JP3197151B2 - Method for producing vinyl chloride polymer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In general, suspension polymerization of vinyl chloride or a monomer mixture containing vinyl chloride (hereinafter referred to as vinyl chloride, etc.) is carried out by adding an aqueous medium and a dispersant to a polymerization vessel equipped with a jacket and a reflux condenser. After charging, a polymerization initiator was charged, and then the inside of the polymerization vessel was evacuated, monomers were charged, and if necessary, other additives were added to prepare an aqueous suspension. This is carried out by raising the temperature of the aqueous suspension by passing water through to initiate a polymerization reaction.

In recent years, as a means of improving productivity, the time required for raising the temperature of a reaction mixture has been reduced. Therefore, in order to shorten the heating time, in the above suspension polymerization, a method of increasing the temperature of hot water passing through a jacket has been adopted. However, when the temperature of the hot water passing through the jacket is increased, an expensive anticorrosive must be used in the hot water for preventing corrosion of the apparatus, which causes an increase in cost. In addition, since this method extends the operating temperature range of the jacket, the loss of heat energy due to replacement of cooling water and hot water in the jacket at the time of temperature rise or temperature decrease is increased, which is not preferable from the viewpoint of energy saving. . In addition, since the scale of the jacket is expanded, the adhesion of the polymer scale to the inner wall surface of the polymerization vessel is also likely to occur. Disadvantages such as an increase in

On the other hand, in order to shorten the heating time, in the above suspension polymerization step, at least one of an aqueous medium and a monomer is preliminarily heated and charged into a polymerization vessel (a so-called hot charge method). It has been proposed (JP-B 62-39601)
No.). This hot charge method increases the size of the polymerization vessel,
It is also excellent in compensating for the lack of heating capacity of the polymerization vessel due to the use of a reflux condenser. However, according to this hot charge method, the polymerization initiator is rapidly decomposed at the same time as the polymerization initiator is charged, so that coarse particles are easily generated in the obtained granular polymer, and polymer scale on the inner wall of the polymerization vessel or the like. There is a problem that adhesion is likely to occur, and as a result, fish eyes after molding increase.

[0005]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to reduce the time required for raising the temperature of an aqueous suspension and to reduce the loss of heat energy during temperature control.
And adhesion of the polymer scale in the polymerization vessel hardly occurs,
Another object of the present invention is to provide a method for producing a vinyl chloride polymer capable of obtaining a polymer having less fish eyes.

[0006]

SUMMARY OF THE INVENTION The present invention provides an aqueous suspension comprising vinyl chloride or a mixture of monomers containing vinyl chloride, an aqueous medium, a polymerization initiator and a dispersing agent. In the method for producing a vinyl chloride polymer having a step of performing a polymerization reaction by raising the temperature of the suspension, the dispersant is a partially saponified polyvinyl alcohol having a cloud point of a 1% aqueous solution of 50 ° C. or more, and It is intended to provide a method for producing a polymer, wherein the temperature of the aqueous suspension immediately before supplying steam is 45 ° C. or less.

Hereinafter, the present invention will be described in detail. Aqueous suspension The aqueous suspension used in the method of the present invention is obtained by charging the following components into a polymerization vessel.

Dispersant In the production method of the present invention, it is necessary to use a partially saponified polyvinyl alcohol having a cloud point of a 1% aqueous solution of 50 ° C. or higher as a dispersant. When a partially saponified polyvinyl alcohol having a cloud point of a 1% aqueous solution having a cloud point of less than 50 ° C. is used, a coarse-grained polymer is formed, or a polymer that gives a molded product having many fish eyes is obtained. The partially saponified polyvinyl alcohol used in the present invention further has a saponification degree of 70 to 90 mol% and a viscosity of a 4% aqueous solution at 20 ° C of 5 to 5 mol%.
Preferably it is 20 cP.

The partially saponified polyvinyl alcohol is, for example, L-9-78 (manufactured by Kuraray Co., Ltd.), OKS-9067K
It can be obtained under trade names such as [Nippon Synthetic Chemical Industry Co., Ltd.] and OKS-9065G [Nippon Synthetic Chemical Industry Co., Ltd.]. These may be used alone or in combination of two or more.

The amount of the partially saponified polyvinyl alcohol to be used is generally 0.01 to 3 parts by weight, preferably 0.03 to 0.5 parts by weight, per 100 parts by weight of the monomer.

Further, in addition to the above partially saponified polyvinyl alcohol, a dispersant used for suspension polymerization of a water-soluble cellulose ether such as methylcellulose, hydroxyethylcellulose and hydroxypropylcellulose may be used in combination.

Polymerization Initiator The polymerization initiator can be used without any particular limitation as long as it is conventionally used for polymerization of vinyl chloride or the like. Examples of such a polymerization initiator include peroxycarbonate compounds such as diisopropylperoxydicarbonate, di-2-ethylhexylperoxydicarbonate, diethoxyethylperoxydicarbonate, t-hexylperoxypivalate, and t-butyl. Peroxyneodecanate, α-cumyl peroxyneodecanate,
Peroxyester compounds such as t-butylperoxyneodecanate and t-hexylperoxyneodecanate; organic peroxides such as acetylcyclohexylsulfonyl peroxide and 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate Azobis-
Azo compounds such as 2,4-dimethylvaleronitrile and azobis (4-methoxy-2,4-dimethylvaleronitrile); persulfates such as potassium persulfate and ammonium persulfate; and hydrogen peroxide. These can be used alone or 2
A combination of more than one species may be used. Among these polymerization initiators, a peroxycarbonate compound and a peroxyester compound are particularly preferable.

The amount of the polymerization initiator used is usually 100
0.01 to 5 parts by weight, preferably 0.03 to 1 part by weight
Parts by weight.

[0014] The monomer production method of the monomer present invention is applied, in addition to vinyl chloride alone, a vinyl chloride as a main component, a monomer mixture containing a copolymerizable therewith comonomer (typically, (Vinyl chloride 50% by weight or more) is used. Examples of the comonomer copolymerizable with vinyl chloride include, for example, vinyl acetate,
Vinyl esters such as vinyl propionate; (meth) acrylates such as methyl acrylate, ethyl acrylate, methyl methacrylate, and ethyl methacrylate; olefins such as ethylene and propylene; maleic anhydride; acrylonitrile; styrene; Is mentioned. In addition to these, any monomer copolymerizable with vinyl chloride can be used without particular limitation.

Aqueous Medium As the aqueous medium, deionized water is usually used. The amount of the aqueous medium is usually 20 to 500 parts by weight, preferably 80 to 200 parts by weight, per 100 parts by weight of the monomer. Since steam drain is mixed into the aqueous suspension by the supply of steam performed at the start of the polymerization, the amount of the aqueous medium to be charged before the start of the polymerization is set by subtracting the amount of the steam drain in consideration of the amount of the steam drain. Good to keep. The aqueous medium is 30
It is advisable to bring the temperature to ~ 45 ° C before charging.

Other additives In the method of the present invention, in addition to the above, a polymerization regulator, a chain transfer agent, a gelling improver, an antistatic agent, and a polymer scale adhering agent which are appropriately used for polymerization of vinyl chloride and the like. Inhibitors and the like can be used as appropriate.

In order to prevent corrosion of the piping, an alkaline steam drain may be used. In such a case, in order to prevent inconvenience associated with an increase in the pH of the aqueous suspension caused by the contamination of the steam drain,
The pH of the aqueous suspension is preferably adjusted in advance to preferably 3.0 to 7.0, more preferably 4.0 to 6.0. For adjusting the pH, it is preferable to use a mineral acid such as sulfuric acid, hydrochloric acid, or nitric acid, and more preferably sulfuric acid. By adjusting the pH of the aqueous suspension, the dispersion stability of the aqueous suspension is favorably maintained, and polymer particles having uniform sizes can be obtained. Temperature condition of aqueous suspension The aqueous suspension prepared above needs to be temperature-controlled to 45 ° C or lower immediately before supplying steam, and further temperature-controlled to 30 to 45 ° C. Is preferred. The temperature of the aqueous suspension is 45 ° C before the steam feed
If the ratio exceeds the above range, a coarse-grained polymer may be formed, or a polymer having many fish eyes may be obtained after molding. The temperature of the aqueous suspension in the feed polymerization vessel of the steam is not more than 45 ° C, preferably 30
~ 45 ° C, more preferably 35-45 ° C, and steam is supplied to raise the aqueous suspension to a polymerization temperature suitable for the polymerization initiator (usually 35-80 ° C, preferably 50-70 ° C). Heating initiates the suspension polymerization.

The supply of steam can be carried out by any method, and may be carried out directly to the aqueous suspension or to the gas phase in the polymerization vessel. Usually, it is preferred to feed directly into the aqueous suspension in the polymerization vessel. For example, a nozzle may be provided on the bottom wall of the polymerization vessel, and steam may be directly blown into the aqueous suspension from the nozzle. Further, it is preferable that the steam is blown into the polymerization vessel uniformly using a movable nozzle.

In the present invention, examples of the nozzle preferably used include a steam silencer, a mixing nozzle, a tank mixing eductor and the like. Although commonly used spray nozzles and the like can be used,
It is not very desirable because the noise during use is large.

Since the polymer scale easily adheres to the nozzle, it is possible to move the inside of the polymerization vessel in order to prevent the deterioration of the polymer quality due to the adhesion of the polymer scale and the clogging of the nozzle. It is advisable to use a nozzle that can be removed from the nozzle. If such a nozzle is used, the nozzle can be moved or removed from the polymerization vessel after the end of steam blowing to isolate the nozzle from the polymerization system, so that the polymer scale hardly adheres to the nozzle. When such a nozzle is not used, it is desirable to flush the water even when the supply of steam is stopped.

The feed rate of steam depends on the polymerization conditions, but is preferably 0.5 kg / 100 kg of the aqueous suspension.
min or less, more preferably 0.1-0.4 kg / m
in. Even after the start of steam supply, the steam supply speed may be increased or decreased within this range. 0.5kg /
If the steam is supplied at a speed exceeding min, the stirring efficiency of the aqueous suspension may be reduced, or the steam supply pipe or the like may be easily damaged by wear or impact,
In some cases, it is necessary to increase the size of the blowing port.

The pressure of the steam may be higher than the maximum pressure in the polymerization vessel, and is preferably 1 kg · f / cm ² or more, more preferably 3 kg · f / cm ^2, higher than the maximum pressure in the polymerization vessel from the viewpoint of safety. It is preferably higher than cm ² .

The supply of steam may be carried out as needed even after the temperature in the polymerization vessel has reached the above-mentioned polymerization temperature in order to regulate the temperature in the polymerization vessel.

The supply of steam is usually terminated when the aqueous suspension reaches the above-mentioned polymerization temperature. In general, the supply of steam may be terminated at any time until the temperature in the polymerization vessel reaches the polymerization temperature described above, but is preferably terminated before reaching the polymerization temperature from 5 ° C before the polymerization temperature. Good to do. Polymerization The general suspension polymerization of the present invention will be specifically described.

A dispersant, an aqueous medium and other additives are charged into a polymerization vessel and uniformly mixed.

Next, the inside of the polymerization vessel is degassed, the degree of vacuum in the gas phase is adjusted to a range of 50 to 100 mmHg (absolute pressure), and monomers are charged into the polymerization vessel. Here, the polymerization initiator may be charged before the supply of steam, and may be before or after charging the monomer.

After preparing the aqueous suspension, as described above,
Supply steam and initiate polymerization.

After the completion of the supply of steam, the polymerization reaction heat is removed by passing cooling water through a jacket provided on the outer periphery of the polymerization vessel, and polymerization is performed while maintaining the polymerization temperature according to the polymerization initiator. During polymerization, one or more of water, a dispersant, and a polymerization initiator can be added as necessary.

When the internal pressure of the polymerization vessel drops to 0 to 7 kgf / cm ² · G, or when the difference between the inlet temperature and the outlet temperature of the cooling water flowing into and out of the jacket becomes almost equal (that is, polymerization occurs). When the heat generated by the reaction has ceased), it is determined that the polymerization reaction has been completed, the exhaust gas is discharged, and the unreacted monomer remaining in the polymer slurry is recovered. At the time of this exhaust gas, usually, the temperature in the polymerization vessel is raised by supplying hot water to the jacket to improve the recovery rate of the unreacted monomer, but in the present invention, instead, steam is supplied again. By doing so, the recovery rate of unreacted monomers can be improved.

The obtained polymer slurry is taken out of the polymerization vessel and dehydrated and dried to obtain a desired vinyl chloride polymer.

[0031]

According to the production method of the present invention, when a 1% aqueous solution is subjected to suspension polymerization of vinyl chloride or the like using a partially saponified polyvinyl alcohol having a cloud point of 50 ° C. or more as a dispersant, the aqueous solution is supplied by supplying steam. Even if the suspension is heated locally,
It is considered that since the protective colloid action of the partially saponified polyvinyl alcohol continues, fine particles of organic compounds such as monomer particles and polymer particles in the aqueous suspension can be stably present. Therefore, according to the production method of the present invention, since such fine particles can be stably present, the production of coarse-grained polymer is reduced, the plasticizer absorbability of the obtained polymer is improved, and fish eye It is considered that a polymer having a small amount is obtained.

[0032]

Examples of the present invention will be described below. The present invention is not limited to the following examples. Examples 1 to 3 and Comparative Examples 1 to 4 In a stainless steel polymerization vessel (with a stirrer and a jacket) having an inner volume of 2.1 m ³ , 780 kg of deionized water (30 ° C.) and Table 1 were added.
Was added as an aqueous solution (concentration 0.03% by weight). While stirring, concentrated sulfuric acid (concentration: 98% by weight) was charged into the polymerization vessel to adjust the pH of the aqueous suspension to 4.6. Further, after degassing the inside of the polymerization vessel to 60 mmHg, 685 kg of a vinyl chloride monomer was charged, and while stirring, the inside temperature was stabilized with a jacket to the temperature before the start of steam blowing shown in Table 2, and then Stop the circulation pump of the jacket, and
380 g of ethylhexyl peroxydicarbonate were pumped in over 1 minute.

After a further two minutes from the injection of the peroxydicarbonate, a nozzle attached to the bottom of the polymerization vessel was used to enter the liquid phase inside the polymerization vessel maintained at the temperature shown in Table 2 before the start of steam blowing. Steam was blown in at a rate of 5.0 kg / min to start raising the temperature of the aqueous suspension. The temperature inside the polymerization vessel
After the temperature reached 54 ° C., the blowing of steam was gradually reduced, and the blowing of steam was stopped immediately before the internal temperature of the polymerization reactor reached 57 ° C. After the steam blowing was completed, the steam blowing nozzle was moved out of the polymerization vessel, and the nozzle was completely shut off from the polymerization system. Drive the jacket circulation pump to pass cold water through the jacket to reduce the temperature inside the polymerization reactor to 57 ° C.
And the polymerization was continued.

When the internal pressure of the polymerization reactor reached 6 kgf / cm ² · G, the polymerization was terminated and unreacted monomers were recovered. The obtained polymer was taken out of the polymerization reactor in the form of a slurry and dehydrated and dried.

The cloud point of the partially saponified polyvinyl alcohol used as the dispersant, and the bulk specific gravity, particle size distribution under the sieve, plasticizer absorption and fish eye of the obtained vinyl chloride polymer were measured by the following methods. Table 1 and Table 2 show the results.
Shown in

(1) Cloud point measuring method: The cloud point was measured by the following method using an ultraviolet spectrophotometer equipped with a thermostat cell holder.

A partially aqueous solution of pure water having a partially saponified polyvinyl alcohol concentration of 1% by weight is prepared at 25 ° C. to prepare a sample solution for cloud point measurement. Pour pure water into the measuring cell and measure the transmittance at a measurement wavelength of 430 nm at 25 ° C.
%). Next, put the sample solution in the measurement cell,
While stirring, the temperature of the sample solution is raised from 25 ° C. by an external thermostat so that the temperature rise rate of the sample solution becomes 1 ° C./min. Measures the change in transmittance due to the temperature change of the sample solution
Measure at 430 nm. The temperature at which the transmittance of the sample solution became (A / 2)% was determined as the cloud point.

(2) Bulk specific gravity: Measured according to JIS K 6721.

(3) Particle size distribution: # 60, according to JIS Z 8801
The mixture was sieved using sieves having mesh sizes of # 80, # 100, # 120, # 150, and # 200, and the passing amount (% by weight) was measured.

(4) Plasticizer absorption: A graph fiber is packed in the bottom of an aluminum alloy container having an inner diameter of 25 mm and a depth of 85 mm, and 10 g of a sample vinyl chloride polymer is sampled and charged.
Add 15cc dioctyl phthalate (DOP)
And leave it for 30 minutes to allow the DOP to fully penetrate the polymer.
The excess DOP is then centrifuged at 1500G acceleration,
The amount of DOP absorbed by 10 g of the polymer was
It was converted per 0g.

(5) Fisheye: 100 parts by weight of a sample vinyl chloride polymer, 1 part by weight of tribasic lead sulfate, 1.5 parts by weight of lead stearate, 0.2 parts by weight of titanium oxide, 0.1 parts by weight of carbon black after the the parts and DOP mixture which was prepared at a ratio of 50 parts by weight were kneaded for 5 minutes at 145 ° C. using a roll, formed into a thickness of 0.2mm sheet, count the number of fish eyes per sheet 100 cm ² did.

Table 2 shows the results of observation of the time required from the temperature before the start of steam blowing to the temperature in the polymerization reactor reaching 57 ° C. and the state of scale adhesion in the polymerization reactor after the polymerization.
Shown in

[0043]

[Table 1] 1) Measured value of 4% aqueous solution at 20 ° C. 2) Measured value of 1% aqueous solution.

[0044]

[Table 2]

[0045]

According to the method for producing a vinyl chloride polymer of the present invention, the time required for raising the temperature of the aqueous suspension can be shortened, and the loss of heat energy during temperature adjustment is small ( That is, since the heating of the aqueous suspension is by steam,
It is sufficient that the temperature adjustment operation substantially only cools the aqueous suspension), and a polymer that hardly adheres to the polymer scale in the polymerization vessel and has less fish eyes can be obtained.

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C08F 2/18-2/20

Claims (2)

(57) [Claims] 1. An aqueous suspension containing vinyl chloride or a mixture of monomers containing vinyl chloride, an aqueous medium, a polymerization initiator and a dispersant is supplied with steam to raise the temperature of the aqueous suspension. The method for producing a vinyl chloride polymer having a step of performing a polymerization reaction, wherein the dispersant is a partially saponified polyvinyl alcohol having a cloud point of a 1% aqueous solution of 50 ° C. or more, and the aqueous solution immediately before supplying the steam. A method for producing a polymer, wherein the temperature of the suspension is 45 ° C or lower. 2. The method according to claim 1, wherein the dispersant is a partially saponified polyvinyl alcohol having a degree of saponification of 70 to 90 mol% and a viscosity of a 4% aqueous solution at 20 ° C. of 5 to 20 cP.