JPH03209627A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To increase the outputs of respective bands and to improve S/N by respectively setting the SFDs of 1st and 2nd magnetic layers formed on a nonmagnetic base to a specific range. CONSTITUTION:The 1st magnetic layer (lower layer) 2 and the 2nd magnetic layer (uppermost layer) 4 are laminated in this order on the nonmagnetic base 1. The SFD is defined by SFD=DELTAH/Hc, where DELTAH denotes the half-amplitude level of the magnetic field relating to the extreme value of the differential coefft. of the hysteresis curve of a magnetic density-magnetic field and Hc denotes a coercive force. The noise components of a video signal are least when the SFD of the magnetic layer is particularly 0.3 to 0.45 and the noise components of a color signal are least particularly when the SFD of the magnetic layer is 0.45 to 0.60, respectively. Namely, the SFD of the 1st magnetic layer 2, designated as SFD1 and the SFD of the 2nd magnetic layer, designated as SFD2 are specified to 0.45<=SFD1<=0.60, 0.3<=SFD2<0.45.

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.

Moreover, with a single layer, emphasis was placed on high-frequency characteristics, so chroma and audio output were relatively neglected.

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.

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. 59172142, Special Publication No. 32-
No. 2218, JP-A-51-64901, JP-A-56-
No. 12937, JP-A-58-56228, JP-A-58
-200425, JP-A-63-146211, JP-A-63-300425, etc.).

According to these known techniques, functions are separated between the upper and lower layers of the magnetic layer, and the upper layer is designed to handle video output, and the lower layer to handle chroma and audio output.

Although these magnetic recording media have the above features,
The dispersibility of magnetic powder is still insufficient, and while it has become possible to achieve high output video signals and chroma (color) signals, S/
The problem remains that the N ratio is insufficient.

C.9 Object of the invention The object of the invention is to output video and color signals as well as to
The objective is to provide a magnetic recording medium with a good S/N ratio.

28 Structure of the Invention The present invention provides a magnetic recording medium in which a first magnetic layer and a second magnetic layer are provided in this order from the non-magnetic support side on a non-magnetic support, SFD=ΔH/Hc (However, ΔH represents the half-width of the magnetic field with respect to the extreme value of the differential coefficient of the magnetic flux density-magnetic field hysteresis curve, and H
e represents coercive force. ) Regarding the magnetic conditions shown in the above, SF of the first magnetic layer is
A magnetic recording medium characterized in that, where D is SFD1 and SFD of the second magnetic layer is SFD2, 0.45≦SFD, ≦0.60 0.30≦S F D, <0.45. This is related to.

First, to explain the above-mentioned SFD in the present invention, the magnetic conditions of the laminated magnetic layer consisting of the first and second magnetic layers as described above are based on the SFD (Switching Field Distribution).
distribution).

Figure 1 (a) shows the magnetization curve (magnetic flux density - magnetic field) of a magnetic material.
The hysteresis curve was shown. Magnetic flux density (B) and magnetic field (
The relationship with H) is B=μ4μ. Denoted by H. μ. is the magnetic permeability in vacuum, and μ4 is the relative magnetic permeability in the medium.

The differential coefficient of the magnetic flux density with respect to the magnetic field is given by the above equation, and in this case μ6 is called differential permeability.

On the other hand, the differential curve along the hysteresis curve is shown in the same figure (c).
forms a loop with the extreme value shown in .

If the half-width of the magnetic field related to this extreme value is ΔH, then the SFD is: SFD-ΔH/Hc (2)
Defined by

Equations (1) and (2) above relate magnetic permeability, SFD, and magnetic field using differential curves and half-value widths at their extreme values, and magnetic permeability can be understood from HC and ΔH1, that is, SFD, which are easy to measure. Ru. If we take magnetic particles as the medium with this permeability, it is linked to Hc fluctuations due to the composition of the magnetic material and crystal defects such as voids in the magnetic material, and if we focus on the magnetic layer, the filling rate of the magnetic particles in the layer also changes. , is linked to Hc fluctuations that control magnetic conditions such as particle number density and dispersity, and SFD
is regarded as a parameter indicating the fluctuation of Hc.

As is clear from the SFD definition formula, SFD and Hc are mutually reciprocal, but depending on the behavior of ΔH, this reciprocity is not necessarily guaranteed, but it has been shown experimentally or from conventionally known hysteresis curves that they are reciprocal. There is no evidence that this is the case; the smaller the Hc, the larger the SFD.

Furthermore, according to experimental findings, magnetic particles with a large BET value give a large SFD. Here, “BET (!
J is the specific surface area of the magnetic material (powder), and BE
The surface area per unit duram is expressed in square meters, as measured by a specific surface area measurement method called the T method.

Regarding this specific surface area and its measurement method, see [Powder Measurement J (J, M, Dallavalle, Clyd
eorr jr.

Co-authored, translated by Benguchi and others; published by Sangyo Toshosha).
171 (edited by the Chemical Society of Japan; published by Maruzen on April 30, 1968). To measure the specific surface area, for example, the powder is heat-treated at around 105°C for 13 minutes while being degassed to remove what is adsorbed to the powder, and then introduced into the measuring device to set the initial pressure of nitrogen. 0.5 kg/
nf, and lower the liquid nitrogen temperature (-195°C) using nitrogen.
) for 10 minutes. The measuring device used was a counter soap (manufactured by Yuasa Ionics ■).

As a result of various studies on the above-mentioned SFD, the present inventor found that the noise component of the video signal is especially 0.3 in the SFD of the magnetic layer.
~0.45, the noise component of the color signal is particularly important when the SFD of the magnetic layer is 0.45.
They found that the values are the lowest when the values are between 45 and 0.60.

That is, in the above laminated magnetic layer, when the SFD of the first magnetic layer (lower layer) is SFD1 and the SFD of the second magnetic layer (upper layer) is SFD, 0.45≦SFD, -≦
0.60 0.30≦S F D, <0.45.

This range is further 0.45≦SFD, ≦0.55 0.32≦SFD, ≦0.42 egoism, 0.45≦SFD, ≦0.52 0.32≦SFD, ≦0.38 - layer is preferred.

In the present invention, the SFD of each of the above magnetic layers is also H
There is also a preferable range for c, and Hc of the first magnetic layer
500-6800 e.

By setting the Hc of the second magnetic layer to 630 to 7500 e, a magnetic recording medium with better output of video signals and color signals and better S/N ratio can be obtained.

In the present invention, since the magnetic layer is composed of multiple layers, the upper layer has good high-frequency recording and playback characteristics such as video output, and the lower layer has relatively low chroma and audio output characteristics. Each layer can be formed to improve the recording and reproducing characteristics of the area. For this purpose, the coercive force (Hc) of the upper layer (especially the top layer) is generally made larger than that of the lower layer,
And the film thickness (or layer thickness) of the upper layer is often thin, especially 0
．． It is desirable that the thickness be 6 μm or less. Further, it is desirable that the thickness of the lower layer adjacent to this upper layer is 1.5 to 4.0 μm.

In the present invention, in addition to the case where a clear boundary substantially exists between each of the magnetic layers described above, with a constant thickness,
Although there may be a boundary area where magnetic powders from both layers coexist, the layer above or below excluding such boundary area is defined as each of the above layers.

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 (lower layer) 2 and a second magnetic layer (top layer) 4 are laminated thereon in this order. Further, a back coat layer 3 is provided on the support surface opposite to this laminated surface. An overcoat layer may be provided on the second magnetic layer.

In the example of FIG. 3, the lower layer is further divided into layer 2a and layer 2b.

In the magnetic recording media shown in FIGS. 2 and 3, the thickness of the first magnetic layer 2 and the thickness of the magnetic layers 2a+2b are 1.5 to 4.
The thickness of the second magnetic layer 4 is preferably 0 μm.
．． The thickness is preferably 6 μm or less (for example, 0.5 μm).

The magnetic layers 2.2a, 2b, and 4 may contain magnetic powder, and examples of such magnetic powder include 1-FezCo-containing 7-
Fe, O,, Fe, o4, Co-containing Fe, 0. Iron oxide magnetic powder such as HFe, Ni, Co, 0°Fe-Ni-Co alloy, Fe-Ni alloy, FeAj2 alloy, Fe-Al-Ni alloy, Fe-AfCO alloy, Fe
-Mn-Zn alloy, Fe-NiZn alloy, Fe-Aff
i-Ni-Co alloy, Fe-Al1! -Ni-Cr alloy, Fe-Affi-Co-Cr alloy, Fe-Co-Ni
-Cr alloy, Fe-C.

Examples include various ferromagnetic powders such as N1-P alloy, Co-Ni alloy, metal magnetic powder mainly composed of Fe, Ni, CO, etc. The SFDs of the outermost magnetic layer 4 and the other magnetic layers 2.2a and 2b are respectively set based on the present invention.

From the above magnetic powder, each of the above magnetic layers 2.2a, 2.
b, one suitable for 4 can be selected. For example, if the upper layer 4 is made of a material having a higher coercive force (Hc) than the lower layer 2, a higher output medium can be obtained.

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. fatty acid esters, etc.), dispersants (lecithin, etc.), abrasives (e.g. fused alumina), antistatic agents (e.g. carbon black)
etc. may be added.

The binder that can be used for the magnetic layers 2.2a, 2b, and 4 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, nitro) cellulose, etc.), styrene-butadiene copolymers, polyester resins, various synthetic rubbers, phenolic resins, epoxy resins, urea resins, melamine resins, phenoxy resins, silicone resins, acrylic reaction resins, high molecular weight polyester resins, and isocyanate resins. mixtures of polymers, 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 -3O3M, -COOM, -PO
Contains a hydrophilic polar group such as (OM') Z (where M is hydrogen or an alkali metal such as lithium, potassium, or sodium, and M' is an alkali metal or hydrocarbon residue such as hydrogen, lithium, potassium, or sodium). Preferably, it is made of resin. 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 coating liquid stability). This can improve the durability of the medium.

Such a binder, especially a vinyl chloride copolymer, can be obtained by copolymerizing a vinyl chloride monomer, a copolymerizable polymer containing an alkali salt of sulfonic acid or phosphoric acid, and other copolymerizable monomers as necessary. I can do it.

Since this copolymer is based on vinyl synthesis, it is easy to synthesize, and various copolymer components can be selected, so that the properties of the copolymer can be optimally adjusted.

The metal of the above-mentioned salts such as sulfonic acid or phosphoric acid is an alkali metal (particularly sodium, potassium, lithium).

In addition, the back coat layer 3 contains carbon black in the above-mentioned binder, and further contains non-magnetic particles such as barium sulfate in some cases, and is coated on the back surface of the support.

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

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

Next, an example of the above-mentioned medium manufacturing apparatus is shown in FIG.

In this manufacturing apparatus, in manufacturing the medium shown in FIG. 2, the film-like support 1 fed out from the supply roll 32 is coated with each of the above-mentioned paints for the magnetic layer 2.4 by extrusion coaters 10 and 11. After that, for example 2000G
It is oriented by a front-stage orientation magnet 33 of Gauss, and further introduced into a dryer 34 equipped with a rear-stage orientation magnet 35 of, for example, 2000 Gauss, where it is dried by blowing hot air from nozzles arranged above and below. Next, the dried support 1 with each coated layer 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 may be fed to extrusion coater 10.11 through an in-line mixer, not shown. In addition, in the figure, arrow O indicates the conveyance direction of the non-magnetic heath film.

Each of the extrusion coaters 10 and 11 has a liquid reservoir 13.
．． 14 are provided to wet and wet the paint from each coater.
Layer using the on-wet method. To produce the media of FIG. 3, one more extrusion coater in FIG. 4 may be added.

FIG. 5 shows an example of an extrusion coater.

The same figure (A) is the same as that shown in Fig. 4 (two heads for sequential wet multi-layer coating), the same figure (B) is one with one head (for sequential wet multi-layer coating), the same figure ( C) is a method in which both magnetic paints 2' and 4' are discharged from one head in an overlapping manner in the cross direction (for simultaneous wet multilayer coating).

Since the above method is an eve-on-wet coating method, it is easy to coat the uppermost layer on the lower layer, and in particular, the thinner uppermost layer can be coated uniformly, and multiple layers can be coated in multiple layers with good reproducibility.

Note that the device used for the multilayer coating described above does not necessarily have to be an extrusion coater, and other known coating devices can be used.

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

The components, 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.

1-7 1-6 <Magnetic paint for first magnetic layer> Co-coated T FezOz (Hc, SFD and Fe''/Fe3+ are shown in Table 1 below.) α-AlzOx Polyvinyl chloride containing sulfonic acid metal salt Co Adhesion 7 Fezes (Hc, SFD and Fe''/Fe3+ are shown in Table 1 below.) 100 parts 5.0 parts 6.0 parts 11.0 parts 8300) 3.0 parts 0.5 parts 0.5 parts 1.0 parts 200 parts 200 parts 100 parts 100 parts α-Ap20. 5.0 parts Polyvinyl chloride resin containing sulfonic acid metal salt 8.0 parts (MRIIO manufactured by Zeon Corporation) Polyurethane resin with functional group 7.0 parts (-3
UR-8300 manufactured by Toyobo Co., Ltd. containing o and - groups) Carbon black 1.0 part stearic acid 0.5 part oleic acid
0.5 parts Butyl stearate
1.0 part methyl ethyl ketone
200 parts toluene
200 parts cyclohexanone
After kneading and dispersing 100 parts of the above first and second magnetic paints, 5.0 parts of each polyisocyanate compound was added,
A first magnetic layer with a dry film thickness of 3.0 μm and a second magnetic layer of 0.5 μm on a polyethylene terephthalate support with a thickness of 14.3 μm.
A 2-inch videotave was manufactured by applying a wet-on-wet simultaneous multilayer coating method so that the coating thickness was .mu.m.

It was coated on both surfaces to a dry thickness of 1.0 μm.

Carbon black (R-1035: manufactured by Columbia Carbon Co., Ltd.) 60 parts Nitrocellulose 30 parts Potassium sulfonate-containing polyurethane resin (UR-8300, manufactured by Toyobo Co., Ltd.) 20 parts Coronate L (manufactured by Nippon Polyurethane Co., Ltd.)
13 parts cyclohexanone 800
1000 parts methyl ethyl ketone 800 parts toluene The following performance evaluations were performed on each of the above tapes, and the results are shown in Table 2 below.

RF-output, Lumi S/N, Chroma S/N: Color video noise meter (sh 1basoku 925 D
/1'' and was expressed as a value (dB) with respect to a reference tape using rHR37000 deck manufactured by Victor Company of Japan.

The frequencies of each signal are as follows.

(Margins below) Table 2 From these results, it can be seen that by determining the SFD of each layer based on the present invention, both the output and the S/N ratio are improved.

Pig 1” 1 Shadow February.

In addition, when the above-mentioned magnetic layer is formed in three layers as shown in Table 3 below (the film thickness is 0.3 μm for the top layer and 0.7 μm for the middle layer),
It was also found that, based on the present invention, by determining the SFD of each of the upper layer, intermediate layer, and lower layer, the characteristics were good as shown in Table 4 below.

(Left below) Table 4 Functions and Effects of the Invention As described above, the present invention has the following advantages: SFD1 of the first magnetic layer,
By setting the SFD2 of each magnetic layer within a specific range, it is possible to increase the output in each band and also improve the SZN ratio.

[Brief explanation of drawings]

The drawings are for illustratively explaining the present invention, and FIG. 1(a) and Φ) are diagrams showing a magnetization curve, a hysteresis curve, and a differential curve, respectively, for explaining the definition of SFD, and FIG. FIG. 3 is a cross-sectional view of an example of a magnetic recording medium, FIG. 4 is a schematic diagram of a magnetic recording medium manufacturing apparatus, and FIGS.
B) and (C) are respective schematic diagrams of each extrusion coater. In addition, in the symbols shown in the drawings, 1...Nonmagnetic support 2.2a...Lower magnetic layer 2b...
...Intermediate magnetic layer 2', 4'...Magnetic paint 3...
. . . Back coat layer 4 . . . Upper magnetic layer 10.11 . . . Extrusion coater.

Claims (1)

[Claims] 1. In a magnetic recording medium in which a first magnetic layer and a second magnetic layer are provided in this order from the non-magnetic support side on a non-magnetic support, SFD=ΔH/Hc ( However, ΔH represents the half-width of the magnetic field with respect to the extreme value of the differential coefficient of the magnetic flux density-magnetic field hysteresis curve, and H
c represents coercive force. ) Regarding the magnetic conditions shown in the above, SF of the first magnetic layer is
D is SFD_1, and SFD of the second magnetic layer is SFD_
2, 0.45≦SFD_1≦0.60 0.30≦SFD_2<0.45.