JPS5941448B2 - Suspension polymerization method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for suspension polymerization of styrenic monomers.

More specifically, the present invention relates to a suspension polymerization method for obtaining styrenic polymer particles having relatively uniform particle sizes. Conventionally, methods for suspension polymerization of styrene monomers include polymerization using organic surfactants such as polyvinyl alcohol and polyvinylpyrrolidone as dispersants, and methods using poorly water-soluble inorganic materials as shown in Japanese Patent Publication No. 1298-1298. A method is known in which a salt and an anionic surfactant are used as a combined dispersant for polymerization.

However, when an organic surfactant is used as a dispersant, it may cause a decrease in thermal stability, deterioration of transparency, or a decrease in mechanical strength due to the incorporation of the dispersant into polymer particles. It is known that this can have undesirable effects such as increasing the COD load of the polymerization effluent. As a method for eliminating these effects, a method such as that shown in Japanese Patent Publication No. 29-1298 is known, but when styrenic monomers are suspension polymerized according to this method, the resulting polymer particles are The particle size distribution width is relatively wide.

Styrenic polymer particles obtained through suspension polymerization are extruded or injection molded and used to make various products, but the wide particle size distribution causes variations in the supply of raw materials to the molding machine, resulting in a high product defect rate. The problem arises that it increases.

In addition, the styrenic polymer particles obtained by suspension polymerization are impregnated with a blowing agent (for example, propane, butane, pentane, etc.).
So-called expanded styrene is obtained.

The uses of expanded styrene can be roughly divided into the following three fields depending on the particle size. (1) Styrene foam with a particle size of approximately 300μ to approximately 700μ is suitable for use in cups such as instant foods and low foaming applications such as shoe soles.

(2) Particles with a particle size of approximately 700μ to approximately 1800μ are used for various packaging purposes. (3) Particle size from about 1300μ to about 3000μ
Styrene foam is used as building material boards, etc. These differences in use require different properties of expanded styrene, so it is necessary to manufacture expanded styrene for each purpose, but if the polymer particles obtained by suspension polymerization have a wide particle size distribution, The goal is difficult to reach.

In order to solve the problem of deception, the present inventors have conducted intensive research and found that polymer particles obtained by suspension polymerization can be polymerized without impairing their thermal stability, transparency, and mechanical strength. We have invented a method that does not increase the COD load of the wastewater and makes the particle size distribution much narrower than known methods.
Here we provide a method.

In the present invention, when carrying out suspension polymerization of styrenic monomers,
The monomer is dispersed in an aqueous medium of a dispersant system consisting of a combination of basic calcium phosphate, sodium α-olefin sulfonate, and a water-soluble metal salt that is neutral in an aqueous system, and then polymerized to reduce the particle size. The purpose is to obtain polymer particles with a narrow distribution width.

The present inventors have confirmed that the total uniformity coefficient UT of the polymer particles obtained by the present invention is 3 or less, whereas in the known suspension polymerization method, the UT is 3.5 or more. There is.

The styrene monomer in the present invention means styrene, but a monomer copolymerizable with styrene may be copolymerized in an amount of 10% by weight or less based on styrene.

Examples of copolymerizable monomers include various substituted styrenes such as chlorstyrene and α-methylstyrene, and vinyl monomers such as acrylonitrile, methyl methacrylate, and stylacrylate. Copolymerization with more than 10% by weight of copolymerizable monomers is not preferred because it significantly changes suspension stability.

Inorganic salts that are neutral in aqueous systems include lithium chloride, potassium chloride, common salt, magnesium chloride, calcium chloride, potassium sulfate, sodium sulfate, magnesium sulfate, and the like.

These inorganic salts may be used alone or in combination. In addition, inorganic salts have the effect of providing particularly good suspension stability and particle size distribution when styrenic monomers are polymerized in the coexistence of methylene bis stearylamide and ethylene bis stearyl amide, which are known as nucleating agents for expanded styrene. It has the effect of narrowing the The amount of inorganic salt used is particularly effective when it is 0.2% by weight or more, and the effect does not change much when it is used in an amount of 1% or more, and there is no reason to use more than that from the viewpoint of economy. Moreover, as the inorganic salt, common salt is preferable because it is inexpensive and exhibits sufficient effects. Sodium α-olefin sulfonate works as a dispersant together with basic calcium phosphate.

The required amount is 0.002% by weight or more based on the monomer.
．． 0.006% by weight or less is preferable. This is because if it exceeds this range, the particle size distribution width becomes wide and suspension stability deteriorates. For basic calcium phosphate, 0.05% by weight or more 1 based on the monomer, depending on the desired particle size.
If amounts between % by weight and below are used, polymer particles sufficient for practical use will be obtained.

In particular, in order to narrow the particle size distribution width, a remarkable effect can be seen by using basic calcium phosphate having a particle size of 2 μm or less, as clearly shown in the examples. Note that basic calcium phosphate may be added in portions during polymerization to balance suspension stability and particle size while polymerization is carried out. Example 1 514 equipped with a stirrer, cooling pipe, thermometer, and nitrogen introduction pipe
2164.5g (130 parts by weight) of water in a two-flask,
Ethylene bisstearylamide 1.339 (0.08 parts by weight), common salt 5.00 g (0.3 parts by weight), basic calcium phosphate 3.33 g (0.20 parts by weight) (tricalcium phosphate, Taihei Chemical Industry ( Co., Ltd., pulverized to a particle size of 1.5μ), α-olefin sodium sulfonate 0.
075f1 (0.0045 parts by weight) was added and uniformly dispersed, and then benzoyl peroxide 7.29 (0.43 parts by weight) and tert-butyl perbenzoate 3.39 (0. 2 parts by weight) was added thereto, and the temperature was raised to 90° C. under a nitrogen stream while thoroughly stirring to initiate polymerization.

True spherical polystyrene polymer particles were obtained which solidified approximately 5 hours after the start of polymerization. After drying, these polymer particles were sieved into various particle sizes, and the average particle size was 1.14 mm, uniformity coefficient U9O/401.24, U6O/101.64, and total uniformity coefficient UT2.88, which is a conventionally known method. The polymer particles had a much narrower particle size distribution width than that obtained by the suspension polymerization method. Example 2 514 equipped with a stirrer, cooling pipe, thermometer, and nitrogen introduction pipe
2164.59 (130 parts by weight) of water in a two-flask,
Ethylene bisstearylamide 1.33g (0.08 parts by weight), common salt 5.009 (0.3 parts by weight), basic calcium phosphate 2.50f1 (0.15 parts by weight) (manufactured by Nihon Kagaku Kogyo Co., Ltd., product) Name "Supertite 10'2, particle size 0.5μ), α-olefin sodium sulfonate 0,
0759 (0.0045 parts by weight) was added and uniformly dispersed, and then benzoyl peroxide 7.29 (0.43 parts by weight) and tert-butyl perbenzoate 3.39 (0. 2 parts by weight) was added thereto, and the temperature was raised to 90° C. under a nitrogen stream while thoroughly stirring to initiate polymerization.

True spherical polystyrene polymer particles that solidified approximately 5 hours after the start of polymerization were obtained. After drying, these polymer particles were sieved into various particle sizes, and the average particle diameter was 1.22 mm with a uniformity coefficient of U9O/401. 18, U60/101.26, total uniformity coefficient UT2.44, and the polymer particles were much narrower than the particle size distribution width obtained by the conventionally known suspension polymerization method.〇Comparative example 514 equipped with a stirrer, cooling tube, thermometer, and nitrogen introduction tube
In a double flask, 2164.5 (130 parts by weight) of water,
Ethylene bis stearylamide 1.331 (0.08 parts by weight), basic calcium phosphate 3.33 g (0.20 parts by weight)
(parts by weight) (tricalcium phosphate, manufactured by Taihei Kagaku Kogyo Co., Ltd., particle size 5μ) and 0.075f1 (0.0045 parts by weight) of α-olefin sodium sulfonate were added and uniformly dispersed. benzoyl peroxide 7 to styrene 16659 (100 parts by weight).

Add a solution of 2f1 (0.43 parts by weight) and tert-butyl perbenzoate 3.39 (0.2 parts by weight), and raise the temperature to 90°C under a nitrogen stream while stirring thoroughly to start polymerization. did.

True spherical polystyrene polymer particles were obtained which solidified approximately 5 hours after the start of polymerization.

After drying these polymer particles, they were sieved into various particle sizes.
The average particle size of turtle is 1.08m17! x uniformity coefficient U9O/40
1.34, U60/102.52, total uniformity coefficient 3.86
This was a typical particle size distribution width.

[Brief explanation of drawings]

The figure shows the particle size on the horizontal axis and the cumulative weight percent of the polymer particles on the vertical axis.The particles obtained by polymerization are sieved into each particle size, and the weight of all particles of each sieved particle size is calculated. , is a curve diagram plotted against particle diameter sequentially starting from particles with a small particle diameter. The particle size C corresponding to 50% of the cumulative weight is referred to as the average particle size t. The value E obtained by dividing the particle diameter E, which accounts for 90% of the cumulative weight, by the particle diameter B, which accounts for 40%, is called the uniformity coefficient U9O/40. The value A obtained by dividing the particle diameter D, which is equivalent to 60% of the cumulative weight, by the particle diameter A, which is equivalent to 10%, is called the uniformity coefficient U6O/10. Uniformity coefficient U9O/40+U6O/10 as total uniformity coefficient UT
It is called. Therefore, the uniformity coefficients U9O/40 and U60/10 are 1.0
The closer the total uniformity coefficient UT is to 2.0, the higher the uniformity of the obtained polymer particles, that is, the narrower the particle size distribution width.

Claims (1)

[Scope of Claims] 1. When carrying out suspension polymerization of a styrenic monomer, the monomer is treated with basic calcium phosphate having a particle size of 2 μm or less, sodium α-olefin sulfonate, and a water-soluble material that is neutral in an aqueous system. A method for suspension polymerization of styrenic monomers, which comprises dispersing them in an aqueous medium containing a dispersant consisting of a combination of metal salts, and then polymerizing them. 2. The polymerization method according to claim 1, wherein the amount of basic calcium phosphate used is 0.05% by weight or more and 1% by weight or less based on the monomer. 3 The amount of sodium α-olefin sulfonate used is 0.002% by weight or more and 0.006% by weight based on the monomer.
The polymerization method according to claim 1, which is as follows. 4. The polymerization method according to claim 1, wherein the water-soluble metal salt exhibiting neutrality in an aqueous system is common salt. 5. The polymerization method according to claim 4, wherein the amount of common salt used is in the range of 0.2% by weight or more and 1% by weight or less based on the monomer. 6. The polymerization method according to claim 1, wherein the polymerization is carried out in the presence of methylene bis-stearylamide and/or ethylene bis-stearylamide.