JP3213825B2 - Method for producing vinyl chloride polymer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aqueous suspension polymerization of a vinyl chloride polymer. The vinyl chloride polymer obtained by the present invention has excellent heat stability and is suitable for various molded articles. It is.

[0002]

2. Description of the Related Art Improving the thermal stability of a vinyl chloride polymer such as polyvinyl chloride obtained by an aqueous suspension polymerization method is an important technical problem in the polymer. Many studies have been made from the viewpoint of improving the polymerization method or blending a heat stabilizer into the polymer. As one example, there is a technical means of suspension polymerization of vinyl chloride in a state where fine powder of hydrotalcite is dispersed in an aqueous medium. According to the suspension polymerization method employing such means, hydrotalcite is used. As compared with a suspension polymerization method in which no vinyl chloride is added, a vinyl chloride-based polymer excellent in thermal stability can be obtained.

[0003] Hydrotalcite has the chemical formula Mg ₆ A
l ₂ (OH) ₁₆ CO ₃ · 4H ₂ O is a name indicating a natural mineral, but recently, an inorganic compound represented by the following general formula and having a structure basically similar to the above-mentioned natural mineral is described below. It is also commonly used as a generic term. Mg _1-x Al _x (OH) ₂ (CO ₃ ) _{x / 2} · mH ₂ O (where x is a number from 0 to 0.33 and m is a number from 0 to 2) Also, the term hydrotalcite is used to mean the hydrotalcites represented by the above general formula.

Hitherto, hydrotalcite surface-treated with a hydrophobic organic compound has been added to a suspension polymerization system of vinyl chloride. Because it was difficult to obtain a liquid, the method was to manually add the powder as it was to a polymerization vessel in a solid state. However, in the method in which the powder is added to the polymerization vessel in a solid state, it is difficult to automate the addition step, and in order to improve the production efficiency of the vinyl chloride polymer, hydrotalcite that enables the step to be automated is improved. There has been a need for a stable aqueous dispersion of powder.

[0005] There has also been proposed a use method in which an aqueous slurry of hydrophilic hydrotalcite is added to an aqueous medium, and polymerization is carried out in the obtained aqueous medium containing hydrotalcite dispersed therein (Japanese Patent Application Laid-Open No. Sho 61-1986). No. 207), such a method has a problem that a part of hydrotalcite aggregates in an aqueous medium.

[0006]

SUMMARY OF THE INVENTION The present invention enables the addition of hydrotalcite to a polymerization medium to be automated,
An object of the present invention is to provide a method for producing a vinyl chloride-based polymer, which can provide a vinyl chloride-based polymer having excellent thermal stability with high production efficiency.

[0007]

Means for Solving the Problems The present inventors have made intensive studies to solve the above problems, and as a result, have completed the present invention. That is, the present invention, when performing a suspension polymerization of a vinyl chloride monomer or a monomer mixture comprising the monomer and a copolymerizable monomer in an aqueous medium, before or during the polymerization, This is a method for producing a vinyl chloride polymer, comprising adding an aqueous hydrotalcite emulsion obtained by a production method comprising the following steps [A] to [C].

[A]: a step of mixing a hydrotalcite powder surface-treated with a water-insoluble organic compound and an emulsifier in a powder mixer. [B]; stirring the dispersion obtained by throwing the powder mixture obtained in the step [A] into water while maintaining the temperature of the dispersion at a temperature equal to or higher than the melting point of the emulsifier, to obtain an aqueous emulsion. Process. [C]: a step of cooling the liquid temperature of the obtained aqueous emulsion to a temperature lower by at least 5 ° C. than the melting point of the emulsifier, while continuing the stirring after the step [B].

Hereinafter, the present invention will be described in more detail. Hydrotalcite used in the present invention,
Hydrotalcite in which a water-insoluble organic compound is treated on the surface of the particles, has poor hydrophilicity, and usually floats in water in the state of fine powder, and does not form an aqueous slurry. Preferably, it is hydrotalcite having a particle size of 0.01 to 1.0 μm.

As the organic compound, higher fatty acids having a long-chain alkyl group, polyvalent metal salts of higher fatty acids and higher fatty acid amides are preferable.
Palmitic acid, myrisnanic acid and the like; calcium stearate, zinc stearate, calcium palmitate and the like; stearylamide, methylene-bis-stearylamide and the like.

The inorganic hydrotalcite to be treated with the organic compound is not particularly limited, and any of the hydrotalcites having the chemical formula shown in the section of the prior art can be used. A typical example of hydrotalcite surface-treated with a water-insoluble organic compound is DHT-4A (trade name, manufactured by Kyowa Chemical Industry Co., Ltd.). Using hydrotalcite that has not been treated with organic substances,
When aqueous emulsification was performed according to the following method, when stirring was stopped, hydrotalcite was directly settled,
A uniform emulsion cannot be obtained.

Preferred emulsifiers used for emulsifying hydrotalcite are nonionic surfactants and anionic surfactants, more preferably nonionic surfactants. As nonionic surfactants,
Glycerin monostearate, glycerin fatty acid esters such as glycerin monooleate and glycerin monolaurate, and sorbitan laurate, sorbitan oleate and sorbitan fatty acid esters such as sorbitan stearate are representative examples, and as the anionic surfactant, Examples include sodium stearate, sodium oleate, potassium laurate and sodium lauryl alcohol sulfate. The melting points of typical emulsifiers are as follows. Glycerin monostearate; 63-68 ° C, glycerin monooleate; 52-58 ° C, sorbitan stearate; 59-6
3 ° C.

The preferred amount of the emulsifier used for hydrotalcite is 10 to 40 parts by weight, more preferably 20 to 40 parts by weight, per 100 parts by weight of hydrotalcite.
35 parts by weight. When the proportion of the emulsifier is less than 10 parts by weight, the resulting aqueous dispersion of hydrotalcite has poor dispersion stability, while the amount of the emulsifier exceeding 40 parts by weight is excessive.

The mixing of the hydrotalcite and the emulsifier in the step [A] is usually carried out dry using a powder mixer. Specifically, for example, if the total amount of the mixture is about 100 g, the product name is KENMIX-C manufactured by Aikosha Seisakusho.
A sufficiently uniform mixture can be obtained by mixing at a temperature of about 20 to 30 ° C. (hereinafter referred to as room temperature) for about 15 to 30 minutes using a powder mixer such as HEF (hereinafter referred to as Kenmix mixer). Due to this mixing, most of the hydrotalcite is assumed to be in a state of being adsorbed on the surface of the emulsifier particles. In the present invention, a mixing step of hydrotalcite and an emulsifier is essential, and if this step is omitted, a hydrotalcite aqueous emulsion having good dispersion stability cannot be obtained.

In the next step [B], the powder mixture obtained by the above mixing is put into water, and the mixture is stirred while maintaining the liquid temperature at or above the melting point of the emulsifier used. Pour the powder mixture into water heated to a temperature equal to or higher than the melting point of the emulsifier, or pour into water at room temperature,
Subsequently, the water temperature may be raised to a temperature higher than the melting point of the emulsifier by heating. Then, the stirring is performed while maintaining the liquid temperature at the above-mentioned temperature until a stable aqueous emulsion is obtained, that is, until the solid content does not separate in the aqueous emulsion even when the stirring is stopped.

As a stirrer used in this step, a stirrer having a stirring blade such as a paddle, a propeller, a turbine, a faudler or a blue margin can be used. The ratio of the powder mixture and the water into which the powder mixture is introduced is preferably 1 to 30% by weight, more preferably 2 to 15% by weight in terms of the solid concentration in the aqueous dispersion. The liquid temperature is
If the temperature is lower than the melting point of the emulsifier, an aqueous hydrotalcite emulsion having excellent dispersion stability cannot be obtained.

In the present invention, the emulsion containing the hydrotalcite and the emulsifier is stirred in water heated to a temperature equal to or higher than the melting point of the emulsifier, whereby the emulsifier is easily made finer and extremely fine micelles are formed. It is presumed that fine particles of hydrotalcite were formed in the micelles.

Step [C] is a step of cooling the aqueous hydrotalcite emulsion which has been heated to a temperature equal to or higher than the melting point of the emulsifier. It is necessary to continue stirring the emulsion until it is cooled to a temperature lower by at least 5 ° C. than the melting point.
It is further preferable that stirring is continued until the temperature is lowered to a lower temperature. Thereafter, during the period of cooling to room temperature, stirring is not essential, but it is preferable to continue stirring. When stirring is stopped at a time when the liquid temperature of the aqueous hydrotalcite emulsion does not drop by 5 ° C. or more from the melting point of the emulsifier, the liquid becomes extremely viscous when cooled to room temperature. When the liquid becomes a viscous liquid, it does not return to a low-viscosity aqueous emulsion even if the liquid is stirred again.

The aqueous emulsion of hydrotalcite obtained by the above method may contain a phenolic antioxidant or an amine antioxidant. In this case, the antioxidant may be added to the hydrotalcite and the emulsifier. At the same time, dry powder mixing is performed, and the following operation may be performed in the same manner as described above. Specific examples of more preferred phenolic antioxidants include triethylene glycol-bis [3- (3-t
-Butyl-5-methyl-4-hydroxyphenyl) propionate], pentaerythritol-tetrakis [3
-(3,5-di-t-butyl-4-hydroxyphenyl) propionate] and octadecyl-3- (3,
5-di-t-butyl-4-hydroxyphenyl) propionate and the like.

In the present invention, the above aqueous emulsion of hydrotalcite is added to the polymerization medium before or during the start of the aqueous suspension polymerization of the vinyl chloride monomer. As an addition method, an automatic addition method using a pump or the like is preferable.
The preferable addition amount of hydrotalcite is 0.01 parts hydrotalcite per 100 parts by weight of the vinyl chloride monomer.
0.003 parts by weight.

The vinyl chloride monomer in the present invention is a vinyl chloride monomer or a monomer mixture comprising the monomer and a monomer copolymerizable with the vinyl chloride monomer. As the active monomer, ethylene, propylene,
Butene, acrylic acid and alkyl acrylate, vinyl acetate, vinyl propionate and maleic acid.

Examples of the polymerization initiator include diisopropyl peroxy dicarbonate, dioctyl peroxy dicarbonate, di-2-ethylhexyl peroxy dicarbonate, dilauryl peroxy dicarbonate, ditertiary butyl peroxy dicarbonate, di (2- (Ethoxyethyl) peroxydicarbonate, tertiary butyl peroxyneodecanate, α-cumylperoxyneodecanate and the like.

Examples of the dispersion stabilizer include polyvinyl alcohol, cellulose derivatives such as methyl cellulose and ethyl cellulose, and gelatin.
The amount of the polymerization initiator and the dispersion stabilizer used, the polymerization temperature, etc.
It may be the same as in the case of a general vinyl chloride monomer suspension polymerization method.

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

Example 1 (Production of an aqueous emulsion of hydrotalcite) 70 g of hydrotalcite whose surface was treated with calcium stearate and 25 g of sorbitan stearate were placed in a Kenmix mixer and mixed for 30 minutes. The obtained mixture was poured into 500 ml of 70 ° C. warm water in a 1000 ml beaker, and stirred for 30 minutes while maintaining the liquid temperature at 70 ° C. to obtain a stable aqueous emulsion. Stirring was continued until the emulsion cooled to room temperature.

(Production of Vinyl Chloride Polymer by Suspension Polymerization) In a polymerization vessel having an internal volume of 400 L, 200 L of deionized water,
60 g of polyvinyl alcohol, 50 ml of the above hydrotalcite emulsion and 90 g of di-2-ethylhexyl peroxydicarbonate were charged. 200 in the polymerization vessel
After degassing until the pressure reached mmHg, 100 kg of a vinyl chloride monomer was charged, the temperature was raised to 57 ° C. with stirring, and polymerization was carried out at this temperature for a time. When the pressure in the polymerization vessel reached 6 kg / cm ² , unreacted monomers were recovered, and then a polymer slurry was extracted. During the above polymerization, the polymerization stability was extremely good.

The vinyl chloride polymer obtained by the above polymerization is mixed with a heat stabilizer and the like at the following ratio, and the mixture is mixed with 16 parts by weight.
The mixture was kneaded with a roll at 0 ° C. for 5 minutes to form a 0.5 mm thick sheet. 100 parts by weight of vinyl chloride polymer Epoxidized soybean oil 2 Ca-Zn heat stabilizer 0.7 (Mark 38 manufactured by Asahi Denka Kogyo Co., Ltd.) Phosphate ester heat stabilizer 0.5 (Asahi Denka Kogyo Co., Ltd.) Mark SC-102 manufactured by the company) The obtained sheet was placed in a gear oven at 180 ° C, and the thermal stability was evaluated based on the time until the sheet turned black. In the sheet of this example, the time required until blackening was 90 minutes.

[0027]

Comparative Example 1 A vinyl chloride polymer was obtained in the same manner as in Example 1 except that hydrotalcite was not added to the polymerization system. The thermal stability of the vinyl chloride polymer was evaluated by the same method as described above, and as a result, the time required until blackening was 70 minutes.

[0028]

Comparative Reference Example 1 500 ml of deionized water was charged into a beaker having an internal volume of 1000 ml, and 70 g of hydrotalcite and 25 g of sorbitan stearate used in Example 1 were mixed therein without mixing with a powder mixer. Each was added separately and stirred at room temperature for 30 minutes. When the stirring was stopped, the hydrotalcite floated on the liquid surface, and a uniform emulsion could not be obtained.

[0029]

Comparative Reference Example 2 The operation of Comparative Reference Example 1 was carried out at a liquid temperature of 70 ° C., and the results were the same as in Comparative Reference Example 1.

Comparative Reference Example 3 In the method for producing an aqueous emulsion of hydrotalcite in Example 1, a mixture of hydrotalcite and sorbitan stearate was charged into deionized water at room temperature, and stirred at room temperature. The result was the same as Comparative Reference Example 1.

[0030]

COMPARATIVE REFERENCE EXAMPLE 4 In the method for producing an aqueous emulsion of hydrotalcite in Example 1, a uniform emulsion was obtained at a liquid temperature of 70 ° C., stirring was stopped, and the mixture was cooled to room temperature. A gel was generated in the obtained liquid.

Comparative Reference Example 5 In the method for producing an aqueous emulsion of hydrotalcite in Example 1, after obtaining a uniform emulsion at a liquid temperature of 70 ° C., stirring was continued until the liquid temperature dropped to 55 ° C. Thereafter, stirring was stopped and the mixture was cooled to room temperature. The obtained liquid was a liquid having an extremely high viscosity.

[0031]

Comparative Reference Example 6 A hydrotalcite emulsion was produced in the same manner as in Example 1, except that hydrotalcite that had not been surface-treated with an organic compound was used. The resulting emulsion underwent a solid-liquid phase separation after 24 hours.

[0032]

The aqueous emulsion of hydrotalcite in the present invention has excellent dispersion stability. Therefore, according to the present invention using the emulsion, for example, a simple equipment such as a pump can be used in a polymerization facility for a vinyl chloride monomer. By adding the apparatus, the addition of hydrotalcite to the polymerization system is automated, and a vinyl chloride polymer having high production efficiency and excellent thermal stability can be produced.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Furuta En 1 Nagoya Research Institute, Toagosei Chemical Industry Co., Ltd. 1-1, Funami-cho, Minato-ku, Nagoya-shi, Aichi (72) Inventor Naori Asada, Minami-ku, Nagoya-shi, Aichi 1 in the town, Nagoya Research Laboratory, Toagosei Chemical Industry Co., Ltd. (56) References JP-A-64-74203 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08F 2 / 18-2/44 C01F 7/00

Claims (1)

(57) [Claims] 1. When suspension polymerization of a vinyl chloride monomer or a monomer mixture comprising the monomer and a monomer copolymerizable with the vinyl chloride monomer in an aqueous medium, prior to or during the polymerization, A method for producing a vinyl chloride polymer, comprising adding an aqueous emulsion of hydrotalcite obtained by a production method comprising steps [A] to [C]. [A]: a step of mixing a hydrotalcite powder surface-treated with a water-insoluble organic compound and an emulsifier with a powder mixer. [B]; stirring the dispersion obtained by throwing the powder mixture obtained in the step [A] into water while maintaining the temperature of the dispersion at a temperature equal to or higher than the melting point of the emulsifier, to obtain an aqueous emulsion. Process. [C]: a step of cooling the liquid temperature of the obtained aqueous emulsion to a temperature lower by at least 5 ° C. than the melting point of the emulsifier, while continuing the stirring after the step [B].