JP4692007B2 - Molding method - Google Patents

Description

  The present invention relates to a molding method in which various parts are insert-molded into a resin, and more particularly to a technique for preventing the occurrence of cracks after molding.

  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, and securing the strength is an important issue in the molding.

From such a situation, for example, an attempt has been made to ensure the strength of the resin molded product by mixing a filler in the resin (see Patent Document 1, etc.). 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

  However, when actually trying to produce resin molded products of various configurations and shapes, even if fillers or the like are mixed, the effect cannot be sufficiently obtained, and cracks and the like frequently occur after molding. Is the actual situation. 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 molding method capable of reliably suppressing the occurrence of cracks and the like in insert molding of a component, suppressing the occurrence of defective products, and improving the yield. And

  The present inventor has intensively studied for a long time to achieve the above object. As a result, when insert molding the part, in consideration of the influence of the part on the resin flow, in the weakest part around the part, inject the resin so that the factor that reduces the strength can be avoided as much as possible, The conclusion was reached that the resin flow needs to be optimized. Further, the weak parts include 1) the thinnest part, 2) a part including “choke” [for example, a curved surface part having a radius of curvature of 1 mm or less, an angle (particularly an acute angle), etc.], and 3) a thermal expansion coefficient. Although there are portions where stress is generated from the difference, it has been found that strength reinforcement is particularly important for the thinnest portion, and the present invention has been completed.

  The present invention has been devised based on such knowledge. When insert molding a part into a resin, the weld does not occur at the thinnest part of the resin around the part. In other words, the resin is injected so that the resin flows in one direction at the thinnest portion of the resin.

  In insert molding, the injected resin is diverted so as to avoid the presence of a part and merges at the end of the part. At the joining portion, that is, at the joint where the resin that has wrapped around avoiding the parts meets again, the weld is caused and the strength is remarkably lowered. In the case of insert molding, since there is always a part, it is difficult to completely eliminate the weld around the part. In addition to the above, when resin is injected from a plurality of gate openings, welds are generated, which also causes a decrease in strength. Therefore, it is necessary to devise a resin flow so that welds do not occur in the thinnest part.

  Therefore, in the present invention, resin is injected so that weld does not occur in the weakest part of the strength, that is, in the part where the resin thickness is the smallest around the part, and in the part where the resin thickness is the thinnest. Ensure that the strength does not decrease. In this case, welds will occur in other parts, but since the resin is thick, the effect of strength reduction will be minor, and no cracks will occur in this part.

  Further, when considering the strength of the molded resin product, it is considered effective to add a fibrous filler in the resin. However, when the fibrous filler is added, the strength of the entire resin molded product is increased. However, when the fibrous filler is oriented in a certain direction, if a force is applied in the direction perpendicular to the fiber direction of the fibrous filler, the strength is increased. However, cracks and the like are easily formed.

Therefore, when the fibrous filler is added, it is necessary to inject the resin so that the orientation direction of the fibrous filler in the portion where the thickness of the resin is the smallest around the part is appropriate. This is defined in the invention according to claim 4 , and the resin is injected so that the fibrous filler is oriented in a direction substantially orthogonal to the minimum cross section of the thinnest portion of the resin. It is characterized by that.

  In the portion where the thickness of the resin is the thinnest, it is most likely to break when a force is applied in a direction perpendicular to the smallest cross section having the smallest cross sectional area. As described above, if the fibrous filler is oriented in a direction substantially orthogonal to the minimum cross section, when a force is applied in the direction orthogonal to the minimum cross section, a force is applied in the direction of stretching the fibrous filler. It works to effectively secure the strength against the force in this direction. As a result, cracks and the like at the thinnest portion of the resin are effectively suppressed.

  Furthermore, when insert molding a part, it is necessary to consider the difference in coefficient of thermal expansion between the part 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. Accordingly, when the rare earth metal magnet is integrated with another substance such as a resin, cracks are likely to occur because it is sensitive to the stress generated when the temperature changes. Therefore, it is necessary to design the process in consideration thereof.

Therefore, it is necessary to inject the resin in consideration of the direction in which the amount of displacement due to heat in the component is maximized, and this is defined in the invention described in claim 1. That is, the component has a negative coefficient of thermal expansion, and the resin is injected from a direction substantially parallel to the direction in which the absolute value of the product αL of the dimension L of the component and the coefficient of thermal expansion α in the dimension direction is the largest. It is characterized by.

  If the resin is injected from the direction, the weld is not formed at the portion where the force is most applied due to the displacement of the component, the strength of the portion is increased, and the crack is suppressed. At the same time, the orientation direction of the fibrous filler is along the direction in which the displacement amount of the component becomes the largest, and the fibrous filler effectively works against the stress due to the difference in thermal expansion coefficient between the component and the resin.

  According to the present invention, when a part is insert-molded, the occurrence of cracks and the like can be reliably suppressed, the generation of defective products can be suppressed, and the yield can be improved. In addition, the above effect is remarkable when a fibrous filler is added to the resin or when the thermal expansion coefficient of the component is negative. By injecting the resin in consideration of these, the reliability without cracks is excellent. Resin molded products can be molded.

  Hereinafter, a molding method to which the present invention is applied will be described in detail with reference to the drawings.

  Actual resin molded products have various shapes and various arrangements of components, but in this embodiment, the basic concept will be described using the simplest model.

First, FIG. 1 shows an example of the shape of a resin molded product when a component 2 is arranged in a mold cavity 1 having a substantially rectangular parallelepiped shape. 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. 2A, when the 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 mold cavity 1 from the resin part C side is blocked by the component 2 and moves while avoiding the component 2. 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 part D, the flow of the resin divided by the component 2 joins, 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. 2B, when the resin is injected from the resin portion A side, the flow of the resin is also divided along the component 2 by the component 2, and the end of the component 2, 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 thinnest resin, a flow of the resin that moves while avoiding the component 2 is formed in this portion, and the weld does not become a joint of the resin flow. 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 is suppressed.

  As described above, the flow of the resin around the component 2 varies depending on the resin injection direction. Therefore, when molding the resin molded product, as shown in FIG. 2B, the resin flow is formed in parallel along the resin portion D where the thickness of the resin is the smallest and the strength is a problem. That is, it is preferable to inject the resin from the resin part A side (or the resin part B side).

  The above is the basic idea of the present invention, but in order to improve the strength of the resin molded product, when a fibrous filler is added to the resin, or the rare earth metal magnet having a negative thermal expansion coefficient is added to the component 2. When used, it is necessary to consider the injection direction of the resin accordingly.

  Therefore, first, a case where a fibrous filler is added to the resin will be described. When considering the strength of the resin molded product, it is well known that the addition of filler to the resin is effective. For example, by adding a fibrous filler such as a glass filler, the strength of the resin molded product Is greatly improved. However, in this case, it is necessary to appropriately control the orientation direction of the fibrous filler.

  FIG. 3 illustrates the orientation direction of the fibrous filler in the resin portion D. Since the resin part D is the part where the thickness of the resin is the thinnest and the strength is weak, it is most effective to optimize the orientation of the fibrous filler in the resin part D.

  When the orientation direction of the fibrous filler f in the resin portion D is considered, the orientation direction changes depending on the resin injection direction. For example, when the resin is injected along the minimum cross section s from the side with respect to the minimum cross section S having the smallest cross sectional area of the resin portion D, the fibrous filler f is substantially parallel to the minimum cross section s. Arrange. As shown in FIG. 3B, even when the resin is injected from above or below the resin portion D, the fibrous fillers f are arranged substantially parallel to the minimum cross section s. In such a case, the fibrous filler f does not act so as to prevent cracks that are substantially parallel to the minimum cross section s, and is torn between the fibrous fillers f. .

  On the other hand, as shown in FIG. 3C, when resin is injected from a direction orthogonal to the minimum cross section s, the resin flows in a direction orthogonal to the minimum cross section s, and the fibrous filler f also extends in this direction. Orient. That is, the fibrous fillers f are arranged in a direction orthogonal to the minimum cross section s. In this case, when a force is applied in a direction perpendicular to the minimum cross section s, the fibrous filler f is pulled, so that the force is resisted. Therefore, the fibrous filler f contributes effectively in preventing the occurrence of cracks, and the occurrence of cracks is effectively suppressed.

  Therefore, when the fibrous filler f is added to the resin, it is preferable to inject the resin from a direction orthogonal to the minimum cross section s of the resin portion D, as shown in FIG. This coincides with the resin injection direction shown in FIG. That is, when the resin molded product shown in FIG. 1 is molded, if the resin is injected from the resin portion A side, no weld occurs in the resin portion D, and the orientation direction of the fibrous filler f is also a direction to prevent cracks. Therefore, strength reduction can be avoided in the resin part D having the most problems in strength.

  Next, the optimization of the resin injection direction when the thermal expansion coefficient of the component 2 is negative will be described. For example, when considering the case where the part 2 to be insert-molded is a rare earth metal magnet, the thermal expansion coefficient of the rare earth metal magnet is negative and the thermal expansion coefficient of the resin is positive. That countermeasure is necessary.

  Rare earth metal magnets are mainly composed of rare earth element R, transition metal element T, and boron B, and are extremely excellent in magnetic properties. Therefore, they are useful for miniaturization and high performance. is there. The composition of the rare earth metal magnet may be arbitrarily selected depending on the application, for example, the rare earth element R is specifically Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb. , Dy, Ho, Er, Tm, Yb or Lu, and one or more of them can be used. Among these, it is preferable that the main component as the rare earth element R is Nd because it is abundant in resources and relatively inexpensive. Moreover, as the transition metal element T, any conventionally used transition metal element can be used. For example, one or more of Fe, Co, Ni and the like can be used. Among these, Fe and Co are preferable from the viewpoint of sinterability, and it is particularly preferable to mainly include Fe from the viewpoint of magnetic characteristics. In addition to the rare earth element R, transition metal element T, and boron B, for the purpose of improving characteristics such as coercive force, an element such as Al may be added. In addition to these elements, for example, carbon and oxygen may be contained as inevitable impurities or trace additives.

In the rare earth metal magnet, there is a close relationship between the magnetic field orientation direction and the thermal expansion coefficient of the rare earth metal powder during molding, and the thermal expansion coefficient is positive in the direction parallel to the magnetic field orientation direction, the magnetic field orientation direction. The coefficient of thermal expansion is negative in the direction orthogonal to. Considering the case where insert molding is performed using a rare earth metal magnet as the component 2 as shown in FIG. 4, when the magnetic field is oriented in the thickness direction of the component 2, the thermal expansion coefficient α in the longitudinal direction of the component 2 is negative. . Here, when the dimension of the component 2 is L, the direction in which the absolute value of the product αL of the thermal expansion coefficient α and the dimension L is the largest (the direction in which the amount of displacement due to the temperature change is the largest) is referred to as the longitudinal direction. It will be.

For the after resin injection, when cooled, the component 2 with the temperature drop extends in the direction of arrow X _1, whereas the resin of the resin portion D tries Chijimimo the direction of arrow X _2. Therefore, a large force is applied to the point F in the resin part D, and cracks are easily generated. Such in order to counteract the force, it is important to secure the strength against the force applied in the arrow X ₁ direction in the resin portion D.

Therefore, it comes to it is preferable to inject the resin so without weld occurs at the resin section D, also fibrous filler to the direction of arrow X ₁ are arranged. This coincides with the direction shown in FIG. 2 (b) and coincides with the orientation of the fibrous filler shown in FIG. 3 (c).

  As described above, when the component 2 is insert-molded, it is necessary to appropriately control the injection direction of the resin, which can surely suppress the occurrence of cracks and the like and suppress the generation of defective products. The yield of resin molded products can be greatly improved. In addition, when a fibrous filler is added to the resin or when the thermal expansion coefficient of the component is negative, it is preferable to determine the resin injection direction in consideration of these factors, thereby further improving the resin. It is possible.

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

Example FIGS. 5A to 5C show the shapes of resin molded products produced in this example. This resin molded product 11 is obtained by insert molding two rare earth metal magnets 13 in a resin portion 12. The resin molded product 11 has a structure in which a resin portion 12 is roughly divided into two parts and these are connected in a casing shape, and a rare earth metal magnet 13 is insert-molded in each of the divided resin portions 12. ing. The rare earth metal magnet 13 is positioned by a guide provided in the mold. Therefore, a guide hole 14 is formed in the resin portion 12 corresponding to the guide.

  As described above, the resin molded product 11 has a structure in which the resin portion 12 is roughly divided into two parts and these are connected in a casing shape, and each of the divided resin portions 12 has one rare earth metal. Although the magnet 13 is insert-molded, the resin portion 12 has the thinnest resin in the portions 12 </ b> A and 12 </ b> B covering the top surface of the rare earth metal magnet 13. Specifically, it is 1.25 mm.

  The rare earth metal magnet 13 inserted into the resin molded product 11 has a size of 10 mm × 10 mm × 3 mm, and was produced by an ordinary powder metallurgy technique. The orientation direction in the rare earth metal magnet 13 is the thickness direction [vertical direction in the plane of FIG. 5A], 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 by injecting resin from the same direction as in the example shown in FIG. That is, in FIG. 5, two gate ports were provided on the left end side in the figure corresponding to the divided part, and resin was injected from here (from the direction of arrow J). Thereby, a resin flow is formed along the longitudinal direction of the rare earth metal magnet 13, and the resin flows in the right direction in the drawing also in the portions 12A and 12B where the resin thickness is the thinnest. The number of produced resin molded products is 200.

  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, a thermal shock test was performed under the conditions of a temperature of −40 ° C. to 85 ° C. and an exposure time of 30 minutes for 15 cycles. After the test, the condition of cracks in the resin molded product was visually observed, the number of resin molded products in which the crack occurred was divided by the number of molded products (200), and the defective product occurrence rate was determined and evaluated. As a result, cracks were slightly generated in the central portions in the longitudinal direction of the peripheral portions 12A and 12B where the resin was the thinnest, but the occurrence rate was as small as 3%, indicating a very good value.

Comparative Example A resin molded product similar to that in Example was molded, but the resin injection direction was the same as that in FIG. That is, in FIG. 5, one gate port was provided on the upper end side in the drawing so as to face the rare earth metal magnet 13, and resin was injected from here (from the direction of arrow H). In this case, in the portion 12B where the resin thickness is the thinnest, the resin flows in one direction and welding does not occur. However, in the peripheral portion 12A where the resin thickness is the smallest, avoid the rare earth metal magnet 13. There is a high possibility that welded resin will merge and weld will occur.

  Actually, many cracks occurred in the central portion in the longitudinal direction of the peripheral portion 12A where the resin was the thinnest, and the occurrence rate was 82%, which was a significantly larger value than in the example.

It is a top view which shows the example of arrangement | positioning of the components in a metal mold 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. It is a schematic diagram which shows the relationship between the injection | pouring direction of resin, and the orientation direction of a fibrous filler, When (a) inject | pours in the width direction of the resin part D, (b) When inject | pours in the thickness direction, (c) Is the case of injection in the longitudinal direction. It is a schematic diagram which shows the direction in which the components are extended at the time of cooling and the direction in which the resin shrinks when the thermal expansion coefficient of the components is negative. The shape of the resin molded product produced in the Example is shown, (a) is a plan view, (b) is a side view, and (c) is a front view.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Mold cavity, 2 parts, 11 resin molded product, 12 resin part, 12A peripheral part (part with the thinnest resin thickness) 13 rare earth metal magnet

Claims (7)

When insert molding a component having a negative coefficient of thermal expansion into the resin, the resin is introduced from a direction substantially parallel to the direction in which the absolute value of the product αL of the dimension L of the component and the coefficient of thermal expansion α in the direction of the dimension is the largest. A molding method characterized by pouring.   The molding method according to claim 1, wherein the resin is injected so that the resin flows in one direction at a portion where the thickness of the resin is the thinnest.   The molding method according to claim 1, wherein the resin contains a fibrous filler. The molding method according to claim 3, wherein the resin is injected so that the fibrous filler is oriented in a direction substantially orthogonal to a minimum cross section of a portion where the thickness of the resin is the thinnest.   The molding method according to claim 1, wherein the component is a rare earth metal magnet. The direction substantially parallel to the direction in which the absolute value of the product αL of the dimension L of the component and the coefficient of thermal expansion α in the dimension direction is the largest is the direction substantially perpendicular to the orientation direction of the rare earth metal magnet. The molding method according to claim 5.   The molding method according to claim 1, wherein the resin is a thermosetting resin.

Images