JP5754156B2 - Injection molding method - Google Patents

Description

  The present invention relates to an injection molding method suitable for molding a thermoplastic resin using an injection molding apparatus, and particularly suitable for preventing appearance defects such as sink marks occurring on the design surface of a molded product. The present invention relates to an injection molding method.

  Conventionally, an injection molding method in which a resin is injected and filled into a mold cavity formed by a fixed mold and a movable mold is well known, but products molded by the injection molding method are, for example, a polybucket or a case. There are a wide variety of daily miscellaneous goods such as automobile parts such as bumpers and instrument panels, and their shapes and sizes vary.

Normally, it is desired that a product molded by an injection molding method be as thin as possible, but ribs and bosses are often formed on the back side (counter-design side).
This is because by placing ribs on the back of the product, product deformation is suppressed (during molding), product rigidity is ensured (the product does not deform even when an external force is applied), alignment during product mounting, and product strength The effect of securing etc. can be expected. Further, if a boss is arranged on the back surface of the product, effects such as fitting of a product mounting jig (for example, screw mounting), positioning at the time of product mounting, and thinning of a rib intersection can be expected. However, as a result, the portions where the ribs and bosses are formed are thicker than other product portions. In addition, products molded as automobile parts are often provided with clips and the like necessary for attachment to other parts, and the parts where the clips are arranged are thicker than other product parts. Become.

When a product with a thick part is injection-molded, there is a possibility that a partial dent called sink will occur in the thick part and cause a defective appearance of the product. Well-known to vendors. In particular, when the design surface is flat, sink marks are conspicuous. Therefore, measures such as embossing the surface may be taken, but even in this case, a defect may be judged in the form of embossed transfer unevenness.

As a measure to prevent sink marks, there is a well-known method of sufficient filling pressure during injection molding to supplement the resin shrinkage in the mold, but a sufficient effect is expected depending on the product shape etc. There is a case that cannot be done.

JP-A-6-315961

In the technique disclosed in Patent Document 1, a heating means is attached at a position close to the concave portion of the mold on the side where the concave portion due to sink marks is generated, and the surface of the concave portion is transferred to the glass of the resin by the heating means at the time of molding. It is characterized by being heated and held above the temperature.

The technique disclosed in Patent Document 1 alleviates a decrease in the temperature of the molten resin filled in the mold by heating and holding the mold on the product visible surface side where sink marks are generated. Since the resin whose temperature drop has been reduced is also reduced in fluidity, it can easily penetrate into fine irregularities on the mold surface, and as a result, the contact part between the irregularities and the resin on the heated mold. However, since it becomes large compared with the case of non-heating, it becomes difficult to release.
In the technique disclosed in Patent Document 1, the heated mold maintains the mold temperature at a high temperature even in the cooling step after filling the mold with the resin. Accordingly, since the temperature drop of the resin in contact with the heated mold is more gradual and the shrinkage is slow, the effect of releasing from the resin surface is less than that of the non-heated mold.

In the technique disclosed in Patent Document 1, for the reason described above, the non-heating-side mold is released from the resin before the heating-side mold.
As a result, the resin molded on the mold cavity surface on the heated side is in close contact with the mold cavity surface, and the resin molded on the mold cavity surface on the non-heated side is released from the mold cavity surface. Condition arises,
In such a case, the resin molded on the mold cavity surface on the non-heated side becomes a free surface without restraint (so-called free surface state).
Accordingly, sink marks generated by the shrinkage are first released and concentrated on the non-heated surface side with less restraint, so that the occurrence of sink marks is suppressed on the resin surface on the heated cavity side.
In this way, the technique disclosed in Patent Document 1 prevents sink marks generated on the design surface by setting the design surface side to the surface to be heated.

In the technique disclosed in Patent Document 1 described above, the mold release state is controlled by the mold temperature to prevent sink marks generated on the design surface.
However, there is a limit to the control of the mold release state by adjusting the mold temperature, and the design side mold cannot be heated to such a high temperature that the resin deforms after taking out the product. Deformation of the molded product sometimes becomes a problem at the mold temperature. In addition, when the release of the resin on the counter-design surface side and the mold is slow, the skin layer on the counter-design surface side develops and the resin on the design surface side is strongly affected by the shrinkage of the resin. The effect of reducing sink marks may be reduced. Similarly, if the mold temperature on the non-design surface side is lowered too much than the mold temperature on the design surface side, the development of the skin layer is promoted and the sink reduction effect may be reduced.

Therefore, in the prior art described above, there are cases where the release state of the resin in the mold cannot be sufficiently controlled, and in such a case, there is a possibility that the sink marks occurring on the design surface cannot be prevented as a result. There is. The present invention has been made in view of the problems of the prior art as described above, and relates to an injection molding method for more effectively preventing sink marks as compared with the prior art.

In order to achieve the above object, an injection molding method according to the present invention comprises:
(1) In a resin injection molding method in which a molten thermoplastic resin is injected and filled into a mold cavity of a mold apparatus formed of a fixed mold and a movable mold, a design surface is provided for the mold cavity. The temperature of the mold cavity surface on the forming side is set to be higher than the temperature of the mold cavity surface on the side forming the counter-design surface within a range of 3 ° C. or more and 30 ° C. and the amorphous resin is molded. In this case, the temperature of the mold cavity surface on the side forming the design surface is set within the range from the glass transition temperature of the resin to be molded to a temperature 20 ° C. lower than the glass transition temperature, and the molten resin is molded After completion of injection filling into the cavity, the pressure of the resin injected and filled into the mold cavity was set to 0 Pa within a time range from 1 second to 7 seconds .

(2) In a resin injection molding method in which a molten thermoplastic resin is injected and filled into a mold cavity of a mold apparatus formed of a fixed mold and a movable mold, a design surface is provided for the mold cavity. When the temperature of the mold cavity surface on the forming side is set to be higher than the temperature of the mold cavity surface on the side forming the counter-design surface within a range of 3 ° C. or more and 30 ° C. In addition, the temperature of the mold cavity surface on the side forming the design surface side is set within a temperature range that is higher than the temperature 20 ° C. lower than the glass transition temperature of the resin to be molded and lower than the melting point of the resin to be molded. After completion of injection filling of the molten resin into the mold cavity, the pressure of the resin injected and filled into the mold cavity was set to 0 Pa within a time range from 1 second to 7 seconds.

(3) In the injection molding method according to (1) or (2), the mold clamping force of the mold apparatus is reduced within a time range from 1 second to 7 seconds after completion of the injection filling.

( 4 ) In the injection molding method according to any one of (1) to ( 3 ), a heat insulating material is disposed on the mold cavity surface on the side forming the design surface side.

( 5 ) In the injection molding method according to any one of (1) to ( 4 ), after the injection filling is completed, the resin pressure becomes 0 Pa and the gold on the counter-design side is within 5 seconds. relative to the mold cavity area 1 cm ^2, to inject gas in a ratio from 0.1Ncm ³ of 10Ncm ^3.

( 6 ) In the injection molding method according to ( 5 ), the gas supply pressure is in the range of 0.1 MPa to 10 MPa.

( 7 ) In the injection molding method according to ( 5 ) or ( 6 ), after the injection filling is completed, two operations of supplying gas into the mold cavity and reducing the clamping force are performed. The mold was opened.

( 8 ) In the injection molding method according to any one of (1) to ( 7 ), a seal portion is arranged on the outer peripheral portion of the mold cavity surface forming the design surface, and the molded resin Prevents air from flowing into.

  In the injection molding method according to the present invention, the mold cavity temperature on the design surface side is set higher than the mold cavity temperature on the counter design surface side within an appropriate range, thereby releasing the part that forms the design surface of the product. In addition to the effect of suppressing sinking by slowing down, the pressure of the resin injected and filled in the mold cavity can be reduced by injection filling the resin so that it becomes 0 Pa within a predetermined time range after completion of injection. By releasing the resin on the design surface side in a short time, the resin on the design surface side is hardly affected by the resin shrinkage and the occurrence of sink marks is suppressed.

Regarding the temperature difference between the mold cavity surface of the design surface and the counter-design surface, if the difference is less than 3 ° C, a temperature reversal region may appear locally. There is a possibility that the cooling rate of the resin becomes too fast and the effect of reducing sink marks is lowered. Therefore, if the temperature of the mold cavity surface on the side forming the design surface is set to be higher in the range of 3 ° C. to 30 ° C. than the temperature of the mold cavity surface forming the counter-design surface side, the design The effect of reducing sink marks can be expected over the entire mold cavity surface on the surface side.

In addition, if the time during which the resin pressure is 0 Pa is shorter than 1 second, there is a possibility that the skin layer is too thin and the shape retainability is inferior. On the contrary, if it is longer than 7 seconds, the mold The skin layer may become too thick while in contact with the cavity, which may reduce the improvement effect. Therefore, if the control is performed so that the pressure becomes 0 Pa within the time range from 1 second to 7 seconds, a high sink reduction effect can be expected.

  Further, when molding an amorphous resin, the temperature of the mold cavity surface on the side where the design surface is formed is 20 ° C. lower than the glass transition temperature of the resin to be molded (−20 ° C. of the glass transition temperature). If it is higher and can be set in a range lower than the glass transition temperature, the adhesiveness of the resin to the mold is further enhanced. At this time, if the temperature of the mold cavity surface is 20 ° C. or more lower than the glass transition point of the resin, it is difficult for the surface temperature of the mold cavity surface to exceed the glass transition point temperature even when the injected resin heat is received. Reduction effect decreases. Conversely, when the temperature of the mold cavity surface is higher than the glass transition point, deformation of the molded product becomes a problem.

In the case of molding a crystalline resin, the temperature of the mold cavity surface on the side forming the design surface side is higher than the temperature 20 ° C. lower than the glass transition temperature of the resin to be molded, and the melting point of the resin to be molded It is preferable to set within a lower temperature range. If the temperature of the mold cavity surface is 20 ° C. or more lower than the glass transition point of the resin, it is difficult for the surface temperature of the mold cavity surface to exceed the glass transition temperature even if the injected resin heat is received. Reduction effect decreases. Conversely, if the temperature of the mold cavity surface is higher than the melting point, the shape of the molded product cannot be maintained, which may cause a problem.

As a method of setting the pressure of the resin injected and filled in the mold cavity to 0 Pa within a time range from 1 second to 7 seconds, a method of reducing the mold clamping force in that time control is possible. Is preferred.

Further, in the present invention, after the resin injection is completed, the resin pressure in the mold becomes 0 Pa, and within 5 seconds, the mold cavity area of 1 cm ² on the counter-design surface side is 0.1 Ncm ^3. If gas is injected at a ratio of (normal cubic centimeter) to 10 Ncm ³ (normal cubic centimeter), the mold cavity surface on the counter-design side and the resin can be reliably separated to create a gap. Further suppression of sink marks can be expected.
In the present invention, when a large amount of gas is blown into the mold cavity as in normal gas assist molding, it induces partial cooling and solidification of the resin. It becomes. Therefore, it is preferable to use a small amount of air instead of using extra air as much as possible.

And the pressure at the time of injecting the gas is preferably a pressure that allows the mold cavity surface on the counter-design surface side and the resin to be separated from each other, and the range is 0.1 MPa or more and 10 MPa or less. .

  In the injection molding method of the present invention, after the molten resin is injected and filled into the mold cavity, the two operations of gas supply and mold clamping force reduction of the mold apparatus are completed, and then the mold is slightly opened. For example, it can be controlled to be 0 Pa more reliably within a time range from 1 second to 7 seconds, and the mold cavity surface on the counter-design side and the resin can be reliably released in a short time. Because it is possible, the effect of preventing sink marks is high.

Furthermore, according to the present invention, if a hole is formed in the mold on the counter-design surface side and an ejector pin is arranged, and gas is introduced into the mold cavity from the gap between the hole and the ejector pin, A gap can be reliably formed between the mold cavity on the design surface side and the product, and release can be promoted to improve sink marks.

  In addition, if a seal portion is arranged on the outer periphery of the mold cavity surface forming the design surface to prevent air from flowing in between the molded resin, the mold cavity surface forming the design surface and the product Since it becomes difficult to impair the adhesion of the film, improvement of sink marks can be expected.

1 is an overall view of an injection molding apparatus used in the present embodiment. It is sectional drawing of the 1st metal mold | die used for this embodiment. It is a behavior figure of resin at the time of implementing the injection molding method used for this embodiment. It is sectional drawing of the 2nd metal mold | die used for this embodiment. It is sectional drawing of the 3rd metal mold | die used for this embodiment. It is a conceptual diagram for demonstrating the structure of an ejector part about a 3rd metal mold | die. It is sectional drawing of the 4th metal mold | die by this embodiment.

Hereinafter, a preferred example of an embodiment of the present invention will be described in detail with reference to the drawings.
1 to 7 relate to an embodiment of the present invention, and FIG. 1 is an overall view of an injection molding apparatus used in this embodiment. FIG. 2 is a cross-sectional view of the first mold used in the present embodiment, and FIG. 3 is a conceptual diagram for explaining the behavior of the resin when the injection molding method according to the present embodiment is performed. FIG. 4 is a sectional view of the second mold, and FIG. 5 is a sectional view of the third mold. FIG. 6 is a conceptual diagram for explaining the structure of the ejector portion of the third mold. FIG. 7 is a cross-sectional view of a fourth mold according to the present embodiment.

  As shown in FIG. 1, the injection molding apparatus 100 used in this embodiment includes a mold apparatus 10, a mold clamping apparatus 20, an injection unit 30, and a control apparatus 60 that controls the mold clamping apparatus 20 and the injection unit 30. It has. The mold apparatus 10 attached to the mold clamping apparatus 20 includes a fixed mold 3 and a movable mold 4, and has a structure in which a mold cavity 15 is formed in the mold mold 10 in a state where both molds are combined. ing.

As shown in FIG. 1, the fixed die 3 is attached to the fixed platen 1, and the movable die 4 is attached to the movable platen 2. Therefore, the movable mold 4 can be freely moved back and forth with respect to the fixed mold 3 by operating the mold clamping device 20 described later.

Next, the mold clamping device 20 used in this embodiment will be described.
A mold clamping device 20 shown in FIG. 1 includes a movable platen 2, a fixed platen 1, an end plate 5, a mold clamping cylinder 22, and a toggle type mold clamping mechanism 8 that operates by driving the mold clamping cylinder 22 (referred to as a toggle mechanism 8). In addition, the movable platen 2 is provided with four tie bars 7 installed between the fixed platen 1 and the end plate 5. The toggle mechanism 8 that is guided and driven by the mold clamping cylinder 22 is configured to move forward and backward together with the movable mold 4.

  In the mold clamping apparatus 20 shown in FIG. 1, a mold clamping force sensor L (not shown) is attached to the tie bar 7, and the extension amount of the tie bar 7 is detected when the mold 10 is clamped by the mold clamping apparatus 20. Thus, the mold clamping force of the mold 10 by the mold clamping device 20 can be measured.

Here, the control device 60 of the injection molding apparatus 100 shown in FIG. 1 controls the mold clamping control valve for supplying hydraulic pressure to the mold clamping cylinder 22 by the mold clamping control device 61 to freely open and close the mold device 10. In addition, it is configured so that it can be clamped.
In the embodiment shown in FIG. 1, a hydraulic and toggle type mold clamping mechanism is used as the driving device of the mold clamping device 20. However, the mold clamping mechanism that can be used in this embodiment is not limited to this. For example, an electric mold clamping device using a ball screw and a servo motor may be used.

  Next, as shown in FIG. 1, the injection unit 30 includes a barrel 32, a screw 34 provided in the barrel 32, a hopper 38 for supplying resin into the barrel 32, an injection cylinder 40 for moving the screw 34 back and forth, and a screw 34. And a hydraulic source (not shown) for supplying desired hydraulic pressure to the injection cylinder 40 and the hydraulic motor 42, and a heater (not shown) and the like are attached to the outer peripheral surface of the barrel 32.

  The injection unit 30 is configured to supply pellet-shaped resin from the hopper 38 into the barrel 32 when the screw 34 is rotated by the hydraulic motor 42, and the supplied pellet-shaped resin is attached to the barrel 32. It is heated by the heated heater and melted by being subjected to a kneading compression action by the rotation of the screw 34 and sent to the front of the screw 34. Resin melted (sometimes referred to as molten resin) sent to the front of the screw 34 can be injected from the nozzle 39 at the tip of the barrel 32 by the screw 34 advanced by the injection cylinder 40.

  The control device 60 includes a mold clamping control unit 61 that controls the mold clamping device, a mold clamping condition setting unit that sets mold clamping conditions in the mold clamping control unit, an injection control device 63 that controls the injection unit 30, and the The injection control unit is provided with an injection condition setting device for setting the injection conditions.

  Here, in the injection molding apparatus 100 shown in FIG. 1, as shown in FIG. 2, a hot runner is disposed as a resin passage in the mold apparatus 10, and the direction toward the mold cavity 15 of the hot runner is provided. The valve gate 31 is arranged on the tip end side.

  In the injection molding apparatus 100 shown in FIG. 1, the above-described configuration enables the resin to flow between the injection unit 30 and the mold cavity 15 with the valve gate 31 open, and the valve gate 31 is closed. In this state, the resin flow between the injection unit 30 and the mold cavity 15 is blocked.

  In the above-described embodiment, the valve gate 31 is arranged in the mold apparatus 10. However, the arrangement is not limited to the above, and it is within the scope of the technical idea of the present invention. It can be changed.

  Hereinafter, the first mold 10 (also referred to as the first mold 10) used in the present embodiment will be described with reference to FIG. The first mold 10 according to the present embodiment includes a fixed mold 3 and a movable mold 4, and has a structure in which a mold cavity 15 is formed in a state in which both molds are combined. The resin molded product molded in the mold 10 is a so-called clog-shaped product in which two large thick ribs are arranged on a rectangular flat plate.

  Here, in the product molded by the first mold 10, the surface on the side where the ribs are not disposed is a visible surface that is visible to the end user when the product is used, and the appearance is required to be beautiful. It is a design surface. Therefore, in FIG. 2, the mold cavity surface formed by the fixed mold 3 is a mold cavity surface on the design surface side that forms the design surface of the product, and the mold cavity surface formed by the movable mold 4 is the anti-design side. This is the mold cavity surface.

  An ejector plate 52, an ejector pin 54, and the like are disposed on the movable mold 4 that forms the mold cavity surface on the counter-design side. Therefore, when attached to the injection molding apparatus 100 in the form shown in FIG. 1, the ejector plate 52 is moved forward and backward by operating the ejector mechanism provided in the mold clamping apparatus 20, thereby ejecting the ejector pins 54. Is driven forward and backward.

Further, the first mold 10 is provided with a temperature adjusting mechanism capable of independently controlling the temperatures of the mold cavity surfaces of the fixed mold 3 and the movable mold 4, and the fixed mold 3 has a fixed mold temperature adjustment. A line T1 (sometimes referred to as a temperature adjustment line T1) and a movable type temperature adjustment line T2 (sometimes referred to as a temperature adjustment line T2) are arranged as separate lines in the movable mold 4.
Therefore, the first mold 10 can be set at a different temperature or raised for the fixed mold 3 that forms the mold cavity surface on the design side and the movable mold 4 that forms the mold cavity surface on the counter design side. Therefore, the temperature can be controlled at a desired temperature.

  Further, the first mold 10 is provided with a sensor capable of measuring the temperature and pressure independently for the mold cavity surfaces of the fixed mold 3 and the movable mold 4, and the fixed mold 3 measures the fixed mold temperature. A sensor TS1 (sometimes referred to as a temperature sensor TS1) and a fixed pressure measurement sensor PS1 (sometimes referred to as a pressure sensor PS1) are provided. And a movable pressure measurement sensor PS2 (sometimes referred to as pressure sensor PS2).

Hereinafter, a preferred example of the embodiment of the injection molding method according to the present embodiment will be described as a first embodiment with reference to FIGS. 2 and 3.
For molding, ABS resin (the glass transition temperature of each of the terpolymers is acrylonitrile: 104 ° C, butadiene: -90 ° C, styrene: 100 ° C, but 104 ° C of acrylonitrile is the glass transition temperature of the copolymer. Dominate).
In the first embodiment, before starting the molding cycle, the mold temperatures of the fixed mold 3 and the movable mold 4 are set in advance to raise the mold 10 to a desired temperature, and then the temperature is maintained. Manage the temperature as you do.

In the first embodiment, the temperature of the temperature adjustment line T1 is set to 90 ° C. for the fixed mold 3, and the temperature of the temperature adjustment line T2 is set to 80 ° C. for the movable mold 4, and the temperature increase is started. One hour after the start of temperature increase, the temperature sensor TS1 of the fixed mold 3 is 89 ° C., 15 ° C. lower than the glass transition temperature 104 ° C. of acrylonitrile in ABS, and the temperature sensor TS2 of the movable mold 4 is 80 ° C. In a state where the temperature difference is 9 ° C., a good temperature management state was obtained.

In the first embodiment, the temperature management is performed by the temperature sensors TS1 and TS2 attached to the fixed mold 3 and the movable mold 4. However, the temperature management is not limited to this method. The temperature may be controlled by adjusting the temperature adjustment line T1 or T2 while the driver is measuring with a portable contact temperature sensor, and as much as possible, the mold is measured while directly measuring the surface portion of the mold cavity surface. The mold temperature is preferably controlled, and the mold cavity temperature immediately after product removal is preferred as the timing for measuring the mold cavity surface temperature during continuous operation of the product.

After the temperature of the first mold 10 is controlled, the process proceeds to the step of FIG. 3 (1), and the molding cycle of the injection molding method is started. In the first embodiment, as the first step, the toggle mechanism 8 is extended by the mold clamping cylinder 22 provided in the mold clamping device 20 and the movable platen 2 is moved in the direction of the fixed platen 1, as shown in FIG. ), The mold 10 is closed, and the mold is clamped with a clamping force applied. The mold clamping force used at this time is 3000 KN, which is a mold clamping force sufficient to mold the resin.

In a state where the mold 10 is clamped with a sufficient clamping force, the process proceeds to the step of FIG. 3 (3), and the injection unit 30 is operated to perform the resin injection operation. The arranged valve gate 31 is opened, and molten resin (ABS resin in this embodiment) is injected into the mold cavity 15.
The resin applicable to the present invention is not limited to the resin used in the first embodiment, and can be applied by, for example, polyamide, polystyrene, PC / ABS, AES, or the like.

In the first embodiment, immediately after the molten resin is injected into the mold cavity 15 and the filling is completed, the process proceeds to the step of FIG. 3 (4), and the toggle mechanism 8 is bent to reduce the clamping force. At this time, an important point is that the mold clamping force is lowered to 0 Pa within the time range from 1 second to 7 seconds with respect to the pressure of the resin injected and filled in the mold cavity 15.
In the first embodiment, the valve gate 31 is immediately closed without using the pressure-holding step of loading the resin pressure in the injection unit 30 in this step.

Then, the pressure of the resin injected and filled in the mold cavity 15 is measured by the pressure sensor PS2 disposed in the mold cavity 15, and the mold is measured until the resin pressure in the mold cavity measured by PS2 becomes 0 Pa. Reduce tightening force. In the first embodiment, the mold clamping force at that time was approximately 0 N (zero).
In the first embodiment, as a preferred embodiment, a pressure sensor is used, and the mold clamping force is reduced while measuring the resin pressure. However, even if measurement is not performed by the sensor, the mold clamping force is almost 0 N (zero). ), The resin pressure in the mold cavity becomes 0 Pa.

  Here, in order to make the pressure of the resin injected and filled in the mold cavity 15 into 0 Pa within the time range from 1 second to 7 seconds, the amount of resin at the time of injection is reduced, after the completion of injection. A method of reducing the mold clamping force or closing the valve gate after forcibly backing the screw of the injection unit after completion of the injection can be considered. As for the method for reducing the resin amount and the method for reducing the mold clamping force, both methods are effective in that the pressure of the resin injected and filled in the mold cavity can be quickly reduced to 0 Pa. Is the range of adaptation. However, as a means for setting the pressure of the resin injected and filled in the mold cavity to 0 Pa, the entire cavity can be uniformly set to 0 Pa, and the time control is simple. The method is preferred. Therefore, in the first embodiment, a method is adopted in which the mold clamping force is reduced and the pressure of the resin injected and filled in the mold cavity is quickly brought to 0 Pa. In particular, in a molded product that is required to be thin, it is effective to reduce the clamping force in order to reduce the pressure of the resin injected and filled within a predetermined time to 0 Pa while avoiding a short shot.

  In the first embodiment, the mold clamping force of the mold clamping device 20 is reduced after the molten resin is injected and filled into the mold cavity, but the toggle mechanism 8 is bent as it is and the mold is slightly opened. For example, this is a more preferable form in that it can be controlled to 0 Pa within the time range from 1 second to 7 seconds more reliably.

  In this embodiment, the mold cavity temperature on the design surface side is made higher than the mold cavity temperature on the counter design surface side, thereby slowing the release of the part forming the design surface of the product, Further, by controlling the pressure of the resin injected and filled in the mold cavity 15 to 0 Pa within a time range from 1 second to 7 seconds, as shown in FIG. The resin on the design surface side is less susceptible to resin shrinkage by releasing the resin on the counter-design surface side in a short time while the resin on the side is in close contact with the mold cavity surface without releasing. Thus, the occurrence of sink marks is suppressed.

In addition, when the time when the resin pressure is 0 Pa is shorter than 1 second, since the melt ratio of the filled resin is high, the shape shaping property is inferior, the skin layer is too thin, the shape retaining property is inferior, and the product design side May cause problems such as poor adhesion to the cavity surface, and if it is longer than 7 seconds, the skin layer grows while it is in contact with the mold cavity and becomes too thick, and the improvement effect diminishes. Since there is a possibility, it is preferable to control to 0 Pa within a time range from 1 second to 7 seconds.

  3 (5), after the resin is cooled and solidified, the mold 10 is completely opened as shown in FIG. 3 (6), and then the ejector mechanism is driven to eject the ejector pin. The product is ejected by 54 to take out the product from the mold 10.

  In this case, although the final product remains in the fixed mold 3 or the movable mold 4 is determined by the product shape or the like, in this embodiment, the movable mold 4 is formed by the rib contraction effect. The product was configured to stay.

Here, as for the first mold, the mold cavity surface of the fixed mold 3 and the movable mold 4 is provided with a temperature adjustment mechanism capable of controlling the temperature independently of each other. It can be adjusted freely so that the temperature falls within the proper range. However, regarding the temperature difference between the mold cavity surface of the design surface and the counter-design surface, if the difference is less than 3 ° C, a temperature reversal region may appear locally. The cooling rate of the resin on the side becomes too fast, and the sink effect is reduced. Therefore, it is preferable to set the temperature of the mold cavity surface on the side forming the design surface to be higher in the range of 3 ° C. or more and within 30 ° C. than the temperature of the mold cavity surface forming the counter-design surface side. .

Further, as a result of examining the temperature setting of the mold 10 by the same method as in the first embodiment described above, the mold cavity surface on the side on which the design surface side is formed is 20 ° C. from the glass transition temperature of the resin to be molded. It was found that there is a favorable effect that the adhesion to the mold cavity surface of the resin is increased by setting and molding in a range higher than the low temperature and not higher than the glass transition temperature. If it is too high, the product will be deformed. Therefore, it is particularly preferable to set the temperature to be higher than the temperature 20 ° C. lower than the glass transition temperature and not higher than the glass transition temperature.

Here, in 1st Embodiment, using the 1st metal mold | die 10, mold temperature control was performed only by the temperature control lines T1 and T2. However, the temperature management of the mold 10 that can be applied to the present invention is not limited to this. For example, a mold such as a second mold 10A (second mold 10A) shown in FIG. The system which arrange | positions the heat insulating materials D, such as a ceramic, inside 10A may be sufficient.
The second mold 10A is a mold cavity surface on the design side of the first mold 10 (mold cavity surface of the fixed mold 3) embedded with a foam ceramic having a heat insulating effect. 10A is a preferable form in that the effect of the heat insulating material D delays the cooling of the product portion molded on the mold cavity surface on the design side, and the effect of preventing sink marks is enhanced.

As another mold 10, for example, a temperature control mold having a temperature control mechanism capable of heating and cooling the mold is used, and predetermined heating is performed to improve sink marks. It is also possible to reduce the temperature of the mold. In this case, there is a possibility that the deformation of the product after the product is taken out can be reduced, and further, an effect of shortening the molding cycle can be expected.
However, when the above-mentioned temperature control mold is used, the resin on the design surface side should not be released from the mold cavity surface quickly due to increased cooling conditions. You need to be careful.

  Hereinafter, a preferable example of the embodiment of the injection molding method according to the present invention will be described as a second embodiment.

  In addition to the molding method described in the first embodiment, the second embodiment is characterized by injecting gas from the mold cavity surface on the counter-design surface side (mold cavity surface of the movable mold 4) during the molding. The mold cavity surface on the counter-design surface side and the resin are surely released from the mold.

  Hereinafter, the second embodiment will be described focusing on differences from the first embodiment. In order to simplify the description, the same reference numerals as those used in the first embodiment may be used for constituent elements having the same functions as those in the first embodiment.

  In 2nd Embodiment, the 3rd metal mold | die 10B (3rd metal mold | die 10B) shown in FIG. 5 was used. About the 3rd metal mold | die 10B, basic structures, such as a product shape, a temperature control mechanism, and sensor arrangement | positioning, are the same as that of the 1st metal mold | die 10. FIG.

A feature of the third mold 10B is that it includes a fixed gas cylinder 80 for injecting gas (air in the present embodiment), and a gap (gas introduction gap) between the ejector pin 54 and a hole portion where the ejector pin 54 is arranged. 57), the gas is introduced into the mold cavity.

FIG. 6 shows the configuration of the third mold 10B. A communication hole 59 through which a gas flows from a fixed gas cylinder 80 attached to the movable mold 4 to a gas introduction gap 57 is formed as a flow path, and is connected to the gas introduction gap 57 through an introduction port 56. Further, in order to prevent the gas supplied from the fixed gas cylinder 80 from escaping from other than the mold cavity, the gap between the hole portion and the ejector pin 54 is sealed on the side opposite to the mold cavity of the gas introduction gap 57. A gas seal 55 is formed.
With the above configuration, the third mold 10B can introduce gas into the mold cavity from the metering gas cylinder.

Hereinafter, the injection molding method according to the second embodiment will be briefly described.
After the temperature of the first mold 10 is controlled at 85 ° C. on the cavity side and 70 ° C. on the core side, the molding cycle of the injection molding method is started, the mold 10 is closed, and the mold is clamped. Clamp with force applied. The mold clamping force used at this time was 3000 KN, which is a mold clamping force sufficient to mold the resin.

  In a state where the mold 10 is clamped with a sufficient mold clamping force, the injection unit 30 is operated to perform the resin injection operation, and at the same time, the valve gate 31 disposed on the front end side of the hot runner is opened to open the mold Molten resin (in this embodiment, polystyrene, glass transition point is 100 ° C.) is injected into the mold cavity 15.

Here, in the second embodiment according to the present invention, after the molten resin is filled in the mold cavity 15, the toggle mechanism 8 is bent to reduce the mold clamping force to 200KN. In this case, an important point is that the mold clamping force is reduced to 0 Pa within the time range from 1 second to 7 seconds with respect to the pressure of the resin injected and filled in the mold cavity 15.
In the second embodiment, the pressure of the resin injected and filled in the mold cavity 15 is measured by the pressure sensor PS2 disposed in the mold cavity 15, and the resin pressure in the mold cavity measured by the PS2 becomes 0 Pa. Until the mold clamping force is reduced, the metering gas cylinder 80 is operated.

As shown in FIG. 6 (1), the gas supplied from the metering gas cylinder 80 flows from the communication hole 59 through the inlet 56 to the gas introduction gap 57 and into the mold cavity 15.
Therefore, in the second embodiment, gas can be reliably supplied between the mold cavity on the counter-design surface side and the product, and the mold release is promoted more than the operational effects obtained in the first embodiment. Can do.

Note that the two operations of gas supply and mold clamping force reduction have been described as being performed substantially simultaneously in the second embodiment described above, but the operations applicable to the present invention are not limited to this, for example, gas supply Thus, the mold clamping force may be reduced, or the gas may be supplied after the mold clamping force is reduced. The order can be changed without departing from the technical idea of the present invention.

  In the second embodiment, the design is performed by releasing the resin on the counter-design surface side in a short time in a state where the resin on the design surface side is in close contact with the mold cavity surface by the above operation. The surface side resin is less affected by resin shrinkage and suppresses the occurrence of sink marks.

Here, in the second embodiment, when a large amount of gas is blown as in normal gas assist molding, a resin molded product (referred to as a resin product) that induces partial cooling and solidification of the resin and is molded with the resin. May cause sinking on the design side.
Therefore, it is preferable to avoid the use of excess air as much as possible, and it is preferable to use a small amount of air. In order to achieve the effect, the pressure of the resin in the mold becomes 0 Pa after the completion of injection for 5 seconds. by within, relative to the mold cavity area 1 cm ² of the anti-design surface side, it is preferable to inject the gas in a ratio from 0.1Ncm ³ of 10Ncm ^3. As a result, the resin product can be reliably released from the counter-design surface side, and the suppression of sink marks can be expected more strongly.

The important point is that the aforementioned gas supply is an action performed mainly for releasing the mold cavity surface on the counter-design surface side and the resin. Therefore, in actual molding, the effect is almost always produced in an amount much smaller than the upper limit of the numerical range.
In addition, in order to send gas quantitatively, it is suitable to use a quantitative gas cylinder 80 having a simple structure and excellent repeatability.

The pressure used is a pressure that allows the mold cavity surface on the side of the anti-design surface and the resin product to be separated from each other, and if the pressure is less than 0.1 MPa, a substantial effect is not seen, so 1 MPa. The above is preferable. In addition, since the effect does not increase in proportion to increasing the pressure, even if the pressure is increased beyond 10 MPa, the effect is not improved. Therefore, a preferable range applicable to this embodiment is 0.1 MPa or more and 10 MPa or less.

Further, as a method of introducing gas from the gas introduction gap 57, for example, a groove is formed in the ejector pin 54 as shown in FIG. 6 (2), or the gap is stepped as shown in FIG. 6 (3). Enlarging the flow path is preferable in that the loss of gas pressure is small.

  Further, in the second embodiment, after injection filling of the molten resin into the mold cavity is completed, the mold clamping force of the mold apparatus is reduced and the mold is slightly opened while supplying the gas. In the time range from 1 second to 7 seconds, the pressure can be controlled to 0 Pa. Furthermore, the resin on the anti-design surface side can be reliably released in a short time, so that the effect of preventing sink is high.

In this case, if a seal portion is arranged on the outer periphery of the mold cavity surface forming the design surface to prevent air from flowing in between the molded resin, the mold cavity forming the design surface The mold release between the surface and the resin can be suppressed.
FIG. 7 shows a fourth mold 10C (fourth mold 10C). On the mold cavity surface of the fixed mold 3 of the fourth mold 10C, a protrusion 85 is formed so as to surround the outer periphery of the mold cavity. When the resin is molded, the resin around the protruding portion 85 contracts and sandwiches the protruding portion 85, thus functioning as a seal portion that blocks the flow of air. Accordingly, since the resin on the design surface side is in close contact with the mold cavity surface without being released, the effect of suppressing the occurrence of sink marks is improved.

  Of course, the design surface sealing method and the like described above may be applied to the first embodiment in which gas is not blown using the metering gas cylinder 80. In addition, although the effect is inferior in that gas is not actively blown in, it is a preferable mode that air naturally flows into the mold cavity on the counter-design surface side at the time of mold release. Therefore, in the first embodiment, the method of the second embodiment in which the air flow path is formed by processing the ejector pin 54 without using the gas metering cylinder 80 is applicable and preferable.

  Moreover, in 1st Embodiment and 2nd Embodiment which were mentioned above, when injection-filling resin as a preferable form, the metal mold | die 10 was clamped with sufficient mold clamping force. However, the present invention can also be applied to, for example, injection compression in which the mold clamping force is reduced and injection filling is performed, or an injection press in which resin is filled in a slightly opened mold and then mold-clamped.

  As described above, some preferred examples have been described as embodiments of the present invention. However, it is needless to say that embodiments to which the present invention can be applied are not limited thereto, and are within the scope not departing from the technical idea of the present invention. Can be changed.

The injection molding method according to the present invention is suitable for molding a product that has a design surface on one side of the product and has ribs or bosses on the side of the non-design surface and is easy to sink.

DESCRIPTION OF SYMBOLS 1 Fixed platen 2 Movable platen 3 Fixed type 4 Movable type 5 End plate 7 Tie bar 8 Toggle mechanism 10 Mold apparatus (die)
15 Mold cavity 20 Clamping device 30 Injection unit 31 Valve gate 52 Ejector plate 54 Ejector pin 55 Gas seal 56 Introduction port 57 Gas introduction gap 59 Communication hole 80 Fixed gas cylinder T1 Fixed mold temperature adjustment line (fixed mold temperature control line)
T2 Movable temperature control line (movable temperature control line)
100 Injection molding apparatus 10A Second mold (second mold)
10B Third mold (third mold)
10C 4th mold (4th mold)
PS1 Pressure sensor (fixed type)
PS2 Pressure sensor (movable type)
TS1 Temperature sensor (fixed type)
TS2 Temperature sensor (movable type)

Claims (8)

In a resin injection molding method in which a molten thermoplastic resin is injected and filled into a mold cavity of a mold apparatus formed of a fixed mold and a movable mold,
About mold cavity is set so that the temperature of the mold cavity surface on the side for forming the design surface is increased to within 30 ° C. 3 ° C. or higher than the temperature of the mold cavity surface on the side for forming the anti-design surface With
When molding an amorphous resin, the temperature of the mold cavity surface on the side where the design surface is formed is set within the range from the glass transition temperature of the resin to be molded to a temperature 20 ° C. lower than the glass transition temperature. ,
A resin injection molding method in which after the molten resin is injected and filled into the mold cavity, the pressure of the resin injected and filled into the mold cavity is 0 Pa within a time range from 1 second to 7 seconds . In a resin injection molding method in which a molten thermoplastic resin is injected and filled into a mold cavity of a mold apparatus formed of a fixed mold and a movable mold,
The mold cavity is set so that the temperature of the mold cavity surface on the side where the design surface is formed is higher than the temperature of the mold cavity surface on the side where the counter surface is formed within a range of 3 ° C. or more and 30 ° C. or less. With
When the crystalline resin is molded, the temperature of the mold cavity surface on the side where the design surface is formed is higher than a temperature 20 ° C. lower than the glass transition temperature of the resin to be molded and lower than the melting point of the resin to be molded. Set within the temperature range,
A resin injection molding method in which after the molten resin is injected and filled into the mold cavity, the pressure of the resin injected and filled into the mold cavity is 0 Pa within a time range from 1 second to 7 seconds . The injection molding method according to claim 1 or 2 , wherein the mold clamping force of the mold apparatus is reduced within a time range from 1 second to 7 seconds after completion of the injection filling. The injection molding method according to any one of claims 1 to 3 , wherein a heat insulating material is disposed on a mold cavity surface on a side forming the design surface side. Billing after completion the injection filling, the resin pressure in to within 5 seconds becomes 0 Pa, the counter-design surface side of the mold cavity area 1 cm ^2, to inject the gas in a ratio from 0.1Ncm ³ of 10Ncm ³ The injection molding method according to any one of claims 1 to 4 . The injection molding method according to claim 5 , wherein a supply pressure of the gas is in a range of 0.1 MPa to 10 MPa. The injection molding method according to claim 5 or 6 , wherein, after completion of the injection filling, the mold is slightly opened by performing two operations of supplying a gas into the mold cavity and reducing a clamping force. By arranging a seal on the outer periphery of the mold cavity surface that forms the design surface, according to any one of during the molding resin of claims 1 to prevent air from flowing to claim 7 Injection molding method.

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