US1921540A - Manufacture of glassine papers - Google Patents

Description

Patented Aug. 8, 1933 UNITED STATES PATENT; OFFICE George A. Richter, Berlin, N. 11., assignmto Brown Company, Berlin, N. IL, a Corporation of Maine No Drawing. Application September 19, 1932 Serial No. 633,852

io Claims.

This invention relates to the manufacture of glassine papers, i. e., translucent or semi-transparent papers, characterized by their excellent all-round qualities. I have found that such papers may be prepared from raw manila or sisal as the starting or raw cellulosic material, provided that such starting material is first converted into a pulp in a special way before it is put through the usual steps of glassine paper manufacture.

v Chemical wood pulps, such as sulphite, have heretofore been generally used in making glassine papers. I have found that pulps whose characteristics for glassine paper are markedly superior to those of the usual chemical wood pulps can be secured by pulping raw manila or sisal in solutions containing sodium sulphite as the essential fiber-liberating chemical. Indeed, unless pulping is done in this special way, one does not realize the various advantageous qualities hereinafter described as residing in the glassine papers of the present invention. For instance, when pulping is done by digesting manila rope or the like at elevated temperatures in hot solutions of caustic soda, as practised in rope paper mills, the resulting pulp, although quite satisfactory for making tough papers of high tear resistance, nevertheless does not lend itself to making glassine papers possessed of the transparency and other valuable characteristics inhering in the glassine papers of the present invention. The fact is, that when caustic soda solutions serve to bring about the pulping of raw manila and sisal, they largely solubilize and destroy the pentosans associated with the raw material, whereas sodium sulphite solutions, and more especially those which are devoid of any substantial amount of strong acid or caustic soda or equivalent alkali, and are hence neither highly acid nor alkaline, conduce to a pulp of high pentosan content. It is evidently the high pentosan content of the latter pulp that contributes to the improved physical characteristics of the glassine papers made therefrom. Thus, glassine papers fabricated from such manila or sisal pulp have a uniformity or homogeneity of texture which is better than that attainable through the use of chemical wood pulps, assuming that the various,

pulps have received similar beating action. They are also distinguished by having considerably greater toughness, strength, tear resistance, and folding endurance than glassine papers prepared from the usual chemical wood pulps. Aside from the fact that such manila and sisal pulps are comparatively easily transformed by beater action into l l ?gelatinized or hydrated stock, such as is required for glassine paper manufacture, the glassine papers made from such stock have better translucency or clarity and are brighter in color than glassine papers composed of wood pulp fibers beaten to a similar extent. This is true of the glassine papers of the pr sent invention, irrespective of whether they have eqrprepared from pulp in a partially bleached or in a completely bleached condition,- as the pulp at any stage of whiteness can be formed into glassine papers which are notably superior to those consisting of wood pulp fibers bleached to a similar stage of whiteness. The glassine papers of the present invention are also more permanent or stable than papers made in the same way from the usual chemical wood pulps, e. g., the ordinary sulphite wood pulp, and, in this respect, are comparable to papers whose base is a highly refined wood pulp or a high grade rag stock. The quality of permanence or stability is of significance in glassine papers, because, as currently made from the usual chemical wood pulps, glassine papers are of comparatively poor stability, especially when agents such'as resins, waxes, and the like are incorporated thereinto for the purpose of enhancing their translucency or clarity. Moreover, such papers made from the usual chemical wood pulp are of inferior heat stability and are impaired when such agents as waxes or resins are applied thereto in molten condition, that is, at high temperature. These agents, which are apt to detract from the stability of the papers, are unnecessary in the glassine papers of the-present invention, which, as already indicated, are characterized by their high clarity or translucency; and, when these agents are applied for the purpose of imparting the quality of water-repellency to the papers, the fibers are able to resist the deteriorating action of the olten agents far better than chemical wood pu p fibers, such as sulphite.

The conversion of the raw manila and sisal into pulps such as are necessary for producing the glassine papers of the present invention may be accomplished substantially as follows. The raw manila or sisal may be placed in a digester and covered with a plain solution of sodium sulphite, which need not be of greater than about 2% strength. The digester may then be closed and its contents heated to a temperature of about 300 to 335 F. After cooking at such temperature for about three hours,it is found that the raw material has been resolved into a pulp characterized by its excellent strength and other papermaking characteristics. At this time, the digester contents may-be discharged and the pulp washed free of cooking liquor. The washed pulp may then be bleached to the desired whiteness with a, bleach liquor containing the appropriate amount of calcium hypochlorite or other bleaching agent. When a fully bleached or white pulp is desired, as isusually the case, the practice disclosed in my application Serial No. 571,462, filed October 27, 1931, may be advantageously employed. According to such practice, the raw manila or the like is treated with an oxidizing reagent of the nature of chlorine water and hypochlorite liquor before it is subjected to the pulping'action of a solution containing sodium sulphite as the essential fiber-liberating agent. Specifically, the raw manila fiber or the like may be steeped in chlorine water containing, say, about 5% to 8% chlorine, based on the weight of dry fiber. After the chlorine has been practically consumed, for which purpose a thirtyminute period is ample, the material is preferably washed free of residual chlorine and reaction products. It may'then undergo the pulping action of a plain solution 'of sodium sulphite, as

hereinbefore described. The resulting pulp, after washing, is of comparatively light color and may be used as such, or be brought to higher whiteness with a bleaching liquor containing as little as 2% to 3% calcium hypochlorite, based on the weight of dry pulp.

' The. partially or fully bleached pulps produced as hereinbefore described may be beaten in the usual stone-roll heaters employed in the glassine paper industry, until a highly gelatinized or hydrated stock, such as conduces to a translucent paper is attained. The pulp is characterized by its capacity to be gelatinized or hydrated with comparative ease to that stage at which papers made therefrom are remarkably translucent. This ease of hydration or gelatinization is evidently ascribableto the high pentosan content of the pulp, for I have observed that in the case of chemical wood pulps, too, ease of hydration or gelatinization is associated with the pentosan content of such pulps. The properly hydrated or gelatinized stock can be delivered to a cylinder or Fourdrinier papermaking machine designed to produce a glassine paper of the desired caliper. It is, of course, possible to use a multi-cylinder papermaking machine when a multi-ply paper is in new.

be used in those various connections wherein the usual glassine papers have heretofore served. In

' all these connections, its superior translucency,

texture, strength, tear resistance, folding endurance, and stability are of great value. Its high translucency and general toughness render it particularly useful for tracing work, forwhich purpose the ordinary glassine papers are quite unsatisfactory.

The glassine papers of the present invention may, of course, be finished in the same ways as the usual glassine papers. For instance, they may be advantageously water-finished, i. e., moistened with water and then calendered. A super-calendering operation is especially to be desired, as it enhances the clarity and other qualities desired inglassine papers. The ordinary wood pulp glassine papers require at least about 1% rosin size or similar sizing agent to withstand water-finishing without being torn, but the glassine papers of the present invention are so strong as to require no sizing agent whatever to The glassine paper of the present invention may undergo a water-finishing treatment. Other finishing treatments may be applied to the glassine papers of the present invention, including waxing, coating with lacquer, or the like, depending upon the ultimate use which they are to serve. They may, if desired, contain rosin size, wax, or other sizing agents, especially in those instances when they are to be used for wrapping foodstuffs or the like associated with water and/or fats or grease. They may, as already indicated, be advantageously waxed, as with molten parafiin,

or impregnated with other hot or molten waterrepellent materials, as they may in this way be made highly water-repellent inan inexpensive way without suffering material damage on account of exposure to elevated temperature! The pulping procedure hereinbefore described admits of some variation, but in any event the cooking liquor should be one containing sodium sulphite as the essential and predominating fiberliberating agent, although it can advantageously also contain sodium carbonate and/or sodium sulphide in substantial amounts. It should not, however, contain any appreciable amount of caustic soda, which, as hereinbefore observed, is destructive of pentosan groups desired in the pulp. Nor should it contain more than a slight amount of acid, as acid tends to injure the cellulose fibers, as well as to hydrolyze and dissolve the pentosans. The temperature at which pulping is effected may also be varied. For instance, pulping may be accomplished at temperatures even as low as 212 F. when sufllcient chlorine, say from 6% to 12% based on raw material, is used in the pre-treatment. No matter which pulping procedure along the foregoing lines is adopted, it is possible to produce the pulps for making the glassine papers of the present invention at a cost such that these glassine papers can, by virtue of their superior qualities, readily compete with the usual glassine papers whose base consists of the ordinary chemical wood pulps, suchas sulphite.

I claim:

1. A process which comprises pulping raw fibrous material of the character of manila and sisal in a cooking liquor containing sodium sulphite as the essential fiber-liberating agent, beating the resulting plup to the hydrated condition requisite for making translucent paper, and forming the beaten pulp into such paper.

2. A process which comprises pulping raw fibrous material of the character of manila and sisal in a cooking liquor which is neither high in acidity nor high in alkalinity and which contains sodium sulphite as the essential fiber-liberating agent, beating the resulting pulp to the hydrated condition requisite for making translucent paper, and forming the beaten pulp into such paper.

3. A process which comprises pulping raw fibrous material of the character of manila and sisal in a cooking liquor containing sodium sulphite as the essential fiber-liberating agent, beating the resulting pulp to the hydrated condition requisite for making paper of substantial clarity, forming the beaten pulp into such paper, and super-calendering the paper.

A process which comprises pulping raw fibrous material of the character of manila and sisal in a cooking liquor containing sodium sulphite as the essential fiber-liberating agent, beating the resulting pulp to the hydrated condition requisite for making paper of substantial clarity, forming the beaten pulp into such paper, and

impregnating the paper with hot, water-repellent material.

5. A process which comprises pulping raw fibrous material of the character of manila. and

sisal in a cooking liquor containing sodium sulphite as the essential fiber-liberating agent, beating the resulting pulp to the hydrated condition requisite for making paper of substantial clarity, forming the beaten pulp into such paper, and impregnating the paper with molten paraflin wax.

6. A translucent paper whose base consists of well-beaten and hydrated fibers derived from raw cellulosic material of the nature of manila and sisal, through the pulping action of a cooking liquor containing sodium sulphite as the essential fiber-liberating chemical.

'7. A translucent paper whose base consists of well-beaten and hydrated fibers derived from raw cellulosic material of the nature of manila and sisal, through the pulping action of a cooking liquor neither high in acidity nor high in alkalinity and containing sodium sulphite as the essential fiber-liberating chemical.

8. A super-calendered paper of substantial clarity whose base consists of well-beaten and hydrated fibers derived from raw cellulosic material of the nature of manila and sisal, through the pulping action of a cooking liquor containing sodium sulphite as the essential fiber-liberating chemical.

9. A paper of substantial clarity containing a water-repellent material and whose base consists of well-beaten and hydrated fibers derived from raw cellulosic material of the nature of manila and sisal, through the pulping action of a cooking liquor containing sodium sulphite as the essential fiber-liberating chemical.

10. A paper of substantial clarity impregnated with paraflin wax and whose base consists of well-beaten and hydrated fibers derived from raw cellulosic material of the nature of manila and sisal, through the pulping action of a cooking liquor containing sodium sulphite as the essential fiber-liberating chemical.

GEORGE A. RICHTER.