JP3359425B2 - Magnetic recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium capable of maintaining high electromagnetic conversion characteristics obtained before storage without deterioration even when stored for a long time under high temperature and high humidity.

[0002]

2. Description of the Related Art In recent years, demands for high-density magnetic recording media have been increasingly higher. In response to this requirement, a method for improving the recording density by using a ferromagnetic metal magnetic powder as the magnetic powder is well known. However, this method alone has not been able to sufficiently satisfy the demand for a high recording density magnetic recording medium that has been desired in recent years.

Therefore, as another method, in order to improve the reproduction output over a wide range from high frequency to low frequency,
2. Description of the Related Art A multilayer structure of a magnetic recording medium has been developed. This is a method in which an upper layer corresponding to a high frequency and a lower layer corresponding to a low frequency are provided so as to correspond to a wide range of frequencies to improve the recording density. In particular, the technique required at this time is to make the upper layer thinner.

Further, to meet the demand for higher recording density, there is a method of reducing self-demagnetization and reproduction demagnetization by reducing the thickness of the magnetic layer. This is a method in which, in a multilayer structure of a magnetic recording medium, the upper layer is a thin magnetic layer and the lower layer is a non-magnetic layer. In addition to these methods, the magnetic powder is further improved to improve the recording density.

As described above, it is relatively easy to obtain a magnetic recording medium having a high recording density before storage, but when stored for a long time in any environment, particularly under high temperature and high humidity, high electromagnetic conversion is obtained. It is extremely difficult to maintain the properties. For example, Japanese Patent Application Laid-Open No. 4-146519 discloses that the amount of water-soluble calcium in a magnetic powder is reduced to 100 ppm or less as a solution to a decrease in reproduction output and an increase in dropout after storage under high temperature and high humidity. However, with this method, it was not possible to obtain a magnetic recording medium that maintains the high electromagnetic conversion characteristics obtained before storage when stored under high temperature and high humidity, and stored under high temperature and high humidity even if this condition was satisfied. At this time, it was not possible to sufficiently prevent a decrease in reproduction output and an increase in dropout.

Accordingly, the present inventors have obtained a magnetic recording medium that has maintained high electromagnetic conversion characteristics obtained before storage when stored for a long period of time under high temperature and high humidity, and has ensured sufficient reliability. In order to perform preservation experiments in all environments,
As a result of investigation, when a magnetic recording medium is stored for a long time under high temperature and high humidity, the reproduction output obtained before storage is greatly reduced, the dropout increases, and the phenomenon of clogging of the head occurs. I found it. It has been found that this phenomenon occurs even when the magnetic layer of the magnetic recording medium is a single layer, but particularly occurs in a multilayer structure. As a result of earnest research on the cause of this phenomenon, the present inventors have found that the following is caused.

[0007] A problem that is likely to occur when stored under high temperature and high humidity is considered to be deterioration of the magnetic powder due to oxidation of the ferromagnetic metal powder. Although the possibility was examined, no result was obtained that the ferromagnetic metal powder was oxidized. However, it was found that a large number of protrusions were generated on the surface of the magnetic layer when stored for a long time under high temperature and high humidity. The inventor of the present invention has found that the projection causes spacing loss and leads to a decrease in reproduction output, and the projection falls off from the surface of the magnetic layer when the projection collides with the head,
It is presumed that the dropouts accumulate on the head to cause clogging of the head, and that dropout frequently occurs to increase dropout.

Next, the present inventors conducted an analysis at the location where the protrusions occurred. As a result, it was found that a peculiar substance was present at the place of occurrence. The material was a crystal of a fatty acid metal salt (eg, barium stearate, calcium stearate, etc.). By suppressing the generation of the fatty acid metal salt (metal soap insoluble in water) at the location where the projections are generated, it is sufficient to store the battery for a long time under high temperature and high humidity, which is the above-mentioned problem. Reliability is guaranteed,
It is considered that a magnetic recording medium that maintains the high electromagnetic conversion characteristics obtained before storage can be provided.

[0009]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to prevent dropout, decrease in reproduction output, and clogging of a head even when stored under a high temperature and a high humidity for a long period of time. Another object of the present invention is to provide a magnetic recording medium that maintains high electromagnetic conversion characteristics obtained before storage.

[0010]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have provided a magnetic layer containing a specific ferromagnetic metal powder on a nonmagnetic support and containing a fatty acid. The present inventors have found that a magnetic recording medium having high electromagnetic conversion characteristics obtained before storage even after storage for a long time under high temperature and high humidity can be obtained, and the present invention has been accomplished. That is,
The object of the present invention is achieved by the following configurations.

1. A magnetic layer containing at least a ferromagnetic metal powder on a non-magnetic support, and in a magnetic recording medium containing a fatty acid, an element forming the surface of the ferromagnetic metal powder that has been orientation-treated in the magnetic layer; The average abundance ratio is such that the number of Na atoms is less than 1, the number of alkaline earth elements is 40 or less, and the number of rare earth elements is 1 with respect to 100 Fe atoms.
50, wherein the fatty acid has 12 to 24 carbon atoms.

Here, as the alkaline earth element, M
g, Ca, Sr, Ba, Ra, etc., and contains at least one element selected from these. Rare earth elements include Sm, Nd, Y, La, Pr, and the like. Contains more than one element.

2. A magnetic recording medium containing at least a ferromagnetic metal powder on a nonmagnetic support, and a fatty acid-containing magnetic recording medium, wherein the weight ratio of elements in the entire ferromagnetic metal powder is 100 parts by weight of Fe atoms. Al
2 to 10 parts by weight of atoms, 1 to 8 parts by weight of atoms of rare earth element,
0.1 to 5 parts by weight of alkaline earth element atoms and less than 0.01 part by weight of Na atoms, and the average abundance of the elements forming the surface of the ferromagnetic metal powder is 10 atoms of Fe atoms.
For 0, the number of Al atoms is 70 to 300, the number of rare earth elements is 0.5 to 60, the number of alkaline earth elements is 40 or less,
A magnetic recording medium, wherein the number of Na atoms is less than 4, and the fatty acid has 12 to 24 carbon atoms.

3. In a magnetic recording medium having a magnetic layer containing at least a ferromagnetic metal powder on a non-magnetic support, and containing a fatty acid, when the ferromagnetic metal powder is immersed in water, an alkali released from the ferromagnetic metal powder. Magnetic recording wherein the metal ion of the earth element is less than 30 ppm, the sodium ion is less than 200 ppm, the sodium dissolved in the hydrochloric acid solution is less than 300 ppm, and the fatty acid has 12 to 24 carbon atoms. Medium.

4. In a magnetic recording medium having a magnetic layer containing at least a ferromagnetic metal powder on a nonmagnetic support, and containing a fatty acid, the ferromagnetic metal powder has a metal ion released when immersed in water of 90 ppm or less. The acid dissociation constant in the free state is 8 or more and less than 14, and the metal ion released when immersed in water is less than 200 ppm, and the acid dissociation constant in the free state where the amount dissolved in the hydrochloric acid solution is less than 300 ppm is Contains 14 or more elements,
A magnetic recording medium, wherein the fatty acid has 12 to 24 carbon atoms.

5. A magnetic recording medium comprising an upper layer containing a ferromagnetic metal powder and a lower layer containing a magnetic powder or a non-magnetic powder on a non-magnetic support, wherein the magnetic powder or the non-magnetic powder has a magnetic property when immersed in water. Less than 100 ppm of sodium ions released from the powder or non-magnetic powder,
A magnetic recording medium, wherein sodium dissolved in a hydrochloric acid solution is less than 130 ppm, and at least one of the upper layer and the lower layer contains a fatty acid having 12 to 24 carbon atoms.

6. A magnetic layer containing at least a ferromagnetic metal powder on a non-magnetic support, and in a magnetic recording medium containing a fatty acid, an element forming the surface of the ferromagnetic metal powder that has been orientation-treated in the magnetic layer; The average abundance ratio is such that the number of Na atoms is 1 or more, the number of alkaline earth elements is 40 or less, and the number of rare earth elements is 1 with respect to 100 Fe atoms.
-50, the number of carbon atoms of the fatty acid is 12-24, and the free fatty acid amount of the fatty acid is 8.0 m.
g / m ² or less.

[7] A magnetic recording medium containing at least a ferromagnetic metal powder on a nonmagnetic support, and a fatty acid-containing magnetic recording medium, wherein the weight ratio of elements in the entire ferromagnetic metal powder is 100 parts by weight of Fe atoms. Al
2 to 10 parts by weight of atoms, 1 to 8 parts by weight of atoms of rare earth element,
0.1 to 5 parts by weight of alkaline earth element atoms and less than 0.1 part by weight of Na atoms, and the average abundance of the elements forming the surface of the ferromagnetic metal powder is 100 atoms of Fe atoms.
The number of Al atoms is 70 to 300, the number of rare earth elements is 0.5 to 60, the number of alkaline earth elements is 1 to 40, and N
a has 4 or more atoms, and the fatty acid has 12 carbon atoms.
A magnetic recording medium, wherein the number of free fatty acids in the fatty acids is 8.0 mg / m ² or less.

8. In a magnetic recording medium having a magnetic layer containing at least a ferromagnetic metal powder on a non-magnetic support and containing a fatty acid, the ferromagnetic metal powder is alkaline earth released from the ferromagnetic metal powder when immersed in water. 30 ppm or less of metal ions of the similar elements and 2 sodium ions
00 ppm or more, and the sodium dissolved in the hydrochloric acid solution is 300 ppm or more, the number of carbon atoms of the fatty acid is 12 to 24, and the free fatty acid amount of the fatty acid is 8.0 mg / m ² or less. A magnetic recording medium characterized by the above-mentioned.

9. In a magnetic recording medium having a magnetic layer containing at least a ferromagnetic metal powder on a nonmagnetic support, and containing a fatty acid, the ferromagnetic metal powder has a metal ion released when immersed in water of 90 ppm or less. An element having an acid dissociation constant of 8 to less than 14 in a free state and a metal ion released when immersed in water is less than 200 ppm, or an acid dissociation constant in a free state of not more than 300 ppm in a hydrochloric acid solution of 14 or less. A magnetic recording medium containing the above elements, wherein the fatty acid has 12 to 24 carbon atoms, and the free fatty acid content of the fatty acid is 8.0 mg / m ² or less.

10. A magnetic recording medium comprising an upper layer containing a ferromagnetic metal powder and a lower layer containing a magnetic powder or a non-magnetic powder on a non-magnetic support, wherein the magnetic powder or the non-magnetic powder has a magnetic property when immersed in water. 100 ppm or more of sodium ions released from powder or non-magnetic powder, and 130 ions of sodium ions dissolved in hydrochloric acid solution
ppm or more, wherein at least one of the upper layer and the lower layer contains a fatty acid having 12 to 24 carbon atoms, and a free fatty acid amount of the fatty acid is 8.0 mg / m ² or less. Magnetic recording medium.

The following embodiments are more preferable.
Between the non-magnetic support and the magnetic layer, at least one
Preferably, the magnetic recording medium is provided with a lower layer of the layer,
The dry thickness of the magnetic layer is preferably from 0.02 to 1.0 μm, more preferably from 0.1 to 0.6 μm. The dry film thickness of the lower layer in the multilayer structure is 0.2 to 2.0.
μm is preferable, and more preferably 0.3 to 1.5 μm
It is.

In the invention according to any one of claims 1 to 4, and 6 to 9, the magnetic powder or the non-magnetic powder contained in the lower layer is immersed in the magnetic powder or the non-magnetic powder when immersed in water. 13 sodium ions released from powder
Preferably it is less than 0 ppm. Preferably, the magnetic or non-magnetic powder in the lower layer is acicular, and the lower layer is preferably achieved by a magnetic recording medium containing a fatty acid having 12 to 24 carbon atoms.

Hereinafter, the present invention will be described in detail. The present inventors have found that protrusions are generated on the surface of the magnetic layer during long-term storage under high temperature and high humidity, and that there is a correlation between the protrusions and the deterioration of the electromagnetic conversion characteristics of a high recording density magnetic recording medium. I found it. As a result of examining the conditions under which the projections occur, it was found that the projections occurred when the following three conditions were satisfied.

The first condition is the presence of the fatty acid in the layer on the non-magnetic support, and the second condition is the properties of the ferromagnetic metal powder contained in the magnetic layer or the ferromagnetic metal contained in the magnetic layer. Properties of magnetic powder or non-magnetic powder contained in powder and lower layer,
The third condition is high temperature and high humidity (40-60 ° C / 70-90% R
H) to be stored below.

That is, if at least one of these conditions is removed, the occurrence of projections can be prevented. However, the third condition listed above is a storage state and cannot be controlled from the magnetic recording medium.
Therefore, by controlling the other two conditions, it was possible to obtain a magnetic recording medium that maintains the high electromagnetic conversion characteristics obtained before storage even after long-term storage under high temperature and high humidity.

Although the mechanism of the formation of the projections is not clear, the following reaction is expected. a. Sodium ions are eluted from the magnetic powder or non-magnetic powder in the magnetic recording medium into water attached to the medium under high temperature and high humidity. B. Free fatty acids dissolve in water attached to medium under high temperature and high humidity c. Reaction of sodium ions with fatty acids dissolved in water RCOOH + Na ⁺ → RCOONa + H ⁺ RCOOH: RCOONa such as stearic acid, palmitic acid and myristic acid has high solubility in water. D. c. By the H ^+, calcium a magnetic powder or nonmagnetic powder in the magnetic recording medium ions, barium ions are eluted e. RCOONa reacts with calcium ions, barium ions, etc. eluted in water ₂ RCOONa + Ca ²⁺ → (RCOO) ₂
^{Ca ↓ + 2Na + 2RCOONa + Ba} 2+ → (RCOO) 2
Ba ↓ + 2Na ^{+ In} this reaction, metal ions (Ca ²⁺ , Ba ^2+, etc.) show the same reaction as long as they are elements that form a metal soap insoluble in water. F. Since (RCOO) ₂ Ca and (RCOO) ₂ Ba are insoluble in water, they crystallize and precipitate, which causes projections.

The above reaction is one of the methods for industrially producing metal soap. General methods for producing metal soaps are roughly classified into two types: metathesis method (aqueous solvent system, alcohol solvent system) and direct method (melt method, semi-molten method, slurry method, solid phase method, solvent method). .

Features of metathesis method: The reaction rate is high and the reaction proceeds easily even at low temperatures. Since metal soaps are generally insoluble in water, by mixing an alkali soap (water soluble) and an aqueous solution of a metal salt, The generated metal soap is immediately precipitated as a precipitate, and the reaction is completed instantly. RCOOH + NaOH → RCONa + H
₂ O (neutralization reaction) 2RCOONa + CaCl ₂ → (RCOO) ₂ Ca + 2
NaCl (double decomposition)

Characteristics of the direct method: The reaction rate is low and the reaction temperature is high. The temperature generated is higher than the melting point of the metal soap that forms fatty acids and metal oxides and hydroxides. 2RCOOH + CaO → (RCOO) ₂ Ca
+ H ₂ O ₂ RCOOH + Ca (OH) ₂ → (RCOO) ₂ Ca +
2H ₂ O

In the reaction by the above-mentioned direct method, the reaction must be carried out at a temperature higher than the melting point of the produced metal soap (for example, in the case of calcium stearate, the melting point is about 150 ° C.). Separation,
It is unlikely that the reaction of the direct method occurs during storage of the magnetic recording medium.

Therefore, the reaction occurring in the present invention is the above-mentioned metathesis method. As is clear from the reaction, the characteristic of this reaction is that fatty acids and elements such as calcium and barium which form metal insoluble in water such as soap. It is considered that the reaction is occurring indirectly, not directly.

In order to suppress the formation of projections, if the reactions a and b described above are suppressed, the reaction c is suppressed, and the subsequent reactions are less likely to occur. Therefore, suppressing the reactions a and b largely depends on the generation of protrusions. The solution is shown below.・ Suppresses the dissolution of sodium ions into water ・ Suppresses the dissolution of fatty acids into water ・ Suppresses the dissolution of water-insoluble metal soap-generating elements such as calcium and barium Is suppressed, and a magnetic recording medium that maintains high electromagnetic conversion characteristics even after storage under high temperature and high humidity can be obtained.

In order to suppress the elution of sodium ions into water, the amount of sodium ions eluted is controlled by controlling the average abundance ratio of elements present on the surface of the ferromagnetic metal powder having been subjected to the orientation treatment of the magnetic layer. . In addition, in order to suppress the elution of sodium ions into water and the elution of elements that generate water-insoluble metal soap such as calcium and barium, by controlling the overall composition and surface state of the ferromagnetic metal powder, sodium Controls the elution amount of ions and alkaline earth elements.

The average abundance ratio of the elements forming the surface of the ferromagnetic metal powder present in the oriented and dried magnetic coating film according to claim 1 used in the present invention is determined using an XPS surface analyzer. Measure.

Next, the method will be described. The XPS surface analyzer is set under the following conditions. X-ray anode; Mg resolution; 1.5 to 1.7 eV (resolution is clean Ag3d
The XPS surface analyzer is not particularly limited, and any model can be used. In the present invention,
ESCALAB-200R manufactured by VG was used.

A narrow scan is performed in the following measurement range,
The spectrum of each element was measured. At this time, the data capturing interval is set to 0.2 eV, and it is necessary to integrate the target peaks until a count equal to or more than the minimum count shown below is obtained.

[0038] For peak measurement range minimum detected intensity (binding energy eV) (counts) C1s three hundred and five to two hundred eighty any Fe2p3 / 2 730~700 60 million in _{Na (KL 23 L 23) 280~250} 60 million in Auger peak resulting spectrum The peak position of C1s is 2
The energy position is corrected so as to be 84.6 eV.

Next, COMMON DATA PROCESSING S manufactured by VAMAS-SCA-JAPAN
YSTEM Ver. 2.3 (hereinafter referred to as “VAMAS software”), the above spectra were converted to VAMAS software using software provided by each device manufacturer.
Transfer to a computer where you can use the software. Then, using the VAMAS software, the transferred spectrum is converted into the VAMAS format, and then data processing is performed.

Before starting the quantitative processing, Co
Unscale is calibrated, and a 5-point smoothing process is performed. With the peak position of each element as the center, the peak area intensity (cps * eV) is determined in the quantitative range shown in the following table. Using the sensitivity coefficients shown below, the atomic% of each element is determined. The number of atoms is converted into the number of atoms with respect to 100 Fe atoms, and is used as a quantitative value. Element Peak position Quantification range Sensitivity coefficient (BE: ev) (BE: ev) Around 719.8 Fe High B. E. FIG. Side 5ev, 10.54 Low B. E. FIG. Side 7ev Na around 264.0 High B. E. FIG. Side 2ev, local minimum near 7.99, low B.P. E. FIG. Side 6ev Measured under the following conditions except for the above elements.

[0041]

[Table 1]

<Sample preparation method> Before performing the above measurement, pretreatment of the medium (magnetic tape) is performed.

The binder resin is removed from the magnetic tape by a plasma low-temperature incineration method to expose the magnetic particles. As the treatment method, a condition is selected in which the binder resin is ashed but the magnetic particles are not damaged. For example, after treatment under the apparatus and treatment conditions described below, the average abundance ratio of the elements forming the surface of the ferromagnetic metal powder subjected to the orientation treatment was measured.

Apparatus; Alliwa Shoji PL-850X Processing conditions: FORWARD POWER 100 W REFLECTED POWER 5 W Vacuum degree 10 Pa Introduced gas type Air Discharge time 1 min Further, the weight of the elements in the entire ferromagnetic metal powder according to claims 2 and 7 The ratio was measured using a wavelength-dispersive X-ray fluorescence spectrometer (W
DX), after measuring the fluorescent X-ray intensity of each element,
It is calculated and determined according to the fundamental parameter method (hereinafter referred to as the FP method).

For measurement of X-ray fluorescence, WD manufactured by Rigaku Denki
The X system 3080 is used under the following conditions.

X-ray tube; Rhodium tube output; 50 KV, 50 mA spectral crystal; LiF (Fe, Co, Ni, Nd, La,
Y, Sr, Ca, Ba), PET (for Al), RX-4 (for Si), RX-40 (for Na) Absorber (for Al); 1/1 (Fe only 1/1
0) Slit; COARSE filter; OUT PHA; 15-30 (for Al, Si, Na), 10-30 (Fe, Co, Ni, Nd, La,
Count time; peak = 40 seconds, background = 40 seconds (measure two points before and after the peak). The measurement of the fluorescent X-ray is limited to the above-mentioned apparatus. Instead, various devices can be used.

The following eight kinds of metal compounds are used as standard samples.

The standard sample 1 is an Analytical R
experience Materials intern
National SRM1219 (C is 0.1
5 wt%, Mn 0.42 wt%, P 0.03 wt%, Si 0.55 wt%, Cu 0.16 wt%, N
i: 2.16% by weight, Cr: 15.64% by weight, Mo
Is 0.16% by weight and V is 0.06% by weight).

The standard sample 2 is an Analytical R
experience Materials intern
National SRM1250 (Ni 3
7.78% by weight, 0.08% by weight of Cr, 0.0% of Mo
1% by weight, 16.10% by weight of Co, and 0.99% by weight of Al).

The standard sample 3 was made of a magnetic iron oxide powder (Mn: 0.14% by weight, P: 0.15% by weight, S: 0.19% by weight, Si: 0.36% by weight, Co: 3.19%). weight%,
1.26% by weight of Zn, 0.07% by weight of Ca, and 0.02% by weight of Na).

The standard sample 4 is a ferromagnetic metal powder (containing 2.73% by weight of Nd and 0.001% by weight of Na).

The standard sample 5 was made of a ferromagnetic metal powder (Sr was set to 0.1%).
97% by weight).

The standard sample 6 was made of a ferromagnetic metal powder (Ba was 1.
40% by weight and 0.40% by weight of Ca).

The standard sample 7 was a ferromagnetic metal powder (La: 2.
69% by weight).

Standard sample 8 was a ferromagnetic metal powder (Y was 1.9).
8% by weight).

The weight percentages of the elements in the standard samples 1 and 2 are data sheet values provided by the manufacturer, and the weight percentages of the elements in the standard samples 3 to 8 are analysis values by an ICP emission spectrometer. This value is input as the element composition value of the standard sample in the calculation of the FP method below. FP
The calculation of the method is performed using the fundamental parameter software Version 2.1 manufactured by Technos under the following conditions.

Sample model; Bulk sample Balance component sample; Fe input component; Measured X-ray intensity (KCPS) Analytical unit: Weight% The calculated weight ratio of each element is 100% by weight of Fe atoms and 100% by weight of other elements. As a quantitative value.

Furthermore, the average abundance ratio of the constituent elements on the surface of the ferromagnetic metal powder can be determined by the following method.

F in the composition on the surface of the ferromagnetic metal powder
e, Co, Ni, Nd, Si, Al, Sr, Ca, B
About the average abundance ratio of each element of a, Y, Na, La,
The value was determined using an XPS surface analyzer.

The method will be described below.

First, the XPS surface analyzer is set under the following conditions.

X-ray anode; Mg separation ability: 1.5 to 1.7 eV (resolution is clean A
It is defined by the half width of 3d5 / 2 peak of g. Note that a so-called adhesive tape is not used for fixing the sample. The model of the XPS surface analyzer is not particularly limited, and various apparatuses can be used. In the present invention, ESCALAB-200R manufactured by VG was used.

A narrow scan is performed in the following measurement range.
The spectrum of each element was measured. At this time, the data acquisition interval was set to 0.2 eV, and integration was performed until a count equal to or more than the minimum count shown in Table 2 was obtained.

The energy position of the obtained spectrum is corrected so that the peak position of C becomes 284.6 eV.

Next, in order to perform data processing on the VAMAS software, the spectrum is transferred to a computer that can use the VAMAS software by using software provided by each device maker.

Then, after the transferred spectrum is converted into the VAMAS format using the VAMAS software, the following data processing is performed.

Before starting the quantitative processing, Co for each element
Unscale is calibrated, and a 5-point smoothing process is performed.

The quantitative processing is as follows.

The peak area intensity is determined in the quantitative range shown in the table below with the peak position of each element as the center. Next, using the sensitivity coefficients shown in the following table, the atomic number% of each element was determined. The number of atoms% was converted into the number of atoms with respect to the number of Fe atoms of 100, and was defined as a quantitative value.

[0070]

[Table 2]

Another method for suppressing the elution of sodium ions into water according to the third, fourth, fifth, eighth, ninth and tenth aspects is to release the sodium ions from the ferromagnetic metal powder when the ferromagnetic metal powder is immersed in water. There is a method of controlling the amount of alkaline earth metal ions or sodium ions and the amount of sodium dissolved in the hydrochloric acid solution. The amounts of alkaline earth metal ions and sodium ions released from the ferromagnetic metal powder and sodium dissolved in the hydrochloric acid solution are determined by the boiling method described below.

The sample is crushed in a mortar. 5.00 g of the crushed sample is precisely weighed with a balance. It is put into a 200 ml Teflon beaker. 100 ml of pure water is taken with a hole pipette and put into a beaker. Boil for 5 minutes. Cool to about 20 ° C with tap water. Filter with a funnel using a 5C filter paper (use the filter paper well after washing with pure water beforehand). Take 10 ml of the filtrate with a whole pipette and dilute it to the measurement concentration range (0 to 5 ppm). (Example: 5 times → 5
0 ml 10 times → 100 ml 20 times → 200 ml) Measure the diluted solution for each element with an atomic absorption spectrometer. At this time, the extraction method by adding hydrochloric acid solution adds 2 ml of 0.24N-HCl together with pure water at the time of the above. Only the other measurement methods are the same as those described above.

The amount can be determined by substituting the obtained measured value into (measured value (ppm) × dilution ratio × 100 ÷ 5).

The present invention can also be achieved by controlling the amount of metal ions released when an element having a specific acid dissociation constant contained in a ferromagnetic metal powder is immersed in water and the amount of the element dissolved in a hydrochloric acid solution. Are solved. That is, the acid dissociation constant of the metal ion is 8 or more and 1
Even if the elution amount of the element less than 4 into the aqueous solution is small, if the elution amount of the element having an acid dissociation constant of metal ions of 14 or more into the aqueous solution is large, protons are generated by the reaction of c, and the reaction of d Are promoted, and an element having an acid dissociation constant of 8 or more and less than 14 is eluted with the metal ions, and reacts with the alkali soap to generate a metal soap insoluble in water, which causes the generation of projections. At this time, it is necessary to suppress the above reaction a.

Therefore, the dispersibility and stability of the coating material are improved by suppressing the amount of the element having an acid dissociation constant of from 8 to less than 14 and the amount of the element having an acid dissociation constant of 14 or more to a specific amount. And high electromagnetic conversion characteristics can be obtained.

The acid dissociation constant of the metal ion is 8 or more and 14 or less
The full element is Tl⁺, Ni²⁺, Co²⁺, M
n²⁺, Ba²⁺, Ca²⁺, Sr²⁺, Mg²⁺,
Nd³⁺, Pr³⁺, Ce³⁺, La³⁺, Y³⁺Is good
Preferably, more preferably, Ba ²⁺, Ca²⁺, S
r²⁺, Nd³⁺, La³⁺, Y³⁺Element.

Elements having an acid dissociation constant of 14 or more in metal ions include Na ⁺ , Li ⁺ , K ⁺ , Rb ⁺ , C
s ⁺ .

The ferromagnetic metal powder of the present invention uses, as a starting stock solution, iron oxyhydroxide obtained by blowing an oxidizing gas into an aqueous suspension in which a ferrous salt and an alkali are mixed.
As the type of the iron oxyhydroxide, α-FeOOH is preferable. As a method for producing the iron oxyhydroxide, a ferrous salt is neutralized with an alkali hydroxide to form an aqueous suspension of Fe (OH) _2. There is a first production method in which an oxidizing gas is blown into the mixture to obtain acicular α-FeOOH. On the other hand, there is a second production method in which a ferrous salt is neutralized with an alkali carbonate to form an aqueous suspension of FeCO ₃ , and an oxidizing gas is blown into the suspension to form a spindle-shaped α-FeOOH. Such an iron oxyhydroxide may be obtained by reacting an aqueous solution of ferrous salt with an aqueous alkali solution to obtain an aqueous solution containing ferrous hydroxide, and oxidizing the aqueous solution by air oxidation or the like. preferable. At this time, a nickel salt, a salt of an alkaline earth element such as a Ca salt, a Ba salt, or a Sr salt, a Cr salt, a Zn salt, or the like may coexist in the ferrous salt aqueous solution, and such a salt is appropriately selected. By using them, the particle shape (axial ratio) and the like can be controlled.

As the ferrous salt, ferrous chloride and sulfuric acid
Iron and the like are preferred. As the alkali, NaOH, NH
₄ OH, (NH ₄ ) ₂ CO ₃ , Na ₂ CO _{3 and the} like are preferable. Examples of the Ni salt include nickel chloride, Ca salt, and B salt.
As the salt a and the salt Sr, chlorides such as calcium chloride, barium chloride, strontium chloride, chromium chloride, and zinc chloride are preferable.

Using the above iron oxide hydroxide as a starting material,
The following operation is performed using this slurry. In the present invention, Co is introduced before Al and / or Si or a rare earth element is introduced as described above. Specifically, a Co compound such as cobalt sulfate or cobalt chloride is used. By stirring and mixing the aqueous solution with the slurry of iron oxyhydroxide.

Next, Al and / or Si are introduced as follows. That is, preferably, after preparing a slurry of iron oxyhydroxide containing Co, an aqueous solution containing an Al compound and / or a Si compound and an aqueous solution containing a compound of a rare earth element are added to the slurry, and the mixture is stirred. What is necessary is just to mix.

The concentration of the aqueous solution containing the Al compound and the Si compound may be 0.5 to 1.5 M, and may contain only one of the compounds, or may contain both compounds. In this case, the total amount may be within the above range. As the Al compound to be used, sodium aluminate,
Examples include sodium metaaluminate, and examples of the Si compound include sodium silicate.

The rare earth elements preferably introduced in the present invention include Nd, Sm, Pr, La, Y and the like.

Examples of the rare earth element compound used for preparing the above aqueous solution include chlorides such as neodymium chloride, samarium chloride, praseodymium chloride, lanthanum chloride and yttrium chloride, and nitrates such as neodymium nitrate and gadolinium nitrate. Can be Further, two or more rare earth elements may be used in combination.

In the present invention, it is preferable to separately prepare and add an aqueous solution containing Al and / or Si and an aqueous solution containing a rare earth element as described above. You may prepare and add the aqueous solution containing and a rare earth element.

In the mode of separately preparing and adding, both liquids may be added at the same time, or one liquid may be added, and then the other liquid may be added. When the latter method is adopted, it is preferable to add an aqueous solution containing a rare earth element first, followed by an aqueous solution containing Al and / or Si.

In the present invention, an iron oxyhydroxide containing an alkaline earth element, Al and / or Si and a rare earth element, more preferably Co, is thus obtained.

This is sufficiently washed with water, dried, and heat-treated at a temperature of 300 to 800 ° C. in a non-reducing atmosphere. When the heat treatment temperature is 300 ° C. or lower, the number of vacancies in α-Fe ₂ O ₃ particles generated by dehydration of α-FeOOH increases, and as a result, the properties of the reduced ferromagnetic metal powder deteriorate. When the heat treatment temperature exceeds 800 ° C., α
-Fe ₂ O ₃ melting may change the shape of the particles start of particles, or sintering proceeds, the properties of the resulting ferromagnetic metal powder is deteriorated. Next, the ferromagnetic metal powder after the heat treatment is reduced at a temperature of 300 to 600 ° C. in a hydrogen gas stream, and an oxide film is formed on the surface by a known method to obtain a ferromagnetic metal powder.

Further, the amount of Na in the ferromagnetic metal powder (Claims 1 to 5)
4) can be achieved by washing with water before or after heat treatment in a non-reducing atmosphere or after forming an oxide film.

Further, by suppressing the amount of sodium ions eluted not only from the ferromagnetic metal powder but also from the magnetic powder or the non-magnetic powder contained in the lower layer, the ferromagnetic metal powder, the magnetic powder or the non-magnetic It is possible to prevent an element that forms an insoluble metal soap when the powder is submerged from being eluted into the aqueous solution.

In the present invention, it is also possible to suppress the generation of crystals of the fatty acid metal salt, which is the cause of the projections, by suppressing the elution of fatty acids into water. Therefore, it is solved by suppressing the amount of free fatty acids among the fatty acids, that is, the amount of fatty acids not adsorbed on the magnetic powder and the like. At this time, of the elements forming the surface of the ferromagnetic metal powder that has been subjected to the orientation treatment on the magnetic layer, It is not necessary to keep the number of sodium atoms with respect to the number of Fe atoms to a certain amount, and the weight ratio of the elements in the entire ferromagnetic metal powder does not keep the amount of sodium atoms with respect to the Fe atoms to a certain amount. Can be suppressed.

The amount of the free fatty acid is preferably 8.0 mg / m ² or less, more preferably 4.0 mg / m ² or less, further preferably 1.0 mg / m ² of the fatty acids contained in the magnetic recording medium.
0 mg / m ² or less. The amount of the free fatty acid is determined by the measurement method described in the examples below.

The fatty acid may be present at any place as long as it is contained in the magnetic recording medium, but it is preferable that the lower layer contains a fatty acid having 12 to 24 carbon atoms.

In a preferred embodiment of the present invention, at least one lower layer is provided between the nonmagnetic support and the magnetic layer. The magnetic or non-magnetic powder contained in the lower layer contains 130 ppt of sodium ions released from the magnetic or non-magnetic powder when immersed in water.
pm, more preferably less than 50p
pm or less.

The magnetic powder used in the lower layer of the present invention is described in JP-A-4-248177, paragraph 0018,0.
No. 019, and any magnetic powder such as ferromagnetic iron oxide powder, ferromagnetic metal powder, and hexagonal plate-like powder may be used. Among these, ferromagnetic iron oxide powder and ferromagnetic metal powder are preferred.

As the non-magnetic powder, various known non-magnetic powders can be appropriately selected and used. Organic powders such as azo organic pigments, carbon black, graphite, TiO ₂ , barium sulfate, ZnS , MgCO ₃ ,
CaCO ₃ , ZnO, CaO, tungsten disulfide, molybdenum disulfide, boron nitride, MgO, SnO ₂ , SiO
₂ , Cr ₂ O ₃ , α-Al ₂ O ₃ , α-Fe ₂ O ₃ , α
-FeOOH, SiC, cerium oxide, corundum, artificial diamond, α-iron oxide, garnet, garnet,
Silica stone, silicon nitride, silicon carbide, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, tripoly,
Examples include inorganic powders such as diatomaceous earth and dolomite. Preferred among these are carbon black, C
aCO ₃ , TiO ₂ , barium sulfate, α-Al ₂ O ₃ ,
It is an inorganic powder such as α-Fe ₂ O ₃ , α-FeOOH and Cr ₂ O ₃ . More preferably, carbon black, T
iO ₂ and α-Fe ₂ O ₃ , and α-Fe ₂ O ₃ is most preferable. When TiO ₂ is used, it is preferably used in combination with carbon black.

The magnetic powder or non-magnetic powder may be of any shape, but is preferably acicular. In the present invention, if the powder has a needle shape, the smoothness of the surface of the lower layer can be improved, and the smoothness of the surface of the magnetic layer laminated thereon can also be improved. Its average major axis diameter is less than 0.3 μm, preferably less than 0.20 μm, and its average minor axis diameter is less than 0.05 μm, preferably less than 0.03 μm. The axial ratio of the non-magnetic powder is usually 2 to 15, preferably 3 to 10. The axis ratio here is the ratio of the average major axis diameter to the average minor axis diameter (average major axis diameter /
Average minor axis diameter). The acicular powder used at this time is Co-coated γ-Fe ₂ O ₃ , α-Fe ₂ O ₃ , Ti
O ₂ is preferred, and needle-like α-Fe ₂ O ₃ is particularly preferred.

The specific surface area of the nonmagnetic powder is usually 10 to 250 m ² / g, preferably 20 to 15 m ² / g.
0 m ² / g. Here, the specific surface area of the nonmagnetic powder is BE
The surface area measured by a specific surface area measurement method called the T method is expressed in square meters per unit gram. About this specific surface area and the measuring method,
"Powder Measurement" (JM Dallavelle, Cl
yearrJr. Co-author, Muta et al .; Sangyo Toshosha Publishing Co., Ltd.)
Pages 0 to 1171 (edited by The Chemical Society of Japan; Showa 41, Maruzen Co., Ltd.)
Issued on April 30, 2003).

For the measurement of the specific surface area, for example,
While heating for 13 minutes before and after, degassing was performed to remove the substance adsorbed on the powder, and then the powder was introduced into a measuring device, and the initial pressure of nitrogen was set to 0.5 kg / m ² ,
The measurement is performed with liquid nitrogen at a liquid nitrogen temperature (−105 ° C.) for 10 minutes. As a measuring device, for example, a counter soap (manufactured by Yuasa Ionics) is used.

It is preferable that the non-magnetic powder is surface-treated with a Si compound and / or an Al compound.
The use of the non-magnetic powder subjected to such a surface treatment can improve the surface condition of the upper layer which is the magnetic layer. The content of Si and / or Al is preferably 0.1 to 10% by weight for both Si and Al based on the nonmagnetic powder. Further, an overcoat layer may be provided on the surface of the magnetic layer.

The present invention provides a magnetic recording medium having the same high electromagnetic conversion characteristics as obtained before storage even when stored under high temperature and high humidity for a long period of time by suppressing the above reaction by various methods. Can be obtained.

In the present invention, the form of the nonmagnetic support is not particularly limited, and may be mainly a tape, a film, a sheet, or the like.
It can take the form of a card, disk, drum, etc.
The optimum thickness of the nonmagnetic support is appropriately selected according to the application. The non-magnetic support may have been subjected to a surface treatment such as a corona discharge treatment.

Further, on the surface of the non-magnetic support on which the magnetic layer is not provided (the back surface), the running property of the magnetic recording medium is improved.
A back coat layer is preferably provided for the purpose of preventing static charge and transfer, and an undercoat layer may be provided between the magnetic layer and the non-magnetic support.

The magnetic layer or lower layer is not particularly limited except that it contains the above-mentioned specific ferromagnetic metal powder, magnetic powder or non-magnetic powder, and can be formed by various methods.

The magnetic layer or the lower layer may contain a binder and other components.

As the binder used for the magnetic layer or the lower layer, for example, vinyl chloride resins such as polyurethane, polyester, vinyl chloride copolymer and the like are representative. These resins are -SO ₃ M, -OSO ₃ M, -CO
OM and -PO (OM ¹⁾ preferably contains a repeating unit having at least one polar group selected from ₂ sulfobetaine group.

[0107] However, M in the polar group is a hydrogen atom or Na, K, an alkali metal such as Li, also ^{M 1} represents a hydrogen atom, Na, K, alkali metal or an alkyl group such as Li.

In the present invention, the resin may be used as a binder in an amount of 20 to 80% by weight of the total binder.

In the present invention, in order to improve the quality of the magnetic layer or the lower layer, additives such as abrasives, lubricants, hardeners, dispersants, antistatic agents and conductive fine powders are used as other components. It can be contained.

As the polishing agent, for example, JP-A-4-214
Known substances described in paragraph No. 0105 of JP-A-218 can be used. The average particle size of the abrasive is usually 0.05 to 0.6 μm, preferably 0.05 to 0.6 μm.
0.5 μm, particularly preferably 0.05 to 0.3 μm
m. The content of the abrasive in the magnetic layer or the lower layer is usually 3 to 20 parts by weight, preferably 5 to 20 parts by weight.
15 parts by weight.

Fatty acids and / or fatty acid esters can be used as lubricants. In this case, the amount of the fatty acid added is 0.2 to 10 with respect to the magnetic powder or the non-magnetic powder.
% By weight, particularly preferably 0.5 to 5% by weight. When it is desired to enhance the lubricating effect by using a fatty acid and a fatty acid ester in combination, the weight ratio of the fatty acid and the fatty acid ester is preferably from 10:90 to 90:10. The fatty acid may be a monobasic acid or a dibasic acid, and preferably has 6 to 30 carbon atoms, more preferably 12 to 2 carbon atoms.
There are four.

Specific examples of the fatty acid include JP-A No. 4-21.
As a specific example of the fatty acid ester, the fatty acid described in paragraph No. 0102 of No.
And fatty acid esters described in No. 3 above.

As the lubricant other than the above fatty acids and fatty acid esters, known substances can be used. For example, silicone oil, carbon fluoride, fatty acid amide, α-olefin oxide and the like can be used.

As the dispersing agent, the same publication, paragraph number 009 can be used.
The compounds described in No. 3 can be mentioned. These dispersants are usually 0.5 to 0.5 to the magnetic powder or non-magnetic powder.
It is used in the range of 5% by weight.

The antistatic agent is described in paragraph 0 of the publication.
And surfactants described in No. 107. This antistatic agent is usually used in an amount of 0.01 to 40 with respect to the binder.
It is added in the range of weight%. Further, in the present invention, conductive fine powder can be preferably used as an antistatic agent. Examples of the antistatic agent include carbon black, graphite, tin oxide, silver powder, silver oxide, silver nitrate, silver organic compounds, metal particles such as copper powder, zinc oxide, barium sulfate, and metal oxides such as titanium oxide. Pigments coated with a conductive substance such as a tin oxide film or an antimony solid solution tin oxide film can be used.

The average particle diameter of the conductive fine powder is as follows:
5 to 700 nm, more preferably 5 to 200 nm
It is. The content of the conductive fine powder is 1 to 20 parts by weight, preferably 2 to 7 parts by weight, based on 100 parts by weight of the magnetic powder or the nonmagnetic powder.

The magnetic recording medium according to the present invention has a so-called wet-type, in which the magnetic layer is applied when the lower layer is in a wet state.
It is preferable to apply by an on-wet coating method. As the wet-on-wet coating method, a known method used for manufacturing a magnetic recording medium having a multilayer structure can be appropriately adopted.

For example, generally, a high-concentration magnetic paint is prepared by kneading a magnetic powder, a binder, a dispersant, a lubricant, an abrasive, an antistatic agent, and a solvent, and then diluting the high-concentration magnetic paint. After adjusting the magnetic paint, the magnetic paint is applied to the surface of the nonmagnetic support. Examples of the solvent include, for example, paragraph No. 0119 of JP-A-4-21418.
Can be used. These various solvents can be used alone, or two or more of them can be used in combination.

In kneading the components for forming the magnetic layer, various kneading and dispersing machines can be used. Examples of the kneading and dispersing machine include those described in paragraph number 0112 of the publication.

Among the kneading and dispersing machines, 0.05 to 0.5 KW
The kneading and dispersing machines capable of providing a power consumption load (per kg of magnetic powder) are a pressure kneader, an open kneader, a continuous kneader, a two-roll mill, and a three-roll mill.

In applying the paint, in the wet-on-wet coating method, a combination of a reverse roll and an extrusion coater, a combination of a gravure roll and an extrusion coater, and the like can be used.
Further, an air doctor coater, blade coater, air knife coater, squeeze coater, impregnation coater, transfer roll coater, kiss coater, cast coater, spray coater, and the like can be combined.

In the multi-layer coating in the wet-on-wet coating method, since the upper layer is coated while the lower layer is kept wet, the surface of the lower layer (that is, the boundary surface with the upper layer) is used.
And the surface properties of the upper layer are improved, and the adhesion between the upper and lower layers is also improved.

As a result, the performance particularly required for a high-density magnetic recording medium is satisfied. Also, the film strength is improved, the durability is sufficient, and the drop-out can be reduced by the wet-on-wet coating method,
Reliability is also improved.

Next, the surface may be smoothed by calendaring. Thereafter, slitting is performed by performing burnishing or blade treatment as necessary.

In the surface smoothing treatment, temperature, linear pressure, treatment speed (C / S) and the like can be listed as calendering conditions.
C, the linear pressure is 50 to 1200 kg / cm, and the C /
It is preferable to keep S at 20 to 600 m / min. Outside of these ranges, it is difficult to maintain the surface properties of the magnetic recording medium in a good condition.

[0126]

EXAMPLES The structure and effect of the present invention will be specifically described with reference to the following examples. However, the components, ratios, and operation orders shown below can be variously changed without departing from the scope of the present invention. It goes without saying that the present invention is not limited to the embodiments. In the following examples, "parts" are all parts by weight. or. ***, *** in each table
* Means not contained or below the detection limit.

The components of the magnetic paint for the uppermost layer and the paint for the lower layer having the following compositions were kneaded and dispersed using a kneader and a sand mill, respectively, to prepare a magnetic paint for the upper layer and a paint for the lower layer. << Magnetic paint for upper layer >> Ferromagnetic metal powder (major axis diameter: 0.12 μm, Hc (coercive force): 1900 Oe, BET: 55 m ² / g, σs (saturation magnetization): 125 emu / g, crystallite size: 150} , Needle ratio: 8, pH: 9.0) 100 parts (compositions are shown in Tables 3, 4, 6, 7, 9, 11, 13 and 15) Potassium sulfonate group-containing vinyl chloride resin 10 parts (Japan ZEON Corporation MR-110) Sodium sulfonate group-containing polyurethane resin 10 parts (Toyobo Co., Ltd., UR-8700) α-alumina (average particle size 0.15 μm) 8 parts Fatty acid 1 part (designated in the table) 100 parts Methyl ethyl ketone 100 parts 100 parts of toluene stearate) butyl stearate 1 part cyclohexanone except for the {underlying paint _{A} Co-γ-Fe 2} O 3 ( Table 3,5,6 7,8,9,12,13,15 and shown in 1 7) 100 parts of [(major axis diameter: 0.20 [mu] m, Hc (coercive force): 700 Oe, BET ^{value: 45 m 2 / g, σs} ( saturation Magnetization): 75 emu / g, crystallite size: 250 °, pH: 8.5, acicular ratio: 10, surface treatment with Si and Al compounds, Si content 0.1% by weight, Al content 0.3 Weight%, water-soluble Na content, hydrochloric acid-soluble Na] 12 parts of potassium sulfonate group-containing vinyl chloride resin (MR-110 manufactured by Zeon Corporation) 8 parts of sodium sulfonate group-containing polyurethane resin (Toyobo Co., Ltd. Co., Ltd., UR-8700) α-alumina (average particle size: 0.2 μm) 5 parts Carbon black (DBP oil absorption: 85 ml / 100 g, pH: 8.2, BET value: 260 m ² / g, volatile matter: 1.2%, coloring power: 140 %) (15 nm) 10 parts Fatty acid 1 part (The number of carbon atoms is shown in Tables 3, 5, 6, 7, 8, 9, 12, 13, 15, 15 and 17) Butyl stearate 1 part Cyclohexanone 100 parts Methyl ethyl ketone 100 parts Toluene 100 parts To each of the obtained upper layer magnetic paint and lower layer paint A was added 5 parts of a polyisocyanate compound (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.).塗料 Lower layer paint B｝ Lower layer paint B is needle-like α-Fe ₂ O instead of Co-γ-Fe ₂ O ₃ in lower layer paint A.
₃ [Long axis diameter: 0.13 μm, axial ratio: 7, BET value: 55]
m ^{2 /} g, pH: 7.5, crystallite size: 200 °, S
i, surface treatment with Al compound (Si: 0.1 wt%, A
l: 0.3 wt%)] except that the lower layer paint A was used.塗料 Lower layer paint C｝ Co-γ-Fe in lower layer paint A
₂ O ₃ spherical instead of _alpha-Fe 2 _{O 3} [average particle size: 35n
m, BET: 40 m ^{2 /} g, pH: 6.5, Si, Al
Surface treatment with compound (Si: 0.1 wt%, Al: 0.3
wt%)] except for using the lower layer paint A. (Examples 1-1 to 10-5 and Comparative Examples 5-1 to 10-
4) Using the above-mentioned magnetic paint for the upper layer and the paint for the lower layer containing the ferromagnetic metal powder shown in each table, the composition was applied on a 10 μm-thick polyethylene terephthalate film by a wet-on-wet method, and then applied. Perform the magnetic field orientation treatment while the film is not dried, and then perform drying,
The surface was smoothed with a calender to form a magnetic layer consisting of a lower layer and an upper layer having the thickness shown in each table.

Further, a coating material having the following composition is applied to the surface (back surface) of the polyethylene terephthalate film opposite to the magnetic layer, and after this coating film is dried, calendering is performed according to the above-described calendering conditions. Thereby, a 0.8 μm thick back coat layer is formed,
A wide raw magnetic tape was obtained.

Carbon black (Raven 1035 manufactured by Columbia Carbon Co., Ltd.) (average particle size 25 nm) 40 parts Barium sulfate (average particle size 300 nm) 10 parts Nitrocellulose 25 parts Polyurethane resin 25 parts (Nippon Polyurethane Co., Ltd., N 2301) Polyisocyanate compound 10 parts (Nippon Polyurethane Co., Ltd., Coronate L) Cyclohexanone 400 parts Methyl ethyl ketone 250 parts Toluene 250 parts The raw magnetic tape thus obtained was slit into 8 m.
A magnetic recording medium for video having a width of m was prepared. This magnetic recording medium was evaluated as follows. Tables 3 and 5 show the results.
To 8, 10, 12, 14, 16, and 17. << Evaluation >><Surface composition of ferromagnetic metal powder present in magnetic coating film>; measured by the method described in the text. <Overall composition of ferromagnetic metal powder>; measured by the method described in the text. <Surface composition of ferromagnetic metal powder>; measured by the method described in the text. <Amount of metal ions released from ferromagnetic powder when immersed in water>; measured by the method described in the text. <Amount of sodium released from ferromagnetic powder when immersed in hydrochloric acid solution>; measured by the method described in the text. <Method of measuring free fatty acid> a. 50 ml of cyclohexane was added to a 253 cm ² sample, which was refluxed and boiled for 1 hour, returned to room temperature, washed with a small amount of cyclohexane, and combined with the extract (refluxed liquid). b. To this extract, 5 ml of a methyl palmitate / cyclohexane solution adjusted to a concentration of 40 ppm is added. c. The cyclohexane is evaporated from this solution using a rotary evaporator. d. Add 0.2m of cyclohexane to the concentrated extract
and add 1 μl to it for gas chromatography. e. From the relationship between the concentrations of methyl palmitate and the fatty acid and the peak area, the amount of the fatty acid extracted from the calibration curve prepared in advance is determined. This value is converted per unit area of 1 m ² . * Gas chromatography is "HP5" manufactured by Yokogawa Electric Corporation.
890A "and" Ultra 1 "manufactured by Hewlett-Packard Company as a column. <Reproduction output> Sony 8mm video camera CCDV-
900, the RF power at 7 MHz and 9 MHz (d
B) was measured. * Both samples were measured before storage and after storage at 50 ° C / 80% RH for 120 hours (cassette state).

<Head Clog> The number of times head clog (head clogging) occurred when using a Sony Corporation 8 mm video deck EVO-550 and running a full-length recorded tape under the environment shown in the table. It was measured. * Before storage, 50 ° C / 80% RH12
After storage for 0 hours (state of the cassette), both samples were measured.

<Dropout> Measurement is performed before and after storing the sample. Sony 8mm
The measurement was performed in a Hi8 mode using a video deck EVS-900. As an input signal, a staircase wave of a monochrome signal is recorded, and a Shibasoku drop-out counter VH01 is used.
Using BZ, the average value of the number of times the output decreased by 5 μs / −8 dB or more per unit time per minute was determined. * Both samples were measured before storage and after storage (in cassette) at 50 ° C / 80% RH for 120 hours.

[0132]

[Table 3]

[0133]

[Table 4]

[0134]

[Table 5]

[0135]

[Table 6]

[0136]

[Table 7]

[0137]

[Table 8]

[0138]

[Table 9]

[0139]

[Table 10]

[0140]

[Table 11]

[0141]

[Table 12]

[0142]

[Table 13]

[0143]

[Table 14]

[0144]

[Table 15]

[0145]

[Table 16]

[0146]

[Table 17]

Next, another embodiment of the present invention (an example using titanium oxide) will be described.

The components of the magnetic paint for the uppermost layer and the paint for the lower layer having the following composition were kneaded and dispersed using a kneader and a sand mill, respectively, to prepare a magnetic paint for the upper layer and a paint for the lower layer.

<< Magnetic paint for upper layer >> Examples 1-1 to 10-
Same as 5. However, the composition of the ferromagnetic metal powder is shown in Tables 18 and 1,
9, 21, 22, 24, 26, 27 and 28.

{Lower Layer Coating C} Instead of Co-γ-Fe ₂ O ₃ in the lower layer coating A, spherical α-Fe ₂ O was used.
₃ [Average particle size: 35 nm, BET value: 40 m ² / g, p
H: 6.5, surface treatment with Si and Al compounds (Si: 0.
1 wt%, Al: 0.3 wt%)].

{Lower Layer Coating D} A lower layer coating A was obtained in the same manner as the lower layer coating A except that spherical TiO ₂ was used instead of Co-γ-Fe ₂ O ₃ in the lower layer coating A. Spherical TiO
₂ [Average particle size: 32 nm, BET value: 40 m ² / g, p
H: 7.5, crystal system: surface treatment with rutile, Si, Al compound (Si: 0.1 wt%, Al: 0.3 wt%)]

{Lower Layer Coating E} A lower layer coating A was obtained in the same manner as the lower layer coating A, except that needle-like TiO ₂ was used instead of Co-γ-Fe ₂ O ₃ in the lower layer coating A. Acicular TiO
₂ [Long axis diameter: 0.12 μm, axial ratio: 6, BET: 40 m
^{2 /} g, pH: 7.0, crystallite size: 220 °, S
i, surface treatment with Al compound (Si: 0.1 wt%, A
l: 0.4 wt%)]

(Examples 1-12 to 10-8) Using the above-mentioned upper layer magnetic paint and lower layer paint containing the ferromagnetic metal powder shown in each table, the wet-on-wet method was used. After coating on a 10 μm polyethylene terephthalate film, a magnetic field orientation treatment was performed while the coating film was not dried, followed by drying, followed by a surface smoothing treatment with a calendar, and a thickness indicated in each table. A magnetic layer consisting of a lower layer and an upper layer having a thickness was formed.

Further, a coating material having the above composition is applied to the surface (back surface) of the polyethylene terephthalate film opposite to the magnetic layer, and after this coating film is dried, calendering is performed according to the above-described calendering conditions. Thereby, a 0.8 μm thick back coat layer is formed,
A wide raw magnetic tape was obtained.

Thereafter, slitting was performed in the same manner as in Examples 1-1 to 10-5, and evaluation was made. The results are shown below.

[0156]

[Table 18]

[0157]

[Table 19]

[0158]

[Table 20]

[0159]

[Table 21]

[0160]

[Table 22]

[0161]

[Table 23]

[0162]

[Table 24]

[0163]

[Table 25]

[0164]

[Table 26]

[0165]

[Table 27]

[0166]

[Table 28]

[0167]

[Table 29]

[0168]

[Table 30]

[0169]

[Table 31]

[0170]

[Table 32]

As is clear from the results in the above table, the present invention is extremely excellent.

[0172]

The magnetic recording medium according to the present invention can be obtained before storage without increasing dropouts, lowering reproduction output, or clogging the head even when stored for a long time under high temperature and high humidity. High electromagnetic conversion characteristics can be maintained.

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Akira Saito 1-13-1 Nihonbashi, Chuo-ku, Tokyo Inside TDK Corporation (72) Inventor Akihiko Seki 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDK (56) References JP-A-3-80424 (JP, A) JP-A-5-54371 (JP, A) JP-A-4-267503 (JP, A) JP-A-64-78423 (JP, A A) JP-A-62-244106 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 5/62-5/82

Claims (10)

(57) [Claims] In a magnetic recording medium having a magnetic layer containing at least a ferromagnetic metal powder on a non-magnetic support and containing a fatty acid, the surface of the ferromagnetic metal powder which is oriented on the magnetic layer is provided. The average abundance of the elements that form
Fe number of atoms is less than 1 for 100 atoms of Na, number of atoms of alkaline earth element is 40 or less, number of atoms of rare earth element is 1 to 5
0, wherein the fatty acid has 12 to 24 carbon atoms. 2. In a magnetic recording medium having a magnetic layer containing at least a ferromagnetic metal powder on a nonmagnetic support and containing a fatty acid, the weight ratio of elements in the entire ferromagnetic metal powder is Fe atom. 2 to 10 parts by weight of Al atom, 1 to 8 parts by weight of atom of rare earth element, 0.1 to 5 parts by weight of atom of alkaline earth element, 0.0 part by weight of Na atom per 100 parts by weight
It is less than 1 part by weight, and the average abundance ratio of the elements forming the surface of the ferromagnetic metal powder is 70 to 300 Al atoms per 100 Fe atoms and 0. 0 for rare earth elements.
5 to 60, the number of atoms of the alkaline earth element is 40 or less, the number of Na atoms is less than 4, and the fatty acid has 12 carbon atoms.
A magnetic recording medium, wherein the number is from 24 to 24. 3. A magnetic recording medium having a magnetic layer containing at least a ferromagnetic metal powder on a nonmagnetic support and containing a fatty acid, wherein the ferromagnetic metal powder is immersed in water when the ferromagnetic metal powder is immersed in water. Less than 30 ppm of alkaline earth metal ions and 20 sodium ions released from the powder
Less than 0 ppm and 3% sodium dissolved in hydrochloric acid solution
Less than 00 ppm and the fatty acid has 1 carbon atom
2 to 24 magnetic recording media. 4. In a magnetic recording medium having a magnetic layer containing at least a ferromagnetic metal powder on a non-magnetic support and containing a fatty acid, the ferromagnetic metal powder contains metal ions released when immersed in water. Is an element having an acid dissociation constant of not less than 8 and less than 14 in a free state of not more than 90 ppm, and a metal ion released when immersed in water is less than 200 ppm, and a dissolved amount in a hydrochloric acid solution is less than 300 ppm. A magnetic recording medium comprising an element having an acid dissociation constant of 14 or more, and wherein the fatty acid has 12 to 24 carbon atoms. 5. A magnetic recording medium comprising a nonmagnetic support and an upper layer containing a ferromagnetic metal powder and a lower layer containing a magnetic powder or a nonmagnetic powder, wherein the magnetic powder or the nonmagnetic powder is immersed in water. Sometimes, the sodium ion released from the magnetic powder or the non-magnetic powder is less than 100 ppm, and the sodium dissolved in the hydrochloric acid solution is less than 130 ppm, and at least one of the upper layer and the lower layer has 12 to 24 carbon atoms. A magnetic recording medium comprising a fatty acid. 6. A magnetic recording medium having at least a ferromagnetic metal powder containing a ferromagnetic metal powder on a non-magnetic support and a fatty acid-containing magnetic recording medium, the surface of the ferromagnetic metal powder being oriented on the magnetic layer. The average abundance of the elements that form
The number of Na atoms is 1 or more, the number of alkaline earth elements is 40 or less, and the number of rare earth elements is 1 to 5 for 100 Fe atoms.
0, the fatty acid has 12 to 24 carbon atoms, and the free fatty acid content of the fatty acid is 8.0 mg /
The magnetic recording medium, characterized in that at m ² or less. 7. In a magnetic recording medium having a magnetic layer containing at least a ferromagnetic metal powder on a non-magnetic support and containing a fatty acid, the weight ratio of elements in the entire ferromagnetic metal powder is Fe atom. 2 to 10 parts by weight of Al atoms, 1 to 8 parts by weight of atoms of rare earth elements, 0.1 to 5 parts by weight of atoms of alkaline earth elements, 0.1 of Na atoms per 100 parts by weight
Less than parts by weight, and the average abundance of elements forming the surface of the ferromagnetic metal powder is such that the number of Al atoms is 70 to 300 and the number of rare earth elements is 0.5
-60, the number of atoms of an alkaline earth element is 1-40, the number of Na atoms is 4 or more, and the number of carbon atoms of the fatty acid is 12-24.
And the amount of free fatty acids among the fatty acids is 8.0
mg / m ² or less. 8. A magnetic recording medium having a magnetic layer containing at least a ferromagnetic metal powder on a nonmagnetic support and containing a fatty acid, wherein the ferromagnetic metal powder is immersed in water when the ferromagnetic metal powder is immersed in water. 30 ppm or less of metal ions of alkaline earth element liberated from the
ppm or more, and sodium dissolved in the hydrochloric acid solution is 30 ppm or more.
0 ppm or more, and the fatty acid has 12 carbon atoms.
A magnetic recording medium, wherein the number of free fatty acids is not more than 8.0 mg / m ² . 9. A magnetic recording medium having a magnetic layer containing at least a ferromagnetic metal powder on a non-magnetic support and containing a fatty acid, wherein the ferromagnetic metal powder contains metal ions released when immersed in water. Is 90 ppm or less acid dissociation constant in the free state of 8 or more and less than 14 and less than 200 ppm of metal ions released when immersed in water,
Or an element having an acid dissociation constant of 14 or more in a free state in which the amount of dissolution in a hydrochloric acid solution is 300 ppm or more, wherein the fatty acid has 12 to 24 carbon atoms, and a free fatty acid among the fatty acids A magnetic recording medium having an amount of 8.0 mg / m ² or less. 10. A magnetic recording medium comprising a nonmagnetic support and an upper layer containing a ferromagnetic metal powder and a lower layer containing a magnetic powder or a nonmagnetic powder, wherein the magnetic powder or the nonmagnetic powder is immersed in water. Sometimes, the sodium ion released from the magnetic powder or the non-magnetic powder is 100 ppm or more, and the sodium ion dissolved in the hydrochloric acid solution is 130 ppm
As described above, at least one of the upper layer and the lower layer contains a fatty acid having 12 to 24 carbon atoms, and a free fatty acid amount of the fatty acid is 8.0 mg / m ² or less. Magnetic recording medium.