JPH0363923A - Thermomagnetic transfer medium - Google Patents

Abstract

PURPOSE:To ameliorate the transfer performance especially in the shortwave region and to improve the protective performance against the external magnetic field by providing a magnetic layer having a higher coercive force on a magnetic layer contg. CrO2. CONSTITUTION:The first magnetic layer contains CrO2 acicular crystal, the coercive force of the second magnetic layer at ordinary temp. is made higher than that of the first magnetic layer at ordinary temp., and the coercive force of the first and second magnetic layers at 150 deg.C is controlled to <=200Oe. When thermomagnetic transfer is applied to such a thermomagnetic transfer medium, the long-wave component is transferred mainly to the first magnetic layer and the shortwave component to the second magnetic layer. As a result, the demagnetization loss of the shortwave component transferred to the second magnetic layer having a higher coercive force at ordinary temp. than the first magnetic layer is minimized, the second magnetic layer having a higher coercive force exerts a shielding effect from the external disturbance magnetic field, and the safety of the transferred information is maintained.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention provides CrO! Regarding the improvement of conventional thermomagnetic transfer media having a magnetic layer containing a magnetic material such as The present invention relates to a thermomagnetic transfer medium that has improved characteristics and also has improved protection performance of the transfer state due to the shielding effect of high coercive force.

<Prior Art> When recording audio or video, it is generally necessary to record various signal components ranging from long wavelengths to short wavelengths. With the trend toward higher density audio and video recording, there is a need for a method to reliably record signals with shorter wavelengths.
For example, in the recording of digital audio signals and video signals, high-density recording with a shortest recording wavelength of 1- or less has been realized.

It is well known that the shorter the recording wavelength, that is, the higher the density of recording, the more the signal recorded on the magnetic layer is recorded only in a very shallow region on the surface of the magnetic layer. On the other hand, it is known that the long wavelength component recording region becomes deeper from the surface if the magnetic layer is sufficiently thick.

In this way, the recording area in the magnetic layer depends on the wavelength of the recording signal, so the magnetic layer has a double layer structure, and the surface area of the medium near the magnetic head (called the upper layer) is specially designed to improve short wavelength characteristics. Many technologies have been proposed.

For example, in order to reduce demagnetization loss due to shorter wavelengths, there is a method of making the coercive force of the upper layer larger than that of the magnetic layer below it (called the lower layer), and also making the upper layer thicker than the lower layer. Method of thinning (for example, Japanese Patent Application Laid-open No. 54-213048)
No. 54-143113, No. 58-175
Publication No. 39, Publication No. 61-165820, Publication No. 62-7
Publication No. 8718, Japanese Patent Publication No. 37-2218, Publication No. 39 of the same
-23678 publication, 52-28364 publication, etc.)
In addition, in order to make effective use of the perpendicular magnetization component, which increases as the wavelength becomes shorter, there is a method in which the distribution of the easy axis of magnetization in the upper layer is made spatially uniform, or a method in which it is perpendicularly aligned (Japanese Patent Laid-Open No. 6
2-43833, Japanese Patent Publication No. 40-5351, etc.) Furthermore, there is a method of using barium ferrite fine particles as a magnetic material suitable for these orientations (Japanese Patent Laid-Open No. 5
7-195329, 58-119610, etc.).

By the way, for mass copying of recorded tapes for video or digital audio, since these recording frequency bands are already high, the speed of the copy tape can be increased simply by increasing the frequency, as in mass copying for normal analog audio. It is not possible to increase the speed by several tens of times, and the situation has become such that copying from the parent deck must be done in real time on a 1:1 ratio. For this reason, contact magnetic transfer methods and thermomagnetic transfer methods have been developed to increase the copying speed.
is being considered.

Among these methods, the contact magnetic transfer method involves bringing the magnetic surfaces of a master medium having a high coercive force magnetic layer and a slave medium (transferring medium) having a low coercive force magnetic layer into contact with each other, so that the coercive force of the master medium is greater than that of the slave medium. This is a method of transferring magnetic information from a master medium to a slave medium by applying an alternating current attenuating magnetic field smaller than the coercive force.

In addition, the thermomagnetic transfer method is a method that uses heat instead of an alternating magnetic field, and the temperature of the heated part by laser beam irradiation is raised to above the Curie point of the slave medium and below the Curie point of the master medium. This method transfers magnetic information from the master medium to the slave medium during the cooling process.

Compared to the contact magnetic transfer method, the thermomagnetic transfer method has features such as no need to apply a magnetic field during transfer, higher transfer efficiency, and less S/N reduction.

The magnetic material used in the slave medium for thermomagnetic transfer (hereinafter referred to as thermomagnetic transfer medium) must be capable of thermal transfer at a temperature below the Curie point of the master magnetic recording medium. Therefore, a magnetic material with a relatively low Curie point is required.

These transfer recording media are required to have characteristics that can reliably transfer short-wavelength magnetic information due to the trend toward higher density audio and video recording as described above, so they are required to have high coercive force at room temperature. Magnetic materials are preferred.

Under these circumstances, in order to improve short-wavelength recording characteristics, media that utilize the perpendicular magnetization component of barium ferrite fine particles and media that increase the perpendicular orientation component of needle-shaped CrOz particles (Japanese Patent Laid-Open No. 10417-1982) have been developed. (publication) has become promising as a slave medium.

However, barium ferrite fine particles have a high Curie point, which makes them unsuitable for thermomagnetic transfer media, and Cr
Currently, Oz acicular particles are used as the only magnetic material for thermomagnetic transfer media.

<Problem to be solved by the invention> In ordinary magnetic recording, in order to improve high-density recording, that is, short wavelength recording characteristics, it is necessary to reduce various losses associated with shortening wavelengths. It is also desirable for the medium to have a high coercive force in order to improve short wavelength characteristics.

However, the coercive force of ordinary CrOz acicular particles is 500~
The coercive force is approximately 900 Oe, and it is difficult to put a coercive force of 1000 Oe or more into practical use.

Furthermore, the needle-like shape of the CrO* particles poses an obstacle to increasing the vertically oriented component to improve the transfer efficiency of the short wavelength component, and it is estimated that it is difficult to obtain a uniform and highly filled perpendicular magnetization stable film. Ru.

On the other hand, with barium ferrite fine particles suitable for vertical alignment, it is difficult to lower the Curie point while maintaining dispersibility and saturation magnetization at the current levels.

In addition, from the perspective of preserving records against external disturbance magnetic fields, the strength of the magnetic field generated near magnets used in daily life can generally reach nearly 2000 Oe, so as mentioned above, the coercive force can reach 1000 Oe. In a thermomagnetic transfer medium using CrO* that does not reach the target temperature, there is a fear that the transfer signal may be altered or even destroyed by the proximity of these magnets.

The present invention was developed in view of the above circumstances, and is capable of reliably performing thermomagnetic transfer of short wavelength components of wavelength 1 or less, and also capable of successfully transferring long wavelength components. It is an object of the present invention to provide a thermomagnetic transfer medium with high protection performance for transferred information.

<Means for Solving the Problems> These objects are achieved by the following inventions (1) to (4).

(1) A thermomagnetic transfer medium having a first magnetic layer and a second magnetic layer sequentially on a substrate, wherein the first magnetic layer contains CrO□acicular particles, and the coercive force of the second magnetic layer at room temperature is higher than the coercive force of the first magnetic layer at room temperature, and 15% of the first magnetic layer and the second magnetic layer.
A thermomagnetic transfer medium having a coercive force of 200 Oe or less at 0°C.

(2) The coercive force of the second magnetic layer at room temperature is 1000 Oe
The thermomagnetic transfer medium according to (1) above.

(3) The thermomagnetic transfer medium according to (1) or (2) above, wherein the thickness of the second magnetic layer is equal to or less than the thickness of the first magnetic layer.

(4) The magnetic material contained in the second magnetic layer is Fe, Co
and (1) to 3) above, which are ferromagnetic ultrafine particles having a F e t P type hexagonal crystal structure containing P as a main component.
The thermomagnetic transfer medium according to any one of the above.

<Function> The thermomagnetic transfer medium of the present invention has a first magnetic layer and a second magnetic layer on a substrate.
and magnetic layers in sequence. The i-th magnetic layer is made of Cr.
Ox acicular particles are contained, and the coercive force of the second magnetic layer at room temperature is higher than the coercive force of the first magnetic layer at room temperature.

When thermomagnetic transfer is performed on such a thermomagnetic transfer medium of the present invention, long wavelength components are mainly transferred to the first magnetic layer, and short wavelength components are mainly transferred to the second magnetic layer.

In thermomagnetic transfer, the first and second magnetic layers of the transfer medium are first heated to near or above their Curie points. After heating, the coercive force of the transfer medium increases from around zero to the value at room temperature while the temperature decreases to room temperature.

Signals are transferred during this process, and the greater the coercive force at room temperature, the greater the rate of increase in coercive force during the cooling process, and the demagnetization loss of the short wavelength component of the signal can be reduced.

Therefore, the demagnetization loss of the short wavelength component transferred to the second magnetic layer, which has a coercive force larger than that of the first magnetic layer at room temperature, is extremely small.

Moreover, since the second magnetic layer having a high coercive force exhibits a shielding effect against external disturbing magnetic fields, the safety of transferred information is maintained.

Furthermore, since the Cry and acicular particles contained in the first magnetic layer are easily oriented within the plane of the magnetic layer, long wavelength components that utilize in-plane magnetization components at a high rate can be efficiently transferred.

In addition, the magnetic material used for the 21st ifl layer is Fe, C
In the case of ferromagnetic ultrafine particles having a Fe2P type hexagonal crystal structure mainly composed of It is easy to orient the magnetic layer in the perpendicular direction. Therefore, it is possible to efficiently transfer the short wavelength component, which uses the perpendicular magnetization component at a high rate.

Specific composition> Hereinafter, the specific configuration of the present invention will be explained in detail.

The thermomagnetic transfer medium of the present invention has a first magnetic layer and a second magnetic layer sequentially on a substrate, the first magnetic layer contains CrOz acicular particles, and the coercive force of the second magnetic layer at room temperature is is configured to be higher than the coercive force of the first magnetic layer at room temperature.

There is no particular limit to the coercive force of the second magnetic layer at room temperature, and it may be set to an appropriate value depending on the wavelength of the magnetic information to be transferred, the external magnetic field strength to be protected, etc. For transfer, it is preferably 1000 Oe or more, and if ferromagnetic ultrafine particles described below are used, it is 2000 Oe or more.
It can be set to 5000 Oe. If the coercive force at room temperature is below the above level, it will be difficult to improve short wavelength characteristics, and the transferred information will be easily disturbed by external magnetic fields.
Although there is no upper limit to the coercive force at room temperature, when using ultrafine particles described below, it is difficult to increase the coercive force to 5000 Oe or more.

The coercive force of the first magnetic layer containing CrOt as a magnetic material at room temperature is usually about 500 to 900 Oe, although it varies depending on the coercive force, shape, orientation, etc. of the CrOz used.

The coercive force of the first magnetic layer and the second magnetic layer at 150° C. is preferably 200 Oe or less, particularly 150 Oe or less. If the coercive force at 150° C. exceeds the above range, it becomes difficult to perform thermomagnetic transfer at a temperature where the thermal influence on the thermomagnetic transfer medium and the master medium can be ignored.

The Curie points of the first Fii layer and the second magnetic layer are 80
The temperature is preferably about 90 to 160°C, particularly about 200°C. If the Curie point is less than the above range, the magnetic thermal stability of the magnetic layer will be insufficient, and if it exceeds the above range, the heating temperature to lower the coercive force to a level suitable for transfer will be high, and the above-mentioned This makes it substantially difficult to perform thermomagnetic transfer.

These magnetic layers are preferably configured such that the second magnetic layer is thinner than the first magnetic layer.

Specifically, the thickness of the second magnetic layer is 0.1 to 1, particularly 0.
．． It is preferable that it is 2-0.8 micrometer. If the thickness of the second magnetic layer is less than this range, the amount of magnetization will be small and the short wavelength characteristics will be deteriorated. Moreover, when this range is exceeded, long wavelength characteristics deteriorate.

Although there is no particular restriction on the thickness of the first magnetic layer, it is preferably about 1 to 6 mm thick.

The thermomagnetic transfer medium of the present invention is a so-called coated medium in which a magnetic material, a binder, and various additives are kneaded and then coated on a nonmagnetic substrate to form a first magnetic layer and a second magnetic layer. .

There are no particular restrictions on the magnetic material contained in the second magnetic layer, but
Since it is easy to obtain the above characteristics, it is preferable to use ferromagnetic ultrafine particles containing Fe, Go$; and P as main components, and such ferromagnetic ultrafine particles are dispersed in a binder to form a second magnetic material. It is preferable to constitute a layer.

Such ferromagnetic ultrafine particles (hereinafter abbreviated as ultrafine particles) usually have a hexagonal Fe*P structure as a main body.

The content of these elements in the ultrafine particles is preferably within the following range.

F e / Co = 95 / 5 ~ 70 / 30
, more preferably Fe/GO=90/10 to 80/20
It is.

If the content of CO relative to Fe is less than the above range, the Curie temperature will drop significantly and the coercive force at room temperature will drop to about 500 Oe or less. Also,
If the above range is exceeded, the magnetocrystalline anisotropy decreases, so that the coercive force also decreases to about 500 Oe or less.

On the other hand, (F e 1 G o ) / P = 85 /
15 to 60/40, more preferably (Fe+C
o) / P = 80 / 20 ~ 65 / 35
It is.

When the content of P in Fe+Go is less than the above range, the effect of P that contributes to increasing the magnetocrystalline anisotropy decreases,
The coercive force becomes about 500 Oe or less.

For a stoichiometric hexagonal F e 2 P structure, the theoretical amount of P is about 33%. When the P content is 30% or less, it is generally considered that a F e t P single phase structure is not formed.
% and up to 15%, almost hexagonal Fe
A tP single-phase structure can be formed.

The reason for this is thought to be that since fine particles are synthesized by rapid cooling from a high-temperature gaseous state by the method described below, the hexagonal crystal structure, which is stable at high temperatures, is frozen as is. If the amount of P is less than the stoichiometric composition, the lattice points of P may remain as vacancies, and other elements added in the raw materials or during the reaction process, such as C,
N, Si%Sn, B%Ni%Zn.

A structure in which Ti, Mn, Al, Cr, etc. are substituted at the P position is also conceivable.

In addition, if the amount of P exceeds the stoichiometric composition, the amount of P in the ultrafine particles will be excessive, but if it is at least within the above range,
No change was observed in the line diffraction image, and no adverse effects occurred on the magnetic properties. However, when the amount of P exceeds the above range, the saturation magnetization decreases to 35 emu/g or less, which is not preferable.

Such ultrafine particles may contain C in addition to the main components Fe, Co and P.

C is incorporated into the ultrafine particles from the raw material powder, the reactor constituent materials, or the atmosphere in the reactor, which will be described later, and is thought to have a stabilizing effect on the hexagonal Fe*P structure. .

More specifically, the inclusion of C is effective in reducing the electrical resistance and improving the dispersibility of ultrafine particles.

Further, the presence of C during the reaction is effective in effectively reducing and evaporating the raw material when it is an oxide.

Thereby, the raw material oxide can be reduced and phosphorized using only nitrogen gas without using dangerous hydrogen.

Further, C has the effect of preventing ultrafine particles from being fused together and forming a chain shape during generation of ultrafine particles, and improving corrosion resistance.

When C is contained, the content of C in the ultrafine particles is preferably 20 wt% or less, more preferably 0.1 to 10 wt%. If the content of C is less than the above range, the effect of containing it will be insufficient,
If it exceeds the above range, the saturation magnetization will decrease.

In the ultrafine particles, most of Fe, Co and P are
Forms a hexagonal Few P structure.

Therefore, ultrafine particles with high coercive force and low Curie temperature are realized. The existence of the hexagonal Few P structure can be confirmed by X-ray diffraction.

In addition, in addition to the hexagonal F e t P structure, the ultrafine particles contain some F e s P as long as it does not interfere with the magnetic properties.
structure or αFe structure may be present.

The composition of such ultrafine particles can be determined by plasma emission spectroscopy, C,
It can be measured by H, N element analyzer, fluorescent X-ray analysis, other chemical analysis, etc.

In addition to the above-mentioned elements, the ultrafine particles may contain N%Si%Sn%B as additional elements if necessary.

Nf, Zn, Ti%Mn%AI2, Cr, etc. may be contained.

The ultrafine particles produced by the method described below are spherical particles, and this appearance can be confirmed using a transmission electron microscope or the like.

The average particle size of such ultrafine particles is preferably 0.00
5 to 0.1μ, more preferably 0.01 to 0.
It is 05-.

When the average particle size is less than the above range, superparamagnetic behavior becomes significant and the coercive force decreases significantly. Moreover, if it exceeds the above range, the agglomeration effect between the particles becomes large, making it difficult to disperse, which is not preferable.

According to the manufacturing method described below, ultrafine particles having such an average particle size can be obtained as a single, substantially spherical particle without the need for pulverization or other means. Therefore, highly dispersible ferromagnetic ultrafine particles can be easily realized.

The ultrafine particles obtained by the manufacturing method described below have a coercive force of 500 Oe or more, particularly 800 Oe or more, and even 100 Oe or more.
oOe or more, and 2000O
It is suitable for the thermomagnetic transfer medium of the present invention because it can be made larger than e, particularly from 2100 to 5000 Oe.

In addition, the saturation magnetization is 35 emu/g or more, especially 50 to
80 emu/g.

In addition, the Curie temperature of such ultrafine particles is 80 to 2
It is suitable for the thermomagnetic transfer medium of the present invention because it can be set at 00°C, particularly 90 to 160°C.

According to the manufacturing method described below, in all of the composition ranges of Fe, Co and P as described above, hexagonal F e t
Since ultrafine particles based on the P structure can be produced, it is possible to freely control mainly the coercive force and the Curie temperature within the above ranges depending on the purpose.

Next, a method for manufacturing such ultrafine particles will be explained.

Such ultrafine particles are preferably produced by a gas phase reaction method.

As the gas phase reaction method, it is preferable to use a method in which raw material powder containing at least Fe and CO is evaporated in a gas phase and then rapidly cooled to obtain ultrafine particles.

In the raw material powder, Fe and Co may be contained alone or in the form of compounds such as oxides, phosphides, or phosphates. Also,
A mixture of these may be used.

There is no particular restriction on the type of compound used, but Fe and C
Oxide of O, iron phosphate, etc. can be suitably used.

P may be contained in the raw material powder, or may be contained in the gas phase.

When P is contained in the raw material powder, it may be contained alone in the same way as above, or it may be contained in the form of a compound. Alternatively, a mixture of these may be used.

There is no particular restriction on the type of compound used, but particularly preferably used P compounds include ammonium phosphate, iron phosphate, cobalt phosphate, phosphorus oxide, and the like.

Containing P in the gas phase can be realized, for example, by introducing hydrogen phosphide gas such as phosphine, which serves as a P supply source, into the reaction system.

In order to contain C in the ultrafine particles, these elements may be contained in the raw material powder or in the gas phase. Alternatively, it can also be supplied from reactor constituent materials used in manufacturing.

When supplying from raw material powder, carbon black or the like may be used as the C source.

When supplying from the gas phase, the C source may include Co, various hydrocarbons, carbonyl compounds, etc. in the carrier gas that transports the raw material.

In addition to these elements, the raw material powder may contain, as additives, the above-mentioned additional elements, alloys or compounds thereof, or mixtures thereof.

Each of the above-mentioned elements and these additives may be contained in the raw material powder so as to have a desired content when formed into ultrafine particles.

Moreover, scrap, ore, mill scale, etc. can also be used as a mixture containing each of the above-mentioned elements.

Even when such low-cost raw materials are used, substantially spherical ultrafine particles with good magnetic properties can be obtained.

The average particle size of the raw material particles constituting the raw material powder containing each of the above elements is preferably 100 or less, particularly preferably 1074 or less.

By setting the average particle size to this level, the evaporation efficiency of Fe, Co, etc. can be increased, and the raw material particles can be easily quantitatively supplied into the reactor.

Such raw material particles can be obtained by pulverizing and mixing raw materials such as the above-mentioned elements or compounds using a known pulverizing means such as a jet mill or a ball mill.

Furthermore, in order to improve the fluidity of the raw material particles, a known binder may be used to granulate the raw material particles. In addition, it is preferable to use spray drying etc. for granulation. Although there is no particular restriction on the binder used, examples of suitable binders include polyvinyl alcohol, polyvinylpyrrolidone, and ethyl cellulose.

Next, in a reactor, the raw material particles as described above are heated in a gas phase to instantaneously evaporate the entire raw material particles, and then rapidly cooled and condensed to form ultrafine particles.

In this case, the entire reaction system is preferably carried out in an inert or reducing atmosphere at atmospheric pressure or lower.

The heating means to be used is not limited as long as it can instantaneously evaporate raw material particles, but thermal plasma, particularly plasma jet, is preferably used.

Examples of means for generating a plasma jet include:
DC plasma is an example of DC plasma, which generates a direct current arc discharge between the inner surface of the tip of a nozzle-shaped anode and the cathode tip provided within this anode, and heats the plasma gas supplied into the anode to an extremely high temperature. It is heated to create thermal plasma, which is ejected as a jet from a nozzle at the tip of the anode.

In addition, a plasma jet using inductively coupled plasma (hereinafter abbreviated as ICP) is also preferably used.

In this method, plasma is generated inductively by a high-frequency magnetic field generated by flowing gas into a quartz tube and passing a high-frequency current through a coil wound around the quartz tube.

By introducing raw material particles into such a plasma jet, the raw material particles are instantaneously heated and instantaneously evaporated.

FIG. 2 and FIG. 3 show a preferred example of an apparatus for producing ultrafine particles.

The reactor 1 shown in FIGS. 2 and 3 has an evaporating section 2, a cooling section 3, and a collecting section 4 in series.

A plasma jet 211 is ejected into the furnace of the evaporation section 2 by the plasma jet generating means 21 . As the plasma jet generating means 21, a DC plasma generator is used in FIG. 2, and an ICP generator is used in FIG. 3.

Raw material powder is introduced into the plasma jet 211 by a carrier gas from the raw material powder supply means 22 .

In the case of the DC plasma shown in FIG. 2, the flow rate of the ultra-high temperature plasma gas is very fast, so the raw material powder does not reach the center of the plasma and is likely to be blown off on the outside of the fast-flowing flame. For this reason, it is better to bring the inner wall of the furnace in the evaporation section as close as possible to the plasma flame, maintain the inside of the furnace at a high temperature, and create a turbulent flow of plasma to prolong the residence time of the raw material powder under high temperature. .

For this reason, the inner wall surface of the furnace of the evaporation section 2 is covered with a heat-resistant material 23. As the material of the heat-resistant material 23, it is preferable to use graphite, boron nitride, tungsten, or other heat-resistant alloy materials. Note that when a carbon-containing material such as graphite is used as the heat-resistant material, C can be supplied to the ultrafine particles from this material.

The heat resistant material 23 is further covered with a heat insulating material 24.

Preferable materials for the heat insulating material 24 include fibrous carbon, alumina, and zirconia.

Heat is retained within the evaporation section by the heat resistant material 23 and the heat insulating material 24. In addition, in this case, the inner wall of the evaporation section 2 is
It is preferable that the temperature is maintained at a high temperature of at least 1000°C or higher.

On the other hand, in ICP, the diameter of the flame of plasma is larger than that of DC plasma, the gas flow rate is slower, and the raw material powder can be supplied from the central axis of the plasma. Residence time can be increased. Therefore, by increasing the inner wall diameter of the reactor shown in FIG. 3 and lowering the temperature of the reactor wall, the evaporation reaction can proceed effectively while preventing other substances from being mixed in. In this case, as shown in FIG. 3, the raw material powder supply means 22 is installed on the central axis of the plasma jet generation means 21, and the raw material can be directly conveyed to the center of the plasma jet 211.

Gas generated by evaporation of the raw material powder in the evaporation section 2 is carried to the cooling section 3 by the carrier gas.

Then, it is rapidly cooled by the cooling gas supplied from the cooling gas supply port 31 and condensed to become the target ultrafine particles 10. The obtained ultrafine particles 10 are transported to the collection section 4 by a carrier gas and discharged outside the reactor 1.

The ultrafine particles obtained in this manner are free from fusion or chain formation between particles, and are monodispersed, substantially spherical particles.

The carrier gas for transporting plasma gas, cooling gas, raw material powder, and its evaporated gas includes Ar, N2, He,
One or more types of Nz, NHs, Co, various hydrocarbons, etc. may be appropriately selected depending on the purpose, but as the plasma gas, Ar-Nz mixed gas, Ar-Nz mixed gas, N
A mixed gas such as z -Ha is preferable, and N2, N2 or NH, etc. are preferable as the cooling gas. When the ultrafine particles contain C or N, an appropriate gas may be selected from these as described above.

Note that the second magnetic layer of the thermomagnetic transfer medium of the present invention is not limited to ultrafine particles produced by such a method, but any magnetic material can be used as long as it satisfies the above-mentioned characteristics. Needless to say.

There is no particular restriction on the binder in which the magnetic material is dispersed, and any binder that can withstand the heat during transfer may be selected from among the binders used in ordinary coated magnetic recording media.

For example, vinyl chloride-vinyl acetate copolymers, polyvinyl butyral resins, cellulose resins, polyurethane resins, polyester resins, epoxy resins, phenol resins, melamine resins, polyvinylphenol resins, isocyanate compounds, etc. are preferably used. .

Such a binder is used in an amount of 1 part by weight per 100 parts by weight of the magnetic material.
It is preferably contained in an amount of about 0 to 100 parts by weight.

These magnetic materials, binders, other additives, etc. are kneaded using a suitable solvent and applied as a magnetic paint.
A magnetic paint is applied, subjected to orientation treatment in a magnetic field, dried, and then calendered to apply a second magnetic layer.

When the above-mentioned ultrafine particles are used in the second magnetic layer, since the ultrafine particles have a substantially spherical shape but have uniaxial magnetic anisotropy, magnetic field orientation can be easily performed. In this case, the squareness ratio of the second magnetic layer dried in the magnetic field is about 0.7 to 0.9 in the direction of the alignment magnetic field. At this time, the magnetic field strength used for orientation was 2000
~8000G is preferable.

In this way, the axis of easy magnetization of the magnetic powder in the second magnetic layer can be aligned in any direction depending on the direction of the orienting magnetic field.
As the recording wavelength to be transferred becomes shorter, the proportion of the perpendicular component of the magnetic flux from the magnetic head increases, so it is more advantageous to orient the medium in the perpendicular direction. Thereby, the perpendicular magnetization component in the second magnetic layer can be effectively utilized, and a thermomagnetic transfer medium with good transfer characteristics at short wavelengths can be obtained.

The second magnetic layer may be a continuous thin film type magnetic layer made of various metals, various oxides, etc., in addition to the coated type as described above.

There is no particular restriction on the CrO□acicular particles contained in the first magnetic layer, and CrOa used in ordinary thermomagnetic transfer media can be used.
Among the acicular particles, one having optimal magnetic properties may be selected depending on the purpose.

CrOz acicular particles suitable for the present invention are e.g.
．． 1~0.5*, axial ratio 3~20. Coercive force 500-900
Oe and Curie point of about 110 to 130°C.

There are no particular restrictions on the non-magnetic substrate on which these magnetic layers are deposited, and in addition to flexible plastic films used for ordinary magnetic tapes, floppy disks, etc., rigid substrates such as aluminum alloys and glass can be used. can.

Further, there is no particular restriction on the shape of the substrate, and the shape of a disk, tape, etc. may be selected depending on the purpose, and there are no particular restrictions on its dimensions.

There is no particular restriction on the method of performing thermomagnetic transfer on the thermomagnetic transfer medium of the present invention as described above, and a conventional thermomagnetic transfer method can be used.

The double-layer thermomagnetic transfer medium of the present invention has an extremely high coercive force in the upper layer at room temperature, so it has excellent short wavelength thermomagnetic transfer characteristics and can be preferably used, for example, in mass duplication of various video tapes.

<Example> Hereinafter, the present invention will be explained in further detail by giving specific examples of the present invention.

[Preparation of ultrafine particle sample] After grinding and mixing iron oxide powder, cobalt oxide powder, iron phosphate powder, and carbon black, they were granulated to obtain raw material particles.

The raw material powder composed of these raw material particles was put into a reactor made of graphite, evaporated by a direct current arc plasma jet, and further rapidly cooled and condensed by cooling gas to obtain ultrafine particle sample No. 1.

Another ultrafine particle sample was produced by changing the composition of the raw material particles and the manufacturing conditions.

Table 1 shows the composition of the raw material particles, plasma gas and cooling gas used to prepare each sample, and the composition and characteristics of each ultrafine particle sample.

The atomic ratios of Fe/Co and (Fe+Co)/P were determined by plasma emission spectroscopy, and the C content was determined by C, H, N.
The average particle size was measured using an elemental analyzer, the average particle size was measured using a transmission electron microscope, and the crystal structure was measured using X-ray diffraction. Moreover, the coercive force was measured by VSM in an applied magnetic field of 10 kOe.

[Preparation of Thermomagnetic Transfer Tape Samples 11 Using each of the ultrafine particle samples shown in Table 1, magnetic paints having the following compositions were prepared.

Ultrafine particles 100 parts by weight Vinyl chloride Vinyl acetate resin 17 parts by weight Urethane resin
17 parts by weight Stearic acid 2 parts by weight Toluene 80 parts by weight MIBK
80 parts by weight MEK
95 parts by weight of these magnetic paints were applied onto a 12-thick polyester film, dried, and calendered to form a magnetic layer to obtain a thermomagnetic transfer tape sample having a single-layer magnetic layer. The coating thickness after calendering was 0.64.

For some samples, the coating film was dried in a vertical magnetic field of 6000 Oe to orient the ultrafine particle sample. Table 2 shows the presence or absence of orientation treatment in a magnetic field.

Table 2 shows the coercive force in the in-plane direction of the magnetic layer, the squareness ratio in the in-plane direction and the perpendicular direction, and the Curie point of the obtained thermomagnetic transfer tape sample.

Further, a graph showing the temperature dependence of the coercive force of each tape sample is shown in FIG.

table No.

Sanbuno I/No, 25℃ 150℃ Direction Direction ('C) 360 570 650 640 100 0.56 0.53 0, 51 0.59 0.52 0.77 0.81 0.66 0.82 0.60 Next, for comparison, coercive force 650 Oe, Curie point 1
A magnetic paint with the following composition was prepared at 25°C using CrOz acicular particles with an average length of 0.34 and an average axial ratio of 6.
A thermomagnetic transfer tape sample having a magnetic layer was prepared.

CrO* 100 parts by weight α-Aβ
*O* 0.5 parts by weight myristic acid
0.5 parts by weight n-butyl stearate 0.
7 parts by weight Vinyl chloride Vinyl acetate resin 12 parts by weight Urethane resin 12 parts by weight MIBK
100 parts by weight cyclohexanone
100 parts by weight THF 100 parts by weight The obtained magnetic paint was applied onto a 16 μm thick polyester film, oriented in a magnetic field in the longitudinal direction of the film, dried, and then calendered. The thickness of the magnetic paint after drying was 3 μs. This was designated as thermomagnetic transfer sample No. 16.

FIG. 1 shows the temperature dependence of the coercive force of this sample No. 16.

From FIG. 1, the sample used in the present invention (NO911-1
5) The coercive force decreases rapidly as the temperature rises, and at temperatures below 150°C, the coercive force of the conventional tape sample using CrO* (N
It can be seen that the coercive force is extremely small as in case 16), and thermomagnetic transfer is possible. Furthermore, since the rate of increase in coercive force from high temperature to room temperature is extremely large compared to CrOx, it is clear that the demagnetization rate during thermomagnetic transfer of short wavelength signals is small and the short wavelength characteristics are improved. It is also clear that magnetic information can be well protected against external disturbing magnetic fields because of the high coercive force at room temperature.

[Preparation of magnetic tape samples 1 Magnetic Tape sample No. 17 Tape sample No. 17 Tape sample No. shown in Table 2 was placed on the CrOx-containing magnetic layer of Tape sample No. 16.

The magnetic paint used in No. 3 was applied, dried and calendered to form a second magnetic layer having a thickness of 0.5-.

This was designated as thermomagnetic transfer tape sample No. 17.

Trajectory Tape Sample No. L8 Tape Sample No. 16 Tape sample No. shown in Table 2 was applied on the magnetic layer containing 16 CrO*.

The magnetic paint used in No. 4 was applied, subjected to perpendicular magnetic field alignment treatment, dried, and then calendered to form a second magnetic layer of 0.37111.

This is designated as tape sample No. 18.

Thermomagnetic transfer tape sample N obtained as above
o, 16. Cut 17 and 18 into 1/2 inch width,
This was used as a transfer tape sample for thermomagnetic transfer.

Next, as a master tape, 1/1 of the coercive force of 1500 Oe was used.
A 2-inch wide metal tape is used with a gap length of 0.
A 2μ Sendust magnetic head generates 7.25MHz (
wavelength 0.8u) and 11.6MHz (wavelength 0.5μ)
A sinusoidal signal was recorded.

After the signal of this master tape was transferred to each of the above-mentioned transferred tape samples using a thermomagnetic transfer device, the reproduction output of the transferred signal at each frequency was measured. Further, the noise level at a frequency 1 MHz apart from the frequency of each signal was measured, and the ratio of the reproduced output to the noise level was determined as C/N.

Table 3 shows the reproduction output and C/N ratio of each tape sample.

Table 3 16 (Comparison) Yes (longitudinal direction) ooo.

17 None +2 +2.
5 44 +3.818 Yes (vertical direction) +3 +3.2 +5 +5
The effects of the present invention are clear from the above examples.

That is, by providing a magnetic layer with a higher coercive force on the magnetic layer containing CrO2, the transfer performance particularly in the short wavelength region is improved, and the protection performance against external magnetic fields is also improved.

<Effects of the Invention> According to the present invention, there is provided a thermomagnetic transfer medium which can successfully and easily transfer magnetic information having an extremely short minimum recording wavelength and a wide recording wavelength range, and which has high security of the transferred information. Realize.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between temperature and coercive force of ferromagnetic ultrafine particles and CrO□ needle-shaped particles. Figure 2 shows a DC
FIG. 1 is a schematic cross-sectional view of a reactor using plasma. FIG. 3 shows an IC which is a preferred example of a ferromagnetic ultrafine particle manufacturing device.
1 is a schematic cross-sectional view of a reactor using P. Explanation of symbols 1 Reaction furnace 10 Ultrafine particles 2 Evaporation section 21 Plasma jet generation means 211 Plasma jet 22 Raw material powder supply means 23 Heat-resistant material 24...Insulating material 3...Cooling section 31...Cooling gas supply port 4...Collection section

Claims (4)

[Claims] (1) A thermomagnetic transfer medium having a first magnetic layer and a second magnetic layer sequentially on a substrate, wherein the first magnetic layer contains CrO_2 acicular particles, and the coercive force of the second magnetic layer at room temperature is The coercive force of the first magnetic layer and the second magnetic layer is higher than the coercive force of the first magnetic layer at room temperature.
A thermomagnetic transfer medium having a coercive force of 200 Oe or less at 50°C. (2) The thermomagnetic transfer medium according to claim 1, wherein the second magnetic layer has a coercive force of 1000 Oe or more at room temperature. (3) The thermomagnetic transfer medium according to claim 1 or 2, wherein the thickness of the second magnetic layer is less than or equal to the thickness of the first magnetic layer. (4) The magnetic material contained in the second magnetic layer is Fe, Co
4. The thermomagnetic transfer medium according to claim 1, wherein the thermomagnetic transfer medium is ferromagnetic ultrafine particles having a Fe_2P type hexagonal crystal structure containing P as a main component.