Method for producing foamed molded article

Abstract

To provide a manufacturing method of a foam molded body capable of improving foaming moldability in foam molding by continuous extrusion.SOLUTION: A manufacturing method of a foam molded body includes an extrusion step and a molding step. In the extrusion step, a foamed parison is formed by continuously extruding a foaming agent-containing resin, containing a physical foaming agent, from a slit of an extrusion head. In the molding step, the foamed parison is molded by a mold. A width of the slit is 0.68-3.50 mm, and mol concentration of the physical foaming agent in the foaming agent-containing resin in the extrusion step is 5-55 mmol / kg.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a foamed molded article. [Background technology]

[0002] Patent Document 1 discloses a method for producing a foamed molded article. In this method, resin is temporarily stored in an accumulator and then extruded from an extrusion head. Therefore, the resin is extruded intermittently. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-70795 Summary of the Invention [Problem to be solved by the invention]

[0004] The inventors of the present invention have been conducting extensive research into a method for producing a foamed molded article by continuous extrusion without using an accumulator. In the course of researching the continuous extrusion foam molding process, unexpected molding defects were actually encountered.

[0005] The present invention has been made in view of the above circumstances, and provides a method for producing a foamed molded article that can improve foam moldability in foam molding by continuous extrusion. [Means for solving the problem]

[0006] According to the present invention, there is provided a method for producing a foamed molded article, comprising an extrusion step and a molding step, wherein in the extrusion step, a foamed parison is formed by continuously extruding a foaming-agent-containing resin containing a physical foaming agent through a slit in an extrusion head, and in the molding step, the foamed parison is molded in a mold, the slit has a width of 0.68 to 3.50 mm, and the molar concentration of the physical foaming agent in the foaming-agent-containing resin in the extrusion step is 5 to 55 mmol / kg.

[0007] As a result of extensive research, the inventors of the present application have discovered that when the molar concentration of the physical foaming agent in the foaming-agent-containing resin and the width of the slit in the extrusion head are set within specific numerical ranges, foam moldability in foam molding by continuous extrusion can be improved, and have completed the present invention.

[0008] Various embodiments of the present invention will be described below as examples, and the embodiments shown below can be combined with each other. Preferably, in the method described above, the width of the slit is 2.85 mm or less. Preferably, in the above-described method, the molar flow rate of the physical foaming agent is 1.00 to 2.80 mol / h. Preferably, in the above-described method, the molar flow rate of the physical foaming agent is 1.00 to 2.35 mol / h. Preferably, the method is as described above, wherein the forming is blow forming, vacuum forming or a combination thereof. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing a foam molding apparatus 100 that can be used in a method for producing a foam molded article according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] The following describes embodiments of the present invention. The various features shown in the following embodiments can be combined with each other. Furthermore, each feature can be an invention independently.

[0011] 1.Foam molding equipment A method for producing a foam molded article according to one embodiment of the present invention can be carried out, for example, using a foam molding apparatus 100 including a foam extruder 1 and a split mold 14 shown in Fig. 1. The foam extruder 1 includes a cylinder 3, a resin inlet 5, a screw 7, a resin extrusion outlet 11, an extrusion head 12, and a foaming agent inlet 16.

[0012] Each component will be described in detail below.

[0013] <Resin inlet 5> The resin inlet 5 is a so-called hopper, and raw resin is introduced from here. The form of the raw resin is not particularly limited, but is usually in pellet form. After being introduced into the cylinder 3 from the resin inlet 5, the raw resin is heated and melted within the cylinder 3 to become a molten resin. Furthermore, the rotation of the screw 7 arranged within the cylinder 3 transports the molten resin toward the resin extrusion outlet 11 provided at one end of the cylinder 3.

[0014] The raw resin is selected from various resin materials. The raw resin is, for example, a thermoplastic resin such as polyolefin. Examples of polyolefin include low-density polyethylene, linear low-density polyethylene, high-density polyethylene, polypropylene, ethylene-propylene copolymer, and mixtures thereof. Any of these thermoplastic resins may be used in the embodiments.

[0015] <Screw 7> The screw 7 is disposed within the cylinder 3, and by its rotation, kneads the molten resin while conveying it toward the resin extrusion port 11. A gear device is provided at one end of the screw 7. The gear device not only drives the screw 7 to rotate, but also controls the rotation speed.

[0016] <Foaming agent injection port 16> The cylinder 3 is provided with a foaming agent injection port 16 for injecting a foaming agent into the cylinder 3. By injecting the physical foaming agent P through the foaming agent injection port 16, a foaming-agent-containing resin in which the physical foaming agent P is injected into the molten resin is obtained. Because a high pressure is maintained inside the foaming extruder 1, the physical foaming agent and the molten resin do not separate into separate lumps, and the physical foaming agent remains dispersed in the molten resin in the form of fine particles.

[0017] Examples of the physical blowing agent P include inorganic physical blowing agents such as air, carbon dioxide, nitrogen gas, and water, as well as organic physical blowing agents such as butane, pentane, hexane, dichloromethane, and dichloroethane, and even supercritical fluids of these. Supercritical fluids are preferably produced using carbon dioxide, nitrogen, or the like, with nitrogen being obtained by adjusting the critical temperature to -149.1°C and the critical pressure to 3.4 MPa or higher, and carbon dioxide being obtained by adjusting the critical temperature to 31°C and the critical pressure to 7.4 MPa or higher. The injection amount may be controlled by controlling the aperture of a control valve (such as an adjustment valve or injector, not shown).

[0018] <Temperature control unit 9> The temperature control unit 9 is configured to individually control multiple temperature adjustment units provided along the cylinder 3 to control the temperature of each part of the cylinder 3. The temperature control unit 9 can also control the temperature of the extrusion head 12 used to form the parison and the temperature of the connecting part 10 between the cylinder 3 and the extrusion head 12. The temperature of each part affects the resin pressure inside the extrusion head 12. Once the temperature setting is completed through conditioning, the temperature of each part may be controlled to be constant so as to minimize deviation from the set temperature.

[0019] <Resin extrusion nozzle 11 · Extrusion head 12> The foaming agent-containing resin is extruded from the resin extrusion port 11 and injected into the extrusion head 12 through the connecting portion 10. The extrusion head 12 has a slit 12a, and the foamed parison 13 is formed by extruding the foaming agent-containing resin through the slit 12a. The shape of the slit 12a is not particularly limited, but may be, for example, annular or linear (e.g., straight). When the slit 12a is annular, a cylindrical foamed parison is obtained. When the slit 12a is linear (e.g., when the extrusion head 12 is a T-die), a sheet-shaped foamed parison is obtained. The width of the slit 12a is variable, so that the thickness of the foamed parison 13 can be changed by changing the width of the slit 12a.

[0020] When the foaming agent-containing resin is extruded through the slit 12a and released into the atmosphere, a pressure gradient is generated due to the difference between the pressure inside the extrusion head 12 and atmospheric pressure, causing the volume of the physical foaming agent to expand and forming a foamed parison 13.

[0021] <Split mold 14> The foam parison 13 is introduced between a pair of split molds 14. A foam molded article is obtained by molding the foam parison 13 using the split mold 14. The molding method using the split mold 14 is not particularly limited, and may be blow molding, in which air is blown into the cavity of the split mold 14 to form the foam parison 13, vacuum molding, in which the pressure inside the cavity of the split mold 14 is reduced from the inner surface of the cavity to form the foam parison 13, or a combination of these.

[0022] 2. Manufacturing method of foam molded product A method for producing a foamed molded article according to one embodiment of the present invention will now be described. The method according to this embodiment includes an extrusion step and a molding step.

[0023] 2-1. Extrusion process In the extrusion step, a foamed parison 13 is formed by continuously extruding a foaming agent-containing resin containing a physical foaming agent P from a slit 12a of an extrusion head 12.

[0024] This embodiment is characterized in that the foaming agent-containing resin is continuously extruded. In foam molding, it is important to appropriately control the timing at which the foaming agent-containing resin starts to foam, and it is also important to appropriately control the pressure applied to the foaming agent-containing resin. For this reason, in foam molding, a certain amount of foaming agent-containing resin is generally stored in an accumulator, and then the stored foaming agent-containing resin is extruded at high speed to form a foam parison.

[0025] In continuous extrusion foam molding without an accumulator, as in this embodiment, it is difficult to strictly control the pressure applied to the foaming-agent-containing resin, which tends to result in poor foam moldability. On the other hand, in continuous extrusion foam molding without an accumulator, the foaming extruder 1 can be continuously operated, which improves the stability of the extrusion rate of the foaming-agent-containing resin from the foaming extruder 1 and increases production efficiency. Furthermore, compared to a foaming extruder 1 with an accumulator, this method has the advantage of being easier to reduce equipment costs and installation space.

[0026] In this embodiment, in order to overcome the above-mentioned problems while enjoying the above-mentioned advantages, the width of the slit 12a of the extrusion head 12 is set to 0.68 to 3.50 mm, and the molar concentration of the physical foaming agent in the foaming-agent-containing resin is set to 5 to 55 mmol / kg. By setting these two parameters within these specific numerical ranges, it is possible to improve the foam moldability even in continuous extrusion foam molding, as will be shown in the examples described later.

[0027] The width [mm] of the slit 12a is preferably 2.85 or less. In this case, foam moldability is further improved. Specific examples of the width [mm] of the slit 12a are 0.68, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.00, 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, 1.50, 1.55, 1.60, 1.65, 1.70, 1.75, 1.80, 1.85, 1.90, 1.95, 2.00, 2.05, 2.10 , 2.15, 2.20, 2.25, 2.30, 2.35, 2.40, 2.45, 2.50, 2.55, 2.60, 2.65, 2.70, 2.75, 2.80, 2.85, 2.90, 2.95, 3.00, 3.05, 3.10, 3.15, 3.20, 3.25, 3.30, 3.35, 3.40, 3.45, 3.50, and may be within a range between any two of the numerical values ​​exemplified here.

[0028] The molar concentration [mmol / kg] of the physical foaming agent in the foaming-agent-containing resin can be calculated by {molar flow rate of physical foaming agent [mol / h] ÷ resin flow rate [kg / h]} × 1000. Specific examples of this molar concentration [mmol / kg] are 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, and 55, and may be within a range between any two of the values ​​exemplified here. and may be in a range between any two of the values ​​given here.

[0029] The molar flow rate [mol / h] of the physical blowing agent is the amount of material of the physical blowing agent injected per unit time (1 hour), and can be adjusted by changing the flow rate of the physical blowing agent P injected through the blowing agent inlet 16. The molar flow rate [mol / h] of the physical blowing agent is, for example, 1.00 to 3.00, preferably 1.00 to 2.80, and more preferably 1.00 to 2.35, because in this case, foam moldability tends to be particularly good. Specific examples of this molar flow rate [mol / h] include 1.00, 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, 1.50, 1.55, 1.60, 1.65, 1.70, 1.75, 1.80, 1.85, 1.90, 1.95, 2.00, 2.05, 2.10, 2.15, 2.20, 2.25, 2.30, 2.35, 2.40, 2.45, 2.50, 2.55, 2.60, 2.65, 2.70, 2.75, 2.80, 2.85, 2.90, 2.95, and 3.00, and may be within a range between any two of the numerical values ​​exemplified here.

[0030] The resin flow rate [kg / h] is the mass (kg) of resin flowing per unit time (1 hr). Specifically, the resin flow rate may be adjusted by controlling the rotation speed of the screw 7, etc. In this embodiment, continuous extrusion is performed, so the resin flow rate corresponds to the resin flow rate flowing into the extrusion head 12, as well as the resin flow rate flowing out of the extrusion head 12.

[0031] The resin flow rate [kg / h] is, for example, 30 to 150, specifically, for example, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, and may be within a range between any two of the numerical values ​​exemplified here.

[0032] 2-2. Molding process In the molding step, the foam parison 13 is molded using a mold. In this embodiment, molding is performed using a pair of split molds 14, but for example, vacuum molding may also be performed using a single mold.

[0033] This molding is preferably blow molding or vacuum molding. In blow molding or vacuum molding, the foam parison is stretched during molding, which tends to deteriorate foam moldability. For this reason, the technical significance of applying the present invention to blow molding or vacuum molding is significant.

[0034] In the method of this embodiment, the foam parison 13 is continuously extruded, so if molding is performed using a single set of molds (one mold or a pair of split molds), it is not possible to ensure time for the foam molded article obtained by molding to cool. Therefore, it is preferable to perform the molding process using multiple sets of molds by sequentially sliding them directly below the extrusion head 12. This improves production efficiency.

[0035] After the molding process, finishing processes including deburring are performed. According to the method of this embodiment, since an accumulator is not used, the accumulator storage process and injection process are omitted, thereby improving manufacturing efficiency.

[0036] An example of a foam molded article obtained by the production method of this embodiment is a duct. The expansion ratio of the foam molded article is, for example, 1.1 to 3.0 times, specifically, for example, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, or 3.0 times, or may be within a range between any two of the values ​​exemplified here. [Example]

[0037] 1. Manufacturing foam moldings A foamed molded article was produced from the foam parison 13 using the apparatus shown in FIG. 1 and the method described in the above embodiment. The raw material composition used was a mixture of polypropylene resin A (manufactured by Borealis AG, trade name "Daploy WB140"), polypropylene resin B (manufactured by Japan Polypropylene Corporation, trade name "Novatec PP BC4BSW"), and polyethylene elastomer (manufactured by Mitsui Chemicals, Inc., trade name "Tafmer DF605") in a mass ratio of 80:10:10 (specific gravity 0.90). The extrusion head 12 had a 150 mm diameter core and a circular slit around it. The width of the circular slit, resin flow rate, type of physical foaming agent, and molar flow rate were adjusted to the values ​​shown in Tables 1 and 2.

[0038] A cylindrical foam parison 13 was placed between split molds 14, and after the molds were closed, blow molding was performed by blowing air into the foam parison 13. In this way, foam molded articles of Examples and Comparative Examples were produced.

[0039] [Table 1]

[0040] [Table 2]

[0041] 2. Evaluation of foamed molded products The specific gravity of the resulting foam molded article was measured, and the expansion ratio was calculated by dividing the specific gravity of the resin composition itself by the specific gravity of the foam molded article. Furthermore, the foam moldability was evaluated according to the following criteria based on the rate of molding defects (defective rate) when 100 foam molded articles were produced. The results are shown in Tables 1 and 2. ◎: Defective rate is 5% or less ○: Defective rate is over 5% and 20% or less △: Defective rate is over 20% and 60% or less ×: Defective rate is over 60%

[0042] As shown in Tables 1 and 2, in all Examples in which the slit width was 0.68 to 3.50 mm and the molar concentration of the physical foaming agent was 5 to 55 mmol / kg, the foam moldability was better than in all Comparative Examples. [Explanation of symbols]

[0043] 1: Foaming extruder 3: Cylinder 5:Resin inlet 7: Screw 9: Temperature control unit 10:Connection part 11: Resin extrusion port 12: Extrusion head 12a: Slit 13: Cylindrical foam parison 14: Split mold 16: Foaming agent injection port 100: Foam molding equipment

Claims

1. A method for producing a foamed molded article comprising an extrusion step and a molding step, In the extrusion step, a foamed parison is formed by continuously extruding a foaming agent-containing resin containing a physical foaming agent through a slit in an extrusion head, In the molding step, the foam parison is molded in a mold, the width of the slit is 0.68 to 3.50 mm, and the molar concentration of the physical foaming agent in the foaming-agent-containing resin in the extrusion step is 5 to 55 mmol / kg.

2. 10. The method of claim 1, The method, wherein the slit has a width of 2.85 mm or less.

3. 3. The method of claim 1 or claim 2, The molar flow rate of the physical blowing agent is 1.00 to 2.80 mol / h.

4. The method according to any one of claims 1 to 3, The method of claim 1, wherein the molar flow rate of the physical blowing agent is 1.00 to 2.35 mol / h.

5. The method according to any one of claims 1 to 4, The method wherein said molding is blow molding, vacuum molding, or a combination thereof.

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