Manufacturing method and manufacturing device for expanded thermoplastic resin particles

Abstract

The purpose of the present invention is to prevent the mutual adhesion of thermoplastic resin foam particles in a manufacturing process, and to obtain thermoplastic resin foam particles having a high foaming ratio. A manufacturing method according to the present invention comprises: a melt-kneading step for melt-kneading a thermoplastic resin and carbon dioxide gas as a foaming agent; and a granulation step for granulating thermoplastic resin foam particles through a hot cut method, wherein in the granulation step, a mixed mist (M) of water and air is sprayed toward die holes (6b) of a die (6), and the flow rate of water sprayed by the mist nozzle (8) is 1 L / h to 9 L / h per nozzle.

Description

[Technical field]

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

[0002] As a method for obtaining expanded thermoplastic resin particles, the extrusion foaming method is known.

[0003] In such a manufacturing method using the extrusion foaming method, first, a thermoplastic resin and a foaming agent are fed into an extruder, melt-kneaded, and cooled to obtain a foamable molten resin (a molten resin containing a foaming agent). The foamable molten resin (a molten resin containing the foaming agent) is then extruded into a low-pressure region through a fine hole die attached to the tip of the extruder, and chopped to obtain foamed thermoplastic resin particles. In addition, the extrusion foaming method using carbon dioxide gas, which has a low environmental impact, as a foaming agent has poor gas retention during foaming compared to the extrusion foaming method using an organic foaming agent. For this reason, it is particularly difficult to obtain foamed particles with a high expansion ratio using the extrusion foaming method using carbon dioxide gas.

[0004] The shredding method for obtaining foamed particles in the extrusion foaming method is roughly divided into the cold cut method and the die face cut method. The cold cut method is a method in which a molten resin containing a foaming agent extruded from a fine hole die is foamed, and a strand-shaped foam is taken out while being cooled through a water tank, and then shredded (strand cut method). The die face cut method is a method in which the molten resin extruded from a fine hole die is cut with a rotating cutter while in contact with the die face or while leaving a small gap.

[0005] The die face cutting method is further divided into three methods based on the difference in the cooling method. That is, the underwater cutting (hereinafter sometimes referred to as UWC) method, the watering cutting (hereinafter sometimes referred to as WRC) method, and the hot cutting (hereinafter sometimes referred to as HC) method. The UWC method is a method in which cooling water adjusted to a predetermined pressure is filled in a chamber attached to the tip of the die so that it contacts the resin discharge surface of the die, and the molten resin extruded from the narrow hole die is cut underwater. In addition, the WRC method is a method in which a cooling drum in which cooling water flows along the inner peripheral surface is connected downstream from the die, and the molten resin cut by the cutter in the air is cooled in the cooling water while foaming or after foaming. The UWC method and the WRC method are characterized in that the cooling water is also used to transport the resin to a water separator while cooling it.

[0006] In addition, the HC method does not use a method of conveying the resin while cooling it, such as by using cooling water flowing through a cooling drum, as in the WRC method. In the HC method, the molten resin cut by the cutter in the air is cooled in the air while foaming or after foaming. In addition, the foamed beads are generally conveyed by air transportation.

[0007] For example, the technology described in Patent Document 1 uses a hot-cut pelletizer used in the HC method. The hot-cut pelletizer described in Patent Document 1 is used to pelletize unfoamed thermoplastic resin into pellets of an appropriate size. Furthermore, Patent Document 2 describes a method for producing a thermoplastic resin by the WRC method.

[0008] Moreover, Patent Documents 3 and 4 disclose techniques for producing expanded thermoplastic resin particles by the UWC method. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 6-170839 [Patent Document 2] Patent No. 3671128 [Patent Document 3] International Publication No. WO2009 / 104671 [Patent Document 4] JP 2011-202077 A Summary of the Invention [Problem to be solved by the invention]

[0010] When attempting to produce expanded thermoplastic resin beads by the HC method as disclosed in Patent Document 1 or the WRC method as disclosed in Patent Document 2, there is a problem that the expanded beads stick to each other during the production process. On the other hand, when attempting to produce expanded thermoplastic resin beads by the UWC method as disclosed in Patent Documents 3 and 4 using carbon dioxide gas as a blowing agent, it is difficult to obtain expanded beads with a high expansion ratio.

[0011] That is, the conventional method is a method for producing thermoplastic resin pellets. Thermoplastic resin pellets are basically strongly influenced by gravity and therefore fall downward. On the other hand, thermoplastic resin foamed particles have a low density and are strongly influenced by the wind generated in the cutter case. For this reason, the thermoplastic resin foamed particles are retained in the cutter case for a long time. As a result, the foamed particles collide with each other many times and tend to stick to each other. Furthermore, static electricity is also easily generated, so the foamed particles tend to aggregate with each other due to static electricity, and the foamed particles tend to stick to each other. Therefore, in the conventional method, it is difficult to prevent the thermoplastic resin foamed particles from sticking to each other during the manufacturing process and obtain thermoplastic resin foamed particles with a high expansion ratio.

[0012] An object of one aspect of the present invention is to prevent the expansion of thermoplastic resin beads from adhering to each other during the production process and to obtain expansion of thermoplastic resin beads having a high expansion ratio. [Means for solving the problem]

[0013] In order to solve the above problems, a manufacturing method according to one embodiment of the present invention is a method for manufacturing expanded thermoplastic resin particles, comprising: a melt-kneading step of melt-kneading a thermoplastic resin and carbon dioxide gas as a blowing agent; and a granulation step of granulating expanded thermoplastic resin particles by a hot-cut method. The hot-cut method is a step of extruding a molten resin containing the thermoplastic resin and the blowing agent through a die hole, cutting the molten resin extruded from the die hole with a cutter in air, and cooling the molten resin in air while foaming or after foaming. The granulation step includes a step of spraying a mixed mist of water and air toward the die hole, and the flow rate of water sprayed by a nozzle in this step is 1 L / h to 9 L / h per nozzle.

[0014] Moreover, a manufacturing apparatus according to one embodiment of the present invention is an apparatus for manufacturing expanded thermoplastic resin particles, comprising an extruder for melt-kneading a thermoplastic resin and carbon dioxide gas as a blowing agent, a die having a hole through which the molten resin containing the thermoplastic resin and the blowing agent extruded from the extruder passes, and a granulation section having a cutter for cutting in air the molten resin that has passed through the die hole, and granulating thermoplastic resin expanded particles by a hot cut method, and characterized in that the apparatus is provided with at least one spray nozzle for spraying water, and the spray nozzle is arranged facing the die hole. Effect of the Invention

[0015] According to one aspect of the present invention, it is possible to prevent the expanded thermoplastic resin beads from adhering to each other during the production process and obtain expanded thermoplastic resin beads having a high expansion ratio. [Brief description of the drawings]

[0016] [Figure 1] 1 is a diagram showing a schematic configuration of a manufacturing apparatus for expanded thermoplastic resin beads according to one embodiment of the present invention. [Diagram 2] 2010 is a front view showing the internal configuration of the granulating unit of the production apparatus shown in FIG. 1, and 2010 is a front view showing a schematic diagram of the positional relationship between the mist nozzle and the die. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] All of the documents described in this specification are incorporated herein by reference. In this specification, when a numerical range is described as "A to B," the description means "A or more and B or less."

[0018] <Expandable thermoplastic resin particle manufacturing equipment> An embodiment of the present invention will be described in detail below. Fig. 1 is a diagram showing a schematic configuration of a manufacturing apparatus 10 for expanded thermoplastic resin beads according to this embodiment. 2010 in Fig. 2 is a front view showing the internal configuration of a granulation section A of the manufacturing apparatus 10. The manufacturing apparatus 10 is an apparatus for granulating expanded thermoplastic resin beads by extruding a molten resin (hereinafter, sometimes simply referred to as molten resin) containing a thermoplastic resin and carbon dioxide gas as a foaming agent, and cutting it in air.

[0019] As shown in FIG. 1, the manufacturing apparatus 10 includes an extruder 1 for extruding a molten resin, a feeder 2, a foaming agent supply unit 3, a transport section 4, a cooling section 5, and a granulation section A. The feeder 2 and the foaming agent supply unit 3 are connected to the extruder 1. The extruder 1, the transport section 4, the cooling section 5, and the granulation section A are connected to each other. The extruder 1, the transport section 4, the cooling section 5, and the granulation section A are arranged in this order from the upstream side to the downstream side in the extrusion direction of the molten resin. In the manufacturing apparatus 10, the transport section 4 can be omitted if the resin pressure in the piping from the extruder 1 to the granulation section A is sufficiently low. The transport section 4 and the cooling section 5 may be arranged in a reversed order with respect to the arrangement order shown in FIG. 1. The transport section 4 may be arranged both upstream and downstream of the cooling section 5. If the resin temperature is sufficiently lowered at the outlet of the extruder 1, the cooling section 5 may be omitted.

[0020] In the manufacturing apparatus 10, (i) raw materials such as thermoplastic resin are supplied into the extruder 1 via the feeder 2, and (ii) the foaming agent is supplied into the extruder 1 via the foaming agent supply unit 3. The thermoplastic resin and the foaming agent are melt-kneaded in the extruder 1. The melt-kneaded molten resin passes through the transport section 4 and the cooling section 5 and reaches the granulation section A. The molten resin is foamed and granulated in the granulation section A to produce expanded particles P. With respect to the flow of the molten resin from the extruder 1 toward the granulation section A, the extruder 1 side is the upstream side, and the granulation section A side is the downstream side.

[0021] The extruder 1 can be appropriately selected from conventionally known extruders depending on the type of resin to be granulated, and examples thereof include extruders using screws. As the extruder using screws, for example, a single screw extruder or a twin screw extruder can be used. When a single screw extruder is used, the feeder 2 can be omitted. When a twin screw extruder is used, the screw rotation directions may be the same or different.

[0022] The feeder 2 is composed of a member for supplying a thermoplastic resin. Although one feeder 2 is provided in Fig. 1, the number of feeders 2 can be appropriately set according to the characteristics, type, number, etc. of the raw material of the thermoplastic resin foamed beads.

[0023] The foaming agent supplying unit 3 is composed of members that supply a foaming agent to the molten resin melt-kneaded in the extruder 1. More specifically, the foaming agent supplying unit 3 includes a foaming agent storage section 3a and a pump 3b. In the foaming agent supplying unit 3, the foaming agent stored in the foaming agent storage section 3a is supplied to the extruder 1 by the pump 3b. When the foaming agent is carbon dioxide gas, the foaming agent storage section 3a is a carbon dioxide gas cylinder, and the pump 3b is a high-pressure pump.

[0024] The transport section 4 is composed of a transport member for transporting the molten resin from the extruder 1 to the granulation section A. The transport member may be a known transport member used in the extrusion foaming method, such as a gear pump. The gear pump is a useful member for maintaining or appropriately increasing the pressure of the flow of the molten resin.

[0025] The cooling section 5 is composed of a cooling member that cools the molten resin transported from the transport section 4 (extruder 1 when the transport section 4 is omitted). The cooling member may be any known cooling member used in the extrusion foaming method. Examples of the cooling member include a single screw extruder or a static mixer. The molten resin is cooled to a predetermined temperature by gradually cooling the resin while mixing it at a low shear rate with the single screw extruder or the static mixer.

[0026] In the manufacturing apparatus 10, raw materials such as thermoplastic resin supplied through the feeder 2 are melted and kneaded in the extruder 1. The barrel temperature for melting the raw materials is not particularly limited, and may be within a range that does not interfere with the supply of the foaming agent to the raw materials. If the thermoplastic resin is not melted at the foaming agent supply position in the extruder 1, the foaming agent may escape to the upstream side of the extruder 1. For this reason, it is preferable to set the barrel temperature so that the thermoplastic resin is completely melted while preventing the foaming agent from vaporizing due to a high resin temperature. For example, when the thermoplastic resin is a polypropylene-based resin, the thermoplastic resin is preferably melted and kneaded at a barrel temperature of 180°C or more and 220°C or less.

[0027] The kneaded material melted at such a resin temperature is mixed with a blowing agent by the blowing agent supply unit 3 in the extruder 1. The molten resin containing the thermoplastic resin and the blowing agent moves while being further kneaded, passes through the transport section 4 and the cooling section 5, and reaches the granulation section A. The molten resin is granulated and foamed in the granulation section A, whereby expanded particles P are produced.

[0028] The granulation unit A includes a die 6, a cutter 7, a mist nozzle 8, and a cutter case 9 (collection unit). The cutter case 9 is a cylindrical housing that houses at least the cutter blade 7a of the cutter 7 and the mist nozzle 8. Although Figs. 1 and 2 show an example of the granulation unit A of a side cut type, it may also be of a center cut type.

[0029] The granulating section A is configured to granulate the molten resin by the HC method, not the UWC method, and therefore the inside of the cutter case 9 is not filled with water or the like.

[0030] The die 6 is disposed on the most downstream side in the flow of the molten resin. The die 6 has a resin discharge surface 6a through which the molten resin extruded from the extruder 1 is discharged. The resin discharge surface 6a has a die hole 6b through which the molten resin extruded from the extruder 1 passes.

[0031] The cutter 7 is a member that cuts the molten resin discharged from the resin discharge surface 6a through the die hole 6b of the die 6. The cutter 7 has a plurality of cutter blades 7a, an air discharge port 7b, and a rotating shaft portion 7c. The cutter blade 7a is provided on the downstream side of the rotating shaft portion 7c and rotates around the axis of the rotating shaft portion 7c. The cutter blade 7a is configured to press against the resin discharge surface 6a of the die 6 or to secure a small gap therebetween while rotating.

[0032] The manufacturing apparatus 10 shown in FIGS. 1 and 2 is a side-cut type apparatus in which the rotation shaft portion 7c of the cutter 7 is disposed offset from the central axis N of the die 6.

[0033] The air outlet 7b is disposed rearward in the rotation direction of the cutter blade 7a. The air outlet 7b is configured to eject air forward in the rotation direction of the cutter blade 7a. As a result, in the granulation section A, air is blown from the air outlet 7b to the molten resin immediately after cutting by the cutter blade 7a. By providing the air outlet 7b in this manner, the molten resin is easily released from the cutter blade 7a after cutting by the cutter blade 7a. In addition, in the manufacturing apparatus 10, a water outlet can be disposed instead of the air outlet 7b.

[0034] The mist nozzle 8 sprays cooling water onto the resin discharge surface 6a of the die 6. 2020 in FIG. 2 is a front view showing a schematic positional relationship between the mist nozzle 8 and the die 6. As shown in 2020 in FIG. 2, the mist nozzle 8 has at least one spray nozzle 8a for spraying water. The mist nozzle 8 is provided at a position where it can spray toward the resin discharge surface 6a of the die 6. That is, the spray nozzle 8a is arranged toward the die hole 6b of the die 6. As a result, the mixed mist M of water and air sprayed from the spray nozzle 8a fills the space near the die hole 6b of the die 6.

[0035] The mist nozzle 8 may be provided in one or more units, so long as cooling water is sprayed to all of the die holes 6b. The spray flow rate of the mist nozzle 8 is 1 L / h to 9 L / h per nozzle, preferably 3 L / h to 9 L / h, and more preferably 3 L / h to 6 L / h. If the spray flow rate is less than 1 L / h, the expanded beads are insufficiently cooled, and the expanded beads are likely to adhere to each other. If the spray flow rate is more than 9 L / h, the die 6 is excessively cooled, and the die holes 6b are likely to be blocked by the molten resin.

[0036] The average spray particle diameter of the water is preferably 40 μm or less, more preferably 35 μm or less. If the average spray particle diameter is larger than 40 μm, the die 6 is easily cooled, and the die holes 6b are easily clogged with the molten resin. This reduces the cooling efficiency of the foamed particles, and the foamed particles are easily stuck to each other. In terms of the average spray particle diameter, the mist nozzle 8 is preferably a two-fluid nozzle. In the two-fluid nozzle, water and air are supplied inside. Then, a mixed mist M of water and air is generated inside the nozzle.

[0037] The cutter case 9 is a portion for accommodating the cutter 7 and recovering the expanded beads P produced by the HC method. A discharge port 9c is provided at the bottom of the cutter case 9 for discharging the expanded beads P produced.

[0038] The side wall surface 9a of the cutter case 9 has a foamed particle collision area 9a1. More specifically, the side wall surface 9a has the foamed particle collision area 9a1, a cylindrical side area 9a2, and a flat area 9a3. The cylindrical side area 9a2 is located between the foamed particle collision area 9a1 and the flat area 9a3. The foamed particle collision area 9a1 is an area that connects the end of the cylindrical side area 9a2 and the discharge port 9c. The flat area 9a3 is an area that connects the end of the cylindrical side area 9a2 opposite to the foamed particle collision area 9a1 and the discharge port 9c. The cylindrical side area 9a2 has a cylindrical side surface that is aligned with the rotational orbit of the cutter blade 7a. The central axis of the cylindrical side area 9a2 is approximately aligned with the rotation shaft portion 7c.

[0039] In addition, the expanded particle collision region 9a1 is subjected to a non-adhesive coating treatment. That is, a coating layer 9b is formed on the expanded particle collision region 9a1. The coating layer 9b is provided to prevent the expanded particles P from adhering to the expanded particle collision region 9a1. By forming the coating layer 9b, the expanded particles P do not adhere to the expanded particle collision region 9a1. The material constituting the coating layer 9b is not particularly limited as long as it is a material that does not adhere to the expanded particles P, but preferable examples include fluororesin, polyether ether ketone, and silicone rubber.

[0040] The molten resin transported to the granulation section A is extruded through the die hole 6b of the die 6. When the molten resin is discharged from the die hole 6b of the resin discharge surface 6a of the die 6, it is cut into granules by the cutter 7 and granulated. Immediately after that, the granulated molten resin is separated from the cutter blade 7a by air from the air discharge port 7b. The molten resin is expanded under the atmospheric pressure atmosphere in the cutter case 9. As a result, expanded particles P expanded to an expansion ratio required for the product are manufactured. The expanded particles P here include not only particles expanded to an expansion ratio desired for the product, but also particles that start to expand after being cut into granules by the cutter 7 and particles in the middle of expanding.

[0041] The expanded particles P cut by the cutter 7 are moved to the discharge port 9c along the trajectory Q shown in Fig. 2 by the airflow generated by the rotation of the cutter blade 7a. More specifically, the expanded particles P move from the cutter blade 7a toward the expanded particle collision region 9a1 (trajectory Q1). After colliding with the expanded particle collision region 9a1 (coating layer 9b), the expanded particles P move along the cylindrical side region 9a2 and the flat region 9a3 (trajectory Q2) and are discharged to the outside of the manufacturing apparatus 10 from the discharge port 9c.

[0042] Here, according to the manufacturing apparatus 10 of this embodiment, a mist nozzle 8 is provided that sprays cooling water onto the molten resin cut by the cutter 7. Therefore, the space in which the expanded particles P exist immediately after cutting by the cutter 7 has an atmosphere with a higher mist concentration than other spaces. Therefore, the cutter 7 cuts the molten resin in an atmosphere with a high mist concentration. Therefore, mist adheres to the surface of the expanded particles P immediately after cutting. The mist adhering to the surface of the expanded particles P evaporates, promoting surface solidification of the expanded particles P, so that the expanded particles P do not stick to each other. Furthermore, this mist prevents aggregation and adhesion of the expanded particles P due to static electricity.

[0043] As described above, according to the manufacturing apparatus 10, the mist nozzle 8 that sprays cooling water onto the molten resin cut by the cutter 7 is provided, so that the expanded particles P can be prevented from adhering to each other.

[0044] In the manufacturing apparatus 10, the molten resin is extruded from the die hole 6b and cut by the cutter blades 7a in sequence. Each time the cutter blades 7a cut the molten resin, the expanded particles P collide with the expanded particle collision area 9a1 in sequence. After being cut by the cutter blades 7a, the expanded particles P collide with the expanded particle collision area 9a1 in a very short time (for example, within 0.02 seconds). At the time of colliding with the expanded particle collision area 9a1, the expanded particles P are not completely solidified. Therefore, the expanded particles P cut by a certain cutter blade 7a (sometimes referred to as the first expanded particles P) adhere to the expanded particle collision area 9a1 after colliding with the expanded particle collision area 9a1 and remain in the expanded particle collision area 9a1. While the first expanded particles P remain in the expanded particle collision area 9a1, the expanded particles P granulated by cutting by the next cutter blade 7a (sometimes referred to as the second expanded particles P) come into contact with the first expanded particles P. Then, the first expanded particles P and the second expanded particles P adhere to each other. Therefore, when the molten resin is cut successively by the cutter blades 7a, the expanded particles P adhere to each other in the expanded particle collision region 9a1.

[0045] Therefore, in the manufacturing apparatus 10, a coating layer 9b is formed in the expanded particle collision area 9a1 where the expanded particles P collide immediately after cutting by the cutter 7. Due to this coating layer 9b, the expanded particles P do not adhere to the expanded particle collision area 9a1 even if they are not completely solidified. Therefore, the expanded particles P cut by a certain cutter blade 7a (first expanded particles P) do not stay in the expanded particle collision area 9a1 after colliding with the expanded particle collision area 9a1, but move along the trajectory Q2. Before the expanded particles P (second expanded particles P) granulated by cutting by the next cutter blade 7a collide with the expanded particle collision area 9a1, the first expanded particles P leave the expanded particle collision area 9a1. As a result, it is possible to prevent the first and second expanded particles P from adhering to each other. And, even if the molten resin is cut in sequence by a plurality of cutter blades 7a, the expanded particles P do not adhere to each other.

[0046] In the configuration shown in Fig. 2, the coating layer 9b is formed only in the expanded particle collision region 9a1. However, the coating layer 9b is not limited to the configuration shown in Fig. 2, and it is sufficient that the coating layer 9b is provided at least on the surface (expanded particle collision region 9a1) where the expanded particles P collide immediately after cutting. The coating layer 9b is sufficient to be formed in a region including the expanded particle collision region 9a1, and may be formed on the entire surface of the side wall surface 9a.

[0047] The coating layer 9b may be made of various known coating materials as long as it can prevent adhesion of the foamed particles P. The coating material is not particularly limited, but examples thereof include fluororesin, polyether ether ketone, and silicone rubber.

[0048] 2, the expanded particle collision area 9a1 is a flat surface. However, the surface that constitutes the expanded particle collision area 9a1 is not limited to a flat surface as long as the expanded particles P can collide with the surface and can move from the collision point. The position of the expanded particle collision area 9a1 in the cutter case 9 can be appropriately set according to the positional relationship between the die hole 6b of the die 6 and the cutter 7, etc.

[0049] 1 and 2 is a side-cut type device. However, the configuration of the manufacturing apparatus 10 according to the present embodiment is not particularly limited as long as it is applicable to the HC method. The manufacturing apparatus 10 may be a center-cut type device.

[0050] In a center-cut type device, the rotation shaft portion 7c of the cutter 7 is disposed so as to coincide with the central axis N of the die 6. Therefore, in the resin discharge surface 6a of the die 6, the die holes 6b are formed around the central axis N. For example, when the die holes 6b are disposed at equal distances all around the central axis N, the expanded particles cut by the cutter 7 move in all directions with respect to the central axis N. Therefore, in this case, the expanded particle collision area 9a1 is formed over the entire side wall surface 9a of the cutter case 9.

[0051] The expansion ratio of the expanded beads P is 9 to 45 times. That is, the manufacturing apparatus 10 is suitable for manufacturing expanded beads P with an expansion ratio of 9 to 45 times. As described above, the granulation section A is configured to granulate the molten resin by the hot cut method, not the UWC method. That is, after the molten resin is cut by the cutter 7, the expanded beads P are released into an atmospheric pressure atmosphere, not into water. Therefore, compared with the UWC method, expanded beads P with a high expansion ratio of 9 to 45 times can be manufactured. The expansion ratio of the expanded beads P is 9 to 45 times, more preferably 15 to 45 times. When the expansion ratio is low, less than 9 times, the molten resin is difficult to solidify, and mutual adhesion of the expanded beads cannot be avoided. Note that the "expansion ratio" referred to here does not mean the expansion ratio of the expanded beads P during expansion after cutting by the cutter 7, but means the desired expansion ratio as a product.

[0052] As described above, the manufacturing apparatus 10 according to this embodiment can prevent the expanded beads P from adhering to each other during the manufacturing process, and can obtain expanded beads P with a high expansion ratio.

[0053] <Raw material for expanded P particles> In this embodiment, in addition to the thermoplastic resin and carbon dioxide gas as a foaming agent, various additives can be added as necessary as raw materials for producing the expanded particles P (hereinafter sometimes simply referred to as "expanded particles"). Examples of such additives include flame retardants, heat stabilizers, radical generators, processing aids, weather resistance stabilizers, nucleating agents, foaming aids, antistatic agents, radiation heat transfer inhibitors, and colorants. These additives can be used alone or in combination of two or more.

[0054] The thermoplastic resin used in this embodiment is not particularly limited as long as it is a thermoplastic resin having a general known foaming property. The manufacturing method according to this embodiment can be suitably applied to a thermoplastic resin having low carbon dioxide gas retention in foaming using carbon dioxide gas. From this viewpoint, the thermoplastic resin used in this embodiment is preferably a crystalline thermoplastic resin. Examples of such thermoplastic resins include polyolefin-based resins, polyester-based resins, polyphenylene ether-based resins, polyamide-based resins, polycarbonate-based resins, and mixtures thereof. The thermoplastic resin is more preferably a polyolefin-based resin or a polyester-based resin.

[0055] Examples of polyester resins include aliphatic polyester resins, aromatic polyester resins, aliphatic-aromatic polyester resins, etc. Specific examples of polyester resins include polyhydroxyalkanoate, polybutylene succinate (PBS), poly(butylene adipate-co-butylene terephthalate) (PBAT), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc. 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).

[0056] The polyolefin resin is not particularly limited, and examples thereof include polypropylene resins. The polypropylene resin may be a general-purpose linear polypropylene resin, or a modified polypropylene resin having a branched structure or a high molecular weight component. Examples of the method for producing the modified polypropylene resin include a method of irradiating a linear polypropylene resin (hereinafter, this resin may be referred to as a "raw polypropylene resin") with radiation, or a method of melt-mixing a linear polypropylene resin, a conjugated diene compound, and a radical polymerization initiator. In this embodiment, the polypropylene resin is preferably a resin having a branched structure, and the method for producing the modified polypropylene resin is preferably a modified polypropylene resin obtained by melt-mixing a linear polypropylene resin, a conjugated diene compound, and a radical polymerization initiator, because it is easy to produce and economically advantageous.

[0057] Examples of linear polypropylene-based resins that can be used in this embodiment include crystalline polymers such as homopolymers, block copolymers, and random copolymers of propylene. As the propylene copolymer, a polymer containing 75% by weight or more of propylene is preferable in that it maintains the crystallinity, rigidity, chemical resistance, etc., which are characteristics of polypropylene-based resins. Examples of copolymerizable α-olefins include α-olefins having 2 or 4 to 12 carbon atoms such as ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene, and 1-decene; cyclic olefins such as cyclopentene, norbornene, and tetracyclo[6,2,11,8,13,6]-4-dodecene; and 5-methylene-2- Examples of the monomer include dienes such as norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, and 7-methyl-1,6-octadiene; vinyl chloride, vinylidene chloride, acrylonitrile, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, ethyl acrylate, butyl acrylate, methyl methacrylate, maleic anhydride, styrene, methylstyrene, vinyltoluene, and divinylbenzene; and the like. In particular, ethylene and 1-butene are preferred from the viewpoints of improving cold brittleness resistance and being inexpensive. These may be used alone or in combination of two or more.

[0058] Among these, from the viewpoints of moldability in in-mold molding of the resulting expanded beads and the physical properties of the resulting molded articles, random copolymers are preferred, and propylene / ethylene / 1-butene random copolymers or propylene / ethylene random copolymers are more preferred.

[0059] The modified polypropylene resin usable in the present embodiment is preferably a modified polypropylene resin obtained by melt-mixing the linear polypropylene resin with a conjugated diene compound and a radical polymerization initiator.

[0060] Examples of the conjugated diene compound include butadiene, isoprene, 1,3-heptadiene, 2,3-dimethylbutadiene, and 2,5-dimethyl-2,4-hexadiene. These may be used alone or in combination of two or more. Among these, butadiene and isoprene are particularly preferred because they are inexpensive, easy to handle, and the reaction proceeds uniformly.

[0061] The amount of the conjugated diene compound added is preferably 0.01 to 20 parts by weight, more preferably 0.05 to 5 parts by weight, relative to 100 parts by weight of the linear polypropylene resin. If the amount of the conjugated diene compound added is less than 0.01 parts by weight, it may be difficult to obtain the effect of modification, and if the amount added exceeds 20 parts by weight, the effect may become saturated and may not be economical.

[0062] Monomers copolymerizable with the conjugated diene compound, for example, vinyl chloride, vinylidene chloride, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, metal acrylates, metal methacrylates, acrylic esters such as methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and stearyl acrylate; methacrylic esters such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, and stearyl methacrylate; and the like may be used in combination.

[0063] Examples of the radical polymerization initiator generally include peroxides and azo compounds. Preferred are initiators capable of abstracting hydrogen from the polypropylene resin or the conjugated diene compound, and generally include organic peroxides such as ketone peroxides, peroxyketals, hydroperoxides, dialkyl peroxides, diacyl peroxides, peroxydicarbonates, and peroxyesters. Among these, initiators with particularly high hydrogen abstraction ability are preferred, such as peroxyketals such as 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, n-butyl 4,4-bis(t-butylperoxy)valerate, and 2,2-bis(t-butylperoxy)butane; dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, α,α'-bis(t-butylperoxy-m-isopropyl)benzene, t-butylcumyl peroxide, di-t-butyl peroxide, and 2,5-dimethyl Examples of the peroxyester include dialkyl peroxides such as 2,5-di(t-butylperoxy)-3-hexyne, diacyl peroxides such as benzoyl peroxide, and peroxyesters such as t-butylperoxyoctate, t-butylperoxyisobutyrate, t-butylperoxylaurate, t-butylperoxy3,5,5-trimethylhexanoate, t-butylperoxyisopropylcarbonate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butylperoxyacetate, t-butylperoxybenzoate, and di-t-butylperoxyisophthalate. These may be used alone or in combination of two or more.

[0064] The amount of radical polymerization initiator added is preferably 0.01 parts by weight or more and 10 parts by weight or less, more preferably 0.05 parts by weight or more and 4 parts by weight or less, relative to 100 parts by weight of linear polypropylene resin. If the amount of radical polymerization initiator added is within the above range, efficient resin modification is possible. If the amount of radical polymerization initiator added is less than 0.01 parts by weight, it may be difficult to obtain the effect of modification, and if the amount added is more than 10 parts by weight, the effect of modification may become saturated and may not be economical.

[0065] Examples of devices for reacting the linear polypropylene resin, the conjugated diene compound, and the radical polymerization initiator include rolls, co-kneaders, Banbury mixers, Brabenders, kneaders such as single-screw extruders and twin-screw extruders, horizontal mixers such as twin-screw surface renewal machines and twin-screw multi-disk devices, and vertical mixers such as double helical ribbon mixers. Of these, it is preferable to use a kneader, and in particular, extruders such as single-screw extruders and twin-screw extruders are preferable from the viewpoint of productivity.

[0066] There is no particular restriction on the order or method of mixing and kneading (stirring) the linear polypropylene resin, the conjugated diene compound, and the radical polymerization initiator. After mixing the linear polypropylene resin, the conjugated diene compound, and the radical polymerization initiator, the mixture may be melt-kneaded (stirred), or after melt-kneading (stirring) the polypropylene resin, the conjugated diene compound or the radical initiator may be mixed simultaneously or separately, all at once or in portions. The temperature of the kneader (stirrer) is preferably 130°C or higher and 300°C or lower, so that the linear polypropylene resin melts and does not thermally decompose. The time for melt-kneading is generally preferably 1 to 60 minutes.

[0067] There is no limitation on the shape or size of the modified polypropylene resin thus obtained, and it may be in the form of pellets.

[0068] The melting point of the polypropylene resin of this embodiment is preferably 130°C or more and 155°C or less, more preferably 135°C or more and 153°C or less, and even more preferably 140°C or more and 150°C or less. If the melting point of the polypropylene resin is within the above range, the dimensional stability and heat resistance of the in-mold foamed molded product are improved. In addition, the pressure of the molding heating steam when the polypropylene resin foam particles are in-mold foamed becomes appropriate. If the melting point of the polypropylene resin is less than 130°C, the dimensional stability of the in-mold foamed molded product tends to decrease or the heat resistance of the foamed molded product tends to be insufficient, and if the melting point exceeds 155°C, the pressure of the molding heating steam when in-mold foamed molding tends to be high.

[0069] Here, the melting point of the polypropylene resin is measured using a differential scanning calorimeter DSC [for example, DSC6200 manufactured by Seiko Instruments Inc.] as follows: That is, 5 to 6 mg of the polypropylene resin is heated from 40°C to 220°C at a heating rate of 10°C / min to melt the resin, then cooled from 220°C to 40°C at a heating rate of 10°C / min to crystallize it, and then heated again from 40°C to 220°C at a heating rate of 10°C / min. The melting point is determined as the melting peak temperature in the DSC curve during the second heating.

[0070] The foaming agent used in this embodiment is carbon dioxide gas. Carbon dioxide gas is a preferred foaming agent from the viewpoint of safety during handling and simplification of required equipment specifications. Furthermore, when carbon dioxide gas is used as a foaming agent, a foam with a high expansion ratio is easily obtained compared to other inorganic foaming agents such as nitrogen and water. The amount of foaming agent added varies depending on the type of thermoplastic resin and the expansion ratio of the targeted foamed particles, so it may be appropriately adjusted, but is preferably 1 part by weight or more and 20 parts by weight or less, more preferably 1 part by weight or more and 10 parts by weight or less, relative to 100 parts by weight of polypropylene resin.

[0071] Furthermore, a bubble nucleating agent may be added for the purpose of controlling the bubble shape of the expanded beads. Examples of bubble nucleating agents include sodium bicarbonate-citric acid mixtures, monosodium citrate, talc, calcium carbonate, etc., which may be used alone or in combination of two or more. The amount of bubble nucleating agent to be added is not particularly limited, but is usually preferably 0.01 parts by weight or more and 5 parts by weight or less per 100 parts by weight of the polypropylene resin.

[0072] In addition, other synthetic resins than the polypropylene resin may be added to the base resin within a range that does not impair the effects of the present invention. Examples of synthetic resins other than the polypropylene resin include ethylene resins such as high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, linear very low-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, and ethylene-methacrylic acid copolymer; styrene resins such as polystyrene, styrene-maleic anhydride copolymer, and styrene-ethylene copolymer; and the like.

[0073] In this embodiment, if necessary, stabilizers such as antioxidants, metal deactivators, phosphorus-based processing stabilizers, ultraviolet absorbers, ultraviolet stabilizers, fluorescent whitening agents, metal soaps, and antacid adsorbents, or additives such as crosslinking agents, chain transfer agents, nucleating agents, lubricants, plasticizers, fillers, reinforcing agents, pigments, dyes, flame retardants, and antistatic agents may be added. Examples of the antacid adsorbents include magnesium oxide and hydrotalcite.

[0074] In this embodiment, there is no limitation on the addition of colorants, and a natural color can be obtained without adding colorants, or a desired color can be obtained by adding colorants such as blue, red, black, etc. Examples of colorants include perylene-based organic pigments, azo-based organic pigments, quinacridone-based organic pigments, phthalocyanine-based organic pigments, threne-based organic pigments, dioxazine-based organic pigments, isoindoline-based organic pigments, carbon black, etc.

[0075] The expanded beads can also be produced by a method in which the inside of the expanded polypropylene resin beads is pressurized with an inert gas and heated to increase the expansion ratio (for example, the method described in JP-A-10-237212).

[0076] In the present embodiment, the weight of the expanded beads is preferably 3 mg / particle or less, more preferably 2 mg / particle or less, because the expanded beads are easily filled and expanded to form a molded article with a beautiful appearance. The lower limit is not particularly limited, but is preferably 0.3 mg / particle or more, taking into consideration productivity, etc.

[0077] In addition, the bubble diameter of the expanded beads in this embodiment is preferably 0.1 to 1.0 mm, and more preferably 0.15 to 0.7 mm, because the expanded beads expand to every corner of the mold during in-mold foam molding and the shrinkage of the obtained in-mold foam molded article is small.

[0078] The in-mold foamed article of the present embodiment can be obtained by filling the foamed beads into a mold that can be closed but cannot be sealed, and then heating and molding with water vapor.

[0079] To form an in-mold foamed article from the expanded beads of this embodiment, for example, (i) a method in which the expanded beads are pressurized with an inorganic gas to impregnate the particles with the inorganic gas and impart a predetermined intra-particle pressure, and then the expanded beads are filled into a mold and heat-fused with steam or the like (e.g., JP-B-51-22951), (ii) a method in which the expanded beads are compressed by gas pressure, filled into a mold, and heat-fused with steam or the like by utilizing the recovery force of the beads (e.g., JP-B-53-33996), or (iii) a method in which the expanded beads are filled into a mold with an expanded gap, the mold is closed to a predetermined gap, the filled expanded beads are compressed, and then heat-fused with steam or the like can be used.

[0080] <Method of manufacturing thermoplastic resin foam beads> The method for producing expanded thermoplastic resin particles according to the present embodiment is a method for producing expanded thermoplastic resin particles, and includes a melt kneading step of melt kneading a thermoplastic resin and carbon dioxide gas as a blowing agent, and a granulation step of granulating expanded thermoplastic resin particles by a hot cut method. The hot cut method is a step of extruding a molten resin containing the thermoplastic resin and the blowing agent through a die hole, cutting the molten resin extruded from the die hole with a cutter in air, and cooling the molten resin in air while foaming or after foaming. The granulation step includes a step of spraying a mixed mist of water and air toward the die hole, and the flow rate of water sprayed by a nozzle in this step is 1 L / h to 9 L / h per nozzle. The production method according to the present embodiment is not particularly limited as long as it has such characteristics. For example, a production method using the above-mentioned production apparatus 10 can be mentioned. Hereinafter, a production method for expanded thermoplastic resin particles using the production apparatus 10 will be described with reference to Figs. 1 and 2.

[0081] First, in the manufacturing method according to the present embodiment, a thermoplastic resin is fed from a feeder 2 into an extruder 1, and for example, in the case of a polypropylene-based resin, the resin is melted at a barrel temperature of 200°C. Next, a foaming agent is added to the extruder 1 from a foaming agent supply unit 3 (melt kneading process). Depending on the type and characteristics of the expanded particles to be manufactured, additives other than the thermoplastic resin described above may be fed into the extruder 1. In this case, the additives can be added simultaneously with the thermoplastic resin by blending the additives with the thermoplastic resin in advance and feeding the blend into the extruder 1. Alternatively, the extruder 1 may be provided with an addition port separate from the feeder 2 for feeding the thermoplastic resin, and the additives may be fed into the extruder 1 from this addition port.

[0082] In this way, in the extruder 1, the molten resin containing the thermoplastic resin and the foaming agent is melt-kneaded, and then the molten resin is sent from the transport section 4 to the cooling section 5. Then, after the molten resin is cooled to a desired resin temperature in the cooling section 5, the molten resin is extruded through the die 6. In the manufacturing method according to this embodiment, the expanded particles P are granulated by a hot cut method (granulation process). In this hot cut method, the molten resin is extruded through the die hole 6b of the die 6, the molten resin extruded from the die hole 6b of the die 6 is cut by the cutter 7 in air, and the molten resin is cooled in air while foaming or after foaming. More specifically, the cutter 7 is driven as the molten resin is extruded through the die 6, and the cutter blade 7a is rotated around the rotating shaft section 7c. Then, the molten resin extruded from the die 6 is cut by the cutter 7. At this time, air or water is sprayed from the cutter 7. For example, after cutting by the cutter 7, air is discharged from the air discharge port 7b to make it easier for the molten resin to separate from the cutter blade 7a. At this time, the linear velocity of the air is preferably 25 m / sec or more. If the linear velocity of the air is less than 25 m / sec, the degree to which the expanded thermoplastic resin particles are separated from the cutter blade 7a becomes poor, and the expanded thermoplastic resin particles tend to stick to each other.

[0083] The pressure of the molten resin in the extruder 1 is kept constant by the transport section 4. The pressure of the molten resin in the extruder 1 should be kept at a level that does not vaporize the foaming agent. For example, when the foaming agent is carbon dioxide gas, the pressure can be set to 10 MPa.

[0084] The temperature of the molten resin immediately before being extruded through the die 6 is cooled to a desired resin temperature by the cooling section 5. The temperature of the molten resin immediately before being extruded through the die 6 can be, for example, 142°C in the case of a polypropylene-based resin.

[0085] In the manufacturing method according to this embodiment, a mist nozzle 8 is used to spray cooling water onto the molten resin cut by the cutter 7. In the granulation step, a mixed mist M of water and air is sprayed toward the die hole 6b of the die 6, and the flow rate of water sprayed by the mist nozzle 8 is 1 L / h to 9 L / h per nozzle. As a result, the mist adheres to the surface of the expanded beads P immediately after cutting. The mist adhering to the surface of the expanded beads P evaporates, promoting surface solidification of the expanded beads P, and therefore the expanded beads P do not stick to each other.

[0086] The water spray flow rate is 1 L / h to 9 L / h per nozzle, preferably 3 L / h to 9 L / h, and more preferably 3 L / h to 6 L / h. If the spray flow rate is less than 1 L / h, the expanded beads are insufficiently cooled, and the expanded beads are likely to adhere to each other. If the spray flow rate is more than 9 L / h, the die 6 is excessively cooled, and the die hole 6b is likely to be blocked by the molten resin.

[0087] The average water spray particle size is preferably 40 μm or less, more preferably 35 μm or less. If the average water spray particle size is larger than 40 μm, the die 6 is likely to cool, and the die holes 6b are likely to become clogged with the molten resin. This reduces the cooling efficiency of the expanded beads, and the expanded beads are likely to stick to each other.

[0088] In addition, after the molten resin is cut by the cutter 7, the expanded particles P are discharged into a cutter case 9 under atmospheric pressure, not underwater. Therefore, compared to the UWC method, expanded particles P with a high expansion ratio of 9 to 45 times can be produced.

[0089] In addition, the manufacturing method according to this embodiment further includes a recovery step of recovering the thermoplastic resin foamed beads formed from the molten resin cut by the cutter, and in the recovery step, it is preferable to collide the thermoplastic resin foamed beads immediately after cutting against a surface that has been subjected to a non-adhesive coating treatment.

[0090] 1 and 2, in the recovery step, the expanded particles P formed from the molten resin cut by the cutter 7 are recovered in a cutter case 9. In the recovery step, the expanded particles P immediately after cutting are collided with the coating layer 9b in the expanded particle collision area 9a1. The coating layer 9b is a layer formed by applying a non-adhesive coating treatment to the expanded particle collision area 9a1. This makes it possible to further prevent the expanded particles P from sticking to each other.

[0091] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. The technical scope of the present invention also includes embodiments obtained by appropriately combining the technical means disclosed in the different embodiments. Furthermore, new technical features can be formed by combining the technical means disclosed in the respective embodiments.

[0092] 〔summary〕 As described above, the manufacturing method according to the first aspect of the present invention is a method for manufacturing expanded thermoplastic resin particles, and includes a melt-kneading step of melt-kneading a thermoplastic resin and carbon dioxide gas as a blowing agent, and a granulation step of granulating expanded thermoplastic resin particles (expanded particles P) by a hot-cut method. The hot-cut method is a step of extruding a molten resin containing the thermoplastic resin and the blowing agent through a hole (die hole 6b) in a die 6, cutting the molten resin extruded from the hole (die hole 6b) in the die 6 with a cutter 7 in air, and cooling the molten resin in air while foaming or after foaming. The granulation step includes a step of spraying a mixed mist M of water and air toward the hole (die hole 6b) in the die 6, and the flow rate of water sprayed by a nozzle (mist nozzle 8) in this step is 1 L / h to 9 L / h per nozzle.

[0093] Furthermore, the manufacturing method according to aspect 2 of the present invention, in accordance with aspect 1, further includes a recovery step of recovering the thermoplastic resin foamed particles (expanded particles P) formed from the molten resin cut by the cutter 7, and the recovery step includes a step of colliding the thermoplastic resin foamed particles immediately after cutting against a surface (coating layer 9b) that has been subjected to a non-adhesive coating treatment.

[0094] Moreover, the production method according to a third aspect of the present invention is the same as that of the first or second aspect, in which the granulation step includes a step of ejecting air or water from the cutter 7.

[0095] In the manufacturing method according to a fourth aspect of the present invention, in the third aspect, the linear velocity of the air discharged from the cutter 7 is 25 m / sec or more.

[0096] In the manufacturing method according to a fifth aspect of the present invention, in any one of the first to fourth aspects, the mixed mist M has an average spray particle size of 40 μm or less.

[0097] In the production method according to a sixth aspect of the present invention, in any one of the first to fifth aspects, the expansion ratio of the expanded thermoplastic resin beads (expanded beads P) is 9 to 45 times.

[0098] In the production method according to a seventh aspect of the present invention, in any one of the first to fifth aspects, the expansion ratio of the expanded thermoplastic resin beads (expanded beads P) is 15 to 45 times.

[0099] In the production method according to an eighth aspect of the present invention, in any one of the first to seventh aspects, the expanded thermoplastic resin particles (expanded particles P) are made of a crystalline thermoplastic resin.

[0100] The manufacturing apparatus 10 according to the ninth aspect of the present invention is a manufacturing apparatus 10 for manufacturing expanded thermoplastic resin particles, and is provided with an extruder 1 for melt-kneading a thermoplastic resin and carbon dioxide gas as a blowing agent, a die 6 having a hole (die hole 6b) through which the molten resin containing the thermoplastic resin and the blowing agent extruded from the extruder 1 passes, and a granulation section A having a cutter 7 for cutting in air the molten resin that has passed through the hole (die hole 6b) of the die 6, and granulating thermoplastic resin expanded particles (expanded particles P) by a hot cutting method, and is provided with at least one spray nozzle 8a for spraying water, and the spray nozzle 8a is configured to be directed toward the hole (die hole 6b) of the die 6.

[0101] A tenth aspect of the present invention relates to the manufacturing apparatus 10 of the ninth aspect. The cutter 7 is provided with an outlet (air outlet 7b) for ejecting air or water.

[0102] The manufacturing apparatus 10 according to aspect 11 of the present invention, in accordance with aspect 9 or 10, further includes a recovery section (cutter case 9) for recovering the thermoplastic resin foamed particles (foamed particles P) formed from the molten resin cut by the cutter 7, and in the recovery section, at least the surface (foamed particle collision area 9a1) with which the thermoplastic resin foamed particles (foamed particles P) collide immediately after cutting is subjected to a non-adhesive coating treatment.

[0103] The manufacturing apparatus 10 of aspect 12 of the present invention is configured in such a manner that, in aspect 11, the recovery section is a cutter case 9 that houses the cutter 7, and the non-adhesive coating treatment is applied to the side wall surface 9a of the cutter case 9. EXAMPLES

[0104] Example 1 Using the production apparatus 10 shown in Figs. 1 and 2, expanded beads P were produced under the following production conditions.

[0105] <Manufacturing conditions> Thermoplastic resins: polypropylene, Thermoplastic resin feed rate: 1kg / hour, Amount of carbon dioxide gas (foaming agent) supplied: 5 parts by weight per 100 parts by weight of thermoplastic resin, Extruder 1: φ15mm twin screw extruder, Screw speed of extruder 1: 150 rpm, Extruder 1 temperature: 200℃, -Temperature of cooling section 5: 148℃, Die 6 temperature: 142℃, Cutter case 9: Teflon (registered trademark) coating layer 9b on side wall surface 9a; Cutter 7 rotation speed: 1000rpm, Mixed Mist M water volume: 4.2L / hour, Mixed mist M spraying method: spray toward die 6, - Average particle size of mixed mist M: 30μm, Air flow rate from cutter blade 7a: 62.5 m / sec.

[0106] As a result, the expansion ratio of the produced expanded beads P was 23.9 times, and the mutual adhesion rate between the expanded beads was 0%.

[0107] Comparative Example 1 The expanded beads P were produced in the same manner as in the <production conditions> of Example 1, except that the mixed mist M was not sprayed toward the die 6. As a result, the expansion ratio of the produced expanded beads P was 21.2 times. In addition, the mutual adhesion rate of the expanded beads was 6%. [Explanation of symbols]

[0108] 1. Extruder 2 Feeder 3. Foaming agent (carbon dioxide) supply unit 4. Transportation Department 5 Cooling section 6 Die 6a Resin discharge surface 6b Die hole (Die hole) 7. Cutter 7b Air outlet 8 Mist nozzle 8a spray nozzle 9 Cutter case (collection section) 9a1 Foam particle collision area (surface where thermoplastic resin foam particles collide) 9b Coating layer (non-adhesive coating) 9c outlet 10 Manufacturing equipment A Granulation section M Mixed Mist P foam particles

Claims

1. A method for producing expanded thermoplastic resin particles, comprising the steps of: A melt-kneading step of melt-kneading a thermoplastic resin and carbon dioxide gas as a foaming agent; A granulation step of granulating the thermoplastic resin foam particles by a hot cut method, The hot cutting method is a process of extruding a molten resin containing the thermoplastic resin and the foaming agent through a die hole, cutting the molten resin extruded from the die hole with a cutter in air, and cooling the molten resin in air while foaming or after foaming, The granulation step includes a step of spraying a mixed mist of water and air toward holes in the die, and the flow rate of water sprayed by nozzles in the step is 1 L / h to 9 L / h per nozzle; The manufacturing method is characterized in that the granulation step includes a step of ejecting air or water from the cutter forward in the direction of rotation, and spraying air or water onto the molten resin immediately after cutting by the cutter.

2. The method further includes a recovery step of recovering expanded thermoplastic resin particles formed from the molten resin cut by the cutter, 2. The manufacturing method according to claim 1, wherein the recovery step includes a step of colliding the foamed thermoplastic resin particles immediately after cutting against a surface that has been subjected to a non-adhesive coating treatment.

3. 3. The method according to claim 1, wherein the linear velocity of the air discharged from the cutter is 25 m / sec or more.

4. 4. The method according to claim 1, wherein the mixed mist has an average spray particle size of 40 μm or less.

5. 5. The method according to claim 1, wherein the expansion ratio of the expanded thermoplastic resin particles is 9 to 45 times.

6. 5. The method according to claim 1, wherein the expansion ratio of the expanded thermoplastic resin particles is 15 to 45 times.

7. 7. The method according to claim 1, wherein the expanded thermoplastic resin particles are made of a crystalline thermoplastic resin.

8. An apparatus for producing expanded thermoplastic resin beads, comprising: an extruder for melt-kneading a thermoplastic resin and carbon dioxide gas as a foaming agent; a die having holes through which the molten resin containing the thermoplastic resin and the foaming agent extruded from the extruder passes; a granulating section having a cutter that cuts the molten resin that has passed through the die holes in air and granulating foamed thermoplastic resin particles by a hot cutting method; At least one spray nozzle for spraying water is provided, the spray nozzle being arranged toward the hole in the die; A manufacturing apparatus characterized in that the cutter is disposed rearward in the direction of rotation of the cutter and is provided with an outlet port for injecting air or water forward in the direction of rotation of the cutter onto the molten resin immediately after cutting.

9. The cutter further includes a recovery section for recovering expanded thermoplastic resin particles formed from the molten resin cut by the cutter.

9. The manufacturing apparatus according to claim 8, wherein in the recovery section, at least a surface against which the foamed thermoplastic resin particles collide immediately after cutting is treated with a non-adhesive coating.

10. the recovery unit is a cutter case that houses the cutter, 10. The manufacturing apparatus according to claim 9, wherein the non-adhesive coating is applied to a side wall surface of the cutter case.

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