US3173830A

US3173830A - Paper comprising collapsed regenerated cellulose fibers

Info

Publication number: US3173830A
Application number: US820602A
Authority: US
Inventors: Harold F Wise; James H Filling; Don S Nelson; Wharton John
Original assignee: Courtaulds PLC
Current assignee: Akzo Nobel UK PLC
Priority date: 1959-06-16
Filing date: 1959-06-16
Publication date: 1965-03-16
Anticipated expiration: 1982-03-16
Also published as: GB945306A

Description

March 16, 1965 H. F. WISE ETAL 3,173,830

PAPER COMPRISING COLLAPSED REGENERA'IYEDCELLULOSE FIBERS Filed June 16 1959' II/II,

I III, III/II WM 0 f llll ll/l ffllllJ fimw M1 United States Patent 3,173,830 PAPER COMPRISTNG (ZOLLAPSED REGEN- ERATED CELLULOSE FIBERS Harold F. Wise, .lames H. Filling, Don S. Nelson, and

John Wharton, Mobile, Ala, assignors, by mesne assignments, to Courtaulds, Limited, London, England, a

British company Filed lane 16, 195?, Ser. No. 320,6tl2 11 Claims. (Cl. 162-446) This invention relates to a new type of paper and to a new paper-making process.

Many proposals have been made over the years for introducing regenerated cellulose fibers into paper. In general, it has been felt that if regenerated cellulose fiber could be incorporated into paper, advantages could be obtained because the fiber could be tailor made as to staple length, denier and the like according to the properties desired in the paper.

In conventional paper made from natural cellulose, i.e. wood pulp, rags, and the like, the paper is bonded by the interlocking of fibrils which are produced when the stock is beaten. Unfortunately, regerenated cellulose fibers cannot be fibrill'ated by beating in the same way that natural cellulose can be, and so with regenerated cellulose fibers, some other source of bonding has to be employed.

It has been proposed to add various adhesives to the paper stock; such techniques, however, add considerably to the cost of the paper. It has also been proposed to treat a newly laid down paper sheet with caustic soda to cause softening and coalescence of the fibers. Treatments of this nature are, however, not Well suited to incorporation in paper-making processes on conventional paper-making machines.

It has now been discovered that certain types of regenerated cellulose fibers have sufiicient natural cohesion to form a strong bond without the addition of any external adhesive. Such fibers are characterized by a crosssection (taken in a direction substantially perpendicular to their axes) in which one dimension is from about five to about fifteen times the other. Preferably, they contain between about 1.5 and about 4.0% by weight of a finely divided inert particulate material. Such fibers can be used by themselves in conventional paper-making processes, without added adhesive, to give a smooth, strong sheet.

The invention, therefore, comprises a paper containing between about 10% and 100% by weight of regenerated cellulose fiber, each of said fibers having a crosssection in a plane perpendicular to its axis such that one dimension is from 5 to 15 times the other.

The invention further comprises in a method for making paper wherein a slurry of fibers is deposited on a surface and liquid is moved therefrom .to form a paper sheet, the improvement which comprises forming said slurry at least in part from generated cellulose fibers having a crosssection in a plane perpendicular to its axis such that one dimension is between about 5 and about 15 times the other.

The drawing is a cross sectional view, greatly enlarged, of a regenerated cellulose fiber as used in the present invention, taken in a plane perpendicular to its axis.

The fibers which are used in the present invention are preferably collapsed hollow fibers made by extruding a viscose containing a suitable gas-forming agent and preferably also containing an inert particulate material, into a ice conventional spinning bath. As they are removed from the spinning bath the fibers are of tubular shape, but upon subsequent washing and drying, they collapse to give fiat filaments.

More specifically, filaments having the dimensions required for the present invention may be made by extruding a conventional viscose containing 1040% on the weight of the cellulose, of an alkali or alkaline earth metal carbonate or bicarbonate into an acid spin bath. Thus, for example, suitable fibers can be made by extruding a viscose containing 610% by Weight cellulose, 57% NaOI-i, 1-4% sodium carbonate, having a total sulfur content of say 1.5 to 3 and a salt number of 5.0 to 7.0 into a spinning containing 11.5-12.5% by weight H 0.5 to 2% ZnSO and 18-25% Na SO Preferably the viscose will also contain from about 0.15% to about 0.40% of an inert particulate material.

After emerging from the spinning bath, the fibers may be cut up to form a blanket of staple fibers and then subjected in the form of a blanket to the various washing treatments customarily given regenerated cellulose fibers, such as a regenerating treatment with dilute acid, a desulfurizing treatment with Na 'S and a sou-ring treatment, again with dilute acid. Following this the blanket may be dried and stored; or it may be sent directly to a papermaking plant, where it can be opened by jets of water to form a suitably slurry.

Instead of being treated as a blanket of cut staple, the fibers may be treatedin the form of a tow with the various washes'outlined above; and cut up into staple at some later time.

Thus, the fiber on coming from the spinning bath may be laid down as a tow in a plaited pattern on a moving belt, and subjected to the various washes in that form. After treatment the tow may be dried and stored. It may be furnished to the paper-making plant as tow; or it may be cut up into staple fiber beforehand.

The fiber as used preferably has a denier of about 1.5 to about 8 and is from say A3" to 1 /2", preferably from A" to ,42 long.

In the drawing a fiber of the type used in the invention is seen in cross section. It will be observed that its width, i.e. the dimension 1:, is from 5 to 15 times its thickness, i.e. the dimension a.

The inert particulate material used in the present invention may be virtually any solid material which is inert with respect to the viscose and the spinning bath. Titanium dioxide is preferred, but alumina, silica, carbon black, and various pigments may also be used. The role of the inert material is twofold. In the first place it aids in forming fibers which are evenly inflated or tubular along their length by providing nuclei for the formation of gas bubbles. Thisfunction of the solid particles has been used hitherto in making inflated fibers. However, were the solid used only as an aid in gas formation, a much smaller amount, say 0.1% on the weight of cellulose, would be sulficient. The second function of the solid material is to raise fiber to fiber friction. The means by which this is accomplished is not known, but at least 1% on the weight of cellulose appears to be necessary for an appreciable effect to be obtained. There is no great advantage in using more than about 4%. The average particle size of the material should be not greater than about 1 micron and, preferably, particles above 5 microns in size should be absent.

Paper according to the present invention may consist wholly of regenerated cellulose fibers or it may consist partly of regenerated cellulose fibers and partly of conventional natural cellulose fibers, e.g. paper pulp.

Besides simple blends of the special regenerated cellulose fibers referred to above with conventional cellulose fibers, other materials, cellulosic and non-eellulosic, may be used in papers according to the invention. Thus, for example, the invention includes blends of the special regenerated cellulose fibers with nylons, acrylic fibers, polyester fibers; cellulose acetate and other cellulose organic ester fibers. Such blends may or may not include conventional cellulose paper-making fibers. Normally at least regenerated cellulose fibers arerequired toappreciably affect the characteristics of the final product.

In making paper according to the invention, the regenerated cellulose staple fiber need not be subjected to the prolonged beating that is required forconventional, natural paper-making fibers, since the cohesion of the novel paper does not depend on fibrillation, which is one of the more important effects of beating conventional fibers. It is desirable, however, to create an even slurry of the fibers for use in paper-making machines and one way to achieve this effect is to run the fibers through a refiner or Jordan engine, as a slurry containing from say .1 to 5.0% by weight fibers. Other mixing devices may be used; for example, in making hand sheets for test purposes, a Waring Blendor and a Tappi Standard Disintegrator have both been used successfully.

In many instances blends of the regenerated cellulose fiber and conventional paper-making fibers are desirable. In preparing such blends, the conventional fibers may be beaten in a beater to the desired freeness (say 500 Canadian) and then the regenerated cellulose component added. After circulating through the beater just enough to disperse large concentrations of regenerated cellulose fiber, the mixture may be sent to a Jordan for further mixing and for further refining of the natural paper. The fiber concentration in the beater (after addition of regenerated cellulose) is about 1.0 to 6.0%. In the Jordan it is about one-half that.

When the fiber has been dispersed as a slurry, it is formed into a paper by any conventional method. In the laboratory, test sheets are made from a slurry having 'a fiber concentration of say 0.05 to 0.2% on a Standard British Sheet Mold. Usually, following Tappi Standard T205 M-53, a concentration of 0.15% is used. For

large scale production, any conventional machine of the Fourdrinier type may be used. In such machines an aqueous slurry containing say 0.1 to 1.0% fiber is formed in the head box of the machine and is then poured onto a moving screen where the water is sucked off to form the paper. The paper may be pressed and dried as desired in accordance with conventional practice.

If desired, conventional sizes may be added to the fiber at any stage in the process, from the beater to the head box of the, paper-making machine. Alternatively, sizes may be applied to the paper after it has been formed. The character and quantity of the size depends on the use to which the paper is to be put, as will be understood by those skilled in the art.

Paper made according to the invention is in general less dense and more porous than comparable paper made from paper pulp. It has, in general, lower tensile strength but greater tear strength, greater fold strength and greater bursting strength than similar papers made from wood pulp.

The invention will be further described with reference to the following specific examples which, it will be understood, are given (for purposes of illustration only and are not to be taken as in any way restricting the invention beyond the scope of the appended claims.

EXAMPLE I A viscose is prepared having the following characteristics:

Cellulose percent by weight 7.5

NaOH do 6.0 Na CO do 2.5 Total sulfur do 2.1 Salt index do 5.0

This is spun into a spinning bath having a temperature of about 48 C. and the following composition (Wt. )1

H 12.0 335 21%? 3. 4 Water balance -at room temperature with a final neutral rinse at 70 C.

The blanket is then dried and stored.

Upon examination it is found that the individual fibers are fiat, deflated tubes each having a cross-section in a plane perpendicular to its axis such that on the average one dimension is about ten times the other.

The fibers made as above are used to make paper test sheets 6%" in diameter on a British Standard Sheet Mold. Four different types of sheets are made up. In trial A the sheets are made solely from pine paper pulp (500 freeness). In trial B the sheets contain 75% by weight pine paper pulp (500 freeness) and 25% of the regenerated cellulose fiber. In trial C the sheets consist of 50% regenerated cellulose fiber and 50% pine paper pulp (500 freeness). In trial D the sheets are regenerated cellulose.

In making the sheets the regenerated cellulose fiber is opened by jets of water to form a slurry. This slurry is then put into a standard Tappi disintegrator with conventional pulp as appropriate and sufiicient water to bring the fiber concentration to about 1.75% by weight. The disintegrator is run for 300 counts to form a smooth dispersion. This dispersion is diluted to 0.15% by weight and the sheets are made on a Standard British Sheet Mold. They are given a first pressing of 50 p.s.i. for five minutes. They are then reversed on a dry blotter and repressed at 50 p.s.i. for two minutes. Finally, they are dried at 50% relative humidity and 23 C. (73 F.) until equilibrium is reached with the conditioning atmosphere. This procedure is in accordance with Tappi Standard T220 M-53. The sheets are then tested for tear factor, porosity (air), tensile strength, breaking length, stretch and fold strength. The results appear in Table I below:

Table I Sample A B C D Percent Rayon (by weight) 0 25 50 100 Percent Pulp (by weight) 100 75 5O 0 Basis Weight Oven Dry (Weight; in

pounds of 500 sheets 24 x 40") 43.0 42.6 42. 1 44. 5 Caliper (Thickness in inches x 0.001) 3. 7 3. 8 4.0 5. 4 Apparent Density (Basis Weight/ Caliper 11.6 11.2 10.5 8. 2 Tear Factor 123 142 189 265 Air Porosity (see/100 cc.) 19 9 4 0 Tensile Strength (lbs/0.5" width) 14. 3 12. 2 9. 5 4. 7 Breaking Length (meters) 7, 270 5, 700 2, 680 Stretch (percent) 3.1 3.7 3. 7 1. 4 Fold (MIT) 909 714 706 644 Details of the tear factor test are found in Tappi Stand-' EXAMPLE II Example I is repeated except that the tow emerging from the spinning bath is subjected to the wash treat ments in that form. After drying it is cut by hand into staple fibers exactly 4" long. These fibers are then used to make up two types of test sheets using the procedure of Example I. Type A contains 25% regenerated cellulose and 75% pine paper pulp (500 freeness). Type B is a 50-50 blend of the same stocks. Test results are shown in Table II.

Table II Sample Percent Rayon (by weight) 25 50 Percent Pulp (by weight) 75 50 Basis Weight Oven Dry 42. 6 40. 6 Caliper 4. 7 5. Apparent density 9. 1 7. 4 Tear Factor 231 438 Air Porosity (Sec [100 cc 3 1 Tensile Strength (lbs l 10.2 6. 5 Breaking Length (Ineters) 6,080 4,080 Stretch (percent) 3. 0 2. 3 Fold Strength (MIT) 548 1,047

EXAMPLE III The procedure of Example I is repeated except that the viscose has the following composition: Cellulose percent by weight 7.5 NaOH do 6.0 Na CO do 25 TiO do 0.19 Total sulfur do 2.1 Salt index 6.0

The staple fibers after washing and drying are found to have a cross-section in which, on the average, one dimension is 12 times the other.

Hand sheets are made up as in Example I. Sheet A is 100% pine pulp (500 freeness), sheet B 25% regenerated cellulose and 75% pine pulp, sheet C 50% regenerated cellulose and 50% pine pulp, and sheet D 100% regenerated cellulose. The characteristics of these sheets are shown in Table III.

Table 111 Sample A B o D Percent Rayon (by weight) 0 25 50 100 Percent Pulp (1) weight) 100 75 50 0 Basis Wei ht Oven Dr 40.8 42.1 17.0 14.3 Caliper 3. 9 4. 2 4. 6 4. 3 Apparent Dens 10.5 10.1 10.4 10.4 Tear Factor 137 123 153 348 Air Porosity (sen/100 ee.) 11 18 18 Tensile Strength (lbs./% width 12.7 11.0 10.6 0.1 Breaking length meters) 7,020 7, 000 5, 620 3,473 Stretch (percent) 3.1 3.8 3.5 2. 0 Fold Strength (MIT) 403 713 685 702 EXAMPLE IV To show the difierence between fibers according to the invention and conventional rayon, sheets are made up with varying proportions of normal textile grade rayon staple fiber and pine pulp. Sample A has 10% rayon, sheet B rayon and sheet C 50% rayon. Sheets made from 100% rayon are so weak that they cannot be tested. The results of tests on the other sheets are shown in Table IV.

Table IV Sample Percent Rayon (by weight) 1O 25 50 Percent Pulp (by weight)- 75 50 Fold Strength (MIT) 699 333 50 Mullen Bursting Strength 111 87 50 Sheets made according to the process of Example I have Mullen factors as follows:

90% pulp/10% rayon 543 75% pulp/25% rayon 560 50% pulp/50% rayon 584 rayon 644 100% pulp 523 What is claimed is:

1. Paper comprising regenerated cellulose fibers, each of which has a cross-section in a plane perpendicular to its axis such that one dimension is between about 5 and about 15 times the other.

2. The paper claimed in claim 1 wherein the regenerated cellulose fiber comprises between about 10% and 100% of the weight of the paper.

3. Paper comprising regenerated cellulose fibers, each of said fibers having a cross-section in a plane perpendicular to its axis such that one dimension is between about 5 and about 15 times the other and containing be tween about 1.5% and about 4.0% by weight of an inert particulate material.

4. The paper claimed in claim 3 wherein the regenerated cellulose fiber comprises between about 10% and 100% of the weight of the paper.

5. Paper comprising regenerated cellulose staple fibers, each of said fibers being in the shape of a collapsed tube and having a cross-section in a plane perpendicular to its axis such that, on the average, one dimension is between about 5 and about 15 times the other.

6. Paper as claimed in claim 5 wherein the fiber contains from about 1.5% to about 4.0% by weight of an inert particulate material.

7. Paper as claimed in claim 6 wherein the inert particulate material is titanium dioxide.

8. Paper comprising wood pulp and not less than 10% by weight regenerated cellulose fibers, each of said rcgenerated cellulose fibers having across section in a plane perpendicular to its axis such that one dimension of said cross-section is fi'om 5 to 15 times the other.

9. Paper containing as its sole fibrous component, regenerated cellulose fibers each of which is characterized in having a width from 5 to 15 times its thickness and in containing from about 1.5% to about 4.0% by weight titanium dioxide.

10. Paper comprising regenerated cellulose fibers wherein a predominate portion of said fibers is composed of fibers, each of which has a cross-section in a plane perpendicular to its axis such that one dimension is between about 5 and about 15 times the other.

11. Paper comprising regenerated cellulose fibers which have a ratio of width to thickness of from about 5:1 to about 15 :1.

References Cited by the Examiner UNITED STATES PATENTS 1,464,048 8/23 Rousset 28-82 2,798,283 7/57 Magat et a1. 2882 FOREIGN PATENTS 674,577 6/52 Great Britain. 687,041- 2/53 Great Britain.

DONALL H. SYLVESTER, Primary Examiner.

RICHARD D. NEVIUS, JOSEPH B. SPENCER,

MORRIS O. WOLK, Examiners.

Claims

11. PAPER COMPRISING REGENERATED CELLULOSE FIBERS WHICH HAVE A RATIO OF WIDTH TO THICKNESS OF FROM ABOUT 5:1 TO ABOUT 15:1.