CA2095554A1

CA2095554A1 - Bleached chemithermomechanical hardwood fibers for soft tissue

Info

Publication number: CA2095554A1
Application number: CA 2095554
Authority: CA
Inventors: William D. Lloyd
Original assignee: Kimberly Clark Corp
Current assignee: Kimberly Clark Corp
Priority date: 1993-02-05
Filing date: 1993-05-05
Publication date: 1994-08-06

Abstract

ABSTRACT OF THE DISCLOSURE

Hardwood bleached chemithermomechanical pulp (BCTMP) fibers at amounts of about 5 weight percent or greater provide a soft tissue useful for use as facial or bath tissue. These fibers are relatively inexpensive compared to conventional chemical pulps having lower yields.

Description

2095~
PATENT

BLEACHED CHEMITHERMOMECHANICAL HARDWOOD FIBERS FOR SOFT TISSUE

Backqround of the Invention In the paper industry, chemithermomechanical pulps such as bleached chemithermomechanical pulp (BCTMP) have been used as a source of relatively inexpensive fiber for produc:ts such as multi-ply board and the like. These pulps are generally produced by a mild chemical treatment of wood chips and bleached with peroxide. Such processes are well known in the industry. Because BCTMP is a high yield pulp (about 90 percent or greater) containing a substantial amount of lignin, paper sheets made with such pulps are generally characterized as having high strength and stiffness. For this reason BCTMP pulps have not been previously used for making high-quality, soft t;ssue products such as facial tissue and bath tissue, where softness is a primary attribute. Instead, pulps used for making soft tissue products have been made using chemical pulps, such as kraft pulps, which have a much lower yield of about 50 percent or less and are therefore significantly more expensive.
Therefore there is a need for fibers or pulps which provide the necessary levels of softness required for today's tissue products, yet which are less costly than the chemical pulps currently in use.

SummarY of the Invention It has now been discovered that hardwood BCTMP pulp fibers, particularly maple BCTMP fibers, have unexpectedly good softness and strength properties which enable one to make a relatively high-quality tissue with a relatively low cost fiber source. As a result, it is not necessary to bury the BCTMP fibers in the middle of the tissue sheet by layering. Instead, the tissue sheets can be blended using a mixture of hardwood BCTMP fibers (for softness) and longer softwood fibers (for strength). If a layered tissue is preferred, the hardwood BCTMP fibers can be utilized in the outer layer(s).
Hence, in general, the invention resides in a soft tissue, useful as a facial or bath tissue, comprising a mixture of softwood fibers and hardwood fibers wherein about 5 dry weight percent or more - -: . ~ :
.. . ~- ~

-2~9~554 of the tissue fibers are hardwood BCTMP fibers. The softness of a tissue can be measured by trained softness panels, consumer testing, or by objective test methods which quantify factors known to contribute to softness, such as stiffness, surface depth, smoothness, protruding surface fibers, bulk, etc.
The amount of hardwood BCTMP fibers in the tissue will depend on the tissue properties desired. Suitable amounts include from about 10 to about 60 weight percent, or alternatively from about 20 to about 40 weight percent.
The softwood fibers can be any softwood fibers useful for tissue, such as southern or northern softwood kraft fibers or fibers produced by other pulping means. The presence of softwood fibers, which are longer than hardwood fibers, provides strength to the tissue. Preferred amounts of softwood fibers in the tissue are from -about 10 to about 60 dry weight percent. Lower amounts will be insufficient to provide adequate strength and stretch and higher amounts will detract from the softness of the tissue.
The hardwood fibers can comprise blends of hardwood species, including chemical pulp fibers or fibers produced by other pulping methods, as well as hardwood BCTMP fibers. Established softness fibers, such as are produced from eucalyptus chemical pulps, can also be blended with the hardwood BCTMP fibers to further enhance the softness. Preferred amounts of hardwood fibers in the tissue are from about 40 to about 90 dry weight percent. Lesser amounts will have little impact on softness, and higher amounts will lack adequate strength or stretch.
Suitable BCTMP fiber species include, without limitation, maple, birch, aspen and eucalyptus. Particularly preferred BCTMP fibers are blends of maple and birch. It is believed that, during the pulping operation, the longer birch fibers improve or enhance the break-up of the shorter maple fibers by some mechanical interaction, thereby resulting in pulp fibers more suitable for making soft tissue.

Examples In order to illustrate the effectiveness of using hardwoGd BCTMP
fibers for making tissue, two-ply, blended, wet-pressed facial tissues were made in a conventional manner using a number of 2 ~

differen-t papermaking furnishes. Specifically, the tissues were made by depositing an aqueous suspension of papermaking fibers on~o a forming fabric to form a web, dewatering and transferring the web to a papermaking felt, pressing the web onto the surface of a Yankee dryer, drying the web, creping the web, and plying the web together with another like web to form a two-ply tissue sheet. The two-ply tissues were calendared in some cases to improve the surface smoothness and hence softness. All of the produc:ts were evaluated by a trained sensory panel to ascertain their softness. Higher Panel Softness numbers correlate with greater softness. The various hardwood BCTMP fibers used herein were purchased from Tembec Company in Canada.
The results are set forth in the Table below:

TABLE
Sample Furnish Calendared? Basis Weiqht Tensile Softness Control 50% SW No 19.2 569 7.54 50% Euc Yes 19.3 540 7.93 1 35% SW No 19.4 610 6.73 35% Euc Yes 19.2 590 7.61 30% Aspen BCTMP
2 35% SW No 19.5 668 6.70 35% Euc Yes 18.5 627 7.40 30/O Birch BCTMP

3 20% SW No 19.3 694 6.30 20% Euc Yes 18.7 694 6.71 60% Birch BCTMP

4 35% SW No 19.0 408 7.55 35% Euc Yes 18.5 432 7.88 30% Maple BCTMP
35% SW No 19.1 473 7.60 35% Euc Yes 18.7 476 8.05 30% Maple BCTMP

6 35% SW No 19.5 593 7.51 35% Euc Yes 18.3 535 7.87 30% Maple BCTMP
7 40% SW No 19.2 488 7.17 60% Maple BCTMPYes 18.7 486 7.80 . ' ~ -' ~: : ' .:

209~4 As shown by these results, tissues containing substantial amounts of hardwood BCTMP pulp fibers exhibit levels of softness comparable to that of the control tissue made from hardwood kraft and softwood kraft fibers.
It will be appreciated that the foregoing examples, given for purposes of illustration, are not to be construed as limiting the scope of this invention, which is defined by the following claims and all equivalents thereto.

Claims

1. A soft tissue comprising a mixture of softwood fibers and hardwood fibers, wherein at least about 5 dry weight percent of the fibers are hardwood bleached chemithermomechanical pulp fibers.

2. The tissue of Claim 1 wherein the amount of hardwood bleached chemithermomechanical pulp fibers is from about 10 to about 60 dry weight percent.

3. The tissue of Claim 1 wherein the amount of hardwood bleached chemithermomechanical pulp fibers is from about 20 to about 40 dry weight percent.

4. The tissue of Claim 1 wherein the hardwood bleached chemithermomechanical pulp fibers comprise maple fibers.

5. The tissue of Claim 4 wherein the hardwood bleached chemithermomechanical pulp fibers comprise a blend of maple fibers and birch fibers.

6. The tissue of Claim 5 wherein the hardwood bleached chemithermomechanical pulp fibers comprise a blend of about 75 percent maple fibers and about 25 percent birch fibers.

7. The tissue of Claim 1 wherein the hardwood bleached chemithermomechanical pulp fibers comprise birch fibers.

8. The tissue of Claim 1 wherein the hardwood bleached chemithermomechanical pulp fibers comprise aspen fibers.

9. The tissue of Claim 1 wherein the hardwood bleached chemithermomechanical pulp fibers comprise eucalyptus fibers.

10. The tissue of Claim 1 comprising about 35 weight percent northern softwood kraft fibers, about 35 weight percent eucalyptus fibers, and about 30 weight percent aspen bleached chemithermomechanical pulp fibers.

11. The tissue of Claim 1 comprising about 35 weight percent northern softwood kraft fibers, about 35 weight percent eucalyptus fibers, and about 30 weight percent birch bleached chemithermomechanical pulp fibers.

12. The tissue of Claim 1 comprising about 20 weight percent northern softwood kraft fibers, about 20 weight percent eucalyptus fibers, and about 60 weight percent birch bleached chemithermomechanical pulp fibers.

13. The tissue of Claim 1 comprising about 35 weight percent northern softwood kraft fibers, about 35 weight percent eucalyptus fibers, and about 30 weight percent maple bleached chemithermomechanical pulp fibers.

14. The tissue of Claim 1 comprising about 40 weight percent softwood kraft fibers and about 60 weight percent maple bleached chemithermomechanical pulp fibers.

15. A soft tissue comprising a mixture of from about 10 to about 60 weight percent softwood fibers and from about 40 to about 90 weight percent hardwood fibers, wherein from about 10 to about 60 weight percent of the fibers are hardwood bleached chemithermomechanical pulp fibers.

16. The tissue of Claim 15 wherein the hardwood bleached chemithermomechanical pulp fibers comprise maple fibers.

17. The tissue of Claim 15 wherein the hardwood bleached chemithermomechanical pulp fibers comprise maple fibers and birch fibers.

18. The tissue of Claim 15 wherein the hardwood bleached chemithermomechanical pulp fibers comprise about 75 weight percent maple fibers and about 25 weight percent birch fibers.