JP2002225077A - Molded body structure and molding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a molded body structure which protects an internally contained part from the external environment while being integrated with the internally contained part without generating a damage or a positional slip, by injection-molding a thermoplastic resin at a melting temperature being lower than a temperature which unfavorably affects the internally contained part, and at the same time, has a mechanical strength being sufficiently bearable to an external force as well. SOLUTION: This molded body structure is equipped with protection objective articles 20 to 24, a first molded body 11 and a second molded body 12. In this case, the first molded body 11 directly covers at least one section of the surfaces of the protection objective articles. The second molded body 12 directly protects at least one section of the surface of the first molded body 11. Then, the first molded body 11 has an elastic coefficient which is smaller than that of the molded body 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compact structure and a molding method suitable for use in a small proximity sensor or the like.

[0002]

2. Description of the Related Art Proximity switches, photoelectric switches, and the like as detection switches are used under various environments. For example, in a production line where a liquid such as water is used, in addition to a mechanical strength, a waterproofing having high mechanical strength is required. Is required. As such a detection switch, for example, JP-A-7-2261
No. 35 discloses a detection switch. This one is
As shown in FIG. 15, an element block 54 having a front cover 53 attached thereto is fitted into a front opening 52 of a main body case 51, and a display cover 55 is fitted on the upper surface. In the assembled state, a joint groove 57 is formed in a region indicated by a two-dot chain line where the joint 56 of each component is located on the bottom surface, and an elastic resin is molded so as to fill the joint groove 57, and the elastic joint is formed. 58 are formed, and each component is integrated with the joint 56 covered with the elastic joint 58.

[0003]

However, in the above-described detection switch having the conventional structure, after a built-in component such as an electric component or an electronic component is assembled in a case which is a primary molded body, a connecting portion is formed outside the case. The work of secondary molding is required, which increases the assembly cost, and increases the number of parts such as the case and the frame, which increases the cost. Further, in order to retrofit the built-in component to the case, a slight dimensional tolerance is required between the case and the built-in component, and the resin of the case material does not adhere to the surface of the built-in component.
Therefore, the performance of protecting the built-in components from the external environment is low. In particular, in the case of a hollow structure, if the size is reduced, the area of the sealing portion must be reduced, so that the sealing performance is reduced. Furthermore, considering the workability of assembly, it is difficult to reduce the size because the arrangement of parts is restricted. The thickness of the case parts is
Since it cannot be made smaller than a certain value due to restrictions on moldability and required strength, there is a problem that the entire shape cannot be reduced in size.

[0004] Instead of the above-mentioned hollow structure, a solid integrated structure in which a thermoplastic resin is injection-molded and integrated around a built-in component placed in a mold is naturally considered. In this case, it is necessary to use a resin having a predetermined strength in order to maintain the mechanical strength of the formed molded body. However, such a resin has a relatively high viscosity even when it is melted, and requires relatively high pressure during injection filling into a mold. And the mounting position is shifted. Also,
It is necessary to raise the melting temperature in order to lower the clay of the molten resin, but there is a problem that it is difficult to raise the temperature of the molten resin when some of the built-in components are easily affected by heat. . Further, since the internal stress generated due to the volume shrinkage of the resin in the cooling process is large, there is a problem that the internal components are damaged, the characteristics are changed, and the mounting position is shifted.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has been made by injection-molding a thermoplastic resin at a melting temperature lower than a temperature that adversely affects built-in components, without causing breakage or displacement. It is an object of the present invention to provide a molded body structure and a molding method having a mechanical strength capable of protecting internal components from an external environment by integrating the same and sufficiently withstanding an external force.

[0006]

In order to achieve the above object, a molded article structure according to claim 1 comprises an object to be protected and a first molded article which directly covers at least a part of the surface of the object to be protected. A second molded body that directly protects at least a part of the surface of the first molded body, wherein the first molded body has a smaller elastic coefficient than the second molded body. I do.

According to a second aspect of the present invention, there is provided the molded article structure according to the first aspect, wherein a part of the first molded article is the second molded article.
Characterized in that the outer surface is formed together with a part of the molded body. The molded body structure according to claim 3 is the molded body structure according to claim 1 or 2, wherein the first molded body has a through-hole, and at least a part of the surface of the through-hole is formed by the second molded body. It is characterized by being coated.

According to a fourth aspect of the present invention, there is provided a molding method, wherein a first molded body directly covering at least a part of an object to be protected is injection-molded using a mold, and at least a part of the first molded body is molded. Injection molding a second molded body to be directly coated using a mold, wherein the first molded body has an elastic modulus smaller than that of the second molded body. Features.

At least a part of the surface of the object to be protected is covered with a first molded body, and the first molded body having a small elastic coefficient is protected by a second molded body, and a part of the first molded body is protected. By forming an external surface together with a part of the second molded body to form a stress relief structure, it is possible to integrally mold while avoiding an adverse effect on a protection target. In addition, at least a part of the surface (inner peripheral surface) of the through hole of the first molded body is covered with the second molded body to secure the strength, and the lower surface contact portion of the screw head and the through hole when attaching with a screw or the like. The deformation or breakage of the object to be protected due to the screw shaft or the like is prevented.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view of a proximity sensor showing a first embodiment of a molded body structure according to the present invention, FIG. 2 is a perspective view of a primary molded body of the proximity sensor shown in FIG. 1, and FIG.
FIG. 3 is a perspective view of a secondary molded body that covers the primary molded body of the proximity sensor illustrated in FIG. 2. The secondary molded body shown in FIG. 3 shows a state in which the primary molded body shown in FIG. 2 has been removed from the proximity sensor shown in FIG. 1 in order to easily understand the shape.

As shown in FIGS. 1 to 3, a proximity sensor (resin molded body) 10 includes a primary molded body (first resin molded body) 11 as a proximity sensor main body and an outer shell that covers the primary molded body 11. (Second resin molded body) 12 and an electric wire 13. The primary molded body 11 is made of a thermoplastic elastomer resin having rubber elasticity as a molding resin for the purpose of sealing insert parts. Further, as the secondary molded body 12, for the purpose of housing the proximity sensor 10, a molding resin satisfying specifications required for the sensor housing is selected, and the molding is performed twice without damaging the insert part. , And a solid integrated structure for realizing the housing of the sensor and the sensor. In addition, it is a matter of course to select a resin that can provide adhesion between the primary molding resin and the secondary molding resin.

As is well known, a thermoplastic elastomer resin is a polymer material having both the properties of rubber and plastic, having the same moldability as plastic, and having rubber-like elasticity. It shows the same properties as vulcanized rubber, and is plasticized at high temperatures and can be molded with a general injection molding machine. Typical thermoplastic elastomer resins include styrene butadiene (TPS), olefin (TPO), polyester (TPEA), polyurethane (TPU), vinyl chloride (TPVC), polyamide (TPEA), and fluorine. There are rubber type and the like. These thermoplastic elastomer resins have a small elastic modulus (for example, a longitudinal elastic modulus of 45 to 460 MPa), but have a large linear expansion coefficient (for example, 8 × 10 ^{−5 to} 20 × 10 ^5).
-5 [K ^-1 ]). The elastic modulus (also referred to as elastic constant) in the present specification is a longitudinal elastic coefficient (Young's modulus) which is a proportional constant between normal stress and vertical strain, a shear elastic modulus which is a proportional constant between shear stress and shear strain, This is a general term for bending elastic modulus, which is a proportionality constant between bending stress and bending strain, and indicates that a material having a larger value of the elastic coefficient has a smaller deformation under a constant load.

The thermoplastic elastomer resin is an engineering plastic (for example, PB) used for structural materials, materials having high heat resistance and high toughness, and parts having a high modulus of longitudinal elasticity.
T, ABS, PC, etc.)
6000 MPa), absorbs the difference in linear expansion coefficient between the insert part and the secondary molding resin of the secondary molding 12, lowers the adhesion between the primary and secondary molding resins due to temperature changes, and cracks Can be suppressed. Further, since the thermoplastic elastomer resin generally has a glass transition point at or below the sensor operating temperature, the absolute value of the thermal stress applied to the insert component itself can be reduced. That is, the glass transition point can be regarded as a temperature at which fluidity is lost. When the glass transition point is equal to or lower than the room temperature at which the sensor is used, the molding resin can be deformed according to the stress even when the sensor is used (at a temperature higher than the glass transition point), so that residual stress is hardly generated.

As shown in FIG. 4, the primary molded body 11 includes a core 21 on which a detection coil as an electric component or an electronic component is wound, a light emitting element (LED) 22, and another circuit element 24.
The circuit board 20 on which the components are mounted is inserted.
The circuit board 20 is, for example, formed by forming a conductive printed pattern on the surface of a glass / epoxy board, and the above-mentioned electric component or electronic component is fixed by soldering, wire wrapping, or the like. The electric wire 13 is connected to a terminal 14 of the covering material 14.
a of the cores 15 to 17 drawn out from the circuit board 2
0 (FIG. 6). In addition, as the primary molded body 11, a semi-transparent resin (for example, in the case of a polyester-based elastomer, a crystalline elastomer is used to make the light of the built-in light emitting element 22 transparent and visible from the outside). (Alloy material containing a conductive resin).

The circuit board 20 and the end of the electric wire 13 are housed in a primary molding die (not shown), and the end portion 14b of the sheath 14 of the electric wire 13 is caulked and narrowed, and the above-mentioned thermoplastic elastomer is formed. Primary molding resin 25 which is resin
Is filled. The primary molding resin 25 is used for the circuit board 2
0, the core 21, the light emitting element 22, and the gap between the circuit element 24, and are filled at a melting temperature lower than the heat resistant temperature when reaching the vicinity of these built-in components. For example, when a molten resin of 250 degrees Celsius is injected into a mold, the skin layer of the molten resin is cooled in the flow path, and the core layer flows to the vicinity of the component while being maintained at a high temperature. The skin layer has a temperature of about 90 degrees Celsius, and there is no problem even if the skin layer contacts a part having a heat resistance temperature of 100 degrees Celsius. Also, at this time, since the skin layer exerts a heat insulating effect, heat from the core layer kept at a high temperature does not reach the components directly and has no adverse effect. Thermoplastic elastomers have good fluidity even in the molten state at a relatively low temperature, so they can be injected at a relatively low pressure, without causing breakage or misalignment of built-in components due to the flow of molten resin. It can be molded integrally.

Further, the primary molding resin 25 enters the inside from the terminal 14a where the coating material 14 is opened, and is prevented from entering the inside from the part 14b because the part 14b near the terminal is caulked. The portion 14b is spread out in a substantially trumpet shape that expands toward the terminal 14a. Of course, the primary molding resin 25 also enters between the core wires 15 to 17 at the terminal 14a. Thereby, the electric wire 1
3, the pull-out strength (tensile strength) from the primary molded body 11 is greatly improved, and the sealing property of the insert part is ensured. Thus, the primary molded body 11 is molded.

As shown in FIG. 2 and FIG.
Has a substantially rectangular parallelepiped shape, and has an upper surface 1 behind the circuit board 20.
1a and a rear lower surface 11b 'are provided with screw mounting holes (step holes) 11c. The screw mounting holes (step holes) 11c further improve the adhesion to the secondary molded body 12, prevent the circuit board 20 from being deformed, etc. In order to position the substrate 20, a plurality of tapered holes 11d are provided from the upper surface 11a to the circuit substrate 20, grooves 11e and 11f are provided before and after both side surfaces, and a groove 11g is provided at the center of the front surface. The lower end of the groove 11g is connected to the front lower surface 11b.

As shown in FIG. 4, the front lower surface 11b of the primary molded body 11 is flush with the end surface (detection surface) 21a of the core 21 fixed to the circuit board 20.
The rear lower surface 11b 'connected to 1b is set at a predetermined height t from the front lower surface 11b. This front lower surface 11b
Is a reference plane (hereinafter referred to as “reference plane 11b”).
Cylindrical protrusions 1 on the left and right sides near the front end of reference surface 11b
1i and 11i are protruded, and the height thereof is
The predetermined height t is set from 1b.

Next, the primary molded body 11 is housed in a mold (not shown) for secondary molding, and two gates 11a, 11f on both sides and a gate 11g provided on the front face are provided. The secondary molding 12 is molded by injecting the molten molding resin 26 for the next molding under pressure. As the secondary molding resin 26, a hard resin is used to secure strength as an outer shell for protecting the primary molded body 11 and to obtain dimensional accuracy.

As described above, the thermoplastic elastomer resin used for the primary molded body 11 has a small coefficient of longitudinal elasticity, but has a large linear expansion coefficient. Therefore, the outer peripheral surface of the primary molded body 11 is formed by the secondary molded body 12 in the sensor package. If a sealing structure that covers and constrains all of the surfaces is adopted, all the strains generated by a change in the surrounding temperature become internal stresses of the primary molded body 11, thereby giving a large stress to the insert part.

Therefore, in the present invention, the secondary molded body 12 has a stress relief structure that restricts only to a portion requiring mechanical strength and dimensional accuracy. That is, by opening a predetermined area with respect to the primary molded body 11 and allowing the primary molded body to expand and contract in accordance with a change in the ambient temperature in that part, an occurrence occurs in the insert part of the primary molded body 11. It has a structure that can radiate thermal stress to the outside. Representative secondary molding resins include PBT, ABS, and PC. These secondary molding resins 26 have a larger longitudinal elastic modulus than the primary molding resin 25 (for example, 2000 to 6000 MP).
a).

As shown in FIGS. 3, 7, and 8, the secondary molded body 12 is formed between the upper plate 12a for protecting the upper surface 11a of the primary molded body 11, the reference surface 11b, and each projection 11i. The lower plate 12b that fills the space and protects the end surface 21a of the core 21, the screw mounting reinforcing portion 12c that covers the inner peripheral surface of the screw mounting hole 11c and the step surface that contacts the screw head, and the holes 11d of the upper surface 11a are filled. 12d for preventing deformation of the circuit board 20 such as warpage, and also serves as a reinforcing portion which is filled in the grooves 11e on both sides to connect the upper plate 12a and the lower plate 12b in series and protect a part of the front side. Connecting portion 12e, reinforcing portion 12 which is filled in grooves 11f on both sides to protect a part of the rear side portion
f, a reinforcing portion 12g which fills the groove 11e on the front surface and protects a part of the front surface, a protection portion 12j which covers the end portion 14b of the covering material 14 of the electric wire 13 and the like.

The lower plate 12b of the secondary molded body 12 is formed in close contact with the reference surface 11b of the primary molded body 11, and the left and right protrusions 1 are formed.
The plate thickness is accurately formed to a predetermined height t by 1i and 11i, and the lower surface is flush with the rear lower surface 11b '. Each projection 11i prevents deformation due to resin filled in the front portion of the upper surface 11a and maintains the space between the front lower surface 11b and the mold at a predetermined interval t. Thereby, the distance from the end surface (detection surface) 21a of the core 21 to the lower surface of the lower plate 12b is accurately set to the predetermined height t (FIG. 7), and variation in the operating distance of the proximity sensor 10 is suppressed. Further, the lower plate 12b is tightly formed on the reference surface 11b to ensure sealing performance, and the end surface 21a of the core 21 is liquid-tightly sealed.

Further, as shown in FIGS. 7 to 9, the inner peripheral surface and the step surface of the screw mounting hole 11c are covered with the reinforcing portion 12c of the secondary molded body 12, so that the strength is secured and the screw 40 (FIG. 9) At the time of attachment, deformation and breakage of the proximity sensor 10 due to the lower surface contact portion of the screw head 40a and the penetrating screw shaft portion 40b are prevented, and the core wires 15 to 17 of the electric wire 13 are prevented.
Is protected and the sealing property is secured. In addition, the reinforcing portion 12c
In the cylindrical portion, a plurality of long holes along the axial direction may be provided at intervals in the circumferential direction, or a large number of small holes may be provided in a mesh shape.

The screw mounting hole 11c of the secondary molded body 12
The reinforcing portion 12c covering the inner peripheral surface may have a shape as shown in FIG. 10 (a) or (b). Further, the reinforcing part 1
A female screw may be engraved on the inner peripheral surface of 2c. In this manner, the proximity sensor 10 includes the primary molded body 11 and the secondary molded body 1.
2, the insert part is sealed by the primary molded body 11 having a large linear expansion coefficient, and the thermal stress generated from the insert part is reduced by two. It is eased by making a part of the next molded body 12 open. Further, the primary molded body 1
By using a material having a small longitudinal elastic modulus (Young's modulus) for 1, peeling of adhesion caused by a difference in linear expansion coefficient between the insert component (built-in material) and the secondary molded body 12 is avoided. With such a structure, a solid structure of the proximity sensor 10 is achieved. As shown in FIG. 1, a window (opening) 12m may be provided on the upper plate 12a of the secondary molded body 12 as shown by a two-dot chain line to provide a further open structure.

FIG. 11 shows a second embodiment of the second molded body, which is a sheet-shaped housing 28 as a secondary molded body. That is, a metal plate is pressed to form a plurality of support portions 28b for reinforcement on both sides of the upper plate 28a, each of which is bent at right angles to one side, and furthermore, the tips 28c of these support portions 28 are bent at right angles inward. The housing 28 is formed by bending. Then, the housing 28 is attached to the primary molded body (not shown) formed as described above.
Assemble to fit. Further, if necessary, the primary molded body and the housing 28 may be bonded to each other using a rubber-based adhesive. The modulus of longitudinal elasticity of the steel sheet is about 200 GPa, and by using the secondary molded body as a sheet metal housing, sufficient strength can be ensured. Further, cost can be reduced. Further, the shape of the primary molded body can be simplified, and molding is facilitated.

FIGS. 12 and 13 show a third embodiment of the present invention, in which a primary molded body 31 of a proximity sensor 30 as a molded body structure has a disk shape, and for example, as a protective object,
A turn-wound coil 33 formed by winding a urethane-coated conductive wire around a bobbin made of high- permeability ferrite is inserted into a stepped screw mounting hole 31c provided through the upper surface 31a and the lower surface 31b at the center. The structure is such that the peripheral surface is covered with a secondary molded body 32. Thereby, the strength of the inner peripheral surface and the step surface of the screw mounting hole 31c is ensured, and the proximity sensor 3 includes a lower surface contact portion of the screw head 40a and a penetrating screw shaft portion 40b when mounting with the screw 40.
0 is prevented from being deformed or damaged, and the coil 33 is also protected and sealed.

The screw mounting hole 31c is shown in FIG.
(A) The central portion of the inner peripheral surface is protruded over the entire circumference to form an annular ridge or a simple hole as shown in FIG. May be coated. Screw mounting holes 31 of these primary molded bodies 31
The shape of c and the shape of the secondary formed body 32 covering the inner peripheral surface thereof may be formed according to the purpose of use. Further, a female screw may be formed on the inner peripheral surface of the secondary formed body 32.

In the above embodiment, the thermoplastic elastomer is used as the material of the primary molded body, but the present invention is not limited to this. That is, the object to be protected is not damaged in molding the primary molded body, and as long as the adverse effects due to thermal stress can be tolerated, it is also within the scope of the present invention to mold the primary molded body with the above-described engineering plastic or the like. is there. Further, in the above embodiments, the detection switches such as the proximity switch and the photoelectric switch have been exemplified, but the scope of the present invention is not limited to this.

[0030]

As described above, according to the molded article structure of the first aspect or the molding method of the fourth aspect, the object to be protected is covered with the first molded article and protected by the second molded article. And the object to be protected or the second
It is possible to perform integral molding while avoiding an adverse effect on the object to be protected due to a difference in the coefficient of linear expansion from the molded article. Accordingly, it is possible to facilitate the assembling work of the proximity sensor or the like as the object to be protected, to improve the sealing performance, or to further reduce the size. The molded body structure according to claim 2, wherein a part of the first molded body forms an external surface together with a part of the second molded body, so that a stress relief structure can be obtained. Accordingly, it is possible to facilitate the assembling work of the proximity sensor or the like as the object to be protected, to improve the sealing property, or to further reduce the size.

According to a third aspect of the present invention, the first molded body has a through-hole, and at least a part of the surface of the through-hole is covered with the second molded body. This prevents deformation or breakage due to the lower surface contact portion of the screw head and the penetrating screw shaft when mounting with a screw or the like.

[Brief description of the drawings]

FIG. 1 is a perspective view of a proximity sensor, showing a first embodiment of a molded body structure according to the present invention.

FIG. 2 is a perspective view of a primary molded body of the proximity sensor shown in FIG.

FIG. 3 is a perspective view of a secondary molded body covering the primary molded body of the proximity sensor shown in FIG. 2;
2 shows a state where the primary molded body shown in FIG.

4 is a cross-sectional view of the primary molded body shown in FIG. 2, taken along the line IV-IV.

FIG. 5 is a bottom view of the primary molded body shown in FIG.

6 is a cross-sectional view of the primary molded body shown in FIG. 4, taken along the line VI-VI.

FIG. 7 is a sectional view of the proximity sensor shown in FIG. 1 taken along the line VII-VII.

8 is a cross-sectional view of the proximity sensor shown in FIG. 7, taken along the line VIII-VIII.

9 is a cross-sectional view of the proximity sensor shown in FIG. 7 taken along the line IX-IX.

FIG. 10 is a sectional view showing another embodiment of the reinforcing portion of the screw mounting hole shown in FIG. 9;

FIG. 11 is a perspective view showing another embodiment of the second molded body of the present invention.

FIG. 12 is a plan view showing a second embodiment of the molded body structure according to the present invention.

FIG. 13 is a sectional view taken along the arrow line XIII-XIII in FIG.

FIG. 14 is a cross-sectional view showing another embodiment of the secondary molded article of FIG.

FIG. 15 is a cross-sectional view illustrating an example of a conventional detection switch.

[Explanation of symbols]

 10, 30 Proximity sensor (molded object) 11, 31 Primary molded body (first molded body) 11a Upper surface 11b Front lower surface 11b 'Rear lower surface 11c Screw mounting hole 12, 32 Secondary molded body (second molded body) 12a Upper plate 12b Lower plate 12c, 12e, 12f Reinforcement part 13 Electric wire 20 Circuit board (object to be protected) 21 Core (object to be protected) 22 Light emitting element (object to be protected) 24 Circuit element (object to be protected) 28 Casing (first object) 2 molded body) 33 Coil (protective symmetric object) 40 Screw

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Koji Seki, Inventor 2-12-19 Shibuya, Shibuya-ku, Tokyo F-term (reference) 4F206 AD03 AG03 AH33 JA07 JB12 JB25 JL02 JM04 JN12 JQ81

Claims (4)

[Claims] An object to be protected, a first molded body that directly covers at least a part of a surface of the object to be protected, and a second body that directly protects at least a part of a surface of the first molded body And a molded body, wherein the first molded body has a smaller elastic modulus than the second molded body. 2. The molded body structure according to claim 1, wherein a part of said first molded body forms an outer surface together with a part of said second molded body. 3. The first molded body has a through-hole, and at least a part of the surface of the through-hole is covered with the second molded body. Molded body structure. 4. A step of injection-molding a first molded body directly covering at least a part of an object to be protected using a mold, and a second step of directly covering at least a part of the first molded body.
A step of injection molding the molded body using a mold, wherein the first molded body has a smaller elastic modulus than the second molded body. .