JP7408405B2 - Method for producing vinyl chloride polymer - Google Patents

Description

The present invention relates to a method for producing a vinyl chloride polymer, and more particularly, to a method for producing a vinyl chloride polymer that reduces the amount of scale adhering to the inner wall of a polymerization tank and improves productivity. The present invention relates to a manufacturing method capable of obtaining a vinyl chloride polymer having fisheye properties and excellent moldability.

Conventionally, as a production technique for obtaining a vinyl chloride polymer having good fisheye properties, Patent Document 1 discloses (A) partial saponification with a degree of saponification of 60 to 90 mol% and a degree of polymerization of 300 to 3000 as a dispersion stabilizer. A method is described in which polyvinyl alcohol and (B) partially saponified polyvinyl alcohol with a degree of saponification of 20 to 55 mol% and a degree of polymerization of 100 to 1000 are used in a ratio of (A)/(B) = 1/9 to 8/2. There is.
However, the above method has the problem that a large amount of scale adheres to the inner wall of the polymerization tank, requiring frequent cleaning in industrial production, and reducing productivity.

As a method for preventing scale adhesion, a method of forming a coating film of a scale adhesion preventive agent in a polymerization tank is known, and various scale adhesion preventive agents have been proposed. Examples of the scale adhesion inhibitor include the agents described in the claims, examples, etc. of Patent Document 2 and Patent Document 3.
However, in the above method, as the number of repeated polymerization batches increases, scale tends to adhere. In particular, when partially saponified polyvinyl alcohol with a degree of saponification of 20 to 55 mol% is used, scale adhesion becomes noticeable.

In addition, as a manufacturing technology that reduces the amount of scale adhering to the inner wall of a polymerization tank for vinyl chloride polymer, Patent Document 4 describes a method in which the temperature of the reaction wall is not raised by 20°C or more than the temperature of the polymerization mixture during the heating step, and There is a method characterized by lowering the temperature of the reaction wall than the temperature of the polymerization mixture during the subsequent polymerization step, and Patent Document 5 describes a method in which water and monomers charged in a polymerization vessel are brought to a predetermined polymerization temperature. To raise the temperature, an internal jacket type polymerization vessel with a heat medium passage provided on the inner surface of the polymerization vessel body is used, and the temperature (Θ) of the heat medium circulated through the jacket is T+5≦Θ for a predetermined polymerization temperature (T). A method for producing a vinyl chloride polymer is disclosed, which is characterized in that the temperature is adjusted to <80 (° C.) and then the polymerization is performed.
However, the method described in Patent Document 4 has a problem in that since the temperature of the heat medium is limited, the temperature rise time becomes long and productivity is reduced. The method described in Patent Document 5 is limited to a polymerization tank having an internal jacket, and it is said that a tank having high heat transfer ability is desirable, and cannot be applied to a polymerization tank having an external jacket.

Japanese Unexamined Patent Publication No. 53-136089 U.S. Patent No. 4,080,173 Special Publication No. 62-3841 Japanese Patent Application Publication No. 49-18984 Patent No. 2574077

Therefore, the purpose of the present invention is to be able to obtain a vinyl chloride polymer that has good fisheye properties and excellent moldability, and also has less scale adhering to the inner wall of the polymerization tank, improving productivity. An object of the present invention is to provide a method for producing a vinyl chloride polymer.

As a result of intensive studies to solve the above problems, the present inventors have discovered a method for producing a vinyl chloride polymer by suspension polymerizing vinyl chloride monomers using a polymerization tank. A part of the specific dispersion stabilizer is charged before the start of polymerization, and after the temperature of the polymerization mixture is raised, the remaining specific dispersion is carried out under the condition that the temperature of the heating medium flowing into the jacket attached to the polymerization tank body is below a predetermined temperature. By adding a stabilizer, hot water and steam used in the jacket can be used without temperature restrictions when the temperature rises, which improves productivity, has good fisheye properties, and has excellent moldability. The present inventors have found that a vinyl chloride polymer can be obtained, and that the amount of scale adhering to the inner wall of a polymerization tank is significantly reduced, leading to the completion of the present invention.

That is, the present invention
Using a polymerization tank, a vinyl chloride monomer , or a mixture of a vinyl chloride monomer and a monomer copolymerizable with the vinyl chloride monomer , the proportion of the copolymerizable monomer being , a mixture (hereinafter referred to as vinyl chloride monomer) in an amount of 20 parts by mass or less per 100 parts by mass of the vinyl chloride monomer is used as a polymerization initiator and a dispersion stabilizer, and (A) the degree of saponification is Partially saponified polyvinyl alcohol having a saponification degree of 65 mol% or more and 90 mol% or less and an average degree of polymerization of 600 or more and 3000 or less, (B) Partially saponified polyvinyl having a saponification degree of 10 mol% or more and 60 mol% or less and an average polymerization degree of 100 or more and 1000 or less In a method for producing a vinyl chloride polymer in which suspension polymerization is carried out in an aqueous medium in the presence of alcohol,
The total amount of the component (B) added is 0.04 parts by mass or more based on 100 parts by mass of the vinyl chloride monomer,
Before the start of polymerization, the above component (B) is added to 100 parts by mass of the vinyl chloride monomer, and 0 parts by mass or more and 0.03 parts by mass or less are added to the jacket attached to the polymerization tank body, and a heat medium of 70° C. or higher is added to the jacket attached to the polymerization tank body. of the vinyl chloride monomer, polymerization initiator, and dispersion stabilizer, the mixture of component (A) and component (B) added before the start of polymerization reaches a predetermined polymerization temperature. After that, the remaining component (B) is added while the temperature of the heat medium flowing through the jacket is 65° C. or less and the polymerization conversion rate is less than 10%. .

According to the method of the present invention, it is possible to obtain a vinyl chloride polymer that has good fisheye properties and excellent moldability.Furthermore, less scale adheres to the inner wall of the polymerization tank, improving productivity. A method for producing a vinyl chloride polymer can be provided. Therefore, the industrial value of the present invention is extremely large.

The present invention will be explained in detail below.
The present invention uses a polymerization tank and uses a vinyl chloride monomer as a polymerization initiator and a dispersion stabilizer. Vinyl chloride subjected to suspension polymerization in an aqueous medium in the presence of the following partially saponified polyvinyl alcohol, (B) partially saponified polyvinyl alcohol having a degree of saponification of 10 mol% or more and 60 mol% or less and an average degree of polymerization of 100 or more and 1000 or less. This is a method for producing a polymer.

The polymerization tank used in the present invention is not particularly limited in the shape of the stirring device, such as stirring blades attached to the polymerization tank and baffles used if desired, except that a jacket is attached to the polymerization tank main body. It is possible to use any of the known methods generally employed for suspension polymerization of vinyl chloride monomers. Examples of the jacket attached to the polymerization tank body include heating jackets such as an external jacket and an internal jacket. Examples of stirring blades attached to the polymerization tank include paddle blades, pitched paddle blades, bull margin blades, Faudler blades, turbine blades, propeller blades, etc. These stirring blades can be used alone or with other stirring blades. May be used in combination. Further, examples of the baffle include a plate type, cylindrical type, D type, loop type, finger type, and the like. Further, a reflux condenser may be used in a polymerization tank equipped with a reflux condenser.

The vinyl chloride polymer used in the present invention is a polymer obtained by polymerizing a vinyl chloride monomer or a mixture of a vinyl chloride monomer and a copolymerizable vinyl monomer. Addition of lubricants, gelling improvers, pH adjusters, chain transfer agents, antistatic agents, crosslinking agents, antifoaming agents, stabilizers, fillers, antioxidants, anti-scaling agents, etc. as appropriate. An agent may be added.

As the monomer copolymerizable with the vinyl chloride monomer, any monomer can be used as long as it is copolymerizable with the vinyl chloride monomer, such as olefins such as ethylene and propylene, Vinyl esters such as vinyl acetate and vinyl stearate, vinyl ethers such as ethyl vinyl ether and cetyl vinyl ether, acrylic esters such as methyl acrylate, ethyl acrylate, butyl acrylate, and propyl acrylate, maleic acid, and fumaric acid. Examples include monomers conventionally known as monomers copolymerizable with vinyl chloride, such as esters or anhydrides, aromatic vinyl compounds such as styrene, and acrylonitrile. The copolymerizable monomer is preferably used in a proportion of usually 20 parts by mass or less based on the vinyl chloride monomer.

The polymerization initiator used in the present invention may be one that is generally used as a polymerization initiator in suspension polymerization, such as tert-butylperoxyneodecanoate and tert-hexylperoxyneodecanoate. , tert-amyl peroxy pivalate, tert-hexyl peroxy pivalate, tert-butyl peroxy pivalate, cumyl peroxy neodecanoate, tert-hexyl peroxy neohexanoate; diisopropyl per ester compounds; Percarbonate compounds such as oxydicarbonate, di-2-ethylhexyl peroxydicarbonate, di-2-ethoxyethyl peroxydicarbonate, dimethoxyisopropyl peroxydicarbonate; benzoyl peroxide, cumene hydroperoxide, 2,4- Peroxide compounds such as dichlorobenzoyl peroxide, acetylcyclohexyl peroxide, diisobutyryl peroxide; azo compounds such as 2,2'-azobisisobutyronitrile and 2,2'-azobis-2,4-dimethylvaleronitrile These can be used alone or in combination of two or more.

In the present invention, component (A) used as a dispersion stabilizer is a partially saponified polyvinyl alcohol having a degree of saponification of 65 mol% or more and 90 mol% or less and an average degree of polymerization of 600 or more and 3000 or less.
If the degree of saponification of component (A) is less than 65 mol%, the particles may become coarse. On the other hand, if the degree of saponification exceeds 90 mol%, it is not preferable because the fish eyes of the molded article will worsen.
Furthermore, if the average degree of polymerization is less than 600, the particles may become coarse. On the other hand, if the average degree of polymerization exceeds 3000, it is not preferable because the fish eyes of the molded product will deteriorate.

In the present invention, component (B) used as a dispersion stabilizer is a partially saponified polyvinyl alcohol having a degree of saponification of 10 to 60 mol% and an average degree of polymerization of 100 to 1000. As component (B), a dispersion stabilizer having characteristics of water dispersibility and/or water solubility is desirable because no organic solvent is used for dissolution and it is easy to handle. In the present invention, water-dispersible refers to a resin that forms particles in an aqueous medium when a compound is dispersed in the aqueous medium, and in which the particles are dispersed in the aqueous medium. do. Water-soluble means that it dissolves at least 1% by mass in water at 25°C.
Specifically, partially saponified polyvinyl alcohol having an ionic group (Japanese Patent No. 2826194, Japanese Patent No. 2566593) and partially saponified polyvinyl alcohol having an oxyalkylene group (Japanese Patent No. 3623562) can be mentioned. In particular, partially saponified polyvinyl alcohol having an ionic group at the end is desirable.
More preferably, the component (B) is a partially saponified polyvinyl alcohol having an ionic group such as a carboxyl group or a sulfonic acid group at the terminal, a degree of saponification of 10 mol% or more and 55 mol% or less, and an average degree of polymerization of 100 or more and 600 or less. When using an aqueous dispersion having as a dispersoid, it is easy to handle because no organic solvent is used, and good fish-eye characteristics can be obtained.
If the degree of saponification of the partially saponified polyvinyl alcohol of component (B) is less than 10 mol% or the average degree of polymerization is less than 100, the particles of the resulting vinyl chloride polymer may become coarse or roll adhesion during calendering may occur. This is not preferable because the occurrence may become noticeable. On the other hand, if the degree of saponification exceeds 60 mol % or if the average degree of polymerization exceeds 1000, fish eyes in the molded article will deteriorate, which is not preferable.

In the present invention, component (B) may be added continuously in a predetermined amount to the polymerization tank within a predetermined period, or may be added instantaneously.

In the present invention, in addition to the above-mentioned components (A) and (B), cellulose derivatives, gelatin, nonionic surfactants, anionic surfactants, etc., which are commonly known as dispersion stabilizers, are used as an auxiliary dispersion stabilizer. You can also use In that case, the amount of other dispersion stabilizers added is preferably 40 parts by mass or less based on the total of 100 parts by mass of the above-mentioned components (A) and (B).

In the present invention, in order to obtain good fisheye characteristics, the total amount of component (B) added must be 0.04 parts by mass or more per 100 parts by mass of the vinyl chloride monomer, and 0. It is desirable to add in a range of .05 parts by mass or more and 0.2 parts by mass or less.
In the present invention, the amount of component (B) added before the start of polymerization has an effect on the amount of scale attached. ) If the concentration of the component is high, scale will adhere, and especially if a heating medium of 80° C. or higher is used, scale will adhere significantly. Therefore, in order to satisfy the purpose of the present invention, the amount of component (B) added before the start of polymerization must be 0.03 parts by mass or less. It is desirable that the content be 0.02 parts by mass or less.

In the present invention, when raising the temperature of the polymerization mixture, the temperature of the heating medium in the jacket attached to the polymerization tank body influences the heating time. In the present invention, the heating time can be shortened by using a heating medium of 70°C or higher, and more preferably, the heating time can be further shortened by using a heating medium of 80°C or higher, improving productivity. . The heat medium may be one commonly used such as water or steam.
When the temperature of the heating medium is 65° C. or lower, the concentration of component (B) within the range used in normal polymerization does not affect scale adhesion. Therefore, after the mixture reaches a predetermined polymerization temperature, it is necessary to add the remaining component (B) at 65° C. or lower. More preferably, the remaining component (B) is added when the heat medium is at 50° C. or lower.

In the present invention, in order to obtain good fisheye properties, it is necessary to add component (B) after the mixture reaches a predetermined polymerization temperature and at a polymerization conversion rate of less than 10%. When the conversion rate exceeds 10%, scale adhesion is good, but fish eyes become worse. It is desirable to add the remaining component (B) at a polymerization conversion rate of less than 5%. The conversion rate can be determined from the amount of heat removed from the jacket attached to the polymerization tank and the reaction heat generated when vinyl chloride monomer polymerizes to polyvinyl chloride.
As explained above, one feature of the present invention is that the amount of component (B) added before the start of polymerization and the conditions for adding the remaining component (B) after the start of polymerization have been found. Conventionally, there are various findings as to why the present invention having such characteristics exhibits the above-mentioned effects, and the following may be considered as an example.

In the polymerization of vinyl chloride monomers, after partially saponified polyvinyl alcohol is added as a dispersion stabilizer, hot water or steam is supplied as a heat medium to the jacket attached to the polymerization tank in order to raise the temperature to a predetermined temperature. do.
When component (B) is dispersed in water, the inner wall of the polymerization tank is heated to a high temperature by hot water or steam, and the partially saponified polyvinyl alcohol (B) near the inner wall of the polymerization tank dispersed in the aqueous phase is It is thought that it aggregates and adheres to the inner wall of the polymerization tank, becoming a starting point for scale adhesion.
On the other hand, when component (B) is dissolved in water, the relationship between the solubility of partially saponified polyvinyl alcohol in water and temperature is as follows: Sakurada et al. have revealed that the negative (heat generation) of increases, the critical temperature for phase separation decreases, and the solubility at high temperatures gradually decreases (Polymer Publishing Association "Poval" P142, Sakurada, Hosono; Takashi et al. (See Molecular Chemistry, 2, 151 (1945)). When the inner wall of the polymerization tank is heated to a high temperature by hot water and steam, the partially saponified polyvinyl alcohol (B) component dissolved in the water phase near the inner wall of the polymerization tank precipitates and adheres to the inner wall of the polymerization tank, causing scale. It is thought that it becomes the starting point of adhesion.
It is considered that the higher the concentration of the partially saponified polyvinyl alcohol (B) component in the mixture, the more likely it is to aggregate or precipitate, and the easier it is for scale to adhere.
From the above findings, by limiting the amount of component (B) added before the start of polymerization, it is possible to prevent component (B) from adhering to the inner wall of the polymerization tank, and to increase the temperature of the polymerization mixture using a heating medium of 70°C or higher in the jacket. By adding the remaining component (B) after the polymerization mixture has reached a predetermined temperature and the jacket has been cooled to below 65°C, scale adhesion is reduced, productivity is further improved, and good fish eyes are achieved. We thought that it would be possible to obtain a vinyl chloride polymer that has these properties and has excellent moldability.

As a result of various studies, we found that (A) a portion with a saponification degree of 65 mol% or more and 90 mol% or less and an average polymerization degree of 600 or more and 3000 or less, using a vinyl chloride monomer as a polymerization initiator and a dispersion stabilizer. In the method of carrying out suspension polymerization in an aqueous medium in the presence of saponified polyvinyl alcohol, (B) partially saponified polyvinyl alcohol having a degree of saponification of 10 mol% or more and 60 mol% or less and an average degree of polymerization of 100 or more and 1000 or less, partial saponification is performed. The total amount of polyvinyl alcohol (B) added is 0.04 parts by mass or more based on 100 parts by mass of the monomer, and before the start of polymerization, the component (B) is added to 0.04 parts by mass or more based on 100 parts by mass of the monomer. At least 0.03 parts by mass is added, and a heating medium of 70°C or higher is flowed through the jacket attached to the polymerization tank body. After the mixture reaches a predetermined polymerization temperature, the temperature of the heating medium flowing through the jacket is 65°C. We have discovered a method for producing a vinyl chloride polymer, characterized in that the remaining component (B) is added at a polymerization conversion rate of less than 10%.

Next, the present invention will be explained in more detail by showing examples, but these are not intended to limit the scope of the present invention in any way. The vinyl chloride polymers obtained in Examples and Comparative Examples were evaluated by the following method.

(1) Fish eye
To 100 parts by mass of the obtained vinyl chloride polymer, 1.5 parts by mass of Ca-Zn powder composite stabilizer, 0.5 parts by mass of organophosphorus stabilizing aid, 3 parts by mass of ultramarine and DOP (dioctyl phthalate). ) 50 parts by mass was blended and kneaded for 3 minutes in a roll forming machine adjusted to 150°C, a sheet with a thickness of 0.35 mm was separated, and the number of transparent particles in the 50 cm ² sheet was evaluated by fish eye. Shown as
(2) Scale adhesion status The scale adhering to the inner wall of the polymerization tank was visually observed and the adhesion status was evaluated based on the following evaluation criteria.
Evaluation criteria for scale adhesion ○: Almost no scale adhesion △: Slight scale adhesion ×: Significant scale adhesion

(Example 1)
720 kg of deionized water was charged into a stainless steel polymerization tank having an internal volume of 2000 liters and equipped with a stirrer, and then 280 g of partially saponified polyvinyl alcohol (component (A)) having a degree of saponification of 80 mol% and an average degree of polymerization of 2600 was charged. 110 g (0.02 parts by mass based on vinyl chloride monomer) of water-dispersible partially saponified polyvinyl alcohol (component (B)) having a carboxyl group at the end with a degree of saponification of 40 mol% and an average degree of polymerization of 550 was charged. . Thereafter, the polymerization tank was degassed using a vacuum pump until the internal pressure became -87 kPa (pressure gauge pressure). After degassing, 550 kg of vinyl chloride monomer and 135 g of tert-butyl peroxyneodecanate and 165 g of tert-cumyl peroxyneodecanate as polymerization initiators were charged into the polymerization tank. While stirring, hot water was passed through the jacket as a heat medium to start raising the temperature. The maximum temperature of the jacket hot water was 81°C. After reaching the target polymerization temperature of 51.7°C, when the jacket hot water temperature was 42°C and the conversion rate was 3.1%, 192g of partially saponified polyvinyl alcohol (B) component having water dispersibility was added. (0.035 parts by mass based on vinyl chloride monomer). The internal pressure of the polymerization tank was 710 kPa (pressure gauge pressure). Thereafter, the reaction was stopped when the internal pressure dropped to 620 kPa (pressure gauge pressure), and the unreacted vinyl chloride monomer was recovered, and the system was replaced with nitrogen, and the vinyl chloride polymer slurry was taken out. A polymer was obtained by dehydration and drying.
Table 1 shows the evaluation results of the obtained vinyl chloride polymer, scale adhesion status, and heating time.
The obtained vinyl chloride polymer had few fish eyes and almost no scale adhering to the inner wall of the polymerization tank was observed. Moreover, the temperature increase time was short and the productivity was also good.

(Example 2)
A polymer was obtained in the same manner as in Example 1 except that the temperature of the jacket hot water during heating was 91°C.
Table 1 shows the evaluation results of the obtained vinyl chloride polymer, scale adhesion status, and heating time.
The obtained vinyl chloride polymer had few fish eyes and almost no scale adhering to the inner wall of the polymerization tank was observed. Moreover, the temperature increase time was short and the productivity was also good.

(Example 3)
A polymer was obtained in the same manner as in Example 1 except that the temperature of the jacket hot water during heating was 75°C.
Table 1 shows the evaluation results of the obtained vinyl chloride polymer, scale adhesion status, and heating time.
The obtained vinyl chloride polymer had few fish eyes and almost no scale adhering to the inner wall of the polymerization tank was observed. Moreover, the temperature increase time was short and the productivity was also good.

(Example 4)
When the jacket hot water was 46°C and the conversion rate was 4.5%, 330g of water-dispersible partially saponified polyvinyl alcohol (B) having a saponification degree of 40 mol%, an average polymerization degree of 550, and a terminal carboxyl group (vinyl chloride monomer) was added. A polymer was obtained in the same manner as in Example 2, except that 0.06 parts by mass (based on the polymer) was added.
Table 1 shows the evaluation results of the obtained vinyl chloride polymer, scale adhesion status, and heating time.
The obtained vinyl chloride polymer had few fish eyes and almost no scale adhering to the inner wall of the polymerization tank was observed. Moreover, the temperature increase time was short and the productivity was also good.

(Example 5)
Same as Example 1 except that partially saponified polyvinyl alcohol having a degree of saponification of 35 mol%, an average degree of polymerization of 300, no terminal ionic groups, and no water dispersibility or solubility was used as component (B). A polymer was obtained in a similar manner.
Table 1 shows the evaluation results of the obtained vinyl chloride polymer, scale adhesion status, and heating time.
The obtained vinyl chloride polymer had few fish eyes and almost no scale adhering to the inner wall of the polymerization tank was observed. Moreover, the temperature increase time was short and the productivity was also good.

(Example 6)
A polymer was prepared in the same manner as in Example 1, except that component (B) was partially saponified polyvinyl alcohol with a degree of saponification of 40 mol%, a degree of polymerization of 250, no ionic groups at the end, and water-soluble characteristics. Obtained.
Table 1 shows the evaluation results of the obtained vinyl chloride polymer, scale adhesion status, and heating time.
The obtained vinyl chloride polymer had few fish eyes and almost no scale adhering to the inner wall of the polymerization tank was observed. Moreover, the temperature increase time was short and the productivity was also good.

(Example 7)
As component (A), 0.04 polymerization part of partially saponified polyvinyl alcohol with saponification degree of 80 mol% and polymerization degree of 2000, and 0.03 polymerization part of partially saponified polyvinyl alcohol with saponification degree of 70 mol% and polymerization degree of 670 were used. A polymer was obtained in the same manner as in Example 1.
Table 1 shows the evaluation results of the obtained vinyl chloride polymer, scale adhesion status, and heating time.
The obtained vinyl chloride polymer had few fish eyes and almost no scale adhering to the inner wall of the polymerization tank was observed. Moreover, the temperature increase time was short and the productivity was also good.

(Comparative example 1)
A polymer was obtained in the same manner as in Example 1 except that the entire amount of component (B) was added before the start of polymerization.
Table 1 shows the evaluation results of the obtained vinyl chloride polymer, scale adhesion status, and heating time.
The obtained vinyl chloride polymer had good fish eyes. However, a lot of scale adhesion was confirmed on the inner wall of the polymerization tank.

(Comparative example 2)
A polymer was obtained in the same manner as in Example 3 except that the entire amount of component (B) was added before the start of polymerization.
Table 1 shows the evaluation results of the obtained vinyl chloride polymer, scale adhesion status, and heating time.
The obtained vinyl chloride polymer had good fish eyes, but significant scale was observed in the polymerization tank.

(Comparative example 3)
A polymer was obtained in the same manner as in Comparative Example 2, except that the maximum temperature of the jacket hot water during heating was 75°C.
Table 1 shows the evaluation results of the obtained vinyl chloride polymer, scale adhesion status, and heating time.
The obtained vinyl chloride polymer had good fish eyes, but some scale adhesion to the inner wall of the polymerization tank was observed.

(Comparative example 4)
A polymer was obtained in the same manner as in Comparative Example 2, except that the maximum temperature of the jacket hot water during heating was 60°C.
Table 1 shows the evaluation results of the obtained vinyl chloride polymer, scale adhesion status, and heating time.
Although the obtained vinyl chloride polymer had good fish eyes and almost no scale adhering to the inner wall of the polymerization tank was observed, the temperature rising time was long and productivity deteriorated.

(Comparative example 5)
The amount of component (B) charged before the start of polymerization was 0.02 parts by mass, and component (B) was not added after reaching the target polymerization temperature of 51.7°C. A polymer was obtained in the same manner as in Example 1 in other respects.
Table 1 shows the evaluation results of the obtained vinyl chloride polymer, scale adhesion status, and heating time.
The fish eyes of the obtained vinyl chloride polymer were significantly deteriorated. Almost no scale was observed adhering to the inner wall of the polymerization tank.

(Comparative example 6)
The amount of component (B) charged before the start of polymerization was 0.04 parts by mass, and after reaching the target polymerization temperature of 51.7°C, when the jacket hot water temperature was 45°C and the polymerization conversion rate was 3.2%, water was added. A polymer was obtained in the same manner as in Example 1, except that 64 g (0.015 parts by mass based on the vinyl chloride monomer) of partially saponified polyvinyl alcohol (B) component having characteristics of dispersibility was added.
Table 1 shows the evaluation results of the obtained vinyl chloride polymer, scale adhesion status, and heating time.
Although the obtained vinyl chloride polymer had good fish eyes, scale was significantly attached to the inner wall of the polymerization tank.

(Comparative Example 7)
After reaching the target polymerization temperature of 51.7°C and when the jacket hot water temperature was 39°C and the polymerization conversion rate was 10.4%, 192g of partially saponified polyvinyl alcohol (B) component having water-dispersible characteristics (monovinyl chloride) was added. A polymer was obtained in the same manner as in Example 1, except that 0.035 parts by mass (based on the polymer) was added.
Table 1 shows the evaluation results of the obtained vinyl chloride polymer, scale adhesion status, and heating time.
The fish eyes of the obtained vinyl chloride polymer deteriorated. Almost no scale was observed on the inner wall of the polymerization tank.

(Comparative example 8)
After reaching the target polymerization temperature of 51.7°C, when the jacket cooling water temperature was 73°C and the polymerization conversion rate was 0.3%, 192g of partially saponified polyvinyl alcohol (B) component having water dispersibility was added (monovinyl chloride). A polymer was obtained in the same manner as in Example 1, except that 0.035 parts by mass (based on the polymer) was added.
Table 1 shows the evaluation results of the obtained vinyl chloride polymer, scale adhesion status, and heating time.
Although the obtained vinyl chloride polymer had good fish eyes, scale was significantly attached to the inner wall of the polymerization tank.

Claims (7)

Using a polymerization tank, a vinyl chloride monomer , or a mixture of a vinyl chloride monomer and a monomer copolymerizable with the vinyl chloride monomer , wherein the proportion of the copolymerizable monomer is , a mixture (hereinafter referred to as vinyl chloride monomer) of 20 parts by mass or less per 100 parts by mass of the vinyl chloride monomer is used as a polymerization initiator and a dispersion stabilizer, and (A) the degree of saponification is Partially saponified polyvinyl alcohol having a saponification degree of 65 mol% or more and 90 mol% or less and an average degree of polymerization of 600 or more and 3000 or less, (B) Partially saponified polyvinyl having a saponification degree of 10 mol% or more and 60 mol% or less and an average polymerization degree of 100 or more and 1000 or less In a method for producing a vinyl chloride polymer in which suspension polymerization is carried out in an aqueous medium in the presence of alcohol,
The total amount of the component (B) added is 0.04 parts by mass or more based on 100 parts by mass of the vinyl chloride monomer,
Before the start of polymerization, the component (B) is added to 100 parts by mass of the vinyl chloride monomer, and a heat medium of 70°C or higher is added to the jacket attached to the polymerization tank body. of the vinyl chloride monomer, polymerization initiator, and dispersion stabilizer, the mixture of component (A) and component (B) added before the start of polymerization reaches a predetermined polymerization temperature. After that, the remaining component (B) is added while the temperature of the heat medium flowing through the jacket is 65° C. or less and the polymerization conversion rate is less than 10%. The method for producing a vinyl chloride polymer according to claim 1, wherein the component (B) has water dispersibility and/or water solubility. The method for producing a vinyl chloride polymer according to claim 1 or 2, wherein the component (B) has a degree of saponification of 10 mol% or more and 55 mol% or less and an average degree of polymerization of 100 or more and 1000 or less. The method for producing a vinyl chloride polymer according to claim 1 or 2, wherein the component (B) has a degree of saponification of 10 mol% or more and 55 mol% or less and an average degree of polymerization of 100 or more and 600 or less. The method for producing a vinyl chloride polymer according to any one of claims 1 to 4, wherein the component (B) has an ionic group at a terminal. The method for producing a vinyl chloride polymer according to claim 5, wherein the ionic group is a carboxyl group or a sulfonic acid group. The method for producing a vinyl chloride polymer according to claim 1, wherein a heat medium of 80° C. or higher is passed through a jacket attached to the polymerization tank main body.