Paper making and fiber liberation – Processes and products – Non-fiber additive
Reexamination Certificate
2000-08-07
2002-04-02
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-fiber additive
C106S206100
Reexamination Certificate
active
06365002
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a process of papermaking wherein amphoteric starch containing a phosphate component and made by a select process is added to the wet end of the papermaking system to provide paper with good drainage and other improved properties.
The term “paper” as used herein, includes sheet-like masses and molded products made from fibrous cellulosic material, which may be derived from natural sources, synthetics such as polyamides, polyesters, rayon and polyacrylic resins as well as from mineral fibers such as asbestos and glass. In addition, paper made from combinations of cellulosic and synthetic materials are applicable herein. Paperboard is also included within the broad term “paper”.
Papermaking, as it is conventionally known, is a process of introducing an aqueous slurry of pulp or wood cellulosic fibers (which have been beaten or refined to achieve a level of fiber hydration and to which a variety of functional additives can be added) onto a screen or similar device in such a manner that the water is removed, thereby forming a sheet of the consolidated fibers, which upon pressing and drying can be processed into dry roll or sheet form. Two well known papermaking processes involve the Fourdrinier machine, the most common, and the cylinder machine. In the Fourdrinier and multicylinder operations, and in other machine operations, as typical in papermaking, the feed or inlet to the machine is an aqueous slurry or water suspension of pulp fibers which is provided from what is called the “wet end” system. In the wet end, the pulp along with other additives are mixed in an aqueous slurry and subject to mechanical and other operations such as beating and refining to improve interfiber bonding and other physical properties of the finished sheet. Additives commonly introduced along with the pulp fibers are pigments such as titanium dioxide, mineral fillers such as clay and calcium carbonate and other materials introduced into paper to achieve such properties as improved brightness, opacity, smoothness, ink receptivity, fire retardance, water resistance, increased bulk, etc.
It has been known to add various materials, including starch, to the pulp, or stock in the papermaking process or prior to the formation of the sheet, to aid in retention, drainage and strength properties.
Starch has been used in the paper industry for many years and, in fact, is the second largest volume raw material component in paper. Starches perform a number of functions in papermaking including strength improvement, increased drainage and increased retention of fibers, fines and other components on the wire. Both unmodified and modified types of starch have been used.
Anionic and cationic starches as well as amphoteric starches have long been used as additives in papermaking for their contributions to strength and pigment retention in the paper. See, for example, U.S. Pat. No. 3,459,632 issued to C. Caldwell et al. on Aug. 5, 1969 and U.S. Pat. No. 3,562,102 issued to K. Moser et al. on Feb. 9, 1971. More recent patents involving the use of starches in papermaking include U.S. Pat. No. 4,876,336 issued to D. Solarek et al. on Oct. 24, 1989 and which discloses the use of amphoteric starch derivatives and U.S. Pat. No. 5,129,989 issued to S. Gosset et al. on Jul. 14, 1992 which discloses the use of cationic and anionic starches in separate additions.
While starch additives of the prior art have shown favorable effects in improving paper properties, it has been found that the use of amphoteric starch additives, prepared as described herein, have high levels of phosphorus substitution, maintain high viscosities, minimize residual salts and other impurites and improve the wet end performance in papermaking operations.
SUMMARY OF THE INVENTION
Now it has been found that the use in papermaking of an amphoteric starch additive which contains a phosphate component and which is made under anhydrous conditions while in a fluidized state, provides advantageous paper properties and improved wet end performance.
More particularly, this invention involves the process of making paper comprising adding to the paper stock prior to or during formation of the sheet, an effective amount of an amphoteric starch which contains a cationic component and an anionic phosphate component and is made by;
a) impregnating a cationic starch with a phosphate reagent to form an impregnated starch;
b) drying the impregnated starch to substantially anhydrous conditions; and
c) heating to phosphorylate the starch.
A preferred embodiment involves the above process wherein the drying and phosphorylation take place in the fluidized state.
DETAILED DESCRIPTION OF THE INVENTION
This invention involves the use of specially prepared amphoteric starches in papermaking. The use of amphoteric starch additives in papermaking has long been known, as noted above, however, amphoteric starches containing a phosphate component and specifically prepared as described herein, have improved characteristics which make them especially useful in papermaking. These amphoteric starches are prepared in a process that has improved reaction efficiency and provides a product with high levels of substitution, particularly bound phosphorus, and minimum amounts of residual salts and other impurities. Such products are also characterized by improved properties such as viscosity, color and uniformity and have been found especially useful as wet end additives in papermaking.
The amphoteric starches as used in this invention contain a cationic functional group and an anionic phosphate functional group and are prepared by impregnating a cationic starch with phosphate and then drying it to substantially anhydrous conditions, preferably when in the fluidized state, before heat treating to effect phosphorylation. By anhydrous or substantially anhydrous conditions is meant less than about 1% moisture content by weight, based on the dry weight of starch. It is preferred that both the drying and phosphorylation steps take place in the fluidized state. While other drying and phosphorylating systems may be used which are not in the fluidized state, the fluidized state is preferred because it provides excellent heat and mass transfer which results in good and desired drying and reaction characteristics.
Impregnation by the phosphate reagent may be accomplished by adding the reagent, at a level of less than about 15% and preferably less than about 10% by weight of starch, either in the dry state or to the wet starch, or by dissolving the reagent in water to form an aqueous solution which is then mixed with the starch. These impregnation techniques are described in U.S. Pat. No. 4,166,173 issued Aug. 28, 1979 to O. Wurzburg et al. and U.S. Pat. No. 4,216,310 issued Aug. 5, 1980 to O. Wurzburg et al., both of which are incorporated herein by reference.
The impregnated starch is first subjected to the fluidized state and dried to anhydrous conditions of less than about 1% by weight moisture content, based on the weight of dry starch, at less than about 140° C., more particularly between about 60 to 140° C. and preferably between about 100 to 125° C. The dried product, while still in the fluidized state, is heated to between about 100 to 185° C., preferably between about 120 to 140° C. for about 30 to 300 minutes. At temperatures higher than about 150° C., the processing time is preferably less than about 45 minutes. Though the heat treatment may be carried out in one step, it is preferably carried out in two steps. When using a one step procedure, once reaction temperature is reached, anhydrous conditions have already or substantially been reached. The important point is that in either the one or two step operation, anhydrous conditions are reached before or in the very early stage of phosphorylation.
The fluidized state is achieved by vigorous mixing of the solid starch particles in vacuum or in a gas whereby a uniform distribution of starch throughout the vacuum or gas may be attained. Vigorous mixing may be accomplished by using air or gas, at or
Altieri Paul A.
Bindzus Wolfgang
Chin Peter
Duncan, Esq. Laurelee
National Starch and Chemical Investment Holding Corporation
Zagarella, Jr. Eugene
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