JPS60195730A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the titled coating-type magnetic recording medium wherein the sliding characteristic of the magnetic layer is particularly improved among other physical characteristics by incorporating a specified organic zinc compd. into the magnetic layer obtained by dispersing ferromagnetic powder in a binder. CONSTITUTION:Ferromagnetic powder or ferromagnetic compd. powder is dispersed in a soln. of zinc dialkyl dithiocarbamate shown by the formula (R is 1-20C alkyl) in an organic solvent, and particles of an abrasive having >=5Mohs hardness are further dispersed and incorporated or said ferromagnetic powder is pretreated in a soln. of the zinc dialkyl dithiocarbamate, filtered, and dried to obtain magnetic powder by whose surface the zinc compd. is adsorbed. The magnetic powder is dispersed in a soln. of a binder to obtain obtain a magnetic paint which is coated on a nonmagnetic supporting body, dried, and then calendered to form a magnetic layer whose surface is smoothed. The organic zinc compd. contg. S is strongly adsorbed by the magnetic powder in this way, and the deterioration of magnetic characteristics due to oxidation is prevented. The sliding characteristic is particularly improved, and the baking on a magnetic head is eliminated. Accordingly, the magnetic recording medium having improved durability is obtained.

Description

[Detailed description of the invention] Ninety-one beans I The present invention uses ferromagnetic powder as the magnetic material.

The present invention relates to improvements in magnetic recording media such as so-called coated IRI magnetic tapes and magnetic sheets, and particularly to coated magnetic recording media with improved physical properties of the magnetic layer, especially sliding properties.

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,
Coating-type magnetic recording media are widely used, which are made by dispersing and coating the magnetic recording medium in a binder such as chlorinated vinyl-vinyl acetate-preic acid copolymer, nitrocellulose, polyester resin, epoxy resin, or polyurethane resin. Generally, oxide magnetic powder such as γ-Fe20H is used as magnetic powder, but in recent years, ferromagnetic metal powder has also been used instead of oxide magnetic powder, mainly for the purpose of improving recording density. It looks like this.

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 (Hc), 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. Such magnetic head materials include:
For example, there are alloy-based magnetic materials such as sendust, but when recording and reproducing on a metal powder-coated recording medium using such an alloy magnetic head, seizure and development may occur on the sliding surface of the head core. be. The mechanism of this burn-in is not necessarily clear, but once it occurs,
This causes gap loss (spacing and loss), which causes a particularly large loss in high-density recording with short recording wavelengths.

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. It has also been proposed to add abrasives or lubricants to the magnetic layer, but satisfactory results have not always been obtained. By adding a large amount of inorganic material 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.
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.

Good” J and 1 cloth The main object of the present invention is to solve the above-mentioned circumstances.

An 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 a magnetic layer.

iJJΣ11 According to the research conducted by the present inventors, it has been found that adding an organic zinc compound having a specific structure to a magnetic layer containing ferromagnetic powder is extremely effective in achieving the above object. 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 zinc compound represented by the general formula (where R is an alkyl group having 1 to 20 carbon atoms).

The above-mentioned organozinc 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. Although it is not necessarily clear why the desired effect is obtained by blending the organozinc compound, the sulfur in the organozinc compound forms a sulfide layer on the surface of the magnetic powder.
It is presumed that this acts as a kind of protective layer and contributes to preventing the magnetic layer from sticking to the magnetic head and improving wear resistance.

The present invention will now be described in more detail. In the following description, "%" and "1 part" indicating the 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 conventional coated magnetic recording media, except for the use of the above-described organic zinc compound.

That is, the magnetic recording medium of the present invention basically includes a magnetic layer containing ferromagnetic powder formed on a nonmagnetic support.

As the non-magnetic support, a film with a thickness of about 3 to 20 IL made of relatively heat-resistant plastic such as polyethylene terephthalate, polycarbonate, polyacetate, polyamide, polyimide, etc. is preferably used, but paper, A non-magnetic metal foil or the like may be used if 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 zinc compound, and a binder.

As the ferromagnetic powder, for example, 20 g of γ-Fe.

Fe, 04. Fe0x with intermediate oxidation degree (1°33<
x < 1.5) or these iron oxides.

Oxide magnetic powder made of powder modified with Fe is also used, but as mentioned above, for high-density recording, Fe
, Co, Ml, etc. as main components are preferably used as the 0 ferromagnetic powder.
Acicular particles having a diameter of 1 to 0.5 or less, preferably a length/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 zinc compound used in the present invention is represented by the above formula (1). These organic zinc compounds are preferably included in the magnetic layer in an amount of 0.5 to 10 parts per 100 parts of ferromagnetic powder; less than 0.5 parts results in poor addition effects, and more than 10 parts When added, the plasticizing effect increases and the durability of the magnetic layer decreases.

In addition to the above-mentioned organozinc 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 is such that the total amount with the above-mentioned organozinc 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, the magnetic layer may contain AI, O, or Cr t Os.
The above-mentioned organozinc compound, which preferably contains abrasive particles having a Mohs hardness of 5 or more, such as SIOt, SIC, TIO2, 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 not only for abrasive particles, but also for strong bonding and contributing to their stable dispersion, but in combination with a relatively small amount of abrasive particles.

It provides a magnetic layer with excellent durability especially for repeated recording and reproduction. The average particle size of the abrasive particles is 0.1 to 1μ.
1-10 parts of ferromagnetic powder per 100 parts of ferromagnetic powder.
It is preferable that the amount is in the range of 10 parts, but if it is added in excess of 10 parts, the surface smoothness of the magnetic layer will deteriorate, which is not preferable.

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 generally includes the above-described organozinc compound, a binder, a magnetic powder, and optionally an abrasive.
If necessary, a known lubricant, dispersant, etc. may be further added, and the magnetic ink obtained by dispersing and kneading with a solvent may be applied to a non-woven material such as a polyester film, which has been subjected to adhesion strengthening treatment such as corona discharge treatment, if necessary. It can be obtained by coating it on a magnetic support by a conventional method, and after orientation treatment and drying, further carrying out a curing reaction if necessary to form a magnetic layer with a thickness of about 1-io.

In addition, the organic zinc 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. These effects can be obtained to some extent by uniformly mixing the organic zinc compound 1 ferromagnetic powder with the binder, as described above.
By pre-treating the ferromagnetic powder with an organic zinc compound and then mixing it with a binder etc., the effect can be considerably increased.

l Mitate JIJ As described above, according to the present invention, in a so-called coated magnetic recording medium, an organic zinc compound having a specific structure is blended into the magnetic layer together with ferromagnetic powder, thereby improving the sliding resistance against the magnetic head. A magnetic recording medium having a magnetic layer that improves dynamic characteristics, particularly the problem of image sticking for alloy magnetic heads, and has good durability can be obtained. Therefore, 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.

Li1" 100 parts of ferromagnetic metal powder (Fe-Ni-Co alloy, major axis 0.2 parts I m, @ ratio 8,
Hc14500e) Vinyl chloride-vinyl acetate-vinyl 15 parts Alcohol copolymer (polymerization molar ratio 91/3/6) Polyurethane elastomer 101J α-AI20s 5 parts (abrasive, particle size 0.4 μm) Stearic acid (dispersant) 1 1 part Methyl ethyl ketone 120 parts Toluene 120 parts Organozinc compound of formula (1) 1 part (R: (CH2) s CHs ) After mixing and dispersing the mixture of the above M in a sand grinder, coronate 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 loJLm,
After the orientation treatment and drying process, calender treatment was performed to smooth one surface to form a magnetic layer with a thickness of about 3 #Lm.

After leaving it at 50℃ for 24 hours, cut it to the specified width.
Obtained magnetic tape.

In Example 1, the amount of organic zinc compound added was 5 parts, α
-A120. A magnetic tape was obtained in the same manner except that the amount added was changed to 3 parts.

Support 11'' In Example 1, one part of butyl stearate was further added as a lubricant, and a magnetic tape was obtained in the same manner.

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

L Gloss 1'' A magnetic tape was obtained using the same amount of butyl stearate in place of the organozinc 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 heating (H, 100 p.a.s.) 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 in the J11 tape durability test because the magnetic head repeatedly slides over the same location on the magnetic tape. Become something. On the other hand, burn-in of the head was observed using an optical microscope.

Looking at the results in the above table, it can be seen that by adding a specified organic zinc 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. 100 parts of 10-mouth ferromagnetic powder (Co-yFe20@, major axis 0.35 g, m, axial ratio 8
, I (c7000e) Vinyl chloride-vinyl acetate-vinyl 15 parts Alcohol copolymer (polymerization molar ratio 91/3/8) Polyurethane elastomer 10 part α-Al t On 3 parts (1j* material, particle size 0.4ILm ) Lecithin (dispersant) 1 part Organozinc compound of formula (1) 2 parts (R: CCHx ) u CHs ) Methyl ethyl ketone 120 parts Toluene 120 parts - A mixture of the following composition was mixed and dispersed using a sand grinder.

Next, 5 parts of Coronae) L were added and thoroughly mixed to obtain a magnetic paint. The magnetic paint obtained in this way has a thickness of topm.
The magnetic layer was coated on a polyester film, 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 #Lm. 50'O
After leaving it for 24 hours, the magnetic tape was cut into a predetermined width to obtain a magnetic tape.In Example 4, the abrasive material α=AI20. Cr2O,
A magnetic tape was obtained in the same manner except that the following was changed.

A magnetic tape was obtained in the same manner as in Example 4, except that the abrasive α-AI, O, was changed to TlO2.

ID A magnetic tape was obtained in the same manner as in Example 4, except that the organic zinc compound was not added and the abrasive was changed to 6 parts.

L Comparison 1'' A magnetic tape was obtained in the same manner as in Example 4 without adding an abrasive.

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

Regarding the various magnetic tapes obtained in this way, Y-5/
N (VHS 3x mode) dropout, still characteristics (time until still out), M life mC40”0
．． 8096RH, the difference between the initial value of the 4MHz signal after the Zoo pass) was investigated. The results are summarized in the table below.

Wood Y-/SN, regenerative demagnetization is OdB for Comparative Example 3.

Looking at the results in the table above, it can be seen that by adding a specified organozinc compound and abrasive particles into the magnetic layer, durability during special playback and repeated recording and playback can be improved 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.

1 piece 1 ferromagnetic metal powder 100 parts (Fe-Nl-Co alloy, major axis 0.25 uLm, axial ratio 8
, Hc14500a) 2 parts of the organic zinc compound of formula (1) (R=-(CH2)s CHs ) 500 parts of methyl ethyl ketone A 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 10 parts α-AI, 0. 5 parts (abrasive, particle size 0.4#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 thus obtained magnetic paint was coated with a thickness of 10IL.
The magnetic layer was coated on a polyester film of 3 pm, subjected to an orientation treatment and a drying process, and then calendered to smooth one surface to form a magnetic layer with a thickness of about 3 pm. After standing at 50° C. for 24 hours, the tape was cut into a predetermined width to obtain a magnetic tape.

Actual J11J In Example 7, the organic zinc compound was changed to R=-(CHt)uCHs in formula (1), and a magnetic tape was obtained in the same manner.

In Example 7, the organozinc compound is represented by formula (1), R= (CHt)+? A magnetic tape was obtained in the same manner except that CHm was used.

1 Gloss 1'' In Example 7, a magnetic tape was obtained in the same manner as in Example 7 using metal magnetic powder without surface treatment.

1. In Example 7, metal magnetic powder was surface-treated using oleic acid instead of the organozinc 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.

d Magnetic properties (initial value) A magnetic recording medium using metal magnetic powder surface-treated with an organozinc 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 subjected to surface treatment with an organic zinc compound also has excellent fractionability.

[Brief explanation of the drawing]

The drawing is a graph showing the difference in the magnetic properties (residual magnetic flux density) of the obtained magnetic recording medium over time, which is caused by whether or not the ferromagnetic metal magnetic powder is treated with an organic zinc compound. Applicant's representative Akio Saruwatari Suitable time (B)

Claims (1)

[Claims]! , 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 magnetic layer having a general formula (where R is a carbon number of 1 to 20
1. A magnetic recording medium comprising an organozinc 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 zinc 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.