Bipopulated latex based on vinyl chloride polymers having a high population level of fine particles, processes for the manufacture thereof and applications thereof

The present invention relates to a latex containing two populations of particles of polymers based on vinyl chloride, respectively exhibiting mean diameters of between 0.9 and 1.3 .mu.m and between 0.15 and 0.3 .mu.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. Other subjects of the present invention are processes for the manufacture of the said latex and its application in fluid plastisols and foams of very good cellular quality.

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 .mu.m and
 between 0.08 and 1 .mu.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 .mu.m and between 0.15 and 0.3 .mu.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
 .mu.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.degree. 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 .mu.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.degree. 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-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,
 alkylarylsulphonates, 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 amounts of emulsifier can represent up to 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.
 In addition, the seeded polymerization according to the present invention
 can be carried out in the presence of one or of several water-soluble
 initiator(s) chosen from hydrogen peroxide and alkali metal or ammonium
 persulphates. Ammonium persulphate is advantageously chosen.
 The water-soluble initiator or initiators is or are preferably introduced
 into the reaction mixture before the beginning of the seeded
 polymerization. The amount of water-soluble initiator(s) used is
 preferably between 10 and 100 ppm with respect to the monomer(s) involved.
 The seeded polymerization temperature is generally between 30 and
 80.degree. C. and the duration of polymerization is between 30 minutes and
 12 hours and preferably between 1 and 8 hours.
 Another method for the preparation of the latex in accordance with the
 present invention consists in choosing the reducing agent from alkyl
 hydrogen phosphates, lactones, ketones, carbazones and mono- or
 polycarboxylic acids, such as ascorbic acid or its derivatives, and in
 carrying out the preparation in the presence of at least one water-soluble
 initiator, preferably ammonium persulphate. Ascorbic acid is
 advantageously chosen as reducing agent.
 According to a third preparation method, the latex of the present invention
 can be obtained by mixing a latex (L1) containing a single population of
 particles of polymers based on vinyl chloride, the mean diameter of which
 is between 0.9 and 1.3 .mu.m, with a second latex (L2) also containing a
 single population of particles of polymers based on vinyl chloride, the
 mean diameter of which is between 0.15 and 0.3 .mu.m, in proportions such
 that the ratio by mass of polymers of the latex (L2) to those of the latex
 (L1) is between 0.4 and 0.7.
 The latex (L1) can be obtained by seeded microsuspension polymerization in
 the presence of a first seeding polymer (P1) based on vinyl chloride, the
 particles of which contain at least one organosoluble initiator, 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 reducing agent.
 The latex (L2) can be obtained by emulsion polymerization of 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.
 According to the first two preparation methods, the amount of two seeding
 polymers used is such that the ratio by mass of the second seeding polymer
 (P2) to (P1) is preferably between 0.7 and 1.8.
 Whatever the preparation method used, the latices thus prepared are then
 advantageously dried by atomization and the resulting powders are
 particularly suitable for the preparation of fluid plastisols and also of
 foams of very good cellular quality. Moreover, the foams thus prepared
 exhibit a high level of whiteness, preferably of the order of 45 (ASTM
 Standard E 313/73 D25/2W).

EXPERIMENTAL T
 (A) Preparation of the seedina polymer (P1)
 The following are successively introduced into an 800 litre reactor stirred
 at 35 revolutions/min and adjusted to 15.degree. C.:
 375 kg of water
 5 l of the buffer solution containing 426 g of potassium
 dihydrogenphosphate and 117 g of pure sodium hydroxide
 11 g of benzoquinone powder
 6 kg of lauroyl peroxide
 320 kg of vinyl chloride
 48 kg of a 10% by weight aqueous sodium dodecylbenzene sulphonate solution,
 the reactor being placed under vacuum just before the introduction of the
 vinyl chloride.
 A fine dispersion of the vinyl chloride in the aqueous mixture is then
 produced at a temperature of less than or equal to 35.degree. C. by
 stirring the said mixture for 105 minutes at 5500 revolutions/min.
 The reaction mixture is then brought to the targeted polymerization
 temperature of 45.degree. C. under autogenous pressure, the rate of
 stirring being 30 revolutions/min. During the polymerization, benzoquinone
 is introduced continuously with a constant throughput of 10.5 g/h.
 After the fall in pressure to a value of 3.5 bars, that is to say after 8
 hours, the unreacted vinyl chloride is degassed. A latex is thus obtained,
 the particles of which have a mean diameter of approximately 0.55 .mu.m
 and contain approximately 2% by weight of lauroyl peroxide with respect to
 the polymer.
 (B) Preparation of the seedinc polymer (P2)
 The following are introduced into an 800 litre reactor equipped with a
 stirrer:
 415 kg of water
 1.25 kg of lauric acid and
 0.8 kg of pure sodium hydroxide.
 The mixture is then brought to a temperature of 65.degree. C. and is
 maintained at this temperature for one hour. The mixture is then cooled to
 55.degree. C. and then the reactor is placed under vacuum. While
 maintaining the temperature of the mixture at 55.degree. C., 400 kg of
 vinyl chloride and 4 litres of an aqueous solution containing 109 g of
 ammonium persulphate are then introduced, followed by the continuous
 addition, with a constant throughput of 3 l/h, of an aqueous solution
 containing, in 30 litres of water, 0.72 g of copper sulphate, 18 g of
 potassium metabisulphite and 0.54 litre of 12N aqueous ammonia. Three
 hours after the introduction of the persulphate, an aqueous solution
 containing 4.56 kg of sodium dodecylbenzene sulphonate per 40 litres of
 water is continuously added to the reaction mixture for 5 hours at 8 l/h.
 When the internal pressure is 4.5 bars, the reaction is halted by rapid
 cooling and an aqueous sodium dodecylbenzene sulphonate solution,
 containing 7.28 kg on a dry basis, is then introduced. The polymer
 particles obtained have a mean diameter in the region of 0.11 .mu.m.
 (C) Preparation of the latex (L2)
 The following are introduced into a 28 litre reactor equipped with a
 stirrer:
 9650 g of water
 100 cm.sup.3 of an aqueous solution containing
 0.975 g of ethylenediaminetetraacetic acid (EDTA)
 0.191 g of iron sulphate
 1.78 g of sodium formaldehydesulphoxylate
 9.8 g of lauric acid and
 3.25 g of pure sodium hydroxide.
 The reactor is then placed under vacuum before the introduction of 7000 g
 of vinyl chloride. The reaction mixture is then brought to the targeted
 temperature of 58.degree. C. As soon as the mixture reaches 45.degree. C.,
 an aqueous solution containing 3.5 g of potassium persulphate per 1 litre
 of water is introduced continuously. One hour after the beginning of the
 introduction of the latter, one litre of solution containing 56 g of
 [lacuna] dodecylbenzene sulphonate is added continuously at a constant
 throughput for 4 hours. When the internal pressure is 4 bars, the reactor
 is re-exposed to the air and then cooled. After polymerizing for 4 hours
 and 30 minutes, the concentration by weight of polymer is 41% and the
 degree of conversion of the vinyl chloride is 93%. The mean diameter of
 the polymer particles is 0.2 .mu.m.
 Comparative Example 1
 The following are successively introduced, by suction, into an 800 litre
 reactor equipped with a stirrer and placed under vacuum beforehand:
 400 kg of demineralized water
 80 g of potassium dihydrogenphosphate
 0.63 g of copper sulphate (CuSO.sub.4.multidot.5H.sub.2 O)
 15.44 kg, on a dry basis, of the seeding polymer P1 latex
 9.08 kg, on a dry basis, of the seeding polymer P2 latex.
 The reactor at room temperature, with stirring and containing the aqueous
 mixture, is again placed under vacuum. 400 kg of vinyl chloride are then
 introduced and the reaction mixture is then brought to the targeted
 temperature of 58.degree. C. As soon as the temperature of the mixture
 reaches 55.degree. C., an aqueous ascorbic acid solution is introduced
 continuously, followed, after one hour, by an aqueous sodium
 dodecylbenzene sulphonate solution.
 When the pressure of the mixture is 4 bars, i.e. after polymerizing for 6
 hours, the introduction of the aqueous solutions and the heating are
 halted and the reactor is cooled.
 The total amount of ascorbic acid and of sodium dodecylbenzene sulphonate
 introduced is 23 g and 3.2 kg respectively.
 A latex is obtained, the polymer If concentration of which is 47%. Particle
 size analysis shows that the polymer is formed of two populations, the
 particles of which have mean diameters of 0.23 .mu.m and 1.09 .mu.m
 respectively. The fine particles represent 15.5% by weight of the polymer.
 Comparative Example 2
 The reaction is carried out as described in Example 1, except that the
 duration of polymerization is 8 hours and that the amount of ascorbic acid
 introduced is 29 g.
 Example 3
 The reaction is carried out as described in Example 1, except that an
 aqueous potassium metabisulphite solution is used instead of ascorbic
 acid.
 Example 4
 The reaction is carried out as described in Example 2, except that 15.6 kg,
 on a dry basis of the seeding polymer (P2) latex are introduced. The
 duration of polymerization is 11 hours and the amount of ascorbic acid
 introduced is 35 g.
 Example 5
 The reaction is carried out as described in Example 2, except that 22 kg,
 on a dry basis, of the seeding polymer (P2) latex are introduced. The
 duration of polymerization is 10 hours and the amount of ascorbic acid
 introduced is 32 g.
 Example 6
 The reaction is carried out as described in Example 2, except that 19.5 kg,
 on a dry basis, of the seeding polymer (P2) latex are introduced, followed
 by 12 g of ammonium persulphate. The duration of polymerization is 7 hours
 and the amount of ascorbic acid introduced is 26 g.
 Example 7
 The reaction is carried out as described in Example 6, except that 21.7 kg,
 on a dry basis, of the seeding polymer (P2) latex are introduced.
 Example 8
 The reaction is carried out as described in Example 7, except that 18 g of
 ammonium persulpipte are introduced and that the duration of
 polymerization is 6 hours.
 Example 9
 The reaction is carried out as described in Example 6, except that, instead
 of an aqueous ascorbic acid solution, an aqueous potassium metabisulphite
 solution is used.
 Example 10
 The reaction is carried out as described in Example 9, except that 13.7 kg,
 on a dry basis, of the seeding polymer (P2) latex are introduced.
 The characteristics of the latex obtained from Examples 2 to 10 are
 reported in Table 1.
 Example 11
 Preparation of the latex (L1)
 The following are successively introduced, by suction, into a 28 litre
 reactor equipped with a stirrer and placed under vacuum beforehand:
 950 g of demineralized water
 1.4 g of potassium dihydrogenphosphate dissolved in 20 ml of water
 52.3 mg of CuSO.sub.4.multidot.5H.sub.2 O dissolved in 20 ml of water and
 245 g of the seeding polymer P1.
 The reactor at room temperature, with stirring and containing the aqueous
 mixture, is again placed under vacuum. 7000 g of vinyl chloride are then
 introduced and the mixture is then heated to the targeted temperature of
 58.degree. C. As soon as the temperature of the reaction mixture reaches
 53.degree. C., one litre of an aqueous solution containing 0.7 g of
 ascorbic acid is introduced continuously and then, after one hour, one
 litre of an aqueous solution containing 56 g of [lacuna] dodecylbenzene
 sulphonate and 175 mg of sodium hydroxide is introduced continuously. When
 the pressure of the mixture reaches 4 bars, i.e. after polymerizing for 8
 hours, introduction of aqueous solution is halted. The reactor is then
 placed under atmospheric pressure and then subjected to rapid cooling.
 The concentration of the polymer in the aqueous mixture is 41% and the mean
 diameter of the particles is 1.21 .mu.m. The degree of conversion of the
 vinyl chloride is 97%.
 Preparation of the Mixture
 A portion of the latex (L1) thus prepared is withdrawn and is mixed with a
 portion of the latex (L2) in proportions such that the ratio by mass of
 the polymer of the latex (L2) to that of the latex (L1) is equal to 0.43.
 Comparative Example 12
 A portion of the latex (L1) is mixed with a portion of the latex (L2), so
 as to obtain a ratio by mass of the polymer of the latex (L2) to that of
 the latex (L1) equal to 0.25.
 Comparative Example 13
 The reaction is carriedzout as described in Example 12, except that the
 ratio by mass of the polymer of the latex (L2) to that of the latex (L1)
 is equal to 1.
 TABLE 1
 Concentration
 of the polymer Mean diameter Mean diameter % by weight
 Exam- in the latex of the fine of the large of the fine
 ple (%) particles (.mu.m) particles (.mu.m) particles
 2 49 0.21 1.1 16
 3 50 0.25 1.06 27
 4 43 0.18 1.13 18.5
 5 49 0.18 1.12 22
 6 50 0.23 1.05 31
 7 50 0.23 1.09 33.5
 8 49 0.23 1.04 38.0
 9 46 0.22 1.01 35.0
 10 48 0.24 1.07 22
 Preparation of the Plastisol
 100 parts of the powder, obtained after atomizing the latex prepared
 according to the preceding examples, are then mixed with 60 parts of
 dioctyl phthalate, 2.5 parts of an expansion agent (azodicarbonamide) and
 2 parts of an activator.
 The viscosity of the plastisol thus prepared is measured at 25.degree. C.
 after half an hour and 24 hours using a rheometer of the Brookfield type.
 Preparation of the foam
 A portion of the plastisol prepared is coated onto a support and then
 placed in an oven for 150 minutes at 195.degree. C.
 The cellular quality of the foam thus obtained is evaluated on a scale from
 -4 to +4.
 The value -4 corresponds to a foam having open, very large and
 heterogeneous cells, whereas the value +4 corresponds to a foam having
 fine, closed and very homogeneous cells.
 The characteristics of the plastisol and of the foam are reported in Table
 2.
 Moreover, the index of whiteness, measured according to ASTM Standard E
 313/73 D25/2W, of the foams obtained from the latices according to
 Examples 3 and 9 are 45.8 and 46.4 respectively, whereas that of the foam
 prepared from the latex of Example 1 is only 39.
 TABLE 2
 Viscosity 1/2 h Viscosity 24 h Cellular
 Example (poises) (poises) quality
 1 35 40 +2
 7 37 47 +3
 9 37 40 +3
 11 46 95 +3
 12 25 70 +1
 13 52 150 +3
 The preceding examples can be repeated with similar success by substituting
 the generically or specifically described reactants and/or operating
 conditions of this invention for those used in the preceding examples.
 The entire disclosure of all applications, patents and publications, cited
 above and below, and of corresponding French application no. 96/10492, are
 hereby incorporated by refrencee.
 From the foregoing description, one skilled in the art can easily ascertain
 the essential characteristics of this invention, and without departing
 from the spirit and scope thereof, can make various changes and
 modifications of the invention to adapt it to various usages and
 conditions.