JPH03203021A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve electromagnetic conversion characteristics, traveling property and durability in good balance by specifying the center line average roughness of the outermost layer to a specified range, incorporating magnetic powder in a magnetic layer and forming projections on the surface of a nonmagnetic supporting body. CONSTITUTION:Magnetic layers 2, 4 are successively laminated on a nonmagnetic supporting body, and a back coating layer 3 is provided on the other side of the supporting body. Projections are formed on the surface of the supporting body at a side where magnetic layers 2, 4 are provided by the distribution of >=1,000 projections/mm<2>. The magnetic layer 2 incorporates magnetic powder having >0.25 mum average major axial length, while the magnetic layer 4 incorporates magnetic powder having<=0.25 mum mean major axial length. The center line average roughness on the outermost surface of the side of the magnetic layer 4 is specified to 0.005-0.015mum. By this method, recording and reproducing characteristics in the high frequency area can be improved in the magnetic layer 4, while recording and reproducing characteristics in the relative low frequency area can be improved in the magnetic layer 2.

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.

In Prior Art II, 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.

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. 172142/1983, Special Publication No. 172142
-2218, JP-A-51-64901, JP-A-56
-12937, JP-A No. 58-56228, JP-A No. 6
3-146211, etc.).

According to these known techniques, relatively fine magnetic powder is used in the upper layer of the magnetic layer, and larger magnetic powder is used in the lower layer, so that the upper layer receives video output and the lower layer receives chroma audio output. It was designed to.

However, in conventional media, it is difficult to properly control the surface properties of the upper magnetic layer because the layer is thin (usually 1.0 μm or less), and as a result, the wear resistance and running properties of the magnetic layer are poor. There is a tendency for electromagnetic conversion characteristics to deteriorate. In other words, if the thin upper magnetic layer has poor surface properties (i.e., is too rough or too smooth), the characteristics of the medium, especially in the high frequency range, may deteriorate or become susceptible to damage. . For example, in conventional media, the surface of the non-magnetic support on the side on which the magnetic layer is provided has a density of 1 oo per Lμm".
There are less than o protrusions, or the surface of the magnetic layer (the outermost surface)
Since the center line average roughness (Ra) of It ends up.

C.1 Purpose of the Invention An object of the present invention is to provide a magnetic recording medium that can improve both electromagnetic conversion characteristics and durability.

23 Structure and effect of the invention, that is, the present invention provides a magnetic recording medium in which a first magnetic layer and a second magnetic layer are laminated in this order on a non-magnetic support. 1000 protrusions/rmn 2 or more protrusions are formed on the surface of the non-magnetic support on the side where the layer is provided, and the first N layer contains magnetic powder with an average major axis length of more than 0°25 μm, Average major axis length is 0.2
Magnetic powder of 5 μm or less is contained in the second vA layer, and the center line average roughness (Ra
) is 0.005 μm or more and less than 0.015 μm.

According to the magnetic recording medium of the present invention, since the magnetic layer is a plurality of layers (multilayer or laminated type), the second magnetic layer has good high-frequency recording and reproduction characteristics such as video output, and the first magnetic layer has good high-frequency recording and reproducing characteristics.
Each layer can be formed so that the magnetic layer has good relatively low-frequency recording and reproduction characteristics such as chroma and audio output. For this purpose, it is generally necessary that the coercive force (Hc) of the second magnetic layer (especially the top layer) be larger than that of the first magnetic layer, and that the film thickness (or layer thickness) of the second magnetic layer be thin. can be,
In particular, it is desirable that the thickness be 0.6 μm or less. The thickness of the first magnetic layer adjacent to the second magnetic layer is 0.1 to 4.0.
It is desirable to set it to μm.

In such a multilayer magnetic layer, the surface of the top layer should be relatively smooth to increase the output in the high frequency band, and the surface should not be too smooth to improve running performance with low friction. However, in the present invention, in order to obtain such appropriate surface properties, 100% is applied to the surface of the non-magnetic support.
00/tm" or more protrusions are formed. In other words,
By providing protrusions at such a ratio (number), the surface of the magnetic layer (specifically, the first magnetic layer) formed thereon,
Furthermore, the surface of the second magnetic layer (the surface of the second magnetic layer) can be appropriately roughened. If the number of protrusions is less than 1,000/ttm, it is too small and the surface of the magnetic layer becomes too smooth. Preferably, the number of protrusions is 1,200 to 2,500/ttm.
more preferably 1,500 to 2,000 pieces/
mm”, and the size of the protrusion is 1 to 30μ in diameter.
m, even 3-20 μm, 0.1-0.6 pm in height
, more preferably 0.3 to 0.5 μm.

In addition to the number of protrusions on the surface of the nonmagnetic support, the center line average roughness (Ra) of the outermost surface on the second magnetic layer side is o, oosμ
It is essential that the thickness be greater than or equal to m and less than 0.015 μm. This Ra range can be controlled by the surface properties of the above-mentioned nonmagnetic support, the structure t2 component of each magnetic layer, layer thickness, etc. In particular, in the present invention, the size of the magnetic powder in each magnetic layer is specified from the viewpoint of improving electromagnetic conversion characteristics.

That is, the first magnetic layer contains magnetic powder with an average major axis length of more than 0.25 μm, and the second magnetic layer contains magnetic powder with an average major axis length of 0.25 μm or less. By making the average major axis length of the magnetic powder of the first magnetic layer larger than 0.25 μm, it is possible to exhibit electromagnetic conversion characteristics as a lower layer, and the surface of the first magnetic layer (interface with the second magnetic layer) is already Appropriate roughness. Since the magnetic powder of the second magnetic layer has a relatively small average long axis length of 0.25 μm or less, it has good high frequency characteristics, and the surface properties of the 21+ff layer are similar to those of the first magnetic layer. It follows the same pattern and becomes even more flat.

In addition to the size of magnetic powder, the particle size of various additives,
The above Ra range is set depending on the amount added. That is, R
If a is less than 0.005 μm, the surface on the second magnetic layer side will be too smooth, and if it is 0.015 μm or more, it will be too rough, and both are inappropriate. Furthermore, this Ra is 0.007 to 0.014 μm.
More preferably, the thickness is 8 to 0.012 μm.

The average major axis length of the magnetic powder is preferably 0.27 to 0.4 um, and 0.30 to 0.35 um in the first VA layer.
tt m is more preferable, and in the second magnetic layer, o, io to 0.23 μm are more preferable, and 0.15 to 0.22 μm.
μm is more preferable.

In the present invention, it is desirable that the thickness of the second magnetic layer does not exceed the thickness of the first FET layer. In addition, magnetic layers (first,
2nd f! ! The total thickness (including the L layer) is 2 μm or more,
The thickness is preferably less than 4 μm.

The number of protrusions on the surface of the nonmagnetic support described above can be controlled by changing the amount and size of the filler contained in the base (nonmagnetic support).

In addition, the above-mentioned protrusions have an area ratio of 7 in the load curve using a surface roughness meter (FK-30K) manufactured by Koita Research Institute.
It refers to a portion with a height of 0.1 μm or more above the 0% level, and the number thereof is counted using an electron microscope (the same applies hereinafter).

In addition, in order to measure the average major axis length of the magnetic powder described above, 2
An electron micrograph is taken at a magnification of approximately 0,000 to 50,000 times, the length of 50 to 100 individual needle-like particles is measured, and the average value is converted according to the magnification (the same applies hereinafter).

Furthermore, the above-described center line average roughness (Ra) is the average value of the amplitude of the surface roughness component, and is calculated by Kosaka Ken (cant off is 0.25++a) (the same applies hereinafter).

In the present invention, a plurality N (first, second
It is desirable that the magnetic layers (magnetic layers) are adjacent to each other. The first magnetic layer may be one layer, or may be two or more layers. 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 each of the above layers. In particular, the media of the present invention are characterized in that each magnetic layer is coated with wet simultaneous multilayer coating (iv).
It is suitable for coating and forming by an et-on-wet method. Of course, it is best to apply the upper layer after drying the lower layer.
-A dry method may also be used.

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 and a second magnetic 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. 2, the upper layer is further divided into layers 5 and 6.

In the magnetic recording media shown in FIGS. 1 and 2, the thickness of the first magnetic layer 2 is preferably 1.5 to 4.0 μm, and the thickness of the second magnetic layer 4 or the second and third The total thickness of the magnetic layer 5.6 is preferably 0.6 μm or less (for example, 0.5 μm).

The magnetic layer 2.4.5.6 may contain magnetic powder, but
Such magnetic powders include 7-Fe2O, Co-containing r
-Fezo3, Fe30s, Go-containing Fe50.
Iron oxide magnetic powder such as; Fe, Ni, Co, Fe-Ni-C
o alloy, Fe-Ni alloy, FeA/2 alloy, Fe-Af
-Ni alloy, Fe-AfCo alloy, Fe-Mn-Zn alloy, Fe-Ni-Zn alloy, Fe-Al-Ni-Co alloy, FeAl-Ni-Cr alloy, Fe-Al-Co-C
r alloy, Fe-Co-Ni-Cr alloy, FC-C0Ni
-P alloy, co-Ni alloy, and various other ferromagnetic powders such as metal magnetic powders containing Fe, Nt, Co, etc. as main components.

Based on the present invention, the outermost magnetic layer 4.6 and the other magnetic layers 2.5 (and/or 2) are such that the former 4.6 is the uppermost layer and the latter 2.5 or 5 and 2 are the lower layers. do.

Among these magnetic powders, one suitable for each of the above-mentioned magnetic layers 2, 4, etc. can be selected.

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.), abrasives (for example, fused alumina), antistatic agents (for example, carbon black, graphite), etc. may be added.

The binder that can be used for the magnetic layer 2.4.5.6 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 501M, -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 such as hydrogen, lithium, potassium, or sodium, or a hydrocarbon residue). Preferably, it is made of resin. In other words, these resins have polar groups in their molecules that
Compatibility with the magnetic powder is improved, which further improves the dispersibility of the magnetic powder and prevents agglomeration of the magnetic powder, further improving the stability of the coating liquid, which in turn improves the durability of the medium. It can be done.

Such a binder, especially a vinyl chloride copolymer, is obtained by copolymerizing a vinyl chloride monomer, a copolymerizable monomer containing an alkali salt of sulfonic acid or phosphoric acid, and, if necessary, other copolymerizable supermers. be able to.

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 salt of sulfonic acid or phosphoric acid is an alkali metal (especially sodium, potassium, lithium), and potassium is particularly preferred in terms of solubility, reactivity, yield, etc.

Further, when providing the back coat layer 3, 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, A1
, 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. 1, 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 an extrusion coater 10.11. 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, the arrow indicates the conveyance direction of the non-magnetic pace film. Each extrusion coater 10.11 has a liquid reservoir 13.1.
4 is provided to wet-on the paint from each coater.
Layer using the wet method. To manufacture the media shown in Figure 2,
In FIG. 3, one more extrusion coater may be added.

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.

First, the following compositions were prepared.

<Magnetic paint A for upper layer> CCo-7-Fe off 100
(The average major axis length is shown in Table 1 below. Hc = 9000
e) 10 parts of potassium sulfonate-containing vinyl chloride resin (
MRllo, manufactured by Nippon Zeon ■) Polyurethane resin 5 parts (Nistan 5701, manufactured by Gnodorinch) α Alz Ox
(Average particle size 0.2 μm) Carbon black myristic acid stearate butyl stearate cyclohexanone methyl ethyl ketone Magnetic paint for lower layer B> Co-7-Fe, ○.

(The average major axis length is shown in Table 1 below.

Potassium sulfonate-containing vinyl chloride resin (MRIIO1 manufactured by Nippon Zeon ■) Polyurethane resin (Nistan 5701. manufactured by Goodlinch) a Afz
() + (Average particle size 0.2 μm) Carbon black myristate stearate butyl stearate 5 parts 0.5 parts 1 part 1 part 0.5 parts 100 parts 100 parts 100 parts Hc = 7000e) 10 parts 5 parts 5 Part 0.5 part 1 part 0.5 part 100 parts Methyl ethyl ketone 100 parts After kneading and dispersing the above compositions (paints A and B), the viscosity was adjusted to 1 to 20p with a solvent (methyl ethyl ketone, toluene). . Then, 5 parts of polyisocyanate: Coronate L (manufactured by Nippon Polyurethane Industries) was added, and a thickness of 1
On a 4.5 μm polyethylene terephthalate base film, various types of lower layer magnetic paint B and upper layer magnetic paint A were sequentially applied using the apparatus shown in Fig. 3, oriented, dried, and then calendered. In this case, the dry film thickness was 0.5 μm for the upper layer and 2.5 μm for the lower layer.

Thereafter, a paint for the BC layer having the following composition was applied to the surface opposite to the magnetic layer to 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-2,301 (manufactured by Nippon Polyurethane Co., Ltd.) 25 parts Coronate L (〃 ) 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 to a width of 3 inches to produce each videotape shown in Table 1 below.

The number of protrusions on the surface of the support was controlled by changing the amount of filler (eg, spherical silica) in the support.

The average major axis length of the magnetic powder can be determined by taking an electron micrograph at a magnification of about 20,000 to 50,000 times, and measuring individual acicular particles at a magnification of 50 to 100 times.
The length was measured and the average value was converted according to the magnification. Further, Ra of the outermost surface of the magnetic layer was measured using a three-dimensional surface roughness meter (3FK) manufactured by Koita Research Institute, and was controlled by various components in the layer.

Then, the following performance evaluations were performed on each of the above tapes, and the results are shown in Table 1 below.

(a), RF-output, Lumi-3/N, Rioma AM-3/
N, chroma-out crab color video noise meter '5hibasoku92
5 D/IJ, "HR-3" made by Japan Victor Co., Ltd.
Reference tape (b) with 7000J deck.

(C).

It is expressed as a value (dB).

The frequencies of each signal are as follows.

RF-output: 6 MHz Le ξ-3/N: 6 MHz Chroma AM-3/N: Secromer output at 629 629 KHz RF output reduction: Video deck HR-37000J (manufactured by Victor Japan) was used, and Shibatsu 925 was used as a noise meter.
D-' was used to record data at a temperature of 20° C. and a relative humidity of 60%, and the decrease in RF output was measured after 100 basses were played back.

Jitter: The value was measured after 100 buses using a VTR jitter meter MK-612A (eye/nose radio wave).

(Left below) From this result, based on the present invention, the center line average roughness (Ra) of the surface of the uppermost layer of the magnetic layer is o, oos μm or more,
less than 0.015 μm, and the average major axis length is 0.25 μm
A larger magnetic powder is contained in the first magnetic layer, a magnetic powder having an average major axis length of 0.25 μm or less is contained in the second magnetic layer, and 1000 particles/1I are contained on the surface of the non-magnetic support.
When protrusions of IIn2 or more are formed, the performance of each magnetic layer is effectively exhibited and the electromagnetic conversion characteristics are improved.
In addition, by adjusting the surface properties to an appropriate level, electromagnetic conversion characteristics, runnability, and durability can be improved in a well-balanced manner.

Next, when the magnetic layer is made up of three layers, layers 2, 5, and 6, as shown in Figure 2 (however, the upper layer 6 is the same as 4 in Figure 1, but the film thickness is 0.3 μm, and the intermediate layer 5 is Hc (=8000e) between 2 and 4 in Fig. 1, the film thickness is 063 μm, and the lower layer 2 is the same as 2 in Fig. 1).The performance evaluation was performed in the same manner as above, and the following table - 2 results were obtained. According to this, 2
As in the case of the layers, it can be seen that the structure of the present invention provides sufficient performance.

8. Effects of the Invention As described above, the present invention has the centerline average roughness (R) of the outermost surface.
a) is 0.005 μm or more and less than 0.015 μm, and the first magnetic layer contains magnetic powder with an average major axis length of more than 0.25 μm; Since it is contained in two magnetic layers and more than 1000 protrusions/IIIz are formed on the surface of the non-magnetic support, the performance of each magnetic layer is effectively exhibited and the electromagnetic conversion characteristics are improved. In addition, by adjusting the surface properties to an appropriate level, electromagnetic conversion characteristics, runnability, and durability can be improved in a well-balanced manner.

[Brief explanation of drawings]

The drawings are for illustratively explaining 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 diagram of an apparatus for manufacturing a magnetic recording medium. In addition, in the reference numerals shown in the drawings, 1...Nonmagnetic support 2...Lower magnetic layer 3...Back coat layer 4. 6... Upper magnetic layer 5... Intermediate magnetic layer.

Claims (1)

[Claims] 1. In a magnetic recording medium in which a first magnetic layer and a second magnetic layer are laminated in this order on a non-magnetic support, the surface of the non-magnetic support on the side where the first and second magnetic layers are provided. The first magnetic layer contains magnetic powder in which 1000 protrusions/mm^2 or more are formed and the average major axis length is greater than 0.25 μm, and the magnetic powder has an average major axis length of 0.25 μm or less. is contained in the second magnetic layer, and the center line average roughness (Ra) of the outermost surface on the second magnetic layer side is 0.005 μm.
A magnetic recording medium characterized in that the diameter is less than 0.015 μm.