Manufacturing apparatus and manufacturing method for expanded particles

Abstract

The purpose of the present invention is to produce expanded particles having a high expansion ratio by a depressurization expansion method using low-cost equipment having a simpler configuration. This production device (100) includes an expansion cylinder (10) that is equipped with a communication port (10b) through which the expansion cylinder (10) communicates with an open-system branch cylinder (21) and that has a space filled with an atmosphere saturated with steam, separately from the space inside the branch cylinder (21). The temperature (T1) inside the expansion cylinder (10) exceeds 102°C but not higher than the higher of 108°C and [(melting point Tm of the thermoplastic resin)-14°C]. The temperature (T2) at the communication port (10b) is 100°C or higher, and the temperature (T1) is higher than the temperature (T2).

Description

Technical Field

[0001] The present invention relates to an apparatus and a method for manufacturing foamed particles.

Background Art

[0002] Thermoplastic resin foamed particles (hereinafter, may be simply referred to as "foamed particles") are known to be manufactured by a pressure-relief foaming method. In the pressure-relief foaming method, thermoplastic resin particles are dispersed in water containing a dispersant in a pressure-resistant container, then a foaming agent is added, and after being impregnated with the foaming agent while maintaining a high temperature and high pressure, it is released into a low-pressure atmosphere.

[0003] For example, Patent Document 1 discloses a technique for manufacturing polyethylene-based resin foamed particles by a pressure-relief foaming method. The apparatus for manufacturing foamed particles described in Patent Document 1 is not usable in actual manufacturing facilities and is considered to be used for manufacturing on a so-called laboratory scale.

[0004] Further, Patent Document 2 discloses a technique for manufacturing polyolefin-based resin foamed particles by a pressure-relief foaming method. Patent Document 2 discloses an apparatus for manufacturing foamed particles on a scale used in actual manufacturing facilities, not on a laboratory scale. The manufacturing apparatus disclosed in Patent Document 2 includes a pressure-resistant container, a discharge valve, a nozzle, a separator, and a foamed particle storage tank. The pressure-resistant container, the discharge valve, the nozzle, the separator, and the foamed particle storage tank are connected by a transport pipe. When the discharge valve is opened, the thermoplastic resin particles impregnated with the foaming agent in the pressure-resistant container are discharged to the nozzle which is in a low-pressure atmosphere. Then, thereby, the thermoplastic resin particles foam and foamed particles are manufactured. The manufactured foamed particles are transported through the transport pipe, pass through the separator, and are stored in the foamed particle storage tank. In the manufacturing apparatus disclosed in Patent Document 2, the range of the pipe and equipment through which the foamed particles are transported from the outlet of the nozzle to the foamed particle storage tank is defined as the foaming chamber.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Patent No. 6547628 [Patent Document 2] International Publication No. WO2019 / 187986 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the above-mentioned prior art, there is still room for improvement in producing expanded beads with a high expansion ratio using actual production equipment.

[0007] According to the inventors' investigations, it has been found that in a method for producing expanded beads using a depressurization expansion method, expanded beads with a high expansion ratio can be produced by releasing thermoplastic resin beads impregnated with a blowing agent in a high-temperature water vapor atmosphere (saturated water vapor atmosphere). However, the inventors have discovered that when a high-temperature water vapor atmosphere is used as the foaming atmosphere in which thermoplastic resin beads are expanded to obtain expanded beads with a high expansion ratio, the production apparatus (production facility) disclosed in Patent Document 2 has the following problem. Specifically, in order to achieve a high-temperature water vapor atmosphere in this production apparatus, it is necessary to make the entire range of piping and equipment (including a separator, etc.) through which the expanded beads are transported from the nozzle outlet to the expanded bead storage tank a sealed system, thereby increasing the vapor partial pressure. Thus, making the entire apparatus a sealed system poses the problem of a complex device configuration.

[0008] An object of one aspect of the present invention is to produce expanded beads with a high expansion ratio by a depressurization foaming method using a simpler configuration and at low equipment costs. [Means for solving the problem]

[0009] In order to solve the above problems, one embodiment of the present invention provides a manufacturing apparatus for expanded beads, which comprises a pressure-resistant container for impregnating crystalline thermoplastic resin beads with a blowing agent, a foaming chamber with a pressure lower than the internal pressure of the pressure-resistant container, and an open transport pipe for transporting the expanded beads, wherein the foaming chamber has a communication port that communicates with the transport pipe and a space with a saturated water vapor atmosphere that is separate from the space inside the transport pipe, and wherein a first temperature inside the foaming chamber is greater than 102°C and is equal to or lower than the greater of 108°C or the melting point Tm of the thermoplastic resin -14°C, and a second temperature at the communication port is equal to or higher than 100°C, and the first temperature is greater than the second temperature.

[0010] In order to solve the above-mentioned problems, one embodiment of the present invention provides a method for producing expanded beads, comprising: an impregnation step in which crystalline thermoplastic resin particles are heated in a pressure-resistant container and impregnated with a blowing agent under pressurized conditions; an expansion step in which the thermoplastic resin particles impregnated with the blowing agent obtained in the impregnation step are released into a foaming chamber whose pressure is lower than the internal pressure of the pressure-resistant container to obtain expanded beads; and a transport step in which the expanded beads are transported through an open transport pipe, wherein the foaming chamber has a communication port communicating with the transport pipe and a space containing a saturated steam atmosphere that is separate from the space inside the transport pipe, wherein a first temperature inside the foaming chamber is greater than 102°C and is equal to or lower than the greater of 108°C or the melting point (Tm) of the thermoplastic resin (Tm-14°C); and a second temperature at the communication port is equal to or higher than 100°C, and the first temperature is greater than the second temperature. [Effects of the Invention]

[0011] According to one aspect of the present invention, expanded beads with a high expansion ratio can be produced by a depressurization foaming method using a simpler configuration and at low equipment costs. [Brief description of the drawings]

[0012] [Figure 1] 1 is a diagram showing a schematic configuration of an expanded bead manufacturing apparatus according to a first embodiment of the present invention. [Diagram 2]It is a cross-sectional view showing a schematic configuration of a foaming cylinder provided in a manufacturing apparatus according to Embodiment 1 of the present invention. [Figure 3] It is a cross-sectional view showing a configuration of a modified example of the foaming cylinder used in Embodiment 1 of the present invention. [Figure 4] It is a cross-sectional view showing a configuration of another modified example of the foaming cylinder used in Embodiment 1 of the present invention. [Figure 5] It is a view showing a schematic configuration of a manufacturing apparatus for foamed particles according to Embodiment 2 of the present invention.

Mode for Carrying Out the Invention

[0013] 〔Embodiment 1〕 Hereinafter, an embodiment of the present invention will be described in detail. FIG. 1 is a view showing a schematic configuration of a manufacturing apparatus 100 for foamed particles according to the present embodiment. The manufacturing apparatus referred to here does not intend a manufacturing apparatus used at the laboratory level, but intends a manufacturing apparatus used in an actual foamed particle production factory or the like. Therefore, the manufacturing apparatus in the present embodiment can also be said to be a production facility or a manufacturing plant.

[0014] As shown in FIG. 1, the manufacturing apparatus 100 includes a foaming cylinder 10 (foaming chamber), a pressure-resistant container 31, a dehydrator 32, a dryer 33, a transport blower 34, a shifter silo, and a filling silo. Further, the manufacturing apparatus 100 includes a transport air circulation line 20 that circulates transport air to the dehydrator 32, the dryer 33, and the transport blower 34. The transport air circulation line 20 is configured as an open system.

[0015] The "open system" means a configuration in which the entire range of pipes and facilities (including systems such as dehydrators) through which foamed particles are transported from the outlet of the nozzle to the dryer 33 is not made into a closed system for increasing the vapor partial pressure in order to realize a high-temperature foaming atmosphere by water vapor. The "open system" is, for example, a system in which at least one of the transport pipes such as the transport air circulation line 20 and various component members connected to the transport pipes is open to the outside.

[0016] The transport air circulation line 20 includes a branch cylinder 21, a transport pipe 22, a transport pipe 23, and a transport pipe 24. The transport pipe 22 is a pipe connecting the dehydrator 32 and the dryer 33. The transport pipe 23 is a pipe connecting the dryer 33 and the transport blower 34. The transport pipe 24 is a pipe connecting the transport blower 34 and the branch cylinder 21. Further, a foaming cylinder 10 is connected to the branch cylinder 21. In the transport air circulation line 20, the moist hot air in the dryer 33 is drawn into the transport pipe 23 by the transport blower 34. Then, the moist hot air passes through the transport pipe 24, the branch cylinder 21, and the transport pipe 22 and flows into the dryer 33 again. By providing the transport air circulation line 20 in this way, in the manufacturing apparatus 100, the moist hot air in the dryer 33 is utilized for transporting the foamed particles, thereby obtaining effects such as energy saving and prevention of bead shrinkage.

[0017] The pressure-resistant container 31 is a container for manufacturing foamed particles by the pressure-release foaming method. An aqueous dispersion containing crystalline thermoplastic resin particles (hereinafter, may be simply referred to as resin particles), an inorganic dispersant, and a dispersion aid, as well as a foaming agent, are charged into the pressure-resistant container 31 together with water. Then, the inside of the pressure-resistant container 31 is heated to a constant pressure and a constant temperature so that the resin particles are impregnated with the foaming agent. The resin particles impregnated with the foaming agent are discharged into the foaming cylinder 10 under a low-pressure atmosphere (pressure-release foaming method) and become foamed particles.

[0018] The foamed particles in the foaming cylinder 10 are transported to the branch cylinder 21 and then from the branch cylinder 21 to the dehydrator 32. The foamed particles are dehydrated in the dehydrator 32 and then dried in the dryer 33 via the transport pipe 22. A shifter silo and a filling silo are provided downstream of the dryer 33. The foamed particles are fed into the shifter silo, classified by a sieve, and stored in the filling silo.

[0019] FIG. 2 is a cross-sectional view showing a schematic configuration of the foaming cylinder 10 provided in the manufacturing apparatus 100 according to the present embodiment. As shown in FIG. 2, the foaming cylinder 10 has a steam inlet 10a and a communication port 10b. The steam inlet 10a is configured such that steam is introduced from a direction intersecting the axis of the foaming cylinder 10. The communication port 10b is an opening that communicates the foaming cylinder 10 with the branch cylinder 21. That is, the foaming cylinder 10 communicates with the branch cylinder 21 through the communication port 10b. The foaming cylinder 10 has a space Q in a saturated steam atmosphere. And this space Q in the saturated steam atmosphere is a separate space from the space inside the branch cylinder 21.

[0020] Further, the foaming cylinder 10 includes a cylinder main body 11, a throttle plate 12 (particle discharge portion) with a cylinder, a connection pipe 13, and a guide pipe 14.

[0021] The cylinder main body 11 has a large-diameter cylinder portion 11a, a reducer portion 11b (throttle portion), and a small-diameter cylinder portion 11c. The reducer portion 11b is a portion that connects the large-diameter cylinder portion 11a and the small-diameter cylinder portion 11c. Also, the large-diameter cylinder portion 11a, the reducer portion 11b, and the small-diameter cylinder portion 11c are connected coaxially. Further, the reducer portion 11b is configured such that the distance between the opposing side walls decreases as it goes toward the communication port 10b.

[0022] The squeezing disk 12 is provided in the large-diameter cylindrical portion 11a of the cylindrical body 11. The squeezing disk 12 is provided on the opposite side of the communication port 10b in the foaming cylinder 10. That is, the squeezing disk 12 is disposed at a position in the foaming cylinder 10 that is farthest from the communication port 10b. The squeezing disk 12 has a cylindrical body. Resin particles impregnated with a foaming agent are released from the cylindrical body of the squeezing disk 12 to become expanded particles P. Here, the squeezing disk 12, which serves as a particle release section, is configured to release the resin particles impregnated with the foaming agent so that the resin particles collide with the side wall surface of the foaming cylinder 10. The cylindrical body of the squeezing disk 12 is preferably disposed at an angle with respect to the axis of the foaming cylinder 10. Therefore, when the resin particles impregnated with the foaming agent are released from the cylindrical body of the squeezing disk 12, they collide with the side wall surface of the large-diameter cylindrical portion 11a. In this way, foam cells are formed by the impact force of the resin particles impregnated with the foaming agent colliding with the side wall surface of the large-diameter cylindrical portion 11a, thereby uniformly expanding each of the foamed particles P and reducing variations in the expansion ratio.In the configuration shown in Figure 2, the cylindrical body of the squeezing plate 12 is arranged at an angle to the axis of the foaming cylinder 10, but the arrangement of the cylindrical body of the squeezing plate 12 is not limited to that shown in Figure 2.

[0023] In addition, in the foaming cylinder 10, the steam inlet 10a is provided near the squeezing disc 12. In other words, in the foaming cylinder 10, the steam inlet 10a is provided at a position opposite to the communication port 10b. Furthermore, in the large-diameter cylinder portion 11a, the steam inlet 10a and the squeezing disc 12 are provided at a position opposite to the reducer portion 11b.

[0024] The connection pipe 13 is a pipe that connects the small-diameter cylindrical portion 11c of the cylindrical body 11 and the branching cylinder 21. The connection pipe 13 and the branching cylinder 21 are in communication with each other via a communication port 10b. The foaming cylinder 10 has an uneven surface 13a on at least the inner wall of the connection pipe 13. An example of the connection pipe 13 having such a configuration is a flexible hose. The inner wall surface of a flexible hose is configured with an uneven surface so that it can be bent freely.

[0025] The guide pipe 14 is provided inside the branch cylinder 21. The guide pipe 14 communicates with the connecting pipe 13 via the communication port 10b. As shown in FIG. 2, the guide pipe 14 has a discharge port 14a for the foamed particles P and stands upright on the inner wall surface of the branch cylinder 21. Further, the guide pipe 14 is arranged so that the transport air W does not flow into the discharge port 14a. For example, the guide pipe 14 has a structure such that the portion in contact with the transport air W is downstream of the most upstream position 10c of the communication port 10b. With such a configuration, the foamed particles P discharged from the discharge port 14a of the guide pipe 14 are easily transported along the flow of the transport air W. That is, it is possible to prevent the re-inflow of the foamed particles P into the foaming cylinder 10 by the transport air W.

[0026] Also, the discharge port 14a preferably has its diameter reduced to be smaller than the diameter of the communication port 10b. Thereby, the flow velocity of the ejection flow due to foaming at the discharge port 14a combined with the introduced steam can be adjusted to be larger than the flow velocity of the transport air W, and it is possible to prevent the transport air W from flowing into the communication port 10b or the inside of the foaming cylinder 10.

[0027] Steam is introduced into the foaming cylinder 10 from the steam inlet 10a. The space Q inside the foaming cylinder 10 is a space with a saturated steam atmosphere. The temperature inside the space Q is controlled as follows: (i) The temperature T1 (the first temperature) inside the foaming cylinder 10 exceeds 102°C and is 108°C or lower or the higher temperature of the melting point Tm - 14°C of the thermoplastic resin. (ii) The temperature T2 (the second temperature) at the communication port 10b is 100°C or higher. (iii) The temperature T1 is higher than the temperature T2. When the temperatures T1 and T2 are within the above ranges, foamed particles P with a high foaming ratio can be obtained. The foaming ratio of the obtained foamed particles P is 10 times or more, preferably 11 times or more, and more preferably 13 times or more.

[0028] Here, regarding the condition (i) above, the melting point Tm of the thermoplastic resin is a value measured by differential scanning calorimetry. Specifically, (a) 5 to 6 mg of the thermoplastic resin is heated from 40°C to 220°C at a heating rate of 10°C / min to be melted, then (b) cooled from 220°C to 40°C at a cooling rate of 10°C / min for crystallization, and (c) further heated from 40°C to 220°C at a heating rate of 10°C / min. And the melting point Tm is a value obtained by determining the melting peak temperature during the second heating as the melting point from the DSC curve obtained by such operations (a) to (c).

[0029] For example, when the thermoplastic resin is polyethylene (PE), although it depends on the type of polyethylene, the melting point Tm is 122 to 128°C. The melting point Tm - 14°C is 108 to 114°C. Therefore, the temperature T1 inside the foaming cylinder 10 is controlled to exceed 102°C and be 108 to 114°C or lower. Note that the upper limit of the temperature T1 is appropriately set according to the type of polyethylene. More specifically, when the melting point Tm of polyethylene (PE) is 122°C, the temperature T1 inside the foaming cylinder 10 is controlled to exceed 102°C and be 108°C or lower. More preferably, the temperature T1 is controlled to be 103°C to 105°C.

[0030] For example, when the thermoplastic resin is polypropylene (PP), although it depends on the type of polypropylene, the melting point Tm is 136 to 155°C. The melting point Tm - 14°C is 122 to 141°C. Therefore, the temperature T1 inside the foaming cylinder 10 is controlled to exceed 102°C and be 122 to 141°C or lower. Note that the upper limit of the temperature T1 is appropriately set according to the type of polypropylene.

[0031] Also, regarding the condition (ii) above, more preferably, the temperature T2 is controlled to be 100°C to 103°C. For example, the difference between the temperature T1 and the temperature T2 is preferably 0°C to 3°C.

[0032] Furthermore, as in the condition (iii) above, since the temperature T1 is higher than the temperature T2, the saturated water vapor pressure inside the foaming cylinder 10 is higher than the saturated water vapor pressure at the communication port 10b. Therefore, the saturated water vapor inside the foaming cylinder 10 flows toward the communication port 10b. However, since the difference between the temperature T1 and the temperature T2 is 6°C or less, the saturated water vapor remains inside the foaming cylinder 10. The resin particles impregnated with the foaming agent are released into the atmosphere where the saturated water vapor remains. Therefore, the expanded particles P produced have a high expansion ratio.

[0033] Here, the measurement location of the temperature T1 is a location that represents the temperature inside the foaming cylinder 10 and is far from the communication port 10b, and can be appropriately set depending on the shape of the foaming cylinder 10. For example, when the foaming cylinder 10 has the structure shown in Fig. 2, the measurement location of the temperature T1 is near the squeezing disc 12. More specifically, it is a location that is 50 to 140 mm away from the squeezing disc 12 and 2000 to 3000 mm away from the communication port 10b. The measurement location of the temperature T1 may also be near the steam inlet 10a.

[0034] Here, in the manufacturing apparatus 100, the space Q of the saturated water vapor atmosphere in the foaming cylinder 10 is a space separate from the space inside the branching cylinder 21. More specifically, the foaming cylinder 10 is provided outside the branching cylinder 21. Therefore, the space Q of the saturated water vapor atmosphere in the foaming cylinder 10 is isolated from the space inside the branching cylinder 21.

[0035] In conventional expanded bead manufacturing devices used in factories, resin particles impregnated with a blowing agent are discharged into a part of the space in the transport air circulation line 20, for example, the space in the branch tube 21. Therefore, in order to discharge the resin particles impregnated with a blowing agent into a space with a saturated water vapor atmosphere, it is necessary to make the entire transport air circulation line 20 a space with saturated water vapor. For this reason, it is necessary to seal the transport air circulation line 20 from the outside and make it a sealed system, which makes the structure of the manufacturing device complex and large, and increases the equipment cost.

[0036] In contrast, in the manufacturing apparatus 100 according to this embodiment, the foaming cylinder 10, into which resin particles impregnated with a foaming agent are released, is separated from the space inside the transport air circulation line 20. Therefore, it is sufficient to make the space Q inside the foaming cylinder 10, not the entire space of the transport air circulation line 20, a space of saturated water vapor atmosphere. Therefore, the transport air circulation line 20 does not need to be a sealed system, but can be an open system that is open to the outside. Therefore, the manufacturing apparatus 100 can achieve depressurization foaming in a high-temperature water vapor atmosphere with a simple structure. Therefore, the depressurization foaming method can manufacture expanded particles with a high expansion ratio with a simpler structure.

[0037] Furthermore, according to the manufacturing apparatus 100 of this embodiment, the cylinder body 11 of the foaming cylinder 10 is cylindrical and has a reducer portion 11b in which the distance between the opposing side walls decreases toward the communication port 10b. As a result, the cylinder body 11 has a reducer shape in which the diameter narrows toward the communication port 10b. Therefore, the water vapor flowing out from the communication port 10b is restricted, and the water vapor tends to remain inside the foaming cylinder 10. Therefore, the expanded particles P have a higher chance of contacting with the water vapor inside the foaming cylinder 10, and thus the expanded particles P can have a high expansion ratio.

[0038] Further, according to the manufacturing apparatus 100, the expansion cylinder 10 is provided outside the branch cylinder 21. The expansion cylinder 10 includes a connecting pipe 13 connected to the branch cylinder 21, and at least the inner wall of the connecting pipe 13 has an uneven surface 13a. By providing the connecting pipe 13 in this manner, the length from the cylinder body 11 to the communication port 10b can be increased by the length of the connecting pipe 13. Therefore, the contact time between the expanded particles P and water vapor is extended. Furthermore, since at least the inner wall of the connecting pipe 13 has an uneven surface 13a, the expanded particles P in the expansion cylinder 10 collide irregularly in the connecting pipe 13 and reach the communication port 10b. As a result, the time it takes for the expanded particles P to reach the communication port 10b while foam cells are formed by the impact force of the collision is extended. Therefore, the contact time between the expanded particles P and water vapor is extended. Since the contact time between the expanded particles P and water vapor is extended in this manner, expanded particles P with a high expansion ratio can be obtained.

[0039] As long as the effect of increasing the contact time between the foamed particles P and the water vapor is achieved, the uneven surface 13a may be formed at least on the inner wall of the connection pipe 13. The uneven surface 13a may be formed on the inner wall of the cylinder main body 11 as well.

[0040] Further, the connection pipe 13 may have a configuration in which the foamed particles P collide irregularly inside. For example, it may have a structure that is repeatedly bent by a straight pipe with a smooth inner surface and a bent pipe.

[0041] Further, the foaming cylinder 10 can be used as an optional facility for existing foamed particle production equipment. The manufacturing apparatus 100 according to the present embodiment may also include existing production equipment provided with the foaming cylinder 10 as such an optional facility.

[0042] (Method for manufacturing foamed particles) The method for manufacturing foamed particles according to the present embodiment includes an impregnation step, a foaming step, and a transportation step. In the impregnation step and the foaming step, after the crystalline thermoplastic resin particles are heated and pressurized in a pressure-resistant container and impregnated with a foaming agent (impregnation step), the thermoplastic resin particles impregnated with the foaming agent are discharged into a foaming chamber at a pressure lower than the internal pressure of the pressure-resistant container to obtain thermoplastic resin foamed particles (foaming step). Further, in the transportation step, the thermoplastic resin foamed particles are transported through an open transportation pipe. In the manufacturing method according to the present embodiment, the foaming chamber is provided with a communication port communicating with the transportation pipe and has a space with a saturated water vapor atmosphere. This space with a saturated water vapor atmosphere is a separate space from the space inside the transportation pipe. Further, the first temperature inside the foaming chamber exceeds 102°C and is 108°C or lower or below the higher temperature of the melting point Tm - 14°C of the thermoplastic resin, the second temperature at the communication port is 100°C or higher, and the first temperature is controlled to be higher than the second temperature. As such a manufacturing method, for example, there is a method for manufacturing foamed particles using the manufacturing apparatus 100 shown in FIG. 1. Regarding the details of this manufacturing method, basically, the description of the above-mentioned manufacturing apparatus is incorporated, and only the non-overlapping parts will be described below.

[0043] The manufacturing method according to this embodiment preferably includes, in the foaming step, a step of discharging the thermoplastic resin particles impregnated with the foaming agent into a cylindrical foaming cylinder 10 having a reducer portion 11b in which the distance between the opposing side walls decreases as it approaches the communication port 10b. This makes it easier for water vapor to stay in the foaming cylinder 10. Therefore, in the foaming cylinder 10, the contact opportunity between the foaming particles P and the water vapor increases, so that highly foamed particles can be obtained.

[0044] Also, when the foaming cylinder 10 is provided outside the branch cylinder 21 and the transport air circulation line 20, and the foaming cylinder 10 includes a connection pipe 13 connected to the branch cylinder 21 and at least the inner wall of the connection pipe 13 has an uneven surface 13a formed thereon, the foaming step preferably includes the following steps. That is, preferably, in the foaming step, it includes a step of discharging the thermoplastic resin particles impregnated with the foaming agent into the foaming cylinder 10 connected to the connection pipe 13. As a result, the contact time between the foaming particles and the water vapor becomes longer, so that highly foamed particles can be obtained.

[0045] The manufacturing method according to this embodiment preferably includes a drying step of drying the foaming particles using a dryer 33, and in the transport step, includes a step of transporting the foaming particles through a transport air circulation line 20 that circulates the air in the dryer 33 as the transport pipe. By using the moist hot air in the dryer 33 for transporting the foaming particles in this way, energy saving and the effect of preventing bead shrinkage can be obtained.

[0046] Also, the manufacturing method according to this embodiment preferably includes, in the foaming step, a step of discharging the thermoplastic resin particles impregnated with the foaming agent so that the thermoplastic resin particles collide with the side wall surface of the foaming cylinder 10. As a result, each of the foaming particles P can be uniformly foamed, and the variation in the foaming ratio can be reduced.

[0047] (Raw material of foaming particles P) In this embodiment, in addition to a crystalline thermoplastic resin and a foaming agent, various additives can be added as raw materials for manufacturing the foamed particles P (hereinafter sometimes simply referred to as "foamed particles"). For example, flame retardants, heat stabilizers, radical generators, processing aids, weather resistance stabilizers, nucleating agents, foaming aids, antistatic agents, radiation heat transfer inhibitors, coloring agents, and the like can be mentioned. These additives can be used singly or in combination of two or more.

[0048] Further, the thermoplastic resin used in this embodiment is not particularly limited as long as it is a crystalline thermoplastic resin having general known foamability. Examples of the thermoplastic resin include polyolefin resins, polyester resins, polyphenylene ether resins, polyamide resins, and mixtures thereof. The thermoplastic resin is preferably a polyolefin resin or a polyester resin.

[0049] Examples of the polyester resin include aliphatic polyester resins, aromatic polyester resins, and aliphatic-aromatic polyester resins. Specific examples of the polyester resin include, for example, polyhydroxyalkanoate, polybutylene succinate (PBS), poly(butylene adipate-co-butylene terephthalate) (PBAT), polyethylene terephthalate (PET), and the like. Further, the polyhydroxyalkanoate is at least one selected from the group consisting of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), poly(3-hydroxybutyrate) (P3HB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB4HB), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), and poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate).

[0050] In addition, the polyolefin resin is not particularly limited, and examples thereof include polypropylene resins and polyethylene resins. Specific examples of the monomer of the polyolefin resin (hereinafter, may also be referred to as an olefin monomer) include, for example, α-olefins having 2 to 12 carbon atoms such as ethylene, propylene, butene-1, isobutene, pentene-1, 3-methyl-butene-1, hexene-1, 4-methyl-pentene-1, 3,4-dimethyl-butene-1, heptene-1, 3-methyl-hexene-1, octene-1, and decene-1. These may be used alone or in combination of two or more.

[0051] In addition, examples of other monomers having copolymerizability with the olefin monomer include cyclic olefins such as cyclopentene, norbornene, and 1,4,5,8-dimethano-1,2,3,4,4a,8,8a,6-octahydronaphthalene, and dienes such as 5-methylene-2-norbornene, �-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, and 7-methyl-1,6-octadiene. These may be used alone or in combination of two or more.

[0052] Specific examples of the polyolefin resin include, for example, polyethylene resins mainly composed of ethylene such as high-density polyethylene, medium-density polyethylene, low-density polyethylene, and linear low-density polyethylene, and polypropylene resins mainly composed of propylene. These polyolefin resins may be used alone or in combination of two or more.

[0053] Among these polyolefin resins, the polyethylene resin mainly composed of ethylene is particularly effective in the production method according to the present embodiment. In particular, a polypropylene resin containing ethylene as a comonomer component in which the α-olefin is ethylene is easily available and excellent in processing moldability.

[0054] The polypropylene resin is not particularly limited as long as it contains propylene as the main component of the monomer. For example, propylene homopolymer, α-olefin-propylene random copolymer, α-olefin-propylene block copolymer, etc. can be mentioned. These may be used alone or in combination of two or more.

[0055] As the foaming agent, volatile hydrocarbon-based foaming agents such as propane, isobutane, butane, pentane, and hexane; inorganic gases such as air, nitrogen, and carbon dioxide; and water can be used. When using an inorganic gas, carbon dioxide is preferred because foamed particles with a relatively high foaming ratio are easily obtained. These foaming agents may be used alone or in combination of two or more.

[0056] In the manufacturing apparatus 100 according to this embodiment, as described above, the space in the saturated steam atmosphere in the foaming cylinder 10 is a separate space from the space inside the branch cylinder 21. The configuration of the "separate space" here means a configuration in which the space in the foaming cylinder 10 and the space in the branch cylinder 21 are isolated. It is not limited to the configuration in which the foaming cylinder 10 is arranged outside the branch cylinder 21 as shown in FIG. 2. For example, a configuration in which a foaming cylinder is formed in the space inside the transport air circulation line 20 (for example, the space inside the branch cylinder 21) may be used. In this case, the space in the foaming cylinder 10 and the space in the branch cylinder 21 are isolated by the wall portion constituting the foaming cylinder 10. Hereinafter, a modified example of the foaming cylinder 10 will be described.

[0057] (Modified Example 1) FIG. 3 is a cross-sectional view showing the configuration of a modified example of the foaming cylinder used in this embodiment.

[0058] As shown in FIG. 3, the branch cylinder 21 has a branch flow path 21a and a main flow path 21b. The foaming cylinder 10A as Modification 1 is disposed in the main flow path 21b of the branch cylinder 21. The foaming cylinder 10A includes a cylindrical cylinder body 11A. The steam inlet 10a is configured such that steam is introduced along the axis of the foaming cylinder 10. The foaming cylinder 10A is configured such that the pressure inside the foaming cylinder 10A due to the steam V flowing in from the communication port 10b is greater than the pressure of the transport air W. Thereby, it is possible to prevent the foamed particles P from flowing backward into the cylinder body 11A by the transport air W.

[0059] (Modification 2) FIG. 4 is a cross-sectional view showing the configuration of another modification of the foaming cylinder used in the present embodiment.

[0060] As shown in FIG. 4, in Modification 2, the foaming cylinder 10 shown in FIG. 2 is disposed in the main flow path 21b of the branch cylinder 21. That is, in Modification 2, the foaming cylinder 10 is not provided outside the branch cylinder 21 but inside the branch cylinder 21. The foaming cylinder 10 is configured such that the pressure inside the foaming cylinder 10 due to the steam V flowing in from the communication port 10b is greater than the pressure of the transport air W. Thereby, it is possible to prevent the foamed particles P from flowing backward into the cylinder body 11 by the transport air W.

[0061] 〔Embodiment 2〕 Another embodiment of the present invention will be described below. For the sake of convenience of explanation, components having the same functions as those described in the above embodiment are denoted by the same reference numerals, and the description thereof will not be repeated. FIG. 5 is a diagram showing a schematic configuration of a manufacturing apparatus 101 according to the present embodiment.

[0062] As shown in FIG. 5, the manufacturing apparatus 101 according to this embodiment is different from the first embodiment in that it does not include a transport pipe 23. The manufacturing apparatus 101 includes a branch cylinder 21, a transport pipe 22, and a transport pipe 24. The transport pipe 22 is a pipe connecting the dehydrator 32 and the dryer 33. The transport pipe 24 is a pipe connecting the transport blower 34 and the branch cylinder 21. Further, a foaming cylinder 10 is connected to the branch cylinder 21. In the manufacturing apparatus 101, transport air is drawn into the transport pipe 24 from the outside by the transport blower 34. Then, the transport air passes through the branch cylinder 21 and the transport pipe 22 and flows into the dryer 33. The manufacturing apparatus 101 according to this embodiment is preferable because it has a simpler equipment configuration than the first embodiment, and has the advantage of lower equipment costs.

[0063] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in 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. Furthermore, by combining the technical means disclosed in each embodiment, new technical features can be formed.

[0064] (Summary) The manufacturing apparatus 100 according to Aspect 1 of the present invention is a manufacturing apparatus 100 for foamed particles P, and includes a pressure-resistant container 31 for impregnating crystalline thermoplastic resin particles with a foaming agent, a foaming chamber (foaming cylinder 10) having a pressure lower than the internal pressure of the pressure-resistant container 31, and an open transport pipe (branch cylinder 21, transport air circulation line 20) for transporting foamed particles. The foaming chamber is provided with a communication port 10b communicating with the transport pipe, and has a space with a saturated water vapor atmosphere that is a separate space from the space inside the transport pipe. The first temperature (temperature T1) inside the foaming chamber exceeds 102°C and is equal to or lower than the higher of 108°C or the melting point Tm - 14°C of the thermoplastic resin. The second temperature (temperature T2) at the communication port 10b is 100°C or higher, and the first temperature is higher than the second temperature.

[0065] In the manufacturing apparatus 100 according to Embodiment 2 of the present invention, in Embodiment 1, the foaming chamber (foaming cylinder 10) is cylindrical, and has a throttle portion (reducer portion 11b) in which the distance between the side walls facing each other becomes smaller as it goes toward the communication port 10b.

[0066] In the manufacturing apparatus 100 according to Embodiment 3 of the present invention, in Embodiment 1 or 2, the foaming chamber (foaming cylinder 10) is provided outside the transport pipe (branch cylinder 21, transport air circulation line 20), and the foaming chamber includes a connection pipe 13 connected to the transport pipe, and has a concavo-convex surface 13a at least on the inner wall of the connection pipe 13.

[0067] In the manufacturing apparatus 100 according to Embodiment 4 of the present invention, in any one of Embodiments 1 to 3, it includes a dryer 33 for drying the foamed particles P, and the transport pipe constitutes a circulation line (transport air circulation line 20) for circulating the air in the dryer.

[0068] In the manufacturing apparatus 100 according to Embodiment 5 of the present invention, in any one of Embodiments 1 to 4, it includes a particle discharge portion (throttle plate 12) for discharging the thermoplastic resin particles impregnated with the foaming agent into the foaming chamber (foaming cylinder 10), and the particle discharge portion is configured to discharge the thermoplastic resin particles so as to collide with the side wall surface of the foaming chamber.

[0069] A manufacturing method according to a sixth aspect of the present invention is a method for manufacturing expanded beads P, comprising: an impregnation step of impregnating crystalline thermoplastic resin particles with a blowing agent under heated and pressurized conditions in a pressure-resistant vessel 31; an expansion step of releasing the thermoplastic resin particles impregnated with the blowing agent obtained in the impregnation step into an expansion chamber (expansion tube 10) whose pressure is lower than the internal pressure of the pressure-resistant vessel 31 to obtain expanded beads P; and a transport step of transporting the expanded beads P through an open transport piping (branch tube 21, transport air circulation line 20). The expansion chamber has a communication port 10b communicating with the transport piping and has a space with a saturated water vapor atmosphere that is separate from the space inside the transport piping. A first temperature (temperature T1) inside the expansion chamber exceeds 102°C and is equal to or lower than the greater of 108°C or the melting point Tm of the thermoplastic resin - 14°C. A second temperature at the communication port 10b is equal to or higher than 100°C, and the first temperature is higher than the second temperature.

[0070] A manufacturing method according to a seventh aspect of the present invention is a method in which, in the foaming step of the sixth aspect, the thermoplastic resin particles impregnated with the foaming agent are released into the cylindrical foaming chamber (foaming cylinder 10) having a constriction portion (reducer portion 11b) in which the distance between opposing side walls becomes smaller toward the communication port 10b.

[0071] A manufacturing method according to an eighth aspect of the present invention is a method according to the sixth or seventh aspect, wherein the foaming chamber (foaming cylinder 10) is provided outside the transport piping (branch cylinder 21, transport air circulation line 20), the foaming chamber is provided with a connecting pipe 13 connected to the transport piping, and at least the inner wall of the connecting pipe is provided with an uneven surface 13a, and the foaming step includes a step of releasing the thermoplastic resin particles impregnated with the foaming agent into the foaming chamber.

[0072] The manufacturing method according to aspect 9 of the present invention is a method according to any one of aspects 6 to 8, which includes a drying step of drying the expanded beads P using a dryer 33, and a transporting step of transporting the expanded beads P using a circulation line (transport air circulation line 20) that circulates air within the dryer as the transport piping.

[0073] In the manufacturing method according to Embodiment 10 of the present invention, in any one of Embodiments 6 to 9, in the foaming step, a step of discharging the thermoplastic resin particles impregnated with the foaming agent is included so as to collide with the side wall surface of the foaming chamber (foaming cylinder 10).

Example

[0074] (Examples 1 to 5, Comparative Example 1) Using the manufacturing apparatus 100 shown in FIG. 1, polyethylene-based resin foamed particles were manufactured on the scale of an actual production facility. Polyethylene-based resin foamed particles are usually manufactured by two-stage foaming. The apparatus configuration and foaming conditions of the manufacturing apparatus 100 are as shown in Table 1. Note that as the temperature T1, the temperature near the throttle plate 12 in the foaming cylinder 10 was measured. Also, as the temperature T2, the temperature near the communication port 10b was measured.

[0075] Then, the expansion ratio of the manufactured foamed particles was evaluated. The results are shown in Table 1. "〇" in Table 1 means that the expansion ratio of the foamed particles is 10 times or more and is good. Also, "×" means that the expansion ratio of the foamed particles is less than 10 times and is bad.

[0076]

Table 1

[0077] On the other hand, in Comparative Example 1, the temperature T1 is 102°C and the temperature T2 is 99°C. Therefore, in Comparative Example 1, the foaming conditions deviate from the conditions (i) and (ii) above. In Comparative Example 1, the expansion ratio was 9 times, and foamed particles with a high expansion ratio could not be obtained.

[0078] Also, in Examples 4 and 5, similar to Examples 1 to 3, the foaming conditions satisfy the above conditions (i) to (iii). In Examples 4 and 5, it was possible to obtain foamed particles with a high foaming ratio (foaming ratio of 11 times or more).

Explanation of Signs

[0079] 10, 10A Foaming cylinder (foaming chamber) 10b Communication port 11b Reducer section (constriction section) 12 Constriction plate (particle discharge section) 13 Connecting pipe 13a Concave-convex surface 20 Transport air circulation line (circulation line) 21 Branch cylinder (transport pipe) 21a Branch flow path (transport pipe) 21b Main flow path (transport pipe) 22, 23, 24 Transport pipes (transport pipes) 31 Pressure-resistant container 33 Dryer 100, 101 Manufacturing apparatus T1 Temperature (first temperature) T2 Temperature (second temperature) Q Space (space with saturated water vapor atmosphere)

Claims

1. An apparatus for manufacturing foamed particles, comprising: a pressure-resistant container for impregnating crystalline polyethylene resin particles with a foaming agent; a foaming chamber at a pressure lower than the internal pressure of the pressure-resistant container; a transport blower; a dehydrator; a dryer; a branch cylinder; a transport pipe connecting the transport blower, the branch cylinder, the dehydrator, and the dryer to transport the foamed particles; the foaming chamber is connected to the branch cylinder, and the foamed particles are transported from the branch cylinder to the dehydrator via the transport pipe, dehydrated by the dehydrator, and dried by the dryer; at least one of the transport pipe and various components connected to the transport pipe is an open system open to the outside; the foaming chamber is provided with a communication port communicating with the transport pipe and has a space with a saturated water vapor atmosphere, which is a space separate from the space inside the transport pipe; the space inside the foaming chamber and the space inside the transport pipe are isolated; the foaming chamber is cylindrical and has a throttle portion in which the distance between opposing side walls decreases as it approaches the communication port; the first temperature inside the foaming chamber exceeds 102°C and is equal to or lower than the higher temperature of 108°C or the melting point Tm - 14°C of the polyethylene resin; the second temperature at the communication port is 100°C or higher; the manufacturing apparatus, wherein the first temperature is higher than the second temperature.

2. the foaming chamber is provided outside the transport pipe; the foaming chamber is provided with a connection pipe connecting to the transport pipe, and at least the inner wall of the connection pipe has an uneven surface. The manufacturing apparatus according to claim 1.

3. The manufacturing apparatus according to claim 1 or 2, wherein the transport pipe constitutes a circulation line for circulating air inside the dryer.

4. comprising a particle discharge portion for discharging the polyethylene resin particles impregnated with the foaming agent into the foaming chamber; the manufacturing apparatus according to any one of claims 1 to 3, wherein the particle discharge portion discharges the polyethylene resin particles so as to collide with the side wall surface of the foaming chamber.

5. A method for manufacturing foamed particles, comprising: an impregnation step of heating crystalline polyethylene resin particles in a pressure-resistant container and impregnating them with a foaming agent under heating and pressurization conditions; a foaming step of obtaining foamed particles by discharging the polyethylene resin particles impregnated with the foaming agent obtained in the impregnation step into a foaming chamber at a pressure lower than the internal pressure of the pressure-resistant container; a transport step of transporting the foamed particles through a transport pipe. The transport pipe connects a transport blower, a dehydrator, a dryer, and a branch cylinder. The foaming chamber is connected to the branch cylinder. The foamed particles are conveyed from the branch cylinder to the dehydrator via the transport pipe, dehydrated in the dehydrator, and dried in the dryer. At least one of the transport pipe and various components connected to the transport pipe is an open system that is open to the outside. The foaming chamber is provided with a communication port that communicates with the transport pipe, and has a space with a saturated water vapor atmosphere, which is a space separate from the space inside the transport pipe. The space inside the foaming chamber and the space inside the transport pipe are isolated from each other. The foaming chamber is cylindrical and has a throttle portion where the distance between opposing side walls decreases as it approaches the communication port. The first temperature inside the foaming chamber exceeds 102°C and is equal to or lower than the higher temperature of 108°C or the melting point Tm - 14°C of the polyethylene-based resin. The second temperature at the communication port is 100°C or higher. The manufacturing method wherein the first temperature is higher than the second temperature.

6. The foaming chamber is provided outside the transport pipe. The foaming chamber includes a connection pipe that connects to the transport pipe, and at least the inner wall of the connection pipe has an uneven surface. The manufacturing method according to claim 5, wherein the foaming step includes a step of discharging the polyethylene-based resin particles impregnated with the foaming agent into the foaming chamber.

7. The manufacturing method includes a drying step of drying the foamed particles using a dryer. The manufacturing method according to claim 5 or 6, wherein in the transport step, the transport pipe includes a step of transporting the foamed particles in a circulation line that circulates air inside the dryer.

8. The manufacturing method according to any one of claims 5 to 7, wherein the foaming step includes a step of discharging the polyethylene-based resin particles impregnated with the foaming agent so as to collide with the side wall surface of the foaming chamber.

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