Process for the production for multimodal latices of vinyl chloride polymers

The multimodal latices are produced by nonmicellar aqueous emulsion polymerization of vinyl chloride in the presence of a seed consisting of a multimodal latex originating from a preceding polymerization cycle. The mean size of the elementary particles of the multimodal latices produced is identical to that of the elementary particles of the seed. The latter preferably consists of three classes of elementary particles which have mean diameters of between 0.15-0.30 .mu.m, between 0.45-0.60 .mu.m and between 1.05-1.25 .mu.m respectively. The vinyl chloride polymers originating from the multimodal latices are-particularly suitable for the manufacture of low-viscosity plastisols.

The present invention relates to a process for the production of multimodal 
latices of vinyl chloride polymers. It relates more particularly to a 
process for the production of multimodal latices of vinyl chloride 
polymers by seeded aqueous emulsion polymerization of vinyl chloride, 
which are particularly suitable for the manufacture of low-viscosity 
plastisols. 
Vinyl chloride polymers intended for the manufacture of plastisols, also 
called pastes, usually take the form of a fine powder consisting of 
particles whose volume average diameter is between 5 and 20 .mu.m, which 
is obtained by milling coenospheres resulting from the spray-drying of 
vinyl chloride polymer latices whose elementary particles have mean 
diameters of between 0.1 and 2 microns (.mu.m). It is known that 
plastisols or pastes of higher quality and of low viscosity are obtained 
when use is made of vinyl chloride polymers originating from multimodal 
latices comprising a number of classes of elementary particles whose 
respective mean diameters fall within the abovementioned range. Known 
techniques for producing multimodal latices consist, for example, in 
mixing a number of monomodal seed latices in known proportions or in 
polymerising vinyl chloride with seeding by means of a number of monomodal 
seed latices, this latter technique being sometimes called "multiseeding". 
These processes have the disadvantage of requiring, in each polymerization 
cycle, the use of a number of monomodal seed latices which are prepared 
beforehand in stages which are separate from those of obtaining the 
multimodal latex intended for the manufacture of pastes. They consequently 
demand considerable capital investments and leave much to be desired where 
production efficiency is concerned. 
The present invention is aimed at providing an improved process for the 
production of multimodal latices of vinyl chloride polymers, which does 
not exhibit the abovementioned disadvantages and which makes it possible 
to obtain vinyl chloride polymer latices suitable for the manufacture of 
low-viscosity plastisols 
To this end, the invention provides a process for the production of 
multimodal latices of vinyl chloride polymers by seeded aqueous emulsion 
polymerization of vinyl chloride, characterised in that the nonmicellar 
aqueous emulsion polymerisation of vinyl chloride is initiated in the 
presence of a seed consisting of a multimodal latex originating from a 
preceding polymerization cycle. 
A surprising effect of the process according to the invention lies in the 
fact that seeding by means of the multimodal vinyl chloride polymer latex 
originating from a preceding polymerization cycle results in multimodal 
latices in which the classes of elementary particles have mean particle 
sizes identical to those of the seed. In other words, once the initial 
multimodal seed latex has been prepared and the seeded polymerization 
process has been initiated, it is no longer necessary to produce and to 
store seed latices, the seed consisting of a portion of the latex produced 
during a preceding polymerization cycle. The process according to the 
invention thus stems, in a way, from a self-regulating phenomenon 
permitting the tailor-made manufacture of multimodal latices containing a 
number of classes of elementary particles whose mean size is 
preestablished as a function of the mean size of the classes of elementary 
particles of the initiating multimodal seed latex. 
For the purposes of the present invention, vinyl chloride polymers are 
intended to mean vinyl chloride homopolymers and copolymers containing at 
least 80% and, preferably, 90% by weight of vinyl chloride. The process 
according to the invention applies, therefore, both to the 
homopolymerisation of vinyl chloride and to its copolymerisation with 
ethylenically unsaturated monomers such as, for example, vinyl acetate. 
Nevertheless, it applies preferably to the homopolymerisation of vinyl 
chloride. 
Nonmicellar aqueous emulsion polymerization is intended to mean the 
polymerisation in the presence of emulsifier in a quantity lower than the 
critical micelle concentration. 
The critical micelle concentration of an emulsifier is identical to the 
concentration corresponding to a change in the slope of the curves 
describing the variation of a physical property of a solution of 
emulsifier, such as, for example, the surface tension, as a function of 
its emulsifier concentration. The critical micelle concentration of many 
emulsifiers is dealt with in the work "Polymer Handbook" edited by J. 
Brandrup and E. H. Immergut, second edition, 1975, II-483 to II-497. 
The seeding ratio, that is to say the weight quantity of seed expressed as 
solids, used per 100 parts by weight of monomer(s) is not really critical 
and is, as a general rule, between 0.5 and 20% and, preferably, between 1 
and 10% by weight. 
Plastisols of excellent quality are obtained when vinyl chloride polymers 
originating from trimodal latices are employed to prepare them. 
According to a preferred embodiment of the present invention, trimodal 
latices of vinyl chloride polymers are produced. To do this, use is made 
as seed of a trimodal latex consisting of three classes of elementary 
particles and still more particularly a trimodal seed latex including the 
three classes of elementary particles which have mean diameters of between 
0.15-0.30 .mu.m, between 0.45-0.60 .mu.m and between 1.05-1.25 .mu.m 
respectively, originating from a preceding polymerization cycle. 
The method in which the initiating multimodal seed latex is obtained is not 
critical. The initiating seed latex can therefore be produced in any known 
and suitable manner, for example by mixing a number of monomodal latices 
or by seeded polymerization in the presence of a number of monomodal seed 
latices. 
The preferred initiating trimodal seed latex is preferably produced by 
mixing, in weight proportions of the order of 2 to 1, a monomodal latex 
whose elementary particles have a mean diameter of beween 0.45-0.60 .mu.m 
with a bimodal latex whose two classes of elementary particles have mean 
diameters of between 0.15-0.30 .mu.m and between 0.85-1.20 .mu.m 
respectively. 
The monomodal seed latex whose elementary particles have a mean diameter of 
between 0.45-0.60 .mu.m is itself obtained advantageously by nonmicellar 
seeded polymerisation of vinyl chloride on a monomodal seed latex whose 
elementary particles have a mean diameter of 0.15-0.30 .mu.m with a 
seeding ratio of 10 to 15%, so as to enlarge the seed particles without 
creating new particles. A part of the monomodal latex thus obtained can 
then be used as seed for producing, by nonmicellar seeded polymerization 
with a seeding ratio of 5 to 10%, a bimodal seed latex whose two classes 
of elementary particles have mean diameters of between 0.15-0.30 .mu.m 
(new particles) and between 0.85-1.20 .mu.m respectively (enlarged 
particles). 
Apart from the presence of a multimodal seed latex and the initiation of 
the seeded polymerisation in the presence of emulsifier in a quantity 
lower than its critical micelle concentration, the seeded aqueous emulsion 
polymerisation of vinyl chloride according to the process of the invention 
takes place in the usual conditions of aqueous emulsion polymerisation of 
vinyl chloride. Thus, the polymerization temperature generally lies 
between 40.degree. and 70.degree. C. and the polymerisation is carried out 
with the use of water-soluble initiators and emulsifying agents, more 
particularly of anionic emulsifiers, present in the usual quantity. By way 
of examples of usual initiators there may be mentioned water-soluble 
peroxides such as sodium, potassium or ammonium persulphates, hydrogen 
peroxide, perborates and t-butyl hydroperoxide, which are employed by 
themselves or in combination with a reducing agent. The initiators are 
usually used in a proportion of approximately 0.020 to 0.040% by weight 
relative to vinyl chloride monomer. By way of examples of usual anionic 
emulsifiers there may be mentioned the alkali-metal salts of fatty acids, 
of sulphonic acids, of sulphosuccinic acids or of sulphuric esters. The 
nature of the emulsifier has no influence on the mean size of the 
elementary particles. The overall quantity of emulsifier used commonly 
varies between 0.5 and 2.5% by weight relative to vinyl chloride monomer 
and, more particularly, between 0.5 and 1.5% by weight. As mentioned 
above, it is essential to initiate the seeded polymerization in the 
presence of emulsifier in a quantity lower than its critical micelle 
concentration. The remainder of the emulsifier is introduced gradually 
during polymerization with a view to ensuring an effective protection of 
the polymer particles at all times. The beginning of gradual introduction 
of the remaining emulsifier advantageously takes place at a time when the 
number of particles is fixed, in other words, generally when the degree of 
conversion is between 5 and 20%, preferably between 5 and 15%, and more 
particularly in the region of 10%. The introduction may be continued until 
the end of polymerization. Nevertheless, arrangements are preferably made 
for all the emulsifier to be used to be introduced before the degree of 
conversion exceeds 80%. 
After polymerization, the latex is sprayed mechanically, for example by 
means of a centrifugal disc or of compressed air jets, into a stream of 
hot air, so as to produce the evaporation of the water present in each 
droplet. The dry vinyl chloride polymer is in the form of a powder 
consisting of hollow spheres (coenospheres) whose mean diameter is between 
10 and 100 .mu.m and, preferably, between 15 and 25 mm. The coenospheres 
are then milled mechanically with a view to obtaining a fine powder 
consisting of particles whose volume-average diameter is between 5 and 20 
.mu.m and preferably between 8 and 13 .mu.m. 
After milling so as to reduce them to fine powders of appropriate size, the 
vinyl chloride polymers originating from the latices produced according to 
the process of the invention can be employed for the formulation of 
low-viscosity plastisols. The plastisols are formulated in a well-known 
manner, by mixing the milled powders with the usual ingredients such as 
plasticisers, heat stabilisers, filling substances, lubricants, pigments 
and the like. The vinyl chloride polymer plastisols usually contain from 
35 to 120 and, preferably, from 40 to 55 parts by weight of plasticiser 
per 100 parts by weight of vinyl chloride polymers. 
The present invention also relates to the use of the vinyl chloride 
polymers originating from the multimodal latices produced according to the 
process of the invention for the formulation of plastisols.

The example which follows is intended to illustrate the process according 
to the invention. 
All the tests are carried out in a stainless steel laboratory reactor of 
3.4 liter capacity, fitted with a jacket in which a heat-transfer fluid 
circulates, and a conventional stainless steel bladed stirrer. 
1. Manufacture of the Initiating Trimodal Seed Latex 
A. Monomodal seed latex (mean diameter of the elementary particles: 
0.15-0.30 .mu.m) 
1440 g of demineralised water and 0.0042 g of copper sulphate pentahydrate 
(that is, 42 ml of an aqueous solution at a concentration of 0.1 g/l) are 
introduced in succession into the reactor at room temperature. The reactor 
is closed and the stirrer s set to run at 250 rev/min. Vacuum (130 mm of 
mercury absolute) is then applied twice and, between the two operations, 
the reactor is purged with technical-grade nitrogen at a pressure of 600 
mm of mercury absolute. 1200 g of vinyl chloride are then introduced and 
the temperature of the reactor contents is gradually raised to 52.degree. 
C. At the time when it reaches 52.degree. C., taken to be the zero time of 
the polymerization (t.sub.0), 0.48 g of ammonium persulphate (that is 24 
ml of an aqueous solution at a concentration of 20 g/l) are introduced. 
After 15 minutes 1.16 g of ammonia (that is 33 ml of 2N aqueous ammonia) 
are introduced. Between t.sub.0 +1 hour and t.sub.0 +5H, 15, 12 g of 
ammonium myristate (that is 109 ml of an 11% solution) are introduced 
gradually. After a pressure drop of 0.5 bar the temperature is raised to 
80.degree. C. When this temperature is reached, 1.16 g of ammonia are 
introduced again. The stirring rate is reduced to 50 rev/min and after 
antifoaming agent has been introduced, the residual vinyl chloride is 
removed by degassing and stripping with boiling. 
2780 g of monomodal polyvinyl chloride latex are collected, with a solids 
content of 39.6% as elementary particles whose mean diameter (determined 
by the photosedimentometry method) is 0.25 .mu.m. 
B. Monomodal seed latex (mean diameter of the elementary particles: 
0.45-0.60 .mu.m) 
1700 g of demineralised water, 0.0035 g of copper sulphate pentahydrate 
(that is 35 ml of a solution at a concentation of 0.1 g/l) and 140 g of 
polyvinyl chloride in the form of the latex originating from stage 1.A. 
(that is 353 g of latex) are introduced in succession into the reactor. 
The procedure is identical to that described above. The nature and the 
quantity of the polymerisation ingredients used are repeated below: 
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ammonium persulphate: 0.40 g 
ammonia (initial): 1.07 g 
ammonium myristate: 7 g 
vinyl chloride: 1000 g 
ammonia (end of polymerization): 
1.07 g 
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3214 g of monomodal polyvinyl chloride latex are collected, with a solids 
content of 33% as elementary particles whose mean diameter is 0.55 .mu.m. 
Alternative version: This procedure consists in manufacturing, in the same 
single reactor, a first monomodal seed latex whose elementary particles 
have a mean diameter of 0.25 .mu.m and, without isolating the said latex, 
in enlarging it by subsequent polymerization of a new quantity of vinyl 
chloride. 
In a first stage, a reduced quantity of vinyl chloride, that is 150 g is 
polymerised under conditions identical to those described under point 1.A. 
The nature and the quantity of the polymerization ingredients used are 
repeated below: 
______________________________________ 
demineralised water: 1845 g 
ammonium persulphate: 0.615 g 
ammonia (initial): 1.144 g 
______________________________________ 
After a pressure drop of 4 bars 1080 g of vinyl chloride are introduced. 15 
minutes after the introduction of vinyl chloride, 9.84 g (that is 89.5 
cm.sup.3 of an 11% solution) of ammonium myristate are introduced 
gradually. After a pressure drop of 1 bar the temperature is raised to 
80.degree. C. and 1.144 g of ammonia are introduced. The stirring rate is 
reduced to 50 rev/min, 7.5 g of antifoaming agent are introduced and the 
unconverted vinyl chloride is removed by degassing and stripping with 
boiling. 
3170 g of monomodal latex are collected, with a solids content of 35.7% of 
elementary particles whose mean diameter is 0.55 .mu.m. 
C. Bimodal seed latex (mean diameter of the two classes of elementary 
particles: 0.15-0.30 .mu.m and 0.85-1.20 .mu.m) 
70 g of polyvinyl chloride are introduced into the reactor in the form of 
the latex produced according to either of the variants described under 
point 1.B., whose elementary particles have a mean diameter of 0.45-0.60 
.mu.m. The general conditions of the (seeded) polymerisation are those 
described under point 1.A. The nature and the quantity of the 
polymerization ingredients are detailed below. 
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demineralised water 1015 g 
copper sulphate pentahydrate 
0.004 g 
ammonium persulphate 0.46 g 
ammonia 1.242 g 
ammonium myristate 10 g 
vinyl chloride 1150 g 
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2507 g of bimodal latex are collected, with a solids content of 45%, 
containing two classes of elementary particles whose mean diameters are 
0.25 .mu.m and 0.95 .mu.m respectively. 
D. The initiating trimodal seed latex is obtained by mixing two parts by 
weight of monomodal latex produced under point 1.B. with 1 part by weight 
of bimodal latex produced under point 1.C. 
2. Manufacture of Trimodal Latex by Seeding Using the Initiating Trimodal 
Latex 
70 g of polyvinyl chloride are introduced into the reactor in the form of 
the seed latex produced under point 1.D. 
The general polymerization conditions, the nature and the quantity of the 
polymerisation ingredients and the quantity of latex collected and its 
concentration are identical to those of Example 1.C. 
The trimodal latex produced is made up of three classes of elementary 
particles whose mean diameters are between 0.15-0.30 .mu.m, 0.45-0.60 
.mu.m and 1.05-1,25 .mu.m respectively. 
3. Manufacture of Trimodal Latex by Seeding Using the Trimodal Latex 
Originating from a Preceding Polymerisation Cycle 
70 g of polyvinyl chloride are introduced into the reactor in the form of 
the latex obtained under point 2. 
The general polymerization conditions, the nature and the quantity of the 
polymerisation ingredients and the quantity of latex collected and its 
concentration are identical to those of Example 1.C. 
The trimodal latex produced is made up of three classes of elementary 
particles whose mean diameters are between 0.15-0.30 .mu.m, 0.45-0.60 
.mu.m and 1.05-1.25 .mu.m respectively. 
A 155-g portion of the trimodal latex produced (that is 70 g of polyvinyl 
chloride) is taken out before isolating the polymer with a view to using 
it as a seed latex in a following polymerization cycle. 
4. Drying and Milling of the Trimodal Latex 
The trimodal latex produced under point 3. is dried in a spray drier in 
which the temperature of the hot air is 175.degree.-200.degree. C. at the 
entry and 75.degree.-85.degree. C. at the exit. At the exit of the drier 
the dry polyvinyl chloride is recovered in the form of a powder consisting 
of coenospheres whose mean diameter is 45 .mu.m. 
The dried polyvinyl chloride is then milled in a pin mill so as to reduce 
the mean particle diamter to 12 .mu.m. 
5. Preparation and Evaluation of a Plastisol 
A plastisol in accordance with ISO standard 4612 
by mixing, in a planetary mixer, 100 g of milled polyvinyl chloride 
produced under point 4. with 40 g of dioctyl phthalate (temperature: 
23.degree. C.; stirring rate: 1 minute at 60 rev/min, 19 min at 120 
rev/min) (Plastisol E). 
By way of comparison, an identical plastisol is prepared, except that the 
polyvinyl chloride originates from the bimodal latex produced under point 
1.C., dried and milled under the conditions detailed under point 4. 
(Plastisol C). 
The initial viscosity of the two plastisols is evaluated in a rotary 
viscometer in accordance with ISO standard 3219. The results of the 
evaluation of the initial viscosity at two velocity gradients appear in 
the table below. 
TABLE 
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Plastisol Velocity gradient, s.sup.-1 
Viscosity, Pa s 
______________________________________ 
E (example) 1.4 17 
400 16 
C (comparative) 
1.4 35 
400 32 
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