JP3584591B2 - Method for producing vinyl chloride polymer - Google Patents

Description

【００３０】
【表２】

【００３１】
【発明の効果】
本発明によれば、ゲル化溶融が速く、かつ、ゲル化時のトルクが低い塩化ビニル系重合体を得ることができる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a vinyl chloride polymer. More specifically, the present invention relates to a method for producing a vinyl chloride-based polymer having improved properties, particularly a high melting rate during gelation and a low torque during gelation.
[0002]
[Prior art]
The vinyl chloride polymer is a vinyl chloride monomer or a mixture of copolymerizable monomers mainly composed of vinyl chloride (hereinafter, collectively referred to as “vinyl chloride monomer”, The polymer obtained by polymerizing is sometimes referred to as "vinyl chloride-based polymer."), In the presence of a polymerization initiator, in an aqueous medium containing a dispersant or an emulsifier, suspension polymerization, or It is manufactured by emulsion polymerization.
In general, the processability of a vinyl chloride polymer strongly depends on the particle shape, aggregation state, and molecular structure, but in particular, increasing the bulk specific gravity and increasing the gelation / melting rate is important for the processability. It is an important factor for improvement.
[0003]
[Problems to be solved by the invention]
As a method of increasing the bulk specific gravity and the gelation / melting rate of a vinyl chloride polymer, when a vinyl chloride monomer is polymerized in an aqueous medium to produce a vinyl chloride polymer, the polymerization reaction proceeds. There has been proposed a method (Japanese Patent Publication No. 3-57121) of performing polymerization while raising the polymerization temperature during a specific ratio of the entire period. The vinyl chloride polymer produced by this method has a high specific gravity, thereby improving the extrusion discharge amount, and has a good gelling and melting property, so that the molded article has excellent surface smoothness and gloss. .
[0004]
However, when trying to increase the extrusion discharge rate while improving the product quality by improving the vinyl chloride polymer, the extrusion torque increases due to the increase in the discharge rate and the gelation melting rate. Eventually, a phenomenon occurs in which the limit of the extruder motor load governs the limit of the extrusion discharge amount. For this reason, there is a need for a vinyl chloride-based polymer that has a large discharge rate, a high gelling / melting rate, and can maintain a low torque during processing.
[0005]
[Means for Solving the Problems]
According to the present invention, in a method for producing a vinyl chloride polymer by polymerizing a vinyl chloride monomer in an aqueous medium in the presence of a polymerization initiator, a cross-linking agent is added to the polymerization reaction system. 0.01 to 2.0 parts by weight per 100 parts by weight of the system monomer and a chain transfer agent are added, and the polymerization temperature is raised by 2 to 35 ° C. with time in a period of 50% or more of the entire period in which the polymerization reaction proceeds. By causing the polymerization reaction to proceed while producing the polymer, it is possible to produce a vinyl chloride-based polymer that has good gelling meltability and can maintain a low torque during processing and molding.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
To explain the present invention in detail,
The vinyl chloride monomer used for the polymerization in the method of the present invention is a mixture of a vinyl chloride monomer alone and a copolymerizable monomer mainly composed of the vinyl chloride monomer. As the other monomer copolymerizable with the vinyl chloride monomer, any of those conventionally used generally in a suspension polymerization method of a vinyl chloride monomer can be used, for example, Vinyl esters such as vinyl acetate, alkyl vinyl ethers such as cetyl vinyl ether, α-olefins such as ethylene and propylene, alkyl (meth) acrylates such as methyl acrylate and methyl methacrylate, and vinylidene compounds such as vinylidene chloride And the like. These monomers are generally used in a proportion of 20% by weight or less based on the vinyl chloride monomer.
[0007]
As the dispersant for dispersing the vinyl chloride-based monomer in the aqueous medium, those commonly used in the suspension polymerization method of the vinyl chloride-based monomer can be used. Water-soluble polymers such as polyvinyl acetate (so-called polyvinyl alcohol), cellulose derivatives such as hydroxypropylmethylcellulose, and gelatin. In addition, an anionic surfactant such as sodium lauryl sulfate and a nonionic surfactant such as sorbitan fatty acid esters and glycerin fatty acid esters may be used in combination as a dispersing aid. These dispersants and dispersion aids can be used alone or in combination of two or more. The amount of the dispersant used is not particularly limited, and the type, stirring strength, polymerization temperature, composition of the vinyl chloride monomer used for the reaction, and the desired particle size for the vinyl chloride polymer to be produced Although it varies slightly depending on the type of the vinyl chloride monomer, it is generally used in the range of 0.001 to 2% by weight, preferably 0.03 to 1% by weight, based on the vinyl chloride monomer.
[0008]
The polymerization initiator may be any of those conventionally used generally in the suspension polymerization method of a vinyl chloride monomer. Examples thereof include t-butyl peroxypivalate, t-butyl peroxy neodecanoate, and t-hexyl peroxy. Pivalate, t-hexyl peroxy neodecanoate, perester compounds such as α-cumyl peroxy neodecanoate, peroxide compounds such as dilauroyl peroxide, diisopropyl peroxy dicarbonate, di-2-ethylhexyl peroxy dicarbonate and the like Examples include percarbonate compounds, azo compounds such as azobis (2,4-dimethylvaleronitrile) and azobisisobutyronitrile. These polymerization initiators can be used alone or in combination of two or more. The amount of the polymerization initiator used varies depending on the type of the initiator, the polymerization temperature, the desired reaction time and the like, but is generally in the range of 0.01 to 1% by weight based on the vinyl chloride monomer.
[0009]
As the cross-linking agent to be added to the polymerization reaction system in the present invention, those generally used conventionally in a suspension polymerization method of a vinyl chloride monomer can be used, for example, diallyl phthalate, diallyl maleate, Examples include polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, bisphenol A-modified dimethacrylate, triallyl cyanurate, triallyl isocyanurate, diallyl succinate, divinylbenzene, and trimethylolpropane triacrylate.
[0010]
These crosslinking agents can be used alone or in combination of two or more. The amount of the crosslinking agent varies depending on the crosslinking efficiency and the degree of polymerization of the crosslinking agent, but may vary from 0.01 to 2.0% by weight, preferably from 0.05 to 2.0% by weight, based on the vinyl chloride monomer. Used in the range of 0.51% by weight.
In the present invention, by adding a chain transfer agent to the polymerization reaction system, it is possible to further increase the gelation and melting rate of the obtained vinyl chloride polymer and to reduce the torque.
[0011]
As the chain transfer agent, those generally known, for example, trichloroethylene, 2-mercaptoethanol, 2-pentene, isopropyl alcohol and the like are used. The chain transfer agent can be added at any time, but is preferably added after the reaction has progressed to some extent. Usually, when the polymerization conversion is in the range of 40 to 70%, it is preferable to add 50% or more, particularly 80% or more of the chain transfer agent. The method of adding the chain transfer agent is arbitrary, and may be added at once, intermittently, or continuously.
Further, in the present invention, if necessary, various polymerization aids such as an antioxidant, a pH adjuster, and a scale adhesion inhibitor used in the polymerization of the vinyl chloride-based monomer can be appropriately used. The amounts of these components to be charged may be the same as those generally used in the polymerization of vinyl chloride monomers.
[0012]
In the present invention, it is necessary to perform at least a part of the polymerization reaction while increasing the reaction temperature over time. Usually, the reaction temperature is raised during a period of 50% or more of the total polymerization reaction period.
As is well known, a suspension polymerization reaction of a vinyl chloride-based monomer is usually a so-called constant-temperature reaction in which a reaction system is rapidly heated to a predetermined reaction temperature, and thereafter, the reaction is performed while maintaining the reaction temperature by cooling. Is performed by The degree of polymerization of the obtained vinyl chloride polymer is determined exclusively by the reaction temperature. Therefore, when producing a vinyl chloride polymer, the reaction temperature is determined according to the degree of polymerization required for the product.
[0013]
On the other hand, in the present invention, rapidly heating the reaction system to a predetermined reaction temperature, that is, a temperature at which polymerization is substantially started is the same as the conventional constant temperature reaction, but the reaction temperature is maintained to the end. Instead, the temperature is raised one after the other. In the present invention, 50% of the entire reaction period (that is, the period from the time when the polymerization reaction is substantially started when a predetermined reaction temperature is reached to the time when the polymerization reaction reaches a target polymerization rate) is completed. The reaction temperature is raised over the above period. If desired, the reaction temperature may be increased over the entire period.
[0014]
In the present invention, the degree of polymerization of the vinyl chloride polymer is basically determined by the reaction temperature, as in the case of the conventional constant temperature reaction. However, in the present invention, since the reaction temperature itself gradually increases, the finally obtained product is a collection of vinyl chloride polymers having a degree of polymerization determined by the reaction temperature at each time point. . Therefore, according to the present invention, a product having a much more complicated composition at the molecular level can be obtained, even if the average degree of polymerization is the same, as compared with the isothermal reaction. It is considered that the property that the speed is high and the torque at the time of gelation is small is given.
[0015]
Therefore, the physical properties of the product obtained by the present invention depend not only on the period during which the reaction temperature is gradually raised, but also on the degree of the temperature rise during that period. According to the findings of the present inventors, it is necessary to raise the temperature by at least 2 ° C. in order to exert the effect of raising the temperature. Usually, it is preferable to raise the temperature to 3.5 ° C. or higher. When the degree of temperature rise is small, the increase in the gelation / melting rate of the obtained product is small, and the degree of improvement in the surface smoothness and gloss of the molded product obtained by molding is also small.
[0016]
The upper limit of the temperature rise is regulated by the polymerization initiator and equipment restrictions. That is, when the width of the temperature increase is large, it becomes difficult to find a stable polymerization initiator over the entire range of the wide reaction temperature. As a result, there arises a problem that the reaction rate is lowered at the end of the reaction or the reaction becomes unstable. In addition, if the width of the temperature rise is large, refrigeration equipment is required for temperature control on the low temperature side, and the vapor pressure of the vinyl chloride monomer increases on the high temperature side, and a reaction vessel with high pressure resistance is required. There's a problem. From these points, the upper limit of the temperature rise should be 35 ° C. Usually, it is preferable to limit the temperature to 30 ° C. or lower, especially 20 ° C. or lower.
[0017]
The pattern of the temperature rise is arbitrary. Normally, the temperature is raised uniformly over the entire temperature raising period, that is, when the temperature raising period is set to H hours and the temperature raising width is set to ΔT ° C., the temperature is raised at a constant rate of ΔT / H. It is advantageous. If desired, the heating rate can be changed midway, but the capacity of the reactor heating / cooling equipment must be increased. From the viewpoint of reaction control, the rate of temperature rise is preferably 10 ° C./hr or less. In the present invention, the term “temperature rising period” refers to a period in which the polymerization reaction system is rapidly heated to reach a predetermined reaction temperature (T ₁ ) to substantially start the polymerization, and then the temperature is raised from the predetermined reaction temperature T _1. It refers to a period until maximum reaction temperature T ₂ Te.
[0018]
In the present invention, the degree of polymerization of the product obtained is basically determined by the average reaction temperature. Therefore, the average reaction temperature may be determined according to the degree of polymerization required for the product. The average reaction temperature is defined as a value obtained by integrating the reaction temperature by the reaction time and dividing by the total reaction time. Therefore, when the temperature is raised uniformly over the entire reaction period, the average reaction temperature is the arithmetic average of the temperatures at the start and end of the reaction, but the temperature is uniformly started from the middle of the reaction. When the polymerization is carried out to reach the maximum temperature at this temperature and then reaches the desired polymerization rate at this temperature, the average reaction temperature is not always the arithmetic average of the temperatures at the start and end of the reaction. Also, the amount of weight produced at each point in the reaction is not necessarily constant. Further, in the present invention, a crosslinking agent and a chain transfer agent are present in the polymerization reaction system, and the former acts in the direction of increasing the degree of polymerization and the latter acts in the direction of decreasing the degree of polymerization. Therefore, taking into account the increase or decrease in the degree of polymerization due to these additives, a tentative average polymerization temperature is determined from the relationship between the polymerization temperature and the degree of polymerization in the well-known constant temperature reaction according to the degree of polymerization desired for the product, and then defined as described above. It is preferable to determine the polymerization initiation temperature from the heating pattern so that the average polymerization temperature to be made coincides with the provisional average polymerization temperature, and further determine the actual polymerization initiation temperature by correcting the polymerization initiation temperature by experiment. .
[0019]
In the present invention, it is considered that increasing the degree of polymerization with the crosslinking agent is closely related to the resulting product having excellent physical properties. In order to sufficiently exert the effect on the physical properties of the crosslinking agent, it is preferable that the increase in the degree of polymerization by the crosslinking agent is a value corresponding to at least 1.5 ° C. as the reaction temperature. That is, it is preferable that the average polymerization temperature be 1.5 ° C. or higher than the polymerization temperature when a vinyl chloride polymer having the same polymerization degree is produced by constant temperature polymerization without adding a crosslinking agent. When a chain transfer agent is used in addition to the cross-linking agent, it is preferable that the effect of the cross-linking agent on the degree of polymerization be substantially offset by the chain transfer agent. That is, when both are used in combination, the average polymerization temperature is at least 10 higher than the polymerization temperature at the time of producing a vinyl chloride polymer having the same degree of polymerization by constant temperature polymerization without adding a crosslinking agent or a chain transfer agent. It is preferred that the temperature not exceed ℃.
[0020]
In carrying out the present invention, an aqueous medium, a vinyl chloride-based monomer, a dispersant, a polymerization initiator and various polymerization auxiliaries to a polymerization reactor, the charging ratio, the charging method, and the like are those conventionally used in general. It does not matter under conditions. In addition, agitating blades, baffles, and the like, which are auxiliary devices of the polymerization reactor, may also be those generally used in the related art.
[0021]
Examples of the method for terminating the polymerization include a method of adding a so-called polymerization inhibitor or a polymerization terminator, and a method of recovering an unreacted monomer from a polymerization reactor. For the dehydration and drying of the generated vinyl chloride polymer slurry, dehydration and drying means such as centrifugal dehydration and fluidized drying can be used.
Removal of residual vinyl chloride from the obtained vinyl chloride-based polymer may be performed by using a known method, and removal of residual monomer is easy.
[0022]
Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless departing from the gist thereof.
The physical properties of the obtained vinyl chloride polymer were evaluated by the following physical property measuring methods.
{Circle around (1)} Average degree of polymerization Determined according to the method described in JIS K6721.
{Circle around (2)} A gel blending time, 100 parts by weight of a torque vinyl chloride polymer, 3 parts by weight of a lead-based powder stabilizer, and 0.5 part by weight of a barium-based powder stabilizer were mixed with 70 g of a sample, and the mixture was mixed with a Labo Plastmill roller type mixer ( The mixture was kneaded at 170 ° C. and 70 rpm, and the maximum torque and the time until the maximum torque was shown were measured.
[0023]
Comparative Example 1
A 400-liter stainless steel polymerization vessel equipped with a stirrer and jacket was charged with 150 kg of deionized water, 55 g of partially saponified polyvinyl acetate, and 100 g of a crosslinking agent (diallyl phthalate), and degassed. 100 kg of a vinyl chloride monomer and 27 g of a polymerization initiator (dioctyl peroxydicarbonate) were added thereto, and the mixture was rapidly heated to 57.5 ° C. to start polymerization. After the polymerization was carried out for 1 hour, the temperature was raised, and the temperature was raised to 63.5 ° C. over 9 hours at a uniform rate, and thereafter, this temperature was maintained. After reaching the target polymerization conversion rate in 12.6 hours, the reaction was terminated, and after removing the vinyl chloride monomer in the polymerization vessel to atmospheric pressure, the inside of the vessel was evacuated. Next, the slurry was taken out and dehydrated, and then dried.
Table 2 shows the results of evaluation of the physical properties of the obtained vinyl chloride polymer.
[0024]
Example 1
Polymerization was carried out in the same manner as in Comparative Example 1 except that the amount of the polymerization initiator used was 31 g, the polymerization initiation temperature was 55.5 ° C., and the temperature raising end temperature was 61.5 ° C. However, when the reaction conversion reached 60%, 15 g of 2-mercaptoethanol was added. The reaction was terminated when the target polymerization conversion was reached in 12.3 hours.
Post-treatment was performed in the same manner as in Comparative Example 1, and the physical properties of the obtained vinyl chloride polymer were evaluated. Table 2 shows the results.
[0025]
Comparative Example 2
Polymerization was carried out in the same manner as in Comparative Example 1 except that 80 g of triallyl isocyanurate was used as a cross-linking agent, the polymerization initiation temperature was 58.5 ° C., and the temperature raising end temperature was 62.5 ° C. The polymerization time was 13.1 hours.
Post-treatment was performed in the same manner as in Comparative Example 1, and the physical properties of the obtained vinyl chloride polymer were evaluated. Table 2 shows the results.
[0026]
Comparative Example 3
Polymerization was carried out in the same manner as in Comparative Example 1 except that no crosslinking agent was used, the amount of the polymerization initiator used was 26 g, and the reaction temperature was kept constant at 58.0 ° C. The polymerization time was 11 hours.
Post-treatment was performed in the same manner as in Comparative Example 1, and the physical properties of the obtained vinyl chloride polymer were evaluated. Table 2 shows the results.
[0027]
Comparative Example 4
Polymerization was carried out in the same manner as in Comparative Example 1 , except that the amount of the polymerization initiator used was 30 g, the polymerization initiation temperature was 55.0 ° C., and the temperature raising end temperature was 61.0 ° C., without using a crosslinking agent. . The polymerization time was 12.5 hours.
Post-treatment was performed in the same manner as in Comparative Example 1, and the physical properties of the obtained vinyl chloride polymer were evaluated. Table 2 shows the results.
[0028]
Comparative Example 5
Polymerization was carried out in the same manner as in Comparative Example 1 , except that the amount of the crosslinking agent used was 80 g, the amount of the polymerization initiator used was 23 g, and the reaction temperature was kept constant at 61.0 ° C. The polymerization time was 13.1 hours.
Post-treatment was performed in the same manner as in Comparative Example 1, and the physical properties of the obtained vinyl chloride polymer were evaluated. Table 2 shows the results.
[0029]
[Table 1]

[0030]
[Table 2]

[0031]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, gelatinization melting | fusing is quick and the torque at the time of gelation can obtain the low vinyl chloride polymer.

Claims (5)

In a method for producing a vinyl chloride polymer by polymerizing a vinyl chloride monomer or a copolymerizable monomer mixture mainly composed of a vinyl chloride monomer in an aqueous medium in the presence of a polymerization initiator. The polymerization reaction system is added with a crosslinking agent in an amount of 0.01 to 2.0 parts by weight per 100 parts by weight of a monomer and a chain transfer agent , and the polymerization temperature is not less than 50% of the entire period during which the polymerization reaction proceeds. A vinyl chloride-based polymer, wherein the polymerization reaction is carried out while raising the temperature by 2 to 35 ° C. over time. The method for producing a vinyl chloride polymer according to claim 1, wherein the crosslinking agent is added in an amount of 0.05 to 0.51 part by weight per 100 parts by weight of the monomer. To the extent the polymerization conversion rate is 40% to 70%, the production method of the vinyl chloride polymer according to claim 1 or 2, wherein the addition of more than 50% of the chain transfer agent. The average polymerization temperature is not less than 1.5 ° C. and less than 10 ° C. than the polymerization temperature at the time of producing a vinyl chloride polymer having the same degree of polymerization by constant temperature polymerization without adding a crosslinking agent and a chain transfer agent. The method for producing a vinyl chloride-based polymer according to any one of claims 1 to 3, wherein the method is increased. The chloride according to any one of claims 1 to 4, wherein the polymerization reaction is carried out while increasing the polymerization temperature by 3.5 to 20 ° C over time in a period of 50% or more of the entire period in which the polymerization reaction proceeds. A method for producing a vinyl polymer.