Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-07-28
2003-05-06
Wilson, D. R. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S367000, C525S369000, C525S328200
Reexamination Certificate
active
06559227
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for producing a vinylamine-vinyl alcohol copolymer, more particularly, a process for easily obtaining the copolymer in the form of powder, and uses of the copolymer as a hair setting composition or a hair conditioning composition.
BACKGROUND OF THE INVENTION
Vinylamine-vinyl alcohol copolymers are known to have various functions. For example, JP-A-62-74902 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) describes the function as a chemical to be used in papermaking. U.S. Pat. No. 4,713,236 teaches application to hair care products including shampoos. JP-A-9-87144 discloses use in a hair conditioning composition. JP-A-9-87151 proposes use in hair styling cosmetics.
Although N-vinylformamide, which is a starting material of the vinylamine-vinyl alcohol copolymer, has recently come to be available in industry, the vinylamine-vinyl alcohol copolymer itself is not manufactured on an industrial scale for the time being because an economical process of production has not been established as yet.
Processes of producing the copolymer that have hitherto been reported include a process comprising acid-hydrolysis of an N-vinylformamide-vinyl acetate copolymer in water (see JP-A-62-74902) and a process comprising polymerizing N-vinylformamide and vinyl acetate in an alcohol followed by hydrolysis (see JP-B-6-51741; the term “JP-B” as used herein means an “examined Japanese patent publication”). The former process yields the polymer in the form of an aqueous solution, which is inconvenient in transportation or purification. The latter process has an advantage of easy purification because the polymer is obtained in the form of powder but is disadvantageous in that, for one thing, a large quantity of an alcohol is required, which leads to an increase of cost, and, for another, complicated production steps are involved.
SUMMARY OF THE INVENTION
The present invention has been completed in the light of the above-described circumstances. An object of the present invention is to provide a vinylamine-vinyl alcohol copolymer in a powdered form at a low cost.
As a result of extensive studies, the present inventors have found that the vinylamine-vinyl alcohol copolymer precipitates in a powdered form where a copolymer comprising an N-vinylamide unit and a vinyl acetate unit as dispersed in water is hydrolyzed under a basic condition. Where the N-vinylamide-vinyl acetate copolymer is hydrolyzed in water in an acidic condition as in the known process, the vinylamine unit of the hydrolysate takes the form of a salt (e.g., a hydrochloride) so that the resulting polymer dissolves in water. On the other hand, where the hydrolysis is conducted under a basic condition according to the invention, the vinylamine unit takes the form of a free amine, and the desired polymer is salted out by the influence of hydrolysis by-produced salts such as sodium acetate and sodium formate.
The polymer obtained by hydrolysis under a basic condition unavoidably contains by-produced salts, such as sodium acetate and sodium formate. Washing with water is a conceivable method for removing these salts. However, the polymer, being water-soluble, will be dissolved when merely washed with water, resulting in a considerable washing loss, which eventually leads to an increase of the polymer price.
The present inventors have continued their study to settle the above problem of washing loss and, as a result, found a specific means for washing the hydrolysis reaction mixture which is obtained by hydrolyzing a copolymer comprising an N-vinylamide unit and a vinyl acetate unit under a basic condition to remove only the impurities without being accompanied by dissolution of the desired polymer.
The gist of the present invention consists in a process for producing a powdered water-soluble polymer comprising hydrolyzing a copolymer comprising an N-vinylamide unit and a vinyl acetate unit while dispersed in water under a basic condition and then washing the resulting powdered water-soluble polymer with at least one washing liquid selected from an alcohol, water at 20° C. or lower, and salt water.
DETAILED DESCRIPTION OF THE INVENTION
The polymer which can be used in the invention as a starting material is a copolymer mainly comprising an N-vinylamide unit and a vinyl acetate unit. The monomer providing the N-vinylamide unit includes N-vinylformamide and N-vinylacetamide, with N-vinylformamide being preferred. The starting copolymer usually comprises about 1 to 50 mol % of the N-vinylamide unit and about 50 to 99 mol % of the vinyl acetate unit.
The molar ratio of the N-vinylamide unit and the vinyl acetate unit in the copolymer usually ranges from 1:99 to 50:50, preferably 5:95 to 50:50. Where the N-vinylamide unit content is too high, the hydrolyzed polymer tends to dissolve.
The starting copolymer may further comprise other arbitrary monomer units as long as the desired characteristics of the resulting polymer are not impaired. The content of the other monomer units, while varying depending on the monomer, is usually 30 mol % or less based on the total monomer units.
The N-vinylamide-vinyl acetate copolymer can be prepared by known techniques such as emulsion polymerization or suspension polymerization in water. Emulsion polymerization is recommended for ease in handling the resulting polymer. Polymerization is carried out by radical polymerization preferably in the presence of an azo initiator. The monomer concentration in the polymerization system is usually 1 to 50% by weight, preferably 10 to 45% by weight. If desired, assistants, such as an emulsifying agent used in emulsion polymerization or a chain transfer agent as a molecular weight modifier, can be used. The reaction mixture as obtained by emulsion polymerization or suspension polymerization is a white emulsion or a slurry, respectively.
The polymerization is followed by hydrolysis. The polymerization reaction mixture (e.g., an emulsion or a slurry) can be subjected to hydrolysis as such or, if desired, with the polymer concentration in water adjusted by dilution with water or concentration by, for example, evaporation of water. The concentration of the polymer to be hydrolyzed is usually in the range of 1 to 50% by weight, preferably 10 to 45% by weight. If the polymer concentration is too low, the hydrolysate polymer may dissolve. Too high a polymer concentration requires much power for stirring.
The hydrolysis should be carried out under a basic condition. The basic condition is preferably such as created in the presence of a strong alkali, particularly a caustic alkali such as caustic soda or caustic potash.
The alkali is usually added in an amount of 0.1 to 10 equivalents, preferably 0.5 to 5 equivalents, per equivalent of the total monomers. It should be noted that the polymer after hydrolysis is water-soluble. It is the salt by-produced by the hydrolysis that causes the water-soluble polymer to precipitate. Therefore, where the amount of the base is small, and the degree of hydrolysis is low or where the reaction system has a low concentration or in like situations, the salt concentration may be so low that the polymer easily dissolves or swells, resulting in a filtration failure. Such a case can be managed by adding a supplementary salt to accelerate precipitation (salting-out) of the polymer. Salts which can be added include sodium acetate, potassium acetate, sodium formate, potassium formate, sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, calcium chloride, sodium carbonate, and potassium carbonate. In particular, addition of a salt of a polybasic acid, such as sulfuric acid, phosphoric acid or carbonic acid, is effective in precipitating the polymer. The salt concentration in the precipitation system, i.e., the total of the salt by-produced by the hydrolysis and the supplementary salt added to accelerate salting-out, is usually 0.5 to 50% by weight, preferably 1 to 30% by weight. The supplementary salt, if needed, is preferably added after compl
Mori Yasuharu
Satoh Kohichi
Ueno Nobuhiko
Mitsubishi Chemical Corporation
Wilson D. R.
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