JP2787120B2 - Method for producing vinyl chloride polymer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention suppresses the generation of bubbles by using a polymerization vessel equipped with a foam sensor in the internal gas phase, thereby preventing scale in the polymerization vessel. The present invention relates to a method for producing a vinyl chloride polymer.

[Conventional technology]

In the case of suspension polymerization or emulsion polymerization of a vinyl chloride monomer or a monomer mixture mainly composed of vinyl chloride in an aqueous medium, in order to increase the production efficiency, the size of the polymerization vessel, the polymerization time, and the amount of unreacted monomer are increased. The entire polymerization cycle is shortened by shortening the time for recovering the body, the time for washing in the polymerization vessel after the polymerization, and the like.

In order to shorten the polymerization time, it is important how to efficiently remove the heat of the polymerization reaction. In addition to the conventional cooling jacket, a reflux condenser has been adopted for heat removal. The size of the reflux condenser is increasing, and the ratio of heat removal by the reflux condenser to the total heat removal is increasing. Incidentally, heat removal by the reflux condenser is performed by liquefaction of gaseous monomers. As a result of this liquefaction, the gas-liquid equilibrium between the monomer in the gas phase and the monomer in the liquid phase is disrupted, so that the vaporization of the monomer in the liquid phase is promoted. This vaporization necessarily involves foaming at the liquid phase surface. This foam causes scale formation in the gas phase part of the polymerization vessel, and polymer particles accompanying the foam enter the condenser communication port, raw material charging port, etc., and if they remain, they will be included in the polymerized product at the next polymerization. When mixed, it causes fish eyes and lowers the quality. If the temperature is further increased, polymer particles may enter the inside of the reflux condenser and generate scale in the reflux condenser, which may reduce the heat removal capability of the reflux condenser. Also,
Occasionally, the piping is clogged with polymer particles, making it impossible to operate the reflux condenser. The bubbles generated on the liquid phase surface cause such an adverse effect. However, since the above-described increase in the size of the reflux condenser further increases the amount of bubbles generated, an appropriate method for suppressing bubbles is required.

The composition of the reaction mixture (polymerization system) in the polymerization varies depending on the type of the target polymer, the degree of polymerization, and the like. Has been done by making the temperature sufficiently low or performing the heat removal operation at a sufficiently safe site. However, this method is extremely unreasonable and unsatisfactory in view of the demand for shortening the polymerization cycle by efficient operation in order to reduce the heat removal capability of the reflux condenser to an unnecessary degree. That is, in this method, the efficient operation of the reflux condenser is hindered, so that the shortening of the polymerization time is limited, and in order to improve the productivity,
It was a major obstacle.

In order to solve this problem, a method has been proposed in which polymerization is carried out while crushing bubbles generated on the liquid surface by mechanical means attached to the gas phase (Japanese Patent Application Laid-Open No. 56-26908).

[Problems to be solved by the invention]

However, the method of crushing foams by mechanical means is not economically disadvantageous because the polymerization apparatus becomes complicated due to the installation of the mechanical means, and the cost of the polymerization apparatus itself increases.

[Means for solving the problem]

An object of the present invention is to provide a polymerization method capable of rationally suppressing the generation of bubbles with a simple structure and without impairing productivity.

That is, the present invention provides a method comprising the step of polymerizing a vinyl chloride monomer or a monomer mixture mainly composed of vinyl chloride in an aqueous medium in a polymerization vessel. In the gas phase portion, a foam sensor set to detect foam when the foam generated on the liquid phase surface reaches a predetermined amount or more is provided; Provided is a method for producing a vinyl chloride polymer, wherein an antifoaming agent is added when bubbles reaching the above are detected, and bubbles generated during polymerization are suppressed.

According to the method of the present invention, regardless of the composition of the polymerization system,
When the foam sensor detects more than a certain amount of foam, foaming is suppressed at the same time as defoaming by adding an antifoaming agent, so there is no need to reduce the heat removal amount of the reflux condenser to suppress foaming, so efficient operation Can be. Since bubbles are suppressed in a timely manner, it is possible to effectively prevent adhesion of polymer scale due to bubbles, intrusion and adhesion of polymer particles in a raw material charging port, an unreacted monomer recovery port, various pipes, and the like.
Therefore, the polymerization cycle can be shortened without causing inconveniences such as blockage of the pipe, as well as deterioration of the quality of the polymer.

Foam Sensor As a sensor for detecting foam, for example, a capacitance type sensor, an ultrasonic type sensor, a radiation type sensor, an infrared type sensor, a conductivity cell and the like can be used. Among these, the capacitance type sensor that detects bubbles by measuring the change in capacitance between two electrodes is easy to be made to have an explosion-proof structure, and it is easy to configure it into a simple shape, and it is heavy. It is particularly suitable in that adhesion of coalesced scale, adhesion of polymer particles, and residue are unlikely to occur.

As such a capacitance-type sensor, for example, a sensor that detects a change in capacitance between a case where a bubble is present between two electrodes and a case where a bubble is not present by a built-in circuit is exemplified. A detecting device having the same principle as that described in Japanese Unexamined Patent Publication No. 62-269021 as a level (liquid level) detecting device can be used as a foam sensor. Such a capacitive sensor is specifically a capacitive level sensor DS
It can be obtained from Yamamoto Electric Co., Ltd. under the product name of the mold.

In the present invention, the foam sensor is attached to the gas phase in the polymerization vessel. The height is set in consideration of the distance from the liquid surface and the height of the reflux condenser inlet, etc., so that bubbles can be detected when the amount of bubbles exceeds an unacceptable certain amount or more. That is, if the bubble sensor is too close to the liquid surface, bubbles are detected even with a small amount of foaming, and a foaming suppression operation is unnecessary, resulting in a decrease in productivity. vice versa,
If the position of the foam sensor is too far from the liquid surface, or if the vertical distance from the reflux condenser inlet, etc., is too small, the foam suppression operation after the detection of foam cannot be made in time, and the foam accompanying the polymer particles will be introduced into the inlet, etc. Can not be prevented from invading. Depending on the shape and size of the foam sensor used, the volume of the polymerization vessel, etc.,
For example, it is desirable that the lower end of the foam sensor is separated from the reflux condenser inlet or the like in a general polymerization vessel by 100 mm or more in vertical direction and 200 mm or more from the liquid surface.

Antifoaming Agent and Foaming Inhibition Method Examples of the antifoaming agent used in the present invention include silicone oils such as polysiloxane, dimethylpolysiloxane, diphenylpolysiloxane, etc .;
Aliphatic or aromatic alcohols; surfactants such as polyvinyl alcohols having a low degree of saponification; homopolymers, random copolymers and block copolymers of alkylene oxides such as ethylene oxide, propylene oxide and butylene oxide And the like. These can be used alone or in combination of two or more.

The addition of these defoaming agents to the polymerization system is performed as it is or in a state of being dissolved or dispersed in a solvent such as water.

The total amount of the defoaming agent added throughout the polymerization is usually a ratio of 0.00001 to 0.05 part by weight per 100 parts by weight of the monomer subjected to the polymerization, and the defoaming effect is obtained by adding at such a ratio. Can be If the amount is less than 0.0001 part by weight, the defoaming effect cannot be obtained during the polymerization, and if it exceeds 0.05 part by weight, the obtained vinyl chloride polymer has various physical properties and quality such as particle size distribution, gelling characteristics and the like. It is not preferable because it may adversely affect the image quality.

Foaming during polymerization mainly occurs when the balance between the liquid phase and the gas phase in the polymerization vessel is disrupted due to heat removal by the reflux condenser, and the monomer moves (vaporizes) from the liquid phase to the gas phase.

Therefore, the foam suppression operation at this stage, for example,
It is performed by adding an antifoaming agent into the polymerization reaction system until the detection signal of the foam sensor is turned off when the detection signal of the foam sensor is output, thereby suppressing foaming without reducing the heat removal capacity of the reflux condenser An operation is performed. Specifically, this foam suppression operation is performed by receiving the output of the foam generation signal from the foam sensor and starting the press-fitting pump for adding the antifoaming agent based on the output. This operation may be performed manually or easily.

As a method of adding the defoaming agent, a method of adding it over the entire liquid surface of the liquid phase portion in the polymerization system using a spray such as a nozzle spray is effective and desirable.

The method of the present invention is applied to suspension polymerization, emulsion polymerization, and the like of a vinyl chloride monomer or a monomer mixture mainly composed of vinyl chloride in an aqueous medium.

Kind of Monomer The monomer polymerized by the method of the present invention is a vinyl chloride monomer or a mixture of a vinyl chloride monomer and a monomer (comonomer) copolymerizable with vinyl chloride. In the case of the monomer mixture, the proportion of the vinyl chloride monomer contained in all the monomers is usually 50% by weight or more.

Examples of comonomers copolymerizable with vinyl chloride include vinyl esters such as vinyl acetate and vinyl propionate; acrylates or methacrylates such as methyl acrylate and ethyl acrylate; olefins such as ethylene and propylene; lauryl vinyl ether. And vinyl ethers such as isobutyl vinyl ether; maleic anhydride; acrylonitrile; styrene; and vinylidene chloride. These comonomers can be used alone or in combination of two or more.

Polymerization conditions Other polymerization conditions in the method of the present invention may be the same as those usually used for suspension polymerization or emulsion polymerization of vinyl chloride or a monomer mixture mainly containing vinyl chloride in an aqueous medium.

That is, examples of the polymerization initiator to be used include an oil-soluble catalyst or a water-soluble catalyst used in the production of a conventional vinyl chloride polymer.

Examples of the oil-soluble catalyst include percarbonate compounds such as diisopropyl peroxydicarbonate, bis (2-ethylhexyl) peroxycarbonate and bis (2-ethoxyethyl) peroxydicarbonate;
-Butyl peroxy neodecanoate, t-butyl peroxy pivalate, t-hexyl peroxy pivalate, α-cumyl peroxy neodecanoate and other perester compounds; acetylcyclohexylsulfonyl peroxide, 2,4, Peroxides such as 4-trimethylpentyl-2-peroxyphenoxyacetate, 3,5,5-trimethylhexanoyl peroxide and lauroyl peroxide; azobis-2,4-dimethylvaleronitrile, azobis (4-methoxy-2 And azo compounds such as 4-dimethylvaleronitrile).

Examples of the water-soluble catalyst include potassium peroxodisulfate, ammonium peroxodisulfate, hydrogen peroxide, cumene hydroperoxide and the like.

These polymerization initiators can be used alone or in combination of two or more.

The dispersant used in the method of the present invention may be any of those conventionally known. Such dispersants include, for example, water-soluble cellulose ethers such as methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, and hydroxypropylmethylcellulose; acrylic polymers; water-soluble polymers such as gelatin; sorbitan monolaurate, sorbitan trio Oil-soluble emulsifiers such as acrylate, sorbitan monostearate, glycerin tristearate, ethylene oxide propylene oxide block copolymer; water-soluble emulsifiers such as polyoxyethylene sorbitan monolaurate, polyoxyethylene glycerin oleate, sodium lauryl sulfate; calcium carbonate, phosphorus Caustic acid, sodium dodecylbenzenesulfonate, and the like. These can be used alone or in combination of two or more.

Other polymerization conditions may be the same as the conventional polymerization conditions in the polymerization of a vinyl chloride monomer or a monomer mixture mainly composed of vinyl chloride.

For example, an aqueous medium, a vinyl chloride monomer, and a comonomer, a polymerization initiator, a dispersant, and the like, which are provided for polymerization as required, may be prepared in the same manner as in the related art, and the polymerization temperature may be the same as that in the related art. Same as above.

Further, if necessary, a polymerization regulator, a chain transfer agent, a pH regulator, a gelling improver, an antistatic agent, a crosslinking agent, a stabilizer, which are appropriately used for the polymerization of the monomer or the monomer mixture, The addition of fillers, antioxidants, buffers, scale inhibitors and the like is optional.

〔Example〕

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. In the examples and comparative examples, the apparatus shown in FIG. 1 was used.

As shown in FIG. 1, the apparatus includes a polymerization vessel 1, a stirrer 3 for stirring a polymerization liquid 2 charged in the polymerization vessel 1 during polymerization, and a motor 4 for driving the stirrer 3. It is a thing. A reflux condenser 5, a deionized water charging line 6, a polymerization initiator charging line 7, a monomer charging line 8, an unreacted monomer recovery line 9, and an antifoaming agent supply line 10 are provided above the polymerization vessel 1. Connected and further foam sensor
11 is provided such that its lower end is located at a height of 200 mm from the liquid level. The foam sensor 11 used in the examples and comparative examples is a capacitive sensor DS manufactured by Yamamoto Electric Co., Ltd.
Type.

In this device, a signal from the foam sensor 11 is output to the controller 12, and in response to this signal, the controller 12 outputs a signal to instruct the high-pressure supply pump 13 of the antifoaming agent supply line 10 to operate and stop the operation. Although the addition of the antifoaming agent can be controlled by adding the antifoaming agent, the addition of the antifoaming agent can be performed manually as needed. In Examples and Comparative Examples, the control of the addition of the antifoaming agent was manually performed based on the detection of foam by a sensor.

Example 1 Capacity 1,000 with a reflux condenser (heat transfer area: 4.5 m ² )
48 stainless steel polymerization vessel 1 with deionized water
0 kg, partially saponified polyvinyl alcohol 210 g, and bis (2-ethylhexyl) peroxydicarbonate 28
After 0 g was charged and the inside of the polymerization vessel 1 was evacuated, 350 kg of a vinyl chloride monomer was charged. While stirring these, the temperature was raised to 57 ° C. to start the polymerization, and the heat was removed at 40,000 kcal / H from 0.5 H after the start of the temperature to the end of the polymerization. The amount of heat removal was controlled by the amount of cooling water to the reflux condenser 5. During the polymerization, a 20% by weight aqueous solution of a random copolymer of ethylene oxide and propylene oxide (antifoaming agent)
Was continuously added 2 hours after the start of heating according to the instruction of the foam sensor 11. The total amount of addition is 200 p
pm.

Thereafter, when the pressure in the polymerization vessel 1 dropped to 6.0 kg / cm ² G, the polymerization was stopped, and unreacted monomers were slowly recovered over 1 hour. Next, before the inside of the polymerization vessel 1 is washed, the inner wall of the gas phase part in the polymerization vessel 1 and the reflux condenser conduit 14 are not used.
The adhesion of the polymer inside was observed.

Example 2 An experiment was performed in the same manner as in Example 1 except that the type of the antifoaming agent added during the polymerization was changed.

The antifoam added was a 50% by weight aqueous emulsion of dimethylpolysiloxane. This defoaming agent was continuously added in the same manner as in Example 1 in accordance with the instruction of the foam sensor 2H after the start of the temperature rise. The total amount of addition is 200 p
pm.

Comparative Example 1 Polymerization of vinyl chloride was carried out in the same manner as in Example 1 except that a polymerization vessel not provided with the foam sensor 11 was used and no defoaming agent was added.

Comparative Example 2 Polymerizer 1 used in Example 1 and provided with foam sensor 11 was used, but no defoamer was added. The heat removal by the reflux condenser 5 during the polymerization was performed under the following conditions.

The heat was removed at 42,000 kcal / H from 0.5 H after the start of the temperature rise, and the heat removal amount was reduced to 30,000 kcal / H after 2 H according to the instruction of the foam sensor 11, and the heat was removed until the polymerization was completed. Other polymerization conditions are the same as in Examples 1 and 2.

Comparative Example 3 A 20% by weight aqueous solution (antifoaming agent) of a random copolymer of ethylene oxide and propylene oxide was added to a charged monomer using a polymerization vessel without the foam sensor 11.
Polymerization of vinyl chloride was carried out in the same manner as in Example 1 except that 700 ppm was added before the start of the polymerization.

Comparative Example 4 Using a polymerization vessel without the foam sensor 11, a 20% by weight aqueous solution of an ethylene oxide random copolymer (defoaming agent) was added at 700 ppm to the charged monomers before the start of polymerization. Except for the above, vinyl chloride was polymerized in the same manner as in Example 1.

Table 1 shows the observation results of polymer adhesion on the inner wall surface of the gas phase portion in the polymerization vessel and the reflux condenser conduit in Examples 1 and 2 and Comparative Examples 1 to 4.

The fish eyes of the vinyl chloride polymers obtained in Examples 1 and 2 and Comparative Examples 1 and 2 were measured by the following measurement method.

Fisheye measurement method Vinyl chloride polymer 100 parts by weight DOP (dioctyl phthalate) 50 parts by weight Tribasic lead sulfate 0.5 parts by weight Lead stearate 1.5 parts by weight Titanium oxide 0.1 parts by weight Carbon black 0.05 parts by weight Prepared according to the above formulation 25 g of the blended composition was mixed at 140 ° C. for 5 minutes on a two-roll mill with a 6 ″ roll for kneading.
Kneading for 10 minutes to form a sheet 10 cm wide and 0.2 cm thick.
The number of transparent particles (fish eyes) per 100 cm ^{2 of the} obtained sheet is counted.

 Table 1 shows the measurement results.

With respect to the vinyl chloride polymers obtained in Examples 1 and 2 and Comparative Examples 3 and 4, the passing amount (% by weight) of the polymers was measured using a sieve specified in JIS Z 8801. Table 2 shows the results.

As can be seen from Tables 1 and 2, in Comparative Examples 1 and 2 in which no defoaming agent was added, there were many scale adhesions and many fish eyes.
No comparison with 2. In Comparative Example 3, the type and total amount of the defoaming agent were the same as in Example 1, but since the defoaming agent was added before the start of polymerization, the defoaming effect was small, and the scale adhered. Further, the quality (fish eye, particle size distribution) of the obtained polymer was worse than that of Examples 1 and 2. Furthermore, in Comparative Example 4, scale adhesion was prevented because a large amount of antifoaming agent was added in order to obtain an antifoaming effect, but the quality (fish eye, particle size distribution) of the obtained polymer was It dropped further than 3.

On the other hand, in the case of the first and second embodiments to which the present invention is applied,
Since the addition of the defoamer was properly performed based on the detection of the foam sensor, the amount of the defoamer added was minimized. For this reason,
The influence on the quality (fish eye, particle size distribution) of the obtained product polymer was also reduced by the small amount of the defoaming agent added, and the vinyl chloride polymer could be produced effectively.

〔The invention's effect〕

According to the method of the present invention, foaming of a certain amount or less that does not cause any trouble is allowed, and only foaming exceeding the certain amount is suppressed, which is reasonable.

That is, in the polymerization of a vinyl chloride monomer or a monomer mixture mainly composed of vinyl chloride in an aqueous medium in a polymerization vessel, regardless of the composition of the polymerization system, defoaming is performed based on detection of foam by a foam sensor. By adding the agent as needed, the equipment can be operated efficiently without lowering the heat removal capacity of the condenser, so shortening the polymerization time, improving the operation rate of the polymerization equipment and improving the productivity Can be. In addition, a high-quality vinyl chloride polymer having few fish eyes can be produced with high productivity.

[Brief description of the drawings]

FIG. 1 is a schematic view showing the structure of a polymerization vessel equipped with a foam sensor.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C08F 2/00-2/60

Claims (1)

(57) [Claims] 1. A method comprising the step of polymerizing a vinyl chloride monomer or a monomer mixture containing vinyl chloride as a main component in an aqueous medium in a polymerization vessel, wherein a liquid phase is added to a gas phase of the polymerization vessel. A foam sensor set to detect foam when the foam generated on the surface reaches a predetermined amount or more is provided, and the foam sensor detects the foam that has reached the predetermined amount or more. A method for producing a vinyl chloride polymer, wherein an antifoaming agent is sometimes added to suppress foaming generated during polymerization.