Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2001-01-31
2001-10-23
Cameron, Erma (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S393000, C427S396000, C427S397000, C427S408000
Reexamination Certificate
active
06306464
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to products and processes to improve the strength of lignocellulosic materials.
BACKGROUND OF THE INVENTION
Lignocellulosic materials, such as paper and cardboard, can be strengthened by treating them (e.g. coating, impregnating, etc.) with solutions or dispersions of various strengthening agents. Examples of these solutions or dispersions are aqueous solutions of lignosulfonates. Lignosulfonates are metal or ammonium salts of lignosulfonic acids. The lignosulfonates are either by-products of the sulfite pulping process, or products of sulfonation of other lignin derivatives. Lignin derivatives include, but are not limited to, kraft lignin, organosolv lignin, chemically modified lignin derivatives, and mixtures thereof. However, one major problem with using these strengthening agents is that they bleed off the lignocellulosic materials when touched with wet hands. This results in poor aesthetics and increased messiness. Another major problem is that these strengthening agents exhibit low retention of strength at high humidity compared to that at normal humidity (e.g. 50% RH). Again, this problem is expected to be caused by their high affinity to water and moisture.
One common method to increase the strength of the lignocellulosic material under high humidity conditions is to add additional fiber to the material. However, this method is not cost effective as well because of the additional fiber/material costs. Another method to eliminate or reduce the bleeding of the water-soluble strengthening agents is to coat the treated lignocellulosic materials with wax or polymer films. However, this method is not an effective solution because the secondary coating materials are expensive to purchase, process, and apply, and typically not repulpable under normal conditions.
Yet another method to eliminate or reduce bleeding of the water-soluble strengthening agents is to insolubilize them by crosslinking. In the case of lignosulfonates the crosslinking reactions that have been reported in the literature include the following: condensation reaction with strong mineral acids at elevated temperatures (via the SO
3
2−
units), oxidative coupling reaction with hydrogen peroxide and catalysts (via the OH
31
groups), reaction with bis-diazonium salts (via the &agr;-position to the OH
−
groups), reaction with bifunctional acid chlorides (via the OH
−
groups), reaction with cyanuric chloride (via the OH
31
groups), reaction with formaldehyde (via the CH
2
groups), reaction with furfural (via the &agr;-position to the OH
−
groups), and reaction with epichlorohydrin (via the OH
−
groups). However, the above reactions/processes include various processing problems, such as cost, low pH, long reaction times, harsh conditions (e.g. temperature), health hazards, etc.
What has been missing is an inexpensive product and a simple, inexpensive, and fast process to improve the strength of treated lignocellulosic materials under humid conditions by reacting the water-soluble strengthening agents so as to substantially reduce or eliminate the bleeding of the water-soluble strengthening agents from the material when touched with wet hands or contacted under humid conditions.
SUMMARY OF THE INVENTION
The present invention relates to products and processes to improve the strength of lignocellulosic materials. The strength improvement is achieved by treating the lignocellulosic materials with water-soluble strengthening agents having at least one sulfonic unit and rendering these agents water-insoluble by reacting them with compounds having at least one epoxide ring and at least one quaternary ammonium group. This results in a substantial reduction or elimination of the bleeding problem of the originally water-soluble strengthening agents from the lignocellulosic materials when touched with wet hands or contacted under humid conditions.
DETAILED DESCRIPTION OF THE INVENTION
It is known that the strength of lignocellulosic materials (e.g. paper, linerboard, corrugated, cartonboard, etc.) can be improved by treating them with various aqueous solutions of strengthening agents (e.g. sodium silicate, starch, carboxy methyl cellulose—CMC, xylan, etc.). Unfortunately, these water-soluble strengthening agents bleed off the materials when touched by wet hands or contacted under humid conditions.
Lignosulfonates are water-soluble strengthening agents that can also be used to strengthen lignocellulosic materials. The lignosulfonates contain sulfonic units (HSO
3
−
; also called hydrogen sulfite units) and sulfonate units (SO
3
2−
; also called sulfite units), and for the purposes of this disclosure the term “sulfonic” will be used to encompass both “sulfonic” and “sulfonate” units. It is expected that the lignosulfonates strengthen the lignocellulosic materials by reinforcing their fibers and/or fiber bonds, via encapsulation and/or penetration. Lignosulfonates are examples of a variety of possible lignin derivatives which may be used. Lignin derivatives include, but are not limited to, kraft lignin, organosolv lignin, chemically modified lignin derivatives wherein the nucleophilic sulfonic unit is preserved, and mixtures thereof.
Unexpectedly it was found that an aqueous calcium lignosulfonate solution (LIGNOSITE 50 containing 40% calcium lignosulfonate and 10% inert solids; from Georgia-Pacific Inc.; Atlanta, Ga.) when mixed together with an aqueous polyamine polyamide epichlorohydrin resin containing epoxide rings and quaternary ammonium groups exhibits a virtually instantaneous reaction that results in a precipitate. This precipitate exhibits water-insoluble properties. This mixing is a simple, inexpensive, and fast process that is carried out under ambient conditions and without the need for complex pieces of equipment. It was also unexpectedly found that aqueous sodium lignosulfonate (LIGNOSITE 458 from Georgia-Pacific Inc.) and ammonium lignosulfonate (LIGNOSITE 1740 from Georgia-Pacific Inc.) when independently mixed together with an aqueous polyamine polyamide epichlorohydrin resin containing epoxide rings and quaternary ammonium groups exhibit a virtually instantaneous reaction that results in a precipitate.
One commercially available polyamine polyamide epichlorohydrin resin {also referred to as a) polyaminoamide epichlohydrin (PAE), b) poly(aminoamide) epichlorohydrin, c) amino polyamide epichlorohydrin, d) polyamide epichlorohydrin, e) amine polymer-epichlorohydrin (APE), and f) polyalkylenepolyamine-epichlorohydrin (PAPAE)} containing epoxide rings and quaternary ammonium groups is KYMENE (KYMENE 450 and KYMENE 2064, both containing 20% solids; from Hercules Inc.; Wilmington, Del.). For the purposes of this disclosure the term “KYMENE” shall refer to the class of polyamine polyamide epicholorhydrin resins containing epoxide rings and quaternary ammonium groups. KYMENE is a compound that is used as a wet-strength agent in paper applications. Preparation of KYMENE is described in great details in Keim, U.S. Pat. No. 3,700,623, issued Oct. 24, 1972; and Keim, U.S. Pat. No. 4,537,657, issued Aug. 27, 1985. Although it is known that KYMENE has a strong affinity for itself (as it crosslinks primarily with itself) and a slight affinity for cellulose or CMC (via the cellulose's carboxyl and hydroxy groups), it has never been disclosed or found that KYMENE has a strong affinity for lignosulfonates.
One commercial source of a useful polyamide polyamine epichlorohydrin compound containing epoxide rings and quaternary ammonium groups is Hercules, Inc. of Wilmington, Del., which markets such compound under the trademark KYMENE 450 and KYMENE 2064. As referenced in U.S. Pat. No. 4,537,657, KYMENE 450 polyamide polyamine epichlorohydrin wet-strength resin has the formula
As referenced in U.S. Pat. No. 3,700,623, KYMENE 2064 polyamide polyamine epichlorohydrin wet-strength resin has the formula
Another commercial source of a useful polyamide polyamine epichlorohydrin compound containing epoxide rings and qua
Collias Dimitris Ioannis
Owens Blair Alex
Wnuk Andrew Julian
LandOfFree
Strengthening compositions and treatments for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Strengthening compositions and treatments for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Strengthening compositions and treatments for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2602930