JP3817864B2 - Injection molding method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention injects a resin smaller than the cavity capacity into a cavity of an injection mold, and injects a fluid such as a gas or other resin into the injected resin, thereby forming a hollow resin molded body or a multilayer resin molded body. The present invention relates to a method and an apparatus for manufacturing.
[0002]
[Prior art]
In order to reduce the weight of resin molded products, hollow ones or those with a resin layer such as a foamed resin layer formed inside are used. To produce such resin molded products, an injection mold is used. A resin having a volume smaller than the cavity capacity is injected into the cavity, and a compressed gas or other resin is injected into the injected resin to produce a hollow molded product or a sandwich-shaped molded product (for example, JP-A-3-248937).
[0003]
In this case, generally, after injecting the resin as the outer layer, the gas or resin filled in the inner layer is injected immediately. However, on the surface of the manufactured molded product, a line called a “hesitation mark” is used. A mark is formed. This mark is presumed to be caused by temporarily stopping the flow of the injected resin in the cavity when switching between injection of resin and injection of fluid such as compressed gas.
[0004]
FIGS. 7A, 7B, and 7C are schematic cross-sectional views illustrating an estimated formation process of a hesitation mark. In FIG. 7, reference numeral 1 denotes an injection mold, which has a structure in which a cavity 4 is formed between a cavity mold 2 and a core mold 3. The cavity mold 2 has a mold surface 5 that forms a decorative surface of the molded product, and the core mold 3 has a mold surface 6 that forms the back surface of the molded product.
[0005]
FIG. 7A shows a state in which the resin 7 forming the outer layer is injected into the cavity 4, and the resin 7 proceeds in the direction of the arrow p. After the resin 7 is injected by an amount smaller than the capacity of the cavity 4, a compressed gas is injected into the injected resin 7 in the direction of the arrow q as shown in (c), and the resin 7 is expanded by the action of the gas. A hollow portion 8 is formed inside. At this time, even if the gas is injected simultaneously with the stop of the injection of the resin 7, the movement of the resin 7 temporarily (instantaneously) is stopped with the switching, and the stop state of (b) appears.
[0006]
While the resin 7 is moving, it flows while maintaining a molten state in the middle part of the resin flow, moves while being divided from the front end of the resin 7 into the upper and lower sides in the drawing, and is crimped to the mold surfaces 5 and 6. . While the resin 7 is flowing in this way, the molten resin inside appears sequentially on the surface and is crimped to the mold surfaces 5 and 6, so that the fine recesses 9 formed on the mold surfaces 5 and 6 Also, the resin 7 is filled to form a uniform surface.
[0007]
However, as shown in (b), when the resin 7 is temporarily stopped, the surface of the tip 7a of the resin 7 is in contact with the room temperature atmosphere in the cavity 4 for a long time. . For this reason, as shown in (c), when the resin 7 resumes moving in the p direction by subsequently injecting gas, immediately after the restart, the tip 7a in (b) becomes a solidified portion 7b and is divided into both sides. Since it is pressed against the mold surfaces 5 and 6, the solidified portion 7b cannot enter into the fine recesses 9 of the mold surfaces 5 and 6, leaving the fine recesses 9a that are not filled with the resin 7. It is presumed that such a solidified portion 7b forms a hesitation mark. The same applies when another molten resin is injected instead of the compressed gas.
[0008]
[Problems to be solved by the invention]
An object of the present invention is to inject a resin having a volume smaller than the cavity capacity into a cavity of an injection mold, and inject a fluid such as gas or other resin into the injected resin, thereby forming a hollow resin molded body or a multilayer resin. An object of the present invention is to propose an injection molding method and apparatus that do not cause an appearance abnormality such as a hesitation mark in the production of molded articles and the like.
[0009]
[Means for Solving the Problems]
The present invention is the following injection molding method and apparatus.
(1) A resin smaller than the cavity capacity is injected into the cavity of the injection mold, and another fluid is injected into the injection resin to fill the resin layer, and the resin layer is pushed into the cavity to expand the mold. a injection molding process for producing a molded article by compression to the surface, to stop emission of the tree fat in the course you start the injection of other fluids, to supply heated gas to the distal end of the injected resin, the cavity An injection molding method characterized in that a tip portion of injection resin injected into the inside is heated or kept warm to maintain a molten state.
(2) Injection of a resin smaller than the cavity capacity into the cavity of the injection mold, injecting another fluid into the injection resin, filling the resin layer, and expanding the resin layer into the cavity An injection molding method in which a molded product is manufactured by pressure bonding to a surface. In the process of stopping injection of resin and starting injection of another fluid, infrared light is irradiated to the tip of the injection resin and injected into the cavity. An injection molding method characterized by heating or keeping a temperature of a tip portion of the injected resin to maintain a molten state.
(3) The injection molding method according to the above (1) or (2 ), wherein the other fluid is a compressed gas.
(4) The injection molding method according to the above (1) or (2) , wherein the other fluid is another molten resin.
(5) An injection mold having a cavity for molding a molded article, a first gate for injecting a molten liquid resin in an amount smaller than the cavity capacity into the cavity, and another fluid in the injection resin In the process of stopping the injection of the resin and starting the injection of another fluid, the heating gas is supplied to the tip portion of the injection resin, and the tip portion of the injection resin is maintained in a molten state. An injection molding apparatus having heating or heat retaining means.
(6) An injection mold having a cavity for molding a molded product, a first gate for injecting a molten liquid resin in an amount smaller than the cavity capacity into the cavity, and another fluid in the injection resin In the process of stopping the injection of the resin and starting the injection of another fluid, the second gate for injecting the resin is heated to irradiate the tip of the injection resin with infrared rays and maintain the injection resin in the molten state Or an injection molding apparatus having a heat retaining means.
(7) The injection molding apparatus according to (5) or (6 ), wherein the second gate is a gate for injecting compressed gas.
(8) The injection molding apparatus according to (5) or (6 ), wherein the second gate is a gate for injecting another molten resin.
[0010]
The molded product to be manufactured in the present invention is a resin injection molded product, and is a molded product having a hollow portion, a foamed resin layer, or other resin layers inside. There is no restriction | limiting in particular in the shape of a molded product, a structure, a material, etc., It can select arbitrarily.
[0011]
The basic configuration of an apparatus for manufacturing such a molded product is the same as that conventionally used, and has an injection mold having a cavity for molding the molded product. An apparatus including a first gate for injecting a resin smaller than the cavity capacity into the cavity and a second gate for injecting another fluid into the injection resin is used.
[0012]
The first gate is a gate for injecting resin for molding the outer layer of the molded product, and is configured to inject an amount of resin smaller than the cavity capacity. The second gate is a gate that ejects another fluid, and its shape, size, position, and the like can be changed depending on the type of the other fluid. For example, when manufacturing a hollow molded product, a compressed gas injection gate, when forming a foamed resin layer inside, a foamable resin injection gate, when forming another resin layer inside, another resin injection gate To do. The first and second gates may be shared or provided separately.
[0013]
In the present invention, in such an injection molding apparatus, a heating or heat retaining means for heating or heat retaining the tip of the injection resin is provided. This heating or heat insulation means all SANYO which holds the tip of the injection resin injected into the cavity in the heated state to maintain the softened state, I De apparatus for supplying heated gas to the distal end portion of the resin, the injected resin equipment and the like for irradiating infrared rays to the tip portion.
[0014]
Apparatus for supplying a pressurized heat gas is required to be one in which to stop the injection of the tree fat in the process of starting the injection of other fluids can be supplied pressurized thermal gas. The gas is preferably a chemically inert gas such as nitrogen, but may be air.
[0015]
If the mold is heated by the heating means, the cooling time of the mold after molding becomes longer, so the heating means is the limit necessary to heat the tip of the injection resin, and the injection mold is more than necessary. In order to maintain a short molding cycle, it is preferable not to heat.
[0016]
The injection molding method of the present invention performs injection molding using the injection molding apparatus as described above to produce a resin molded product. In this case, an amount of molten resin less than the cavity capacity is injected into the cavity of the injection mold, and another fluid is injected into the injection resin injected into the cavity to fill the resin layer and the resin layer into the cavity. when producing a molded article by compression to the mold surface pushed open, stop the injection of the tree fat in the course you start the injection of other fluids, by supplying heated gas to the distal end of the injected resin, the cavity The tip of the injected resin injected into the inside is heated or kept warm to maintain a molten state.
[0017]
As a result, the resin after the flow of the resin has been resumed by the injection of another fluid can be brought into close contact with the mold surface, thereby preventing the occurrence of an abnormal shape such as a hesitation mark. That is, when the injection of the resin is stopped and another fluid is injected, the flow of the injection resin temporarily stops due to the time loss at the time of switching, but the tip of the injection resin is heated or kept warm by the heating or heat retaining means. When the molten resin is maintained in a molten state, the resumed injection resin is pressure-bonded to the mold surface under substantially the same conditions as before stopping, so that the molded product has a uniform appearance and no hesitation mark is generated.
[0018]
As a method for heating or heat retaining the leading end of the resin, a method of supplying the heated gas to the tip in the process from the injection stop tree fat to the injection of other fluids, heated or kept warm tip of the injection resin, There is a method of irradiating infrared rays in the process from stopping the injection of the resin to injecting another fluid to heat or keep the tip of the injection resin.
[0019]
In either case, the heating since it is sufficient in process from the injection stop tree fat to the injection of another fluid tip of the injection resin is heated or kept warm is maintained in a molten state, unnecessarily injection mold In a non-limiting manner, the heating or heat retention time by these heating means can be extended back and forth.
[0020]
【The invention's effect】
According to the injection molding method and apparatus of the present invention, a small amount of resin than the cavity capacity injection mold cavity by injection, during injection of other fluids in the injected resin, to stop emission of the tree butter In the process of starting the injection of other fluids , heated gas was supplied to the tip of the injection resin, or infrared rays were applied to heat or keep the tip of the injection resin injected into the cavity. The tip portion of the injection resin can be maintained in a softened state, whereby the injection resin can be uniformly adhered to the mold surface, and a molded product having no appearance abnormality such as a hesitation mark can be manufactured.
[0022]
By supplying a heating gas in a process from the injection stop of the resin to the injection of other fluids, or to heat the tip of the injection resin by infrared radiation, it is only heated or kept warm certain parts at a particular time It is possible to prevent the temperature of the entire mold from rising and shorten the time required for cooling.
[0023]
When the other fluid is compressed gas, it is possible to efficiently produce a hollow molded article having no appearance abnormality, and when the other fluid is another molten resin, efficiently producing a multilayer molded article having no appearance abnormality. be able to.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described with reference to the drawings.
1 is a cross-sectional view showing an injection molding apparatus of a reference example , FIGS. 2A and 2B are enlarged cross-sectional views of a part thereof, and FIGS. 3A, 3B, and 3C show manufacturing processes. It is typical sectional drawing, and the same code | symbol as FIG. 7 shows the same or equivalent part.
[0025]
This apparatus shows an example in which the gas inside the cavity is heated in advance. 1 to 3, reference numeral 1 denotes an injection mold, which has a structure in which a cavity 4 is formed between split surfaces (parting surfaces) of a cavity mold 2 and a core mold 3. The cavity mold 2 has a mold surface 5 that forms a decorative surface of the molded product, and the core mold 3 has a mold surface 6 that forms the back surface of the molded product.
[0026]
The core mold 3 has a first gate 11 for injecting resin so as to open to one side of the cavity 4, a second gate 12 for injecting compressed gas as another fluid, and a heating gas as heating or heat retaining means A hot air outlet 13 is provided in the vicinity, and a gas discharge port 14 is provided at a position where the resin injected into the cavity 4 finally reaches, that is, the opposite side of the cavity 4 in this embodiment. .
[0027]
The first gate 11 is connected to an injection nozzle 17 a of an injection molding machine 17 through a sprue 15 and a runner 16. The second gate 12 is connected to the injection portion 18 a of the compressed gas injection device 18, and the gas injection device 18 is connected to the gas supply device 20 via the flow path 19. 21 is a gas vent valve which discharges | emits compressed gas to air | atmosphere.
[0028]
The blower outlet 13 is connected to the blowing part 22 a of the hot air blowing device 22. A blower pipe 24 communicates with the hot air blowing device 22 from a blower 23. The detailed structure of the hot air blowing device 22 is shown in FIG. A tapered valve seat 25 is formed at the upper part of the hot air blowing part 22a, and an on-off valve 26 that is in close contact with the valve seat 25 is attached to the rod 27 and can be opened and closed by moving in the directions of arrows r and s. A heater (heating wire) 28 is arranged around the air pipe 24 and communicates with the blower pipe 24. The rod 27 is provided so as to be able to advance and retreat from a fluid pressure cylinder constituting the hot air blowing device 22. The hot air blowing device 22 is preferably surrounded by a heat insulating material (not shown) so as not to heat the mold.
[0029]
The gas discharge port 14 is connected to a suction chamber 33 provided in the cavity mold 2 through a ventilation path 32 having a ventilation material 31 such as sintered metal provided in the core mold 3, and is further connected to a suction pump via a flow path 34. 35 is connected. This ventilation material 31 allows the passage of gas but prevents the passage of molten resin. 36 is a temperature sensor, and 37 is a sealing material. Reference numeral 38 denotes a mold temperature control medium flow path such as cooling water, which is disposed in a portion surrounding the cavity 4 of the cavity mold 2 and the core mold 3, but only a part is illustrated. Reference numeral 30 denotes a control device.
[0030]
The above injection molding apparatus is for producing a hollow resin molded product, and molding is performed by the following method. First, the cavity mold 2 and the core mold 3 of the injection mold 1 are closed, and the suction chamber 33 is hermetically sealed by the sealing material 37, and the suction pump 35 is operated by the signal a from the control device 30 to Inhale (air). At this time, the temperature signal b is input from the temperature sensor 36 to the control device 30.
[0031]
At the same time or before and after this, the blower 23 and the heater 28 are operated by the signals c and d from the control device 30 and at the same time, the on-off valve 26 is opened and hot air (chemically inert N ₂ gas is preferred in the cavity 4. May be air) to maintain the temperature of the gas in the cavity 4 at a predetermined temperature. In this case, nitrogen gas or air sent from the blower 23 through the blower pipe 24 is heated by the heater 28 and becomes hot air and enters the cavity 4 from the hot air outlet 13.
[0032]
The original air in the cavity 4 passes through the ventilation path 32 from the gas exhaust port 14 and is exhausted from the suction chamber 33 through the flow path 34 by the suction pump 35. In this state, when the temperature sensor 36 detects a predetermined temperature, preferably slightly higher than the temperature of the injected resin, the on-off valve 26 is closed. At this time, the suction pump 35, the blower 23, and the heater 28 are preferably stopped. In addition, since the determination of predetermined temperature changes with resin materials to shape | mold, it is good to determine by a prior test shot.
[0033]
Next, the injection molding machine 17 is operated by a signal h from the control device 30, and the liquid thermoplastic resin heated and melted from the injection nozzle 17 a is injected into the cavity 4 through the runner 16, the sprue 15 and the first gate 11. At this time, as shown in FIG. 3A, the resin 7 advances in the cavity 4 in the direction of the arrow p. When the injection of the resin from the injection molding machine 17 is stopped at a stage where a predetermined amount of resin smaller than the capacity of the cavity 4 is injected, the tip 7a of the resin 7 is temporarily in the middle of the cavity 4 as shown in FIG. To stop. At this time, since the tip 7a is in contact with the heated gas in the cavity 4, it is heated or kept warm to prevent cooling and maintain a molten state.
[0034]
Immediately (not strictly at the same time, it may be within the time when the resin injected into the cavity 4 does not start to solidify), the inert gas is added from the gas supply device 20 by the signals e and f of the control device 30. The gas injection device 18 is operated at the same time as the pressure is supplied (the pressure may be increased to several hundred kgf / cm ² in advance), and the compressed gas is injected into the resin 7 as shown in FIG. A hollow portion 8 is formed inside and the hollow portion 8 is gradually enlarged to expand the apparent volume of the resin 7. In this case, the gas vent valve 21 is closed, and the resin 7 flows toward an unfilled portion in the cavity 4 due to apparent volume expansion. At this time, the resin 7 and the front end portion 7a are kept in a softened state because the resin at the central portion sequentially comes out to the front end portion, so that the resin 7 and the front end portion 7a are pressure-bonded to the mold surfaces 5 and 6, and the fine recess 9 is filled with the resin 7. By continuing the injection of the compressed gas in this way, the cavity 4 is filled with the resin 7 having the hollow portion 8 inside.
[0035]
The resin 7 is solidified by supplying a medium such as cooling water to the temperature control medium flow path 38 while the expansion pressure of the compressed gas is acting toward the mold surfaces 5 and 6 in this way. Thereafter, the operation of the gas supply device 20 and the gas injection device 18 is stopped, and the gas vent valve 21 is opened by the signal g of the control device 30 to discharge the gas in the cavity 4. Then, the injection mold 1 is opened and the resin molded product is taken out.
[0036]
The resin molded product thus obtained has a hollow portion 8 and has an excellent appearance without hesitation marks.
As described above, when the heating gas is filled in the cavity before the injection of the resin, it is not necessary to strictly control the stop position of the front end portion 7a of the resin 7, and thus the operation is easy.
[0037]
In the above apparatus, the blowing portion 22a of the hot air blowing device 22 may be opened at the position 22b, that is, the position of the first gate 11. The injection portion 18a of the gas injection device 18 may also be opened at the position 18b or 18c, that is, the runner 16 or the injection nozzle 17a. Further, when the hot air supply device is provided outside, the heater 28 can be omitted by connecting the hot air supply path 24a to the hot air blowing device 22 in FIG.
[0038]
FIG. 2B shows another open / close valve structure, in which the valve seat 25a is inclined on the cavity 4 side of the core mold 3, and the open / close valve 26a is umbrella-shaped and protrudes into the cavity 4. Formed and moved in the directions of arrows u and v to open and close. In this case, the resin is closed when the resin is injected, and the on-off valve 26a is pressed against the valve seat 25a by the resin pressure. 2A and 2B, when the valve 26a is closed, the surface of the valve is continuous with the mold surface 6 of the core mold 2 to form a core mold surface.
[0039]
4 and 5 show an embodiment of the present invention . In FIG. 4, the hot air blowing device 22 is provided in the vicinity of the tip 7a of the resin 7 stopped at the end of the resin injection process. Here, the hot air blowing device 22 is configured to supply hot air to the front end portion 7 a of the resin 7 by ventilating the heater 28 disposed in the ventilation member 31 from the blower 23 through the blower pipe 24.
[0040]
In this apparatus, the resin injection is stopped at the same time as the resin injection or when the tip 7a of the resin 7 reaches a predetermined position in the cavity 4, the blower 23 and the heater 28 are started, and hot air is blown to the tip 7a. Thus, the resin at the tip 7a is heated or kept warm to be kept in a molten state. The hot air may be blown before or after the injection is stopped, but it must be before the gas is injected.
[0041]
In FIG. 5, the heat generating device 39 composed of the transparent glass 39a and the infrared irradiator 39b is arranged so as to face the front end portion 7a at the stop position. In this apparatus, the infrared irradiator 39b is activated simultaneously with the injection of the resin 7 or when the injection is stopped, and the tip 7a is irradiated with infrared rays to heat or keep the tip 7a in a molten state.
[0042]
4 and 5, only the front end portion 7a of the resin 7 is heated, so that the amount of heat of heating is small and the mold itself is not heated, so that cooling is easy. In these cases, the temperature sensor 36, the suction pump 35, etc. are not necessarily required.
[0043]
FIG. 6 is a cross-sectional view of an embodiment in which a molten resin is injected as another fluid. In the injection mold 1, a cavity 4 is formed between a cavity mold 2 and a core mold 3. Through the sprue 15 and the first gate 11, the resin 7 that forms the outer layer and the molten inner layer resin 10 that forms the inner layer are injected from the injection nozzle 17 a of the injection molding machine 17. The core mold 3 is provided with a hot air blowing device 22 having a hot air outlet 13 opened on a mold surface at a position different from that of the gate 11 and connected with a hot air supply path 24a.
[0044]
As in FIG. 1, the gas discharge port 14, the air passage 32, the suction pump 35, and the like are provided, but the illustration is omitted. An inner cylinder nozzle 41 is slidable on the inner periphery of the injection nozzle 17a, and a needle 42 is slidable on the inner periphery of the inner cylinder nozzle 41. An outer layer resin flow path 43 is formed between the injection nozzle 17 a and the inner cylinder nozzle 41. An inner layer resin flow path 44 is formed between the inner cylinder nozzle 41 and the needle 42.
[0045]
In the above apparatus, first, hot air is supplied from the hot air supply path 24 a to the hot air blowing device 22, and blown out from the hot air outlet 13 to the cavity 4 to replace the air in the cavity 4. Then, the resin 7 is injected from the outer resin flow path 43 by an amount smaller than the capacity of the cavity 4 in a state where the inner resin flow path 44 is blocked by the needle 42 of the injection nozzle 17a, and then the injection of the resin 7 is stopped. Thereafter, the needle 42 is retracted and the inner layer resin 10 is injected from the inner layer resin flow path 44 to manufacture a sandwich-shaped multilayer resin molded product.
[0046]
In this method, blowing of hot air, at the time of stop of the tip portion 7a, it may be performed toward the tip portion 7a.
[0047]
In each of the above examples, a remarkable effect can be obtained when a mold surface having an embossed pattern is used. However, the mold surface is not necessarily limited to an embossed pattern and may have a smooth surface. Further, the structure of the mold 1, the shape of the cavity 4 and the like can be changed according to the molded product, and the heating method of the tip 7a of the resin 7 can also be changed.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an injection molding apparatus of a reference example .
2A and 2B are enlarged cross-sectional views of a part of FIG.
FIGS. 3A, 3B and 3C are schematic cross-sectional views showing a manufacturing process. FIGS.
FIG. 4 is a cross-sectional view showing an injection molding apparatus according to an embodiment of the present invention .
FIG. 5 is a cross-sectional view showing an injection molding apparatus according to another embodiment.
FIG. 6 is a cross-sectional view showing an injection molding apparatus according to still another embodiment.
FIG. 7 is a schematic cross-sectional view showing a conventional manufacturing process.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Injection mold 2 Cavity type | mold 3 Core type | mold 4 Cavity 5, 6 Mold surface 7 Resin 8 Hollow part 9 Fine recessed part 10 Inner layer resin 11 1st gate 12 2nd gate 13 Hot-air blower outlet 14 Gas exhaust port 15 Sprue 16 Runner DESCRIPTION OF SYMBOLS 17 Injection molding machine 17a Injection nozzle 18 Gas injection apparatus 19,34 Flow path 20 Gas supply apparatus 21 Gas vent valve 22 Hot air blowing apparatus 23 Blower 24 Blowing pipe 25 Valve seat 26 On-off valve 27 Rod 28 Heater 30 Control apparatus 31 Ventilation material 32 Ventilation Path 33 Suction chamber 35 Suction pump 36 Temperature sensor 37 Sealing material 38 Temperature control medium flow path 39 Heat generating device 41 Inner cylinder nozzle 42 Needle 43 Outer layer resin flow path 44 Inner layer resin flow path

Claims (8)

A smaller amount of resin than the cavity capacity is injected into the cavity of the injection mold, and other fluids are injected into the injection resin to fill the resin layer, and the resin layer is expanded into the cavity and crimped to the mold surface. a injection molding method not producing molded article is, to stop the injection of the tree fat in the course you start the injection of other fluids, to supply heated gas to the distal end of the injected resin, injected into the cavity An injection molding method characterized by heating or keeping a temperature of a tip portion of the injected resin to maintain a molten state. A smaller amount of resin than the cavity capacity is injected into the cavity of the injection mold, and other fluids are injected into the injection resin to fill the resin layer, and the resin layer is pushed into the cavity and crimped to the mold surface. An injection molding method for producing a molded product by irradiating the tip of the injection resin with infrared rays in the process of stopping the injection of the resin and starting the injection of another fluid, and the injection injected into the cavity An injection molding method characterized in that the tip of the resin is heated or kept warm to maintain a molten state. The injection molding method according to claim 1 or 2 , wherein the other fluid is a compressed gas. The injection molding method according to claim 1 or 2 , wherein the other fluid is another molten resin. An injection mold having a cavity for molding a molded article, a first gate for injecting a molten liquid resin in an amount less than the cavity capacity into the cavity, and injecting another fluid into the injection resin In the process of stopping the injection of the second gate and the resin and starting the injection of another fluid, heating or heat retention is performed to supply the heating gas to the tip portion of the injection resin and maintain the tip portion of the injection resin in a molten state. Means for injection molding. An injection mold having a cavity for molding a molded article, a first gate for injecting a molten liquid resin in an amount less than the cavity capacity into the cavity, and injecting another fluid into the injection resin In the process of stopping the injection of the second gate and other fluid and starting the injection of another fluid, heating or heat retaining means for irradiating the tip of the injection resin with infrared rays and maintaining the tip of the injection resin in a molten state An injection molding apparatus. The injection molding apparatus according to claim 5 or 6, wherein the second gate is a gate for injecting compressed gas. The injection molding apparatus according to claim 5 or 6 , wherein the second gate is a gate for injecting another molten resin.

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