US1948943A - Conditioning paper for nitration - Google Patents

Description

Patented Feb. 27, 1934 OFFICE 1,948,943 CONDITIONING PAPER FOR NITRATION Milton 0. Schur, Benjamin G. Hoos, and Thomas C. Morris, Berlin, N. H.,' assignors to Brown Company, Berlin, N. H., a'corporation of Maine No Drawing. Application March 21, 1929 I Serial No. 348,987

13 Claims. (01. 260-146) This invention relates to the conditioning of cellulose fiber for nitration, being more particularly concerned with fiber in the form of waterleaf paper as a raw material.

It is sometimes of advantage to subject cellulose fiber to a conditioning treatment before it is nitrated. For instance, as disclosed in application Serial No. 336,633, filed Jan. 31, 1929, by Milton 0. Schur and Benjamin G. Hoos, it has been found advantageous to treat the fiber uniformly with a trace of acid-repellent material, e. g., an aqueous dispersion of paraffin wax, and then to fix such material on the fibers, before treating with nitrating acid. Such conditioning of the fiber makes possible the realization of improved results upon nitration, the nitrocellulose yield being increased and the product dissolving in suitable media to give solutions of remarkable clarity and sparkle. The function of the acidrepellent material is to retard the action of the nitrating acid, acid-repellent materials such as waxes even when used in exceedingly small amount producing films or coatings on the fiber and seemingly rendering the fiber resistant to undesirable secondary reactions. Our theory is that the sulphuric acid in the nitratingbath tends to gelatinize and to hydrolyze the cellulose fibers, especially when the pulp is highly absorptive. If, however, the fiber is first treated with an acid-repellent material, side reaction is retarded or eliminated and nitration proceeds smoothly. The protecting coatings or films of acid-repellent material on the fiber probably allow nitric acid to penetrate into the fiber wall more easily than they do the sulphuric acid, and thus perhaps readily allow water within the fiber during nitrating to diffuse into the main body of the nitrating acid, so that within the fiber wall there is believed to be a nitric-acidrich mixture which has a greatly reduced hydrolyzing tendency and which nitrates the cellulose before hydrolysis proceeds to any troublesome degree. It is well known, for example, that nitrating acids rich in nitric acid give high yields, but that acids rich in sulphuric acid cause hydrolysis and accordingly give lower yields. The acid-repellent material applied to the fiber prior to nitration, by slowing up the reaction, eliminates local over-heating in the acid bath, and thus may prevent loss in yield, for the higher the temperature of nitration, the greater the tendency for the yield to drop because of side reaction.

We have discovered that when cellulose fiber in the form of paper is used as a raw material plied directly to the surface of the paper.

for the production of nitrocelluloses, remarkably good results may be obtained when acid-repellent material of the character described is ap- For instance, when parafiin wax is rubbed on a smooth iron plate at room temperature, and then the wax is almost entirely removed from the plate as by wiping with cheesecloth, and the plate with the trace of wax is then rubbed over the surface of the paper to be nitrated, excellent results are obtained upon the nitration of such paper. This discovery is of commercial importance, for the application of a thin film of suitable acid-repellent material in solid condition to the surface of the paper is an easy and inexpensive procedure which possesses features of advantage over the use of organic solvent solutions or aqueous dispersions of the acid-repellent material. In such latter case, the solvent or water must be removed from the fiber in order 5 to prevent dilution of the nitrating acid, this involving the use of drying equipment, and the recovery of solvents when organic solvent solutions are used, as the loss of such solvents would render the cost of the conditioning treatment excessive.

Various non-cellulosic, acid-repellent materials, including oils and waxes, may be used in the process of this invention, e. g., parafiin oil, spermaceti, stearic acid, paraffin, and the like, but parafiin wax, stearic acid, or mixtures'of paraifin wax and stearic acid which are inexpensive and easy to handle, are especiallysatisfactory for the purpose. Paraffin wax readily lends itself to the application of uniform, thin films on paper, and in some cases may be advantageously compounded with stearic acid. For instance, a stearic acidparafiin mixture containing, say, 10% to 25% paraffin has been found to be eminently satisfactory. In carrying out the treatment commercially, the acid-repellent material, e. g., parafiin wax or a stearic acid-paraffin wax mixture, may be applied or transferred to a continuous sheet of paper from a suitable transfer surface containing a film of the material. For instance, the sheet may be passed progressively between resilient rolls covered with waxed paper, between calender rolls on which exceedingly thin films of such material are maintained, or between rolls such as are commonly used in printing machines, but which have received a very thin, uniform film of such material as by contact with other rolls carrying such material in place of the ink used in the case of printing machines. Or acid-repellent material may be applied or transferred to the surface of the paper, as by drawing the paper across slabs of wax or other solid, acid-repellent material lightly pressed against both its sides. The treatment may be carried out in the paper mill while 5 the paper is on the dry end of the paper machine or as it comes off the paper machine, thus avoiding the necessity of special equipment.

The amount of acid-repellent material necessary to produce the results desired is exceedingly small, in fact so small that the treated paper gives little evidence in appearance or feel that it has been treated. Indeed, only the outermost fibers are treated, the pores and interstices of the paper remaining substantially unaffected. When nitrated at, say, 40 0., the yield is practically theoretically perfect, and the product gives solutions of remarkable clarity and sparkle, which may be formed into films of excellent appearance, strength, and elasticity. The amount of acidrepellent material used may be 0.07% to 0.10% by weight, based on fiber, more than this amount being unnecessary and perhaps detrimental, in that it may retard nitration to too great an extent and accordingly necessitate an excessively long time of reaction for complete nitration. The surface treated paper has little or no tendency to stick to the sides of the nitrating pot, and has little, if any, tendency to float to the surface of the acid.

Ihe following table gives the results obtained when a mixture containing 25 paraffin wax and 75% stearic acid was applied directly to the surface of a waterleaf paper of 30 pounds basis weight, prepared from refined wood pulp,beta and gamma celluloses and resinous impurities having been removed from such pulp by cooking with caustic soda containing oleic acid. The results obtained from similar untreated paper are also given, for the purpose of comparison.

5Q A (In all cases a nitrating acid containing 20.5% HNOS, 60.8% H2804,

and 18.7% 1120 is used, the ratio of acid to paper being to l, and the time of nitration 30 minutes.)

While the process of the present invention may be employed when using cellulose fiber of various origins as a raw material, it has especial utility in the case of wood pulps, such as refined wood pulps of high alpha cellulose content. Thus, there are wood pulps which have been refined to high alpha cellulose content and so are largely free from natural occurring impurities such as beta and gamma celluloses, lignin, and resins. When used as a raw material for nitration, they yield nitrocelluloses which are comparable in quality with those obtained from a more expensive raw material, such as highly refined cotton fiber, but they may suffer from the disadvantage of giving under certain conditions a lower yield of product, probably because such pulps are highly absorbent and so undergo a slight hydrolysis during nitration. By treating waterleaf paper composed of refined wood pulp with a trace of acid-repellent material such as described, it becomes possible to increase the nitrocellulose yield without injuring the nitrocellulose, as the acid-repellent material is of controllable composition and may be so chosen that it does not act as a contamination.

Having thus described certain modes of procedure in practising the process of the present invention, and the product resulting therefrom, it should be evident to-those skilled in the art that various changes and modifications might be made therein without departing from the spirit or scope of invention'as defined by the appended claims.

We claim:

1. A process which comprises transferring waxy material from a transfer surface to the outermost fibers of paper, and nitrating the paper.

2. A process which comprises transferring paraffin wax from a transfer surface to the outermost fibers of paper, and nitrating the paper.

3. A process which comprises applying stearic acid to the outermost fibers of paper, and nitrating the paper.

4. A process which comprises applying a mixture of paraffin wax and stearic acid to the outermost fibers of paper, and nitrating the paper.

5. Waterleaf paper the outermost fibers only of which carries stearic acid.

6. Waterleaf paper the outermost fibers only 110 of which carries stearic acid and paraffin wax.

'7. Waterleaf paper the outermost fibers only of which carries stearic acid containing about 10% to 20% paraffin wax.

8. A process which comprises transferring solid, acid-repellent material from a transfer surface to the outermost fibers of paper, and then nitrating the paper.

9. A process which comprises transferring noncellulosic, acid-repellent material from a transfer 12o surface to the outermost fibers of paper, and then nitrating the paper.

10. A process which comprises transferring solid, non-cellulosic, acid-repellent material from a transfer surface to the outermost fibers of paper, and then nitrating the paper.

11. A process which comprises transferring acid-repellent material from a transfer surface to the outermost fibers of paper, and nitrating the paper.

12. Waterleaf paper carrying not more than about 0.10% by weight of acid-repellent mate.- rial only on its outermost fibers.

13. Waterleaf paper carrying not more than about 0.10% by weight of paraffin wax only 5 on its outermost fibers.

MILTON O. SCHUR. BENJAMIN G. HOOS. THOMAS C. MORRIS.