US2005397A - Manufacture of strengthened absorptive paper - Google Patents

Description

Patented June 18, 1935 MANUFACTURE OF STRENGTHENED ABSORPTIVE PAPER Milton Schur, Berlin, N. H., assignor to Brown 1ialoarinpany, Berlin, N. 11., a corporation oi.

No Drawing. Continuation of application Serial UNITED STATE No. 554,598, August 1, 1931. This application January 21, 1933, Serial No. 652,939

4 Claims.

. The subject of this invention is the manufacture of strengthened absorptive paper more especially of the kind intended for use as toweling. The primary aim of this invention is to produce for toweling or analogous purposes a paper whose wet strength has been enormously increased without serious impairment of its water-absorptivity either in the sense of water-holding capacity or in the sense of rate of imbibition or take-up of water.

It has been found possible to increase enormously the wet strength of paper without appreciably detracting from its ultimate water-holding capacity by the incorporation of a small amount of wet-strengthening agent such as .viscose, glue, gelatin, or their equivalents throughout the paper. Thus, the presence in waterleaf paper of only about of cellulose regenerated from viscose or other cellulose derivatives brings about a multifold increase in the wet strength-of such paper without significantly impairing its water-holding capacity. Such a paper is eminently useful for toweling purposes on account of the fact that it does not tend to disintegrate even when subjected to vigorous wiping with wet hands. served that while the ultimate water-holding capacity of a wet-strengthened towel is practically the same as similar waterleai' towel (i e., a towel which lacks a strengthening agent), nevertheless the strengthening agent may greatly reduce the rate at which water is imbibed by the towel and consequently tends to give the towel a cold, slipv pery feel when wet hands are brought in contact therewith. I have found that these defects arising from the presence of wet-strengthening agents in the towel can be practically nullified by associating so-called wetting-out agents with the towel, for these wetting-out agents have the property of phenomenally increasing the rate at which water penetrates into paper evenafter the paper has been dried with an inclusion of regenerated cellulose or other wet-strengthening agent. Apparently they function to dissolve immediately in water brought into contact with the paper to form a solution having the proper surface tension relationships in contact with the wet-strengthening agent so that it penetrates instantaneously through the wet-strengthening agent to the cellulose fibers themselves.

There are various wetting-out agents which are )0 commercially available for use in accordance with my invention, for instance the wetting-out agents sold under the trade names Nekal A, Nekal AEM, "Indrapid, Nekal S, Nekal BX, Neomerpin, Neomerpin N, all of which are either 55 benzene, naphthalene, or anthracene derivatives I have ob-.

having side chains. 'Thus, Nekal BX, which is a highly effective wetting-out agent, is the sodium salt of a naphthalene sulphonic acid with'slde chains. Nekal A is the crude sodium salt of .octohydro-anthracene meta'sulphonic acid, while 5 Indrapid and Nekal S are similar but contain the free acid. Nekal AEM is a combination of Nekal A with methylhexalin. Neomerpin N is a high molecular weight sulphonic acid. While it is pos-- sible to add any one of the wetting-out agents to the paper toweling independently of the wet-" strengthening agent, yet the two types of. agents may be advantageously-mixed and incorporated into the toweling in a. single step, In this connection, I have found that the wetting-out agents 5 may be added directly to the viscose solution to be employed as the impregnant for waterleai pa-. per toweling while preserving the cellulose in solution and otherwise maintaining the solution fit for its intended use. I have further discovered that the inclusion of a wetting-out agent is highly desirable when a-viscose-treated toweling is to undergo a deodoriz'ation treatment with a suitable oxidant as disclosed in my application Serial No. 535,293, filed May 5, 1931. As pointed out in that application, the viscose-treated toweling may be freed from malodors by a suitable oxidizing solution or oxidizing atmosphere. The presence of water in such toweling during the deodorizing treatment, either as a result of introduction thereinto by the oxidizing solution or of a previous Q wetting step, has been found to promote deodorization. Indeed, I have stated in my previously filed application that even when the toweling web is passed through an oxidizing atmosphere like chlorine gas, it is distinctly preferable that the web be moist in order to foster the removal of foul odors. Unfortunately, however, the presence of moisture in the sheet during the deodorizing treatment so slows up the rate at which water is absorbed by the finished toweling, especially in the first few seconds, that in practical operation one is forced to choose between either of two evils, viz., the imperfectly deodorized toweling ensuing from the lack of moisture therein during deodorization, or the'toweling which is slow in its rate of water absorption. Through the presence of wetting-out agents in the toweling along with the viscose, I have found that I can keep the toweling sufliciently moist or wet during the deodorizing treatment to eliminate all traces of foul odor and at the same time to realize an exceedingly high rate of absorptivity in the fln-. ished toweling.

A specific example of procedure falling within wet-strengthening agent and the wetting-out.

the purview of the present invention may be substantially as follows. A waterleaf web of toweling may, as ordinarily, be made of any suitable cellulose pulp or mixture of pulps, such as ground-wood, sulphite, kraft, refined wood pulp, or the like, on a paper machine, and the continuous web comingoff the dry end of the machine may then be passed through a bath of both the agent, thence through squeeze rolls, and over a bank of redrying cylinders. Specifically, the wetstrengthening agent may be a solution containing about $6, of soluble cellulose in the form of cellulose xanthate. About 1% of boric acid is preferably added to the solution for the purpose of promoting the regeneration of cellulose in the web as it passes over the redrying cylinders; and about 1% of ammonium carbonate is preferably also added for the purpose of combining with sulphur impurities in the web to form sulphur compounds and especially ammonium sulphide, which can be expelled under the heat of redrying. The wetting-out agent in the solution may be Nekal B1! in amount varying, say, from .05% to 0.25%. More wetting-out agent may be added to the solution but with comparatively little additional benefit. As a demonstration of what my invention means in the way of improving the rate of water imbibition by viscose-treated toweling, theresults of a number of tests will be given. The samples used in all the tests were made similarly, except in respect of content of wetting-out agent. In fact, the various test samples were made by passing similar webs of dry waterleaf to'weling through viscose solutions containing various amounts of Nekal Bx but otherwise of the same composition, and then squeezing them to a solution content equal to the weight of dry web, that is, so that the redried web had a viscose and Nekal BX content equal to that present in the solution. Each sample sheet was tested for rate of water absorptivity by adding a V cc. drop of water thereto while supported horizontally, and noting how long it took for the drop or tiny puddle of water to disappear completely by diffusion into the sheet. In the case of a sample containing 7 of regenerated cellulose and which had been chlorinated while wet to remove malodors, it was found that the time of disappearance was 600 seconds. This sample was lacking in any content of wetting-out agent. A sample containing .05% Nekal BX had a time of 71 seconds. Another sample containing 0.1% Nekal BX had the short time of 38 seconds. Still another sample containing 02 Nekal BX had the remarkably short time of 14 seconds. The fact is that samples containing as little as .08% Nekal BX have a time of 60 seconds, despite the fact that they are taken from a web which has been run through a chlorinated atmosphere in sufliciently moist condition to be rid of all traces of objectionable odor.

An ordinary paper towel which is lacking in regenerated cellulose or other wet-strengthening agent and is reasonably fast in absorbing water, for instance, a waterleaf paper towel prepared so as to have a water absorptivity of lessthan600 seconds when tested as hereinbefore described, has a wet tensile strength of 0.6 pounds,in most cases considerably less than this. The paper towel of the present invention has a wet strength of 1.5 pounds, the web of towelling described in the specific example of procedure hereinbefore given, for example, having a wet strength of 2 pounds or greater. In determining the wet tensile strength values herein given, a one-half inch paper strip of a length, say, 4 to 6 inches, is clamped while dry in a tensile strength tester, preferably of the Schopper type. and is streaked across the width of the sheet with water applied from a camel-hair brush carrying a large excess of water. Ten seconds later, the tensile load is applied and the maximum force exerted in pulling apart the specimen is recorded as the wet tensile strength of the specimen. The tests are made in both the with and the "across" directions (paper-machine directions) of the paper and the tensile strength values hereinbefore given .represent the average of the tests in both directions. It is thus seen that the absorptive paper of the present invention has combined therein the qualities of high capacity and rate of water absorption and the quality of high wet strength. This combination of qualities is of preeminent value when the paper is to serve for such purposes as paper towels, diapers, napkins, orthe like.

One may depart from the procedure hereinbefore outlined in producing the product of the present invention. For instance, it is possible to associate both the wet-strengthening agent and the wetting-out agent with the paper while it is being fabricated rather than with the prefabricated and dried web. In other words, it is possible to introduce both these agents into the papermaking stock or to add these agents to the nascentor partially dried web on the paper machine, as by spraying a mixed solution of both these agents onto the web. So, too, one might add one of the agents while the paper web is in the course of fabrication, and then add the other agent to the prefabricated and dried web. The deodorizing treatment with chlorine gas or other oxidant may be practiced immediately after the web has been impregnated with a solution of the viscose and wetting-out agent or after the impregnated paper has been dried, in which lat ter case it is preferable, as already indicated, to remoisten the paper in order to secure maximum deodorization.

I am aware of the fact that wetting-out agents have been proposed for use in some connections and that their power of increasing water-penetrability is known. In such cases, however, the wetting-out agents were proposed for use in dyeing solutions or the like to overcome the waterrepelling action of the material being dyed, which action may ensue from naturally occurring impurities, such as the wax in cotton goods, or from lubricating oils or the like previously added to textile threads to facilitate fabrication. My invention is distinguished from such previous proposals or practices in that I use its wetting-out agent conjunctively with a wet-strengthening agent, and more especially viscose, in dry papers of substantially unimpaired water-holding capacity, in which case I have found that the wetting-out agent can be made to offset practically completely the otherwise retarded rate at which the wet-strengthened, dry paper may absorb water. In fact, the resulting paper can be accurate- 1y described as one which in addition to possessing a wet strength several times that of similar waterleaf paper, is capable of imbibing water practically instantaneously.

So far as concerns subject matter, this application is a continuation of my application Serial No. 554,598, filed August 1, 1931.

I claim:--

1. As an article of manufacture intended especially for such use as toweling, a dry paper web containing distributed therethrough about of regenerated cellulose, said web also containing distributed therethrough a smaller amount of solid wetting-out agent of sufliciently high wetting-out eflectiveness to render said web capable of imbibing water practically instantaneously.

2. As an article of manufacture designed to be exposed to the action of water and to absorb the water quickly, a dry paper web containing distributed therethrough only a small percentage oi regenerated cellulose imparting thereto a wet strength several times that of similar waterleat paper and further containing distributed therethrough even a smaller amount of solid wettingout agent of sufllciently high wetting-out effectiveness to impart thereto the property of imbibing water practically instantaneously, said paper having a water-holding capacity substantially equal to that of a similar waterleaf paper.

3. As an article of manufacture intended especially for such use as toweling, a dry paper web, the fibers of which are so thinly coated and bonded together with a wet-strengthening agent selected from a class consisting oi regenerated cellulose, glue and'gelatin as to detract inappreciably from the water-holding capacity of said web, said wet-strengthening agent containing invfused therein a smaller amount of solid wettingout agent which dissolves substantially immedi- 5 ately in water brought into contact with the paper web and which is of sufliciently high wetting-out efiectiveness to cause said water to penetrate substantially instantaneously through said thin coating of wet-strengthening agent to the fibers themselves.

4. As an article of manufacture intended especially for such purpose as toweling, a dry paper containing both a wet-strengthening agent and a wetting-out agent, said wet-strengthening agent being selected from a class consisting of regenerated cellulose, glueand gelatin, and being present in such restricted amount as not to detract from the water-holding capacity of the paper and said wetting-out agent being a solid of such high wetting-out efiectiveness as to render said paper capable of imbibing water practically instantaneously even when present therein in amount less than 0.25%.

MILTON O. SCHUR.