US2033485A - Waterlaid felt - Google Patents

Description

Patented Mar. 10, 1936' PATENT OFFICE WATEBLAID FELT I Milton 0. Sohur and Walter L. Hearn, Berlin,

N. 11., assignors to Brown Company, Berlin, N. H., a corporation of Maine No Drawing. Application November 19, 1932,

Serial No. 643,544

2 Claims.

This invention relates to porous and absorptive waterlaid felts such as are designed to undergo impregnation with binders of various kinds.

We have found that in making waterlaid felts, it is highly advantageous to blend 2. refined, preliberated pulp, preferably refined wood pulp, and rag pulp. Such a blend is advantageous, not only by reason of the fact that the rag pulp may be prepared directly from waste rags, which are far less expensive than refined wood pulp, but also by reason of the fact that the felts made from such a blend are, as will hereinafter appear in greater detail, of improved characteristics. In making impregnated products, e. g., bituminized sheets or ielts, from such a blend, it is distinctly preferable that the refined wood pulp be maintained in substantially unhydrated condition, whereas the rags may be reduced to a beaten or hydrated halfstufi by beating as ordinarily in a hollander or heater engine. The blend made up of substantially unhydrated but refined wood pulp and hydrated but unrefined rag pulp, may be formed into a waterlaid felt. The felt may be impregnated with various binders, e. g., latex, natural or synthetic resins, cellulose ester solutions, waxes, bitumens, or other binders of a thermoplastic, water-dispersed, or dissolved Va riety. For instance, the felt may be bituminized to form a product possessed of improved utility in the roofing and flooring industries.

While not limited thereto, we shall hereinafter deal with our invention as applied to the manufacture of bitumlnized sheets of a character highly prized in. the roofing and flooring in dustries. In these industries, waste rags have heretofore been employed as the raw material for making the felt base, which is bituminized and put through the finishing operations. In the roofing industry, the bituminized sheet is surfaced with talc, sand, mica, or the like, when roll roofing is in view, or is coated with blown asphalt and then surfaced with crushed slate or similar granular material when roofing shingles are in view. In the flooring industry, the bituminized sheet is put through a printing or painting machine, which applies an ornamental coating to the sheet. In both these industries, the finished article has heretofore been easy-tearing and of poor pliancy or flexibility.

It has been found that when the felt base is made from refined wood pulp, and more especially refined wood pulp in a substantially unhydrated condition, the bituminized felt is vastly improved in its tear resistance and in other respects. We have discovered that, notwithstanding the inferiority of a rag base felt, it is possible to realize a felt which represents an improvement over the refined wood pulp base felt by using both rag pulp and refined wood pulp as the felt-making fibrous materials. In other words, we have found that a blend or mixture of the two fibrous materials gives better results than does either fibrous material alone. This holds true especially when the refined wood pulp is used in amount preponderating over the rag pulp and is kept from becoming substantially hydrated before the felt-making operation, whereas, on the other hand, the rag pulp is hydrated to the extent which necessarily ensues from its having been produced by the beating and reduction of rags in water in the ordinary hollander or beater engine.

A specific example of procedure falling within the purview of our invention and applicable in the manufacture of roofing and flooring materials may be practised substantially as follows. The usual rags currently employed in making roofing and flooring felts may be used in amount up to about 50% by weight of the fibrous furnish prepared in the beater engine. Therags may contain some wool fiber in addition to the cotton. The usual hollander may be charged with the rags and suflicicnt water to ensure circulation, whereupon beating of the rags may be carried on until the fibers have been reduced to the desired extent and an aqueous pulp suspension or rag halfstuff fit for felt-making has been produced. The beater roll may then be raised from the bedplate and the refined wood pulp may then be added to the rag halfstufi and the engine kept running until a physically homogeneous mixture of the two kinds of fiber has been effected. The refined wood pulp is hence kept in a substantially unhydrated state by reason of the fact that the beater roll is operated merely to effect a mixing of such pulp with the previously beaten rags, and further by reason of the fact that refined wood pulp is comparatively difficultly hydratable. The mixed fiber furnish is delivered from the beater engine into the stock chest, wherein it is diluted to the appropriate consistency for delivery to the felt-making machine. The diluted pulp is further thinned with large volumes of water, most of which is white water recirculated from the forming or wet end of the felt machine. It is highly advantageous that the pulp be fed onto the felt-forming screen or wire cloth in a highly diluted state, in order that good formation shall be obtained. In the case of a cylinder mould, for

example, it is preferred to operate at consistencies 55 lid below, say, about 0.35%, in order to avoid lumpy definite range, depending upon whether the felt is to be bituminized for roofing or for flooring purposes.

In connection with roofing, where it is desired that the felt absorb a maximum amount of asphalt, the compactness may be comparatively low,so much so that the felt will be able to absorb up to about 250% to 300% or more of its own dry weight of asphalt. In such case, we may prepare felts having a compactness ranging from about to about 45. When felts for fiooring purposes are in view, the compactness should be higher, in order that the bituminized felts may have the desired mechanical properties, especially resistance to indentation or distortion, without being so dense that difiiculties will be encountered, especially during impregnation. For fiooring purposes, therefore, our felts' are preferably prepared so as to have a compactness ranging from about 50 to 70. By compactness, we mean the ratio of the basis weight of the felt in terms of pounds per 2880 square feet, divided by the felt thickness expressed in hundreds of an inch.

The felts prepared as hereinbefore described may be put through a bituminizing operation, such as is currently practised in the roofingand fiooring industries. The bituminized roofing felt may, as already indicated, contain up to about 250% to 300%, or more, of its own dry weight of asphalt, whereas the bituminized flooring felt may contain much less asphalt, say only about 100% to 175%, more or less, of its own dry weight of asphalt. The bituminized roofing felt may then be finished in the usual manner, depending upon whether roll roofing or roofing shingles are in view. So, too, the bituminized flooring felt may be ornamentally finished in accordance with the conventional finishing steps employed in fiooring manufacture.

There. are various important advantages in using rag pulp along with refined, preliberated, substantially unhydrated cellulose pulp in the fiber furnish employed for making felts to be bituminized as hereinbefore described. Aside from the fact that unrefined rags constitute an inexpensive raw material, being far less expensive than alkali-refined, chemically preliberated wood pulp, the rag halfstuif prepared in the beater engine enhances the qualities of the raw or un impregnated felt without detracting from the qualities of the bituminized felt. The felt of the present invention in its raw or unimpregnated state is superior to a felt made substantially entirely from refined and substantially unhydrated wood pulp. Thus, in such important respects as tensile strength, tear resistance, and flexibility, the raw or unimpregnated felt of the present invention constitutes a definitely superior article. In connection with the quality of improved flexibility, it might be mentioned that during the saturating and finishing operations, the felt generally undergoes flexing about a great many rollers of comparatively small diameter, say about 4 inches. When a felt is made practically wholly from refined but substantially unhydrated wood pulp, the fiexing which it undergoes, as hereinbefore described, is apt to cause rupture of the felt surface, owing to the tendency of the surface fibers to separate or part from one another under flexing and/or tension. This tendency exists to a much reduced degree in the felts of the present invention. The improvement effected through the inclusion of pulped rags in the felt-making furnish is surprising, particularly when one considers the fact that rag pulp alone yields a felt of a stiff and boardy character, which not only tends to crack or break comparatively easily when bent upon itself, but which after bituminization has relatively low pliancy and tear resistance.

While the felts of the present invention may be made from various proportions of rag pulp and refined but substantially unhydrated wood pulp, nevertheless, as already indicated, we prefer to employ a preponderating proportion of the refined but substantially unhydrated wood pulp. Indeed, we prefer to prepare a fiber furnish containing not more than about 35% to 40% by weight on a dry basis of the rag pulp, the rest of the furnish being refined but substantially unhydrated wood pulp.

The refined cellulose pulps employed in accordance with our invention are produced by taking the ordinary wood pulps of commerce, such as sulphite and kraft, and putting them through the refining action of an alkaline liquor under suitable conditions of temperature, time, and concentration of alkali in the liquor. Thus, the refined wood pulp may be one which has been prepared by subjecting an unbleached chemical wood pulp, such as sulphite, to the action of hot solutions of caustic soda or equivalent alkaline refining agents in moderate concentration. Or the refined wood pulp may be one which has been prepared by exposing chemical wood pulp, such as unbleached sulphite or kraft, to the action of alkaline liquors at about room or even lower temperatures, whose alkalinity is comparatively high and so is capable of extracting non-alpha cellulose components from the fiber under such temperature conditions. In some instances, the

refinement of the pulp may take place in alkaline liquors of such high alkalinity and/or at such low temperature as to result in an incipient or complete mercerization, as well as refinement of the fiber. This latter effect, that is, mercerization, is had through the use of caustic soda solutions of about 18% or greater strength, at room temperature, or through the use of solutions of lower causticity at lower temperatures. A refined pulp whose refinement has been brought about through the use of strong alkaline refining liquors, e. g., liquors of sufficient strength to be mercerized, is of a puffy and resilient or springy character, and consequently must be handled on the felt-forming machine somewhat differently than-other types of refined pulps. The felts formed from such pulps in admixture with rag pulp may require considerable squeezing or compacting while they are in freshly formed condition on the wet end of the felt-forming machine, in order to be delivered from the dry end of the machine at a compactness such as is desired in the roofing and/or flooring industries, especially the latter industry. Otherwise, they may be too soft and spongy and, after being bituminized, lack the required firmness and defacementresisting qualities desired more particularly in a fioor covering material. As hereinbefore noted, however, our felts are in all cases composed largely of the refined but substantially unhydrated wood pulp, irrespective of whether such pulp has become incipiently or completely mercerized during the previous refining operation, or has been preserved in an unmercerized condition.

Inasmuch as refined wood pulp is an essential component in the bituminized sheets of our invention, we wish to define what we mean by the expression refined wood pulp, so that it may be understood in the patented claims and their scope be ascertainable. This expression is meant to exclude the ordinary wood pulps of commerce, such as sulphite, kraft, and soda, whose alpha cellulose content is invariably below 90%. It is designed to include only those preliberated pulps which have undergone refinement or purification in alkaline liquors to an alpha cellulose content upwards of 90% as the lower limit. The refined wood pulp to be used in the felt-making furnishes hereinbefore described may be one having an alpha cellulose content of about 94%, as this represents a pulp which can be produced economically and yield excellent results. Refined wood pulps of higher than 94% alpha cellulose content may perhaps be employed to better advantage, but their cost of preparation is higher, and on this account their use does not appear to be warranted. It is evidently the removal of that portion of non-alpha cellulose components or preliberated wood pulp, such as sulphite and craft, that conduces to the most marked improvement in the bituminized sheets whose felt base contains the refined wood pulp as a preponderating ingredient. In other words, the over-all improvement curve for our bituminized sheets rises sharply as the preliberated wood pulp component undergoes the initial stages of refinement. In any event, however, it is necessary to stay within the range of wood pulps whose alpha cellulose content is above 90%, in order to arrive at bituminized sheets answering the requirements of our invention.

While it may be possible to treat cellulose pulp from other sources, such as cotton, cotton rags, flax, manila, hemp, ramie, sisal, and the like, as by suitable treatment with alkaline liquors, and to utilize the principles of the present invention in producing the results of the present inminimum of effort, equipment, and cost, the production of felts possessed of fine-grained, smooth surface. texture. A bituminized sheet prepared from such felt can be directly and economically finished to produce a flooring, for example, having an ornamented face free from imperfections or blemishes.

We claim:

1. A porous, absorptive, flexible waterlaid felt comprising a blend of substantially unhydrated but alkali-refined cellulose pulp having an alpha cellulose content of at least 90% and of beaten and hydrated but unrefined rag halfstufi in amount up to about of the dry weight of the blended fibrous materials, said felt having less tendency to he ruptured at its surface under flexing than a felt made from only said substantially un-= hydrated but alkali-refined cellulose pulp and further being less stiff and boardy than a felt made from only said beaten and hydrated but unrefined rag halfstuif.

2. A porous, absorptive, flexible waterlaid felt comprising a blend of substantially unhydrated but alkali-refined chemical wood pulp having an alpha cellulose content of at least and of beaten'and hydrated but unrefined rag halfstufi in proportion amounting up to about 50% of the dry weight of the blended fibrous materials, said felt having less tendency to be ruptured at its surface under flexing than a felt made from only said substantially unhydrated but alkali-refined chemical wood pulp and further being less stiff and boardy than a felt made from only said beaten and hydrated but unrefined rag halfstuff.

. MILTON O. SCHUR.

WALTER L. HEARN.