KR100599847B1 - Method for manufacturing expandable polystyrene particles with excellent thermal insulation capability - Google Patents

Abstract

The present invention relates to a method for producing expandable polystyrene particles comprising graphite particles. Expandable polystyrene particles including graphite particles are obtained by heating graphite, a blowing agent, and a C ₆ -C ₁₀ aromatic hydrocarbon into aqueous suspended polystyrene particles. The expandable polystyrene particles obtained by this method have a good thermal conductivity improvement effect, and form fine bubbles upon foaming to provide expandable polystyrene particles having excellent thermal insulation properties.

Thermal Conductivity, Graphite, Bubbles, Heat Insulation, Foaming, Polystyrene, Particles

Description

Method for manufacturing expandable polystyrene particles with excellent thermal insulation capability}

1 is a cross-sectional photograph (bubble diameter: 300 to 500 µm) of a product obtained by foaming and molding expandable polystyrene particles prepared by simultaneously adding styrene and graphite.

2 is a cross-sectional photograph (bubble diameter: 80 to 100㎛) of the product obtained by foaming and molding the expandable polystyrene particles according to the present invention.

The present invention relates to a method for producing expandable polystyrene particles containing graphite, and more particularly, expandable polystyrene particles comprising heating by adding graphite, a blowing agent and a C ₆ -C ₁₀ aromatic hydrocarbon to the aqueous suspended polystyrene particles. It relates to a manufacturing method.

Polystyrene foam is generally pre-expanded foamed polystyrene particles to obtain pre-foamed granules, filled in a closed mold having a plurality of small holes, and then heat-foamed by pressurized steam or the like to fill the voids between the foam granules and at the same time After fusion to each other, it is produced by cooling and releasing from the mold.

Such polystyrene foam is mainly used as a heat insulator, and is interposed between panels to be used for walls of buildings, and so on, such as low thermal conductivity, low water absorption, and high strength are required. In particular, in order to obtain the same thermal insulation performance, the improvement of the insulation material has the advantage of reducing the production cost by reducing the amount of expanded polystyrene particles or slimming the outer wall by reducing the thickness of the insulation material, thereby increasing the living space. As such, the demand for his improvement has continued.

As one method for improving the performance of the heat insulating material, a method of identifying and improving the heat transfer mechanism of the resin foam has been proposed. In general, the thermal conductivity of a resin foam can be divided from its conduction mechanism into (a) conduction in solid phase, (b) conduction in gas phase, (c) radiation between bubble membranes, and (d) convection of gas in bubbles. In the case of a high foaming body, the volume occupied by resin by high foaming is very small, and the ratio of conduction of the solid phase (resin) of (a) to thermal conductivity is small. The conduction of the gas phase in (b) is advantageous for reducing the thermal conductivity when using a high molecular weight freon-based gas in the foam, but gradually decreases the effect on the thermal conductivity as the gas is dispersed and replaced with air from the foam. do. Convection of the gas in the bubble of (d) is confirmed when the bubble diameter is 4 mm or more and can be ignored in a conventional resin foam. Therefore, the highest degree of influence on thermal conductivity is radiation between the bubble films of (c). Radiation refers to heat transfer that occurs between two opposing surfaces at different surface temperatures and has a great effect of attenuating radiant heat transfer due to the solid (resin) surface constituting the bubbles in the foam. Therefore, the bubble diameter of the foam is closely related to the blocking of radiant heat, and the smaller the bubble diameter, the more the number of heat flow blocks per unit thickness increases, and consequently, the thermal conductivity is lowered.

In addition, the larger the bubble diameter of the foam, the more water is absorbed in the bubble, which causes a rapid increase in thermal conductivity, which is about 0.52 kcal / mhr ° C at room temperature, while water is about 0.5 It originates from the point which is kcal / mhr degreeC. In addition, since the moisture in the heat insulating material is severe, the surface of the interior and exterior materials that are in contact with the heat insulating material may be corroded, and in particular, the organic heat insulating material may corrode the heat insulating material itself. very important.

As another way to improve the thermal conductivity of polystyrene foam, a method of introducing an inorganic heatless material has been proposed. EP-A-620 246 describes moldings of expanded polystyrene foams containing particulate heatless materials, in particular carbon black and graphite. The incorporation of the particulate heatless material into the molding is preferably carried out by coating the surface of the prefoamed polystyrene foam granules or by embedding them in polystyrene particles which have not yet been foamed. However, this method makes it difficult to distribute the graphite uniformly in the polystyrene foam, greatly impairs the adhesion of the prefoamed foam granules, causing a low quality foam, and causes the problem of the graphite particles peeling off the surface of the molding. do.

In order to solve this problem, attempts have been made to polymerize styrene monomers in the presence of graphite particles to introduce graphite into the expandable polystyrene particles, but this leads to bubble alleles and non-uniformities, which lead to important physical properties such as absorption and strength of the foam. This may result in a deterioration.

Therefore, there is a continuing demand for a heat insulating material having a low thermal conductivity by including an inorganic heatless material without deteriorating the properties of the heat insulating material such as water absorption or strength.

It is an object of the present invention to provide a novel process for producing expandable polystyrene particles containing graphite particles.

Another object of the present invention is to provide novel expandable polystyrene particles in which graphite particles are introduced in part.

It is still another object of the present invention to provide a novel foam obtained by foaming of expandable polystyrene containing graphite particles having excellent thermal insulation properties such as low thermal conductivity, water absorption and strength.

The present invention for achieving the above object

It consists of a process for producing expandable polystyrene particles containing graphite particles comprising heating by adding graphite, blowing agent and C ₆ -C ₁₀ aromatic hydrocarbons to the aqueous suspended polystyrene particles.

In the practice of the present invention, the polymerized polystyrene particles are styrene; Alkyl styrenes such as ethyl styrene, dimethyl styrene and para-methyl styrene; Alpha-alkylstyrenes such as alpha-methylstyrene, alpha-ethylstyrene, alpha-propylstyrene and alpha-butylstyrene; Halogenated styrenes such as chlorostyrene, and bromostyrene; And polymers and / or copolymers of styrene monomers composed of vinyl toluene, monomers copolymerizable with the styrene monomers, for example acrylonitrile, butadiene, alkyl acrylates, for example methyl acrylate, alkyl methacrylates, for example Copolymers with methyl methacrylate, isobutylene, vinyl chloride, isoprene and mixtures thereof.

In the present invention, the aqueous suspended polystyrene particles means particles in which the polymerization of the monomers is made at least 80% or more, and the specific gravity of the particles is 1 or more, or the gel effect is exhibited. In the practice of the present invention, preferably for the stability of the aqueous suspended polystyrene particles, the aqueous suspended polystyrene particles are particles having at least 90% or more, more preferably 95%, and most preferably polymerization of the monomers. .

In one embodiment of the invention, the polymerized polystyrene particles are subjected to aqueous suspension to obtain aqueous suspended polystyrene particles. Suspended polystyrene particles can be obtained by emulsion polymerization, bulk polymerization, dispersion polymerization and suspension polymerization known in the art. Preferably, considering that the present invention provides expandable polystyrene particles for use in thermal insulation, it is preferable to use the aqueous suspension of the polystyrene particles polymerized by suspension polymerization which easily provides the size of conventional expandable polystyrene particles. .

In one preferred embodiment of the invention, the aqueous suspended polystyrene particles are obtained by resuspension of primary polystyrene obtained by suspension polymerization. First, a suspension agent is added to pure water, followed by styrene monomer and a flame retardant, followed by an initiator. The type of suspending agent has a great influence on the particle size distribution of the prepared particles. In the present invention, a tree which is an inorganic suspending agent, which is generally known to be effective in narrow particle size distribution and uniform particle growth during suspension polymerization of styrene foam, is used. Calcium phosphate system was used. The flame retardant used hexabromocyclododecane which is generally used. The initiator may use a peroxide initiator. The polymerization was carried out using benzoyl peroxide as an initiator to maintain the temperature in the range of 80-90 ° C. for 6-7 hours, followed by 120-130 using tertiary butylperoxide, an initiator that decomposed at high temperature to sufficiently react the residual monomers. The reaction is carried out for 30 minutes-2 hours at a high temperature of ℃. The obtained polystyrene suspension can be used after being discharged, dehydrated and dried, and then resuspended, or the obtained polystyrene suspension can be used directly.

In one preferred embodiment of the invention, when used resuspended, the discharged, dehydrated and dried polystyrene particles can be used by dispersing in the water added suspension. The suspending agent used may be a conventional suspending agent used in polystyrene suspending polymerization, and it is preferable to use a tricalcium phosphate suspending agent.

In one embodiment of the present invention, aqueous suspended polystyrene particles are obtained by suspension polymerization of styrene monomer. In this case, the polystyrene particles are polystyrene particles having a polymerization degree of at least 80% by weight, and mean polystyrene particles having a density of 1 or more or gelation of the particles. Preferably, after styrene is at least 80% or more suspended polymerized, graphite, blowing agent, C ₆ -C ₁₀ aromatic hydrocarbons may be added, more preferably at least 99% or more after polymerization, and most preferably the polymerization is completed. It is most preferable to add after. In the state where the styrene monomer is not polymerized, graphite is completely penetrated into the particles, thereby degrading the physical properties of the foamed particles.

In the present invention, the graphite used for reducing the thermal conductivity may use natural graphite or synthetic graphite, the particle size is preferably 1-50 microns, particularly preferably 2-10 microns, the bulk density is 100- 500 g / l and specific surface area of 5-20 m ² / g. In the present invention, the graphite particles are preferably used 0.05 to 25 parts by weight, more preferably 0.5 to 10% by weight based on the styrene polymer.

In the present invention, the blowing agent used for the foaming of the polystyrene particles may be a conventional blowing agent used for the expandable styrene polymer, and preferably the blowing agent is added in an amount of 3 to 10% by weight based on the styrene polymer. Suitable blowing agents may use aliphatic hydrocarbons having 4 to 6 carbon atoms, preferably pentane.

In the present invention, the C ₆ -C ₁₀ aromatic hydrocarbon used for improving the charging performance of the graphite particles is preferably used 0.1 to 1% by weight based on the polystyrene particles, when the amount of the aromatic hydrocarbon is less, the graphite The permeation efficiency of is lowered, and if the amount of aromatic hydrocarbon is too large, the heat resistance of the final molded product may be lowered. The C ₆ -C ₁₀ aromatic hydrocarbon includes benzene, toluene, p-xylene, o-xylene, m-xylene, ethylbenzene, propylbenzene, isopropylbenzene, and the like, preferably toluene, ethyl benzene .

In the present invention, it is preferable that the aqueous suspended polystyrene particles and the graphite, blowing agent and C ₆ -C ₁₀ aromatic hydrocarbons introduced are heated above the glass transition temperature Tg of the polystyrene particles so that the polystyrene particles can be softened. In order to improve the permeability of graphite, it is preferable to heat at a high temperature of 10 ° C. or higher than the glass transition temperature of the suspended polystyrene particles. In one embodiment of the invention, the heating time can be adjusted so that the graphite is properly penetrated into the polystyrene particles, it is preferable to heat more than 3 hours. When heated for a long time or heated at an excessively high temperature, it is possible to cause the foaming decrease by exhaustion of the unreacted monomer. In one embodiment of the invention, in the case of the polystyrene homopolymer, when heated to a temperature of 110-130 ℃ for about 3-7 hours it is possible to obtain an appropriate graphite introduction effect.

In the practice of the present invention, in addition to the above-mentioned graphite, blowing agent, and C ₆ -C ₁₀ aromatic hydrocarbon, a flame retardant having a melting point that can be melted at the heating temperature can be introduced. If the melting point is higher than the heating temperature, the flame retardant may proceed unmelted at the heating temperature, thereby increasing process instability. In one preferred embodiment of the present invention, when the polystyrene homopolymer is heated to 110-130 ℃, the flame retardant having a melting point that can be melted at the heating temperature is tetrabromo cyclooctane, tetrabromo vinylcyclohexane, 2, 2 '-(4-allyloxy-3,5-dibromophenyl) propane and tribromophenyl allyl ether may be used, preferably tetrabromo cyclooctane, and the melting point of the flame retardant is 105 ° C.

In the practice of the present invention, the flame retardant used may be used to increase the penetration efficiency of graphite in the final product, and also exhibit the effect of strengthening the flame retardancy. The amount of the flame retardant to be added is preferably used 0.1 to 2.0% by weight based on the polystyrene particles. When the amount added is low, the efficiency of graphite is lowered, and when the flame retardant is added in the above range, there is a problem that the heat resistance of the final product is lowered.

In the present invention, novel expandable polystyrene particles into which graphite particles are introduced are obtained by heating graphite, a blowing agent, and a C ₆ -C ₁₀ aromatic hydrocarbon into aqueous suspended polystyrene particles. Since the expandable polystyrene particles obtained by the present invention are added after the reaction is completed or at least 80% by weight or more of the monomers are polymerized, the graphite is not uniformly distributed inside the expandable polystyrene particles, and is mostly in the portion close to the surface while forming a surface layer. It will exist. In a preferred embodiment of the invention, the graphite is uniformly present by introducing or penetrating the surface of the expandable polystyrene particles.

In the present invention, the foamed polystyrene foam containing graphite particles having excellent thermal insulation properties such as low thermal conductivity, water absorption, and strength is heated by injecting graphite, a blowing agent, and a C ₆ -C ₁₀ aromatic hydrocarbon into the aqueous suspended polystyrene particles. The expandable polystyrene particles obtained by the above step are obtained by foaming. The foaming conditions may use the conventional conditions used for the foaming of the expandable polystyrene, there is no particular limitation. Foams containing foamed graphite can be foamed by those skilled in the art to have a diameter of 70-200 microns, and have the advantage of excellent properties such as absorption and strength, including thermal conductivity. In FIG. 2, the cross section obtained by foaming the graphite-containing expandable polystyrene obtained by the present invention is a photograph taken by a scanning electron microscope (SEM).

For reference, the expandable polystyrene particles have a specific gravity of 1.04 and evenly contain a blowing agent for foaming. The particle diameter is about 0.5-1.2 mm in diameter and is spherical particles. The polystyrene foam, which is the final product, is completed through physical foaming by high temperature steam, and its cross-sectional shape has a honeycomb-shaped interface between the preliminary foams, and each foam is composed of numerous bubbles. do. In the present invention, when graphite is introduced into the expandable polystyrene particles, the foaming agent is not evenly distributed within the polystyrene particles and is concentrated around the graphite particles, resulting in large bubbles and non-uniformity of the final polystyrene foam, resulting in a decrease in physical properties. Graphite is present in the surface layer of the polystyrene particles within a range that does not affect the thermal conductivity without affecting the bubble diameter.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited by the Examples.

<Example 1>

Polystyrene manufacturing

Pure water, styrene monomer, suspending agent, and flame retardant were injected into the reactor at room temperature as follows based on 100 kg, and the initiator was added to the polymerization temperature at 88 ° C (near 60 ° C).

The mixture was reacted for 6 hours while maintaining the polymerization temperature at 88 ° C, cooled after reaction for 1 hour at 125 ° C to remove unreacted styrene monomer, and then discharged, dehydrated, and dried to obtain polystyrene particles. The size of the obtained polystyrene particles was in the range of 0.5-1.2 mm.

(Polymerization of Polystyrene Particles)

Styrene monomer 49.59 wt%

Pure 49.59 wt%

0.25 wt% of suspending agent (tricalcium phosphate, Dubon Co .; DET-10)

0.37 wt% flame retardant (hexabromocyclododecane, GLC; CD75P ^TM )

Initiator [Benzoyl Peroxide (Hansol Chemical; PEROX-B75):

Tertiary butyl peroxide (Century Atopina; Luperox P) = 3: 1] 0.20 wt%

Pure water, suspending agent, polystyrene particles, graphite, and solvent were sequentially added to the obtained styrene polymer in a separate reactor as follows based on 100 kg, and after the completion of the temperature increase of 120 ° C., a blowing agent was added and maintained for 5 hours.

(Graphite injection process prescription)

Pure 47.62 wt%

47.62 wt% polystyrene particles

0.24 wt% of suspending agent (tricalcium phosphate, Dubon Co .; DET-10)

Graphite (natural graphite; average particle 5㎛, Korea Coma Industry; HCN-905) 0.48 wt%

Solvent (Toluene, M Chemical Co., Ltd.) 0.24 wt%

Foaming agent (pentane, SK) 3.80 wt%

The graphite input product thus obtained was subjected to the physical property evaluation by coating the blending agent after dehydration and drying, and are shown in Table 1.

Example 2

Using the same styrene polymer as in <Example 1>, graphite was introduced into the polystyrene particles in which polymerization was completed in the same manner, but ethyl benzene (SK) was added instead of toluene as a suitable solvent. The physical properties of the foamed and molded products are shown in Table 1.

Example 3

The same polystyrene as in <Example 1> was used, and the graphite addition process was the same. Graphite was added to the polystyrene particles in which polymerization was completed, but a few weight% of a flame retardant was added. The melting point of the flame retardant is 105 ° C.

The physical properties of the product obtained by foaming and molding the obtained graphite input product are shown in Table 1.

(Graphite injection process prescription)

Pure 47.39 wt%

47.39 wt% polystyrene particles

0.24 wt% of suspending agent (tricalcium phosphate, Dubon Co .; DET-10)

Graphite (natural graphite; average particle 5㎛, Korea Coma Industry; HCN-905) 0.47 wt%

Solvent (Toluene, M Chemical Co., Ltd.) 0.24 wt%

Foaming agent (pentane, SK) 3.80 wt%

Flame retardant (tetrabromocyclooctane, Albemarle; Saytex BC-48) 0.47 wt%

Comparative Example 1

In the manufacturing method of the expandable polystyrene particles, pure water, styrene monomer, suspending agent and flame retardant are introduced into the reactor at room temperature, and the initiator is added to the polymerization temperature at 88 ° C. (near 60 ° C.) as in the conventional styrene suspension polymerization. It was.

After the reaction was conducted for 6 hours while maintaining the polymerization temperature at 88 ° C, the reaction was cooled after cooling at 125 ° C for 4 hours in order to remove unreacted styrene monomer and give foamability after adding the blowing agent, and then coated with a blending agent after discharge, dehydration and drying. It was.

The physical properties of the product obtained by foaming and molding the obtained expandable polystyrene particles are shown in Table 1.

(Preparation of Preparation of Foamable Polystyrene Particles)

Styrene Monomer 47.70 wt%

Pure 47.70 wt%

0.24 wt% of suspending agent (tricalcium phosphate, Dubon Co .; DET-10)

0.36 wt% flame retardant (hexabromocyclododecane, GLC; CD75P ^TM )

Initiator [Benzoyl Peroxide (Hansol Chemical; PEROX-B75):

Tertiary butyl peroxide (Century Atopina; Luperox P) = 3: 1] 0.19 wt%

Foaming agent (pentane, SK) 3.81 wt%

Comparative Example 2

In Comparative Example 2, ordinary foamable polystyrene particles were foamed to apply an electrodeposition agent such as polyethylene glycol having a molecular weight of 400 to the foam granules, and then graphite was coated to observe thermal conductivity effects and physical properties.

The manufacturing method of the expandable polystyrene particles is the same as in <Comparative Example 2>, and the expandable polystyrene particles thus obtained are foamed to incorporate and apply 10% polyethylene glycol (Korea Polyol; PEG-400) to the weight of the foam granules, followed by 5 % Of graphite (natural graphite; average particle 5㎛, Korea Coma Industry; HCN-905) was coated and molded to evaluate the physical properties.

The physical properties of the molded product of the obtained graphite coated article are shown in Table 1.

Comparative Example 3

[Comparative Example 3] is to observe the physical properties of the final molded article by adding graphite during the polymerization, the polymerization process of the expandable polystyrene particles is dissolved in a certain amount of polystyrene particles in the styrene monomer in order to increase the stability of the suspension proceeds the polymerization The same is true except that

First, pure water, a polystyrene solution, a suspending agent, a flame retardant, and graphite were sequentially added to a reactor at room temperature, and an initiator was added to a polymerization temperature of 88 ° C. (near 60 ° C.).

The mixture was reacted for 6 hours while maintaining the polymerization temperature at 88 ° C, cooled after reaction for 4 hours at 125 ° C to remove unreacted styrene monomer and giving foamability, and then coated with a blending agent after discharge, dehydration and drying.

The physical properties of the product obtained by foaming and molding the expandable polystyrene particles into which graphite was added during polymerization thus obtained are shown in Table 1.

(Preparation of Preparation of Expandable Polystyrene Particles Filled with Graphite During Polymerization)

Pure 47.25 wt%

Styrene monomer 42.52 wt%

4.72% by weight polystyrene particles

0.24% by weight of suspending agent (Polyvinyl Alcohol, KURARAY; PVA-217)

0.35% by weight of flame retardant (hexabromocyclododecane, GLC; CD75P ^TM )

Graphite (natural graphite; average particle 5㎛, Korea Coma Industry; HCN-905) 0.95 wt%

Initiator [Benzoyl Peroxide (Hansol Chemical; PEROX-B75):

Tertiary butyl peroxide (Century Atopina; Luperox P) = 3: 1] 0.19 wt%

Foaming agent (pentane, SK) 3.78 wt%

Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Density (g / cm 3) 0.020 0.020 0.021 0.020 0.021 0.021 Thermal conductivity (kcal / mhr ℃) 0.0276 0.0275 0.0266 0.0324 0.0312 0.0268 Bubble diameter (㎛) 80-100 80-100 80-100 80-100 80-100 300-500 Absorption rate (g / 100㎠) 0.47 0.52 0.48 0.42 3.02 2.67 Compressive strength (kgf / ㎠) 1.205 1.183 1.202 1.213 0.724 0.389 Self-firing (sec) 1.0 1.1 0.7 1.3 1.1 0.9

In Table 1, the physical property evaluation was specifically performed as follows.

1. Density: Mass of the molded article (g) / Volume of the molded article (m ³ )

2. Thermal conductivity: The value measured by the plate heat flow meter method among the thermal conductivity measurement methods of the thermal insulation material specified in KS L 9016 (Kcal / mhr ℃).

3. Bubble diameter: Average diameter between bubble wall and wall (μm; measured under microscope)

4. Absorption rate: It is the numerical value divided by the surface area of water absorbed according to the absorption method of expanded polystyrene insulation according to KS M 3808. (g / 100cm ² )

5. Compressive strength: According to the method of measuring the compressive strength of expanded polystyrene insulation specified in Korean Industrial Standard KS M 3808 (kg _f / cm ² )

6. Self-firing: According to the soft plastic test method of expanded polystyrene insulation specified in Korean Industrial Standard KS M 3808 (sec)

From the results of Table 1, the introduction of graphite in the expandable polystyrene particles can be confirmed that the effect of improving the thermal conductivity except the coating on the foam granules, and when the graphite is added during polymerization, the thermal conductivity due to the bubble alleles improved Although there was an effect, it was observed that the water absorption and the strength decreased.

When the high temperature operation and the proper solvent were selected and added in order to efficiently inject graphite into the polystyrene particles, the thermal conductivity was improved while maintaining the bubble diameter, absorption rate, and strength of the existing polystyrene foam, and in particular, <Example 3 In the present invention, it was confirmed that tetrabromocyclooctane was introduced into the polystyrene particles to increase the graphite-injection efficiency in the particles and to improve self-plasticity.

Although the present invention has been described in detail in the above embodiments, the above embodiments are not described to limit the scope of the present invention, but are described for illustrative purposes only.

Those skilled in the art will recognize that modifications of the invention are possible without departing from the scope and spirit of the invention.

According to the present invention, a novel method for producing polystyrene particles containing graphite has been provided, and expandable polystyrene particles containing graphite in a part of the particles have also been provided. By foaming the polystyrene particles, it is possible to adhere to the bubble diameter of the existing polystyrene foam to significantly lower the thermal conductivity while maintaining the physical properties such as absorption rate, strength, thereby producing a foam having excellent thermal insulation properties.

Claims (14)

A process for producing expandable polystyrene particles containing graphite particles, comprising heating graphite at higher temperature than the Tg of the polystyrene particles by adding graphite, a blowing agent, and a C ₆ -C ₁₀ aromatic hydrocarbon to the aqueous suspended polystyrene particles. The method of claim 1 wherein the polystyrene particles are styrene, ethylstyrene, dimethylstyrene, para-methylstyrene, alpha-methylstyrene, alpha-ethylstyrene, alpha-propylstyrene, alpha-butylstyrene, chlorostyrene, bromostyrene and vinyl. A polymer or copolymer of monomers of toluene, a copolymer of monomers with acrylonitrile, butadiene, methylacrylate, methylmethacrylate, isobutylene, vinyl chloride, isophorene and mixtures thereof. delete The method according to claim 1, which is heated to a temperature of 110 to 130 ° C. for 3 to 7 hours. The method of claim 1, wherein the aqueous suspended polystyrene particles are made by suspension of polystyrene particles or suspension polymerization of styrene monomers. The method of claim 1, wherein the aqueous suspended polystyrene particles are at least 80% polymerized polystyrene particles. The method of claim 1 wherein the graphite particles are 1-50 microns in size. The method of claim 1 wherein the graphite is 0.05-25% by weight based on the polystyrene particles. The method of claim 1, wherein the C ₆ -C ₁₀ aromatic hydrocarbon is selected from the group consisting of toluene, ethylbenzene, and mixtures thereof. The method of claim 1, wherein the aromatic hydrocarbon uses 0.1-1 wt% based on the polystyrene particles. The method according to claim 1, further comprising adding 0.1 to 2% by weight of a flame retardant dissolved at a heating temperature based on the polystyrene particles. The flame retardant according to claim 1, wherein the flame retardant has a melting point of 120 C or less, tetrabromocyclooctane, tetrabromo vinylcyclohexane, 2,2 '-(4-allyloxy-3,5-dibromophenyl) prop Plate, tribromophenyl allyl ether. delete delete

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