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
2001-06-12
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
Reexamination Certificate
active
06245848
ABSTRACT:
The present invention relates to a latex containing two populations of particles of polymers based on vinyl chloride. Other subjects of the present invention are processes for producing this latex and its applications.
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. These latices are prepared by seeded microsuspension polymerization of the corresponding monomer or monomers in the presence of a first seeding polymer, the particles of which contain at least one organosoluble initiator, of a second seeding polymer, of a surface-active agent and of a soluble metal salt, in an amount such that the molar ratio of the metal salt to the organosoluble initiator is between 0.1 and 10 (FR 2 309 569). The polymerization is carried out in the absence of supplementary addition of initiator.
Moreover, U.S. Pat. No. 5,151,476 teaches us that the metal salt/organosoluble initiator molar ratio can be reduced and that the polymerization can even be carried out in the absence of metal salt.
Bipopulated latices currently known, in particular those prepared by seeded microsuspension polymerization, lead either to fluid plastisols or to foams of good cellular quality. Until the present application, it was not possible to obtain both fluid plastisols and foams of high cellular quality from the same latex.
It has now discovered a latex containing two populations of particles of polymers based on vinyl chloride, respectively exhibiting mean diameters of between 0.9 and 1.3 &mgr;m and between 0.15 and 0.3 &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 0.4 and 0.7.
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 or itaconic acid, 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, in an amount such that the metal salt/organosoluble initiator molar ratio is less than 0.09, and of a reducing agent.
This process is characterized in that the reducing agent is the metabisulphite of an alkali metal and preferably potassium metabisulphite. The amount of reducing agent used is preferably between 30 and 120 ppm with respect to the monomer(s) involved.
The first seeding polymer (P1) necessary for the polymerization can be prepared according to conventional microsuspension polymerization techniques. It is used in the form of an aqueous dispersion of its particles, the mean diameter of which is preferably between 0.4 and 0.7 &mgr;m.
A means for preparing this seeding polymer consists in making use of water, vinyl chloride, alone or in combination with one or a number of copolymerizable monomer(s), an organosoluble inkiator and an anionic emulsifier, optionally in combination with a non-ionic emulsifier. The monomer or monomers are finely dispersed in water using an energetic mechanical means, such as, for example, colloid mill, fast pump, vibratory agitator or ultrasonic device. The microsuspension obtained is then heated under autogenous pressure and with moderate stirring at a temperature generally of between 30 and 65° C. After the fall in the pressure, the reaction is halted and the unconverted monomer or monomers are degassed.
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.
The choice of the organosoluble initiator depends on its rate of decomposition at the reaction temperature adopted. This is because the said initiator must be sufficiently reactive to make it possible to carry out the seeding polymerization within times of between 4 and 12 hours and with normal doses, of the order of 0.1 to 3% by weight with respect to the monomer or to the mixture of monomers, and its rate of decomposition must be such that the amount of initiator decomposed in the preparation of the seeding polymer does not exceed half the amount of initiator employed. For this, it is therefore necessary to choose an initiator with a half-life such that the proportion of initiator destroyed during the preparation of the seeding polymer is between 5 and 50% by weight of all the initiator employed.
Moreover, the organosoluble initiator chosen must be insoluble in water. 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 polymer 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 polymer (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 a number of 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.
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 advantageously chosen.
The presence of the anionic emulsifier, optionally in combination with at least one non
Ernst Benoit
Espiard Philippe
Peres Richard
Elf Atochem S.A.
Millen White Zelano & Branigan P.C.
Mulcahy Peter D.
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