JPH11228606A - Suspension polymerization for vinyl chloride-based resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for suspension polymerization for a vinyl chloride-based resin, in which resin scale adhesion doesn't occur on the inner wall of a polymerization reactor and the produced vinyl chloride-based resin has high porosity, sharp particle size distribution, high bulk density, almost free from skin layers on the surface of particles and is very excellent in molding processability. SOLUTION: When suspension polymerizing a vinyl chloride-based monomer in the presence of oil-soluble polymerization initiator in an aqueous medium, the method production comprises adding a dispersant, an emultifier, a higher fatty acid and a thickener to the reaction system followed by initiating the polymerization and then discharging vinyl chloride-based monomer in a quantity of 5-20 wt.% based on vinyl chloride-based monomer existing at that time from the polymerization system while the weight ratio of the vinyl chloride-based monomer to the aqueous medium ranges from 0.1 to 0.6, followed by continuing the polymerization.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for suspension polymerization of a vinyl chloride resin.

[0002]

2. Description of the Related Art Conventionally, vinyl chloride resins (hereinafter referred to as P
VC) is widely used in fields such as piping materials and building materials because of its excellent mechanical strength, weather resistance, chemical resistance and the like. However, the moldability is not always excellent, and further improvement is required.

[0003] Typical methods for evaluating the moldability of PVC include a method for measuring the absorbency of a plasticizer and a method for measuring torque and gel time using a plastmill. In the former, the plasticizer penetrates into the inside of PVC in a short time, and in the latter, the maximum torque is low and the gelation time is short.

[0004] What is considered as the biggest factor inhibiting the moldability is the presence of a skin layer on the surface of PVC particles. The skin layer is a skin layer present on the surface of the PVC particles, and is formed by firmly grafting partially saponified polyvinyl acetate, a cellulose derivative, or the like, which has been used as a dispersant in polymerization, to PVC. It is considered a layer.

[0005] Originally, the skin layer functions to protect the surface of the monomer oil droplets in the polymerization system and to stabilize the polymerization system by adjusting the splitting and coalescence of the oil droplets. However, at the stage of molding and processing PVC, it is necessary to grind the vinyl chloride resin particles to submicron units (primary particles or less), and the existence of a strong skin layer is rather a major obstacle. Conceivable.

Accordingly, in order to obtain PVC having excellent moldability, it is desirable that the skin layer on the surface of the PVC particles has little or no skin layer. In addition, in order to easily diffuse and absorb the liquid stabilizer, plasticizer, and the like taken into the PVC particles, there are many fine pores between the primary particles inside the PVC particles, and the porosity is excellent. Deemed important.

As a method for producing PVC having excellent moldability as described above, for example, Japanese Patent Publication No. 36-22445 discloses a method using a combination of a higher fatty acid ester of sorbitan and a higher fatty acid ester of polyoxyethylene sorbitan. Although a suspension polymerization method is disclosed, the resulting PVC has poor porosity, and there is a problem that a large amount of resin scale adheres to the inner wall of the polymerization vessel.

[0008] Numerous methods have been proposed to solve the above problems, for example, Japanese Patent Publication No. 53-1339.
No. 5 uses a dispersant in which a lipophilic sorbitan higher fatty acid and a hydrophilic polyoxyethylene sorbitan higher fatty acid ester are combined in the presence of a basic compound, and the polymerization conversion of PVC is 5 to 40% by weight. %, Or a method of adding a water-soluble cellulose derivative, or Japanese Patent Publication No. 5-86408, uses sorbitan higher fatty acid ester as a dispersant, and initiates polymerization under stirring with a Faudler blade. The polymerization conversion rate of PVC is 5
A method of adding a water-soluble dispersant when reaching に 40% by weight is disclosed.

However, in these polymerization methods, although a resin scale does not adhere to the inner wall of the polymerization vessel during polymerization, a highly porous PVC can be obtained, but the bulk specific gravity becomes low, and a dispersing agent is added later. In the polymerization step, the operation becomes complicated, and a large amount of the dispersant remains on the surface of the PVC, thereby deteriorating the physical properties of the obtained PVC.

Japanese Patent Application Laid-Open No. 5-295008 discloses that
There is disclosed a method in which a known suspension dispersant, a nonionic surfactant such as partially saponified polyvinyl acetate having a low saponification degree, and sorbitan monolaurate are added at a specific ratio to carry out polymerization. However, PVC obtained by this method is:
Although the skin layer portion on the particle surface is reduced, it is necessary to control the power required for stirring in the initial stage of polymerization, and the gelling properties, plasticizer absorbency and the like of the obtained PVC are still insufficient.

Further, Japanese Patent Application Laid-Open No. 8-59731 discloses that
A method of polymerizing a suspension / dispersant having a specific cloud point or a sorbitan-based higher fatty acid ester having a specific HLB value and a specific thickener, a higher fatty acid having 8 to 25 carbon atoms in combination with a cellulose derivative. It has been disclosed. In these methods, various additives can be added all at once, there is no complicated production, and there is a great improvement in reducing the number of PVC skin layers, but the moldability of PVC has not been improved.

Further, Japanese Patent Application Laid-Open No. H8-3206,
-109207 discloses partially saponified polyvinyl alcohol and high-viscosity hydroxypropylmethylcellulose,
Alternatively, a method using a crosslinked copolymer having a carboxyl group is disclosed. However, although the PVC obtained by this method is excellent in plasticizer absorption, it has a low bulk specific gravity and is not satisfactory.

As described above, a problem of the prior art is that a resin having no skin layer inevitably reduces the bulk specific gravity. Along with improving the bulk specific gravity, further improvements in productivity per volume of the polymerization vessel and measures for preventing scale adhesion have been demanded. One solution is disclosed in JP-A-4-325506.
And JP-A-8-100004 disclose an addition method during the polymerization of an aqueous medium.

In Japanese Patent Application Laid-Open No. 4-325506, an attempt is made to achieve a method for producing PVC which causes less generation of fish eyes when absorbing a plasticizer by using a specific dispersant and further adding an aqueous medium during polymerization. Although
The improvement of the bulk specific gravity and the plasticizer absorption were not improved.

In Japanese Patent Application Laid-Open No. Hei 8-100004, a specific heat exchanger is used to remove reaction heat, and an aqueous medium corresponding to the volume reduced by polymerization is added to improve productivity and scale adhesion. It is aimed at prevention, but no improvement in bulk specific gravity was observed.

Another solution is disclosed in JP-A-8-8150.
No. 9, the polymerization conversion is between 10 and 18% by weight,
It is disclosed that 2 to 15% by weight of the vinyl chloride-based monomer is discharged out of the system to improve initial coloring, thermal stability, and prevent scale adhesion. No effect of improving specific gravity was observed.

[0017]

SUMMARY OF THE INVENTION In view of the above, the method of the present invention for suspending and polymerizing PVC does not cause resin scale to adhere to the inner wall of the polymerization vessel, and the resulting PVC has a high porosity and sharpness. It is an object of the present invention to provide a method of suspension polymerization of PVC, which has an excellent particle size distribution and a high bulk specific gravity, has almost no skin layer on the particle surface, and has extremely good moldability.

[0018]

SUMMARY OF THE INVENTION The present invention relates to a method for preparing a partially saponified polyvinyl acetate in a reaction system when a vinyl chloride monomer is subjected to suspension polymerization in an aqueous medium in the presence of an oil-soluble polymerization initiator. (A) and at least one dispersant of the cellulose derivative (b), at least one emulsifier of the higher sorbitan fatty acid ester (c) having an HLB value of 3 to 10 and an anionic emulsifier (d), A higher fatty acid (e) having 8 to 25 carbon atoms and a thickener (f) having a Brookfield viscosity of 10 to 200 cP in a 0.1% by weight aqueous solution at normal temperature and normal pressure were added to initiate polymerization. Thereafter, the weight ratio of the vinyl chloride-based monomer / aqueous medium is between 0.1 and 0.6, and the weight ratio of the vinyl chloride-based monomer 1 existing at that time is 0.05 to 0. 2. Excluding the vinyl chloride monomer out of the polymerization system Characterized by further continued polymerization. Hereinafter, the present invention will be described in detail. Incidentally, the vinyl chloride monomer is referred to as VCM.

In the present invention, VCM is subjected to suspension polymerization in an aqueous medium in the presence of an oil-soluble polymerization initiator. VC above
As M, in addition to vinyl chloride alone, a mixture with a monomer copolymerizable with vinyl chloride can be used. The monomer copolymerizable with the vinyl chloride is not particularly limited, and includes, for example, alkyl vinyl esters such as vinyl acetate; α-monoolefins such as ethylene and propylene;
Alkyl (meth) acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, and octyl acrylate; alkyl vinyl ether; maleimides;
Vinylidene chloride; styrene and the like. These may be used alone or in combination of two or more. When vinyl chloride is copolymerized with a monomer copolymerizable with vinyl chloride, the content of vinyl chloride is preferably 50% by weight or more.

As the above oil-soluble polymerization initiator, generally, P
A known radical polymerization initiator or the like used for the polymerization of VC is used. The radical polymerization initiator is not particularly limited, and for example, t-butyl peroxy neodecanoate, t-hexyl peroxy neodecanoate, t-hexyl peroxy pivalate, α-cumyl peroxy neodecanoate Eate, t-hexyl neohexanoate,
2,4,4-trimethylpentyl-2-peroxy-2
A perester compound such as neodecanoate; a percarbonate compound such as diisopropylperoxydicarbonate, di-2-ethylhexylperoxydicarbonate, di-2-ethoxyethylperoxydicarbonate, dimethoxyisopropylperoxydicarbonate; decanoylper; Oxide, lauroyl peroxide, benzoyl peroxide, cumene hydroperoxide, cyclohexanone peroxide, 2,4-dichlorobenzoyl peroxide, p-menthane hydroperoxide, 3,5,5-trimethylhexanoyl peroxide, isobutyl peroxide Peroxide compounds such as α, α′-azobisisobutyronitrile, α, α ′
Azo compounds such as -azobis (dimethylvaleronitrile) and α, α'-azobis (4-methoxy-2,4-dimethylvaleronitrile). These may be used alone or in combination of two or more.

The partially saponified polyvinyl acetate (a) is used as a dispersant, and has a saponification degree of 60 to 90 mol%.
Is preferable, and 70 to 85 mol% is more preferable. If the saponification degree is less than 60 mol%, the oil solubility becomes strong and the ability to disperse VCM becomes insufficient, so that the selected PVC has many coarse particles. On the other hand, if it exceeds 90 mol%, the protective colloid property becomes strong, so that a strong skin layer is formed on the particle surface, and the gelling properties are deteriorated.

The average degree of polymerization of the partially saponified polyvinyl acetate (a) is preferably 500 to 3000,
~ 1500 is more preferable. If the average degree of polymerization is less than 500, the dispersing ability of VCM is lacking, and the PVC tends to become coarse particles or blocks. If it exceeds 3000, the skin layer becomes thicker and the porosity becomes insufficient, and the moldability decreases.

The partially saponified polyvinyl acetate (a) is added in an amount of 150 to 1500 ppm based on VCM.
Is preferred. If the amount is less than 150 ppm, the oil droplets of VCM become unstable, so that the PVC tends to become blocky, and
If it exceeds 00 ppm, the skin layer on the surface of the PVC particles becomes thicker, the molding processability becomes worse, and glass ball particles called fish eyes increase.

Examples of the cellulose derivative (b) include methyl cellulose, ethyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose and the like.

The amount of the cellulose derivative (b) to be added is preferably 150 to 2000 ppm based on VCM. If it is less than 150 ppm, the oil droplets of the VCM become unstable, so that the PVC tends to become blocky,
If it exceeds pm, the skin layer on the surface of the PVC particles becomes thick, the moldability deteriorates, and glass ball particles called fish eyes increase.

The at least one dispersant of the partially saponified polyvinyl acetate (a) and the cellulose derivative (b) refers to various dispersants selected from (a) and (b) alone. Or two or more of them may be used in combination.

The above sorbitan higher fatty acid ester (c)
Is limited to those having an HLB value of 3 to 10, and preferably 4 to 9. If the HLB value is less than 3, since the lipophilicity is strong, the emulsifying and dispersing ability of the VCM in water is low, and the particle size distribution of the obtained PVC is broad including coarse particles. Is large, the oil droplets of the above-mentioned VCM during polymerization become unstable, and the above-mentioned particles of the above-mentioned VCM tend to agglomerate, and the obtained PVC becomes block-like or aggregates of coarse particles.

The above-mentioned HLB value is a hydrophilic-lipophilic equilibrium value. C. Griffin [J. soc. Cos
metic Chem. , 1, 311 (1949)
Year)), which means the balance between the hydrophilic group and the hydrophobic group of the nonionic surfactant. The larger the value, the greater the hydrophilicity, and the smaller the value, the greater the hydrophobicity.

The sorbitan higher fatty acid ester (c) having an HLB value of 3 to 10 includes, for example, sorbitan monolaurate, sorbitan monomyristate, sorbitan monopalmitate, sorbitan monostearate, sorbitan distearate, sorbitan tristearate Sorbitan saturated higher fatty acid esters such as stearate and sorbitan unsaturated higher fatty acid esters are exemplified. These may be used alone or in combination of two or more.

The above sorbitan higher fatty acid ester (c)
When the amount of addition is small, the skin layer of the obtained PVC particles is formed thick, lacks porosity, the moldability is reduced, and when the amount is large, the particle size distribution of the obtained PVC is wide, 500 to 5,000 ppm with respect to the weight of the VCM is preferable,
00 to 2,500 ppm is more preferable.

Examples of the anionic emulsifier (d) include fatty acid salts such as sodium stearate soap, alkyl sulfate salts such as sodium lauryl sulfate, alkyl benzene sulfonates such as sodium dodecyl benzene sulfonate, and octyl naphthalene sulfonic acid. Alkyl naphthalene sulfonates such as sodium, alkyl sulfosuccinates such as sodium didodecyl sulfosuccinate,
Alkyl diphenyl ether disulfonate, alkyl phosphate, polyoxyethylene alkyl sulfate,
Examples include a naphthalenesulfonic acid formalin condensate, a special polycarboxylic acid type polymer surfactant, a polyoxyethylene alkyl phosphate, and a reactive surfactant. These may be used alone or in combination of two or more.

The amount of the anionic emulsifier (d) added is
When the amount is small, the obtained PVC particles have a thick skin layer, which results in poor porosity and poor moldability, and when the amount is large, the obtained PVC has a wide particle size distribution and a large amount of resin scale adheres to the inner wall of the polymerization vessel. And in some cases P
Since VC particles are blocked, the content is preferably 5 to 1,000 ppm, more preferably 25 to 1,000 ppm based on the weight of the VCM.
750 ppm is more preferred.

The at least one emulsifier of the higher sorbitan fatty acid ester (c) having an HLB value of 3 to 10 and the anionic emulsifier (d) is selected from (c) and (d). Various emulsifiers may be used alone or in combination of two or more.

The higher fatty acid (e) having 8 to 25 carbon atoms is preferably a straight-chain saturated fatty acid, although its effect is not reduced by the degree of unsaturation or branching of the main chain. When the number of carbon atoms is small, the higher fatty acid (e) is hydrophilic, so that the higher fatty acid (e) is not distributed to the oil layer of the VCM during polymerization, and does not exhibit a gelation promoting effect. Since the melting point is high, even if the obtained PVC is processed at a molding temperature, it is difficult to exhibit the gelation promoting effect. Therefore, the above range is preferable, and the carbon number of 11 to 22 is more preferable.

As the above higher fatty acid (e), for example,
Examples include isostearic acid, stearic acid, n-heptadecanoic acid, palmitic acid, n-pentadecanoic acid, myristic acid, arginic acid, nonadecanoic acid, n-tridecanoic acid, lauric acid, and undecylic acid. These may be used alone or in combination of two or more. The added amount of the higher fatty acid (e) is preferably 300 to 20,000 ppm based on the weight of the VCM.

As the above thickener (f), a thickener having a Brookfield viscosity of 10 to 200 cP of a 0.1% by weight aqueous solution at normal temperature and normal pressure is used. PVC obtained at less than 10 cP or more than 200 cP
Is in the above range, and more preferably 11 to 140 cP.

Examples of the thickener (f) include polyethylene oxide, polyvinylpyrrolidone, polyacrylamide, polyacrylamide copolymer, crosslinked (meth) acrylic resin, methylcellulose calcium,
Examples include sodium starch glycolate, sodium starch phosphate, sodium alginate, propylene glycol alginate, sodium carboxymethylcellulose, and calcium carboxymethylcellulose. These may be used alone or in combination of two or more.

The polyethylene oxide used as the thickener (f) preferably has an average molecular weight of 1.7 to 5.5 million. In particular, it is preferable to use an aqueous solution of 4.3 to 4.8 million as a 0.1% by weight aqueous solution because the Brookfield viscosity becomes 12 cP.

The amount of the thickener (f) to be added depends on the VCM
Is preferably 5 to 2,000 ppm based on the weight of. If it is less than 5 ppm, the viscosity is low, so the effect of improving the particle size distribution of the obtained PVC is low, and 2,000 ppm
If it exceeds, a strong skin layer is formed on the surface of the obtained PVC particles, so that the gelation rate is reduced. More preferably, it is 25 to 900 ppm.

In the present invention, VCM during polymerization is used.
Elimination was achieved at a weight ratio of VCM / aqueous medium of 0.6 to 0.1%.
1, preferably at a time of 0.5 to 0.2. 0.
If it is eliminated before time 6, a large amount of VCM must be eliminated in order to obtain the effect of eliminating VCM, resulting in a decrease in polymerization yield and a decrease in productivity. If it is excluded at a point of time less than 0.1, since the polymerization is at the end stage of polymerization, the PVC particles are almost completed and the residual VCM is small, so that the effect of eliminating VCM cannot be expected.

The weight of VCM rejected is 0.05 per weight of the remaining VCM in the polymerization system at the time of rejection.
Limited to ~ 0.2. If it is less than 0.05, the effect of improving the bulk specific gravity by exclusion is small, and if it exceeds 0.2, the decrease in the yield per batch due to the elimination of VCM during polymerization cannot be ignored, and the productivity decreases, which is not preferable. .

The operation of the present invention is as follows. By eliminating a part of VCM in suspended oil droplets during polymerization, gas phase monomers are reduced, and liquid phase monomers, ie, monomers in oil droplets are reduced. It is presumed that the oil droplets, that is, the polymerized PVC particles are compacted and become "clamped", and that many fine pores of the PVC particles are formed. As a result, the porosity is maintained or increased, and the bulk specific gravity increases.

The shape and structure of the polymerization vessel (pressure-resistant autoclave) used in the present invention are not particularly limited, and a conventionally known polymerization vessel is used. Examples of the stirring blade include a Faudler blade, a paddle blade, a turbine blade, a fan turbine blade, and a blue margin blade, and any of them is used. Among them, the Faudler blade is preferable. The combination of the wing and the baffle is not particularly limited.

In the suspension polymerization method of the present invention, a suspension dispersant, emulsifier, thickener, water-soluble nitrogen atom-containing substance,
The method of introducing CM and the like is performed by a conventionally known method, and depending on polymerization conditions, a polymerization regulator, a chain transfer agent, an antistatic agent,
A crosslinking agent, a stabilizer, a filler, a scale inhibitor, a pH adjuster, and the like may be appropriately added. The addition may be batch addition or intermittent addition or continuous addition as long as the reaction is completed within the preferable range of the present invention.

[0045]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

(Example 1) 45 kg of deionized water was put into a polymerization vessel (pressure-resistant autoclave) having an internal volume of about 100 liters, and was further partially saponified as shown in Table 1 based on the weight of VCM. Polyvinyl acetate (a) (Saponification degree 7
2 mol%, average polymerization degree 700) 500 ppm, sorbitan monolaurate (c) (HLB = 8.6) 1,400
ppm, lauric acid (e) 1,400 ppm, polyethylene oxide (f) (average molecular weight, 4.3 million to 480
100 ppm of t, 12 cP / 0.1% aqueous solution) and 500 ppm of t-butyl peroxy neodecanoate. Next, after degassing the inside of the polymerization vessel to 40 mmHg,
45 kg of CM was charged and stirring was started. Polymerization temperature is 5
The temperature was adjusted to 7 ° C., and this temperature was maintained until the polymerization was completed.

After the polymerization temperature reaches a constant temperature, when about 31 kg of VCM is consumed by polymerization (monomer / aqueous medium = about 0.3), about 1.5 kg of VCM (residual monomer 1 in the polymerization vessel) (Corresponding to a weight ratio of about 0.1) to the outside of the system by exhaust gas operation and led to a VCM recovery device. The polymerization is further continued, and the reaction is terminated when the polymerization conversion rate reaches 95%. After the unreacted VCM in the polymerization vessel is recovered, the polymer is taken out of the system in the form of a slurry, and is obtained after dehydration and drying. PV
C was evaluated for plasticizer absorbency, particle size distribution, bulk specific gravity, porosity, maximum torque, gel time, skin-free rate, and scale adhesion according to the test method described below. The results are shown in Table 3. Was.

Examples 2 to 4 Under the conditions shown in Table 1,
In the same manner as in Example 1, PVC was prepared and its performance was evaluated. The results are shown in Table 3.

(Comparative Examples 1 to 5) Under the conditions shown in Table 2,
In the same manner as in Example 1, PVC was prepared and its performance was evaluated. The results are shown in Table 3.

[0050]

[Table 1]

[0051]

[Table 2]

[0052]

[Table 3]

[Performance Evaluation Method] (Measurement of Plasticizer Absorbency) 5 g of the obtained PVC was put into a centrifuge tube equipped with a glass filter, an excess of plasticizer DOP (10 mL) was added to the PVC, and mixed well. , Left for 1 hour. Thereafter, the mixture was treated with a centrifuge (H-200N, rotation speed: 3000 rpm, manufactured by Domestic Centrifuge) for 30 minutes to separate excess DOP, and 100 g of PVC was obtained.
Per DOP absorption was determined.

(Measurement of Particle Size Distribution) JIS Z8801
The obtained PVC was fractionated using a sieve of 60, 100, or 200 mesh according to the above, and the weight% of the passing amount was determined.

(Measurement of Bulk Specific Gravity) The bulk specific gravity of the obtained PVC was measured according to JIS Z6721.

(Measurement of Porosity) Using a mercury intrusion porosimeter (Porosimeter 2000, manufactured by ACOM),
The porosity was determined by measuring the volume of mercury injected per 100 g of PVC obtained at 2,000 kg / cm ² .

(Measurement of Bulk Specific Gravity) The bulk specific gravity of the obtained PVC was measured according to JIS Z6721.

[Measurement of processability (maximum torque, gel time)] Compound for test; 100 parts by weight of obtained PVC,
Dibutyltin mercapto (organotin-based stabilizer: JF-10
B, 2 parts by weight (manufactured by Sankyo Co., Ltd.) and 0.5 parts by weight of a montanic acid ester (lubricant: WAX OP, manufactured by Hoechst) were added, and the mixture was mixed with a supermixer (manufactured by Mitsui Miike) to obtain 120 parts.
After raising the temperature to and mixing at 40 ° C., the mixture was cooled at 40 ° C. to obtain a test compound.

Apparatus: Plastmill: manufactured by Toyo Seiki Co., Ltd. Model: Haake Rheocord 90 Test conditions: 60 g of the test compound was put into a test chamber at a temperature of 120 ° C., and the temperature was increased at a rate of 5 ° C./min. The mixture was kneaded at 200 rpm at 50 rpm, and the maximum torque and the gelation time were measured.

[Evaluation of Surface Condition (Skin Free Ratio)] The obtained PVC particles were subjected to a scanning electron microscope (FE-SEM).
S-4200, manufactured by Hitachi, Ltd.)
V, 130x magnification, particle outline, skin part,
A portion where the skin was not present (a portion where the primary particles were exposed, hereinafter referred to as a skin-free portion) was copied to a tracing paper (or an OHP sheet). Next, the tracing paper (or OHP sheet) is introduced into an image analysis device (PIAS-III, manufactured by Pierce) and image analysis is performed to calculate a particle area and a skin-free area.
The skin-free rate was determined according to the following equation. Skin free ratio = (skin free area / particle area) × 100

[0061]

The suspension polymerization method of PVC of the present invention is as described above, so that the resin scale does not adhere to the inner wall of the polymerization vessel, and has a sharp particle size distribution and a high bulk specific gravity.
It is possible to obtain a PVC having high polymerization productivity, having almost no skin layer portion on the particle surface, and having extremely good moldability.

Claims (1)

[Claims] When a vinyl chloride monomer is subjected to suspension polymerization in an aqueous medium in the presence of an oil-soluble polymerization initiator, a partially saponified polyvinyl acetate (a) and a cellulose derivative ( at least one dispersant of b), at least one emulsifier of sorbitan higher fatty acid ester (c) having an HLB value of 3 to 10 and anionic emulsifier (d);
A higher fatty acid (e) having 8 to 25 carbon atoms and a thickener (f) having a Brookfield viscosity of 10 to 200 cP in a 0.1% by weight aqueous solution at normal temperature and normal pressure were added to initiate polymerization. Thereafter, the weight ratio of the vinyl chloride monomer / aqueous medium is between 0.1 and 0.6, and the weight ratio of the vinyl chloride monomer 1 existing at that time is 0.05
A suspension polymerization method for a vinyl chloride-based resin, wherein the vinyl chloride-based resin is excluded from the polymerization system and the polymerization is further continued.