US2199750A - Process of making paper - Google Patents

Description

Patented May 7, 1940 UNITED STATES PATENT OFFICE PROCESS OF MAKING PAPER Howard D. Meincke, Glencoc, Ill., assignor to A. M. Meincke & Son, Inc, Chicago, 111., a corporation of Illinois 1 Claim.

This invention relates to processes of makin paper; and it includes a process of making an improved open textured paper with the fibers thereof cemented together by minute particles of a dried irreversible starch gel, which process comprises beating paper pulp with the usual fillers and additions, adding to the pulp in the later stages of beating, a fine-grained partly converted starch of a character readily-dispersible in cold water and swelling therewith, adding silicate of soda to the pulp to maintain the pulp at about pH '7 during the beating, adding acidic sizing material to the pulp in the later stages of beating to drop the pH to about 5, and converting the beaten pulp into paper; all as more-fully hereinafter set forth and as claimed.

In making paper, paper pulp is beaten for a long time with water and various additions, the beaten pulp then going to the fourdrinier, or wire, to be made into paper. There are operations supplemental to the beating, in jordans, etc., but in principle the operation is as stated. After formation the web is dried, using heat. Sometimes the .web temperature becomes rather high. Commercial paper is, of course, based on cellulose fiber but it contains all sorts of other additions and there are many types of paper. The use of fillers, inert non-fibrous material, is common and sometimes mineral matter forms a major fraction of the paper. Sizes and cementing bodies are often used. But as a rule, in opentextured paper, there is a fiber-to-fiber union with fibers in frictional engagement.

One of the additions often made to the pulp in the beater is starch, either as raw starch or as cooked starch. Neither material gives entirely satisfactory'results. Raw starch, even in its finely divided form, is heavy and tends to settle out of water if given opportunity, so that securing uniform distribution of starch in the heater and in the paper is not easy. Raw starch is dispersed.

And if complete and uniform dispersion is seon each of the several fibers. A cemented union of this sort is too stiff; the paper produced is not desirable for most purposes.

The strength shown in various tests of paper varies considerably and depends on the way the paper is made. Sometimes the strength is due to the fiber-to-fiber union and sometimes there are agglutinatives or cementing materials in the mixtures, which sheath or coat the fibers and give a cemented unionbetween fibers. But whatever the fiber union may be, it is made, so far as possible, uniform all over the sheet; there is no localization of cementing material as far as this can be avoided. Either the paper relies for its strength and its other properties largely on a fiber-to-fiber bond or it relies on a cemented.

union between coated fibers. Both types of bond have their advantages.

I have discovered that I can produce a better and stronger paper which is of a diiierent type; there being spot-wise union of fibersthrough a cementing material with fibers elsewhere in the usual fiber-to-fiber engagement. In so doing, I secure two types of bond in the paper, securing the advantages of both so far as strength and other characters are concerned. The new paper has many of the properties and. advantages of both pure cellulose papers and starch-sized papers. The appearance of the paper does not suffer since the spots of localized cementation are small; to the naked eye, and even under a low power magnification, the paper appears uniform. Its properties as regards taking ink are somewhat better than those of a wholly unsized paper and of a completely sized paper. There is a moderate and desirable degree of penetration in the uncemented portions of the paper. Spot cementation of fibers, in other words, gives two desirable results: a better type of strength and a paper of intermediate properties as regards taking ink.

I have discovered that by the use of specially treated starch I can secure the desired result of spot-wise cemented engagement between the fibers. Starch on cooking with water swells and is hydrated with the ultimate production of a gel. The final gels are irreversible; on drying and rewetting the gel does not re-appear. But if the starch be cooked with a limited amount of water for a limited time and the gel comminuted and dried, particles can be secured which in water swell and hydrate, giving a gel particle. There is little tendency for these hydrated gel particles to coalesce or reunite when stirred up in water. If the gel particle be again dried, it

becomes irreversible. These properties are utilized in the present invention: a granular modified starch of the character described being placed in the beater and incorporated with the pulp. It may be added dry or as a pulped suspension. The particles can be readily distributed uniformly through the beater contents in the same sense that mineral particles can be distributed. When the beater mixture is made into paper on the wire, modified starch particles pass forward and are dried down with the web giving a cemented engagement between adjacent fibers wherever they occur. The particles persist, so to speak, in the finished web. The fibers are, so to speak, spot welded. There is no cooking or further gelling as in using raw starch in the web.

In this operation control of the pH is important. For the best results the liquid in the .beater, which may be, largely, returned white water, is kept at a pH of about 7 by additions of silicate of soda. At the end of the beating an acidic sizing material such as alum, is added to the pulp to drop the pH to about 5. At a-pH of '7 the modified starch particles have little stickiness; they do not tend to clump and coagulate in the water, while at a pH of 5 in making the web, stickiness does develop. In other words, modified starch particles are kept non-sticky during incorporation in the beater charge and are allowed to develop stickiness, or adhesive power, afterwards.

There are various conmiercial starch preparations, some made for food purposes, which are useful in the described invention. However, a good preparation may be made by heating starch under pressure with four or five times its volume of water until there is complete interaction between the starch and the water and then delivering the hot material on a heated drying roll. After drying it is removed from the roll and mechanically comminuted. Better results are obtained by feeding the starch between a pair of heated rollers. The comminution should be to a moderately fine powder; fine enough so that in the paper it is not quite visible to the naked eye. In this operation the original starch granules disappear and the new particles bear no necessary relation to the original starch granules. A preparation of this sort resembles ordinary tapioca except for the size of the grains. In fact, a preparation useful for the present purposes can be made by fine grinding commercial tapioca.

In carrying out my process, I mix a suitable quantity of converted starch w'ith the pulp in the beater. The starch may be added either in dry granular form or in water suspension, and in a typical case is added in a proportionof about 6o 1 to 2 per cent by weight on'the (dry) pulp.

The pulp in the beater is kept at a pH of about 7, that is, about at neutrality, during the addition of the starch and the following beating. Since it is common practice to return back-water from the save-ails to the beater, (white water) and as this water is acid, to maintain the proper pH it is usually necessary to add an alkaline agent to the pulp. Silicate of soda is best.

When beating is finished or nearly so, I drop the pH of the pulp to about 5. This is conveniently done by adding alum or other sizing material to the pulp.

The beaten pulp is then refined in Jordan engines in the usual way and is made into paper.

As a result of this process there is obtained a paper which has distributed isolated spots where the fibers are bonded by the dry gel with other areas where the ordinary fiber-.to-fiber union exists. If the starch product be ground to the proper fineness, a paper. is secured of uniform appearance to the naked eye, but under a low power lens showing spots of cemented fiber and areas of uncemented fiber. On bluing the paper with iodine it presents a uniformly blue appearance, but under the lens shows deep blue spots of cemented union and paler areas where uncemented fibers occur. If coarser starch product is used, the spots of starch bonded fibers may become large enough to be visible and give the paper an uneven or mottled look.-

Paper with localized spot union as described is considerably stronger by all the usual tests, bending, tension, fold, etc., than ordinary papers including starch-sized papers, while it has much of the open-textured and other desirable characteristics of ordinary paper. Moreover the new paper is less subject to changes due to variations in humidity and temperature. It is quite possible to size, coat and otherwise treat the new paper in ways in which prior paper is treated, there being a sufficient total area where the texture is open, and the union of the ordinary type, to permit this.

What I claim is:

The process of making an open-textured high strength paper which comprises beating paper pulp in a beater for a prolonged period; adding to and beating into the contents of the beater a readily dispersible fine-grained starch product produced by heating starch under pressure with 4 to 5 times its volume of water until interaction between starch and water is complete and heating the suspension to dryness in thin layers and comminuting the dried product to subvisible powder particles; maintaining the pH oi. the' starch-pulp mixture in the beater at about pH '7 by addition of sodium silicate; adding alum to the beater mixture to reduce the pH to about 5 and converting the mixture into paper.

HOWARD D. MEINCKE.