JP6214448B2 - Method for producing carbon black-containing composite resin particles - Google Patents

Description

  The present invention relates to a method for producing carbon black-containing composite resin particles. More specifically, the present invention relates to a method for producing carbon black-containing composite resin particles, which can provide a foamed molded article with improved blackness and good appearance and beauty.

Foamed molded articles made of polystyrene resin are widely used as packaging materials and heat insulating materials because they have excellent buffering properties and heat insulating properties and are easy to mold. However, since the impact resistance and flexibility are insufficient, cracks and chips are likely to occur, and it is not suitable, for example, for packaging precision instrument products.
On the other hand, a foam-molded article made of polypropylene resin is excellent in impact resistance and flexibility, but requires a large facility for molding. Also, due to the nature of the resin, it must be transported from the raw material manufacturer to the molding processing manufacturer in the form of pre-expanded particles. Therefore, bulky pre-expanded particles are transported, and there is a problem that the manufacturing cost increases.
Therefore, various polystyrene composite resin particles having the characteristics of the two different resins and foamed molded products using them have been proposed.
Moreover, depending on the use, a black foam molded article may be desired, and carbon black is mainly used as a colorant.

  For example, JP-A-2008-266583 (Patent Document 1) contains a carbon-containing polypropylene resin, 100 to 400 parts by mass of a polystyrene resin with respect to 100 parts by mass of the carbon-containing polypropylene resin, Carbon-containing modified polystyrene resin particles having a polystyrene resin ratio at the center of the particle being 1.2 times or more of the polystyrene resin ratio of the entire particle are disclosed.

  JP 2006-257150 A (Patent Document 2) discloses carbon-containing styrene-modified polyethylene resin particles containing 120 to 400 parts by weight of styrene resin with respect to 100 parts by weight of carbon-containing polyethylene resin. And the polyethylene resin is an ethylene-vinyl acetate copolymer obtained by copolymerizing 5.5 to 8% by weight of vinyl acetate and 94.5 to 92% by weight of ethylene, and 30 to 40% of crystals. Carbon-containing styrene-modified polyethylene resin particles having a degree of conversion and containing 1 to 8 parts by weight of a halogenated flame retardant with respect to 100 parts by weight of carbon-containing styrene-modified polyethylene resin particles are disclosed.

  Furthermore, in Japanese Patent Application Laid-Open No. 2006-111862 (Patent Document 3), a styrene monomer is dispersed in a dispersion liquid in which carbon-containing polyethylene resin particles are dispersed in an aqueous suspension containing a dispersant. A first polymerization initiator which comprises a suspension polymerization in the presence of a polymerization initiator, generates a tertiary alkoxy radical and has a 10-hour half-life temperature of 100 ° C. or less, A method for producing black styrene-modified polyethylene resin particles using a second polymerization initiator that is 2-bis (t-butylperoxy) butane is disclosed.

Japanese Patent Application Laid-Open No. 2009-108237 (Patent Document 4) has an average particle diameter of 0.5 to 10 mm and an apparent density of 0.013 to 0.15 g / cm ^{3 using} a styrene resin as a base resin. A number of depressions having a maximum diameter of 5 to 100 μm are formed on the surface of the foamed particles, and the foamed particles are secondarily foamed under the conditions of a heating steam temperature of 107 ° C. and a heating time of 120 seconds, The secondary foaming rate obtained by dividing the apparent density (g / cm ³ ) of the expanded particles before secondary foaming by the apparent density (g / cm ³ ) of the expanded particles after secondary foaming satisfies a specific formula. Styrenic resin expanded particles are disclosed.

JP 2008-266583 A JP 2006-257150 A JP 2006-111862 A JP 2009-108237 A

  However, the foam molded body obtained by foam-molding the prior art pre-expanded particles as described above is not sufficient in blackness and appearance, and further improvement is required.

  Then, this invention solves said subject, and it is a subject to provide the manufacturing method of carbon black containing composite resin particle which can provide the foaming molding which blackness is improved more, and has a favorable external appearance beauty And

  The inventors of the present invention, as a result of intensive studies to solve the above problems, impregnated and polymerized a carbon black-containing polypropylene resin with a styrene monomer in two stages to obtain carbon black-containing composite resin particles. When manufacturing, by using a water-soluble polymerization inhibitor and an oil-soluble polymerization inhibitor in combination as a polymerization inhibitor, and further adjusting the timing of their addition, the blackness is further improved, and a good appearance It has been found that a foamed molded article having a beautiful appearance can be obtained, and the present invention has been completed.

In the above prior art, there is no description or suggestion of the combined use of a water-soluble polymerization inhibitor and an oil-soluble polymerization inhibitor as a polymerization inhibitor.
That is, Patent Document 1 does not describe the addition of a polymerization inhibitor. Patent Documents 2 and 3 exemplify water-soluble polymerization inhibitors and oil-soluble polymerization inhibitors together with other additives as additives that may be added to the styrene-based monomer. As an additive that may be added to the monomer, a polymerization inhibitor is exemplified together with other additives, but there is no description of a specific polymerization inhibitor, and color unevenness (blackness) of the obtained foamed molded product ) And its appearance and beauty are not described or suggested.

Thus, according to the present invention, there is provided a method for producing carbon black-containing composite resin particles containing 100 to 400 parts by mass of a polystyrene resin with respect to 100 parts by mass of the carbon black-containing polypropylene resin.
(A) a suspension preparation step for obtaining a suspension by dispersing carbon black-containing polypropylene-based resin particles in an aqueous medium containing a dispersant;
(B) Next, a styrene monomer and a polymerization initiator are added to the obtained suspension, and the styrene monomer is heated to a temperature at which the styrene monomer is not substantially polymerized, so that the carbon black-containing polypropylene resin is obtained. A first polymerization step of allowing the particles to absorb the styrene monomer and heating the obtained reaction liquid to polymerize the styrene monomer;
(C) Next, a styrene monomer and a polymerization initiator are further added to the obtained reaction solution, and the styrene monomer is absorbed into the carbon black-containing polypropylene resin particles while the styrene monomer is absorbed. Is included in the suspension or reaction solution up to the step (C), and a water-soluble polymerization inhibitor and an oil-soluble polymer as a polymerization inhibitor. There is provided a method for producing carbon black-containing composite resin particles characterized in that a polymerization inhibitor is present.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the carbon black containing composite resin particle which can provide the foaming molding which blackness is improved more and has a favorable external appearance beauty can be provided.
That is, according to the present invention, the polystyrene on the surface of the carbon black-containing composite resin particles is caused by the polymerization reaction after the styrene monomer absorbed by the polypropylene resin particles during polymerization by the polymerization inhibitor penetrates more inside. The amount of carbon-based resin present (surface polystyrene-based resin amount: surface PS amount) is reduced, and color development due to carbon contained in the carbon black-containing polypropylene-based resin is not suppressed, so the blackness in the resulting foam molded article is improved. It is thought that.

Further, the method for producing the carbon black-containing composite resin particles of the present invention,
(1) A water-soluble polymerization inhibitor is added to the suspension of step (A) or the reaction solution of step (B), and an oil-soluble polymerization inhibitor is added to the reaction solution of step (C).
(2) a 10~400ppm amount of the water-soluble polymerization inhibitor is an aqueous medium, the amount of the oil-soluble polymerization inhibitor is 100~1000ppm against styrene monomer,
(3) The water-soluble polymerization inhibitor is sodium nitrite, and the oil-soluble polymerization inhibitor is 2,2-methylenebis (4-methyl-6-t-butylphenol).

(4) (D) A flame retardant treatment step of adding a flame retardant and a flame retardant aid to the reaction liquid obtained in step (C) and heat treating it to make the carbon black-containing composite resin particles flame retardant. (5) The flame retardant is 1.5 to 6.0% by mass of tri (2,3-dibromopropyl) isocyanate based on the carbon black-containing composite resin particles, and the flame retardant aid is a carbon black-containing composite. The above excellent effect is further exhibited when at least one condition of 0.1 to 2.0 parts by mass of 2,3-dimethyl-2,3-diphenylbutane is satisfied with respect to the resin particles.

The method for producing carbon black-containing composite resin particles (hereinafter also referred to as “composite resin particles”) of the present invention includes carbon black containing 100 to 400 parts by mass of a polystyrene resin with respect to 100 parts by mass of the carbon black-containing polypropylene resin. A method for producing composite resin particles,
(A) a suspension preparation step for obtaining a suspension by dispersing carbon black-containing polypropylene-based resin particles in an aqueous medium containing a dispersant;
(B) Next, a styrene monomer and a polymerization initiator are added to the obtained suspension, and the styrene monomer is heated to a temperature at which the styrene monomer is not substantially polymerized, so that the carbon black-containing polypropylene resin is obtained. A first polymerization step of allowing the particles to absorb the styrene monomer and heating the obtained reaction liquid to polymerize the styrene monomer;
(C) Next, a styrene monomer and a polymerization initiator are further added to the obtained reaction solution, and the styrene monomer is absorbed into the carbon black-containing polypropylene resin particles while the styrene monomer is absorbed. Is included in the suspension or reaction solution up to the step (C), and a water-soluble polymerization inhibitor and an oil-soluble polymer as a polymerization inhibitor. It is characterized by the presence of a polymerization inhibitor.

In the method for producing composite resin particles of the present invention, steps (A) to (C), that is, absorption (impregnation) of styrene monomer into carbon black-containing polypropylene resin particles (hereinafter also referred to as “polypropylene resin particles”). ) And polymerization are repeated twice to obtain composite resin particles.
What is necessary is just to divide | segment suitably the quantity of the styrene-type monomer used for superposition | polymerization so that the mass ratio of polypropylene resin and polystyrene resin may become above.

Further, the method for producing composite resin particles of the present invention is such that a water-soluble polymerization inhibitor and an oil-soluble polymerization inhibitor are present as polymerization inhibitors in the suspension or reaction liquid up to step (C), that is, styrene. In the polymerization of the monomer, the main feature is that a water-soluble polymerization inhibitor and an oil-soluble polymerization inhibitor are used in combination as a polymerization inhibitor.
The addition timing of each polymerization initiator is not particularly limited, but the water-soluble polymerization inhibitor is added to the suspension of step (A) or the reaction solution of step (B), and the oil-soluble polymerization inhibitor is added to the step (C ) Is preferably added to the reaction solution.

  The water-soluble polymerization inhibitor is not particularly limited as long as it is a polymerization inhibitor used in the technical field. For example, sodium nitrite, potassium nitrite, ammonium nitrite, calcium nitrite, silver nitrite, strontium nitrite, nitrous acid Cesium, barium nitrite, magnesium nitrite, lithium nitrite, dicyclohexylammonium nitrite, thiocyanate such as ammonium thiocyanate, zinc thiocyanate, sodium thiocyanate, potassium thiocyanate, aluminum thiocyanate, mercaptoethanol Monothiopropylene glycol, thioglycerol, thioglycolic acid, thiohydroacrylic acid, thiolactic acid, thiomalic acid, thioethanolamine, 1,2-dithioglycerol, 1,3-dithioglycerol Water-soluble sulfur-containing organic compounds, further ascorbic acid, and ascorbic acid sodium. Among them, sodium nitrite is particularly preferred in that less impact on the physical properties after polymerization composite resin particles.

Moreover, it is preferable that the addition amount of a water-soluble polymerization inhibitor is 10-400 ppm with respect to an aqueous medium.
When the addition amount of the water-soluble polymerization inhibitor is less than 10 ppm, a large amount of polymer powder may be generated. On the other hand, when the addition amount of the water-soluble polymerization inhibitor exceeds 400 ppm, the polymerization may not be completed and the monomer may remain. A more preferable addition amount of the water-soluble polymerization inhibitor is 30 to 200 ppm.

  The oil-soluble polymerization inhibitor is not particularly limited as long as it is a polymerization inhibitor used in the technical field. For example, 2,2-methylenebis (4-methyl-6-tert-butylphenol), t-butylhydroquinone, para Methoxyphenol, 2,4-dinitrophenol, t-butylcatechol, sec-propylcatechol, N-methyl-N-nitrosoaniline, N-nitrosophenylhydroxylamine, triphenyl phosphite, tris (nonylphenyl phosphite), triethyl Phosphite, tris (2-ethylhexyl) phosphite, tridecyl phosphite, tris (tridecyl) phosphite, diphenyl mono (2-ethylhexyl) phosphite, diphenyl monodecyl phosphite, diphenyl mono (to Decyl) phosphite, dilauryl hydrogen phosphite, tetraphenyldipropylene glycol diphosphite, tetraphenyltetra (tridecyl) pentaerythritol tetraphosphite and other phenol polymerization inhibitors, nitroso polymerization inhibitors, aromatic amine polymerization Inhibitors, phosphite ester polymerization inhibitors, thioether polymerization inhibitors, and the like. Among these, 2,2-methylenebis (4-methyl) is preferred because it has little effect on the physical properties of the composite resin particles after polymerization. -6-t-butylphenol) is particularly preferred.

Moreover, it is preferable that the addition amount of an oil-soluble polymerization inhibitor is 100-1000 ppm with respect to the styrene-type monomer used at a 2nd polymerization process.
When the addition amount of the oil-soluble polymerization inhibitor is less than 100 ppm, the polypropylene resin particles may not sufficiently absorb the styrene monomer. On the other hand, when the addition amount of the oil-soluble polymerization inhibitor exceeds 1000 ppm, polymerization may be suppressed and particle coalescence may occur. A more preferable addition amount of the oil-soluble polymerization inhibitor is 300 to 700 ppm.

Below, each process is demonstrated.
(1) Step (A): Step of preparing suspension Suspension is obtained by dispersing polypropylene resin particles in an aqueous medium containing a dispersant.

(1-1) Carbon Black-Containing Polypropylene Resin Particles Polypropylene resin particles become core resin particles (also referred to as “seed particles”). For example, after melt-kneading a polypropylene resin with an extruder, the resin is extruded in a strand shape and desired. It can obtain by cutting with the particle diameter of.

The die for obtaining core resin particles of a predetermined size has a resin discharge hole diameter of preferably 0.2 to 1.0 mm, and the land length of the resin flow path is to maintain high dispersibility of the polystyrene resin. The resin temperature at the die inlet of the resin extruded from the extruder is adjusted to 200 to 270 ° C. so that the pressure at the die resin flow path inlet can be maintained at 10 to 20 MPa at 2.0 to 6.0 mm. It is preferable.
Desired core resin particles can be obtained by combining an extruder and a die having the screw structure, extrusion conditions, and underwater cutting conditions.
Moreover, the said core resin particle can contain additives, such as a compatibilizer of a polypropylene resin and a polystyrene resin, a bubble regulator, and an antistatic agent, unless the effect of this invention is impaired.

  The particle diameter of the core resin particles can be adjusted as appropriate according to the average particle diameter of the composite resin particles, and the preferable particle diameter is in the range of 0.4 to 1.5 mm, more preferably 0.4 to 1.0 mm. The average mass is 30 to 90 mg / 100 grains. In addition, examples of the shape include a true spherical shape, an elliptical spherical shape (egg shape), a cylindrical shape, and a prismatic shape.

  The carbon black constituting the polypropylene resin is not particularly limited as long as it is carbon black used in the technical field, and examples thereof include furnace black, ketjen black, channel black, thermal black, acetylene black, graphite, and carbon fiber. Specifically, commercially available products such as those used in the examples can be mentioned.

The polypropylene resin constituting the polypropylene resin is not particularly limited as long as it is a polypropylene resin used in the technical field, and may be a resin obtained by a known polymerization method, which may be cross-linked. For example, polyethylene resins such as branched low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-methyl methacrylate copolymer, and cross-linked products of these polymers And polypropylene resins such as propylene, ethylene-propylene random copolymer, propylene-1-butene copolymer, and ethylene-propylene-butene random copolymer. These low-density polyethylene preferably has a density of 0.90~0.94g / cm ^3, more preferably having a density of 0.91~0.94g / cm ^3, 0.91~0. Most preferably, it has a density of 93 g / cm ³ . Specifically, commercially available products such as those used in the examples can be mentioned.

The composite resin particles of the present invention preferably have a carbon black content of 0.5 to 5.0% by mass.
If the carbon black content of the composite resin pre-expanded particles is less than 0.5% by mass, sufficient blackness may not be imparted to the foamed molded product. On the other hand, if the carbon black content of the composite resin pre-expanded particles exceeds 5.0% by mass, it may be difficult to ensure the flame retardancy of the foam molded article. The carbon black content of the more preferable composite resin particles is 1.5 to 3.0% by mass.

(1-2) Dispersant (suspension stabilizer)
The dispersant is used to stabilize the dispersibility of the styrene monomer droplets and the core resin particles. Therefore, the dispersant is also referred to as a suspension stabilizer.
The dispersant is not particularly limited as long as it is a dispersant used in the technical field, in particular, conventionally used for suspension polymerization of styrene monomers. For example, polyvinyl alcohol, methyl cellulose, polyacrylamide, Examples include water-soluble polymers such as polyvinylpyrrolidone, and poorly soluble inorganic compounds such as tricalcium phosphate, hydroxyapatite, and magnesium pyrophosphate.
Moreover, when using a poorly soluble inorganic compound, an anionic surfactant is used together normally.

  Examples of such anionic surfactants include fatty acid soaps, N-acyl amino acids or salts thereof, carboxylates such as alkyl ether carboxylates, alkylbenzene sulfonates (for example, sodium dodecylbenzenesulfonate), and alkylnaphthalenes. Sulfonates such as sulfonates, dialkylsulfosuccinates, alkylsulfoacetates, α-olefin sulfonates, higher alcohol sulfates, secondary higher alcohol sulfates, alkyl ether sulfates, polyoxyethylene Examples thereof include sulfuric acid ester salts such as alkylphenyl ether sulfates, and phosphoric acid ester salts such as alkyl ether phosphoric acid ester salts and alkyl phosphoric acid ester salts.

(1-3) Water-soluble polymerization inhibitor As described above, the water-soluble polymerization inhibitor is preferably added to the suspension in the step (A) or the reaction solution in the step (B). Specific compounds and their addition amounts are as described above.

(1-4) Stirring In order to obtain a suspension by dispersing the core resin particles in an aqueous medium containing a dispersant, the aqueous medium containing these may be mechanically stirred by a known method.
The stirring conditions, agitation power it takes to stir the aqueous medium 1 m ³ (Pv) is adjusted condition so as to 0.06~0.8kw / m ³ is preferred.
The power required for stirring corresponds to the net energy per unit volume received by the contents in the reaction vessel, and is preferably 0.1 to 0.5 kw / m ³ .

Here, the power required for stirring can be measured in the following manner.
For example, an aqueous medium having a volume V (m ³ ) containing core resin particles and the like is supplied into a polymerization vessel of a polymerization apparatus, and the aqueous medium is stirred by rotating a stirring blade at a predetermined rotational speed. At this time, the rotational driving load necessary to rotate the stirring blade is measured as a current value A ₁ (ampere), and a value obtained by multiplying the current value A ₁ by an effective voltage (volt) is defined as P ₁ (watt). .
On the other hand, when the polymerization vessel is empty, the stirring blade is rotated at the same rotational speed as described above, and the rotational driving load necessary to rotate the stirring blade is measured as a current value A ₂ (ampere). A value obtained by multiplying A ₂ by an effective voltage (volt) is defined as P ₂ (watt).
The required power for stirring is calculated from the obtained measured value and the following equation.
Power required for stirring (Pv) = (P ₁ −P ₂ ) / V

The shape and structure of the polymerization vessel are not particularly limited as long as they are conventionally used for the polymerization of styrene monomers.
The stirring blade is not particularly limited as long as the power required for stirring can be set within a predetermined range.
Specifically, paddle blades such as V-type paddle blades, inclined paddle blades, flat paddle blades, fiddler blades, pull margin blades, turbine blades such as turbine blades and fan turbine blades, propeller blades such as marine propeller blades, etc. Can be mentioned. Of these stirring blades, paddle blades are preferable, and V-type paddle blades, inclined paddle blades, flat paddle blades, Ferdler blades, and pull margin blades are more preferable. The stirring blade may be a single-stage blade or a multi-stage blade.
The size of the stirring blade is not particularly limited as long as the required power for stirring can be set within a predetermined range, and a baffle plate may be provided in the polymerization vessel.
About said stirring, it is common also to the polymerization process of the styrene-type monomer of the process (B) and (C) mentioned later.

(2) Step (B): First polymerization step A styrene monomer and a polymerization initiator are added to the suspension obtained in step (A), and the styrene monomer is not substantially polymerized. The styrenic monomer is absorbed by the polypropylene resin particles by heating to a temperature, and the resulting reaction solution is heated to polymerize the styrenic monomer.

(2-1) Styrene monomer The polystyrene resin (PS) constituting the composite resin particle is not particularly limited as long as it is a resin mainly composed of a styrene monomer used in the technical field, A styrene or a styrene derivative may be used alone or as a copolymer.
Examples of the styrene derivative include α-methyl styrene, vinyl toluene, chlorostyrene, ethyl styrene, isopropyl styrene, dimethyl styrene, bromostyrene, and the like. These styrenic monomers may be used alone or in combination.
In the step (B), those monomers are used.

The polystyrene resin may be a combination of a vinyl monomer copolymerizable with a styrene monomer. Examples of the vinyl monomer include o-divinylbenzene and m-divinyl. Polyfunctional monomers such as benzene, divinylbenzene such as p-divinylbenzene, alkylene glycol di (meth) acrylate such as ethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate; (meth) acrylonitrile, methyl (Meth) acrylate, butyl (meth) acrylate, etc. are mentioned. Among these, polyfunctional monomers are preferable, ethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate having 4 to 16 ethylene units, and divinylbenzene are more preferable, and divinylbenzene, ethylene glycol di ( Particularly preferred is (meth) acrylate. In addition, a monomer may be used independently or may be used together.
Moreover, when using a monomer together, it is preferable that the content is set so that it may become the quantity (for example, 50 mass% or more) which a styrene-type monomer becomes a main component.
In the present invention, “(meth) acryl” means “acryl” or “methacryl”.

The composite resin particle of the present invention contains 100 to 400 parts by mass of polystyrene resin with respect to 100 parts by mass of polypropylene resin.
If the polystyrene-based resin is less than 100 parts by mass, the ability to hold the foaming agent of the composite resin particles may be lowered, and high foaming may not be achieved, and the rigidity of the foamed molded product may be lowered. On the other hand, when the polystyrene resin exceeds 400 parts by mass, the polystyrene resin is not sufficiently impregnated inside the polypropylene resin particles, and a large amount of polystyrene resin is present on the surface of the composite resin particles, and white particles are generated. This is not preferable. In addition, it is not preferable because not only the crack resistance of the foamed molded product is lowered but also the chemical resistance may be lowered.
Preferably, the polystyrene resin is 120 to 300 parts by mass with respect to 100 parts by mass of the polypropylene resin.
What is necessary is just to divide | segment suitably the quantity of the styrene-type monomer used for superposition | polymerization so that the mass ratio of polypropylene resin and polystyrene resin may become above.

(2-2) Polymerization initiator The polymerization initiator is not particularly limited as long as it is a dispersant used in the technical field, in particular, as long as it is conventionally used for suspension polymerization of a styrene monomer. Benzoyl peroxide, lauryl peroxide, t-butyl peroxybenzoate, t-butyl peroxy-2-ethylhexanoate, t-butyl peroxide, t-butyl peroxypivalate, t-butyl peroxyisopropyl carbonate T-butyl peroxyacetate, 2,2-bis (t-butylperoxy) butane, t-butylperoxy-3,3,5-trimethylhexanoate, di-t-butylperoxyhexahydroterephthalate, 2,2-di-t-butylperoxybutane, di-t-hexyl peroxide, di Examples thereof include organic peroxides such as cumyl peroxide and azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile. These may be used alone or in combination, but it is preferable to use a plurality of types of polymerization initiators having a decomposition temperature of 60 to 130 ° C. for obtaining a half-life of 10 hours.

(2-3) First polymerization In order to polymerize the styrene monomer by causing the polypropylene resin particles to absorb the styrene monomer and heating the obtained reaction liquid, for example, It is sufficient to process as follows.
First, a reaction liquid is obtained by heating to a temperature at which the styrene monomer is not substantially polymerized and impregnating the polypropylene resin particles with the styrene monomer.
The temperature at which the styrene monomer is not substantially polymerized may be appropriately set according to the type and blending ratio of the raw material resin, the physical properties of the composite resin particles to be produced, etc., but is usually 45 to 80 ° C.
The time for impregnating the styrene monomer inside the polypropylene resin particles is suitably 30 minutes to 2 hours. When polymerization proceeds before sufficient impregnation, polystyrene polymer powder is likely to be formed.
The production method of the present invention has an effect of suppressing the formation of the polymer powder and coalesced particles.

Next, when the melting point of the polypropylene resin in the polypropylene resin particles is T ° C., the obtained reaction liquid is heated to a temperature of (T−10) ° C. to (T + 20) ° C. Is polymerized.
When the polymerization temperature is less than (T-10) ° C., there are few polystyrene-based resins in the center of the obtained resin particles, and resin particles and foamed molded articles showing good blackness and mechanical properties may not be obtained. is there. On the other hand, if the polymerization temperature exceeds (T + 20) ° C., the polymerization starts before the styrene monomer is sufficiently impregnated with the polypropylene resin particles, so that the resin particles exhibit good blackness and mechanical properties. In some cases, foam molded articles cannot be obtained.
For example, when the melting point of the polypropylene resin is 140 ° C, the polymerization temperature is 130 to 160 ° C.

Other polymerization conditions may be appropriately set depending on the composition of the composite resin particles to be produced.
The polymerization time per polymerization is usually about 1 to 6 hours, and preferably 1.5 to 3 hours, considering the quality and productivity of the resulting composite resin particles.
Moreover, the pressure in the system at the time of polymerization is usually about 0.05 to 0.5 MPa, and preferably 0.1 to 0.3 MPa in consideration of safety in terms of workability of polymerization stability.
The polymerization can be performed after the monomer is absorbed into the core resin particles or while the monomer is absorbed into the core resin particles. The amount of the monomer and the amount of polystyrene resin obtained after polymerization are almost the same.
In addition, the temperature increase or decrease time to the set temperature of each process varies depending on the outside air temperature, but when converted in the entire section from the start temperature to the target temperature, 0.3 ° C / min to 3.0 ° C / min is appropriate.
In particular, if the temperature rise rate is too high, polymerization starts before the styrene monomer is sufficiently impregnated with the polypropylene resin particles, so resin particles and foam molding exhibiting good blackness and mechanical properties. The body may not be obtained. On the other hand, if the rate of temperature increase is too slow, the process becomes longer and the manufacturing cost is increased. More preferably, it is 0.4 degreeC / min-2.5 degreeC / min.

(2-4) Other Additives The composite resin particles of the present invention include a plasticizer, a binding inhibitor, a cell regulator, a flame retardant and a flame retardant aid, which will be described later, within a range that does not impair physical properties. Additives such as a crosslinking agent, a filler, a lubricant, a fusion accelerator, an antistatic agent, and a spreading agent may be added.
These additives may be added to the reaction solution in the polymerization step.

The composite resin particles can contain a plasticizer having a boiling point exceeding 200 ° C. under 1 atm in order to maintain good foam moldability even when the pressure of water vapor used at the time of heat foaming is low.
Examples of the plasticizer include glycerin fatty acid esters such as phthalic acid ester, glycerin diacetomonolaurate, glycerin tristearate and glycerin diacetomonostearate, adipic acid esters such as diisobutyl adipate, and plasticizers such as coconut oil. .
The content of the plasticizer in the composite resin particles is preferably 0.1 to 3.0% by mass.

Examples of the binding inhibitor include calcium carbonate, silica, zinc stearate, aluminum hydroxide, ethylene bis stearamide, tricalcium phosphate, and dimethyl silicon.
Examples of the air conditioner include ethylene bis stearamide and polyethylene wax.
As a crosslinking agent, 2,2-di-t-butylperoxybutane, 2,2-bis (t-butylperoxy) butane, dicumyl peroxide, 2,5-dimethyl-2,5-di-t -Organic peroxides such as butylperoxyhexane.
Examples of the filler include silicon dioxide produced synthetically or naturally.

Examples of the lubricant include paraffin wax and zinc stearate.
Examples of the fusion accelerator include stearic acid, stearic acid triglyceride, hydroxystearic acid triglyceride, sorbitan stearate, and polyethylene wax.
Examples of the antistatic agent include polyoxyethylene alkylphenol ether, stearic acid monoglyceride, polyethylene glycol and the like.
Examples of the spreading agent include polybutene, polyethylene glycol, and silicone oil.

(3) Step (C): Second polymerization step A styrene monomer and a polymerization initiator are further added to the reaction solution obtained in step (B), and the styrene monomer is absorbed into the polypropylene resin. Then, the styrene monomer is polymerized to obtain composite resin particles.

(3-1) Styrene monomer The same as (2) and (2-1) in the previous section.
(3-2) Polymerization initiator The same as (2) and (2-2) in the previous section.
(3-3) Oil-soluble polymerization inhibitor As described above, the oil-soluble polymerization inhibitor is preferably added to the reaction solution in step (C). Specific compounds and their addition amounts are as described above.

(3-4) Second polymerization In order to polymerize the styrene monomer while allowing the polypropylene resin to absorb the styrene monomer, for example, the melting point of the polypropylene resin in the polypropylene resin particles is set to T When it is set to ° C, the resulting reaction liquid is heated to a temperature of (T-25) to (T + 15) ° C to polymerize the styrene monomer.
When the polymerization temperature is less than (T-25) ° C., there are few polystyrene-based resins in the center of the obtained resin particles, and resin particles and foamed molded articles showing good blackness and mechanical properties may not be obtained. is there. On the other hand, if the polymerization temperature exceeds (T + 15) ° C., the polymerization starts before the styrene monomer is sufficiently impregnated with the polypropylene resin particles, so that the resin particles exhibit good blackness and mechanical properties. In some cases, foam molded articles cannot be obtained.
For example, when the melting point of the polypropylene resin is 140 ° C., the polymerization temperature is 115 to 155 ° C. What is necessary is just to process according to said 1st superposition | polymerization about other superposition | polymerization conditions.

Next, the reaction solution obtained in the second polymerization step is long at a temperature of (T-10) ° C. to (T + 20) ° C. when the melting point of the polypropylene resin in the polypropylene resin particles is T ° C. It is preferred to hold for a time, ie anneal.
Here, the necessity of annealing will be described.
In the process up to the annealing process, the styrene monomer and polymerization initiator absorbed in the core resin particles have not completely completed the reaction, and there are not a few unreacted substances inside the composite resin particles. Existing. Therefore, when a foamed molded product is obtained using composite resin particles obtained without annealing, the mechanical properties and heat resistance of the foamed molded product are degraded due to the influence of low molecular weight unreacted materials such as styrene monomers. And odor caused by volatile unreacted materials becomes a problem. Therefore, by introducing an annealing step, it is possible to secure a time for the unreacted material to undergo a polymerization reaction, and to remove the remaining unreacted material so as not to affect the physical properties of the foam molded article.

The composite resin particles of the present invention preferably have an average particle diameter of 0.5 to 3.0 mm.
When the average particle diameter of the composite resin particles is less than 0.5 mm, high foamability may not be obtained. On the other hand, when the average particle diameter of the composite resin particles exceeds 3.0 mm, the pre-expanded particles may not be sufficiently filled during the molding process. More preferably, the average particle size of the composite resin particles is 0.5 to 2.0 mm.

(4) Process (D): Flame retardant process The manufacturing method of the composite resin particle of this invention adds a flame retardant and a flame retardant adjuvant to the reaction liquid obtained at the process (C), heat-processes, and is composite. It is preferable to further include a flame retardant treatment step for making the resin particles flame retardant. Conditions such as the temperature and time of the heat treatment may be appropriately set depending on the flame retardant used, the flame retardant aid and the amount added.

(4-1) Flame retardant and flame retardant auxiliary Examples of the flame retardant include tri (2,3-dibromopropyl) isocyanate, bis [3,5-dibromo-4- (2,3-dibromopropoxy) phenyl] sulfone, Tetrabromocyclooctane, hexabromocyclododecane, trisdibromopropyl phosphate, tetrabromobisphenol A, tetrabromobisphenol A-bis (2,3-dibromo-2-methylpropyl ether), tetrabromobisphenol A-bis (2,3 -Brominated flame retardants such as -dibromopropyl ether). Among these, tri (2,3-dibromopropyl) isocyanate is particularly preferable in that it can be efficiently flame retardant.
Examples of the flame retardant aid include organic peroxides such as 2,3-dimethyl-2,3-diphenylbutane, 3,4-dimethyl-3,4-diphenylhexane, dicumyl peroxide and cumene hydroperoxide. It is done.

If the addition amount of the flame retardant is less than 1.5 parts by mass, the flame retardancy may not be sufficiently imparted. On the other hand, when the addition amount of the flame retardant exceeds 6.0 parts by mass, the heat resistance of the foamed molded product may be lowered. The addition amount of a preferable flame retardant is 2.0-5.0 mass parts with respect to 100 mass parts of composite resin pre-expanded particles.
If the addition amount of the flame retardant aid is less than 0.1 parts by mass, the flame retardancy may not be sufficiently imparted. On the other hand, when the addition amount of the flame retardant aid exceeds 2.0 parts by mass, the heat resistance of the foamed molded product may be lowered. The addition amount of a preferable flame retardant aid is 1.0 to 2.0 parts by mass with respect to 100 parts by mass of the composite resin pre-expanded particles.

  Therefore, in the step (D), the flame retardant is 1.5 to 6.0% by mass of tri (2,3-dibromopropyl) isocyanate based on the composite resin particles, and the flame retardant aid is based on the composite resin particles. 0.1 to 2.0 parts by mass of 2,3-dimethyl-2,3-diphenylbutane is preferred.

(5) Foam molded body The composite resin particles of the present invention have a carbon black content of polypropylene resin particles of 0.5 to 5% by mass, and the composite resin particles are impregnated with a foaming agent by a known method. When pre-foamed to obtain composite resin pre-foamed particles, the resulting composite resin pre-foamed particles were subjected to in-mold foam molding,
In color difference measurement based on JIS Z8729-2004 “Color Display Method—L ^* a ^* b ^* Color System”, the following formula:
ΔE ′ = L ^* + | a ^* | + | b ^* | <30
(Where ΔE ′ is blackness, L ^* is lightness, a ^* and b ^* are color coordinates)
Resin particles that satisfy the relational expression shown below, satisfy the relation that the standard deviation σ of ΔE ′ is σ <1.0, and have a surface polystyrene-based resin amount of 5 to 50% by mass. Is preferred.

(5-1) Blackness A method for measuring blackness will be described in detail in Examples.
When the blackness ΔE ′ is less than 30, it is good, and when the blackness ΔE ′ exceeds 30, it is bad.
Further, when the standard deviation σ of the blackness ΔE ′ is less than 1.0, it is good, and when the standard deviation σ exceeds 1.0, it is bad.

(5-2) Surface Polystyrene Resin Amount If the surface polystyrene resin amount of the foamed molded product is less than 5% by mass, appearance defects such as unevenness in blackness may occur. On the other hand, if the surface polystyrene-based resin content of the foamed molded product exceeds 50% by mass, sufficient blackness may not be imparted, and at the same time chemical resistance and impact resistance may be lowered.
The surface polystyrene-type resin amount of a preferable foaming molding is 5-30 mass%.

EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, the following Examples are only illustrations of this invention and this invention is not limited only to the following Examples.
In Examples and Comparative Examples, the polymerization state and the obtained foamed molded products were evaluated as follows.

"Polymerized powder"
The amount (g) of polymer powder produced as a by-product during polymerization is weighed, and the ratio to the total amount of the polymer is calculated (mass%), and then evaluated according to the following criteria.
The polymer powder is filtered and dried from the reaction solution using filter paper, and separated from the composite resin particles.
◎ (very good): less than 0.1% by mass ○ (good): 0.1% by mass or more and less than 0.15% by mass × (defect): 0.15% by mass or more

"Mixed particles"
The coalesced particles (g) produced during the polymerization are weighed, and the ratio to the total amount of the polymer is calculated (mass%), and then evaluated according to the following criteria.
Separation is carried out by sieving the product after polymerization using a sieve with an aperture that normally passes through the composite resin particles that are produced and particles through which two or more resin particles are coalesced. To do.
◎ (very good): less than 1.5% by mass ○ (good): 1.5% by mass or more and less than 2.5% by mass × (defect): 2.5% by mass or more

“Amount of surface polystyrene resin (PS) in the molded product (%)”
The absorbance ratio (D698 / D1376) of the surface of the molded body is measured as follows.
In addition, each light absorbency obtained from an infrared absorption spectrum says the height of the peak originating in the vibration of each resin component contained in a molded object.
Ten randomly selected compact samples are subjected to surface analysis by infrared spectroscopic ATR measurement to obtain infrared absorption spectra. In this analysis, an infrared absorption spectrum in a depth range of several μm (about 2 μm) from the surface of the molded body is obtained.
The individual absorbance ratio (D698 / D1376) is calculated from each infrared absorption spectrum, and the arithmetic average of the individual absorbance ratios calculated for the surface layer is defined as the absorbance ratio.
The polystyrene resin ratio (% by mass) is calculated from the absorbance ratio (D698 / D1376) based on a calibration curve described later.
The absorbances D698 and D1376 are measured under the following conditions using a measuring device manufactured by Nicolet; trade name “Fourier Transform Infrared Spectrometer MAGNA 560” and “Thunder Dome” manufactured by Spectra-Tech as an ATR accessory.

(Measurement condition)
High refractive index crystal seed: Ge (germanium)
Incident angle: 45 ° ± 1 °
Measurement area: 4,000 cm ^{-1 to} 675 cm ^-1
Fractional dependence of measurement depth: No correction Number of reflections: 1 Detector: DTGS KBr
Resolution: 4cm ^-1
Number of integrations: 32 times Others: An infrared absorption spectrum is measured under the above conditions without contacting the sample, and the measured infrared absorption spectrum is used as the background. When measuring the sample, the measurement data is processed so that the background does not contribute to the measurement spectrum. In the ATR method, the intensity of the infrared absorption spectrum changes depending on the degree of adhesion between the sample and the high refractive index crystal. Therefore, the maximum load that can be applied by the “Thunder Dome” of the ATR accessory is applied to perform the measurement with a substantially uniform contact degree.

About the infrared absorption spectrum obtained on the above conditions, the peak process is performed as follows and each light absorbency is calculated | required.
The absorbance D698 at 698 cm ⁻¹ obtained from the infrared absorption spectrum is an absorbance corresponding to the absorption spectrum derived from the out-of-plane vibration of the benzene ring contained in the polystyrene resin. In this absorbance measurement, peak separation is not performed even when other absorption spectra overlap at 698 cm ⁻¹ . Absorbance D698 is a straight line connecting the 1,280Cm ^-1 and 860 cm ^-1 as a baseline, means the maximum absorbance between 710 cm ^-1 and 685cm ^-1.
Further, the absorbance D1376 at 1,376 cm ⁻¹ obtained from the infrared absorption spectrum is the absorbance corresponding to the absorption spectrum derived from the symmetrical bending vibration of CH ₃ of —C—CH ₃ hydrocarbon contained in the polypropylene resin. It is. In this absorbance measurement, peak separation is not performed even when other absorption spectra overlap at 1376 cm ⁻¹ . Absorbance D1376 is a straight line connecting the 1,414Cm ^-1 and 1,340Cm ^-1 as a baseline, means the maximum absorbance between 1,400Cm ^-1 and 1,350cm ^-1.

As a method for obtaining the composition ratio of polystyrene resin and polypropylene resin from the absorbance ratio, a plurality of types of standard samples are prepared by uniformly mixing polystyrene resin and polypropylene resin at a predetermined composition ratio, and each standard is prepared. The sample is subjected to surface analysis by ATR infrared spectroscopy to obtain an infrared absorption spectrum. The absorbance ratio is calculated from each of the obtained infrared absorption spectra. A calibration curve is drawn by taking the composition ratio (polystyrene resin ratio (% by mass) in the standard sample) on the vertical axis and the absorbance ratio (D698 / D1376) on the horizontal axis. Based on the calibration curve, the composition ratio of the polystyrene resin and the polypropylene resin in the molded product produced by the method of the present invention is determined from the absorbance ratio of the molded product produced by the method of the present invention.
The calibration curve is approximated by the following equation.
・ When D698 / D1376 <2.35,
Y = −2.5119X ₁ ² + 22.966X ₁
If 10.0> (D698 / D1376)> 2.35,
Y = 27.591Ln (X ₁₎ +16.225
X ₁ = (D698 / D1376), Y = polystyrene resin amount (%)

"Folding multiple of foamed molded product"
The expansion ratio of the foamed molded product is measured as follows.
A test piece of 10 cm × 10 cm × 5 cm (volume V) is cut out from the obtained foamed molded article, and its weight W is weighed at the second decimal place.
From the weight W of the obtained foamed molded product and the volume V of the foamed molded product, the expansion factor (times) is calculated by the following formula.
Foam multiple of the foamed molded product (times) = 1 / (bulk density of the foamed molded product) = 1 / (W / V) = V / W

“Blackness ΔE ′ of foam molded product and its standard deviation σ”
The blackness ΔE ′ of the foamed molded product is evaluated by color difference measurement based on JIS Z8729-2004 “Color Display Method—L ^* a ^* b ^* Color System”.
For the measurement, a color difference meter (manufactured by Konica Minolta, model: CR-400) and a standard white plate calibration plate (Y: 94.3, x: 0.3144, y: 0.3208) are used in accordance with the standard.
Specifically, from any 10 points on the vertical and horizontal surfaces of the foamed molded product, the measurement area was measured as φ8 mm, and the average value was calculated from the lightness L ^* value, color coordinate a ^* value, and b ^* value. ΔE ′ is calculated as the degree.
ΔE ′ = L ^* + | a ^* | + | b ^* |
From the obtained ΔE ′, the blackness is evaluated according to the following criteria.
ΔE ′ <30: Good (◯)
ΔE ′ ≧ 30: Defect (×)
Further, in order to evaluate the color unevenness of the foamed molded product, the standard deviation σ of the blackness ΔE ′ at the 10 arbitrary measurement points is calculated.
σ <1.0: Good (◯)
σ ≧ 1.0: Defect (×)

"Appearance of foam molding"
The appearance (color texture / color unevenness / novi) of the foamed molded product is evaluated according to the following criteria.
A (very good): There is no composite resin pre-expanded particle of ΔE ′ ≧ 30 per 100 cm ^{2 of the} molding surface, and the molding surface is uniformly molded and smooth. ○ (Good): per 100 cm ^{2 of the} molding ΔE ′ ≧ 30 composite resin pre-expanded particles are not more than one, and the surface of the molded body is uniformly molded and smooth Δ (partially defective): ΔE ′ ≧ 30 composite resin per 100 cm ^{2 of the} molded body The number of pre-expanded particles is 1 or more and less than 2, and the surface of the molded body is uniformly formed and is smooth. X (defect): 2 or more composite resin pre-expanded particles of ΔE ′ ≧ 30 per 100 cm ^{2 of the} molded body Or a gap between the pre-foamed composite resin particles and an aggregate of polystyrene resin are confirmed on the surface of the molded body.

Example 1
(Preparation of core resin particles)
Polypropylene resin (manufactured by Prime Polymer Co., Ltd., trade name “Prime Polypro (film)”, brand name “F-744NP”, melting point 140 ° C.) 1,900 g, and furnace black (manufactured by Mitsubishi Chemical Corporation, 100 g of trade name “Mitsubishi Carbon Black” and brand “Intermediate Color (MCF) # 900”) were put into a tumbler mixer and mixed for 7 minutes.
Next, the obtained mixture is supplied to an extruder (Toshiba Machine Co., Ltd., model: SE-65), heated and melted, extruded, and granulated into pellets by an underwater cut method, so that furnace black is added to polypropylene resin. A spherical polypropylene resin particle containing 5% by mass of was obtained. The resin particles at this time were adjusted to 80 mg per 100 particles and an average particle diameter of about 1 mm.
In the following Examples / Comparative Examples, polymerization, flame retardancy, and production of expandable composite resin particles were performed at a temperature rising / falling rate of 1 ° C./min.

(Preparation of carbon black-containing composite resin particles)
(Preparation of suspension)
Next, 760 g of the obtained polypropylene resin particles were put into a 5 liter autoclave with a stirrer (manufactured by Nitto Koatsu Co., Ltd.), and further 2,000 g of pure water as an aqueous medium and 20 g of magnesium pyrophosphate as a dispersant. Then, 0.5 g of sodium dodecylbenzenesulfonate as a surfactant and 150 mg of sodium nitrite as a water-soluble polymerization inhibitor (75 ppm with respect to the aqueous medium) were added. The resulting mixture was stirred and suspended in an aqueous medium, held at 25 ° C. for 10 minutes, and then heated to 70 ° C. to obtain a suspension.

(First polymerization)
Next, 320 g of a styrene monomer prepared by dissolving 0.7 g of dicumyl peroxide as a polymerization initiator in advance is added dropwise to the resulting suspension over 30 minutes to obtain a polypropylene resin. The particles were allowed to absorb styrene monomer. Next, the temperature of the reaction solution was raised to 140 ° C. and held at the same temperature for 2 hours to polymerize the styrene monomer in the polypropylene resin particles.

(Second polymerization)
Next, the reaction solution was cooled (cooled) to 125 ° C. which was 15 ° C. lower than the melting point of the polypropylene resin in the polypropylene resin particles, and 2.7 g of sodium dodecylbenzenesulfonate as a surfactant was added to the reaction solution. Thereafter, 3.6 g of dicumyl peroxide as a polymerization initiator and 387 mg of 2,2-methylenebis (4-methyl-6-tert-butylphenol) as an oil-soluble polymerization inhibitor (450 ppm with respect to the styrene monomer) 860 g of a styrene monomer prepared by dissolving the styrene monomer was dropped over 4 hours, and the styrene monomer was polymerized while being absorbed by polypropylene resin particles. After completion of dropping, the reaction solution was held at the same temperature for 1 hour, and then the reaction solution was heated to 140 ° C. and held at the same temperature for 3 hours to complete the polymerization, thereby obtaining composite resin particles.

(Flame retardant)
Next, the temperature of the reaction solution is lowered (cooled) to 60 ° C., and 60 g of tri (2,3-dibromopropyl) isocyanate (manufactured by Nippon Kasei Co., Ltd.) as a flame retardant and a flame retardant aid in the reaction solution. Of 2,3-dimethyl-2,3-diphenylbutane (manufactured by Kayaku Akzo Corporation) was charged. After the addition, the temperature of the reaction solution was raised to 140 ° C. and held at the same temperature and stirring for 4 hours to flame-treat the composite resin particles.
Next, after the reaction solution was cooled to 25 ° C., the dispersant was removed by acid washing using a 20% aqueous hydrochloric acid solution, and 2,000 g of composite resin particles were taken out from the autoclave.

(Production of expandable composite resin particles)
Next, 2,000 g of the taken out composite resin particles and 2,000 g of water were again put into an autoclave with a capacity of 5 liters equipped with a stirrer, and further 300 g of butane (normal butane: isobutane = 7: 3) as a blowing agent. Injected. After the injection, the mixture was heated to 70 ° C. and kept at the same temperature and stirring for 4 hours.
Thereafter, the mixture was cooled to 25 ° C., the composite resin particles were taken out from the autoclave, dehydrated and dried, and 2,100 g of expandable composite resin particles were obtained.

(Preparation of composite resin pre-expanded particles)
Next, 1,000 g of the obtained expandable composite resin particles was put into a pre-foaming machine having a capacity of 40 liters (manufactured by Kasahara Kogyo Co., Ltd., model: PSX40), and steam with a gauge pressure of 0.04 MPa was introduced into the can The mixture was then heated and pre-expanded to a bulk expansion ratio of 42 times to obtain composite resin pre-expanded particles.

(Production of composite resin foam molding)
Next, the pre-expanded particles obtained were left at 25 ° C. for 1 day, and then filled into a cavity of a mold having an internal dimension of 400 mm long × 300 mm wide × 30 mm thick. The steam was introduced for 50 seconds and heated, and then cooled until the maximum surface pressure of the foamed molded product was reduced to 0.001 MPa to obtain a foamed molded product.
Using the obtained composite resin foam molded article, the expansion ratio, blackness and appearance were evaluated. The blackness was good and the color variation was small.
The obtained results are shown in Table 1 together with the raw materials and production conditions.

(Example 2)
2. 387 mg of 2,2-methylenebis (4-methyl-6-tert-butylphenol) as an oil-soluble polymerization inhibitor in (second polymerization) was changed to 568 mg (660 ppm) with respect to styrene monomer. Except for the above, composite resin pre-foamed particles and foamed molded products were obtained in the same manner as in Example 1, and they were evaluated.
The obtained results are shown in Table 1 together with the raw materials and production conditions.

(Example 3)
(Preparation of suspension) As in Example 1, except that 150 mg of sodium nitrite (75 ppm with respect to the aqueous medium) as the water-soluble polymerization inhibitor was changed to 335 mg (168 ppm with respect to the aqueous medium). The composite resin pre-expanded particles and the expanded molded body were obtained and evaluated.
The obtained results are shown in Table 1 together with the raw materials and production conditions.

Example 4
(Preparation of suspension) As in Example 1, except that 150 mg of sodium nitrite (75 ppm with respect to the aqueous medium) as the water-soluble polymerization inhibitor was changed to 64 mg (32 ppm with respect to the aqueous medium). The composite resin pre-expanded particles and the expanded molded body were obtained and evaluated.
The obtained results are shown in Table 1 together with the raw materials and production conditions.

(Example 5)
282 mg (based on styrene monomer) of 387 mg (450 ppm relative to styrene monomer) 2,2-methylenebis (4-methyl-6-tert-butylphenol) as an oil-soluble polymerization inhibitor in (second polymerization) The composite resin pre-foamed particles and the foamed molded product were obtained and evaluated in the same manner as in Example 1 except that the content was changed to 328 ppm).
The obtained results are shown in Table 1 together with the raw materials and production conditions.

(Example 6)
Except for the following steps, composite resin pre-expanded particles and a foam-molded product were obtained in the same manner as in Example 1 and evaluated.
The obtained results are shown in Table 1 together with the raw materials and production conditions.
(Preparation of suspension)
600 g of polypropylene resin particles obtained in the same manner as in Example 1 (preparation of core resin particles) was placed in a 5 liter autoclave (manufactured by Nitto Koatsu Co., Ltd.) equipped with a stirrer, and further purified as an aqueous medium. 2,000 g of water, 20 g of magnesium pyrophosphate as a dispersant, 0.5 g of sodium dodecylbenzenesulfonate as a surfactant, and 150 mg of sodium nitrite as a water-soluble polymerization inhibitor (75 ppm based on an aqueous medium) were added. . The resulting mixture was stirred and suspended in an aqueous medium, held at 25 ° C. for 10 minutes, and then heated to 70 ° C. to obtain a suspension.

(First polymerization)
Next, 252 g of a styrene monomer prepared by dissolving 0.5 g of dicumyl peroxide as a polymerization initiator in advance is added dropwise to the resulting suspension over 30 minutes to obtain a polypropylene resin. The particles were allowed to absorb styrene monomer. Next, the temperature of the reaction solution was raised to 140 ° C. and held at the same temperature for 2 hours to polymerize the styrene monomer in the polypropylene resin particles.

(Second polymerization)
Next, the reaction solution was cooled (cooled) to 125 ° C. which was 15 ° C. lower than the melting point of the polypropylene resin in the polypropylene resin particles, and 2.7 g of sodium dodecylbenzenesulfonate as a surfactant was added to the reaction solution. Thereafter, 4.2 g of dicumyl peroxide as a polymerization initiator and 517 mg of 2,2-methylenebis (4-methyl-6-tert-butylphenol) as an oil-soluble polymerization inhibitor (450 ppm with respect to the styrene monomer) 1148 g of the styrene monomer prepared by dissolving the styrene monomer was dropped over 4 hours, and the styrene monomer was polymerized while being absorbed by the polypropylene resin particles. After completion of dropping, the reaction solution was held at the same temperature for 1 hour, and then the reaction solution was heated to 140 ° C. and held at the same temperature for 3 hours to complete the polymerization, thereby obtaining composite resin particles.

(Example 7)
Except for the following steps, composite resin pre-expanded particles and a foam-molded product were obtained in the same manner as in Example 1 and evaluated.
The obtained results are shown in Table 1 together with the raw materials and production conditions.
(Preparation of suspension)
1000 g of polypropylene resin particles obtained in the same manner as in Example 1 (preparation of core resin particles) was placed in a 5 liter autoclave (manufactured by Nitto Koatsu Co., Ltd.) equipped with a stirrer, and further purified as an aqueous medium. 2,000 g of water, 20 g of magnesium pyrophosphate as a dispersant, 0.5 g of sodium dodecylbenzenesulfonate as a surfactant, and 150 mg of sodium nitrite as a water-soluble polymerization inhibitor (75 ppm based on an aqueous medium) were added. . The resulting mixture was stirred and suspended in an aqueous medium, held at 25 ° C. for 10 minutes, and then heated to 70 ° C. to obtain a suspension.

(First polymerization)
Next, 420 g of a styrene monomer prepared by dissolving 0.8 g of dicumyl peroxide as a polymerization initiator in advance is added dropwise to the resulting suspension over 30 minutes to obtain a polypropylene resin. The particles were allowed to absorb styrene monomer. Next, the temperature of the reaction solution was raised to 140 ° C. and held at the same temperature for 2 hours to polymerize the styrene monomer in the polypropylene resin particles.

(Second polymerization)
Next, the reaction solution was cooled (cooled) to 125 ° C. which was 15 ° C. lower than the melting point of the polypropylene resin in the polypropylene resin particles, and 2.7 g of sodium dodecylbenzenesulfonate as a surfactant was added to the reaction solution. Thereafter, 3.0 g of dicumyl peroxide as a polymerization initiator and 261 mg of 2,2-methylenebis (4-methyl-6-t-butylphenol) as an oil-soluble polymerization inhibitor (450 ppm with respect to the styrene monomer) 580 g of a styrene monomer prepared by dissolving the styrene monomer was dropped over 4 hours, and the styrene monomer was polymerized while being absorbed by polypropylene resin particles. After completion of dropping, the reaction solution was held at the same temperature for 1 hour, and then the reaction solution was heated to 140 ° C. and held at the same temperature for 3 hours to complete the polymerization, thereby obtaining composite resin particles.

(Example 8)
Example except that addition of oil-soluble polymerization inhibitor in (second polymerization) was 144 mg (450 ppm with respect to styrene monomer) with respect to 320 g of styrene monomer in (first polymerization). In the same manner as in No. 1, composite resin pre-foamed particles and a foam-molded product were obtained and evaluated.
The obtained results are shown in Table 1 together with the raw materials and production conditions.

Example 9
Except that the (flame retardant) step was not carried out, the composite resin pre-foamed particles and the foamed molded product were obtained and evaluated in the same manner as in Example 1.
The obtained results are shown in Table 1 together with the raw materials and production conditions.

(Comparative Example 1)
In the same manner as in Example 1 except that no water-soluble polymerization inhibitor was added in (Preparation of suspension) and no oil-soluble polymerization inhibitor was added in (Second polymerization), Expanded particles and a molded foam were obtained and evaluated.
The obtained results are shown in Table 1 together with the raw materials and production conditions.

(Comparative Example 2)
Composite resin pre-expanded particles and expanded molded articles were obtained and evaluated in the same manner as in Example 1 except that the oil-soluble polymerization inhibitor was not added in (second polymerization).
The obtained results are shown in Table 1 together with the raw materials and production conditions.

(Comparative Example 3)
In the same manner as in Example 1 except that no water-soluble polymerization inhibitor was added in (Preparation of suspension), composite resin pre-foamed particles and foamed molded products were obtained and evaluated.
The obtained results are shown in Table 1 together with the raw materials and production conditions.

  From the results of Table 1, in the method for producing composite resin particles of the present invention (Examples 1 to 9), a water-soluble polymerization inhibitor is used particularly in the first polymerization step, and an oil-soluble polymerization inhibitor is used in the second polymerization step. In Examples 1 to 7 and 9 used, the formation of polymer powder and coalesced particles was suppressed, and the molded foam produced using the obtained composite resin particles was improved in blackness and good. It can be seen that it has a beautiful appearance.

Claims (6)

It is a method for producing carbon black-containing composite resin particles containing 100 to 400 parts by mass of a polystyrene resin with respect to 100 parts by mass of a carbon black-containing polypropylene resin.
(A) a suspension preparation step for obtaining a suspension by dispersing carbon black-containing polypropylene-based resin particles in an aqueous medium containing a dispersant;
(B) Next, a styrene monomer and a polymerization initiator are added to the obtained suspension, and the styrene monomer is heated to a temperature at which the styrene monomer is not substantially polymerized, so that the carbon black-containing polypropylene resin is obtained. A first polymerization step of allowing the particles to absorb the styrene monomer and heating the obtained reaction liquid to polymerize the styrene monomer;
(C) Next, a styrene monomer and a polymerization initiator are further added to the obtained reaction solution, and the styrene monomer is absorbed into the carbon black-containing polypropylene resin particles while the styrene monomer is absorbed. Is included in the suspension or reaction solution up to the step (C), and a water-soluble polymerization inhibitor and an oil-soluble polymer as a polymerization inhibitor. A method for producing carbon black-containing composite resin particles, characterized by comprising a polymerization inhibitor.   The water-soluble polymerization inhibitor is added to the suspension of the step (A) or the reaction solution of the step (B), and the oil-soluble polymerization inhibitor is added to the reaction solution of the step (C). Item 2. A process for producing a carbon black-containing composite resin particle according to Item 1. The additive amount of the water-soluble polymerization inhibitor is 10~400ppm to the aqueous medium, the amount of the oil-soluble polymerization inhibitor is 100~1000ppm to said styrenic monomers claim 1 or 2. A method for producing a carbon black-containing composite resin particle according to 2.   The water-soluble polymerization inhibitor is sodium nitrite, and the oil-soluble polymerization inhibitor is 2,2-methylenebis (4-methyl-6-t-butylphenol). Of producing carbon black-containing composite resin particles.   (D) It further includes a flame retardant treatment step of adding a flame retardant and a flame retardant aid to the reaction liquid obtained in the step (C) and heat-treating the carbon black-containing composite resin particles. The manufacturing method of the carbon black containing composite resin particle as described in any one of Claims 1-4.   The flame retardant is 1.5 to 6.0% by mass of tri (2,3-dibromopropyl) isocyanate based on the carbon black-containing composite resin particles, and the flame retardant aid is added to the carbon black-containing composite resin particles. The method for producing carbon black-containing composite resin particles according to claim 5, wherein 0.1 to 2.0 parts by mass of 2,3-dimethyl-2,3-diphenylbutane is present.