Paper making and fiber liberation – Processes and products – Non-fiber additive
Reexamination Certificate
1994-06-01
2001-02-27
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-fiber additive
C162S176000, C162S177000
Reexamination Certificate
active
06193843
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to polycationic reagents, to novel cationic polysaccharide derivatives produced by reaction of polysaccharides with these reagents, and to the use of these polysaccharide derivatives in paper manufacturing. The polycationic reagents have at least two cationic groups and one polysaccharide-reactive group. Certain of these reagents are novel compositions of matter.
The modification of starch and other polysaccharides by chemical derivatization to produce various cationic polysaccharides is well known. Cationic polysaccharides, i.e., polysaccharides which have been modified so that they have a positive electrostatic charge, are used for a large number of applications and are particularly useful in the manufacture of paper due to their superior performance in the paper production as compared to unmodified polysaccharides. Amphoteric polysaccharides, i.e., polysaccharides which have been modified so they have cationic groups, together with a controlled amount of anionic (e.g., phosphate) groups, are used in a similar manner, with superior performance as compared to unmodified polysaccharides.
As used herein, the term “paper” includes sheet-like masses and molded products made from fibrous cellulosic material, which may be derived from natural sources as well as from synthetics such as polyamides, polyesters and polyacrylic resins, as well as from mineral fibers such as asbestos and glass. Also included are papers made from combinations of cellulosic and synthetic materials.
Various materials, including starch, are added to the pulp, or stock, during the paper-making process, prior to the formation of the sheet. One purpose of such additives is to bind the individual fibers to one another, thus aiding the formation of a stronger paper. Alum is employed in paper-making processes which are conducted under acidic conditions, however, alum-free, alkaline conditions in paper-making processes are becoming common in the industry.
In the case of those papers which contain added pigments, such as titanium dioxide, it has been known to add materials to the pulp, or stock, for the specific purpose of retaining a greater proportion of such pigments in the paper (rather than have them drain off in the water that is removed during the formation of the sheet). Such additives are often referred to as “pigment retention agents.” Cationic starches have long been employed as additives in paper production for their contributions to drainage, strength and pigment and fine pulp retention in paper.
Starches used in paper manufacturing are typically used in dispersed form and starch inhibition is avoided. Starch inhibition refers to crosslinking modifications to the starch granule which limit or prevent granule hydration or swelling and disintegration during cooking (gelatinizing) to form a hydrated colloidal dispersion of starch molecules. Inhibited starches cannot form desirable dispersions and are not as effective in paper production as uninhibited starches. Other polysaccharides perform in a similar manner.
The polycationic reagents which have been used in the past to prepare polysaccharide derivatives contain more than one polysaccharide-reactive group or require reaction conditions which provide an opportunity for crosslinking of the polysaccharide. Thus, cationic polysaccharide derivatives prepared from these known reagents are only useful in paper production so long as the crosslinking, or inhibition, is controlled. Unlike the known reagents, the polycationic reagents of the present invention contain only one polysaccharide-reactive site (and therefore are not susceptible to undesirable crosslinking) and polysaccharide derivatives made therefrom are useful in paper production without any need for control of crosslinking of the polysaccharide derivative.
It has now been discovered that unexpected superior performance in paper production may be achieved by the use of novel cationic polysaccharide derivatives which are prepared by reaction of a polysaccharide with a reagent containing a single polysaccharide-reactive group and more than one cationic group. Where the cationic group is an amine, the performance of these derivatives far exceeds their expected performance based on degree of substitution or nitrogen content alone. These advantages are most advantageous in alum-free processes for making paper under alkaline conditions. It is believed that the high charge density per saccharide monomer unit which is produced by reaction with the reagents disclosed herein is responsible for the unexpected improvement in performance.
Accordingly, this invention provides a new class of cationic polysaccharide derivatives and polycationic reagents useful in the preparation of these polysaccharide derivatives. This invention also provides cationic polysaccharides for use in paper manufacturing showing improved drainage, pigment and pulp retention and paper strength as compared to cationic polysaccharides of the prior art.
SUMMARY OF THE INVENTION
The cationic polysaccharides of the present invention are polysaccharide derivatives which contain two or more cationic groups on the same substituent. The derivatives are prepared by reacting a suitable polysaccharide with a reagent containing a single polysaccharide-reactive group and two or more cationic groups. The reagent introduces a substituent group which provides a highly cationic polysaccharide at relatively low levels of substitution in comparison to the charge distribution of known cationic polysaccharides. Thus, where cationic polysaccharides of the prior art have substituents with a single cationic group, the cationic polysaccharides of the present invention have substituents with two or more cationic groups located on the derivatized saccharide monomer units.
The cationic polysaccharides of this invention are prepared by reaction of a polysaccharide with a reagent selected from a group of polycationic compositions having a single polysaccharide-reactive group. Thus, in contrast to cationic polysaccharides known in the art (e.g., graft copolymers of cationic monomers and polysaccharides), the polysaccharides herein are advantageously provided by a simple one-step reaction with a reagent. These reagents are polycationic alkyl, aryl, alkaryl, cycloaliphatic or heterocyclic amines, some of which are novel compositions of matter.
Cationic polysaccharides prepared from these reagents are more effective in paper manufacturing than polysaccharides of the prior art where the two polysaccharides have the same cationic group content (e.g., equal nitrogen content), particularly under alum-free, alkaline conditions. It follows that these polysaccharides are effective at a lower degree of substitution than the polysaccharides of the prior art.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The starches which may be used in preparing the cationic polysaccharide derivatives of the present invention may be derived from any plant source including corn, potato, sweet potato, wheat, rice, waxy rice, sago, tapioca, waxy maize, sorghum, high amylose corn, etc. Also included are derivatized starches such as starch ethers and esters; crosslinked starches; the conversion products derived from starches including, for example, dextrins prepared by the hydrolytic action of acid and/or heat; oxidized starches prepared by treatment with oxidants such as sodium hypochlorite; and fluidity or thin boiling starches prepared by enzyme conversion or by mild acid hydrolysis. In particular, starch derivatized to contain substituents carrying an anionic charge (e.g., phosphate containing starch) may be reacted with the polycationic reagents disclosed herein to yield amphoteric starch derivatives. These polycationic amphoteric starch derivatives are particularly useful in paper manufacturing.
The use of the term “starch” herein includes any amylaceous substance, whether untreated or chemically modified which, however, still retains free hydroxyl groups capable of entering into the reaction of this invention. If the desired product is to be a granular
Billmers Robert L.
Philbin Michael T.
Rutenberg Morton W.
Tessler Martin M.
Trzasko Peter T.
Chin Peter
Duncan Laurelee A.
Kaisler, Esq. Karen G.
National Starch and Chemical Investment Holding Corporation
Zagarella Eugene
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