Polyolefinic resin foam molding composite body and use of the same

Abstract

To provide a polyolefinic resin foam molding which is lightweight and is excellent in sound absorption performance in a low frequency region.SOLUTION: A polyolefinic resin foam molding composite body includes at least a first layer and a second layer, wherein porosities of both layers are set to be predetermined ranges so that porosity of the first layer is smaller than porosity of the second layer, and a ratio in thickness between both layers is set to be a predetermined range.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyolefin resin foam molded composite and its use. [Background technology]

[0002] Polyolefin resin foam molded articles obtained by molding expanded polyolefin resin particles made of polyolefin resin are used in a variety of applications, including automobile interior components, core materials for automobile bumpers, heat insulating materials, cushioning packaging materials, returnable containers, etc. In particular, for automobile interior components, foamed materials with sound-absorbing properties are required.

[0003] To achieve sound absorption performance, the material must have an appropriate amount of voids, and miniaturizing the voids tends to absorb lower frequency sounds. For this reason, technologies using fiber-based materials as sound-absorbing materials targeting low frequency sounds have been disclosed, but the problem is that fiber-based materials are heavy. On the other hand, foamed molded bodies are lightweight, but until now, there has been insufficient knowledge about the relationship between the void ratio of foamed molded bodies and their sound absorption performance (especially for low frequency sounds).

[0004] Patent Document 1 describes a method of laminating a nonwoven fabric having a predetermined air permeability as a face material onto a resin foam molding having interconnected voids, with the aim of providing a laminate that is thin but has excellent sound absorption performance.

[0005] Patent Document 2 describes a method for providing a foamed molded article having a high porosity and shape retention, in which rod-shaped pre-expanded particles and spherical pre-expanded particles are packed approximately in a compartment and molded to obtain a foamed molded article having a high porosity inside and a low porosity on the periphery of the foamed molded article.

[0006] Patent Document 3 discloses an automobile storage member having a sound-absorbing layer formed of a foamed bead molding on the underside, with the aim of providing an automobile storage member that is lightweight and has excellent sound-absorbing properties for high-frequency sounds, and describes that the sound-absorbing layer has a porosity of 15% or more in the surface portion, which is greater than or equal to the porosity of the interior. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2018-171829 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-240285 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-143046 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the conventional foam molded articles or laminates thereof described above have room for improvement in terms of providing materials with excellent sound absorption performance in the low frequency range. Specifically, the laminate described in Patent Document 1 does not fully utilize the weight-saving benefits of the foam molded article. Furthermore, none of the technologies described in Patent Documents have been studied regarding sound absorption performance in the low frequency range.

[0009] An object of one aspect of the present invention is to provide a polyolefin resin foam molded article that has excellent sound absorption performance in the low frequency range. [Means for solving the problem]

[0010] In order to solve the above-mentioned problems, one embodiment of the present invention includes the following configuration.

[0011] [1] A polyolefin resin foam molded body composite comprising at least a first polyolefin resin foam molded body layer and a second polyolefin resin foam molded body layer, the thickness of the first polyolefin resin foam molded body layer is 8% or more and 35% or less of the total thickness of the first polyolefin resin foam molded body layer and the second polyolefin resin foam molded body layer; the porosity of the first polyolefin resin foam molded body layer is 20.0% or more and 32.0% or less, the thickness of the second polyolefin resin foam molded body layer is 65% or more and 92% or less of the total thickness of the first polyolefin resin foam molded body layer and the second polyolefin resin foam molded body layer; The polyolefin resin foam molded composite, wherein the second polyolefin resin foam molded layer has a porosity of more than 32.0% and 45.0% or less.

[0012] [2] The polyolefin resin foam molded body composite according to [1], wherein the second polyolefin resin foam molded body layer is in contact with the first polyolefin resin foam molded body layer.

[0013] [3] The polyolefin resin foam molded body composite according to [1] or [2], wherein the first polyolefin resin foam molded body layer is positioned closer to the sound source than the second polyolefin resin foam molded body layer.

[0014] [4] The polyolefin resin foam molded body composite according to any one of [1] to [3], wherein the first polyolefin resin foam molded body layer and / or the second polyolefin resin foam molded body layer is a foam molded body obtained by molding expanded polyolefin resin beads in a mold.

[0015] [5] The polyolefin resin foam molded composite according to [4], wherein the polyolefin resin foam particles are irregularly shaped particles.

[0016] [6] A sound-absorbing member comprising the polyolefin resin foam molded composite according to any one of [1] to [5]. [Effects of the Invention]

[0017] According to one aspect of the present invention, it is possible to provide a polyolefin resin foam molded composite having excellent sound absorption performance in the low frequency range. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a front view image showing an example die configuration. [Figure 2] Figure 2 is an image of star-shaped polyolefin resin particles. [Figure 3] Figure 3 is an image of star-shaped expanded polyolefin resin beads. [Figure 4] FIG. 4 is a front view image showing an alternative die configuration to that of FIG. [Figure 5] FIG. 5 is a front view image showing an alternative die configuration to those of FIGS. DETAILED DESCRIPTION OF THE INVENTION

[0019] One embodiment of the present invention will be 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. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic literature and patent documents described in this specification are incorporated herein by reference. Furthermore, unless otherwise specified in this specification, "A to B" representing a numerical range means "greater than or equal to A (including and greater than A) and less than or equal to B (including and less than B)."

[0020] It is known that miniaturizing voids tends to result in better sound absorption in the low frequency range, and in the course of conducting research to solve the above-mentioned problem, the inventors produced a composite consisting of two layers of polyolefin resin foam molded bodies with different porosities, each with a relatively large void ratio of 20.0% or more, and placed the layer with the lower porosity on the sound source side.Unexpectedly, they found that the composite had a peak sound absorption coefficient in the low frequency range of 1000 Hz or less, and that this sound absorption coefficient was high.Since there is no correlation between the degree of miniaturization of voids and the void ratio, it is assumed that the composite achieves improved sound absorption performance in the low frequency range through a principle other than miniaturization of voids.

[0021] Based on this knowledge, the inventors conducted further research and discovered that by setting the porosity of both layers within a predetermined range so that the porosity of the layer located on the sound source side is smaller than the porosity of the layer located on the opposite side of the sound source and by setting the thickness ratio of the two layers within a predetermined range, it is possible to realize a polyolefin resin foam molded product that is lightweight and has excellent sound absorption performance in the low frequency range, and this led to the completion of the present invention.

[0022] That is, a polyolefin resin foam molded body composite according to one embodiment of the present invention is a polyolefin resin foam molded body composite comprising at least a first polyolefin resin foam molded body layer and a second polyolefin resin foam molded body layer, wherein the thickness of the first polyolefin resin foam molded body layer is 8% to 35% of the total thickness of the first polyolefin resin foam molded body layer and the second polyolefin resin foam molded body layer, the porosity of the first polyolefin resin foam molded body layer is 20.0% to 32.0%, the thickness of the second polyolefin resin foam molded body layer is 65% to 92% of the total thickness of the first polyolefin resin foam molded body layer and the second polyolefin resin foam molded body layer, and the porosity of the second polyolefin resin foam molded body layer is more than 32.0% and 45.0% or less.

[0023] In this specification, "polyolefin resin particles" may be referred to as "resin particles," "expanded polyolefin resin particles" may be referred to as "expanded particles," "polyolefin resin foam molded body" may be referred to as "foam molded body," "polyolefin resin foam molded body composite" may be referred to as "foam molded body composite," "first polyolefin resin foam molded body layer" may be referred to as "first layer," and "second polyolefin resin foam molded body layer" may be referred to as "second layer." In this specification, "a polyolefin resin foam molded body composite according to one embodiment of the present invention" may be referred to as "the present foam molded body composite."

[0024] Furthermore, in this specification, a "structural unit derived from an X monomer" contained in a polymer, copolymer, or resin may be referred to as an "X unit."

[0025] Unless otherwise specified in this specification, the structural unit is X 1 Units and X 2 Units, ... and X n A copolymer containing X units (n is an integer of 2 or more) is referred to as "X 1 / X 2 / ··· / X n Also called "copolymer". X 1 / X 2 / ··· / X n Unless otherwise specified, the polymerization mode of the copolymer is not particularly limited, and the copolymer may be a random copolymer, an alternating copolymer, a block copolymer, or a graft copolymer.

[0026] [1. Polyolefin resin foam molded composite] Before describing a polyolefin-based resin foam molded body composite according to one embodiment of the present invention, the polyolefin-based resin foam beads used in the production of this foam molded body composite and the polyolefin-based resin particles that are the raw material (material) for the polyolefin-based resin foam beads will be described.

[0027] [1-1] Polyolefin resin particles In this specification, the term "polyolefin-based resin particles" refers to resin particles containing a polyolefin-based resin.

[0028] <Polyolefin resin> In this specification, the term "polyolefin resin particles" refers to a resin having the highest content of olefin units among all the constituent units constituting the resin. The polyolefin resin preferably contains olefin units in an amount of 60 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, and particularly preferably 90 mol% or more, based on 100 mol% of all constituent units.

[0029] Examples of the polyolefin resin include polyethylene resins such as low / medium / high density polyethylene, linear low / very low density polyethylene, and ethylene / vinyl acetate copolymer; and polypropylene resins such as polypropylene and ethylene / propylene copolymer.

[0030] Among these, the polyolefin resin is preferably a polypropylene resin having the highest propylene unit content among all the structural units constituting the resin. The polypropylene resin contains, for example, 50 mol% or more of propylene units out of 100 mol% of all structural units. The polypropylene resin may be (i) a propylene homopolymer, (ii) a block copolymer, impact copolymer, alternating copolymer, random copolymer, or graft copolymer of propylene and a monomer other than propylene, or (iii) a mixture of two or more of these.

[0031] It is more preferable that the polypropylene-based resin is a random copolymer of propylene and a monomer other than propylene, since this has the advantage that the resin particles and expanded particles can be processed at a low heating temperature during expansion of the resin particles and molding of the expanded particles.

[0032] The polypropylene-based resin may have, in addition to the propylene unit, one or more units or types of structural units derived from a monomer other than the propylene monomer.

[0033] Examples of the monomer 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.

[0034] Specific examples of polypropylene-based 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-based resins.

[0035] As the polypropylene-based resin, one of the above-mentioned specific examples may be used alone, or two or more may be used in combination. Among the above-mentioned specific examples, ethylene / propylene random copolymer and / or 1-butene / ethylene / propylene random copolymer are preferred as the polypropylene-based resin, in view of the good expandability of the resin particles and the good moldability of the expanded particles.

[0036] The polyolefin resin may contain a polypropylene resin and a polyolefin resin other than the polypropylene resin. Examples of the polyolefin resin 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 very 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 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, relative to 100 parts by weight of the polypropylene resin. When the content of the polyolefin resin other than the polypropylene resin is within the above range, there is an advantage that the expandability of the resin particles and / or the moldability of the expanded particles tend to be good.

[0037] 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 having excellent heat resistance can be obtained. When the melting point is (ii) 160°C or lower, it becomes easy to increase the expansion ratio of the foamed beads in the production of the foamed beads. Furthermore, when the melting point of the polyolefin resin is within the above-mentioned range, there is an advantage that a polypropylene resin foamed molded article having excellent sound absorption performance and little deformation can be obtained. The method for measuring the melting point of the polyolefin resin will be described in detail in the Examples below.

[0038] 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, 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. The MI is sometimes also referred to as "melt flow rate (MFR)." This configuration has the advantage of being able to produce a polyolefin resin foam molded product with excellent sound absorption performance and little deformation. The method for measuring the MI of the polyolefin resin will be described in detail in the Examples below.

[0039] The polyolefin resin can be obtained by a known method. The polymerization catalyst used in synthesizing the polyolefin resin is not particularly limited, and for example, a Ziegler catalyst or a metallocene catalyst can be used.

[0040] <Other resins, etc.> The resin particles may further contain, as a resin component, a resin other than the polyolefin-based resin (sometimes referred to as "other resins"), provided that the effects of the present invention are not impaired. Examples of the other resins include (a) vinyl-based / acrylic-based resins such as ethylene / vinyl acetate copolymer, ethylene / acrylic acid copolymer, and ethylene / methacrylic acid copolymer; (b) polyphenylene ether-based resins such as polyphenylene ether and modified polyphenylene ether; and (c) polystyrene-based resins and hydrogenated styrene-based copolymers. Note that polyphenylene ether-based resins are amorphous resins.

[0041] When the resin particles contain other resins, the content of the other resins in the resin 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, relative to 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 expandability of the resin particles and / or the moldability of the expanded particles tend to be good.

[0042] <Additives> The resin particles may contain any additives in addition to the polyolefin resin. Examples of the additives include colorants, hydrophilic compounds, crystal nucleating agents, antistatic agents, flame retardants, antioxidants, light stabilizers, conductive agents, lubricants, etc. Such additives may be contained in the resin particles, or may be added directly to the dispersion when the resin particles are foamed.

[0043] The hydrophilic compound is a substance used for the purpose of increasing the amount of water impregnated in the resin particles. The hydrophilic compound can impart foamability to the resin particles. The foamability imparting effect of the hydrophilic compound to the resin particles is particularly remarkable when water is used as the foaming agent.

[0044] 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.

[0045] The nucleating agent to be blended with the resin particles is a substance that can become foam nuclei when the resin particles are foamed. The resin particles preferably contain a nucleating agent.

[0046] 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 oxide, bentonite, barium sulfate, zinc borate, etc., each having an average particle size of more than 1000 nm. These nucleating agents may be used alone or in combination of two or more.

[0047] <Physical properties of polyolefin resin particles> (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 improving the productivity of the polyolefin-based resin particles and the mechanical properties of the polyolefin-based resin expansion molded products.

[0048] (shape of resin particles) The resin particles are preferably, but not limited to, irregularly shaped resin particles. In other words, the shape of the resin particles is preferably, but not limited to, a shape other than the shapes (spherical and cylindrical) generally used in producing expanded beads, and is preferably one selected from the group consisting of star, anchor cross, macaroni, cross, L-shape, Y-shape, T-shape, U-shape, and polygonal, more preferably one selected from the group consisting of star, anchor cross, and macaroni, and even more preferably star-shaped. This configuration has the advantage of being able to produce a polypropylene resin foam molded product with excellent sound absorption performance and little deformation.

[0049] In other words, the shape of the resin particles is preferably such that the degree of irregularity of the resulting expanded beads satisfies the preferred numerical range of the degree of irregularity of the expanded beads described below, and for example, star-shaped, anchor-cross-shaped, macaroni-shaped, etc. are preferred.

[0050] Here, Fig. 1 is a front view image showing an example of a die configuration. Specifically, Fig. 1 is a front view image showing the configuration of a die for obtaining star-shaped resin particles that are the raw material for star-shaped expanded beads. The star-shaped resin particles are resin particles obtained by extrusion through the die shown in Fig. 1. Fig. 2 is an image of star-shaped polyolefin resin particles.

[0051] Figures 4 and 5 are front views showing a die configuration different from that shown in Figure 1. Specifically, Figure 4 shows the configuration of a die for obtaining anchor-cross-shaped resin particles, which are the raw material for anchor-cross-shaped expanded beads. The anchor-cross-shaped resin particles are resin particles obtained by extrusion through the die shown in Figure 4. Figure 5 shows the configuration of a die for obtaining macaroni-shaped resin particles, which are the raw material for macaroni-shaped expanded beads. The macaroni-shaped resin particles are resin particles obtained by extrusion through the die shown in Figure 5. In this specification, the term "macaroni-shaped" refers to a cylindrical shape with a hollow hole formed therein.

[0052] The resin particles may or may not form hollow holes.

[0053] [1-2] Polyolefin resin foam particles The expanded polyolefin resin particles are formed by expanding the polyolefin resin particles described in the section [1-1] Polyolefin Resin Particles. That is, the expanded polyolefin resin particles contain the components (e.g., polyolefin resin) contained in the polyolefin resin particles.

[0054] <Physical properties of expanded polyolefin resin beads> (Bulk density of expanded particles) The bulk density of the expanded beads 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 providing expanded beads with little variation in expansion ratio and good moldability. The method for measuring the bulk density of the expanded beads will be described in detail in the Examples below.

[0055] (Degree of irregularity of foamed particles) The expanded polyolefin resin particles preferably have a degree of deformation represented by the following formula of 2.20 or more: Degree of irregularity = true density of expanded polyolefin resin beads / bulk density of expanded polyolefin resin beads.

[0056] In this specification, the irregularity is an index showing the bulkiness of the expanded beads. The irregularity of the expanded beads is preferably 2.20 or more, more preferably 2.40 or more, and even more preferably 2.50 or more. This configuration has the advantage that it is possible to obtain a polyolefin resin foam molded product that has excellent sound absorption performance and little deformation.

[0057] The upper limit of the degree of irregularity of the expanded beads is not particularly limited, but is preferably 3.00 or less, more preferably 2.90 or less, even more preferably 2.80 or less, and particularly preferably 2.70 or less. This configuration has the advantage of producing a foamed molded article with high mechanical properties. Details of the method for measuring the degree of irregularity of the expanded beads will be explained in detail in the Examples below.

[0058] Examples of shapes of expanded beads that satisfy the above-mentioned preferred range of irregularity include shapes other than those generally used in the production of expanded beads (spherical and cylindrical). A "shape other than spherical and cylindrical" is sometimes referred to as an "irregular shape." That is, the expanded beads are preferably irregular-shaped particles. The shape of the expanded beads is preferably one selected from the group consisting of star, anchor cross, macaroni, cross, L-shape, Y-shape, T-shape, U-shape, and polygonal, more preferably one selected from the group consisting of star, anchor cross, and macaroni, even more preferably star or anchor cross, and even more preferably star. This configuration has the advantage of being able to produce a polyolefin resin foam molded product that has excellent sound absorption performance and little deformation.

[0059] The shape of the expanded beads is the same or substantially the same as the shape of the resin beads. When the resin beads are irregularly shaped resin beads, the expanded beads obtained by expanding the resin beads are irregularly shaped expanded beads. Specifically, for example, when the resin beads are star-shaped, the expanded beads obtained by expanding the resin beads are also star-shaped. Here, FIG. 3 is an image of star-shaped expanded polyolefin resin beads.

[0060] In one embodiment of the present invention, the expanded polyolefin resin particles may or may not have hollow holes.

[0061] <Method of manufacturing expanded polyolefin resin beads> The method for producing expanded beads is not particularly limited, and known production methods can be used as appropriate. One embodiment of the method for producing expanded beads will be described in detail below, but the above descriptions (for example, the description in the section on <Additives>) will be used as appropriate for matters other than those described in detail below. Note that the method for producing expanded beads is not limited to the following production method.

[0062] (Polyolefin resin particle manufacturing process) When producing expanded beads, a step of producing polyolefin resin beads (resin bead production step) may be carried out first.

[0063] The resin particle production process is not particularly limited as long as it can produce resin particles, and known methods can be used. One example of the resin particle production process is a method in which the following steps (S1) to (S3) are carried out in order: (S1) a predetermined amount of polyolefin resin and, if necessary, additives are melt-kneaded using an extruder to prepare a melt-kneaded product; (S2) the melt-kneaded product is extruded through a die provided in the extruder; and (S3) the extruded melt-kneaded product is chopped to a desired length to obtain polyolefin resin particles.

[0064] In the step (S1), a blend may be prepared in advance by blending a predetermined amount of polyolefin resin and, if necessary, additives, and the blend may be fed to an extruder and melt-kneaded to prepare a melt-kneaded product.

[0065] In the step (S2), the shape of the die may be selected according to the desired shape of the expanded beads. Here, the shape of the die is the same as or approximately the same as the desired shape of the expanded beads. For example, when resin beads obtained by extruding a resin composition using the die shown in FIG. 5 are used, macaroni-shaped expanded beads can be obtained.

[0066] In the above (S3), before the molten kneaded material is chopped, the extruded molten kneaded material may be cooled and solidified using a cooling medium such as water.

[0067] (Dispersion process) In producing the expanded beads, a step (dispersion step) of dispersing the polyolefin resin particles and the blowing agent in an aqueous dispersion medium in a vessel may next be carried out.

[0068] Examples of the container include a pressure vessel and an autoclave-type pressure vessel. The container may be equipped with a stirrer inside.

[0069] Examples of aqueous dispersion media include (a) dispersion media obtained by adding methanol, ethanol, ethylene glycol, glycerin, or the like 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.

[0070] Examples of the blowing agent include (a) (a-1) inorganic blowing agents such as inorganic gases such as nitrogen, carbon dioxide, and air, and (a-2) water; and (b) organic blowing agents such as (b-1) saturated hydrocarbons having 3 to 5 carbon atoms such as propane, normal butane, isobutane, normal pentane, isopentane, and neopentane, (b-2) ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether, and (b-3) halogenated hydrocarbons such as monochloromethane, chloroethane, and hydrofluoroolefins.

[0071] In the production of expanded beads, it is preferable to use a dispersant (e.g., an inorganic substance such as tricalcium phosphate, kaolin, or talc) and a dispersing aid (e.g., an anionic surfactant such as sodium dodecylbenzenesulfonate). This configuration can reduce adhesion of resin particles (sometimes called blocking) and improve the stability of the dispersion in the container. As a result, it has the advantage of enabling stable production of expanded beads.

[0072] The aqueous dispersion medium and the blowing agent may each be used alone or in combination of two or more.

[0073] The amounts of the aqueous dispersion medium, blowing agent, dispersant, and dispersion aid used are not particularly limited, and can be appropriately set taking into consideration (i) the stability of the dispersion (dispersibility of resin particles), (ii) the density of the resulting expanded beads, (iii) the fusion properties of the expanded molded article obtained by molding the resulting expanded beads, (iv) productivity, and (v) economic efficiency.

[0074] In the method for producing expanded beads, it is preferable to use a pH adjuster (for example, citric acid, malic acid, succinic acid, tartaric acid, oxalic acid, etc.), which has the advantage of being able to suppress corrosion of equipment.

[0075] The amount of the pH adjuster 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, relative to 100 parts by weight of the polyolefin resin particles. This configuration has the advantages of high productivity of the expanded beads and suppressing corrosion of equipment.

[0076] The method for dispersing the polyolefin resin particles and the blowing agent in the aqueous dispersion medium in the container, i.e., the specific method for the dispersion step, is not particularly limited, and examples thereof include a method in which the aqueous dispersion medium, the polyolefin resin particles, and the blowing agent are supplied to the container, and the mixture in the container is stirred with a stirrer provided in the container.

[0077] (Temperature-pressure increase process and holding process) In the production of expanded beads, it is preferable to further include, after the dispersing step and before the releasing step, (1) a temperature-pressure increasing step in which the temperature in the container is increased to a constant temperature and the pressure in the container is increased to a constant pressure, and (2) a holding step in which the temperature and pressure in the container are held at a constant temperature and constant pressure, in this order. In this specification, the (a) constant temperature in the temperature-pressure increasing step and the holding step may be referred to as the foaming temperature, and the (b) constant pressure in the foaming pressure may be referred to as the foaming pressure.

[0078] The expansion temperature is preferably 130.0° C. to 170.0° C., more preferably 135.0° C. to 165.0° C., further preferably 138.0° C. to 162.0° C., and particularly preferably 140.0° C. to 160.0° C. This configuration has the advantage that expanded beads with good expandability and moldability can be easily obtained.

[0079] The expansion 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). When the expansion pressure is 0.5 MPa (gauge pressure) or more, expanded particles with a suitable density can be obtained.

[0080] In the holding step, the time (holding time) for holding the dispersion in the container at near the foaming temperature and foaming pressure is not particularly limited, but is, for example, preferably 10 to 60 minutes, more preferably 12 to 50 minutes, and even more preferably 15 to 40 minutes.

[0081] (Release process) When producing expanded beads, a step (releasing step) of releasing the dispersion obtained in the dispersing step into a region where the pressure is lower than the pressure inside the container may be carried out.

[0082] The discharging step can expand the resin particles, resulting in expanded particles. The discharging step can also be described as a step of opening one end of the container and discharging the dispersion liquid in the container into a region (space) with a pressure lower than the expansion pressure (i.e., the pressure inside the container).

[0083] In the releasing step, the "region under a pressure lower than the foaming pressure" refers to a "region under a pressure lower than the foaming pressure" or a "space under a pressure lower than the foaming pressure", and can also be referred to as "an atmosphere under a pressure lower than the foaming pressure". The region under a pressure lower than the foaming pressure may be, for example, a region under atmospheric pressure.

[0084] (Foaming process) The process from the dispersing step to the releasing step is sometimes called the expansion step. The process of producing expanded beads from resin beads in this way is called the "first-stage expansion step," and the resulting expanded beads are called "first-stage expanded beads."

[0085] (2-stage foaming process) In order to obtain expanded beads with a high expansion ratio, the first-stage expanded beads obtained in the first-stage expansion step may be expanded again. The step of increasing the expansion ratio of the first-stage expanded beads is called the "second-stage expansion step," and the expanded polyolefin resin beads obtained by the second-stage expansion step are called "second-stage expanded beads." The specific method for the second-stage expansion step is not particularly limited, and any known method can be used.

[0086] [1-3] Polyolefin resin foam molding composite A polyolefin resin foam molded body composite according to one embodiment of the present invention is a polyolefin resin foam molded body composite comprising at least a first polyolefin resin foam molded body layer and a second polyolefin resin foam molded body layer, and it is preferred that the thickness of the first polyolefin resin foam molded body layer is 8% to 35% of the total thickness of the first and second polyolefin resin foam molded body layers, the porosity of the first polyolefin resin foam molded body layer is 20.0% to 32.0%, the thickness of the second polyolefin resin foam molded body layer is 65% to 92% of the total thickness of the first and second polyolefin resin foam molded body layers, and the porosity of the second polyolefin resin foam molded body layer is more than 32.0% and 45.0% or less. The first and second layers included in the polyolefin resin foam molded body composite according to one embodiment of the present invention are both polyolefin resin foam molded body layers made of polyolefin resin foam molded bodies. Therefore, the polyolefin resin foam molded body composite according to one embodiment of the present invention has the advantage of being lightweight. Furthermore, because the polyolefin resin foam molded body composite according to one embodiment of the present invention has the above-mentioned configuration, it has the advantage of being able to realize a polyolefin resin foam molded body with excellent sound absorption performance in the low frequency range.

[0087] The first and second layers may be layers of a polyolefin resin foam molded article having a porosity within the aforementioned range. Therefore, the polyolefin resin contained in the polyolefin resin foam molded article constituting the first layer and the polyolefin resin contained in the polyolefin resin foam molded article constituting the second layer may be the same or different in monomer composition, molecular weight, melting point, melt flow rate, etc. Furthermore, the foamed particles contained in the polyolefin resin foam molded article constituting the first layer and the foamed particles contained in the polyolefin resin foam molded article constituting the second layer may be the same or different in shape, particle size, density, color, etc.

[0088] If the expanded beads contained in the polyolefin resin expanded molded body constituting the first layer and the second layer are the same, there is no need to separately manufacture different expanded beads. The first layer and the second layer can be prepared by using the same expanded beads and changing the conditions (compression ratio, filling air pressure, amount of cracking, etc.) during molded body manufacturing.

[0089] The porosity of the first layer, in other words, the porosity of the polyolefin resin foam molded product constituting the first layer, is preferably 20.0% or more and 32.0% or less. The porosity of the first layer is more preferably 22.0% or more, even more preferably 23.0% or more, and particularly preferably 24.0% or more. If the porosity of the first layer is 20.0% or more, the present foam molded product composite has the advantage of being excellent in sound absorption performance when the first layer is placed on the sound source side. Therefore, the first layer is preferably located closer to the surface of the present foam molded product laminate than the second layer. The porosity of the first layer is more preferably 30.0% or less, even more preferably 29.0% or less, and particularly preferably 28.0% or less. If the porosity of the first layer is 32.0% or less, the present foam molded product composite has the advantage of being excellent in sound absorption performance in the low frequency range when the first layer is placed on the sound source side.

[0090] The degree of deformation of the expanded beads constituting the first layer is preferably 2.00 or more, and more preferably 2.20 or more.

[0091] The closed cell rate of the expanded beads constituting the first layer is preferably 90% or more, and more preferably 95% or more.

[0092] Furthermore, the thickness of the first layer having a porosity in the above-mentioned range is preferably 8% to 35% of the total thickness of the first and second layers. The thickness of the first layer is more preferably 10% or more, and even more preferably 20% or more. If the thickness of the first layer is 8% or more, the foam molded composite has the advantage of being excellent in sound absorption performance in the low frequency range when the first layer is placed on the sound source side. The thickness of the first layer is more preferably 30% or less, and even more preferably 28% or less. If the thickness of the first layer is 35% or less, the foam molded composite has the advantage of being excellent in sound absorption performance when the first layer is placed on the sound source side.

[0093] Furthermore, the porosity of the second layer, in other words the porosity of the polyolefin resin foam molded product constituting the second layer, is preferably greater than 32.0% and less than 45.0%. The porosity of the second layer is more preferably 34.0% or greater, even more preferably 35.0% or greater, and particularly preferably 36.0% or greater. If the porosity of the second layer is greater than 32.0%, the foam molded composite has the advantage of being excellent in sound absorption performance when the first layer is placed on the sound source side. The porosity of the second layer is more preferably 43.0% or less, even more preferably 42.0% or less, and particularly preferably 41.0% or less. If the porosity of the second layer is 45.0% or less, the foam molded composite has the advantage of being excellent in sound absorption performance when the first layer is placed on the sound source side.

[0094] The degree of deformation of the expanded beads constituting the second layer is preferably 2.0 or more, and more preferably 2.2 or more.

[0095] The closed cell rate of the expanded beads constituting the second layer is preferably 90% or more, and more preferably 95% or more.

[0096] Furthermore, the thickness of the second layer having a porosity in the aforementioned range is preferably 65% ​​to 92% of the total thickness of the first and second layers. The thickness of the second layer is more preferably 70% or more, and even more preferably 72% or more. If the thickness of the second layer is 65% or more, the foam molded composite has the advantage of being excellent in sound absorption performance when the first layer is placed on the sound source side. The thickness of the second layer is more preferably 90% or less, and even more preferably 72% or less. If the thickness of the second layer is 92% or less, the foam molded composite has the advantage of being excellent in sound absorption performance in the low frequency range when the first layer is placed on the sound source side.

[0097] The difference between the porosity of the second layer and the porosity of the first layer (porosity of the second layer - porosity of the first layer) is not particularly limited. From the viewpoint of reducing peak frequencies, the difference between the porosity of the second layer and the porosity of the first layer (porosity of the second layer - porosity of the first layer) is preferably 5.0% or more, more preferably 7.0% or more, even more preferably 9.0% or more, and particularly preferably 11.0% or more. Furthermore, from the viewpoint of improving sound absorption coefficient, the difference between the porosity of the second layer and the porosity of the first layer (porosity of the second layer - porosity of the first layer) is preferably 19.0% or less, more preferably 18.5% or less, even more preferably 18.0% or less, and particularly preferably 17.5% or less.

[0098] The ratio of the porosity of the second layer to the porosity of the first layer (porosity of second layer / porosity of first layer) is not particularly limited. From the viewpoint of reducing peak frequencies, the ratio of the porosity of the second layer to the porosity of the first layer (porosity of second layer / porosity of first layer) is preferably 1.1 or more, more preferably 1.2 or more, even more preferably 1.4 or more, and particularly preferably 1.5 or more. Furthermore, from the viewpoint of improving sound absorption coefficient, the ratio of the porosity of the second layer to the porosity of the first layer (porosity of second layer / porosity of first layer) is preferably 2.0 or less, more preferably 1.9 or less, even more preferably 1.8 or less, and particularly preferably 1.7 or less.

[0099] The difference between the thickness (%) of the second layer and the thickness (%) of the first layer (thickness (%) of the second layer - thickness (%) of the first layer) is not particularly limited. From the viewpoint of improving the sound absorption coefficient, the difference between the thickness (%) of the second layer and the thickness (%) of the first layer (thickness (%) of the second layer - thickness (%) of the first layer) is preferably 25% or more, more preferably 30% or more, even more preferably 35% or more, and particularly preferably 40% or more. Furthermore, from the viewpoint of reducing peak frequency, the difference between the thickness (%) of the second layer and the thickness (%) of the first layer (thickness (%) of the second layer - thickness (%) of the first layer) is preferably 85% or less, more preferably 80% or less, even more preferably 75% or less, and particularly preferably 70% or less.

[0100] The ratio of the thickness (%) of the second layer to the thickness (%) of the first layer (thickness (%) of the second layer / thickness (%) of the first layer) is not particularly limited. From the viewpoint of improving the sound absorption coefficient, the ratio of the thickness (%) of the second layer to the thickness (%) of the first layer (thickness (%) of the second layer / thickness (%) of the first layer) is preferably 1.6 or more, more preferably 1.8 or more, even more preferably 2.0 or more, and particularly preferably 2.2 or more. Furthermore, from the viewpoint of reducing peak frequency, the ratio of the thickness (%) of the second layer to the thickness (%) of the first layer (thickness (%) of the second layer / thickness (%) of the first layer) is preferably 18 or less, more preferably 15 or less, even more preferably 12 or less, and particularly preferably 10 or less.

[0101] The present foam molded composite only needs to include at least a first layer and a second layer. Therefore, the first and second layers may have another layer between them, or they may be in contact with each other. From the viewpoint of improving sound absorption performance in the low-frequency range, it is more preferable that the first and second layers be in contact with each other. When the first and second layers are in contact with each other, the present foam molded composite may be a laminate in which the first and second layers are foam-molded separately, or a foam molded product in which the first and second layers are integrally molded so that they are in contact with each other. When another layer is present between the first and second layers, the layer is not particularly limited as long as it does not adversely affect the effects of the present invention, and may be a layer made of foamed particles with a high degree of irregularity, for example. The other layer may be a single layer or a multilayer consisting of two or more layers. When another layer is present between the first layer and the second layer, the foamed molded composite may be a laminate in which the first layer and the second layer, which have been foamed separately, are laminated together with the other layer interposed therebetween, or may be a foamed molded product in which the first layer and the second layer are integrally molded with the other layer interposed therebetween.

[0102] When the first layer and the second layer are in contact with each other, the foam molded composite may have at least the first layer and the second layer in contact with the first layer, and may have a multilayer structure of three or more layers. In such a case, the number of layers in the multilayer structure is not particularly limited and may be three, four, five, or the like. For example, when the foam molded composite has at least the first layer and the second layer in contact with the first layer and has a multilayer structure of three or more layers, it is preferable that an additional layer be provided on the second layer side in addition to the first and second layers. This configuration has the advantage that when the first layer is positioned on the sound source side, the foam molded composite has excellent sound absorption performance in the low frequency range. Similarly, when another layer is present between the first layer and the second layer, it is preferable that an additional layer be provided on the second layer side.

[0103] Furthermore, when the foam molded composite has a multilayer structure of three or more layers, layers other than the first and second layers (including layers when other layers exist between the first and second layers) may also be polyolefin resin foam molded articles. In such cases, the porosity and thickness of the polyolefin resin foam molded article layers other than the first and second layers are not particularly limited and may be selected appropriately depending on the application, usage environment, etc.

[0104] For example, the foam molded composite may include, in addition to the first and second layers, a third polyolefin resin foam molded body layer on the second layer side, where the thickness of the third polyolefin resin foam molded body layer is 8% to 35% of the total thickness of the first and second layers, and the porosity of the third layer may be 20.0% to 32.0%. This configuration has the advantage of providing excellent sound absorption performance in the low frequency range when sound sources are present on both the first and third layer sides of the foam molded composite. In this configuration, the first and second layers may be in contact with each other, or another layer may be present between the first and second layers. The second and third layers may be in contact with each other, or another layer may be present between the second and third layers. It is particularly preferred that the first and second layers are in contact with each other, and that the second and third layers are in contact with each other.

[0105] Alternatively, the foam molded composite may include, in addition to the first and second layers, a third polyolefin resin foam molded body layer around the second layer, the thickness of the third polyolefin resin foam molded body layer being 8% to 35% of the total thickness of the first and second layers, and the porosity of the third layer being 20.0% to 32.0%. Here, the "around the second layer" refers to the four side surfaces of the second layer and the surface of the second layer opposite to the surface of the second layer that contacts the first layer when the first and second layers are in contact. Furthermore, the "around the second layer" refers to the four side surfaces of the other layer and the second layer and the surface of the second layer opposite to the first layer when another layer is present between the first and second layers. This configuration offers the advantage of excellent sound absorption performance in the low-frequency range when sound sources are present in all directions around the foam molded composite. In this configuration, the first layer and the second layer may be in contact with each other, or another layer may be present between the first layer and the second layer, or the second layer and the third layer may be in contact with each other, or another layer may be present between the second layer and the third layer. Of these, it is more preferable that the first layer and the second layer are in contact with each other, and that the second layer and the third layer are in contact with each other.

[0106] In this specification, the porosity of a polyolefin resin foam molded article can be measured by the measurement method described in the Examples. The porosity is a value measured by the measurement method described in the Examples after molding, drying, and cooling to room temperature (for example, after leaving the foam molded article at room temperature for 1 hour, curing and drying for 24 hours in a thermostatic chamber at 75°C, and then leaving it at room temperature for another 4 hours).

[0107] The porosity of each layer of the polyolefin resin foam molded article in the present foam molded article composite can be measured by cutting out each layer and using the method for measuring the porosity of a foam molded article described in the Examples.

[0108] In addition, the thickness of each layer in this foamed molded composite can be measured by thinly slicing the foamed molded composite, measuring the porosity of each slice using the method for measuring the porosity of foamed molded bodies described in the examples, and adding up the thicknesses of the slices until the porosity changes.

[0109] When the first layer is disposed on the sound source side, the maximum sound absorption coefficient of the foam molded composite is preferably 0.80 or more, more preferably 0.85 or more, even more preferably 0.90 or more, still more preferably 0.96 or more, and particularly preferably 0.97 or more. With this configuration, the foam molded composite can be said to have excellent sound absorption performance.

[0110] The peak frequency at which the normal incidence sound absorption coefficient of this foam molded composite is maximum, when the first layer is positioned on the sound source side, is preferably 300 Hz or more and 1000 Hz or less, more preferably 980 Hz or less, even more preferably 950 Hz or less, and particularly preferably 900 Hz or less. This configuration allows the foam molded composite to have excellent sound absorption performance in the low frequency range. The maximum sound absorption coefficient and peak frequency of the polyolefin resin foam molded composite can be measured by the measurement methods described in the Examples.

[0111] The composite density of the present foam molded composite is preferably 25.5 g / L to 31.0 g / L, more preferably 26.0 g / L to 30.5 g / L, even more preferably 26.5 g / L to 30.0 g / L, and particularly preferably 27.0 g / L to 29.5 g / L. A composite density of the present foam molded composite of 25.5 g / L or more is preferred because the composite has high strength, and a composite density of 31.0 g / L or less is preferred because the composite is lightweight. The composite density of the polyolefin resin foam molded composite can be measured by the measurement method described in the Examples.

[0112] The total thickness of the first and second layers in the foamed molded composite is not particularly limited, but is, for example, 20 mm to 40 mm. The overall thickness of the foamed molded composite is not particularly limited, but is, for example, 30 mm to 60 mm.

[0113] [1-4] Method for producing polyolefin resin foam molded composite The method for producing the polyolefin resin foam molded composite according to one embodiment of the present invention is not particularly limited.

[0114] The present foam molded composite can be produced, for example, by separately producing a first layer and a second layer, each of which is a polyolefin resin foam molded product, and then laminating the resulting first layer and second layer together. That is, the method for producing the present foam molded composite can include, for example, a foam molded product production step for producing the first layer, a foam molded product production step for producing the second layer, and a lamination step for laminating the resulting first layer and second layer together. The foam molded product production step for producing the first layer and the foam molded product production step for producing the second layer can be steps for producing foam molded products by in-mold molding.

[0115] Alternatively, the present foamed molded composite may be produced, for example, by forming a first layer, then filling a mold with expanded polyolefin resin beads to form the second layer together with the first layer, and expanding the resulting mixture, thereby integrally molding the first and second layers. More specifically, for example, the first layer may be formed by filling a mold with expanded polyolefin resin beads to form the first layer, and then filling the mold with expanded polyolefin resin beads to form the second layer together with the first layer, and expanding the resulting mixture, thereby integrally molding the first and second layers. That is, another method for producing the present foamed molded composite may include, for example, a foamed molded product production step for producing the first layer, and a foamed molded product production step for integrally molding the first and second layers. In this manufacturing method, after producing the first layer, expanded polyolefin resin particles for forming the second layer are filled together with the first layer and foamed to form the first and second layers. However, after producing the second layer, expanded polyolefin resin particles for forming the first layer are filled together with the second layer and foamed to form the first layer, so that the first and second layers are integrally molded.

[0116] Therefore, in the present foam molded composite, the first layer and / or the second layer is preferably a foam molded article obtained by molding expanded polyolefin resin beads in a mold.

[0117] <Method of manufacturing foam molded article> As an example of a method for producing a foam molded article in the foam molded article production process for producing the first layer, the foam molded article production process for producing the second layer, and the foam molded article production process for integrally molding the first and second layers, a method for producing a foam molded article by in-mold molding using a mold will be described below. This method includes a heating step of heating polyolefin resin foam beads in a mold, and a water-cooling step of water-cooling the pre-polyolefin resin foam molded article obtained in the heating step, or both the pre-polyolefin resin foam molded article and the mold, by spraying water for at least one second. However, the method for producing a foam molded article is not limited to this production method.

[0118] The method has the advantage that a foamed molded article having a large porosity and excellent sound-absorbing properties can be obtained. The mold preferably includes, for example, a fixed mold that cannot be driven and a movable mold that can be driven. The fixed mold and the movable mold can be configured so that a molding space can be formed inside the fixed mold and the movable mold by driving the movable mold toward the fixed mold (this operation is sometimes referred to as "mold closing").

[0119] (filling process) A filling step of filling the molding space of the mold with expanded polyolefin resin particles may be included before the heating step. The filling step may include, for example, a configuration including the following (b1) to (b4) in order, but is not limited to the following configurations: (b1) A mold consisting of a fixed mold that cannot be driven and a movable mold that can be driven is mounted on an in-mold foam molding machine; (b2) The movable mold is driven toward the fixed mold so that a small gap (also called cracking) is formed between the fixed mold and the movable mold so that they are not completely closed; (b3) Filling the molding space formed inside the fixed mold and the movable mold with foam particles, for example, through a filling machine; (b4) The movable mold is driven so that the fixed mold and the movable mold are completely closed (that is, the molds are completely closed).

[0120] The expanded beads that are filled into a mold and heated may be those that have been pressurized in advance with an inorganic gas (e.g., air, nitrogen, oxygen, carbon dioxide, helium, neon, argon, etc.) to impregnate the expanded beads with the inorganic gas, thereby giving them internal pressure, or they may be expanded beads that have not been given internal pressure. Using expanded beads that have not been given internal pressure allows for the production of foamed molded articles with a higher porosity. Expanded beads that have not been given internal pressure can also be said to be polyolefin resin expanded beads with an internal pressure of 0.1 MPa (absolute pressure).

[0121] (Heating process) The heating step is, for example, a step of heating the expanded beads filled in the molding space of the mold with steam in the filling step. In the heating step, the expanded beads in the mold (in the molding space of the mold) are heated, so that the expanded beads in the mold can be fused together, thereby obtaining a foamed molded article.

[0122] In this specification, the foam molded article present in the mold obtained after the heating step, which has not been water-cooled or is in the process of being water-cooled, may be referred to as a "pre-polyolefin resin foam molded article" for convenience in order to distinguish it from the polyolefin resin foam molded article finally obtained.

[0123] In the heating step, the temperature of the steam is not particularly limited, but is preferably 143° C. to 170° C., more preferably 145° C. to 168° C., even more preferably 147° C. to 165° C., and particularly preferably 148° C. to 162° C. This configuration has the advantage of producing a polyolefin resin foam molded article with good fusion.

[0124] In the heating step, the pressure of the steam is not particularly limited, but is preferably 0.20 MPa (gauge pressure) to 0.40 MPa (gauge pressure), more preferably 0.24 MPa (gauge pressure) to 0.36 MPa (gauge pressure), further preferably 0.26 MPa (gauge pressure) to 0.34 MPa (gauge pressure), and particularly preferably 0.28 MPa (gauge pressure) to 0.32 MPa (gauge pressure). This configuration has the advantage of producing a polyolefin resin foam molded product with good fusion.

[0125] (Water cooling process) In the water-cooling step, water is sprayed for one second or more onto the pre-polyolefin resin foam molded article obtained in the heating step, or onto both the pre-polyolefin resin foam molded article and the mold, to water-cool the pre-polyolefin resin foam molded article. A polyolefin resin foam molded article can be obtained by the water-cooling step. Furthermore, by carrying out the water-cooling step having the above-described configuration, there is an advantage that a polyolefin resin foam molded article with little deformation can be obtained.

[0126] The temperature of the water is preferably 10° C. to 70° C., more preferably 12° C. to 65° C., even more preferably 14° C. to 60° C., and particularly preferably 15° C. to 55° C. This configuration has the advantages of improving the productivity of polyolefin resin foam molded articles and reducing the cost of steam used in molding.

[0127] The water spray pressure is preferably 0.3 MPa (gauge pressure) to 0.7 MPa (gauge pressure), more preferably 0.4 MPa (gauge pressure) to 0.65 MPa (gauge pressure), further preferably 0.4 MPa (gauge pressure) to 0.6 MPa (gauge pressure), and particularly preferably 0.4 MPa (gauge pressure) to 0.55 MPa (gauge pressure). This configuration has the advantage of allowing water (cooling water) to be effectively sprayed onto both the pre-polyolefin resin foam molded article and the mold, or onto the pre-polyolefin resin foam molded article.

[0128] The time for spraying water (sometimes referred to herein as "water cooling time") is 1 second or more, preferably 1 to 90 seconds, more preferably 3 to 60 seconds, even more preferably 5 to 50 seconds, and particularly preferably 10 to 45 seconds. This configuration has the advantage that a polyolefin resin foam molded article with little deformation can be obtained.

[0129] When spraying water onto the pre-polyolefin resin foam molded article, a method of directly spraying water onto the foam molded article can be used.

[0130] When spraying water onto both the pre-polyolefin resin foam molded article and the mold, the method for spraying water is not particularly limited, and examples include a method of directly spraying water onto a mold having holes formed therein. When water is directly sprayed onto a mold having holes formed therein, the water is ultimately sprayed onto the pre-polyolefin resin foam molded article in the mold through the holes. In this way, when the water sprayed onto the mold is ultimately sprayed onto the pre-polyolefin resin foam molded article in the mold, it is considered that "water is sprayed onto both the pre-polyolefin resin foam molded article and the mold."

[0131] As described above, in the water cooling step, spraying water directly onto the pre-polyolefin resin foam molded article or onto both the pre-polyolefin resin foam molded article and the mold has the advantage of allowing the pre-polyolefin resin foam molded article to be cooled efficiently.

[0132] (Mold release and drying process) After the water-cooling step, a demolding and drying step may be included in which the in-mold foam molded article is removed from the mold and dried to obtain a foam molded article.

[0133] The method for releasing the in-mold foam molded article from the mold is not particularly limited, but examples thereof include a method using air and a method using a demolding tool.

[0134] The drying temperature is not particularly limited, but is preferably 70° C. to 85° C., more preferably 75° C. to 83° C., even more preferably 75° C. to 81° C., and particularly preferably 75° C. to 80° C. This configuration has the advantage that a polyolefin resin foam molded article with a low moisture content can be obtained with little energy consumption.

[0135] The drying time is not particularly limited, but is preferably 10 to 24 hours, more preferably 12 to 24 hours, even more preferably 14 to 24 hours, and particularly preferably 16 to 24 hours. This method has the advantage that a polyolefin resin foam molded article with a low moisture content can be obtained with little energy consumption.

[0136] Alternatively, the drying may be performed by cooling at room temperature for 0.5 to 2 hours, followed by drying at the aforementioned temperature and for the aforementioned time, and then cooling at room temperature for 1 to 6 hours. In this specification, room temperature means 20°C to 25°C.

[0137] <Adjusting the porosity of foamed molded products> In the foam-molded article production process for producing the first layer, the foam-molded article production process for producing the second layer, and the foam-molded article production process for integrally molding the first layer and the second layer, the method for adjusting the porosity of the resulting foam-molded article is not particularly limited.

[0138] The porosity of the resulting foamed molded article can be adjusted to a predetermined range in the first and second layers, for example, by adjusting the compression ratio of the expanded beads. The compression ratio of the expanded beads can be adjusted, for example, by adjusting the size of the gap (cracking) between the fixed mold and the movable mold that form the molding space into which the expanded beads are filled (hereinafter, sometimes referred to as the "cracking amount"). If the cracking amount is large (high compression ratio), the porosity of the foamed molded article will be small, and if the cracking amount is small (low compression ratio), the porosity of the foamed molded article will be large.

[0139] Other methods for adjusting the void ratio of the resulting foamed molded body include adjusting the pressurized state of the hopper when filling the molding space of the mold with polyolefin resin foam particles, adjusting the internal pressure when applying internal pressure, and adjusting the peak pressure during molding of the foamed molded body.

[0140] <Production of Polyolefin Resin Foam Molded Composite> In a method for producing a foam molded composite, which includes a foam molded product production step for producing a first layer, a foam molded product production step for producing a second layer, and a lamination step for laminating the obtained first layer and second layer, the method for laminating the first layer and second layer in the lamination step is not particularly limited. Examples include a method in which the surfaces of the first layer and the second layer obtained in the foam molded product production step are overlapped with each other, and then at least one of the four sides of the laminated surfaces of the obtained laminate is fixed with a fixture, fixing tape, or the like, or a method in which the obtained laminate is molded again and heat-sealed to each other.

[0141] The method may include a thickness adjusting step of adjusting the thickness of the first layer and / or the second layer produced in the foam molded article production step, prior to the laminating step.

[0142] In a method for producing a foam molded composite, which includes a foam molded product production step for producing the first layer (or the second layer) and a foam molded product production step for integrally molding the first and second layers, after the water cooling step in the foam molded product production step for producing the first layer (or the second layer), the in-mold foam molded product obtained is not removed from the mold but is left in the mold. Then, using methods (b2) to (b4) in the filling step, polyolefin resin foam particles for forming the second layer (or the first layer if the foam molded product left in the mold is the second layer) are filled and expanded, thereby foam-molding the second layer (or the first layer), thereby integrally molding the first and second layers. In this case, the foam molded product left in the mold may be present on either the fixed mold side or the movable mold side. However, the method for integrally molding the first and second layers is not limited to this.

[0143] [2. Sound-absorbing materials] The polyolefin resin foam molded composite according to one embodiment of the present invention can be suitably used as a sound absorbing material, and therefore the present invention also includes sound absorbing materials.

[0144] A sound-absorbing member according to one embodiment of the present invention may include the foam molded composite, and is configured, for example, so that a first layer of the foam molded composite is positioned closer to the sound source than the second layer.

[0145] A sound-absorbing member according to one embodiment of the present invention may be, for example, a sound-absorbing member for automobiles. The sound-absorbing member for automobiles is suitably used for automobile ceiling materials, floor materials, dash insulators, tibia pads, etc. Alternatively, a sound-absorbing member according to one embodiment of the present invention may be a sound-absorbing member for architecture. The sound-absorbing member for architecture is suitably used for interior decoration such as ceilings, walls, and floors of buildings. Alternatively, a sound-absorbing member according to one embodiment of the present invention may also be suitably used as a sound-absorbing member for aircraft; railway vehicles such as electric trains and bullet trains, etc. [Example]

[0146] The present invention will be specifically explained below with reference to examples, but the technical scope of the present invention is not limited to these examples.

[0147] 〔material〕 The materials used in the examples and comparative examples are shown below.

[0148] (Polyolefin resin) Polypropylene resin: 1-butene / ethylene / propylene random copolymer (melting point 149°C, propylene unit 96 mol%, 1-butene content 3.8 wt%, ethylene content 0.5 wt%, MI = 10.1 g / 10 min) (additives) Glycerin: Refined glycerin D (manufactured by Lion Corporation) Talc: Talc Powder (registered trademark) PK-S (manufactured by Hayashi Kasei Co., Ltd.).

[0149] [Measurement method] The measurement and evaluation methods for various items carried out in the examples and comparative examples will be explained below.

[0150] <Melting point of polyolefin resin> The melting point of the polyolefin resin was determined by measurement using a DSC method using a differential scanning calorimeter (manufactured by Seiko Instruments Inc., DSC6200 model). The specific operating procedures were as follows (1) to (4): (1) The temperature of 5 mg to 6 mg of polyolefin-based resin was raised from 40.0°C to 220.0°C at a heating rate of 10.0°C / min to melt the polyolefin-based resin; (2) The temperature of the molten polyolefin-based resin was then lowered from 220.0°C to 40.0°C at a heating rate of 10.0°C / min to crystallize the polyolefin-based resin; (3) The temperature of the crystallized polyolefin-based resin was then further raised 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-based resin obtained during the second heating (i.e., at the time of (3)) was determined as the melting point of the polyolefin-based resin. In addition, when there are multiple peaks (melting peaks) in the DSC curve of the polyolefin resin obtained during the second heating by the above-mentioned method, the temperature of the peak (melting peak) with the largest heat of fusion was taken as the melting point of the polyolefin resin.

[0151] The MI of polyolefin resins was measured using an MI measuring instrument specified in JIS K7210:1999 under the following conditions: orifice diameter 2.0959±0.005 mmφ, orifice length 8.000±0.025 mm, load 2.16 kgf, and temperature 230°C (230±0.2°C).

[0152] <Degree of irregularity of foamed beads> The degree of deformation of the expanded polyolefin resin beads was calculated by dividing the "true density" measured by the method described below by the "bulk density" measured by the method described below. Specifically, it was measured by the following formula: Degree of irregularity = true density of expanded particles (g / L) / bulk density of expanded particles (g / L).

[0153] (True density of foamed particles) The weight M1 (g) of the expanded polyolefin resin beads was accurately measured to the nearest 0.001 g (rounded off to the fourth decimal point). The weighed expanded polyolefin resin beads were immersed in a measuring cylinder containing 100 mL of water at 23°C. The volume V1 (cm3) of the expanded polyolefin resin beads was determined from the rising scale. 3 The true density of the expanded beads was calculated using the following formula: True density of foamed beads (g / L) = Weight of foamed beads M1 (g) / {Volume of foamed beads V1 (cm 3 ) / 1000}.

[0154] (Bulk density of expanded particles) The method for measuring the bulk density of the expanded beads was as follows (1) to (3): (1) The expanded beads were placed in a container with a volume of V2 (L) until the expanded beads overflowed from the container; (2) The powder surface (top end) of the container was scraped off, and the weight M2 (g) of the expanded beads in the container was measured; (3) The bulk density of the expanded beads was calculated using the following formula: Bulk density of expanded particles (g / L) = weight of expanded particles M2 (g) / volume of container V2 (L).

[0155] <Maximum sound absorption coefficient and peak frequency of foam molded material> In accordance with JIS A1405, normal incidence sound absorption coefficients were measured in the frequency range of 500 Hz to 6400 Hz using a normal incidence sound absorption coefficient measurement sample with a sample thickness of 40.0 mm.

[0156] The normal incidence sound absorption coefficient was measured with the sample in close contact with a rigid wall that reflects sound waves, meaning there was no air behind it. The evaluation sample was placed with the first layer facing the sound source and the second layer facing the rigid wall, and measurements were taken. The normal incidence sound absorption coefficient was measured using an Ono Sokki normal incidence sound absorption coefficient measuring device, SR-4100. From the obtained frequency-normal incidence sound absorption coefficient curve, the frequency at which the normal incidence sound absorption coefficient first becomes maximum, viewed from the low frequency side, and the normal incidence sound absorption coefficient were read as the peak frequency and maximum sound absorption coefficient, respectively.

[0157] <Porosity of foam molded body> The volume of the sample on which the maximum sound absorption coefficient and peak frequency were measured was determined as Vc (cm) according to the method described in Procedure C of ASTM D2856-87. 3 ) and the porosity (%) was calculated according to the following formula: Porosity (%)={(Va-Vc)×100} / Va In addition, Vc(cm 3 ) was measured using an air comparison type hydrometer Model 1000 manufactured by Tokyo Science Co., Ltd. The volume Va (cm 3 ) is the apparent volume calculated by the following formula, using a vernier caliper to measure the diameter D (cm) and height H (cm) of the polyolefin resin foam molded article after measuring Vc with the air comparison type hydrometer: Volume Va (cm 3 )=πD 2 H / 4.

[0158] <Composite density> The weight W (g) of the sample for which the maximum sound absorption coefficient and peak frequency were measured was measured and calculated using the following formula: Composite density (g / L)=W / Vc×1000.

[0159] [Production Example 1] (Preparation of polyolefin resin particles) 100 parts by weight of polypropylene resin, 0.15 parts by weight of glycerin, and 0.05 parts by weight of talc were weighed and dry-blended using a small tumbler manufactured by O.N. Machine Co., Ltd. to obtain a mixture. The resulting mixture was melt-kneaded at a resin temperature of 200°C using a twin-screw extruder (Toshiba Machine Co., Ltd., TEM26-SX) and extruded into strands from a five-baseline die (die shown in Figure 1) attached to the tip of the extruder. The extruded product (strands) were water-cooled in a 2-m-long water tank. The water-cooled product was then taken up and chopped into star-shaped columns using a chopping device (Ishinaka Iron Works Co., Ltd.) (chopping process). This procedure yielded polyolefin resin particles (weight per particle: 2.5 mg). The resulting polyolefin resin particles were used as polyolefin resin particles for foaming.

[0160] (Preparation of polyolefin resin foam particles) A 10-L pressure vessel was charged with 100 parts by weight of expandable polyolefin resin particles, 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 dispersing aid, 0.03 parts by weight of citric acid as a pH adjuster, and 3.5 to 4.5 parts by weight of carbon dioxide as a blowing agent, depending on the foaming pressure, to prepare a dispersion containing the foaming agent. The resulting dispersion was stirred while the foaming temperature (temperature inside the pressure vessel) was raised to 151.0°C. After the temperature and pressure inside the pressure vessel reached the predetermined foaming temperature and foaming pressure, the temperature and pressure inside the pressure vessel were maintained at the predetermined foaming temperature and foaming pressure for an additional 30 minutes. Carbon dioxide was then introduced, and the pressure inside the pressure vessel was maintained at the foaming pressure of 2.5 MPa. The valve at the bottom of the pressure vessel was opened, and the dispersion inside the pressure vessel was released into atmospheric pressure through a 4.0 mm diameter orifice, yielding expanded polyolefin resin particles. The expanded polyolefin resin beads were dried for 24 hours at 75° C. The resulting first-stage expanded beads showed two peaks derived from the polyolefin resin in a DSC curve measured by a DSC method.

[0161] (Production of polyolefin resin foam molded body) The resulting polyolefin-based resin foam particles were loaded into a mold (370 mm long x 320 mm wide x 60 mm high) for a plate-shaped molded product mounted on a polyolefin in-mold foam molding machine (manufactured by Daisen Co., Ltd.) with the mold open by a cracking distance of 5 mm. The mold was then completely closed, and the polyolefin-based resin foam particles were heated and pressed with steam at 0.28 MPa (gauge pressure). After that, 30°C cooling water was sprayed onto the mold at 0.4 MPa for 40 seconds to cool the in-mold foam molded product. The mold was then opened, and the polyolefin-based resin in-mold foam molded product was removed from the mold using air or a mold release tool. The resulting in-mold foam molded product was left at room temperature for 1 hour, then cured and dried in a constant-temperature chamber at 75°C for 16 hours, and then left at room temperature for another 4 hours to obtain a polyolefin-based resin foam molded product. The porosity of the resulting polyolefin-based resin foam molded product was 39.3%, as shown in Table 1.

[0162] [Table 1]

[0163] [Production Examples 2 to 8] Polyolefin resin foam molded articles were produced in the same manner as in Production Example 1, except that the cracking amount was changed to the cracking amount shown in Table 1. The cracking amount and the porosity of the resulting molded article in each Production Example are shown in Table 1. The polyolefin resin foam beads obtained in Production Examples 1 to 8 were star-shaped and had an irregularity degree of 2.50. These foamed beads are referred to as foamed beads A.

[0164] [Production Examples 9-10] In the production of polyolefin resin particles, the die attached to the tip of the extruder was changed from a five-line die to an anchor-cross die (as shown in Figure 4), thereby obtaining anchor-cross-shaped polyolefin resin particles (weight per particle: 2.5 mg). These polyolefin resin particles were used to obtain anchor-cross-shaped expanded polyolefin resin particles. In the production of polyolefin resin foam molded articles, the same procedures as in Production Example 1 were carried out, except that the cracking amount was changed to the cracking amount shown in Table 1. The first-stage expanded polyolefin resin beads obtained in the production of the expanded polyolefin resin beads showed two peaks derived from the polyolefin resin in the DSC curve measured by the DSC method. The expanded polyolefin resin beads obtained in Production Examples 9 and 10 had an anchor-cross shape and an irregularity degree of 2.69. These expanded beads are designated as expanded beads B.

[0165] Table 1 shows the amount of cracking and the porosity of the resulting molded body in each production example.

[0166] [Production Example 11] In the production of polyolefin resin particles, the die attached to the tip of the extruder was changed from a five-line die to a circumferential die (die shown in Figure 5) to obtain macaroni-shaped polyolefin resin particles (weight per particle: 2.5 mg). These polyolefin resin particles were used to obtain macaroni-shaped expanded polyolefin resin particles. In the production of polyolefin resin foam molded articles, the cracking amount was changed to the cracking amount shown in Table 1. The same procedures as in Production Example 1 were performed to produce polyolefin resin foam molded articles, except for this. The first-stage expanded particles obtained in the production of polyolefin resin foam beads showed two peaks derived from the polyolefin resin in the DSC curve measured by the DSC method. The expanded polyolefin resin particles obtained in Production Example 11 had a macaroni-shaped shape and a degree of irregularity of 2.24. These expanded beads are designated as expanded beads C.

[0167] Table 1 shows the amount of cracking and the porosity of the resulting molded body in each production example.

[0168] Example 1 (Production of two-layer polyolefin resin foam molding) Samples measuring φ29 mm and 60 mm thick were cut out from the polyolefin resin foam having a porosity of 37.7% produced in Production Example 2 and the polyolefin resin foam having a porosity of 26.8% produced in Production Example 6. The cylindrical samples were cut and removed from the bottom and top surfaces of the cylinder along planes parallel to the bottom and top surfaces, thereby adjusting the thickness of the sample with a porosity of 37.7% to 30 mm (second layer) and the sample with a porosity of 26.8% to 10 mm (first layer). The two samples with adjusted thicknesses were stacked so that their circular surfaces were in contact with each other, and the circumferential surfaces were fixed by wrapping tape around them.

[0169] (Evaluation of two-layer polyolefin resin foam moldings) The obtained two-layer polyolefin resin foam molded article was used as a sample for measuring normal incidence sound absorption coefficient, and the maximum sound absorption coefficient and peak frequency were measured. In addition, the volume and weight of the normal incidence sound absorption coefficient measurement sample whose maximum sound absorption coefficient and peak frequency were measured were measured, and the composite density was calculated. The results are shown in Table 2.

[0170] [Table 2]

[0171] [Examples 2 to 9, Comparative Examples 1 to 6] Two-layer polyolefin resin foam molded articles were produced in the same manner as in Example 1, except that the porosity of the foam constituting the first and second layers, the type of foamed beads constituting the first and second layers, and the thickness of each layer were changed as shown in Table 2. The physical properties of the obtained two-layer polyolefin resin foam molded articles were measured and evaluated. The results are shown in Table 2.

[0172] 〔summary〕 A comparison of Examples 1 to 5 with Comparative Example 1 reveals that when the porosity of the molded body constituting the first layer placed on the sound source side is 32% or less, the peak frequency is lower and sound absorption performance is superior in the low frequency range compared to Comparative Example 1, where the porosity exceeds 32%. On the other hand, a comparison of Examples 1 to 5 with Comparative Example 3 reveals that when the porosity of the molded body constituting the first layer placed on the sound source side is 20% or more, the maximum sound absorption coefficient is higher compared to Comparative Example 3, where the porosity is less than 20%.

[0173] A comparison of Examples 1 to 3 with Comparative Example 2 reveals that when the porosity of the molded body constituting the second layer located on the opposite side from the sound source exceeds 32%, the maximum sound absorption coefficient is higher than in Comparative Example 2, where the porosity is 32% or less. Furthermore, a comparison of Example 7 with Comparative Example 4 reveals that when the porosity of the molded body constituting the second layer located on the opposite side from the sound source is 45% or less, the maximum sound absorption coefficient is higher than in Comparative Example 4, where the porosity is more than 45%.

[0174] The above results show that the porosity of the molded body constituting the layer placed on the sound source side has a greater effect on the peak frequency than the porosity peak frequency of the molded body constituting the layer placed on the opposite side of the sound source. [Industrial Applicability]

[0175] According to the present invention, it is possible to provide a polyolefin resin foam molded article that is lightweight and has excellent sound-absorbing performance in the low frequency range, and therefore can be suitably used as a sound-absorbing member for vehicles such as automobiles and trains, aircraft, buildings, etc.

Claims

1. A polyolefin resin foam molded body composite comprising at least a first polyolefin resin foam molded body layer and a second polyolefin resin foam molded body layer, the thickness of the first polyolefin resin foam molded product layer is 8% or more and 35% or less of the total thickness of the first polyolefin resin foam molded product layer and the second polyolefin resin foam molded product layer; the first polyolefin resin foam molded body layer has a porosity of 20.0% or more and 32.0% or less; the thickness of the second polyolefin resin foam molded product layer is 65% or more and 92% or less of the total thickness of the first polyolefin resin foam molded product layer and the second polyolefin resin foam molded product layer; A polyolefin resin foam molded composite, wherein the second polyolefin resin foam molded layer has a porosity of more than 32.0% and not more than 45.0%.

2. The polyolefin resin foam molded composite according to claim 1 , wherein the second polyolefin resin foam molded body layer is in contact with the first polyolefin resin foam molded body layer.

3. The polyolefin resin foam molded body composite according to claim 1, wherein the first polyolefin resin foam molded body layer is positioned closer to a sound source than the second polyolefin resin foam molded body layer.

4. 2. The polyolefin resin foam molded body composite according to claim 1, wherein the first polyolefin resin foam molded body layer and / or the second polyolefin resin foam molded body layer is a foam molded body obtained by molding polyolefin resin foam beads in a mold.

5. The polyolefin resin foam molded composite according to claim 4, wherein the expanded polyolefin resin particles are irregularly shaped particles.

6. A sound-absorbing member comprising the polyolefin resin foam molded composite according to any one of claims 1 to 5.

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