Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1997-08-27
2001-10-02
Mulcahy, Peter D. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S834000, C526S075000
Reexamination Certificate
active
06297316
ABSTRACT:
The present invention relates to a latex containing two populations of particles of polymers based on vinyl chloride. Other aims of the present invention are processes for producing this latex and its use in the manufacture of fluid plastisols which are stable on storage.
Bipopulated latices of particles of polymers based on vinyl chloride, respectively exhibiting mean diameters of between 0.4 and 2.5 &mgr;m and between 0.08 and 1 &mgr;m, in a ratio of the diameters of between 1 and 20 and a ratio by weight of between 0.1 and 10, are known (FR 2 309 569). In the examples which illustrate the invention, these latices are prepared by seeded microsuspension polymerization in the presence of a first seeding polymer, the particles of which contain at least one organosoluble initiator and have a mean diameter of at most 0.48 &mgr;m.
Moreover, a process for producing a latex of polymers based on vinyl chloride, capable of giving fluid plastisols which are stable on storage, is described in Patent JP-A-6 107 711. This process is characterized in that the seeded microsuspension polymerization is carried out in the presence of a specific surface-active agent, such as, for example, nonylpropenylphenol (ethylene oxide)
20
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Plastisols comprising polymers based on vinyl chloride having a low viscosity and exhibiting good stability on storage are much sought after. They have numerous applications in coating and in the manufacture of moulded articles. Their low viscosity makes them easier to use and also makes it possible to increase the productivity during conversion.
The Applicant Company has now discovered a latex containing two populations of particles of polymers based on vinyl chloride, respectively exhibiting mean diameters of between 1.2 and 2 &mgr;m and between 0.15 and 0.30 &mgr;m, in proportions such that the ratio by weight of the population with the lesser mean diameter to that with the greater mean diameter is between 0.1 and 0.3. The powder resulting from the atomization of this latex, optionally followed by milling, is very particularly suitable for the manufacture of fluid plastisols which are stable on storage.
Polymers based on vinyl chloride is understood to mean homo- and copolymers, the latter containing at least 50% by weight of vinyl chloride and at least one monomer which is capable of copolymerizing with vinyl chloride. The copolymerizable monomers are those generally employed in conventional techniques for the copolymerization of vinyl chloride. Mention may be made of vinyl esters of mono- and polycarboxylic acids, such as vinyl acetate, propionate or benzoate; unsaturated mono- and polycarboxylic acids, such as acrylic, methacrylic, maleic, fumaric and itaconic acids, and their aliphatic, cycloaliphatic or aromatic esters, their amides or their nitriles; alkyl, vinyl or vinylidene halides; alkyl vinyl ethers and olefins.
The preferred polymers based on vinyl chloride are vinyl chloride homopolymers.
The latex according to the present invention can be obtained by seeded microsuspension polymerization of the corresponding monomer or monomers in the presence of a first seeding polymer (P1), the particles of which contain at least one organosoluble initiator, of a second seeding polymer (P2), the particles of which have a mean diameter less than that of the particles of the first seeding polymer (P1), of water, of an anionic emulsifier, of a soluble metal salt and of a reducing agent.
This process is characterized in that the mean diameter of the particles of the first seeding polymer (P1) is between 0.6 and 0.9 &mgr;m.
The first seeding polymer (P1) necessary for the polymerization can be prepared according to conventional microsuspension polymerization techniques, such as that described in Patent FR 2 309 569, but the time for dispersion of the monomer or monomers is less than that commonly used. It is then used in the form of an aqueous dispersion of its particles.
The organosoluble initiators to be employed in the preparation of the first seeding polymer (P1) are represented by organic peroxides, such as lauroyl, decanoyl and caproyl peroxides, tert-butyl diethylperacetate, diethylhexyl percarbonate, diacetyl peroxide and dicetyl peroxide carbonate.
Lauroyl peroxide is advantageously chosen.
In the case where a number of organosoluble initiators are employed, it is advantageous to choose them with different reactivities; the most reactive initiators act mainly during the preparation of the seeding polymer, whereas the least reactive initiators act in particular during the seeded polymerization.
The second seeding polymer (P2) is provided in the form of an aqueous dispersion of its particles, the mean diameter of which is preferably between 0.1 and 0.14 &mgr;m.
This particle dispersion can be obtained by conventional microsuspension or emulsion polymerization techniques.
When the second seeding (P2) is prepared by microsuspension polymerization, the preparation is carried out as described above but the homogenization is more developed.
The second seeding polymer (P2) is preferably prepared by emulsion polymerization, which consists in making use of water, vinyl chloride, alone or in combination with one or more copolymerizable monomer(s), a water-soluble initiator and an anionic emulsifier, optionally in combination with a non-ionic emulsifier.
The reaction mixture is heated under autogenous pressure and moderate stirring at a temperature of between 30 and 65° C. After fall in pressure, the reaction is halted and the unconverted monomer or monomers are degassed.
The water-soluble initiators necessary for the preparation of the second seeding polymer (P2) are generally represented by hydrogen peroxide or alkali metal or ammonium persulphates, optionally in combination with water-soluble reducing agents, such as alkali metal sulphites or bisulphites. The highly variable amounts used depend on the initiator system chosen and are just sufficient to provide for the polymerization within reasonable times.
The reducing agents can be chosen from alkyl hydrogen phosphates, lactones, ketones, carbazones, alkali metal metabisulphites and mono- or polycarboxylic acids, such as ascorbic acid and its derivatives. The amount of reducing agent used is preferably between 30 and 120 ppm with respect to the monomer(s) involved. Ascorbic acid is advantageously chosen.
In the process according to the present invention, the rate of polymerization is accelerated by the action of the water-soluble metal salt and of the reducing agent on the organosoluble initiator. The metal salt is employed in an amount such that the metal salt/initiator molar ratio is preferably between 0.001 and 0.1 and more particularly between 0.001 and 0.03. The metal is generally chosen from iron, copper, cobalt, nickel, zinc, tin, titanium, vanadium, manganese, chromium and silver. Copper is advantegeously chosen.
The presence of the anionic emulsifier, optionally in combination with at least one non-ionic emulsifier, improves the stability of the microsuspension. The emulsifier or emulsifiers can be added to the reaction mixture before and/or after and/or during polymerization. The anionic emulsifiers are preferably chosen from alkaline alkyl phosphates, alkyl sulphosuccinates, allylsulphonates, vinylsulphonates, alkylarysulphonates, alkylsulphonates, ethoxylated alkyl sulphates, alkyl sulphates or fatty acid soaps. The preferred non-ionic emulsifiers are polycondensates of ethylene or propylene oxide with various hydroxylated organic compounds.
The total amount of emulsifier employed is preferably between 1 and 3% by weight of the monomer or monomers involved.
The amount of water necessary for the polymerization according to the invention is such that the initial concentration of seeding polymers, plus the monomer or monomers involved, is between 20 and 80% and preferably between 45 and 75% by weight with respect to the reaction mixture.
The seeded polymerization temperature is generally between 30 and 80° C. and the duration of polymerization is between 30 minutes and 12 hours and preferably between 1 and 8 ho
Ernst Benoit
Espiard Philippe
Peres Richard
Elf Atochem S.A.
Millen White Zelano & Branigan P.C.
Mulcahy Peter D.
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