JP2021109932A - Method for producing vinyl chloride-based polymer - Google Patents

Abstract

To provide a method for producing a vinyl chloride-based polymer which has good fish-eye characteristics and excellent molding processability and further has less scale adhering to an inner wall of a polymerization tank and is improved in productivity.SOLUTION: There is provided a method for producing a vinyl chloride-based polymer by suspension polymerization of a vinyl chloride-based monomer using a polymerization tank, wherein a part of a specific dispersion stabilizer is charged before the start of polymerization, after increasing the temperature of a polymerization mixture, the remaining part of the specific dispersion stabilizer is added under the condition that the temperature of a heating medium flowing into a jacket attached to a polymerization tank body is below a predetermined temperature.SELECTED DRAWING: None

Description

The present invention relates to a method for producing a vinyl chloride-based polymer, and more particularly, to a method for producing a vinyl chloride-based polymer in which the amount of scale adhering to the inner wall of the polymerization tank is small and the productivity is improved. The present invention relates to a production method capable of obtaining a vinyl chloride-based polymer having fisheye characteristics and excellent molding processability.

Conventionally, as a production technique for obtaining a vinyl chloride-based polymer having good fish-eye characteristics, Patent Document 1 describes (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 of using polyvinyl alcohol, (B) partially saponified polyvinyl alcohol having a degree of saponification of 20 to 55 mol% and a degree of polymerization of 100 to 1000 at a ratio of (A) / (B) = 1/9 to 8/2 is described. There is.
However, the above method has a problem that a large amount of scale adheres to the inner wall of the polymerization tank, frequent cleaning or the like is required in industrial production, and the productivity is lowered.

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

Further, as a manufacturing technique in which the amount of scale adhering to the inner wall of the polymerization tank of the vinyl chloride polymer is small, the temperature of the reaction wall is not made higher than the temperature of the polymerization mixture by 20 ° C. or more during the heating step in Patent Document 4, and In the subsequent polymerization step, the temperature of the reaction wall is made lower than the temperature of the polymerization mixture, and Patent Document 5 describes that the water and the monomer charged in the polymerizer are brought to a predetermined polymerization temperature. When raising the temperature, an internal jacket type polymer having a heat medium passage provided on the inner surface of the polymer body is used, and the temperature (Θ) of the heat medium circulated in the jacket is T + 5 ≦ Θ with respect to a predetermined polymerization temperature (T). A method for producing a vinyl chloride-based polymer is disclosed, which comprises adjusting the temperature to <80 (° C.), raising the temperature, and subsequently performing polymerization.
However, the method described in Patent Document 4 has a problem that the temperature of the heat medium is limited, so that the temperature rising time becomes long and the productivity decreases. The method described in Patent Document 5 is a method limited to a polymerization tank having an inner jacket, and it is said that a method having a high heat transfer ability is desirable, and cannot be applied to a polymerization tank having an outer jacket.

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

Therefore, an object of the present invention is to obtain a vinyl chloride-based polymer having good fish-eye characteristics and excellent molding processability, and further, the scale adhering to the inner wall of the polymerization tank is small, and the productivity is improved. The present invention is to provide a method for producing a vinyl chloride-based polymer.

As a result of diligent studies to solve the above problems, the present inventors have found a method for producing a vinyl chloride-based polymer by suspend-polymerizing a vinyl chloride-based monomer using a polymerization tank. A part of a specific dispersion stabilizer is charged before the start of polymerization, the temperature of the polymerization mixture is raised, and then the temperature of the heat medium flowing through the jacket attached to the main body of the polymerization tank is equal to or lower than a predetermined temperature, and the remaining specific dispersion is dispersed. By adding a stabilizer, hot water or steam used for the jacket at the time of temperature rise can be used without temperature limitation, so that the productivity is improved, the fisheye characteristics are good, and the molding processability is excellent. It has been found that a vinyl chloride-based polymer can be obtained and the amount of scale adhering to the inner wall of the polymerization tank is remarkably reduced, and the present invention has been completed.

That is, in the present invention, using a polymerization tank, vinyl chloride or a mixture of vinyl chloride and a copolymerizable vinyl chloride (hereinafter referred to as vinyl chloride-based monomer) is used as a polymerization initiator and. As dispersion stabilizers, (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, and (B) a degree of sacrifice of 10 mol% or more and 60 mol% or less and In a method for producing a vinyl chloride-based polymer which is suspended-polymerized in an aqueous medium in the presence of a partially saponified polyvinyl alcohol having an average degree of polymerization of 100 or more and 1000 or less.
The total amount of the component (B) added is 0.04 parts by mass or more with respect to 100 parts by mass of the vinyl chloride monomer.
Before starting the polymerization, the component (B) was added in an amount of 0 to 0.03 parts by mass based on 100 parts by mass of the vinyl chloride monomer, and a heat medium at 70 ° C. or higher was passed through a jacket attached to the main body of the polymerization tank. After the vinyl chloride-based mixture reaches a predetermined polymerization temperature, the remaining component (B) is added under the condition that the temperature of the heat medium flowing through the jacket is 65 ° C. or lower and the polymerization conversion rate is less than 10%. This is a method for producing a vinyl chloride-based polymer, which is characterized by the above.

According to the method of the present invention, a vinyl chloride-based polymer having good fish-eye characteristics and excellent molding processability can be obtained, and further, the scale adhering to the inner wall of the polymerization tank is small, and the productivity is improved. A method for producing a vinyl chloride polymer can be provided. Therefore, the industrial value of the present invention is very large.

Hereinafter, the present invention will be described in detail.
In the present invention, using a polymerization tank, a vinyl chloride monomer is used as a polymerization initiator and a dispersion stabilizer, and (A) the degree of polymerization is 65 mol% or more and 90 mol% or less and the average degree of polymerization is 600 or more and 3000. Vinyl chloride subjected to suspension polymerization in an aqueous medium in the presence of the following partially saponified polyvinyl alcohol and (B) partially saponified polyvinyl alcohol having a degree of sacrifice 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 system polymer.

The polymerization tank used in the present invention has no particular limitation on the shape of the stirring device such as the stirring blade attached to the polymerization tank and the baffle used as desired, except that the jacket is attached to the main body of the polymerization tank. As a suspension polymerization method for vinyl chloride-based monomers, a known method generally used can be used. Examples of the jacket attached to the main body of the polymerization tank include a jacket for heating such as an outer jacket and an inner jacket. Examples of the stirring blade attached to the polymerization tank include paddle blades, pitched paddle blades, bull margin blades, Faudler blades, turbine blades, propeller blades, etc. It may be used in combination. Examples of the baffle include a plate type, a cylindrical type, a D type, a loop type, and a finger type. Further, the reflux capacitor may be used in the polymerization tank accompanied by the reflux capacitor.

The vinyl chloride-based polymer used in the present invention contains a vinyl chloride monomer or a polymer obtained by polymerizing a mixture of a vinyl chloride monomer and a copolymerizable vinyl-based monomer as a main component. Addition of lubricant, gelling improver, pH adjuster, chain transfer agent, antistatic agent, cross-linking agent, antifoaming agent, stabilizer, filler, antioxidant, scale adhesion inhibitor, etc. The agent may be added.

As the monomer copolymerizable with the vinyl chloride monomer, any monomer copolymerizable with the vinyl chloride monomer can be used, for example, 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 acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate and propyl acrylate, maleic acid and fumaric acid. Examples thereof include esters or anhydrides, aromatic vinyl compounds such as styrene, and monomers such as acrylonitrile which are conventionally known as monomers copolymerizable with vinyl chloride. The copolymerizable monomer is preferably used in a proportion of 20 parts by mass or less with respect to the vinyl chloride monomer.

The polymerization initiator used in the present invention may be generally used as a polymerization initiator in the suspension polymerization method, for example, tert-butylperoxyneodecanoate and tert-hexylperoxyneodecanoate. Perester compounds such as, tert-amylperoxypivalate, tert-hexylperoxypivalate, tert-butylperoxypivalate, cumylperoxyneodecanoate, tert-hexylperoxyneohexanoate; diisopropylper. Percarbonate compounds such as oxydicarbonate, di-2-ethylhexyl peroxydicarbonate, di-2-ethoxyethylperoxydicarbonate, dimethoxyisopropylperoxydicarbonate; benzoyl peroxide, cumene hydroperoxide, 2,4- Peroxide compounds such as dichlorobenzoyl peroxide, acetylcyclohexyl peroxide, diisobutyryl peroxide; azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis-2,4-dimethylvaleronitrile These can be used alone or in combination of two or more.

In the present invention, the component (A) used as the dispersion stabilizer is a 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.
If the saponification degree of the component (A) is less than 65 mol%, the particles may become coarse. On the other hand, when the saponification degree exceeds 90 mol%, the fish eye of the molded product deteriorates, which is not preferable.
If the average degree of polymerization is less than 600, the particles may become coarse. On the other hand, when the average degree of polymerization exceeds 3000, the fish eye of the molded product deteriorates, which is not preferable.

In the present invention, the component (B) used as the dispersion stabilizer is a partially saponified polyvinyl alcohol having a saponification degree of 10 mol% or more and 60 mol% or less and an average degree of polymerization of 100 or more and 1000 or less. As the component (B), a dispersion stabilizer having the characteristics of water dispersibility and / or water solubility is desirable from the viewpoint of ease of handling without using an organic solvent for dissolution. In the present invention, the water dispersibility means a resin indicating that when a compound is dispersed in an aqueous medium, particles are formed in the aqueous medium and the particles are dispersed in the aqueous medium. do. Water-soluble means that it dissolves in water at 25 ° C. in an amount of 1% by mass or more.
Specific examples thereof include partially saponified polyvinyl alcohol having an ionic group (Patent No. 2826194, Japanese Patent No. 2566593), partially saponified polyvinyl alcohol having an oxyalkylene group (Patent No. 3623562), and the like. Partially saponified polyvinyl alcohol having an ionic group at the terminal is particularly desirable.
More preferably, the partially saponified polyvinyl alcohol in which the component (B) has an ionic group such as a carboxyl group or a sulfonic acid group at the terminal and has a saponification degree 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 an aqueous dispersion liquid containing the above-mentioned dispersoid is used, it is easy to handle because no organic solvent is used, and good fish-eye characteristics can be obtained.
When the degree of saponification of the partially saponified polyvinyl alcohol of the component (B) is less than 10 mol% or the average degree of polymerization is less than 100, the particles of the obtained vinyl chloride polymer become coarse or the roll adherence in calendar processing. It is not preferable because the occurrence becomes remarkable. On the other hand, when the saponification degree exceeds 60 mol% or the average degree of polymerization exceeds 1000, the fish eye of the molded product deteriorates, which is not preferable.

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

In the present invention, in addition to the above-mentioned components (A) and (B), a cellulose derivative, gelatin, a nonionic surfactant, an anionic surfactant, etc., which are usually known as dispersion stabilizers, are used as auxiliary dispersion stabilizers. It can also be used. In that case, the amount of the other dispersion stabilizer added is preferably 40 parts by mass or less with respect to 100 parts by mass in total of the above-mentioned component (A) and component (B).

In the present invention, in order to obtain good fisheye characteristics, the total addition amount of the component (B) needs to be 0.04 part by mass or more with respect to 100 parts by mass of the vinyl chloride monomer, which is 0. It is desirable to add in the range of 0.05 parts by mass or more and 0.2 parts by mass or less.
In the present invention, the amount of the component (B) added before the start of polymerization affects the amount of scale adhesion, and when the temperature of the polymerization mixture is raised and a heat medium of 70 ° C. or higher is passed through the jacket, the polymerization mixture (B) is added. ) When the concentration of the component is high, the scale adheres, and especially when a heat medium of 80 ° C. or higher is used, the scale adheres remarkably. Therefore, in order to satisfy the object of the present invention, the amount of the component (B) added before the start of polymerization needs to be 0.03 parts by mass or less. It is desirable that it is 0.02 parts by mass or less.

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

In the present invention, in order to obtain good fisheye characteristics, it is necessary to add the component (B) within a polymerization conversion rate of less than 10% after the mixture reaches a predetermined polymerization temperature. When the conversion rate exceeds 10%, the scale adhesion is good, but the fish eye deteriorates. It is desirable to add the remaining component (B) with a polymerization conversion rate of less than 5%. The conversion rate can be obtained from the amount of heat removed from the jacket attached to the polymerization tank and the heat of reaction when the vinyl chloride monomer polymerizes into polyvinyl chloride.
As described above, one of the features of the present invention is that the amount of the 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. There have been various findings in the past as the reason why the present invention having such characteristics exhibits the above-mentioned effects, but the following contents can be considered as an example.

In the polymerization of vinyl chloride-based monomers, 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 after adding partially saponified polyvinyl alcohol or the like as a dispersion stabilizer. do.
When the component (B) is dispersed in water, the inner wall of the polymerization tank is heated to a high temperature by hot water and steam, so that the partially saponified polyvinyl alcohol (B) in the vicinity of the inner wall of the polymerization tank dispersed in the aqueous phase is released. It is considered that the aggregates and adheres to the inner wall of the polymerization tank becomes the starting point of scale adhesion.
On the other hand, when the component (B) is dissolved in water, the relationship between the solubility of the partially saponified polyvinyl alcohol in water and the temperature is such that the acetic acid group of the partially saponified polyvinyl alcohol increases (the lower the degree of saponification) and the heat of dissolution. It has been clarified by Sakurada et al. That the negative (heat generation) of the saponification increases, the critical temperature of phase separation decreases, and the solubility at high temperature gradually decreases (Polymer Publishing Association "Poval" P142, Sakurada, Hosono; High). 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 in the vicinity of the inner wall of the polymerization tank dissolved in the aqueous phase is precipitated and adheres to the inner wall of the polymerization tank to scale. It is considered to be 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 easier it is for aggregation or precipitation, and the easier it is for scale to adhere.
From the above findings, by limiting the amount of the component (B) added before the start of polymerization, the component (B) is prevented from adhering to the inner wall of the polymerization tank, and the temperature of the polymerization mixture using a heat medium of 70 ° C. or higher for the jacket is raised. After the polymerization mixture reaches a predetermined temperature and the jacket is cooled to 65 ° C. or lower, the remaining component (B) is added to reduce scale adhesion, further improve productivity, and provide good fish eyes. It was considered that a vinyl chloride-based polymer having characteristics and excellent molding processability could be obtained.

As a result of various studies, (A) a portion having a degree of polymerization of 65 mol% or more and 90 mol% or less and an average degree of polymerization of 600 or more and 3000 or less, using a vinyl chloride-based monomer as a polymerization initiator and a dispersion stabilizer. Partially saponified in a method of suspend polymerization in an aqueous medium in the presence of sausified polyvinyl alcohol, (B) partially sausible polyvinyl alcohol having a degree of sacrifice of 10 mol% or more and 60 mol% or less and an average degree of polymerization of 100 or more and 1000 or less. The total amount of polyvinyl alcohol (B) added is 0.04 parts by mass or more with respect to 100 parts by mass of the monomer, and the component (B) is 0 with respect to 100 parts by mass of the monomer before the start of polymerization. Add 70 parts by mass or more and 0.03 parts by mass or less, flow a heat medium of 70 ° C. or higher through the jacket attached to the polymerization tank body, and after the mixture reaches a predetermined polymerization temperature, the temperature of the heat medium flowing through the jacket is 65 ° C. We have found a method for producing a vinyl chloride-based polymer, which comprises adding the remaining component (B) within the following and with a polymerization conversion rate of less than 10%.

Next, the present invention will be described in more detail with reference to Examples, but these do not limit the scope of the present invention in any way. The vinyl chloride-based polymers obtained in Examples and Comparative Examples were evaluated by the following methods.

(1) Fish eye
With respect to 100 parts by mass of the obtained vinyl chloride polymer, 1.5 parts by mass of Ca—Zn-based powder composite stabilizer, 0.5 parts by mass of organic phosphorus-based stabilizing aid, 3 parts by mass of ultramarine, and DOP (dioctylphthalate). ) 50 parts by mass was mixed and kneaded in a roll molding machine adjusted to 150 ° C. for 3 minutes, a sheet having a thickness of 0.35 mm was separated, and the number of transparent particles in the ^{sheet 50 cm 2 was evaluated for fish eyes.} Shown as.
(2) Scale adhesion status The scale adhered to the inner wall of the polymerization tank was visually observed and the adhesion status was judged according to the following evaluation criteria.
Evaluation Criteria for Scale Adhesion ○: Almost no scale adhesion △: Slight scale adhesion ×: Significant scale adhesion is observed

(Example 1)
720 kg of deionized water was charged into a stainless steel polymerization tank equipped with a stirrer having an internal volume of 2000 liters, and then 280 g of partially saponified polyvinyl alcohol (component (A)) having a saponification degree of 80 mol% and an average degree of polymerization of 2600 was charged. 110 g (0.02 parts by mass with respect to the vinyl chloride monomer) of water-dispersible partially saponified polyvinyl alcohol (component (B)) having a carboxyl group at the end having a saponification degree of 40 mol% and an average degree of polymerization of 550 was charged. .. Then, it was degassed with a vacuum pump until the pressure inside the polymerization tank reached −87 kPa (pressure gauge gauge pressure). After degassing, 550 kg of vinyl chloride monomer and 135 g of tert-butylperoxyneodecaneate and 165 g of tert-cumylperoxyneodecaneate as a polymerization initiator 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%, 192 g of a partially saponified polyvinyl alcohol (B) component having a characteristic of water dispersibility was added. (0.035 parts by mass with respect to the vinyl chloride monomer). The internal pressure of the polymerization tank was 710 kPa (pressure gauge gauge pressure). Then, when the internal pressure dropped to 620 kPa (pressure gauge pressure), the reaction was stopped, then the unreacted vinyl chloride monomer was recovered, the inside of the system was replaced with nitrogen, and then the vinyl chloride polymer slurry was taken out. It was dehydrated and dried to obtain a polymer.
Table 1 shows the evaluation results of the obtained vinyl chloride polymer, the scale adhesion status, and the temperature rise time.
The obtained vinyl chloride polymer had few fish eyes, and almost no scale was observed on the inner wall of the polymerization tank. In addition, the temperature rising time was short and the productivity was good.

(Example 2)
A polymer was obtained by the same method as in Example 1 except that the temperature of the jacket hot water at the time of raising the temperature was set to 91 ° C.
Table 1 shows the evaluation results of the obtained vinyl chloride polymer, the scale adhesion status, and the temperature rise time.
The obtained vinyl chloride polymer had few fish eyes, and almost no scale was observed on the inner wall of the polymerization tank. In addition, the temperature rising time was short and the productivity was good.

(Example 3)
A polymer was obtained by the same method as in Example 1 except that the temperature of the jacket hot water at the time of raising the temperature was set to 75 ° C.
Table 1 shows the evaluation results of the obtained vinyl chloride polymer, the scale adhesion status, and the temperature rise time.
The obtained vinyl chloride polymer had few fish eyes, and almost no scale was observed on the inner wall of the polymerization tank. In addition, the temperature rising time was short and the productivity was good.

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

(Example 5)
Example 1 except that partially saponified polyvinyl alcohol having no ionic group at the terminal having a saponification degree of 35 mol% and an average degree of polymerization of 300 and having no water dispersibility and water solubility was used as the component (B). A polymer was obtained by the same method.
Table 1 shows the evaluation results of the obtained vinyl chloride polymer, the scale adhesion status, and the temperature rise time.
The obtained vinyl chloride polymer had few fish eyes, and almost no scale was observed on the inner wall of the polymerization tank. In addition, the temperature rising time was short and the productivity was good.

(Example 6)
The polymer was prepared by the same method as in Example 1 except that a partially saponified polyvinyl alcohol having a saponification degree of 40 mol%, a degree of polymerization of 250, no ionic group at the terminal, and a water-soluble characteristic was used as the component (B). Obtained.
Table 1 shows the evaluation results of the obtained vinyl chloride polymer, the scale adhesion status, and the temperature rise time.
The obtained vinyl chloride polymer had few fish eyes, and almost no scale was observed on the inner wall of the polymerization tank. In addition, the temperature rising time was short and the productivity was good.

(Example 7)
As the component (A), 0.04 polymerized part of partially saponified polyvinyl alcohol having a degree of saponification of 80 mol% and 2000 degree of polymerization, and 0.03 polymerized part of partially saponified polyvinyl alcohol having a degree of saponification of 70 mol% and 670 degree of polymerization were used. Obtained a polymer by the same method as in Example 1.
Table 1 shows the evaluation results of the obtained vinyl chloride polymer, the scale adhesion status, and the temperature rise time.
The obtained vinyl chloride polymer had few fish eyes, and almost no scale was observed on the inner wall of the polymerization tank. In addition, the temperature rising time was short and the productivity was good.

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

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

(Comparative Example 4)
A polymer was obtained by the same method as in Comparative Example 2 except that the maximum temperature of the jacket hot water at the time of temperature rise was set to 60 ° C.
Table 1 shows the evaluation results of the obtained vinyl chloride polymer, the scale adhesion status, and the temperature rise time.
The obtained vinyl chloride polymer had good fish eyes, and almost no scale was observed on the inner wall of the polymerization tank, but the temperature rising time was long and the productivity deteriorated.

(Comparative Example 5)
The amount of the component (B) charged before the start of the polymerization was 0.02 parts by mass, and the component (B) was not added after reaching the target polymerization temperature of 51.7 ° C. Other than that, a polymer was obtained by the same method as in Example 1.
Table 1 shows the evaluation results of the obtained vinyl chloride polymer, the scale adhesion status, and the temperature rise time.
The fish eye of the obtained vinyl chloride polymer was significantly deteriorated. Almost no scale was observed on the inner wall of the polymerization tank.

(Comparative Example 6)
The amount of the component (B) charged before the start of polymerization was 0.04 parts by mass, and when the jacket hot water temperature was 45 ° C. and the polymerization conversion rate was 3.2% after reaching the target polymerization temperature of 51.7 ° C., water was used. A polymer was obtained by the same method as in Example 1 except that 64 g (0.015 parts by mass with respect to the vinyl chloride monomer) of the partially saponified polyvinyl alcohol (B) component having a dispersibility characteristic was added.
Table 1 shows the evaluation results of the obtained vinyl chloride polymer, the scale adhesion status, and the temperature rise time.
The fisheye of the obtained vinyl chloride polymer was good, but scale was remarkably adhered to the inner wall of the polymerization tank.

(Comparative Example 7)
After reaching the target polymerization temperature of 51.7 ° C., when the jacket hot water temperature is 39 ° C. and the polymerization conversion rate is 10.4%, 192 g (monovinyl chloride) of the partially saponified polyvinyl alcohol (B) component having a characteristic of water dispersibility is added. A polymer was obtained by the same method as in Example 1 except that 0.035 parts by mass was added to the polymer.
Table 1 shows the evaluation results of the obtained vinyl chloride polymer, the scale adhesion status, and the temperature rise time.
The fisheye of the obtained vinyl chloride polymer deteriorated. Almost no scale was seen 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 is 73 ° C. and the polymerization conversion rate is 0.3%, 192 g (monovinyl chloride) of the partially saponified polyvinyl alcohol (B) component having a characteristic of water dispersibility is added. A polymer was obtained by the same method as in Example 1 except that 0.035 parts by mass was added to the polymer.
Table 1 shows the evaluation results of the obtained vinyl chloride polymer, the scale adhesion status, and the temperature rise time.
The fisheye of the obtained vinyl chloride polymer was good, but scale was remarkably adhered to the inner wall of the polymerization tank.

Claims (7)

Using a polymerization tank, vinyl chloride or a mixture of vinyl chloride and a copolymerizable vinyl chloride (hereinafter referred to as vinyl chloride-based monomer) is used as a polymerization initiator and a dispersion stabilizer. , (A) Partially saponified polyvinyl alcohol with 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, (B) Degree of sacrifice of 10 mol% or more and 60 mol% or less and an average degree of polymerization of 100 In a method for producing a vinyl chloride-based polymer which is suspended-polymerized in an aqueous medium in the presence of 1000 or less partially saponified polyvinyl alcohol.
The total amount of the component (B) added is 0.04 parts by mass or more with respect to 100 parts by mass of the vinyl chloride monomer.
Before starting the polymerization, the component (B) is added in an amount of 0 part by mass or more and 0.03 part by mass or less with respect to 100 parts by mass of the vinyl chloride monomer, and a heat medium at 70 ° C. or higher is added to the jacket attached to the polymerization tank body. After the vinyl chloride-based mixture reaches a predetermined polymerization temperature, the remaining component (B) is added while the temperature of the heat medium flowing through the jacket is 65 ° C. or lower and the polymerization conversion rate is less than 10%. A method for producing a vinyl chloride-based polymer. 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-based polymer according to claim 1 or 2, wherein the component (B) has a saponification degree 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-based polymer according to claim 1 or 2, wherein the component (B) has a saponification degree 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 the 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-based polymer according to claim 1, wherein a heat medium having a temperature of 80 ° C. or higher is passed through a jacket attached to the main body of the polymerization tank.