JP2001266332A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium excellent in surface smoothness and wear resistance and having excellent running properties without emboss deforming. SOLUTION: γ-Alumina particulates are incorporated into a back coating layer. Thereby, the surface of the back coating layer can be made smooth and the emboss deforming can be prevented. Since the hardness of γ-alumina is lower compared with that of γ-alumina and the like, a guide pin or the like is not scraped. And since change of the frictional coefficient of γ-alumina at the time of sliding is smaller than that of material comprising primarily carbon, enhancement of durability of a magnetic surface can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a magnetic recording medium, and more particularly to a technique for improving the surface smoothness and abrasion resistance of a back coat layer and preventing the occurrence of emboss deformation.

[0002]

2. Description of the Related Art Conventionally, a magnetic recording medium such as a magnetic tape has a non-magnetic layer opposite to a magnetic layer for the purpose of improving strength, preventing deformation and damage, and preventing turbulence during winding and rewinding. A back coat layer is provided on the magnetic support. For example,
JP-A-63-131321 discloses an Al ₂ O ₃ .x
A magnetic recording medium having a back coat layer containing an alumina hydrate represented by H ₂ O is shown. Also, JP-A-58-240931 and JP-A-63-27172.
0, JP-A-3-80426, JP-A-9-3
JP-A-26111 and JP-A-10-11736 disclose a magnetic recording medium provided with a back coat layer containing α-alumina.

[0003]

However, when alumina hydrate is contained in the back coat layer, the magnetic layer is easily oxidized and the corrosion resistance is reduced. Further, since α-alumina has extremely high hardness (Mohs hardness of 9), if it is contained in the back coat layer, it may damage guide pins and the like. The particle size of α-alumina contained in the back coat layer is generally 0.1% in primary particle size.
Although the particle size is as small as 2 to 0.8 μm, the adhesion between particles is so strong that it is difficult to disperse. Therefore, a relatively large number of aggregates of secondary particles or more are present, and the surface state of the back coat layer becomes rough (average Ra6).
When the magnetic recording media are stored or left standing in a stacked state, the surfaces of the magnetic layers adjacent to each other are damaged, so-called emboss deformation is caused, dropouts and the like are generated, and electric characteristics such as output characteristics are deteriorated. In some cases. When the surface of the back coat layer is smoothed, emboss deformation is prevented and high output is obtained, but stable running cannot be obtained. Also, if the smooth surface of the back coat is easily worn, the tape is scraped by contact with a guide or the like during running of the tape, so that irregularities are generated, and as a result, emboss deformation is caused.

An object of the present invention is to provide a magnetic recording medium which is excellent in corrosion resistance, surface smoothness, and abrasion resistance, does not cause embossing deformation, and has excellent running properties.

[0005]

[Means for Solving the Problems] For such problems,
The present inventors have found that the inclusion of fine particles of γ-alumina in the back coat layer is effective for improving the surface smoothness and abrasion resistance and for preventing the occurrence of embossing deformation, and the present invention Was completed.

That is, the present invention is directed to a magnetic recording medium having a magnetic layer on one surface of a non-magnetic support and a back coat layer containing a binder in which inorganic powder is dispersed and contained on the other surface. And The back coat layer has a particle size of 0.02 to 0.2 μm.
It is assumed that 5 to 70 parts by weight of γ-alumina is contained with respect to the total powder, and the balance is carbon black having a particle size of 15 to 60 μm.

The average roughness Ra of the surface of the back coat layer is:
Desirably, the thickness is 2 to 5 nm. Carbon black has an electric resistance of 10 ⁵ to 10 ⁸ Ω and a friction coefficient of 0.15 to 0.15.
Desirably, it is 0.20. In the back coat layer,
Further, hematite may be contained.

The γ-alumina used in the present invention is fine particles having a particle size of 0.02 to 0.2 μm. γ-alumina has a lower hardness than Mo-alumina (Mohs hardness 6)
It has the characteristic of. For this reason, even if it is contained in the back coat layer, the guide pins, the magnetic head, and the like are not worn and damaged. Further, by using γ-alumina as fine particles having a particle diameter of 0.02 to 0.2 μm, the average roughness Ra of the surface of the back coat layer can be set to 2 to 5 nm, and the back coat layer can be smoothed. This allows
Even when stored or left for a long time in a state where the magnetic recording media are stacked, the surface of the magnetic layer adjacent to each other is damaged,
It is possible to prevent so-called embossing deformation, thereby preventing the occurrence of dropout and the deterioration of electrical characteristics such as output characteristics. In addition, γ-alumina does not cause deterioration of the corrosion resistance of the magnetic layer as in the case of alumina hydrate.

Specific examples of commercially available γ-alumina include:
AKP-G015 manufactured by Sumitomo Chemical Co., Ltd.
08 μm) and AKP-G025 (particle size 0.05 μm).

On the other hand, the carbon black added to the back coat layer simultaneously with the above-mentioned γ-alumina powder is added for the purpose of preventing the back coat layer from being charged. It is preferable to use one having a thickness of 60 nm. When the particle size is less than 15 nm, the dispersion in the back coat layer is poor, which may adversely affect the running property. On the other hand, if it is larger than 60 nm,
The antistatic effect cannot be obtained. In particular, the electric resistivity of the back coat layer is preferably 10 ⁵ to 10 ⁸ Ω,
Within this range, a good antistatic effect can be obtained.

The coefficient of friction of the back coat layer is 0.1.
It is preferably from 15 to 0.20. If it is less than 0.15, running becomes unstable, and there is a possibility of adverse effects such as edge damage. If it is larger than 0.20, there is a possibility that emboss deformation may occur.

As the carbon black, any of channel black, furnace black, acetylene black and thermal black can be used, but acetylene black is particularly preferred. Also, Japanese Patent Application Laid-Open No. Sho 61-22424
A graphitized carbon black whose surface is wrapped with a graphite layer as disclosed in Japanese Patent Application Laid-Open Publication No. H10-209, can also be used.

Specific examples of commercially available carbon black products include those manufactured by Cabot Corporation in the United States, Black Pearl 700 having a particle size of 18 μm, Mogal L having a particle size of 20 μm, ELFTEX pellet-115 having a particle size of 27 μm, and Legal 3001 having the same size. Vulcan XC-72 with a particle size of 30 μm, manufactured by Columbia Carbon Co., Ltd., having a particle size of 13 μm Raben 8000, particle size of 20 μm Raben 5250, particle size of 30 μm Raben 890, manufactured by Asahi Carbon Co., Ltd. # 60H of 35 μm, Seat 5H with a particle size of 20 μm for Tokai Carbon Co., Ltd., Ketjen Black EC with a particle size of 35 μm for Akzo, The Netherlands, and particle size of Ketjen Black EC for Mitsubishi Kasei 20
# 4040 μm, # 4330BS having a particle size of 23 μm, # 4350BS having a particle size of 45 μm, and the like can be preferably used.

The mixing ratio of the γ-alumina and the carbon black is such that the γ-alumina is 5 to 70 parts by weight and the balance is carbon black. With such a mixing ratio, the change in the coefficient of friction during sliding can be suppressed smaller than that of the carbon black-based one, whereby the durability of the magnetic surface can be improved. If the compounding ratio of γ-alumina is less than 5 parts by weight, wear is liable to occur, resulting in an increase in friction coefficient and emboss deformation. When the compounding ratio of γ-alumina is more than 70 parts by weight, the surface smoothness is improved, but the electric resistance is increased, the dust and the like are adsorbed, which causes dropout.

The back coat layer containing γ-alumina and carbon black as described above is prepared by mixing and dispersing γ-alumina and carbon black together with a binder component, an organic solvent and other additives. Is prepared, applied to the back surface of a non-magnetic support having a magnetic layer formed on the front surface, and dried. The order of application may be in the order of the back coat layer and the magnetic layer.

Here, as the binder, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-acrylic acid copolymer,
Vinyl chloride resin such as vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, thermoplastic polyurethane resin, thermosetting polyurethane resin, polyester resin, phenoxy resin , A polyvinyl butyral resin, a cellulose derivative, an epoxy resin or a mixture thereof. In addition, by introducing hydrophilic polar groups such as carboxylic acid, sulfonic acid, sulfonic acid salt, phosphoric acid, phosphate, amine and ammonium salt into these resins, the dispersibility of powder particles as coating film constituent materials is improved. Alternatively, an acrylic double bond may be introduced to cure by irradiation with an electron beam.

Solvents used for preparing paints for forming these coating films include alcohols such as ethanol, propanol and butanol, esters such as methyl acetate, ethyl acetate and butyl acetate, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone. Ketones, ethers such as tetrahydrofuran and dioxane, benzene, toluene, aromatic hydrocarbons such as xylene, heptane, hexane, aliphatic hydrocarbons such as cyclohexane, methylene chloride, ethylene chloride,
Examples thereof include chlorinated hydrocarbons such as chloroform, and a mixed solvent of cyclohexanone-toluene is more preferable.

In addition, the above-mentioned coating film may further include, as an additive,
Lubricants such as saturated and unsaturated higher fatty acids, higher fatty acid amides, fatty acid esters, higher alcohols, silicone oils, mineral oils, edible oils, and fluorine oils can be used.

Such a composition can be achieved by dispersing a predetermined amount in a ball mill or a sand mill and applying it as a backcoat coating composition on the non-magnetic substrate. As an application method, an air doctor coat, a blade coat, an air knife coat, an air knife coat, a reverse roll coat, a transfer roll coat, a gravure coat, a kiss coat, a cast coat, a spray coat and the like can be used.

In the magnetic recording medium of the present invention, the magnetic powder used for the magnetic layer is not particularly limited, and iron oxide-based magnetic powder, ferrite-based magnetic powder, and metal or alloy magnetic powder can be used. The method of applying the same is also the same as the method of applying the back coat layer described above.

The material of the non-magnetic support on which the back coat layer and the magnetic layer as described above are coated may be any material as long as it is generally used for this type of magnetic recording medium. Examples include polyesters such as polyethylene terephthalate, polyolefins such as polyethylene, cellulose derivatives such as cellulose acetate, vinyl resins such as polyvinyl chloride, plastics such as polycarbonate, metals such as aluminum, and single crystal silicon.

The thickness of the back coat layer is 0.2 to 0.4.
μm is preferable, and the thickness of the magnetic recording medium including the magnetic layer, the non-magnetic support, and the back coat layer is preferably 10 μm or less. When the thickness of the back coat layer is less than 0.2 μm, the thickness unevenness increases, and the electrical resistance increases in a portion having a small thickness. When the thickness is more than 0.4 μm, the nonmagnetic support needs to be thinned, resulting in insufficient strength. . In addition, by suppressing the thickness of the magnetic recording medium to 10 μm or less, there is an effect that a long tape can be stored in a limited cartridge and the storage capacity can be increased.

The back coat layer may contain hematite (acicular or spherical iron oxide) having low abrasiveness.
A typical hematite has a major axis length of 0.11 × a minor axis length of 0.02 μm. Since hematite has good dispersibility, smoothness is not impaired. This has the effect of increasing the density in the backcoat layer and increasing the rigidity of the entire tape.

[0024]

The present invention will be described in detail with reference to the following Examples, but it should not be construed that the invention is limited thereto. (Example 1) << Coating component for magnetic layer >> (1) Ferromagnetic iron-based metal powder (Co / Fe: 10 at%, Y / (Fe + Co): 3 at%, Al / (Fe + Co): 5 wt%, σs : 130 A · m ² / kg, Hc: 133.0 kA / m, pH: 9.4, major axis length: 0.17 μm) 100 parts Vinyl chloride-hydroxypropyl acrylate copolymer 11 parts (contained -SO ₃ Na group) : 0.7 × 10 ^-4 equivalents / g) Polyester polyurethane resin 5 parts (contained -SO ₃ Na group: 1.0 × 10 ^-4 equivalents / g) α-alumina (average particle size: 0.2 μm) 10 parts Carbon black 2.0 parts (Average particle size: 75 nm, DBP oil absorption: 72 cc / 100 g) Methyl acid phosphate 2 parts Palmitic acid amide 1.5 parts N-butyl stearate 1.0 parts Tetrahydrofuran 65 parts Methi Ethyl ketone 245 parts 85 parts of toluene (2) Polyisocyanate 4 parts Cyclohexanone 167 parts

After kneading the magnetic layer coating component (1) with a kneader, the mixture is dispersed in a sand mill with a residence time of 45 minutes, and the magnetic layer coating component (2) is added thereto. And The above coating material for a magnetic layer was coated with an aromatic polyamide film (4.4 μm in thickness, MD = 11GP).
a, MD / TD = 0.70, trade name: Mictron, manufactured by Toray Co., Ltd.) and applied so that the thickness of the magnetic layer after the magnetic field orientation treatment, drying and calendering treatment becomes 1.6 μm. After the magnetic field orientation treatment, drying was performed to obtain a magnetic sheet. Note that the magnetic field orientation treatment is performed before the dryer by using an NN counter magnet (5
kG) and two NN counter magnets (5 kG) 50 cm from the near side of the finger coating dry position of the coating film in the dryer.
The test was performed at intervals of cm. The coating speed was 100 m / min.

<< Coating component for back coat layer >> Carbon black (particle size: 25 nm) 93 parts γ-alumina AKP-G015 particle size: 80 nm 7 parts (Sumitomo Chemical Co., Ltd.) Nitrocellulose 45 parts Polyurethane resin ( (Containing SO ₃ Na group) 30 parts Cyclohexanone 260 parts Toluene 260 parts Methyl ethyl ketone 525 parts

After the above-mentioned coating composition for a backcoat layer was dispersed in a sand mill with a residence time of 60 minutes, 15 parts of polyisocyanate was added to prepare a coating for the backcoat layer, followed by filtration. The coating was applied to the opposite surface so that the thickness after drying and calendering became 0.5 μm, followed by drying.

The magnetic sheet obtained in this manner was heated at a temperature of 100.degree.
The surface of the magnetic layer was wrapped with a magnetic sheet wound on a core, aged at 70 ° C. for 72 hours, cut to a DAT width, and run at 200 m / min. After polishing, blade polishing and surface wiping, post-processing was performed to produce a magnetic tape. At this time, K10000 on the wrapping tape,
The treatment was performed with a running tension of 30 g using a carbide blade for the blade and Toraysee for wiping the surface. The magnetic tape obtained as described above was assembled in a cartridge to produce a computer tape.

(Examples 2 to 5) Examples 2 to 5 were performed in the same manner as in Example 1 except that some of the conditions were changed to the conditions shown in Table 1.
5 was produced.

(Comparative Examples 1 to 3) Comparative Examples 1 to 3 were performed in the same manner as in Example 1 except that some of the conditions were changed to the conditions shown in Table 1.
The tape for computer No. 3 was produced.

The evaluation was performed as follows. Deterioration rate: The magnetic tape was stored in a cartridge in a 60 ° C., 80% RH ring for 7 days. The saturation magnetization .sigma.s0 of the tape before storage and the saturation magnetization .sigma.s1 of the tape after storage were measured by VSM. The deterioration rate was determined by the following equation. Deterioration rate (%) = (σs0−σs1) / σs0 × 100 Average roughness: Surface roughness meter SE-3FA (manufactured by Kosaka Laboratories)
It measured using. The magnetic layer surface of the magnetic tape is stuck on a smooth semi-cylindrical glass, and the magnetic layer surface has a stylus curvature of 5 μm.
R, magnification 100,000 times, cut-off 0.08 mm, the center line average roughness Ra was determined and defined as the roughness of the magnetic surface.
Similarly, the roughness of the back coat surface was determined.・ Output: To the rotating cylinder around which the tape sample is wound
The head was brought into contact with the magnetic surface from the outside, and recording / reproduction was performed under the condition that the recording wavelength was 0.67 μm. The evaluation was made relatively based on the output of the tape sample of Example 1. Coefficient of friction of the back coat layer: A tape sample having a length of 400 mm is prepared and brought into contact with a metal pin of SUS304 having a diameter of 5 mm so as to have a winding angle of 90 °, and the tape is loaded at one end with a load of 10 g (T1). Is attached to the tension detection side (T2), and the tension detection side is set to 10 mm / sec.
T2 was read by moving at the speed shown in FIG. Friction coefficient is T2
/ T1. The number of repetitions was performed up to 1000 passes, and the friction coefficient at 10 passes and 1000 passes was determined. -Scratch property of friction pin: After measuring the friction coefficient, the back coat surface was observed with an optical microscope at a magnification of x100, and the scratch property of the pin used in the measurement of the friction coefficient was evaluated. The evaluation results were expressed in five stages of ◎, ○, △, ▲, × in the order of goodness.・ Dropout: Sony DAT deck DTC-1000
Using ES, dropout was counted at a slice level of -16 dB for 5 minutes. The number of dropouts was expressed as an average number / minute.

[0032]

[Table 1]

As is clear from Table 1, the magnetic recording media of Examples 1 to 5 according to the present invention have a small effect on the magnetic layer because the roughness of the back coat layer is small, and even when the friction coefficient is 1000P. It can be seen that the pin does not become large and does not damage the friction pin when the back coat layer slides. As a result, it can be seen that the dropout has not increased.

[0034]

[Table 2]

On the other hand, in Comparative Examples 1 to 3, when the alumina hydrate was present in the back coat layer, the saturation magnetization of the magnetic layer was reduced and the corrosion resistance was poor (the deterioration rate was large). I understand. Also, it can be seen that the dropout increases when the amount of carbon black is small as in Comparative Examples 2 and 3, and when the amount of γ-alumina is small.

[0036]

As described in detail above, the inclusion of the fine particles of γ-alumina in the back coat layer provides excellent surface smoothness and abrasion resistance, does not cause embossing deformation, and is excellent. It is possible to provide a magnetic recording medium exhibiting running properties.

Claims (4)

[Claims] 1. A magnetic recording medium having a magnetic layer on one side of a non-magnetic support and a back coat layer comprising a binder and inorganic powder dispersedly contained on the other side, wherein the back coat layer is A magnetic recording medium comprising 5 to 70 parts by weight of γ-alumina having a particle size of 0.02 to 0.2 μm with respect to all powders, and the balance being carbon black having a particle size of 15 to 60 nm. 2. The average roughness Ra of the surface of the back coat layer.
Is 2 to 5 nm. 3. The method according to claim 1, wherein the back coat layer has an electric resistance of 10 ⁵ to 1.
0 ⁸ Omega, magnetic recording medium according to claim 1 or 2, wherein the coefficient of friction from 0.13 to 0.22. 4. The magnetic recording medium according to claim 1, wherein the back coat layer further contains hematite.