JP6657883B2 - Method for producing composite resin particles - Google Patents

Description

  The present invention relates to a method for producing composite resin particles in which core particles containing an ethylene-based resin are impregnated with a styrene-based monomer and polymerized in the presence of a polymerization initiator.

  BACKGROUND ART Foamed particle molded articles are utilized in a wide range of applications such as packaging materials, building materials, and vehicle members by making use of characteristics such as excellent cushioning properties, lightweight properties, vibration-proof properties, sound-proof properties, and heat-insulating properties. A foamed particle molded article is obtained by fusing foamed particles to each other in a mold. In addition, foamed particles are obtained by foaming resin particles obtained by impregnating resin particles with an organic physical foaming agent such as propane, butane, and pentane or an inorganic physical foaming agent such as carbon dioxide, nitrogen, and air by heating or the like. Can be Styrene-based resins, propylene-based resins, ethylene-based resins, and the like are mainly used as resin components constituting the foamed particle molded body.

  In particular, packaging containers used for plate products such as liquid crystal panels and solar power panels do not suffer from abrasion, cracking, chipping due to press scratches or rubbing, and because they can be used multiple times, A foamed particle molded article made of a propylene-based resin has been used. However, due to the increase in packing weight accompanying the recent increase in panel size, when a foamed particle molded article made of a propylene-based resin is used as a packing container, there has been a problem that the amount of deflection in a packed state increases. If the amount of deflection at the time of packing is large, there is a possibility that the container may fall off when both ends of the packed container are supported and lifted by a transporter or the like, or the liquid crystal panel may be damaged due to the bending.

  On the other hand, a foamed particle molded article made of a composite resin of an ethylene-based resin and a styrene-based resin (hereinafter, appropriately referred to as a “foamed composite resin molded article”) has attracted attention (see Patent Documents 1 to 3). The expanded composite resin molded body is, for example, as described above, foamed the composite resin particles obtained by impregnating and polymerizing the styrene-based monomer into the core particles containing the ethylene-based resin and fusing them together. Manufactured by In such a foamed composite resin molded article, the rigidity can be improved by increasing the ratio of the styrene resin component in the composite resin. As a result, it becomes possible to reduce the amount of deflection of the foamed composite resin molded article and improve the deflection resistance. Therefore, it is possible to avoid the above-described problem at the time of transportation when the foamed composite resin molded body is applied to a packing container. Further, when the proportion of the styrene resin component is increased, it is possible to increase the expansion ratio of the foamed composite resin molded article while maintaining good deflection resistance. Therefore, there is an advantage that the weight of the foamed composite resin molded article can be reduced.

JP 2014-196441 A JP 2014-196444 A Japanese Patent No. 5058866

  In order to increase the proportion of the styrene-based resin component in the composite resin, if the proportion of the styrene-based monomer to be impregnated into the core particles containing the ethylene-based resin is increased, the amount of the styrene-based monomer remaining in the composite resin particles is increased. Increases body volume. As a result, the amount of the styrene monomer remaining in the foamed composite resin molded article obtained by using the composite resin particles may increase. An increase in the amount of residual styrenic monomer is not preferable because it causes VOC (volatile organic compound) when used for automobiles and causes dirt to transfer to packing objects when used for packaging. . On the other hand, by increasing the amount of the polymerization initiator used for the polymerization of the styrene monomer, the amount of the residual styrene monomer can be reduced. There is a possibility that crosslinking of the system resin proceeds. As a result, there is a concern that problems such as a decrease in foaming property of the composite resin particles and an increase in molding pressure may occur. Therefore, the fusion property between the foamed particles is likely to be reduced, the toughness of the foamed composite resin molded product is insufficient, and cracks may easily occur.

  The present invention has been made in view of the above problems, and it is possible to obtain a foamed composite resin molded article that has good internal fusion, is hard to set, has excellent resistance to deflection, and can prevent destruction due to deformation, and has residual styrene. An object of the present invention is to provide a method for producing composite resin particles having a small amount of system monomers and excellent in foaming property during foaming and moldability during molding.

One embodiment of the present invention is a dispersion step of dispersing core particles containing an ethylene-based resin in an aqueous medium,
In the aqueous medium, a modification step of impregnating the core particles with a styrene-based monomer and polymerizing to obtain composite resin particles,
As the styrene-based monomer, styrene alone or used together with styrene together with one or more selected from the group consisting of styrene derivatives and acrylic monomers,
The compounding amount of the styrene monomer is 100 to 1900 parts by mass with respect to 100 parts by mass of the ethylene resin contained in the core particles,
In the polymerization of the styrene-based monomer, as a polymerization initiator, an organic peroxide A having a t-butoxy group, a 10-hour half-life temperature of 80 to 120 ° C., and a t-hexyloxy group are used. And an organic peroxide B having a 10-hour half-life temperature of 80 to 120 ° C.,
The total blending amount of the organic peroxide A and the organic peroxide B with respect to 100 parts by mass of the styrene-based monomer is 0.4 to 1.2 parts by mass, and the organic peroxide A and the organic peroxide In the method for producing composite resin particles, the ratio of the compounding amount of the organic peroxide A to the total compounding amount with the peroxide B is 30 to 85% by mass.

  In the above-mentioned production method, the composite resin particles are produced by performing the above-mentioned dispersion step and the above-mentioned modification step. Then, while using the organic peroxide A having a t-butoxy group and the organic peroxide B having a t-hexyloxy group in combination with the polymerization initiator, the compounding amount and the compounding ratio thereof are adjusted to the predetermined values. Adjusted to the range. Therefore, even if the amount of the styrene-based monomer to be impregnated into the core particles is increased within the above range, the residual styrene-based monomer can be reduced while suppressing the crosslinking of the ethylene-based resin in the composite resin particles. it can. Further, by suppressing the crosslinking of the ethylene-based resin, the foamability of the composite resin particles at the time of foaming and the moldability at the time of molding can be improved. Further, by using such composite resin particles, it is possible to produce a foamed composite resin molded article having good internal fusion, low sag, excellent bending resistance, and prevention of destruction due to deformation.

  Next, a preferred embodiment of the method for producing the composite resin particles will be described. The composite resin particles can be used to produce composite resin expanded particles (hereinafter referred to as “expanded particles”) by impregnating with a physical foaming agent and foaming. As the physical foaming agent, an inorganic physical foaming agent such as carbon dioxide or an organic physical foaming agent such as hydrocarbon may be used. Further, by molding the foamed particles obtained by foaming in a mold, it is possible to produce a molded body in which the foamed particles are fused to each other (that is, a foamed composite resin molded body). As described above, the composite resin particles are manufactured by performing the dispersion step and the modification step.

  In the dispersion step, core particles containing the ethylene-based resin are dispersed in an aqueous medium. In the reforming step, the styrene-based monomer is impregnated into the core particles and polymerized in an aqueous medium. The polymerization of the styrene monomer is performed in the presence of a polymerization initiator. In this modification step, the styrene-based monomer impregnated in the core particles can be polymerized. Therefore, it is possible to obtain composite resin particles containing a styrene resin component and an ethylene resin component generated by polymerization. Hereinafter, each step will be described in detail.

  In the dispersion step, core particles containing an ethylene-based resin are used. Examples of the ethylene resin include linear low-density polyethylene, branched low-density polyethylene, high-density polyethylene, ethylene-acrylic acid copolymer, ethylene-acrylic acid alkyl ester copolymer, and ethylene-methacrylic acid alkyl ester copolymer. A polymer, an ethylene-vinyl acetate copolymer, or the like can be used. The ethylene-based resin may be a single polymer, or a mixture of two or more polymers.

  The content of the linear low-density polyethylene in 100% by mass of the ethylene-based resin is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more. . The linear low-density polyethylene preferably has a branched structure having a linear polyethylene chain and a short branched chain having 2 to 6 carbon atoms. Specific examples include an ethylene-butene copolymer, an ethylene-hexene copolymer, and an ethylene-octene copolymer. Particularly, the ethylene-based resin is preferably a linear low-density polyethylene obtained by polymerization using a metallocene-based polymerization catalyst. In this case, the affinity between the ethylene-based resin component in the composite resin particles and the styrene-based resin component obtained by polymerizing the styrene-based monomer is further improved, and it is possible to obtain more tough composite resin particles. it can. In addition, since the low molecular weight component can be further reduced and the fusion strength between the foamed particles during molding can be further increased, it is possible to produce a foamed composite resin molded article that is less likely to crack. Further, it is possible to obtain a foamed composite resin molded article having both the excellent rigidity of the styrene resin and the excellent tenacity of the ethylene resin at a higher level.

  Further, the melting point Tm (° C.) of the ethylene-based resin is preferably from 95 to 105 ° C. In this case, the ethylene resin can be sufficiently impregnated with the styrene monomer during the production of the composite resin particles, and the suspension system can be prevented from becoming unstable during polymerization. As a result, it is possible to obtain a foamed composite resin molded article having both the excellent rigidity of the styrene resin and the excellent tenacity of the ethylene resin at a higher level. From the same viewpoint, the melting point Tm of the ethylene-based resin is more preferably 100 to 105 ° C. The melting point Tm can be measured as a melting peak temperature by differential scanning calorimetry (DSC) based on JIS K7121 (1987).

  The ethylene-based resin is preferably made of a linear low-density polyethylene whose melting point Tm (° C.) and Vicat softening point Tv (° C.) satisfy the relationship of Tm−Tv ≦ 20 (° C.). It is presumed that such an ethylene-based resin shows a uniform molecular structure, and a network structure due to crosslinking is more uniformly distributed in the ethylene-based resin. Therefore, in this case, the strength and tenacity of the foamed composite resin molded article obtained using the composite resin particles can be further improved. From the same viewpoint, the linear low-density polyethylene more preferably satisfies the relationship of Tm−Tv ≦ 15, and still more preferably satisfies the relationship of Tm−Tv ≦ 10. In addition, the Vicat softening point Tv can be measured based on the A50 method of JIS K 7206 (1999). When the ethylene resin is a mixed resin composed of two or more resins, the melting point and the Vicat softening point of the mixed resin are defined as the melting point and the Vicat softening point of the ethylene resin.

  From the viewpoint that the foamability of the composite resin particles can be further improved, the melt mass flow rate (that is, MFR) of the ethylene-based resin under the conditions of a temperature of 190 ° C. and a load of 2.16 kg is 0.5 to 4.0 g / 10 minutes. Preferably, it is more preferably 1.0 to 3.0 g / 10 minutes. The MFR of the ethylene resin under the conditions of a temperature of 190 ° C. and a load of 2.16 kg is a value measured based on JIS K7210-1 (2014). In addition, a melt indexer (for example, Model L203 manufactured by Takara Kogyo Co., Ltd.) can be used as the measuring device.

  The core particles can contain additives such as a bubble regulator, a colorant, a lubricant, and a dispersion diameter enlarger. In addition, the compounding quantity of an additive can be suitably adjusted according to the required performance of an expanded particle and an expanded composite resin molded object. The core particles can be produced by blending an additive, which is added as necessary, with the ethylene resin, melt-kneading the blend, and then pulverizing the blend. Melt kneading can be performed by an extruder. In order to perform uniform kneading, it is preferable to extrude after mixing the resin components in advance. The mixing of the resin components can be performed using a mixer such as a Henschel mixer, a ribbon blender, a V blender, a Ladyge mixer, or the like. The melt kneading is preferably performed using a high dispersion type screw such as a dalmage type, a mudock type, and a unimelt type, or a twin-screw extruder.

  Further, in order to adjust the cell size of the foamed particles obtained after foaming the composite resin particles, a cell regulator can be added to the core particles in advance. As the cell regulator, for example, an organic substance such as a higher fatty acid bisamide, a higher fatty acid metal salt, or an inorganic substance can be used. In the case where an organic bubble regulator is used, the amount thereof is preferably in the range of 0.01 to 2 parts by mass based on 100 parts by mass of the resin component used for the core particles. When using an inorganic cell regulator, the amount thereof is preferably in the range of 0.1 to 5 parts by mass based on 100 parts by mass of the resin component used for the core particles.

  The refinement of the core particles is performed, for example, by cutting the melt-kneaded compound while extruding the mixture with an extruder or the like. The miniaturization can be performed by, for example, a strand cut method, an underwater cut method, a hot cut method, or the like.

  In the dispersion step, a dispersion in which the core particles are dispersed in an aqueous medium can be obtained. As the aqueous medium, for example, deionized water can be used. The core particles are preferably dispersed in an aqueous medium together with a suspending agent. In this case, the styrene monomer can be uniformly suspended in the aqueous medium. Examples of the suspending agent include tricalcium phosphate, hydroxyapatite, magnesium pyrophosphate, magnesium phosphate, aluminum hydroxide, ferric hydroxide, titanium hydroxide, magnesium hydroxide, barium phosphate, calcium carbonate, and magnesium carbonate. And fine-particle inorganic suspending agents such as barium carbonate, calcium sulfate, barium sulfate, talc, kaolin and bentonite. Further, for example, an organic suspending agent such as polyvinylpyrrolidone, polyvinyl alcohol, ethylcellulose, and hydroxypropylmethylcellulose can also be used. Among these, tricalcium phosphate, hydroxyapatite, and magnesium pyrophosphate are preferred. These suspending agents can be used alone or in combination of two or more.

  The amount of the suspending agent used is 0.05 to 10 parts by mass in terms of solid content with respect to 100 parts by mass of the aqueous medium of the suspension polymerization system (all water in the system containing water such as the reaction product-containing slurry). Is preferable, and 0.3 to 5 parts by mass is more preferable. In this case, the styrene-based monomer can be stably suspended, and the generation of resin lumps can be prevented. As a result, it is possible to narrow the particle size distribution of the composite resin particles obtained after the modification step.

  A surfactant can be added to the aqueous medium. As the surfactant, for example, an anionic surfactant, a nonionic surfactant, a cationic surfactant, an amphoteric surfactant and the like can be used.

Examples of the anionic surfactant include sodium alkyl sulfonate, sodium alkylbenzene sulfonate, sodium lauryl sulfate, sodium α-olefin sulfonate, sodium dodecyl diphenyl ether disulfonate, and the like.
As the nonionic surfactant, for example, polyoxyethylene dodecyl ether, polyoxyethylene nonylphenyl ether, polyoxyethylene lauryl ether and the like can be used.

As the cationic surfactant, an alkylamine salt such as coconutamine acetate and stearylamine acetate can be used. Also, quaternary ammonium such as lauryltrimethylammonium chloride and stearyltrimethylammonium chloride can be used.
As the amphoteric surfactant, alkyl betaines such as lauryl betaine and stearyl betaine can be used. Further, an alkylamine oxide such as lauryldimethylamine oxide can also be used.
One of the above surfactants can be used alone, or two or more can be used in combination.

  Preferably, an anionic surfactant is used as the surfactant. More preferably, an alkali metal salt of an alkylsulfonic acid having 8 to 20 carbon atoms (preferably a sodium salt) is preferred. Thereby, the suspension can be sufficiently stabilized. In the above dispersion step, it is preferable to add 20 to 1000 ppm by mass of a surfactant to the aqueous medium, more preferably 10 to 500 ppm by mass.

If necessary, an electrolyte composed of inorganic salts such as lithium chloride, potassium chloride, sodium chloride, sodium sulfate, sodium nitrate, sodium carbonate, sodium bicarbonate, etc. can be added to the aqueous medium. Further, in order to obtain a foamed composite resin molded article having better toughness and mechanical strength, it is preferable to add a water-soluble polymerization inhibitor to the aqueous medium.
As the water-soluble polymerization inhibitor, for example, sodium nitrite, potassium nitrite, ammonium nitrite, L-ascorbic acid, citric acid and the like can be used.

  The water-soluble polymerization inhibitor hardly impregnates the core particles and dissolves in the aqueous medium. Therefore, the styrene-based monomer impregnated in the core particles is polymerized, but microdroplets of the styrene-based monomer in the aqueous medium not impregnated in the core particles, and the nuclear particles being absorbed by the core particles Polymerization of the styrene monomer near the surface can be suppressed. As a result, it is presumed that the amount of the styrene-based resin on the surface of the composite resin particles can be reduced, and the toughness of the obtained foamed composite resin molded article is improved. The addition amount of the water-soluble polymerization inhibitor is preferably 0.001 to 0.1 part by mass with respect to 100 parts by mass of the aqueous medium (refers to all water in a system containing water such as a reaction product-containing slurry), More preferably, the content is 0.005 to 0.06 parts by mass.

  In the reforming step, the styrene-based monomer is impregnated into the core particles and polymerized in an aqueous medium. The polymerization of the styrene monomer is performed in the presence of a polymerization initiator. In this case, the ethylene-based resin may be crosslinked with the polymerization of the styrene-based monomer. In the polymerization of the styrene monomer, a polymerization initiator is used, but a crosslinking agent can be used in combination as needed. When using a polymerization initiator and / or a crosslinking agent, it is preferable to dissolve the polymerization initiator and / or the crosslinking agent in the styrene-based monomer in advance. When a crosslinking agent is used, a crosslinking agent that does not decompose at the polymerization temperature but decomposes at the crosslinking temperature can be employed. Specific examples include peroxides such as dicumyl peroxide, 2,5-t-butyl perbenzoate, and 1,1-bis-t-butyl peroxycyclohexane. As the crosslinking agent, one type may be used, or two or more types may be used in combination. The compounding amount of the crosslinking agent is preferably 0.1 to 5 parts by mass based on 100 parts by mass of the styrene monomer.

  As the polymerization initiator, an organic peroxide A having a t-butoxy group and a 10-hour half-life temperature of 80 to 120 ° C. and a t-hexyloxy group and having a 10-hour half-life temperature of 80 An organic peroxide B at ~ 120 ° C is used in combination. Organic peroxide A has a strong hydrogen extraction ability and has an effect of reducing residual styrene-based monomers. On the other hand, the organically-modified oxide B has a weak hydrogen-extracting ability and hardly causes crosslinking of the ethylene-based resin. Examples of the organic peroxide A include t-butylperoxy-2-ethylhexyl monocarbonate, t-butylperoxy-2-ethylhexanoate, t-butylperoxylaurate, and t-butylperoxyisopropyl monocarbonate. Carbonate, t-butylperoxybenzoate, di-t-butyl peroxide, 1,1-bis (t-butylperoxy) cyclohexane, and the like can be used. As the organic peroxide A, t-butyl peroxy-2-ethylhexyl monocarbonate is preferable from the viewpoint that the residual styrene-based monomer can be more easily reduced. As the organic peroxide B, for example, t-hexylperoxybenzoate, t-hexylperoxyisopropyl monocarbonate, di-t-hexyl peroxide and the like can be used. From the viewpoint that the residual styrene-based monomer can be more easily reduced, the crosslinking of the ethylene-based resin can be further suppressed, and the decrease in foaming property and moldability can be further prevented, the organic peroxide B is t-hexylperoxy. Benzoate is preferred.

  Further, when an organic peroxide having a 10-hour half-life temperature of less than 80 ° C. is used as the polymerization initiator, there is a possibility that the amount of the residual styrene-based monomer in the composite resin particles increases, There is a possibility that the shape becomes flat and the filling property at the time of molding deteriorates. Therefore, the 10-hour half-life temperature of the organic peroxide A and the organic peroxide B is preferably 80 ° C. or higher as described above. From the same viewpoint, the 10-hour half-life temperature of the organic peroxide A and the organic peroxide B is more preferably 85 ° C or higher, further preferably 90 ° C or higher, and more preferably 95 ° C or higher. Particularly preferred. On the other hand, when an organic peroxide having a 10-hour half-life temperature exceeding 120 ° C. is used, there is a possibility that the amount of the residual styrene monomer in the composite resin particles becomes too large, or the resin particles coagulate during polymerization. There is a fear. Therefore, the 10-hour half-life temperature of the organic peroxide A and the organic peroxide B is preferably 120 ° C. or lower as described above. From the same viewpoint, the 10-hour half-life temperature of the organic peroxide A and the organic peroxide B is more preferably 115 ° C or lower, further preferably 110 ° C or lower, and more preferably 105 ° C or lower. Particularly preferred.

The 10-hour half-life temperature is defined as a temperature at which an organic peroxide is charged in an inert solvent and 50% of the charged amount of the organic peroxide is thermally decomposed in 10 hours. The 10-hour half-life temperature can be measured, for example, as follows. First, an organic peroxide is dissolved in benzene to obtain a solution having a concentration of 0.1 mol / liter. This solution is sealed in a glass tube in which the air inside has been replaced with nitrogen in advance. Next, the organic peroxide is thermally decomposed by immersing the glass tube in a thermostat set at a predetermined temperature. Here, if the decomposition rate constant is k, the time is t, the initial concentration of the organic peroxide is [PO] ₀ , and the concentration of the organic peroxide after the time t is [PO] _t , kt = ln [PO] The relationship ₀ / [PO] _t holds. Therefore, when the relationship between the time t and In [PO] ₀ / [PO] _t is plotted on a graph, the decomposition rate constant k can be obtained from the slope.

Since the half-life time _{t 1/2 [PO] 0 / [} PO] t = 2 relation holds, from the relationship equation t _1/2 = ln2 / k, the half-life time t _1/2 at a certain temperature You can ask. By obtaining the half-life times t _1/2 for a plurality of temperatures and plotting the relationship between lnt _1/2 and 1 / T on a graph, a 10-hour half-life temperature can be obtained. T is an absolute temperature (unit: K). Note that data of the 10-hour half-life temperature described in a catalog or a technical document issued by an organic peroxide manufacturer may be used.

  The difference between the 10-hour half-life temperature of the organic peroxide A and the 10-hour half-life temperature of the organic peroxide B is preferably within ± 20 ° C. In this case, in the reforming step, the organic peroxide A and the organic peroxide B function as the polymerization initiator at the same timing. Therefore, even if the blending amount of the styrene-based monomer to be impregnated into the core particles is increased within the above range, it is possible to reduce the residual styrene-based monomer while suppressing the crosslinking of the ethylene-based resin in the composite resin particles. it can. From the same viewpoint, the difference between the 10-hour half-life temperature of the organic peroxide A and the 10-hour half-life temperature of the organic peroxide B is more preferably ± 15 ° C., and is ± 10 ° C. It is more preferable that the temperature be within ± 5 ° C.

In the reforming process, the total amount C _T of the organic peroxide A and an organic peroxide B to the styrene monomer to 100 parts by mass is 0.4 parts by mass or more. If the total blending amount _CT is less than 0.4 parts by mass, the amount of the residual styrene monomer in the composite resin particles may be too large. The residual styrene monomer content from more viewpoints of reducing further, the total amount C _T is more preferably 0.5 parts by mass or more, more preferably 0.6 parts by mass or more. The total blending amount _CT is 1.2 parts by mass or less. If the total amount C _T exceeds 1.2 parts by mass, there is a possibility that foaming and molding of the composite resin particles is lowered. Further, in this case, when a foamed composite resin molded body is manufactured using the composite resin particles, internal fusion between the foamed particles in the molded body becomes insufficient, and the bending rupture energy of the molded body may decrease. There is. From the viewpoint of further improving the foaming property and moldability of the composite resin particles, and improving the internal fusion between the foamed particles in the foamed composite resin molded article, and improving the bending rupture energy, the total amount C _T is more preferably 1 part by mass or less, further preferably 0.8 part by mass or less.

Also, in the reforming step, the ratio R _A of the amount of the organic peroxide A to the total amount of the organic peroxide A and an organic peroxide B is 30 mass% or more. If the ratio _RA is less than 30% by mass, the foamability and moldability of the composite resin particles may be reduced. Further, in this case, when a foamed composite resin molded body is manufactured using the composite resin particles, internal fusion between the foamed particles in the molded body becomes insufficient, and the bending rupture energy of the molded body may decrease. There is. From the viewpoint of further improving the foaming property and moldability of the composite resin particles, and improving the internal fusion between the foam particles in the foamed composite resin molded article, and improving the bending rupture energy, the ratio _RA is , 40% by mass or more, more preferably 50% by mass or more. The ratio _RA is 85% by mass or less. If the ratio _RA exceeds 85 parts by mass, the amount of the residual styrene monomer in the composite resin particles may increase. Further, in this case, when a foamed composite resin molded body is manufactured using the composite resin particles, internal fusion between the foamed particles in the molded body becomes insufficient, and the bending rupture energy of the molded body may decrease. There is. From the viewpoint of reducing the amount of the residual styrene monomer in the composite resin particles, or improving the internal fusion between the foamed particles in the foamed composite resin molded article, and improving the bending rupture energy, the ratio _RA is more preferably 80% by mass or less, and further preferably 70% by mass or less.

In the reforming process, the amount M _t of styrene monomer is 100 parts by mass or more with respect to 100 parts by weight ethylene-based resin contained in the core particles. When the blending amount _Mt is less than 100 parts by mass, the rigidity of the foamed composite resin molded article obtained using the composite resin particles may be reduced, and the deflection resistance may be insufficient. From the viewpoint of further improving the rigidity and further improving the deflection resistance, the compounding amount _Mt is more preferably more than 400 parts by mass, and still more preferably 500 parts by mass or more. The amount M _t of the styrene monomer to 100 parts by weight of ethylene-based resin contained in the core particles is less 1900 parts by weight. If the amount M _t is more than 1900 parts by weight, it foamed composite resin molded article is easily broken obtained using the composite resin particles, it may become brittle. From the viewpoint of further preventing cracking of the foamed composite resin molded body, the blending amount _Mt is more preferably 1500 parts by mass or less, further preferably 900 parts by mass or less, and is 600 parts by mass or less. Is even more preferred.

  When the core particles are impregnated with the styrene-based monomer and polymerized, the entire amount of the styrene-based monomer to be compounded can be added to the aqueous medium in which the core particles are dispersed, but the mixing is planned. May be divided into, for example, two or more, and these monomers may be added at different timings. Specifically, a part of the total amount of the styrene monomer to be blended is added to the aqueous medium in which the core particles are dispersed, and the styrene monomer is impregnated and polymerized. Further, the rest of the styrene monomer to be blended can be added to the aqueous medium once or twice or more. By dividing and adding the styrene monomer as in the latter case, it is possible to further suppress the resin particles from coagulating during polymerization.

  Further, the polymerization initiator can be added to the aqueous medium in a state of being dissolved in the styrene monomer. As described above, when the styrene monomer to be compounded is divided into two or more times and added at different timings, the polymerization initiator must be dissolved in the styrene monomer added at any timing. It is also possible to add a polymerization initiator to each styrene monomer added at different timing. When the styrene-based monomer is added in portions, it is preferable to dissolve the polymerization initiator in at least the styrene-based monomer added first (hereinafter, referred to as “first monomer”). It is preferable that 75% or more of the total amount of the polymerization initiator to be blended is dissolved in the first monomer, and it is more preferable that 80% or more is dissolved. In this case, the ethylene resin can be sufficiently impregnated with the styrene monomer during the production of the composite resin particles, and the suspension system can be prevented from becoming unstable during polymerization. As a result, it is possible to obtain a foamed composite resin molded article having both the excellent rigidity of the styrene resin and the excellent tenacity of the ethylene resin at a higher level. In addition, as described above, when a part of the styrene-based monomer to be blended is added as the first monomer, the remainder of the total amount of the styrene-based monomer to be blended is defined as the second monomer. After the addition of one monomer, it can be added at a timing different from that of the first monomer. The second monomer may be further divided and added.

  In addition, the seed ratio (mass ratio of the first monomer to the core particles) of the styrene-based monomer (first monomer) is preferably 0.5 or more. In this case, it becomes easy to make the shape of the composite resin particles more spherical. From the same viewpoint, the seed ratio is more preferably 0.7 or more, and further preferably 0.8 or more. Further, the seed ratio is preferably 1.5 or less. In this case, it is possible to further prevent polymerization before the styrene-based monomer is sufficiently impregnated into the core particles, and it is possible to further prevent the generation of resin aggregates. From the same viewpoint, the seed ratio of the first monomer is more preferably 1.3 or less, and further preferably 1.2 or less.

  The styrene-based monomer may include not only styrene but also a monomer copolymerizable with styrene. Examples of monomers copolymerizable with styrene include styrene derivatives and other vinyl monomers. Examples of the styrene derivative include α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-methoxystyrene, pn-butylstyrene, and p-methylstyrene. -T-butylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, 2,4,6-tribromostyrene, divinylbenzene, styrenesulfonic acid, sodium styrenesulfonate and the like. These may be used alone or in combination of two or more.

  Other vinyl monomers include acrylic acid esters, methacrylic acid esters, acrylic acid, methacrylic acid, vinyl compounds containing a hydroxyl group, vinyl compounds containing a nitrile group, vinyl organic acid compounds, olefin compounds, diene compounds, and halogen compounds. Examples include vinyl halide compounds, vinylidene halide compounds, and maleimide compounds. These vinyl monomers may be used alone or in combination of two or more.

  Examples of the acrylate include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and the like. Examples of the methacrylate include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, and the like.

  Examples of the hydroxyl-containing vinyl compound include, for example, hydroxyl-containing vinyl compounds such as hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, and hydroxypropyl methacrylate. Examples of the vinyl compound containing a nitrile group include acrylonitrile and methacrylonitrile. Examples of the organic acid vinyl compound include vinyl acetate and vinyl propionate.

  Examples of the olefin compound include ethylene, propylene, 1-butene and 2-butene. Examples of the diene compound include butadiene, isoprene, and chloroprene. Examples of the vinyl halide compound include vinyl chloride and vinyl bromide. Examples of the vinylidene halide compound include vinylidene chloride. Examples of the maleimide compound include N-phenylmaleimide and N-methylmaleimide.

  As the styrene-based monomer, it is preferable to use styrene alone or to use styrene and an acrylic-based monomer in combination from the viewpoint of enhancing the foamability of the composite resin particles. From the viewpoint of further improving foamability, it is particularly preferable to use styrene and butyl acrylate as the styrene monomer. In this case, the compounding amount of butyl acrylate is preferably adjusted so that the content of the butyl acrylate component in the composite resin is 0.5 to 10% by mass based on the entire composite resin. It is more preferably adjusted to be 8% by mass, and further preferably adjusted to be 2 to 5% by mass.

  When a monomer copolymerizable with styrene is used together with styrene as the styrene monomer, the content of the monomer copolymerizable with styrene in the composite resin particles is preferably set to 10% by mass or less. . In this case, the expandability of the composite resin particles can be improved, and the shrinkage of the expandable particles can be prevented. From the viewpoint of improving foamability, the content of the monomer copolymerizable with styrene in the composite resin particles is more preferably 1 to 8% by mass, and still more preferably 2 to 5% by mass.

  In the reforming step, it is preferable that the melting point Tm (° C.) of the ethylene resin in the core particles and the polymerization temperature Tp (° C.) in the reforming step satisfy the relationship of Tm−10 ≦ Tp ≦ Tm + 30. In this case, the ethylene resin can be sufficiently impregnated with the styrene monomer during the production of the composite resin particles, and the suspension system can be prevented from becoming unstable during polymerization. As a result, it is possible to obtain a foamed composite resin molded article having both the excellent rigidity of the styrene resin and the excellent tenacity of the ethylene resin at a higher level. Further, the impregnation temperature and the polymerization temperature in the reforming step vary depending on the type of the polymerization initiator used, but are preferably from 60 to 105 ° C, more preferably from 70 to 105 ° C. The crosslinking temperature varies depending on the type of the crosslinking agent used, but is preferably from 100 to 150 ° C. The impregnation temperature of the styrene-based monomer is a temperature at which the ethylene-based resin is impregnated with the styrene-based monomer. The polymerization temperature is a temperature at which the polymerization of the styrene monomer impregnated in the ethylene resin proceeds.

  In addition, a bubble regulator can be added to the styrene monomer. As the cell regulator, for example, aliphatic monoamide, fatty acid bisamide, polyethylene wax, methylene bisstearic acid and the like can be used. As the aliphatic monoamide, for example, oleic amide, stearic amide and the like can be used. As the fatty acid bisamide, for example, ethylene bisstearic acid amide and the like can be used. It is preferable to use 0.01 to 2 parts by mass of the cell regulator based on 100 parts by mass of the styrene monomer. Further, a plasticizer, an oil-soluble polymerization inhibitor, a flame retardant, a colorant, a chain transfer agent, and the like can be added to the styrene-based monomer as needed.

  As the plasticizer, for example, fatty acid esters, acetylated monoglycerides, oils and fats, hydrocarbon compounds and the like can be used. As the fatty acid ester, for example, glycerin tristearate, glycerin trioctoate, glycerin trilaurate, sorbitan tristearate, sorbitan monostearate, butyl stearate and the like can be used. Further, as the acetylated monoglyceride, for example, glycerin diacetomonolaurate or the like can be used. As fats and oils, for example, hardened beef tallow, hardened castor oil and the like can be used. As the hydrocarbon compound, for example, cyclohexane, liquid paraffin and the like can be used. As the oil-soluble polymerization inhibitor, for example, para-t-butylcatechol, hydroquinone, benzoquinone and the like can be used. As the flame retardant, for example, hexabromocyclododecane, tetrabromobisphenol A-based compound, trimethyl phosphate, brominated butadiene-styrene block copolymer, aluminum hydroxide and the like can be used. Furnace black, channel black, thermal black, acetylene black, Ketjen black, graphite, carbon fiber, and the like can be used as the coloring agent. As the chain transfer agent, for example, n-dodecyl mercaptan, α-methylstyrene dimer, or the like can be used. The above additives can be added alone or in combination of two or more.

  Additives such as the above-mentioned cell regulator, plasticizer, oil-soluble polymerization inhibitor, flame retardant, colorant, and chain transfer agent can also be dissolved in a solvent and impregnated into core particles. As the solvent, for example, aromatic hydrocarbons such as ethylbenzene and toluene, and aliphatic hydrocarbons such as heptane and octane are used.

Next, the composite resin particles obtained by the above-described dispersion step and modification step will be described.
The composite resin particles contain an ethylene-based resin and a styrene-based resin obtained by polymerizing a styrene-based monomer. The styrene-based resin refers to a resin having a styrene component unit content of 50% by mass or more in the resin. The styrene component unit in the styrene-based resin is preferably at least 80% by mass, more preferably at least 90% by mass.

  The content of the styrene monomer in the composite resin particles is preferably 500 ppm by mass or less (including 0). In this case, using the composite resin particles, a foamed composite resin molded article having a low VOC (volatile organic compound) can be obtained. The content of the styrene monomer in the composite resin particles is more preferably 400 mass ppm or less (including 0), further preferably 300 mass ppm or less (including 0), and 200 mass ppm. The following (including 0) is even more preferred.

  The degree of swelling in methyl ethyl ketone at a temperature of 23 ° C. (hereinafter simply referred to as “swelling degree”) Is preferably 1.25 or more. In this case, the bending rupture energy of the foamed composite resin molded article obtained by using the composite resin particles can be further improved, and the toughness can be further improved. From the same viewpoint, the swelling degree is more preferably 1.5 or more, and further preferably 2 or more. In addition, from the viewpoint of suppressing shrinkage of the foamed composite resin molded body, the degree of swelling of the composite resin particles is preferably 10 or less, more preferably 5 or less.

  The reason why the rigidity and the tenacity are excellent as described above when the swelling degree is equal to or more than the predetermined value is presumed as follows. The degree of swelling (degree of swelling) when a crosslinked ethylene-based resin is immersed in an organic solvent is correlated with the crosslinked structure (three-dimensional network structure) of the resin, and the finer the mesh, the lower the amount of absorption of the organic solvent. Therefore, the degree of swelling decreases. On the other hand, non-crosslinked ethylene resins hardly swell in methyl ethyl ketone at a temperature of 23 ° C. That is, as described above, the xylene-insoluble component of the composite resin particles (that is, the mainly crosslinked ethylene resin component) and the acetone-insoluble component of the xylene-soluble component (that is, the crosslinked ethylene-based component that mainly passed through the mesh) were used. (The sum of the resin component and the non-crosslinked ethylene-based resin component) has a higher degree of swelling in the mixed insoluble portion than in the case where the degree of swelling is low. This means that the network of the obtained three-dimensional network structure contains a large amount of a coarse ethylene resin component. The crosslinked ethylene resin component and the non-crosslinked ethylene resin component each include an ethylene resin component obtained by graft polymerization of a styrene monomer (that is, a PE-g-PS component). Since the crosslinked three-dimensionally structured ethylene resin component having a coarse network is easily stretched at the time of foaming while having strength, it is presumed that a foam film having high strength is formed. Furthermore, in the composite resin expanded particles, when compressed, the ethylene resin in the composite resin is flexible and sufficiently deformable, so that even when the ratio of the styrene resin in the composite resin is high, the bubbles of the expanded particles are reduced. It is presumed that the closed cell structure can be maintained without breaking the film. That is, when the degree of swelling is in a specific range, a foamed composite resin molded article having both high rigidity and high tenacity and a large bending rupture energy can be obtained.

  In the composite resin particles, it is preferable that the mass ratio of the xylene-insoluble component by Soxhlet extraction is 40% by mass or less (including 0). In this case, the foamability of the composite resin particles can be further improved. Further, the mass ratio of the xylene-insoluble component is more preferably 30% by mass or less (including 0), and further preferably 20% by mass or less (including 0). In this case, the rigidity and tenacity of the foamed composite resin molded article obtained using the composite resin particles can be further improved.

  In the composite resin particles, the weight average molecular weight of the styrene resin is preferably 100,000 to 600,000. In this case, the shrinkage of the expanded particles obtained by expanding the composite resin particles can be further prevented. Furthermore, at the time of in-mold molding of the expanded particles, the fusion property between the expanded particles can be further improved. As a result, the dimensional stability of the foamed composite resin molded article can be further improved. From the same viewpoint, the weight average molecular weight of the styrene resin is more preferably 150,000 to 500,000, and further preferably 150,000 to 350,000.

  Further, the glass transition temperature (Tg) of the styrene-based resin is preferably 85 to 100 ° C. In this case, the foamability of the composite resin particles during foaming can be further improved, and shrinkage during foaming can be further prevented. Furthermore, at the time of in-mold molding of the foamed particles obtained after foaming, the fusion property between the foamed particles can be further improved, and the dimensional stability of the foamed composite resin molded article can be further improved.

  The glass transition temperature (Tg) of the styrene resin can be measured, for example, as follows. Specifically, first, 1.0 g of the composite resin particles is put in a wire mesh bag of 150 mesh. Next, about 200 ml of xylene is placed in a round flask having a capacity of 200 ml, and the sample placed in the wire mesh bag is set in a Soxhlet extraction tube. Heat for 8 hours with a mantle heater to perform Soxhlet extraction. The extracted xylene solution is dropped into 600 ml of acetone, decanted, and the supernatant is evaporated to dryness under reduced pressure to obtain a styrene-based resin as an acetone-soluble component. About 2 to 4 mg of the obtained styrene-based resin, a heat flux differential scanning calorimetry is performed using a DSC measuring instrument (Q1000) manufactured by TIA Instruments in accordance with JIS K7121 (1987). Then, the glass transition temperature Tg can be determined as the midpoint glass transition temperature of the DSC curve obtained at a heating rate of 10 ° C./min.

  A conventionally known foaming method can be applied to the foaming of the composite resin particles. Specifically, for example, after dispersing the composite resin particles together with a foaming agent in a dispersion medium such as water in a pressure vessel, heating and softening the resin particles, and impregnating the composite resin particles with the foaming agent, A method (hereinafter, also referred to as a direct foaming method) in which the composite resin particles are released at a temperature lower than the inside of the container at a temperature equal to or higher than the softening temperature of the particles (for example, usually under atmospheric pressure) and foamed. Further, for example, a method in which the expandable composite resin particles containing a foaming agent are taken out of the closed container, and the expandable composite resin particles are heated and foamed by a heating medium such as steam can be used. Among these methods, the direct foaming method is preferably employed. Further, the temperature in the container (ie, the foaming temperature) at the time of discharging the expandable composite resin particles impregnated with the foaming agent from the inside of the pressure-resistant container is determined by the apparent density of the intended foamed particles, the composition of the base resin, or It is determined in consideration of the type and the amount of the foaming agent. The foaming temperature is generally equal to or higher than the glass transition temperature (Tg) of the styrene-based resin component obtained by polymerizing a styrene-based monomer which is one of the constituent components of the composite resin particle, and the decomposition of the resin component constituting the composite resin particle is performed. It can be in the range below the starting temperature.

(Example 1)
Hereinafter, a method for producing the composite resin particles will be described. In this example, composite resin particles are prepared, the composite resin particles are impregnated with a physical foaming agent, the composite resin particles are expanded to prepare expanded particles, and the expanded composite resin molded article is further formed using the expanded particles. To manufacture.

(1) Preparation of core particles Linear low-density polyethylene (specifically, “Nipolon Z HF210K” manufactured by Tosoh Corporation) was prepared as an ethylene-based resin by polymerization using a metallocene polymerization catalyst. The melting point Tm of this ethylene resin is 103 ° C. In addition, “CE-7335” manufactured by Polycor Corp. was prepared as a foam nucleating agent master batch. "CE-7335" manufactured by Polycor Co., Ltd. has a content of zinc borate (cell regulator) of 10% by mass and a content of linear low-density polyethylene ("Nipolon Z HF210K" manufactured by Tosoh Corporation) of 90% by mass. %. 8.65 kg of the ethylene-based resin and 1.35 kg of the air bubble master batch were charged into a Henschel mixer and mixed for 5 minutes to obtain a resin mixture. Next, the resin mixture was melt-kneaded using a 50 mmφ single screw extruder, and cut into 0.5 mg / piece on average by an underwater cutting method to obtain core particles. Melt kneading of the resin mixture was performed by setting the maximum temperature of the extruder to 250 ° C.

(2) Preparation of Composite Resin Particles In a 3 L autoclave equipped with a stirrer, 1000 g of deionized water was added, and 6.0 g of sodium pyrophosphate was further added. Thereafter, 12.9 g of powdery magnesium nitrate hexahydrate was added, and the mixture was stirred at room temperature for 30 minutes. This produced a magnesium pyrophosphate slurry as a suspending agent. Next, 2.0 g of sodium lauryl sulfonate (10 mass% aqueous solution) as a surfactant, 0.2 g of sodium nitrite as a water-soluble polymerization inhibitor, and 75 g of core particles were added to the suspension.

  Next, two types of organic peroxides were prepared as polymerization initiators. Specifically, t-butyl peroxy-2-ethylhexyl monocarbonate (specifically, “Perbutyl E” manufactured by NOF Corporation) is prepared as the organic peroxide A, and as the organic peroxide B, t-Hexyl peroxybenzoate (specifically, "Perhexyl Z" manufactured by NOF Corporation) was prepared. An α-methylstyrene dimer (specifically, “NOFMER MSD” manufactured by NOF Corporation) was prepared as a chain transfer agent. In the tables described below, t-butylperoxy-2-ethylhexyl monocarbonate is indicated as “A1”, and t-hexylperoxybenzoate is indicated as “B1”. Then, 1.72 g of t-butylperoxy-2-ethylhexyl monocarbonate, 0.86 g of t-hexylperoxybenzoate, and 0.63 g of α-methylstyrene dimer were added to the first monomer (styrene-based monomer). Dissolved. Then, while stirring the melt at a rotation speed of 500 rpm, the melt was charged into the above-described autoclave into which the core particles and the like had been charged. Note that a mixed monomer of 60 g of styrene and 15 g of butyl acrylate was used as the first monomer.

  Next, after the air in the autoclave was replaced with nitrogen, the temperature was raised and the temperature in the autoclave was raised to 100 ° C. over 1 hour and 30 minutes. After the temperature was raised, the temperature was kept at 100 ° C. for 1 hour. Thereafter, the stirring speed was reduced to 450 rpm, and the temperature was maintained at 100 ° C. for 7.5 hours. The temperature at this time (specifically, 100 ° C.) is the polymerization temperature. One hour after the temperature reached 100 ° C., 350 g of styrene as the second monomer (styrene-based monomer) was added into the autoclave over 5 hours.

  Next, the inside of the autoclave was heated to a temperature of 125 ° C. over 2 hours, and kept at a temperature of 125 ° C. for 5 hours. Thereafter, the inside of the autoclave was cooled, and the contents (composite resin particles) were taken out. Next, nitric acid was added to dissolve the magnesium pyrophosphate attached to the surfaces of the composite resin particles. Thereafter, dehydration and washing are performed by a centrifugal separator, and moisture adhering to the surface is removed by a flash dryer to obtain composite resin particles having a styrene-based resin-to-ethylene-based resin ratio (mass ratio) of 85:15. Was. The ratio between the styrene-based resin and the ethylene-based resin is determined from the blending ratio (mass ratio) of the styrene-based monomer and the ethylene-based resin used in the production.

The polymerization conditions of the composite resin particles produced in this example are shown in Table 1 below. Specifically, the amount M _T of the styrenic monomer to 100 parts by weight of ethylene-based resin in the core particles, the kind of the organic peroxide A, the 10-hour half-life temperature T _A, organic peroxide B Type, its 10-hour half-life temperature T _B , the ratio R _{A of} the amount of the organic peroxide A to the total amount of the organic peroxide A and the organic peroxide B, based on 100 parts by mass of the styrene monomer. Total blending amount C _T of organic peroxide A and organic peroxide B, difference ΔT of 10-hour half-life temperature of organic peroxide A and organic peroxide B (however, ΔT = T _B −T _A ) Are shown in Table 1. In Table 1 described below, t-butylperoxy-2-ethylhexyl monocarbonate used as the organic peroxide A is represented by “A1”, and t-butylperoxyisopropyl monocarbonate is represented by “A1”. A2 "and t-butyl peroxybenzoate as" A3 ". Further, t-hexylperoxybenzoate used as the organic peroxide B is represented as “B1”, t-hexylperoxyisopropyl monocarbonate is represented as “B2”, and di-t-hexyl peroxide Is represented as “B3”. Further, t-hexylperoxy-2-ethylhexanoate, which is an organic peroxide, is represented as "B4", and t-amylperoxy-2-ethylhexyl monocarbonate is represented as "B5". Table 1 shows the mass ratio of the ethylene resin to the styrene resin (ethylene resin / styrene resin) for the composite resin particles obtained in this example. Further, regarding the composite resin particles, expandability, styrene monomer content (R-SM), degree of swelling, mass ratio of xylene-insoluble component (XY gel amount), and weight average molecular weight (Mw) of the styrene resin are shown. The investigation was performed as follows. Table 1 shows the results.

"Foamability"
1 kg of the composite resin particles was charged together with 3.5 liters of water into a 5 L pressure-resistant vessel equipped with a stirrer, and 5 g of kaolin as a dispersant and 0.6 g of sodium alkylbenzene sulfonate as a surfactant were further added to water. . Next, while the inside of the pressure vessel was heated to a foaming temperature of 165 ° C. while stirring the inside of the pressure vessel at a stirring speed of 300 rpm, 4.0 MPa of carbon dioxide as an inorganic physical foaming agent was injected into the pressure vessel and pressurized. Hold underneath for 20 minutes. Thereafter, by discharging the contents under atmospheric pressure, the composite resin particles were expanded to obtain expanded particles. The bulk density of the obtained expanded particles was measured, and the expandability was evaluated based on the following criteria.

That is, the case where the bulk density is less than 40 kg / m ³ as "◎", the case of less than 40 kg / m ³ or more and 50 kg / m ³ as "○", evaluated in the case of 50 kg / m ³ or more as "×" did. The results are shown in Table 1 below. In Table 1, the numbers in parentheses beside the evaluation results of the expandability indicate the bulk density (kg / m ³ ) of the expanded particles. The bulk density (kg / m ³ ) was measured as follows. First, a 1 L measuring cylinder was prepared, and an empty measuring cylinder was filled with foamed particles to a 1 L mark line. Next, the mass (g) of the foamed particles per liter was measured. Then, the bulk density (kg / m ³ ) was calculated by converting the mass (g) of 1 L of the expanded particles into a unit.

"Content of styrene-based monomer remaining in composite resin particles (R-SM)"
First, the composite resin particles were frozen and pulverized using an IKA analysis mill so that the particle diameter became about 100 μm. About 1 g of the pulverized material was collected, immersed in 25 ml of dimethylformamide (ie, DMF), and left at a temperature of 5 ° C. for 24 hours. The content of the styrene monomer was measured by gas chromatography of the DMF solution. In addition, the measurement conditions of gas chromatography are as follows. Equipment used: Gas chromatograph GC-9A manufactured by Shimadzu Corporation, Column packing: [liquid phase name] PEG-20M, [liquid phase impregnation rate] 25% by weight, [carrier particle size] 60/80 mesh, carrier treatment Method], column material: glass column having an inner diameter of 3 mm and a length of 3000 mm, carrier gas: N ₂ , detector: FID (hydrogen flame ionization detector), quantification: internal standard method.

"Swelling degree"
First, about 1 g of composite resin particles were collected, and the mass (that is, W ₀ ) was weighed to the fourth decimal place and placed in a 150 mesh wire mesh bag. Then, about 200 ml of xylene was put into a 200 ml round flask, and the sample put in the wire mesh bag was set in a Soxhlet extraction tube. Soxhlet extraction was performed by heating with a mantle heater for 8 hours. After completion of the extraction, the mixture was cooled by air cooling. After cooling, the wire net was taken out of the extraction tube, and the sample was washed together with about 600 ml of acetone. Next, the acetone was volatilized and dried at a temperature of 120 ° C. The sample collected from inside the wire mesh after this drying is “xylene-insoluble matter”. Further, the xylene solution after the Soxhlet extraction was thrown into 600 ml of acetone. Then, by filtering using a type A filter paper specified in JIS P3801, components insoluble in acetone were separated and collected, and the collected product was evaporated to dryness under reduced pressure. The obtained solid is “acetone-insoluble matter”.
The mass (i.e., Wa) of the mixed insoluble content of "xylene insoluble content" and "acetone insoluble content" obtained by these operations was measured to four decimal places. In addition, when the mass of the mixed insolubles is less than 0.2 g in other examples and comparative examples, the above operation is repeated to obtain a sufficient amount of the mixed insolubles, and the mixing of 0.2 g or more is performed. An insoluble content was obtained. Next, the mixed insolubles were immersed in 50 ml of methyl ethyl ketone and left at a temperature of 23 ° C. for 24 hours. Thereafter, the mixed insolubles were taken out from the methyl ethyl ketone, gently wiped with filter paper, and then the mass (ie, Wb) of the mixed insolubles was measured to four decimal places. Then, the swelling degree S was determined by the following formula (I) based on the masses of the mixed insoluble components before and after immersion in methyl ethyl ketone (that is, Wa, Wb).
S = Wb / Wa (I)

"Mass ratio of xylene-insoluble matter (XY gel amount)"
First, the mass (that is, W ₂ ) of the xylene-insoluble component obtained in the measurement of the degree of swelling was measured. The ratio of the xylene-insoluble component is the ratio of the mass (W ₂ ) to the mass (that is, W ₀ ) of the composite resin particles measured at the degree of swelling (that is, 100 × W ₂ / W ₀ , unit: mass%). is there.

"Mw of styrene resin"
First, Soxhlet extraction was performed in the same manner as described above. Then, the extracted xylene solution was dropped into 600 ml of acetone, and after decantation, evaporated to dryness under reduced pressure. As a result, a styrene resin was obtained as an acetone-soluble component. The weight average molecular weight of the styrene resin was measured by gel permeation chromatography (ie, GPC) using polystyrene as a standard substance. For the measurement, a mixed gel column for polymer measurement was used. Specifically, using a measuring apparatus manufactured by Tosoh Corporation (specifically, HLC-8320GPC EcoSEC), eluent: tetrahydrofuran (that is, THF), flow rate: 0.6 ml / min, and sample concentration: 0 0.1 wt%, column: TSKguardcolumn SuperH-H x 1 and TSK-GEL SuperHM-H x 2 were connected in series. That is, the weight average molecular weight Mw was determined by measuring the molecular weight of a styrene resin dissolved in tetrahydrofuran by a GPC method and calibrating with a standard polystyrene.

(3) Production of Expanded Particles 500 g of the composite resin particles were charged together with 3500 g of water as a dispersion medium in a 5 L pressure-tight container equipped with a stirrer. Subsequently, 5 g of kaolin as a dispersant and 0.5 g of sodium alkylbenzenesulfonate as a surfactant were further added to the dispersion medium in the pressure tight container. Next, while stirring the inside of the pressure-resistant closed container at a rotation speed of 300 rpm, the inside of the container was heated to a foaming temperature of 165 ° C. Thereafter, carbon dioxide, which is an inorganic physical foaming agent, is injected into the pressure-resistant closed container so that the pressure in the pressure-resistant closed container becomes 3.2 MPa (G: gauge pressure), and the pressure is reduced to 15 at the same temperature (that is, 165 ° C.). Hold for minutes. Thereby, carbon dioxide was impregnated into the composite resin particles to obtain expandable composite resin particles. Next, the foamable composite resin particles were discharged together with the dispersion medium from a closed container under atmospheric pressure to obtain foamed particles having a bulk density of 48 kg / m ³ . Since the foamed particles are a foam of composite resin particles, they can be said to be composite resin foamed particles.

  The foaming conditions of the composite resin particles are shown in Table 1 below. Specifically, the type of the foaming agent and the pressure (gauge pressure) at the time of press-in of the foaming agent are shown in Table 1 described later.

(4) Production of Expanded Particle Molded Article The expanded particles obtained as described above were filled in a mold having a flat-shaped cavity of 250 mm in length, 200 mm in width and 50 mm in thickness. Next, the foamed particles were heated and fused to each other by introducing steam into the mold. Then, after cooling the inside of the mold by water cooling, the foamed composite resin molded product was taken out from the mold. Further, the foamed composite resin molded body was placed in an oven adjusted to a temperature of 60 ° C. for 12 hours to perform drying and curing. Thus, a foamed particle molded body was obtained. The foamed particle molded article is a foamed composite resin molded article because foamed particles obtained by foaming the composite resin particles are mutually fused.

The molding conditions are shown in Table 1 below. Specifically, the molding pressure (MPa) and the water cooling time (second) during molding are shown in Table 1 below. The apparent density (kg / m ³ ), the fusion rate (%), the flexural modulus (MPa), the bending rupture energy (MJ / m ³ ), and the compressive strength (MPa) of the foamed composite resin molded article were as follows. Was measured as described above. The results are shown in Table 1 below.

"Apparent density"
The apparent density can be calculated by dividing the mass of the foamed composite resin molded product by its volume.

"Fusing rate"
The fractured surface of the foamed composite resin molded article was observed, and the number of foamed particles that were broken inside and the number of foamed particles that peeled off at the interface were visually measured. Next, the ratio of the internally broken foamed particles to the total number of the internally broken foamed particles and the foamed particles separated at the interface was calculated, and the value expressed as a percentage was defined as the fusion rate (%).

"Flexural modulus"
The flexural modulus was measured according to a three-point bending test method described in JIS K7221-1 (2006). Specifically, a test piece having a thickness of 20 mm × a width of 25 mm × a length of 120 mm is cut out from the foamed composite resin body so that the entire surface is a cut surface, and left in a constant temperature room at a room temperature of 23 ° C and a humidity of 50% for 24 hours or more. Autograph AGS-10kNG (manufactured by Shimadzu) under the conditions of a distance between fulcrums, a radius of the indenter 100 mm, a radius R 15.0 mm of the indenter, a radius R 15.0 mm of the support base, a test speed of 20 mm / min, a room temperature of 23 ° C. and a humidity of 50%. And the average of the calculated values (5 points or more) was adopted.

"Bending rupture energy"
A three-point bending test was performed in the same manner as the measurement of the bending elastic modulus described above, and the energy (MJ / m ³ ) up to the breaking point was determined from the relationship between the strain (m / m) and the stress (MPa). The bending rupture energy is calculated from the area surrounded by the strain-stress curve up to the breaking point and the horizontal axis (strain).

"Compressive strength"
A rectangular parallelepiped test piece having a length of 50 mm, a width of 50 mm, and a thickness of 25 mm was cut out from the center of the foamed composite resin molded body. Next, a compressive load at 50% strain was determined for this test piece in accordance with JIS K6767 (1999). The compressive strength (50% compressive stress) was calculated by dividing the compressive load by the pressure receiving area of the test piece.

(Example 2)
This example and Example 3 described below are examples in which the type of the organic peroxide B used as the polymerization initiator was changed. Specifically, in this example, 0.86 g of t-hexylperoxyisopropyl monocarbonate (“Perhexyl I” manufactured by NOF Corporation) was used as the organic peroxide B, except that 0.86 g of t-hexylperoxyisopropyl monocarbonate was used. Similarly, composite resin particles, foamed particles, and foamed molded articles were produced.

(Example 3)
In this example, a composite resin was prepared in the same manner as in Example 1 except that 0.86 g of di-t-hexyl peroxide ("Perhexyl D" manufactured by NOF Corporation) was used as the organic peroxide B. Particles, expanded particles, and expanded particle molded bodies were produced.

(Example 4)
This example and Examples 5 and 6 described below are examples in which the amount of the organic peroxide B used as the polymerization initiator is changed. Specifically, in this example, composite resin particles were prepared in the same manner as in Example 1 except that the amount of t-hexylperoxybenzoate used as the organic peroxide B was changed to 0.32 g. Expanded particles and a molded article of expanded particles were produced.

(Example 5)
In this example, composite resin particles, expanded particles, expanded particles were obtained in the same manner as in Example 1 except that the amount of t-hexylperoxybenzoate used as the organic peroxide B was changed to 0.43 g. A molded body was produced.

(Example 6)
In this example, composite resin particles, expanded particles, expanded particles were obtained in the same manner as in Example 1 except that the amount of t-hexylperoxybenzoate used as the organic peroxide B was changed to 1.72 g. A molded body was produced.

(Example 7)
This example and Examples 8 and 9 described below are examples in which the polymerization initiator is dissolved not only in the first monomer but also in the second monomer. Specifically, in this example, t-butyl peroxy-2-ethylhexyl monocarbonate 0.86 g used as the organic peroxide A is dissolved in the first monomer, and t-hexyl peroxide used as the organic peroxide B is dissolved. Except for dissolving 1.72 g of oxybenzoate in the second monomer, composite resin particles, foamed particles, and molded foamed particles were produced in the same manner as in Example 1.

(Example 8)
In this example, 1.5 g of t-butylperoxy-2-ethylhexyl monocarbonate used as the organic peroxide A and 0.76 g of t-hexylperoxybenzoate used as the organic peroxide B were used as the first monomer. Was dissolved. In the second monomer, 0.22 g of t-butylperoxy-2-ethylhexyl monocarbonate used as the organic peroxide A and 0.11 g of t-hexylperoxybenzoate used as the organic peroxide B were dissolved. Was. Otherwise, the procedure of Example 1 was repeated to prepare composite resin particles, foamed particles, and foamed particle molded bodies.

(Example 9)
This example and Examples 10 to 12 described below are examples in which the mixing ratio of the styrene monomer to the core particles is changed. Specifically, in this example, first, except that the amount of the ethylene-based resin was changed from 8.65 kg to 9 kg, and the amount of the foam regulator master batch was changed from 1.35 kg to 1 kg, Nuclear particles were produced in the same manner as in Example 1. Next, the same as Example 1 except that 100 g of the core particles were used, a mixed monomer of 85 g of styrene and 15 g of butyl acrylate was used as the first monomer, and 300 g of styrene was used as the second monomer. In this way, composite resin particles, foamed particles, and foamed molded articles were produced.

(Example 10)
In this example, first, the amount of the ethylene-based resin was changed from 8.65 kg to 8 kg, and the amount of the foam regulator master batch was changed from 1.35 kg to 2 kg, in the same manner as in Example 1. Core particles were prepared. Next, the same as Example 1 except that 53 g of the core particles were used, a mixed monomer of 38 g of styrene and 15 g of butyl acrylate was used as the first monomer, and 394 g of styrene was used as the second monomer. In this way, composite resin particles, foamed particles, and foamed molded articles were produced.

(Example 11)
In the present example, first, the amount of the ethylene-based resin was changed from 8.65 kg to 9.35 kg, and the amount of the foam regulator master batch was changed from 1.35 kg to 0.65 kg. Nuclear particles were produced in the same manner as in Example 1. Next, the same as Example 1 except that 150 g of the core particles were used, a mixed monomer of 135 g of styrene and 15 g of butyl acrylate was used as the first monomer, and 200 g of styrene was used as the second monomer. In this way, composite resin particles, foamed particles, and foamed molded articles were produced.

(Example 12)
In this example, first, the amount of the ethylene-based resin was changed from 8.65 kg to 9.2 kg, and the amount of the foam regulator master batch was changed from 1.35 kg to 0.8 kg. Nuclear particles were produced in the same manner as in Example 1. Next, the same as Example 1 except that 125 g of the core particles were used, a mixed monomer of 110 g of styrene and 15 g of butyl acrylate was used as the first monomer, and 250 g of styrene was used as the second monomer. In this way, composite resin particles, foamed particles, and foamed molded articles were produced.

(Example 13)
This example and Example 14 described below are examples in which the type of the organic peroxide A used as the polymerization initiator was changed. Specifically, in this example, except that 1.72 g of t-butyl peroxyisopropyl monocarbonate ("Perbutyl I" manufactured by NOF Corporation) was used as the organic peroxide A, the same as in Example 1 was used. Similarly, composite resin particles, foamed particles, and foamed molded articles were produced.

(Example 14)
In this example, composite resin particles were prepared in the same manner as in Example 1 except that 1.72 g of t-butyl peroxybenzoate ("Perbutyl Z" manufactured by NOF Corporation) was used as the organic peroxide A. , Foamed particles and foamed molded articles were produced.

(Comparative Example 1)
In this example, composite resin particles, expanded particles, and expanded particle molded bodies were produced in the same manner as in Example 1, except that the organic peroxide B was not used as the polymerization initiator.

(Comparative Example 2)
In this example, 2.58 g of t-butyl peroxy-2-ethylhexyl monocarbonate ("Perbutyl E" manufactured by NOF CORPORATION) was used as the organic peroxide A, and the organic peroxide B was not used. Except for the above, composite resin particles, foamed particles, and molded foamed particles were produced in the same manner as in Example 1.

(Comparative Example 3)
In this example, instead of the t-hexylperoxybenzoate used as the organic peroxide B in Example 1, t-hexylperoxy-2-ethylhexanoate (“Perhexyl O” manufactured by NOF Corporation) was used. Except for the points used, composite resin particles, foamed particles, and foamed particle molded articles were produced in the same manner as in Example 1.

(Comparative Example 4)
In this example, composite resin particles, expanded particles, and expanded particle molding were performed in the same manner as in Example 1 except that the amount of t-hexylperoxybenzoate used as the organic peroxide B was changed to 0.22 g. The body was made.

(Comparative Example 5)
In this example, composite resin particles, expanded particles, and expanded particle molding were performed in the same manner as in Example 1 except that the amount of t-hexylperoxybenzoate used as the organic peroxide B was changed to 4.3 g. The body was made.

(Comparative Example 6)
In this example, first, except that the amount of the ethylene-based resin was changed from 8.65 kg to 9.61 kg, and the amount of the foam regulator master batch was changed from 1.35 kg to 0.39 kg, Nuclear particles were produced in the same manner as in Example 1. Next, 260 g of the core particles were used, and a mixed monomer of 225 g of styrene and 15 g of butyl acrylate was used as the first monomer, except that the second monomer was not used. Thus, composite resin particles, foamed particles, and a foamed particle molded product were produced.

(Comparative Example 7)
In this example, first, the amount of the ethylene-based resin was changed from 8.65 kg to 4.0 kg, and the amount of the foam regulator master batch was changed from 1.35 kg to 6.0 kg. Nuclear particles were produced in the same manner as in Example 1. Next, the same as Example 1 except that 25 g of the core particles were used, a mixed monomer of 10 g of styrene and 15 g of butyl acrylate was used as the first monomer, and 450 g of styrene was used as the second monomer. In this way, composite resin particles, foamed particles, and foamed molded articles were produced.

(Comparative Example 8)
In this example, first, the amount of the ethylene-based resin was changed from 8.65 kg to 9.2 kg, and the amount of the foam regulator master batch was changed from 1.35 kg to 0.8 kg. Nuclear particles were produced in the same manner as in Example 1. Next, 125 g of the core particles were used, a mixed monomer of 110 g of styrene and 15 g of butyl acrylate was used as the first monomer, 250 g of styrene was used as the second monomer, and no organic peroxide B was used. Except for this point, composite resin particles, foamed particles, and foamed molded articles were produced in the same manner as in Example 1. That is, the present example is an example performed in the same manner as in Example 13 except that the organic peroxide B was not used.

(Comparative Example 9)
In this example, instead of the t-hexylperoxybenzoate used as the organic peroxide B in Example 1, t-amylperoxy-2-ethylhexyl monocarbonate ("Luperox TAEC" manufactured by Arkema Yoshitomi Co., Ltd.) was used. Except for the points used, composite resin particles, foamed particles, and foamed particle molded articles were produced in the same manner as in Example 1.

(Comparative Example 10)
In this example, except that the addition amount of t-butyl peroxy-2-ethylhexyl monocarbonate ("Perbutyl E" manufactured by NOF CORPORATION) used as the organic peroxide A was changed to 0.415 g. In the same manner as in Example 1, a composite resin particle, a foamed particle, and a foamed particle molded product were produced.

(Example 15)
This example and Comparative Examples 11 to 12 described below are examples in which foaming was performed using an organic physical foaming agent. Specifically, in this example, first, the amount of the ethylene-based resin was changed from 8.65 kg to 20 kg, and the acrylonitrile-styrene copolymer (electric Core particles were produced in the same manner as in Example 1 except that 1 kg of "AS-XGS, weight average molecular weight: 109,000, acrylonitrile component amount: 28% by mass" manufactured by Chemical Industry Co., Ltd. was used.

  Then, in the same manner as in Example 1, a magnesium pyrophosphate slurry as a suspending agent was prepared in a 3 L internal volume autoclave equipped with a stirring device, and sodium lauryl sulfonate (10% by mass) as a surfactant was further prepared. 2.0 g of an aqueous solution), 0.2 g of sodium nitrite as a water-soluble polymerization inhibitor, and 75 g of core particles. Next, 1.72 g of t-butyl peroxy-2-ethylhexyl monocarbonate ("Perbutyl E" manufactured by NOF CORPORATION) as the organic peroxide A and t-hexyl peroxybenzoate 0 as the organic peroxide B were used. 0.86 g (“Perhexyl Z” manufactured by NOF Corporation) and 0.63 g of α-methylstyrene dimer (“NOFMER MSD” manufactured by NOF Corporation) as a chain transfer agent were dissolved in the first monomer. Then, the melt was poured into the suspension in the autoclave while stirring at a stirring speed of 500 rpm. Note that a mixed monomer of 60 g of styrene and 15 g of butyl acrylate was used as the first monomer.

  Next, after the air in the autoclave was replaced with nitrogen, the temperature was raised and the temperature in the autoclave was raised to 100 ° C. over 1 hour and 30 minutes. After the temperature was raised, the temperature was kept at 100 ° C. for 1 hour. Thereafter, the stirring speed was reduced to 450 rpm, and the temperature was maintained at 100 ° C. for 7.5 hours. One hour after the temperature reached 100 ° C., 350 g of styrene as the second monomer (styrene-based monomer) was added into the autoclave over 5 hours.

  Next, the inside of the autoclave was heated to a temperature of 125 ° C. over 2 hours, and kept at a temperature of 125 ° C. for 5 hours. Thereafter, the mixture was cooled to a temperature of 90 ° C. over 1 hour, the stirring speed was reduced to 400 rpm, and the temperature was maintained at 90 ° C. for 3 hours. When the temperature reached 90 ° C., 20 g of cyclohexane and 65 g of butane (a mixture of 20% by mass of normal butane and 80% by mass of isobutane) were added into the autoclave as an organic physical foaming agent over about 1 hour. Further, the temperature was raised to a temperature of 105 ° C. over 2 hours, kept at a temperature of 105 ° C. for 5 hours, and then cooled to a temperature of 30 ° C. over a period of about 6 hours.

  After cooling, the contents (expandable composite resin particles) were taken out, and nitric acid was added to dissolve magnesium pyrophosphate attached to the surfaces of the resin particles. Thereafter, dehydration and washing were performed by a centrifugal separator, and water adhering to the surface was removed by a flash dryer to obtain expandable composite resin particles. 0.008 parts by mass of N, N-bis (2-hydroxyethyl) alkylamine as an antistatic agent was added to 100 parts by mass of the obtained expandable composite resin particles. Further, 0.12 parts by mass of zinc stearate was added. These were used to coat the expandable composite resin particles.

Next, the composite resin particles containing a foaming agent obtained as described above were placed in a normal pressure batch foaming machine having a volume of 30 L, and steam was supplied into the foaming machine. Thereby, the expandable composite resin particles were expanded to a bulk density of 50 kg / m ³ to obtain expanded particles having a bulk expansion ratio of 20 times. Further, in-mold molding of the foamed particles was performed in the same manner as in Example 1 to obtain a foamed composite resin molded article.

  Regarding the expandable composite resin particles produced in this example and Comparative Examples 10 to 12 described below, the bead life was measured as follows instead of the evaluation of the expandability described above.

"Beads Life"
The expandable composite resin particles were left in an open state at a temperature of 23 ° C. for a predetermined period of time to disperse the foaming agent from the expandable composite resin particles. Thereafter, the expandable composite resin particles were expanded by heating at a heating steam temperature of 107 ° C. for 270 seconds to obtain expanded particles. Next, the foamed particles were dried at a temperature of 23 ° C. for 24 hours. Next, the bulk density (kg / m ³ ) of the dried expanded particles was measured. The method for measuring the bulk density (kg / m ³ ) is as described above. Then, the standing time during which the expanded beads bulk density 20 kg / m ³ is obtained (in days), i.e., standing time until the expanded beads having a bulk density of 20 kg / m ³ can not be obtained (in days) was bead life.

(Comparative Example 11)
In this example, a composite resin particle, a foamed particle, and a foamed composite resin molded product were produced in the same manner as in Example 16, except that the organic peroxide B was not used as the polymerization initiator.

(Comparative Example 12)
In this example, except that the addition amount of t-butyl peroxy-2-ethylhexyl monocarbonate used as the organic peroxide A was changed to 2.58 g and the organic peroxide B was not used, In the same manner as in Example 16, composite resin particles, foamed particles, and a foamed composite resin molded product were produced.

  Tables 1 to 3 also show polymerization conditions, foaming conditions, molding conditions, and evaluation results for Examples 2 to 15 and Comparative Examples 1 to 12, as in Example 1.

  As is known from Tables 1 to 3, by adjusting the composition of the ethylene-based resin and the styrene-based resin, the type of the polymerization initiator, and the amount thereof, the obtained composite resin particles have a low residual styrene monomer, Excellent in moldability and moldability (see Examples 1 to 15). The foamed composite resin molded article obtained by using these composite resin particles has good internal fusion, a high flexural modulus, and a high flexural breaking energy. Therefore, the above-mentioned foamed composite resin molded product is hard to set, has excellent bending resistance, and can prevent destruction due to deformation. Such a foamed composite resin molded article is particularly suitable for a packaging container such as a liquid crystal panel or a solar power panel. Further, as in Examples 1 to 14, the composite resin particles can be foamed with an inorganic gas such as carbon dioxide, and as in Example 15, an organic physical foaming agent such as hydrocarbon is added to the composite resin particles. It is also possible to prepare the expandable composite resin particles by impregnation, and expand the expandable composite resin particles.

  The reasons why the composite resin particles of Examples 1 to 15 exhibit the above-described excellent effects are considered as follows. That is, in these examples, the polymerization initiator has, as the polymerization initiator, an organic peroxide A having a t-butoxy group having a relatively strong hydrogen abstraction ability and a t-hexyloxy group having a relatively weak hydrogen abstraction ability. Organic peroxide B is used in combination at a predetermined ratio. Therefore, while exhibiting the effect of reducing the residual styrene monomer by the organic peroxide A and the effect of suppressing the crosslinking of the ethylene resin by the organic peroxide B, the polymerization of the styrene monomer in the core particles is performed. Can be advanced. As a result, as described above, while reducing the residual styrene-based monomer, the foamability of the composite resin particles and the moldability can be increased, and further, the internal fusion is good, the sag hardly occurs, and the deflection resistance is excellent. It is considered that it is possible to manufacture a foamed composite resin molded article that can prevent destruction due to deformation.

On the other hand, in the composite resin particles of Comparative Example 1, Comparative Example 8, and Comparative Example 11 in which the organic peroxide B was not used as the polymerization initiator, the amount of the residual styrene monomer was increased. Moreover, by reducing the amount of the organic peroxide B, it compares the ratio R _A of the amount of the organic peroxide A to the total amount of the organic peroxide A and an organic peroxide B is higher examples Also in the composite resin particles of No. 4, the amount of the residual styrene monomer was increased.

  Further, in the composite resin particles of Comparative Examples 2 and 12 produced without using the organic peroxide B and increasing the amount of the organic peroxide A, the amount of the residual styrene-based monomer was reduced, but The crosslinking density of the system resin tends to be high, the amount of XY gel is high, and the degree of swelling is too low. For this reason, there is a problem that the bending rupture energy of the foamed composite resin molded product is insufficient, and destruction due to deformation is likely to occur.

  Further, in the composite resin particles of Comparative Example 3 using the organic peroxide B having a low 10-hour half-life temperature, there is a problem that the amount of the residual styrene monomer increases. In the composite resin particles of Comparative Example 3, the crosslink density of the ethylene-based resin tends to be high, the XY gel amount is high, and the swelling degree is too low. For this reason, there is a problem that the bending rupture energy of the foamed composite resin molded product is insufficient, and destruction due to deformation is likely to occur.

Comparative Example 5, since increasing the amount of the organic peroxide B, an organic peroxide A and an organic peroxide B to the ratio R _A of the amount of the organic peroxide A to the total amount of low styrene is an example of the ratio is higher the total amount C _T of the organic peroxide a and an organic peroxide B to the system monomer 100 parts by mass. In the composite resin particles of Comparative Example 5, although the amount of the residual styrene monomer decreases, the crosslink density of the ethylene resin tends to increase, the XY gel amount is high, and the degree of swelling is too low. For this reason, there is a problem that the bending rupture energy of the foamed composite resin molded product is insufficient, and destruction due to deformation is likely to occur.

  The foamed composite resin molded article produced using the composite resin particles of Comparative Example 6 having a small amount of the styrene-based monomer has low rigidity, and thus has low compressive strength and low flexural modulus. For this reason, the foamed composite resin molded article of Comparative Example 6 has a problem that it is easily deformed due to bending and has insufficient deflection resistance. On the other hand, the foamed composite resin molded article produced using the composite resin particles of Comparative Example 7 having a large amount of styrene-based monomer has a high compressive strength and a high flexural modulus, but has insufficient bending rupture energy. There is a problem that destruction is likely to occur.

  In the composite resin particles of Comparative Example 9 using t-amyl peroxy-2-ethylhexyl monocarbonate having no t-hexyloxy group as the organic peroxide B, the residual styrene monomer increased. I was Further, the foamed composite resin molded article produced using the composite resin particles of Comparative Example 9 has a high compressive strength and a high flexural modulus, but has insufficient bending rupture energy, and is liable to be broken by deformation. There is.

Comparative Example 10, by reducing the amount of the organic peroxide A, the ratio of the total amount C _T of the organic peroxide A and an organic peroxide B to the styrene monomer 100 parts by mass lower This is an example. In the composite resin particles of Comparative Example 10, the amount of the residual styrene monomer was significantly increased.

  From the comparison between Example 1 and Comparative Example 1, it can be seen that the combined use of the organically modified oxide A and the organically modified oxide B reduced the residual styrene monomer amount by 91%. From the comparison between Example 12 and Comparative Example 8, it can be seen that the combined use of the organically modified oxide A and the organically modified oxide B reduced the residual styrene monomer amount by 90%.

Claims (3)

A dispersion step of dispersing core particles containing an ethylene-based resin in an aqueous medium,
In the aqueous medium, a modification step of impregnating the core particles with a styrene-based monomer and polymerizing to obtain composite resin particles,
As the styrene-based monomer, styrene alone or used together with styrene together with one or more selected from the group consisting of styrene derivatives and acrylic monomers,
The compounding amount of the styrene monomer is 100 to 1900 parts by mass with respect to 100 parts by mass of the ethylene resin contained in the core particles,
In the polymerization of the styrene-based monomer, as a polymerization initiator, an organic peroxide A having a t-butoxy group, a 10-hour half-life temperature of 80 to 120 ° C., and a t-hexyloxy group are used. And an organic peroxide B having a 10-hour half-life temperature of 80 to 120 ° C.,
The total blending amount of the organic peroxide A and the organic peroxide B with respect to 100 parts by mass of the styrene-based monomer is 0.4 to 1.2 parts by mass, and the organic peroxide A and the organic peroxide A method for producing composite resin particles, wherein the ratio of the amount of the organic peroxide A to the total amount of the peroxide B is 30 to 85% by mass. And 10-hour half-life temperature T _A of the organic peroxide A, the difference between the 10-hour half-life temperature T _B of the organic peroxide B (T _B -T _A) is within ± 20 ° C., claim 2. The method for producing composite resin particles according to 1.   3. The production of the composite resin particles according to claim 1, wherein a blending amount of the styrene-based monomer with respect to 100 parts by mass of the ethylene-based resin contained in the core particles is more than 400 parts by mass and 1900 parts by mass or less. 4. Method.