JPH062766B2 - Method for producing vinyl polymer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a vinyl-based polymer, and more specifically, a vinyl-based polymer having less generation of fine powder particles by suspension polymerization and having a narrow particle size distribution. It relates to a method of producing polymer particles.

[Prior Art] Polymer particles obtained by suspension-polymerizing a vinyl-based polymer, for example polystyrene particles, may be used as expanded polystyrene by impregnating hydrocarbons such as butane and pentane as a foaming agent. Many. The applications of this expanded polystyrene are roughly divided into three fields depending on the particle size. That is, those with a particle size of 0.3 to 0.7 mm are used for instant food cups, those with a particle size of 0.7 to 1.8 mm are used for packaging, fish boxes, and those with a particle size of 1.5 to 3.0 mm are used as building material boards. Has been done. Due to these differences in application, it is desirable to produce expanded polystyrene for each application, but the particle size obtained by suspension polymerization is about 0.1.
It is in the range of up to 3 mm, and the width of the particle size distribution is wide, and it is difficult to manufacture it according to the intended use by narrowing the width of the particle size distribution. However, in recent years, the demand for a large variety of small lots has become more stringent, and there is a strong demand for a suspension polymerization method that does not generate fine powder particles and efficiently obtain beads with a particle size within a specific required range. There is.

In recent years, as a method for narrowing the particle size distribution of polymer particles obtained when a vinyl-based polymer is produced by suspension polymerization, for example, a method of adding an anionic surfactant during the polymerization (Japanese Patent Laid-Open Publication No. S60-12065). No. 52-51483), a method of adding an anionic surfactant and a sparingly soluble phosphate during polymerization (JP-A-52-47881), and the like.

[Problems to be solved by the invention]

In each of these conventional techniques, the particle size is brought close to the target particle size as much as possible to start the polymerization, and thereafter, in order to prevent the growth due to the collision of the particles with each other, an anionic surfactant during the polymerization, or It is a method of narrowing the particle size distribution by adding a sparingly soluble phosphate, and it is possible to suppress the distribution of the maximum particle size, but to suppress the generation of fine particles,
It wasn't enough yet.

The present invention has been made against the background of such conventional technical problems, and in order to be able to deal with a large variety of small lots, the production of fine polymer particles is extremely small, and vinyl polymer particles having a narrow particle size distribution are produced. The purpose is to

[Means for solving problems]

That is, the present invention provides a sparingly soluble inorganic salt, an alkylnaphthalene sulfonate, and a nonionic surfactant in an aqueous medium at a polymerization conversion rate of less than 55% during suspension polymerization of a vinyl-based monomer. To provide a method for producing a vinyl-based polymer, which comprises adding a water-soluble metal salt exhibiting neutrality in an aqueous medium at a polymerization conversion rate of 55 to 75%. is there.

Examples of the vinyl-based monomer applicable to the present invention include styrene, α-methylstyrene, styrene derivatives such as p-chlorostyrene, (meth) acrylic acid esters such as methyl methacrylate and methyl acrylate, vinyltoluene, acrylonitrile, vinyl. Carbazole and the like can be mentioned, but styrene derivatives are preferable, and styrene is particularly preferable.

Such vinyl monomers are suspension polymerized in an aqueous medium, and as a radical initiator used at that time, organic peroxides such as benzoyl peroxide, butyl perbenzoate, and t-butyl peroxybenzoate are used. Polymerization initiators used in general radical polymerization such as azo compounds such as azobisisobutyronitrile are used.

Further, the sparingly soluble inorganic salt acts as a suspension stabilizer during suspension polymerization of the vinyl polymer and functions to keep the suspension system stable. Examples of the sparingly soluble inorganic salt include sparingly soluble inorganic salts in water which is an aqueous medium such as calcium phosphate, basic calcium phosphate, magnesium phosphate, magnesium carbonate and calcium carbonate. This poorly soluble inorganic salt may be used alone or in combination of two or more. The amount of this sparingly soluble inorganic salt used is required to keep the suspension system in the form of fine particles from the early stage to the middle stage of the polymerization. For example, when calcium phosphate is used, 0.05 to 1.0 part by weight is used per 100 parts of the monomer. , Preferably 0.2 to 0.5 parts by weight. If the amount of the hardly soluble inorganic salt used is too small, the stability of the suspension system is deteriorated, and as the amount of the hardly soluble inorganic salt added increases, the particle size growth rate after the addition of the water-soluble metal salt will be described later. Late, 1.
It is not economical to exceed 0 part by weight.

Further, the alkylnaphthalene sulfonate is used as an auxiliary agent of the suspension stabilizer in order to further stabilize the dispersion of the suspension system, and alkali metal salts and ammonium salts are preferable.

The amount of the alkylnaphthalene sulfonate used is in the range of 0.0005 to 0.05 parts by weight, preferably 0.002 to 0.02 parts by weight, based on 100 parts by weight of the vinyl monomer.

If the amount of the naphthalene sulfonate used is less than the above range, the suspension system may become unstable. On the other hand, if the amount exceeds the above range, the particle size of the water-soluble metal salt described below may be increased even if it is added. Growth is hindered, and uniform particles having a desired particle size cannot be obtained.

The alkylnaphthalene sulfonate and other anionic surfactants can be used in combination, and when used in combination, the amount of the other anionic surfactants to be used is particularly the water-soluble metal salt described below. It is necessary to set the amount so as not to hinder the growth of the particle diameter by the addition of.

Examples of the anionic surfactant used in combination with the alkylnaphthalene sulfonate include alkylbenzene sulfonates such as dodecylbenzene sulfonate, higher fatty acid salts such as sodium stearate, higher alcohol sulfate ester salts such as sodium lauryl sulfate, and mono Sulfates of higher fatty acid esters such as sodium stearate sulfate, sulfosuccinate salts such as sodium sulfosuccinate dilauryl ester, and other anionic surfactants used in general suspension polymerization are used. It is not limited to these.

Furthermore, the nonionic surfactant has a function of promoting the growth of the particle size due to the synergistic effect of the addition of the water-soluble metal salt described later.

Examples of the nonionic surfactant include polyoxyethylene alkyl ester, polyoxyethylene alkyl ether, polyoxyalkylphenol ether,
Examples thereof include sorbitan alkyl ester, polyoxyethylene sorbitan alkyl ester, and polyglycerin alkyl ester. The strength of the effect of grain size growth depends on HLB (Hydrop
It has a close relationship with the hile-lypophile balance; the larger the value, the stronger the growth action after addition of the water-soluble metal salt and the faster the particle size growth rate.
Therefore, the HLB of the nonionic surfactant used is 10
The range of -20 is preferable, and the range of 15 or more is particularly preferable. The amount of the nonionic surfactant added at this time varies depending on the particle size of the target polymer particles, but is 0.0001 to 0.05 parts by weight, preferably 0.001 to 100 parts by weight of the monomer. It is 0.01 parts by weight, and if it is too small, the growth of the particles is not promoted even when the water-soluble metal salt described below is added, and the ratio of the particles becomes large in the particle size distribution, while if it is too large, the suspension system becomes unstable. , Not preferable.

The use of this nonionic surfactant is an essential requirement, and unless the surfactant is used, the particle size does not grow even if a large amount of a water-soluble metal salt described later is added.

In the present invention, a water-soluble metal salt that is neutral in an aqueous medium is added while the polymerization conversion rate is 55 to 75% in the course of such suspension polymerization. That is, in the early to middle stages of suspension polymerization (polymerization conversion rate is less than about 55%),
It is a relatively uniform fine particle (for example, a particle size of 0.5 mm or less) and is a stable suspension system, and the particle size division is stopped after the polymerization conversion rate is about 55%.

By adding a water-soluble metal salt to the suspension system during the polymerization, a part of the sparingly soluble inorganic salt is released from the particle surface to accelerate the growth of particles from finer particles and achieve the desired average. Along with obtaining the particle size, an extremely uniform particle size distribution is obtained.

Here, the polymerization conversion rate can usually be easily measured by a specific gravity method, gas chromatography or the like. The polymerization conversion rate is 55 when the water-soluble metal salt is added.
~ 75%, preferably 60-70%, 55
When it is less than 75%, it becomes difficult to control the growth of particles, and the particle size distribution of the particles obtained at this time becomes broad, whereas when it exceeds 75%, the growth of particles is not performed.

The water-soluble metal salt that is neutral in this aqueous medium generally promotes particle size growth by interaction with a nonionic surfactant present in a suspension system, such as sodium sulfate, Examples thereof include monovalent or divalent metal salts such as potassium sulfate, magnesium sulfate, sodium chloride, potassium chloride, calcium chloride and magnesium chloride.

The amount of the water-soluble metal salt added is 0.001 to 5.0 parts by weight, preferably 0.01 to 2.0 parts by weight, based on 100 parts by weight of the monomer.
0.001 to 1.0 parts by weight, preferably 0.01 to 0 parts by weight
Used in the range of 0.5 parts by weight.

If the amount of such a water-soluble metal salt added is absent or too small, it is difficult to obtain polymer particles having a desired particle size, and it is difficult to obtain polymer particles having a desired particle size. The diameter grows undesirably.

Further, in the present invention, after increasing the particle size of fine particles by adding a water-soluble metal salt to obtain a desired average particle size,
It is also possible to add a poorly soluble inorganic salt and / or an anionic surfactant, a water-soluble polymer protective colloid and the like.

In the case of polystyrene particles, for example, the vinyl polymer particles obtained by the present invention have an average particle diameter of 0.8 to 1.1 mm, and easily obtain fine powder particles of 0.5 mm or less in an amount of 0.5% by weight or less.

[Action]

In the present invention, the presence of the sparingly soluble inorganic salt, the anionic surfactant and the nonionic surfactant in the aqueous medium from the early stage to the middle stage of the suspension polymerization (polymerization conversion rate of less than 55%) makes it relatively uniform. It is a water-soluble metal salt that is neutral in an aqueous medium at a polymerization conversion rate of 55 to 75%, which seems to stop particle size division in a stable suspension system with various fine particle sizes. By adding to the suspension system during the polymerization, a part of the sparingly soluble inorganic salt is released from the surface of the particles, thereby promoting the growth of particles from finer particles to obtain a desired particle size. It is possible to obtain an extremely uniform particle size distribution.

〔Example〕

 Hereinafter, the present invention will be described in more detail with reference to examples.

In the examples, the particle size distribution is obtained by blotting the relationship between the particle size of polymer particles and the cumulative weight% of polymer particles as shown in FIG. Is.

That is, FIG. 1 shows the cumulative weight% of the polymer particles on the vertical axis and the particle size on the horizontal axis. The polymer particles obtained by the polymerization are shown in a particle size range of 10 mesh to 35 mesh. The particles are screened in the above, and the weight of each particle size is sequentially plotted from the particle having the smaller particle size to the particle size. In FIG. 1, the particle size C corresponding to 50% by weight in cumulative weight is defined as the average particle size.

Then, the value D / A obtained by dividing D corresponding to 60% by weight in cumulative weight by A corresponding to 5% by weight and the value E / B obtained by dividing E corresponding to 95% by weight by B corresponding to 40% by weight were added. "D / A + E
The value of "/ B" is defined as the total uniformity coefficient. Therefore, the closer D / A and E / B are to 10, respectively, the more “D / A + E”
The closer the value of / B is to 20, the narrower the particle size distribution width of the polymer particles.

Conventionally, there is a method in which 10% by weight is used instead of 5% by weight and 90% by weight is used instead of 95% by weight. Has the drawback that it is not considered at all. Therefore, in the present invention, in order to make up for this drawback, the lower and upper limits are set to 5% by weight and 95% by weight, and the evaluation method for the particle size distribution is made more strict.

Example 1 In a polymerization container with an internal volume of 5 equipped with a stirrer, ion-exchanged water was added.
0.18 g of 1,800 g (100 parts by weight), 9.0 g (0.5 parts by weight) of tricalcium phosphate, sodium alkylnaphthalene sulfonate (Keio Soap Co., Ltd., Perex NB-L, 34% by weight pure) g (0.01 parts by weight), polyoxyethylene alkylphenol ether (HS-2 manufactured by NOF CORPORATION)
70, HLB = 18.7) 0.036 g (0.002 parts by weight) benzoyl peroxide 4.68 g (0.26 parts by weight), t-butyl perbenzoate 1.8 g (0.1 parts by weight) and styrene monomer 1,800 g (100 parts by weight). It was added and sufficiently dispersed, and this was heated to 90 ° C. Polymerization conversion rate is about 60-65%
At that point, 3.6 g (0.2 parts by weight) of sodium sulfate was added to the polymerization system as a 10% by weight aqueous solution, polymerization was continued, and after about 5 hours, the solidified polystyrene polymer particles were obtained by cooling. The particle size distribution of the polymer particles is shown in Table 1.

Example 2 0.09 g (0.005 parts by weight) of sodium alkylnaphthalenesulfonate (manufactured by Kao Soap Co., Ltd., Perex NB-L, pure powder 34% by weight) and sodium alkylbenzenesulfonate (Kao Soap Co., Ltd.) Made, Neoperex N0
0.009 g (0.0005 parts by weight) of pure powder (25, pure powder 25% by weight), and polyoxyethylene alkylphenol ether (Nippon Yushi Co., Ltd. NS-220, HLB =) as a nonionic surfactant. 16.2) 0.1g (0.0056
Suspension polymerization was carried out in the same manner as in Example 1 except that (parts by weight) was added to obtain polystyrene polymer particles. The particle size distribution of the polymer particles is shown in Table 1.

Example 3 2.7 g (0.15 parts by weight) of potassium sulfate was used as the water-soluble metal salt, and polyoxyethylene alkylphenol ether (Nippon Yushi Co., Ltd.) was used as the nonionic surfactant.
Manufactured, NS-240, HLB = 17.9) 0.144 g (0.00
Suspension polymerization was carried out in the same manner as in Example 1 except that 8 parts by weight) was added to obtain polystyrene polymer particles. The particle size distribution of the polymer particles is shown in Table 1.

Comparative Example 1 Suspension polymerization was carried out in the same manner as in Example 1 except that sodium sulfate was not added to obtain polystyrene polymer particles. The particle size distribution of the polymer particles is shown in Table 1.

Comparative Example 2 Suspension polymerization was performed in the same manner as in Example 1 except that polyoxyethylene alkylphenol ether was not added to obtain polystyrene polymer particles. The particle size distribution of the polymer particles is shown in Table 1.

Comparative Example 3 In a polymerization container with an internal volume of 5 equipped with a stirrer, deionized water was added.
0.054 g of pure 1,800 g (100 polymerization parts), tricalcium phosphate 7.2 g (0.4 parts by weight), sodium alkylbenzene sulfonate (Kao Soap Co., Ltd., Neoperex NO25, pure 25% by weight) 0.003 parts by weight), benzoyl peroxide 4.68 g (0.26 parts by weight), t-butyl perbenzoate 1.8 g (0.1 parts by weight) and styrene monomer 1,800
Add g (100 parts by weight) and disperse well.
The temperature was raised to. Polymerization was carried out for about 5 hours, and after the polymerization was completed, it was cooled to obtain solidified polystyrene polymer particles. The particle size distribution of the polymer particles is shown in Table 1.

*) Fine powder particle generation rate: The generation rate of fine powder particles with a particle size of 0.5 mm or less is shown by weight%.

As is clear from Table 1, in Examples 1 to 3, the particle size distribution is extremely sharp and almost no differential particles are generated.
In the systems in which the water-soluble inorganic salt or the nonionic surfactant of Comparative Examples 1 and 2 does not exist, the average particle size is small and the particle size distribution is wide due to insufficient particle growth, and Comparative Example 3
In the system in which the water-soluble inorganic salt and the nonionic surfactant do not exist, the particle size distribution is wide.

〔The invention's effect〕

According to the present invention, the resulting polymer particles have a particle size of about 0.5 m.
Contributes to improved productivity, such as generation of fine powder particles of m or less and production of particles with an extremely narrow particle size distribution, which improves yield and can be used for single products. It is possible.

[Brief description of drawings]

Figure 1 shows the particle size of polymer particles and the cumulative weight% of polymer particles.
It is a relationship diagram which shows the relationship with.

Claims (1)

[Claims] 1. A suspension-polymerizing vinyl-based monomer in an aqueous medium, wherein the polymerization conversion rate is less than 55%, a sparingly soluble inorganic salt, an alkylnaphthalene sulfonate, and a nonionic surfactant in the aqueous medium. A method for producing a vinyl polymer, characterized in that a water-soluble metal salt which is neutral in an aqueous medium at a polymerization conversion rate of 55 to 75% is added in the presence of a water-soluble metal salt.