JP3979758B2 - Foam molding method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a foam molding method, and in particular, a throttle means is provided in a nozzle portion to enable low-pressure foam molding so that the inside of a cylinder such as injection does not become supercritical pressure of an inert gas , and flow rate control. The present invention relates to a novel improvement for providing a valve to control the supply amount of an inert gas in accordance with the rotational speed of a screw.
[0002]
[Prior art]
Conventional foam molding methods of this type include, for example, a first method of foam molding by mixing a thermoplastic foaming agent with a thermoplastic resin, and foam molding using a physical foaming agent for a thermoplastic resin. The second method was adopted.
In addition, as disclosed in Japanese Patent No. 2625576, a third method in which supercritical carbon dioxide is injected into a molten resin to perform foam molding has been adopted.
[0003]
[Problems to be solved by the invention]
Since the conventional foam molding method is configured as described above, the following problems exist.
That is, in the first method described above, the chemical foaming agent is thermally decomposed to perform foam molding, but the cost of the foaming agent is high, and because of the residue of cracked gas, the generation of off-flavors, food Hygiene problems, molding machine, mold quality problems due to mold contamination, etc. have occurred.
On the other hand, the physical foaming method, which is the second method, is a method in which butane, betane, chlorofluorocarbon or the like is kneaded with a resin melted by a molding machine and then injected into a mold to obtain a foam molded product. However, these foaming agents are costly and cause environmental pollution such as ozone layer destruction.
In the case of the third method, since an inert gas such as carbon dioxide is used, the cost is low, there is no generation of a substance harmful to the global environment, and the foamed cell size is 10 μm or less and the moldability is also improved. Although it is good and has the advantage that the strength of the molded product does not decrease, it is difficult to maintain the cylinder in a supercritical state in the pre-injection process. If this supercritical pressure is not maintained, gas will be separated in the cylinder. A sufficient foamed molded product cannot be obtained in the mold.
[0004]
The present invention has been made to solve the above-described problems, and in particular, it is possible to perform low-pressure foam molding by providing a throttle means in the nozzle portion so that the inside of the cylinder before injection does not become below the supercritical pressure. In addition, an object of the present invention is to provide a foam molding method in which a flow rate control valve is provided to control the supply amount of the inert gas according to the rotational speed of the screw.
[0005]
[Means for Solving the Problems]
Foam molding method according to the invention, the inert gas is dissolved in the molten resin is injected from the nozzle portion of the distal end of the cylinder by the screw, the case of forming a foam molded article, a throttle means provided in the nozzle portion, the nozzle portion The internal pressure of the cylinder from the pressure sensor provided in the cylinder is taken into the control unit during injection by touching the touch part of the mold, and the restriction is performed so that the internal pressure does not become lower than the supercritical pressure of the inert gas. the opening of the opening of the nozzle portion by the diaphragm controlled by a command the throttle means from the control unit the operation of the actuator means is variable, and connected to the supply amount of the inert gas into the cylinder in the cylinder the flow control valve, the foam molding method to be controlled according to the rotational speed of the screw, the injection pressure sensor provided in the screw head portion of the cylinder Detecting the injection pressure at the time of injection by the opening of the opening of the nozzle portion by the control to the throttle means the operation of the actuator of the throttle means by the stop command issued from the control unit depending on the injection pressure It is a method of performing insert molding by controlling.
A foam molding method characterized by the above.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of a foam molding method according to the present invention will be described with reference to the drawings.
In FIG. 1, reference numeral 1 denotes a cylinder having an overall cylindrical shape and a heater 1 </ b> A. In a lumen 2 formed in the cylinder 1, a screw 3 is a rotation detector such as an encoder. It is rotatably arranged by a motor M having E.
[0007]
The cylinder 1 has a supply part 7, a first melting part 8, a low pressure part 9 and a second melting part from the raw material supply port 5 side where the hopper 4 is provided to the screw head part 6 side along the longitudinal direction thereof. 10 are sequentially formed.
Nozzle portion 12 having an opening 12a for injection comprising a heater 12A is provided which has a stop means 11 operated by the screw head part 6 actuator Do Ri not shown from the tip throttle valve side or the throttle nozzle like the . The diaphragm means 11 is provided in the opening 12a of the nozzle section 12, and the actuator of the diaphragm means 11 controls the throttle state , that is, the opening degree of the opening 12a based on a diaphragm command 14b from the control section 14 described later. It is configured to be variable.
[0008]
The screw head portion 6 of the cylinder 1 is provided with an injection pressure sensor 13 for detecting the pressure in the screw head portion 6, and the injection pressure 13 a detected by the injection pressure sensor 13 is supplied to the control portion 14. It is configured to be captured. Further, an internal pressure 15 a of a pressure sensor 15 provided at a substantially central position of the cylinder 1 is configured to be taken into the control unit 14.
[0009]
A variable electromagnetic flow control valve 17 is connected to an inlet 16 provided at a substantially central position of the cylinder 1, and the flow control valve 17 is an inert gas made of a liquid or gas such as carbon dioxide or nitrogen. The opening of the flow control valve 17 is configured to be variably controlled by a control signal 14a from the control unit 14.
[0010]
The screw rotation speed V of the screw 3 detected by the rotation detector E provided in the motor M is taken into the control unit 14, and a motor speed command from the control unit 14 is based on the screw rotation speed V. The rotation speed of the motor M, that is, the screw 3 can be controlled to a required speed by Vcom.
[0011]
Next, the operation will be described. First, in the state of FIG. 1, the resin raw material 20 sent into the cylinder 1 from the hopper 4 through the supply port 5 of the cylinder 1 is sent by the screw 3 that rotates based on the motor speed command Vcom from the control unit 14. The resin material 20 is sent to the downstream side while being melted by the heating by the heater 1 </ b> A and the shearing heat by the screw 3.
In this case, the throttle means 11 of the nozzle portion 12 is held in a closed state, and is plasticized and accumulated in the inner chamber 4 of the screw head portion 6 on the tip side of the screw 3.
[0012]
In the above case, the flow rate control valve 17 is opened by the control signal 14a from the control unit 14, the inert gas 18a is supplied into the cylinder 1 through the inlet 16, and the inert gas 18a is mixed into the molten resin. Is done.
In this case, since the mixing amount of the inert gas 18a into the molten resin is preferably 5 to 20 W%, the calculation is performed by the control unit 14 according to the screw rotation speed V as shown in FIG. The level of the signal 14a is controlled and, for example, the control shown in the step characteristic of FIG.
For example, in FIG. 2, when the screw rotation speed is changed to 100%, for example, the plasticizing ability is changed to 100Kg / Hr, 60% (30100Kg / Hr), and 20% (20Kg / Hr), this corresponds to the rotation speed, respectively. The gas supply amount is controlled to keep the gas supply amount to the molten resin constant.
[0013]
The inert gas injected and mixed into the molten resin does not become a supercritical state when the internal pressure 15a in the cylinder 1 falls below a certain level (for example, 7.5 Ma or more). The internal pressure 15a from the pressure sensor 15 of the cylinder 1 is controlled by the control unit 14 so that the nozzle unit 12 can be ejected by touching the touch unit 31 of the mold 30 as shown in FIG. And the operation of an actuator (not disclosed) of the throttle means 11 is controlled while the opening degree of the opening 12a of the nozzle part 12 is controlled to be variable by a throttle command 14b issued from the control part 14 .
As described above, by injecting the inert gas while maintaining the supercritical pressure state, the cylinder 1 does not become a foamed state but foams in the cavity 33 of the mold 30. (For example, a cell diameter of 10 μm or less) is obtained, and the strength of the molded product does not decrease. In addition, since the fluidity of the resin is improved, low-pressure molding is possible, and for example, breakage and damage of electronic parts such as ICs and coils in IC card molding can be prevented.
In the above-described case, the injection pressure sensor 13 provided in the screw head unit 6 detects the injection pressure 13a at the time of injection, and the throttle means 11 is controlled by the throttle command 14b from the control unit 14 according to the injection pressure 13a. The aperture of the opening 12a of the nozzle portion 12 by the throttle means 11 is variably controlled by controlling the operation of the actuator .
The operation of advancing the cylinder 1 and touching the nozzle portion 12 to the touch portion 31 of the mold 30 is not shown, but is advanced by a cylinder means that advances a known cylinder base (not shown). Is done.
[0014]
【The invention's effect】
Since the foam molding method according to the present invention is configured as described above, the following effects can be obtained. That is, during foam molding, the pressure in the cylinder is not always less than or equal to the supercritical pressure of the inert gas , and the injection pressure is also feedback controlled during injection to control the opening of the nozzle opening by the throttle means. Because the internal pressure in the cylinder is kept above a certain level and foaming in the cylinder is controlled, a finely foamed molded product can be obtained in the mold and a strong molded product can be obtained, and low pressure molding is possible. Therefore, for example, damage to electronic components during insert molding of an IC card or the like can be prevented.
In addition, since the opening of the flow control valve is controlled according to the screw rotation speed, the amount of inert gas in the molten resin can be controlled within a certain range, and the foamed state according to the molding purpose Can be controlled, and a constant, foamed molded product can be obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a foam molding method according to the present invention.
FIG. 2 is a characteristic diagram when flow control is performed according to the screw rotation speed in FIG.
FIG. 3 is an enlarged configuration diagram of a nozzle touch state in FIG. 1;
[Explanation of symbols]
1 cylinder 3 screw
6 Screw head part 11 Throttling means 12 Nozzle part
12a opening 13 injection pressure sensor 13a injection pressure
14 control unit
14b aperture command
15 pressure sensor
15a Internal pressure 17 Flow control valve 18a Inert gas 18 Tank
30 molds
31 touch part

Claims (1)

Emitted from the nozzle of the tip of the cylinder (1) by screw inert gas (18a) is dissolved in the molten resin (3) (12), when molding foamed molded diaphragm to the nozzle portion (12) Means (11), the cylinder from the pressure sensor (15) provided on the cylinder (1) during injection by touching the touch part (31) of the mold (30 ) with the nozzle part (12) ( The internal pressure (15a) of 1) is taken into the control unit (14) , and the operation of the actuator of the throttle means (11) is performed so that the internal pressure (15a) does not become lower than the supercritical pressure of the inert gas (18a). the nozzle unit according to the control by the throttle means by the stop command from the control unit (14) (14b) (11) the opening of the opening (12) is made variable, inert gas into said cylinder (1) in ( In the foam molding method in which the supply amount of 18a) is controlled according to the rotational speed of the screw (3) by the flow rate control valve (17) connected to the cylinder (1) .
Wherein detecting the injection time of the injection pressure (13a) by the cylinder screw head portion (1) injection pressure sensor provided in (6) (13), the control unit depending on the injection pressure (13a) (14) The insert command is performed by controlling the opening of the nozzle portion (12) by the throttle means (11) by controlling the operation of the actuator of the throttle means (11 ) by the throttle command (14b) issued from A foam molding method characterized by the above.

Images