Resin molded products

Abstract

This resin molded article comprises a flat-plate-shaped screw fastening part. The screw fastening part has a penetration hole through which a screw penetrates, a contact area which is provided around the penetration hole and with which the head of the screw comes into contact, a notch part which is formed extending in a first direction along a weld line from the penetration hole and which is formed by notching a part of the contact area, and a pair of slits which is formed extending in the first direction further from the notch part and which is symmetrical with respect to the weld line.

Description

Technical Field

[0001] The present invention relates to a resin molded product.

Background Art

[0002] In Patent Document 1 below, for the purpose of providing a resin molded part in which cracks hardly occur starting from the weld line when pressure is applied, in a resin molded part having a disc-shaped main body portion with a through-hole at the center, along a straight line connecting the center of the through-hole and the gate cut portion, a technique is disclosed in which an opening is provided communicating with the through-hole and extending toward the peripheral edge portion of the main body portion away from the gate cut portion.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the technique of Patent Document 1 cannot sufficiently release the stress applied to the weld line line during when tightening the screw. Still, a high stress is applied to the weld line when tightening the screw, and there is a risk of cracks occurring along the weld line.

Means for Solving the Problems

[0005] A resin molded product according to an embodiment is a resin molded product provided with a flat screw fastening portion. The screw fastening portion includes a through-hole through which a screw passes, a contact region provided around the through-hole against which the head of the screw abuts, a notch portion formed by extending in a first direction along the weld line from the through-hole and cutting out a part of the contact region, and a pair of slits formed by further extending in the first direction from the notch portion and symmetric with respect to the weld line.

Effects of the Invention

[0006] According to one embodiment of the resin molded product, it is possible to suppress the stress applied to the weld line when fastening screws. [Brief explanation of the drawing]

[0007] [Figure 1] A perspective view of a resin molded product according to one embodiment, viewed from above. [Figure 2] A perspective view of the resin molded product according to one embodiment, viewed from below. [Figure 3] Exploded perspective view of a resin molded product according to one embodiment. [Figure 4] Cross-sectional view of a resin molded product according to one embodiment. [Figure 5] Bottom view of the battery cover of a portable device according to one embodiment. [Figure 6] A diagram showing one embodiment of a battery cover for a portable device according to one embodiment. [Figure 7] This figure shows a first modified example of a screw fastening portion of a portable device according to one embodiment. [Figure 8] This figure shows a second modified example of a screw fastening portion of a portable device according to one embodiment. [Modes for carrying out the invention]

[0008] An embodiment will be described below with reference to the drawings.

[0009] (Configuration of mobile device 100) Figure 1 is an external perspective view of the portable device 100 according to one embodiment, viewed from above. Figure 2 is an external perspective view of the portable device 100 according to one embodiment, viewed from below. Figure 3 is an exploded perspective view of the portable device 100 according to one embodiment. Figure 4 is a cross-sectional view of the portable device 100 according to one embodiment.

[0010] For convenience, in the following explanation, the Z-axis direction (thickness direction of case 110) in the diagram will be considered the vertical direction, the Y-axis direction (short side direction of case 110) will be considered the horizontal direction, and the X-axis direction (long side direction of case 110) will be considered the front-to-back direction.

[0011] The portable device 100 shown in Figure 1 is a small, portable device that can be carried by the user. For example, the portable device 100 is an electronic key that enables remote control of a vehicle (e.g., locking, unlocking, starting, etc.) by communicating wirelessly with an in-vehicle unit installed in the vehicle. However, the portable device 100 may be used for any purpose other than an electronic key.

[0012] As shown in Figures 1 to 4, the portable device 100 comprises a case 110, a battery cover 120, and a circuit board 130.

[0013] Case 110 is a hollow, container-shaped component made of resin. Case 110 has a generally rectangular parallelepiped shape. Case 110 can be divided into two parts, an upper case 111 and a lower case 112, at an intermediate position in the vertical direction. The external shape of case 110 is generally rectangular parallelepiped, but its front end (the end on the positive X-axis side) is interrupted.

[0014] Instead, the front end (the end on the positive X-axis side) of the case 110 has a roughly rectangular tubular projection 113 that protrudes forward (towards the positive X-axis direction). When the case 110 is divided into two parts, the projection 113 can be divided into an upper projection 113A which is integrally provided on the upper case 111 and a lower projection 113B which is integrally provided on the lower case 112.

[0015] The battery cover 120 is a hollow, container-shaped resin component. The battery cover 120 is an example of a "resin molded product." The battery cover 120 has an external shape that is continuous with the case 110 (i.e., an external shape that complements the gap in the case 110), and by being attached to the front end of the case 110 (the end on the positive X-axis side), it together with the case 110 forms an external shape that is roughly rectangular. Inside the battery cover 120 is a battery (not shown) for supplying power to the circuit board 130.

[0016] The battery cover 120 has a rectangular opening 120A at the rear end portion (the portion on the negative X-axis side) facing the case 110. The battery cover 120 is attached to the front end portion (the end portion on the positive X-axis side) of the case 110 by fitting the convex portion 113 of the case 110 into the opening 120A, and is supported from the inside by the convex portion 113 so as not to easily fall off from the case 110.

[0017] Note that the case 110 and the battery cover 120 are made of a synthetic resin material such as ABS resin or PC resin, and are formed into a predetermined shape by injection molding.

[0018] The circuit board 130 is a resin-made and flat member provided inside the case 110. The circuit board 130 is fixed inside the case 110 in a horizontal posture with respect to the lower case 112. Various electronic components are mounted on the circuit board 130, thereby constructing an integrated circuit for realizing various functions (for example, wireless communication function, control function, etc.) of the resin molded product 10. The integrated circuit operates using the power supplied from a battery (not shown) built in the battery cover 120. As the circuit board 130, for example, a PCB (Printed Circuit Board) is used.

[0019] (Screw fastening structure) Here, the screw fastening structure provided in the portable device 100 will be described. As shown in FIGS. 2 to 4, the battery cover 120 has a main body portion 122 and a flat screw fastening portion 121 that protrudes rearward (in the negative X-axis direction) from the rear end portion (the end portion on the negative "X-axis side) of the lower wall portion 122A of the main body portion 122 and the central portion in the left-right direction (Y-axis direction). In particular, in the present embodiment, the screw fastening portion 121 has a tongue shape because one end portion (the end portion on the positive X-axis side) is connected to the main body portion 122 and the other end portion (the end portion on the negative X-axis side) is not connected to anything. The screw fastening portion 121 has a circular through hole 121A penetrating the screw fastening portion 121 in the vertical direction at the central portion in plan view.

[0020] On the other hand, the lower wall portion 112A of the lower case 112 has recesses 112B formed at the front end (the end on the positive X-axis side) and in the central part in the left-right direction (Y-axis direction), which are substantially the same shape as the screw fastening portion 121. In the central part of the recess 112B in a plan view, a screw hole 112C is formed, which is threaded upward (in the positive Z-axis direction).

[0021] Here, as shown in Figures 2 and 4, in one embodiment of the portable device 100, when the battery cover 120 is attached to the front end (positive X-axis end) of the case 110, the screw fastening portion 121 of the battery cover 120 is fitted into the recess 112B of the lower case 112. Also, in this case, in a plan view from below (negative X-axis direction), the through hole 121A of the screw fastening portion 121 and the screw hole 112C of the recess 112B are aligned.

[0022] Therefore, in one embodiment of the portable device 100, as shown in Figure 4, the screw fastening portion 121 can be screwed into the recess 112B by passing the countersunk screw 140 through the through hole 121A of the screw fastening portion 121 and screwing it into the screw hole 112C of the recess 112B.

[0023] (Detailed configuration of the screw fastening portion 121) Figure 5 is a bottom view of a battery cover 120 provided in a portable device 100 according to one embodiment.

[0024] As shown in Figure 5, the screw fastening portion 121 of the battery cover 120 has a circular through hole 121A in the center of the screw fastening portion 121 in the vertical direction, which penetrates the screw fastening portion 121 in the central direction when viewed from above.

[0025] Furthermore, the screw fastening portion 121 has a tapered surface 121B (an example of a "contact area") formed in an annular shape around the through hole 121A in a plan view, surrounding the through hole 121A. The tapered surface 121B has a tapered shape (conical) in which the diameter gradually decreases toward the depth direction (positive Z-axis direction).

[0026] As a result, when fastening with the countersunk screw 140, the screw fastening portion 121 can receive the fastening force from the conical seating surface of the head 141 of the countersunk screw 140 with its similarly conical tapered surface 121B, and the head 141 of the countersunk screw 140 can be housed inside the tapered surface 121B so as not to protrude from the screw fastening portion 121.

[0027] Here, as shown in Figure 5, a weld line WL extending in the front-to-back direction (X-axis direction) is formed at an intermediate position in the left-to-right direction (Y-axis direction) of the screw fastening portion 121, behind the through hole 121A (negative X-axis side). This weld line WL is formed when the battery cover 120 is injection molded, by the molten resin flowing around the outside of the through hole 121A and the molten resin flowing from one side (positive Y-axis side) merging with the molten resin flowing from the other side (negative Y-axis side). Therefore, the weld line WL can also be described as the "molten resin merging portion". The weld line WL can be determined by performing a flow analysis of the molten resin during the injection molding of the battery cover 120.

[0028] Since a weld line WL is formed in the screw fastening portion 121, when fastening with the countersunk screw 140, stress is applied to the weld line WL, and there is a risk that cracks may occur along the weld line WL.

[0029] Therefore, in the portable device 100 according to one embodiment, as shown in Figure 5, the screw fastening portion 121 is provided with a notch portion 121C and a pair of slits 121D.

[0030] The notch 121C is formed extending from the through hole 121A in a first direction D1 (negative X-axis direction) along the weld line WL, and cuts out a portion of the tapered surface 121B.

[0031] The pair of slits 121D are formed extending further from the notch 121C in a first direction D1 (negative X-axis direction) and are symmetrical with respect to the weld line WL.

[0032] The pair of slits 121D are the parts that form the projection 121E between the pair of slits 121D. The notch 121C is the part that connects the through hole 121A and the pair of slits 121D.

[0033] Furthermore, the screw fastening portion 121 is provided with a pair of slits 121D, and has a projection 121E between the pair of slits 121D that protrudes toward the through hole 121A, so that the weld line WL is located on the projection 121E.

[0034] Therefore, the important thing here is to form the notch 121C and the pair of slits 121D so that the head 141 of the countersunk screw 140 does not come into contact with the projection 121E when fastened with the countersunk screw 140.

[0035] Furthermore, since the tip of the projection 121E (the end on the positive X-axis side) is located at approximately the same position as the outer circumference of the head 141 of the countersunk screw 140, it can function as a positioning and stopper for the outer circumference of the head 141 of the countersunk screw 140.

[0036] In one embodiment, the portable device 100 is provided with a notch 121C and a pair of slits 121D, which allows the stress to be concentrated on the pair of slits 121D (i.e., on both outer sides of the weld line WL) when fastened with countersunk screws 140, thereby suppressing the stress applied to the weld line WL (projection 121E).

[0037] In particular, in this embodiment, a pair of slits 121D are provided parallel to each other as an example of a preferred configuration that can release the stress applied to the weld line WL.

[0038] (Examples) Figure 6 shows one embodiment of a battery cover 120 provided in a portable device 100 according to one embodiment.

[0039] In this example, the battery cover 120 shown in Figure 5 was designated as "Example," and battery covers prepared for comparison were designated as "Comparative Example 1" and "Comparative Example 2." For each of these, the stress applied to the weld line WL was measured by simulation, and the likelihood of crack formation was determined to determine whether they were good or bad.

[0040] In "Comparative Example 1," a model without either a notch or a slit was used. In "Comparative Example 2," a model with a notch but without a slit was used.

[0041] As shown in Figure 6, in "Comparative Example 1," it was found that an extremely large stress of "approximately 48 MPa" was applied to the weld line WL, and the possibility of crack formation was extremely high, so the possibility of crack formation was judged as "× (defective)." This is thought to be because "Comparative Example 1" does not have either a notch or a slit, so the stress cannot be relieved in either direction, and the stress is concentrated on the weld line WL.

[0042] Furthermore, as shown in Figure 6, in "Comparative Example 2," it was found that a relatively large stress of "approximately 8 MPa" was applied to the weld line WL, and the possibility of crack formation was relatively high, so the possibility of crack formation was judged as "× (poor)." In "Comparative Example 2," although the presence of a notch allows some stress to be released into the notch, this is insufficient, and it is thought that stress is still concentrated on the weld line WL.

[0043] On the other hand, as shown in Figure 6, in the "Example," it was found that an extremely small stress of "less than 1 MPa" was applied to the weld line WL, and the possibility of crack occurrence was extremely low, so the possibility of crack occurrence was judged as "○ (Good)." This is thought to be because in the "Example," there is a notch 121C and a pair of slits 121D, so most of the stress can be relieved to the pair of slits 121D.

[0044] (First variation) Figure 7 shows a first modified example of a screw fastening portion 121 provided in a portable device 100 according to one embodiment. The screw fastening portion 121 shown in Figure 7 is a first modified example of the screw fastening portion 121 shown in Figure 5. The screw fastening portion 121 shown in Figure 7 differs from the screw fastening portion 121 shown in Figure 5 in that the groove width of the notch portion 121C is enlarged and the notch portion 121C is extended in the first direction D1.

[0045] Furthermore, the inventors have confirmed through simulation that even when the groove width of the notch 121C is enlarged and the notch 121C is extended in the first direction D1, most of the stress can be relieved to the pair of slits 121D, similar to the case where the pair of slits 121D are provided parallel to each other (configuration in Figure 5), and therefore, an extremely small stress of "less than 1 MPa" is applied to the weld line WL.

[0046] (Second variation) Figure 8 shows a second modified example of a screw fastening portion 121 provided in a portable device 100 according to one embodiment. The screw fastening portion 121 shown in Figure 8 is a second modified example of the screw fastening portion 121 shown in Figure 5. The screw fastening portion 121 shown in Figure 8 differs from the screw fastening portion 121 shown in Figure 5 in that a pair of slits 121D are arranged radially (i.e., the distance between them gradually increases as they extend in the first direction D1 (negative X-axis direction)).

[0047] Furthermore, the inventors confirmed through simulations that even when the pair of slits 121D are arranged radially, most of the stress can be released to the pair of slits 121D, just as in the case where the pair of slits 121D are arranged parallel to each other (configuration in Figure 5), and therefore, an extremely small stress of "less than 1 MPa" is applied to the weld line WL.

[0048] Although one embodiment of the present invention has been described in detail above, the present invention is not limited to these embodiments, and various modifications or changes are possible within the scope of the gist of the present invention as described in the claims.

[0049] For example, in the above embodiment, the left-right width (width in the Y-axis direction) of the screw fastening portion 121 is made smaller than the left-right width of the main body portion 122. However, the left-right width (width in the Y-axis direction) of the screw fastening portion 121 may be equal to the left-right width of the main body portion 122. Even in this case, the stress suppression effect on the weld line by providing the notch portion 121C and the pair of slits 121D is the same.

[0050] Furthermore, from the viewpoint of suppressing stress applied to the weld line WL, it is preferable that at least one pair of slits 121D are provided in a range that is acute angle with respect to the center of the through hole 121A, as is the case with the configurations shown in Figures 5, 7, and 8.

[0051] Furthermore, although the above embodiment describes an example in which the screw fastening portion 121 is fixed using a countersunk screw 140, the method is not limited to this. Even when other screws (those with a flat seating surface rather than a tapered one) are used to fix the screw fastening portion 121, the stress suppression effect on the weld line by providing the notch 121C and the pair of slits 121D is the same.

[0052] This international application claims priority based on Japanese Patent Application No. 2022-123571, filed on 2 August 2022, and the entire contents of said application are incorporated herein by reference. [Explanation of symbols]

[0053] 100 Mobile devices 110 cases 111 Upper case 112 Lower case 112A Lower wall section 112B Recess 112C Screw hole 113 Convex part 113A Upper protrusion 113B Lower protrusion 120 Battery cover (plastic molded product) 120A opening 121 Screw fastening section 121A through hole 121B Tapered surface (contact area) 122 Main body 122A Lower wall section 130 Circuit boards 140 Countersunk screws 141 Head D1 First direction WL Weldline

Claims

1. A resin molded product having a flat screw fastening portion, The screw fastening portion is, A through hole through which the screw passes, A contact area is provided around the through hole, and the head of the screw abuts against it, A notch is formed extending from the through hole in a first direction along the weld line, and a portion of the contact area is cut out, A pair of slits are formed extending further in the first direction from the aforementioned notch and are symmetrical with respect to the weld line. A resin molded product characterized by having [a certain feature].

2. The pair of slits are arranged parallel to each other. The resin molded product according to feature 1.

3. The pair of slits are arranged radially. The resin molded product according to feature 1.

4. The pair of slits are provided in a range that is acute in angle to the center of the through hole. The resin molded product according to feature 1.

5. Equipped with a main body, The screw fastening portion is provided extending from the main body in the first direction. The resin molded product according to feature 1.

6. The aforementioned contact region is a tapered surface that forms a cone. The resin molded product according to feature 1.

7. The pair of slits are portions that form a projection between the pair of slits, The aforementioned notch is the portion that connects the through hole and the pair of slits. The resin molded product according to feature 1.

8. The pair of slits are portions that form a projection between the pair of slits, The notch and the pair of slits are formed so that the head of the screw does not come into contact with the projection when the screw is fastened. The resin molded product according to feature 1.

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