JP2001150512A - Foaming method and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable low pressure foaming by setting the pressure in a cylinder to definite pressure, which exceeds supercritical pressure, or more by controlling the opening degree of the throttle means of a nozzle part. SOLUTION: In a method and an apparatus for performing foaming, the opening degree of the throttle means 11 of the nozzle part 12 is controlled so that the internal pressure of a cylinder 1 during injection does not become supercritical pressure or less and the supply amount of inert gas 18a is controlled corresponding to the rotational speed of a screw 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for foam molding, and more particularly, to a method for forming a nozzle by providing a throttle means so that the inside of a cylinder for injection or the like can be kept at a supercritical pressure or less, thereby enabling low pressure foam molding. In addition, the present invention relates to a novel improvement for providing a flow control valve to control a supply amount of an inert gas according to a rotation speed of a screw.

[0002]

2. Description of the Related Art Conventionally, foam molding methods and apparatuses of this kind include, for example, a first method in which a thermoplastic resin is mixed with a chemical foaming agent and foam molding is performed; A second method of foam molding using an agent has been employed. Further, as disclosed in Japanese Patent No. 2625576, a third method of injecting carbon dioxide in a supercritical state into a molten resin and performing foam molding has been adopted.

[0003]

Since the conventional foam molding method and apparatus have been constructed as described above, the following problems exist. That is, in the first method described above, the foaming is performed by thermally decomposing the chemical foaming agent. However, since the cost of the foaming agent is high and the residue of the decomposed gas generates an unpleasant odor, Hygiene issues, molding machines,
There was a quality problem of the molded product due to contamination of the mold and the like.
On the other hand, the physical foaming method, which is the second method, is a method of kneading butane, betan, freon, and the like into a resin melted by a molding machine, and then injecting the kneaded resin into a mold to obtain a foam molded product. However, these foaming agents are expensive and cause environmental pollution such as depletion of the ozone layer. Further, 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 substances harmful to the global environment, and the foam cell size is 10 μm or less, and the moldability is low. Although it has good characteristics and the strength of the molded product does not decrease, it is difficult to maintain the inside of the cylinder in a supercritical state in the process before injection, and if this supercritical pressure is not maintained, the gas will be separated in the cylinder. In addition, a sufficient foam molded product cannot be obtained in the mold.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and in particular, a low-pressure foam molding method is provided in which a nozzle portion is provided with a throttling means so that the inside of a cylinder before injection does not become lower than supercritical pressure. It is another object of the present invention to provide a method and an apparatus for foam molding in which a flow control valve is provided and a supply amount of an inert gas is controlled according to a rotation speed of a screw.

[0005]

A foam molding method according to the present invention is a foam molding method in which an inert gas is dissolved in a molten resin and injected from a nozzle at the tip of a cylinder by a screw to form a foam molded article. A throttle means provided in the nozzle portion, wherein the throttle amount of the throttle means is made variable so that the internal pressure of the cylinder does not become lower than the supercritical pressure during injection. A method of controlling the supply amount of the active gas by a flow rate control valve connected to the cylinder in accordance with the rotation speed of the screw, detecting an injection pressure of the injection, and controlling the throttle means in accordance with the injection pressure. Is a method of controlling the opening of
Further, the method is such that the pressure in the supercritical pressure state is 7.5 MPa or more. Further, the foam molding device according to the present invention,
In a foam molding apparatus in which an inert gas is dissolved in a molten resin and injected by a screw from a nozzle portion at a tip of a cylinder to form a foam molded article, the nozzle portion is provided with a squeezing means. Further, a flow control valve is provided between the cylinder and the inert gas tank, and an injection pressure sensor is provided in the nozzle portion.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the foam molding method and apparatus according to the present invention will be described below with reference to the drawings. In FIG. 1, a cylinder denoted by reference numeral 1 is a cylinder having an overall shape of a longitudinal cylinder and having a heater 1A. A screw 3 is provided in a bore 2 formed inside the cylinder 1 with a rotation detector such as an encoder. Motor M with E
It is arranged so that it can rotate freely.

The screw 3 has a supply section 7, a first melting section 8, a low-pressure section 9, and a first section from the raw material supply port 5 side provided with the hopper 4 to the screw head section 6 along the longitudinal direction. Two fusion parts 10 are sequentially formed. At the tip end of the screw head 6, there is provided a nozzle unit 12 having a throttle means 11 comprising a throttle valve or a throttle nozzle and a heater 12A. The aperture means 11 is configured to be able to change the aperture state based on an aperture command 14b from the control unit 14 described later.

The screw head 6 of the cylinder 1
Is provided with an injection pressure sensor 13 for detecting the pressure in the screw head section 6, and the injection pressure 13 a detected by the injection pressure sensor 13 is taken into the control section 14. . The internal pressure 15 a of the pressure sensor 15 provided at a substantially central position of the cylinder 1 is configured to be taken into the control unit 14.

A variable electromagnetic type flow control valve 17 is connected to an injection port 16 provided at a substantially central position of the cylinder 1, and the flow control valve 17 is made of a liquid or gas such as carbon dioxide and nitrogen. The flow control valve 17 is connected to a tank 18 containing an inert gas. The opening of the flow control valve 17 is variably controlled by a control signal 14 a from the control unit 14.

The rotation speed V of the screw 3 detected by the rotation detector E provided on the motor M is
And based on the screw rotation speed V, the motor M is controlled by a motor speed command Vcom from the control unit 14.
That is, the rotation speed of the screw 3 is controlled to a required speed.

Next, the operation will be described. First, in the state of FIG. 1, the resin raw material 20 sent from the hopper 4 into the cylinder 1 through the supply port 5 of the cylinder 1 is sent by the screw 3 rotating based on the motor speed command Vcom from the control unit 14. The resin raw material 20 is sent to the downstream side while being melted by heating by the heater 1A and shearing heat insulation by the screw 3. In this case, the throttle unit 1 of the nozzle unit 12
1 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.

In the case described above, the control signal 1 from the control unit 14
4a, the inert gas 18a is opened by the injection port 16a.
And the inert gas 18a is mixed into the molten resin. In this case, the inert gas 18a
Since the mixing amount in the molten resin is preferably 5 to 20 W%, as shown in FIG. 2, the control unit 14 calculates according to the screw rotation speed V and controls the level of the control signal 14 a. For example, the opening degree of the flow control valve 17 is controlled by performing control as shown in the step characteristics of FIG.
For example, in FIG.
%, For example, a plasticizing ability of 100 kg / hr, 60%
(30100 kg / hr), 20% (20 kg / hr)
Is changed, the gas supply amount corresponding to the rotation speed is controlled, and the gas supply amount to the molten resin is kept constant.

The inert gas injected and mixed into the molten resin does not enter a supercritical state when the internal pressure 15a in the cylinder 1 falls below a certain level (for example, 7.5 Ma or more). As shown in FIG. 3, the nozzle 12 is maintained at a certain level so that the pressure does not become lower than the supercritical pressure.
Injection is performed by taking the internal pressure 15a into the control unit 14 and controlling the actuator (not shown) of the squeezing means 11 by the squeezing command 14b so that the squeezing can be performed by touching the touch unit 31 of the mold 30. As described above, by injecting while maintaining the supercritical pressure state, since the foam is formed in the cavity 33 of the mold 30 without being in the foamed state in the cylinder 1, a molded product of fine foam (for example, 10 μm The following cell diameter) is obtained, and the strength of the molded product does not decrease. Further, since the fluidity of the resin is also improved, low-pressure molding becomes possible. For example, breakage or damage of electronic components such as ICs and coils in IC card molding can be prevented. In the case described above, the injection pressure sensor 13 provided on the screw head 6
Thus, the injection pressure 13a at the time of injection is detected, and the opening of the throttle means 11 is variably controlled by the throttle command 14b according to the injection pressure 13a. The aforementioned cylinder 1 is advanced and the nozzle part 12 is moved to the touch part 31 of the mold 30.
Although not shown, the operation of touching is performed by a well-known cylinder means for moving a cylinder table (not shown) forward.

[0014]

The foam molding method and apparatus according to the present invention include:
With the configuration described above, the following effects can be obtained. That is, at the time of foam molding, the internal pressure in the cylinder is kept at a certain level or more by controlling the opening of the throttle means by feedback control of the injection pressure during injection so that the pressure in the cylinder does not always fall below the supercritical pressure. As the foaming in the cylinder is controlled, a molded product of fine foam is obtained in the mold, and a molded product having a high strength is obtained, and low-pressure molding is possible. It is possible to prevent electronic components from being damaged during insert molding. In addition, since the opening of the flow control valve is controlled in accordance with the screw rotation speed, the amount of inert gas mixed in the molten resin can be controlled within a certain range. Control is possible, constant,
A foamed molded product is obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a foam molding method and apparatus according to the present invention.

FIG. 2 is a characteristic diagram when a flow rate is controlled according to a screw rotation speed in FIG.

FIG. 3 is an enlarged configuration diagram of a nozzle touch state in FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cylinder 3 Screw 11 Throttle means 12 Nozzle part 13a Injection pressure 18a Inert gas 18 Tank 17 Flow control valve 13 Injection pressure sensor

Claims (7)

[Claims] An inert gas (18a) is dissolved in a molten resin, and a screw (3) is used to dissolve an inert gas (18a) in a nozzle (12) at a tip of a cylinder (1).
In the foam molding method in which a foaming molded body is molded from the above, a nozzle means (12) is provided with a squeezing means (11), and the internal pressure of the cylinder (1) does not become lower than the supercritical pressure during the injection. Thus, the foaming method is characterized in that the drawing amount of the drawing means (11) is made variable. 2. An inert gas (18a) into the cylinder (1).
Flow control valve (17) connected to the cylinder (1)
The foam molding method according to claim 1, wherein the control is performed in accordance with the rotation speed of the screw (3). 3. The method according to claim 1, wherein an injection pressure (13a) of the injection is detected, and an opening degree of the throttle means (11) is controlled according to the injection pressure (13a). Foam molding method. 4. The pressure in the supercritical pressure state is 7.5MP.
The foam molding method according to any one of claims 1 to 3, wherein the value is not less than a. 5. A nozzle (12) at the tip of a cylinder (1) by dissolving an inert gas (18a) in a molten resin and using a screw (3).
A foaming molding apparatus, which is formed by injecting from a nozzle to form a foamed molded article, characterized in that the nozzle portion (12) is provided with a squeezing means (11). 6. The cylinder (1) and the inert gas (18a).
6. A foam molding apparatus according to claim 5, further comprising a flow control valve (17a) between said tank and said tank (18). 7. An injection pressure sensor (1) is provided at said nozzle portion (12).
7. The foam molding apparatus according to claim 5, wherein 3) is provided.