JPH0718005A - Production of vinyl chloride polymer - Google Patents

Abstract

PURPOSE:To reduce scale buildup in a polymerizer and simultaneously reduce fish eyes in a molded article by specifying the max. temp. of the inner wall of the polymerizer during the suspension polymn. of a vinyl chloride monomer at a specified temp. in the presence of a specific polymn. initiator active at high temp. CONSTITUTION:The max. temp. of the inner wall of a polymerizer is specified to be 75 deg.C or lower during the suspension polymn. of vinyl chloride or a monomer mixture contg. vinyl chloride in the polymerizer at 58 deg.C or higher in the presence of a polymn. initiator which has a 10hr half-life temp. in benzene in a concn. of 0.1mol/l of 55 deg.C or higher.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Generally, suspension polymerization of vinyl chloride or a monomer mixture containing vinyl chloride (hereinafter referred to as vinyl chloride etc.) is carried out, for example, in an aqueous medium, dispersion in a polymerization vessel equipped with a jacket and a reflux condenser. After charging the agent (suspension agent) and the polymerization initiator, then evacuating the inside of the polymerization vessel and charging the above monomer, and further charging various other additives as necessary,
The inside of the polymerization vessel is maintained at a predetermined reaction temperature by passing hot water through the jacket to raise the temperature inside the polymerization vessel to a predetermined polymerization reaction temperature and then passing cooling water through the jacket and the reflux condenser to remove the heat of the polymerization reaction. While carrying out the polymerization reaction, it is carried out.

When a vinyl chloride polymer is produced by suspension polymerization of vinyl chloride or the like, the higher the polymerization reaction temperature, the lower the degree of polymerization of the vinyl chloride polymer. Therefore, when producing a vinyl chloride polymer having an average degree of polymerization of 1000 or less, particularly 800 or less, the polymerization reaction temperature is usually
It must be above 58 ℃.

In recent years, the polymerization time has been shortened in order to improve the productivity. One of the methods for shortening the polymerization time is to charge a large amount of a polymerization initiator. In the case of such a method, in order to shorten the heating time and make the calorific value per unit time almost constant, a low-temperature active polymerization initiator and a high-temperature active polymerization initiator (when the polymerization reaction temperature is 58 ° C or higher, benzene is used). The heat generation due to the polymerization reaction is adjusted in combination with a high-temperature active polymerization initiator with a 10-hour half-life temperature of 55 ° C or higher at a medium concentration of 0.1 mol / L.

When the low temperature active polymerization initiator and the high temperature active polymerization initiator are used in combination as described above, if the use ratio of the low temperature active polymerization initiator is too large, heat generation is concentrated at the end of the temperature rise. Therefore, in order to prevent the concentration of heat generation at the end of temperature rise, it is necessary to enhance the heat removal capacity in the initial stage of polymerization.
However, after the start of the polymerization reaction, if the reflux condenser is used at a time when the polymerization conversion rate is low, there are disadvantages such as generation of coarse particles in the obtained polymer, so that the reflux condenser cannot be used at such time, There is a risk that it becomes difficult to maintain the reaction mixture at a predetermined temperature due to insufficient heat removal ability, and the reaction will run out. Therefore, when a low temperature active polymerization initiator and a high temperature active polymerization initiator are used in combination, it is necessary to increase the use ratio of the high temperature active polymerization initiator.

[0006]

[Problems to be Solved by the Invention] However, the polymerization reaction temperature is as high as 58 ° C. or higher, and the concentration is 0.1 mol / L in benzene.
When the polymerization is carried out with a high use ratio of a high-temperature active polymerization initiator having a 10-hour half-life temperature of 55 ° C or higher at a certain concentration, particularly when a large-scale polymerization reactor having an internal volume of 40 m ³ or more is used, Since the amount of scale attached to the inner liquid phase portion increases, the frequency of scale removal work increases, and further, when the obtained polymer is molded into a sheet or the like, fish eyes increase and the quality deteriorates. is there.

Therefore, an object of the present invention is to produce a scale in a polymerization vessel in the production of a vinyl chloride-based polymer, which comprises suspension-polymerizing vinyl chloride or the like at 58 ° C. or higher in the presence of a high-temperature active polymerization initiator. It is an object of the present invention to provide a method for producing a high-quality polymer with high productivity, which can reduce the amount of adhering substances, and can obtain a molded product with less fish eyes when molded into a sheet or the like.

[0008]

[Means for Solving the Problems] Generally, the 10-hour half-life temperature of vinyl chloride or the like at a concentration of 0.1 mol / L in benzene is
When carrying out suspension polymerization at a polymerization reaction temperature of 58 ° C or higher in the presence of a polymerization initiator of 55 ° C or higher, the temperature of the hot water passed through the jacket in order to raise the temperature in the polymerization reactor to the predetermined polymerization reaction temperature in a short time. Normally, it is as high as 80-95 ℃. Especially, the internal volume of 40m ³
When the above-mentioned large-sized polymerization vessel is used, the ratio of the heat transfer area to the reaction mixture per unit volume decreases and the heat transfer efficiency decreases, so the temperature of the hot water is increased. However, if the temperature of the hot water is too high, the maximum temperature reached on the inner wall surface of the polymerization vessel also becomes high. The present inventors have studied the relationship between the adhesion of the scale of the inner wall surface of the polymerization vessel and the highest temperature reached of the inner wall surface of the polymerization vessel, and if the highest temperature is controlled to 75 ° C. or less, The present invention has been completed by finding that the scale adhesion can be significantly reduced.

In the present invention, vinyl chloride or a monomer containing vinyl chloride is added in a polymerization vessel at 0.1 mol / L in benzene.
In the presence of a polymerization initiator having a 10-hour half-life temperature of 55 ° C or higher at a concentration, in the method for producing a vinyl chloride polymer, which comprises suspension polymerization at a polymerization reaction temperature of 58 ° C or higher, the inner wall surface of the polymerization vessel The method for producing a vinyl chloride polymer is characterized by controlling the maximum temperature reached to 75 ° C. or lower, preferably 70 ° C. or lower.

In the production method of the present invention, a high-temperature active polymerization initiator having a 10-hour half-life temperature of 55 ° C. or higher at a concentration of 0.1 mol / L in benzene is used as the polymerization initiator.
Examples of such a high-temperature active polymerization initiator include t-butylperoxypivalate (10-hour half-life temperature in benzene at a concentration of 0.1 mol / L: 55 ° C.), 3,5,5-trimethylhexanoyl peroxide ( 59.5 ° C), decanoyl peroxide (62 ° C), lauroyl peroxide (62 ° C)
℃), benzoyl peroxide (at the same 74 ℃) and the like.

In the production method of the present invention, benzene is used as a polymerization initiator in order to shorten the temperature rising time.
A 10-hour half-life temperature of 0.1 mol / L in benzene is less than 55 ℃, with a high-temperature active polymerization initiator having a 10-hour half-life temperature of 55 ℃ or higher at a concentration of 0.1 mol / L, preferably 50
It is preferable to use a low temperature active polymerization initiator having a temperature of not higher than 0 ° C, more preferably 40 to 50 ° C. The charging amount of the low temperature active polymerization initiator is usually 10 to 70% by weight, preferably 30 to 50% by weight, of the total amount of the high temperature active polymerization initiator and the low temperature active polymerization initiator charged. is there. If the amount of the low-temperature active polymerization initiator used is too small, the effect of shortening the temperature raising time is small. Further, when the amount of the low-temperature active polymerization initiator used is large, heat generation is concentrated at the end of the temperature rise, making it difficult to maintain the reaction mixture at a predetermined temperature due to lack of heat removal capability,
There is a risk that the reaction will run away, and there is the inconvenience that when the polymer obtained is processed into a molded product such as a sheet, fish eyes increase.

Examples of the above-mentioned low temperature active polymerization initiator include di-2-ethoxyethyl peroxydicarbonate (10-hour half-life temperature at a concentration of 0.1 mol / L in benzene: 43.4 ° C.) and di-2-ethylhexyl. Peroxydicarbonate (43.5 ° C. in the same), t-hexyl peroxy neodecanoate (44.7 ° C. in the same), t-butyl peroxy neodecanoate (46.5 ° C. in the same) and the like can be mentioned.

In the production method of the present invention, the total amount of the polymerization initiator charged is usually 0.02 to 0.2% by weight, preferably 0.04 to 0.1% by weight, based on the charged amount of the monomer.

In the present invention, suspension polymerization of vinyl chloride or the like is carried out, for example, as follows. First, water, a dispersant, a polymerization initiator, and various other additives are charged into a polymerization vessel equipped with a jacket and a reflux condenser, and then a gas phase portion in the polymerization vessel is deaerated. Next, a monomer such as vinyl chloride is charged into the polymerization vessel, and hot water is passed through the jacket while stirring the reaction mixture in the polymerization vessel to a predetermined polymerization reaction temperature (58 ° C).
Above). At that time, the temperature of the hot water is set so that the highest temperature reached on the inner wall surface of the polymerization vessel is 75 ° C. or lower, but is usually about 65 to 70 ° C. Since this temperature is lower than the temperature of conventional hot water, the temperature rising time in the polymerization vessel becomes long. Therefore, it is preferable to shorten the temperature raising time by, for example, blowing steam into the polymerization vessel or heating the water to be charged into the polymerization vessel in advance.

When the temperature in the polymerization vessel reaches a predetermined polymerization reaction temperature, cooling water is passed through the jacket to remove the heat of the polymerization reaction to carry out polymerization. When a predetermined yield is reached, unreacted monomers are recovered. At the time of recovering the unreacted monomer, in order to help desorption of the unreacted monomer, a method in which hot water is again passed through the jacket is generally used. Also in this case, the maximum adhesion temperature of the inner wall surface of the polymerization vessel can be set to 75 ° C. or lower to reduce scale adhesion. After recovering the unreacted monomers, the obtained vinyl chloride polymer is taken out of the container and dehydrated and dried.

In the production method of the present invention, vinyl chloride may be used alone as a monomer, or a monomer mixture containing vinyl chloride as a main component and a comonomer copolymerizable with vinyl chloride ( Usually, a vinyl chloride content of 50% by weight or more) can also be used. Such comonomers include, for example, vinyl esters such as vinyl acetate and vinyl propionate; acrylic acid esters and methacrylic acid esters such as methyl acrylate and ethyl acrylate; olefins such as ethylene and propylene; maleic anhydride; Acrylonitrile; styrene; vinylidene chloride and the like.

The amount of the aqueous medium used for suspending and dispersing the polymer component such as the monomer is the same as in the conventional method, and the charging ratio with the monomer (water / monomer) is 1.0 to. It may be about 1.5, and water may be added during the polymerization, if necessary.

In order to stabilize the polymerization system (suspension dispersion), for example, polyvinyl alcohol, water-soluble and oil-soluble methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose,
Water-soluble cellulose ethers such as hydroxypropylmethyl cellulose, water-soluble polymers such as polyacrylic acid and gelatin, oil-soluble polymers such as sorbitan monolaurate, sorbitan trioleate, sorbitan monostearate, glycerin tristearate, ethylene oxide and propylene oxide block copolymers. Emulsifiers; for example, water-soluble emulsifiers such as polyoxyethylene sorbitan monolaurate, polyoxyethylene gucerin oleate, sodium laurate; other calcium carbonate, calcium phosphate, sodium dodecylbenzene sulfonate, etc. without impairing the object of the present invention A small amount can be used within the range.

The polymerization reaction temperature in the production method of the present invention is
It is at least 58 ° C, and particularly preferably in the range of 58 to 75 ° C. If the temperature exceeds 75 ° C., the internal pressure of the polymerization vessel becomes too high, which may cause inconvenience such as a safety problem.

Further, in the production method of the present invention, the polymerization is carried out at the above-mentioned polymerization reaction temperature, and a chain transfer agent is further used, whereby a low polymerization degree of chloride having an average polymerization degree of 1000 or less, particularly 800 or less is obtained. It is extremely effective when producing a vinyl polymer. As the chain transfer agent, for example, organic mercaptans, halogenated hydrocarbons, chain alkyl vinyls having an epoxy group and the like can be used.

Further, if necessary, it is optional to add a polymerization degree adjusting agent, a pH adjusting agent and the like, which are appropriately used for the polymerization of vinyl chloride and the like, to the polymerization system.

[0022]

EXAMPLES Examples 1 to 5 and Comparative Examples 1 to 4 Polymerization was carried out as follows in each Example and Comparative Example. 900 kg of deionized water at the temperature shown in Table 1 and 760 g of partially saponified polyvinyl alcohol as an aqueous solution were charged into a stainless steel polymerization vessel having an internal volume of 2.1 m ³ .
After degassing the inside of the polymerization vessel to 50 mmHg, 700 kg of vinyl chloride monomer was charged. While stirring the reaction mixture in the polymerization vessel, a polymerization initiator of the amount shown in Table 1 (percentage (% by weight relative to the charged amount of the monomer)) was pumped in, and at the same time, the temperature of the one shown in Table 1 was introduced into the jacket. The inside of the polymerization vessel was heated to 61 ° C., which is the polymerization reaction temperature, by passing hot water. Table 1
Shows the maximum temperature reached and the temperature rising time of the inner wall surface of the polymerization vessel.

The polymerization reaction was carried out while maintaining the temperature in the polymerization vessel at 61 ° C., and after 1 hour and 40 minutes from the start of temperature increase, 200 g of mercaptoethanol was added. The internal pressure of the polymerization vessel is 6.0
Polymerization was stopped when the amount reached kg / cm ² G, unreacted monomers were recovered, and the obtained polymer was taken out of the polymerization vessel in a slurry form and dehydrated and dried. Table 1 shows the time (polymerization time) required from the start of temperature increase to the end of polymerization.

With respect to the vinyl chloride polymers obtained in the respective Examples and Comparative Examples, the bulk specific gravity, particle size distribution, and the number of fish eyes when formed into a sheet were measured by the following methods.
The results are shown in Table 1.

Bulk density measured according to JIS K 6721.

Particle size distribution The particles were sieved using # 60, # 100 and # 200 sieves according to JIS Z 8801, and the passing amount (% by weight) was measured.

Fisheye After mixing 100 parts by weight of the obtained polymer, 3.0 parts by weight of epoxidized soybean oil, 0.7 parts by weight of cetanol, 1.0 part by weight of butyl stearate and 2.5 parts by weight of tin stabilizer with a mixer, The obtained mixture was extruded using a 20 mm extruder at a header temperature of 170 ° C. and a die temperature of 205 ° C., and a sheet having a thickness of 0.1 mm and a width of 30 mm was taken for 50 m. The number of white transparent particles in 1 m ^{2 of the} obtained sheet was counted and used as the number of fish eyes.

Further, the scale adhesion state in the polymerization vessel after the completion of the polymerization was observed and evaluated according to the following criteria. The results are shown in Table 1. A: There is no adhesion of scale, and the metallic mirror surface has gloss. B: The metal mirror surface has some cloudiness. C: Scale is recognized on a part of the metal surface.

[0029]

[Table 1]

Example 6 and Comparative Example 5 Polymerization was carried out as follows in each Example and Comparative Example. In a stainless steel polymerization vessel equipped with a reflux condenser with an internal volume of 80 m ³ , add deionized water at the temperature shown in Table 2.
37 t and 31.5 kg of partially saponified polyvinyl alcohol were added as an aqueous solution. After degassing the inside of the polymerization vessel to 50 mmHg, 29 t of vinyl chloride monomer was charged. While stirring the reaction mixture in the polymerization vessel, the amount of the polymerization initiator shown in Table 2 (ratio (% by weight relative to the charged amount of the monomer)) was pumped into the jacket and, at the same time, the temperature at the temperature shown in Table 2 was applied to the jacket. The inside of the polymerization vessel was heated to 61 ° C., which is the polymerization reaction temperature, by passing hot water. In addition, Table 2 shows the maximum reached temperature and the temperature rising time of the inner wall surface of the polymerization vessel.

The polymerization reaction was carried out while maintaining the temperature in the polymerization vessel at 61 ° C., and after 1 hour and 20 minutes from the start of heating, heat removal by a reflux condenser was started, and 20 minutes after that, 200 g of mercaptoethanol was added. The internal pressure of the polymerization vessel is
The polymerization was stopped when the amount reached 6.0 kg / cm ² G, unreacted monomers were recovered, and the obtained polymer was taken out of the polymerization vessel in a slurry form and dehydrated and dried. Table 2 shows the time (polymerization time) required from the start of temperature increase to the end of polymerization.

With respect to the vinyl chloride polymers obtained in the respective Examples and Comparative Examples, the bulk specific gravity, particle size distribution, and the number of fish eyes when formed into a sheet were measured by the same method as described above. The results are shown in Table 2.

Further, the state of scale adhesion in the polymerization vessel after completion of the polymerization was observed and evaluated according to the same criteria as above. The results are shown in Table 2.

[0034]

[Table 2]

[0035]

According to the method for producing a vinyl chloride polymer of the present invention, the polymerization reaction temperature is as high as 58 ° C. or higher, and the 10-hour half-life temperature at a concentration of 0.1 mol / L in benzene is 55 ° C.
Even if the above high-temperature active polymerization initiator is used in a higher proportion, especially when using a large-sized polymerization vessel with an internal volume of 40 m ³ or more, the polymerization vessel inner wall surface It is possible to reduce the amount of adhered scale. Therefore,
Since the frequency of scale removal work is reduced, productivity is improved. Further, when the polymerization is carried out by applying the production method of the present invention, a high-quality low-polymerization vinyl chloride-based polymer with high productivity can be obtained which gives a molded product with less fish eyes when molded into a sheet or the like. can do.

Claims (1)

[Claims] 1. A vinyl chloride or a monomer containing vinyl chloride is added in a polymerization vessel in the presence of a polymerization initiator having a 10-hour half-life temperature of 55 ° C. or higher at a concentration of 0.1 mol / L in benzene,
In a method for producing a vinyl chloride-based polymer comprising suspension polymerization at a polymerization reaction temperature of 58 ° C or higher, a vinyl chloride-based polymer characterized in that the maximum temperature reached on the inner wall surface of the polymerization vessel is controlled to 75 ° C or lower. Method for producing polymer.