JPS63102037A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve S/N by incorporating magnetic Co-gamma-Fe2O3 powder specified in SBET specific surface area, coercive force and residual magnetic flux density into a 1st magnetic layer and 2nd magnetic layer and forming the 1st magnetic layer to the thickness larger than the thickness of the 2nd magnetic layer. CONSTITUTION:The magnetic Co-gamma-Fe2O3 powder having >=40m<2>/g SBET specific surface area, 350-450Oe coercive force and >=1,650 gauss residual magnetic flux density is incorporated into the 2nd magnetic layer. The magnetic Co-gamma-Fe2O3 powder having 26-40m<2>/g SBET specific surface area, the coercive force equal to or lower than the coercive force of the magnetic powder incorporated into the 2nd magnetic layer and >=1,800 gauss residual magnetic flux density is incorporated into the 1st magnetic layer. The 1st magnetic layer is formed to the thickness larger than the thickness of the 2nd magnetic layer. Since advantage is taken of the feasibility of lowering the noise level possessed by the magnetic powder of the fine particles having the large specific surface areas in the above-mentioned manner, the effect of improving a transfer characteristic by the 1st magnetic layer and the effect of lowering the noise level by the 2nd magnetic layer are interacted with good balance to lower then noise level and to improve the S/N.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a magnetic recording medium, and more specifically, the present invention relates to a magnetic recording medium, which has two magnetic layers, has a high S/N ratio, and has a low transfer rate. It is related to recording media.

[Background of the Invention] In recent years, there has been a demand for audio cassette tapes that have low noise levels, well-balanced frequency characteristics, and good output characteristics in all frequency bands. Recently, music sources have become increasingly digital, such as compact discs, and are becoming ultra-high-fidelity and extremely low-noise, so the above-mentioned demands are becoming stronger for audio cassette tapes as well.

As a means to meet these requirements, when iron oxide-based magnetic powder is used as the magnetic powder used in magnetic recording media (hereinafter sometimes referred to as magnetic tape), it is necessary to use the magnetic properties of fine particles with a large S BET specific surface area. There is a way to reduce the noise level by using powder.

However, when using such fine-grained magnetic powder, the noise level is reduced, but at the same time the transfer characteristics (when a magnetic tape with a signal recorded on it and a magnetic tape with no signal recorded on it are overlapped, the recording starts from the one with the recorded signal) There is a disadvantage that the signal transfers to the side where the signal is not transferred and the level difference decreases (in other words, the transfer becomes more pronounced).

As described above, a single magnetic layer containing fine particles of magnetic powder could not satisfy the requirements of reducing noise and not deteriorating transfer characteristics.

In order to satisfy such requirements, for example,
Japanese Patent No. 1-137402 proposes a magnetic tape consisting of two magnetic layers. However, although the magnetic tape disclosed in this publication secures a bias noise level when the bias is 100%, it cannot be said that the transfer characteristics are at a fully satisfactory level, and the output in the entire frequency band is not sufficient. Since there is a tendency
It cannot be said that the level of magnetic tape for music recording is still sufficiently satisfactory.

[Purpose of the Invention] The present inventor conducted various studies with the aim of improving a tape that has excellent transfer characteristics and good output in all frequency bands while taking advantage of the low noise level of fine particle magnetic powder with a large specific surface area. However, the present invention was achieved.

A first object of the present invention is to provide a magnetic recording medium, such as a magnetic tape, which can dramatically improve the S/N ratio without increasing the noise level.

The second object is to provide a magnetic tape with improved transferability.

The third purpose is MOL (distortion rate in low frequency band),
It is an object of the present invention to provide a magnetic tape having excellent output in all frequency bands, including excellent 5QL (output level in a high frequency band).

[Configuration 1 of the Invention The present invention provides a magnetic recording medium in which a first magnetic layer is provided on the surface of a non-magnetic support and a second magnetic layer is provided thereon, wherein the second magnetic layer has an S BET specific surface area of Co-γ of 40 m2/g or more, coercive force (Hc) of 350 to 450 Oe, and residual magnetic flux density (Br) of 1650 Gauss or more
-Fe2O3 magnetic powder is contained, and the first magnetic layer is S B
ET specific surface area is 26 to 40 m'/g, coercive force (Hc) is equal to or lower than the coercive force of the magnetic powder contained in the second magnetic layer (preferably 0.9 to 1.0 times), and Co with a residual magnetic flux density (Br) of 1800 Gauss or more
- A magnetic recording medium containing γ-Fe2O3 magnetic powder, wherein the first magnetic layer is thicker than the second magnetic layer.

In the present invention, the magnetic powder of the second magnetic layer is C.

-γ-Fe2O. (Cobalt-containing iron trioxide) magnetic powder with an S BET specific surface area of 40rr? /g or more, preferably 40 to 50rr1'/g, and the coercive force (Hc) is 350 to 450 Oe, preferably 360 to 4
000e, and the residual magnetic flux density (Br) is 165
It is a magnetic powder with a strength of 0 Gauss or more.

When the S BET specific surface area of the magnetic powder is less than 40 m2/g, the noise level is high. Further, as the specific surface area increases, the noise level decreases, but transfer becomes more pronounced and Br tends to decrease, so it is preferable that the SBET specific surface area of the magnetic powder is 50 m'/g or less. If Hc is smaller than the lower limit of the above range, the output at high frequencies will be reduced and the high range will be insufficient.If Hc is greater than the upper limit of the above range, the high range will be too emphasized and the low range will be insufficient, resulting in an unbalanced frequency characteristic.

The magnetic powder of the first magnetic layer is Co-γ-Fe2O3 magnetic powder, and has an S BET specific surface area of 26 to 4 orn'/g, preferably 29 to 35 orn'/g, and Hc is contained in the second magnetic layer. Equivalent to or lower than the Hc of the magnetic powder used (
Preferably 0.9 to 1.0 times, more preferably 0.9
2 to 0.98 times) and a Br of 1800 Gauss or more.

If the S BET specific surface area of the magnetic powder contained in the first magnetic layer is smaller than the lower limit of the above range, the noise level will increase, and if it is larger than the upper limit of the above range, Br will decrease and MOL
The value also decreases, making it impossible to obtain high output, and at the same time, transfer becomes noticeable. Furthermore, if the magnification of the Hc of the magnetic powder contained in the first magnetic layer to the Hc of the magnetic powder contained in the second magnetic layer is smaller than the above range, the low and high frequencies will be emphasized, and the mid-range If it is insufficient, the reproduced sound lacks power, and if it is larger than the above range, the electromagnetic conversion characteristics and the perceptual frequency characteristics are insufficient in the low and high frequencies, and the original sound reproduction ability is reduced.

In the magnetic recording medium of the present invention, first, a magnetic paint obtained by kneading magnetic powder of the first magnetic layer with a binder solution is applied onto a non-magnetic support to form a first magnetic layer coating film. Next, a magnetic paint obtained from the magnetic powder of the second magnetic layer and a binder solution is applied thereon to form a second magnetic layer coating film, which is generally adopted in the manufacture of magnetic tapes. It can be manufactured using a method known per se.

As the non-magnetic support, a non-magnetic support known as a support for magnetic recording media can be used. The most common is polyethylene terephthalate film.

The binder solution for manufacturing the first magnetic paint and the second magnetic paint is generally a binder and a solvent used in manufacturing coated magnetic tape, and a binder solution containing a lubricant and an abrasive as necessary. It is.

There are no particular limitations on the binder used in manufacturing the magnetic recording medium of the present invention. For example, vinyl chloride/vinyl acetate resin, vinyl chloride/vinylidene chloride resin, cellulose resin, acetal resin, urethane resin, acrylonitrile φ
There are thermoplastic resins such as butadiene resins, and these can be used alone or in combination.

Examples of solvents used in the production of magnetic paints include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, ethyl isobutyl ketone, and cyclohexanone; esters such as methyl acetate, ethyl acetate, butyl acetate, and acetic acid glycol monoethyl ether; Glycol ethers such as ether, glycol dimethyl ether, and dioxane; Aromatic hydrocarbons such as benzene, toluene, and xylene; Methylene chloride, ethylene chloride,
Carbon tetrachloride, chloroform, ethylene chlorohydrin,
Examples include chlorinated hydrocarbons such as dichlorobenzene, and these solvents can be used alone or in combination. Particularly preferred are polar solvents such as ketones or solvents containing polar solvents.

When manufacturing magnetic paint, ferromagnetic powder is uniformly kneaded with a binder solution containing the above-mentioned specific amount of water.
Spread. This kneading and dispersion is performed using a two-roll mill, a three-roll mill, an oven kneader, a pressure kneader, a continuous kneader, etc., followed by a sand grinder,
A method of post-dispersion using a ball mill or the like is generally used. Note that, as described above, water may be added during the kneading and dispersion operations.

Magnetic paint contains abrasives, lubricants,
Of course, any of various additives such as dispersants and antistatic agents may be added depending on the purpose.

Methods for applying the first magnetic paint and the second magnetic paint include air doctor coating, blade coating, rod coating, extrusion coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, gravure coating, and kiss coating. , cast coat, spray coat, spin code, and other methods can be used, and detailed explanations of these methods can be found in "Coating Engineering" published by Zenkin Shoten, pp. 253-277 (Showa 46゜3.2).
(Published by O).

Further, as a method for layering the second magnetic layer on the first magnetic layer, the first magnetic layer may be coated and dried, and the second magnetic layer may be coated and dried on top of the first magnetic layer. Showa 48-9880
A two-layer simultaneous coating method as described in Japanese Patent Application Laid-Open No. 48-99233 and the like can be adopted. By such a method, the first magnetic paint is applied so that the first magnetic layer has a dry thickness as shown below, and the second magnetic paint is applied so that the second magnetic layer has a dry thickness shown below.

The thickness of the first magnetic layer of the magnetic recording medium of the present invention is 3.5~
The thickness of the second magnetic layer is preferably 5.0 μm, particularly 4.0 to 4.5 μm, and the thickness of the second magnetic layer is preferably 0.5 to 1.5 gm, particularly 0.5 to 11 μm. If the thickness of the second magnetic layer is smaller than the above range, the effect of reducing the noise level is poor, and even if it is larger than the above range, no further noise level reduction effect can be obtained and the thickness remains almost constant. On the contrary, the transfer characteristics deteriorate, the MOL of the low frequency output decreases, and the balance of frequency characteristics deteriorates.

The magnetic coating layer coated on the non-magnetic support is optionally treated to orient the magnetic powder in the layer, and then dried to obtain a desired magnetic layer. Further, if necessary, the magnetic recording medium is manufactured by performing surface smoothing processing and cutting into a desired shape. This surface smoothing process is performed by a smoothing process before drying or a calendering process after drying.

[Effects of the Invention] The magnetic recording medium of the present invention includes a first magnetic layer and a second magnetic layer containing magnetic powder each having specified properties as described above, and each magnetic layer also has specific properties. Since the transfer characteristic improvement effect of the first magnetic layer and the noise level reduction effect of the second magnetic layer interact in a balanced manner, the noise level is low, and therefore the S/N ratio is dramatically improved. It has excellent transfer characteristics and MOL
, SQL, etc., and has good output in all frequency bands.

Next, Examples and Comparative Examples will be shown to further specifically explain the present invention. In each case, 1 part means 1 part by weight unless otherwise specified.

[Comparative Example 1] Magnetic coating composition Co-yFe2O3 100 parts [Hc: 3
80Oe, S BET specific surface area: 30rn”/g, Br
: 1880 Gauss] Vinyl chloride/vinyl acetate/vinyl alcohol copolymer 10 parts [copolymerization ratio,
92:3:5] Polyester polyurethane resin 7 parts Oleic acid 2 parts Dimethylsiloxane (degree of polymerization 400) 0,5 parts Methyl ethyl ketone 200 parts Methyl isobutyl ketone 150 parts The above components were cross-dispersed for 48 hours using a ball mill. After the cross-dispersion was completed, 5 parts by weight of incyanate was added to the ball mill and mixed for 20 minutes. The obtained dispersion liquid was filtered using a filter having an average pore size of 1JLm to prepare a magnetic paint.

The obtained magnetic coating material was applied onto the surface of a polyethylene terephthalate support having a thickness of 7 pm using a reverse roll so that the thickness of the magnetic layer after calendering was 5.5 lm. The support coated with the magnetic paint was subjected to magnetic field orientation treatment using a 1500 gauss magnet while the magnetic paint was not dry, and after drying, supercalender treatment was performed and the support was slit to a width of 3.81 mm to form a magnetic tape. Prepared. This magnetic tape was housed in a cassette to produce a Phillips-type compact cassette tape.

[Comparative Example 2] Magnetic coating composition Go-γFe2O3 100 parts [Hc: 400 Oe, S BET specific surface area: 45 m''7
g, Br: 1640 Gauss] Vinyl chloride/vinyl acetate/vinyl alcohol copolymer 16 parts [Copolymerization ratio 92:3:5] Polyester polyurethane resin 4 parts Oleic acid 2 parts Dimethylsiloxane (degree of polymerization 400) 0, 5 parts Methyl ethyl ketone 200 parts Methyl isobutyl ketone 150 parts A magnetic tape was produced in the same manner as in Comparative Example 1, except that the above components were used and no isocyanate compound was added, and a Phillips-type compact cassette tape was obtained.

[Example 1] Using the magnetic coating composition described in Comparative Example 1 and following the method described therein, a magnetic layer (first magnetic layer) having a layer thickness of 4.5 JLm was formed on a support.

Next, using the magnetic coating composition described in Comparative Example 2 and following the method described therein, a layer thickness of 1. oJL
A magnetic layer (second magnetic layer) of m was formed.

Thereafter, a magnetic tape was manufactured in the same manner as in Comparative Example 1 to obtain a Phillips-type compact cassette tape.

[Comparative Example 3] The magnetic powder of the first magnetic layer was heated to 390 Elsterad (O
e), except for changing to Co-γFe2O3 with a 5BET specific surface area of 30 m'/g and Br of 1740 Gauss,
A first magnetic layer was formed in the same manner as in Example 1.

Next, on the first magnetic layer, Hc was 390 oersted (Oe), 5BET specific surface area was 45 m'/g,
A second magnetic layer was formed in the same manner as in Example 1 except that the magnetic powder was changed to Co-γFe2O3 (Br = 1740 Gauss (cy)).

Thereafter, a magnetic tape was manufactured in the same manner as in Comparative Example 1 to obtain a Phillips-type compact cassette tape.

[Comparative Example 4] The magnetic powder of the first magnetic layer was
e), 5BET specific surface area is 30m2/g, Br is 1
470 Gauss c7) A first magnetic layer was formed in the same manner as in Example 1 except that Co-γFe2O3 was used.

Next, on the above first magnetic layer, He was applied at 300 oersted (Oe), 5BET specific surface area was 45rn'7g, and B
A second magnetic layer was formed in the same manner as in Example 1 except that the magnetic powder was changed to Co-y Fe 2 O3 with r of 1470 Gauss.

Thereafter, a magnetic tape was manufactured in the same manner as in Comparative Example 1 to obtain a Phillips-type compact cassette tape.

[Evaluation of Magnetic Tape] The physical properties of the cassette tapes obtained in the Examples and Comparative Examples were measured as follows using a ZX-9 type cassette deck manufactured by Nakamichi Co., Ltd. as a measuring instrument.

MOL315Hz (dB) Displayed as the output level when the distortion rate at 315Hz is 3%.

5QL10KHz (dB) Displayed at maximum output level at 10KHz.

Transferability (dB) +10dB input of IKHz signal (160 parts wb to 0
dB) within one revolution of the reel, then recorded about 10 revolutions without any signal, then recorded again, repeated this several times, left it at a temperature of 30 ± 1°C for 24 hours, and then played it back. Measure the reproduction output level of the signal and transfer signal.

Bias Noise (BN) (dB) After erasing the magnetic tape with high-frequency magnetic fields from the erasing head and the recording head, and applying a bias, the level of the remaining tape noise is measured.

The conditions for each magnetic tape are summarized in Table 1, and the results obtained for each magnetic tape are shown in Table 2.
Margin below First table Magnetic layer thickness (Le Peng) Upper (second) layer 1.0 - 5.5 Co1,
0 lower (first) layer 4.5 5.5 - L5 4.5
Magnetic powder characteristics Second magnetic layer 5BET (m2/g) 45 - 45 4
5 45He(Oe) 400 - 400
390 300Br (Gauss) 1880
- 1640 1740 1470 Magnetic powder characteristics First magnetic layer 5BET (go/g) 30 30 - 50
50Hc(Oe) 380 380 -
390 300Br (Gauss) 1640 1
640 - 1740 1470 Table 2 M0L315Hz (dB) +0.2 0
-2.0 -0.8 -5.2SQL10KHz(dB
) +0.4' 0 +0. Fl +0.
5 -0.5 Transfer (dB) 53 54
44 45 46BN(dB) -2
, 2O-2, 5-2, 3-2, 3 From the above results, the magnetic tape according to the present invention has no increase in noise level compared to known magnetic tapes having a similar configuration. It is clear that the S/N ratio is improved and the transferability is improved. It is also clear that the magnetic tape according to the present invention has good output in all frequency bands.

Patent Applicant Fuji Photo Film Co., Ltd. Agent Patent Attorney Yasushi Yanagawa Procedural Amendment 1, Indication of the Case 1986 Patent Application No. 246903 2, Name of the Invention Magnetic Recording Medium 3, Person Making the Amendment Related Patent applicant name (52O) Fuji Photo Film Co., Ltd. 4, agent address Mitsuya Yotsuya Building 8, 2-14 Yotsuya, Shinjuku-ku, Tokyo
Floor 6: Number of inventions increased by amendment None 7: Subject of amendment: “Detailed Description of the Invention” column of the specification.

8. Contents of the amendment as shown in the attached sheet.

To the Ship (1) We will amend the "Detailed Description of the Invention" column of the specification as follows.

Note 1) "Extremely low noise" on page 3, line 16 of the specification is corrected to "extremely low noise."

2) Correct "100% bias" in the first line of page 5 of the specification to "99% bias."

3) On the last line of page 6 of the specification, ``Gamma trioxide 1 is corrected to rgamma oxide J.

4) Correct lr1640 count JI on page 15, line 15 of the specification.

5) From the last line of page 16 to the third line of page 18 of the specification, “
The magnetic powder of the first magnetic layer was used to form a second magnetic layer. ”
Correct as shown below.

"Using the magnetic coating composition described in Comparative Example 1 and following the method described therein, a magnetic layer with a thickness of 2.5 lm (
A first magnetic layer) was formed.

Next, using the magnetic coating composition described in Comparative Example 2 and following the method described therein, a layer thickness of 3.5 mm was applied on the first magnetic layer. A magnetic layer (second magnetic layer) of Ogm was formed.

Thereafter, a magnetic tape was manufactured in the same manner as in Comparative Example 1, and a Phillips-type compact cassette tape was obtained.

[Comparative Example 4] The magnetic powder of the first magnetic layer had an Hc of 310 oersted (O
e), S BET specific surface area is 30 m2/g, Br or 14
A magnetic layer (first magnetic layer) with a layer thickness of 4.5 gm was prepared on the support using the magnetic coating composition described in Comparative Example 1 and according to the method described therein, except that Co-γFe2O3 was used at 70 Gauss. was formed.

Next, on the first magnetic layer, Hc is 276 Oe, SBET specific surface area is 45 m2/g, Br14
The magnetic coating composition described in Comparative Example 2 was used, except that Co-γFe2O3 of 50 Gauss was used, and the layer thickness was 1. A magnetic layer (second magnetic layer) of Ogm was formed. "δ) Table 1 on page 18 of the specification is amended as follows.

First table Magnetic layer thickness (lumen) Upper (second) layer 1.0 - 5.5
3.0 1.0 Lower (first) layer 4.5 5.5
-2.5 L5SBET(rn'/g)
a5 4! li 45
45Hc(Oe) 400-40
0 400 310Br (Gauss) 16
70 - 1670 1670 1470 Magnetic powder characteristics 5BET (m2/g) 30 30 -
30 30He(Oe) 380
380-380 276Br(Ga
uss) 1880 1880-18
80 14707) Table 2, Table 1 on page 21 of the specification is corrected as follows.

Table 2 M0L315Hz (dB) +0.2 0 -2
．． 0 -0.8 -5.2SOL101Glz(dB)
+0.4 0 +0.6 +0.5 -0
．． 5 Transcription (dB) 53 54 44
45 46BN (dB) -2,2O
-2,5-2,3-2,3 bye 77! , C%) 1
00 100 100 100 100- or more-

Claims (1)

[Claims] 1. A magnetic recording medium comprising a first magnetic layer provided on the surface of a non-magnetic support and a second magnetic layer provided thereon, wherein the second magnetic layer has an S BET specific surface area of 40 m Co-γ with ^2/g or more, coercive force (Hc) of 350 to 450 Oe, and residual magnetic flux density (Br) of 1650 Gauss or more
- Contains Fe_2O_3 magnetic powder, the first magnetic layer is S
BET specific surface area is 26-40m^2/g, coercive force (Hc
) is equal to or lower than the coercive force of the magnetic powder contained in the second magnetic layer, and the residual magnetic flux density (Br) is 18
1. A magnetic recording medium containing Co-γ-Fe_2O_3 magnetic powder having a magnetic flux of 0.00 Gauss or more, and characterized in that the thickness of the first magnetic layer is greater than the thickness of the second magnetic layer. 2. Claim 1, characterized in that the magnetic powder contained in the first magnetic layer has a coercive force in a range of 0.9 to 1.0 times the coercive force of the magnetic powder contained in the second magnetic layer. Magnetic recording medium described in Section 1. 3. The coercive force (Hc) of the Co-γ-Fe_2O_3 magnetic powder in the first magnetic layer is in the range of 0.92 to 0.98 times the coercive force of the magnetic powder contained in the second magnetic layer. A magnetic recording medium according to claim 1 characterized by: 4. Claim 1, characterized in that the first magnetic layer has a thickness of 2.0 to 5.0 μm, and the second magnetic layer has a thickness of 0.5 to 2.5 μm. magnetic recording media. 5. S of Co-γ-Fe_2O_3 magnetic powder in the second magnetic layer
2. The magnetic recording medium according to claim 1, wherein the BET specific surface area is in the range of 40 to 50 m^2/g. 6. The magnetic recording medium according to claim 1, wherein the Co-γ-Fe_2O_3 magnetic powder of the second magnetic layer has a coercive force (Hc) in the range of 360 to 400 Oe. 7. S of Co-γ-Fe_2O_3 magnetic powder in the first magnetic layer
2. The magnetic recording medium according to claim 1, wherein the BET specific surface area is in the range of 29 to 35 m^2/g.