CA1065481A - Magnetic recording tape - Google Patents
Magnetic recording tapeInfo
- Publication number
- CA1065481A CA1065481A CA233,765A CA233765A CA1065481A CA 1065481 A CA1065481 A CA 1065481A CA 233765 A CA233765 A CA 233765A CA 1065481 A CA1065481 A CA 1065481A
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- CA
- Canada
- Prior art keywords
- coercive force
- magnetic
- layer
- ferromagnetic
- tape
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/62—Record carriers characterised by the selection of the material
- G11B5/68—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent
- G11B5/70—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer
- G11B5/716—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by two or more magnetic layers
Landscapes
- Paints Or Removers (AREA)
- Magnetic Record Carriers (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An improved magnetic recording tape having a dual layer magnetizable coating which provides an improved high frequency response and increased recording sensitivity in the middle and middle-to-high frequency ranges when used in conventional audio recording devices, particularly open reel to reel type recorders operated at a tape speed of 19 cm/sec or 38 cm/sec. The dual magnetizable coatings consist of an inner layer of a ferromagnetic iron oxide powder dispersed in a resinous binder and an upper layer of a mixture of ferromagnetic powders in a resinous binder, the mixture including at least ferro-magnetic chromium dioxide powder and a ferromagnetic iron oxide powder, both layers having a controlled thickness, controlled coercive force and controlled saturation residual flux density. The weight ratio of the ferromagnetic iron oxide to the chromium dioxide in the upper layer is from 1:4 and 4:1, each of the magnetic powders in said mix-ture having coercive force values within specific ranges.
-i-
An improved magnetic recording tape having a dual layer magnetizable coating which provides an improved high frequency response and increased recording sensitivity in the middle and middle-to-high frequency ranges when used in conventional audio recording devices, particularly open reel to reel type recorders operated at a tape speed of 19 cm/sec or 38 cm/sec. The dual magnetizable coatings consist of an inner layer of a ferromagnetic iron oxide powder dispersed in a resinous binder and an upper layer of a mixture of ferromagnetic powders in a resinous binder, the mixture including at least ferro-magnetic chromium dioxide powder and a ferromagnetic iron oxide powder, both layers having a controlled thickness, controlled coercive force and controlled saturation residual flux density. The weight ratio of the ferromagnetic iron oxide to the chromium dioxide in the upper layer is from 1:4 and 4:1, each of the magnetic powders in said mix-ture having coercive force values within specific ranges.
-i-
Description
10~548~
_NV E NTION
Field of the Invelltion Tllis invention relates to a maglletic recording tape consisting o~ fl non-lllagnetizable base over whicll thele is a dual layer magnetizable co~ting consisting of an inner layer adllering to the base and an outer layer over the inner layer, the inner layer containing a ferromagnetic iron oxide, and the outer lay~r containing a mixture o~
a fêrromagnetic iron oxide and chromium clio~ide, the magnetizable powders in both layers being dispersed in rcsinous binders.
DES~RIPTION OF THE PRIOR l~RT_ In recent times, cassette type audio tape recorders which operate at a tape speed of 4. 8 cm/sec have become more popular and more widely used since the quality of reproduction has been steadily improving. For higher quality work, however, an open reel to reel type audio tape recorder which operates at relatively faster speeds of 19 cm/sec or 38 cm/sec is used.
One presently available magnetic recording tape includes a non-magnetizable base film coated with a homogeneous dispersion of ferromagnetic iron oxide powder such as gamma ferric oxide or magnetite having a relatively low coercive force and dispersed in a resinous binder having a coating thickness of 10 to 15 microns. This magnetic tape provides better output sound quality than the cassette tapes, even though the coercive force of the tapes is rather low, being about 250 oersteds or so, because these tapes are operated at rela-tively high speeds of 19 cm/sec or 38 cm/sec in open reel to reel type recorders. However, these tapes ha~ing a low coercive force do not -1- , '~
~ 0~5~1 have a sufficiently good high frequency response, do not provide suf-ficient output in the high frequency range, and do not provide a wide dynamic range. To improve the above disadvantage, magnetic tapes using gamma ferric oxide having an improved coercive force value have been marketed, ~ut such tapes still do not meet the quality stand-ards desired, because these tapes do not provide an improvement in output in the low ~requency range and the high frequency range improve-ment was not suf~iciently great. The use o~ magnetic powders having a high coercive force, such as chromium dioxide was also attempted, but the sensitivity of this material in the frequency range below the middle range was not satisfactory. To obtain a sufficient output level from a ferrite recording head which is used more and more frequently in tape recorders, the recording current has ~o be increasèd. The ferrite head, however, is easily saturated by a current increase and ~ .
distorts the signal to be recorded. ~onsequently, attempts to improve the output level in the low frequency range of chromium dioxide tapes results in a sacrifice of sound quality.
Dual layer magnètic recording tapes have been pre-viously disclosed in U.S. Patent No. 3,775,178 and U.S. Patent No.
3,761,311 both to Perrington et al. The first-named patent disclosed a video tape having a dual layer magnetizable coating. The second patent disclosed àn audio tape especially suitable for use in a cassette tape recorder at a speed of 4.8 cm/sec. In the aforementioned Canadian Patent 1,029,129, there was proposed a dual layer magnetic tape in which each layer had a controlled thic~ness, a controlled coercive force, and a controlled 10~548~
saturation residual flux density. It was found, however, that the output level in the frequency range of 1 KHz to 10 KHz when used in tape recorders and operating at relatively fast speed is descreased so that the frequency response curve for this type of tape is not flat in the middle and middle to high frequency ranges.
U.S. Patent No. 3,824,128 to Akashi et al. disclosed a magnetic recording tape containing a mixture of erromagnetic iron oxide and chromium dioxide having substantially equal coercive force values. However, the magnetic recording tape produced according to this disclosure does not improve the output level in the low frequency range.
SUMM~RY OF THE INVENTION
The present invention provides a magnetic recording tape which has a non-magnetizable base carrying a dual layer magnetizable coating, comprising an inner layer and an outer layer. The inner layer consists of a coating of a uniform dispersion of ferromagnetic iron oxide in a resinous binder, and the outer layer is a coating of a uniform dispersion of a mixture of ferromagnetic chromium dioxide and a ferromagnetic iron oxide in a resinous binder. The inner layer has a thick-; ness of from 7 to 12 microns, a coercive force of 260 to 320 oersteds, and a saturation residual flux density of 1150 to 1600 gauss. The outer layer has a thickness of 1 to 5 microns, a coercive force of 380 to 500 oersteds, and a saturation residual flux density of 1200 to 1600 gauss. The weight ratio of the ferromagnetic chromium dioxide and the ferromagnetic iron oxide in the outer layer is in the range from 1:4 and 4:1.
More particularly, there is provided a magnetic audio recording tape including a non-magnetizable base, a dual layer of magnetizable coating on said base, said dual layer comprising an inner layer and an outer layer, said inner layer being a homogeneous dispersion of ferromagnetic iron oxide 1~ .
., ~ _ 3 _ 10~4~1 powder in a resinous binder, having a coating thickness of 7 to 12 microns, having a coercive orce of 260 to 320 oersteds, and having a saturation residual flux density of 1150 to 1600 gauss, said outer layer being superposed on said inner layer, and being a homogeneous dispersion of ferromagnetic powders in a resinous binder, having a coating thickness of 1 to 5 microns, having a coercive force of 380 to 500 oersteds, and having a saturation residual flux density of 1200 to 1600 gauss, the said magnetic powder of both the layers being oriented in the longitudinal direction wherein said magnetic recording tape being characterized in that said ferromagnetic powders in said outer layer including at least ferromagnetic chromium dioxide powder having a coercive force of 450 to 600 oersteds and a ferromagnetic iron oxide powder having a coercive force of from 320 to 450 oersteds, the weight ratio of said ferromagnetic chromium dioxide and said ferromagnetic iron oxide existing in ` said outer layer being in the range from 1:4 to 4:1.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects, features and advantages of the invent-ion will be readily apparent from the following description of certain preferred :~
.' :
- 3a -.... . .
548~
em~odiments thereof, taken in conjunctiotl with the accompanying drawings, although variations and modifications may be effected with-out departing from the spirit and scope of the novel concepts of the disclosure, and in which:
Figure 1 is a graph plotting frequency response for a typical c:ollllllercial tape for an open reel recorder, a dual layer magneticrecording t~pe of the prior art, and an improved dual layer magnetic recording tape according to the present invention;
Figure 2 is a graph of the frequency response charac-teristics for a typical commercial cassette tape and a dual layer ` cassette tape;
" Figure 3 is a graph plotting the response against the biasing current for a commercial tape used for open reel recorders, and comparing it with the improved dual layer magnetic recording tape of the present invention;
Figure ~ is a graph of the frequency response char-acteristics for a dual layer magnetic recording tape manufactured ac-cording to an example of the present invention;
Figure 5 is a graph plotting distortion factor against the AC biasing current for a commercial tape and for the dual layer tape of the present invention;
Figure 6 is a graph plotting maximum output level for the commercial reel to reel tape, and also for the tape of the present invention; and Figure 7 is a graph of the frequency response char-acteristics for tapes produced accord~lng to other examples of the present invention.
lO~S4~1 DESCRII'TION Oli' T}-IE PRl~FERRED EM130DIMENTS
A suitable magnetic material for the inner layer is gamma ferric oxide because i~ has good printing characteristics, has a low noise level, and can be easily manufactured to obtain a desired coercive force. ~lowever, magnetite (Fe3O4) can also be used. The coercive force of the inner layer should be between 260 and 320 oersteds. If the coercive force of the inner layer is higher than 320 oersteds, it is difficult to increase the output in the low frequency range. The saturation residual flux density should be between 1150 and 1600 gauss. If this value is less than 1150 gauss, a satisfactory output in the low frequency range cannot be obtained, and if it exceeds 1600 gauss, the tendency of the magnetic powder to tear off is in-creased. ~he most suitable value for the saturation residual flux density is between 1250 and 1400 gauss. The coating thickness of the inner layer is closely related to the reproduction characteristics at the low or middle frequency range. According to the results which we have obtained, the thickness of the inner layer should be between about 7 and 12 microns. If it is less than 7 microns, the output in the low frequency range is decreased and if it exceeds 12 microns, the output in the low frequency range is increased too much. Since the output in the middle frequency range is not substantially changed, this makes the frequency response characteristics not flat over the entire audio frequency range.
The coercive force of the outer layer should be between about 380 and 500 oersteds. High frequency signals are recorded on the surface area of the magnetizable~.layer, so that a high coercive force in the outer layer is desirable. If it exceeds 500 oersteds, 1()65481 the output level in the high frequency range l~comes too high This then causes the ~requency response characteristics to deviate from the desired flat char~cteristic. Too high a coercive force in the tape also causes an increase in distortion and difficulty in erasing. A1so, a high coercive force requires an increase in recording current which makes the tape not compatible with conventional recorders, and also may cause a saturation of ferrite type magnetic heads. If the coercive force of the outer layer is less than 380 oersteds, it is not possible to obtain a high output level in the high frequency range.
Chromium dioxide has an excellent sensitivity in the high frequency range and is used in accordance with this invention to obtain the desired coercive force. However, lt is not easy to manu-facture chromium dioxide having a rather low coercive force in combina-tion with a large acicular ratio, and a small acicular ratio causes a decrease of the rectangular ratio of the coated layer. As a practical matter, it is desirable that the coercive force of the chromium dioxide be in the range from about 450 to 600 oersteds. Chromium dioxide shows an excellent sensitivity in the range of recorded wavelengths of less than 10 or 12 microns, and provides a high output in the high frequency range. Consequently, it is necessary to employ a magnet-izable powder other than chromium dioxide in admixture therewith to improve the frequency response in the range of recorded wavelengths longer than 10 or 12 microns to correspond to the middle and middle-high frequencies, According to our experimentation, a suitable dual layer magnetic tape is obtained when using~'a mixture of chromium dioxide and a ferromagnetic iron oxide powder having a coercive force of 10~;5~81 320 to 450 oersteds, with the weight ratio between the two ranging from 1:4 and 4: l in the outer layer. As noted, suitable ferromagnetic iron oxides are gamma ferric oxide or magnetite. If the coercive force of the powder is less than 320 oersteds, the total coercive force of the outer layer is decreased. Thus, an improvement in the high frequency range cannot be obtained. If the coercive force of the iron oxide powder exceeds 450 oersteds, the output in the high frequency range is increased too much, but the output in the middle and middle-high frequency ranges is not increased. In addition, too high a co-ercive force value in the outer layer requires an increase in the re-cording current. If the proportionate amount of the iron oxide powd~r is less than 20 parts by weight per 100 parts of magnetizable particles in the outer layer, it is not effective to increase the output in the middle and middle-high frequency ranges. If the ratio exceeds 80 parts per 100 parts of the mixture, the output in the high frequency range is deteriorated.
The saturation residual flux density of the outer layer should be between 1200 to 1600 gauss, preferably at 1250 to 1400 gauss so that the output in the high frequency range is increased without increasing the tendency of the powder to tear off from the tape. The coating thickness of the outer layer is closely related to the charac-teristics of the inner layer. If the coating thickness is less than 1 micron, the frequency response in the high frequency range is not satisfactory. If it exceeds 5 microns, the frequency response in the low frequency range is not satisfactory. Accordingly, the coating thickness of the outer layer should be from 1 to 5 microns, and preferably should be in the range of 2 to S microns.
Examples of the improved dual layer magnetic record-10~;54~i ing tape of the present invention which can be used with conventional biasing currents in tape recorders and which provide a flat frequency response characteristic over the entire audio frequency range, an excellent high frequency response, and a broad dynamic range are set forth in the following.
EXA MPLE
The inner layer oE the dual layer magnetic recording tape was produced from the following composition:
Material Parts bv weight Gamma ferric oxide particles100 Vinylacetate-vinyl chloride copolymer ("VAG}I" of Union Carbide Corp.) 5 Polyurethane resin ("Estane 5702" of B. F. Goodrich Corp.) 12 Lecithin (dispersant ) Olive oil (lubricant) 0. 5 Methyl ethyl ketone (solvent)80 Toluene (solvent) 80 Cyclohexanone (solvent) 80 The above ingredients were ball-milled for 50 hours, whereupon 3 parts by weight of an isocyanate compound ("Desmodule L"
manufactured by Bayer Corporation) was added to the mixture as a cur-ing agent for the polyurethane resin. The mixture was stirred for an additional 1 hour to produce a magnetic dispersion in the form of a paint.
The backing member employed was a polyethylene terephthalate film of 24 microns in thickness which had been treated with an alkyl titanate and nitrocellulose to improve the adhesion.
lO~S~l The magnetic paint was applied to the backing member by means of a gravure coater so that the thickness of the coating after drying was 9 microns. The coated film was passed through a magnetic field to orient the magnetizable particles in the longitudinal direction of the film before drying, and thereafter the film was dried and wound into a roll form. Then, the film was calendered to improve the magnetic characteristics and the Eilm was heated at 60C for 4 hours to cure the polyurethane resin sufficiently.
The inner layer formed by the above-described pro-cedure had the following characteristics:
Coercive force (Hc) 290 Oe Saturation residual flux density (Br) 1310 gauss Rectangular ratio (Rs = Br/Bm) 85~
~ he outer magnetizable layer of the dual layer magnetic tape was prepared as follows. The following mixture was made up:
Material Parts bv wei~ht Chromium dioxide particles 60 Gamma ferric oxide particles 40 Vinyl acetate-vinyl chloride co-polymer ("VAGH" of Union Carbide Corp. ) 15 Polyurethane resin ("Estane 5702) 5 "Squalane" (lubricant) Lecithin (dispersant) 0. 5 Methyl ethyl ketone (solvent) 80 Toluene (solvent) 80 Cyclohexanone (solvent) ~ 80 After the above mixture was ball-milled for 70 hours, ~ 0~;54~1 3 parts by weight of the isocyanate compound "Desmodule r ~ wag added to the mixture as a curing agent for the polyurethane resin. The mixture was stirred for an additional 30 minutes to provide a magnetic paint. The paint was coated on the previously formed inner layer so that the thickness was 3 microns after drying. The coated layer was also passed through a flat magnetic field to orient the magnetizable particles in the longitudinal direction of the film before drying,and then the film was dried and wound into a roll form. After the film was calendered to improve the magnetic characteristics, the film was heated at 50~ for 2 hours to cure the polyurethane resin sufficiently.
The outer layer formed by the above-described pro-cedure had the following magnetic characteristics:
Coercive force (Hc) 420 Oe Saturation residual flux density (Br) 1300 gauss The magnetic particles themselves employed in the foregoing example had the following characteristics:
Gamma ferric oxide of the inner layer:
Acicular particles of 0.7-0. 8 microns in length, with an axis ratio of 8-10 Magnetization 72 emu/g Coercive force 310 Oe Print through value51 dB
Adsorption 0. 8 m~/g Normalized surface area 17 . 7 m /g Chromium dioxide of the outer layer:
Acicular particles having an average length of 0.4 microns with an axis ratio of 4 to 10 Coercive force 480 oe Magnetization 80 emu/g 10~;54~1 1 Camma ferric oxide of the outer layer:
Acicular particles having an average length of 0. 4 to 0. 5 microns with an axis ratio of 7 to l0 Coercive force 420 Oe Magnetization 76 emu/g Because of the greater acicular ratio of the gamma ferric oxide particles of the inner layer, the inner layer had a higher packing density than the conventional gamma ferric oxide tape.
A dual layer magnetlc tape was manufactured using a different weight ratio of iron oxide to chromium dioxide from that used in Example 1.
Eighty parts by weight of chromium dioxide particles having a coercive force of 480 oersteds and 20 parts by weight of gamma ferric oxide having a coercive force of 420 oersteds were used as the magnetizable particles of the outer layer, in combination with the other ingredients in the coating formulation as indicated in Example 1. The outer layer had a coercive force of 450 oersteds, and a saturation residual flux density of 1350 gauss.
In this example, the outer layer was composed of 20 parts by weight of chromium dioxide having a coercive force of 480 oersteds and 80 parts by weight of gamma ferric oxide having a co-ercive force of 420 oersteds. The other ingredients of the outer layer were as specified in Example 1. The magnetic characteristics of the outer layer included a coercive force of 370 oersteds and a saturation residual flux density of 1250gauss.
In Eiigures 1 and 2, curves 1 to 4, inclusive, illustrate 10~54~1 the freguency response characteristics of various tapes, Curve 1 was derived ~rom a conventional cassette tape having a single magnet-izable layer with a coating thickness of 6 microns and a coercive force of 320 oersteds (Sony C-60FP). Curve 2 was derived from a conven-tional open reel to reel type tape having a single magnetizable layer with a coating thickness of 12 microns and a coercive force of 300 oersteds (Sony SL~I tape). Curve 3 was derived from a dual layer magnetic tape used in cassette type recorders. The inner layer con-tained gamma ferric oxide having a coating thickness of 5 microns and a coercive force of 290 oersteds. The outer layer of the dual layer contained chromium dioxide having a coating thickness of 1 micron and a coercive force of 490 oersteds.
Curve 4 was derived from a dual layer magnetic tape of the type used in open reel to reel recorders. The inner layer of the dual layer contained gamma ferric oxide having a coating thickness of 10 microns and a coercive force of 290 oersteds. The outer layer contained chromium dioxide having a coating thickness of 2 microns and a coercive force of 490 oersteds.
In Figures 1 and 2, the characteristics of the tapes represented by curves 1 and 3 were measured at a tape speed of 4. 8 cm/sec while the characteristics of tapes numbered 2, 4 and 5 were measured at a tape speed of 19 cm/sec. Curve 5 illustrates the characteristics of the improved dual magnetic tape of the present inven-tion and produced according to Example 1.
It will be seen from the foregoing curves that the dual layer magnetic tape for use in casse~tes, exemplified by curve 3, show~ a good frequency response over the audio frequency range. In 10~5~
the case of the dual layer magnetic tape for the open reel to reel recorder exemplified by curve 4, however, the output level in the frequency range of 1 to 10 kilohertz is de~creased con-siderably. The reason for this decrease in output level is that the sensitivity of chromium dioxide powder becomes good for the range in which the recording wavelength is shorter than 10 to 12 microns, corresponding to the fact that the frequency is more than 15 kilohertz at a tape speed of 19 cm/sec, but is not so good for a longer wavelength.
The dual layer magnetic recording tape of the present invention can be operated with the same biasing current as is used in conventional single layer magnetic recording tapes to provide a high frequency response throughout the audio frequency range, together with a wide dynamic range and little distortion.
The best setting of biasing current is 110 + 10% of the biasing current of the conventional single layer magnetic recording tapes. Figure 3 illustrates the biasing characteristics of the conventional SONY SLH tape by means of dotted lines, and the improved magnetic tape of the present invention by means of Z0 the solid line. These characteristics were obtained by using an open reel type recorder, Denon DN-342R-T (Trade Mark), with a ferrite recording head having an eight micron gap and a ferr-ite reproducing head having a four micron gap, the recording level being set to -lOdB (OdB = 200 pwb/mm) and at a tape speed of 19 cm/sec.
The dual layer magnetic tape ~anufactured as described in Example 1 had a frequency response characteristic illustrated in Figure 4. Also, the distortion factor and the maximum out-put level (M.O.L.) characteristics were measured and these results are illustrated in Figures 5 and 6, respectively. In these figures, the characteristics of the magnetic tape of the present invention are indicated by the solid lines while the dotted lines indicate 10~5~
characteristics of the Sony SLI ~ tape. The clistortion factor was measured at 400 ~lertz with a Od~3 output. The M.O.T, was measured using the aforementioned tape deck witll playback equalizer time constant Tl = 3180 microseconds, T2 = 50 microseconds, and at a tape speed of ]9 cm/sec.
As is apparent from Figure 4 of the frequency re-sponse characteristics, the output level in the freguency range from 4 kilohertz to 10 kilohertz was much improved and a flat frequency response characteristic was obtained. ~ccording to a hearing test, the tone quality obtained was satisfactory. The distortion factor was much smaller than with the conventional SLH tape. Also, in the low frequency range, that is, not greater than 3 kilohertz, the M. O. L.
gained 3dB compared with the SLH tap~, and in the high frequency range (above 10 kilohertz) it gained more than 1.5 dB.
The frequency response characteristics of the tapes produced according to Examples 2 and 3 are shown in Figure 7.
Curve a represents the output response characteristic of the tape produced according to Example 2, while curve b represents that ob-tained using the tape produced according to Example 3.
A dual layer magnetic tape containing more than 80 parts by weight of chromium dioxide per 100 parts of mixture in the outer layer did not improve the output level in the middle and the middle-high frequency ranges while the dual layer magnetic tape con-taining more than 80 parts by weight of iron oxide per 100 parts of mixture in the outer layer did not improve the output level at high frequencies. Consequently, it was d~termined that the weight ratio of the chromium dioxide to the ferromagnetic iron oxide in the outer layer 10~S4t~1 ' should be in the range from about 1:4 to 4:1.
As apparent from the foregoing description, the dual layer magnetic recording tape of the present invention when operated at speeds higher than used in conventional cassette tape recorders has advantages over conventional tapes, and also over dual layer magnetic recording tapes of the prior art. The new tape has a high sensitivity over all the audio frequency range. The decrease of out-put in the middle and middle-high frequency ranges is improved so that it has a relatively flat frequency response over the entire audio frequency range at a relatively high tape speed. The distortion factor ¦ .
is small and the M.O.L.characteristics are large and it provides a wide dynamic range. Furthermore, it is compatible with the biasing characteristics of standard tape recorders using ferrite magnetic heads.
It should be evident that various modifications and !
variations can be made to the described embodiments of the invention without departing from the scope of the novel concepts of the present invention.
_NV E NTION
Field of the Invelltion Tllis invention relates to a maglletic recording tape consisting o~ fl non-lllagnetizable base over whicll thele is a dual layer magnetizable co~ting consisting of an inner layer adllering to the base and an outer layer over the inner layer, the inner layer containing a ferromagnetic iron oxide, and the outer lay~r containing a mixture o~
a fêrromagnetic iron oxide and chromium clio~ide, the magnetizable powders in both layers being dispersed in rcsinous binders.
DES~RIPTION OF THE PRIOR l~RT_ In recent times, cassette type audio tape recorders which operate at a tape speed of 4. 8 cm/sec have become more popular and more widely used since the quality of reproduction has been steadily improving. For higher quality work, however, an open reel to reel type audio tape recorder which operates at relatively faster speeds of 19 cm/sec or 38 cm/sec is used.
One presently available magnetic recording tape includes a non-magnetizable base film coated with a homogeneous dispersion of ferromagnetic iron oxide powder such as gamma ferric oxide or magnetite having a relatively low coercive force and dispersed in a resinous binder having a coating thickness of 10 to 15 microns. This magnetic tape provides better output sound quality than the cassette tapes, even though the coercive force of the tapes is rather low, being about 250 oersteds or so, because these tapes are operated at rela-tively high speeds of 19 cm/sec or 38 cm/sec in open reel to reel type recorders. However, these tapes ha~ing a low coercive force do not -1- , '~
~ 0~5~1 have a sufficiently good high frequency response, do not provide suf-ficient output in the high frequency range, and do not provide a wide dynamic range. To improve the above disadvantage, magnetic tapes using gamma ferric oxide having an improved coercive force value have been marketed, ~ut such tapes still do not meet the quality stand-ards desired, because these tapes do not provide an improvement in output in the low ~requency range and the high frequency range improve-ment was not suf~iciently great. The use o~ magnetic powders having a high coercive force, such as chromium dioxide was also attempted, but the sensitivity of this material in the frequency range below the middle range was not satisfactory. To obtain a sufficient output level from a ferrite recording head which is used more and more frequently in tape recorders, the recording current has ~o be increasèd. The ferrite head, however, is easily saturated by a current increase and ~ .
distorts the signal to be recorded. ~onsequently, attempts to improve the output level in the low frequency range of chromium dioxide tapes results in a sacrifice of sound quality.
Dual layer magnètic recording tapes have been pre-viously disclosed in U.S. Patent No. 3,775,178 and U.S. Patent No.
3,761,311 both to Perrington et al. The first-named patent disclosed a video tape having a dual layer magnetizable coating. The second patent disclosed àn audio tape especially suitable for use in a cassette tape recorder at a speed of 4.8 cm/sec. In the aforementioned Canadian Patent 1,029,129, there was proposed a dual layer magnetic tape in which each layer had a controlled thic~ness, a controlled coercive force, and a controlled 10~548~
saturation residual flux density. It was found, however, that the output level in the frequency range of 1 KHz to 10 KHz when used in tape recorders and operating at relatively fast speed is descreased so that the frequency response curve for this type of tape is not flat in the middle and middle to high frequency ranges.
U.S. Patent No. 3,824,128 to Akashi et al. disclosed a magnetic recording tape containing a mixture of erromagnetic iron oxide and chromium dioxide having substantially equal coercive force values. However, the magnetic recording tape produced according to this disclosure does not improve the output level in the low frequency range.
SUMM~RY OF THE INVENTION
The present invention provides a magnetic recording tape which has a non-magnetizable base carrying a dual layer magnetizable coating, comprising an inner layer and an outer layer. The inner layer consists of a coating of a uniform dispersion of ferromagnetic iron oxide in a resinous binder, and the outer layer is a coating of a uniform dispersion of a mixture of ferromagnetic chromium dioxide and a ferromagnetic iron oxide in a resinous binder. The inner layer has a thick-; ness of from 7 to 12 microns, a coercive force of 260 to 320 oersteds, and a saturation residual flux density of 1150 to 1600 gauss. The outer layer has a thickness of 1 to 5 microns, a coercive force of 380 to 500 oersteds, and a saturation residual flux density of 1200 to 1600 gauss. The weight ratio of the ferromagnetic chromium dioxide and the ferromagnetic iron oxide in the outer layer is in the range from 1:4 and 4:1.
More particularly, there is provided a magnetic audio recording tape including a non-magnetizable base, a dual layer of magnetizable coating on said base, said dual layer comprising an inner layer and an outer layer, said inner layer being a homogeneous dispersion of ferromagnetic iron oxide 1~ .
., ~ _ 3 _ 10~4~1 powder in a resinous binder, having a coating thickness of 7 to 12 microns, having a coercive orce of 260 to 320 oersteds, and having a saturation residual flux density of 1150 to 1600 gauss, said outer layer being superposed on said inner layer, and being a homogeneous dispersion of ferromagnetic powders in a resinous binder, having a coating thickness of 1 to 5 microns, having a coercive force of 380 to 500 oersteds, and having a saturation residual flux density of 1200 to 1600 gauss, the said magnetic powder of both the layers being oriented in the longitudinal direction wherein said magnetic recording tape being characterized in that said ferromagnetic powders in said outer layer including at least ferromagnetic chromium dioxide powder having a coercive force of 450 to 600 oersteds and a ferromagnetic iron oxide powder having a coercive force of from 320 to 450 oersteds, the weight ratio of said ferromagnetic chromium dioxide and said ferromagnetic iron oxide existing in ` said outer layer being in the range from 1:4 to 4:1.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects, features and advantages of the invent-ion will be readily apparent from the following description of certain preferred :~
.' :
- 3a -.... . .
548~
em~odiments thereof, taken in conjunctiotl with the accompanying drawings, although variations and modifications may be effected with-out departing from the spirit and scope of the novel concepts of the disclosure, and in which:
Figure 1 is a graph plotting frequency response for a typical c:ollllllercial tape for an open reel recorder, a dual layer magneticrecording t~pe of the prior art, and an improved dual layer magnetic recording tape according to the present invention;
Figure 2 is a graph of the frequency response charac-teristics for a typical commercial cassette tape and a dual layer ` cassette tape;
" Figure 3 is a graph plotting the response against the biasing current for a commercial tape used for open reel recorders, and comparing it with the improved dual layer magnetic recording tape of the present invention;
Figure ~ is a graph of the frequency response char-acteristics for a dual layer magnetic recording tape manufactured ac-cording to an example of the present invention;
Figure 5 is a graph plotting distortion factor against the AC biasing current for a commercial tape and for the dual layer tape of the present invention;
Figure 6 is a graph plotting maximum output level for the commercial reel to reel tape, and also for the tape of the present invention; and Figure 7 is a graph of the frequency response char-acteristics for tapes produced accord~lng to other examples of the present invention.
lO~S4~1 DESCRII'TION Oli' T}-IE PRl~FERRED EM130DIMENTS
A suitable magnetic material for the inner layer is gamma ferric oxide because i~ has good printing characteristics, has a low noise level, and can be easily manufactured to obtain a desired coercive force. ~lowever, magnetite (Fe3O4) can also be used. The coercive force of the inner layer should be between 260 and 320 oersteds. If the coercive force of the inner layer is higher than 320 oersteds, it is difficult to increase the output in the low frequency range. The saturation residual flux density should be between 1150 and 1600 gauss. If this value is less than 1150 gauss, a satisfactory output in the low frequency range cannot be obtained, and if it exceeds 1600 gauss, the tendency of the magnetic powder to tear off is in-creased. ~he most suitable value for the saturation residual flux density is between 1250 and 1400 gauss. The coating thickness of the inner layer is closely related to the reproduction characteristics at the low or middle frequency range. According to the results which we have obtained, the thickness of the inner layer should be between about 7 and 12 microns. If it is less than 7 microns, the output in the low frequency range is decreased and if it exceeds 12 microns, the output in the low frequency range is increased too much. Since the output in the middle frequency range is not substantially changed, this makes the frequency response characteristics not flat over the entire audio frequency range.
The coercive force of the outer layer should be between about 380 and 500 oersteds. High frequency signals are recorded on the surface area of the magnetizable~.layer, so that a high coercive force in the outer layer is desirable. If it exceeds 500 oersteds, 1()65481 the output level in the high frequency range l~comes too high This then causes the ~requency response characteristics to deviate from the desired flat char~cteristic. Too high a coercive force in the tape also causes an increase in distortion and difficulty in erasing. A1so, a high coercive force requires an increase in recording current which makes the tape not compatible with conventional recorders, and also may cause a saturation of ferrite type magnetic heads. If the coercive force of the outer layer is less than 380 oersteds, it is not possible to obtain a high output level in the high frequency range.
Chromium dioxide has an excellent sensitivity in the high frequency range and is used in accordance with this invention to obtain the desired coercive force. However, lt is not easy to manu-facture chromium dioxide having a rather low coercive force in combina-tion with a large acicular ratio, and a small acicular ratio causes a decrease of the rectangular ratio of the coated layer. As a practical matter, it is desirable that the coercive force of the chromium dioxide be in the range from about 450 to 600 oersteds. Chromium dioxide shows an excellent sensitivity in the range of recorded wavelengths of less than 10 or 12 microns, and provides a high output in the high frequency range. Consequently, it is necessary to employ a magnet-izable powder other than chromium dioxide in admixture therewith to improve the frequency response in the range of recorded wavelengths longer than 10 or 12 microns to correspond to the middle and middle-high frequencies, According to our experimentation, a suitable dual layer magnetic tape is obtained when using~'a mixture of chromium dioxide and a ferromagnetic iron oxide powder having a coercive force of 10~;5~81 320 to 450 oersteds, with the weight ratio between the two ranging from 1:4 and 4: l in the outer layer. As noted, suitable ferromagnetic iron oxides are gamma ferric oxide or magnetite. If the coercive force of the powder is less than 320 oersteds, the total coercive force of the outer layer is decreased. Thus, an improvement in the high frequency range cannot be obtained. If the coercive force of the iron oxide powder exceeds 450 oersteds, the output in the high frequency range is increased too much, but the output in the middle and middle-high frequency ranges is not increased. In addition, too high a co-ercive force value in the outer layer requires an increase in the re-cording current. If the proportionate amount of the iron oxide powd~r is less than 20 parts by weight per 100 parts of magnetizable particles in the outer layer, it is not effective to increase the output in the middle and middle-high frequency ranges. If the ratio exceeds 80 parts per 100 parts of the mixture, the output in the high frequency range is deteriorated.
The saturation residual flux density of the outer layer should be between 1200 to 1600 gauss, preferably at 1250 to 1400 gauss so that the output in the high frequency range is increased without increasing the tendency of the powder to tear off from the tape. The coating thickness of the outer layer is closely related to the charac-teristics of the inner layer. If the coating thickness is less than 1 micron, the frequency response in the high frequency range is not satisfactory. If it exceeds 5 microns, the frequency response in the low frequency range is not satisfactory. Accordingly, the coating thickness of the outer layer should be from 1 to 5 microns, and preferably should be in the range of 2 to S microns.
Examples of the improved dual layer magnetic record-10~;54~i ing tape of the present invention which can be used with conventional biasing currents in tape recorders and which provide a flat frequency response characteristic over the entire audio frequency range, an excellent high frequency response, and a broad dynamic range are set forth in the following.
EXA MPLE
The inner layer oE the dual layer magnetic recording tape was produced from the following composition:
Material Parts bv weight Gamma ferric oxide particles100 Vinylacetate-vinyl chloride copolymer ("VAG}I" of Union Carbide Corp.) 5 Polyurethane resin ("Estane 5702" of B. F. Goodrich Corp.) 12 Lecithin (dispersant ) Olive oil (lubricant) 0. 5 Methyl ethyl ketone (solvent)80 Toluene (solvent) 80 Cyclohexanone (solvent) 80 The above ingredients were ball-milled for 50 hours, whereupon 3 parts by weight of an isocyanate compound ("Desmodule L"
manufactured by Bayer Corporation) was added to the mixture as a cur-ing agent for the polyurethane resin. The mixture was stirred for an additional 1 hour to produce a magnetic dispersion in the form of a paint.
The backing member employed was a polyethylene terephthalate film of 24 microns in thickness which had been treated with an alkyl titanate and nitrocellulose to improve the adhesion.
lO~S~l The magnetic paint was applied to the backing member by means of a gravure coater so that the thickness of the coating after drying was 9 microns. The coated film was passed through a magnetic field to orient the magnetizable particles in the longitudinal direction of the film before drying, and thereafter the film was dried and wound into a roll form. Then, the film was calendered to improve the magnetic characteristics and the Eilm was heated at 60C for 4 hours to cure the polyurethane resin sufficiently.
The inner layer formed by the above-described pro-cedure had the following characteristics:
Coercive force (Hc) 290 Oe Saturation residual flux density (Br) 1310 gauss Rectangular ratio (Rs = Br/Bm) 85~
~ he outer magnetizable layer of the dual layer magnetic tape was prepared as follows. The following mixture was made up:
Material Parts bv wei~ht Chromium dioxide particles 60 Gamma ferric oxide particles 40 Vinyl acetate-vinyl chloride co-polymer ("VAGH" of Union Carbide Corp. ) 15 Polyurethane resin ("Estane 5702) 5 "Squalane" (lubricant) Lecithin (dispersant) 0. 5 Methyl ethyl ketone (solvent) 80 Toluene (solvent) 80 Cyclohexanone (solvent) ~ 80 After the above mixture was ball-milled for 70 hours, ~ 0~;54~1 3 parts by weight of the isocyanate compound "Desmodule r ~ wag added to the mixture as a curing agent for the polyurethane resin. The mixture was stirred for an additional 30 minutes to provide a magnetic paint. The paint was coated on the previously formed inner layer so that the thickness was 3 microns after drying. The coated layer was also passed through a flat magnetic field to orient the magnetizable particles in the longitudinal direction of the film before drying,and then the film was dried and wound into a roll form. After the film was calendered to improve the magnetic characteristics, the film was heated at 50~ for 2 hours to cure the polyurethane resin sufficiently.
The outer layer formed by the above-described pro-cedure had the following magnetic characteristics:
Coercive force (Hc) 420 Oe Saturation residual flux density (Br) 1300 gauss The magnetic particles themselves employed in the foregoing example had the following characteristics:
Gamma ferric oxide of the inner layer:
Acicular particles of 0.7-0. 8 microns in length, with an axis ratio of 8-10 Magnetization 72 emu/g Coercive force 310 Oe Print through value51 dB
Adsorption 0. 8 m~/g Normalized surface area 17 . 7 m /g Chromium dioxide of the outer layer:
Acicular particles having an average length of 0.4 microns with an axis ratio of 4 to 10 Coercive force 480 oe Magnetization 80 emu/g 10~;54~1 1 Camma ferric oxide of the outer layer:
Acicular particles having an average length of 0. 4 to 0. 5 microns with an axis ratio of 7 to l0 Coercive force 420 Oe Magnetization 76 emu/g Because of the greater acicular ratio of the gamma ferric oxide particles of the inner layer, the inner layer had a higher packing density than the conventional gamma ferric oxide tape.
A dual layer magnetlc tape was manufactured using a different weight ratio of iron oxide to chromium dioxide from that used in Example 1.
Eighty parts by weight of chromium dioxide particles having a coercive force of 480 oersteds and 20 parts by weight of gamma ferric oxide having a coercive force of 420 oersteds were used as the magnetizable particles of the outer layer, in combination with the other ingredients in the coating formulation as indicated in Example 1. The outer layer had a coercive force of 450 oersteds, and a saturation residual flux density of 1350 gauss.
In this example, the outer layer was composed of 20 parts by weight of chromium dioxide having a coercive force of 480 oersteds and 80 parts by weight of gamma ferric oxide having a co-ercive force of 420 oersteds. The other ingredients of the outer layer were as specified in Example 1. The magnetic characteristics of the outer layer included a coercive force of 370 oersteds and a saturation residual flux density of 1250gauss.
In Eiigures 1 and 2, curves 1 to 4, inclusive, illustrate 10~54~1 the freguency response characteristics of various tapes, Curve 1 was derived ~rom a conventional cassette tape having a single magnet-izable layer with a coating thickness of 6 microns and a coercive force of 320 oersteds (Sony C-60FP). Curve 2 was derived from a conven-tional open reel to reel type tape having a single magnetizable layer with a coating thickness of 12 microns and a coercive force of 300 oersteds (Sony SL~I tape). Curve 3 was derived from a dual layer magnetic tape used in cassette type recorders. The inner layer con-tained gamma ferric oxide having a coating thickness of 5 microns and a coercive force of 290 oersteds. The outer layer of the dual layer contained chromium dioxide having a coating thickness of 1 micron and a coercive force of 490 oersteds.
Curve 4 was derived from a dual layer magnetic tape of the type used in open reel to reel recorders. The inner layer of the dual layer contained gamma ferric oxide having a coating thickness of 10 microns and a coercive force of 290 oersteds. The outer layer contained chromium dioxide having a coating thickness of 2 microns and a coercive force of 490 oersteds.
In Figures 1 and 2, the characteristics of the tapes represented by curves 1 and 3 were measured at a tape speed of 4. 8 cm/sec while the characteristics of tapes numbered 2, 4 and 5 were measured at a tape speed of 19 cm/sec. Curve 5 illustrates the characteristics of the improved dual magnetic tape of the present inven-tion and produced according to Example 1.
It will be seen from the foregoing curves that the dual layer magnetic tape for use in casse~tes, exemplified by curve 3, show~ a good frequency response over the audio frequency range. In 10~5~
the case of the dual layer magnetic tape for the open reel to reel recorder exemplified by curve 4, however, the output level in the frequency range of 1 to 10 kilohertz is de~creased con-siderably. The reason for this decrease in output level is that the sensitivity of chromium dioxide powder becomes good for the range in which the recording wavelength is shorter than 10 to 12 microns, corresponding to the fact that the frequency is more than 15 kilohertz at a tape speed of 19 cm/sec, but is not so good for a longer wavelength.
The dual layer magnetic recording tape of the present invention can be operated with the same biasing current as is used in conventional single layer magnetic recording tapes to provide a high frequency response throughout the audio frequency range, together with a wide dynamic range and little distortion.
The best setting of biasing current is 110 + 10% of the biasing current of the conventional single layer magnetic recording tapes. Figure 3 illustrates the biasing characteristics of the conventional SONY SLH tape by means of dotted lines, and the improved magnetic tape of the present invention by means of Z0 the solid line. These characteristics were obtained by using an open reel type recorder, Denon DN-342R-T (Trade Mark), with a ferrite recording head having an eight micron gap and a ferr-ite reproducing head having a four micron gap, the recording level being set to -lOdB (OdB = 200 pwb/mm) and at a tape speed of 19 cm/sec.
The dual layer magnetic tape ~anufactured as described in Example 1 had a frequency response characteristic illustrated in Figure 4. Also, the distortion factor and the maximum out-put level (M.O.L.) characteristics were measured and these results are illustrated in Figures 5 and 6, respectively. In these figures, the characteristics of the magnetic tape of the present invention are indicated by the solid lines while the dotted lines indicate 10~5~
characteristics of the Sony SLI ~ tape. The clistortion factor was measured at 400 ~lertz with a Od~3 output. The M.O.T, was measured using the aforementioned tape deck witll playback equalizer time constant Tl = 3180 microseconds, T2 = 50 microseconds, and at a tape speed of ]9 cm/sec.
As is apparent from Figure 4 of the frequency re-sponse characteristics, the output level in the freguency range from 4 kilohertz to 10 kilohertz was much improved and a flat frequency response characteristic was obtained. ~ccording to a hearing test, the tone quality obtained was satisfactory. The distortion factor was much smaller than with the conventional SLH tape. Also, in the low frequency range, that is, not greater than 3 kilohertz, the M. O. L.
gained 3dB compared with the SLH tap~, and in the high frequency range (above 10 kilohertz) it gained more than 1.5 dB.
The frequency response characteristics of the tapes produced according to Examples 2 and 3 are shown in Figure 7.
Curve a represents the output response characteristic of the tape produced according to Example 2, while curve b represents that ob-tained using the tape produced according to Example 3.
A dual layer magnetic tape containing more than 80 parts by weight of chromium dioxide per 100 parts of mixture in the outer layer did not improve the output level in the middle and the middle-high frequency ranges while the dual layer magnetic tape con-taining more than 80 parts by weight of iron oxide per 100 parts of mixture in the outer layer did not improve the output level at high frequencies. Consequently, it was d~termined that the weight ratio of the chromium dioxide to the ferromagnetic iron oxide in the outer layer 10~S4t~1 ' should be in the range from about 1:4 to 4:1.
As apparent from the foregoing description, the dual layer magnetic recording tape of the present invention when operated at speeds higher than used in conventional cassette tape recorders has advantages over conventional tapes, and also over dual layer magnetic recording tapes of the prior art. The new tape has a high sensitivity over all the audio frequency range. The decrease of out-put in the middle and middle-high frequency ranges is improved so that it has a relatively flat frequency response over the entire audio frequency range at a relatively high tape speed. The distortion factor ¦ .
is small and the M.O.L.characteristics are large and it provides a wide dynamic range. Furthermore, it is compatible with the biasing characteristics of standard tape recorders using ferrite magnetic heads.
It should be evident that various modifications and !
variations can be made to the described embodiments of the invention without departing from the scope of the novel concepts of the present invention.
Claims (6)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A magnetic audio recording tape including a non-magnetizable base, a dual layer of magnetizable coating on said base, said dual layer comprising an inner layer and an outer layer, said inner layer being a homogeneous dispersion of ferromagnetic iron oxide powder in a resinous binder, having a coating thickness of 7 to 12 microns, having a coercive force of 260 to 320 oersteds, and having a saturation residual flux density of 1150 to 1600 gauss, said outer layer being superposed on said inner layer, and being a homogeneous dispersion of ferromagnetic powders in a resinous binder, having a coating thickness of 1 to 5 microns, having a coercive force of 380 to 500 oersteds, and having a saturation residual flux density of 1200 to 1600 gauss, the said magnetic powder of both the layers being oriented in the longitudinal direction wherein said magnetic recording tape being characterized in that said ferromagnetic powders in said outer layer including at least ferromagnetic chromium dioxide powder having a coercive force of 450 to 600 oersteds and a ferromagnetic iron oxide powder having a coercive force of from 320 to 450 oersteds, the weight ratio of said ferromagnetic chromium dioxide and said ferromagnetic iron oxide existing in said outer layer being in the range from 1:4 to 4:1.
2. A magnetic recording tape according to claim 1 in which the coating thickness of the outer layer is in the range from 2 to 5 microns.
3. A magnetic recording tape according to claim 1 in which the saturation residual flux density of the inner layer is in the range from 1250 to 1400 gauss.
4. A magnetic recording tape according to claim 1 in which the saturation residual flux density of the outer layer is in the range from 1250 to 1400 gauss.
5. A magnetic recording tape according to claim 1 in which the inner layer is a homogeneous dispersion of ferromagnetic gamma ferric oxide powder in a resinous binder.
6. A magnetic recording tape of claim 1 in which the outer layer is the homogeneous dispersion of a mixture of ferro-magnetic chromium dioxide powder and ferromagnetic gamma ferric oxide powder in a resinous binder.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP9705574A JPS5725893B2 (en) | 1974-08-26 | 1974-08-26 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1065481A true CA1065481A (en) | 1979-10-30 |
Family
ID=14181961
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA233,765A Expired CA1065481A (en) | 1974-08-26 | 1975-08-19 | Magnetic recording tape |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS5725893B2 (en) |
| CA (1) | CA1065481A (en) |
| DE (1) | DE2538005A1 (en) |
| GB (1) | GB1484958A (en) |
| NL (1) | NL7510080A (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3825619A1 (en) * | 1988-07-28 | 1990-02-01 | Agfa Gevaert Ag | METHOD FOR PRODUCING A MAGNETIC RECORDING CARRIER |
| JP2821280B2 (en) * | 1991-04-19 | 1998-11-05 | 富士写真フイルム株式会社 | Magnetic recording media |
| US5747593A (en) * | 1993-07-14 | 1998-05-05 | Nippon Steel Chemical Co., Ltd. | Process for producing rubber-modified styrene resin |
-
1974
- 1974-08-26 JP JP9705574A patent/JPS5725893B2/ja not_active Expired
-
1975
- 1975-08-19 GB GB3450275A patent/GB1484958A/en not_active Expired
- 1975-08-19 CA CA233,765A patent/CA1065481A/en not_active Expired
- 1975-08-26 NL NL7510080A patent/NL7510080A/en not_active Application Discontinuation
- 1975-08-26 DE DE19752538005 patent/DE2538005A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5125104A (en) | 1976-03-01 |
| NL7510080A (en) | 1976-03-01 |
| GB1484958A (en) | 1977-09-08 |
| DE2538005A1 (en) | 1976-03-18 |
| JPS5725893B2 (en) | 1982-06-01 |
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