JPH01210406A - Suspension polymerization of styrene resin - Google Patents

Abstract

PURPOSE:To make it possible to decrease fine powdery beads without changing a mean particle diameter of styrene resin beads, by initiating polymn. of styrene monomer in an aq. medium contg. a hardly soluble inorg. compd. and an anionic surface active agent and supplementing the hardly soluble inorg. compd. when the conversion rate of the polymn. is in a specified range. CONSTITUTION:In preparing a styrene resin by suspension polymn. of styrene monomer. polymn. of the monomer is initiated in an aq. medium contg. a hardly soluble inorg. compd. and an anionic surface active agent and the hardly soluble inorg. compd. is supplemented while the conversion rate of the polymn. is in the range of 5-25%. As the hardly soluble inorg. compd., hardly-soluble phosphates, e.g., calcium phosphate or magnesium phosphate are pref. As to the loading of the hardly soluble inorg. compd., the total loading is 0.3-0.5wt.% based on the aq. medium, the initial loading is 0.05wt.% or more and the rest is pref. supplemented at once or in two or more portions while the conversion rate of the polymn. is 5-25%. The anionic surface active agent is pref. used in an amount of 0.003-0.005wt.% based on the aq. medium.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to improvements in suspension polymerization of styrenic resins. More specifically, the present invention relates to a method for suspension polymerization of styrenic resin that can reduce the amount of fine beads without changing the average particle size of the styrenic resin beads.

[Prior Art] Conventionally, as a method for producing styrenic resin by suspension polymerization of styrenic monomers, for example, in an aqueous medium containing a sparingly soluble inorganic compound and an anionic surfactant,
A method of suspension polymerizing the styrenic monomer is well known. However, this suspension polymerization method has the disadvantage that the resulting styrenic resin inevitably has a wide particle size distribution.

As a method to improve these drawbacks and narrow the particle size distribution of the resulting styrenic resin, for example, the use of water-soluble neutral inorganic salts such as sparingly soluble phosphates, anionic surfactants, and sodium sulfate is effective. In the aqueous medium containing the styrenic monomer, the polymerization of the styrenic monomer is started, and the polymerization conversion rate is 30 to 7.
A method of adding a sparingly soluble phosphate in the range of 0% has been proposed (Japanese Unexamined Patent Publication No. 71901/1983). However, in this method, although the yield of polymer particles with a particle size of 1.0 to 2.4 mm is high and the number of fine beads is reduced, the average particle size of the polymer particles also becomes large and the suspension becomes unstable. In addition, large particles tend to contain air bubbles, and it is difficult to wash away the impurities that exist there.
It has problems such as adversely affecting physical properties.

[Problems to be Solved by the Invention] The present invention overcomes the drawbacks of the conventional suspension polymerization method for styrenic resin, and reduces the amount of fine beads without changing the average particle size of the beads of styrenic resin. The purpose of this invention was to provide a suspension polymerization method for wet styrenic resins.

[Means for Solving the Problems] As a result of intensive research to achieve the above object, the present inventors found that styrene-based It was discovered that the purpose could be achieved by starting the polymerization of the monomer and adding a sparingly soluble inorganic compound until the polymerization conversion rate was within a predetermined range.Based on this knowledge, the present invention was completed. That's it.

That is, the present invention provides a method for producing a styrenic resin by suspension polymerizing a styrenic monomer in an aqueous medium containing a sparingly soluble inorganic compound and an anionic surfactant. The present invention provides a suspension polymerization method for styrenic resins, which is characterized in that a poorly soluble inorganic compound is added at a polymerization conversion rate of 5 to 25%.

The present invention will be explained in detail below.

The styrenic monomer used in the present invention includes:
Examples include styrene, α-methylstyrene, chlorostyrene, etc., which may be used alone or in combination of two or more, and copolymerizable monomers such as acrylonitrile, It may also be copolymerized with methyl methacrylate, butyl acrylate, etc.

Further, as the poorly soluble inorganic compound, for example, poorly soluble phosphates such as calcium phosphate and magnesium phosphate are generally preferably used. This poorly soluble inorganic compound is 0
．． Those having a particle size of 0.05 to 0.2 μm are preferred.

Regarding the amount of the sparingly soluble inorganic compound used in the method of the present invention, the total amount added is usually 0.1 to 0.
It is used in an amount of 6% by weight, preferably 0.3 to 0.5% by weight. In the method of the present invention, the polymerization conversion rate is 5
It is necessary to additionally add the poorly soluble inorganic compound in an amount between 25% and 25%. In this case, the initial addition amount of the poorly soluble inorganic compound is 0.05% by weight or more, and the remainder is added at a polymerization conversion rate of 5%.
It is desirable to add between 25% and 25% at once or in two or more portions. If the total amount added is less than 0.1% by weight, the average particle size becomes large and the suspension tends to become unstable;
If it exceeds 6% by weight, the average particle size tends to become too small. Moreover, if the initial addition amount is less than 0.05% by weight, the average particle size becomes too large, which is not preferable. Furthermore, if the poorly soluble inorganic compound is added when the polymerization conversion rate is less than 5%, the number of fine particles will increase, and if it is added after the polymerization conversion rate exceeds 25%, the average particle size will increase, making suspension difficult. It becomes stable.

Examples of anionic surfactants used in the method of the present invention include those conventionally used in suspension polymerization of styrenic monomers, such as alkylbenzenesulfonates such as sodium dodecylbenzenesulfonate, alkylsulfonates, Acid sulfonates such as β-tetrahydronaphthalene sulfonate or sodium N-isopropylcyclohoxidyl acid sulfonate, higher fatty acid salts such as sodium oleate, and dialkyl sulfosuccinates such as di-2-ethylhexyl sodium sulfosuccinate. etc. can be mentioned. These anionic surfactants may be used alone or in combination of two or more, but generally alkylbenzenesulfonates such as sodium dodecylbenzenesulfonate are preferably used.

These anionic surfactants are used as dispersion aids, and the amount used is usually 0.001 to 0.01% by weight, preferably 0.003% by weight based on the aqueous medium.
- o, oos weight% range. If the amount of the anionic surfactant used exceeds the above range, the polymerization system will become unstable, which is not preferred.

In the uninvented method, the aqueous medium is optionally further supplemented with water-soluble inorganic salts such as sodium sulfate, potassium sulfate,
Sulfates such as magnesium sulfate, chlorides such as potassium chloride, magnesium chloride, and sodium chloride can also be added.

Next, to explain one example of a preferred embodiment of the method of the present invention, first, a required amount of a poorly soluble inorganic compound and an anionic surfactant are added to an aqueous medium, and then a styrene monomer is added. , polymerization is initiated at a predetermined temperature while stirring. At this time, it is desirable for the ratio of the styrene monomer to the aqueous medium to be 0.8 or more by weight in terms of suspension stability. After the start of polymerization, the polymerization conversion rate is 5-25%.
A required amount of the poorly soluble inorganic compound is added at once or in two or more portions, and the reaction is further advanced to complete the polymerization. A polymerization initiator is appropriately used in this polymerization.

Examples of the heavy initiator include those conventionally used in radical polymerization of styrenic monomers, such as organic peroxides such as benzoyl peroxide and butyl perbenzoate, and azo compounds such as azobisisobutyronitrile. is used. Furthermore, various additives commonly used in radical polymerization of styrenic monomers, such as a chain transfer agent such as mercaptan, can be added to the polymerization reaction, if necessary.

[Effects of the Invention] According to the method of the present invention, the number of types of suspension stabilizers used can be reduced, and the average particle diameter of the styrene resin particles can be reduced to 0.
．． Since the particle size can be controlled within the range of 3 to 0.6+a+++ and the amount of fine beads can be reduced, unstable extruder discharge due to fine particles and poor physical properties due to large beads containing air bubbles can be prevented. Therefore, the styrenic resin obtained by the method of the present invention allows stable operation in an extruder and improves the haze of the product.

[Example] Next, the present invention will be explained in more detail with reference to Examples.
The present invention is not limited in any way by these examples.

Examples 1 to 6, Comparative Examples 1 to 5 To 25 to 9 parts of water, tricalcium phosphate and sodium dodecylbenzenesulfonate were added in the amounts shown in Table 1, and to this, benzoyl peroxide, a polymerization initiator, was added to styrene monomer. The added materials were added in the amounts shown in Table 1, and the mixture was heated to 80°C in a nitrogen atmosphere with stirring to initiate polymerization. When the polymerization conversion rate reached the desired value, tricalcium phosphate was further added in the amount shown in Table 1, and the temperature was raised appropriately to complete the reaction. The average particle size of the styrene resin thus obtained and the fine powder beads (diameter: 0.074 mm)
Find the amount of (below) t;. The results are shown in Table 1.

(Margin below)

Claims (1)

[Claims] 1. When producing a styrenic resin by suspension polymerization of a styrenic monomer, the polymerization of the styrenic monomer is started in an aqueous medium containing a sparingly soluble inorganic compound and an anionic surfactant. , and its polymerization conversion rate is 5 to 25%
A suspension polymerization method for styrenic resins characterized by the addition of a sparingly soluble inorganic compound between the layers.