KR100884817B1 - Method for producing expandable polystyrene beads - Google Patents

Abstract

A method for producing expandable polystyrene beads is provided to reduce the thermal conductivity and to proceed nucleus polymerization for the increase of introduction graphite volume and fuse improvement by introducing graphite. A method for producing expandable polystyrene beads comprises (S1) a step for obtaining the polystyrene particles coated with graphite by suspending styrene-based resin particles in water, adding a styrene-based monomer, fat soluble initiator and graphite and performing the first nucleus polymerization; and (S2) a step for forming and dipping a resin protecting film on the graphite-coated layer by adding a styrene-based monomer, fat soluble initiator and water soluble initiator or resin melting liquid to the graphite-coated polystyrene particles, and performing the second nucleus polymerization.

Description

Method for Producing Expandable Polystyrene Beads {Method for Producing Expandable Polystyrene Beads}

The present invention relates to a method for producing expandable polystyrene particles in which graphite is introduced, and more particularly, to a manufacturing method consisting of two stages in which nuclear polymerization is carried out stepwise to increase graphite introduction amount and improve fusion.

As a general method for producing polystyrene, a production method by emulsion polymerization, suspension polymerization, and dispersion polymerization is widely known. Japanese Patent Publication No. 46-15112, Japanese Patent Publication No. 5-317688, US Patent Publication 5,559,202, US Patent Publication 2,652,392, UK Patent 1,188,252, and Korean Patent Publication No. 10-1999-0024927 are in suspension. A method for producing expandable polystyrene particles by law is disclosed. The suspension polymerization method can be largely classified into a one-stage process of adding a blowing agent together with suspension polymerization and a two-stage process of selecting polystyrene particles obtained in polymerization, injecting only necessary particles into the reactor, and then suspending them to impregnate the foaming agent at high temperature. In addition, nuclear polymerization techniques are known in which small particles are used to grow styrene monomers up to a desired particle size.

As a method for preparing expanded polystyrene particles into which graphite is introduced, Korean Patent No. 10-0599847 discloses foamability in which graphite is uniformly coated on the surface of polystyrene particles by suspending polymerized polystyrene particles in water together with graphite and impregnated at high temperature. Techniques for producing polystyrene particles have been published. However, the expanded polystyrene with graphite introduced in this manner has an effect of lowering the thermal conductivity in part than the general expanded polystyrene, but there is a limit in increasing the amount of graphite introduced, and it is difficult to further improve the thermal conductivity.

Accordingly, it is an object of the present invention to provide a novel method for producing expandable polystyrene particles in which graphite is introduced, which can reduce the thermal conductivity and compensate for the chronology of the thermal conductivity.

It is another object of the present invention to provide a novel method for producing expandable polystyrene particles having graphite introduced therein which can increase the amount of graphite introduced into the polystyrene particles to further reduce the thermal conductivity.

It is still another object of the present invention to provide a novel method for preparing expanded polystyrene particles into which graphite is introduced, which has improved fusion characteristics through surface modification of the graphite coated layer of graphite coated polystyrene particles.

In the present invention, in order to increase the amount of graphite introduced into the expanded polystyrene particles, which are prepared by suspending the polymerized polystyrene particles in the prior art, which is prepared by suspending water together with graphite and impregnating at high temperature, a nuclear polymerization process is applied. In this nuclear polymerization process, an additional styrene monomer is added to the polystyrene particles in which polymerization is completed, thereby lowering the viscosity of the polystyrene particles, thereby increasing the coating amount of graphite. However, the expanded polystyrene particles coated with graphite simply by increasing the amount of graphite is excellent in improving thermal insulation performance, but graphite desorption may occur during processing due to the excessive coating of graphite, and may cause a decrease in fusion due to the graphite coating layer during molding. In order to improve this, second polynuclear polymerization, in which a resin protective film is formed on the graphite coating layer, may be performed in steps to prepare expanded polystyrene particles having graphite having excellent thermal insulation performance and fusion characteristics.

The expanded polystyrene particles incorporating graphite obtained by this method have excellent thermal insulation performance while maintaining the same or higher quality of mechanical properties, including fusion characteristics, than general expandable polystyrene products.

In addition, the two-stage nuclear polymerization technology that introduces inorganic materials such as graphite into the polystyrene particles and forms a resin protective film on the inorganic coating layer is not only graphite, but also inorganic materials such as carbon black, inorganic pigments, expanded graphite, and the like, and gold, silver, copper, aluminum, and the like. It can be used for various purposes such as introduction of metal materials.

In particular, the nuclear polymerization technology for forming the resin protective film may be applied to various fields for improving not only fusion but also various mechanical properties through surface modification of the expandable polystyrene particles.

The present invention relates to a two-step process for producing expandable polystyrene particles, which incorporates graphite and has improved thermal insulation performance and fusion characteristics. Suspending the styrene resin particles in water to add a styrene monomer, a fat soluble initiator and graphite, and performing primary nuclear polymerization to obtain graphite coated polystyrene particles; A styrene-based monomer, a fat-soluble initiator and a water-soluble initiator or a resin solution are added to the graphite-coated polystyrene particles, followed by secondary nuclear polymerization, and a blowing agent is added to form and impregnate a resin protective film in the graphite coating layer.

In the practice of the present invention, the styrene-based resin is 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; Styrene halides, 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 a preferred embodiment of the present invention, the styrene resin is a polystyrene resin having a weight average molecular weight of 100,000 to 300,000 g / mol.

In the practice of the present invention, the dispersant used to suspend the styrene resin particles in water can be prepared using all dispersants used in the production of ordinary expandable polystyrene particles, for example, an inorganic dispersant; Tricalcium phosphate, magnesium pyrophosphate, organic dispersants; Polyvinyl alcohol, methyl cellulose, polyvinyl pyrrolidone and the like can be used. The dispersant is 0.5 to 1.0 parts by weight based on 100 parts by weight of ultrapure water, preferably tricalcium phosphate.

In the practice of the present invention, the styrene monomer is styrene, styrene; Alkyl styrenes such as ethyl styrene, dimethyl styrene and para-methyl styrene; Alpha-alkylstyrene, for example alpha-methylstyrene, alpha-ethylstyrene, alpha-propylstyrene and alpha-butylstyrene can be used. In the second nuclear polymerization, the weight ratio of graphite-coated polystyrene particles and styrene monomer is 10 to 90:90 to 10. Depending on the type and content, a variety of high functional and physical properties can be produced.

 In the practice of the present invention, the fat-soluble initiator can be used all the initiators usually used in effervescent polystyrene polymerization, preferably two kinds of benzoyl peroxide (BPO), t-butyl peroxy benzoate (TBPB) Initiator is used. A fat-soluble initiator uses 0.1-5 weight part with respect to 100 weight part of styrene type monomers injected | thrown-in.

In the practice of the present invention, the graphite has a particle size of 0.1 to 20 µm and 0.1 to 25 parts by weight based on 100 parts by weight of polystyrene particles.

In the practice of the present invention, in order to form a resin protective film on the graphite coating layer of the graphite coated polystyrene particles, a nuclear polymerization may be performed by adding a water-soluble initiator or a resin solution. The water-soluble initiator does not polymerize inside the polystyrene particles due to the hydrophilic group at the terminal, and polymerization occurs at the interface between the water and the graphite-coated polystyrene particles, thereby forming a resin protective film on the graphite layer. In addition, monomers such as styrene easily penetrate into the particles during the nuclear polymerization, but polymer materials including styrene resins and waxes having different structures are difficult to penetrate into the particles. By dissolving waxes and injecting a resin solution, the polymer resin and waxes were further coated on the graphite coating layer to achieve surface modification.

The water-soluble initiator may be used a conventional water-soluble initiator such as ammonium persulfate, potassium persulfate, sodium persulfate, preferably ammonium persulfate. The water-soluble initiator is used in the amount of 0.01 to 0.5 parts by weight based on 100 parts by weight of the injected styrene monomer.

The concentration of the polymer material and the waxes relative to the styrene monomer of the resin solution is not particularly limited.

 In the practice of the present invention, the blowing agent may be used blowing agents C4 to C6 used in the production of general expandable polystyrene, and preferred blowing agents in the practice of the present invention are n-pentane, i-pentane and cyclopentane. Such a blowing agent is used in an amount of 4 to 15 parts by weight based on the total amount of the expandable polystyrene particles into which graphite is introduced.

In the practice of the present invention, additives may be added to impart various properties of the expandable polystyrene particles, and specifically, C6 to C10 aromatic hydrocarbons, bubble control agents, and flame retardants may be used.

The C6 to C10 aromatic hydrocarbons serve as a solvent to improve the foaming power, and include benzene, toluene, p-xylene, o-xylene, m-xylene, ethylbenzene, propylbenzene, i-propylbenzene, and the like. Preferably, toluene and ethyl benzene are used. It is preferable to use 0.01-5.0 weight part with respect to the total amount of expandable polystyrene particle which graphite was introduce | transduced, More preferably, it is 0.1-1.0 weight part. When the amount of the aromatic hydrocarbon is small, the foamability of the expandable polystyrene particles is lowered, and when the amount of the aromatic hydrocarbon is too large, the heat resistance of the final molded product is lowered.

The bubble control agent may be polyethylene wax and ethylene bis stearamide, calcium carbonate, talc, clay, silica, diatomaceous earth, citric acid and sodium bicarbonate, and 0.01 to the total amount of expanded polystyrene particles into which graphite is introduced. It is preferable to use ˜3.0 parts by weight, which can reduce the size of the bubble to improve the thermal insulation and molded article properties.

Examples of the flame retardant include hexabromo cyclododecane, tetrabromo sclooctane, tetrabromo vinylcyclohexane, 2,2 ′ (4allyloxy-3,5-dibromophenyl) propane, tribromophenyl allyl Bromine type flame retardants, such as ether, and a conventional chlorine type and phosphorus type flame retardant can be used, Preferably it is hexabromo cyclododecane. The flame retardant is 0.1 to 5.0 parts by weight based on the total amount of expandable polystyrene particles in which graphite is introduced.

In the practice of the present invention, the process of introducing the graphite and performing the two-step nuclear polymerization of the expandable polystyrene particles with improved heat insulating performance and fusion characteristics are as follows.

First, the first nuclear polymerization step of obtaining graphite-coated polystyrene particles is maintained by dispersing ultrapure water, polystyrene particles, and a dispersant into a reactor. When this process is completed, the temperature of the reactor is maintained between 60 ° C and 90 ° C and graphite is added. And a styrene monomer and a fat-soluble initiator are gradually added over 2-3 hours. Thereafter, the manhole of the reactor was closed, and the temperature was raised from 60 ° C. to 90 ° C. to 100 ° C. to 130 ° C. for 3 to 6 hours while slowly adding the remaining styrene monomer to complete polymerization.

The step of forming and impregnating a resin protective film on the graphite coating layer by using the graphite-coated polystyrene particles thus completed polymerization is carried out by adding ultrapure water, graphite-coated polystyrene particles, dispersant to the reactor to maintain dispersion. When this process is completed, the temperature of the reactor is raised and maintained between 60 ° C. and 90 ° C., and a styrene monomer, a fat-soluble initiator, a bubble control agent, a flame retardant, and a C 6 -C 10 aromatic hydrocarbon are gradually added over 2 to 3 hours. Then, a water-soluble initiator was added, and then, the manhole of the reactor was closed, and the resin solution was gradually added while gradually raising the temperature from 60 ° C. to 90 ° C. to 100 ° C. to 130 ° C. to complete the polymerization. After the polymerization is completed, the impregnation may be terminated while maintaining at 100 ° C. to 130 ° C. for 3 to 6 hours to obtain expanded polystyrene particles into which graphite is introduced.

Expandable polystyrene particles of the present invention comprises the steps of suspending the styrene resin particles in water to add a styrene monomer, a fat-soluble initiator and graphite, and subjected to the first nuclear polymerization to obtain a graphite coated polystyrene particles; A styrene-based monomer, a fat-soluble initiator, a water-soluble initiator, and a resin dissolving solution are added to the graphite-coated polystyrene particles, followed by secondary nuclear polymerization, and a blowing agent is added to form and impregnate a resin protective film in the graphite coating layer. The step of foaming the expandable polystyrene particles into which the graphite thus obtained is introduced may use ordinary foaming conditions, and there is no particular limitation. Expandable polystyrene incorporating graphite can be foamed by those skilled in the art to have a diameter of 70 to 300 microns, and has the advantage of excellent mechanical properties including thermal insulation and welding properties including high foaming properties.

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

Comparative Example 1 Experiment of Manufacturing Expandable Polystyrene Particles Incorporating Graphite (Introduction of Graphite at High Temperature Impregnation)

0.2 kg of a dispersant (tricalcium phosphate; Dubon emulsifier) was added to 40 kg of ultrapure water and stirred, and 40 kg of polystyrene particles and 1.0 kg of graphite (GRAPHITE; Hyundai-Coma; HC-905) were added thereto. Then, the temperature of the reactor was raised to 125 ° C, 3 kg of blowing agent (pentane; SK) was introduced into the reactor at nitrogen pressure, and impregnation was performed for 5 hours while maintaining the final reactor pressure of 13 kgf / cm 2. After cooling to 30 ° C. or below, the product was discharged, washed with water, dried, and applied to the blending agent used in conventional expandable polystyrene was evaluated for physical properties. The results are published in Table 1 below. A cross section photograph is posted in FIG. 1.

Example 1 Production Experiment of Expandable Polystyrene Particles Incorporated with Graphite (To Increase Graphite Introduction)

0.2 kg of a dispersant (tricalcium phosphate; Dubon emulsifier) was added to 40 kg of ultrapure water and stirred, and 20 kg of polystyrene particles were added thereto. After that, the reactor temperature was raised to 60 ° C., and 1.0 kg of graphite (GRAPHITE; Hyundai Comma Industry; HC-905) was charged. 6 kg of styrene monomer (SM; SK), 1 kg of flame retardant (hexabromocyclododecane; GLC; CD75P ™), 0.1 kg of low temperature initiator (benzoyl peroxide; Hansol Chemical), high temperature initiator (t-butyl peroxy benzoate) 0.03 kg) was dissolved and added for 3 hours. After the reactor manhole was closed and the polymerization was carried out by slowly adding 14 kg of styrene monomer while raising the temperature from 60 ° C. to 125 ° C. for 4 hours, 3 kg of blowing agent (pentane; SK) was added to the reactor at 125 ° C. under nitrogen pressure, and the final reactor pressure. Was impregnated for 5 hours while maintaining 13 kgf / cm 2. After cooling to 30 ° C. or below, the product was discharged, washed with water, dried, and applied to the blending agent used in conventional expandable polystyrene was evaluated for physical properties. The results are published in Table 1 below. A cross section photograph is posted in FIG. 2.

<Example 2> Experiment for preparing expanded polystyrene particles into which graphite particles are introduced (two-step nuclear polymerization for graphite coating and resin protective film formation; resin melt introduction)

0.2 kg of a dispersant (tricalcium phosphate; Dubon emulsifier) was added to 40 kg of ultrapure water and stirred, and 20 kg of polystyrene particles were added thereto. After that, the reactor temperature was raised to 60 ° C and maintained, and 2.0 kg of graphite (GRAPTIE; Hyundai Comma; HC-905) was added thereto. And 6 kg of styrene monomer (SM; SK), 1 kg of flame retardant (hexabromocyclododecane; GLC; CD75P ™), 0.1 kg of low temperature initiator (benzoyl peroxide; Hansol Chemical), high temperature initiator (t-butyl peroxy benzoate; 0.03 kg) was dissolved and added for 3 hours. After the reactor manhole was closed and the polymerization was carried out by slowly adding 14 kg of styrene monomer while raising the temperature from 60 ° C to 125 ° C for 4 hours, the reaction was terminated while maintaining at 125 ° C for 1 hour. After cooling below 30 ° C., the product was discharged and washed with water and dried. 20 kg of the graphite-coated polystyrene particles thus obtained were put in a 100 L reactor suspended in 0.2 kg of a dispersant (tricalcium phosphate; dubon emulsifier) in 40 kg of ultrapure water, and then the reactor temperature was raised to 60 ° C., and the styrene monomer ( SM; SK) 6 kg flame retardant (hexabromocyclododecane; GLC; CD75P ™) 1 kg, low temperature initiator (benzoyl peroxide; Hansol Chemical) 0.05 kg, high temperature initiator (t-butyl peroxy benzoate; Hosung Chemical) 0.02 kg was dissolved and added for 2 hours. Thereafter, the reactor manhole was closed and 14 kg of the resin solution (polystyrene 6 kg + styrene monomer 8 kg) prepared in advance was slowly added while heating the temperature from 60 ° C. to 125 ° C. for 3 hours, and then 3 kg of a blowing agent (pentane; SK) was added at 125 ° C. Into the reactor at nitrogen pressure and impregnation was carried out for 5 hours while maintaining the final reactor pressure 13kgf / ㎠. After cooling to 30 ℃ or less, the product was discharged, washed with water, dried, and applied to the blending agent used in conventional expandable polystyrene was evaluated for physical properties. The results are published in Table 1 below. The cross section picture is posted in FIG. 3.

Example 3 Production Experiment of Expandable Polystyrene Particles Incorporating Graphite Particles (2-Step Nuclear Polymerization for Graphite Coating and Resin Protective Film Formation; Water-Solution Initiator Introduction)

0.2 kg of a dispersant (tricalcium phosphate; Dubon emulsifier) was added to 40 kg of ultrapure water and stirred, and 20 kg of polystyrene particles were added thereto. After that, the reactor temperature was raised to 60 ° C and maintained, and 2.0 kg of graphite (GRAPTIE; Hyundai Comma; HC-905) was added thereto. 6 kg of styrene monomer (SM; SK), 1 kg of flame retardant (hexabromocyclododecane; GLC; CD75P ™), 0.1 kg of low temperature initiator (benzoyl peroxide; Hansol Chemical), high temperature initiator (t-butyl peroxy benzoate) 0.03 kg) was dissolved and added for 3 hours. After the reactor manhole was closed and the polymerization was carried out by slowly adding 14 kg of styrene monomer while raising the temperature from 60 ° C to 125 ° C for 4 hours, the reaction was terminated while maintaining at 125 ° C for 1 hour. After cooling below 30 ° C., the product was discharged and washed with water, dried. 20 kg of the graphite-coated polystyrene particles thus obtained were put in a 100 L reactor suspended in 0.2 kg of a dispersant (tricalcium phosphate; dubon emulsifier) in 40 kg of ultrapure water, and then the reactor temperature was raised to 60 ° C., and the styrene monomer ( SM; SK) 6 kg flame retardant (hexabromocyclododecane; GLC; CD75P ™) 1 kg, low temperature initiator (benzoyl peroxide; Hansol Chemical) 0.05 kg, high temperature initiator (t-butyl peroxy benzoate; Hosung Chemical) 0.02 kg was dissolved and added for 2 hours. Finally, 0.01 kg of a water-soluble initiator (ammonium persulfate: SK) was added, and then 14 kg of styrene monomer was slowly added while proceeding polymerization by closing the reactor manhole and raising the temperature from 60 ° C to 125 ° C for 3 hours, and then blowing agent at 125 ° C. 3 kg (pentane; SK) was introduced into the reactor at a nitrogen pressure, and impregnation was performed for 5 hours while maintaining a final reactor pressure of 13 kgf / cm 2. After cooling to 30 ℃ or less, the product was discharged, washed with water, dried, and applied to the blending agent used in conventional expandable polystyrene was evaluated for physical properties. The results are published in Table 1 below. The cross section picture is posted in FIG. 4.

The density of the polystyrene foam specimens for the physical property evaluation was 30 kg / m 3, and the physical property evaluation was specifically performed as follows.

1) 5-minute effervescent: foamed drainage (doubled) when foamed for 5 minutes at 0.3kgf / cm ² steam pressure

2) Bubble size: Average diameter between bubble wall and bubble (㎛: measured by microscope)

3) Absorption amount: It is the numerical value divided by the surface area of water absorbed according to the absorption method of expanded polystyrene insulation according to Korea Industrial Standard KS M 3808 (g / 100㎠)

4) Fusion: It shows the state in which the foamed granules of the molded products are in close contact with each other, and the ratio of the breakage of the foamed granules among the fractured surfaces (%)

5) Compressive strength: According to the method of measuring compressive strength of expanded polystyrene insulation specified in Korean Industrial Standard KS M 3808 (kgf / ㎠)

6) Flexural strength: According to the method of measuring flexural strength of foamed polystyrene insulation specified in Korean Industrial Standard KS M 3808 (kgf / ㎠)

7) Compressive strength: According to the method of measuring flammability of expanded polystyrene insulation specified in Korean Industrial Standard KS M 3808 (sec)

8) Thermal conductivity: measured value (W / mK) using Netzsch's thermal conductivity device (HFM 436/3/1)

9) Graphite content: Graphite impregnation measured value (%) based on 100 parts by weight of expandable polystyrene particles into which graphite was introduced

10) Graphite desorption amount: Graphite falling compared to the initial graphite content (%) when spraying the foam granules with compressed air for 30 minutes after foaming the expanded polystyrene particles into which graphite was introduced 50 times

Comparative Example 1 Example 1 Example 2 Example 3 5 minutes effervescent 75 70 70 71 Bubble size (㎛) 80-120 80-120 80-110 80-110 Absorption amount (g / 100㎠) 0.45 0.45 0.40 0.43 Fusion (%) 30 30 50 70 Compressive strength (kgf / ㎠) 1.87 1.86 1.85 1.85 Flexural Strength (kgf / ㎠) 3.84 3.75 3.91 3.94 Self-firing (sec) 1.2 1.1 1.0 0.9 Graphite content (%) 1.0 1.8 1.9 1.9 Graphite Desorption Amount (%) 23 48 25 10 Thermal Conductivity (W / mK) 0.0325 0.0305 0.0303 0.0304

From the results of Table 1, it was confirmed that the expanded polystyrene particles into which graphite obtained from the nuclear polymerization technology were introduced exhibited a level of equivalent or more mechanical properties including fusion and excellent thermal insulation performance, compared to general expandable polystyrene. In the case of carrying out the nuclear polymerization as in Examples 1 to 3, in the graphite introduction step, the styrene monomer may lower the viscosity of the polystyrene particles, thereby increasing the amount of graphite introduced than the comparative example. In addition, Example 2 and Example 3 from the results of the graphite desorption amount of Table 1 confirmed that the graphite desorption amount was reduced under the processing conditions such as drying, conveying after foaming to form a resin protective film, foaming in Figures 3 to 4 It was confirmed that a resin protective film was formed on the outermost side of the polystyrene particles.

Expanded polystyrene with graphite prepared by the method of the present invention is excellent in strength and heat insulating properties can be usefully used as a variety of heat insulating materials such as building heat insulating material.

1 is a disregard of expandable polystyrene particles in which graphite is introduced by a process of introducing graphite during conventional high temperature impregnation (Comparative Example 1)

2 is a disintegration of expandable polystyrene particles in which graphite is introduced by nuclear polymerization (Example 1)

3 is a disintegration of expandable polystyrene particles in which graphite is introduced by two-step nuclear polymerization using a resin melt (Example 2)

4 is a disintegration of expandable polystyrene particles in which graphite is introduced by two-step nuclear polymerization using a water-soluble initiator (Example 3).

Claims (8)

Styrene, ethyl styrene, dimethyl styrene, para-methylstyrene, alpha-methylstyrene, alpha-ethylstyrene, alpha-propylstyrene, alpha-butylstyrene, chlorostyrene, bromostyrene; And a copolymer of a monomer selected from the group consisting of vinyl toluene or a copolymer of this monomer with at least one monomer selected from the group consisting of acrylonitrile, butadiene, methylacrylate, methylmethacrylate, isobutylene, vinyl chloride and isoprene. Suspending the styrenic resin particles in water to add the styrene monomer, the initiator, and the graphite, followed by primary nuclear polymerization to obtain the graphite coated polystyrene particles; To the graphite-coated polystyrene particles, a styrene-based monomer, an initiator and a compound selected from the group consisting of ammonium persulfate, potassium persulfate and sodium persulfate dissolved in a styrene-based monomer or a solution of the styrene-based resin or wax are added. A method for producing expanded polystyrene particles into which graphite is introduced, comprising performing secondary nuclear polymerization and simultaneously adding a blowing agent to form and impregnate a resin protective film on the graphite coating layer. The method of claim 1, wherein the styrenic resin has a weight average molecular weight of 100,000 to 300,000 g / mol. The method according to claim 1, wherein the graphite has a particle size of 0.1 to 20 µm and is used at 0.1 to 25 parts by weight based on 100 parts by weight of polystyrene particles. The method of claim 1, wherein the weight ratio of the graphite-coated polystyrene particles to the styrene monomers during the second nuclear polymerization is 10 to 90: 90 to 10. The method of claim 1, wherein the styrene monomer is selected from the group consisting of styrene, ethyl styrene, dimethyl styrene, para-methyl styrene, alpha-methyl styrene, alpha-ethyl styrene, alpha-propyl styrene and alpha-butyl styrene. How to feature. The method of claim 1, wherein the compound selected from the group consisting of ammonium persulfate, potassium persulfate and sodium persulfate is used in an amount of 0.01 to 0.5 parts by weight based on 100 parts by weight of a styrene monomer. delete The method of claim 1, wherein the amount of blowing agent is used in an amount of 4 to 15 parts by weight based on the total amount of expandable polystyrene particles into which graphite is introduced.

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