JP5754187B2 - 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.

  2. Description of the Related Art 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. Products molded by the injection molding method are diverse, such as daily miscellaneous goods such as poly buckets and cases, or automobile parts such as bumpers and instrument panels, and the shapes and sizes thereof are various.

Incidentally, it is usually desired that a product molded by the injection molding method be as thin as possible. For this reason, ribs and bosses are often formed on the back surface side (counter-design surface side) of the design surface that forms the appearance of the product. Because by arranging ribs on the back of the product, you can expect effects such as suppressing product deformation (during molding), ensuring product rigidity (the product will not deform even when external force is applied), ensuring product strength, etc. This leads to a thin product.
In addition, if a boss is arranged on the rear 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, for the reasons described above, the portion where the ribs and bosses are formed is thicker than the other product portions. In addition, many products molded as automobile parts are often provided with clips and the like necessary for attachment to other parts, and the portions where clips etc. are arranged are thicker than other product parts. Become meat.

And when a product with a thick part is partially 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. Are well known to those skilled in the art. 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. As described above, the technique disclosed in Patent Document 1 prevents sink marks generated on the design surface of the product by setting the design surface side of the product as a 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 surface side mold cannot be heated to such a high temperature that the resin is deformed after taking out the product. Therefore, deformation of the molded product sometimes becomes a problem at a mold temperature higher than the glass transition 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 In addition, the effect of preventing sink marks may be reduced. Similarly, if the mold temperature on the counter-design surface side is too much lower than the mold temperature on the design surface side, the development of the skin layer is also 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, the anti-design surface of the mold cavity Apply a material that is gasified by the amount of heat of the injection-filled resin to the mold cavity surface on the side, and make the temperature of the mold cavity surface on the design surface side higher than the temperature of the mold cavity surface on the counter-design surface side The pressure of the resin injected and filled in the mold cavity was set to 0 Pa within the time range from 1 second to 7 seconds after completion of injection.

(2) In the injection molding method according to (1), the gasifying material was baking soda.

(3) In the injection molding method according to (1) or (2), the clamping force of the mold apparatus is reduced within a time range of 1 second to 5 seconds after completion of the injection filling.

(4) The injection molding method according to (3), wherein after the injection is completed, the mold clamping force is reduced and then the mold is slightly opened.

(5) In the injection molding method according to any one of (1) to (4), a seal portion is arranged on the outer peripheral portion of the mold cavity surface forming the design surface, and the molded resin The air was prevented from flowing into.

  The mold used in the injection molding method of the present invention is gasified by a thermal decomposition reaction with the amount of heat of injection-filled resin on the mold cavity surface on the counter-design side, or by a gasification reaction such as evaporation or sublimation. The pressure of the resin injected and filled in the mold cavity during molding was set to 0 Pa within the time range from 1 second to 7 seconds after the injection was completed.

According to the injection molding method of the present invention, the material applied to the mold cavity surface on the counter-design surface side is quickly heated by quickly setting the pressure of the resin filled in the mold cavity to 0 Pa during molding. Decomposes into gas. As a result, the resin on the anti-design surface side is surely released from the mold cavity surface in a short time, so that the resin on the design surface side is less susceptible to resin shrinkage, and as a result, sink marks that occur on the design surface are generated. Is suppressed.
Baking soda (sodium hydrogen carbonate) is one of the materials that can be gasified by the heat quantity of the injection-filled resin. Sodium bicarbonate is pyrolyzed into gas, which is harmless and safe for the human body and is environmentally friendly. It is suitable in terms of excellent workability and the like, and is also excellent in that it is generally commercially available and easy to purchase.

In addition, if the time when 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 deteriorated. The skin layer may become too thick while in contact with the cavity, which may reduce the improvement effect.
Therefore, a high improvement effect can be expected by controlling to 0 Pa within a time range from 1 second to 7 seconds.

Further, 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, for example, there is a method of adjusting the filling amount of the resin. A method of reducing the clamping force is preferable in terms of simple control.
Therefore, as a method of setting the resin pressure in the mold to 0 Pa within the time range from 1 second to 7 seconds, the mold clamping of the mold apparatus is performed within the time range from 1 second to 5 seconds after completion of the injection filling. A method of reducing the force is preferred.

  Furthermore, in the injection molding method of the present invention, after the injection filling of the molten resin into the mold cavity is completed, the mold clamping force is reduced, and then the mold is slightly opened, so that the process can be performed more reliably from 1 second to 7 seconds. Within the time range, the resin pressure in the mold can be controlled to be 0 Pa. As a result, the mold cavity surface on the counter-design surface side and the resin can be reliably released in a short time. The effect of preventing sink marks is high.

  In addition, for the mold cavity surface that forms the design surface, a mold cavity surface that forms the design surface and the product can be provided by providing a seal portion on the outer periphery of the mold cavity surface to make it difficult for air to flow in between the molded resin. Since it is difficult to damage the adhesiveness, 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 performing the injection molding method by this embodiment. It is sectional drawing of the 2nd metal mold | die used for 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 4 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 cross-sectional view of the second mold used in this 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.
The mold clamping device 20 shown in FIG. 1 is 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 toggle type mold clamping mechanism is used as the driving device of the mold clamping device 20, but the mold clamping mechanism that can be used in the present 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 20 placement, a mold clamping condition setting unit that sets the mold clamping conditions in the mold clamping control unit, and an injection control device 63 that controls the injection unit 30. And an injection condition setting device for setting an injection condition in the injection control unit.

  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 inside the two molds in a combined state. The molded product of the resin molded in the first 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 the 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 surface. It becomes the mold cavity surface of the side.

  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 surface 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 temperature and pressure independently in the vicinity of the mold cavity surface of the fixed mold 3 and the movable mold 4. A temperature measurement sensor TS1 (sometimes referred to as temperature sensor TS1) and a fixed pressure measurement sensor PS1 (sometimes referred to as pressure sensor PS1) are provided. And a movable pressure measurement sensor PS2 (also referred to as pressure sensor PS2).

Here, the feature of the mold used in the present invention is that the gas generating material C is a material that is thermally decomposed and gasified by the amount of heat of the resin injected and filled in the mold cavity surface on the side that forms the counter-design surface. It is being applied.
In the first mold 10, the baking soda is applied as the gas generating material C to the mold cavity surface on the side that forms the counter-design surface (in this embodiment, the mold cavity surface on the movable mold 4 side). It has become. FIG. 2 shows the situation. Baking soda is applied along the mold cavity surface of the movable mold 4 on the counter-design surface side, and is applied to the entire mold cavity surface on the counter-design surface side.
Of course, the coating material that can be used in the present embodiment is not limited to this, and any material that is thermally decomposed and gasified at the resin temperature at the time of injection, or vaporized by evaporation or sublimation, etc. Other materials may be used without departing from the technical idea of the present invention.
For example, in addition to the baking soda used in the above-described embodiment, water may be used as a material that is vaporized by evaporation to become a gas, while taking into account the safety of work and the negative impact on the product. It is possible to use a known material that is gasified with the amount of heat of the present invention.

As a method for coating the mold cavity surface, for example, baking soda is directly applied to the mold cavity surface by means such as printing, or sprayed on the mold cavity in a state where the baking soda is dissolved in a solvent. Various known methods such as a method of attaching and solidifying can be used.

Baking soda powder basically decomposes into carbon dioxide, sodium carbonate, and water when heated, but it may decompose at room temperature if it contains moisture in the air. Therefore, it is necessary to control the amount of water so that it can be gasified properly.

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.
Note that ABS resin was used for molding. 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, the temperature of the temperature adjustment line T2 is set to 80 ° C. for the movable mold 4, and the temperature increase is started. When the temperature rise is started, the heating medium circulates through the temperature adjustment line T1a processed into the fixed mold 3 by the temperature adjustment line T1 in the fixed mold 3, and the movable mold 4 by the temperature adjustment line T2 in the movable mold 4. A heating medium circulates in the temperature control line T2a processed into a temperature, and the mold is heated to a set temperature. It should be noted that one hour after the start of temperature increase, the temperature difference is 10 ° C., and a good temperature management state is 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.

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.

  In the first embodiment, since the pressure holding process by the injection filling pressure of the injection unit 30 is not used, the energy of the injection unit 30 can be reduced, leading to energy saving. Further, since the mold clamping force is immediately reduced without a pressure holding step, there is a secondary effect that the life of the mold 10 is extended.

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 is normally 0 Pa.

If the resin filled in the mold cavity 15 is thermally shrunk and the resin pressure in the mold cavity becomes 0 Pa, the product becomes sinked.
However, in the first embodiment, baking soda is applied to the mold cavity surface on the counter-design surface side, and gas is generated by thermal decomposition by the amount of heat of the filled resin. Therefore, as shown in FIG. 3 (5), the resin on the counter-design surface side is surely released from the mold cavity surface earlier than the resin on the design surface side. Therefore, the resin on the design surface side is hardly affected by resin shrinkage, and the occurrence of sink marks is suppressed.

If the temperature of the mold cavity surface on the design surface side is set to be higher than the temperature of the mold cavity surface on the counter design surface side, the resin on the counter design surface side is released from the resin on the design surface side. The effect that it becomes easy to do can be expected. However, according to the present invention, the mold surface on the design surface side is formed during molding by applying the material that generates heat and decomposes by the amount of heat of the filled resin to the mold cavity surface on the anti-design surface side. Gas can be generated between the cavity surface and the resin to further enhance the mold release effect. As a result, sink marks generated on the design surface of the product can be more reliably suppressed. Therefore, it is possible to adapt even under a situation where the resin on the counter-design surface side is difficult to release from the mold cavity surface due to the product shape or the like.

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.
Further, at this time, whether the product finally remains in the fixed mold 3 or the movable mold 4 is determined by the product shape or the like, but in this embodiment, the movable mold 4 is formed by the rib contraction effect. The product was configured to stay.

  In order to make the pressure of the resin injected and filled in the mold cavity 15 into 0 Pa in the time range from 1 second to 7 seconds in the above-described process, the amount of resin at the time of injection is reduced. A method is conceivable in which the mold clamping force is reduced after completion of injection, or the valve gate is closed after forcibly backing the screw of the injection unit after completion of injection. 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 3 seconds after the completion of injection, and the pressure of the resin injected and filled in the mold cavity is quickly set 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, after the molten resin is injected and filled into the mold cavity, the mold clamping force of the mold clamping device 20 is reduced, 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 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.

Further, in the first mold 10 described above, the mold cavity surface on the side of the counter-design surface is configured to be coated with baking soda. However, the applicable range of the present invention is not limited to this, and the mold release is performed. The application range of the present invention is also applicable to a case where a portion that is difficult to be selectively selected is selectively applied.

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. .

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.

  In the first embodiment described above, after injection and filling of the molten resin into the mold cavity, the mold clamping force of the mold apparatus is reduced and then the mold is opened slightly to ensure more reliable operation from 1 second. Within a time range of up to 7 seconds, it can be controlled to 0 Pa, and furthermore, the resin on the anti-design surface side can be surely released in a short time, so that the effect of preventing sink marks 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. 4 shows a second mold 10B (second mold 10B). On the mold cavity surface of the fixed mold 3 of the second mold 10B, 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.

  Moreover, in 1st Embodiment 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 has a design surface on one side of the product, and has ribs and bosses on the side of the non-design surface, and is suitable for molding products that are 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)
DESCRIPTION OF SYMBOLS 15 Mold cavity 20 Clamping apparatus 30 Injection unit 31 Valve gate 52 Ejector plate 54 Ejector pin 85 Projection part 100 Injection molding apparatus 10B 2nd mold (2nd mold)
C Gas generation material T1 Fixed temperature control line (fixed temperature control line)
T2 Movable temperature control line (movable temperature control line)
PS1 Pressure sensor (fixed type)
PS2 Pressure sensor (movable type)
TS1 Temperature sensor (fixed type)
TS2 Temperature sensor (movable type)

Claims (5)

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,
For the mold cavity, a material that is gasified by the amount of heat of the injection-filled resin is applied to the mold cavity surface on the counter-design surface side, and the temperature of the mold cavity surface on the design-surface side is the mold surface on the counter-design surface side. Set to be higher than the mold cavity surface temperature,
A resin injection molding method in which the pressure of a resin injected and filled in a mold cavity is 0 Pa within a time range from 1 second to 7 seconds after completion of injection. The injection molding method according to claim 1, wherein the material to be gasified is baking soda. The injection molding method according to any one of claims 1 to 2, wherein the clamping force of the mold apparatus is reduced within a time range of 1 second to 5 seconds after the completion of the injection filling.   The injection molding method according to claim 3, wherein after completion of the injection, the mold clamping force is reduced and then the mold is slightly opened. 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 4 Injection molding method.

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