JP2511800B2 - Resin molded product, its molding method, and its molding device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin molded product having a shape having different thickness portions, a molding method for obtaining a molded product by injection molding, and an injection molding apparatus.

[0002]

2. Description of the Related Art A method called a gas counter pressure method is known as an injection molding method for a resin having a thick portion. That is, a gas counter pressure (hereinafter referred to as compressed air) is injected into the mold cavity with a gas (air, N ₂ gas, etc.) pressurized above the atmosphere before injection of the resin, and a foaming gas, that is, an organic solvent ( Alcohol), inorganic liquid (H ₂
O), organic gas (Cl ₃ H), inorganic gas (N ₂ , C)
(O ₂ , CO) etc. or a molten resin in which a mixture thereof is melted is maintained in a pressurized melted state even when injected into the mold cavity, and compressed air is released to the atmosphere immediately before or after the injection of the resin to lower the compressed air. As a result, the inside of the molded product is foamed to perform foam molding. A method called gas-assisted injection is also known. That is, the resin holding pressure is replaced by injecting gas into the molded product after (or while inserting) the resin into the mold cavity to fill the mold cavity (or less) with the primary injection.

[0003]

[SUMMARY OF THE INVENTION A gas counter-flop LESSON shea <br/> catcher method skins foaming power and has no thickness to some extent the foam layer surface which hold the sink by foaming power of the internal molded article when the It cannot overcome the sinking force of the layer (Fig. 6).
Therefore, there is a problem that the shape thickness of the molded product is greatly limited. In order to obtain a molded product having a smooth surface and a foamed layer inside, the wall thickness in the arrow direction (hereinafter, the wall thickness means the arrow direction) generally needs to be 5 to 6 mm or more (FIG. 7).

In the case of the gas-assisted injection method, since sink marks are prevented by the injection gas pressure, unlike the foam molding, in the case of a thick-walled molded product, the cooling of the thick-walled part does not proceed, so that high pressure gas Among them, there is a problem that the hollow portion is not conveniently formed (FIG. 8) and the gas spreads in the molded product so that the strength of the molded product is lowered. In a shape with a thick rib on a thin wall (Fig. 9), the thin portion will cool first, so the gas does not spread to that location and only the rib portion creates a hollow portion, and the gas pressure inside the hollow reduces Is prevented. Therefore, it is desirable that the wall thickness be up to about 5 mm. The present invention has been made in view of such problems of the conventional technique, and an object thereof is to provide a fine foam cell in a thick wall portion of an injection molded product having a thick wall portion and a thin wall portion, and An object of the present invention is to provide an injection-molded article which forms a hollow portion and has no surface defects such as sink marks, a molding method thereof and a molding apparatus thereof.

[0005]

SUMMARY OF THE INVENTION The present invention in order to achieve the above object, a hollow portion is formed in the resulting <br/> have Yasu thick portion of shrinkage of the resin molded article is injection molded, further surface A layer and a hollow part or a hollow part, and foam cells are scattered between them. Also, when injecting the molten resin into the mold cavity of the injection molding machine, contain the foaming gas in the molten resin,
Before injection of resin, compressed air above atmospheric pressure is supplied to the mold cavity, and high-pressure gas is injected into the hollow part forming position of the molded product during or after the injection of molten resin to form a hollow part. After holding the high-pressure gas for a predetermined time to suppress the expansion of the foaming gas in the molten resin, it is withdrawn from the mold cavity and the molded product to expand the foaming gas in the molten resin to expand the foam cells into the surface layer and the hollow part or It is formed on the hollow portion between them.

Further, there is provided a first means for injecting / exhausting a gas having an atmospheric pressure or more such as air or an inert gas into a mold cavity of the injection molding machine, and a first detecting means for detecting a timing for operating the first means. And a gas injection nozzle for air, an inert gas or the like is provided in at least one position in a mold corresponding to a position where a hollow part is desired to be formed in the thick part of the molded product, and the gas injection nozzle is advanced and retracted. Drive means is provided, second detection means is provided for detecting the timing of operating the drive means, and second means for supplying high pressure gas to the gas injection nozzle is provided,
A third detecting means for detecting a timing for operating the second means is provided, a means for collecting or discharging the injected high pressure gas communicated by the retreat of the gas injection nozzle is provided, and the first detecting means is provided.
A control means for operating the means, the second means, and the driving means in relation to each other is provided, and the foaming gas and the hollow portion are mixed in the resin molded product by melting the foaming gas in the molten resin.
It is desirable that the second means for supplying the high-pressure gas can control the gas pressure in multiple stages.

[0007]

When the compressed air is sent to the mold cavity by the first means, the molten resin in which the foaming gas is melted is injected into the mold cavity by the injection screw. Corresponding to the injection, a high-pressure gas having a predetermined pressure is injected from the second means from the gas injection nozzle into the thick portion of the molded product, and the compressed air is exhausted before and after. When the hollow portion held for a predetermined time is formed, the gas injection nozzle is retracted and the high pressure gas is recovered. When the air pressure and gas pressure inside the mold cavities and the molded product are lower than atmospheric pressure, the foaming gas foams and expands and reaches the surface of the molded product and the hollow part or hollow part to form a foam cell therebetween.

[0008]

Embodiments of the present invention will be described below with reference to FIGS. A mold cavity 2 which is a mold of a molded product is formed on the joint surface of the movable side mold 1A and the fixed side mold 1B which are coupled by a fastening member of a hydraulic actuator (not shown), and molten resin is injected into the mold cavity 2 at a high pressure. By doing so, a desired molded product can be obtained. A resin injection passage 1c is provided in the center of the mold 1B, and an injection screw nozzle 3 of a known injection molding machine is advanced at the time of molding and joined to the mouth of the resin injection passage 1c. Gas injection nozzle for injecting high-pressure gas into one or more places in the mold 1A corresponding to the position where the sink of the molded product is likely to occur.
Le 5, the molded product gas supply path 1e to the ejector 4 and gas supply-discharge passage 1d and the high-pressure gas injection nozzle 5 is taken out from the mold, the gas <br/> scan the injection nozzle 5 for high pressure operation of the hydraulic actuator (not shown) The recovery path 1f is provided. An O-ring is interposed on the joint surface between the fixed mold 1B and the movable mold 1A, and a gap for allowing only air and gas to pass through the mold cavity 2 from the compressed air supply / discharge passage 1d.

Next, the structure for supplying high-pressure gas to the gas supply passage 1e will be described. N ₂ pressure gas (typically 150 kg /
A N ₂ gas cylinder 11 having a pressure of about 1 cm ² ) is passed through a manual opening / closing valve 12, a pressure gauge 13 and a pressure control valve 14, a pressure gauge 15 and a safety valve 16 and a check valve 17. Is connected to the reserve tank 19.
The reserve tank 19 is provided with a pressure gauge 21, a safety valve 22, and a manual exhaust valve 23 communicating with the drain. The N ₂ gas once stored in the reserve tank 19 is supplied from the flow passage 27 to the diaphragm hoop 28 via the check valve 26 and is compressed to a high pressure (max 500 kg / cm ² ) to the check valve 2.
It is stored in the high-pressure reserve tank 32 from the flow path 31 through the passage 9.

The high pressure reserve tank 32 has a pressure gauge 33,
A safety valve 34 and a manual exhaust valve 35 leading to the drain are provided. The high-pressure gas stored in the high-pressure reserve tank 32 is supplied from three parallel circuits 36A, 36B, 36C for controlling the pressure in three stages, through a check valve 37 and a circuit 38.
Is connected to the supply path 1e. Circuits 36A, 36B, 3
6C is composed of the following elements and is connected to the check valve 37. That is, from the high pressure reserve tank 32 to the check valve 4
1 is an electromagnetic switching valve 44 with a pressure gauge 43 interposed via a pressure control valve 42.

Next, the circuit configuration of the gas recovery passage 1f will be described. The recovery passage 1f is connected to the reserve tank 19 by a recovery passage 45, an automatic opening / closing valve 46, and a recovery passage 48 passing through a check valve 47. Further, the circuit configuration of the compressed air supply / discharge path 1d will be described. Air from the air compressor 51 at a normal pressure or higher to about 30 kg / cm ² is connected to the reserve tank 55 by a circuit 54 passing through a filter 52 and a check valve 53. The reserve tank 55 is provided with a pressure gauge 56, a safety valve 57, and a manual opening / closing valve 58 communicating with the drain. A circuit 62 that passes through a check valve 59 and a three-way three-position electromagnetic switching valve 61 from the reserve tank 55 is connected to the compressed air supply / discharge path 1d.

Further, an N ₂ gas cylinder 62 of pressure N ₂ gas is supplied to reduce the oxygen concentration in the mold cavity 2.
A manual flow control valve 63 is provided with a pressure gauge 64, a pressure control valve 65, a pressure gauge 66 and a safety valve 67, and a check valve 68.
It is connected to the. As the N ₂ gas, a liquefied N ₂ gas cold evaporator or an N ₂ gas generator may be used. In this case, the booster boosts the pressure to a pressure higher than the constant pressure 51. Both may be used together.

Next, FIG. 2 showing the gas injection nozzle 5 in detail.
I will explain based on this. One or more gas injection nozzles are provided in a portion where a hollow portion is desired to be formed corresponding to the shape of the molded product, and a position corresponding to the thick portion of the molded product is provided on the surface of the mold cavity 2 of the movable mold 1A. A needle fitting hole 1a that opens to the inside is provided and a stepped portion 1b having a small diameter is formed in the opening, which serves as a forward end stopper of the gas injection needle outer cylinder 501. The gas injection needle outer cylinder 501 slidably fitted in the needle fitting hole 1a has a recess 5 on the end surface on the mold cavity 2 side.
01a and needle shaft cylinder 502 with a flange in the center hole
Is fixed with the tip conical portion 502a protruding into the recess 501a. The gas injection needle outer cylinder 501 is connected to the end of the piston rod 504 of the hydraulic actuator 503 provided on the machine base and is moved forward and backward.

The needle shaft cylinder 502 has a central portion formed to have a small diameter to form a space 502b of a central hole, and a tip portion thereof is shown in FIG.
As shown in (4), four outer peripheral portions are cut out to form an axial gap 502c through which the molten resin cannot enter but the pressure gas can pass. A flow path 501b that connects the space 502b and the gas supply path 1e is formed in the gas injection needle outer cylinder 501 at the forward end position of the gas injection needle outer cylinder 501. Further, the flow path 1f of the mold 1A is opened at the retracted position of the gas injection needle outer cylinder 501 between the flow path 1f and the stopper 1b so as to communicate with the mold cavity 2. Further, an O-ring for preventing gas leakage is interposed in the joint portion and the sliding portion.

The operation of the present invention configured as described above will be described. An injection molding machine in which one or more gas injection nozzles 5 are incorporated in the movable mold 1A of the molds 1A and 1B corresponding to the molded product to be molded, corresponding to the thick walled part of the molded product. Install on. Thermoplastic resins such as vinyl chloride, polycarbonate, styrene-grafted polyphenylene ether, polystyrene, acrylic / nitrile / butadiene / styrene copolymer resin (ABS), high-impact polystyrene, styrene-modified polyphenylene oxide are used for the heating cylinder of the injection molding machine. , Polypropylene and all other thermoplastic resin pellets and foaming gas eg N
₂ gas, hydrocarbon gas, etc. blowing agent, for example, inorganic blowing agent such as sodium bicarbonate, amonium bicarbonate, sodium borohydride, etc. Is melted by heat and the density of the resin is increased while pressure is applied by the back pressure so that the gas from the simultaneous foaming agent is melted under pressure.

When the preparation for injection is completed, it is confirmed by a detector (not shown) that the molds 1A and 1B are closed, and then pressure air above atmospheric pressure is fed into the mold cavity 2. That is, the air compressor 51 is operated to temporarily supply high pressure air (max 25 kg / cm ² ) above atmospheric pressure to the reserve tank 55.
To store. Close the 3-port 3-position solenoid switch valve 61 (b)
The position is switched to the position (c), the flow paths 54 and 62 are connected, and the pressurized air is sent from the flow path 1d of the mold into the mold cavity 2 through the gap between the mold bonding surfaces. When it is necessary to reduce the oxygen concentration in the mold cavity 2, the pressure gas is changed to pressure air and the manual opening / closing valve 63 is opened to adjust the gas pressure of the inert gas N ₂ gas cylinder 62 with the pressure control valve 65. It is sent from the flow path 69 into the mold cavity 2.
As this gas, N ₂ , Ar, CO ₂ , CO, or other nonflammable gas is used.

The injection screw nozzle 3 of the injection molding machine is advanced and brought into contact with the connection port of the resin injection passage 1c to inject the molten resin in which the foaming gas has been melted into the mold cavity 2. The resin is filled in the mold cavity or in a slightly smaller amount. The resin in the mold cavity 2 suppresses the foaming expansion of the foaming gas by the compressed air. The molten resin is filled in the mold cavity 2 and the completion of the injection is confirmed mechanically or electrically by the detector of the movement of the injection screw, and when the timer is up, the hydraulic actuator 503 contacts the stopper 1b to advance. The gas injection needle outer cylinder 501 is located at the end. The gas injection nozzle 5 injects a high-pressure gas at atmospheric pressure or higher, for example, a gas such as air, N ₂ , Ar, or CO ₂ . That is, the pressure control valve 13 is 10 to 30 k from the N ₂ gas cylinder 11.
The N ₂ gas whose pressure is adjusted to g / cm ² is temporarily stored in the reserve tank 19 through the flow path 18.

Then, it is compressed to a high pressure of max 500 kg / cm ^{2 by} a pressure boosting device such as a diaphragm pump 28 and stored in a high pressure reserve tank 32. Channel 36A, 36
B and 36C are adjusted to three stages of pressure by the respective pressure control valves 42 depending on the large shape of the molded product. For example, channel 3
6A is the lowest first-stage pressure for introducing gas into the molded product, channel 36B is the second-stage intermediate pressure for expanding the gas inside the molded product, and channel 36C is melted by the gas pressure. Adjust the flow pressure to the highest pressure, which is the third stage pressure, that suppresses the foaming gas that is being generated so that it does not expand.
After the automatic switching valve 44 of 6A is opened, the automatic switching valve 44 of the flow path 36B is opened after a time set by a timer (not shown) corresponding to the molded product, and the timer (not shown) similarly handles the molded product after opening. After the set time, the flow path 36
The automatic switching valve 44 of C is opened. Of course, when the same pressure may be applied to all three stages, it is necessary to use only one flow path instead of using three flow paths. The first stage is low, the second stage is high, and the third stage is high.
Decrease the pressure in steps or in steps. It may also be a two-stage adjustment.

The high-pressure N ₂ gas passes through the circuit 38, the flow path 1e of the mold 1A, the flow path 501b of the gas injection needle outer cylinder 501, the space 502b of the needle shaft cylinder 502, and the gap 502c into a resin molded product. Injected. The thick part of the molded product is cooled by the mold and the surface is solidified, but the inside is in a molten state due to solidification, so high pressure gas is injected into this molten part and a hollow part is formed to absorb sink marks due to cooling. . This injection time is several seconds to several seconds depending on the shape of the molded product. After the passage of a predetermined time (before or after the completion of resin injection), the compressed air is operated by operating the electromagnetic switching valve 61 and the passage 62
Is released to the atmosphere and released, and the flow paths 69 and 54 are closed. Further, the hydraulic actuator 503 is operated to retract the gas injection needle outer cylinder 501 so that the flow passage 1f communicates with the needle fitting hole 1a, and the electromagnetic switching valve 46 (b) position is set, so that the high pressure gas passes through the flow passages 1f, 45, 48. It is collected and stored in the reserve tank 19.

When the compressed air or high pressure gas is exhausted in this way, the foaming gas, which is suppressed by the high pressure due to the pressure drop, expands to form foam cells and hollow portions, which complement the volume contraction and increase the thickness of the thick portion. I get hurt. The compressed air and the like injected into the mold cavity 2 may be discharged before or after the high pressure gas is injected, or may be discharged simultaneously.
Further, the injection of the high-pressure gas is not limited to after the injection of the molten resin but may be performed during the injection of the resin, and the injection timing is controlled by the detector that detects the screw position of the injection molding machine. All of these are selected according to the shape of the molded product.
If an inert gas is used instead of the pressure injected into the mold cavity 2, it may be recovered if necessary.

Experimental Example A molded product having the shape shown in FIG. 4 was molded from an acrylonitrile-butadiene-styrene copolymer resin (ABS). An injection molding machine having a capacity of 120 t was used. As the foaming agent, a molten resin containing 0.1% of azodicarbonamide (ADCA) was used. N ₂ gas used as compressed air was injected into the mold cavity 2 at a pressure of 18 kg / cm ² . The high-pressure gas injected into the molded product was injected and held at two locations at 50 kg / cm ² for 5 seconds. The resin molding process in FIG. 5A of the cross-sectional view taken along the line BB of FIG. 4 is performed by injecting the foamed resin in FIG. A hollow portion is formed as shown in 5 (c). 5s
When the high-pressure gas is discharged after ec, since the foaming force of the portion a is larger than the sinking force, the hollow portion disappears to form a foam layer. Since part b has a large sinking force, it remains as a hollow part, foam cells Wa and hollow part Wb are formed inside, and no sink mark defect is found on the surface. The expansion ratio reached around 5% and the hollow ratio reached 3%.

[0022]

Since the present invention is constructed as described above, the present invention has the following effects. Defects such as sink marks due to volume shrinkage of the thick part of the molded product do not occur on the surface of the molded product due to the sinking force being absorbed and complemented by the foam cells and hollow parts, and a molded product with a smooth surface can be obtained. , Product quality yield is improved and quality is improved. Since the foam cells are mixed everywhere, the strength of the molded product is higher than that of the hollow part alone. It also has the effect of heat insulation and sound deadening, and the cushioning property is enhanced to improve the impact resistance.

[Brief description of drawings]

FIG. 1 is a diagram showing a circuit for compressed air and high pressure gas.

FIG. 2 is an explanatory diagram of a gas injection nozzle.

FIG. 3 is an enlarged cross-sectional view taken along line AA of FIG. 2;

FIG. 4 is a diagram of an injection-molded product of an experimental example.

5 is a cross-sectional view taken along the line BB of FIG. 4, (a) is a contour diagram of the product shape, (b) is a diagram immediately after injection of the foamable resin, (c) is a diagram of high pressure gas injection pressure holding state, (D) is a figure after discharge of compressed air and high pressure gas.

FIG. 6 is a diagram showing sink marks in the case where a molded product made of a foamable resin has a small thickness.

FIG. 7 is a view without sink marks in the case where the thickness of the formed product made of the foamable resin is large.

FIG. 8 is a diagram showing a hollow portion formation state by high-pressure gas injection when a molded product made of resin has a large thickness.

FIG. 9 is a diagram showing a hollow portion forming state by high-pressure gas injection when a molded product made of resin has a small thickness.

[Explanation of symbols]

1A, 1B Mold 2 Mold Cavity 3 Injection Nozzle 4 Edge Ecta 5 Gas Injection Nozzle 11,62 N
₂ Gas cylinder 19,55 Reserve tank 28 Diaphragm pump 32 High pressure reserve tank 51 Air compressor 501 Gas injection needle outer cylinder 502 Needle shaft cylinder 503 Hydraulic actuator

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location // B29K 105: 04 B29K 105: 04 B29L 24:00 B29L 24:00

Claims (4)

(57) [Claims] 1. A occur shrinkage of the resin molded article is injection molded <br/> to form a hollow portion in the thick portion has Yasu, point the foamed cells further depends on the surface layer and the hollow portion or hollow portion therebetween A resin molded product characterized by being present. 2. When injecting a molten resin into a mold cavity of an injection molding machine, a foaming gas is contained in the molten resin,
Before injection of resin, compressed air above atmospheric pressure is supplied to the mold cavity, and high-pressure gas is injected into the hollow part forming position of the molded product during or after the injection of molten resin to form a hollow part. After holding the high-pressure gas for a predetermined time to suppress the expansion of the foaming gas in the molten resin, it is withdrawn from the mold cavity and the molded product to expand the foaming gas in the molten resin to expand the foam cells into the surface layer and the hollow part or A method for molding a resin molded product, which comprises forming a hollow portion and forming a space therebetween. 3. A first cavity for injecting / exhausting a gas such as air or an inert gas above atmospheric pressure into a mold cavity of an injection molding machine.
Means, and a first detecting means for detecting the time when the first means is operated, and at least one position of air, an inert gas or the like corresponding to the position where a hollow part is desired to be formed in the thick part of the molded product is provided. A gas injection nozzle is provided in the mold so that the gas injection nozzle can move forward and backward, a drive means for moving the gas injection nozzle forward and backward is provided, and a second detection means for detecting a timing of operating the drive means is provided, and a high-pressure gas is supplied to the gas injection nozzle. A second means for operating the second means, a third detecting means for detecting a time when the second means is operated, a means for collecting or discharging the injected high pressure gas communicated by the retreat of the gas injection nozzle, Controlling means for operating the first means, the second means, and the driving means in relation to each other, and melting the foaming gas in the molten resin to mix the foamed cells and the hollow portion in the resin molded product. Product molding equipment . 4. The molding apparatus for a resin molded product according to claim 3, wherein the second means for supplying the high-pressure gas can control the gas pressure in a plurality of stages.