Method of production of polyvinyl chloride resin for paste processing

A method of production of polyvinyl chloride resin for paste processing comprises recovering in 98% or more the polyvinyl chloride resin from an aqueous dispersion of the polyvinyl chloride resin for paste processing as aggregates by adding an organic fluid which is at most barely soluble in water and does not dissolve or swell the polyvinyl chloride resin to the aqueous dispersion in the presence of an aggregating agent, followed by separating the aggregated polyvinyl chloride resin particles from the aqueous phase of the aqueous dispersion. By the addition of the aggregating agent, dispersion of the resin particles into a medium is improved, fluidity of a sol thereof and the physical properties of molded articles formed therefrom are improved and blocking during the drying process is prevented.

BACKGROUND OF THE INVENTION 
1. Field of the invention 
The present invention relates to a novel method of production of polyvinyl 
chloride resin for paste processing. 
2. Description of the prior art 
Paste processing of a polyvinyl chloride resin comprises the preparation of 
a liquid plastisol by mixing a polyvinyl chloride plastisol prepared 
specifically for the paste processing with compounding ingredients, such 
as plasticizers, stabilizers and, when necessary, pigments, fillers and 
the like, curing of the liquid plastisol by a suitable method, such as 
molding, coating, dipping and the like, and melting by heating followed by 
solidification of the plastisol to obtain a cured product. 
The flow property of the plastisol naturally affects the workability of the 
paste processing to a great extent and much effort has actually been paid 
for improvement of the flow property. 
Along with the flow property of the plastisol, the degree of dispersion of 
powder compounding components into the liquid compounding components 
affects the properties, particularly appearance and strength, of the 
molded product to a great extent. 
A plastisol contains aggregated resin particles formed by the aggregation 
of a number of small particles of the resin. When the plastisol contains 
rough and large aggregates of the resin particles without being dispersed 
into small particles, the flow property of the plastisol is adversely 
affected and furthermore problems, such as clogging of the plastisol 
during transportation, streaking during coating, rough surfaces on the 
molded product, decrease in gloss of the cured product, decrease of 
strength in the cured product and like other problems, arise. 
To overcome the problems of the paste processing described above, it is 
proposed that the material resin is supplied as a very fine powder which 
completely passes a sieve of 325 mesh of Tyler Standard Sieves. The fine 
powder is prepared by polymerizing vinyl chloride or a monomer mixture 
containing vinyl chloride as the main component in the presence of a 
radical generating polymerization initiator and an emulsifier by the 
method of emulsion polymerization or by the method of microsuspension 
polymerization. An aqueous suspension of spherical resin particles having 
a diameter of 0.05 to 5 .mu.m is obtained by the polymerization, which is 
then dried by spraying. 
However, conventional resins prepared by the above method have problems 
caused by the fine powdery form of the resin, such as deteriorated working 
conditions because of scattering of the powder during charging into a bag, 
discharging from the bag for production of the plastisol and mixing in the 
production of the plastisol and difficulties in automatic weighing and 
automatic transportation because of the inferior flow property. 
For overcoming the problems described above, a method of production of 
vinyl chloride resin for paste processing in which the polyvinyl chloride 
resin is recovered from a dispersion by separating it as aggregates from 
the aqueous phase with addition of an organic fluid which is at least 
barely soluble in water and does not dissolve or swell the polyvinyl 
chloride resin and then dried with or without granulation in advance is 
proposed in Japanese Patent Publication Heisei 1-42282. 
Though the problems described above are improved, other problems, such as 
formation of blocking during the drying process, inhomogeneous drying and 
formation of particulate protrusions at the surface of the cured product 
by the presence of larger particles, are caused by the formation of too 
strong aggregates of the wet resin. The yield of recovery of the resin 
powder is about 96% at most and the 4% rest of the resin which is lost 
material creates a serious problem for a large production. It is 
absolutely necessary that the resin left in the aqueous phase is 
additionally effectively recovered. 
SUMMARY OF THE INVENTION 
The present invention accordingly has an object to provide a method of 
production of the polyvinyl chloride resin for paste processing having 
excellent dispersing property with easy decomposition into small particles 
with a high yield of recovery without causing blocking during the drying 
process. 
Extensive investigations undertaken by the present inventors with the 
objects described above lead to a discovery that, when the polyvinyl 
chloride resin is recovered by separating it as aggregates from the 
aqueous phase with addition of an organic fluid which is barely soluble in 
water and does not dissolve or swell the polyvinyl chloride resin in the 
presence of an aggregating agent, the yield of recovery of the resin is 
increased to 98% or more because of the enhanced aggregation by the 
organic fluid and an additional recovery process of the resin is not 
necessary. At the same time, the aggregated particles are unexpectedly 
more easily decomposed and a good dispersion is formed more easily from 
the wet resin aggregates obtained after the recovery in the presence of 
the aggregating agent. 
Thus, the method of production of polyvinyl chloride resin for paste 
processing comprises recovering the polyvinyl chloride resin from an 
aqueous dispersion of the polyvinyl chloride resin for paste processing as 
aggregates by adding an organic fluid, which is at most barely soluble in 
water and does not dissolve or swell the polyvinyl chloride resin, to the 
aqueous dispersion in the presence of an aggregating agent, followed by 
separating the polyvinyl chloride resin from the aqueous phase of the 
aqueous dispersion. 
Other and further objects, features and advantages of the invention will 
appear more fully from the following description.

DETAILED DESCRIPTION OF THE INVENTION 
The method of the invention comprises essentially the following processes: 
process 1 in which an aggregating agent is added to and mixed with an 
aqueous dispersion of the polyvinyl chloride resin; process 2 in which an 
organic fluid which is at most barely soluble in water is added to and 
mixed with the aqueous dispersion of the resin to form aggregates of the 
resin by the organic fluid acting as a binder; process 3 in which the 
aqueous phase is removed from the aqueous dispersion of the aggregates of 
the resin; and process 4 in which the aggregates of the resin, separated 
from the aqueous phase are dried. 
The aqueous dispersion of polyvinyl chloride resin for paste processing 
utilized in the invention is an aqueous dispersion of a homopolymer of 
vinyl chloride or a copolymer of vinyl chloride comprising vinyl chloride 
as the main component thereof, generally in an amount of 70 weight % or 
more, which is prepared by conventional emulsion polymerization or micro 
suspension polymerization. Examples of the vinyl chloride copolymers are 
copolymers with olefinic monomers, such as vinyl acetate, vinylidene 
chloride, ethylene, propylene, butene, acrylonitrile, esters of acrylic 
acid, esters of methacrylic acid, maleic acid and the like. Aqueous 
dispersions of polyvinyl chloride which can be utilized in conventional 
paste processing are utilized without particular restriction. Polyvinyl 
chloride resins utilized as filler may be present in the resin of the 
invention when necessary. 
Any aqueous dispersion comprising 10 to 70 weight % of the polyvinyl 
chloride resin can be utilized in the invention. The aqueous dispersion 
prepared by the polymerization can be advantageously utilized without 
additional treatment. However, when necessary, a part of water in the 
dispersion may be removed or a suitable amount of water may be added to 
the dispersion. When the content of the polyvinyl chloride is less than 10 
weight %, too much water needs to be removed in comparison with the amount 
of the product and the process is not economically advantageous and, when 
the content of the polyvinyl chloride is more than 70 weight %, viscosity 
of the mixture of the aqueous dispersion and the organic fluid is 
increased dramatically, which causes difficulty on the operation of the 
processes. 
The aggregating agent utilized in the method of the invention is an agent 
having the property of forming aggregates from dispersed particles, such 
as inorganic low molecular weight aggregating agents, inorganic 
macromolecular aggregating agents, organic macromolecular nonionic 
aggregating agents, organic macromolecular anionic aggregating agents and 
organic macromolecular cationic aggregating agents. 
Examples of the inorganic low molecular weight aggregating agent are 
aluminum sulfate, aluminum chloride, aluminum sulfate containing iron, 
ammonium alum, potassium alum, ferrous sulfate, ferric sulfate, ferric 
chloride, cuprous chloride, zinc chloride, zinc sulfate, magnesium 
carbonate, magnesium oxide, magnesium sulfate, sodium aluminate, calcium 
chloride, sodium silicate and the like. 
Examples of the inorganic macromolecular aggregating agent are polyaluminum 
chloride, polyaluminum sulfate, polyferric chloride, polyferric sulfate 
and the like. 
Examples of the organic macromolecular nonionic aggregating agent are 
polyacrylamide, polyethylene oxide, polyvinyl alcohol, starch and the 
like. 
Examples of the organic macromolecular anionic aggregating agent are 
polysodium acrylate, polysodium vinylsulfonate, sodium of alginate, 
partial hydrolyzates of polyacrylamide, copolymers of acrylamide and 
acrylic acid, partially sulfomethylated products of polyacrylamide, 
carboxymethyl cellulose and the like. 
Examples of the organic macromolecular cationic aggregating agent are 
polyethyleneimine, condensation products of dicyandiamide and 
formaldehyde, polymethacrylic esters, polyacrylic esters, polyamines and 
the like. 
The concentration of the aggregating agent in the aqueous dispersion of the 
resin is suitably selected according to the aggregating activity of the 
aggregating agent. It is generally in the range from 10 to 1000 ppm and 
preferably in the range from 60 to 800 ppm based on the total amount of 
the aqueous dispersion. It is preferable for exhibiting the desirable 
physical properties of the resin that the concentration of the aggregating 
agent is kept at the low end of the range where the effect of the agent is 
exhibited. 
The organic fluid added to the aqueous dispersion of polyvinyl chloride 
resin is at most barely soluble in water and does not dissolve or swell 
the resin during the separation and recovery process of the resin. The 
organic fluid generally has a melting point of 20.degree. or lower and a 
boiling point at the atmospheric pressure which is not less than the 
temperature of the separation and recovery process and preferably 
200.degree. C. or higher. When an organic fluid having a boiling point 
which is lower than the temperature of the separation and recovery process 
is utilized, the organic fluid evaporates during the process and an 
additional apparatus is required for recovery of the organic fluid, thus 
rendering the process economically disadvantageous. The organic fluid may 
be utilized singly or as a mixture of two or more kinds. When two or more 
kinds of the organic fluid are utilized as a mixture, the mixture 
preferably has the property described above and the component fluids are 
not necessarily required to have the property described above. 
The organic fluid utilized in the invention is required to be at most 
barely soluble in water by the following reasons. Firstly, when the 
organic fluid is mixed with the aqueous dispersion and then separated from 
the aqueous phase, the amount of the organic fluid separated with the 
aqueous part is kept low to prevent loss of the organic fluid and to 
reduce the cost of treatment of the waste water. Secondly, to form 
aggregates of the resin particles dispersed in water by the action of 
layer of the organic fluid formed between the particles, it is necessary 
that the organic fluid is present on the surface of the particle of the 
resin to prevent water from being in direct contact with the particles. 
When the organic fluid utilized in the invention dissolves or swells the 
resin at the temperature of the separation and recovery process, the resin 
particles are deformed or modified and the process is not advantageous. 
Because a major part of the organic fluid utilized in the invention 
remains in the resin of the product article, organic fluids having adverse 
effects on workability and operability during the paste processing and on 
the quality of the product article must be avoided. From the reasons 
described above, it is natural and advantageous that liquid compounding 
ingredients generally utilized for the paste processing are adopted. 
Examples of the organic fluid of the invention are plasticizers, process 
oils, lubricants and the like as shown in the following: 
(1) Alkyl phthalate plasticizers, such as dioctyl phthalate, dinonyl 
phthalate, butyl lauryl phthalate, methyl oleyl phthalate and the like; 
(2) Aromatic carboxylic acid ester plasticizers, such as trioctyl 
trimellitate, diethyleneglycol dibenzoate and the like; 
(3) Aliphatic dibasic acid ester plasticizers, such as dioctyl adipate, 
dibutyl sebacate, dioctyl tetrahydrophthalate and the like; 
(4) Phosphoric acid ester plasticizers, such as trioctyl phosphate, 
trichloroethyl phosphate and the like; 
(5) Aliphatic glycol ester plasticizers, such as diethyleneglycol 
dicaprylate, 1,4-butyleneglycol di-2-ethylhexanoate and the like; 
(6) Polyester plasticizers; 
(7) Secondary plasticizers, such as aliphatic esters like butyl oleate, 
methyl acetylricinolate, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate and 
the like, epoxy plasticizers like epoxidized soy bean oil, octyl 
epoxystearate and the like, chlorinated paraffin plasticizers like 
chlorinated aliphatic fatty acid methyl esters, chlorinated paraffin and 
the like, aliphatic dibasic acid esters like dioctyl succinate and the 
like, dioctyl succinate and the like other plasticizers; 
(8) Diluents, such as petroleum diluents like mineral spirit, mineral 
terpene and the like, long chain alkylbenzene diluents like dodecylbenzene 
and the like and the like other diluents; and 
(9) Liquid lubricants, such as higher alcohols, liquid paraffin, alkyl 
esters of higher fatty acids and the like. 
The amount of the organic fluid added to the aqueous dispersion can be 
selected suitably according to the concentration of the resin in the 
aqueous dispersion and to the required properties of the dried resin as 
the product within the range from 0.5 to less than 15 weight parts per 100 
weight parts of the resin in the aqueous dispersion. When the amount of 
the organic fluid is 15 weight parts or more, the safety of the operation 
during the mixing with the resin is not maintained well and blocking 
during storage tends to take place. When the concentration of the resin in 
the aqueous dispersion is more than 40%, it is preferred that the amount 
of the organic fluid added to the aqueous dispersion is kept to 10 weight 
parts or less so that the continuous process is not disrupted by the 
formation of excessively large and coarse resin aggregates in the mixture 
solution. When the concentration of the resin in the aqueous dispersion is 
approximately in the range from 10 to 20%, it is effective that the 
organic fluid is added in an amount of 10 weight parts or more so that the 
efficiency of the formation of the aggregates is enhanced. 
Mixing of the organic fluid and the aqueous dispersion of the resin in the 
presence of the aggregating agent according to the method of the invention 
is conducted at such a temperature that the organic fluid utilized does 
not dissolve or swell the resin and within the range from 20.degree. to 
70.degree. C. The temperature is preferably 50.degree. C. or lower because 
a higher temperature increases the rate of swelling of the resin by the 
organic fluid. When the temperature is higher than 70.degree. C., 
absorption of the organic fluid into the resin is further enhanced and, 
furthermore, the resin is softened to form a block. It is thus highly 
probable that the product made at a temperature higher than 70.degree. C. 
is not suitable for paste processing. 
In the method of the invention, the order of the addition of the 
aggregating agent and the organic fluid to the aqueous dispersion of the 
resin is not particularly limited. When the mixture is stirred 
sufficiently, the effect of the order of the addition is absent. As the 
method of mixing after the aggregating agent and the organic fluid are 
added to the aqueous dispersion of the resin, conventional methods can be 
adopted. However, because the degree of the mixing greatly affects the 
efficiency of the aggregation of the resin by the aggregating agent and 
the organic fluid, it is preferred that the mixing power of the mixing 
apparatus per unit volume is 1 KW/M.sup.3 (1 kilowatt per 1 cubic meter) 
or more and the product of the mixing power and the mixing time is 4 
KW.Hr/M.sup.3 or more. As the apparatus of mixing, a high speed rotatory 
continuous mixer and a multiblade continuous mixing vessel are preferably 
utilized because of homogeneity and continuity of the mixing. However, 
conventional stirred vessel mixers and static mixers may be utilized as 
well. 
Separation of the aqueous phase from the resin aggregates formed by the 
effect of the organic fluid can be conducted by utilizing conventional 
methods suitably selected according to the condition of the resin mixture 
formed. The temperature of the separation is preferably in the range from 
20.degree. to 70.degree. C. to prevent softening and blocking of the 
resin. When the separation is conducted at a low resin concentration with 
a relatively large amount of the organic fluid (in the range from 5 to 
less than 15 weight % of the resin) for a long mixing time, the aggregates 
can be obtained as spherical particles having relatively large diameters 
and high strengths and the aqueous part can be separated by screening and 
the like methods. When the separation is conducted at a higher 
concentration of the resin with a smaller amount of the added organic 
fluid, the aggregates obtained have smaller diameters and a significant 
portion of the resin particles are not aggregated. In the latter 
condition, methods like centrifugal separation can be utilized. 
The resin particles separated at the separation process are sent to the 
drying process and the organic fluid and the remaining water are removed. 
In the drying process, it is necessary that the condition of the operation 
is selected suitably so that strength of the aggregation and blocking of 
the resin do not have an adverse effect on the dispersion during the paste 
processing. The temperature of the resin treated in the drying process is 
70.degree. C. or lower and preferably 50.degree. C. or lower. As the 
drying apparatus, a vacuum dryer is preferred to keep the resin to be 
dried at a low temperature. When the particle size is distributed rather 
uniformly, a fluidized bed drier is preferred because of the lower 
temperature and the increased efficiency of the operation. However, 
various kinds of other conventional drying apparatuses can be utilized as 
well. Resins having random shapes or broad distribution of the particle 
size can be obtained as the product by suitably selecting the apparatus of 
the drying. The shape of the resin particles can also be made uniform by 
incorporation of a pelletizing apparatus like an extrusion pelletizer into 
the drying process. In this case again, care must be taken so that the 
dispersion during the paste processing is not adversely affected by 
melting of the resin or by absorption of the organic fluid under heat and 
pressure during the pelletizing process. According to the method of 
production of the invention, the resin aggregates are easily decomposed by 
the effect of addition of the aggregating agent and the dispersion 
property as the particles for the past processing is improved. 
When the method of the invention is conducted as an industrial process, the 
presence of the aggregating agent enhances the yield of recovery of the 
resin by the organic fluid in process 2 because of the proper effect of 
the aggregating agent. 
It is important for increasing the yield of recovery of the resin that the 
amount of water remaining in the resin in the process 3 is kept low. The 
kind of the organic fluid must be selected suitably for this purpose in 
process 2. It is also important for increasing the yield of recovery that 
various factors of mixing affecting the aggregation of the resin are 
optimized by conventionally available methods. Suitable selection of the 
separation apparatus in the process 3 is also desirable for the same 
purpose. 
In the method of the invention, the recovery yield of the resin can be 98% 
or more, particularly 99% or more, without recovering the residual resin 
in the aqueous phase in process 3, by selecting the conditions of the 
recovery suitably as described above unlike conventional methods. 
The addition of the aggregating agent exhibits an additional effect of 
preventing blocking of the dried particles in process 4. 
In the method of the invention, only a small amount of the resin is left 
remaining in the aqueous phase and recovery of the resin therefrom is not 
necessary. However, for reduction of cost accompanied with the treatment 
of waste water, a process for complete recovery of the residual resin and 
the organic fluid from the aqueous part separated in process 3 may be 
added to the process of the invention. The residual resin thus recovered 
may be disposed as an industrial waste or recycled by adding it to the 
resin in the method of the invention when the purity of the recovered 
residual resin is good enough to do so. 
The residual resin can be recovered by a physical method of recovery, such 
as a centrifugal method, a floatation method like aeration, a coagulation 
method by addition of a coagulating agent and a method of ultrafiltration. 
As the method of recovery of the residual resin from the aqueous part, the 
coagulation method can be adopted in the same way as process 1. The 
organic fluid emulsion remaining in the aqueous part is coagulated 
together with the resin and the content of substances other than the resin 
in the thus obtained coagulated product is increased. When the cake or the 
mud-like material recovered from the aqueous phase is utilized as a part 
of the resin product, it is preferably recycled to process 1 or process 2. 
In the method of recovery of the residual resin in the aqueous part by 
coagulation, the aggregating agent described above in the method of the 
production of the invention can be utilized. 
When the recovery of the residual resin in the aqueous phase is 
additionally adopted in the process of the invention, the method of 
ultrafiltration using a semipermeable membrane can be favorably utilized. 
In the ultrafiltration, the rate of filtration is varied to a great degree 
depending on the concentration of the dispersed material in the dispersion 
to be treated. The concentration of the dispersed material in the aqueous 
part to be treated in the invention is 1% at most, which is within the 
general range of the concentration effectively treated by the 
ultrafiltration. Emulsifiers and other low molecular weight water soluble 
components are removed from the resin to the aqueous filtrate and the 
resin recovered from the aqueous part does not contain undesirable 
substances. Mixing of the thus recovered resin from the aqueous phase to 
the main resin of the process does not adversely affect the water 
resistance and the transparency of the molded product. Thus, the method is 
advantageous and can be favorably adopted. The resin obtained by the 
method can be directly added to the drying process of the invention. 
To summarize the advantages obtained by the invention: the yield of the 
aggregated resin particles can be increased to 98 % or more by the 
addition of the aggregating agent; the resin particles obtained are easily 
decomposed; the property of dispersion into a medium is improved; the 
fluidity of the sol and physical properties of the molded articles are 
improved; and blocking during the drying process is prevented. 
The invention will be understood more readily with reference to the 
following examples; however, these examples are intended to illustrate the 
invention and are not to be construed to limit the scope of the invention. 
Methods of testing in Examples and Comparative Examples are described in 
the following: 
[Properties of the resin as powder] 
Rest angle shows degree of fluidity of a powder and a smaller value means 
larger fluidity. 
Bulk density shows apparent density of powder and a larger value means 
better handling property. 
[Dispersion property of sol] 
The property was evaluated by measuring the NF value (North Finess value) 
of resin particles in a sol prepared by mixing 50 g of a resin and 30 g of 
di-2-ethylhexylphthalate in a grinder. 
[Method of measurement of the NF value] 
A sample of sol is placed on the base line of a steel gauge which is at the 
maximum depth of a ditch of the gauge having 0.5 inch width and the ditch 
of linearly varying depth. The sample is scraped to the direction of 
shallower depth by a scraper and the position where many points of rough 
aggregated particles are observed is recorded. The number 0 means the 
roughest and the number 8 means the finest. The numbers 8, 4 and 0 
correspond to diameters of the particle of 0, 51 and 102 .mu.m, 
respectively. A larger NF value means that the particles are finer and 
dispersed better. 
[Method of testing of easiness of decomposition of a wet cake] 
Into a Tyler standard sieve of 12 mesh, 10 grams of a wet cake were placed 
and treated with a tap shaker for 1 minute. The degree of decomposition of 
the wet cake was evaluated by the following criterion. 
.smallcircle.: all passed the sieve. 
.increment.: less than 5 g of the cake remaining in the sieve. 
x: 5 g or more of the cake remaining in the sieve. 
[Method of measurement of amount of rough particles] 
Into a Tyler standard sieve of six mesh, 25 g of a resin powder after 
drying were placed and treated with a tap shaker for 10 minutes. Weight of 
the resin powder remaining on the sieve was measured and recorded as the 
ratio to the original weight of 25 g. 
[Yield of recovery] 
Yield of recovery=weight of the resin obtained after drying/weight of the 
resin in the aqueous dispersion before the aggregation.times.100 
The yield and the amount of recovery do not include the resin recovered 
from the separated aqueous part. 
EXAMPLE 1 
An aqueous dispersion of polyvinyl chloride for paste processing was passed 
through a screen attached with a sieve of 250 .mu.m mesh and water was 
added to the screened aqueous dispersion to adjust the concentration of 
the solid component to 35 weight %. Into a mixing vessel of 20 cm diameter 
and 12 liter inner volume, 11000 g (solid PVC=11000.times.0.35=3850 g) of 
the aqueous dispersion and 12 g of a 10% aqueous solution of polyaluminum 
chloride were charged. As soon as stirring was started at 1100 rpm, 
diisononyl phthalate was injected into the bottom of the mixing vessel for 
60 minutes at a rate of 3.2 g per minute (3.2.times.60=192 g). The mixture 
was further stirred for 60 minutes at 1100 rpm to obtain an aqueous 
dispersion of resin particles. The dispersion thus obtained was filtered 
in a vacuum using a filter cloth having an air passage of 80 
cc/sec.cm.sup.2 to separate the resin particles and 5750 g of wet 
particles were obtained. The wet particles were dried in a small fluidized 
bed dryer in a stream of 40.degree. C. air to obtain 4020 g of polyvinyl 
chloride resin particles (A). 
EXAMPLE 2 
An aqueous dispersion of polyvinyl chloride for paste processing was passed 
through a screen attached with a sieve of 250 .mu.m mesh and the 
concentration of the solid component of the aqueous dispersion passed 
through the screen was adjusted to 35 weight %. Into a mixing vessel of 20 
cm diameter and 12 liter inner volume, 11000 g of the aqueous dispersion 
and 65 g of a 10 % aqueous solution of aluminum sulfate were charged. As 
soon as stirring was started at 1100 rpm, di-2-ethylhexyl phthalate was 
injected into the bottom of the mixing apparatus for 30 minutes at a rate 
of 7.7 g per minute. The mixture was further stirred for 60 minutes at 
1100 rpm to obtain an aqueous dispersion of resin particles. The 
dispersion thus obtained was filtered in a vacuum using a filter cloth 
having an air passage of 80 cc/sec.cm.sup.2 to separate the resin 
particles and 5150 g of wet particles were thus obtained. The wet 
particles were dried in a small fluidized bed dryer in a stream of 
40.degree. C. air to obtain 3500 g of polyvinyl chloride resin particles 
(B). 
EXAMPLE 3 
An aqueous dispersion of polyvinyl chloride for paste processing was passed 
through a screen attached with a sieve of 250 .mu.m mesh and the 
concentration of the solid component of the aqueous dispersion passed 
through the screen was adjusted to 40 weight %. Into a mixing vessel of 20 
cm diameter and 12 liter inner volume, 11000 g of the aqueous dispersion 
and 650 g of a 1% aqueous solution of polyacrylamide were charged. As soon 
as stirring was started at 1100 rpm, diisodecyl phthalate was injected 
into the bottom of the mixing vessel for 40 minutes at a rate of 11 g per 
minute. The mixture was further stirred for 50 minutes at 1100 rpm to 
obtain an aqueous dispersion of resin particles. The dispersion thus 
obtained was filtered in a vacuum using a filter cloth having an air 
passage of 80 cc/sec.cm.sup.2 to separate the resin particles and 6870 g 
of wet particles were thus obtained. The wet particles were dried in a 
small fluidized bed dryer in the air stream of 40.degree. C. to obtain 
4810 g of polyvinyl chloride resin particles (C). 
Comparative Example 1 
Employing the same operations and the same materials as those in Example 1 
except that polyaluminum chloride was not used, 5470 g of wet resin 
particles were obtained. The wet resin particles were dried in a small 
fluidized bed dryer in a stream of 40.degree. C. air to obtain 3830 g of 
polyvinyl chloride resin particles (D). 
Comparative Example 2 
Employing the same operations and the same materials as those in Example 2 
except that aluminum sulfate was not used, 4720 g of wet resin particles 
were obtained. The wet resin particles were dried in a small fluidized bed 
dryer in a stream of 40.degree. C. air to obtain 3400 g of polyvinyl 
chloride resin particles (E). 
Comparative Example 3 
Employing the same operations and the same materials as those in Example 3 
except that polyacrylamide was not used, 6400 g of wet resin particles 
were obtained. The wet resin particles were dried in a small fluidized bed 
dryer in a stream of 40.degree. C. air to obtain 4670 g of polyvinyl 
chloride resin particles (F). 
The results of the above Examples and Comparative Examples are listed in 
Table 1. 
TABLE 1 
______________________________________ 
Example 1 2 3 -- -- -- 
Comparative 
Example -- -- -- 1 2 3 
______________________________________ 
resin particles 
A B C D E F 
amount of added 
ca 300 ca 2000 ca 1500 
0 0 0 
aggregating agent 
(ppm) 
yield of recovery 
99.4 99.0 99.2 95.0 96.1 96.4 
(%) 
ease of .largecircle. 
.largecircle. 
.largecircle. 
X X X 
decomposition of 
wet cake after 
separation of 
aqueous phase 
properties of resin 
as powder 
rest angle 37 38 36 38 39 37 
bulk density 
0.52 0.52 0.53 0.51 0.51 0.52 
content of coarse 
1.2 1.2 1.5 5.5 5.8 6.5 
particles (%) 
dispersion property 
4.0 4.0 4.5 4.0 4.0 4.5 
of sol (NF value) 
______________________________________ 
While the invention has been particularly shown and described with 
reference to preferred embodiments thereof, it will be understood by those 
skilled in the art that the foregoing and other changes in form and 
details can be made therein without departing from the spirit and scope of 
the invention.