JPH0677314B2 - Magnetic recording medium - Google Patents

Description

Detailed Description of the Invention a. TECHNICAL FIELD The present invention relates to a magnetic recording medium such as a magnetic tape, a magnetic sheet and a magnetic disk.

B. 2. Description of the Related Art Generally, a magnetic recording medium such as a magnetic tape is manufactured by applying a magnetic coating material composed of magnetic powder, a binder resin and the like on a support and drying it.

In such magnetic recording media, especially videotapes,
In order to color the magnetic coating film or prevent electrification, carbon black having excellent colorability and conductivity was contained in the magnetic layer. An average particle size of 30m for carbon with excellent coloring properties
Carbon for pigment less than μ was used (Japanese Patent Publication No. 55-2416).
No. 8). As the conductive carbon, a carbon having a high oil absorption, which is easy to form a structure structure, was used (Japanese Patent Publication No. 56-15052, Japanese Patent Publication No. 57-4968, and Japanese Patent Laid-Open No. 53-1).
34406, JP-A-55-55431).

However, the pigment carbon having a particle diameter of 30 mμ or less, which is used in the above-mentioned prior art, has good dispersibility and high colorability, but has low conductivity and high surface specific resistance of the magnetic layer. As a result, static electricity is easily generated, which sucks dust and the like and causes dropout.

On the other hand, carbon, which has a high oil absorption amount, can easily have a structure structure in the magnetic layer, has high conductivity, and can reduce the surface specific resistance, but has poor dispersibility and increases the surface roughness of the magnetic layer. As a result, the electromagnetic conversion characteristics are deteriorated.

Further, it was discovered that when the above magnetic coating liquid containing carbon was applied to the base, the electromagnetic conversion characteristics of the tape were deteriorated as the coding speed increased.

C. OBJECT OF THE INVENTION The object of the present invention is to provide a high level of electromagnetic conversion characteristics (Lumi S /
N, chroma S / N), the surface resistivity of the magnetic layer is low, dropout is small, and runnability (40 ℃,
There is little decrease in the RF output during the running durability test (80% RH), and the magnetic coating properties do not deteriorate as the coating speed of the magnetic coating liquid increases, and high electromagnetic conversion characteristics are achieved. It is an object of the present invention to provide a magnetic recording medium that can be maintained and has a low friction coefficient of the magnetic layer to realize stable running.

D. Structure of the invention and its action and effect That is, the present invention, the specific surface area is 20 ~ 80m ² / g in BET value, and the oil absorption is 160 ~ 210ml / 100g carbon black carbon black magnetic material 100 weight. The magnetic recording medium is characterized in that it is contained in the magnetic layer in a ratio of 0.5 to 5 parts by weight with respect to 10 parts by weight, and that the surface roughness Ra (cutoff 0.25 μm) of the magnetic layer is 0.025 μm or less. It is related.

First, the superiority of the carbon black used in the present invention will be described.

Generally, carbon having a BET value of about ²⁰ to 70 m ² / g can be roughly classified into those having an oil absorption of 150 ml / 100 g or less and those having an oil absorption of 300 ml / 100 g or more. Many of the former carbons are known, such as Colombian Leven 450, R-410, R-420, Cabot's Sterling V, Sterling-NS, Mitsubishi Kasei's # 22B, # 20B, # 60, # 50. Has been.

However, the drawbacks of these carbons are that they have a low oil absorption, making it difficult to form a structure structure, lowering the conductivity, and increasing the surface specific resistance of the magnetic layer. Usually, when 5 parts by weight of these carbons are mixed in the magnetic layer with respect to 100 parts by weight of the magnetic material, the surface resistivity becomes 5 × 10 ¹⁰ Ω or more.
If the surface resistivity is about this level, static electricity is likely to be generated, resulting in increased drops.

In the latter case, the BET is 20 to 70 m ² / g and the oil absorption is 300 ml / 100 or more, but the surface specific resistance is slightly lowered, but the oil absorption is large, so the dispersibility is poor and the electromagnetic conversion characteristics are remarkable. Will lower it. In particular, with these carbons, when the coating speed of the magnetic coating liquid is increased, the surface of the magnetic layer is roughened, and electromagnetic conversion characteristics are deteriorated. Specific examples of the latter carbon include JP-B-52-18561 and JP-B-53
-Asahi Carbon HS-500 used in No. 20203 and Japanese Patent Publication No. 54-9041.

Now, the carbon used in the present invention is in a region (BET 20-80 m ² / g and oil absorption 160-
It is characterized by being present in 210ml / 100g). That is, oil absorption
160 to 210 (ml / 100g) carbon is well dispersed in the magnetic coating liquid, forms an appropriate structure structure, and has a low surface specific resistance, which results in less dropout. In particular, since the dispersion is good, the surface roughness of the magnetic layer does not deteriorate when the magnetic coating liquid is applied at a high speed, and the electromagnetic conversion characteristics of the tape can be maintained at a high level. Further, since the present carbon is well dispersed in various binders (binders), the mutual binding force between the carbon, the magnetic substance and the binder becomes extremely good. As a result, in the running durability test (Runnability) under high temperature and high humidity of 40 ° C. and 80% RH, RF output did not decrease and good results were shown.

Further, the present carbon has the effect of drastically reducing the dynamic friction coefficient of the magnetic layer by adding a small amount of 5 parts by weight or less (preferably 2 parts by weight or less) to 100 parts by weight of the magnetic material. For example,
Addition of 1 part by weight to 100 parts by weight of the magnetic material resulted in a dynamic friction coefficient of 0.14 for HS-100. Surface roughness Ra at this time
The (cutoff 0.25 μm) was 0.015. The use of this carbon improves the dispersion and improves the surface roughness Ra of the magnetic layer.
0.025 μm or less (In order to obtain high electromagnetic conversion characteristics, R
The smaller the value of a, the better), so the electromagnetic conversion characteristics are greatly improved.

BET value of the carbon is preferably 20 to 50 m ² / g, more preferably 20 to 40 m ² / g. Oil absorption is preferably 160
~ 190 ml / 100 g, more preferably 170-190 ml / 100 g.

The carbon is mixed in an amount of 5 parts by weight or less with respect to 100 parts by weight of the magnetic material, preferably 3 parts by weight or less, more preferably 2 parts by weight or less.
It is less than or equal to parts by weight. Surface roughness of magnetic layer Ra (cut off 0.25
μm) is 0.025 μm or less, preferably 0.022 μm
The following is more preferable and 0.018 μm or less is more preferable.

Specific examples of carbon that can be used in the present invention are as follows.

In addition to the carbon used in the present invention, carbon black having another BET value and oil absorption may be used in combination. For example, Conductance made by Colombian
SC, Cabot's Vulcan-P, Vulcan-9, BP
(Black Pearls) -1000, BP-880, BP-L, Sterling V and the like.

In the above, the "specific surface area" means a surface area per unit weight, and is a physical quantity which is completely different from the average particle diameter, and for example, even if the average particle diameter is the same, the specific surface area is large, Some have a small specific surface area. To measure the specific surface area, for example, first of all, magnetic powder at
Degas while heating for 0 to 60 minutes to remove those adsorbed on the powder, then introduce into the measuring device, set the initial pressure of nitrogen to 0.5 kg / m ^2, and Adsorption measurement at liquid nitrogen temperature (-195 ℃) (generally called BET method for measuring specific surface area. For details, see J. Ame. Chem.
Soc, 60 309 (1938)). This specific surface area (BET
As a measuring device for the “value”, a “powder and granular material measuring device (canter soap)” jointly manufactured by Yuasa Battery Co., Ltd. and Yuasa Ionics Co., Ltd. can be used. A general explanation of the specific surface area and its measurement method is described in detail in "Measurement of powder" (co-authored by JMDALLAVALLE, CLYDEORR Jr, translated by Benda et al. Edited, pp. 1170-1171, edited by The Chemical Society of Japan,
It is also described in Maruzen Co., Ltd., April 30, 1966 (In the above "Chemical Handbook", the specific surface area is simply referred to as the surface area (m ² / gr), but in the present specification The same as the specific surface area.)

Regarding the above-mentioned "oil absorption (DBP method)", DBP (Dibutylphthalate) was added little by little to 100 g of pigment powder, the state of the pigment was observed while kneading, and the point of forming one lump from the state of being dispersed dispersively DBP ml when found
Let the number be the DBP oil absorption.

The magnetic recording medium of the present invention is, for example, as shown in FIG.
The magnetic layer 2 is provided on the support 1. A BC layer 3 is provided on the surface opposite to the magnetic layer 2. This BC layer may or may not be provided. Magnetic powders used in the magnetic layer 2, particularly ferromagnetic powders, include γ-Fe ₂ O ₃ and Co.
Examples of the magnetic powder include γ-Fe ₂ O ₃ , Fe ₃ O ₄ , and Co-containing Fe ₃ O ₄ . Of these, Co-containing iron oxide is preferable. Further, when the BET value of the magnetic powder is 25 m ² / g or more, further 40 m ² / g or more, the effect is remarkable. In the magnetic layer 2, in addition to the above-mentioned carbon black, a lubricant (for example, silicone oil, graphite, molybdenum disulfide, tungsten disulfide, monobasic fatty acid having 12 to 20 carbon atoms (for example, stearic acid))
And fatty acid ester consisting of monohydric alcohol having 3 to 26 carbon atoms), antistatic agent (eg graphite)
Etc. may be added. In addition, non-magnetic abrasive particles may be added, but alumina (α-Al ₂ O ₃ (corundum)
Etc.), artificial corundum, fused alumina, silicon carbide, chromium oxide, diamond, artificial diamond, garnet, emery (main components: corundum and magnetite), etc. are used. The content of the abrasive is preferably 20 parts by weight or less with respect to the magnetic powder, and the average particle size thereof is preferably 0.5 μm, more preferably 0.4 μm or less.

Further, at least polyurethane can be used as the binder resin of the magnetic layer, which can be synthesized by the reaction of polyol and polyisocyanate. When a phenoxy resin and / or a vinyl chloride-based copolymer is contained together with polyurethane, the dispersibility of the magnetic powder when applied to the magnetic layer is improved and its mechanical strength is increased. However, the layer becomes too hard only with the phenoxy resin and / or the vinyl chloride copolymer, but this can be prevented by the inclusion of polyurethane, and the adhesion to the support or the underlayer becomes good. In addition to the above, as the binder resin, a fibrous resin, a thermoplastic resin, a thermosetting resin, a reactive resin, or an electron beam irradiation curable resin may be used.

Further, the carbon black according to the present invention used for the magnetic layer 2 may also be added to the BC layer 3. It may be used in combination with two or more kinds of carbon, and may be used as a filler such as CaCO ₃ or Zn
You may use together with O, BaCO _3, etc.

The magnetic recording medium shown in FIG. 1 may have an undercoat layer (not shown) provided between the magnetic layer 2 and the support 1, or may not have the undercoat layer ( The same applies below).
Further, the support may be subjected to corona discharge treatment.

As the material of the support 1, polyethylene terephthalate, plastics such as polypropylene, metals such as Al and Zn, glass, BN, Si carbide, porcelain, ceramics such as pottery, etc. are used.

It is desirable that a predetermined amount of polyfunctional isocyanate as a cross-linking agent is added to the coating material when the above-mentioned magnetic layer or the like is formed by coating, in order to strengthen the magnetic layer. As such a cross-linking agent, in addition to the polyfunctional polyisocyanate described above,
Triphenylmethane triisocyanate, Tris- (p
-Isocyanate phenyl) thiophosphite, polymethylene polyphenyl isocyanate and the like, methylene diisocyanate type and tolylene diisocyanate type are preferable. When the magnetic layer is cured by electron beam irradiation or the like, the addition of the isocyanate compound may be omitted or may be added.

FIG. 2 shows another magnetic recording medium.
An OC layer 4 is provided on the magnetic layer 2 of the medium shown. this
The OC layer 4 is provided in order to protect the magnetic layer 2 from damage and the like, but it is necessary for the OC layer 4 to have sufficient lubricity. Therefore, as the binder resin for the OC layer 4, the urethane resin used for the magnetic layer 2 described above (preferably in combination with a phenoxy resin and / or a vinyl chloride-based copolymer) is used.

FIG. 3 shows a magnetic recording medium configured as a magnetic disk, in which the same magnetic layer 2 and OC layer 4 as described above are provided on both sides of the support 1, respectively. A binder resin containing as a main component may be included.

E. EXAMPLES Hereinafter, the present invention will be described with reference to specific examples. However,
In the following, "part" represents part by weight.

The following components were prepared for the magnetic paint.

Co-containing magnetic iron oxide 100 parts Vinyl chloride-vinyl acetate copolymer 13〃 (UCGH VAGH) Polyurethane resin 7〃 (Goodrich Estane 5701) α-Al ₂ O ₃ 5〃 Myristic acid 1〃 Butyl stearate 1 〃 Lecithin 3 〃 Carbon black (listed in the table below) Polyisocyanate 13 〃 Cyclohexanone 130 〃 Toluene 70 〃 A magnetic powder dispersion coating solution in which these components are dispersed with a ball mill,
After the polyisocyanate was added, one side of polyethylene terephthalate having a thickness of 15 μm was coated with an extrusion coater, dried, subjected to calender surface treatment, and then cut into 1/2 inch width. At this time, the film thickness of the magnetic layer was 40 μm on average.

When the following measurements were performed on each video tape, the results shown in the following table were obtained.

RF output: RF output at 4 MHz was measured using a VTR deck for measuring RF output, and a value decreased after 100 times of reproduction was taken as a reference (0 dB) in Example 9 (unit: dB). S / N: Shiba Soku noise meter (925D /
1) was used, Comparative Example 1 was used as a reference tape (0 dB), and the difference was displayed. The high pass filter is 4.2MHz,
The low pass filter was performed at 10 kHz. VTR is JVC HR-D
120 was used.

Chroma S / N: Same as RF output.

Friction coefficient: Measure the tape tension at the inlet and outlet of the head cylinder I asked.

Dropout: The number of scratches on the playback screen.

From these results, it can be seen that when carbon black is used according to the present invention (Sample Nos. 4 to 6), it is superior to the comparative examples in the following points.

Electromagnetic conversion characteristics at high level (Lumi S / N, Chroma S /
Must have N).

 There are few dropouts.

Little decrease in RF output during Runnability (running durability test under the conditions of 40 ° C and 80% RH).

As the coating speed of the magnetic coating liquid increases, the coating properties of the magnetic coating film do not deteriorate, and high electromagnetic conversion characteristics can be maintained.

The friction coefficient of the magnetic layer is low, and stable running can be realized.

Next, the BET value and the oil absorption of the carbon black were changed for the sample according to Example 5 above.
The results shown in FIGS. 5 and 5 were obtained. From this result, the BET value of carbon black was set to 20 to 80 m ² / g, and the oil absorption amount was set to 160 to
When it is set to 210 ml / 100 g, the dynamic friction coefficient can be lowered while maintaining Lumi S / N. Thus, it can be seen that the advantage of limiting the scope of the present invention is remarkable.

[Brief description of drawings]

The drawings show an embodiment of the present invention. FIGS. 1, 2, and 3 are enlarged cross-sectional views of a part of a magnetic recording medium according to each example, and FIGS. 4 and 5 are carbon blacks. 6 is a graph showing each characteristic when the physical quantity of is changed. In the reference numerals used in the drawings, 1 ... Support 2 ... Magnetic layer 3 ... Backcoat layer (BC layer) 4 ... Overcoat layer (OC layer).

Claims (1)

[Claims] 1. A carbon black having a specific surface area of 20 to 80 m ² / g as a BET value and an oil absorption of 160 to 210 ml / 100 g as a DBP value of 0.5 to 5 parts by weight per 100 parts by weight of a magnetic material. A magnetic recording medium, characterized in that the magnetic layer is contained in a ratio of 1 part, and the surface roughness Ra (cutoff 0.25 μm) of the magnetic layer is 0.025 μm or less.