WO2014098360A1 - Method for preparing vinyl chloride-based resin by using suspension polymerization - Google Patents

Abstract

The present invention relates to a method for preparing a vinyl-based polymer and a vinyl-based copolymer including a vinyl chloride-based material through suspension polymerization in which the generation of foam is prevented while maintaining the pressure by slowly increasing the reaction temperature when the pressure starts to drop at a reaction terminal stage. In the method for preparing a vinyl-based resin, a vinyl chloride-based monomer is suspension polymerized to reduce the generation of foam and improve the quality of protrusions, thermal stability and the like.

Description

Method for preparing vinyl chloride resin using suspension polymerization

The present invention relates to a method for producing a vinyl chloride-based resin, and more particularly, by gradually increasing the polymerization temperature by a predetermined temperature per minute at the time of the pressure drop in the second half of the reaction during the production of the vinyl chloride-based resin to prevent pressure drop and foam generation. It relates to a method for producing a vinyl chloride-based resin to improve the quality of the projections and to improve the quality by solving the thermal stability of the residual initiator.

Vinyl chloride-based resins are inexpensive and have excellent processability, chemical resistance, durability, insulation properties, and are widely used as hard and soft materials such as pipes, wallpaper, window frames, wire coatings, wrap films, and sheets. However, as vinyl chloride-based resins are widely used, customer's eye level on molding processing has been increased, and improvement of molding processability is continuously required.

In general, the processability of the vinyl chloride-based resin is affected by the internal porosity, particle diameter, particle distribution, and morphology of the particles and is intended to increase the meltability of the resin. One of the quality criteria for evaluating the melting characteristics of these resins is called protrusions or fish-eyes, which can confirm the difference in the degree of melting and the quality of the final product.

The difference in the meltability of the particles is suspected as a cause of the deterioration of the protrusion quality, and the production of such unmelted particles may be associated with the foam generated during the reaction. In detail, foam is generated by crossing the high usage and pressure drop of the reflux condenser at the end of the reaction, and the dry foam containing the particles floats to the top of the reactor and to the reflux condenser. However, due to the difficulty of sufficient cleaning in each batch, the particles floated by the foam remain inside the reactor and the reflux condenser, and are subjected to repolymerization as they are included in the next reaction to generate large, low internal porosity particles. The production of particles of low meltability deteriorates the projection quality.

As a conventional technique for solving such a problem, as can be seen in US Patent No. 5,087,678 and Japanese Patent Application Laid-Open No. 2007-284510, a method for inhibiting foam generation during a reaction may be used alone or by using an antifoaming agent with other additives. Methods have been used to suppress the occurrence of foam by mixing. However, it is difficult to suppress the occurrence of dry foam by using antifoaming agent alone.In order to add antifoaming agents and additives during the reaction, there are economic problems such as investment in equipment and the price of the amount of antifoaming agent and additives added. There is a problem of deterioration.

An object of the present invention is to solve the problems of the prior art, the present invention is to increase the polymerization temperature by a predetermined temperature per minute from the reference temperature at the time when the pressure drop occurs at the end of the reaction to prevent the pressure drop and foam generation repolymerization And scale generation.

In addition, the present invention induces decomposition of the initiator by the elevated temperature to lower the content of the initiator remaining after the end of the reaction to produce a vinyl chloride-based resin with less projections and excellent thermal stability, so the problem of scale generation of the existing method An object of the present invention is to provide a method for producing a resin without quality problems due to protrusions and thermal stability.

The above and other objects of the present invention can be achieved by the present invention described below.

In order to achieve the object of the present invention, the present invention is a method for producing a vinyl chloride resin by suspension polymerization, the polymerization temperature of the vinyl chloride resin, characterized in that to increase the temperature from the time point at which the pressure is reduced at the end of the reaction It provides a manufacturing method.

In addition, the present invention after the start of the suspension polymerization reaction from the time when the reaction pressure is lowered more than 0.01 kgf / cm ² to less than 0.5 kgf / cm ² , at a temperature rising rate of more than 0.008 ℃ / min to less than 0.8 ℃ / min, more than 10 minutes It provides a method for producing a vinyl chloride-based resin, characterized in that to increase the temperature for less than 90 minutes.

The decreasing reaction pressure is characterized in that more than 0.01 kgf / cm ² to less than 0.2 kgf / cm ² as an example.

The temperature increase rate is, for example, characterized in that more than 0.008 ℃ / min less than 0.65 ℃ / min.

The temperature increase rate is characterized by adjusting the temperature control system as an example.

The reaction temperature of the polymerization is characterized in that within 30 to 80 ℃ range, for example.

The temperature increase time is, for example, characterized in that 30 to 60 minutes.

In another aspect, the present invention provides a vinyl chloride-based resin prepared by the method for producing a vinyl chloride-based resin.

The vinyl chloride-based resin, for example, is characterized in that the residual initiator concentration is less than 0.002 parts by weight based on 100 parts by weight of the vinyl chloride-based resin.

In another aspect, the present invention provides a vinyl chloride-based resin composition comprising the vinyl chloride-based resin, inorganic filler and stabilizer.

The inorganic filler is characterized in that the carbon black as an example.

The vinyl chloride-based resin composition is characterized in that the number of fish-eyes (thickness 0.3 mm, area 400 cm ² ) is less than 10.

In addition, the present invention is a vinyl chloride system, characterized in that the temperature rises for 20 to 60 minutes at a temperature increase rate of 0.01 to 0.5 ℃ / min from the time when the reaction pressure is lowered from 0.05 to 0.1 kgf / cm ² after starting the suspension polymerization reaction It provides a method for producing a resin.

As described above, according to the method of the present invention, in the step of preparing the vinyl chloride-based resin by suspension polymerization, it is possible to control the temperature increase rate for each polymerization temperature and to prevent the pressure drop at the end of the reaction, thereby increasing the reflux condenser. It has the advantage of suppressing the foam generation appearing while overlapping the heat removal point. In addition, it is possible to solve the problem of protrusion quality and thermal stability due to the conventional scale problem and repolymerization problem.

In the present invention, in order to solve the disadvantages of the prior art, by raising the temperature gradually at the time of the end of the pressure drop occurs to prevent the pressure drop, the possibility of foam that can occur at the time of the intersection of the high amount of reflux condenser and the pressure drop It provides a method for producing a resin that is removed, and induces decomposition of the initiator remaining at the end of the reaction to improve the quality after the reaction.

In the present invention, foam does not occur after the reaction to prevent the inflow of particles that can be repolymerized in the next reaction, and the residual initiator is not left so that the thermal stability is simultaneously improved, thereby improving quality.

According to the present invention, in the method for producing a vinyl chloride-based resin by suspension polymerization while adding different polymerization temperatures and different polymerization initiators according to the degree of polymerization, in order to minimize the generation of foam generated during the reaction and to minimize the content of the residual initiator It provides a method of producing a vinyl chloride-based resin, characterized in that the polymerization temperature is raised by a predetermined temperature per minute to prevent the pressure drop appearing at the end of the reaction to control the generation of foam.

Hereinafter, the present invention will be described in more detail.

In the present invention, the amount of defrosting by the reflux condenser is increased at the end of the reaction of the prior art and the polymerization conversion rate is increased, and a dry foam containing particles is generated at the end of the pressure drop at the end of the reaction. It is a technical feature to provide a new method for producing a vinyl chloride-based resin that can overcome the problems of quality improvement by solving the problem that repolymerization occurs, and solve the high level of residual initiator.

In order to achieve the above technical features, at the end of the reaction at the time when the pressure is lowered by gradually raising the reaction temperature by more than 0.008 ℃ to less than 0.8 ℃ per minute to control the pressure drop occurs while not exceeding the defined defrost limit in the reactor by By preventing foam generation due to pressure change, the meltability of the final resin obtained can be improved. Preferably it can raise a temperature below 0.01 degreeC-0.65 degreeC or 0.02 degreeC-0.65 degreeC, More preferably, 0.05 degreeC-0.6 degreeC. When the temperature increase rate is adjusted beyond the temperature range per minute at the time when the pressure is lowered at the end of the reaction, the temperature is rapidly increased, which adversely affects the quality while disturbing the pressure and the stability of the reaction. On the other hand, if the temperature increase rate is lower than the above temperature range, the temperature rise becomes slow and the pressure drop cannot be prevented, so that the problems of the prior art appear in the same manner.

The present invention the time for raising the temperature at the time of pressure decrease caused the reaction end is described in the time shown is about 0.01kgf / cm ² to less than 0.5kgf / cm ² the pressure drop. Preferably, the temperature is increased at a pressure drop time of 0.05 to less than 0.2 kgf / cm ² . If the temperature is raised before the pressure drop in the above range, a pressure change may occur to the elevated temperature, resulting in unstable quality problems, and if the temperature is increased after the pressure drop exceeds the above range, the heat removal amount and the pressure drop of the reflux condenser are Since foam containing particles is generated, this causes protrusions and internal scales of the reactor, which adversely affects it.

The polymerization temperature is generally determined by the degree of polymerization of the resin, and the temperature generally applied is 55 to 60 ° C. for the number average degree of polymerization of 1000 products, 61 to 65 ° C. for the number average degree of polymerization of 800 products and 700 number average degree of polymerization of the products. In the case of it is determined in the range of 66 to 70 ℃.

It is preferable that the polymerization temperature in this invention satisfy | fills the range of 30-80 degreeC. More preferred polymerization reference temperatures are within the range from 40 to 70 ° C, even more preferably from 50 to 65 ° C.

The degree of polymerization refers to the number of repeated units, ie units or monomers, constituting the polymer, and the number average degree of polymerization is used in the present invention.

Since the reaction pressure also varies depending on the polymerization temperature, the degree to which the pressure falls is also different. Accordingly, it is possible to control the temperature increase rate according to the difference in the pressure decreases at the end of the reaction according to the polymerization temperature, so that the reaction stability does not have a burden on the reaction stability.

In addition, the pressure drop occurs to increase the temperature at the existing polymerization temperature for 30 minutes to 60 minutes, preferably 30 minutes to 50 minutes, even more preferably 30 minutes to 40 minutes after the pressure drop occurs.

This does not significantly affect the overall polymerization time and is to proceed until the end of the reaction. If the temperature increase time is too short, the pressure drop may occur rapidly after the temperature stops, and the possibility of foam generation may increase, thereby causing protrusion and scale in the reactor. In addition, if the time to increase the temperature too long may affect the internal morphology of the particles, the polymerization time is too long has the disadvantage that the output per unit time decreases. Additionally, as the polymerization temperature is raised, the maximum temperature range for raising the temperature does not deviate from the above-mentioned polymerization temperature range of 30 ° C to 80 ° C.

Suitable initiators in the above polymerizations are as follows.

α, α'-bis (neotecanoyl peroxy) diisopropyl benzene, cumene peroxyneodecanoate, di-n-propyl peroxy dicarbonate, diisopropyl peroxy dicarbonate, 1,1,3 , 3-tetramethylbutyl peroxy neodecanoate, bis (4-t-butylcyclohexyl) peroxy dicarbonate, 1-cyclohexyl-1-methylethyl peroxy neodecanoate, di-2-ethoxy Ethyl peroxy dicarbonate, di-2-ethylhexyl peroxy dicarbonate, t-hexyl peroxy neodecanoate, dimethoxybutyl peroxy dicarbonate, bis (3-methyl-3-methoxybutyl) peroxy di Peroxides such as carbonate, t-butyl peroxy neodecanoate, t-hexyl peroxy pivalate, 2,2'-azobis (2,4-dimethylvaleronitrile), 2,2'-azobis (Isobutyronitrile), one or more selected from azo compounds such as dimethyl 2.2'-azobis (isobutyrate) may be used. I, and the like.

The amount of the polymerization initiator to be injected into the reactor is characterized in that the same amount as the polymerization initiator used in the conventional polymerization, it is characterized in that 0.02 to 0.3 parts by weight, or 0.03 to 0.2 parts by weight based on 100 parts by weight of the vinyl chloride monomer As another example, use of 0.04 to 0.15 parts by weight is appropriate.

The present invention provides a vinyl chloride-based resin, characterized in that it is prepared by the method for producing a vinyl chloride-based resin as described above.

The vinyl chloride-based resin has a residual initiator concentration of less than 0.002 parts by weight, or 0.0005 to 0.0015 parts by weight, more preferably 0.0006 to 0.001 parts by weight based on 100 parts by weight of the vinyl chloride-based resin.

For reference, the vinyl chloride-based resin of the present invention is a copolymer of a vinyl chloride monomer composed mainly of a vinyl chloride monomer as well as a resin composed of a vinyl chloride monomer and copolymerizable with the vinyl chloride monomer (the content of the vinyl chloride monomer in the total composition of the resin 50 wt% or more).

Vinyl monomers copolymerizable with such vinyl chloride monomers include olefin compounds such as ethylene and propylene; Unsaturated nitriles such as vinyl esters such as vinyl acetate and vinyl propionate and acrylonitrile; Vinyl alkyl ethers such as vinyl methyl ether and vinyl ethyl ether; Unsaturated fatty acids such as acrylic acid, methacrylic acid itaconic acid and maleic acid; And anhydrides of these fatty acids; may be used alone or in combination of two or more selected from the group consisting of.

Hereinafter, preferred examples are provided to help understanding of the present invention, but the following examples are merely for exemplifying the present invention, and various changes and modifications within the scope and spirit of the present invention are apparent to those skilled in the art. Naturally, changes and modifications belong to the appended claims.

EXAMPLE

Example 1

100 parts by weight of a vinyl chloride monomer, 130 parts by weight of deionized water, 0.04 part by weight of a polyvinyl dispersant having a degree of saponification of 72%, and 0.02 part by weight of a 55% polyvinyl dispersant were introduced into a 1 cubic meter reactor.

As the polymerization initiator, 0.02 parts by weight of t-butyl peroxyneodecanoate (BND) was added thereto, and the reactor was depressurized to remove air and nitrogen.

It is heated to maintain the target polymerization temperature of 58 ° C, and when the pressure in the reactor at the end of the reaction drops by about 0.1kgf / cm ² , the polymerization temperature is continuously controlled by 0.2 ° C / min by controlling the temperature using steam or cooling water of a specific temperature. Increasing pressure to maintain pressure. After the temperature was raised for about 35 minutes, the temperature was stopped and when the pressure reached 7.0 kgf / cm ² , the reactor was cooled down and stopped by adding 0.02 parts by weight of Irganox 245 and 0.01 parts by weight of sodium bicarbonate as an antioxidant. Unreacted vinyl chloride monomer was recovered through devacuum and the vinyl chloride resin slurry was recovered.

The resulting slurry was washed and dried to obtain a vinyl chloride resin polymer having a number average degree of polymerization of 1000.

Example 2

In Example 1, the polymerization was repeated under the same conditions as in Example 1 except that the polymerization temperature was increased by 0.4 占 폚 from the time when the pressure drop occurred at the end of the reaction to obtain a vinyl chloride resin polymer having a number average degree of polymerization of 1000.

Example 3

In Example 1, the polymerization was repeated under the same conditions as in Example 1 except that the polymerization temperature was increased by 0.6 ° C from the time when the pressure drop occurred at the end of the reaction to obtain a vinyl chloride resin polymer having a number average degree of polymerization of 1000.

Example 4

In Example 1, the polymerization was repeated under the same conditions as in Example 1 except that the polymerization temperature was increased by 0.05 ° C from the time when the pressure drop occurred at the end of the reaction to obtain a vinyl chloride resin polymer having a number average degree of polymerization of 1000.

Example 5

In Example 1, the polymerization was repeated under the same conditions as in Example 1 except that the polymerization temperature was increased when the pressure reduction degree at the end of the reaction was 0.05 kgf / cm ² , thereby obtaining a vinyl chloride resin polymer having a number average degree of polymerization of 1000.

Example 6

In Example 1, the polymerization was repeated under the same conditions as in Example 1 except that the polymerization temperature was increased when the pressure reduction degree at the end of the reaction was 0.15 kgf / cm ² , thereby obtaining a vinyl chloride resin polymer having a number average degree of polymerization of 1000.

Example 7

In Example 1, the polymerization was repeated under the same conditions as in Example 1 except that the temperature was increased for 30 minutes after the end of the pressure drop occurred, thereby obtaining a vinyl chloride resin having a number average degree of polymerization of 1000.

Example 8

In Example 1, the polymerization was repeated under the same conditions as in Example 1 except that the temperature was increased for 50 minutes after the pressure drop occurred at the end of the reaction to obtain a vinyl chloride resin having a number average degree of polymerization of 1000.

Comparative Example 1

In order to compare with the vinyl chloride resin production method of Example 1, the same method was repeated except that the polymerization temperature was not increased even after the pressure drop occurred at the end of the reaction in Example 1, to obtain a vinyl chloride resin having a number average degree of polymerization of 1000. Prepared.

Comparative Example 2

In Example 1, the polymerization was repeated under the same conditions as in Example 1 except that the polymerization temperature was increased by 0.008 ° C from the time when the pressure drop occurred at the end of the reaction to obtain a vinyl chloride resin polymer having a number average degree of polymerization of 1000.

Comparative Example 3

In Example 1, the polymerization was repeated under the same conditions as in Example 1 except that the polymerization temperature was increased by 0.8 ° C at the end of the reaction at the end of the reaction to obtain a vinyl chloride resin polymer having a number average degree of polymerization of 1000.

Comparative Example 4

In Example 1, except that the degree of pressure drop at the end of the reaction was 0.01 kgf / cm ² , the polymerization was repeated under the same conditions as in Example 1 to obtain a vinyl chloride resin polymer having a number average degree of polymerization of 1000.

Comparative Example 5

In Example 1, the polymerization was repeated under the same conditions as in Example 1 except that the degree of pressure drop at the end of the reaction was 0.5 kgf / cm ² to obtain a vinyl chloride resin polymer having a number average degree of polymerization of 1000.

Comparative Example 6

In Example 1, the polymerization was repeated under the same conditions as in Example 1 except that the temperature was increased for 10 minutes after the pressure drop occurred at the end of the reaction to obtain a vinyl chloride resin having a number average degree of polymerization of 1000.

Comparative Example 7

In Example 1, the polymerization was repeated under the same conditions as in Example 1 except that the temperature was increased for 90 minutes after the pressure drop occurred at the end of the reaction to obtain a vinyl chloride resin having a number average degree of polymerization of 1000.

Comparative Example 8

In Example 1, the polymerization was repeated under the same conditions as in Example 1 except that after the pressure drop occurred at the end of the reaction, the inlet of the cooling water was stopped in the jacket to raise the temperature of the polymerization reactor contents from 58 ° C to 70 ° C irregularly. A vinyl chloride resin having an average degree of polymerization of 1000 was obtained.

 [Test Example]

The physical properties of the vinyl chloride resins prepared in Examples 1 to 8 and Comparative Examples 1 to 8 were evaluated by the following method.

* Number average degree of polymerization: The number average degree of polymerization was measured according to ASTM D1243-79.

* Polymerization time measurement: The time from when the polymerization initiator was added until the reaction was completed was measured.

* Processing whiteness measurement: 5 parts by weight of complex stabilizer (WPS-60, lead stabilizer, Songwon Industries), 100 parts by weight of vinyl chloride resin, 1.5 parts by weight of processing aid (PA-822, acrylic processing aid, LG Chemical) 2 parts by weight of titanium oxide was added and roll-milled at 180 ° C. for 3 minutes to obtain a sheet having a thickness of 0.5 mm.

Thereafter, the whiteness (W.I) value was measured using Nippon Denshoku's NR-3000, and the results are summarized in Tables 1 and 2. Thermal stability can be measured from the whiteness value, and the higher the value, the better the thermal stability.

* Residual initiator concentration measurement: Iodine titration was used to measure the content of residual initiator present in the produced vinyl chloride resin. That is, 50 parts by weight of the prepared resin, 80 parts by weight of isopropyl alcohol (IPA) was mixed, and 20 ml of 10% acetic acid solution and 20 ml of 10% potassium iodide solution were mixed and sufficiently mixed.

* Fish-eye number: 100 parts by weight of vinyl chloride resin, 45 parts by weight of DOP, 0.1 part by weight of barium stearate, 0.2 part by weight of tin stabilizer, and 0.1 part by weight of carbon black using a 6-inch roll at 140 ° C. After mixing and kneading for 5 minutes, a sheet having a thickness of 0.3 mm was formed, and the sheet was expressed as the number of white transparent particles in 400 cm ² .

* Particle size distribution measurement: The obtained resin was measured for particle size using Sumpatec's HELOS particle size analyzer, and the span value at that time was defined as the particle size distribution. In this case, the lower the span value, the smaller the deviation.

Table 1

division	Example 1	Example 2	Example 3	Example 4	Example 5	Example 6	Example 7	Example 8
Temperature rise rate (℃ / min)	0.2	0.4	0.6	0.05	0.2	0.2	0.2	0.2
Pressure drop (△ P, kgf / cm 2 )	0.1	0.1	0.1	0.1	0.05	0.15	0.1	0.1
Temperature rise time (minutes)	35	35	35	35	35	35	30	50
Polymerization time (minutes)	264	264	263	267	261	268	260	280
Whiteness	75	75	76	74	75	74	73	76
Residual initiator concentration (ppm)	10	8	5	12	7	11	14	4
Whiskey (number)	5	5	4	5	4	7	6	6

TABLE 2

division	Comparative Example 1	Comparative Example 2	Comparative Example 3	Comparative Example 4	Comparative Example 5	Comparative Example 6	Comparative Example 7	Comparative Example 8
Temperature increase rate (℃ / min)	-	0.008	0.8	0.2	0.2	0.2	0.2	-
Pressure drop (△ P, kgf / cm 2 )	-	0.1	0.1	0.01	0.5	0.1	0.1	0.1
Temperature rise time (minutes)	-	35	35	35	35	10	90	35
Polymerization time (minutes)	260	264	256	253	266	260	349	264
Whiteness	72	72	68	73	72	71	69	74
Residual initiator concentration (ppm)	35	26	2	13	8	29	3	8
Whiskey (number)	10	11	16	20	23	12	38	15

As can be seen from the results of Tables 1 and 2 above, in the comparative example 1 in which the whiteness and the whiskey of Example 1, which proceeded to raise the temperature at the time when the pressure drop occurred to prevent the pressure drop, did not increase the polymerization temperature at the end of the reaction, It was confirmed that the improvement.

In addition, as in Examples 2 and 3, by controlling the temperature increase rate, the whiteness and the polymerization time may be controlled, thereby improving the whiteness and the whiskey.

In addition, when the temperature increase rate was too slow or too fast, as in Comparative Examples 2 and 3, the decrease in the number of fish eye was relatively small.

In addition, as shown in Comparative Example 8 in which the temperature rising method stopped the inflow of the cooling water of the jacket, the degree of temperature rise was not constant, and it was difficult to prevent foam generation.

Therefore, according to the present invention, the pressure drop was prevented by raising the temperature above the polymerization temperature using a temperature control system according to the degree of pressure drop at the end of the reaction at which the pressure drop occurred, and the pressure drop at the end of the reaction and the high heat removal amount of the reflux condenser By suppressing the foam generated, it was possible to efficiently produce a whiskey and a high vinyl chloride-based resin.

Claims (11)

1. From the point of time when the reaction pressure drops from more than 0.01 kgf / cm ² to less than 0.5 kgf / cm ² after the start of the suspension polymerization reaction, at a temperature rising rate of more than 0.008 ° C./min to less than 0.8 ° C./min, more than 10 minutes to less than 90 minutes Characterized in that during

   Method for producing vinyl chloride resin.
2. The method of claim 1,

   The decreasing reaction pressure is characterized in that more than 0.01 kgf / cm ² to less than 0.2 kgf / cm ²

   Method for producing vinyl chloride resin.
3. The method of claim 1,

   The temperature increase rate is characterized in that more than 0.008 ℃ / min to less than 0.65 ℃ / min

   Method for producing vinyl chloride resin.
4. The method of claim 1,

   The temperature increase rate is characterized in that for adjusting the temperature control system

   Method for producing vinyl chloride resin.
5. The method of claim 1,

   The reaction temperature of the polymerization is a method for producing a vinyl chloride resin, characterized in that in the range of 30 to 80 ℃.
6. The method of claim 1,

   The temperature increase time is 30 to 60 minutes, characterized in that the vinyl chloride-based resin production method.
7. Claim 1 to 6 characterized in that it is prepared by the method for producing a vinyl chloride-based resin of any one of

   Vinyl chloride resin.
8. The method of claim 7, wherein

   The vinyl chloride resin is characterized in that the residual initiator concentration is less than 0.002 parts by weight based on 100 parts by weight of the vinyl chloride-based resin.

   Vinyl chloride resin.
9. Claim 7 comprising a vinyl chloride-based resin, inorganic filler and stabilizer

   Vinyl chloride-based resin composition.
10. The method of claim 9,

    The inorganic filler is characterized in that the carbon black

    Vinyl chloride-based resin composition.
11. From the time when the reaction pressure is lowered from 0.05 to 0.1 kgf / cm ² after the start of the suspension polymerization reaction, the temperature is increased for 20 to 60 minutes at a temperature increase rate of 0.01 to 0.5 ℃ / min

    Method for producing vinyl chloride resin .