Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carbohydrate or derivative as a reactant
Reexamination Certificate
1999-01-13
2001-07-03
Hampton-Hightower, P. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carbohydrate or derivative as a reactant
C527S306000, C527S309000, C527S310000, C527S311000, C527S312000, C527S313000, C527S314000
Reexamination Certificate
active
06255427
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
Polymer dispersions on an aqueous basis are characterized by the presence of dispersely distributed polymer particles in an aqueous dispersion fluid. For stabilizing a system of this type in which discrete polymer particles, for thermodynamic reasons, tend to coagulate, as a rule, surface active substances are used. The capability of using starch and the derivatives thereof as surface active substances of this type for generating aqueous polymer dispersions has already repeatedly been suggested.
2. Description of the Related Art
EP 0 276 770 is concerned with a sizing agent in the form of an aqueous polymer dispersion wherein a monomer mix of 20-65% acrylonitrile, 80-35% acrylic acid ester and 0-10% of other ethylenically unsaturated monomers in the aqueous phase is copolymerized in one step, using modified starch of a reduced viscosity of 0.04 to 0.12 dl/g.
EP 0 536 597 A1 describes aqueous polymer dispersions obtainable by radical polymerisation of unsaturated monomers containing at least one reduced starch product obtainable by hydrolysis in the aqueous phase and having an average molecular weight of between 2.500 and 25.000. In none of the aforementioned cases, the way of carrying out the radical polymerisation is suitable for preparing an amphoteric copolymer. The afore-mentioned patent applications do not describe any charge characteristics actually required for these systems in order to judge their suitability for special applications, such as sizing and coating.
EP 0 479 245 A2 describe polymers usable as adsorbents for aqueous media, with the polymers being formed by copolymerisation of an ampholytic ion-pair and at least one additional monomer, wherein the said second monomer can be acrylamide, methacrylamide or acrylonitrile. Moreover, the said polymers also contain so called cross-linking agents carrying, in turn, at least 2 olefinic functional groups, with each of these groups being suitable for cross-linking. The polymer, in addition, contains polysaccharides, polypropylene or polyethylene forming in conjunction with the afore-mentioned comonomers a graft polymer. The resultant polymer exclusively contains water-soluble monomers and is formed in a one-step reaction. U.S. Pat. No. 4,552,940 discloses a starch-containing graft polymer generated in the form of an aqueous solution. It was the object of that invention to adjust the viscosity of the starch solution by the addition of styrene. The so adjusted starch solutions can then be employed as adhesives or coating agents. The problem underlying the present invention resides in providing amphoteric aqueous polymer dispersions which with the aid of a suitable process using starch and/or the derivatives thereof, can be generated free of coagulate. Polymer dispersions of this type, with a uniform particle size distribution, should be of a high stability and, through their surface charge, should be compatible both with anionic and cationic systems, and safeguard the use thereof over a wide pH-range.
SUMMARY OF THE INVENTION
The amphoteric polymer dispersions of the invention are available in a multi-step emulsion polymerization, with a finely divided anionic polymer dispersion being generated in the first process step based on a monomer mixture composed of ethylenically unsaturated monomers which, in addition, contain in the mixture unsaturated carbonic, sulphonic and phosphonic acids (monomers A) up to 30% by weight, with the said mixture being polymerized in the presence of starch and/or the derivatives thereof modified by enzyme or acid hydrolysis and with the starch and/or the derivatives thereof being of an average molecular weight of 500-2000, preferably 800-1500 g/mol and an intrinsic viscosity of under 0.1 dl/g. The concentration of the present aqueous starch solutions can amount to up to 40% by weight, preferably 10-35% by weight. The weight ratio of starch to monomeric mixture is between (20:1) and (1:20). The solids content of the so obtained anionic dispersion amounts to between 15 and 45% by weight, preferably 20 to 40% by weight and has a Zeta-potential of between −3 and −70 mV, preferably between −5 and −30 mV. In the presence of the anionic dispersion obtained in step 1 the same is then polymerized with another monomeric mixture which in addition to the ethylenically unsaturated monomers also contains monomers of a cationic (basic) character (monomers B) having a weight of up to 35% by weight, preferably 5 to 20% by weight. The weight ratio between the dispersion prepared in step 1 and the share of monomers added in step 2 is between (10:1) and (1:10), with the solids content of the so produced amphoteric polymer dispersion amounting to between 20 and 55% by weight, preferably between 25 and 45% by weight and having a uniform particle size distribution smaller than 300 nm. To be considered as radically polymerizable monomers are, in particular, monoethylenically unsaturated monomers, such as olefins, vinyl aromatic monomers such as styrene, alpha-methyl styrene, chlorostyrene or vinyl toluene, esters of vinyl alcohol and monocarbonic acids preferably containing 1-18 C-atoms, such as vinyl acetate, vinyl butyrate, vinyl stearate, esters of alpha-, beta mono-ethylenically unsaturated mono- and dicarbonic acids preferably containing 3-6 C-atoms, in particular, acrylic acid, methacrylic acid, maleic acid, fumaric acid with alkanols generally containing 1-2, preferably 1-8, more preferably 1-4 C-atoms, in particular, acrylic acid and methacrylic acid methyl, ethyl, n-butyl, isobutyl, ethyl hexyl and cyclohexyl esters as well as acrylonitrile and conjugated dienes, such as 1,3-butadiene. In addition, functional monomers, such as hydroxyethylacrylate and methacrylate, hydroxypropylacrylate and methacrylate, n-vinyl pyrrolidene, acrylamide, methacrylamide and trimethylolpropane triacrylate are used.
The typical anionic charge characteristic of the dispersion prepared in the first process step is obtained by copolymerization of ethylenically unsaturated carbonic, sulphonic or phosphonic acids. For example, acrylic acid, methacrylic acid, maleic acid, fumaric acid, vinyl sulphonic acid, vinyl phoshonic acid, 2-acrylamidopropane sulphonic acid and styrne sulphonic acid or the alkaline and or alkaline earth salts or ammonium salts can be used in this respect. The weight ratio of starch to monomers, in the first process step, is between 20:1 and 1:20. The share of unsaturated carbonic, sulphonic or phosphonic acids, based on the monomeric amount of the first process step, amounts to up to 30% by weight. In the first process step, the monomeric mixture containing the monomers A is continuously fed to the aqueous starch solution. The reaction temperature is between 40 and 95° C. To the aqueous starch solution both peroxides such as ammonium or alkaline metal peroxide disulphate or H
2
O
2
, and azocompounds are added as water-soluble radical initiators. In combinations with reducing components, such as ascorbic acid, hydroxymethane sulphinic acid, sodium sulphite, sodium hydrogen sulphite of the reducing metal compounds, such as Fe(II)- Ce(IV)- or Mn(II) salts, the initiators, alternatively, can also be dosed in the continuous admixing process. The second process step is characterized in that in the presence of the dispersion prepared in the first process step ethylenically unsaturated monomers are polymerized which also contain nitrogen-containing monomers of a basic character (monomers B), with the polymerization, using water-soluble radical starters and/or a redox system, being carried out at temperatures of between 20 and 95° C. The monomers B are selected from the group of acrylic acid and/or methacrylic acid diaminoalkylesters, for example dimethyl aminoethylmethacrylate, dimethyl aminoethylacrylate and from the group of acrylic acid and/or methacrylic acid diaminoalkylamides, for example, dimethyl aminopropylmethacrylamide, dimethyl aminopropylacrylamide, and from additional basic vinyl compounds, such as n-vinylimidazol, n-vinyl-2-m
Exner Reiner
Hetterich Karl
Ulubay Hasen
Giulini Chemie GmbH
Hampton-Hightower P.
Spencer George H.
Venable
Wells Ashley J.
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