An apparatus for producing expanded beads, a method for controlling the temperature of the apparatus, and a method for producing expanded beads of a thermoplastic resin.

Abstract

To precisely control an internal temperature of a foam tank, in an apparatus for producing foam particles.SOLUTION: A temperature control part (6) of a production apparatus (1) includes a first PID controller (6a) for outputting an internal temperature SV, and a jacket steam temperature SV from the internal temperature PV, a pressure converter (6b) for converting the jacket steam temperature SV into a jacket steam pressure SV, and a second PIC controller (6c) for outputting an opening of a control valve (5) from the jacket steam pressure SV and the jacket steam pressure PV, and changes the parameter of the first PID control in the middle of a foaming process.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] A known method for producing expanded beads is the depressurization foaming method, in which a jacket is provided around the outer periphery of a foaming tank and steam is supplied to the jacket to control the internal temperature of the foaming tank.

[0003] Furthermore, in recent years, a technique has been disclosed for controlling the temperature of a general reactor by controlling the steam pressure in the jacket portion of the reactor.

[0004] For example, Patent Document 1 discloses a thin-film dehydration device in which a thermosetting resin syrup in the final stage of reaction is caused to flow down the heated wall surface of a metal cylinder with a heating jacket attached to the outer periphery, thereby completing the reaction and dehydrating the material. The device discloses a temperature control method for the thin-film dehydration device, in which the valve supplying high-temperature steam to the jacket is operated by constant-value control using feedback of the steam pressure of the jacket at the beginning of the device startup, and then switches to constant-value control using feedback of the temperature inside the device at steady-state.

[0005] Patent Document 2 also discloses a method for heating tanks, pots, and kettles, in which a metal or magnetic jacket or double pipe is installed on the bottom, sides, and periphery of the tank, pot, or kettles, the jacket or double pipe is heated directly by a heat source, and the heat generated in the jacket or double pipe keeps the tank, pot, or kettles warm and heats them. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 57-51724 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-236878 Summary of the Invention [Problem to be solved by the invention]

[0007] However, when the above-mentioned conventional techniques are applied to a foaming tank, there is room for improvement in terms of controlling the internal temperature of the foaming tank.

[0008] One aspect of the present invention has been made in consideration of the above-mentioned problems, and an object of the present invention is to provide an expanded bead manufacturing apparatus, a temperature control method for the manufacturing apparatus, and a method for manufacturing expanded thermoplastic resin beads, which are capable of precisely controlling the internal temperature of a foaming tank. [Means for solving the problem]

[0009] As a result of intensive research into solving the above-mentioned problems, the present inventors have found that, in a temperature control method in which a first PID control is performed based on a target value of the inner temperature of the foaming tank and a measured value of the inner temperature of the foaming tank, and a second PID control is performed based on a target value of the steam pressure of the jacket section and a measured value of the steam pressure of the jacket section, changing the sensitivity of the parameters of the first PID control during foaming correlates with the controllability of the inner temperature of the foaming tank. Therefore, by changing the parameters of the first PID control, it becomes possible to more accurately control the temperature of the expanded beads manufacturing apparatus, and have arrived at the present invention.

[0010] That is, one aspect of the present invention includes the following configuration. <1> an expansion tank for expanded beads, a jacket portion provided on the outer periphery of the expansion tank, a supply pipe for supplying steam to the jacket portion, a control valve provided on the supply pipe for adjusting the amount of steam, and a temperature control unit for controlling an internal temperature of the expansion tank to a predetermined temperature, wherein the temperature control unit comprises: a first PID controller that performs a first PID control calculation based on a target internal temperature of the expansion tank and a measured internal temperature of the expansion tank, and outputs a target steam temperature value of the jacket portion; a pressure converter that converts the target steam temperature value of the jacket portion into a pressure and outputs a target steam pressure value of the jacket portion; and a second PID controller that performs a second PID control calculation based on the target steam pressure value of the jacket portion and the measured steam pressure value of the jacket portion, and outputs an aperture of the control valve, wherein: (a) the amount of steam in the jacket portion is adjusted by controlling opening and closing of the control valve using the aperture, thereby controlling the internal temperature of the expansion tank to a predetermined temperature; and (b) the temperature control unit changes a parameter of the first PID control calculation during an expansion process of the expanded beads. <2> The temperature control unit controls the sensitivity of the parameter of the first PID control calculation during the expansion process of the expanded beads so as to be lower than the sensitivity at the start of the expansion process. <1> An apparatus for producing expanded beads according to claim 1. <3> The temperature control unit controls the sensitivity of the parameter P to be reduced among the parameters of the first PID control calculation. <2> An apparatus for producing expanded beads according to claim 1. <4> 1. A temperature control method for an expanded bead manufacturing apparatus, the expanded bead manufacturing apparatus comprising: an expansion tank for expanded beads; a jacket portion provided on the outer periphery of the expansion tank; a supply pipe for supplying steam to the jacket portion; and a control valve provided in the supply pipe for regulating the amount of steam. The temperature control method includes a first PID control step of performing a first PID control calculation based on an internal temperature target value and an internal temperature measured value in the expansion tank to output a steam temperature target value for the jacket portion; a pressure conversion step of converting the steam temperature target value of the jacket portion into a pressure value and outputting a steam pressure target value for the jacket portion; and a second PID control step of performing a second PID control calculation based on the steam pressure target value of the jacket portion and the steam pressure measured value of the jacket portion to output an aperture of the control valve. 2. The temperature control method for an expanded bead manufacturing apparatus, the expanded bead manufacturing apparatus comprising: an expansion tank for expanded beads; a jacket portion provided on the outer periphery of the expansion tank; a supply pipe for supplying steam to the jacket portion; and a control valve provided in the supply pipe for regulating the amount of steam. <5> The temperature control step includes a step of controlling the sensitivity of the parameter of the first PID control calculation during the expansion step of the expanded beads so as to be lower than the sensitivity at the start of the expansion step. <4> A method for controlling the temperature of the expanded bead manufacturing apparatus according to claim 1. <6> The temperature control step includes a step of controlling the sensitivity of a parameter P among the parameters of the first PID control calculation so as to decrease the sensitivity. <5> A method for controlling the temperature of the expanded bead manufacturing apparatus according to claim 1. <7> <4> ~ <6> 10. A method for producing expanded beads of a thermoplastic resin, comprising the temperature control method according to any one of the preceding items as one step. <8> The thermoplastic resin is a polyolefin resin. <7> 1. A method for producing expanded beads of the thermoplastic resin according to claim 1. [Effects of the Invention]

[0011] According to one aspect of the present invention, it is possible to provide an expanded bead manufacturing apparatus capable of precisely controlling the internal temperature of the expansion tank, and a method for controlling the temperature of the manufacturing apparatus. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a diagram schematically illustrating an entire expanded bead manufacturing apparatus according to one embodiment of the present invention. [Figure 2] 1 is a graph showing an example of setting the internal temperature of an expansion tank in a method for controlling the temperature of an expanded bead manufacturing apparatus according to one embodiment of the present invention. [Figure 3] 1 is a graph showing changes over time in the internal temperature, internal temperature deviation, jacket steam pressure SV, and jacket steam pressure PV in the foaming step in Examples and Comparative Examples. [Figure 4] 1 is a graph showing changes in the internal temperature, internal temperature deviation, jacket steam pressure SV, and jacket steam pressure PV during the foaming process relative to the progress of foaming (initiation of foaming: 0%, completion of foaming: 100%) in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0013] One embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the respective configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments or examples obtained by combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic literature and patent documents described in this specification are incorporated herein by reference. Furthermore, unless otherwise specified in this specification, the term "A to B" representing a numerical range means "greater than or equal to A (including and greater than A) and less than or equal to B (including and less than B)."

[0014] A depressurization foaming method is known as one of the methods for producing expanded beads. In the depressurization foaming method, a jacket part is provided on the outer periphery of a foaming tank, and the inner temperature of the foaming tank can be controlled by supplying steam to the jacket part by adjusting the aperture of a control valve.

[0015] Conventionally, the control of the internal temperature of the foaming tank has generally been performed by controlling the aperture of a control valve for supplying steam to the jacket section using two PID controls, namely, a first PID control and a second PID control. In the first PID control, a PID control calculation is performed based on an internal temperature target value of the foaming tank (hereinafter, sometimes referred to as an internal temperature target value) and a measured internal temperature value of the foaming tank (hereinafter, sometimes referred to as a measured internal temperature value), and a target steam temperature value of the jacket section (hereinafter, sometimes referred to as a jacket steam temperature target value) is output. In addition, in the second PID control, a PID control calculation is performed based on the above-mentioned jacket steam temperature target value and a measured steam temperature value of the jacket section (hereinafter, sometimes referred to as a measured jacket steam temperature value), and an aperture of a control valve (hereinafter, sometimes referred to as a control valve MV) is output. However, in the method of performing PID control calculation based on the jacket steam temperature target value and the measured jacket steam temperature in the second PID control, it takes time for the temperature of the jacket section to rise after the control valve is opened, and a response delay time when the control valve is opened or closed is long. Therefore, the conventional method for controlling the internal temperature of the foaming tank has a drawback in that the response when the control valve is opened and closed is poor, and therefore the internal temperature controllability is poor.

[0016] Recently, a technology has been disclosed for controlling the internal temperature of a typical reaction vessel by controlling the aperture of a control valve through jacket pressure control. The method of controlling the aperture of a control valve through jacket pressure control improves the response delay time when opening and closing the control valve and the internal temperature controllability of the reaction vessel, and this technology is expected to be applied to a foaming vessel. Therefore, the present inventors have considered that the internal temperature controllability of a foaming vessel can be improved by controlling the aperture of the control valve through jacket pressure control in the second PID control. Specifically, in the second PID control, a PID control calculation is performed based on the target steam pressure of the jacket (hereinafter sometimes referred to as the jacket steam pressure target value) and the measured steam pressure of the jacket (hereinafter sometimes referred to as the jacket steam pressure measurement value).

[0017] However, even if the aperture of the control valve is controlled by controlling the pressure of the jacket part in the second PID control, the responsiveness is improved to some extent, but there is room for further improvement in terms of precisely controlling the internal temperature of the foaming tank.Therefore, there is a demand for an internal temperature control method of the foaming tank that can precisely control the internal temperature of the foaming tank even when the aperture of the control valve is controlled by controlling the pressure of the jacket part in the second PID control.

[0018] In light of these circumstances, the inventors of the present invention have conducted extensive research with the aim of developing a method for controlling the internal temperature of a foaming tank that satisfies the above requirements, and have focused on changes in the internal liquid of the foaming tank during the foaming process.

[0019] In the depressurization foaming method, the amount of liquid in the foaming tank gradually decreases as the resin particles foam. Therefore, the inventors of the present application discovered that when the internal temperature of the foaming tank is controlled by keeping the first and second PID control parameters constant over the foaming time, the internal temperature of the foaming tank deviates from the target value, and that there is a correlation between the amount of liquid in the foaming tank and the first PID control parameters. They also discovered that when the first PID control parameters are changed during the foaming process, control according to changes in the internal liquid in the foaming tank becomes possible, allowing for precise control of the internal temperature of the foaming tank, i.e., improving the controllability of the internal temperature of the foaming tank.

[0020] An expanded beads manufacturing apparatus according to one embodiment of the present invention (hereinafter, sometimes referred to as "the manufacturing apparatus") includes an expansion tank for expanded beads, a jacket portion provided on the outer periphery of the expansion tank, a supply pipe for supplying steam to the jacket portion, a control valve provided on the supply pipe for adjusting the amount of steam, and a temperature control unit for controlling an inner temperature of the expansion tank to a predetermined temperature, wherein the temperature control unit is a first PID controller that performs a first PID control calculation based on an inner temperature target value of the expansion tank and a measured inner temperature value of the expansion tank, and outputs a steam temperature target value of the jacket portion; and a second PID controller that performs a second PID control calculation based on the target steam pressure of the jacket section and the measured steam pressure of the jacket section to output an aperture of the control valve, wherein (a) the opening and closing of the control valve is controlled by the aperture to adjust the amount of steam in the jacket section and control the internal temperature of the foaming tank to a predetermined temperature, and (b) parameters of the first PID control calculation are changed during the expansion process of the expanded beads. This configuration has the advantage of providing an expanded beads manufacturing apparatus and a temperature control method for the manufacturing apparatus that can precisely control the internal temperature of the foaming tank.

[0021] A temperature control method for an expanded bead manufacturing apparatus according to one embodiment of the present invention (hereinafter, sometimes referred to as "this control method") is a temperature control method for an expanded bead manufacturing apparatus, the expanded bead manufacturing apparatus including an expansion tank for expanded beads, a jacket portion provided on the outer periphery of the expansion tank, a supply pipe for supplying steam to the jacket portion, and a control valve provided in the supply pipe for regulating the amount of steam, the method comprising a temperature control step of controlling an internal temperature of the expansion tank to a predetermined temperature, the temperature control step including: a first PID control step of performing a first PID control calculation based on an internal temperature target value and an internal temperature measured value in the expansion tank, and outputting a steam temperature target value for the jacket portion; a pressure conversion step of converting the steam temperature target value of the jacket portion into a pressure value and outputting a steam pressure target value for the jacket portion; and a second PID control step of performing a second PID control calculation based on the steam pressure target value of the jacket portion and the steam pressure measured value of the jacket portion, and outputting an aperture of the control valve, and the method changes parameters of the first PID control calculation during the expansion process of the expanded beads. This method has the advantage of being able to provide an expanded bead manufacturing apparatus and a temperature control method for the manufacturing apparatus, which are capable of precisely controlling the internal temperature of the expansion tank.

[0022] In this specification and drawings, the target value may be referred to as "SV" and the measured value as "PV." Accordingly, the target value of the inner temperature of the foaming tank, the measured value of the inner temperature of the foaming tank, the target value of the steam temperature of the jacket part, the target value of the steam pressure of the jacket part, and the measured value of the steam pressure of the jacket part may be referred to as the inner temperature SV, the inner temperature PV, the jacket steam temperature SV, the jacket steam pressure SV, and the jacket steam pressure PV, respectively.

[0023] An expanded bead manufacturing apparatus and a method for controlling the temperature of the manufacturing apparatus according to one embodiment of the present invention will be described below with reference to Fig. 1. Fig. 1 is a diagram schematically illustrating the entire expanded bead manufacturing apparatus according to this embodiment.

[0024] As shown in Fig. 1, an expanded bead manufacturing apparatus 1 according to one embodiment of the present invention includes a foaming tank 2, a jacket section 3, a supply pipe 4, a control valve 5, a temperature control section 6, a foaming tank thermometer 7, a jacket steam pressure gauge 8, a stirrer 9, a steam drain 10, and a resin particle discharge valve 11. The supply pipe 4 is a pipe for supplying steam to the jacket section 3. The control valve 5 is provided in the supply pipe 4 and is a valve for adjusting the amount of steam supplied to the jacket section 3. The temperature control section 6 controls the internal temperature of the foaming tank 2 to a predetermined temperature. The foaming tank thermometer 7 is for measuring the internal temperature of the foaming tank 2. The jacket steam pressure gauge 8 is for measuring the steam pressure in the jacket section 3.

[0025] The expansion tank 2 is a container for producing expanded beads by the depressurization foaming method. The expanded beads are produced by charging the expansion tank 2 with water, an aqueous dispersion containing resin particles, an inorganic dispersant, and a dispersion aid, and a volatile blowing agent, and then heating and maintaining a constant pressure and temperature to impregnate the resin particles with the blowing agent. The material is then released into a low-pressure atmosphere (depressurization foaming method), and then dried. The material charged in the expansion tank 2 is stirred by the mixer 9 and discharged from the resin particle discharge valve 11.

[0026] In one embodiment of the present invention, the jacket part 3 is provided on the outer periphery of the foaming tank 2 and contains steam therein. When the control valve 5 is opened, the steam is ventilated into the jacket part 3 through the supply pipe 4. That is, in the production apparatus 1, the amount of steam in the jacket part 3 is adjusted by opening and closing the control valve 5, thereby controlling the internal temperature of the foaming tank 2.

[0027] More specifically, when the control valve 5 is opened and steam is ventilated to the jacket part 3 through the supply pipe 4, the steam does not condense into water, but the heat of condensation is transferred to the foaming tank 2, causing the internal temperature of the foaming tank 2 to rise. On the other hand, by reducing the opening of the control valve 5, the amount of steam supplied to the jacket part 3 decreases, and the internal temperature of the foaming tank 2 does not rise. After the steam condenses into water, it is discharged from the steam drain 10.

[0028] The temperature control unit 6 includes a first PID controller 6a, a pressure converter 6b, and a second PID controller 6c.

[0029] Here, PID control is a type of control action that is applied according to the difference between a target value and a measured value. In this specification, an action that changes the manipulated variable according to the control deviation is called P action, an action that changes the manipulated variable according to the integral value of the control deviation is called I action, and an action that changes the manipulated variable according to the differential value of the control deviation is called D action. In this specification, PID control refers to a process that controls by a combination of three actions: P action, I action, and D action. In this specification, a parameter based on P action is called parameter P, a parameter based on D action is called parameter D, and a parameter based on I action is called parameter I.

[0030] The first PID controller 6a performs a first PID control calculation based on the internal temperature target value (internal temperature SV) of the foaming tank 2 and the internal temperature measurement value (internal temperature PV) of the foaming tank 2, and outputs a steam temperature target value (jacket steam temperature SV) of the jacket part 3. More specifically, the first PID controller 6a compares the internal temperature PV with the internal temperature SV, and outputs the jacket steam temperature SV by a PID control calculation so that the internal temperature PV becomes the internal temperature SV. The internal temperature measurement value (internal temperature PV) of the foaming tank 2 is measured by a foaming tank thermometer 7.

[0031] The pressure converter 6b converts the jacket steam temperature SV output from the first PID controller 6a into a steam pressure target value (jacket steam pressure SV) for the jacket section 3. A known method for converting from steam temperature to steam pressure can be used to convert from the jacket steam temperature SV to the jacket steam pressure SV. For example, the conversion method may be based on the Antoine equation, which will be described later.

[0032] The second PID controller 6c performs a second PID control calculation based on the steam pressure target value (jacket steam pressure SV) of the jacket section 3 and the steam pressure measurement value (jacket steam pressure PV) of the jacket section 3, and outputs the opening degree (control valve MV) of the control valve 5. More specifically, the second PID controller 6c compares the jacket steam pressure SV with the jacket steam pressure PV, and outputs the control valve MV by a PID control calculation so that the jacket steam pressure PV becomes the jacket steam pressure SV. The steam pressure measurement value of the jacket section 3 (jacket steam pressure PV) is measured by a jacket steam pressure gauge 8.

[0033] In the manufacturing apparatus 1, the temperature control unit 6 operates as follows (a) and (b): (a) The control valve MV output from the second PID controller 6c controls the opening and closing of the control valve 5, thereby adjusting the amount of steam in the jacket unit 3 and controlling the internal temperature of the foaming tank 2 to a predetermined temperature. (b) During the expansion process of the expanded beads, the parameters of the first PID control calculation are changed. According to the manufacturing apparatus 1, the internal temperature of the foaming tank can be precisely controlled by the above (a) and (b).

[0034] The manufacturing apparatus to which this control method can be applied is not particularly limited as long as it includes an expansion tank for expanded beads, a jacket portion provided on the outer periphery of the expansion tank, a supply pipe for supplying steam to the jacket portion, and a control valve provided on the supply pipe for regulating the amount of steam. An example of such a manufacturing apparatus is the manufacturing apparatus 1 shown in FIG. 1. Hereinafter, as this control method, a method for controlling the internal temperature of the expansion tank 2 to a predetermined temperature by a temperature control unit 6 in the manufacturing apparatus 1 will be described in detail. The temperature control step by the temperature control unit 6 includes a first PID control step, a pressure conversion step, and a second PID control step.

[0035] In the first PID control step, a first PID control calculation is performed based on the target internal temperature value and the measured internal temperature value in the foaming tank 2, and a target steam temperature value for the jacket section 3 is output. Specifically, first, the internal temperature of the foaming tank 2 is measured by the foaming tank thermometer 7. The foaming tank thermometer 7 is provided inside the foaming tank 2, and the temperature measured by the foaming tank thermometer 7 is input to the first PID controller 6a as the measured internal temperature value. Based on the target internal temperature value, which is the set target internal temperature, and the measured internal temperature value described above, a target jacket steam temperature value is calculated by PID control calculation by the first PID controller 6a.

[0036] Next, in the pressure conversion step, the target steam temperature value of the jacket section 3 is converted into pressure and the target steam pressure value of the jacket section 3 is output. Specifically, in the pressure converter 6b, the temperature is converted into pressure using, for example, the Antoine equation, to calculate the target jacket steam pressure value corresponding to the target jacket steam temperature value.

[0037] Then, in the second PID control step, a second PID control calculation is performed based on the steam pressure target value of the jacket section 3 and the steam pressure measurement value of the jacket section 3, and the opening degree of the control valve 5 is output. More specifically, the second PID controller 6c performs a PID control calculation based on the jacket steam pressure target value and the pressure of the jacket section measured by the jacket steam pressure gauge 8, i.e., the jacket steam pressure measurement value, to calculate the opening degree of the control valve 5.

[0038] Here, the temperature control unit 6 controls the first PID controller 6a to change the parameter of the first PID controller 6a during the expansion of the expanded beads. Changing the parameter of the first PID controller 6a preferably means changing the sensitivity of the parameter of the first PID controller 6a to be lower than the value at the start of expansion. That is, in a preferred configuration, the temperature control unit 6 controls the sensitivity of the parameter of the first PID control calculation during the expansion process of the expanded beads to be lower than the sensitivity at the start of the expansion process. In this control method, the temperature control step preferably includes a step of controlling the sensitivity of the parameter of the first PID control calculation during the expansion process of the expanded beads to be lower than the sensitivity at the start of the expansion process. This configuration has the advantage of further improving the controllability of the internal temperature of the expansion tank.

[0039] The following describes in detail the case where the sensitivity of the parameter P of the first PID controller 6a is reduced. Note that reducing the sensitivity of the parameter P of the first PID controller 6a means reducing the value of the parameter P of the first PID controller 6a.

[0040] In one embodiment of the present invention, at the start of foaming, the value of P of the first PID controller 6a is not particularly limited, but is preferably 5 to 30, and more preferably 10 to 20. This configuration has the advantage of further improving the controllability of the internal temperature of the foaming tank.

[0041] During the foaming process, it is preferable to reduce the value of P in the first PID controller 6a. If the value of P at the start of foaming is 100%, it is preferable to reduce the value of P to 30 to 70%, and more preferably to 40 to 60%.

[0042] Specifically, in the middle stage of the expansion of the expanded beads, the value of P of the first PID controller 6a is preferably 5 to 15, and more preferably 8 to 12. This configuration has the advantage of further improving the controllability of the internal temperature of the foaming tank.

[0043] Furthermore, the "intermediate stage of expansion of expanded beads" specifically refers to a stage where the degree of expansion is 30 to 70%, preferably 40 to 60%, assuming that the degree of expansion at the start of expansion is 0% and the degree of expansion at the end of expansion is 100%.

[0044] The sensitivity of P of the first PID controller 6a may be lowered by a large amount at once or may be lowered in stages. The number of times the sensitivity of P of the first PID controller 6a is lowered is not particularly limited, and may be one degree, two degrees, or three degrees or more. Of these, a three degree lowering is preferable. This configuration has an advantage that the internal temperature of the foaming tank 2 can be controlled more precisely.

[0045] Next, a detailed description will be given of a case where the sensitivity of the parameter I of the first PID controller 6a is reduced. Note that reducing the sensitivity of the parameter I of the first PID controller 6a means increasing the value of the parameter I of the first PID controller 6a.

[0046] In one embodiment of the present invention, at the start of foaming, the value of I of the first PID controller 6a is not particularly limited, but is preferably 100 to 500, and more preferably 200 to 300. This configuration has the advantage of further improving the controllability of the internal temperature of the foaming tank.

[0047] During the foaming process, it is preferable to increase the I value of the first PID controller 6a. If the I value at the start of foaming is 100%, it is preferable to increase the I value to 150 to 250%, and more preferably to 180 to 220%.

[0048] Specifically, in the middle stage of the expansion of the expanded beads, the value of I of the first PID controller 6a is preferably 300 to 600, and more preferably 400 to 500. This configuration has the advantage of further improving the controllability of the internal temperature of the foaming tank.

[0049] Furthermore, the "intermediate stage of expansion of expanded beads" specifically refers to a stage where the degree of expansion is 30 to 70%, preferably 40 to 60%, assuming that the degree of expansion at the start of expansion is 0% and the degree of expansion at the end of expansion is 100%.

[0050] The parameter D of the first PID controller 6a may be changed during the foaming process.

[0051] In one embodiment of the present invention, when changing the three parameters of the first PID controller 6a, all three parameters may be changed, two parameters may be changed, or one parameter may be changed during the foaming stage. Specifically, for example, during the foaming stage, the value of P of the first PID controller 6a may be decreased and the value of I may be increased.

[0052] The timing for lowering the sensitivity of the parameters of the first PID controller 6a may be three or two at the same time.

[0053] Note that the change to reduce the sensitivity of the parameters of the first PID controller 6a is preferably a change to reduce the sensitivity of P among the parameters of the first PID controller 6a. That is, in a preferred configuration, the temperature control unit 6 controls the parameters of the first PID control calculation to reduce the sensitivity of the parameter P during the expansion process of the expanded beads. In this control method, the temperature control step preferably includes a step of controlling the parameters of the first PID control calculation to reduce the sensitivity of the parameter P during the expansion process of the expanded beads. This configuration has the advantage of improving the controllability of the internal temperature of the foaming tank.

[0054] As described above, the temperature control unit 6 has the pressure converter 6b, which calculates the jacket steam pressure target value from the jacket steam temperature target value based on the Antoine equation.

[0055] In this specification, the Antoine equation and Antoine constants shown below are used. The Antoine equation is an empirical formula relating the saturated vapor pressure and temperature of a pure substance, and is expressed as Equation 1. The Antoine constants A, B, and C are constants that depend on the substance; for water vapor, A = 23.1964, B = 3816.44, and C = -46.13. In the temperature control of the present invention, Equation 1 is used to convert the jacket steam temperature SV to the jacket steam pressure SV. Equation 1: lnP[Pa]=AB / (T[K]+C) P: Vapor pressure [Pa] A, B, C: Antoine constants T: Temperature [K] The conversion formula used in the pressure converter 6b is not particularly limited, and the Antoine formula, the Clausius-Clapeyron formula, etc. may be used, with the Antoine formula being most preferably used.

[0056] As described above, the second PID controller 6c adjusts the opening of the control valve 5 by performing PID control calculations based on the jacket steam pressure target value and the pressure in the jacket section measured by the jacket steam pressure gauge 8, i.e., the jacket steam pressure measurement value.

[0057] In the second PID controller 6c, the value of P is not particularly limited, but is preferably 3 to 20, and more preferably 5 to 10. This configuration has the advantage of further improving the controllability of the internal temperature of the foaming tank.

[0058] In the second PID controller 6c, the value of I is not particularly limited, but is preferably 300 to 700, and more preferably 400 to 600. This configuration has the advantage of further improving the controllability of the internal temperature of the foaming tank.

[0059] In one embodiment of the present invention, the internal temperature of the foaming tank in the first half of the foaming step (foaming progress of 0 to 50%) is preferably less than (internal temperature SV) ±0.13°C, more preferably (internal temperature SV) ±0.12°C or less, further preferably less than (internal temperature SV) ±0.11°C, and particularly preferably (internal temperature SV) ±0.10°C or less.

[0060] In one embodiment of the present invention, the internal temperature of the foaming tank in the latter half of the foaming step (when the foaming progress is 50 to 80%) is preferably less than (internal temperature SV) ±0.23°C, more preferably (internal temperature SV) ±0.22°C or less, more preferably less than (internal temperature SV) ±0.21°C, more preferably (internal temperature SV) ±0.20°C or less, more preferably (internal temperature SV) ±0.19°C or less, more preferably (internal temperature SV) ±0.18°C or less, further preferably (internal temperature SV) ±0.17°C or less, and particularly preferably (internal temperature SV) ±0.16°C or less.

[0061] The method for producing expanded beads of a thermoplastic resin according to one embodiment of the present invention is a method including, as one step, the method for controlling the temperature of the expanded beads production apparatus described above.

[0062] The method for producing expanded beads that can include the present control method as one step is not particularly limited, and known methods (WO2018 / 008445) and the like can be used.

[0063] The thermoplastic resin that is the base resin of the expanded beads is preferably a polyolefin resin, and although there are no particular limitations on the polyolefin resin, polypropylene and polyethylene are particularly preferred. [Example]

[0064] The method for controlling the temperature of the expanded bead manufacturing apparatus according to the present invention will be described in detail below with reference to examples and comparative examples, although the present invention is not limited to these examples.

[0065] The evaluation methods implemented in the examples and comparative examples will be described.

[0066] 〔Experimental method〕 <Inner temperature control of the foaming tank> An example of the inner temperature setting of the foaming tank is shown in Fig. 2. As shown in Fig. 2, temperature control was performed such that the inner temperature SV (°C) of the foaming tank became T1 °C at t1 minutes after the start of the temperature rise of the foaming tank, T2 °C at t2 minutes, and T3 °C at t3 minutes. When the period from the start of the temperature rise of the foaming tank to t1 minutes was defined as the P1 process, the period from t1 minutes to t2 minutes was defined as the P2 process, and the period from t2 minutes to t3 minutes was defined as the P3 process, the magnitude of the temperature rise rate of the foaming tank was P1 > P2 > P3.

[0067] In the P3 process (foaming process), since the inner liquid in the foaming tank was drained, the amount of the inner liquid gradually decreased. At the end of foaming, all the inner liquid was drained. Also, as the process advanced from the P1 process to the P3 process, the necessity for the accuracy of the inner temperature control increased, so the inner temperature control in the foaming process (P3 process) was particularly important. In the examples, inner temperature control was implemented in the foaming process, and the inner temperature deviation (inner temperature PV - inner temperature SV) in the foaming process was compared to evaluate the respective inner temperature controllabilities.

[0068] <Antoine equation> In this specification, the Antoine equation and the Antoine constants used the following equations and constants, respectively. The Antoine equation is an empirical equation regarding the saturated vapor pressure and temperature of a pure substance, and is represented by Equation 1. The Antoine constants A, B, and C are constants that depend on the substance. In the case of water vapor, A = 23.1964, B = 3816.44, and C = -46.13. In the temperature control of the present invention, the jacket steam temperature SV was converted to the jacket steam pressure SV using Equation 1. Equation 1: lnP[Pa] = A - B / (T[K] + C) P: Vapor pressure [Pa] A, B, C: Antoine constants T: Temperature [K] (Example 1) The inner temperature of the foaming tank was controlled according to the following (1) to (5). The PID parameters in the foaming process (P3 process) were set to the values shown in Table 1.

[0069] (1) 3m of the shape shown in Figure 1 3 2m of pure water in the foaming tank 3 was prepared.

[0070] (2) After adding pure water to the foaming tank, the agitator was turned on and the agitation was continued until the end of the experiment.

[0071] (3) The temperature in the foaming tank was raised by supplying steam from a supply pipe with a diameter of 80A (diameter 80 mm) to the jacket (average thickness approximately 2.5 cm) for approximately 30 minutes until the temperature inside the foaming tank PV reached T1 (130°C). During the temperature increase, the opening of the control valve of the supply pipe with a diameter of 80A was kept constant.

[0072] (4) After the internal temperature PV of the foaming tank reached T1, the temperature was raised by supplying steam from a supply pipe with a diameter of 80A for about 20 minutes until it reached T2 (150°C). The jacket steam temperature SV was calculated from the internal temperature SV and internal temperature PV of the foaming tank by the first PID control. Then, the jacket steam temperature SV was converted to jacket steam pressure SV by using the Antoine equation in a pressure converter. The internal temperature of the foaming tank was controlled by calculating the control valve opening from the jacket steam pressure SV and jacket steam pressure PV by the second PID control.

[0073] (5) After the internal temperature PV of the foaming tank reached T2, the beads discharge valve was opened to start foaming. Then, steam was supplied from a supply pipe with a diameter of 80A to raise the temperature inside the foaming tank until the internal temperature PV of the foaming tank reached T3 (152°C). As in (4), the jacket steam temperature SV was calculated by the first PID controller from the internal temperature SV and the internal temperature PV of the foaming tank. The first PID parameters from the start of foaming to 10 minutes after the start of foaming were P: 18 and I: 240. The first PID parameters from 10 minutes after the start of foaming to the completion of foaming were P: 9 and I: 240. The jacket steam pressure SV was then converted into the jacket steam pressure SV using the Antoine equation in a pressure converter. The internal temperature of the foaming tank was controlled by calculating the control valve opening using the second PID controller from the jacket steam pressure SV and the jacket steam pressure PV. The second PID parameters were kept constant from the start of foaming to the completion of foaming, being P: 8 and I: 500.

[0074] (Comparative Example 1) The same procedure as in Example 1 was carried out, except that the PID parameters in the foaming step were changed to the values ​​shown in Comparative Example 1 in Table 1.

[0075] (Comparative Example 2) The same procedure as in Example 1 was carried out, except that the PID parameters in the foaming step were changed to the values ​​shown in Comparative Example 2 in Table 1.

[0076] [Table 1]

[0077] The evaluation results are shown in Figures 3 and 4. Figure 3 is a graph showing the changes over time in the internal temperature, internal temperature deviation, jacket steam pressure SV, and jacket steam pressure PV during the foaming process in Examples and Comparative Examples. Figure 4 is a graph showing the changes over time in the internal temperature, internal temperature deviation, jacket steam pressure SV, and jacket steam pressure PV during the foaming process with respect to the degree of foaming progress (0% at the start of foaming, 100% at the end of foaming) in Examples and Comparative Examples. Table 2 also shows the internal temperature deviations in the first half (foaming progress of 0-50%) and second half (foaming progress of 50-80%) of the foaming process in Examples and Comparative Examples. Note that the internal liquid temperature (internal temperature PV - internal temperature SV) in the foaming tank drops significantly at the end of foaming (foaming progress of 80-100%). Therefore, the internal temperature deviation at the end of foaming was excluded from the comparison and verification.

[0078] [Table 2]

[0079] (summary) As shown in Table 2, the internal temperature deviation in the latter half of foaming was large, reaching a maximum of 0.23°C, in Comparative Example 1. This is thought to be because the fluctuations in the jacket steam pressures SV and PV in the latter half of foaming were larger than those in the first half of foaming.

[0080] In Comparative Example 2, fluctuations in the jacket steam pressures SV and PV in the latter half of foaming were kept small, and the internal temperature deviation in the latter half of foaming was improved to 0.15°C. However, the internal temperature deviation in the first half of foaming was 0.13°C, which was worse than in Comparative Example 1.

[0081] In Example 1, by using the PID parameter values ​​of Comparative Example 1 in the first half and the parameter values ​​of Comparative Example 2 in the second half, the internal temperature deviation in the first half of foaming was 0.10°C and the internal temperature deviation in the second half of foaming was 0.16°C. In other words, Example 1 achieved better internal temperature controllability than Comparative Examples 1 and 2. [Explanation of symbols]

[0082] 1 Manufacturing equipment 2 Foaming tank 3 Jacket section 4 Supply pipe 5 Control valve 6 Temperature control unit 6a First PID controller 6b Pressure converter 6c Second PID controller 7. Foam bath thermometer 8 Jacketed steam pressure gauge 9 Mixer 10 Steam drain 11 Resin particle discharge valve

Claims

1. a foaming tank for foam particles; a jacket portion provided on the outer periphery of the foaming tank; a supply pipe for supplying steam to the jacket portion; a control valve provided in the supply pipe for adjusting the amount of steam; a temperature control unit that controls the internal temperature of the foaming tank to a predetermined temperature, The temperature control unit a first PID controller that performs a first PID control calculation based on an internal temperature target value of the foaming tank and a measured internal temperature value of the foaming tank, and outputs a steam temperature target value of the jacket portion; a pressure converter that converts the steam temperature target value of the jacket section into pressure and outputs the steam pressure target value of the jacket section; a second PID controller that performs a second PID control calculation based on the steam pressure target value of the jacket section and the steam pressure measurement value of the jacket section, and outputs an opening degree of the control valve, (a) By controlling the opening and closing of the control valve according to the opening degree, the amount of steam in the jacket part is adjusted, and the internal temperature of the foaming tank is controlled to a predetermined temperature, (b) An expanded bead manufacturing apparatus that changes a parameter of the first PID control calculation during an expansion process of the expanded beads.

2. The expanded bead manufacturing apparatus according to claim 1, wherein the temperature control unit controls the sensitivity of the parameter of the first PID control calculation to be lower during the middle stage of the expansion process of the expanded beads than the sensitivity at the start of the expansion process.

3. 3. The expanded bead manufacturing apparatus according to claim 2, wherein the temperature control section controls the first PID control calculation parameters so as to reduce the sensitivity of the parameter P.

4. a foaming tank for foam particles; a jacket portion provided on the outer periphery of the foaming tank; a supply pipe for supplying steam to the jacket portion; a control valve provided in the supply pipe for adjusting the amount of steam; and a temperature control method for an expanded bead manufacturing apparatus, the method comprising: a temperature control step of controlling an internal temperature of the expansion tank to a predetermined temperature, The temperature control step includes: a first PID control step of performing a first PID control calculation based on an internal temperature target value and an internal temperature measurement value in the foaming tank, and outputting a steam temperature target value of the jacket portion; a pressure conversion step of converting the steam temperature target value of the jacket section into a pressure and outputting the steam pressure target value of the jacket section; a second PID control step of performing a second PID control calculation based on the steam pressure target value of the jacket section and the steam pressure measurement value of the jacket section, and outputting an aperture of the control valve, A temperature control method for an expanded bead manufacturing apparatus, comprising changing a parameter of the first PID control calculation during an expansion step of the expanded beads.

5. 5. The temperature control method for an expanded bead manufacturing apparatus according to claim 4, wherein the temperature control process includes a process of controlling the sensitivity of the parameters of the first PID control calculation to be lower than the sensitivity at the start of the expansion process during an intermediate stage of the expansion process of the expanded beads.

6. 6. The temperature control method for an expanded bead manufacturing apparatus according to claim 5, wherein the temperature control step includes a step of controlling so as to reduce the sensitivity of a parameter P among the parameters of the first PID control calculation.

7. A method for producing expanded beads of a thermoplastic resin, comprising the temperature control method according to any one of claims 4 to 6 as one step.

8. The method for producing expanded thermoplastic resin beads according to claim 7, wherein the thermoplastic resin is a polyolefin resin.

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