Paper making and fiber liberation – Processes and products – Non-fiber additive
Reexamination Certificate
2001-03-07
2003-06-24
Fortuna, Jose A. (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-fiber additive
C162S009000, C162S158000, C162S179000, C162S109000, C162S135000
Reexamination Certificate
active
06582560
ABSTRACT:
BACKGROUND OF THE INVENTION
In the manufacture of paper products, it is often desirable to enhance physical and/or optical properties by the addition of chemical additives. Typically, chemical additives such as softeners, colorants, brighteners, strength agents, etc. are added to the fiber slurry upstream of the headbox in a paper making machine during manufacturing to impart certain attributes to the finished product. These chemical additives 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 additive at each paper machine is that the manufacturer has to install equipment on each paper machine to accomplish the chemical additive 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 additive was added, variations in chemical additive uniformity and concentrations, the exact point of chemical additive 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 additive addition is that the water soluble or water dispersible chemical additives are suspended in water and are not completely adsorbed or retained onto the fibers prior to formation of the wet mat. To improve adsorption of wet end chemical additives, the chemical additives are often modified with functional groups to impart an electrical charge when in water. The electrokinetic attraction between charged chemical additives and the anionically charged fiber surfaces aids in the deposition and retention of chemical additives onto the fibers. Nevertheless, the amount of the chemical additive that can be adsorbed or 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. The use of water insoluble chemical additives in the water systems of papermaking processes is even more problematic and typically provides even poorer loading levels. Water insoluble chemical additives or water nondispersible chemical additives cannot typically be used in such water systems unless in the form of an emulsion.
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 or unretained 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 or unretained 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 an improved method for using water insoluble chemical additives, providing more consistent water insoluble chemical additive additions to the pulp fiber and a reduction or elimination of unretained water insoluble 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 water insoluble chemical additives can be applied to pulp fibers at high and/or consistent levels with reduced amounts of unretained water insoluble chemical additives present in the papermaking process water after the treated pulp fiber has been redispersed in water. This is accomplished by treating a fibrous web prior to the finishing operation at a pulp mill with a water insoluble chemical additive, completing the finishing operation, redispersing the finished pulp at the paper mill and using the finished pulp in the production of a paper product.
Hence in one aspect, the invention resides in a method for preparing chemically treated pulp fibers. The method comprises creating a fiber slurry comprising process water and virgin pulp fibers. The fiber slurry is transported to a web-forming apparatus of a pulp sheet machine and formed into a wet fibrous web. The wet fibrous web is dried to a predetermined consistency thereby forming a dried fibrous web. The dried fibrous web is treated with a water insoluble chemical additive thereby forming a chemically treated dried fibrous web containing chemically treated pulp fibers wherein the chemically treated pulp fibers have an increased or improved level of chemical retention of the water insoluble chemical additive and have a level of chemical retention of the water insoluble chemical additive is between about 25 to about 100 percent retention of the applied amount of the water insoluble chemical additive when the chemically treated pulp fibers are redispersed in water. The level of chemical retention of the water insoluble chemical additive may range from between about 60 to about 100 percent or between about 80 to about 100 percent retention of the water insoluble chemical additive. The improved level of chemical retention of the water insoluble chemical additive, measured as the change in the level of chemical retention of adding by typical wet-end addition, may range from a lower limit of about 5 percent, about 15 percent, about 25 percent, about 35 percent, about 45 percent, about 55 percent, about 65 percent, and about 75 percent to a higher limit of about 25 percent, about 35 percent, about 45 percent, about 55 percent, about 65 percent, about 75 percent, about 85 percent, about 95 percent, and about 100 percent retention of the water insoluble chemical additive. It is understood that the value for the lower limit is less than the value for the upper limit. The chemically treated pulp fiber may be then used in a separate process to produce paper products.
In another aspect, the invention resides in a method for applying a water insoluble chemical additive to pulp fiber. The method comprises mixing pulp fibers with process water to form a fiber slurry. The fiber slurry is transported to a web-forming apparatus of a pulp sheet machine and forming a wet fibrous web. The wet fibrous web is dewatered to a predetermined consistency thereby forming a dewatered fibrous web. A water insoluble chemical additive is applied to the dewatered fibrous web, thereby forming a chemically treated dewatered fibrous web containing chemically treated pulp fibers wherein the chemically treated pulp fibers have an increased or improved level of chemical retention of the water insoluble chemical additive wherein the level of chemical retention of the water insoluble chemical additive is between about 25 to about 100 percent of the applied amount of the water insoluble chemical additive when the chemically treated pulp fibers are redispersed in water. The level of chemical retention of the water insoluble chemical additive may range from between about 60 to about 100 percent or between about 80 to about 100 percent retention of the water insoluble chemical additive. The improved level of chemical retention of the water insoluble chemical additive, measured as the change in the level of chemical retention of adding by typical wet-end addition, may rang
Coe Louise Cynthia Ellis
Goulet Mike Thomas
Hu Sheng-Hsin
Runge Troy Michael
Charlier Patricia A.
Fortuna Jos'e A.
Kimberly--Clark Worldwide, Inc.
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