JPH08290447A - Injection molding method and machine - Google Patents

Abstract

PURPOSE: To safely and rationally mold a complicated resin product having thin-walled and thick-walled parts within a short time at low cost without generating molding inferiority. CONSTITUTION: A process injecting water 200 being a liquid having a b.p. lower than the m.p. of a resin into the predetermined part of the resin (molded product part 100) before solidified in a mold 50 for a predetermined time is provided after a filling process filling the mold 50 with a molten resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin product having a thick wall portion, a resin having a complicated shape such that a thin wall portion and a thick wall portion such as a case or a housing of a home electric appliance and a precision mechanical component are mixed. When molding products, warpage, deformation,
The present invention relates to an injection molding method that eliminates defects such as sink marks and achieves a high cycle by shortening the cooling time.

[0002]

2. Description of the Related Art Generally, a resin product is injection-molded by using an injection-molding machine equipped with a mold,
The injection process, the pressure holding process, the cooling process, and the molded product removing process are performed as one cycle.

In the injection molding of a resin product having a shape having a thick portion, sink marks are generated on the surface of the thick portion, and the pressure-holding step and the cooling step require a longer time than other steps. It becomes a problem. As a measure against this problem, a pressurized metal such as nitrogen gas is passed through the void insertion pin for gas injection into the thick part of the resin that has not been solidified after being filled (full shot) in the mold. A method of injecting from the mold side and pressurizing so that the resin spreads throughout the mold has been proposed and implemented. Such a method of injecting the pressurized gas into the thick portion is generally called gas injection, and is disclosed in, for example, Japanese Patent Application Laid-Open No. 6-79758 (hereinafter referred to as Conventional Example 1). According to this gas injection, the pressurized gas enters instead of the resin in the thick portion, so that the thickness of the thick portion is reduced. That is, the actual thick state of the thick portion is eliminated while maintaining the shape on the cavity side. And as the thickness of the thick part decreases,
Cooling time is reduced. For example, when a molded article of the same size and shape is to be obtained by injection molding, if gas injection is used, the cooling time is expected to be shortened by about 20% as compared with the case where it is not used. In addition, since the resin in the thick wall portion in contact with the gas is pressed toward the cavity side, the problem of sink marks on the surface of the thick wall portion is improved without forcibly increasing the holding pressure. When the pressurized gas is injected, the thick-walled resin is cooled on the surface side in contact with the mold and its viscosity increases, so that the pressurized gas is retained inside the resin and There is no breakthrough.

In addition to gas injection, for example, Japanese Unexamined Patent Publication No. 5-261750 (hereinafter referred to as Conventional Example 2)
)), A method of molding a hollow resin product using a liquid such as water without using a high-pressure gas is disclosed.
In Conventional Example 2, a liquid such as water is pressed into the resin during the filling step, that is, before the resin is filled into every corner of the cavity, so that the resin is pressurized by its expansion force. Injection molding methods have been proposed.

[0005]

By the way, when a case or housing of a home electric appliance or the like or a precision mechanical component is made of resin, the resin product has a thin portion (thickness is, for example, 1.0 mm). In many cases, a thick part (thickness is 2.5 mm, for example) is present in a complicated shape in a mixed state. Therefore, as described above, warpage, deformation, sink marks, etc. do not occur in the injection molding of not only a resin product having only a thick portion but also a resin product having a complicated shape in which a thin portion and a thick portion are mixed. It is required to solve the problems and achieve a high cycle by shortening the cooling time.

On the other hand, for example, in the case of molding a resin product having a complicated shape in which a thin wall portion and a thick wall portion are mixed according to Conventional Example 1, since the thick wall portion has a relatively thin wall thickness. The void insertion pin for injecting the pressurized gas needs to have a fairly small outer diameter. Therefore, it is very difficult to provide a valve mechanism for opening and closing the pin inner hole at the tip of the thin void insertion pin. After setting the void insertion pin without this valve mechanism in the thick part, before injecting the pressurized gas, the high-temperature resin before solidification enters near the tip of the void insertion pin due to the resin pressure and clogging occurs. I have something to do. Therefore, Conventional Example 1 has a problem in reliability.

Further, in Conventional Example 1, although the holding pressure lower than that normally required for sink mark prevention is required due to the pressurizing effect of the pressurized gas, the cooling efficiency for the thick wall portion is not improved. Since there is no such reduction, the reduction of the cooling process is practically limited to about 20% reduction as described above, and further reduction cannot be realized. Therefore, a large reduction in the time of the entire injection molding process has not been realized.

Further, in Conventional Example 1, stable injection molding is difficult unless the portion into which the pressurized gas is to be injected has a certain thickness. That is, the resin in contact with the mold is cooled, while the resin in contact with the pressurized gas is not particularly cooled by the pressurized gas, so the solidification timing differs between the two. For this reason, even if it is a thick portion, when injecting the pressurized gas into a portion where the wall thickness is comparatively thin, the gap between the mold sandwiching the resin and the pressurized gas tends to be small, and the shallow portion near the resin surface Resins having different solidification times are present in the region. As a result, molding defects such as poor appearance and insufficient strength may occur.

Further, in the conventional example 1, since a high pressure gas is used, the equipment used is relatively expensive, and the operator who carries out this method needs a person who has passed the regulations for the reason of ensuring safety. In some cases, it is inconvenient for implementation.

On the other hand, in Conventional Example 2, if a hollow resin product having only a thick wall portion is molded, relatively good injection molding with less sink marks can be performed, but a thin wall portion and a thick wall portion It is not suitable for injection molding of a resin product having a complicated shape in which parts are mixed. This will be described with reference to FIG. FIG. 6 shows the mold internal pressure (indicated by a solid line in the figure), the injection pressure (indicated by a broken line in the figure) in the injection molding of a resin product having a thin portion, and the expansion pressure of liquid (water) injection according to Conventional Example 2. It is a figure which shows the maximum value (indicated by a dashed line in the figure). Referring to FIG. 6, in Conventional Example 2, water or the like is injected before the resin is filled in the cavity of the mold. Therefore, a hollow resin product (which basically has no thin portion) can be formed into a desired shape by the expansion pressure of water (200 to 300 Kgf / cm ^{2 at} maximum). is there. However, it is not possible to mold (transfer molding) a thin-walled portion existing in a case or housing of a home electric appliance as described above into a desired shape even with a swelling pressure of water of about 200 to 300 Kgf / cm ^{2 at} maximum. It is possible. That is, according to Conventional Example 2, even if an attempt is made to obtain a resin product having a complicated shape in which a thin portion and a thick portion are mixed, only the thick portion has a desired shape, and the thin portion becomes a short shot. It is not possible to mold the entire structure including the thin portion to the desired shape.

An object of the present invention is to prevent molding defects such as warpage, deformation and sink marks in injection molding of a complicated resin product in which a thin portion and a thick portion are mixed, as is the case with ordinary resin products. An object of the present invention is to provide an injection molding method which can be solved and which can achieve a high cycle by significantly shortening the cooling time which could not be achieved by gas injection or the like.

Another object of the present invention is to provide an injection molding method capable of molding a resin product safely, rationally and at low cost.

Still another object of the present invention is to provide an injection molding machine for realizing the above injection molding method.

[0014]

According to the present invention, the injection molding methods of the following modes 1 to 5, and modes 6 and 7 are as follows.
Injection molding machine is obtained.

(1) After the filling step of filling the molten resin into the mold is completed, a liquid having a boiling point lower than the melting point of the resin is applied to a predetermined portion of the resin before being solidified in the mold. An injection molding method having a step of injecting for a predetermined time.

(2) In injection molding a complicated resin product in which a thin portion and a thick portion are mixed, in the filling step, the molten resin is filled in the mold and then the resin is compressed. Then, the thin-walled portion is formed by transfer molding, and after the filling step is completed, the liquid is injected into the thick-walled portion as the predetermined portion.

(3) Aspect 1 or 2 in which the step of injecting the liquid for a predetermined time is performed after the filling step is completed and after switching to a pressure holding step of holding the filled resin at a predetermined pressure holding value. Injection molding method.

(4) Injection molding of aspect 3 in which, in the filling step, an injection pressure value higher than the holding pressure value is maintained for a predetermined time after the resin is filled in the mold for a predetermined time. Method.

(5) The injection molding method according to any one of Modes 1 to 4, which has a step of sucking a residual portion of the liquid injected into the predetermined portion to the outside of the resin.

(6) Aspects 1 to 5 having a liquid injecting section arranged in the mold so that a tip is located at the predetermined portion, and a liquid injecting apparatus for injecting the liquid through the liquid injecting section. An injection molding machine used for any of the injection molding methods.

(7) A liquid injecting section arranged in the mold so that a tip thereof is located at the predetermined section, a liquid injecting apparatus capable of injecting the liquid through the liquid injecting section, and injecting into the predetermined section. A liquid suction device capable of sucking the remaining portion of the liquid that has been sucked to the outside of the resin through the liquid injection unit, and an insertion arrangement in a tube that connects the liquid injection unit to the liquid injection device and the liquid suction device. An injection mode for the flow of the liquid in the tube,
An injection molding machine for use in the injection molding method according to aspect 5, comprising a direction switching valve that switches between a suction mode and a shutoff mode.

[0022]

Embodiments of the present invention will be described below with reference to the drawings.

[Embodiment 1] FIG. 1 is a schematic view showing a main part of an injection molding machine used in an injection molding method according to Embodiment 1 of the present invention. In this injection molding machine, as in the conventional example, a fixed platen 31 fixed to a body frame (not shown) and a tie bar (not shown) are supported and driven by a mold clamping mechanism (not shown) with respect to the fixed platen 31. And a nozzle 3 at the tip of a heating cylinder (not shown) equipped with a screw.
3 and an eject plate, which will be described later, as movable platen 32.
And an ejector rod 34 for driving independently. In addition, this injection molding machine has a fixed platen 3
1. Fixed mold 51 attached to 1 and movable platen 32
Movable die 52 attached to the movable die 52, an eject plate 53 disposed on the back side of the movable die 52, and a plurality of eject pins 54 attached to the eject plate 53 and penetrating the movable die 52 to reach the inside of the die. (In the figure, only two are shown).

FIGS. 2A and 2B are views showing a part of the present injection molding machine shown in FIG. Referring to FIG. 1 and FIGS. 2A and 2B together, this injection molding machine has a sleeve that is attached to the eject plate 53 like the eject pin 54 and penetrates the movable mold 52 to reach the inside of the mold. It has a needle 11 as an example of a liquid injection part that penetrates through the pin 12 and projects, and a liquid injection device 20 connected to the needle 11 via a tube 13.
The needle in the present invention is not limited to the illustrated form, and may have a sliding pin shape or a thin open / close valve shape.

FIG. 3 is a schematic view showing the liquid injection device 20. In FIG. 3, the liquid injection device 20 includes a liquid chamber 21a having a liquid supply port 211a and a liquid output port 212a.
And a cylinder 21 having an oil chamber 21b having two oil outflow ports 211b and 212b, a piston 22 capable of reciprocating in the cylinder 21, a hydraulic pump 23, a variable throttle valve 24, and a relief valve 25, A direction switching valve 26,
It has a hopper 27 and a check valve 28.

The piston 22 in the cylinder 21 is driven by the pressure of the oil which is pumped up by the hydraulic pump 23 and flows into and out of the oil chamber 21b by switching the relief valve 25 and the direction switching valve 26 through the variable throttle valve 24. On the other hand, water 200 as a liquid having a lower boiling point than the melting point of the resin material (for example, 170 ° C. when the resin material is polyacetal) is supplied from the hopper 27 into the liquid chamber 21a. The water 200 in the liquid chamber 21a is generated by the piston 2
2 is injected into the mold through the liquid output port 212a and the tube 13. The liquid in the present invention is
The liquid is not limited to water, and any liquid having a boiling point lower than the melting point of the resin may be used. In particular, a liquid that is easily vaporized and has a large volume and expands is preferable. According to the experiments by the inventors, as will be described later, with water easily obtained,
It has been found that a sufficiently effective effect can be obtained. It should be noted that it is possible to inject a liquid in the form of a mist, although the cooling effect described later is relatively low. In the present invention, the melting point of the resin means the temperature at which the solid resin material becomes a fluid.

Next, the injection molding method according to the present invention will be described with reference to FIGS. 1 and 2A and 2B. In the following description, injection molding of a molded product having a thick portion on a scale that requires about 1 minute for one molding cycle is taken as an example.

First, while the resin charged into the heating cylinder is being melted, the resin is weighed and kneaded with a screw, and the molten resin is stored in front of the screw.

On the other hand, in the mold defined by the fixed mold 51 and the movable mold 52, the needle 11 is arranged so that the tip is located at a position corresponding to the thick part of the molded product.

Next, the screw is moved forward by the hydraulic cylinder mechanism, that is, toward the mold, so that the stored resin is filled in the mold through the nozzle 33. When the filling of the molded product section 100 is completed as shown in FIGS. 1 and 2A, the pressure holding step is started.

During the pressure-holding step, water 200 is injected by the liquid injection device 20 through the needle 11 into the thick part of the molded part 100 of the resin before solidification. The injected water 200 vaporizes after about 2 seconds. Where 1 mol 1
As is clear from the principle that 8 g of water becomes a gas having a volume of 22.4 liters in the atmosphere, the water 200 that is vaporized in the state of being contained in the resin will generate a pressure of several hundred atmospheric pressure. Therefore, the vaporized water 200 spreads to a predetermined volume as shown in FIG. As described above, since the water 200 (liquid) injected into the resin vaporizes and expands, so to speak, in the present invention, it can be said that the pressure for injecting the liquid is sufficient even if it is relatively low. In FIG. 2 (b), reference numeral 100 a is a solidified layer that is cooled and solidified by the water 200. This cooling action is mainly due to the fact that when the water 200 vaporizes, heat is taken from the resin in contact with the water 200. Therefore, the cooling effect is large. Since the part of the molded part 100 that comes into contact with the water 200 is cooled, the water 200
Does not diffuse irregularly in the molded product part 100. Further, unlike the conventional method using a pressurized gas, the high-temperature resin before solidification does not enter the opening at the tip of the needle 11 due to the resin pressure and is not clogged. This is because the liquid such as water 200 has a characteristic (incompressibility) that it is hardly compressed even when the same pressure (pressure by resin) is applied as compared with the pressurized gas, and the place The most likely resin to enter the opening at the tip of the needle 11 is water 2
It is due to the fact that the viscosity is increased (flowability is lowered) by being cooled to 00 itself. However, a check valve may be provided near the tip of the needle 11.

By the way, if a large amount of water 200 is injected into the resin, the entire amount may remain in the cavity of the molded product without being vaporized. When there is a problem that water remains in the molded product, the liquid injection device 20 is used after the water 200 is vaporized.
The injection molding machine according to the present invention may be configured so that the piston 22 of FIG.

After that, a molded product is obtained through a cooling process and a molded product removing process. According to the injection molding method of the present invention described above, not only the pressure-holding process time required to prevent sink marks is shortened but also the cooling efficiency for the thick wall portion is greatly improved, so the cooling process is also shortened. Thus, the entire injection molding process is shortened. In addition, in the thick-walled portion, the resin and water 200 which are in contact with the mold (movable mold 52)
Since both of the resins in contact with each other are cooled, the solidification time between them is almost the same, the thickness of the thick part is relatively thin, and even when the interval between the mold for sandwiching the resin and the water 200 is small. Molding defects such as poor appearance and insufficient strength are unlikely to occur. That is, even if the thick portion of the resin does not have a certain thickness, stable injection molding can be realized. Therefore,
In the present invention, the location where the liquid is injected is not limited to the thick portion. In addition to the molded part 100 of the resin, the liquid may be injected into the sprue 101 or the runner in FIG. For example, sprue 101 to water 10
In the case of injecting at a pressure of about 20 atm, it has been found from experiments by the inventors that by setting the resin temperature relatively high, the same effect as in the case of injecting into the above-mentioned molded article part 100 can be obtained. . However, when the gate is thin, that is, when the area of the cross section of the gate perpendicular to the resin advancing direction is small, injecting the liquid into the molded product portion is more excellent in the pressure application effect and the cooling effect.

Further, since the injection molding method according to the present invention does not use a high-pressure pressurized gas, the equipment used is relatively inexpensive and the operator is not limited to those who have passed the regulations.

In addition, in order to adjust the water pressure of the water 200 by the liquid injection device 20, a pressure sensor for detecting each of the mold internal pressure and the water pressure, and a control unit for controlling the water pressure based on the detected values of these pressure sensors are provided. It may be provided in the injection molding machine.

[Embodiment 2] FIG. 4 is a schematic view showing a main part of an injection molding machine used in an injection molding method according to Embodiment 2 of the present invention. In the figure, the same parts as those of the conventional example or the same parts are designated by the same reference numerals as those in FIG. In FIG. 4, the injection molding machine has a fixed platen 31, a movable platen 32, a nozzle 33 at the tip of a heating cylinder (not shown) equipped with a screw, and an ejector rod 34, as in the first embodiment. ing. Further, in this injection molding machine, the fixed mold 5 attached to the fixed platen 31 is used.
1'and movable mold 5 attached to the movable platen 32
2 ', an eject plate 53' disposed on the back side of the movable mold 52 ', and a plurality of eject pins 54' attached to the eject plate 53 'and penetrating the movable mold 52' to reach the inside of the mold. (Only one is shown in the figure). The mold 50 'is
This is a type that can obtain multiple resin products (only one is shown in the figure) with one shot.

This injection molding machine is also attached to the eject plate 53 ', and passes through the movable mold 52' and the mold 5 '.
The sleeve pin 62 reaching the inside of 0'and the sleeve pin 6
Needle 6 as a liquid injecting portion that penetrates through 2 and projects
1, a pipe 64 to which the plurality of needles 61 are connected, a tube 63 connected to the pipe 64, and a direction switching valve 80 connected to the plurality of needles 61 via the tube 63 and the pipe 64. The direction switching valve 80 is also connected to the liquid injection device 20 ′ described in the first embodiment and the liquid suction device 70 described later. The liquid injection device 20 ′ has a configuration in which the liquid suction device 20 (FIG. 3) of the first embodiment is excluded from the configuration related to liquid suction such as the direction switching valve 26. That is, the combination of the liquid injection device 20 ′, the liquid suction device 70, and the direction switching valve 80 in the second embodiment is the same as the liquid injection device 20 in the first embodiment.
Equivalent to.

The liquid injecting device 20 'is a device for injecting water 200 as a liquid having a boiling point lower than the melting point of the resin material into the mold, as in the first embodiment. Also in the second embodiment, the liquid is not limited to water, but may be any liquid having a boiling point lower than the melting point of the resin, and a liquid that easily vaporizes and expands greatly in volume is preferable.

FIG. 5 is a flow chart showing the main steps of the injection molding method according to the second embodiment of the present invention. Hereinafter, the injection molding method according to the second embodiment will be described with reference to FIGS. 4 and 5. In the second embodiment, injection molding of a complicated resin product in which a thin molding portion and a thick molding portion 300 '(FIG. 4) are mixed on a scale requiring about 1 minute for one molding cycle is also taken as an example. To However, in FIG. 4, the thin portion is not specifically shown in order to avoid complexity of the drawing.

First, the resin charged into the heating cylinder is melted and weighed and kneaded with a screw to store the molten resin in front of the screw. On the other hand, in the mold 50 'defined by the fixed mold 51' and the movable mold 52 ', a needle 61 is arranged so that its tip is located at a position corresponding to the thick part of the molded product. The direction switching valve 80 is in the shutoff mode 81.

When the mold clamping is completed in step S1, the screw is moved to the mold 50 'side by the hydraulic cylinder mechanism, and the stored resin is discharged from the nozzle 33 to the sprue 3'.
01, filling (injection) into the mold 50 'through the runner 302 is started (step S2). At the time of step S2, the control device (not shown) of the present injection molding machine stores the position of the screw at this time as the initial screw position L ₀ . After that, the control device detects the screw position L.

In step S3, the control device determines that (screw position L-initial screw position L ₀ ), that is, the moving amount of the screw is equal to or more than the full moving amount L _s set in advance according to the full state of the resin. It is determined whether or not, that is, whether or not the resin is full in the mold 50 ', and if it is the full movement amount L _s or more, the process proceeds to step S4.

In step S4, the injection pressure is maintained at a predetermined value for a predetermined period. The holding of the injection pressure will be described in detail later. After that, the holding pressure is switched, that is, the filling step is switched to the holding step (step S5).

Further, at this time, the direction switching valve 80 is switched to the injection mode 82, and the liquid injection device 20 '
Molded product part 30 of the resin before being solidified during the pressure holding step
Injecting the water 200 into the thick part 300 ′ of 0 through the needle 61 is started (step S6). At the same time, the control unit starts measuring the liquid injection time that is set in advance according to the amount to be injected (step S7). It should be noted that instead of the liquid injection time, the expansion pressure of the liquid may be detected and the amount to be injected may be injected in advance.

Here, the injected water 200 is vaporized, for example, after about 2 seconds. Here, as is clear from the principle that 1 mol of 18 g of water turns into a gas having a volume of 22.4 liters in the atmosphere, the water 200 that is vaporized in the state of being enclosed in the resin is, for example, 200 to 300 Kgf / cm ^2. So-called bubbles having a pressure of. Therefore, the vaporized water 200 spreads to a predetermined volume as shown in FIG. As described above, since the water 200 (liquid) injected into the resin vaporizes and expands, so to speak, in the present invention, it can be said that the pressure for injecting the liquid is sufficient even if it is relatively low. When the water 200 is vaporized, heat is directly taken from the resin in contact with the water 200, so that the cooling effect is great.

Liquid injection time has expired (step S8)
Then, the direction switching valve 80 is switched to the suction mode 83, and the remaining water 200 is sucked through the needle 61 by the liquid suction device 20 'composed of a vacuum device or the like (step S9). However, when water is used as the liquid as in the present embodiment, most of the amount is usually vaporized and the remaining amount is small.

After this, the cooling process is completed (step S1).
0), the molded product is obtained through the molded product take-out process (step S11).

Here, the holding of the injection pressure in step S4 described above will be described. At the time when the resin is full in the mold 50 'in step S3, the necessary injection pressure is not high because of the fine bubbles and cushioning properties in the resin, that is, the absorbing element by the resin. Therefore, if the injection pressure is greatly reduced at the time of the full state, there is a possibility that the resin will not be cut all the way to the thin portion or the like. Therefore, in the present invention, the injection pressure is maintained at a predetermined pressure value and is not significantly reduced until the resin is completely distributed including the thin portion. However, if the injection pressure is held for a long time, defects such as sink marks, burrs, and deformation are likely to occur, and a high mold clamping force is also required. Therefore, the injection pressure holding time is, for example, about 0.2 seconds ( (It depends on the shape of the molded part, the type of resin, etc.) and the following, and the process proceeds to the holding pressure switching in step S5 (the holding pressure value is lower than the injection pressure holding pressure).
To do. Now, merely by shifting to the holding pressure switching, sink marks are likely to occur in the thick portion 300 ′ with large shrinkage. Therefore,
In the present embodiment, liquid injection is started in step S6 after switching the holding pressure. However, in the present invention, the liquid injecting step is not limited to the one after the holding pressure is switched as long as it is after the filling step.

Also in the second embodiment described above, in addition to the substantial thickness of the thick portion 300 'being reduced, the thick portion 300' is cooled by the heat of vaporization, so as to prevent sink marks. In addition to shortening the pressure-holding process time conventionally required, the cooling process can be shortened, and the entire injection molding process can be shortened. For example, as described above, in the gas injection method, the limit was that the cooling time was shortened by 20% as compared with the usual injection molding. However, according to the present invention, except for the gist, the same conditions as in the gas injection method were used. if you did this,
A reduction of about 50% was achieved compared to usual. Further, unlike the conventional case, it is not necessary to make the sprue 301 and the runner 302 a large diameter in order to perform sufficient holding pressure and prevent sink marks, so that the cooling time can be shortened by that amount and the waste of the resin material can be omitted. .

[0050]

The injection molding method according to the present invention has a melting point lower than the melting point of a resin in a predetermined portion of the resin before solidified in the mold after the filling step of filling the molten resin into the mold is completed. Since there is a step of injecting a liquid having a boiling point for a predetermined time, this liquid is, so to speak, vaporized and expanded, and exerts a pressure application effect and a cooling effect. As a result, when molding a resin product in which a thin portion and a thick portion are mixed, as is the case with ordinary resin products, warping, deformation, molding defects such as sink marks are eliminated, and gas injection etc. It is possible to achieve a high cycle by greatly reducing the cooling time that could not be achieved. In addition, resin products can be molded safely, reasonably and at low cost.

The injection molding machine according to the present invention can realize the injection molding method with a simple and inexpensive structure.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a main part of an injection molding machine used in an injection molding method according to a first embodiment of the present invention.

2A and 2B are schematic views showing a part of the injection molding machine shown in FIG. 1, where FIG. 2A is a state before liquid injection and FIG. 2B is a state after liquid injection.

FIG. 3 is a schematic view showing a liquid injection device of the injection molding machine shown in FIG.

FIG. 4 is a schematic diagram showing a main part of an injection molding machine used in an injection molding method according to a second embodiment of the present invention.

FIG. 5 is a flowchart of an injection molding method according to a second embodiment of the present invention.

FIG. 6 is a diagram for explaining a comparison between the expansion pressure and the injection pressure of the liquid in the injection molding method using the liquid.

[Explanation of symbols]

 11, 61 Needle 12, 62 Sleeve pin 13, 63 Tube 20, 20 'Liquid injection device 21 Cylinder 21a Liquid chamber 21b Oil chamber 22 Piston 23 Hydraulic pump 24 Variable throttle valve 25 Relief valve 26 Direction switching valve 27 Hopper 28 Check valve 31 Fixed platen 32 Movable platen 33 Nozzle 50, 50 'Mold 51, 51' Fixed mold 52, 52 'Movable mold 53, 53' Eject plate 54, 54 'Eject pin 80 Direction switching valve 100, 300 Molded part 101,301 Sprue 200 Water 300 'Thick wall 302 Runner

Claims (7)

[Claims] 1. A liquid having a boiling point lower than the melting point of the resin is predetermined at a predetermined portion of the resin before solidification in the mold after the filling step of filling the molten resin into the mold is completed. An injection molding method having a step of time injection. 2. When injection molding a complicated resin product in which a thin portion and a thick portion are mixed, in the filling step, the molten resin is filled in the mold and then the resin is compressed. The injection molding method according to claim 1, wherein the thin wall portion is formed by transfer molding, and the liquid is injected into the thick wall portion as the predetermined portion after the filling step is completed. 3. The step of injecting the liquid for a predetermined time is performed after the completion of the filling step and after switching to a holding pressure step of holding the filled resin at a predetermined holding pressure value. The injection molding method described in. 4. The injection according to claim 3, wherein in the filling step, an injection pressure value higher than the holding pressure value is held for a predetermined time after the resin is filled in the mold to a predetermined full state. Molding method. 5. The injection molding method according to claim 1, further comprising a step of sucking a remaining portion of the liquid injected into the predetermined portion to the outside of the resin. 6. A liquid injecting section arranged in the mold so that a tip thereof is located at the predetermined portion, and a liquid injecting apparatus for injecting the liquid through the liquid injecting section. An injection molding machine used in any one of the injection molding methods. 7. A liquid injecting section disposed in the mold so that a tip is located at the predetermined section, a liquid injecting device capable of injecting the liquid through the liquid injecting section, and a liquid injecting section for injecting the liquid into the predetermined section. A liquid suction device capable of sucking the remaining portion of the liquid to the outside of the resin through the liquid injection unit, and is inserted and arranged in a tube connecting the liquid injection unit, the liquid injection device, and the liquid suction device. The injection molding machine used in the injection molding method according to claim 5, further comprising: a direction switching valve that switches a flow of the liquid in the tube between an injection mode, a suction mode, and a cutoff mode.