Paper making and fiber liberation – Processes and products – Non-fiber additive
Reexamination Certificate
2000-02-28
2002-04-30
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-fiber additive
C162S180000, C162S183000
Reexamination Certificate
active
06379498
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to paper or tissue products. More particularly, the invention concerns methods for applying adsorbable chemical additives to the fibers of pulps during the pulp processing and the paper products that can be obtained by the methods.
In the manufacture of paper products, it is often desirable to enhance physical and/or optical properties by the addition of chemical additives. Typically, chemicals such as softeners, colorants, brighteners, strength agents, etc. are added to the fiber slurry upstream of the headbox in a paper making machine during the manufacturing or converting stages of production to impart certain attributes to the finished product. These chemicals are usually mixed in a stock chest or stock line where the fiber slurry has a fiber consistency of from between about 0.15 to about 5 percent or spraying the wet or dry paper or tissue during production.
One disadvantage of adding a chemical at each paper machine is that the manufacturer has to install equipment on each paper machine to accomplish the chemical addition. This, in many cases, is a costly proposition. In addition, the uniformity of the finished product coming off of each paper machine may vary depending upon how the chemical was added, variations in chemical uniformity and concentrations, the exact point of chemical introduction, water chemistry differences among the paper machines as well as personnel and operational differences of each paper machine.
Another difficulty associated with wet end chemical addition is that the water soluble or water dispersible chemical additives are suspended in water and are not completely adsorbed onto the fibers prior to formation of the wet mat. To improve adsorption of wet end additives, chemical additives are often modified with functional groups to impart an electrical charge when in water. The electrokinetic attraction between charged additives and the anionically charged fiber surfaces aids in the deposition and retention of chemical additives onto the fibers. Nevertheless, the amount of chemical additive that can be retained in the paper machine wet end generally follows an adsorption curve exhibiting diminishing incremental adsorption with increasing concentration, similar to that described by Langmuir. As a result, the adsorption of water soluble or water dispersible chemical additives may be significantly less than 100 percent, particularly when trying to achieve high chemical additive loading levels.
Consequently, at any chemical addition level, and particularly at high addition levels, a fraction of the chemical additive is retained on the fiber surface. The remaining fraction of the chemical additive remains dissolved or dispersed in the suspending water phase. These unadsorbed chemical additives can cause a number of problems in the papermaking process. The exact nature of the chemical additive will determine the specific problems that may arise, but a partial list of problems that may result from unadsorbed chemical additives includes: foam, deposits, contamination of other fiber streams, poor fiber retention on the machine, compromised chemical layer purity in multi-layer products, dissolved solids build-up in the water system, interactions with other process chemicals, felt or fabric plugging, excessive adhesion or release on dryer surfaces, physical property variability in the finished product.
Therefore, what is lacking and needed in the art is a method for applying adsorbable chemical additives onto pulp fiber surfaces in the initial or primary pulp processing, providing more uniform chemical additions to the pulp fiber and a reduction or elimination of unadsorbed chemical additives in the process water on a paper machine. The method minimizes the associated manufacturing and finished product quality problems that would otherwise occur with conventional wet end chemical addition at the paper machine.
SUMMARY OF THE INVENTION
It has now been discovered that adsorbable chemical additives can be adsorbed onto pulp fibers that have never been dried at high and/or uniform levels with at most a minimal amount of unadsorbed chemical additives present in the papermaking process water after the treated pulp fiber has been redispersed in water. This is accomplished by treating a fiber slurry comprising pulp fiber and water with an excess of the adsorbable chemical additive, allowing sufficient residence time for adsorption to occur, and filtering or otherwise dewatering the fiber slurry to remove water and unadsorbed chemical additives.
Hence in one aspect, the invention resides in a method for applying adsorbable chemical additives to the pulp fibers. The method comprises creating a fiber slurry comprising water, pulp fibers that have never been dried, and an adsorbable chemical additive. The fiber slurry having the chemical additive may be formed into a wet fibrous web using a web forming apparatus. The wet fibrous web is dried to a predetermined consistency. In other embodiments of the present invention, the process may include further dewatering thereby forming a crumb-form. The dried fibrous web may have retained from between about 10 to about 100 percent of the adsorbable chemical additive.
According to another embodiment of the present invention is a method for adding an adsorbable chemical to the pulp fiber during the pulp processing prior to the drying stage. During the pulp processing, upstream of a paper machine, one can obtain chemically treated pulp fiber that is essentially homogeneous in chemical adsorption. Furthermore, the chemically treated pulp fiber can be transported to several different paper machines that may be located at various sites, and the quality of the finished product from each paper machine will be more consistent. Also, by chemically treating the pulp fiber before the pulp fiber is available for use on multiple paper machines or multiple runs on a paper machine, the need to install equipment at each paper machine for the adsorbable chemical addition can be eliminated.
This method for processing pulp fibers also enables higher and more uniform concentrations of adsorbable chemical additives to be adsorbed by the pulp fibers while at the same time maintaining significantly lower levels of unadsorbed chemical additive in the water phase of a papermaking machine compared to paper machine wet end chemical additions.
The term “adsorbable” is used herein to refer to a chemical additive that can be assimilated by the surface of a pulp fiber, in the absence of any chemical reaction involving the chemical additive and the fiber. Once the chemical additive is adsorbed, it may or may not be absorbed into the pulp fiber. The term “unadsorbed” refers to any portion of the adsorbable chemical additive that is not adsorbed by the pulp fiber and thus remains suspended in the process water. The term “web-forming apparatus” includes fourdrinier former, twin wire former, cylinder machine, press former, crescent former, and the like known to those skilled in the art.
The consistency of the fiber slurry is from about 0.5 to about 15 percent. In other embodiments, the consistency of the fiber slurry is from about 2 to about 10 percent or from about 3 to about 5 percent. The consistency of the dried fibrous web is from about 45 to about 100 percent. In other embodiments, the consistency of the dried fibrous web is from about 60 to about 100 percent or from about 85 to about 95 percent. The consistency of the wet fibrous web is from about 30 to about 45 percent. In other embodiments, the consistency of the wet fibrous web is from about 35 to about 45 percent or from about 40 to about 45 percent. The consistency of the crumb form is from about 50 to about 85 percent. In other embodiments, the consistency of the crumb form is from about 60 to about 85 percent or from about 80 to about 85 percent.
The present method allows for the production of pulp fibers that are useful for making paper products. This results in a pulp fiber, which after drying, has different mechanical properties th
Burns Barbara Jean
Coe Louise Cynthia Ellis
Goulet Mike Thomas
Rekoske Michael John
Charlier Patricia A.
Chin Peter
Kimberly--Clark Worldwide, Inc.
Lopez Carlos
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