JP2018030923A - Composite resin foam particle, antistatic composite resin foam particle, and composite resin foam particle molded body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide composite resin foam particles capable of obtaining a molded body which has a high ratio of a styrenic resin component in a composite resin, has good internal fusion, and is stably excellent in antistatic performance; antistatic composite resin foam particles; and a molded body using the same.SOLUTION: There are provided composite resin foam particles which use a composite resin obtained by impregnation-polymerizing an ethylenic resin with a styrenic monomer as a base material resin; antistatic composite resin foam particles in which foam particles are covered with an antistatic agent; and a molded body of the same. The composite resin contains a component derived from the ethylenic resin and a component derived from the styrenic monomer with a predetermined ratio. The ethylenic resin is a mixture of linear low density polyethylene and an ethylenic copolymer having a polar group, and a content of the ethylenic copolymer having the polar group in the ethylenic resin is adjusted to a predetermined range. An amount of water vapor absorption of the composite resin foam particles is 0.50 cm/g or more.SELECTED DRAWING: None

Description

  The present invention relates to a composite resin foam particle, an antistatic composite resin foam particle, and an antistatic composite resin foam particle having a base resin as a composite resin in which a styrene monomer is impregnated and polymerized with an ethylene resin. The present invention relates to a fused molded body.

  Molded composite resin foam particles (that is, composite resin foam particles) containing an ethylene-based resin component and a styrene-based resin component are widely used as packaging and buffer packaging materials for electronic equipment and precision equipment parts. ing. In general, an antistatic property may be imparted to a molded body for such use in order to prevent electrical damage due to dust adhesion or generation of overcurrent such as discharge.

  As a method for obtaining the composite resin expanded particles, for example, the following method is known. Specifically, first, a core resin containing an ethylene resin component is impregnated with a styrene monomer and polymerized, whereby a composite resin containing an ethylene resin component and a styrene resin component is used as a base resin. A composite resin particle is obtained. Next, composite resin foam particles can be obtained by impregnating the composite resin particles with a foaming agent and foaming the composite resin particles (see Patent Documents 1 to 3). As the ethylene resin, linear low density polyethylene, ethylene copolymer having a polar group such as ethylene-vinyl acetate copolymer, a mixture thereof, and the like are used.

  Further, as a method of imparting antistatic performance to the foamed particle molded body, a method of adding an antistatic agent composed of a surfactant or the like is generally used. Specifically, a method is known in which an antistatic agent is impregnated at the time of or after impregnation of a volatile foaming agent into composite resin particles. A method of applying an antistatic agent to the composite resin foam particles is also known.

  In the method of impregnating the antistatic agent when impregnating the volatile foaming agent, the resin particles are excessively plasticized by the antistatic agent, so that the heat resistance of the foamed particles may be reduced during molding and the molded body may be deformed. There is a possibility that the fusion property between the expanded particles may be lowered. Therefore, as in Patent Document 4, a method of applying a predetermined amount of a cationic antistatic agent to composite resin foam particles has been developed.

International Publication No. 2007/138916 JP2015-189911A JP-A-2005-97555 Japanese Patent Laying-Open No. 2015-81274

  On the other hand, in order to further improve the rigidity while maintaining the toughness and resilience of the composite resin foamed particle molded body, a technique for increasing the ratio of the styrene resin component in the composite resin has been developed. However, an ethylene resin containing an ethylene copolymer having a polar group such as an ethylene-vinyl acetate copolymer is used as a core particle, such as the composite resin foam particles disclosed in Patent Documents 1 to 3. In some cases, when the ratio of the styrene resin component in the composite resin is increased, the fusibility of the expanded particles may be reduced. In this case, when the content of the ethylene copolymer having a polar group is reduced, the fusibility of the expanded particles tends to be improved, but there is still room for further improvement. In addition, when the content of the ethylene copolymer having a polar group is further reduced, the fixability of the antistatic agent may be lowered. For this reason, it has been difficult to obtain foamed particles having a high ratio of the styrene-based resin component in the composite resin and excellent fusion and antistatic agent fixing properties.

  Further, as described in Patent Document 4, in the method of applying an antistatic agent to the composite resin foamed particles, the antistatic agent may have insufficient fixability, and depending on the heating conditions during in-mold molding, for example, There is a possibility that the antistatic agent attached to the foamed particles may partially flow out by a heating medium such as steam, and depending on the part of the molded body, the amount of antistatic agent attached may decrease, etc. It was difficult to stably obtain a molded product having the same.

  The present invention has been made in view of such a background, and it is possible to obtain a molded article having a high ratio of a styrene-based resin component in a composite resin, good internal fusion, and stably excellent antistatic performance. An object of the present invention is to provide a foamed composite resin particle, an antistatic composite resin foam particle, and a molded body using the antistatic composite resin foam particle.

One aspect of the present invention is a composite resin foamed particle using a composite resin obtained by impregnating and polymerizing an ethylene resin with a styrene monomer as a base resin,
The composite resin contains 5% by mass or more and less than 20% by mass of the ethylene resin-derived component and more than 80% by mass of 95% by mass or less of the styrene monomer-derived component (however, The total is 100% by mass).
The ethylene resin is a mixture of a linear low density polyethylene and an ethylene copolymer having a polar group,
Content of the said ethylene-type copolymer which has the said polar group in the said ethylene-type resin is 1-45 mass%,
The composite resin foam particles have a water vapor adsorption amount of 0.50 cm ³ / g or more.

  Another aspect of the present invention resides in an antistatic composite resin foamed particle in which the surface of the composite resin foamed particle is coated with an antistatic agent containing a cationic surfactant.

Yet another embodiment of the present invention is a molded article in which the antistatic composite resin foam particles are fused to each other, and the composite resin foam particles molded article has a surface resistivity of less than 1 × 10 ¹² Ω.

  The composite resin foamed particles (hereinafter referred to as “foamed particles” as appropriate) are styrene-based monomer at a high blending ratio with respect to an ethylene-based resin containing linear low-density polyethylene and an ethylene-based copolymer having a polar group. The composite resin in which the body is impregnated and polymerized is used as the base resin, and the specific ethylene copolymer is contained in the specific amount, and the amount of water vapor that can be adsorbed by the expanded particles, that is, the water vapor adsorption amount is adjusted to the predetermined value or more ing. Therefore, even if an antistatic agent is applied to the foamed particles, for example, the foamed particles can sufficiently adsorb and hold the antistatic agent, and the outflow of the antistatic agent at the time of molding can be suppressed. A composite resin foamed particle molded body (hereinafter referred to as “molded body” as appropriate) having good antistatic performance can be obtained. Further, even when an ethylene resin containing an ethylene copolymer having a polar group and a high proportion of the styrene resin component in the composite resin is used, internal fusion of the molded product, that is, expanded particles Excellent fusion between each other. Therefore, the molded body can exhibit strength properties such as compression rigidity and deflection resistance, which are originally excellent in the composite resin based on the composition of the ethylene-based resin or the styrene-based resin. The antistatic composite resin foamed particles can also exhibit the same effects as the above-mentioned foamed particles.

In addition, the molded product having antistatic composite resin foam particles fused to each other and having a surface resistivity of less than 1 × 10 ¹² Ω is not only excellent in antistatic performance, but also the expanded particles constituting the molded product Since it is sufficiently fused, it has excellent strength characteristics such as compression rigidity and deflection resistance as described above. Therefore, the molded body obtained by using the antistatic composite resin foamed particles is suitable for applications such as packaging containers and buffer packaging materials for parts of electronic devices such as liquid crystal panels and photovoltaic power generation panels or precision devices.

  Next, a preferred embodiment of the expanded particles will be described. The expanded particles are used, for example, in applications where an antistatic agent is applied to the surface thereof. It can be said that the expanded particles for such use have an antistatic agent contact surface on the surface to which the antistatic agent adheres.

  The expanded particles are used to obtain a molded body by in-mold molding. That is, a molded body having a desired shape can be obtained by filling a large number of foamed particles in a mold and fusing the composite resin particles with each other in the mold.

  The foamed particles use a composite resin in which an ethylene resin is impregnated and polymerized with a styrene monomer as a base resin. In this specification, the composite resin is a resin in which an ethylene resin is impregnated and polymerized in an ethylene resin as described above, and a component derived from an ethylene resin and a component derived from a styrene monomer It is resin containing. The component derived from the styrene monomer is, for example, a styrene resin, and the main component of the component derived from the styrene monomer is usually a styrene resin obtained by polymerizing the styrene monomer. Further, when polymerizing styrene monomers, not only polymerization of styrene monomers but also graft polymerization of styrene monomers may occur in the polymer chain constituting the ethylene resin. In this case, the composite resin not only contains an ethylene resin component and a styrene resin component obtained by polymerizing a styrene monomer, but also contains an ethylene resin component (grafted with a styrene monomer) ( That is, it contains a PE-g-PS component). In addition, when the styrene monomer is polymerized, the ethylene resin may be cross-linked. In this case, the composite resin is an ethylene resin that is cross-linked with an uncrosslinked ethylene resin as an ethylene resin component. including. Therefore, the composite resin is a concept different from a mixed resin obtained by melt-mixing a polymerized ethylene resin and a polymerized styrene resin.

  The amount of the styrene monomer to be impregnated and polymerized in the ethylene resin can be appropriately adjusted according to desired physical properties. Specifically, when the ratio of the component derived from the ethylene-based resin in the composite resin is increased, the toughness and the restorability of the molded body are improved, but the rigidity tends to be lowered. On the other hand, when the ratio of the component derived from the styrene monomer, that is, the component derived from the styrene monomer in the polymer chain constituting the composite resin is increased, the rigidity of the molded body is improved, Restorability tends to decrease.

  In the foamed particles, the composite resin contains a component derived from an ethylene-based resin in an amount of 5% by mass to less than 20% by mass and a component derived from a styrene-based monomer in an amount of more than 80% by mass and 95% by mass or less (both Therefore, it is possible to obtain a molded article that is particularly excellent in rigidity while maintaining toughness and restorability. From the viewpoint of further improving the rigidity of the molded body, the composite resin contains 19% by mass or less of an ethylene resin-derived component and 81% by mass or more of a styrene monomer-derived component (however, both The total is 100% by mass.) And more preferably contains 18% by mass or less of an ethylene resin-derived component and 82% by mass or more of a component derived from a styrene monomer. More preferably, it is 100% by mass. Moreover, in order to improve the toughness and restorability of the molded body, the composite resin contains 10% by mass or more of an ethylene resin-derived component and 90% by mass or less of a styrene monomer-derived component. (However, the total of both is 100% by mass.) More preferably, it contains 11% by mass or more of an ethylene resin-derived component and 89% by mass or less of a styrene monomer-derived component (however, The total of both is 100% by mass). In addition, in this specification, the preferable range regarding the upper limit and lower limit of a numerical range, a more preferable range, and a more preferable range can be determined from all the combinations of an upper limit and a minimum.

  The ethylene resin contains linear low-density polyethylene and an ethylene copolymer having a polar group. In the present specification, the linear low density polyethylene is hereinafter appropriately referred to as “LLDPE”, and the ethylene copolymer having a polar group is hereinafter appropriately referred to as “polar copolymer”. The ethylene-based resin is preferably mainly composed of linear low-density polyethylene, and specifically, the content of linear low-density polyethylene in the ethylene-based resin is preferably 50% by mass or more, More preferably, it is 55 mass% or more, More preferably, it is 60 mass% or more. Examples of the ethylene-based resin other than the linear low-density polyethylene and the polar copolymer include branched low-density polyethylene and high-density polyethylene.

The linear low density polyethylene preferably has a structure having a linear polyethylene chain and a short-chain branched chain having 2 to 6 carbon atoms. Specific examples include an ethylene-butene copolymer, an ethylene-hexene copolymer, an ethylene-octene copolymer, and the like. In particular, a linear low density polyethylene obtained by polymerization using a metallocene polymerization catalyst. It is preferable that In this case, the affinity between the ethylene resin component in the composite resin and the styrene resin component obtained by polymerizing the styrene monomer is further improved, and the toughness of the molded body can be increased. The linear low density polyethylene preferably has a density of approximately 0.910 to 0.925 g / cm ³ .

  The melt mass flow rate (that is, MFR) of LLDPE under the conditions of a temperature of 190 ° C. and a load of 2.16 kg is preferably from 0.5 to 4.0 g / 10 minutes, and preferably from 1.0 to 3. 0 g / 10 min is more preferable. In addition, MFR of polar copolymers, such as ethylene-type resin, such as LLDPE, and ethylene-vinyl acetate copolymer, is measured based on JIS K7210-1 (2014), temperature 190 degreeC, load 2.16kg. The value in the condition. Moreover, a melt indexer (for example, model L203 manufactured by Takara Kogyo Co., Ltd.) can be used as the measuring device.

  Moreover, it is preferable that melting | fusing point Tm of LLDPE is 80 to 115 degreeC. In this case, since the ethylene resin can be sufficiently impregnated with the styrene monomer, it is possible to prevent the suspension system from becoming unstable during the polymerization. As a result, it is possible to obtain a molded body that combines 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 LLDPE is more preferably 85 to 110 ° C. The melting point Tm can be measured as a melting peak temperature by differential scanning calorimetry (DSC) based on JIS K7121 (1987).

  The ethylene resin contains a polar copolymer. Polar copolymers include ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-acrylic acid alkyl ester copolymer, ethylene-methacrylic acid copolymer, ethylene-methacrylic acid alkyl ester copolymer. 1 or more types can be used. Examples of the polar group in the polar copolymer include functional groups such as a carboxy group, a hydroxy group, a carbonyl group, a nitro group, an amino group, and a sulfo group. By including a polar copolymer in the composite resin, it is considered that the hydrophilicity of the expanded particles can be increased, and the water vapor adsorption amount of the expanded particles described later can be increased. As a result, it is considered that the fixing property of the antistatic agent is improved and the outflow of the antistatic agent during molding can be suppressed. Preferably, it has a carbonyl group as a polar group.

  Content of the polar copolymer in ethylene-type resin is 1-45 mass%. If it exceeds 45% by mass, crosslinking of the ethylene resin is likely to occur during the impregnation polymerization, and the fusion property between the expanded particles may be lowered. Furthermore, in this case, since the content of LLDPE in the ethylene-based resin is inevitably lowered, the bending fracture energy of the molded body may be insufficient. From the viewpoint of improving the fusibility and bending fracture energy, the content of the polar copolymer in the ethylene-based resin is preferably 35% by mass or less, and more preferably 30% by mass or less. On the other hand, when the content of the polar copolymer is less than 1% by mass, the hydrophilicity of the surface of the expanded particles cannot be increased, and the retention of the antistatic agent may be insufficient. From the viewpoint of further improving the retention of the antistatic agent, the content of the polar copolymer in the ethylene-based resin is preferably 2% by mass or more, and more preferably 5% by mass or more.

  The content of the polar copolymer in the composite resin is preferably 0.1 to 7% by mass. In this case, it is possible to further improve the tenacity of the molded body to further suppress cracking of the molded body and to further improve the retention of the antistatic agent for the foamed particles. From the viewpoint of further suppressing cracking of the molded body, the content of the polar copolymer in the composite resin is more preferably 5% by mass or less, and further preferably 4.5% by mass or less. On the other hand, from the viewpoint of further improving the retention of the antistatic agent for the expanded particles, the content of the polar copolymer in the composite resin is more preferably 0.5% by mass or more, and 1% by mass or more. More preferably it is.

  The content of the structural unit derived from the monomer containing a polar group in the polar copolymer is preferably 10 to 50% by mass. In this case, the hydrophilicity of the expanded particles can be increased without impairing the mechanical properties when formed into a molded body, and the fixability of the antistatic agent can be further improved. From the viewpoint of further suppressing the outflow of the antistatic agent, the content of the structural unit derived from the monomer containing a polar group in the polar copolymer is more preferably 15 to 50% by mass. In addition, the component (namely, structural unit) derived from the monomer having a polar group in the polar copolymer is a component derived from vinyl acetate when the polar copolymer is an ethylene-vinyl acetate copolymer, for example. is there.

  The polar copolymer is preferably an ethylene-vinyl acetate copolymer. In this case, it is possible to obtain a molded body that combines the excellent rigidity of the styrene resin and the excellent tenacity of the ethylene resin at a higher level. The ethylene-vinyl acetate copolymer is a polymer obtained by copolymerizing ethylene and vinyl acetate by, for example, high-pressure radical polymerization. The ethylene-vinyl acetate copolymer generally has a long chain composed of a polyethylene chain and a short chain derived from vinyl acetate branched from the long chain.

  The MFR of the ethylene-vinyl acetate copolymer is preferably 1 to 120 g / 10 min (190 ° C., load 2.16 kg). In this case, the fusion rate of the composite resin foamed particle molded body obtained by molding the composite resin foamed particles in the mold can be further improved, and the toughness of the composite resin foamed particle molded body can be further improved. From the same viewpoint, the MFR (190 ° C., load 2.16 kg) of the ethylene-vinyl acetate copolymer is more preferably 2 to 30 g / 10 min, and further preferably 2 to 10 g / 10 min.

The water vapor adsorption amount per 1 g of the foamed particles is 0.50 cm ³ / g or more. When the water vapor adsorption amount is less than 0.50 cm ³ / g, the fixability of the antistatic agent for the expanded particles becomes insufficient. As a result, for example, the antistatic agent tends to flow out during molding, and the antistatic performance of the molded body may be insufficient. From the viewpoint of improving fixing property of the antistatic agent of the expanded beads, the amount of adsorbed water vapor of the expanded beads is preferably 0.60 cm ³ / g or more, more preferably at least ^{0.70cm 3 / g, 0.80cm 3 /} g The above is more preferable. Further, it is preferable that the water vapor adsorption amount of the expanded particles is approximately 4.0 cm ³ / g or less.

  Since conventional foamed particles based on a composite resin in which a styrene monomer is impregnated and polymerized with an ethylene resin are basically hydrophobic, for example, when an antistatic agent having a hydrophilic property is attached. Low fixability. Therefore, depending on the heating conditions when molding the conventional foamed particles in the mold, the antistatic agent attached to the foamed particles may be partially detached by steam or the like as a heating medium. It has been difficult to stably obtain a molded article having a desired antistatic performance due to a decrease in the amount of the antistatic agent attached. Further, in order to improve the water vapor adsorption amount of the foamed particles, when an ethylene resin having a large content of polar copolymer as shown in Patent Documents 1 to 3 described above is used as the core particle, the ethylene resin itself There has been a risk that physical properties such as compression rigidity and deflection resistance of the molded product may be reduced due to the lowering of the toughness of the resin and the ease of crosslinking of the ethylene-based resin resulting in a decrease in the fusibility of the expanded particles. Further, in the methods shown in Patent Documents 1 to 3, when the blending ratio of the styrene monomer is increased, the amount of the styrene monomer to be impregnated and polymerized in the core particle is increased. It became difficult to impregnate uniformly, and the styrene resin component increased in the surface layer portion of the resin particles, which may reduce the fusibility of the expanded particles and the fixing property (water vapor adsorption amount) of the antistatic agent. .

On the other hand, for example, the expanded particles disclosed in the present specification obtained by the production method described later have a high ratio of components derived from the styrenic monomer in the composite resin, and the polar copolymer with respect to the total amount of the composite resin. Despite the low content, the water vapor adsorption amount of the expanded particles is high, so that the fixability of the antistatic agent can be improved while maintaining the fusibility of the expanded particles. Therefore, according to the said foamed particle, the molded object which can be compatible with the outstanding mechanical physical property and antistatic performance can be obtained.
In addition, it is thought that the quantity of the polar copolymer of the surface is increasing compared with the conventional expanded particle by the said expanded particle being manufactured by the manufacturing method mentioned later. Therefore, it is not necessary to excessively increase the blending ratio of the polar copolymer and the content of the polar group component with respect to the total amount of the composite resin, and the surface area of the expanded particles is not affected by the low content of the polar copolymer. It is thought that it can be made hydrophilic.

  In this specification, the water vapor adsorption amount of the expanded particles is the amount of water vapor that can be adsorbed by the expanded particles. That is, the water vapor adsorption amount at the maximum relative pressure is the water vapor adsorption amount of the foam particles in the adsorption isotherm at a temperature of 25 ° C. of the foam particles measured using the vapor adsorption amount measuring device. Specific measurement methods will be described later in Examples.

  The composite resin contains a styrene resin component obtained by polymerizing a styrene monomer. In the present specification, styrene constituting the styrene resin component and a monomer copolymerizable with styrene added as necessary may be collectively referred to as a styrene monomer. The proportion of styrene in the styrenic 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-methyl styrene, o-methyl styrene, m-methyl styrene, p-methyl styrene, p-ethyl styrene, 2,4-dimethyl styrene, p-methoxy styrene, pn-butyl styrene, p. -T-butylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, 2,4,6-tribromostyrene, divinylbenzene, styrene sulfonic acid, sodium styrene sulfonate and the like. These may be used alone or in combination of two or more.

  Other vinyl monomers include acrylic acid esters, methacrylic acid esters, acrylic acid, methacrylic acid, vinyl compounds containing hydroxyl groups, vinyl compounds containing nitrile groups, organic acid vinyl compounds, olefin compounds, diene compounds, halogens. Vinyl halide compounds, vinylidene halide compounds, maleimide compounds, and the like. 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, and 2-ethylhexyl acrylate. Examples of the methacrylic acid ester include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, and 2-ethylhexyl methacrylate. These may be used alone or in combination of two or more.

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

  Examples of the olefin compound include ethylene, propylene, 1-butene, and 2-butene. Examples of the diene compound include butadiene, isoprene, chloroprene and the like. Examples of the vinyl halide compound include vinyl chloride and vinyl bromide. Examples of the vinylidene halide compound include vinylidene chloride. Examples of maleimide compounds include N-phenylmaleimide and N-methylmaleimide. These may be used alone or in combination of two or more.

  From the viewpoint of enhancing foamability, it is preferable to use styrene or a combination of styrene and an acrylic monomer as the styrene monomer. Further, from the viewpoint of enhancing foamability, it is preferable to use styrene and butyl acrylate in combination. 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 and more preferably 1 to 8% by mass with respect to the entire composite resin. Preferably, it is 2 to 5% by mass.

  Moreover, in the range which does not inhibit the effect of this invention, composite resin can contain other resin components other than an above-described ethylene resin component and a styrene resin component. Examples of other resin components include polymethyl methacrylate, polycarbonate, and polyvinyl alcohol. In that case, the content of the other resin component is preferably approximately 10% by mass or less, more preferably 5% by mass or less, and further preferably 100% by mass with respect to 100% by mass of the composite resin (including other resin components). Is 3% by mass or less.

  An antistatic agent can be attached to the surface of the expanded particles. The adhesion amount of the antistatic agent is preferably 0.4 to 3.5 parts by mass with respect to 100 parts by mass of the expanded particles, although it depends on the type of antistatic agent used. In this case, sufficient antistatic performance can be obtained, and a decrease in fusion property can be further prevented. From the viewpoint of obtaining sufficient antistatic performance, the adhesion amount of the antistatic agent to 100 parts by mass of the expanded particles is more preferably 0.5 parts by mass or more, and further preferably 0.6 parts by mass or more. preferable. Further, from the viewpoint of further preventing a decrease in fusion property, the adhesion amount of the antistatic agent is more preferably 2.7 parts by mass or less, and further preferably 2.5 parts by mass or less.

  As the antistatic agent, for example, a cationic surfactant, a nonionic surfactant, an amphoteric surfactant and the like can be used. These surfactants can be used alone or in combination. As the antistatic agent, for example, various commercially available products can be used.

  As the cationic surfactant, for example, octyldimethylethylammonium ethyl sulfate, lauryl dimethylethylammonium ethyl sulfate, didecyldimethylammonium chloride, tetraalkylammonium salt, trialkylbenzylammonium salt and the like can be used. As the nonionic surfactant, for example, hydroxyalkylamine, hydroxyalkyl monoetheramine, polyoxyalkylene alkylamine, glycerin fatty acid ester, polyoxyethylene alkyl ether, polyoxyethylene alkyl ether and the like can be used. As the anionic surfactant, for example, an alkyl sulfonate, an alkyl benzene sulfonate, an alkyl phosphate, or the like can be used.

  The antistatic agent preferably contains at least a cationic surfactant. In this case, the antistatic agent is more easily fixed to the expanded particles, and the antistatic performance can be further improved. This is presumably because the surface of the foamed particles has a negative electrostatic charge, so that an antistatic agent containing a cationic surfactant is easily fixed. And even if it is a small amount of antistatic agent, it can show the more excellent antistatic performance, and can prevent the fall of a meltability, the filling property to a metal mold | die, etc. further.

Moreover, Ge (i.e., germanium) infrared total reflection absorption measurement method using the prism (i.e., ATR method) of at wavenumbers 1740 cm ^-1 and a wavenumber 2850 cm ^-1 in an infrared absorption spectrum of the surface of the expanded beads as measured by The absorbance ratio D _{1740 / 2850-Ge} is preferably 0.2 or more. In other words, in the infrared absorption spectrum of the surface of the composite resin foamed particles measured by ATR method using Ge prism, and the absorbance D _1740-Ge at a wave number 1740 cm ^-1, the absorbance at a wave number 2850cm ^-1 D _2850- It is preferable that _Ge and the absorbance ratio D _{1740 / 2850-Ge} satisfy the relationship of the following formula I.
D _{1740 / 2850-Ge} = D _1740-Ge / D _2850-Ge ≧ 0.2 (Formula I)
When the carbonyl group is included as the polar group in the polar copolymer, the amount of the carbonyl group on the surface of the expanded particle is sufficiently large by satisfying the above formula, and therefore the hydrophilicity of the expanded particle surface is more reliably increased. Conceivable. As a result, it is considered that the fixability of the antistatic agent can be improved more reliably, and the outflow of the antistatic agent during molding can be more reliably suppressed. From the viewpoint of further increasing the hydrophilicity of the surface of the expanded particle, the absorbance ratio D _{1740 / 2850-Ge on} the surface of the expanded particle is more preferably 0.23 or more, and further preferably 0.25 or more. The absorbance ratio D _{1740 / 2850-Ge} is preferably about 0.5 or less. Incidentally, the absorbance D ₂₈₅₀ at wave number 2850 cm ^-1 is the height of the peak derived from C-H between stretching vibration of methylene group contained in both the ethylene-based resin and a styrene resin, at wave number 1740 cm ^-1 Absorbance D ₁₇₄₀ is the height of a peak mainly derived from C═O stretching vibration of a carbonyl group contained in a polar copolymer such as a component derived from vinyl acetate in an ethylene-vinyl acetate copolymer.

Absorbance ratio D _{1740 / 2850-Ge} is the ratio between the styrene monomer (that is, the first monomer) and the core particles introduced in the initial stage of the polymerization and the impregnation temperature of the styrene monomer in the foamed particle production method described later. By adjusting the ratio to an appropriate range and sufficiently impregnating the ethylene-based resin core particles with the styrene-based monomer, the ratio can be adjusted to the predetermined value or more. As a result, the amount of the polar copolymer in the surface layer portion of the expanded particles can be increased despite the small content of the polar copolymer relative to the total amount of the composite resin.

ZnSe (i.e., zinc selenide) absorbance ratio D _{1740/2850-ZnSe} at wavenumbers 1740 cm ^-1 and a wavenumber 2850 cm ^-1 in an infrared absorption spectrum of the surface of the composite resin foamed particles measured by ATR method using a prism It is preferable that the ratio D _{1740 / 2850-Ge} / D _{1740 / 2850-ZnSe of the} above and the absorbance ratio D _{1740 / 2850-Ge} exceeds 1. In other words, in the infrared absorption spectrum of the surface of the composite resin foamed particles measured by ATR method using a ZnSe prism, and the absorbance D _1740-ZnSe at a wave number 1740 cm ^-1, absorption at a wave number 2850 cm ^-1 degree D _{2850- ZnSe} and the absorbance ratio D _{1740 / 2850-ZnSe} satisfy the relationship of the following formula II, and the absorbance ratio D _{1740 / 2850-Ge} and the absorbance ratio D _{1740 / 2850-ZnSe} of the following formula III It is preferable to satisfy the relationship.
D _{1740 / 2850-ZnSe} = D _1740-ZnSe / D _2850-ZnSe (Formula II)
D _{1740 / 2850-Ge} / D _{1740 / 2850-ZnSe} > 1 (Formula III)
When the carbonyl group is included as a polar group in the polar copolymer, the amount of carbonyl in the vicinity of the surface of the expanded particle is increased by satisfying the above formula, and thus the hydrophilicity of the surface of the expanded particle is more reliably increased. . As a result, it is considered that the fixability of the antistatic agent can be improved more reliably, and the outflow of the antistatic agent during molding can be more reliably suppressed. From the viewpoint of further enhancing the hydrophilicity of the foam particle surface, the absorbance ratio D _{1740 /} ratio D _{1740 /} absorbance ratio D _1740/2850-Ge for _{2850-ZnSe 2850-Ge / D} 1740/2850-ZnSe 1.1 More preferably, it is more preferably 1.2 or more. Further, it is preferable that the ratio _{D 1740/2850-Ge / D} 1740/2850-ZnSe absorbance ratio D _1740/2850-Ge to the absorbance ratio D _{1740/2850-ZnSe} is approximately 5 or less.

  In the ATR method, measurement can be performed by changing the penetration depth of infrared rays with respect to a sample by utilizing the property that the refractive index varies depending on the prism material. Specifically, when Ge is used as the prism material, the infrared penetration depth becomes shallower than when ZnSe is used, so that the infrared absorption spectrum of the surface layer portion of the expanded particles can be measured. When Ge is used, an infrared absorption spectrum having a depth of about 0.2 to 0.5 μm from the outermost surface is obtained. When ZnSe is used, a depth of about 0.6 to 0.6 is formed from the outermost surface. An infrared absorption spectrum in the range of 1.5 μm is obtained.

Absorbance ratio D _{1740 / 2850-Ge} and ratio D _{1740 / 2850-Ge} / D _{1740 / 2850-ZnSe} are the impregnation temperature of styrenic monomer (that is, impregnation polymerization temperature) By adjusting the ratio of the styrene monomer (that is, the first monomer) and the core particles to be introduced in the initial stage of polymerization to an appropriate range and sufficiently impregnating the ethylene resin core particles with the styrene monomer, It can be adjusted to a predetermined value or more.

  The content of xylene-insoluble matter in the expanded particles is preferably 20% or less. In this case, the content of the cross-linked ethylene-based resin in the composite resin is small, and the foamability at the time of producing foamed particles described later and the moldability at the time of producing the molded body can be improved. The content ratio of the xylene-insoluble matter is hereinafter referred to as “XY gel amount” as appropriate. From the viewpoint of further improving foamability and moldability, the amount of XY gel of the foamed particles is more preferably 18% or less. A method for measuring the amount of XY gel of the expanded particles will be described later in Examples.

  The amount of XY gel in the surface layer of the expanded particles is preferably 25% or less. In this case, since the content of the cross-linked ethylene resin component in the surface layer of the expanded particles is small, it is considered that the fusion property between the expanded particles can be improved. That is, the foamed particles contain a polar copolymer that can improve hydrophilicity on the surface layer even though the content of the polar copolymer is small relative to the total amount of the composite resin. It is considered that the gel amount (specifically, the content of the crosslinked ethylene resin component) is small. Therefore, the expanded particles can combine the excellent fixing property of the antistatic agent and the excellent fusion property between the expanded particles at a high level. The method for measuring the amount of XY gel in the surface layer of the expanded particles will be described later in the Examples, but a surface layer portion sample is prepared by cutting out the surface layer portion of a molded product obtained by fusing a large number of expanded particles. By measuring the amount of XY gel, the amount of XY gel on the surface of the expanded particles is obtained. From the viewpoint of further improving the fusibility, the amount of XY gel in the surface layer of the expanded particles is preferably 23% or less, more preferably 21% or less, and even more preferably 20% or less.

From the viewpoint of achieving both moldability and light weight and mechanical properties when formed into a molded body, the bulk density of the expanded particles is preferably about 5 kg / m ³ or more, and preferably about 10 kg / m ³ or more. More preferred. On the other hand, the bulk density of the expanded particles is preferably about 200 kg / m ³ or less, more preferably 100 kg / m ³ or less.

In addition, from the viewpoint of achieving both lightness and mechanical properties, the apparent density of the molded body in which the expanded particles are fused to each other is preferably approximately 5 kg / m ³ or more, and preferably 10 kg / m ³ or more. More preferred. On the other hand, the apparent density of the molded body is preferably approximately 200 kg / m ³ or less, and more preferably 100 kg / m ³ .

The surface resistivity of the molded body in which the expanded particles are fused to each other is preferably less than 1 × 10 ¹² Ω. When the surface resistivity is in the above range, the antistatic performance required for a packaging container such as a liquid crystal panel and a photovoltaic power generation panel and a buffer packaging material can be sufficiently exhibited. The surface resistivity of the molded body is more preferably 7 × 10 ¹¹ Ω or less, and further preferably 5 × 10 ¹¹ Ω or less.

  Next, an embodiment of a method for producing expanded particles will be described. Expanded particles are obtained by performing a dispersion process, a modification process, and a foaming process. Hereinafter, each step will be described in detail.

  In the dispersion step, an ethylene-based resin containing LLDPE and a polar copolymer is used as the core particles, and the core particles include other resins, foam nucleating agents, bubble regulators, colorants, lubricants, dispersion diameter expanding agents, and the like. The additive may be further contained. The core particles can be produced by blending the above-described additives and the like, which are added as necessary, into an ethylene-based resin, melt-kneading the blend, and then finely granulating it. Melt kneading can be performed by an extruder. In order to perform uniform kneading, it is preferable to perform extrusion after mixing the resin in advance. The resin can be mixed using, for example, a mixer such as a Henschel mixer, a ribbon blender, a V blender, or a ladyge mixer. The melt kneading is preferably performed using a single-screw extruder or a twin-screw extruder provided with a highly dispersed screw such as a dull image type, a Maddock type, or a unimelt type.

  The granulation of the core particles is performed, for example, by cutting the melt-kneaded compound while extruding it with an extruder or the like. Granulation 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 core particles are dispersed in an aqueous medium can be obtained. As the aqueous medium, for example, deionized water can be used. The core particles are preferably dispersed in an aqueous medium together with a suspending agent. In this case, the styrenic 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, magnesium carbonate. Fine particulate inorganic suspending agents such as barium carbonate, calcium sulfate, barium sulfate, talc, kaolin and bentonite can be used. In addition, organic suspending agents such as polyvinyl pyrrolidone, 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 0.1% by solid content with respect to 100 parts by mass of the suspension polymerization aqueous medium (specifically, all water in the system including water such as the reaction product-containing slurry). 05-10 mass parts is preferable. More preferably, 0.3-5 mass parts is good. By making the suspending agent in the above range, the styrene monomer can be stably suspended in the modification step, and the particle size distribution of the composite resin particles obtained after the modification step can be expanded. Can be suppressed.

  A dispersant such as a surfactant can be added to the aqueous medium. As the surfactant, for example, an anionic surfactant or a nonionic surfactant is preferably used. These surfactants can be used alone or in combination.

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

  In addition, an electrolyte made of an inorganic salt such as lithium chloride, potassium chloride, sodium chloride, sodium sulfate, sodium nitrate, sodium carbonate, or sodium bicarbonate can be added to the aqueous medium as necessary. In addition, in order to obtain a molded article superior in 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. From the viewpoint of reducing the amount of styrenic resin in the vicinity of the outermost surface of the composite resin particles, the addition amount of the water-soluble polymerization inhibitor is determined in the aqueous medium (specifically, in the system containing water such as a reaction product-containing slurry). 0.001-0.1 mass part is preferable with respect to 100 mass parts of all the water), More preferably, 0.005-0.06 mass part is good.

  In the reforming step, the styrene monomer is impregnated into the core particles and polymerized in an aqueous medium. The polymerization of styrene monomers and the like can be performed in the presence of a polymerization initiator. In this case, the ethylene resin may be cross-linked with the polymerization of the styrene monomer or the like. Moreover, a crosslinking agent can be used together as needed. When using a polymerization initiator and a crosslinking agent, it is preferable to previously dissolve the polymerization initiator and the crosslinking agent in a styrene monomer.

  As a polymerization initiator, what is used for the suspension polymerization method of a styrene-type monomer can be used. For example, a polymerization initiator that is soluble in a styrene monomer and has a 10-hour half-life temperature of 50 to 120 ° C. can be used. Examples of the polymerization initiator include cumene hydroxy peroxide, dicumyl peroxide, t-butylperoxy-2-ethylhexanoate, t-butylperoxybenzoate, benzoyl peroxide, t-butylperoxyisopropyl carbonate, t Organic peroxides such as -butyl peroxy-2-ethylhexyl carbonate, t-amyl peroxy-2-ethylhexyl carbonate, hexyl peroxy-2-ethylhexyl carbonate, lauroyl peroxide, and the like can be used. As the polymerization initiator, an azo compound such as azobisisobutyronitrile can be used. These polymerization initiators can be used alone or in combination of two or more. Further, t-butylperoxy-2-ethylhexanoate is preferred from the viewpoint of easily reducing the residual styrene monomer. The polymerization initiator is preferably used in an amount of 0.01 to 3 parts by mass with respect to 100 parts by mass of the styrene monomer.

  Further, as the crosslinking agent, it is preferable to use a substance that does not decompose at the polymerization temperature but has a 10 hour half-life temperature that is 5 to 50 ° C. higher than the polymerization temperature. Specifically, for example, peroxides such as dicumyl peroxide, 2,5-t-butyl perbenzoate, and 1,1-bis-t-butyl peroxycyclohexane can be used. A crosslinking agent can be used individually or in combination of 2 or more types. It is preferable that the compounding quantity of a crosslinking agent is 0.1-5 mass parts with respect to 100 mass parts of styrene-type monomers. In addition, the same compound can also be employ | adopted as a polymerization initiator and a crosslinking agent.

  When the core particles are impregnated with the styrene monomer and polymerized, the total amount of the styrene monomer to be blended is divided into two or more in an aqueous medium in which the core particles are dispersed, and these monomers are different. It is preferable to add at a timing. Specifically, a part of the total amount of the styrene monomer to be blended is added to an aqueous medium in which core particles are dispersed, and the styrene monomer is impregnated and polymerized. Furthermore, the remainder of the styrene monomer to be blended can be added to the aqueous medium in one or more portions. Like the latter, by adding the styrenic monomer in a divided manner, the condensation of the resin particles during polymerization can be suppressed, and the content of the polar copolymer on the surface of the composite resin foamed particles can be increased. Is possible.

  The polymerization initiator can be added to the aqueous medium in a state dissolved in the styrene monomer. As described above, when the styrene 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 monomer added at any timing. It is possible to add a polymerization initiator to each styrene monomer added at different timings. When the styrene monomer is added in portions, it is preferable to dissolve the polymerization initiator at least in the styrene monomer added first (hereinafter referred to as “first monomer”). In the first monomer, it is preferable to dissolve 75% or more of the total amount of the polymerization initiator to be blended, and it is more preferable to dissolve 80% or more. In this case, it is possible to prevent the suspension system from becoming unstable during the polymerization. As a result, it is possible to obtain a molded body that combines 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 monomer to be blended is added as the first monomer, the remaining part of the total amount of the styrene 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, or the second monomer can be continuously added over a predetermined time.

  In addition, it is preferable that the seed ratio (namely, mass ratio of the 1st monomer with respect to a nucleus particle) of the styrene-type monomer added as a 1st monomer is 0.5 or more. In this case, even if the ratio of the styrene resin component in the composite resin is high, the amount of the second monomer added can be suppressed from being excessively increased, so that the styrene monomer is uniformly impregnated. And the styrene-based resin component on the particle surface can be reduced. Moreover, it becomes easy to make the shape of the composite resin particles more spherical. From the same viewpoint, the seed ratio is more preferably 0.7 or more, and further preferably 0.8 or more. The seed ratio is preferably 1.5 or less. In this case, even if the ratio of the styrene resin component in the composite resin is high, the styrene monomer can be sufficiently impregnated into the core particles. Further, it is possible to further prevent the styrene monomer from being polymerized before the core particles are sufficiently impregnated, and it is possible to further prevent the generation of a resin mass. 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. By setting the seed ratio of the first monomer within the above range, the amount of the polar copolymer on the surface of the expanded particles can be increased even when the ratio of the styrene resin component in the composite resin is high. The hydrophilicity of the particle surface can be improved.

  It is preferable that the melting point Tm (° C.) of the ethylene-based resin in the core particles and the impregnation polymerization temperature Tp (° C.) in the modification step satisfy the relationship of Tm−10 ≦ Tp ≦ Tm + 30. In this case, even when the ratio of the styrene resin component in the composite resin is high, the ethylene resin can be sufficiently impregnated with the styrene monomer, and the suspension system becomes unstable during polymerization. Can be prevented. In particular, by combining the range of the polymerization temperature and the range of the seed ratio of the first monomer described above, even if the ratio of the styrene resin component in the composite resin is high, the polar co-polymerization on the surface of the expanded particles The amount of coalescence can be increased, and the hydrophilicity of the surface of the expanded particles can be improved even if the content of the polar copolymer is small relative to the total amount of the composite resin. As a result, it is possible to obtain a foamed particle molded body that combines the excellent rigidity of the styrene-based resin and the excellent tenacity of the ethylene-based resin at a higher level and is excellent in fixability of the antistatic agent. The impregnation polymerization temperature in the modification step varies depending on the type of polymerization initiator used, but is preferably 60 to 105 ° C, more preferably 70 to 105 ° C. Moreover, although a crosslinking temperature changes with kinds of crosslinking agent to be used, it is preferable that it is 100-150 degreeC.

Moreover, a plasticizer, an oil-soluble polymerization inhibitor, a flame retardant, a coloring agent, a chain transfer agent, etc. can be added to a styrene-type monomer as needed. As the plasticizer, for example, fatty acid esters, acetylated monoglycerides, fats and oils, hydrocarbon compounds and the like can be used. Examples of fatty acid esters that can be used include glycerin tristearate, glycerin trioctoate, glycerin trilaurate, sorbitan tristearate, sorbitan monostearate, and butyl stearate. Moreover, as an acetylated monoglyceride, glycerol diacetomonolaurate etc. can be used, for example. As fats and oils, hardened beef tallow, hardened castor oil, etc. can be used, for example. As a hydrocarbon compound, cyclohexane, a liquid paraffin, etc. can also be used, for example. 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 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, or 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 said additive can be added individually or in combination of 2 or more types.

Additives such as the above-mentioned plasticizers, oil-soluble polymerization inhibitors, flame retardants, colorants, chain transfer agents and the like can be dissolved in a solvent and impregnated into core particles. As the solvent, for example, aromatic hydrocarbons such as ethylbenzene and toluene, aliphatic hydrocarbons such as heptane and octane, and the like can be used.

  In the foaming step, the composite resin particles are foamed. The foaming method is not particularly limited, and examples thereof include a gas impregnation preliminary foaming method, a dispersion medium discharge foaming method, and other foaming methods based on these methods and principles.

  In the gas-impregnated pre-foaming method, foamable composite resin particles are produced by impregnating composite resin particles during and / or after polymerization with a foaming agent such as a physical foaming agent. Thereafter, the foamable composite resin particles are put into a pre-foaming machine and heated with a heating medium such as water vapor, hot air, or a mixture thereof to foam the foamable composite resin particles to obtain expanded particles. Alternatively, the composite resin particles after production can be filled in a pressure vessel, and a foaming agent can be impregnated into the composite resin particles by press-fitting a foaming agent to produce foamable composite resin particles.

  On the other hand, in the dispersion medium discharge foaming method, first, foamable composite resin particles are prepared by impregnating a composite resin particle dispersed in an aqueous medium in a pressure vessel with a foaming agent under heating and pressure. Next, the foamable composite resin particles can be expanded to obtain foamed particles by releasing the foamable composite resin particles together with the aqueous medium from the pressure vessel under a lower pressure than in the pressure vessel under an appropriate foaming temperature condition. .

  For impregnation with the foaming agent, a liquid phase impregnation method and a gas phase impregnation method can be appropriately selected. Physical foaming agents include inorganic gases such as nitrogen, carbon dioxide, argon, air, helium, water; methane, ethane, propane, normal butane, isobutane, cyclobutane, normal pentane, isopentane, neopentane, cyclopentane, normal hexane, cyclohexane Organic volatile gases such as 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, and 2,3-dimethylbutane. An inorganic foaming agent is preferable. In this case, the foaming agent diffuses from the foamed particles after foaming, and the foaming agent does not remain in the foamed particles. Therefore, the internal pressure of the foamed particles is unlikely to rise excessively at the time of molding, and cooling of the molded body can be completed in a short time and taken out from the mold.

  Examples of the method of applying the antistatic agent to the expanded particles include spray coating, airless coating, dip coating, blending, and other coating methods based on these methods and principles. Spray coating is a method in which an antistatic agent solution is atomized and sprayed onto foamed particles together with high-pressure air. Airless coating is a method in which an antistatic agent solution is made high and sprayed onto the foamed particles from the spray nozzle using the pressure. In addition, it is preferable to make foamed particles into a fluid state at the time of spraying, or to stir after spraying to adhere the antistatic agent solution to the entire surface of the foamed particles. Immersion coating is a method in which expanded particles are pulled up after being immersed in an antistatic agent solution. The blending method is a method of applying foamed particles and a small amount of an antistatic agent solution by stirring.

  There is no restriction | limiting in the density | concentration of the antistatic agent used for application | coating, Dilution liquids, such as a stock solution, powder, water, or alcohol, may be sufficient. Furthermore, the container for applying the antistatic agent to the expanded particles may be either a closed system or an open system, and the temperature at the time of application only needs to be equal to or lower than the heat resistant temperature of the expanded particles. It is preferable to stir the foamed particles well during or after coating so that the antistatic agent adheres to the entire surface of the composite foamed particles. The application method can be any of the above, or a combination thereof.

  The antistatic agent is not particularly limited, and examples thereof include nonionic surfactants such as hydroxyalkylamines, hydroxyalkyl monoetheramines, polyoxyalkylene alkylamines, glycerin fatty acid esters, polyoxyethylene alkyl ethers; alkyl sulfonates, Anionic surfactants such as alkylbenzene sulfonates and alkyl phosphates; Cationic interfaces such as octyldimethylethylammonium ethyl sulfate, lauryl dimethylethylammonium ethyl sulfate, didecyldimethylammonium chloride, tetraalkylammonium salts and trialkylbenzylammonium salts Examples include activators. Further, these antistatic agents can be used alone or in combination.

  From the viewpoint of exhibiting excellent antistatic performance, at least a cationic surfactant is preferably used as the antistatic agent, and at least octyldimethylethylammonium ethyl sulfate is more preferably used.

  In the application process of the antistatic agent, it is preferable to apply 0.4 to 4 parts by mass of the antistatic agent to 100 parts by mass of the composite resin foam particles so that the adhesion amount of the antistatic agent is within the above range. . In this case, it is possible to impart sufficiently excellent antistatic performance to the foamed particles, to prevent the fluidity of the foamed particles from being lowered, and to prevent filling defects during molding. The amount of the antistatic agent applied to 100 parts by mass of the composite resin foamed particles is more preferably 0.5 to 3.5 parts by mass, and still more preferably 0.6 to 3 parts by mass. As for the adhesion (coating) of the antistatic agent, the foamed particle surface does not necessarily have to be completely covered as long as the desired antistatic performance can be obtained. You may have the part which is not covered by.

  The molded body can be manufactured by a known in-mold molding method using steam heating. That is, a molded body can be obtained by filling a large number of foamed particles in a mold such as a mold, and introducing steam into the mold to fuse the foamed particles together.

Example 1
Below, the expanded particle concerning an Example is demonstrated.
The foamed particle according to the example uses, as a base resin, a composite resin in which an ethylene resin is impregnated and polymerized with a styrene monomer. That is, the composite resin contains an ethylene resin component and a styrene resin component obtained by polymerizing a styrene monomer. Hereinafter, the manufacturing method of the expanded particle of this example is demonstrated. In this example, a molded body is produced by further molding the obtained foamed particles in a mold.

(1) Preparation of core particles LLDPE (manufactured by Tosoh Corporation, trade name: Nipolon Z HF210K) polymerized with a metallocene polymerization catalyst as an ethylene resin, and ethylene-vinyl acetate copolymer (Asahi Kasei Chemicals Corporation) Product name: EF1531, and the content of vinyl acetate component (that is, structural unit) in the ethylene-vinyl acetate copolymer is 15% by mass). The ethylene-vinyl acetate copolymer contains a carbonyl group as a polar group and corresponds to the above-mentioned polar copolymer. The ethylene-vinyl acetate copolymer is hereinafter referred to as “EVA” as appropriate. Moreover, zinc borate (Tonda Pharmaceutical Co., Ltd., zinc borate 2335) was prepared as a foam nucleating agent.

  LLDPE 7.5 kg, EVA 2.5 kg, and zinc borate 0.144 kg were added to a Henschel mixer (Mitsui Miike Chemical Co., Ltd .; model: FM-75E) and mixed for 5 minutes to obtain a resin mixture. Subsequently, the resin mixture was melt-kneaded at a temperature of 230 to 250 ° C. using a 26 mmφ twin-screw extruder (specifically, model TEM-26SS manufactured by Toshiba Machine Co., Ltd.). The melt-kneaded product was extruded and cut into an average of 0.5 mg / piece by an underwater cutting method to obtain core particles containing an ethylene-based resin.

(2) Production of Composite Resin Particles 1000 g of deionized water was added to an autoclave with an internal volume of 3 L equipped with a stirrer, and 6.0 g of sodium pyrophosphate was further added. Thereafter, 12.9 g of powdered magnesium nitrate hexahydrate was added and stirred at room temperature for 30 minutes. This produced the magnesium pyrophosphate slurry as a suspending agent. Next, 2.0 g of sodium lauryl sulfonate (specifically, 10% by weight aqueous solution) as a surfactant and 0.21 g of sodium nitrite as a water-soluble polymerization inhibitor in an aqueous medium containing this suspending agent. And 75 g of core particles were charged.

  Next, t-butyl peroxy-2-ethylhexyl monocarbonate (specifically, “Perbutyl E” manufactured by NOF Corporation) and t-hexyl peroxybenzoate (specifically, manufactured by NOF Corporation) as polymerization initiators. “Perhexyl Z”) was prepared. In addition, α-methylstyrene dimer (specifically, “NOFMER MSD” manufactured by NOF Corporation) was prepared as a chain transfer agent. Then, 1.67 g of t-butylperoxy-2-ethylhexyl monocarbonate, 0.835 g of t-hexylperoxybenzoate, and 0.665 g of α-methylstyrene dimer are mixed with the first monomer (that is, styrene monomer). ). Then, while stirring the melt at a rotational speed of 500 rpm, the melt was put into the above-described autoclave into which the core particles were put. As the first monomer, a mixed monomer of 60 g of styrene and 15 g of butyl acrylate was used.

  Next, after the air in the autoclave was replaced with nitrogen, the temperature was raised and the temperature inside the autoclave was raised to 100 ° C. over 1 hour and 30 minutes. After the temperature increase, the temperature was maintained at 100 ° C. for 1 hour. Thereafter, the stirring speed was lowered to 450 rpm and maintained at a temperature of 100 ° C. for 7.5 hours. When 1 hour had passed since the temperature reached 100 ° C., 350 g of styrene as a second monomer (specifically, a styrene 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 kept at the temperature of 125 ° C. for 5 hours. Thereafter, the inside of the autoclave was cooled, and the contents (specifically, composite resin particles) were taken out. Next, nitric acid was added to dissolve the magnesium pyrophosphate adhering to the surface of the composite resin particles. Thereafter, dehydration and washing were performed with a centrifugal separator, and water adhering to the surface was removed with an airflow drying device to obtain composite resin particles. The mass ratio of the component derived from the styrene monomer and the component derived from the ethylene resin in the composite resin from the blending ratio (mass ratio) of the styrene monomer and ethylene resin used during the production. Asked.

  Regarding the composite resin particles obtained as described above, the composition and polymerization conditions are shown in Table 1 described later. Moreover, about the obtained composite resin particle, mass ratio of the component (namely, PE) derived from ethylene-type resin and the component (namely, PS) derived from a styrene-type monomer, EVA content, vinyl acetate component The content of is shown in Table 2. The composite resin particles were measured for the XY gel amount, the glass transition temperature Tg of the acetone-soluble component, and the weight average molecular weight Mw of the acetone-soluble component as follows, and the results are shown in Table 2.

“Amount of xylene insoluble matter (XY gel) W _XY ”
First, about 1 g of composite resin particles were collected, and its weight 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 bottom flask having a capacity of 200 ml, and the sample placed in the wire mesh bag was set in a Soxhlet extraction tube. Soxhlet extraction was performed by heating with a mantle heater for 8 hours. After the extraction, it was cooled by air cooling. After cooling, the wire mesh was taken out from the extraction tube, and the sample together with the wire mesh was washed with about 600 ml of acetone. Next, acetone was volatilized and dried at a temperature of 120 ° C. The sample collected from the wire net after this drying is “xylene-insoluble matter”. The weight W ₁ of the xylene-insoluble matter obtained by these operations was weighed to the fourth decimal place. The content ratio of xylene insolubles, that is, the XY gel amount W _XY is the ratio of the weight W ₁ of xylene insolubles to the weight W ₀ of the composite resin particles (that is, 100 × W ₁ / W ₀ , unit:%). In addition, since the XY gel amount of the composite resin particles, the XY gel amount of the foamed particles obtained using the composite resin particles, and the XY gel amount of the molded body are substantially the same, the XY gel amount of the composite resin particles The value can be regarded as the XY gel amount of the expanded particles and the XY gel amount of the molded body. It is also possible to directly measure the XY gel amount of the foamed particles and the XY gel amount of the molded body by performing the same operation as described above using the foamed particles and the molded body instead of the composite resin particles. It is.

"Glass transition temperature Tg of acetone solubles"
First, 1.0 g of composite resin particles are placed in a 150 mesh wire mesh bag. Next, about 200 ml of xylene is placed in a round bottom flask having a volume of 200 ml, and the sample (that is, composite resin particles) placed in the wire mesh bag is set in a 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 obtain an acetone-soluble component. About the obtained acetone soluble part 2-4 mg, heat flux differential scanning calorimetry is performed based on JISK7121-1987 using DSC measuring instrument Q1000 made from TI Instruments. And the glass transition temperature Tg of an acetone soluble part can be calculated | required as a midpoint glass transition temperature of the DSC curve obtained on the conditions of a heating rate of 10 degree-C / min. The acetone-soluble component obtained by further dissolving the xylene-soluble component in the composite resin in acetone is mainly a styrene resin.

"Mw of acetone soluble part"
First, Soxhlet extraction was performed in the same manner as the measurement of the glass transition temperature described above. Then, the extracted xylene solution was dropped into 600 ml of acetone, and after decantation, by evaporation under reduced pressure, an acetone-soluble component was obtained. Mw of acetone-soluble content was measured by gel permeation chromatography (that is, GPC) method using polystyrene as a standard substance. For the measurement, a polymer gel mixed gel column was used. Specifically, using a measuring device manufactured by Tosoh Corporation (specifically, HLC-8320GPC EcoSEC), eluent: tetrahydrofuran (that is, THF), flow rate: 0.6 ml / min, sample concentration: 0 Measurement was performed under the measurement condition of 1 wt%. As the column, a column in which TSK guard column Super H-H × 1 and TSK-GEL Super HM-H × 2 were connected in series was used. That is, Mw was determined by measuring the molecular weight of acetone-soluble component dissolved in tetrahydrofuran by GPC method and calibrating with standard polystyrene.

(3) Production of expanded particles 500 g of composite resin particles were charged into a 5 L pressure vessel equipped with a stirrer together with 3500 g of water as a dispersion medium. 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 container. Next, the inside of the container was heated to a foaming temperature of 165 ° C. while stirring the inside of the container at a rotation speed of 300 rpm. Thereafter, carbon dioxide, which is an inorganic physical foaming agent, was pressed into the container so that the pressure in the container was 3.6 MPa (however, gauge pressure), and held at the same temperature (ie, 165 ° C.) for 15 minutes. Thereby, the composite resin particles were impregnated with carbon dioxide to obtain expandable composite resin particles. Next, the foamable composite resin particles were discharged together with the dispersion medium from the container under atmospheric pressure to obtain expanded particles having a bulk density of 50 kg / m ³ . Since the expanded particle is a foam of composite resin particles, it can also be said to be composite resin expanded particles. The foaming conditions are shown in Table 2 below.
The bulk density (kg / m ³ ) of the foamed particles after drying is such that the foamed particles dried for 24 hours at a temperature of 23 ° C. are filled in an empty 1 L graduated cylinder up to a 1 L marked line. The mass (g) of was measured, and it was determined by converting the unit.

For the expanded particles obtained as described above, the absorbance ratio D _{1740 / 2850-Ge} measured by the ATR method using a _Ge prism and the absorbance measured by the ATR method using a ZnSe prism are as follows. The ratio _{D1740 / 2850-ZnSe} , the ratio _{D1740 / 2850-Ge} / _{D1740 / 2850-ZnSe} , the water vapor adsorption amount, and the surface XY gel amount were measured as follows. The results are shown in Table 2 below.

"Water vapor adsorption of foam particles"
The amount of water vapor adsorbed by the expanded particles is the amount of water vapor adsorbed at the maximum relative pressure (specifically 0.9) of the adsorption isotherm at 25 ° C. (however, the set relative pressure: 0.005 to 0.9). means. The relative pressure means the ratio of the pressure in the measurement atmosphere to the saturated vapor pressure. The saturated water vapor pressure at a temperature of 25 ° C. is 3.169 kPa. The measurement is performed using a vapor adsorption amount measuring apparatus BELSORP-max manufactured by Nippon Bell Co., Ltd. First, a foamed particle group having an average particle diameter of 4 mm per foamed particle was dried at a temperature of 60 ° C. for 24 hours under atmospheric pressure, and then 100 foamed particles were collected from the foamed particle group and weighed. The total weight of the expanded particle group determined from the measurement result was 0.20 g. Next, all of the weighed foam particles are placed in a sample cell of the apparatus, the relative pressure is set to 0.005 to 0.9, and the water vapor adsorption isotherm at a temperature of 25 ° C. is measured for the foam particles in the cell. did. Next, the water vapor adsorption amount per 1 g of the foam particles (cm ³ / g) was determined from the water vapor adsorption amount of the foam particle group at the maximum relative pressure of the adsorption isotherm (ie 0.9). The adsorption amount at the maximum relative pressure is defined as the water vapor adsorption amount of the expanded particles. In the measurement, a group of expanded particles having an average weight per expanded particle of 1 to 3 mg and an average particle diameter of 3 to 5 mm is used. Moreover, the average particle diameter per foamed particle was measured as follows.
First, a graduated cylinder containing water at a temperature of 23 ° C. was prepared, and an arbitrary amount of expanded particle group (mass Wα of the expanded particle group) left for 2 days under the conditions of 50% relative humidity, 23 ° C. and 1 atm. The tool was submerged in water in the graduated cylinder using a tool such as a wire mesh. Then, taking into account the volume of the tool such as a wire mesh, the volume Vα (L) of the expanded particle group read from the rise in the water level is measured, and this volume Vα is determined by the number of expanded particles (N) in the measuring cylinder. By dividing (Vα / N), the average volume per foamed particle was calculated. And the diameter of the virtual sphere which has the same volume as the obtained average volume was made into the average particle diameter per foamed particle.

"Absorbance ratio D _{1740 / 2850-Ge} , Absorbance ratio D _{1740 / 2850-ZnSe} , Ratio D _{1740 / 2850-Ge} / D _{1740 / 2850-ZnSe} "
The absorbance ratio D _{1740 / 2850-Ge} and the absorbance ratio D _{1740 / 2850-ZnSe on} the surface of the expanded particles can be obtained from an infrared absorption spectrum measured by the ATR method. As a measuring apparatus, an infrared spectrophotometer “FT / IR-460plus” manufactured by JASCO Corporation and a total reflection absorption measuring apparatus “ATR PRO 450-S type” manufactured by JASCO Corporation were used. The absorbance ratio D _{1740 / 2850-Ge} is measured using a Ge prism, and the absorbance ratio D _{1740 / 2850-ZnSe} is measured using a ZnSe prism. The specific measurement conditions are prism: Ge or ZnSe, incident angle: 45 °, and the foamed particles are pressed against the prism of the total reflection absorption measuring device with a pressure of 170 kg / cm ² to be in close contact with the surface of the foamed particles. An external absorption spectrum (but no ATR correction) was obtained.

First, an infrared absorption spectrum (but no ATR correction) measured by the ATR method using a Ge prism is measured using the above measuring apparatus and measurement conditions, and the absorbance in the vicinity of a wave number of 1740 cm ⁻¹ in this infrared absorption spectrum. Absorbance D _2850-Ge in the vicinity of D _1740-Ge and wave number ₂₈₅₀ cm ⁻¹ was measured. Then, the ratio of the absorbance D _{1740 -Ge} to the absorbance D _2850-Ge , that is, the absorbance ratio D _{1740 / 2850-Ge} was calculated. Further, an infrared absorption spectrum (without ATR correction) measured by the ATR method using a ZnSe prism is measured, and the absorbance D _1740-ZnSe near the wave number 1740 cm ⁻¹ in this infrared absorption spectrum, the wave number 2850 cm ^−. Absorbance D _2850-ZnSe in the vicinity of ¹ was measured. Then, the ratio of the absorbance D _{1740 -ZnSe} to the absorbance D _2850-ZnSe , that is, the absorbance ratio D _{1740 / 2850-ZnSe} was calculated. Moreover, to calculate the ratio _{D 1740/2850-Ge / D} 1740/2850-ZnSe absorbance ratio D _1740/2850-Ge to the absorbance ratio D _{1740/2850-ZnSe.} The results are shown in Table 2 below. In calculating each absorbance ratio, the same measurement was performed on five expanded particles, and the average value of these was obtained.

"Amount of surface xylene insoluble matter (surface layer XY gel)"
First, a molded body was produced by the method described later using the foamed particles produced as described above. Next, using a Super Deluxe Slicer WSD-2P & 3P manufactured by Watanabe Fumak Co., Ltd. as a slicer, a surface layer portion having a depth of 0.1 mm from the outermost surface of the molded body was cut out. Then, a surface layer sample of about 1 g was taken, and its weight W ₀₀ was measured to the fourth decimal place. The weighed surface layer sample was placed in a 150 mesh wire mesh bag. Next, about 200 ml of xylene was placed in a round bottom flask having a capacity of 200 ml, and the surface layer sample placed in the wire mesh bag was set in a Soxhlet extraction tube. Soxhlet extraction was performed by heating with a mantle heater for 8 hours. After the extraction, it was cooled by air cooling. After cooling, the wire mesh was taken out from the extraction tube, and the surface layer sample was washed together with the wire mesh with about 600 ml of acetone. Next, acetone was volatilized and dried at a temperature of 120 ° C. A sample collected from the wire net after this drying is “surface xylene insoluble matter”. The weight W ₀₁ insoluble in the surface layer xylene obtained by these operations was weighed to the fourth decimal place. The content ratio of the surface xylene insolubles, that is, the surface layer XY gel amount W _XY-S is the ratio of the weight W ₀₁ insoluble in the surface layer xylene to the weight W ₀₀ of the surface layer sample (ie 100 × W ₀₁ / W ₀₀ , unit:%) ). Here, the surface layer XY gel amount of the molded body was measured. However, since the surface layer XY gel amount of the foamed particles and the molded body is approximately the same, the surface layer XY gel amount of the molded body was measured as described above. Can be the surface layer XY gel amount of the expanded particles.

"Amount of antistatic agent"
About 5 g of expanded particles with an antistatic agent attached and about 5 g of expanded particles with no antistatic agent attached were weighed. Let W ₀₀₀ (W ₀₀₀ ≈5) be the weight of the expanded particles to which no antistatic agent is attached. Each foamed particle after weighing was washed three times with 100 cm ³ (ml) of a washing liquid (specifically ethanol). About 300 cm ³ of the cleaning liquid after cleaning was collected and kept at a temperature of 40 ° C. for 24 hours to evaporate the cleaning liquid. Was then measured and residue weight W _A after evaporation of the cleaning liquid of the expanded beads of the antistatic agent adheres, after evaporation of the cleaning liquid of the expanded beads of the antistatic agent does not adhere to the residue weight W _B. Based on these residue weights W _A and W _B , and the weight W ₀₀₀ of the expanded particles, the adhesion amount A (parts by mass) of the antistatic agent to 100 parts by mass of the expanded particles was calculated from the following (formula IV). . The results are shown in Table 2.
A = (W _A −W _B ) / W ₀₀₀ × 100 (Formula IV)

(4) Application of antistatic agent As an antistatic agent, octyldimethylethylammonium ethyl sulfate (specifically, "Katiogen ES-O" manufactured by Daiichi Kogyo Seiyaku Co., Ltd .; active ingredient 50%) was prepared. The foamed particles are put together with an antistatic agent in a 50 L plastic bag, and the mouth of the plastic bag is closed. Then, the foamed particles and the antistatic agent were well shaken and mixed in the plastic bag, and then the whole bag was placed in a tumbler and mixed for 30 minutes to apply the antistatic agent to the foamed particles. The coated composite resin foamed particles were dried in an oven at 40 ° C. for 12 hours. Thus, foamed particles (antistatic foamed particles) having an antistatic agent attached to the surface were obtained. The addition amount of the antistatic agent was 2 parts by mass with respect to 100 parts by mass of the expanded particles. The amount of the active ingredient is 1 part by mass with respect to 100 parts by mass of the expanded particles.

(5) In-mold molding Next, the foamed particles coated with the antistatic agent were filled into 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. Next, by introducing water vapor into the mold, the expanded particles were heated and fused to each other. Then, after cooling the inside of a metal mold | die by water cooling, the molded object was taken out from the metal mold | die. Furthermore, the molded body was dried and cured by placing it in an oven adjusted to a temperature of 60 ° C. for 12 hours. In this way, a molded body in which a large number of expanded particles were fused to each other was obtained.

  The molded body produced as described above was measured for apparent density, fusion rate, surface resistivity, flexural modulus, breaking energy, and compressive strength. The results are shown in Table 2. The measuring method is as follows.

"Apparent density"
The apparent density was calculated by dividing the mass of the compact by its volume.

"Fusion rate"
The molded body was bent and broken into approximately equal parts. The fracture surface was observed, and the number of foam particles broken inside, that is, the material destroyed, and the number of foam particles peeled at the interface were measured. Next, the ratio of the internally broken foam particles to the total number of foam particles peeled at the interface and the foam particles peeled at the interface was calculated, and the value expressed as a percentage was defined as the fusion rate (%).

"Surface resistivity"
The antistatic performance of the molded body was evaluated by measuring the surface resistivity of the molded body. The surface resistivity was measured by a method based on JIS K 6271-1-2015. In the measurement, first, a rectangular parallelepiped test piece having a length of 100 mm, a width of 100 mm and a thickness of 25 mm was cut out from the vicinity of the center of a molded body cured at a temperature of 23 ° C. and 50% RH for one day. At this time, the test piece was cut out so that one of the two surfaces of 100 mm length × 100 mm width existing in the rectangular parallelepiped was the surface of the foamed particle molded body (ie, skin surface). And the surface resistivity in the skin surface of a test piece was measured using "Hiresta MCP-HT450" by Mitsubishi Chemical Corporation. As a probe, “UR100” manufactured by Mitsubishi Chemical Corporation was used, and the measurement was performed under the condition that 23 ° C., 50% RH, and an applied voltage of 500 V were held for 30 seconds. The measurement was performed at arbitrary four locations on the same test piece, and the maximum value, the minimum value, and the arithmetic average value were obtained. The skin surface is the surface of the foamed particle molded body obtained by in-mold molding.

"Bending elastic modulus"
The flexural modulus was measured according to the three-point bending test method described in JIS K7222-1-2006. Specifically, first, five test pieces each having a thickness of 20 mm, a width of 25 mm, and a length of 120 mm were cut from an arbitrary portion of the molded body so that the entire surface became a cutting surface. After leaving the test piece for 24 hours or more in a constant temperature room at 23 ° C. and a humidity of 50%, the distance between supporting points 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 bending elastic modulus was measured with an autograph AGS-10 kNG tester manufactured by Shimadzu Corporation under the condition of humidity 50%. The arithmetic average value of the five measured values was adopted as the measurement result of the flexural modulus.

"Bending fracture energy"
A three-point bending test is performed in the same manner as the measurement of the flexural modulus described above, and the energy (unit: MJ / m ³ ) from the relationship between strain (unit: m / m) and stress (unit: MPa) to the breaking point is calculated. It calculated | required from the arithmetic average value of the measured value of 5 points | pieces. The bending rupture energy is calculated from the area surrounded by the strain-stress curve up to the rupture point and the horizontal axis (ie, strain).

"Compressive strength"
A rectangular parallelepiped test piece having a length of 50 mm, a width of 50 mm, and a thickness of 25 mm was cut out from the center portion of the foamed particle molded body. Next, the compression load at the time of 50% strain was calculated | required based on JISK6767-1999 with respect to this test piece. 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)
In this example, the amount of LLDPE used when producing the core particles is changed to 6 kg, the amount of EVA is changed to 4 kg, and the foaming conditions during foaming (specifically, the CO ₂ pressure in the container during foaming) are shown in Table 2 below. Except for the points changed as shown, foamed particles and molded bodies were produced in the same manner as in Example 1.

(Example 3)
In this example, the amount of LLDPE used when producing the core particles is changed to 9.8 kg, the amount of EVA is changed to 0.2 kg, and the foaming conditions during foaming (specifically, the CO ₂ pressure in the container during foaming) will be described later. Except for the points changed as shown in Table 2, foamed particles and molded articles were produced in the same manner as in Example 1.

Example 4
In this example, the amount of the core particles used when producing the composite resin particles was changed to 100 g, except that 85 g of styrene and 15 g of butyl acrylate were used as the first monomer, and 300 g of styrene was used as the second monomer. Produced composite resin particles in the same manner as in Example 1. Next, Example 1 was used except that the composite resin particles were used and the foaming conditions during foaming (specifically, the CO ₂ pressure in the container during foaming) were changed as shown in Table 2 described below. In the same manner, foamed particles and molded bodies were produced.

(Example 5)
In this example, the amount of the core particles used when producing the composite resin particles was changed to 50 g, except that 35 g of styrene and 15 g of butyl acrylate were used as the first monomer, and 400 g of styrene was used as the second monomer. Produced composite resin particles in the same manner as in Example 1.
Next, Example 1 was used except that the composite resin particles were used and the foaming conditions during foaming (specifically, the CO ₂ pressure in the container during foaming) were changed as shown in Table 2 described below. In the same manner, foamed particles and molded bodies were produced.

(Example 6)
In this example, first, except that 14 g of polytetrafluoroethylene (manufactured by Seishin Enterprise Co., Ltd., TFW1000, average particle size: 10 μm) was used as the foam nucleating agent used in the preparation of the core particles, the examples In the same manner as in Example 1, core particles were prepared. Next, composite resin particles were produced in the same manner as in Example 1 except that this core particle was used and 52.5 g of styrene and 22.5 g of butyl acrylate were used as the first monomer. At the time of foaming, in addition to 5 g of kaolin and 0.5 g of sodium alkylbenzene sulfonate, 1 g of stearic acid (“Stear Deer Class 1” manufactured by Kanto Chemical) is added to the container charged with the composite resin particles. In the same manner as in Example 1, except that the foaming conditions during foaming (specifically, the CO ₂ pressure in the container during foaming) were changed as shown in Table 2 below, Was made.

(Example 7)
In this example, the amount of LLDPE used at the time of producing the core particles is changed to 9 kg, and EVA is a EVA acetate EV-45LX manufactured by Mitsui DuPont Polychemical Co., Ltd., with a vinyl acetate component content of 46% by mass. The core particles were prepared in the same manner as in Example 1 except that the amount of EVA was changed to 1 kg. Next, with the use of this core particle, Example 1 except that the foaming conditions at the time of foaming (specifically, the CO ₂ pressure in the container at the time of foaming) were changed as shown in Table 2 described later. Similarly, foamed particles and molded bodies were produced.

(Comparative Example 1)
In this example, the amount of LLDPE used when producing the core particles is changed to 10 kg, EVA is not used, and the foaming conditions during foaming (specifically, the CO ₂ pressure in the container during foaming) are shown in Table 4 below. Except for the points changed as shown in Table 1, foamed particles and molded articles were produced in the same manner as in Example 1.

(Comparative Example 2)
In this example, the amount of LLDPE used when producing the core particles is changed to 5 kg, the amount of EVA is changed to 5 kg, and the foaming conditions during foaming (specifically, the CO ₂ pressure in the container during foaming) are shown in Table 4 below. Except for the points changed as shown, foamed particles and molded bodies were produced in the same manner as in Example 1.

(Comparative Example 3)
In this example, the amount of the core particles used when producing the composite resin particles is changed to 150 g, except that 135 g of styrene and 15 g of butyl acrylate are used as the first monomer, and 200 g of styrene is used as the second monomer. Produced composite resin particles in the same manner as in Example 1. Next, Example 1 was used except that the composite resin particles were used and the foaming conditions during foaming (specifically, the CO ₂ pressure in the container during foaming) were changed as shown in Table 4 described below. In the same manner, foamed particles and molded bodies were produced.

(Comparative Example 4)
In this example, the amount of the core particles used when preparing the composite resin particles was changed to 24 g, except that 9 g of styrene and 15 g of butyl acrylate were used as the first monomer, and 452 g of styrene was used as the second monomer. Produced composite resin particles in the same manner as in Example 1. Next, Example 1 was used except that the composite resin particles were used and the foaming conditions during foaming (specifically, the CO ₂ pressure in the container during foaming) were changed as shown in Table 4 described below. In the same manner, foamed particles and molded bodies were produced.

(Comparative Example 5)
In this example, foamed particles and a molded body were produced as follows. Specifically, first, nuclear particles were produced in the same manner as in Example 1. Next, a magnesium pyrophosphate slurry as a suspending agent was prepared in the same manner as in Example 1 in an autoclave with an internal volume of 3 L equipped with a stirrer. Next, 2.0 g of sodium lauryl sulfonate (specifically, a 10% by mass aqueous solution) as a surfactant and 75 g of core particles were added to the suspension.

  Subsequently, as a polymerization initiator, benzoyl peroxide (specifically, “Nyper BW” manufactured by NOF Corporation), t-butylperoxy-2-ethylhexyl monocarbonate (specifically, “manufactured by NOF Corporation” Perbutyl E "), 1,1-bis-t-butylperoxycyclohexane (specifically," Lupelox 331M70 "manufactured by Arkema Yoshitomi). Then, 1.5 g of benzoyl peroxide, 0.25 g of t-butylperoxy-2-ethylhexyl monocarbonate, and 5.36 g of 1,1-bis-t-butylperoxycyclohexane are mixed with the first monomer (ie, (Styrene monomer). Then, while stirring the melt at a rotational speed of 500 rpm, the melt was put into the above-described autoclave into which the core particles were put. As the first monomer, a mixed monomer of 410 g of styrene and 15 g of butyl acrylate was used.

  Next, after the air in the autoclave was replaced with nitrogen, the temperature was raised and the temperature inside the autoclave was raised to 88 ° C. over 1 hour and 30 minutes. After the temperature increase, the temperature was maintained at 88 ° C. for 1 hour. Thereafter, the stirring speed was lowered to 450 rpm and maintained at a temperature of 88 ° C. for 5 hours. Next, the temperature inside the autoclave was raised to a temperature of 130 ° C. over 2 hours, and kept at the temperature of 130 ° C. for 10 hours. Thereafter, the inside of the autoclave was cooled, and the contents (specifically, composite resin particles) were taken out. Next, nitric acid was added to dissolve the magnesium pyrophosphate adhering to the surface of the composite resin particles. Thereafter, dehydration and washing were performed with a centrifugal separator, and water adhering to the surface was removed with an airflow drying device to obtain composite resin particles. Except for using the composite resin particles thus obtained, foamed particles and molded bodies were produced in the same manner as in Example 1.

(Comparative Example 6)
In this example, the composite resin particles were prepared in the same manner as in Example 1 except that 10 g of styrene and 15 g of butyl acrylate were used as the first monomer, and 400 g of styrene was used as the second monomer. Particles were made. Next, Example 1 was used except that the composite resin particles were used and the foaming conditions during foaming (specifically, the CO ₂ pressure in the container during foaming) were changed as shown in Table 4 described below. In the same manner, foamed particles and molded bodies were produced.

(Comparative Example 7)
In this example, linear low-density polyethylene is not used as the ethylene-based resin, and EVA (produced by Tosoh Corporation, trade name: content of vinyl acetate component in Ultrasen 515 EVA is 6% by mass) is 10 kg. Except for the points used, core particles were produced in the same manner as in Example 1. Next, Example 1 was used except that the core particles were used and the foaming conditions during foaming (specifically, the CO ₂ pressure in the container during foaming) were changed as shown in Table 4 described below. Similarly, foamed particles and molded bodies were produced.

  For Examples 2 to 7 and Comparative Examples 1 to 7, the evaluation results and the like are shown in Tables 1 to 4 as in Example 1.

As can be seen from Tables 1 and 2, the molded article to which the antistatic agent obtained by using the foamed particles of Examples adhered had excellent antistatic performance with a surface resistivity of less than 1 × 10 ¹² Ω. In addition, the foamed particles to which the antistatic agent is attached are excellent in fusion property while exhibiting the above-described excellent antistatic performance. Therefore, it is possible to produce a molded article having good internal fusion, excellent compressive strength and deflection resistance, and capable of preventing breakage due to deformation. Therefore, the molded body obtained by using the expanded particles of the examples is suitable for an electronic device such as an automobile member, a liquid crystal panel, and a solar power generation panel, a packaging container for a precision device, and the like.

  On the other hand, as can be seen from Tables 3 and 4, Comparative Example 1 in which the content of the polar copolymer was 0 had insufficient antistatic performance. This is presumably because the cationic antistatic agent has low fixability and the antistatic agent outflow suppressing effect of the polar copolymer was not obtained.

  Moreover, in Comparative Example 2 and Comparative Example 7 in which the amount of the polar copolymer is excessive, the fusion rate of the molded product was insufficient. It is considered that this is mainly due to the increase in the amount of the surface layer XY gel of the expanded particles because the ethylene resin is easily crosslinked. As a result, the bending rupture energy of the molded body was insufficient, and breakage due to deformation was likely to occur.

  In Comparative Example 3 with a small amount of styrene-based monomer, the molded article has insufficient rigidity, a small compressive strength, and a low flexural modulus. Therefore, the molded body of Comparative Example 3 was easily deformed by bending and had insufficient deflection resistance. On the other hand, in Comparative Example 4 having a large amount of styrene-based monomer, the compression strength and flexural modulus of the molded product were high, but the bending fracture energy was insufficient, and breakage due to deformation was likely to occur.

In Comparative Example 5 where the seed ratio was too high, a resinous mass was generated during polymerization. Further, the fusion rate of the molded body was insufficient. This is because the suspension amount during polymerization became unstable due to the large amount of styrene monomer added, and the ethylene resin could not be sufficiently impregnated with the styrene monomer. The main cause is thought to be an increase in the styrene resin component on the particle surface. As a result, the molded body of Comparative Example 5 had insufficient bending fracture energy, and was easily broken by deformation. In Comparative Example 5, the absorbance ratio D _{1740 / 2850-Ge} and the ratio D _{1740 / 2850-Ge} / D _{1740 / 2850-ZnSe} were small, the water vapor adsorption amount was small, and the antistatic performance was insufficient.

On the other hand, in Comparative Example 6 where the seed ratio was too low, flat composite resin particles were generated. When the particles are flattened, defective filling of the expanded particles is likely to occur during molding. Further, the fusion rate of the molded body was insufficient. This is mainly because the addition amount of the second monomer is too large to make it difficult to uniformly impregnate the styrene monomer, and the styrene resin component on the surface of the expanded particles is increased. It is believed that there is. As a result, the bending rupture energy of the molded body was insufficient, and breakage due to deformation was likely to occur. In Comparative Example 7, the absorbance ratio D _{1740 / 2850-Ge} and the ratio D _{1740 / 2850-Ge} / D _{1740 / 2850-ZnSe} were small, the water vapor adsorption amount was small, and the antistatic performance was insufficient.

  As described above, the embodiments have been described. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention.

Claims (12)

Composite resin foamed particles using a composite resin obtained by impregnating and polymerizing an ethylene resin with a styrene monomer as a base resin,
The composite resin contains 5% by mass or more and less than 20% by mass of the ethylene resin-derived component and more than 80% by mass of 95% by mass or less of the styrene monomer-derived component (however, The total is 100% by mass).
The ethylene resin is a mixture of a linear low density polyethylene and an ethylene copolymer having a polar group,
The content of the ethylene copolymer having the polar group in the ethylene resin is 1 to 45% by mass,
The composite resin foam particles, wherein the composite resin foam particles have a water vapor adsorption amount of 0.50 cm ³ / g or more.   2. The composite resin foamed particle according to claim 1, wherein the content of the structural unit derived from the monomer containing the polar group in the ethylene-based copolymer is 10 to 50 mass%.   The composite resin expanded particle according to claim 1 or 2, wherein the content of the ethylene copolymer having the polar group in the composite resin is 0.1 to 7% by mass.   The composite resin foamed particle according to any one of claims 1 to 3, wherein the ethylene copolymer having the polar group contains a carbonyl group as the polar group.   The composite resin expanded particle according to any one of claims 1 to 4, wherein the ethylene copolymer having a polar group is an ethylene-vinyl acetate copolymer. Ge ratio of absorbance at wave number 1740 cm ^-1 and a wavenumber 2850 cm ^-1 in an infrared absorption spectrum of the surface of the composite resin foamed particles as measured by infrared total reflection absorption measurement using a prism D _1740/2850-Ge is 0 The composite resin foamed particle according to claim 4 or 5, which is 2 or more. Absorbance ratio D _{1740/2850-ZnSe} and said at wavenumbers 1740 cm ^-1 and a wavenumber 2850 cm ^-1 in an infrared absorption spectrum of the surface of the composite resin foamed particles as measured by infrared total reflection absorption measurement method using a ZnSe prism The composite resin foamed particle according to claim 6, wherein the ratio D _{1740 / 2850-Ge} / D _{1740 / 2850-ZnSe} to the absorbance ratio D _{1740 / 2850-Ge} is greater than 1.   The composite resin foamed particle according to any one of claims 1 to 7, wherein a content ratio of xylene insolubles in a surface layer of the composite resin foamed particle is 25% or less.   The composite resin includes a component derived from 10 to 18% by mass of an ethylene resin and a component derived from 82 to 90% by mass of a styrene monomer (however, the total of both is 100% by mass). The composite resin foamed particles according to any one of claims 1 to 8.   An antistatic composite resin foamed particle, wherein the surface of the composite resin foamed particle according to any one of claims 1 to 9 is coated with an antistatic agent containing a cationic surfactant.   The antistatic composite resin foam particles according to claim 10, wherein the amount of the antistatic agent attached is 0.4 to 3.5 parts by mass with respect to 100 parts by mass of the composite resin foam particles. ^12. A molded article in which the antistatic composite resin foam particles according to claim 10 or 11 are fused to each other, and the molded article has a surface resistivity of less than 1 × 10 ¹² Ω.