JPH06151162A - Induction coil - Google Patents

Abstract

PURPOSE:To eliminate distortion between a bobbin and a molding material and also increase strength of close contactness at the boundary between the bobbin and molding material. CONSTITUTION:A coil 7 is wound on a polyester bobbin 1 and it is then placed in a metal die 9 for injection molding. Thereafter, melted polyester having the melting point higher than that of the polyester of the bobbin 1 is supplied into the metal die 9. The coil 7 is integrally covered with a molding member formed of the hardened polyester.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention covers a coil wound around a bobbin with a molding member so as not to expose the coil at all, for example, a solenoid, a magnetic sensor, a magnetic switch,
The present invention relates to an induction coil used for pickups and the like.

[0002]

2. Description of the Related Art In the induction coil, a synthetic resin is exclusively used as a material for a bobbin and a molding member. A coil is wound around a bobbin made of a primary material, and the coil is housed in a mold. The coil is integrally covered by injecting a secondary material for forming the molding member into the mold. As a synthetic resin used in a conventional induction coil, various thermoplastic resins such as a polyamide-based one are selected and used depending on the application in consideration of productivity, price, durability and the like.

[0003]

One of the uses of the induction coil is a solenoid, and this solenoid is used in many automobile parts. The environmental conditions in the engine room of a car are bad, and the solenoid placed in such a place makes the coil unreasonable due to the distortion of the bobbin of the induction coil or the molding member when the engine room changes from a low temperature atmosphere to a high temperature atmosphere. Power is added,
There is a risk of disconnection. Also, if a sudden temperature drop is applied or if a void exists inside the molded product, the interface between the bobbin and the molding member and the periphery of the coil will be depressurized due to resin shrinkage, etc. If the joining is insufficient at the boundary between the bobbin and the molding member, water may be allowed to enter there from, and the thin metal coil may be corroded by the water. Among these drawbacks, the former is due to the fact that the polyamide-based resin or the like has a high hygroscopic property and thus easily causes distortion,
Also, in the latter case, since the boundary between the bobbin and the molding member is obtained by closely curing the cured primary material with the secondary material in a molten state, regardless of the type of resin, the adhesion strength is generally increased. This is because it cannot be secured enough.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide an induction coil in which strain due to temperature change is reduced and which has a high adhesion strength between a bobbin formed of a primary material and a molding member formed of a secondary material. In that structure, the polyesters having different melting points are selected for the primary material and the secondary material, and the melting point of the polyester used as the primary material is
The combination is lower than the melting point of the polyester used as the secondary material.

[0005]

By using polyester having a low water absorption rate for both the primary material and the secondary material, the bobbin and the molding member are less likely to be distorted due to temperature changes, and the degree of stress applied to the coil is small. When the molten secondary material is injected into the mold, the primary material having a lower melting point than the secondary material
The surface layer that is in contact with the secondary material is melted, and the boundary surfaces between the primary material and the secondary material are both in a molten state, and when hardened, they are fused together and the clear boundary disappears.

[0006]

EXAMPLE A modified PBT (polybutylene terephthalate) obtained by controlling the induction coil according to the present invention by copolymerizing DMI (dimethyl isophthalate) as a polyester for a general material, and a PBT (polyester for a secondary material). The example applied to the induction coil for the solenoid valve adopting (polybutylene terephthalate),
A description will be given based on FIG. Reference numeral 1 is a slender modified PBT bobbin, which is provided with flange portions 2.3 at both ends, one flange portion 2 is provided with a metal terminal 4, and the other side flange portion 3 is provided with a nipple type port 5. No. 6 is integrally formed by protruding molding. The bobbin 1 includes the flange portion 2.
A coil 7 made of a copper thin wire coated with an insulator is wound between 3 and the metal terminal 4 is connected to an end of the coil 7.

A bobbin 1 formed of modified PBT and wound with a coil 7 is set in a mold 8 for injection molding, and a secondary material is inserted in a gap between the mold 8 and a sprue (not shown). Inject some molten PBT. This injected PB
T is a polyester having a melting point higher than that of the modified PBT which is the primary material forming the bobbin 1. Therefore, PBT, which is the secondary material injected in the molten state, is naturally higher in temperature than the melting point of the modified PBT, which is the primary material. The layers are melted and both cure in contact in the molten state. As a result, the boundary between the bobbin 1 and the molding member 9 formed by the hardening of the molten PBT becomes unclear, and the airtightness is secured by the perfect heat-sealing effect in the same state as when the boundary disappears. A lead wire system may be used instead of the metal terminal.

The induction coil thus formed is commercialized as a solenoid valve by incorporating a valve unit (not shown) in the bobbin 1. Since the solenoid valve that has been commercialized is made of resin with a low water absorption rate for both the bobbin and the molding member, there is little distortion due to temperature changes, there is no risk of disconnection due to the stress applied to the coil, and the coil is completely Since the bobbin and the molding material are completely sealed with each other due to the high airtightness,
It is completely waterproof and does not allow water to enter through the interface that causes corrosion of the metal coil.

Although the above embodiment has described the induction coil for the solenoid valve, the present invention can be applied to induction coils other than the solenoid valve. Next, an example implemented in the induction coil for the magnetic sensor will be described. The same reference numerals are used for the same parts as those in the above embodiment. 2 and 3, the elongated bobbin 1 has flange portions 2.
3 is provided, and the core accommodating portion 10 is integrally formed continuously with the one flange portion 2. A metal terminal 4 is projected from the core accommodating portion 10, and a coil 7 made of a copper fine wire coated with an insulator is wound between the flange portions 2.3 of the bobbin 1, and the end of the coil 7 is wound. The part is connected to the metal terminal 4.

The bobbin 1 formed of DMI-modified PBT and wound with the coil 7 is set in the injection molding die 8 and the tip of the metal terminal 4 is headed out of the cavity, as in the previous embodiment. Then, molten PBT, which is the secondary material, is injected into the gap between the mold 8 and the mold 8, and the mold is released after curing. In the induction coil according to the present embodiment as well, the coil is surely protected by the molding member 9 as in the above embodiments, and the core (not shown) in which the metal and the permanent magnet are combined is incorporated into the core storage portion to thereby provide a magnetic sensor. Will be commercialized as.

In order to find the optimum combination of polyesters used in each of the above-mentioned examples, the applicant selected polyesters having different characteristics and conducted an experiment on the adhesion strength exhibited by those combinations. Next, the experimental example will be described. First, the cross section is 3.0 mm × 20.0 mm, and the length is
A test piece 11 having a stepwise adhesive surface of 150.0 mm and a stepwise adhesive surface of 10.0 mm was set in the central portion in the length direction (Fig. 4), and the preformed primary material side test piece was set in the mold and the secondary A molten resin, which is a material, is injected and cured to obtain a test piece bonded at the bonding portion. The evaluation was performed by measuring the strength of peeling of the adhesive portion by a tensile test of the test piece. The selected polyesters have three melting temperatures of 205 ° C., 215 ° C., and 225 ° C., respectively. The former two kinds are modified PBT modified by copolymerizing DMI (dimethyl isophthalate), and the latter one is a normal one. P
It is BT. The results are shown below, in which the resins A, B, and C are sequentially used, the resin C is used as the secondary material, and the cylinder temperature at the time of molding is changed.

[0012]

[Table 1]

From these results, when the cylinder temperature was set to 260 ° C., the resin C. Practical adhesion strength cannot be expected between Cs, but relatively high adhesion strength is exhibited only by raising the cylinder temperature by 20 ° C. Further, even when the cylinder temperature is 260 ° C., when it is combined with the resin B, the adhesion strength becomes higher, and with the resin A, a better result is obtained. Further, when the cylinder temperature is raised by 10 ° C., respectively, the adhesion strength is remarkably improved, but in both cases, the adhesion strength tends to decrease when the cylinder temperature is increased more than that. It was also found that there is a range of.

In order to find the optimum combination of polyesters in the examples following the above experiments, the applicant formed an induction coil in which the combination of the primary material and the secondary material was changed, and the airtightness exhibited by each combination was examined. Experiments were also conducted. Next, the experimental example will be described. The polyesters selected have melting temperatures of 205 ° C, 215 ° C, and 2
There are four types at 25 ° C and 257 ° C, the former two types are DMI modified P
BT and the latter two kinds are ordinary PBT and PET (polyethylene terephthalate). These are the resins A, B,
Let C and D. The inspection method is 60 in an atmosphere of 130 ° C.
After exposing for a minute, soak it in water at 0 ° C for 60 minutes,
A heating / cooling cycle of taking out from water and leaving at room temperature for 15 minutes was repeated 50 times, and the resistance value between the metal terminals was measured. Further, after the measurement, highly penetrable ink is dropped on the boundary part between the primary material and the secondary material (a and b in FIG. 1) and the boundary part between the secondary material and the core part (c in FIG. 3), The state of ink penetration was also observed. Incidentally, in the case where disconnection was confirmed in the resistance value measurement experiment, the ink invasion condition was observed at that time, and the ink invasion condition was inspected by destroying the ink after it had dried. The conditions of injection molding and the results of each inspection are as follows.

[0015]

[Table 2]

[Table 3]

From the results, it can be seen that although the resin C is used as both the primary material and the secondary material, the airtightness is poor.
Or when B is used and C is used as the secondary material,
It was found that when C was used as the primary material and D was used as the secondary material, the airtightness was excellent, and if the melting point of the primary material was a combination lower than the melting point of the secondary material, it was severe. It was possible to obtain the confirmation that the coil can be protected reliably even under various conditions.

The present invention is not limited to the combination of the primary material and the secondary material used in the above Examples and Experimental Examples,
If it is a polyester type, the same effect can be expected by combining the melting point of the primary material with the melting point of the secondary material. The polyester used may be various substances generally added to the resin, depending on the purpose and application, such as antioxidants, heat stabilizers, stabilizers such as ultraviolet absorbers,
Antistatic agent, lubricant, plasticizer, mold release agent, flame retardant, flame retardant aid, crystallization accelerator, dye, pigment, or fibrous, powdery,
It may be a mixture of plate-shaped fillers.

The induction coil of the present invention is not limited to the solenoid valve and the magnetic sensor shown in the embodiments, but can be applied to a single solenoid or other various devices using the induction coil, and the shape and size thereof can be improved. The size and the like are arbitrary.

[0019]

According to the present invention, since there is little influence on strain and airtightness due to temperature change, there is no trouble due to coil breakage or water ingress, and reliability that is sufficient for utilization under adverse conditions is outstanding. I can say.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example in which an induction coil according to the present invention is used for a solenoid valve.

FIG. 2 is an explanatory cross-sectional view showing an example in which the induction coil according to the present invention is used for a magnetic sensor.

FIG. 3 is a sectional view taken along line XX of FIG.

FIG. 4 is an explanatory view showing the shape of a test piece.

[Explanation of symbols]

1 ··· Bobbin 2.3 · · Flange part 4 · · Metal terminal 5.6 · · Port 7 · · Coil 8 · · Lead wire 9 · · Mold 10 · · Molding member 11・
・ Core storage part, 12 ・ ・ Metal terminal, 13 ・ ・ Test piece.

Claims (1)

[Claims] 1. An induction coil in which a coil is wound around a bobbin made of a primary material, and the wound coil is completely covered with a molding member made of a secondary material. An induction coil in which polyesters having different melting points are selected as the next material, and the melting point of the polyester used as the primary material is lower than the melting point of the polyester used as the secondary material.