JPH03295024A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium excellent in electromagnetic conversion characteristics for the ball frequency band by providing plural magnetic layers on a nonmagnetic supporting body and specifying Hc and BET value of magnetic powder for each magnetic layer. CONSTITUTION:On a nonmagnetic supporting body 1, there are successively formed a first magnetic layer 2, second magnetic layer 3, third magnetic layer 4 and forth magnetic layer 5 in this order. The magnetic powder used in the first magnetic layer 2 has Hc of 800 - 1,000 Oe, BET value of 30 - 40m<2>/g and 1.0 - 3.0mum thickness. The magnetic powder used in the second magnetic layer 3 has Hc of 800 - 1,000 Oe, BET value of 35 - 45m<2>/g and 0.1 - 0.2mum thickness. The magnetic powder used in the third magnetic layer 4 has Hc of 650 - 800 Oe, BET value of 35 - 45m<2>/g and 0.1 - 0.2mum thickness. The magnetic powder used in the forth magnetic layer 5 has Hc of >=800 Oe, BET value of >=45m<2>/g and 0.2 - 0.3mum thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to magnetic recording media such as magnetic tapes, magnetic sheets, and magnetic disks.

BACKGROUND OF THE INVENTION Generally, magnetic recording media such as magnetic tapes are manufactured by applying a magnetic paint made of magnetic powder, binder resin, etc. onto a support and drying it. Since conventional magnetic recording media have only one magnetic layer, it is necessary to cover a wide frequency band from low to high frequencies with one type of magnetic powder.

In particular, with the recent trend toward higher recording densities, magnetic powders with high Hc and high BET values are used because recording characteristics in high frequencies are improved and low noise is required.

However, since magnetic recording media are composed of a single type of magnetic powder (magnetic layer), high-H
c. Since it is necessary to use magnetic powder with a high BET value, the low-frequency characteristics become insufficient. Furthermore, the output of HiFi audio, whose recording band is lower than that of the video U degree signal, was insufficient to be covered by magnetic powder with high Hc and high BET values.

On the other hand, in magnetic recording media for video, media having multiple magnetic layers have been proposed in order to increase the magnetic recording capacity or to improve and balance the magnetic recording characteristics of the medium in both the high frequency region and the low frequency region. (Unexamined Japanese Patent Publication No. 48-9
No. 8803, Japanese Patent Publication No. 172142, Publication No. 172142, Publication No. 172142
-2218, JP-A-51-64901, JP-A-56
~12937, JP-A No. 58-56228, JP-A-Sho 6
3-146211, etc.).

However, even with these media, color signal output, video brightness output, HiFi audio output, and linear audio output are all enhanced in a well-balanced manner, and high frequencies,
It is still insufficient to improve electromagnetic conversion characteristics in the entire frequency band ranging from mid-range to low-range.

The purpose of the present invention is to provide excellent electromagnetic conversion characteristics in all frequency bands (specifically, excellent in all video brightness signal output, HiFi audio signal output, linear audio output, and color signal output). The objective is to provide a magnetic recording medium with special characteristics.

20 Structure of the invention and its effects, that is, the present invention comprises a first magnetic layer on a non-magnetic support,
A second magnetic layer, a third magnetic layer, and a fourth magnetic layer are laminated in this order, and the H of the magnetic powder of the first magnetic layer is
c is 800~10000e, BET value is 30~
40%/g, the layer thickness is 1.0-3.0 pm,
Hc of the magnetic powder of the second magnetic layer is 800 to 10,000
e, BET value is 35 to 45 m/g, the layer thickness is 0.1 to 0.2 μm, Hc of the magnetic powder of the third magnetic layer is 650 to 800 Oe, and BET value is 35 to 45.
po/g, the layer thickness is 0.1 to 0.2 μm, and
Hc of the magnetic powder of the fourth magnetic layer is 800 Oe or more, B
ET value is 45 bo/g or more, and the layer thickness is 0.2 to 0.3μ
This relates to a magnetic recording medium of m.

According to the present invention, the magnetic layer is composed of the first, second, third, and fourth magnetic layers described above, and the Hc (coercive force) of the magnetic powder in the upper layer (fourth magnetic layer) is 800 Oe. Above, BET value (
specific surface area) of 45 rrr/g or more, layer thickness of 0.2 to 0.
Since the thickness is 3 μm, high-density recording is possible, and electromagnetic conversion characteristics such as S/N ratio and output can be particularly improved in a high frequency band.

Therefore, this fourth magnetic layer allows the video luminance signal output to be successfully recorded and reproduced. In order to achieve this effect even better, if magnetic powder with Hc of 850 Oe or more and BET value of 50 m2/g or more is used, and the layer thickness is set to 0.2 to 0.25 μm, the electromagnetic conversion characteristics will be even better. Become.

Regarding the third magnetic layer under the fourth magnetic layer, the Hc of the magnetic powder is 650 to 800 Oe, the BET value is 35 to 45 Bo/g, and the layer thickness is 0.1 to 0.2 μm. Therefore, although the frequency range is lower than that of the video luminance signal, the color luminance signal can be sufficiently recorded and reproduced. Hc is further 700-750 Oe, BET value is further 38
The layer thickness is preferably 0.15 to 0.20 μm.

A second magnetic layer is provided under this third magnetic layer, and the Hc of the magnetic powder is set to be 800 Oe or more (however, 10,000 e or less) like the fourth magnetic layer, but the BET value is 35 to 4.
5 bo/g and the layer thickness is 0.1 to 0.2 μm,
This means that HiFi audio signals can be sufficiently recorded and reproduced. Hc is further 850 to 950 Oe, B
ET value is further 38~42rr? /g, layer thickness is 0.12~
It is preferable to set it to 0.17 μm.

In addition to this, the present invention further includes a magnetic layer below the second magnetic layer with an Hc of 800 to 10,000 e and a BET value of 30 to less than 40 m2/g, and a layer thickness of 1.5 m2/g.
Since the first magnetic layer is provided with a thickness of 0 to 3.0 μm, low-frequency linear audio output characteristics are improved. This further increases Hc to 820-9000 e and BET value to 3.
It is further improved by setting the layer thickness to 2 to 35 rrr/g and 2.5 to 3.0 μm. In addition, since the BET (J) of this first magnetic layer is relatively small and the particle size of the magnetic powder is correspondingly relatively large, the Young's modulus of the lower layer and, by extension, the stiffness of the entire magnetic layer are improved. In addition, since the magnetic powder in the lower layer has a relatively large particle size, the dispersibility is improved, and the surface properties of the fourth magnetic layer, which is the upper layer, can be controlled appropriately.

As mentioned above, the fourth magnetic layer, the third magnetic layer, and the second magnetic layer share the frequency characteristics in the high range and the middle range, respectively, and as a result, the frequency characteristics in the high range and the middle range are respectively shared, and as a result, the frequency characteristics in the high range and the middle range are respectively shared, and as a result, the video brightness and color signals are Recording and playback characteristics of HiFi audio signals can be greatly improved. Furthermore, since the first magnetic layer improves the low-frequency linear audio output, together with the second and third magnetic layers, it becomes possible to improve the frequency characteristics over the entire range.

In addition, in the present invention, the above-mentioned first, second, third, and fourth
It is desirable that the respective magnetic layers are adjacent to each other. However, in addition to cases where there is substantially a clear boundary between each layer, there may also be a boundary area where magnetic powder from both layers coexist at a certain thickness; The removed upper or lower layer is referred to as each of the above magnetic layers. In particular, the media of the present invention utilize wet-coating (wet-o-coating) of each magnetic layer.
It is suitable for coating and forming by the n-wet method. Of course, it is an et-on-dr method in which the upper layer is applied after drying the lower layer.
The y method may also be used.

Furthermore, each of the above magnetic layers may be further divided into a plurality of layers. For example, the first magnetic layer is Hc900Oe, BET
Value 35nf/g, lower layer part with thickness 2.0μm, Hc
900Oe, BET value 45rrr/g, thickness 1.0μm
It may be formed separately from the upper layer portion. In this case, the same magnetic layer is used including the boundary region as described above.

In the present invention, the above rBET value refers to the surface area per unit weight, and is a physical quantity that is completely different from the average particle diameter.For example, even if the average particle diameter is the same, there are Some have a small surface area. To measure the specific surface area, for example, first, the powder is heat-treated at around 250 ° C for 30 to 60 minutes and degassed to remove what is adsorbed to the powder, and then introduced into a measuring device. The initial pressure of nitrogen is set to 0.5 kg/rrr, and the adsorption measurement is performed using nitrogen at a liquid nitrogen temperature (-195°C) (a specific surface area measurement method generally referred to as the B, E, T method).

For details, see J, Ame, CheIIl, Soc,
60309 (1938)). This specific surface area (BE
The measuring device for T value) is a "Powder/Grain Material Measuring Device" (Kanter-T value), which is jointly manufactured by Digestion Batteries■ and Digestion Ionics■.
Sorb)" can be used. For a general explanation of the specific surface area and its measurement method, see "Measurement of Granules"
(J, M, DALLAVALLE, CLYDEO
Co-authored by RR Jr., translated by Benta and others; published by Sangyo Toshosha).
Pages 0 to 1171, Nippon Kagakujojo, Maruzen, published on April 30, 1960). (However, it is the same as the specific surface area in this specification.)

The magnetic recording medium of the present invention has, for example, as shown in FIG.
Non-magnetic support 1 made of polyethylene terephthalate etc.
A first magnetic layer 2, a second magnetic layer 3, a third magnetic layer 4, and a fourth magnetic layer 5 are laminated thereon in this order. Further, although a back coat layer 6 is provided on the support surface opposite to the laminated surface, this need not necessarily be provided.

An overcoat layer may be provided on the fourth magnetic layer.

In the magnetic recording medium of FIG. 1, the layer thickness of the first magnetic layer 2 is 1.0 to 3.0 μm, and the layer thickness of the second magnetic layer 3 is 0.1 μm.
~0.2 μm, and the layer thickness of the third magnetic layer 4 is 0.1 to 0.2
.mu.m, and the layer thickness of the fourth magnetic layer 5 is 02 to 0.3 .mu.m.

The first to fourth magnetic layers 2.4.5 may contain magnetic powder, such as γFez O, C
o-containing r-Few o3, Fe+ 04, Co-containing F
e: Iron oxide magnetic powder such as +04; Fe, Ni, Co, Fe
-Ni-Co alloy, Fe-Ni alloy, Fe-Af gold alloy Fe-Al-Ni alloy, Fe-Al-Co alloy, Fe-
Mn-Zn alloy, Fe-Ni-Zn alloy, Fe-Al
-Ni-C.

Alloy, Fe-Af! -N 1-Cr alloy, Fe-A/
lCo-Cr alloy, Fe-Co-Ni-Cr alloy, Fe
-Co-N1-P alloy, Co-Ni alloy, etc. Fe, Ni,
Examples include various ferromagnetic powders such as metal magnetic powders containing Co or the like as a main component.

Among these magnetic powders, those having Hc and BET values suitable for each of the above-mentioned magnetic layers 2, 3, 4, and 5 can be selected based on the present invention.

Each magnetic layer also contains lubricants such as silicone oil, graphite, molybdenum disulfide, tungsten disulfide, monobasic fatty acids with 12 to 20 carbon atoms (such as stearic acid), and lubricants with a total of 13 to 40 carbon atoms. Abrasives (eg, fused alumina), antistatic agents (eg, carbon black, graphite), etc. may be added.

The binder that can be used in the magnetic layer 2.3.4.5 preferably has an average molecular weight of about 10,000 to 200,000, such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, etc. , 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, nitrocellulose, etc.), styrene-butadiene copolymer, polyester resin, various synthetic rubbers, phenolic resin, epoxy resin, urea resin, melamine resin, phenoxy resin, silicone resin, acrylic reaction Examples include resins, mixtures of high molecular weight polyester resins and isocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, mixtures of low molecular weight glycols/high molecular weight diols/isocyanates, and mixtures thereof.

These binders are -3O,M, -COOM, -PO(
OM')z (where M is hydrogen or an alkali metal such as lithium, potassium, or sodium; M' is hydrogen, an alkali metal such as lithium, potassium, or sodium, or a hydrocarbon residue); It is good to be. In other words, the polar groups in the molecules of these resins improve their compatibility with the magnetic powder, which further improves the dispersibility of the magnetic powder and prevents agglomeration of the magnetic powder, further improving the stability of the coating liquid. This can also improve the durability of the medium.

Such a binder, especially a vinyl chloride copolymer, can be used by copolymerizing a copolymerizable monomer containing vinyl chloride monomer, an alkali salt of sulfonic acid or phosphoric acid, and other copolymerizable monomers as necessary. You can definitely get it.

Since this copolymer is based on vinyl synthesis, it is easy to synthesize, and the copolymer components can be selected to suitably adjust the properties of the copolymer.

The metal salts of the above-mentioned sulfonic acid or phosphoric acid are alkali metals (especially sodium, potassium, lithium), and potassium is particularly preferred in terms of solubility, reactivity, yield, etc.

Further, when providing the bank coat layer 6, the above-described binder contains non-magnetic particles such as barium sulfate and is applied to the back surface of the support.

Further, as the material of the support 1, plastics such as polyethylene terephthalate and polypropylene, Aj
! , metals such as Zn, glass, BN.

Ceramics such as Si carbide, porcelain, and earthenware are used.

Next, FIG. 2 shows an example of the above-mentioned medium manufacturing apparatus.

In this manufacturing apparatus, first, the film-like support 1 fed out from the supply roll 32 is transferred to an extrusion coater 10.1.
After applying each coating material for the magnetic layer 2.3.4.5 described above in accordance with 1.12.16, it is oriented by the front-stage orientation magnet 33 of, for example, 2000 Gauss, and further, for example, 2000 Gauss.
The material is introduced into a dryer 34 equipped with a Gauss rear-stage orientation magnet 35, where it is dried by blowing hot air from nozzles arranged above and below. Next, the dried support 1 with each coated layer is
is led to a supercalender device 37 consisting of a combination of calender rolls 38, where it is calendered and then wound onto a winding roll 39. Each paint is extruded through an in-line mixer (not shown) and coated in a coater 1.
0.11.12.16. In addition, in the figure, arrow O indicates the conveyance direction of the nonmagnetic base film. Each of the extrusion coaters 10.11.12.16 is provided with a reservoir 13.14.15.17 to deposit the paint from each coater in a wet-on-wet manner.

In addition to the extrusion coater shown in Fig. 2, the extrusion coater shown in Figs.
An extrusion coater as shown in FIG. 9 can be used (18 in the figure is a guide roller). Here, the one in Figure 3 is a four-layer simultaneous multi-layer coating method, the one in Figure 6 is a combination of two-layer simultaneous multi-layer coating method and sequential multi-layer coating, and the other methods are also simultaneous multi-layer coating and sequential multi-layer coating. It is a combination of each.

E, Example The present invention will be explained in detail below.

The ingredients, proportions, order of operations, etc. shown below may be changed in various ways without departing from the spirit of the invention. In addition, in the following examples, all "parts" are parts by weight. Also,
"Actual J" indicates an example, and "Riko" indicates a comparative example.

First, the compositions shown in Table 1 below were kneaded and dispersed,
Each magnetic paint was prepared.

Table note) In the above, Co-7-Fe, 03 means Co-containing (or deposited) 7-Fe2O, and PVC copolymer contains -3O3K (MRIIO: manufactured by Nippon Zeon Co., Ltd.). The polyurethane resin is a polyurethane containing the following structural formula, and the polyisocyanate is Coronate (manufactured by Nippon Polyurethane Co., Ltd.).

The above paint was kneaded using a kneader, and then mixed and dispersed using a sand mill. The polyisocyanate was added immediately before coating, and each of the above magnetic paints was extruded using the extrusion coater shown in Figure 2, and the dry thickness of the upper layer, lower layer, and middle layer was coated onto a 14 μm thick polyethylene terephthalate base. The coating was applied to a film thickness as shown in Table 2 below, subjected to orientation and drying treatment, and then subjected to supercalender treatment.

Thereafter, a bank coating paint having the following composition was applied to the opposite side of the magnetic layer to a dry thickness of 1.0 am.

Carbon black (average particle size 20 mμ) 40 parts Carbon black (average particle size 300 mμ) 5 parts Nitrocellulose 25 parts (Seltsuba BTH% manufactured by Asahi Kasei Co., Ltd.) N-2301 (manufactured by Nippon Polyurethane Co., Ltd.) 25 parts Coronate (manufactured by Nippon Polyurethane Co., Ltd.) 10 parts cyclohexanone 400 parts methyl ethyl ketone 250 parts toluene
250 copies of a wide magnetic film was thus obtained and wound up. This film was cut into 2-inch widths to make each videotape. The following performance evaluations were performed on each of these tapes, and the results are shown in Table 2.

(a), RF-output, Lumi-3/N, Rl:l? -AM
S/N, chroma output crab color video noise meter r 5hibasoku9
25 D/l J was used, and “HR-
Expressed as a value (dB) with respect to a reference tape using an S 7000J deck.

The frequencies of each signal are as follows.

RF-output = 6M 7Silmy 3/N
: 6M se(b).

(C).

Rumi-AM-3/N: 629 to 629 K7 HiFi-Audio output using a HR-57000J deck manufactured by Victor Japan Co., Ltd., and expressed as a value (dB) relative to a reference tape.

The frequency of this output signal was IKHz.

Linear Audio Output The same test device as above was used, but the output signal frequency was 333Hz.

(The following is a margin, continued on the next page) From the above results, by forming each magnetic layer based on the present invention, RF, luminance, chroma output, chroma S/N,
It was excellent in HiFi audio and linear audio output, and a good balance between them was obtained.

[Brief explanation of the drawing]

The drawings are for illustratively explaining the present invention, and FIG. 1 is a cross-sectional view of an example of a magnetic recording medium, FIG. 2 is a schematic diagram of a magnetic recording medium manufacturing apparatus, FIGS. 3, 4, 5, 6, 7, 8, and 9 are schematic sectional views showing various extrusion coaters. In addition, in the symbols shown in the drawings, 1...Nonmagnetic support 2...First magnetic layer 3...Second magnetic layer 4...Third magnetic layer 5...Fourth magnetic layer 6...Back coat layer.

Claims (1)

[Claims] 1. A first magnetic layer, a second magnetic layer, a third magnetic layer, and a fourth magnetic layer are laminated in this order on a nonmagnetic support, and the first magnetic layer Hc of magnetic powder is 800~
1000 Oe, the BET value is 30 to 40 m^2/g, and the layer thickness is 1.0 to 3.0 μm, and the Hc of the magnetic powder of the second magnetic layer is 800 to 1000 Oe, and the BET value is 35.
~45 m^2/g, the layer thickness is 0.1 to 0.2 μm, and the Hc of the magnetic powder of the third magnetic layer is 650 to 800.
Oe, BET value is 35 to 45 m^2/g, and the layer thickness is 0
．． 1 to 0.2 μm, and the Hc of the magnetic powder of the fourth magnetic layer is 800 Oe or more, and the BET value is 45 m^2/
A magnetic recording medium having a layer thickness of 0.2 to 0.3 μm.