US2103640A

US2103640A - Paper manufacture

Info

Publication number: US2103640A
Application number: US13989A
Authority: US
Inventors: George A Richter
Original assignee: Brown Co
Current assignee: Brown Co
Priority date: 1935-03-30
Filing date: 1935-03-30
Publication date: 1937-12-28
Anticipated expiration: 1954-12-28

Description

P wn e 19 Georgob. Brown ofllalne '1 No serliv-llfllo. 13,9

Co m. Ber

munracruu ll'ichteaherlin, N. 11., assignor to- N. 11., a corporation (cl. ill-68) This invention relates to the manufacture of papers having the cofijunctive properties of high absorbency and high wet-strength. When paper is put to such .uses as toweling.

napkins, diaper linings; handkerchiefs, etc., it

should preferably benot only of high absorbency but. also of sufficient wet-strength to resist the disintegrating action of the water or aqueous medium absorbed thereby. Within recent years, it has been discovered that an absorptive paper base can be made -to acquire high wet-strength while substantially retaining its absorptive capacity by thinly enveloping substantially all of its fibers with regenerated cellulose produced in situ in thebase from viscose or other'cellulose derivative and serving to bind together the fibers. It was then discovered that an albuminous adhesive, such as 'gluefalthough of radically different chemical composition from regenerated cellulose, functions in a way similar to regenerated cellulose provided that the albumen is in-. 'solubilized or tanned by formaldehyde or its equivalent. Both 'regenerated cellulose and glue, however, have the common property of being water-absorbing to a considerable-extent; and it is evidently this property that permits water to difiuse or penetrate through the thin envelops or coatings of binder to the fibers of the paper base while at the same time performing the role of binding together the. fibers quite strongly and thus of resisting fiber-separation under manipulation that would bespeak rupture of the base lacking the binder-reinforcement.

I have now found that despite the fact that.

cellulose acetate is decidedly diflerent from both regenerated cellulose and glue in that it is water repellent, it can be incorporated to good ad- 'vantage' as a wet-strengthening agent into a paper I base to yield a paper product of high water-ab- '40 sorptivity and high wet-strength and hence especially .adapted for such uses as have hereinbefore' been mentioned. When I say that cellulose acetate is water-repellent, I mean that, unlike a dried glue film, which swells appreciably when soaked in water, a dried cellulose acetate film formed from an organic solventsolution of cellubase of high p rosity and absorbency and to in- 7 corporate the cellulose acetate 'thereinto in a state of attenuation so great that the pore or void space in the base is substantially'the same as that .55

hazard than ordinary papers.

it has'undergone. Thus, a refined wood pulp in a similar base lacking the acetate. This means the water-holding capacity m: the base is substantially unaflfected by the cellulose acetate, whereas the wet-strength of the base is greatly in-- creased by reason of the bonding action of the cellulose acetate on the flbera- The resulting 5 paper products are substantially odorless. and non-toxic. Because of the presence therein of the cellulose acetate, they present even less fire If desired, the paper product of the present invention may be softened as by being led into frictional or rubbi contact with the edge of a doctor blade or by being impregnated with such cellulose-softenin or plasticizing agents as glycerine, ethylene glycol, oils, or the like.

In producing a paper product embodying the present invention for such purposes, for instance, as toweling, the procedure may be as follows:-. The absorptive paper base may be fabricated from substantially unbeaten or only lightly beaten 20 papermaking stock on a high-speed papermak- 'ing machine, 'as usual; and the paper may be creped while still on the machine as ordinarilf and collected in rolls as it is being delivered by the machine. The paper base thus fabricated 25 may have pore or void space therein amounting to, say, or more ofthe space occupied by the solid fibers alone. In other words, the waterholding capacity of the paper may amount roughly to 100% or more, by weight of the dry fibers, the particular water-holding capacity de-' pending upon the cellulose pulp used as raw material and the conditioning treatment, for in stance, the degree of preliminary beating, that consisting essentially of alpha cellulose, such as I may advantageously employ as raw material,

.wouldunder given conditioning treatment lead to a more absorptive paper base than such ordinary pulps as kraft and/or sulphite, such asI may also employ. The dried creped paper base may be progressively withdrawn from a roll and passed progressively through a bath of cellulose acetate solution containing any one of the usual volatile cellulose acetate solvents, such as acetone, ethyl acetate, etc. It is necessary that the cellulose acetate solution used as the impregnant for the paper base be quite dilute in order to deposit cellulose acetate in the desired highly attenuated state in the paper body, that is, without detracting significantly from its void or interstitial space. To this end, the cellulose acetate solution constituting the bath is preferably one whose cellulose acetate concentration or strength ranges from 0.5 to 2%. Such a solution containing,

limited small amount of cellulose acetate dis-' for instance, acetone as the solvent, is quite thin and fluent and so penetrates the paper base quickly and substantially uniformly throughout. As the impregnated paper base leaves the bath of cellulose acetate solution, free or excess solution may be removed therefrom, as by the action of squeeze rolls, to leave only the desired tributed substantially uniformly through the paper body. It is preferable that only about 0.5 to 2.0% of cellulose acetate, based on the dry weight of fiber, remain in the paper body in order to impart thereto the desired characteristics.

The particular amount of cellulose acetate with-- in the foregoing range that may be incorporated into the paper base for the purpose of the present invention. depends upon the compactness of the The impregnated paper sheet may then be dried as by passage through a hot air chamber or over drier drums, the particular dryer employed preferably being equipped with a solvent-recovery system. The cause of the comparatively small amount of solvent present in the impregnated paper and the volatility of the solvent, drying of the impregnated paper may be effected rapidly, insomuch that it is possible to employ in. a continuous process, such as described, only one large drier drum such as constitutes the dry end of a so-called Yankee papermaking machine.

. the Oils such as castor oil do like- If desired, the dilute cellulose acetate solution may be applied to the paper base other than by immersion of the base therein. Thus, the' solution may be spread on a face of the base or be picked up by the base from an applicator or kissing roll rotating partially submerged in the solution, in which case the solution because of its high fluidity penetrates quickly and substantially uniformly throughout the paper body. The amount of cellulose acetate thus introduced into the base is controlled as in the immersion and squeezing treatments already described.

. The dried impregnated product may be softened, if desired, as hereinbefore described. when softening agents are used, however, thermal?- be added to the cellulose acetate solution so as to obviate. a separate "softening treatment. For

instance, rather than glycerinating' the dried impresnated product, 'glycerine may. be added in appropriate amount to the impregnating cellulose acetate solution, particularly when the cellulose acetate solvent is acetone, since glycerine is conipatible with acetone. cresyl phosphate, dibutyl phthalate, etc. may also be added tothe cellulose acetate solution to develop soft or emollient quality in-the finished paper product. These latter plasticizers act as softeners upon both the cellulose acetate and The rate at which water is or imbibed by the finished paper product may be increased by adding small amounts of suitable so-called wetting-out agents to the paper base or to the imcellulose acetate solution. Among such agents may be mentioned Nekal BX,

.for the crepe to pull out.

Such plasticizers as triwhich is the sodium salt of naphthalene sulphonic acid with side chains; Nekal A", which is the crude sodium salt of octohydro-anthracene metasulphonic acid; "Nekal AEM, which is a combination of Nekal A with methylhexalin; "Neomerpin N", which is a high molecular weight sulphonic acid; etc.

The finished impregnated paper product has substantially the creped form imparted to the paper base during the papermaking operation by reason of the fact that the organic solvent solution of cellulose acetate does not hydrate or swell the fiber as does water or an aqueous solution and, accordingly, there is very little tendency Since the cellulose acetate solution is colorless, a white paper base treated as hereinbefore described is not dis-- colored; nor does the cellulose acetate undergo any decomposition necessitating any chemical after-treatment of the impregnated paper product.

The absorptivityof the finished paper product may be increased by causing a precipitation of the cellulose acetate inthe freshly impregnated paper base. Thus, rather than passing the paper base immediately after impregnation with the dilute cellulose acetate solution to a dryer,the wet, impregnated base may be treated with water, as by running it through a water bath, to cause the acetate'to precipitate out of solution onto the fibers, whereupon excess water may be removed from the sheet as by squeeze rolls and the sheet then dried. Such a practice works to good advantage when the cellulose acetate solvent is, like acetone, ,water-miscible. The cellulose acetate solvent ,leached out of the sheetby the water bath may, when the bath becomes overconcentrated therewith, be recovered by distillation from the bath eilluent. In such case, the fibers of the finished paper product carry minute discrete particles of cellulose acetate which perform a fiber-bonding service but do not prevent quick access of water to the individual fibers themselves.

Other water-repellent cellulose esters might be used in lieu of cellulose acetate according to-the present invention, but cellulose acetate is the preferable ester, possessing the advantage of lower cost over such esters-as the formate and butyrate and being 'without the fire and ex-- plo'sion hazard of the less expensive cellulose nitrate. I

It is a surprising phenomenon that despite their content ofwater-repellent material, the paper products of the present invention have high water-holding ability. In other words, they do not tend to shed water as do so-called sized papers. While I cannot account with precision for the water-holding ability of. the paper products of the present invention, it is my theory that, unlike the initially water-soluble wet-strengthening agents, namely, the regenerated cellulose and the glue, hereinbefore mentioned, which are believed to attach themselves'tightly on the fiber walls and to wet all of the wall surface but nevertheless to permit water to diffuse therethrough to the fiber walls, the cellulose esters by virtue of 1 deposition from organic solvent solutions do not become so intimately attached to the fiber walls as not .to permit seepage in between them and the fiber walls and further do not "wet orcover all the fiber surfaces. In other words, it maybe the case that even though practically all of the fiber surface is thinly coated with the waterrepellent cellulose ester, there aremyriad microscopic loci on the fiber walls that have escaped wetting by the ester and that constitute startin points for the water to hold onto the paper and to spread by capillary action into the bodies of the fibers as well as to stay in the interstitial or void space of the paper body. This does not happen when a paper base is treated with a comparatively strong solution of cellulose ester; and in terms of my theory this could not happen, since the amount of cellulose ester available for coating the fiber walls and occupying the pores and interstices of the paper is so large as leave no uncoated starting points on the wall surfaces for the influx of water into and throughout the fiber bodies or walls. I

It might be remarked that when a cellulose acetate film is cast or set from an acetone solution, it is necessary to take certain precautions in order to avoid what is sometimes termed a milky or smoky effect in the film. Indeed, it

is quite difilcult to produce from acetone solutions of cellulose acetate films which are per.- fectly transparent. The presence of small amounts of water in the solvent is responsible for impairment in the transparency of the film; and, unless precaution is taken to exclude water-from the acetone solvent, residual traces of water in the film will spoil its transparency. Undoubtedly, the acetone evaporates more rapidly than the water and as the last traces of water are expelled from the cellulose acetate film, there is a crazing action on the film, which is very apparent. So far as I have been able to ascertain, when a very dilute cellulose acetate solution-is applied to a porous paper sheet, as hereinbefore described, and when the solvent, for instance, the acetone, is evaporated, there-is no continuous film of acetate deposited in the sheet but only multitudinous partly connected cellulose acetate particles between which there is a definite lack of the kind of continuity that exists in a cellulose acetate film. This is particularly true if the paper base is treated with the dilute cellulose acetate solution in the presence of a small amount of moisture, that is, when the base sheet carries moisture therein and/or when the cellulose acetate solution itself is notcompletely anhydrous but carries a small amount of water dispersed or dissolved therein. Accordingly, it may be distinctly desirable in accordance with the present invention to treat the paper base while it contains a small percentage of moisture, say, about 5 to 12% of moisture and/or to use as the treating solution a dilute cellulose acetate solution containing, say, about 2% to 5% of water;

dissolved or dispersed inthe volatile organic solvent solution, for instance, an acetone solution of cellulose acetate containing such percentage of water dissolved therein.

. prises impregnating I claim:

1. A water-absorbing paper product of high wet-strength comprising a highly porous paper body and containing substantially uniformly distributed therethrough a water-repellent cellulose ester in the amount of about 0.5%, to 2.0%, based on the dry weight of the paper body, deposited in said body from organic solvent solution in an attenuated and discontinuous such that water brought into contact with said paper product spreads by capillary action to the bodies of the fibers as well as entering the pores and interstices in said paper body.

2. A water-absorbing paper product of high wet-strength comprising a highly porous body and containing substantially uniformly distributed therethrough cellulose acetate in the amount of about 0.5% to 2.0%, based on the dry weight of the paper body, deposited in said paper body from organic solvent solution in an attenuated and discontinuous film suchthat water brought into contact with said paper product spreads by capillary action to the bodies of the fibers as well as entering the pores and interstices in said paper body.

3. A method of producing a water-absorbing paper product of high wet-strength, which comprises impregnating a highly porous paper body substantially unif rmly throughout with a dilute organic solvent solution of a water-repellent cellulose ester in such amount as to incorporate into said body about 0.5%to 2.0% of said cellulose ester, based on thedry weight of said paper body, and removing the organic solvent from the impregnated paper body, and depositing said celluloseester therein from solution in an attenuated and discontinuous film such that water brought into contact with the resulting paper product spreads by capillary action to the bodies of the fibers as well as entering the pores and interstices in'said paper body.

4. A method of producing a paper product of high wet-strength, which coma highly porous paper body substantially. uniformly throughout with a dilute organic solvent solution of cellulose acetate in such amount as to incorporate into said body about 0.5% to 2.0% of cellulose acetate, based on the dry weight 01' said paper body, and nemoving the organic solvent from the impreg GEORGE a. RICIHI'ER.

the pores and interwater-absorbing