JPH1190952A - Gas injection device for gas injection molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable stable continuous molding without generating a defective appearance such as silver and a flow mark and to attempt response to wide molding conditions by installing a depressurization valve for discharging gas between a gas shutoff valve and a gas injection valve in a gas channel equipped with a gas source, the gas shutoff valve and the gas injection valve. SOLUTION: An actuation valve 29 is actuated by the signal of a gas injection controller, a gas shutoff valve 23 is opened, and a gas injection port is opened by gas pressure to inject gas into a molten resin. After the completion of gas injection, the valve 23 is closed by the actuation valve 29, an actuation valve 30 is actuated, the gas pressure in a channel is decreased by a depressurization valve 26, and when gas in the channel is unnecessary, the intrusion of gas into a cylinder is prevented. Gas is injected to inject/pack molten resin containing gas into a mold cavity, a molding which is cooled and molded is demolded by extracting gas in a hollow part, and a molding cycle is completed. The molding without generation of silver, a flow mark, and others having a good appearance can be molded stably and continuously, and molding conditions can be set finely.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas injection / injection molding gas injection apparatus used for injection molding of a molded article containing a hollow portion by gas injection. More specifically, the present invention relates to a gas injection device for injection molding, which is used for molding a hollow portion-containing resin molded product to be injected into a mold cavity after injecting a gas into a plasticized molten resin in an injection cylinder.

[0002]

2. Description of the Related Art Conventionally, thermoplastic resins such as a polypropylene resin and a polystyrene resin have been manufactured by using an injection molding method for molded articles such as automobile parts, home electric parts, and electric parts. However, there is a drawback that the weight cannot be reduced by general injection molding, and in molded products having different thicknesses, particularly molded products with ribs and molded products having thick portions, sinks occur in the rib portions and thick portions, and integrated molding is performed. There was a problem that it was impossible. As a method of solving this, there is a method using a foamable resin, but it is possible to reduce the weight, but in addition to the insufficient strength and poor surface properties, the cooling time is long, and as a result, the molding cycle is long. Disadvantages such as poor productivity.

In recent years, as another method, a gas injection molding method has been adopted. Gas injection injection molding method,
This is a molding method in which after injecting a molten resin into a mold cavity, a pressurized gas such as nitrogen is injected into the molten resin from an injection nozzle, a runner in a mold, and a mold cavity wall. The gas forms a hollow part over the entire molded product, or forms a hollow part in the rib part or thick part, and the gas pressure transfers the mold cavity surface, resulting in sink, warp, deformation A lightweight resin molded product with excellent dimensional accuracy can be obtained.
For this reason, molded products have many excellent features such as being able to perform low-pressure molding compared to general injection molding, being lighter in weight, having higher rigidity, complex product design, and being applicable to large molded products. Has been deployed in the field.

However, in the conventional gas injection injection molding, a gas is injected into a molten resin in a mold cavity. Generally, it is necessary to use a high-pressure gas of 3 MPa or more as a gas. There are problems such as the need for equipment for gas injection and complicated control for injection. For these reasons, it has not yet been widely adopted in the field of injection molding, and is in fact limited to molding in special fields.

[0005] A gas injection molding method based on a new concept to improve these drawbacks has been proposed (Japanese Patent Laid-Open No. 9-164).
No. 547). In this method, the conventional gas injection is performed using an injection nozzle, a runner in a mold, a mold cavity, or the like as an injection point. The injection point is essentially changed. That is, a gas is injected into the plasticized molten resin in the injection cylinder, and the molten resin containing the gas is injection-molded to obtain a hollow-portion-containing resin molded product. Specifically, from the tip of the plasticizing screw or the cylinder wall, a gas is injected after the completion of the first resin plasticization, and the second resin plasticization is further performed to form a cavity by the gas in the plasticized resin. Let it form
This gas and the plasticized resin are integrally formed by injection molding.

[0006] This injection molding method is a very excellent injection molding method such that gas injection molding can be performed with a relatively low pressure gas and equipment can be simplified. However, in the gas injection device disclosed in the above publication, outside the gas injection step, the pressure in the cylinder is higher than the pressure in the gas supply path before the gas injection valve (the pressure at the time of completion of gas injection remains). When it becomes low, the gas may be automatically injected into the cylinder from the gas injection valve. There is a problem that it is not possible to manufacture a stable and constant molded product, for example, a surface appearance defect occurs due to the unintended gas injection.

Further, in the disclosure of the above-mentioned publication, the opening / closing control of the gas shut-off valve is performed by detecting the retreat position of the screw with the first limit switch and opening it, and when injecting a certain amount of gas, using the second limit switch or the timer. It is stated to close. However, in the opening of the shut-off valve by this limit switch, although there is no particular problem in the case where the injection of gas is performed while the resin is being plasticized and melted, that is, when the screw is being retracted, there is no particular problem. Irrespective of the timing, there is room for improvement and there remains a problem that molding conditions are limited, for example, when plasticization and metering are completed and the screw does not move backward, the molding cannot be performed.

[0008]

SUMMARY OF THE INVENTION Under such circumstances, the present invention relates to injection molding of a hollow part-containing resin molded article which is formed by directly injecting a gas into a plasticized molten resin in a plasticizing cylinder and then performing injection molding. , Stable continuous molding without appearance defects such as silver and flow mark, and
An object of the present invention is to provide a gas injection device for gas injection and injection molding, which can cope with a wide range of molding conditions depending on a molded product.

[0009]

Means for Solving the Problems The inventors of the present invention relate to a method of injecting a gas into a molten resin in a plasticizing cylinder and then performing injection molding of a resin molded article containing a hollow portion to be injection-molded. As a result of intensive studies on the relationship between appearance and molding stability, it was found that not only gas injection control but also other control, particularly control of the gas supply line, was necessary.
The present invention has been completed based on such findings.

That is, the present invention provides (1) a gas injection for injection molding gas injection for use in molding a hollow part-containing resin molded product which is injected into a mold cavity after injecting a gas into a plasticized molten resin in an injection cylinder. Apparatus, in a gas flow path provided with a gas source, a gas cutoff valve, and a gas injection valve, provided with a depressurization valve for discharging gas between the gas cutoff valve and the gas injection valve. Gas injection device. (2) The gas injection device for gas injection injection molding according to (1), wherein the opening and closing of the gas shutoff valve is position-controlled and / or time-controlled. (3) An object of the present invention is to provide the gas injection device for gas injection injection molding according to the above (1) or (2), wherein the opening and closing of the depressurizing valve is time-controlled.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The resin used for the injection molding method of the hollow part-containing resin molded product of the present invention is a thermoplastic resin, and is not particularly limited as long as it is a resin that can be injection molded. For example, polypropylene, ethylene-propylene block copolymer or random copolymer, polyolefin resin such as high-density polyethylene, polystyrene resin, rubber-modified polystyrene resin, ABS resin, AS resin, polyvinyl chloride resin, P
MMA resin, polyamide resin, polycarbonate resin,
Examples include polyacetate resin. As impact modifiers, ethylene-propylene copolymer rubber, polybutadiene rubber, styrene-butadiene-styrene block copolymer rubber (SBS), styrene-ethylene-butylene-styrene block copolymer rubber with SBS hydrogenated (S
Rubbers such as EBS) can also be added. Also,
If necessary, consider the required characteristics of the molded product, etc.
Carbon black, graphite, talc, mica, clay, calcium carbonate, silica, aluminum hydroxide,
Inorganic fillers such as magnesium hydroxide, calcium sulfate, glass fiber, carbon fiber, calcium titanate whisker, fibrous magnesium oxysulfate, crystallization accelerators, antioxidants (phosphorous, phenolic, sulfuric, etc.), Neutralizer, lubricant, dispersant, peroxide, heat stabilizer, ultraviolet absorber, light stabilizer, antistatic agent, flame retardant, flame retardant auxiliary, plasticizer, epoxy compound, metal deactivator, pigment ,
Additives such as dyes can also be added.

In the present invention, these thermoplastic resins are blended with known additional additives, if necessary, and then melt-kneaded. The pellets are used as raw materials in an injection cylinder containing a plasticizing screw. And plasticized by rotation of a screw to form a plasticized molten resin at the tip of the cylinder, and gas is injected into the molten resin during or after the formation of the molten resin. Next, the molten resin containing the gas is injected into a cavity in a mold to obtain a hollow-part-containing resin molded product.

According to the present invention, as the gas injection device, a gas from a gas source is led to a gas shutoff valve, and when the shutoff valve is opened, a gas injection valve provided downstream of the gas shutoff valve is opened by gas pressure to allow the molten resin to enter. To improve a gas flow path for injecting gas into a gas. That is, a depressurizing valve for discharging gas between the gas shutoff valve and the gas injection valve is provided. This depressurization valve works to depressurize the gas supply path to provide a clear difference between the pressure in the cylinder and the pressure in the gas supply path, and to close the gas injection valve when it is necessary to complete the gas injection. It is what you do. Simply closing the gas shut-off valve may cause the gas injection valve to open if the pressure in the cylinder subsequently drops. For this reason, after the end of the gas injection, the gas in the gas flow path confined between the gas injection valve and the gas injection valve is discharged by closing the gas shutoff valve, and the pressure is reduced or completely released to the atmosphere.

In the present invention, the injection of gas into the molten resin is generally performed by a check valve which can be opened and closed at the tip of the screw. It can be subject to considerable temperatures and therefore also the pressure of the gas, which is of particular importance in this case. The gas can be injected from the cylinder wall in addition to the screw tip described above. However, with a single gas injection valve, gas injection into the molten resin can be performed at any stage of melt plasticization of the resin, and further, it is possible to freely respond to changes in the amount of plasticized metered resin. At the tip of the screw. In addition, as a method of injecting gas from the injection valve,
Although there is no particular limitation, it is preferable to inject in the direction of reflection and reflection based on the direction perpendicular to the screw axis. In this case, the angle α in the injection direction is 10 degrees or more and about 20 to 60 degrees. A poppet valve can be used as an injection valve that enables this.

The present invention further provides a gas injection device provided with the above-mentioned depressurizing valve, wherein position control and / or time control of opening and closing of the gas cutoff valve are provided. Accordingly, the timing of gas injection can be controlled not only at the position of the screw by melt plasticization of the resin but also at completely free timing. That is, in addition to the position control, from a specific reference point such as a resin injection start signal, a specified amount of a plasticization measurement signal, or a plasticization measurement completion signal, the gas shutoff valve is directly or at an arbitrary time such as a time delay from this point. Open,
Gas injection can be performed. Opening of the depressurizing valve after completion of gas injection cannot be performed only by position control, but is controlled by time.

Hereinafter, the present invention will be described with reference to the drawings. FIG. 1 is a conceptual diagram showing a partial cross section of an entire injection molding apparatus to which a gas injection apparatus for gas injection and injection molding of the present invention is applied. 1 is an injection molding apparatus, 2 is a cylinder, 3 is a screw, 4 is an injection nozzle, 5 is a nozzle shutoff valve, 6 is a gas supply path, 7 is a gas injection valve, 8 is a fixed mold, 9 is a moving mold, 10 Is a mold cavity, 11 is a hopper, 12 is a plasticized molten resin, 13 is a sprue, 14 is a screw position detecting device, 15 is a gas injection device, and 16 is a gas injection control device.

FIG. 2 is a detailed view of the gas injection device according to the embodiment of the present invention. 21 is a gas supply pipe, 22 is a pressure reducing valve A, 2
3 is a gas shut-off valve, 24 is a flow control valve, 25 is a gas injection pipe, 26 is a depressurizing valve, 27 is a pressure reducing valve B, 28 is a low-pressure nitrogen line for operating a valve, 29 is an operating valve for a gas shut-off valve, and 30 is a degassing valve. This is an operating valve for a pressure valve. In the figure, reference numerals 29 and 30 denote current flow and excitation, the flow path is opened, and the respective valves 23 and 26 are opened and closed by operating nitrogen gas.

Next, an example of gas injection / injection molding using the gas injection / injection molding gas injection apparatus of the present invention will be described. After the nozzle shutoff valve 5 is closed, the pellets of the raw material are supplied from the hopper 11 to the screw 3, and are plasticized by rotation of the screw, and are plasticized and supplied to the tip of the cylinder by the retreat of the screw to form a plasticized molten resin 12.
The measurement of the molten resin is controlled so as to correspond to the volume excluding the hollow portion of the molded product.

Next, a gas from a gas supply source such as a gas cylinder (not shown) is supplied to the molten resin through a gas supply pipe 21.
The pressure reducing valve 22 is actuated and guided, and the signal from the gas injection control device 16 is actuated to actuate the actuating valve 29 to open the gas shut-off valve 23, through the gas supply path 6 provided at the center of the screw, and by the gas pressure. The gas injection port of the gas injection valve 7 is opened to inject gas. The pressure of the injected gas is usually controlled by the pressure reducing valve 22 and is usually in the range of 0.5 to 2.8 MPa.

The timing of gas injection is as follows:
There is no particular limitation as long as the molten resin necessary for injection is formed to some extent at the tip of the cylinder, but during the plasticization continuation, a back pressure is applied to the molten resin, so there is considerable pressure,
Near the end of plastification, especially after plastification and metering,
Injecting while sucking back (retreating the screw) may be preferable in that gas can be injected at a low pressure. When the gas injection is completed, the gas shutoff valve 23 is closed by the operation valve 29, and then the operation valve 30 is operated to reduce the gas pressure in the flow path by the depressurization valve 26. It is sufficient that the degree of the gas pressure drop is lower than the pressure in the cylinder including the step after the injection of the molten resin into the cavity, whereby the gas injection valve 7 is completely closed. This eliminates the possibility that the gas in the flow path will flow into the cylinder when unnecessary. It is preferable that the depressurization is maintained at a pressure slightly higher than the atmospheric pressure in order to prevent air from entering the injection gas flow path.

Gas is injected and molten resin 12 containing gas
Is injected and filled into the mold cavity 10 through the opened nozzle shutoff valve 5, the injection nozzle 4, and the sprue 13.
Next, the molded product that has been cooled and shaped is degassed as necessary, and then the mold is opened to release the molded product, thereby completing the molding cycle. In addition, it is not clear what form the molten resin and gas exist in the cylinder at the time of injection into the mold cavity, and they may exist in any state.

According to the present invention, in a gas injection device provided with a depressurizing valve, the opening and closing of the gas cutoff valve is controlled by position control and / or time control, that is, independently or in combination. Further, the opening and closing of the depressurizing valve is time-controlled. In the conventional gas injection method, the opening and closing of the gas shut-off valve is position control by moving the screw forward and backward,
Another problem is that residual gas in the flow path between the gas shut-off valve and the gas injection valve is opened by the check valve action of the injection valve due to a decrease in pressure downstream of the gas injection valve. On the other hand, in the present invention, in addition to providing the depressurizing valve,
Gas injection, stop, depressurization, etc., combined with time control in addition to basic position control by forward / backward position change by plasticization of the screw, enables arbitrary shape, size, degree of hollow part, resin It is possible to freely control the gas injection with respect to many molding variation factors such as the type of the resin and the melt viscosity of the resin.

[0023]

EXAMPLES Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. Injection molding machine 350MG manufactured by Mitsubishi Heavy Industries, Ltd. [clamping force: 350 tons, screw diameter: 62
mm] using a side molding for automobiles [length: 1100
mm, width: 70 mm, thickness: 2.5 mm] using a metal mold and polypropylene [IDEMISUPP
J-950H (MI = 20 g / 10 min: 230 ° C.,
2.16 kg load)] and molding was performed by injecting nitrogen gas. The molding conditions are shown below. (1) Molding temperature: 200 ° C (2) Mold temperature: 40 ° C (3) Start of gas injection: After completion of measurement (4) Gas injection pressure: 2.2 MPa (5) Gas injection time: 5 seconds (6) Gas Injection poppet valve: opening diameter = 23 mm, injection direction α = 35 degrees [reflection and outgoing direction angle based on the direction perpendicular to the screw axis] The gas shut-off valve at the start of gas injection is based on the screw metering completion position signal. . Based on this time, the closing of the gas cutoff valve was controlled after 5 seconds, and after 5.5 seconds, the depressurizing valve was operated to control the pressure in the flow path to 0.2 MPa.

The obtained side molding for automobiles had an average thickness of 2.5 mm, was free of silver and flow marks, had an excellent surface appearance, and could be repeatedly molded stably.

[0025]

According to the present invention, a light-weight molded article having a hollow portion with good appearance without generation of silver, flow mark, etc. can be continuously and stably formed. Further, gas injection timing, injection time, pressure, and the like can be finely set to molding conditions suitable for a molded product. In addition, equipment costs, molding costs,
It has excellent effects such as no generation of defective products.

[Brief description of the drawings]

FIG. 1 is a partial sectional conceptual view showing an entire injection molding machine used in an embodiment of the present invention.

FIG. 2 is an explanatory view of a gas injection device, which is a main part of an injection molding machine used in an embodiment of the present invention.

[Explanation of symbols]

 1: Injection molding device 2: Cylinder 3: Screw 4: Injection nozzle 5: Nozzle shutoff valve 6: Gas supply path 7: Gas injection valve 8: Fixed mold 9: Moving mold 10: Mold cavity 11: Hopper 12: Plasticized molten resin 13: Sprue 14: Screw position detecting unit 15: Gas injection device 16: Control device 21: Gas supply pipe 22: Pressure reducing valve A 23: Gas shutoff valve 24: Flow control valve 25: Gas injection pipe 26: Degassing Pressure valve 27: Pressure reducing valve B 28: Low pressure nitrogen line for valve operation 29: Operating valve for gas shutoff valve 30: Operating valve for depressurizing valve

Claims (3)

[Claims] 1. A gas injection device for injection molding, which is used for molding a resin molded article containing a hollow portion which is injected into a mold cavity after injecting a gas into a plasticized molten resin in an injection cylinder. A gas injection device for gas injection injection molding, characterized in that a gas pressure path provided with a gas shutoff valve and a gas injection valve is provided with a depressurization valve for discharging gas between the gas shutoff valve and the gas injection valve. 2. The gas injection device for gas injection injection molding according to claim 1, wherein the opening and closing of the gas shutoff valve is controlled in position and / or time. 3. The gas injection device for gas injection injection molding according to claim 1, wherein the opening and closing of the depressurizing valve is time-controlled.