DECOMPOSITION PROCESS AND DECOMCOMPOSITION DEVICE FOR RESIN

Abstract

A decomposition process and a resin decomposition device capable of safely and efficiently decomposing a resin are provided.A resin decomposition device (10) comprises: a cylinder (12); a resin feeder (11) that supplies a thermoplastic resin to the cylinder (12); a screw (12a) that transports the supplied thermoplastic resin and a melt-plasticized thermoplastic resin; a fluid feeder (13) that supplies a heated and pressurized fluid to the cylinder to decompose the melt-plasticized thermoplastic resin in a subcritical or supercritical state; an extruder (14) provided at a tip of the cylinder (12) that discharges a decomposed thermoplastic resin product to the outside of the cylinder; a rotary drive mechanism (15) that rotates the screw (12a); and a backflow suppression mechanism (16) that suppresses the backflow of the melt-plastic thermoplastic resin in the cylinder (12).

Description

Resin decomposition treatment method and decomposition treatment device

[0001] The present invention relates to a resin decomposition method and decomposition treatment device, and more particularly to a resin decomposition method and decomposition treatment device that prevents backflow toward the resin supply section when performing resin decomposition treatment under high temperature and high pressure conditions.

[0002] Currently, plastic products are used in a wide range of fields, and the amount of plastic used is enormous. However, disposal of plastic products is costly, and the environmental impact of plastic products, such as their components being released into rivers and oceans when left in the natural environment, is a problem.

[0003] Therefore, various studies have been conducted on various resins to effectively utilize resources by recycling them. For example, a method is known in which acrylic resin is thermally decomposed using a twin-screw extruder to recover and reuse the resulting monomer (see, for example, Patent Document 1).

[0004] In recent years, research has also been conducted into a method of decomposing resins by exposing them to a fluid in a subcritical or supercritical state to obtain monomers.

[0005] Japanese Patent Application Publication No. 11-106427

[0006] When utilizing a subcritical or supercritical state, it is necessary to set a predetermined temperature and pressure depending on the liquid (fluid) used, and since high temperature and high pressure conditions are usually required, a sealed decomposition treatment device is considered for use in such applications.

[0007] On the other hand, if a decomposition treatment device capable of withstanding such subcritical or supercritical conditions is to be prepared, for example, a dedicated device must be fabricated, which increases the initial cost and the total treatment cost.

[0008] Therefore, an object of the present invention is to provide a resin decomposition method and decomposition treatment device that can safely and continuously perform resin decomposition treatment in order to promote the recycling of such resins.

[0009] The resin decomposition method disclosed in the present application includes the steps of: (a) supplying a thermoplastic resin from a resin supply unit to a cylinder; (b) heating and pressurizing the supplied thermoplastic resin in the cylinder to melt and plasticize it; (c) supplying a heated and pressurized fluid from a fluid supply unit to the melt-plasticized thermoplastic resin and mixing them; (d) decomposing the melt-plasticized thermoplastic resin by exposing it to a subcritical or supercritical state using the supplied fluid; and (e) extruding the decomposed thermoplastic resin obtained in step (d) from an extrusion unit provided at the tip of the cylinder.

[0010] Here, in this decomposition treatment method, in step (b), at least one selected from the temperature of the thermoplastic resin, the pressure of the thermoplastic resin, and the temperature of the cylinder is measured, and a backflow suppression step is started in accordance with the measured value to suppress the backflow of the molten plasticized thermoplastic resin.

[0011] The resin decomposition treatment device disclosed in the present application comprises a cylinder; a resin supply section that supplies the thermoplastic resin to be decomposed to the cylinder; a screw that transports the supplied thermoplastic resin and the melt-plasticized thermoplastic resin in the cylinder; a fluid supply section that supplies a heated and pressurized fluid into the cylinder in order to decompose the melt-plasticized thermoplastic resin in a subcritical or supercritical state; and an extrusion section that is provided at the tip of the cylinder and discharges decomposed products of the thermoplastic resin outside the cylinder.

[0012] Furthermore, this decomposition treatment device has at least one selected from a resin thermometer that measures the temperature of the thermoplastic resin, a resin pressure gauge that measures the pressure of the thermoplastic resin, a cylinder thermometer that measures the temperature of the cylinder, and a screw measurement gauge that measures the energy consumption or drive torque of the rotary drive mechanism that drives the screw, in a cylinder provided between the resin supply section and the fluid supply section, and has a backflow suppression mechanism that suppresses backflow of the molten plasticized thermoplastic resin in response to a change in at least one of the measured values ​​of the resin thermometer, the resin pressure gauge, the cylinder thermometer, and the screw measurement gauge.

[0013] According to the resin decomposition treatment method and decomposition treatment device disclosed in the present application, it is possible to provide a resin decomposition treatment method and decomposition treatment device that can be carried out safely and continuously.

[0014] FIG. 1 is a side view showing a schematic configuration of a resin decomposition treatment device of embodiment 1. FIG. 2 is a side view illustrating a screw arranged in a cylinder of the decomposition treatment device of FIG. 1. FIG. 3 is a view illustrating in more detail a backflow prevention mechanism in the decomposition treatment device of FIG. 1. FIG. 4 is a view illustrating in more detail a backflow prevention mechanism in the decomposition treatment device of FIG. 1. FIG. 5 is a flow chart illustrating the operation of a resin decomposition treatment device of embodiment 1. FIG. 6 is a side view showing a schematic configuration of a resin decomposition treatment device of embodiment 2. FIG. 7 is a flow chart illustrating the operation of a resin decomposition treatment device of embodiment 2. FIG. 8 is a side view showing a schematic configuration of a resin decomposition treatment device of embodiment 3. FIG. 9 is a flow chart illustrating the operation of a resin decomposition treatment device of embodiment 3.

[0015] Hereinafter, the embodiments will be described in detail with reference to examples and drawings. In all drawings for explaining the embodiments, components having the same functions are designated by the same or related reference numerals, and repeated explanations thereof will be omitted.

[0016] <Background of the Study> First, the background of the study of the present invention will be described. As described above, when decomposing a resin (depolymerizing a resin) using a fluid in a subcritical or supercritical state, a sealed processing vessel capable of withstanding the processing conditions is usually prepared. However, the present inventors studied whether a resin extrusion device used in forming a resin material could be used for the decomposition of this resin.

[0017] In other words, the inventors thought that by utilizing such a resin extrusion device, it would be possible to carry out resin decomposition processing continuously and efficiently using an existing extrusion device as is, or with slight modifications to make it suitable for decomposition processing, without having to prepare special processing equipment for resin decomposition processing.

[0018] In an extrusion device, a thermoplastic resin as a raw material is typically supplied from one side of a cylindrical cylinder, gradually heated and kneaded within the cylinder, and the molten, plasticized resin is transported by a screw. The molten, plasticized resin is then thoroughly kneaded as it is transported within the cylinder, and is extruded from a die at the tip of the cylinder as a uniformly mixed resin material. Because the inside of this cylinder is subjected to heated and pressurized conditions, it was anticipated that the device could be used as is for the decomposition treatment of the resin, by mixing the resin with a fluid in a subcritical or supercritical state within the cylinder.

[0019] In fact, the inventors tried to decompose resin under such conditions and confirmed that a subcritical state could be maintained within the cylinder and that resin decomposition could also be carried out.

[0020] However, when this decomposition process was continued, the melted and plasticized resin and the unmelted resin sometimes flowed back and spurted out from the resin supply section of the extrusion device. This is thought to be because the resin supply section of the extrusion device is usually not sealed and is open to the atmosphere, and the pressure of the molten resin melted and plasticized in the cylinder becomes greater than the pressure of the unmelted resin on the resin supply section side.

[0021] Therefore, in order to provide a decomposition treatment apparatus that can continue and safely perform the decomposition treatment of resin without backflow of molten plasticized resin even when performing the decomposition treatment of resin in a subcritical state using an extrusion device, various studies were conducted and a resin decomposition treatment method and decomposition treatment apparatus that can suppress backflow were found. The resin decomposition treatment apparatus and decomposition treatment method in this embodiment will be described in detail below.

[0022] <Embodiment 1> [Resin decomposition treatment device] Fig. 1 is a diagram showing an example of the configuration of a resin decomposition treatment device according to embodiment 1. Fig. 2 is a diagram for explaining a screw arranged in a cylinder of the resin decomposition treatment device shown in Fig. 1, as viewed from the side.

[0023] The resin decomposition treatment device 10 shown in FIG. 1 is a device used for decomposing a resin to be decomposed by exposing the resin to a fluid in a subcritical or supercritical state.

[0024] This resin decomposition treatment device 10 has a resin supply section 11, a cylinder 12 having a screw, a fluid supply section 13 that supplies fluid to the cylinder 12, an extrusion section 14, a rotation drive mechanism 15 that drives the screw of the cylinder 12, and a backflow prevention mechanism 16.

[0025] The resin supply unit 11 supplies the resin to be decomposed to the cylinder 12. In this embodiment, a thermoplastic resin is supplied as the resin to be decomposed. The thermoplastic resin to be supplied may be in various forms such as pellets, powder, or flakes. For example, the thermoplastic resin is fed from above into the resin supply unit 11, which has a hopper, using a feeder or the like, and then supplied into the cylinder 12. The following description will be given taking as an example a case where the thermoplastic resin to be supplied is in the form of pellets.

[0026] The cylinder 12 has a screw 12a inside. Figure 2 shows a cross-sectional view of the cylinder 12 so that the internal structure of the cylinder 12 of the resin decomposition treatment device 10 in Figure 1 can be seen. The cylinder 12 in Figure 2 also shows a fluid supply hole 12b in which the fluid supply unit 13 is disposed and a relief hole 12c through which the molten plasticized thermoplastic resin can be discharged from inside the cylinder 12 to the outside.

[0027] By rotating the screw 12a, the supplied resin is gradually transported inside the cylinder 12 toward the extrusion section 14 (downstream side). If a twin screw having two screws is used as the screw 12a, a twin-screw extruder can be configured. Twin-screw extruders are flexible in that operating conditions such as the screw rotation speed and barrel temperature setting can be freely changed, and also have various advantages such as high transportability and continuous processability.

[0028] The cylinder 12 is formed by, for example, connecting a plurality of cylinder blocks, and each cylinder block has a space inside which the thermoplastic resin can be transported. A screw 12a is provided in this space, and the screw 12a is connected to a rotation drive mechanism 15. The rotation drive mechanism 15 rotates the screw 12a, so that the resin to be decomposed can be transported in the cylinder 12.

[0029] The cylinder 12 is also provided with a heater so that its temperature can be adjusted. The thermoplastic resin to be decomposed is transported from the resin supply section 11 toward the extrusion section 14, and is gradually heated by the heater so that a molten, plasticized thermoplastic resin can be easily obtained. The molten, plasticized thermoplastic resin thus obtained can be easily transported within the cylinder 12 and further downstream.

[0030] The molten resin in the cylinder 12 and the fluid supplied from the fluid supply unit 13 are pressurized by the screw 12a and reach a subcritical or supercritical state.

[0031] During this process, when a fluid is supplied from a fluid supply unit 13 (described later), the molten plasticized thermoplastic resin and the fluid are mixed, and at this time, the inside of the cylinder 12 is adjusted to a predetermined temperature and pressure by the heater and screw provided in the cylinder 12 as described above, and the inside of the cylinder 12 is brought into a subcritical or supercritical state. Then, while the thermoplastic resin is further transported inside the cylinder 12 in this subcritical or supercritical state, the decomposition process of the thermoplastic resin is allowed to proceed.

[0032] The fluid supply unit 13 supplies a heated and pressurized fluid to the melted and plasticized thermoplastic resin in the cylinder 12. The fluid supply unit 13 is disposed so that the fluid is supplied into the cylinder 12 after the thermoplastic resin has been melted and plasticized in the cylinder 12.

[0033] The fluid supplied from the fluid supply unit 13 exposes the melt-plasticized thermoplastic resin downstream thereof to the fluid in a subcritical or supercritical state and decomposes it. The fluid supplied from the fluid supply unit 13 only needs to be in a subcritical or supercritical state within the cylinder 12, and does not need to be in a subcritical or supercritical state immediately before being supplied to the cylinder 12. It is preferable to bring the supplied fluid to a subcritical or supercritical state before being supplied to the cylinder 12 and supply the fluid into the cylinder 12 while maintaining that state, because this will start decomposition of the melt-plasticized thermoplastic resin immediately after the fluid is supplied.

[0034] The fluid is added to the molten and plasticized thermoplastic resin as described above, but since the inside of the cylinder 12 is heated and pressurized at this time, the fluid supplied here is supplied into the cylinder 12 against that pressure.

[0035] Furthermore, after the fluid is supplied as described above, in order to bring it into a subcritical or supercritical state, it is preferable that the supplied fluid has a temperature equal to or higher than the temperature of the molten plasticized thermoplastic resin in the fluid supply section 13.

[0036] Therefore, it is preferable that the fluid supply unit 13 is provided with a heating means that can heat the supplied fluid to a predetermined heated state. For example, Fig. 1 shows a diagram in which the fluid supply unit 13 is connected to a heated water production device 13a. In this way, the heated water production device 13a can produce a fluid heated to a predetermined heated state, and the resulting fluid can be supplied from the fluid supply unit 13 to the inside of the cylinder 12 through piping using a pump such as a plunger pump.

[0037] The extrusion section 14 is a member that discharges the decomposition products of the thermoplastic resin transported inside the cylinder 12 to the outside of the decomposition treatment device 10, and has an extrusion hole or a restrictor at the extrusion port. The extrusion section 14 may be configured to discharge the decomposition products to the outside while maintaining the pressure inside the device.

[0038] The extrusion section 14 may be connected to a container for recovering raw materials, or may be connected to a different processing device so that the decomposition products of the extruded thermoplastic resin are subjected to further predetermined processing.

[0039] The rotation drive mechanism 15 is a device for rotating the screw 12a provided in the cylinder 12. The thermoplastic resin to be decomposed is transported inside the cylinder 12 by the screw rotated by the rotation drive mechanism 15.

[0040] The extrusion device may be a twin-screw extruder having two screws in the cylinder 12, or a single-screw extruder having one screw. In the case of a twin-screw extruder, the two screws are arranged parallel to each other and rotate. The two shafts may be arranged to intermesh with each other, or may not be arranged to intermesh with each other. When the number of screws is two, the extrusion rate can be increased compared to a single-screw extruder having one screw, given that the screw diameter is the same, due to the high efficiency of conveying the raw materials and the high kneading performance. Furthermore, the extension direction of the cylinder 12 and the extension direction of the screws in the cylinder 12 are the same.

[0041] The backflow prevention mechanism 16 is a mechanism for preventing backflow of the supplied thermoplastic resin or the molten plasticized thermoplastic resin from being ejected from the resin supply section 11 side within the cylinder 12 .

[0042] In this embodiment, the backflow suppression mechanism 16 is configured to include at least one measurement sensor 16a selected from a resin thermometer, a resin pressure gauge, and a cylinder thermometer, a relief valve 16b provided in the cylinder 12, and a control unit 16c that controls the operation of the relief valve 16b in accordance with the measurement value obtained by the measurement sensor 16a. Here, the measurement sensor 16a may include a screw measurement meter (not shown) that measures the energy consumption of the rotation drive mechanism 15 that drives the screw and / or the rotation torque of the rotation drive mechanism 15.

[0043] As described above, the measurement sensor 16a is at least one measurement sensor selected from a resin thermometer, a resin pressure gauge, a cylinder thermometer, and a screw measurement gauge. The measurement sensor 16a may be one of the resin thermometer, the resin pressure gauge, the cylinder thermometer, and the screw measurement gauge, or a combination of multiple sensors. While FIG. 1 shows an example in which one measurement sensor 16a is provided, multiple sensors of the same type may also be provided. When multiple sensors are provided, it is preferable to provide each sensor in a different cylinder block that constitutes the cylinder 12. Note that when a screw measurement gauge is provided as the measurement sensor 16a, it is not necessary to provide it in the cylinder block; it is provided in the rotation drive mechanism 15 so that its energy consumption and / or rotational torque can be measured.

[0044] The relief valve 16b is an on-off valve that can open and close the relief hole 12c, which connects the inside of the cylinder 12 with the external atmosphere, at any timing. The relief valve 16b may be opened and closed manually or automatically. By opening the relief valve 16b, the pressure inside the cylinder 12 is reduced, and backflow can be effectively suppressed. Note that FIG. 1 shows an example configuration in which the control unit 16c is provided to enable automatic opening and closing. With this configuration, the relief valve 16b can be opened immediately when a predetermined measurement value is detected, and the backflow suppression operation can be performed without delay.

[0045] This relief valve 16b is provided so as to be placed in the cylinder 12 after the thermoplastic resin has been melted and plasticized, and its placement position is preferably closer to the extrusion section 14 (downstream) than the fluid supply section 13, more preferably closer to the extrusion section 14 between the fluid supply section 13 and the extrusion section 14, and particularly preferably in the cylinder block adjacent to the extrusion section 14.

[0046] The control unit 16c is connected to the measurement sensor 16a and the relief valve 16b, and constantly monitors the temperature or pressure measured by the measurement sensor 16a. When the measured value exceeds a predetermined threshold or the rate of change of the measured value exceeds a predetermined magnitude, the control unit 16c automatically opens the relief valve 16b and operates to discharge the molten plasticized resin in the cylinder 12 outside the device.

[0047] The backflow prevention mechanism 16 may be configured to monitor the measurement value of the measurement sensor 16a, issue a warning when a predetermined measurement value is detected, and manually open the relief valve 16b when the warning is issued. In this case, the control unit 16c may not be provided.

[0048] <Resin Decomposition Treatment Method> Next, each step of the resin decomposition treatment method of this embodiment will be described using the resin decomposition treatment device 10 of FIG. 1 described above as an example.

[0049] First, a thermoplastic resin is supplied from a resin supply unit 11 to a cylinder 12 (step (a): resin supply step). In this step, the thermoplastic resin to be decomposed is supplied into the cylinder 12, which is the main body of the decomposition treatment device.

[0050] The resin product to be decomposed and supplied here is not particularly limited as long as it is made of a thermoplastic resin and undergoes hydrolysis, and examples of the resin include polyamide (PA) resin, polycarbonate (PC) resin, polyethylene terephthalate (PET) resin, polybutylene terephthalate (PBT) resin, etc. In this example, an example of hydrolysis of polyamide (PA) resin will be introduced.

[0051] Next, the supplied thermoplastic resin is heated and pressurized in the cylinder 12 to be melted and plasticized (step (b): melt-plasticizing step). Here, the thermoplastic resin supplied in the resin supplying step is heated and pressurized while being conveyed by the screw 12a through the cylinder 12 toward the extrusion section 15.

[0052] Here, the temperature is gradually increased as the material is conveyed by a heater provided on the outer periphery of the cylinder 12, and the material is gradually pressurized as the material is conveyed by a screw inside the cylinder 12. Heated and pressurized in this manner, the thermoplastic resin can be easily conveyed by the screw 12a in a molten and plasticized state.

[0053] Although this varies depending on the type of resin used, it is preferable to heat and pressurize the resin before the fluid supplying step described below so that the resin temperature is 250 to 400°C and the resin pressure is 15 to 22 MPa. It is preferable to set the temperature to 150 to 250°C and the pressure to 15 to 20 MPa immediately before the fluid supplying step. More specifically, when the resin to be decomposed contains polyamide (PA) resin, it is preferable to set the resin temperature to 300 to 350°C and the resin pressure to 15 to 18 MPa, for example.

[0054] Next, the heated and pressurized fluid is supplied from the fluid supply unit 13 to the molten and plasticized thermoplastic resin in the cylinder 12 (step (c): fluid supply step). The supplied fluid is mixed with the molten and plasticized thermoplastic resin.

[0055] The fluid supplied at this time is a fluid that can be brought to a subcritical or supercritical state in order to decompose the melt-plasticized resin, and examples thereof include water and alcohols such as methanol, with water being preferred. The supercritical state refers to a state in which the liquid has activity in a region above its critical point, similar to an intermediate state between a liquid and a gas, and the subcritical state refers to a liquid phase state in which the liquid has activity in a region slightly lower than the supercritical state.

[0056] The conditions for the subcritical and supercritical states differ depending on the fluid used. In the case of water, the subcritical state may be, for example, a pressure that is equal to or greater than the saturation pressure at 150 to 350°C (for example, the saturation pressure at 300°C is 8.59 MPa, and the saturation pressure at 350°C is 16.54 MPa), and the supercritical state may be, for example, equal to or greater than 374°C and equal to or greater than 22 MPa.

[0057] The subcritical or supercritical state may be achieved either before or after the fluid is supplied to the molten plasticized thermoplastic resin, and in this fluid supplying step, the heating and pressurizing conditions are adjusted so that the supplied fluid meets the desired conditions. Preferably, the fluid is brought to a subcritical or supercritical state before supplying, and then supplied into the cylinder 12. In this way, when the fluid is supplied into the cylinder 12, the molten plasticized thermoplastic resin is mixed with the fluid, and the decomposition process can begin simultaneously with the mixing.

[0058] After the fluid is supplied, the melted and plasticized thermoplastic resin in the cylinder 12 is mixed with a fluid in a subcritical or supercritical state and decomposed by this (step (d): decomposition step). This decomposition step is preferably carried out for a time period that allows the thermoplastic resin to be sufficiently decomposed, and this can be adjusted by the length of the cylinder 12, the conveying speed due to the rotation of the screw 12a, etc.

[0059] The time for the decomposition treatment is, for example, preferably 2 to 5 minutes, more preferably 5 to 10 minutes, and even more preferably 10 to 15 minutes.

[0060] The thermoplastic resin exposed to a subcritical or supercritical state in this way becomes a decomposition product of the resin, in which the bonds are cut and the resin is decomposed (depolymerized) into the raw material monomers.

[0061] The decomposition product of the thermoplastic resin obtained in this decomposition step is then extruded from the extrusion section 14 provided at the tip of the cylinder 12 (step (e): extrusion step). The extruded decomposition product of the resin is recovered. This decomposition product can be reused as a raw material when producing resin again.

[0062] In addition, when the decomposition product is reused, it is preferable to remove impurities contained in the decomposition product, and an impurity removal step may be carried out when the decomposition product is recovered.

[0063] Next, the backflow suppression process, which is characteristic of this embodiment, will be described. When the above steps (a) to (e) are performed, the thermoplastic resin fed into the cylinder 12 is, for example, in the form of granular pellets for easy handling. After being fed, the resin is melted and plasticized by heating and pressurization as described above. At this time, as shown in FIG. 3, solid pellets 50 fed from the resin feed section 11 are transported downstream and become semi-molten, and then completely melted into molten resin 51.

[0064] At this time, if the pressure on the pellet 50 side and the pressure on the molten resin 51 side are balanced, continuous operation is possible and decomposition processing can be performed efficiently. However, if this balance is lost and the pressure on the molten resin 51 side becomes higher than the pressure on the pellet 50 side, the molten resin 51 will flow back while pushing the pellet 50 back toward the resin supply section 11, and eventually the molten resin 51 and pellet 50 may be ejected from the resin supply section 11 in a mixed state.

[0065] In this embodiment, in order to suppress such backflow, the cylinder 12 is provided with a measurement sensor 16a, as shown in FIG. 1. FIG. 3 shows an example in which the measurement sensor 16a includes a resin thermometer 16a-1, a resin pressure gauge 16a-2, and a cylinder thermometer 16a-3. However, as described above, the number of measurement sensors 16a may be one, two, or three. Furthermore, the measurement sensor 16a may be a screw measurement sensor alone (in this case, the screw measurement sensor is provided in the rotary drive device 15), or the screw measurement sensor may be combined with at least one of the resin thermometer 16a-1, the resin pressure gauge 16a-2, and the cylinder thermometer 16a-3. The following description will be given with reference to FIG. 3, in which the measurement sensor 16a is provided in the cylinder block.

[0066] Here, Figure 3 shows an example in which the resin thermometer 16a-1, resin pressure gauge 16a-2, and cylinder thermometer 16a-3 are provided in the cylinder block of the cylinder 12 from the resin supply section 11 to the fluid supply section 13, but it is also possible to provide measurement sensors in one cylinder block.

[0067] Even if the measurement sensor 16a is provided in one cylinder block, there is no problem because it can detect the imbalance of the pressure. Furthermore, if the measurement sensor 16a is provided in multiple cylinder blocks, it is preferable because it can detect the imbalance of the pressure more accurately.

[0068] The cylinder block where the measurement sensor 16a is provided is preferably the cylinder block on the resin supply unit 11 side where most of the resin is in pellet form. In this way, if there is a change in the value measured by the measurement sensor 16a in the cylinder block on the resin supply unit 11 side, the occurrence of backflow can be accurately detected and the suppression operation described below can be initiated.

[0069] For example, if the decomposition process is continued in the state shown in FIG. 3, but the pressure on the molten resin 51 side increases and the molten resin starts to backflow toward the resin supply unit 11 as shown in FIG. 4, the control unit 16c detects a fluctuation in the measured value of at least one of the resin thermometer 16a-1, resin pressure gauge 16a-2, and cylinder thermometer 16a-3 and determines that backflow is occurring. If this is the case, the control unit 16c opens the relief valve 16b and discharges the molten resin 51 from inside the cylinder 12 to the outside through the opening. This reduces the pressure of the molten resin in the cylinder 12, preventing the molten resin 51 from flowing back toward the resin supply unit 11 together with the pellets 50 and spouting. As a specific example, the relief valve 16b may be opened when the temperature on the resin thermometer 16a-1 rises by 10%, for example, from 240°C to 265°C.

[0070] The control unit 16c may set a threshold value based on the measured value of the measuring sensor 16a to control the operation of the relief valve 16b, or may monitor the change over time and set a threshold value based on the fluctuation value. The threshold value may be set appropriately depending on the cylinder in which the measuring sensor 16a is installed, the resin or fluid used, the conditions of the decomposition process, etc.

[0071] In the case of a decomposition process using polyamide resin as the thermoplastic resin to be decomposed and water as the supplied fluid, threshold values ​​based on measured values ​​can be set, for example, at 50 to 225°C for the resin temperature, 1 to 8 MPa for the resin pressure, and 25 to 250°C for the cylinder temperature.Furthermore, threshold values ​​based on fluctuation values ​​can be set, for example, at 5 to 30% for the resin temperature, 5 to 30% for the resin pressure, and 5 to 30% for the cylinder pressure.

[0072] <Operation of Decomposition Treatment Apparatus> The resin decomposition treatment apparatus and decomposition treatment method of this embodiment have been described above. A series of operations of this resin decomposition treatment apparatus 10 will now be described with reference to the flowchart of FIG.

[0073] First, the resin decomposition treatment device 10 is started up, and the measurement values ​​(temperature, pressure) are displayed by the measurement sensor 16a (S1-1). Next, the relief valve 16b is closed (S1-2), and the operation of the decomposition treatment device 10 is started (S1-3). When the operation starts, the cylinder 12 is heated to a predetermined temperature, and the screw 12a also starts to be driven.

[0074] The supply of pellets 50 to the resin supply section 11 as the resin to be decomposed is started (S1-4), and after confirming that the resin has been sufficiently melted and plasticized and is being transported through the cylinder 12, the supply of heated and pressurized fluid is started from the fluid supply section 13 (S1-5).

[0075] Furthermore, the pressure inside the cylinder 12 is started to be increased to a predetermined pressure (S1-6). At the same time as the pressure increase is started, it is determined whether there are any signs of backflow based on the measurement value of the measurement sensor 16a (S1-7). If there are no signs of backflow, operation is continued (S1-8). Thereafter, it is confirmed that the pressure has reached the specified pressure (S1-9), and it is again determined whether there are any signs of backflow based on the measurement value of the measurement sensor 16a (S1-10). If there are no signs of backflow here either, operation is continued, and the resin decomposition process is continued (S1-11).

[0076] On the other hand, when the presence of any signs of backflow is checked (S1-7, S1-10), if any signs of backflow are detected, the relief valve 16b is opened (S1-12, S1-13). By opening the relief valve 16b, the pressure inside the cylinder 12 can be quickly reduced, thereby suppressing (preventing) backflow. Furthermore, by constantly checking for any signs of backflow even after continuing operation (S1-11), backflow can be reliably suppressed (prevented).

[0077] When operation is resumed after the relief valve 16b is opened, the relief valve 16b is closed (S1-14), and pressure increase is resumed (S1-6), and operation is continued while checking for signs of backflow (S1-7 to S1-14). Note that once the relief valve is opened, it is preferable to eliminate the cause of backflow, if any, before resuming operation.

[0078] If there are no problems, the operation continues until the decomposition treatment of the resin is completely completed, and then the decomposition treatment device is stopped.

[0079] (Embodiment 2) <Apparatus for manufacturing a resin composite material> In this embodiment 2, the backflow suppression mechanism suppresses backflow by varying the amount of resin supplied from the resin supply unit, and other configurations can be the same as those in embodiment 1. Figure 6 is a diagram showing an example of the configuration of a resin decomposition treatment apparatus in embodiment 2.

[0080] The resin decomposition treatment device 20 shown in Figure 6 has a resin supply section 11, a cylinder 12 having a screw, a fluid supply section 13 that supplies fluid to the cylinder 12, an extrusion section 14, a rotation drive mechanism 15 that drives the screw of the cylinder 12, and a backflow prevention mechanism 26.

[0081] Here, the resin supply unit 11, cylinder 12, fluid supply unit 13, extrusion unit 14, and rotation drive mechanism 15 are the same as those described in embodiment 1, and therefore their description will be omitted. In embodiment 2, backflow is suppressed by varying the amount of resin supplied from the resin supply unit 11 as described above, and is characterized by the inclusion of a backflow suppression mechanism 26. The backflow suppression mechanism 26 will be described in detail below.

[0082] In this embodiment, the backflow prevention mechanism 26 is configured to have at least one measurement sensor 26a selected from a resin thermometer, a resin pressure gauge, and a cylinder thermometer, a feeder 26b that can adjust the amount of resin supplied to the resin supply section 11, and a control section 16c that controls the operation of the feeder 26b in accordance with the measurement value obtained by the measurement sensor 26a.

[0083] The measurement sensor 26a can have the same configuration as the measurement sensor 16a described in the first embodiment, and therefore a description thereof will be omitted here.

[0084] A known feeder can be used as the feeder 26b, which is a device that supplies the resin to be decomposed to the resin supply unit 11. The feeder 26b used in this embodiment has a function that can adjust the amount of resin supplied, and is connected to a control unit 26c, which will be described next, so that the amount of resin supplied can be changed depending on the situation.

[0085] The control unit 26c is connected to the measurement sensor 26a and the feeder 26b, and constantly monitors the temperature or pressure measured by the measurement sensor 26a. When the measured value exceeds a predetermined threshold or the rate of change of the measured value exceeds a predetermined magnitude, the control unit 26c operates to increase the amount of resin supplied from the feeder 26b to the resin supply unit 11.

[0086] The backflow prevention mechanism 26 may be configured to monitor the measurement value of the measurement sensor 26a, issue a warning when a predetermined measurement value is detected, and manually increase the amount of resin supplied from the feeder when the warning is issued. In this case, the control unit 26c may not be provided.

[0087] <Resin Decomposition Treatment Method> Next, each step of the resin decomposition treatment method of this embodiment will be described using the resin decomposition treatment device 20 of FIG. 6 described above as an example.

[0088] The resin decomposition treatment method in this embodiment shares steps (a) to (e) with the resin decomposition treatment method described in the first embodiment, and therefore the description thereof will be omitted. The present embodiment is characterized by the backflow suppression step, which is different from the first embodiment, and therefore the following description will mainly focus on this difference.

[0089] 3, when the above steps (a) to (e) are performed, the solid pellets 50 supplied from the resin supply unit 11 become semi-molten while being conveyed downstream, and then become completely melted molten resin 51. When the balance between the pressure on the pellet 50 side and the pressure on the molten resin 51 side is lost, the molten resin 51 flows back while pushing the pellets 50 back toward the resin supply unit 11, and eventually the molten resin 51 and the pellets 50 may be ejected from the resin supply unit 11 in a mixed state.

[0090] In this embodiment, in order to suppress such backflow, as shown in Fig. 6, the cylinder 12 is provided with at least one measurement sensor 26a selected from a resin thermometer, a resin pressure gauge, and a cylinder thermometer. This measurement sensor 26a can have the same configuration as the measurement sensor 16a in the first embodiment.

[0091] In this embodiment, the decomposition process is continued in the state shown in Fig. 3, but if the pressure on the molten resin 51 side increases and the molten resin starts to flow back toward the resin supply unit 11 side as shown in Fig. 4, the control unit 26c detects a fluctuation in the measured value of at least one of the resin thermometer 16a-1, resin pressure gauge 16a-2, and cylinder thermometer 16a-3, and determines that backflow is occurring, and increases the amount of resin supplied in the feeder 26b to increase the pressure on the pellet 50 side. This adjusts the balance between the pressure of the pellets 50 and the molten resin 51 in the cylinder 12, making it possible to prevent the molten resin 51 from flowing back toward the resin supply unit 11 side together with the pellets 50 and spouting out.

[0092] At this time, the threshold value and the fluctuation value explained in the first embodiment may be set as the measurement value of the measurement sensor 26a, and the measurement may be performed.

[0093] The amount of resin may be increased by any amount that can prevent the backflow from spouting, and is preferably increased by, for example, 1.5 to 2.5 times the amount of resin originally supplied.

[0094] After the amount of resin is increased, the measurement value of the measuring sensor 26a is checked again to see if the backflow has been suppressed. If the backflow has not been suppressed, the amount of resin may be further increased, and this process may be repeated until the backflow is suppressed. In this case, the amount of resin may be increased in stages by about 1.1 to 1.5 times the amount of resin originally supplied.

[0095] <Operation of Decomposition Treatment Apparatus> The resin decomposition treatment apparatus and decomposition treatment method of this embodiment have been described above. A series of operations of this resin decomposition treatment apparatus 20 will now be described with reference to the flowchart of FIG.

[0096] First, the resin decomposition treatment device 20 is started up, and the measurement values ​​(temperature, pressure) are displayed by the measurement sensor 26a (S2-1). Next, operation of the decomposition treatment device 20 is started (S2-2). When operation starts, the cylinder 12 is heated to a predetermined temperature, and the screw 12a also starts to be driven.

[0097] The supply of pellets 50 to the resin supply section 11 as the resin to be decomposed is started (S2-3), and after confirming that the resin has been sufficiently melted and plasticized and is being transported through the cylinder 12, the supply of heated and pressurized fluid is started from the fluid supply section 13 (S2-4).

[0098] Furthermore, the pressure in the cylinder 12 is started to be increased to a predetermined pressure (S2-5). At the same time as the pressure increase is started, it is determined whether there are any signs of backflow based on the measurement value of the measurement sensor 26a (S2-6). If there are no signs of backflow, operation is continued (S2-7).

[0099] Thereafter, it is confirmed that the pressure has reached the specified pressure (S2-8), and again, it is determined whether there are any signs of backflow based on the measurement value of the measurement sensor 26a (S2-9). If there are no signs of backflow here either, operation continues, and the resin decomposition process continues (S2-10).

[0100] On the other hand, when the presence of any signs of backflow is confirmed (S2-6, S2-9), if any signs of backflow are detected, the amount of resin supplied from the feeder 26b is increased (S2-11, S2-12). After increasing the amount of resin supplied, the measurement value of the measurement sensor 26a is checked to see if the signs have disappeared (S2-13). If the signs have disappeared, operation is continued and the decomposition process is continued (S2-9). If the signs have not disappeared, the resin supply is increased again (S2-11, S2-12), and this process is repeated until the signs have disappeared. By increasing the amount of resin supplied, the balance of pressure between the pellets 50 and the molten resin 51 within the cylinder 12 can be adjusted, thereby suppressing (preventing) backflow. Furthermore, by constantly checking for signs of backflow, even after continuing operation (S2-10), backflow can be reliably suppressed (prevented).

[0101] If there are no problems, the operation continues until the decomposition treatment of the resin is completely completed, and then the decomposition treatment device is stopped.

[0102] (Embodiment 3) In this embodiment 3, the backflow prevention mechanism suppresses backflow by stopping the supply of fluid from the fluid supply unit, and other configurations can be the same as those in embodiment 1. Figure 8 is a diagram showing an example of the configuration of a resin decomposition treatment device in embodiment 3.

[0103] The resin decomposition treatment device 30 shown in Figure 8 has a resin supply section 11, a cylinder 12 having a screw, a fluid supply section 13 that supplies fluid to the cylinder 12, an extrusion section 14, a rotation drive mechanism 15 that drives the screw of the cylinder 12, and a backflow prevention mechanism 36.

[0104] Here, the resin supply unit 11, cylinder 12, fluid supply unit 13, extrusion unit 14, and rotation drive mechanism 15 are the same as those described in embodiment 1, and therefore will not be described again. In embodiment 3, backflow is suppressed by stopping the supply of fluid from the fluid supply unit 13 as described above, and is characterized by the inclusion of a backflow suppression mechanism 36. The backflow suppression mechanism 36 will be described in detail below.

[0105] In this embodiment, the backflow prevention mechanism 36 is configured to include at least one measurement sensor 36a selected from a resin thermometer, a resin pressure gauge, and a cylinder thermometer, a valve 36b connected to the fluid supply unit 13 and provided in the piping for supplying the fluid, and a control unit 36c that can control the opening and closing of the valve 36b according to the measurement value obtained by the measurement sensor 36a.

[0106] The measurement sensor 36a can have the same configuration as the measurement sensor 16a described in the first embodiment, and therefore a description thereof will be omitted here.

[0107] A known valve can be used as the valve 36b, and is provided on a pipe connected to supply fluid from the fluid supply unit 13 to the cylinder 12. By opening and closing this valve 36b, it is possible to control whether or not to supply fluid to the cylinder 12 and the amount of fluid supplied.

[0108] The control unit 36c is connected to the measurement sensor 36a and the valve 36b, and constantly monitors the temperature or pressure measured by the measurement sensor 36a. When the measured value exceeds a predetermined threshold or the rate of change of the measured value exceeds a predetermined magnitude, the control unit 36c closes the valve 36b and stops the fluid being supplied to the cylinder 12.

[0109] The backflow prevention mechanism 36 may be configured to monitor the measurement value of the measurement sensor 36a, issue a warning when a predetermined measurement value is detected, and manually stop the fluid supply from the fluid supply unit 13 when the warning is issued. In this case, the control unit 36c may not be provided.

[0110] <Resin Decomposition Treatment Method> Next, each step of the resin decomposition treatment method of this embodiment will be described using the resin decomposition treatment device 30 of FIG. 8 described above as an example.

[0111] The resin decomposition treatment method in this embodiment shares steps (a) to (e) with the resin decomposition treatment method described in the first embodiment, and therefore the description thereof will be omitted. The present embodiment is characterized by the backflow suppression step, which is different from the first embodiment, and therefore the following description will mainly focus on this difference.

[0112] 3, when the above steps (a) to (e) are performed, the solid pellets 50 supplied from the resin supply unit 11 become semi-molten while being conveyed downstream, and then become completely melted molten resin 51. When the balance between the pressure on the pellet 50 side and the pressure on the molten resin 51 side is lost, the molten resin 51 flows back while pushing the pellets 50 back toward the resin supply unit 11, and eventually the molten resin 51 and the pellets 50 may be ejected from the resin supply unit 11 in a mixed state.

[0113] In this embodiment, in order to suppress such backflow, as shown in Fig. 8, the cylinder 12 is provided with at least one measurement sensor 36a selected from a resin thermometer, a resin pressure gauge, and a cylinder thermometer. This measurement sensor 36a can have the same configuration as the measurement sensor 16a in the first embodiment.

[0114] In this embodiment, the decomposition process was continued in the state shown in Fig. 3, but if the pressure on the molten resin 51 side increases and the molten resin starts to flow back toward the resin supply unit 11 side as shown in Fig. 4, the control unit 36c detects a fluctuation in the measured value of at least one of the resin thermometer 16a-1, resin pressure gauge 16a-2, and cylinder thermometer 16a-3, and determines that backflow is occurring, and closes the valve 36b to stop the supply of fluid to the cylinder 12. This adjusts the balance between the pressure of the pellets 50 and the molten resin 51 in the cylinder 12, making it possible to prevent the molten resin 51 from flowing back toward the resin supply unit 11 side together with the pellets 50 and spraying out.

[0115] At this time, the threshold value and the fluctuation value explained in the first embodiment may be set as the measurement value of the measurement sensor 36a, and the measurement may be performed.

[0116] <Operation of Decomposition Treatment Apparatus> The resin decomposition treatment apparatus and decomposition treatment method of this embodiment have been described above. A series of operations of this resin decomposition treatment apparatus 30 will now be described with reference to the flowchart of FIG.

[0117] First, the resin decomposition treatment device 30 is started up, and the measurement values ​​(temperature, pressure) are displayed by the measurement sensor 36a (S3-1). Next, operation of the decomposition treatment device 30 is started (S3-2). When operation starts, the cylinder 12 is heated to a predetermined temperature, and the screw 12a also starts to be driven.

[0118] The supply of pellets 50 to the resin supply section 11 as the resin to be decomposed is started (S3-3), and after confirming that the resin has been sufficiently melted and plasticized and is being transported through the cylinder 12, the supply of heated and pressurized fluid is started from the fluid supply section 13 (S3-4).

[0119] Furthermore, the pressure in the cylinder 12 is started to be increased to a predetermined pressure (S3-5). At the same time as the pressure increase is started, it is determined whether there are any signs of backflow based on the measurement value of the measurement sensor 36a (S3-6). If there are no signs of backflow, operation continues (S3-7).

[0120] Thereafter, it is confirmed that the pressure has reached the specified pressure (S3-8), and again, it is determined whether there are any signs of backflow based on the measurement value of the measurement sensor 36a (S3-9). If there are no signs of backflow here either, operation continues, and the resin decomposition process continues (S3-10).

[0121] On the other hand, when the presence of the above-mentioned signs of backflow is checked (S3-6, S3-9), if there is a sign of backflow, the valve 36b is closed to stop the supply of fluid from the fluid supply unit 13 (S3-11, S3-12). After the fluid supply is stopped, the operating conditions are changed (S3-13). The operating conditions to be changed here may be any conditions that can suppress backflow, such as the resin supply amount, fluid supply amount, screw rotation speed, cylinder temperature, etc.

[0122] After the operating conditions are changed, the valve 36b is opened to resume the fluid supply (S3-4). By stopping the fluid supply, the balance of pressure between the pellets 50 and the molten resin 51 in the cylinder 12 can be adjusted, thereby suppressing (preventing) backflow. Furthermore, by constantly checking for signs of backflow even after continuing operation (S3-10), backflow can be reliably suppressed (prevented).

[0123] If there are no problems, the operation continues until the decomposition treatment of the resin is completely completed, and then the decomposition treatment device is stopped.

[0124] The present invention has been specifically described above using embodiments and examples, but it should be understood that the present invention should not be construed as being limited to these embodiments and examples, and that various modifications are possible within the scope of the gist of the present invention.

[0125] 10, 20, 30 Resin decomposition treatment device 11 Resin supply section 12 Cylinder 12a Screw 12b Fluid supply hole 12c Relief hole 13 Fluid supply section 14 Extrusion section 15 Rotation drive mechanism 16, 26, 36 Backflow prevention mechanism 16a, 26a, 36a Measurement sensor 16c, 26c, 36c Control section 16b Relief valve 26b Feeder 36c Valve

Claims

1. A method for decomposing a resin, comprising the following steps: (a) supplying a thermoplastic resin from a resin supply unit to a cylinder; (b) heating and pressurizing the supplied thermoplastic resin in the cylinder to melt and plasticize it; (c) supplying a heated and pressurized fluid from a fluid supply unit to the melt-plasticized thermoplastic resin and mixing them; (d) decomposing the melt-plasticized thermoplastic resin by exposing it to a subcritical or supercritical state using the supplied fluid; and (e) extruding the decomposition product of the thermoplastic resin obtained in step (d) from an extrusion unit provided at the tip of the cylinder, wherein in step (b), at least one selected from the temperature of the thermoplastic resin, the pressure of the thermoplastic resin, and the temperature of the cylinder is measured, and a backflow suppression step is initiated in which a backflow of the melt-plasticized thermoplastic resin is suppressed according to the measured value.

2. A resin decomposition treatment method according to claim 1, wherein the backflow suppression step is a step of discharging the molten plasticized thermoplastic resin from the cylinder downstream of the fluid supply section to the outside.

3. A resin decomposition treatment method according to claim 2, wherein the molten resin is discharged to the outside through a relief hole provided in the cylinder adjacent to the extrusion section.

4. A resin decomposition treatment method according to claim 1, wherein the backflow suppression step is a step of increasing the supply amount of the thermoplastic resin in step (a).

5. A method for decomposing a resin according to claim 4, wherein the amount of the thermoplastic resin supplied is increased by 1.5 to 2.5 times.

6. A resin decomposition treatment method according to claim 1, wherein the backflow suppression step is a step of stopping the supply of the fluid in step (c).

7. A method for decomposing a resin according to claim 1, wherein the thermoplastic resin is a polyamide resin.

8. A resin decomposition treatment device, comprising: a cylinder; a resin supply unit that supplies a thermoplastic resin to be decomposed to the cylinder; a screw that transports the supplied thermoplastic resin and the melt-plasticized thermoplastic resin in the cylinder; a fluid supply unit that supplies a heated and pressurized fluid into the cylinder to decompose the melt-plasticized thermoplastic resin in a subcritical or supercritical state; an extrusion unit that is provided at the tip of the cylinder and extrudes decomposed products of the thermoplastic resin to the outside of the cylinder; and a backflow suppression mechanism that is provided in the cylinder between the resin supply unit and the fluid supply unit and has at least one selected from a resin thermometer that measures the temperature of the thermoplastic resin, a resin pressure gauge that measures the pressure of the thermoplastic resin, a cylinder thermometer that measures the temperature of the cylinder, and a screw measurement gauge that measures the energy consumption or drive torque of a rotation drive mechanism that drives the screw, and that can suppress backflow of the melt-plasticized thermoplastic resin in accordance with at least one of the measurements of the resin thermometer, the resin pressure gauge, the cylinder thermometer, and the screw measurement gauge.

9. A resin decomposition treatment device as described in claim 8, wherein the backflow prevention mechanism comprises a relief valve provided in the cylinder downstream of the fluid supply section so as to be able to open and close a relief hole connecting the inside of the cylinder with the external atmosphere, and a control section which controls the opening and closing of the relief valve in accordance with the measured value.

10. A resin decomposition treatment device according to claim 9, wherein the relief valve is provided in the cylinder adjacent to the extrusion section.

11. A resin decomposition treatment device as described in claim 8, wherein the backflow prevention mechanism has a feeder capable of adjusting the amount of resin supplied from the resin supply unit, and a control unit that increases the amount of resin supplied from the resin supply unit to the cylinder by the feeder according to the measured value.

12. A resin decomposition treatment device according to claim 8, wherein the backflow prevention mechanism comprises a valve connected to the fluid supply unit and provided in a pipe for supplying the fluid, and a control unit capable of controlling the opening and closing of the valve in accordance with the measured value.

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