Paper making and fiber liberation – Processes and products – Non-fiber additive
Reexamination Certificate
2000-08-07
2002-07-02
Fortuna, José S. (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-fiber additive
C162S135000, C162S158000, C162S164600, C106S206100, C106S210100
Reexamination Certificate
active
06413372
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an improved process of papermaking wherein polymer combinations of cationic and anionic starches having a select zeta potential are added to the stock or furnish in the wet end to provide improved retention as well as drainage and strength 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 subjected 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 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. 3,562,103 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 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.
Despite the various and well known use of different starches in papermaking, there is the continuing need and desire to provide improved papermaking properties and especially improved retention.
SUMMARY OF THE INVENTION
Now, it has been found that significantly improved retention properties can be obtained in the process of papermaking by the addition or combination of cationic starch and starch phosphate having a select zeta potential, to the stock or furnish in the wet end.
More particularly, this invention involves the process of making paper comprising adding to the paper stock or furnish prior to or during formation of the sheet, a combination of cationic starch and starch phosphate, the combination having a zeta potential of from about +20 to −18 mV (millivolts).
In another embodiment of this invention, paper is made using the combination of cationic starch and starch phosphate having a select zeta potential as described herein, and wherein the starch phosphate is made by impregnating the starch with a phosphate reagent and then drying to substantially anhydrous conditions, preferably while in a fluidized state, prior to heat treating to effect phosphorylation. Preferably both the drying and heat treatment take place while in the fluidized state.
DETAILED DESCRIPTION OF THE INVENTION
This invention involves a combination of modified cationic starches and starch phosphates in amounts to provide a selected zeta potential range for use in papermaking.
The modified starches which are used in this invention can be prepared by methods known and described in the art. Cationization of the starch can be produced by well known chemical reactions with reagents containing amino, imino, ammonium, sulfonium and phosphonium groups as disclosed, for example, in “Cationic Starches” by D. B. Solarek,
Modified Starches: Properties and Uses
, Chapter 8, pp. 113-129, 1986, and in U.S. Pat. No. 4,119,487 issued Oct. 10, 1978 to M. Tessler. Such cationic derivatives include those containing nitrogen groups comprising primary, secondary, tertiary and quaternary amines and sulfonium and phosphonium groups attached through either ether or ester linkages. The preferred derivatives are those containing the tertiary amino and quaternary ammonium ether groups.
The general method for preparing starches containing tertiary amine groups, which method involves reacting starch under alkaline conditions with a dialkylaminoalkyl halide is described in U.S. Pat. No. 2,813,093 issued on Nov. 12, 1957 to C. Caldwell, et al. Another method, therefore, is disclosed in U.S. Pat. No. 4,675,394 issued Jan. 23, 1987 to D. Solarek et al. The primary and secondary amine starches may be prepared by reacting the starch with aminoalkyl anhydrides, amino epoxides or halides, or the corresponding compounds containing aryl in addition to the alkyl groups.
Quaternary ammonium groups may be introduced into the starch by suitable treatment of the tertiary aminoalkyl ether or starch, as described in the previously noted U.S. Pat. No. 2,813,093. Alternatively, quaternary groups may be introduced directly into the starch by treatment with the reaction product of an epihalohydrin and a tertiary amine or tertiary amine salt, to provide, for example, (3-trimethylammonium chloride)-2-hydroxypropyl ether substituent groups as disclosed in the noted U.S. Pat. No. 4,119,487. The above noted patents, i.e., '487, '093 and '394 are incorporated herein by reference.
The preparation of cationic sulfonium derivatives is described in U.S. Pat. No. 2,989,520 issued June, 1961 to M. Rutenberg et al. and essentially involves the reaction of starch in an aqueous alkaline medium with a beta-halogenoalkylsulfonium salt, vinylsulfonium salt or epoxyalkylsulfonium salt. The preparation of cationic phosphonium derivatives is disclosed in U.S. Pat. No. 3,077,469 issued Feb. 12, 1963 to A. Aszalos and involves reaction of starch in an aqueous alkaline medium with a beta-halogenoalkylphosphonium salt. The above noted patents, i.e. '520 and '469 are incorporated herein be reference.
Other suitable cationic starches may be provided using reagents and methods that are well known in the art as illustrated in the above references. Further description of useful cationic starches are disclosed in U.S. Pat. No. 2,876,217 issued Mar. 3, 1959 to E. Paschall, U.S. Pat. No. 2,970,140 issued Jan. 31, 1961 to C. Hullinger et al., U.S. Pat. No. 5,004,808 issued Apr. 2, 1991 to M. Yalpani et al., U.S. Pat. No. 5,093,159 issued Mar. 3, 1992 to J. Fernandez et al., and EP 406 837 published Jan. 1, 1991 (corresponding to U.S. application Ser. No. 516,024 filed Apr. 26,
Altieri Paul A.
Bindzus Wolfgang
Maliczyszyn Walter
Duncan, Esq. Laurelee A.
Fortuna Jose S.
National Starch and Chemical Investment Holding Corporation
Zagarella, Esq. Eugene
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