WO2000058094A1

WO2000058094A1 - Use of cotton fibers in filter paper

Info

Publication number: WO2000058094A1
Application number: PCT/US2000/006429
Authority: WO
Inventors: Homan B. Kinsley, Jr.
Original assignee: Fibermark, Inc.
Priority date: 1999-03-26
Filing date: 2000-03-24
Publication date: 2000-10-05
Also published as: AU3739900A

Abstract

Provided is a filter paper, and method making same, using cotton fibers having a diameter between 9 and 23 micrometers. The source of the cotton fibers can be cotton rags, and in particular the off-cuts from denim clothes, with the pieces being chopped to the desired length. The use of such cotton fiber surprisingly results in a filter paper which has a high dust capacity as well as a high dust removal efficiency.

Description

USE OF COTTON FIBERS IN FILTER PAPER

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. provisional application Serial No. 60/126,321 filed on March 26, 1999.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to the use of cotton fiber in filter paper, and to a method of manufacturing such paper. More particularly, the invention concerns the use of cotton fiber derived from w.aste cotton rags, or pieces of waste cut as excess during the making of clothing.

Description of Related Art

The usefulness of filter paper can be measured by two attributes, which are its dust capacity and dust removal efficiency. Dust capacity is related to the bulk of the paper. The higher the bulk, the more volume there is within a sheet for dust to be retained. Dust removal efficiency, however, is related to the size of the pores in a sheet of paper. Therefore, in the manufacture of filter paper, the desire is to produce a paper with a high bulk, but with a small pore size.

Currently, filter paper is typically made so as to achieve high dust capacity, and this is achieved by using a stiff fiber which has a large diameter. Such fibers may be derived from a wood pulp such as Buckeye's HZP (a mercerized southern pine) and HBA (a chemically crosslinked southern pine), and these fibers have a diameter of about 45 micrometers. Filter papers made from these pulps tend to have high bulk, and thus high dust capacity, but disadvantageously have low dust removal efficiency due to a large pore size. The use of cotton fibers in conventional paper making is well known. Cotton fibers are harvested from the cotton plant (Gossypium hirsutium) . The cotton fibers are the seed hairs that were formed by the plant for the distribution of the seeds by the agent of the wind. The individual hairs are known as lint. They are typically from 9 to 23 micrometers wide and 12 to 64 millimeters long, with a cell wall thickness of 2.5 to 6 micrometers.

After the lint fibers are harvested, there remains a short, thick walled stub attached to the cotton seed. This short piece is milled off of the seed hull. The cleaned seed is pressed for the production of cotton seed oil. The short length of cotton fuzz that has been removed is known as linter.

Some of the best writing, book, and drawing papers are made from the lint fibers found in cotton rags. Lint fibers are converted into pulp by cooking in a mild alkaline liquor. Such cooking liquor can also contain wetting agents or detergents, and the cooking can continue with the use of steam, for between three and ten hours. After cooking, the pulp must be reduced in length by beating or refining, if the pulp is to be used in paper. The beating or refining of the cooked product also increases the swelling action of water to produce a softened and plastic fiber.

Cotton linter fibers have a different morphology than lint fibers. They are rounder, thicker, .and stiffer than lint fibers. Being stiff, if they are not overly beaten they produce an excellent filter pulp for automobile and industrial uses.

Thus, we observe that cotton lint fibers are mildly cooked and refined or beaten to produce a high strength, low porosity paper. Linter fibers are cooked, mildly refined, and used for the production of porous bulky fibers. Due to the vast availability of cotton waste, it would be of great economic value to find an appropriate use for the cotton. An object of the present invention, therefore, is to successfully utilize waste cotton fibers, and in particular chopped cotton fibers available from cotton waste materials, such as that chopped in making denim clothes.

Yet another object of the present invention is to provide a filter paper which is economical, employs cotton fibers, and exhibits good dust capacity and dust removal efficiency.

Still another object of the present invention is to provide a bulky paper which is economical and employs cotton fibers available from waste cotton materials.

These and other objects of the present invention will become apparent upon a review of the following specification and the claims appended thereto.

SUMMARY OF THE INVENTION

The present invention accordingly provides filter paper comprised of cotton fibers having a diameter between about 9 and 23 micrometers. Preferably, the fibers have been chopped to a length of between 2 and 8 millimeters. The use of such cotton fibers results in a filter paper which has high dust capacity and also high dust removal efficiency.

The present invention also provides a method of making stock for manufacturing such filter paper from cotton cloth which includes the steps of

(a) chopping cotton material into pieces preferably having a length between 2 and 8 millimeters,

(b) slurry ing the small pieces in water to form a slurry of cotton fibers,

(c) refining the fibers in the slurry, and

(d) removing the water to form a sheet.

This process is particularly suitable for using waste cotton cloths, and also cotton off-cuts resulting from the manufacture of cotton clothing, e.g., denim jeans. In another embodiment, the present invention relates to bulky paper comprised of cotton fibers having a diameter between about 9 and 23 micrometers. The use of such cotton fibers can provide a bulky paper exhibiting excellent absorbance and blotting characteristics, thereby making the paper useful, for example, as paper towel.

It is preferred that the filter paper, and bulky paper, of the present invention comprise at least 40% by weight, preferably at least a majority, 50% by weight, and can successfully be comprised of from 70-100% of cotton fibers having a diameter between about 9 and 23 micrometers. The preferred fiber length is between 2 and 8 mUl-Lmeters, more preferably between 3 and 6 millimeters (1/8 to 1/4 inch), and most preferably between 3 and 5 millimeters (1/8 to 3/16 inch). The fiber diameter preferably lies between 17 and 22 micrometers, and is most preferably around 19 micrometers.

It is further preferred that the cotton fibers in the filter paper are not water swollen. In the method of making stock for manufacturing filter paper according to the invention, it is further preferred that the slurry is refined using disk or conical refiners.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides an opportunity to utilize the scraps of cloth which are formed when demm (or other cotton cloth) is cut into the shapes needed for clothing. It has been found that the cotton fibers of these scraps are generally lint fibers, and they can be easily handled in conventional paper making equipment. By this, it is meant that these small threads can be slurried in a pulper designed for wood pulps, pumped by conventional stock pumps, and refined with convention^ disk refiners. The resulting stock has been found suitable for making filter papers, which provide superior filtration performance. The cotton pulp slurry can also be used to make excellent bulky paper, useful in paper towels. The cotton fiber that is used is a cotton fiber which has a very small diameter, such as that of the lint cotton fiber, between about 9 and 23 micrometers. The fiber diameter is preferably in the range between about 17 and 22 micrometers, and most preferably from about 18 to 20 micrometers. The fiber can be advantageously obtained from waste cotton rags or pieces of waste cut as excess during the making of clothing. Of particular interest are cotton scraps of deriim, cut, for example, in the making of jeans, which cotton scraps have been found to provide good results.

The cotton fiber is also preferably cut or chopped, most advantageously to a length between 2 and 8 millimeters. It is more preferred for filter paper to use a fiber length ranging from 3 to 6 millimeters (Vs to ^xk inch), and most preferably between 3 and 5 millimeters (Vs to 3/16 inch).

The preferred source for the cotton fibers is deriim, which generally comprises uncooked lint fibers. It has been noted that by eliminating the cooking process, lint fibers become very resistant to the refining process. By resistant to the refining process is meant a fiber which remains stiff. The uncooked lint fibers are thus stiff and unswollen. By mechanically cutting the lint fibers into short lengths, one is able to avoid the hydration and softening of the fiber that would occur if one were to rely on fiber refining to achieve the desired fiber shorting. The cotton fibers used in the paper of the present invention can therefore be described as mechanically cut "raw" cotton fiber, with the raw referring to a fiber which has not been subjected to chemical cooking.

There is a distinct advantage in using lint fibers over linter fibers in that the fiber diameter of the lint fiber is smaller (between about 9 and 23 micrometers as described above) than the coarser linter fiber. This is important in filter paper since the filter efficiency is related to the fiber diameter. When papers are made of these chopped cotton fibers, they are found to deliver superior filtration performance. There are two important attributes of filter paper: dust capacity and dust removal efficiency. As had been learned, dust capacity is related to the bulk of the paper. The higher the bulk, the more volume there is within a sheet for dust to be retained. Dust removal efficiency, however, is related to the size of the pores in a sheet of paper. As is well accepted in the filtration industry, the size of the pores in a sheet of paper is determined by the fiber diameter. Small diameter fibers yield small pores and high dust removal efficiency. Paper made from the chopped cotton fiber surprisingly excels in both dust capacity and dust removal efficiency.

Therefore, there is a significant advantage gained by using the cotton fibers of the present invention. One can obtain the required bulk with a smaller diameter fiber. This translates into a filter with both high dust capacity and high dust removal efficiency. It is normally considered impossible to achieve both capacity and efficiency with one pulp. The wood based pulps which give high dust capacity deliver low dust removal efficiency. Wood pulps with small fiber diameters, like hardwoods, deliver low capacity. Only the chopped cotton fiber of the present invention does both. Since the chopped cotton fiber is smaller in diameter than hardwood pulps, it delivers a higher efficiency. It has been found that use of the cotton fiber of the present invention, of small diameter and uncooked, provides a filter paper that is more bulky and much more porous than what would be obtained using wood pulp under the same kinds of refining.

While the papers made with the cotton fibers of the present invention are particularly useful as filter paper, the papers can also be used as bulky paper for its blotting or absorbancy characteristics. Bulky papers are papers having a high void fraction, higher th.an normal paper. The void fraction is often greater than 70% by volume. Such bulky papers would be applicable in paper towels, blotters or coasters. The papers of the present invention, whether filter or bulky, can be comprised of substantially all cotton fibers of the present invention having a diameter between about 9 and 23 micrometers. The fibers can also be mixed with other fibers, wood pulp or synthetic or glass fibers. Generally, however, the papers are comprised of at least 40% by weight of the cotton fibers of small diameter of the present invention, preferably at least a majority, 50% by weight, and up to 100% by weight of the cotton fibers.

The papers are made by chopping or cutting cotton material comprised of cotton fibers having a diameter between about 9 and 23 micrometers into pieces having a length preferably in the range of from 2 to about 8 millimeters. The chopping or cutting procedure will generally result in most of the pieces being of the desired length, however, a distribution of lengths is achieved which will include some longer fibers/pieces. Once the pieces are cut, the pieces are slurried in water to form a slurry of cotton fibers, which are then refined, generally using conical or disk refiners, preferably a disk refiner. The water is then removed from the slurry to form a sheet, which can occur on a Fourdrinier machine. Once formed, the sheet is dried, e.g., on a dryer or in an oven. The sheet can then be pleated, etc. to form a filter paper, optionally with resin impregnation, or simply cut to size for use as bulky paper, e.g., paper towel.

The present invention will be further illustrated by the following Examples, which are provided purely for illustration and are not meant to be limiting.

EXAMPLE 1

450 grams of furnish was placed into a Valley Laboratory Beater, to which was added 24 liters of water. The beater was run with an unloaded bed plate for five minutes to disperse the fibers. The bed plate was then loaded with a standard 5,500 gram weight and the pulp was beat until it achieved 700 ml Canadian Standard Freeness. The pulp fibers were added to a handsheet mold and diluted to standard level. A handsheet was formed on a removable forming wire mesh. The forming wire mesh was removed with the handsheet and the handsheet was transferred to a drying blotter, and pressed very lightly. The handsheet was then transferred to a steam heated drum and allowed to dry.

Four handsheets were conditioned to TAPPI standards (50% Relative Humidity and 72 degrees F.). The handsheets were then tested to determme its physical properties. The four handsheets that were made and tested used the following furnishes:

Furnish A B C

Cut demm (3/16 inch), % 00 82.8 82.8

Polyester Fiber 1.5 denier x 0.25 inch, % 0 17.2 17.2

Lycoid Gum #260 (formation aid), % 0 0.7 0.7

Furnish for commercial grade filter paper

HP11 (Southern Softwood Kraft), % 20.4

Eucalyptus pulp, % 21.3

HBA (Cross-linked southern softwood kraft) 10.5

HPZ (Mercerized southern softwood kraft) 26.6

410 (Glass microfiber) 3.3

Polyester fiber 1.5 denier x 0.25 inch 17.7 Results of Physical Testing

The denim papers were nearly equivalent in permeability, pore size, and strength with the commercial grade filter paper. This was accomplished without the addition of expensive bulky wood pulps and glass microfibers. Thus, by using scrap cotton material as the source of cotton fibers, one can provide an excellent filter paper most economically and quite easily.

EXAMPLE 2

The following furnish was prepared in accordance with the present invention:

Furnish: Pounds Blue Denim Cotton Fiber 49.4% 1500

Westuaco Hardwood 34.1 1035

Polyester 1.5 denier ¹ " 16.5% 500

3035

Filter paper was prepared and tested as follows: Slurry fiber in pulper with 5,000 6. water (6.78% consistency)

Refining with double D refiner at 240 amp load and Bauer refiner at 190 amp load.

Run on 80" wide Fourdrinier at 210 ft/minute - No wet pressing, no calendering. Paper characteristics: Basis weight 99.7 lb/3000 ft² (161 g/m²) Caliper 0.0340 inch (0.864 mm) Permeability 44.6 cubic feet air at (no equivalent) 0.5 inch water pressure drop for 1 sq. ft area

3rd Bubble Pressure, 6.93 inches of water (176 mm water)

Kerosene Fluid

A standard commercial grade paper was prepared as follows using the following furnish:

Furnish: % > Pounds

HPII (Southern Softwood Kraft) 20.4 575 Eucalyptus Pulp 21.3 400

HBA (Crosslinked Southern Softwood Kraft 10.5 900 HPZ (Mercerized Southern Softwood Kraft) 26.6 375

410 (Glass Microfiber) 3.5 50 Polyester Fiber 1.5 denier x 0.25 inch 17.7 250

Refine with Double D refiner and Bauer Disk- Refine as needed to achieve specification.

Run on 80" wide Fourdrinier at 210 ft/rnin,

No wet pressing, no calendering Both papers were saturated with a phenol formaldehyde resin applied from methanol. Resin contents 19% . Both sheets were corrugated to a 0.019 inch corrugation depth and cured 15 minutes at 350°F. Both sheets were then tested, with the results tabulated below:

Physical and Filtration Results on Saturated, Corrugated, and Cured Paper

Denim Trial

11/10/97 Standard 964

Permeability, Frazier 45 48

Caliper, inch 33 34

Tensile, lb/inch width 6.1 8.4

Stiffness, Gurley mg : 1168 1447

Average of MD & CD

Mullen Burst, psi 6.1 8.5

3rd Bubble, inches water 6.9 5.8

Mean flow Pore, micrometers 26.5 25.9

BetaCom capacity mg/sq inch 107 108

BetaCom efficiency at particle size: 2μ 5μ 10jLl 15 i 20/χ 25_/x

Standard Grade 11 24 31 42 51 57

Denim 16 28 50 69 80 86

Conclusions: Denim paper slightly weaker, Denim paper equal in dust capacity, Denim paper more efficient at all sizes, and Can achieve efficiency without glass microfiber. The conclusions suggest that the filter paper of the present invention is not only more economical, but also more efficient than an expensive standard grade filter paper.

While the invention has been described with preferred embodiments, it is to be understood that variations and modifications may be resorted to, as will be apparent to those skilled in the art. Such variations and modifications are to be considered within the purview and the scope of the claims appended hereto.

Claims

WHAT IS CLAIMED IS:

1. A filter paper comprised of cotton fibers having a diameter between about 9 and 23 micrometers.

2. The filter paper of claim 1, comprised of at least 40% of said cotton fibers.

3. The filter paper of claim 1, comprised of at least 50% of said cotton fibers.

4. The filter paper of claim 1, comprised of at least 70% of said cotton fibers.

5. The filter paper of claim 1, the filter paper further comprising synthetic or cellulosic fiber.

6. The filter paper of claim 1 , wherein the cotton fibers have a length between 2 and 8 millimeters.

7. The filter paper of claim 1 , wherein the cotton fibers have a length between 3 and 6 millimeters.

8. The filter paper of claim 1, wherein the cotton fibers have a diameter between 17 and 22 micrometers.

9. The filter paper of claim 1, wherein the cotton fibers have a diameter of between about 18 and 20 micrometers.

10. The filter paper of claim 1, wherein the cotton fibers are not substantially water swollen.

11. The filter paper of claim 1, wherein the cotton fibers are obtained from denim material.

12. The filter paper of claim 11, wherein the cotton fibers have a length between 2 and 8 millimeters.

13. The filter paper of claim 1, wherein the cotton fiber is lint cotton fiber.

14. A filter paper comprised of mechanically cut raw cotton fiber having a diameter between about 9 and 23 micrometers.

15. A bulky paper comprised of cotton fibers having a diameter between about 9 and 23 micrometers.

16. The bulky paper of claim 15, wherein the cotton fibers are mechanically cut raw cotton fibers.

17. A method of making filter paper comprising the steps of:

(a) chopping cotton material into pieces where the cotton fibers of the material have a diameter between about 9 and 23 micrometers;

(b) slurry ing said pieces in water; (c) refining said slurry; and

(d) removing the water to form a sheet.

18. The method of claim 17, wherein the slurry is refined using disk refiners.