US2013841A - Manufacture of fiber articles - Google Patents

Description

Patented Sept. 10, 1935 UNITED s'm'rss MANUFACTURE OF FIBER- ARTICLES George A. Richter, Berlin, N. 11., assignor to Brown Company, Berlin, N. H., a corporation of Maine No Drawing. Application December 10, 1932, Serial No. 646,741

, -Claims.

This invention relates to the manufacture of I or free condition. Otherwise, the hydrated or gelatinized cellulose tends to bind together the pulp fibers of the article into which the pulp is formed and, although enhancing the strength, tear resistance and other physical qualities of the article, detracts from'its absorptive capacity, i. e., from the amount of impregnant which the article takes up and from the speed and uniformity with which the impregnant diffuses into and throughout the article. Moreover, despite the fact that a fiber article may be possessed of good strength, tear resistance and other physical qualities by virtue of the fact that its pulp component has been hydrated or gelatinized, nevertheless, it has been established that it is those articles whose pulp component has been kept in a substantially unhydrated or free condition thatacquire the best physical qualities after they have undergone impregnation with a given impregnant. For instance, water-laid felts made from cellulose .pulp which has been preserved in as free a condition. as possible, may be quite tender and lacking in tensile strangth, tear resistance, and other qualities to begin with, but when they are impregnated with various binders such as asphalt, rubber and the like, they acquire remarkable toughness, body, strength, tear resistance, and other valuable physical properties. Again, they can imbibe quickly and unipaper-making type, e. g., a felt-forming machine.

In other words, the cellulosic stock must undergo mechanical fiber-liberating or pulping action in the presence of water before it can be satisfactorily formed into such articles as water-laid felts. The subjection of rags, rope stock or similar cellulosic material to beater action, however, is inevitably accompanied by the hydration or gela- 6 tinization of the pulp thereby prepared, wherefore, the conditioned pulp or halfstuff rather than being a free one, possesses a comparatively high slowness and accordingly leads to felts of a relatively denseand boardy character. 1

In accordance with the present invention, a

- cellulose pulp or halfstufl' which has been hydratchemicals might be used for the purpose of destroying the hydrated or gelatinized cellulose present in the pulp, I prefer to use alkaline reagents of such a type and under such conditions as will ensure the destruction of the hydrated or gelatinized cellulose without sensibly damaging 25 the pulp fibers. Indeed, by the selection of the appropriate alkaline compound and treating conditions, it is possible to destroy the undesirable hydratedor. gelatinized cellulose while at the same time improving the pulp fibers for formation into water-laid felts or other fiber articles designed to undergo an impregnating treatment. Thus, the hydrated or gelatinized cellulose may be destroyed while enhancing the absorbency and purity of the pulp fibers so that water-laid felts 35 made from the pulp lend themselves better to impregnation not only because they are essentially free from undesirable cellulosic binding or cementing ingredients, but because the pulp fibers themselves are soft and absorbent and so. contlgiglblte such qualities to the felts in which they There are various ways in which the principles of the present invention may be availed of and there are various kinds of cellulos'ic materials to 5 which these principles may be applied to greater or less advantage. Inasmuch as rag stock constitutes a form of cellulose in connection with which the present invention may, so far as I am now aware, be practiced to greatest advantage, 5

I shall describe specifically the conditioning of rag stock in accordance with my invention for the preparation of water-laid felts. Thus a rag stock such as is commonly used as raw material in the manufacture of roofing or floor-covering 55 felts, may-constitute my starting material. If desired, the rags may be cut or shredded while substantially dry into the smallest pieces or cloth fragments economically producible in this way, thereby minimizing the work that need be done by the beater engine and hence the generation of hydrated or gelatinized cellulose during the beating operation. The rags in a normal or reduced condition may then bedelivered into a hollander or beater engine together with suflicient water to ensure circulation and the beater roll may be run in the usual cutting relationship with the bed-plate until the rags have been reduced to a pulp or halfstuff which can be formed into a felt which is satisfactory from the standpoint of uniformity of texture and smoothness of surface. Inasmuch as the resulting pulp or halfstuff will normally be a dilute aqueous pulp suspension, that is, have a fiber content of about 5% .or less, as does the usual beaten stock, it may be desirable to thicken or partially dewater the beaten pulp before it undergoes the action of a chemical which destroys in large measure or practically entirely its hydrated or gelatinized cellulose constituent. To this end, the beaten pulp may be delivered 'to thickeners or other dewateringjnstrumentalities which raise its fiber content to, say, about 10% or greater.

. The pulp thus thickened may then be treated with an alkali under suitable conditions of alkalinity and temperature to effect the desired change in the properties of the pulp.

According to one procedure, the thickened pulp is boiled in dilute caustic soda solution, say one of about 1% to 3% strength under atmospheric or superatmospheric pressure for about one to three hours, whereupon the pulp is washed free of alkaline liquor. The washed pulp is characterized by its high freeness and softness. According to a second procedure,the pulp may be treated at or below room temperature conditions with a caustic soda solution of greater strength, say, one of about 5% to 8% soda concentration,

for about 30 minutes to 2 hours, and then washed.

In such case too, the hydrated cellulose is dissolved or destroyed and the pulp fibers transformed into a soft, absorbent condition. Accord' ing to a third procedure, the pulp may be subjected to the action of a caustic soda solution of mercerizing activity at or below room temperature conditions. At about room temperature, 20 C., a solution of about 18% or greater strength has full mercerizing activity, but inasmuch as such activity exists to some extent in solutions of as low as about 10% strength at room temperature, such latter solutions may also be considered for the purposes of my invention as having mercerizing activity. At lower than room temperature, say at 5 C., or at C., solutions of lower causticity than 10% caustic soda strength are characterized by their ability to mercerize ce1lulose fiber and to destroy hydrated cellulose associated therewith. It is thus possible to employ various conditions of causticity and temperaturebe separated from the pulp as in a countercurrent washer designed to effect washing of the pulp with minimum dilution of the liquor so that the separated liquor may be re-used in the treatwashing the stock free from the liquor, the excess liquor may be separated without dilution as in a centrifuge, thickener, or other separating apparatus. A portion of the liquormay thus be recovered in an undiluted condition and be refreezing point, in which case mercerization may be effected with even more dilute caustic soda so* lution as in such case ice or water crystals separate out from the solution, in consequence of which the unfrozen or liquid portion of the solution becomes more ooncentrated in caustic'soda and functions more effectively as a mercerizing agent. In the event that the treatment of the pulp is performed with a refrigerated or partially frozen mercerizingliquor, it is of decided advantage to separate out the excess refrigerated liquor from the pulp so as to conserve it in a refrigerated as well as undiluted condition for the treatment of other pulp. Should a portion of the mercerstance, the so-called white liquor of a kraft pulp 50' The-alkaline liquor may, if desired, contain suit- 55 izing liquor be frozen, it may be thawed out to permit a separation of as much liquor as possible from the pulp before the pulp is washed.

The alkaline liquor used for the purpose of the present invention may have its alkalinity furnished in whole or in part by alkalies other than caustic soda. For instance, when the treatment of the pulp is performed more particularly at elevated temperature, the liquor may have its 1 alkalinity furnished by sodium sulphide,' sodium carbonate, lime, sodium borate, sodium phosphate, sodium sulphite, or like salts, which undergo 4o hydrolysis in water to yield an alkaline aqueous medium. Some of these salts, like the borates, phosphates, and. sulphites, may require the use of higher treating temperatures to give the same effect as that attainable through the use of caustic soda, sodium sulphide and sodium carbonate at lower temperatures.- It is of course possible to use various combinations of alkalies or salts which give an alkaline aqueous medium. For inmlll, which as is well known,- contains sodium sulphide as well as caustic soda, may in some instances be advantageously employed, either under mercerizing or under non-mercerizing conditions.

able oxidants such as hypochlorite bleach, so-

.dium peroxide, hydrogen peroxide, permanganate, or the like, particularly when it is strongly alkaline or is used under mercerizing conditions.

An oxidant should not, however, be used in an alkaline liquor when a reducing agent like'sodium sulphide is present therein. An alkaline*" liquor containing an oxidant is of 'valuemore particularly in connection with a colored pulp, as it makes possible partial or complete decolorization r of the pulp. The fact is that in some cases it, may be advantageous to treat the rags or other starting material before they undergo beater action or while they are undergoing beater action with oxidants such as chlorine, hypochlorite bleach, permanganate or the like, and then to wash the'pulp before it is treated with an alkaline liquor containing, if desired, additional oxidant.

ment of other pulp. If desired, rather than Insome instances, the rags maybecookedinan alkaline liquor and/or chlorinated or bleached prior to beating. In other instances, the beaten stock may be chlorinated or bleached and then treated with alkaline liquor, as hereinbefore described, to destroy hydrated cellulose present therein; or the beaten stock may be treated with alkaline liquor, as hereinbefore described, to destroy hydrated cellulose present therein and then bleached. The stock is preferably washed between the bleaching and alkaline treatments. It is of course possible to apply the foregoing chemical treatments in other combinations or sequences, but in each case, the principle of destroying hydrated cellulose generated during the beating operation is utilized, thereby increasing the freeness of the pulp or halfstufi after the beating operation. I may, however, state that it is preferable to carry out such alkali treatment as is desired or necessary only after the beating operation so as to refine or purify the pulp at the same time as its hydrated cellulose constituent is being destroyed. The chlorinating or bleaching treatment may, however, advantageously be performed on the raw rags, as such treatment tends to promote subsequent disintegration in the beater engine, whereas an alkali treatment of refinement of the rags, as by cooking in alkaline liquors, works the other way, that is, tends to diminish ease of disintegration in the beater engine. If desired, however, the chlorinating or bleaching treatment maybe performed partly before beating and partly after beating; or it may be performed in entirety after the beating operation, whereupon the rag pulp may then have its hydrated cellulose ingredient destroyed by the action of an alkaline liquor which may simultaneously serve to remove oxycellulose or other undesirable products formed during bleaching and otherwise to refine or purify the pulp. As already indicated, the rags may be preliminarily cut or shredded in a dry way to facilitate subsequent chemical treatment as well as beating.

When pulp or halfstuif containing hydrated or gelatinized cellulose is processed in accordance with any one of the foregoing procedures of my invention, it is rendered so free that when made into felts on the usual felt-making machines, the felts are comparatively tender or lacking in tensile strength and tear resistance and are high- 1y .porous, bibulous, soft and flexible. Notwithstanding the fact that such felts are thus poor in their physical qualities as unimpregnated felts, they can be impregnated quickly and uniformly with various binders such as latex, natural and synthetic resins, cellulose ester solutions, waxes, bitumen, or other'binders of a thermoplastic, water-dispersed or dissolved variety, to form impregnated products of a high binder content and characterized by a highly desirable combination of characteristics. The felt may, for example, be

bituminized to form a sheet which is highly pliant and practically proof against tear, especially the initiation of tear, and hence highly valtear resistance in a-bituminized sheet, for example, since it is quite likely that when a tearing stress is applied to the sheet, the stress rather than becoming localized and giving rise to rupture of the sheet, is not confined to any particular subjected to beater action.

locus, but it is distributed and/or dissipated over a large areaon account of the freedom of the fibers to slip or move past one another.

In making the water-laid felts or foundations of the present invention, it may be of advantage 5 to admix with the free pulp or halfstuff a suitable small proportion of pulp in a partially hydrated or well hydrated condition. The well'hydrated pulp may be prepared by beating rag stock as hereinbefore described or by over-beating such stock or other suitable cellulose fiber in much the same way as is done in connection with the manufacture of glassine papers. The best kinds of hydrated or gelatinized cellulose for blending with the free pulp or halfstuff is-that prepared in aso-called stone-rolled beater from kraft or other wood pulps refined by alkali to higher alpha cel-' lulose content. In connection with pulps which have been rendered free by the use'of caustic soda solutions of mercerizing activity, it is desirable to use a suitable proportion of unmercerized cellulose pulp which may be in a substantially unhydrated, partially hydrated or well hydrated condition. The use of some unmercerized pulp together with the mercerized pulp facilitates the production of uniformly textured felts, serving to offset the clumping or bunching tendencies in mercerized pulp. It is, however, possible to avoid clumpy or non-uniformfelt formation even when the entire felt-making furnish is mercerized by delivering the furnish in an extremely dilute and well mixed condition to the felt-forming machine. The use of hot water as a suspending medium for the mercerized pulp also mitigates the clumping or bunching tendencies of the mercerized fibers. It is to be observed that in accordance with my invention, the beating of rags, rope stock or other similar cellulosic materials, which shall be designated in the appended claims by the generic expression "rag stock" and which must be reduced to fibers of the appropriate size for uniform felting on machinery of the paper-making type, is practiced in water containing little, if any, alkali. While it may be possible to inhibit the generation of hydrated or gelatinized cellulose by using a large amount of alkali in the water in which beating is being effected, nevertheless, the presence of considerable alkali in the beater water would interfere seriously with the rate at which the rags or similar cellulosic material would of friction between the cutting edges of the beater roll and the fibrous material.

I have observed, 60 for example, that it is much more difficult to reduce refined rag stock, for instance, rag stock which has been mercerized, than unrefined rag stock into a pulp or halfstuff even though substantially all of the alkali has been removed from the refined or mercerized rag stock before it is By adopting the practice of the present invention, it is possible to take advantage of the ease with which unrefined rag stock can be reduced to a pulp or halfstuif in the beater engine and then to destroy through the use of a suitable chemical reagent, preferably alkali, the undesirable constituents and more especially the hydrated or gelatinized cellulose present in the resulting pulp or halfstuff.

'without substantial subsequent beating of the fibers forming the resultant pulp with its fibers at essentially the same length as after the beating operation, into a waterlaid felt.

2. A process which comprises bleaching rag stock whose fibers must be reduced in size 'in order to be uniformly feltable, beating the bleached rag stock in the presence of -water to form a hydrated, uniformly feltable 'pulp or halfstuff, thereafter treating the beaten pulp with an alkaline liquor to destroy hydrated cellulose and thereby to increase itsfreeness without sen sibly damaging the pulp fibers, washing the treated pulp, and, without substantial subsequent beating of the fibers, forming the resultant pulp with its fibers at substantially the same length as after the beating operation, into a waterlaid felt.

3. A process which comprises beating ray stock whose fibers must be reduced in size in order to be uniformly feltable, in the presence of water to form a hydrated, uniformly feltable pulp or halfstufi', bleaching the beaten pulp, thereafter treating the bleached pulp with an alkaline liquor to destroy the hydrated cellulose and thereby to increase its freeness without sensibly damaging the pulp fibers, washing the treated pulp, and, without substantial subsequent beating of the fibers, forming the resultant pulp with its fibers at essentially the same length as after the beating operation, into a waterlaid felt.

4. A process of producing a waterlaid felt which 5 comprises beating rag stock, whose fibers must be reduced in size in order to be uniformly feltable, in the presence of water to form a hydrated, substantially uniformly feltable pulp or halfstufi containing the fibers in substantially their final felt-making size, thereafter treating the pulp with an alkaline liquor to destroy hydrated cellulose and thereby to increase .the freeness of the pulp without sensibly damaging the pulp fibers, washing the treated pulp, and, without hydrating 1'5 of the pulp thereafter, forming the resultant freer pulp, with its fibers at essentially the same length as after the beating operation, into a waterlaid felt.

5. A process of producing a waterlaid felt which comprises beating rag stock, whose fibers must be reduced in size in order to be uniformly feltable, in the presence of suflicient water to form-a hydrated, substantially uniformly feltable pulp or halfstuff of a fiber content downwards of about 5% and containing the fibers in substantially their final felt-making size, thickening the hydrated pulp-to a fiber content of at least about 10%, thereafter treating the thickened pulp with an alkaline liquor to destroy hydrated cellulose and thereby to increase the freeness of the pulp without sensibly damaging the pulp fibers, wash- .ing the treated pulp, and, without lwdration of the pulp thereafter, forming the resultant freer pulp, with its fibers at essentially the same length as after the beating operation, into a waterlaid felt. v

GEORGE A. RICHTER.