JP3353348B2 - Magnetic recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium having a back coat layer formed thereon, and more particularly to a magnetic recording medium having excellent running durability.

[0002]

2. Description of the Related Art Generally, a magnetic recording medium is subjected to a high-speed relative motion with a magnetic head in the process of recording / reproducing a magnetic signal, in which case the running must be performed smoothly and stably. . Therefore, a back coat layer has been provided for measures against static electricity during running and a reduction in friction coefficient.

[0003] With the increase in recording density and miniaturization of magnetic recording media, it has become necessary to sufficiently smooth the surface of the back coat layer. However, in general, the smoother the surface of the back coat layer, the larger the friction coefficient, the lower the running property of the tape, and in some cases, the running becomes impossible or the tape may be stretched.
There are many problems such as scratches easily occurring on the surface of the back coat layer, resulting in reduced durability.

For this reason, at present, the backcoat layer cannot be unnecessarily smoothed. In order to avoid the above-mentioned problems, various measures have been taken such as adding various pigments and lubricants to the paint for the back coat layer to reduce friction and reduce damage.

[0005]

However, in reality, a sufficient lubricating effect cannot be obtained or guide shaving occurs due to the inclusion of a pigment, and the abrasion powder is transferred to the magnetic layer to cause dropout. Or become
The problems of running durability, such as the fact that the friction coefficient increases due to the shaving of the guide and the change in surface, causing edge damage and jitter, have not been solved.

Accordingly, the present invention has been proposed in view of the above circumstances, and has as its object to provide a magnetic recording medium having good lubricity on the surface of a back coat layer and excellent running durability.

[0007]

Means for Solving the Problems The inventors of the present invention have made intensive studies to achieve the above-mentioned object, and as a result, carbon black and titanium oxide and heptyl stearate having an average particle diameter of 1 μm or less have been formed on the back coat layer. Was found to be a magnetic recording medium having excellent running durability by containing the compound in an appropriate compounding ratio, and the present invention was completed.

That is, according to the present invention, in a magnetic recording medium having at least a magnetic layer and a back coat layer on a non-magnetic support, the back coat layer is oxidized with carbon black having an average particle size of 0.3 μm or more and 1 μm or less. Containing titanium and heptyl stearate, and at least 1 part by weight of titanium oxide based on 100 parts by weight of carbon crack,
It is characterized in that the mixing ratio of heptyl stearate is 10 parts by weight or less and heptyl stearate is 1 part by weight or more and 5 parts by weight or less.

In the present invention, titanium oxide plays a role of a dispersant and a role of forming surface projections. The average particle size is preferably 1 μm or less, and if it exceeds 1 μm, the smoothness of the surface of the back coat layer is deteriorated, which affects the magnetic layer side and reduces the magnetic properties. More preferably, the average particle size is 0.4 μm or less, but if it is too small, the effect of adding titanium oxide cannot be obtained, so the lower limit is set to 0.3 μm.

The mixing ratio of the above-mentioned titanium oxide is preferably 10 parts by weight or less with respect to 100 parts by weight of carbon black, and if it exceeds this, the smoothness of the surface of the back coat layer deteriorates. If the amount is too small, the effect of the addition cannot be obtained, so the lower limit is 1 part by weight.

The compounding ratio of heptyl stearate is as follows:
The amount is preferably 5 parts by weight or less with respect to 100 parts by weight of carbon black, and if it exceeds this, the bonding force of the coating film of the back coat layer is reduced, and powder falling on guide pins and the like becomes remarkable. Therefore, the mixing ratio is more preferably 3 parts by weight or less, but if the amount is too small, the effect of addition cannot be obtained, so the lower limit is 1 part by weight.

The back coat layer of the present invention is formed by adding carbon black as a main component, and a conventionally known one can be used for this. For example, Mitsubishi Kasei's product name MA-7, MA-8, C
F-9, # 4000, MA-600, MA-100, manufactured by Cabot Corporation Product names Black Pearls-L, Black Pearls-800, Black Pearls-880, Black Pearls-900, Black Pearls-1000,
Black Pearls-1300, Black Pearls-20
00, trade names Raven-1150, Raven-1250, Raven-125 manufactured by Colombian Carbon
5, Raven-1040, Raven-760, Raven-1060, Raven-780, Raven-1000,
Product name PRINTEX-55, PRINT manufactured by Degussa
EX-75, PRINTEX-80 and the like.

The average particle size of carbon black is 10 nm.
To 50 nm, more preferably 1 to 50 nm.
It is 5 nm to 30 nm. If the particle size of the carbon black exceeds 30 nm, there is a tendency that the smoothness of the back coat layer surface is deteriorated. The amount of carbon black to be added is usually preferably from 10 to 400 parts by weight, more preferably from 100 to 300 parts by weight, based on 100 parts by weight of the binder.

The back coat layer of the present invention contains the above-mentioned carbon black, titanium oxide and heptyl stearate in a binder. The binder usable here is a modified or unmodified binder. Vinyl chloride resin,
Polyurethane resin or polyester resin, etc., further used in combination with fibrous resin, phenoxy resin or thermoplastic resin having a specific use method, thermosetting resin, reactive resin, electron beam irradiation curing resin, etc. May be. The group introduced for the above modification includes -SO ₃ M, -OSO which can improve the dispersibility of carbon black.
₃ M, -COOM, -PO (OM ') _{2 and the} like (M is an alkali metal atom such as Na, and M' is the same alkali metal atom or alkyl group).

As the above-mentioned fiber-based resin, cellulose ether, cellulose inorganic acid ester, cellulose organic acid ester and the like can be mentioned. In addition,
The phenoxy resin has advantages such as high mechanical strength, excellent dimensional stability, good heat resistance, water resistance, chemical resistance, and good adhesiveness.

Further, it is preferable to add a curing agent to such a binder in order to further improve durability. As the curing agent, a polyfunctional isocyanate can be used, and in particular, tolylene diisocyanate (T
DI) systems are preferred. The addition amount of the curing agent is preferably 5 to 30 parts by weight based on the total binder material.

The magnetic recording medium to which the present invention is applied is not particularly limited as long as a magnetic layer is formed on a non-magnetic support and a back coat layer is provided on the surface opposite to the magnetic layer. However, for example, in the case of a so-called coating type magnetic recording medium in which a magnetic powder is dispersed in a binder and coated on a non-magnetic support, the magnetic powder constituting the non-magnetic support and the magnetic coating film, a resin binder, etc. Any known ones can be used and are not limited at all.

As the magnetic powder used in the magnetic layer, any conventionally known magnetic powder can be used. As the oxide magnetic powder, for example, γ-Fe ₂ O ₃ ,
-Fe ₂ O ₃ , Co-containing γ-Fe ₂ O ₃ , Fe ₃ O ₄ ,
Co-coated γ-Fe ₃ O ₄ , Co-containing γ-Fe ₃ O ₄ , C
rO _{2 and the} like. Also, hexagonal ferrite such as barium ferrite, iron carbide such as Fe ₅ C ₂ , iron nitride, and the like can be used.

Examples of usable ferromagnetic metal magnetic powder include ferromagnetic metal materials such as Fe, Co, and Ni, and Fe—C
o, Fe-Ni, Fe-Co-Ni, Co-Ni, Fe
-Mn-Zn, Fe-Ni-Zn, Fe-Co-Ni-
Cr, Fe-Co-Ni-P, Fe-Co-B, Fe-
Fe, Co, Ni such as Co-Cr-B and Fe-Co-V
Ferromagnetic metal particles composed of various ferromagnetic alloy materials containing as a main component.

In the above ferromagnetic powder for a magnetic recording medium, Al, Si, Ti, and C are used for the purpose of improving various characteristics.
Elements such as r, Mn, Cu, Zn, Mg, and P may be added.

The binder used in the magnetic layer is as follows:
Any of the aforementioned binders that can be used in the backcoat layer can be used. Further, a dispersant such as lecithin, a lubricant such as stearic acid, an antistatic agent such as carbon black, an abrasive such as alumina, a rust preventive, and the like may be added to the magnetic layer as needed. These dispersants, lubricants,
As the antistatic agent and the rust preventive, any conventionally known materials can be selected, and there is no particular limitation.

Examples of the non-magnetic support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polyamides and polycarbonates. Is mentioned. Cu,
Substrates made of alloys such as Al and Zn, glass, and ceramics such as BN and SiC can also be used. The shape is not limited at all, and may be any shape such as a tape shape, a sheet shape, and a drum shape.

In order to form the back coat layer and the magnetic layer, for example, the constituent materials of each layer are dispersed in a binder, and ethers, esters, ketones, aromatic hydrocarbons, fatty A coating material is prepared by kneading with an organic solvent selected from the group consisting of a group hydrocarbon and an organic chlorine compound-based solvent, and the coating material is applied to each surface of the nonmagnetic support.

Of course, the configuration of the magnetic recording medium according to the present invention is not limited to this, but may be modified without departing from the scope of the present invention, for example, if necessary, an undercoat layer may be formed on a non-magnetic support. Or forming a layer of a lubricant, a rust preventive, or the like. In this case, any conventionally known materials can be used as the material contained in the undercoat layer, the lubricant and the rust preventive layer.

[0025]

Since the titanium oxide particles have good dispersibility, the dispersibility of the back coat layer is improved as a whole, and the surface properties of the back coat layer are improved. Further, since the titanium oxide particles have a certain size and are dispersed in the carbon black particles, projections due to the titanium oxide particles are formed on the surface of the back coat layer. This reduces the coefficient of friction and improves the running performance of the magnetic recording medium.

Further, since the presence of heptyl stearate improves lubricity, protrusions of titanium oxide and falling off of carbon black particles are reduced, and the surface of the back coat layer is not damaged.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described, but it goes without saying that the present invention is not limited to these embodiments.

Example 1 First, a backcoat paint and a magnetic paint having the following compositions were prepared.

Composition of back coat paint Carbon black: (Raven-1255, trade name, manufactured by Colombian Carbon Co., Ltd.) 100 parts by weight Titanium oxide: (average particle diameter 0.3 μm) 1 part by weight heptyl Stearate 1 part by weight Binder: Polyester polyurethane (containing polar group -SO ₃ Na: Toyobo Co., Ltd., trade name UR-8300) 70 parts by weight Solvent: methyl ethyl ketone 220 parts by weight Parts Methyl isobutyl ketone: 220 parts by weight Toluene: 220 parts by weight

Composition of magnetic paint Magnetic powder: Co-γ-Fe ₂ O ₃ (specific surface area: 45 m ² / g: BET value) 100 parts by weight Binder: polyester polyurethane (containing polar group-SO ₃ Na: Toyobo) 10 parts by weight Nitrocellulose 7 parts by weight Abrasive: alumina (Al ₂ O ₃ ) 5 parts by weight Additive: carbon (average) Particle size 23 nm: manufactured by Colombian Carbon Co., Ltd., trade name: RAVEN-1255) 5 parts by weight Lubricant: butyl stearate 1 part by weight Solvent: methyl ethyl ketone 80 parts by weight methyl isobutyl Ketone: 80 parts by weight Toluene: 80 parts by weight

After mixing the above-mentioned materials for the backcoat paint in a ball mill for 48 hours, 20 parts by weight of a curing agent (manufactured by Nippon Polyurethane Co., trade name: Coronate L) were added, and this paint was applied to a 7 μm-thick polyethylene terephthalate film. It was applied at a thickness of 0.8 μm. Next, the above-mentioned magnetic paint material was mixed in a ball mill for 48 hours, and a paint containing 5 parts by weight of a curing agent (trade name: Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) was added to the opposite side where the above-mentioned back coat paint was applied. Was coated with a thickness of 5 μm.

Thereafter, a calendering treatment and a curing treatment were performed, and the resultant was cut into a ３ inch width to produce a sample tape as shown below.

Examples 2 to 9 Sample tapes were prepared in the same manner as in Example 1 except that the amount of titanium oxide or the average particle diameter and the amount of heptyl stearate added to the backcoat paint were changed as shown in Table 1. Was prepared.

[0034]

[Table 1]

Comparative Examples 1 to 8 Sample tapes were prepared in the same manner as in Example 1 except that heptyl stearate was not added and titanium oxide was not added. Table 2 shows the difference in the back coat paint material between the sample tapes of the comparative examples.

[0036]

[Table 2]

In Comparative Example 7, 5 parts by weight of myristic acid (MA) was added instead of heptyl stearate, and in Comparative Example 8, 5 parts by weight of butyl stearate (BS) was added instead of heptyl stearate. did.

The surface roughness Ra and the coefficient of friction of the sample tapes of Examples and Comparative Examples prepared as described above were measured, and the results are shown in Tables 1 and 2.

The surface roughness Ra was measured by Kosaka Laboratory Co., Ltd.
The measurement was performed using a surface roughness meter having a trade name of SE-30H. The measurement conditions were a magnification of 50,000 times, a measurement length of 2 mm, and a cutoff value of 0.08 mm. Here, 20
Those having a small surface roughness of not more than nm are preferred.

The coefficient of friction was measured as the coefficient of friction of the surface of the back coat layer with respect to the stainless steel guide pins. Here, the number of tape shuttles is 200 for the 10th pass.
At the time of the pass, the values are compared, but it is preferable that the change of the numerical value at this time is small, and the numerical value is preferably 0.20 or less.

Further, for each of the sample tapes, the surface of the back coat layer was observed to be scratched, and powder was dropped onto stainless steel guide pins. The results are also shown in Tables 1 and 2.

The scratch on the surface of the back coat layer is indicated as "scratch" in the table. After the above-mentioned measurement of the coefficient of friction (after 200 passes), the degree of the scratch is ranked A, B and C. It is attached. This damage occurs when the strength of the surface of the back coat layer is low, when the friction coefficient is large, and the like. The evaluation criteria are as follows. A: A good state in which no damage has occurred.

B: Some scratches have occurred. Not at a usable level. C: Large scratch has occurred. Unavailable.

The powder dropping on the guide pin is indicated by “Powder dropping” in the table.
Similarly, after the measurement of the friction coefficient (after 200 passes), the degree of powder falling was ranked A, B, and C. This powder drop occurs when the bonding strength of the back coat layer is low, when the friction coefficient is large, and the like, and the evaluation criterion is based on the above evaluation of the back coat layer surface.

Further, the RF output of each of the produced sample tapes was measured, and the results are also shown in Tables 1 and 2. The above RF output is made by Sony Corporation, product name DVR
The measurement was performed at 6 MHz using an apparatus of −1000. The output of the sample tape of Example 1 was set to 0, and the outputs of the other sample tapes were indicated by relative values.

As a result of the above measurement, the sample tape to which titanium oxide was not added was excellent in RF output, but the coefficient of friction increased sharply as the number of shuttles of the tape increased, and the surface of the back coat layer surface increased. There is a tendency for scratches and powder dropping on the guide pins to occur easily. Further, it can be seen that, even if titanium oxide is added, if the compounding ratio is too large or the average particle size is too large, the smoothness of the surface of the back coat layer is impaired and the RF output is inferior.

Further, in a sample tape to which heptyl stearate is not added as a lubricant, the friction coefficient sharply increases as the number of shuttles of the tape increases, and the surface of the back coat layer tends to be easily scratched. I understand. Further, as compared with those to which myristic acid or butyl stearate is added, the surface of the back coat layer is more excellent in scratches, generation of powder on guide pins, and RF output.

[0048]

As is clear from the above description, titanium oxide and heptyl stearate having an average particle diameter of 0.3 μm or more and 1 μm or less are added to the back coat layer, and the mixing ratio of the titanium oxide is adjusted to carbon. By setting the blending ratio of heptyl stearate to 1 part by weight or more and 5 parts by weight or less for 1 part by weight or more and 10 parts by weight or less with respect to 100 parts by weight of black, the surface property of the back coat layer becomes good. And a magnetic recording medium having excellent output characteristics.

Further, since the coefficient of friction is low and the lubricating effect is excellent, it is possible to prevent the projections of titanium oxide and carbon black particles from falling off and to prevent the back coat layer surface from being damaged, and to improve running durability. An excellent magnetic recording medium can be obtained.

Claims (1)

(57) [Claims] 1. A magnetic recording medium having at least a magnetic layer and a back coat layer on a nonmagnetic support, the average particle size of carbon black in the backcoat layer is
0.3μm or more, are contained in the following titanium oxide and heptyl stearate 1 [mu] m, and carbon blanking rack 1
00 of titanium oxide relative to the weight part 1 part by weight or more, with 10 parts by weight or less, heptyl stearate 1 part by weight or more, 5
A magnetic recording medium having a mixing ratio of not more than parts by weight.