Injection molding method

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DESCRIPTION

Injection molding method.

Technical field

The present invention relates to injection molding technologies.

Previous technique

An injection mold is provided with a gate and a cavity connected to the gate. A molten resin is injected into the cavity from the gate. When the molten injected resin has solidified in the cavity, the mold is opened to remove a molded product from the mold.

The resin shrinks when it solidifies. When the molten resin with which the cavity has been filled shrinks during solidification, the external shape of the molded product no longer matches the shape of the cavity. It is impossible to form the molded product into the desired external shape.

To solve this problem, the following technology was developed. This technology continues to apply pressure to the molten resin within the cavity from the gate while the molten resin within the cavity is solidifying. That is, the amount of molten resin necessary to compensate for the shrinkage is replenished. This technology can prevent the outer surface of the molded product from separating from the cavity surface, even as the molten resin shrinks. As a result, a molded product with the desired external shape can be obtained.

A technology that supersedes the technology mentioned above is disclosed in Japanese Patent Application Publication No. H10-58493. This technology focuses on the fact that many molded products have both a surface that must be finished with a desired shape (this surface is called the "design surface"), and a surface whose finish is not important (this surface is called a "surface later"). In this prior art method, when filling of the cavity with molten resin from the gate ends, the pressure applied to the molten resin is stopped. A fluid under pressure is injected towards the rear surface of the molded product. When the fluid under pressure is injected towards the rear surface of the molded product, the rear surface is separated from the cavity surface, but the design surface of the molded product is pushed against the surface of the cavity. Accordingly, the design surface of the molded product can be finished to the desired shape. It is explained that this technology does not require an additional amount of resin, since the pressure applied to the molten resin from the gate stops when the cavity has been filled with the molten resin.

US Patent 5,972,276 discloses a method for injection molding a resin to produce a shaped resin article having, on a back surface thereof, a locally protruding portion of a greater thickness, in which it is uses an excess of fill resin that reaches 100.5% or more by weight and a pressurized gas is applied.

Description of the invention

In order to form an excellent molded product using technology that continues to apply pressure to the molten resin from the gate, it is necessary to continue to apply high pressure. For example, to form a car bumper, it is necessary to continue applying a pressure of about 16 MPa to end zones (zones that are distant from the hatch) where shrinkage can become a problem. This makes it necessary to continue applying a pressure of approximately 40 MPa in the vicinity of the gate. Therefore, an injection mold for the bumper must be able to withstand a pressure of 40 MPa or higher. A large and expensive injection mold is required.

Even when using the technology that injects a fluid under pressure towards the rear surface of the molded product, a high fluid pressure is required to form an excellent molded product. The aforementioned Japanese Patent Application Publication No. H10-58493 injects a fluid at a pressure of about 18 MPa. Therefore, the injection mold must be able to withstand a pressure of 18 MPa or higher. A large and expensive injection mold is required.

The present invention reduces the pressure that needs to be applied to the resin within the cavity. Therefore, the required pressure resistance of the injection mold is reduced. As a result, the injection mold can be undersized, and the cost of injection molding can be reduced.

In the injection molding method disclosed by this specification, an injection mold is used. The injection mold is provided with a gate, a cavity connected to the gate, a flow channel having an opening that opens towards a rear surface of a molded product. In this method, a molten resin injection step is executed that injects the molten resin from the gate into the cavity. Furthermore, a pressure application stage to apply pressure from the gate against the resin injected into the cavity after the molten resin injection stage and a fluid injection stage to inject a fluid towards the back surface of the product are simultaneously executed. molded.

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The present injection molding method implements both the technology that continues to apply pressure from the gate and the technology that injects a fluid under pressure towards the back surface of the molded product. By simultaneously executing these two technologies, the present injection molding method is successful in obtaining an unexpected synergistic effect. That is, it is successful in significantly reducing the pressure required to form the desired design shape. In the example described above, if only the technology that continues to apply pressure from the gate is used, a pressure of approximately 16 MPa is required in the end zones. If only the technology that injects a fluid under pressure towards the back surface of the molded product is used, a pressure of approximately 18 MPa is required. On the contrary, when both technologies are used simultaneously, the pressure that needs to be applied from the gate in the pressure application stage can be halved to about 8 MPa and a pressure of only about 1 MPa becomes sufficient in the pressure setting. fluid injection stage. Therefore, both the pressure applied from the gate and the injection pressure of the fluid can be low. The design surface of the molded product can be formed to the desired surface shape, under conditions where both types of pressure are low. Note that the pressure values ​​mentioned above are provided merely as examples, and are not to be construed as limiting the technical scope of the invention.

This injection molding method achieves a synergistic effect using both the technology that the back surface of the molded product separates from the cavity surface before the design surface of the molded product separates from the cavity surface, and the technology that pressure is continuously applied to the molten resin from the gate. The step of injection of the fluid from the flow channel is one of the steps that ensures that the back surface of the molded product is separated from the surface of the cavity before the design surface of the molded product is separated from the surface of the cavity, and another stage may be used instead of the fluid injection stage.

Expressed more generally, the present injection molding method can be considered an injection molding method that simultaneously executes the pressure application step and a separation step to separate the back surface of the molded product from the cavity surface.

In order to ensure that the back surface separates from the cavity surface before the design surface separates from the cavity surface, it is also possible to use a pull pin or the like to mechanically separate the back surface from the cavity. molded product from the cavity surface.

Brief description of the drawings

Figure 1 is a perspective diagram illustrating an example of a molded product that is formed using the technology of one embodiment.

Fig. 2 is a schematic cross-sectional diagram of an injection molding apparatus of a first embodiment.

Figure 3 is a diagram explaining how the upper surface of a molded product separates from the surface of the cavity. Figure 3 (a) is a diagram explaining technology that prevents the design surface of the molded product from being separated from the cavity surface simply by replenishing the molten resin; Figure 3 (b) is a diagram explaining technology that prevents the design surface of the molded product from being separated from the cavity surface simply by applying pressure to the rear surface of the molded product; and Figure 3 (c) is a diagram explaining the technology that prevents the design surface of the molded product from separating from the cavity surface by simultaneously executing the step of replenishing the molten resin and the step of applying pressure to the surface. rear of the molded product.

Fig. 4 is a diagram explaining a process diagram of the first embodiment in comparison with a conventional example.

Fig. 5 is a diagram explaining the pressure required in the embodiment compared to a conventional example.

Fig. 6 is a schematic cross-sectional diagram of the injection molding apparatus of the second embodiment.

Figure 7 is a diagram explaining the various stages of injection molding and changes in pressure within the cavity.

Figure 8 is a diagram explaining how the resin flows into the cavity.

Figure 9 is a diagram explaining how the resin flows into the cavity.

Figure 10 is a diagram explaining the state of the resin inside the cavity when the fluid injection step ends.

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Figure 11 is a diagram explaining how the resin flows into the cavity.

Fig. 12 is a diagram explaining the state in which the molded product has been formed.

Fig. 13 is a diagram explaining the state in which the molded product has been formed.

Fig. 14 is a diagram explaining the state in which the molded product has been formed.

Fig. 15 is a diagram explaining the results of injection molding when a pressure holding time and pressure within the cavity are varied.

Best mode of carrying out the invention

The next section describes an assumed reason why pressure can be lowered by simultaneously executing the pressure application stage and the fluid injection stage. Note, however, that the technology disclosed in this specification is not limited for this presumed reason, and conforms to the objective elements described in the claims section.

As the resin within the cavity cools and shrinks, it becomes difficult to apply pressure to the resin in distant parts of the gate. If the pressure that is applied to the resin falls below the pressure that is being applied to the back surface of the resin at an opening in a flow channel of a pressurized fluid, the pressurized fluid begins to infiltrate between the back surface. of the molded product and the cavity surface. This causes the rear surface of the molded product to separate from the surface of the cavity. As a result, the back surface of the molded product does not end with the surface of the cavity. However, the back surface of the molded product does not affect the performance of the product. The pressure near the back surface of the molded product decreases as the resin shrinks. Thus, low pressure fluid can easily infiltrate between the rear surface of the molded product and the surface of the cavity. As the resin shrinks, the pressure near the design surface of the molded product also decreases. However, the fluid under pressure enters the space between the back surface of the molded product and the cavity surface before the design surface separates from the cavity surface, and the back surface of the molded product separates from the cavity surface before the design surface separates from the cavity surface.

After the back surface of the molded product separates from the cavity surface but before the shape of the design surface of the molded product solidifies, pressure is continuously applied to the molten resin from the gate to prevent it from the design surface of the molded product separates from the cavity surface. During this process, the back surface of the molded product, which has been separated from the cavity surface, can shrink so that it moves towards the design surface and becomes thinner. Accordingly, although the pressure to be applied continuously to the molten resin from the gate is adjusted so that it is less than that required in conventional technologies, it is possible to prevent the design surface of the molded product from separating from the surface. of the cavity.

It is preferable to simultaneously start the pressure application stage and the fluid injection stage. It is preferable to start simultaneously the step of applying pressure to the molten resin and the step of fluid injection immediately after completing the step of injection of molten resin. In this case, no unnecessary molding time is required. However, it is also possible to have an interval between the molten resin injection stage and the pressure application stage.

Alternatively, it is also possible to start the fluid injection step without waiting for the filling of the cavity with the molten resin to complete. That is, it is preferred that the fluid injection step is started during the molten resin injection step. In this case, the pressure application step is started after the fluid injection step is started.

When a molten resin is being injected into a cavity, the molten resin flows into the cavity, with the tip of the molten resin moving. If the fluid injection stage is to be started without waiting for the molten resin injection stage to be completed, it is preferable to start the fluid injection stage after the tip of the molten resin flowing into the cavity has passed through the flow channel opening. In this case, it is preferable to start the fluid injection step after the tip of the molten resin has passed through the opening but before the molten resin begins to shrink. In this case, it is possible to allow the molten resin to continue to solidify, the rear surface of the molded product being separated from the surface of the corresponding cavity. This allows the design surface to be finished to the desired shape.

The cavity surface facing the rear surface of the molded product can be formed by combining multiple divided molds in some cases. Consequently, lumps sometimes occur in these split molds. If there are lumps on the surface of the cavity, even on the back surface, the thickness of the molded product changes sharply. As a result, the shrinkage does not occur uniformly. So even when the design surface of the cavity is smooth, deformation corresponding to the bumps on the back surface may appear on the design surface of the molded product. With the present injection molding method, the divided mold lumps on the back surface side of the molded product do not affect the thickness of the molded product. Therefore, the deformation can be suppressed.

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After finishing the step of applying pressure to the molten resin, it is preferable to continue the fluid injection step. If the fluid injection step continues, although the resin shrinks on the design surface side of the molded product, this shrinkage will not cause the design surface to separate from the cavity surface. That is, since a fluid is injected from the flow channel, it is possible to maintain a state in which the design surface is not easily separated from the cavity surface. Therefore, the time of applying pressure to the resin can be significantly reduced, resulting in a significantly shorter cycle time.

It is preferable to create a state in which the design surface is not separated from the cavity surface both by the pressure applied in the pressure application stage and by the pressure applied in the fluid injection stage. Even when the pressure in the pressure application stage and the pressure in the fluid injection stage are both low, it is preferable to use pressure levels that are sufficient to prevent the design surface from separating from the cavity surface to through a compound effect between these pressure values.

The pressure of the resin to be applied in the pressure application stage may be a pressure that would not be sufficient to prevent the design surface of the molded product from separating from the cavity surface, unless the injection stage fluid run simultaneously. Also, the fluid pressure to be applied in the fluid injection step may be a pressure that would not be sufficient to prevent the design surface of the molded product from separating from the cavity surface, unless the step of pressure application runs simultaneously. In the pressure application stage, the present technology can use a pressure that is too low to be able to prevent the design surface of the molded product from separating from the cavity surface unless the fluid injection stage is run simultaneously. . Furthermore, it is sufficient to inject a fluid having a pressure that is too low to prevent the design surface of the molded product from separating from the cavity surface unless the pressure applying step is executed simultaneously. Taking advantage of the characteristics of both stages, it is possible to use low pressure for both.

The present technology can also be implemented in an injection molding apparatus. This injection molding apparatus uses an injection mold having a gate, a cavity connected to the gate, and a flow channel provided with an opening that opens into the cavity. The opening opens towards the rear surface of the molded product. The injection molding apparatus is provided with a pressure applying device for continuously applying pressure from the gate after filling the cavity with the molten resin and a fluid injection device for injecting a fluid from the flow channel.

According to the present injection molding apparatus, even when both the pressure to be applied to the molten resin and the pressure of the fluid to be injected from the flow channel are reduced, the shape of the surface of the molded product can be formed with the desired shape. Therefore, the required pressure resistance of the injection mold can be reduced. As a result, the injection mold can be reduced in size and the cost of injection molding can be lowered.

The injection mold may have a plug arranged in the opening. The plug prevents molten resin from entering through the opening. The plug referred to in this case prevents the passage of the molten resin, but allows the passage of a fluid having a lower viscosity level. Such a plug is normally used to degas a mold, etc.

To injection mold a molded product having a hole, an injection mold having a columnar area is used to form the hole in the molded product. When the columnar area is formed within the cavity, when a molten resin is injected into the cavity from the gate, the molten resin that has passed to the right side of the columnar area and the molten resin that has passed to the left side of the columnar zone merge with each other on the downstream side of the columnar zone. In this case, it is preferable to form the opening of the flow channel in the vicinity of the boundary where the molten resin is fused.

At the boundary where two or more resin streams merge, a molding defect called a "weld line" tends to occur. This molding defect tends to occur more frequently if the pressure to be applied continuously to the molten resin after the cavity has been filled with the molten resin is high. This is because the higher the pressure to be applied continuously to the molten resin, the greater the pressure difference between the left and right side of the columnar zone. As a result the boundary tends to shift. When the boundary is shifted, the weld line tends to be produced more easily. To prevent the generation of the weld line, it is effective to lower the pressure to be applied continuously to the molten resin. However, doing so causes the design surface of the molded product to separate more easily from the cavity surface. There is no technology available that prevents weld line generation while ensuring surface shape accuracy. Manufacturers suffer from this problem. The apparatus of the present invention solves this problem.

If the flow channel for the fluid is provided in the vicinity of the boundary where two or more flows of molten resin merge, it is possible to decrease the pressure to be applied continuously to the molten resin to ensure precision of the shape of the design surface. As a result, the generation of the welding line can be prevented.

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Furthermore, it is preferable that the fluid injection device begins to inject the fluid after a tip of the molten resin flowing into the cavity has passed through the opening of the flow channel.

This injection molding apparatus can allow the molten resin to solidify as long as the rear surface of the molded product separates from the surface of the corresponding cavity. The design surface can be finished to the desired shape. Although there are lumps on the surface of the cavity facing the rear surface of the molded product, it is possible to ensure that no deformation appears on the design surface of the molded product.

Preferred embodiments of the present technology are explained below .

(1) An opening of a flow channel is provided in the terminal areas of an injection mold, in which a molten resin cannot easily reach when it is being injected into a cavity of an injection mold from a gate.

(2) The openings of a flow channel are dispersed at positions corresponding to a rear surface of a molded product.

(3) A fluid under pressure is injected towards the rear surface of the molded product before raising the pressure of the injected resin in the terminal regions of the cavity by the step of applying pressure to the resin.

(4) A fluid under pressure is injected towards the rear surface of the molded product, after raising the pressure of the injected resin in the terminal areas of the cavity by the step of applying pressure to the resin, and the pressure subsequently drops due to to cooling.

(5) A fluid under pressure is injected towards the rear surface of the molded product, without waiting for the cavity to fill with the molten resin.

(6) The moment at which the molten resin that has been injected into the cavity passes through the opening of the flow channel is measured in advance, and the injection of the pressurized fluid begins when that moment has passed.

(7) The fluid under pressure is air under pressure.

(8) Air from an air supply already provided within a factory is used as pressurized air. No need for new equipment.

Embodiment 1

Embodiment 1 is explained below with reference to the drawings. Fig. 1 is a perspective diagram of a molded product that has been formed using the injection molding technology of the present embodiment. Fig. 2 is a schematic cross-sectional diagram of the injection molding apparatus of the present embodiment. Fig. 3 is a diagram comparing the injection molding method of the present embodiment with a conventional injection molding method. Fig. 4 is a process diagram for the injection molding method of the present embodiment. Fig. 5 is a diagram illustrating the pressure required in the injection molding method of the present embodiment compared to that of a conventional example.

The molded product 10 illustrated in Figure 1 is a molded resin product that is injection molded by the injection molding apparatus 18 illustrated in Figure 2. A typical example is a resin molded bumper for an automobile.

In the molded product 10, a surface 12 is a design surface (front surface) that must be precisely finished with the desired surface shape, and a surface 14 is a rear surface whose surface shape is not critical. A through hole 16, running through from the front to the rear, is formed in the molded product 10.

Figure 2 illustrates a cross section of a mold 20 of the injection molding apparatus 18 in the position corresponding to the line II-II in the molded product in Figure 1. The mold 20 comprises a female mold 22 for molding the surface 12 of the molded product 10 and a male mold 24 for molding the rear surface 14 of the molded product 10. The shape of a cavity 26, which is formed by combining the female mold 22 and the male mold 24, corresponds to the shape of the molded product 10 to be obtained. That is, the surface 22a of the cavity of the female mold 22 corresponds exactly to the design surface 12 of the molded product 10. The surface 24a of the cavity of the male mold 24 approximately coincides with the rear surface 14 of the molded product 10. A columnar zone 24b extending from the cavity surface 24a to the cavity surface 22a is formed in the male mold 24. The shape of the columnar area 24b corresponds to the shape of the through hole 16 to be formed in the molded product 10.

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A gate 28, connecting the outside of the female mold 22 with the cavity surface 24a, is formed in the female mold 22. A nozzle 30 of a secondary channel 32 is installed at the location where the gate 28 opens to the outside of the female mold 22. Gate 28 and secondary channel 32 constitute a resin injector 34. The secondary channel 32 pushes the molten resin out at a predetermined pressure. The secondary channel injects molten resin into cavity 26 from gate 28.

Two fluid injection flow channels 24d and 24f are formed in the male mold 24. Fluid injection flow channels 24d and 24f connect the outside of the male mold 24 with the cavity surface 24a. The fluid injection flow channels 24d and 24f open towards the cavity surface 24a, and their openings 24c and 24e are provided in the terminal areas where the molten resin cannot easily reach when it is being injected into the chamber. cavity 26 from gate 28. Openings 24c and 24e are provided with vents 36c and 36e. Vent holes 36c and 36e have small holes with diameters that do not allow molten resin to pass through but allow air to pass through.

Furthermore, a third fluid injection flow channel 24g is provided. The opening of the fluid injection flow channel 24g is formed at a position where the molten resin that has passed to the right side of the columnar zone 24b and the molten resin that has passed to the left side of the columnar zone 24b are fused. to each other on the downstream side of the columnar zone 24b. Columnar zone 24b is used to form through hole 16. The opening of the fluid injection flow channel 24g is also provided with a vent hole.

A fluid tube 38 is connected to the locations where the fluid injection flow channels 24d, 24f and 24g open toward the outside of the male mold 24. One end of the fluid tube 38 is connected to a pump 42. The pump 42 increases the pressure and delivers a fluid. A valve 40 for adjusting the flow rate and pressure of the fluid is provided in the middle of the fluid tube 38. Valve 40 regulates the pressure of the air supplied by pump 42 to 0.5 MPa. A controller not shown in the figure controls the degree of opening of the valve 40. The fluid under pressure (air in this embodiment) that is sent by the pump 42 is regulated by the valve 40 at 0.5 MPa. Pressurized fluid is injected into cavity 26 through fluid tube 38 and fluid injection flow channels 24d, 24f, and 24g. The openings of the fluid injection flow channels 24d, 24f and 24g are provided on the side of the male mold 24 and send the pressurized air which has been set at 0.5 MPa towards the rear surface of the molded product.

In addition, a group of grooves extending in a radial pattern from the opening of the fluid injection flow channels 24d may be formed on the surface of the male mold 24. Also, grooves may be formed extending in a radial pattern from the opening of fluid injection flow channels 24f and 24g. The grooves draw air under pressure into a wide area of ​​the rear surface 14 of the molded product 10. This causes the rear surface 14 of the molded product 10 to separate from the male mold 24 rapidly.

Instead of forming the grooves, a molding lubricant can be used. The molding lubricant can be applied to the surface of the male mold 24. The rear surface 14 of the molded product 10 can be detached from the male mold 24 easily. If a molding lubricant is also used for the female mold 22, it is preferred that the molding lubricant for the male mold 24 is different from the molding lubricant for the female mold 22. A molding lubricant that can separate the molded product 10 from the male mold 24 before the female mold 22 is used as a molding lubricant for the male mold 24.

As described above, it is preferred to adopt means to separate the rear surface 14 of the molded product 10 from the male mold 24 easily. In addition to the above examples, the following means can be adopted. That is, the male mold 24 can be made of a low thermal conductivity material, and the female mold 22 can be made of a high thermal conductivity material. This also causes the rear surface 14 of the molded product 10 to separate from the male mold 24 before separating from the female mold 22.

The process diagram of the injection molding method based on the above-mentioned injection molding apparatus 18 will be explained below, referring to Fig. 4.

First, female mold 22 and male mold 24 combine to close mold 20. At this time, valve 40 on fluid injector 44 is kept closed. From this state, a molten resin is pushed out of the secondary channel 32 of the mold injector 34 at an injection pressure of approximately 50 MPa. Molten resin that is pushed out is injected into cavity 26 through nozzle 30 and from gate 28. In the vicinity of columnar zone 24b, the molten resin passes to the right and left sides of columnar zone 24b and merges with the downstream side of columnar zone 24b.

When the cavity 26 has been filled with the molten resin, the injection pressure of the secondary channel 32 is lowered to 20 MPa, and the process proceeds to the step of maintaining the pressure of the molten resin.

When the filling of the cavity 26 with the molten resin ends, that is, when the pressure maintenance step is started, the valve 40 of the fluid injector 44 opens. Air pressure increased to 0.5 MPa is sent to fluid injection flow channels 24d, 24f and 24g.

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The relationship between the pressure that is applied to the molten resin within the cavity 26 from the gate 28 and the pressure of the pressurized fluid that is applied to the fluid injection flow channels 24d, 24f and 24g produces the phenomenon described above. .

The pressure of the molten resin within the cavity 26 is higher than the pressure of the pressurized fluid when the pressurized fluid injection step is initiated. The pressure of the resin decreases as the molten resin solidifies, and when the pressure of the resin falls below the fluid pressure, the fluid under pressure is injected onto the rear surface side 14 of the molded product 10.

Since fluid under pressure is injected onto the rear surface 14 of the molded product 10 from the fluid injection flow channels 24d, 24f, and 24g, the design surface 12 of the molded product 10 does not separate from the surface 22a of the cavity.

Molten resin that has been injected into cavity 26 cools and shrinks. During this process, fluid under pressure is injected onto the rear surface 14 of the molded product 10. At the same time, the pressure of about 20 MPa is applied continuously from the secondary channel 32. As shown in Fig. 5, when the pressure of about 20 MPa is applied continuously from the secondary channel 32, the pressure of the resin in the end zones becomes about 8 MPa.

This resin pressure is about half that required in conventional resin pressure holding technology indicated as conventional example 1 in Fig. 5. This resin pressure in this embodiment is low.

Figure 3 is a diagram comparing the injection molding technology of the present embodiment with a conventional injection molding technology. Figure 3 (a) corresponds to a technology that prevents the design surface of the molded product from separating from the surface of the cavity simply by continuously applying pressure P1 from gate 28. This technology does not guarantee that the back surface of the molded product will separate from the cavity surface first, and the design surface of the molded product cannot separate from the cavity surface first. In such a case, the composite force resulting from shrinkage of the molded product on both its design and rear sides becomes the force that separates the design surface of the molded product from the cavity surface. To counteract this force and prevent the design surface of the molded product from separating from the surface of the cavity, it is necessary to increase the pressure P1, which is to be applied continuously to the molten resin from the gate 28. As shown in Figure 5, a high make-up pressure is required which can produce a pressure of about 40 MPa in the gate area (16 MPa in the end areas).

Figure 3 (b) corresponds to a technology that prevents the design surface of the molded product from separating from the cavity surface simply by injecting a fluid under pressure towards the rear surface of the molded product. With this technology, it is necessary to push the molded product from the rear surface against the front surface with a fairly large pressure. As shown in figure 5, it is necessary to push the molded product from the back surface against the design surface with a pressure of about 18 MPa.

Figure 3 (c) corresponds to the present embodiment and continues to apply the pressure P1 to the molten resin and at the same time injects air under pressure towards the rear surface 14 of the molded product 10. Even when the air injection pressure is low, it is ensured that the rear surface of the molded product will separate from the cavity surface 24a before the design surface of the molded product separates from the cavity surface 22a. The pressure P1 to be applied to the molten resin can be lowered. As shown in figure 5, only a pressure of about 20 MPa is required in the gate zone (8 MPa in the end zones).

These numerical values ​​are presented as examples only and should not be considered as limiting the technical scope of the invention. Also, the above explanation is presented to explain the alleged motive. The technology of the present invention is not limited for this supposed reason. Strictly speaking, the technology of the present invention is a technology that simultaneously executes a stage that continuously applies pressure to the molten resin from gate 28 and a stage that injects a fluid under pressure from a flow channel 24d, 24f, 24g. .

The molten resin pressure maintenance step can be completed prior to the pressurized fluid injection step. In the present embodiment, the implementation of the pressurized fluid injection step reduces the force that attempts to cause the design surface 12 of the molded product 10 to separate from the cavity surface 22a. Although the resin pressure maintenance step is completed in a phase where the strength of the design surface 12 of the molded product 10 is relatively low, it is possible to prevent the design surface 12 of the molded product 10 from separating. of the cavity surface 22a. Therefore, the pressure holding time of the resin can be shortened significantly.

Since the pressure holding time of the resin can be significantly shortened, subsequent steps can be executed earlier. In figure 4, the dotted lines indicate the moments of execution of the process based on the conventional technique. The present embodiment can speed up the time for opening the mold and thus can speed up the time for disconnecting the product. As a result, the cycle time is shortened and the efficiency of series production is improved.

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The present embodiment can almost halve the pressure required in the pressure maintenance stage of the molten resin. Therefore, the boundary, in which the molten resin that has passed to the right side of the columnar zone 24b and the molten resin that has passed to the left side of the columnar zone 24b are fused together on the downstream side of the zone 24b columnar, does not change during the resin pressure maintenance stage. It is possible to mold a product in which a resin melting boundary (weld line) is not very visible. To achieve this effect, it is preferable to form the fluid injection flow channel 24g in the vicinity of the melting boundary.

Furthermore, it is also possible to simultaneously execute the step of continuously applying pressure to the molten resin from the gate 28 and a step of mechanically separating the rear surface 14 of the molded product 10 from the cavity surface 24a. These steps are performed after filling the cavity 26 of the injection mold 20 with the molten resin but before the mold 20 is opened. A removal pin or the like may be used to separate the rear surface 14 of the molded product 10 from the cavity surface 24a before the design surface 12 of the molded product 10 is separated from the cavity surface 22a.

Embodiment 2

Embodiment 2 is explained below with reference to the drawings. In Embodiment 2, an injection molding apparatus 50 illustrated in Fig. 6 is used to mold molded product 10 having the same shape as in Embodiment 1 (see Fig. 1). The injection molding apparatus 50 comprises a mold 51 and a pressurizer 52. Figure 6 shows only the part of the mold 51 that molds an end zone of the molded product 10. The mold 51 comprises a female mold 53 and a male mold 54. Male mold 54 has a core 59. A cavity 55 is formed by combining female mold 53 and male mold 54. The cavity surface 56 of the female mold 53 corresponds to the design surface 12 of the molded product 10. The cavity surface 57 of the male mold 54 approximately coincides with the rear surface 14 of the molded product 10. To open the mold 51, the female mold 53 and the male mold 54 are vertically separated.

A fluid injection flow channel 58 is formed in the male mold 54. One end of the fluid injection flow channel 58 opens toward the cavity surface 57 at an opening 60. The other end 61 of the fluid injection flow channel 58 opens toward the outside of the male mold 54. The opening 60 is provided with a ventilation hole 62. The vent hole has holes to link cavity 55 with fluid injection flow channel 58. The size of this link hole is adjusted so that resin does not flow into fluid injection flow channel 58 when a molten resin is injected into cavity 55.

Although not shown in Figure 6, the injection molding apparatus 50 of Embodiment 2, like the injection molding apparatus 18 of Embodiment 1, has a resin injector 34 comprising a secondary channel 32, a nozzle 30 and a gate 28.

The pressurizer 52 is provided with an autocoupler 63, a fluid tube 64, a solenoid valve 70, a regulator 68, a filter 67, a timer 71, and a molding controller 72. The autocoupler 63 is attached to the outside of the male mold 54. The autocoupler 63 is connected to the fluid injection flow channel 58. One end 65 of fluid tube 64 is connected to autocoupler 63. Factory air is supplied as fluid under pressure to the other end 66 of fluid tube 64. Filter 67, regulator 68, and solenoid valve 70 are connected to fluid tube 64. Filter 67 removes foreign substances contained in the factory air. Regulator 68 regulates the factory supplied air at the predetermined pressure (eg, 0.5 MPa). Solenoid valve 70 opens and closes fluid tube 64. When the solenoid valve 70 is open, a pressurized fluid whose pressure has been regulated by the regulator 68 is supplied to the fluid injection flow channel 58 of the mold 51. The solenoid valve 70 is connected to the timer 71, which at it is in turn connected to the molding controller 72. The molding controller 72 exhaustively controls the injection molding apparatus 50.

The mold controller 72 issues an injection start signal to the timer 71 when injection of a molten resin into the mold 51 is started. In addition, the mold controller 72 issues a mold open signal to the timer 71 when it starts. an opening action of the mold 51. In addition, the mold controller 72 issues a close-mold signal to the timer 71 when a closing action of the mold 51 is initiated.

Based on the injection start signal, the mold open signal and the mold close signal that have been input, the timer 71 outputs an open signal or close signal to the solenoid valve 70. The time when the timer 71 issues the open / close signal is described in detail later.

The step of molding the molded product 10 by means of the injection molding apparatus 50 is explained below, with reference to FIG. 7. Changes in pressure within the cavity 55 are also explained below. The lower half of Figure 7 is a molding process diagram. The upper half of Figure 7 is a graph showing the pressure within cavity 55. The horizontal axis of the molding process diagram indicates time (seconds). The time on this horizontal axis is also applicable to the graph showing the pressure inside cavity 55. The curve X shown inside the graph showing the pressure inside cavity 55 corresponds to the internal pressure of the cavity near the gate 28 (see Figures 1 and 2). The triangles assigned the letters A to D in Figure 7 will be used later in the detailed explanation of when to start or stop the injection of a pressurized fluid.

ES 2 335 784 T3

As shown in Fig. 7, to mold the molded product 10, a step of closing the mold 51 is first carried out by combining the female mold 53 and the male mold 54. When the mold close step is started, the mold close signal is output to the solenoid valve 70. As a result, the solenoid valve 70 closes. Therefore, pressurized air is not supplied to the fluid injection flow channel 58 of the mold 51. Next, a step of injecting a molten resin from the gate 28 into the cavity 55 is carried out.

The injected molten resin begins to fill the cavity 55. The internal pressure of the cavity (curve X) near the gate 28 increases rapidly to approximately 60 (MPa) when the injection is started. Even when molten resin is injected into cavity 55, its pressure does not immediately propagate in the vicinity of opening 60 of fluid injection flow channel 58. Therefore, it is near the end of the injection stage that the pressure (curve Y) in the vicinity of the opening 60 begins to increase.

Molten resin injected flows into cavity 55. Figure 8 illustrates the state before the tip (leading edge) 75 of molten resin 74 injected into cavity 55 passes through opening 60 of channel 58 fluid injection flow. Hereinafter, the tip 75 of the molten resin 74 is referred to as "molten front 75". Figure 9 illustrates the state immediately after the molten front 75 of the molten resin 74 has passed through the opening 60 of the fluid injection flow channel 58.

The timer 71 counts the elapsed time since the mold close signal was input from the mold controller 72. Then, the timer 71 issues an open signal to the solenoid valve 70 when the molten front 75 of the resin 74 has passed through the opening 60 of the fluid injection flow channel 58. This moment is indicated by triangle B in Figure 7, and will hereinafter be referred to as "injection moment". The injection moment has been predetermined by estimating the moment when the molten front 75 passes through the opening 60 using the measurement data on the pressure in the cavity surface 57 near the opening 60 and the results of the analysis. fluid dynamics, within cavity 55, resin 74, etc. It is also possible to start counting the time when the injection start signal is input, and output the open signal to the solenoid valve 70 based on this counted time.

When the solenoid valve 70 is opened at the time of injection, a pressurized fluid in the form of air is supplied to the fluid injection flow channel 58 and the fluid injection step begins. At this time, the resin 74 near the opening 60 has not solidified. Air is injected from the vent hole 62 towards the rear surface of the resin 74, which has not solidified. This step causes the back surface of the resin 74 to separate from the cavity surface 57.

Although only one is shown in Figure 6, multiple openings are actually provided for injecting a fluid into cavity 55 at cavity surface 57. The timing of a fluid injection into each port is individually adjusted by a solenoid valve. This solenoid valve is installed in the fluid tube linked to each opening and is controlled by timer 71.

As shown in Fig. 7, after completion of the molten resin injection step, the step passes to the molten resin pressure maintenance step ("pressure maintenance step"). A cooling stage is also started in conjunction with the pressure maintenance stage, and the decreasing temperature within cavity 55 favors solidification of resin 74. As a result of the fluid injected from the vent hole 62, the resin 74 solidifies while the rear surface of the resin 74 is pulling away from the cavity surface 57. Even after the pressure maintenance stage has ended, the fluid injection stage (air injection) and the cooling stage continue, and these two stages are subsequently terminated simultaneously.

The internal pressure of the cavity near gate 28 (curve X) drops rapidly as the process moves to the pressure holding stage. The internal pressure of the cavity near the gate 28 is maintained at approximately 35 (MPa) until the cooling stage ends. The internal pressure of the cavity near opening 60 (curve Y) continues to increase even after the pressure maintenance stage starts, it reaches its maximum point (at approximately 10 (MPa)) midway through the pressure maintenance stage. pressure, and then drops. The internal pressure of the cavity near the opening 60 returns to zero upon completion of the pressure holding step. Thus, the internal pressure of the cavity near the opening 60 exceeds the pressure (0.5 (MPa)) of the pressurized fluid once. However, even though the internal pressure of the cavity near the opening 60 exceeds the pressure (0.5 (MPa)) of the fluid under pressure, the back surface of the resin 74 soon separates from the cavity surface 57 due to that the resin 74 shrinks due to cooling and the pressure of the resin becomes less than the pressure of the fluid under pressure.

Figure 10 illustrates the state of resin 74 when the fluid injection step is complete (indicated by triangle D in Figure 7). The rear surface of the resin 74 has been separated, but the front surface of the resin is in fixed contact with the cavity surface 56 of the female mold 53. As shown in Figure 6, even when there is a step 69 between the core 59 and the male mold 54, since solidification continues with the back surface of the resin 74 moving away from the step 69, no bulging area is formed in the rear surface of resin 74 due to step 69. Since no bulging area is formed on the rear surface of resin 74, design surface 12 is not affected at all (i.e., no bulging occurs).

ES 2 335 784 T3 deformation corresponding to a bulging area in the design surface 12). Therefore, the design surface 12 of the molded product 10 is correctly molded.

When the fluid injection stage and the cooling stage are completed, the timer 71 issues a close signal to the solenoid valve 70. When solenoid valve 70 closes, the supply of pressurized fluid to cavity 55 stops. After completion of the fluid injection stage and the cooling stage, the process proceeds to the mold opening stage to open the mold 51. Figure 14 illustrates the state in which the mold 51 has been opened.

Finally, a product disconnection step is executed to disconnect (remove) the molded product 10 from the mold 51.

As explained above, by injecting the fluid towards the back side of the resin 74 immediately after the molten front 75 of the resin 74 has passed through the opening 60 (at the time of injection), it is possible to mold a product 10 molded having an excellent design surface 12. In contrast, if a fluid is injected into cavity 55 before the molten front 75 of resin 74 has passed through aperture 60 (indicated by triangle A in Figure 7), the fluid is blown front 75 cast as shown in FIG. 11. Consequently, flow marks are generated in the molded product 10.

As the cooling step proceeds, the resin 74 that has been injected into the cavity 55 shrinks during the solidification process. Injection of the fluid towards the rear surface of the resin 74 once the cooling stage has started (triangle C in FIG. 7) causes the design surface 12 of the molded product 10 to deform. That is, injection of the fluid after the resin 74 has begun to shrink causes the design surface 12 to deform. Specifically, as shown in Figure 12, deformations 77 in the design surface 12 and the back surface 14 of the molded product 10 are generated if the shrinkage occurs before the fluid has sufficiently entered the back surface side of resin 74. Although the injection of the fluid begins immediately after the molten front 75 of the resin 74 has passed through the opening 60 (that is, at the time of injection, indicated by triangle B in Figure 7), if the fluid injection stops prematurely (eg triangle C in figure 7) while resin 74 is still in the solidification process, molded product 10 will not form properly. More specifically, as shown in FIG. 13, the range F in which the design surface 12 of the molded product 10 can be correctly molded (the range in which the fluid injection is effective) becomes narrow.

The inventor has tried to mold the molded product 10 while varying the pressure holding time and the pressure within the cavity 55, the fluid being injected towards the back side of the resin 74. Figure 15 shows the results. The horizontal axis in figure 15 corresponds to the pressure holding time. The vertical axis corresponds to the pressure (MPa) within the terminal zone (near the opening 60) of the cavity 55. Note that this internal cavity pressure was measured in the pressure hold state.

In Figure 15, O indicates a point where the molded product 10 was correctly molded. Mark X with "1" indicates a point where burrs occurred in the molded product. Mark X with "2" indicates a point where voids occurred in the molded product. Mark X with "3" indicates a point where deformation occurred in the molded product 10. In other words, the molded product 10 cannot be formed correctly in the J, K, or L regions.

On the contrary, it is possible to correctly mold the molded product 10 if the pressure holding time and the internal pressure of the cavity are combined in the region G indicated with thick hatch lines and the region H indicated with thin hatch lines.

When no fluid is injected to the back surface of the resin 74, as in the conventional example, the molded product 10 can only be correctly molded in the G region. That is, with conventional technology, a minimum of 8 (seconds) is required. as pressure hold time. On the contrary, the technology of the present invention can correctly mold the molded product 10 even when the pressure holding time is shortened to 3 (seconds). Since a shorter pressure holding time shortens the molding time, a greater number of products can be molded per unit time. Furthermore, while conventional technology requires an internal cavity pressure of at least 20 (MPa), the technology of the present invention can correctly mold the molded product 10 even when said pressure is reduced to 10 (MPa). Since the internal pressure of the cavity can be lowered, it becomes possible to mold larger molded products even though the clamping pressure of the mold is not increased.

The numerical values ​​mentioned above are presented only as examples and should not be considered as limiting the technical scope of the invention. Furthermore, the above explanation is presented to explain the alleged reason, and the technology of the present invention is not limited by this alleged reason.