Foamed particle shaped body

Abstract

This invention relates to a foamed particle molded body, which is composed of multiple layers of foamed particles. The multiple layers of foamed particles have a core layer in a foamed state, using polypropylene resin as the base resin, and a coating layer covering the core layer. The coating layer is in a non-foamed state and uses a thermoplastic elastomer as the base polymer. The dynamic friction coefficient of the foamed particle molded body is 1.0 to 3.0, the ratio of the static friction coefficient to the dynamic friction coefficient is 0.4 to 0.9, and the molded body density is 30 kg / m³. 3 Above 300kg / m 3 the following.

Description

Technical Field

[0001] This invention relates to foamed particle molded articles. Background Technology

[0002] Compared to polystyrene foam particles, polypropylene resin foam particles formed by in-mold molding exhibit superior chemical resistance, impact resistance, and compressive strain recovery. Therefore, polypropylene resin foam particles are widely used as impact-absorbing materials, thermal insulation materials, and various packaging materials in a wide range of fields, including food containers, packaging cushioning materials for electrical and electronic components, automotive bumpers, interior components, building components such as residential insulation materials, and general merchandise. However, to address the molding and processing difficulties caused by the crystallinity and heat resistance of propylene resins, improvements to the in-mold molding method using propylene resin foam particles are being sought, and research is underway on molded bodies using propylene resin foam particles coated with a resin different from the foam layer.

[0003] Patent documents 1 and 2 disclose a multilayer foamed particle structure consisting of a core layer and an outer layer of polypropylene resin, with the aim of obtaining a molded body having good formability, rigidity, and heat resistance under low pressure. For example, Patent document 1 discloses a method for manufacturing polypropylene resin foamed particles and a molded body, in which the melting point of the polypropylene resin in the outer layer and the melting point of the polypropylene resin in the core layer satisfy a specific relationship, the multilayer foamed particles with an outer layer thickness of 30 μm or less are impregnated with a foaming agent, and the multilayer resin particles impregnated with the foaming agent in a heated and softened state are foamed.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2004-68016

[0007] Patent Document 2: Japanese Patent Application Publication No. 2012-126816 Summary of the Invention

[0008] The technical problem that the invention aims to solve

[0009] As mentioned above, when polypropylene foamed particle molded bodies are used, for example, as bundled containers, they exhibit superior strength compared to polystyrene foamed particle molded bodies. Furthermore, compared to conventional polyethylene containers and other plastic containers, polypropylene foamed particle molded bodies are lightweight and offer superior protection. However, when handling such bundled containers with the bundled items wrapped around them, the surface of the foamed particle molded body changes due to friction with the bundled items. This may lead to a deterioration in the appearance of the foamed particle molded body surface in contact with the bundled items, or a reduction in the gripping force of the foamed particle molded body in contact with the bundled items. Moreover, if the appearance of the molded body deteriorates, it may become difficult to maintain the original gripping performance of the foamed particle molded body during repeated use.

[0010] Therefore, the technical problem of the present invention is to provide a foamed particle molded body with excellent grip, whose appearance is not easily changed by friction, and which can withstand repeated use.

[0011] Solution to the above technical problems

[0012] After in-depth research, the inventors discovered that by setting the foamed particles constituting the polypropylene resin foamed particle molded body as multi-layered foamed particles, setting the coating layer of the multi-layered polypropylene resin foamed particles as non-foamed and composed of thermoplastic elastomer, and setting the dynamic friction coefficient, static friction coefficient, and density of the molded body to a specific range, the above-mentioned technical problems can be solved.

[0013] That is, the present invention is a foamed particle molded body composed of multiple layers of foamed particles. The multiple layers of foamed particles have a core layer in a foamed state, using polypropylene resin as the base resin, and a coating layer covering the core layer. The coating layer is in a non-foamed state and uses a thermoplastic elastomer as the base polymer. The dynamic friction coefficient of the foamed particle molded body is 1.0 to 3.0, the ratio of the static friction coefficient to the dynamic friction coefficient is 0.4 to 0.9, and the molded body density is 30 kg / m³. 3 Above 300kg / m 3 the following.

[0014] Furthermore, details are as follows: [1]

[0016] A foamed particle molded body is composed of multiple layers of foamed particles having a core layer in a foamed state with polypropylene resin as the base resin and a covering layer covering the core layer.

[0017] The coating layer is in a non-foamed state.

[0018] The coating layer uses a thermoplastic elastomer as the base polymer.

[0019] The coefficient of dynamic friction of the foamed particle molded body is above 1.0 and below 3.0.

[0020] The ratio of the static friction coefficient to the dynamic friction coefficient of the foamed particle molded body is between 0.4 and 0.9.

[0021] The bulk density of the foamed particle molded body is 30 kg / m³. 3 Above 300kg / m 3 the following. [2]

[0023] As described above [1], the coefficient of dynamic friction of the substrate polymer of the coating layer is 1 or higher. [3]

[0025] As described in [1] or [2] above, the flexural modulus of the substrate resin of the core layer is between 500 MPa and 1500 MPa. [4]

[0027] The foamed particle molded body as described in any of [1] to [3] above, wherein the core layer contains an antistatic agent. [5]

[0029] The foamed particle molded body described in any of [1] to [4] above has a static friction coefficient of 0.7 or more and 2 or less. [6]

[0031] The foamed particle molded body as described in any of [1] to [5] above, wherein the static friction coefficient of the substrate polymer of the coating layer is 2 or higher. [7]

[0033] The foamed particle molded body as described in any of [1] to [6] above, wherein the thermoplastic elastomer is one or more selected from the group consisting of olefin thermoplastic elastomers, styrene thermoplastic elastomers and polyurethane thermoplastic elastomers. [8]

[0035] The foamed particle molded body as described in any of [1] to [7] above, wherein the hardness of the substrate polymer of the coating layer is 65 or higher and 95 or lower according to a hardness tester. [9]

[0037] In the foamed particle molded body described in any of [1] to [8] above, the mass ratio of the core layer to the coating layer (core layer / coating layer) is 85 / 15 or more and 99.5 / 0.5 or less.

[10]

[0039] The foamed particle molded body described in any of [1] to [9] above has a 25% compressive stress of 0.20 MPa or more and 0.80 MPa or less.

[11]

[0041] A packaging container comprising a foamed particle molded body as described in any one of [1] to

[10] above.

[0042] Invention Effects

[0043] According to the present invention, a foamed particle molded article with excellent grip, minimal change in appearance due to friction, and the ability to withstand repeated use can be obtained. Furthermore, the foamed particle molded article is particularly suitable for use as a packaging container. Attached Figure Description

[0044] Figure 1 This is a conceptual diagram of the load-displacement curve when the coefficient of friction is measured using the foamed particle molded body of the present invention.

[0045] Figure 2 This is a conceptual diagram of the load-displacement curve when a stick-slip phenomenon occurs due to the measurement of the coefficient of friction using a foamed particle molded body that does not meet the conditions of this invention. Detailed Implementation

[0046] [Foamed Particle Molding Body]

[0047] The foamed particle molded body of the present invention is a foamed particle molded body composed of multiple layers of foamed particles. The multiple layers of foamed particles have a core layer in a foamed state, using polypropylene resin as the base resin, and a covering layer encapsulating the core layer. The covering layer is in a non-foamed state and uses a thermoplastic elastomer as the base polymer. The dynamic friction coefficient of the foamed particle molded body is 1.0 to 3.0, the ratio of the static friction coefficient to the dynamic friction coefficient is 0.4 to 0.9, and the molded body density is 30 kg / m³. 3 Above 300kg / m 3 the following.

[0048] Furthermore, in this specification (the present invention), "A or above" is synonymous with "A and above," indicating the value (A) and values ​​greater than the value (A). Similarly, in this specification (the present invention), "B or below" is synonymous with "B and below," indicating the value (B) and values ​​less than the value (B). That is, in this specification (the present invention), both "above" and "below" include the value.

[0049] <Friction coefficient of foamed particle molded body>

[0050] In the foamed particle molded body of the present invention, the ratio of the static friction coefficient of the foamed particle molded body to the dynamic friction coefficient of the foamed particle molded body is 0.4 or more and 0.9 or less.

[0051] By making the ratio of the static friction coefficient to the dynamic friction coefficient of the foamed particle molded body within the aforementioned range, it is possible to make it a foamed particle molded body with excellent grip, especially one whose appearance is not easily altered by friction, and which can withstand repeated use. Although the reason for this is not yet clear, it can be considered as follows.

[0052] In the foamed particle molded body of the present invention, since the ratio of the static friction coefficient of the foamed particle molded body to the dynamic friction coefficient of the molded body is within the aforementioned range, that is, the dynamic friction coefficient and the static friction coefficient have similar values, it becomes difficult for stick slip phenomenon caused by friction to occur when the packaged object moves due to vibration, etc., and the appearance is less likely to change due to friction, thus allowing it to withstand repeated use. On the other hand, since the dynamic friction coefficient becomes a relatively large value, it can be considered to have excellent grip.

[0053] In particular, in this invention, it can be considered that the above-mentioned frictional properties can be achieved by making the foamed particles constituting the foamed particle molded body into multi-layered foamed particles, and by making its coating layer a thermoplastic elastomer as the substrate and in a non-foamed state.

[0054] From the above perspective, the lower limit of the ratio of the static friction coefficient to the dynamic friction coefficient of the foamed particle molded body is preferably 0.45 or more, more preferably 0.47 or more, even more preferably 0.60 or more, and even more preferably 0.70 or more. Furthermore, the upper limit of this ratio is preferably 0.80 or less, more preferably 0.75 or less. If the static friction coefficient of the foamed particle molded body is within the above-mentioned preferred range, the strength and cushioning properties of the molded body are also excellent.

[0055] Furthermore, in the foamed particle molded body of the present invention, the coefficient of kinetic friction of the foamed particle molded body is 1.0 or more and 3.0 or less. The lower limit of the coefficient of kinetic friction is 1.0 or more, preferably 1.1 or more, and more preferably 1.2 or more. In addition, the upper limit of the coefficient of kinetic friction is 3.0 or less, preferably 2.5 or less, and more preferably 2.0 or less.

[0056] By ensuring that the frictional characteristics of the foamed particle molded body satisfy the above-mentioned relationship, and the coefficient of dynamic friction is within the range described above, it becomes easier to retain the packaged item again when the molded body moves due to vibration, etc., resulting in excellent grip.

[0057] Furthermore, the dynamic friction coefficient can be measured according to JIS K7125 using the method described in the embodiments. Similarly, the static friction coefficient can be measured according to JIS K7125 using the method described in the embodiments. Based on the obtained static friction coefficient and the dynamic friction coefficient, the ratio of the static friction coefficient of the foamed particle molded body to its dynamic friction coefficient can be calculated.

[0058] In the foamed particle molded body of the present invention, the static friction coefficient of the foamed particle molded body is preferably 0.7 or more and 2 or less. The lower limit of the static friction coefficient is preferably 0.7 or more, more preferably 0.8 or more, and even more preferably 0.9 or more. Furthermore, the upper limit of the static friction coefficient is preferably 2 or less, more preferably 1.8 or less, and even more preferably 1.19 or less.

[0059] exist Figure 1 A conceptual diagram showing the load-displacement curve when measuring the friction coefficient of the foamed particle molded body of the present invention is presented. Furthermore, in Figure 2 A conceptual diagram showing the load-displacement curve when measuring the friction coefficient of a foamed particle molded body that does not meet the conditions of this invention is presented. Figure 2 The load-displacement curve of the foamed particle molded body is as follows: the coating layer is not in a non-foamed state, the substrate polymer of the coating layer does not contain thermoplastic elastomers, and the ratio of the static friction coefficient to the dynamic friction coefficient of the foamed particle molded body exceeds 0.9.

[0060] exist Figure 2 As can be seen from the load-displacement curve, vibration occurs due to friction during the friction coefficient measurement, resulting in a stick-slip phenomenon. On the other hand, in Figure 1 As can be seen from the load-displacement curve, there is no vibration due to friction during the friction coefficient measurement, thus making it difficult to produce stick-slip phenomenon and exhibiting excellent grip.

[0061] <Bulk density of foamed particle molded body>

[0062] In the foamed particle molded body of the present invention, the molded body density is 30 kg / m³. 3 Above 300kg / m 3 The lower limit of the density of the molded body is 30 kg / m³. 3 The above is preferably 40kg / m 3 The above, more preferably 55 kg / m 3 That's all. Furthermore, the upper limit of the density of the molded body is 300 kg / m³. 3 The following is preferred: 100 kg / m 3 The following is more preferably 70 kg / m 3 the following.

[0063] By making the density of the molded body within the aforementioned range, a lightweight molded body with excellent cushioning properties is obtained. Furthermore, it can be considered that by forming bubbles and bubble films of foamed particles with a molded body density as described above, the contact state between the surface of the foamed particle molded body and the packaged object becomes capable of exhibiting the aforementioned frictional properties.

[0064] [Multi-layer foamed particles]

[0065] The foamed particle molded body of the present invention is composed of multiple layers of foamed particles. The multiple layers of foamed particles have a core layer in a foamed state with polypropylene resin as the base resin and a covering layer covering the core layer. The covering layer is in a non-foamed state and the covering layer is a thermoplastic elastomer as the base polymer.

[0066] <Covering layer>

[0067] The core layer is covered by a coating layer of the multilayer foamed particles, and the coating layer is in a non-foamed state. By making the coating layer non-foamed, it is possible to make it exhibit specific frictional properties on its surface when it becomes a foamed particle molded body. Furthermore, it can be considered that by making the coating layer non-foamed, it is possible to reduce the unevenness caused by air bubbles on the surface of the foamed particles, resulting in a foamed particle molded body with a good appearance.

[0068] Here, the non-foaming state refers not only to a state in which there are absolutely no bubbles in the coating layer, but also to a state in which there are only a very small number of extremely tiny bubbles, which is essentially a non-foaming state. Furthermore, the state in which there are absolutely no bubbles in the coating layer also includes the state in which temporarily formed bubbles burst and disappear.

[0069] The coating layer preferably covers more than 50% of the surface area of ​​the core layer, more preferably more than 70%, although it can practically cover 100% of the area, but as an upper limit, it is approximately 90%.

[0070] The manufacturing method of multilayer foamed particles will be described below, but by, for example, omitting bubble nucleating agents from the polymer used as the coating layer, increasing the melting point difference between the coating layer and the core layer, and setting the mass ratio of the core layer to the coating layer (core layer / coating layer) to a specific range, the coating layer can be made into a non-foamed state. Furthermore, the coating layer can be formed into a non-foamed state under conditions where the core layer foams but the coating layer does not, or under conditions where even if the coating layer foams, the bubbles cannot be stably maintained and bubble rupture occurs. From the above viewpoint, the amount of bubble nucleating agent in the coating layer is preferably less than 2 parts per 100 parts of the base polymer of the coating layer, more preferably less than 1 part, and even more preferably, the coating layer does not contain bubble nucleating agents.

[0071] The coating layer preferably contains a lubricant such as erucamide or calcium stearate. The amount of the lubricant added is preferably 0.05 parts by weight or less than 0.2 parts by weight relative to 100 parts by weight of the substrate polymer of the coating layer.

[0072] (The substrate polymer of the coating layer)

[0073] The coating layer uses a thermoplastic elastomer as the base polymer. It can be considered that by using a thermoplastic elastomer as the base polymer for the coating layer, the coating layer becomes exceptionally soft, and the surface of the foamed particle molded body exhibits excellent gripping properties. On the other hand, since the coating layer can be considered to be in a non-foamed state, the surface of the foamed particle molded body forms a smooth surface condition. Therefore, it can be considered that while maintaining excellent gripping properties, it is difficult to produce a stick-slip phenomenon, thus forming a surface condition of the foamed particle molded body with specific frictional characteristics.

[0074] "The coating layer uses a thermoplastic elastomer as the base polymer" means that the polymer of the coating layer uses a thermoplastic elastomer as the main component. Specifically, the content of thermoplastic elastomer in the polymer of the coating layer is preferably 90% by mass or more, more preferably 95% by mass or more, further preferably 97% by mass or more, and even more preferably 99% by mass or more. There is no upper limit, and it can be 100% by mass or less. The polymer of the coating layer may also be composed solely of thermoplastic elastomer.

[0075] Furthermore, other thermoplastic resins may be included in the coating layer without impairing the effects of the present invention. Examples of other thermoplastic resins include polyolefin resins and polystyrene resins, with polyolefin resins being preferred, and polypropylene resins being more preferred.

[0076] The lower limit of the coefficient of dynamic friction of the substrate polymer of the coating layer is preferably 1 or more, more preferably 1.2 or more, and even more preferably 1.5 or more. In addition, the upper limit is preferably 3 or less.

[0077] The static friction coefficient of the substrate polymer of the coating layer is preferably 2 or higher, more preferably 2.3 or higher, and even more preferably 2.5 or higher. Furthermore, the upper limit of the static friction coefficient of the substrate polymer of the coating layer is preferably 3.5 or lower.

[0078] In this invention, the coefficient of friction of the substrate polymer of the coating layer is preferably within the range described above.

[0079] The dynamic and static friction coefficients of the substrate polymer of the coating layer can be determined according to JIS K7125 using the same method as that used for the friction coefficients of the aforementioned foamed particle molded articles. The test was conducted at a speed of 500 mm / min.

[0080] The ratio of the static friction coefficient to the dynamic friction coefficient of the substrate polymer of the coating layer [static friction coefficient / dynamic friction coefficient] is preferably 1.5 or more and 2 or less.

[0081] When the substrate polymer of the coating layer is crystalline and has a melting point, the melting point of the substrate polymer of the coating layer is preferably 5°C or lower than that of the substrate resin of the core layer, more preferably 8°C or lower, and even more preferably 10°C or lower. Furthermore, the substrate polymer of the coating layer is preferably 30°C or lower than that of the substrate resin of the core layer, more preferably 20°C or lower, and even more preferably 15°C or lower.

[0082] Furthermore, from the viewpoint of improving formability, the lower limit of the melting point of the substrate polymer of the coating layer is preferably 116°C or higher, more preferably 120°C or higher, and even more preferably 120°C or higher. Furthermore, the upper limit of the melting point of the substrate polymer of the coating layer is preferably 143°C or lower, more preferably 140°C or lower, and even more preferably 130°C or lower. Additionally, the melting point of the substrate polymer is measured based on differential scanning calorimetry of heat flux as described in JIS K7121:2012.

[0083] The lower limit of the heat of fusion of the substrate polymer of the coating layer is preferably 20 J / g or more, more preferably 30 J / g or more, and even more preferably 40 J / g or more. Furthermore, the upper limit of the heat of fusion of the substrate polymer is preferably 100 J / g or less, more preferably 80 J / g or less.

[0084] In addition, the heat of fusion of the substrate polymer of the coating layer is measured using a differential scanning calorimeter based on JIS K7122:2012.

[0085] From the viewpoint of flexibility, the lower limit of the flexural modulus of the substrate polymer of the coating layer is preferably 10 MPa or more, more preferably 15 MPa or more, and even more preferably 20 MPa or more. Furthermore, the upper limit of the flexural modulus of the substrate polymer of the coating layer is preferably 50 MPa or less, more preferably 35 MPa or less, and even more preferably 25 MPa or less.

[0086] In addition, the flexural modulus of the substrate polymer of the coating layer is a value measured according to JIS K7171:2016.

[0087] Furthermore, the lower limit of the hardness of the substrate polymer of the coating layer is preferably 65 or higher, more preferably 70 or higher. Furthermore, the upper limit of the hardness of the substrate polymer of the coating layer is preferably 95 or lower, more preferably 90 or lower. The hardness is measured using a Type A hardness tester. That is, the hardness (HDA, Shore A) of the substrate polymer measured using a Type A hardness tester is preferably 65 or higher, more preferably 70 or higher. Furthermore, it is preferably 95 or lower, more preferably 90 or lower. If the hardness of the substrate polymer is within the above range, a foamed particle molded body with superior softness can be obtained.

[0088] In addition, the hardness (HDA) of the substrate polymer is measured according to JIS K7215:1986.

[0089] Furthermore, the proportion of ethylene component units in the substrate polymer is preferably 45% by mass or more, more preferably 55% by mass or more, and even more preferably 65% ​​by mass or more.

[0090] The substrate polymer constituting the coating layer preferably contains a lubricant such as erucamide or calcium stearate. The content of the lubricant is preferably 0.05 parts by weight or more and 0.2 parts by weight or less per 100 parts by weight of the substrate polymer of the coating layer.

[0091] (Thermoplastic elastomer)

[0092] The thermoplastic elastomer used as the substrate polymer for the coating layer is not particularly limited, and examples include olefin-based thermoplastic elastomers (TPO), styrene-based thermoplastic elastomers (TPS), and polyurethane-based thermoplastic elastomers (TPU). Specifically, the thermoplastic elastomer is preferably one or more selected from the group consisting of olefin-based thermoplastic elastomers (TPO), styrene-based thermoplastic elastomers (TPS), and polyurethane-based thermoplastic elastomers (TPU). These thermoplastic elastomers can be used alone or in combination. From the viewpoint of adhesion between the core layer and the coating layer, olefin-based thermoplastic elastomers (TPO) are preferred.

[0093] [Olefin thermoplastic elastomers (TPO)]

[0094] Examples of TPOs include thermoplastic elastomers with polyolefins such as polypropylene and polyethylene as hard segments and α-olefin copolymers and ethylene rubbers as soft segments; and block copolymers having hard segments composed of polyethylene blocks and soft segments composed of ethylene / α-olefin copolymer blocks.

[0095] In block copolymers having hard segments composed of polyethylene blocks and soft segments composed of ethylene / α-olefin copolymer blocks, examples of polymers constituting the polyethylene blocks include ethylene homopolymers and copolymers of ethylene with α-olefins having 3 to 8 carbon atoms. On the other hand, examples of ethylene / α-olefin copolymer blocks include blocks of copolymers of ethylene with α-olefins having 3 to 20 carbon atoms. Furthermore, examples of α-olefins copolymerized with ethylene include propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 3-methyl-1-butene, and 4-methyl-1-pentene. From the viewpoint of industrial availability, various properties, and economic efficiency, α-olefins copolymerized with ethylene are preferably propylene, 1-butene, 1-hexene, or 1-octene, with 1-octene being particularly preferred.

[0096] The content of polyethylene component in the block copolymer is preferably 45% or more, more preferably 65% ​​or more.

[0097] The proportion of ethylene units in the polyethylene block is preferably 95% by mass or more, more preferably 98% by mass or more, relative to the mass of the polyethylene block. On the other hand, the proportion of α-olefin units in the ethylene / α-olefin copolymer block is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more, relative to the mass of the ethylene / α-olefin copolymer block.

[0098] Furthermore, the proportion of ethylene components in the TPO is preferably 45% by mass or more, more preferably 55% by mass or more, and even more preferably 65% ​​by mass or more.

[0099] In addition, the proportions of polyethylene blocks and ethylene / α-olefin copolymer blocks can be calculated based on data obtained from differential scanning calorimetry (DSC) or nuclear magnetic resonance (NMR).

[0100] Commercially available products can be used as TPOs. Examples include "Infuse" (an olefin block copolymer manufactured by Dow Chemical Co., Ltd.), "Affinity" (another olefin block copolymer manufactured by Dow Chemical Co., Ltd.), "THERMORUN" (a olefin block copolymer manufactured by Mitsubishi Chemical Co., Ltd.), "MILASTOMER" (a olefin block copolymer manufactured by Mitsui Chemical Co., Ltd.), "TAFMER" (a olefin block copolymer manufactured by Mitsui Chemical Co., Ltd.), "Sumitomo TPE" (a olefin block copolymer manufactured by Sumitomo Chemical Co., Ltd.), and "PRIME TPO" (a olefin block copolymer manufactured by Priman Polymer Co., Ltd.).

[0101] The lower limit of the density of the olefin-based thermoplastic elastomer is preferably 700 kg / m³. 3 The above, more preferably 800 kg / m 3That's all. Furthermore, the upper limit of the density is preferably 1000 kg / m³. 3 The following is more preferably 900 kg / m 3 Below. If within the above range, foamed particle molded articles with excellent heat resistance can be easily obtained.

[0102] When the olefin-based thermoplastic elastomer is crystalline, the lower limit of its melting point is preferably 110°C or higher, more preferably 115°C or higher, even more preferably 116°C or higher, and still more preferably 120°C or higher. Furthermore, the upper limit of its melting point is preferably 150°C or lower, more preferably 145°C or lower, even more preferably 143°C or lower, still more preferably 140°C or lower, and still more preferably 130°C or lower. When the melting point of the olefin-based thermoplastic elastomer is within the above range, it becomes a foamed particle molded body with particularly excellent heat resistance.

[0103] In addition, the melting point of the olefin thermoplastic elastomer is measured based on the differential scanning calorimetry of heat flux as described in JIS K7121:2012.

[0104] The melting point of the olefin-based thermoplastic elastomer is preferably at least 5°C lower than that of the core layer's base resin, more preferably at least 8°C lower, and even more preferably at least 10°C lower. Furthermore, the melting point of the olefin-based thermoplastic elastomer is preferably at least 30°C lower than that of the core layer's base resin, more preferably at least 20°C lower, and even more preferably at least 15°C lower.

[0105] The heat of fusion of the olefin-based thermoplastic elastomer is preferably 20 J / g or more, more preferably 30 J / g or more, and even more preferably 40 J / g or more. Furthermore, the heat of fusion of the TPO is approximately 80 J / g or less.

[0106] In addition, the heat of fusion of the olefin thermoplastic elastomer was measured using a differential scanning calorimeter based on JIS K7122:2012.

[0107] The lower limit of the melt flow rate (MFR) of the olefin-based thermoplastic elastomer is preferably 2 g / 10 min or more, more preferably 3 g / 10 min or more, and even more preferably 4 g / 10 min or more, under conditions of 190°C and a load of 2.16 kg. Furthermore, the upper limit of the MFR is preferably 10 g / 10 min or less, more preferably 8 g / 10 min or less, and even more preferably 7 g / 10 min or less. Within the above range, the formation of the coating layer becomes easier when forming multilayer foamed particles. The melt flow rate of the olefin-based thermoplastic elastomer is a value measured according to JIS K7210-1:2014 under conditions of 190°C and a load of 2.16 kg.

[0108] The lower limit of the hardness (HDA, Shore A) of the olefin-based thermoplastic elastomer measured using a Type A hardness tester is preferably 65 or higher, more preferably 70 or higher. Furthermore, the upper limit of the hardness (HDA, Shore A) is preferably 95 or lower, more preferably 90 or lower. If the hardness of the thermoplastic elastomer is within the above range, a foamed particle molded body with superior softness can be obtained.

[0109] In addition, the hardness (HDA) of the olefin thermoplastic elastomer is measured according to JIS K7215:1986.

[0110] From the viewpoint of flexibility, the lower limit of the flexural modulus of the olefin-based thermoplastic elastomer is preferably 10 MPa or more, more preferably 15 MPa or more, and even more preferably 20 MPa or more. Furthermore, the upper limit of the flexural modulus is preferably 50 MPa or less, more preferably 35 MPa or less, and even more preferably 25 MPa or less.

[0111] In addition, the flexural modulus of the olefin thermoplastic elastomer is a value measured according to JIS K7171:2016.

[0112] The lower limit of the coefficient of kinetic friction of the olefin-based thermoplastic elastomer is preferably 1 or more, more preferably 1.2 or more, and even more preferably 1.5 or more. Furthermore, the upper limit is preferably 3 or less.

[0113] The static friction coefficient of the olefin-based thermoplastic elastomer is preferably 2 or higher, more preferably 2.3 or higher, and even more preferably 2.5 or higher. Furthermore, the upper limit of the static friction coefficient of the olefin-based thermoplastic elastomer is preferably 3.5 or lower.

[0114] The dynamic and static friction coefficients of the olefin-based thermoplastic elastomer can be determined according to JIS K7125 using the same method as that used for the friction coefficients of the aforementioned foamed particle molded bodies. The test was conducted at a speed of 500 mm / min.

[0115] The ratio of the static friction coefficient of the olefin-based thermoplastic elastomer to the dynamic friction coefficient of the substrate polymer of the coating layer [static friction coefficient / dynamic friction coefficient] is preferably 1.5 or more and 2 or less.

[0116] Furthermore, from the viewpoint of improving formability, the lower limit of the melting point of the olefin-based thermoplastic elastomer is preferably 116°C or higher, more preferably 120°C or higher, and even more preferably 120°C or higher. Furthermore, the upper limit of the melting point of the olefin-based thermoplastic elastomer is preferably 143°C or lower, more preferably 140°C or lower, and even more preferably 130°C or lower. Additionally, the melting point of the olefin-based thermoplastic elastomer is measured based on differential scanning calorimetry of heat flux as described in JIS K7121:2012.

[0117] The lower limit of the heat of fusion of the olefin-based thermoplastic elastomer is preferably 20 J / g or more, more preferably 30 J / g or more, and even more preferably 40 J / g or more. Furthermore, the upper limit of the heat of fusion of the olefin-based thermoplastic elastomer is preferably 100 J / g or less, more preferably 80 J / g or less.

[0118] In addition, the heat of fusion of the olefin thermoplastic elastomer was measured using a differential scanning calorimeter based on JIS K7122:2012.

[0119] From the viewpoint of flexibility, the lower limit of the flexural modulus of the olefin-based thermoplastic elastomer is preferably 10 MPa or more, more preferably 15 MPa or more, and even more preferably 20 MPa or more. Furthermore, the upper limit of the flexural modulus of the olefin-based thermoplastic elastomer is preferably 50 MPa or less, more preferably 35 MPa or less, and even more preferably 25 MPa or less.

[0120] In addition, the flexural modulus of the olefin thermoplastic elastomer is a value measured according to JIS K7171:2016.

[0121] Furthermore, the hardness (HDA, Shore A) of the olefin-based thermoplastic elastomer measured using a Type A hardness tester is preferably 65 or higher, more preferably 70 or higher. It is also preferably 95 or lower, more preferably 90 or lower. If the hardness of the olefin-based thermoplastic elastomer is within the above range, a foamed particle molded body with superior softness can be obtained.

[0122] In addition, the hardness (HDA) of the olefin thermoplastic elastomer is measured according to JIS K7215:1986.

[0123] The thickness of the coating layer is preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 3 μm or more. On the other hand, its upper limit is preferably 25 μm or less, more preferably 18 μm or less, and even more preferably 15 μm or less.

[0124] If within the above range, it will not hinder the fusion of foamed particles with each other, and the frictional characteristics of the surface of the foamed particle molded body can be set to specific characteristics.

[0125] Furthermore, the mass ratio of the core layer to the covering layer, i.e., the mass ratio of the core layer to the covering layer (core layer / covering layer), is more preferably 85 / 15 or more, further preferably 88 / 12 or more, and even more preferably 90 / 10 or more. More preferably, it is 99.5 / 0.5 or less, further preferably 99 / 1 or less, and even more preferably 95 / 5 or less. By constituting the covering layer within the above-mentioned range, it becomes particularly possible to exert the frictional properties unique to the present invention within the covering layer, and by setting the core layer to a foamed state, foamed particles with excellent cushioning properties for the bundled object can be formed.

[0126] <Core Layer>

[0127] The core layer of the multilayer foamed particles is in a foamed state and uses polypropylene resin as the base resin. Furthermore, "using polypropylene resin as the base resin" means that the resin constituting the core layer uses polypropylene resin as the main component. In this specification, using polypropylene resin as the main component means that the content of polypropylene resin in the base resin is 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more. Although there is no particular upper limit, it is 100% by mass or less.

[0128] (Polypropylene resins)

[0129] In this invention, polypropylene resin refers to, for example, propylene homopolymers, propylene copolymers or mixtures thereof, preferably propylene copolymers or mixtures of propylene homopolymers and propylene copolymers, and more preferably propylene copolymers.

[0130] When the polypropylene resin is an propylene copolymer or a mixture of propylene homopolymer and propylene copolymer, the content of propylene-derived structural units in the polypropylene resin is preferably 50% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass or more, and even more preferably 90% by mass or more. The content of propylene-derived structural units in the polypropylene resin is preferably 99% by mass or less, more preferably 98% by mass or less, further preferably 97% by mass or less, and even more preferably 96% by mass or less.

[0131] Examples of propylene copolymers include copolymers of propylene with ethylene and / or α-olefins having 4 to 20 carbon atoms, such as 1-butene, 1-pentene, 1-hexene, 1-octene, and 4-methyl-1-butene, with copolymers of propylene and ethylene being preferred. Furthermore, the ethylene content in the copolymer of propylene and ethylene is preferably 2% by mass or more, more preferably 2.5% by mass or more. It is also preferably 5% by mass or less, more preferably 4.5% by mass or less.

[0132] To the extent that it does not impede the objective effect of the present invention, the polypropylene resin may also contain resins or elastomers other than the propylene homopolymer or propylene copolymer.

[0133] The content of resins or elastomers other than the propylene homopolymer or propylene copolymer in the polypropylene resin is preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, and even more preferably 1% by mass or less.

[0134] The flexural modulus of the polypropylene resin is preferably 500 MPa or more, more preferably 850 MPa or more, and even more preferably 900 MPa or more. Furthermore, it is preferably 1500 MPa or less, more preferably 1300 MPa or less, and even more preferably 1100 MPa or less. By keeping the flexural modulus within the above range, the bubble film during foaming becomes more robust, further increasing the strength of the foamed particle molded body obtained by molding the foamed particles, making it particularly useful as a packaging container. The flexural modulus can be determined based on JIS K7171 (2008).

[0135] The melting point of the polypropylene resin is preferably 130°C or higher, more preferably 132°C or higher, and even more preferably 135°C or higher. From the viewpoint of heat resistance, the melting point of the polypropylene resin is preferably 148°C or lower, more preferably 145°C or lower, and even more preferably 142°C or lower.

[0136] Furthermore, additives may be appropriately added to the base resin of the core layer, provided that they do not impair the effects of the present invention. Examples of additives include antioxidants, ultraviolet absorbers, antistatic agents, flame retardants, pigments, dyes, nucleating agents, and bubble nucleating agents. The core layer preferably contains an antistatic agent. The content of these additives is preferably 20 parts by weight or less per 100 parts by weight of the base resin forming the core layer, more preferably 5 parts by weight or less. When the core layer contains an antistatic agent, the content of the antistatic agent is preferably 0.2 parts by weight or more per 100 parts by weight of the base resin of the core layer, more preferably 0.5 parts by weight or more. Furthermore, it is preferably 2 parts by weight or less per 100 parts by weight of the base resin of the core layer, more preferably 1 part by weight or less.

[0137] The flexural modulus of the substrate resin of the core layer is preferably 500 MPa or more, more preferably 850 MPa or more, and even more preferably 900 MPa or more. Furthermore, the upper limit of the flexural modulus is preferably 1500 MPa or less, more preferably 1300 MPa or less, and even more preferably 1100 MPa or less. By keeping the flexural modulus within the above range, the bubble film during foaming becomes stronger, and the strength of the foamed particle molded body obtained by molding the foamed particles can be further increased, making it particularly useful as a packaging container. The flexural modulus can be determined based on JIS K7171 (2008).

[0138] The lower limit of the ratio of the flexural modulus of the core layer's substrate resin to the flexural modulus of the coating layer's substrate polymer [core layer / coating layer] is preferably 10, more preferably 26, and even more preferably 30. Furthermore, the upper limit of this ratio is preferably 50, more preferably 50, and even more preferably 50.

[0139] The lower limit of the melting point of the substrate resin is preferably 130°C or higher, more preferably 132°C or higher, and even more preferably 135°C or higher. From the viewpoint of heat resistance, the upper limit of the melting point of the substrate resin is preferably 148°C or lower, more preferably 145°C or lower, and even more preferably 142°C or lower.

[0140] The multilayer foamed particles preferably have one or more melting peaks (high temperature peaks) on the high-temperature side of the inherent melting peak (resin-inherent peak) of the base resin, i.e., polypropylene resin, in the DSC curve of differential scanning calorimetry (DSC).

[0141] These melting peaks can be obtained using the method shown below.

[0142] Specifically, the foamed particles were heated from 23°C to 200°C at a rate of 10°C / minute using a differential scanning calorimeter to obtain DSC curves with more than two melting peaks. The peak with the largest heat of melting was designated as the inherent melting peak of polypropylene resin (resin-specific peak), and the melting peak that appeared at a higher temperature was designated as the high-temperature peak.

[0143] It can be assumed that the DSC curve in this case refers to the DSC curve obtained by the measurement method for the first heating. The endothermic peak caused by the inherent melting of the resin (resin inherent peak) refers to the endothermic peak caused by the inherent melting of the polypropylene resin constituting the foamed particles. It is the peak caused by the endothermic melting of the crystals originally present in the resin constituting the core layer of the foamed particles.

[0144] On the other hand, the endothermic peak on the high-temperature side of the inherent resin peak (high-temperature peak) refers to the endothermic peak that appears in the first DSC curve further up the temperature range than the inherent resin peak. The presence of this high-temperature peak suggests secondary crystallization in the resin. Furthermore, in the DSC curve obtained after heating from 23°C to 200°C at a heating rate of 10°C / min, cooling from 200°C to 23°C at a cooling rate of 10°C / min, and then heating again from 23°C to 200°C at a heating rate of 10°C / min (the second heating DSC curve), only the endothermic peak caused by the melting of the polypropylene resin inherent in the core layer of the multilayer foamed particles is observed. This inherent resin peak appears in both the first and second heating DSC curves; sometimes the temperature of the peak tip differs slightly between the first and second heating curves, but the difference is usually less than 5°C. Therefore, it is possible to identify which peak is the inherent resin peak. This endothermic peak varies depending on the composition of the resin, etc.

[0145] The lower limit of the heat of fusion at the high-temperature peak of the multilayer foamed particles is preferably 5 J / g or more, more preferably 7 J / g or more, and even more preferably 10 J / g or more. Furthermore, the upper limit of the heat of fusion is preferably 40 J / g or less, more preferably 30 J / g or less, and even more preferably 20 J / g or less.

[0146] It can be assumed that by setting the melting heat of the high-temperature peak within such a range, due to the presence of secondary crystallization as a high-temperature peak, the foamed particles become foamed particles with particularly excellent mechanical strength and excellent in-mold formability.

[0147] The lower limit of the average mass of each multilayer foamed particle (the arithmetic mean of the masses of 200 randomly selected particles) is preferably 0.1 mg or more, more preferably 0.2 mg or more, further preferably 0.3 mg or more, and even more preferably 0.4 mg or more. Furthermore, the upper limit of the average mass is preferably 20 mg or less, more preferably 10 mg or less, further preferably 5 mg or less, and even more preferably 2 mg or less.

[0148] <Foamed Particle Molding Body>

[0149] The foamed particle molded body of the present invention is a foamed particle molded body composed of multiple layers of foamed particles. The multiple layers of foamed particles have a core layer in a foamed state, using polypropylene resin as the base resin, and a covering layer encapsulating the core layer. The covering layer is in a non-foamed state and uses a thermoplastic elastomer as the base polymer. The dynamic friction coefficient of the foamed particle molded body is 1.0 to 3.0, the ratio of the static friction coefficient to the dynamic friction coefficient is 0.4 to 0.9, and the molded body density is 30 kg / m³.3 Above 300kg / m 3 the following.

[0150] Due to the frictional properties of the foamed particle molded body as described above, the packaged object has excellent grip, making it difficult to cause surface damage and change its appearance, thus making it suitable for repeated use.

[0151] Such frictional properties can be considered to be related to the fact that the foamed particle molded body is formed from multiple layers of foamed particles, the coating layer of which uses a thermoplastic elastomer as the base polymer, and the coating layer is in a non-foamed state. Specifically, it can be considered that the gripping force is provided by the softness of the thermoplastic elastomer in the coating layer, and that the non-foamed state of the coating layer makes it difficult to produce a sticky or slippery phenomenon, thus exhibiting the unique frictional properties of the foamed particle molded body of the present invention. Furthermore, it can be considered that by making the molded body density of the foamed particle molded body within the above-mentioned range, the foamed layer is in a specific foamed state, thereby providing cushioning for the packaged object and exhibiting the frictional properties within the foamed particle molded body.

[0152] The lower limit of the 25% compressive stress of the foamed particle molded article of the present invention is preferably 0.20 MPa or more, and more preferably 0.30 MPa or more. Furthermore, the upper limit of the 25% compressive stress is preferably 0.80 MPa or less, and more preferably 0.50 MPa or less.

[0153] Within the aforementioned range, it becomes a foamed particle molded body with particularly excellent cushioning properties.

[0154] The aforementioned 25% compressive stress is based on the compressive stress (MPa) at 25% deformation when compressed at a rate of 10 mm / min, as measured by JIS K6767:1999.

[0155] On the surface of the foamed particle molded body, the area ratio of the exposed area of ​​the coating layer of the foamed particles constituting the foamed particle molded body is preferably more than 50% and less than 80%.

[0156] In particular, when the shape of the foamed particles used in this invention is cylindrical, from the viewpoint of making the obtained foamed particle molded body have good frictional characteristics, it is preferable to set the area ratio of the coating layer component of the foamed particles in the foamed particle molded body (the proportion of the area exposed by the coating layer of the foamed particles) to be 50% or more. The ratio of the length L to the diameter D of the foamed particles, L / D, is 1.2 or more.

[0157] The area ratio of the foam particle coating layer component on the surface of the foam particle molded body can be obtained by image analysis of the surface of the foam particle molded body using image analysis software such as NS2K-Pro manufactured by Nano System Co., Ltd. Specifically, a photograph is taken of the surface of the foam particle molded body, which is as flat as possible, with an appropriate wide range. In this photograph, the portions of the foam particle coating layer component and the portions of the foam particle core layer component on the surface of the foam particle molded body are binarized into black and white using image analysis software, and the area ratio of each portion is calculated. The area ratio of the foam particle coating layer component can be calculated using the following formula.

[0158] The percentage of the coating layer component in the foamed particles = (Area occupied by the coating layer component of the foamed particles / (Area occupied by the coating layer component of the foamed particles + Area occupied by the core layer component of the foamed particles) × 100

[0159] Furthermore, when it is difficult to distinguish the exposed portion of the foam particle coating layer on the surface of the foam particle molded body, image analysis can be easily performed by coloring the resin forming the coating layer.

[0160] <Manufacturing Method of Multilayer Foamed Particles>

[0161] There are no restrictions on the manufacturing method of the multilayer foamed particles, but the following method is preferred.

[0162] As a preferred manufacturing method for the multilayer foamed particles, the following method can be used: dispersing multilayer particles having a core layer with a polypropylene resin as the base resin and a coating layer covering the core layer with a thermoplastic elastomer as the base polymer in a dispersion medium, impregnating the multilayer particles with a foaming agent, and releasing it under low pressure (dispersion medium release foaming method).

[0163] (Manufacturing of multilayer particles)

[0164] The multilayer foamed particles used in the manufacture of the present invention have a core layer and a coating layer.

[0165] First, the resin used as the core layer, including bubble nucleating agents and other additives as needed, is blended with the polypropylene resin and supplied to the first extruder for heating and kneading to form the resin melt of the core layer.

[0166] Furthermore, other additives, as needed, are blended with the polymer of the coating layer and supplied as a coating layer to a second extruder for heating and kneading to form a resin melt for the coating layer. Additionally, it is preferable not to incorporate a bubble nucleating agent into the coating layer at this time. By omitting the bubble nucleating agent, it becomes easier to obtain a non-foamed coating layer.

[0167] Next, the resin melt of the core layer and the resin melt of the coating layer are fed into a co-extrusion die, where the fluids of the resin melt of the core layer and the resin melt of the coating layer are combined and layered. The layered resin melt can then be granulated from the extruder using methods such as wire harness cutting, thermal cutting, or underwater cutting.

[0168] Furthermore, when manufacturing multilayer particles, the lower limit of the mass ratio of the core layer to the coating layer (core layer / coating layer) is preferably set to 85 / 15 or more, more preferably 88 / 12 or more, and even more preferably 90 / 10 or more. The upper limit of this ratio is preferably set to 99.5 / 0.5 or less, more preferably 99 / 1 or less, and even more preferably 95 / 5 or less. In addition, when manufacturing multilayer particles, the core layer can contain additives such as zinc borate, antistatic agents, and weather-resistant agents as bubble nucleating agents. Furthermore, the coating layer can also contain additives such as lubricants, antistatic agents, and weather-resistant agents.

[0169] In particular, when an antistatic agent is added to the core layer, although the reason is not clear, it is preferable because it facilitates demolding during molding. The core layer preferably contains an antistatic agent. There are no particular limitations on the antistatic agent; examples include nonionic surfactants such as hydroxyalkylamines, hydroxyalkyl monoetheramines, polyoxyalkylene alkylamines, glycerol fatty acid esters, and polyoxyethylene alkyl ethers; anionic surfactants such as alkyl sulfonates, alkylbenzene sulfonates, and alkyl phosphates; and cationic surfactants such as octyl dimethyl ethyl ammonium ethyl sulfate, lauryl dimethyl ethyl ammonium ethyl sulfate, dialcyl dimethyl ammonium chloride, tetraalkyl ammonium salts, and trialkyl benzyl ammonium salts. Furthermore, these antistatic agents can be used alone or in combination. Nonionic surfactants are preferred. The content of the antistatic agent in the core layer is preferably 0.2 parts by mass or more, more preferably 0.5 parts by mass or more, relative to 100 parts by mass of the base resin of the core layer. Furthermore, it is preferably less than 1 part by mass, more preferably less than 1 part by mass, relative to 100 parts by mass of the base resin of the core layer.

[0170] From the viewpoint of manufacturing stability, it is preferable to include a lubricant such as erucamide or calcium stearate in the coating layer. The content of the lubricant is preferably 0.05 parts by weight or more and 0.2 parts by weight or less relative to 100 parts by weight of the substrate polymer constituting the coating layer.

[0171] In this case, it also makes demolding during molding easier.

[0172] The particle size of the multilayer particles is preferably 0.1 mm or more, more preferably 0.3 mm or more. Furthermore, it is preferably 3.0 mm or less, more preferably 1.5 mm or less. Furthermore, the length-to-diameter ratio of the multilayer particles is preferably 0.5 or more, more preferably 1.0 or more. Furthermore, it is preferably 5.0 or less, more preferably 3.0 or less. Furthermore, the average mass of each particle (the arithmetic mean of the masses of 200 randomly selected particles) is preferably adjusted to be 0.1 mg or more and 20 mg or less, more preferably 0.2 mg or more, further preferably 0.3 mg or more, and even more preferably 0.4 mg or more. Furthermore, it is more preferably 10 mg or less, further preferably 5 mg or less, and even more preferably 2 mg or less. The multilayer particles are cylindrical in shape.

[0173] In addition, the particle size, length / diameter ratio and average mass of multilayer particles in the wire harness cutting method can be adjusted by appropriately changing the extrusion speed, pull speed and cutting speed when extruding the resin melt.

[0174] (Manufacturing of multi-layer foamed particles)

[0175] An aqueous dispersion medium can be used as the dispersion medium for dispersing the multilayer particles obtained as described above within a closed container. This aqueous dispersion medium is a dispersion medium with water as its main component.

[0176] In the preferred dispersion medium release foaming method used in this invention, a dispersant is preferably added to the dispersion medium to prevent the multilayer particles heated in the container from melting together. As a dispersant, any material that prevents the multilayer particles from melting together in the container can be either organic or inorganic; for ease of processing, particulate inorganic materials are preferred. Examples include natural or synthetic clay minerals such as alumina, kaolin, mica, and clay; alumina; titanium dioxide; basic magnesium carbonate; basic zinc carbonate; calcium carbonate; and iron oxide. One type or a combination of two or more types can be used. Natural or synthetic clay minerals are preferred. The dispersant is preferably added at a rate of 0.001 to 5 parts by mass per 100 parts by mass of the multilayer particles.

[0177] Furthermore, when using a dispersant, it is preferable to use anionic surfactants such as sodium dodecylbenzenesulfonate, sodium alkyl sulfonate, or sodium oleate as dispersing aids. The dispersing aid is preferably added at a rate of 0.001 to 1 part by weight per 100 parts by weight of the multilayer particles.

[0178] As a blowing agent for foaming multilayer particles, a physical blowing agent is preferred. Examples of physical blowing agents include inorganic and organic types. Inorganic physical blowing agents include carbon dioxide, air, nitrogen, helium, and argon. Organic physical blowing agents include aliphatic hydrocarbons such as propane, butane, and hexane; cyclic aliphatic hydrocarbons such as cyclopentane and cyclohexane; and halogenated hydrocarbons such as chlorofluoromethane, trifluoromethane, 1,1-difluoromethane, 1-chloro-1,1-dichloroethane, 1,2,2,2-tetrafluoroethane, chloromethane, chloroethane, and dichloromethane. Furthermore, the physical blowing agent can be used alone or in combination with two or more other types. In addition, inorganic and organic physical blowing agents can also be mixed. From the viewpoint of environmental impact and manageability, inorganic physical blowing agents are preferred, and carbon dioxide is more preferred.

[0179] The amount of foaming agent added relative to 100 parts by weight of the multilayer particles is preferably 0.1 parts by weight or more, more preferably 0.5 parts by weight or more. Furthermore, it is preferably 30 parts by weight or less, more preferably 15 parts by weight or less.

[0180] In the foamed particle manufacturing process, as a method for impregnating multilayer particles with a foaming agent, it is preferable to use an aqueous dispersion medium in which multilayer particles are dispersed in a closed container, and a foaming agent is injected while heating, thereby impregnating the multilayer particles with the foaming agent.

[0181] The internal pressure of the sealed container during foaming is preferably 0.5 MPa(G) or higher, more preferably 0.8 MPa(G) or higher. On the other hand, the upper limit of the internal pressure of the sealed container is preferably 4 MPa(G) or lower, more preferably 3 MPa(G) or lower. If it is within the above range, foamed particles can be safely manufactured without the danger of damage or explosion of the sealed container. In addition, the temperature is raised to 100°C or higher and 200°C or lower, preferably 130°C or higher and 160°C or lower, and maintained at this temperature for about 5 minutes or 30 minutes, after which the foamable multilayer particles are released from the sealed container under low pressure to foam them.

[0182] The lower limit of the average bubble diameter of the foamed particles is preferably 20 μm or more, more preferably 50 μm or more, and even more preferably 80 μm or more. Furthermore, the upper limit of the average bubble diameter is preferably 400 μm or less, more preferably 300 μm or less, and even more preferably 200 μm or less. If the average bubble diameter is within this range, a foamed particle molded body with excellent in-mold formability, excellent dimensional recovery after molding, and excellent mechanical properties such as compressibility can be obtained.

[0183] The lower limit of the apparent density of the multilayer foamed particles is preferably 10 kg / m³. 3 The above, preferably 30 kg / m3 That's all. Furthermore, the upper limit of the apparent density is preferably 100 kg / m³. 3 The following is more preferably 80 kg / m 3 The following applies. If the range is specified, the resulting foamed particles are preferred due to their cushioning and frictional properties for the packaged material.

[0184] Furthermore, the multilayer foamed particles obtained as described above can be further foamed with a higher foaming ratio (lower apparent density) by increasing the internal pressure through air pressurization and then heating them with steam or the like to make them foam (two-stage foaming).

[0185] <Manufacturing of Foamed Particle Moldings>

[0186] The foamed particle molded body of the present invention is a molded body composed of the aforementioned multilayer foamed particles, which can be obtained by in-mold molding of the foamed particles.

[0187] Specifically, it can be obtained by in-mold molding of multilayer foamed particles having a foamed core layer with polypropylene resin as the base resin and a covering layer covering the core layer, wherein the covering layer is in a non-foamed state and the covering layer uses a thermoplastic elastomer as the base material.

[0188] In-mold forming involves filling foamed particles into a mold and heating them using a heating medium such as steam. Specifically, after filling the mold with foamed particles, a heating medium such as steam is introduced into the mold to heat the particles, causing them to foam and fuse together, thereby obtaining a foamed particle molded body with a formed space. Furthermore, the in-mold forming in this invention is preferably performed using a pressure forming method (for example, Japanese Patent Publication No. 51-22951). That is, the foamed particles are pre-pressurized using a pressurized gas such as air to increase the pressure inside the bubbles of the foamed particles. After adjusting the pressure inside the foamed particles to a pressure 0.01 MPa to 0.3 MPa higher than atmospheric pressure, the foamed particles are filled into the mold under atmospheric pressure or reduced pressure. Then, a heating medium such as steam is supplied into the mold to heat and fuse the foamed particles. In addition, molding can be performed using a compression filling molding method (Japanese Patent Publication No. Hei 4-46217), in which foamed particles pressurized to above atmospheric pressure are filled into a molding die using compressed gas, and then a heating medium such as steam is supplied to the mold cavity for heating, causing the foamed particles to fuse. Alternatively, molding can be performed using an atmospheric pressure filling molding method (Japanese Patent Publication No. Hei 6-49795), in which foamed particles with high secondary foaming power obtained under special conditions are filled into the mold cavity of a molding die under atmospheric pressure or reduced pressure, and then a heating medium such as steam is supplied for heating, causing the foamed particles to fuse. Molding can also be performed using a method combining the above methods (Japanese Patent Publication No. Hei 6-22919), etc.

[0189] In the manufacture of foamed particle molded articles, the shrinkage rate is preferably 3% or less, more preferably 2.5% or less.

[0190] Furthermore, in the obtained foamed particle molded body, the weld ratio is preferably 80% or more, and more preferably 90% or more. If it is within the above range, the foamed particles will not be damaged when gripping the packaged object, thus resulting in superior grip.

[0191] In the obtained foamed particle molded body, the bending strength of the molded body is preferably 0.2 MPa or more and 2 MPa or less, and from the viewpoint of being able to form a better packaging container, it is preferably 0.3 MPa or more and 1.5 MPa or less.

[0192] Furthermore, the compressive strength (25%) of the foamed particle molded body is preferably 0.1 MPa or more and 1 MPa or less, and from the viewpoint of protecting the packaged item, it is preferably 0.2 MPa or more and 0.8 MPa or less.

[0193] [Packaging Containers]

[0194] The packaging container of the present invention is composed of the foamed particle molded body. Specifically, the packaging container of the present invention is composed of a foamed particle molded body, which is composed of multiple layers of foamed particles. The multiple layers of foamed particles have a core layer in a foamed state with polypropylene resin as the base resin and a covering layer covering the core layer. The covering layer is in a non-foamed state and is made of thermoplastic elastomer as the base polymer. The dynamic friction coefficient of the foamed particle molded body is 1.0 to 3.0, the ratio of the static friction coefficient to the dynamic friction coefficient of the foamed particle molded body is 0.4 to 0.9, and the molded body density of the foamed particle molded body is 30 kg / m³. 3 Above 300kg / m 3 the following.

[0195] Since the packaging container of the present invention is composed of the foamed particle molded body, its shape can be adjusted by the shape of the mold used for molding. The shape of the packaging container can be selected to be most suitable according to the shape, size, weight, and material of the packaged item. Examples of packaging container shapes include box-shaped, tray-shaped, and sheet-shaped.

[0196] The foamed particle molded body constituting the packaging container of the present invention has excellent grip and its appearance is not easily changed by friction, allowing it to withstand repeated use. Therefore, the packaging container of the present invention is suitable for packaging heavy objects or precision parts. In addition, it is also suitable for packaging items that are easily deteriorated or damaged by dropping or vibration during handling.

[0197] [Example]

[0198] The invention will then be described in further detail by way of examples, but the invention is not limited to these examples in any way.

[0199] [Physical Properties and Evaluation]

[0200] The following measurements and evaluations were performed on the resins, foamed particles, and foamed particle molded articles used in the examples and comparative examples. The results are shown in Tables 1 and 2. Furthermore, the evaluation of the foamed particles or foamed particle molded articles was conducted after they were conditioned for 2 days at 50% relative humidity, 23°C, and 1 atm.

[0201] (Coefficient of friction)

[0202] The coefficient of friction of the foamed particle molded body was measured according to JIS K7125 by the following method.

[0203] A sample with a single-sided skin (63mm x 63mm x 10mm, referring to the surface in contact with the mold during in-mold forming, not the cutting surface) was cut from the foamed particle molded body obtained through the examples and comparative examples, and used as a test piece. Furthermore, the foamed particle molded body of the test sample was obtained through in-mold forming on a smooth mold surface.

[0204] A 3mm thick, smooth, soft polyvinyl chloride resin sheet was placed on a horizontal surface, with the sample positioned with its surface area (40cm²) as the guide. 2 The sample is placed on top of the vinyl chloride sheet with the sheet facing down, and a counterweight is then placed on top to achieve a normal force of 9.8 N. Additionally, a 1 mm thick felt is used to cover the top of the sample to apply uniform pressure.

[0205] The measurements were performed using a TENSILON universal testing machine. The sample was moved horizontally for 70 mm at a speed of 100 mm / min on a soft vinyl chloride sheet, and the load (unit: N) and the distance moved were recorded to obtain the load-displacement curve.

[0206] A conceptual diagram of the load-displacement curve is shown below. Figure 1 and Figure 2 As shown.

[0207] In the load-displacement curve, the initial maximum load value (static load) (F) is... S The static friction coefficient (μ) is obtained by dividing by the normal force (9.8 N). S Specifically, this is expressed by the following formula. Furthermore, the maximum value can be obtained, for example, by obtaining the load-displacement curve ( Figure 1 Use a magnified image to make a judgment.

[0208] static friction coefficient (μ) S ) = F S / 9.8

[0209] In the load-displacement curve, the average value of the dynamic load in the detected measured displacements with a displacement (movement distance) of 10mm to 60mm is defined as the dynamic load (F). D Divide this by the normal force (9.8 N) to obtain the coefficient of kinetic friction (μ) in this invention. D Specifically, it is represented by the following formula.

[0210] coefficient of kinetic friction (μ) D ) = F D / 9.8

[0211] In addition, in this invention, since the value of dynamic friction after the relative displacement movement is initially unstable due to the sample being a foam, a value starting from a displacement of 10 mm is adopted.

[0212] In addition, besides changing the test speed from 100 mm / min to 500 mm / min, non-foamed test samples were prepared to measure the test conditions and operations of the foamed particle molded body. The dynamic and static friction coefficients of the base polymer or thermoplastic elastomer of the coating material were calculated using the formula. Furthermore, the accuracy of the displacement gauge was 0.001 mm or higher.

[0213] Table 3 shows the dynamic friction coefficient, static friction coefficient, and the ratio of static friction coefficient to dynamic friction coefficient of the substrate polymer of the coating material.

[0214] (Density of the molded body)

[0215] The volume of the foamed particle molded body is calculated based on its external dimensions. The mass of the foamed particle molded body is divided by the aforementioned volume, and the resulting value is taken as the density of the molded body ρ(D) [kg / m³]. 3 ].

[0216] (Melting point and heat of fusion)

[0217] The melting point (Tm) was determined using the method described in JIS K7121 (1987) as "the melting temperature was measured after a certain heat treatment" (the heating and cooling rates in the condition adjustment of the test piece were both set to 10°C / minute).

[0218] A DSC curve was plotted using a DSC apparatus (TA Instruments DSC Q1000) with a heating rate of 10°C / min. The temperature of the peak at which the resin melts was absorbed on the DSC curve was taken as the melting point. Furthermore, if multiple endothermic peaks were present on the DSC curve, the peak with the largest endothermic peak area was taken as the melting point.

[0219] The heat of melting is calculated from the peak area of ​​the endothermic peak accompanying the melting of the resin on the DSC curve from the start to the end of melting.

[0220] (Flexural modulus)

[0221] The flexural modulus was determined according to JIS K7171:2008. As a test piece, a 4mm sheet was produced by hot-pressing the test piece at 230°C. A standard test piece (80mm long × 10mm wide × 4mm thick) was cut from this sheet. Furthermore, the radius of the indenter (R1) and the radius of the support platform (R2) were both 5mm, the distance between the support points was 64mm, and the test speed was 2mm / minute.

[0222] (Heat of fusion at the high temperature peak of the foamed particles)

[0223] 1–3 mg of the inner layer of the foamed particles were collected and measured using a differential scanning calorimeter (TA Instruments DSC Q1000) at a rate of 10 °C / min, from 23 °C to 200 °C, to obtain a DSC curve with more than one melting peak. The resin-specific peaks mentioned below are designated as A, and the high-temperature peaks appearing at higher temperatures are designated as B.

[0224] Draw a straight line (α-β) connecting point α on the DSC curve, which corresponds to 80°C, and point β on the DSC curve, which corresponds to the melting point T of the foaming particles. The melting point T refers to the intersection of the DSC curve on the high-temperature side of high-temperature peak B and the high-temperature side baseline. Next, starting from point γ on the DSC curve corresponding to the valley between the resin's inherent peak A and the high-temperature peak B, draw a straight line parallel to the vertical axis of the graph. The point intersecting this line (α-β) is designated as δ.

[0225] The area of ​​resin intrinsic peak A is the area enclosed by the curve, line segment (α-δ), and line segment (γ-δ) of the resin intrinsic peak A portion of the DSC curve, and is used as the melting heat of the resin intrinsic peak.

[0226] The area of ​​high temperature peak B is the area enclosed by the curve, line segment (δ-β), and line segment (γ-δ) of the high temperature peak B part of the DSC curve, and it is used as the melting heat of the high temperature peak.

[0227] (Shrinkage rate)

[0228] The shrinkage rate [%] of the foamed particle molded body is defined as the ratio of the long side length of the foamed particle molded body to the long side length of the mold. Specifically, it is calculated by (mold long side length [mm] - molded body long side length [mm]) / mold long side length [mm] × 1000. Furthermore, "molded body long side length [mm]" refers to the value obtained by measuring the length of the long side of the foamed particle molded body obtained through the examples and comparative examples after curing at 80°C for 12 hours, slowly cooling, and further curing at 23°C for 6 hours.

[0229] (Welding rate)

[0230] The weld ratio of the foamed particle molded body can be evaluated by the material failure rate on the fracture surface of the bending test. Specifically, the bending fracture surface of the foamed particle molded body (a fracture surface containing more than 100 foamed particles) is observed, and the number of broken foamed particles and the number of foamed particles detached at the interface are counted visually. Then, the percentage of the number of broken foamed particles relative to the total number of broken foamed particles and the number of foamed particles detached at the interface is defined as the weld ratio.

[0231] (Friction test)

[0232] A sample with a length of 50 mm, a width of 50 mm, and a thickness of 15 mm, and a skin surface on at least one side, was cut from the foamed particle mold and fixed in place. A piece of 400-grit sandpaper, with a length of 30 mm and a width of 30 mm, was placed in contact with the skin surface. Under conditions of a load of 1000 g, a test travel distance (horizontal movement) of 8 mm, and a test speed of 60 times / minute, the skin surface of the sample was rubbed with the sandpaper 500 times, and the results were evaluated using the following criteria. Furthermore, referring to the test conditions described in JIS K7204:1999, the test was stopped every 100 rubs to check for sandpaper clogging and remove any powder adhering to the sandpaper.

[0233] (Evaluation Criteria)

[0234] A: The amount of friction (the mass of the foamed particle molded body reduced by the test) is less than 1 mg, and no surface fuzzing was observed after the friction test, and the appearance is good.

[0235] B: The amount of friction (the mass of the foamed particle molded body reduced by the test) is more than 1mg, and fuzzing and poor appearance are observed after the friction test.

[0236] (Grip test)

[0237] When the above friction coefficient measurement was performed using a single-sided skin sample cut from a foamed particle molded body with dimensions of 63mm in length, 63mm in width, and 10mm in thickness, the following benchmarks were used to evaluate whether stick-slip phenomenon occurred.

[0238] (Evaluation Criteria)

[0239] A: No sticky or slippery phenomenon occurred, nor did any frictional noise (the sound produced by the friction of the foamed particle molding during the aforementioned friction coefficient measurement). (Excellent grip)

[0240] B: It produces a slippery feel and a frictional sound. (Poor grip)

[0241] (Bending properties)

[0242] Under the conditions described in the examples and comparative examples, only the mold was changed to produce a plate-shaped foamed particle molded body with dimensions of 300mm in length, 75mm in width, and 25mm in thickness, instead of the molded body with dimensions of 300mm in length, 250mm in width, and 60mm in thickness produced in the examples and comparative examples. Using this molded body as a test piece, a three-point bending test was performed according to the bending test method for large test pieces described in Appendix 1 of JIS K7221-2 (1999), and the stress-strain curve was obtained. The bending stress in the maximum load calculated based on the stress-strain curve was taken as the bending strength of the foamed particle molded body. In addition, the three-point bending test was conducted using a universal testing machine (Autograph (registered trademark) manufactured by Shimadzu Corporation) with a distance of 200mm between the lower support points and a test speed of 10mm / min.

[0243] (Compressive strength (25% compressive stress of the foamed particle molded body))

[0244] As a measure of the stiffness of the foamed particle molded body, test pieces with dimensions of 50 mm in length, 50 mm in width, and 25 mm in thickness were cut from the resin foamed particle molded bodies obtained through the examples and comparative examples without a skin layer. Based on JIS K6767:1999, the compressive stress (MPa) at 25% deformation when compressed at a speed of 10 mm / min was measured.

[0245] (Average bubble diameter)

[0246] The average bubble diameter of the foamed particles was measured according to ASTM D3576-77 as follows.

[0247] More than 50 foamed particles were randomly selected from the foamed particle group. Each particle was cut in half lengthwise, passing through its center, and magnified photographs of its cross-sections were taken. In each cross-sectional photograph, four line segments were drawn at equal angles from the outermost surface of the foamed particle through its center to the outermost surface on the opposite side. The number of bubbles intersecting each line segment was measured. The average chord length of the bubbles was calculated by dividing the total length of the four line segments by the total number of bubbles intersecting the line segments. This average chord length was then divided by 0.616 to calculate the average bubble diameter of each foamed particle. Finally, the average bubble diameter of the foamed particle was calculated by taking the arithmetic mean of these values.

[0248] [raw material]

[0249] The resins and elastomers used in the examples and comparative examples are shown below.

[0250] (1) Abbreviated as PP1 (density 900 g / cm³) 3MFR (2.16 kg, 190 °C) 7 g / 10 min, melting point 141 °C, flexural modulus 950 MPa, ethylene content 3.1%): manufactured by Prattmann Polymers; polypropylene resin, ethylene-propylene random copolymer "J832MZV"

[0251] (2) Abbreviated as PP2 (density 900 g / cm³) 3 MFR (2.16 kg, 190 °C) 7 g / 10 min, melting point 134 °C, flexural modulus 600 MPa, ethylene content 4.2%): manufactured by Prattmann Polymers; polypropylene resin, ethylene-propylene random copolymer "F744NP".

[0252] (3) Abbreviated as PP3 (density 900g / cm³) 3 MFR (2.16 kg, 190℃) 7 g / 10 minutes, melting point 131℃, flexural modulus 650 MPa, ethylene content 3.1%: manufactured by POLYPRO Co., Ltd., Japan; polypropylene resin, propylene / 1-butene / ethylene copolymer "FX4ET"

[0253] (4) Abbreviated as TPO (density 887 g / cm³) 3 MFR (2.16 kg, 190℃) 5 g / 10 min, melting point 119℃, Shore hardness A83, flexural modulus 34 MPa, ethylene content 68%, heat of fusion 54 J / g): manufactured by Dow Chemical Company; olefin thermoplastic elastomer "INFUSE 9530".

[0254] (5) Bubble nucleating agent masterbatch; trade name "CP-130786F" (polypropylene resin (PP); J832MZV, zinc borate concentration 10% by mass)

[0255] (Example 1: Manufacturing of foamed particle molded articles)

[0256] Using only the polypropylene resins shown in Table 1 as the base resin for the core layer, the polypropylene resins are melt-kneaded in an extruder at 180–240°C to obtain a resin melt for the core layer. Simultaneously, using only the elastomers shown in Table 1 as the base polymer for the coating layer, the elastomers are melt-kneaded in an extruder at 180–240°C to obtain a resin melt for the coating layer.

[0257] Next, the resin melt for the core layer and the resin melt for the coating layer are fed into a co-extrusion die. In the die, the resin melt for the coating layer is stacked around the resin melt for the core layer, extruded into a wire bundle shape, water-cooled, cut with a granulator to achieve a mass of about 1.0 mg, and dried to obtain multilayer particles.

[0258] At this point, the mass ratio of the resin melt for the core layer to the resin melt for the coating layer is set to 90 / 10. Furthermore, during the manufacturing of multilayer particles, zinc borate (as a bubble nucleating agent), an antistatic agent (manufactured by Kao Corporation), and an electro-stripping agent TS-8B (0.9 parts per 100 parts by mass of the base resin) (a mixture of higher alcohols, hydroxyalkyl diethanolamide, and glyceryl monostearate) are supplied to the extruder for the resin melt for the core layer. Thus, the base resin contains the aforementioned additives. Additionally, a lubricant (1000 ppm erucamide (0.1 parts per 100 parts by mass of the base polymer)) is supplied to the extruder for the resin melt for the coating layer. Thus, the base polymer contains additives. Then, the resin melt for the coating layer and the resin melt for the core layer are co-extruded to obtain multilayer particles. At this time, the bubble nucleating agent is supplied in the form of masterbatch, so that the substrate resin of the core layer contains 1000 ppm of zinc borate as a bubble nucleating agent, and the substrate polymer of the coating layer does not contain the bubble nucleating agent.

[0259] 50 kg of the multilayer particles and 280 L of water as the dispersion medium were placed together in a 400 L sealed container. Further, for 100 parts by mass of the multilayer particles, 0.008 parts by mass of kaolin as a dispersant, 0.004 parts by mass of a surfactant (sodium alkylbenzene sulfonate), and 0.0002 parts by mass of aluminum sulfate as a dispersing aid were added to the sealed container. Carbon dioxide as a foaming agent was added to the sealed container to achieve a pressure of 1.5 MPa (carbon dioxide pressure). The container was heated to 150.6 °C (foaming temperature) under stirring and maintained at this temperature for 6 minutes. The contents of the container were then released to atmospheric pressure, thus obtaining multilayer foamed particles 1. When the resin particles were foamed with a core layer resin melt to coating layer resin melt mass ratio of 90 / 10, the coating layer thickness in the multilayer foamed particles was 10 μm.

[0260] After applying an internal pressure of 0.18 MPa (G) to a flat molding die measuring 300 mm in length, 250 mm in width, and 60 mm in thickness using air, multiple layers of foamed particles 1 are filled to achieve a 10x ratio. Steam is supplied from both sides of the die for 5 seconds for preheating (venting process). Then, heating is performed from one side of the die until a steam pressure 0.08 MPa (G) lower than the molding pressure of 0.34 MPa (G) is reached. This is repeated from the other side of the die until a steam pressure 0.04 MPa (G) lower than the molding pressure is reached. Heating continues until the molding pressure reaches 0.34 MPa (G) (main heating). After heating, the pressure is released, and the molded body is water-cooled until the surface pressure caused by the foaming force reaches 0.04 MPa (G) (water cooling time 51 seconds). The die is then opened, and the molded body is removed. The resulting molded body is cured in an oven at 80°C for 12 hours to obtain the foamed particle molded body.

[0261] (Examples 2-5)

[0262] Except for changing the raw materials and conditions as shown in Table 1, multilayer foamed particles and foamed particle molded bodies were obtained in the same manner as in Example 1.

[0263] (Comparative Example 1)

[0264] Except for obtaining single-layer resin particles by using only the resin melt for the core layer instead of the resin melt for the coating layer in Example 1, and changing the conditions as shown in Table 2, multi-layer foamed particles and foamed particle molded articles were obtained in the same manner as in Example 1.

[0265] (Comparative Example 2)

[0266] Except that in Example 1 only polypropylene resin (propylene / 1-butene / ethylene copolymer (FX4ET)) was used as the base polymer for the coating layer, and the conditions were changed as shown in Table 2, multilayer foamed particles and foamed particle molded articles were obtained in the same manner as in Example 1.

[0267] (Comparative Examples 3-5)

[0268] Except for using a mixture of olefin thermoplastic elastomer and polypropylene resin as the base polymer for the coating layer in Example 1, and changing the conditions as shown in Table 2, foamed particles and foamed particle molded articles were obtained in the same manner as in Example 1.

[0269] In addition, granules of olefin-based thermoplastic elastomer and polypropylene resin were placed into an extruder for coating layers in the proportions shown in Table 2, and the mixture was fed to a co-extrusion die in the same manner as in Example 1. Furthermore, in Comparative Examples 3 and 5, a bubble nucleating agent was also supplied to the extruder for the resin melt used in the coating layers. This resulted in the coating layers containing 1000 ppm by mass of zinc borate as a bubble nucleating agent.

[0270] [Table 1]

[0271]

[0272] [Table 2]

[0273]

[0274] [Table 3]

[0275]

[0276] It is understood that the foamed particle molded body of the embodiment, by forming the coating layer of the foamed particles with a thermoplastic elastomer, has specific frictional characteristics, thereby exhibiting excellent grip. Therefore, since the foamed particle molded body of the embodiment does not exhibit stick-slip phenomenon in the grip test, its appearance is unlikely to change due to friction, and it can withstand repeated use.

Claims

1. A foamed particle molded body, comprising multiple layers of foamed particles having a core layer in a foamed state with polypropylene resin as the base resin and a covering layer covering the core layer, characterized in that, The coating layer is in a non-foamed state. The coating layer uses a thermoplastic elastomer as the base polymer. The coefficient of dynamic friction of the foamed particle molded body is above 1.0 and below 3.

0. The ratio of the static friction coefficient to the dynamic friction coefficient of the foamed particle molded body is between 0.4 and 0.

8. The bulk density of the foamed particle molded body is 30 kg / m³. 3 Above 300kg / m 3 the following.

2. The foamed particle molded body as described in claim 1, characterized in that, The coefficient of dynamic friction of the substrate polymer of the coating layer is greater than 1.

3. The foamed particle molded body as described in claim 1 or 2, characterized in that, The flexural modulus of the substrate resin of the core layer is between 500 MPa and 1500 MPa.

4. The foamed particle molded article as described in claim 1 or 2, characterized in that, The core layer contains an antistatic agent.

5. The foamed particle molded article as described in claim 1 or 2, characterized in that, The static friction coefficient of the foamed particle molded body is above 0.7 and below 2.

6. The foamed particle molded article as described in claim 1 or 2, characterized in that, The substrate polymer of the coating layer has a static friction coefficient of 2 or higher.

7. The foamed particle molded article as described in claim 1 or 2, characterized in that, The thermoplastic elastomer is selected from one or more of the group consisting of olefin-based thermoplastic elastomers, styrene-based thermoplastic elastomers, and polyurethane-based thermoplastic elastomers.

8. The foamed particle molded article as described in claim 1 or 2, characterized in that, The substrate polymer of the coating layer has a hardness of 65 or higher and 95 or lower on a hardness tester.

9. The foamed particle molded article as described in claim 1 or 2, characterized in that, The mass ratio of the core layer to the covering layer is 85 / 15 or more and 99.5 / 0.5 or less.

10. The foamed particle molded article as described in claim 1 or 2, characterized in that, The 25% compressive stress of the foamed particle molded body is above 0.20 MPa and below 0.80 MPa.

11. A packaging container, characterized in that, It is composed of the foamed particle molded body according to any one of claims 1 to 10.

Images