JPS6239601B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved suspension polymerization method for vinyl chloride monomers. Suspension polymerization of vinyl chloride is usually carried out in a batch process, in which an aqueous medium, a dispersion aid (suspending agent), a polymerization initiator, and vinyl chloride monomer are charged into a polymerization vessel, and then the necessary In this method, the polymerization reaction is carried out by adding the additives and then raising the temperature. However, in order to shorten the time required for one batch of polymerization in order to improve productivity, it is necessary to shorten the temperature raising time as well as shorten the preparation time and reaction time. In particular, in large polymerization vessels and polymerization vessels with condensers, the heating capacity of jackets and the like is relatively small compared to the internal volume, and therefore it is necessary to develop a more effective temperature raising method. In order to achieve this purpose, a method can be considered in which the charging water or vinyl chloride monomer is heated in advance before charging, but if the polymerization initiator is charged together with the heated aqueous medium, the polymerization initiator will rapidly decompose. However, if vinyl chloride monomer and polymerization initiator are charged after heating water, polymerization will begin during the charging process, and in either case, scale will form on the walls of the polymerization vessel, and the resulting polymer will be extremely It will have a lot of fish eyes. Furthermore, if a polymerization initiator is added and polymerized after the heated aqueous medium and vinyl chloride monomer are added, the amount of fisheye will increase. Similar disadvantages arise when the monomers are heated and charged. The present inventors completed the present invention as a result of intensive research to develop a polymerization method that greatly shortens the time required for one batch of polymerization without the above-mentioned drawbacks. The aqueous medium, vinyl chloride monomer, and polymerization initiator are heated in advance so that the temperature of the polymerization system becomes -5≦T≦2 with respect to the set polymerization temperature (T°C) during and at the completion of the preparation. At the same time, the homogeneous mixture is charged within 30 minutes at a feeding rate adjusted to maintain the above-mentioned temperature conditions, and within this feeding time, a dispersion aid is charged to start the polymerization reaction, and the mixture is heated for 2 hours. The present invention relates to a method for suspension polymerization of vinyl chloride monomers, which is characterized in that the polymerization reaction is completed while removing the reaction heat while maintaining the temperature at which the polymerization rate after the elapse of time is maintained at 5% or less. According to the above-mentioned method of the present invention, the time required for one batch from preparation to completion of polymerization can be significantly shortened, and it is possible to obtain high-quality vinyl chloride polymers with less fissures at extremely high productivity. It gives you the advantage of being able to. The present invention will be explained in detail below. To carry out the method of the present invention, first, a heated aqueous medium and a homogeneous mixture of a vinyl chloride monomer and a polymerization initiator are simultaneously charged into a polymerization vessel. It is necessary that the mixing system of polymer and polymerization initiator be a homogeneous mixture, and if this mixing system is non-uniform, the resulting polymer will be of low quality with a lot of stickiness, which is disadvantageous. . This homogeneous mixture may be charged by a method in which the vinyl chloride monomer and the polymerization initiator are uniformly mixed in advance in a suitable tank or continuous mixer, and then the mixture is charged into the polymerization vessel. When preparing a homogeneous mixture of the vinyl chloride monomer and the polymerization initiator, the temperature of the mixture must be kept below the temperature at which the polymerization initiator substantially decomposes. Although it is acceptable that a slight decomposition may occur,
The temperature must be at least such that the polymerization rate of the mixed system after 2 hours is 5% or less. If the above conditions are not maintained, scale will be produced and the resulting polymer will have a lot of fisheye. Therefore, depending on the type of polymerization initiator and the charging ratio to the monomer, it is effective not only to use the above temperature conditions but also to add a small amount of a polymerization inhibitor or polymerization inhibitor, and in the present invention, these additions are also effective. You may do so as appropriate. On the other hand, at the same time as the homogeneous mixture of vinyl chloride monomer and polymerization initiator is charged, a heated aqueous medium is charged to start the polymerization reaction, and the heating temperature of this aqueous medium varies during and at the completion of the preparation. It is necessary to set the temperature of the polymerization system so that -5≦T≦2 with respect to the set polymerization temperature (T℃).If the temperature of the polymerization system during and at the completion of charging is too high, the polymerization reaction will occur. If the temperature is too low, it will take time to raise the temperature to the set polymerization temperature, which is disadvantageous in achieving the purpose of the present invention. Both preparations must be carried out with stirring, but it is desirable to make the preparation speed as fast as possible, and usually it is necessary to complete the preparation within 30 minutes. If the preparation takes longer than this, the amount of scale adhering to the polymerization vessel will increase, and the resulting polymer will be of low quality with a lot of stickiness.
A dispersing agent (suspending agent) for uniformly dispersing the monomer in the polymerization system is used together with the vinyl chloride monomer in the case of oil-soluble monomers, and together with the heated aqueous medium in the case of water-soluble monomers. However, it is desirable that this is added and dissolved as uniformly as possible. Note that it may be added as a highly concentrated aqueous solution, and in this case, it is preferably added mainly at the initial stage of preparation. If this happens after preparation, it will lead to the formation of scale and an increase in the size of the fish. The above-mentioned dispersion aids may be those commonly used in the polymerization of vinyl chloride in an aqueous medium, including water-soluble cellulose ethers such as methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, and hydroxypropylmethylcellulose; polyvinyl alcohol,
Acrylic acid polymers, water-soluble polymers such as gelatin, oil-soluble emulsifiers such as sorbitan monolaurate, sorbitan triolate, glycerin tristearate, ethylene oxide propylene oxide block copolymer, polyoxyethylene sorbitan monolaurate, polyoxyethylene glycerin oleate , and water-soluble emulsifiers such as sodium laurate, which may be added singly or in combination of two or more. On the other hand, the polymerization initiator may also be one conventionally used in the polymerization of vinyl chloride, including percarbonates such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethyl peroxydicarbonate. Compound, t-butylperoxyneodecanate, α-cumylperoxyneodecanate, t-
Perester compounds such as butyl peroxyneodecanate, acetylcyclohexylsulfonyl peroxide, 2,4,4-trimethylpentyl-
Peroxides such as 2-peroxyphenoxy acetate, azo compounds such as azobis-2,4-dimethylvaleronitrile, azobis(4-methoxy-2,4-dimethylvaleronitrile), and potassium persulfate, Ammonium sulfate, hydrogen peroxide, etc. can be used alone or in combination. Furthermore, it is also optional to add polymerization regulators, chain transfer agents, PH regulators, gelling improvers, antistatic agents, etc. that are appropriately used in the polymerization of vinyl chloride. The vinyl chloride monomer to be polymerized in the method of the present invention includes not only vinyl chloride alone, but also a monomer mixture mainly composed of vinyl chloride (50% by weight or more of vinyl chloride), which can be copolymerized with vinyl chloride. Examples of comonomers include vinyl esters such as vinyl acetate and vinyl propionate, acrylic esters or methacrylic esters such as methyl acrylate and ethyl acrylate, olefins such as ethylene and propylene, maleic anhydride, acrylonitrile, styrene, and vinylidene chloride. , and other monomers copolymerizable with vinyl chloride. In carrying out the method of the present invention, the charging ratio of each component, polymerization temperature, etc. may be determined according to the conditions conventionally employed in suspension polymerization of vinyl chloride.
There is no particular reason to limit it. The method of the present invention has the advantage that the polymerization time for one batch can be significantly shortened. If the heating capacity is small compared to the internal volume,
In other words, it is effective when the ratio of the maximum heat removal capacity of the condenser to that of the jacket is large, and high productivity can be achieved. Of course, the same applies to polymerizers without condensers. Next, a specific example will be given. Example 1 (Experiment Nos. 1 to 8) The following polymerization was carried out using a polymerization vessel equipped with a stirring device and having a jacket around the outer periphery and having an internal volume of 1.2 m ³ . Mixture A: 350 kg of vinyl chloride (VC) and 200 g of di-2-ethylhexyl peroxydicarbonate
A homogeneous mixture of dissolved The temperature of this mixture in each experiment No. is as shown in Table 1, and the polymerization rate after 2 hours at that temperature is also listed. Mixture B: Partially saponified polyvinyl alcohol 150
g and 50 g of hydroxypropyl methylcellulose
A mixture of 480 kg of water (aqueous medium). The aqueous medium was preheated to the temperatures shown in Table 1. The above mixture A and mixture B were charged into a polymerization vessel while maintaining a weight ratio of 1.37, and a polymerization reaction was carried out while controlling the internal temperature at 57°C. The temperature of the polymerization system during and at the completion of charging mixture A and mixture B was as shown in Table 1. When the polymerization approached the end and the internal pressure decreased to 7 kg/cm ² G, unreacted monomers were collected and dehydrated and dried to obtain a vinyl chloride resin. The state of scale adhesion of the thus produced resin to the fish eye and the inner wall of the polymerization vessel was as shown in Table 1. However, Experiment No. 8* shows the case where heated water in which no suspending agent was dissolved and Mixture A were prepared in the same manner, and then the suspending agent was added to cause polymerization. . Polymerization rate (%) of a homogeneous mixture of vinyl chloride and polymerization initiator after 2 hours: 20 ml of the homogeneous mixture was left in a glass sealed tube for 2 hours, and the polymerization rate at that time was measured. Fisheries (pieces): 100 parts by weight of vinyl chloride resin obtained by polymerization,
1 part by weight of tribasic lead sulfate, 1.5 parts by weight of lead stearate
25g of a compound containing 0.2 parts by weight of titanium oxide, 0.1 parts by weight of carbon black, and 50 parts by weight of DOP was kneaded for 5 minutes with a roll at 145°C, separated into a 0.2 mm thick sheet, ^and the The number of transparent particles is also shown. Scale adhesion condition: 〇: Almost no scale adhesion. △: Scale adhesion at the air-liquid interface. ×: There was scale adhesion all over the inner wall of the polymerization vessel.

[Table] Example 2 (Experiment Nos. 9 to 12) Internal volume 40 with a condenser with a heat transfer area of 40 m ²
13 tons of vinyl chloride and 18 m ³ of heated water were charged into ^a 3 m 3 polymerization reactor at a rate of 0.65 t/min and at a rate of 0.9 m ³ /min, respectively, while stirring simultaneously. In addition, di(ethoxyethyl) is used as a polymerization initiator in the middle of the line where vinyl chloride is charged into the polymerization vessel.
50% toluene solution of peroxydicarbonate 14
Kg was injected at a rate of 0.7 Kg/min and further mixed with a static mixer. Similarly, 3.0 kg of partially saponified polyvinyl alcohol and hydroxypropyl methylcellulose are added to water.
2.5 kg of water dissolved in 100 g of water was mixed at a rate of 5 minutes. The preparation was carried out as described above, and the polymerization reaction was carried out while maintaining the internal temperature at 57°C. When the polymerization was nearing its end and the internal pressure had dropped to 7 kg/cm ² G, unreacted vinyl chloride was collected and dehydrated and dried. The results were as shown in Table 2. However, Experiment No. 12* shows the results obtained using the most common method of charging, i.e., charging the same formulation in the order of aqueous medium, polymerization initiator, and vinyl chloride monomer. As is clear from the above examples, the results according to the present invention (Experiment Nos. 1, 2, 4, 7, 9, and 10) showed that no scale was formed despite the shortening of the polymerization time. In addition, a high quality vinyl chloride polymer with less fibers was obtained.

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Claims (1)

[Claims] 1. An aqueous medium which is preheated in a polymerization vessel so that the temperature of the polymerization system during charging and at the completion of charging is -5≦T≦2 with respect to the set polymerization temperature (T°C);
A homogeneous mixture of vinyl chloride monomer and polymerization initiator is simultaneously charged within 30 minutes at a feeding rate adjusted to maintain the above-mentioned temperature conditions, and a dispersion aid is charged within this feeding time. A vinyl chloride monomer characterized in that the polymerization reaction is started, the polymerization rate of the mixture is maintained at a temperature of 5% or less after 2 hours, and the polymerization reaction is completed while removing the reaction heat. suspension polymerization method. 2. The suspension polymerization method according to claim 1, characterized in that the charging is carried out quickly with stirring. 3. The suspension polymerization method according to claim 1, characterized in that a polymerization vessel equipped with a stirrer, a jacket for removing heat, and a condenser is used.