CN113321843A

CN113321843A - Expanded particles and expanded particle molded article

Info

Publication number: CN113321843A
Application number: CN202110220906.4A
Authority: CN
Inventors: 永木雅纮; 平晃畅
Original assignee: JSP Corp
Current assignee: JSP Corp
Priority date: 2020-02-28
Filing date: 2021-02-26
Publication date: 2021-08-31
Also published as: JP7421092B2; CN117567787A; JP2021134332A

Abstract

The invention provides expanded particles capable of producing an expanded particle molded body having excellent weldability, exhibiting electric conductivity or electrostatic diffusion, and having a small variation in surface resistance value, and an expanded particle molded body comprising the expanded particles. The foamed particles (1) have: a pellet body (2) having a foamed layer made of an olefin resin; and a single-walled carbon nanotube (3) attached to the surface of the particle body (2). The expanded particles (1) have conductivity or semiconductivity. To the hairThe foamed molded article of foamed particles obtained by in-mold molding of the foamed particles (1) has an average surface resistivity of 1X 10. omega. or more and 1X 10 omega. or less¹⁰Omega is less than or equal to.

Description

Expanded particles and expanded particle molded article

Technical Field

The present invention relates to expanded particles and an expanded particle molded body.

Background

Foamed molded particles comprising olefin resins are sometimes used as packaging materials such as spacers and cases, because of their excellent impact absorption properties. Examples of the object to be protected by the packaging material include precision instruments, electronic devices, and electronic components.

A packaging material used for packaging electronic devices, electronic components, and the like is sometimes required to have electrostatic diffusibility and other electrical characteristics in addition to shock absorbability. The foamed particles used for producing such a packaging material may contain a conductive material. As the conductive material, conductive carbon black or the like is often used. The electrostatic diffusibility refers to a property of being able to release static electricity slowly.

Patent document 1 describes a foam molding material obtained by adding an aqueous gel in which a plurality of layers of carbon nanotubes are dispersed to pre-expanded polystyrene beads and heating and mixing the mixture.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2012 and 87041

Disclosure of Invention

Problems to be solved by the invention

However, when semiconductive or conductive foamed particles obtained by adhering a conductive material to expandable particles made of an olefin-based resin or foamed particles are subjected to in-mold molding, it is difficult to maintain the weldability of the foamed particles in the foamed particle molded article. In this case, the conductive material cannot be sufficiently prevented from falling off from the surface of the foamed molded particle. When the conductive material falls off from the surface of the expanded particle molded body, a portion having a high surface resistance and a portion having a low surface resistance are easily formed on the surface of the expanded particle molded body. In this case, it may be difficult to obtain a foamed molded article of expanded particles having desired electrical characteristics. On the other hand, if the amount of the conductive material adhering to the expanded beads is reduced in order to improve the weldability of the expanded beads, the surface of the expanded bead molded article obtained from such expanded beads may not have a desired surface resistance value.

The present invention has been made in view of the above-mentioned circumstances, and an object thereof is to provide expanded beads which can produce an expanded bead molded body having excellent weldability, and which has small variations in electrical conductivity, electrostatic diffusion properties, and surface resistance values. It is another object of the present invention to provide a foamed molded article of foamed particles comprising such foamed particles, which has excellent weldability, and which has electrical conductivity, electrostatic diffusibility, and small variations in surface resistance.

Means for solving the problems

A first aspect of the invention is a foamed particle,

the foamed particles have:

a pellet body having a foamed layer made of an olefin resin; and

a single-walled carbon nanotube attached to the surface of the particle body,

the foamed particles have conductivity or semiconductivity.

The second aspect of the present invention is a foamed molded article of expanded particles obtained by in-mold molding the expanded particles of the above aspect,

the foamed molded article has an average surface resistivity of 1X 10. omega. or more and 1X 10¹⁰Omega is less than or equal to.

Effects of the invention

Single-walled carbon nanotubes as a conductive material are attached to the surface of the foamed particles of the first aspect. This can prevent the conductive material from falling off from the main body of the pellet made of the olefin resin. Therefore, by in-mold molding the expanded beads, a molded article of expanded beads having excellent weldability, exhibiting electric conductivity or electrostatic diffusibility, and exhibiting small variations in surface resistance can be produced.

Drawings

Fig. 1 is an electron micrograph (30000 times) of the surface of the expanded particles in example 1.

Fig. 2 is an electron micrograph (30000 times) of the surface of the expanded beads in comparative example 2.

Description of the reference numerals

1: foaming particles; 2: a particle body; 3: a single-walled carbon nanotube.

Detailed Description

The foamed particles include a particle body having a foamed layer, and a single-walled carbon nanotube attached to a surface of the particle body. Hereinafter, the single-walled carbon nanotube may be simply referred to as "SWCNT".

The expanded particles have conductivity or semiconductivity by adhering SWCNTs to the surface of the particle body. The foamed particles having conductivity or semiconductivity mean that, when the foamed particles are subjected to in-mold molding, the surface resistivity of a foamed particle molded article obtained by in-mold molding the foamed particles is 1 × 10 Ω or more and 1 × 10 Ω or more¹⁰Electrical characteristics of Ω or less.

The expanded bead in-mold molded article using the expanded beads of the present invention is excellent in electrical conductivity and electrostatic diffusibility. In the present specification, the term "electrostatic diffusibility" specifically means that the surface resistivity of the foamed molded particle is 1 × 10⁴1 × 10 over omega¹⁰The "electrical conductivity" means that the surface resistivity of the foamed molded particle is less than 1X 10⁴Electrical properties in the range of Ω.

The foamed layer of the pellet body is a foam made of an olefin resin. Examples of the olefin resin forming the foamed layer include homopolymers of propylene (h-PP), copolymers of a propylene component and another polymerizable monomer component, and mixtures of two or more of these. Examples of the other polymerizable monomer component include an α -olefin having 4 to 10 carbon atoms such as ethylene, 1-butene, isobutylene, 1-pentene, 3-methyl-1-butene, 1-hexene, 3, 4-dimethyl-1-butene, and 3-methyl-1-hexene. The copolymer may be a random copolymer or a block copolymer, and may be a binary copolymer or a ternary copolymer. The content of the other polymerizable monomer copolymerizable with propylene in the copolymer in the olefin-based resin is preferably 25% by mass or less, more preferably 15% by mass or less. More specifically, as the copolymer, a propylene-ethylene random copolymer, a propylene-ethylene-butene random copolymer (r-PP), a propylene-ethylene block copolymer (b-PP), or the like can be used.

As the olefin-based resin, a general-purpose polypropylene-based resin having excellent rigidity, abrasion resistance and processability and also having low cost is preferably used. Examples of the polypropylene resin include (1) a propylene homopolymer, (2) a propylene copolymer having a propylene component ratio of 50% by mass or more, such as a propylene random copolymer, (3) a propylene homopolymer, and a mixture of two or more polymers selected from the group consisting of propylene copolymers, such as a propylene-ethylene random copolymer, a propylene-butene random copolymer, and a propylene-ethylene-butene terpolymer.

In addition to the polymer or the mixture, additives such as other resins, catalyst neutralizers, lubricants, and crystal nucleating agents may be added to the olefin-based resin in a range that does not impair the above effects. The content of the additive is, for example, preferably 15 parts by mass or less, more preferably 10 parts by mass or less, further preferably 5 parts by mass or less, and particularly preferably 1 part by mass or less, based on 100 parts by mass of the olefin-based resin.

The particle body may have a foamed single-layer structure composed only of the foamed layer. The main particle body may have a multilayer structure including the foamed layer and a coating layer for coating the foamed layer. The coating layer may be in a foamed state or in an unfoamed state. The resin constituting the coating layer may be, for example, the same polymer or mixture as the foamed layer.

The softening temperature of the surface of the particle body is preferably 145 ℃ or lower. The "softening temperature" refers to a temperature at which the surface of the particle body starts to melt. In this case, the weldability of the expanded beads to each other at the time of in-mold molding can be further improved. The melting characteristics of the surface of the particle body can be evaluated based on, for example, a melting point obtained by a differential thermal analysis, so-called differential thermal analysis, in which a probe of a scanning probe microscope is brought into contact with a measurement object.

In the expanded beads, SWCNTs are adhered to the surface of the main particle body. By using SWCNTs as the conductive material, desired conductivity or semiconductivity can be imparted to the expanded particles, and the amount of SWCNTs applied to the expanded particles can be reduced as compared with the case of applying another conductive material. In addition, SWCNTs can be attached to the surface of the particle body in a state of being entangled with the particle body, other components attached to the particle body, or other SWCNTs. Therefore, compared to other conductive materials such as conductive carbon black and multilayered carbon nanotubes, the SWCNTs can be prevented from falling off from the particle body. Therefore, the foamed particle molded body obtained by in-mold molding the foamed particles can reduce variations in the amount of SWCNTs adhering thereto. As a result, variation in surface resistivity of the surface of the expanded particle molded body can be reduced.

In addition, the foamed particles are in a state where desired conductivity or semiconductivity is secured, and the amount of the conductive substance applied to the surface of the particle body is reduced. This can improve the weldability of the expanded beads to each other. Therefore, if the expanded beads are used, even when the molding is performed at a lower molding pressure, a molded article of expanded beads having good weldability can be obtained. In addition, when the expanded beads are molded at a low molding pressure, the dropping of the SWCNTs attached to the expanded beads can be more effectively suppressed. Therefore, the variation in the surface resistivity of the expanded particle molded body can be further reduced by the synergistic effect with the effect of suppressing the shedding of the SWCNTs from the particle body.

The coating amount of SWCNT is preferably 1m²The surface of the main particle body of (3) is 0.1mg to 10.0 mg. In this case, SWCNTs can be more uniformly attached to the particle body. As a result, variation in the surface resistivity of the surface of the expanded particle molded body can be further reduced.

The lower limit of the amount of SWCNT to be coated is preferably 0.2mg/m²More preferably 0.5mg/m². In this case, the SWCNTs adhering to the expanded particles constituting the expanded particle molded body can form a sufficient electrostatic conductive path on the expanded particle molded body. As a result, the expanded bead molded body can be provided with electric conductivity or electrostatic diffusibility more reliably.

The upper limit of the amount of SWCNT to be coated is preferably 9.0mg/m²More preferably 8.0mg/m²More preferably 7.0mg/m². In this case, a foamed molded article of foamed particles having desired electrical characteristics and excellent weldability between foamed particles can be obtained more easily. Further, in this case, the coating amount of the SWCNTs can be reduced as compared with the case of coating a conductive material other than the SWCNTs. As a result, the influence of SWCNTs adhering to the expanded beads on the color tone of the expanded beads can be further reduced, and a foamed molded article with brighter color tone can be produced.

The coating amount of SWCNTs can be calculated from the concentration of the SWCNT dispersion, the amount of the SWCNT dispersion added when the particle host is mixed with the SWCNT dispersion, and the surface area of the particle host. As another method, for example, the following method may be employed: SWCNTs were separated from the surface of the expanded beads, the total carbon content of the separated SWCNTs was measured by quantitative analysis, and the total carbon content was converted into the coating weight by a standard curve method or the like.

The upper limit of the average diameter of the SWCNTs is preferably 10nm, more preferably 5 nm. The lower limit of the average diameter of the SWCNTs is preferably 1nm, more preferably 1.2 nm. The average length of the SWCNTs is preferably 1 μm or more, and more preferably 3 μm or more. The L/D of the SWCNT, i.e., the value obtained by dividing the average length by the average diameter, is preferably 100 or more, and more preferably 200 or more. In this case, on the surface of the particle body, the winding of the particle body and the SWCNTs and the winding of the SWCNTs with each other become more complicated, and therefore, the SWCNTs can be more effectively suppressed from falling off from the particle body.

The average diameter and average length of SWCNTs can be measured, for example, by the following methods. First, a surface image of the expanded particles is obtained by a scanning electron microscope. The diameter of the SWCNTs present in the surface image was determined at 50 randomly selected locations. Then, the average value of the obtained diameters can be regarded as the average diameter of the SWCNTs.

Similarly, 50 SWCNTs were randomly selected from the surface image obtained by a scanning electron microscope, and the length of each SWCNT was measured by image analysis. In the case where the SWCNT is not linear but curved, the length along the shape of the SWCNT may be measured using a curvature meter or the like. The average of the lengths thus obtained can be taken as the average length of the SWCNTs.

The above expanded beads are preferably those obtained by JIS Z8722: in 2009, the value (a) of L obtained by measuring the cross section of the particle body is 40 to 80, and the differences (a) - (B) between the value (a) and the value (B) obtained by measuring the surface of the expanded particle are greater than 0 and 10 or less. In addition, the L value refers to L value in CIE1976L a b color system. The L value is a value indicating the lightness of the expanded beads, and a larger value indicates a brighter color tone. Specifically, the L value of the expanded beads can be measured by a method based on JIS Z8722: 2009 by the measurement method.

Since SWCNTs exhibit a black color or a color close to black, the larger the coating amount of SWCNTs applied to expanded particles, the larger the L value (B) obtained by measuring the surface of the expanded particles. On the other hand, since SWCNTs adhere to the surface of the particle body, the SWCNTs do not adhere to the cross section of the particle body, that is, the bubble film portion of the surface exposed when the particle body is cut at an arbitrary cross section. Therefore, the L value (a) measured for the cross section of the particle body substantially coincides with the L value of the particle body before the SWCNTs are attached. Therefore, the differences (a) - (B) between the aforementioned L value (a) and the L value (B) measured on the surface of the expanded particle indirectly indicate the amount of SWCNTs adhering to the surface of the particle body. The larger the values of (A) to (B), the larger the amount of SWCNT adhered.

When the value of L × of the cross section of the particle body (a) and the values of the differences (a) - (B) between the value of L × of the cross section of the particle body (a) and the value of L × of the surface of the expanded particle (B) are within the above-described specific ranges, electrical conductivity or electrostatic diffusibility can be imparted to the expanded particle molded body, and the color tone of the expanded particle molded body can be brighter than before. The upper limit of the values of (a) to (B) is more preferably 10, still more preferably 7, and particularly preferably 5, from the viewpoint of imparting a desired electrical conductivity or electrostatic diffusibility to the expanded particle molded article and making the color tone of the expanded particle molded article brighter. The lower limit of the value of (a) to (B) is more preferably 1, and still more preferably 2.

In addition, for the purpose of identifying the contents and improving the design, it is desirable that the foamed molded particle be colored in a chromatic color such as red, blue, green, or yellow in addition to an achromatic color such as white, gray, or black. The colored foamed particle molded article is made of foamed particles colored in color. In such applications, it is strongly desired to increase the number of visually recognizable colors of the expanded bead molded article. By setting the values of the difference (a) - (B) between the L value (a) and the L value (B) on the surface of the expanded beads and the L value (a) on the cross section of the bead main body in the above-described specific ranges, the color tone of the expanded beads can be sufficiently brightened even in a state where the SWCNTs are adhered to the bead main body. As a result, the influence on the color tone of the particle main body can be reduced as compared with the conventional conductive material, and the number of types of colors of the foamed particle molded body that can be visually recognized can be increased.

A coefficient of variation L of the L value (B) of the surface of the expanded beads_cvPreferably 0.15 or less. Coefficient of variation L of L value (B)_cvIndicates the degree of variation in the color tone of the expanded beads. I.e. the coefficient of variation L_cvIndicating the degree of variation in the amount of SWCNTs adhering to the surface of the particle body, the smaller the value of the coefficient of variation, the smaller the variation in the electrical characteristics and color tone of the expanded particles.

Specifically, the coefficient of variation L of the L-value (B)_cvIs a value calculated by the following equations (1) and (2). L in the following formulae (1) to (2)_avIs a symbol representing the average value of L values (B), n is a symbol representing the total number of L values (B) obtained by measurement, and L is a symbol_iIs a symbol indicating the L value (B) obtained by the i-th measurement.

[ number 1 ]

Number 2

The larger the value of n, the more accurate the average value L of L-values (B) can be calculated_avAnd a coefficient of variation L_cvThe value of (c). The value of n may be 50 or more, for example.

By varying the coefficient of variation L of the aforementioned L-value (B)_cvSetting to 0.15 or less can further improve the weldability of the expanded beads, and can more reliably impart electrical conductivity or electrostatic diffusibility to the resulting expanded bead molded body. In particular, by varying the coefficient of variation L of the value of L (B)_cvWithin the above-specified range, the variation in the electrostatic conductive path in the expanded particle molded body can be reduced, and desired electrical characteristics can be stably exhibited.

From the viewpoint of more reliably exhibiting the above-described effects, the coefficient of variation L of L × value (B) is L_cvPreferably 0.12 or less, more preferably 0.10 or less, and still more preferably 0.05 or less.

In the production of the expanded beads, for example, a dispersion liquid composed of an aqueous solution containing SWCNTs is preferably mixed with the main particles while applying shear. Thereby, SWCNTs can be uniformly attached to the surface of the particle body. As the dispersion liquid, for example, TB002L grade manufactured by KJ Special paper Co. The dispersion liquid preferably does not contain a binder that inhibits fusion of olefin resin foamed particles. In order to further enhance the effect of the step of mixing with the particle main body while applying the shear, the SWCNT concentration of the dispersion is preferably 0.1 mass% to 1.0 mass%. The lower limit of the viscosity of the dispersion is preferably 8 mPas, more preferably 10 mPas, and still more preferably 12 mPas at 25 ℃. The upper limit of the viscosity of the dispersion is preferably 150 mPas, more preferably 50 mPas, and still more preferably 30 mPas at 25 ℃.

By using SWCNT as the conductive material, the foamed particles can be provided with conductivity or semiconductivity to the surface of the foamed particles while suppressing a decrease in L value (B) on the surface of the foamed particles due to adhesion of the conductive material. The obtained expanded beads are excellent in moldability. Therefore, the expanded particles in the expanded particle molded article obtained by in-mold molding the expanded particles are sufficiently welded to each other, and therefore, breakage of the expanded particles, falling off from the expanded particle molded article, and the like can be suppressed.

The apparent density of the expanded beads is preferably 20g/L to 100 g/L. In this case, the quality can be reduced without impairing the impact absorbability of the expanded particle molded body. When the resin particles in an unfoamed state are foamed, the resin particles are foamed so that the apparent density is within the specific range, whereby the resin on the surface of the resin particles can be appropriately stretched to form a particle body having a specific surface state.

The surface of the particle body having an apparent density in this range is considered to have a concave-convex shape suitable for attaching SWCNTs. Furthermore, as described above, SWCNTs can be easily fixed to the surface of the particle body by using shearing or friction. In particular, it is considered that in expanded beads having a high expansion ratio and an apparent density of 20g/L to 100g/L, unevenness is more likely to be formed on the surface of the beads than in expanded beads having a low expansion ratio, and the main body of the beads has an uneven shape suitable for adhesion of SWCNTs. From the above viewpoint, the lower limit of the apparent density of the expanded beads is preferably 25g/L, and more preferably 30 g/L. The upper limit of the apparent density of the expanded beads is preferably 90g/L, and more preferably 80 g/L.

The expanded beads having an apparent density in the above-described specific range can be produced, for example, by the following method. That is, first, the olefin-based resin pellets in an unfoamed state are dispersed in a dispersion medium such as water in a pressure-resistant vessel together with a blowing agent in an amount corresponding to a desired apparent density. Next, heating is performed to soften the resin particles and to impregnate the foaming agent into the resin particles. Then, the dispersion medium and the resin particles impregnated with the foaming agent are released from the container under a pressure lower than the pressure in the container (for example, usually atmospheric pressure) at a temperature equal to or higher than the softening temperature of the olefin-based resin and corresponding to a desired apparent density, and the resin particles are foamed.

The apparent density of the expanded beads can be measured, for example, by the following method. First, the foamed particles whose mass is measured in advance are sunk into a measuring cylinder filled with water, and the volume of the foamed particles is determined according to the rising amount of the water level of the measuring cylinder. The apparent density of the expanded beads can be calculated by dividing the mass of the expanded beads by the volume of the expanded beads thus obtained.

The color of the expanded beads is not particularly limited, and the expanded beads may be colored, for example. In this case, a colored foamed molded article of expanded particles can be produced. The foamed molded article of colored expanded particles is more excellent in design than the foamed molded article of achromatic foamed particles. In addition, for example, by using a colored foamed molded particle as the packing material, the object to be protected by the packing material can be easily recognized from the color of the foamed molded particle. Therefore, the colored expanded bead molded article is suitable for use in, for example, a container for transporting an object between production steps.

The colored expanded particles can be produced, for example, by attaching SWCNTs to a particle body containing a colorant and colored with the colorant to be colored in a colored manner. The colorant may be a pigment or a dye. Further, the effect of the present invention is more easily exhibited by using SWCNTs because the weldability of expanded beads with colored expanded beads is more easily reduced than that of expanded beads without colored expanded beads. More specifically, as the colorant, an organic pigment, an organic dye, an inorganic pigment, and an inorganic dye can be used.

Examples of the organic pigments include monoazo-based, condensed azo-based, anthraquinone-based, isoindolinone-based, heterocyclic-based, perinone-based, quinacridone-based, perylene-based, thioindigo-based, dioxazine-based, phthalocyanine-based, nitroso-based, phthalocyanine-based, and organic fluorescent pigments.

Examples of the inorganic pigment include titanium oxide, titanium yellow, iron oxide, ultramarine, cobalt blue, calcined pigment, metal pigment, mica, pearl pigment, zinc white, precipitated silica, and cadmium red.

Examples of the dye include organic dyes such as anthraquinone-based, heterocyclic-based and violanthrone-based dyes, basic dyes, acid dyes and mordant dyes.

As the colorant, one of the above-mentioned pigments and dyes may be used alone, or two or more thereof may be used in combination. Among these colorants, organic pigments or inorganic pigments are preferably used from the viewpoint of weather resistance. The amount of the colorant contained in the pellet body is not particularly limited, and for example, the upper limit of the amount of the colorant is preferably 10 parts by mass, and more preferably 5 parts by mass, based on 100 parts by mass of the olefin-based resin. The lower limit of the amount of the colorant is preferably 1 part by mass, and more preferably 0.1 part by mass, based on 100 parts by mass of the olefin-based resin.

The expanded beads can be produced, for example, by the following method. First, resin particles in an unfoamed state, which are a raw material of a particle main body, are produced. The resin pellets can be obtained, for example, by preparing strands of an olefin resin by extrusion molding and then cutting the strands into desired sizes by a pelletizer. When the pellet body is colored, the colorant and the olefin resin are supplied to the extruder together, and the two are kneaded under heating and extrusion-molded. In the colored resin particle body thus produced, the colorant is impregnated into the interior of the resin particle body. In this case, the L value (a) measured on the cross section of the resin particle body substantially coincides with the L value of the particle body before the SWCNTs are attached. The mass of the resin particles may be, for example, 0.1mg to 5mg, more preferably 0.5mg to 2mg, and still more preferably 0.8mg to 1.8 mg.

When the foamed pellet is produced, if the pellet body composed only of the foamed layer is to be produced, the resin pellet composed of a single olefin resin may be produced. When it is desired to produce a pellet body having a sheath-core type multilayer structure including a foamed layer and a coating layer, a two-layer structure strand in which the olefin resin as the foamed layer is covered with the olefin resin as the coating layer is produced in extrusion molding, and then a resin pellet may be produced from the strand.

Next, the obtained resin particles are dispersed in an aqueous dispersion medium such as water, and then sealed in a pressurized container such as an autoclave together with the dispersion medium. The foaming agent is added to the pressurized container, and the pressure and heat are applied while stirring, thereby impregnating the foaming agent into the resin particles. By releasing the pressurized state of the pressurized container after the foaming agent is sufficiently impregnated in the resin particles, bubbles are formed in the resin particles by the expansion of the foaming agent. As a result, the particle body can be obtained.

In addition, in the dispersion medium, a dispersant and/or a dispersion aid may be added as necessary to uniformly disperse the resin particles in the dispersion medium. Examples of the dispersant include inorganic substances that are hardly soluble in water, such as alumina, tricalcium phosphate, magnesium pyrophosphate, zinc oxide, kaolin, mica, and talc. These dispersants may be used alone, or two or more of them may be used in combination. The lower limit of the mass ratio of the resin particles to the dispersant (resin particles/dispersant) is preferably 20, and more preferably 30. The upper limit of the mass ratio of the resin particles to the dispersant (resin particles/dispersant) is preferably 2000, and more preferably 1000. The dispersant remains on the surface of the expanded main particle body. It is considered that by coating SWCNTs on the surface of such a particle body, the SWCNTs on the surface of the expanded particle are wound around the surface of the particle body in a state of including the above-described dispersant present on the surface of the particle body, and adhere to the surface of the particle body.

Examples of the dispersing aid include anionic surfactants such as sodium dodecylbenzenesulfonate and sodium alkane sulfonate. These dispersing aids may be used alone or in combination of two or more. The lower limit of the mass ratio of the dispersant to the dispersion aid (dispersant/dispersion aid) is preferably 1, and more preferably 2. The upper limit of the mass ratio of the dispersant to the dispersing aid (dispersant/dispersing aid) is preferably 500, and more preferably 100.

Examples of the blowing agent include hydrocarbons such as butane, pentane and hexane, halogenated hydrocarbons such as trichlorofluoromethane, dichlorofluoromethane and tetrachlorodifluoroethane, inorganic gases such as carbon dioxide, nitrogen and air, and water. These blowing agents may be used alone or in combination of two or more.

After the particle body having the foamed layer is obtained as described above, the surface of the particle body is coated with the dispersion liquid in which SWCNTs are dispersed. In this case, it is preferable to stir the dispersion and the particle body in a state where a shearing force or a frictional force is applied to the dispersion and the particle body in a state where the volume of the dispersion is sufficiently smaller than the volume of the particle body. More specifically, the lower limit of the coating amount of SWCNT is preferably 1m²The surface of the above-mentioned main particle body is stirred so as to be 0.1mg, preferably 0.3 mg. Further, the upper limit of the coating amount of SWCNT is preferably 1m²The surface of the above-mentioned main particle body is stirred so as to be 10.0mg, preferably 8.0mg or less.

In this case, when the particle host is brought into contact with the SWCNTs, a large shear load is applied to attach the SWCNTs to the particle host, and therefore, the SWCNTs can be more effectively inhibited from falling off from the particle host. Further, in this case, the variation in the amount of SWCNTs adhering to the particle body can be further reduced. When the apparent density of the particle body is set to a specific range as described above, the particle body has a specific surface shape suitable for SWCNT adhesion. Therefore, by stirring while applying a shear force to the particle body, the variation in the amount of SWCNTs adhering to the particle body can be further reduced. As a result, SWCNTs can be more firmly and uniformly held on the surface of the particle body.

After that, the dispersion liquid is dried to remove the dispersion medium from the particle main body, whereby expanded particles can be obtained.

When the expanded beads are used to produce an expanded bead molded article, for example, a method of filling the cavity of a mold with expanded beads and then introducing a high-temperature gas such as steam into the cavity can be employed. The foamed particles in the cavity are heated by the high temperature gas. This makes it possible to obtain a foamed molded article of expanded particles corresponding to the shape of the cavity while welding the expanded particles to each other.

The foamed molded article obtained in this way has1 × 10 omega of 1 × 10¹⁰Average surface resistivity of Ω or less. The average surface resistivity of the foamed particle-shaped article is less than 1X 10⁴In the case of Ω, the expanded particle molded article has electrical conductivity, and therefore, when used as a packaging container, for example, electrification of the packaged article can be suppressed. The average surface resistivity of the expanded-particle molded article was 1X 10⁴1 × 10 over omega¹⁰When Ω or less, the foamed molded particle has electrostatic diffusibility. The foamed molded particle having electrostatic diffusibility is useful for protecting a packaged object having a relatively low withstand voltage, such as an organic EL device or a high-density integrated circuit, because it can release static electricity slowly when it comes into contact with the charged packaged object.

On the other hand, the average surface resistivity in the foamed molded article of the expanded particles exceeds 1X 10¹⁰In the case of Ω, the foamed particle molded article itself may be easily charged. Therefore, when the charged expanded particle molded body comes into contact with an object, static electricity is easily discharged from the expanded particle molded body to the object. From the viewpoint of more easily avoiding such troubles due to static electricity, the upper limit of the average surface resistivity of the expanded particle molded article is preferably 1 × 10⁹Ω, more preferably 1 × 10⁸Omega. The lower limit of the average surface resistivity of the expanded particle molded article is preferably 1 × 10⁵Ω, more preferably 1 × 10⁶Ω。

In the expanded particle molded article obtained by in-mold molding the expanded particles, SWCNTs more uniformly adhere to each expanded particle constituting the expanded particle molded article than in the conventional expanded particle molded article to which a conductive substance adheres. Therefore, even a molded body having a complicated shape can exhibit uniform electrical conductivity and electrostatic diffusibility, as compared with the case where a dispersion liquid of SWCNT or the like is directly applied to the molded body. Therefore, even a molded article having a complicated shape is less likely to cause coating unevenness. In addition, when the surface resistivity is measured at various positions on the surface of the molded body, variations in the surface resistivity of the molded body can be reduced. Specifically, the ratio (C)/(D) of the maximum value (C) of the surface resistivity to the minimum value (D) of the surface resistivity of the expanded particle molded article is preferably 2.9 or less, more preferably 2.8 or less, still more preferably 2.5 or less, and particularly preferably 2.0 or less. The lower limit of the ratio (C)/(D) of the maximum value (C) of the surface resistivity to the minimum value (D) of the surface resistivity of the expanded particle molded article is substantially 1.

In addition, SWCNTs are uniformly adhered to the respective expanded beads of the expanded bead molded article obtained by in-mold molding the expanded beads. Therefore, unlike the case where a conductive material such as SWCNT is directly applied to the surface of the molded article, the cut surface of the molded expanded particle has electrical conductivity or electrostatic diffusibility even when the molded article is cut. This is believed to be because SWCNTs adhere to individual foam particles. The upper limit of the surface resistivity of the inside (i.e., cut surface) of the expanded particle molded article is preferably 1 × 10¹⁴Omega, more preferably 1 × 10¹⁰Omega. In addition, the lower limit of the surface resistivity of the inside (i.e., cut surface) of the expanded particle molded body is preferably 1 × 10⁵Omega, more preferably 1 × 10⁷Ω。

[ examples ] A method for producing a compound

Examples of the expanded beads and the expanded bead molded article will be described. In this example, expanded particles having SWCNTs adhered to the surface of the particle body were produced using the following materials (table 1, examples 1 to 3). In order to compare these examples, expanded particles were prepared in which multi-walled carbon nanotubes (hereinafter referred to as "MWCNTs") as conductive materials were attached to the surfaces of the particle bodies (table 1, comparative examples 1 to 2).

The materials used in this example are specifically as follows.

Particle body (achromatic): the particle comprises a foamed layer comprising an ethylene-propylene random copolymer and a coating layer comprising an ethylene-butene-propylene random copolymer in a non-foamed state, the coating layer covering the surface of the foamed layer.

Particle body (coloured): granules comprising a foamed layer comprising an ethylene-propylene random copolymer.

Kind of dispersion

TB002L：SWCNT Dispersion (manufactured by KJ Special paper Co., Ltd., SWCNT having an average diameter of 1.6nm, an average length of 5 μm or more, and a specific surface area of 500m²/g)。

K1004M: MWCNT dispersion (MWCNT made by KJ Special paper Co., Ltd., having an average diameter of 8 to 15nm, an average length of 26 μm, and a specific surface area of 260m²/g)

N7006L: MWCNT dispersion (MWCNT having an average diameter of 9.5nm, an average length of 1.5 μm, and a specific surface area of 250 to 300m, manufactured by KJ Special paper Co., Ltd.)²/g)

Colorants

As the colorant, a master batch containing a quinacridone-based red pigment is used.

The method of making the particle body is as follows.

An achromatic particle body

In the production of the pellet body, a co-extruder was used, in which a foaming layer forming extruder having an inner diameter of 65mm and a covering layer forming extruder having an inner diameter of 30mm were arranged in parallel, and a die capable of performing multi-strand co-extrusion was attached to the outlet side. A master batch of an ethylene-propylene random copolymer (MFR: 7g/10 min, melting point 142 ℃) as a polypropylene resin and zinc borate as a cell regulator was fed to a foaming layer-forming extruder, and they were melt-kneaded at 200 to 230 ℃ in the extruder. An ethylene-butene-propylene random copolymer (MFR: 6g/10 min, melting point 131 ℃) was fed to an extruder for forming a coating layer, and the resultant was melt-kneaded at 200 to 230 ℃ in the extruder.

Then, the mass ratio of the foaming layer to the coating layer from the co-extruder is defined as the foaming layer: coating layer 97: mode 3 the melt-kneaded product was co-extruded into a strand shape and water-cooled to obtain a strand having a plurality of layers. The obtained strand was cut by a pelletizer so that the mass of the resin pellets was 1.3mg on average, to obtain resin pellets in an unfoamed state having a plurality of layers. The L/D ratio, i.e., the ratio of the length to the diameter, of the resin pellets was 2.5, and the content of zinc borate in the foamed layer was 1000 mass ppm.

1kg of the above resin particles, 0.3 parts by mass of a dispersant, 0.01 parts by mass of a dispersion aid, and 0.004 parts by mass of a surfactant were sealed in a closed container together with 3L of water as a dispersion medium, based on 100 parts by mass of the resin particles. In this example, kaolin was used as a dispersant, sodium alkylbenzenesulfonate was used as a surfactant, and aluminum sulfate was used as a dispersion aid.

Next, carbon dioxide as a blowing agent was supplied into the closed container until the pressure in the container reached 3.1 MPa. Thereafter, the inside of the vessel was heated while being stirred, so that the temperature in the vessel became 145 ℃. After the temperature in the vessel reached 145 ℃, the temperature was maintained for 15 minutes. Thereafter, the closed vessel was opened, and the contents were released to atmospheric pressure, thereby foaming the resin particles. Through the above operations, a multilayered particle body was obtained.

Coloured particle bodies

When producing a colored particle body, first, a master batch of a colorant is produced by the following method. The colorant and the ethylene-propylene random copolymer were heated and melted at 160 ℃ and kneaded, and then formed into a sheet. The obtained sheet was cut with a pelletizer to obtain a master batch in which 20 mass% of the colorant was dispersed in the ethylene-propylene random copolymer.

A master batch of an ethylene-propylene random copolymer (MFR: 7g/10 min, melting point 142 ℃, ethylene ratio 3.1%) as a polypropylene resin and zinc borate as a bubble control agent were fed to an extruder together with the master batch of the colorant, and melt-kneaded at 200 to 230 ℃ in a single-layer extruder. Subsequently, the ethylene-propylene random copolymer in a molten state was extruded into a strand shape and water-cooled to obtain a strand. The obtained strands were cut in the same manner as for the achromatic particle bodies, to obtain resin particles in an unfoamed state. Further, the content of zinc borate in the resin particles was 500 mass ppm, and the content of the colorant was 10000 mass ppm.

The resin particles obtained above were foamed in the same manner as the achromatic particle body, thereby obtaining an achromatic single-layer particle body.

As shown in table 1, the color tone of the particle body used in examples 1 to 3 and comparative examples 1 to 2 was an achromatic color, and the color tone of the particle body used in example 4 was a chromatic color shown in the table.

Immobilization of Carbon Nanotubes (CNTs)

After the dispersion liquid in the amount shown in table 1 was added to 100g of the main particle body, the main particle body and the dispersion liquid were stirred by a paddle stirrer under the conditions shown in these tables. While stirring, the CNTs in the dispersion repeatedly contact the particle body and apply a shearing force to the particle body, thereby immobilizing the CNTs in the dispersion on the surface of the particle body. Thereby, SWCNTs or MWCNTs can be attached to the surface of the particle host.

The expanded beads (Table 1, examples 1 to 4 and comparative examples 1 to 2) thus obtained were measured for apparent density and color tone. Further, a foamed particle molded body was produced using the foamed particles, and evaluation of the fusion rate, measurement of the density of the molded body, measurement of the surface resistivity, and measurement of the color tone were performed. The coating amount of CNTs shown in table 1 was calculated based on the CNT concentration of the dispersion, the addition amount of the dispersion to the particle body, and the surface area of the particle body.

Apparent density of the expanded particles

After accurately weighing the mass of the foamed particle group composed of a plurality of foamed particles, a measuring cylinder filled with water is prepared, and the foamed particle group is completely submerged in water using a metal mesh or the like. The amount of rise of the liquid surface at this time was defined as the volume of the expanded particle group. The apparent density of the expanded beads was calculated by dividing the mass of the expanded beads thus obtained by the volume. The apparent density of the expanded beads is shown in the column "apparent density" of table 1.

Color tone of the cross section of the particle body

The expanded beads are cut in approximately halved fashion to expose the cross section of the bead main body. The cross section of the main particle body was measured using a micro-facet spectrocolorimeter ("VSS 7700" manufactured by japan electro-chromatic industries, ltd.) to obtain color coordinates in CIE1976L a b color space. In the acquisition of color coordinates, five randomly selected positions were measured for the bubble film portion of the cross section of one particle body using 50 foamed particles.

More specifically, as the light source, JIS Z8720: 2012, and a standard light source which emits the light source C in accordance with JIS Z8722: 2009 by the method for measuring a reflecting object. The measurement light was irradiated to the measurement area of 0.5mm phi, and a value based on the tristimulus value of the 2-degree visual field was obtained. This value is converted to color coordinates in L a b color space. The column "L × value (a) of the particle body" in table 1 shows the arithmetic mean of L × values (a) of the cross section of the particle body. Further, although not shown in table 1, the particle body of example 4 having a chromatic color had an a value (F) of 46.9 and a b value (G) of-5.9.

Color tone of expanded particles

The color tone of the surface of the expanded particles was measured by the same method as the method for measuring the color tone of the particle main body except that the measurement position was changed from the cross section of the particle main body to the surface of the expanded particles, and color coordinates in the CIE1976L a b color space were obtained. In the columns "L value (B) of expanded beads" and "coefficient of variation of L value (B)" of table 1, the average value L of L value (B) is shown_avAnd the coefficient of variation L of the value of L_cv. Further, although not shown in table 1, the expanded beads of example 4 having a chromatic color had an a value (H) of 44.9 and a b value (I) of-5.7.

Production of expanded bead molded article, evaluation of minimum molding pressure, and evaluation of fusion bonding ratio

A mold having a flat-plate-shaped cavity having a length of 250mm, a width of 200mm and a thickness of 50mm was prepared, and the cavity was filled with foamed particles. Subsequently, steam was supplied into the cavity at a gauge pressure of 0.3mpa (g), and the expanded beads were heated and fused to each other, and were molded into a shape corresponding to the cavity. The expanded particle molded article was obtained by the above-described procedure. In this example, the molded expanded beads taken out of the mold were left to stand in an oven adjusted to 60 ℃ for 12 hours, and the molded expanded beads were dried and cured.

The column entitled "fusion rate" in table 1 shows the fusion rate of the expanded bead molded article. Specifically, the value of the welding ratio is a value measured by the following method. First, the expanded bead molded body is bent and broken so as to be approximately equally divided in the longitudinal direction. The number of expanded beads having peeled off from the interface between expanded beads and the number of expanded beads having broken inside were counted by visually observing the broken surface thus exposed. Then, the ratio of the number of expanded particles broken inside the expanded particles to the total number of expanded particles exposed at the broken surface, that is, the total of the number of expanded particles peeled at the interface between expanded particles and the number of expanded particles broken inside is calculated. The welding ratio was defined as a value of the ratio in percent (%). The fusion bonding ratio of the expanded bead molded article is preferably 60% or more, more preferably 70% or more, and still more preferably 80% or more. The upper limit of the fusion rate of the expanded bead molded article is 100%.

Measurement of molded body Density of expanded particle molded body

The molded body density of the expanded particle molded body was determined by dividing the mass of the expanded particle molded body by the volume of the expanded particle molded body. The expanded particle molded article is submerged in water, and the apparent volume of the expanded particle molded article is determined by the rise in the water level. The molded article density of the expanded particle molded article is shown in the column of "molded article density" in table 1.

Surface resistivity

By a method based on JIS C2170: in the method 2004, the surface resistivity of the expanded particle molded article was measured. Specifically, the expanded bead molded article was first allowed to stand for 1 day at a temperature of 23 ℃ and 50% RH for curing. Next, ten measurement positions were randomly set from the flat portion on the skin surface of the expanded particle molded body at the center portion. At the ten measurement positions, the surface resistivity was measured using a resistivity meter ("Hiresta MCP-HT 450" manufactured by Mitsubishi chemical analysis and science corporation). As the probe, "URS" manufactured by Mitsubishi chemical analysis science and technology Co., Ltd was used.

Further, the surface resistivity is less than 1X 10⁴In the case of Ω, the surface resistivity was measured in the same manner as in the above method except that "Loresta MCP-T610" manufactured by mitsubishi chemical analysis co.

The column entitled "average surface resistivity" in table 1 shows the arithmetic average of the surface resistivities of six points excluding the upper two points and the lower two points from among the ten-point measurement values of the surface resistivities obtained by the above measurement. In the column of "maximum value (C) of surface resistivity", the third measurement value from the upper level among the ten-point measurement values of surface resistivity obtained by the above measurement is described. In the column of "minimum value of surface resistivity (D)", the third measured value from the lower position among the ten-point measured values of surface resistivity obtained by the above measurement is described. In the column "(C)/(D)" in the table, the value obtained by dividing the maximum value (C) by the minimum value (D) is shown.

L value of expanded particle shaped body

The color tone of the surface of the molded foam particles was measured using a spectrophotometer ("CM-5" manufactured by konica minolta japan), and color coordinates in CIE1976L a b color space were obtained. The color coordinates are acquired a plurality of times by using different measurement objects. The column "L value (E)" in table 1 shows the average value of L values of the expanded bead molded bodies obtained by the multiple measurements. In the column "(B)/(E)" in the table, the ratio of the L value (B) of the surface of the expanded beads divided by the L value (E) of the expanded bead molded body is shown. Although not shown in table 1, the expanded molded article of example 4 having a colored color had an a value of 45.4 and a b value of-3.1.

(Electron microscope photograph of expanded beads)

The surfaces of the expanded beads of example 1 and comparative example 2 were observed with a scanning electron microscope, and an electron micrograph was taken at a magnification of 30000 times. FIG. 1 shows an electron micrograph of the expanded beads of example 1, and FIG. 2 shows an electron micrograph of the expanded beads of comparative example 2.

TABLE 1

As shown in table 1, SWCNTs as a conductive material were attached to the surfaces of the particle bodies of examples 1 to 4. As shown in the electron micrograph of fig. 1, SWCNTs adhere to the surface of the expanded particle 1 so as to be entangled with the surface of the particle body 2, kaolin remaining on the surface of the particle body 2, and other SWCNTs. Therefore, by in-mold molding the expanded beads of examples 1 to 4, the SWCNTs can be prevented from falling off from the expanded beads during in-mold molding. As a result, the in-mold molded article of the expanded particles has a desired surface resistivity and a small variation in surface resistance value. Further, by using SWCNT as the conductive substance, desired electrical conductivity or electrostatic diffusibility can be imparted to the foamed molded particle, and the color tone of the foamed molded particle can be made bright.

In comparative examples 1 to 2, MWCNTs were used as the conductive material, and therefore, the amount of MWCNTs to be coated for ensuring the electrical conductivity or electrostatic diffusivity of the expanded particle molded body was larger than in examples 1 to 4. Therefore, the expanded beads of comparative examples 1 to 2 and the expanded bead molded bodies produced using these expanded beads have darker color tones than those of examples 1 to 4.

As shown in the electron micrograph of fig. 2, MWCNTs adhere to the surface of the expanded particles 4 so as to overlap with each other. In such an attached state, it is assumed that a part of the MWCNTs exposed to the outermost surface is not directly in contact with the particle body, but is indirectly held in the particle body via other MWCNTs. Furthermore, it is considered that such MWCNTs are more likely to fall off from the expanded particles than MWCNTs that are in direct contact with the particle bulk.

In addition, the expanded bead molded bodies of comparative examples 1 to 2 have a larger value of the ratio (C)/(D) of the maximum value (C) to the minimum value (D) of the surface resistivity than the expanded bead molded bodies of examples 1 to 4.

This is considered to be because the MWCNT coating amount is increased and the MWCNT is more likely to fall off from the particle bulk than the SWCNT, and therefore the amount of MWCNT falling off from the expanded particle during in-mold molding is increased, and variation in the amount of MWCNT present on the surface of the expanded particle molded body is increased.

The embodiment of the expanded particles and the expanded particle molded article according to the present invention is not limited to the embodiment of the above example, and the configuration can be appropriately modified within a range not to impair the gist thereof.

Claims

1. A foamed particle characterized by comprising, in a main particle,

the expanded particles have:

a pellet body having a foamed layer made of an olefin resin; and

a single-layered carbon nanotube attached to a surface of the particle body,

the foamed particles are conductive or semiconductive.

2. The expanded particles according to claim 1,

the coating amount of the single-layer carbon nano tube is 1m per²The surface of the main particle body of (a) is 0.1mg to 10.0 mg.

3. The expanded particles according to claim 1 or 2,

by JIS Z8722: 2009 is 40 to 80, and the difference (a) - (B) between the L value (a) and the L value (B) measured on the surface of the expanded particle is more than 0 and 10 or less.

4. The expanded particles according to any one of claims 1 to 3,

the single-walled carbon nanotube has an average diameter of 1nm to 10nm and an average length of 1 [ mu ] m or more.

5. The expanded particles according to any one of claims 1 to 4,

the pellet body has a foamed layer made of an olefin resin and a coating layer made of an olefin resin and coating the foamed layer.

6. The expanded particles according to any one of claims 1 to 5,

the softening temperature of the surface of the particle body is 145 ℃ or lower.

7. The expanded particles according to any one of claims 1 to 6,

the particle body has a foamed layer comprising a propylene-ethylene random copolymer.

8. The expanded particles according to any one of claims 1 to 7,

the single-walled carbon nanotube has an average diameter of 1nm to 10nm, and the value obtained by dividing the average length of the single-walled carbon nanotube by the average diameter is 100 or more.

9. The expanded particles according to any one of claims 1 to 8,

by JIS Z8722: the coefficient of variation of the L value (B) measured on the surface of the expanded beads by the method specified in 2009 is 0.15 or less.

10. The expanded particles according to any one of claims 1 to 9,

the foamed particles are colored.

11. The expanded particles according to any one of claims 1 to 10,

the expanded beads have an apparent density of 20g/L to 100 g/L.

12. An expanded-particle molded article obtained by in-mold molding the expanded particles according to any one of claims 1 to 11,

the foamed molded article has an average surface resistivity of 1X 10 omega to 1X 10 omega¹⁰Omega is less than or equal to.

13. The expanded particle molding according to claim 12,

the ratio (C)/(D) of the maximum value (C) of the surface resistivity of the expanded particle molded article to the minimum value (D) of the surface resistivity is 2.9 or less.