Method for producing polyolefin resin foam particles and polyolefin resin foam particles

Abstract

A method for producing polyolefin resin foam particles that enables a high foaming ratio and suppresses the formation of excessive foam using talc, and polyolefin resin foam particles containing talc that exhibit a high foaming ratio and suppress the formation of excessive foam are provided. The above manufacturing method involves releasing polyolefin resin particles containing carbon dioxide, which are dispersed in an aqueous medium within a sealed container, from the sealed container under a pressure lower than the pressure inside the container to cause foaming. The polyolefin resin particles contain one or more compounds A selected from the group consisting of magnesium nitrate, tripotassium phosphate, trisodium phosphate, potassium carbonate, and calcium nitrate, and talc. The amounts of talc and compound A added are adjusted within a predetermined range. The polyolefin resin foam particles have an average bubble diameter of 20 μm or more and 200 μm or less, and contain a polyolefin resin, one or more compounds A selected from magnesium nitrate, tripotassium phosphate, trisodium phosphate, potassium carbonate, and calcium nitrate, and talc, and the content of talc and compound A is adjusted to a predetermined range.

Description

[Technical Field]

[0001] This invention relates to a method for producing polyolefin resin foam particles and to polyolefin resin foam particles. [Background technology]

[0002] Conventionally, when manufacturing foamed polyolefin resin particles, it is a known technique to typically add a bubble nucleating agent.

[0003] For example, Patent Document 1 discloses a manufacturing method for producing polyolefin resin foam particles using an inorganic blowing agent, exemplified by carbon dioxide, and resin particles containing a polyolefin resin and a water-containing inorganic compound. In the same document, talc is given as an example of the water-containing inorganic compound, and it is disclosed that compounds that are insoluble or sparingly soluble in water are preferable for exhibiting the effect of a bubble nucleating agent. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2009-215485 [Overview of the project] [Problems that the invention aims to solve]

[0005] When talc is included as a bubble nucleating agent and carbon dioxide is used as a blowing agent, the ability of carbon dioxide to impregnate polyolefin resins tends to be very low. Therefore, although it is possible to produce resin particles using polyolefin resin and talc as disclosed in Patent Document 1 and then foam them to obtain polyolefin resin foamed particles, it was difficult to obtain a sufficient foaming ratio in this case. Furthermore, in Patent Document 1, foamed particles manufactured to have a high foaming ratio tend to have a significantly larger average bubble diameter, and when such foamed particles are molded in a mold, they have poor secondary foaming properties, which may lead to reduced moldability or a narrower range of pressures in which they can be molded.

[0006] Patent Document 1 also discloses an example of using an inorganic compound such as sodium sulfate as a gas nucleating agent instead of talc. However, in this case as well, it was difficult to obtain polyolefin-based resin foamed particles with a high expansion ratio as in the case of using talc. Further, in Patent Document 1, when attempting to obtain polyolefin-based resin foamed particles with a high expansion ratio, oversized bubbles may be scattered in the foamed particles, and as the expansion ratio increases, the tendency to promote oversized bubbling becomes more pronounced. When using polyolefin-based resin foamed particles with such advanced oversized bubbling for in-mold molding, it was difficult to provide a foamed particle molded body with good appearance.

[0007] The present invention has been made in view of the above problems, and provides a method for producing polyolefin-based resin foamed particles that enables a high expansion ratio and suppresses oversized bubbling, and polyolefin-based resin foamed particles.

Means for Solving the Problems

[0008] The method for producing polyolefin-based resin foamed particles of the present invention is a method for producing polyolefin-based resin foamed particles by discharging polyolefin-based resin particles containing carbon dioxide, which are dispersed in an aqueous medium, from within a sealed container to a pressure lower than the pressure within the sealed container in the sealed container to cause foaming. The polyolefin-based resin particles contain at least one compound A selected from the group consisting of magnesium nitrate, tripotassium phosphate, trisodium phosphate, potassium carbonate, and calcium nitrate, and talc. The addition amount of the talc is 0.01 part by mass or more and 0.5 part by mass or less with respect to 100 parts by mass of the resin constituting the polyolefin-based resin particles, and the ratio of the addition amount of the compound A to the addition amount of the talc is 0.5 or more and 5 or less in terms of mass ratio.

[0009] The polyolefin resin foam particles of the present invention are polyolefin resin particles, wherein the average cell diameter of the polyolefin resin foam particles is 20 μm or more and 200 μm or less, and one or more compounds A selected from magnesium nitrate, tripotassium phosphate, trisodium phosphate, potassium carbonate and calcium nitrate and talc are contained in the polyolefin foam particles. The content of the talc is 0.01 part by mass or more and 0.5 part by mass or less with respect to 100 parts by mass of the resin constituting the polyolefin resin foam particles, and the ratio of the content of the compound A to the content of the talc is 0.5 or more and 5 or less in terms of mass ratio, which is characterized in that.

Effects of the Invention

[0010] The method for producing polyolefin resin foam particles of the present invention can produce polyolefin resin foam particles with a high expansion ratio despite using talc as a cell nucleating agent. The polyolefin resin foam particles produced by the production method of the present invention suppress the formation of oversized cells, and it is possible to easily obtain a foam particle molded body with a good appearance by in-mold molding. In addition, the polyolefin resin foam particles of the present invention are suppressed from having a significantly large average cell diameter and can exhibit an excellent expansion ratio. Further, the polyolefin resin foam particles of the present invention suppress the formation of oversized cells even at a high expansion ratio, and it is possible to easily obtain a foam particle molded body with a good appearance by in-mold molding.

Brief Description of the Drawings

[0011] [Figure 1] It is a photograph of a cut surface formed by cutting the foam particles of Example 1 into approximately two equal parts. [Figure 2] It is a photograph of a cut surface formed by cutting the foam particles of Comparative Example 2 into approximately two equal parts.

Modes for Carrying Out the Invention

[0012] The outline of the present invention will be described below. In the following, the method for producing polyolefin resin foam particles of the present invention may be referred to as the "production method of the present invention." In the following description, preferred numerical ranges of the present invention may be indicated as appropriate. In this case, preferred ranges, more preferred ranges, and particularly preferred ranges regarding the upper and lower limits of the numerical range can be determined from all combinations of the upper and lower limits. Furthermore, regarding the number of carbon atoms in the present invention, the notation "Y (number) ~ X (number)" should be read as "Y or more and X or less." The present invention relates to a method for producing foamed polyolefin resin particles, in which polyolefin resin particles containing carbon dioxide, dispersed in an aqueous medium, are released from a sealed container under a pressure lower than the pressure inside the sealed container to cause foaming. In the manufacturing method of the present invention, one or more compounds A selected from the group consisting of magnesium nitrate, tripotassium phosphate, trisodium phosphate, potassium carbonate, and calcium nitrate, and talc are blended into the polyolefin resin particles. The amount of talc added is adjusted to be between 0.01 parts by mass and 0.5 parts by mass per 100 parts by mass of the resin constituting the polyolefin resin foam particles, and the ratio of the amount of compound A added to the amount of talc added is adjusted to be between 0.5 and 5 by mass. According to the manufacturing method of the present invention, which has the above configuration, it is possible to produce foamed particles with a high foaming ratio by using talc as a foaming nucleation agent and using a specific inorganic compound. Furthermore, the bubbles inside the foamed particles produced by the manufacturing method of the present invention are suppressed from becoming air bubbles. Therefore, when polyolefin resin foamed particles produced by the manufacturing method of the present invention are subjected to in-mold molding, a lightweight polyolefin resin foamed particle molded article with a good appearance can be provided. Of course, it is also possible to produce polyolefin resin foamed particles with an appropriately suppressed foaming ratio using the manufacturing method of the present invention, and it is possible to provide a polyolefin resin foamed particle molded article using such particles. Further details of the present invention will be described below.

[0013] <Polyolefin resin particles> The polyolefin resin particles used in the manufacturing method of the present invention include a polyolefin resin, talc, and a predetermined inorganic compound. The polyolefin resin particles consist of polyolefin resin at a concentration of 50% or more by mass of 100% by mass of the resin constituting the resin particles, and other resins other than polyolefin resin may be mixed in as appropriate. As the polyolefin resin, for example, polyethylene resins, polypropylene resins, polybutene, polypentene, and copolymers of olefin monomers and other monomers can be used. Preferably, the polyolefin resin is one or more selected from polyethylene resins and polypropylene resins, and more preferably a polypropylene resin. In the present invention, the resin that is added in the largest amount, making up 50% by mass or more of the total resin that constitutes the resin particles, is called the base resin. That is, in the present invention, a polyolefin resin is the base resin. The amount of the polyolefin resin in 100% by mass of the total resin is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 100% by mass. Furthermore, the resin constituting the polyolefin resin particles is preferably 85% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, based on 100% by mass of the polyolefin resin particles. On the other hand, the upper limit of the amount of resin added per 100% by mass of the polyolefin resin particles can be determined by considering the amount of talc and compound A added to the polyolefin resin particles.

[0014] [Polypropylene resin] The polypropylene-based resin, which is the base resin, refers to a propylene copolymer containing 50% by mass or more of propylene homopolymers and / or structural units derived from propylene. Examples of the propylene homopolymers include isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene. These resins, as exemplified as propylene homopolymers, may be used individually or as a mixture of two or more. The propylene copolymer preferably contains 80% by mass or more, and more preferably 90% by mass or more, structural units derived from propylene in the polypropylene resin. The content of structural units derived from propylene in the propylene copolymer is preferably 99% by mass or less, and more preferably 98% by mass or less. Examples of such propylene copolymers include copolymers of propylene and ethylene and / or α-olefins having 4 to 20 carbon atoms. Examples of the α-olefins include 1-butene, 1-pentene, 1-hexene, 1-octene, and 4-methyl-1-butene. Other examples of propylene copolymers include ethylene-propylene random copolymers, propylene-butene random copolymers, and ethylene-propylene-butene random copolymers. These propylene copolymers may be, for example, random copolymers or block copolymers, but random copolymers are preferred. Examples of the propylene copolymer include impact-resistant polypropylene (block polypropylene) composed of two or more phases, including a continuous phase of propylene polymer and a rubber phase dispersed within that continuous phase. An example of a material constituting the rubber phase is ethylene-α-olefin copolymer. These resins, exemplified as propylene copolymers, may be used individually or as a mixture of two or more. Furthermore, the polypropylene resin may be a linear polypropylene resin, a branched polypropylene resin, or a combination thereof.

[0015] [Polyethylene resin] Examples of polyethylene-based resins used as the base resin include ethylene homopolymers or ethylene copolymers containing more than 50% by mass of structural units derived from ethylene. Specific examples of polyethylene-based resins include low-density polyethylene, high-density polyethylene, linear low-density polyethylene, ultra-low-density polyethylene, ethylene-vinyl acetate copolymers, ethylene-methyl methacrylate copolymers, ethylene-methacrylic acid copolymers, and ionomer resins in which the intermolecules of ethylene-methacrylic acid copolymers are crosslinked with metal ions. When the polyethylene-based resin is a copolymer, the copolymer may be a block copolymer, a random copolymer, or a graft copolymer. Furthermore, the polymer described above may be crosslinked, but it is preferable that it be uncrosslinked.

[0016] The melting point of the polypropylene resin used as the polyolefin resin is preferably 155°C or lower. By using the foamed particles of the present invention made with a polypropylene resin exhibiting the above melting point range, a foamed particle molded article with superior appearance can be molded at a lower molding temperature. From the viewpoint of improving this effect, the melting point of the polypropylene resin is more preferably 150°C or lower, and even more preferably 145°C or lower. On the other hand, from the viewpoint of further improving the heat resistance and mechanical strength of the foamed particle molded article, the melting point of the polypropylene resin is preferably 130°C or higher, more preferably 135°C or higher, and even more preferably 138°C or higher.

[0017] Furthermore, the melting point of the polyethylene resin used as the polyolefin resin particles is preferably 140°C or lower. By using the foamed particles of the present invention made of polyethylene resin exhibiting the above melting point range, it is possible to mold foamed particle molded articles that have excellent fusion properties and moldability even when molded at low molding temperatures. From the viewpoint of improving this effect, the melting point of the polyethylene resin is more preferably 135°C or lower, and even more preferably 130°C or lower. On the other hand, from the viewpoint of ensuring that the molded article released after in-mold molding is less prone to shrinkage and deformation and has excellent recovery properties, the melting point of the polyethylene resin is preferably 110°C or higher, more preferably 115°C or higher, and even more preferably 120°C or higher.

[0018] [Other resins] The resin constituting the polyolefin resin particles may consist solely of the polyolefin resin described above, or it may contain other resins together with the polyolefin resin, to the extent that it does not hinder the purpose and effects of the invention. The other resins used in the resin may be one type or a combination of two or more types. Other resins include, but are not limited to, resins selected from the group consisting of thermoplastic resins other than polyolefin resins and thermoplastic elastomers. In the context of this invention, "other resins" also includes elastomers that can be used in the production of foamed particles, in addition to general resins. Examples of the thermoplastic resins include polystyrene resins, polycarbonate resins, polyvinyl chloride resins, polymethacrylic resins, acrylonitrile resins, polyester resins, polyamide resins, and blends thereof. Examples of the aforementioned thermoplastic elastomers include olefin-based thermoplastic elastomers (TPO) and urethane-based thermoplastic elastomers (TPU).

[0019] The amount of the other resin added to 100% by mass of the aforementioned resin is preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, and particularly preferably 0% by mass. In other words, it is particularly preferable that the resin constituting the polyolefin resin particles is substantially composed solely of polyolefin resin.

[0020] [talc] In this invention, talc refers to a mineral whose main component is hydrated magnesium silicate (3MgO·4SiO2·H2O).

[0021] For example, as shown in Patent Document 1, it is known that talc is added to polypropylene resin particles as a bubble nucleating agent. However, when carbon dioxide is used as a blowing agent and talc is used as a bubble nucleating agent, it is difficult to achieve a high foaming ratio. The inventors of this invention have therefore diligently investigated this problem. When talc is blended into resin particles, carbon dioxide, as a blowing agent, makes it difficult to increase the foaming ratio of the foamed particles, and attempting to increase the foaming ratio tends to generate excessive bubbles in the foamed particles. The inventors of this invention have found that when carbon dioxide is used as a blowing agent, it is possible to achieve a high foaming ratio and suppress the formation of excessive bubbles in the foamed particles by adding a specific inorganic compound together with talc in a predetermined ratio. In this invention, the specific inorganic compound that can be added together with talc is referred to as compound A. In this invention, excessive bubbles refer to bubbles that have an area of ​​5% or more of the area of ​​the cut surface formed by cutting the obtained foamed particles into approximately two equal parts.

[0022] From the viewpoint of efficiently increasing the foaming ratio of foamed particles while suppressing the amount of talc added, the amount of talc added is preferably 0.01 parts by mass or more and 0.5 parts by mass or less, more preferably 0.05 parts by mass or more and 0.4 parts by mass or less, and more preferably 0.07 parts by mass or more and 0.3 parts by mass or less, per 100 parts by mass of resin constituting the polyolefin resin particles. In other words, the amount of talc added is 0.01 parts by mass or more, preferably 0.05 parts by mass or more, and more preferably 0.07 parts by mass or more, per 100 parts by mass of resin constituting the polyolefin resin particles. Furthermore, the amount of talc added is 0.5 parts by mass or less, preferably 0.4 parts by mass or less, and more preferably 0.3 parts by mass or less, per 100 parts by mass of resin constituting the polyolefin resin particles. The talc content in the foamed particles can be appropriately calculated from the materials used to manufacture the resin particles used to produce the foamed particles. Alternatively, the talc content in the foamed particles may be directly measured using conventionally known methods.

[0023] [Compound A] The polyolefin resin particles in the manufacturing method of the present invention contain compound A along with the talc described above. Compound A is one or more inorganic compounds selected from the group consisting of magnesium nitrate, tripotassium phosphate, trisodium phosphate, potassium carbonate, and calcium nitrate. Compound A may be used alone or in combination of two or more compounds.

[0024] Our investigations have shown that when talc and an inorganic compound are used in combination, excess bubbles tend to be observed in the foamed particles. In particular, the number of excess bubbles tended to increase as the foaming ratio of the foamed particles increased. On the other hand, in the manufacturing method of the present invention, by using talc in combination with a specific inorganic compound shown as compound A, it was found that polyolefin resin foamed particles with low apparent density and suppressed excess bubbles can be obtained due to the synergistic effect of talc and the specific inorganic compound.

[0025] The thermal decomposition temperature of compound A is 250°C or higher. When the thermal decomposition temperature is 250°C or higher, for example, when compound A and resin are kneaded in an extruder, the risk of compound A being decomposed by heat and yellowing occurring in the foamed particles produced can be suppressed. Furthermore, non-chlorinated compounds A, including calcium nitrate, are preferable because they do not require consideration of rust formation on metal equipment used in the manufacturing process. The thermal decomposition temperature can be measured using thermogravimetry (TG) and differential thermal analysis (DTA). By heating compound A in an oven-dried state, the thermal decomposition temperature can be determined from the peak temperature of the endothermic reaction when there is a change in the weight of TG and a peak due to the endothermic reaction is observed in DTA.

[0026] Furthermore, it is preferable that compound A includes one or more compounds a selected from the group consisting of calcium nitrate and potassium carbonate, and more preferably that compound A is one or more compounds a selected from the group consisting of calcium nitrate and potassium carbonate. The inclusion of calcium nitrate and / or potassium carbonate as compound A not only increases the foaming ratio and suppresses excessive foaming, but also makes compound A less susceptible to decomposition by the heat generated when resin particles are produced by the extruder.

[0027] The shape of compound A is not particularly limited, but it is preferably solid, and more preferably powder. Here, powder means a state in which fine particles can be seen with the naked eye. When compound A is in powder form, it is preferable because it is easier to precisely adjust the amount of compound A added when compound A is blended in the production of resin particles. From this viewpoint, it is preferable that compound A has a 50% volume average particle diameter (d50) of 0.1 μm or more and 30 μm or less, more preferably 0.5 μm or more and 20 μm or less, and even more preferably 1 μm or more and 15 μm or less. If the average particle diameter of compound A is large, it is preferable to crush it into small particles that satisfy the volume average particle diameter using a crusher or the like as appropriate.

[0028] The amount of compound A added to the resin constituting the polyolefin resin particles is not particularly limited. For example, from the viewpoint of easily balancing the amount of talc added and facilitating in-mold molding of foamed particle molded bodies with excellent appearance, the amount of compound A added is preferably 0.05 parts by mass or more and 0.6 parts by mass or less per 100 parts by mass of the resin constituting the polyolefin resin particles, more preferably 0.07 parts by mass or more and 0.55 parts by mass or less, and even more preferably 0.09 parts by mass or more and 0.5 parts by mass or less. In other words, the amount of compound A added is preferably 0.05 parts by mass or more, more preferably 0.07 parts by mass or more, even more preferably 0.09 parts by mass or more, and also preferably 0.6 parts by mass or less, more preferably 0.55 parts by mass or less, and even more preferably 0.5 parts by mass or less, based on 100 parts by mass of the resin constituting the polyolefin resin particles. Furthermore, the content of compound A in the resin particles can be determined using the same method as for the talc content.

[0029] [Ratio of talc and inorganic additives] From the viewpoint of efficiently increasing the foaming ratio of foamed particles while suppressing the amount of talc and compound A added, the total amount of talc and compound A added is preferably 0.02 parts by mass or more and 1 part by mass or less, more preferably 0.05 parts by mass or more and 0.9 parts by mass or less, and even more preferably 0.1 parts by mass or more and 0.8 parts by mass or less, per 100 parts by mass of the resin constituting the polyolefin resin particles. In other words, the total amount of talc content and compound A added is preferably 0.02 parts by mass or more, more preferably 0.05 parts by mass or more, even more preferably 0.1 parts by mass or more, and also preferably 1 part by mass or less, more preferably 0.9 parts by mass or less, and even more preferably 0.8 parts by mass or less, based on 100 parts by mass of the resin constituting the polyolefin resin foam particles.

[0030] In the manufacturing method of the present invention, the ratio of the amount of compound A added to the amount of talc added is 0.5 or more and 5 or less by mass ratio. Foamed particles produced by the manufacturing method of the present invention that satisfies the above ratio have a high foaming ratio and suppress excess bubbles in the foamed particles. The reason for this is not clear, but it is thought to be due to the interaction between talc, which functions as a bubble nucleating agent, and compound A. From the viewpoint of obtaining foamed particles with a higher foaming ratio, the ratio of the amount of compound A added to the amount of talc added is preferably 0.7 or more by mass ratio, and more preferably 1 or more. On the other hand, from the viewpoint of more reliably suppressing excess bubbles in the foamed particles, the ratio of the amount of compound A added to the amount of talc added is preferably 4 or less by mass ratio, more preferably 3 or less, and even more preferably 2 or less.

[0031] [Other additives] In addition to the resin, talc, and compound A described above, the polyolefin resin particles may also contain other additives as appropriate. Other additives include, for example, one or more combinations of functional additives such as colorants (exemplified by carbon black), organic compounds for adjusting bubbles, antioxidants, antistatic agents, surfactants, heat stabilizers, light stabilizers, UV absorbers, and flame retardants.

[0032] Carbon Black: Black polyolefin resin foam particle molded articles are used in various fields, including the automotive sector. Therefore, it is a preferred embodiment that carbon black is included as an additional additive in the polyolefin resin foam particles. Examples of carbon blacks used in the present invention include gas furnace black, oil furnace black, acetylene black, channel black, roller black, thermal black, and Ketjen black. When producing the polyolefin resin foam particles containing carbon black, the amount of carbon black added is preferably 0.5 parts by mass or more and 5.0 parts by mass or less per 100 parts by mass of resin, more preferably 1 part by mass or more and 4.5 parts by mass or less, and even more preferably 1.5 parts by mass or more and 4.0 parts by mass or less. This makes it possible to provide a sufficiently black foam particle molded article while adding an appropriate amount of carbon black. In other words, the amount of carbon black added is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, even more preferably 1.5 parts by mass or more, and also preferably 5.0 parts by mass or less, more preferably 4.5 parts by mass or less, and even more preferably 4.0 parts by mass or less. In particular, when producing black polyolefin resin foam particles containing carbon black, compound A is preferably one or more selected from the group consisting of calcium nitrate and tripotassium phosphate, and more preferably calcium nitrate. By using these compounds A and carbon black in combination, it is possible to provide foam particle molded articles with good uniformity of blackness.

[0033] When producing the polyolefin resin foam particles containing carbon black, the ratio of the amount of carbon black added to the amount of compound A added is preferably 1 to 50, and more preferably 5 to 40. By adjusting the ratio to this range, it is easy to produce polyolefin resin foam particles that exhibit sufficient blackness while sufficiently solving the problems of the present invention, namely increasing the foaming ratio and suppressing excessive foaming.

[0034] Organic compounds for bubble control: To more effectively solve the problems of the present invention, in addition to compound A, which is an inorganic compound, an organic compound for adjusting bubbles may be added to the polyolefin resin particles. Examples of the organic compound for adjusting bubbles include one or more organic compounds selected from the group consisting of aliphatic carboxylate metal salts having 4 to 20 carbon atoms (where the metal of the aliphatic carboxylate metal salt is an alkali metal or an alkaline earth metal) and aliphatic hydroxycarboxylate metal salts having 4 to 20 carbon atoms (where the metal of the aliphatic hydroxycarboxylate metal salt is an alkali metal or an alkaline earth metal). In particular, it is preferable that the organic compound for adjusting bubbles is one or more organic compounds selected from the group consisting of aliphatic carboxylate metal salts having 16 to 20 carbon atoms (where the metal of the aliphatic carboxylate metal salt is an alkali metal or an alkaline earth metal) and aliphatic hydroxycarboxylate metal salts having 16 to 20 carbon atoms (where the metal of the aliphatic hydroxycarboxylate metal salt is an alkali metal or an alkaline earth metal). By adding the organic compound for adjusting bubbles, the bubble diameter of the foamed particles can be made appropriately larger, making it easier to obtain foamed particles with a lower apparent density.

[0035] [Method for producing polyolefin resin particles] In the manufacturing method of the present invention, the production of polyolefin resin particles can be carried out by known methods for producing resin particles, except for adding talc and compound A to a resin containing polyolefin resin. Specifically, for example, the following method can be used. First, the resin containing the polyolefin resin described above, talc, compound A, and other additives added as needed are supplied to an extruder and melt-kneaded to obtain a molten mixture. Then, the molten mixture is extruded in strand form from a strand-forming die attached to the downstream side of the extruder, the extruded strands are water-cooled, and cut with a device exemplified by a pelletizer. In this way, pellet-shaped resin particles containing the polyolefin resin, talc, and compound A can be obtained.

[0036] The method for incorporating talc and compound A into polyolefin resin particles is not limited to the method described above. However, from the viewpoint of incorporating talc and compound A into the polyolefin resin particles as evenly as possible, the method of preparing a molten mixture by kneading a resin containing polyolefin resin, talc, and compound A using an extruder, as described above, is preferred. Furthermore, from the viewpoint of incorporating talc and compound A into the polyolefin resin particles as evenly as possible while suppressing the thermal decomposition of compound A, it is preferable to set the maximum temperature when molten mixing in the extruder to 200°C or higher and 250°C or lower. Moreover, from the viewpoint of stably producing foamed particles with a high foaming ratio and suppressed excessive bubbles in the foamed particles, it is preferable to prepare a mixture of talc and compound A in advance during the resin particle production process, and to supply the mixture and the resin to the extruder and mix them in the extruder. Similarly, from the viewpoint of preparing a masterbatch containing talc, compound A, and resin during the resin particle production process, and to supply the masterbatch to the extruder, it is also preferable to prepare a masterbatch containing talc, compound A, and resin, and to supply the masterbatch to the extruder.

[0037] <Foaming Process> The manufacturing method of the present invention produces polyolefin resin foam particles by carrying out a foaming process that foams the polyolefin resin particles described above. The foaming process involves releasing polyolefin resin particles containing carbon dioxide, which are dispersed in an aqueous medium within a sealed container, from the sealed container under a pressure lower than the pressure inside the container to cause foaming, thereby producing foamed polyolefin resin particles. A more specific example of the foaming process described above is explained below.

[0038] First, resin particles are dispersed in a sealed container containing an aqueous medium, such as water, and an inorganic dispersant, such as a sparingly soluble inorganic salt or clay mineral, or a dispersion aid, such as a surfactant. Next, a foaming agent is added to the sealed container to impregnate the resin particles with the foaming agent. Then, the resin particles containing the foaming agent and the aqueous medium are released together from the sealed container into an atmosphere with a pressure lower than the pressure inside the sealed container, causing the resin particles to foam. From the viewpoint of increasing the productivity of foamed particles, it is preferable to perform the impregnation of resin particles with a foaming agent and the foaming of resin particles containing the foaming agent as a series of processes using a single sealed container, as described above.

[0039] In this invention, carbon dioxide is used as the blowing agent. Other blowing agents other than carbon dioxide may be used in combination, as long as they do not hinder the purpose and effects of this invention. Examples of other blowing agents include the following inorganic and organic physical blowing agents. Examples of the inorganic physical blowing agent include air, nitrogen, argon, helium, oxygen, and neon. Examples of the organic physical blowing agent include aliphatic hydrocarbons such as propane, n-butane, isobutane, n-pentane, isopentane, and n-hexane; alicyclic hydrocarbons such as cyclohexane and cyclopentane; halogenated hydrocarbons such as ethyl chloride, 2,3,3,3-tetrafluoropropene, trans-1,3,3,3-tetrafluoropropene, and trans-1-chloro-3,3,3-trifluoropropene; and dialkyl ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether. The blowing agents described above can be used individually or in combination of two or more types. The amount of foaming agent added is determined considering the desired apparent density of the foamed particles, the type of resin used, the type of foaming agent, etc., but the amount of carbon dioxide added is preferably 0.1 parts by mass or more and 30 parts by mass or less, and more preferably 0.5 parts by mass or more and 15 parts by mass or less, per 100 parts by mass of resin particles.

[0040] Furthermore, the foamed particles obtained as described above can be further foamed in multiple stages to produce foamed particles with a higher foaming ratio. For example, by pressurizing the obtained foamed particles with air or the like to increase the pressure inside the bubbles of the foamed particles, and then heating them with steam or the like to further foam them, a two-stage foaming process can be performed to produce foamed particles with a higher foaming ratio.

[0041] The foamed particles produced by the manufacturing method of the present invention may be single-layer foamed particles having only a particulate foamed layer, or they may be multi-layer foamed particles. Examples of multi-layer foamed particles include multi-layer foamed particles comprising a core layer made of a foamed layer and a fusion layer covering at least a part of the surface of the core layer. The fusion layer is a layer for improving the fusion properties between foamed particles during in-mold molding, and may be present on the entire surface of the foamed particles or on only a part of the surface. The fusion layer may be a foamed layer or a non-foamed layer. Examples of resins constituting the fusion layer include polyolefin resins. The melting point or softening point of the resin constituting the fusion layer should be adjusted to be lower than the melting point of the resin constituting the core layer. The method for forming a fusion layer on the surface of foamed particles is not particularly limited. Examples include foaming resin particles having a fusion layer on their surface, or obtaining single-layer foamed particles and then attaching a fusion layer to the surface of those foamed particles. When obtaining foamed particles by foaming resin particles having a fusion layer on their surface, it is preferable to use an extruder capable of co-extrusion to co-extrude a molten mixture for forming the core layer and a molten mixture for forming the fusion layer, thereby providing a fusion layer on the surface of the resin particles. When producing multilayer foamed particles in the manufacturing method of the present invention, it is preferable that the core layer has the same configuration as the foamed particles described herein.

[0042] From the viewpoint of adjusting the foamed particles of the present invention to a good crystalline state, it is preferable that in the DSC curve obtained by differential scanning calorimetry of heat flux, in accordance with JIS K7121-1987, where the foamed particles are heated from 23°C to a temperature 30°C higher than the end of the melting peak at a heating rate of 10°C / min, a melting peak (high-temperature peak) appears that has a peak temperature higher than the peak temperature of the main melting peak (intrinsic peak) of the foamed particles. In this case, the DSC curve refers to the DSC curve obtained by heating the foamed particles using the measurement method described above (the DSC curve for the first heating). Furthermore, the main melting peak (intrinsic peak) of the foamed particles refers to the peak that arises from the melting of the intrinsic crystals of the base resin constituting the foamed particles. It should be noted that the intrinsic peak is considered to be a peak that appears due to the melting of the crystals normally present in the base resin constituting the foamed particles. On the other hand, a melting peak (high-temperature peak) with its peak temperature on the high-temperature side of the intrinsic peak is a peak located at a higher temperature than the intrinsic peak that can be confirmed in the first DSC curve. When this high-temperature peak appears, it is presumed that secondary crystals different from the crystals normally present in the base resin constituting the foam particles are present. The DSC curve obtained when the foam particles are heated at a heating rate of 10°C / min from 23°C to a temperature 30°C higher than the end of the melting peak (first heating), then cooled from a temperature 30°C higher than the end of the melting peak to 23°C at a cooling rate of 10°C / min, and then heated again at a heating rate of 10°C / min from 23°C to a temperature 30°C higher than the end of the melting peak (second heating) is called the DSC curve for the second heating. In the DSC curve for the second heating, only the intrinsic peak due to the melting of the crystals normally present in the base resin constituting the foam particles appears. Since this intrinsic peak appears in both the DSC curve from the first heating and the DSC curve from the second heating, it is possible to determine which peak is the intrinsic peak and which is the high-temperature peak by comparing the shape of the DSC curves and the peak position of each from the first and second heating. From the viewpoint of obtaining a foam particle molded article with an excellent balance of cushioning and rigidity using foam particles, the heat of fusion of the high-temperature peak is preferably 10 J / g or more and 50 J / g or less, more preferably 110 J / g or more and 30 J / g or less, and even more preferably 13 J / g or more and 20 J / g or less.

[0043] [Apparent density of foamed particles] The manufacturing method of the present invention can produce polyolefin-based resin foam particles having a low apparent density as compared with the case where only talc is used as a member for bubble adjustment. The apparent density of the foam particles produced by the manufacturing method of the present invention is lower than that of the comparative foam particles produced in the same manner except that compound A was not used, and from the viewpoint of exhibiting excellent lightness, it is 100 kg / m 3 It is preferably as follows, 95 kg / m 3 It is more preferably as follows, 90 kg / m 3 It is still more preferably as follows, 85 kg / m 3 It is even more preferably as follows, 80 kg / m 3 It is particularly preferably as follows. The upper limit of the apparent density of the foam particles produced by the manufacturing method of the present invention is not particularly limited, but from the viewpoint of ensuring good rigidity of the foam particle molded body obtained by in-mold molding using the foam particles, it is 30 kg / m 3 It is preferably above, 40 kg / m 3 It is more preferably above, 50 kg / m 3 It is still more preferably above. In other words, the foam particles produced by the manufacturing method of the present invention preferably have an apparent density of 30 kg / m 3 or more and 100 kg / m 3 or less.

[0044] By using the above-mentioned polyolefin-based resin particles, the manufacturing method of the present invention can produce polyolefin-based resin foam particles showing the above-mentioned desirable range of apparent density. For example, by the manufacturing method of the present invention, it is possible to provide polyolefin-based resin foam particles having an apparent density of 30 kg / m 3 or more and 100 kg / m 3 or less.

[0045] The measurement method of the apparent density of the foam particles is determined by the following measurement method. First, prepare a graduated cylinder filled with water at 23°C. Then, using a tool such as a wire mesh, submerge approximately 500 ml of polyolefin resin foam particles (mass W1), which have been left for two days under conditions of 50% relative humidity, 23°C, and 1 atm, into the graduated cylinder. Then, taking into account the volume of the wire mesh or other tool, measure the volume V1 (cm³) of the polyolefin resin foam particles, which can be read from the rise in water level. 3 By measuring the volume (W1 / V1) of the polyolefin resin foam particles placed in a graduated cylinder, the apparent density of the polyolefin resin foam particles can be determined.

[0046] <Polyolefin-based resin foam particles> Next, the polyolefin resin foam particles of the present invention will be described. In the following description, the polyolefin resin foam particles of the present invention may be referred to as the foam particles of the present invention. The manufacturing method of the present invention described above is an example of a preferred manufacturing method of the foam particles of the present invention, but it does not limit the manufacturing method of the foam particles of the present invention. The foamed particles of the present invention are obtained by foaming polyolefin resin particles as described in the manufacturing method of the present invention. Therefore, descriptions of the resin, base resin, talc, compound A, and other additives constituting the foamed particles of the present invention should be appropriately referenced from the description of the manufacturing method of the present invention described above.

[0047] The foamed particles of the present invention are polyolefin resin foamed particles with a polyolefin resin as the base resin, and the foamed particles contain one or more compounds A selected from magnesium nitrate, tripotassium phosphate, trisodium phosphate, potassium carbonate, and calcium nitrate, and talc. The talc content in the foamed particles of the present invention is 0.01 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of the resin constituting the polyolefin resin foamed particles, and the ratio of the amount of compound A added to the amount of talc added is 0.5 or more and 5 or less by mass ratio. The foamed particles of the present invention having such a configuration have a higher foaming ratio and suppress the formation of excess bubbles compared to comparison foamed particles having a similar composition except for the absence of compound A. Therefore, by subjecting the foamed particles of the present invention to in-mold molding, it is possible to provide a foamed particle molded article with excellent lightness and appearance. The foamed particles of the present invention, in which the formation of excess bubbles is suppressed, are thought to produce relatively uniform secondary foaming when molded in a mold due to the suppression of excess bubbles, making it difficult for wrinkles and irregularities to form on the outer surface of the foamed particle molded article.

[0048] In the foamed particles of the present invention, the total content of talc and compound A is preferably 0.02 parts by mass or more and 1 part by mass or less, more preferably 0.05 parts by mass or more and 0.9 parts by mass or less, and even more preferably 0.1 parts by mass or more and 0.8 parts by mass or less, per 100 parts by mass of the resin constituting the polyolefin-based foamed particles. The content of talc and compound A in the foamed particles can be appropriately calculated from the materials used to manufacture the resin particles used to manufacture the foamed particles.

[0049] The compound A preferably contains one or more compounds selected from the group consisting of calcium nitrate and potassium carbonate, and more preferably the compound A is one or more compounds selected from the group consisting of calcium nitrate and potassium carbonate.

[0050] The content of compound A is preferably 0.05 parts by mass or more and 0.6 parts by mass or less per 100 parts by mass of the resin constituting the foamed particles of the present invention, more preferably 0.07 parts by mass or more and 0.55 parts by mass or less, and even more preferably 0.09 parts by mass or more and 0.5 parts by mass or less. Furthermore, it is preferable that compound A is in powder form.

[0051] [Average bubble diameter] The average bubble diameter of the foamed particles of the present invention is in the range of 20 μm to 200 μm, exhibiting an appropriate bubble diameter while suppressing significant variation in bubble diameter or the inclusion of extremely large bubbles. When foamed particles in which the average bubble diameter is within a specific range and the inclusion of extremely large bubbles is suppressed are used, the pressure range in which the foamed particles can be molded during in-mold molding is wide, and a foamed particle molded article with excellent appearance can be easily obtained. From the viewpoint of easily obtaining a foamed particle molded article with excellent appearance, the average bubble diameter of the foamed particles of the present invention is preferably 40 μm to 180 μm, more preferably 60 μm to 160 μm, even more preferably 70 μm to 140 μm, and even more preferably 80 μm to 130 μm. In other words, the average bubble diameter of the foamed particles of the present invention is 20 μm or more, preferably 40 μm or more, more preferably 60 μm or more, even more preferably 70 μm or more, even more preferably 80 μm or more, and also 200 μm or less, preferably 180 μm or less, more preferably 160 μm or less, even more preferably 140 μm or less, and even more preferably 130 μm or less.

[0052] The average bubble diameter of the foamed particles is measured as follows: A randomly selected foam particle is cut into approximately two equal parts, and a magnified photograph of one of the cross-sections is taken from the surface image obtained using a scanning electron microscope. In the magnified photograph, four line segments are drawn from the surface of the foam particle toward the center at equal angles (45 degrees) apart. The number of bubbles intersecting each line segment is counted. The average bubble diameter of the foam particle is then calculated by dividing the total length of the four line segments by the number of bubbles. The total length refers to the actual length considering the magnification, not the length in the magnified photograph. This operation is performed for 20 foam particles, and the arithmetic mean of the average bubble diameters of the individual foam particles obtained is taken as the average bubble diameter.

[0053] [Average number of excessive bubbles] The foamed particles of the present invention have suppressed formation of excess bubbles inside. In the foamed particles of the present invention, the number of excess bubbles is preferably 5 or less, more preferably 4 or less, even more preferably 3 or less, and particularly preferably 0. An excess bubble in foamed particles refers to a bubble that occupies 5% or more of the area of ​​the cut surface formed by cutting the foamed particle in approximately two equal parts. If the average number of excess bubbles is 5 or less, it can be determined that the formation of excess bubbles has been suppressed.

[0054] The average number of superbubbles can be determined as follows: First, randomly selected foam particles are cut in approximately two equal parts, and the area of ​​the resulting cut surface is measured. Then, bubbles with an area of ​​5% or more of the cut surface area are counted. This operation is performed for 20 foam particles, and the arithmetic mean of the number of superbubbles for each individual foam particle is taken to determine the average number of superbubbles.

[0055] [Closed cell ratio] Furthermore, the closed-cell ratio of the foamed particles used in the present invention is preferably 80% or more. When the closed-cell ratio is within the above range, the foamed particles exhibit excellent secondary foaming properties, resulting in a wide range of moldable pressures and making it easier to obtain foamed particle molded articles with excellent appearance. From this viewpoint, the closed-cell ratio of the foamed particles is more preferably 85% or more, and even more preferably 90% or more. The closed-cell ratio of foamed particles can be measured as follows: First, the foamed particles are left to cure for 10 days in a constant-temperature room under atmospheric pressure, relative humidity of 50%, and temperature of 23°C. Next, in the same constant-temperature room, a volume of approximately 20 cm³ is measured. 3 The cured foam particles are used as measurement samples, and their apparent volume Va is accurately measured by the immersion method as described below. After thoroughly drying the measurement samples from which the apparent volume Va has been measured, the true volume Vx of the measurement samples is measured according to procedure C described in ASTM-D2856-70, for example, using a Toshiba Beckmann 930 air-comparative hydrometer. Based on these volumes Va and Vx, the closed-cell ratio is calculated using the following formula (1), and the closed-cell ratio of the foam particles can be determined from the average value of N=5 or more. [Formula 1] Closed cell ratio = (Vx-W / ρ)×100 / (Va-W / ρ) (1) However, Vx in formula (1) above (unit: cm) 3 ) is the true volume of the foamed particle (i.e., the sum of the volume of the resin constituting the foamed particle and the total volume of the closed-cell portion of the foamed particle), and Va (unit: cm) 3 ) is the apparent volume of the foaming particle (i.e., the volume measured from the rise in the liquid level when the foaming particle is submerged in a graduated cylinder of water), W (unit: g) is the mass of the sample used for measurement, and ρ (unit: g / cm³) is the apparent volume of the foaming particle (i.e., the volume measured from the rise in the liquid level when the foaming particle is submerged in a graduated cylinder of water), W (unit: g / cm³) is the apparent volume of 3 ) is the density of the polyolefin resin that constitutes the foamed particles. The density of the polyolefin resin referred to here is the density of the base resin that constitutes the foamed particles being measured.

[0056] [Apparent Density] The apparent density of the foamed particles of the present invention is 100 kg / m³. 3 Preferably, it is 95 kg / m 3 It is more preferable that the following is true: 90 kg / m 3 It is even more preferable that the following conditions apply: 85 kg / m 3 It is even more preferable that the following conditions are met: 80 kg / m 3 The following is particularly preferable: The upper limit of the apparent density of the foamed particles of the present invention is not particularly limited, but is 30 kg / m³.3 Preferably, it is 40 kg / m 3 It is more preferable that it be 50 kg / m 3 It is even more preferable that the above conditions are met. In other words, the foamed particles of the present invention have an apparent density of 30 kg / m³. 3 More than 100kg / m 3 The following is preferable. Note that the method for measuring the apparent density of the foamed particles of the present invention will be appropriately described in the description of foamed particles produced by the manufacturing method of the present invention, so a detailed explanation is omitted here.

[0057] The foamed particles of the present invention can be used to produce polyolefin-based resin foamed particles exhibiting the desired apparent density range described above. For example, the foamed particles of the present invention have an apparent density of 30 kg / m³. 3 More than 100kg / m 3 The following is preferable:

[0058] [Carbon Black] The foamed particles of the present invention may contain carbon black. The carbon black content in the foamed particles of the present invention is preferably 0.5 parts by mass or more and 5.0 parts by mass or less, more preferably 1 part by mass or more and 4.5 parts by mass or less, and even more preferably 1.5 parts by mass or more and 4.0 parts by mass or less, per 100 parts by mass of the resin constituting the foamed particles of the present invention. This makes it possible to provide a foamed particle molded article that is sufficiently black while adding an appropriate amount of carbon black. In other words, the carbon black content in the foamed particles of the present invention is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, even more preferably 1.5 parts by mass or more, and preferably 5.0 parts by mass or less, more preferably 4.5 parts by mass or less, and even more preferably 4.0 parts by mass or less, based on 100 parts by mass of the resin constituting the foamed particles of the present invention. In particular, the foamed particles of the present invention containing carbon black preferably contain one or more compounds selected from the group consisting of calcium nitrate and tripotassium phosphate as compound A, and more preferably calcium nitrate. By using these compounds A and carbon black in combination, it is possible to provide a foamed particle molded article with good uniformity of blackness.

[0059] The carbon black content in the foamed particles can be appropriately calculated from the materials used to manufacture the resin particles used to produce the foamed particles. Alternatively, the carbon black content in the foamed particles may be directly measured from test pieces cut from the foamed particles. One measurement method is to use a thermogravimetric differential thermal analyzer (TG-DTA). In this case, the foamed particles are first measured according to JIS K7120-1987. Specifically, the weight of the test piece is measured, and the test piece is heated from 40°C to 500°C at a rate of 10°C / min under a nitrogen atmosphere to decompose the resin constituting the test piece. Then, the atmosphere is changed to an air atmosphere and the temperature is raised to 800°C to decompose the carbon black, and the weight difference from 500°C to 800°C can be measured as the carbon black content. As described above, the carbon black content relative to 100 parts by mass of resin constituting the test specimen can be determined using the measured resin content and carbon black content.

[0060] In the foamed particles of the present invention that contain carbon black, the ratio of the carbon black content to the compound A content is preferably 1 to 50 by mass, and more preferably 10 to 40 by mass. In other words, the ratio of the carbon black content to the compound A content is preferably 1 or more by mass, more preferably 10 or more, more preferably 50 or less, and more preferably 40 or less. By adjusting the ratio within this range, it is possible to provide polyolefin resin foam particles that exhibit sufficient blackness while fully solving the problems of the present invention, namely increasing the foaming ratio and suppressing excessive foaming.

[0061] <Polyolefin-based resin foam particle molded product> A polyolefin resin foam particle molded article can be produced by subjecting the foam particles produced by the manufacturing method of the present invention described above, or by subjecting the foam particles of the present invention to in-mold molding. Such a foam particle molded article enjoys the effects of the present invention, is lightweight, and has an excellent appearance. In the following, a polyolefin resin foam particle molded article obtained by subjecting the foam particles produced by the manufacturing method of the present invention, or by subjecting the foam particles of the present invention to in-mold molding, may be referred to as a foam particle molded article relating to the present invention.

[0062] The in-mold molding method can be appropriately selected from known in-mold molding methods using foamed particles. For example, foamed particles are filled into a mold having a cavity corresponding to the shape of the desired foamed particle molded body, and the foamed particles filled in the mold are heated by applying a predetermined molding pressure using a heating medium, such as steam. The molding pressure can be adjusted, for example, in the range of 0.2 MPa(G) or more and 0.5 MPa(G) or less. In this specification, (G) refers to gauge pressure, that is, the pressure value relative to atmospheric pressure. By heating the foamed particles in the cavity in this way, the foamed particles are further foamed and fused to each other. Next, after heating with the heating medium, such as steam, is completed, the pressure in the cavity is released, and cooling of the mold and the molded body inside the mold is started immediately. When it is confirmed that the pressure (surface pressure) generated on the inner surface of the mold has decreased to below a predetermined value, cooling is stopped, and the foamed particle molded body is removed from the mold. The cooling method here is not particularly limited, but water cooling is one example. Through this series of molding steps, a foamed particle molded body corresponding to the shape of the cavity is obtained.

[0063] The foamed particle molded article according to the present invention has excellent lightness and appearance because the foamed particles used in its manufacture have a high foaming ratio and the formation of excessive bubbles is suppressed. The appearance of the foamed particle molded article according to the present invention is evaluated by visual observation, based on the presence or absence of wrinkles and irregularities on the surface of the foamed particle molded article.

[0064] Furthermore, a foam particle molded article according to the present invention, which is molded using foam particles containing carbon black, may exhibit a black color suitable for use as a vehicle component.

[0065] The molded density of the foamed particle molded article according to the present invention is 30 kg / m³. 3 More than 120kg / m 3 Preferably, it is 40 kg / m 3 More than 115kg / m 3 More preferably, it is 50 kg / m 3 More than 110kg / m 3 The following is even more preferable: The density of the molded body (kg / m³) 3 ) is calculated by dividing the mass of the foamed particle molded body by the volume calculated based on its dimensions. [Examples]

[0066] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. First, the raw materials of the examples and comparative examples will be described. In the examples and comparative examples described below, a polyolefin resin was used as the resin constituting the polyolefin resin particles. Compounds A1 to A5 described later all have a thermal decomposition temperature of 250°C or higher. The parts by mass of the raw materials shown in the example table indicate the amount blended relative to 100 parts by mass of the resin used. The parts by mass of carbon black indicates the amount blended in pure form relative to 100 parts by mass of the resin used.

[0067] • Polypropylene resin: Propylene-ethylene random copolymer, melting point 142°C, density 900 kg / m³ 3 • Polyethylene resin: Linear low-density polyethylene, melting point 124°C, density 926 kg / m³ 3 Talc: A mineral whose main component is hydrated magnesium silicate (3MgO·4SiO2·H2O), manufactured by Matsumura Sangyo Co., Ltd., [Product name: High Filler #12], particle size (d50) 7.5 μm ·Inorganic compounds Compound A1: Calcium nitrate (Ca(NO3)2), manufactured by Kishida Chemical Co., Ltd., reagent grade. Compound A2: Potassium carbonate (K2CO3), manufactured by Kishida Chemical Co., Ltd., Grade 1. Compound A3: Tripotassium phosphate (K3PO4), manufactured by Kishida Chemical Co., Ltd., Grade 1. Compound A4: Trisodium phosphate (Na3PO4), manufactured by Kishida Chemical Co., Ltd., anhydrous, primary grade. Compound A5: Magnesium nitrate (Mg(NO3)2), manufactured by Nacalai Tesque Co., Ltd., JIS reagent grade. Inorganic compound 1 other than compound A: Magnesium carbonate (MgCO3), manufactured by Nacalai Tesque Co., Ltd., thermal decomposition temperature 350°C Inorganic compound 2 other than compound A: Zinc carbonate (ZnCO3), manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Wako Grade 1, thermal decomposition temperature 140℃ Inorganic compound 3 other than compound A: Sodium sulfate (Na2SO4), manufactured by Kishida Chemical Co., Ltd., thermal decomposition temperature 890°C • Carbon Black: Carbon black-containing masterbatch: Product name "PP Black Master Batch, BT920F-JSJ" (manufactured by B&Tech Corporation, CB concentration 45% by weight)

[0068] (Example 1) <Preparation of polyolefin resin particles> A manufacturing apparatus was prepared that included an extruder with an inner diameter of 50 mm and a strand-forming die attached to the downstream side of the extruder. Polyolefin resin and the raw materials shown in Table 1 were supplied to an extruder and melt-kneaded to obtain a molten mixture. In addition, talc and compound A were pre-mixed to form a mixture, which was then supplied to the extruder. The molten mixture was introduced into a strand-forming die, and strands were extruded. The extruded strands were water-cooled and cut with a pelletizer to an average weight of 1 mg per strand. This yielded polyolefin resin particles with added talc and compound A. In Example 1, polypropylene resin was used as the polyolefin resin.

[0069] <Preparation of polyolefin-based resin foam particles> As described above, 1 kg of the obtained polyolefin resin particles was supplied together with 3 L of water, an aqueous medium, into a pressurized, sealed container with a capacity of 5 L. In addition, 0.3 parts by mass of kaolin as an inorganic dispersant and 0.2 parts by mass of a surfactant (product name: Neogen, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., sodium dodecylbenzenesulfonate) (as active ingredients) were added to 100 parts by mass of the polyolefin resin particles into the sealed container. Next, the sealed container was heated at a rate of 5°C / min while being stirred until it reached the foaming temperature. Then, carbon dioxide was injected into the sealed container as a foaming agent, and the pressure was increased to 2.1 MPa(G). This was then maintained at the same temperature and pressure for 15 minutes. This adjusted the crystalline structure of the resulting foam particles so that a high-temperature peak would appear in the DSC curve obtained by differential scanning calorimetry. Subsequently, the contents of the sealed container (polyolefin resin particles and water) were released to atmospheric pressure, resulting in an apparent density of 87 kg / m³. 3 Polyolefin-based resin foam particles were obtained. In the examples and comparative examples, the foaming temperature was appropriately adjusted to foam the resin particles so that they would have a predetermined apparent density. The average bubble diameter and average number of superbubbles of the foamed particles, as described later, were measured using foamed particles that had been conditioned by standing for 24 hours under conditions of 50% relative humidity, 23°C, and 1 atm.

[0070] <Manufacturing of polyolefin-based resin foam particle molded products> The obtained polyolefin resin foam particles were filled into a mold having a molding cavity capable of forming a plate-shaped foam particle mold measuring 250 mm in length, 200 mm in width, and 20 mm in height, and heated using the following heating method. A metal mold was used as the molding die. The heating method involved preheating (exhaust process) by supplying steam to the mold with drain valves on both sides of the mold open. Then, steam was supplied from one side of the mold to heat it, and then from the other side to heat it further. Subsequently, steam was supplied from both sides of the mold to heat it at the lower limit molding pressure shown in the example table. After heating was complete, the pressure was released and water cooling was started immediately, and water cooling was carried out until the pressure generated on the inner surface of the mold by the foaming force of the foamed particle molded body reached 0.04 MPa (G). After water cooling was complete, the foamed particle molded body was removed from the mold, and this was the foamed particle molded body of Example 1. Furthermore, the evaluation of the appearance and uniformity of blackness of the foamed particle molded body, as described later, was performed using foamed particle molded bodies that had been conditioned by standing for 12 hours under conditions of 50% relative humidity, 80°C, and 1 atm after demolding.

[0071] As described above, the polyolefin resin foam particles obtained in Example 1 exhibited a synergistic effect between talc and compound A1, resulting in a low apparent density and suppressed excessive foaming.

[0072] (Examples 2-11, Comparative Examples 1-8) Except for the changes described in Tables 1 and 2, polyolefin resin particles, polyolefin resin foam particles, and polyolefin resin foam particle molded articles were manufactured in the same manner as in Example 1 described above, and these were designated as Examples 2-11 and Comparative Examples 1-8. In Examples 2-11 and Comparative Examples 1-8, polypropylene resin was used as the polyolefin resin.

[0073] In Examples 2 to 5, polyolefin resin particles, polyolefin resin foam particles, and polyolefin resin foam particle molded articles were produced in the same manner as in Example 1 described above, except that compounds A2 to A5 were used instead of compound A1. Even when compounds A2 to A5 were used, a synergistic effect with talc was obtained, resulting in polyolefin resin foam particles with low apparent density and suppressed excessive bubbles.

[0074] In Example 6, polyolefin resin particles, polyolefin resin foam particles, and polyolefin resin foam particle molded articles were produced in the same manner as in Example 1 described above, except that the amount of compound A1 was 0.5 parts by mass. Even when the amount of compound A1 was 0.5 parts by mass, a synergistic effect with talc was obtained, and polyolefin resin foam particles with particularly low apparent density and no excessive bubbles were obtained.

[0075] In Example 7, polyolefin resin particles, polyolefin resin foam particles, and polyolefin resin foam particle molded articles were produced in the same manner as in Example 3 described above, except that 2.6 parts by mass of carbon black were used. Even when carbon black was used, a synergistic effect between talc and compound A3 was obtained, resulting in polyolefin resin foam particles with low apparent density and suppressed excessive bubbles.

[0076] In Example 8, polyolefin resin particles, polyolefin resin foam particles, and polyolefin resin foam particle molded articles were produced in the same manner as in Example 1 described above, except that 0.05 parts by mass each of compound A1 and compound A2 were used. Even when 0.05 parts by mass each of compound A1 and compound A2 were used, a synergistic effect with talc was obtained, resulting in polyolefin resin foam particles with low apparent density and suppressed excessive bubbles.

[0077] In Example 9, polyolefin resin particles, polyolefin resin foam particles, and polyolefin resin foam particle molded articles were produced in the same manner as in Example 1 described above, except that the amount of compound A1 was 0.3 parts by mass. Even when the amount of compound A1 was 0.3 parts by mass, a synergistic effect with talc was obtained, and polyolefin resin foam particles with particularly low apparent density and no excessive bubbles were obtained.

[0078] In Example 10, polyolefin resin particles, polyolefin resin foam particles, and polyolefin resin foam particle molded articles were produced in the same manner as in Example 1 described above, except that the amount of talc was 0.3 parts by mass and the amount of compound A1 was 0.3 parts by mass. Even when the amount of talc and compound A1 was 0.3 parts by mass, a synergistic effect between talc and compound A1 was obtained, and polyolefin resin foam particles with low apparent density and no excessive bubbles were obtained.

[0079] In Example 11, polyolefin resin particles, polyolefin resin foam particles, and polyolefin resin foam particle molded articles were produced in the same manner as in Example 1 described above, except that 2.6 parts by mass of carbon black were used. Even when carbon black was used, a synergistic effect between talc and compound A was obtained, resulting in polyolefin resin foam particles with low apparent density and no excess bubbles. Furthermore, in Example 11, since there were no excess bubbles in the foam particles, relatively uniform secondary foaming occurred when the foam particles were molded in a mold, making it difficult for wrinkles and irregularities to form on the outer surface of the foam particle molded article, and resulting in a molded article with excellent uniformity of blackness.

[0080] In Comparative Example 1, polyolefin resin particles, polyolefin resin foam particles, and polyolefin resin foam particle molded articles were produced in the same manner as in Example 1 described above, except that the amount of compound A1 added was 0.02 parts by mass. In Comparative Example 1, the ratio of the amount of compound A1 added to the amount of talc added was 0.2 by mass, which was below the predetermined numerical range. As a result, a synergistic effect with talc was not obtained, and polyolefin resin foam particles with insufficient high magnification were obtained.

[0081] In Comparative Example 2, polyolefin resin particles, polyolefin resin foam particles, and polyolefin resin foam particle molded articles were produced in the same manner as in Example 1 described above, except that the amount of compound A1 added was 1 part by mass. In Comparative Example 2, the ratio of the amount of compound A1 added to the amount of talc added was 10 by mass, which was below the predetermined numerical range. Therefore, a synergistic effect with talc was not obtained, and many excess bubbles were observed in the foam particles, resulting in a molded article with poor moldability and poor appearance. In addition, in Comparative Example 2, the average bubble diameter of the foam particles was large and many excess bubbles were present, resulting in poor secondary foaming during in-mold molding and no pressure range in which molding was possible. In Comparative Example 2, a molded article molded at a molding pressure of 0.3 MPa (G) was used for evaluating the appearance and measuring the density of the molded article.

[0082] Comparative Examples 3 to 5 were produced in the same manner as in Example 1 described above, except that compound A was not used and the amount of talc used was as shown in Table 3. Polyolefin resin particles, polyolefin resin foam particles, and molded polyolefin resin foam particle articles were produced. Because compound A was not used, a synergistic effect with talc was not obtained, and polyolefin resin foam particles with insufficient high magnification were obtained.

[0083] In Comparative Example 6, polyolefin resin particles, polyolefin resin foam particles, and polyolefin resin foam particle molded articles were produced in the same manner as in Example 1 described above, except that magnesium carbonate was used instead of the inorganic compound shown above. When magnesium carbonate was used, a synergistic effect with talc was not obtained, and polyolefin resin foam particles with insufficient high magnification were obtained.

[0084] In Comparative Example 7, polyolefin resin particles, polyolefin resin foam particles, and polyolefin resin foam particle molded articles were produced in the same manner as in Example 1 described above, except that zinc carbonate was used instead of the inorganic compound shown above. When zinc carbonate was used, a synergistic effect with talc was not obtained, and polyolefin resin foam particles with insufficient high magnification were obtained.

[0085] In Comparative Example 8, polyolefin resin particles, polyolefin resin foam particles, and polyolefin resin foam particle molded articles were produced in the same manner as in Example 1, except that sodium sulfate was used instead of the inorganic compound described above. When sodium sulfate was used, a synergistic effect with talc was not obtained, and polyolefin resin foam particles with insufficient high magnification were obtained.

[0086] (Example 12) Example 12 was produced in the same manner as in Example 2, except that a polyethylene resin was used as the polyolefin resin, to manufacture polyolefin resin particles, polyolefin resin foam particles, and a molded polyolefin resin foam particle article.

[0087] (Comparative Example 9) Comparative Example 9 was prepared in the same manner as in Example 12, except that potassium carbonate was not used, by producing polyolefin resin particles, polyolefin resin foamed particles, and a molded polyolefin resin foamed particle article.

[0088] (Reference example 1) Except for the changes described in Table 3, the use of zinc borate as a bubble nucleating agent, and the absence of the inorganic compounds described above, polyolefin resin particles, polyolefin resin foam particles, and molded polyolefin resin foam particle articles were manufactured in the same manner as in Example 1 described above, and this was designated as Reference Example 1. In Reference Example 1, polypropylene resin was used as the polyolefin resin.

[0089] As described above, the following measurements or evaluations were performed on polyolefin resin particles, polyolefin resin foam particles, and polyolefin resin foam particle molded articles for each example, comparative example, and reference example 1 obtained. The results are shown in Tables 1 to 3.

[0090] <Apparent density of foamed particles> Apparent density of polyolefin resin foam particles (kg / m³) 3 The following measurement method was used to determine the value. First, a graduated cylinder filled with water at 23°C was prepared. Approximately 500 ml of polyolefin resin foam particles (mass W1), which had been conditioned by standing for 48 hours under conditions of 50% relative humidity, 23°C, and 1 atm, was submerged in the graduated cylinder using a wire mesh. Then, taking into account the volume of the wire mesh, the volume V1 (cm³) of the polyolefin resin foam particles, which could be read from the rise in water level, was calculated. 3 The apparent density of the polyolefin resin foam particles was determined by measuring the volume (W1 / V1) and dividing the mass W1 (g) of the polyolefin resin foam particles placed in a graduated cylinder by the volume V1.

[0091] <Average bubble diameter of foaming particles> Randomly selected foam particles were cut into approximately two equal parts, and a magnified photograph of one of the cross-sections was taken from the surface image obtained using a scanning electron microscope. In the magnified photograph, four line segments were drawn from the surface of the foam particle toward the center at equal angles (45 degrees) apart. The number of bubbles intersecting each line segment was counted. The average bubble diameter of the foam particle was then calculated by dividing the total length of the four line segments by the number of bubbles. The total length here refers to the actual length considering the magnification, not the length in the magnified photograph. This operation was performed for 20 foam particles, and the arithmetic mean of the average bubble diameters of the individual foam particles obtained was taken as the average bubble diameter.

[0092] <Average number of excess bubbles in foamed particles> Randomly selected polyolefin resin foam particles were cut in approximately two equal parts, exposing the resulting cross-sections. A scanning electron microscope was used to photograph the entire cross-section. The area of ​​each bubble observed in the cross-section was measured by image analysis. The image analysis device used was WinROOF2021 manufactured by Mitani Corporation. For each bubble, the equivalent circle diameter was determined from the Ferret diameter, and the bubble area was calculated from the equivalent circle diameter. Similarly, for the area of ​​the cross-section of the foam particle, the equivalent circle diameter was determined from the Ferret diameter, and the area of ​​the cross-section was calculated from the equivalent circle diameter. Bubbles with an area of ​​5% or more of the cross-section area were counted. This procedure was performed for 20 foam particles, and the arithmetic mean of the number of oversized bubbles in each individual foam particle was calculated to obtain the average number of oversized bubbles.

[0093] <Percentage of closed cells in foamed particles> The percentage of closed cells in the foamed particles was measured as follows: First, the foamed particles were left to cure for 10 days in a constant temperature room under atmospheric pressure, relative humidity of 50%, and temperature of 23°C. Next, in the same constant temperature room, a volume of approximately 20 cm³ was measured. 3 The cured foamed particles were used as measurement samples, and their apparent volume Va was accurately measured by the immersion method as described below. After thoroughly drying the measurement samples from which the apparent volume Va was measured, the true volume Vx of the measurement samples was measured using a Toshiba Beckmann 930 air-comparative hydrometer, in accordance with procedure C described in ASTM-D2856-70. Based on these volumes Va and Vx, the closed-cell ratio was calculated using equation (1) below, and the average value for N=5 was taken as the closed-cell ratio of the foamed particles. [Formula 2] Closed cell ratio = (Vx-W / ρ)×100 / (Va-W / ρ) (1) However, Vx in formula (1) above (unit: cm) 3 ) is the true volume of the foamed particle (i.e., the sum of the volume of the resin constituting the foamed particle and the total volume of the closed-cell portion of the foamed particle), and Va (unit: cm) 3 ) is the apparent volume of the foaming particle (i.e., the volume measured from the rise in the liquid level when the foaming particle is submerged in a graduated cylinder of water), W (unit: g) is the mass of the sample used for measurement, and ρ (unit: g / cm³) is the apparent volume of the foaming particle (i.e., the volume measured from the rise in the liquid level when the foaming particle is submerged in a graduated cylinder of water), W (unit: g / cm³) is the apparent volume of 3 ) is the density of the polyolefin resin that constitutes the foamed particles. The density of the polyolefin resin referred to here is the density of the base resin that constitutes the foamed particles being measured.

[0094] <Heat of fusion at high temperature peak of foamed particles> Based on JIS K7122-2024, differential scanning calorimetry (DSC) was used to obtain the first DSC curve measured when a 2 mg foamed particle was heated at a heating rate of 10 °C / min from 23 °C to a temperature 30 °C higher than the end of the melting peak. Then, in the first DSC curve, a straight line was drawn connecting point I, which corresponds to 80°C on the DSC curve, and point II, which corresponds to the melting end temperature of the foamed particles. Point II, which indicates the melting end temperature, is the high-temperature endpoint of the high-temperature peak, and is the intersection point of the high-temperature peak and the baseline on the high-temperature side of the DSC curve. As described above, after drawing a straight line connecting point I and point II, point IV was defined as the intersection of a straight line parallel to the vertical axis of the graph and passing through the maximum point III, which lies between the eigenpeak and the high-temperature peak, with the straight line connecting point I and point II. The area enclosed by the straight line connecting point IV and point II, the straight line connecting point III and point IV, and the DSC curve connecting point III and point II was defined as the area of ​​the high-temperature peak. The value of the heat of fusion of the high-temperature peak was calculated from the area of ​​the high-temperature peak obtained as described above.

[0095] <Evaluation of the appearance of foamed particle molded products> The appearance of the obtained polyolefin resin foam particle molded articles was visually observed and evaluated as follows. A: No wrinkles or irregularities were observed on the outer surface of the foam particle molded body. B: Almost no wrinkles and / or irregularities were observed on the outer surface of the foamed particle molded body. C: Multiple wrinkles and / or irregularities were observed on the outer surface of the foamed particle molded body.

[0096] <Evaluation of uniformity of blackness in foamed particle molded products> The uniformity of the blackness of the foam particle molded bodies obtained in Examples 7 and 11 was evaluated as follows. Visually, the color unevenness on the surface of the molded bodies was evaluated using the following 5-point scale, and the color unevenness of the foam particle molded bodies was evaluated based on the average value of the evaluations of 5 observers according to the following criteria. (5-point rating scale) 5 points: The surface of the molded body exhibits a uniform black color. 4. The surface of the molded body exhibits a generally uniform black color. 3. Slight color unevenness was observed on the surface of the molded product. Two points: Color inconsistencies were observed on the surface of the molded product. 1. Significant color unevenness was observed in multiple locations on the surface of the molded product. (Evaluation of blackness) A: 4 points or more B: 3 points or more but less than 4 points C: 2 points or more but less than 3 points D: Less than 2 points

[0097] <Density of molded foam particle molded body> The mass of the foamed particle molded body was calculated by dividing it by the volume, which is determined based on its dimensions.

[0098] <Moldable pressure range for foam particle molded bodies> The foamed particles obtained in the examples and comparative examples were used for in-mold molding as described below, and evaluated as follows. In the examples and comparative examples using polypropylene resin, in-mold molding was performed to experimentally mold foam particle molded bodies by varying the molding pressure in 0.02 MPa increments between 0.20 MPa(G) and 0.40 MPa(G). In other words, in-mold molding was performed at a total of 11 different molding pressures. The lowest molding pressure confirmed within the moldable range, as described below, is referred to as the lower limit molding pressure. Furthermore, in the examples and comparative examples using polyethylene resin, in-mold molding was performed by experimentally molding foamed particle molded bodies by varying the molding pressure in 0.02 MPa increments between 0.08 MPa(G) and 0.20 MPa(G). In other words, in-mold molding was performed at a total of seven different molding pressures. As described above, the foam particle molded bodies obtained by in-mold molding were judged to meet the following three criteria (fusion properties, appearance, and recovery properties). Foam particle molded bodies that met all criteria were considered acceptable products, and the moldable pressure range in which such acceptable products could be obtained was evaluated according to the following criteria (moldable pressure range). Note that MPa(G) indicates gauge pressure. In-moldability was evaluated by examining the moldable pressure range. A wider range from the lower limit to the upper limit of the moldable pressure indicates a wider moldable range and is therefore more desirable.

[0099] (Fusibility) The fusion properties of the foam particle molded body were evaluated by the following method. The plate-shaped foam particle molded body was bent and fractured, and the number of foam particles present on the fracture surface (C1) and the number of foam particles that were destroyed (C2) on the fracture surface were determined. The ratio of the number of destroyed foam particles (C2) to the number of foam particles (C1) (C2 / C1 × 100) was calculated as the material destruction rate, and a value of 80% or higher was considered acceptable. (exterior) A 100mm x 100mm rectangle was drawn near the center of a 250mm x 200mm surface of a foam particle molded body. Lines were drawn diagonally from the corners of this rectangle, and the number of voids with a minor axis of 1mm or more and a major axis of 1mm or more along these lines was counted. If the number of voids was less than 5, the product was deemed to have a good appearance and passed the test. Specifically, voids refer to the gaps between foam particles. (Recoverability) The foam particle molded body was left standing for 24 hours in an environment of 23°C and 50% relative humidity. After that, the surface of the foam particle molded body was observed to check for the presence or absence of wrinkles. In addition, the thickness of the central part of the main surface (i.e., the surface with the largest area) and the four corners of the main surface of the flat molded body were measured, and the ratio of the thickness of the central part to the thickness of the thickest part of the four corners was calculated. A product was considered acceptable if no wrinkles were observed at all or very few, and the ratio was 95% or more.

[0100] (Moldable pressure range) A: There are three or more molding pressures that allow for the formation of a satisfactory product. B: There are two molding pressures at which a satisfactory product can be formed. C: There is one molding pressure point at which a satisfactory product can be formed. D: We were unable to mold any acceptable product at any of the molding pressures.

[0101] Figure 1 shows a photograph of a cross-section formed by cutting the foamed particles of Example 1 into approximately two equal parts. There were no excessive bubbles, and no significant variation in bubble diameter was observed.

[0102] Figure 2 shows a photograph of the cross-section formed by cutting the foamed particles of Comparative Example 2 into approximately two equal parts. Multiple over-air bubbles were formed, and a significant variation in bubble diameter was observed.

[0103] [Table 1]

[0104] [Table 2]

[0105] [Table 3]

[0106] The above embodiment encompasses the following technical concepts. (1) A method for producing foamed polyolefin resin particles, wherein polyolefin resin particles containing carbon dioxide, dispersed in an aqueous medium inside a sealed container, are released from the sealed container under a pressure lower than the pressure inside the sealed container to cause foaming, The polyolefin resin particles contain one or more compounds A selected from the group consisting of magnesium nitrate, tripotassium phosphate, trisodium phosphate, potassium carbonate, and calcium nitrate, and talc. The amount of talc added is 0.01 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of the resin constituting the polyolefin resin particles. A method for producing polyolefin resin foam particles, characterized in that the ratio of the amount of compound A added to the amount of talc added is 0.5 or more and 5 or less by mass ratio. (2) The method for producing polyolefin resin foam particles according to (1), characterized in that the sum of the amount of talc added and the amount of compound A added is 0.02 parts by mass or more and 1 part by mass or less per 100 parts by mass of the resin constituting the polyolefin resin particles. (3) The method for producing polyolefin resin foam particles according to (1) or (2), characterized in that compound A is one or more compounds a selected from the group consisting of calcium nitrate and potassium carbonate. (4) A method for producing polyolefin resin foam particles according to any one of (1) to (3), characterized in that the amount of compound A added is 0.05 parts by mass or more and 0.6 parts by mass or less per 100 parts by mass of the resin constituting the polyolefin resin particles. (5) A method for producing polyolefin resin foam particles according to any one of (1) to (4) above, characterized in that compound A is a powder. (6) The apparent density of the polyolefin resin foam particles is 30 kg / m³ 3 More than 100kg / m 3 A method for producing polyolefin resin foam particles according to any one of the above (1) to (5), characterized in that it is as follows: (7) The polyolefin resin foam particles contain carbon black, A method for producing polyolefin resin foam particles according to any one of (1) to (6) above, characterized in that the amount of carbon black added is 0.5 parts by mass or more and 5 parts by mass or less per 100 parts by mass of resin. (8) The method for producing polyolefin resin foam particles according to (7), characterized in that the ratio of the amount of carbon black added to the amount of compound A added is 1 or more and 50 or less by mass ratio. (9) Polyolefin resin foam particles, The average bubble diameter of the polyolefin resin foam particles is 20 μm or more and 200 μm or less. The polyolefin foam particles contain one or more compounds A selected from magnesium nitrate, tripotassium phosphate, trisodium phosphate, potassium carbonate, and calcium nitrate, and talc. The talc content is 0.01 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of the resin constituting the polyolefin-based foamed particles. Polyolefin resin foam particles characterized in that the ratio of the content of compound A to the content of talc is 0.5 or more and 5 or less by mass ratio. (10) The polyolefin resin foam particle according to (9), characterized in that the sum of the talc content and the compound A content is 0.02 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of the resin constituting the polyolefin resin foam particle. (11) The polyolefin resin foam particles according to (9) or (10), characterized in that compound A is one or more compounds selected from the group consisting of calcium nitrate and potassium carbonate. (12) The polyolefin resin foam particle according to any one of (9) to (11), characterized in that the content of compound A is 0.05 parts by mass or more and 0.3 parts by mass or less per 100 parts by mass of the resin constituting the polyolefin resin foam particle. (13) Polyolefin resin foam particles according to any one of the above (9) to (12), characterized in that compound A is a powder. (14) Apparent density of 50 kg / m³ 3 More than 100kg / m 3 Polyolefin resin foam particles according to any one of the above items (9) to (13), characterized in that they are as follows: (15) Contains carbon black, The polyolefin resin foam particle according to any one of (9) to (14), characterized in that the carbon black content is 0.5 parts by mass or more and 5 parts by mass or less per 100 parts by mass of resin. (16) The polyolefin resin foam particles according to (15), characterized in that the ratio of the carbon black content to the compound A content is 1 or more and 50 or less by mass ratio.

Claims

1. A method for producing foamed polyolefin resin particles, comprising releasing polyolefin resin particles containing carbon dioxide, which are dispersed in an aqueous medium inside a sealed container, from the sealed container under a pressure lower than the pressure inside the sealed container to cause foaming, The polyolefin resin particles contain one or more compounds A selected from the group consisting of magnesium nitrate, tripotassium phosphate, trisodium phosphate, potassium carbonate, and calcium nitrate, and talc, wherein the amount of talc added is 0.01 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of the resin constituting the polyolefin resin particles. A method for producing polyolefin resin foam particles, characterized in that the ratio of the amount of compound A added to the amount of talc added is 0.5 or more and 5 or less by mass ratio.

2. A method for producing polyolefin resin foam particles according to claim 1, wherein the total amount of talc added and the amount of compound A added is 0.02 parts by mass or more and 1 part by mass or less per 100 parts by mass of the resin constituting the polyolefin resin particles.

3. A method for producing polyolefin resin foam particles according to claim 1 or 2, wherein the compound A is one or more compounds a selected from the group consisting of calcium nitrate and potassium carbonate.

4. A method for producing polyolefin resin foam particles according to any one of claims 1 to 3, wherein the amount of compound A added is 0.05 parts by mass or more and 0.6 parts by mass or less per 100 parts by mass of the resin constituting the polyolefin resin particles.

5. The apparent density of the polyolefin resin foam particles is 30 kg / m³ 3 More than 100kg / m 3 A method for producing polyolefin resin foamed particles according to any one of claims 1 to 4 below.

6. Polyolefin resin foam particles, The average bubble diameter of the polyolefin resin foam particles is 20 μm or more and 200 μm or less. The polyolefin foam particles contain one or more compounds A selected from magnesium nitrate, tripotassium phosphate, trisodium phosphate, potassium carbonate, and calcium nitrate, and talc. The talc content is 0.01 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of the resin constituting the polyolefin-based foamed particles. Polyolefin resin foam particles characterized in that the ratio of the content of compound A to the content of talc is 0.5 or more and 5 or less by mass ratio.

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