JPH06139550A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve running property and durability by incorporating carbon black and barium zirconate particles having prescribed characteristics into a back coat layer in a prescribed weight ratio. CONSTITUTION:A magnetic layer 2 is formed on the front side of a nonmagnetic substrate 1 and the back coat layer 3 is formed on the rear side. This back coat layer 3 contains carbon black and barium zirconate particles having <=0.5mum average particle diameter in (99:1)-(80:20) weight ratio. Since the back coat layer 3 has the improved dispersibility, surface properties of the rear side are improved. Running property is improved by the reduced coefft. of friction of the rear side, scuffing is prevented and durability is improved. The scuffing of a guide pin or other running system coming into contact with the rear side can also be prevented.

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 such as a magnetic tape or a magnetic disk, and more particularly to a magnetic recording medium excellent in running property and durability.

[0002]

2. Description of the Related Art Conventionally, for example, in a magnetic tape, further smoothness and thinness have been demanded along with high density recording and miniaturization.

The back surface as well as the magnetic surface side having the magnetic layer must be sufficiently smooth. However, in general, the smoother the back surface is, the larger the friction coefficient becomes, and the tape running property deteriorates. In some cases, the tape may not run or the tape may stretch, and the back surface may be scratched. Sticking is likely to occur and durability is reduced.

Therefore, at present, the back surface cannot be unduly smoothed. Then, in order to avoid the above-mentioned problems, a pigment (TiO ₂ , Al ₂ O ₃ ,
(Measures such as large particle size carbon) have been added to form a large number of protrusions on the surface of a smooth back coat layer, thereby taking measures to reduce friction.

However, in reality, the protrusions are apt to fall off or peel off, which increases friction and scratches, while the guide pins (for example, VT) with which the back surface contacts.
A problem may occur that the traveling system stainless guide pin used for R is damaged by the protrusion.

As described above, in the conventional magnetic tape, not only the running property and durability of the back surface are insufficient, but also the durability of the guide pin is easily deteriorated at the same time, and each of these problems is solved. Has become very difficult.

[0007]

The object of the present invention is not only to improve the surface properties of the backcoat surface by improving the dispersibility of the backcoat layer, but also to improve the running property by reducing the friction coefficient of the back surface. Another object of the present invention is to provide a magnetic recording medium capable of eliminating scratches and the like.

[0008]

That is, the invention according to claim 1 is a magnetic recording medium in which a magnetic layer is formed on one surface of a non-magnetic support and a back coat layer is formed on the other surface. In the above, the back coat layer contains carbon black and barium zirconate (BaZrO ₃ ) particles having an average particle size of 0.5 μm or less, and the content ratio of the carbon black and the barium zirconate particles is 99 by weight. 1 to 8
The present invention relates to a magnetic recording medium characterized by being 0:20.

According to a second aspect of the present invention, the barium zirconate particles have an average particle diameter of 0.3 μm or less, and the content ratio of the carbon black and the barium zirconate particles is 99: 1 by weight. To 90:10 from the magnetic recording medium according to claim 1.

According to a third aspect of the present invention, the average particle size of the carbon black is in the range of 10 to 50 nm, and
The magnetic recording medium according to claim 1 or 2, wherein the blending ratio of the carbon black to 100 parts by weight of the binder in the back coat layer is in the range of 10 to 400 parts by weight.

As a result of various studies on the problems of the prior art as described above, the present inventor has found that the above problems can be solved by devising an additive to be added to the back coat layer.

The characteristics required of the back coat layer are compatibility of smoothness, low friction, running property and high durability. In order to satisfy these characteristics, various additives and pigments are often blended in addition to the main carbon black and the binder, but the present invention is to blend barium zirconate particles as a pigment in the back coat layer coating material. It is characterized by.

That is, as an additive for the back coat layer, barium zirconate (BaZrO ₃ ) particles having an average particle size of 0.5 μm or less are added together with carbon black to carbon black: barium zirconate = 99: 1 to 80:20 (weight ratio). By adding it in the compounding ratio of (4), the following remarkable effects (1) to (4) can be obtained.

(1) Since the barium zirconate particles have good dispersibility, the dispersibility of the back coat layer is improved as a whole, and the surface property of the back surface becomes good. This is advantageous for high-density recording of the medium, because when the magnetic layer adjacent to the back coat layer comes into contact (for example, when the tape is wound), the unevenness is not transferred to the surface of the magnetic layer.

(2) The surface property of the back surface is good, and the barium zirconate particles are appropriately dispersed among the carbon black particles on the back surface to form protrusions. Is reduced (for example, friction with respect to the stainless guide pin is reduced), and the running property of the medium is improved.

(3) By improving the running property of the back surface, scratches that may occur on the back surface can be eliminated, and
The presence of barium zirconate particles makes it difficult for carbon black protrusions to fall off or be scraped off, and reliably achieves low friction and prevention of scratches.

(4) The size of barium zirconate particles is as small as 0.5 μm or less in average particle size, and the content thereof is appropriate. Therefore, it is possible to satisfy all of the above-mentioned effects and at the same time, the guide which the back surface contacts. Pins etc. will not be damaged.

The barium zirconate particles used in the present invention have an average particle size of 0.5 μm or less. If the average particle size exceeds 0.5 μm, they are too large and the smoothness of the back surface is deteriorated. Also, damage the guide pin (made of stainless steel) that comes into contact with the back surface.

The average particle size of the barium zirconate particles is preferably 0.3 μm or less, but if it is too small, the effect due to addition tends to be invisible, so the lower limit is preferably 0.2 μm.

Further, in the present invention, the blending ratio of barium zirconate particles is such that the weight ratio of carbon black and barium zirconate particles is within the range of 99: 1 to 80:20, but the blending ratio is less than 99: 1. In the ratio, the effect of the addition of barium zirconate is not seen, which leads to deterioration of running property and damage to the back surface. Further, when the compounding ratio exceeds 80:20, the barium zirconate particles are too much and the surface smoothness is deteriorated, and
Scratches such as guide pins occur. This compounding ratio is 9
It is desirable to use 9: 1 to 90:10.

The above-mentioned "average particle diameter" is an average of 100 or more diameters of arbitrary particles measured from a transmission electron microscope (TEM) photograph.

Carbon black is added as a main component to the back coat layer of the present invention, and known ones can be used.

For example, MA-7 and MA- manufactured by Mitsubishi Kasei Co.
8, CF-9, # 4000, MA-600, MA-100, Cabot's Black Pearls-L, Black Pearls-800, Black Pearls-880, Black Pearls-
900, Black Pearls-1000, Black Pearls-13
00, Black Pearls-2000, Raven-1150, Raven-1250, Raven-12 made by Colombian Carbon Co.
55, Raven-1040, Raven-760, Raven-106
0, Raven-780, Raven-1000, Printex-55, Printex-75, Printex-80 and the like manufactured by Degussa.

The average particle size of carbon black is from 10 nm
The thickness is preferably 50 nm, more preferably 15 nm to 30 nm. When the particle size of carbon black exceeds 50 nm, the smoothness of the back coat layer tends to be deteriorated.
If it is less than nm, dispersion may not be sufficiently performed.

The amount of carbon black added is usually 10 to 400 parts by weight per 100 parts by weight of the binder.
It is more desirable that the amount is up to 300 parts by weight.

The back coat layer of the present invention comprises the above-mentioned carbon black and barium zirconate particles dispersed in a binder. The usable binder is a modified or non-modified vinyl chloride resin. , A polyurethane resin or a polyester resin can be used, and further a fibrin resin, a phenoxy resin, or a thermoplastic resin having a specific usage system, a thermosetting resin, a reactive resin,
You may use electron beam irradiation hardening type resin etc. together.

The group introduced for the above modification can improve the dispersibility of carbon black --SO ₃ M,-
It may be OSO ₃ M, —COOM, —PO (OM ′) ₂ or the like (M is an alkali metal atom such as Na, M ′ is the same alkali metal atom or an alkyl group).

As the usable fibrin resin, cellulose ether, cellulose inorganic acid ester, cellulose organic acid ester and the like can be used. 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 this curing agent, a polyfunctional isocyanate can be used, and particularly tolylene diisocyanate (T
The DI) system is preferred. The amount of the curing agent added is preferably 5 to 30% by weight based on the total amount of the binder.

In the magnetic recording medium of the present invention, a magnetic layer is provided on the surface of the non-magnetic support opposite to the back layer. The magnetic powder used for this magnetic layer is any of those conventionally known. Can also be used. It is possible to use oxide magnetic powders, which include, for example, γ-
Fe ₂ O ₃ , Co deposition γ-Fe ₂ O ₃ , Co-containing γ-Fe ₂ O ₃ , Fe
₃ O ₄ , Co-deposited γ-Fe ₃ O ₄ , Co-containing γ-Fe ₃ O ₄ , CrO _{2 and the} like can be mentioned. Further, hexagonal ferrite such as barium ferrite, iron carbide such as Fe ₅ C ₂ and iron nitride can also be used.

Further, as usable metal magnetic powders,
Fe, Co, Ni, Fe-Co, Fe-Ni, Fe-Co-B, Fe-Co-Cr
-B, Co-Ni, Mn-Bi, Mn-Al, Fe-Co-V, and the like, and Al, Si, for the purpose of improving various characteristics of these.
A metal component such as Ti, Cr, Mn, Cu or Zn may be added.

For the magnetic layer, the above-mentioned binder that can be used in the back coat layer can be used. If necessary, a dispersant such as lecithin, a lubricant such as stearic acid, an antistatic agent such as carbon black, an abrasive such as alumina, and a rust preventive may be added. These dispersants,
As the lubricant, antistatic agent, and rust preventive, any conventionally known material can be used, and the lubricant is not limited at all.

The non-magnetic support usable in the present invention includes polyethylene terephthalate and polyethylene-
Polyesters such as 2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate,
Examples include plastics such as polyamide and polycarbonate. In addition, metals such as Cu, Al, Zn, glass, BN, SiC
Ceramics and the like can also be used.

To form the back coat layer and the magnetic layer, for example, various constituent components are dispersed in a binder, and ethers, esters, ketones, aromatic hydrocarbons, and fats are used depending on the kind of the binder. Group hydrocarbon, dispersed with an organic solvent selected from organic chlorine compound-based solvent and the like, to prepare a backcoat layer coating material, a magnetic coating material, and apply these coating materials to the back and front surfaces of the non-magnetic support, respectively, and dry, Perform calendar processing.

FIG. 1 shows an example (magnetic tape for video) of the magnetic recording medium of the present invention. That is, a magnetic layer 2 containing magnetic powder, a binder and the like is provided on one surface of the non-magnetic support 1. Further, on the other surface, there is a back coat layer 3 mainly composed of the above-mentioned carbon black, barium zirconate particles and a binder.

[0036]

EXAMPLES The present invention will be described below with reference to specific examples, but it goes without saying that the present invention is not limited to these examples.

Raw materials having the following compositions were mixed in a ball mill for 48 hours to prepare a back coat layer coating material. Pigment + 100 parts by weight of carbon black (Koronbiyan Carbon Co. "RAVEN-1255") Binder: polyester polyurethane (polar group -SO ₃ Na content) 70 parts by weight (manufactured by Toyobo Co., Ltd. "UR-8300") dissolved Agent: Methyl ethyl ketone 220 parts by weight Methyl isobutyl ketone 220 parts by weight Toluene 220 parts by weight

Further, the raw materials having the following composition were ball milled.
The mixture was mixed for 48 hours to prepare a magnetic paint. Magnetic powder: Co-γ-Fe ₂ O ₃ (Specific surface area BET value = 45 m ² / g) 100 parts by weight Binder: Polyester polyurethane 10 parts by weight (containing polar group-SO ₃ Na) (manufactured by Toyobo Co., Ltd.) UR-8300 ") Nitrocellulose 7 parts by weight Abrasive: Alumina (Al ₂ O ₃ ) 5 parts by weight Additive: Carbon black (average particle size 23 nm) 5 parts by weight (Colombian Carbon Co., Ltd." RAVEN-1255 ") Sliding Agent: 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

Then, after adding 20 parts by weight of a curing agent (Coronate L) to the back coat layer coating material obtained above, 7
Thickness on μm thick polyethylene terephthalate film
After applying 0.7 μm, the above magnetic coating is applied on the opposite side of the film to a thickness of 5 after adding 5 parts by weight of a curing agent (Coronate L).
It was applied to a thickness of μm. After that, calendering treatment and curing treatment were performed to cut into a width of 3/4 inch to prepare corresponding magnetic tapes of the following examples.

Example 1 In the above-mentioned coating composition for the back coat layer, barium zirconate (BaZrO ₃ ) particles having an average particle diameter of 0.3 μm were mixed in a weight ratio of 10 and carbon black was mixed in a ratio of 90.

Example 2 In the above coating composition for the back coat layer, barium zirconate (BaZrO ₃ ) particles having an average particle diameter of 0.3 μm were blended in a weight ratio of 1 and carbon black in a ratio of 99.

Example 3 In the above coating composition for the back coat layer, barium zirconate (BaZrO ₃ ) particles having an average particle diameter of 0.3 μm were mixed in a weight ratio of 5 and carbon black in a ratio of 95.

Example 4 In the above coating composition for the back coat layer, barium zirconate (BaZrO ₃ ) particles having an average particle diameter of 0.3 μm were blended in a weight ratio of 15 and carbon black in a ratio of 85.

Example 5 In the above coating composition for back coat layer, barium zirconate (BaZrO ₃ ) particles having an average particle diameter of 0.3 μm were blended in a weight ratio of 20 and carbon black in a ratio of 80.

Example 6 In the above coating composition for the back coat layer, barium zirconate (BaZrO ₃ ) particles having an average particle diameter of 0.1 μm were blended in a weight ratio of 10 and carbon black in a ratio of 90.

Example 7 In the above coating composition for back coat layer, barium zirconate (BaZrO ₃ ) particles having an average particle diameter of 0.5 μm were blended in a weight ratio of 10 and carbon black in a ratio of 90.

Comparative Example 1 In the above coating composition for the back coat layer, barium zirconate (BaZrO ₃ ) particles having an average particle diameter of 0.7 μm were blended in a weight ratio of 10 and carbon black in a ratio of 90.

Comparative Example 2 In the above coating composition for the back coat layer, barium zirconate (BaZrO ₃ ) particles having an average particle diameter of 0.3 μm were blended at a weight ratio of 25 and carbon black at a ratio of 75.

Comparative Example 3 In the above coating composition for the back coat layer, barium zirconate (BaZrO ₃ ) particles having an average particle diameter of 0.3 μm were blended in a weight ratio of 0.5 and carbon black in a proportion of 99.5.

Comparative Example 4 In the above coating composition for the back coat layer, chromium oxide (Cr ₂ O ₃ ) particles having an average particle diameter of 0.3 μm were mixed in a weight ratio of 10 and carbon black was mixed in a ratio of 90.

Comparative Example 5 In the coating composition for the back coat layer described above, alumina (Al ₂ O ₃ ) particles having an average particle diameter of 0.3 μm were mixed in a weight ratio of 10 and carbon black was mixed in a ratio of 90.

Comparative Example 6 In the above coating composition for the back coat layer, alumina (Al ₂ O ₃ ) particles having an average particle diameter of 0.3 μm were mixed in a weight ratio of 5 and carbon black was mixed in a ratio of 95.

Comparative Example 7 In the above coating composition for the back coat layer, carbon black having an average particle diameter of 0.3 μm was blended at a weight ratio of 10 and carbon black was blended at a ratio of 90.

The following performances were measured for the 3/4 inch video tapes obtained in each of the above examples, and the results are shown in Table 1 below.

Surface Roughness-Ra: Measured with a surface roughness meter "SE-30H" manufactured by Kosaka Laboratory Ltd. Measurement conditions: Magnification 50,0
The measurement was performed at 00 times, a measurement length of 2 mm, and a cutoff value of 0.08 mm. The smaller the number, the better, and 20nm or less is desirable.

Friction coefficient: The coefficient of friction with respect to the stainless steel guide pin. The smaller the value, the lower the friction. It is directly related to the running property of the tape. Looking at the data for the 10th and 200th passes of the tape shuttle, there are few fluctuations in the numerical value, and it is desirable that the numerical value is 0.18 or less.

Scratch on the back surface: After the measurement of the above friction coefficient
The degree of scratches on the back surface (after 200 passes) is A, B and C
The one ranked. If the strength of the back surface is weak, scratches will occur. A: A good condition in which no scratches occur. B: Some scratches have occurred. Not at a usable level. C: Large scratches are seen. I can't use it at all.

Scratch of stainless guide pin: The degree of scratch of the stainless guide pin after the above friction coefficient was measured (after 200 passes) was ranked A, B and C. If the back surface is too strong, scratches will occur. The rank is based on the above "Scratch on back surface".

RF output: Using a DVR-1000 deck manufactured by Sony Corporation, the RF output at 6 MHz was measured. Example 1 was set to 0 dB and shown as a relative value. The larger the number, the better.

[0060]

[0061]

From these results, based on the present invention, the average particle diameter of barium zirconate particles to be incorporated in the back coat layer was set to 0.5 μm or less, and the amount of the mixture was 99% by weight ratio of carbon black and barium zirconate particles. By adding it within the range of 1 to 80:20, it was possible to improve the smoothness of the back surface and at the same time satisfy the running property and the high durability.

[0063]

The dispersibility of the back coat layer improves the surface property of the back surface, and the friction (coefficient) of the back surface is reduced to improve the running property and prevent scratches and durability. In addition, it is possible to prevent damage to the traveling system such as guide pins that come into contact with the back surface.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a structural example of a magnetic recording medium to which the present invention is applied.

[Explanation of symbols]

 1 ... Non-magnetic support 2 ... Magnetic layer 3 ... Back coat layer

Claims (3)

[Claims] 1. A magnetic layer on one surface of a non-magnetic support,
In a magnetic recording medium having a back coat layer formed on the other surface thereof, the back coat layer contains carbon black and barium zirconate particles having an average particle size of 0.5 μm or less, and the carbon black and the zircon. The content ratio with barium acid particles is 99: 1 to 80:20 by weight.
A magnetic recording medium characterized by: 2. The barium zirconate particles have an average particle diameter of 0.3 μm or less, and the content ratio of the carbon black and the barium zirconate particles is 9 by weight.
The magnetic recording medium according to claim 1, which is 9: 1 to 90:10. 3. The average particle size of the carbon black is 10.
The magnetic recording according to claim 1 or 2, wherein the content is in the range of 50 nm to 50 nm and the compounding ratio thereof is in the range of 10 to 400 parts by weight with respect to 100 parts by weight of the binder in the back coat layer. Medium.