JPH0322882B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved method for polymerizing vinyl chloride monomers. More specifically, vinyl chloride monomers or mixtures of vinyl chloride monomers with copolymerizable monomers (hereinafter collectively referred to as "vinyl chloride monomers"),
The polymer obtained by polymerizing this monomer is called a "vinyl chloride polymer." ), in polymerizing
The present invention relates to a method for preventing polymer scale from forming on the inner wall surface of a polymerization vessel and/or on the surface of equipment attached to a polymerization vessel. Polymerization of vinyl chloride monomers is usually carried out by emulsifying or suspending the vinyl chloride monomers in an aqueous medium containing an emulsifier or dispersant in the presence of a polymerization initiator. In this polymerization process, the inner wall of the polymerization vessel,
The parts where the vinyl chloride monomer comes into contact with the ancillary equipment of the polymerization vessel, such as the stirring blades, bubbles, the walls of the reflux condenser, and the walls of various piping installed in the polymerization vessel (hereinafter, these are collectively referred to as the ``polymerization vessel''). Polymer scale adheres to the inner walls, etc.), which reduces the polymer yield and reduces the cooling capacity of the polymerization reactor. In addition, the peeled scale mixed into the product deteriorates the physical properties of the product (e.g. At the same time, excessive labor and time are required to remove the attached scale, and the operating rate of the polymerization reactor is reduced.
Furthermore, if one attempts to remove attached scale by entering the polymerization vessel, one will be exposed to vinyl chloride monomer, which is not favorable from an occupational hygiene standpoint. Therefore, solving these problems has been a long-standing concern for manufacturers of vinyl chloride polymers. Conventionally, as a method to prevent polymer scale from adhering to the inner walls of polymerization vessels, polar compounds such as amine compounds, quinone compounds, and aldehyde compounds (Japanese Patent Publication No. 45-30343), dyes (Japanese Patent Publication No. 45-30835) and a free radical inhibitor (Japanese Patent Application Laid-open No. 48-44375). However, these methods have the disadvantage that they do not have a sufficient effect of preventing scale adhesion, and that the sustainability of the preventive effect is low. In addition, in the method of applying a mixture of a film-forming resin and a polymerization inhibitor (Japanese Patent Application Laid-Open No. 52-98081), the film-forming resin is insoluble in water, so it is necessary to dissolve it in an organic solvent before use. There are problems with toxicity and safety due to organic solvents. As a result of intensive studies in order to solve the problems of conventional methods, the present inventors have developed a hydrophilic polymer substance that can form a crosslinked polymer substance by reacting a hydrophilic polymerization inhibitor with methylolmelamine and methylolmelamine. By applying it as a fixing agent, it has an extremely remarkable effect on preventing scale adhesion, and
The present invention was completed based on the discovery that the preventive effect can be maintained for a long period of time. That is, the purpose of the present invention is to industrially advantageously carry out the polymerization reaction of vinyl chloride monomers, and the purpose is to carry out the polymerization reaction of vinyl chloride monomers mainly using vinyl chloride monomers or vinyl chloride monomers. When a mixture with a copolymerizable monomer is polymerized in an aqueous medium, a hydrophilic polymerization inhibitor, methylolmelamine, and a compound capable of crosslinking with methylolmelamine is applied to the inner wall of the polymerization vessel and/or the surface of ancillary equipment of the polymerization vessel in advance. This is easily accomplished by coating the three components of the hydrophilic polymeric material in their respective solvent solutions or in a combined solvent solution. The present invention will be explained in more detail below. The present invention is a method in which a hydrophilic polymerization inhibitor, methylol melamine, and a hydrophilic polymer substance capable of reacting with methylol melamine to form a crosslinked polymer substance are coated onto the inner wall of a polymerization vessel, etc., as essential ingredients. In this method, only two components, methylolmelamine used as a fixing agent for a hydrophilic polymerization inhibitor, and a hydrophilic polymer substance capable of reacting with methylolmelamine to form a crosslinked polymer substance are coated on the inner wall of a polymerization vessel, etc. When carrying out a polymerization reaction of vinyl chloride monomers, a sufficient scale adhesion prevention effect cannot be obtained. In addition, when a hydrophilic polymerization inhibitor alone is applied to the inner wall of a polymerization vessel to perform a polymerization reaction of vinyl chloride monomers, a relatively good effect of preventing scale adhesion can be obtained, but scale adhesion occurs in a short period of time. The preventive effect will be lost. However, as mentioned above, by using a hydrophilic polymerization inhibitor with a low lasting scale prevention effect in combination with methylolmelamine and a hydrophilic polymer substance according to the method of the present invention, an excellent scale prevention effect can be obtained. The unexpected effect is that the preventive effect can be maintained for a long time. Hydrophilic polymerization inhibitors used in the method of the present invention include both so-called polymerization inhibitors, which capture radicals and inhibit the polymerization reaction of vinyl chloride monomers, and so-called polymerization retarders, which suppress or delay the polymerization reaction. Among these, those soluble in water (those having sufficient water solubility to be used as a coating solution) are included, such as phenol, hydroquinone, t-butylcatechol, cresol, catechol, resorcinol, Phenols such as pyrogallol and hydroxyhydroquinone, disodium ethylenediaminetetraacetate, triethylamine,
Amines such as N-nitrosophenylhydroxylamine ammonium salt, 2-vinylpyridine, 3
- Vinylpyridines such as vinylpyridine, nitrites such as sodium nitrite, potassium nitrite, ammonium nitrite, diisopropylammonium nitrite, triethylamine nitrite, sodium dithiocarbamates such as dimethyldithiocarbamate, diethyldithiocarbamate, diisopropyldithiocarbamate salt, lithium salt,
Examples include metal salts such as potassium salts, dithiocarbamates such as ammonium salts, molybdates, phosphomolybdates, and inorganic metal salts such as cupric chloride, ferric chloride, and stannous chloride. These may be used alone or in a mixture of two or more. In addition, methylolmelamine includes monomethylolmelamine, dimethylolmelamine, trimethylolmelamine, tetramethylolmelamine,
Examples include pentamethylolmelamine and hexamethylolmelamine, and these may be used alone or in a mixture of two or more. Further, a condensate of methylolmelamine may be contained in the methylolmelamine to the extent that it is soluble in water. Furthermore, alkylated methylolmelamine obtained by alkylating the methylolmelamine with alcohol or the like, such as methylated methylolmelamine, can also be used. Next, as the hydrophilic polymer substance, a hydrophilic polymer substance that reacts with methylolmelamine to form a crosslinked polymer substance is used, and a functional group that can react with the methylol group, imino group, or alkoxy group of methylolmelamine is used. For example, those having a hydroxyl group, a carboxyl group, an amide group, etc. and are hydrophilic are used. Specific examples include polyvinyl alcohol, polyacrylic acid, polyacrylamide, polyethyleneimine, partially saponified polyvinyl acetate, and the like, and these may be used alone or in a mixture of two or more. In order to apply a hydrophilic polymerization inhibitor to the inner wall of a polymerization vessel using methylolmelamine and a hydrophilic polymer substance as a fixing agent according to the method of the present invention, a solution of these components (from the working surface, it is better to use an aqueous solution) is used. ) may be applied to surfaces such as the inner wall of the polymerization vessel, either singly or in combination, but in order to carry out the application process more efficiently, it is necessary to first apply a hydrophilic polymerization inhibitor and a hydrophilic polymer substance. It is preferable to dissolve these in water, add methylolmelamine immediately before coating, and apply as a three-component mixed aqueous solution. The mixing ratio of the above three components is not particularly limited, but in order to obtain good coating performance, the ratio of hydrophilic polymerization inhibitor/methylol melamine/hydrophilic polymer substance should be 100/10 to 1000 by weight. It is preferably within the range of /10 to 1000. Further, from the viewpoint of coating workability due to viscosity, etc., it is preferable to use an aqueous solution containing 0.1 to 30% by weight of the above three components. This aqueous solution may be applied to the inner wall of the polymerization vessel by a commonly used application means such as spraying. In the coating film, the methylolmelamine and the hydrophilic polymer substance undergo a crosslinking reaction and become water-insoluble, thereby firmly adhering the hydrophilic polymerization inhibitor to surfaces such as the inner wall of the polymerization vessel. Although this crosslinking reaction can be carried out by leaving it at room temperature for a long time, it is preferable to accelerate the reaction by heating to 50 to 150°C. The amount of the three components to be applied is usually 0.01% of the surface to which the total amount is applied, i.e., the inner wall of the polymerization vessel, etc.
g/m ² or more, preferably in the range of 0.01 to 10 g/m ² . If the coating amount is less than 0.01 g/m ² , scale generation cannot be sufficiently suppressed, and if the coating amount is 10 g/m ²
Above this, no increase in the prevention effect can be expected, and on the contrary, the adhesion of the coating material to the wall surface becomes weaker, which is not preferable. It is preferable to use a coating agent obtained by adding a xanthate to the above three components, since this further improves the sustainability of the scale adhesion prevention effect.
Examples of the xanthate include sodium salts such as methylxanthate, ethylxanthate, and propylxanthate, metal salts such as lithium salts, potassium salts, and ammonium salts. The amount of xanthate added is preferably in the range of 10 to 300 parts by weight per 100 parts by weight of the hydrophilic polymerization inhibitor. The polymerization of vinyl monomers in the method of the present invention includes:
All commonly known polymerization formulations are adopted, and the dispersants, emulsifiers, polymerization initiators, etc. used do not need to be special ones; commonly used dispersants,
Emulsifiers and polymerization initiators can be used. For example, dispersants and emulsifiers include protective colloidal agents such as partially saponified polyvinyl acetate, acrylic acid copolymers, maleic anhydride copolymers, cellulose derivatives, gelatin, starch, etc., or natural polymers. Compounds, esters of higher fatty acids and polyhydric alcohols, nonionic surfactants such as polyoxyethylene derivatives, metal salts of higher fatty acids, anionic surfactants such as alkali salts of higher alcohol sulfates, and the like are used. Examples of polymerization initiators include organic peroxides such as benzoyl peroxide, lauroyl peroxide, dioctyl peroxycarbonate, and acetylcyclohexylsulfonyl peroxide, azo compounds such as azobisisobutyronitrile and dimethylvaleronitrile, potassium persulfate, ammonium persulfate, etc. persulfates are used. The vinyl chloride monomer used in the method of the present invention may be a vinyl chloride monomer itself or a mixture of a vinyl chloride monomer as a main component and a monomer copolymerizable with it. Commonly used copolymerizable monomers include olefins such as ethylene and propylene, vinyl esters such as vinyl acetate and vinyl stearate, vinyl ethers such as ethyl vinyl ether and cetyl vinyl ether, acrylic esters, maleic acid, and Any conventionally known monomer copolymerizable with vinyl chloride can be used, such as fumaric acid esters and anhydrides, aromatic vinyl compounds such as styrene, and nitrile compounds such as acrylonitrile. According to the method of the present invention, during the polymerization reaction, there is no or an insignificant amount of scale attached to the inner walls of the polymerization vessel, so the occurrence of scales in the final processed product is drastically reduced and the quality of the product is improved. Furthermore, since the number of times the inner walls of the polymerization vessel must be fixed is significantly reduced, operation can be continued for a long period of time without cleaning, productivity is improved, and extremely advantageous results can be obtained from a cost perspective. In addition, not only does operational management such as cooling become easier, but it also becomes possible to use a reflux condenser as a new cooling means. Other coating materials used in the method of the present invention are water-soluble and are used after being dissolved in water.
There are no adverse effects such as recovery of the solvent when using an organic solvent or deterioration of the working environment during drying of the coating film. Furthermore, the method of the present invention is applicable to cases where low-boiling point polymerization initiators, such as t-butyl peroxypivalate or diisopropyl peroxydicarbonate, which have conventionally caused particularly significant scale deposition, are used, or when special polymerization initiators are used for quality improvement. Even when an auxiliary agent such as sorbitan ester is added, a stable scale adhesion prevention effect is exhibited. Example 1 Methylolmelamine (manufactured by Sumitomo Chemical Co., Ltd., trade name Sumimaru M-50W), sodium dimethyldithiocarbamate, and water were added and mixed in specific amounts to a 2% by weight aqueous solution of polyvinyl alcohol, and 1% by weight of polyvinyl alcohol and 5% by weight of methylolmelamine were added. Weight% and sodium dimethylcarbamate
An aqueous coating solution containing 0.2% by weight was prepared.
This coating liquid was sprayed onto the inner wall of a stainless steel polymerization vessel with an internal volume of 400 mm and the surface of the stirring blade using an iron sprayer in an amount of 100 g of coating liquid per 1 m ² of coating area, and heated and dried at 80°C for 30 minutes. A film was formed on the inner wall surface. Using this polymerization vessel, 150 kg of deionized water, 60 g of partially saponified polyvinyl acetate,
100 kg of vinyl chloride monomer and 25 g of t-butyl peroxypivalate were charged, and polymerization was carried out at about 58°C until a predetermined polymerization rate was reached. After the reaction was completed, the inside of the vessel was washed with water, and after drying, the amount of scale attached was measured.
The results are shown in Table 1. Furthermore, the same polymerization as above was carried out for 30
Table 1 shows the measurement results of the amount of scale deposited when the measurements were carried out continuously in batches. Example 2 The same procedure as in Example 1 was carried out except that partially saponified polyvinyl acetate was used instead of polyvinyl alcohol. The results are shown in Table 1. Example 3 The same procedure as in Example 1 was carried out except that polyacrylic acid was used instead of polyvinyl alcohol. The results are shown in Table 1. Example 4 The same procedure as in Example 1 was carried out except that the concentration of sodium dimethyldithiocarbamate in the coating solution was changed to 1% by weight. The results are shown in Table 1. Example 5 Same as Example 1 except that an aqueous solution containing 5% by weight of methylolmelamine, 1% by weight of partially saponified polyvinyl acetate, and 1% by weight of sodium dimethyldithiocarbamate was used as the coating liquid. I did it. The results are shown in Table 1. Example 6 The same procedure as Example 5 was carried out except that polyethyleneimine was used instead of partially saponified polyvinyl acetate. The results are shown in Table 1. Example 7 The same procedure as in Example 1 was carried out except that t-butylcatechol was used instead of sodium dimethyldithiocarbamate.
The results are shown in Table 1. Example 8 The same procedure as in Example 1 was carried out except that hydroquinone was used instead of sodium dimethyldithiocarbamate. The results are shown in Table 1. Example 9 The same procedure as in Example 1 was carried out except that N-nitrosophenylhydroxylamine ammonium salt was used instead of sodium dimethyldithiocarbamate. The results are shown in Table 1. Example 10 The same procedure as in Example 1 was carried out except that sodium molybdate was used instead of sodium dimethyldithiocarbamate. The results are shown in Table 1. Example 11 Example 1 was carried out in the same manner as in Example 1, except that an aqueous solution containing 1% by weight of methylolmelamine, 1% by weight of polyethyleneimine and 0.5% by weight of sodium molybdate was used as the coating liquid. The results are shown in Table 1. Example 12 The same procedure as Example 11 was carried out except that the concentration of polyethyleneimine in the coating liquid was changed to 0.5% by weight. The results are shown in Table 1. Example 13 In Example 1, the coating liquid contained 5% by weight of methylolmelamine, 1% by weight of partially saponified polyvinyl acetate, and sodium dimethyldithiocarbamate.
0.2% by weight and potassium ethylxanthate 0.2
Example 1 was carried out in the same manner as in Example 1, except that an aqueous solution containing % by weight was used. The results are shown in Table 1. Example 14 The same procedure as in Example 13 was carried out except that the concentrations of sodium dimethyldithiocarbamate and potassium ethylxanthate in the coating solution were changed to 0.5% by weight and 0.5% by weight, respectively. The results are shown in Table 1. Example 15 Example 13 was carried out in the same manner as in Example 13, except that the concentration of methylolmelamine in the coating liquid was changed to 2% by weight. The results are shown in Table 1. Example 16 Same as Example 1 except that an aqueous solution containing 2% by weight of methylolmelamine, 1% by weight of polyacrylic acid, 0.2% by weight of hydroquinone and 0.2% by weight of potassium ethylxanthate was used as the coating solution. I did the same thing. The results are shown in Table 1. Example 17 Example 16 was carried out in the same manner as Example 17 except that the concentration of polyacrylic acid in the coating liquid was changed to 0.5% by weight. The results are shown in Table 1. Comparative Example 1 The same procedure as in Example 1 was carried out except that the coating liquid was not applied at all to the inner wall of the polymerization vessel and the surface of the stirring blade. The results are shown in Table 1. Comparative Example 2 Example 1 except that an aqueous solution containing 5% by weight of methylolmelamine and 1% by weight of polyvinyl alcohol was used as the coating liquid.
I did the same thing. The results are shown in Table 1. Comparative Example 3 In Example 1, 5% by weight of methylolmelamine and 1% of partially saponified polyvinyl acetate were used as the coating liquid.
Example 1 was carried out in the same manner as in Example 1, except that an aqueous solution containing % by weight was used. The results are shown in Table 1. Comparative Example 4 In Example 1, 5% by weight of methylolmelamine and 1% by weight of polyacrylamide were used as the coating liquid.
The same procedure as in Example 1 was carried out except that an aqueous solution containing . The results are shown in Table 1. Comparative Example 5 The same procedure as in Example 1 was conducted except that an aqueous solution containing 5% by weight of methylolmelamine and 1% by weight of polyethyleneimine was used as the coating liquid. The results are shown in Table 1. Comparative Example 6 The same procedure as in Example 1 was conducted except that a 1% by weight aqueous solution of potassium ethylxanthate was used as the coating liquid. The results are shown in Table 1. Comparative Example 7 The same procedure as in Example 1 was conducted except that a 0.2% by weight aqueous solution of sodium dimethyldithiocarbamate was used as the coating liquid. The results are shown in Table 1.

【table】

[Table] Reference Examples 1 to 3 In Example 1, Comparative Example 1 or Comparative Example 7,
The quality of vinyl chloride polymers obtained by specific batches of polymerization reactions was evaluated by the following method. A mixture obtained by sufficiently mixing 100 parts of vinyl chloride polymer, 50 parts of dioctyl phthalate, and 3 parts of a lead-based stabilizer was kneaded for 5 minutes with a roll at 155°C. The number of fish eyes observed in 25 cm ² of the obtained rolled sheet was counted. The results are shown in Table 2.

【table】

Claims (1)

[Claims] 1. Before polymerizing vinyl chloride monomer or a mixture of vinyl chloride monomer and copolymerizable monomers in an aqueous medium, the surface of the inner wall of the polymerization vessel and/or the incidental equipment of the polymerization vessel must be prepared in advance. The method is characterized in that the three components, a hydrophilic polymerization inhibitor, methylolmelamine, and a hydrophilic polymer substance capable of crosslinking with methylolmelamine, are applied in a solvent solution of each or a combination of the three components. A method for polymerizing vinyl chloride monomers.