JPH0144722B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for obtaining vinyl polymer particles having a large particle size and a narrow particle size distribution by suspension polymerizing vinyl monomers. In particular, when polymerizing styrene monomer using the suspension polymerization method, it is important to produce polymer particles with a narrow particle size distribution centered on large particle sizes of 1.4 to 2.4 mm with good yield. It is related to a method of characteristics. Generally, polymer particles produced by suspension polymerization are polymerized in the form of at least one type of vinyl monomer that is dispersed in water through stirring and the action of a suspending agent (dispersing agent). It is generated by The suspending agent has the function of preventing vinyl monomers or mixtures of monomers and polymers, that is, oil particles, from coalescing into lumps. Conventionally, suspending agents used for suspension polymerization of vinyl monomers mainly composed of styrene include sparingly soluble phosphates as the main suspending agent and anionic surfactants as the suspending aids. This is well known. Specifically, tricalcium phosphate and sodium dodecylbenzenesulfonate are the most common suspending agents.
The particle size of the polymer particles produced by suspension polymerization using this suspending agent was in the range of about 0.1 to 3 mm, and the particle size distribution was wide. Conventionally, it has been possible to arbitrarily control the particle diameter of polymer particles by mechanical factors such as suspending agent concentration and stirring effect. However, it has been extremely difficult to narrow the particle size distribution of polymer particles. The styrene-based polymer particles obtained as a suspension polymer are impregnated with a blowing agent (eg, propane, butane, pentane, etc.) to obtain the desired expandable polystyrene resin. The uses of expandable polystyrene resin can be divided into the following three fields depending on the particle size. In other words, (1) particle size from about 300μ
Expandable polystyrene particles with a diameter of 700μ are suitable for cups such as instant foods, (2) particles with a particle size of approximately 700μ to 1800μ are used for various packaging and fish boxes, and (3) particles with a diameter of approximately 1500μ to 3000μ are used for various packaging and fish boxes. Used for building boards, etc. Due to these differences in use, the required properties of expandable polystyrene also differ, so it is necessary to manufacture expandable polystyrene for each purpose. It is difficult to achieve that goal. In order to solve this problem, the inventors of the present invention have conducted extensive research, and as a result have found a method for obtaining only polymer particles with a required size at a high yield. That is, in the present invention, when carrying out suspension polymerization of vinyl monomers, in the presence of a sparingly soluble phosphate and an anionic surfactant, 0.5 to 0.01% by weight of a water-soluble inorganic salt that is neutral in an aqueous system is used. After starting suspension polymerization at an aqueous medium/monomer weight ratio of 1.5/1 to 1.1/1, the polymerization conversion rate of the vinyl monomer is 30% by weight and 70% by weight. Production of vinyl polymer particles characterized by adding a poorly soluble phosphate one or more times between the steps of 1 to 3 to advance the polymerization to obtain polymer particles having a particle size distribution centered on 1.4 to 2.4 mm. Regarding the method. Examples of the vinyl monomer in the present invention include styrene, styrene derivatives such as α-methylstyrene and chlorostyrene, acrylonitrile, methyl methacrylate, and butyl acrylate, and one or more of these may be used. In particular, it is preferable to use styrene or a styrene derivative in an amount of 50% by weight or more. As poorly soluble phosphates, tricalcium phosphate,
Magnesium phosphate, etc., and those with a size of 0.2 to 0.05 μ, which is called a submicron unit, are useful. The total amount of poorly soluble phosphate used is 0.01% by weight or more based on the total amount of substances present in the polymerization system, and there is no particular upper limit, but if it exceeds 1% by weight, it exceeds the necessary amount. It will be wasted. Preferably 0.05-0.4% by weight is used. If the amount is less than 0.01% by weight, the particle size distribution of the produced polymer particles cannot be narrowed. The amount of the poorly soluble phosphate initially present in the reaction system is not particularly limited within the above range, but it is preferably used from 1/4 to 3/4 of the total amount of the poorly soluble phosphate. Examples of anionic surfactants include alkylbenzene sulfonates such as sodium dodecylbenzenesulfonate, alkyl sulfonates with SO 3 Na added directly to the alkyl group, and naphthalene with _{SO 3 Na} added directly to the alkyl group.
β-tetrahydronaphthalenesulfonic acid fumes added with, acidosulfonic acids such as sodium N-isopropylcyclohexyl acidosulfonate, higher fatty acid salts such as sodium oleate, dialkyl sulfosuccinates such as di-2-ethylhexyl sodium sulfosuccinate, etc. used. The amount of these additives is appropriately determined depending on the target particle size, mechanical conditions, suspending agent concentration, water-soluble inorganic salt or dispersion medium to monomer ratio, etc., and the amount cannot be determined unconditionally. However, as a general guideline, it is 0.0002 to 0.02% by weight, preferably 0.001 to 0.02% by weight based on the total capacity.
It is in the range of 0.01% by weight. Water-soluble inorganic salts that are neutral in aqueous systems include sulfates such as sodium sulfate, potassium sulfate, and magnesium sulfate, and chlorides such as potassium chloride, magnesium chloride, and sodium chloride. These inorganic salts may be used alone or in combination. The amount used is 0.5 to 0.5 to the total amount of substances present in the polymerization system.
In the range of 0.01% by weight, preferably 0.3-0.02% by weight
used within the range. If there is too much water-soluble inorganic salt that is neutral in an aqueous system, the suspended system becomes unstable and tends to form lumps, whereas if it is too little, the particle size distribution of the produced polymer particles cannot be narrowed. As the polymerization initiator, polymerization initiators that are generally used for radical polymerization of vinyl monomers can be used, such as organic peroxides such as benzoyl peroxide and butyl perbenzoate, and azo compounds such as azobisisobutylnitrile. . In addition, various additives used in radical polymerization such as chain transfer agents such as mercaptans can be added as necessary. The aqueous medium/monomer is used in a weight ratio of 1.1/1 or more, but there is no particular upper limit on the amount of aqueous medium to monomer, but if it exceeds 1.5/1, the effect will not change much. There is no need to increase the amount more than that because it also reduces productivity. If the aqueous medium/monomer weight ratio is less than 1.1/1, the suspension system becomes unstable and tends to form lumps, making it impossible to narrow the particle size distribution of the produced polymer particles. In addition, the smaller the ratio of the amount of dispersion medium to the monomer, the wider the particle size distribution because when the poorly soluble phosphate is added during polymerization, the oil droplets that have grown to the desired particle size will be dispersed again. Therefore, only particles having the desired particle size can be obtained with a low yield. The sparingly soluble phosphate salt added during the polymerization is added once or in two or more portions. The timing of addition is when the polymerization conversion rate of the vinyl monomer is between 30% and 70% by weight. This is done by adding a sparingly soluble phosphate when the final particle size of the vinyl polymer particles is determined to prevent the particles from growing beyond the desired particle size. The polymerization conversion rate can be measured, for example, by gas chromatography, specific gravity liquid method, or the like. In general, in the suspension polymerization process, after polymerization is started at a predetermined polymerization temperature, if the poorly soluble phosphate is not added during the reaction, the initial concentration of the poorly soluble phosphate will be the same as that of the polymer oil droplets. It is preferable that it be slightly darker than the limit that does not form lumps. As the polymerization progresses, the polymer oil droplets repeat the dispersion and coalescence phenomenon by stirring, but due to the increase in viscosity of the oil droplets during polymerization, coalescence becomes more dominant, and the particle size of the oil droplets decreases. gradually grows larger. If polymerization continues, the oil droplets may continue to coalesce and eventually form a lump. Alternatively, the width of the particle size distribution is wide, and only particles having the desired particle size can be obtained in a low yield. In this method, the initial concentration of the sparingly soluble phosphate is slightly low to allow polymerization to start and proceed, and when the particles have grown to a desired particle size, the sparingly soluble phosphate is added and the polymerization is continued. At this point, the polymerization has progressed to the point where the polymer oil droplets can no longer be dispersed into small particles by stirring, and the particle size is gradually determined with slight coalescence, and the polymerization is finally completed. When sparingly soluble phosphate is added, the concentration of sparingly soluble phosphate after additional addition of the sparingly soluble phosphate is such that the polymer oil droplets are dispersed again in the subsequent process of polymerization completion and do not become small particles. The concentration of yeast must be adjusted. In other words, if the additional amount of poorly soluble phosphate is too large, the polymer oil droplets will be dispersed again in the subsequent polymerization process and become small particles, and conversely, if the total amount of poorly soluble phosphate added is too small. In the subsequent polymerization process, the polymer oil droplets coalesce and become larger, making it impossible to obtain particles with the desired particle size, or forming agglomerates during polymerization.
It has been difficult to find the optimal amount of sparingly soluble phosphate to be used. Examples of the present invention are shown below. In examples, “part”
means "parts by weight". Example 1 In a 3-separable flask, 1 part of tribasic calcium phosphate, 5 parts of a 1% aqueous solution of sodium dodecylbenzenesulfonate, and 1 part of sodium sulfate were dispersed and dissolved in 1100 parts of distilled water, and 2.5 parts of benzoyl peroxide was added thereto. A solution of 1,000 parts of styrene was added with stirring, and the temperature was raised to 90°C to initiate polymerization. Then, when the polymerization rate reached 40 to 50%, 0.5 part of tribasic calcium phosphate was added, and the mixture was directly polymerized at 90° C. for 8 hours to obtain polymer particles. Example 2 The procedure of Example 1 was followed except that the amount of distilled water was changed to 1200 parts. Example 3 The procedure of Example 1 was repeated except that 5 parts of sodium chloride was used instead of sodium sulfate. Example 4 The procedure of Example 1 was repeated except that sodium sulfate was changed to 5 parts of sodium chloride and distilled water was changed to 1200 parts. Comparative Example 1 In a 3-separable flask, 1 part of tribasic calcium phosphate and 5 parts of a 1% aqueous solution of sodium dodecylbenzenesulfonate were dispersed and dissolved in 1000 parts of distilled water, and 2.5 parts of benzoyl peroxide was added to 1000 parts of styrene. The dissolved material was added while stirring, and the temperature was raised to 90°C to start polymerization. Then, when the polymerization rate reached 40 to 50%, 0.5 part of tribasic calcium phosphate was added, and the mixture was directly polymerized at 90° C. for 8 hours to obtain polymer particles. Comparative Example 2 Comparative Example 1 was followed except that 1 part of sodium sulfate was also used. Table 1 shows the particle size distribution of the polymer particles obtained in each of the above Examples and Comparative Examples.

[Table] As is clear from Table 1, in Examples 1 to 4, the particle size distribution was centered around the B-1, B-2, and B-3 cuts, with fewer particles and fine particles in the A cut. Although small particles were obtained, in Comparative Examples 1 and 2, there were many A-cut particles and fine particles.
Moreover, only particles with a wide particle size distribution are obtained. As is clear from the above, according to the present invention, by suspension polymerizing vinyl monomers,
It is possible to obtain narrow vinyl polymer particles with a particle distribution centered on a particle diameter of 2.4 mm.

Claims (1)

[Scope of Claims] 1. When carrying out suspension polymerization of vinyl monomers, in the presence of a sparingly soluble phosphate and an anionic surfactant, a water-soluble inorganic salt that is neutral in an aqueous system contains 0.5 to 0.01
After starting suspension polymerization at a range of % by weight and an aqueous medium/monomer weight ratio of 1.1/1 or more,
The polymerization is proceeded by adding a sparingly soluble phosphate to the polymerization system at least once at a polymerization conversion rate of the vinyl monomer between 30% and 70% by weight, and the particle size distribution of the polymer particles is
A method for producing vinyl polymer particles, characterized in that particles having a diameter of 1.4 to 2.4 mm are obtained. 2. Production of vinyl polymer particles according to claim 1, wherein the poorly soluble phosphate is basic tricalcium phosphate (hydroxyapatite) and the anionic surfactant is sodium dodecylbenzenesulfonate. Method. 3. The method for producing vinyl polymer particles according to claim 1, wherein the water-soluble inorganic salt is sodium sulfate. 4. Production of vinyl polymer particles according to claim 1, in which a sparingly soluble phosphate is added once or twice between 30% and 70% by weight of the vinyl monomer polymerization conversion rate. Method.