JP3986500B2 - Supply device for supercritical fluid to injection molding machine - Google Patents

Description

The present invention relates to a supercritical fluid supply technique used when a supercritical fluid serving as a plasticizer or a foaming agent is mixed into a resin in an injection molding machine.
In the present invention, the upstream side of a certain device is called a primary side, the upstream pressure is called a primary pressure, the downstream side of the device is called a secondary side, and the downstream pressure is called a secondary pressure.

  FIG. 4 is a state diagram of a substance, in which the horizontal axis indicates temperature and the vertical axis indicates pressure. As is well known, the boundary line between a gas and a solid is a sublimation curve, and the boundary line between a gas and a liquid is an evaporation curve. Generally, there is an end point on the high pressure and high temperature side of the evaporation curve, and this end point is called a supercritical point. The temperature Tc corresponding to this supercritical point is called the supercritical temperature, and the corresponding pressure Pc is called the supercritical pressure. In the region higher than the supercritical point, it becomes a supercritical fluid with no change in evaporation or solidification.

  FIG. 5 is a state diagram of carbon dioxide, in which the horizontal axis indicates pressure and the vertical axis indicates density. Since the density increases as the pressure on the horizontal axis increases, supercritical carbon dioxide has a gaseous nature.

FIG. 6 is a graph comparing physical properties of gas, liquid, and supercritical fluid.
(A) is a density comparison diagram, and the density of the gas is about 1/1000 times the density of the liquid. On the other hand, the density of the supercritical fluid is 0.2 to 1.0 times the density of the liquid, and the supercritical fluid is close to the liquid in terms of density.
(B) is a comparative diagram of viscosity, and it can be seen that the supercritical fluid is close to gas in terms of viscosity.

  If a low-viscosity fluid is mixed with the resin in the injection machine, the fluidity of the resin increases, and the resin can be injected into the mold with a lower injection pressure. Therefore, a supercritical fluid having a viscosity much lower than that of a normal plasticizer is promising as a plasticizer in injection molding.

Since a normal plasticizer is a liquid or solid powder and is a non-compressed product, it is not affected by pressure, and a predetermined amount can be easily mixed into the resin, and the mixing ratio can be stabilized.
On the other hand, since supercritical fluid has both fluid (incompressible) and gas (compressible) properties, the conventional supply method that manages the supply amount by pressure mixes resin and plasticizer. It becomes difficult to stabilize the ratio.

Therefore, conventionally, a technique for adding supercritical carbon dioxide to a thermoplastic resin using a metering pump has been proposed (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 2000-84968 (FIG. 1)

Patent document 1 is demonstrated based on the following figure.
FIG. 7 is a diagram for explaining the basic configuration of the prior art. (1) is a liquefied carbon dioxide cylinder, (2) is a metering pump, (3) is a pressure holding valve, (4) is a molding machine, and (5) is A refrigerant circulator, (6) is a heater, and (7) is a flow meter.

To summarize the description from paragraph No. [0036] line 1 to paragraph No. [0040] line 10 of Patent Document 1, in FIG. 8, “Liquefied carbon dioxide in liquefied carbon dioxide cylinder (1) is metered in pump (2) And heated by the heater (6) and supplied to the molding machine (4).
In order to obtain a supercritical fluid, the pressure is controlled by the pressure-holding valve (3), and the temperature is controlled by the heater (6).
The flow rate is measured with a high-precision mass flow meter (7), and the information is fed back to the metering pump (2) to suppress fluctuations in the flow rate. Is explained.

However, the technique of Patent Document 1 has the following problems.
First, the high-accuracy mass flow meter (7) is extremely expensive and causes an increase in equipment costs.
Next, since there is a heater (6) next to the pressure holding valve (3), even if the pressure is kept constant by the pressure holding valve (3), the pressure changes greatly when heated by the heater (6). This pressure fluctuation appears as a flow fluctuation.

Further, when the supercritical fluid is continuously supplied to the molding machine (4), the influence is small, but the supply stop may be alternately repeated for the convenience of the molding process. When stopped, the metering pump (2) is stopped and the reading of the mass flow meter (7) becomes zero. When the supply is started, the flow rate is not stable until the metering pump (2) reaches a predetermined rotational speed.
Further, the supercritical fluid is compressible, and even if the metering pump (2) responds upon receiving a feedback signal from the mass flow meter (7), it is difficult to control due to a time delay due to the compression characteristics.
That is, the technique of Patent Document 1 is not suitable for a molding machine that repeatedly stops supply.

The present invention can omit a flow meter, and to provide a supply technique supercritical fluid supercritical fluid of a predetermined amount even after repeated outages can be stably supplied.

According to the first aspect of the present invention, in order to mix the fluid in the supercritical state with the resin material in the heating cylinder, the liquefied fluid is taken out from the liquefied fluid storage means by the constant discharge pump, and the heating cylinder side from the constant discharge pump Supplying the supercritical fluid that changes the liquefied fluid into a supercritical fluid by adjusting the pressure and temperature up to the supply port, and supplying the supercritical fluid into the heating cylinder when necessary Device,
A first flow path for changing the liquefied fluid to a supercritical fluid between the constant discharge pump and the heating cylinder side supply port, and a second channel from the outlet of the first flow path to the heating cylinder side supply port. A flow path and a return flow path for returning the fluid from the middle of the first and second flow paths to the inlet of the constant discharge pump, and the return flow path is closed when the primary pressure is less than a predetermined pressure. In the supercritical fluid supply device having a return flow path holding valve that keeps the primary pressure and opens when the primary pressure is equal to or higher than the predetermined pressure, and maintains the primary pressure at the predetermined pressure,
A first on / off valve is provided in the second flow path, a second on / off valve is provided in the return flow path, the second on / off valve is closed when the first on / off valve is opened, and the second on / off valve is opened. Rutotomoni a valve control unit for executing closing control of the first on-off valve when,
A throttle valve is provided on the outlet side of the first flow path .

According to the second aspect of the present invention, the first flow is closed on the outlet side of the first flow path when the primary pressure is less than a predetermined pressure to keep the primary pressure, and when the primary pressure is higher than the predetermined pressure, the primary flow is kept at the predetermined pressure. A road holding valve is interposed.

The invention according to claim 1 includes a first on / off valve in the second flow path, a second on / off valve in the return flow path, and closes the second on / off valve when opening the first on / off valve, The valve control part which performs control which closes a 1st on-off valve when opening a 2nd on-off valve was provided.
When the fluid is not supplied to the heating cylinder side supply port, the second flow path is closed by closing the first on / off valve, the fluid is circulated through the first flow path and the return flow path by opening the second on / off valve, At this time, the pressure at the inlet of the second flow path can be kept constant by the action of the pressure holding valve.

When supplying the fluid to the heating cylinder side supply port, the return channel is closed by closing the second on / off valve, and the fluid is allowed to flow through the first channel and the second channel by opening the first on / off valve. In addition, a constant amount of fluid is supplied to the heating cylinder side supply port by the action of the constant discharge pump.
As an apparatus, the first and second on / off valves are provided in the flow path and only the valve control unit is provided, so that an increase in the apparatus cost can be suppressed.
Furthermore, the invention according to claim 1 is characterized in that a throttle valve is provided on the outlet side of the first flow path. The constant discharge pump is set to the maximum discharge, and the flow rate can be controlled by the opening of the throttle valve. In addition, if a variable needle valve is used, the needle valve can always be set to an opening corresponding to the required flow rate, so that it is possible to suppress the occurrence of a surge flow accompanying a change in the opening of the valve.

The invention according to claim 2 is characterized in that a first flow path pressure-retaining valve is interposed on the outlet side of the first flow path. With the first flow path holding valve, a constant flow rate can always be discharged from the outlet of the first flow path by making the pressure on the primary side of the valve the same as the discharge pressure of the pump.
In addition, the holding valve can avoid a phenomenon in which the discharge pressure of the constant discharge pump is abnormally reduced, and can also protect the constant discharge pump.

The best mode for carrying out the present invention will be described below with reference to the accompanying drawings. The drawings are viewed in the direction of the reference numerals.
Figure 1 is a principle diagram of a supply device of the supercritical fluid into the molding machine out morphism, illustrating the injection mechanism 10 the configuration of the supply device 30 of the supercritical fluid in order.

  The injection mechanism 10 includes a two-stage screw 11 (detailed structure will be described later), a heating cylinder 12 that accommodates the screw 11 so as to be movable forward and backward, a heater 13 provided in the heating cylinder 12, and heating. A nozzle valve 14 provided at the tip of the cylinder 12, a heating cylinder side supply port 15 provided substantially at the center of the heating cylinder 12, a hopper 16 provided at the rear of the heating cylinder 12, and a rear end of the heating cylinder 12 The injection cylinder 17 includes a screw rotating means 18 provided at the rear end of the injection cylinder 17 and a resin pressure sensor 19 that measures the resin pressure in the heating cylinder 12.

The two-stage screw 11 melts the resin 22 and raises the pressure in the first stage 23 to form a leak barrier portion of the supply gas to the heating tube side supply port 15.
The second stage 25 serving as a gas supply part is provided with a resin pressure decompression part depending on the screw pitch and groove depth so as not to interfere with the gas supply. To advance.
21 is a flight in the first stage 23, 24 is a flight in the second stage 25, 26 is a partition for partitioning both stages 23 and 25, and 27 is a supply port.
The screw 11 is not limited to a two-stage screw, and any type can be used as long as it is a screw used in an injection machine.

  When the nozzle valve 14 is closed and the screw 11 is rotated in a predetermined direction by the screw rotating means 18, the resin 22 in the hopper 16 is kneaded by the first stage 23 to become high-pressure resin and travels toward the partition wall 26. The high pressure resin reaches the second stage 25 through the supply port 27 and is reduced in pressure.

  This resin is plasticized by the action of kneading and compression, and accumulates in the resin reservoir 28 on the primary side of the nozzle valve 14. The resin reservoir 28 increases with time, and the screw 11 moves backward accordingly. This series of steps is called a metering step, and resin is metered in this metering step.

This measurement is predetermined according to the cavity of the mold. When the metering is completed, the nozzle valve 14 is opened, the injection cylinder 17 is operated, the screw 11 is advanced, and the molten resin is injected from the heating cylinder 12.
The main action of the injection mechanism 10 is the above plasticization, metering, and injection in which holding pressure is applied.

  The supercritical fluid supply device 30 stores a liquefied fluid such as liquefied carbon dioxide, and a first flow path 32 and a second flow path 33 that connect a liquefied fluid storage means 31 such as a cylinder and the heating cylinder side supply port 15 in series. And a return flow path 34 branched from the inlet of the second flow path 33 and returning to the entrance of the first flow path 32, and the basic flow paths 32, 33, and 34 are used as the basic flow paths. It is provided.

  That is, a cooling unit 35 that cools the liquefied fluid to the first flow path 32, a constant discharge pump 36 that discharges the liquefied fluid in a certain amount, a variable speed motor 37 that drives the pump 36, and the liquefied fluid in a supercritical state. A heater unit 38 that heats up to a temperature necessary to achieve a temperature and a first flow path pressure-retaining valve 39 that maintains a pressure necessary to bring the liquefied fluid into a supercritical state are interposed.

  A safety valve 41 is a device that opens and lowers the pressure when the secondary pressure of the constant discharge pump 36 abnormally increases. Reference numeral 42 denotes a primary pressure sensor of the first flow path holding valve 39.

  A first on / off valve 44 is interposed in the second flow path 33. Reference numeral 45 is a supercritical fluid pressure sensor, and 46 is a flow measurement position where a mass flow meter is attached during the test.

The return channel 34 is provided with a second on / off valve 47, a return channel holding valve 48, and a check valve 49.
The first on / off valve 44 and the second on / off valve 47 close the second on / off valve 47 when the first on / off valve 44 is opened, and close the first on / off valve 44 when the second on / off valve 47 is opened. A valve control unit 50 that executes control is connected.

Next, the operation of the supercritical fluid supply device 30 will be described.
When the fluid is not supplied to the heating cylinder side supply port 15, the first on / off valve 44 is closed and the second on / off valve 47 is opened to close the second flow path 33, and to the first flow path 32 and the return flow path 34. Circulate the fluid.

  At this time, the first flow path pressure-retaining valve 39 is opened and plays the role of keeping the primary pressure (which can be read by the primary pressure sensor 42) constant. This primary pressure affects the discharge pressure of the constant discharge pump 36. If the discharge pressure fluctuates abnormally, the constant discharge pump 36 will be damaged. Thus, the constant discharge pump 36 can be protected by keeping the primary pressure constant by the first flow path pressure-retaining valve 39.

  At the same time, the return flow pressure holding valve 48 is opened and plays the role of keeping its primary pressure (which can be read by the supercritical fluid pressure sensor 45) constant.

  Next, when supplying fluid to the heating cylinder side supply port 15, the second on / off valve 47 is closed, the return flow path 34 is closed, and the first on / off valve 44 is opened. Then, the fluid discharged by the constant discharge amount pump 36 flows through the first flow path 32 and the second flow path 33 and reaches the heating cylinder side supply port 15. During this time, the first flow path holding valve 39 continues to protect the constant discharge pump 36.

  In general, when the first on / off valve 44 is switched from closed to open, the secondary pressure of the first on / off valve 44 rapidly increases (referred to as a transition period), and the primary pressure and flow rate fluctuate accordingly. It has been known. It is practically important whether or not this variation is significant.

Therefore, a mass flow meter was attached to the flow measurement point 46, and the flow rate of the supercritical fluid in the transition period was measured, and the pressure was measured at the same time.
FIG. 2 is an actual measurement graph of the flow rate, pressure, and resin pressure of the supercritical fluid in the transition period.
The bottom (c) shows the resin pressure measured by the resin pressure sensor 19 in FIG. 1, and the resin pressure gradually decreases with time from the point P1 to the point P2. By retreating, the volume of the low-pressure stage 25 increases and no supercritical fluid is supplied.

  The first on / off valve is opened and the second on / off valve is closed at the point P2 in FIG. 2 (c), but the pressure decreases until the point P3 due to the time delay. Since the supercritical fluid is supplied from the point P3 to the point P4, the pressure rises.

(A) is a graph showing the relationship between the flow rate of supercritical fluid and time, and the flow rate was measured with a mass flow meter attached to the flow rate measurement point 46.
The flow rate began to increase from the point P11 immediately after the first on / off valve opened, peaked at the point P12, rapidly decreased to the point P13, and gradually decreased from the point P13 to the point 14. Point P12 was 19 g / min, point P13 was 15 g / min, and point P14 was 13.8 g / min.

The line drawn horizontally from the vertical axis of 15 g / min corresponds to the set value of the discharge flow rate of both constant discharge pumps. From the experimental results, it can be confirmed that the flow rate is quantitatively stable without being affected by the surge. It was. This 15 g / min is the basis for the following comparison.
The deviation at the point P12 is +4 g / min (= 19-15), and the variation rate is (+4/15) × 100 = + 26%. The deviation at the point P14 is -1.2 g / min (= 13.8-15), and the variation rate is (-1.2 / 15) × 100 = -8%.
In particular, the flow rate is substantially constant between points P13 and P14.

(B) shows the pressure measured by the supercritical fluid pressure sensor 45 of FIG. 1, and the pressure increased from point P21 to point P22. This is considered to be influenced by the closing of the second on / off valve. However, this increase is slight, the pressure decreases with the supply into the heating cylinder, and the pressure increases with the pressure increase in the heating cylinder to point 23.
As is clear from the figure, the pressure fluctuation was slight, and the pressure fluctuation could be suppressed even in the transition period in which the on / off valve transitioned from closing to opening.

The supercritical fluid pressure of (b) was added to (c) with a fine line. In the present invention, since a constant flow rate is supplied, it can be said that the supercritical fluid pressure is obtained by adding a substantially constant pressure ΔP to the resin pressure. That is, the present invention can perform flow rate control that supplies a fixed amount of quantitative flow rate, not pressure control. If the flow rate is excessive, the pump discharge pressure increases abnormally. However, according to the present invention, this is not a concern, and the pump discharge pressure can be kept constant.
Remove the mass flow meter when the experiment is complete.

  From the above graph, it is possible to stably supply a predetermined amount of supercritical fluid to the heating cylinder even if the supply of the supercritical fluid is repeatedly stopped. Moreover, a stable supply of fluid can be realized without using an expensive flow meter.

As the supercritical fluid, carbon dioxide or nitrogen is preferable for the following reason.
Carbon dioxide has a critical temperature of 31.3 ° C. and a critical pressure of 7.4 MPa, and can be processed at a relatively low temperature and a relatively constant pressure. In addition, since carbon dioxide gas is a non-toxic gas, it can be spontaneously released into the atmosphere from the molded product after molding.

  Nitrogen has a critical temperature of −147 ° C., a critical pressure of about 3.4 MPa, and can be easily produced by simply pressurizing at normal temperature (it should be −147 ° C. or higher). Therefore, it can be spontaneously released into the atmosphere from the molded product after molding.

FIG. 3 is a principle diagram of a supercritical fluid supply apparatus to an injection molding machine according to the present invention . The common parts with FIG. That is, in the present invention, to remove the safety valve 41 of FIG. 1, the first flow path pressure holding valve of Figure 1 is replaced with a deformable throttle valve 52, further primary and return flow path pressure holding valve of the diaphragm valve 52 48 A bypass channel 53 is passed to the secondary side of the first channel, and a first channel pressure-retaining valve 39 is interposed in the bypass channel 53.

The constant discharge pump is selected so that the primary pressure is equal to or higher than the critical pressure when the required flow rate is set to the opening.
The pressure holding valve 39 is set to an arbitrary pressure lower than or equal to the set pressure of the safety valve 41.

  When the fluid is not supplied to the heating cylinder side supply port 15, the second flow path 33 is closed by the first on / off valve 44, and the fluid is circulated using the first flow path 32, the return flow path 34, and the bypass flow path 53, When the return flow pressure holding valve 48 is used to keep the pressure at the inlet of the second flow path 33 constant and fluid is supplied to the heating cylinder side supply port 15, the return flow path 34 is closed by the second on / off valve 47. The fluid can be flowed through the first flow path 32 and the second flow path 33, and the required flow rate of fluid can be supplied to the heating cylinder by the throttle valve.

  Further, as described above, since the pressure holding valve 39 functions and relieves the safety valve, the pressure on the primary side of the pressure holding valve can be maintained at a predetermined pressure, and the discharge pressure of the constant discharge pump Can be avoided, and the constant discharge pump can be protected. At the same time, resource loss can be suppressed.

The invention is suitable for that equipment to supply the supercritical fluid into the heating chamber of the injection molding machine.

It is a principle diagram of the supply device of the supercritical fluid into the morphism molding machine. It is an actual measurement graph of the flow volume, pressure, and resin pressure of a supercritical fluid in a transition period. It is a principle diagram of the supply device of the supercritical fluid into an injection molding machine according to the present invention. It is a state diagram of a substance. It is a phase diagram of carbon dioxide. It is the graph which compared the physical-property value of gas, a liquid, and a supercritical fluid. It is a figure explaining the basic composition of the conventional technology.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Injection mechanism, 12 ... Heating cylinder, 15 ... Heating cylinder side supply port, 19 ... Resin pressure sensor, 30 ... Supercritical fluid supply apparatus, 31 ... Liquefied fluid storage means, 32 ... 1st flow path, 33 ... 1st 2 flow paths, 34 ... return flow path, 36 ... constant discharge pump, 39 ... first flow path holding valve, 44 ... first on / off valve, 45 ... supercritical fluid pressure sensor, 47 ... second on / off valve, 48 ... Return flow pressure maintaining valve, 50... Valve control unit, 52.

Claims (2)

In order to mix the fluid in the supercritical state with the resin material in the heating cylinder, the liquefied fluid is taken out from the liquefied fluid storage means with a constant discharge pump, and the pressure and pressure between the constant discharge pump and the heating cylinder side supply port are taken out. The liquefied fluid is changed to a supercritical fluid by adjusting the temperature, and the supercritical fluid supply device supplies the supercritical fluid into the heating cylinder when necessary.
A first flow path for changing the liquefied fluid to a supercritical fluid between the constant discharge pump and the heating cylinder side supply port, and a second channel from the outlet of the first flow path to the heating cylinder side supply port. A flow path and a return flow path for returning the fluid from the middle of the first and second flow paths to the inlet of the constant discharge pump, and the return flow path is closed when the primary pressure is less than a predetermined pressure. In the supercritical fluid supply device having a return flow path holding valve that keeps the primary pressure and opens when the primary pressure is equal to or higher than the predetermined pressure, and maintains the primary pressure at the predetermined pressure,
A first on / off valve is provided in the second flow path, a second on / off valve is provided in the return flow path, the second on / off valve is closed when the first on / off valve is opened, and the second on / off valve is opened. Rutotomoni a valve control unit for executing closing control of the first on-off valve when,
An apparatus for supplying a supercritical fluid to an injection molding machine, wherein a throttle valve is provided on the outlet side of the first flow path . On the outlet side of the first flow path, a first flow path pressure maintaining valve is provided that closes and maintains the primary pressure when the primary pressure is less than a predetermined pressure, and opens and keeps the primary pressure at a predetermined pressure when the primary pressure is equal to or higher than the predetermined pressure. The supercritical fluid supply apparatus for an injection molding machine according to claim 1 .

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