JP7759824B2 - 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. - Google Patents

Description

The present invention relates to an apparatus for manufacturing expanded beads, a method for controlling the temperature of the manufacturing apparatus, and a method for manufacturing expanded beads of a thermoplastic resin.

The depressurization foaming method is known as a method for producing expanded beads. In this method, a jacket is provided around the outer periphery of the foaming tank, and steam is supplied to the jacket to control the internal temperature of the foaming tank.

Furthermore, in recent years, technology has been disclosed for controlling the temperature of a typical reactor by controlling the steam pressure in the jacket.

For example, Patent Document 1 discloses a thin-film dehydration device in which thermosetting resin syrup in the final stage of reaction is caused to flow down the heated wall surface of a metal cylinder fitted with a heating jacket on the outer periphery, 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 jacket's steam pressure during the initial start-up of the device, and switches to constant-value control using feedback of the temperature inside the device during steady-state operation.

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 around 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 by the jacket or double pipe is used to heat and insulate the tank, pot, or kettles.

Japanese Unexamined Patent Publication No. 57-51724 Japanese Patent Application Laid-Open No. 2007-236878

However, when the above-mentioned conventional technology is used in a foaming tank, there is room for improvement in terms of controlling the internal temperature of the foaming tank.

One aspect of the present invention was conceived in consideration of the above-mentioned problems, and its purpose is to provide an expanded bead manufacturing apparatus and a temperature control method for the manufacturing apparatus, as well as a method for manufacturing expanded thermoplastic resin beads, that are capable of precisely controlling the internal temperature of the expansion tank.

As a result of extensive research to solve the above-mentioned problems, the inventors discovered that in a temperature control method that performs first PID control based on the target value of the foaming tank's internal temperature and the measured value of the foaming tank's internal temperature, and second PID control based on the target value of the jacket section's steam pressure and the measured value of the jacket section's steam pressure, changing the sensitivity of the first PID control parameters during foaming correlates with the controllability of the foaming tank's internal temperature. Therefore, by changing the parameters of the first PID control, it is possible to more accurately control the temperature of the expanded bead manufacturing equipment, leading to the present invention.

That is, one aspect of the present invention includes the following configuration.
<1> An expanded beads 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; a control valve provided on the supply pipe for adjusting the amount of steam; and a temperature control portion for controlling an internal temperature of the expansion tank to a predetermined temperature, wherein the temperature control portion 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 pressure-converts the target steam temperature value of the jacket portion, 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) changing a parameter of the first PID control calculation during an expansion process of the expanded beads.
<2> The expanded bead manufacturing apparatus described in <1>, wherein the temperature control unit controls the sensitivity of the parameters 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> The expanded bead manufacturing apparatus according to <2>, wherein the temperature control unit controls the sensitivity of the parameter P among the parameters of the first PID control calculation so as to decrease the sensitivity.
<4> 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 measurement value in the expansion 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 portion into a pressure value and outputting a steam pressure target value of 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 measurement value of the jacket portion, and outputting an aperture of the control valve, wherein a parameter of the first PID control calculation is changed during the expansion step of the expanded beads.
<5> The temperature control method for the expanded bead manufacturing apparatus described in <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> The temperature control method for the expanded bead manufacturing apparatus according to <5>, wherein the temperature control step includes a step of controlling so as to reduce the sensitivity of the 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 <4> to <6> as one step.
<8> The method for producing expanded thermoplastic resin beads according to <7>, wherein the thermoplastic resin is a polyolefin resin.

One aspect of the present invention provides an expanded bead manufacturing apparatus that can precisely control the internal temperature of the expansion tank, and a method for controlling the temperature of the manufacturing apparatus.

1 is a diagram schematically illustrating an entire expanded bead manufacturing apparatus according to one embodiment of the present invention. 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. 1 is a graph showing 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. 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.

One embodiment of the present invention is described below, but the present invention is not limited to this. The present invention is not limited to the 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 created by combining the technical means disclosed in each embodiment. All academic and patent literature described in this specification is incorporated herein by reference. Furthermore, unless otherwise specified in this specification, the expression "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)."

One known method for producing expanded beads is the depressurization foaming method. In this method, a jacket is provided around the outer periphery of the foaming tank, and the internal temperature of the foaming tank can be controlled by adjusting the opening of a control valve to supply steam to the jacket.

Conventionally, the internal temperature of a foaming tank has been controlled by controlling the opening of a control valve for supplying steam to the jacket section using two PID controls: a first PID control and a second PID control. The first PID control calculates a PID control value based on the internal temperature target value of the foaming tank (hereinafter sometimes referred to as the internal temperature target value) and the internal temperature measurement value of the foaming tank (hereinafter sometimes referred to as the internal temperature measurement value) to output a steam temperature target value for the jacket section (hereinafter sometimes referred to as the jacket steam temperature target value). The second PID control calculates a PID control value based on the above-mentioned jacket steam temperature target value and the measured steam temperature of the jacket section (hereinafter sometimes referred to as the jacket steam temperature measurement value) to output a control valve opening (hereinafter sometimes referred to as the control valve MV). However, with the second PID control, which calculates a PID control value based on the jacket steam temperature target value and the jacket steam temperature measurement value, it takes time for the jacket temperature to rise after the control valve is opened, resulting in a long response delay when the control valve is opened or closed. Therefore, conventional methods for controlling the internal temperature of a foaming tank have the drawback of poor response when opening and closing the control valve, resulting in poor internal temperature controllability.

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. This 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, making this technology expected to be used in foaming vessels. Therefore, the inventors of the present application believed that controlling the aperture of the control valve through jacket pressure control using the second PID control would improve the internal temperature controllability of the foaming vessel. Specifically, in the second PID control, PID control calculations are performed based on the target steam pressure value of the jacket (hereinafter sometimes referred to as the jacket steam pressure target value) and the measured steam pressure value of the jacket (hereinafter sometimes referred to as the jacket steam pressure measurement value).

However, even when the opening of the control valve is controlled by controlling the pressure in the jacket section using the second PID control, the responsiveness is improved to some extent, but there is still room for improvement in terms of precisely controlling the internal temperature of the foaming tank. Therefore, there is a demand for a method of controlling the internal temperature of the foaming tank that can precisely control the internal temperature of the foaming tank even when the opening of the control valve is controlled by controlling the pressure in the jacket section using the second PID control.

Based on these considerations, the inventors of the present application conducted extensive research with the aim of developing a method for controlling the internal temperature of a foaming tank that would meet the above requirements. They focused on changes in the liquid inside the foaming tank during the foaming process.

In the depressurization foaming method, the liquid inside the foaming tank gradually decreases as the resin particles foam. Therefore, the inventors 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 inside the foaming tank and the first PID control parameters. They also discovered that changing the first PID control parameters during the foaming process enables control in response to changes in the liquid inside the foaming tank, 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.

An expanded bead manufacturing apparatus according to one embodiment of the present invention (hereinafter sometimes referred to as "the manufacturing apparatus") comprises 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 the internal temperature of the expansion tank to a predetermined temperature. The temperature control unit comprises a first PID controller that performs a first PID control calculation based on the internal temperature target value of the expansion tank and the internal temperature measured value of the expansion tank, and outputs a steam temperature target value for the jacket portion. and a pressure converter that converts the target steam temperature value of the jacket section into a pressure value and outputs the target steam pressure value of the jacket section, and a second PID controller that performs a second PID control calculation based on the target steam pressure value of the jacket section and the measured steam pressure value of the jacket section to output the aperture of the control valve, whereby (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 bead manufacturing apparatus and a temperature control method for the manufacturing apparatus that can precisely control the internal temperature of the foaming tank.

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 comprising an expanded bead expansion tank, 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 adjusting the amount of steam. The method includes a temperature control process for controlling the internal temperature of the expansion tank to a predetermined temperature. The temperature control process includes a first PID control process for performing a first PID control calculation based on an internal temperature target value and a measured internal temperature value in the expansion tank to output a steam temperature target value for the jacket portion; a pressure conversion process for converting the steam temperature target value for the jacket portion into a pressure value and outputting a steam pressure target value for the jacket portion; and a second PID control process for performing a second PID control calculation based on the steam pressure target value for the jacket portion and the measured steam pressure value for the jacket portion to output the opening degree of the control valve. This method changes parameters of the first PID control calculation during the expansion process of the expanded beads. This method has the advantage of providing an expanded bead manufacturing apparatus and a temperature control method for the manufacturing apparatus that can precisely control the internal temperature of the expansion tank.

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

The expanded bead manufacturing apparatus and temperature control method for the manufacturing apparatus according to one embodiment of the present invention will be described below with reference to Figure 1. Figure 1 is a schematic diagram showing the entire expanded bead manufacturing apparatus according to this embodiment.

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 3, a supply pipe 4, a control valve 5, a temperature control unit 6, a foaming tank thermometer 7, a jacket steam pressure gauge 8, an agitator 9, a steam drain 10, and a resin particle discharge valve 11. The supply pipe 4 supplies steam to the jacket 3. The control valve 5 is provided on the supply pipe 4 and adjusts the amount of steam supplied to the jacket 3. The temperature control unit 6 controls the internal temperature of the foaming tank 2 to a predetermined temperature. The foaming tank thermometer 7 measures the internal temperature of the foaming tank 2. The jacket steam pressure gauge 8 measures the steam pressure in the jacket 3.

Exposure tank 2 is a container for producing expanded beads using the depressurization foaming method. Expanded beads are produced by charging resin particles, an aqueous dispersion containing an inorganic dispersant and a dispersion aid, and a volatile blowing agent together with water into the expansion tank 2, raising the temperature to a constant pressure and temperature to allow the resin particles to be impregnated with the blowing agent, and then releasing the mixture into a low-pressure atmosphere (depressurization foaming method), followed by drying. The materials charged in the expansion tank 2 are agitated by the agitator 9 and discharged through the resin particle discharge valve 11.

In one embodiment of the present invention, the jacket portion 3 is provided on the outer periphery of the foaming tank 2 and contains steam inside. When the control valve 5 is open, the steam is ventilated into the jacket portion 3 through the supply pipe 4. In other words, in the manufacturing apparatus 1, the internal temperature of the foaming tank 2 is controlled by adjusting the amount of steam in the jacket portion 3 by opening and closing the control valve 5.

More specifically, when the control valve 5 is opened and steam is vented into the jacket section 3 through the supply pipe 4, the steam does not condense into water, but instead 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 narrowing the opening of the control valve 5, the amount of steam supplied to the jacket section 3 is reduced, preventing the internal temperature of the foaming tank 2 from rising. After the steam condenses into water, it is discharged through the steam drain 10.

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

Here, PID control is a type of control action applied according to the difference between a target value and a measured value. In this specification, the action of changing the manipulated variable according to the control deviation is called P action, the action of changing the manipulated variable according to the integral value of the control deviation is called I action, and the action of changing 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 of control using a combination of the three actions of P action, I action, and D action. Note that in this specification, the parameter resulting from P action is called parameter P, the parameter resulting from D action is called parameter D, and the parameter resulting from I action is called parameter I.

The first PID controller 6a performs a first PID control calculation based on the target internal temperature value (internal temperature SV) of the foaming tank 2 and the measured internal temperature value (internal temperature PV) of the foaming tank 2, and outputs the target steam temperature value (jacket steam temperature SV) of the jacket section 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 through a PID control calculation so that the internal temperature PV becomes the internal temperature SV. The measured internal temperature value (internal temperature PV) of the foaming tank 2 is measured by the foaming tank thermometer 7.

The pressure converter 6b converts the jacket steam temperature SV output from the first PID controller 6a into the target steam pressure value (jacket steam pressure SV) for the jacket section 3. The method for converting the jacket steam temperature SV into the jacket steam pressure SV can be a known method for converting steam temperature into steam pressure. For example, one such conversion method is based on the Antoine equation, which will be described later.

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 measured steam pressure value (jacket steam pressure PV) of the jacket section 3, and outputs the opening degree of the control valve 5 (control valve MV). 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 through a PID control calculation so that the jacket steam pressure PV becomes the jacket steam pressure SV. The measured steam pressure value of the jacket section 3 (jacket steam pressure PV) is measured by the jacket steam pressure gauge 8.

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 section 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. With the manufacturing apparatus 1, the internal temperature of the foaming tank can be precisely controlled by the above (a) and (b).

The manufacturing apparatus to which this control method can be applied is not particularly limited, as long as it comprises an expansion tank for expanded beads, a jacket portion attached to the outer periphery of the expansion tank, a supply pipe for supplying steam to the jacket portion, and a control valve attached to the supply pipe for adjusting the amount of steam. An example of such a manufacturing apparatus is the manufacturing apparatus 1 shown in Figure 1. Below, as this control method, a method for controlling the internal temperature of the expansion tank 2 to a predetermined temperature using the temperature control unit 6 in the manufacturing apparatus 1 is described in detail. The temperature control process performed by the temperature control unit 6 includes a first PID control process, a pressure conversion process, and a second PID control process.

In the first PID control process, a first PID control calculation is performed based on the internal temperature target value and the internal temperature measurement value in the foaming tank 2, and a steam temperature target value for the jacket section 3 is output. Specifically, the internal temperature of the foaming tank 2 is first measured using the foaming tank thermometer 7. The foaming tank thermometer 7 is installed 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 internal temperature measurement value. The jacket steam temperature target value is calculated through PID control calculation by the first PID controller 6a based on the internal temperature target value, which is the set target internal temperature, and the internal temperature measurement value described above.

Next, in the pressure conversion process, the target steam temperature value for the jacket section 3 is converted to pressure and the target steam pressure value for the jacket section 3 is output. Specifically, the pressure converter 6b converts temperature to pressure using, for example, the Antoine equation, to calculate the target jacket steam pressure value corresponding to the target jacket steam temperature value.

Then, in the second PID control process, a second PID control calculation is performed based on the target steam pressure value of the jacket section 3 and the measured steam pressure 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 target jacket steam pressure value and the pressure of the jacket section measured by the jacket steam pressure gauge 8, i.e., the measured jacket steam pressure value, to calculate the opening degree of the control valve 5.

Here, the temperature control unit 6 controls the parameters of the first PID controller 6a to change during the expansion of the expanded beads. Changing the parameters of the first PID controller 6a preferably involves changing the sensitivity of the parameters 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 parameters 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 process preferably includes a step of controlling the sensitivity of the parameters 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.

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.

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

During the middle stage of foaming, it is preferable to lower the P value of the first PID controller 6a. If the P value at the start of foaming is 100%, it is preferable to lower the P value to 30-70%, and more preferably to 40-60%.

Specifically, during the intermediate stage of foaming of the foam 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.

In addition, "an intermediate stage in the expansion of expanded beads" specifically refers to a stage where the expansion progress is preferably 30-70%, and more preferably 40-60%, assuming that the expansion progress at the start of expansion is 0% and the expansion progress at the end of expansion is 100%.

The sensitivity of P of the first PID controller 6a may be lowered by a large amount in one go, or by a gradual decrease. Furthermore, the number of times the sensitivity of P of the first PID controller 6a is lowered is not particularly limited, and it may be by one degree, two degrees, or three degrees or more. Of these, a decrease of three degrees is preferable. This configuration has the advantage of enabling more precise control of the internal temperature of the foaming tank 2.

Next, we will explain in detail the case where the sensitivity of parameter I of the first PID controller 6a is reduced. Note that reducing the sensitivity of parameter I of the first PID controller 6a means increasing the value of parameter I of the first PID controller 6a.

In one embodiment of the present invention, the I value of the first PID controller 6a at the start of foaming 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.

During the middle stage of foaming, 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 150-250%, and more preferably to 180-220%.

Specifically, during the intermediate stage of foaming of the foam beads, the I value 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.

In addition, "an intermediate stage in the expansion of expanded beads" specifically refers to a stage where the expansion progress is preferably 30-70%, and more preferably 40-60%, assuming that the expansion progress at the start of expansion is 0% and the expansion progress at the end of expansion is 100%.

In addition, parameter D of the first PID controller 6a may be changed during the foaming process.

In one embodiment of the present invention, when changing the three parameters of the first PID controller 6a, it is possible to change all three parameters, two parameters, or one parameter during the foaming process. Specifically, for example, during the foaming process, it is possible to decrease the value of P in the first PID controller 6a and increase the value of I.

Furthermore, the timing for reducing the sensitivity of the parameters of the first PID controller 6a may be three or two at the same time.

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

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

In this specification, the Antoine equation and Antoine constants shown below are used. The Antoine equation is an empirical equation 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, and 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.
Formula 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.

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 jacket pressure measured by the jacket steam pressure gauge 8, i.e., the jacket steam pressure measurement value.

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

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

In one embodiment of the present invention, the internal temperature of the foaming tank during the first half of the foaming process (foaming progress 0-50%) is preferably less than (internal temperature SV) ±0.13°C, more preferably (internal temperature SV) ±0.12°C or less, even more preferably less than (internal temperature SV) ±0.11°C, and particularly preferably (internal temperature SV) ±0.10°C or less.

In one embodiment of the present invention, the internal temperature of the foaming tank in the latter half of the foaming process (foaming progress 50-80%) 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, even more preferably (internal temperature SV) ±0.17°C or less, and particularly preferably (internal temperature SV) ±0.16°C or less.

A method for producing expanded thermoplastic resin beads according to one embodiment of the present invention is a method that includes, as one step, the method for controlling the temperature of the expanded bead production apparatus described above.

The method for producing expanded beads that can include this control method as one step is not particularly limited, but known methods such as those described in WO2018/008445 can be used.

The thermoplastic resin that is the base resin of the expanded beads is preferably a polyolefin-based resin. There are no particular limitations on the polyolefin-based resin, but polypropylene and polyethylene are particularly preferred.

The method for controlling the temperature of the expanded bead manufacturing apparatus according to the present invention will be explained in detail below using examples and comparative examples. Note that the present invention is not limited to these examples.

The evaluation methods used in the examples and comparative examples are described below.

[Experimental Method]
<Controlling the internal temperature of the foaming tank>
An example of the setting of the internal temperature of the foaming tank is shown in Fig. 2. As shown in Fig. 2, the temperature was controlled so that the internal temperature SV (°C) of the foaming tank was T1°C at t1 minute after the start of temperature increase of the foaming tank, T2°C at t2 minute after the start of temperature increase of the foaming tank, and T3°C at t3 minute after the start of temperature increase of the foaming tank. When the period from the start of temperature increase of the foaming tank to t1 minute was defined as process P1, the period from t1 minute to t2 minutes was defined as process P2, and the period from t2 minutes to t3 minutes was defined as process P3, the magnitude of the temperature increase rate of the foaming tank was P1>P2>P3.

During the P3 process (foaming process), the liquid inside the foaming tank was drained, gradually reducing the amount of liquid inside. When foaming was complete, all of the liquid inside had been drained. Furthermore, as the process progressed from P1 to P3, the need for precision in internal temperature control increased, making internal temperature control particularly important during the foaming process (P3 process). In the examples, internal temperature control was performed during the foaming process, and the internal temperature deviation (internal temperature PV - internal temperature SV) during the foaming process was compared to evaluate the internal temperature controllability of each process.

<Antoine style>
In this specification, the Antoine equation and Antoine constants used are the equations and constants shown below. The Antoine equation is an empirical equation 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, and for water vapor, A = 23.1964, B = 3816.44, and C = -46.13. In the temperature control of the present invention, Equation 1 was used to convert the jacket steam temperature SV to the jacket steam pressure SV.
Formula 1: lnP[Pa]=AB/(T[K]+C)
P: Vapor pressure [Pa]
A, B, C: Antoine constants T: temperature [K]
Example 1
The internal temperature of the foaming tank was controlled according to the following (1) to (5). The PID parameters in the foaming step (P3 step) were set to the values shown in Table 1.

(1) 2 ^m³ of pure water was charged into a 3 ^m³ foaming tank having the shape shown in Figure 1.

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

(3) The temperature inside 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). The opening of the control valve of the supply pipe with a diameter of 80A was kept constant throughout the temperature increase.

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

(5) After the internal temperature PV of the foaming tank reached T2, the bead discharge valve was opened to initiate foaming. Steam was then supplied from a supply pipe with an 80A diameter 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 using the first PID controller from the internal temperature SV and 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 to 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 jacket steam pressure PV. In this case, the second PID parameters were kept constant from the start of foaming to the end of foaming, with P: 8 and I: 500.

(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.

(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.

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 the examples and comparative examples. Figure 4 is a graph showing the changes in the internal temperature, internal temperature deviation, jacket steam pressure SV, and jacket steam pressure PV during the foaming process versus the foaming progress (0% at the start of foaming, 100% at the end of foaming) in the examples and comparative examples. Table 2 also shows the internal temperature deviations in the first half (foaming progress 0-50%) and second half (foaming progress 50-80%) of the foaming process in the examples and comparative examples. Note that the internal liquid temperature of the foaming tank (internal temperature PV - internal temperature SV) drops significantly at the end of foaming (foaming progress 80-100%). Therefore, the internal temperature deviation at the end of foaming was excluded from the comparison and verification.

(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 due to the fact that 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.

In Comparative Example 2, fluctuations in jacket steam pressure 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, worse than in Comparative Example 1.

In Example 1, by using the PID parameter values of Comparative Example 1 in the first half and 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.

REFERENCE SIGNS LIST 1 Manufacturing apparatus 2 Foaming tank 3 Jacket section 4 Supply pipe 5 Control valve 6 Temperature control section 6a First PID controller 6b Pressure converter 6c Second PID controller 7 Foaming tank thermometer 8 Jacket steam pressure gauge 9 Agitator 10 Steam drain 11 Resin particle discharge valve

Claims (8)

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. The expanded bead manufacturing apparatus of claim 1, wherein the temperature control unit controls the sensitivity of the parameters 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. The expanded bead manufacturing apparatus described in claim 2, wherein the temperature control unit controls the first PID control calculation parameters to reduce the sensitivity of parameter P. 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, the method comprising: a temperature control step of controlling an internal temperature of the foaming tank to a predetermined temperature in the expanded bead manufacturing apparatus;
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. The temperature control method for an expanded bead manufacturing apparatus described in claim 4, wherein the temperature control process includes a process of controlling the sensitivity of the parameters 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. The temperature control method for an expanded bead manufacturing apparatus described in claim 5, wherein the temperature control process includes a control process for reducing the sensitivity of parameter P, one of the parameters of the first PID control calculation. A method for producing expanded thermoplastic resin beads, comprising the temperature control method described in any one of claims 4 to 6 as one step. The method for producing expanded thermoplastic resin beads according to claim 7, wherein the thermoplastic resin is a polyolefin-based resin.