Magnetic head
This is a continuation, of application Ser. No. 14,849, filed Feb. 26, 1979 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a magnetic head improved in the electromagnetic converting characteristics and abrasion resistance by providing thin plates of a high magnetic permeability with an adhesive layer comprising a granular substance. 
     2. Description of the Prior Art 
     The magnetic head, being designed for information recording and playback by friction contact with a magnetic tape, is gradually abraded at its contact surface with the magnetic tape to lose the recording performance in the higher frequency region in the beginning and to eventually result in a deterioration of the recording performance over the entire frequency range as the abrasion proceeds. Such drawback can be prevented by increasing the abrasion resistance to reduce the amount of abrasion and to cause the abrasion to occur in a uniform manner. For example in case of an audio cassette tape recorder with a recording track width of ca. 0.6 mm, the stereo magnetic head is composed of four laminated thin plates each 0.15 mm thick to obtain the above-mentioned track width, since a single plate of a 0.6 mm thickness will result in a significant eddy current loss, leading to a loss in the electromagnetic converting efficiency. In such structure said laminated thin plates have to be mutually insulated electrically, and are therefore composed of a material of a high magnetic permeability such as permalloy or sendust each provided on the surfaces thereof with a resinous insulating adhesive. Consequently the track face of the magnetic head is composed of an alternating laminated structure of said material of high magnetic permeability and said adhesive layer. Such laminated structure is generally obtained by forming a thin layer for example of an epoxy resin, for example by spraying, on thin plates of a high magnetic permeability and compressing such plates under heating. In such structure, however, said resin layer tends to generate a stress along the surface of said thin plates at the hardening of resin after lamination, thus resulting in a deterioration of magnetic properties. On the other hand a resin with a low stress generation generally provides an excessively low adhesive force. In the conventional magnetic heads said material of high magnetic permeability has been changed from permalloy to less-abradable materials such as hard permalloy or sendust while said adhesive has been of a lower abrasion resistance than that of said material of high magnetic permeability in order to ensure a satisfactory adhesion, but it is to be noted that the abrasion resistance of the entire magnetic core is also affected by the abrasion resistance of said adhesive. Furthermore said magnetic core, after coil winding, is inserted into a head case and fixed therein by means of a fixing material to be filled between said core and said case, so that a part of said fixing material will constitute, together with said magnetic core, the contact face with the magnetic tape. It is therefore necessary, in order to maintain the initial performance of the head for a prolonged period, that said core and said fixing material are evenly abraded to always maintain a flat contact face. In the conventional magnetic heads, however, the service life has been inevitably limited due to unbalanced abrasion of the head core and the fixing material. 
     SUMMARY OF THE INVENTION 
     A first object of the present invention is to provide a magnetic head of improved high frequency characteristics through relaxation of stress generated at the hardening of the adhesive thereby preventing the loss in the effective magnetic permeability of the core. 
     A second object of the present invention is to provide a magnetic head with an improved abrasion resistance of the core by rendering said adhesive harder than the thin plates of a high magnetic permeability constituting the core. 
     A third object of the present invention is to provide a magnetic head wherein the sensitivity loss resulting from the presence of said adhesive is reduced. 
     A fourth object of the present invention is to provide a magnetic head wherein the core and the fixing material present therearound are evenly abraded to ensure stable electromagnetic converting performance over a prolonged period. 
     A fifth object of the present invention is to provide a magnetic head of a prolonged service life. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a head element adapted for use in the present invention and formed by winding coil on a core; 
     FIG. 2 is a perspective view of the head element shown in FIG. 1 placed in a head casing; 
     FIG. 3 is a cross-sectional view of the magnetic head of the present invention in a state in contact with a magnetic tape and a tape pad; 
     FIG. 4 is a chart of effective permeability-frequency relationship in a comparison of the head of the present invention with a conventional magnetic head; 
     FIG. 5 is a chart showing a relationship of the abraded depth of the core vs. the tape traveling time in comparison of the magnetic head of the present invention with that of a conventional head; 
     FIG. 6(a) is a partial cross-sectional view of a conventional multi-element magnetic head showing an abraded state thereof; and 
     FIG. 6(b) is a partial cross-sectional view of a multi-element embodiment of the magnetic head of the present invention showing an abraded state thereof. 
     FIG. 7 is a perspective view of a head element of the present invention, similar to that shown in FIG. 1, but wherein only a single magnetically permeable plate is provided. 
     FIG. 8 is a perspective view of the head element shown in FIG. 7 placed in a head casing. 
     FIG. 9 is a cross-sectional view of the magnetic head of FIG. 8 in contact with a magnetic tape and tape pad. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1 there is shown, in a perspective view, a head core composed of core halves 1, 2 and provided partially thereon with a coil 3. The thin plates 1a, 1b, 1c and 1d constituting said core half 1 are respectively composed of a material of a high magnetic permeability such as permalloy (hardness Hv 139) or sendust (hardness Hv 480) of a determined thickness and are provided on the surfaces thereof with an insulating adhesive layer of an abrasion resistance higher than that of said high permeability material and of a thickness sufficiently smaller than the above-mentioned determined thickness of thin plates. The core half 1 formed in this manner from the laminated thin plates 1a-1d with interleaved adhesive layers is adjoined to another core half 2 similar to said core half 1 as shown by the chain lines to form a core cap 4, whereby said core halves 1 and 2 constituting a closed magnetic circuit. 
     In FIG. 2 there is shown, in a partial perspective view, the magnetic head of the present invention composed of the core halves, 1, 2 and coil 3 of FIG. 1 which are placed in a head case 6 and fixed therein by means of a fixing material 7 filled into said case. 
     FIG. 3 is a cross-sectional view of the magnetic head in FIG. 2 along the chain line 5 and seen from the direction of arrow A, wherein there are additionally shown a tape pad 8 and a magnetic tape 9. In FIG. 3 the afore-mentioned adhesive 10 is present in the spaces between said thin plates 1a-1d to mutually adhere said thin plates of a high magnetic permeability and to mutually insulate said thin plates thereby reducing the eddy current loss therein. Said adhesive 10 is for example composed of an insulating and adhesive epoxy resin comprising a granular substance of a particle size in a range of 0.5 to 15 microns. Said granular substance is an inorganic material composed of at least a member selected from metal oxides such as SiO 2 , Al 2  O 3  (hardness Hv 1950), Zr(SiO 4 ), Al 2  O 3  -SiO 2  compounds (each of the following compounds is understood to include all the family compounds), Al 2  O 3  -MgO (MgO hardness Hv 600), Al 2  O 3  -MgO-SiO 2 , MgO-SiO 2 , K.sub. 2 O-Al 2  O 3  -SiO 2 , Ti-O, Zr-O, Hf-O, V-O, Nb-O, Ta-O, Cr-O, Pd-O, Re-O, Mo-O, W-O, Mn-O, Fe-O, Co-O, Rh-O, Ir-O, Ni-O, Pt-O, Ti-Zr-O, Ti-Hf-O, Ti-Ta-O, Ti-Co-O, Ti-V-O, Ti-Nb-O, Ti-W-O, Ti-Mn-O, Ti-Fe-O, Zr-Hf-O, Zr-V-O, Zr-Nb-O, Zr-Ta-O, Zr-Cr-O, Zr-Mo-O, Zr-W-O, Zr-Mn-O, Zr-Re-O, Zr-Fe-O, Zr-Co-O, Zr-Ni-O, V-Nb-O, V-Ta-O, V-Cr-O, V-Mo-O, V-W-O, V-Mn-O, V-Re-O, V-Fe-O, V-Co-O, V-Ni-O, Nb-Ta-O, Nb-Cr-O, Nb-Mo-O, Nb-W-O, Nb-Mn-O, Nb-Re-O, Nb-Fe-O, Nb-Co-O, Nb-Ni-O, Ta-Cr-O, Ta-Mo-O, Ta-W-O, Ta-Mn-O, Ta-Re-O, Ta-Fe-O, Ta-Co-O, Ta-Ni-O, Cr-Mo-O, Cr-W-O, Cr-Mn-O, Cr-Re-O, Cr-Fe-O, Cr-Co-O, Cr-Ni-O, Mo-W-O, Mo-Mn-O, Mo-Fe-O, Mo-Co-O, Mo-Ni-O, W-Mn-O, W-Re-O, W-Fe-O, W-Co-O, W-Ni-O, Mn-Re-O, Mn-Co-O, Mn-Ni-O, Re-Fe-O, Re-Co-O, Re-Ni-O, Co-Ni-O etc., metal carbides such as Ti-C (hardness Hv 3000), Zr-C, Hf-C, V-C, Nb-C, Ta-C, Cr-C, Mo-C, W-C, Mn-C, Fe-C, Fe-W-C, Fe-Mo-C, Co-Fe-C, Co-Mo-C, Ni-W-C, V-Zr-C, Cr-Nb-C, Mn-Mo-C, Mn-W-C, Ni-Mo-C etc., metal nitrides such as Ti-N, Zr-N, V-N, Nb-N, Ta-N, Cr-N, Mo-N, W-N, Mn-N, Fe-N, Co-N, Ti-Zr-N, Ti-Hf-N, Ti-V-N, Ti-Nb-N, Ti-Ta-N, Ti-Co-N, Ti-Ni-N, Zr-Nb-N, V-Nb-N, V-Ta-N, Ta-Cr-N, Ta-Mn-N, Ta-Fe-N, Ta-Co-N, Ta-Ni-N, Cr-Mo-N, Cr-Mn-N, Cr-Fe-N, Mo-(Mn, Fe, Co, Ni)-N, Mo-Co-N, Mo-Ni-N, Mn-Fe-N, Fe-Ni-N, Fe-Pd-N etc., metal borides such as Ti-B, Zr-B, Hf-B, V-B, Nb-B, Ta-B, Cr-B, Mo-B, W-B, Mn-B, Ni-B, Pd-B, Ti-Zr-B, Ti-Hf-B, Zr-Hf-B, Ti-V-B, Ti-Nb-B, Ti-Ta-B, Ti-Cr-B, Ti-Mo-B, Zr-Nb-B, Zr-Ta-B, Zr-Mo-B, V-Cr-B, Nb-Cr-B, Ta-Cr-B, Ta-Fe-B, Ta-Co-B, Ta-Ni-B, Cr-Mo-B, Cr-Mn-B, Cr-Fe-B, Cr-Co-B, Cr-Ni-B, Mo-Fe-B, Mo-Co-B, Mo-Ni-B, Mn-Fe-B, Mn-Co-B, Mn-Ni-B, Fe-Co-B, Mo-Al-B, Co-Al-B, Ni-Al-B, Co-Mg-B, Ni-Mg-B, Co-Zn-B, Ni-Zn-B, Co-Ga-B, Ni-Ga-B, Co-Ge-B, Ni-Ge-B, Co-Sn-B, Ni-Sn-B, Co-In-B, Ni-In-B etc., and metal silicides such as T-Si (hardness Hv 700), Zr-Si, Hf-Si, V-Si, Nb-Si, Ta-Si, Cr-Si, Mo-Si, W-Si, Mn-Si, Fe-Si, Co-Si, Rh-Si, Ir-Si, Ni-Si, Pb-Si, Pt-Si, Ti-Zr-Si, Ti-Hf-Si, Ti-V-Si, Ti-Ta-Si, Ti-Cr-Si, Ti-Mo-Si, Ti-W-Si, Ti-Ni-Si, Ti-Mn-Si, Ti-Re-Si, Zr-V-Si, Zr-Nb-Si, Zr-Ta-Si, Zr-Mo-Si, Zr-W-Si, Hf-W-Si, Zr-Co-Si, Zr-Ni-Si, Hf-Ni-Si, Zr-Fe-Si, Hf-Fe-Si, V-Nb-Si, V-Mo-Si, V-Mn-Si, V-Fe-Si, V-Co-Si, V-Ni-Si, Nb-Gr-Si, Ta-Cr-Si, Ta-Mo-Si, Nb-W-Si, Ta-W-Si, Nb-Fe-Si, Nb-Co-Si, Ta-Co-Si, Nb-Ni-Si, Ta-Ni-Si, Nb-Mo-Si, Cr-Mo-Si, Cr-W-Si, Cr-Mn-Si, Cr-Fe-Si, Cr-Co-Si, Cr-Ni-Si, Mo-W-Si, W-Mn-Si, Mo-Re-Si, Mo-Fe-Si, W-Fe-Si, Mo-Co-Si, W-Co-Si, Mo-Ni-Si, W-Ni-Si etc. The amount of such inorganic granular substance should at least equal to 20% for achieving a satisfactory effect, but at the same time should not exceed 70% in order to avoid deterioration of the adhesion to the thin plates and also to prevent inefficient coating work at a high viscosity. Consequently the preferred range of the amount of said inorganic granular substance is from 20 to 70%. 
     The inorganic granular substance of a particle size in excess of 15 microns will excessively enlarge the spacing between the thin plates and thus will deteriorate the sensitivity of the magnetic head since the effective thickness of the magnetic layer on the tape contact face is reduced for a given track width. Also the presence of such large granules will locally reduce the amount of resinous binder, thereby reducing the adhering force thereof. 
     On the other hand the granules of a size smaller than 0.5 microns can only be mixed in a limited amount with the epoxy resin due to significant increase in the viscosity and are therefore unable to perform sufficient stress relaxation. Also a minimum particle diameter of 0.5 microns is required in order to prevent mutual contact of the high permeability thin plates which generally show surface irregularity in the order of ±0.2 microns. Consequently the preferred range for the particle size of said inorganic granular substance is from 0.5 to 15 microns. In this manner the above-explained adhesive layer employed in the magnetic head of the present invention shows satisfactory electric insulation, abrasion resistance, coating efficiency, adhering force and stress relaxation, wherein said stress relaxation functions to prevent the eventual deformation of core at the hardening of the resinous binder, thereby preventing the loss in the effective magnetic permeability. 
     FIG. 4 shows the plotting of effective permeability in ordinate against frequency in abscissa, wherein the curve 11 shows the results of measurements on a conventional ring-shaped core sample laminated with an epoxy resin alone while the curve 12 shows those of a ring-shaped core sample laminated with an epoxy resin containing powdered alumina (Al 2  O 3 ) of an average particle size of 1 micron in an amount of 30% by weight. It will be observed that the curve 12 and the magnetic tape can be increased to avoid the loss of sensitivity. 
     FIG. 5 shows the abrasion depth of magnetic core as a function of tape running time at a tape speed of 4.75 cm/sec, wherein the line 13, representing a first example of the present invention with a track width of ca. 0.6 mm prepared by laminating six hard permalloy plates each 0.1 mm thick and respectively coated with an adhesive in a thickness of 0.001 mm having a higher hardness and a higher abrasion resistance than said hard permalloy, shows abrasion depth of 8 microns at a running time of 300 hours, while the line 15 representing an identical example except for utilizing another adhesive of a lower abrasion resistance shows an abrasion depth of 48 microns after a running time of 300 hours. Also a second example of the magnetic head of the present invention with a track width of ca. 0.6 mm, prepared by laminating two high permeability sendust thin plate each 0.3 mm thick and respectively coated with an adhesive in a thickness of 0.01 mm having a higher hardness and a higher abrasion resistance than said sendust, shows an abrasion depth of 6 microns after a running time of 300 hours as shown by the line 14, while an identical head except for employing an adhesive of an abrasion resistance lower than that of said sendust shows an abrasion depth of 18 microns after a running time of 300 hours as shown by the line 16. Also the heads of the first and second examples of the present invention show almost no change in the electromagnetic converting characteristics before and after the running test. 
     Although the foregoing examples utilize plural laminated thin plates, it is also possible to improve the abrasion resistance even when a single plate of high magnetic permeability is employed if said plate is coated on both sides thereof with an adhesive material of a high abrasion resistance. For example, the core is of a non-laminated structure for a magnetic head with a track width of 0.1-0.03 mm such as a video recording head, but also in such case the abrasion of the core can be reduced by coating an adhesive as aforementioned on both sides of the core plate. Thus, as explained in the foregoing, it is rendered possible to realize a magnetic head with an extended service life without deteriorating the electromagnetic converting characteristics by selecting the abrasion resistance of said adhesive higher than that of the said high permeability thin plates and also selecting the thickness of said adhesive satisfactorily smaller than that of said thin plates. 
     In this regard, reference is made to FIGS. 7, 8 and 9, showing a single plate embodiment of the invention, wherein the same reference numerals are used to refer to elements corresponding to those shown in FIGS. 1, 2 and 3. 
     FIGS. 6a and 6b are cross-sectional views of the magnetic head of FIG. 2 along the chain line 5 and seen from the direction of arrow A, wherein said head is constructed with four channels, and c and d representing the boundaries of the contact area with the magnetic tape. FIG. 6a illustrates the cross section of a conventional multichannel magnetic head as a reference, wherein the chain line 17a and the full line 17b respectively indicate the tape contact surfaces before and after the abrasion test, while FIG. 6b illustrates the cross section of the magnetic head of the present invention, wherein the line 18a and the full line 18b respectively indicate the tape contact surfaces before and after the abrasion test. In FIGS. 6a and 6b the abrasion is caused by a running test for 200 hours with an unrepresented magnetic tape with a tape speed of 4.75 cm/sec, and the vertical dimension is enlarged 100 times with respect to the horizontal dimension in order to clarify the state of abrasion. From the comparison of these two drawings it will be apparent that the magnetic head of the present invention, shown in FIG. 6b has a superior abrasion resistance. In this third example of the present invention shown therein, the adhesive 10a is provided in the spacings between the laminated thin plates 1a-1d to electrically insulate the adjacent thin plates of a high permeability thereby reducing the eddy current loss therein and also to improve the abrasion resistance. Said adhesive 10a is composed of an epoxy resin added with an inorganic granular substance consisting of at least a member selected from the aforementioned metal oxides, metal carbides, metal nitrides, metal borides, and metal silicides. Said inorganic granular substance is preferably added in an amount within a range from 20 to 70% as already explained in connection with FIG. 3, and is most preferably composed of alumina. 
     The fixing material 7a is composed of an epoxy resin added with SiO 2  (silica) in an amount of 20-50 wt.% or Al 2  O 3  (alumina) in an amount of 1-5 wt.%. Further CaCO 3  (calcium carbonate) is added in such a manner that the total amount of the above-mentioned additives represents 30-80 wt.% of the mixture, in order to prevent time-dependent deteriorating and to relax the stress caused by the contraction at the hardening. 
     The magnetic head of the present invention prepared with the adhesive and the fixing material of the above-explained compositions is provided with an elevated abrasion resistance at the tape contact surface and is abraded evenly on said surface as shown in FIG. 6b. Consequently it is rendered possible to maintain satisfactory magnetic characteristics over a prolonged period and thus to achieve an extended service life.