Sugar – starch – and carbohydrates – Products – Modified starches
Reexamination Certificate
2001-09-27
2004-06-08
Bell, Mark L. (Department: 1755)
Sugar, starch, and carbohydrates
Products
Modified starches
C127S067000, C127S071000, C162S164600, C162S168200, C162S175000, C525S054240, C525S054260
Reexamination Certificate
active
06746542
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for modifying starch by heating starch with at least one cationic polymer in an aqueous medium to temperatures above the gelatinization temperature of said starch, to the modified starches obtainable by said process, and to the use of said modified starches as paper, paperboard and cardboard dry strength enhancer.
2. Description of the Background
Ullmann's Enzyklopädie der Technischen Chemie, 4
th
edition, Verlag Chemie, Weinheim, 1979, vol. 17, pages 581 ff., gives a general description of the use of digested, water-soluble starches and of water-soluble starch derivatives as assistants for papermaking, in particular for enhancing the strength of paper. However, the retention of the dissolved starches in paper is low, leading to a considerable wastewater loading.
U.S. Pat. No. 3,467,608 describes a process for preparing a cationic starch by heating an aqueous starch slurry in the presence of a polyalkyleneimine, for example polyethyleneimine, or of a polyalkylenepolyamine, for example polyethylenepolyamine. The molecular weight of the modifying polymer used is not less than 50,000 in either case. The reaction mixture contains 0.5 to 40% by weight of the polymer and 60 to 99.5% by weight of starch, the percentages being based on the solids content. The possibility of using starches modified by hydrolysis, oxidation, esterification and etherification is described here in general terms. The resulting cationic starch derivatives are used as flocculants.
U.S. Pat. No. 4,097,427 describes a process for cationizing starch by reacting an aqueous starch slurry under alkaline reaction conditions in the presence of an oxidizing agent with a water-soluble polymer which contains quaternary ammonium groups. Only unmodified or minimally degraded starches are used, preferably maize and tapioca starch. The polymers containing quaternary ammonium groups are selected from polymers containing epichlorohydrin units, quaternized polyethyleneimines, quaternized diallyldialkylamine polymers, etc. The oxidizing agent is for example ammonium persulfate, hydrogen peroxide, sodium hypochlorite, ozone or tert-butyl hydroperoxide. The pH of the starch slurry is adjusted to about 8 using water-soluble bases. The modified cationic starches thus prepared are added to paper stock to enhance the dry strength of the paper being produced. In this process, however, the wastewater has a very high chemical oxygen demand (COD).
U.S. Pat. No. 4,146,515 discloses a process for preparing cationic starch used for surface sizing and coating paper and paper products. In this process, an aqueous slurry of oxidized starch is digested together with a cationic polymer in a continuous cooker. The cationic polymers are selected from the group consisting of epichlbrohydrin-dimethylamine condensate, diallyldimethylanmonium chloride polymer, quaternized ethylene chloride dichloride ammonia reaction product and also quaternized polyethyleneimine, inter alia.
DE-A-3719480 discloses a process for producing paper, paperboard and cardboard by using a dry strength enhancer comprising a mixture obtained by heating native potato starch in an aqueous medium in the presence of polyethyleneimine at above or below the gelatinization temperature of the starch.
EP-A-0282761 discloses a process for producing paper, paperboard and cardboard by using a dry strength enhancer comprising a mixture obtainable by heating native potato starch with polyvinylamine in aqueous solution at 70 to 110° C.
EP-A-0301372 discloses a process for producing paper of high dry strength by using a dry strength enhancer comprising a mixture obtained by heating enzymatically degraded starch and cationic polymers such as polyvinylamines at up to 170° C.
U.S. Pat. No. 4,880,497 and U.S. Pat. No. 4,978,427 disclose the production of paper of high dry and wet strength by adding, either to the surface of the paper or to the paper stock prior to sheet formation, a hydrolyzed copolymer strength enhancer obtainable by polymerizing N-vinylformamide and ethylenically unsaturated monomers such as vinyl acetate or alkyl vinyl ethers and hydrolyzing from 30 to 100 mol % of the formyl groups of the copolymer to form the amino groups. WO-A-96/135525 [sic] discloses a process for the cationic modification of starch by reacting starch with polymers, diamino [sic] and/or ammonium groups contain [sic] in an aqueous medium at 115 to 180° C. under superatmospheric pressure with only minimal degradation of the starch.
WO-A-98/31711 discloses a process for modifying starch by, for example, reacting an anionic starch with a cationic polymer, for example polyvinylamine, at 80 to 220° C. in an aqueous medium. The aqueous solutions thus obtainable are used as dry and wet strength enhancers and also as drainage and retention aids for paper, paperboard and cardboard.
WO-A-98/45536 relates to a process for preparing paper, paperboard and cardboard of high dry strength by adding starches which are digested in an aqueous medium in the presence of cationic polymers. The paper stock is additionally admixed with a cationic polymer as retention aid for starch. The higher retention reduces the COD of the machine wastewater.
Yet, with all the processes mentioned above, where a cationic modified starch dry strength enhancer is added to paper stock, the sheet-forming step is accompanied by an unwelcome reduction in the drainage rate of the paper stock, which is particularly pronounced when comparatively high starch levels are used.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide modified starch which, in the production of paper, paperboard and cardboard, combines an enhanced retention of starch in the paper with a drainage rate superior to that of existing cationic modified starches.
We have found that this object is achieved by a process for modifying starch by heating starch with at least one cationic polymer in an aqueous medium to temperatures above the gelatinization temperature of said starch, which comprises effecting said modifying of said starch in the presence of
(a) a polymeric cationizer selected from the group consisting of the polymers containing vinylamine units and having molar masses of up to 1 million, the polyethyleneimines, the polydiallyldimethylammonium chlorides, the condensates of dimethylamine with epichlorohydrin or dichloroalkanes, the condensates of dichloroethane and ammonia, and the mixtures thereof, and
(b) polymeric papermaking drainage aids selected from the group consisting of the water-soluble crosslinked polyamidoamines with or without an ethyleneimine graft, the nonionic or cationic polymers containing acrylamide and/or methacrylamide units and having molar masses of more than 1 million, the polymers containing vinylamine units and having molar masses of more than 1 million, and the mixtures thereof.
The present invention also provides the reaction products of starch with cationic polymers obtainable by the process described above.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
All starches can be modified according to the invention, for example native starches, oxidized native starches, starch ethers, starch esters, oxidized starch ethers, oxidized starch esters, cationic modified starches or amphoteric starches.
The native starches used may be starches from the group consisting of maize starch, potato starch, wheat starch, rice starch, tapioca starch, sago starch, sorghum starch, casaba starch, pea starch, or mixtures thereof. It is also possible to use starches which have an amylopectin content of at least 80% by weight. Such starches are obtainable for example by fractionation of customary native starches or by cultivation of such plants as produce virtually pure amylopectin starch, as described in Günther Tegge, Stärke und Stärkederivate, Hamburg, Behr's-Verlag 1984, pages 157-160. Starches having an amylopectin content of at least 80% by weight are commercially available. They are generally known as w
Diehl Kurt
Lorencak Primoz
Mahr Norbert
Stange Andreas
BASF - Aktiengesellschaft
Bell Mark L.
Hailey Patricia L.
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