JP3414026B2 - Method for producing vinyl chloride polymer - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a suspension of vinyl chloride or a mixture of vinyl chloride-based copolymerizable monomers (hereinafter, collectively referred to as “vinyl chloride-based monomer”) in an aqueous medium. The present invention relates to a method for producing a vinyl chloride polymer by carrying out suspension polymerization. Specifically, it relates to a method for producing a vinyl chloride polymer having a high bulk density and good product quality.

[0002]

2. Description of the Related Art Generally, the molding processability of a vinyl chloride resin made of a vinyl chloride polymer strongly depends on the properties of particles constituting the vinyl chloride resin. In particular, increasing the bulk density is
Not only is the volume and area required for transporting and storing the resin small and efficient, but the discharge rate at the time of extrusion molding increases and the throughput per unit time increases, improving productivity. Is important in that it does.

In order to increase the bulk density, conventionally, partially saponified polyvinyl acetate having a specific degree of saponification and degree of polymerization is used in combination at a specific ratio as a dispersant, or vinyl chloride is used during the polymerization reaction. A method of additionally charging a system monomer (JP-A-61-195101, JP-A-59-
No. 168008) has been proposed.

[0004]

However, the method of using a specific dispersant is insufficient in the effect of improving the bulk density, while the conventional method of additionally charging a vinyl chloride-based monomer has been obtained. During the processing of the polymer, particles that are difficult to melt called fish eyes (hereinafter sometimes abbreviated as "FE") are likely to be generated, and as a result, the surface condition of the final product such as a film or a molded product may be impaired. There were many.

Fish eyes can be reduced by prolonging the kneading time, but the polymer deteriorates due to heat and shearing force.
There is a problem that it may decompose, and it takes a long time for processing to lower the productivity. Therefore, a vinyl chloride-based resin that can sufficiently reduce fish eyes by kneading for a short time is desired.

Further, the method of additionally charging a vinyl chloride monomer makes it difficult to remove the vinyl chloride monomer remaining in the polymer particles (hereinafter abbreviated as "residual VCM"). If the vinyl chloride monomer is processed while being occluded in the polymer particles, it may be released into the environment during processing, but the vinyl chloride monomer has hygiene problems such as carcinogenicity. Therefore, preventing this release is extremely important. However, the conventional method of reducing the residual VCM is to increase the surface area by making the generated resin particles porous so as to increase the surface area, thereby promoting the migration of the vinyl chloride monomer to the outside of the particles, which tends to lower the bulk density. On the other hand, in the method of treating the produced polymer under reduced pressure at high temperature for a long time, the productivity may be lowered or the resulting polymer may be subjected to excessive heat history, which may deteriorate the product quality. A compatibility between a high bulk density and a low residual VCM concentration of 10 ppm or less has not been achieved so far.

[0007]

DISCLOSURE OF THE INVENTION The inventors of the present invention have conducted intensive studies in view of the above-mentioned problems of the prior art, and as a result, carry out additional charging of vinyl chloride-based monomer so as to satisfy specific conditions. It has been found that the high bulk density and the low residual VCM concentration are compatible with each other, and the present invention has been completed.

That is, the gist of the present invention is to disperse vinyl chloride or a mixture of vinyl chloride-based copolymerizable monomers (hereinafter collectively referred to as “vinyl chloride-based monomer”) as a dispersant and an oil-soluble polymer. When a vinyl chloride polymer is produced by suspension polymerization in an aqueous medium in the presence of an initiator, additional charging of a vinyl chloride monomer is started while the polymerization conversion rate is 30% by weight to 60% by weight. Then, the weight of the vinyl chloride monomer charged before the start of the polymerization is W ₁ (kg), and the vinyl chloride monomer is additionally charged. Where W ₂ (kg) is the total weight and t (hours) is the time required for additional charging, the following relation is established between them: . .

[0009]

## EQU00003 ## 0.02W ₁ ≤W ₂ ≤0.3W ₁ (k
g)

[0010]

[Equation 4] W ₂ /t≦0.2 W ₁ (k
g / h)

The present invention will be described in detail below. The polymerization method of the vinyl chloride monomer to which the method of the present invention is applied is a suspension polymerization method carried out in an aqueous medium using a dispersant and an oil-soluble polymerization initiator.

The vinyl chloride type monomer used in the method of the present invention includes vinyl chloride monomer alone and a mixture of copolymerizable monomers mainly composed of vinyl chloride monomer. As the other monomer copolymerizable with the vinyl chloride monomer, those generally used in the related art can be used and are not particularly limited. As the other monomer above,
For example, vinyl acetates such as vinyl acetate, vinyl propionate and vinyl stearate, methyl vinyl ether, ethyl vinyl ether, octyl vinyl ether,
Alkyl vinyl ethers such as lauryl vinyl ether and cetyl vinyl ether, α such as ethylene and propylene
-Olefins, acrylic acid, monounsaturated acids such as methacrylic acid, alkyl esters such as methyl esters of these monounsaturated acids, divalent unsaturated acids such as maleic acid, fumaric acid, itaconic acid, Examples thereof include alkyl esters of these diunsaturated acids, vinylidene compounds such as vinylidene chloride, unsaturated nitriles such as acrylonitrile, and mixtures of two or more thereof. These other monomers are used in a proportion of usually 30% by weight or less, preferably 20% by weight or less, with respect to the vinyl chloride monomer, but there is no particular limitation.

The dispersant used in the method of the present invention is
The suspension polymerization method of a vinyl chloride-based monomer may be one conventionally used and is not particularly limited. Examples of the dispersant include partially saponified polyvinyl acetate (so-called polyvinyl alcohol), cellulose derivatives such as hydroxypropylmethyl cellulose, and water-soluble polymers such as gelatin. In addition, anionic surfactants such as sodium lauryl sulfate and nonionic surfactants such as sorbitan fatty acid esters and glycerin fatty acid esters may be used as a dispersion aid. These dispersants or dispersion aids can be used alone or in combination of two or more. The amount of these dispersants used is not particularly limited, and the type, stirring strength, polymerization temperature, type and composition of other monomers to be copolymerized with the vinyl chloride monomer, and the vinyl chloride-based weight to be produced. Although it varies somewhat depending on the particle size of the coalesced particles and the like, it is generally 0.001 to 2% by weight, preferably 0.1% to the total amount of vinyl chloride-based monomers.
It is used within the range of 03 to 1% by weight.

The oil-soluble polymerization initiator used in the method of the present invention may be one generally used in the suspension polymerization method of vinyl chloride type monomers, and is not particularly limited. For example, t-
Butyl peroxypivalate, t-butyl peroxy neodecanoate, t-hexyl peroxypivalate,
Perester compounds such as t-hexyl peroxy neodecanoate and α-cumyl peroxy neodecanoate, diacyl peroxide compounds such as dilauroyl peroxide, percarbonates such as diisopropyl peroxy dicarbonate and di-2-ethylhexyl peroxy dicarbonate Compounds, azo compounds such as azobis (2,4-dimethylvaleronitrile), azobisisobutyronitrile and the like can be used. These polymerization initiators can be used alone or in combination of two or more. Although the amount of the polymerization initiator used varies depending on the type of the initiator, the polymerization temperature, the desired reaction time, etc., it is generally in the range of 0.01 to 1% by weight based on the total amount of the vinyl chloride monomer.

Further, in the method of the present invention, a polymerization degree adjusting agent (chain transfer agent, cross-linking agent), an antioxidant, a pH adjusting agent, a redox starting agent used for the polymerization of vinyl chloride-based monomers, if necessary. Various polymerization aids such as an activator of the agent can be appropriately added. The charging method and the charging amount of each of these components may be the general conditions conventionally used for the polymerization of vinyl chloride-based monomers.

As the degree-of-polymerization regulator used for the polymerization of vinyl chloride-based monomers, trichlorethylene, carbon tetrachloride, chain transfer agents such as 2-methylcaptoethanol, octyl mercaptan, diallyl phthalate and isocyanuric acid. Triallyl, ethylene glycol diacrylate,
Examples of the crosslinking agent include trimethylolpropane trimethacrylate.

The additional charging of the vinyl chloride-based monomer, which is a feature of the method of the present invention, has a polymerization conversion rate (hereinafter sometimes simply referred to as "conversion rate") of 30% by weight to 60 at the start of charging. % By weight, and the conversion is 55% to 80% by weight when the charging is completed. If the conversion rate at the start and end of the additional charging is too low, the increase in bulk density will be insufficient, and if it is too late, the fish eye will deteriorate and the residual VCM concentration will tend to increase.

The term "polymerization conversion rate" as used herein means a value (percentage) obtained by dividing the weight of the polymer formed by a certain time by the weight of the charged monomers up to that time. Therefore, the weight of the monomer charged additionally is included in the weight of the monomer charged during the additional charging or at the end of the additional charging. In addition, the weight W ₂ (kg) of the monomer charged additionally, the weight W ₁ (kg) of the monomer charged before the start of the polymerization, and the time t (hour) required for the additional charge
The following relational expression must be satisfied during the period.

[0019]

## EQU00005 ## 0.02W ₁ ≤W ₂ ≤0.3W ₁ (k
g)

[0020]

[Equation 6] W ₂ /t≦0.2 W ₁ (k
g / h)

That is, W ₂ must be in the range of 2% by weight to 30% by weight of W ₁ , and the additional charging rate of the monomer is 20% of that of the initial charging monomer (W ₁ ). weight%
This means that the speed of charging in 1 hour is not exceeded. When these relationships are satisfied, a vinyl chloride-based polymer having a high bulk density and low fish eyes and residual VCM can be obtained.

When W ₂ is less than 0.02 W ₁ , the bulk density is low, and when it exceeds 0.3 W ₁ , fish eyes tend to increase, and the additional charging rate (kg / h) of the monomer is 0.2 W / hr. Fisheye when it grows larger than ₁ ,
Both the residual VCM concentration tends to increase.

The polymerization conversion rate at a certain point can be estimated from a time-conversion rate curve obtained by collecting a slurry during the reaction at a predetermined time in a separately conducted reaction, or during the reaction from the polymerization can during the test. It can be determined by a method of collecting and calculating the slurry (all are calculated from the total weight of the charged material, the amount of the collected slurry, and the amount of the polymer in the collected slurry).

The polymerization temperature adopted in the method of the present invention varies depending on the kind of the polymerization initiator used, the polymerization method, the presence or absence of the polymerization degree adjusting agent, the target degree of polymerization and the like, but it is generally 0 to 90 ° C. In particular, the range of 40 to 70 ° C. is often used. In the reaction, the polymerization may be carried out at a constant temperature or the polymerization temperature may be changed during the polymerization.

In particular, the reaction is carried out while increasing the polymerization temperature with the reaction time over 50% or more of the entire polymerization reaction period, and the polymerization temperature is controlled so that the temperature change range is in the range of 2 to 35 ° C. By controlling, the bulk density can be further increased, which is preferable. In this case, the polymerization reaction period means that a raw material such as vinyl chloride-based monomer is charged into a polymerization vessel, heated and heated to reach a predetermined polymerization temperature, and the internal pressure of the polymerization vessel is vinyl chloride at that temperature. It refers to the period from the saturation pressure of the system monomer to the time when it falls by ² kg / cm ² .

When the polymerization temperature is increased with the progress of the reaction by the above-mentioned method, the temperature rising start temperature, the temperature ending temperature and the temperature rising rate (hereinafter collectively referred to as "temperature rising pattern") are as follows: It is determined according to the target degree of polymerization of the vinyl chloride-based polymer produced by the reaction.For example, it may be selected such that the amount of the polymer formed is the same before and after reaching the temperature corresponding to the target degree of polymerization. Good.

The reaction rate is the same throughout the entire polymerization period regardless of the polymerization temperature, that is, the amount of polymer produced per hour is constant over the entire reaction period, and the degree of polymerization of the produced polymer is proportional to the polymerization temperature. Considering the case of, the temperature rising pattern can be determined as follows. Vertical axis (y
On a graph with temperature on the axis and time on the horizontal axis,
Let f (x) be a function that represents the change in the polymerization temperature with time,
The temperature that gives the target degree of polymerization (P) is T (° C), f
The time when (x) = T is M, and the time when the reaction is started is M
a, when the time when the reaction is completed is Mb, the weight average degree of polymerization of all the polymers produced in this reaction is P, in order to obtain the amount of the polymer produced from the start of the reaction (Ma) to M. The amount of polymer produced from M to the end of the reaction (Mb) may be the same. That is, the section [Ma,
M], the integrated value of the function u (x) = T−f (x),
Function v (x) = f (x) -T in the interval [M, Mb]
It is only necessary that the integral values of are equal. Therefore, whether or not the polymerization carried out according to a certain heating pattern can give a polymer having a target degree of polymerization depends on a curve or a straight line of the heating pattern on the graph and a straight line in the case of a constant temperature reaction and at the start of the reaction and at the end of the reaction. The determination can be made by obtaining the area of the figure enclosed by the straight line indicating the time.

In practice, however, the rate of the polymerization reaction often changes depending on the temperature and the type of the initiator, and the degree of polymerization measured by the commonly used viscosity method is not always directly proportional to the "weight average value" of the produced polymer. Because it does not
In determining the temperature rise pattern, it is often necessary to confirm and correct it by experiments, but basically it is possible to organize it according to the above concept.

The range of change in the polymerization temperature is preferably in the range of 2 to 35 ° C, more preferably in the range of 15 to 25 ° C. If the change width is less than 2 ° C, the effect of improving the bulk density by adopting this method is not so great.
In the case of a change width of more than 5 ° C., since a polymerization initiator (or a combination thereof) that can cope with such a wide reaction temperature range has not been found, the controllability of the reaction often deteriorates, In addition, since the polymerization temperature generally increases at the end of the temperature rise, the internal pressure of the can also increases, and a polymerization can with high pressure resistance is required, resulting in increased equipment costs.

The period during which the reaction is carried out while raising the polymerization temperature with the reaction time is preferably 50% or more of the entire polymerization reaction period. If this period is less than 50%, it tends to be difficult to remove the unreacted vinyl chloride monomer from the produced polymer.

An aqueous medium to the polymerization vessel in the method of the present invention,
Regarding the method of charging the dispersant, the polymerization initiator and various polymerization aids, the method usually used in the suspension polymerization method of vinyl chloride-based monomers may be used, and the method is not particularly limited. Also, as a method of stopping the polymerization, a method of adding a so-called polymerization inhibitor or a polymerization terminator, a method of collecting unreacted monomer from a polymerization vessel, or the like can be used.

In order to remove the unreacted vinyl chloride monomer from the vinyl chloride polymer, for example, the slurry is passed under reduced pressure through a plate distillation column, or steam is blown into the slurry under reduced pressure. And adjusting the processing conditions (temperature, residence time, etc.) in the fluidized dryer,
The method usually used for removing the residual vinyl chloride monomer can be used without particular limitation. The operations such as dehydration / drying of the resulting vinyl chloride polymer slurry include dehydration / drying such as generally performed centrifugal dehydration / fluid drying.
Drying means may be used without any particular limitation.

The shape of the stirring blades, baffles, etc., which are the auxiliary equipment of the polymerization can used in the method of the present invention, is not particularly limited, and the equipment and equipment generally used in the suspension polymerization method are used. can do.

In addition to the method of additionally charging the vinyl chloride monomer in the above-mentioned specific amount and condition during the polymerization reaction, the polymerization temperature is increased with the reaction time over 50% or more of the entire polymerization reaction period. By carrying out the reaction and controlling the polymerization temperature so that the range of temperature change is within the range of 2 to 35 ° C., a high bulk density and a low residual VCM which have hitherto not been achieved can be obtained. It became possible to achieve both concentration.

As a result, a vinyl chloride polymer having a bulk density of 0.59 g / ml or more and 0.69 g / ml, preferably 0.67 g / ml or less and a residual VCM concentration of 10 ppm or less can be obtained.

Generally, the higher the bulk density is, the more convenient it is. However, when the bulk density is higher than 0.69 g / ml, the removal rate of residual vinyl chloride monomer is decreased, and the target residual VC is increased.
It becomes difficult to achieve the M level. In addition, the plasticizer absorption rate during processing is also reduced, which requires a long time for processing. The upper limit of the bulk density is preferably 0.67 g / ml or less from the viewpoint of maintaining workability.

The lower the residual VCM concentration, the better, but 1
If it is 0 ppm or less, the load on the environment is considered to be small. Here, the bulk density is a value measured according to the method specified in JIS K 6721, and the residual VCM concentration can be measured by a gas chromatographic analysis method using a tetrahydrofuran solution of a vinyl chloride polymer.

[0038]

EXAMPLES Next, specific embodiments of the method of the present invention will be described with reference to examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. The vinyl chloride polymer obtained was evaluated by the following methods.

<Evaluation Method> Bulk Density It was measured according to the method specified in JIS K6721. Fisheye (FE) 100 parts by weight of a vinyl chloride polymer, 50 parts by weight of a plasticizer (Diaysizer (registered trademark) DOP, manufactured by Mitsubishi Chemical Co., Ltd.), and 3 parts by weight of tribasic lead sulfate are added to the vinyl chloride system. 100 g of the combined product is weighed out, pre-mixed in a beaker and kneaded using a mill roll at 155 ° C., and kneading times are 3, 4, 5, and 7 minutes, respectively, and a thickness of 0.4 mm
I made a roll sheet of. The number of fish eyes found in a square of 5 cm on each side (area: 25 cm ² ) of the obtained roll sheet was counted and expressed as the number of FE.

Porosity A mercury porosimetry porosimeter (manufactured by Shimadzu Corporation, Micromeritics Poisizer Model 9310) was used to measure the pore volume of the pore size 75 to 7500Å, and dried resin 1
It is shown as a value per gram (cc / g).

Residual VCM Concentration About 0.5 g of a vinyl chloride polymer after drying was precisely weighed and 10
Tetrahydrofuran (THF) in a ml volumetric flask
Dissolve in. After constant volume, 5 μl of this solution was sampled with a microsyringe, and gas chromatograph (GC-7A manufactured by Shimadzu Corporation, column packing material 20% Ucon oil) was used.
LB550 / chromosolve W), and the peak area of vinyl chloride monomer on the obtained gas chromatogram is
The content of vinyl chloride monomer is calculated by collating with the calibration curve prepared separately using vinyl chloride monomer standard solution, and the residual vinyl chloride monomer weight per unit weight of dry polymer is ppm Displayed in units.

<Examples 1 to 4, Comparative Examples 2 to 5> Internal volume 4
A stainless steel polymerization can equipped with a 00 liter stirrer and a jacket was charged with 150 kg of deionized water and deaerated, and then 60 g of partially saponified polyvinyl acetate, 100 kg of initially charged vinyl chloride monomer, and a predetermined type shown in the table. -The amount of polymerization initiator was charged. Hot water was circulated through the jacket of the polymerization vessel to raise the temperature to 57 ° C. to start the polymerization.

After the initiation of the reaction, at a predetermined polymerization conversion rate,
Additional charging of vinyl chloride monomer was carried out at the addition rates and amounts shown in the table. The reaction was stopped by collecting the unreacted monomer out of the system when the reaction was completed when the internal pressure of the polymerization vessel dropped by ² kg / cm ² from the saturated vapor pressure of the vinyl chloride monomer at 57 ° C.

After the internal pressure of the polymerization vessel became equal to the atmospheric pressure, the internal temperature of the polymerization vessel was kept at 80 ° C. and vacuum suction was performed (at the steam pressure at 80 ° C.) to remove the residual vinyl chloride monomer. It was The vinyl chloride polymer slurry collected at the treatment times of 15, 30, and 120 minutes was spin-dried and then dried, and the residual VCM concentration of the obtained polymer was measured by the above method. Further, the bulk density and FE of the sample having a processing time of 120 minutes were evaluated by the above-mentioned methods.

The results are summarized in the table. The abbreviations of the polymerization initiators in the table have the following meanings.

[0046]

[Table 1] SEC: di-secondary butyl peroxydicarbonate HPV: tert-hexyl peroxypivalate CND: α-cumyl peroxy neodecanoate OPP: di-2-ethylhexyl peroxydicarbonate

<Comparative Example 1> Polymerization and residual vinyl chloride monomer removal treatment were carried out in the same manner as in Example 1 except that the vinyl chloride monomer was not added after the start of the reaction to give a vinyl chloride polymer. Obtained and evaluated. The results are shown in the table.

<Examples 5 and 6, Comparative Examples 8 to 12> Polymerization and additional vinyl chloride monomer were added in the same manner as in Example 1, and the polymerization reaction was started for 1 hour. After the lapse of time, the polymerization reaction was carried out while raising the reaction temperature at a constant rate under the conditions shown in the table.

In Comparative Example 10, the heat generation was remarkably increased, and the polymerization initiator was rapidly decomposed during the temperature rise, and remarkable heat generation was observed. However, from the end of the temperature rise, the polymerization initiator became insufficient and the reaction became slow, and the reaction time greatly exceeded the desired time.

Determination of end of reaction and removal of residual VCM,
Evaluation of the produced polymer was carried out in the same manner as in Example 1. The results are also shown in the table.

<Comparative Examples 6 and 7> Polymerization and residual vinyl chloride monomer removal treatment were carried out in the same manner as in Example 5 except that the vinyl chloride monomer was not added. An evaluation was made. The results are also shown in the table.

[0052]

[Table 2]

<Evaluation of Results> (1) When polymerization is carried out at a constant reaction temperature (Examples 1 to 4), the following tendencies can be read. Presence of additional charging of vinyl chloride monomer: Compared to Comparative Example 1, it is found that the bulk density is increased by the method of the present invention. Conversion rate during additional charging: When the charging time is too early (Comparative Example 2), the bulk density does not increase and FE also deteriorates. If it is too late (Comparative Example 3), the FE tends to deteriorate.

Amount of additional charging: When the amount of vinyl chloride monomer to be additionally charged is too large (Comparative Example 4), the residual VCM concentration tends to increase and the FE is also inferior. Additional charging rate: When the additional charging rate of the vinyl chloride monomer is too high (Comparative Example 5), FE increases.

(2) In the method of keeping the reaction temperature constant (Examples 1 to 4) and the method of raising the temperature during the reaction (Examples 5 and 6), the method of raising the temperature during the reaction is more bulk density. Although it is possible to obtain a high polymer, the FE and residual VCM concentrations tend to increase slightly although they are within the practically acceptable range.

(3) When polymerization is carried out while raising the reaction temperature during the reaction (Examples 5 and 6), the following tendencies occur. (Comparison with the constant temperature reaction is as described above) Presence of additional charging of vinyl chloride monomer: When additional charging is not performed (Comparative Example 7), the effect of improving bulk density is small.

Conversion rate during additional charging: When charging is started too early (Comparative Example 11), the bulk density does not increase, and the FE and residual VCM concentrations are inferior. If it is too slow (Comparative Example 12, but the additional charging speed is too high in this case), the FE and residual VCM concentrations are significantly deteriorated. Additional charging rate: When the additional charging rate of the vinyl chloride monomer is higher than the preferable range (Comparative Examples 8 to 10), the FE and residual VCM concentrations are deteriorated.

[0058]

EFFECT OF THE INVENTION By using the method of the present invention, it is possible to produce a vinyl chloride polymer having a high bulk specific gravity, less fish eyes, and a residual VCM concentration of 10 ppm or less, which is excellent in quality. . In particular, the residual VCM concentration can be maintained while maintaining the fisheye level, which is practically unproblematic, by using the method in which the reaction is performed while raising the polymerization temperature by a specific temperature range with the reaction time during the polymerization reaction period. Of 10 ppm or less, a bulk density of 0.59 to 0.69 g / ml, which is extremely high, can be produced.

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Claims (2)

(57) [Claims] 1. A vinyl chloride or a mixture of vinyl chloride-based copolymerizable monomers (hereinafter collectively referred to as “vinyl chloride-based monomer”) in the presence of a dispersant and an oil-soluble polymerization initiator. When producing a vinyl chloride polymer by suspension polymerization in an aqueous medium, additional charging of a vinyl chloride monomer is started at a polymerization conversion rate of 30% by weight to 60% by weight and 55% by weight. To 80% by weight, the weight of the vinyl chloride-based monomer charged before the start of the polymerization is W ₁ (kg), and the total weight of the vinyl chloride-based monomer additionally charged is W. ₂ (kg), when the time required for additional charging is t (hours), the following relationship is established between them, and a method for producing a vinyl chloride polymer. [Equation 1] 0.02 W ₁ ≤ W ₂ ≤ 0.3 W ₁ (kg) [Equation 2] W ₂ / t ≤ 0.2 W ₁ (kg / h) 2. The method according to claim 1, wherein the reaction is carried out while increasing the polymerization temperature with the reaction time over 50% or more of the entire polymerization reaction period, and the temperature change range is in the range of 2 to 35 ° C. 1. A method for producing a vinyl chloride polymer according to claim 1.