JP2017203144A - Composite resin foam particle, method for producing the same, and composite resin foam particle molded body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide composite resin foam particles capable of obtaining a molded body which has good internal fusion and is excellent in compression rigidity and deflection resistance, and is excellent in antistatic performance; a method for producing the same; and a molded body using the composite resin foam particles.SOLUTION: There are provided composite resin foam particles using a composite resin obtained by impregnating and polymerizing an ethylenic resin with a (meth)acrylic acid and a styrenic monomer, as a base resin; a method for producing the same; and a molded body using the same. The composite resin contains 100-1,900 pts.mass of a structural unit derived from the styrenic monomer with respect to 100 pts.mas of the ethylenic resin. A glass transition temperature Tg of an acetone soluble content obtained by further dissolving a xylene soluble content in the composite resin in acetone is 105°C or lower. An amount of carbonyl on the surface of the composite resin foam particles is 0.03 mol% or more.SELECTED DRAWING: None

Description

  The present invention relates to a composite resin foam particle using a composite resin in which a styrene monomer is impregnated and polymerized with an ethylene resin as a base resin, a manufacturing method thereof, and a molded body in which the composite resin foam particles are fused to each other.

  In-mold molded products of composite resin foam particles (ie composite resin foam particle molded products) using a composite resin in which a styrene monomer is impregnated and polymerized in an ethylene resin as a base resin are components for electronic equipment and precision equipment. Widely used as packing material and buffer packaging material. In general, an antistatic property may be imparted to a molded body for such use in order to prevent electrical damage due to dust adhesion or generation of overcurrent such as discharge.

  As a method for obtaining the composite resin expanded particles, for example, the following method is known. Specifically, first, a seed resin containing an ethylene resin is impregnated with a styrene monomer and polymerized to obtain a composite resin obtained by impregnating and polymerizing the ethylene resin with the styrene monomer. A composite resin particle is obtained. Subsequently, 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 of imparting antistatic performance to the foamed particle molded body, a method of adding an antistatic agent composed of a surfactant or the like is generally used. Specifically, a method is known in which an antistatic agent is impregnated at the time of or after impregnation of a volatile foaming agent into composite resin particles. A method of applying an antistatic agent to the composite resin foam particles is also known.

  In the method of impregnating the antistatic agent when impregnating the volatile foaming agent, the resin particles are excessively plasticized by the antistatic agent, so that the heat resistance of the foamed particles may be reduced during molding and the molded body may be deformed. There is a possibility that the fusion property between the expanded particles may be lowered. Therefore, as in Patent Document 1, a method of applying a predetermined amount of a cationic antistatic agent to composite resin foam particles has been developed. Further, as in Patent Document 2, a method has been developed in which a composite resin particle is impregnated and polymerized with polyethylene glycol (meth) acrylate, and then an antistatic agent is impregnated when the foaming agent is impregnated.

Japanese Patent Laying-Open No. 2015-81274 Japanese Patent Laid-Open No. 10-147660

  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 depending on the heating conditions during in-mold molding, There is a possibility that the antistatic agent adhering to the foamed particles is partially detached by steam or the like as a medium. Therefore, further improvement in antistatic performance is desired. Further, as described in Patent Document 2, in the method in which the composite resin particles are impregnated and polymerized with a reactive surfactant, polyethylene glycol (meth) acrylate, and then impregnated with an antistatic agent, antistatic performance is improved. Improvement is possible. However, since polyethylene glycol (meth) acrylic acid ester is a highly water-soluble reactive surfactant, it is difficult to impregnate into composite resin particles during impregnation polymerization, and polyethylene glycol (meth) acrylic is very close to the surface of composite resin particles. Polymerization of the acid ester occurs. As a result, the polyethylene glycol (meth) acrylic acid ester polymer is unevenly distributed near the surface of the composite resin particles, so that the fusion property when foamed particles are reduced, and the strength of the molded product such as compression rigidity and deflection resistance is reduced. 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, there is a possibility that the fusion property between the foamed particles is lowered as described above.

  The present invention has been made in view of such problems, and is a composite resin foamed particle capable of obtaining a molded article having good internal fusion, excellent compression rigidity and deflection resistance, and excellent antistatic performance, and its production The present invention intends to provide a method and a molded body using the composite resin expanded particles.

One aspect of the present invention is a composite resin foamed particle using a composite resin obtained by impregnating and polymerizing (meth) acrylic acid and a styrene monomer in an ethylene resin,
The composite resin contains 100 to 1900 parts by mass of a structural unit derived from a styrene monomer with respect to 100 parts by mass of an ethylene 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 less,
In the composite resin foamed particles, the amount of carbonyl on the surface of the composite resin foam particles is 0.03 mol% or more.

Another aspect of the present invention is a composite resin foamed particle molded body in which the 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 that, in a dispersion in which ethylene resin seed particles are dispersed in an aqueous medium, 100 to 1900 parts by mass of styrene with respect to 100 parts by mass of the ethylene resin in the ethylene resin seed particles. A monomer and (meth) acrylic acid are added, and the ethylene resin seed particles are impregnated with the styrene monomer and (meth) acrylic acid and polymerized to obtain composite resin particles. Process,
A foaming step of foaming the composite resin particles using a foaming agent to obtain composite resin foam particles,
The glass transition temperature Tg of the acetone soluble part obtained by further dissolving the xylene soluble part in the composite resin expanded particles in acetone is 105 ° C. or less,
In the method for producing composite resin foam particles, the amount of carbonyl on the surface of the composite resin foam particles is 0.03 mol% or more.

  In the composite resin expanded particles (hereinafter referred to as “expanded particles” as appropriate), a composite resin in which (meth) acrylic acid and a styrene monomer are impregnated and polymerized with an ethylene resin is used as a base resin, and the composite resin expanded particles The amount of carbonyl on the surface is adjusted to a predetermined amount or more. For this reason, even if an antistatic agent is applied to the composite resin foam particles, the antistatic agent can be prevented from flowing out during molding, and the composite resin foam particles having good antistatic performance (hereinafter referred to as “molding” as appropriate). Body)). In addition, 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 below a predetermined value, the internal fusion of the molded product, that is, the fusion between the expanded particles Good. Therefore, the molded body can exhibit strength properties such as compression rigidity and deflection resistance, which are originally excellent in the composite resin based on the composition of the ethylene-based resin or the styrene-based resin.

In addition, a molded article having a surface resistivity of less than 1 × 10 ¹² Ω, in which the foam particles are fused to each other, is excellent not only in antistatic performance but also in strength properties such as compression rigidity and deflection resistance as described above. ing. Therefore, the molded body obtained by using the composite resin particles is suitable for uses such as packaging containers and buffer packaging materials for electronic equipment such as liquid crystal panels and photovoltaic power generation panels, or parts for precision equipment.

  The foamed particles can be produced by performing a modification process and a foaming process. In the modification step, a predetermined amount of styrene monomer and (meth) acrylic acid are added to a dispersion in which ethylene resin seed particles are dispersed in an aqueous medium, and styrene is added to the ethylene resin seed particles. Impregnation and polymerization of a monomer and (meth) acrylic acid. Thereby, composite resin particles in which a styrene monomer and (meth) acrylic acid are impregnated and polymerized in an ethylene resin can be obtained. In the foaming step, the composite resin particles are foamed using a foaming agent to obtain foamed particles. Even when an antistatic agent is applied to the foamed particles thus obtained, the outflow of the antistatic agent during molding can be suppressed as described above, and a molded article having good antistatic performance can be obtained. Can do. Further, the molded body has good internal fusion and excellent strength properties such as compression rigidity and deflection resistance.

The relationship figure of the amount of styrene and an absorbance ratio in an Example. The relationship figure of the amount of carbonyl and an absorbance ratio in an Example.

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

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

  The foamed particles use a composite resin obtained by impregnating and polymerizing an ethylene resin with a styrene monomer and (meth) acrylic acid (hereinafter also referred to as a styrene monomer). In this specification, the composite resin is a resin obtained by impregnating and polymerizing an ethylene resin with a styrene monomer as described above, and is a resin containing an ethylene resin component and a styrene resin component. . The styrene resin component includes a component obtained by polymerizing styrene monomers and a component obtained by copolymerizing a styrene monomer and (meth) acrylic acid. Furthermore, during the polymerization of styrene monomers and the like, not only polymerization of styrene monomers but also graft polymerization of styrene monomers may occur in the polymer chain constituting the ethylene resin. In this case, the composite resin not only contains an ethylene resin component composed of an ethylene resin and a styrene resin component obtained by polymerizing a styrene monomer, but also a styrene monomer graft-polymerized. Contains an ethylene-based resin component (ie, PE-g-PS component). Therefore, the composite resin is a concept different from a mixed resin obtained by mixing a polymerized ethylene resin and a polymerized styrene resin.

  The amount of the styrene monomer to be impregnated and polymerized in the ethylene resin can be appropriately adjusted according to desired physical properties. Specifically, when the proportion of the ethylene resin in the composite resin is increased, toughness and restorability are improved, but the rigidity tends to decrease. On the other hand, when the proportion of the structural unit derived from the styrene monomer is increased, the rigidity is improved, but the toughness and the restoring property tend to be lowered. As described above, the composite resin contains a structural unit derived from a styrene 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 resin, and thus has a good balance of toughness, restorability, and rigidity. A molded body can be obtained. In order to obtain a molded article having a better balance of toughness, restorability, and rigidity, the composite resin has a structural unit derived from a styrene monomer that exceeds 150 parts by mass with respect to 100 parts by mass of the ethylene resin and 1900. It is preferable to contain below part by mass. Furthermore, from the viewpoint of further improving the rigidity of the molded body, the content of the structural unit derived from the styrenic monomer with respect to 100 parts by mass of the ethylene-based resin is more preferably more than 400 parts by mass, and more than 450 parts by mass. More preferably, it is particularly preferably 500 parts by mass or more. In order to further improve the toughness and restoration property of the molded body, the content of the structural unit derived from the styrene monomer with respect to 100 parts by mass of the ethylene resin is more preferably 1000 parts by mass or less, and 900 More preferably, it is at most part by mass. In addition, in this specification, the preferable range regarding the upper limit and lower limit of a numerical range, a more preferable range, and a more preferable range can be determined from all the combinations of an upper limit and a minimum.

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

  The ethylene resin is preferably composed of 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 resin is preferably less than 10% by mass, and more preferably less than 5% by mass. Most preferably, the ethylene-based resin does not contain a vinyl acetate copolymer. Further, the ethylene-based resin is preferably mainly composed of linear low density polyethylene. Specifically, the content of the linear low density polyethylene in the ethylene-based resin is preferably 50% by mass or more, more preferably 70% by mass or more, and further preferably 80% by mass or more. Preferably, it is particularly preferably made of only linear low density polyethylene.

  The linear low density polyethylene preferably has a structure having a linear polyethylene chain and a short-chain branched chain having 2 to 6 carbon atoms. Specific examples include an ethylene-butene copolymer, an ethylene-hexene copolymer, and an ethylene-octene copolymer. In particular, the ethylene resin is preferably a linear low-density polyethylene having a melting point of 105 ° C. or lower obtained by polymerization using a metallocene 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. Moreover, since the fusion strength between the foamed particles at the time of molding can be increased while reducing the low molecular weight component, it becomes possible to obtain a molded product having a low VOC and hardly cracking. Furthermore, it is possible to obtain a molded body that combines the excellent rigidity of the styrene resin and the excellent tenacity of the ethylene resin at a higher level.

  Moreover, it is preferable that melting | fusing point Tm of ethylene-type resin is 95-105 degreeC. In this case, since the ethylene resin can be sufficiently impregnated with the styrene monomer, it is possible to prevent the suspension system from becoming unstable during the polymerization. As a result, it is possible to obtain a molded body that combines the excellent rigidity of the styrene resin and the excellent tenacity of the ethylene resin at a higher level. From the same viewpoint, the melting point Tm of the ethylene-based resin is more preferably 100 to 105 ° C. The melting point Tm can be measured as a melting peak temperature by differential scanning calorimetry (ie, DSC) based on JIS K7121-1987.

  The ethylene-based resin may be composed of linear low-density polyethylene in which the melting point Tm (unit: ° C) and the Vicat softening point Tv (unit: ° C) satisfy the relationship Tm-Tv ≦ 20 (unit: ° C). preferable. Such an ethylene resin exhibits a uniform molecular structure, and it is presumed that the network structure formed by crosslinking is more uniformly distributed in the ethylene resin. Accordingly, in this case, the strength and tenacity of the foamed particle molded body obtained using the foamed particles can be improved. From the viewpoint of further improving the strength and tenacity of the molded article, the linear low density polyethylene more preferably satisfies Tm-Tv ≦ 15 (unit: ° C), and Tm-Tv ≦ 10 (unit: ° C). It is further preferable to satisfy 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). In the case where the ethylene resin is a mixed resin composed of two or more kinds of resins, the melting point and Vicat softening point of the mixed resin are measured, and are used as the melting point and Vicat softening point of the ethylene resin.

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

  The composite resin contains a component obtained by copolymerizing a styrene monomer and (meth) acrylic acid. In this specification, styrene constituting the styrenic resin component and monomers (but excluding (meth) acrylic acid) that can be copolymerized with styrene that are added as necessary, together with the styrene monomer May be called. The proportion of styrene in the styrenic monomer is preferably 50% by mass or more, more preferably 80% by mass or more, and further preferably 90% by mass or more. Examples of the monomer copolymerizable with styrene include the following styrene derivatives and other vinyl monomers.

  Examples of styrene derivatives include α-methyl styrene, o-methyl styrene, m-methyl styrene, p-methyl styrene, p-ethyl styrene, 2,4-dimethyl styrene, p-methoxy styrene, pn-butyl styrene, p. -T-butylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, 2,4,6-tribromostyrene, divinylbenzene, styrene sulfonic acid, sodium styrene sulfonate and the like. These may be used alone or in combination of two or more.

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

  Examples of the acrylate ester include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate. Examples of the methacrylic acid ester include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, and 2-ethylhexyl methacrylate. These may be used alone or in combination of two or more.

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

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

  From the viewpoint of enhancing foamability, it is preferable to use styrene or a combination of styrene and an acrylate monomer as the styrene monomer. Further, from the viewpoint of enhancing foamability, it is preferable to use styrene and butyl acrylate in combination. In this case, the content of the structural unit derived from butyl acrylate in the composite resin is preferably 0.5 to 10% by mass and more preferably 1 to 8% by mass with respect to the entire composite resin. Preferably, it is 2 to 5% by mass.

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

  That is, since (meth) acrylic acid has moderate water solubility, it has high polymerization stability and hardly causes condensation. Furthermore, (meth) acrylic acid is copolymerized with a styrene monomer, so that the composite resin has a copolymer component having a structural unit derived from a styrene monomer and a structural unit derived from (meth) acrylic acid. It is considered that this copolymer component can be contained on the particle surface while being contained. Therefore, it becomes possible to improve the fixability of the antistatic agent while maintaining the fusibility of the expanded particles.

  The structure derived from (meth) acrylic acid is preferably present in the vicinity of the surface more than the center of the foamed 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 foamed particles, which will be described later, a structure derived from (meth) acrylic acid tends to exist near the surface of the foamed particles. Specifically, when the styrene monomer is added in several times during the impregnation polymerization of the styrene monomer, (meth) acrylic acid is added together with the styrene monomer added after the second time. By adding, a structure derived from (meth) acrylic acid tends to exist near the surface of the expanded particles.

  If possible, add (meth) acrylic acid at least with the last added styrenic monomer, or after adding the last added styrenic monomer, More preferably, (meth) acrylic acid is added until the polymerization is completed. In this case, it becomes easy to increase the amount of carbonyl derived from (meth) acrylic acid on the surface of the expanded particles.

  Moreover, it is preferable that the styrene monomer added last does not contain the monomer copolymerizable with styrene, such as the above-mentioned acrylic ester, for example. Specifically, the styrenic monomer added last is more preferably styrene. In this case, the fixing property of the antistatic agent can be improved efficiently 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 less, preferably 102 ° C. or less. On the other hand, the lower limit of the glass transition temperature Tg is preferably approximately 85 ° C. or higher. In this case, the foamability at the time of foaming of the composite resin particles can be further improved, and shrinkage at the time of foaming can be further prevented. Furthermore, at the time of in-mold molding of the foamed particles obtained after foaming, the fusion property between the foamed particles can be further improved, and the dimensional stability of the foamed particle molded body can be further improved.

  The glass transition temperature Tg can be measured, for example, as follows. First, 1.0 g of composite resin particles are placed in a 150 mesh wire mesh bag. Next, about 200 ml of xylene is placed in a round flask having a volume of 200 ml, and the sample placed in the wire mesh bag is set in a Soxhlet extraction tube. Heat with a mantle heater for 8 hours to extract Soxhlet. The extracted xylene solution is dropped into 600 ml of acetone, decanted, and the supernatant is evaporated to dryness under reduced pressure to obtain an acetone-soluble component. About the obtained acetone soluble part 2-4 mg, heat flux differential scanning calorimetry is performed based on JISK7121 (1987) using DSC measuring instrument Q1000 made from TI Instruments. Then, Tg of acetone-soluble matter is obtained as the midpoint glass transition temperature of the DSC curve obtained at a heating rate of 10 ° C./min, and obtained by further dissolving xylene-soluble matter in the composite resin in acetone. It is set as Tg of the acetone soluble part to be obtained. 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 carbonyl on the surface of the expanded particles (hereinafter also referred to as surface carbonyl amount) is 0.03 mol% or more. If it is less than 0.03 mol%, the effect of improving the fixability of the antistatic agent may be insufficient. As a result, the antistatic performance of the molded body 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 particles is more preferably 0.07 mol% or more, and further preferably 0.1 mol% or more.

  On the other hand, if the amount of carbonyl in the entire expanded particle is too large, the glass transition temperature Tg exceeds 105 ° C., and the fusion property of the expanded particle may be lowered. From the viewpoint of further improving the fixability of the antistatic agent while maintaining the fusibility of the expanded particles without increasing the glass transition temperature, the amount of carbonyl on the surface of the expanded particles is preferably 0.2 mol% or less. 0.16 mol% or less is more preferable, and 0.15 mol% or less is more 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 obtained by multiplying the amount of styrene on the surface of the expanded particles by the amount of carbonyl to the amount of styrene on the surface. First, the amount of styrene and the amount of carbonyl with respect to the amount of styrene are measured as follows.
(A) Styrene amount In measuring the styrene amount, an infrared absorption spectrum (but no ATR correction) of the surface of the expanded particles is obtained using an infrared spectrophotometer and a total reflection absorption measuring device as a measuring device. Next, the absorbance D _{698 at 698} cm ^{−1 and} the absorbance D ₂₈₅₀ at ₂₈₅₀ cm ⁻¹ obtained from the infrared absorption spectrum (however, without ATR correction) are measured, and the absorbance ratio D ₆₉₈ / D ₂₈₅₀ is obtained. These average values are taken 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 amount of polystyrene 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. In addition, the absorbance D ₂₈₅₀ obtained from the infrared absorption spectrum (without ATR correction) is the peak height derived from the C—H stretching vibration of the methylene group contained in both the ethylene resin and the styrene resin. is there. The amount of styrene on the surface of the expanded particles can be determined using a calibration curve.
(B) Amount of carbonyl with respect to the amount of styrene The amount of carbonyl is determined by the same measurement apparatus and measurement conditions as those for the above-mentioned measurement of the amount of styrene. Next, the absorbance D _{698 at 698} cm ^{−1 and} the absorbance D ₁₇₃₀ at ₁₇₃₀ cm ⁻¹ obtained from the infrared absorption spectrum (however, without ATR correction) are measured, and the absorbance ratio D ₁₇₃₀ / D ₆₉₈ is determined. The same measurement is performed for five expanded particles, and the average of these is taken as the absorbance ratio D ₁₇₃₀ / D ₆₉₈ of the composite resin expanded particles. The absorbance D ₁₇₃₀ obtained from the infrared absorption spectrum (without ATR correction) is the peak height derived from the carboxy group of the (meth) acrylic acid component unit. And the amount of carbonyl with respect to the amount of styrene is calculated | required using the analytical curve created beforehand. And the amount of carbonyls on the surface of the expanded particles can be determined from the multiplication of the amount of styrene and the amount of carbonyl to the amount of styrene.

  The styrenic 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 styrenic resin component has at least a structural unit derived from methacrylic acid. In this case, the fixing property of the antistatic agent and the fusibility of the expanded particles can be improved in a balanced manner.

  In the foamed particles, the content of the structural unit derived from (meth) acrylic acid with respect to 100 parts by mass of the composite resin is preferably 0.1 to 2 parts by mass. In this case, the fixing property of the antistatic agent and the fusibility of the expanded particles can be improved in a balanced manner. From the viewpoint of further improving the fixability of the antistatic agent, 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 0.2 parts by mass or more, and 0.5 parts by mass or more. Further preferred. On the other hand, from the viewpoint of further suppressing a decrease in fusibility, 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. Further preferred.

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

  Note that the composite resin foamed particles based on a composite resin in which a styrene monomer is impregnated and polymerized with an ethylene resin are basically hydrophobic, so that when a hydrophilic antistatic agent is attached, The antistatic agent attached to the foamed particles may be partially detached by steam or the like as a heating medium depending on the heating conditions when the foamed particles are molded in the mold. However, since the expanded particles contain a specific amount of structural units derived from (meth) acrylic acid as described above, the vicinity of the surface is appropriately hydrophilized without hindering the fusion between the expanded particles, It is considered that the fixing property of the antistatic agent is improved. That is, according to the composite resin foam particles, it is possible to obtain a molded body having both excellent mechanical strength and antistatic performance.

  The antistatic agent is not particularly limited, and examples thereof include nonionic surfactants such as hydroxyalkylamine, hydroxyalkyl monoetheramine, polyoxyalkylene alkylamine, glycerin fatty acid ester, polyoxyethylene alkyl ether, polyoxyethylene alkyl ether and the like. 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 salts, trialkyl benzyl And cationic surfactants such as ammonium salts. Further, 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 more preferably at least octyldimethylethylammonium ethyl sulfate. In this case, the antistatic agent is more easily fixed to the expanded 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 expanded particles are fused to each other is preferably less than 1 × 10 ¹² Ω. When the surface resistivity is in the above range, the antistatic performance required for a packaging container such as a liquid crystal panel and a photovoltaic power generation panel and a buffer packaging material can be sufficiently exhibited. The surface resistivity of the molded body is more preferably 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 expanded 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 particles 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 amount of water vapor adsorbed indicates how much water vapor can be adsorbed on the surface of the expanded particles. This amount of water vapor adsorption is an indicator of the hydrophilicity of the expanded particles, and when the amount of carbonyl on the surface of the expanded particles increases, the amount of water vapor adsorbed on the surface of the expanded particles tends to increase.

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

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

  In the reforming step, ethylene-based resin seed particles (hereinafter, referred to as “seed particles” as appropriate) containing an ethylene-based resin component as a main component are used. In addition to the ethylene-based resin component, the seed particles can further contain additives such as a bubble adjusting agent, a colorant, a lubricant, and a dispersion diameter expanding agent. Seed particles can be produced by blending the above-described additives, which are added as necessary, into the ethylene-based resin component, melt-kneading the blend, and then refining. Melt kneading can be performed by an extruder. In order to perform uniform kneading, it is preferable to perform extrusion after mixing the resin components in advance. The mixing of the resin components can be performed using a mixer such as a Henschel mixer, a ribbon blender, a V blender, or a ladyge mixer. The melt kneading is preferably performed using a single-screw extruder or a twin-screw extruder provided with a highly dispersed screw such as a dull image type, a Maddock type, or a unimelt type.

  The seed particles are granulated, for example, by cutting the melt-kneaded compound while extruding it with an extruder or the like. Granulation can be performed by, for example, a strand cut method, an underwater cut method, a hot cut method, or the like.

  In the modification step, first, a dispersion is obtained by dispersing seed particles in an aqueous medium. As the aqueous medium, for example, deionized water can be used. The seed particles are preferably dispersed in an aqueous medium together with a suspending agent. In this case, a styrene monomer described later 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. Fine particulate inorganic suspending agents such as barium carbonate, calcium sulfate, barium sulfate, talc, kaolin and bentonite can be used. In addition, organic suspending agents such as polyvinyl pyrrolidone, polyvinyl alcohol, ethyl cellulose, and hydroxypropyl methyl cellulose can also be used. Preferred are tricalcium phosphate, hydroxyapatite, and magnesium pyrophosphate. These suspending agents can be used alone or in combination of two or more.

  The amount of the suspending agent used is 0.1% by solid content with respect to 100 parts by mass of the suspension polymerization aqueous medium (specifically, all water in the system including water such as the reaction product-containing slurry). 05-10 mass parts is preferable. More preferably, 0.3-5 mass parts is good. When the amount of the suspending agent is too small, it becomes difficult to stably suspend the styrene monomer in the reforming step, and there is a possibility that a lump of resin is generated. On the other hand, when there are too many suspending agents, not only manufacturing cost will increase, but there exists a possibility that the particle size distribution of the composite resin particle obtained after a modification | reformation process may spread.

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

  Examples of the anionic surfactant include sodium alkyl sulfonate, sodium alkylbenzene sulfonate, sodium lauryl sulfate, sodium α-olefin sulfonate, sodium dodecyl diphenyl ether disulfonate, and the like. As the nonionic surfactant, for example, polyoxyethylene nonylphenyl ether, polyoxyethylene lauryl ether, or the like can be used. More preferably, an anionic surfactant made of an alkali metal alkyl sulfonate (preferably a sodium salt) having 8 to 20 carbon atoms is preferably used as the dispersant. Thereby, the suspension can be sufficiently stabilized.

  In addition, an electrolyte made of an inorganic salt such as lithium chloride, potassium chloride, sodium chloride, sodium sulfate, sodium nitrate, sodium carbonate, or sodium bicarbonate can be added to the aqueous medium as necessary. In addition, in order to obtain a molded article superior in toughness and mechanical strength, it is preferable to add a water-soluble polymerization inhibitor to the aqueous medium. As the water-soluble polymerization inhibitor, for example, sodium nitrite, potassium nitrite, ammonium nitrite, L-ascorbic acid, citric acid and the like can be used.

  The water-soluble polymerization inhibitor is hardly impregnated in the seed particles and dissolves in the aqueous medium. Therefore, the polymerization of the styrene monomer impregnated in the seed particles is performed, 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 Polymerization of the styrene monomer near the surface can be suppressed. As a result, it is presumed that the amount of the styrene resin component in the vicinity of the outermost surface of the composite resin particles can be reduced, and the toughness of the obtained molded body is improved. The addition amount of the water-soluble polymerization inhibitor is 0.001 to 0.1 parts by mass with respect to 100 parts by mass of the aqueous medium (specifically, all water in the system including water such as the reaction product-containing slurry). Is preferable, and 0.005 to 0.06 parts by mass is more preferable.

  In the modifying step, the seed particles are impregnated and polymerized with the styrene monomer and (meth) acrylic acid in the dispersion liquid in which the seed particles are dispersed in the aqueous medium as described above. The polymerization of styrene monomers and the like can be performed in the presence of a polymerization initiator. In this case, the ethylene resin may be cross-linked together with the copolymerization of the styrene monomer or the like. Moreover, a crosslinking agent can be used together as needed. When using a polymerization initiator and a crosslinking agent, it is preferable to previously dissolve the polymerization initiator and the crosslinking agent in a styrene monomer.

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

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

  Moreover, it is preferable that (meth) acrylic acid is previously dissolved in the styrene monomer. That is, it is preferable to impregnate and polymerize seed particles dispersed in an aqueous medium with a styrene 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 monomer.

  When the seed particles are impregnated with a styrene monomer and polymerized, the entire amount of the styrene 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 styrenic monomer into two or more and add these monomers at different timings. Specifically, a part of the total amount of the styrene monomer to be blended is added to an aqueous medium in which seed particles are dispersed, and the styrene monomer is impregnated and polymerized, and then Furthermore, the remainder of the styrene monomer to be blended can be added to the aqueous medium in one or more portions. As in the latter case, by adding the styrene monomer separately, it is possible to further suppress the condensation of the resin particles during the polymerization.

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

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

  In addition, it is preferable that the seed ratio (namely, mass ratio of the 1st monomer with respect to a seed particle) of the styrene-type monomer added as a 1st monomer is 0.5 or more. In this case, it becomes easy to make the shape of the composite resin particles more spherical. From the same viewpoint, the seed ratio is more preferably 0.7 or more, and further preferably 0.8 or more. The seed ratio is preferably 1.5 or less. In this case, it is possible to further prevent polymerization before the styrenic monomer is sufficiently impregnated into the seed particles, and it is possible to further prevent generation of a resinous mass. From the same viewpoint, the seed ratio of the first monomer is more preferably 1.3 or less, and further preferably 1.2 or less.

  It is preferable that the melting point Tm (° C.) of the ethylene-based 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 suspension system can be prevented from becoming unstable during the polymerization. As a result, it is possible to obtain a foamed particle molded body that combines the excellent rigidity of the styrene resin and the excellent tenacity of the ethylene resin at a higher level. Moreover, although the impregnation temperature and polymerization temperature in a modification | reformation process change with kinds of the polymerization initiator to be used, it is preferable that it is 60-105 degreeC, and it is more preferable that it is 70-105 degreeC. Moreover, although a crosslinking temperature changes with kinds of crosslinking agent to be used, it is preferable that it is 100-150 degreeC.

  Moreover, additives, such as a plasticizer, an oil-soluble polymerization inhibitor, a flame retardant, a coloring agent, a chain transfer agent, can be added to a styrene-type monomer as needed. When these additives are added to the styrenic monomer, they are preferably added to the first monomer. Of these additives, it is preferable not to add an additive having a carbonyl group to at least the styrenic monomer added last.

  As the plasticizer, for example, fatty acid esters, acetylated monoglycerides, fats and oils, hydrocarbon compounds and the like can be used. Examples of fatty acid esters that can be used include glycerin tristearate, glycerin trioctoate, glycerin trilaurate, sorbitan tristearate, sorbitan monostearate, and butyl stearate. Moreover, as an acetylated monoglyceride, glycerol diacetomonolaurate etc. can be used, for example. As fats and oils, hardened beef tallow, hardened castor oil, etc. can be used, for example. As a hydrocarbon compound, cyclohexane, a liquid paraffin, etc. can also be used, for example. As the oil-soluble polymerization inhibitor, for example, para-t-butylcatechol, hydroquinone, benzoquinone and the like can be used. As the flame retardant, for example, hexabromocyclododecane, tetrabromobisphenol A compound, trimethyl phosphate, brominated butadiene-styrene block copolymer, aluminum hydroxide and the like can be used. As the colorant, furnace black, channel black, thermal black, acetylene black, ketjen black, graphite, carbon fiber, or the like can be used. As the chain transfer agent, for example, n-dodecyl mercaptan, α-methylstyrene dimer and the like can be used. The said additive can be added individually or in combination of 2 or more types.

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

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

  In the gas impregnation 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 are put into a pre-foaming machine, and heated with a heating medium such as water vapor, hot air, or a mixture thereof to foam the expandable composite resin particles to obtain expanded particles. Also, the composite resin particles obtained by polymerization in a pressure vessel are filled in another pressure vessel, and the foaming agent is impregnated by press-fitting a foaming agent to produce foamable composite resin particles. You can also

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

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

  Examples of the shape of the expanded particles include a columnar shape, a rugby ball shape, and a spherical shape. The size of the expanded particles is about 0.5 mm to 5 mm in diameter, although it depends 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 expanded particles include spray coating, airless coating, dip coating, blending, and other coating methods based on these methods and principles. Spray coating is a method in which an antistatic agent solution is atomized and sprayed onto foamed particles together with high-pressure air. Airless coating is a method in which an antistatic agent solution is made high and sprayed onto the foamed particles from the spray nozzle using the pressure. In addition, it is preferable to make foamed particles into a fluid state at the time of spraying, or to stir after spraying to adhere the antistatic agent solution to the entire surface of the foamed particles. Immersion coating is a method in which expanded particles are pulled up after being immersed in an antistatic agent solution. The blending method is a method of applying foamed particles and a small amount of an antistatic agent solution by stirring.

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

  In the application process of 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 expanded 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 foamed particles, to prevent the fluidity of the foamed particles from being lowered, and to prevent filling defects during molding. As for the application quantity of the antistatic agent with respect to 100 mass parts of composite resin foamed particles, it is more preferable that it is 0.5-4 mass parts, and it is further more preferable that it is 1-3 mass parts. The antistatic agent may be coated as long as the antistatic agent is present on the surface of the expanded particles, and an embodiment in which the surface of the expanded particles is completely covered is more preferable. Therefore, the foamed particles coated with the antistatic agent do not necessarily need to be completely covered with the surface, and may have a portion not covered with the antistatic agent on the surface of the foamed particles.

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

  Examples of producing foamed particles and molded products will be described in detail below.

Example 1
(1) Preparation of seed particles A linear low-density polyethylene resin (specifically, “Nipolon Z HF210K” manufactured by Tosoh Corporation) prepared by polymerization using a metallocene polymerization catalyst was prepared as an ethylene-based resin. The melting point Tm of this ethylene resin is 103 ° C. 20 kg of this ethylene-based resin and 0.144 kg of zinc borate (specifically, zinc borate 2335 manufactured by Tomita Seiyaku Co., Ltd.) are mixed with a Henschel mixer (specifically, manufactured by Mitsui Miike Chemical Co., Ltd.). Model FM-75E) and mixed for 5 minutes to obtain a resin mixture.

  Subsequently, the resin mixture was melt-kneaded at a temperature of 230 to 250 ° C. using a 26 mmφ twin-screw extruder (specifically, model TEM-26SS manufactured by Toshiba Machine Co., Ltd.). The melt-kneaded material was extruded and cut into an average of 0.5 mg / piece by an underwater cutting method to obtain seed particles.

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

  Next, t-butyl peroxy-2-ethylhexyl monocarbonate (specifically, “Perbutyl E” manufactured by NOF Corporation) and t-hexyl peroxybenzoate (specifically, manufactured by NOF Corporation) as polymerization initiators. “Perhexyl Z”) was prepared. In addition, α-methylstyrene dimer (specifically, “NOFMER MSD” manufactured by NOF Corporation) was prepared as a chain transfer agent. Then, 1.72 g of t-butylperoxy-2-ethylhexyl monocarbonate, 0.86 g of t-hexylperoxybenzoate, and 0.63 g of α-methylstyrene dimer are mixed with the first monomer (that is, a styrene monomer). ). Then, the dissolved product was put into an aqueous medium in the autoclave while stirring at a rotation speed of 500 rpm. As the first monomer, a mixed monomer of 60 g of styrene and 15 g of butyl acrylate was used.

  Next, after the air in the autoclave was replaced with nitrogen, the temperature was raised and the temperature inside the autoclave was raised to 100 ° C. over 1 hour and 30 minutes. After the temperature increase, the temperature was maintained at 100 ° C. for 1 hour. Thereafter, the stirring speed was lowered to 450 rpm and maintained at a temperature of 100 ° C. for 7.5 hours. The temperature at this time (specifically, 100 ° C.) is the polymerization temperature. When 1 hour has passed since the temperature reached 100 ° C., 346.25 g of styrene as a second monomer (specifically, a styrene monomer) and 3.75 g of methacrylic acid (ie, MAA) It was added into the autoclave over time. Note that MAA was added in a state of being previously dissolved in styrene as the second monomer.

  Next, the temperature inside the autoclave was raised to a temperature of 125 ° C. over 2 hours, and kept at the temperature of 125 ° C. for 5 hours. Thereafter, the inside of the autoclave was cooled, and the contents (specifically, composite resin particles) were taken out. Next, nitric acid was added to dissolve the magnesium pyrophosphate adhering to the surface of the composite resin particles. Thereafter, dehydration and washing were performed with a centrifugal separator, and water adhering to the surface was removed with an airflow drying device to obtain composite resin particles. The mass ratio of the component derived from the ethylene resin and the component derived from the styrene monomer in the composite resin from the blending ratio (mass ratio) of the styrene monomer and ethylene resin used at the time of manufacture. Asked.

  For the composite resin particles obtained as described above, the blending amount of the styrene monomer, the amount of MAA, the addition time of MAA, the addition time, the ethylene resin component (ie, PE) and the styrene resin component (ie, , PS) are shown in Table 1 below. In addition, the quantity of MAA is the quantity with respect to a total of 100 mass parts of ethylene-type resin, a styrene-type monomer, and MAA. Further, for the composite resin particles, a glass transition temperature Tg of an acetone-soluble component obtained by further dissolving the xylene-soluble component in the composite resin in acetone as follows (hereinafter referred to as “acetone-soluble component Tg” as appropriate). And the foamability was further evaluated. The results are shown in Table 1.

“Tg of acetone soluble part”
First, 1.0 g of composite resin particles are placed in a 150 mesh wire mesh bag. Next, about 200 ml of xylene is placed in a round flask having a volume of 200 ml, and the sample (that is, composite resin particles) placed in the wire mesh bag is set in a Soxhlet extraction tube. Heat with a mantle heater for 8 hours to extract Soxhlet. The extracted xylene solution is dropped into 600 ml of acetone and decanted, and the supernatant is evaporated to dryness under reduced pressure to separate the acetone-soluble component. About the obtained acetone soluble part 2-4 mg, heat flux differential scanning calorimetry is performed based on JISK7121 (1987) using DSC measuring instrument Q1000 made from TI Instruments. And Tg of acetone soluble part can be calculated | required as a midpoint glass transition temperature of the DSC curve obtained on the conditions of a heating rate of 10 degree-C / min.

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

That is, the case where the bulk density is less than 40 kg / m ³ as "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, while showing the value of the bulk density in foaming evaluation, the evaluation result is shown in a parenthesis. The bulk density (unit: kg / m ³ ) was measured as follows. First, a 1 L graduated cylinder was prepared, and foam particles were filled to a 1 L marked line in an empty graduated cylinder. Subsequently, the mass (unit: g) of the expanded particles per liter was measured. And the bulk density (unit: kg / m < ³ >) was computed by converting the mass (unit: g) of 1 L of expanded particles into a unit.

(3) Production of expanded particles 500 g of the composite resin particles produced as described above were charged into a 5 L pressure vessel equipped with a stirrer together with 3500 g of water as a dispersion medium. Subsequently, 5 g of kaolin as a dispersant and 0.5 g of sodium alkylbenzene sulfonate as a surfactant were further added to the dispersion medium in the container. Next, the inside of the container was heated to a foaming temperature of 165 ° C. while stirring the inside of the container at a rotation speed of 300 rpm. Thereafter, carbon dioxide, which is an inorganic physical foaming agent, was pressed into the container so that the pressure in the container was 3.9 MPa (however, gauge pressure), and held at the same temperature (ie, 165 ° C.) for 15 minutes. Thereby, the composite resin particles were impregnated with carbon dioxide to obtain expandable composite resin particles. Next, the foamable composite resin particles were discharged together with the dispersion medium from the container under atmospheric pressure to obtain expanded particles having a bulk density of 50 kg / m ³ . Since the expanded particle is a foam of composite resin particles, it can also be said to be composite resin expanded particles. The foaming conditions are shown in Table 1 below.

  About the foamed particle produced as mentioned above, the amount of surface carbonyl and the amount of water vapor adsorption were measured as follows. The results are shown in Table 1.

"Carbonyl content"
The amount of carbonyl on the surface of the expanded particles is expressed 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 with respect to the amount of styrene are measured as follows.

(A) Styrene amount In measuring styrene amount, infrared spectrophotometer “FT / IR-460plus” manufactured by JASCO Corporation and total reflection absorption measuring device “ATR PRO 450-S type” manufactured by the same company are used as measuring devices. Was used. The measurement conditions of the total reflection absorption measuring apparatus were prism: ZnSe and incident angle: 45 °. Specifically, first, the foamed particles are pressed and adhered to the prism of the total reflection absorption measuring device at a pressure of 170 kg / cm ² to measure the infrared spectrum of the surface of the foamed particles, and the infrared absorption spectrum (however, ATR 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 (however, 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 defined as the absorbance ratio D ₆₉₈ / D ₂₈₅₀ of the expanded particles. The results are shown in Table 1.

Absorbance D ₆₉₈ obtained from an infrared absorption spectrum (but no ATR correction) is the height of a peak derived from an out-of-plane bending vibration of a benzene ring mainly contained in a styrene resin. In addition, the absorbance D ₂₈₅₀ obtained from the infrared absorption spectrum (without ATR correction) is the peak height derived from the C—H 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 foamed particle is substituted by the absorbance ratio D ₆₉₈ / D ₂₈₅₀ of the foamed particle obtained from the infrared absorption spectrum in the following (formula 1) obtained from the calibration curve. The amount of styrene on the surface was determined. The results are shown in Table 1.
(Formula 1) Styrene amount = 0.7622 × (absorbance ratio D ₆₉₈ / D ₂₈₅₀ ) ² + 7.4831 × (absorbance ratio D ₆₉₈ / D ₂₈₅₀ ) +1.635

A calibration curve for styrene was prepared as follows. That is, first, using an extruder, polyethylene (specifically, “Nipolon Z HF210K” manufactured by Tosoh Corp.) and polystyrene (specifically, “680” manufactured by PS Japan Co., Ltd.) are converted into 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 (but 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 scale so that the specific mass ratio is obtained. By doing so, the pellet which has said mol ratio can be produced. Subsequently, the pellet was formed into a film by a press machine heated at a temperature of 180 ° C. to obtain a film. The infrared absorption spectrum (without ATR correction) of the film was measured using the total reflection absorption measuring apparatus described above. Next, 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 described above, and the absorbance ratio D ₆₉₈ / D ₂₈₅₀ is obtained. A calibration curve as illustrated in FIG. 1 can be obtained 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. .

(B) Amount of carbonyl relative to the amount of styrene In measuring the amount of carbonyl, the same measuring device as that for measuring the amount of styrene described above was used, and the measurement conditions of the total reflection absorption measuring device were the same as those for measuring the amount of styrene. Specifically, first, the foamed particles are pressed and adhered to the prism of the total reflection absorption measuring device at a pressure of 170 kg / cm ² to measure the infrared spectrum of the surface of the foamed particles, and the infrared absorption spectrum (however, ATR 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 (however, without ATR correction) are measured, and the absorbance ratio D ₁₇₃₀ / D ₆₉₈ is determined. The same measurement is performed for five expanded particles, and the average value of these is 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 the peak derived from the stretching vibration between C = O of the carboxy group of the (meth) acrylic acid component unit. Then, by preparing a calibration curve in advance and substituting the absorbance ratio D ₁₇₃₀ / D ₆₉₈ of the expanded particles obtained from the infrared absorption spectrum into the following (formula 2) obtained from the calibration curve, the amount of carbonyl relative to the amount of styrene Asked. The results are shown in Table 1.
(Formula 2) Amount of carbonyl with respect to amount of styrene = 6.4838 × (absorbance ratio D ₁₇₃₀ / D ₆₉₈ ) −0.0523

A calibration curve for the amount of carbonyl was prepared as follows. That is, using styrene and butyl acrylate, polymer particles having butyl acrylate amounts of 0 mol%, 0.8 mol%, 2.5 mol%, and 4.1 mol%, respectively, were prepared 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 (without ATR correction) of the film was measured using the total reflection absorption measuring apparatus described above. Next, the absorbance D ₆₉₈ and absorbance D ₁₇₃₀ obtained from the infrared absorption spectrum (without ATR correction) were measured in the same manner as described above, and the absorbance ratio D ₁₇₃₀ / D ₆₉₈ was determined. A calibration curve as illustrated in FIG. 2 can be obtained by taking the amount of carbonyl in the standard sample (unit: mol%) on the horizontal axis and the absorbance ratio D ₁₇₃₀ / D ₆₉₈ on the vertical axis. .

(C) Surface carbonyl amount The value obtained by multiplying the styrene amount on the surface of the expanded particles obtained by the above-mentioned method by 100 and multiplying the styrene amount by the carbonyl amount was defined as the surface carbonyl amount of the composite resin expanded particles. The results are shown in Table 1.

"Water vapor adsorption amount of composite resin foam particles"
The water vapor adsorption amount is measured using a vapor adsorption amount measuring device (BELSORP-max (manufactured by Nippon Bell Co., Ltd.)) and measuring the adsorption isotherm (set relative pressure: 0.005 to 0.9) at 25 ° C. 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 foamed 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 are placed in a sample cell, and using BELSORP-max (made by Nippon Bell Co., Ltd.), an adsorption isotherm of water vapor at 25 ° C. (set relative pressure: 0.005 to 0.9) 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 foam particles. The results are shown in Table 1.

(4) Application process of antistatic agent Octyldimethylethylammonium ethyl sulfate (specifically, “Katiogen ES-O” manufactured by Daiichi Kogyo Seiyaku Co., Ltd .; active ingredient 50%) was prepared as an antistatic agent. . The foamed particles were put together with an antistatic agent in a plastic bag, shaken well, and then the whole bag was placed in a tumbler and mixed for 30 minutes to apply the antistatic agent to the foamed particles. The addition amount of the antistatic agent was 2 parts by mass with respect to 100 parts by mass of the expanded particles. The amount of the active ingredient is 1 part by mass with respect to 100 parts by mass of the expanded particles. Thereafter, the expanded particles 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 were obtained. With respect to the expanded particles, the adhesion amount of the antistatic agent was measured as follows.

"Amount of antistatic agent"
About 5 g of expanded particles with an antistatic agent attached and about 5 g of expanded particles with no antistatic agent attached were weighed. Let W ₀ (W ₀ ≈5) be the weight of the expanded particles to which no antistatic agent is attached. Each foamed particle after weighing was washed three times with 100 cm ³ (ml) of a washing liquid (specifically ethanol). About 300 cm ³ of the washing liquid after washing was recovered and kept at a temperature of 40 ° C. for 24 hours to evaporate the washing liquid. Was then measured and residue weight W _A after evaporation of the cleaning liquid of the expanded beads of the antistatic agent adheres, after evaporation of the cleaning liquid of the expanded beads of the antistatic agent does not adhere to the residue weight W _B. Based on these residue weights W _A and W _B , and the weight W ₀ of the expanded particles, the adhesion amount A (mass part) of the antistatic agent 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 foamed particles coated with the antistatic agent were filled into a mold having a flat plate-shaped cavity having a length of 250 mm, a width of 200 mm, and a thickness of 50 mm. Next, by introducing water vapor into the mold, the expanded particles were heated and fused to each other. Then, after cooling the inside of a metal mold | die by water cooling, the molded object was taken out from the metal mold | die. Furthermore, the molded body was dried and cured by placing it in an oven adjusted to a temperature of 60 ° C. for 12 hours. In this way, a molded body in which a large number of expanded particles were fused to each other was obtained.

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

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

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

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

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

"Compressive strength"
A rectangular parallelepiped test piece having a length of 50 mm, a width of 50 mm, and a thickness of 25 mm was cut out from the center portion of the foamed particle molded body. Next, the compression load at the time of 50% strain was calculated | required based on JISK6767-1999 with respect to this test piece. The compressive strength (that is, 50% compressive stress) was calculated by dividing this compressive load by the pressure receiving area of the test piece.

(Example 2)
Examples 2 to 4 are examples in which the composition of MAA was changed. Specifically, in this example, expanded 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 molded bodies 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, expanded particles and a molded body 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 for adding MAA and the time for addition were changed. Specifically, in this example, the amount of sodium nitrite used as the water-soluble polymerization inhibitor is changed from 0.21 g to 0.15 g, and the autoclave temperature reaches 100 ° C. and the first time elapses. 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, as in Example 1. 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 when the autoclave temperature reached 100 ° C., the second monomer, styrene 347 0.5 g was added to 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 made.

(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 is changed to 150 g, a mixed monomer of styrene 135 g and butyl acrylate 15 g is used as the first monomer, and styrene 196 is used as the second monomer. Except for using .25 g, expanded particles and molded bodies were produced in the same manner as in Example 1.

(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. Except for the points, foamed particles and molded bodies were produced in the same manner as in Example 1.

Example 9
In this example, MAA is changed to acrylic acid (that is, AA). Specifically, in this example, expanded 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 foamed particles produced without using methacrylic acid and acrylic acid, and a molded article. Specifically, in this example, expanded particles and a molded body were produced in the same manner as in Example 1 except that 350 g of styrene was used as the second monomer without adding methacrylic acid.

(Comparative Example 2)
In this example, the amount of methacrylic acid added is made too small. Specifically, in this example, expanded particles and a molded body 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 added excessively. Specifically, in this example, expanded particles and a molded body 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)
In this example, the amount of the styrene monomer added to the ethylene 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. In addition, a mixed monomer of 221.25 g of styrene and 15 g of butyl acrylate was used as the first monomer, 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 foamed particles and molded bodies.

(Comparative Example 5)
In this example, the amount of the styrene monomer added to the ethylene resin is excessive. Specifically, in this example, the amount of seed particles added to the autoclave was changed to 24 g. In addition, 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 foamed particles and molded bodies.

(Comparative Example 6)
In this example, methacrylic acid (ie, MAA) is changed to methyl methacrylate (ie, MMA) as the second monomer. Specifically, in this example, 346.25 g of styrene as a second monomer (specifically, a styrene 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 previously dissolved in styrene as the second monomer. Others were the same as in Example 1 to produce foamed particles and molded bodies.

  For Examples 2 to 9 and Comparative Examples 1 to 6, the same evaluation as in Example 1 was performed, and the results are shown in Tables 1 and 2.

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

  On the other hand, as can be seen from Table 2, in Comparative Examples 1 and 2 in which the amount of surface carbonyl of the composite resin foamed particles was small, sufficient antistatic performance was not obtained. Moreover, in the comparative example 3 which increased the addition amount of (meth) acrylic acid, the glass transition temperature of acetone soluble part was high, and foamability and melt | fusion property were inadequate. In Comparative Example 4 in which the addition amount of the styrene monomer is small, the rigidity of the molded body is lowered, so that the compression strength is small and the flexural modulus is low. Therefore, the molded body of Comparative Example 4 is easily deformed by bending and has insufficient deflection resistance. On the other hand, in Comparative Example 5 in which the addition amount of the styrene monomer is large, the compression strength and bending elastic modulus of the molded body are increased, but the bending rupture energy is insufficient. Therefore, the molded body of Comparative Example 5 is liable to break due to deformation. Further, in Comparative Example 6, sufficient anti-static performance could not be obtained.

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

Claims (10)

A composite resin foamed particle using a composite resin obtained by impregnating and polymerizing (meth) acrylic acid and a styrene monomer in an ethylene resin,
The composite resin contains 100 to 1900 parts by mass of a structural unit derived from a styrene monomer with respect to 100 parts by mass of an ethylene 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 less,
Composite resin foamed particles, wherein the amount of carbonyl on the surface of the composite resin foamed particles is 0.03 mol% or more.   2. The composite resin expanded particle according to claim 1, wherein the content of the structural unit derived from (meth) acrylic acid with respect to 100 parts by mass of the composite resin is 0.1 to 2 parts by mass. The composite resin foamed particles according to claim 1 or 2, wherein the composite resin foamed particles have a water vapor adsorption amount of 0.5 cm ³ / g or more.   The ethylene-based resin is composed of linear low-density polyethylene, or linear low-density polyethylene and an ethylene-vinyl acetate copolymer, and the ethylene-vinyl acetate copolymer content in the ethylene-based resin is 10 mass. The composite resin expanded particles according to any one of claims 1 to 3, wherein the composite resin expanded particles are less than%.   5. The composite resin according to claim 1, wherein the structural unit derived from the styrene monomer contains more than 400 parts by mass and 1900 parts by mass or less with respect to 100 parts by mass of the ethylene resin. The composite resin expanded particle as described.   The surface of the composite resin foam 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 composite resin foam particles. The composite resin foamed particle according to any one of 5. A molded article in which the composite resin foam particles according to claim 6 are fused to each other, wherein the molded article has a surface resistivity of less than 1 × 10 ¹² Ω. In a dispersion in which ethylene resin seed particles are dispersed in an aqueous medium, 100 to 1900 parts by weight of a styrene monomer with respect to 100 parts by weight of the ethylene resin in the ethylene resin seed particles, and (meth) A modification step of adding acrylic acid, impregnating and polymerizing the ethylene resin seed particles with the styrene monomer and the (meth) acrylic acid to obtain composite resin particles;
A foaming step of foaming the composite resin particles using a foaming agent to obtain composite resin foam particles,
The glass transition temperature Tg of the acetone soluble part obtained by further dissolving the xylene soluble part in the composite resin expanded particles in acetone is 105 ° C. or less,
The method for producing composite resin foamed particles, wherein the amount of carbonyl on the surface of the composite resin foam particles is 0.03 mol% or more.   In the modification step, the styrenic monomer is added to the aqueous medium in a plurality of times, and the (meth) acrylic acid is added to the ethylene together with the styrenic monomer added at least last. The method for producing composite resin foamed 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 with respect to 100 parts by mass of the total amount of the (meth) acrylic acid, the ethylene resin, and the styrene monomer. Item 10. The method for producing composite resin foamed particles according to Item 8 or 9.

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