Resin for foam molding, method for manufacturing foamed molded products

Abstract

To provide a method for producing a resin for foam molding which has excellent foam moldability, where a polypropylene-based resin having no long-chain branch structure can be used.SOLUTION: A method for producing a resin for foam molding includes a step of melting and kneading a raw material resin 4 containing a polypropylene-based resin and low density polyethylene using an extruder 2, wherein the extruder has a cylinder 2a to which the raw material resin is charged and a screw 2b rotatably arranged in the cylinder; the screw has a central part and a flight part; the central part extends along a rotation axis of the screw; the flight part is provided so as to project to the radial outside from the central part; the flight part has such a shape as to convey the raw material resin toward the tip of the screw along with rotation of the screw; and when a diameter of the flight part in the screw is represented by D, and an area of the flight surface facing the inner surface of the cylinder in the flight part is represented by S, S / D is 800-1,500.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a resin for foam molding, a method for producing the same, and a method for producing a foamed molded article. [Background technology]

[0002] As examples of foamed molded products, various air conditioning ducts installed in the instrument panels of automobiles are well known. Foamed ducts, which are molded from foamed resin materials, are widely used for these air conditioning ducts. Foamed ducts are lightweight and can be easily manufactured by adding a foaming agent to a resin material such as polyolefin resin, melt-kneading it, and blow-molding the foamed parison extruded from the die of an extruder.

[0003] Polyolefin resins are widely used as resin materials for foamed molded articles, and among them, polypropylene resins are the most common (Patent Document 1).

[0004] Patent Document 1 discloses a foamed molded article obtained by blow molding a mixture of long-chain branched homopolypropylene, long-chain branched block polypropylene, and polyethylene-based elastomer, to which a foaming agent is added. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2018-141031 [Overview of the project] [Problems that the invention aims to solve]

[0006] Incidentally, most commercially available polypropylene and block polypropylene do not have a long-chain branched structure, and long-chain branched homopolypropylene and long-chain branched block polypropylene can be expensive or difficult to obtain. Therefore, it is desirable to manufacture foamed molded articles using polypropylene that does not have a long-chain branched structure.

[0007] On the other hand, polypropylene resins that do not have a long-chain branched structure do not have a three-dimensional network structure, so when foamed molded articles are manufactured using such polypropylene resins, there is a problem that bubbles tend to burst on the surface and bubbles coalesce together.

[0008] This invention has been made in view of these circumstances, and provides a method for producing a foam molding resin that can be used with polypropylene resins that do not have a long-chain branched structure and has excellent foam molding properties. [Means for solving the problem]

[0009] The present invention provides a method for producing a foam molding resin, comprising the step of melt-kneading a raw material resin containing a polypropylene resin and low-density polyethylene using an extruder, wherein the content of the low-density polyethylene relative to the total of the polypropylene resin and the low-density polyethylene is 20 to 50% by mass, the extruder comprises a cylinder into which the raw material resin is fed, and a screw rotatably disposed within the cylinder, the screw comprises a central portion and a flight portion, the central portion extends along the rotation axis of the screw, the flight portion is provided so as to protrude radially outward from the central portion, the flight portion is shaped to convey the raw material resin toward the tip of the screw as the screw rotates, and if the diameter of the screw at the flight portion is D and the area of ​​the flight surface of the flight portion facing the inner surface of the cylinder is S, then S / D is 800 to 1500.

[0010] The inventors first focused on the fact that low-density polyethylene (hereinafter referred to as "LDPE") has a long-chain branched structure, and considered mixing polypropylene (hereinafter referred to as "PP") resin with LDPE. In fact, they used an extruder to melt-knead the raw material resin containing PP resin and LDPE to produce a foam molding resin, and then used the obtained foam molding resin to produce a foamed molded article. However, the resulting foamed molded article had many broken bubbles on the surface, and the foaming moldability of the foam molding resin obtained by this method was not good.

[0011] An investigation into the reasons for the poor foaming moldability revealed that PP resin and LDPE have low compatibility, and therefore, in commonly used extruders, the two are not sufficiently mixed. Consequently, the effect of adding LDPE on improving foaming moldability was limited.

[0012] Based on this finding, a foam molding resin was produced by melt-kneading raw resins containing PP-based resin and LDPE using an extruder with a screw having an S / D ratio of 800 to 1500, and a foam molded article was produced using the obtained foam molding resin. The obtained foam molded article showed fewer surface bubbles, indicating that the foam molding resin obtained by this method has excellent foam moldability, leading to the completion of the present invention.

[0013] The following are examples of various embodiments of the present invention. The embodiments shown below can be combined with each other. Preferably, the foam molding resin is composed of a raw material resin containing a polypropylene resin and low-density polyethylene, wherein the content of the low-density polyethylene relative to the total of the polypropylene resin and the low-density polyethylene is 20 to 50% by mass, the foam molding resin has a melt flow rate of 3.20 to 3.80 g / 10 min, and a melt tension of 35 to 90 mN. Preferably, the method for manufacturing a foamed molded article comprises the steps of forming a foamed parison using a foamed molding resin manufactured by the method described above, and molding the foamed parison to obtain a foamed molded article. Preferably, the method described above, wherein the molding is blow molding or vacuum molding.

Brief Description of the Drawings

[0014] [Figure 1] An example of a foam molding machine 1 that can be used in the method for manufacturing a foam molded body according to an embodiment of the present invention is shown. [Figure 2] FIG. 2A is an enlarged view of region A in FIG. 1, and FIG. 2B is a view excluding the cylinder 2a from FIG. 2A.

Embodiments for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be described. Various characteristic matters shown in the following embodiments can be combined with each other. Also, an invention can be established independently for each characteristic matter.

[0016] 1. Method for Producing Resin for Foam Molding Using FIG. 1, the method for producing a resin for foam molding according to an embodiment of the present invention will be described. This method includes a step of melt-kneading a raw material resin 4 containing a PP-based resin and LDPE using an extruder. Hereinafter, each component will be described in detail.

[0017] <Raw Material Resin 4> The raw material resin 4 contains a PP-based resin and LDPE. The raw material resin 4 may contain only a PP-based resin and LDPE, or may contain other resins. The ratio of the PP-based resin and LDPE in the raw material resin 4 is, for example, 60% by mass or more. This ratio is, for example, 60 to 100% by mass, specifically, for example, 60, 65, 70, 75, 80, 85, 90, 95, 100% by mass, and may be within the range between any two of the values exemplified here. Various additives (nucleating agents, colorants, antioxidants, etc.) may be added to the raw material resin 4. The content of the additive is preferably 10 parts by mass or less with respect to 100 parts by mass of the resin.

[0018] <PP-Based Resin> PP-based resin is a resin whose main component is PP. The proportion of propylene units in the monomer units constituting the PP-based resin is 60% by mass, preferably 80% by mass or more. This proportion is, for example, 60 to 100% by mass, specifically, for example, 60, 65, 70, 75, 80, 85, 90, 95, and 100% by mass, and may be within the range of any two of the values ​​exemplified here, or greater than or equal to either of them.

[0019] The PP resin may be a homopolymer of propylene (i.e., homopolypropylene), a copolymer of propylene and another olefin (such as ethylene) (random copolymer or block copolymer; hereinafter, random copolymer will be referred to as "random polypropylene" and block copolymer as "block polypropylene"), or a mixture thereof. From the viewpoint of heat resistance, the PP resin is preferably homopolypropylene or block polypropylene.

[0020] PP resins may have a long-chain branched structure, but the present invention is characterized by the fact that good foam moldability is achieved even when the PP resin does not have a long-chain branched structure. Therefore, the technical significance of applying the present invention when the PP resin does not have a long-chain branched structure is remarkable. Furthermore, when the PP resin has a long-chain branched structure, main chain splitting due to shear and oxidative degradation is likely to occur, so it is preferable that the PP resin does not have a branched structure.

[0021] The degree of long-chain branching in PP resins can be evaluated using the branching index g'. g' is given by the ratio of the intrinsic viscosity [η]br of the polymer under evaluation to the intrinsic viscosity [η]lin of a linear polymer having the same molecular weight as the polymer under evaluation, i.e., [η]br / [η]lin. The definition is described, for example, in "Developments in Polymer Characterization-4" (JV Dawkinsed. Applied Science Publishers, 1983), and is a well-known index to those skilled in the art. The smaller the value of g', the more pronounced the degree of long-chain branching.

[0022] The g' value of the PP resin is, for example, 0.95 or higher, and preferably between 0.95 and 1.00. Specifically, this value may be, for example, 0.95, 0.96, 0.97, 0.98, 0.99, or 1.00, and may be within the range of any two of the values ​​exemplified here.

[0023] The melt tension (hereinafter referred to as "MT") of PP resin is not particularly limited, but the MT tends to be lower when the PP resin does not have a long-chain branched structure, so the technical significance of applying the present invention when the MT is low is remarkable. From this viewpoint, the MT of the PP resin is preferably 100 mN or less, and more preferably 50 mN or less. This MT is, for example, 1 to 100 mN, specifically, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 mN, and may be within the range between any two of the values ​​exemplified here or less than or equal to any two of them. In this specification, MT refers to the tension obtained when a strand is extruded from an orifice with a diameter of 2.095 mm and a length of 8 mm using a melt tension tester (manufactured by Toyo Seiki Seisakusho Co., Ltd.) at a test temperature of 230°C and an extrusion speed of 10 mm / min, and this strand is wound onto a roller with a diameter of 80 mm at a winding speed of 16 rpm.

[0024] The melt flow rate (hereinafter referred to as "MFR") of PP resin is not particularly limited, but for example, it is 0.5 to 10 (g / 10 min), specifically, for example, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 (g / 10 min), and may be within the range of any two of the values ​​exemplified here. In this specification, MFR means the value obtained by measurement in accordance with JIS K-7210 at a test temperature of 230°C and a test load of 2.16 kg.

[0025] <ldpe> LDPE is polyethylene with a long-chain branched structure. Density of LDPE (g / cm³) 3 The density is 0.910 or more and less than 0.930, preferably 0.915 or more and 0.925 or less. Specifically, this density may be, for example, 0.910, 0.915, 0.920, 0.925, 0.929, or within the range of any two of the values ​​exemplified here. LDPE can be polymerized, in one example, using a radical initiator such as oxygen in the air or a peroxide as a catalyst, with ethylene polymerized using a multi-stage gas compressor in an environment of 1,000 to 4,000 atmospheres and 100 to 350°C.

[0026] Because LDPE has a long-chain branched structure, incorporating LDPE can improve the foaming properties of foam molding resins.

[0027] The MFR of LDPE is not particularly limited, but for example, it is 0.5 to 10 (g / 10 min), specifically, for example, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 (g / 10 min), and may be within the range of any two of the values ​​exemplified here.

[0028] The LDPE content relative to the total of PP resin and LDPE is 20-50% by mass. If the LDPE content is too low, the effect of improving foam moldability tends to be insufficient, and if the LDPE content is too high, the heat resistance and weldability with polypropylene tend to be insufficient. Specifically, this content is, for example, 20, 25, 30, 35, 40, 45, or 50% by mass, and may be within the range of any two of the values ​​exemplified here.

[0029] <Extruder 2> As shown in Figure 1, the extruder 2 comprises a cylinder 2a into which the raw material resin 4 is fed, and a screw 2b rotatably positioned inside the cylinder 2a.

[0030] The raw material resin 4 preferably contains PP-based resin pellets 4a and LDPE pellets 4b. The raw material resin 4 is introduced into the cylinder 2a via a hopper 2c attached to the cylinder 2a.

[0031] The screw 2b is configured to be rotatably driven by the motor 2d. By rotating the screw 2b, the raw resin 4 is melted and kneaded, and the raw resin 4 is conveyed toward the tip of the cylinder 2a and extruded through the discharge port 2e provided at the tip of the cylinder 2a.

[0032] As shown in Figure 2, the screw 2b comprises a central portion 2b1 and a flight portion 2b2. The central portion 2b1 extends along the axis of rotation of the screw 2b. The flight portion 2b2 is provided so as to project radially outward from the central portion 2b1. The flight portion 2b2 only needs to have a shape that can transport the raw resin 4 toward the tip of the screw 2b as the screw 2b rotates, and in one example it is helical, but it may have a different shape.

[0033] A clearance C is provided between the flight section 2b2 and the inner surface of the cylinder 2a. As the raw material resin 4 in the cylinder 2a passes through the clearance C, a shear force is applied to the raw material resin 4, causing the PP-based resin and LDPE contained in the raw material resin 4 to mix together. The size of the clearance C is, for example, in the range of 0.10 to 0.20 mm.

[0034] If D is the diameter of the screw 2b at the flight section 2b2 (or, in other words, the diameter of the rotational trajectory of the flight surface 2b3 of the flight section 2b2 that faces the inner surface of the cylinder 2a), then D is, for example, between 10 and 300 mm, specifically, for example, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 250, and 300 mm, and may also be within the range of any two of the values ​​exemplified here.

[0035] If the area of ​​the flight surface 2b3 is S, then S / D is preferably 800 to 1500. The area S can be calculated, for example, by (width W of the flight surface 2b3) × (length of the flight section 2b2 in the longitudinal direction). The larger the S / D, the greater the shear force applied to the raw material resin 4, and the better the dispersibility of the PP resin and LDPE in the foam molding resin obtained by melt-kneading the PP resin and LDPE. On the other hand, if the shear force applied to the raw material resin 4 is too large, the raw material resin 4 may overheat and deteriorate. Specifically, S / D can be, for example, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250, 1300, 1350, 1400, 1450, or 1500, and may also be within the range of any two of the values ​​exemplified here.

[0036] If L is the length of the screw 2b in the area where the flight section 2b2 is provided, then L / D is, for example, 20 to 80, specifically, for example, 20, 30, 40, 50, 60, 70, 80, and may be within the range of any two of the values ​​exemplified here.

[0037] If the flight section 2b2 has a helical shape, and L1 is the longitudinal length of the ellipse constituting the helix, then L1 / D is, for example, between 1.05 and 2, specifically, for example, 1.05, 1.1, 1.15, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, and 2.0, and may also be within the range of any two of the values ​​exemplified here.

[0038] If W is the width of the flight surface 2b3 (the length perpendicular to the longitudinal direction of the flight section 2b2), then W / 0.1D is, for example, 0.5 to 2, specifically, for example, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, and may also be within the range of any two of the values ​​exemplified here.

[0039] The rotational speed of screw 2b is not particularly limited, but is, for example, 10 to 200 rpm, and preferably 30 to 120 rpm. Specifically, this rotational speed is, for example, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, and 200 rpm, and may be within the range of any two of the values ​​exemplified here.

[0040] If V is the extrusion speed of the foam molding resin from extruder 2, then V / D 2 (g / hr·mm 2 The value is between 1 and 50, specifically, for example, 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, and may also be within the range of any two of the numbers exemplified here.

[0041] The heating temperature of the raw material resin 4 is, for example, 150 to 250°C, specifically, for example, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, and 250°C, and may be within the range of any two of the values ​​exemplified here.

[0042] <Injector 3> The cylinder 2a of the extruder 2 is equipped with an injector 3 for injecting a foaming agent into the cylinder 2a. The foaming agent injected from the injector 3 can be a physical foaming agent, a chemical foaming agent, or a mixture thereof, but a physical foaming agent is preferred. As a physical foaming agent, inorganic physical foaming agents such as air, carbon dioxide, nitrogen gas, and water, and organic physical foaming agents such as butane, pentane, hexane, dichloromethane, and dichloroethane, as well as supercritical fluids thereof, can be used. Among these, it is preferable to use air, carbon dioxide, or nitrogen gas as the foaming agent. By using these, it is possible to prevent the inclusion of organic matter and suppress the deterioration of durability, etc. By using a supercritical fluid, foaming can be achieved uniformly and reliably. As a supercritical fluid, it is preferable to use carbon dioxide or nitrogen, and if nitrogen is used, it can be obtained by setting the critical temperature to -149.1°C and the critical pressure to 3.4 MPa or higher, and if carbon dioxide is used, the critical temperature to 31°C and the critical pressure to 7.4 MPa or higher. Examples of chemical blowing agents include those that generate carbon dioxide gas through a chemical reaction between an acid (e.g., citric acid or its salt) and a base (e.g., baking soda). The chemical blowing agent may be added from hopper 2c instead of being injected from injector 3.

[0043] <Resin for foam molding> The foam molding resin produced by the above method (hereinafter referred to as "the foam molding resin of this embodiment") has a high dispersion of PP-based resin and LDPE, and it is preferable that the LDPE is dispersed in the matrix of PP-based resin as fine particles. Since this foam molding resin has the same composition as the raw material resin 4, the above description of the raw material resin 4 also applies to the foam molding resin.

[0044] The foam molding resin of this embodiment maintains to some extent the properties of PP-based resins while also possessing to some extent the properties of LDPE. Since LDPE has superior foam moldability compared to PP-based resins, the foam molding resin of this embodiment also has superior foam moldability compared to PP-based resins. Furthermore, since LDPE has superior low-temperature impact resistance compared to PP-based resins, the foam molding resin of this embodiment also has superior low-temperature impact resistance compared to PP-based resins.

[0045] Furthermore, since PP-based resins have superior heat resistance and weldability with PP compared to LDPE, the foam molding resin of this embodiment also has superior heat resistance and weldability with PP compared to LDPE.

[0046] Furthermore, the foam molding resin of this embodiment preferably has an MFR of 3.20 to 3.80 g / 10 min and an MT of 35 to 90 mN. The above technical effects are achieved by having such novel physical properties. Specifically, the MFR is, for example, 3.20, 3.30, 3.40, 3.50, 3.60, 3.70, 3.80 g / 10 min, and may be within the range of any two of the values ​​exemplified here. Specifically, the MT is, for example, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90 mN, and may be within the range of any two of the values ​​exemplified here.

[0047] 2. Method for manufacturing foamed molded articles A method for manufacturing a foamed molded article according to one embodiment of the present invention comprises the steps of forming a foamed parison using a foamed molding resin manufactured by the above method or the above foamed molding resin, and molding the foamed parison to obtain a foamed molded article.

[0048] The method of this embodiment can be carried out, for example, using a foam molding machine 1 illustrated in Figure 1. The foam molding machine 1 comprises an extruder 2, an injector 3, a head 18, and a split mold 19. The extruder 2 and the head 18 are connected by a connecting pipe 25.

[0049] <Extruder 2> In the extruder 2, the raw resin and the foaming agent are melt-kneaded together to form a foam molding resin containing the foaming agent, and this foam molding resin is discharged through the discharge port 2e and injected into the head 18.

[0050] <Head 18> The head 18 is provided with a slit, and a foamed parison 23 can be formed by extruding a foaming resin containing a foaming agent through this slit. The shape of the foamed parison 23 is not particularly limited and may be cylindrical or sheet-shaped. An accumulator may be provided, which is configured to extrude a predetermined amount of foaming resin containing a foaming agent in one go after it has been stored. The accumulator may be provided between the extruder 2 and the head 18, or it may be built into the head 18.

[0051] <Split mold 19> The foamed parison 23 is guided between a pair of split molds 19. A foamed molded body is obtained by molding the foamed parison 23 using the split molds 19. The molding method using the split molds 19 is not particularly limited and may be blow molding, in which air is blown into the cavity of the split mold 19 to perform molding, or vacuum molding, in which the foamed parison 23 is molded by reducing the pressure inside the cavity from the inner surface of the cavity of the split mold 19, or a combination thereof. In the case of blow molding, the air is blown in at a pressure range of, for example, 0.05 to 0.15 MPa. In blow molding and vacuum molding, the foamed parison 23 is stretched, so it is prone to bubble bursting. For this reason, the technical significance of applying the present invention in the case of blow molding or vacuum molding is particularly pronounced.

[0052] After molding, the parts of the resin material that have cooled and solidified other than the finished product can be crushed and used as recovered resin material, which can then be used again in the manufacture of foamed molded products.

[0053] <Foam molded product> As described above, the foam molding resin of this embodiment has excellent foam moldability, so by using this foam molding resin, a foamed molded article can be obtained in which surface rupture and coalescence of air bubbles are less likely to occur.

[0054] Furthermore, the foam molding resin of this embodiment also has excellent low-temperature impact resistance, heat resistance, and weldability with PP. Therefore, by using this foam molding resin, a foamed molded article with excellent low-temperature impact resistance, heat resistance, and weldability with PP can be obtained.

[0055] The foaming ratio of the foamed molded article is not particularly limited, but is, for example, 1.1 to 8 times, and preferably 1.5 to 6 times. Specifically, this foaming ratio may be, for example, 1.1, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, or 8.0 times, and may be within the range of any two of the values ​​exemplified here.

[0056] The foamed molded body is preferably hollow, and its average wall thickness is, for example, 1.5 to 5 mm, specifically, for example, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, or 5.0 mm, and may be within the range of any two of the values ​​exemplified here. [Examples]

[0057] 1. Preparation of Screw 2b As screw 2b, screws S1-S4 and CS1-CS4 shown in Table 1 were prepared. All of these screws have a helical shape in the flight section 2b2, with L1 (length in the longitudinal direction of the ellipse constituting the flight section 2b2) / D being 1.12 and W (width of the flight surface 2b3) / 0.1D being 1. The diameter D of the flight section and the area S of the flight surface of these screws are as shown in Table 1. The area S of the flight surface was changed by changing the length L of the screw 2b.

[0058] [Table 1]

[0059] 2. Manufacturing of foamed molded products <Example 1> In Example 1, a foamed molded body was produced using the foam molding machine 1 shown in Figure 1. Screw S1 was used as the screw 2b of the extruder 2. The clearance C was set to 0.15 ± 0.05 mm. As raw material resins, pellets of PP resin (Novatec PP·BC4BSW, manufactured by Nippon Polypropylene Co., Ltd.) and LDPE (Suntec-LD·M1820, manufactured by Asahi Kasei Corporation) were blended in the proportions shown in Table 2. In addition, 1.0 part by weight of an LDPE base masterbatch (product name "FineCell Master P0217K," manufactured by Dainichi Seika Kogyo Co., Ltd., containing 20 wt% sodium bicarbonate-based foaming agent as a nucleating agent) and 1.0 part by weight of an LLDPE base masterbatch containing 40 wt% carbon black as a coloring agent were added per 100 parts by mass of resin. The temperature of each part was controlled so that the resin temperature inside the extruder 2 was 190 to 200°C. The rotation speed of the screw was set to 60 rpm. The foaming agent was N2 gas, injected via injector 3. The injection volume was 0.4 [wt.%] (N2 injection volume / resin extrusion volume). The thickness of the foamed parison 23 was adjusted so that the thickness of the foamed molded body was 2 mm.

[0060] After placing the foamed parison 23 formed under the above conditions between the divided molds 19, the divided molds 19 were clamped to obtain a hollow foamed molded body.

[0061] <Examples 2-8 and Comparative Examples 1-13> A foamed molded article was manufactured in the same manner as in Example 1, except that the type of screw and the composition of the raw material resin were changed as shown in Tables 2 to 4.

[0062] [Table 2]

[0063] [Table 3]

[0064] [Table 4]

[0065] 2. Physical property measurement Sample pieces were cut out from the foamed molded bodies of each example and comparative example, and the MFR and MT were measured. The results are shown in Tables 2 to 4.

[0066] 3. Evaluation For the produced foamed molded bodies, the foamability, heat resistance, weldability with PP, and low-temperature impact resistance were evaluated by the following methods. The results are shown in Tables 2 to 4. As shown in Tables 2 to 4, in all the examples, all the evaluation results were ◎ or ○. On the other hand, in all the comparative examples, at least one evaluation result was △ or ×.

[0067] <Foamability> The foamability was evaluated by measuring the expansion ratio of the foamed molded body according to the following criteria. ◎: 2.8 times or more ○: 1.8 times or more and less than 2.8 times △: 1.4 times or more and less than 1.8 times ×: Less than 1.4 times

[0068] <Heat resistance> The heat resistance was evaluated according to JIS 7161-2. Test pieces were cut from the foamed molded body, and the tensile modulus at 80 °C was measured for these test pieces according to the following criteria. ◎: 75 MPa or more ○: 55 MPa or more and less than 75 MPa △: 35 MPa or more and less than 55 MPa ×: Less than 35 MPa

[0069] <Weldability with PP> The weldability with PP was evaluated based on the magnitude of the tensile load required for tensile fracture by performing a tensile fracture test at room temperature on a member obtained by ultrasonically welding the foamed molded body to a polypropylene plate according to the following criteria. ◎: 20 N / cm 2 or more ○: 15 N / cm 2 or more and less than 20 N / cm 2 less than △: 10 N / cm 2 Above, 15 N / cm 2 Less than ×: 10 N / cm 2 Less than

[0070] <Low-temperature impact resistance> The low-temperature impact resistance was measured for the foamed molded body at -10°C in accordance with JIS K 7110, and evaluated according to the following criteria. ◎: 10 kJ / m 3 Above ○: 8 kJ / m 2 Above, less than 10 kJ / m 2 Less than △: 5 kJ / m 2 Above, less than 8 kJ / m 2 Less than ×: 5 kJ / m 2 Less than

Explanation of symbols

[0071] 1: Foaming molding machine 2: Extruder 2a: Cylinder 2b: Screw [[ID=四十九]]2b1: Central part 2b2: Flight part 2b3: Flight surface 2c: Hopper 2d: Motor 2e: Discharge port<00003?3: Injector 4: Raw material resin 4a: Pellet 4b: Pellet 18: Head 19: Split mold 23: Foamed parison 25: Connecting pipe< / ldpe>

Claims

1. A foam molding resin is formed by melt-kneading a raw material resin containing a polypropylene resin and low-density polyethylene, The content of the low-density polyethylene relative to the total of the polypropylene resin and the low-density polyethylene is 20 to 50% by mass. The foam molding resin has a melt flow rate of 3.20 to 3.80 g / 10 min and a melt tension of 35 to 90 mN.

2. A method for manufacturing a foamed molded article, comprising the steps of forming a foamed parison using the foamed molding resin described in Claim 1, and molding the foamed parison to obtain a foamed molded article.

3. The method according to Claim 2, The molding is performed by blow molding or vacuum molding.

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