Method for producing foam molded article

Abstract

Provided is a method for producing a foam molded article, which can improve the mass production efficiency of a highly expanded polyethylene foam molded article. According to the present invention, provided is a method for producing a foam molded body having a foaming ratio of 2.0 times or more, the method comprising an input step in which a raw material resin is input through a hopper into an inner space of a cylinder of an extruder, a parison forming step in which the raw material resin is molded into the inner space of the cylinder of the extruder, and a molding step in which the raw material resin is molded into the inner space of the cylinder of the extruder. And a molding step in which a foaming agent-containing resin in a molten state, which is obtained by melt-kneading the starting material resin and the foaming agent in the internal space, is extruded from a head to form a foamed parison, and the foamed parison is molded using a mold to form a foamed molded body, the raw material resin contains 50% by mass or more of a polyethylene-based resin, the raw material resin contains a crushed material produced by crushing a foamed body using a crusher, the foamed body is composed of a resin containing 50% by mass or more of a polyethylene-based resin, and the foaming ratio is 2.0 times or more. The pulverizer is configured so that the pulverized material passes through an opening provided in a screen and is discharged from the pulverizer, and the diameter of the opening is 8.0 mm or less.

Description

Technical Field

[0001] The invention relates to a method for producing a foamed molded body. Background Art

[0002] For example, in an air conditioning device for a car or the like, a tubular air conditioning duct is used for ventilating air.

[0003] As air conditioning pipes, there are known foamed molded articles using a foamed resin obtained by foaming a thermoplastic resin with a foaming agent. The demand for foamed molded articles is increasing because they can achieve both high thermal insulation and light weight.

[0004] As a method for producing such a foamed molded article, foam blow molding is widely known, in which a foamed resin in a molten state is molded together with split molds and air is blown into the inside to expand it (for example, Patent Document 1).

[0005] Prior art literature Patent Literature Patent Document 1: Japanese Patent Application Publication No. 2017-064932 Summary of the invention Problem that the invention aims to solve In foam blow molding, a molten resin containing a foaming agent is extruded from a head portion by melt-kneading a raw material resin and a foaming agent in an extruder to form a foamed parison, and the foamed parison is molded using a mold to obtain a foamed molded body. Subsequently, the foamed molded body is post-processed to remove burrs or pockets, etc., to obtain a foamed molded product as a desired product.

[0006] The removed part is usually crushed by a crusher to form a crushed material, which is fed into an extruder and used for the production of the next foamed molded body.

[0007] However, when developing mass production equipment for highly expanded polyethylene foam molded products, it is known that crushed materials frequently clog the hopper of the extruder, thereby reducing mass production efficiency.

[0008] The present invention has been made in view of such circumstances, and provides a method for producing a foamed molded product, which method can improve the mass production efficiency of a highly foamed polyethylene-based foamed molded product.

[0009] Means used to solve problems According to the present invention, the following inventions are provided.

[0010] [1] (First aspect) A method for producing a foamed molded article, the foamed molded article having an expansion ratio of 2.0 times or more, the method comprising a feeding step, a parison forming step, and a molding step, wherein in the feeding step, a raw material resin is fed into an internal space of a cylinder of an extruder through a hopper, in the parison forming step, a molten resin containing a foaming agent obtained by melt-kneading the raw material resin and a foaming agent in the internal space is extruded from a head to form a foamed parison, and in the molding step, the foamed parison is molded using a mold to form a foamed molded article, the raw material resin containing 50% by mass or more of a polyethylene resin, the raw material resin containing a pulverized material produced by pulverizing a foamed article using a pulverizer, the foamed article being composed of a resin containing 50% by mass or more of a polyethylene resin and having an expansion ratio of 2.0 times or more, the pulverizer being configured so that the pulverized material passes through an opening provided in a screen and is discharged from the pulverizer, the diameter of the opening being 8.0 mm or less.

[0011] In the mass production of foamed products, crushed materials are generally used. In the mass production of polypropylene foamed products and the mass production of polyethylene foamed products with low foaming ratio, the phenomenon of crushed materials blocking the hopper does not occur. Therefore, the phenomenon that crushed materials easily block the hopper is a unique phenomenon that occurs in the mass production of polyethylene foamed products. In order to solve this problem, in-depth research was conducted, and it was found that by making the diameter of the aperture of the screen provided at the outlet of the pulverizer less than 8.0 mm, the blockage of crushed materials in the hopper can be suppressed, thereby completing the present invention.

[0012] [2] The method according to [1], wherein the expansion ratio of the foamed molded article and the foam is 3.2 times or more.

[0013] [3] According to the method described in [1] or [2], the head has a core and a shell surrounding the core, and the resin containing the foaming agent flows through the flow path between the core and the shell and is extruded from the head through an annular gap to form the foamed blank. In the front end area within a range of 20 mm in the vertical direction from the annular gap, the core and the shell respectively have a core side flow path forming surface and a shell side flow path forming surface, and the angle between the core side flow path forming surface and the shell side flow path forming surface is greater than 3.0 degrees.

[0014] [4] (Second Aspect) A method for producing a foamed molded article having a foaming ratio of 2.0 or more, the method comprising a feeding step, a parison forming step, and a molding step, wherein in the feeding step, a raw material resin is fed into an internal space of a cylinder of an extruder through a hopper, in the parison forming step, a molten resin containing a foaming agent obtained by melt-kneading the raw material resin and a foaming agent in the internal space is extruded from a head to form a foamed parison, and in the molding step, the foamed parison is molded using a mold to form a foamed molded article. The raw material resin contains more than 50% by mass of polyethylene resin, the head has a core and a shell surrounding the core, the resin containing the foaming agent flows through the flow path between the core and the shell and is extruded from the head through the annular gap to form the foamed blank, in the front end area within the range of 20 mm in the vertical direction from the annular gap, the core and the shell respectively have a core side flow path forming surface and a shell side flow path forming surface, and the gap angle between the core side flow path forming surface and the shell side flow path forming surface is more than 3.0 degrees.

[0015] [5] The method according to [4], wherein in the front end region, the inclination angle of the flow path forming surface on the shell side relative to the horizontal plane is greater than 45 degrees.

[0016] [6] The method according to any one of [1] to [5], wherein the resin constituting the foamed molded product contains 80% by mass or more of a polyethylene-based resin. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1A It is a structural diagram of a molding device 100 according to one embodiment of the present invention. Figure 1B yes Figure 1A BB cross-section diagram in.

[0018] Figure 2 It is a cross-sectional view showing the structure of the pulverizer 15 .

[0019] Figure 3 yes Figure 2 A three-dimensional view of the screen 15a in FIG.

[0020] Figure 4A It is an enlarged cross-sectional view of the vicinity of the front end of the head portion 12 in FIG. 1 . Figure 4B yes Figure 4A Magnified view of area B in FIG.

[0021] Figure 5 It is a cross-sectional view showing a state in which the split molds 14 a and 14 b are closed and the foamed parison 13 is blow-molded to form a foamed molded body 18 .

[0022] Fig. 6AThis is a perspective view showing a foamed molded body main body 18b obtained by removing burrs 18c from the foamed molded body 18. Figure 6B It is a perspective view showing a foam molded product 18a obtained by removing the pocket portion 18d from the foam molded body main body 18b. DETAILED DESCRIPTION

[0023] The following describes the embodiments of the present invention. The various features shown in the embodiments described below can be combined with each other. In addition, the invention is independent for each feature.

[0024] The embodiments described below relate to the first and second viewpoints. However, the technical matters related to the first viewpoint are arbitrary structures in the second viewpoint, and the technical matters related to the second viewpoint are arbitrary structures in the first viewpoint.

[0025] 1. Molding device 100 In one example, the method for producing a foamed molded article 18 according to an embodiment of the present invention can be implemented using a molding device 100 including an extruder 1, a head 12, and a mold 14 as shown in Fig. 1. The extruder 1 has a barrel 3, a hopper 5, a screw 7, a foaming agent injection unit 8, a temperature control unit 9, and a resin extrusion port 11.

[0026] Hereinafter, the raw material resin 2 used for manufacturing the foam molded body 18 will be described first, and then the molding device 100 will be described.

[0027] <Raw material resin 2> The raw material resin 2 contains 50% by mass or more of a polyethylene resin. The proportion of the polyethylene resin in the raw material resin 2 is, for example, 50 to 100% by mass, preferably 80 to 100% by mass, specifically, for example, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100% by mass, and may be a range between any two of the numerical values ​​exemplified here.

[0028] Polyethylene resin refers to a resin in which 80% by mass (preferably 85, 90 or 95% by mass) or more of the monomer unit is polyethylene. As polyethylene resins, ethylene homopolymers, copolymers of ethylene and other olefins (e.g., α-olefins such as 1-butene), i.e., ethylene copolymers, acid-modified polyethylene, etc. can be cited. As ethylene homopolymers, high-density polyethylene (HDPE) and low-density polyethylene (LDPE) can be cited. As ethylene copolymers, linear low-density polyethylene (LLDPE) can be cited. The proportion of other olefin units in the ethylene copolymer is, for example, 1 to 20% by mass, specifically, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20% by mass, and can also be a range between any two of the values ​​exemplified here. Regarding the polyethylene resin in the raw material resin 2, for example, if the total of HDPE and LDPE is set to 100% by mass, the proportion of HDPE is preferably 20 to 60% by mass, and more preferably 30 to 50% by mass. The density of HDPE is, for example, 0.941 g / cm 3 Above, the density of LDPE is 0.910~0.940g / cm 3 .

[0029] As the resin other than the polyethylene resin in the raw material resin 2, polyolefins other than the polyethylene resin can be cited, and as such polyolefins, polypropylene (homopolypropylene, random polypropylene, block polypropylene, etc.) can be exemplified. In addition to the resin, various additives such as a foaming nucleating agent (such as sodium bicarbonate and citric acid), an antioxidant, and a colorant can be formulated in the raw material resin 2.

[0030] In the invention of the first aspect, as shown in FIG. 1 to FIG. Figure 2 As shown, the raw resin 2 contains a crushed material 17 produced by crushing a foam 16 with a crusher 15. The particles constituting the crushed material 17 are preferably irregular in shape or size. The proportion of the crushed material 17 in the raw resin 2 is, for example, 50 to 100% by mass, preferably 85 to 95% by mass, specifically, for example, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100% by mass, and may also be in the range between any two of the numerical values ​​exemplified here. The resin other than the crushed material 17 in the raw resin 2 is preferably a virgin resin 26. The virgin resin 26 is preferably in the form of a pellet, and the diameter of the pellet is, for example, 1 to 6 mm. In this case, the raw resin 2 is obtained by mixing the crushed material 17 and the virgin resin 26.

[0031] As an example of the foam body 16, there can be cited a foam body which is manufactured in the past. Figure 6B As an example of waste, Figure 5As shown in Figure 6, there can be cited the end materials (burrs 18c, bag portions 18d cut off to form opening portions 18e, etc.) generated when the foamed molded body 18 is processed into the desired foamed molded product 18a, and the foamed molded product 18a that failed the inspection. In this case, the foamed body 16 has the same composition and foaming ratio as the foamed molded body 18. In addition, the composition and / or foaming ratio of the foamed body 16 may also be different from those of the foamed molded body 18. For example, in the case of using the following specific scrap, the composition and / or foaming ratio of the foamed body 16 is different from that of the foamed molded body 18, and the specific scrap is generated in the manufacture of a foamed molded body having a composition and / or foaming ratio different from that of the foamed molded body 18 manufactured in the present embodiment.

[0032] The foam 16 is composed of a resin containing 50% by mass or more of a polyethylene resin, and has an expansion ratio of 2.0 or more. The description of the resin is the same as that of the raw resin 2. The expansion ratio is preferably 3.2 or more, more preferably 3.5 or more, specifically, for example, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 5.0, 5.5, 6.0 times, and may be a range between any two of the numerical values ​​exemplified here or any one or more. The present inventors have found that when the foam 16 used in the manufacture of the crushed material 17 has such a composition and expansion ratio, clogging is likely to occur in the hopper 5, so when the foam 16 has such a composition and expansion ratio, the technical significance of applying the present invention is particularly significant. Examples of the reasons why clogging is likely to occur in the hopper 5 when the foam 16 has the above composition and expansion ratio are as follows: since polyethylene resin is softer than polypropylene resin, the crushed materials 17 are likely to adhere to each other; and since the expansion ratio is high, the downward force applied to the crushed material 17 is likely to become insufficient.

[0033] like Figure 2-3As shown, the pulverizer 15 is preferably configured so that the pulverized material 17 passes through the opening 15a1 provided on the screen 15a and is discharged from the pulverizer 15. The diameter of the opening 15a1 is preferably 8.0 mm or less, and more preferably 7.5 mm or less or 7.0 mm or less. In this case, as shown in the following embodiment, clogging in the hopper 5 can be suppressed. The lower limit of the diameter of the opening 15a1 is not particularly specified, and is, for example, 3.0 mm. By not making the diameter of the opening 15a1 too small, the time required for pulverization can be suppressed from becoming too long. The diameter of the opening 15a1 is specifically, for example, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0 mm, and can also be a range between any two of the numerical values ​​exemplified here. The spacing of the openings 15a1 (that is, the distance between the centers of adjacent openings 15a1) is preferably the diameter of the opening 15a1 × P. P is, for example, 1.1 to 2, preferably 1.3 to 1.7, and specifically, for example, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, and may also be a range between any two of the numerical values ​​exemplified herein. In addition, in the case where the opening 15a1 is not circular, "diameter" means an equivalent circular diameter. Preferably, a plurality of openings 15a1 are provided on the screen 15a. Preferably, the diameters of the plurality of openings 15a1 are the same. In the case where the diameters of the plurality of openings 15a1 are different from each other, the proportion of the openings 15a1 with a diameter of 8.0 mm (preferably 7.5 or 7.0 mm) or less is preferably 50% or more, and more preferably 80% or more. The proportion is specifically, for example, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100%, and may also be a range between any two of the numerical values ​​exemplified herein. The average value of the diameters of the plurality of openings 15a1 is preferably 8.0 mm (preferably 7.5 or 7.0 mm) or less, and the maximum value of the diameters of the plurality of openings 15a1 is more preferably 8.0 mm (preferably 7.5 or 7.0 mm) or less. The above description of the diameter of the openings 15a1 can also be applied to the average value and the maximum value.

[0034] In one example, the pulverizer 15 includes an input portion 15b, a pulverizing portion 15c, and a screen 15a. The foam 16 input from the input portion 15b is pulverized in the pulverizing portion 15c to become a pulverized material 17, which passes through the screen 15a and is discharged from the pulverizer 15. In one example, the pulverizing portion 15c includes a fixed blade 15e fixed to a housing 15d and a rotating blade 15f rotating around a rotating shaft 15f2. The rotating shaft 15f2 is, for example, an axis extending in the horizontal direction. Preferably, the edges 15e1 and 15f1 of the fixed blade 15e and the rotating blade 15f are respectively along the axial direction ( Figure 2The gap between the edges 15e1 and 15f1 when the edges 15e1 and 15f1 are closest to each other is, for example, 0.3 to 2.0 mm, preferably 0.5 to 1.2 mm. The gap is specifically, for example, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 2.0 mm, and may be a range between any two of the values ​​exemplified here.

[0035] According to this structure, as the rotating blade 15f rotates, the fixed blade 15e and the rotating blade 15f apply shear force to the foam 16, so that the foam 16 is cut. When the foam 16 is cut into a size that can pass through the opening 15a1, it passes through the opening 15a1 and is discharged as a crushed material 17. In order to improve the crushing efficiency, it is preferable to provide two or more fixed blades 15e and two or more rotating blades 15f.

[0036] like Figure 2 As shown, the screen 15a preferably has an arc shape in a cross section perpendicular to the rotation axis 15f2, and it is further preferred that the center of the arc coincides with the rotation axis 15f2. In this case, since the edge of the rotating blade 15f moves concentrically with the inner surface of the screen 15a, the foam 16 that is cut and thinned by the fixed blade 15e and the rotating blade 15f is transported along the inner surface of the screen 15a by the rotating blade 15f. According to this structure, the foam 16 that is sized to pass through the opening 15a1 can be easily and quickly discharged through the opening 15a1. The gap between the inner surface of the screen 15a and the edge of the rotating blade 15f is, for example, 1 to 10 mm, preferably 2 to 7 mm. The gap is specifically, for example, 1.0, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 8.0, 9.0, 10.0 mm, or may be a range between any two of the values ​​exemplified here. If the gap is too large, the foam body 16 cut into small pieces will be difficult to be transported by the rotating blade 15f and difficult to be discharged through the opening 15a1.

[0037] <Hopper 5> The hopper 5 is connected to the internal space 3b of the barrel 3 through the opening 3a provided on the side of the barrel 3, and the raw resin 2 is put into the internal space 3b from the hopper 5. The raw resin 2 is heated and melted in the internal space 3b to become a molten state. In addition, by the rotation of the screw 7 arranged in the internal space 3b, the molten resin is transported toward the resin extrusion port 11 provided at the front end of the internal space 3b.

[0038] like Figure 1BAs shown, the opening area of ​​the passage 19 through which the raw material resin 2 fed into the hopper 5 passes (the area of ​​the smallest portion in the horizontal cross section of the passage 19) is preferably 50 to 500 cm 2 , more preferably 150 to 400 cm 2 The area is specifically, for example, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500 cm 2 , or it can be a range between any two of the values ​​exemplified here. The shape of the passage 19 is not particularly limited. In one example, it is preferably a flat shape such as a rectangle, an oblong or an ellipse. "Oblong" refers to the shape of the outer edge of the trajectory of the circle when it moves in parallel. Here, the direction parallel to the rotation axis of the screw 7 is set as the major axis direction, the direction perpendicular to the major axis direction in the horizontal plane is set as the minor axis direction, the length of the passage 19 in the major axis direction at the position where the length of the passage 19 in the major axis direction is the largest is set as LL, and the length of the passage 19 in the minor axis direction at the position where the length of the passage 19 in the minor axis direction is the largest is set as SL.

[0039] LL is, for example, 10 to 40 cm, preferably 15 to 25 cm, specifically, for example, 10, 15, 20, 25, 30, 35, 40 cm, and may be a range between any two of the values ​​exemplified herein. SL is, for example, 4 to 15 cm, preferably 6 to 12 cm, specifically, for example, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 cm, and may be a range between any two of the values ​​exemplified herein. LL / SL is, for example, 1.2 to 4.0, preferably 1.5 to 2.5, specifically, for example, 1.2, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, and may be a range between any two of the values ​​exemplified herein.

[0040] When the passage 19 has such a shape, clogging of the raw resin 2 is likely to occur, and therefore the technical significance of applying the present invention is significant.

[0041] <Screw 7> The screw 7 is disposed in the internal space 3b of the barrel 3, and the molten resin is conveyed toward the resin extrusion port 11 while being kneaded by its rotation. A motor 4 is provided at one end of the screw 7. The motor 4 can drive the screw 7 to rotate and can also control the rotation speed.

[0042] <Foaming agent injection portion 8> The foaming agent injection portion 8 is a portion for injecting the foaming agent into the cylinder 3. There is no particular restriction on the position of the foaming agent injection portion 8. When the end position of the hopper 5 side of the internal space 3b of the cylinder 3 is set to 0 and the end position of the resin extrusion port 11 side is set to L, the foaming agent injection portion 8 is preferably set at a position of 0.3L to 0.7L (preferably 0.4 to 0.6L). If the foaming agent injection portion 8 is set at a position closer to the hopper 5 side than 0.3L, the foaming agent is sometimes injected in a state where the molten resin is not sufficiently kneaded, and the dispersion of the foaming agent becomes insufficient. In addition, because the temperature of the molten resin is usually controlled to gradually decrease toward the resin extrusion port 11, if the foaming agent injection portion 8 is set at a position closer to the resin extrusion port 11 than 0.7L, the temperature of the molten resin at the portion where the foaming agent is injected is sometimes too low, and the injection amount of the foaming agent is reduced.

[0043] The foaming agent injected from the foaming agent injection part 8 can include physical foaming agents, chemical foaming agents and mixtures thereof, preferably physical foaming agents. As physical foaming agents, inorganic physical foaming agents such as air, carbon dioxide gas, nitrogen, water, and organic physical foaming agents such as butane, pentane, hexane, dichloromethane, and dichloroethane, as well as their supercritical fluids can be used. As a supercritical fluid, it is preferably made using carbon dioxide, nitrogen, etc. If it is nitrogen, it is obtained by setting the critical temperature to -149.1°C and the critical pressure to 3.4MPa or more. If it is carbon dioxide, it is obtained by setting the critical temperature to 31°C and the critical pressure to 7.4MPa or more. As a chemical foaming agent, a foaming agent that produces carbon dioxide gas by a chemical reaction of an acid (e.g., citric acid or its salt) and an alkali (e.g., sodium bicarbonate) can be cited. In addition, the foaming agent injection part 8 can also be an opening connected to the hopper 5.

[0044] <Temperature control unit 9> The temperature control unit 9 is configured to control the temperature of each portion by controlling a plurality of temperature adjustment units provided in the barrel 3 and the head 12 .

[0045] <Head 12, mold 14> The resin containing the foaming agent in a molten state obtained by melt-kneading the raw material resin 2 and the foaming agent in the internal space 3b is extruded from the resin extrusion port 11 and injected into the head 12. The head 12 has a slit, and the resin containing the foaming agent is extruded from the slit to form a foamed parison 13. The shape of the slit is not particularly limited, and it is, for example, annular or linear (e.g., linear). In the case where the slit is annular, a cylindrical foamed parison is obtained. In the case where the slit is linear (e.g., when the head 12 is a T-die), a sheet-shaped foamed parison is obtained. In addition, the resin containing the foaming agent extruded from the resin extrusion port 11 can also be accumulated in an accumulator (not shown) for a certain amount, and then the plunger of the accumulator is operated to extrude from the head 12 to form the foamed parison 13. In this case, since the extrusion speed of the foamed parison 13 can be increased, there is an advantage that the foaming state of the foamed parison 13 is easily stabilized. The extrusion rate of the resin containing the foaming agent is preferably 250 to 1250 g / sec, specifically, for example, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250 g / sec, and may be a range between any two of the values ​​exemplified here.

[0046] The foamed parison 13 is molded by a mold 14. The mold 14 is preferably a split mold 14a, 14b that can be opened and closed, and the foamed parison 13 is guided between the split molds 14a, 14b. The foamed molded body 18 is obtained by molding the foamed parison 13 using the mold 14. The foamed molded body 18 is preferably hollow. There is no particular limitation on the molding method using the mold 14, and it can be blow molding in which air is blown into the cavity of the mold 14 to perform molding, or vacuum molding in which the foamed parison 13 is molded by depressurizing the cavity from the inner surface of the cavity of the mold 14, or a combination thereof.

[0047] The description of the composition of the foamed molded article 18 is the same as that of the raw resin 2. The foaming ratio of the foamed molded article 18 is the same as that of the foamed article 16. The average wall thickness of the foamed molded article 18 is, for example, 1 to 5 mm, or preferably 2 to 4 mm.

[0048] <Foamed molded article 18> However, the inventor observed the inner surface of the hollow foaming molded body 18 composed of a resin containing 50% or more of polyethylene resin and having a foaming ratio of 2.0 or more, and found that there was a case where an undesirable striped concave-convex shape was formed. When air is circulated inside the foaming molded body 18 like a pipeline, such a concave-convex shape will cause increased circulation resistance or noise, so it is not desirable. Such a concave-convex shape does not occur in the mass production of polypropylene foaming molded bodies or polyethylene foaming molded bodies with a low foaming ratio, so it is a unique phenomenon that occurs in the manufacture of highly foamed polyethylene foaming molded bodies.

[0049] In order to suppress the occurrence of such a phenomenon, the inventors conducted intensive research and found that the occurrence of the above phenomenon can be suppressed by improving the structure of the head 12 for forming the foamed parison 13, thereby completing the invention of the second aspect. The head 12 of the invention of this aspect will be described below.

[0050] According to the invention in this viewpoint, as shown in Fig. 4, the head 12 has a core 21 and a shell 22 surrounding the core 21. The resin containing the foaming agent flowing through the flow path 23 between the core 21 and the shell 22 passes through the annular slit 24 and is extruded from the head 12, thereby forming a foamed parison 13.

[0051] As shown in FIG4 , in the front end region 25 within the range of 20 mm in the vertical direction from the annular gap 24, the core 21 and the shell 22 have a core side flow path forming surface 21a and a shell side flow path forming surface 22a, respectively. The gap angle α between the core side flow path forming surface 21a and the shell side flow path forming surface 22a is 3.0 degrees or more. As shown in the following embodiment, when it is confirmed that the head 12 of the molding device that produces the above-mentioned undesirable striped concave-convex shape is generated, the gap angle α between the core side flow path forming surface 21a and the shell side flow path forming surface 22a is less than 3.0 degrees, and it can be confirmed that by increasing this angle, the striped concave-convex shape can be suppressed.

[0052] The gap angle α is, for example, 3.0 to 45 degrees, preferably 3.3 to 30 degrees, and specifically, for example, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.65, 3.7, 3.8, 3.9, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10, 15, 20, 25, 30, 35, 40, 45 degrees, and may be a range between any two of the values ​​exemplified here or any one or more thereof. When the angle is 3.0 degrees or more, pulsation when the resin containing the foaming agent is extruded from the head 12 is suppressed, thereby suppressing the generation of stripe-like concavo-convex shapes.

[0053] In the front end region 25, the inclination angle β of the flow path forming surface 22a on the shell side relative to the horizontal plane is preferably 45 degrees or more. In this case, the generation of striped concave and convex shapes is further suppressed. The inclination angle β is, for example, 45 to 85 degrees, and specifically, for example, 45, 49.4, 50, 55, 60, 65, 70, 75, 80, 85 degrees, and can also be a range between any two of the values ​​exemplified here or any one or more. The flow path forming surface 21a on the core side is preferably inclined in a manner that the front end of the core 21 becomes pointed.

[0054] The diameter D of the core 21 at the height position where the annular gap 24 is provided is, for example, 50 to 300 mm, preferably 100 to 200 mm. Specifically, the diameter D is, for example, 50, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 250, 300 mm, and may be a range between any two of the values ​​exemplified here.

[0055] The width of the annular gap 24 can be adjusted by changing the height position of the core 21 relative to the shell 22. For example, the width of the annular gap 24 can be increased by raising the core 21 relative to the shell 22. The width of the annular gap 24 is appropriately set to obtain a foamed molded body 18 having a desired wall thickness.

[0056] 2. Method for producing foamed molded article A method for producing a foamed molded article according to one embodiment of the present invention will be described. The method of this embodiment includes a charging step, a parison forming step, and a molding step.

[0057] <Input process> In the charging step, the raw material resin 2 is charged into the internal space 3b of the cylinder 3 of the extruder 1 through the hopper 5. The raw material resin 2 contains the above-mentioned crushed material 17, so that clogging of the raw material resin 2 can be suppressed, and mass production efficiency can be improved.

[0058] <Parison Forming Process> In the parison forming step, as shown in Fig. 1 and Fig. 4, the raw material resin 2 and the foaming agent are melt-kneaded in the internal space 3b, and the resin containing the foaming agent in a molten state is extruded from the head 12 to form the foamed parison 13. As described above, by forming the foamed parison 13 using the head 12 in which the angle between the core side flow path forming surface 21a and the shell side flow path forming surface 22a is 3.0 degrees or more, it is possible to suppress the formation of stripe-like concavo-convex shapes on the inner surface of the foamed molded body 18.

[0059] <Molding process> like Figure 5 As shown, in the molding step, the foamed parison 13 is molded using a mold 14 to form a foamed molded body 18 .

[0060] The foamed molded body 18 is formed by connecting the burr 18c outside the cavity of the mold 14 with the foamed molded body 18b inside the cavity of the mold 14. By removing the burr 18c from the foamed molded body 18, a foamed molded body 18 can be obtained. Fig. 6A Next, as required, the pocket 18d provided on the foamed molded body 18b is cut away along the line indicated by the dotted line 18f to form an opening, such as Figure 6B As shown, a desired foamed molded product (eg, foamed pipe) 18a can be obtained. In addition, when post-processing such as forming an opening in the foamed molded body 18b is not required, the foamed molded body 18b can be directly used as the foamed molded product 18a.

[0061] In the mass production process of the foam molded product 18a, waste materials consisting of end materials (burrs 18c or pockets 18d, etc.) generated when the foam molded body 18 taken out of the mold 14 is processed into the desired foam molded product 18a and foam molded products 18a that failed in inspection are generated. By feeding the waste materials into the grinder 15 as the foamed body 16 and crushing them, a crushed material 17 can be obtained. The crushed material 17 can be fed into the hopper 5 as the raw material resin 2 directly or mixed with virgin resin. According to the above method, the waste materials generated in the previous process can be used to efficiently mass-produce high-quality foam molded products 18.

[0062] [Example] 1. Comparative Example 1 Using the manufacturing apparatus for a foamed molded body shown in FIG1 , a foamed molded body 18 having a foaming ratio of 4.0 times was manufactured. As the raw material resin 2, a resin prepared by mixing virgin resin and crushed material 17 at a mass ratio of 1:9 was used. The virgin resin was prepared by mixing HDPE / LDPE / foaming nucleating agent (sodium bicarbonate and citric acid) / antioxidant / black masterbatch at a mass ratio of 40 / 60 / 1 / 4 / 1. The crushed material 17 was prepared by crushing waste generated in the previous manufacture of the foamed molded body 18 using a crusher 15. The diameter of the opening 15a1 of the screen 15a of the crusher 15 was set to 9.0 mm, and the pitch of the opening 15a1 was set to 13.0 mm.

[0063] The horizontal cross-sectional shape of the passage 19 through which the raw material resin 2 introduced into the hopper 5 passes is an oval shape, and the length LL in the major axis direction is 300 mm and the length SL in the minor axis direction is 100 mm.

[0064] The temperature control unit 9 is set so that the temperature of the foamed parison 13 is 190-200°C. N2 gas is used as the foaming agent, which is injected from the foaming agent injection unit 8 set at the 0.5L position. The foaming ratio is adjusted by changing the amount of injected gas. After a certain amount of resin containing a foaming agent extruded from the resin extrusion port 11 of the extruder 1 is accumulated in an accumulator (not shown), the plunger of the accumulator is operated to extrude from the head 12 to form a foamed parison 13. The extrusion speed of the resin containing a foaming agent is 554g / sec. The head 12 uses a head with a core 21 having a diameter of 120mm, a gap angle α of 2.26 degrees, and an inclination angle β of 41.8 degrees.

[0065] The foamed parison 13 formed under the above conditions is blow-molded to produce the foamed molded article 18. The foamed molded article 18 is repeatedly produced by using scraps generated when producing the foamed molded article 18.

[0066] Under the above conditions, the raw resin 2 frequently clogs the passage 19 , and the clog must be eliminated each time, resulting in poor mass production efficiency. In addition, stripe-like concavo-convex shapes are formed on the inner surface of the foamed molded body 18 .

[0067] 2. Example 1 The foamed molded body 18 is repeatedly manufactured by the same method as in Comparative Example 1, except that the diameter of the opening 15a1 of the screen 15a is set to 7.0 mm, the spacing of the opening 15a1 is set to 10.5 m, and a head 12 having a core 21 with a diameter of 140 mm, a gap angle α of 3.65 degrees, and an inclination angle β of 49.4 degrees is used.

[0068] Under the above conditions, the raw material resin 2 hardly blocks the passage 19, and the mass production efficiency is excellent. In addition, no stripe-like concavo-convex shape is formed on the inner surface of the foamed molded body 18.

[0069] Description of Reference Numerals 1: Extruder, 2: Raw material resin, 3: Cylinder, 3a: Opening, 3b: Internal space, 4: Motor, 5: Hopper, 7: Screw, 8: Foaming agent injection part, 9: Temperature control part, 11: Resin extrusion port, 12: Head, 13: Foaming parison, 14: Mold, 14a: Split mold, 14b: Split mold, 15: Crusher, 15a: Screen, 15a1: Opening, 15b: Feeding part, 15c: Crushing part, 15d: Basket, 15e: Fixed blade, 15e1: Edge, 15f: Rotating blade, 15f1 : edge, 15f2: rotating shaft, 16: foam body, 17: crushed material, 18: foamed molded body, 18a: foamed molded product, 18b: foamed molded body main body, 18c: burr, 18d: bag part, 18e: opening part, 18f: dotted line, 19: passage, 21: core, 21a: flow path forming surface on the core side, 22: shell, 22a: flow path forming surface on the shell side, 23: flow path, 24: annular gap, 25: front end area, 26: virgin resin, 100: molding device, α: gap angle, β: tilt angle.

Claims

1. A method for producing a foamed molded article, wherein: The foaming ratio of the foamed molded body is 2.0 times or more, The method comprises an input step, a parison forming step and a molding step. In the feeding step, the raw material resin is fed into the inner space of the cylinder of the extruder through the hopper. In the parison forming step, the raw material resin and the foaming agent are melt-kneaded in the internal space to obtain a molten resin containing the foaming agent, which is extruded from the head to form a foamed parison. In the molding step, the foamed parison is molded using a mold to form a foamed molded body. The raw material resin contains 50% by mass or more of a polyethylene resin, The raw material resin contains a pulverized material produced by pulverizing a foamed body using a pulverizer, The foam is composed of a resin containing 50% by mass or more of a polyethylene resin, and has a foaming ratio of 2.0 times or more. The pulverizer is configured to allow the pulverized material to pass through an opening provided in the screen and be discharged from the pulverizer. The diameter of the opening is 8.0 mm or less.

2. The method according to claim 1, wherein: The expansion ratios of the foamed molded article and the foamed article are each 3.2 times or more.

3. The method according to claim 1, wherein: The head has a mold core and a mold shell surrounding the mold core. The resin containing the foaming agent flowing through the flow path between the core and the shell is extruded from the head through the annular slit to form the foamed parison. In the front end region within the range of 20 mm in the vertical direction from the annular gap, the core and the shell have a core-side flow path forming surface and a shell-side flow path forming surface, respectively. The angle between the core-side flow path forming surface and the shell-side flow path forming surface is 3.0 degrees or more.

4. A method for producing a foamed molded article, wherein: The foaming ratio of the foamed molded body is 2.0 times or more, The method comprises an input step, a parison forming step and a molding step. In the feeding step, the raw material resin is fed into the inner space of the cylinder of the extruder through the hopper. In the parison forming step, the raw material resin and the foaming agent are melt-kneaded in the internal space to obtain a molten resin containing the foaming agent, which is extruded from the head to form a foamed parison. In the molding step, the foamed parison is molded using a mold to form a foamed molded body. The raw material resin contains 50% by mass or more of a polyethylene resin, The head has a mold core and a mold shell surrounding the mold core. The resin containing the foaming agent flowing through the flow path between the core and the shell is extruded from the head through the annular slit to form the foamed parison. In the front end region within the range of 20 mm in the vertical direction from the annular gap, the core and the shell have a core-side flow path forming surface and a shell-side flow path forming surface, respectively. A gap angle between the core-side flow path forming surface and the shell-side flow path forming surface is 3.0 degrees or more.

5. The method according to claim 4, wherein: In the front end region, the inclination angle of the flow path forming surface on the formwork side relative to the horizontal plane is greater than or equal to 45 degrees.

6. The method according to any one of claims 1 to 5, wherein: The resin constituting the foamed molded product contains 80% by mass or more of a polyethylene-based resin.

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