JPS6338407Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to an erasing head used in video tape recorders, etc., and more specifically, the head body, glass, and block are attached to each other with epoxy resin and mounted inside a plastic case. A magnetic head of a type fixed with adhesive,
This invention relates to an erasing head which prevents malfunctions caused by differences in expansion coefficients due to temperature or humidity between a case, a block, a glass, and a head main body.

Erasing heads used in video tape recorders and the like are assembled by inserting the head body into a case molded from a plastic material such as phenolic resin, but the part of the head that comes into contact with the tape, that is, the front surface, is Because of the severe wear caused by the front head, blocks made of ceramic material such as non-magnetic ferrite or barium titanate are usually fixed to both sides of the front head with epoxy adhesive. The situation is as shown in FIGS. 1 and 2 (a view of the - section in FIG. 1 viewed in the direction of the arrow). In other words, in both figures, a case 1 of the erasing head includes a head body 2 which is a combination of a front core 2A, a back core 2B, and a coil (not shown in Figure 2), and is fixed to the front core 2A via adhesive. The three glass blocks 4A and 4B are attached and fixed to the case 1 with adhesive. Conventionally, there was almost no gap between the front core 2A and the inner surface of the case 1 (usually about 0.1 mm), as shown in Figure 2, and the adhesive for bonding the two was located near the front surface (as shown in Figure 2). Even if it is applied only to the upper part (as shown), it will penetrate into the entire gap between the two by capillary action,
The front core 2A and the case 1 were fixed to each other over their entire opposing surfaces.

On the other hand, when comparing the physical properties of plastic materials such as phenolic resin used for the case and ceramic materials such as ferrite, glass, or barium titanate, the former has a lower expansion rate due to temperature and humidity than the latter.
The value is more than 10 times higher. This has resulted in the problem shown in FIG. 4 in the conventional erase head. Figure 4 is a view of the - cross section in Figure 1 viewed in the direction of the arrow, showing only the vicinity of the front surface, with A showing the initial state, B and C showing the high temperature and humidity state, and showing the top and bottom. The directional dimensions are shown much more exaggerated than the lateral dimensions. In the figure, the front surface of the erasing head is initially aligned with the surfaces of blocks 4A, 4B, front core 2A, and glass block 3, as shown in A, but in high temperature and humid conditions, the front core 2A
Only the surface (Fig. This dimension C is usually about 0 to 5μ.

The cause of this problem is shown in FIG. 3 (a view of the - section in FIG. 1 viewed in the direction of the arrow) and FIG. 2. As mentioned above, the expansion rate of plastic is more than 10 times that of ferrite, glass, or ceramic, so when discussing dimensional changes due to changes in temperature or humidity of the erase head,
Approximately, only the expansion rate of the plastic needs to be considered. If the expansion coefficient of plastic at the current temperature or humidity is α or β, respectively, then the front surface of block 4B and the bottom surface of the case (-
The dimensional change between the two surfaces is b×α or b×β (see FIG. 3). As described above, the front core 2A and the case 1 are fixed to each other over their entire opposing surfaces, and the expansion of that portion depends on the expansion of the front core. Therefore, the dimensional change between the front surface and the negative surface of the front core is a×α or a×β. This is the cause of the unevenness of the front surface as shown in FIG. 4 described above, and C=(ba)α or C=(ba)β.

Conventionally, even when the front surface of the erasing head is hot and humid, there are cases where the unevenness shown in Figure 4 (b) and (c) does not occur, but in such cases, cracks often occur in the front core. It was. This is because a crack occurs in the front core due to stress caused by the difference in expansion coefficient between the case 1 and the front core 2A.

Needless to say, the unevenness of the front surface and the cracks occurring in the front core lead to poor performance of the erase head.

The object of the present invention is to prevent the above-mentioned drawbacks of conventional erasing heads and to provide an erasing head whose performance does not deteriorate even under high temperature and humidity.

The present invention was developed based on the fact that the drawback of conventional erasing heads is that the facing surfaces of the front core and case are completely fixed with adhesive. The above objective is achieved by setting the thickness to 1.0 mm or more.

Embodiments of the present invention will be described below based on the drawings. FIG. 5 is a front view of the erasing head according to the present invention, and FIG. 6 is a cross-sectional view taken in the direction of the arrow in FIG. In both figures, a groove 1A is provided on the surface of the case 1 facing the front core 2A. Therefore, a gap d of 1.0 mm or more is provided between the case surface and the front core surface in this portion. The structure of other parts is no different from the conventional erasing head described above. In this example, the case contains the head body 2, glass 3, block 4.
After inserting A and 4B, adhesive 5 is applied to the gap between case 1 and front core 2A to bond them, but since the gap d is more than 1.0 mm, the adhesive 5 spreads over the entire opposing surface due to capillary action. There is no fear that it will spin. If the adhesive 5 is thixotropic, it will not flow downwards even after heating and hardening, and will remain in the applied position as shown in FIG. If the distance e between the lower end of this painted position and the surface is eb, then even if the case 1 expands due to high temperature and humidity, the distance between the reference surface and the front core 2A, block 4
The distance between each front surface of A and 4B is equal,
There is no risk of unevenness or cracks due to stress.

As mentioned above, the present invention is based on the temperature of the erase head.
This prevents unevenness on the front surface caused by changes in humidity or cracks in the front core, and greatly contributes to improving the performance and durability of the erasing head.

[Brief explanation of the drawing]

1 and 2 are diagrams showing the general structure of a conventional erasing head. FIG. 2 is a cross-sectional view of FIG. 1 viewed in the direction of the arrow, and FIG. A diagram of the cross section viewed in the direction of the arrow,
4A to 4C are cross-sectional views of FIG. 1 showing the unevenness of the front head surface, FIG. 5 is a front view of the erasing head according to the present invention, and FIG. - A cross-sectional view seen in the direction of the arrow. 1...Case, 1A...Groove, 2...Head body, 2A...Front core, 2B...Back core, 3...Glass, 4A, 4B...Block, 5
……glue.

Claims (1)

[Scope of utility model registration request] A head body, which is a combination of a front core, a back core, and a coil, and a glass block made of ceramic material and fixed to the front core with adhesive are inserted and fixed into a case molded from a plastic material. 1. An erasing head for a tape recorder comprising: a groove of a predetermined depth is provided in a case surface facing the front core, and a gap therebetween is 1.0 mm or more.