JPH09115134A - Magnetic tape - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic tape which has excellent electromagnetic transducing characteristics and traveling durability even in the case of forming the magnetic tape to have a relatively small thickness over the entire part and thickness of a back coating layer, has high reliability to recording and reading out of data, and is useful as the magnetic tape for computer. SOLUTION: The back coating layer of the magnetic tape consisting of a nonmagnetic base, a magnetic layer and the back coating layer having the thickness of 0.2 to 0.8μm and the total thickness of 3 to 10μm contains particulate carbon black having an average particle size of 10 to 20μm and coarse particulate carbon black having an average particle size of 230 to 300μm. Further, the back coating layer contains calcium carbonate having an average particle size of 30 to 50μm and an inorg. powder having an average particle size of 80 to 250μm and Mohs hardness of 5 to 9 and the surface roughness Ra thereof is 0.030 to 0.060μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic tape which can be particularly advantageously used as an external recording medium for recording computer data.

[0002]

2. Description of the Related Art In recent years, with the spread of office computers such as minicomputers and personal computers, magnetic tapes (so-called backup tapes) for storing computer information have been actively researched as external storage media. There is. In practical application of magnetic tapes for such purposes, there is a strong demand for improvement in recording capacity in order to achieve larger recording capacities and smaller recording capacities, especially in conjunction with smaller computers and increased information processing capabilities. In addition, the use environment of magnetic tapes is widespread, so it can be used under a wide range of environmental conditions (especially in the circumstance where temperature and humidity fluctuates rapidly). Reliability for performance such as recording and reading is required more than before.

Generally, a magnetic tape has a structure in which a magnetic layer is provided on a non-magnetic support made of a flexible material such as synthetic resin. In order to achieve the above-mentioned large recording capacity (volume recording capacity), the particle size of the magnetic powder is reduced, its dispersibility is improved, or the magnetic layer itself is further thinned. It is said that an effective method is to increase the recording density and reduce the total thickness of the magnetic tape. Further, in order to maintain good sensitivity (especially output in a high frequency region), it is preferable that the magnetic layer is smooth. However, in order to prevent winding disorder and deterioration of running property due to this smoothing, the above support is A back coat layer is usually provided on the surface opposite to the magnetic layer. In particular, when the total thickness is reduced, the self-supporting property and strength of the magnetic tape are also deteriorated, so that the backcoat layer must be attached to maintain good running durability against repeated use. However, as the magnetic tape becomes thinner as described above, it is necessary to provide the back coat layer with a relatively small thickness.

A magnetic tape in which the total thickness of the magnetic tape and the thickness of the back coat layer are relatively thin is disclosed in, for example, JP-A-6-215350. As a specific example of the magnetic tape described in this publication, an embodiment in which the total thickness of the magnetic tape is 10 μm and the layer thickness of the back coat layer is 0.5 μm, or the total thickness is 9.5 μm And a mode in which the layer thickness of the back coat layer is set to 0.5 μm. In the back coat layer in these embodiments, relatively fine carbon black is used alone in the former embodiment, and in the latter embodiment, in order to provide antistatic and stable running properties, and in the latter embodiment, a relatively fine carbon black is used. Two types of carbon black, fine particle carbon black and relatively coarse particle carbon black, are used.

On the other hand, the high surface smoothness of the back coat layer,
For the purpose of reducing the friction coefficient with respect to the guide pin and obtaining good running stability, fine carbon black particles having an average particle diameter of 0.01 to 0.08 μm and an average particle diameter of 0.2 to A magnetic tape containing 0.5 μm of coarse-grained carbon black and fine-grained calcium carbonate having an average particle diameter of 0.01 to 0.045 μm has been proposed (JP-A-2-7223). Further, it is described that an inorganic powder (for example, α-iron oxide or the like) may be further added to the back coat layer.

[0006]

DISCLOSURE OF THE INVENTION The inventors of the present invention have made a computer of a magnetic tape in which the total thickness of the magnetic tape is as thin as 10 μm or less and the layer thickness of the back coat layer is kept very thin as 0.2 to 0.8 μm. We examined its use as an external recording medium. As a result, it was found that the magnetic tape described in Japanese Patent Laid-Open No. 6-215350 cannot provide sufficiently satisfactory performance. For example, probably because the strength of the tape itself becomes insufficient as the magnetic tape becomes thinner, carbon black falls off from the back coat layer during repeated running, increasing the friction coefficient and deteriorating running performance. It has been found that the thinning of the coat layer itself tends to cause adverse effects on the running property and output due to the abrasion of the back coat layer. In addition, since the unevenness of the surface of the backcoat layer is generally transferred to the magnetic layer, it is preferable that the surface of the backcoat layer is also smooth in response to the demand for smoothing of the magnetic layer, but when the magnetic tape is made thin. It was also found that when the smoothness of the surface of the back coat layer is excessively increased as in the magnetic tape described in JP-A-2-7223, on the contrary, the friction coefficient tends to increase.

The object of the present invention is to provide excellent performances such as electromagnetic conversion characteristics and running durability even when the overall thickness and the thickness of the back coat layer are formed to be relatively thin as described above. It is an object of the present invention to provide a magnetic tape which has high reliability in recording and reading and which can be advantageously used particularly for recording computer data.

[0008]

As a result of the research conducted by the present inventor,
In a relatively thin magnetic tape, in the back coat layer, two kinds of carbon black having a specific average particle size, calcium carbonate having a specific average particle size, and high hardness and a specific average particle size of The inorganic powder is allowed to coexist, and the surface roughness Ra of the back coat layer is
The inventors have found that a magnetic tape having a performance suitable for computer data recording can be obtained by adjusting the thickness to be 0.030 to 0.060 μm, and arrived at the present invention.

The present invention provides a non-magnetic support, a magnetic layer provided on one side thereof, and a back coat layer having a thickness of 0.2 to 0.8 μm provided on the other side. In a magnetic tape of 3 to 10 μm, the back coat layer contains fine particle carbon black having an average particle size of 10 to 20 mμ and coarse particle carbon black having an average particle size of 230 to 300 mμ, and further has an average particle size of 30 to 30 μm. It contains 50 mμ of calcium carbonate and an inorganic powder having an average particle size of 80 to 250 mμ and a Mohs hardness of 5 to 9, and has a surface roughness Ra (cutoff value 0.08 m).
m) is 0.030 to 0.060 μm.

The present invention preferably has the following aspects. (1) 10 to 20 mμ of particulate carbon black and 2
The content ratio (weight ratio) of 30 to 300 mμ of coarse-grained carbon black is as follows: former: latter = 98: 2 to 75:25.
(More preferably 95: 5 to 85:15). (2) The content of calcium carbonate is carbon black 1
It is in the range of 35 to 100 parts by weight with respect to 00 parts by weight. (3) The inorganic powder having a Mohs hardness of 5 to 9 is α-iron oxide or α-alumina. (4) The content of the inorganic powder having a Mohs hardness of 5 to 9 is 3 to 20 parts by weight with respect to 100 parts by weight of carbon black. (5) The magnetic tape is for recording computer data.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The magnetic tape of the present invention will be described below. The magnetic tape of the present invention comprises a non-magnetic support, a magnetic layer provided on one side of the support, and a back coat layer provided on the other side. Then, the magnetic tape of the present invention is formed except that the thickness of the entire magnetic tape is formed to be relatively thin as 3 to 10 μm (preferably 3 to 9 μm), and the back coat layer itself is made thin and has a specific composition. The tape can be constructed similarly to an ordinary magnetic tape. The back coat layer will be described in detail below. The backcoat layer contains two kinds of carbon blacks having different average particle sizes, calcium carbonate as an inorganic powder, and an inorganic powder having a Mohs hardness of 5-9.

The carbon black contained in the back coat layer is a particulate carbon black having an average particle size of 10 to 20 mμ and an average particle size of 230 to 300 mμ.
Is a coarse particle carbon black. In general, the surface electric resistance of the back coat layer can be set low and the light transmittance can be set low by the addition of the fine carbon black as described above. Depending on the magnetic recording apparatus, many of them use the light transmittance of the tape for the operation signal, and in such a case, the addition of particulate carbon black is particularly effective. In addition, fine particulate carbon black is generally excellent in retaining force of the lubricant, and contributes to reduction of the friction coefficient when used in combination with the lubricant. On the other hand, 230-30
Coarse-grained carbon black of 0 mμ has a function as a solid lubricant, and also forms fine protrusions on the surface of the back layer to reduce the contact area and contribute to the reduction of the friction coefficient. However, the coarse-grained carbon black has a drawback that in a harsh traveling system, the tape easily slides to fall off from the back coat layer, leading to an increase in error ratio.

Specific products of the particulate carbon black that can be used in the present invention include the following. RAVEN2000B (18m
μ), RAVEN1500B (17 mμ) (above, Columbia Carbon Co., Ltd.), BP800 (17 mμ) (Cabot Co.), PRINTEX90 (14 mμ), P
RINTEX95 (15mμ), PRINTEX85
(16 mμ), PRINTEX 75 (17 mμ) (above, manufactured by Degussa), # 3950 (16 mμ) (manufactured by Mitsubishi Kasei Co., Ltd.). Further, as an example of a specific product of coarse particle carbon black, thermal black (270 mμ)
(Manufactured by Khan Kalb Co.), RAVEN MTP (275m
μ) (manufactured by Columbia Carbon Co., Ltd.).

In the present invention, the content ratio (weight ratio) of the particulate carbon black of 10 to 20 mμ and the coarse carbon black of 230 to 300 mμ is the former: the latter =
The range of 98: 2 to 75:25 is preferable, and the range of 95: 5 to 85:15 is more preferable. The content of carbon black (the total amount of fine particles and coarse particles) in the back coat layer is usually in the range of 30 to 80 parts by weight with respect to 100 parts by weight of the binder described below, and preferably, It is in the range of 45 to 65 parts by weight.

In general, a magnetic tape for recording computer data as in the present invention is strongly required to have repetitive running property as compared with a video tape and an audio tape. In such a tape, the addition of calcium carbonate is
It contributes to the stabilization of the friction coefficient during repeated running and does not scrape the sliding guide pole. The calcium carbonate contained in the back coat layer of the present invention has an average particle size of 30.
˜50 mμ. If the average particle size exceeds 50 mμ, the particles repeatedly fall off the surface of the back coat layer due to repeated sliding of the tape, which causes dropout. In addition, the surface of the back coat layer becomes rough, and in the rolled state, it is reflected on the surface of the magnetic layer of the tape, which easily leads to a reduction in output. Further, when the tape is wound and stored in a high temperature and high humidity environment, a reaction with the lubricant contained in the magnetic layer may occur in a state where the back coat layer and the magnetic layer are in contact with each other. On the other hand, when the average particle size is 3
If it is less than 0 μm, the amount of calcium carbonate present on the surface of the back coat layer will be small, and a sufficient effect will not be achieved. In the present invention, the content of calcium carbonate is 10 to 1 with respect to 100 parts by weight of carbon black.
It is in the range of 40 parts by weight, preferably 35 to 100 parts by weight.

The inorganic powder having a Mohs hardness of 5 to 9 is used for the purpose of imparting durability to repeated running of the tape and strengthening the back coat layer. When these inorganic powders are used together with the above-mentioned carbon black or calcium carbonate, the backcoat layer becomes a strong backcoat layer with little deterioration due to repeated sliding due to its filler effect. Moreover, since the inorganic powder used in the present invention has a relatively high Mohs hardness of 5 to 9, it has an appropriate polishing force and also has an action of reducing adhesion to a tape guide pole or the like, and particularly when used in combination with calcium carbonate, It is possible to stabilize the friction coefficient of the back coat layer with respect to the sliding characteristics with respect to the guide pole having a rough surface. However, an inorganic powder having a high Mohs hardness of more than 9 is not preferable because it scrapes the guide pole and causes dropout. The inorganic powder having a Mohs hardness of 5 to 9 used in the present invention has an average particle size in the range of 80 to 250 mμ, and preferably in the range of 100 to 210 mμ. Examples of the inorganic powder having a Mohs hardness of 5 to 9 that can be used in the present invention include α-iron oxide, α-alumina, and chromium oxide (Cr ₂ O ₃ ). These powders may be used alone or in combination. Of these, α-iron oxide or α-alumina is preferable. The content of the inorganic powder having a Mohs hardness of 5 to 9 is usually 3 with respect to 100 parts by weight of carbon black.
To 30 parts by weight, preferably 3 to 20 parts by weight.

The back coat layer according to the present invention comprises the above components dispersed in a binder described below.
It is preferable to add a dispersant and a lubricant as other optional components. As the dispersant, for example, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid,
Stearic acid, behenic acid, oleic acid, elaidic acid,
1 carbon atom such as linoleic acid, linolenic acid and stearolic acid
2 to 18 fatty acids (RCOOH, R is 11 to 1 carbon atoms
7 alkyl groups, or alkenyl groups), a metal soap comprising an alkali metal or an alkaline earth metal of the above fatty acid, a fluorine-containing compound of the above fatty acid ester,
Amides of the above fatty acids, polyalkylene oxide alkyl phosphates, lecithin, trialkyl polyolefin oxy quaternary ammonium salts (where alkyl is 1 carbon atom)
~ 5, olefin is ethylene, propylene, etc.),
Sulfate ester, copper phthalocyanine, etc. can be used. These may be used alone or in combination. Among the above, copper oleate, copper phthalocyanine,
And barium sulfate are preferred. Dispersant is binder resin 1
It is added in the range of 0.5 to 20 parts by weight with respect to 00 parts by weight.

The lubricant can be appropriately selected and used from the lubricants that have been conventionally used for magnetic tapes. In the present invention, a fatty acid having 18 or more carbon atoms or a fatty acid ester is particularly useful for improving the running property. Is preferred. The lubricant is usually added in the range of 1 to 5 parts by weight with respect to 100 parts by weight of the binder resin.

Examples of the binder that can be used in the present invention include thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof. Examples of the thermoplastic resin include vinyl chloride-vinyl acetate copolymer, vinyl chloride-
Vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, acrylic ester-styrene copolymer, methacrylic ester-acrylonitrile Copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-
Acrylonitrile copolymer, polyamide resin, polyvinyl butyral, fibrin resin (cellulose acetate butyrate, cellulose diacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymer, polyester resin, chlorovinyl ether-acrylic acid Examples thereof include ester copolymers, amino resins and various rubber resins.

Examples of the thermosetting resin or reactive resin include phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, acrylic reaction resin, formaldehyde resin, silicone resin, epoxy polyamide. Resins and polyisocyanates can be mentioned.

The back coat layer is provided on the side of the non-magnetic support opposite to the side on which the magnetic layer is provided according to a conventional method. That is, a back coating layer is provided on a non-magnetic support by preparing a coating solution in which each of the above components is dissolved and dispersed in an appropriate organic solvent, and coating and drying the coating solution according to a conventional coating method. be able to. In the present invention, the backcoat layer has a surface roughness (cutoff of 0.
08mm center line average roughness) Ra is 0.030-0.
It is in the range of 060 μm. This surface roughness is in the above range because the surface of the back coat layer is transferred to the surface of the magnetic layer when the tape is wound, which affects the reproduction output and the friction coefficient with respect to the guide pole. It needs to be adjusted. The adjustment of the surface roughness Ra is usually performed by adjusting the material of the calender roll to be used, its surface property, pressure, etc. in the calender surface treatment step after coating and forming the back coat layer. In the present invention, the back coat layer has a thickness of 0.2 to 0.
It is in the range of 8 μm.

[0022]

The present invention will be described more specifically with reference to the following Examples and Comparative Examples. The "parts" shown below are
Represents "parts by weight".

Example 1 A magnetic layer containing ferromagnetic metal powder was provided on the surface of a polyethylene terephthalate base having a thickness of 6 μm (2.3 μm), and a back coat layer having the following composition was formed on the opposite surface to a thickness of 0 μm. It was applied so as to have a thickness of 0.6 μm. After drying, calendering was performed and heat treatment was performed. Next, the obtained coated material was slit into a width of 3.8 mm, subjected to surface polishing treatment, and then incorporated into a predetermined cartridge to obtain a sample (magnetic tape). The surface roughness Ra of the back coat layer of the obtained sample is 0.04 μm.
m.

Coating Liquid Composition for Backcoat Layer Formation 100 parts of fine carbon black powder (manufactured by Cabot, BP-800, average particle size: 17 mμ) 10 parts of coarse carbon black powder (manufactured by Kahn Kalb, thermal black, average) Particle size: 270 mμ) Calcium carbonate 80 parts (manufactured by Shiraishi Industry Co., Ltd., white luster O, average particle size: 40 mμ) α-iron oxide 15 parts (manufactured by Toda Kogyo Co., Ltd., TF100, average particle size: 110 mμ, Mohs hardness : 5.5) Nitrocellulose resin 140 parts Polyurethane resin 15 parts Polyisocyanate resin 40 parts Polyester resin 5 parts Dispersant: Copper oleate 5 parts Copper phthalocyanine 5 parts Barium sulfate 5 parts Methyl ethyl ketone 2200 parts Butyl acetate 300 parts Toluene 600 parts

[Example 2] In Example 1, the particulate carbon black powder was R
A sample was prepared in the same manner except that the average particle size was changed to 18 mμ.

[Example 3] In Example 1, the particulate carbon black powder was used as PRINTEX manufactured by Degussa.
90, average particle size: A sample was prepared in the same manner except that the average particle size was changed to 14 mμ.

[Example 4] In Example 1, coarse particle carbon black powder was used as R
Samples were prepared in the same manner except that the average particle size was changed to 275 mμ.

Example 5 In Example 1, the inorganic powder α-iron oxide was mixed with α-alumina (Sumitomo Chemical Co., Ltd.).
Manufactured by HIT55, average particle size: 200 mμ, Mohs hardness: 8.5) A sample was prepared in the same manner except that the content was changed to 5 parts.

[Embodiment 6] In Embodiment 1, the thickness is 6 μm.
A sample was prepared in the same manner, except that a polyethylene naphthalate base having a thickness of 6 μm was used instead of the polyethylene terephthalate base having a thickness of m.

[Embodiment 7] In Embodiment 1, the thickness is 6 μm.
A sample was prepared in the same manner except that an aromatic polyamide base having a thickness of 4.4 μm was used instead of the polyethylene terephthalate base of m.

Comparative Example 1 A sample was prepared in the same manner as in Example 1, except that the average particle size of calcium carbonate was changed to 20 mμ.

[Comparative Example 2] A sample was prepared in the same manner as in Example 1 except that the average particle size of calcium carbonate was changed to 70 mμ.

[Comparative Example 3] A sample was prepared in the same manner as in Example 1 except that the average particle size of α-iron oxide was changed to 50 mμ.

Comparative Example 4 A sample was prepared in the same manner as in Example 1, except that the α-iron oxide was changed to α-alumina having an average particle size of 270 mμ.

[Comparative Example 5] In Example 1, except that the surface roughness Ra of the back coat layer was changed to 0.02 μm.
A sample was prepared in the same manner.

[Comparative Example 6] In Example 1, except that the surface roughness Ra of the back coat layer was changed to 0.08 μm.
A sample was prepared in the same manner.

[Comparative Example 7] A sample was prepared in the same manner as in Example 1 except that calcium carbonate was not used.

[Comparative Example 8] A sample was prepared in the same manner as in Example 1 except that α-iron oxide was not used.

[Comparative Example 9] A sample was prepared in the same manner as in Example 1 except that calcium carbonate and α-iron oxide were not used.

[Performance Evaluation as Magnetic Tape] The following performance evaluation was performed using each sample obtained as described above. (1) Friction coefficient of the first pass on the backcoat layer surface (μ
Value) and the friction coefficient at the 500th pass (μ value) The back coat layer surface of the magnetic tape is brought into contact with the guide pole of the back surface touch used in the DDS drive, and a load of 10 g (T1) is applied, and 8 mm T / T1 by applying tension (T2) so that the speed becomes / sec.
The coefficient of friction of the back layer surface with respect to the guide pole was determined. The measurement was repeated up to 500 passes to determine the friction coefficient μ1 of the first pass and the friction coefficient μ500 of the 500th pass.

(2) Dirt on the guide pole The back coat layer surface of the magnetic tape was brought into contact with the guide pole and a load of 40 g was applied to the guide pole at a speed of 8 mm / sec.
We ran the 00 pass repeatedly. Dirt on the guide pole after running was visually observed and observed with a microscope, ranked as follows, and evaluated. A: Dirt is not seen at all. B: Stain is observed, but there are more unstained portions. C: There are more stained portions than unstained portions.

(3) Dropout (DO) A signal having a frequency of 2.35 MHz was written at an optimum current value on a DAT deck, and the reproduced signal was counted by a dropout counter (Shiba Soku Co., Ltd.). The measurement was performed for 5 minutes, and the average number of DOs of −16 dB for 15 μsec per minute was obtained.

(4) 4.7 MHz reproduction output A single frequency signal of 4.7 MHz was recorded at the optimum recording current with a DDS drive, and the reproduction output was measured. The output value is shown as a relative value with the reproduction output of Example 1 being 100. Table 1 shows the above results.

[0044]

[Table 1] Table 1 ──────────────────────────────────── μ-value guide pad DO ( 15μs) Reproduction output μ1μ500 Dirt (unit / min) 4.7MHz (%) ────────────────────────────── Example 1 0.27 0.32 A 5 100 2 0.26 0.34 A 5 99 3 0.27 0.34 A 5 100 4 0.28 0.32 A 6 100 50 .27 0.32 A 5 101 6 0.28 0.33 A 5 102 7 0.28 0.34 A 5 110 ─────────────────────── ────────────── Comparative Example 1 0.29 0.48 B 5 101 2 0.26 0.33 A 12 90 3 0.27 0.40 C 6 99 4 0.2 7 0.32 A 18 88 5 0.30 0.55 C 15 106 6 0.24 0.27 B 8 81 7 0.28 0.52 C 8 102 8 0.27 0.35 C 6 101 9 0.9. 28 0.60 C 22 104 ─────────────────────────────────────

From the results of Table 1 above, when the sample according to the present invention is used, the increase in the friction coefficient (μ value) of the back surface due to repeated running is small and stable. Further, it can be seen that the guide pole is not dirty, dropouts are less likely to occur, and the reproduction output is hardly reduced, which is good.

On the other hand, when calcium carbonate having a smaller average particle size than that of the present invention was used (Comparative Example 1), the increase in μ value was large, and when calcium carbonate having a large average particle size was used (comparison). In Example 2), dropouts are more likely to occur due to dropping. When α-iron oxide having an average particle size smaller than that of the present invention is used (Comparative Example 3), the dirt on the guide pole increases as the μ value increases. On the contrary, α- with a large average particle size
In the case of using iron oxide (Comparative Example 4), dropout due to falling off is more likely to occur, and transfer of the surface state of the backcoat layer to the magnetic layer is more likely to result in lower output. Further, when the surface roughness Ra of the back coat layer is small (Comparative Example 5), the output is high, but the μ value is remarkably increased, and the guide pole is also heavily soiled. On the contrary, when the surface roughness Ra of the back coat layer is large (Comparative Example 6),
Similar to Comparative Example 4, the output is significantly reduced probably because the transfer of the surface state of the back coat layer to the magnetic layer is increased. Further, as in Comparative Examples 7 and 8, when calcium carbonate or α-iron oxide is not added, the μ value during repeated running increases and the dirt on the guide pole increases.
Further, as in Comparative Example 9, when the calcium carbonate and α-iron oxide are not added, similarly, the μ value during repeated running increases, the dirt of the guide pole increases, and the dropout also increases. .

[0047]

INDUSTRIAL APPLICABILITY The magnetic tape of the present invention has a small increase in the friction coefficient due to repeated running while maintaining excellent electromagnetic conversion characteristics, regardless of the total thickness and the thickness of the back coat layer being thin, and the guide is It has good running durability without the pole getting dirty. In addition to these performances, the reliability of recording and reading of data is high, and therefore the magnetic tape of the present invention can be particularly advantageously used as a magnetic tape for recording computer data.

Claims (3)

[Claims] 1. A non-magnetic support, a magnetic layer provided on one side of the non-magnetic support, and a thickness of 0.2 on the other side.
The total thickness of the back coat layer is 0.8 to 0.8 μm.
In a magnetic tape of μm, the backcoat layer contains fine particle carbon black having an average particle size of 10 to 20 mμ and coarse particle carbon black having an average particle size of 230 to 300 mμ, and further has an average particle size of 30 to 30 μm.
50mμ of calcium carbonate and average particle size of 80-2
A magnetic tape comprising 50 mμ of inorganic powder having a Mohs hardness of 5 to 9 and having a surface roughness Ra of 0.030 to 0.060 μm. 2. An inorganic powder having a Mohs hardness of 5-9 is α-
The magnetic tape according to claim 1, which is iron oxide or α-alumina. 3. The magnetic tape according to claim 1, wherein the magnetic tape is for recording computer data.