JPH0677312B2 - 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,
The technology of using carbon black together in order to simultaneously satisfy some of the characteristics such as conductivity, friction coefficient, surface property (that is, electromagnetic conversion characteristics), and wear resistance of the medium is
Conventionally, JP-A-59-5426, 59-16141, 58-218039
No. 58-211321, Japanese Patent Publication No. 53-202020, 54-9041 and the like are known.

However, a recording medium having excellent conductivity and a low friction coefficient (that is, good running property and excellent wear resistance) without roughening the surface (that is, without deteriorating the electromagnetic conversion characteristics of the magnetic recording medium). Was insufficient to provide.

That is, in the above-mentioned conventional technique, the conductivity is not always enhanced by using carbon black having a particle size of 40 mμ or less. For example, when carbon having a particle diameter of 23 mμ is used alone, the surface resistivity is 10 ¹⁰ unless the magnetic layer contains 15 parts by weight or more with respect to 100 parts by weight of magnetic powder.
Does not fall below Ω / sq. However, when such a large amount of carbon is added, the electromagnetic conversion characteristics deteriorate. Further, with carbon black having a particle diameter of 40 mμ or less, friction on the surface of the magnetic layer becomes large. If a large amount of lubricant is added to compensate for this, phenomena such as deterioration of electromagnetic conversion characteristics and bleed-out occur. If a large amount of carbon black having a particle size of 50 mμ or more is used, the electromagnetic conversion characteristics deteriorate. Also, carbon black having a particle size of 50 mμ or more does not always improve conductivity. B with particle size smaller than 30 mμ
Both ET500 m ² / g or more carbon black and carbon black with a particle size of 40 mμ or more generally reduce the electromagnetic conversion characteristics.

C. OBJECT OF THE INVENTION It is an object of the present invention to provide a medium having a high conductivity and a low coefficient of friction without deteriorating the surface property (that is, having a high level of electromagnetic conversion characteristics).

D. Structure of the invention and its action and effect The present invention has a specific surface area of BET value of 15 m ² / g or more and less than 50 m ² / g, oil absorption of DBP value of 40 ml / 100 g or more, less than 100 ml / 100 g, and, A first carbon black having a particle size of 50 mμ or more and less than 75 mμ, a specific surface area of 50 m ² / g or more in BET amount and less than 900 m ² / g, and an oil absorption amount of 40 ml / 1 in DBP value
A second carbon black having a content of 00 g or more and less than 160 ml / 100 g is contained in the magnetic layer, and the BET values of the first carbon black and the second carbon black are different from each other by 25 m ² / g or more. The present invention relates to a characteristic magnetic recording medium.

According to the present invention, since the first carbon black and the second carbon black each having a BET value and an oil absorption in a specific range are used in combination, the above-mentioned deficiencies of the prior art are sufficiently solved. It turns out. That is,
The BET value and oil absorption of the first carbon black are in appropriate ranges, and good dispersibility is maintained. In addition, since the particle size is less than 75 mμ, the dispersibility is good and the friction coefficient is improved. It also reduces the light shielding property. Moreover,
For improving conductivity, the second carbon black is 16
Since it exhibits an oil absorption of less than 0 ml / 100 g (desirably less than 140 ml / 100 g), it can relatively easily have a structure structure and exhibit high conductivity. At the same time, BET value is 50m
^Since it is relatively large at ² / g or more (actually less than 900 m ² / g), it is easy to exhibit high conductivity also in this respect, but the value is further 60 m ² / g or more and less than 400 m ² / g It is desirable to do.

In the present invention, in order to obtain the above effects, the addition amount of carbon black is preferably 1 to 20 parts by weight based on 100 parts by weight of the magnetic powder in the total amount of the first and second carbon blacks, Even more preferably 3 to 15 parts by weight. There is also a desirable range for the ratio of both carbon blacks, and the weight ratio of the first carbon black to the second carbon black =
(6: 4) to (1: 9) are preferable, and (5: 5) to (2: 8) are more preferable.

The first carbon black usable in the present invention includes:
Examples include Raven 410, Raven 420, Raven 430, and Raven 450 manufactured by Colombian Carbon. The second carbon blacks are Raven 1255, Raven 1035, Raven 1000, Raven 2000, Raven 5000, Conductex-SC manufactured by Colombian Carbon, and Black Pearls manufactured by Cabot. ) -L, Black Pearls 100
0, Black Pearls 880, Black Pearls 1300,
Vulcan-P, Vulcan-9, Mitsubishi Kasei CF-9, # 4000 and the like can be mentioned.

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, the effect is remarkable when the BET value of the magnetic powder is 35 m ² / g or more, and further 40 m ² / g or more. In addition to the above-described first and second carbon blacks, the magnetic layer 2 includes a lubricant (for example, silicone oil, graphite, molybdenum disulfide, tungsten disulfide, a monobasic fatty acid having 12 to 20 carbon atoms (for example, stearin). Acid) and a fatty acid ester consisting of a monohydric alcohol having 3 to 26 carbon atoms), an antistatic agent (eg graphite) and the like may be added. In addition, non-magnetic abrasive particles may be added, but this may include 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.

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.
The surface roughness of the OC layer 4 is Ra ≦ 0.02 especially in relation to the color S / N.
It is preferable that μm and Rmax ≦ 0.13 μm. In this case, the surface roughness of the support 1 is Ra ≦ 0.03 μm and Rmax ≦ 0.13 μm,
It is desirable to use a smooth support 1.

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 magnetic powder dispersion coating liquid dispersed in a ball mill with each composition of Examples 1 to 7 and Comparative Examples 1 to 5 shown in FIG. 4 was extruded on one side of a polyethylene terephthalate base having a thickness of 15 μm after addition of polyisocyanate to a coater. Was applied, dried, and subjected to calender surface treatment, and then cut into 1/2 inch widths. At this time, the thickness of the magnetic layer was 4.0 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 4MHz was measured using a VTR deck for RF output measurement, and after 100 times of reproduction, the value decreased with reference to Comparative Example 1 (0 dB) (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.

Surface resistivity: Measured with a surface electrometer.

From these results, it can be seen that when two types of carbon black are used in combination according to the present invention (Examples 1 to 7), they are superior to the comparative examples in the following points.

(1) A high level of electromagnetic conversion characteristics can be obtained.

(2) A surface resistivity of 1 × 10 ¹⁰ Ω / sq or less can be obtained.

(3) The coefficient of friction on the surface of the magnetic layer is lowered (running durability is good).

(4) The surface of the magnetic layer is unlikely to be scratched by a head or the like.

(5) Little powder drop when repeatedly run.

(6) Since the electromagnetic conversion characteristics do not deteriorate even with a high addition amount, it is possible to reduce the film thickness with VHS tape.

Next, as shown in FIGS. 5 and 6, with respect to Example 8 and Comparative Examples 6 to 21 in which various kinds of carbon black were further used, the characteristics of the obtained media were measured in relation to each physical quantity of carbon black. The results are shown in FIGS. 7 to 11.

Fig. 7: RF according to the BET value of the second carbon black with the first carbon black (Raven-420) fixed
The output is shown (data of Examples 1, 2, 3, 4, 5 and Comparative Examples 6, 7, 8).

FIG. 8: Shows the RF output according to the DBP oil absorption of the second carbon black with the first carbon black (Raven-420) fixed (Examples 1, 2, 3, 4, 5 and comparison). (Data of Examples 9, 10, and 11).

Fig. 9: Second carbon black (Conductex-
SC) was fixed and the dynamic friction coefficient according to the BET value of the first carbon black was shown (Examples 2, 6, 7 and Comparative Examples).
Data for 12, 13, 14, 15, 16, 19, 20, and 21).

Fig. 10: Second carbon black (Conductex-
SC) was fixed and the surface resistivity was shown according to the DBP oil absorption of the first carbon black (data of Examples 2, 6, 7 and Comparative Examples 13, 14, 15, 17, 18).

Fig. 11: Second carbon black (Conductex-
The RF output when the particle size of the first carbon black was changed by fixing SC) was shown (data of Examples 2, 6, 7, 8 and Comparative Examples 12, 13, 14).

From the above, the BET value of the first carbon black 15 m ² / g or more, 50 m ² / not less than g, the not be obtained a low coefficient of friction, the oil absorption amount output less than 100 ml / 100 g was markedly enhanced, also By improving the RF output when the particle size is less than 75 mμ, and further improving the output by setting the BET value of the second carbon black to 50 m ² / g or more, and by increasing the oil absorption amount to less than 160 ml / 100 g, The output can be improved. 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 FIG. Tables collectively showing the coating composition, FIGS. 5 and 6 are tables collectively showing the magnetic coating compositions of the tapes according to other examples, FIG. 7, FIG. 8, FIG. 9, FIG. Figure 11 is a graph showing each characteristic when the physical quantity of carbon black is changed. Incidentally, in the reference numerals used in the drawings, 2 ... magnetic layer 3 ... back coat layer (BC layer).

Claims (1)

[Claims] 1. A specific surface area of BET value of 15 m ² / g or more and less than 50 m ² / g, and oil absorption amount of DBP value of 40 ml / 100 g or more, 100 ml / 100 g
And a first carbon black having a particle size of 50 mμ or more and less than 75 mμ and a specific surface area of BET value of 50 m ² / g
Above, less than 900m ² / g, and oil absorption is 40ml in DBP value
The second carbon black having a density of / 100 g or more and less than 160 ml / 100 g is contained in the magnetic layer, and the BET values of the first carbon black and the second carbon black are different by 25 m ² / g or more. A magnetic recording medium characterized by: