JP5114827B2 - Molding method of resin molded products - Google Patents

Description

  The present invention relates to a resin molded product in which various parts are insert-molded in a resin, and further relates to a molding method thereof.

  In the field of resin molded products, insert molding of electronic components and mechanical components is widely performed, and by incorporating these components integrally, various functions can be added to the resin molded products. Here, insert molding requires only placing the parts in the mold and injecting the resin, making it possible to easily produce resin molded products that integrate electronic parts and mechanical parts, reducing man-hours. This is an effective method for reducing costs.

  In recent years, with the progress of miniaturization of electronic devices and the like, miniaturization is required for components incorporated in the device, and the resin molded product is no exception. In order to reduce the size of the resin molded product, it is necessary to reduce the resin thickness of the molded product as much as possible. In the molding, first, ensuring the strength is an issue.

From such a situation, an attempt has been made to ensure the strength of the resin molded product by adding a filler to the resin, for example (see Patent Document 1 and the like). Patent Document 1 relates to molding of a lens holder. The lens holder is molded with a resin containing filler having shape anisotropy, and the filler is oriented in the axial direction of the central axis. Thereby, it is said that it is possible to provide a lens holder that is excellent in dimensional accuracy and that is thin and light but has high mechanical rigidity.
JP-A-6-27360

  By the way, in the insert molding, since the viscosity of the resin at the time of insert molding is high, a large force is applied to the insert part due to the flow of the resin, and as a result, the part often rises. Normally, in order to prevent displacement of the insert parts, for example, a guide is provided in the mold, and the insert parts are arranged here to perform molding. However, when a guide that simply supports one side of the insert parts is arranged. As a result of the stress due to the viscosity of the resin being applied to the insert part, the insert part rises from the guide.

  When the above-described lifting of the insert part occurs, a problem of degassing when a thermosetting resin is used becomes a serious problem. When a thermosetting resin is used, a reaction gas is generated as the resin hardens. Normally, this reaction gas is used along the guides or the like, for example, using a micro space between the insert part and the mold. Escaped to the outside. Here, when the insert part is lifted, a film is formed by the encircling resin, and a minute space along the guide is closed by the film. As a result, it becomes impossible to vent the reaction gas, and dissociation occurs between the resin and the insert part, or troubles such as gas accumulation and deformation of the resin causing blisters and cracks occur.

  Further, even if the above-described degassing failure due to the floating of the component does not occur, for example, when a rare earth metal magnet or the like is used as the component, there is a possibility that the degassing failure due to the thermal expansion coefficient may occur. For example, a rare earth metal magnet has a negative coefficient of thermal expansion in a direction orthogonal to the orientation direction, and expands in this direction during cooling. At this time, since the surrounding resin shrinks, it is difficult to form a gap between the rare earth metal magnet and the resin, and it is difficult to sufficiently discharge the gas.

  In order to prevent the component from lifting up, for example, a fixing pin is inserted from the outside, and the insert component is sandwiched between the fixing pin and the guide and fixed so that the component does not lift up due to the stress of the resin. is there.

  However, when fixing the insert part by inserting a fixing pin from the outside, very high pressure is applied to the inside of the mold, and it is necessary to devise measures that do not hinder the flow of the resin so that the resin is evenly filled Therefore, the implementation is accompanied with great difficulty.

  For example, when the insert part is fixed with the tip of the fixing pin, it is necessary to apply a large force against the pressure applied to the inside of the mold. However, since the insert part has a certain amount of dimensions, excessive force is required. May add to the insert and damage it.

  In addition, degassing is eventually performed using a gap between the guide or the fixing pin and the resin or component, but as described above, it is not sufficient. Furthermore, when an insert part is fixed by inserting a fixing pin from the outside, a large opening (hole) is formed in the resin portion after the fixing pin is pulled out, which may cause a decrease in strength. In particular, the fixing pin may be provided at the thinnest portion of the resin, and after molding, stress is suddenly released at the opening, and cracks and the like are likely to occur. When these cracks occur, they cannot be provided as a product, and therefore, a decrease in yield due to the occurrence of defective products becomes a serious problem.

  The present invention has been proposed in view of such a conventional situation. That is, the present invention has an object to provide a resin molded product that can reliably vent the reaction gas when insert-molding a part and does not cause swelling or deformation, and a molding method therefor. And

  The present inventor has intensively studied for a long time to achieve the above object. As a result, when insert molding a part, it came to the conclusion that the degassing of a reactive gas was promoted remarkably by using the negative pressure by pulling out a core pin.

The present invention has been devised based on such knowledge. That is, in the molding method of the present invention, when a component placed in a cavity of a mold is insert-molded with a thermosetting resin, a core pin that contacts the surface of the component is provided on the mold, and the resin is placed in the mold. After the resin has been cured, the core pin is pulled out before the curing is completely completed.

  In insert molding, when a thermosetting resin is used as the resin, a reaction gas is generated. If the degassing is not sufficient, dissociation occurs between the resin and the parts, and troubles such as gas accumulation and deformation of the resin occur. In the present invention, degassing is promoted by utilizing a negative pressure (reduced pressure state) due to drawing of the core pin. That is, the space generated by the operation of pulling out the core pin is in a reduced pressure state compared to the surroundings. As a result, the reaction gas gathers in this space, and the degassing is promoted.

  According to the present invention, it is possible to reliably vent the reaction gas, and it is possible to provide a high-quality resin molded product that is free from blisters and deformation caused by a gas vent failure. Further, in the present invention, the fixing pin can be minimized, and depending on the case, there is no need for the fixing pin.

  Hereinafter, a resin molded product to which the present invention is applied and a molding method thereof will be described in detail with reference to the drawings. In addition, although the actual resin molded product has various shapes and the arrangement of parts and the like are various, in this embodiment, the basic concept will be described using the simplest model.

  FIG. 1 shows a schematic configuration of a resin molded product 1 to which the present invention is applied. 1A is a plan view, FIG. 1B is a side view, and FIG. 1C is a front view.

  This resin molded product 1 is obtained by insert-molding two parts (for example, a rare earth metal magnet) in a resin portion made of, for example, a thermosetting resin. The resin molded product 1 has a structure in which the resin portion is largely divided into two parts, and each of the resin portions 2A and 2B is connected in a casing shape, and each of the divided resin portions 2A and 2B has a structure. Part 3 is insert molded. The component 3 is positioned by a guide provided in the mold, and therefore, a guide hole 4 is formed in the resin portion 2A, 2B corresponding to the guide.

  Moreover, in the resin molded product 1 of this invention, the vent hole 5 is formed corresponding to each said part 3, This is the big characteristic. The degassing hole 5 is for accelerating the degassing of the reaction gas at the time of molding, and is formed so that a part of the surface of the component 3 is exposed. The gas vent hole 5 only needs to have an opening diameter sufficient to promote gas venting, and is preferably formed with a diameter as small as possible.

  The vent hole 5 may be formed so as to overlap with a part of the surface of the component 3, but it is preferable to form the opening shape so as to be within one surface of the component 3. If the gas vent hole 5 is formed so as to protrude from the surface of the component 3, resin pressure is applied to the core pin forming the gas vent hole 5, which may lead to burrs, blockage of the gas vent hole 5, or the like. Moreover, it is preferable to form the said vent hole 5 corresponding to each component 3, Therefore, when there are two or more components 3 to insert, it is preferable to also provide two or more vent holes.

  The resin molded product 1 is provided with the guide hole 4 in addition to the gas vent hole 5, but these openings are preferably arranged only on one surface side of the component 3. For example, if an opening formed by a fixing pin or the like is formed on the opposite side of the guide hole 4 or the gas vent hole 5, there is a possibility that a decrease in strength or generation of cracks may be a problem.

  Here, for example, when insert molding is performed using an upper mold and a lower mold as molds, the resin molded product 1 is normally positioned in the lower mold when the mold is opened after molding. Therefore, the gas staying in the upper part of the resin molded product 1 is released relatively easily by opening the mold. On the other hand, the gas retained in the lower part of the resin molded product 1 is not easily released because it is contained between the lower mold and the resin molded product 1 or between the resin molded product 1 and the part 3 to be inserted. Therefore, when the mold is opened, a sudden pressure change is generated in the upper and lower portions of the resin molded product 1, and the occurrence of blisters and cracks becomes more remarkable. Therefore, in order to eliminate such inconvenience, the core pin (gas vent hole 5) is a mold on the side where the resin molded product 1 is located, in the above-described example, a guide pin for positioning a component when molding the lower mold. It is desirable to be on the surface side where there is an opening (guide hole 4) formed by.

  In the resin molded product 1 having the above configuration, since the gas vent hole 5 is provided, there is no occurrence of blistering, deformation, cracking, or the like due to poor gas venting. Normally, blistering and deformation are likely to occur in a thin resin portion around the part 3, for example, a portion indicated by an arrow in the example shown in FIG. 1, but such trouble is caused by smooth degassing. Can be resolved.

  Next, a method for molding the resin molded product 1 will be described. When molding the resin molded product 1, it is necessary to insert-mold the component. When the component is insert-molded in this way, it is necessary to consider the difference in thermal expansion coefficient between the component and the resin. Since the component to be incorporated and the resin usually have different coefficients of thermal expansion, cracks are likely to occur after integral molding. In particular, in the case of a rare earth metal magnet having anisotropy, the above tendency is remarkable. This is because the thermal expansion coefficient in the direction orthogonal to the orientation direction is negative. When insert molding a rare earth metal magnet, the resin surrounding the rare earth metal magnet shrinks during cooling after integral molding due to the thermal expansion coefficient, whereas the rare earth metal magnet surrounded by the resin expands. To do. As a result, a large stress is generated. Therefore, when the rare earth metal magnet is integrated with another substance such as a resin, it is susceptible to a stress generated when the temperature changes, and therefore, the rare earth metal magnet is liable to crack. Therefore, it is necessary to design the process in consideration thereof. Further, when resin molding is performed, gas may be generated. In this case, the generated gas may not be discharged to the outside due to wraparound of the resin or the like, and may accumulate at the interface between the resin and the magnet. In such a case, at the time of cooling, the resin contracts while the magnet expands, and the interface gas is crushed to generate a high internal pressure. Therefore, it is also necessary to design the process so that the gas can be quickly degassed. The molding method of the present embodiment is an optimized process in consideration of these matters.

  That is, in order to mold the resin molded product 1 in the present embodiment, as shown in FIG. 2, for example, the component 3 is placed in the cavity of a mold 6 having a rectangular parallelepiped shape, and so-called insert molding is performed. FIG. 2A shows a part setting state before resin injection, and a plurality of guides 7 are provided on the bottom surface 6 a of the mold 6, and the parts 3 are placed in the plane of the bottom surface 6 a by these guides 7. Positioning is done in the direction.

  In this example, the guides 7 are provided at four locations corresponding to the four corners of the component 3, and each guide 7 is a rising wall 7 a that supports the peripheral surface of the component 3, for example, as shown in FIG. 3. And a mounting surface 7 b that supports the bottom surface of the component 3. Therefore, the inserted component 3 is positioned in the height direction by the mounting surface 7b of the guide 7, and the movement in the in-plane direction is restricted by the rising wall 7a.

  Further, in the present invention, the core pin 8 for venting gas is installed in the mold 6 so that the venting is smoothly performed during molding. The core pin 8 is a pin with a predetermined diameter and a circular cross section, and can be inserted into and removed from the mold 6 by a hydraulic device 9. The number and diameter of the core pins 8 may be set in consideration of the size of the resin molded product 1, the amount of gas generated, the degree of outgassing from other parts, and the like. A plurality of them may be provided. The device for pressurizing the core pin 8 is not limited to the hydraulic device 9 and may be a device that pressurizes with a spring or the like, for example. Before the resin injection, the core pin 8 is pushed in by the hydraulic device 9 so that the tip of the core pin 8 is at the same height as the mounting surface 7 b of the guide 7.

  In this state, the resin is injected. At this time, since the component 3 is only placed on the placement surface 7b of the guide 7, it can move upward. Therefore, there is a concern that the resin may wrap around due to the floating of the component 3. Due to the wraparound of the resin, the generated gas may be difficult to escape. Therefore, in this embodiment, it is more effective if the flow of the resin 3 is used to prevent the component 3 from being lifted.

  Specifically, in the mold 6, a gate 10 is provided at a position higher than the part 3, and resin is injected therefrom. As described above, when the resin is injected from the gate 10 provided at a position higher than the part 3, the flow of the resin becomes a so-called down flow, and as shown by an arrow in FIG. It becomes a flow. Further, a part of the resin flow passes over the component 3.

  Due to such a resin flow, a force in the direction indicated by the arrow F is applied to the component 3, and as a result, the component 3 is placed on the mold surface 6 a on which the guide 7 of the mold 6 is formed, that is, the placement of the guide 7. It is pressed toward the surface 7b. Therefore, the component 3 does not float when the resin is injected, the positioning state by the guide 7 is maintained, and the component 3 can be molded without positional deviation.

In this case, the height of the resin injection port (gate 10) with respect to the component 3 is important. Specifically, first, the bottom surface of the component 3 whose height is determined by the mounting surface 7b of the guide 7 is used as a reference. If this bottom surface is the reference h ₀ , the position of the top surface of the component 3 is the height h. In this case, it is necessary to provide the gate 10 at a position higher than the height of the center of gravity of the component 3 with the bottom surface as the reference h ₀ . When the component 3 has a vertically symmetrical shape, it is necessary to provide the gate 10 at a position higher than ½ of the height h. If the gate 10 is provided at a position lower than this, the flow of the resin rises with respect to the component 3 and the possibility of the component 3 being lifted increases. Preferably, the gate 10 is provided at a position higher than the height h of the component 3.

  After filling the resin, the core pin 8 is moved backward by operating the hydraulic device 9 as shown in FIG. The timing of retracting the core pin 8 is after the resin has been cured and before the curing is completely completed. If the timing is too early, the uncured resin may flow into the space where the core pin 8 is retracted. There is. Further, if the core pin 8 is pulled out after the resin is completely cured, there is a possibility that a sufficient effect cannot be obtained. Accordingly, it is preferable to retract the core pin 8 at any time between the start of resin cooling and the opening of the mold 6, preferably from the middle of the period until the mold is opened, and further, the mold It is preferable to retract the core pin 8 immediately before opening.

  The core pin 8 may be retracted, for example, by retracting the core pin 8 by a predetermined amount, or may be performed by completely pulling the core pin 8 out of the mold 6. In the former case, the space k is formed by the retreat of the core pin 8 and the inside of the space k is in a reduced pressure state as compared with the surroundings. In the latter case, the reaction gas quickly escapes to the outside from the hole from which the core pin 8 has been pulled out.

  In the present invention having the above-described configuration, any resin material can be used as the resin material constituting the resin molded product, but the effect can be obtained by applying it particularly when a thermosetting resin is used. It can be pulled out. This is because when a thermosetting resin is used for the resin molded product, gas is easily generated, and the effect of degassing is remarkable.

  The above is the basic idea of the molding method of the present invention. In molding, in addition to this, for example, a substantially longitudinal direction of the component 3 is formed so that a resin flow is formed along the longitudinal direction of the component 3. It is preferable to inject the resin. This is because the molding method can prevent blisters and cracks due to the generated gas as described above, but in addition to this, cracks due to the structure of the integrally molded product can be prevented by considering the flow of the resin.

For example, when the component 3 is insert-molded, in a molded resin molded product, the resin thickness of the portion formed along the longitudinal direction of the component 3 is often thin. FIG. 4 shows a typical shape example of a resin molded product when the component 2 is arranged in the mold 6. This resin molded product has resin parts A, B, C, and D corresponding to the four sides of the part 2, and the thicknesses of the resin parts A, B, C, and D are t ₁ , t _{2, respectively.} , T ₃ , t ₄ . Then, t ₁ , t ₂ , t ₃ > t ₄ , and the portion with the smallest resin thickness is defined as a resin portion D. Therefore, the resin part D has the weakest strength in the molded resin product to be molded.

  When a resin molded product having such a shape is molded, for example, as shown in FIG. 5A, when resin is injected from the resin portion C side, the flow of the resin is as indicated by arrows in the figure. That is, the flow of resin injected into the cavity of the mold 6 from the resin part C side is blocked by the component 3 and moves while avoiding the component 3. And about the resin part D, after flowing around the resin part A and the resin part B, the flow of resin arrives. At this time, in the resin portion D, the flow of the resin divided by the component 3 merges, and as a result, a so-called weld is caused at the position indicated by w in the figure. The weld causes a significant decrease in strength, and if this occurs in the resin portion D having the weakest strength, it leads to the occurrence of cracks in this portion and remarkably deteriorates the reliability.

  On the other hand, as shown in FIG. 5B, when the resin is injected from the resin portion A side, the flow of the resin is also divided along the component 3 by the component 3, and the end of the component 3, in this case, the resin portion B Join at. Accordingly, weld occurs in the resin part B, but the resin part B is thick in resin, and even if the weld occurs, the influence of the strength reduction is slight, and no cracks are caused due to this. Further, regarding the resin portion D having the smallest resin thickness, a flow of the resin that moves while avoiding the component 3 is formed in this portion, and there is no joint between the resin flows, so that a weld occurs. There is no. Therefore, the strength does not decrease in the resin part D, which is the most problematic in terms of strength, and the occurrence of cracks can be suppressed.

  As described above, the resin flow around the component 3 varies depending on the resin injection direction. Therefore, when molding a resin molded product, as shown in FIG. 5B, the resin flow is formed in parallel along the resin portion D having the smallest thickness of the resin and causing a problem in strength. That is, it is preferable to inject the resin from the resin part A side (or the resin part B side).

  In addition, when a fibrous filler is added to the resin in order to improve the strength of the resin molded product, or when a rare earth metal magnet having a negative coefficient of thermal expansion is used for the component 2, the resin is changed accordingly. It is preferable to consider the injection direction.

  As described above, according to the present invention, the reaction gas can be surely vented by pulling out the core pin 8, and a high-quality resin molded product free from blistering or deformation due to poor venting can be produced. Is possible. In addition to the above, by properly controlling the injection of the resin in order to suppress the displacement of the parts, the effect of degassing can be further increased, the occurrence of defective products can be suppressed, and the resin can be suppressed. It is possible to greatly improve the yield of molded products. In addition to the above, by appropriately controlling the injection of the resin, it is possible to reliably suppress the occurrence of cracks and the like, coupled with the suppression of the occurrence of defective products due to the effect of degassing, the resin It is possible to greatly improve the yield of molded products.

  In the following, a resin molded product was actually molded to confirm the effect of the present invention.

EXAMPLE The shape of the resin molded product produced in this example is as shown in FIG. 1, and two rare earth metal magnets were insert-molded in the resin part. The rare earth metal magnet insert-molded in the resin is 10 mm × 10 mm × 3 mm, and was produced by a usual powder metallurgy technique. The orientation direction in the rare earth metal magnet was the thickness direction (3 mm direction), and the surface was plated with Ni. As the resin to be injected, a thermosetting resin filled with 40% by mass of a glass filler was used.

  The resin molded product was molded according to the method shown in FIG. The number of produced resin molded products is 200. In this example, after the resin was injected, the core pin was retracted immediately before the mold was opened, thereby degassing. Therefore, as shown in FIG. 1, a vent hole is formed in the molded resin molded product.

  About each resin molded product, after resin solidified, it took out from the metal mold | die and performed aging at 180 degreeC for 3 hours. Thereafter, the occurrence of swelling, deformation, cracks, and the like in the resin portion was visually confirmed. The number of resin molded products in which blisters, deformation, cracks, etc. occurred was divided by the number of molded products (200), and the defective product occurrence rate was determined and evaluated. As a result, the defective product generation rate was an extremely good value of 0%.

Although the resin molded product similar to the comparative example was molded, the gas was not removed by drawing the core pin. Therefore, the vent hole is not formed in the produced resin molded product. In this case, the defective product generation rate due to blistering, deformation, cracks, etc. was 96%, which was a significantly large value compared to the example.

An example of the resin molded product to which this invention is applied is shown, (a) is a top view, (b) is a side view, (c) is a front view. It is a schematic diagram which shows an example of a shaping | molding process, (a) is a setting state, (b) is a resin injection | pouring state, (c) shows the degassing state by pulling out a core pin, respectively. It is a principal part schematic perspective view which shows the example of a shape of the guide provided in the metal mold | die, and a core pin. It is a top view which shows the example of arrangement | positioning of components in a metal mold | die cavity. (A) is a schematic diagram showing the flow of resin when the resin is injected from the direction orthogonal to the longitudinal direction of the component, and (b) is the resin flow when the resin is injected from the direction parallel to the longitudinal direction of the component. It is a schematic diagram which shows a flow.

Explanation of symbols

1 resin molded product, 2A, 2B resin part, 3 parts, 4 guide hole, 5 vent hole, 6 mold, 7 guide, 7a rising wall, 7b mounting surface, 8 core pin, 9 hydraulic device, 10 gate

Claims (5)

When insert-molding parts placed in the mold cavity with thermosetting resin,
The mold is provided with a core pin that comes into contact with the surface of the component, the resin is filled in the mold, and after the resin has been cured, the core pin is withdrawn before the curing is completely completed. A method for molding a resin molded product. 2. The method for molding a resin molded product according to claim 1, wherein gas is vented in a reduced pressure state by pulling out the core pin. 2. The method for molding a resin molded product according to claim 1 , wherein the gas is vented by pulling out the core pin from the mold and opening a core pin hole into which the core pin is inserted. The method for molding a resin molded product according to any one of claims 1 to 3, wherein the component is a rare earth metal magnet. Positioning the part with a guide provided on a predetermined mold surface, and injecting resin so that a force by a resin flow is applied to the part toward the mold surface provided with the guide The method for molding a resin molded product according to any one of claims 1 to 4, characterized in that:

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