Methods for the reduction of bleeding of lignosulfonates...

Details Methods for the reduction of bleeding of lignosulfonates... Methods for the reduction of bleeding of lignosulfonates...

2001-08-06

2002-10-01

Cameron, Erma (Department: 1762)

Coating processes

With post-treatment of coating or coating material

Heating or drying

C427S389900, C427S391000, C427S392000

Reexamination Certificate

active

06458419

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to methods of reducing the bleeding of lignosulfonates from lignosulfonate-treated substrates when contacted under humid conditions by rendering the lignosulfonates water insoluble.
BACKGROUND OF THE INVENTION
Lignosulfonates are water-soluble materials. They are used in various applications and products, such as preparation of concrete admixtures, feed pellets, oil drilling muds, road stabilization, emulsion and dispersion stabilization, plant nutrition, leather tanning, dust collection, road de-icing and other applications. Lignosulfonates are metal or ammonium salts of lignosulfonic acids, and 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.
Lignosulfonates can also be used to strengthen various substrates by treating them (e.g. coating, impregnating, etc.) with lignosulfonate solutions. Examples of these substrates are lignocellulosic-based substrates (such as paper, cardboard, and webs containing mixtures of lignocellulosic and polymer fibers). Note that for the purposes of this disclosure the terms “lignocellulosic-based substrates” and “substrates” will be used interchangeably. However, one major problem with using the lignosulfonates in the strengthening applications above is that they bleed off the substrates when contacted under humid conditions (e.g. touched with wet hands). This results in poor aesthetics, increased messiness, and poor strength retention. One method to reduce or eliminate this bleeding is to coat the treated substrates with wax or polymer films. However, this coating method is not an effective solution because the secondary coating materials are expensive to purchase, process and apply. Yet another method to reduce or eliminate the bleeding of the water-soluble lignosulfonates is to insolubilize them by crosslinking.
The crosslinking reactions for lignosulfonates that have been reported in the literature include the following: 1) condensation reaction with strong mineral acids at elevated temperatures (via the SO
3
2−
units); 2) oxidative coupling reaction with hydrogen peroxide and catalysts (via the OH
−
groups); 3) reaction with bis-diazonium salts (via the &agr;−position to the OH
−
groups); 4) reaction with bifunctional acid chlorides (via the OH
−
groups); 5) reaction with cyanuric chloride (via the OH
−
groups); 6) reaction with formaldehyde (via the CH
2
groups); 7) reaction with final (via the &agr;-position to the OH
−
groups); and 8) 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 have been missing are simple and inexpensive methods to render lignosulfonates water insoluble, thus reducing or eliminating their bleeding from the lignosulfonate-treated substrates when contacted under humid conditions.
SUMMARY OF THE INVENTION
The present invention relates to methods of rendering lignosulfonates water insoluble by reacting them with an amine polymer-epichlorohydrin adduct containing at least one quaternary ammonium group under acidic conditions. This results in reduction of the bleeding problem of the originally water-soluble lignosulfonates from the substrates when contacted under humid conditions.
DETAILED DESCRIPTION OF THE INVENTION
It is known that the strength of lignocellulosic-based substrates (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 substrates when contacted under humid conditions.
Lignosulfonates are water-soluble strengthening agents that can also be used to strengthen lignocellulosic-based substrates. 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-based substrates by reinforcing their fibers and/or fiber bonds, via encapsulation and/or penetration. Lignosulfonates are examples of a variety of possible lignin derivatives that 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; Georgia-Pacific Inc.; Atlanta, Ga.), containing 40% calcium lignosulfonate and 10% inert solids, when mixed together with aqueous amine polymer-epichlorohydrin adducts containing quaternary ammonium groups under acidic conditions 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. At acidic pH levels, such as pH=3, amine polymer-epichlorohydrin adducts contain quaternary ammonium groups and have a charge density of about 3.2 meq/g. It was also unexpectedly found that aqueous sodium lignosulfonate (LIGNOSITE 458; Georgia-Pacific Inc.) and ammonium lignosulfonate (LIGNOSITE 1740; Georgia-Pacific Inc.) when independently mixed together with an aqueous amine polymer-epichlorohydrin adduct containing quaternary ammonium groups under acidic conditions exhibit a virtually instantaneous reaction that results in a precipitate.
For the purpose of this disclosure, the term “amine polymer-epichlorohydrin adduct(s)” refers to any resins made by the reaction of a polyamine or an amine-containing polymer with an epoxide an possessing an epichlorohydrin second functional group. Two commercially available amine polymer-epichlorohydrin adducts containing quaternary ammonium groups at pH=3 are KYMENE® 450 and KYMENE® 557H from Hercules Inc. (Wilmington, Del.). These KYMENE® products contain 20% and 12.5% solids, respectively. The amine polymer-epichlohydrin is also referred to as either: a) polyamide polyamine epichlorohydrin (PAE), or b) poly(aminoamide) epichlorohydrin, or c) amino polyamide epichlorohydrin, or d) polyamide epichlorohydrin, or e) amine polymer-epichlorohydrin (APE), or f) polyalkylenepolyamine-epichlorohydrin (PAPAE). For the purposes of this disclosure the term “KYMENE®” shall refer to the class of amine polymer-epichlorohydrin adducts, more commonly known as polyamide polyamine epichlorohydrin resins, containing quaternary ammonium groups at pH=3. 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. 2,926,116, issued Feb. 23, 1960; Keim, U.S. Pat. No. 3,332,901, issued Jul. 25, 1967; 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), it has never been disclosed or found that KYMENE® has a strong affinity for lignosulfonates.
As referenced in U.S. Pat. No. 4,537,657, KYMENE® 450 amine polymer-epichlorohydrin adduct at pH=3 has the general formula
Another commercial source of a useful polyamide polyamine epichlorohydrin compound containing quaternary ammonium groups at pH=3 is Henkel Inc. (Düsseldorf, Germany), which markets such compound under the trademark Fibr

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