Paper making and fiber liberation – Processes and products – Non-fiber additive
Reexamination Certificate
2000-09-28
2002-04-30
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-fiber additive
C162S173000, C162S181200
Reexamination Certificate
active
06379499
ABSTRACT:
BACKGROUND OF THE INVENTION
The paper industry uses additives to improve the properties of paper. Additives may be added to paper pulp slurry prior to sheet formation (wet-end addition), or applied to paper after sheet formation (dry-end addition). Some properties that are desired in paper depending on its application include wet strength, dry strength, folding endurance, oil resistance and solvent/stain resistance.
For ease of processing and commercial applicability, the curing temperature of the paper should be as low as possible, the time of treatment should be short, and the cost of the additives used should be low. Also, the treatments should not emit environmentally harmful products. Additives currently used to improve wet strength, such as urea-formaldehyde (UF), melamine-formaldehyde (MF), and polyamide/polyamide-epichlorohydrin (PAE) are believed to emit formaldehyde (UF and MF) or absorbable organic halogens (AOX).
In an attempt to produce paper with desired properties, as well as decrease the amount of environmentally harmful chemicals being produced from paper production, various additives have been studied.
The dry properties of the paper are affected by the nature of crosslinks produced in the paper network. Small molecules such as glutaraldehyde are able to penetrate readily into cellulosic fibers and produce crosslinks between cellulosic molecules inside the fiber (Linke, W. F., (1968)
Tappi J
. 51(11):59A-65A). These crosslinks are located predominantly in the amorphous regions of the fiber wall and restrict the mobility of microstructural units of fibers. The intrafiber crosslinks produced by the small molecules such as glutaraldehyde alone do not contribute to fiber bonding and thus have little effect on the dry strength of paper. However, the intrafiber crosslinks increase the rigidity of fibers, and thus impart a more heterogeneous distribution of stress in the paper network. The result of intrafiber crosslinks is the reduction in the stretch of treated paper. The decrease in the stretching ability of paper also leads to premature breakage of paper, thus leading to an overall reduction in dry strength. Paper treated with high levels of glutaraldehyde exhibits loss of dry strength and decreased folding endurance.
Certain dialdehydes have been studied as crosslinking agents of cellulose to impart wrinkle resistance to cotton fabric (Frick, J. G., et al., (1982)
J. Appl. Polym. Sci
. 27:983-988; Frick, J. G., et al. (1984)
J. Appl. Polym. Sci
. 29:1433-1447). The reaction between certain dialdehydes and cellulose is promoted by using metallic salts and ammonium salts as catalysts (Petersen, H. A. (1983) in
Chemical Processing of Fibers and Fabrics: Functional Finishes Part A
”, Chapter 2, Lewin, M et al. (eds.), New York, pp. 47-327). The most frequently used metallic catalysts include inorganic salts of aluminum, magnesium and zinc.
Glyoxal has been used to provide temporary wet strength for paper (Eldred, N. R. et al. (1963)
Tappi
46(10):608-612). Glyoxal crosslinks cellulose molecules by formation of hemiacetal links, which are sensitive to water. If an acid catalyst is used, more stable acetal linkages are reported to be formed. However, the use of glyoxal, especially in an acidic treatment process, leads to serious embrittlement of paper, similar to the use of small polycarboxylic acids.
U.S. Pat. No. 4,547,807 (Chan et al.) relates to a method of temporarily improving the wet strength of pre-moistened towelette paper by reacting the paper with an adhesive formed from the reaction of a polyvinyl alcohol with glyoxal or related dialdehydes. Papers produced by the disclosed process reportedly exhibit enhanced wet strength when stored in an acidic medium and decreased wet strength when immersed in a basic medium. No catalyst is used.
U.S. Pat. No. 4,888,093 (Dean et al.) reports the use of certain dialdehydes to reportedly provide individualized, crosslinked cellulosic fibers.
Fully hydrolyzed polyvinyl alcohol (PVA) is a polymer with high tensile strength, excellent flexibility, good water resistance, and outstanding binding capacity (Finch, C. A. Ed., “Polyvinyl Alcohol: Properties and Applications,” John Wiley & Sons, (1973), pp.277-230). Polyvinyl alcohol (PVA) has been used in the paper processing industry for surface and internal sizing of paper and to impart water resistance to paper.
Large amounts of PVA (approximately 10% on an oven-dried basis of the pulp) have been added to pulp in wet-end processing to reportedly enhance paper wet strength (U.S. Pat. No. 2,402,469 (Toland et al.), discussed in U.S. Pat. No. 5,328,567 (Kinsley)). The PVA product described is water soluble at 130° F. PVA has been reported to control pitch deposition on processing equipment used when paper is formed (U.S. Pat. No. 4,871,424 (Dreisbach et al.)). PVA has also been reported to control “stickies” that may form during paper processing from the adhesives, ink and coating binders remaining from papers used in the recycled paper industry (U.S. Pat. No. 4,886,575 (Moreland)).
U.S. Pat. No. 5,281,307 (Smigo et al.) discloses the use of polyvinyl alcohol/vinylamine copolymers with a crosslinking agent to treat paper in a dry-end process. No catalysts are used. The process disclosed required a heat treatment of 150° C. for 5 minutes after the paper was formed.
U.S. Pat. No. 5,380,403 (Robeson et al.) discloses the use of an amine functionalized polyvinyl alcohol in combination with a cyclic ester or anhydride in a wet-end process to reportedly improve the wet strength of recycled paper.
Even though many additives have been studied in an attempt to improve the properties of paper, there is a continuing need for an environmentally-friendly treatment that imparts permanent improvement in wet strength, dry strength and folding endurance to the paper.
All references cited herein are hereby incorporated by reference to the extent not inconsistent with the disclosure herein.
SUMMARY OF THE INVENTION
A method of treating paper with a hydroxy-containing polymer and a multifunctional aldehyde in the presence of a catalyst to improve the strength properties of paper including wet strength, dry strength and folding endurance is provided. As used herein, “paper” includes paper sheets after formation, or paper pulp before sheet formation, among other forms as known in the art. In the method of the invention, the aldehyde is present in amounts of between about 50% to 800% weight percent of the polymer present, and all intermediate ranges therein. Preferably, the aldehyde is used in an amount of greater than 100% the weight percent of polymer. The catalyst is preferably present at a percentage weight ratio between about 1:0.1 to about 1:2 aldehyde:catalyst and all intermediate ranges therein, and more preferably present at a weight ratio of 1:0.2 to 1:1 aldehyde:catalyst. The treatment chemicals are typically used in total amounts of between about 0.1% to about 10% based on dry weight of pulp fibers, and all intermediate ranges therein. The presently preferred treatment uses between about 0.25% to about 4% by weight of treatment chemicals, based on dry weight of pulp fibers.
Also provided is a method of treating paper comprising: contacting said paper with a non amine-functionalized hydroxy-containing polymer and a multifunctional aldehyde, wherein the multifunctional aldehyde has formula:
where R is a divalent aliphatic, cycloaliphatic, aromatic or heterocyclic group having from 1 to 12 carbon atoms; the multifunctional aldehyde is present at a concentration of about 50% to about 800% weight percent of the polymer present; and the total weight of hydroxy-containing polymer and multifunctional aldehyde is about 0.1% to about 10% based on the dry weight of pulp fibers. The hydroxy-containing polymer and multifunctional aldehyde composition may further comprise a catalyst selected from the group consisting of AlCl
3
, Al
2
(SO
4
)
3
, Al(NO
3
)
3
, alum, ZnCl
2
, Zn(NO
3
)
2
, Zn(CH
3
COO)
2
, MgCl
2
, Mg(NO
3
)
2
, Mg(CH
3
COO)
2
, NH
4
Cl and amino acids; wherein said catalyst is pres
Xu Guozhong
Yang Charles Q.
Chin Peter
Greenlee Winner & Sullivan, P.C.
Hug Eric J.
University of Georgia Research Foundation Inc.
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