JPH0142281B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a suspension polymerization method for monomers mainly composed of styrene, and more specifically to a method for obtaining particles with a narrow particle size distribution synthesized by suspension polymerization. It relates to suspension polymerization.

Conventionally, in the suspension polymerization of monomers mainly composed of styrene, benzoyl peroxide is used as a polymerization initiator, and organic surfactants such as polyvinyl alcohol and polyvinylpyrrolidone, or poorly water-soluble inorganic surfactants are used as polymerization dispersants. Combinations of salts and anionic surfactants have been used, but in either case the resulting polymer particles have a relatively wide particle size distribution.

Polymer particles mainly composed of polystyrene obtained through suspension polymerization are extruded or injection molded and made into various products, but if the particle size distribution is wide, there will be variations in the supply of raw materials to the molding machine, resulting in product defects. The problem arises that the rate increases.

In addition, polymer particles mainly composed of styrene obtained through suspension polymerization are used for purposes such as expanded styrene, but depending on the size of the particles, the expanded styrene is used in the following three fields. Can be divided.

1. Styrene foam with a particle size of approximately 0.3 to 0.7 mm is used in cups for instant foods.

2. Styrene foam with a particle size of approximately 0.7 to 1.8 mm is used for various packaging materials.

3. Styrene foam with a particle size of approximately 1.3 to 3.0 mm is a board for building materials.

These different uses require different properties of expanded styrene, so it is necessary to manufacture expanded styrene for each use, but if the polymer particles obtained by suspension polymerization have a wide particle size distribution, this purpose can be achieved. hard.

In order to solve this problem, the present inventors have conducted intensive research and have found that the polymer particles obtained by suspension polymerization can be produced without impairing their thermal stability, transparency, and mechanical strength, and in which polymerization effluent can be We have found a method that significantly narrows the particle size distribution compared to known methods without increasing the COD load of the particles, and we hereby provide that method.

According to the present invention, when suspension polymerizing a styrenic monomer, the monomer is made of a combination of an anionic surfactant, a poorly water-soluble inorganic salt, and a water-soluble metal salt that is neutral in an aqueous system. After being dispersed in an aqueous dispersion medium, polymer particles having a narrow particle size distribution width can be obtained by polymerizing using tert-butyl peroxy (2-ethylhexanoate) as a polymerization initiator. The total uniformity coefficient U _T of the polymer particles obtained by the present invention is about 2.7, whereas
In known suspension polymerization methods, U _T is usually a value of 3.2 or more.

The styrenic monomer in the present invention means styrene, but a monomer copolymerizable with styrene may be mixed with 10 parts by weight or less of styrene for copolymerization. Copolymerizable monomers include various substituted styrenes such as chlorstyrene and α-methylstyrene;
Alternatively, vinyl monomers such as acrylonitrile, methyl methacrylate, and methyl acrylate are used. Copolymerization with more than 10 parts by weight of a copolymerizable monomer is not preferred because it significantly changes suspension stability.

In the present invention, it is essential to use tert-butyl peroxy (2-ethylhexanoate) as a polymerization initiator in order to achieve the object of the present invention. The amount of the polymerization initiator used is
It can be determined depending on the degree of polymerization of the target polymer particles, but usually 0.10 to 0.40 parts by weight based on the monomer is sufficient, and in practice, 0.15 to 0.32 parts by weight is sufficient for polymer particles with a sufficient degree of polymerization. can get. In addition to the polymerization initiator, common catalysts such as benzoyl peroxide and t-butyl peroxybenzoate may be used in combination. When used in combination, the amount of other polymerization initiators used is preferably 20% by weight or less of tert-butyl peroxy (2-ethylhexanoate). Furthermore, for the purpose of reducing the residual monomer, the effects of the present invention will not change even if a high temperature polymerization initiator such as tertiary butyl perbenzoate is used in an amount of, for example, 0.01 to 0.30 parts by weight based on the monomer. do not have.

The poorly water-soluble inorganic salt is an inorganic salt that is poorly soluble in water, such as calcium phosphate, magnesium phosphate, calcium carbonate, and magnesium carbonate, and acts as a dispersant when polymerizing styrene monomers. The amount used can be adjusted depending on the target particle size of the polymer. For example, when using basic calcium phosphate,
It is practically sufficient to select an amount in the range of 0.05 parts by weight or more and 1.0 parts by weight or less. Moreover, those having a particle size of 2 μm or less are preferably used.

The poorly water-soluble inorganic salt may be added in portions during the polymerization, and the polymerization may be carried out while maintaining a balance between suspension stability and particle size.

The anionic surfactant acts as a dispersant together with a poorly water-soluble inorganic salt, and common sodium alkylbenzene sulfonate, sodium α-olefin sulfonate, etc. can be used.

Examples of inorganic salts that are neutral in aqueous systems include lithium chloride, potassium chloride, common salt, magnesium chloride, calcium chloride, and the like. These inorganic salts can be used alone or in combination, but the amount used is particularly effective at 0.2 parts by weight or more based on the monomer, and 1.0 parts by weight or more.
There is no reason to use more than 1 part by weight because the effect does not change much and it is economical. Among these inorganic salts, common salt is particularly preferred because it is inexpensive and exhibits sufficient effects.

Hereinafter, this will be explained in more detail with reference to Examples.

Example 1 1700 g (90 parts by weight) of water was placed in a 5-volume 4-necked flask equipped with a stirrer, thermometer, etc., and then 2.38 g of basic calcium phosphate was added while stirring.
(0.125 parts by weight) (manufactured by Nippon Kagaku Kogyo Co., Ltd., trade name Supertite 10, solid content 10%), sodium α-olefin sulfonate 0.076 g (0.0040 parts by weight), salt 6.38 g (0.336 parts by weight), ethylene Bisstearylamide 1.33g (0.07 parts by weight), tert-butylperoxy (2-ethylhexanoate) 3.42
g (0.180 parts by weight) (manufactured by NOF Corporation, trade name Perbutyl 0), tertiary butyl perbenzoate 2.85 g
(0.150 parts by weight) was added and uniformly dispersed, then 1900 g (100 parts by weight) of styrene was added, and the temperature was raised to 94° C. with thorough stirring to initiate polymerization. True spherical polystyrene polymer particles solidified in about 5 hours after the start of polymerization were obtained. After drying these polymer particles, they were sieved to various particle sizes, and the average particle size was 1.20 mm.
The uniformity coefficient U90/40 = 1.34, U60/10 = 1.39, and the total uniformity coefficient U _T = 2.74, which are significantly narrower than the particle size distribution width obtained by conventionally known suspension polymerization methods. It was hot.

Example 2 According to the process of Example 1, sodium dodecyl phenyl oxide disulfonate (Kao soap) was used instead of sodium α-olefin sulfonate.
Manufactured by Co., Ltd., trade name: Perex SSH (purity 50%)
When 0.076 g (0.0040 parts by weight) was used, the average particle size of the obtained polymer particles was 1.19 mm, and the uniformity coefficient was
U90/40=1.31, U60/10=1.38, total uniformity coefficient=
2.69, and the polymer particles had a particle size distribution width significantly narrower than that obtained by conventionally known suspension polymerization methods.

Comparative Example 1 According to the process of Example 1, the same amount of common benzoyl peroxide was used in place of tert-butyl peroxy (2-ethylhexanoate). The average particle size of the obtained polymer particles is
1.06mm, uniformity factor U90/40=1.66, U60/10=
1.55, and the total uniformity coefficient U _T =3.20, which was a typical particle size distribution.

[Brief explanation of drawings]

The figure shows the particle size (mm) on the horizontal axis and the cumulative weight percentage of polymer particles on the vertical axis, and the weight of all particles of each particle size obtained by sieving the particles obtained by polymerization into each particle size. The graph is plotted against the particle size in order from the smallest particle size. The particle diameter C corresponding to 50% of the cumulative weight is referred to as the average particle diameter dB~. in cumulative weight
Particle size E, which is equivalent to 90%, and particle size B, which is equivalent to 40%.
The value E/B divided by is called the uniformity coefficient U90/40. The value D/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 U60/10. Uniformity coefficient U90/40 + U60/10 is total uniformity coefficient
It is called _UT . Therefore, uniformity coefficients U90/40, U60/10
The closer to 1.0 and the closer the total uniformity coefficient U _T is to 2.0, the higher the uniformity of the obtained polymer particles, that is, the narrower the particle size distribution width. C: average particle diameter dB~, E/B: uniformity coefficient U90/40,
D/A: uniformity coefficient U60/10, E/B+D/A: total uniformity coefficient _UT .

Claims (1)

[Claims] 1. When carrying out suspension polymerization of styrenic monomers,
After dispersing the monomer in an aqueous medium containing a dispersant consisting of a combination of an anionic surfactant, a poorly water-soluble inorganic salt, and a water-soluble metal salt that is neutral in an aqueous system, tert-butyl peroxide was added as a polymerization initiator. A suspension polymerization method for styrenic monomers, characterized by polymerization using oxy(2-ethylhexanoate). 2. The polymerization method according to claim 1, wherein the poorly water-soluble inorganic salt is basic calcium phosphate. 3. The polymerization method according to claim 2, wherein the amount of basic calcium phosphate used is 0.05 parts by weight or more and 1.0 parts by weight or less based on the monomer. 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 0.2 parts by weight or more and 1.0 parts by weight or less based on the monomer.