US 2683088 A
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Patented July 6, 1954 UNITED sr r- NT orslcs sor'r BIBULOUS SHEET N Drawing. Application June 10, 1952,
Serial No. 292,719
The present invention relates to bibulous cellulosic paper and paper tissues of .improved softness and to a method for the manufacture therefor. More particularly, the present invention relates to a process for the manufacture of bibulous paper and paper tissues of improved softness by a process wherein a substantially non-ionic water-dispersible, water-insoluble alkylene oxide adduct of a hydroxyalkyl amide of a carboxylic acid of 14-22 carbon atoms is added to a stock of cellulosic fibers in aqueous suspension and said adduct is adsorbed by the fibers. The invention includes the use of these adducts in conjunction with hydrophilic, cationic wetstrength resins, and further includes the formation of bibulous paper and paper tissues from the adduct-treated fibers with or without the wet-strength resins.
The manufacture of soft paper, and particularly personal bibulous tissues, of the type of expendable facial cleansing tissues, is an important rapidly growing specialty of the paper industry. These papers are characterized by their freedom from harshness, lack of odor, open texture, high absorbency for water and body fluids, and particularly by their softnessand physical limpness. In these respects, the personal tissues approximate, or even excel, the best grades of plain woven cotton towelling or handkerchief stock. 7
The problem of producing papers and paper tissues having the characteristics mentioned is a difficult one, as evidenced by the fact that many distinct procedures have been suggested for attaining this result. The papers and tissues produced by these processes, however, while frequently of considerable merit, are characterized by their high cost, whichrefiects the cost of the special pulps frequently employed, the cost of the special reagents utilized, and the additional labor and equipment usually required.
It is a particular object of the present invention to devise a method for manufacturing tissues of the type described from ordinary papermakers pulp or ordinary papermaking equipment, without the use of extra labor, spe cial machines, or costly reagents.
The discovery has now been made that soft bibulous paperand tissues of the type described can be prepared by forming a stock of cellulosic resins.
fibers in the ordinary way, adding to the stock a very small proportion, for example from 0.1% to 5% of a water-dispersible, water-insoluble alkylene oxide adduct of a hydroxyalkyl amide of a carboxylic acid having between about 14 and about 22 carbon atoms, aging the stock for a few minutes until adsorption of the adduct by the fibers is substantially complete, sheeting the stock at an appropriate basis weight, and drying the water-laid sheet.
Cellulosic fibers in aqueous suspension are negatively charged, and in the past it has been generally believed that such fibers are substantive only to positively charged or cationic particles. The amide adducts of the present invention, however, are almost if not entirely nonionic in nature. The reason why these adducts are substantively adsorbed in so rapid a manner by cellulosic fibers is therefore unknown, and I do not wish to be limited. to any particular theory.
The further discovery has been made that after adsorption of the above-described substantially non-ionic adducts by the fibers is complete, the fibers possess substantially unimpaired substantivity for cationic, hydrophilic, wet strength It has been found that after the fibers have been treated with a small proportion of the adduct within the range specified above, and while still in aqueous suspension, they may be treated with a small proportion of a cationic, hydrophilic, wet strength resinous colloid and then sheeted and cured at an elevated temperature in accordance with appropriate practice to develop the properties of the particular wet strength .resin used. A paper of substantially v the expected wet strength is thereby obtained.
. negatived, resulting in the formation of a paper of satisfactory wet strength which is even softer a ,9 than normal paper having substantially no wet strength at all.
The mechanism by which the amide adducts referred to reduce the harshness of cellulosic sheets is not understood, and again I do not wish to be limited to any particular theory. It is believed, however, that the action of these adducts is to interfere in some manner with the mutual adhesiveness of the fibers or the fiberto-fiber bonding which occurs when ordinary untreated cellulosic fibers are sheeted and dried. Thus, when the adducts of the present invention are employed, the fibers in the dry paper sheets appear to retain considerable freedom of movement causing the sheet to be apparently soft to the touch.
That the action of these compounds is not merely a lubricating one is proved by the fact that the softness of the sheet is not impaired when the adduct is extracted or leached from the sheet by the use of a suitable solvent, for example ethanol, as may be readily done.
Cellulosic papers and tissues prepared by the use of these adducts alone, in the absence of wetstrength resin, find use as facial tissues, toilet paper, blotting paper, diaper fillers, and paper intended for similar applications. Paper produced by the use of these adducts, followed by treatment with a wet-strength resin, find use as paper napkins, paper towels, and paper towelling.
Marked improvements have been obtained by the use of the present invention on papers made both from the widely available bleached and unbleached northern kraft pulps. Alpha pulp may also be formed into bibulous sheets of improved softness, according to the present invention, as well as the inherently soft pulps prepared by cooking cellulosic chips and bleaching and degrading the fibers by the use of sodium hypochlorite. Thus it appears that the benefits of the present invention extend to bibulous papers and tissues prepared from any of the commercial papermakers cellulosic pulps.
Adducts suitable for the practice of the present invention may be produced by known means by a variety of processes. Preferably, they will be prepared by a two-step process in which a hydroxyalkyl amide is formed by the reaction of a hydroxyalkylamine with an appropriate acid, followed by reaction of the amide with an alkylene oxide such as propylene oxide or butylene oxide. Ethylene oxide is preferred. In the first step, the acid is agitated with a slight excess of a primary or secondary hydroxylamine at about 200 C. until the calculated amount of water has evolved. Any excess or unreac-ted amine remaining in the reaction mixture is then stripped off. The residue is reacted with the alkylene oxide at about 120 C. in the presence of strong aqueous sodium hydroxide as catalyst, until the desired amount of the oxide has combined. A similar method is disclosed and claimed in copending application Serial No. 177,776 filed on August 4, 1950, by J. J. Carnes et al. now abandoned.
Any fatty acid, saturated or unsaturated, containing about 14-22 carbon atoms may be used in pure form or admixed with similar acids. Acids of this type are represented by such monobasic acids as coconut, palmitic, linoleic, linolenic, oleie and stearic acids and by abietic acid and rosin acids. Since mixtures may be used, both refined and crude tall oil fall within this class, crude tall oil consisting of about 40%-60% of fatty acids, %-10% of unsaponifiables, chiefly,
lignins and sterols, and the balance abietic and other rosin acids. Refined tall oil is crude tall oil from which most of the unsaponifiables and frequently a part of the abietic and other rosin acids have been removed. Since crude tall oil constitutes the most readily available source of fatty acids and yields results substantially equal to the results obtained by the use of the less readily available types of acid mentioned, crude tall oil is the raw material of choice for the practice of the present invention. In general, the preferred acids are those selected from the group of acids consisting of the fatty acids and rosin acids of about 14 to about 22 carbon atoms.
In addition certain of the higher di or poly basic acids formed by dimerizing or polymerizing one or more of the unsaturated monobasic acids of the class described have given comparable results. The cost of these acids, however, is prohibitively high, and therefore these acids fall outside the preferred group of acids set forth above.
The hydroxyalkylamines used in the synthesis described above are the short-chain amines having a chain length not in "excess of 4 carbon atcms, for example, 4-aminobutanol, 4,4- iminodibutanol and 2,2-iminodiethanol. Generally, however, superior results are obtained by the use of the readily available mono and diethanolamines. By the use of these amines, as described above, suitable substituted amides may readily be prepared.
The amount of alkylene oxide reacted should be at least sufficient to form an adduct which is freely dispersible when gently agitated with ten times its weight of water at 20 0., forming a stable, cloudy dispersion therein. At the other extreme, insufficient alkylene oxide should be used to form an adduct which is freely watersoluble, that is, which forms a clear, transparent mixture with ten times its weight of water at 20 C.
In the case of the mono substituted amides of monocarboxylic fatty acids, the minimum amounts of the alkylene oxide is about 3.5 mols and the maximum about 10 mols. Beyond this limit, water-soluble adducts form which exhibit reduced capacity to soften. In the case of the disubstituted amides of these acids considerably more alkylene oxide is necessary, and in the case of the tetrasubstituted diamides of the dicarboxylic fatty acids a larger amount still. In each instance the exact amount of oxide needed varies with the character of the acid selected, and the number of hydrcxyalkyl groups present. As a result, no numerical limit can be set to the amount of the alkylene oxide required in every instance.
For best results, the minimum proportion of the alkylene oxide which should be reacted is the proportion which is just sufficient to permit the amide to form a stable dispersion in water, and in this range, the softening action of the compound is at its peak while minimizing consumption of the more costly oxide. The use of more alkylene oxide usually confers no added benefit. When sunicient alkylene oxide is used to form an adduct which is freely soluble in water, forming a clear solution therewith, a paper of considerably reduced softness results.
The amide-ethylene oxide condensates prepared as described above are viscous pastes or waxy solids, and it is therefore advantageous to use them as 5% or more dilute, water dispersions thereof.
tween about 0.5% and 5.0%.
A noticeable degree of: softening results. when as little as 0.1% of the adduct is added, based on the weight. of the dry fibers. The improvement in softness continues rapidly through the range of roughly 0.5% toi.5%. The addition of further amounts of the adduct' causes'an additional degree of softening, but this generally is less than proportional to the additional amount added. Beyond 4%, the improvement-effected is slight, and the maximum proportion of amide which. can beused to advantage in most instances is about 5%, based on the weight of the fibers. As a result, it is preferred to add about 0.5% to 1.5% of the adduct.
The consistency of the stock during addition of. the adduct should be at a normal value hethe stock is stirred gently to distribute the adduct rapidly and uniformly therethrough. Thereafter, the stock is aged. ,In numerous instances,
depending on the character of the pulp and the adduct, a few seconds are 'sufiicient for this purpose whereas in other instances, -15 minutes should be allowed. For maximum efilciency the aging should be extended until adsorption of the added adduct is substantially complete, any unadsorbed adduct being wasted with the white water withoutbenefit to the paper.
The pH of the stock is not critical as adsorption of the adducts takes. place with the stock at any pH between about 2 and 9. Somewhat better results are obtained, however, when the stock is on the acid side, particularly between pH 4 and 6. Asa result, the choice of pH will depend primarily on other considerations such as the character of. the stock andits tendency to foam,- and the. presenceor absence of Wet'strength resins and pH sensitive fillers and colorants... A paper having a pH. of as high asabout 8.0 may be obtained, permitting the incorporation of acidsensitive fillers and. colorants into the stock, together with those wet strength resins: which are rapidly adsorbed under alkaline conditions. A suitable'wet. strength resin of this type may be formed by the reaction of ammonium with epichlorohydrin'as disclosed and claimed in 00- pending application Serial No. 277,741 filed on March- 20, 1952 by J. H. Daniel, Jr., et a1.
After sheetin the adduct treated fibers need only be dried, as the adducts of the present invention are not benefitted by subjecting them tocuring...conditions. .Thewaterlaid sheets will therefore be dried at about 200 F. as is normal; the
duration of the drying depending principally on the basis weight of the sheet. Where, however, a thermosetting wet strength resin has been added, the temperature and duration of the drying should be such as will develop the wet strength properties of the resin. While this varies with the specific wet strength resin employed, good results with ordinary paper are generally obtained when the resin is cured at 200 F. to 260 F. for 025 to 3.minutes. With very light weight papers and tissues the time is reduced, decreasing to about 1 second in the case of facial tissues.
The invention has been fully disclosed above and will be illustrated by the following examples which constitute preferred embodiments thereof, without being limitations thereon. Parts are by Weight unless otherwise noted.
Example 1 1350 parts (4 mols) of crude tall oil (Arizona Crude Tall Oil III, Acid No. 168) containing 48% During addition..
denser and a gas inlet tube.
ance abietic acid and resin acids, was mixed with 4.4 mols (280 parts) of technical monoethanolamine and charged into a reaction vessel equipped with an agitator, distilling column, and reflux condenser. The temperature of the mixture was raised to the point at which water evolution began, and then slowly raised to about 200 C. and maintained atthat temperature until no more water distilled. The heating was then continued for one additional hour at that temperature, the total reaction time being about 6.5 hours. Stirring was continued throughout. Vacuum was applied and excess monoethanolamine was distilled from the product. The product was a viscous syrup. On titration with 0.1 N-sodium hydroxide solution, the product was found to contain less than 3% acid, calculated as abietic acid.
From this amide a series of adducts were prepared as follows. The amide prepared above was charged into a reaction flask, together with 20 parts (5 mol percent of 40% aqueous sodium hydroxide solution as catalyst. The reaction flask was fitted with a stirrer, an ice-water-cooled con- The amide was heated to C. and ethylene oxide gas passed in at such a rate as maintained, a slow rate of reflux, the reflux condenser being opened to atmospheric pressure. During the addition, the temperature fluctuated up to C. The flask was wei hed from time to time to determine the amount of ethylene oxide adsorbed, and samples periodically withdrawn. The products were dark,
green-brown liquids, easily miscible with water and, forming a stable cloudy dispersion therewith. The adducts prepared contained the following amounts of combined ethylene oxide:
Adduct: Ethylene oxide A mols 3.7
C do 8.0
D do 10.0
A stock of northern bleached kraft pulp stocks were prepared by 'beatingxthe pulp to a green freeness of 475 cc. and diluting the stock to 0.6%
consistency. The pH of the stock was then adjusted to 4.5 by the use of dilute sulfuric acid and divided into aliquots. One aliquot was retained as control. To the other aliquots were added a"10% aqueous dispersion of a'dductAabove in the amounts shown. The amounts shown rep resent the weight of the'addu'ct' as such, based and their tensile strength in pounds per inch determined in their long direction, in their short direction, and the results averaged. The results were then corrected to a 25 x 47-500 basis weight. The results are shown in the table which follows. Three series of tests are shown, each with its own control, indicating performance of the tests at different times with separately prepared batches of the northern kraft stock.
Adducts Added Dry l lsljigtrcngth,
Test Amt Direction Average Desig. per; gg O een 1'- Short Long Found meted Control. None 49. 3 28. 4 31. 0 29. 7 28. 4 1 l 0. 5 3. 7 45. 8 19. 8 25. 6 22. 7 23. 3 3. 7 46. 2 18. 8 21. 2 20. 0 20. 3 3.7 47.1 14.4 15.6 15.0 15.0
Example 2 A stock was prepared by beating northern unbleached kraft pulp to a Green freeness of 525 cc., diluting the slurry thus obtained to 0.6% consistency and adjusting the pH to 4.5 with hydrochloric acid. The slurry was divided into four aliquots. One aliquot was retained as control. To the second aliquot was added 1% of adduct A above, as a 10% water dispersion. To the third aliquot was added 1% of the adduct, and after minutes, 1% of the cationic hydrophilic melamine-formaldehyde colloid prepared according to Example 1 of U. S. Patent No. 2,345,543, followed by aging for minutes. The percentages are based on the weight of thefibers. The fourth aliquot was treated only with melamine colloid as described. Handsheets were formed from all four aliquots as in Example 1, and their dry tensile 1 Estimated. after standing in water 1 hour.
I claim: 1. A soft bibulous sheet of felted cellulosic fibers having uniformly adsorbed thereon between 0.1% and 5.0% of their weight of a water-dispersible,
water-insoluble alkylene oxide adduct of a short chain hydroxyalkyl amide of an acid selected from thegroup of fatty acids and rosin acids of about 14 to 22 carbon atoms and mixtures thereof.
2. A sheet according to claim 1 wherein the amide is a hydroxyethyl amide.
3. A sheet according to claim 2, wherein the adduct is an ethylene oxide adduct.
4. A sheet according to claim 3, wherein the mixture of acids is the mixture of acids present in crude tall oil.
5. A soft bibulous sheet of felted cellulosic fibers having uniformly adsorbed thereon between about 0.1% and 5.0% of their Weight of a waterdispersible water-insoluble alkylene oxide adduct of a short chain hydroxyalkyl amide of anacid selected from the group of fatty acids and rosin acids of 14 to 22 carbon atoms and mixtures thereof, and between about 0.1% and 4% of its weight of cured cationic hydrophilic wet strength resin.
6. A sheet according to claim 5, wherein the adduct is an ethylene ovide adduct.
7. A sheet according to claim 6, wherein the mixture of acids is the mixture of acids present in crude tall oil.
8. A sheet according to claim 7, wherein the wet strength resin is a melamine-formaldehyde Wet strength resin.
References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Re. 21,530 Kritchevsky Aug. 13, 1940 2,325,302 Britt July 27, 1943 2,338,602 Schur Jan. 4, 1944 2,343,090 Smith Feb. 29, 1944 2,373,690 Kenda Apr. 17, 1945 2,387,429 Cate Oct. 23, 1945 2,400,544 Kline May 21, 1946 2,402,160 Heritage June 18, 1946 2,487,899 Sherman Nov. 15, 1949 2,510,284 Haggard June 6, 1950 2,601,671 Wilson et a1. June 24, 1952 I FOREIGN PATENTS Number Country Date 467,571 Great Britain June16, 1937 OTHER REFERENCES Boehm, Paper Trade J., May 2, 1940, pages -38.
Miskel, Paper Trade J June 29, 1944, page 27.