JP2007060138A - Coil antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coil antenna which meets specifications such as L value necessary for transceiving, sensitivity, impedance value and the like, as a matter of course; moreover, whose core is hard to crack even when it is thin, and whose heat resistance is so high that it is not deformed during reflow. <P>SOLUTION: A sheet-like magnetic substance 4 which is formed of a hybrid of powder of soft magnetic body and an organic bonding material and exhibits flexibility is covered with a heat-resistant resin 5 to form the core 2. Wire 3 is directly wound on the core 2 to form the coil antenna 1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a magnetic sheet and a coil antenna for a coil antenna used for transmission and / or reception of a radio signal of a low and medium wave band used for a remote key system such as a vehicle key or a house key, or a radio clock. In particular, the present invention relates to a coil antenna suitable for transmission and reception of a radio signal at a frequency in the range of 10 kHz to 20 MHz.

  In recent years, communication terminals have become smaller and more versatile, and there are many terminals that use radio waves in the low and medium wave bands. For example, there is a coil antenna in the vehicle keyless system disclosed in Patent Document 1, and many coil antennas using a ferrite material magnetic core (sintered ferrite) as a coil antenna in a low and medium wave region are widely used. .

  In this Patent Document 1, a multi-axis coil antenna using three types of ferrite magnetic core shapes is prototyped and the result is described. However, when the magnetic core size is 10 × 10 × 1 mm (described as “sample product B”), it is wound using a plastic bobbin instead of a coil wound directly around the magnetic core. It is stated in the text that this is done to stabilize the winding quality.

JP 2003-249816 A

  However, coil antennas that use ferrite material magnetic cores (sintered ferrite) have a market demand for impact resistance (preventing defects such as magnetic core cracking) and diversification of shapes (different shapes, multi-axis with directivity) , Lightness, shortness, and enlargement), there are problems such as impact resistance and poor manufacturability.

  Moreover, recent remote keys for automobiles, etc. have a predetermined LF wave by pressing a switch on the vehicle body side with the remote key in the pocket or by touching a door handle having a capacitance sensor or the like. The door can be opened and closed by receiving a signal transmitted from the vehicle body side and receiving a signal from the vehicle body side with this remote key. However, while being constantly required to be thin and light due to the characteristics of carrying (pocket, bag, etc.), damage to the magnetic core due to a drop impact becomes a fatal failure, so impact resistance is required.

  Actually, when the sintered ferrite core is left alone as it is dropped from the height of about 0.5 m to 1 m on the floor surface, even a ferrite core having a thickness of about 2 to 3 mm is cracked with considerable frequency. Therefore, although there is an advantage in static characteristics, it is difficult to reduce the size and height (thinner). In many cases, a resin case or a rubber material protection mechanism is attached so that the impact is not directly propagated to the magnetic core. However, these measures are factors that hinder downsizing and height reduction.

  In addition, plastic ferrites combined with resin have been studied, but impact properties and manufacturability are improved to some extent. However, pursuing characteristics as an antenna requires increasing the ferrite filling rate, and eventually antenna characteristics. The plastic ferrite material satisfying the condition causes a problem that the impact resistance becomes weak as in the case of sintered ferrite.

  Now, in the case of a portable remote key for in-vehicle use or residential use, an unlocking / locking signal circuit and an antenna system of another system may be mixedly mounted inside, and in achieving the above-mentioned thinning and integration, SMD It is desired to be a part and to be compatible with reflow. In addition, due to the full-scale introduction of lead-free solder, the reflow temperature is higher (about 240 to 250 ° C.) than conventional lead solder reflow.

  Further, the demand for thinning is increasing due to the design as a portable remote key. For example, in the case of a remote key, a card type design of about 1 to 2 mm or less is desired.

  Accordingly, the present invention has been made to solve the above-described problems. In addition to satisfying specifications such as L value, sensitivity, impedance value, etc. required for transmission / reception, the magnetic core of the coil antenna is also provided. As a first object, it is intended to provide a coil antenna that is not cracked even if it is thinned, and secondly that ensures heat resistance without deformation during reflow.

  In order to solve the above-mentioned problems, the present invention has been made by finding out a synergistic effect as a result of investigating the anchor effect and the adhesive effect of the resin on the surface roughness of the joint surface.

  That is, according to the present invention, there is provided a coil antenna in which a flexible sheet-like magnetic body composed of a mixture of soft magnetic powder and an organic binder is directly wound on a magnetic core covered with a heat-resistant resin. can get.

  Further, according to the present invention, a coil is formed by attaching a bobbin to a magnetic core made of a flexible sheet-like magnetic body made of a mixture of soft magnetic powder and an organic binder, and winding the bobbin. An antenna is obtained.

  Further, according to the present invention, the soft magnetic powder has a high magnetic permeability at a high frequency, such as iron aluminum silicon alloy (Sendust), iron nickel alloy (Permalloy), iron cobalt alloy, iron cobalt silicon alloy, iron silicon vanadium alloy. A coil antenna made of any one of iron cobalt boron alloy, cobalt-based amorphous alloy, iron-based amorphous alloy, carbonyl iron, molybdenum permalloy, pure iron powder, or a combination thereof can be obtained.

  According to the present invention, the organic binder is a thermoplastic resin such as a polyester resin, a polyvinyl chloride resin, a polyvinyl butyral resin, a polyurethane resin, a cellulose resin, a nitrile-butadiene rubber, or a styrene-butadiene rubber. Resin, or copolymer thereof, epoxy resin, phenol resin, amide resin, imide resin, and other thermosetting resins, or organic flame retardant halides, brominated polymers, or combinations thereof A coil antenna is obtained.

  In addition, according to the present invention, a coil antenna is obtained, in which a flexible sheet-like magnetic body made of a soft magnetic amorphous material is covered with a heat-resistant resin and a winding is directly applied to the magnetic core.

  Further, according to the present invention, a coil antenna is obtained in which a bobbin is attached to a magnetic core made of a flexible sheet-like magnetic body made of a soft magnetic amorphous material, and the bobbin is wound.

  According to the present invention, since the magnetic core is a flexible sheet-like magnetic body made of a mixture of soft magnetic powder and an organic binder or a soft magnetic amorphous material, the magnetic core is bent during use. However, even if it is used while being kept bent, it satisfies specifications such as L value, sensitivity, impedance value, etc. necessary for transmission and reception in the frequency band of 10 kHz to 20 MHz. At the same time, it is possible to obtain a coil antenna that is difficult to break even if it is thin, and that ensures heat resistance without deformation of the magnetic core during reflow.

  Embodiments of the present invention will be described below.

  FIG. 1 is a perspective view of a coil antenna according to an embodiment of the present invention. In FIG. 1, a coil antenna 1 is constituted by a winding 3 wound around a magnetic core 2, and the magnetic core 2 has a structure in which a sheet-like magnetic body 4 is covered with a resin 5.

  First, assuring impact resistance that is difficult to break can be greatly improved by using a flexible sheet-like magnetic body 4 made of soft magnetic powder and an organic binder for the magnetic core 2 as compared with a sintered ferrite material. .

  As the soft magnetic powder in the sheet-like magnetic body 4 used in the present invention, iron aluminum silicon alloy (Sendust), iron nickel alloy (Permalloy), iron cobalt alloy, iron cobalt silicon alloy having a high magnetic permeability at high frequency, Any of iron silicon vanadium alloy, iron cobalt boron alloy, cobalt-based amorphous alloy, iron-based amorphous alloy, carbonyl iron, molybdenum permalloy, pure iron powder, or a combination thereof is used.

  In addition, there are a wide variety of organic binders that bind soft magnetic powder, including polyester resins, polyvinyl chloride resins, polyvinyl propylar resins, polyurethane resins, cellulose resins, nitrile-butadiene polymers, styrene-butadiene rubbers. And thermoplastic resins such as these, or their copolymers, thermosetting resins such as epoxy resins, phenol resins, amide resins, and imide resins, halides that are organic flame retardants, and brominated polymers.

  In addition, some of these organic binders have insufficient resistance to the lead-free solder reflow process conditions (temperature and time). In the sheet-like magnetic body 4 using this organic binder, In the coil antenna 1 in which the magnetic core 2 is formed, some of the deformation of the magnetic core 2 and the organic binder deteriorate due to heating in the reflow process at the time of assembly, and as a result, the quality of the antenna characteristics deteriorates.

  Therefore, in the present invention, in order to solve the problem of ensuring heat resistance without deformation of the magnetic core 2 made of the sheet-like magnetic body 4 in reflow, the present invention examined two methods. One is a method of correcting the deformation during heating by holding the magnetic core 2 with a bobbin (not shown) from the outside, and the other is an organic binder constituting the sheet-like magnetic body 4. This is a method of changing to one having reflow heat resistance.

  When a bobbin (not shown) is used, the magnetic core 2 can be pressed from the outside due to its structure, so that at least expansion and deformation during heating can be suppressed. However, from the viewpoint of reducing the thickness, the thickness of the resin bobbin causes the thickness of the magnetic core 2 to be reduced, and the cross-sectional area of the magnetic core 2 is reduced. Decreases. Further, the heating in the reflow process is far from the actual use environment temperature, and therefore it is not desirable from the viewpoint of cost to add a bobbin.

  Moreover, it is not always easy to change the organic binder of the sheet-like magnetic body 4 in the manufacturing process of the sheet-like magnetic body 4, and compatibility with each soft magnetic material, production equipment, and a change in the construction method occur. As a result, considerable development man-hours may be required.

  From the above, the present invention focuses on preventing deformation of the magnetic core 2 during reflow, and by directly applying the heat-resistant resin 5 to the sheet-like magnetic body 4, Provided is a method for obtaining a structure that can be applied as it is while maintaining the configuration of the sheet-like magnetic body 4 used for the internal magnetic core 2 while having an effect. As the resin 5 having heat resistance, for example, a liquid epoxy resin is appropriate.

  Further, as a method for forming a film on the sheet-like magnetic body 4 with the resin 5 having heat resistance, it can be applied by dipping, potting, spin coating or the like. The spin coating method is a particularly suitable method for forming a uniform resin film on a wide plane with a small amount of dripping.

  In the present invention, as one method of covering the small pieces of the sheet-like magnetic body 4 with the resin 5, a method of forming the resin 5 in two stages was performed. First, the resin film 5 is formed by using the above-mentioned resin on one side or both sides of a sheet-like magnetic plate having a sufficiently large size (for example, 150 mm □) compared to the dimension of the magnetic core 2 used for a portable key or the like. To do. Thus, the sheet-like magnetic plate is more easily handled than the sheet-like magnetic plate by the hardness of the resin film.

  Next, after cutting into a sheet-like magnetic body 4 having a desired dimension (for example, a width of 5 mm, a length of 20 mm, and a thickness of 0.5 mm to 1 mm) as the magnetic core 2, the outer periphery is covered with the same or different resin as described above. Thus, a thin magnetic core 2 having both resistance to cracking and heat resistance is obtained. By applying the winding 3 to the magnetic core 2, a coil antenna 1 that can be mounted on a card-shaped key having a thickness of less than several millimeters is obtained.

  The resin film 5 is insulative and can also serve as an insulating layer between the winding 3 and the magnetic core 2. Further, as a secondary matter, when the winding 3 is applied to the magnetic core 2 on which the resin film 5 is formed, a certain degree of hardness is advantageous from the viewpoint of the winding process. The effect of stabilizing workability can be expected.

  As another method, it is also possible to form a film on the outer peripheral surface of the sheet-like magnetic body 4 with a liquid resin in the same step after first cutting into small pieces. As another method, a structure in which a film-like resin (for example, a polyimide resin film) is first attached to a small piece of the sheet-like magnetic body 4 may be used.

  In addition, when the outer periphery of the small piece of the sheet-like magnetic body 4 is covered with the resin 5, if possible, the entire structure of the small piece is covered with the resin 5 and the structure in which the sheet-like magnetic body 4 is confined inside is the best. It does not have to be completely closed. For example, when the shape of the magnetic core 2 is elongated such that L × W × H is 5 × 20 × 2 mm, the two narrow surfaces formed by L × H may not be closed. Is whether or not the L value characteristic change amount after reflow is acceptable.

  That is, in the present invention, a coil antenna that is miniaturized as the casing is thinned, includes a flexible magnetic core 2 that is flexible and difficult to break, and a winding 3 wound around the magnetic core 2. In addition, the coil antenna 1 having reflow resistance is obtained.

Below, the specific example of a coil antenna of this invention is demonstrated. A sheet of magnetic material plate was prepared by cutting a flexible 1 mm thick sheet made of a soft magnetic powder and an organic binder into 60 mm □. After applying a liquid epoxy resin (viscosity of about 100 cp) to this sheet-like magnetic plate with a spin coater, baking is performed for 1 hour in a N ₂ atmosphere at 70 ° C., and the liquid epoxy resin is again applied to the opposite surface under the same conditions. This was applied and baked again in an N ₂ atmosphere at 70 ° C. for 1 hour. The sheet-like magnetic body plate covered with the resin thus produced was cut to produce a 5 × 20 × 2 mm sheet-like magnetic body 4.

  When a plurality of the sheet-like magnetic bodies 4 are provided on the tray, the same resin is dropped from above and cured at 100 ° C. for 2 hours to produce the magnetic core 2. Furthermore, a coil wire 3 was formed by winding a 0.3 mmφ polyurethane wire around the magnetic core 2 (direct winding, about 1200 T), and the coil antenna 1 was obtained. Note that the sheet-like magnetic body 4 is a composite made of soft magnetic powder and an organic binder, and is flexible in itself, but it is appropriate to cover the surface of the sheet-like magnetic body 4 with an epoxy resin 5. A magnetic core 2 having a sufficient surface hardness is obtained.

  In order to verify the transmitting coil antenna and the receiving coil antenna thus manufactured, the characteristics of the coil antenna were measured. As comparative examples, two coil antennas having a sintered ferrite magnetic core were prepared for transmission and reception. The coil antenna of the comparative example has the same structure, shape and size as the present embodiment except that the magnetic core material is different. In addition, the characteristics of the coil antenna of the comparative example were also measured.

  The transmission coil antenna according to the present embodiment had better transmission characteristics than the transmission coil antenna of the comparative example. Similarly, the receiving coil antenna according to the present embodiment had better receiving characteristics than the receiving coil antenna of the comparative example.

  Further, the transmission / reception characteristics according to these embodiments were not particularly deteriorated even when the coil antenna 1 was bent. This is because the soft magnetic powder particles operate independently as "microcores". In the present embodiment, since each powder particle is coated with an oxide film, the total number of microcores does not change even when the coil antenna 1 is bent, and therefore excellent transmission / reception characteristics are maintained. Seems to be able to do.

  From the above, when using sintered ferrite as a magnetic core in a keyless system, a radio timepiece, or an electronic device that is required to be thin, the problem of cracking when using a thin ferrite is to use the sheet-like magnetic body 4 that is difficult to break as the magnetic core 2. In this way, the thin flat coil antenna 1 is manufactured, and the influence of heat in the reflow process is covered with an appropriate resin 5 on the outside of the sheet-like magnetic body 4 to prevent deformation and deterioration of characteristics due to heat. It was possible to provide the coil antenna 1 capable of suppressing the above.

  The coil antenna according to the present invention is applicable to a wireless transmission / reception system capable of transmitting / receiving a radio signal of 10 kHz to 20 MHz, and a time adjustment mechanism that automatically adjusts the time according to the radio signal received using the coil antenna. It can be applied to a radio wave wristwatch equipped with Moreover, in a remote keyless entry system, it can also be used as an antenna for receiving a user identification signal transmitted from an object carried by the user. Further, when the coil antenna of the present invention is mounted on a door, a handle portion or the like of an automobile, a remote keyless entry system automobile is obtained.

1 is a perspective view of a coil antenna according to an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Coil antenna 2 Magnetic core 3 Winding 4 Sheet-like magnetic body 5 Resin (resin film)

Claims (6)

  A coil antenna comprising a magnetic core made of a mixture of soft magnetic powder and an organic binder and having a flexible sheet-like magnetic body covered with a heat-resistant resin, and is directly wound.   A coil antenna comprising: a bobbin attached to a magnetic core made of a flexible sheet-like magnetic body made of a mixture of soft magnetic powder and an organic binder; and winding the bobbin.   The soft magnetic powder has high magnetic permeability at high frequencies, such as iron aluminum silicon alloy (Sendust), iron nickel alloy (permalloy), iron cobalt alloy, iron cobalt silicon alloy, iron silicon vanadium alloy, iron cobalt boron alloy, cobalt series The coil antenna according to claim 1 or 2, comprising any one of an amorphous alloy, an iron-based amorphous alloy, carbonyl iron, molybdenum permalloy, and pure iron powder, or a combination thereof.   The organic binder is a thermoplastic resin such as polyester resin, polyvinyl chloride resin, polyvinyl butyral resin, polyurethane resin, cellulose resin, nitrile-butadiene rubber, styrene-butadiene rubber, or a copolymer thereof. 2. A thermosetting resin such as an epoxy resin, a phenol resin, an amide resin or an imide resin, or a halide or brominated polymer which is an organic flame retardant, or a combination thereof. The coil antenna according to any one of claims 3 to 4.   A coil antenna comprising a magnetic sheet made of a soft magnetic amorphous material and having a flexible sheet-like magnetic body covered with a heat-resistant resin, and is directly wound.   A coil antenna comprising: a bobbin attached to a magnetic core made of a soft sheet-like magnetic material made of a soft magnetic amorphous material; and winding the bobbin.

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