Expanded particle manufacturing method and manufacturing device

Abstract

The purpose of the present invention is to improve the variation in foaming magnification of foamed particles in a depressurization foaming method using a flush valve. In this manufacturing method for foamed particles according to the present invention, foamed particles (P) discharged from the flush valve (20) are led out in an oblique direction with respect to the direction of extension of the valve body (22) of the flush valve (20) in a foaming step.

Description

[Technical Field]

[0001] The present invention relates to a method and an apparatus for producing expanded beads. [Background technology]

[0002] It is known that expanded beads made of a thermoplastic resin are produced by a method (hereinafter referred to as depressurization foaming method) in which thermoplastic resin particles are dispersed in water containing a dispersant in a pressure-resistant vessel, a blowing agent is then added, the mixture is maintained under high temperature and high pressure to be impregnated with the blowing agent, and then the mixture is released into a low-pressure atmosphere. An example of a method for producing expanded beads using the depressurization foaming method is a technology described in Patent Document 1.

[0003] In this depressurization foaming method, a pressure vessel is charged with thermoplastic resin particles, mini-pellets containing an inorganic dispersant and a dispersion aid, and a blowing agent together with water. The pressure vessel is then heated to adjust the mixture in the pressure vessel to a predetermined temperature, and the pressure in the pressure vessel is then adjusted to a predetermined pressure. This allows the blowing agent to impregnate the thermoplastic resin particles in the pressure vessel.

[0004] In the technique described in Patent Document 1, a flush valve provided at the bottom of a pressure-resistant container is opened to release thermoplastic resin particles impregnated with a foaming agent into a low-pressure atmosphere. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2020 / 158061 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the depressurization foaming method using a flash valve as described in Patent Document 1 leaves room for improvement in terms of reducing the variation in the expansion ratio of the expanded beads.

[0007] One aspect of the present invention aims to realize a method and an apparatus for manufacturing foamed particles with improved variation in the expansion ratio of foamed particles in a pressure-relief foaming method using a flash valve.

Means for Solving the Problems

[0008] In order to solve the above problems, a method for manufacturing foamed particles according to one aspect of the present invention disperses polyolefin resin particles in an aqueous dispersion medium in a pressure-resistant container, heats and pressurizes the polyolefin resin particles to a temperature equal to or higher than the softening temperature of the polyolefin resin, and then releases them into a container with a pressure lower than the internal pressure in the pressure-resistant container, thereby foaming the polyolefin resin particles to obtain polyolefin resin foamed particles. The foaming step includes a first step of releasing the polyolefin resin particles from the pressure-resistant container into a low-pressure container through a flash valve including a valve body and a valve element, and a second step of guiding the foamed particles discharged from the flash valve in a direction obliquely from the direction in which the valve element of the flash valve extends. In the second step, when the angle of the导出 direction of the foamed particles with respect to the direction in which the valve element of the flash valve extends is C, the angle C is such that 40° < C < 90°.

[0009] In order to solve the above problems, a manufacturing apparatus for foamed particles according to one aspect of the present invention includes a pressure-resistant container for foaming polyolefin resin particles, a flash valve for discharging the polyolefin resin particles in the pressure-resistant container into a low-pressure container, and a discharge pipe for discharging the foamed particles discharged from the flash valve. The flash valve includes a valve body and a valve element, and the discharge pipe is connected to the valve body of the flash valve so as to be inclined with respect to the direction in which the valve element extends. When the angle of the导出 direction of the foamed particles with respect to the direction in which the valve element of the flash valve extends is C, the angle C is such that 40° < C < 90°.

Effects of the Invention

[0010] According to one aspect of the present invention, in a depressurization foaming method using a flash valve, the variation in the expansion ratio of expanded beads can be improved. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram schematically illustrating an example of an expanded bead manufacturing apparatus used in a manufacturing method according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing a schematic configuration of a flush valve provided in the manufacturing apparatus shown in FIG. [Figure 3] 3 shows a schematic diagram of the state when the flush valve shown in FIG. 2 is opened, with 301 being a side view and 302 being a view seen from above. DETAILED DESCRIPTION OF THE INVENTION

[0012] One embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the respective configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments and examples obtained by appropriately combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in the embodiments. Furthermore, all academic literature and patent documents described in this specification are incorporated herein by reference. Furthermore, unless otherwise specified in this specification, the term "A to B" representing a numerical range means "greater than or equal to A (including and greater than A) and less than or equal to B (including and less than B)."

[0013] (Method of manufacturing expanded beads) As a result of intensive research into the above-mentioned problems, the present inventors have independently discovered that, when discharging the contents of a pressure-resistant container using a flush valve, the expansion ratio variation can be improved by discharging the expanded beads discharged from the flush valve in a direction oblique to the direction in which the valve body of the flush valve extends. Based on this discovery, the present inventors have arrived at the present embodiment.

[0014] The method for producing expanded beads according to this embodiment (hereinafter simply referred to as this method) includes an expansion step in which expanded polyolefin resin beads are obtained by a depressurization expansion method. In this expansion step, polyolefin resin particles are dispersed in an aqueous dispersion medium in a pressure-resistant vessel, and the polyolefin resin particles are heated and pressurized to a temperature equal to or higher than the softening temperature of the polyolefin resin. The polyolefin resin particles are then released into a vessel with a pressure lower than the internal pressure of the pressure-resistant vessel, thereby expanding the polyolefin resin particles and obtaining expanded polyolefin resin beads.

[0015] In this method, the expansion step includes a first step and a second step. In the first step, the polyolefin resin particles are released from the pressure-resistant container into a low-pressure container through a flush valve including a valve body and a valve element. In the second step, the expanded particles released from the flush valve are guided in a direction oblique to the direction in which the valve element of the flush valve extends.

[0016] Fig. 1 is a diagram schematically illustrating an example of an expanded bead manufacturing apparatus 10 used in this method. As shown in Fig. 1, the manufacturing apparatus 10 includes a pressure-resistant container 1, a flush valve 20, a discharge pipe 3 (low-pressure container), and a transport pipe 4 (low-pressure container) for transporting the expanded beads. Here, with respect to the pressure-resistant container 1, the side of the flush valve 20 is defined as the lower side, and the side opposite the flush valve 20 is defined as the upper side.

[0017] The pressure vessel 1 is a vessel for producing expanded beads by a depressurization foaming method. The pressure vessel 1 is charged with polyolefin resin particles P0 (hereinafter sometimes referred to as resin particles P0), a blowing agent, and an aqueous dispersion medium S. The pressure vessel 1 is then heated to adjust the temperature of the contents therein to a temperature equal to or higher than the softening temperature of the resin particles P0, and the pressure within the pressure vessel 1 is then adjusted to a predetermined pressure. As a result, the resin particles P0 in the pressure vessel 1 are impregnated with the blowing agent.

[0018] The flush valve 20 is provided at the bottom of the pressure vessel 1. The flush valve 20 is also called a tank valve. By opening the flush valve 20, the resin particles P0 pass through the flush valve 20 and are released into the low-pressure spaces of the release pipe 3 and the transport pipe 4, where they become foamed particles P.

[0019] The discharge pipe 3 is a pipe for discharging the foamed particles P discharged from the flush valve 20 to the transport pipe 4. The discharge pipe 3 is a pipe that connects the flush valve 20 and the transport pipe 4. The discharge pipe 3 has a conical cylindrical shape that tapers toward the flush valve 20.

[0020] The transport pipe 4 is a pipe for transporting the expanded particles P. In the transport pipe 4, the expanded particles P are transported together with the transport air, and are stored in a predetermined storage tank after undergoing at least cleaning treatment, drainage treatment, dehydration treatment, and drying treatment.

[0021] In the manufacturing apparatus 10, the various equipment and facilities other than the pressure vessel 1, the flush valve 20, the discharge pipe 3, and the transport pipe 4 are not particularly limited as long as they are capable of performing at least the cleaning process, drainage process, dehydration process, and drying process described above, and are, for example, shown in Figures 6 and 7 of International Publication WO2020 / 158061.

[0022] 2 is a cross-sectional view showing a schematic configuration of the flush valve 20 provided in the manufacturing apparatus 10. As shown in FIG. 2, the flush valve 20 includes a valve body 21, a valve element 22, and an operating part 23.

[0023] The valve body 21 has an inlet 21a, a guide surface 21b, and a connecting port 21c. The inlet 21a is formed at the top of the valve body 21. The pressure-resistant container 1 and the valve body 21 are in communication with each other via the inlet 21a. Therefore, the resin particles P0 in the pressure-resistant container 1 flow into the valve body 21 via the inlet 21a. The guide surface 21b is a surface inclined with respect to the axis E of the valve element 22, and is configured to guide the resin particles P0 that have flowed into the valve body 21 to the connecting port 21c. The guide surface 21b is inclined so that the end 21d on the connecting port 21c side is at the lowest point. The connecting port 21c is formed at the connection portion between the valve body 21 and the discharge pipe 3. The valve body 21 and the discharge pipe 3 are in communication with each other via the connecting port 21c.

[0024] The valve element 22 is a piston that moves up and down within the valve body 21, and opens and closes the inlet 21a. The tip portion of the valve element 22 on the inlet 21a side has a truncated cone shape that narrows toward the inlet 21a. In the portion above the guide surface 21b, a gap is provided between the inner surface of the valve body 21 and the valve element 22. This gap serves as a flow path for the resin particles P0 that flow in from the inlet 21a. Furthermore, in the portion below the guide surface 21b, there is no gap between the inner surface of the valve body 21 and the valve element 22. In other words, within the valve body 21, the resin particles P0 do not flow below the guide surface 21b.

[0025] The operating unit 23 is a part that operates the valve element 22. By operating the operating unit 23, the valve element 22 moves in the up and down direction. The operating unit 23 may be operable automatically or manually.

[0026] In the flush valve 20, the valve element 22 is lowered from the valve body 21 by operation of the operating part 23. In the flush valve 20, the area occupied by the gap between the inlet 21a and the valve element 22 is changed by changing the distance that the valve element 22 is lowered, thereby making it possible to adjust the valve opening. When the inlet 21a is opened by the valve element 22 in this way, the resin particles P0 flow into the low-pressure valve body 21 and foam, thereby obtaining foamed particles P.

[0027] According to the manufacturing apparatus 10 of this embodiment, the discharge pipe 3 is connected to the valve body 21 of the flush valve 20 so as to be inclined with respect to the extending direction of the valve element 22. In other words, the axis F of the discharge pipe 3 is inclined with respect to the axis E of the valve element 22.

[0028] Therefore, when the flush valve 20 is opened, the resin particles P0 flow in from the inlet 21a together with the aqueous dispersion medium S. The resin particles P0 then come into contact with the guide surface 21b, are guided to the connecting port 21c, and are released into the release pipe 3 to become expanded particles P. In this way, the resin particles P0 come into contact with the guide surface 21b and change their moving direction before becoming expanded particles P, so that good expanded particles with little variation in expansion ratio can be obtained.

[0029] Here, the guide surface 21b is a surface inclined with respect to the axis E of the valve body 22. Furthermore, the guide surface 21b is inclined so that the end 21d on the connecting port 21c side is lowest. Therefore, the resin particles P0 contact the guide surface 21b and smoothly reach the connecting port 21c, making it less likely for the resin particles P0 to collide with each other or to be compressed at the guide surface 21b. As a result, it is possible to prevent the generation of expanded particles P with finer cells on the particle surface or flattened expanded particles P. Note that the guide surface 21b is not limited to a configuration inclined so that the end 21d on the connecting port 21c side is lowest, as long as it is inclined to an extent that allows smooth guidance to the connecting port 21c. When the guide surface 21b is inclined so that the end 21d on the connecting port 21c side is lowest, the inclination angle of the guide surface 21b with respect to a plane perpendicular to the axis E is preferably greater than 0° and less than 60°, and more preferably greater than 15° and less than 45°.

[0030] In this way, according to this method, the expanded beads P released from the flush valve 20 are guided in a direction oblique to the direction in which the valve body 22 of the flush valve 20 extends. Therefore, good expanded beads with little variation in expansion ratio can be obtained.

[0031] In this method, preferably, when the angle between the direction of导出 of the expanded particles P and the direction of elongation of the valve body 22 of the flash valve 20 is C, the angle C is such that 40° < C < 90°, preferably 50° ≤ C ≤ 70°. In other words, the angle C at which the axis F of the discharge pipe 3 is inclined with respect to the axis E of the valve body 22 is 40° < C < 90°, preferably 50° ≤ C ≤ 70°. The range of the angle C is more preferably 50° ≤ C ≤ 60°. By setting the angle C within such a range, the variation in the expansion ratio of the expanded particles can be made smaller.

[0032] Here, as a result of further study by the present inventor, it has been found that the pressure release rate of the resin particles P0 when the flash valve 20 is opened affects the variation in the expansion ratio. FIG. 3 schematically shows the state when the flash valve 20 is opened. 301 in FIG. 3 is a side view, and 302 in FIG. 3 is a view seen from above.

[0033] As shown in 301 and 302 of FIG. 3, when the valve body 22 is lowered and the closing of the inlet 21a by the valve body 22 is released, a clearance G is formed between the valve body 21 and the valve body 22. The walls constituting the clearance G are constituted by the inner surface of the valve body 21 and the outer surface of the valve body 22, and are annular in top view. The above-mentioned pressure release rate can be adjusted by the area of the clearance G.

[0034] The clearance G is defined by A (see FIG. 2), which is the diameter of the inlet 21a, and H1 (see FIG. 2), which is the diameter of the tip portion of the valve body 22 on the inlet 21a side. Further, the pressure release rate is defined by the clearance G, B / A, and H2 (see FIG. 2), which is the diameter of the middle portion of the valve body 22. Note that H2 is larger than A and smaller than B. Also, H1 is smaller than A.

[0035] From the viewpoint of reducing the variation in the expansion ratio, A and B are preferably 1.0.

[0036] Also, A is preferably 20 to 30 mm. H1 is preferably 7 to 19 mm. Furthermore, H2 is preferably A+2 to 8 mm.

[0037] (About expanded particles P) The raw materials for the expanded beads P used in this embodiment may be any materials that can be expanded by the depressurization foaming method described above, and include at least polyolefin resin particles, a blowing agent, and an aqueous dispersion medium S. In addition to the polyolefin resin particles and the blowing agent, various additives may also be added as needed to the raw materials for the expanded beads. Examples of such additives include flame retardants, heat stabilizers, radical generators, processing aids, weathering stabilizers, nucleating agents, foaming aids, antistatic agents, radiation heat transfer inhibitors, and colorants. These additives may be used alone or in combination of two or more.

[0038] The polyolefin-based resin used in this embodiment is not particularly limited, and examples thereof include the polyolefin-based resins exemplified in International Publication WO2020 / 158061.

[0039] (summary) ​The method for producing foamed particles according to Aspect 1 of the present invention disperses polyolefin resin particles (resin particles P0) in an aqueous dispersion medium S in a pressure-resistant container 1, heats and pressurizes the polyolefin resin particles to a temperature equal to or higher than the softening temperature of the polyolefin resin, and then releases them into a container (discharge pipe 3, transport pipe 4) having a pressure lower than the internal pressure in the pressure-resistant container 1, thereby foaming the polyolefin resin particles to obtain polyolefin resin foamed particles (foamed particles P). The foaming step includes a first step of discharging the polyolefin resin particles from the pressure-resistant container 1 into a low-pressure container through a flash valve 20 including a valve body 21 and a valve element 22, and a second step of导出 the foamed particles discharged from the flash valve 20 in an oblique direction from the direction in which the valve element 22 of the flash valve 20 extends (the direction of axis E). In the second step, when the angle between the direction of导出 of the foamed particles (the direction of axis F) and the direction in which the valve element 22 of the flash valve 20 extends is C, the angle C satisfies 40° < C < 90°.

[0040] The method for producing foamed particles according to Aspect 2 of the present invention is, in Aspect 1, in the first step, when the diameter of the inlet 21a of the valve body 21 of the flash valve 20 is A and the inner diameter of the valve body 21 is B, 1.0 < B / A ≤ 4.0, and the polyolefin resin particles are discharged from the pressure-resistant container into a low-pressure container.

[0041] The method for producing foamed particles according to Aspect 3 of the present invention is, in Aspect 1 or 2, in the first step, when the diameter of the middle part of the valve element 22 is H2 and the inner diameter of the valve body 21 is B, B and H2 are set such that 1.0 < B / H2 ≤ 3.0.

[0042] The method for producing foamed particles according to Aspect 4 of the present invention is, in any of Aspects 1 to 3, the diameter A of the inlet 21a of the valve body 21 of the flash valve 20 is 20 to 30 mm.

[0043] The manufacturing method of the foamed particles according to Aspect 5 of the present invention is the method in any one of Aspects 1 to 4, wherein the diameter H1 of the tip portion of the valve body 22 is 7 to 19 mm.

[0044] The manufacturing method of the foamed particles according to Aspect 6 of the present invention is the method in any one of Aspects 1 to 5, wherein the diameter H2 of the middle portion of the valve body 22 is the diameter A + 2 to 8 mm of the inlet 21a of the valve body 21 of the flash valve 20.

[0045] The manufacturing method of the foamed particles according to Aspect 7 of the present invention is the method in any one of Aspects 1 to 6, wherein the variation in magnification of the foamed particles is less than 10%.

[0046] The manufacturing apparatus 10 of the foamed particles according to Aspect 8 of the present invention includes a pressure-resistant container 1 for foaming polyolefin resin particles (resin particles P0), a flash valve 20 for discharging the polyolefin resin particles in the pressure-resistant container 1 to a low-pressure container (transport pipe 4), and a discharge pipe 3 for discharging the foamed particles P discharged from the flash valve 20. The flash valve 20 includes a valve body 21 and a valve body 22. The discharge pipe 3 is connected to the valve body 21 of the flash valve 20 so as to be inclined with respect to the direction in which the valve body 22 extends (the direction of the axis E). When the angle of the derivation direction (the direction of the axis F) of the foamed particles with respect to the extending direction of the valve body 22 of the flash valve 20 is C, the angle C is 40° < C < 90°.

[0047] The manufacturing apparatus 10 of the foamed particles according to Aspect 9 of the present invention is, in Aspect 8, the valve body 21 communicates with the discharge pipe 3 through a connection port 21c. The valve body 21 has a guide surface 21b for guiding the polyolefin resin particles (resin particles P0) flowing into the valve body 21 to the connection port 21c. The guide surface 21b is a surface inclined with respect to the axis E of the valve body 22.

[0048] The expanded beads manufacturing apparatus 10 according to a tenth aspect of the present invention is the same as in the eighth or ninth aspect, wherein, when the diameter of the inlet 21a of the valve body 21 of the flush valve 20 is A and the inner diameter of the valve body 21 is B, A and B are 1.0

[0049] The expanded beads manufacturing apparatus 10 according to an eleventh aspect of the present invention is any one of the eighth to tenth aspects, wherein when the diameter of the intermediate portion of the valve element 22 is H2 and the inner diameter of the valve main body 21 is B, B and H2 are 1.0

[0050] The expanded beads manufacturing apparatus 10 according to a twelfth aspect of the present invention is configured as in any one of the eighth to eleventh aspects, wherein the diameter A of the inlet 21a of the valve body 21 of the flush valve 20 is 20 to 30 mm.

[0051] The expanded beads manufacturing apparatus 10 according to a thirteenth aspect of the present invention is configured as in any one of the eighth to twelfth aspects, wherein the diameter H1 of the tip portion of the valve body 22 is 7 to 19 mm.

[0052] The expanded bead manufacturing apparatus 10 according to a fourteenth aspect of the present invention is configured in any one of the eighth to thirteenth aspects such that the diameter H2 of the middle part of the valve element 22 is the diameter A of the inlet 21a of the valve body 21 of the flush valve 20 + 2 to 8 mm.

[0053] The expanded beads manufacturing apparatus 10 according to a fifteenth aspect of the present invention is configured in any one of the eighth to fourteenth aspects, such that the expansion coefficient variation of the expanded beads is less than 10%.

[0054] The expanded beads manufacturing apparatus 10 according to a sixteenth aspect of the present invention is configured in such a manner that, in the ninth aspect, the guide surface 21b is inclined so that the end 21d on the side of the connecting port 21c is at the lowest position.

[0055] ​​The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Example]

[0056] The present invention will be described in more detail below using examples and comparative examples, but the present invention should not be construed as being limited to these examples.

[0057] <Measurement of variation in expansion ratio of expanded beads> 1 kg of expanded polyolefin resin particles was sieved using JIS Z8801 standard sieves (11 types of sieves with nominal dimensions of 1, 1.18, 1.4, 1.7, 2, 2.36, 2.8, 3.35, 4, 4.75, and 5.6). The weight fraction Wi and expansion ratio Ki of the expanded polyolefin resin particles remaining on each sieve were measured, and the average expansion ratio Kav was calculated using the following formula (1).

[0058]

number

number

number

[0059] The expansion ratio Ki of the expanded polyolefin resin particles remaining on each sieve was determined as follows. First, the weight Gi of the expanded polyolefin resin particles remaining on each sieve was accurately weighed to 0.001 g (rounded to the fourth decimal point). Next, the weighed expanded polyolefin resin particles with a known weight were submerged in 100 ml of water at 23°C in a measuring cylinder, and the volume yi (cm) of the expanded polyolefin resin particles was calculated from the rise in the scale. 3 The weight Gi (g) of the expanded polyolefin resin particles was then calculated as the volume yi (cm 3 The apparent density di of the expanded polyolefin resin particles for each sieve was calculated by dividing the density by the density of the expanded polyolefin resin and converting it to g / L. Finally, the expansion ratio Ki = ds / di was calculated from the ratio to the density ds (= 900 g / L) of the base resin.

[0060] Example 1 (Production of resin particles) Ethylene-propylene random copolymer (density 0.90 g / cm), a polyolefin resin 3 The resulting mixture (ethylene content: 3%, melting point: 145°C, MI=7.5g / 10min, flexural modulus: 1000MPa) was fed into a 26mmφ twin-screw extruder [TEM26-SX, manufactured by Toshiba Machine Co., Ltd.] and melt-kneaded. It was then extruded through a cylindrical die with a diameter of 1.2mmφ, cooled with water, and cut with a cutter to obtain cylindrical resin composition particles (pellets) (1.2mg / particle) made of polyolefin resin. The resulting resin particles had a melting point of 145°C and a density of 0.90g / cm3 measured according to JIS K7112. 3 It was.

[0061] (Production of expanded beads) 100 parts by weight of the resulting resin particles, 0.5 parts by weight of tribasic calcium phosphate (manufactured by Taihei Chemical Industry Co., Ltd.) as a dispersant, and 0.03 parts by weight of sodium alkylsulfonate (n-paraffin sulfonate sodium) (manufactured by Kao Corporation, Latemul PS) as a dispersant were placed in a pressure vessel along with 200 parts by weight of water. Then, 3.5 parts by weight of carbon dioxide gas was placed in the pressure vessel, and the aqueous dispersion was heated to 151°C while stirring. The pressure inside the pressure vessel at this time was approximately 1.7 MPa. Additional carbon dioxide gas was then injected to raise the pressure to 2.2 MPa. After maintaining the predetermined foaming temperature and foaming pressure for 20 minutes, the aqueous dispersion in the pressure vessel was released from the pressure vessel through a flush valve into a lower-pressure vessel, yielding expanded particles. In this process, the inlet diameter (A) of the flush valve was 25 mm, the inner diameter (B) of the valve body of the flush valve was 38 mm, and the angle (C) of the direction in which the expanded beads were discharged relative to the direction in which the valve body of the flush valve extended was 60°. The expansion ratio and the variation in expansion ratio of the obtained expanded beads were measured.

[0062] Example 2 Except for changing the angle (C) to 50°, expanded beads were obtained in the same manner as in Example 1. The expansion ratio and the variation in expansion ratio of the obtained expanded beads were measured.

[0063] Example 3 Except for changing the angle (C) to 70°, expanded beads were obtained in the same manner as in Example 1. The expansion ratio and the variation in expansion ratio of the obtained expanded beads were measured.

[0064] Example 4 Except for setting the inlet diameter (A) of the flush valve to 25 mm and the inner diameter (B) of the valve body of the flush valve to 75 mm, expanded beads were obtained in the same manner as in Example 1. The expansion ratio and the variation in expansion ratio of the obtained expanded beads were measured.

[0065] Comparative Example 1 Except for changing the angle (C) to 40°, expanded beads were obtained in the same manner as in Example 1. The expansion ratio and the variation in expansion ratio of the obtained expanded beads were measured.

[0066] Comparative Example 2 Except for changing the angle (C) to 90°, expanded beads were obtained in the same manner as in Example 1. The expansion ratio and the variation in expansion ratio of the obtained expanded beads were measured.

[0067] The results of measuring the variations in the expansion ratios of the expanded beads of Examples 1 to 4 and Comparative Examples 1 and 2 are shown in Table 1.

[0068] [Table 1] From the results in Table 1, the expanded beads of Examples 1 to 4 had a good expansion ratio variation of 10% or less. On the other hand, the expanded beads of Comparative Examples 1 and 2 had a poor expansion ratio variation of more than 10%. Therefore, it was found that the expanded beads of Examples 1 to 4 had a reduced expansion ratio variation compared to the expanded beads of Comparative Examples 1 and 2. Furthermore, a comparison of Examples 1 to 3 with Comparative Examples 1 and 2 revealed that the expansion ratio variation was good when 50°≦C≦70°. [Explanation of symbols]

[0069] 1. Pressure vessel 3 discharge tube 4 Transport pipe 10 Manufacturing equipment 20 Flush valve 21 Valve body 21a Entrance 22 Valve body P0 resin particles P foam particles S Aqueous dispersion medium

Claims

1. an expansion step of dispersing polyolefin resin particles in an aqueous dispersion medium in a pressure-resistant vessel, heating and pressurizing the polyolefin resin particles to a temperature equal to or higher than the softening temperature of the polyolefin resin, and then releasing the polyolefin resin particles into a vessel having a pressure lower than the internal pressure of the pressure-resistant vessel, thereby expanding the polyolefin resin particles to obtain expanded polyolefin resin particles; The foaming step includes: a first step of discharging the polyolefin resin particles from the pressure-resistant container into a low-pressure container through a flush valve including a valve body and a valve element; a second step of directing the foamed particles released from the flush valve in a direction oblique to the direction in which the valve body of the flush valve extends, In the second step, The method for producing expanded beads, wherein when the angle of the direction in which the expanded beads are discharged relative to the direction in which the valve body of the flush valve extends is defined as C, the angle C is 40°<C<90°.

2. In the first step, 2. The method for producing expanded beads according to claim 1, wherein the polyolefin resin particles are released from the pressure-resistant container into a low-pressure container in a manner such that 1.0<B / A≦4.0 is satisfied, where A is the diameter of the inlet of the valve body of the flush valve and B is the inner diameter of the valve body.

3. In the first step, 3. The method for producing expanded beads according to claim 1, wherein when the diameter of the intermediate portion of the valve body is H2 and the inner diameter of the valve body is B, B and H2 are set so as to satisfy the relationship 1.0<B / H2≦3.

0.

4. 4. The method for producing expanded beads according to claim 1, wherein the diameter A of the inlet of the valve body of the flush valve is 20 to 30 mm.

5. 5. The method for producing expanded beads according to claim 1, wherein the diameter H1 of the tip portion of the valve body is 7 to 19 mm.

6. 6. The method for producing expanded beads according to claim 1, wherein a diameter H2 of the middle portion of the valve body is a diameter A of the inlet of the valve body of the flush valve plus 2 to 8 mm.

7. 7. The method for producing expanded beads according to claim 1, wherein the expansion coefficient variation of the expanded beads is less than 10%.

8. a pressure-resistant container for foaming the polyolefin-based resin particles; a flush valve for discharging the polyolefin resin particles in the pressure-resistant container into a low-pressure container; a discharge pipe for discharging the foam particles discharged from the flush valve; The flush valve includes a valve body and a valve element, the discharge pipe is connected to the valve body of the flush valve so as to be inclined with respect to the direction in which the valve body extends; The expanded bead manufacturing device, wherein when the angle between the direction in which the valve body of the flush valve extends and the direction in which the expanded beads are discharged is defined as C, the angle C satisfies 40°<C<90°.

9. The valve body is in communication with the discharge pipe via a connecting port, the valve body has a guide surface that guides the polyolefin resin particles that have flowed into the valve body to the connecting port, The expanded bead manufacturing apparatus according to claim 8 , wherein the guide surface is a surface inclined with respect to the axis of the valve body.

10. 10. The expanded beads manufacturing apparatus according to claim 8, wherein when the diameter of the inlet of the valve body of the flush valve is A and the inner diameter of the valve body is B, A and B are set so as to satisfy the relationship 1.0<B / A≦3.

5.

11. The expanded beads manufacturing device according to any one of claims 8 to 10, wherein when a diameter of the middle portion of the valve body is H2 and an inner diameter of the valve body is B, B and H2 are set so as to satisfy the relationship 1.0 < B / H2 ≦ 3.

0.

12. 12. The expanded bead manufacturing apparatus according to claim 8, wherein the diameter A of the inlet of the valve body of the flush valve is 20 to 30 mm.

13. 13. The expanded bead manufacturing device according to claim 8, wherein the diameter H1 of the tip portion of the valve body is 7 to 19 mm.

14. 14. The expanded bead manufacturing device according to claim 8, wherein a diameter H2 of the middle portion of the valve body is a diameter A of the inlet of the valve body of the flush valve plus 2 to 8 mm.

15. The expanded beads manufacturing apparatus according to any one of claims 8 to 14, wherein the expansion coefficient variation of the expanded beads is less than 10%.

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