JPS60195729A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve particularly the sliding characteristic of a magnetic layer among other physical characteristics and to obtain the titled coating-type magnetic recording medium by incorporating a specified organic molybdenum compd. into a magnetic layer obtained by dispersing ferromagnetic power in a binder. CONSTITUTION:A magnetic paint is obtained by dissolving molybdenum dialkyl dithiophosphate shown by the formula (R is 1-20C alkyl), mixing ferromagnetic metallic powder or the powder of a ferromagnetic metallic oxide, etc. into said soln., and adding, if necessary, the particles of an abrasive such as Al2O3, Cr2 O3, and SiC having >=5Mohs hardness. The paint is coated on a nonmagnetic body which is oriented, dried, and then calendered to form a magnetic layer having a smooth surface. The magnetic powder can also be pretreated in a soln. of the organic molybdenum compd., filtered, dried, and then dispersed in the soln. of the binder. The organic molybdenum compd. is strongly adsorbed by the ferromagnetic powder and the abrasive due to the presence of S in the organic molybdenum compd. in this way, and the sliding characteristic is particularly improved. The baking on a magnetic head is also prevented, and the magnetic medium having excellent characteristics such as stillness at low temps. is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the improvement of magnetic recording media such as so-called coated magnetic tapes and magnetic sheets that use ferromagnetic powder as a magnetic material, and particularly relates to improvements in the physical properties of the magnetic layer, In particular, it relates to a coated magnetic recording medium with improved sliding characteristics.

11. Conventionally, magnetic powder is coated on a non-magnetic support made of a film or sheet of polyethylene terephthalate, cellulose triacetate, polycarbonate, polyacetate, polyvinyl chloride, etc., and a vinyl chloride-vinyl acetate copolymer,
Nitrocellulose is a combination of vinyl chloride, vinyl acetate, and malein.

Coated magnetic recording media are widely used, which are made by dispersing the magnetic recording medium in a binder such as polyester resin, epoxy resin, or polyester resin and then coating it. Generally, oxide magnetic powder such as γ-Fe20g is used as magnetic powder, but in recent years, mainly for the purpose of improving recording density,
Instead of oxide magnetic powders, ferromagnetic metal powders are also being used.

Typical applications of these coating-type magnetic recording media include audio tapes, video tapes, etc., and the characteristics required for video tapes in particular have become more severe as video decks have progressed and become more widespread. Specifically, the magnetic layer is required to have severe durability for special photography such as still and picture search, or for repeated recording and reproduction of the same tape. Furthermore, from the viewpoint of electromagnetic conversion characteristics, higher density is also required by narrowing the track width.

As mentioned earlier, in response to the demand for higher density recording,
Ferromagnetic metal powders made of iron, nickel, cobalt, etc. or alloys containing these as main components, which have high residual magnetic flux density (Br) and coercive force (He), are now being used. Although these ferromagnetic metal powders have excellent magnetic properties, they also have a large coercive force. Therefore, in order to record on a metal powder-coated magnetic recording medium coated with these ferromagnetic metal powders, a soft magnetic material with a high saturation magnetic flux density is required. It is necessary to use a magnetic head made of material. Examples of such magnetic head materials include alloy-based magnetic materials such as sendust, but when recording and reproducing a metal powder-coated recording medium using such an alloy magnetic head, the head core slides. Burn-in development may occur on the surface. Although the mechanism of this burn-in is not necessarily clear, once it occurs, it causes spacing loss, which causes a large loss, especially in high-density recording with a short recording wavelength.

In order to improve the sliding characteristics of the magnetic layer, including improving the durability of the magnetic layer and preventing seizure on the sliding surface of the helad core, as described above, 1. Adding an abrasive or lubricant to the magnetic layer However, satisfactory results have not always been obtained.In other words, if a large amount of an inorganic material such as Cr20B or Al2O, which has a high Mohs hardness, is added to the magnetic layer as an abrasive, its effect will The durability of the magnetic layer can be improved and seizure can be prevented. However, in this case, even though the sliding properties are improved, the reduction in surface smoothness of the magnetic layer due to the addition of these abrasive powders cannot itself be ignored as a cause of gap loss in high-density recording.
Furthermore, since the amount of wear on the head increases, even if an abrasive is added, it should be kept to a small amount. On the other hand, adding lubricants such as higher fatty acids or their esters, modified silicones, and paraffin wax has some effect on preventing seizure, but these lubricants have a relatively low molecular weight and do not coat the magnetic layer. It also has a large plasticizing effect, and if it is added to the extent that it exhibits a sufficient effect of improving sliding properties, problems will arise in terms of the durability of the magnetic layer.

In view of the above-mentioned circumstances, the main object of the present invention is to provide a magnetic layer with improved sliding properties while maintaining good physical properties of the magnetic layer in a coated magnetic recording medium. The goal is to provide recording media.

LLΩJJ According to the research conducted by the present inventors, it has been found that adding an organic molybdenum compound having a specific structure to a magnetic layer containing ferromagnetic powder is extremely effective in achieving the above objective. The magnetic recording medium of the present invention is based on such findings, and more specifically, the magnetic recording medium of the present invention is a magnetic recording medium in which a magnetic layer formed by dispersing ferromagnetic powder in a binder is formed on a non-magnetic support. The medium is characterized in that the magnetic layer contains an organic molybdenum compound represented by the general formula (where R is alkyl having 1 to 20 carbon atoms).

The above-mentioned organic molybdenum compound itself has traditionally been added as an extreme pressure agent to machine oils such as gear oil, cutting oil, and engine oil to strengthen the oil film strength. It was discovered for the first time by the present inventors that it exerts an excellent effect when added to the liquid. The reason why the desired effect is obtained by blending the organic molybdenum compound is not necessarily clear, but the bacteria in the organic molybdenum compound form a sulfide layer on the surface of the magnetic powder, which acts as a kind of protective layer.
It is presumed that this contributes to preventing the magnetic layer from sticking to the magnetic head and improving wear resistance.

The present invention will be explained in more detail below. In the following description, "%" and "part" indicating composition are based on weight unless otherwise specified.

The structure of the magnetic recording medium of the present invention is not particularly different from that of a conventional coated magnetic recording medium, except for the use of the above-mentioned organic molybdenum compound. Specifically, on a non-magnetic support,
A magnetic layer containing ferromagnetic powder is formed.

As the non-magnetic support, a film with a thickness of about 3 to 20 μm made of relatively heat-resistant plastic such as polyethylene terephthalate, polycarbonate, polyacetate, polyamide, polyimide, etc. is preferably used. , non-magnetic metal foil, etc. can be used as necessary, and basically any non-magnetic solid material that provides a desired magnetic layer formation surface can be used.

The magnetic layer is formed by coating on the non-magnetic support as described above, after performing adhesion strengthening treatment such as corona treatment and primer treatment, if necessary. It can also be formed by transferring a magnetic layer formed on a support to a non-magnetic support as described above.

The magnetic layer of the magnetic recording medium of the present invention basically consists of ferromagnetic powder, the above-mentioned organic molybdenum compound, and a binder.

Examples of ferromagnetic powder include γ-Fe20B, Fe, O
,, Fe0x with intermediate oxidation degree (1,33<x<1.
5) Alternatively, oxide magnetic powders made of these iron oxides modified with Co can also be used, but as mentioned above, in order to achieve high-density recording, powders containing Fe, Co, N1, etc. as the main components are used. A powder of a ferromagnetic alloy is preferably used.As the ferromagnetic powder, acicular particles having an average particle size of 0.1-0.5p or less and preferably a length/breadth ratio of 5 or more are preferably used. It will be done.

As the binder, thermoplastic resins, thermosetting resins, or mixtures thereof, which themselves have excellent film-forming properties and can uniformly disperse the above-mentioned ferromagnetic powder, are preferably used, such as vinyl chloride-vinyl acetate copolymer. Used are combinations or partially saponified products thereof, combinations of vinyl chloride, vinyl acetate, and maleic acid, nitrocellulose, polyurethane elastomers, polyester resins, epoxy resins, acrylic resins, and mixtures of two or more thereof. These binders are used in an amount of 10 to 40 parts per 100 parts of the above-mentioned ferromagnetic powder as a solid content.

The organic molybdenum compound used in the present invention has the above formula (
1). These organic molybdenum compounds are contained in the magnetic layer at 0%,
It is preferable to include in the range of 5 to 10 parts; if it is less than 0.5 parts, the effect of addition is poor, and if it is added in excess of 10 parts, the plasticizing effect becomes large and the durability of the magnetic layer decreases.

In addition to the above-mentioned organic molybdenum compounds, ordinary lubricants such as higher fatty acids or their esters can also be used together, but in this case as well, the amount of lubricant added must be such that the total amount with the above-mentioned organic molybdenum compounds is ferromagnetic. Preferably, the amount does not exceed 10 parts per 100 parts of powder.

In order to particularly improve the durability of the magnetic layer of the magnetic recording medium of the present invention, Al2O, or Cr20* is added to the magnetic layer.
The above-mentioned organic molybdenum compound, which preferably contains abrasive particles having a Mohs hardness of 5 or more, such as , S i 02 , S I C, T f Ot, etc., is a ferromagnetic powder only due to the presence of sulfur atoms in the molecule. It is thought that this is because it has a strong adsorption power to the abrasive particles, and it bonds firmly and contributes to their stable dispersion. Provides a magnetic layer with excellent durability. As abrasive particles,
It is preferable to include particles with an average particle size of about 0.11-1 pL in the range of 1 to 10 parts per 100 parts of the ferromagnetic powder. If more than 10 parts is added, the surface smoothness of the magnetic layer will deteriorate. This is not preferable because it lowers the temperature.

In addition, auxiliary agents such as surfactants and dispersants may be added to the magnetic layer in commonly used amounts, if necessary.

The magnetic recording medium of the present invention is generally produced by adding the above-mentioned organic molybdenum compound, binder, magnetic powder, and optionally an abrasive, further adding known lubricants, dispersants, etc. as necessary, and dispersing and kneading them together with a solvent. The obtained magnetic ink,
It is coated by a conventional method on a non-magnetic support such as a polyester film which has been subjected to adhesion strengthening treatment such as corona discharge treatment as necessary, and after orientation treatment and drying, a further curing reaction is performed as necessary to determine the thickness. is obtained by forming a magnetic layer having a thickness of about 1 to 10 µl.

In addition, the organic molybdenum compound has strong adsorption to ferromagnetic powder and has the effect of improving the dispersion of ferromagnetic powder into the binder. This coating has the effect of suppressing deterioration of magnetic properties over time due to oxidation. As mentioned above, these effects can be obtained to some extent by uniformly mixing the ferromagnetic powder of organic molybdenum compound 1 with the binder, but after treating the ferromagnetic powder with the organic molybdenum compound in advance, the ferromagnetic powder is mixed with the binder etc. By mixing, the effect can be increased considerably.

As described above, according to the present invention, in a so-called coating-type magnetic recording medium, a magnetic head can be made It is possible to obtain a magnetic recording medium having a magnetic layer, which improves the sliding characteristics of the magnetic head, particularly the problem of seizure with respect to alloy magnetic heads, and has good durability. For this reason,
By using the magnetic recording medium of the present invention, gap loss can be kept low even in high-density recording with a short recording wavelength.

Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples.

100 parts of old 0-mouth ferromagnetic metal powder (Fe-NI-Co alloy, major axis 0.25 pm, axial ratio 8,
Hc14500e) Vinyl chloride-vinyl acetate-vinyl 15 parts Alcohol copolymer (polymerization molar ratio 91/3/6) Polyurethane elastomer 10 parts α-A I 201 5 parts (abrasive, particle size 0.4#Lm) Stearic acid (Dispersant) 1 part methyl ethyl ketone 120 parts Toluene 120 parts Organic molybdenum compound of formula (1) 1 part (R: -
(CH2)CHi) After mixing and dispersing the mixture having the above composition using a sand grinder, 5 parts of Coronate L was added as a hardening agent and mixed uniformly to obtain a magnetic paint. The magnetic paint thus obtained was applied onto a polyester film with a thickness of 1071 m,
After an orientation treatment and a drying process, a calender treatment was performed to smooth the surface to form a magnetic layer with a thickness of about 3 pm.

After being left at 50° C. for 24 hours, it was cut into a predetermined width to obtain a magnetic tape.

1 pot 1" In Example 1, the amount of organic molybdenum compound added was 5
A magnetic tape was obtained in the same manner except that the amount of α-A1203 added was changed to 3 parts.

A magnetic tape was obtained in the same manner as in Example 1 except that one part of butyl stearate was further added as a lubricant.

A magnetic tape was obtained in the same manner as in Example 1 without adding the organic molybdenum compound.

Il A magnetic tape was obtained using the same amount of butyl stearate in place of the organic molybdenum compound in Example 1.

Concerning the various magnetic tapes thus obtained.

Low temperature still characteristics at 0℃ and high temperature running (40℃,
80%RH, 100pass) Afterwards, the seizing state of the dust head was investigated. The results are summarized in the table below.

In the above table, still characteristics indicate the time (minutes) until a still image deteriorates significantly, and is the most severe durability test for magnetic tapes because the magnetic head repeatedly slides over the same location on the magnetic tape. becomes. On the other hand, burn-in of the head was observed using an optical microscope.

Looking at the results in the table above, it can be seen that by adding a specified organic molybdenum compound to the magnetic coating film according to the present invention, a magnetic recording medium that prevents head seizure and has excellent durability can be obtained. can be understood.

Length 1 leg A 100 parts of ferromagnetic powder (Co-7F e 20 m, major axis 0.35 gm,
Axial ratio 8, Hc 7000e) Vinyl chloride-vinyl acetate-vinyl 15fl alcohol copolymer (polymerization molar ratio 91/3/6) Polyurethane elastomer 10 parts a-AI2013 parts (abrasive, particle size 0.4p, m) Lecithin ( fractional agent) 1 part organic molybdenum compound of formula (1) 2 parts CR: (
CH2)s CHs) Methyl ethyl ketone 120 parts Toluene 120 parts A mixture having the above composition was mixed and dispersed using a sand grinder.

Next, add 5% of the polyisocyanate crosslinking agent (Coronate L).
% and mixed thoroughly to obtain a magnetic paint. The magnetic paint thus obtained was applied onto a polyester film with a thickness of loILm, and after going through an orientation treatment and drying process, it was calendered to smooth the surface, resulting in a thickness of approximately 31L.
m magnetic layers were formed. After standing at 50° C. for 24 hours, the tape was cut into a predetermined width to obtain a magnetic tape.

In Example 4, the abrasive α-A I,O, was Cr20
A magnetic tape was obtained in the same manner except that the number was changed to 1.

In Example 4, the abrasive α-AI 20s was
A magnetic tape was obtained in the same manner except that o2 was used.

1 Gloss 1" In Example 4, no organic molybdenum compound was added,
A magnetic tape was also obtained in the same manner except that the abrasive was changed to 6 parts.

A magnetic tape was obtained in the same manner as in Example 4 without adding an abrasive.

1 Gloss 1'' A magnetic tape was obtained in the same manner as in Example 4 except that the organic molybdenum compound was changed to butyl stearate.

Regarding the various magnetic tapes obtained in this way, Y-3/
N (VH3 3x mode) dropout, still characteristics (time until still out), regenerative demagnetization (40℃,
80% R) I, the difference between the initial value of the 4 MHz signal after 100 buses) was investigated. The results are summarized in the table below.

*Y-/SN, reproduction demagnetization is OdB for Comparative Example 3.

Looking at the results in the above table, by adding a specified organic molybdenum compound and abrasive particles into the magnetic layer, durability can be achieved through special playback and repeated recording and playback while maintaining electromagnetic conversion characteristics suitable for high-density recording. It can be seen that a magnetic recording medium with excellent properties can be obtained.

100 parts of ferromagnetic metal powder (Fe-Ni-Co alloy, major axis 0.251 parts m, axial ratio 8
, Hc14500e) 2 parts of the organic molybdenum compound of formula (1) (R= (
CH2)sCHs) Methyl ethyl ketone 500 parts The mixture having the above composition was stirred and mixed using a stirrer for 8 hours. After filtering this, it was dried to obtain a surface-treated metal magnetic powder.

Next, a magnetic tape was created using the following method.

Ferromagnetic metal powder subjected to the above treatment 100 parts Vinyl chloride-vinyl acetate-vinyl 15 parts Alcohol copolymer (polymerization molar ratio 91/3/6) Polyurethane elastomer 10 parts α-A1203 5 parts (1 grain of abrasive) Diameter: 0.4 JLm) Lecithin (dispersant) 1 part Methyl ethyl ketone 120 parts Toluene 120 parts The mixture having the above composition was mixed and dispersed using a sand grinder.

Next, 5 parts of Coronate L was added and thoroughly mixed to obtain Magnetic Paint 4. The magnetic paint obtained in this way has a thickness of 1071 mm.
The magnetic layer was coated on a polyester film of 3 m in thickness, subjected to an orientation treatment and a drying process, and then calendered to smooth the surface to form a magnetic layer with a thickness of about 3 m. After standing at 50° C. for 24 hours, the tape was cut into a predetermined width to obtain a magnetic tape.

In Example 7, the organic molybdenum compound was changed to R=(CH2)ucH* in formula (1), and a magnetic tape was obtained in the same manner.

Support m In Example 7, the organic molybdenum compound is represented by formula (1), R= (CH2) 1? A magnetic tape was obtained in the same manner except that CH* was used.

A magnetic tape was obtained in the same manner as in Example 7 using metal magnetic powder without surface treatment.

L Drawing 11 In Example 7, the metal magnetic powder was surface-treated using oleic acid instead of the organic molybdenum compound, and a magnetic tape was obtained in the same manner.

The magnetic tape thus obtained was heated at 60°C and 90% R.
The amount of change in the maximum residual magnetic flux density was examined after being left under H conditions. The results are shown in the attached drawings.

The initial magnetic properties are shown in the table below.

"C2 Magnetic properties (initial value) A magnetic recording medium using metal magnetic powder surface-treated with an organic molybdenum compound has less deterioration of magnetic properties due to oxidation reaction and has excellent stability over time. Furthermore, since the initial magnetic properties are good, it can be seen that the metal magnetic powder surface-treated with an organic molybdenum compound also has excellent dispersibility.

[Brief explanation of drawings]

The drawing is a graph showing the difference in the change over time in the magnetic properties (residual magnetic flux density) of the obtained magnetic recording medium, which occurs depending on whether or not the ferromagnetic metal magnetic powder is treated with an organic molybdenum compound. Q 5 10 15 20 25 30 mF4-MC
8)

Claims (1)

[Claims] 1. A magnetic recording medium in which a magnetic layer formed by dispersing ferromagnetic powder in a binder is formed on a non-magnetic support, wherein the magnetic layer has a general formula (where R is Carbon number 1-20
1. A magnetic recording medium comprising an organic molybdenum compound represented by an alkyl group of 2. The magnetic recording medium according to claim W41, wherein the ferromagnetic powder is composed of ferromagnetic metal powder. 3. The magnetic recording medium according to claim 2, wherein the ferromagnetic metal powder is previously treated with the organic molybdenum compound and then dispersed in the Fii magnetic inder. 4. The magnetic recording medium according to any one of claims 1 to 3, wherein the magnetic layer further contains abrasive particles having a Mohs hardness of 5 or more.