Polypropylene resin foam particle composite molded article and method for manufacturing the same

Abstract

The present invention provides a polypropylene-based resin foam particle composite molded article capable of forming a resin layer with few defects, and a method for manufacturing the same. [Solution] First, a pre-molded product 10 is prepared, which is composed of a foam particle fusion body 20 formed by the fusion of first foam particles of polypropylene resin with each other, and a preliminary resin layer 40 made of polypropylene resin is provided on a part of the surface of the foam particle fusion body 20. Then, the pre-molded product 10 is placed in the molding cavity 50 of the mold 5. Then, the remaining space of the molding cavity 50 is filled with second foam particles 300. Then, a heating medium is supplied into the molding cavity 50, and the temperature of the heating surface 524 of the mold 5 is raised to form a resin layer 4 and obtain a composite molded product. The melt mass flow rate of the resin layer 4 is 9 g / 10 min or more.

Description

[Technical Field]

[0001] The present invention relates to a polypropylene resin foam particle composite molded article, which comprises a foam layer composed of polypropylene resin foam particles and a resin layer composed of polypropylene resin, and a method for producing the same. [Background technology]

[0002] Polypropylene resin foam particle molded articles are manufactured by a method called in-mold molding, in which polypropylene resin foam particles are filled into the molding cavity of a mold, and then heated by supplying a heating medium such as steam into the mold. When a heating medium is supplied into the mold in the in-mold molding method, the foam particles inside the mold undergo secondary foaming and fuse together. As a result, a molded article with a shape corresponding to the shape of the molding cavity can be obtained.

[0003] The surface of a molded body obtained by in-mold molding forms patterns originating from the boundaries of adjacent foam particles and traces of slits used to supply a heating medium to the mold. However, depending on the application of the molded body, there are cases where a molded body with a superior appearance is required, without patterns originating from the boundaries of foam particles or traces of slits on the surface. In such cases, a composite molded body in which a foam layer composed of polypropylene resin foam particles and a resin layer composed of polypropylene resin are integrated may be required.

[0004] As an example of this type of composite molded article, Patent Document 1 describes a foamed synthetic resin molded article in which, on the surface of the molded article corresponding to a portion of the molded surface of the molded die for in-mold foam molding that has been heated above the melting point of the foamable synthetic resin raw material particles, the raw material particles are brought into contact with the heated portion of the molded surface and melted, forming a molten resin layer in that portion, and then this molten resin layer is cured to form a continuous surface hardened layer during the in-mold foam molding process.

[0005] In the molded product of Patent Document 1, when forming the surface hardened layer, first, foam particles are filled into the mold with a cracking gap formed between the cavity mold and the core mold in the mold for in-mold foam molding. Then, the mold is clamped while the molding surface of the core mold is heated, and a molten resin layer is formed by melting the foam particles pressed against the molding surface. After that, the surface hardened layer is formed by hardening the molten resin layer. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 5-124126 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, when using polypropylene resin foam particles to produce molded articles as described in Patent Document 1, depending on the shape of the molded article and the arrangement of the surface hardened layer, it is difficult to form a uniform surface hardened layer on the surface, and defects such as holes, bubbles, unevenness, and wrinkles tend to occur in the surface hardened layer. In particular, when attempting to form the surface hardened layer on the surface of the molded article along the mold clamping direction, it is difficult to form a surface hardened layer with few defects because the foam particles are not easily pressed against the molded surface.

[0008] This invention has been made in view of the above background, and aims to provide a polypropylene-based resin foam particle composite molded article having a resin layer with few defects, and a method for producing a polypropylene-based resin foam particle composite molded article that can form a resin layer with few defects. [Means for solving the problem]

[0009] One aspect of the present invention relates to a method for producing a polypropylene resin foam particle composite molded article according to the following [1] to [8].

[0010] [1] A method for manufacturing a polypropylene-based resin foam particle composite molded body having a resin layer on a part of its surface, using a mold having a molding cavity having a shape corresponding to the shape of the composite molded body, and a heating surface provided on a part of the surface of the inner wall forming the molding cavity, A premolding preparation step involves preparing a premolding product which is composed of a foam particle fused body formed by the fusion of first foam particles of polypropylene resin with each other, and a pre-resin layer made of polypropylene resin is provided on a part of the surface of the foam particle fused body. A filling step is to place the premolded object in the molding cavity with the heating surface and the pre-resin layer of the premolded object in contact, and then fill the remaining space of the molding cavity with polypropylene resin second foam particles. The molding process includes supplying a heating medium into the molding cavity, further foaming the foam particle fusion body and the second foam particles, fusing them together to form a foam particle molded body, and raising the temperature of the heating surface to melt the pre-resin layer of the pre-molded material and at least a portion of the first foam particles to form the resin layer and obtain the composite molded body. A method for producing a polypropylene resin foam particle composite molded article, wherein the melt mass flow rate of the polypropylene resin constituting the resin layer of the composite molded article is 9 g / 10 min or more, as measured under conditions of a temperature of 230°C and a load of 2.16 kg.

[0011] [2] In the preform preparation step, a preform mold is prepared that includes a preform cavity having a shape corresponding to the shape of the preform and a heating surface provided on a part of the surface of the inner wall forming the preform cavity. The first foamed particles are filled into the pre-molded cavity. A method for producing a composite molded body of polypropylene - based resin foamed particles according to [1], wherein a heating medium is supplied into the molding cavity of the pre - molding die, the first foamed particles are further foamed and fused to each other to form the foamed particle fused body, and the temperature of the heating surface of the pre - molding die is raised to melt at least a part of the first foamed particles to form the preliminary resin layer, thereby obtaining the pre - molded article. 〔3〕The bulk density M1 of the first foamed particles is 30 kg / m 3 or more and 450 kg / m 3 or less, and the bulk density M2 of the second foamed particles is 15 kg / m 3 or more and 120 kg / m 3 or less, and the ratio M2 / M1 of the bulk density M2 of the second foamed particles to the bulk density M1 of the first foamed particles is less than 1.0. The method for producing a composite molded body of polypropylene - based resin foamed particles according to [1] or [2].

[0012] 〔4〕The first foamed particles are composed of a polypropylene - based resin having a melt mass flow rate measured under the conditions of a temperature of 230 °C and a load of 2.16 kg of 9 g / 10 min or more, and the second foamed particles are composed of a polypropylene - based resin having a melt mass flow rate measured under the conditions of a temperature of 230 °C and a load of 2.16 kg of 2 g / 10 min or more and less than 9 g / 10 min. The ratio of the melt mass flow rate of the polypropylene - based resin constituting the first foamed particles to the melt mass flow rate of the polypropylene - based resin constituting the second foamed particles is 2 or more and 5 or less. The method for producing a composite molded body of polypropylene - based resin foamed particles according to any one of [1] to [3]. 〔5〕The difference T - Tm1 between the temperature T (unit: °C) of the heating surface in the main molding step and the melting point Tm1 (unit: °C) of the polypropylene - based resin constituting the first foamed particles is 10 °C or more and 40 °C or less. The method for producing a composite molded body of polypropylene - based resin foamed particles according to any one of [1] to [4].

[0013] The manufacturing method of the polypropylene - based resin foamed particle composite molded body according to any one of [1] to [5], wherein the average particle diameter based on the particle size distribution of the first foamed particles is 1 mm or more and 4 mm or less. The manufacturing method of the polypropylene - based resin foamed particle composite molded body according to any one of [1] to [6], wherein the resin layer of the composite molded body has a flat portion parallel to the mold - clamping direction of the molding die.

[0014] The manufacturing method of the polypropylene - based resin foamed particle composite molded body according to any one of [1] to [7], wherein the composite molded body has a bottomed box - like shape having a bottom plate and side plates erected from the edges of the bottom plate, and the resin layer of the composite molded body is provided on at least one of the inner surface facing the inner space of the box of the composite molded body and the outer surface facing the outer space of the box.

[0015] Another aspect of the present invention relates to the polypropylene - based resin foamed particle composite molded bodies according to the following [9] to

[10] .

[0016] A polypropylene - based resin foamed particle composite molded body comprising a foamed particle molded body having a first foamed layer formed by fusing polypropylene - based resin first foamed particles to each other and a second foamed layer formed by fusing polypropylene - based resin second foamed particles to each other, and a resin layer composed of a polypropylene - based resin, wherein the resin layer is integrated with the first foamed layer and provided on a part of the surface of the composite molded body, the average thickness of the resin layer is 0.05 mm or more and 2 mm or less, and the melt mass - flow rate of the resin layer measured under the conditions of a temperature of 230 °C and a load of 2.16 kg is 9 g / 10 min or more. 〔10〕The polypropylene - based resin foamed particle composite molded body according to [9], wherein the density of the composite molded body is 20 kg / m 3 or more and 150 kg / m 3 or less.

Advantages of the Invention

[0017] According to the above embodiment, it is possible to provide a polypropylene-based resin foam particle composite molded article having a resin layer with few defects, and a method for manufacturing a polypropylene-based resin foam particle composite molded article that can form a resin layer with few defects. [Brief explanation of the drawing]

[0018] [Figure 1] Figure 1 is an explanatory diagram showing the method for calculating the area of ​​the high-temperature peak. [Figure 2] Figure 2 is a perspective view of a polypropylene-based resin foam particle composite molded article obtained by the manufacturing method of Example 1. [Figure 3] Figure 3 is a cross-sectional view taken along the line III-III in Figure 2. [Figure 4] Figure 4 is a cross-sectional view showing the main parts of the mold used in the manufacturing method of Example 1. [Figure 5] Figure 5 is a cross-sectional view showing the main part of the mold with the spacer in place in the manufacturing method of Example 1. [Figure 6] Figure 6 is a cross-sectional view showing the main part of the mold in the manufacturing method of Example 1, with the first foamed particles filled inside. [Figure 7] Figure 7 is a cross-sectional view showing the main part of the mold in which the premolded product is placed in the manufacturing method of Example 1. [Figure 8] Figure 8 is a cross-sectional view showing the main part of the mold in the manufacturing method of Example 1, with the second foamed particles filled inside. [Figure 9] Figure 9 is a magnified photograph of a cross-section of a polypropylene resin foam particle composite molded article obtained by the manufacturing method of Example 3. [Figure 10] Figure 10 is a magnified photograph of the surface of the resin layer in a polypropylene-based resin foam particle composite molded article obtained by the manufacturing method of Example 1. [Figure 11] Figure 11 is a magnified photograph of the surface of the resin layer in a polypropylene-based resin foam particle composite molded article obtained by the manufacturing method of Comparative Example 1. [Modes for carrying out the invention]

[0019] In the pre-molded product preparation step in the manufacturing method of the polypropylene resin foam particle composite molded product (hereinafter referred to as the "composite molded product"), a pre-molded product is prepared which is composed of a foam particle fused body formed by the fusion of the first polypropylene resin foam particles (hereinafter referred to as the "first foam particles") with each other, and a pre-resin layer made of polypropylene resin is provided on a part of the surface of the foam particle fused body. In the filling step, the pre-molded product is placed in the molding cavity of the mold with the heating surface and the pre-resin layer of the pre-molded product in contact, and then the remaining space in the molding cavity is filled with second polypropylene resin foam particles (hereinafter referred to as the "second foam particles"). In the molding step, a heating medium is supplied into the molding cavity of the mold, and the temperature of the heating surface of the mold is increased.

[0020] In this molding process, when a heating medium is supplied into the mold, the second foam particles in the mold undergo secondary foaming, and the first and second foam particles constituting the foam particle fusion body fuse together and become one. At this time, the entire pre-molded resin layer is pressed against the heating surface by the expansion of the second foam particles. Therefore, by increasing the temperature of the heating surface along with the supply of the heating medium to the mold, and forming a resin layer made of a polypropylene resin having a melt mass flow rate within the specified range while the second foam particles are expanding, defects such as air bubbles present in the resin layer of the pre-molded product can be repaired. As a result, even when attempting to manufacture a composite molded product with a relatively thin resin layer, a resin layer with few defects can be formed on the surface of the composite molded product.

[0021] Furthermore, in the molding process described above, the expansion of the second foam particles can be used to press the pre-resin layer against the heating surface. Therefore, the pre-resin layer can be pressed against the heating surface without generating pressure between the pre-resin layer and the heating surface by clamping the mold. Consequently, the manufacturing method can form a resin layer with fewer defects even when attempting to form a resin layer on a surface that is difficult to press against the mold even when the mold is clamped, such as a surface parallel to the clamping direction of the mold. In addition, the manufacturing method can form a resin layer with fewer defects even when attempting to form a resin layer on the surface of the composite molded body along the clamping direction of the mold, thereby more easily increasing the degree of freedom in the shape of the composite molded body. The steps of the manufacturing method described above will be explained in detail below.

[0022] [Pre-molded product preparation process] In the pre-molded product preparation step, a pre-molded product is prepared having a foam particle fused body formed by the fusion of first foam particles with each other, and a pre-resin layer provided on a part of the surface of the foam particle fused body. The shape of the pre-molded product is not particularly limited, and it is sufficient to have an appropriate shape according to the shape of the final composite molded product and the arrangement of resin layers in the composite molded product. For example, when manufacturing a flat composite molded product having a resin layer on its surface, a pre-molded product having a flat foam particle fused body and a pre-resin layer provided on the surface of the foam particle fused body can be prepared in the pre-molded product preparation step. Alternatively, for example, when manufacturing a bottomed box-shaped composite molded product having a resin layer on its inner surface, a pre-molded product having a bottomed box-shaped foam particle fused body and a pre-resin layer provided on the inner surface of the foam particle fused body, that is, the region of the surface of the foam particle fused body facing the space inside the box can be prepared.

[0023] The foamed particle fused body is formed by the fusion of first foamed particles with each other. Preferably, voids are formed between the first foamed particles in the foamed particle fused body. In this case, the heating medium supplied into the mold during the molding process can easily spread throughout the foamed particle fused body through the voids, and the total surface area of ​​the heated foamed particle fused body can be increased, thereby further enhancing the expansion force of the foamed particle fused body. As a result, in the molding process, the pre-resin layer of the pre-molded product can be pressed more strongly against the heating surface, and defects in the resin layer of the composite molded body can be further reduced.

[0024] Furthermore, in order to form a foamed particle fused body having voids between the first foamed particles, for example, the amount of heating medium supplied when producing the foamed particle fused body can be adjusted to an appropriate range. More specifically, by adjusting the amount of heating medium supplied, the first foamed particles can be secondarily foamed to the extent that voids are formed between them, and adjacent first foamed particles can be bonded together at the contact points on their surfaces and in the vicinity thereof, thereby forming a foamed particle fused body with voids.

[0025] A pre-resin layer is provided on a portion of the surface of the pre-molded product. The pre-resin layer is formed when the first foam particles melt and then solidify. The pre-resin layer may have defects such as pores, minute bubbles, wrinkles, and unevenness, or it may be a film with a smooth surface without these defects. In the above manufacturing method, in the main molding step, the pre-molded product is pressed against the heating surface using the expansion force of the second foam particles, and the pre-resin layer of the pre-molded product is melted. As a result, even if defects exist in the pre-resin layer, the defects can be repaired in the main molding step, and furthermore, the unevenness in the thickness of the pre-resin layer can be reduced, making it possible to form a composite molded product with a good resin layer.

[0026] In the pre-molded product preparation process, there are various methods for preparing the pre-molded product. For example, in the pre-molded product preparation process, the pre-molded product may be prepared by obtaining a pre-made pre-molded product. Alternatively, in the pre-molded product preparation process, the pre-molded product may be prepared by manufacturing the pre-molded product.

[0027] In-mold molding can be used to produce preforms. The preform mold used for in-mold molding of preforms has a preform cavity having a shape corresponding to the shape of the preform. In addition, a heating surface is provided on a part of the surface of the inner wall of the mold that forms the preform cavity in the preform mold.

[0028] For example, in a first embodiment of the method for manufacturing a premolded product, a premolded product can be manufactured by preparing a premolding mold having the above-described configuration and simultaneously forming a foam particle fused body and a resin layer within the premolding mold. More specifically, first, first foam particles are filled into the premolding cavity of the premolding mold. Then, the temperature of the heating surface of the premolding mold is increased, and a pre-resin layer is formed by melting at least a portion of the first foam particles, specifically the first foam particles present near the heating surface. While the first foam particles present near the heating surface are melting, a heating medium is supplied into the premolding cavity, and a foam particle fused body is formed by fusing the first foam particles together, and the foam particle fused body and the resin layer are fused together to integrate them. For example, steam can be used as the heating medium. After that, cooling of the premolding cavity is performed to stabilize the shape of the foam particle fused body and the pre-resin layer within the premolding cavity, thereby obtaining a premolded product having a foam particle fused body and a pre-resin layer.

[0029] As in this embodiment, by supplying a heating medium into the pre-molding cavity while the first foam particles present near the heating surface are melting, the first foam particles heated by the heating medium can be expanded, pressing the first foam particles near the heating surface against the heating surface. As a result, defects in the pre-resin layer of the pre-molded product can be further reduced. In this case, it is also easier to reduce the number of operations such as cooling performed to stabilize the shape of the foam particle fused body and the pre-resin layer, and to shorten the molding cycle.

[0030] On the other hand, the formation of the foam particle fused body may be carried out in parallel with the formation of the pre-resin layer, as shown in the first embodiment, or it may be carried out before the formation of the pre-resin layer. For example, in the second embodiment of the method for manufacturing a pre-molded product, after filling the pre-molding cavity with first foam particles, the temperature of the heating surface is increased to melt the first foam particles. Then, the molten portion of the first foam particles is solidified by cooling the pre-molding cavity, etc., to first form a pre-resin layer. After the formation of the pre-resin layer is completed, a heating medium is supplied to the pre-molding cavity to form a foam particle fused body and fuse the pre-resin layer and the foam particle fused body together to integrate them. In this way, a pre-molded product can also be obtained by forming the foam particle fused body after forming the pre-resin layer.

[0031] Furthermore, in the method for manufacturing a premolded product, a pre-resin layer may be formed after the formation of the foam particle fused body is complete. That is, in a third embodiment of the method for manufacturing a premolded product, first, first foam particles are filled into the premolding cavity. Then, a heating medium is supplied into the premolding cavity to fuse the first foam particles together, thereby forming a foam particle fused body. After stabilizing the shape of the foam particle fused body by cooling, the temperature of the heating surface of the premolding mold is increased to melt the first foam particles present near the heating surface. Then, the molten portion of the first foam particles is solidified to form a pre-resin layer on the surface of the foam particle fused body. In this way, a premolded product can also be obtained by forming a pre-resin layer after forming the foam particle fused body.

[0032] Thus, since the pre-resin layer of the pre-molded body and the resin layer of the composite molded body are formed by melting the first foamed particles, the polypropylene resin constituting the resin layer of the composite molded body and the polypropylene resin constituting the pre-resin layer of the pre-molded body both have the same properties as the polypropylene resin constituting the first foamed particles.

[0033] The maximum thickness of the premolded material, that is, the thickness of the thickest part of the premolded material, is preferably 1 mm to 30 mm, more preferably 1.5 mm to 20 mm, and even more preferably 2 mm to 10 mm. In this case, the fusion properties of the entire composite molded body can be more easily improved. Furthermore, even when foam particles with a relatively high bulk density are used as the first foam particles, it is expected that the weight of the composite molded body can be easily reduced.

[0034] In the manufacturing process of a premolded product, methods such as cracking filling or compression filling may be used when filling the premolding mold with first foam particles. Cracking filling is a method in which first foam particles are filled into the premolding cavity while the premolding mold is not completely closed, and then the premolding mold is completely closed. Compression filling is a method in which the pressure in the transport path of the first foam particles and inside the premolding mold is increased by pressurized gas, the first foam particles compressed by the pressurized gas are filled into the premolding cavity, and then the pressure inside the premolding mold is released to restore the shape of the first foam particles.

[0035] The first foamed particles used in the production of the premolded product may have internal pressure applied to them beforehand. Methods for applying internal pressure to the first foamed particles include, for example, placing the first foamed particles in a pressure vessel and then pressurizing the inside of the pressure vessel with an inorganic gas such as air or carbon dioxide to impregnate the foamed particles with the inorganic gas.

[0036] When manufacturing a preform, it is preferable to fill the preform cavity with first foam particles that have not been subjected to internal pressure by cracking filling. In this case, the first foam particles can be filled into the preform cavity more efficiently, and the fusion properties of the resulting preform can be more easily improved.

[0037] When producing a premolded product, the difference T0-Tm1 between the heating surface temperature T0 (unit: °C) and the melting point Tm1 (unit: °C) of the polypropylene resin constituting the first foamed particles is preferably between 10°C and 40°C. In this case, the first foamed particles present near the heating surface can be melted more easily, forming a pre-resin layer. Furthermore, by keeping the heating surface temperature within the above range, deterioration of the resin components due to excessively high heating temperatures can be prevented. In addition, deformation of the premolded product can be prevented, and the release properties and appearance of the composite molded product can be improved more easily.

[0038] The method for heating the heating surface in a pre-molding die is not particularly limited and can take various forms. For example, the pre-molding die may be configured to supply a heating medium such as steam to the heating surface from outside the pre-molding cavity, thereby raising the temperature of the heating surface. Alternatively, the pre-molding die may have a heater for raising the temperature of the heating surface, and may be configured to raise the temperature of the heating surface by the heater.

[0039] The first foamed particles used in the production of premolded articles are composed of a polypropylene resin. In this specification, a polypropylene resin refers to a propylene copolymer containing 50% by mass or more of a homopolymer of propylene monomers and a propylene copolymer containing 50% by mass or more of constituent units derived from propylene. Examples of propylene copolymers include copolymers of propylene and α-olefins having 4 to 10 carbon atoms, such as ethylene-propylene copolymer, propylene-butene copolymer, hexene-propylene copolymer, and ethylene-propylene-butene copolymer. The propylene copolymer may be a random copolymer or a block copolymer. The first foamed particles may be composed of one type of polypropylene resin or of two or more types of polypropylene resins.

[0040] The first foamed particles may contain other resins or elastomers other than polypropylene resins, to the extent that they do not impair the objectives and effects of the present invention. Examples of resins other than polypropylene resins include thermoplastic resins other than polypropylene resins, such as polyethylene resins, polystyrene resins, polyamide resins, and polyester resins. Examples of elastomers include olefin-based thermoplastic elastomers and styrene-based thermoplastic elastomers. The proportion of polymers other than polypropylene resins in the first foamed particles is preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, and particularly preferably 0% by mass, that is, the first foamed particles contain only polypropylene resin as a polymer.

[0041] Furthermore, the first foamed particles may contain additives such as foam regulators, nucleating agents, flame retardants, flame retardant aids, plasticizers, antistatic agents, antioxidants, UV inhibitors, light stabilizers, conductive fillers, antibacterial agents, and colorants, to the extent that they do not impair the effects described above. The amount of additives in the first foamed particles is preferably, for example, 0.01 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the polypropylene resin constituting the first foamed particles.

[0042] The first foamed particles are preferably composed of a polypropylene resin having a melt mass flow rate of 9 g / 10 min or more, measured under conditions of a temperature of 230°C and a load of 2.16 kg. In this case, a resin layer having a melt mass flow rate within the aforementioned specific range can be formed more reliably. As a result, defects in the resin layer in the composite molded article can be reduced more easily. From the viewpoint of more reliably obtaining this effect, the melt mass flow rate of the polypropylene resin constituting the first foamed particles is more preferably 13 g / 10 min or more, even more preferably 17 g / 10 min or more, and particularly preferably 20 g / 10 min or more.

[0043] On the other hand, the melt mass flow rate of the polypropylene resin constituting the first foam particles is preferably 40 g / 10 min or less, more preferably 35 g / 10 min or less, even more preferably 32 g / 10 min or less, particularly preferably 28 g / 10 min or less, and most preferably 27 g / 10 min or less. In this case, shrinkage during the manufacturing process of the premolded product is suppressed, and a composite molded product having the desired dimensions can be manufactured more easily. The melt mass flow rate of the polypropylene resin is a value measured under the conditions of a test temperature of 230°C and a load of 2.16 kg, based on JIS K7210-1:2014.

[0044] In determining the preferred range for the melt mass flow rate of the polypropylene resin constituting the first foamed particles, the upper and lower limits of the melt mass flow rate mentioned above can be arbitrarily combined. For example, the preferred range for the melt mass flow rate of the polypropylene resin constituting the first foamed particles may be 9 g / 10 min to 40 g / 10 min, 13 g / 10 min to 35 g / 10 min, 17 g / 10 min to 32 g / 10 min, 20 g / 10 min to 28 g / 10 min, or 20 g / 10 min to 27 g / 10 min.

[0045] The melting point Tm1 of the polypropylene-based resin constituting the first foamed particles is preferably 120 °C or higher, more preferably 125 °C or higher, even more preferably 127 °C or higher, and particularly preferably 130 °C or higher. In this case, the releasability of the preform and the composite molded body can be enhanced, and the dimensional accuracy of the composite molded body can be more easily enhanced. Further, the melting point Tm1 of the polypropylene-based resin is preferably 155 °C or lower, more preferably 150 °C or lower, even more preferably 145 °C or lower, and particularly preferably 140 °C or lower. In this case, the heating temperature and the molding pressure during the production of the preform or the foamed particle composite molded body can be more easily reduced.

[0046] The melting point Tm1 of the polypropylene-based resin can be determined based on the differential scanning calorimetry (i.e., DSC) performed in accordance with JIS K7121-1987 and based on the obtained DSC curve. Specifically, first, the test piece is conditioned according to “(2) Measuring the melting temperature after performing a certain heat treatment”. The temperature range in the conditioning is from 30 °C to 200 °C. The conditioned test piece is heated from 30 °C to 200 °C at a heating rate of 10 °C / min to obtain a DSC curve, and the peak temperature of the melting peak appearing in the DSC curve is taken as the melting point Tm1 of the polypropylene-based resin. When a plurality of melting peaks appear in the DSC curve, the peak temperature of the melting peak having the largest area is taken as the melting point Tm1 of the polypropylene-based resin.

[0047] The bulk density M1 of the first foamed particles is 30 kg / m 3 or more and 450 kg / m 3 or less, preferably 60 kg / m 3 or more, more preferably 90 kg / m 3 or more, even more preferably 120 kg / m 3 or more, particularly preferably. In this case, the ratio of the polypropylene-based resin in the first foamed particles can be increased. As a result, in this molding step, the polypropylene-based resin can be more easily supplied in the vicinity of the heating surface, and the defects in the resin layer in the composite molded body can be more easily reduced.

[0048] Furthermore, the bulk density M1 of the foamed particles is 450 kg / m³. 3 Preferably, it is 400 kg / m 3 It is more preferable that the following conditions are met: 350 kg / m 3 It is even more preferable that the following conditions apply: 300 kg / m 3 The following is particularly preferable: 250 kg / m 3 The following is most preferable. In this case, the first foam particles fuse more easily with each other, making it easier to produce a pre-molded product. In addition, in this case, it is easier to reduce the weight of the composite molded product.

[0049] The method for measuring the bulk density M1 of the first foamed particles is as follows: First, the first foamed particles are allowed to stand for 24 hours under conditions of 50% relative humidity, 23°C, and 1 atm to adjust their state. Next, the adjusted first foamed particles are filled into a graduated cylinder so that they naturally accumulate, and the bulk volume (unit: L) of the first foamed particles in the graduated cylinder is read from the scale on the graduated cylinder. Then, the mass (unit: g) of the first foamed particles in the graduated cylinder is divided by the aforementioned bulk volume, and the bulk density M1 (unit: kg / m³) of the first foamed particles is obtained by further unit conversion. 3 Calculate ).

[0050] The average particle diameter based on the particle size distribution of the first foamed particles is preferably 4 mm or less, more preferably 3.4 mm or less, even more preferably 2.8 mm or less, and particularly preferably 2.4 mm or less. In this case, the first foamed particles can be packed more densely into the pre-molded cavity, making it easier to reduce defects in the resin layer of the composite molded article.

[0051] The average particle diameter based on the particle size distribution of the first foamed particles is preferably 1 mm or more, more preferably 1.2 mm or more, even more preferably 1.5 mm or more, and particularly preferably 1.7 mm or more. In this case, the manufacturability of the first foamed particles can be further improved. In this case, when the first foamed particles are filled into the pre-molded cavity, the distribution of the first foamed particles within the pre-molded cavity can be made more uniform.

[0052] A laser diffraction / scattering particle size distribution analyzer (for example, "Millitrack JPA" manufactured by Nikkiso Co., Ltd.) can be used to measure the particle size distribution of the first foamed particles based on the number of particles. More specifically, the volume-based particle size distribution of the first foamed particles can be measured using a laser diffraction / scattering particle size distribution analyzer, and then converted to a number-based particle size distribution by assuming the particle shape is spherical. Furthermore, the average particle diameter based on the number of particles of the first foamed particles is specifically the arithmetic mean diameter in the number-based particle size distribution.

[0053] Preferably, the polypropylene resin constituting the first foamed particles has a crystalline structure such that the DSC curve obtained when heated from 23°C to 200°C at a heating rate of 10°C / min shows an endothermic peak due to the melting of crystals inherent to the polypropylene resin constituting the first foamed particles, and one or more melting peaks located at a higher temperature than this endothermic peak. First foamed particles composed of such a polypropylene resin have excellent mechanical strength and moldability. In the following, the endothermic peak due to the melting of crystals inherent to the polypropylene resin that appears in the DSC curve is called the "resin-specific peak," and the melting peak that appears at a higher temperature than the resin-specific peak is called the "high-temperature peak." The resin-specific peak is caused by endothermic heat when the crystals inherent to the polypropylene resin constituting the first foamed particles melt. On the other hand, the high-temperature peak is presumed to be caused by the melting of secondary crystals formed in the polypropylene resin during the manufacturing process of the first foamed particles. That is, if a high-temperature peak appears in the DSC curve, it is presumed that secondary crystals have been formed in the polypropylene resin.

[0054] Whether or not the polypropylene resin constituting the first foamed particles has the aforementioned crystalline structure can be determined based on the DSC curve obtained by performing differential scanning calorimetry (DSC) under the conditions described above, in accordance with JIS K7121:1987. Furthermore, when performing DSC, 1 to 3 mg of the first foamed particles should be used as a sample.

[0055] Specifically, the DSC curve obtained when heating from 23°C to 200°C at a heating rate of 10°C / min (i.e., the first heating) shows both a high-temperature peak and a resin-specific peak of the polypropylene resin constituting the first foamed particles. In contrast, the DSC curve obtained when cooling from 200°C to 23°C at a cooling rate of 10°C / min after the first heating, and then heating again from 23°C to 200°C at a heating rate of 10°C / min (i.e., the second heating), shows only the resin-specific peak of the polypropylene resin constituting the first foamed particles. Therefore, by comparing the DSC curve obtained during the first heating and the DSC curve obtained during the second heating, it is possible to distinguish between the resin-specific peak and the high-temperature peak. The temperature at the peak of this resin-specific peak may differ slightly between the first and second heating, but the difference is usually within 5°C.

[0056] The heat of fusion of the high-temperature peak of the polypropylene resin constituting the first foamed particle is preferably 5 J / g or more and 40 J / g or less, more preferably 7 J / g or more and 30 J / g or less, and even more preferably 10 J / g or more and 20 J / g or less.

[0057] The heat of fusion of the aforementioned high-temperature peak is determined as follows. First, the foamed particles are allowed to stand for 24 hours under conditions of 50% relative humidity, 23°C, and 1 atm to adjust the state of the first foamed particles. Using 1 to 3 mg of the first foamed particles after adjustment as a sample, a differential scanning calorimetry (DSC) curve is obtained by heating them from 23°C to 200°C at a heating rate of 10°C / min. An example of a DSC curve is shown in Figure 1. When the polypropylene resin constituting the first foamed particles has a high-temperature peak, the DSC curve shows a resin-specific peak ΔH1 and a high-temperature peak ΔH2, whose peak is at a higher temperature than the peak of the resin-specific peak ΔH1, as shown in Figure 1.

[0058] Next, draw a straight line L1 connecting point α, which corresponds to 80°C on the DSC curve, and point β, which corresponds to the melting termination temperature Te of the first foamed particle. Note that the melting termination temperature Te is the high-temperature endpoint of the high-temperature peak ΔH2, that is, the intersection point of the high-temperature peak ΔH2 and the baseline on the high-temperature side of the DSC curve.

[0059] After drawing the straight line L1, a straight line L2 is drawn parallel to the vertical axis of the graph, passing through the maximum point γ located between the resin intrinsic peak ΔH1 and the high-temperature peak ΔH2. This straight line L2 separates the resin intrinsic peak ΔH1 and the high-temperature peak ΔH2. The amount of heat absorbed by the high-temperature peak ΔH2 can be calculated based on the area enclosed by the portion of the DSC curve that constitutes the high-temperature peak ΔH2, and the straight lines L1 and L2.

[0060] The method for producing the first foamed particles is not particularly limited, and known methods can be employed. For example, the first foamed particles may be produced by a method called direct foaming, in which polypropylene resin particles dispersed in an aqueous medium in a container are impregnated with a foaming agent, and then the resin particles are released together with the aqueous medium into an atmosphere at a lower pressure than the pressure inside the container to cause foaming. Alternatively, for example, the first foamed particles may be produced by a method called extrusion foaming, in which a foaming agent is added to a molten polypropylene resin in an extruder, and the molten material is extruded from the extruder and foamed.

[0061] [Filling process] The mold used in the filling process has a molding cavity shaped to correspond to the desired shape of the composite molded body. Furthermore, a heating surface is provided on a portion of the inner wall surface of the mold that forms the molding cavity. In the filling process, a pre-molded object is placed in the molding cavity of the mold with the heating surface and the pre-resin layer in contact. Then, the remaining space in the molding cavity, i.e., the space between the pre-molded object and the inner wall forming the molding cavity, is filled with second foam particles.

[0062] The placement of the premolded product into the molding cavity may be done before filling with the second foam particles. For example, first, the premolded product may be placed into the molding cavity of the mold with the pre-resin layer separated from the heating surface of the mold, and then the premolded product may be moved within the molding cavity to bring the heating surface and the pre-resin layer into contact so that at least a large portion of the heating surface and the pre-resin layer are in contact. After placing the premolded product into the molding cavity in this manner, the second foam particles may be filled into the space between the premolded product and the mold. Alternatively, for example, first, the mold may be clamped while keeping the pre-resin layer in close contact with the heating surface of the mold, and the premolded product may be placed into the molding cavity. After that, the second foam particles may be filled into the space between the premolded product and the mold. From the viewpoint of forming a space for filling with the second foam particles between the premolded product and the mold, the volume of the molding cavity in the mold may be larger than the volume of the premolding cavity in the premolding mold, and may have a shape corresponding to the desired composite molded product.

[0063] The molding die may be a different mold from the pre-molding die. For example, if the pre-molded product has a shape with recesses or protrusions, such as a box with a bottom, the molding die can be provided with a portion that corresponds to the recesses or protrusions of the pre-molded product. This allows the pre-molded product to be placed in the molding die, and also creates a space between the pre-molded product and the molding die for filling with second foam particles.

[0064] Furthermore, a portion of the pre-molded mold can be shared with the main mold. For example, the pre-resin layer of the pre-molded product formed in the pre-molded product preparation process is in close contact with the heating surface of the pre-molded mold. Therefore, even after the pre-molded product preparation process is completed and the pre-molded mold is opened, the pre-resin layer can remain attached to the heating surface. Thus, after opening the pre-molded mold, the portion of the pre-molded mold including the heating surface, i.e., the portion in contact with the pre-resin layer of the pre-molded product, can be used as part of the main mold, and the portion not including the heating surface can be replaced with the corresponding portion of the main mold. This allows the pre-molded product to be placed in the main mold and a space to fill the second foam particles between the pre-molded product and the main mold.

[0065] Furthermore, by using a mold configured to allow changes in the volume of the molding cavity, the mold can also be used as a pre-molding mold. For example, after forming a pre-molded product in the molding cavity of the mold during the pre-molded product preparation process, the volume of the molding cavity can be increased during the filling process to position the pre-molded product in the mold and to create a space between the pre-molded product and the mold for filling with second foam particles.

[0066] After placing the premolded product in the molding cavity of the mold in this manner, the remaining space in the molding cavity, that is, the space formed between the premolded product and the inner wall of the mold forming the molding cavity, is filled with second foam particles. The method of filling the space with the second foam particles is not particularly limited and can take various forms. For example, the space may be filled with the second foam particles with the mold completely clamped, or the second foam particles in the space may be compressed to a state greater than their natural state by methods such as cracking filling or compression filling. Furthermore, the space may be filled with second foam particles that have been pre-pressurized. By employing these filling methods or by applying internal pressure, pressure can be generated between the heated surface of the mold and the pre-resin layer in this molding process, making it easier to improve the appearance of the resin layer of the composite molded product.

[0067] The second foamed particles may be composed of a polypropylene resin, and their specific form can take various forms. For example, the second foamed particles may be composed of the same polypropylene resin as the first foamed particles, or they may be composed of a different polypropylene resin. Furthermore, the bulk density M2 of the second foamed particles may be the same as or different from the bulk density M1 of the first foamed particles. In addition, the average particle diameter based on the particle size distribution of the second foamed particles may be the same as or different from the average particle diameter based on the particle size distribution of the first foamed particles.

[0068] The second foamed particles may contain other resins or elastomers other than polypropylene resins, to the extent that they do not impair the objectives and effects of the present invention. Examples of resins other than polypropylene resins include thermoplastic resins other than polypropylene resins, such as polyethylene resins, polystyrene resins, polyamide resins, and polyester resins. Examples of elastomers include olefin-based thermoplastic elastomers and styrene-based thermoplastic elastomers. The proportion of polymers other than polypropylene resins in the second foamed particles is preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, and particularly preferably 0% by mass, that is, the second foamed particles contain only polypropylene resin as a polymer.

[0069] Furthermore, the polypropylene resin constituting the second foamed particles may contain additives such as foam regulators, nucleating agents, flame retardants, flame retardant aids, plasticizers, antistatic agents, antioxidants, UV inhibitors, light stabilizers, conductive fillers, antibacterial agents, and colorants, to the extent that they do not impair the effects described above. The amount of additives in the second foamed particles is preferably, for example, 0.01 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the polypropylene resin constituting the second foamed particles.

[0070] The bulk density M2 of the second foamed particle is 15 kg / m³ 3 More than 120kg / m3 The following conditions apply, and it is preferable that the ratio of the bulk density M2 of the second foamed particle to the bulk density M1 of the first foamed particle, M2 / M1, is less than 1.0. Second foamed particles having such a bulk density M2 tend to expand during the molding process because the volume of air bubbles within the foamed particles is large. Therefore, by performing the molding process using second foamed particles in which the bulk density M2 and the bulk density ratio M2 / M1 are both within the specified range, the pre-resin layer can be pressed more easily against the heated surface of the mold. As a result, the appearance of the resin layer in the composite molded body can be improved, and the thickness of the resin layer can be increased more easily while reducing variations in thickness.

[0071] From the perspective of further enhancing the aforementioned effects, the bulk density M2 of the second foamed particle should be 18 kg / m³. 3 More than 130kg / m 3 Preferably, it is 20 kg / m 3 More than 120kg / m 3 It is more preferable that the following conditions are met: 22 kg / m 3 More than 110kg / m 3 The following is even more preferable. The method for measuring the bulk density M2 of the second foamed particle is the same as the method for measuring the bulk density M1 of the first foamed particle described above, except that the second foamed particle is used instead of the first foamed particle.

[0072] From a similar viewpoint, the ratio M2 / M1 of the bulk density of the second foamed particle to the bulk density M1 of the first foamed particle is more preferably 0.8 or less, and even more preferably 0.6 or less. From the viewpoint of enhancing the aforementioned effects, there is no particular lower limit to the bulk density ratio M2 / M1, but it is preferable that the bulk density ratio M2 / M1 is, for example, 0.05 or more.

[0073] The second foamed particles are preferably composed of a polypropylene resin having a melt mass flow rate of 2 g / 10 min or more and less than 9 g / 10 min, measured under conditions of a temperature of 230°C and a load of 2.16 kg. Second foamed particles composed of such a polypropylene resin exhibit excellent secondary foaming properties. Therefore, by setting the melt mass flow rate of the polypropylene resin constituting the second foamed particles within the aforementioned specific range, the pre-resin layer can be more easily pressed against the heated surface of the mold during the molding process. As a result, the appearance of the resin layer in the composite molded article is improved, and the thickness of the resin layer can be increased more easily while reducing variations in thickness. From the viewpoint of further enhancing the above effects, the melt mass flow rate of the polypropylene resin constituting the second foamed particles is more preferably 4 g / 10 min or more and less than 9 g / 10 min, even more preferably 5 g / 10 min or more and less than 9 g / 10 min, and particularly preferably 6 g / 10 min or more and less than 9 g / 10 min.

[0074] The ratio of the melt mass flow rate of the polypropylene resin constituting the first foamed particle to the melt mass flow rate of the polypropylene resin constituting the second foamed particle is preferably 2 to 5, more preferably 2 to 4, even more preferably 2.5 to 3.9, and particularly preferably 3 to 3.8. In this case, it is possible to increase the thickness of the resin layer in the composite molded article more easily while reducing variations in thickness.

[0075] The melting point Tm2 (unit: °C) of the polypropylene resin constituting the second foamed particles is preferably 120 °C or higher, more preferably 125 °C or higher, even more preferably 127 °C or higher, and preferably 130 °C or higher. In this case, the release properties when manufacturing a composite molded article using the second foamed particles can be improved. Furthermore, the melting point Tm2 of the polypropylene resin constituting the second foamed particles is preferably 155 °C or lower, more preferably 150 °C or lower, even more preferably 145 °C or lower, and particularly preferably 140 °C or lower. The method for measuring the melting point Tm2 of the polypropylene resin constituting the second foamed particles is the same as the method for measuring the melting point Tm1 of the polypropylene resin constituting the first foamed particles described above, except that the polypropylene resin constituting the second foamed particles is used instead of the polypropylene resin constituting the first foamed particles.

[0076] The average particle diameter of the second foamed particles, based on the particle size distribution on a number basis, is preferably 1.0 mm or more and 7.0 mm or less, more preferably 2.0 mm or more and 6.0 mm or less, even more preferably 3.0 mm or more and 5.5 mm or less, and particularly preferably 3.3 mm or more and 5.0 mm or less. In this case, the packing ability of the second foamed particles can be further improved, and the secondary foaming ability of the second foamed particles in this molding process can be further enhanced. The method for measuring the particle size distribution on a number basis of the second foamed particles is the same as the method for measuring the particle size distribution on a number basis of the first foamed particles described above. Furthermore, the average particle diameter based on the number basis of the second foamed particles is specifically the arithmetic mean diameter in the particle size distribution on a number basis.

[0077] The ratio of the average particle diameter of the first foamed particles to the average particle diameter of the second foamed particles is preferably 0.2 or more and 1.5 or less, preferably 0.3 or more and 1.2 or less, and more preferably 0.4 or more and 0.8 or less. In this case, the secondary foaming properties of the second foamed particles can be made higher than those of the first foamed particles that constitute the foamed particle fusion body of the premolded product. As a result, the pre-resin layer can be pressed more easily against the heated surface of the mold in this molding process, making it easier to reduce variations in the thickness of the resin layer and to reduce defects in the resin layer.

[0078] The second foamed particle preferably has a crystalline structure in which, when heated from 23°C to 200°C at a heating rate of 10°C / min, the DSC curve obtained shows an endothermic peak due to the melting of crystals inherent to the polypropylene resin constituting the second foamed particle, and one or more melting peaks located at a higher temperature than this endothermic peak. The second foamed particle having such a crystalline structure has excellent mechanical strength and moldability.

[0079] Furthermore, the heat of fusion of the high-temperature peak of the second foamed particle is preferably 5 J / g or more and 40 J / g or less, more preferably 7 J / g or more and 30 J / g or less, and even more preferably 10 J / g or more and 20 J / g or less.

[0080] The method for obtaining the DSC curve of the second foamed particle and the method for measuring the heat of fusion of the high-temperature peak are the same as the method for obtaining the DSC curve of the first foamed particle and the method for measuring the heat of fusion of the high-temperature peak described above, except that the second foamed particle is used instead of the first foamed particle.

[0081] The method for producing the second foamed particles is not particularly limited, and known methods can be used, similar to those for the first foamed particles. For example, the second foamed particles may be produced by a direct foaming method or by an extrusion foaming method.

[0082] [Main molding process] In this molding process, a heating medium is supplied into the molding cavity of the mold, and the temperature of the heating surface of the mold is increased to melt the pre-molded resin layer. When a heating medium is supplied into the molding cavity of the mold in this molding process, the pre-molded product is pressed against the heating surface by the expansion of the second foam particles. Therefore, by melting the pre-molded resin layer and expanding the second foam particles, defects such as holes, minute bubbles, wrinkles, and unevenness that were present in the pre-molded product's pre-molded resin layer can be repaired. As a result, a resin layer with fewer defects and less variation in thickness can be formed on the surface of the composite molded product.

[0083] The resin layer formed in this molding process contains almost no cellular structures. The resin layer is formed when the pre-molded resin layer is pressed against the heating surface, causing holes, minute bubbles, and bubbles of the first foam particles present in the pre-molded resin layer to disappear.

[0084] In this molding process, the second foam particles in the molding cavity should be expanded while the pre-molded resin layer of the pre-molded product is molten. By expanding the second foam particles while the pre-molded resin layer is molten, the pre-molded resin layer can be pressed more firmly against the heating surface. As a result, defects present in the pre-molded resin layer can be repaired more easily, and variations in the thickness of the resin layer can be reduced. Therefore, as long as the above-described state can be achieved, the timing of raising the temperature of the heating surface and the timing of supplying the heating medium into the mold in this molding process may be simultaneous or different. Furthermore, the temperature of the heating surface in this molding process should be within a range that allows the pre-molded resin layer to melt to the extent that the resin layer of the composite molded product is formed and defects are repaired. In other words, in this molding process, the pre-molded resin layer does not necessarily need to be completely molten; it is sufficient that the pre-molded resin layer is softened to the extent that defects are repaired.

[0085] The specific embodiment of this molding process can take various forms. For example, in the first embodiment of this molding process, first, the temperature of the heating surface of the mold is increased to melt the pre-molded resin layer. Then, while the pre-molded resin layer is melted, a heating medium such as steam is supplied into the molding cavity of the mold to expand at least the second foam particles, thereby repairing defects originating from the pre-molded resin layer and reducing variations in the thickness of the resin layer. After that, the composite molded body inside the mold is cooled to stabilize its shape. As a result, a composite molded body with fewer defects and a resin layer with small variations in thickness can be obtained.

[0086] Furthermore, in this molding process, the heating medium can be supplied to the mold before the temperature of the heating surface rises. For example, in a second embodiment of this molding process, first, the heating medium is supplied to the molding cavity of the mold to expand at least the second foam particles. While the second foam particles are expanding, the temperature of the heating surface of the mold is raised to melt the pre-molded resin layer. After that, the composite molded body inside the mold is cooled to stabilize its shape. As a result, a composite molded body with fewer defects and a resin layer with less variation in thickness can be obtained.

[0087] Furthermore, the melt mass flow rate of the polypropylene resin constituting the resin layer of the composite molded body, measured under conditions of a temperature of 230°C and a load of 2.16 kg, is 9 g / 10 min or higher. By keeping the melt mass flow rate of the polypropylene resin constituting the resin layer of the composite molded body within the specified range, it is possible to reduce local variations in the thickness of the resin layer and eliminate defects in the resin layer, even when the thickness of the resin layer is relatively small. The melt mass flow rate of the polypropylene resin constituting the resin layer is a value measured under conditions of a test temperature of 230°C and a load of 2.16 kg, based on JIS K7210-1:2014.

[0088] As a method for adjusting the melt mass flow rate of the resin layer of the composite molded article to within the specified range, for example, a method of adjusting the melt mass flow rate of the polypropylene resin constituting the first foam particles can be employed. From the viewpoint of more easily adjusting the melt mass flow rate of the resin layer of the composite molded article to within the specified range, it is preferable to set the melt mass flow rate of the polypropylene resin constituting the first foam particles to 9 g / 10 min or more.

[0089] In this molding process, the difference T-Tm1 between the temperature T (unit: °C) of the heated surface and the melting point Tm1 (unit: °C) of the polypropylene resin constituting the first foamed particles is preferably between 10°C and 40°C. In this case, the first foamed particles can be easily melted when heated within the specified temperature range, and a resin layer with few defects can be formed on the surface of the composite molded article.

[0090] The method for heating the heating surface in a mold is not particularly limited and can take various forms, similar to the method for heating the heating surface in a pre-molded mold. For example, the mold may be configured to supply a heating medium such as steam to the heating surface from outside the molding cavity, thereby raising the temperature of the heating surface. Alternatively, the mold may have a heater for raising the temperature of the heating surface, and may be configured to raise the temperature of the heating surface by the heater.

[0091] (Polypropylene resin foam particle composite molded product) The polypropylene resin foam particle composite molded article obtained by the above manufacturing method comprises a foam particle molded article having a first foam layer formed by the fusion of the first foam particles with each other, a second foam layer formed by the fusion of the second foam particles with each other, and a resin layer made of polypropylene resin. The resin layer is integrated with the first foam layer. Furthermore, the resin layer is present in a part of the surface of the composite molded article.

[0092] The thickness of the resin layer in the composite molded article is 0.05 mm or more and 2 mm or less. In the above manufacturing method, as described above, the resin layer of the composite molded article is formed by pressing the pre-molded resin layer onto the heating surface using the expansion that occurs when the second foamed particles are heated with a heating medium in the main molding process. The resin layer of the composite molded article may be composed of, for example, a layer formed from the solidified molten material of the first foamed particles. In this case, the resin layer fills the recesses of the first foamed layer, integrating the foamed particle molded article and the resin layer. This easily avoids the uneven shape of the foamed layer affecting the surface of the composite molded article, and the surface of the composite molded article can be flattened by the resin layer. Furthermore, the surface of the resin layer has a shape that reflects the heating surface of the mold.

[0093] Thus, by utilizing the expansion of the second foam particles in this molding process, local variations in the thickness of the resin layer can be reduced, the strength of the resin layer can be improved, and the thickness of the resin layer can be easily reduced while ensuring the strength of the resin layer. As a result, the composite molded article is lightweight. From the viewpoint of lightweightness, the average thickness of the resin layer of the composite molded article is preferably 0.1 mm or more and 1.5 mm or less, and more preferably 0.2 mm or more and 1 mm or less.

[0094] The melt mass flow rate of the resin layer of the composite molded body measured under the conditions of a temperature of 230°C and a load of 2.16 kg is 9 g / 10 min or more. By keeping the melt mass flow rate of the resin layer of the composite molded body within the specified range, local variations in the thickness of the resin layer can be reduced even when the thickness of the resin layer is relatively small, and a composite molded body with a good surface appearance can be easily obtained. The melt mass flow rate of the resin layer is a value measured using a resin layer separated from the composite molded body by methods such as cutting as a sample, under the conditions of a test temperature of 230°C and a load of 2.16 kg, in accordance with JIS K7210-1:2014.

[0095] Furthermore, as a method for adjusting the melt mass flow rate of the resin layer of the composite molded body to within the specified range, for example, a method of adjusting the melt mass flow rate of the polypropylene resin constituting the first foam particles can be employed. From the viewpoint of more reliably adjusting the melt mass flow rate of the resin layer of the composite molded body to within the specified range, it is preferable that the first foam particles are composed of the polypropylene resin having a melt mass flow rate of 9 g / 10 min or more.

[0096] The first foam layer and the second foam layer in the composite molded article may be composed of foam particles of the same type. Such a composite molded article can be obtained, for example, by filling the molding cavity with second foam particles having the same composition as the first foam particles in the filling step of the manufacturing method and then performing the molding step.

[0097] Furthermore, the first foam layer and the second foam layer in the composite molded article may be composed of different types of foam particles. Such a composite molded article can be obtained, for example, by filling the molding cavity with second foam particles having a different composition from the first foam particles in the filling step of the manufacturing method described above.

[0098] Preferably, the first foam particles constituting the first foam layer are different from the second foam particles constituting the second foam layer. In this case, for example, foam particles with superior secondary foaming properties than the first foam particles can be used as the second foam particles. By using foam particles with superior secondary foaming properties as the second foam particles, the secondary foaming properties of the second foam particles in this molding process are further enhanced, local variations in the thickness of the resin layer are reduced, the strength of the resin layer is improved, and the thickness of the resin layer can be easily reduced while ensuring the strength of the resin layer.

[0099] The melt mass flow rate of the second foam layer, measured under conditions of a temperature of 230°C and a load of 2.16 kg, is preferably 3 g / 10 min to 18 g / 10 min, more preferably 4 g / 10 min to 12 g / 10 min, and even more preferably 5 g / 10 min to 9 g / 10 min. In this case, the lightweight properties and appearance of the composite molded article can be improved in a balanced manner. The melt mass flow rate of the second foam layer is a value measured using the second foam layer separated from the composite molded article by methods such as cutting as a sample, under conditions of a test temperature of 230°C and a load of 2.16 kg, in accordance with JIS K7210-1:2014. In addition, when measuring the melt mass flow rate of the second foam layer, it is also possible to use foam particles that have undergone degassing treatment to the extent that the physical properties of the resin are not significantly impaired as a measurement sample.

[0100] The ratio of the melt mass flow rate of the first foam layer to the melt mass flow rate of the second foam layer is preferably 1.5 or more and 6 or less, more preferably 1.7 or more and 5 or less, and even more preferably 2 or more and 4.5 or less. In this case, the lightweight properties and appearance of the resulting composite molded article can be improved in a more balanced manner.

[0101] The shape of the composite molded body is not particularly limited and can take various forms. For example, the composite molded body may have a flat plate shape or a bottomed box shape. The composite molded body may also comprise a flat plate portion and an upright portion erected from the flat plate portion. Furthermore, the resin layer may be provided on a part of the surface of the composite molded body.

[0102] The resin layer of the composite molded body preferably has a flat portion parallel to the mold clamping direction of the mold. As described above, the manufacturing method allows the entire resin layer of the pre-molded body to be efficiently pressed against the heating surface by expanding and fusing the second foamed particles in the molding process. Therefore, even when the heating surface is located in a part of the mold where it is difficult to generate pressure between it and the resin layer, that is, when the heating surface is located in a part corresponding to the flat portion of the composite molded body, defects in the flat portion can be reduced, and variations in the thickness of the flat portion can be reduced. As a result, defects can be easily reduced throughout the entire resin layer, including the flat portion.

[0103] Furthermore, the positional relationship referred to as "parallel" above includes both a positional relationship in which the mold clamping direction of the molding die and the flat portion are geometrically strictly parallel, and a positional relationship in which the flat portion is slightly inclined from a geometrically parallel positional relationship. In other words, the flat portion may have a positional relationship that is strictly parallel to the mold clamping direction of the molding die, or it may have a positional relationship that is generally considered parallel. The angle between the surface of the flat portion and the direction parallel to the mold clamping direction of the molding die may be, for example, within 5°.

[0104] From the viewpoint of making more effective use of such effects, it is preferable that the composite molded body has a bottomed box shape having a bottom plate and side plates erected from the edge of the bottom plate, and that the resin layer is provided on at least one of the inner surface facing the space inside the box or the outer surface facing the space outside the box. As described above, according to the manufacturing method, it is possible to form a resin layer with few defects on both the surface perpendicular to the mold clamping direction and the surface along the mold clamping direction of the composite molded body. Therefore, the manufacturing method can easily reduce defects in the resin layer even when forming a resin layer on the inner or outer surface of a composite molded body having a bottomed box shape.

[0105] The maximum thickness of the composite molded article is preferably 8 mm to 100 mm, more preferably 10 mm to 80 mm, and even more preferably 15 mm to 60 mm. In this case, the overall fusion properties of the composite molded article can be improved. Furthermore, even when the composite molded article is manufactured using first foamed particles with a relatively high bulk density, the overall weight of the composite molded article can be reduced. [Examples]

[0106] (Example 1) An example of the manufacturing method for the composite molded body described above will be explained with reference to Figures 2 to 8. The composite molded body 1 obtained by the manufacturing method of this example has a bottomed box shape, as shown in Figures 2 and 3, and comprises a bottom plate 11 and side plates 12 erected from the edge of the bottom plate 11. The outer dimensions of the composite molded body 1 in the vertical direction are 365 mm, the outer dimensions in the horizontal direction are 440 mm, and the outer dimensions in the height direction are 177 mm. The thickness of the bottom plate 11 is 20 mm, and the thickness of the side plates 12 is 25 mm.

[0107] Furthermore, the bottom plate 11 and the side plate 12 each have a foamed particle molded body 100 comprising a second foamed layer 3 exposed to the external space of the composite molded body 1 and a first foamed layer 2 arranged adjacent to the second foamed layer 3, and a resin layer 4 provided on a part of the surface of the foamed particle molded body 100 in an integrated state with the first foamed layer 2. Both the first foamed layer 2 and the second foamed layer 3 have the maximum thickness on the side plate 12 of the composite molded body 1. The maximum thickness of the first foamed layer 2 is 3 mm, and the maximum thickness of the second foamed layer 3 is 22 mm. The first foamed layer 2 is composed of a plurality of polypropylene resin first foamed particles fused together. The second foamed layer 3 is composed of a plurality of polypropylene resin second foamed particles fused together.

[0108] The first foam layer 2 and the second foam layer 3 are fused together, thereby integrating them into a single unit. Furthermore, the first foam layer 2 and the resin layer 4 are fused together, thereby integrating the foam particle molded body 100 and the resin layer 4 into a single unit. Thus, the composite molded body 1 is formed by the integration of the first foam layer 2, the second foam layer 3, and the resin layer 4.

[0109] As shown in Figure 3, the resin layer 4 is provided on the inner surfaces of the bottom plate 11 and the side plates 12, that is, on the surfaces facing the internal space of the box of the composite molded body 1. In this example, the resin layer 4 has a flat portion 41 formed on the inner surface of the bottom plate 11 and a flat portion 42 formed on the inner surface of the side plate 12.

[0110] In the manufacture of the composite molded body 1 in this example, a mold 5 is used, which comprises a first mold 51 and a second mold 52, as shown in Figure 4, and is configured to form a molding cavity 50 having a shape corresponding to the composite molded body 1 between the first mold 51 and the second mold 52. When the mold 5 is completely closed, the molding cavity 50 consists of a space enclosed by the inner wall 510 of the first mold 51 and the inner wall 520 of the second mold 52. The mold 5 also has a heating surface 524 on a part of the surface of the inner walls 510 and 520 that form the molding cavity 50. A more detailed configuration of the mold 5 will be described below.

[0111] The first mold 51 has a hollow structure and includes a first steam supply valve 511 that supplies steam as a heating medium into the first mold 51, a first drain valve 512 that discharges the steam supplied into the first mold 51 to the outside of the first mold 51, and a foam particle supply unit 513 that supplies first foam particles and second foam particles into the molding cavity 50.

[0112] Furthermore, the portion of the first mold 51 facing the molding cavity 50 is provided with a recess 514 having a shape corresponding to the outer surface of the composite molded body 1, that is, the surface facing the space outside the box. Although not shown in the figure, the recess 514 is provided with a slit for guiding the steam supplied from the first steam supply valve 511 into the molding cavity 50.

[0113] The second mold 52 has a hollow structure and includes a second steam supply valve 521 that supplies steam as a heating medium into the second mold 52, and a second drain valve 522 that discharges the steam supplied into the second mold 52 to the outside of the second mold 52.

[0114] The portion of the second mold 52 facing the molding cavity 50 is provided with a protrusion 523 having a shape corresponding to the inner surface of the composite molded body 1. In this example, the heating surface 524 of the mold 5 is provided on the surface of the protrusion 523 on the inner wall 520 of the second mold 52. The mold 5 is configured so that the temperature of the heating surface 524 can be increased by heating the protrusion 523 with steam supplied from the second steam supply valve 521.

[0115] [Method for manufacturing composite molded articles] Next, the manufacturing method of the composite molded body 1 in this example will be described. In manufacturing the composite molded body 1, first, as shown in Figure 5, a spacer 515 was placed in the recess 514 of the first mold 51, and then the first mold 51 and the second mold 52 were combined to close the mold 5. Specifically, the spacer 515 in this example has a shape corresponding to the second foam layer 3 of the composite molded body 1 and is provided with a slit (not shown) for steam to pass through. Therefore, by placing the spacer 515 in the first mold 51, the volume of the molding cavity 50 can be reduced, and a pre-molding cavity 50a having a shape corresponding to the first foam layer 2 of the composite molded body 1 can be formed between the first mold 51 and the second mold 52. In this example, the mold 5 in which the spacer 515 was placed in this manner was used as a pre-molding mold 501, and a pre-molded product was manufactured by in-mold molding (pre-molded product preparation step).

[0116] • Fabrication of preforms After constructing the pre-molding mold 501 shown in Figure 5, the first foamed particles 200 were filled into the pre-molding cavity 50a as shown in Figure 6. Note that, for convenience, some of the first foamed particles 200 are omitted from Figure 6. The first foamed particles 200 used in this example are made of a polypropylene resin having the melting point and melt mass flow rate shown in Table 1. The high-temperature peak heat of fusion, bulk density M1, and average particle diameter of the first foamed particles 200 are also shown in Table 1. In this example, the first foamed particles 200 were filled by cracking.

[0117] Next, the second steam supply valve 521 and the second drain valve 522 were opened, and steam was supplied into the second mold 52 from the second steam supply valve 521. This raised the temperature of the heating surface 524 to the temperature shown in Table 1, melting the first foamed particles 200 near the heating surface 524 and forming the preliminary resin layer 40.

[0118] Furthermore, while the first foam particles 200 near the heating surface 524 were melting, the first steam supply valve 511 and the first drain valve 512 were opened, and steam was supplied from the first steam supply valve 511 into the first mold 51, while the first foam particles 200 in the pre-molding cavity 50a were heated by the steam. The first foam particles 200 were then fused together to form a foam particle fused body 20. The pressure of the steam supplied into the first mold 51 was as shown in the "Molding Pressure" column of Table 1.

[0119] After the foam particle fusion body 20 was formed in the pre-molding cavity 50a, the supply of steam from the first steam supply valve 511 and the second steam supply valve 521 was stopped. Then, cooling water was supplied from the first steam supply valve 511 and the second steam supply valve 521 to cool the pre-resin layer 40 and the foam particle fusion body 20 and stabilize their shapes. With this, the pre-molded product preparation process was completed and the pre-molded product 10 was obtained. The pre-molded product 10 has a foam particle fusion body 20 formed by the fusion of first foam particles with each other, and a pre-resin layer 40 formed on the surface of the pre-molded product 10 in the portion that was in contact with the heated surface 524.

[0120] ·Filling process After preparing the pre-molded product as described above, the first mold 51 was separated from the second mold 52 while maintaining the state in which the pre-resin layer 40 of the pre-molded product 10 was attached to the heating surface 524 of the second mold 52. Then, after removing the spacer 515 from inside the first mold 51, the first mold 51 and the second mold 52 were reassembled to close the mold 5. As a result, as shown in Figure 6, the pre-molded product 10 was placed inside the molding cavity 50 of the mold 5 with the pre-resin layer 40 in contact with the heating surface 524.

[0121] Subsequently, as shown in Figure 7, the second foam particles 300 were filled into the space formed between the pre-molded product 10 and the mold 5 in the molding cavity 50 of the mold 5. Note that, for convenience, some of the second foam particles 300 are omitted from Figure 7. The second foam particles 300 used in this example are composed of a polypropylene resin having the melting point and melt mass flow rate shown in Table 1. The high-temperature peak heat of fusion, bulk density M2, and average particle diameter of the second foam particles 300 are also shown in Table 1. In this example, the second foam particles 300 were filled by compression filling. After filling was complete and the second foam particles 300 in the molding cavity 50 were restored within the molding cavity 50, they were in a more compressed state than their natural state.

[0122] ·Main molding process After the filling process was completed, the molding process was carried out as follows. First, the second steam supply valve 521 and the second drain valve 522 were opened, and steam was supplied into the second mold 52 from the second steam supply valve 521. This raised the temperature of the heating surface 524 to the temperature shown in Table 1, melting the pre-molded product 10's pre-resin layer 40.

[0123] Furthermore, while the preliminary resin layer 40 was melting, the first steam supply valve 511 and the first drain valve 512 were opened, and steam was supplied from the first steam supply valve 511 into the first mold 51. At the same time, the second foam particles 300 in the molding cavity 50 and the first foam particles of the foam particle fusion body 20 were heated by the steam. The second foam particles 300 and the first foam particles were then expanded and fused together. As a result, the second foam layer 3 was formed, and the preliminary molded product 10 and the second foam layer 3 were integrated to form a composite molded body 1 comprising a resin layer 4, a first foam layer 2 derived from the foam particle fusion body 20, and a second foam layer 3. The pressure of the steam supplied into the first mold 51 was as shown in the "Molding Pressure" column of Table 1.

[0124] After the composite molded body 1 was formed in the molding cavity 50, the supply of steam from the first steam supply valve 511 and the second steam supply valve 521 was stopped. Subsequently, cooling water was supplied from the first steam supply valve 511 and the second steam supply valve 521 to cool the resin layer 4, the first foam layer 2, and the second foam layer 3 and stabilize their shapes. This completed the molding process.

[0125] (Examples 2-3) In these examples, composite molded articles were prepared in essentially the same manner as in Example 1, except that the bulk density M2 of the second foamed particles was changed as shown in Table 1.

[0126] (Examples 4-5) In these examples, composite molded articles were prepared in essentially the same manner as in Example 2, except that the bulk density M1 and average particle diameter of the first foamed particles were changed as shown in Table 2.

[0127] (Examples 6-7) In these examples, composite molded articles were prepared in generally the same manner as in Example 2, except that the melt mass flow rate of the polypropylene resin constituting the first foamed particles was changed as shown in Table 2.

[0128] (Comparative Example 1) In Comparative Example 1, a composite molded article was prepared in essentially the same manner as in Example 2, except that the melt mass flow rate of the polypropylene resin constituting the first foamed particles, the bulk density M1 of the first foamed particles, and the average particle size of the first foamed particles were changed as shown in Table 3.

[0129] (Comparative Example 2) In Comparative Example 2, a composite molded article was prepared in essentially the same manner as in Example 2, except that the polypropylene resin constituting the first foamed particles was changed as shown in Table 3.

[0130] (Comparative Example 3) The molded article of Comparative Example 3 is composed solely of first foam particles. The manufacturing method of the molded article of Comparative Example 3 is generally the same as that of Comparative Example 1, except that no pre-molded product is made, and the first foam particles are filled into the mold 5 to perform the main molding process.

[0131] The composite molded articles obtained in this manner were used to evaluate the various properties shown in Tables 1 to 3. The evaluation methods for each item shown in Tables 1 to 3 are as follows.

[0132] (Melting point of polypropylene resins) Differential scanning calorimetry (DSC) was performed in accordance with JIS K7121-1987, and the melting point of the polypropylene resin constituting each foam particle was measured based on the acquired DSC curve. Specifically, test specimens made of polypropylene resin were prepared, and the specimens were conditioned according to "(2) When measuring the melting temperature after performing a certain heat treatment." The heating and cooling rates in conditioning were set to 10°C / min, and the temperature range was from 30°C to 200°C. The DSC curve was obtained by raising the temperature of the conditioned specimens from 30°C to 200°C at a heating rate of 10°C / min. The peak temperature of the melting peak that appeared in the DSC curve was taken as the melting point of the polypropylene resin. If multiple melting peaks appeared in the DSC curve, the peak temperature of the melting peak with the largest area was taken as the melting point.

[0133] (Heat of fusion at high temperature peak of polypropylene resin) Following the method described above, the heat of fusion of the high-temperature peak of the polypropylene resin constituting each foam particle was measured.

[0134] (Meltmass flow rate of polypropylene resin) Based on JIS K7210-1:2014, the melt mass flow rate (MFR1) of the polypropylene resin constituting the first foamed particle and the melt mass flow rate (MFR2) of the polypropylene resin constituting the second foamed particle were measured under the conditions of a test temperature of 230°C and a load of 2.16 kg.

[0135] (Bulk density of foamed particles) Each foamed particle was allowed to stand for 24 hours under conditions of 50% relative humidity, 23°C, and 1 atm to adjust its state. Next, the adjusted foamed particles were filled into a graduated cylinder so that they would naturally accumulate, and the bulk volume (in L) of the foamed particles in the graduated cylinder was read from the scale on the cylinder. Then, the mass (in g) of the foamed particles in the graduated cylinder was divided by the aforementioned bulk volume, and the bulk density M1 of the first foamed particle and the bulk density M2 (in kg / m³) of the second foamed particle were obtained by further unit conversion. 3 ) was calculated.

[0136] (Average particle size of foaming particles) Approximately 3,000 first or second foamed particles were used as measurement samples, and the volume-based particle size distribution of each foamed particle was measured using a particle size distribution analyzer ("Millitrack JPA" manufactured by Nikkiso Co., Ltd.). Based on this particle size distribution, the particle shape was assumed to be spherical, and the distribution was converted to a number-based particle size distribution to obtain the number-based particle size distribution. The arithmetic mean diameter based on this number-based particle size distribution was defined as the average particle diameter D1 of the first foamed particles and the average particle diameter D2 of the second foamed particles.

[0137] (Thickness of the resin layer) The flat portions 41 and 42 of the resin layer 4 of the composite molded body 1 (i.e., the portions of the resin layer 4 excluding corners, etc.) were cut in the thickness direction to expose the cut surface. Magnified photographs of these cut surfaces were taken, and the thickness of the resin layer 4 shown in the magnified photographs was measured at multiple locations. As an example, Figure 9 shows a magnified photograph of the cut surface of the bottom plate 11 of the composite molded body 1 of Example 3. The bottom plate 11 has a second foam layer 3 exposed on the bottom surface of the composite molded body 1, a first foam layer 2 adjacent to the second foam layer 3, and a flat portion 41 of the resin layer 4 provided on the first foam layer 2. In such magnified photographs, more than 10 measurement positions were randomly selected, and the arithmetic mean of the thickness of the resin layer 4 at these measurement positions was taken as the thickness of the resin layer in each magnified photograph. The above operation was then performed for more than 5 locations on the composite molded body, and the arithmetic mean of the thickness of the resin layer in 5 magnified photographs was taken as the average thickness of the resin layer.

[0138] (Meltmass flow rate of the resin layer) The resin layer 4 was separated from the composite molded body 1 by cutting it. The melt mass flow rate (MFR(R)) of this resin layer 4 was measured according to JIS K7210-1:2014 under the conditions of a test temperature of 230°C and a load of 2.16 kg.

[0139] (Meltmass flow rate of the second foam layer) The second foam layer 3 was separated from the composite molded body 1 by cutting it. The melt mass flow rate (MFR(S)) of this second foam layer 3 was measured according to JIS K7210-1:2014 under the conditions of a test temperature of 230°C and a load of 2.16 kg.

[0140] (Surface properties of the resin layer) For each of the flat portions 41 on the bottom plate 11 and 42 on the side plate 12 of the resin layer 4, magnified photographs were obtained by photographing the surface at a magnification of 100 to 200 times. The appearance of each flat portion was evaluated by visually observing these magnified photographs. As an example, Figure 10 shows a magnified photograph taken at a magnification of 200 times of the surface of the resin layer 4 in the composite molded body E1 obtained by the manufacturing method of Example 1. Also, Figure 11 shows a magnified photograph taken at a magnification of 200 times of the surface of the resin layer 4 in the composite molded body C1 obtained by the manufacturing method of Comparative Example 1. In the "Surface Properties" column of Tables 1 to 3, the symbol "A" is written if the flat portion has a smooth surface and there are no defects such as holes, bubbles, wrinkles, or unevenness; the symbol "B" is written if slight defects are found in the flat portion; and the symbol "C" is written if obvious defects are found in the flat portion.

[0141] (Density of composite molded material) The mass (in kg) of composite molded body 1 is calculated from the volume (in m³) of composite molded body 1 based on its external dimensions. 3 By dividing by ), the density of the composite molded body (unit: kg / m³) can be calculated. 3 ) was obtained.

[0142] (Water leak resistance) To evaluate defects in the resin layer of a composite molded body that cannot be visually confirmed, a leak resistance test was performed by filling the box of composite molded body 1 with either water or a 2% by mass aqueous solution of a surfactant, and leaving it for 24 hours. In the "Leak Resistance" column of Tables 1 to 3, "Excellent" was written if the water level did not change after 24 hours and no leaks were confirmed, regardless of whether water or the surfactant aqueous solution was used; "Good" was written if the water level did not change when water was used, but decreased when the surfactant aqueous solution was used; and "Poor" was written if the water level decreased and leaks were confirmed, regardless of whether water or the surfactant aqueous solution was used.

[0143] [Table 1]

[0144] [Table 2]

[0145] [Table 3]

[0146] As shown in Tables 1 and 2, in Examples 1 to 7, a premolded product was prepared using the first foamed particles, and then the main molding process was carried out with the second foamed particles filling the area around the foamed particle fused body in the premolded product. Furthermore, the melt mass flow rate of the resin layer in these examples was within the specified range. Therefore, in these examples, the expansion of the second and first foamed particles during the main molding process repaired defects present in the premolded resin layer, and a resin layer with few defects was formed on the surface of the composite molded product.

[0147] Furthermore, the heating surface 524 in the mold 5 used in these embodiments is provided on the protrusion 523 of the second mold 52, as shown in Figure 4. Also, the portion of the surface of the protrusion 523 that contacts the side plate 12 of the composite molded body 1 is parallel to the clamping direction of the mold 5. Therefore, according to these embodiments, even in portions having surfaces parallel to the clamping direction of the mold 5, such as the flat portion 42 formed on the inner surface of the side plate 12, defects in the resin layer 4 can be reduced, as shown in Figure 10.

[0148] In contrast, as shown in Table 3, the melt mass flow rate of the resin layer in Comparative Example 1 is lower than the specified range. As a result, large defects 43 were formed in the resin layer of the composite molded article obtained by the manufacturing method of Comparative Example 1, as shown in Figure 11 as an example. This is thought to be because the fluidity of the molten resin layer and the first foam particles in this molding process was low, and defects that existed in the pre-molded resin layer were not sufficiently repaired.

[0149] In Comparative Example 2, first foamed particles with a higher bulk density M1 than those used in Comparative Example 1 were used, but the defects present in the pre-molded resin layer could not be adequately repaired.

[0150] In Comparative Example 3, the main molding process was performed without using a pre-molded product, resulting in numerous defects in the resin layer of the molded body obtained after in-mold molding. This is thought to be because the secondary foaming properties of the first foam particles were relatively low, resulting in insufficient force pressing the first foam particles against the heating surface during the main molding process.

[0151] Although embodiments of the method for manufacturing the polypropylene-based resin foam particle composite molded article have been described above based on the examples, the specific embodiments of the method for manufacturing the polypropylene-based resin foam particle composite molded article according to the present invention are not limited to the embodiments described in the examples, and the configuration can be appropriately changed without impairing the spirit of the present invention. [Explanation of symbols]

[0152] 10 Preformed parts 4 resin layer 40. Pre-resin layer 20 Foamed particle fusion body 300 Second foaming particles 5 Molding mold 50 molded cavities 524 Heating surface

Claims

1. A method for manufacturing a polypropylene-based resin foam particle composite molded body, wherein the polypropylene-based resin foam particle composite molded body having a resin layer on a part of its surface is manufactured using a mold having a molding cavity having a shape corresponding to the shape of the composite molded body, and a heating surface provided on a part of the surface of the inner wall forming the molding cavity, A premolding preparation step involves preparing a premolding product which is composed of a foam particle fused body formed by the fusion of first foam particles of polypropylene resin with each other, and a pre-resin layer made of polypropylene resin is provided on a part of the surface of the foam particle fused body. A filling step is to place the premolded object in the molding cavity with the heating surface and the pre-resin layer of the premolded object in contact, and then fill the remaining space of the molding cavity with polypropylene resin second foam particles. The molding process includes supplying a heating medium into the molding cavity, further foaming the foam particle fusion body and the second foam particles, fusing them together to form a foam particle molded body, and raising the temperature of the heating surface to melt the pre-resin layer of the pre-molded material and at least a portion of the first foam particles to form the resin layer and obtain the composite molded body. A method for producing a polypropylene resin foam particle composite molded article, wherein the melt mass flow rate of the polypropylene resin constituting the resin layer of the composite molded article is 9 g / 10 min or more, as measured under conditions of a temperature of 230°C and a load of 2.16 kg.

2. In the preform preparation step, a preform mold is prepared that includes a preform cavity having a shape corresponding to the shape of the preform, and a heating surface provided on a part of the surface of the inner wall forming the preform cavity. The first foamed particles are filled into the pre-molded cavity. A method for producing a polypropylene-based resin foam particle composite molded article according to claim 1, comprising supplying a heating medium into the molding cavity of the pre-molding mold, further foaming the first foam particles and fusing them together to form the foam particle fused body, and raising the temperature of the heating surface of the pre-molding mold to melt at least a portion of the first foam particles and form the pre-resin layer.

3. The bulk density M1 of the first foamed particle is 30 kg / m³. 3 More than 450kg / m 3 The following conditions apply, and the bulk density M2 of the second foamed particle is 15 kg / m³. 3 More than 120kg / m 3 A method for producing a polypropylene resin foam particle composite molded article according to claim 1 or 2, wherein the ratio M2 / M1 of the bulk density M2 of the second foam particle to the bulk density M1 of the first foam particle is less than 1.

0.

4. A method for producing a polypropylene resin foam particle composite molded article according to claim 1 or 2, wherein the first foam particles are composed of a polypropylene resin having a melt mass flow rate of 9 g / 10 min or more, measured under conditions of a temperature of 230°C and a load of 2.16 kg, the second foam particles are composed of a polypropylene resin having a melt mass flow rate of 2 g / 10 min or more and less than 9 g / 10 min, measured under conditions of a temperature of 230°C and a load of 2.16 kg, and the ratio of the melt mass flow rate of the polypropylene resin constituting the first foam particles to the melt mass flow rate of the polypropylene resin constituting the second foam particles is 2 or more and 5 or less.

5. A method for producing a polypropylene resin foam particle composite molded article according to claim 1 or 2, wherein the difference T-Tm1 between the temperature T (unit: °C) of the heated surface in the molding step and the melting point Tm1 (unit: °C) of the polypropylene resin constituting the first foam particle is 10°C or more and 40°C or less.

6. A method for producing a polypropylene resin foam particle composite molded article according to claim 1 or 2, wherein the average particle diameter based on the particle size distribution on a number basis of the first foam particles is 1 mm or more and 4 mm or less.

7. The method for manufacturing a polypropylene-based resin foam particle composite molded article according to claim 1 or 2, wherein the resin layer of the composite molded article has a flat portion parallel to the mold clamping direction of the mold.

8. The method for manufacturing a polypropylene-based resin foam particle composite molded article according to claim 1 or 2, wherein the composite molded article has a bottomed box shape having a bottom plate and side plates erected from the edge of the bottom plate, and the resin layer of the composite molded article is provided on at least one of the inner surface facing the space inside the box and the outer surface facing the space outside the box of the composite molded article.

9. A polypropylene resin foam particle composite molded body comprising a foam particle molded body having a first foam layer formed by the fusion of first foam particles of polypropylene resin with each other, a second foam layer formed by the fusion of second foam particles of polypropylene resin with each other, and a resin layer made of polypropylene resin, The resin layer is integrated with the first foam layer and is provided on a part of the surface of the composite molded body. The average thickness of the aforementioned resin layer is 0.05 mm or more and 2 mm or less. A polypropylene-based resin foam particle composite molded article, wherein the melt mass flow rate of the resin layer, measured under conditions of a temperature of 230°C and a load of 2.16 kg, is 9 g / 10 min or more.

10. The density of the aforementioned composite molded body is 20 kg / m³. 3 More than 150kg / m 3 The polypropylene resin foam particle composite molded article according to claim 9, which is as follows:

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