JPS5814047B2 - Method for manufacturing magnetic recording material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new material for use in high-resolution magnetic recording, particularly a high-resolution magnetic material containing doped triiron tetroxide, and a method for producing the same.

Magnetic recording is finding increasing use in a wide variety of technical fields, and its potential uses are also expanding.

It is particularly desirable to have a magnetic tape that is capable of recording high density signals without compromising the quality of signal reproduction.

The characteristics of the magnetic materials used to record and reproduce images or other signals are closely related to the properties of the magnetic pigments that contribute to the finished product of these materials.

It is particularly known that one of the essential factors in the field of magnetic recording is the use of magnetic compounds with high coercive fields.

Currently, the most widely used magnetic product is gamma ferric oxide, or ferric maghemite oxide (γFe203), which is in the form of acicular particles with a length on the order of microns.

It has been proposed to dope the ferric oxide with cobalt to enable this product to exhibit a reasonably high coercive field for short wavelength recording.

However, this improvement in the coercive field is accompanied by a number of drawbacks, particularly in the profile of the magnetostatic properties with respect to temperature and mechanical stress.

Moreover, the output level tends to decrease regularly during continuous reading of the magnetic tape.

These drawbacks of gamma ferric monoxide doped with cobalt are discussed, for example, in the IEEE Transactions on Electronic Computers.
nic Computers Vol. EC-15, No. 5 (
J. R. Morrison (1966), pp. 782-793.
and D. E. Spelio
tis).

On the other hand, it is well known that magnetic recording materials usually have drawbacks related to electrostatic phenomena.

Therefore, in general, for example, French Patent No. 11190
Incorporating carhon into the magnetic layer as described in French Patent No. 985701; Synchronous No. 1273
No. 334; using a conductive subbing layer as described in Synchronous No. 1,479,574 or as described in French Patent No.
A conductive backing layer is used to correct this drawback, as described in US Pat. No. 2,733,334.

It would therefore be desirable to have a material that does not have any of the aforementioned drawbacks associated with the characteristics of doped gamma ferric oxide for magnetic recording.

Accordingly, an object of the present invention is to provide a high-resolution magnetic recording material, and in particular to provide a high-resolution magnetic recording material containing doped triiron tetroxide.

The magnetic recording material of the present invention consists of one or more magnetic layers and has the following characteristics.

That is, the magnetic recording material of the present invention has a layer consisting of doped triiron tetroxide alone or together with another magnetic substance dispersed in a nonmagnetic binder, In addition to the doping agent, iron oxide contains at least one elemental ion selected from the group consisting of alkali metals and alkaline earth metals in such a form that it imparts basicity to the oxide, and has an acicular shape. The ratio is at least equal to about 15.

The magnetic material of the invention can in particular be in the form of a disk or a tape.

The magnetic recording material of the present invention has very low sensitivity to heat and also exhibits positive magnetostriction (ie, a force in the direction of improving magnetic properties).

Furthermore, this material does not have any of the drawbacks associated with static phenomena, and moreover, the output level is significantly superior to that of conventional tape (ie tape containing gamma ferric monoxide).

There is virtually no change in the output level after several readings of the magnetic recording material.

According to one embodiment of the invention, the magnetic recording material comprises triiron tetroxide doped with a divalent metal of the group consisting of nickel, cobalt, chromium, zinc, manganese and cadmium.

According to an advantageous embodiment of the invention, the magnetic tape comprises triiron tetroxide doped with cobalt and furthermore at least one ion selected from the alkali metals and optionally one of the alkaline earth metals. or more ions,
These contain the oxides in such a way as to give the base silica and exhibit an acicular ratio at least approximately equal to 15.

The acicular ratio herein refers to the length/diameter ratio of oxide particles.

The doped triiron tetroxide used in this invention can be obtained from doped ferric oxide obtained by the following method.

That is, for example, a solution of a ferrous salt containing a small amount of cobalt salt (hereinafter referred to as a ferrous salt solution) is prepared in excess of the stoichiometric amount required at a temperature of 60° C. or lower and in the absence of an oxidizing agent. Disperse in the alkaline solution used.

Dispersion is carried out by directing the solution of the ferrous salt into a suction zone created in the center of the alkaline solution.

That is, in this suction region, the ferrous salt solution extends in a thin layer so as to penetrate into the alkaline solution in the form of a sheet with a large specific area.

As a result, the ferrous salt has virtually no local excess.

The hydrated iron oxide in the final dispersion, i.e. goethite (
The concentration of α-FeOOH) is 15 g/1 or less.

The resulting dispersion of ferrous hydroxide is heated between approximately 20°C and 60°C.
oxidized using an oxygen-containing gas stream (eg air) at a temperature of 200 mL, followed by boiling, separation (eg filtration), washing and drying.

The general method for producing hydrated iron oxide is described in French patent 2060.
It is described in No. 273.

According to a variant of this method, water that has been at least partially freed of mineral elements is used for the precipitation.

Furthermore, washing water containing calcium ions is used.

As mentioned above, the temperature at which precipitation is carried out is below 60°C, whereas the temperature used for oxidation is in the range 20-60°C.

If the temperature exceeds 60° C., the length of the crystals does not change significantly, but the diameter of the crystals increases and the acicular ratio decreases accordingly.

At even higher temperatures, cubic triiron tetroxide crystals form directly.

The length of the cube-shaped crystal ridges is approximately equal to the length of the needle-shaped crystals that would form at lower temperatures.

Furthermore, crystal heterogeneity increases with increasing oxidation time.

According to this phenomenon, the initially precipitated hexagonal lattice ferrous hydroxide is slowly oxidized to acicular α-ferric monoxide hydrate.

After a certain point, the two acid compounds described above are present.

The operating conditions are therefore such that the growth of existing needles and the formation of new microcrystalline needles occur simultaneously, thereby increasing the heterogeneity of the product.

Using a minimum oxidation temperature of 20° C. ensures that the oxidation reaction is completed within a reasonable time without introducing undesirable heterogeneity.

The excess alkyl hydroxide or alkaline earth metal hydroxide used in the process of the invention must be at least 500% free.

That is, at least five times the amount of alkali or earth metal hydroxide required to convert all of the ferrous salt to ferrous hydroxide must be present in the solution.

Precipitations carried out at lower concentrations produce complexes that are oxidized to alpha ferric monoxide hydrate only after a very long oxidation time, and the final properties of the resulting crystals also improve by at least 500%. The properties are inferior to those of crystals produced using a stoichiometric excess.

The starting ferrous solution of the present invention must be of such a concentration or amount that the alpha ferric monoxide hydrate of the oxidized dispersion does not exceed 15 g/l.

Beyond this limit, the length of the α ferric monoxide crystal is 0.
It becomes 5 microns or more.

For example, at a concentration of 18 g/l and oxidation for 2 hours, the median length of the crystals is 0.65 microns.

Moreover, the crystal length increases with increasing oxidation time.

The hydrated iron, or goethite, containing a certain amount of cobalt ions (obtained by the method described above) is then converted into doped triiron tetroxide by the following heat treatment.

In other words, the doped goutite has 270
Dehydration at temperatures around °C yields doped alpha ferric monoxide.

This ferric oxide, in the presence of a reducing gas (e.g. hydrogen),
It is heated at a temperature between 300°C and 500°C.

The product thus obtained is cooled to room temperature in an inert atmosphere (eg nitrogen atmosphere).

The composition of the resulting doped triiron tetroxide varies depending on the reduction time and reduction temperature.

For example, at a temperature between about 325°C and 450°C and between 10 minutes and 45°C.
It is advantageous to carry out the reduction time in minutes.

The doped triiron tetroxide of the present invention contains sodium or sodium and calcium in addition to a component called a dope component.

The triiron tetroxide of this invention exhibits a basic reaction.

This basicity can be balanced by dispersing the oxide in crystallizable acetic acid with vigorous stirring.

This balancing is carried out using a potentiometer with the aid of a solution of perchloric acid in nitromethane.

The alkalinity ratio of the doped triiron tetroxide sample of the invention thus determined is at least equal to 0.04 meq/g of oxide, preferably between 0.04 and 0.04 meq/g of oxide. It is between .2 meq/g.

Since this alkalinity is enhanced by the presence of calcium, the oxides of the invention advantageously contain calcium, i.e. Ca(OH)2 on the already formed goethite.
Contains precipitated calcium in the form of

This ratio is 25/10000 to 1/10 to the oxide.
The weight of calcium is between 0.

The acicularity ratio of the particles of the oxide of this invention is at least 15, but can reach 40 or more in some cases.

On the other hand, according to an examination using an electron microscope, the crystal size of the oxide of this invention is uniform.

This uniformity is determined by counting the number of particles of the same length or by examining the distribution curve.

This operation is preferably carried out with the intermediate non-magnetic goethite.

Each crystal is used to obtain a usable image.
This is because it is easy to divide into two parts.

The grain size distribution of goethite crystals follows the following formula.

dN 7[1t,/; −=N −-exp (tog −)”1d
7 π t Lm where N represents the number of l crystals, Lm represents the average length, and K is the polydispersity coefficient.

This factor K is taken from the above equation and is greater than or equal to 2 for the oxides preferred in one embodiment of the invention.

As mentioned above, the doped triiron tetroxide of the present invention advantageously contains cobalt as a doping component.

The coercive field of a doped oxide is usually related to the amount of cobalt present in the oxide and the temperature at which the doped goethite is converted to doped triiron tetroxide. .

The amount of cobalt in the oxide is advantageously between about 12 and 6 g of cobalt metal per 100 g of oxide.

According to one method of the invention, the amount of metallic cobalt is 1
It is between about 2g and about 4g per 00g.

The coercive magnetic field of the oxide is about 600 Oe to 900 Oe.

The coercive field of the doped oxide of this invention is always about 100 to 150 Oe higher than that of doped gamma ferric monoxide with the same goethite.

Furthermore, the residual induction of the doped oxide of this invention is about 10% higher than that of doped gamma ferric monoxide with the same goethite.

In making the doped triiron tetroxide magnetic tape of this invention, the oxide is dispersed in a polymeric binder.

The binder used in the embodiment of the present invention is particularly a copolymer of vinyl acetate and vinyl chloride, a copolymer of vinylidene chloride and acrylonitrile, a copolymer of acrylic acid and/or methacrylic acid ester, polyvinyliptyral. , copolymers of butadiene and styrene, terpolymers of acrylonitrile, vinylidene chloride, and maleic anhydride or maleimide, reticular or non-reticular copolymer condensates, such as polyamides, polyurethanes, polyesters, etc., or mixtures of such binders. It is.

Particularly advantageous results are obtained with copolymers of vinyl acetate and partially hydrolyzed vinyl chloride, preferably reticulated with isocyanates, or with polyurethanes or mixtures of such binders.

The amount of binder to magnetic oxide is between about 10% and about 40% by weight, advantageously between about 15% and about 25% by weight.

The magnetic recording layer of the invention may also contain other additives, such as oleic acid, or other dispersants to facilitate dispersion, lubricants, such as compounds such as those described in French Patent No. 2094663, or charges, such as Colloidal silica may be added without changing the desired properties.

The magnetic layer of the invention can be applied to a flexible film, such as a support of cellulose triacetate, polyvinyl chloride, or polyester, such as ethylene glycol polytetraphthalate.

Alternatively, other supports such as flat disks may be coated with this magnetic layer.

The magnetic material of the invention consists of a support coated with one or more layers as described above, one of which includes:
Doped ferrous and ferric oxides are included alone or with other magnetic materials (eg, gamma ferric monoxide).

According to one embodiment of the invention, the magnetic material is coated, in order from the support, with a layer containing conventional gamma ferric monoxide, and then on its surface with a doped triiron tetroxide (preferably It consists of a layer containing a cobalt-doped oxide).

According to a preferred embodiment, the magnetic material of the invention consists of a single layer comprising the doped triiron tetroxide (particularly the cobalt-doped oxide) of the invention.

The magnetic recording material of this invention, especially the single layer magnetic tape, has a high coercive field.

This coercive field is related to the triiron tetroxide used, as mentioned above, and in particular to the content of the doping components, as well as to the temperature carried out during the process of converting the goethite to triiron tetroxide.

This coercive field typically ranges from about 600 oersteds to about 110 oersteds.
It is about 0 oersteds, preferably about 700 oersteds to 900 oersteds.

The oxides of this invention have extremely high coercive fields, making it possible to record high density data on tape.

Magnetic recording materials, and in particular, as mentioned above, the single-layer magnetic tape of the present invention have excellent thermal stability.

This thermal stability can be measured by the change in coercive field as a function of temperature.

For the same coercive field at 20° C., the tape of the invention exhibits a decrease in coercive field with increasing temperature, a decrease that is observed for magnetic tapes containing doped gamma ferric oxide. It is about half of that.

Doped triiron tetroxide magnetic tape exhibits positive magnetostriction.

When measurements are made on a doped gamma ferric monoxide magnetic tape with a polyester support 6.3 mm wide and 25 microns thick (although the magnetic layer itself is 5 microns thick), The tape used is 1kg.
When pulled longitudinally with a force of , the tape loses up to 10% of its coercive field.

It has been found that when the same force is applied to a tape of the invention having the same support, the same width, and the same thickness but with a doped triiron tetroxide layer, the magnetic properties of the tape are improved. Ta.

That is, the coercive field of a tape containing cobalt-doped triiron tetroxide (approximately 25/1000 cobalt to oxide) increases to approximately 3%.

The magnetic tape of the present invention thus represents a substantial advance over commercially available magnetic tapes.

In fact, in a recording/reading device, this magnetic tape is
Applying a force that causes a decrease in the coercive field results in signal alternation.

The magnetic tapes of the invention do not exhibit such drawbacks; on the contrary, a slight increase in the coercive field is observed, especially in the case of tapes consisting of a single layer of doped triiron tetroxide.

The magnetic recording material of the invention also provides substantially higher output power for shorter wavelengths (e.g., wavelengths used to record images) than the output levels obtained with magnetic tape containing gamma ferric monoxide. Indicates level.

For a set coercive field (eg, on the order of 700 to 900 oersteds), the output level of the magnetic tape of the present invention is always at least about 2 to 3 dB higher than that of gamma ferric monoxide tape.

Measurements of this output level should be made using a Philips magnetoscope model LDL1002.

Then, the curve representing the output level (dB) as a function of MA writing speed for the magnetic tape of the present invention or a gamma ferric monoxide magnetic tape with the same coercive field can be examined.

The maximum value of the curve corresponding to the tape of the invention, which consists of a layer containing triiron tetroxide doped with cobalt (approximately 3 parts by weight of cobalt to oxide), is It is noted that it is approximately 4 dB higher than the maximum value of the curve corresponding to ferric oxide magnetic tape.

Furthermore, surprisingly, the signal loss of the tape of the present invention is negligible even after several consecutive passes, and is virtually negligible compared to doped gamma ferric monoxide magnetic tape. Things are getting attention.

For example, triiron tetroxide doped with cobalt (however,
Power level measurements are made on magnetic tapes of the invention having an amount of cobalt of approximately 3% relative to oxide.

Measurements are made under the same conditions on a doped gamma ferric monoxide magnetic tape.

Although it exhibits the same coercivity and surface condition as the inventive tape, the signal loss after 10 passes of the inventive tape for recording at a wavelength of 2.5 μ is 0.5 dB, whereas gamma monoxide The signal loss of double iron tape is 2dB to 3
It is about dB.

The magnetic tape of the present invention, particularly the magnetic tape with heavily doped triiron tetroxide, also exhibits superior characteristics with respect to static phenomena compared to conventional ferric oxide magnetic tapes.

The electrical resistivity of the doped triiron tetroxide of this invention is about 1.104 ohm·cm, whereas that of the corresponding gamma ferric monoxide is 1.104 ohm·cm. 109 oh
It reaches ms・cm.

Volume resistivity is measured using oxide samples in the form of pellets.

These pellets are obtained by solidifying oxide powder under a pressure of about 200 MPa.

The doped triiron tetroxide of this invention has a low resistivity which greatly assists in electrostatic charge flow.

This property makes it possible to substantially reduce the manufacturing costs of magnetic recording tapes.

Generally, the tapes of this invention do not require a conductive subbing layer or conductive backing layer other than one or several magnetic layers.

The manufacture of magnetic tape is therefore substantially simplified and less cumbersome.

The invention is further illustrated in the following examples.

Example 1 Using water from which mineral components have been removed in a 10 liter container, 1
A 3.5 liter solution containing 157 g of NaOH per liter is made.

This solution was stabilized by warming to 40°C, and 1 liter of a solution containing 225 g of ferrous sulfate and 10 1 of cobalt sulfate was quickly poured into the above solution and then diluted with 2 liters of demineralized water. do.

The stirring and dispersion methods described in French Patent No. 1,157,156 are used to introduce this solution.

After the precipitation is complete, stir for 40 minutes using the stirring method described above.
Compressed air is blown into the suspension at a flow rate between 1/hr and 201/hr.

After oxidation for 2 hours and 40 minutes, boil for 45 minutes, filter,
After washing with 100 ml of calcium ion-containing water per 4 ml and then drying, the cobalt-doped goethite needles (length 0.3 to 0.4 μ, needle ratio 3
0 to 35).

The doped goethite thus obtained is
It is placed in an electric furnace with controlled conditions.

Gradually increase the temperature of the furnace at a rate of 8°C per minute to 375°C.
℃.

Then, the obtained dehydrated oxide of αFe203 is reduced by the following procedure.

The furnace, after purging with nitrogen and at a temperature of 375° C., is fed with a stream of hydrogen containing water vapor at a flow rate of 1.5 l/min.

After 40 minutes, the heating is stopped and the triiron tetroxide thus obtained is cooled to room temperature under nitrogen.

This oxide had a coercive field of 900 oersteds.

A magnetic tape is made by applying a layer containing cobalt-doped triiron tetroxide (dispersed in a polyvinylacetochloride binder) to a support.

The magnetic tape thus obtained is calendered and then tested using a Philips magnetoscope model LDL 1002.

The output level is approximately 4 dB lower than that of a tape with the same coercive field, but containing doped gamma ferric monoxide instead of the doped triiron tetroxide of the present invention.
expensive.

The output level after 10 passes of this tape did not decrease substantially.

Example 2 In a 10 liter container, prepare 3.5 liters of solution containing 160 g of NaOH per liter.

Into this solution, add ferrous sulfate 22 as in Example 1.
5 g of cobaltous sulfate, 7.5 g of cobaltous sulfate and 6 g of zinc sulfate are quickly poured and diluted with 2.5 liters of demineralized water.

After oxidation, boil for 40 minutes as described in Example 1, filter and treat with water until the unwanted salts are removed.

This oxide is then dehydrated and reduced as described in Example 1.

The triiron tetroxide doped with cobalt and zinc thus obtained had a coercivity of 680 Oe.

A magnetic tape was made by applying a layer of this oxide dispersed in a polyvinylacetochloride binder to a support.

The tape thus produced is calendered and then tested using a Philips magnetoscope model LDL 1002.

The output level was about 3 dB higher than that of a doped gamma ferric monoxide tape with the same coercivity.

No change occurred in the output level after 10 passes through the tape.

Claims (1)

[Claims] 1. Doped triiron tetroxide alone or as a mixture with other magnetic materials is dispersed in a non-magnetic binder, and the dispersion thus obtained is applied to a support. In the method for manufacturing a magnetic recording material consisting of one or more magnetic layers, the doped triiron tetroxide is (a) cobalt alone or cobalt and cobalt and An aqueous solution of a ferrous salt containing a doping divalent metal ion consisting of zinc is added to an aqueous solution of a stoichiometrically excess alkali metal hydroxide and, optionally, an alkaline earth metal hydroxide. An iron salt is added while preventing local excess to form an aqueous dispersion of ferrous hydroxide particles, wherein the alkali metal or alkaline earth metal hydroxide is present in the aqueous dispersion. 500 to
% or more in stoichiometric excess; (b) in the aqueous dispersion, the ferrous hydroxide particles are converted into crystals of α-ferric monoxide hydrate at a temperature of 20 to 60°C; Oxygen is introduced for a sufficient time to convert, wherein the concentration of the ferrous salt in the aqueous solution is such that the concentration of the alpha ferric monoxide hydrate formed in the aqueous dispersion is 15 g/min. (c) stopping the introduction of oxygen into the dispersion; (b) heating the dispersion by boiling to produce the α-ferric monoxide hydrate; further crystallize the crystals; (e) dehydrate the pre-right α ferric monoxide hydrate crystals to form α ferric monoxide; (f) reduce the α ferric monoxide; A method for producing a magnetic recording material, characterized in that it is produced by a method comprising each step of forming and recovering triiron tetroxide.