JP6701943B2 - Expanded composite resin particles, method for producing the same, molded composite resin foam particles - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a composite resin foamed particle having a composite resin obtained by impregnating and polymerizing an styrene-based monomer in an ethylene resin as a base resin, a method for producing the same, and a molded body in which the composite resin foamed particles are mutually fused.

  In-mold molded products of composite resin expanded particles (that is, composite resin expanded particle molded products) whose base resin is a composite resin obtained by impregnating and polymerizing an styrene-based monomer with an ethylene-based resin are parts of electronic devices and precision equipment. Widely used as packaging materials and cushioning packaging materials. A molded article for such a purpose is generally provided with an antistatic property in order to prevent dust from adhering and electrical damage due to generation of overcurrent such as discharge.

  For example, the following method is known as a method of obtaining composite resin expanded particles. Specifically, first, by impregnating and polymerizing a styrene-based monomer in seed particles containing an ethylene-based resin, a composite resin in which the styrene-based monomer is impregnated and polymerized in the ethylene-based resin is used as a base resin. To obtain composite resin particles. Next, the composite resin particles can be obtained by impregnating the composite resin particles with a foaming agent and foaming the composite resin particles. Further, as a method for imparting antistatic performance to the expanded particle molded article, a method of adding an antistatic agent such as a surfactant is generally used. Specifically, a method of impregnating a composite resin particle with an antistatic agent during or after impregnation of a volatile foaming agent is known. Further, a method of applying an antistatic agent to the composite resin expanded particles is also known.

  In the method of impregnating the antistatic agent at the time of impregnating the volatile foaming agent, the resin particles are excessively plasticized by the antistatic agent, which may lower the heat resistance of the foamed particles at the time of molding and deform the molded body. However, there is a possibility that the fusibility of the foamed particles may deteriorate. Therefore, as in Patent Document 1, a method of applying a predetermined amount of a cationic antistatic agent to foamed composite resin particles has been developed. Further, as in Patent Document 2, a method has been developed in which polyethylene glycol (meth)acrylic acid ester is impregnated and polymerized into composite resin particles, and then an antistatic agent is impregnated when impregnating a foaming agent.

JP, 2005-81274, A JP, 10-147660, A

  However, as described in Patent Document 1, in the method of applying the antistatic agent to the composite resin foamed particles, the fixing property of the antistatic agent may be insufficient, and heating may be performed depending on heating conditions during in-mold molding. The antistatic agent adhering to the expanded particles may be partially released by steam or the like as a medium. Therefore, further improvement in antistatic performance is desired. Further, as described in Patent Document 2, in a method of impregnating and polymerizing a composite resin particle with a polyethylene glycol (meth)acrylic acid ester which is a reactive surfactant, and then impregnating with an antistatic agent, Improvements are possible. However, since polyethylene glycol (meth)acrylic acid ester is a highly water-soluble reactive surfactant, it is difficult for it to be impregnated into the composite resin particles during the impregnation polymerization, and polyethylene glycol (meth)acrylic acid ester is very close to the surface of the composite resin particles. Polymerization of the acid ester occurs. As a result, the polyethylene glycol (meth)acrylic acid ester polymer is unevenly distributed in the vicinity of the surface of the composite resin particles, so that the melt-bonding property when the foamed particles are formed is lowered, and the compression rigidity and flexural resistance of the molded body are reduced. The physical properties may be insufficient. Further, in the method of Patent Document 2, since the antistatic agent is impregnated when the foaming agent is impregnated, the fusibility of the foamed particles to each other may decrease as described above.

  The present invention has been made in view of the above problems, and is a composite resin foamed particle capable of obtaining a molded article excellent in antistatic performance as well as having excellent internal fusion and excellent compression rigidity and bending resistance, and the production thereof. It is intended to provide a method and a molded article using the composite resin expanded particles.

One embodiment of the present invention is a composite resin foamed particle having a base resin of a composite resin obtained by impregnating ethylene resin with (meth)acrylic acid and a styrene monomer.
The composite resin contains 100 to 1900 parts by mass of a structural unit derived from a styrene-based monomer with respect to 100 parts by mass of an ethylene-based resin,
The glass transition temperature Tg of the acetone-soluble component obtained by further dissolving the xylene-soluble component in the composite resin in acetone is 105° C. or lower,
The foamed composite resin particles have a carbonyl content of 0.03 mol% or more on the surface of the foamed composite resin particles.

Another aspect of the present invention is a molded composite resin foamed particle, wherein the molded composite resin foamed particles are fused to each other, and the surface resistivity of the molded body is less than 1×10 ¹² Ω. ..

Still another aspect of the present invention is to add 100 to 1900 parts by mass of styrene to 100 parts by mass of the ethylene resin in the ethylene resin seed particles in a dispersion liquid in which the ethylene resin seed particles are dispersed in an aqueous medium. Modification to obtain composite resin particles by adding a system monomer and (meth)acrylic acid, impregnating and polymerizing the styrene monomer and the (meth)acrylic acid in the ethylene resin seed particles Process,
A foaming step of foaming the composite resin particles using a foaming agent to obtain composite resin expanded particles,
The glass transition temperature Tg of the acetone-soluble component obtained by further dissolving the xylene-soluble component in the composite resin expanded beads in acetone is 105° C. or lower,
The method for producing a foamed composite resin particle has a carbonyl amount of 0.03 mol% or more on the surface of the foamed composite resin particle.

  In the composite resin expanded particles (hereinafter, appropriately referred to as “expanded particles”), the composite resin expanded particles obtained by impregnating and polymerizing the ethylene-based resin with (meth)acrylic acid and a styrene-based monomer are used as the base resin. The amount of carbonyl on the surface of the is adjusted to a predetermined amount or more. Therefore, even when the antistatic agent is applied to the composite resin expanded particles, the outflow of the antistatic agent at the time of molding can be suppressed, and the composite resin expanded particle molded article having good antistatic performance (hereinafter, referred to as "molding as appropriate" Can be obtained). Further, since the glass transition temperature of the acetone-soluble component obtained by further dissolving the xylene-soluble component in the composite resin in acetone is equal to or lower than a predetermined value, internal fusion of the molded body, that is, fusion of the expanded particles to each other. The quality is good. Therefore, the molded body can exhibit strength properties such as excellent compression rigidity and flexure resistance, which are inherent in the composite resin based on the composition of the ethylene resin or the styrene resin.

In addition, the molded product having the surface resistivity of less than 1×10 ¹² Ω, in which the foamed particles are fused to each other, has not only excellent antistatic performance but also excellent strength physical properties such as compression rigidity and flexure resistance as described above. ing. Therefore, the molded product obtained by using the above-mentioned composite resin particles is suitable for applications such as a packaging container for parts of electronic equipment such as liquid crystal panels and solar power generation panels or precision equipment, buffer packaging material, and the like.

  The expanded beads can be produced by performing a modification step and an expansion step. In the modification step, a predetermined amount of styrene monomer and (meth)acrylic acid are added to a dispersion liquid in which ethylene resin seed particles are dispersed in an aqueous medium, and styrene is added to the ethylene resin seed particles. A system monomer and (meth)acrylic acid are impregnated and polymerized. This makes it possible to obtain composite resin particles in which an ethylene resin is impregnated and polymerized with a styrene monomer and (meth)acrylic acid. In the foaming step, the composite resin particles are foamed with a foaming agent to obtain expanded particles. Even if the antistatic agent is applied to the expanded particles thus obtained, it is possible to suppress the outflow of the antistatic agent at the time of molding as described above, and to obtain a molded article having good antistatic performance. You can Further, the molded body has good internal fusion bonding and is excellent in strength characteristics such as compression rigidity and bending resistance.

FIG. 3 is a diagram showing the relationship between the amount of styrene and the absorbance ratio in the examples. FIG. 3 is a diagram showing the relationship between the amount of carbonyl and the absorbance ratio in the examples.

  Next, a preferred embodiment of the expanded beads will be described. The expanded particles are used, for example, for applications in which an antistatic agent is applied to the surface thereof. It can be said that the foamed particles for such an application have an antistatic agent contact surface for adhering the antistatic agent on the surface. In the present specification, the expanded particles are a concept including both particles having an antistatic agent attached to the surface thereof and particles having no antistatic agent attached thereto.

  The expanded particles are used to obtain a molded product by in-mold molding. That is, it is possible to obtain a molded product having a desired shape by filling a large number of expanded particles in a molding die and fusing the composite resin particles to each other in the molding die.

  The expanded beads have a base resin of a composite resin obtained by impregnating and polymerizing an styrene-based monomer and (meth)acrylic acid (hereinafter, also referred to as a styrene-based monomer or the like) in an ethylene-based resin. In the present specification, the composite resin is a resin obtained by impregnating an ethylene-based resin with a styrene-based monomer or the like and polymerized as described above, and is a resin containing an ethylene-based resin component and a styrene-based resin component. .. The styrene-based resin component includes a component formed by polymerizing styrene-based monomers and a component formed by copolymerization of the styrene-based monomer and (meth)acrylic acid. Furthermore, during the polymerization of styrene-based monomers and the like, not only styrene-based monomers may be polymerized with each other, but also styrene-based monomers may be graft-polymerized on the polymer chains constituting the ethylene-based resin. In this case, the composite resin not only contains an ethylene-based resin component composed of an ethylene-based resin and a styrene-based resin component formed by polymerization of a styrene-based monomer, but also a styrene-based monomer is graft-polymerized. It contains an ethylene resin component (that is, a PE-g-PS component). Therefore, the composite resin is a different concept from the mixed resin formed by mixing the polymerized ethylene resin and the polymerized styrene resin.

  The amount of the styrene-based monomer to be impregnated and polymerized in the ethylene-based resin can be appropriately adjusted according to desired physical properties. Specifically, if the proportion of the ethylene resin in the composite resin is increased, the toughness and the resilience are improved, but the rigidity tends to be lowered. On the other hand, when the ratio of the structural unit derived from the styrene-based monomer is increased, the rigidity is improved, but the toughness and the resilience tend to be decreased. As described above, since the composite resin contains the structural unit derived from the styrene-based monomer in an amount of 100 parts by mass or more and 1900 parts by mass or less with respect to 100 parts by mass of the ethylene-based resin, it has a good balance of toughness, resilience, and rigidity. A molded body can be obtained. In order to obtain a molded product having a better balance of toughness, resilience, and rigidity, the composite resin has a structural unit derived from a styrene-based monomer exceeding 150 parts by mass and 1900 parts by mass with respect to 100 parts by mass of the ethylene-based resin. It is preferably contained in an amount of not more than mass parts. Further, from the viewpoint of further improving the rigidity of the molded body, the content of the structural unit derived from the styrene-based monomer with respect to 100 parts by mass of the ethylene-based resin is more preferably more than 400 parts by mass, and is 450 parts by mass or more. It is more preferable that the amount is 500 parts by mass or more. Further, in order to further improve the toughness and the resilience of the molded body, the content of the structural unit derived from the styrene-based monomer is more preferably 1000 parts by mass or less based on 100 parts by mass of the ethylene-based resin, and 900 It is more preferable that the amount is not more than parts by mass. In the present specification, a preferable range, a more preferable range, and a further preferable range regarding the upper limit and the lower limit of the numerical range can be determined from all combinations of the upper limit and the lower limit.

  Examples of the ethylene-based resin include low-density polyethylene, linear low-density polyethylene, branched low-density polyethylene, high-density polyethylene, ethylene-acrylic acid copolymer, ethylene-acrylic acid alkyl ester copolymer, ethylene-methacrylic acid. Acid alkyl ester copolymers, ethylene-vinyl acetate copolymers and the like can be used. As the ethylene resin, one kind of polymer may be used, but a mixture of two or more kinds of polymers can also be used.

  The ethylene resin is preferably linear low-density polyethylene, or linear low-density polyethylene and an ethylene-vinyl acetate copolymer. The content of the ethylene-vinyl acetate copolymer in the ethylene-based resin is preferably less than 10% by mass, more preferably less than 5% by mass. Most preferably, the ethylene resin does not contain a vinyl acetate copolymer. Furthermore, it is preferable that the ethylene-based resin contains linear low-density polyethylene as a main component. Specifically, the content of the linear low-density polyethylene in the ethylene resin is preferably 50% by mass or more, more preferably 70% by mass or more, and further preferably 80% by mass or more. It is particularly preferable that the linear low-density polyethylene is exclusively used.

  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 ethylene-butene copolymers, ethylene-hexene copolymers, ethylene-octene copolymers, and the like. In particular, the ethylene-based resin is preferably linear low-density polyethylene having a melting point of 105° C. or lower, which is obtained by polymerization using a metallocene-based polymerization catalyst. 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 composite resin can be increased. Further, since the fusion strength between the foamed particles at the time of molding can be increased while reducing the amount of low molecular weight components, it becomes possible to obtain a molded product having a low VOC and being hard to break. Further, it becomes possible to obtain a molded product having a higher level of the excellent rigidity of the styrene resin and the excellent tenacity of the ethylene resin.

  The melting point Tm of the ethylene resin is preferably 95 to 105°C. 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 becomes possible to obtain a molded product having both the excellent rigidity of the styrene resin and the excellent tenacity of the ethylene resin at a higher level. From the same viewpoint, the melting point Tm of the ethylene resin is more preferably 100 to 105°C. The melting point Tm can be measured as a melting peak temperature by differential scanning calorimetry (that is, DSC) based on JIS K7121-1987.

  The ethylene-based resin may be made of a linear low-density polyethylene that has a melting point Tm (unit: °C) and a Vicat softening point Tv (unit: °C) satisfying a relationship of Tm-Tv ≤ 20 (unit: °C). preferable. It is presumed that such an ethylene-based resin has a uniform molecular structure and the network structure due to crosslinking is more evenly distributed in the ethylene-based resin. Therefore, in this case, it is possible to improve the strength and tenacity of the expanded particle molded product obtained by using the expanded particles. From the viewpoint of further improving the strength and tenacity of the molded product, the linear low-density polyethylene more preferably satisfies Tm-Tv ≤ 15 (unit: °C), and Tm-Tv ≤ 10 (unit: °C). It is more preferable to satisfy the above requirement. Usually, the melting point Tm is higher than the Vicat softening point Tv. The Vicat softening point Tv can be measured based on the A50 method of JIS K7206 (2016). When the ethylene-based resin is a mixed resin composed of two or more kinds of resins, the melting point and the Vicat softening point of the mixed resin are measured and used as the melting point and the Vicat softening point of the ethylene-based resin.

  From the viewpoint of further improving the foamability, the melt mass flow rate (that is, MFR) of the ethylene resin under the conditions of a temperature of 190° C. and a load of 2.16 kg is preferably 0.5 to 4.0 g/10 minutes, and 0 to 3.0 g/10 minutes is more preferable. The MFR of the ethylene resin under the conditions of a temperature of 190° C. and a load of 2.16 kg is a value measured based on JIS K7210-1 (2014). A melt indexer (for example, model L203 manufactured by Takara Industry Co., Ltd.) can be used as the measuring device.

  The composite resin contains a component obtained by copolymerizing a styrene-based monomer and (meth)acrylic acid. In addition, in the present specification, styrene constituting the styrene resin component, and a monomer copolymerizable with styrene which is added as necessary (however, excluding (meth)acrylic acid) are also combined with the styrene monomer. Sometimes called. The proportion of styrene in the styrene-based monomer is preferably 50% by mass or more, more preferably 80% by mass or more, and further preferably 90% by mass or more. Examples of the monomer copolymerizable with styrene include the following styrene derivatives and other vinyl monomers.

  Examples of the styrene derivative include α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-methoxystyrene, pn-butylstyrene and p-methylstyrene. Examples thereof include -t-butylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, 2,4,6-tribromostyrene, divinylbenzene, styrenesulfonic acid, and sodium styrenesulfonate. These may be used alone or as a mixture of two or more kinds.

  Further, as other vinyl monomers, acrylic acid ester, methacrylic acid ester, vinyl compound containing a hydroxyl group, vinyl compound containing a nitrile group, organic acid vinyl compound, olefin compound, diene compound, halogenated vinyl compound, halogenated compound Examples thereof include vinylidene compounds and maleimide compounds. These vinyl monomers may be used alone or as a mixture of two or more kinds.

  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, 2-ethylhexyl methacrylate and the like. These may be used alone or as a mixture of two or more kinds.

  Examples of the vinyl compound having 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 as a mixture of two or more kinds.

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

  From the viewpoint of enhancing the foamability, it is preferable to use styrene or a combination of styrene and an acrylate monomer as the styrene monomer. From the viewpoint of further enhancing the foamability, it is preferable to use styrene and butyl acrylate together. 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. It is preferably 2 to 5% by mass, and further preferably.

  The styrene resin component further contains a structural unit derived from (meth)acrylic acid. In the present specification, “(meth)acrylic acid” is a concept including “acrylic acid” and “methacrylic acid”, and means one or both of them. Since (meth)acrylic acid has a carbon-carbon double bond in its structure, it can be copolymerized with the styrene-based monomer during impregnation polymerization of the styrene-based monomer. The presence of the structural unit derived from (meth)acrylic acid, for example, on the surface of the expanded particles makes it possible to improve the fixability of the antistatic agent while suppressing the decrease in the fusion property of the expanded particles. The reason for this is considered as follows.

  That is, since (meth)acrylic acid has appropriate water solubility, it has high polymerization stability and is unlikely to cause coagulation. Furthermore, by copolymerizing (meth)acrylic acid with a styrene-based monomer, the composite resin has a copolymer component having a structural unit derived from a styrene-based monomer and a structural unit derived from (meth)acrylic acid. It is considered that the copolymer component can be contained on the surface of the particle as well as the content. Therefore, it becomes possible to improve the fixing property of the antistatic agent while maintaining the fusion property of the expanded particles.

  The structure derived from (meth)acrylic acid is preferably present in the vicinity of the surface more than in the central part of the expanded particles. In this case, the fixability of the antistatic agent for the expanded particles can be further improved. By adjusting the timing of adding (meth)acrylic acid in the process for producing expanded particles described below, a structure derived from (meth)acrylic acid is likely to exist near the surface of the expanded particles. Specifically, during impregnation polymerization of a styrene-based monomer, when the styrene-based monomer is added in a plurality of times, (meth)acrylic acid is added together with the styrene-based monomer added after the second time. By the addition, the structure derived from (meth)acrylic acid easily exists near the surface of the expanded beads.

  Whenever possible, add (meth)acrylic acid together with at least the last styrene-based monomer, or add the styrene-based monomer after the last-added styrene-based monomer. It is more preferable to add (meth)acrylic acid by the time the polymerization is completed. In this case, the amount of carbonyl derived from (meth)acrylic acid on the surface of the expanded particles can be easily increased.

  Further, it is preferable that the styrene-based monomer added last does not include a monomer copolymerizable with styrene such as the above-mentioned acrylic acid ester. Specifically, the styrene-based monomer added last is more preferably styrene. In this case, the fixability of the antistatic agent can be efficiently enhanced according to the amount of (meth)acrylic acid added.

  The glass transition temperature Tg of the acetone-soluble component obtained by further dissolving the xylene-soluble component in the composite resin in acetone is 105° C. or lower, and preferably 102° C. or lower. On the other hand, the lower limit of the glass transition temperature Tg is preferably about 85° C. or higher. In this case, the foamability of the composite resin particles during foaming can be further improved, and the shrinkage during foaming can be further prevented. Furthermore, during in-mold molding of the expanded beads obtained after foaming, the fusibility of the expanded particles can be further improved, and the dimensional stability of the expanded particle molded product can be further improved.

  The glass transition temperature Tg can be measured, for example, as follows. First, 1.0 g of the composite resin particles is put in a wire mesh bag of 150 mesh. Next, about 200 ml of xylene is placed in a round flask having a volume of 200 ml, and the Soxhlet extraction tube is set with the sample placed in the wire mesh bag. Soxhlet extraction is performed by heating with a mantle heater for 8 hours. 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. With respect to the obtained acetone-soluble content of 2 to 4 mg, a heat flux differential scanning calorimetry is performed using a DSC measuring instrument Q1000 manufactured by TA Instruments in accordance with JIS K7121 (1987). Then, the Tg of the acetone-soluble component was obtained as the midpoint glass transition temperature of the DSC curve obtained under the heating rate of 10° C./min, which was obtained by further dissolving the xylene-soluble component in the composite resin in acetone. It is the Tg of the acetone-soluble component. The acetone-soluble component obtained by further dissolving the xylene-soluble component in the composite resin in acetone is mainly a styrene resin.

  The amount of carbonyls on the surface of the expanded beads (hereinafter, also referred to as the amount of surface carbonyls) is 0.03 mol% or more. If it is less than 0.03 mol %, the effect of improving the fixing property of the antistatic agent may be insufficient. As a result, the antistatic performance of the molded product may be insufficient. From the viewpoint of further improving the fixability of the antistatic agent, the amount of carbonyl on the surface of the expanded beads is more preferably 0.07 mol% or more, and further preferably 0.1 mol% or more.

  On the other hand, if the amount of carbonyls in the entire expanded particles is too large, the glass transition temperature Tg becomes higher than 105° C., and the fusion property of the expanded particles may decrease. The carbonyl content on the surface of the foamed particles is preferably 0.2 mol% or less from the viewpoint of further improving the fixability of the antistatic agent while maintaining the fusibility of the foamed particles without increasing the glass transition temperature. , 0.16 mol% or less is more preferable, and 0.15 mol% or less is further preferable.

The amount of carbonyl on the surface of the expanded particles can be determined from the infrared absorption spectrum of total reflection absorption (ATR method). Specifically, it is determined by multiplying the amount of styrene on the surface of the expanded particles by the amount of carbonyl on the amount of styrene on the surface. First, the amount of styrene and the amount of carbonyl relative to the amount of styrene are measured as follows.
(A) Amount of styrene In measuring the amount of styrene, an infrared spectrophotometer and a total reflection absorption measuring device are used as a measuring device to obtain an infrared absorption spectrum (without ATR correction) of the surface of the expanded particles. Next, the absorbance D _{698 at 698} cm ^{−1 and} the absorbance D ₂₈₅₀ at ₂₈₅₀ cm ⁻¹ obtained from the infrared absorption spectrum (without ATR correction) are measured to obtain the absorbance ratio D ₆₉₈ /D ₂₈₅₀ . The average value of these is defined as the absorbance ratio D ₆₉₈ /D ₂₈₅₀ of the expanded particles. The absorbance ratio D ₆₉₈ /D ₂₈₅₀ is an index for estimating the polystyrene content on the surface of the expandable modified resin particles. The absorbance D ₆₉₈ obtained from the infrared absorption spectrum (without ATR correction) is the height of the peak derived from the out-of-plane bending vibration of the benzene ring mainly contained in the styrene resin. Further, the absorbance D ₂₈₅₀ obtained from the infrared absorption spectrum (without ATR correction) is the height of the peak derived from the CH stretching vibration of the methylene group contained in both the ethylene resin and the styrene resin. is there. Then, the calibration curve can be used to determine the amount of styrene on the surface of the expanded particles.
(B) Carbonyl amount relative to styrene amount When measuring the carbonyl amount, it can be determined by the same measuring device and measuring conditions as the above-mentioned measurement of the styrene amount. Next, the absorbance D _{698 at 698} cm ^{−1 and} the absorbance D ₁₇₃₀ at ₁₇₃₀ cm ⁻¹ obtained from the infrared absorption spectrum (without ATR correction) are measured to obtain the absorbance ratio D ₁₇₃₀ /D ₆₉₈ . The same measurement is performed for five expanded particles, and the average value of these is taken as the absorbance ratio D ₁₇₃₀ /D _{698 of the} expanded resin particles of the composite resin. The absorbance D ₁₇₃₀ obtained from the infrared absorption spectrum (without ATR correction) is the height of the peak derived from the carboxy group of the (meth)acrylic acid component unit. Then, the carbonyl amount with respect to the styrene amount is obtained using the calibration curve prepared in advance. Then, the amount of carbonyl on the surface of the expanded particles can be obtained by multiplying the amount of styrene by the amount of carbonyl with respect to the amount of styrene.

  The styrene resin component has a structural unit derived from methacrylic acid, a structural unit derived from acrylic acid, or a structural unit derived from methacrylic acid and a structural unit derived from acrylic acid. Preferably, the styrene resin component should have at least a structural unit derived from methacrylic acid. In this case, the fixing property of the antistatic agent and the fusion property of the expanded particles can be improved in a better balance.

  In the expanded beads, the content of the structural unit derived from (meth)acrylic acid is preferably 0.1 to 2 parts by mass with respect to 100 parts by mass of the composite resin. In this case, the fixing property of the antistatic agent and the fusion property of the expanded particles can be improved in a better balance. From the viewpoint of further improving the fixability of the antistatic agent, the content of the structural unit derived from (meth)acrylic acid relative to 100 parts by mass of the composite resin is more preferably 0.2 parts by mass or more, and 0.5 parts by mass or more. More preferable. On the other hand, the content of the structural unit derived from (meth)acrylic acid with respect to 100 parts by mass of the composite resin is more preferably 1.5 parts by mass or less, and preferably 1 part by mass or less, from the viewpoint of further suppressing the decrease in fusion property. More preferable.

  An antistatic agent can be attached to the surface of the expanded beads. The amount of the antistatic agent attached depends on the type of the antistatic agent used, but is preferably 0.3 to 5 parts by mass with respect to 100 parts by mass of the expanded particles. In this case, sufficient antistatic performance can be obtained and the fusion property can be prevented from lowering. From the viewpoint of obtaining more sufficient antistatic performance, the amount of the antistatic agent attached to 100 parts by mass of the expanded particles is more preferably 0.5 parts by mass or more. Further, from the viewpoint that the fusion property can be further prevented from decreasing, the amount of the antistatic agent attached is more preferably 3 parts by mass or less, and further preferably 2 parts by mass or less.

  In addition, since the composite resin foamed particles using the composite resin in which the styrene-based monomer is impregnated and polymerized with the ethylene-based resin as the base resin have basically hydrophobic properties, when an antistatic agent having hydrophilicity is attached, The fixing property is low and the antistatic agent attached to the expanded particles may be partially released by steam or the like which is a heating medium depending on the heating conditions for in-mold molding of the expanded particles. However, since the foamed particles contain a specific amount of the structural unit derived from (meth)acrylic acid as described above, the vicinity of the surface is appropriately hydrophilized without inhibiting the fusibility of the foamed particles, It is considered that the fixability of the antistatic agent is improved. That is, according to the composite resin expanded particles, it becomes possible to obtain a molded product having both excellent mechanical strength and antistatic performance.

  The antistatic agent is not particularly limited, and examples thereof include nonionic surfactants such as hydroxyalkyl amine, hydroxyalkyl monoether amine, polyoxyalkylene alkyl amine, glycerin fatty acid ester, polyoxyethylene alkyl ether, and polyoxyethylene alkyl ether. Agents: anionic surfactants such as alkyl sulfonates, alkyl benzene sulfonates, alkyl phosphates; octyl dimethyl ethyl ammonium ethyl sulfate, lauryl dimethyl ethyl ammonium ethyl sulfate, didecyl dimethyl ammonium chloride, tetraalkyl ammonium salt, trialkyl benzyl Examples include cationic surfactants such as ammonium salts. In addition, these antistatic agents can be used alone or in combination. As the antistatic agent, for example, various commercially available products can be used.

  The antistatic agent preferably contains at least a cationic surfactant, and at least octyldimethylethylammoniumethylsulfate is more preferably used. In this case, the antistatic agent is more easily fixed to the foamed particles containing the structural unit derived from (meth)acrylic acid, and the antistatic performance of the molded product can be further improved.

The surface resistivity of the molded body in which the foamed 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 packing containers such as liquid crystal panels and solar power generation panels and buffer packing materials can be sufficiently exhibited. The surface resistivity of the molded body is more preferably equal to or less than 5 × 10 ¹¹ Ω, more preferably 2.5 × 10 ¹¹ Ω or less.

The water vapor adsorption amount of the foamed particles is preferably 0.5 cm ³ /g or more. In this case, the fixing property of the antistatic agent on the surface of the expanded beads can be more reliably and sufficiently improved. In view of the above, the water vapor adsorption amount of the foamed particles is more preferably 0.7 cm ³ / g or more, further preferably 0.8 cm ³ / g or more. The water vapor adsorption amount shows how much water vapor can be adsorbed on the surface of the expanded particles. The amount of water vapor adsorbed is an index of the hydrophilicity of the expanded particles, and when the amount of carbonyls on the surface of the expanded particles increases, the amount of water vapor adsorbed on the surface of the expanded particles also tends to increase.

  The vapor adsorption amount of the composite resin foamed particles is measured by measuring an adsorption isotherm (set relative pressure: 0.005 to 0.9) at 25° C. using a vapor adsorption amount measuring device to obtain a maximum relative pressure of 0.9. The amount of adsorbed water vapor can be obtained as the amount of adsorbed water vapor of the expanded resin beads of the present invention. Specifically, for example, about 0.2 g of composite resin particles is weighed in advance, then the weighed composite resin particles are put in a sample cell, and the adsorption isotherm of water vapor at 25° C. (set relative pressure: 0.005 .About.0.9), and the amount of water vapor adsorbed at the maximum relative pressure of 0.9 can be determined as the amount of water vapor adsorbed by the composite resin expanded particles of the present invention.

  Next, an embodiment of a method for producing expanded beads will be described. Expanded particles can be obtained by performing a modifying step and a foaming step. Hereinafter, each step will be described in detail.

  In the modifying step, ethylene-based resin seed particles containing an ethylene-based resin component as a main component (hereinafter referred to as “seed particles” as appropriate) are used. The seed particles may further contain additives such as a bubble control agent, a colorant, a lubricant, and a dispersion diameter expanding agent, in addition to the ethylene resin component. The seed particles can be produced by blending the above-mentioned additives, which are added as necessary, with the ethylene resin component, melt-kneading the blend, and then finely granulating the blend. Melt kneading can be performed by an extruder. In order to carry out uniform kneading, it is preferable to extrude after mixing the resin components in advance. The resin components can be mixed using a mixer such as a Henschel mixer, a ribbon blender, a V blender, and a Ledige mixer. The melt-kneading is preferably performed using a single-screw extruder or a twin-screw extruder equipped with a high dispersion type screw such as a dullage type, a mudock type, a unimelt type.

  The seed particles are granulated by, for example, cutting the melt-kneaded mixture 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 modification step, first, seed particles are dispersed in an aqueous medium to obtain a dispersion liquid. For example, deionized water can be used as the aqueous medium. The seed particles are preferably dispersed in an aqueous medium together with the suspending agent. In this case, the styrene-based monomer described below can be uniformly suspended in the aqueous medium in which the seed particles are dispersed. 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. Inorganic suspending agents in the form of fine particles such as barium carbonate, calcium sulfate, barium sulfate, talc, kaolin and bentonite can be used. In addition, for example, an organic suspending agent such as polyvinylpyrrolidone, polyvinyl alcohol, ethyl cellulose, hydroxypropylmethyl cellulose can be used. Preferred are tricalcium phosphate, hydroxyapatite, and magnesium pyrophosphate. These suspending agents can be used alone or in combination of two or more kinds.

  The amount of the suspending agent used is 100 parts by mass with respect to 100 parts by mass of the aqueous medium of the suspension polymerization system (specifically, all the water in the system containing water such as the reaction product-containing slurry). 05 to 10 parts by mass is preferable. More preferably, it is 0.3 to 5 parts by mass. If the amount of the suspending agent is too small, it becomes difficult to stably suspend the styrene-based monomer in the modifying step, and a lump of resin may be generated. On the other hand, if the amount of the suspending agent is too large, not only the manufacturing cost will increase, but also the particle size distribution of the composite resin particles obtained after the modifying step may be broadened.

  A dispersant composed of a surfactant can be added to the aqueous medium. As the surfactant, it is preferable to use, for example, an anionic surfactant or a nonionic surfactant. These surfactants can be used alone or in combination of two or more.

  Examples of the anionic surfactant that can be used 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, etc. can be used. More preferably, as the dispersant, an anionic surfactant composed of an alkyl sulfonic acid alkali metal salt (preferably sodium salt) having 8 to 20 carbon atoms may be used. Thereby, the suspension can be sufficiently stabilized.

  If necessary, an electrolyte composed of inorganic salts such as lithium chloride, potassium chloride, sodium chloride, sodium sulfate, sodium nitrate, sodium carbonate and sodium bicarbonate can be added to the aqueous medium. Further, in order to obtain a molded product excellent 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.

  The water-soluble polymerization inhibitor is difficult to impregnate in the seed particles and is soluble in the aqueous medium. Therefore, the styrenic monomer impregnated in the seed particles is polymerized, but the styrene monomer fine droplets in the aqueous medium not impregnated in the seed particles, and the seed particles being absorbed by the seed particles. It is possible to suppress the polymerization of the styrene-based monomer near the surface. As a result, it is presumed that the amount of the styrene resin component near the outermost surface of the composite resin particles can be reduced, and the toughness of the obtained molded product is improved. The amount of the water-soluble polymerization inhibitor added is 0.001 to 0.1 part by mass with respect to 100 parts by mass of the aqueous medium (specifically, all the water in the system including water such as the reaction product-containing slurry). Is preferable, and 0.005-0.06 parts by mass is more preferable.

  In the modification step, the styrene-based monomer and (meth)acrylic acid are impregnated and polymerized in the dispersion liquid in which the seed particles are dispersed in the aqueous medium as described above. The polymerization of the styrene-based monomer and the like can be performed in the presence of a polymerization initiator. In this case, the ethylene resin may be crosslinked together with the copolymerization of the styrene monomer and the like. Further, a cross-linking agent can be used together if necessary. When using the polymerization initiator and the crosslinking agent, it is preferable to dissolve the polymerization initiator and the crosslinking agent in the styrene monomer in advance.

  As the polymerization initiator, those used in the suspension polymerization method of styrene-based monomers can be used. For example, a polymerization initiator which is soluble in a styrene-based monomer and has a 10-hour half-life temperature of 50 to 120° C. can be used. Examples of the polymerization initiator include cumene hydroxyperoxide, dicumyl peroxide, t-butylperoxy-2-ethylhexanoate, t-butylperoxybenzoate, benzoyl peroxide, t-butylperoxyisopropyl carbonate, t. Organic peroxides such as -butylperoxy-2-ethylhexyl carbonate, t-amylperoxy-2-ethylhexyl carbonate, hexylperoxy-2-ethylhexyl carbonate and lauroyl peroxide can be used. Moreover, as the polymerization initiator, an azo compound such as azobisisobutyronitrile can be used. These polymerization initiators may be used alone or in combination of two or more. Further, t-butylperoxy-2-ethylhexanoate is preferable from the viewpoint of easily reducing the residual styrene-based 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-based monomer.

  As the cross-linking agent, it is preferable to use a substance that does not decompose at the polymerization temperature but decomposes at the cross-linking temperature and has a 10-hour half-life temperature higher by 5 to 50° C. than the polymerization temperature. Specifically, for example, peroxides such as dicumyl peroxide, 2,5-t-butylperbenzoate, and 1,1-bis-t-butylperoxycyclohexane can be used. The cross-linking agents can be used alone or in combination of two or more kinds. The compounding amount of the crosslinking agent is preferably 0.1 to 5 parts by mass with respect to 100 parts by mass of the styrene-based monomer. The same compound may be used as the polymerization initiator and the crosslinking agent.

  Further, (meth)acrylic acid is preferably dissolved in the styrene-based monomer in advance. That is, it is preferable to impregnate and polymerize seed particles dispersed in an aqueous medium with a styrene-based monomer in which (meth)acrylic acid is dissolved. In this case, (meth)acrylic acid is more easily taken in during the polymerization of the styrene-based monomer.

  When impregnating the seed particles with the styrene-based monomer for polymerization, the total amount of the styrene-based monomer to be blended can be added all at once to the aqueous medium in which the seed particles are dispersed. It is also possible to divide the total amount of the styrene-based monomer of, for example, into two or more and add these monomers at different timings. Specifically, a part of the total amount of the styrenic monomer to be blended is added to the aqueous medium in which the seed particles are dispersed, the styrenic monomer is impregnated, and the polymerization is performed. Further, the balance of the styrenic monomer to be blended can be added once or twice or more to the aqueous medium. By adding the styrene-based monomer in a divided manner as in the latter case, it becomes possible to further suppress the coagulation of the resin particles during the polymerization.

  In addition, as described above, when the total amount of the styrenic monomer to be blended is divided into two or more and these monomers are added at different timings, together with the styrenic monomer added after the second time ( It is preferred to add (meth)acrylic acid. More preferably, it is preferable to add (meth)acrylic acid together with at least the styrene-based monomer added last. In this case, the styrene resin component containing the structural unit derived from (meth)acrylic acid is likely to be present near the surface of the expanded beads. As a result, the fixability of the antistatic agent on the expanded particles can be further improved.

  Further, the polymerization initiator can be added to the aqueous medium in a state of being dissolved in the styrene-based monomer. As described above, when the styrenic monomer to be mixed is divided into two or more parts and added at different timings, the polymerization initiator should be dissolved in the styrenic monomer added at any timing. It is also possible to add a polymerization initiator to each styrene monomer added at different timings. When the styrene-based monomer is divided and added, it is preferable that the polymerization initiator is dissolved in at least the styrene-based monomer (hereinafter referred to as “first monomer”) added first. It is preferable to dissolve 75% or more, and more preferably 80% or more of the total amount of the polymerization initiator to be mixed in the first monomer. In this case, the ethylene resin can be sufficiently impregnated with the styrene monomer during the production of the composite resin particles, and the destabilization of the suspension system during the polymerization can be prevented. As a result, it becomes possible to obtain a molded product having both the excellent rigidity of the styrene resin and the excellent tenacity of the ethylene resin at a higher level. Further, as described above, when a part of the styrenic monomer to be blended is added as the first monomer, the rest of the total amount of the styrenic 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 added in a divided manner.

  The seed ratio of the styrene-based monomer added as the first monomer (that is, the mass ratio of the first monomer to the seed particles) is preferably 0.5 or more. In this case, it becomes easy to make the shape of the composite resin particles more spherical. From the same viewpoint, the seed ratio is more preferably 0.7 or more, further preferably 0.8 or more. The seed ratio is preferably 1.5 or less. In this case, it is possible to further prevent the styrene-based monomer from polymerizing before being sufficiently impregnated in the seed particles, and it is possible to further prevent the formation of resin lumps. From the same viewpoint, the seed ratio of the first monomer is more preferably 1.3 or less, and further preferably 1.2 or less.

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

  In addition, additives such as a plasticizer, an oil-soluble polymerization inhibitor, a flame retardant, a colorant, and a chain transfer agent can be added to the styrene-based monomer, if necessary. When these additives are added to the styrene-based monomer, it is preferable to add them to the above-mentioned first monomer. Of these additives, it is preferable not to add an additive having a carbonyl group to at least the styrene-based monomer added last.

  As the plasticizer, for example, fatty acid ester, acetylated monoglyceride, fats and oils, hydrocarbon compounds and the like can be used. Examples of the fatty acid ester that can be used include glycerin tristearate, glycerin trioctoate, glycerin trilaurate, sorbitan tristearate, sorbitan monostearate, and butyl stearate. As the acetylated monoglyceride, for example, glycerin diacetomonolaurate or the like can be used. As the fats and oils, for example, hardened beef tallow, hardened castor oil, etc. can be used. As the hydrocarbon compound, for example, cyclohexane, liquid paraffin, etc. can be used. Further, as the oil-soluble polymerization inhibitor, for example, para-t-butylcatechol, hydroquinone, benzoquinone or 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. Furnace black, channel black, thermal black, acetylene black, Ketjen black, graphite, carbon fiber and the like can be used as the colorant. As the chain transfer agent, for example, n-dodecyl mercaptan, α-methylstyrene dimer or the like can be used. The above additives can be added alone or in combination of two or more.

  The above-mentioned additives such as the plasticizer, the oil-soluble polymerization inhibitor, the flame retardant, the colorant, and the chain transfer agent can be dissolved in a solvent and impregnated in the seed particles. As the solvent, for example, aromatic hydrocarbons such as ethylbenzene and toluene, and aliphatic hydrocarbons such as heptane and octane 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-impregnated pre-foaming method, a dispersion medium releasing foaming method, and these methods, and other foaming methods based on the principle.

  In the gas-impregnated pre-foaming method, a foaming agent such as a physical foaming agent is impregnated into the composite resin particles during polymerization, after polymerization, or during and after polymerization. Hereinafter, the composite resin particles impregnated with the foaming agent are appropriately referred to as "expandable composite resin particles". Next, the expandable composite resin particles can be obtained by charging the expandable composite resin particles into a pre-expanding machine and heating with a heating medium such as steam, hot air, or a mixture thereof. Also, the composite resin particles obtained by polymerization in the pressure vessel are filled in another pressure vessel, and the foaming agent is impregnated with the foaming agent by press-fitting the foaming agent to produce expandable composite resin particles. You can also do it.

  On the other hand, in the dispersion medium discharging foaming method, first, the composite resin particles dispersed in the aqueous medium in the pressure vessel are impregnated with a foaming agent under heating and pressure to produce expandable composite resin particles. Then, under proper foaming temperature conditions, the expandable composite resin particles can be foamed by discharging the expandable composite resin particles together with the aqueous medium from the pressure vessel under a lower pressure than in the pressure vessel. .

  For the impregnation of the foaming agent, a liquid phase impregnation method or a vapor phase impregnation method can be appropriately selected. As a physical foaming agent, an inorganic gas such as nitrogen, carbon dioxide, argon, air, helium, water; methane, ethane, propane, normal butane, isobutane, cyclobutane, normal pentane, isopentane, neopentane, cyclopentane, normal hexane, cyclohexane , 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, 2,3-dimethylbutane, and other organic volatile gases. An inorganic foaming agent is preferable. In this case, the foaming agent is diffused from the foamed particles after foaming, and the foaming agent does not remain in the foamed particles. Therefore, the internal pressure of the expanded beads is unlikely to rise excessively during molding, and the molded body can be cooled in a short time and taken out from the molding die.

  Examples of the shape of the foamed particles include a columnar shape, a rugby ball shape, and a spherical shape. The size of the foamed particles is about 0.5 mm to 5 mm in diameter, depending on the amount of the foaming agent and the size of the resin particles.

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

  There is no limitation on the concentration and properties of the antistatic agent used for coating, and it may be a stock solution or a powder, or a diluting solution such as water or alcohol. Furthermore, the container for applying the antistatic agent to the expanded beads may be either a closed system or an open system, and the temperature at the time of application may be below the heat resistant temperature of the expanded particles. It is preferred that the antistatic agent be adhered to the entire surface of the composite expanded particles by stirring the expanded particles well during or after the application. The coating method may be any of the above or a combination thereof.

  In the step of applying the antistatic agent, it is preferable to apply 0.3 to 5 parts by mass of the antistatic agent to 100 parts by mass of the foamed particles so that the amount of the antistatic agent attached falls within the above range. In this case, it is possible to impart sufficiently excellent antistatic performance to the expanded beads, prevent deterioration of the fluidity of the expanded particles, and prevent defective filling during molding. The amount of the antistatic agent applied to 100 parts by mass of the composite resin expanded particles is more preferably 0.5 to 4 parts by mass, further preferably 1 to 3 parts by mass. The antistatic agent may be coated as long as the antistatic agent is present on the surface of the expanded beads, and it is more preferable that the surface of the expanded beads is completely covered. Therefore, the expanded particles coated with the antistatic agent do not necessarily have to have their surfaces completely covered, and may have a portion not covered with the antistatic agent on the surface of the expanded particles.

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

  Examples for producing expanded particles and molded products will be described in detail below.

(Example 1)
(1) Preparation of seed particles As the ethylene resin, a linear low-density polyethylene resin (specifically, "Nipolon Z HF210K" manufactured by Tosoh Corporation) prepared by polymerization using a metallocene polymerization catalyst was prepared. The melting point Tm of this ethylene resin is 103°C. 20 kg of this ethylene resin and 0.144 kg of zinc borate (specifically, zinc borate 2335 manufactured by Tomita Pharmaceutical Co., Ltd.) were mixed with a Henschel mixer (specifically, manufactured by Mitsui Miike Kakoki Co., Ltd.). The mixture was put into a model FM-75E) and mixed for 5 minutes to obtain a resin mixture.

  Next, 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.). Seed particles were obtained by extruding the melt-kneaded product and cutting it into an average of 0.5 mg/piece by an underwater cutting method.

(2) Preparation of Composite Resin Particles 1000 g of deionized water was placed in an autoclave with an internal volume of 3 L equipped with a stirrer, and 6.0 g of sodium pyrophosphate was further added. Then, 12.9 g of powdery magnesium nitrate hexahydrate was added, and the mixture was stirred at room temperature for 30 minutes. As a result, a magnesium pyrophosphate slurry as a suspending agent was prepared. Next, in an aqueous medium containing this suspending agent, 2.0 g of sodium lauryl sulfonate (specifically, a 10 mass% aqueous solution) as a surfactant and 0.21 g of sodium nitrite as a water-soluble polymerization inhibitor. , And 75 g of seed particles.

  Then, as a polymerization initiator, t-butylperoxy-2-ethylhexyl monocarbonate (specifically, “Perbutyl E” manufactured by NOF CORPORATION) and t-hexylperoxybenzoate (specifically manufactured by NOF CORPORATION). "Perhexyl Z") was prepared. In addition, α-methylstyrene dimer (specifically, “NOFMER MSD” manufactured by NOF CORPORATION) was prepared as a chain transfer agent. Then, 1.72 g of t-butylperoxy-2-ethylhexyl monocarbonate, 0.86 g of t-hexylperoxybenzoate, and 0.63 g of α-methylstyrene dimer were added as a first monomer (that is, a styrene-based monomer). ). Then, the melt was put into an aqueous medium in the autoclave while stirring at a rotation speed of 500 rpm. A mixed monomer of 60 g of styrene and 15 g of butyl acrylate was used as the first monomer.

  Next, after replacing the air in the autoclave with nitrogen, the temperature rise was started, and the temperature in the autoclave was raised to 100° C. over 1 hour and 30 minutes. After the temperature was raised, the temperature was kept at 100° C. for 1 hour. Then, the stirring speed was reduced to 450 rpm, and the temperature was maintained at 100° C. for 7.5 hours. The temperature at this time (specifically 100° C.) is the polymerization temperature. In addition, 1 hour after the temperature reached 100° C., 56.4 g of styrene as the second monomer (specifically, styrene-based monomer) and 3.75 g of methacrylic acid (that is, MAA) were added. It was added to the autoclave over time. MAA was added in a state of being dissolved in styrene as the second monomer in advance.

  Then, the temperature inside the autoclave was raised to a temperature of 125°C over 2 hours, and the temperature was kept at 125°C for 5 hours. Then, 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 attached to the surfaces of the composite resin particles. After that, dehydration and washing were performed with a centrifuge, and water adhering to the surface was removed with an airflow drying device to obtain composite resin particles. From the compounding ratio (mass ratio) of the styrene-based monomer and the ethylene-based resin used during production, the mass ratio of the component derived from the ethylene-based resin and the component derived from the styrene-based monomer in the composite resin I asked.

  Regarding the composite resin particles obtained as described above, the amount of styrene-based monomer, the amount of MAA, the timing of addition of MAA, the time of addition, the ethylene-based resin component (that is, PE) and the styrene-based resin component (that is, PE) , PS) are shown in Table 1 below. The amount of MAA is the amount based on 100 parts by mass of the total of the ethylene resin, the styrene monomer, and the MAA. Further, regarding the composite resin particles, the glass transition temperature Tg of the acetone-soluble component obtained by further dissolving the xylene-soluble component in the composite resin in acetone as described below (hereinafter, appropriately referred to as “Tg of acetone-soluble component”). Was measured, and the foamability was evaluated. The results are shown in Table 1.

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

"Evaluation of foamability"
1 kg of the composite resin particles was charged with 3.5 liters of water in a pressure-resistant container of 5 L equipped with a stirrer, and 5 g of kaolin as a dispersant and 0.6 g of sodium alkylbenzenesulfonate as a surfactant were further added to water. .. Next, while stirring the pressure vessel at a stirring speed of 300 rpm, the pressure vessel was heated to a foaming temperature of 165° C., and then carbon dioxide as an inorganic physical foaming agent was added to the pressure vessel at 4.0 MPa (however, with a gauge. Pressure), and kept under stirring for 20 minutes. Then, the composite resin particles were foamed by releasing the contents under atmospheric pressure to obtain expanded particles. The bulk density of the obtained expanded beads was measured, and the foamability was evaluated according to the following criteria.

That is, the case where the bulk density is less than 40 kg / m ³ as "excellent", a case of less than 40 kg / m ³ or more and 50 kg / m ³ as "good", rating the case of 50 kg / m ³ or more as "poor" did. The results are shown in Table 1 below. In addition, in Table 1, the value of the bulk density in the evaluation of foaming property is shown, and the evaluation result is shown in parentheses. The bulk density (unit: kg/m ³ ) was measured as follows. First, a 1-liter graduated cylinder was prepared, and the empty graduated cylinder was filled with the expanded particles up to the 1-L marked line. Then, the mass (unit: g) of the expanded particles per 1 L was measured. Then, the bulk density (unit: kg/m ³ ) was calculated by converting the mass (unit: g) of the foamed particles 1 L into a unit.

(3) Preparation of Expanded Particles 500 g of the composite resin particles prepared as described above was charged together with 3500 g of water as a dispersion medium in a 5 L pressure vessel equipped with a stirrer. Then, 5 g of kaolin as a dispersant and 0.5 g of sodium alkylbenzenesulfonate as a surfactant were further added to the dispersion medium in the 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. Then, carbon dioxide, which is an inorganic physical foaming agent, was pressed into the container so that the pressure in the container was 3.9 MPa (however, gauge pressure), and held at the same temperature (that is, 165° C.) for 15 minutes. Thus, the composite resin particles were impregnated with carbon dioxide to obtain expandable composite resin particles. Next, the expandable 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 foamed particles are a foamed body of composite resin particles, they can be said to be composite resin foamed particles. The foaming conditions are shown in Table 1 below.

  With respect to the expanded particles produced as described above, the amount of carbonyl on the surface and the amount of water vapor adsorbed were measured as follows. The results are shown in Table 1.

"Carbonyl amount"
The amount of carbonyl on the surface of the expanded beads is represented by the amount of styrene on the surface of the expanded particles and the product of the amount of styrene and the amount of styrene on the surface. First, the amount of styrene and the amount of carbonyl relative to the amount of styrene are measured as follows.

(A) Amount of styrene In measuring the amount of styrene, an infrared spectrophotometer “FT/IR-460plus” manufactured by JASCO Corporation and a total reflection absorption measurement device “ATR PRO 450-S type” manufactured by the same company are used as measuring devices. Was used. Moreover, the measurement conditions of the total reflection absorption measurement apparatus were prism: ZnSe and incident angle: 45°. Specifically, first, the foamed particles are pressed against the prism of the total reflection absorption measurement device at a pressure of 170 kg/cm ² to be in close contact with the prism, and the infrared spectrum of the surface of the foamed particles is measured. (Without correction).

Next, the absorbance D ₆₉₈ near ₆₉₈ cm ^{−1 and} the absorbance D ₂₈₅₀ near ₂₈₅₀ cm ⁻¹ obtained from the infrared absorption spectrum (without ATR correction) are measured, and the absorbance ratio D ₆₉₈ /D ₂₈₅₀ is obtained. The same measurement is performed on five expanded particles, and the average value of these is taken as the absorbance ratio D ₆₉₈ /D ₂₈₅₀ of the expanded particles. The results are shown in Table 1.

The absorbance D ₆₉₈ obtained from the infrared absorption spectrum (without ATR correction) is the height of the peak derived from the out-of-plane bending vibration of the benzene ring mainly contained in the styrene resin. Further, the absorbance D ₂₈₅₀ obtained from the infrared absorption spectrum (without ATR correction) is the height of the peak derived from the CH stretching vibration of the methylene group contained in both the ethylene resin and the styrene resin. is there. Then, a calibration curve of styrene is prepared in advance, and the absorbance ratio D ₆₉₈ /D ₂₈₅₀ of the foamed particles obtained from the infrared absorption spectrum is substituted into the following (formula 1) obtained from the calibration curve to obtain the foamed particles. The amount of styrene on the surface was determined. The results are shown in Table 1.
(Equation 1) Styrene amount=0.7622×(absorbance ratio D ₆₉₈ /D ₂₈₅₀ ) ² +7.4831×(absorbance ratio D ₆₉₈ /D ₂₈₅₀ )+1.165

The calibration curve of styrene was prepared as follows. That is, first, using an extruder, polyethylene (specifically, "Nipolon Z HF210K" manufactured by Tosoh Corporation) and polystyrene (specifically, "680" manufactured by PS Japan Co., Ltd.) were mixed with 100/0, 91. Pellets were prepared by melt-kneading at a molar ratio of 8/8.2, 78.8/21.2, 55.3/44.7 and 0/100 (however, polyethylene/polystyrene). Specifically, based on a molar mass of ethylene of 28 g/mol and a molar mass of styrene of 104 g/mol, the molar ratio is converted into a mass ratio, and then polyethylene and polystyrene are weighed with a specific mass ratio. By doing so, a pellet having the above molar ratio can be produced. Next, a film was obtained by molding the pellets into a film with a press machine heated at a temperature of 180°C. The infrared absorption spectrum (however, without ATR correction) of the film was measured using the above-mentioned total internal reflection absorption measuring device. Then, the absorbance D ₆₉₈ and the absorbance D ₂₈₅₀ obtained from the infrared absorption spectrum (without ATR correction) are measured in the same manner as the above-mentioned method, and the absorbance ratio D ₆₉₈ /D ₂₈₅₀ is obtained. Then, by taking the amount of styrene (unit: mol%) in the standard sample on the horizontal axis and the absorbance ratio D ₆₉₈ /D ₂₈₅₀ on the vertical axis, a calibration curve as illustrated in FIG. 1 can be obtained. .

(B) Amount of carbonyl relative to the amount of styrene When measuring the amount of carbonyl, the same measuring device as that used for measuring the amount of styrene described above is used, and the measurement conditions of the total reflection absorption measuring device are the same as those for measuring the amount of styrene. Specifically, first, the foamed particles are pressed against the prism of the total reflection absorption measurement device at a pressure of 170 kg/cm ² to be in close contact with the prism, and the infrared spectrum of the surface of the foamed particles is measured. (Without correction). Next, the absorbance D ₆₉₈ near ₆₉₈ cm ^{−1 and} the absorbance D ₁₇₃₀ near ₁₇₃₀ cm ⁻¹ obtained from the infrared absorption spectrum (without ATR correction) are measured to obtain the absorbance ratio D ₁₇₃₀ /D ₆₉₈ . The same measurement is performed for five expanded particles, and the average value of these is taken as the absorbance ratio D ₁₇₃₀ /D ₆₉₈ of the expanded particles. The absorbance D ₁₇₃₀ obtained from the infrared absorption spectrum (without ATR correction) is the height of a peak derived from stretching vibration between C═O of the carboxy group of the (meth)acrylic acid component unit. Then, a calibration curve is created in advance, and the absorbance ratio D ₁₇₃₀ /D ₆₉₈ of the expanded particles obtained from the above infrared absorption spectrum is substituted into the following (formula 2) obtained from the calibration curve to obtain the amount of carbonyl relative to the amount of styrene. I asked. The results are shown in Table 1.
(Formula 2) Amount of carbonyl relative to amount of styrene=6.4838×(Absorbance ratio D ₁₇₃₀ /D ₆₉₈ )−0.0523

The calibration curve for the amount of carbonyl was prepared as follows. That is, styrene and butyl acrylate were used to prepare polymer particles in which the amounts of butyl acrylate were 0 mol%, 0.8 mol%, 2.5 mol%, and 4.1 mol% by suspension polymerization. Next, the polymer particles were formed into a film by a press machine heated at a temperature of 180° C. to obtain a film. The infrared absorption spectrum (however, without ATR correction) of the film was measured using the above-mentioned total internal reflection absorption measuring device. Next, the absorbance D ₆₉₈ and the absorbance D ₁₇₃₀ obtained from the infrared absorption spectrum (without ATR correction) were measured in the same manner as the above-mentioned method to obtain the absorbance ratio D ₁₇₃₀ /D ₆₉₈ . Then, by taking the carbonyl amount (unit: mol%) in the standard sample on the horizontal axis and the absorbance ratio D ₁₇₃₀ /D ₆₉₈ on the vertical axis, a calibration curve as illustrated in FIG. 2 can be obtained. ..

(C) Surface carbonyl amount The value obtained by dividing the styrene amount on the surface of the expanded beads obtained by the above method by 100 and the carbonyl amount relative to the styrene amount was taken as the surface carbonyl amount of the composite resin expanded beads. The results are shown in Table 1.

"Amount of water vapor adsorbed on composite resin foam particles"
For the measurement of the water vapor adsorption amount, a vapor adsorption amount measuring device (BELSORP-max (manufactured by Bell Japan Ltd.)) is used, and an adsorption isotherm (set relative pressure: 0.005-0.9) is measured at 25°C. Then, the water vapor adsorption amount at the maximum relative pressure of 0.9 was determined as the water vapor adsorption amount of the composite resin expanded particles in the present invention. Specifically, first, about 0.2 g of composite resin particles was weighed in advance. Next, the weighed composite resin particles were put in a sample cell, and using BELSORP-max (manufactured by Bell Japan Ltd.), an adsorption isotherm of water vapor at 25° C. (set relative pressure: 0.005 to 0.9). Was measured, and the water vapor adsorption amount at the maximum relative pressure of 0.9 was determined as the water vapor adsorption amount of the composite resin expanded particles. The results are shown in Table 1.

(4) Step of Applying Antistatic Agent As an antistatic agent, octyldimethylethylammoniumethylsulfate (specifically, “Cationogen ES-O” manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.; active ingredient 50%) was prepared. .. The antistatic agent was applied to the expanded particles by placing the expanded particles in a polybag together with the antistatic agent, thoroughly shaking and mixing, and then putting the entire bag in a tumbler and mixing for 30 minutes. The amount of the antistatic agent added 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. Then, the expanded beads were dried in an oven at a temperature of 40° C. for 12 hours. In this way, expanded particles having an antistatic agent attached to the surface thereof were obtained. The amount of the antistatic agent attached to the expanded particles was measured as follows.

"Amount of antistatic agent deposited"
About 5 g of the expanded particles to which the antistatic agent was attached and about 5 g of the expanded particles to which the antistatic agent was not attached were weighed. The weight of the expanded particles to which the antistatic agent is not attached is W ₀ (W ₀ ≈5). Each weighed expanded particle was washed three times with 100 cm ³ (ml) of a washing liquid (specifically, ethanol). About 300 cm ³ of the washing liquid after washing was collected and kept at a temperature of 40° C. for 24 hours to evaporate the washing liquid. Then, the weight W _A of the residue of the foamed particle cleaning liquid to which the antistatic agent adhered after evaporation and the weight W _B of the residue of the foamed particle cleaning liquid to which the antistatic agent did not adhere after evaporation were measured. Based on these residue weights W _A , W _B and the weight W ₀ of the expanded particles, the amount A (parts by mass) of the antistatic agent adhering to 100 parts by mass of the expanded particles was calculated from the following (formula 3). .. The results are shown in Table 1.
(Formula 3) A=(W _A −W _B )/W ₀ ×100

(5) In-mold molding Next, the expanded particles coated with the antistatic agent were filled in a mold having a flat plate-shaped cavity having a length of 250 mm, a width of 200 mm, and a thickness of 50 mm. Next, by introducing water vapor into the mold, the expanded particles were heated and fused to each other. Then, after cooling the inside of the mold by water cooling, the molded body was taken out from the mold. Furthermore, the molded body was placed in an oven adjusted to a temperature of 60° C. for 12 hours to dry and cure the molded body. In this way, a molded body was obtained in which a large number of expanded particles were fused to each other.

  The apparent density, the fusion rate, the surface resistivity, the flexural modulus, the breaking energy, and the compressive strength of the molded body produced as described above were measured. The results are shown in Table 1. The measuring method is as follows.

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

"Fusion rate"
The molded body was bent and broken into approximately equal parts. The fractured surface was observed, and the number of foamed particles broken inside and the number of foamed particles separated at the interface were measured. Next, the ratio of the foamed particles broken inside to the total number of the foamed particles broken inside and the foamed particles peeled off at the interface was calculated, and the value expressed as a percentage was taken as the fusion rate (%).

"Surface resistivity"
The antistatic performance of the molded product was evaluated by measuring the surface resistivity of the molded product. The surface resistivity was measured by the 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 the molded body that was aged 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 in length×100 mm in width present in the rectangular parallelepiped was the surface of the expanded particle molded body (that is, the skin surface). Then, the surface resistivity of the skin surface of the test piece was measured using "HIRESTA MCP-HT450" manufactured by Mitsubishi Chemical Corporation. As the probe, "UR100" manufactured by Mitsubishi Chemical Co., Ltd. was used, and the measurement was performed under the conditions of holding 23° C., 50% RH, and an applied voltage of 500 V for 30 seconds. The measurement was performed at arbitrary four points on the same test piece, and the maximum value, the minimum value, and the arithmetic mean value were obtained. The skin surface is the surface of the expanded particle molded body obtained by in-mold molding.

"Flexural modulus"
The flexural modulus was measured according to the three-point bending test method described in JIS K7221-1 (2006). Specifically, first, five test pieces having a thickness of 20 mm, a width of 25 mm, and a length of 120 mm were cut out from an arbitrary portion of the molded body so that the entire surface became the cut surface. After leaving the test piece for 24 hours or more in a constant temperature room at a room temperature of 23° C. and a humidity of 50%, a distance between fulcrums 100 mm, an indenter radius R15.0 mm, a support base radius R15.0 mm, a test speed 20 mm/min, a room temperature 23° C. The flexural modulus was measured with an Autograph AGS-10kNG tester manufactured by Shimadzu Corporation under the condition of a humidity of 50%. The arithmetic mean value of the measured values of the five test pieces 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 above-mentioned measurement of the bending elastic modulus, and the energy (unit: MJ/m ³ ) to the break point is calculated from the relationship between strain (unit: m/m) and stress (unit: MPa). It was determined from the arithmetic mean value of the measured values of five test pieces. The bending fracture energy is calculated from the area surrounded by the strain-stress curve up to the fracture point and the horizontal axis (that is, strain).

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

(Example 2)
Examples 2 to 4 are examples in which the composition of MAA was changed. Specifically, in this example, foamed particles and a molded body were produced in the same manner as in Example 1 except that 345 g of styrene as the second monomer and 5 g of MAA were used.

(Example 3)
In this example, expanded particles and a molded body were produced in the same manner as in Example 1 except that 347.5 g of styrene as the second monomer and 2.5 g of MAA were used.

(Example 4)
In this example, foamed particles and a molded product were produced in the same manner as in Example 1 except that 348.75 g of styrene as the second monomer and 1.25 g of MAA were used.

(Example 5)
Examples 5 and 6 are examples in which the composition of MAA was changed, and the timing of addition of MAA and the time required for addition were also changed. Specifically, in this example, the amount of sodium nitrite used as a water-soluble polymerization inhibitor was changed from 0.21 g to 0.15 g, and when the autoclave temperature reached 100° C., 1 hour later, As in Example 1, except that 348.75 g of 2 monomer styrene was added into the autoclave over 4 hours and 50 minutes and 1.25 g of MAA was added into the autoclave over 10 minutes after the addition of styrene. Foamed particles and molded bodies were produced.

(Example 6)
In this example, the amount of sodium nitrite used as the water-soluble polymerization inhibitor was changed from 0.21 g to 0.15 g, and 1 hour after the temperature of the autoclave reached 100° C., the second monomer, styrene 347 0.5 g of the foamed particles were added into the autoclave over 4 hours and 50 minutes, and 2.5 g of MAA was added into the autoclave over 10 minutes after the addition of styrene. Was produced.

(Example 7)
Examples 7 and 8 are examples in which the mass ratio of the ethylene resin and the styrene resin in the composite resin was changed. Specifically, in this example, the amount of seed particles added to the autoclave was changed to 150 g, a mixed monomer of styrene 135 g and butyl acrylate 15 g was used as the first monomer, and styrene 196 was used as the second monomer. Foamed particles and a molded product were produced in the same manner as in Example 1 except that 0.25 g was used.

(Example 8)
In this example, the amount of seed particles added to the autoclave was changed to 50 g, a mixed monomer of 35 g of styrene and 15 g of butyl acrylate was used as the first monomer, and 396.25 g of styrene was used as the second monomer. Foamed particles and a molded product were produced in the same manner as in Example 1 except for the above points.

(Example 9)
This example is an example in which MAA is changed to acrylic acid (that is, AA). Specifically, in this example, foamed particles and a molded body were produced in the same manner as in Example 1 except that AA was used instead of MAA.

(Comparative Example 1)
This example is an example of a foamed particle and a molded body produced without using methacrylic acid and acrylic acid. Specifically, in this example, expanded particles and a molded body were produced in the same manner as in Example 1 except that methacrylic acid was not added and 350 g of styrene was used as the second monomer.

(Comparative example 2)
This example is an example in which the amount of methacrylic acid added was too small. Specifically, in this example, foamed particles and a molded product were produced in the same manner as in Example 1 except that 349.55 g of styrene as the second monomer and 0.45 g of MAA were used.

(Comparative example 3)
Comparative Example 3 is an example in which methacrylic acid was excessively added. Specifically, in this example, foamed particles and a molded product were produced in the same manner as in Example 1 except that 337.55 g of styrene as the second monomer and 12.5 g of MAA were used.

(Comparative example 4)
This example is an example in which the amount of styrene-based monomer added to the ethylene-based resin is made too small and methacrylic acid is added together with the first monomer. Specifically, in this example, the amount of seed particles added to the autoclave was changed to 260 g. As the first monomer, a mixed monomer of 221.25 g of styrene and 15 g of butyl acrylate was used, and 3.75 g of methacrylic acid was added to the autoclave together with the first monomer. Others were the same as in Example 1 to produce expanded particles and a molded body.

(Comparative example 5)
This example is an example in which the amount of the styrene-based monomer added to the ethylene-based resin is excessive. Specifically, in this example, the amount of seed particles added to the autoclave was changed to 24 g. Further, a mixed monomer of 9 g of styrene and 15 g of butyl acrylate was used as the first monomer. Further, 448.25 g of styrene was used as the second monomer. Others were the same as in Example 1 to produce expanded particles and a molded body.

(Comparative example 6)
In this example, methacrylic acid (that is, MAA) is changed to methyl methacrylate (that is, MMA) as the second monomer. Specifically, in this example, 346.25 g of styrene as the second monomer (specifically, styrene-based monomer) and 3.75 g of methyl methacrylate were added to the autoclave over 5 hours. Note that MMA was added in a state of being dissolved in styrene as the second monomer in advance. Others were the same as in Example 1 to produce expanded particles and a molded body.

  The same evaluations as in Example 1 were performed for Examples 2 to 9 and Comparative Examples 1 to 6, and the results are shown in Tables 1 and 2.

As is known from Table 1, the molded articles to which the antistatic agent obtained by using the expanded beads of the Examples adhered showed excellent antistatic performance of surface resistivity of less than 1×10 ¹² Ω. In addition, the expanded particles to which the antistatic agent is attached are excellent in fusion property while exhibiting the above-mentioned excellent antistatic performance. Therefore, it is possible to manufacture a molded body that has good internal fusion bonding, is excellent in compression rigidity and flexure resistance, and can prevent damage due to deformation. Therefore, the molded product obtained by using the foamed particles of the examples is suitable for a packaging container for electronic devices such as automobile members, liquid crystal panels, solar power generation panels, and precision devices.

  On the other hand, as known from Table 2, sufficient antistatic performance was not obtained in Comparative Examples 1 and 2 in which the amount of surface carbonyls of the composite resin expanded particles was small. Further, in Comparative Example 3 in which the amount of (meth)acrylic acid added was increased, the acetone-soluble component had a high glass transition temperature, and the foaming property and the fusion property were insufficient. In Comparative Example 4 in which the amount of the styrene-based monomer added was small, the rigidity of the molded body was lowered, so the compressive strength was low and the flexural modulus was low. Therefore, the molded body of Comparative Example 4 is easily deformed by bending and has insufficient flexure resistance. On the other hand, in Comparative Example 5 in which the addition amount of the styrene-based monomer is large, the compression strength and the bending elastic modulus of the molded body are high, but the bending rupture energy is insufficient. Therefore, the molded body of Comparative Example 5 is likely to be broken due to deformation. Further, in Comparative Example 6, sufficient anti-static performance was not obtained.

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

Claims (10)

A composite resin foamed particle comprising a composite resin obtained by impregnating and polymerizing an ethylene-based resin with (meth)acrylic acid and a styrene-based monomer,
The composite resin contains 100 to 1900 parts by mass of a structural unit derived from a styrene-based monomer with respect to 100 parts by mass of an ethylene-based resin,
The glass transition temperature Tg of the acetone-soluble component obtained by further dissolving the xylene-soluble component in the composite resin in acetone is 105° C. or lower,
Composite resin foamed particles, wherein the amount of carbonyls on the surface of the composite resin foamed particles is 0.03 mol% or more.   The expanded composite resin particles according to claim 1, wherein the content of the structural unit derived from (meth)acrylic acid is 0.1 to 2 parts by mass with respect to 100 parts by mass of the composite resin. The expanded composite resin particles according to claim 1 or 2, wherein the water vapor adsorption amount of the expanded composite resin particles is 0.5 cm ³ /g or more.   The ethylene-based resin is a linear low-density polyethylene, or a linear low-density polyethylene and an ethylene-vinyl acetate copolymer, and the content of the ethylene-vinyl acetate copolymer in the ethylene-based resin is 10 mass. % Of the composite resin expanded particles according to any one of claims 1 to 3.   The composite resin contains the structural unit derived from the styrene-based monomer in an amount of more than 400 parts by mass and 1900 parts by mass or less based on 100 parts by mass of the ethylene-based resin, according to any one of claims 1 to 4. Expanded composite resin particles.   The surface of the foamed composite resin particles is coated with an antistatic agent, and the amount of the antistatic agent attached is 0.3 to 5 parts by mass with respect to 100 parts by mass of the foamed composite resin particles. 5. The expanded composite resin particle according to any one of 5 above. A molded product in which the expanded foamed composite resin particles according to claim 6 are fused to each other, and the molded product has a surface resistivity of less than 1×10 ¹² Ω. 100 to 1900 parts by mass of a styrene-based monomer, relative to 100 parts by mass of the ethylene-based resin in the ethylene-based resin seed particles, in a dispersion liquid in which the ethylene-based resin seed particles are dispersed in an aqueous medium, (meth) Acrylic acid is added, the ethylene-based resin seed particles are impregnated with the styrene-based monomer and the (meth)acrylic acid, and a polymerization step of polymerizing to obtain composite resin particles,
A foaming step of foaming the composite resin particles using a foaming agent to obtain composite resin expanded particles,
The glass transition temperature Tg of the acetone-soluble component obtained by further dissolving the xylene-soluble component in the composite resin expanded beads in acetone is 105° C. or lower,
A method for producing a foamed composite resin particle, wherein the amount of carbonyls on the surface of the foamed composite resin particle is 0.03 mol% or more.   In the modification step, the styrene-based monomer is added to the aqueous medium in a plurality of divided portions, and the (meth)acrylic acid is added to the ethylene-based ethylene at least with the styrene-based monomer added last. The method for producing composite resin expanded particles according to claim 8, wherein the seed particles are impregnated and polymerized.   The addition amount of the (meth)acrylic acid is 0.1 to 2 parts by mass based on 100 parts by mass of the total amount of the (meth)acrylic acid, the ethylene resin, and the styrene monomer. Item 10. A method for producing expanded composite resin particles according to Item 8 or 9.

Images