Polyolefin resin foam particles and method for producing the same

Abstract

The objective is to provide polyolefin-based resin foam particles that can provide a foamed molded article with excellent sound absorption performance and reduced moisture content. [Solution] The above problem is solved by using polyolefin resin foam particles that have a degree of irregularity of 2.2 or higher and contain an antistatic agent present in a specific amount on their surface.

Description

[Technical Field]

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

[0002] Polyolefin resin foam molded products, which are formed by molding polyolefin resin foam particles, are widely used in various applications, including automotive interior components, core materials for automotive bumpers, as well as insulation materials, cushioning materials, and reusable containers. In particular, there is a demand for foam materials with sound-absorbing properties in automotive interior components.

[0003] Various types of polyolefin-based resin foam particles and polyolefin-based resin foam molded articles have been developed (for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. WO2024 / 204495 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, the conventional technologies described above were insufficient in terms of the moisture content of the foamed molded body, and there was room for further improvement. Furthermore, as mentioned above, foamed molded bodies are sometimes required to have sound-absorbing properties.

[0006] One embodiment of the present invention has been made in view of the above-mentioned problems, and its objective is to provide polyolefin resin foam particles that can provide a foamed molded article with excellent sound absorption performance and reduced moisture content. [Means for solving the problem]

[0007] To solve the aforementioned problems, one embodiment of the present invention includes the following configuration.

[0008] [1] Polyolefin resin foam particles having a degree of irregularity of 2.2 or more, wherein the polyolefin resin foam particles contain an antistatic agent present on the surface of the polyolefin resin foam particles, and the amount of the antistatic agent is 0.0010 parts by weight or more per 100 parts by weight of the polyolefin resin foam particles.

[0009] [2] The polyolefin resin foam particles according to [1], wherein the content of the antistatic agent is 1.0000 parts by weight or less per 100 parts by weight of polyolefin resin foam particles.

[0010] [3] The polyolefin resin foam particles are the polyolefin resin foam particles according to [1] or [2], comprising more than 50 parts by weight of polyolefin resin per 100 parts by weight of polyolefin resin foam particles.

[0011] [4] The antistatic agent comprises at least one selected from the group consisting of nonionic surfactants, anionic surfactants, and cationic surfactants, as described in any of [1] to [3].

[0012] [5] The polyolefin resin foam particles according to any one of [1] to [4], wherein the polyolefin resin foam particles contain a polypropylene resin, and the melt index of the polypropylene resin at 230°C is 3.0 g / 10 min to 30.0 g / 10 min.

[0013] [6] The polyolefin resin foam particles according to any one of [1] to [5], wherein the polyolefin resin foam particles contain a polypropylene resin, and the melting point of the polypropylene resin is 135°C to 160°C.

[0014] [7] The polyolefin resin foam particles according to any one of [1] to [6], wherein the bulk density of the polyolefin resin foam particles is 10.0 g / L to 300.0 g / L.

[0015] A polyolefin-based resin expanded molded article obtained by molding the polyolefin-based resin expanded particles according to any one of [8] and [1] to [7].

[0016] [9] A method for producing polyolefin-based resin expanded particles having an irregularity degree of 2.2 or more, wherein the polyolefin-based resin expanded particles contain an antistatic agent present on a surface of the polyolefin-based resin expanded particles, and the method comprises a step of applying the antistatic agent to a surface of polyolefin-based resin particles before expansion, and / or a step of applying the antistatic agent to a surface of a main body of the polyolefin-based resin expanded particles, and a content of the antistatic agent is 0.0010 parts by weight or more based on 100 parts by weight of the polyolefin-based resin expanded particles. [Effects of the Invention]

[0017] According to one aspect of the present invention, there can be provided polyolefin-based resin expanded particles capable of providing an expanded molded article that is excellent in sound absorption performance and has a reduced moisture content. [Brief Description of Drawings]

[0018] [Figure 1] FIG. 1 is a front view image showing an example of a configuration of a die. [Figure 2] FIG. 2 is an image of star-shaped polyolefin-based resin particles. [Figure 3] FIG. 3 is an image of star-shaped polyolefin-based resin expanded particles. [Figure 4] FIG. 4 is a front view image showing a configuration of another die different from that of FIG. 1. [Figure 5] FIG. 5 is a front view image showing a configuration of another die different from those of FIG. 1 and FIG. 4. [Mode for Carrying Out the Invention]

[0019] One embodiment of the present invention is described below, but the present invention is not limited to the configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments or examples obtained by combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Moreover, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic and patent documents mentioned herein are incorporated as references herein. Furthermore, unless otherwise specified herein, "A to B" representing a numerical range means "A or greater (including A and greater than A) and B or less (including B and less than B)."

[0020] [Technical concept relating to one embodiment of the present invention] For example, in the conventional manufacturing of foamed molded articles as described in Patent Document 1, polyolefin resin foam particles are heated, and then the foam is cooled by spraying water onto the mold, or onto both the foamed molded article and the mold. However, foamed molded articles with high porosity and sound-absorbing properties become heavier and their water content increases when cooled in this manner. Specifically, even when cooling water is sprayed directly onto the foamed molded article, or / or indirectly onto the mold by spraying water onto the mold, the cooling water that enters the molding space through grooves called core vents in the mold is absorbed between the foam particles in the molding space, which has cooled from a steam-filled state to a reduced pressure, thus increasing the water content. When the foamed molded article becomes heavy, cracking and chipping may occur during demolding, or deformation may occur on the chute. In addition, if the water content of the foamed molded article is high, a lot of time and energy is required for drying.

[0021] Therefore, the inventors diligently conducted research with the aim of providing polyolefin resin foam particles that can provide a foam molded article with excellent sound absorption performance and reduced moisture content (especially the moisture content after cooling by water injection during manufacturing). The inventors have found that foam molded articles obtained from foam particles whose irregularity, an index indicating the bulkiness of polyolefin resin foam particles, is greater than a predetermined value have excellent sound absorption performance. In their research to solve the above problem, the inventors have independently discovered a novel finding: foam molded articles obtained from polyolefin resin foam particles with an irregularity of 2.2 that can provide a foam molded article with excellent sound absorption performance, by adding an antistatic agent to the foam particles on which the antistatic agent is present, not only have excellent sound absorption performance, but also, surprisingly, a reduced moisture content after cooling by water injection during manufacturing. The inventors have further found that a similar effect can be obtained from foam molded articles obtained from foam particles obtained by adding an antistatic agent to polyolefin resin particles before foaming and then foaming them. As a result, the inventors have completed the present invention.

[0022] [1. Polyolefin resin foam particles] The polyolefin resin foam particles according to one embodiment of the present invention are polyolefin resin foam particles having a degree of irregularity of 2.2 or more, and the polyolefin resin foam particles contain an antistatic agent present on the surface of the polyolefin resin foam particles, and the content of the antistatic agent is 0.0010 parts by weight or more per 100 parts by weight of the polyolefin resin foam particles.

[0023] In this specification, polyolefin-based foamed resin particles to which no additives have been added after foaming may be referred to as "polyolefin-based foamed resin particle body." Polyolefin-based foamed resin particles are the final obtained polyolefin-based foamed resin particles containing an antistatic agent present on the surface, and if no additives are added after foaming the polyolefin-based resin particles, then "polyolefin-based foamed resin particle body" can be said to be polyolefin-based foamed resin particles. Furthermore, in this specification, "polyolefin-based resin particles" may be referred to as "resin particles," "polyolefin-based foamed resin particles" may be referred to as "foamed particles," "polyolefin-based foamed particle body" may be referred to as "foamed particle body," and "polyolefin-based foamed molded article" may be referred to as "foamed molded article."

[0024] Because the polyolefin resin foam particles according to one embodiment of the present invention have the above-described configuration, it is possible to provide a foamed molded article with excellent sound absorption performance. If the maximum sound absorption coefficient of the foamed molded article measured by the method described in detail in the following examples is, for example, 0.8 or higher, the foamed molded article can be considered to have excellent sound absorption performance. Because the polyolefin resin foam particles according to one embodiment of the present invention have the above-described configuration, it is possible to provide a foamed molded article with reduced moisture content, particularly the moisture content after cooling by water injection during manufacturing. If the moisture content of the foamed molded article measured by the method described in detail in the following examples is, for example, 200% or less, the foamed molded article can be considered to have excellent moisture content.

[0025] In this specification, "polyolefin resin foam particles contain an antistatic agent present on the surface of the polyolefin resin foam particles" means any of the following: (i) the entire amount of antistatic agent contained in the foam particles forms a layer on the surface of the foam particles; (ii) the entire amount of antistatic agent contained in the foam particles is impregnated into the surface layer of the foam particles; or (iii) a portion of the entire amount of antistatic agent contained in the foam particles forms a layer on the surface of the foam particles, and the remaining portion is impregnated into the surface layer of the foam particles.

[0026] Also, in the present specification, the "structural unit derived from an X monomer" contained in a polymer, copolymer or resin may be referred to as an "X unit".

[0027] Unless otherwise specified in the present specification, as a structural unit, X 1 unit, X 2 unit, ... and X n unit (n is an integer of 2 or greater), the copolymer containing these units is also referred to as "X 1 / X 2 / ... / X n copolymer". For the X 1 / X 2 / ... / X n copolymer, unless explicitly stated, the polymerization mode is not particularly limited, and it may be a random copolymer, an alternating copolymer, a block copolymer, or a graft copolymer.

[0028] [1-1. Polyolefin-based resin, polyolefin-based resin particles] In one embodiment of the present invention, the expanded polyolefin-based resin particles are particles obtained by expanding the polyolefin-based resin particles described later, and contain a predetermined amount of an antistatic agent present on the surface thereof. In one embodiment of the present invention, the expanded polyolefin-based resin particles may contain components contained in the polyolefin-based resin particles (for example, the polyolefin-based resin, and optionally other resins and / or additives).

[0029] <Polyolefin-based resin> In one embodiment of the present invention, the term "polyolefin-based resin" refers to a resin in which the content of olefin units is the highest among all structural units constituting the resin. The polyolefin-based resin contains 50 mol% or more, preferably 60 mol% or more, more preferably 70 mol% or more, still more preferably 80 mol% or more, and particularly preferably 90 mol% or more of olefin units based on 100 mol% of all structural units.

[0030] Examples of the polyolefin resins include polyethylene resins such as low, medium, and high-density polyethylene, linear low and ultra-low-density polyethylene, and ethylene / vinyl acetate copolymers; and polypropylene resins such as polypropylene and ethylene / propylene copolymers. These may be used individually or in combination of two or more types.

[0031] In particular, polyolefin resins are more preferably polypropylene resins in which propylene units have the highest content among all constituent units of the resin. For example, a polypropylene resin contains 50 mol% or more propylene units per 100 mol% of all constituent units. A polypropylene resin may be (i) a homopolymer of propylene, (ii) a block copolymer, impact copolymer, alternating copolymer, random copolymer or graft copolymer of propylene and monomers other than propylene, or (iii) a mixture of two or more of these.

[0032] In foaming resin particles and molding foamed particles, it is preferable that the polypropylene resin be a random copolymer of propylene and a monomer other than propylene, as this offers the advantage of being able to process the resin particles and foamed particles at low heating temperatures.

[0033] Polypropylene resins may have one or more constituent units derived from monomers other than propylene monomers, in addition to propylene units, and may have one or more of these units.

[0034] Examples of monomers other than the propylene monomer include α-olefins having 2 or 4 to 12 carbon atoms, such as ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene, and 1-decene.

[0035] Specific examples of polypropylene resins include polypropylene homopolymers, ethylene / propylene random copolymers, 1-butene / propylene random copolymers, 1-butene / ethylene / propylene random copolymers, ethylene / propylene block copolymers, 1-butene / propylene block copolymers, propylene / chlorinated vinyl copolymers, propylene / maleic anhydride copolymers, and styrene-modified polypropylene resins.

[0036] As the polypropylene resin, one of the examples described above may be used alone, or two or more may be used in combination. Among the examples described above, ethylene / propylene random copolymer and / or 1-butene / ethylene / propylene random copolymer are preferred as the polypropylene resin because the resin particles have good foaming properties and the foamed particles have good moldability.

[0037] The polyolefin resin may contain a polypropylene resin and a polyolefin resin other than the polypropylene resin. Examples of polyolefin resins other than the polypropylene resin include (a) ethylene resins such as high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, linear ultra-low-density polyethylene, ethylene / vinyl acetate copolymer, ethylene / acrylic acid copolymer, and ethylene / methacrylic acid copolymer; (b) polyolefin waxes such as propylene / α-olefin wax; and (c) olefin rubbers such as ethylene / propylene rubber, ethylene / butene rubber, ethylene / hexene rubber, and ethylene / octene rubber. When the polyolefin resin contains a polypropylene resin and a polyolefin resin other than the polypropylene resin, the content of the polyolefin resin other than the polypropylene resin is, for example, 0.1 parts by weight to 20.0 parts by weight, and more preferably 0.5 parts by weight to 15.0 parts by weight, per 100 parts by weight of the polypropylene resin. When the content of polyolefin resins other than polypropylene resins is within the aforementioned range, there is an advantage that the foaming properties of the resin particles and / or the moldability of the foamed particles tend to be good.

[0038] The melting point of the polyolefin resin is not particularly limited, but is preferably 135°C to 160°C, more preferably 138°C to 158°C, more preferably 140°C to 156°C, more preferably 143°C to 154°C, even more preferably 145°C to 152°C, and particularly preferably 148°C to 150°C. When the melting point of the polyolefin resin is (i) 135°C or higher, a foamed molded article with excellent heat resistance can be obtained, and when it is 160°C or lower, it becomes easier to increase the foaming ratio of the foamed particles in the production of the foamed particles. Furthermore, when the melting point of the polyolefin resin is within the above range, there is an advantage in that a polyolefin resin foamed molded article with high strength can be obtained. The method for measuring the melting point of the polyolefin resin will be explained in detail in the examples described later.

[0039] The melt index (MI) of the polyolefin resin at 230°C (230±0.2°C) is preferably 3.0 g / 10 min to 30.0 g / 10 min, more preferably 4.0 g / 10 min to 20.0 g / 10 min, even more preferably 5.0 g / 10 min to 15.0 g / 10 min, even more preferably 7.0 g / 10 min to 13.0 g / 10 min, and particularly preferably 8.5 g / 10 min to 12.0 g / 10 min. MI is sometimes referred to as "melt flow rate (MFR)". The above configuration has the advantage of being able to obtain a polyolefin resin foam molded article with high foaming properties. The method for measuring the MI of the polyolefin resin will be explained in detail in the examples described later.

[0040] Polyolefin resins can be obtained by known methods. There are no particular restrictions on the polymerization catalyst used when synthesizing polyolefin resins; for example, Ziegler catalysts and metallocene catalysts can be used.

[0041] In one embodiment of the present invention, the polyolefin resin foam particles preferably contain more than 50 parts by weight, more preferably 60 parts by weight or more, even more preferably 70 parts by weight or more, and particularly preferably 80 parts by weight or more of the polyolefin resin per 100 parts by weight of the polyolefin resin foam particles. If the polyolefin resin foam particles contain more than 50 parts by weight of the polyolefin resin, there is an advantage that a polyolefin resin foam with high strength and excellent heat resistance can be obtained. The upper limit of the content of the polyolefin resin contained per 100 parts by weight of the polyolefin resin foam particles may be, for example, 99 parts by weight or less.

[0042] <Other resins> In one embodiment of the present invention, the polyolefin resin particles may contain resins other than polyolefin resins (sometimes referred to as other resins). Therefore, foamed polyolefin resin particles obtained by foaming polyolefin resin particles may further contain other resins derived from the polyolefin resin particles. The other resins are not particularly limited as long as they are resins other than the resin in which the olefin unit content is the highest among all constituent units of the resin. Examples of the other resins include (a) vinyl / acrylic resins such as ethylene / vinyl acetate copolymer, ethylene / acrylic acid copolymer, and ethylene / methacrylic acid copolymer, (b) polyphenylene ether resins such as polyphenylene ether and modified polyphenylene ether, and (c) polystyrene resins, hydrogenated styrene copolymers, etc.

[0043] When the polyolefin resin foam particles contain other resins, the content of the other resins in the foam particles is, for example, 0.1 to 20.0 parts by weight, more preferably 0.5 to 15.0 parts by weight, even more preferably 1.0 to 10.0 parts by weight, and even more preferably 3.0 to 8.0 parts by weight, per 100 parts by weight of the polyolefin resin. When the content of the other resins is within the above range, there is an advantage that the foaming properties of the resin particles and / or the moldability of the foam particles tend to be good.

[0044] <Additives contained within resin particles> In one embodiment of the present invention, the polyolefin resin particles may optionally contain additives inside the resin particles in addition to the polyolefin resin. Examples of such additives include colorants, hydrophilic compounds, nucleating agents, antistatic agents, flame retardants, antioxidants, light stabilizers, conductive agents, and lubricants. The additives contained inside the resin particles are added during the process leading up to the preparation of the resin particles. That is, since the additives are contained inside the polyolefin resin particles or washed away from the polyolefin resin particles during their preparation, they are distinguished from additives present on the surface of the polyolefin resin particles. Furthermore, even in foamed particles formed by foaming the resin particles, the additives are contained inside the foamed particles, and are therefore distinguished from additives present on the surface of the foamed particles.

[0045] The hydrophilic compound is a substance used to increase the amount of water impregnated in the resin particles. The hydrophilic compound can impart foaming properties to the resin particles. The foaming effect of the hydrophilic compound on the resin particles is particularly pronounced when water is used as a foaming agent. The hydrophilic compound that can be used in one embodiment of the present invention is preferably one or more selected from the group consisting of glycerin, polyethylene glycol, aliphatic alcohols having 12 to 18 carbon atoms (e.g., pentaerythritol, cetyl alcohol, stearyl alcohol), melamine, isocyanuric acid, melamine-isocyanuric acid condensate, and zinc borate. One of these hydrophilic compounds may be used alone, or two or more may be used in combination.

[0046] The aforementioned nucleating agent is a substance that can act as a foaming nucleus when the resin particles are foamed. It is preferable that the resin particles contain the nucleating agent. Examples of nucleating agents that can be used in one embodiment of the present invention include talc, feldspar, zeolite, kaolin, mica, calcium stearate, calcium carbonate, silica, titanium dioxide, bentonite, barium sulfate, zinc borate, etc., with an average particle diameter per particle exceeding 1000 nm. One of these nucleating agents may be used alone, or two or more may be used in mixture form.

[0047] The aforementioned light stabilizer is a substance used for purposes such as protecting the foam from degradation by ultraviolet light and stabilizing the dispersion state of resin particles during foaming. Examples of light stabilizers that can be used in one embodiment of the present invention include hindered amine light stabilizers (HALS) and ultraviolet absorbers. One of these light stabilizers may be used alone, or two or more may be used in combination.

[0048] <Additives contained on the surface of resin particles (post-additives)> In one embodiment of the present invention, the polyolefin resin particles may include an additive present on the surface of the resin particles. Here, "present on the surface of the resin particles" means any of the following: (i) the entire amount of the additive forms a layer on the surface of the resin particles; (ii) the entire amount of the additive is impregnated into the surface layer of the resin particles; or (iii) a portion of the entire amount of the additive forms a layer on the surface of the resin particles, and the remaining portion is impregnated into the surface layer of the resin particles. The additive is an additive that is added after the resin particles are prepared and present on the surface of the resin particles (hereinafter referred to as "post-resin particle additive" in this specification).

[0049] If an antistatic agent is included as a post-addition for resin particles, the antistatic agent is present on the surface of the resin particles. When these resin particles are foamed, foamed particles containing the antistatic agent present on the surface of the foamed particles are obtained.

[0050] The resin particle post-additive may include other resin particle post-additives other than antistatic agents, as long as they do not undesirably affect the effects of the present invention. Examples of other resin particle post-additives include surfactants, lubricants, conductive materials, flame retardants, scratch-resistant materials, etc. The resin particle post-additive is also present on the surface of foamed particles formed by foaming resin particles.

[0051] [1-2] Antistatic agent The polyolefin resin foam particles according to one embodiment of the present invention contain an antistatic agent present on the surface of the polyolefin resin foam particles. The polyolefin resin foam particles according to one embodiment of the present invention have the advantage of being able to provide a foamed molded article with reduced water content (particularly the water content after cooling by water injection during manufacturing) by containing an antistatic agent present on the surface of the polyolefin resin foam particles.

[0052] The antistatic agent is not particularly limited as long as it is a substance that is normally used as an antistatic agent. Examples of the antistatic agent include nonionic surfactants such as alkylamide-type nonionic surfactants, ethylene oxide condensation-type nonionic surfactants, and polyhydric alcohol ester-type nonionic surfactants; anionic surfactants such as sodium alkyldiphenyl ether disulfonate, carboxylate-type anionic surfactants, phosphate ester-type anionic surfactants, sulfonate-type anionic surfactants, and sulfate ester-type anionic surfactants; cationic surfactants such as N-hydroxyethyl(2-hydroxyalkyl)amine-inorganic acid salts, aliphatic quaternary ammonium salt-type cationic surfactants, aliphatic amine salt-type cationic surfactants, aliphatic quaternary ammonium salt-type cationic surfactants, heterocyclic quaternary ammonium salt-type cationic surfactants, and aromatic quaternary ammonium salt-type cationic surfactants; and amphoteric surfactants such as glycine-type amphoteric surfactants and aminoacetic acid betaine-type amphoteric surfactants. The antistatic agent may be used alone as one of the above-mentioned specific examples, or two or more may be used in combination. In particular, from the viewpoint of providing a foamed molded article with a further reduced water content, the antistatic agent is more preferably (i) comprising at least one selected from the group consisting of nonionic surfactants, anionic surfactants, and cationic surfactants, and may consist only of at least one selected from the group; (ii) comprising at least one selected from the group consisting of nonionic surfactants and cationic surfactants, and may consist only of at least one selected from the group; and (iii) comprising a cationic surfactant, and may consist only of a cationic surfactant.

[0053] The antistatic agent preferably contains, in total at least 50% by weight or more of at least one selected from the group consisting of nonionic surfactants, anionic surfactants, and cationic surfactants, and is more preferably 60% by weight or more, more preferably 70% by weight or more, more preferably 80% by weight or more, and even more preferably 90% by weight or more, in 100% by weight of the antistatic agent. The antistatic agent may also contain, in total at least 100% by weight of at least one selected from the group consisting of nonionic surfactants, anionic surfactants, and cationic surfactants, in 100% by weight of the antistatic agent.

[0054] In one embodiment of the present invention, the content of the antistatic agent is 0.0010 parts by weight or more, more preferably 0.0030 parts by weight or more, even more preferably 0.0050 parts by weight or more, and even more preferably 0.0100 parts by weight or more, per 100 parts by weight of the polyolefin resin foam particle body. If the content of the antistatic agent is 0.0010 parts by weight or more, it is possible to provide polyolefin resin foam particles that have excellent sound absorption performance and a reduced water content after cooling by water spraying during manufacturing. The upper limit of the content of the antistatic agent is not particularly limited, but for example, it is 1.0000 parts by weight or less, more preferably 0.9000 parts by weight or less, and even more preferably 0.8000 parts by weight or less, per 100 parts by weight of the polyolefin resin foam particle body.

[0055] Furthermore, in one embodiment of the present invention, the content of the antistatic agent is 0.0010 parts by weight or more, more preferably 0.0030 parts by weight or more, even more preferably 0.0050 parts by weight or more, and even more preferably 0.0100 parts by weight or more, per 100 parts by weight of polyolefin resin foam particles. If the content of the antistatic agent is 0.0010 parts by weight or more, it is possible to provide polyolefin resin foam particles that have excellent sound absorption performance and a reduced water content after cooling by water spraying during manufacturing. The upper limit of the content of the antistatic agent is not particularly limited, but for example, it is 1.0000 parts by weight or less, more preferably 0.9000 parts by weight or less, and even more preferably 0.8000 parts by weight or less, per 100 parts by weight of polyolefin resin foam particles.

[0056] Here, the amount of antistatic agent contained in the polyolefin resin foam particles can be measured by the method described in JIS K3362.

[0057] [1-3] Other additives present on the surface of the foamed particle body The foamed particles may contain other additives on their surface in addition to the antistatic agent. Hereinafter, in this specification, other additives present on the surface of the foamed particles will be referred to as other "external additives." Examples of such other external additives include surfactants, lubricants, conductive materials, flame retardants, scratch-resistant materials, and the like. These other external additives may be post-additives added to the resin particles after preparation but before foaming, and / or additives added to the foamed particle body itself.

[0058] The total amount of the other external additives is, for example, 10 parts by weight or less, or 5 parts by weight or less, per 100 parts by weight of the foaming particles.

[0059] [1-4] Method for producing polyolefin resin foam particles A method for producing polyolefin resin foam particles according to one embodiment of the present invention is a method for producing polyolefin resin foam particles having a degree of irregularity of 2.2 or more, wherein the polyolefin resin foam particles contain an antistatic agent present on the surface of the polyolefin resin foam particles, and the method includes the steps of applying the antistatic agent to the surface of the polyolefin resin particles before foaming, and / or applying the antistatic agent to the surface of the polyolefin resin foam particle body, wherein the content of the antistatic agent is 0.0010 parts by weight or more per 100 parts by weight of the polyolefin resin foam particles. A method for producing polyolefin resin foam particles according to one embodiment of the present invention allows the presence of an antistatic agent on the surface of the foam particles by including either or both of the steps of applying the antistatic agent to the surface of the polyolefin resin particles before foaming, and applying the antistatic agent to the surface of the polyolefin resin foam particle body. This has the advantage of providing a foamed molded article with reduced moisture content (especially the moisture content after cooling by water injection during manufacturing).

[0060] The method for producing foamed particles is not particularly limited to any other steps, as long as it includes steps other than the step of applying the antistatic agent to the surface of polyolefin resin particles before foaming, and / or the step of applying the antistatic agent to the surface of the polyolefin resin foamed particle body (antistatic agent application step). Known manufacturing methods can be used as appropriate. One embodiment of the method for producing foamed particles will be described in detail below, but the method for producing foamed particles is not limited to the method described below. In the following embodiment, the step of applying the antistatic agent to the surface of the resin particles is performed on the polyolefin resin particles obtained in the polyolefin resin particle manufacturing step described below, and the step of applying the antistatic agent to the surface of the foamed particle body is performed on the foamed particle body obtained in the release step described below. If a two-stage foaming process is performed, it is sufficient to perform it on the obtained foamed particle body in at least one of the stages.

[0061] (Polyolefin resin particle manufacturing process) In manufacturing foamed particles, a process for manufacturing polyolefin-based resin particles (resin particle manufacturing process) may be carried out first. Here, polyolefin-based resin particles refer to resin particles containing the aforementioned polyolefin-based resin.

[0062] The resin particle manufacturing process is not particularly limited as long as resin particles can be obtained, and known methods can be employed. An example of a resin particle manufacturing process is a method in which the following (S1) to (S3) are carried out in order: (S1) A predetermined amount of the polyolefin resin, and if necessary, the other resin and the additive are melt-kneaded together using an extruder to prepare a molten mixture; (S2) The molten mixture is extruded from a die provided in the extruder; (S3) The extruded molten mixture is shredded to a desired length to obtain polyolefin resin particles.

[0063] In (S1) above, a blend may be prepared in advance by blending a predetermined amount of polyolefin resin with, if necessary, the other resin and the additive. The blend may then be subjected to an extruder and melt-kneaded to prepare a melt-kneaded product.

[0064] In (S2) above, the die shape can be selected to match the desired shape of the foam particle body. Here, the die shape is the same as or substantially the same as the desired shape of the foam particle body. Furthermore, the shape of the foam particle body is the same as or substantially the same as the shape of the foam particle containing the antistatic agent present on its surface. Also, when a post-additive is added to the resin particles, the shape of the resin particles after the addition is the same as or substantially the same as the shape of the resin particles before the addition. For example, when resin particles obtained by extruding a resin composition using the die shown in Figure 5 are used, macaroni-shaped foam particle bodies and foam particles can be obtained.

[0065] In (S3) above, before shredding the molten mixture, the extruded molten mixture may be cooled and solidified using a cooling medium such as water.

[0066] (Dispersion process) In manufacturing the foamed particle body, a subsequent step (dispersion step) may be performed in which polyolefin resin particles and a foaming agent are dispersed in an aqueous dispersion medium within a container.

[0067] As a container, for example, a pressure-resistant vessel such as an autoclave-type pressure vessel can be used. The container may also be equipped with a stirrer inside.

[0068] Examples of aqueous dispersion media include (a) dispersion media obtained by adding methanol, ethanol, ethylene glycol, and glycerin to water, (b) water such as ultrapure water, pure water, tap water, and industrial water, and (c) solutions (aqueous solutions) containing salts such as sodium chloride or sodium sulfate.

[0069] Examples of blowing agents include (a) (a-1) inorganic gases such as nitrogen, carbon dioxide, and air, and (a-2) water, and other inorganic blowing agents; and (b) (b-1) saturated hydrocarbons having 3 to 5 carbon atoms such as propane, n-butane, isobutane, n-pentane, isopentane, and neopentane; (b-2) ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether; and (b-3) halogenated hydrocarbons such as monocormethane, chloroethane, and hydrofluoroolefin.

[0070] In the production of foamed particle bodies, it is preferable to use dispersants (e.g., inorganic substances such as tricalcium phosphate, kaolin, and talc) and dispersion aids (e.g., anionic surfactants such as sodium dodecylbenzenesulfonate). This configuration reduces adhesion between resin particles (sometimes referred to as blocking) and improves the stability of the dispersion liquid in the container. As a result, it has the advantage of being able to produce foamed particle bodies stably.

[0071] The aforementioned aqueous dispersion medium and foaming agent may be used individually or in combination of two or more types.

[0072] The amounts used for the aqueous dispersion medium, foaming agent, dispersant, and dispersion aid are not particularly limited and can be set appropriately considering (i) the stability of the dispersion (dispersibility of resin particles), (ii) the density of the resulting foamed particle body, (iii) the fusion properties of the foamed molded article formed by molding the resulting foamed particle body, (iv) productivity, and (v) economic efficiency.

[0073] In the method for producing the foamed particles, it is preferable to use a pH adjusting agent (for example, citric acid, malic acid, succinic acid, tartaric acid, and oxalic acid). This configuration has the advantage of suppressing equipment corrosion.

[0074] The amount of pH adjusting agent used is not particularly limited, but is preferably 0.001 to 1.00 parts by weight, more preferably 0.003 to 0.50 parts by weight, and even more preferably 0.005 to 0.30 parts by weight per 100 parts by weight of polyolefin resin particles. This configuration has the advantages of high productivity of the foamed particle body and suppression of equipment corrosion.

[0075] The method for dispersing polyolefin resin particles and a foaming agent in an aqueous dispersion medium within a container, i.e., the specific method of the dispersion process, is not particularly limited. For example, one method involves supplying an aqueous dispersion medium, polyolefin resin particles, and a foaming agent into a container and stirring the mixture in the container with a stirrer provided in the container.

[0076] (Heating-pressure boosting process and holding process) In the production of the foamed particle body, it is preferable to further include, in this order, (1) a heating-pressure step in which the temperature inside the container is raised to a constant temperature and the pressure inside the container is raised to a constant pressure, and (2) a holding step in which the temperature and pressure inside the container are maintained at a constant temperature and a constant pressure, after the dispersion step and before the release step. In this specification, (a) the constant temperature in the heating-pressure step and the holding step may be referred to as the foaming temperature, and (b) the constant pressure may be referred to as the foaming pressure.

[0077] The foaming temperature is preferably 130.0°C to 170.0°C, more preferably 135.0°C to 165.0°C, even more preferably 138.0°C to 162.0°C, and particularly preferably 140.0°C to 160.0°C. This configuration has the advantage of easily obtaining foamed particle bodies with good foaming properties and moldability.

[0078] The foaming pressure is preferably 0.5 MPa (gauge pressure) to 10.0 MPa (gauge pressure), more preferably 0.6 MPa (gauge pressure) to 5.0 MPa (gauge pressure), and even more preferably 0.6 MPa (gauge pressure) to 3.5 MPa (gauge pressure). If the foaming pressure is 0.5 MPa (gauge pressure) or higher, foamed particles with a suitable density can be obtained.

[0079] In the holding process, the time for holding the dispersion in the container at or near the foaming temperature and pressure (holding time) is not particularly limited, but for example, 10 to 60 minutes is preferred, 12 to 50 minutes is more preferred, and 15 to 40 minutes is even more preferred.

[0080] (Release process) In manufacturing the foamed particle body, a step (release step) may be performed in which the dispersion obtained in the dispersion step is released into a region with a pressure lower than the pressure inside the container.

[0081] The release process allows the resin particles to foam, resulting in the formation of foamed particles. The release process can also be described as a process of releasing the dispersion liquid inside the container into a region (space) with a pressure lower than the foaming pressure (i.e., the pressure inside the container) by opening one end of the container.

[0082] In the release process, the "region with a pressure lower than the foaming pressure" refers to the "region under a pressure lower than the foaming pressure" or the "space under a pressure lower than the foaming pressure," and can also be described as "an atmosphere with a pressure lower than the foaming pressure." The region with a pressure lower than the foaming pressure may, for example, be a region under atmospheric pressure.

[0083] (Foaming process) The process from dispersion to release is sometimes referred to as the foaming process. Furthermore, the process of manufacturing foamed particle bodies from resin particles in this manner is called the "single-stage foaming process," and the resulting foamed particle bodies are called "single-stage foamed particle bodies."

[0084] (Two-stage foaming process) To obtain foamed particle bodies with a high foaming ratio, the foamed particle bodies obtained in the first foaming step may be foamed again. The step of increasing the foaming ratio of the foamed particle bodies in the first foaming step is called the "second foaming step," and the foamed polyolefin resin particles obtained in the second foaming step are called the "second foamed particle bodies." The specific method of the second foaming step is not particularly limited, and known methods can be used.

[0085] (Antistatic agent application process) In one embodiment of the present invention, the step of applying the antistatic agent to the surface of the foamed particle body may be, for example, a method of adding the antistatic agent to the foamed particle body and mixing the resulting mixture. If the antistatic agent is a liquid, it may be added as is, or it may be added in a solution dissolved in any solvent. If the antistatic agent is a solid, it may be added in a solid state, or it may be added in a solution dissolved in any solvent. Furthermore, when adding two or more types of antistatic agents, the order of addition is not particularly limited.

[0086] The method of adding the antistatic agent to the foamed particle body is not particularly limited; it may be added all at once, in multiple stages, or continuously. Among these, a method of spraying the antistatic agent onto the foamed particle body in liquid form is preferred. This method allows the antistatic agent to be applied more uniformly to the surface of the foamed particle body.

[0087] The method of mixing the mixture obtained by adding the antistatic agent to the foamed particle body is not particularly limited, but can be done by stirring, for example.

[0088] One preferred embodiment involves placing the foam particle body in a container that allows the antistatic agent sprayed from the outside to pass through, and spraying the antistatic agent while stirring the foam particle body inside the container. The container can be a mesh container, a mesh bag, a mesh container, etc. The material of the container is not particularly limited and may be metal, resin, fiber, etc. Alternatively, a mixing device having a spray nozzle inside may be used. Examples of such mixing devices include (a) mixers such as Super Mixer, Nauter Mixer, Universal Mixer, Prosher Mixer, Apex Mixer, Henschel Mixer, and Rediger Mixer; and (b) blenders such as Ribbon Blender and Tumbler Blender. Conditions such as mixing time can be adjusted considering the mixing capacity, the amount of foam particle body, the amount applied, etc.

[0089] In one embodiment of the present invention, the step of applying the antistatic agent to the surface of the resin particles before foaming can also be performed by the same operation as the step of applying the antistatic agent to the surface of the foamed particle body.

[0090] In the antistatic agent application process, the amount of antistatic agent applied (amount added) should be such that the total amount applied in the process of applying the antistatic agent to the surface of the polyolefin resin particles before foaming and the process of applying the antistatic agent to the surface of the foamed polyolefin resin particles is equal to the content described in section "[1-2] Antistatic Agent".

[0091] A method for producing polyolefin resin foam particles according to one embodiment of the present invention may include a step of applying the antistatic agent to the surface of the polyolefin resin particles and / or the surface of the polyolefin resin foam particle body, but may further include a step of curing the resin particles and / or polyolefin resin foam particles after the application of the antistatic agent and / or a drying step of removing the solvent contained in the sprayed liquid. In the curing and drying step, it is preferable to cure and dry at 20°C to 40°C, and the curing and drying time is preferably 6 to 24 hours.

[0092] If the polyolefin resin foam particles contain other external additives, the method and order of adding the other additives are not particularly limited. The method of adding the other additives may be the same as the method of applying the antistatic agent to the surface of the foam particle body.

[0093] <Physical properties of polyolefin resin particles> (Particle weight of resin particles) The particle weight of the resin particles is not particularly limited, but is preferably 0.50 mg / particle to 6.0 mg / particle, more preferably 1.0 mg / particle to 5.0 mg / particle, even more preferably 1.5 mg / particle to 4.0 mg / particle, and particularly preferably 1.8 mg / particle to 3.0 mg / particle. This configuration has the advantage of good productivity of polyolefin resin particles and good mechanical properties of polyolefin resin foam molded articles.

[0094] (Shape of resin particles) The resin particles are not particularly limited, but are preferably irregularly shaped. In other words, the shape of the resin particles is not particularly limited, but is preferably a shape other than those generally used when manufacturing foamed particles (spherical, ellipsoidal, and cylindrical). For example, it is preferably one selected from the group consisting of star, anchor cross, macaroni, cross, L-shape, Y-shape, T-shape, U-shape, and polygon, more preferably one selected from the group consisting of star, anchor cross, and macaroni, and even more preferably a star shape. This configuration has the advantage of being able to obtain a polyolefin-based resin foamed molded article with excellent sound absorption performance.

[0095] In other words, the shape of the resin particles is preferably such that the degree of irregularity of the resulting foamed particles satisfies the preferred numerical range for the degree of irregularity of the foamed particle body, and consequently the degree of irregularity of the foamed particles, as described later. For example, star-shaped, anchor-cross-shaped, macaroni-shaped, etc., are preferred. Here, the degree of irregularity of the foamed particle body is the same as or approximately the same as the degree of irregularity of the foamed particles containing the antistatic agent present on the surface.

[0096] Here, Figure 1 is a front view image showing an example of the die configuration. Specifically, Figure 1 is a front view image of the die, showing the configuration of the die used to obtain the star-shaped foamed particle body and the star-shaped resin particles that serve as the raw material for the foamed particles. The star-shaped resin particles are the resin particles obtained by extruding them from the die shown in Figure 1. Figure 2 is an image of star-shaped polyolefin resin particles.

[0097] Figures 4 and 5 are front views showing a different die configuration from that in Figure 1. Specifically, Figure 4 shows the configuration of a die for obtaining anchor-cross shaped foam particles and anchor-cross shaped resin particles that serve as the raw material for the foam particles. The anchor-cross shaped resin particles are the resin particles obtained by extruding from the die shown in Figure 4. Figure 5 shows the configuration of a die for obtaining macaroni-shaped foam particles and macaroni-shaped resin particles that serve as the raw material for the foam particles. The macaroni-shaped resin particles are the resin particles obtained by extruding from the die shown in Figure 5. In this specification, "macaroni-shaped" refers to a cylindrical shape with a hollow hole formed within it.

[0098] Furthermore, the resin particles may or may not form hollow pores.

[0099] <Physical properties of polyolefin-based resin foam particles> The polyolefin resin foam particle body is a foam particle obtained by foaming the polyolefin resin particles.

[0100] (Bulk density of the foamed particle itself) The bulk density of the foamed particle body is preferably 10.0 g / L to 300.0 g / L, more preferably 12.0 g / L to 100.0 g / L, even more preferably 14.0 g / L to 60.0 g / L, even more preferably 15.0 g / L to 50.0 g / L, and particularly preferably 16.0 g / L to 40.0 g / L. This configuration has the advantage of yielding foamed particle bodies with less variation in foaming ratio and good moldability. The method for measuring the bulk density of the foamed particle body will be explained in detail in the examples described later.

[0101] (Degree of irregularity of the foamed particle itself) The polyolefin resin foam particle body preferably has a degree of irregularity represented by the following formula of 2.2 or higher: Degree of deformation = True density of polyolefin resin foam particles / Bulk density of polyolefin resin foam particles.

[0102] In this specification, the degree of irregularity is an index indicating the bulk height of the foamed particle body. The degree of irregularity of the foamed particle body is preferably 2.2 or higher, more preferably 2.4 or higher, and even more preferably 2.5 or higher. This configuration has the advantage of being able to obtain a polyolefin resin foamed molded article with excellent sound absorption performance.

[0103] Furthermore, while there is no particular upper limit to the degree of irregularity of the foamed particle body, it is preferably 3.0 or less, more preferably 2.9 or less, even more preferably 2.8 or less, and particularly preferably 2.7 or less. This configuration has the advantage of yielding a foamed molded article with high mechanical properties. Details of the method for measuring the degree of irregularity of the foamed particle body will be explained in detail in the examples described later.

[0104] The shape of the foam particle body that satisfies the preferred numerical range of irregularity mentioned above is a shape other than the shapes (spherical and cylindrical) generally used when manufacturing the foam particle body. A shape other than spherical and cylindrical may be referred to as an "irregular shape." In other words, it is preferable that the foam particle body is an irregularly shaped particle. The shape of the foam particle body is preferably one selected from the group consisting of star shape, anchor cross shape, macaroni shape, cross shape, L shape, Y shape, T shape, U shape, and polygon, more preferably one selected from the group consisting of star shape, anchor cross shape, and macaroni shape, even more preferably a star shape or anchor cross shape, and even more preferably a star shape. This configuration has the advantage of being able to obtain a polyolefin resin foam molded article with excellent sound absorption performance.

[0105] The shape of the foamed particle body is the same as or approximately the same as the shape of the resin particle. If the resin particle is an irregularly shaped resin particle, the foamed particle body obtained by foaming the resin particle will be an irregularly shaped foamed particle body. Specifically, for example, if the resin particle is star-shaped, the foamed particle body obtained by foaming the resin particle will also be star-shaped. Here, Figure 3 is an image of a star-shaped polyolefin resin foamed particle, and the foamed particle body is the same or approximately the same shape.

[0106] Furthermore, in one embodiment of the present invention, the polyolefin resin foam particle body may or may not form hollow holes.

[0107] [1-5] Physical properties of polyolefin resin foam particles The shape of the polyolefin foam particles is the same as or nearly the same as the shape of the foam particle body. If no additives are added after the polyolefin resin particles are foamed, the "polyolefin resin foam particle body" is the polyolefin foam resin particle. If additives are added after the foaming process, and the foam particle body is an irregularly shaped resin particle, then the foam particles containing the antistatic agent present on the surface will also be irregularly shaped foam particles. Specifically, for example, if the resin particles are star-shaped, then the foam particle body obtained by foaming the resin particles will also be star-shaped, and the foam particles containing the antistatic agent present on the surface will also be star-shaped.

[0108] The bulk density and morphology of the polyolefin resin foam particles are the same as or approximately the same as those of the foam particles themselves.

[0109] [2. Polyolefin-based resin foam molded product] The polyolefin resin foam molded article according to one embodiment of the present invention is preferably a foam molded article obtained by the manufacturing method described in the section "[2-2] Method for manufacturing a polyolefin resin foam molded article" described later. With this configuration, a polyolefin resin foam molded article with excellent sound absorption performance can be obtained.

[0110] [2-1] Physical properties of polyolefin-based foamed molded articles (Moisture content of foamed molded material) The moisture content of the foamed molded article according to one embodiment of the present invention is 0% to 250%, preferably 20% to 185%, more preferably 50% to 180%, even more preferably 80% to 160%, and even more preferably 90% to 140%. This configuration has the advantage of reducing cracking and chipping during demolding or deformation on the chute during the manufacturing of the foamed molded article. The method for measuring the moisture content of the polyolefin resin foamed molded article will be described in detail in the examples below.

[0111] (Void ratio of foamed molded material) The porosity of this foamed molded article is 25% or more, preferably 27% or more, more preferably 28% or more, and even more preferably 30% or more. This configuration has the advantage of being able to produce a polyolefin-based resin foamed molded article with excellent sound absorption performance.

[0112] The porosity of the foamed molded article is preferably 60% or less, more preferably 55% or less, even more preferably 50% or less, and particularly preferably 45% or less. This configuration has the advantage of being able to produce a polyolefin resin foamed molded article with excellent mechanical strength. The porosity of the polyolefin resin foamed molded article can be measured by the method described in International Publication WO2024 / 204495. The porosity is measured after the foamed molded article has been left at room temperature for 1 hour after molding, then cured and dried in a constant temperature room at 75°C for 24 hours, and then left at room temperature for 4 hours again.

[0113] (Maximum sound absorption coefficient of foamed molded material) The maximum sound absorption coefficient of this foamed molded article is preferably 0.85 or higher, and more preferably 0.90 or higher. This configuration allows the foamed molded article to exhibit excellent sound absorption performance. There is no particular upper limit to the maximum sound absorption coefficient of this foamed molded article, but it is, for example, 1.00 or lower. The method for measuring the maximum sound absorption coefficient of the polyolefin resin foamed molded article will be described in detail in the examples below.

[0114] [2-2] Method for producing a foamed polyolefin resin molded product The method for producing a polyolefin resin foamed molded article is not particularly limited as long as it is a method for molding foamed particles, and conventional methods such as in-mold foaming can be used. In-mold foaming is a method in which foamed particles are filled into a mold, a heating medium such as steam is blown into the mold to heat the foamed particles, causing the foamed particles to foam and fuse together to obtain a foamed molded article. The molding of foamed particles by the in-mold foaming method is sometimes referred to as in-mold molding. The foamed molded article according to one embodiment of the present invention is preferably made by in-mold molding of the foamed particles described in the section [1. Polyolefin Resin Foamed Particles] above.

[0115] The apparatus and molding conditions used for forming the foamed particles can be set appropriately according to the composition of the foamed particles and / or the desired foaming ratio, and are not particularly limited.

[0116] (Filling the mold with foamed particles) As the aforementioned mold, it is preferable to use a mold that consists of a fixed mold that cannot be driven and a movable mold that can be driven. Here, the fixed mold and the movable mold may be configured to form a molding space inside the fixed mold and the movable mold by driving the movable mold toward the fixed mold (this operation may be referred to as "mold closing").

[0117] The foamed particles filled into the mold may be pressurized, but from the viewpoint of sound absorption performance, it is more preferable to use foamed particles that are not pressurized.

[0118] (Heating process) The heating process involves blowing a heating medium such as steam into the mold to heat the foam particles, causing them to foam up and fuse together to obtain a foamed molded product.

[0119] In this specification, a foamed molded body present in the mold after the heating process, which has not been water-cooled or is in the process of water-cooling, may be referred to as a "pre-polyolefin-based foamed molded body" for convenience, in order to distinguish it from the final polyolefin-based resin foamed molded body.

[0120] In the heating process, polyolefin resin foam particles are heated without applying internal pressure. In other words, the heating process involves heating polyolefin resin foam particles with an internal pressure of 0.1 MPa (absolute pressure). With this configuration and a deformation degree of 2.2 or higher for the foam particles, a polyolefin resin foam molded article with excellent sound absorption performance can be obtained.

[0121] In the heating step, the temperature of the steam is not particularly limited, but is, for example, 130°C to 170°C. With this configuration, a polyolefin resin foam molded article with good fusion properties can be obtained.

[0122] In the heating step, the pressure of the steam is not particularly limited, but it is preferably 0.2 MPa (gauge pressure) to 0.7 MPa (gauge pressure). This configuration has the advantage of yielding a polyolefin resin foam molded article with good fusion properties.

[0123] (Water cooling process) The water cooling process involves water cooling the pre-polyolefin resin foam molded body obtained in the heating process by spraying water onto the mold, or both the pre-polyolefin resin foam molded body and the mold, for at least one second.

[0124] The water temperature is preferably 10°C to 70°C, and more preferably 15°C to 55°C. This configuration has the advantage of improving the productivity of polyolefin resin foam molded articles and reducing the cost of steam used for molding.

[0125] The spray pressure of the water is preferably 0.3 MPa (gauge pressure) to 0.7 MPa (gauge pressure), and more preferably 0.4 MPa (gauge pressure) to 0.65 MPa (gauge pressure). This configuration has the advantage of effectively spraying water (cooling water) onto both the pre-polyolefin resin foam molded article and the mold, or onto the mold or the pre-polyolefin resin foam molded article.

[0126] The water spraying time is 1 second or longer, preferably between 1 and 90 seconds, and more preferably between 3 and 60 seconds.

[0127] (Release and drying) A foamed molded body is obtained by removing a water-cooled in-mold foamed molded body from the mold and drying it. The method for removing the in-mold foamed molded body from the mold is not particularly limited, but examples include using air or using a release device.

[0128] The drying temperature is not particularly limited, but is preferably 70°C to 85°C, and more preferably 75°C to 83°C. This configuration has the advantage of being able to produce a polyolefin resin foam molded article with low water content with low energy consumption.

[0129] The drying time is not particularly limited, but it is preferably 10 to 24 hours, and more preferably 12 to 24 hours. This configuration has the advantage of being able to obtain a polyolefin resin foam molded article with low water content with low energy consumption.

[0130] Alternatively, during drying, the material may be allowed to cool at room temperature for 20 minutes to 1 hour, then dried at 70°C to 85°C for 10 to 24 hours, and then allowed to cool at room temperature for 2 to 6 hours. In this specification, room temperature refers to 20°C to 25°C. [Examples]

[0131] The present invention will be specifically described below with reference to examples, but the technical scope of the present invention is not limited by these examples.

[0132] 〔material〕 The materials used in the examples and comparative examples are shown below.

[0133] (Polyolefin resin) • Polyolefin resin A: 1-butene / ethylene / propylene random copolymer (propylene units 96 mol%, melting point 149°C, 1-butene content 3.8 wt%, ethylene content 0.5 wt%, MI = 10.1 g / 10 min) • Polyolefin resin B: Ethylene / propylene random copolymer (96 mol% propylene units, melting point 144°C, ethylene content 2.8% by weight, MI = 8.4 g / 10 min) • Polyolefin resin C: Linear low-density polyethylene (melting point 122℃, MI = 2.0 g / 10 min, density 0.926 g / cm³) 3 ) (Additives) • Additive A: Glycerin (Purified Glycerin D, manufactured by Lion Corporation) • Additive B: Talc (Talcan Powder (registered trademark) PK-S, manufactured by Hayashi Chemical Co., Ltd.) • Additive C: Hindered amine light stabilizer (HALS) (Tinuvin® 622 (manufactured by BASF)) (Antistatic agent) • Antistatic agent A: Alkyloramide-type nonionic surfactant (nonionic surfactant) (Profan 128 Extra®, manufactured by Sanyo Chemical Industries, Ltd.) • Antistatic agent B: Sodium alkyldiphenyl ether disulfonate (anionic surfactant) (Takesurf A-43-S (registered trademark), manufactured by Takemoto Co., Ltd.) • Antistatic agent C:N-hydroxyethyl(2-hydroxyalkyl)amine-inorganic acid salt (cationic surfactant) (EC-4®, manufactured by Kitahiro Chemical Co., Ltd.) [Measurement method] The measurement and evaluation methods for various items used in the examples and comparative examples are described below.

[0134] <Melting point of polyolefin resins> The melting point of the polyolefin resin was determined by measuring it using the DSC method with a differential scanning calorimeter (DSC6200 model, manufactured by Seiko Instruments Inc.). The specific operating procedure was as follows (1) to (4): (1) The polyolefin resin was melted by raising the temperature of 5 mg to 6 mg of polyolefin resin from 40.0°C to 220.0°C at a heating rate of 10.0°C / min; (2) The molten polyolefin resin was then crystallized by lowering the temperature from 220.0°C to 40.0°C at a cooling rate of 10.0°C / min; (3) The crystallized polyolefin resin was then further heated from 40.0°C to 220.0°C at a heating rate of 10.0°C / min; (4) The temperature of the peak (melting peak) of the DSC curve of the polyolefin resin obtained during the second heating (i.e., at (3)) was taken as the melting point of the polyolefin resin. Furthermore, if multiple peaks (melting peaks) exist in the DSC curve of the polyolefin resin obtained during the second heating step using the method described above, the temperature of the peak with the largest heat of fusion (melting peak) was defined as the melting point of the polyolefin resin.

[0135] The MI of the polyolefin resin was determined using an MI measuring instrument described in JIS K7210:1999, under the following conditions: orifice diameter of 2.0959 ± 0.005 mmφ, orifice length of 8.000 ± 0.025 mm, load of 2.16 kgf, and temperature of 230 °C (230 ± 0.2 °C).

[0136] <Degree of irregularity of foamed particles> The degree of irregularity of polyolefin resin foam particles was calculated by dividing the "true density," measured by the method described below, by the "bulk density," also measured by the method described below. Specifically, it was measured using the following formula: Degree of deformation of foamed particles = True density of foamed particles (g / L) / Bulk density of foamed particles (g / L). The degree of irregularity of the foamed particles themselves was also measured using this method.

[0137] (True density of foam particles) The weight M1 (g) of polyolefin resin foam particles was accurately weighed to 0.001g (rounded to the fourth decimal place). The volume V1 (cm³) of the polyolefin resin foam particles was determined from the rise in the scale when the weighed, weight-known polyolefin resin foam particles were immersed in 100mL of ethanol at 23°C in a graduated cylinder. 3 The following formula was used to calculate the true density of the foam particles: True density of foamed particles (g / L) = Weight of foamed particles M1 (g) / Volume of foamed particles V1 (cm³) 3 ) × 1000.

[0138] (Bulk density of foamed particles) The method for measuring the bulk density of the foamed particles was as follows (1) to (3): (1) The foamed particles were placed in a container of volume V2 (L) until the foamed particles overflowed from the container; (2) The weight M2 (g) of the foamed particles in the container was measured by scraping the surface (top) of the powder in the container; (3) The bulk density of the foamed particles was calculated using the following formula: The bulk density of foamed particles (g / L) = weight of foamed particles M² (g) / volume of container V² (L).

[0139] <Moisture content of foamed molded material> Except for using a mold for a cushioning box for storing goods, the same procedure as described later (Preparation of a polyolefin resin foam molded body) was performed to foam-mold the obtained foam particles in the mold and remove the polyolefin resin foam molded body from the mold. The cushioning box had dimensions of 400 mm in the length direction × 300 mm in the width direction × 145 mm in the depth direction. After removing the obtained polyolefin resin foam molded body from the mold, the weight A (g) of the molded body was measured after being left at room temperature for 30 minutes. Subsequently, the molded body was cured and dried in a constant temperature room at 75°C for 15 hours, and after being left at room temperature for another 4 hours, the weight B (g) of the molded body was measured, and the moisture content was calculated using the following formula. Moisture content (%)={(AB) / B}×100 <Maximum sound absorption coefficient and peak frequency of foamed molded material> A sample measuring φ29 mm and 60 mm in thickness was cut from a polyolefin resin foam molded product (370 mm long x 320 mm wide x 60 mm thick). Both skin surfaces of this sample were cut to adjust the thickness to 40 mm, and this sample was used for measuring the normal incidence sound absorption coefficient. Using this sample, the normal incidence sound absorption coefficient at a thickness of 40 mm was measured at 500 Hz to 6400 Hz in accordance with JIS A1405.

[0140] The measurement of the normal incidence sound absorption coefficient was performed with the sample in close contact with a rigid wall reflecting sound waves, i.e., without any air behind it. A SR-4100 normal incidence sound absorption coefficient measuring device manufactured by Ono Sokki Co., Ltd. was used for the measurement. From the obtained frequency-normal incidence sound absorption coefficient curve, the frequency and normal incidence sound absorption coefficient at the point where the normal incidence sound absorption coefficient is first maximized when viewed from the low-frequency side were read as the peak frequency and maximum sound absorption coefficient, respectively.

[0141] [Example 1] (Preparation of polyolefin resin particles) Polyolefin resin A was weighed to a concentration of 100 parts by weight, additive A to 0.20 parts by weight, and additive B to 0.10 parts by weight. A mixture was obtained by dry blending these components using a small tumbler manufactured by ON Machinery Co., Ltd. This mixture was then melt-kneaded at a resin temperature of 200°C using a twin-screw extruder (Toshiba Machine Co., Ltd., TEM26-SX) and extruded in strand form from a 5-baseline die attached to the tip of the extruder. The extruded product (strand) was cooled in a 2m long water tank. Subsequently, the water-cooled product was shredded into a star-shaped form using a shredding device (Ishinaka Iron Works Co., Ltd.) (shredding process). Through this operation, polyolefin resin particles with a star-shaped cross-section (weight per particle: 2.5mg) were obtained.

[0142] (Preparation of polyolefin resin foam particles) A dispersion containing the foaming agent was prepared by adding 100 parts by weight of the obtained polyolefin resin particles for foaming, 442 parts by weight of water as an aqueous dispersion medium, 0.33 parts by weight of kaolin as a dispersant, 0.05 parts by weight of sodium dodecylbenzenesulfonate as a dispersion aid, 0.03 parts by weight of citric acid as a pH adjuster, and 3.5 to 7.5 parts by weight of carbon dioxide as a foaming agent, according to the foaming pressure, to a 10 L pressure vessel. The resulting dispersion was heated to a foaming temperature (temperature inside the pressure vessel) of 151.0°C while stirring. After the temperature and pressure inside the pressure vessel reached the predetermined foaming temperature and pressure, the temperature and pressure inside the pressure vessel were maintained at the predetermined foaming temperature and pressure for another 30 minutes. Then, carbon dioxide was introduced and the pressure inside the pressure vessel was maintained at the foaming pressure of 3.0 MPa (gauge pressure). The valve at the bottom of the pressure vessel was opened, and the dispersion liquid inside the pressure vessel was released to atmospheric pressure through a 4.0 mm diameter orifice to obtain polyolefin resin foam particles. The polyolefin resin foam particles were dried at 75°C for 24 hours. The obtained single-stage foam particles showed two peaks originating from the polyolefin resin in the DSC curve obtained by measurement using the DSC method. The bulk density of the obtained polyolefin resin foam particles was evaluated. The results are shown in Table 1.

[0143] (Preparation of polyolefin resin foam particles: Application of antistatic agent to the surface of the polyolefin resin foam particle body) 100 parts by weight of polyolefin resin foam particles were placed in a mesh bag, and 2.0 parts by weight of antistatic agent A (antistatic agent A with a concentration of 99% by weight of alkylamide-type nonionic surfactant diluted with distilled water to a concentration of 4% by weight of alkylamide-type nonionic surfactant) was sprayed while stirring the polyolefin resin foam particles. In this case, 0.08 parts by weight of the pure component of antistatic agent A was sprayed. The polyolefin resin foam particles after spraying were cured at room temperature for 24 hours to remove moisture from the surface of the foam particles and obtain polyolefin resin foam particles. The bulk density and morphology of the obtained polyolefin resin foam particles were evaluated. The results, along with the shape of the beads, are shown in Table 1.

[0144] (Preparation of polyolefin resin foam molded products) The obtained polyolefin resin foam particles were filled into a mold for a box-shaped molded body using a polyolefin mold foam molding machine (manufactured by Dabo Co., Ltd.). After heating and pressing the polyolefin resin foam particles with steam at 0.30 MPa (gauge pressure), 30°C water (cooling water) was sprayed onto the mold at a spray pressure of 0.4 MPa (gauge pressure) for 40 seconds to cool the mold-filled foamed molded body (pre-polyolefin resin foamed molded body). Specifically, the water was sprayed directly onto the mold through a cooling water nozzle from a copper pipe. Since the mold has holes through which steam can pass, spraying water directly onto the mold resulted in water being sprayed not only onto the mold but also onto the pre-polyolefin resin foamed molded body. In other words, water was sprayed onto both the pre-polyolefin resin foamed molded body and the mold for 40 seconds. After that, the mold was opened and the polyolefin resin mold-filled foamed molded body was removed from the mold using air or a release jig. The obtained in-molded foamed body was left at room temperature for 30 minutes, then cured and dried in a constant temperature room at 75°C for 15 hours, and then left at room temperature for another 4 hours to obtain a polyolefin resin foamed body. The maximum sound absorption coefficient, peak frequency, and water content of the obtained polyolefin resin foamed body were measured. The results are shown in Table 1.

[0145] [Table 1]

[0146] [Examples 2, 4, 5] Foamed particles and foamed molded articles were obtained using the same method as in Example 1, except that the types and quantities of each material were changed as shown in Table 1. The physical properties of the obtained foamed particle bodies, foamed particles, and foamed molded articles were measured and evaluated. The results are shown in Table 1.

[0147] [Example 3] Foamed particles and foamed molded articles were obtained using the same method as in Example 1, except that the concentration of antistatic agent A was changed to 0.4% by weight, and the amount sprayed onto the polyolefin resin foamed particle body was changed so that the amount of pure components was as shown in Table 1. The physical properties of the obtained foamed particle body, foamed particles, and foamed molded articles were measured and evaluated. The results are shown in Table 1.

[0148] [Example 6] The types and quantities of each material were changed as shown in Table 1, and foamed particles and foamed molded articles were obtained using the same method as in Example 1, except that the foaming temperature was changed to 123.7°C and the foaming pressure to 3.4 MPa in the preparation of the polyolefin resin foamed particle body. The physical properties of the obtained foamed particles and foamed molded articles were measured and evaluated. The results are shown in Table 1.

[0149] [Example 7] Foamed particles and foamed molded articles were obtained using the same method as in Example 1, except that the types and amounts of each material were changed as shown in Table 1. As an antistatic agent, 2.5 parts by weight of antistatic agent B (concentration of alkyl diphenyl ether disulfonate sodium: 4% by weight) was sprayed onto the polyolefin resin foamed particle body while stirring. The physical properties of the obtained foamed particle body, foamed particles, and foamed molded articles were measured and evaluated. The results are shown in Table 1.

[0150] [Example 8] Foamed particles and foamed molded articles were obtained using the same method as in Example 1, except that the types and amounts of each material were changed as shown in Table 1. As an antistatic agent, 2.5 parts by weight of an aqueous solution of antistatic agent C (antistatic agent C with a hindered amine light stabilizer concentration of 20% by weight was diluted with distilled water to a hindered amine light stabilizer concentration of 4.0% by weight) was sprayed onto the polyolefin resin foamed particle body under stirring. The physical properties of the obtained foamed particle body, foamed particles, and foamed molded articles were measured and evaluated. The results are shown in Table 1.

[0151] [Example 9] In the preparation of polyolefin resin particles, the die attached to the tip of the extruder was changed from a 5-baseline die to an anchor cross die (the die shown in Figure 4) to obtain anchor cross-shaped polyolefin resin particles (weight per particle: 2.5 mg). These polyolefin resin particles were used to obtain anchor cross-shaped polyolefin resin foam particle bodies. Foam particles and foam molded articles were obtained using the same method as in Example 1, except that the types and amounts of each material were changed as shown in Table 1. The physical properties of the obtained foam particle bodies, foam particles, and foam molded articles were measured and evaluated. The results are shown in Table 1. The single-stage foam particles obtained in the preparation of the polyolefin resin foam particle bodies showed two peaks originating from the polyolefin resin in the DSC curve obtained by measurement using the DSC method.

[0152] [Example 10] In the production of polyolefin resin particles, macaroni-shaped polyolefin resin particles (weight per particle: 2.5 mg) were obtained by changing the die attached to the tip of the extruder from a 5-baseline die to a circumferential die (the die shown in Figure 5). Macaroni-shaped polyolefin resin foam particle bodies were obtained using these polyolefin resin particles. Foam particles and foam molded articles were obtained by the same method as in Example 1, except that the types and amounts of each material were changed as shown in Table 1. The physical properties of the obtained foam particle bodies, foam particles, and foam molded articles were measured and evaluated. The results are shown in Table 1. The single-stage foam particles obtained in the production of the polyolefin resin foam particle bodies showed two peaks originating from the polyolefin resin in the DSC curve obtained by measurement using the DSC method.

[0153] [Comparative Example 1] Foamed particles and foamed molded articles were obtained using the same method as in Example 1, except that the concentration of antistatic agent A was changed to 0.04% by weight, and the amount sprayed onto the polyolefin resin foamed particle body was changed so that the amount of pure components was as shown in Table 1. The physical properties of the obtained foamed particle body, foamed particles, and foamed molded articles were measured and evaluated. The results are shown in Table 1.

[0154] [Comparative Example 2] In the preparation of polyolefin resin particles, elliptic polyolefin resin particles (weight per particle of 2.5 mg) were obtained by changing the die attached to the tip of the extruder from a 5-baseline die to a circular die; elliptic polyolefin resin foam particle bodies were obtained using these polyolefin resin particles; and foam particles and foam molded articles were obtained by the same method as in Example 1, except that the types and amounts of each material were changed as shown in Table 1. The physical properties of the obtained foam particle bodies, foam particles, and foam molded articles were measured and evaluated. The results are shown in Table 1. The single-stage foam particles obtained in the preparation of the polyolefin resin foam particle bodies showed two peaks originating from the polyolefin resin in the DSC curve obtained by measurement using the DSC method. [Industrial applicability]

[0155] According to one embodiment of the present invention, polyolefin resin foam particles can be provided that offer a foamed molded article with excellent sound absorption performance and reduced moisture content. Therefore, one embodiment of the present invention can be suitably used as a sound-absorbing component in vehicles such as automobiles and trains, aircraft, buildings, and the like.

Claims

1. Polyolefin resin foam particles with a degree of irregularity of 2.2 or higher, The polyolefin resin foam particles contain an antistatic agent present on the surface of the polyolefin resin foam particles. Polyolefin resin foam particles, wherein the content of the antistatic agent is 0.0010 parts by weight or more per 100 parts by weight of polyolefin resin foam particles.

2. The polyolefin resin foam particles according to claim 1, wherein the content of the antistatic agent is 1.0000 parts by weight or less per 100 parts by weight of polyolefin resin foam particles.

3. The polyolefin resin foam particles according to claim 1, wherein the polyolefin resin foam particles contain more than 50 parts by weight of polyolefin resin per 100 parts by weight of polyolefin resin foam particles.

4. The polyolefin resin foam particles according to claim 1, wherein the antistatic agent comprises at least one selected from the group consisting of nonionic surfactants, anionic surfactants, and cationic surfactants.

5. The polyolefin resin foam particles contain a polypropylene resin, The polyolefin resin foam particles according to claim 1, wherein the melt index of the polypropylene resin at 230°C is 3.0 g / 10 min to 30.0 g / 10 min.

6. The polyolefin resin foam particles contain a polypropylene resin, The polyolefin resin foam particles according to claim 1, wherein the melting point of the polypropylene resin is 135°C to 160°C.

7. The polyolefin resin foam particles according to claim 1, wherein the bulk density of the polyolefin resin foam particles is 10.0 g / L to 300.0 g / L.

8. A polyolefin resin foam molded article obtained by molding polyolefin resin foam particles according to any one of claims 1 to 7.

9. A method for producing polyolefin resin foam particles with a degree of irregularity of 2.2 or higher, The polyolefin resin foam particles contain an antistatic agent present on the surface of the polyolefin resin foam particles. The process includes the steps of applying the antistatic agent to the surface of polyolefin resin particles before foaming, and / or applying the antistatic agent to the surface of the foamed polyolefin resin particles. A method for producing polyolefin resin foam particles, wherein the content of the antistatic agent is 0.0010 parts by weight or more per 100 parts by weight of the polyolefin resin foam particles.

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