Polypropylene-based resin foamed particles, polypropylene-based resin

Abstract

The present invention provides polypropylene resin foamed particles capable of improving the dimensional stability of a molded body, a polypropylene resin foamed particle molded body comprising the foamed particles, a bumper core material for a motor vehicle, and a tool box for a motor vehicle. The foamed particles (1) have a foamed layer (2) comprising a polypropylene resin, and have a specific shape having one or more defect portions (11). The polypropylene resin constituting the foam layer (2) includes a polypropylene resin (A) having a melting point of 135-150 DEG C and a flexural modulus of less than 1000 MPa, and a polypropylene resin (B) having a melting point of 145-160 DEG C and a flexural modulus of 1000 MPa or more. The mass ratio of the resin (A) to the resin (B) in the polypropylene resin is (resin (A)): (resin (B)) = 65: 35-35: 65.

Description

TECHNICAL FIELD

[0001] The present application relates to a polypropylene resin foamed particle, a polypropylene resin foamed particle molded body, a bumper core for a motor vehicle, and a tool box for a motor vehicle. BACKGROUND

[0002] A polypropylene resin foamed particle molded body is used for various purposes because it is lightweight and excellent in cushioning property, rigidity, and the like. The polypropylene resin foamed particle molded body is manufactured, for example, by a method called in-mold molding method, which is a method of filling polypropylene resin foamed particles into a molding die, and then supplying steam to the molding die to heat. In the in-mold molding method, if steam is supplied to the molding die, the foamed particles are secondarily foamed, and their surfaces are melted. Thereby, the foamed particles in the molding die are fused to each other, and a molded body having a shape corresponding to the shape of the molding cavity of the molding die can be obtained. The molded body immediately after molding is easily expanded by secondary foaming, and thus is cooled by water, air, or the like in the molding die, and then demolded from the molding die.

[0003] In the manufacturing process of the molded body described above, if the molded body demolded from the molding die is stored at normal temperature, the steam flowing into the bubbles of the molded body at the time of in-mold molding is condensed in the bubbles, and the inside of the bubbles becomes underpressure. As a result, there is a case where the molded body is volumetrically shrunk and is largely deformed. Therefore, after the molded body is demolded from the molding die, a curing process of standing the molded body in a high-temperature atmosphere adjusted to a temperature of about 60°C to 80°C for a predetermined time to recover the shape of the molded body is performed, for example. However, since the curing process is required in the in-mold molding of the polypropylene resin foamed particles, equipment investment is required, and the process requires work and time, and thus it is desired to omit the curing process and greatly improve the productivity of the molded body.

[0004] From the above viewpoint, a foamed particle molded body composed of a tubular polypropylene resin foamed particle is proposed in Patent Literature 1, for example.

[0005] PRIOR ART DOCUMENTS PATENT LITERATURE Patent Literature 1: International Publication No. 2022 / 270425 SUMMARY PROBLEMS TO BE SOLVED BY THE INVENTION The molded body described in Patent Literature 1 has room for further improvement in dimensional stability after in-mold molding depending on its shape and the like, and it is desired to reduce the amount of change in the size of the molded body from the time point of demolding to the time point at which the shape is stabilized by the curing process or the like.

[0006] The present application has been made in view of the above-described background, and aims to provide a polypropylene resin expanded particle capable of improving dimensional stability of a molded body, a polypropylene resin expanded particle molded body composed of the expanded particle, a bumper core material for a motor vehicle, and a tool box for a motor vehicle.

[0007] Means for solving the problem One embodiment of the present application is a polypropylene resin expanded particle according to any one of the following 〔1〕 to 〔6〕.

[0008] 〔1〕 A polypropylene resin expanded particle having a foamed layer composed of a polypropylene resin, wherein the expanded particle has a columnar shape, and has one or both of a defect portion selected from the group consisting of a through-hole that penetrates the inside of the expanded particle in the axial direction of the expanded particle, and a groove that extends in the axial direction on the side peripheral surface of the expanded particle, a ratio Ca / A of an average cross-sectional area Ca of each of the defect portions in a cross section obtained by cutting the expanded particle at the center in the axial direction of the expanded particle with a plane perpendicular to the axial direction with respect to an average cross-sectional area A of the expanded particle is 0.01 or more and 0.20 or less, and a ratio Ct / A of a total cross-sectional area Ct of the defect portions with respect to the average cross-sectional area A of the expanded particle is 0.02 or more and 0.20 or less, the polypropylene resin that constitutes the foamed layer contains a polypropylene resin (A) having a melting point of 135°C or more and 150°C or less and a flexural elastic modulus of less than 1000 MPa, and a polypropylene resin (B) having a melting point of 145°C or more and 160°C or less and a flexural elastic modulus of 1000 MPa or more, a mass ratio of the polypropylene resin (A) to the polypropylene resin (B) in the polypropylene resin is polypropylene resin (A) : polypropylene resin (B) = 65 : 35 to 35 : 65.

[0009] 〔2〕 The polypropylene resin expanded particle according to 〔1〕, wherein an absolute value of a difference between the flexural elastic modulus of the polypropylene resin (A) and the flexural elastic modulus of the polypropylene resin (B) is 200 MPa or more and 500 MPa or less.

[0010] 〔3〕 The polypropylene resin expanded particle according to 〔1〕 or 〔2〕, wherein the polypropylene resin (B) is one or more kinds of propylene-based copolymers selected from the group consisting of an ethylene-propylene copolymer, a butylene-propylene copolymer, and an ethylene-butylene-propylene copolymer.

[0011] 〔4〕 The polypropylene-based resin expanded particles according to any one of 〔1〕 to 〔3〕, wherein the content of the ethylene component and the content of the butene component in the polypropylene-based resin (B) are 0.5 mass% or more and 2.5 mass% or less in total.

[0012] 〔5〕 The polypropylene-based resin expanded particles according to any one of 〔1〕 to 〔4〕, wherein the polypropylene-based resin expanded particles have a crystal structure in which a resin-inherent peak derived from melting of a crystal inherent to the polypropylene-based resin and a high-temperature peak having a peak temperature higher than that of the resin-inherent peak appear in a DSC curve obtained when the expanded particles are heated from 23°C to 200°C at a heating rate of 10°C / minute, and the heat of fusion of the high-temperature peak is 8 J / g or more and 25 J / g or less.

[0013] 〔6〕 The polypropylene-based resin expanded particles according to any one of 〔1〕 to 〔5〕, wherein the apparent density of the polypropylene-based resin expanded particles is 15 kg / m 3 or more and 200 kg / m 3 or less.

[0014] Another aspect of the present application is a polypropylene-based resin expanded particle molded article according to any one of 〔7〕 or 〔8〕.

[0015] 〔7〕 A polypropylene-based resin expanded particle molded article, wherein the polypropylene-based resin expanded particle molded article is produced by in-mold molding the polypropylene-based resin expanded particles according to any one of 〔1〕 to 〔6〕.

[0016] 〔8〕 The polypropylene-based resin expanded particle molded article according to 〔7〕, wherein the maximum length of the polypropylene-based resin expanded particle molded article is 600 mm or more.

[0017] Still another aspect of the present application is a bumper core for a motor vehicle according to 〔9〕.

[0018] 〔9〕 A bumper core for a motor vehicle, wherein the bumper core for a motor vehicle is produced by in-mold molding the polypropylene-based resin expanded particles according to any one of 〔1〕 to 〔6〕.

[0019] Still another aspect of the present application is a tool box for a motor vehicle according to 〔10〕.

[0020] 〔10〕 A tool box for a motor vehicle, wherein the tool box for a motor vehicle is produced by in-mold molding the polypropylene-based resin expanded particles according to any one of 〔1〕 to 〔6〕.

[0021] Effects of the Invention According to the above-described manner, it is possible to provide a polypropylene resin expanded particle capable of improving dimensional stability of a molded body, a polypropylene resin expanded particle molded body composed of the expanded particle, a bumper core material for a motor vehicle, and a tool box for a motor vehicle. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a schematic view of the appearance of an expanded particle having a through-hole as a defect.

[0023] Figure 2 is a schematic view of the appearance of an expanded particle having a groove as a defect. Figure 1 is a schematic view of the appearance of an expanded particle having a groove as a defect.

[0024] Figure 3 is a schematic view of the appearance of an expanded particle having a through-hole as a defect.

[0025] Figure 4 is a schematic view of the appearance of an expanded particle having a through-hole as a defect. Figure 3 is a schematic view of the appearance of an expanded particle having a through-hole as a defect.

[0026] Figure 5 is a schematic view of the appearance of an expanded particle having a through-hole as a defect.

[0027] Figure 6 is a schematic view of the appearance of an expanded particle having a through-hole as a defect. Figure 5 is a schematic view of the appearance of an expanded particle having a through-hole as a defect.

[0028] Figure 7 is an explanatory view of a calculation method of the area of a high-temperature peak.

[0029] Figure 8 is a schematic view of the appearance of an expanded particle D in the example.

[0030] Figure 9 is a schematic view of the appearance of an expanded particle having a through-hole as a defect. Figure 8 is a schematic view of the appearance of an expanded particle having a through-hole as a defect.

[0031] Figure 10 is a front view of a bumper core material in Example 1-1.

[0032] Figure 11 is a schematic view of the appearance of an expanded particle having a through-hole as a defect. Figure 10 is a schematic view of the appearance of an expanded particle having a through-hole as a defect.

[0033] Figure 12 is a perspective view of a tool box in Example 1-3.

[0034] Figure 13 is a plan view of a tool box in Example 1-3.

[0035] BRIEF DESCRIPTION OF DRAWINGS 1: Foamed particle; 11: Defect portion; 111: Through-hole; 112: Groove; 2: Foamed layer. DETAILED DESCRIPTION

[0036] (Polypropylene resin foamed particle) The polypropylene resin foamed particle (hereinafter, referred to as "foamed particle") has a columnar shape, and has one or both of a defect portion selected from the group consisting of a through-hole that penetrates an inside of the foamed particle in an axial direction and a groove that extends in the axial direction on a side peripheral surface of the foamed particle. In other words, the foamed particle has one or both of a defect portion constituted by a through-hole that penetrates an inside of the foamed particle in an axial direction and a defect portion constituted by a groove that extends in the axial direction on a side peripheral surface of the foamed particle. In addition, a ratio Ca / A of an average cross-sectional area Ca of each of the defect portions in a cut surface of the foamed particle obtained by cutting the foamed particle at a center thereof in the axial direction with a surface perpendicular to the axial direction with respect to an average cross-sectional area A of the foamed particle is 0.01 or more and 0.20 or less, and a ratio Ct / A of a total cross-sectional area Ct of the defect portions with respect to the average cross-sectional area A of the foamed particle is 0.02 or more and 0.20 or less. Furthermore, a foamed layer of the foamed particle is constituted by a polypropylene resin containing the polypropylene resin (A) and the polypropylene resin (B) in the specific mass ratio.

[0037] In the past, in in-mold foaming of a polypropylene resin foamed particle molded body (hereinafter, referred to as "molded body"), a desired size of the molded body is manufactured by adjusting a molding condition or the like in consideration of a dimensional change of the molded body from a time point of demolding from a molding mold to a time point at which a shape is stabilized by a curing process or the like. However, in a case where the molded body is manufactured while omitting the curing process or shortening a time of the curing process, the dimensional change of the aforementioned molded body tends to be large. In addition, particularly, in a case where a molded body having a maximum length longer, a molded body having a complex shape such as a shape having a recess, or a molded body in which high dimensional accuracy is pursued, there is a risk that it becomes difficult to adjust the dimension of the molded body to be within a desired range.

[0038] On the contrary, the foamed particle can easily improve the dimensional stability of the molded body, and reduce the dimensional change from the time point of demolding to the time point at which the shape is stabilized. Therefore, even in a case where, for example, a molded body having a maximum length longer, a molded body having a complex shape, or a molded body in which high dimensional accuracy is pursued, which is relatively high in difficulty in in-mold foaming, is manufactured while omitting the curing process or shortening a time of the curing process, a molded body having a desired dimension can be easily obtained. In addition, the foamed particle can significantly improve the productivity of the molded body even in a case where the molded body which is relatively high in difficulty in in-mold foaming as described above is molded, since the curing process can be omitted or the time of the curing process can be shortened.

[0039] In addition, the foamed particles can easily shorten the drying time of the molded body after demolding, and further improve the productivity of the molded body. Further, the foamed particles can shorten the cooling time of the molded body in the molding die, and improve the surface properties and the fusion properties of the molded body.

[0040] As a reason why the foamed particles exhibit the above effects, for example, the following reasons are considered.

[0041] As described above, the foamed particles have one or more defect portions selected from the group consisting of grooves and through-holes. It is considered that, if such foamed particles are filled into a molding die, the defect portions of the foamed particles such as the through-holes, the grooves, the gaps between the foamed particles, and the like are intricately connected in the molding cavity of the molding die, and thereby a fine passage through which steam can pass is formed in the molding cavity. Therefore, it is considered that, when steam is supplied into the molding die, the steam easily reaches the inside of the molding die via the fine passage, and the entire foamed particles in the molding die can be easily heated. In addition, it is considered that the foamed particles having the defect portions moderately expand when heated by the steam because of having a moderate secondary foaming property. It is considered that, as a result, even in a condition where the molding temperature during in-mold molding is low, a molded body having excellent fusion properties and a good appearance can be obtained by using the foamed particles.

[0042] In addition, since the foamed particles having the defect portions have a moderate secondary foaming property, the secondary foaming can be sufficiently performed in the molding die even in a case where no internal pressure is applied in advance, or in a case where the magnitude of the applied internal pressure is relatively low. Further, it is considered that, since the foamed particles have the aforementioned defect portions, excessive expansion of the molded body at the time point when heating based on the steam ends can be avoided. Thereby, the time required from the end of heating of the foamed particles to the time when the shape of the molded body is stabilized in the molding die can be shortened. It is considered that, as a result, the time required for cooling of the molded body in the molding die can be shortened.

[0043] Further, a moderate open-cell structure is formed in the molded body after the end of in-mold molding. The open-cell structure is a minute space portion that communicates with the outside of the molded body. The open-cell structure is formed by intricately connecting the gaps formed by the communication of the gaps between the foamed particles, the continuous bubble portions of the foamed particles constituting the molded body, and the defect portions, and the like. It is considered that, since the foamed particles have the specific range of the ratio Ca / A and the ratio Ct / A and can suppress the formation of a bulky open-cell structure in the inside of the molded body, the time required for drying of the molded body after demolding can be shortened.

[0044] In addition, it is considered that if the molded body having the open-cell structure is taken out of the molding die, air rapidly flows into the cells inside the molded body via the open-cell structure, as a result, the internal pressure of the molded body stabilizes early. Further, since the foamed layer of the foamed particle is composed of the polypropylene-based resin containing the polypropylene-based resin (A) and the polypropylene-based resin (B) in the specific mass ratio, it is possible to improve the dimensional stability of the molded body and reduce the change in the size of the molded body after being taken out of the molding die. In addition, it is considered that since the foamed particle has a small change in the size of the molded body after being taken out, even in the case where a molded body having a relatively high degree of difficulty in in-mold molding is manufactured without performing a curing process or shortening the time of the curing process, it is possible to easily obtain a molded body having a desired size.

[0045] In the case where in-mold molding is performed using a foamed particle having no defect portion, it is difficult for the molded body to form an open-cell structure, the dimensional stability of the molded body easily decreases, and the change in the size of the molded body from after being taken out to shape stabilization easily becomes large. Therefore, in this case, there is a risk that it is difficult to adjust the size of the molded body to a desired size, for example, when a molded body having a relatively high degree of difficulty in in-mold molding is manufactured without performing a curing process or shortening the time of the curing process. In addition, in the case where in-mold molding is performed using a foamed particle having no defect portion, there is a risk that fusion failure of the foamed particles to each other occurs, the cooling time of the molded body in the molding die increases, and the productivity of the molded body significantly deteriorates.

[0046] Even in the case where there is a defect portion, in the case where the ratio Ca / A of the average cross-sectional area Ca of each of the defect portions to the average cross-sectional area A of the foamed particle and / or the ratio Ct / A of the total cross-sectional area Ct of the defect portions to the average cross-sectional area A of the foamed particle is excessively small, it is difficult to obtain the effect of the defect portion. Therefore, in this case, there is a risk that the dimensional stability of the molded body decreases, and fusion failure of the foamed particles to each other occurs. In addition, in this case, there is a risk that the cooling time of the molded body in the molding die excessively becomes long, and the productivity decreases.

[0047] By using a foamed particle in which the ratio Ca / A is 0.01 or more and the ratio Ct / A is 0.02 or more, it is possible to exhibit the effect of the defect portion, improve the moldability of the foamed particle, and improve the dimensional stability of the molded body. In addition, it is possible to shorten the cooling time of the molded body in the molding die at the time of in-mold molding. From the viewpoint of further improving the above effects, the ratio Ca / A is preferably 0.02 or more. From the same viewpoint, the ratio Ct / A is more preferably 0.03 or more.

[0048] On the other hand, in a case where the ratio Ca / A of the average cross-sectional area Ca of each of the defective portions to the average cross-sectional area A of the foamed particle and / or the ratio Ct / A of the total cross-sectional area Ct of the defective portions to the average cross-sectional area A of the foamed particle is excessively large, there is a risk that the secondary foaming property of the foamed particle is reduced. As a result, there is a risk that a relatively large void is easily formed in the obtained molded body, leading to an increase in the moisture content and an increase in the drying time. On the other hand, if the amount of steam supplied into the molding die during in-mold foaming or the temperature of the steam is increased in order to reduce the voids originating from the defective portions, there is a risk that the dimensional stability of the molded body is reduced.

[0049] By using a foamed particle having a ratio Ca / A of 0.20 or less and a ratio Ct / A of 0.20 or less, these problems can be easily avoided and the dimensional stability of the molded body can be improved. In addition, such a foamed particle can shorten the drying time of the molded body after demolding and can easily obtain a molded body excellent in surface properties and rigidity. From the viewpoint of more reliably obtaining these effects, the ratio Ca / A is preferably 0.15 or less, more preferably 0.10 or less, further preferably 0.08 or less, and particularly preferably 0.05 or less. From the same viewpoint, the ratio Ct / A is preferably 0.18 or less, more preferably 0.15 or less, further preferably 0.10 or less, and particularly preferably 0.08 or less. Furthermore, the calculation method of the average cross-sectional area A of the foamed particle, the average cross-sectional area Ca of each of the defective portions, and the total cross-sectional area Ct of the defective portions will be described later.

[0050] In constituting the preferable range of the value of the ratio Ca / A, the upper limit value and the lower limit value of the aforementioned ratio Ca / A can be arbitrarily combined. For example, the preferable range of the value of the ratio Ca / A can be 0.01 or more and 0.15 or less, can be 0.01 or more and 0.10 or less, can be 0.02 or more and 0.08 or less, or can be 0.02 or more and 0.05 or less. Similarly, in constituting the preferable range of the value of the ratio Ct / A, the upper limit value and the lower limit value of the aforementioned ratio Ct / A can be arbitrarily combined. For example, the preferable range of the value of the ratio Ct / A can be 0.02 or more and 0.18 or less, can be 0.02 or more and 0.15 or less, can be 0.03 or more and 0.10 or less, or can be 0.03 or more and 0.08 or less.

[0051] The shape of the foamed particle can more specifically adopt the following modes. Furthermore, in the following description, for convenience, the foamed particle having a through-hole and the foamed particle having a groove are described separately, but the shape of the foamed particle according to the present application also includes a mode having a through-hole and having a groove.

[0052] 〔Foamed particle having a through-hole〕 Figure 1 and Figure 2 An example of a foamed particle 1 (1a) having a through-hole 111 as a defect portion 11 is shown. Figure 1 The foamed particle 1a shown is composed of a foamed layer 2, and has a cylindrical shape having the through-hole 111. The shape of the foamed particle as a whole can be, for example, a cylindrical shape as shown in Figure 1 The through-hole is preferably in the axial direction of the foamed particle. The number of through-holes can be one or more.

[0053] In the case where the foamed particle has the through-hole as the defect portion, the average pore diameter d of the through-hole is preferably 0.1 mm or more and less than 1 mm. In this case, it is possible to easily adjust Ca / A and / or Ct / A of the foamed particle to the above range. By making the average pore diameter d of the through-hole 0.1 mm or more, it is possible to suppress the case where the through-hole of the foamed particle is flattened and plugged at in-mold foaming, and more reliably exert the effect of the through-hole as the defect portion. From the same viewpoint, the average pore diameter d of the through-hole is more preferably 0.2 mm or more, further preferably 0.3 mm or more, particularly preferably 0.4 mm or more, and most preferably 0.5 mm or more.

[0054] On the other hand, in the case where the average pore diameter d of the through-hole is excessively large, there is a risk that Ca / A and / or Ct / A of the foamed particle becomes excessively large. Therefore, there is a risk that drying of the molded body requires an excessively long time. In addition, there is a risk that it becomes easy to form a gap between foamed particles, a concave-convex of the through-hole, and the like on the surface of the molded body, and there is a risk that the rigidity of the molded body decreases.

[0055] In addition, if the amount of steam supplied into the molding die at in-mold foaming or the temperature of the steam is increased in order to avoid the formation of a gap between foamed particles, a concave-convex of the through-hole, and the like, there is a risk that the dimensional stability of the molded body decreases and the change in the size of the molded body from after demolding to when the shape is stabilized becomes large. By making the average pore diameter d of the through-hole 1 mm or less, it is possible to easily avoid these problems, and even in the case of manufacturing a molded body having a long maximum length or a molded body having a complex shape, it is possible to make the appearance and the rigidity of the molded body more favorable, and more easily improve the dimensional stability. From the viewpoint of more reliably obtaining the above effects, the average pore diameter d of the through-hole is more preferably 0.95 mm or less, further preferably 0.9 mm or less, and particularly preferably 0.85 mm or less.

[0056] In setting the preferable range of the average pore diameter d of the through-hole, the upper limit value and the lower limit value of the average pore diameter d described above can be combined arbitrarily. For example, the preferable range of the average pore diameter d can be 0.2 mm or more and less than 1 mm, 0.3 mm or more and 0.95 mm or less, 0.4 mm or more and 0.9 mm or less, or 0.5 mm or more and 0.85 mm or less.

[0057] The average pore diameter d of the through-hole 111 of the foamed particle 1a is calculated as follows. First, the foamed particle 1a is cut at the center in the axial direction with a plane perpendicular to the axial direction, so that a cut surface as shown in FIG. 2 is exposed. Next, a photograph of the cut surface is taken, and the cross-sectional area (specifically, the opening area) of the through-hole in the cut surface is calculated. Then, the diameter of an imaginary right circular circle having the same area as the cross-sectional area of the through-hole is calculated, and this value is taken as the pore diameter of the through-hole of each foamed particle. The above operation is performed on 50 or more foamed particles, and the arithmetic mean of the pore diameters of the through-holes thus obtained is taken as the average pore diameter d of the through-hole of the foamed particle. Furthermore, even in the case where the pore diameters of the through-holes of the respective foamed particles are not the same in the through-hole direction, the pore diameters of the through-holes of the respective foamed particles are determined as described above from the pore diameters of the through-holes in the cut surface. Figure 2

[0058] The average pore diameter d of the through-hole can be adjusted to the specific range by adjusting the size of the average pore diameter dr of the through-hole in the resin particles described later, the apparent density of the foamed particle, and the like. In addition, by making the foamed particle a secondary foamed particle produced by secondary foaming, the average pore diameter d can be more easily adjusted to a small value.

[0059] From the viewpoint of increasing the wall thickness of the foamed particle and improving the secondary foaming property of the foamed particle and the rigidity of the molded body, and from the viewpoint of suppressing deformation and shrinkage of the molded body when the curing process is omitted, the average outer diameter D of the foamed particle is preferably 2 mm or more, more preferably 2.5 mm or more, and further preferably 3 mm or more. On the other hand, from the viewpoint of improving the fillability of the foamed particle into the molding die, the average outer diameter D of the foamed particle is preferably 8 mm or less, more preferably 5 mm or less, and further preferably 4.5 mm or less.

[0060] In setting the preferable range of the average outer diameter D of the foamed particle, the upper limit value and the lower limit value of the average outer diameter D described above can be combined arbitrarily. For example, the preferable range of the average outer diameter D can be 2 mm or more and 8 mm or less, 2.5 mm or more and 5 mm or less, or 3 mm or more and 4.5 mm or less. Furthermore, the method of calculating the average outer diameter D of the foamed particle will be described later.

[0061] ​The ratio d / D of the average pore diameter d of the through-hole to the average outer diameter D of the foamed particle is preferably 0.4 or less, more preferably 0.35 or less, further preferably 0.3 or less, and particularly preferably 0.25 or less. By making the ratio d / D 0.4 or less, the secondary foaming property of the foamed particle at the in-mold foaming can be moderately improved, and the molded body having excellent surface properties and rigidity can be more easily obtained. On the other hand, from the viewpoint of more suppressing the through-hole of the foamed particle from being crushed and blocked at the in-mold foaming and more reliably exerting the effect of the through-hole, the ratio d / D is preferably 0.05 or more, and more preferably 0.1 or more.

[0062] In the preferable range of the value of the ratio d / D, the upper limit value and the lower limit value of the ratio d / D described above can be arbitrarily combined. For example, the preferable range of the value of the ratio d / D can be 0.05 or more and 0.4 or less, 0.05 or more and 0.35 or less, 0.1 or more and 0.3 or less, or 0.1 or more and 0.25 or less.

[0063] The average wall thickness t of the foamed particle having the through-hole is preferably 1.1 mm or more. If the average wall thickness t is in this range, the secondary foaming property at the in-mold foaming is more improved because the wall thickness of the foamed particle is sufficiently thick. In addition, the foamed particle is more difficult to be crushed with respect to an external force, and the rigidity of the molded body is more improved. From the above viewpoint, the average wall thickness t of the foamed particle is more preferably 1.2 mm or more. The average wall thickness t of the foamed particle having the through-hole can be 1.1 mm or more and 2.5 mm or less, or 1.2 mm or more and 2.0 mm or less.

[0064] The average wall thickness t of the foamed particle is the distance from the surface (in other words, the outer surface) of the foamed particle to the outer edge of the through-hole (in other words, the inner surface of the foamed particle), and is a value obtained by the following formula (1).

[0065] t = (D - d) / 2 • • • (1) d: average pore diameter of the through-hole (unit: mm) D: average outer diameter of the foamed particle (unit: mm) In addition, the ratio t / D of the average wall thickness t of the foamed particle to the average outer diameter D is preferably 0.30 or more and 0.50 or less. If t / D is in the above range, the filling property of the foamed particle becomes more favorable at the in-mold foaming of the foamed particle. In addition, the cooling time can be maintained short, and the secondary foaming property is more improved. Thus, the molded body having excellent appearance and rigidity can be favorably produced at a lower molding pressure (in other words, a heating temperature). From the above viewpoint, the ratio t / D of the average wall thickness t of the foamed particle to the average outer diameter D is more preferably 0.32 or more and 0.50 or less, and further preferably 0.35 or more and 0.50 or less.

[0066] 〔Foamed particles with grooves〕 Figure 3 and Figure 4 indicates an example of a foamed particle 1 (1b) having a groove 112 as a defective portion 11. Figure 3 The foamed particle 1b illustrated in the drawing is composed of a foamed layer 2. In addition, the foamed particle 1b has a columnar shape, and has at least one groove 112 in its side peripheral surface.

[0067] The aforementioned "groove" refers to a recess provided in the side peripheral surface of the foamed particle 1b and extending in the axial direction of the foamed particle 1b. More specifically, as illustrated in the drawing, the groove 112 of the foamed particle 1b is observed as a portion in which the profile of the foamed particle is recessed inward in a cross section that appears when the foamed particle 1b is cut with a plane perpendicular to the axial direction of the foamed particle 1b. Figure 4

[0068] The shape and the like of the foamed particle 1b can be adopted in various ways. For example, as illustrated in the drawings, the foamed particle 1b can also be a columnar shape in which the cross section perpendicular to the axial direction is a cross shape. The foamed particle 1b having such a shape has four grooves 112 in its side peripheral surface. The cross-sectional shape of the foamed particle in the cross section perpendicular to the axial direction is not limited to the shape illustrated in the drawings, and can be adopted in various ways such as a shape based on a circle, a shape based on a triangle, a shape based on a quadrangle, and the like. Figure 3 Figure 4 Figure 3 Figure 4

[0069] The number of the grooves 112 provided in the foamed particle can be one or more. In addition, the cross-sectional shape of the groove 112 in the cross section perpendicular to the axial direction of the foamed particle is not limited to the V shape illustrated in the drawings, and can be adopted in various ways such as a semicircular shape, a quadrangular shape, and a U shape. In the case where the foamed particle has two or more grooves 112, all of the grooves 112 can have the same cross-sectional shape, or can have mutually different cross-sectional shapes. Figure 3 Figure 4

[0070] The foamed particle preferably has two or more grooves and six or fewer grooves. In this case, it is more likely that an open-cell structure is formed in the molded article. Therefore, the foamed particle can more easily improve the dimensional stability of the molded article.

[0071] ​​​​​​​Furthermore, when the foamed particles have two or more grooves, these grooves are preferably arranged at equal intervals on the side circumferential surfaces of the foamed particles. In other words, when the foamed particles have multiple grooves, these grooves are preferably arranged symmetrically with respect to the central axis of the foamed particles. If such foamed particles are molded in-mold, the open bubble structure is more easily and uniformly formed in the molded body. Therefore, the foamed particles can more easily improve the dimensional stability of the molded body.

[0072] The average cross-sectional area of ​​each groove in the cut surface of the foamed granules is preferably 0.05 mm. 2 Above and 1.2mm 2 Below, by ensuring that the ratio of the average cross-sectional area Ca of each defect to the average cross-sectional area A of the aforementioned foamed particles, Ca / A, is within the specified range, and further ensuring that the average cross-sectional area of ​​each groove is within the specified range, the effects of the aforementioned grooves can be obtained more reliably. From the same viewpoint, the average cross-sectional area of ​​each groove is more preferably 0.1 mm. 2 Above and 1.0mm 2 Hereinafter, 0.2mm is further preferred. 2 Above and 0.8mm 2 The following is an explanation of the method for calculating the average cross-sectional area of ​​each groove in the cut surface of the foamed particle, except that the total cross-sectional area C of the grooves 112 is used instead of the total cross-sectional area of ​​the defective parts 11 in each foamed particle 1 in the method for calculating the average cross-sectional area Ca of each defective part described later.

[0073] The ratio H / D of the average depth H of each groove in the cut surface of the foamed particle to the average outer diameter D of the foamed particle is preferably 0.20 or less. In this case, it is easy to form an open bubble structure in the molded body, and shrinkage and deformation of the molded body when the curing process is omitted can be more effectively suppressed. Furthermore, in this case, the rigidity of the molded body can be improved on the basis of the aforementioned effects. From the viewpoint of further improving the above-mentioned effects, the ratio H / D of the average depth H of each groove to the average outer diameter D of the foamed particle is more preferably 0.18 or less, and more preferably 0.15 or less.

[0074] From the same point of view, the average depth H of each groove in the cut surface of the foamed particles is preferably less than 1.0 mm, more preferably less than 0.8 mm, and even more preferably less than 0.5 mm.

[0075] In addition, from the viewpoint of inhibiting excessive reduction in the open cell ratio of the molded article, the ratio H / D of the average depth H of each groove in the cross section of the expanded particle to the average outer diameter D of the expanded particle is preferably 0.02 or greater, more preferably 0.05 or greater. In addition, from the same viewpoint, the average depth H of each groove in the cross section of the expanded particle is preferably 0.1 mm or greater, more preferably 0.2 mm or greater. In setting the preferable range of the value of the ratio H / D, the upper limit value and the lower limit value of the aforementioned ratio H / D can be arbitrarily combined. For example, the preferable range of the value of the ratio H / D can be 0.02 or greater and 0.20 or less, 0.02 or greater and 0.18 or less, or 0.05 or greater and 0.15 or less. In addition, in setting the preferable range of the value of the average depth H, the upper limit value and the lower limit value of the aforementioned average depth H can be arbitrarily combined. For example, the preferable range of the value of the average depth H can be 0.1 mm or greater and 1.0 mm or less, 0.1 mm or greater and 0.8 mm or less, or 0.2 mm or greater and 0.5 mm or less.

[0076] The average depth H of each groove in the cross section of the expanded particle is calculated as follows. First, the expanded particle 1 is cut at the center in the axial direction with a plane perpendicular to the axial direction, and the cross section shown in FIG. 1 is exposed. Next, on the outer side of each groove 112 in the cross section, a tangent line L1 is drawn which touches the outline of the expanded particle 1 at two points Q1 and Q2 and does not pass through the inside of the expanded particle 1. The maximum value h of the distance from the tangent line L1 to the circumference of the groove 112 (in other words, the outline of the expanded particle) in the direction perpendicular to the tangent line L1 is measured. Then, the maximum value h of the distance is measured for all of the grooves 112, and the arithmetic mean value thereof is taken as the depth of the groove of each expanded particle. Furthermore, the measurement of the depth of the groove of each expanded particle in the cross section can be performed, for example, by taking a photograph of the cross section of the expanded particle and performing image analysis. Figure 4 and Figure 9 The average depth H of each groove in the cross section of the expanded particle is calculated as follows. First, the expanded particle 1 is cut at the center in the axial direction with a plane perpendicular to the axial direction, and the cross section shown in FIG. 1 is exposed. Next, on the outer side of each groove 112 in the cross section, a tangent line L1 is drawn which touches the outline of the expanded particle 1 at two points Q1 and Q2 and does not pass through the inside of the expanded particle 1. The maximum value h of the distance from the tangent line L1 to the circumference of the groove 112 (in other words, the outline of the expanded particle) in the direction perpendicular to the tangent line L1 is measured. Then, the maximum value h of the distance is measured for all of the grooves 112, and the arithmetic mean value thereof is taken as the depth of the groove of each expanded particle. Furthermore, the measurement of the depth of the groove of each expanded particle in the cross section can be performed, for example, by taking a photograph of the cross section of the expanded particle and performing image analysis.

[0077] Then, the arithmetic mean value of the depths of the grooves obtained by the measurement for 100 or more expanded particles 1 is taken as the depth H of the groove of the expanded particle.

[0078] 〔Method for calculating average cross-sectional area Ca of each defective portion, total cross-sectional area Ct of defective portions, and average cross-sectional area A of expanded particle〕 The ratio Ca / A of the average cross-sectional area Ca of each of the defective portions in the cut surface of the foamed particle cut at the center in the axial direction with a surface perpendicular to the axial direction with respect to the average cross-sectional area A of the foamed particle is 0.01 or more and 0.20 or less, and the ratio Ct / A of the total cross-sectional area Ct of the defective portions with respect to the average cross-sectional area A of the foamed particle is 0.02 or more and 0.20 or less. As described above, the foamed particle having the specific shape can improve the dimensional stability of the molded body. In addition, the foamed particle can significantly improve the productivity of the molded body, and can easily improve the surface properties and the fusion properties of the molded body.

[0079] The average cross-sectional area A of the foamed particle is calculated as follows. First, the foamed particle is cut at the center in the axial direction with a surface perpendicular to the axial direction, and the cut surface is exposed. The cross-sectional area of the foamed particle 1 in the cut surface is measured. For example, as shown in Figure 2 and Figure 4 shown, in the case where the foamed particle 1 is composed only of the foamed layer 2, the cross-sectional area of the foamed particle 1 is equal to the cross-sectional area of the foamed layer 2 in the cut surface. In addition, as described later in Figure 6 shown, in the case where the foamed particle 1 has the foamed layer 2 and the coating layer 3 that coats the foamed layer 2, the cross-sectional area of the foamed particle 1 is the total of the cross-sectional area of the foamed layer 2 and the cross-sectional area of the coating layer 3 in the cut surface. Furthermore, the measurement of the cross-sectional area of the foamed particle 1 in the cut surface can be performed, for example, by taking a photograph of the cut surface of the foamed particle and performing image analysis. In addition, the cross-sectional area of the defective portion is not included in the cross-sectional area of the foamed particle.

[0080] The above operation is performed for 100 or more foamed particles, and the arithmetic mean of the cross-sectional areas of the foamed particles obtained is taken as the average cross-sectional area A of the foamed particle in the cut surface.

[0081] The average cross-sectional area Ca of each of the defective portions and the total cross-sectional area Ct of the defective portions are calculated as follows. First, the foamed particle is cut at the center in the axial direction with a surface perpendicular to the axial direction, and the cut surface is exposed. As Figure 2 and Figure 6 shown, in the case where the defective portion 11 is the through hole 111, the cross-sectional area C of the through hole 111 in the cut surface is measured.

[0082] In addition, in the case where the defective portion 11 is the groove 112, as Figure 4 and Figure 9As shown, on the outer side of each groove 112 in the cut surface, a tangent line L1 is drawn that connects to the outline of the foamed particle 1 at two points Q1 and Q2, but does not pass through the interior of the foamed particle 1. Then, the area of ​​the region enclosed by the outline of the foamed particle 1 and the tangent line L1 is calculated, and this area is taken as the cross-sectional area C of each groove 112. That is, the cross-sectional area C of each groove 112 is... Figure 4 as well as Figure 9 The area of ​​the region indicated by the diagonal line in the middle.

[0083] By summing the cross-sectional area C of the through hole 111 and the cross-sectional area C of the groove 112 obtained in this way, the total cross-sectional area of ​​the defect portion 11 in each foamed particle 1 is calculated. In addition, the total cross-sectional area of ​​the defect portion 11 is divided by the number of defect portions 11 to calculate the cross-sectional area of ​​each defect portion in each foamed particle 1.

[0084] The above operations are performed on more than 100 foamed particles, and the arithmetic mean of the total cross-sectional areas of the defective parts is taken as the total cross-sectional area Ct of the defective parts. Furthermore, the average cross-sectional area of ​​each defective part is taken as the average cross-sectional area Ca of each defective part.

[0085] [Calculation method for the average outer diameter D of foamed particles] The method for calculating the average outer diameter D of the foamed particles is as follows. First, the foamed particle 1 is cut at its center along the axial direction with a plane perpendicular to the axial direction, so that... Figure 2 as well as Figure 4 The cut surface is exposed as shown. Two points Q3 and Q4, with the longest distance between them, are determined on the outline of the foamed particles 1 in this cut surface. The distance between these two points (in other words, the maximum outer diameter of the foamed particles in the cut surface) is taken as the outer diameter r of each foamed particle 1. Then, the arithmetic mean of the outer diameters r measured for more than 100 foamed particles 1 is taken as the average outer diameter D of the foamed particles. Furthermore, the measurement of the outer diameter of the foamed particles 1 in the cut surface can be performed, for example, by taking a photograph of the cut surface of the foamed particles and performing image analysis. Additionally, even when the outer diameters of the individual foamed particles are different in the penetrating direction, the outer diameter of each foamed particle is determined by the outer diameter at the cut surface as described above.

[0086] [Apparent density and bulk density of foamed particles] The bulk density of the foamed granules is preferably 10 kg / m³. 3 Above and 100kg / m 3 The following is more preferably 15 kg / m 3 Above and 75kg / m 3 The following is a further preferred value: 20 kg / m 3 Above and 50kg / m 315 kg / m 3 20 kg / m 3 20 kg / m 3 30 kg / m 3 30 kg / m 3 40 kg / m 3 40 kg / m 3 In these cases, the lightweight property and the rigidity of the molded body can be improved in good balance. In addition, in the past, particularly in cases where a molded body having a low density (in other words, a molded body having a high molded body ratio) is manufactured, the molded body is likely to be significantly deformed after demolding, and it is difficult to omit the curing process. In contrast, the foamed particles can omit the curing process even in cases where a molded body having a low density is manufactured, and thus a lightweight molded body having a good appearance can be manufactured even without curing.

[0087] The ratio of the apparent density of the foamed particles to the bulk density of the foamed particles (in other words, apparent density / bulk density) is preferably greater than 1.6, and more preferably 1.7 or greater. In this case, the cooling time after in-mold molding can be shortened even more, and a lightweight molded body having a good appearance can be obtained even more easily. In addition, the deformation and shrinkage of the molded body in cases where the curing process is omitted or the time of the curing process is shortened can be suppressed even more reliably. In addition, the ratio of the apparent density of the foamed particles to the bulk density of the foamed particles (in other words, apparent density / bulk density) is preferably less than 2.0, and more preferably 1.9 or less. In this case, the drying time of the molded body can be shortened even more. In addition, the surface property and the rigidity of the obtained molded body can be made even better.

[0088] In the preferred range of the value of the ratio of the apparent density of the foamed particles to the bulk density of the foamed particles, the upper limit value and the lower limit value of the aforementioned ratio can be combined arbitrarily. For example, the preferred range of the value of the apparent density / bulk density can be greater than 1.6 and less than 2.0, or 1.7 or greater and 1.9 or less.

[0089] The calculation method of the bulk density of the foamed particles is described below. First, the foamed particles are left to stand for 24 hours or more in an environment of a relative humidity of 50%, a temperature of 23°C, and an atmospheric pressure of 1 atm, and the state of the foamed particles is adjusted. The foamed particles in the state adjusted are filled into a graduated cylinder in a natural packed manner, and the bulk volume of the foamed particles (unit: L) is read from the scale of the graduated cylinder. Then, the value obtained by dividing the mass (unit: g) of the foamed particles in the graduated cylinder by the aforementioned bulk volume is unit-converted, and thus the bulk density of the foamed particles (unit: kg / m 3). In addition, the bulk density of the expanded particles is a value measured using the expanded particles in a natural state without being compressed, in an environment of 1 atm of air pressure.

[0090] The method for calculating the apparent density of the expanded particles is described below. First, the expanded particle group is left to stand for 1 day in an environment of 50% relative humidity, 23°C, and 1 atm of air pressure, and the state of the expanded particles is adjusted. After measuring the mass of the expanded particle group (unit: g), the volume of the expanded particle group (unit: L) is found using a metal mesh or the like sunk in a graduated cylinder containing 23°C alcohol (for example, ethanol), from the amount of rise in the liquid level. Thereafter, the value obtained by dividing the mass of the expanded particle group by the volume of the expanded particle group is unit-converted, whereby the apparent density of the expanded particles (unit: kg / m 3 ).

[0091] 〔Foamed layer〕 The expanded particles have a foamed layer composed of a polypropylene-based resin. In the present specification, the polypropylene-based resin refers to a homopolymer of a propylene monomer and a propylene-based copolymer containing 50% by mass or more of a structural unit derived from propylene. As the propylene-based copolymer, a copolymer of propylene and an α-olefin having 4 to 10 carbon atoms such as an ethylene-propylene copolymer, a butene-propylene copolymer, a hexene-propylene copolymer, an ethylene-propylene-butene copolymer, and the like is preferably exemplified. These copolymers can be, for example, random copolymers, block copolymers, or the like, but are preferably random copolymers.

[0092] The polypropylene-based resin constituting the foamed layer contains a polypropylene-based resin (A) having a melting point of 135°C or higher and 150°C or lower and a flexural modulus of less than 1000 MPa, and a polypropylene-based resin (B) having a melting point of 145°C or higher and 160°C or lower and a flexural modulus of 1000 MPa or more. In addition, the mass ratio of the polypropylene-based resin (A) to the polypropylene-based resin (B) in the polypropylene-based resin is polypropylene-based resin (A) : polypropylene-based resin (B) = 65 : 35 to 35 : 65 (where the total amount of both is 100% by mass).

[0093] As the polypropylene-based resin constituting the foamed layer of the expanded particles, a polypropylene-based resin containing the polypropylene-based resin (A) and the polypropylene-based resin (B) in the specified mass ratio is used, whereby the dimensional stability of the molded body can be easily improved, and the change in the dimensions of the molded body from the time point of demolding to the time point of shape stabilization can be reduced. In addition, by using the above-described expanded particles, even in the case of manufacturing a molded body that is relatively difficult to in-mold form without performing a curing process or shortening the time of the curing process, a molded body having a desired dimension can be easily obtained.

[0094] 〔Polypropylene-based resin (A)〕 The polypropylene-based resin (A) can be a homopolymer of a propylene monomer or a propylene-based copolymer. From the viewpoint of more reliably obtaining the effect of improving the dimensional stability of the molded body, the polypropylene-based resin (A) is preferably a propylene-based copolymer, more preferably one or more propylene-based copolymers selected from the group consisting of an ethylene-propylene copolymer, a butene-propylene copolymer, and an ethylene-butene-propylene copolymer, and further preferably an ethylene-propylene random copolymer. The polypropylene-based resin (A) can be a virgin resin or a recycled resin. In addition, the polypropylene-based resin (A) can be a resin derived from fossil fuels or a resin containing a monomer component derived from biomass.

[0095] The total of the content of the ethylene component and the content of the butene component in the polypropylene-based resin (A) is preferably 1.5% by mass or more and 4.5% by mass or less, more preferably 2.0% by mass or more and 3.5% by mass or less, and further preferably more than 2.5% by mass and 3.5% by mass or less.

[0096] Further, the aforementioned "ethylene component" refers to a structural unit derived from ethylene in the propylene-based copolymer. In addition, the content of the ethylene component is the mass ratio of the ethylene component in the case where the total of the structural unit derived from propylene and the structural unit derived from other monomers included in the propylene-based copolymer is 100% by mass. The content of the ethylene component in the propylene-based copolymer can be found based on the results of IR spectroscopy measurement.

[0097] In addition, the aforementioned "butene component" refers to a structural unit derived from butene in the propylene-based copolymer. In addition, the content of the butene component is the mass ratio of the butene component in the case where the total of the structural unit derived from propylene and the structural unit derived from other monomers included in the propylene-based copolymer is 100% by mass. The content of the butene component in the propylene-based copolymer can be found based on the results of IR spectroscopy measurement.

[0098] The flexural modulus of the polypropylene-based resin (A) is preferably 600 MPa or more and less than 1000 MPa, more preferably 700 MPa or more and less than 1000 MPa, further preferably 800 MPa or more and less than 1000 MPa, and particularly preferably 900 MPa or more and 980 MPa or less. In this case, the moldability of the foamed particles can be more easily improved. Further, the flexural modulus of the polypropylene-based resin (A) can be found based on JIS K7171:2008.

[0099] The melting point of the polypropylene-based resin (A) is more preferably 136°C or higher and 148°C or lower, further preferably 137°C or higher and 146°C or lower, particularly preferably 138°C or higher and 145°C or lower, and most preferably 140°C or higher and less than 145°C. In this case, the moldability of the expanded particles can be more easily improved.

[0100] The melting point of the polypropylene-based resin (A) can be determined based on differential scanning calorimetry (in other words, DSC) in accordance with JIS K7121-1987. First, the state adjustment of the test piece is performed in accordance with "(2) Measurement of the melting temperature after a certain heat treatment". The heating rate and the cooling rate in the state adjustment are 10°C / min. The test piece after the state adjustment is heated from 30°C to 200°C at a heating rate of 10°C / min, whereby a DSC curve is obtained, and the temperature at the peak of the melting peak appearing in the DSC curve is taken as the melting point of the polypropylene-based resin (A). In addition, in the case where a plurality of melting peaks appear in the DSC curve, the temperature at the peak of the melting peak having the largest area is taken as the melting point of the polypropylene-based resin (A).

[0101] From the viewpoint of further improving the expandability and the moldability of the expanded particles, the melt flow rate (in other words, MFR) of the polypropylene-based resin (A) is preferably 5 g / 10 min or more and 15 g / 10 min or less, more preferably 6 g / 10 min or more and 12 g / 10 min or less, and further preferably 7 g / 10 min or more and 10 g / 10 min or less. In addition, the MFR of the polypropylene-based resin (A) is a value determined based on JIS K7210-1:2014 under the conditions of a test temperature of 230°C and a load of 2.16 kg.

[0102] 〔Polypropylene-based resin (B)〕 The polypropylene-based resin (B) can be a homopolymer of a propylene monomer or a propylene-based copolymer. From the viewpoint of more reliably obtaining the effect of improving the dimensional stability of the molded body, the polypropylene-based resin (B) is preferably a propylene-based copolymer, and more preferably one or more kinds of propylene-based copolymers selected from the group consisting of an ethylene-propylene copolymer, a butylene-propylene copolymer, and an ethylene-butylene-propylene copolymer. In this case, a molded body excellent in appearance and rigidity can be molded at a lower molding temperature (in other words, a lower molding pressure). In addition, in this case, the shape of the molded body is more easily restored after demolding from the molding die, and the time of the curing process can be more easily shortened. In addition, the polypropylene-based resin (B) can be a virgin resin or a recycled resin. In addition, the polypropylene-based resin (B) can be a resin derived from fossil fuels or a resin containing a monomer component derived from biomass.

[0103] From the viewpoint of further improving the aforementioned effects, the total of the content of the ethylene component and the content of the butene component in the polypropylene-based resin (B) is preferably 0.5% by mass or more and 2.5% by mass or less, more preferably 0.5% by mass or more and less than 2.5% by mass, further preferably 0.8% by mass or more and 2.0% by mass or less, particularly preferably 1.0% by mass or more and 1.8% by mass or less.

[0104] The flexural modulus of the polypropylene-based resin (B) is preferably 1000 MPa or more and 1800 MPa or less, more preferably 1050 MPa or more and 1700 MPa or less, further preferably 1100 MPa or more and less than 1600 MPa, particularly preferably 1150 MPa or more and 1500 MPa or less. In this case, the effect of improving the dimensional stability of the molded body can be further improved. From the same viewpoint, the absolute value of the difference between the flexural modulus of the polypropylene-based resin (A) and the flexural modulus of the polypropylene-based resin (B) is preferably 200 MPa or more and 500 MPa or less. Furthermore, the flexural modulus of the polypropylene-based resin (B) can be found based on JIS K7171:2008.

[0105] The melting point of the polypropylene-based resin (B) is more preferably 148°C or more and 158°C or less, further preferably 150°C or more and 155°C or less. In this case, the effect of improving the dimensional stability of the molded body can be further improved.

[0106] The measuring method of the melting point of the polypropylene-based resin (B) is the same as the aforementioned measuring method of the melting point of the polypropylene-based resin (A), except that the polypropylene-based resin (B) is used instead of the polypropylene-based resin (A).

[0107] 〔Mass ratio of polypropylene-based resin (A) to polypropylene-based resin (B)〕 The mass ratio of the polypropylene-based resin (A) to the polypropylene-based resin (B) in the polypropylene-based resin constituting the foamed layer is polypropylene-based resin (A) : polypropylene-based resin (B) = 65 : 35 to 35 : 65 (wherein the total amount of both is 100% by mass). That is, the mass ratio of the polypropylene-based resin (A) with respect to the total 100% by mass of the polypropylene-based resin (A) and the polypropylene-based resin (B) is 35% by mass or more and 65% by mass or less.

[0108] The foamed particles can improve the dimensional stability of the molded body and reduce the dimensional change from the time point at which the molded body is demolded to the time point at which the shape is stabilized, by making the mass ratio of the polypropylene-based resin (A) to the polypropylene-based resin (B) be within the specific range. Therefore, even in the case where a curing process is omitted or the time of a curing process is shortened to manufacture a molded body having a long maximum length, a molded body having a complex shape, or the like, which is relatively high in difficulty of in-mold molding, the molded body having a desired dimension can be easily obtained.

[0109] In the case where the mass ratio of the polypropylene-based resin (A) is lower than 35% with respect to 100% by mass of the total of the polypropylene-based resin (A) and the polypropylene-based resin (B), the molding pressure at the time of in-mold molding is likely to be excessively high. In this case, particularly in the case of manufacturing a molded body having a long maximum length or a molded body having a complex shape, the secondary foaming property at the time of in-mold molding is likely to be reduced, and there is a risk of causing deterioration of the appearance of the molded body.

[0110] By making the mass ratio of the polypropylene-based resin (A) be 35% by mass or more, preferably 38% by mass or more, more preferably 40% by mass or more, further preferably 45% by mass or more, particularly preferably 50% by mass or more, and most preferably 55% by mass or more, with respect to 100% by mass of the total of the polypropylene-based resin (A) and the polypropylene-based resin (B), the above problems can be easily avoided and a molded body having a good appearance can be easily obtained.

[0111] In the case where the mass ratio of the polypropylene-based resin (A) is greater than 65% with respect to 100% by mass of the total of the polypropylene-based resin (A) and the polypropylene-based resin (B), there is a risk of causing a reduction in the dimensional stability of the molded body. In particular, in the case of manufacturing a molded body which is relatively high in difficulty of in-mold molding, there is a risk that the dimensional change from the time point at which the molded body is demolded to the time point at which the shape is stabilized becomes large, and it is difficult to adjust the dimension of the molded body to a desired range. By making the mass ratio of the polypropylene-based resin (A) be 65% by mass or less, preferably 64% by mass or less, more preferably 63% by mass or less, further preferably 62% by mass or less, and particularly preferably 61% by mass or less, with respect to 100% by mass of the total of the polypropylene-based resin (A) and the polypropylene-based resin (B), these problems can be easily avoided and the dimensional stability of the molded body can be improved.

[0112] In the preferable range of the mass ratio of the polypropylene-based resin (A) to the polypropylene-based resin (B), the upper limit and the lower limit of the mass ratio of the polypropylene-based resin (A) to the polypropylene-based resin (B) can be combined arbitrarily. For example, the preferable range of the mass ratio of the polypropylene-based resin (A) to the polypropylene-based resin (B) can be polypropylene-based resin (A) : polypropylene-based resin (B) = 65 : 35 to 38 : 62, can be polypropylene-based resin (A) : polypropylene-based resin (B) = 64 : 36 to 40 : 60, can be polypropylene-based resin (A) : polypropylene-based resin (B) = 63 : 37 to 45 : 55, can be polypropylene-based resin (A) : polypropylene-based resin (B) = 62 : 38 to 50 : 50, or can be polypropylene-based resin (A) : polypropylene-based resin (B) = 61 : 39 to 55 : 45 (in which the total amount of both is 100% by mass).

[0113] [Other polymer] The polypropylene-based resin constituting the foamed layer can also contain, within a range not impeding the aforementioned effects, other polymers than the polypropylene-based resin (A) and the polypropylene-based resin (B). As the other polymers, for example, polypropylene-based resins other than either of the polypropylene-based resin (A) and the polypropylene-based resin (B), polyethylene-based resins, polyamide resins, polystyrene-based resins, and the like, thermoplastic resins, elastomers, and the like are exemplified. The content of the other polymers in the foamed layer is preferably 20% by mass or less, more preferably 10% by mass or less, further preferably 5% by mass or less, and particularly preferably 0, in other words, it is particularly preferable that the foamed layer substantially contain only the polypropylene-based resin (A) and the polypropylene-based resin (B) as the polymers.

[0114] In addition, in the polypropylene-based resin constituting the foamed layer, additives such as a bubble regulator, a crystallization nucleating agent, a flame retardant, a flame retardant aid, a plasticizer, an antistatic agent, an antioxidant, an ultraviolet inhibitor, a light stabilizer, an electrically conductive filler, an antibacterial agent, a coloring agent, and the like can be contained within a range not impairing the aforementioned effects. The content of the additives in the foamed layer is, for example, preferably 0.01 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the polypropylene-based resin.

[0115] The coloring agent contained in the polypropylene-based resin constituting the foamed layer is preferably carbon black. In this case, a high-class appearance can be imparted to the molded body. The content of the carbon black in the foamed layer is preferably 0.1% by mass or more and 5% by mass or less, more preferably 0.5% by mass or more and 4% by mass or less, and further preferably 1% by mass or more and 3.5% by mass or less.

[0116] [Coating layer] The foamed particle can also have a foamed layer, and a coating layer composed of a thermoplastic resin and covering the foamed layer. In this case, the coating layer can cover the entire surface of the foamed layer, or can cover a part of the foamed layer. For example, as shown in Figure 5 and Figure 6 The coating layer 3 can also be provided to the side peripheral surface of the foamed particle 1 (1c) and cover the foamed layer 2.

[0117] The coating layer is a layer provided to the surface of the foamed particle in order to improve the fusion of the foamed particles with each other in in-mold molding. The thermoplastic resin constituting the coating layer preferably has a lower melting point or a lower softening point than the melting point of the polypropylene-based resin constituting the foamed layer.

[0118] The thermoplastic resin constituting the coating layer can be a crystalline thermoplastic resin, or can be a non-crystalline thermoplastic resin. As a crystalline thermoplastic resin for the coating layer, for example, a polyolefin-based resin or the like is exemplified. In addition, as a non-crystalline thermoplastic resin for the coating layer, for example, a polystyrene-based resin or the like is exemplified. From the viewpoint of adhesion to the foamed layer, the thermoplastic resin constituting the coating layer is preferably a polyolefin-based resin, more preferably a polyethylene-based resin and / or a polypropylene-based resin, and further preferably a polypropylene-based resin. As a polypropylene-based resin for the coating layer, for example, an ethylene-propylene copolymer, a propylene-butene copolymer, an ethylene-propylene-butene copolymer, a propylene homopolymer, and the like can be exemplified. Among them, the coating layer is particularly preferably composed of an ethylene-propylene copolymer and / or an ethylene-propylene-butene copolymer.

[0119] In the case where the coating layer is composed of a crystalline polyolefin-based resin, the melting point of the crystalline polyolefin-based resin is preferably 110°C or higher and 150°C or lower, more preferably 120°C or higher and 145°C or lower, and further preferably 125°C or higher and 142°C or lower.

[0120] In addition, the difference [Tmc-Tms] between the melting point Tmc of the base resin constituting the foamed layer and the melting point Tms of the crystalline polyolefin-based resin constituting the coating layer is preferably 1°C or higher and 40°C or lower, more preferably 2°C or higher and 35°C or lower, and further preferably 5°C or higher and 30°C or lower. In this case, the in-mold moldability of the foamed particle can be more easily improved even in the case where the molding pressure is low.

[0121] In the thermoplastic resin constituting the coating layer, a crystalline nucleating agent, a flame retardant, a flame retardant aid, a plasticizer, an antistatic agent, an antioxidant, an ultraviolet inhibitor, a light stabilizer, an electrically conductive filler, an antibacterial agent, a coloring agent, and the like can also be contained within a range not impairing the aforementioned effects. The content of the additive in the coating layer is, for example, preferably 0.01 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the thermoplastic resin.

[0122] The coloring agent contained in the thermoplastic resin constituting the coating layer is preferably carbon black. In this case, a high-class appearance can be imparted to the molded body. The content of carbon black in the coating layer is preferably 0.1% by mass or more and 5% by mass or less, more preferably 0.5% by mass or more and 4% by mass or less, and further preferably 1% by mass or more and 3.5% by mass or less.

[0123] In addition, the melt flow rate of the thermoplastic resin constituting the coating layer, which is measured in accordance with JIS K7210-1:2014 under conditions of a temperature of 230°C and a load of 2.16 kg, is preferably higher than 15 g / 10 minutes. In this case, the formation of a striped pattern on the surface of the molded body can be suppressed without impairing the rigidity of the foamed layer. Furthermore, the upper limit of the melt flow rate of the thermoplastic resin constituting the coating layer, which is measured in accordance with JIS K7210-1:2014 under conditions of a temperature of 230°C and a load of 2.16 kg, is generally 35 g / 10 minutes.

[0124] The coating layer of the foamed particle can be in a foamed state or a non-foamed state, but is preferably in a substantially non-foamed state. "Substantially non-foamed" means a state in which the coating layer is not foamed and does not contain bubbles, a state in which bubbles disappear after foaming, and a state in which there is almost no bubble structure in the coating layer. The thickness of the coating layer is, for example, 0.5 μm or more and 100 μm or less. In addition, an intermediate layer can be further provided between the foamed layer and the coating layer.

[0125] From the viewpoint of maintaining the rigidity of the molded body and improving the moldability, the mass ratio (ratio in % by mass) of the polypropylene-based resin constituting the foamed layer to the thermoplastic resin constituting the coating layer is preferably foamed layer:coating layer = 99.5:0.5 to 80:20, more preferably 99:1 to 85:15, and further preferably 97:3 to 88:12.

[0126] [High-temperature peak] The foamed particle preferably has a crystal structure in which a resin-specific peak derived from the melting of crystals inherent to the polypropylene-based resin constituting the foamed layer and a high-temperature peak having a peak temperature higher than that of the resin-specific peak appear in a DSC curve obtained when the foamed particle is heated from 23°C to 200°C at a heating rate of 10°C / minute. The foamed particle having such a crystal structure is excellent in mechanical strength and also excellent in moldability. Furthermore, the resin-specific peak is generated by the heat absorption at the time of melting of the crystals inherently possessed by the polypropylene-based resin constituting the foamed layer. On the other hand, it is presumed that the high-temperature peak is generated by the melting of secondary crystals formed in the polypropylene-based resin constituting the foamed layer during the production of the foamed particle. That is, in the case where the high-temperature peak appears in the DSC curve, it is presumed that secondary crystals are formed in the polypropylene-based resin.

[0127] Whether or not the foamed particles have the aforementioned crystal structure can be determined based on a DSC curve obtained by differential scanning calorimetry (DSC) under the aforementioned conditions according to JIS K7121: 1987. In addition, in performing DSC, 1 to 3 mg of the foamed particles can be used as a sample.

[0128] Specifically, both the high-temperature peak and the inherent peak of the polypropylene-based resin constituting the foamed layer appear in the DSC curve obtained when the foamed particles are heated from 23°C to 200°C at a heating rate of 10°C / minute (in other words, first heating) as described above. Furthermore, in the DSC curve obtained when the first heating is performed, the resin inherent peak also appears on the basis of the high-temperature peak. In contrast, in the DSC curve obtained when, after the first heating, the temperature is cooled from 200°C to 23°C at a cooling rate of 10°C / minute and then the temperature is again heated from 23°C to 200°C at a heating rate of 10°C / minute (in other words, second heating), only the resin inherent peak of the polypropylene-based resin constituting the foamed layer appears. Therefore, by comparing the DSC curve obtained at the first heating with the DSC curve obtained at the second heating, it is possible to distinguish the resin inherent peak from the high-temperature peak. The temperature of the apex of the resin inherent peak is sometimes slightly different between the first heating and the second heating, but the difference is usually within 5°C.

[0129] From the viewpoint of further improving the moldability of the foamed particles, the viewpoint of obtaining a molded body having more excellent rigidity, and the viewpoint of further improving the dimensional stability when a molded body having a relatively high degree of difficulty in in-mold foaming is intended to be obtained, the heat of fusion of the high-temperature peak of the foamed particles is preferably 8 J / g or more and 25 J / g or less, more preferably 10 J / g or more and 24 J / g or less, further preferably 15 J / g or more and 23 J / g or less, and particularly preferably 18 J / g or more and 22 J / g or less.

[0130] The heat of fusion of the aforementioned high-temperature peak is a value obtained as follows. First, 1 to 3 mg of the foamed particles after state adjustment is used as a sample, and a DSC curve is obtained by performing differential scanning calorimetry under conditions in which the temperature is heated from 23°C to 200°C at a heating rate of 10°C / minute. Figure 7 An example of a DSC curve is shown. In the case where the foamed particles have a high-temperature peak, as shown in FIG. 1, a resin inherent peak ΔH1 and a high-temperature peak ΔH2 having an apex on the high-temperature side of the apex of the resin inherent peak ΔH1 appear in the DSC curve. Figure 7

[0131] ​Next, a straight line L2 connecting a point a on the DSC curve corresponding to 80°C and a point β corresponding to the end temperature of melting of the expanded particles T is drawn. Further, the end temperature of melting T is the end point on the high temperature side in the high temperature peak ΔH2, in other words, the intersection point of the high temperature peak ΔH2 and the base line on the high temperature side than the high temperature peak ΔH2 in the DSC curve.

[0132] After the straight line L2 is drawn, a straight line L3 passing through a maximum point γ present between the resin inherent peak ΔH1 and the high temperature peak ΔH2 and parallel to the ordinate of the graph is drawn. The resin inherent peak ΔH1 and the high temperature peak ΔH2 are divided by this straight line L3. The heat of fusion of the resin inherent peak ΔH1 can be calculated based on the area of the portion enclosed by the portion of the DSC curve constituting the resin inherent peak ΔH1, the straight line L2, and the straight line L3. Further, the heat of fusion of the high temperature peak ΔH2 can be calculated based on the area of the portion enclosed by the portion of the DSC curve constituting the high temperature peak ΔH2, the straight line L2, and the straight line L3.

[0133] (Method for producing expanded polypropylene resin particles) The expanded particles can be produced, for example, by a method in which polypropylene resin particles (hereinafter referred to as "resin particles") composed of a polypropylene resin are dispersed in a dispersion medium, and a blowing agent is impregnated in the resin particles, and then the resin particles containing the blowing agent are released together with the dispersion medium under a low pressure. Further, such a foaming method is sometimes referred to as a "direct foaming method".

[0134] The resin particles can be produced, for example, by a wire cutting method. In the wire cutting method, first, a polypropylene resin (A) and a polypropylene resin (B) constituting the foaming layer, and an additive such as a bubble nucleating agent, which is supplied as necessary, are supplied into an extruder, and heated and kneaded to produce a resin melt-kneaded product. Thereafter, the resin melt-kneaded product is extruded from a small hole of a die attached to the front end of the extruder to form an extrudate. The extrudate is cooled and cut to a desired length, whereby resin particles of a single layer structure composed of a core layer of a polypropylene resin as a base resin can be obtained.

[0135] In the case where expanded particles having a multilayer structure of a foaming layer and a coating layer are desired to be obtained, a multilayer structure resin particle can be produced using a co-extrusion device having a core layer forming extruder, a coating layer forming extruder, and a co-extrusion die connected to both of the extruders. In this case, in the core layer forming extruder, a polypropylene resin (A) and a polypropylene resin (B) constituting the foaming layer, and an additive, etc. added as necessary, are melt-kneaded to produce a core layer forming resin melt-kneaded product. Further, in the coating layer forming extruder, a thermoplastic resin constituting the coating layer, and an additive, etc. added as necessary, are melt-kneaded to produce a coating layer forming resin melt-kneaded product.

[0136] By co-extruding these resin melt mixtures and merging them in a die, a composite of a multilayer structure composed of a core layer in a non-foamed state and a clad layer in a non-foamed state that clads the outer surface of the core layer is formed. The composite is extruded from a small hole of the die to form an extrudate. By cooling the extrudate and cutting it to a desired length, a resin particle of a multilayer structure can be obtained. In addition, the method of producing the resin particle is not limited to the above-described method, and a hot cutting method, a water cutting method, or the like can be employed.

[0137] In the direct foaming method, the resin particle is foamed in a state that substantially maintains the shape of the resin particle. Therefore, the shape of the foamed particle obtained by the direct foaming method substantially becomes a shape in which the shape of the resin particle is enlarged. Therefore, in the case where a foamed particle of a cylindrical shape having a through hole is desired, the resin particle of a cylindrical shape having a through hole is foamed. Such a resin particle can be produced, for example, by using a die having a small hole of a circular ring corresponding to the shape of the cross section of the desired cut surface of the resin particle in the above-described wire cutting method.

[0138] Similarly, in the case where a foamed particle having a cross shape in the cross section of the cut surface is desired, a columnar resin particle having a cross shape in the cross section of the cut surface is foamed. Such a resin particle can be produced, for example, by using a die having a small hole of a cross shape corresponding to the shape of the cross section of the desired cut surface of the resin particle in the above-described wire cutting method.

[0139] In producing the resin particle, a wire cutting method in which the extrudate is cooled in water and then cut is preferably employed. In this case, the accuracy of the shape of the resin particle can be further improved, and the shape of the defective portion in the finally obtained foamed particle can be more easily made into a desired shape. According to the wire cutting method, the extrusion direction of the extrudate used for producing the resin particle becomes the axial direction of the resin particle. In addition, the axial direction of the foamed particle corresponds to the axial direction of the resin particle used for its production.

[0140] The particle diameter of the resin particle is preferably 0.1 mm or more and 3.0 mm or less, and more preferably 0.3 mm or more and 1.5 mm or less. In addition, the ratio of the length of the resin particle to the outer diameter is preferably 0.5 or more and 5.0 or less, and more preferably 1.0 or more and 3.0 or less.

[0141] In addition, the average mass of each resin particle is preferably 0.1 mg or more and 20 mg or less, more preferably 0.2 mg or more and 10 mg or less, further preferably 0.3 mg or more and 5 mg or less, and particularly preferably 0.4 mg or more and 2 mg or less. In addition, the average mass of each resin particle is a value obtained by dividing the mass of 200 resin particles selected at random by the number of the resin particles.

[0142] In the case where the resin particles have a core layer and a clad layer, the mass ratio of the core layer to the clad layer is preferably core layer: clad layer = 99.5:0.5 to 85:15, more preferably 99:1 to 92:8, and further preferably 97:3 to 90:10.

[0143] In the foamed particles having the through-holes, by adjusting the average pore diameter dr of the through-holes of the core layer in the resin particles, it is possible to adjust the average pore diameter d of the through-holes of the foamed layer to the aforementioned specific range. More specifically, by making the average pore diameter dr of the through-holes of the resin particles 0.10 mm or more and less than 0.25 mm, preferably 0.12 mm or more and less than 0.24 mm, and more preferably 0.15 mm or more and less than 0.22 mm, it is possible to easily produce the foamed particles in which the average pore diameter d of the through-holes is 0.1 mm or more and less than 1 mm. The average pore diameter dr of the through-holes of the core layer of the resin particles can be adjusted, for example, by the pore diameter of the small holes of the die for forming the through-holes, in other words, the inner diameter of the die.

[0144] In addition, by adjusting the particle diameter, average mass of the resin particles, it is possible to adjust the average outer diameter of the foamed particles to the aforementioned range. More specifically, by making the ratio dr / Dr of the average pore diameter dr of the through-holes of the resin particles to the average outer diameter Dr 0.4 or less, preferably 0.3 or less, more preferably 0.25 or less, and further preferably 0.2 or less, it is possible to easily produce the foamed particles in which the ratio d / D of the average pore diameter d of the through-holes of the foamed particles to the average outer diameter D is 0.4 or less. Furthermore, from the viewpoint of the stability of the production of the resin particles, the average pore diameter dr of the through-holes of the resin particles is preferably 0.1 mm or more, and the ratio dr / Dr of the average pore diameter dr of the through-holes of the resin particles to the average outer diameter Dr is preferably 0.1 or more.

[0145] The calculation method of the average pore diameter dr of the through-holes of the resin particles and the average outer diameter Dr of the resin particles is the same as the aforementioned calculation method of the average pore diameter d of the through-holes of the foamed particles and the average outer diameter D of the foamed particles except that the resin particles are used instead of the foamed particles.

[0146] Furthermore, in the case where the line cutting method, in other words, the method of cutting into an appropriate length after cooling in water while pulling the cylindrical extrudate extruded from the die is employed in the cutting of the extrudate, by cutting by appropriately changing the extrusion speed, pulling speed, cutting speed, and the like at the time of the extrusion of the resin melt mixture, it is possible to adjust the particle diameter, length / outer diameter ratio, and average mass of the resin particles.

[0147] After the resin particles are produced as described above, the resin particles are dispersed in a dispersion medium. The operation of dispersing the resin particles in the dispersion medium can be performed in a closed container used in the foaming process described later, or can be performed in a container different from the closed container used in the foaming process. From the viewpoint of simplification of the manufacturing process, it is preferable to perform the dispersion process in the closed container used in the foaming process.

[0148] As the dispersion medium, an aqueous dispersion medium in which water is the main component is used. In the aqueous dispersion medium, in addition to water, a hydrophilic organic solvent such as ethylene glycol, glycerol, methanol, ethanol, or the like can be contained. The proportion of water in the aqueous dispersion medium is preferably 60% by mass or more, more preferably 70% by mass or more, and further preferably 80% by mass or more.

[0149] It is preferable to add a dispersant to the dispersion medium. By adding a dispersant to the dispersion medium, in the foaming process, the fusion of the resin particles heated in the container with each other can be suppressed. The amount of the dispersant to be added is preferably 0.001 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the resin particles. As the dispersant, an organic dispersant, an inorganic dispersant, and from the viewpoint of ease of handling, a particulate inorganic substance is preferably used as the dispersant. More specifically, as the dispersant, for example, aluminomagnesium stone, kaolin, mica, clay minerals such as clay, alumina, titania, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, iron oxide, or the like can be used. These dispersants can be used alone, or two or more kinds of dispersants can be used in combination. Among them, as the dispersant, a clay mineral is preferably used. The clay mineral can be a natural clay mineral, or a synthetic clay mineral.

[0150] Further, in the case where a dispersant is used, as the dispersing aid, an anionic surfactant such as sodium dodecylbenzenesulfonate, sodium alkylbenzenesulfonate, sodium laurylsulfate, sodium oleate, or the like is preferably used in combination. The amount of the dispersing aid to be added is preferably 0.001 parts by mass or more and 1 part by mass or less with respect to 100 parts by mass of the resin particles.

[0151] After dispersing the resin particles in the dispersion medium, the foaming agent is impregnated into the resin particles in a closed container. The foaming agent impregnated into the resin particles is preferably a physical foaming agent. As the physical foaming agent, inorganic physical foaming agents such as carbon dioxide, air, nitrogen, helium, argon, and the like; organic physical foaming agents such as aliphatic hydrocarbons such as propane, butane, hexane, and the like; cyclic aliphatic hydrocarbons such as cyclopentane, cyclohexane, and the like; halogenated hydrocarbons such as chlorofluoromethane, trifluoromethane, 1,1-difluoromethane, 1-chloro-1,1-dichloroethane, 1,2,2,2-tetrafluoroethane, chloromethane, chloroethane, dichloromethane, and the like; and the like can be exemplified. These physical foaming agents can be used alone or in combination of two or more kinds of physical foaming agents. In addition, the inorganic physical foaming agent and the organic physical foaming agent can be used in combination. From the viewpoint of the load on the environment and the operability, it is preferable to use the inorganic physical foaming agent, and more preferable to use carbon dioxide.

[0152] The amount of the foaming agent added with respect to 100 parts by mass of the resin particles is preferably 0.1 parts by mass or more and 30 parts by mass or less, and more preferably 0.5 parts by mass or more and 15 parts by mass or less.

[0153] In the manufacturing process of the foamed particles, as a method of impregnating the foaming agent into the resin particles, a method of supplying the foaming agent into a closed container and raising the pressure in the closed container to impregnate the foaming agent into the resin particles in the dispersion medium can be employed. At this time, by heating the resin particles together with the dispersion medium, the impregnation of the foaming agent into the resin particles can be further promoted.

[0154] The pressure in the closed container at the time of foaming is preferably 0.5 MPa (G) or more in terms of gage pressure. On the other hand, the pressure in the closed container is preferably 4.0 MPa (G) or less in terms of gage pressure. If it is within the above range, the foamed particles can be safely manufactured without the risk of breakage or explosion of the closed container.

[0155] In addition, in the case of heating the dispersion medium, by setting the temperature increasing rate of the dispersion medium to be within a range of 1°C / min or more and 5°C / min or less, the temperature at the time of foaming can also be set to an appropriate range.

[0156] After the impregnation of the foaming agent into the resin particles is completed, the content of the closed container is released to an environment having a lower pressure than the closed container. Thereby, the core layer of the resin particles is foamed to form a bubble structure, and the bubble structure is stabilized by cooling with the outside air, and the foamed particles are obtained.

[0157] In the impregnation of the foaming agent into the core layer, heating and foaming are preferably performed in the following manner. That is, first, a primary holding step of holding at a temperature of (melting point of the resin particles - 20°C) or higher and less than (end temperature of the melting of the resin particles) for a sufficient time, preferably for about 10 to 60 minutes, is performed, and then the temperature is adjusted from (melting point of the resin particles - 15°C) to less than (end temperature of the melting of the resin particles + 10°C). Then, as necessary, a secondary holding step of further holding at the temperature for a sufficient time, preferably for about 10 to 60 minutes, is performed. Thereafter, the contents of the closed container are preferably released to the outside in a state in which the temperature in the closed container is (melting point of the resin particles - 10°C) or higher, to foam the resin particles. The temperature in the closed container at the time of foaming is more preferably (melting point of the resin particles) or higher and (melting point of the resin particles + 20°C) or lower. By heating the resin particles in this manner to foam them, secondary crystals are formed in the polypropylene-based resin constituting the foamed layer, and foamed particles having excellent mechanical strength and also excellent moldability can be easily obtained.

[0158] Further, the method of measuring the melting point of the resin particles is the same as the aforementioned method of measuring the melting point of the polypropylene-based resin (A), except that the resin particles are used instead of the polypropylene-based resin (A). In addition, the end temperature of the melting of the resin particles is the end point on the high-temperature side in the DSC curve obtained in the measurement of the melting point of the resin particles, in other words, the temperature at which the melting peak intersects with the baseline on the high-temperature side of the melting peak.

[0159] In the production of the molded body, the foamed particles obtained above can also be used directly. In addition, the foamed particles obtained by the aforementioned direct foaming method can be further foamed, and a molded body can be produced using foamed particles having an increased bulk factor. Further, in the case where the foaming of the resin particles is performed in two stages in this manner, the foaming step of the first stage is referred to as a primary foaming step, and the foamed particles obtained by the primary foaming step are referred to as primary foamed particles. In addition, the foaming step of the second stage is referred to as a secondary foaming step. The foamed particles obtained by the secondary foaming step are sometimes referred to as secondary foamed particles.

[0160] The method of increasing the bulk factor of the foamed particles by secondary foaming is described below, for example. First, as the primary foaming step, the resin particles are foamed by the aforementioned direct foaming method to obtain primary foamed particles. Thereafter, internal pressure is applied to the primary foamed particles. More specifically, after the primary foamed particles are put into a pressure-resistant container, the pressure-resistant container is pressurized with an inorganic gas such as air or carbon dioxide to impregnate the inorganic gas into the foamed particles. Thus, the pressure in the bubbles of the primary foamed particles is made to be atmospheric pressure or higher. Thereafter, the primary foamed particles taken out of the pressure-resistant container are heated with a heating medium such as steam or heated air in an environment having a lower pressure than the pressure in the bubbles of the primary foamed particles, to further foam the primary foamed particles.

[0161] (polypropylene resin foamed particle molded body) By in-mold forming the foamed particles, a polypropylene resin foamed particle molded body can be obtained. The molded body formed by in-mold forming the foamed particles has an open cell structure. The open cell structure is a minute space portion that communicates with the outside of the molded body. The open cell structure is formed in a complicated manner by, for example, a through hole, a gap, or the like of the foamed particles, a gap formed by the defect portions of the foamed particles communicating with each other, a gap formed by the defect portions of the foamed particles communicating with a gap formed between the foamed particles, a gap formed by the gaps between the foamed particles communicating with each other, a continuous bubble portion of the foamed particles constituting the molded body, or the like.

[0162] The density of the molded body is preferably 10 kg / m 3 or more and 150 kg / m 3 or less. In this case, the lightweight property and the rigidity of the molded body can be improved in a well-balanced manner. From the viewpoint of further improving the rigidity of the molded body, the density of the molded body is more preferably 15 kg / m 3 or more, and further preferably 18 kg / m 3 or more, and particularly preferably 20 kg / m 3 or more. From the viewpoint of further improving the lightweight property of the molded body, the density of the molded body is more preferably 100 kg / m 3 or less, and further preferably 60 kg / m 3 or less, and particularly preferably 50 kg / m 3 or less, and most preferably 45 kg / m 3 or less. The density of the molded body is calculated by dividing the mass (unit: g) of the molded body by the volume (unit: L) calculated from the outer dimensions of the molded body and performing unit conversion. In addition, in a case where the molded body has a complicated shape at least in part, for example, it is not easy to calculate the volume from the outer dimensions of the molded body, and the volume of the molded body can be calculated from the water displacement.

[0163] In the preferable range of the density of the molded body, the upper limit value and the lower limit value of the density of the molded body described above can be combined arbitrarily. For example, the preferable range of the density of the molded body can be 10 kg / m 3 or more and 100 kg / m 3 or less, and also can be 15 kg / m 3 or more and 60 kg / m 3 or less, and also can be 18 kg / m 3 or more and 50 kg / m 3 or less, and also can be 20 kg / m 3 or more and 45 kg / m 3 or less.

[0164] In the past, in the case of manufacturing a molded body having a small density, it was particularly difficult to omit the curing process because the molded body was likely to be significantly deformed after demolding. In contrast, the molded body molded by the foamed particles can omit the curing process even in the case of having a small density, and can be in a desired shape and have an excellent appearance and rigidity even without curing. From the viewpoint of effectively exerting this effect, it is also preferable that the density of the molded body be in the above range.

[0165] The shape of the molded body is not particularly limited, and various shapes can be adopted depending on its use. The maximum length of the molded body, in other words, the maximum value of the length when the length of the molded body is measured in various directions, is preferably 600 mm or more. In the past, it was particularly difficult to omit the curing process or shorten the time of the curing process because such a long molded body was likely to shrink after demolding. In contrast, since the molded body has a foamed layer composed of the specific polypropylene-based resin and is composed of foamed particles having the specific shape, it can have excellent dimensional stability as described above, and the dimensional change of the molded body from the time point of demolding to the time point of shape stabilization can be reduced. Therefore, the molded body can reduce the dimensional change of the molded body after demolding even in the case of having a relatively long maximum length of, for example, 600 mm or more. As a result, even in the case of omitting the curing process or shortening the time of the curing process, the molded body having a desired dimension can be easily obtained. The molded body having such a shape is used, for example, for a bumper core material for a motor vehicle, a tool box for a motor vehicle, a seat core material for a motor vehicle, and the like.

[0166] The molded body is used, for example, for a wide variety of uses such as sound-absorbing materials, impact-absorbing materials, cushioning materials, and the like in the field of vehicles such as motor vehicles, the field of construction, and the like. From the viewpoint of more effectively utilizing the excellent dimensional stability based on the foamed particles, the molded body is preferably configured as a bumper core material for a motor vehicle, a tool box for a motor vehicle.

[0167] The bumper core material for a motor vehicle has a shape in which the maximum length is longer compared to the cross-sectional area, and thus has a problem in that the dimensional change of the molded body after demolding is likely to be large. In addition, the tool box for a motor vehicle has a complex shape having at least one recess for accommodating tools and a wall portion provided upright around the recess, and has a problem in that the wall portion is likely to be deformed due to the dimensional change of the molded body after demolding. In contrast, since the molded body is composed of the foamed particles, the dimensional stability can be improved even in the case of manufacturing such a molded body having a relatively long maximum length, a molded body having a complex shape. Therefore, the bumper core material for a motor vehicle, the tool box for a motor vehicle composed of the foamed particles have high dimensional accuracy.

[0168] (Method for manufacturing polypropylene-based resin foamed particle molded body) In producing the shaped body, for example, after the foamed particles are filled into a molding die, in-mold molding is performed by supplying steam as a heating medium into the molding die. Specifically, first, foamed particles are filled into a molding die having a molding cavity corresponding to the shape of the desired shaped body. As a method of filling the foamed particles, a split gate filling method, a compression filling method, or the like can be employed. Further, the split gate filling method refers to a method in which the foamed particles are filled into the molding die in a state in which a gap called a split gate is provided in the molding die, and then the molding die is completely closed, thereby mechanically compressing the foamed particles in the molding die. In addition, the compression filling method refers to a method in which foamed particles in a state in which they are preliminarily compressed by a pressurized gas or the like are filled into the molding die.

[0169] As the foamed particles filled into the molding die, foamed particles obtained by the production method described above can also be used directly. Alternatively, for example, foamed particles to which internal pressure is applied by impregnating a gas such as compressed air into the foamed particles in a pressure-resistant container can be used. In the case where internal pressure is applied to the foamed particles, the internal pressure of the foamed particles filled into the molding die can be appropriately set within a range of, for example, 0.3 MPa (G) or less in terms of gage pressure. The internal pressure of the foamed particles is preferably 0.20 MPa (G) or less. Alternatively, the foamed particles can be molded without applying internal pressure thereto. Further, the pressure (internal pressure) in the bubbles can be measured, for example, by the method described in Japanese Patent Application Publication No. 2003-201361.

[0170] After the filling of the foamed particles is completed, the foamed particles are heated by supplying steam into the molding die. The foamed particles in the molding die are heated by the steam, undergo secondary foaming, and are fused to each other. Thus, the foamed particles in the molding die can be integrated to form a shaped body.

[0171] After the heating of the foamed particles is completed, the shaped body in the molding die is cooled to stabilize the shape. Thereafter, the in-mold molding is completed by taking out the shaped body from the molding die. In the production method, as needed, a curing process in which the shaped body after demolding is left to stand in a high-temperature atmosphere for a predetermined time can be performed. The temperature of the atmosphere in the curing process can be appropriately set, for example, within a range of 60°C to 80°C. Alternatively, the standing time in the curing process can be, for example, 12 hours or more.

[0172] Further, in the production method, even in the case where the shaped body after demolding is not subjected to the curing process, the shrinkage and deformation of the shaped body can be suppressed. In the case where the curing process is omitted, for example, by leaving the shaped body after demolding to stand in an environment at 23°C for 12 hours, the shape of the shaped body can be stabilized. Alternatively, in the case where the time of the curing process is shortened, for example, by leaving the shaped body after demolding to stand in a high-temperature atmosphere adjusted to a temperature of about 60°C to 80°C for 3 hours, the shape of the shaped body can be stabilized.

[0173] [Examples] Embodiments of the foamed particles and the shaped bodies will be described.

[0174] (Polypropylene-based resin) Table 1 shows properties and the like of the polypropylene-based resin used for the production of the foamed particles. The polypropylene-based resins PP-A, PP-B, and PP-C used in this example are all virgin ethylene-propylene random copolymers derived from fossil fuels.

[0175] [Table 1]

[0176] 〔Melt flow rate of polypropylene-based resin〕 The melt flow rate (in other words, MFR) of the polypropylene-based resin was measured in accordance with JIS K7210-1:2014 under the conditions of a temperature of 230°C and a load of 2.16 kg.

[0177] 〔Melting point of polypropylene-based resin〕 The melting point of the polypropylene-based resin was found based on JIS K7121:1987. Specifically, first, the state of a test piece composed of the polypropylene-based resin was adjusted based on "(2) After a certain heat treatment, the case where the melting temperature is measured" described in JIS K7121:1987. The heating rate and the cooling rate in the state adjustment were set to 10°C / minute. The DSC curve was obtained by raising the temperature of the test piece after the state adjustment from 30°C to 200°C at a heating rate of 10°C / minute. Then, the vertex temperature of the melting peak appearing in the DSC curve was taken as the melting point. In addition, the flow rate of nitrogen in the measurement environment was set to 30 mL per minute. As the measurement device, a heat flux differential scanning calorimetry device (manufactured by SII NanoTechnology, Inc., model number: DSC7020) was used. In the case where a plurality of melting peaks appeared in the DSC curve, the vertex temperature of the melting peak with the largest area was taken as the melting point of the polypropylene-based resin.

[0178] 〔Crystallization temperature of polypropylene-based resin〕 The crystallization temperature of the polypropylene-based resin was measured based on JIS K7121-1987. Specifically, using a heat flux differential scanning calorimetry measuring device (manufactured by SII NanoTechnology (Shanghai) Co., Ltd., model number: DSC7020), a test piece composed of the polypropylene-based resin was warmed from 23°C to 200°C at a heating rate of 10°C / min, and then cooled from 200°C to 30°C at a cooling rate of 10°C / min, whereby a DSC curve was obtained. The peak temperature of the crystallization peak in the DSC curve was taken as the crystallization temperature. Further, the flow rate of nitrogen in the measurement environment was set to 30 mL per minute. In the case where a plurality of crystallization peaks appeared in the DSC curve, the vertex temperature of the crystallization peak with the largest area was taken as the crystallization temperature of the polypropylene-based resin.

[0179] 〔Melting heat of polypropylene-based resin〕 The melting heat of the polypropylene-based resin was calculated from a DSC curve obtained by performing differential scanning calorimetry in accordance with JIS K7122-1987. Specifically, first, the state of a test piece was adjusted based on "(2) After a certain heat treatment, the case where the melting temperature is measured" in "3. Adjustment of the state of the test piece" in JIS K7122-1987, using the polypropylene-based resin as the test piece. In the state adjustment, the heating rate and the cooling rate were set to 10°C / min. Thereafter, by heating the test piece after the state adjustment again from 23°C to 200°C at a rate of 10°C / min, a DSC curve (DSC curve at the second heating) was obtained. Further, the flow rate of nitrogen in the measurement environment was set to 30 mL per minute.

[0180] On the thus obtained DSC curve, a straight line connecting a point corresponding to 80°C in the DSC curve and an end point on the high-temperature side in the melting peak having the highest vertex temperature was drawn. Then, the melting heat of the polypropylene-based resin was calculated based on the area of the region surrounded by the thus determined straight line and the melting peak of the DSC curve.

[0181] 〔Flexural modulus of polypropylene-based resin〕 A 4-mm-thick sheet was produced by hot pressing the polypropylene-based resin at 230°C, and a test piece having a length of 80 mm, a width of 10 mm, and a thickness of 4 mm was cut out from the sheet. The flexural modulus of the test piece was calculated in accordance with JIS K7171:2008. Further, the radius R1 of the indenter and the radius R2 of the support table were both 5 mm, the distance between the fulcrums was 64 mm, and the test speed was 2 mm / min.

[0182] 〔Ethylene component content and butene component content of polypropylene-based resin〕 The ethylene component content and the butene component content in the polypropylene-based resin are determined by a publicly known method according to IR spectrum. Specifically, the ethylene component content and the butene component content are determined by a method described in "Polymer Analysis Handbook" (published by the Society of Polymer Science, Japan, published on January 1995, publisher: Kiiko-do Shoten, page numbers and item names: 615-616 "II.2.3 2.3.4 Polypropylene / Ethylene Copolymer", 618-619 "II.2.3 2.3.5 Polypropylene / Butene Copolymer"), in other words, a method for quantifying the relationship between the values corrected with predetermined coefficients for the absorbances of ethylene and butene and the thickness of a film-shaped test piece and the like.

[0183] More specifically, first, the polypropylene-based resin is heat-pressed at 180°C to be shaped into a film, and a plurality of test pieces having different thicknesses are produced. Next, by measuring the IR spectrum of each test piece, the absorbances (A -1 , A -1 ) at 722 cm 722 and 733 cm 733 derived from ethylene, and the absorbance (A -1 ) at 766 cm 766 derived from butene are read. Next, for each test piece, the ethylene component content (unit: mass%) in the polypropylene-based resin is calculated using the following equations (2) to (4). The value obtained by arithmetically averaging the ethylene component contents obtained for each test piece is taken as the ethylene component content (unit: mass%) in the polypropylene-based resin.

[0184] (K´ 733 ) c = 1 / 0.96 {(K´ 733 ) a - 0.268 (K´ 722 ) a} • • • (2) (K´ 722 ) c = 1 / 0.96 {(K´ 722 ) a - 0.150 (K´ 733 ) a} • • • (3) Ethylene component content = 0.575 {(K´ 722 ) c + (K´ 733 ) c} • • • (4) wherein K´ a in the equations (2) to (4) is the apparent light absorption coefficient (K´ a = A / pt) at each wave number, and K´ cis the corrected absorbance coefficient, A is the absorbance, p is the density of the resin (unit: g / cm 3 ), and t is the thickness of the test piece in film form (unit: cm). Furthermore, the above-described equations (2) to (4) can be applied to random copolymers.

[0185] In addition, the butene component content (unit: mass%) in the polypropylene-based resin was calculated for each test piece using the following equation (5). The value obtained by arithmetically averaging the butene component contents obtained for each test piece was used as the butene component content (unit: mass%) in the polypropylene-based resin.

[0186] Butene component content = 12.3 (A 766 / L) • • • (5) In equation (5), A is the absorbance, and L is the thickness of the test piece in film form (unit: mm).

[0187] Next, the configuration and the production method of the foamed particle used in this example will be described.

[0188] (Foamed particle A) As shown in Figure 5 and Figure 6 , the foamed particle A has a cylindrical shape having a through-hole 111 as a defective portion 11. In addition, the foamed particle A has a multilayer structure having a foamed layer 2 and a non-foamed covering layer 3 covering the foamed layer 2. As shown in Table 2, in the polypropylene-based resin constituting the foamed layer 2, PP-A (refer to Table 1) as a polypropylene-based resin (A) and PP-B as a polypropylene-based resin (B) are contained in a mass ratio of PP-A:PP-B = 60:40. The covering layer 3 is constituted by PP-C (refer to Table 1) as a thermoplastic resin.

[0189] In producing the foamed particle A, first, a multilayer resin particle was produced by a wire cutting method. In the production of the multilayer resin particle, a co-extrusion device having a core layer forming extruder, a covering layer forming extruder, and a co-extrusion die connected to these two extruders was used. Specifically, in the core layer forming extruder, PP-A, PP-B, carbon black, and zinc borate as a bubble regulator were melt-kneaded to obtain a core layer forming resin melt-kneaded product. Furthermore, the amount of zinc borate added was 500 mass ppm with respect to the total of the mass of PP-A and the mass of PP-B, and the amount of carbon black added to the core layer forming resin melt-kneaded product was 2.6 mass% in the core layer forming resin melt-kneaded product. In parallel therewith, in the covering layer forming extruder, PP-C and carbon black were melt-kneaded to obtain a covering layer forming resin melt-kneaded product. The amount of carbon black added to the covering layer forming resin melt-kneaded product was 2.6 mass% in the covering layer forming resin melt-kneaded product.

[0190] By bringing these resin melt mixtures together in a co-extrusion die, a composite was formed that consisted of a core layer in a non-foamed state, and a clad layer in a non-foamed state that clad the side periphery of the core layer. After extruding the composite from the orifice of the co-extrusion die, the extrudate was drawn while being cooled in water whose temperature was adjusted to 10°C, and was cut to an appropriate length using a pelletizer, whereby a multilayer resin pellet was obtained that consisted of a core layer and a clad layer that clad the side periphery of the core layer, and that had a through-hole formed in the core layer. The mass ratio of the core layer to the clad layer in the multilayer resin pellet was core layer:clad layer = 95:5 (in other words, the mass ratio of the clad layer was 5%). In addition, the mass of each multilayer resin pellet was about 1.5 mg.

[0191] Next, the multilayer resin pellet was made to foam in two stages, whereby a foamed pellet was produced. In the primary foaming process, the multilayer resin pellet was made to foam by a direct foaming method, whereby a primary foamed pellet was obtained. Specifically, 1 kg of the multilayer resin pellet was put into a 5-L container together with 3 L of water as a dispersion medium. Next, 0.3 parts by mass of a dispersant, 0.004 parts by mass of a dispersing aid, relative to 100 parts by mass of the multilayer resin pellet, were added to the container, and the multilayer resin pellet was dispersed in the dispersion medium. Kaolin was used as the dispersant. In addition, a surfactant (sodium alkylbenzenesulfonate) was used as the dispersing aid.

[0192] Next, while the container was closed, carbon dioxide as a physical foaming agent was supplied to the closed container while stirring was performed in the container, and the temperature in the container was raised to the foaming temperature shown in Table 2. The foaming pressure at this time (in other words, the pressure in the container) is shown in Table 2. After the temperature in the container reached the foaming temperature, the temperature was maintained for 15 minutes, whereby the physical foaming agent was impregnated in the multilayer resin pellet. After the impregnation of the physical foaming agent was completed, the container was opened, and the contents were released at atmospheric pressure while the foaming pressure in the container was maintained, whereby the multilayer resin pellet was made to foam. By the above, a primary foamed pellet was obtained that had a foamed layer in which the core layer was foamed, and a clad layer in a non-foamed state that clad the foamed layer.

[0193] Next, the primary foamed pellet was further foamed by performing a secondary foaming process, whereby a foamed pellet A was obtained. In the secondary foaming process, first, the primary foamed pellet was put into a pressure-resistant container (specifically, a metal drum), and air was supplied to the pressure-resistant container, whereby the pressure in the container was raised, and the air was impregnated in the bubbles. The internal pressure of the bubbles of the primary foamed pellet taken out of the pressure-resistant container is shown in Table 2. After that, the primary foamed pellet was put into a metal drum, and steam was supplied so that the drum pressure became the value shown in Table 2, and the primary foamed pellet was heated, whereby the foamed pellet A was obtained.

[0194] (Foaming Granules B) Except for differences such as the melting heat at the high-temperature peak, foamed particle B has a largely the same composition as foamed particle A. The manufacturing method of foamed particle B is the same as that of foamed particle A, except that the conditions of the first-stage foaming process and the second-stage foaming process are changed to the points shown in Table 2.

[0195] (Foaming Granules C) Foamed granules C have a substantially the same composition as foamed granules B, except that the mass ratio of PP-A to PP-B is changed to the ratio shown in Table 2. The manufacturing method of foamed granules C is the same as that of foamed granules B, except that the mass ratio of PP-A to PP-B and the foaming temperature in the primary foaming process are changed to the points shown in Table 2.

[0196] (Foaming Granules D) like Figure 8 as well as Figure 9 As shown, the foamed particle D has a columnar shape with grooves 112 serving as defect portions 11. Furthermore, the foamed particle D has a multi-layer structure comprising a foamed layer 2 and a coating layer 3 covering the foamed layer 2 in a non-foamed state. More specifically, the foamed particle D has a cross-shaped columnar shape with respect to its axial direction, or in other words, with respect to the direction connecting the bottom surface 12 and the top surface 13 (in other words, the shape of the cut surface of the foamed particle). Four grooves 112 are evenly spaced on the side circumferential surface 14 of the foamed particle D. The side circumferential surface 14 of the foamed particle D is covered by the coating layer 3, the inner side of which is composed of the foamed layer 2. The grooves 112 of the foamed particle D have a V-shaped cross-sectional shape. The average depth H of each groove in the foamed particle D is 0.45 mm.

[0197] The manufacturing method of foamed granules D is the same as that of foamed granules A, except that the shape of the die head is changed to produce resin granules with a cross-shaped cross section, and the conditions of the first-stage foaming process and the second-stage foaming process are changed to the points shown in Table 3.

[0198] (Foaming Granules E) Foamed granules E have a composition largely the same as foamed granules A, except that the polypropylene resin does not contain PP-B and is composed only of PP-A. The manufacturing method of foamed granules E is the same as that of foamed granules A, except that the core layer forming resin melt compound is made without PP-B and the conditions of the first-stage foaming process and the second-stage foaming process are changed to those shown in Table 3.

[0199] (Foamed Granules F) The foamed particle F has substantially the same configuration as the foamed particle A except that the mass ratio of PP-A to PP-B is changed to the ratio shown in Table 2. The manufacturing method of the foamed particle F is the same as that of the foamed particle A except that the mass ratio of PP-A to PP-B, the conditions of the primary foaming step, and the conditions of the secondary foaming step are changed to those shown in Table 3.

[0200] (Foamed particle G) The foamed particle G has substantially the same configuration as the foamed particle A except that the polypropylene-based resin does not include PP-A but is composed of only PP-B. The manufacturing method of the foamed particle G is the same as that of the foamed particle A except that the resin melt-mixed material for forming the core layer is produced without using PP-A, and the conditions of the primary foaming step are changed to those shown in Table 4.

[0201] (Foamed particle H) The foamed particle H has substantially the same configuration as the foamed particle A except that it has a cylindrical shape having no defective portion. The manufacturing method of the foamed particle H is the same as that of the foamed particle A except that the shape of the die is changed to produce a cylindrical resin particle having no through-hole, and the conditions of the primary foaming step and the conditions of the secondary foaming step are changed to those shown in Table 4.

[0202] (Foamed particle I) The foamed particle I has substantially the same configuration as the foamed particle A except that the pore diameter of the through-hole is larger than that of the foamed particle A. The manufacturing method of the foamed particle I is the same as that of the foamed particle A except that the shape of the die is changed to change the average pore diameter of the through-hole in the resin particle to that shown in Table 4, and the conditions of the primary foaming step are changed to those shown in Table 4.

[0203] (Example 1-1) The molded body 5 of the present example is a bumper core 51 for a motor vehicle. As shown in FIG. 1, the bumper core 51 has a cylindrical shape. In addition, as shown in FIG. 2, the cross-sectional shape of the bumper core 51 in a cross section perpendicular to the length direction is substantially C-shaped. The length of the bumper core 51 of the present example is about 1300 mm, the width (specifically, the outer dimension in the longitudinal direction) is about 150 mm, the depth (specifically, the outer dimension in the lateral direction) is 75 mm, and the wall thickness is about 30 mm. The manufacturing method of the molded body 5 of the present example is described below. Figure 10 Figure 11 Figure 11 Figure 11

[0204] ​​​​First, the foamed particles A were put into a pressure-resistant container, and compressed air was impregnated in the pressure-resistant container, thereby applying an internal pressure of 0.15 MPa (G) in terms of gage pressure to the foamed particles. Next, the foamed particles A were filled in a molding die for bumper core material molding. As a filling method into the molding die, a split filling method was adopted, and a split amount was set to 10%. Thereafter, steam was supplied into the molding die, and the foamed particles A in the molding die were secondarily foamed and fused with each other, thereby forming a molded body. At this time, a molding pressure, in other words, a pressure of the steam supplied into the molding die was 0.32 MPa (G) in terms of gage pressure. Next, the pressure in the molding die was released, and the molded body in the molding die was cooled with water until a surface pressure generated on an inner surface of the molding die by a foaming force of the molded body became 0.04 MPa (G), and the molded body was demolded from the molding die. The demolded molded body was left to stand in an atmosphere of 23°C. By the above, the molded body (specifically, a bumper core material) of Example 1-1 was obtained.

[0205] (Example 1-2) The production method of the molded body of Example 1-2 was the same as that of the molded body of Example 1-1 except that the molded body demolded from the molding die was left to stand in an atmosphere of 80°C for 3 hours for curing.

[0206] (Example 1-3) The molded body 5 of Example 1-3 was a tool box 52 for a motor vehicle. As shown in Figs. 1 and 2, the tool box 52 had a rectangular parallelepiped shape, and was provided with two recesses 521 (521a, 521b) for housing tools. More specifically, the tool box 52 had a floor portion 522, four side wall portions 523 (523a to 523d) which were vertically provided at outer peripheral end edges of the floor portion 522, and a partition wall portion 524 which divided a space surrounded by the side wall portions 523 into a first recess 521a and a second recess 521b. The partition wall portion 524 extended in a direction parallel to a width direction of the tool box 52. Figure 12 Figure 13 As shown in Figs. 1 and 2, the tool box 52 had a rectangular parallelepiped shape, and was provided with two recesses 521 (521a, 521b) for housing tools. More specifically, the tool box 52 had a floor portion 522, four side wall portions 523 (523a to 523d) which were vertically provided at outer peripheral end edges of the floor portion 522, and a partition wall portion 524 which divided a space surrounded by the side wall portions 523 into a first recess 521a and a second recess 521b. The partition wall portion 524 extended in a direction parallel to a width direction of the tool box 52.

[0207] ​The tool box 52 of this example has a length of about 900 mm, a width of about 450 mm, and a height of about 400 mm. The first recess 521a has internal dimensions of about 550 mm in length, about 350 mm in width, and about 300 mm in depth, and the second recess 521b has internal dimensions of about 100 mm in length, about 250 mm in width, and about 100 mm in depth. Of the four side wall portions 523, the first side wall portion 523a and the second side wall portion 523b provided at both ends in the length direction of the tool box 52 each have a thickness of about 100 mm. In addition, the portions of the third side wall portion 523c and the fourth side wall portion 523d provided at both ends in the width direction of the tool box 52 each have a thickness of about 50 mm toward the first recess 521a and a thickness of about 100 mm toward the second recess 521b. Furthermore, the partition wall portion 524 has a thickness of about 50 mm. The manufacturing method of the shaped body 5 of this example is described below.

[0208] First, the expanded particles A were put into a pressure-resistant container, and compressed air was impregnated in the pressure-resistant container, whereby an internal pressure of 0.15 MPa (G) in terms of gage pressure was applied to the expanded particles. Next, the expanded particles A were filled in a molding die for tool box molding. As the filling method into the molding die, a split filling method was employed, and the split amount was set to 10%. Thereafter, steam was supplied into the molding die, and the expanded particles A in the molding die were secondarily foamed and fused to each other, whereby a shaped body was formed. The molding pressure at this time, in other words, the pressure of the steam supplied into the molding die, was 0.34 MPa (G) in terms of gage pressure. Next, the pressure in the molding die was released, and the shaped body in the molding die was cooled with water until the surface pressure generated on the inner surface of the molding die by the foaming force of the shaped body became 0.04 MPa (G), and the shaped body was demolded from the molding die. Then, the demolded shaped body was left to stand in an atmosphere of 23°C. By the above, the shaped body (specifically, a tool box) of Example 1-3 was obtained.

[0209] (Example 1-4) The manufacturing method of the shaped body of Example 1-4 was the same as that of the shaped body of Example 1-3 except that the shaped body demolded from the molding die was left to stand in an atmosphere of 80°C for 3 hours for curing.

[0210] (Examples 2-1, 3-1, 4-1 and Comparative Examples 1-1, 2-1, 3-1, 4-1, 5-1) The molded bodies of these examples and comparative examples are automobile bumper cores having the same shape as the molded body of Example 1-1, and are composed of the expanded particles shown in Tables 6 to 13. The production method of the molded bodies of these examples and comparative examples is generally the same as the production method of the molded body of Example 1-1, except for the point of using the expanded particles shown in Tables 6 to 13 instead of expanded particles A, and the point of changing the molding pressure as shown in Tables 6 to 13.

[0211] (Examples 2-2, 3-2, 4-2 and Comparative Examples 1-2, 2-2, 3-2, 4-2, 5-2) The molded bodies of these examples and comparative examples are automobile bumper cores having the same shape as the molded body of Example 1-2, and are composed of the expanded particles shown in Tables 6 to 13. The production method of the molded bodies of these examples and comparative examples is generally the same as the production method of the molded body of Example 1-2, except for the point of using the expanded particles shown in Tables 6 to 13 instead of expanded particles A, and the point of changing the molding pressure as shown in Tables 6 to 13.

[0212] (Examples 2-3, 3-3, 4-3 and Comparative Examples 1-3, 2-3, 3-3, 4-3, 5-3) The molded bodies of these examples and comparative examples are automobile tool boxes having the same shape as the molded body of Example 1-3, and are composed of the expanded particles shown in Tables 6 to 13. The production method of the molded bodies of these examples and comparative examples is generally the same as the production method of the molded body of Example 1-3, except for the point of using the expanded particles shown in Tables 6 to 13 instead of expanded particles A, and the point of changing the molding pressure as shown in Tables 6 to 13.

[0213] (Examples 2-4, 3-4, 4-4 and Comparative Examples 1-4, 2-4, 3-4, 4-4, 5-4) The molded bodies of these examples and comparative examples are automobile tool boxes having the same shape as the molded body of Example 1-4, and are composed of the expanded particles shown in Tables 6 to 13. The production method of the molded bodies of these examples and comparative examples is generally the same as the production method of the molded body of Example 1-4, except for the point of using the expanded particles shown in Tables 6 to 13 instead of expanded particles A, and the point of changing the molding pressure as shown in Tables 6 to 13.

[0214] Various physical properties of the expanded particles A to I are shown in Tables 2 to 4. In addition, various physical properties of the molded bodies of the examples and comparative examples are shown in Tables 5 to 13. The measurement method and evaluation method of the various physical properties shown in Tables 2 to 13 are as described below.

[0215] (Bulk density) First, the foamed particles were left to stand for 24 hours or more in an environment of a relative humidity of 50%, a temperature of 23°C, and an atmospheric pressure of 1 atm, and the state of the foamed particles was adjusted. The foamed particles after the state adjustment were filled in a graduated cylinder in a natural packed state, and the bulk volume of the foamed particle group (unit: L) was read from the scale of the graduated cylinder. Thereafter, the bulk density of the foamed particles (unit: kg / m 3 ).

[0216] (apparent density) First, the foamed particles were left to stand for 24 hours or more in an environment of a relative humidity of 50%, a temperature of 23°C, and an atmospheric pressure of 1 atm, and the state of the foamed particles was adjusted. After the mass of the foamed particle group after the state adjustment was measured, a metal mesh was immersed in a graduated cylinder to which ethanol at a temperature of 23°C was added. Then, the volume of the foamed particle group read from the water level rise amount was measured, taking into account the volume of the metal mesh. After the mass of the foamed particle group thus obtained (unit: g) was divided by the volume (unit: L), the unit was converted, and thus the apparent density of the foamed particles (unit: kg / m 3 ).

[0217] (average pore diameter d of through holes) First, the foamed particle group was left to stand for 24 hours or more in an environment of a relative humidity of 50%, a temperature of 23°C, and an atmospheric pressure of 1 atm, and the state of the foamed particles was adjusted. With respect to 100 foamed particles randomly selected from the foamed particle group after the state adjustment, the central portion in the axial direction was cut with a plane perpendicular to the axial direction, and thus the cut surface was exposed. A photograph of the cut surface of each foamed particle was taken, and the cross-sectional area (opening area) of the through hole portion in the cross-sectional photograph was calculated. The diameter of an imaginary right circle having the same area as the cross-sectional area was calculated, and the value obtained by arithmetically averaging these was taken as the average pore diameter d (unit: mm) of the through holes of the foamed particles.

[0218] (average outer diameter D of foamed particles) First, the foamed particle group was left to stand for 24 hours or more in an environment of a relative humidity of 50%, a temperature of 23°C, and an atmospheric pressure of 1 atm, and the state of the foamed particles was adjusted. With respect to 100 foamed particles randomly selected from the foamed particle group after the state adjustment, the central portion in the axial direction was cut with a plane perpendicular to the axial direction, and thus the cut surface was exposed. Figure 6 and Figure 9The cross section is exposed. Two points Q3, Q4 that are farthest apart on the outline of the foamed particle 1 in the cross section are determined, and the distance between the two points (in other words, the maximum outer diameter of the foamed particle in the cross section) is taken as the outer diameter r of each foamed particle 1. Then, the arithmetic mean of the outer diameters r measured for 100 or more foamed particles 1 is taken as the average outer diameter D of the foamed particles. Furthermore, the measurement of the outer diameter of the foamed particle 1 in the cross section is performed by taking a photograph of the cross section of the foamed particle and performing image analysis.

[0219] (Average cross-sectional area A of foamed particle) First, the foamed particle group is left to stand for 24 hours or more in an environment of relative humidity 50%, temperature 23°C, and atmospheric pressure 1 atm, and the state of the foamed particles is adjusted. The foamed particles after the state adjustment are cut at the center in the axial direction with a plane perpendicular to the axial direction, whereby the cross section is exposed. The cross-sectional area of the foamed particle in the cross section is measured. The cross-sectional area of the foamed particle having a multilayer structure is specifically the sum of the cross-sectional area of the foamed layer and the cross-sectional area of the clad layer in the cross section, and the cross-sectional area of the defective portion is not included in the cross-sectional area of the foamed particle. The measurement of the cross-sectional area of the foamed particle in the cross section is performed by taking a photograph of the cross section of the foamed particle and performing image analysis. The above operation is performed for 100 foamed particles, and the arithmetic mean of the cross-sectional areas of the foamed particles obtained is taken as the average cross-sectional area A of the foamed particles.

[0220] (Average cross-sectional area Ca of each defective portion, total cross-sectional area Ct of defective portions) First, the foamed particle group is left to stand for 24 hours or more in an environment of relative humidity 50%, temperature 23°C, and atmospheric pressure 1 atm, and the state of the foamed particles is adjusted. From the foamed particle group after the state adjustment, 100 foamed particles are randomly selected, and these foamed particles are cut at the center in the axial direction with a plane perpendicular to the axial direction, whereby the cross section is exposed. Next, a photograph of the cross section of the foamed particle is taken, and image analysis is performed, whereby the cross-sectional area of the defective portion of each foamed particle is measured.

[0221] Next, the total of the cross-sectional areas of the defective portions thus obtained is calculated for each foamed particle. In addition, the cross-sectional area of each defective portion in each foamed particle is calculated by dividing the total of the cross-sectional areas of the defective portions by the number of defective portions.

[0222] The arithmetic mean of the total cross-sectional area of the defects for the 100 foamed particles was taken as the total cross-sectional area of the defects Ct. In addition, the average of the cross-sectional area of each defect for the 100 foamed particles was taken as the average cross-sectional area of each defect Ca. The ratio of the total cross-sectional area of the defects Ct to the average cross-sectional area A of the foamed particles Ct / A and the ratio of the average cross-sectional area of each defect Ca to the average cross-sectional area A of the foamed particles Ca / A in the cut surface are shown in Table 2 and Table 3.

[0223] (Independent bubble ratio of foamed particle) The independent bubble ratio of the foamed particles was measured using an air comparison pycnometer based on ASTM-D2856-70 Step C. Specifically, first, the foamed particles were left to stand for 24 hours or more in an environment of a relative humidity of 50%, a temperature of 23°C, and an atmospheric pressure of 1 atm, and the state of the foamed particles was adjusted. The foamed particles of which the bulk volume was about 20 cm 3 after the adjustment of the state were taken as a measurement sample, and the measurement sample was sunk into a graduated cylinder to which ethanol was added. The apparent volume Va of the measurement sample was measured from the amount of rise of the liquid surface at this time. After the measurement sample of which the apparent volume Va was measured was sufficiently dried, the value Vx of the true volume of the measurement sample measured by an air comparison pycnometer (manufactured by Tokyo Science Co., Ltd., "Beckman Model 1000 Air Comparison Pycnometer") was measured in accordance with Step C described in ASTM-D2856-70. Then, using these volume values Va and Vx, the independent bubble ratio of the measurement sample (unit: %) was calculated based on the following formula (6). The above operation was performed five times with a change in the measurement sample, and the arithmetic mean (N = 5) of the independent bubble ratios of the five measurement samples was taken as the independent bubble ratio (unit: %) of the foamed particles.

[0224] Independent bubble ratio = (Vx - W / ρ) x 100 / (Va - W / ρ) • • • (6) In the above formula (6), the symbols have the following meanings.

[0225] Vx: The true volume of the measurement sample measured by the above method, that is, the sum of the volume of the resin constituting the foamed particles and the total volume of the bubbles in the independent bubble portion within the foamed particles (unit: cm 3 ) Va: The apparent volume of the measurement sample measured from the amount of rise of the liquid surface when the measurement sample was sunk into the graduated cylinder to which ethanol was added (unit: cm 3 ) W: The mass of the measurement sample (unit: g) ρ: Density of the resin constituting the foamed particles (unit: g / cm³) 3 ) (Heat of fusion of high temperature peak, heat of fusion of resin inherent peak, total heat of fusion) The peak temperature and heat of fusion of the high-temperature peak were determined using a DSC curve obtained according to JIS K7122:1987. Specifically, firstly, approximately 3 mg of foamed particles were used as a sample, and the sample was heated from 23°C to 200°C at a heating rate of 10°C / min, and a differential scanning calorimeter was performed to obtain the DSC curve. Next, as in... Figure 7 As shown in the example, a straight line L2 is drawn connecting point α on the DSC curve, corresponding to 80°C, and point β, corresponding to the melting end temperature T of the foamed particles. Further, a straight line L3 is drawn passing through the maximum point γ between the resin intrinsic peak ΔH1 and the high-temperature peak ΔH2, and parallel to the vertical axis of the graph. Line L3 separates the resin intrinsic peak ΔH1 and the high-temperature peak ΔH2.

[0226] Then, the heat of fusion of the high-temperature peak ΔH2 was calculated based on the area enclosed by the portion of the DSC curve constituting the high-temperature peak ΔH2, line L2, and line L3. Similarly, the heat of fusion of the resin-specific peak ΔH1 was calculated based on the area enclosed by the portion of the DSC curve constituting the resin-specific peak ΔH1, line L2, and line L3. Furthermore, the total heat of fusion was calculated based on the area enclosed by the portion of the DSC curve constituting the resin-specific peak ΔH1, the portion of the DSC curve constituting the high-temperature peak ΔH2, and line L2.

[0227] The above operation was performed five times using different samples. The arithmetic mean of the fusion heat of the high-temperature peak ΔH2 obtained in each measurement was taken as the fusion heat Q of the high-temperature peak ΔH2 of the foamed particles. H2 Similarly, the arithmetic mean of the fusion heats of the resin intrinsic peak ΔH1 obtained in each measurement will be taken as the fusion heat Q of the resin intrinsic peak ΔH1 of the foamed particles. H1 In addition, the arithmetic mean of the total heat of fusion obtained from each measurement will be taken as the total heat of fusion Q of the foamed particles. H1 +Q H2 .

[0228] (Formable range, lower limit pressure for forming) In the evaluation of the formability range and the lower limit of forming pressure, in-mold forming was performed by varying the forming pressure during formal heating by 0.02 MPa (G) from 0.24 MPa (G) to 0.44 MPa (G) in increments of 0.02 MPa to produce a flat molded body. The formability range was determined based on the surface properties, weldability, and resilience of the resulting molded body.

[0229] The manufacturing method of the molded body for the evaluation of the moldable range is described below. First, the expanded particles were put into a pressure-resistant container, and the pressure-resistant container was pressurized with air to impregnate the air into the expanded particles, and the internal pressure of 0.12 MPa (G) was applied to the expanded particles. Next, the expanded particles after the internal pressure application were filled in a molding die by a split filling method. In this example, a molding die having a molding cavity capable of molding a flat plate-shaped molded body of 300 mm in length, 250 mm in width, and 60 mm in thickness was used. In the split filling, the expanded particles were filled in the molding die in a state where a split gap of 6 mm (in other words, a split amount of 10%) was opened in the thickness direction of the molded body, and then the molding die was completely closed, and thus the expanded particles in the molding die were mechanically compressed.

[0230] Next, in-mold molding was performed by supplying steam into the molding die. In the in-mold molding, first, preheating was performed by supplying steam into the molding die for 5 seconds in a state where a discharge valve of the molding die was opened. Next, the discharge valve was closed, and first one-way heating was performed by supplying steam into the molding cavity from one face of the molding die until reaching a pressure that was 0.08 MPa (G) lower than the molding pressure at the time of formal heating. Next, second one-way heating was performed by supplying steam into the molding cavity from the other face of the molding die until reaching a pressure that was 0.04 MPa (G) lower than the molding pressure at the time of formal heating. Thereafter, formal heating was performed by supplying steam into the molding cavity from both faces of the molding die until reaching the molding pressure at the time of formal heating. After the formal heating was completed, the pressure in the molding die was released, and the molded body in the molding die was cooled until the surface pressure based on the foaming force of the molded body became 0.04 MPa (G).

[0231] Thereafter, the molded body taken out from the molding die was subjected to a curing process by being left in an oven at 80°C for 12 hours. After the curing process, the molded body was left for 24 hours under conditions of a relative humidity of 50%, 23°C, and 1 atm, and a state adjustment of the molded body was performed. The surface properties, the fusion properties, and the recovery properties of the molded body after the state adjustment were evaluated, and the range of the molding pressure (in other words, the molding pressure at which a good product could be obtained) in which any one item was satisfactory according to the evaluation criteria described later was recorded as the moldable range in the "molding pressure" column of Tables 2 to 4. In addition, the number of conditions in which a good product could be obtained was recorded in the "number of conditions" column of Tables 2 to 4. The wider the moldable range, the more excellent the moldability could be judged to be.

[0232] In addition, the lowest molding pressure in the moldable range determined by the above method was recorded as the lower limit molding pressure in Tables 2 to 4. Since the lower the moldable molding pressure, the in-mold molding with a smaller amount of steam could be performed, the productivity could be judged to be excellent.

[0233] The evaluation method of the surface property, the fusion property, and the recovery property in the evaluation of the moldable range and the lower limit pressure of molding is described below.

[0234] [Surface Property] A 100 mm x 100 mm square was drawn in the central portion of the skin surface on one side in the thickness direction of the molded body, and then a diagonal line was drawn from any one corner of the square. Then, the number of pores present on the diagonal line, in other words, the number of pores having a size of 1 mm x 1 mm or more formed in the gaps between the foamed particles, was counted. Then, in the case where the number of pores was two or less, it was judged to be acceptable, and in the case where it was three or more, it was judged to be unacceptable.

[0235] [Fusion Property] The molded body was broken in such a manner that it was roughly equally divided in the length direction. By visually observing 100 or more of the foamed particles randomly selected from the foamed particles exposed on the broken surface, it was judged whether the foamed particles that were broken inside the particles, in other words, the foamed particles in which the material was broken, or the foamed particles that were broken at the interface between the foamed particles. Then, the value expressed as a percentage of the ratio of the number of the foamed particles observed that were broken inside the particles to the total number of the foamed particles, in other words, the material breakage rate, was calculated, and this value was taken as the fusion rate. Then, in the case where the fusion rate was 80% or more, it was judged to be acceptable, and in the case where it was less than 80%, it was judged to be unacceptable.

[0236] [Recovery Property] When the molded body was observed from above, the thickness of the molded body at four positions 10 mm inward from each vertex in the central direction, and the thickness of the molded body at the central portion were measured, respectively. Then, the ratio of the thickness of the thinnest portion among the measured portions to the thickness of the thickest portion (unit: %) was calculated. In the case where the thus obtained thickness ratio was 95% or more, it was judged to be acceptable, and in the case where it was less than 95%, it was judged to be unacceptable.

[0237] (Water Cooling Time) In the in-mold molding of each molded body in the examples and the comparative examples, the required time from the point in time at which the supply of steam to the molding die ended to the point in time at which the surface pressure reached 0.04 MPa (G) based on the foaming force of the molded body was recorded as the water cooling time in Tables 5 to 13.

[0238] (Density of Molded Body) The density of the molded body (unit: kg / m 3 ) was calculated by dividing the mass (unit: g) of each molded body in the examples and the comparative examples by the volume (unit: L) of the molded body calculated by the water displacement method, and then performing unit conversion.

[0239] (External Appearance) Based on the results of visual observation of each of the molded bodies in the examples and the comparative examples, evaluation of appearance was performed. The symbols described in the column of "appearance" in Tables 5 to 13 mean the following.

[0240] A: a beautiful surface having no interstices (pores) between the foamed particles on the surface of the molded body, and no obvious unevenness derived from the defective portions.

[0241] B: a surface having slightly many interstices (pores) between the foamed particles on the surface of the molded body, and / or slightly obvious unevenness derived from the defective portions.

[0242] C: a surface having many interstices (pores) between the foamed particles on the surface of the molded body, and / or obvious unevenness derived from the defective portions.

[0243] (Dimension stability) Depending on the shape of the molded body and the curing conditions, evaluation of dimension stability was performed by the following method.

[0244] (Examples 1-1, 2-1, 3-1, 4-1 and Comparative Examples 1-1, 2-1, 3-1, 4-1, 5-1) In the evaluation of dimension stability of the molded bodies of these examples and comparative examples, the molded bodies after demolding were left to stand in an atmosphere of 23°C, and the dimensions of predetermined portions of the molded bodies were measured at a time point 6 hours after the time point of demolding from the molding die, and at a time point 5 days after the time point of demolding from the molding die. In addition, as a reference sample, a molded body molded under the same conditions as each of the examples and the comparative examples, and left to stand in an atmosphere of 80°C for 12 hours after demolding from the molding die was prepared. Then, the dimensions of predetermined portions of this reference sample were measured. Based on these dimensions, the values of the index a1 and the index β1 described later were calculated, and the evaluation of dimension stability was performed.

[0245] With respect to the molded bodies of these examples and comparative examples, the symbols described in the column of "dimension stability" in Tables 5 to 13 mean the following.

[0246] A: a1 is 1% or less, and β1 is 13 mm or less.

[0247] B: neither A nor C.

[0248] C: a1 is more than 1%, and β1 is more than 13 mm.

[0249] Not evaluated: no evaluation was performed because of unqualified appearance.

[0250] Further, the dimensions of the predetermined portion of the aforementioned molded body refer to the outer dimension Xl (unit: mm) in the longitudinal direction of the bumper core 51, in other words, the distance from one end to the other end in the longitudinal direction of the bumper core 51.

[0251] The index a1 (unit: %) uses the outer dimension Xl of the bumper core 51 at the time point after 6 hours from the time point of demolding from the molding die 无养护，6h , and the outer dimension Xl of the bumper core 51 at the time point after 5 days from the time point of demolding from the molding die 无养护，5d , and is calculated based on the following equation (7). The smaller the value of the index a1, the smaller the change in the dimension from the time point after demolding to the time point of shape stabilization.

[0252] a1 = ([ (Xl 无养护，5d - Xl 无养护，6h ) ] / Xl 无养护，6h ) x 100 • • • (7) Further, the index b1 (unit: mm) uses the outer dimension Xl of the bumper core 51 at the time point after 6 hours from the time point of demolding from the molding die 无养护，6h , and the outer dimension Xl of the aforementioned reference sample in the longitudinal direction ref , and is calculated based on the following equation (8). The smaller the value of the index b1, the more easily the molded body having the desired dimension is obtained even if the standing time after molding is short.

[0253] b1 = | Xl ref - Xl 无养护，6h | • • • (8) [Examples 1-2, 2-2, 3-2, 4-2, and Comparative Examples 1-2, 2-2, 3-2, 4-2, 5-2] In the evaluation of the dimensional stability of the molded bodies for these examples and comparative examples, after the demolded molded body was cured by standing in an atmosphere of 80°C for 3 hours, the molded body was moved to an atmosphere of 23°C and further stood. Then, the dimensions of the predetermined portion of the molded body were measured at the time point after 6 hours from the time point of demolding from the molding die, and at the time point after 5 days from the time point of demolding from the molding die. Further, as a reference sample, a molded body that was molded under the same conditions as each example and comparative example, and cured by standing in an atmosphere of 80°C for 12 hours after demolding from the molding die was prepared. Then, the dimensions of the predetermined portion of this reference sample were measured. Based on these dimensions, the values of the index a2 and the index b2 described later were calculated, and the evaluation of the dimensional stability was performed.

[0254] The meaning of the symbols described in the "dimensional stability" column of Tables 5 to 13 for the shaped bodies of these examples and comparative examples is as follows.

[0255] A: α2 is 1% or less, and β2 is 13 mm or less.

[0256] B: neither A nor C.

[0257] C: α2 is more than 1%, and β2 is more than 13 mm.

[0258] Not evaluated: evaluation was not performed because of unqualified appearance.

[0259] Further, the dimension of the predetermined portion of the shaped body described above specifically refers to Figure 10 the outer dimension Xl (unit: mm) of the bumper core 51 in the length direction.

[0260] The index α2 (unit: %) is calculated based on the following equation (9) using the outer dimension Xl of the bumper core 51 in the length direction at the time point 6 hours after the time point of demolding from the molding die 3h养护，6h and the outer dimension Xl of the bumper core 51 in the length direction at the time point 5 days after the time point of demolding from the molding die 3h养护，5d . The smaller the value of the index α2, the smaller the change in dimension from the time point of demolding to the time point of shape stabilization.

[0261] α2 = ([ (Xl 3h养护，5d - Xl 3h养护，6h ) ] / Xl 3h养护，6h ) x 100 ••• (9) Further, the index β2 (unit: mm) is calculated based on the following equation (10) using the outer dimension Xl of the bumper core 51 in the length direction at the time point 6 hours after the time point of demolding from the molding die 3h养护，6h and the outer dimension Xl of the reference sample in the length direction ref . The smaller the value of the index β2, the more easily a shaped body having a desired dimension is obtained even if the shaped body is left to stand for a short time after molding.

[0262] β2 = | Xl ref - Xl 3h养护，6h | ••• (10) [Examples 1-3, 2-3, 3-3, 4-3 and Comparative Examples 1-3, 2-3, 3-3, 4-3, 5-3] In the evaluation of the dimensional stability of the molded bodies for these examples and comparative examples, the molded bodies after demolding were left to stand in an atmosphere of 23°C, and the dimensions of predetermined portions of the molded bodies were measured at a time point 6 hours after the time point of demolding from the mold, and at a time point 5 days after the time point of demolding from the mold. In addition, as a reference sample, a molded body that was molded under the same conditions as in each example and comparative example, and was left to stand in an atmosphere of 80°C for 12 hours after demolding from the mold was prepared, and was cured. Then, the dimensions of predetermined portions of this reference sample were measured. Based on these dimensions, the values of the indexes α3, α4, β3, and β4 described later were calculated, and the evaluation of the dimensional stability was performed.

[0263] The symbols described in the column of "dimensional stability" in Tables 5 to 13 mean the following for the molded bodies of these examples and comparative examples.

[0264] A: All of the four conditions that α3 is 1% or less, α4 is 1% or less, β3 is 9 mm or less, and β4 is 5 mm or less are satisfied.

[0265] B: Neither A nor C.

[0266] C: All of the four conditions that α3 is greater than 1%, α4 is greater than 1%, β3 is greater than 9 mm, and β4 is greater than 5 mm are satisfied.

[0267] Not evaluated: Evaluation was not performed because of unqualified appearance.

[0268] Further, the dimensions of the predetermined portions of the molded bodies described above specifically mean Figure 13 the length direction outer dimension X2 (unit: mm) and the width direction outer dimension Y2 (unit: mm) of the tool box 52 in the upper surface (in other words, the face on which the recess 521 opens) of the tool box 52, as shown in FIG. 6. The length direction outer dimension X2 of the tool box 52 specifically means the outer dimension from the upper end of the first side wall portion 523a to the upper end of the second side wall portion 523b measured at the center in the width direction of the tool box 52. In addition, the width direction outer dimension Y2 of the tool box 52 specifically means the outer dimension from the upper end of the third side wall portion 523c to the upper end of the fourth side wall portion 523d measured at the center in the length direction of the tool box 52.

[0269] The index α3 (unit: %) uses the length direction outer dimension X2 of the tool box 52 at a time point 6 hours after the time point of demolding from the mold 无养护，6h and the length direction outer dimension X2 of the tool box 52 at a time point 5 days after the time point of demolding from the mold 无养护，5dand is calculated based on the following equation (11). The smaller the value of the index a3, the smaller the change in the lengthwise dimension from the time point of demolding to the time point of shape stabilization.

[0270] a3= ( [ (X2 无养护，5d - X2 无养护，6h ) ] / X2 无养护，6h ) x 100 • • • (11) The index a4 (unit: %) uses the outer dimension Y2 of the tool box 52 at the time point 6 hours after the time point of demolding from the molding die 无养护，6h , and the outer dimension Y2 of the tool box 52 at the time point 5 days after the time point of demolding from the molding die 无养护，5d and is calculated based on the following equation (12). The smaller the value of the index a4, the smaller the change in the widthwise dimension from the time point of demolding to the time point of shape stabilization.

[0271] a4= ( [ (Y2 无养护，5d - Y2 无养护，6h ) ] / Y2 无养护，6h ) x 100 • • • (12) The index β3 (unit: mm) uses the outer dimension X2 of the tool box 52 at the time point 6 hours after the time point of demolding from the molding die 无养护，6h , and the outer dimension X2 of the reference sample described above in the lengthwise direction ref and is calculated based on the following equation (13). The smaller the value of the index β3, the more easily a molded body having a desired lengthwise dimension is obtained even with a short period of standing after molding.

[0272] β3= | X2 ref - X2 无养护，6h | • • • (13) The index β4 (unit: mm) uses the outer dimension Y2 of the tool box 52 at the time point 6 hours after the time point of demolding from the molding die 无养护，6h , and the outer dimension Y2 of the reference sample described above in the widthwise direction ref and is calculated based on the following equation (14). The smaller the value of the index β4, the more easily a molded body having a desired widthwise dimension is obtained even with a short period of standing after molding.

[0273] β4= | Y2 ref - Y2 无养护，6h | • • • (14) [Examples 1-4, 2-4, 3-4, 4-4 and Comparative Examples 1-4, 2-4, 3-4, 4-4, 5-4] In the evaluation of the dimensional stability of the molded bodies of these examples and comparative examples, the molded bodies after demolding were left to stand for 3 hours in an atmosphere of 80°C to perform curing, and then the molded bodies were moved to an atmosphere of 23°C to further stand. Then, the dimensions of predetermined portions of the molded bodies were measured at a time point 6 hours after the time point of demolding from the mold, and at a time point 5 days after the time point of demolding from the mold. In addition, as a reference sample, a molded body molded under the same conditions as in each example and comparative example, and left to stand for 12 hours in an atmosphere of 80°C after demolding from the mold was prepared. Then, the dimensions of predetermined portions of this reference sample were measured. Then, based on these dimensions, the values of the indexes α5, α6, β5, and β6 described later were calculated, and the evaluation of the dimensional stability was performed.

[0274] The symbols described in the column of "dimensional stability" in Tables 5 to 13 mean the following with respect to the molded bodies of these examples and comparative examples.

[0275] A: All of the four conditions that α5 is 1% or less, α6 is 1% or less, β5 is 9 mm or less, and β6 is 5 mm or less are satisfied.

[0276] B: Neither A nor C.

[0277] C: All of the four conditions that α5 is larger than 1%, α6 is larger than 1%, β5 is larger than 9 mm, and β6 is larger than 5 mm are satisfied.

[0278] Not evaluated: Not evaluated because of unqualified appearance.

[0279] Further, the dimensions of predetermined portions of the molded bodies described above mean the outer dimensions X2 (unit: mm) in the length direction and the outer dimensions Y2 (unit: mm) in the width direction of the tool case 52 on the upper surface of the tool case 52 shown in FIG. 1. Figure 13

[0280] The index α5 (unit: %) is calculated based on the following equation (15) using the outer dimensions X2 in the length direction of the tool case 52 at a time point 6 hours after the time point of demolding from the mold 3h养护，6h and the outer dimensions X2 in the length direction of the tool case 52 at a time point 5 days after the time point of demolding from the mold 3h养护，5d . The smaller the value of the index α5, the smaller the change in the length direction from the time point of demolding to the time point of shape stabilization.

[0281] α5= ([(X2 3h养护，5d -X2 3h养护，6h ) / X2 3h养护，6h ] x 100 ••• (15)​ Index a6 (unit: %) uses the outer dimension Y2 of the tool box 52 at the time point after 6 hours from the time point of demolding from the molding die in the width direction 3h养护，6h , and the outer dimension Y2 of the tool box 52 at the time point after 5 days from the time point of demolding from the molding die in the length direction 3h养护，5d , and is calculated based on the following equation (16). The smaller the value of the index a6, the smaller the change in the dimension in the width direction from the time point of demolding to the time point of shape stabilization.

[0282] a6= ( [ (Y2 3h养护，5d - Y2 3h养护，6h ) ] / Y2 3h养护，6h ) x 100 • • • (16) Index b5 (unit: mm) uses the outer dimension X2 of the tool box 52 at the time point after 6 hours from the time point of demolding from the molding die in the length direction 3h养护，6h , and the outer dimension X2 of the reference sample in the length direction ref , and is calculated based on the following equation (17). The smaller the value of the index b5, the more easily the molded body having the desired dimension in the length direction is obtained even if the standing time is short after molding.

[0283] b5= | X2 ref - X2 3h养护，6h | • • • (17) Index b6 (unit: mm) uses the outer dimension Y2 of the tool box 52 at the time point after 6 hours from the time point of demolding from the molding die in the width direction 3h养护，6h , and the outer dimension Y2 of the reference sample in the width direction ref , and is calculated based on the following equation (18). The smaller the value of the index b6, the more easily the molded body having the desired dimension in the width direction is obtained even if the standing time is short after molding.

[0284] b6= | Y2 ref - Y2 3h养护，6h | • • • (18) [Table 2]

[0285] [Table 3]

[0286] [Table 4]

[0287] [Table 5]

[0288] [Table 6]

[0289] [Table 7]

[0290] [Table 8]

[0291] [Table 9]

[0292] [Table 10]

[0293] [Table 11]

[0294] [Table 12]

[0295] [Table 13]

[0296] As shown in Table 2 and Table 3, the foamed particles A to D have the specific shape. In addition, the foamed layer of the foamed particles A to D is composed of the polypropylene-based resin containing the polypropylene-based resin (A) and the polypropylene-based resin (B) in the specific mass ratio. Therefore, these foamed particles, as shown in Table 5, Examples 1-1 to 1-4, Table 6, Examples 2-1 to 2-4, Table 7, Examples 3-1 to 3-4, and Table 8, Examples 4-1 to 4-4, can improve the dimensional stability of the molded body even in the case where the curing process is not performed, or the time of the curing process is shortened. In addition, the molded body obtained by the in-mold foaming of the foamed particles A to D does not have the striped pattern observed.

[0297] In addition, as shown in Table 5 to Table 8, the molded body composed of these foamed particles can reduce the dimensional change after the demolding. Therefore, according to these results, by using the foamed particles A to D, it is possible to manufacture a molded body having a longer maximum length, a molded body having a complex shape, or a molded body pursuing high dimensional accuracy, by omitting the curing process or shortening the time of the curing process.

[0298] On the other hand, the foamed layer of the foamed particle E shown in Table 3 is composed only of the polypropylene-based resin (A) and does not contain the polypropylene-based resin (B). Therefore, as shown in Table 9, the molded bodies of Comparative Examples 1-1 to 1-4 composed of the foamed particle E have poor dimensional stability compared to the molded bodies of the Examples.

[0299] The foamed layer of the foamed particles F shown in Table 3 contains the polypropylene-based resin (A) and the polypropylene-based resin (B), but the mass ratio of the polypropylene-based resin (B) is less than the specific range. Therefore, as shown in Table 10, the molded bodies of Comparative Examples 2-1 to 2-4 composed of the foamed particles F have poor dimensional stability compared with the molded bodies of the examples.

[0300] The foamed layer of the foamed particles G shown in Table 4 is composed of only the polypropylene-based resin (B) and does not contain the polypropylene-based resin (A). Therefore, as shown in Table 11, the molding pressure becomes excessively high when the molded bodies of Comparative Examples 3-1 to 3-4 composed of the foamed particles G are manufactured. In addition, the foamed particles G have insufficient secondary foaming property, and the appearance of the molded bodies of Comparative Examples 3-1 to 3-4 is not qualified.

[0301] The foamed particles H shown in Table 4 have no defect portions. Therefore, as shown in Table 12, the molded bodies of Comparative Examples 4-1 to 4-4 composed of the foamed particles H have poor dimensional stability compared with the molded bodies of the examples. In addition, the time required for cooling at the time of in-mold molding of the molded bodies of Comparative Examples 4-1 to 4-4 (in other words, the water cooling time) is long, and the productivity is poor.

[0302] The foamed particles I shown in Table 4 have larger through-holes than the foamed particles A to D, and the ratio Ca / A of the average cross-sectional area Ca of each defect portion to the average cross-sectional area A of the foamed particles and the ratio Ct / A of the total cross-sectional area Ct of the defect portions to the average cross-sectional area A of the foamed particles are larger than the specific ranges. Therefore, as shown in Table 13, the appearance of the molded bodies of Comparative Examples 5-1 to 5-4 composed of the foamed particles I is not qualified.

[0303] The above describes the polypropylene-based resin foamed particles, the polypropylene-based resin foamed particle molded body, the bumper core for a motor vehicle, and the tool box for a motor vehicle according to the present application based on the examples, but the specific modes of the polypropylene-based resin foamed particles, the polypropylene-based resin foamed particle molded body, the bumper core for a motor vehicle, and the tool box for a motor vehicle according to the present application are not limited to the modes of the examples, and the constitution can be appropriately changed within a range not impairing the gist of the present application.

Claims

1. A polypropylene resin foamed granule, comprising a foamed layer composed of polypropylene resin, wherein, The foamed particles have a columnar shape and have one or more defects selected from one or two of the following groups: a through hole penetrating the interior of the foamed particle in the axial direction and a groove extending axially on the side circumferential surface of the foamed particle. The ratio of the average cross-sectional area Ca of each defect portion to the average cross-sectional area A of the foamed particle in the cut surface obtained by cutting the foamed particle at its center with a plane perpendicular to the axial direction is 0.01 or more and 0.20 or less, and the ratio of the total cross-sectional area Ct of the defect portions to the average cross-sectional area A of the foamed particle is Ct / A is 0.02 or more and 0.20 or less. The polypropylene resin constituting the foam layer comprises a polypropylene resin (A) with a melting point of 135°C or higher and 150°C or lower and a flexural modulus of less than 1000 MPa, and a polypropylene resin (B) with a melting point of 145°C or higher and 160°C or lower and a flexural modulus of more than 1000 MPa. The mass ratio of polypropylene resin (A) to polypropylene resin (B) in the polypropylene resin is 65:35 to 35:

65.

2. The polypropylene resin foamed granules according to claim 1, wherein, The absolute value of the difference between the flexural modulus of the polypropylene resin (A) and the flexural modulus of the polypropylene resin (B) is 200 MPa or more and 500 MPa or less.

3. The polypropylene resin foamed granules according to claim 1 or 2, wherein, The polypropylene resin (B) is one or more propylene copolymers selected from the group consisting of ethylene-propylene copolymers, butene-propylene copolymers, and ethylene-butene-propylene copolymers.

4. The polypropylene resin foamed granules according to claim 3, wherein, The total content of ethylene and butene in the polypropylene resin (B) is 0.5% by mass or more and 2.5% by mass or less.

5. The polypropylene resin foamed granules according to claim 1 or 2, wherein, The polypropylene resin foamed particles have a crystal structure in which the DSC curve obtained when the foamed particles are heated from 23°C to 200°C at a heating rate of 10°C / min shows a resin-inherent peak originating from the melting of the inherent crystals of the polypropylene resin and a high-temperature peak having a peak temperature higher than that of the resin-inherent peak, wherein the heat of fusion of the high-temperature peak is 8 J / g or more and 25 J / g or less.

6. The polypropylene resin foamed granules according to claim 1 or 2, wherein, The apparent density of the polypropylene resin foamed particles is 15 kg / m³. 3 Above and 200kg / m 3 the following.

7. A polypropylene resin foamed granule molded body, wherein, The polypropylene resin foamed granule molded body is formed by in-mold molding of the polypropylene resin foamed granules as described in claim 1 or 2.

8. The polypropylene resin foamed granule molded article according to claim 7, wherein, The maximum length of the polypropylene resin foamed granules is 600 mm or more.

9. A bumper core material for motor vehicles, wherein, The core material for the motor vehicle bumper is formed by in-mold molding of polypropylene resin foam particles as described in claim 1 or 2.

10. A toolbox for a motor vehicle, wherein, The motor vehicle toolbox is formed by in-mold molding of polypropylene resin foam particles as described in claim 1 or 2.

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