JP6964962B2 - Composite resin particles - Google Patents

Description

The present invention relates to composite resin particles using a composite resin obtained by impregnating and polymerizing an ethylene resin with a styrene monomer as a base resin.

The foamed particle molded product is used in a wide range of applications such as packaging materials, building materials, and vehicle members, taking advantage of its excellent properties such as cushioning property, light weight, vibration isolation property, soundproofing property, and heat insulating property. The foamed particle molded product is obtained by fusing a plurality of foamed particles to each other in a molding mold. The foamed particles are obtained by foaming the resin particles obtained by impregnating the resin particles with an organic physical foaming agent such as propane, butane, or pentane or an inorganic physical foaming agent such as carbon dioxide, nitrogen, or air by heating or the like. Be done. Styrene-based resin, propylene-based resin, ethylene-based resin and the like are mainly used as the resin component constituting the foamed particle molded body.

In particular, packaging containers used for plate-shaped products such as liquid crystal panels and photovoltaic power generation panels do not wear, crack, or chip due to scratches or rubbing, and can be used multiple times. A foamed particle molded product made of a propylene resin was used. However, due to the increase in the packing weight due to the increase in the panel size in recent years, there has been a problem that the amount of deflection in the packed state increases when the foamed particle molded product made of the propylene resin is used as the packing container. If the amount of deflection during packing is large, there is a risk that the container will fall off when both ends of the packed container are supported and lifted by a conveyor or the like, or the liquid crystal panel may be damaged due to the deflection.

On the other hand, a foamed particle molded body made of a composite resin of an ethylene-based resin and a styrene-based resin has attracted attention (see Patent Documents 1 to 3). In the foamed particle molded body made of such a composite resin, for example, the composite resin particles obtained by impregnating and polymerizing the nuclear particles containing an ethylene resin with a styrene monomer are foamed as described above. Manufactured by fusing to each other. In the foamed particle molded product thus obtained, the rigidity can be improved by increasing the ratio of the styrene-based resin component in the composite resin. As a result, it becomes possible to reduce the amount of deflection of the foamed particle molded product and improve the deflection resistance. Therefore, it is possible to avoid the above-mentioned problem during transportation when the foamed particle molded product is applied to the packaging container. Further, by increasing the proportion of the styrene resin component, it is possible to increase the foaming ratio of the foamed particle molded product while maintaining good deflection resistance. Therefore, there is an advantage that the weight of the foamed particle molded product can be reduced.

Japanese Unexamined Patent Publication No. 2014-196441 Japanese Unexamined Patent Publication No. 2014-196444 Japanese Patent No. 5058866

Increasing the blending ratio of the styrene-based monomer impregnated in the ethylene-based resin in order to increase the proportion of the styrene-based resin component in the composite resin increases the amount of the styrene-based monomer remaining in the composite resin particles. It becomes easier to do. As a result, the amount of the styrene-based monomer remaining in the foamed particle molded product obtained by using the composite resin particles may also increase. An increase in the amount of residual styrene-based monomer is not preferable because it causes VOC (volatile organic compounds) when used for automobiles and causes stains to be transferred to the packaged object when used for packing. .. On the other hand, if the amount of the polymerization initiator used for the polymerization of the styrene-based monomer is increased, the amount of the residual styrene-based monomer can be decreased. In this case, ethylene is produced during the polymerization of the styrene-based monomer. There is a risk that the cross-linking of the styrene resin will proceed. This may cause problems such as a decrease in foamability of the composite resin particles and an increase in molding pressure, and as a result, the cohesiveness between the foamed particles tends to decrease, and the tenacity of the foamed particle molded product is insufficient. , There is a risk that cracks are likely to occur.

The present invention has been made in view of the above problems, and it is possible to obtain a foamed particle molded product which has good internal fusion, is hard to settle, has excellent bending resistance, and can prevent fracture due to deformation, and is a residual styrene type. It is an object of the present invention to provide composite resin particles having a small amount of monomers and excellent foamability at the time of foaming and moldability at the time of molding.

One aspect of the present invention is a composite resin particle using a composite resin obtained by impregnating and polymerizing an ethylene resin with a styrene monomer as a base resin.
The ethylene resin has a melting point of 95 to 105 ° C.
The composite resin contains a structural unit derived from a styrene-based monomer in an amount of more than 400 parts by mass and 900 parts by mass or less with respect to 100 parts by mass of the ethylene-based resin.
The content of the styrene-based monomer present as a monomer in the composite resin particles is 0 to 500 mass ppm.
The composite content W _XY xylene insoluble content of the resin particles is 0 Ri 23% by mass,
The surface layer of the composite resin particles has a morphology in which the ethylene resin forms a continuous phase and the styrene resin composed of a polymer of the styrene monomer forms a dispersed phase, and the dispersed phase in the surface layer. The average diameter X ₁ μm of the composite resin particles satisfies the relationship of 0.01 ≦ X _{1 ≦ 0.2.}

Although the composite resin particles are made of a composite resin having a high content of structural units derived from the styrene-based monomer as described above, is the content of the styrene-based monomer present as a monomer low? It is 0. Further, although the content of the styrene-based monomer is low or 0, the content ratio of the xylene insoluble component is low or 0. That is, the cross-linking of the ethylene resin in the composite resin is suppressed. Therefore, the foamability of the composite resin particles at the time of foaming and the moldability at the time of molding can be improved. Further, although the content of the styrene-based monomer is low or 0, the fusion property is excellent. As a result, by using the composite resin particles, it becomes possible to produce a foamed particle molded product which has good internal fusion, is hard to settle, has excellent bending resistance, and can prevent fracture due to deformation. Further, by using the composite resin particles, it is possible to obtain a foamed particle molded product having a small amount of residual styrene-based monomer and excellent rigidity and toughness. Therefore, the foamed particle molded body obtained by using the composite resin particles is suitable for applications such as automobile members, and packaging containers such as liquid crystal panels and photovoltaic power generation panels.

(A) Cross-sectional view of the composite resin particles, (b) Cross-sectional view of the composite resin particles having a single-phase outermost layer. The figure which shows the transmission electron micrograph at a magnification of 10000 times in the central cross section of the composite resin particle of Example 1. FIG. The figure which shows the transmission electron micrograph of the composite resin particle of Example 1 with a magnification of 10000 times in the surface layer cross section. The figure which shows the transmission electron micrograph of the composite resin particle of Example 1 with a magnification of 50,000 times in the surface layer cross section. The figure which shows the transmission electron micrograph at a magnification of 10000 times in the central cross section of the composite resin particle of Comparative Example 1. FIG. The figure which shows the transmission electron micrograph of the composite resin particle of the comparative example 1 in the surface layer cross section of the magnification 10000 times. The figure which shows the transmission electron micrograph of the composite resin particle of Example 12 with a magnification of 10000 times in the central cross section. The figure which shows the transmission electron micrograph of the composite resin particle of Example 12 with a magnification of 50,000 times in the surface layer cross section. The figure which shows the relationship between the value of _{W XY / Mw × 10000 and bending fracture energy.}

Next, a preferred embodiment of the composite resin particles will be described. The composite resin particles can be used for producing composite resin foamed particles (hereinafter, referred to as “foamed particles”) by impregnating with a physical foaming agent and foaming the composite resin particles. As the physical foaming agent, an inorganic physical foaming agent such as carbon dioxide may be used, or an organic physical foaming agent such as a hydrocarbon may be used. The composite resin particles in the present specification are not only those that do not contain a physical foaming agent, but are also a concept that includes foamable composite resin particles that contain, for example, an organic physical foaming agent. Further, by in-mold molding of the foamed particles obtained by foaming the composite resin particles, a molded product (that is, a foamed particle molded product) in which a plurality of foamed particles are fused to each other can be produced.

The composite resin particles are made of a composite resin obtained by impregnating and polymerizing an ethylene resin with a styrene monomer as a base resin. In the present specification, the composite resin is a resin obtained by impregnating an ethylene resin with a styrene monomer and polymerizing it as described above, and is a styrene resin obtained by polymerizing an ethylene resin component and a styrene monomer. Although it is a resin containing a resin component, it is a different concept from a mixed resin obtained by mixing a polymerized ethylene resin and a polymerized styrene resin. When the styrene-based monomer is polymerized, not only the polymerization of the styrene-based monomers but also the graft polymerization of the styrene-based monomer on the polymer chain constituting the ethylene-based resin may occur. Therefore, the composite resin not only contains the ethylene-based resin component and the styrene-based resin component obtained by polymerizing the styrene-based monomer, but also the ethylene-based resin component obtained by graft-polymerizing the styrene-based monomer (that is, that is). , PE-g-PS component) may be contained.

The composite resin contains a structural unit derived from a styrene-based monomer in an amount of more than 400 parts by mass and 1900 parts by mass or less with respect to 100 parts by mass of the ethylene-based resin. When the content of the structural unit derived from the styrene-based monomer is 400 parts by mass or less, the rigidity of the foamed particle molded body obtained by using the composite resin particles may decrease, and the deflection resistance may become insufficient. .. From the viewpoint of further improving the rigidity and the deflection resistance, the content of the structural unit derived from the styrene-based monomer with respect to 100 parts by mass of the ethylene-based resin is preferably 450 parts by mass or more, preferably 500 parts by mass or more. Is more preferable. On the other hand, when the content of the structural unit derived from the styrene-based monomer exceeds 1900 parts by mass, the foamed particle compact obtained by using the composite resin particles becomes fragile and brittle. From the viewpoint of further preventing cracking of the foamed particle molded body, the content of the structural unit derived from the styrene-based monomer with respect to 100 parts by mass of the ethylene-based resin is preferably 1500 parts by mass or less, preferably 1000 parts by mass or less. More preferably, it is more preferably 900 parts by mass or less. The structural unit derived from the styrene-based monomer is a styrene-based monomer that constitutes a part of the ethylene-based resin component contained in the composite resin particles and the styrene-based resin component. The ethylene-based resin component may contain a styrene-based monomer as a graft chain or the like, but may not contain a styrene-based monomer. In the present specification, a preferable range, a more preferable range, and a more preferable range regarding the upper limit and the lower limit of the numerical range can be determined from all combinations of the upper limit and the lower limit.

Further, the content of the styrene-based monomer present as a monomer in the composite resin particles is 500 mass ppm or less, and may be 0. When the content of the styrene-based monomer existing as the monomer exceeds 500 mass ppm, it becomes impossible to obtain a foamed particle compact having a low content of the volatile organic compound (VOC), or the foamed particles. Dirt may be transferred from the molded body to the packaged object. Therefore, if the content of the styrene-based monomer is too large, the foamed particle molded product cannot be suitably used for, for example, an automobile member or a packaging material. From the viewpoint of more reliably obtaining a foamed particle molded product having a low VOC and capable of hindering the transfer of dirt, the content of the styrene-based monomer present as a monomer in the composite resin particles in the composite resin particles is It is preferably 400 mass ppm or less, more preferably 300 mass ppm or less, and further preferably 200 mass ppm or less. The content of the styrene-based monomer is most preferably 0, but from the viewpoint of further improving the feasibility, ease of realization, and fusion property of the composite resin particles obtained by impregnation polymerization, the styrene-based monomer is used. The content of the above is preferably 50% by mass or more, more preferably 80% by mass or more, and further preferably 100% by mass or more.

_{The content ratio W XY} of the xylene insoluble matter in the composite resin particles is 40% by mass or less, and may be 0. If the content ratio W _XY of the xylene insoluble matter exceeds 40% by mass, the foamability of the composite resin particles during foaming and the moldability during in-mold molding may be insufficient. From the viewpoint of further improving the rigidity and tenacity of the foamed particle molded body obtained by using the composite resin particles, the content ratio W _XY of the xylene insoluble matter is preferably 30% by mass or less, preferably 20% by mass or less. More preferably, it is more preferably 15% by mass or less, and particularly preferably 11% by mass or less. On the other hand, _{the lower limit of the content ratio W XY} of the xylene insoluble matter is preferably 1% by mass or more, and more preferably 5% by mass or more. The xylene insoluble component is obtained as a component insoluble in xylene when the composite resin particles are soxhlet-extracted with xylene.

The degree of swelling in methyl ethyl ketone at a temperature of 23 ° C., which is a mixture of the xylene insoluble component when the composite resin particles are soxhlet-extracted with xylene and the acetone-insoluble component contained in the xylene solution after the soxhlet extraction (hereinafter, simply "swelling degree"). ”) Is preferably 1.25 or more. In this case, the bending breaking energy of the foamed particle molded product obtained by using the composite resin particles can be further improved, and the toughness can be further improved. From the same viewpoint, the degree of swelling is more preferably 1.5 or more, and even more preferably 2 or more. Further, from the viewpoint of suppressing the shrinkage of the foamed particle molded product, the swelling degree of the composite resin particles is preferably 10 or less, and more preferably 5 or less.

The reason why the rigidity and tenacity are excellent as described above when the degree of swelling is equal to or higher than the above-mentioned predetermined value is presumed as follows. The degree of swelling (that is, the degree of swelling) when the crosslinked ethylene resin is immersed in the organic solvent has a correlation with the crosslinked structure (that is, the three-dimensional network structure) of the resin, and the finer the network, the more the organic solvent is absorbed. As the amount decreases, the degree of swelling decreases. On the other hand, the non-crosslinked ethylene resin also hardly swells 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 crosslinked ethylene-based resin component), the acetone-insoluble component in the xylene-soluble component (that is, the crosslinked ethylene-based resin component that has passed through the mesh, and the crosslinked ethylene-based resin component). When the degree of swelling of the insoluble component mixed with the uncrosslinked ethylene resin component (total) is large, the degree of swelling is small, and the degree of swelling is three-dimensionally crosslinked in the ethylene resin constituting the composite resin. It means that the mesh structure of the network structure contains a large amount of coarse ethylene resin components. The crosslinked ethylene resin component and the non-crosslinked ethylene resin component each include an ethylene resin component graft-polymerized with a styrene monomer (that is, a PE-g-PS component). It is presumed that the ethylene-based resin component having a crosslinked three-dimensional network structure and a coarse mesh forms a bubble film having high strength because it has strength but is moderately stretchable at the time of foaming. Further, in the composite resin foamed particles, the ethylene resin component in the composite resin is flexible and sufficiently deformable when compressed, so that the foamed particles even when the ratio of the styrene resin component in the composite resin is high. It is presumed that the closed cell structure can be maintained without breaking the bubble film. That is, when the degree of swelling is within a specific range, a foamed particle molded product having a high level of rigidity and tenacity and a large bending breaking energy can be obtained.

The weight average molecular weight Mw of the styrene resin component composed of the polymer of the styrene monomer and the content ratio W _XY mass% _{of the xylene insoluble matter in the composite resin particles are W XY} / Mw × 10000 ≦ 1. It is preferable to satisfy the relationship of 5. In this case, the bending fracture energy of the foamed particle molded product obtained by using the composite resin particles can be further improved. From the same viewpoint, more preferably _{W XY / Mw × 10000 ≦ 1} , and more preferably a W _XY /Mw×10000≦0.8.

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. A polymer, an ethylene-vinyl acetate copolymer, or the like can be used. As the ethylene resin, one kind of polymer may be used, but a mixture of two or more kinds of polymers may also be used.

The ethylene resin preferably contains linear low-density polyethylene as a main component. The linear low-density polyethylene preferably has a branched structure having a linear polyethylene chain and a short-chain branched chain having 2 to 6 carbon atoms. Specific examples thereof include an ethylene-butene copolymer, an ethylene-hexene copolymer, and an ethylene-octene copolymer. In particular, the ethylene-based resin is preferably a linear low-density polyethylene having a melting point of 105 ° C. or lower, which is polymerized 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 the toughness of the composite resin can be enhanced. Further, since the fusion strength between the foamed particles at the time of molding can be increased while reducing the low molecular weight component, it is possible to obtain a foamed particle molded product having a low VOC and being hard to break. Further, it becomes possible to obtain a foamed particle molded product having both the excellent rigidity of the styrene resin and the excellent tenacity of the ethylene resin at a higher level.

The melting point Tm of the ethylene resin is preferably 95 to 105 ° C. In this case, since the ethylene-based resin can be sufficiently impregnated with the styrene-based monomer during the production of the composite resin particles, it is possible to prevent the suspension system from becoming unstable during the polymerization. As a result, it becomes possible to obtain a foamed particle molded product 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 resin is more preferably 100 to 105 ° C. The melting point Tm can be measured as the melting peak temperature by differential scanning calorimetry (DSC) based on JIS K7121 (1987).

The ethylene resin is preferably made of linear low-density polyethylene in which the melting point Tm (° C.) and the Vicat softening point Tv (° C.) satisfy the relationship of Tm−Tv ≦ 20 (° C.). It is presumed that such an ethylene-based resin exhibits a uniform molecular structure, and the network structure by cross-linking is more uniformly distributed in the ethylene-based resin. Therefore, in this case, the strength and tenacity of the foamed particle molded product obtained by using the composite resin particles can be improved. From the viewpoint of further improving the strength and toughness of the molded product, the linear low-density polyethylene more preferably satisfies Tm-Tv ≦ 15 (° C.), and more preferably Tm-Tv ≦ 10 (° C.). Is even more preferable. 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 kinds of resins, the melting point of the mixed resin and the Vicat softening point of the mixed resin are defined as the melting point of the ethylene resin and the Vicat softening point.

From the viewpoint of further improving the foamability of the composite resin particles, the melt mass flow rate (that is, MFR) of the ethylene 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, 1.0 to 3.0 g / 10 minutes is more preferable. 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). As the measuring device, a melt indexer (for example, model L203 manufactured by Takara Kogyo Co., Ltd.) can be used.

The composite resin contains a styrene-based resin component obtained by polymerizing a styrene-based monomer. In the present specification, the styrene constituting the styrene-based resin component and the monomer copolymerizable with the styrene added as needed may be collectively referred to as a styrene-based monomer. The ratio of styrene in the styrene-based monomer is preferably 50% by mass or more, more preferably 80% by mass or more, and further preferably 90% by mass or more. Examples of the monomer copolymerizable with styrene include the following styrene derivatives and other vinyl monomers.

Examples of styrene derivatives include α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-methoxystyrene, pn-butylstyrene, and p. Examples thereof include -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 a mixture of two or more types.

Examples of other vinyl monomers include acrylic acid esters, methacrylic acid esters, acrylic acids, methacrylic acid, vinyl compounds containing hydroxyl groups, vinyl compounds containing nitrile groups, vinyl organic acid compounds, olefin compounds, diene compounds, and halogens. Examples thereof include vinyl oxide 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 ester include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate and the like. Examples of the methacrylic acid ester include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate and the like. These may be used alone or in a mixture of two or more types.

Examples of the hydroxyl group-containing vinyl compound include hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate and the like. Examples of the vinyl compound containing a nitrile group include acrylonitrile and methacrylonitrile. Examples of the vinyl acetate compound include vinyl acetate and vinyl propionate. These may be used alone or in a mixture of two or more types.

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 halogenated vinylidene compound include vinylidene chloride and the like. Examples of the maleimide compound include N-phenylmaleimide and N-methylmaleimide. These may be used alone or in a mixture of two or more types.

As the styrene-based resin component, polystyrene or a copolymer of styrene and an acrylic monomer is preferable from the viewpoint of enhancing the foamability of the composite resin particles. From the viewpoint of further enhancing foamability, it is preferable to use styrene and butyl acrylate as the styrene-based monomer constituting the styrene-based resin component. In this case, the content of the structural unit derived from butyl acrylate in the composite resin is preferably 0.5 to 10% by mass, more preferably 1 to 8% by mass, based on the entire composite resin. It is preferably 2 to 5% by mass, more preferably 2 to 5% by mass.

In general, there are three forms in the morphology of a composite resin obtained by impregnating and polymerizing an ethylene resin with a styrene monomer. Specifically, there is a morphology (this is called a "sea-sea structure") in which an ethylene-based resin component and a styrene-based resin component form a co-continuous phase. A morphology in which the ethylene-based resin component forms a dispersed phase (also called an island phase) and the styrene-based resin component forms a continuous phase (this is also called a sea phase) (this is called an "island sea structure"). Exists. In addition, morphology (this is called "sea island structure") in which the ethylene resin component forms a continuous phase (also called a sea phase) and the styrene resin component forms a dispersed phase (this is also called an island phase). exist.

The surface layer of the composite resin particles has a morphology in which the ethylene-based resin component forms a continuous phase and the styrene-based resin component formed by the polymerization of the styrene-based monomer forms a dispersed phase consisting of a discontinuous phase. It is preferable that _{the average diameter X 1} μm of the dispersed phase in the surface layer satisfies the relationship of 0.01 ≦ X _{1 ≦ 0.2.} In this case, although the amount of residual styrene-based monomer is small, the internal fusion of the foamed particle molded product obtained by using the composite resin particles can be improved, and the foamed particles have better toughness. It becomes possible to manufacture a molded product. Here, as shown in FIG. 1A, the surface layer is a region R of 2 μm from the outermost surface 19 of the composite resin particles toward the center O of the composite resin particles on the cut surface passing through the center O of the composite resin particles 1. It is _1. In FIG. 1 (a), W ₁ = 2 μm. Further, as shown in FIG. 1 (b), when the outermost surface layer 10 made of a single-phase styrene resin is formed on the outermost surface 19 on the cut surface passing through the center O of the composite resin particles, it is combined with the surface layer. _{Is a region R 1} from the virtual surface 18 (that is, the boundary 18 between the outermost layer and the composite resin) excluding the outermost layer 10 of the single phase to 2 μm toward the center O of the composite resin particles. In FIG. 1 (b), W ₂ = 2 μm. The inside is a region R ₂ that includes the center O of the composite resin and its surroundings, and _{does not include the above-mentioned surface layer R 1} . In FIGS. 1 (a) and 1 (b), the surface layer is represented by the region R ₁ marked with dark dots hatching relatively density, inside, denoted by the thin dot hatching a relatively density regions It is represented by R _2. From the viewpoint of further increasing the toughness of the foamed particle molded body, _{it is more preferable that the average diameter X 1} μm of the dispersed phase in the surface layer of the composite resin particles satisfies the relationship of 0.02 ≤ X ₁ ≤ 0.15, and 0.03. It is more preferable to satisfy the relationship of ≦ X ₁ ≦ 0.13, and it is particularly preferable to satisfy the relationship of _{0.04 ≦ X 1 ≦ 0.09.}

Further, both the surface layer and the inside of the composite resin particles are dispersed phases in which the ethylene-based resin component forms a continuous phase and the styrene-based resin component formed by the polymerization of the styrene-based monomer is a discontinuous phase. _{The average diameter X 1} μm of the dispersed phase in the surface layer and the average diameter X ₂ μm of the dispersed phase inside are 0.01 ≤ X ₁ ≤ 0.2 and 0.1 ≤ X. ₂ ≦ 2, and it is preferable to satisfy the relation of X ₁ ≦ X _2/4. In this case, the internal fusion of the foamed particle molded product obtained by using the composite resin particles becomes better, and the foamed particle molded product can exhibit better toughness. From the viewpoint of further improving the toughness of the foamed particle molded body, the average diameter X ₂ μm of the dispersed phase inside preferably satisfies the relationship of 0.5 ≤ X ₂ ≤ 1.7, and is 0.7. It is more preferable to satisfy the relationship of ≦ X _{2 ≦ 1.5.} It is more preferable to satisfy the relation of X ₁ ≦ X _2/6, it is more preferable to satisfy the relation of X ₁ ≦ X _2/10.

The morphology of the composite resin particles can be observed by the following method. As a specific method for observing the morphology inside the composite resin particles, first, a sample for observation is cut out from the center of the composite resin particles. Next, this observation sample is embedded in an epoxy resin, stained with ruthenium tetroxide, and then an ultrathin section is prepared from the sample using an ultramicrotome or the like. This ultrathin section is placed on a grid, and the morphology of the central cross section of the composite resin particles is observed with a transmission electron microscope (for example, JEM1010 manufactured by JEOL Ltd.) at a magnification of 10000 times or 50,000 times, and a cross-sectional photograph (that is, TEM) is observed. Take a photo). From the cross-sectional photograph, the morphology of the phase of the ethylene-based resin component and the phase of the styrene-based resin component in the composite resin particles is visually observed. In addition, the average diameter of the dispersed phase can be calculated from the TEM photograph. Specifically, the longest diameters of 100 dispersed phases randomly selected in the TEM photograph were measured, and the measured values were arithmetically averaged to obtain _{the average diameter x 2 μm of the dispersed phases.} When the shape of the dispersed phase in the cross-sectional photograph is, for example, a perfect circle, the diameter is the longest diameter of the dispersed phase, and when the shape of the dispersed phase is, for example, an ellipse, the major axis is the largest of the dispersed phases. It has a major axis. Further, the morphology of the surface layer of the composite resin particles can be observed in the same manner as the above method except that a sample for observation is cut out from the surface layer of the composite resin particles.

The weight average molecular weight Mw of the styrene resin component composed of the polymer of the styrene monomer is preferably 100,000 to 400,000. In this case, shrinkage of the foamed particles obtained by foaming the composite resin particles can be further prevented. Further, when the foamed particles are molded in the mold, the fusion property between the foamed particles can be further improved. As a result, the dimensional stability of the foamed particle molded product can be further improved. From the same viewpoint, the weight average molecular weight of the styrene resin component is more preferably 150,000 to 350,000.

The glass transition temperature (that is, Tg) of the styrene resin component 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. Further, when the foamed particles obtained after foaming are molded in the mold, the fusion property between the foamed particles can be further improved, and the dimensional stability of the foamed particle molded product can be further improved.

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

The composite resin particles are produced, for example, by performing the following dispersion step and modification step. In the dispersion step, nuclear particles containing an ethylene resin component as a main component are dispersed in an aqueous medium. In the modification step, the nuclei are impregnated with a styrene-based monomer and polymerized in the presence of a polymerization initiator in an aqueous medium. Further, the composite resin particles are used for producing foamed particles as described above. The foamed particles are subjected to a foaming step in which the resin particles are impregnated with a physical foaming agent during and / or after the polymerization of the styrene-based monomer to prepare composite resin particles containing the foaming agent, and the composite resin particles are foamed. It can be manufactured by doing. Hereinafter, each step will be described in detail.

In the dispersion step, nuclear particles containing an ethylene-based resin component as a main component are used, and the nuclear particles can contain additives such as a bubble modifier, a colorant, a lubricant, and a dispersion diameter expanding agent. The nuclei particles can be produced by blending the above-mentioned additives, which are added as needed, with the ethylene-based resin component, melt-kneading the blend, and then atomizing the mixture. Melt kneading can be performed by an extruder. In order to perform uniform kneading, it is preferable to mix the resin components in advance and then extrude. The resin components can be mixed by using a mixer such as a Henschel mixer, a ribbon blender, a V blender, or a Ladyge mixer. Melt-kneading is preferably carried out using, for example, a screw or a twin-screw extruder of a high dispersion type such as a dalmage type, a madock type, and a unimelt type.

Further, in order to adjust the bubble size of the foamed particles obtained after the foaming of the composite resin particles, a bubble adjusting agent can be added to the core particles in advance. As the bubble adjusting agent, for example, an organic substance such as a higher fatty acid bisamide or a higher fatty acid metal salt, or an inorganic substance can be used. When an organic bubble modifier is used, the blending amount thereof is preferably in the range of 0.01 to 2 parts by mass with respect to 100 parts by mass of the resin component used for the nuclear particles. When an inorganic bubble adjusting agent is used, the blending amount thereof is preferably in the range of 0.1 to 5 parts by mass with respect to 100 parts by mass of the resin component used for the nuclear particles.

The miniaturization of the nuclear particles is performed, for example, by cutting the melt-kneaded compound while extruding it 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 liquid in which nuclear particles are dispersed in an aqueous medium can be obtained. As the aqueous medium, for example, deionized water can be used. The nuclear particles are preferably dispersed in an aqueous medium together with the suspending agent. In this case, the styrene-based 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. , Calcium carbonate, calcium sulfate, barium sulfate, talc, kaolin, bentonite and other fine-grained inorganic suspending agents can be used. Further, for example, an organic suspending agent such as polyvinylpyrrolidone, polyvinyl alcohol, ethyl cellulose, and hydroxypropyl methyl cellulose can also be used. Preferred are tricalcium phosphate, hydroxyapatite, and magnesium pyrophosphate. 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 is preferable. More preferably, 0.3 to 5 parts by mass is preferable. If the amount of the suspending agent is too small, it becomes difficult to stably suspend the styrene-based monomer in the reforming step, and a lump of resin may be generated. On the other hand, if the amount of the suspending agent is too large, not only the production cost increases, but also the particle size distribution of the composite resin particles obtained after the modification step may be widened.

Surfactants 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. These surfactants can be used alone or in combination of two or more.

As the anionic surfactant, for example, sodium alkylsulfonate, sodium alkylbenzenesulfonate, sodium laurylsulfate, sodium α-olefin sulfonate, sodium dodecyldiphenyl ether disulfonate and the like can be used.
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, alkylamine salts such as coconutamine acetate and stearylamine acetate can be used. Further, quaternary ammonium such as lauryltrimethylammonium chloride and stearyltrimethylammonium chloride can also 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.

Preferably, an anionic surfactant may be used as the surfactant. More preferably, an alkyl sulfonic acid alkali metal salt (preferably a sodium salt) having 8 to 20 carbon atoms is preferable. This allows the suspension to be sufficiently stabilized.

Further, if necessary, an electrolyte composed of inorganic salts such as lithium chloride, potassium chloride, sodium chloride, sodium sulfate, sodium nitrate, sodium carbonate and sodium bicarbonate can be added to the aqueous medium. Further, in order to obtain a foamed particle molded product 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 is difficult to impregnate in the nuclear particles and dissolves in the aqueous medium. Therefore, the styrene-based monomer impregnated in the nuclear particles is polymerized, but the fine droplets of the styrene-based monomer in the aqueous medium not impregnated in the nuclear particles and the nuclear particles being absorbed by the nuclear particles. It is possible to suppress the polymerization of styrene-based monomers near the surface. As a result, it is presumed that the amount of the styrene-based resin on the surface layer of the composite resin particles can be reduced, and the toughness of the obtained foamed particle molded body is improved. The amount of the water-soluble polymerization inhibitor added is 0.001 to 0.1 parts by mass with respect to 100 parts by mass of an aqueous medium (specifically, all water in the system containing water such as a reaction product-containing slurry). Is preferable, and 0.005 to 0.06 parts by mass is more preferable.

In the modification step, the nuclei are impregnated with a styrene-based monomer and polymerized in an aqueous medium. The polymerization of the styrene-based monomer is carried out in the presence of a polymerization initiator. In this case, cross-linking of the ethylene resin may occur with the polymerization of the styrene monomer. A polymerization initiator is used in the polymerization of the styrene-based monomer, but a cross-linking agent can be used in combination if necessary. Further, when using the polymerization initiator and / or the cross-linking agent, it is preferable to dissolve the polymerization initiator and / or the cross-linking agent in the styrene-based monomer in advance.

The polymerization initiator has 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 has a 10-hour half-life temperature of 80. It is preferable to use it in combination with the organic peroxide B at ~ 120 ° C. In this case, even if the amount of the styrene-based monomer impregnated in the nuclei particles is increased, it is possible to produce composite resin particles in which the content of the residual styrene-based monomer is small and the content ratio of the xylene insoluble content is small. Become. Examples of the organic peroxide A include t-butylperoxy-2-ethylhexyl monocarbonate, t-butylperoxy-2-ethylhexanoate, t-butylperoxylaurate, and t-butylperoxyisopropylmono. Carbonate, t-butylperoxybenzoate, di-t-butyl peroxide, 1,1-bis (t-butylperoxy) cyclohexane and the like can be used. From the viewpoint that the residual styrene-based monomer can be more easily reduced, t-butylperoxy-2-ethylhexyl monocarbonate is preferable as the organic peroxide A. As the organic peroxide B, for example, t-hexyl peroxybenzoate, t-hexyl peroxyisopropyl monocarbonate, di-t-hexyl peroxide and the like can be used. The t-hexylper is used as the organic peroxide B from the viewpoint that the residual styrene-based monomer can be more easily reduced, the cross-linking of the ethylene-based resin component can be further suppressed, and the deterioration of foamability and moldability can be further prevented. Oxybenzoate is preferred.

Further, when an organic peroxide having a 10-hour half-life temperature of 80 ° C. or higher is used as the polymerization initiator, the amount of residual styrene-based monomer in the composite resin particles can be reduced. Further, in this case, it is possible to prevent the shape of the composite resin particles from becoming flat, and it is possible to obtain substantially spherical composite resin particles. As a result, substantially spherical foamed particles can be obtained, and such substantially spherical foamed particles are excellent in filling property into the molding mold at the time of in-mold molding. 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 90 ° C. or higher, and further preferably 95 ° C. or higher. Further, even when an organic peroxide having a 10-hour half-life temperature of 120 ° C. or less is used, the amount of residual styrene-based monomer in the composite resin particles can be reduced, and the resin particles can be condensed at the time of polymerization. Can be prevented. 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 particularly preferably 105 ° C. or lower. preferable. The above-mentioned substantially spherical shape means that the shape is spherical in appearance, and includes not only a spherical shape but also a shape close to a spherical shape.

The 10-hour half-life temperature is defined as the 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 internal air is previously replaced with nitrogen. Next, the organic peroxide is thermally decomposed by immersing the glass tube in a constant temperature bath set at a predetermined temperature. Here, assuming that 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 of ₀ / [PO] _{t holds.} Therefore, if the relationship between the time t and ln [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 Can be sought. The half-life temperature t _1/2 is obtained _{for a plurality of temperatures, and the relationship between lnt 1/2} and 1 / T is plotted on a graph to obtain a 10-hour half-life temperature. T is the absolute temperature (unit: K). The data of the 10-hour half-life temperature described in the catalog or technical data issued by the manufacturer of the organic peroxide may be used.

Further, it is preferable that 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 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 impregnated in the core particles is increased within the above range, the residual styrene-based monomer can be reduced while suppressing the cross-linking of the ethylene-based resin in the composite resin particles. Can be done. 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 within ± 15 ° C., and more preferably within ± 10 ° C. Is more preferable, and it is particularly preferable that the temperature is within ± 5 ° C.

_{In the reforming step, the total amount C T} of the organic peroxide A and the organic peroxide B with respect to 100 parts by mass of the styrene-based monomer is preferably 0.4 parts by mass or more. In this case, the amount of residual styrene-based monomer in the composite resin particles can be reduced. From the viewpoint of further reducing the amount of residual styrene-based monomer, the total blending amount C _T is more preferably 0.5 parts by mass or more, and further preferably 0.6 parts by mass or more. Further, the total blending amount C _T is preferably 1.2 parts by mass or less. In this case, the foamability and moldability of the composite resin particles can be improved. Further, in this case, when the foamed particle molded product is manufactured using the composite resin particles, the foamed particles in the molded product are more sufficiently internally fused to each other, and the bending and breaking energy of the molded product can be improved. .. From the viewpoint of further improving the foamability and moldability of the composite resin particles, improving the internal fusion of the foamed particles in the foamed particle molded product, and further improving the bending breaking energy, the total blending amount C _T is more preferably 1 part by mass or less, and further preferably 0.8 part by mass or less.

Also, in the reforming step, it is preferred that 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. In this case, it is possible to prevent an increase in the xylene insoluble content in the composite resin particles and improve the foamability and moldability of the composite resin particles. Further, in this case, when the foamed particle molded product is manufactured using the composite resin particles, the foamed particles in the molded product are more sufficiently internally fused to each other, and the bending and breaking energy of the molded product can be improved. .. From the viewpoint of further improving the foamability and moldability of the composite resin particles, and from the viewpoint of improving the internal fusion of the foamed particles in the foamed particle molded product and further improving the bending break energy, the ratio _RA is It is more preferably 40% by mass or more, and further preferably 50% by mass or more. Further, the ratio _RA is preferably 85% by mass or less. In this case, the amount of residual styrene-based monomer in the composite resin particles can be reduced. Further, in this case, when the foamed particle molded product is manufactured using the composite resin particles, the foamed particles in the molded product are more sufficiently internally fused to each other, and the bending and breaking energy of the molded product can be improved. .. From the same viewpoint, the ratio _RA is more preferably 80% by mass or less, and further preferably 70% by mass or less.

When the nuclei are impregnated with the styrene-based monomer and polymerized, the entire amount of the styrene-based monomer to be blended can be added all at once to the aqueous medium in which the nuclei are dispersed. The total amount of the styrene-based monomers in the above can be divided into, for example, two or more, and these monomers can be added at different timings. Specifically, a part of the total amount of the styrene-based monomer to be blended is added to an aqueous medium in which nuclear particles are dispersed to impregnate and polymerize the styrene-based monomer, and then Further, the balance of the styrene-based monomer to be blended can be added to the aqueous medium once or twice or more. By adding the styrene-based monomer in a divided manner as in the latter case, it is possible to further suppress the condensation of the resin particles during the polymerization.

Further, the polymerization initiator can be added to the aqueous medium in a state of being dissolved in the styrene-based monomer. As described above, when the styrene-based monomer to be blended is divided into two or more times and added at different timings, the polymerization initiator should be dissolved in the styrene-based monomer added at any timing. It is also possible to add a polymerization initiator to each styrene-based monomer added at different timings. When the styrene-based monomer is added in a divided manner, 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 the first monomer. 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 the polymerization. As a result, it becomes possible to obtain a foamed particle molded product having both the excellent rigidity of the styrene resin and the excellent tenacity of the ethylene resin at a higher level. Further, as described above, when a part of the styrene-based monomer to be blended is added as the first monomer, the rest of the total amount of the styrene-based monomer to be blended is used 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 can be further divided and added.

The seed ratio of the styrene-based monomer added as the first monomer (that is, the mass ratio of the first monomer to the nuclear particles) is preferably 0.5 or more. In this case, it becomes easy to make the shape of the composite resin particles closer to a spherical shape. From the same viewpoint, the seed ratio is more preferably 0.7 or more, and further preferably 0.8 or more. The seed ratio is preferably 1.5 or less. In this case, it is possible to further prevent the styrene-based monomer from being polymerized before the nuclear particles are sufficiently impregnated, and it is possible to further prevent the generation of resin lumps. 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.

It is preferable that the melting point Tm (° C.) of the ethylene resin in the nuclear 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 the polymerization. As a result, it becomes possible to obtain a foamed particle molded product having both the excellent rigidity of the styrene resin and the excellent tenacity of the ethylene resin at a higher level. The impregnation temperature and the polymerization temperature in the reforming step vary depending on the type of the polymerization initiator used, but are preferably 60 to 105 ° C, more preferably 70 to 105 ° C. The cross-linking temperature varies depending on the type of cross-linking agent used, but is preferably 100 to 150 ° C.

Further, a bubble adjusting agent can be added to the styrene-based monomer. As the bubble adjusting agent, 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 acid amide, stearic acid amide and the like can be used. As the fatty acid bisamide, for example, ethylene bisstearic acid amide or the like can be used. The bubble adjusting agent is preferably used in an amount of 0.01 to 2 parts by mass with respect to 100 parts by mass of the styrene-based 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, if necessary.

As the plasticizer, for example, fatty acid ester, acetylated monoglyceride, fats and oils, hydrocarbon compound and the like can be used. As the fatty acid ester, for example, glycerin tristearate, glycerin trioctate, glycerin trilaurate, sorbitan tristearate, sorbitan monostearate, butyl stearate and the like can be used. Further, as the acetylated monoglyceride, for example, glycerin diacet monolaurate or the like can be used. As the 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 also be used. Further, 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. As the colorant, furnace black, channel black, thermal black, acetylene black, ketjen black, graphite, carbon fiber and the like can be used. As the chain transfer agent, for example, n-dodecyl mercaptan, α-methylstyrene dimer and 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 bubble modifier, plasticizer, oil-soluble polymerization inhibitor, flame retardant, colorant, and chain transfer agent can be dissolved in a solvent and impregnated into the nuclear particles. As the solvent, for example, aromatic hydrocarbons such as ethylbenzene and toluene, and aliphatic hydrocarbons such as heptane and octane can be used.

For foaming of composite resin fat particles, a preliminary foaming method in which the composite resin particles are impregnated with a foaming agent in advance and then heated with steam, hot water or warm air, or after heating with a foaming agent in a pressure vessel, the particles are released to a lower pressure. A direct foaming method can be adopted. As the foaming agent to be used, an organic foaming agent such as butane, pentane or propane can be used, or an inorganic foaming agent such as carbon dioxide gas, air or nitrogen can be used. An inorganic foaming agent is preferable. In this case, the foaming agent is released from the foamed particles after foaming, and the foaming agent does not remain in the foamed particles. Therefore, the internal pressure of the particles is unlikely to increase during molding, and the molded product can be cooled in a short time and taken out from the molding mold.

The foamed particle molded product can be produced by a known in-mold molding method by steam heating. That is, a foamed particle molded product can be obtained by filling a large number of foamed particles in a molding mold such as a mold and introducing steam into the molding mold to fuse the foamed particles to each other.

(Example 1)
The composite resin particles according to the examples will be described below.
The composite resin particles of this example are composite resin particles using a composite resin obtained by impregnating and polymerizing an ethylene-based resin with a styrene-based monomer as a base resin. That is, the composite resin contains an ethylene-based resin component and a styrene-based resin component obtained by polymerizing a styrene-based monomer. The content of the structural unit derived from the styrene-based monomer with respect to 100 parts by mass of the ethylene-based resin in the composite resin particles is 574 parts by mass. The content of the styrene-based monomer present as a monomer in the composite resin particles is 150 mass ppm. _{The content ratio W XY} of the xylene insoluble matter in the composite resin particles is 6% by mass. Hereinafter, a method for producing the composite resin particles of this example will be described. In this example, the obtained composite resin particles are foamed to produce foamed particles, and the foamed particles are further used to produce a foamed particle molded product.

(1) Preparation of Nuclear Particles As an ethylene resin, linear low-density polyethylene (specifically, "Niporon Z HF210K" manufactured by Tosoh Corporation) polymerized using a metallocene polymerization catalyst was prepared. The melting point Tm of this ethylene resin is 103 ° C. In addition, "CE-7335" manufactured by Polycol Co., Ltd. was prepared as a masterbatch of foam nucleating agent. "CE-7335" manufactured by Polycol Co., Ltd. contains 10% by mass of zinc borate (bubble adjusting agent) and 90% by mass of linear low-density polyethylene ("Niporon Z HF210K" manufactured by Tosoh Corporation). %. 8.65 kg of an ethylene resin and 1.35 kg of a bubble adjusting agent masterbatch were put 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 to an average of 0.5 mg / piece by an underwater cutting method to obtain nuclear particles containing an ethylene resin as a main component. The melt kneading of the resin mixture was carried out by setting the maximum temperature of the extruder to 250 ° C.

(2) Preparation of Composite Resin Particles 1000 g of deionized water was placed in an autoclave having an internal volume of 3 L equipped with a stirrer, and 6.0 g of sodium pyrophosphate was further added. Then, 12.9 g of powdered magnesium nitrate hexahydrate was added, and the mixture was stirred at room temperature for 30 minutes. As a result, a magnesium pyrophosphate slurry as a suspending agent was prepared. Next, 2.0 g of sodium lauryl sulfonate (10% by mass aqueous solution) as a surfactant, 0.2 g of sodium nitrite as a water-soluble polymerization inhibitor, and 75 g of nuclear particles were added to this suspending agent.

Next, two types of organic peroxides were prepared as polymerization initiators. Specifically, t-butylperoxy-2-ethylhexyl monocarbonate (specifically, "Perbutyl E" manufactured by NOF CORPORATION) was prepared as the organic peroxide A, and the organic peroxide B was prepared. t-hexyl peroxybenzoate (specifically, "Perhexyl Z" manufactured by NOF CORPORATION) was prepared. In the table described later, t-butylperoxy-2-ethylhexyl monocarbonate is indicated as "A1", and t-hexyl peroxybenzoate is indicated as "B1". Further, as a chain transfer agent, α-methylstyrene dimer (specifically, “NOFMER MSD” manufactured by NOF CORPORATION) was prepared. Then, 1.72 g of t-butylperoxy-2-ethylhexyl monocarbonate, 0.86 g of t-hexyl peroxybenzoate, and 0.63 g of α-methylstyrene dimer were added to the first monomer (styrene-based monomer). It was dissolved. Then, while stirring the melt at a rotation speed of 500 rpm, it was put into the above-mentioned autoclave into which nuclear particles and the like were put. As the first monomer, a mixed monomer of 60 g of styrene and 15 g of butyl acrylate was used.

Then, after replacing the air in the autoclave with nitrogen, the temperature was started, 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 maintained at 100 ° C. for 1 hour. Then, the stirring speed was lowered to 450 rpm, and the mixture was maintained at a temperature of 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 a second monomer (specifically, a styrene-based monomer) was added into the autoclave over 5 hours.

Next, the temperature inside the autoclave was raised to a temperature of 125 ° C. over 2 hours, and the temperature was maintained at 125 ° C. for 5 hours. Then, the inside of the autoclave was cooled, and the contents (composite resin particles) were taken out. Then, nitric acid was added to dissolve magnesium pyrophosphate adhering to the surface of the composite resin particles. After that, dehydration and washing are performed with a centrifuge, and moisture adhering to the surface is removed with an airflow drying device, so that the ratio (mass ratio) of the structural unit derived from the styrene-based monomer to the ethylene-based resin is 85: Composite resin particles using 15 composite resins as a base resin were obtained. The ratio of the structural unit derived from the styrene-based monomer to the ethylene-based resin can be obtained from the compounding ratio (mass ratio) of the styrene-based monomer and the ethylene-based resin used at the time of 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 organic peroxides a and the ratio of the amount of the organic peroxide a to the total amount of the organic peroxide B R _a, for styrene monomer 100 parts by organic peroxides a and an organic peroxide B to the total amount C _T of the organic peroxide a and an organic peroxide 10-hour half-life difference in temperature [Delta] T of B (provided that, [Delta] T = T _B -T _a) Is shown in Table 1. In Table 1 described later, t-butylperoxy-2-ethylhexyl monocarbonate used as the organic peroxide A is represented as "A1". Further, t-hexyl peroxybenzoate used as organic peroxide B is represented as "B1", t-hexyl peroxyisopropyl monocarbonate is represented as "B2", and di-t-hexyl peroxide is represented. Is expressed as "B3". Further, the organic peroxide t-hexylperoxy-2-ethylhexanoate is represented as "B4", and the t-amylperoxy-2-ethylhexyl monocarbonate is represented as "B5".

Further, regarding the composite resin particles obtained in this example, the mass ratio of the ethylene-based resin component in the composite resin particles to the structural unit derived from the styrene-based monomer (structural unit derived from the ethylene-based resin / styrene-based monomer). ) Is shown in Table 1. Further, the composite resin particles have (a) foamability, (b) content of styrene-based monomer remaining as a monomer (R-SM), (c) swelling degree, and (d) content of xylene insoluble matter. Ratio (that is, XY gel amount W _XY ), (e) Weight average molecular weight Mw of the styrene resin component, (f) _{Relationship between XY gel amount W XY} and the weight average molecular weight of the styrene resin component (that is, W _XY / Mw × 10000), (g) morphology of the inside and surface of the composite resin particles, (h) the average diameter X _{2 of the dispersed phase inside the composite resin particles and the average diameter X 1} of the dispersed phase in the surface layer are as follows. Examined. The results are shown in Table 1.

(A) 1 kg of effervescent composite resin particles are charged together with 3.5 liters of water in a 5 L pressure-resistant container equipped with a stirrer, and further, 5 g of kaolin as a dispersant and sodium alkylbenzene sulfonate as a surfactant 0 in water. .6 g was added. Next, while stirring the inside of the pressure-resistant container at a stirring speed of 300 rpm, the inside of the pressure-resistant container is heated to a foaming temperature of 165 ° C., and then carbon dioxide as an inorganic physical foaming agent is added to the pressure-resistant container at 4.0 MPa (however, a gauge). It was press-fitted so as to be (pressure), and kept under stirring for 20 minutes. Then, the contents were released under atmospheric pressure to foam the composite resin particles to obtain foamed particles. The bulk density of the obtained foamed particles was measured, and the foamability was evaluated according to 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 "×" bottom. The results are shown in Table 1 below. In Table 1, the numbers in parentheses next to the evaluation result of foamability indicate the bulk density (unit: kg / m ³ ) of the foamed particles. The bulk density (unit: kg / m ³ ) was measured as follows. First, a 1 L graduated cylinder was prepared, and foamed particles were filled in an empty graduated cylinder up to the 1 L marked line. Next, the mass (unit: g) of the foamed particles per 1 L was measured. ^{Then, the bulk density (unit: kg / m 3} ) was calculated by converting the mass (unit: g) of 1 L of the foamed particles into a unit.

(B) Content of styrene-based monomer remaining in the composite resin particles (that is, R-SM)
First, the composite resin particles were frozen and pulverized with an analysis mill manufactured by IKA so that the particle size was about 100 μm. About 1 g of the ground product 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-based monomer was measured by gas chromatography of the DMF solution. The measurement conditions for gas chromatography are as follows. Equipment used: Gas chromatograph GC-9A manufactured by Shimadzu Corporation, Column packing material: [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 with 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.

(C) Degree of swelling First, about 1 g of composite resin particles were collected, their mass W ₀ was weighed to the fourth decimal place, and placed in a 150 mesh wire mesh bag. Next, about 200 ml of xylene was placed in a round flask having a capacity of 200 ml, and the sample placed in the wire mesh bag was set in the Soxhlet extraction tube. Soxhlet extraction was performed by heating with a mantle heater for 8 hours. After the extraction was completed, it was cooled by air cooling. After cooling, the wire mesh was taken out from the extraction tube, and the sample was washed together with the wire mesh with about 600 ml of acetone. Acetone was then volatilized and then dried at a temperature of 120 ° C. The sample recovered from the wire mesh after this drying is the "xylene insoluble matter". Moreover, the xylene solution after the extraction of the Soxhlet was put into 600 ml of acetone. Then, by filtering using a filter paper of type 5 A specified in JIS P3801, components insoluble in acetone were separated and recovered, and the recovered product was evaporated to dryness under reduced pressure. The obtained solid is "acetone insoluble".
The mass Wa of the mixed insoluble matter of "xylene insoluble matter" and "acetone insoluble matter" obtained by these operations was measured to the fourth decimal place. When the mass of the mixed insoluble matter is less than 0.2 g in the other Examples and Comparative Examples, the above operation is repeated in order to obtain a sufficient amount of the mixed insoluble matter, and 0.2 g or more is mixed. Insoluble content was obtained. Next, the mixed insoluble matter was immersed in 50 ml of methyl ethyl ketone and left at a temperature of 23 ° C. for 24 hours. Then, the mixed insoluble matter was taken out from methyl ethyl ketone, wiped lightly with a filter paper, and then the mass Wb of the mixed insoluble matter was measured to the fourth decimal place. Then, the swelling degree S was determined by the following formula (I) based on the mass of the mixed insoluble matter before and after immersion in methyl ethyl ketone (that is, Wa, Wb).
S = Wb / Wa ... (I)

(D) Content ratio of xylene insoluble matter W _XY (that is, XY gel amount W _XY )
_{First, the mass W 2} of the xylene insoluble matter obtained by measuring the degree of swelling was measured. The content ratio W _XY of the xylene insoluble matter is the ratio of the mass W _{2 of the xylene insoluble matter to the mass W 0} of the composite resin particles measured in the measurement of the degree of swelling (that is, 100 × W ₂ / W ₀ , unit: mass%). Is.

(E) 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, evaporation to dryness under reduced pressure was performed. As a result, a styrene resin was obtained as an acetone-soluble component. Then, the weight average molecular weight of the styrene resin was measured by a gel permeation chromatography (that is, GPC) method using polystyrene as a standard substance. A mixed gel column for polymer measurement was used for the measurement. Specifically, using a measuring device manufactured by Toso Co., Ltd. (specifically, HLC-8320GPC EcoSEC), eluent: tetrahydrofuran (that is, THF), flow rate: 0.6 ml / min, sample concentration: 0. .1 wt%, column: TSKguardcolum 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 the styrene-based resin dissolved in tetrahydrofuran by the GPC method and calibrating with standard polystyrene.

(F) Relationship between XY gel amount W _XY and weight average molecular weight of styrene resin From the above-mentioned xylene gel amount W _XY and Mw of styrene resin, _{the value of the relationship W XY} / Mw × 10000 between the two was calculated.

(G) Morphology inside and on the surface of the composite resin particles Morphology was performed by observing the cross section of the composite resin particles with a transmission electron microscope (TEM). As the TEM, JEM1010 manufactured by JEOL Ltd. was used. Specifically, first, an observation sample was cut out from the central portion and the surface layer of the composite resin particles. This observation sample was embedded in an epoxy resin, stained with ruthenium tetroxide, and then ultrathin sections were prepared from the sample using an ultramicrotome. The ultrathin section was placed on a grid for TEM, and cross-sectional photographs of the central portion and the surface layer of the composite resin particles were taken at a magnification of 10,000 times or 50,000 times. FIG. 2 shows a transmission electron micrograph (that is, a TEM photograph) at a magnification of 10000 times in the central cross section of the composite resin particles of this example. Further, a TEM photograph having a magnification of 10000 times in the surface layer cross section is shown in FIG. 3, and a TEM photograph having a magnification of 50,000 times in the surface layer cross section is shown in FIG. In FIGS. 2 to 4, the dark gray portion is the ethylene resin component, and the light gray portion is the styrene resin component. Then, in the TEM photograph, when the ethylene-based resin component and the styrene-based resin component form a co-continuous phase, it is determined that the morphology has a sea-sea structure, the ethylene-based resin component forms a dispersed phase, and styrene. When the based resin component forms a continuous phase, the morphology determines that it has an island-sea structure, and when the ethylene-based resin component forms a continuous phase and the styrene-based resin component forms a dispersed phase, the morphology has a sea-island structure. It was determined that there was. As shown in FIGS. 2 to 4, in the composite resin particles 1 of this example, the ethylene-based resin component forms the continuous phase 11 and the styrene-based resin component forms the dispersed phase 12 both inside and on the surface layer. The morphology was a sea-island structure. When the outermost layer 10 made of a single-phase styrene resin is formed on the outermost surface of the composite resin particles 1, for example, as shown in FIGS. 3 and 4, the outermost layer 10 of the single phase is excluded. The morphology was judged. The surface layer is a region having a depth of 2 μm from the virtual surface (specifically, the boundary between the single-phase outermost layer and the composite resin) excluding the above-mentioned single-phase outermost layer. The inside is a region that includes the center of the composite resin particles and the periphery thereof, and does not include the above-mentioned surface layer.

(H) Average Diameter of Dispersed Phases The diameters of 100 randomly selected dispersed phases were measured from the above TEM photographs, and this measurement was performed on three randomly selected composite resin particles. Next, the average value (unit: μm) of the dispersed phase was determined by the arithmetic mean of each diameter. _{The average diameter X 1} of the dispersed phase in the surface layer was obtained from the TEM photograph of the surface cross section of the composite resin particles, and _{the average diameter X 2} of the dispersed phase inside was obtained from the TEM photograph of the cross section of the central portion. The diameter of the dispersed phase is the maximum diameter of the dispersed phase, that is, the longest length between two points on the outer shape of the dispersed phase in the TEM photograph. Therefore, when the outer shape of the dispersed phase on the TEM photograph is a perfect circle, the diameter is the longest diameter of the dispersed phase, and when the outer shape of the dispersed phase is, for example, an ellipse, the major axis is the longest diameter of the dispersed phase. It becomes.

(I) Single-phase outermost layer made of styrene resin In the above TEM photograph, it is determined whether or not the single-phase outermost layer 10 made of styrene resin is formed on the composite resin particles 1, and the outermost layer is determined. The thickness of 10 was measured (see FIGS. 3 and 4). The thickness of the outermost layer 10 is represented by the average value of the measured values at five randomly selected locations so as not to be extremely biased. The case where the thickness of the outermost layer 10 is 0.05 μm or more and 0.3 μm or less is evaluated as “◯”, and the case where the thickness of the outermost layer 10 is less than 0.05 μm or the case where the outermost layer 10 is not formed is evaluated as “×”. Was evaluated as.

(3) Production of Foamed Particles 500 g of composite resin particles were charged together with 3500 g of water as a dispersion medium in a 5 L pressure-resistant airtight container equipped with a stirrer. Subsequently, 5 g of kaolin as a dispersant and 0.5 g of sodium alkylbenzene sulfonate as a surfactant were further added to the dispersion medium in the pressure-resistant airtight container. Next, the temperature inside the container was raised to a foaming temperature of 165 ° C. while stirring the inside of the pressure-resistant airtight container at a rotation speed of 300 rpm. After that, carbon dioxide, which is an inorganic physical foaming agent, is press-fitted into the pressure-resistant airtight container so that the pressure in the pressure-resistant airtight container becomes 3.2 MPa (G: gauge pressure), and 15 at the same temperature (that is, 165 ° C.). Hold for minutes. As a result, carbon dioxide was impregnated into the composite resin particles to obtain foamable composite resin particles. Next, the foamable composite resin particles were discharged from the closed container together with the dispersion medium under atmospheric pressure to obtain foamed particles having ^{a bulk density of 48 kg / m 3.} Since the foamed particles are foams of composite resin particles, they can also 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 foaming agent and the pressure (specifically, gauge pressure) when the foaming agent is press-fitted are shown in Table 1 below.

(4) Production of Foamed Particle Mold The foamed particles obtained as described above were filled in a mold having a flat plate-shaped cavity having a length of 250 mm, a width of 200 mm, and a thickness of 50 mm. Then, by introducing water vapor into the mold, the foamed particles were heated and fused to each other. Then, after cooling the inside of the mold by water cooling, the foamed particle molded product was taken out from the mold. Further, the foamed particle molded product was placed in an oven adjusted to a temperature of 60 ° C. for 12 hours to dry and cure. In this way, a foamed particle molded product was obtained. The foamed particle molded product can be said to be a foamed composite resin molded product because the foamed particles formed by foaming the composite resin particles are fused to each other.

The molding conditions are shown in Table 1 below. Specifically, the molding pressure (unit: MPa) and the water cooling time (unit: seconds) at the time of molding are shown in Table 1 described later. Further, regarding the foamed particle molded body, (i) apparent density (unit: kg / m ³ ), (j) fusion coefficient (unit:%), (k) flexural modulus (unit: MPa), (l) bending Breaking energy (unit: MJ / m ³ ) and (m) compression strength (unit: MPa) were measured as follows. The results are shown in Table 1 below.

(I) Apparent density The apparent density can be calculated by dividing the mass of the foamed particle molded product by its volume.

(J) Fusing rate The fracture surface of the foamed particle molded body was observed, and the number of foamed particles fractured inside and the number of foamed particles peeled off at the interface were visually measured. Next, the ratio of the foamed particles broken inside to the total number of the foamed particles broken inside and the foamed particles peeled off at the interface was calculated, and the value expressed as a percentage was taken as the fusion rate (%).

(K) Flexural modulus The flexural modulus was measured according to the three-point bending test method described in JIS K7221-1 (2006). Specifically, first, a test piece having a thickness of 20 mm, a width of 25 mm, and a length of 120 mm was cut out from the foamed particle molded body so that the entire surface was a cutting surface. After leaving the test piece in a room at room temperature of 23 ° C and humidity of 50% for 24 hours or more, the distance between fulcrums is 100 mm, the radius of the indenter is R15.0 mm, the radius of the support is R15.0 mm, the test speed is 20 mm / min, and the room temperature is 23 ° C. The flexural modulus was measured with an Autograph AGS-10kNG tester manufactured by Shimadzu Corporation under the condition of humidity of 50%.

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

(M) 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 central portion of the foamed particle molded product. Next, the compressive load at 50% strain was determined for this test piece in accordance with JIS K6767 (1999). The compressive strength (that is, 50% compressive stress) was calculated by dividing this compressive load by the pressure receiving area of the test piece.

(Example 2)
This example and Example 3 described later are examples in which the type of organic peroxide B used as the polymerization initiator is changed. In this example, except that 0.86 g of t-hexyl peroxyisopropyl monocarbonate (specifically, “Perhexyl I” manufactured by NOF CORPORATION) was used as the organic peroxide B in Examples. Composite resin particles, foamed particles, and foamed particle molded bodies were produced in the same manner as in No. 1, and various evaluations were performed. The t-hexyl peroxyisopropyl monocarbonate is represented as "B2" in the table described later.

(Example 3)
In this example, the composite resin is the same as in Example 1 except that 0.86 g of dit-hexyl peroxide (“Perhexyl D” manufactured by NOF CORPORATION) is used as the organic peroxide B. Particles, foamed particles, and foamed particle molded bodies were prepared and evaluated in various ways. The di-t-hexyl peroxide is referred to as "B3" in the table described later.

(Example 4)
This example and Examples 5 and 6 described later are examples in which the amount of the organic peroxide B added as the polymerization initiator is changed. Specifically, in this example, the composite resin particles are the same as in Example 1 except that the addition amount of t-hexyl peroxybenzoate used as the organic peroxide B is changed to 0.32 g. Foamed particles and foamed particle molded bodies were prepared and evaluated in various ways.

(Example 5)
In this example, the composite resin particles, the foamed particles, and the foamed particles are the same as in Example 1 except that the addition amount of t-hexyl peroxybenzoate used as the organic peroxide B is changed to 0.43 g. A molded body was prepared and various evaluations were performed.

(Example 6)
In this example, the composite resin particles, foamed particles, and foamed particles are the same as in Example 1 except that the amount of t-hexyl peroxybenzoate used as the organic peroxide B is changed to 1.72 g. A molded product was prepared and various evaluations were performed.

(Example 7)
This example and Examples 8 and 9 described later 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, 0.86 g of t-butylperoxy-2-ethylhexyl monocarbonate used as the organic peroxide A is dissolved in the first monomer and used as the organic peroxide B. Composite resin particles, foamed particles, and foamed particle compacts were prepared in the same manner as in Example 1 except that 1.72 g of oxybenzoate was dissolved in the second monomer, and various evaluations were performed.

(Example 8)
In this example, the first monomer contains 1.5 g of t-butylperoxy-2-ethylhexyl monocarbonate used as the organic peroxide A and 0.76 g of t-hexyl peroxybenzoate used as the organic peroxide B. Was dissolved. Further, 0.22 g of t-butylperoxy-2-ethylhexyl monocarbonate used as the organic peroxide A and 0.11 g of t-hexyl peroxybenzoate used as the organic peroxide B are dissolved in the second monomer. rice field. Other than that, composite resin particles, foamed particles, and foamed particle molded products were produced in the same manner as in Example 1, and various evaluations were performed.

(Example 9)
This example and Example 10 described later are examples in which the mixing ratio of the styrene-based monomer to the nuclear particles is changed. Specifically, in this example, first, the amount of the ethylene resin was changed from 8.65 kg to 9 kg, and the amount of the bubble adjusting agent masterbatch was changed from 1.35 kg to 1 kg. Nuclear particles were prepared in the same manner as in Example 1. Next, the same as in 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. Then, composite resin particles, foamed particles, and foamed particle molded bodies were prepared and evaluated in various ways.

(Example 10)
In this example, first, the amount of the ethylene resin is changed from 8.65 kg to 8 kg, and the amount of the bubble adjusting agent masterbatch is changed from 1.35 kg to 2 kg in the same manner as in Example 1. Nuclear particles were prepared. Next, the same as in 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. Then, composite resin particles, foamed particles, and foamed particle molded bodies were prepared and evaluated in various ways.

(Comparative Example 1)
In this example, composite resin particles, foamed particles, and foamed 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, and various evaluations were performed. went. A transmission electron micrograph with a magnification of 10000 times in the central cross section of the composite resin particles of this example is shown in FIG. 5, and a transmission electron micrograph with a magnification of 10000 times in the surface layer cross section is shown in FIG. In the composite resin particles 9 of this example, the ethylene-based resin component formed a continuous phase 91 and the styrene-based resin component formed a dispersed phase 92 both inside and on the surface layer, and the morphology was a sea-island structure. .. Further, as shown in FIG. 6, since the outermost layer 90 made of a single-phase styrene resin was formed on the outermost surface of the composite resin particles 1, the morphology was determined by excluding the outermost layer 90 of the single phase. ..

(Comparative Example 2)
In this example, except that the amount of t-butylperoxy-2-ethylhexyl monocarbonate used as the organic peroxide A was changed to 2.58 g and the organic peroxide B was not used. Composite resin particles, foamed particles, and foamed particle molded bodies were produced in the same manner as in Example 1, and various evaluations were performed.

(Comparative Example 3)
In this example, instead of t-hexyl peroxybenzoate used as the organic peroxide B in Example 1, t-hexyl peroxy-2-ethylhexanoate (“Perhexyl O” manufactured by NOF CORPORATION) is used. Composite resin particles, foamed particles, and foamed particle compacts were produced in the same manner as in Example 1 except for the points used, and various evaluations were performed. In addition, t-hexylperoxy-2-ethylhexanoate is described as "B4" in the table described later.

(Comparative Example 4)
In this example, composite resin particles, foamed particles, and foamed particle moldings are carried out in the same manner as in Example 1 except that the addition amount of t-hexyl peroxybenzoate used as the organic peroxide B is changed to 0.22 g. A body was prepared and various evaluations were performed.

(Comparative Example 5)
In this example, composite resin particles, foamed particles, and foamed particle moldings are carried out in the same manner as in Example 1 except that the amount of t-hexyl peroxybenzoate used as the organic peroxide B is changed to 4.3 g. A body was prepared and various evaluations were performed.

(Comparative Example 6)
In this example, first, the amount of the ethylene resin was changed from 8.65 kg to 9.35 kg, and the amount of the bubble adjusting agent masterbatch was changed from 1.35 kg to 0.65 kg. Nuclear particles were prepared in the same manner as in 1. Next, the same as in 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. Then, composite resin particles, foamed particles, and foamed particle molded bodies were prepared and evaluated in various ways.

(Comparative Example 7)
In this example, first, the amount of the ethylene resin was changed from 8.65 kg to 4.0 kg, and the amount of the bubble adjusting agent masterbatch was changed from 1.35 kg to 6.0 kg. Nuclear particles were prepared in the same manner as in 1. Next, the same as in 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. Then, composite resin particles, foamed particles, and foamed particle molded bodies were prepared and evaluated in various ways.

(Comparative Example 8)
In this example, instead of t-hexyl peroxybenzoate used as the organic peroxide B in Example 1, t-amylperoxy-2-ethylhexyl monocarbonate (“Luperox TAEC” manufactured by Alchema Yoshitomi Co., Ltd.) was used. Composite resin particles, foamed particles, and foamed particle compacts were produced in the same manner as in Example 1 except for the points used, and various evaluations were performed. The t-amylperoxy-2-ethylhexyl monocarbonate is referred to as "B5" in the table below.

(Example 11)
This example and Comparative Examples 9 to 11 described later are examples of foaming using an organic physical foaming agent. Specifically, in this example, first, the amount of the ethylene resin was changed from 8.65 kg to 20 kg, and 1 kg of the acrylonitrile-styrene copolymer was used as the dispersion diameter expanding agent without using the bubble adjusting agent masterbatch. Nuclear particles were prepared in the same manner as in Example 1 except for the points used. Specifically, as the acrylonitrile-styrene copolymer, AS-XGS manufactured by Denki Kagaku Kogyo Co., Ltd. having a weight average molecular weight of 109,000 and an acrylonitrile component content of 28% by mass was used.

Next, in the same manner as in Example 1, a magnesium pyrophosphate slurry as a suspension agent was prepared in an autoclave having an internal volume of 3 L equipped with a stirrer, and a 10 mass% sodium lauryl sulfonate aqueous solution as a surfactant was further prepared. 2.0 g, 0.2 g of sodium nitrite as a water-soluble polymerization inhibitor, and 75 g of nuclear particles were added. Next, 1.72 g of t-butylperoxy-2-ethylhexyl monocarbonate as the organic peroxide A (specifically, "Perbutyl E" manufactured by NOF CORPORATION) and t- as the organic peroxide B. 0.86 g of hexyl peroxybenzoate (“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 dissolved product was put into the suspending agent in the autoclave while stirring at a stirring speed of 500 rpm. As the first monomer, a mixed monomer of 60 g of styrene and 15 g of butyl acrylate was used.

Then, after replacing the air in the autoclave with nitrogen, the temperature was started, 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 maintained at 100 ° C. for 1 hour. Then, the stirring speed was lowered to 450 rpm, and the mixture was maintained at a temperature of 100 ° C. for 7.5 hours. When 1 hour had passed after the temperature reached 100 ° C., 350 g of styrene as a second monomer (styrene-based monomer) was added into the autoclave over 5 hours.

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

After cooling, the contents (that is, effervescent composite resin particles containing a foaming agent) were taken out, and nitric acid was added to dissolve magnesium pyrophosphate adhering to the surface of the resin particles. Then, it was dehydrated and washed with a centrifuge, and the moisture adhering to the surface was removed with an air flow drying device to obtain effervescent composite resin particles (hereinafter referred to as effervescent composite resin particles). To 100 parts by mass of the obtained foamable composite resin particles, 0.008 parts by mass of N, N-bis (2-hydroxyethyl) alkylamine as an antistatic agent was added. Further, 0.12 parts by mass of zinc stearate was added. Then, the foamable composite resin particles were coated with these.

FIG. 7 shows a transmission electron micrograph at a magnification of 10000 times in the central cross section of the foamable composite resin particles of this example, and FIG. 8 shows a transmission electron micrograph at a magnification of 50,000 times in the surface layer cross section. In the foamable composite resin particles 2 of this example, the ethylene resin formed the continuous phase 21 and the styrene resin formed the dispersed phase 22 both inside and on the surface layer, and the morphology was a sea-island structure. .. Further, as shown in FIG. 8, since the outermost layer 20 made of a single-phase styrene resin was formed on the foamable composite resin particles 2, the morphology was determined by excluding the outermost layer 20 of the single phase.

Next, the foamable composite resin particles 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. As a result, the foamable composite resin particles were foamed to a bulk density of 50 kg / m ³ to obtain foamed particles having a bulk foaming ratio of 20 times. Further, an in-mold molding of the foamed particles was carried out in the same manner as in Example 1 to obtain a foamed particle molded product.

The foamable composite resin particles and the foamed particle molded product obtained in this example were also evaluated in the same manner as in Example 1. For the effervescent composite resin particles produced in this example and Comparative Examples 9 to 11 described later, the bead life was measured as follows instead of the evaluation of the effervescence in Example 1.

"Beads Life"
The foamable composite resin particles were left in an open state at a temperature of 23 ° C. for a predetermined time to dissipate the foaming agent from the foamable composite resin particles. Then, the foamable composite resin particles were heated at a heating steam temperature of 107 ° C. for 270 seconds to foam the particles to obtain foamed particles. The foamed particles were then dried at a temperature of 23 ° C. for 24 hours. Next, the bulk density (kg / m ³ ) of the foamed particles after drying 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 9)
In this example, composite resin particles, foamed particles, and foamed particle molded bodies were prepared in the same manner as in Example 12 except that the organic peroxide B was not used as the polymerization initiator, and various evaluations were performed. rice field.

(Comparative Example 10)
In this example, the amount of t-butylperoxy-2-ethylhexyl monocarbonate used as the organic peroxide A was changed to 2.58 g, except that the organic peroxide B was not used. Composite resin particles, foamed particles, and foamed particle molded bodies were produced in the same manner as in Example 12, and various evaluations were performed.

(Comparative Example 11)
In this example, the amount of t-butylperoxy-2-ethylhexyl monocarbonate added as the organic peroxide A without using α-methylstyrene dimer (“Nofmer MSD” manufactured by Nichiyu Co., Ltd.) as the chain transfer agent is used. Composite resin particles, foamed particles, and foamed particle molded bodies were prepared in the same manner as in Example 12 except that the amount was changed to 2.58 g and no organic peroxide B was used, and various evaluations were performed.

In Examples 2 to 11 and Comparative Examples 1 to 11, the polymerization conditions, foaming conditions, molding conditions, and evaluation results are shown in Tables 1 to 3 in the same manner as in Example 1.

As is known from Tables 1 to 3, the composite resin particles of the examples are styrene-based particles that exist as monomers even though they are made of a composite resin having a high content of structural units derived from styrene-based monomers. Low monomer content. Further, although the content of the styrene-based monomer is small, the content ratio of the xylene-insoluble component is low or 0, and the cross-linking of the ethylene-based resin in the composite resin particles is suppressed. Therefore, the foamability of the composite resin particles at the time of foaming and the moldability at the time of molding can be improved. Further, although the content of the styrene-based monomer is low or 0, the fusion property is excellent. As a result, by using the composite resin particles of the example, the content of the styrene-based monomer is small, the internal fusion is good, the settling is hard, the bending resistance is excellent, and the foamed particles can be prevented from being broken by deformation. The body can be manufactured. Further, by using the composite resin particles of the example, a foamed particle molded product having excellent rigidity and toughness can be obtained. Therefore, the foamed particle molded body obtained by using the composite resin particles of the examples is suitable for applications such as automobile members and packaging containers such as liquid crystal panels and photovoltaic power generation panels.

The reason why the composite resin particles of the examples exert the above-mentioned excellent effects is considered as follows. That is, in these examples, the polymerization initiator has 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 abstracting ability. Organic peroxide B is used in combination at a predetermined ratio. Therefore, the polymerization of the styrene-based monomer in the nuclear particles is exhibited while the organic peroxide A has the effect of reducing the residual styrene-based monomer and the organic peroxide B has the effect of suppressing the cross-linking of the ethylene-based resin. Can be advanced. As a result, the structural unit derived from the styrene-based monomer is contained in the composite resin particles in an amount of more than 400 parts by mass and 1900 parts by mass or less with respect to 100 parts by mass of the ethylene-based resin, and is present as the monomer. _{It is possible to realize composite resin particles in which the content of the monomer is 0 to 500% by mass and the content ratio W XY} of the xylene insoluble matter in the composite resin particles is 0 to 40% by mass. Such composite resin particles are excellent in foamability at the time of foaming and moldability at the time of molding, and by using such composite resin particles, internal fusion is good, they are hard to settle, they are excellent in bending resistance, and they are broken by deformation. It becomes possible to manufacture a foamed particle molded product that can prevent the above.

Further, the composite resin particles of the examples can be foamed by an inorganic gas such as carbon dioxide as in Examples 1 to 10, and foamed by an organic physical foaming agent such as a hydrocarbon as in Example 11. You can also let it.

On the other hand, in the composite resin particles of Comparative Example 1, Comparative Example 9, and Comparative Example 11 in which the organic peroxide B was not used as the polymerization initiator, the amount of the residual styrene-based monomer was increased. Further, the composite resin particles of Comparative Example 11 had a relatively high weight average molecular weight of the styrene resin component, a short bead life, and insufficient foamability. Further, in Comparative Example 4 in which the ratio of the blending amount of the organic peroxide A to the total blending amount of the organic peroxide A and the organic peroxide B was increased by reducing the addition amount of the organic peroxide B. The amount of residual styrene-based monomer was also increased in the composite resin particles.

Further, in the composite resin particles of Comparative Example 2 and Comparative Example 10 produced by increasing the amount of organic peroxide A without using organic peroxide B, the amount of residual styrene monomer is reduced, but that of the ethylene resin. The crosslink density tends to be high, the amount of XY gel is high, and the degree of swelling is too low. Therefore, there is a problem that the bending fracture energy of the foamed particle molded product is insufficient and the fracture 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 half-life temperature of 10 hours, there is a problem that the amount of the residual styrene-based monomer is large. Further, in the composite resin particles of Comparative Example 3, the crosslink density of the ethylene resin component tends to be high, the amount of XY gel is high, and the degree of swelling is too low. Therefore, there is a problem that the bending fracture energy of the foamed particle molded product is insufficient and the fracture due to deformation is likely to occur.

In Comparative Example 5, since the addition amount of the organic peroxide B was increased, the ratio of the blending amount of the organic peroxide A to the total blending amount of the organic peroxide A and the organic peroxide B was low, and the styrene-based monomer was used. This is an example in which the ratio of the total blending amount of the organic peroxide A and the organic peroxide B to 100 parts by mass is high. In the composite resin particles of Comparative Example 5, the amount of the residual styrene-based monomer decreases, but the crosslink density of the ethylene-based resin tends to be high, the amount of XY gel is high, and the degree of swelling is too low. Therefore, there is a problem that the bending fracture energy of the foamed particle molded product is insufficient and the fracture due to deformation is likely to occur.

The foamed particle compact produced by using the composite resin particles of Comparative Example 6 in which a small amount of styrene-based monomer is added has low rigidity, so that the compressive strength is low and the flexural modulus is low. Therefore, the foamed particle molded product of Comparative Example 6 has a problem that it is easily deformed by bending and has insufficient deflection resistance. On the other hand, the foamed particle compact produced by using the composite resin particles of Comparative Example 7 containing a large amount of styrene-based monomers has high compressive strength and flexural modulus, but has insufficient bending breaking energy and fracture due to deformation. There is a problem that is likely to occur.

In the composite resin particles of Comparative Example 8 in which a t-amyl-based organic peroxide having no t-hexyloxy group was used as the organic peroxide B, the residual styrene-based monomer was increased. .. Further, the foamed particle molded body produced by using the composite resin particles of Comparative Example 8 has a high compressive strength and a flexural modulus, but has a problem that the bending breaking energy is insufficient and the fracture due to deformation is likely to occur. be.

Further, with respect to Examples 1 to 9, Comparative Examples 1 to 5, and Comparative Example 8 in which the ratio of the ethylene resin component and the styrene resin component of the composite resin is the same, W _XY / Mw × 10000. The relationship between the value and bending fracture energy was investigated. The result is shown in FIG. As is known from FIG. 9, in order to further improve the bending fracture energy of the foamed particle molded product, it is preferable to satisfy the relationship of _{W XY / Mw × 10000 ≦ 1.5.}

1 Composite resin particles 11 Continuous phase 12 Dispersed phase

Claims (5)

Composite resin particles using a composite resin obtained by impregnating and polymerizing an ethylene-based resin with a styrene-based monomer as a base resin.
The ethylene resin has a melting point of 95 to 105 ° C.
The composite resin contains a structural unit derived from a styrene-based monomer in an amount of more than 400 parts by mass and 900 parts by mass or less with respect to 100 parts by mass of the ethylene-based resin.
The content of the styrene-based monomer present as a monomer in the composite resin particles is 0 to 500 mass ppm.
The composite content W _XY xylene insoluble content of the resin particles is 0 Ri 23% by mass,
The surface layer of the composite resin particles has a morphology in which the ethylene resin forms a continuous phase and the styrene resin composed of a polymer of the styrene monomer forms a dispersed phase, and the dispersed phase in the surface layer. Composite resin particles in which the average diameter X ₁ μm of the above satisfies the relationship of 0.01 ≤ X _{1 ≤ 0.2.} And weight-average molecular weight Mw of styrene resin comprising a polymer of the styrene monomer, the content of W _XY of the xylene-insoluble content, satisfying the relationship of _{W XY / Mw × 10000 ≦ 1} , claim 1 The composite resin particles described in. The degree of swelling in methyl ethyl ketone at a temperature of 23 ° C., which is a mixture of the xylene insoluble component when the composite resin particles are soxhlet-extracted with xylene and the acetone-insoluble component contained in the xylene solution after the soxhlet extraction, is 1.25 or more. in it, the composite resin particles according to claim 1 or 2. Both the surface layer and the inside of the composite resin particles have a morphology in which the ethylene resin forms a continuous phase and the styrene resin composed of a polymer of the styrene monomer forms a dispersed phase. _{The average diameter X 1} μm of the dispersed phase in the surface layer _{and the average diameter X 2} μm of the dispersed phase inside the inside are 0.01 ≦ X ₁ ≦ 0.2 and 0.1 ≦ X ₂ ≦ 2. satisfy the relation: X ₁ ≦ X _2/4, the composite resin particles according to any one of claims 1 to 3. The composite resin particles according to any one of claims 1 to 4, wherein the styrene resin composed of the polymer of the styrene monomer has a weight average molecular weight Mw of 100,000 to 400,000 .

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