US2874618A - Creped paper with improved softness and process of making the same - Google Patents

Description

Feb. 24, 1959 CHRISTEN H. c. YANG CREPED P ER WITH IMPRQVED SOFTNESS AND CESS O AKING THE SAME Filed 7, 1955 I VEN CHRISTE .C.Y 0

L P ATTORNEY CREPED PAPER WITH IMPROVED SOFTNESS AND PROCESS OF MAKING THE SAME Application February 7, 1955, Serial No. 486,545 4 Claims. (CI. 92-70) This invention relates in general to the manufacture of creped paper and, more particularly, to the manufacture of creped paper specifically intended for such use as paper towels and tissues, wherein softness is an important requirement.

It is common practice for paper intended for towels and tissues to be creped.- The creping of the paper results in certain well known advantages. The fine wrinkles produced by the creping provide stretch, increase the bulk of the paper web by increasing its caliper, and, to some degree and with some types of paper, add increased softness.

In the customary process of creping paper the fine wrinkles are formed by means of a doctor blade engaging the web on a rotating roll and causing the web to be contracted longitudinally, and the creping wrinkles form a wavy pattern with the waves extending substantially transversely with respect to the longitudinal or general direction of travel of the paper web. However, while such creping increases the longitudinal flexibility of the paper web to some extent, it also increases its stiffness transversely. Such increased stiffness, in combination with the ridged formation produced by the creping, causes the resulting surface to feel harsh to the touch. This is particularly truewith creped papers made from some species of wood-fibers, notably Douglasfir and western hemlock commonto the Pacific Northwestern portion of the country.

The primary object of the present invention is to provide a creped paper, especially creped paper in the grades suitable for paper towels, 'tissues and the like, with markedly improved softness.

An important related object is to provide a creped paper which will have increased softness while still retaining its creping wrinkles.

Another object of the invention is to provide a simple mechanical process for softening creped paper without destroying the creping Wrinkles or sacrificing any of the advantages initially obtained by the creping.

A further specific object of the present invention is to provide a practical and continuous process for softening a transversely creped traveling web of light weight paper, which will considerably reduce the transverse stiffness of the paper web and improve its overall softness without eliminating the creping wrinkles or causing any appreciable change in tensile strength, water absorbency or caliper of the creped Web.

The manner in which the above objects and other incidental advantages are attained will be readily understood from the following brief description wherein reference is made to the accompanying drawings:

In the drawings:

Figure 1 is a more or less diagrammatic side elevation of the pair of rolls which comprise the means by which the present invention is carried out, this figure illustrating the creped paper in passage between the treating rolls;

Figure 2 is an enlarged fragmentary elevation of the treating rolls for the creped paper, the view being taken on the line 2-2 of Figure 1;

Figure 3 is a fragmentary sectional elevation, drawn 2,874,618 Patented Feb. 24, 1959 tea considerably enlarged scale, taken on line 33 of Figure 1;

Figure 4 is a face view, drawn to an enlarged scale, of a piece of creped paper before treatment in accordance with the present invention; and

Figure 5 is a corresponding face view, on an enlarged scale, of a piece of the same creped. paper after such treatment.

In the carrying out of my invention the paper or paper web, of the weight and'quarity selected as desired for the particular use for which the finished product is intended, is creped, as previously indicated, by conventional or suitable means, which creping results in the customary wavelike wrinkles extending substantially transversely across the paper web. As a result the paper or paper web presents a creped surface of familiar appearance as illustrated in Figure 4.

Subsequent to such creping the paper or paper web is passed between a pair of rolls, indicated at 10 and 11 respectively, in Figures 1, 2 and 3. These rolls rotate in opposite directions, as indicated by the arrows in Figure 1. The two rolls 10 and 11 may 'or may not be of the same diameter, but in any event have the same peripheral speed. Both rolls may be driven by any suitable means (not shown), or one roll may be driven and the other roll have rotation imparted to it by the rotation of the companion roll and the passage of the paper between the rolls.

One of the rolls, for example the lower roll 11, as shown in the drawings, has a smooth surface. The sur-' face of the other roll 10 is grooved or engraved so as to have parallel, uniform, equally spaced grooves 12 sepa-' rated by parallel, uniform lands 13. The parallel planes of the grooves and lands, while preferably perpendicular to the axis of the roll as shown, may, in the carrying out of my invention, be disposed at any angle from about 30 to with respect to the roll axis.

The width of each of the lands 13 should not exceed its inch, and preferably, depending upon the quality and thickness of the paper web, should be from to 5 inch. The width of the grooves 12, and thus the spacing between the lands 13, should not be greater than V2 inch nor less than & inch, and preferably should be from to A: inch. Although the depth of the grooveslZ is not critical, the depth should be at least greater than the thickness of the creped paper or paper web to be treated so that there will be. no contact between the bottom of the grooves and the surface of the paper.

The two rolls 10 and 11 are mounted in any suitable and adjustable supporting means (not shown) so that the pressure exerted on thepaper or paper web 14 passing between them will be of a predetermined amount sufiicient to impress permanent thin lines in the surface without eliminating the creping wrinkles. Also, when desired, the rolls should be so mounted that there is a limit to the minimum spacing between their peripheries, depend ing'upon the thickness and the nature of the paper being treated. The pressure exerted on the paper or paper web 14 by the lands 13 of the roll 10 must not be such as to cut into the surface or even to produce permanent smoothening out of the wrinkles at the lines of compression, but, on the other hand, must be suflicient to impress permanent continuous, thin, fine lines in the surface, and this, of course, causes a partial breaking down of the wrinkles, at the points where they are crossed by the continuous lines. As a result, due to the thinness of the impressed lines and the proper control of the pressure, the wrinkles give the general appearance of being unaltered although the continuous lines will nevertheless be visible. Preferably, but not necessarily, the engravedor grooved roll contacts the top face of the creped web of paper rather than the wire side of the web of paper.

higher or lower basis weight can be Preferably the rolls 10 and 11 are constructed of metal, and I consider steel most desirable because of its resistance to wear. It is necessary that the surfaces of both rolls be hard and non-yielding. The rolls may comprise either solid or hollow cylinders, and if hollow cylinders are employed these may be heated. Preferably, in the carrying out of my invention, the rolls 10 and 11 are installed on a conventional paper machine which is furnished with creping equipment and the rolls are located between the drying section of the machine and the take-up roll of the finished paper, so that the softening of the paper in accordance with my invention is eifectuated on a substantially dry paper web. If the paper machine is provided with a calender stack one of the calender rolls may be grooved or engraved and thus made to correspond to the roll 10 shown in the drawings. Also the treatment of the paper in accordance with my invention could also take place subsequently and thus during the paper converting operations after the making of the creped paper is completed.

My invention may be carried out with creped paper made from any desired pulps. Thus, for example, I have obtained satisfactory results with paper made from sulfite, kraft, or groundwood pulps, either bleached or unbleached, or from mixtures thereof. Preferably, the basis weight of the light-weight paper to be softened should be from about 8 pounds to about 50 pounds per ream (thus 8-50 pounds per 3,000 square feet), although paper of used. The amount of crepe in the paper may vary from as little as about 2 percent up to 20 percent, or higher. However, if there is a relatively high amount of crepe in the paper the lands on the grooved or engraved roll should be very narrow and close together, for example spaced of an inch apart.

The following examples illustrate the increased softness obtained in grades of creped paper toweling which were treated in accordance with my invention. In these examples a pair of steel rolls of the same diameter, both being driven at the same speed were used, the upper of the two rolls being grooved in the manner illustrated by roll 10 of Figures 2 and 3. The width of the lands on this roll was ,4 of an inch. The width of the grooves, or the spacing between the lands was 4, inch, and the grooves were inch deep. The two rolls constituted part of the calender stack of the paper machine, the grooved or engraved roll being the top roll of the stack and the stack being located between the last drier of a Fourdrinier type paper machine and the take-up roll for the finished paper. The transversely creped paper web was substantially dry as it was passed between the nip formed by the two rolls. The position of the rolls in the calender stack in these examples was such that their peripheries were barely in contact.

Tests for softness were made in each case before and after the treatment. The testing was done by cutting a strip V2 inch wide and about 6 inches long from the paper and placing one end of the strip between a pair of horizontal holding jaws so that a free portion 4 inches in length extended from the jaws. The free portion was allowed to deflect from the horizontal under its own weight and the amount of such deflection of the free end was tabulated in degrees by using a chart placed in vertical position behind the strip as it was tested, the chart being scaled from to 90, with 0 corresponding to the horizontal and 90 corresponding to the vertical. Thus, the softness was measured in terms of flexibility. To arrive at a numerical index for the softness, a test was made with a strip cut from the paper longitudinally, thus for ascertaining the flexibility in the machine direction, and the same test was repeated with a strip cut transversely across the paper, thus ascertaining the flexibility in the cross machine direction. The two results were then added together. An average was computed; from five such tests made for each grade of paper tested on both the wire side and the felt side of the paper.

EXAMPLE 1 This example shows the improvement in softness of two grades of creped toweling treated in accordance with my invention as described above, the two grades having approximately the same basis weight and having approximately the same amount of crepe.

This example shows the resulting improvement in softness in the machine direction and cross-machine direction of creped toweling of varying basis weights. The toweling was made from paper furnish consisting of 70% bleached sulfite pulp and 30% groundwood and had 5% crepe.

Softuess Before Treatment After Treatment Percent lbs. Softness per Improveream Ma- Cross Ma- Cross ment chine Machine Ma- Dir'ecchine Total Direcchine Total tlon Direction Direction tion Paper furnish==70% bleached sulfite.

30% groundwood. Percent crepe=5%.

EXAMPLE 3 This example shows the resulting improvement in softness of a toweling grade of a basis weight of 36 lbs. per ream, made from 70% bleached sulfite pulp and 30% groundwood and having various percentages of crepe.

This example shows the effect on some of the physical properties of creped paper of 32 lbs. per ream basis weight, made from 100% bleached sulfite pulp, when given the softening treatment in accordance with this invention.

Before After 7 Treatment Treatment Dry tensile machine direction, lbs 2.4 2. 4 Wet tensile machine direction, oz. 12 12 Water absorbency, see 45 42 Caliper, in- 0.0090 0. 0089 Snftnn s l EXAMPLE 5 Tests which I have made have shown that my process will also produce increased softness in creped paper containing mineral fillers such as clay, as well as 'in creped paper Which has previously been treated with chemical softening agents or wetting agents. This example, given by way of illustration, shows the improvement in softness obtained with my process when used on a tissue grade creped paper which had been treated with 1% based on the dry weight of pulp of a softening agent supplied by the Harshaw Chemical Company and known as Uversoft D.

Soitness Percent softness Before After Increase Treatment Treatment Thus, as shown by the examples given, the treatment of creped paper in accordance with my invention can improve its softness up to an extent of about 35%. Furthermore, this is accomplished without affecting the dry and Wet tensile strength of the paper, without changing its water absorbency and caliper to any significant extent, and without eliminating the creping wrinkles. The lightly impressed thin lines give the creped paper a distinctive finished appearance, and impart a pleasant feel to the creped surface of the paper.

The greatest utility of this invention is in the manufacture of paper toweling, tissue and other light-weight paper grades, where over-all softness is of paramount importance.

I claim:

l. The improved process in the manufacture of paper toweling which comprises creping the paper by forming creping wrinkles all extend g substantially in the same direction, impressing continuous thin fine lines into one face only of the creped paper, said impressed lines having an angularity of from 30 to 90 with said creping wrinkles, and controlling the pressure with which said thin fine lines are formed in the paper so that said wrinkles will give the general appearance of being unaltered although said impressed continuous fine lines will nevertheless be visible in the finished sheet, whereby the softness and flexibility of the paper will be increased while the caliper and tensile strength will remain substantially unchanged.

2. The improved process in the manufacture of paper toweling which comprises creping the paper by forming creping wrinkles all extending substantially in the sam direction, impressing continuous thin fine lines into on face only of the creped paper, said impressed lines havin an angularity of approximately with said crepin, wrinkles and the spacing between said thin fine lines no exceeding A; inch, and controlling the pressure wit] which said thin fine lines are formed in the paper so tha said wrinkles will give the general appearance of being unaltered although said impressed continuous fine line: will nevertheless be visible in the finished sheet, whereb; the softness and flexibility of the paper will be increased while the caliper and tensile strength will remain substantially unchanged.

3. A sheet of paper of such softness as to be suitable for toweling and like uses, said sheet having creped wrinkles extending substantially all in the same direction and having thin, fine, continuous, substantially parallel lines impressed into one face only of said sheet, said fine lines intersecting said crepmg Wrinkles at an angularity of from 30 to 90 and being visible in said sheet with the creping wrinkles appearing unaltered, said sheet having the tensile strength and caliper substantially unchanged and being characterized by greater over-all softness and flexibility and less surface roughness than the same sheet without said intersecting lines, while having the same tensile strength as creped paper without said intersecting lines.

4. An improved paper toweling consisting of creped paper having creped wrinkles extending substantially all in the same direction and having thin, fine, continuous, substantially parallel lines impressed into one face only of said paper, said fine lines intersecting said creping wrinkles at an angularity of approximately 90, being spaced apart a distance not exceeding inch, and being visible in said paper with the creping wrinkles appearing unaltered, said toweling having the tensile strength and caliper substantially unchanged and being characterized by greater over-all softness and flexibility and less surface roughness than the same toweling without said intersecting lines, While having the same tensile strength as creped paper without said intersecting lines.

References Cited in the file of this patent UNITED STATES PATENTS 1,680,203 Cannard Aug. 7, 1928 2,007,047 Gibbs July 2, 1935 2,020,928 Asnes Nov. 12, 1935 2,043,351 Fourness et a1 June 9, 1936 2,154,940 Ives Apr. 18, 1939 2,168,896 Asnes Aug. 8, 1939 2,729,267 Walton Jan. 3, 1956 2,780,573 Davidson Feb. 5, 9 7

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