JP2637538B2 - Method for producing expandable thermoplastic polymer particles - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing expandable thermoplastic polymer particles having a uniform particle size, in particular, expandable styrene resin particles at a high yield.

[Prior Art] Among the expandable thermoplastic polymer particles, particles having a small particle diameter easily lose a volatile foaming agent and lose their foaming power in a short time. Therefore, when polymer particles in which small particles are mixed are foamed, a difference occurs in the expansion ratio between the particles, and even if the density is the same, the strength of the molded body is reduced, and conversely, large particles are mixed. In such a case, there arises a problem that the filling property into the mold is deteriorated and a good foamed molded product cannot be obtained.

Furthermore, the molded product obtained from the particles having a wide particle size distribution width,
Since the size of the particles is small and the appearance of the molded product is not good, it is not desirable.

In order to avoid such problems, when forming a foam from expandable thermoplastic polymer particles, it is desirable to use particles having a narrow particle size distribution and uniform particle size.

As the conventional known methods for obtaining the expandable thermoplastic polymer particles, for example, the following methods can be listed: (1) After the polymerizable monomer is subjected to suspension polymerization and impregnation with a blowing agent,
A method of obtaining particles having a desired particle size distribution width by sieving; (2) a method of suspension polymerizing a polymerizable monomer and then sieving to impregnate only particles having a desired particle size distribution width with a blowing agent; (3) a method of pelletizing a polymer to a desired size and impregnating the pellet with a foaming agent; and (4) a method of suspension-polymerizing a polymerizable monomer, followed by sieving to obtain particles having a desired particle size distribution width. Only in water, polymerizable monomers are added continuously or intermittently to polymerize,
A method of impregnating the particles with a blowing agent.

However, in the above method (1), since all the particles are impregnated with the blowing agent, if particles having a particle size distribution width suitable as the expandable particles are sieved, the particles are not suitable for foaming use. It is necessary to separately dispose the blowing agent-containing particles. When the demand for the expandable particles increases and the production amount increases, there is a problem that the absolute amount of unnecessary particles increases.

Since the above method (2) uses particles that have already been polymerized, a process of polymerizing a polymerizable monomer and a process of impregnating a foaming agent are required to obtain the expandable particles. The manufacturing process becomes complicated, and the manufacturing cost is disadvantageous. Furthermore, even when this method is employed, it is necessary to separately dispose of particles outside the desired particle size distribution range.

Even when the above method (3) is employed, two steps of a monomer polymerization step and a foaming agent impregnation step are required, and a pelletizing step is further required, which significantly complicates the steps. In addition, when the expandable particles obtained in this way are expanded, the cells become extremely fine, and another problem arises in that it is difficult to obtain a good expanded molded article.

In order to solve the problems described above, Japanese Patent Publication No. 49-29
No. 94 proposes the above method (4). However, even if this method is adopted, small particles obtained by suspension polymerization are sieved in advance, and only particles having a desired particle size are used. Unnecessary disposal of particles is necessary, and in order to obtain extremely uniform particles, the sieve width of the particles must be extremely narrow. In addition, for each of these to grow by impregnation polymerization to a certain particle size,
Complicated management must be performed, and to avoid this, the sieving width must be increased to some extent, and the resulting expandable thermoplastic polymer particles have only a somewhat broad particle size distribution. Will not be able to do it.

[Problems to be Solved by the Invention] Therefore, when producing expandable thermoplastic polymer particles, the problems of the conventional method as described above are solved, and expandable thermoplastic polymer particles having a uniform particle size distribution are produced. It is an object of the present invention to provide a method for manufacturing.

[Means for Solving the Problems] In view of the problems of the conventional method as described above, the present inventors have conducted intensive studies and as a result, have obtained a desired particle size (or particle size distribution width) without generating unnecessary particles. The present inventors have found a method for easily and efficiently producing expandable thermoplastic polymer particles capable of efficiently molding a foamed molded article having good appearance and excellent strength.

That is, the present invention provides a liquid column of a polymerizable monomer which jets out of a nozzle hole into an aqueous dispersion medium by applying regular vibrational disturbance to form a group of droplets having a uniform diameter in the aqueous dispersion medium. A first step of obtaining small thermoplastic polymer particles having a substantially uniform particle size by polymerizing under conditions that do not cause coalescence or additional dispersion, and a first step obtained by the first step. The suspended thermoplastic polymer particles are suspended in an aqueous medium, and the polymerizable monomer is added continuously or intermittently to polymerize. A method for producing expandable thermoplastic polymer particles, comprising a second step of adding an agent.

The monomer that can be used in the method of the present invention is not particularly limited as long as it can be used in a usual suspension polymerization technique. Such monomers include, for example, styrene-based derivatives such as styrene, α-methylstyrene, paramethylstyrene, t-butylstyrene and chlorostyrene, methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate and cetyl. Esters of acrylic acid or methacrylic acid such as methacrylate, or acrylonitrile, dimethyl fumarate, ethyl fumarate and the like are included. These monomers can be used alone or in a mixture of two or more. Further, bifunctional monomers such as divinylbenzene and alkylene glycol dimethacrylate may be used in combination.

In the method of the present invention, when the polymerizable monomers used in the first step and the second step are a mixture, the composition of the monomers used in each step may be the same or different.

As the polymerization initiator of the monomer in the present invention, a radical-generating polymerization initiator generally used for producing a thermoplastic polymer can be used. Examples of such a polymerization initiator include, for example, benzoyl peroxide, lauroyl peroxide, t-butyl perbenzoate, t-butyl perbenzoate and t-butyl perbenzoate.
-Butyl perpivalate, t-butyl peroxyisopropyl carbonate, t-butyl peroxy acetate, 2,2-di-t-butyl peroxybutane, t-butyl peroxy-3,3,5-trimethylhexanoate Organic peroxides such as, di-t-butylperoxyhexahydroterephthalate, 1,1-di-t-butylperoxy-3,3,5-trimethylcyclohexane and 1,1-di-t-butylperoxycyclohexane And azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile.

These polymerization initiators can be used alone or in a mixture of two or more. In order to adjust the molecular weight and to reduce the amount of residual monomers, two or more initiators having different decomposition temperatures are used. It is effective to use them together.

The foaming agent used in the present invention is liquid under normal conditions or gaseous under normal conditions and liquefies under pressure. Suitable volatile organic compounds have a boiling point not higher than the softening point of the polymer. Examples of such a foaming agent include aliphatic hydrocarbons such as propane, butane, pentane and hexane, alicyclic hydrocarbons such as cyclobutane, cyclopentane and cyclohexane, methyl chloride, dichlorodifluoromethane, and dichlorotetrafluoroethane. And the like.

Furthermore, in the present invention, in addition to the above-mentioned raw materials, plasticizers, solvents, nucleating agents, flame retardants and other additive materials commonly used in the production of expandable thermoplastic polymer particles may be used in combination. Is no problem.

As described above, the method of the present invention can be applied to various polymerization systems, but the production amount of expandable styrene-based polymer particles is particularly large, and when produced by a conventional method, particles that are not suitable for foaming applications are produced. The method of the present invention is particularly useful in the production of expandable styrene-based polymer particles that are generally used as a porous foam because of the burden of separately formulating.

In the method of the present invention, the first step can be further subdivided into two steps.

On the other hand, in the subdivision process, a group of liquid droplets having a substantially uniform diameter is formed by regularly applying vibrational disturbance to a liquid column of a monomer containing an initiator which is ejected from a nozzle hole into an aqueous dispersion medium. It is a process.

The particle size of the droplet group to be formed depends on the nozzle hole diameter, the speed of the monomer passing through the nozzle, the viscosity of the monomer, the type of vibration disturbance applied to the liquid column generated after the monomer passes through the nozzle, the frequency and the amplitude. It is determined by factors, and a droplet group having a desired particle size distribution can be obtained by appropriately combining these factors.

The nozzle that can be used in the subdivision step is not particularly limited, and for example, a nozzle formed of an orifice plate having one or more small holes or a nozzle into which a thin tube is inserted can be used.
A particularly preferred nozzle is an orifice plate, and such nozzles are usually used alone or in combination.

Examples of the method of applying the disturbance vibration include, but are not limited to, a method of transmitting the vibration of the vibrator to the monomer ejected from the nozzle.

For example, when styrene is suspended in an aqueous dispersion medium having a charged amount of 0.72 kg / Hr and polyvinyl alcohol as a suspending agent, a nozzle having a pore diameter of 0.2 mm is used, and a vibrator is used as a disturbance imparting means at a frequency of 500 Hz. Thus, droplets having a particle size of 0.53 mm can be obtained.

Another subdivision step included in the first step is a step of polymerizing a group of droplets having a uniform diameter generated under conditions that do not cause coalescence or additional dispersion.

Here, "conditions under which coalescence or additional dispersion does not occur" means that a droplet ejected from a nozzle and generated by disturbance vibration merges with another droplet to form a larger droplet. Or conversely, a condition under which the liquid does not substantially re-divide into smaller droplets.

Methods for achieving such conditions include, for example, a method of adding a suspending agent to an aqueous dispersion medium to increase the dispersion stability of droplets, and a method of maintaining an aqueous dispersion medium containing droplets in a fluidized state. And the like.

As a method of performing the fragmentation step, a normal polymerization method can be adopted.For example, the droplet group generated by the fragmentation step described above is introduced into a reactor containing an aqueous dispersion medium containing a suspending agent. Then, a layer of the droplet group is formed in the upper layer of the reactor, and the polymerization reaction is carried out while circulating and supplying the aqueous dispersion medium from the lower part of the reactor to the upper part. At the time when the amount of the aqueous dispersion medium increases, the circulation of the aqueous dispersion medium is stopped, and at this time, a method in which the stirring blade provided in the reactor is driven to complete the polymerization can be employed.

As another method, a method using a tower reactor can be exemplified.
While extracting the aqueous dispersion medium containing the suspending agent from the lower part of the tower reactor and circulating and supplying it to the upper part, the droplet group is introduced into the tower reactor, and a fluidized bed of the droplet group is formed in the reactor. The polymerization reaction is carried out while the specific gravity of the droplets has increased to a value close to the specific gravity of the aqueous dispersion medium, and the polymerization can be completed by sending the liquid to another reactor following the tower reactor. . In this case, the other reactor may be an ordinary stirred reactor, or may be a tower reactor in which the aqueous dispersion medium is withdrawn from the upper portion of the reactor and supplied to the lower portion.

Further, by adding a salt, the specific gravity of the aqueous dispersion medium is made larger than the specific gravity of the polymer formed in the first stage formed by polymerization of the droplets, and the specific gravity of the desired final polymer is obtained. The polymerization can be completed only with the vessel. These polymerizations can be carried out batchwise or continuously.

It is not always necessary to perform the subdivision step and the subdivision step in separate reactors, and the subdivision step can be performed after the subdivision step using a single apparatus.

In the first step, those which have hitherto been widely used as a suspending agent can be used, and examples thereof include water-soluble polymers such as polyvinyl alcohol, methylcellulose, polyacrylamide, and polyvinylpyrrolidone, and tricalcium phosphate and magnesium pyrophosphate. In the case where a poorly soluble inorganic substance is used, a suspension stabilizing effect is increased when an anionic surfactant such as sodium dodecylbenzenesulfonate is used in combination. The combined use of a water-soluble polymer and a poorly soluble inorganic substance also enhances the suspension stabilizing effect.

The thermoplastic polymer small particles obtained in the first step of the present invention have at least 90% by weight or more, preferably 99% by weight or more of the particles have a particle size in the range of 0.9 to 1.1 times the volume average particle size, It is a group of substantially uniform particles.

On the other hand, the monomer is suspended and dispersed in an aqueous dispersion medium containing a suspension protective agent by the power of a stirring propeller in a conventional suspension polymerization technique, for example, a tank-type reactor having a paddle-shaped stirring propeller. When using the polymerization method, only about 30-40% by weight of the particles have a particle size within the range of 0.9-1.1 times the volume average particle size.

Therefore, in order to obtain a uniform particle group as in the present invention by a conventional suspension polymerization method, sieving operation of at least three or more divisions is required, and further, from the sieved particle group of each particle diameter, In order to obtain expandable thermoplastic polymer particles having a certain particle size, it is necessary to control the amount of the added monomer according to each particle group.

However, by using the first step of the method of the present invention, polymer particles having a uniform particle size can be obtained without such complicated and complicated management.

In the second step, the thermoplastic polymer small particles having a uniform particle size obtained in the first step as described above are suspended as core particles in an aqueous dispersion medium, and a monomer is added to polymerize the particles. Can be obtained.

That is, in the second step of the present invention, the thermoplastic polymer small particles having a uniform particle size obtained in the first step are suspended in an aqueous dispersion medium in a polymerization reactor, and the polymerizable monomer is removed. The monomer is impregnated or polymerized in the thermoplastic polymer small particles by adding continuously, intermittently or intermittently, and the volatile foaming agent is added at any time from the start to the end of the polymerization in the second step. This is a step of obtaining polymer particles containing a foaming agent and having a uniform particle size grown to a desired particle size by addition.

As a method for suspending the small particles in the second step,
A method of dispersing droplets in the first step can be adopted.

D is the desired diameter of the finally obtainable expandable thermoplastic polymer particles, d is the particle size of the small particles obtained in the first step, and x is the ratio of the weight of the small particles to the weight of the final polymer particles. % (Ie, using x weight% of the total monomer amount to form small particles in the first step to obtain the desired polymer particles), the relational expression: D = (100 / x) ^{1 / 3} × d is obtained. This means that the particle size of the thermoplastic polymer small particles generated in the first step and the amount thereof determine the particle size of the expandable thermoplastic polymer particles obtained in the second step. Therefore, by appropriately selecting the particle size of the thermoplastic polymer particles to be suspended in the aqueous dispersion medium in the second step and the amount of the monomer used in the first step, foaming having a desired particle size can be achieved. Thermoplastic polymer particles can be obtained.

If the amount of the small particles used as the core particles is too small (that is, x is too small), the polymerization of monomers not impregnated or polymerized in the small particles increases, and the amount of the powdery polymer increases. In order to prevent this, it is necessary to add a monomer while maintaining a fixed ratio to the small particles, so that the polymerization time becomes longer and the particle diameter (D) of the growing particles with respect to the particle diameter (d) of the small particles And the particle size distribution becomes non-uniform.

Conversely, if the amount of the small particles used is too large (that is, x is too large), the ratio of the particle diameter (D) of the grown particles to the particle diameter (d) of the small particles becomes small, and the polymer once produced becomes It is economically disadvantageous because the rate of reuse as nuclear particles increases.

For these reasons, the amount of the small particles suspended in the aqueous dispersion medium in the second step is 1 to the total amount of the polymer at the end of the polymerization.
It is preferably 60% by weight, especially 5 to 30% by weight.

In the second step of the present invention, the ratio of the amount of the monomer in the polymerization system to the sum of the amount of the monomer in the polymerization system and the amount of the polymer does not exceed 60% by weight, preferably 30 to 50% by weight. % Of the monomer is preferably added. If the ratio of the monomer amount is more than 60% by weight, particle splitting and coalescence of particles will occur, and it will be difficult to stably maintain small polymer particles containing a large amount of monomer. (If the amount of the monomer is large, generation of split particles due to a decrease in the conversion rate and generation of coalescence of the particles by the monomer occur), and the amount of the polymer not having a desired particle size is large. It is because it becomes.

As the polymerization initiator and the suspending agent used in the second step of the present invention, the types of substances listed in relation to the description of the first step can be used.

The polymerization initiator may be added before, after, or together with the monomer in the polymerization vessel.
In the second step, an easily volatile foaming agent is added to the polymerization reaction system. The timing of adding the foaming agent may be divided into one or several times at any time from the start to the end of the polymerization. Or may be added continuously.

By the method for producing expandable thermoplastic polymer particles of the present invention as described above, it is possible to obtain expandable thermoplastic polymer particles having a substantially uniform particle size and a desired particle size in high yield. It is possible to produce almost no polymer unsuitable for foam molding applications.

Next, the present invention will be specifically described with reference to Examples and Comparative Examples. The present invention is not limited to these Examples.

Example 1 A circulation line was provided to take out the aqueous dispersion medium from a aqueous dispersion medium outlet provided at the lower part of a 5 l tank type reactor equipped with a stirrer by a vortex pump and to introduce the aqueous dispersion medium into the reactor from an upper inlet of the reactor.

In this reactor, 3000ppm of tricalcium phosphate fine powder,
Polyvinyl alcohol 50ppm, anionic surfactant 50p
3 l of an aqueous dispersion medium adjusted to pm was added, and the dispersion medium was circulated through a circulation line using a vortex pump.

The droplet generation device inserts a nozzle that ejects a monomer into a column containing an aqueous dispersion medium, the upper end of the nozzle is formed of an orifice plate having small holes, and the lower end is provided with a vibration plate that transmits vibration. The diaphragm was connected to a shaker. The droplet generator was connected to the bottom of the reactor via an inlet tube.

Next, benzoyl peroxide was added to the styrene monomer.
The polymerizable monomer in which 0.25% by weight was dissolved was supplied at 0.8 l / Hr to a droplet generating apparatus having a nozzle formed of an orifice plate having five small holes having a diameter of 0.2 mm, and a vibrator was used. 500
By applying mechanical vibration at Hz, a group of droplets of the polymerizable substance was generated in the aqueous dispersion medium, and introduced into the above-mentioned 5 l reactor by using the buoyancy of the droplets via an introduction tube.

After 500 g of the polymerizable monomer was introduced into the reactor, the solution in the reactor was kept at 90 ° C. for 2 hours to carry out heat polymerization.

Next, the circulation of the aqueous dispersion medium was stopped, and a stirrer (plate blade) provided in the reactor was driven at 60 rpm and reacted at 90 ° C. for 3 hours to obtain spherical polymer small particles. After the polymerization was completed, the slurry in the reactor was cooled and dehydrated and dried.

As a result of measuring the particle size distribution of the obtained particles, the average particle diameter was determined.
The yield of particles having a particle size in the range of 0.53 mm and 28 to 32 mesh (0.59 to 0.50 mm) was 99% by weight, which was a group of true spherical particles having a substantially uniform particle size.

 The obtained particle group is referred to as a core particle A.

Example 2 Nozzle hole diameter 0.15 mm, supply rate of polymerizable substance 0.5 l / H
A polymer particle group was obtained in the same manner as in Example 1 except that r was used.

When the particle size distribution of the obtained particles was measured, the average particle size was 0.47 mm, and the yield of particles having a particle size in the range of 32 to 35 mesh (0.5 to 0.42 mm) was 98% by weight.

 The obtained particle group is referred to as a core particle B.

Example 3 A polymer particle group was obtained in the same manner as in Example 1, except that the polymerizable substance was a polymerizable monomer containing a mixture of 70% by weight of a styrene monomer and 30% by weight of acrylonitrile.

When the particle size distribution of the obtained particles was measured, the average particle size was 0.53 mm, and the yield of particles having a particle size of 28 to 32 mesh was 97% by weight. The obtained particle group is referred to as a core particle C.

Comparative Example 1 1.8 l of pure water, 7.2 g of tribasic calcium phosphate and 6 ml of a 1% by weight aqueous solution of sodium α-olefin sulfonate were added to a 5 l flask equipped with a stirrer, and benzoyl peroxide 0.3 was stirred.
1.8 kg of a styrene monomer containing 10% by weight was added, and the mixture was heated to 90 ° C. and polymerized for 5 hours.

The obtained polymer was cooled, dehydrated and dried, and then the particle size distribution was measured. The results are shown in Table 1.

The particles were sieved and the resulting 24-32 mesh (0.71
Particles having a diameter of about 0.5 mm) are referred to as core particles D.

Example 4 To a 5 l autoclave equipped with a stirrer, 7.2 g of tribasic calcium phosphate, 20 cc of a 1% by weight aqueous solution of α-olefin sulfonate and 360 g of the core particles A obtained in Example 1 were added, and the temperature in the autoclave was adjusted to 90 ° C while stirring. The temperature rose.

Next, a mixed solution of 12.6 g of coconut oil dissolved in 1800 g of styrene monomer, and 5 g of benzoyl peroxide and 1,1
-Di-t-butylperoxy-3,3,5-trimethylcyclohexane (3.6 g) was dissolved in 50 g of styrene monomer to give 0.2 g.
Emulsified liquids emulsified in 50 g of an aqueous solution of hydroxyethyl cellulose by weight were charged into autoclaves at the rates shown in Table 2 and polymerized while maintaining the temperature at 90 ° C.

Immediately after the preparation of the mixture and the emulsion, 32 g of cyclohexane and 126 g of butane as a foaming agent were added, the temperature was raised to 115 ° C., and polymerization and impregnation of the foaming agent were performed for 3 hours.

After cooling, the obtained expandable styrene polymer particles were taken out, dehydrated and dried, and the particle size distribution was measured.

 The results are shown in Table 3.

After storing the particles at 15 ° C. for 7 days, they were prefoamed 60 times with steam. The cells of the expanded particles were uniform and fine from the surface to the inside.

After curing the pre-foamed granules for 1 day, length 45cm, width 30cm, thickness
A molded product was manufactured using a Pearl Star 90 molding machine (manufactured by Toyo Kikai Metal Co., Ltd.) having a 2 cm mold.

The density of the obtained molded body was 0.019 g / cm ³ , and the appearance was beautiful with a uniform particle diameter.

The flexural strength of the molded article was measured according to the method of JIS-A-9511 to be 3.6 kg / cm ² .

Examples 5 to 8 and Comparative Example 2 Expandable styrene resin particles were obtained in the same manner as in Example 4 using the core particles shown in Table 3, and the particle size distribution and the bending strength of the molded product were measured.

 Table 3 shows the measurement results.

Comparative Example 3 In a 5 l autoclave with a stirrer, 1.8 l of pure water, 2.7 g of tribasic calcium phosphate, and sodium α-olefin sulfonate 1
Of benzoyl peroxide 0.22% by weight and 1,1-di-t-butylperoxy-
1.8 kg of a styrene monomer containing 0.15% by weight of 3,3,5-trimethylcyclohexane was added, the temperature was raised to 90 ° C., and polymerization was carried out for 5 hours.

Then, cyclohexane 32 g, butane 126 as blowing agent
g, the temperature was raised to 115 ° C., and polymerization and impregnation with a blowing agent were performed for 3 hours.

The obtained expandable styrene resin particles were molded in the same manner as in Example 4.

 The results are shown in Table 3.

Examples 9 to 11 In Example 4, after initially charging the styrene monomer mixture in the amount shown in Table 4, the remaining styrene monomer mixture and the initiator emulsion were added dropwise.
Polymerization was carried out while controlling the polymerization conversion to the value shown in Table 4.

After the completion of the dropwise addition, when the polymerization conversion reached 90%, a blowing agent was charged in the same manner as in Example 4, and the evaluation results are shown in Table 4.

From these results, it can be seen that as the proportion of the monomer in the polymerization system increases, the particle size distribution deteriorates, so that it is necessary to keep the proportion of the monomer in the polymerization system low.

Examples 12 and 13 Expandable styrene resin particles were obtained in the same manner as in Example 4 except that the polymerization temperature was set to 110 ° C. and the core particles shown in Table 5 were used. Was measured.

 The results are shown in Table 5.

Example 14 Expandable resin particles were obtained in the same manner as in Example 4, except that 1260 g of α-methylstyrene monomer and 540 g of acrylonitrile were used instead of 1800 g of the styrene monomer, and that core particles C were used as the core particles.

 The results are shown in Table 5.

From the results shown in Table 5, by increasing the polymerization temperature, it is possible to increase the polymerization rate without deteriorating the particle size distribution, and to obtain a good particle size distribution even when using a monomer other than styrene. It can be seen that expandable particles are obtained.

[Effects of the Invention] As described above, expandable thermoplastic polymer particles having a uniform particle size distribution can be easily and efficiently produced by the method of the present invention.

Claims (5)

(57) [Claims] Claims: 1. A liquid column of a polymerizable monomer ejected from a nozzle hole into an aqueous dispersion medium is subjected to regular vibrational disturbance to form droplet groups having a uniform diameter in the aqueous dispersion medium. A first step of obtaining small thermoplastic polymer particles having a substantially uniform particle size by polymerizing under conditions that do not cause coalescence or additional dispersion, and a first step obtained by the first step. The thermoplastic polymer small particles are suspended in an aqueous medium, the polymerizable monomer is added continuously or intermittently to polymerize, and further, at any time from the start to the end of the polymerization, a volatile foaming agent is added. A process for producing expandable thermoplastic polymer particles, comprising: 2. The polymerizable monomer is a styrene monomer or a monomer mixture containing styrene as a main component, and the expandable thermoplastic polymer particles are expandable styrene polymer particles. The method for producing expandable thermoplastic polymer particles according to claim 1, wherein 3. The method according to claim 1, wherein in the second step, the amount of the small particles suspended in the aqueous dispersion medium is 1 to 60% by weight of the total amount of the polymer at the end of the polymerization. Item 3. The method for producing expandable thermoplastic polymer particles according to item 2 or 2. 4. The method according to claim 2, wherein in the second step, the polymerizable monomer is added in such a ratio that the amount of the monomer in the polymerization system does not exceed 60% by weight of the total amount of the monomer and the polymer. The method for producing expandable thermoplastic polymer particles according to any one of claims 1 to 3, characterized in that: 5. The method according to claim 1, wherein at least 90% by weight of the small thermoplastic polymer particles obtained in the first step has a volume average diameter in the range of 0.9 to 1.1 times the volume average diameter.
The production method according to any one of the above items.