JPH0935247A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium for high density recording having high output, less liable to cause the contamination and wear of a head and blocking, less liable to the reduction of output caused by repeated running and the reduction of output caused by storage and less liable to cause the contamination of a roll caused by the seizing and sticking of the magnetic layer in a calendering process. SOLUTION: This magnetic recording medium has one or more magnetic layers on the nonmagnetic substrate has a nonmagnitic layer if necessary. Each of the magnetic layers consists of acicular ferromagnetic metal powder having 0.04-0.12μm major axis size and an acicularity ratio of 3-10 and a resin binder. The metal powder contains 5×10<-4> -0.2at.% Ca atoms, 5×10<-4> -2at.% alkali metal and 5×10<-5> -0.4at.% Ni atom based on the amt. of Fe atoms.

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, in particular, a high output, high density recording with less head deterioration, wear and clogging, less output reduction due to repeated running, and less output reduction due to storage and storage. Relates to a magnetic recording medium. Further, the present invention relates to a magnetic recording medium in which roll contamination due to sticking of a magnetic layer in a calendar process is small.

[0002]

2. Description of the Related Art Magnetic recording media are widely used as recording tapes, video tapes, computer tapes, disks, and the like. The magnetic recording medium basically comprises a magnetic layer in which a ferromagnetic powder is dispersed in a binder, which is provided on a non-magnetic support. Basically, a magnetic recording medium is required to be at a high level in various characteristics such as electromagnetic conversion characteristics, running performance, running durability. Especially with high density recording, in a new VCR system, there is a tendency to increase the rotational speed of the cylinder to increase the relative speed of the head / tape.

Further, when the head / tape relative speed is high and the head projection rate from the cylinder is high, the tape is likely to hit the head, so that the head projection amount tends to be set low. This is because the magnetic recording medium itself is also thin, and if the stiffness of the medium also weakens and the protrusion of the head is large, it does not hit the projected portion of the head. Therefore, there is a tendency that the evaluation of output reduction due to head dirt and clogging that occurs when a scraped magnetic layer adheres to the head becomes more severe. This is because the head hitting the magnetic layer is not so strong that the self-cleaning action of the deposit by the magnetic layer is weakened.

Further, the amount of head wear increases due to high-speed sliding, and the amount of protrusion of the head is low, which causes a problem of head life (life of head). In consideration of the above trend, it is necessary for the magnetic recording medium to suppress as much as possible the head contamination and the generation of shavings from the tape due to running. or,
In the past, the tape's polishing power was increased to prevent head dirt and head clogging by removing it, but with the new system, the above head protrusion amount cannot be made large. Polishing power cannot be increased. That is, it is desired to use a tape that has a low polishing power and does not cause head contamination or clogging.

In the first place, head contamination and head wear have a trade-off relationship for a magnetic recording medium, and if one is improved, the other is reduced. Further, it has been desired that the head is less worn and the head is less contaminated, but there is a problem in that it is difficult to find a point where both are well balanced in the related art. That is, it has been confirmed that the effect of increasing the amount of binder resin in the magnetic layer and covering the magnetic substance with the binder resin has been confirmed as a means for suppressing head contamination due to the burning of the magnetic substance. Since the degree of filling of the magnetic material is decreased, the output is lowered and high density recording cannot be performed. This head sticking is observed as sticking due to the sticking to the magnetic head to form a thin film due to part of the magnetic material itself or some of the components including impurities in the magnetic material. The main cause of head sticking is It is thought to be in a magnetic material.

In a high density magnetic recording medium, it is important to improve the output by increasing the filling degree of the magnetic material in the magnetic layer. Therefore, heat and pressure are applied to the magnetic layer by calendering to compress it. It is effective to do. Therefore, the material of the calender roll is preferably a metal roll, and the magnetic layer forming treatment of the medium is performed while applying a high temperature with the calender roll made of the metal roll. that time,
When dirt adheres to the metal roll in contact with the magnetic layer and causes seizure, the surface property of the roll surface is deteriorated and the surface roughness of the magnetic layer is generated. The work of removing (calender roll surface correction) is required, and there is a problem that the operation is reduced and the productivity is reduced. When the polishing power of the tape magnetic layer is lowered, the calendar roll is apt to be contaminated, which further reduces the production operation and raises the cost.

With the recent spread of 8 mm video tape recorders and the like, video tapes are required to have particularly high electromagnetic output characteristics such as high video output and excellent original image reproduction capability. There are various methods for improving the electromagnetic conversion characteristics of the magnetic recording medium, and the method of improving the characteristics of the ferromagnetic powder is direct and effective. Therefore, the ferromagnetic powder has been gradually made into fine powder so that high density recording is possible. Also, a means for suppressing self-demagnetization by increasing the thickness of the magnetic layer and increasing the output has been proposed (for example, Japanese Patent Publication No. 4-71244). For a high-output magnetic recording medium, it is as important to suppress output reduction due to repeated running and output reduction during storage / storage as to increase output. Conventionally, as a measure to reduce the output during repeated running, a means such as adding an abrasive having a large particle size or an abrasive having a high hardness to the medium, increasing the amount of the abrasive, or increasing the binder amount in the magnetic layer, There is used a means for increasing the amount of binder adsorbed on the magnetic material to suppress head contamination due to magnetic layer sticking. However, with the above measures, there is a problem that the head wear becomes large and the filling degree of the magnetic material in the magnetic layer is lowered, so that the output is lowered.

Further, in the recent high-density recording system such as DVC, the storability in an environment more severe than before,
Running durability and high output are desired. Then, in order to increase the output, the surface of the magnetic layer is made smooth, the gap between the magnetic head and the magnetic layer is narrowed to reduce so-called spacing loss, and the rigidity of the non-magnetic support is adjusted so that the magnetic head with respect to the magnetic tape. Means such as strengthening the hit have been tried. This requirement is that the magnetic head is likely to be contaminated, and the magnetic head is severely worn.

The present invention has been made against the background of such technical trends, and one of the constituent elements thereof is a specific ferromagnetic metal powder having a limited content of a trace amount of metal component. On the other hand, the present applicants have disclosed various inventions in which various trace components of the ferromagnetic metal powder are specified. For example,
JP-A-24032 discloses an invention for improving magnetic properties by suppressing the amount of alkaline earth metal in a raw metal compound of a ferromagnetic metal powder, and JP-A-52-97711.
The publication discloses a magnetic recording medium in which the amount of calcium ions in the magnetic material is reduced to suppress the formation of deposits at high humidity and to prevent dropout and head clogging. Further, Japanese Patent Laid-Open No. 56-101649 discloses a magnetic material which is excellent in aging stability especially under high humidity using a ferromagnetic metal powder whose rust resistance is improved by suppressing the elution amount of ferromagnetic metal into water. It is said that a recording medium will be provided. Japanese Unexamined Patent Publication No. 60-150228 discloses a magnetic recording medium having improved weather resistance by reducing the amount of water-soluble metal ions eluted from the surface of the magnetic layer. Japanese Patent Application Laid-Open No. 7-78331 discloses that the storage stability of a magnetic recording medium under high humidity is improved by specifying the contents of Na and alkaline earth metal elements in the magnetic material and the carbon number of fatty acid. There is.

Further, Japanese Patent Laid-Open No. 63-103424 discloses a magnetic recording medium having a structure in which a specific amount of a specific abrasive is used in an Al-containing ferromagnetic metal powder, and Japanese Patent Publication No. 6-1.
Japanese Patent No. 0360 discloses a magnetic recording medium having a configuration in which a polar group is defined as a binder resin in an Al-containing ferromagnetic metal powder, and that the output and running durability can be improved. . In addition, JP-A-6-215360
The publication discloses improving running durability by specifying the amounts of Al, rare earth elements, and other elements.

However, by simply combining these conventional techniques, high output of a high density recording magnetic recording medium, prevention of head clogging and head contamination, and prevention of calendar roll contamination are maintained while maintaining good electromagnetic conversion characteristics and storage stability. I couldn't find a condition to satisfy both.

[0012]

SUMMARY OF THE INVENTION Therefore, the object of the present invention is to provide a high output, less head contamination, head wear and clogging, and output reduction and storage due to repeated running,
It is an object of the present invention to provide a magnetic recording medium for high-density recording, in which the output is less decreased by storage and the roll contamination due to sticking of the magnetic layer in the calendering process is small.

[0013]

The above object of the present invention can be achieved by the following constitutions. (1) In a magnetic recording medium having at least one magnetic layer on a non-magnetic support, the uppermost magnetic layer has a major axis length of 0.04 to 0.12 μm and an acicular ratio of 3 to 10 is a magnetic layer mainly composed of a needle-shaped ferromagnetic metal powder and a binder resin, and the ferromagnetic metal powder has a Ca atom content of 5 × 10 ^{−4 to} 0 with respect to Fe atoms. .2 atom%, the content of alkali metal is 5 × 10 ^{−4 to} 0.2 atom%, and the content of Ni atom is 5 × 10 ^{−4 to} 0.4 atom%.
A magnetic recording medium characterized by the following. (2) The content of Mg atoms in the ferromagnetic metal powder is F
The magnetic recording medium as described in (1) above, wherein the content is 0.2 to 1.5 atom% with respect to e atoms. (3) A non-magnetic layer mainly composed of an inorganic non-magnetic powder and a binder resin is provided on a non-magnetic support, and at least one magnetic layer mainly composed of a ferromagnetic metal powder and a binder resin is formed on the non-magnetic layer. In the magnetic recording medium having the magnetic layer, the magnetic layer is mainly composed of acicular ferromagnetic metal powder having a major axis length of 0.04 to 0.12 μm and an acicular ratio of 3 to 10 and a binder resin. And the ferromagnetic metal powder is
The content of Ca atom is 5 × 10 ^{−4 to} 0.2 atom%, the content of alkali metal is 5 × 10 ^{−4 to} 0.2 atom%, and the content of Ni atom is 5 × 10 ^{−4 to} 0. A magnetic recording medium having a content of 4 atom% and a content of Mg atom of 0.1 to 2.0 atom%. (4) The coercive force Hc of the ferromagnetic metal powder is 1700 to 3
000 Oe, the saturation magnetization amount is 135 to 170 emu / mg, The magnetic recording medium as described in (1) above. (5) A fatty acid is contained in one of the coating layers on the magnetic layer side of the non-magnetic support, and the amount of fatty acid extracted from all the coating layers on the magnetic layer side is 1 to 50 mg / cm 3 per volume of the entire coating layer. ^3. The magnetic recording medium according to (1) above, which is ³ .

In the present invention, C contained in the ferromagnetic metal powder is used.
By defining the amounts of a, alkali metal and Ni, and specifying the major axis length and the needle-like ratio of the needle-shaped ferromagnetic metal powder, the output is high and head wear, head contamination and head clogging are reduced. In addition, the magnetic recording medium is a magnetic recording medium which is less likely to be deteriorated in output due to storage and storage, and which further satisfies all of the excellent characteristics that there is little stain on the calender roll due to sticking of the magnetic layer in the calendering process.

In the present invention, the major axis length and acicular ratio of the acicular ferromagnetic metal powder and the composition of the ferromagnetic powder are optimized so that head wear and head contamination do not occur, and particularly marked output The magnetic recording medium of the present invention has high characteristics, excellent electromagnetic conversion characteristics, and excellent characteristics that it is possible to prevent output reduction due to repeated running and output reduction due to storage and storage.

In the present invention, the coercive force Hc of the ferromagnetic metal powder is 1700 to 30000e and the saturation magnetization is 1
It is preferably 35 to 170 emu / mg. As a result, a high-output magnetic recording medium suitable for higher density recording can be obtained.

Further, the head burn-in stain (remarkably in a low humidity environment) during repeated running is an Fe atom containing a trace amount of contaminating elements from the analysis result of ESCA and the like, and since it is not in the form of a magnetic substance, A part was scraped off,
It is thought that it adhered. In addition, stains on the calender roll in contact with the magnetic layer are detected as Fe and N atoms by analysis of EDAX or the like, so that a part of the magnetic material is scraped off or used as a curing agent for the binder resin in the magnetic layer. It is considered that isocyanate or the like is attached.

In the present invention, the strength of the magnetic substance itself is enhanced by defining Ni atoms with respect to Fe atoms in the ferromagnetic metal powder. That is, by setting the content of Ni atoms to Fe atoms in the ferromagnetic metal powder to 5 × 10 ^{−4 to} 0.4 at%, preferably 5 × 10 ^{−4 to} 0.2 at%, Since it is possible to reduce the crystal structure of Fe-Ni or the like in the powder, increase the strength of the Fe crystal structure itself, and prevent the powder surface layer from being scraped, it is considered that the head contamination, head clogging, and calendar roll contamination can be prevented. To be

In the present invention, M is contained in the ferromagnetic metal powder.
It is preferable that g atoms are contained in an amount of 0.1 to 2.0 atomic% with respect to Fe atoms, more preferably 0.2 to 1.5 atomic% in Mg atoms, and particularly preferably 0.4 to 1.5 atomic%. Preferably there is. Mg has the effect of increasing the number of nucleation points during firing of the magnetic material, and the resulting ferromagnetic metal powder can be miniaturized. In the ferromagnetic metal powder of the present invention, it was particularly effective to adjust the major axis length of the ferromagnetic metal powder by adjusting the amount of Mg added. Further, since the surface of the ferromagnetic metal powder is hardened and the magnesium oxide formed is hard, it has excellent wear resistance to the head and can further effectively prevent the head from becoming dirty.

In the present invention, the ferromagnetic metal powder Ca
The atomic weight is 5 × 10 ^{−4 to} 0.2 atomic%, preferably 5 × 1.
0 ^{-4 to} 0.1 atomic% and an amount of alkali metal of 5 x 10 ^-4
Since the amount of the binder resin adsorbed on the ferromagnetic metal powder is increased and the adsorbed layer of the binder resin on the surface of the magnetic body is thickened, the magnetic body directly contacts the magnetic head. Can be prevented, and the burn-in stain on the head can be reduced. Further, since the strength of the magnetic layer is increased as the adsorbability of the binder resin to the ferromagnetic metal powder is increased, it is possible to prevent the occurrence of clogging and the like due to abrasion of the magnetic layer. It is most effective to define the amount of Ca and alkali metal, especially Na, but it is necessary to suppress other alkaline earth metals and alkali metal elements mixed as impurities during the preparation of the magnetic material, and the total amount of 1 atomic% It is preferable to suppress it to

In the present invention, it is preferable that the magnetic layer and / or the non-magnetic layer contain a fatty acid. By defining the Ca content and the alkali metal content of the ferromagnetic metal powder, it is possible to suppress the formation of salts of Ca and the alkali metal with the fatty acid, and it is possible to reduce the free fatty acid content. It is possible to suppress salt formation due to reaction with alkali metals and Ca, prevent head contamination, reduce head wear, and suppress output reduction. The amount of fatty acid used in the present invention is
When added to the magnetic layer, it is 0.2 to
5.0% by weight is preferable, and 0.5 to 2.0% by weight is particularly preferable.

The ferromagnetic metal powder used in the present invention preferably contains the following elements with respect to Fe atoms in the range shown below. 4 to 15 atomic% of Al atoms,
Rare earth element 0.1 to 10 atomic%, especially 1.0 to 3.0
Atomic%, Si atom 5 × 10 ^{−4 to} 1.5 atom%, especially 5
× 10 ^{-4 to} 0.1 atom%, Co atom to 5 to 35 atom%,
In particular, each range is 10 to 35 atomic%. The ferromagnetic metal powder-containing element has the following functions, and the optimum content can be determined to exert those functions.

Rare earth elements such as Al atoms and Y atoms have the function of increasing the strength of the ferromagnetic metal powder itself, are present in the surface layer of the ferromagnetic metal powder, and enter deeper from the surface layer.
The respective atoms are decreasing at almost the same ratio. Further, Si atoms are in a form existing in the surface layer more than Al atoms. Al atoms in the surface layer of the ferromagnetic metal powder combine with O atoms to form alumina, which is hard and has high polishing power. However, if the crystal bonding state between the inside of the ferromagnetic metal powder and the surface layer portion of Al atoms is weak, the hard surface layer portion will be scraped off. Therefore, in the present invention, by setting the content of the Ni atom to 5 × 10 ^{−4 to} 0.4 atom%, the crystal structure of Fe—Ni—Al or the like in the ferromagnetic metal powder is reduced to obtain the Fe crystal structure itself. Strength and Fe-Al
It is possible to increase the strength of the crystal structure such as, and prevent the surface layer of the ferromagnetic metal powder from being scraped.

When Co atoms are present, the strength of the crystal structure is increased, and the abrasion of the surface layer of the ferromagnetic metal powder can be further prevented. The addition of a rare earth element such as Si atom or Y atom has the function of adjusting the hardness of the surface layer of the ferromagnetic metal powder. That is, the polishing power can be lowered by increasing the ratio of Si atoms or rare earth elements to Al atoms, and by adjusting the content of these atoms, the durability of the tape can be ensured while suppressing head wear. Exert function. Further, since Si atoms in the ferromagnetic metal powder are on the surface layer portion of the ferromagnetic metal powder and are not hard as compared with Al atoms, they are easily scraped and suppress the curing reaction of the isocyanate in the binder resin. Have a function.

Therefore, when the amount of Si atoms increases, the curing reaction of isocyanate is suppressed, so that the surface layer portion of the magnetic layer is cohesively destroyed and scraped off, and head contamination occurs. In particular, it is remarkable when there is no thermotreatment (heating treatment for accelerating the curing of the binder resin after coating and drying the magnetic layer). For the above countermeasures, Al is used as a sintering inhibitor for ferromagnetic metal powder.
Rare earth elements such as Y and Y are used, and a small amount of Si atoms mixed in in the manufacturing process of the ferromagnetic metal powder are removed in the cleaning process by heating the cleaning water, adjusting the pH, etc. It is effective to reduce the Si atom content of the metal powder.

In the present invention, the use of the ferromagnetic metal powder having the above composition improves the adhesion rate of the binder resin to the ferromagnetic metal powder, so that a burn-in head can be obtained even if the amount of the binder resin in the magnetic layer is reduced. It is possible to produce a magnetic recording medium that does not cause stains or clogging due to insufficient strength of the magnetic layer and reduces stains on the calender roll in contact with the magnetic layer side. Further, by lowering the amount of the binder resin, the filling rate of the ferromagnetic metal powder is substantially improved, which can contribute to securing the output. In the present invention, the amount of the binder resin in the magnetic layer is preferably 12 to 28 parts by weight, more preferably 15 to 23 parts by weight, based on 100 parts by weight of the ferromagnetic metal powder.
Parts by weight. Here, the binder resin is meant to include a crosslinking agent.

Further, it is possible to strongly adsorb an organic phosphorus compound such as phenylphosphonic acid on the ferromagnetic metal powder or to use a binder resin having a specific polar group such as a vinyl chloride copolymer or urethane. The dispersibility of the magnetic metal powder is enhanced, and the above-mentioned effects are more remarkable. Furthermore, a wet simultaneous coating multilayer structure (upper magnetic material: ferromagnetic metal powder / lower magnetic material: γ-iron oxide, upper magnetic material: ferromagnetic metal powder /
The lower layer inorganic non-magnetic powder, etc.) tends to have a higher surface binder resin amount from the viewpoint of coating and drying conditions and liquid physical properties than a single-layer magnetic layer mainly composed of ferromagnetic metal powder. The effect of the invention becomes clearer. Further, even the fine particles of the ferromagnetic metal powder increase the amount of the binder resin in the surface layer of the magnetic layer, so that the effect becomes more remarkable. However, if there is a large amount of free binder resin that is not adsorbed on the ferromagnetic metal powder on the surface of the magnetic layer, it causes flow deformation of the binder resin during repeated running, or the binder resin adheres to the head etc. Since stains are generated, it is necessary to optimize the amount of binder resin added as described above.

As the method for producing the ferromagnetic metal powder of the present invention, conventionally known production methods can be applied, but alkali metal, C
It is necessary to control a and Ni so as to be in the above range. As the control means for the alkali metal and Ca, it is effective to insert a cleaning step in the manufacturing step of the ferromagnetic metal powder. That is, iron oxyhydroxide powder, iron oxide powder or metal powder is washed with water. In particular, trace elements tend to segregate on the surface of the particles as iron oxyhydroxide, iron oxide, and metal progress in the process, and therefore their removal becomes easy by washing. Washing can be carried out more efficiently by heating the washing water, adjusting the pH of the washing water, and selecting the acid and base to be added to the washing water. Also, it goes without saying that it is effective to reduce the impurity elements in the raw materials as much as possible.

The control means of Ni is Ni in each manufacturing process from the ferromagnetic metal powder raw material to the ferromagnetic metal powder.
Is added, and specifically, quantitative addition of Ni in the raw material of the ferromagnetic metal powder can be mentioned. Further, as means for incorporating Mg, Al, rare earth elements, Si, Co or other trace elements described below into the ferromagnetic metal powder, Mg or the like is used in each manufacturing process from the ferromagnetic metal powder raw material to the ferromagnetic metal powder. (Including the same treatment as the above-mentioned Ca and alkali metal removal treatment) or an addition treatment, and the addition treatment is specifically quantitative in the sintering prevention treatment of the ferromagnetic metal powder. It is possible to add Al, a rare earth element or the like to form an oxide of each element in the ferromagnetic metal powder. The amount of the trace element is 5 × 1 with respect to Fe.
It is 0 ^-4 to 1 atomic%. The trace elements include S and T
i, V, Cr, Cu, Mo, Rh, Pd, Ag, Sn,
Sb, Te, Ta, W, Re, Au, Hg, Pb, B
Examples thereof include i, P, Mn, Zn and B. The ferromagnetic metal powder used in the present invention may be previously treated with a dispersant, a lubricant, a surfactant, an antistatic agent, etc. described below before the dispersion.

Specifically, Japanese Patent Publication Nos. 44-14,090 and 4
5-18,372, Japanese Examined Sho 47-22,062, Japanese Examined Sho 47-22,513,
Japanese Patent Publication No. 46-28,466, Japanese Publication No. 46-38,755, Japanese Publication No. 47-4,2
86, Japanese Examined Sho 47-12,422, Japanese Examined Sho 47-17,284, Japanese Examined Sho
47-18,509, Japanese Patent Sho 47-18,573, Japanese Sho 39-10,307
No. 48-39,639, U.S. Patent No. 3,026,215, and No. 3,0
3,1341, 3,100,194, 3,242,005, 3,389,01
It is described in No. 4 etc.

The ferromagnetic metal powder may contain a small amount of hydroxide or oxide. As the ferromagnetic metal powder, a powder obtained by a known production method can be used, and the following method can be used. A method of reducing a complex organic acid salt (mainly oxalate) and a reducing gas such as hydrogen, or reducing Fe oxide with a reducing gas such as hydrogen to Fe or F
a method of obtaining e-Co particles or the like, a method of thermally decomposing a metal carbonyl compound, a method of adding a reducing agent such as sodium borohydride, hypophosphite or hydrazine to an aqueous solution of a ferromagnetic metal to reduce the metal, And evaporating in a low-pressure inert gas to obtain fine powder. The ferromagnetic metal powder thus obtained is subjected to a known gradual oxidation treatment,
That is, a method of immersing in an organic solvent and then drying, a method of immersing in an organic solvent and then feeding an oxygen-containing gas to form an oxide film on the surface and then drying, a partial pressure of oxygen gas and an inert gas without using an organic solvent. Any of the methods of adjusting and forming an oxide film on the surface can be used.

The average major axis length of the acicular ferromagnetic metal powder of the magnetic layer of the present invention is 0.04 to 0.12 μm, preferably 0.
06 to 0.10 μm, and in terms of specific surface area by BET method, it is 25 to 80 m ² / g, preferably 40 to 7
0 m ² / g. If it is less than 25 m ² / g, noise increases, and if it is more than 80 m ² / g, it is difficult to obtain surface properties, which is not preferable. The acicular ferromagnetic metal powder having a specific average major axis length and acicular ratio according to the present invention is obtained by adding a trace amount of a third component element such as Mg and Y, and appropriately adding the amount depending on the element species. By selecting, the formation of nuclei of the non-magnetic precursor is controlled, and ferromagnetic metal powders having various major axis lengths and acicular ratios are produced. The crystallite size of the ferromagnetic metal powder of the magnetic layer of the present invention is 100 to 450 angstroms, preferably 100 to 350 angstroms, and more preferably 100 to 250 angstroms. The saturation magnetization (σ _S ) is preferably 100 to 200 emu / g, more preferably 135 emu / g to 170 emu / g. The coercive force is preferably 1,700 to 3,000 Oe, more preferably 1,700 to 2700 Oe. Needle ratio is 3-1
It is 0, preferably 4 to 10. Moisture content is 0.0
It is preferable to set it to 1 to 2%. The water content is preferably optimized depending on the type of binder. Tap density is 0.2 ~
0.8 g / ml is preferable, and if it is more than 0.8 g / ml, oxidation easily proceeds in the consolidation process of the ferromagnetic metal powder, and sufficient σ _S
Will be difficult to obtain. If the tap density is less than 0.2 g / ml, the dispersion tends to be insufficient. The pH is preferably optimized by the combination with the binder used. Its range is from 4 to 12, preferably from 6 to 10.

The ferromagnetic metal powder used in the present invention preferably has few voids, and the value is 0 to 20% by volume, more preferably 0 to 5% by volume. The SFD is preferably 0.1 to 0.6, and the distribution of Hc is preferably small. For that purpose, there are methods such as improving the particle size distribution of goethite and preventing the sintering of γ-hematite. The amount of the lubricant such as fatty acid adsorbed on the ferromagnetic metal powder according to the present invention is usually 0.
5 mg / m ² or less, preferably 0.01 to 0.25 mg
/ M ² . In the present invention, even if the coating layer is a single magnetic layer, the coating layer has a multilayer structure, for example, from a plurality of layers including a magnetic layer and a non-magnetic layer (also referred to as a lower layer) provided between the magnetic layer and the non-magnetic support. You can make it. In the latter case, fatty acids can be contained in the non-magnetic layer. The magnetic layer and the non-magnetic layer may each be a multilayer. When the magnetic layer has a multilayer structure, the layer farthest from the non-magnetic support is called the uppermost layer (also called the upper magnetic layer), and the other layers are called the lower magnetic layer. This lower magnetic layer contains γ-FeOx (x = 1.33.
~ 1.5), Co-modified γ-FeOx (x = 1.33 ~
1.5), ferromagnetic metal powder or the like can be used. In the present invention, since the above-mentioned ferromagnetic metal powder is used, it is possible to specifically improve the adsorption amount of the binder resin, particularly the polar group-containing binder resin to the ferromagnetic metal powder, and to bond with the binder resin. Since the force can be improved, even if the amount of resin is lowered, a mechanically strong coating film is formed, which is effective for head wear. Based on the ferromagnetic metal powder, 5 to 15% by weight when a vinyl chloride resin is used, 2 to 10% by weight when a polyurethane resin is used, and 2 to 1% by weight of polyisocyanate.
It is in the range of 0% by weight, and it is preferable to use these in combination. In the present invention, when polyurethane is used, the glass transition temperature is −50 to 100 ° C., and the elongation at break is 1
0 to 2,000%, breaking stress 0.05 to 10 kg /
cm ² and the yield point are preferably 0.05 to 10 kg / cm ² .

The fatty acid used in the present invention has 8 to 2 carbon atoms.
4 monobasic fatty acids can be used, and monobasic fatty acids having 8 to 18 carbon atoms are preferable. Specific examples thereof include lauric acid, caprylic acid, capric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, linoleic acid, linolenic acid and elaidic acid. Next, the nonmagnetic layer provided between the magnetic layer and the nonmagnetic support will be described in detail. The inorganic non-magnetic powder used in the non-magnetic layer can be selected from inorganic compounds such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides and metal sulfides. Examples of the inorganic compound include α-alumina, β-alumina, γ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, silicon nitride, titanium carbide, and titanium oxide having an α conversion rate of 90 to 100%. , Silicon dioxide, tin oxide, magnesium oxide, tungsten oxide, zirconium oxide, boron nitride, zinc oxide, barium sulfate, molybdenum disulfide, etc. are used alone or in combination. Particularly preferred are titanium dioxide, zinc oxide, iron oxide and barium sulfate, and more preferred is titanium dioxide. Calcium carbonate is not preferable because it serves as a source of water-soluble metal ions.

The average particle size of these inorganic non-magnetic powders is 0.
The thickness is preferably 005 to 2 μm, but if necessary, inorganic non-magnetic powders having different average particle diameters may be combined, or a single inorganic non-magnetic powder may be used to broaden the particle diameter distribution to obtain the same effect. Particularly preferably, the average particle size of the inorganic non-magnetic powder is 0.01 μm to 0.2 μm. Tap density is 0.05 to 2 g / ml, preferably 0.2 to
It is 1.5 g / ml. The water content of the inorganic non-magnetic powder is 0.1 to 5% by weight, preferably 0.2 to 3% by weight. The specific surface area of the inorganic non-magnetic powder is 1 to 100 m ² /
g, preferably 5 to 50 m ² / g, more preferably 7 to
40 m ² / g. The crystallite size of the inorganic non-magnetic powder is preferably 0.01 μm to 2 μm. Oil absorption using DBP is 5-100ml / 100g, preferably 10-80ml / 100
g, more preferably 20 to 60 ml / 100 g. Specific gravity is 1
-12, preferably 3-6. The shape is acicular, spherical,
It may be a polyhedron or a plate.

The ignition loss of the inorganic nonmagnetic powder is preferably 0 to 20% by weight. The inorganic non-magnetic powder used in the present invention preferably has a Mohs hardness of 4 to 10. The roughness factor of the surface of these powders is 0.8 to 1.5.
Is preferable, and a more preferable roughness factor is 0.9.
１．２1.2. The amount of SA (stearic acid) adsorbed on the inorganic non-magnetic powder is 1 to 20 μmol / m ² , and more preferably 2 to
It is 15 μmol / m ² . 2 of inorganic non-magnetic powder of non-magnetic layer
Wetting heat to water at 5 ℃ is 200erg / cm ^{2 to} 600erg / cm ²
Is preferably within the range. Further, a solvent having a range of the heat of wetting can be used. 100-400 ° C
The suitable amount of water molecules on the surface is 1 to 10 / 100Å. The pH of the isoelectric point in water is preferably between 3 and 6.

Al ₂ O is formed on the surface of these inorganic non-magnetic powders.
Surface treatment with ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , Sb ₂ O ₃ , and ZnO is preferable. Al ₂ O ₃ and S are particularly preferable for dispersibility.
iO ₂ , TiO ₂ and ZrO ₂ are preferable, but Al ₂ O ₃ and Si are more preferable.
O ₂ and ZrO ₂ . These may be used in combination or may be used alone. Further, a co-precipitated surface treatment layer may be used according to the purpose, or a method of first treating with alumina and then treating the surface layer with silica, or vice versa, may be employed. Although the surface treatment layer may be a porous layer depending on the purpose, it is generally preferable that the surface treatment layer be homogeneous and dense.

Specific examples of the inorganic non-magnetic powder used in the non-magnetic layer of the present invention include Nanotite manufactured by Showa Denko, HIT-100, ZA-G1 manufactured by Sumitomo Chemical, DPN-250, DPN- manufactured by Toda Kogyo Co., Ltd. 250BX,
DPN-245, DPN-270BX, Ishihara Sangyo TTO-51B, TTO-55A, TTO-5
5B, TTO-55C, TTO-55S, TTO-55D, SN-100, E270, E271, Titanium Industry STT-4D, STT-30D, STT-30, STT-65C, TAKEA
MT-100S, MT-100T, MT-150W, MT-500B, MT-600B, MT-100F, MT
-500HD, Sakai Chemical FINEX-25, BF-1, BF-10, BF-20, ST-M, Dowa Mining DEFIC-Y, DEFIC-R, Nippon Aerosil AS2BM, TiO2
Examples include P25, Ube Industries 100A and 500A, titanium industry Y-LOP, and fired products thereof.

By mixing carbon black into the non-magnetic layer, Rs, which is a known effect, can be lowered. For this purpose, furnace for rubber, thermal for rubber, black for color, acetylene black and the like can be used.
The specific surface area of carbon black is 100 to 500 m ² /
g, preferably 150 to 400 m ² / g, DBP oil absorption is 20 to 400 ml / 100 g, preferably 30 to 200 ml / 10
It is 0g. The average particle size of carbon black is 5 mμ to 80
mμ, preferably 10 to 50 mμ, more preferably 1
It is 0 to 40 mμ. The pH of carbon black is 2-1
0, water content is 0.1-10%, tap density is 0.1-1
g / ml is preferred.

Specific examples of carbon black used in the present invention include BLACKPEAR manufactured by Cabot Corporation.
LS 2000, 1300, 1000, 900, 80
0,880,700, VULCAN XC-72, Mitsubishi Kasei Co., Ltd., # 3050B, 3150B, 3250.
B, # 3750B, # 3950B, # 950, # 650
B, # 970B, # 850B, MA-600, Columbia Carbon Co., CONDUCTEX SC, RAVE
N 8800,8000,7000,5750,5250,3500,2100,2000,1800,1
500,1255,1250, Ketjen Black EC manufactured by Akzo, etc. Carbon black may be used after being surface-treated with a dispersant or the like or grafted with a resin, or may be one obtained by partially graphitizing the surface. Further, the carbon black may be dispersed in a binder before adding it to the paint. These carbon blacks can be used in the range of 0 to 50% by weight based on the inorganic nonmagnetic powder, and in the range of 0 to 40% of the total weight of the nonmagnetic layer. These carbon blacks can be used alone or in combination.

The carbon black that can be used in the nonmagnetic layer in the present invention can be referred to, for example, "Carbon Black Handbook" (edited by Carbon Black Association). In addition, an organic powder can be added to the non-magnetic layer according to the purpose. For example, acrylic styrene-based resin powder, benzoguanamine resin powder, melamine-based resin powder, phthalocyanine-based pigment, but also polyolefin-based resin powder, polyester-based resin powder, polyamide-based resin powder, polyimide-based resin powder, polyfluorinated ethylene resin also Can be used. As the manufacturing method, those described in JP-A-62-18,564 and JP-A-60-255,827 can be used.

Binder, lubricant, dispersant for the non-magnetic layer,
Additives, solvents, dispersion methods and the like can be applied to those of the magnetic layer. In particular, with respect to the amount and type of binder, the amount and type of additive and dispersant added, known techniques relating to the magnetic layer described later can be applied.

Next, the contents other than the ferromagnetic metal powder and fatty acid used for the magnetic layer will be described in detail. As the binder used in the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof are used.
As a thermoplastic resin, the glass transition temperature is -100 to 1
50 ° C., number average molecular weight of 1,000 to 200,000,
It is preferably 10,000 to 100,000 and the degree of polymerization is about 50 to 1,000.

Examples of such binders are vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene, butadiene, ethylene, There are polymers or copolymers containing vinyl butyral, vinyl acetal, vinyl ether, etc. as constituent units, polyurethane resins, and various rubber resins. Further, as the thermosetting resin or the reactive resin, phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin,
Examples thereof include acrylic reaction resins, formaldehyde resins, silicone resins, epoxy-polyamide resins, polyester resin / isocyanate prepolymer mixtures, polyester polyol / polyisocyanate mixtures, polyurethane / polyisocyanate mixtures, and the like. These resins are described in detail in "Plastic Handbook" published by Asakura Shoten. It is also possible to use a known electron beam curable resin for the non-magnetic layer or the upper magnetic layer.

Examples of these binders and their production methods are given below.
Are described in detail in JP-A-62-256,219.
I have. The above resins can be used alone or in combination,
Preferred are vinyl chloride resin and vinyl acetate vinyl acetate.
Nyl resin, vinyl chloride, vinyl acetate, vinyl alcohol
Fat, vinyl chloride vinyl acetate maleic anhydride copolymer
A combination of at least one selected from the group and polyurethane resin
Or combined with polyisocyanate
There are things. The structure of polyurethane resin is Polyes
Ter polyurethane, polyether polyurethane, polyether
-Polyester polyester polyurethane, polycarbonate
Polyurethane, Polyurethane Polycarbonate Polyurethane
Polycaprolactone polyurethane polyolefin
Known materials such as urethane can be used. Shown here
Greater dispersibility and durability for all binders
To obtain, if necessary, -COOM, -SO_ThreeM,-
OSO_ThreeM, -P = O (OM ')_Two, -OP = O (O
M ')_Two, (M is hydrogen atom or alkali
Indicates a metal atom. M'is a hydrogen atom or an alkali metal atom
Alternatively, it represents a lower hydrocarbon group. ), -OH, -NR_Two,
-N⁺R_Three(R represents a hydrocarbon group having 1 to 12 carbon atoms
You. ), Epoxy group, -SH, -CN, sulfobetatai
, Carboxybetaine, phosphobetaine, etc., preferably
Is -COOM, -SO _ThreeM, -OSO_ThreeM, -P = O (O
M ')_TwoAt least one selected from
In addition reaction, preferably polyurethane resin and vinyl chloride type
It is preferable to use one introduced into at least one of the resins.
Good. The amount of such polar groups is 10^-8-10^-1Mol / g
And preferably 10^-6-10^-2Mol / g, more preferred
Ku 3 × 10^-Five~ 20 x 10^-FiveMol / g.

Specific examples of these binders used in the present invention include VAGH and V manufactured by Union Carbide.
YHH, VMCH, VAGF, VAGD, VROH, V
YES, VYNC, VMCC, XYHL, XYSG, P
KHH, PKHJ, PKHC, PKFE, manufactured by Nissin Chemical Industries, MPR-TA, MPR-TA5, MPR-TA
L, MPR-TSN, MPR-TMF, MPR-TS,
MPR-TM, MPR-TAO, manufactured by Denki Kagaku Co., Ltd. 1000
W, DX80, DX81, DX82, DX83, 100
FD, ZEON MR-104, MR-105,
MR110, MR100, 400X-110A, Nipporan N2301, N2302, N
2304, Pandex T-510 manufactured by Dainippon Ink and Chemicals, Inc.
5, T-R3080, T-5201, Burnock D-4
00, D-210-80, Crisbon 6109, 720
9. Byron UR8200, UR8300, manufactured by Toyobo Co., Ltd.
UR-8600, UR-5500, UR-4300, R
V530, RV280, FB-84, manufactured by Dainichiseika, Daiferamine 4020, 5020, 5100, 530
0, 9020, 9022, 7020, Mitsubishi Kasei Co., Ltd., M
X5004, Sanpre Chemical Co., Ltd. Samprene SP-150, T
Examples include IM-3003, TIM-3005, Saran F310, F210 manufactured by Asahi Kasei. MR-
104, MR110, UR8300, UR-8600,
UR-5500, UR-4300 and TIM-3005 are preferred.

The magnetic recording medium of the present invention includes the case where it is composed of two or more layers as described above. Therefore, the amount of binder, the amount of vinyl chloride resin, polyurethane resin, polyisocyanate, or other resin in the binder, the molecular weight of each resin forming the magnetic layer, the amount of polar groups, or the resins described above. It is of course possible to change the physical properties and the like of the non-magnetic layer and the magnetic layer as necessary, and known techniques relating to the multilayer magnetic layer can be applied. For example, when changing the amount of binder in the upper and lower layers, it is effective to increase the amount of binder in the upper magnetic layer in order to reduce scratches on the surface of the magnetic layer, and to improve the head touch to the head,
This is achieved by increasing the amount of binder in the non-magnetic layer other than the upper magnetic layer to give flexibility.

As the polyisocyanate used in the present invention, tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,
Isocyanates such as 5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate and triphenylmethane triisocyanate, products of these isocyanates and polyalcohols, and polyisocyanates produced by condensation of isocyanates are used. can do. Commercially available trade names of these isocyanates include Nippon Polyurethane Co., Ltd., Coronate L, Coronate HL, Coronate 2030, Coronate 2031 and Millionate M.
R, Millionate MTL, Takeda Yakuhin, Takenate D
-102, Takenate D-110N, Takenate D-2
00, Takenate D-202, Sumitomo Bayer Co., Ltd., Desmodur L, Desmodur IL, Desmodul N, Desmodul HL, and the like. These are used alone or by utilizing the difference in curing reactivity. It can be used as a non-magnetic layer and an upper magnetic layer in combination.

As the carbon black used in the present invention, those exemplified above for the non-magnetic layer can be applied to the magnetic layer. Before adding the carbon black to the magnetic paint, the carbon black may be dispersed in a binder in advance. These carbon blacks can be used alone or in combination. When carbon black is used, it is preferably used in an amount of 0.1 to 10% based on the ferromagnetic metal powder. Carbon black has functions such as antistaticity of the magnetic layer, reduction of friction coefficient, provision of light-shielding properties, and improvement of film strength, and these differ depending on the carbon black used. From the viewpoint of improving the film strength and reducing head wear, it is more preferable that the amount of carbon black added is 0.2 to 3% by weight based on the ferromagnetic powder. Therefore, these carbon blacks used in the present invention are different in type, amount, and combination in the upper magnetic layer and the non-magnetic layer, and the average particle diameter, oil absorption, electric conductivity,
Of course, it is possible to use differently according to the purpose based on the above-mentioned various properties such as pH. The carbon black that can be used in the magnetic layer of the present invention can be referred to, for example, “Carbon Black Handbook” (edited by Carbon Black Association).

As the raw material of the abrasive used in the magnetic layer of the present invention, the inorganic non-magnetic powder exemplified in the above-mentioned non-magnetic layer can be applied to the magnetic layer. It is needless to say that the abrasive used in the present invention can be selectively used depending on the purpose by changing the type, amount and combination of the non-magnetic layer, the lower magnetic layer and the upper magnetic layer. These abrasives may be dispersed in a binder in advance and then added to the magnetic paint. Examples of preferable abrasives include α-alumina, red iron oxide, chromium oxide, titanium oxide and the like. The shape of the abrasive is not particularly limited and may be spherical, needle-like, plate-like, etc., but is preferably spherical or plate-like. The abrasive present on the magnetic layer surface and the magnetic layer end surface of the magnetic recording medium of the present invention is 5
~ 130 pieces / 100 μm ² is preferable, 5 to 90 pieces / 1
00 μm ² is particularly preferable.

As the additives used in the present invention, those having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect, etc. are used. Molybdenum disulfide, tungsten graphite disulfide, boron nitride, graphite fluoride, silicone oil, silicone with polar groups, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol,
Fluorine-containing esters, polyolefins, polyglycols, alkyl phosphates and alkali metal salts thereof,
Alkyl sulfate and its alkali metal salt, polyphenyl ether, fluorine-containing alkyl sulfate and its alkali metal salt, monobasic fatty acid having 10 to 24 carbon atoms (may contain unsaturated bond or may be branched) ) Metal salt (Li, Na, K, Cu, etc.) or a monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent alcohol having 12 to 22 carbon atoms (including an unsaturated bond, It may be branched), an alkoxy alcohol having 12 to 22 carbon atoms, a monobasic fatty acid having 10 to 24 carbon atoms (which may contain an unsaturated bond, or may be branched) and 2 to 12 carbon atoms. Mono-fatty acid ester or di-alcohol consisting of any one of 12 monohydric, dihydric, trihydric, tetrahydric, pentahydric, and hexahydric alcohols (which may include unsaturated bonds or may be branched) Fatty acid esters or tri-fatty acid esters, fatty acid esters of monoalkyl ethers of alkylene oxide polymers, fatty acid amides having 8 to 22 carbon atoms, aliphatic amine having 8 to 22 carbon atoms, or the like can be used.

Specific examples thereof include butyl stearate, octyl stearate, amyl stearate, isooctyl stearate, octyl myristate, butoxyethyl stearate, anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydro. Examples include sorbitan tristearate, oleyl alcohol, and lauryl alcohol. Also, nonionic surfactants such as alkylene oxides, glycerin, glycidol, alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphonium or sulfoniums, etc. Cationic surfactants, carboxylic acids, sulfonic acids, phosphoric acids, sulfate groups, phosphate groups, anionic surfactants containing acidic groups such as amino acids, aminosulfonic acids, sulfuric acid or phosphates of amino alcohols, An amphoteric surfactant such as an alkylbedine type can also be used. These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents and the like are not necessarily 100% pure, and may contain impurities such as isomers, unreacted products, by-products, decomposed products and oxides in addition to the main components. These impurities are preferably 0 to 30%, more preferably 0 to 10%.
It is.

The types and amounts of these lubricants and surfactants used in the present invention can be properly selected in the non-magnetic layer and the magnetic layer. For example, fatty acids with different melting points in the non-magnetic layer and magnetic layer are used to control bleeding to the surface, esters with different boiling points and polarities are used to control bleeding to the surface, and the amount of surfactant is adjusted. By doing so, it is considered that the stability of the coating is improved, the amount of the lubricant added is increased in the non-magnetic layer, and the lubricating effect is improved. Of course, the present invention is not limited to the examples shown here.

All or a part of the additives used in the present invention may be added in any step of the magnetic coating production, for example, in the case of mixing with a ferromagnetic metal powder before the kneading step, a ferromagnetic metal powder is used. It may be added in the kneading step of the metal powder, the binder and the solvent, in the dispersing step, after the dispersing, or just before the coating.
In some cases, the purpose may be achieved by applying a part or all of the additives simultaneously or sequentially after applying the magnetic layer according to the purpose. Depending on the purpose, a lubricant may be applied to the surface of the magnetic layer after calendering or after the slit is completed.

The organic solvent used in the present invention is any ratio of ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, tetrahydrofuran, methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol. , Alcohols such as methylcyclohexanol, esters such as methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycol acetate, glycol dimethyl ether, glycol monoethyl ether, dioxane, and other glycol ethers, benzene, etc. Aromatic hydrocarbons such as toluene, xylene, cresol, chlorobenzene, methylene chloride, ethylene chloride, carbon tetrachloride, chlorine Chloroform, ethylene chlorohydrin, dichlorobenzene, chlorinated hydrocarbons and the like, N,
Those such as N-dimethylformamide and hexane can be used. These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted substances, by-products, decomposition products, oxides, and water in addition to the main components. The content of these impurities is preferably 0 to 30%, more preferably 0 to 10%.

The organic solvent used in the present invention is preferably the same type in the magnetic layer and the non-magnetic layer. The amount added may be changed. A solvent having a high surface tension (cyclohexane, dioxane, etc.) can be used for the nonmagnetic layer to improve the stability of coating. Specifically, it is important that the arithmetic mean value of the solvent composition of the upper magnetic layer does not fall below the arithmetic mean value of the solvent composition of the non-magnetic layer. In order to improve the dispersibility, it is preferable that the polarity is strong to some extent, and it is preferable that the solvent composition contains a solvent having a dielectric constant of 15 to 25 in an amount of 50 to 80%. Further, the dissolution parameter is preferably from 8 to 11.

The thickness of the magnetic recording medium of the present invention is such that the non-magnetic support has a thickness of 1 to 20 μm, and is particularly effective when a thin non-magnetic support having a thickness of 1 to 10 μm is used. The thickness of the single magnetic layer or the total thickness of the upper magnetic layer and the nonmagnetic layer is 1/100 to 2 times the thickness of the nonmagnetic support. In the case of a single magnetic layer, its thickness is usually 0.7.
~ 4.0 [mu] m, preferably 1.5-3.5 [mu] m,
In the case of the upper magnetic layer and the non-magnetic layer, the thickness of the upper magnetic layer is
Usually 0.1 to 1.5 μm, preferably 0.1 to 0.5
The thickness of the non-magnetic layer is usually 0.8 to 3.5 μm.
m, preferably 1.2 to 3.0 μm. An adhesive layer for improving adhesion is provided between the non-magnetic support and the non-magnetic layer. The thickness of the adhesive layer is 0.005 to 0.5 μm, preferably 0.02 to 0.3 μm. Further, a back coat layer may be provided on the side of the non-magnetic support opposite to the side of the magnetic layer. This thickness is 0.1 to 2 μm, preferably 0.3 to
It is 1.0 μm. Known adhesive layers and back coat layers can be used. The total thickness of the magnetic recording medium, including the thickness of the adhesive layer and the back coat layer, is usually 5 to
The range is 25 μm, preferably 5 to 20 μm.

As the non-magnetic support used in the present invention, known films such as biaxially stretched polyethylene terephthalate, polyethylene naphthalate, polyamide, polyimide, polyamide imide, aromatic polyamide, polybenz oxidazole and the like can be used. . In particular, a non-magnetic support using polyethylene terephthalate, polyethylene naphthalate, or aramid resin is preferable. The micro-Vickers hardness of the non-magnetic support is preferably 75 to 100 kg / mm ^2, and can be adjusted by adjusting the heating conditions, relaxation conditions, stretching conditions, etc. during film formation and selecting the materials. . These non-magnetic supports may be previously subjected to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment, and the like.

The non-magnetic support of the present invention has a center line average surface roughness of 0.001 to 0.03 μm, preferably 0.001.
To 0.02 μm, more preferably 0.001 to 0.0
It is 1 μm. Further, it is preferable that these non-magnetic supports have not only a small center line average surface roughness but also no coarse protrusions of 1 μm or more. The surface roughness shape can be freely controlled by the size and amount of the filler added to the non-magnetic support as needed. Examples of these fillers include Al, Ca, Si,
In addition to crystalline or amorphous oxides and carbonates such as Ti, organic fine powders such as acrylic and melamine-based powders can be used.

The F-5 value in the tape running direction of the non-magnetic support used in the present invention is preferably 10 to 50 Kg / mm.
^2. The F-5 value in the tape width direction is preferably 10 to 30K.
g / mm ² , and the F-5 value in the longitudinal direction of the tape is generally higher than the F-5 value in the tape width direction. However, especially when the strength in the width direction needs to be increased, Not. The heat shrinkage rate of the non-magnetic support in the tape running direction and width direction at 100 ° C. for 30 minutes is preferably 0 to 3.
%, More preferably 0 to 1.5%, the heat shrinkage at 80 ° C. for 30 minutes is preferably 0 to 1%, more preferably 0.
~ 0.5%. Breaking strength is 5 to 100K in both directions
The g / mm ² and the elastic modulus are preferably 100 to 2,000 Kg / mm ² .

The step of producing the magnetic coating material for the magnetic recording medium of the present invention comprises at least a kneading step, a dispersing step, and a mixing step provided before and after these steps, if necessary. Each step may be divided into two or more steps. Ferromagnetic metal powder, binder, carbon black, abrasive, antistatic agent, lubricant used in the present invention,
All raw materials such as a solvent may be added at the beginning or during any step. Further, individual raw materials may be added in two or more steps in a divided manner. For example, polyurethane may be divided and supplied in a kneading step, a dispersing step, and a mixing step for adjusting the viscosity after dispersion. In order to achieve the object of the present invention, it is needless to say that conventionally known manufacturing techniques can be used as a part of the steps, but those having a strong kneading force such as a continuous kneader or a pressure kneader in the kneading step. It is preferable to obtain high Br of the magnetic recording medium by using. When a continuous kneader or a pressure kneader is used, all or a part of the ferromagnetic metal powder and the binder (however, 30% or more of the total binder is preferable) and the range of 15 to 500 parts per 100 parts of the ferromagnetic metal powder. Is kneaded. Details of the kneading treatment are described in JP-A-1-106,338 and JP-A-64-79,274.
No. Further, when adjusting the non-magnetic layer liquid, it is desirable to use a dispersion medium having a high specific gravity, and zirconia beads are suitable.

The following constitution can be proposed as an example of an apparatus and method for coating a magnetic recording medium having a multilayer constitution as in the present invention. 1, the lower layer is first coated by gravure coating, roll coating, blade coating, extrusion coating equipment, etc. that are commonly used for coating magnetic paint, and while the lower layer is in a wet state, Japanese Patent Publication No. 1-46,186 Kaisho 60-238,179,
The upper magnetic layer is coated by the support pressure type extrusion coating apparatus disclosed in JP-A-2-265672. 2, JP-A-63-88,080, JP-A-2-17,971, and JP-A-2-26
The upper and lower layers are coated almost simultaneously by one coating head having two slits for passing the coating liquid as disclosed in Japanese Patent No. 5,672. 3. The upper and lower layers are coated almost simultaneously by the extrusion coating apparatus with a backup roll disclosed in Japanese Patent Laid-Open No. 2-174965. In order to prevent the deterioration of the electromagnetic conversion characteristics of the magnetic recording medium due to the aggregation of the ferromagnetic metal powder, the inside of the coating head is coated by the method disclosed in JP-A-62-95,174 or 1-236,968. It is desirable to apply shear to the coating solution of. Further, regarding the viscosity of the coating liquid, JP-A-3-8,
It is preferable to satisfy the numerical range disclosed in No. 471.

In order to obtain the magnetic recording medium of the present invention, it is necessary to perform strong orientation. It is preferable to use a solenoid of 1,000 G or more and a cobalt magnet of 2,000 G or more in the same polarity facing each other, and to provide an appropriate drying step before orientation so that the orientation after drying is the highest. preferable. Further, when the present invention is applied to a disk medium, an orientation method that randomizes the orientation is rather required. Further, when there are a plurality of magnetic layers, the orientation direction of each is changed, for example, not only the in-plane direction but also the vertical direction,
It can also be oriented in the width direction.

Further, as a calendering roll, various metal rolls and heat-resistant plastic rolls such as epoxy, polyimide, polyamide, polyimide amide are used. In the present invention, it is particularly preferable that the treatment is carried out by metal rolls. The treatment temperature is preferably 70 to 150 ° C, more preferably 80 to 150 ° C. The linear pressure is preferably 200 to 500 Kg / cm, more preferably 30.
It is 0 to 400 Kg / cm.

The friction coefficient of the magnetic layer surface of the magnetic recording medium of the present invention and the surface opposite thereto to SUS420J is preferably 0.1 to 0.5, more preferably 0.15 to 0.3, and the surface resistivity is preferably 10 ⁴ to. 10 ¹² ohm / sq, the elastic modulus at 0.5% elongation of the magnetic layer is preferably 100 to 2,000 Kg / mm ^{2 in} the running direction and the width direction, and the breaking strength is preferably 1 to 30 Kg / cm ² , magnetic recording. The elastic modulus of the medium is preferably 100 to 1,500 in both the running direction and the width direction.
Kg / mm ² , residual elongation is preferably 0-0.5%, 1
The heat shrinkage at any temperature below 00 ° C is preferably 0
˜1%, more preferably 0 to 0.5%, most preferably 0 to 0.1%. Glass transition temperature of magnetic layer (1
(Maximum loss elastic modulus in dynamic viscoelasticity measurement measured at 10 Hz)
Is preferably 50 ° C. or more and 120 ° C. or less, and that of the nonmagnetic layer is preferably 0 ° C. to 100 ° C. Loss elastic modulus is 1 × 10 ⁸
The loss tangent is preferably in the range of 8 × 10 ⁹ dyne / cm ² , and the loss tangent is preferably 0-0.2. If the loss tangent is too large, adhesion failure is likely to occur.

The residual solvent contained in the magnetic layer is preferably 0 to 100 mg / m ² , more preferably 0 to 10 mg.
/ M ² , and the residual solvent contained in the upper magnetic layer is preferably smaller than the residual solvent contained in the non-magnetic layer. The porosity of the magnetic layer is preferably 0 in both the non-magnetic layer and the magnetic layer.
-30% by volume, more preferably 0-20% by volume. The porosity is preferably small in order to achieve high output, but it may be better to secure a certain value depending on the purpose. For example, in a magnetic recording medium for data recording in which repetitive use is emphasized, a higher porosity is often preferable in running durability.

The magnetic characteristic of the magnetic recording medium of the present invention is the magnetic field 5
When measured with KOe, the squareness ratio in the tape running direction is 0.
70 to 1.00, preferably 0.80 to 1.00
And more preferably 0.90 to 1.00.
The squareness ratio in the two directions perpendicular to the tape running direction is preferably 80% or less of the squareness ratio in the running direction. The SFD of the magnetic layer is preferably 0.1 to 0.6.

The center line surface roughness Ra of the magnetic layer is 1 nm to 1
0 nm is preferable, but the value should be appropriately set depending on the purpose. Ra is preferably as small as possible in order to improve electromagnetic conversion characteristics, but is preferably as large as it is in order to improve running durability. The RMS surface roughness RRMS determined by AFM evaluation is preferably in the range of 2 nm to 15 nm.

The magnetic recording medium of the present invention can have a non-magnetic layer and an upper magnetic layer, but it is easily presumed that the physical properties of the non-magnetic layer and the magnetic layer can be changed according to the purpose. That is. For example, the elastic modulus of the magnetic layer is increased to improve running durability, and at the same time, the elastic modulus of the non-magnetic layer is made lower than that of the magnetic layer to improve the contact of the magnetic recording medium with the head.

[0070]

Next, the present invention will be described in detail with reference to examples and comparative examples of the present invention. In the examples, "parts" indicates "parts by weight".

Examples 1 to 4 and Comparative Examples 1 to 8 Nonmagnetic Layer (Nonmagnetic) Inorganic Nonmagnetic Powder TiO ₂ Crystalline Rutile 85 parts Average Primary Particle Diameter 0.035 μm Specific Surface Area by BET Method 40 m ² / g pH 7 0.0 TiO ₂ content 90% or more DBP oil absorption 27-38 g / 100 g, surface treatment agent Al ₂ O ₃ carbon black 15 parts Average primary particle size 16 mμ DBP oil absorption 80 ml / 100 g pH 8.0 BET specific surface area 250 m ² / g Volatile content 1.5% Vinyl chloride copolymer 14 parts MR110 SO ₃ Na, manufactured by Nippon Zeon Co., containing epoxy group Polymerization degree 300 Polyester polyurethane resin 5 parts Neopentyl glycol / caprolactone polyol / MDI = 0. 9 / 2.6 / 1-SO ₃ Na 1 × 10 ^-4 eq / g content Butyl stearate 1 part Stearic acid 1 part Methyl ethyl ketone 150 parts Cyclohexano 50 copies

Magnetic layer (upper magnetic layer) Ferromagnetic metal powder Composition: described in Table-1 100 parts Vinyl chloride copolymer 13 parts Zeon Corporation “MR110” SO ₃ Na-containing, epoxy group-containing Polymerization degree 300 Polyester polyurethane resin 5 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group 1 × 10 ^-4 eq / g content α-Al ₂ O ₃ (average particle size 0.23 μm ) 12.5 parts Carbon black (average particle size 0.10 μm) 0.5 part Butyl stearate 1.0 part Stearic acid 0.5 part Methyl ethyl ketone 150 parts Cyclohexanone 50 parts

Each component of each of the above coating materials was kneaded with a continuous kneader and then dispersed using a sand mill. To the obtained dispersion liquid, 5.5 parts of polyisocyanate (Coronate L manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to the coating liquid of the non-magnetic layer, 5 parts to the coating liquid of the upper magnetic layer, and butyl acetate was added to each. 40 parts was added and the mixture was filtered using a filter having an average pore size of 1 μm to prepare coating solutions for forming the non-magnetic layer and the magnetic layer, respectively. The resulting non-magnetic layer coating solution was applied with a center line of 7 μm so that the thickness after drying was 2.7 μm and immediately after that the thickness of the magnetic layer was 0.3 μm. Simultaneous multilayer coating is performed on the above-mentioned non-magnetic support having a surface roughness of 0.01 μm, and while both layers are still in a wet state, a cobalt magnet having a magnetic force of 3000 G and a solenoid having a magnetic force of 1500 G are used for orientation and drying. Then, using a 7-stage calender consisting of only metal rolls, the temperature was 90 ° C, and the linear pressure was 300 Kg / cm.
It was processed at m / min. and slit into a width of 8 mm to produce an 8 mm video tape.

[0074]

[Table 1]

[0075]

[Table 2]

[0076]

[Table 3]

Examples 5 to 7 and Comparative Examples 9 to 15 An upper layer prepared in the same manner as in Example 1 except that the ferromagnetic metal powders shown in Table 2 below were used in the upper layer coating solution described in Example 1. 8 according to Table 2 according to Example 1 except that only the magnetic layer coating material was applied to a single layer having a thickness of 2.4 μm.
mm video tape manufactured.

[0078]

[Table 4]

[0079]

[Table 5]

[0080]

[Table 6]

Each sample of the above obtained 8 mm video tape (Examples 1 to 7 and Comparative Examples 1 to 15) was evaluated as follows. Evaluation method <Method of measuring thickness of magnetic layer> Non-magnetic layer + upper magnetic layer Cut to a thickness of about 0.1 μm with a diamond cutter over the longitudinal direction of the magnetic recording medium, and magnify it with a transmission electron microscope at a magnification of 30,000 times. Observed and photographed. The print size of the photo is A4 size. After that, the interface was visually judged by paying attention to the shape difference between the ferromagnetic metal powder and the inorganic non-magnetic powder in the magnetic layer and the non-magnetic layer, and the surface of the magnetic layer was also black. Thereafter, the interval between the bordered lines was measured by an image processing apparatus IBAS2 manufactured by Zeiss. The length of the sample photograph was over a range of 21 cm, and measurement was performed by taking measurement points. The simple average value of the measured values at that time was defined as the thickness of the magnetic layer. In the case of a single layer The magnetic layer was peeled off from the non-magnetic support and the thickness was measured.

<Magnetic Characteristics Hc, Br, Squareness Ratio> Using a vibrating sample type magnetometer (manufactured by Toei Industry Co., Ltd.), measurement was performed at Hm of 10 kOe.

<Average Particle Diameter of Ferromagnetic Metal Powder and Inorganic Non-Magnetic Powder> A method of taking a transmission electron microscope photograph and directly reading the minor axis diameter and the major axis diameter of the ferromagnetic metal powder from the photograph and image analysis. The average particle size was determined by appropriately using a method of tracing and reading a transmission type micrograph with an apparatus Carl Zeiss IBASS1.

<Ferromagnetic metal powder crystallite size> It was determined from the half-width broadening of the diffraction lines of the (1,1,0) plane and the (2,2,0) plane by X-ray diffraction.

<Metal component in ferromagnetic metal powder> 5 g of a ferromagnetic metal powder sample was dissolved in 6N HCl, and the dissolved metal was analyzed by an atomic absorption method to determine the atomic% with respect to Fe.

[Head wear (μm)] Sony EVO-
Using a deck of 9500, the tape was made to run for 120 minutes in an atmosphere of 5 ° C. and a relative humidity of 80%, and the head projection change before and after the running was changed by Union His.
It was measured by an omet optical microscope.

[Head dirt] <23 ° C., relative humidity 10%, output reduction after 10 passes (d
B)> In the measurement of the above-mentioned reproduction output, a tape having a length of 120 minutes was repeatedly used in an atmosphere of 23 ° C. and a relative humidity of 10%.
The output reduction after running on a pass was measured.

<Head Contamination> The head contamination at the time of the measurement of <23 ° C., relative humidity 10%, output decrease (dB) after 10 passes> was evaluated. The surface of the magnetic head was observed, and the presence or absence of dirt was observed with a Machida Borescope. ○: No stain, △: No stain was observed on the sliding surface, but deposits were observed on the shoulders, ×: There were deposits on the sliding surface.

<40 ° C., 20% relative humidity, output reduction after 10 passes (dB)> In the measurement of the above reproduction output, 40
The decrease in output was measured after the tape having a length of 120 minutes was repeatedly run for 10 passes in an atmosphere of ° C and a relative humidity of 20%. <Head dirt> Above <40 ° C, relative humidity 20%, 10
The head stain at the time of measurement of output reduction (dB) after passing> was evaluated. The evaluation method is the same as above.

<Glass bulb stain> 23 ° C., relative humidity 10%
Or, in an atmosphere of 40 ° C. and a relative humidity of 20%, a load of 30 g is applied to a 1/4 inch glass ball, and 2 is applied on the magnetic layer.
It was reciprocated 10 times at a distance of 0 mm, and by contact with the magnetic layer, the ratio of the area occupied by the magnetic layer on the abraded glass spherical surface was determined. The evaluation criteria are as follows. None ... Magnetic layer adhered small ... The area where the magnetic layer adheres is 1/5 or less of the worn glass sphere area. Medium: A state in which the same ratio is in the range of 1/5 to 1/2. Large ... A state in which the ratio is 1/2 or more.

[Calendar Staining] The change in lightness index (ΔL) of a colorimeter (GR-200) manufactured by Minolta Co., Ltd. was measured after calendering 10,000 m of the magnetic recording medium. [Clogging] 1 for Sony, EV-C45, 8 decks
After recording the 20-length tape, the tape was run for 10 passes, and the number of times that the RF output reduction dropped by 3 dB within 30 seconds was counted. ○: within 5 times, Δ: less than 10 times, ×: 10 times or more or 3
If the output drops for 0 seconds or more

[Reproduction output of 7 MHz] A 7 MHz signal was recorded using a "FUJIX8" 8 mm video deck manufactured by Fuji Photo Film Co., Ltd., and the reproduction output of the 7 MHz signal when this signal was reproduced was measured with an oscilloscope. The reference is 8 mm tape SAG, P6-120 manufactured by Fuji Photo Film. The reproduction output before storage is preferably 5 dB or more. [High temperature storability] <Output decrease (dB) during high temperature storage> 60 ° C, 90%
The reproduction output after storage for 1 week at RH was measured in the same manner as the reproduction output at 7 MHz, and its decrease was determined.

The results of evaluation of each sample as described above are shown in Tables 1 and 2 above. In Table-1 and Table-2,
In B / M and B / F, B represents a binder resin, M represents a ferromagnetic metal powder, and F represents an inorganic non-magnetic powder + carbon black. The B binder resin of B / M contains a curing agent.

As shown in Tables 1 and 2 above, the magnetic recording medium of the present invention has a remarkably high reproduction output, a low output reduction after repeated running, a reduction in output during high temperature storage is prevented, and There is no adhesiveness, it is possible to reduce head dirt, prevent clogging, and prevent calendar dirt, but in the comparative example, the electromagnetic conversion characteristics are inferior to those of the present invention, and the adhesion to glass, head dirt. ,
It can be seen that at least one of clogging and calendar stain is not improved.

[0095]

The magnetic recording medium of the present invention has a high output and a low output drop after repeated running, prevents output drop during high temperature storage, has no adhesion to glass, and suppresses head wear. It is possible to reduce stains, prevent clogging, and prevent calendar stains.

Claims (3)

[Claims] 1. In a magnetic recording medium having at least one magnetic layer on a non-magnetic support, the uppermost magnetic layer has a major axis length of 0.04 to 0.12 μm and is needle-shaped. A magnetic layer mainly composed of a needle-like ferromagnetic metal powder having a ratio of 3 to 10 and a binder resin, wherein the ferromagnetic metal powder is F
The content of Ca atom is 5 × 10 ^{−4 to} 0.
2 atomic%, content of alkali metal is 5 × 10 ^{−4 to} 0.2
A magnetic recording medium characterized by having an atomic% and a Ni atom content of 5 × 10 ^{−4 to} 0.4 atomic%. 2. The magnetic recording medium according to claim 1, wherein the content of Mg atoms in the ferromagnetic metal powder is 0.1 to 2.0 atom% with respect to Fe atoms. 3. A non-magnetic layer comprising an inorganic non-magnetic powder and a binder resin as a main component on a non-magnetic support, and at least one magnetic layer mainly comprising a ferromagnetic metal powder and a binder resin thereon. In the magnetic recording medium having a layer, the magnetic layer has a major axis length of 0.04 to 0.12 μm and an acicular ratio of 3-1.
A needle-like ferromagnetic metal powder of 0 and a magnetic layer mainly composed of a binder resin, wherein the ferromagnetic metal powder has a Ca atom content of 5 × 10 ^{−4 to} 0.2 with respect to Fe atoms. Atomic%, content of alkali metal 5 × 10 ^{−4 to} 0.2 atomic%, Ni
A magnetic recording medium having an atomic content of 5 × 10 ^{−4 to} 0.4 atomic% and an Mg atomic content of 0.1 to 2.0 atomic%.