JP2002053601A - Method for producing vinyl chloride polymer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method capable of obtaining a vinyl chloride polymer little in the generation of fish eyes and the adhesion of scales during polymerization, and little in the formation of crude product. SOLUTION: The method for producing a vinyl chloride polymer is carried out as follows: a vinyl monomer mainly composed of a vinyl chloride monomer is subjected to suspension polymerization in an aqueous solvent containing a dispersant by using a polymerization vessel provided with a reflux condenser; the suspension polymerization is carried out by adding 0.005-0.08 pt.wt. of a polyethylene oxide having a viscosity-average molecular weight of 2,000,000-8,000,000 based on 100 pts.wt. of the vinyl monomer as the dispersant; and the polymerization temperature is elevated continuously or intermittently so that the polymerization initiation temperature (T1) is 45-60 deg.C, the polymerization termination temperature (T2) is 50-75 deg.C, and the temperature difference between T1 and T2 is 3-15 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a vinyl chloride polymer.

[0002]

2. Description of the Related Art Generally, polymerization of vinyl chloride monomer is carried out by heating and
It is carried out by a batch type water suspension polymerization method using a polymerization vessel equipped with a jacket for cooling, a stirrer, and the like. That is, an aqueous medium and a dispersant are charged into a polymerization vessel, then a polymerization initiator is charged, and then the inside of the polymerization vessel is degassed under vacuum, vinyl chloride monomer is charged, and the temperature is raised to a predetermined polymerization temperature to carry out polymerization. The reaction was carried out, and when the heat of reaction came out, the jacket was cooled by passing cooling water through the jacket.The polymerization was maintained at a predetermined temperature to proceed with the polymerization.After the polymerization was completed, the vinyl chloride monomer was recovered and vinyl chloride was recovered. It is polymerized by a series of operations for removing the polymer.

[0003] With the recent increase in the size of polymerization vessels,
There is a problem that the heat transfer area for the polymer is reduced, so that the time required for raising the temperature is increased or the cooling capacity is insufficient. Therefore, a method in which one or both of the aqueous medium and the vinyl chloride monomer is preliminarily heated and charged (hot charge method), and a method in which the size of the reflux condenser is increased to increase the amount of slow heat are adopted.

[0004] However, in the former method, when the polymerization initiator is charged, the polymerization initiator is rapidly decomposed and the polymerization is started, the control of the polymerization becomes difficult, and the scale adhesion to the polymerization vessel increases. The obtained vinyl chloride polymer has an increase in fish eyes and an increase in coarse particles.

[0005] In the latter method, foaming occurs during the reaction, the scale adheres to the polymerization vessel, and the gradual heat effect gradually decreases. If the reflux condenser is used at the beginning of the reaction, the particle size of the vinyl chloride polymer obtained is reduced. However, there is a disadvantage that the coarseness increases and the coarse-grained product increases.

Various proposals have been made to solve these problems. For example, Japanese Patent Publication No. 2-12963 discloses that when a vinyl chloride-based monomer is subjected to suspension polymerization, the amount of heat gradually controlled by a condenser is controlled while gradually increasing the polymerization temperature after a polymerization conversion of 50%. There has been proposed a method of performing polymerization while suppressing foaming.

Japanese Patent Application Laid-Open No. 7-173203 discloses that when a vinyl chloride monomer is subjected to suspension polymerization, a specific oil-soluble polymerization initiator is used and the polymerization temperature is continuously increased over a range of 10 ° C. or more. There has been proposed a method of performing polymerization while causing the polymerization.

However, in the above polymerization method, the polymerization temperature rises at the end of the polymerization, the reaction speed increases, and the polymer rapidly increases, so that the viscosity of the reaction system sharply increases. As a result, the stirring state deteriorated, and there still remained defects such as generation of fish eyes and an increase in coarse-grained products due to increased scale adhesion.

On the other hand, Japanese Patent Application Laid-Open No. 5-125105 proposes a polymerization method in which a partially saponified polyvinyl alcohol, polyethylene oxide and hydroxypropylmethylcellulose are used as a dispersant when a vinyl chloride monomer is subjected to suspension polymerization. Have been. However,
Even with the above polymerization method, the improvement of the generation of fish eyes was still insufficient.

[0010]

SUMMARY OF THE INVENTION In view of the above-mentioned drawbacks, an object of the present invention is to provide a vinyl chloride-based polymer having less fish eyes, less scale adhesion during polymerization, and less coarse particles. It is an object of the present invention to provide a manufacturing method capable of performing the above.

[0011]

According to the method for producing a vinyl chloride polymer of the present invention, a vinyl monomer mainly composed of a vinyl chloride monomer is produced by using a polymerizer equipped with a reflux condenser.
Upon suspension polymerization in an aqueous medium containing a dispersant, polyethylene oxide having a viscosity average molecular weight of 2,000,000 to 8,000,000 is added as a dispersant in an amount of 0.005 to 0.08 parts by weight based on 100 parts by weight of the vinyl monomer. And the polymerization initiation temperature (T
₁ ) is 45 to 60 ° C. and the polymerization end temperature (T ₂ ) is 5
0 to 75 ° C. and the temperature difference between T ₁ and T ₂ is 3 to ₁
The polymerization is carried out while continuously or intermittently increasing the polymerization temperature so as to reach 5 ° C.

The vinyl monomer used in the present invention is mainly composed of a vinyl chloride monomer. That is, it is a mixture of a vinyl chloride monomer and a polymerizable vinyl monomer mainly containing the vinyl chloride monomer or containing the vinyl chloride monomer as a main component (including 50% by weight or more).

Examples of the vinyl monomer include vinyl esters such as vinyl acetate and vinyl propionate;
(Meth) acrylic esters such as methyl (meth) acrylate and ethyl (meth) acrylate; olefins such as ethylene and propylene; (meth) acrylic acid, maleic anhydride, acrylonitrile, styrene, and vinylidene chloride. .

The polyethylene oxide used in the present invention has a viscosity average molecular weight of 2,000,000 to 8,000,000. When the viscosity average molecular weight is less than 2,000,000, the stirring state is deteriorated at the end of polymerization, fish eyes and coarse particles are easily generated, and those having a viscosity average molecular weight exceeding 8,000,000 are difficult to produce, so Polyethylene oxide is used.

[0015] If the amount of polyethylene oxide is small, the stirring state is deteriorated at the end of polymerization, and fish eyes and coarse particles are liable to be generated. If the amount is large, the effect becomes saturated and it is not economical. 0.005 to 0.08 parts by weight is added to 100 parts by weight.

Since the ability of polyethylene oxide as a dispersant is low, it is preferable to use a commonly used dispersant in the production of a vinyl chloride polymer.

Examples of the dispersant include partially saponified polyvinyl alcohol; water-soluble cellulose such as methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose and hydroxypropylmethylcellulose; water-soluble polymers such as polyacrylic acid and gelatin; sorbitan monolau. Rate, sorbitan monostearate,
Oil-soluble emulsifiers such as glycerin tristearate and ethylene oxide propylene oxide block polymer;
Examples include water-soluble emulsifiers such as polyoxyethylene sorbitan monolaurate, polyoxyethylene glycerin oleate, and sodium laurate, and partially saponified polyvinyl alcohol and water-soluble cellulose are preferably used.

The above dispersant may be used alone,
Two or more kinds may be used in combination. If the amount of the dispersing agent is small, the dispersing effect is reduced, and an abnormal reaction is liable to occur.If the amount is too large, the effect of polyethylene oside is hindered and fish eyes and coarse particles are easily generated. And the weight ratio of the dispersing agent to 1: 0.5 to 20
Is preferred.

In the present invention, a vinyl monomer mainly composed of a vinyl chloride monomer is subjected to suspension polymerization in an aqueous medium containing a dispersant using a polymerization vessel equipped with a reflux condenser. The reflux condenser is a device for cooling and condensing a gas vaporized from a liquid layer to return to a liquid state to remove heat of polymerization, and a conventionally known device is used.

The suspension polymerization method may be any of the methods employed in the conventional suspension polymerization of vinyl monomers. For example, an aqueous medium, polyethylene oxide and a dispersant are charged into a polymerization vessel. Then, a polymerization initiator is charged, and then the inside of the polymerization vessel is vacuum degassed, then a vinyl monomer is charged, the temperature is raised to a predetermined polymerization temperature, and a polymerization reaction is performed. There is a method of cooling by passing cooling water through a reflux condenser, maintaining the polymerization temperature at a predetermined temperature, and allowing the polymerization to proceed. After completion of the polymerization, a vinyl chloride monomer is recovered and a vinyl chloride polymer is removed.

In the present invention, the polymerization temperature is such that the polymerization start temperature (T ₁ ) is 45 to 60 ° C., the polymerization end temperature (T ₂ ) is 50 to 75 ° C., and T ₁ and T ₂ The polymerization is carried out while continuously or intermittently increasing the polymerization temperature such that the temperature difference of

It is preferable that the polymerization initiation temperature (T ₁ ) is low, because the temperature-raising step can be shortened. However, if it is too low, the polymerization initiator does not react, and if it is too high, the polymerization degree decreases.
Set to 60 ° C.

The polymerization start temperature (T ₁ ) and the polymerization end temperature (T
₂ ) If the temperature difference is less than 3 ° C., the reaction rate does not increase, and the polymerization takes time. If the temperature difference exceeds 15 ° C., the reaction rate sharply increases, and it becomes difficult to control the reaction. And preferably 5 to 10 ° C.

If the polymerization end temperature (T ₂ ) exceeds 75 ° C., the adhesion of scale increases, the amount of coarse particles increases, and the washing time after the end of the reaction becomes longer, so that it is set at 50 to 75 ° C.

The increase in the polymerization temperature is affected by the type and amount of the polymerization initiator used, and the degree of polymerization of the obtained polymer is affected by the polymerization temperature. The temperature may be kept constant for a certain time.

As the above-mentioned polymerization initiator, a polymerization initiator generally used in suspension polymerization of a vinyl monomer may be used, for example, diisopropyl peroxycarbonate, di-2-ethylhexyl peroxycarbonate, Peroxycarbonate compounds such as diethoxyethyl peroxycarbonate; α-cumyl peroxyneodecanate, t-butyl peroxyneodecanate, t
Peroxyester compounds such as -butylperoxypivalate and t-hexylperoxyneodecanate; acetylcyclohexylsulfonyl peroxide;
Peroxides such as 4,4-trimethylpentyl-2-peroxyphenoxyacetate; azobis-2,4-dimethylvaleronitrile, azobis (4-methoxy-2,4-
Azo compounds such as dimethylvaleronitrile); potassium persulfate, ammonium persulfate, and hydrogen peroxide; and the like, which may be used alone or in combination of two or more.

The method of adding the polymerization initiator may be a method generally used in the suspension polymerization of vinyl monomers. For example, the polymerization initiator may be dissolved in an organic solvent or dispersed in an aqueous medium. Into an emulsion or suspension,
There is a method of adding together with or after charging the aqueous medium and / or dispersant. Also, after the vinyl monomer is charged, it may be press-fitted with a pump.

The above polyethylene oxide and dispersant are
Generally, when the aqueous medium is charged, the aqueous medium is charged together with the aqueous medium, but a part of the aqueous medium may be dividedly added during the polymerization. Alternatively, only the dispersant may be added together with the aqueous medium, and the polyethylene oxide may be added in portions during the polymerization.

Furthermore, polymerization regulators, chain transfer agents, pH regulators, gelling improvers, antistatic agents, and polymer scale adhesion inhibitors conventionally used in suspension polymerization of vinyl monomers. Etc. may be added.

[0030]

Example 1 A 600 liter polymerization vessel equipped with a reflux condenser having a heat transfer area of 0.5 m ² and a stirring blade was charged with 130 parts by weight of water and polyethylene oxide 0.04 having a viscosity average molecular weight of 4.5 million. Parts by weight, supplying 0.03 parts by weight of partially saponified polyvinyl alcohol having a saponification degree of 72 mol% and 0.03 parts by weight of hydroxypropyl methylcellulose,
Each component was dissolved by stirring. Next, 0.028 parts by weight of α-cumyl peroxy neodecanoate and 0.039 parts by weight of di-2-ethylhexyl peroxydicarbonate were added, and then air in the polymerization reactor was removed to remove 100 parts by weight of a vinyl chloride monomer. Was charged, and the inside of the polymerization vessel was heated to 54.5 ° C. to start a polymerization reaction. The reflux condenser was operated immediately after the start of the polymerization.

Thereafter, the polymerization temperature was gradually raised, and when the pressure in the polymerization vessel reached 0.75 MPa, unreacted vinyl chloride monomer was recovered, the polymerization was terminated, and a vinyl chloride polymer was obtained. Was. The polymerization termination temperature was 60.5 ° C., and the reaction time was 3 hours and 40 minutes.

Example 2 Polymerization was started in the same manner as in Example 1 except that the polymerization initiation temperature was set at 56.0 ° C., and the temperature was kept at that temperature for 2 hours and 30 minutes, and then the polymerization temperature was gradually raised. Thus, a vinyl chloride polymer was obtained. The polymerization termination temperature was 68.0 ° C., and the reaction time was 3 hours and 46 minutes.

Comparative Example 1 A vinyl chloride polymer was obtained in the same manner as in Example 1 except that no polyethylene oxide was added. The reaction time was 3 hours and 54 minutes.

Comparative Example 2 A vinyl chloride polymer was obtained in the same manner as in Example 1 except that the polymerization temperature was kept constant at 57.0 ° C. The reaction time was 4 hours and 9 minutes.

Comparative Example 3 A vinyl chloride polymer was obtained in the same manner as in Example 1 except that polyethylene oxide having a viscosity average molecular weight of 150,000 was used as polyethylene oxide. The reaction time was 3 hours and 43 minutes.

The stirring conditions of the above Examples and Comparative Examples were observed, and the average degree of polymerization, fish eye and coarseness of the obtained vinyl chloride polymer were measured. The results are shown in Table 1.
In addition, the evaluation method of a stirring state and the measuring method of a polymer are as follows.

(1) Stirring state Since it is difficult to measure the viscosity of the suspension during the reaction, the viscosity of the suspension after the start of polymerization is measured through an observation window provided at the top of the polymerization vessel for internal observation.
At the time, the stirring condition was observed.

；: The movement of the suspension was active and involved, and a drop in the liquid level at the center was observed. (Low viscosity state) △: The movement of the suspension was poor and there was entrainment, but no decrease in the liquid level at the center was observed. (Viscosity is very high) x; no movement of suspension. (Very high viscosity)

(2) Average degree of polymerization Measured according to JIS K6721.

(3) Fisheye 100 parts by weight of the obtained vinyl chloride polymer, 50 parts by weight of dioctyl phthalate, 0.5 parts by weight of barium stearate, 0.5 parts by weight of zinc stearate, 0.1 parts by weight of titanium dioxide.
A mixture consisting of 5 parts by weight and 0.1 part by weight of carbon black was supplied to a 6-inch roll and kneaded at 140 ° C. for 5 minutes to obtain a sheet having a thickness of 0.3 mm. The number of transparent particles in 100 cm ² of the obtained sheet was counted.

(4) Degree of Coarse Grain According to JIS Z8801, a standard sieve of 42 mesh was used, and the ratio (% by weight) of vinyl chloride polymer particles remaining on the sieve was measured.

[0042]

[Table 1]

[0043]

As described above, the method for producing the vinyl chloride polymer of the present invention can be efficiently stirred, the adhesion of scale due to the stirring is small, and the polymerization can be performed in a short time. The resulting vinyl chloride polymer has less fisheye and less coarse particles.

Claims (1)

[Claims] In a suspension polymerization of a vinyl monomer mainly composed of a vinyl chloride monomer in an aqueous medium containing a dispersant using a polymerization vessel equipped with a reflux condenser, a dispersant is used. Polyethylene oxide having a viscosity average molecular weight of 2,000,000 to 8,000,000 as 0.0 parts by weight based on 100 parts by weight of the vinyl monomer.
The polymerization start temperature (T ₁ ) is 45 to 60 ° C. and the polymerization end temperature (T ₂ ) is 50 to 7 parts by weight.
A vinyl chloride-based polymer, wherein the polymerization is performed while continuously or intermittently increasing the polymerization temperature so that the temperature is 5 ° C. and the temperature difference between T ₁ and T ₂ is 3 to 15 ° C. Production method.