JPH05274649A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve running property and to prevent scratch by improving the surface properties of the back side of a back coat layer and reducing the coefft. of friction of the back side. CONSTITUTION:A magnetic layer is formed on one side of a nonmagnetic substrate and a back coat layer contg. carbon black and calcium titanate (CaTiO3) of 0.5mum average particle diameter in (99:1)-(80:20) weight ratio is formed on the other side of the substrate to obtain the objective magnetic recording medium.

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 required in accordance with high density recording and miniaturization. Like the magnetic surface side having the magnetic layer, the back surface must be sufficiently smooth. However, generally, the smoother the back surface is, the larger the friction coefficient is, the tape running property is deteriorated, and in some cases, the tape cannot be run and the tape may be stretched, and the back surface is scratched. It is likely to occur and there is a problem that durability is reduced.

For this reason, the back surface can be made to be unduly smooth.
The current situation is that there are none. And avoid the problems mentioned above
In order to achieve this, the pigment for the back coat layer paint (TiO 2₂, Al
₂O ₃, Large particle size carbon etc.) is added to reduce friction.
Measures have been taken. That is, on the back side,
The coating material for the coat layer is properly dispersed between the pigments to form protrusions.
The friction coefficient of the back surface is reduced.

However, in reality, the protrusions are apt to fall off or be scraped, which increases friction and scratches, while the guide pins (for example, VTR) with which the back surface contacts.
The stainless guide of the traveling system used in (1) may be damaged by the protrusion.

[0005]

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 easily deteriorates. It has become very difficult to solve the problems of. Therefore, the present invention not only improves the surface property of the back surface by improving the dispersibility of the back coat layer, but also improves the running property by reducing the friction coefficient of the back surface and can prevent scratches and the like. The purpose is to provide.

[0006]

The present inventor has conducted extensive studies as a means to achieve the above-mentioned object, and as a result, a magnetic layer was formed on one surface of a non-magnetic support and a back coat layer was formed on the other surface. In the magnetic recording medium having the above-mentioned structure, the backcoat layer contains carbon black and calcium titanate having an average particle size of 0.5 μm or less, and the content ratio of the carbon black and the calcium titanate is 99. :
The present invention has been completed by finding that a magnetic recording medium characterized by being 1 to 80:20 is suitable for this purpose.

The calcium titanate used in the present invention has an average particle size of 0.5 μm or less.
If it exceeds 5 μm, it is too large and the smoothness of the surface of the back surface is deteriorated, and the guide pin (made of stainless steel) contacting the back surface is damaged.

The average particle size of calcium titanate 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.

In the present invention, the compounding ratio of calcium titanate is such that the weight ratio of carbon black and calcium titanate is within the range of 99: 1 to 80:20, but the compounding ratio of less than 99: 1. However, the effect of the addition of calcium titanate is not observed, which leads to deterioration of running property and scratches on the back surface. Further, if the compounding ratio exceeds 80:20, the smoothness of the surface is deteriorated and the guide pin is scratched. Further, it is desirable that the mixing ratio be 99: 1 to 90:10.

The "average particle diameter" is an average of 100 or more arbitrary particles selected from transmission electron microscope (TEM) photographs and the diameters of the particles are measured and averaged.

Carbon black is added as a main component to the back coat layer of the present invention, and a conventionally known one can be used for this. For example, MA-7, MA-8, CF-9, # 4000, MA-6 manufactured by Mitsubishi Kasei.
00, MA-100, Cabot Black Pearls-L, Black Pearls-800, Black Pearls-
880, Black Pearls-900, Black Pearls-1000, Black Pearls-1300, Black Pearls 2000, Raven-1150, Raven-1250, Raven-125 manufactured by Colombian Carbon Co.
5, Raven-1040, Raven-760, Raven-1060, Raven-780, Raven-1000,
Detexa Printex-55, Printex-
75, Printex-80 and the like.

The average particle size of carbon black is 10 nm.
To 50 nm, more preferably 15 nm
To 30 nm. Particle size of carbon black is 30
If it exceeds nm, the smoothness of the back coat layer tends to be deteriorated.

The amount of carbon black added is 10
Usually, 10 to 400 parts by weight is preferable with respect to 0 parts by weight, but 100 to 300 parts by weight is more preferable.

The back coat layer of the present invention comprises the carbon
Disperse black and calcium titanate in the binder
However, the usable binders are modified or
Is a non-modified vinyl chloride resin, polyurethane resin or
Polyester resin can be used and also fiber
Has a base resin, phenoxy resin, or specific usage method
Thermoplastic resin, thermosetting resin, reactive resin, electron beam
A radiation-curable resin or the like may be used together. Due to the denaturation
The group introduced into the carbon black is the dispersibility of carbon black.
Can be better-SO₃M, -OSO₃M, -COOM,-
PO (OM ') ₂Etc. (M is an alkali such as Na
Li metal atom, M'is the same alkali metal atom or alkyl
Group).

As the usable fibrin resin, cellulose ether, cellulose inorganic acid ester, cellulose organic acid ester and the like can be used. 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, polyfunctional isocyanates can be used, especially tolylene diisocyanate (TD
The I) 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, the back layer
A magnetic layer on the side of the non-magnetic support opposite to
However, the magnetic powder used for this magnetic layer is conventionally
Any known material can be used. Oxide magnetic powder
It is possible to use powders such as γ-
Fe₂O₃, Co deposition γ-Fe₂O₃, Co-containing γ-F
e₂O₃, Fe₃O_Four, Co deposition γ-Fe₃O_Four, Co
Contains γ-Fe₃O_Four, CrO₂Etc. Again
Hexagonal ferrite such as strontium ferrite and Fe _FiveC₂
It is also possible to use iron carbide, iron nitride, etc.

Further, as usable metal magnetic powders,
For example, Fe, Co, Ni, Fe-Co, Fe-Ni,
Fe-Co-B, Fe-Co-Cr-B, Mn-Bi,
Mn-Al, Fe-Co-V and the like are mentioned, and Al, Si, Ti, C are further added for the purpose of improving various characteristics of these.
A metal component such as r, 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 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. Also, metals such as Cu, Al and Zn, glass, B
Ceramics such as N and SiC can also be used.

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

[0022]

According to the present invention, as a result of various studies on the problems of the prior art as described above, it was 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 added in addition to the main carbon black and the binder,
The present invention is characterized in that calcium titanate is blended as a pigment in the back coat paint.

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

(1) Since the dispersibility of the calcium titanate particles is good, the dispersibility of the back coat layer is improved as a whole, and the surface property of the back surface is good. This is advantageous for high density recording of the medium.

(2) In order to improve the surface property of the back surface, the calcium titanate particles are appropriately dispersed among the carbon black particles on the back surface to form protrusions. (For example, the friction against 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
Due to the presence of calcium titanate, the protrusions due to carbon black are less likely to fall off or be scraped, and low friction and prevention of scratches can be reliably achieved.

(4) Since the size of calcium titanate is as small as 0.5 μm or less in average particle size and the content thereof is appropriate, it is possible to satisfy both of the above-mentioned effects and at the same time, and at the same time, the guide which the back surface contacts. The pin will not be damaged.

[0029]

EXAMPLES Hereinafter, specific examples of the present invention will be described, but it goes without saying that the present invention is not limited to these examples. Raw materials having the compositions shown in Table 1 were mixed in a ball mill for 48 hours to prepare a back coat layer coating material.

[0030]

[Table 1]

Further, the raw materials having the compositions shown in Table 2 were mixed in a ball mill for 48 hours to prepare a magnetic paint.

[0032]

[Table 2]

Then, after adding 20 parts by weight of a curing agent (Coronate-L) to the obtained coating material for back coat layer, 7
After coating a polyethylene terephthalate film having a thickness of 0.7 μm with a thickness of 0.7 μm, the above magnetic coating material was applied to the opposite surface of the film with a thickness of 5 μm after adding 5 parts by weight of a curing agent (Coronate-L). After that, calendering treatment and curing treatment were carried out and cut into 3/4 inch widths to prepare corresponding magnetic tapes of the following examples.

Example 1 In the above coating composition for the back coat layer, calcium titanate (CaTiO ₃ ) 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.

Example 2 In the coating composition for the back coat layer described above, calcium titanate (CaTiO ₃ ) having an average particle diameter of 0.3 μm was blended at a weight ratio of 1 and carbon black was blended at a ratio of 99.

Example 3 In the above-mentioned coating composition for the back coat layer, calcium titanate (CaTiO ₃ ) having an average particle diameter of 0.3 μm was mixed in a weight ratio of 5 and carbon black was mixed in a ratio of 95.

Example 4 Calcium titanate (CaTiO ₃ ) having an average particle size of 0.3 μm was blended in a weight ratio of 15 and carbon black was blended in a ratio of 85 in the above-mentioned coating composition for the back coat layer.

Example 5 In the above coating composition for the back coat layer, calcium titanate (CaTiO ₃ ) having an average particle diameter of 0.3 μm was mixed in a weight ratio of 20 and carbon black was mixed in a ratio of 80.

Example 6 Calcium titanate (CaTiO ₃ ) having an average particle diameter of 0.1 μm was blended in a weight ratio of 10 and carbon black was blended in a ratio of 90 in the coating composition for the back coat layer described above.

Example 7 In the above coating composition for the back coat layer, calcium titanate (CaTiO ₃ ) having an average particle diameter of 0.5 μm was blended in a weight ratio of 10 and carbon black was blended in a ratio of 90.

Comparative Example 1 In the above coating composition for the back coat layer, calcium titanate (CaTiO ₃ ) having an average particle diameter of 0.7 μm was mixed in a weight ratio of 10 and carbon black was mixed in a ratio of 90.

Comparative Example 2 In the coating composition for the back coat layer described above, 25 parts by weight of calcium titanate (CaTiO ₃ ) having an average particle diameter of 0.3 μm and 75 parts by weight of carbon black were blended.

Comparative Example 3 In the above coating composition for the back coat layer, calcium titanate (CaTiO ₃ ) having an average particle diameter of 0.3 μm was blended in a weight ratio of 0.5, and carbon black was blended in a ratio of 99.5.

Comparative Example 4 In the above coating composition for the back coat layer, chromium oxide (Cr ₂ O ₃ ) having an average particle diameter of 0.3 μm was used in a weight ratio of 1: 1.
0 and carbon black were mixed in a ratio of 90.

Comparative Example 5 In the above coating composition for the back coat layer, alumina (Al ₂ O ₃ ) having an average particle diameter of 0.3 μm was used in a weight ratio of 1: 1.
0 and carbon black were mixed in a ratio of 90.

Comparative Example 6 In the above coating composition for the back coat layer, alumina (Al ₂ O ₃ ) having an average particle diameter of 0.3 μm was added in a weight ratio of 5,
Carbon black was blended at 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 mixed in a weight ratio of 10 and carbon black was mixed in a ratio of 90.

The following performances were measured for the 3/4 inch video tapes obtained in the above examples, and the results are shown in Table 3 (Examples) and Table 4 (Comparative Examples) below.

Surface Roughness-Ra The surface roughness was measured with a surface roughness meter "SE-30H" manufactured by Kosaka Laboratory Ltd. The measurement conditions are a magnification of 50,000 times and a measurement length of 2 m.
m, cutoff value 0.08 mm. The smaller the value, the better, and 20 nm or less is desirable.

Friction coefficient This is 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 of the 10th and 200th passes of the tape shuttle, there is little fluctuation in the numerical value, and it is desirable that the numerical value is 0.18 or less.

Scratch on the back surface The degree of scratches on the back surface after the measurement of the friction coefficient (after 200 passes) is ranked A, B and C. 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 on Stainless Guide Pin The degree of scratch on the stainless guide pin after the measurement of the friction coefficient (after 200 passes) is ranked A, B and C. If the back surface is too strong, scratches will occur. Regarding ranking, it is in accordance with "Scratch on back surface".

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

[0054]

[Table 3]

[0055]

[Table 4]

From these results, the average particle size of calcium titanate to be incorporated into the back coat layer according to the present invention was set to 0.5 μm or less, and the amount of the mixture was 99: 1 by weight ratio of carbon black and calcium titanate. 80:20
By adding it within the range, it was possible to improve the smoothness of the back surface and at the same time satisfy the running property and durability.

As is apparent from the above description, the magnetic recording medium of the present invention has a magnetic layer formed on one surface of a non-magnetic support and a back coat layer formed on the other surface, Carbon black and average particle size 0.5 in the back coat
It is characterized by containing calcium titanate of μm or less, and the content ratio of the carbon black and the calcium titanate is 99: 1 to 80:20 by weight ratio. By improving the dispersibility of the back coat layer, not only the surface property of the back surface is improved, but also the running property is improved by the reduction of the friction coefficient of the back surface, and scratches are eliminated.

Claims (1)

[Claims] 1. A magnetic layer on one surface of a non-magnetic support,
A magnetic recording medium having a back coat layer formed on the other surface, wherein the back coat layer contains carbon black and calcium titanate having an average particle diameter of 0.5 μm, and
A magnetic recording medium characterized in that the content ratio of the carbon black and the calcium titanate is 99: 1 to 80:20 by weight.