JPS60195732A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the titled high-density magnetic recording medium whose sliding characteristic is particularly improved and which has excellent durability by providing a magnetic layer contg. a specified organic molybdenum compd. along with ferromagnetic powder on a nonmagnetic supporting body. CONSTITUTION:Ferromagnetic metallic powder is immersed in a soln. of molybdenum xanthate shown by the formula (R is 1-20C alkyl) to adsorb the compd., and dried. Then a magnetic paint is prepared by dispersing said ferromagnetic powder in a soln. of a binder along with a suitable amt. of the particles of an abrasive having >=5Mohs hardness or by dispersing magnetic powder which is not allowed to adsorb previously said compd. in a soln. of the organic molybdenum compd. along with the abrasive. The paint is coated on a nonmagnetic supporting body, oriented, dried, and calendered to smooth the surface, and a magnetic layer is formed. The baking on a magnetic head is especially eliminated, and the magnetic recording medium having excellent durability and small space loss is obtained in this way.

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., vinyl chloride-vinyl acetate copolymer,
Coated type magnetic recording media are widely used, which are made by dispersing and coating vinyl chloride-vinyl acetate-maleic copolymer in a binder such as nitrocellulose, polyester resin, epoxy resin, or polyurethane resin. Generally, γ-F e 2 o s 'I oxide magnetic powder is used as magnetic powder, but in recent years, ferromagnetic metal powder has been used instead of oxide magnetic powder, mainly for the purpose of improving recording density. Powders are also being used.

Typical applications of these coating-type magnetic recording media include audio tapes and video tapes, but video tapes in particular have been developed due to advances in video decks.

As they become more popular, the characteristics required are becoming even more stringent. To be more specific, the magnetic layer is required to have severe durability for special photography such as methyl 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 ferromagnetic metal powder has excellent magnetic properties, it also has a large coercive force, so in order to record on a metal powder-coated magnetic recording medium coated with ferromagnetic metal powder, a soft magnetic material with a high saturation magnetic flux density is required. It is necessary to use a magnetic head consisting of: 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, as abrasives, Cr20g, AI, 0.5g, which have a high Mohs hardness, etc. have been proposed. By adding a large amount of inorganic substances such as, to the magnetic layer, 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.
Further, 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 in preventing seizure, but these lubricants have a relatively low molecular weight and do not protect the magnetic layer #i. 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.

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, the main object of the present invention is to provide a coating-type magnetic recording medium that has improved sliding properties while maintaining good physical properties of the magnetic layer. It's about doing.

According to the research conducted by the present inventors, 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 in which a
In a magnetic recording medium in which a magnetic layer is formed by dispersing ferromagnetic powder in a binder, the magnetic layer is
It is characterized by containing an organic molybdenum compound represented by the general formula (where R is an alkyl group 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 sulfur in the organic molybdenum compound forms 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.

Snow 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. Basically, on a non-magnetic support,
A magnetic layer containing ferromagnetic powder is formed.

As the non-magnetic support, a film having a thickness of about 3 to 20 parts of relatively heat-resistant plastic such as polyethylene terephthalate, polycarbonate, polyacetate, polyamide, polyimide, etc. is preferably used. Paper, nonmagnetic metal foil, etc. can also be used as needed, and basically any nonmagnetic solid material that provides the 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.

As the ferromagnetic powder, 1, for example, γ-Fe, O,, Fe50
．． , FeOx (1.

33<x<1.5) or these iron oxides with C.

Oxide magnetic powder made of powder modified with Fe is also used, but as mentioned above, for high-density recording, Fe
, C01N1, etc., as the main components.
1 to 0.51L or less, preferably major axis/
Acicular particles having a breadth-to-breadth ratio of 5 or more are preferably used.

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. One or a mixture of two or more of coalesced or partially saponified products thereof, vinyl chloride-vinyl acetate-maleic acid copolymer, nitrocellulose, polyurethane elastomer, polyester resin, epoxy resin, acrylic resin, etc. can be used. 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 0.00 parts per 100 parts of the ferromagnetic powder.
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, it is preferable to include AI in the magnetic layer. or Cr20g, S
Mohs hardness of i02, Sic, TlO2 etc. is 5
Due to the presence of sulfur atoms in the molecule, the above-mentioned organic molybdenum compound, which preferably contains the abrasive particles, has a strong adsorption force not only to the ferromagnetic powder but also to the abrasive particles, and forms a strong bond. This is thought to be because it contributes to its stable dispersion, but the combination with a relatively small amount of abrasive particles provides a magnetic layer with excellent durability, especially against repeated recording and reproduction. The abrasive particles have an average particle size of 0.
It is preferable to include about 1 to 10 parts per 100 parts of ferromagnetic powder.Adding more than 10 parts is not preferable because the surface smoothness of the magnetic layer decreases.

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 that 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 reduce the thickness. This can be obtained by forming about 1-10 parts of the magnetic layer.

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 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 an organic molybdenum compound and ferromagnetic powder with a binder, but after treating the ferromagnetic powder with an organic molybdenum compound in advance, the binder etc. By mixing, the effect can be increased considerably.

As described above, according to the present invention, in a so-called coated magnetic recording medium, an organic molybdenum compound having a specific structure is blended into the magnetic layer together with ferromagnetic powder, thereby improving the sliding movement against the magnetic head. It is possible to obtain a magnetic recording medium having a magnetic layer that has improved properties, particularly the problem of image sticking in alloy magnetic heads, and also 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.

Round lid 1 100 parts of ferromagnetic metal powder (Fe-NI-Co alloy, major axis 0.25 pm, axial ratio 8,
I (c14500e) Vinyl chloride-vinyl acetate-vinyl 15 parts Alcohol copolymer (wc combined molar ratio 91/3/6) Polyurethane elastomer 10 parts α-AI203 5 parts (abrasive, particle size 0.4 Im) Stearin 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 Coronet) L as a hardening agent were added and mixed uniformly to obtain a magnetic paint. The magnetic paint thus obtained was spread on a polyester film with a thickness of 10 pm, and after undergoing an orientation treatment and a drying process, a calender treatment was performed.
The surface was smoothed to form a magnetic layer with a thickness of about 3 gm.

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

In Example 1, the amount of organic molybdenum compound added was 5
A magnetic tape was obtained in the same manner except that the amounts of α-AI and Oa were changed to 3 parts.

Support m 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.

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

Regarding the various magnetic tapes obtained in this way, low-temperature still characteristics at 0°C and high-temperature running (40°C, 80% R
The seizing state of the Sendust head after 100 passes was investigated. The results are summarized in the table below.

In the table above, 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.

夾jLL! LA ferromagnetic powder 100 parts (Co-yFe20s, major axis 0.35 pm, axial ratio 8,
Hc7000e) Vinyl chloride-vinyl acetate-vinyl 15 parts Alcohol copolymer (polymerization molar ratio 91/3/6) Polyurethane elastomer 10 parts a-A12013 parts (abrasive, particle size 0.4 μ! 11 l) Lecithin (dispersant) 1 part organic molybdenum compound of formula (1) 2 parts (R: -
(CHt) I? CHi) 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 a magnetic paint. The thus obtained magnetic paint was coated with a thickness of 10#L.
The magnetic layer was coated on a polyester film having a thickness of about 3 m and was subjected to an orientation treatment and a drying process, followed by calendering 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 4, the abrasive α-A12Q was replaced with Cr2O5
A magnetic tape was obtained in the same manner except that the following was changed.

In Example 4, the abrasive material α-A120. A magnetic tape was obtained in the same manner except that TlO2 was used instead.

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.

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=S/
N (3x vH3 mode) dropout, still characteristics (time until still out), regenerative demagnetization (40℃,
The results were summarized in the table below.

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.

Tom 100 parts of ferromagnetic metal powder (Fe-Ni-Co alloy, major axis 0.257 parts m, axial ratio 8
, Hc14500a) 2 parts of the organic molybdenum compound of formula (1) (R= (
CH2)sCHm) Methyl ethyl ketone 500 parts The mixture having the above composition was stirred and mixed for 8 hours using a stirrer. 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 1 part α-AI20. 5 parts (abrasive, particle size 0.47 Lm) 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 a magnetic paint. The magnetic paint obtained in this way is coated with a thickness of lop.
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.

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

LLL! In Example 7, a magnetic tape was obtained in the same manner as above except that the organic molybdenum compound was changed to R=(CH2)rycHs in formula (1).

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

In LLf 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.

jL! -111 characteristics (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 reactions and has excellent stability over time. In addition, the magnetic properties of magnetic recording media with good initial magnetic properties (
3 is a graph showing differences in changes over time in residual magnetic flux density (residual magnetic flux density).

Q 5 10 15 20 25 Over 30 companies? jN5
(B)

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 1, wherein the ferromagnetic powder comprises 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 magnetic layer binder. 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.