JPS6312481B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for obtaining vinyl polymer particles having a narrow particle size distribution and without air bubbles within the particles by suspension polymerization of vinyl monomers. Generally, polymer particles produced by suspension polymerization are polymerized particles of at least one type of vinyl monomer that are dispersed in water by stirring and the action of a suspending agent (dispersing agent). 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 such as styrene and methyl methacrylate include sparingly soluble phosphates as the main suspending agent and anionic surfactants as suspension aids. is known to be used. Specifically, tricalcium phosphate and sodium dodecylbenzenesulfonate are the most common suspending agents. The particle size of polymer particles produced by suspension polymerization using this suspending agent is approximately 0.1
-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. Polymer particles are generally required to have a uniform particle size depending on the use. For example, if we take polymer particles mainly composed of styrene such as polystyrene,
The polymer particles 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. That is, (1) particle size approx.
Expandable polystyrene particles with a particle size of 300μ to 700μ are used for instant food cups, (2) particles with a particle size of about 700μ to 1800μ are used for various packaging and fish boxes, and (3) particles with a particle size of about 1500μ to 3000μ are used for various packaging and fish boxes. It is 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. It is conventionally known to add a water-soluble sulfite or its precursor during suspension polymerization of vinyl monomers, but simply adding such a substance will not produce spherical particles of the desired particle size. This is insufficient to obtain high yields. Furthermore, in suspension polymerization, air bubbles may be present in the obtained polymer particles, but this is not preferable in terms of improving the utility value of the polymer particles. The present invention solves these problems. That is, the present invention provides a method for suspension polymerizing a vinyl monomer in the presence of a sparingly soluble phosphate and an anionic surfactant, before the start of polymerization or at a polymerization conversion rate.
Up to 30% by weight, 0.0001 to 0.05% by weight of a water-soluble sulfite or its precursor is added to the vinyl monomer, and after the addition of the water-soluble sulfite or its precursor, Vinyl polymer particles characterized in that the polymerization is proceeded by adding a sparingly soluble phosphate to the polymerization system at least once while the polymerization conversion rate of the vinyl monomer is between 20% and 60% by weight. Regarding manufacturing methods. Examples of the vinyl monomer in the present invention include styrene or α-methylstyrene, styrene derivatives such as vinyltoluene and parachlorostyrene, acrylonitrile, acrylic esters, methacrylic esters such as methyl methacrylate, vinyl pyridine, vinyl carbazole, and At least one selected from the group consisting of butadiene is used. As poorly soluble phosphates, tricalcium phosphate,
Examples include magnesium phosphate, and those with a size of 0.2 to 0.05 μ, called submicron units, are useful. The total amount of sparingly 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 and is wasted. become. Preferably 0.05-0.5% 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 poorly soluble phosphate initially present in the reaction system is not particularly limited within the above range, but it is preferable that the amount of poorly soluble phosphate present in the reaction system is 1/
4 to 3/4 used. 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.
β-tetrahydronaphthalene sulfonate with SO ₃ Na added, acid sulfonate such as sodium N-isopropylcyclohexyl acid sulfonate, higher fatty acid salt such as sodium oleate,
Dialkyl sulfosuccinates such as di-2-ethylhexyl sodium sulfosuccinate are used. The amount of these additions is not determined by the target particle size, mechanical conditions, suspending agent concentration, etc., but as a rough guide, it is based on the total volume.
It ranges from 0.0002 to 0.02% by weight, preferably from 0.001 to 0.01% by weight. The presence of water-soluble sulfites or their precursors reduces the amount of particles larger and smaller than the target particle size. Water-soluble sulfites or their precursors that have been found to be particularly effective include sodium sulfite, sodium pyrosulfite, sodium bisulfite, sodium pyrosulfate, sodium dithionite, sodium hydrogen sulfate, sodium thiosulfate, and hydrosulfite. Includes sodium, sodium metabisulfite, sodium formaldehyde sulfoxylate and sulfite. These sulfites and their precursors may be used alone or in combination. The amount of these used is in the range of 0.0001 to 0.05% by weight based on the monomer. If it is less than 0.0001% by weight, it is not possible to narrow the particle size distribution of the produced polymer particles, and if it is used in excess of 0.05% by weight, no increase in the effect can be expected. Furthermore, by adding these before the start of polymerization or at a polymerization conversion rate of up to 30% by weight, the particle size distribution can be narrowed. In addition, it is preferable that polyvinyl alcohol, a water-soluble cellulose derivative such as alkyl cellulose, hydroxyalkyl cellulose, or carboxyalkyl cellulose, sodium polyacrylate, etc. be present in the polymerization system as a water-soluble polymeric protective colloid. These may be used alone or in combination of two or more. The range of use of these is preferably 0.0002 to 0.05% by weight, particularly preferably 0.0002 to 0.005% by weight, based on the total amount of substances present in the polymerization system. By using a water-soluble polymeric protective colloid, the suspension system can be further stabilized.
This is preferable for narrowing the particle size distribution. The amount of poorly soluble phosphate, anionic surfactant, and sulfite or their precursors initially present in the reaction system is an important factor for the resulting vinyl polymer particles, but the amounts are as described above. It is appropriately determined within the range depending on the particle size of the objective vinyl polymer particles. For example, in order to increase the desired particle size, first reduce the amount of poorly soluble phosphate present in the reaction system or increase the amount of anionic surfactant. In order to reduce the target particle size, the opposite may be used. The poorly soluble phosphate salt added during the reaction is added once or in two or more portions. The timing of addition is after the addition of sulfite or its precursor, when the polymerization conversion rate is 20 to 60% by weight. This is because the final particle size of the vinyl polymer particles is determined at this stage, so the poorly soluble phosphate is added to prevent the particles from growing beyond the desired particle size. Examples of the polymerization initiator in the present invention include organic peroxides such as benzoyl peroxide and butyl perbenzoate;
Polymerization initiators generally used for radical polymerization of vinyl monomers can be used, such as azo compounds such as azobisisobutyronitrile. The polymerization initiator is preferably used in an amount of 0.05 to 1% by weight based on the vinyl monomer, and is preferably added to the polymerization system after being dissolved in the vinyl monomer. The suspension polymerization in the present invention is preferably carried out at a temperature of 50 to 100°C, preferably 70 to 93°C. Further, in the suspension polymerization of the present invention, it is preferable that the ratio of the vinyl monomer and the aqueous medium used is such that the former/latter is in a weight ratio of 0.9/1 to 1.5/1. The polymerization conversion rate can be measured, for example, by gas chromatography, specific gravity liquid method, or the like. Examples of the present invention are shown below. In examples, “part”
means "parts by weight". Example 1 In a three-separable flask, 1.7 g of tricalcium phosphate, 4.2 g of a 1% aqueous solution of sodium dodecylbenzenesulfonate, 0.2 g of a 1% aqueous solution of polyvinyl alcohol (saponyl value 90-99%), and 0.16 g of sodium sulfite were added. g to 1200g of ion-exchanged water
dispersed and dissolved in A solution of 3 parts of benzoyl peroxide dissolved in 1000 g of styrene was added to this with stirring, and the temperature was raised to 90°C to initiate polymerization.
Then, when the polymerization conversion rate reached 30 to 35% by weight, 1.1g of tribasic calcium phosphate was added and the mixture was left as it was.
Polymerization was carried out at 90°C for 8 hours to obtain polymer particles. Example 2 Polymer particles were obtained in the same manner as in Example 1 except that 0.16 g of sodium sulfite was changed to 0.07 g. Example 3 Polymer particles were obtained in the same manner as in Example 1 except that 0.16 g of sodium sulfite was replaced with 0.12 g of sodium dithionite. Example 4 0.16g of sodium sulfite was added to sodium hydrogen sulfate
The same procedure as in Example 1 was carried out except that the amount was changed to 0.2 g.
Polymer particles were obtained. Comparative Example 1 In a 3-separable flask, 1.7 g of tricalcium phosphate, 4.2 g of a 1% aqueous solution of sodium dodecylbenzenesulfonate, and 0.2 g of a 1% aqueous solution of polyvinyl alcohol (saponyl value 90-99%) were dispersed in 1200 g of ionized water. and dissolved. A solution of 3 g of benzoyl peroxide dissolved in 1000 g of styrene was added to this with stirring, and the temperature was raised to 90° C. to initiate polymerization. Then, when the polymerization conversion rate reached 30 to 35% by weight, 1.1 g 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 1.7 g of tribasic calcium phosphate, polyvinyl alcohol (saponyl value 90~
99%) and 0.16 g of sodium bisulfite were dispersed and dissolved in 1200 g of deionized water. A solution of 3 g of benzoyl peroxide dissolved in 1000 g of styrene was added to this with stirring, and the temperature was raised to 90° C. to initiate polymerization. 90 as is
Polymerization was carried out at ℃ for 8 hours to obtain polymer particles. Comparative Example 3 0.16g of sodium sulfite was added to 0.16g of sodium sulfite
Polymer particles were obtained in the same manner as in Example 1, except for changing the amount to g. The particle size distribution of the polymer particles obtained in each of the above Examples and Comparative Examples is shown in the following table.

[Table] Example 5 In a three-separable flask equipped with a cooling tube, 2 g of tribasic calcium phosphate, 4.2 g of a 1% aqueous solution of sodium dodecylbenzenesulfonate, and a 1% aqueous solution of polyvinyl alcohol (Saponidity 90-99%) were added. 0.2 g and 0.15 g of sodium sulfite were dispersed and dissolved in 1200 g of ion-exchanged water. Add 3g of lauroyl peroxide to this and 1000ml of methyl methacrylate.
The solution was added with stirring, and the temperature was raised to 70° C. while nitrogen gas was passed through at 60 ml/min to initiate polymerization. Then, when the polymerization conversion rate reached 25 to 30% by weight, 1g of tricalcium phosphate was added, and when the polymerization rate reached 40 to 45% by weight, 1g was added, and the polymer particles were polymerized at 70°C for 7 hours. Obtained. Comparative Example 4 Polymer particles were obtained in the same manner as in Example 5 except that 0.15 g of sodium sulfite was removed. Example 6 Polymer particles were obtained in the same manner as in Example 5, except that 0.15 g of sodium sulfite was replaced with 0.12 g of sodium dithionite. Example 7 In a three-separable flask equipped with a cooling tube, 2 g of tribasic calcium phosphate, 4.2 g of a 1% aqueous solution of sodium dodecylbenzenesulfonate, 0.2 g of a 1% aqueous solution of polyvinyl alcohol (saponification degree 90-99%), and 0.15 g of sodium bisulfite were dispersed and dissolved in 1200 g of ion-exchanged water. Add 3g of lauroyl peroxide to this and methyl methacrylate.
A solution of 700 g of vinylcarbazole and 300 g of vinylcarbazole dissolved in a mixed monomer was added with stirring, and the temperature was raised to 70° C. while nitrogen gas was bubbled through at 60 ml/min to initiate polymerization. Then, when the polymerization conversion rate reached 25 to 30% by weight, 1g of tribasic calcium phosphate was added, and when the polymerization rate reached 40 to 45% by weight, 1g was added,
Polymerization was continued at 70°C for 7 hours to obtain polymer particles. Comparative Example 5 Polymer particles were obtained in the same manner as in Example 7 except that 0.15 g of sodium bisulfite was removed. Table 2 shows the particle size distribution of the polymer particles obtained in Examples 5 to 7 and Comparative Examples 4 to 5.

[Table] According to the present invention, by carrying out aqueous suspension polymerization of vinyl monomers, it is possible to obtain vinyl polymer particles with extremely few air bubbles being entrained within the particles and with a narrow particle size distribution. Can be done. Therefore, for example, when used as expandable particles, the quality and bead utilization rate are improved.

Claims (1)

[Claims] 1. In the presence of a poorly soluble phosphate and an anionic surfactant, at least one vinyl monomer selected from the group consisting of styrene, styrene derivatives, acrylonitrile, acrylic esters, methacrylic esters, vinylpyridine, vinyl carbazole and butadiene. When carrying out suspension polymerization of polymers, a polymerization initiator or a polymerization conversion rate of up to 30% by weight,
0.0001 to 0.05% by weight based on the above vinyl monomer
of a water-soluble sulfite or its precursor;
After adding the water-soluble sulfite or its precursor, 1 % of the sparingly soluble phosphate is added to the polymerization system in which the polymerization conversion rate of the vinyl monomer is between 20% and 60% by weight.
A method for producing vinyl polymer particles, which comprises adding the particles more than once to advance polymerization.