JP2565606B2 - Suspension polymerization method for vinyl monomers - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a suspension polymerization method for vinyl monomers. In general, vinyl resin particles represented by polystyrene and polymethylmethacrylate obtained by suspension polymerization are extruded or injection-molded to produce various molded articles. Further, by impregnating a volatile foaming agent such as propane, butane or pentane, foamable resin particles known as expanded polystyrene can be obtained.
Applications of the expandable resin particles are roughly classified into three fields depending on the size of the particles. Particle sizes of 0.2 to 0.5 mm are for cups of instant foods or for full molding in casting, 0.5 to 1.2 mm are for various packaging or fish boxes, and 0.9 to 2.0 mm are for building material boards and soft ground countermeasures. For blocks such as the lightweight embankment method (EPS civil engineering method).

The present invention relates to a method for producing resin particles having a size suitable for these fields of use with a high yield, that is, a suspension polymerization method for vinyl monomers capable of obtaining resin particles having a narrow particle size distribution.

[0003]

2. Description of the Related Art Generally, suspension polymerization of a vinyl monomer in water requires the addition of a suspension stabilizer to water in order to keep oil droplets of the monomer produced by stirring stable. Suspension stabilizers used for this purpose include water-soluble polymer colloids such as starch, alkyl cellulose, hydroxyalkyl cellulose, polyvinyl alcohol, and polyvinylpyrrolidone, or magnesium oxide, calcium carbonate, magnesium carbonate, calcium pyrophosphate, magnesium pyrophosphate. , Powders of poorly water-soluble inorganic salts such as tricalcium phosphate and hydroxyapatite.

However, when the former water-soluble polymer colloid is used as a suspension stabilizer, it is easy to form partially emulsified micelles in water, so that fine particles are generated, which results in a broad particle distribution and a high water solubility. Mixing of the molecular colloid into the produced polymer causes a problem of deterioration of thermal stability, mechanical strength and transparency, which is not preferable. On the other hand, when the latter poorly water-soluble inorganic salt is used, it has a poor affinity with oil droplets of the monomer and has little effect as a suspension stabilizer, so a small amount of anionic surfactant (for example, todecyl) is used. Sodium benzene sulfonate, sodium α-olefin sulfonate, etc.) is usually used together as a suspension stabilizing aid. However, even in this case, the resin particles finally obtained have a wide particle diameter, and it was very difficult to make the resin particles have a specific particle diameter range.

When the particle size distribution is wide, small particles and large particles are separated by a raw material hopper in the extrusion molding and injection molding, and defective products are generated due to variations in raw material supply. Further, in the expandable resin particles, since the characteristics of the expandable resin particles required due to the difference in the application are different, it is inevitably necessary to carry out the production according to the application, particularly from 0.2 to 0.
When producing 5 mm particles, a large amount of off-sized particles are generated, resulting in a significant decrease in productivity and a cost increase.

[0006] Several methods have already been tried to improve these drawbacks. For example, in JP-A-59-176309, a method of using a combination of a poorly water-soluble inorganic salt and a water-soluble neutral water-soluble metal salt with dodecylphenyl oxide disulfonate (which is an anionic surfactant) is used. Is disclosed. However, when the present inventors re-tried this method, as shown in the examples of the publication,
When obtaining resin particles with an average particle diameter of 0.8 mm or less, although resin particles with an average particle diameter of about 1.0 mm can be obtained with a relatively narrow particle diameter distribution, a large amount of fine particles that cannot be used as expandable resin particles are generated. , There is no difference from the method that uses sodium dodecylbenzene sulfonate, sodium α-olefin sulfonate, etc., and the particle size distribution remains wide. It is difficult to obtain a high yield.

Further, in JP-A-58-71901, a water-soluble inorganic salt which is neutral in an aqueous system is used in combination in the presence of a sparingly soluble phosphate and an anionic surfactant. After initiating suspension polymerization in the range of the monomer weight ratio of 1.1 / 1 or more, once the polymerization conversion rate of the vinyl monomer is between 30 and 70% by weight, the sparingly soluble phosphate is once added to the polymerization system. The method of adding the above to proceed the polymerization is disclosed. However, in this method, the weight ratio of the aqueous medium / monomer needs to be 1.1 or more, the production amount per batch is small, and the productivity is not good. The initial concentration of the sparingly soluble phosphate is rather low. Then start the polymerization, and add a sparingly soluble phosphate when the monomer oil droplets grow to the target particle size, so that the particles do not grow above the target particle size. When obtaining resin particles with a particle size of 1.0 mm or less, the degree of growth of monomer oil droplets must be reduced, and the particle size distribution remains wide after all. Fluctuates, and thus the final particle size varies greatly.

[0008]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The purpose of the present invention is to solve the following problems of the prior art, to reduce the thermal stability, transparency and mechanical strength of the resin particles obtained, and to improve the particle size distribution. A suspension polymerization method for vinyl monomers that solves the problems that a large number of fine particles are generated, etc., and ensures that vinyl resin particles of the required size can be reliably produced in high yield by a simple process. Is to provide.

[0009]

[Means for Solving the Problems] As a result of earnest studies, the inventors of the present invention have developed a soap-free novel method that does not substantially use the water-soluble polymer colloid (polymer surfactant) or anionic surfactant. It was found that the above problems can be solved by a simple suspension polymerization method. That is, in the present invention, when suspension-polymerizing a vinyl-based monomer in the presence of a poorly water-soluble inorganic salt and an oil-soluble catalyst, substantially no anionic surfactant is used, and 4,4′-azobis ( 4-cyanopentanoic acid) is used in an amount of 0.1 to 0.0001% by weight with respect to an aqueous medium.

Hereinafter, the present invention will be described in detail. The vinyl-based monomer that can be used in the present invention preferably has a solubility in water of 0.001% by weight or more at 20 ° C., such as styrene, α-methylstyrene, p-
Styrene-based monomers such as methylstyrene, t-butylstyrene and chlorostyrene, acrylate monomers such as ethyl acrylate and 2-ethylhexyl acrylate, methacrylate monomers such as methyl methacrylate, butyl methacrylate and isobutyl methacrylate, acrylonitrile and methacryl Examples include vinyl cyanide-based monomers such as ronitrile, maleimides, N-methylmaleimide, N-phenylmaleimide, maleimide-based monomers such as N-cyclohexylmaleimide, and conjugated diolefins such as butadiene and isoprene. it can. These monomers may be used alone or in combination of two or more, and in addition, a small amount of a polyfunctional monomer such as divinylbenzene, polyethylene glycol dimethacrylate or triacyl cyanurate may be used together.

When a monomer having a solubility in water of less than 0.001% by weight, such as stearyl methacrylate, is used, it takes a very long time to stabilize the dispersion of oil droplets of the monomer. For the purpose of increasing the amount, it is preferable to add a water-soluble organic solvent such as methanol or ethanol to water. The sparingly water-soluble inorganic salt is a sparingly water-soluble inorganic salt such as tricalcium phosphate, hydroxyapatite, magnesium pyrophosphate, calcium carbonate, or magnesium carbonate as described above, and preferably a sparingly water-soluble phosphate. so,
Particularly, tricalcium phosphate and / or hydroxyapatite is preferable. These are generally 0.
It is used by adding 01 to 5% by weight.

As the oil-soluble catalyst, benzoyl peroxide,
Uses polymerization initiators used for suspension polymerization of ordinary vinyl monomers such as organic peroxides such as butyl perbenzoate and azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile. it can. The amount used is usually 0.10 to 0.50% by weight with respect to the monomer. The present invention, in addition to the hardly water-soluble inorganic dispersant and oil-soluble catalyst as described above,
4,4'-azobis (4-cyanopentanoic acid), a water-soluble radical polymerization initiator represented by the following formula

[0013]

Embedded image

It is characterized by using 4,4 '
By suspension-polymerizing a vinyl-based monomer using -azobis (4-cyanopentanoic acid), it is possible to obtain resin particles having a narrow particle size distribution, which is far superior to the conventionally known methods. . At present, this mechanism is unknown, but in water, 4,4'-azobis (4-cyanopentanoic acid) generates free radicals by heating, so vinyl-based compounds partially dissolved in suspended water are used. Initiate polymerization of monomer and carboxyl group at terminal (hydrophilic)
It is believed that a polymer having Since this polymer exhibits an appropriate surface activity, it acts as a dispersion aid by combining with the poorly water-soluble inorganic dispersant, and the oil droplet dispersibility of the vinyl-based monomer is significantly improved. It is assumed that the particle size distribution is narrowed.

The amount of 4,4'-azobis (4-cyanopentanoic acid) used is 0.1 to 0.00 with respect to the aqueous medium.
The amount is 01% by weight, preferably 0.01 to 0.0005% by weight. If it exceeds 0.1% by weight, a part of the milk may be suspended and the suspension stability may be significantly deteriorated. Also, 0.0001% by weight
When it is less than the above range, the particles are likely to be coarsened, and the effect of narrowing the particle size distribution is reduced.

In the present invention, the amount of the poorly water-soluble inorganic salt and the amount of the 4,4'-azobis (4-cyanopentanoic acid) may be changed, or the mechanical condition, the aqueous medium and the monomer may be changed. It is possible to control the particle size of the vinyl resin particles produced by changing the ratio of the, and the like, and to use an alkaline agent such as sodium hydroxide, potassium hydroxide, sodium phosphate, sodium acetate in the aqueous medium. , Sodium carbonate-sodium hydrogen carbonate based solution, sodium phosphate-sodium hydrogen phosphate based solution, phosphoric acid-
Add a buffer such as potassium-borax solution to adjust the pH.
It is also possible to adjust.

The present invention is characterized in that when the vinyl monomer is suspension-polymerized in the presence of the poorly water-soluble inorganic salt, substantially no anionic surfactant is used.
Here, substantially means that the conversion rate of the vinyl monomer is about 50.
This means that the surfactant is not present until the weight% is reached, and the final particle size of the vinyl resin particles is generally determined by this time. Therefore, if necessary, the water-soluble polymer colloid or the anionic surfactant may be added after this time without any problem.

In the polymerization method of the present invention, known additives such as a lubricant, a flame retardant, a colorant, a nucleating agent, etc. can be added. For other polymerization conditions, known methods can be applied correspondingly. You can

[0019]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited thereto.

[0020]

Example 1 In a polymerization vessel having an internal volume of 5 L, 2000 g of water, 7.2 g of tricalcium phosphate and 4,4'-azobis (4-
0.12 g of cyanopentanoic acid), followed by 2400 g of styrene and 6.0 of benzoyl peroxide while stirring.
g was added and the temperature was raised to 90 ° C. to initiate polymerization. Then, polymerization was carried out as it was at 90 ° C. for 7 hours to obtain resin particles. When the resin particles were dried and sieved to each particle size, the resin particles were significantly narrower than the particle size distribution obtained by a conventionally known method. The results are shown in Table 1.

[0021]

Examples 2 to 4 In Example 1, the amount of 4,4'-azobis (4-cyanopentanoic acid) was adjusted to 0.
Polymerization was carried out under the same conditions except that the amounts were changed to 16 g [Example 2], 0.08 g [Example 3] and 0.04 g [Example 4]. The particle size distribution of the obtained resin particles is shown in Table 1.

[0022]

Example 5 2000 g of water and 7.2 g of tricalcium phosphate were placed in a polymerization vessel having an internal volume of 5 L, 2400 g of styrene and 6.0 g of benzoyl peroxide were added with stirring, and the temperature was raised to 90 ° C. After 30 minutes 4,4'-azobis (4-
0.08 g of cyanopentanoic acid) was added and further polymerized for 6 hours and 30 minutes to obtain resin particles. The particle size distribution of the obtained resin particles is shown in Table 1.

Example 6 In a polymerization container having an internal volume of 5 L,
2000 g of water, 7.2 g of tricalcium phosphate and 0.08 g of 4,4'-azobis (4-cyanopentanoic acid) were added, and subsequently 2400 g of styrene and 6.0 g of benzoyl peroxide were added with stirring, and the mixture was heated to 90 ° C. The temperature was raised. After 20 minutes, add 0.02 g of sodium hydroxide and continue for 6 hours 40
Polymerization was carried out to obtain resin particles. The particle size distribution of the obtained resin particles is shown in Table 1.

Example 7 In a polymerization container having an internal volume of 5 L,
2000 g of water, 6.0 g of tricalcium phosphate and 0.10 g of 4,4'-azobis (4-cyanopentanoic acid) were added, followed by stirring with 1930 g of methyl methacrylate,
70 g of α-methylstyrene and 10.0 g of benzoyl peroxide
Was added and the temperature was raised to 75 ° C. to initiate polymerization. Then, polymerization was carried out as it was at 75 ° C. for 6 hours to obtain resin particles. After the resin particles were dried, they were sieved according to each particle size. The results are shown in Table 1.

[Comparative Example 1] In Example 1, 4,4'-
The same operation was performed except that azobis (4-cyanopentanoic acid) was not used. However, at the polymerization temperature of 90 ° C, the dispersion of the monomer oil droplets collapsed after only 2 hours and 10 minutes,
It became mochi. [Comparative Example 2] 2000 g of water, 0.18 g of sodium dodecylphenyl oxide disulfonate were placed in a polymerization vessel having an internal volume of 5 L.
3.6 g of sodium chloride and 7.2 g of tricalcium phosphate were added, 2400 g of styrene and 6.0 g of benzoyl peroxide were subsequently added with stirring, and the temperature was raised to 90 ° C. to initiate polymerization. Then, polymerization was carried out as it was at 90 ° C. for 7 hours to obtain resin particles. When the resin particles were dried and sieved to each particle size, the particle size distribution was wide and many fine particles passing through 80 mesh were generated. Table 2 shows the results.

[Comparative Examples 3 and 4] Polymerization was carried out under the same conditions as Comparative Example 2 except that the amount of tricalcium phosphate was changed to 6.0 g [Comparative Example 3] or 4.8 g [Comparative Example 4]. It was Table 2 shows the particle size distribution of the obtained resin particles. [Comparative Examples 5 to 7] In Comparative Example 2, 0.12 g of sodium α-olefin sulfonate was used instead of sodium dodecylphenyl oxide disulfonate, and the amount of tricalcium phosphate was 9.6 g [Comparative Example 5], 7.2. Polymerization was performed under the same conditions except that the amount was changed to g [Comparative Example 6] or 3.6 g [Comparative Example 7]. Table 2 shows the particle size distribution of the obtained resin particles.

[Comparative Example 8] In a polymerization container having an internal volume of 5 L,
2000 g of water and 0.04 g of sodium dodecylbenzene sulfonate
And 6.0 g of tricalcium phosphate, and subsequently, with stirring, 1930 g of methyl methacrylate, 70 g of α-methylstyrene and 10 g of benzoyl peroxide,
The temperature was raised to 75 ° C. to initiate polymerization. Then, polymerization was carried out as it was at 75 ° C. for 6 hours to obtain resin particles. The results of sieving the resin particles into particles after drying are shown in Table 2.

In Tables 1 and 2, the average particle size is the particle size (mm) corresponding to a cumulative weight percentage of 50%.

Here, based on the cumulative passage distribution curve screened as a display method showing the particle size distribution of the obtained resin particles, 10% by weight, 40% by weight, 60% by weight and 90% by weight of the particles are obtained. The openings (mm) of the passing sieve are d10, d40, d6, respectively.
Obtained as 0 and d90, and from these data, A = d60
/ D10, B = d90 / d40 and C = A + B were determined. Then, this C was used to define a narrow and wide particle size distribution. Here, the larger C is, the wider the distribution is, and the smaller C is, the narrower the distribution is.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

As is apparent from the above description, according to the present invention, vinyl resin particles having a narrow particle size distribution and a small number of fine particles can be obtained, and the productivity can be greatly improved. .

Claims (3)

(57) [Claims] 1. When suspension-polymerizing a vinyl monomer in the presence of a poorly water-soluble inorganic salt and an oil-soluble catalyst, substantially no anionic surfactant is used, and 4,4′-azobis (4 −
Cyanopentanoic acid) in an aqueous medium of 0.1
~ 0.0001% by weight of a suspension polymerization method of a vinyl-based monomer, which is used. 2. The suspension polymerization method for vinyl monomers according to claim 1, wherein the poorly water-soluble inorganic salt is a poorly water-soluble phosphate. 3. The suspension polymerization method for vinyl monomers according to claim 2, wherein the poorly water-soluble phosphate is tricalcium phosphate and / or hydroxyapatite.