JP2009172780A - Manufacturing process of foamed injection-molded article - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the manufacturing process of a foamed injection-molded article, by which a metallic mold is not complicated, there is no problem in durability of the metallic mold, a molded article surface has no nonfoaming nor foaming pattern called a swirl mark, and the foamed injection-molded article having a foamed inside and high appearance is provided. <P>SOLUTION: A foaming resin composition containing a chemical foaming agent is charged by injection into a metallic mold cavity in a state where a gas is poured in so that gas pressure in the metallic mold cavity is (atmospheric pressure +0.3 MPa) to (atmospheric pressure +6 MPa). A gas in the metallic mold cavity is discharged during time from charge start till charge finish from a gas discharge part provided at a part facing a position where flow of the foaming resin composition in the metallic mold cavity stops, so that the gas pressure in the metallic mold cavity at the time of charge finish is positive pressure of (atmospheric pressure +0.25 MPa) or below. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a foam injection molded product using a counter pressure method.

  Cases of information devices such as personal computers, home appliances, OA devices, and interior panels of automobiles are not only excellent in surface appearance, but can also be reduced in weight, so thermoplastic resin molded products are used. ing. Further, as these resin molded products, foamed injection molded products are being used for further weight reduction.

  Conventionally, two methods have been considered as an injection foam molding method of the foam injection molded product. One method uses a chemical foaming agent such as an azo compound or sodium hydrogen carbonate. A thermal decomposition gas is generated by applying a temperature higher than the thermal decomposition temperature of the chemical foaming agent, and dissolved and kneaded in a thermoplastic resin. The melted foamable resin composition is injected and filled into a mold cavity and foamed in the mold cavity. Another method is to inject and fill a molten foamable resin composition in which a gas such as nitrogen or carbon dioxide is dissolved in a molten state of a thermoplastic resin as a physical foaming agent into the mold cavity. This is a method of foaming.

  In addition, as a method of obtaining a foamed injection molded product in which the surface of the molded product is non-foamed and the inside is foamed, a molding generally called a counter pressure method is performed in order to improve the surface state and the surface strength of the molded product. Methods (see Patent Documents 1 and 2), methods using a heat insulating mold (see Patent Document 3), and methods using a heating control mold (see Patent Document 4) have been proposed.

However, each molding method has the following problems.
That is, the counter pressure method is to inject a foamable resin composition into a mold cavity pressurized to a gas pressure higher than the foaming pressure of a foamable resin composition filled with gas and dissolving a foaming agent. A non-foamed molded product or a molded product without a swirl mark is obtained on the surface, and then the inside of the molded product is foamed by expanding the volume of the mold cavity to obtain a product having a non-foamed layer on the surface However, in this method, when the foamable resin composition is injected and filled into the mold cavity, a pressurized gas is filled in the mold cavity. May cause poor transfer and poor foam such as sink marks.

  On the other hand, in the case of the method using the heat insulating mold, a heat insulating layer such as polyimide resin is provided on the mold surface corresponding to the design surface of the molded product, and the surface temperature of the foamable resin composition flowing in contact with the heat insulating layer is set. By keeping the solidification temperature above the state and maintaining the fluidity of the surface in a good state until the gas generated from the flow front of the foamable resin composition at the time of injection is discharged to the outside of the mold cavity, Although it is made to cool and solidify without generating a swirl mark, since the heat insulating layer provided on the design surface of the mold is made of polyimide resin or the like as described above, there is a problem in the durability of the mold. In addition, there is a problem that it takes time to cool and solidify the molded product and the molding cycle becomes long.

  On the other hand, in the case of a method using a heating control mold, by maintaining the mold surface temperature on the visible surface (design surface) side of the molded product at a high temperature from the start to the end of filling, it is generated from the flow front of the foamable resin composition at the time of injection. Until the exhausted gas is discharged outside the mold cavity, the surface fluidity is kept in a good state to cool and solidify without generating swirl marks. A heating control mold with a device that can raise and control the temperature only where the surface of the surface is desired to be non-foamed must be used, resulting in a complicated mold, and due to thermal expansion of the mold, etc. There is a possibility that distortion may occur and the durability of the mold may be lowered.

Japanese Examined Patent Publication No. 62-1616 JP 2004-216578 A JP 2004-66751 A Japanese Patent Laid-Open No. 10-80932

  In view of the above circumstances, the present invention does not complicate the mold, and there is no problem in the durability of the mold, and the surface of the molded product has no foaming pattern called non-foamed or swirl marks, and the interior is It is an object of the present invention to provide a method for producing a foamed injection molded product from which a foamed high appearance foamed injection molded product can be obtained.

In order to achieve the above object, the inventors of the present invention provide a molded article by foam injection molding using a chemical foaming agent such as an azo compound or sodium hydrogen carbonate, using a counter pressure method and foaming in a molten state. The pressurized gas in the mold cavity is exhausted from the portion of the mold cavity facing the position where the flow of the foamable resin composition stops as the mold resin cavity is filled into the mold cavity, and the mold cavity By precisely controlling the gas pressure in the mold cavity, it has been found that there is no foam pattern called swirl marks, and that foam defects such as transfer defects and sink marks can be prevented, and the present invention has been completed.
That is, the method for producing a foam injection molded product according to the present invention includes a foam injection molding in which a foamable resin composition is injected into a mold cavity to obtain a resin molded product having a foam structure inside and a non-foamed surface. Foaming resin containing a chemical foaming agent in a mold cavity in which gas is injected so that the gas pressure in the mold cavity is (atmospheric pressure + 0.3 MPa) to (atmospheric pressure + 6 MPa) While injecting and filling the composition, the gas in the mold cavity is exhausted from the exhaust part provided at the portion of the mold cavity facing the position where the flow of the foamable resin composition stops between the start of filling and the completion of filling. The gas pressure in the mold cavity at the completion of filling with the foamable resin composition is set to a positive pressure of (atmospheric pressure +0.25 MPa) or less.

In the present invention, the gas pressure of the gas injected into the mold cavity is (atmospheric pressure + 0.3 MPa) to (atmospheric pressure + 6 MPa) [gage pressure of pressure gauge is 0.3 to 6 MPa, hereinafter, in the specification, All pressures are described in gauge pressure.] The reason is that if the gas pressure is less than 0.3 MPa, swirl marks may occur. If the gas pressure exceeds 6 MPa, the foaming resin This is because poor filling of the composition or sink marks may occur.
Further, the gas pressure in the mold cavity at the completion of filling of the foamable resin composition is limited to a positive pressure of 0.25 MPa or less, more preferably 0.1 to 0.2 MPa, for the reason: This is because if the gas pressure is too high, sink marks may occur, and if the gas pressure is too low, swirl marks may be generated.

As a method of adjusting the gas pressure in the mold cavity to a positive pressure of 0.25 MPa or less upon completion of filling, the gas pressure in the mold cavity is detected by a gas pressure sensor, and the foamable resin composition is filled. Is completed, there is a method of adjusting an on-off valve connected to the exhaust gas hole so that the gas pressure is a positive pressure of 0.25 MPa or less, preferably 0.1 to 0.2 MPa.
The gas pressure sensor is not particularly limited, and an appropriate one can be used. For example, a commercially available product such as a pressure sensor with a built-in medium / high pressure amplifier manufactured by VALCOM may be used.

  In the present invention, the position where the flow of the foamable resin composition stops is a flow terminal of the foamable resin composition in the mold cavity, and in the case of a multipoint gate, a weld portion is also included.

  In the present invention, the mechanism for exhausting the injected gas is not particularly limited. For example, an exhaust gas hole facing the outside of the mold cavity is provided in the mold, and the gas hole and the mold cavity are provided. In order to prevent molten resin from entering, a mechanism in which a groove of about 100 to 200 μm is connected, or a porous sintered metal block is interposed between the gas hole and the mold cavity, so that the sintered metal There is a mechanism for exhausting the gas in the mold cavity from the gas hole through the small hole.

  In the present invention, the gas injected into the mold cavity is not particularly limited, and examples thereof include inert gases such as nitrogen gas, carbon dioxide gas, and argon gas, and these may be used in combination. .

  Although it does not specifically limit as resin used for the manufacturing method of the foam injection molding product of this invention, For example, polyolefin resin, such as a polypropylene, polyethylene, a polystyrene, a propylene / ethylene copolymer, is mentioned.

  Although it does not specifically limit as a chemical foaming agent, Bicarbonate (inorganic compound), such as azodicarbonamide (organic compound) and sodium bicarbonate, etc. are mentioned.

  In addition to the thermoplastic resin and the chemical foaming agent, the foamable resin composition includes, as necessary, known foaming aids, foam nucleating agents, foam molding stabilizers, stabilizers, ultraviolet absorbers, Antioxidants, antistatic agents, lubricants, colorants, flame retardants, crosslinking agents and / or fillers can be blended.

Incidentally, as the foaming aid, for example, stearates such as sodium stearate, calcium stearate, magnesium stearate, potassium stearate, zinc stearate, montanates such as calcium montanate (octadocosanoate), zinc montanate, etc. Higher fatty acid metal salts such as urea, urea or urea compounds, paraffin, and other stearamides.
Examples of the foam nucleating agent include inorganic fillers such as talc, silica, calcium carbonate, and calcium silicate.

  As described above, the method for manufacturing a foam injection molded product according to the present invention includes a chemical foaming agent in a mold cavity in a state where gas is injected so that the gas pressure in the mold cavity is 0.3 to 6 MPa. Injecting and filling the foamable resin composition, and filling the mold cavity from the exhaust portion provided at the portion of the mold cavity facing the position where the flow of the foamable resin composition stops from the start of filling to the completion of filling. Since the gas pressure in the mold cavity was set to a positive pressure of 0.25 MPa or less when the filling of the foamable resin composition was completed, the surface of the molded product was not foamed or foamed called a swirl mark. It is possible to obtain a high appearance foam injection molded product having no pattern and having no foamed inside. In addition, since the exhaust part is only provided at the part facing the position where the flow of the foamable resin composition stops, the structure of the mold is not so complicated. In addition, since there is no need to provide a heat insulating layer made of resin on the cavity surface, there is no problem with the durability of the mold.

Hereinafter, the present invention will be described in detail with reference to the drawings showing embodiments thereof.
FIG. 1 shows an example of a foam injection molding apparatus used in a method for producing a foam injection molded product according to the present invention.

As shown in FIG. 1, the foam injection molding apparatus 1 includes a mold 2 and an injection machine 3.
The injection machine 3 includes an injection cylinder 31, an injection screw 32, and an injection nozzle 33.
The mold 2 includes a fixed mold 4, a movable mold 5, and a counter pressure device 6.

  The fixed mold 4 includes a cavity part 41 that forms a mold cavity C with a cavity part 51 of the movable mold 5 to be described later by closing, and a foamable resin composition that fills the mold cavity C from the injection machine 3. A flow path 42, a gas pressure sensor 43, an O-ring 44, and a pressure gauge 45 that displays the gas pressure measured by the gas pressure sensor 43 are provided. The gas pressure sensor 43 can feed back the measured pressure to an electromagnetic opening / closing valve 56a described later.

As shown in FIGS. 1 and 2, the movable mold 5 includes a cavity portion 51, and an insufflation gas hole 52 that is a passage of gas infused from the cavity portion 51 and a counter pressure device 6 described in detail later. A slit-like groove 53 connecting the cavity 51 and the gas supply gas hole 52, an exhaust gas hole 54 for exhausting the gas injected into the mold cavity C, and the cavity 51 and the exhaust gas. A slit-like groove 55 connecting the holes 54, a gas exhaust pipe 56 with an electromagnetic on-off valve 56 a connected to the exhaust gas hole 54, an O-ring fitting groove 57, and a gate 58 are provided.
The slit-like groove 55 is provided at a position farthest from the gate 58 that is a position where the flow of the foamable resin composition stops.
The counter pressure device 6 is connected to an air supply gas hole 52 and includes a nitrogen gas cylinder 61 and a gas air supply pipe 62 with a pressure control valve 62a and an electromagnetic open / close valve 62b.

  The foam injection molding apparatus 1 includes a controller (not shown) including a controller, a timer for opening / closing an electromagnetic opening / closing valve, and the timer starts simultaneously with completion of mold clamping, The exhaust timing can be controlled.

And the said foam injection molding apparatus 1 can manufacture a foam injection molded article as follows.
That is, first, the movable mold 5 starts mold clamping, and when the mold clamping is completed as shown in FIG. 1, the timers of the gas inlet side electromagnetic on-off valve 62b and the gas exhaust side electromagnetic on-off valve 56a are started. . Then, when the set time for starting the gas injection that has been empirically obtained in advance is reached, the valve of the electromagnetic on-off valve 62b is opened, and the gas pressure in the mold cavity C is set to 0.3 to 6 MPa. When the nitrogen gas is injected into the mold cavity C from the pressure device 6 and the set time for the end of the gas injection determined in advance is reached, the valve of the electromagnetic on-off valve 62b is closed. The control of the gas pressure is set by the pressure control valve 62a.

After that, when the set time for starting gas exhaust, which is empirically obtained in advance, comes, the valve of the electromagnetic on-off valve 56a opens, the gas in the mold cavity C starts to be exhausted, and the gas measured by the gas pressure sensor 43 is measured. When the gas pressure in the mold cavity C is exhausted until the gas pressure in the mold cavity C reaches a positive pressure of 0.25 MPa or less, preferably 0.1 to 0.2 MPa at the completion of filling, The valve of the electromagnetic opening / closing valve 56a is closed.
Further, as described above, the foamable resin composition P1 is filled into the mold cavity C as shown in FIG. 3 while the electromagnetic on-off valves 62b and 56a are operating.

When a predetermined time has elapsed from the start of filling of the foamable resin composition P1 and the filling of the foamable resin composition P1 into the mold cavity C is completed, as shown in FIG. It moves by the distance of L1, and the foamable resin composition P1 foams.
After completion of cooling and solidification, the mold 2 is opened, and the foam injection molded product P2 is taken out from the mold 2.

Specific examples of the present invention will be described below together with comparative examples.
With a foam injection molding apparatus 1 as shown in FIG. 1, a foaming agent master batch (trade name, manufactured by Eiwa Kasei Kogyo Co., Ltd.) is added to 100 parts by weight of polypropylene (trade name: Prime Polypro J830HV, manufactured by Prime Polymer Co., Ltd.) under the following basic conditions. Using an injection molding machine (EC160N manufactured by Toshiba Machine Co., Ltd.), a foamable resin composition to which 5 parts by weight of Polyslene EE275F) has been added, gas pressure in the mold cavity at the start of filling the foamable resin composition shown in Table 1, foaming Each foamed injection-molded product is manufactured at the gas pressure inside the mold cavity when filling the resin composition, and the resulting molded product is visually inspected for the presence of swirl marks and sink marks. Valve opening start time (seconds) of the electromagnetic on-off valve 62b for gas, valve closing time (seconds) of the electromagnetic on-off valve 62b for gas injection, and valve opening of the electromagnetic on-off valve 56a for gas exhaust It is shown in Table 1 together with the start time (in seconds).
The valve opening start time (seconds) of the electromagnetic opening / closing valve 62b, the valve closing time (seconds) of the electromagnetic opening / closing valve 62b, and the valve opening start time (seconds) of the electromagnetic opening / closing valve 56a indicate the time from the completion of mold clamping. . The gas pressure is measured by the gas pressure sensor 43. The gas pressure before the start of injection filling was adjusted by the pressure control valve 62a.
(Basic conditions)
Temperature of foamable resin composition P1: 200 ° C.
Number of rotations of injection screw 32: 80 rpm
Mold 2 temperature: 60 ° C
Thickness of mold cavity C upon injection of foamable resin composition P1: 1.43 mm
Size of mold cavity C: 330mm (width) x 130mm (length)
Mold opening width at core back (L1): 1.55mm
Mold opening waiting time: 0.5 seconds Filling time: 2.1 seconds Thickness of molded product P2: 2.73 mm (foaming ratio 1.9 times)
Cooling time: 40 seconds

  From Table 1, the foamable resin composition containing a chemical foaming agent was injected and filled into the mold cavity in a state where gas was injected so that the gas pressure in the mold cavity was 0.3 to 6 MPa, and from the start of filling. Until the filling is completed, the gas in the mold cavity is exhausted from the exhaust part provided at the portion facing the position where the flow of the foamable resin composition of the mold stops, and when the filling of the foamable resin composition is completed If the gas pressure in the mold cavity is controlled so that the gas pressure in the mold cavity is a positive pressure of 0.25 MPa or less, the surface of the molded product has no foaming pattern called non-foaming or swirl marks. It can be clearly seen that a high appearance foam injection molded product free from sinked foam or the like is obtained.

  The method for manufacturing a foam injection-molded product according to the present invention is suitably used for manufacturing information equipment such as personal computers, housings such as home appliances and OA equipment, and interior products such as automobiles.

FIG. 2 is a diagram showing a partial cross-sectional view of an example of an injection molding apparatus used in the method for manufacturing a foam injection molded product of the present invention. It is a top view of the movable mold | type of the injection molding apparatus of FIG. It is a figure which shows the state just before the core back of the metal mold | die of the injection molding apparatus of FIG. It is a figure which shows the state immediately after the core back of the metal mold | die of the injection molding apparatus of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Foam injection molding apparatus 2 Mold 3 Injection machine 31 Injection cylinder 32 Injection screw 33 Injection nozzle 4 Fixed mold 41 Cavity part 42 Flow path 43 Gas pressure sensor 44 O-ring 45 Pressure gauge 5 Movable type 51 Cavity part 52 Gas for inflating Hole 53 Slit groove 54 Exhaust gas hole 55 Slit groove 56 Gas exhaust pipe 56a Electromagnetic on-off valve 57 O-ring fitting groove 58 Product gate 6 Counter pressure device 61 Nitrogen gas cylinder 62 Gas inlet pipe 62a Pressure control valve 62b Electromagnetic on-off valve C Mold cavity P1 Foamable resin composition P2 Foamed injection molded product

Claims (2)

  In a method for producing a foamed injection molded product in which a foamable resin composition is injected into a mold cavity to obtain a resin molded product having a foamed structure inside and a non-foamed surface, the gas pressure in the mold cavity is large ( Injecting and filling a foamable resin composition containing a chemical foaming agent into a mold cavity in a state where gas is injected so that the pressure becomes + atmospheric pressure + 0.3 MPa) to (atmospheric pressure + 6 MPa), and from filling start to filling completion. The mold cavity when the filling of the foamable resin composition is completed by exhausting the gas in the mold cavity from the exhaust part provided in the part facing the position where the flow of the foamable resin composition of the mold cavity stops A method for producing a foam injection molded product, wherein the internal gas pressure is set to a positive pressure of (atmospheric pressure +0.25 MPa) or less.   The method for producing a foam injection molded article according to claim 1, wherein the gas pressure in the mold cavity at the time of filling is set to (atmospheric pressure + 0.1 MPa) to (atmospheric pressure + 0.2 MPa).

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