JP2789129B2 - Magnetic recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION 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 In general, a magnetic recording medium such as a magnetic tape is manufactured by applying a magnetic paint composed of a magnetic powder, a binder resin and the like on a support and drying the magnetic paint. Since a conventional magnetic recording medium has only one magnetic layer, it is necessary to cover a wide frequency band from a low band to a high band with one kind of magnetic powder. In particular, in the trend of higher recording density in recent years, a magnetic powder having a high Hc and a high BET value has been used since a recording characteristic in a high frequency range and low noise are required.

However, since the magnetic recording medium is composed of one type of magnetic powder (magnetic layer), the emphasis on high-frequency characteristics is too high.
Since magnetic powder having a high Hc and a high BET value must be used, the low-frequency characteristics become insufficient.

On the other hand, in a magnetic recording medium for video, carbon black is contained in a plurality of magnetic layers in order to increase the magnetic recording capacity or to improve the magnetic recording characteristics of the medium both in a high frequency range and a low frequency range, and to balance them. (Japanese Patent Application Laid-Open No. 1-263926).

According to this known technique, a plurality of magnetic layers are provided, and the lower layer contains 1.0 to 20% by weight of carbon having a pH of less than 6 and the upper layer contains 0.1 to 10.0% by weight of carbon having a pH of 6 or more.

However, it has been found that with this medium, calendar rolls are stained during calendaring. This is presumably because, because the pH of the carbon black in the upper layer is high, an extra curing agent that does not react with the carbon black precipitates on the roll surface, and the calender roll is contaminated. In addition, the carbon black in the upper layer has a high pH, has a low affinity for the binder and the organic solvent, and increases the viscosity of the dispersion, thereby increasing the aggregation of the carbon black and reducing the smoothness of the upper layer surface. easy.

C. The object of the present invention is to improve the high-frequency side RF output and Lumi S / N etc. as well as the low-frequency side chroma output and the chroma S / N etc. in a magnetic recording medium having a magnetic layer composed of a plurality of layers. While showing
It is an object of the present invention to provide a magnetic recording medium capable of greatly reducing calender roll contamination.

D. Constitution of the invention That is, the present invention comprises at least two magnetic layers provided on a non-magnetic support, of which the uppermost layer has carbon black of pH 4 or less and an average major axis length of 0.25.
The present invention relates to a magnetic recording medium characterized by containing a ferromagnetic metal powder having a crystallite size of 200 μm or less and a crystallite size of less than 200 °.

In the magnetic recording medium of the present invention, it is desirable that the magnetic layer is composed of a plurality of layers (the uppermost layer and at least one lower layer), and the plurality of layers are adjacent to each other. The lower layer may be a single layer or two or more layers.

High frequency recording such as RF output and Lumi S / N in the upper layer,
Each layer can be formed so that the reproduction characteristics are good and the recording and reproduction characteristics of a relatively low band such as chroma output and chroma S / N are good in the lower layer.

For this purpose, it is generally preferable that the coercive force (Hc) of the upper layer (especially the uppermost layer) be larger than that of the lower layer, and that the film thickness (or layer thickness) of the upper layer be smaller, more preferably 1.5 μm or less. The thickness of the lower layer adjacent to the upper layer is 1.5 to
It is desirable to be 4.0 μm.

However, in addition to the case where a clear boundary substantially exists between each layer, there may be a boundary region where both layers coexist with a certain thickness. The lower layer is each of the above layers.

In particular, the medium of the present invention is suitable when each magnetic layer is formed by wet-on-wet coating.
Of course, a wet-on-dry method of applying the upper layer after drying the lower layer may be used.

According to the magnetic recording medium of the present invention, the pH
It was found that since 4 or less carbon black was contained, it was possible to prevent calendar roll contamination. Since the carbon black has a pH of 4 or less, the excess hardener in the upper layer reacts with and is captured by the carbon black, so that the hardener can be prevented from being deposited on the calender roll. It is considered possible. In addition, pH4
Because of the following carbon black, the dispersibility (and, consequently, the dispersibility of the magnetic powder) is improved, whereby the surface properties of the magnetic layer are improved and the electromagnetic conversion characteristics are improved.

The pH of the carbon black in the present invention was measured as follows. 5 g of carbon black was boiled for 10 minutes together with 100 g of ion-exchanged water, and then cooled for 30 minutes. The pH of the resulting solution was measured with a pH meter, and this was taken as the pH of the carbon black.

The amount of carbon black added is 100
The amount is preferably 0.1 to 10 parts by weight, and the average particle size of the carbon black is preferably 20 to 75 μm.

The uppermost layer contains a ferromagnetic metal powder together with the carbon black. In order to improve the high-frequency recording and reproduction characteristics, the present invention has an average major axis length of the metal powder obtained by a transmission electron microscope of 0.25 μm or less,
The crystallite size obtained by the X-ray diffraction method is less than 200 °. Due to such physical properties, high magnetization can be achieved by high density filling.

When the uppermost layer contains ferromagnetic metal powder, particularly metal powder having an average major axis length of 0.25 μm or less and a crystallite size of less than 200 mm, p
When carbon black of H4 or less is used, dirt on the calendar roll is greatly reduced.

In the above, the “average major axis length” of the magnetic powder is
50 or more of each were measured from a photograph taken by a transmission electron microscope (in the case of the uppermost layer), and the average was obtained for each. The crystallite size can be determined from the Debye-Scherrer equation using the X-ray diffraction method. For details, Isamu Nita, "X-ray crystallography"
Is obvious.

In addition, when the lower layer contains iron oxide containing Co as a magnetic powder, the chroma output is particularly improved, but at the same time,
Free acid is likely to be present, so the free acid also increases in the adjacent uppermost layer, the hardener is more easily captured in the uppermost layer, and the friction coefficient between the heat roll and the magnetic layer also decreases, It is believed that the calender roll stain is reduced.

The pH of the carbon black added to the uppermost layer should be 4 or less, but is preferably 2.0 to 3.5, more preferably 2.0 to 3.0.

The magnetic recording medium of the present invention has a structure in which a first magnetic layer 2 and a second magnetic layer 4 are laminated in this order on a nonmagnetic support 1 made of polyethylene terephthalate or the like, as shown in FIG. 1, for example. is there. Further, the back coat layer 3 is provided on the surface of the support opposite to the lamination surface, but this is not necessarily required. An overcoat layer may be provided on the second magnetic layer. In the example of FIG. 2, the upper layer is further divided into layers 5 and 6.

In the magnetic recording medium of FIGS. 1 and 2, the thickness of the first magnetic layer 2 is preferably 1.5 to 4.0 μm (for example, 2.5 μm), and the thickness of the second magnetic layer 4 or 2nd, 3rd
Has a total thickness of 0.1 to 1.5 μm (for example, 0.5 to 1.5 μm).
μm).

The second magnetic layer 4 or the third magnetic layer 6 contains carbon black having a pH of 4 or less (preferably having an average particle diameter of 20 to 75 μm).

Examples of such carbon black include the following (provided that pH is shown in parentheses).

Made by Columbian Carbon: Royal Spectra (4.0), Neo Spectra Mark I (4.0), Neo Spectra Mark II (3.0), Raven 5000 (2.8), Raven 7000 (2.1), Raven 3500 (2.5), Raven 1255 (2.5) ), Raven 1035 (3.5), Raven 14 (3.0) Cabot Corporation: Monarch 1300 (2.5), Monarch 1000 (2.5), Black Pearls 1300 (2.5), Black Pearls 1000 (2.5), Black Pearls L (3.0) Magnetic The layers 2, 4, 5, and 6 may contain magnetic powder. Examples of such magnetic powder include γ-Fe ₂ O ₃ and Co-containing γ-F.
Iron oxide magnetic powder such as e ₂ O ₃ , Fe ₃ O ₄ , Co-containing Fe ₃ O ₄ ; Fe, Ni, C
o, Fe-Ni-Co alloy, Fe-Ni alloy, Fe-Al alloy, Fe-Al
-Ca alloy, Fe-Al-Ni alloy, Fe-Al-Co alloy, Fe-Mn-
Zn alloy, Fe-Ni-Zn alloy, Fe-Al-Ni-Co alloy, Fe-Al
-Ni-Cr alloy, Fe-Al-Co-Cr alloy, Fe-Co-Ni-Cr alloy, Fe-Co-Ni-P alloy, Co-Ni alloy, etc. Various ferromagnetic powders such as magnetic powders can be used. The outermost magnetic layers 4 and 6 and the other magnetic layers 2 and 5 (and / or
Or 2) means that the former 4, 6 is the uppermost layer,
The latter 2, 5 or 5 and 2 are the lower layer.

From these magnetic powders, a ferromagnetic metal powder suitable for the magnetic layers 4 and 6 can be selected, and a metal oxide suitable for the magnetic layers 2 and 5 can be selected.

Each magnetic layer also contains a lubricant (eg, silicone oil, graphite, molybdenum disulfide, tungsten disulfide, a monobasic fatty acid having 12 to 20 carbon atoms (eg, stearic acid), and a total of 13 to 40 carbon atoms. , An abrasive (eg, fused alumina), a dispersant (eg, powdered lecithin), an antistatic agent (eg, carbon black), and the like.

The binder usable for the magnetic layers 2, 4, 5, and 6 preferably has an average molecular weight of about 10,000 to 200,000. For example, a vinyl chloride-vinyl acetate copolymer, a vinyl chloride-vinylidene chloride copolymer , Vinyl chloride-acrylonitrile copolymer, polyvinyl chloride, urethane resin, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitro Cellulose), styrene-butadiene copolymer, polyester resin, various synthetic rubbers, phenolic resin, epoxy resin, urea resin, melamine resin, phenoxy resin, silicone resin, acrylic reaction resin, high molecular weight polyester resin and isocyanate Mixtures of bets prepolymer,
Mixture of polyester polyol and polyisocyanate, urea formaldehyde resin, low molecular weight glycol /
Examples thereof include a mixture of a high molecular weight diol / isocyanate, and a mixture thereof.

These _{binders, -SO 3 M, -COOM, -PO} (OM ') 2
(Where M is hydrogen or an alkali metal such as lithium, potassium, and sodium, and M ′ is an alkali metal such as hydrogen, lithium, potassium, and sodium, or a hydrocarbon residue). Good. That is, such a resin improves the compatibility with the magnetic powder due to the polar group in the molecule, thereby further improving the dispersibility of the magnetic powder, and also preventing the aggregation of the magnetic powder to further improve the coating liquid stability. Therefore, the durability of the medium can be improved.

Such a binder, in particular, a vinyl chloride copolymer is obtained by copolymerizing a copolymerizable monomer containing a vinyl chloride monomer, an alkali salt of sulfonic acid, carboxylic acid or phosphoric acid and, if necessary, other copolymerizable monomers. Obtainable. Since this copolymer is obtained by vinyl synthesis, it can be easily synthesized, and various copolymer components can be selected, so that the properties of the copolymer can be adjusted optimally.

The above-mentioned metals such as sulfonic acid, carboxylic acid and phosphoric acid are alkali metals (particularly sodium, potassium and lithium), and potassium is particularly preferable in terms of solubility, reactivity, yield and the like.

In the case where the back coat layer 3 is provided, non-magnetic particles such as barium sulfate are contained in the above-mentioned binder and applied to the back surface of the support.

The material of the support 1 is a plastic such as polyethylene terephthalate or polypropylene;
Metals such as l, Zn and the like, glass, BN, Si carbide, ceramics such as porcelain, pottery and the like are used.

Next, FIG. 3 shows an example of the above-described medium manufacturing apparatus.

In this manufacturing apparatus, when manufacturing the medium shown in FIG. After that, for example, it is oriented by the pre-aligned magnet 33 of 2000 Gauss, and further, for example, 2000 Gauss
Is introduced into a dryer 34 provided with a second-stage oriented magnet 35, where it is dried by blowing hot air from nozzles arranged above and below. Next, the dried support 1 with each coating layer is guided to a super calender device 37 comprising a combination of calender rolls 38, where it is calendered, and then wound up by a take-up roll.
Winded up at 39. Each paint may be supplied to extrusion coaters 10 and 11 through an inline mixer (not shown). Note that, in the figure, the arrow D indicates the transport direction of the non-magnetic base film. Extrusion coaters 10 and 11 are provided with liquid reservoirs 13 and 14, respectively, so that paint from each coater can be wet-coated.
Stack on-wet. In order to manufacture the medium of FIG. 2, one more extruder coater may be added in FIG.

E. Examples Hereinafter, examples of the present invention will be described.

The components, ratios, operation orders, and the like shown below can be variously changed without departing from the spirit of the present invention. In the following examples, "parts" are all parts by weight.

(Example 1) First, each of the following compositions was kneaded in a kneader and then dispersed in a sand mill to prepare a magnetic paint for the upper layer and a magnetic paint for the lower layer.

<Upper layer magnetic paint> ferromagnetic metal powder 100 parts (Composition: Fe: Al = 100: 5 , Hc: 1580Oe, σ s: 120emu / g, average major axis length: 0.20 [mu] m, crystallite size: 170 Å) sulfonic acid Potassium-containing PVC resin 10 parts [Zeon Corporation, trade name MR110] Sodium sulfonate-containing polyurethane 5 parts [Toyobo Co., Ltd., trade name UR-8300] Alumina (average particle size 0.2 μm) 5 parts Carbon black 3 parts [Product name Raven1255, pH2.5] Myristic acid 1 part Stearic acid 1 part Butyl stearate 1 part Methyl ethyl ketone 100 parts Cyclohexanone 100 parts Toluene 100 parts Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) 5 parts <Lower layer Magnetic Coatings for Coating> Co-containing iron oxide 100 parts (Hc: 650 Oe, average major axis length: 0.32μ) Potassium sulfonate-containing PVC resin 10 parts [Nippon Zeon Co., Ltd., trade name MR110] Sodium sulfonate-containing Poly Rethane 5 parts [Toyobo Co., Ltd., product name UR-8300] Alumina (average particle size 0.2 μm) 5 parts Carbon black 1 part [Product name Raven1255, pH2.5] Myristic acid 1 part Stearic acid 1 part Butyl steer Rate 1 part Methyl ethyl ketone 100 parts Cyclohexanone 100 parts Toluene 100 parts Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) 5 parts Next, on a polyethylene terephthalate base film having a thickness of 10.0 μm, a lower magnetic paint B and an upper magnetic paint are provided. A was wet-on-wet coated in an upper layer thickness of 0.5 μm and a lower layer thickness of 2.5 μm sequentially using the apparatus shown in FIG. 3, oriented, dried, and then calendered.

Thereafter, a paint for a BC layer having the following composition was applied to the surface on the opposite side of the magnetic layer or the like so as to have a dry thickness of 0.8 μm.

Carbon black (Raven1035) 40 parts Barium sulfate (average particle size 300 mμm) 10 parts Nitrocellulose 25 parts N-2301 (Nippon Polyurethane Industry Co., Ltd.) 25 parts Coronate L (Nippon Polyurethane Industry Co., Ltd.) 10 parts Cyclohexanone 400 Part: 250 parts of methyl ethyl ketone: 250 parts of toluene In this way, a wide magnetic film was obtained and wound up. This film was cut into an 8 mm width to produce an 8 mm tape.

(Examples 2 and 3) In Example 1, carbon black was added to each of Raven 14
(PH 3.0), and 8 mm tapes were produced in the same manner as in Example 1 except that Black Pearls 1000 (pH 2.5) was used.

(Comparative Example 8) In the same manner as in Example 1, except that the magnetic powder in the upper layer was changed to Co-containing iron oxide (Hc: 800 Oe, average major axis length: 0.16 μm), An inch wide videotape was made.

(Example 5) In the upper layer of Example 1, the ferromagnetic metal powder was changed to 8 m in the same manner as in Example 1 except that the powder had the following composition.
m tape was produced.

Ferromagnetic metal powder (composition: Fe: Al = 100: 5 , Hc: 1600Oe, σ s: 121emu / g, average major axis length: 0.18 .mu.m, crystal size: 150 Å) in the upper layer (Comparative Example 9) Example 1 8m in the same manner as in Example 1 except that the ferromagnetic metal powder was changed to one having the following composition.
m tape was produced.

Ferromagnetic metal powder (composition: Fe: Al = 100: 5, Hc: 1560 Oe, _s : 120 emu / g, average major axis length: 0.27 µm, crystallite size: 250Å) (Example 7) Upper layer of Example 1 To use carbon black in Royal
Except having changed to Spectra (pH 4.0), an 8 mm tape was produced in the same manner as in Example 1.

Example 8 In the lower layer of Example 1, a ferromagnetic metal powder (composition: Fe: Al = 100: 5, Hc: 1560 Oe, σ _s : 120 emu / g, average major axis length) was used in place of the Co-containing iron oxide. An 8 mm tape was produced in the same manner as in Example 1 except that 0.27 μm, crystallite size: 250 °) was used.

(Comparative Examples 1, 2, 3) In Example 1, carbon black
An 8 mm tape was produced in the same manner as in Example 1 except that uctexSC, Conductex975, and SterlingV were changed.

(Comparative Example 4) In Example 1, the carbon black was changed to ConductexS
C, a 1/2 inch tape was produced in the same manner as in Example 1, except that the magnetic powder in the upper layer was changed to Co-containing iron oxide (Hc: 800 Oe, average major axis length: 0.16 μm).

(Comparative Example 5) In Example 1, the carbon black was replaced with VULCANXC-72.
An 8 mm tape was produced in the same manner as in Example 1 except that the pH was changed to 5.0.

(Comparative Example 6) In Comparative Example 1, Raven1255 having a pH of 2.5 was formed under the magnetic layer.
An 8 mm tape was produced in the same manner as in Comparative Example 1 except that was used.

(Comparative Example 7) In Example 1, carbon black was replaced with Raven having a pH of 6.0.
An 8 mm tape was produced in the same manner as in Example 1 except that the tape was changed to 1000.

<Method of Measuring Characteristics in Examples and Comparative Examples> The following performance evaluations were performed on the above tapes, and the results are shown in Table 1 below.

In the case of RF output and Lumi S / N: 8 mm tape, a 100% white signal was input and reproduced at a reference level on a porcelain recording medium using a Sony "V-900" deck. Also, if the playback video signal is 921D / 1
Input to [Noise meter made by Shibasoku Co., Ltd.] and read Lumi S / N from the obtained absolute noise value.

In the case of a 1/2 inch tape, a color video noise meter "Shibasoku925 D / 1" was used, and a value (dB) with respect to a reference tape was shown on a deck of "HR-S7000" manufactured by Victor Company of Japan. The frequency of each signal is as follows.

RF output: 6 MHz Rumi S / N: 6 MHz Chroma S / N, Chroma: output: In the case of 8 mm tape, playback was performed using a Sony "V-900" deck. Further, using a noise meter manufactured by Shibasoku Co., Ltd., the difference between the S / N of the sample in the chroma signal was determined in comparison with the reference tape.

In the case of a 1/2 inch tape, a color video noise meter "Shibasoku925 D / 1" was used, and a value (dB) with respect to a reference tape was shown on a deck of "HR-S7000" manufactured by Victor Company of Japan. The frequency of each signal is as follows.

Chroma S / N: 629 KHz Chroma output: 629 KHz Calender heat roll stain; In the above tape manufacturing process, the degree of stain on the calender roll used for calender treatment was visually observed.

◎ No dirt ○ No dirt △ Dirt × Dirt From this result, based on the present invention, the pH of the uppermost magnetic layer was
It can be seen that when carbon black of 4 or less is contained, the stain on the calendar roll is greatly improved, and the RF output, the Lumi S / N, the chroma output, and the chroma S / N are also good.
In addition, to reduce calender roll stains,
It is desirable to include a Co-containing iron oxide.

Next, as shown in FIG. 2, when the magnetic layer is made into three layers, layers 2, 5, 6 (provided that the compositions of the upper layer 6 and the lower layer 2 are the same as above, but the intermediate layer is composed of the upper layer and the lower layer. Middle Hc (850 Oe)
The other composition is the same as the lower layer, the thickness is 0.3 μm,
When the performance of the intermediate layer was 0.3 μm and the lower layer was 2.5 μm) in the same manner as described above, the results shown in Table 2 below were obtained. According to this, as in the case of the two layers, it can be seen that the configuration of the present invention provides sufficient performance.

F. Advantageous Effects of the Invention As described above, the present invention has at least two magnetic layers provided on a nonmagnetic support, and the uppermost layer among these layers contains carbon black having a pH of 4 or less. Therefore, the extra curing agent reacts with and is captured by the carbon black, so that the extra curing agent is prevented from depositing on the calender roll, and the contamination of the calender roll is greatly improved. Further, since the magnetic layer is composed of at least two layers, a wide frequency band can be covered, and RF output and luminance S /
Chroma output, chroma S / N, etc. are good. This can be further improved by improving the dispersibility of carbon black having a pH of 4 or less in the uppermost layer.

[Brief description of the drawings]

 BRIEF DESCRIPTION OF THE DRAWINGS The drawings are intended to exemplify the present invention, and FIGS. 1 and 2 are cross-sectional views of an example of a magnetic recording medium, and FIG. 3 is a schematic view of a magnetic recording medium manufacturing apparatus. In the reference numerals shown in the drawings, 1 is a non-magnetic support 2... A lower magnetic layer 3... A back coat layer 4, 6... An upper magnetic layer 5.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Nobuyuki Sekiguchi 1 Konica Corporation, Sakura-cho, Hino-shi, Tokyo (56) References JP-A-59-19234 (JP, A) JP-A-1-263926 ( JP, A) JP-A-62-239320 (JP, A) JP-A-63-14323 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11B 5/716 G11B 5/708 G11B 5/706

Claims (1)

(57) [Claims] A magnetic layer provided on a non-magnetic support comprises at least two layers.
A magnetic recording medium comprising the following carbon black and a ferromagnetic metal powder having an average major axis length of 0.25 μm or less and a crystallite size of less than 200 °.