-soluble content, including tanning agent, would be extracted therefrom; and they would become markedly shortened in length.

The composite fiber furnish is withdrawn into a stuff chest, pumped to the usual wet machine wherein it is diluted to a consistency of about 1%, and run off'into sheets of the desired caliper or thickness, for instance 3 to 3% irons, which is'the usual range of thickness of counterboard for both mens and womens shoes. (The iron, which is the standard gage of measuring thickness of leather, equals 1/48 of an inch). The sheets are then dried, calendered, cut into counter blanks, and molded into counters by the usual method.

While my invention has been described as applied to the production of counterboard, wherein, so far as I am now aware, it has the greatest utility, the principles thereof may have application to the production of sheet material useful for articles other than counters, or in the production of fiber products other than sheets. The novel fiber furnish which I employ may include Wood pulps, such as soda or sulphite pulp. It may include cellulose fibers differing in origin and in proportion from those given in the example, but it is preferable in the case of counterboard to use a preponderant proportion of cellulose fiber consisting of a mixture of equal parts of kraft pulp and groundwood pulp, as stated in the example. Not only are both these wood pulps virgin materials, but they are quite inexpensive, especially the groundwood pulp. The kraft pulp is advantageous in that it lends strength to the product, especially after it is well beaten. While it is possible to apply a waterproofing agent to the finely shredded leather scrap without an aqueous vehicle, for instance in a liquid condition brought about by melting the size or by dissolving it in suitable organic solvents of a readily volatile nature, it is, from the standpoint of simplicity and low cost, distinctly preferable to work with sizing or waterproofing agents carried by an aqueous vehicle and from which the agent is precipitated by mere contact with the acid leather fibers. If desired, the fixation of the sizing agent to the leather fibers so sized may then be ensured by the addition of a solution of an acid substance such as alum thereto.

What I claim is:

1. A composite fiber furnish comprising waterproofed, previously-tanned leather fiber in substantially unbeaten condition comingled with well-beaten, sized cellulose fiber.

2. A composite fiber furnish comprising waterproofed, previously-tanned leather fiber in substantially unbeaten condition comingled with well-beaten, sized wood pulp.

3. A composite fiber furnish comprising a subordinate proportion of waterproofed, previously-tanned leather fiber in substantially unbeaten condition comingled with a preponderant proportion of well-beaten, sized wood pulp.

4. A composite fiber furnish comprising waterproofed, previously-tanned leather fibers in substantially unbeaten condition comingled with well-beaten sized kraft pulp and mechanical wood pulp. said fiber components being present in substantially equal proportions.

5. An interfelted fiber sheet all of whose fibers are sized and comprising previouslytanned leather fibers in substantially unbeaten condition and associated with substantial- 1y all of their water soluble constituent, including tanning agent, and well-beaten cellulose fibers.

6. A process which comprises beating cellulose fiber in water until it is well-hydrated, sizing the resulting aqueous fiber suspension, and comingling therewith sized,-previousl'ytanned leather fiber while keeping associated with such latter fiber substantially all ofits water-soluble constituent, including tanning agent.

7 A process which comprises beating cellulose fiber in water until it is well-hydrated, sizing the resulting aqueous fiber suspension, comingling therewith sized, previouslytanned leather fiber while keeping associated with such latter fiber substantially all of its water-soluble constituent, including tanning agent, and interfelting the mixture of sized fibers into sheets.

In testimony whereof I have aflixed my signature.

GEORGE F. DAVIS.