JP2748014B2 - Magnetic recording medium, manufacturing method and manufacturing apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium such as a magnetic tape, a magnetic sheet, and a magnetic disk, and a method and an apparatus for manufacturing the same.

B. 2. Description of the Related Art In general, a magnetic recording medium such as a magnetic tape is manufactured by applying a magnetic paint composed of a magnetic powder, a binder resin and the like on a support and drying it.

In recent years, in a magnetic recording medium, particularly a video magnetic recording medium that requires short-wavelength recording, the magnetic recording capacity is increased, or the magnetic recording characteristics in both the high frequency range and the low frequency range of the medium are both improved and balanced. Therefore, a medium having a plurality of magnetic layers has been proposed (Japanese Patent Laid-Open No. 48-98803,
JP-A-59-172142, JP-B 32-2218, JP-A-51-64
No. 901 and JP-A-56-12937).

However, all conventional media form the upper magnetic layer without being affected by the lower magnetic layer (ie,
To obtain high output and high S / N with moderate surface properties of the medium)
There is no one that achieves both the prevention of the separation of particles from the magnetic layer (that is, the prevention of dropout). In particular, the upper magnetic layer is considerably thinner than the lower magnetic layer (for example, the lower layer is 3 μm and the upper layer is 0.3 μm).
m), it is difficult to obtain the above surface properties, and the upper layer surface is roughened by the lower layer. This is remarkable when a magnetic powder having a relatively large particle size is used as the lower magnetic powder. Also,
Even if the above surface properties can be obtained, if particles such as powder fall off, dropouts will cause image flaws in the reproduced screen, resulting in serious defects.

C. Object of the invention It is an object of the present invention to form an upper magnetic layer without being affected by a lower magnetic layer (with appropriate surface properties, high output, high S /
It is an object of the present invention to provide a magnetic recording medium which achieves both N (obtaining N) and preventing separation of particles from a magnetic layer (preventing dropout), and a method and apparatus for manufacturing the same.

D. In other words, the present invention comprises a first non-magnetic layer, a first magnetic layer, a second non-magnetic layer, and a second magnetic layer on a non-magnetic support. The first magnetic layer has a thickness of 1.5 to 4.0 μm, the second magnetic layer has a thickness of 1.0 μm or less, and the first magnetic layer and the second magnetic layer the second non-magnetic layer sandwiched _{in, -SO 3 M, -COOM, -PO} (OM ') 2 ( where, M
Is hydrogen or an alkali metal, and M ′ is a resin having a hydrophilic polar group selected from the group consisting of hydrogen, an alkali metal and a hydrocarbon residue).

Further, according to the present invention, a first nonmagnetic layer, a first magnetic layer, a second nonmagnetic layer, and a second magnetic layer are laminated on a nonmagnetic support in this order, first magnetic layer and the second nonmagnetic layer sandwiched between the second magnetic _{layer, -SO 3 M, -COOM, -PO} (OM ') 2 ( where, M
Is a hydrogen or alkali metal, and M ′ is a hydrogen, alkali metal or hydrocarbon residue), comprising a resin having a hydrophilic polar group selected from the group consisting of: The first magnetic paint is superimposed on the paint to form a first laminated paint, and thereby, at the upstream position separated by a predetermined distance, the -SO ₃ M,
—COOM, —PO (OM ′) ₂ (where M is hydrogen or an alkali metal, M ′ is a hydrogen, alkali metal or hydrocarbon residue) containing a resin having a hydrophilic polar group selected from the group 2
Forming a second laminated paint by superimposing a second magnetic paint on the non-magnetic paint, and guiding the second laminated paint on the first laminated paint to be superimposed on the first laminated paint. It is another object of the present invention to provide a method for manufacturing a magnetic recording medium, wherein the superposed paint is applied on the non-magnetic support after being guided by a predetermined distance.

Further, according to the present invention, a first nonmagnetic layer, a first magnetic layer, a second nonmagnetic layer, and a second magnetic layer are laminated on a nonmagnetic support in this order, first magnetic layer and the second nonmagnetic layer sandwiched between the second magnetic _{layer, -SO 3 M, -COOM, -PO} (OM ') 2 ( where, M
Is a hydrogen or alkali metal, and M 'is a hydrogen, alkali metal or hydrocarbon residue), a magnetic recording medium containing a resin having a hydrophilic polar group selected from the group consisting of: A downstream paint discharge section for forming a first laminated paint by superimposing a first magnetic paint on the paint, whereby at the upstream position separated by a predetermined distance, the -SO ₃ M,
—COOM, —PO (OM ′) ₂ (where M is hydrogen or an alkali metal, M ′ is a hydrogen, alkali metal or hydrocarbon residue) containing a resin having a hydrophilic polar group selected from the group 2
An upstream paint discharging unit for forming a second laminated paint by superposing a second magnetic paint on the non-magnetic paint, and guiding the second laminated paint onto the first laminated paint to form the first laminated paint. A magnetic recording medium comprising: a guide portion for superimposing on the laminated paint; and a guide portion for guiding the superimposed paint for a predetermined distance and then applying the paint on the non-magnetic support. A manufacturing apparatus is also provided.

In the magnetic recording medium according to the present invention, the non-magnetic layer is provided between the first magnetic layer and the second magnetic layer. Second
Can be provided. Therefore, the surface of the second magnetic layer is not affected by the surface condition of the first magnetic layer, and the non-magnetic layer can reproduce an appropriate surface property. The contact with the head is improved, the output is improved, and a high S / N ratio can be realized. In addition, since the first non-magnetic layer is provided between the first magnetic layer and the non-magnetic support, it is possible to improve the adhesion of the magnetic layer to the non-magnetic support via the non-magnetic layer. Can be. For this reason, it is possible to prevent the magnetic powder from peeling off due to the separation between the magnetic layer and the support due to the slitting of the medium material and the like, and it is also possible to sufficiently prevent the powder from falling off during the running of the medium, so that the dropout is drastically reduced. The performance of the medium can be greatly improved in combination with the improvement in the surface properties described above.

Such an excellent effect is effective when the thickness of the second magnetic layer is small, but such a thickness is desirably 1.0 μm or less. This is because if the thickness of the second magnetic layer exceeds 1.0 μm and becomes too thick, the function of the lower first magnetic layer (for example, signal recording and reproduction in a low frequency range) becomes weak.

Further, the second magnetic layer sandwiched between the first magnetic layer and the second magnetic layer
The nonmagnetic _{layer, -SO 3 M, -COOM, -PO} (OM ') 2 ( where
M is hydrogen or an alkali metal, and M 'is a resin having a hydrophilic polar group selected from the group consisting of hydrogen, an alkali metal and a hydrocarbon residue. Roughness can be prevented more than enough. In addition, the adhesion between the first magnetic layer and the second magnetic layer is good.

As shown in FIG. 1, for example, a magnetic recording medium of the present invention has a first nonmagnetic layer (undercoat layer) 5, a first magnetic layer 2, a nonmagnetic layer 5 on a nonmagnetic support 1 made of polyethylene terephthalate or the like. The second nonmagnetic layer (intermediate layer) 6 and the second magnetic layer 4 are laminated in this order. Further, the back coat layer 3 is provided on the surface of the support opposite to the lamination surface, but this is not necessarily required. An overcoat layer may be provided on the second magnetic layer.

In the magnetic recording medium of FIG. 1, 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 is preferably 1.0 μm or less (particularly 0.3 to 1.0 μm). .

The first and second magnetic layers 2 and 4 may contain magnetic powder. Examples of such magnetic powder include γ-Fe ₂ O ₃ , Co-containing γ-Fe ₂ O ₃ , Fe ₃ O ₄ , and Co-containing Iron oxide magnetic powder such as Fe ₃ O ₄ ; Fe,
Ni, Co, Fe-Ni-Co alloy, Fe-Ni alloy, Fe-Al alloy, Fe
-Al-Ni alloy, Fe-Al-Co alloy, Fe-Mn-Zn alloy, Fe-
Ni-Zn alloy, Fe-Al-Ni-Co alloy, Fe-Al-Ni-Cr alloy, Fe-Al-Co-Cr alloy, Fe-Co-Ni-Cr alloy, Fe-Co
-Ni-P alloys, Co-Ni alloys, etc. Various ferromagnetic powders such as metal magnetic powders mainly composed of Fe, Ni, Co and the like can be mentioned.

Among these magnetic powders, those suitable for the magnetic layers 2 and 4 can be selected. For example, a medium having a higher coercive force (Hc) than the lower layer 2 can be used for the upper layer 4 to provide a medium with high output and good frequency characteristics.

The magnetic layer also contains a lubricant (for example, silicone oil, graphite, molybdenum disulfide, tungsten disulfide, a monobasic fatty acid having 12 to 20 carbon atoms (for example, stearic acid), and 13 to 40 carbon atoms. Abrasives (eg, fused alumina), antistatic agents (eg, carbon black, graphite), etc., such as fatty acid esters, may be added.

Further, the nonmagnetic layers 5 and 6 can be formed from various binder resins, respectively. The binder which can be used for the magnetic layers 2 and 4 including such a binder resin preferably has an average molecular weight of about 10,000 to 200,000. For example, a vinyl chloride-vinyl acetate copolymer, a vinyl chloride-vinylidene chloride copolymer may be used. Coalescence, vinyl chloride-acrylonitrile copolymer,
Urethane resin, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (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 resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, mixture of polyester polyol and polyisocyanate, urea Examples thereof include a formaldehyde resin, a mixture of low molecular weight glycol / high molecular weight diol / isocyanate, and a mixture thereof.

These _{binders, -SO 3 M, -COOM, -PO} (OM ') 2
(Where M is hydrogen or an alkali metal such as lithium, potassium, and sodium, and M ′ is an alkali metal such as hydrogen, lithium, potassium, and sodium, or a hydrocarbon residue). Good. That is, such a resin improves the compatibility with the magnetic powder due to the polar group in the molecule, thereby further improving the dispersibility of the magnetic powder, and also preventing the aggregation of the magnetic powder to further improve the coating liquid stability. Therefore, the durability of the medium can be improved.
Further, when the resin having the polar group is used for the second nonmagnetic layer (intermediate layer), the adhesiveness to the upper and lower layers is improved, and the surface roughness of the second magnetic layer is reduced by more than 12%. Can be prevented in minutes.

Such a binder, in particular, a vinyl chloride copolymer can be 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 monomers. it can. Since this copolymer is obtained by vinyl synthesis, it can be easily synthesized, and various copolymer components can be selected, so that the properties of the copolymer can be adjusted optimally.

The metal of a salt such as the above-mentioned sulfonic acid or phosphoric acid is an alkali metal (particularly sodium, potassium, lithium), and potassium is particularly preferable in terms of solubility, reactivity, yield and the like.

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

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

Next, an example of a coating head used at the time of forming each layer will be described with reference to FIG.

The coating head 10 is configured as an extrusion heater of an extrusion type. The coating head 10 is formed by superposing a magnetic paint 2 ′ for the magnetic layer 2 on a non-magnetic paint 5 ′ for the non-magnetic layer 5 to form a first laminated paint. A second paint layer is formed by superimposing the magnetic paint layer 4 'for the magnetic layer 4 on the non-magnetic paint layer 6' for the non-magnetic layer 6 at a predetermined distance away from the downstream paint discharge section 15 to be formed. An upstream paint discharging section 16 to be formed, and the second laminated paint is guided on the first laminated paint to form the first laminated paint.
And a guide section 18 for guiding the superposed paint by a predetermined distance and then applying the paint on the non-magnetic support 1. Each of the above discharge units
The guides 15 and 16 and the guides 17 and 18 are provided along the slope 20 of the head main body 19 as shown. Then, each discharge unit 15,
In 16, the slits 2 are formed from the respective liquid pools 11, 12, and 13, 14.
The coating liquids 5 ', 2' and 6 ', 4' extruded through 1, 22, 23, and 24, respectively, are immediately superimposed immediately after the discharge to form the above-described first and second laminated paints. At this time, it is important that each paint is in an undried state (so-called wet-on-wet) and the non-magnetic paint 5 '
And 6 'have lower viscosities than the magnetic paints 2' and 4 ', respectively, so that the magnetic paint is extruded on the non-magnetic paint in a slippery manner, and each laminated paint can be formed well, and It can be guided in the direction as it is. Then, the second laminated paint descends so as to slide on the above-mentioned guide portion 17, and is superimposed on the first laminated paint as it is, and is coated with four kinds of paints 5 ', 2', 6 ', 4'. The liquid 25 can be easily formed. In this case, the second laminated paint rises on the first laminated paint while descending at a constant speed due to the presence of the guide portion 17, and at the same time, the paint 2 'has a higher viscosity than the paint 6', so that the second laminated paint rides well. And the components do not mix unexpectedly between the paints. Therefore,
The four layers of paint 25 are smoothly guided along the guide portion 18 onto the support 1 in a layer-separated state, and are applied as they are.

Thus, each layer can be applied smoothly and at high speed with good reproducibility, and the magnetic recording medium shown in FIG. 1 can be manufactured.

 FIG. 3 shows an example of an apparatus for performing this manufacturing method.

In this manufacturing apparatus, first, the film-like support 1 pulled out from the supply roll 32 is applied with each paint as described above by the extrusion coater 10, and is oriented by the orientation magnet 33, and is introduced into the dryer 34. Here, hot air is blown from nozzles arranged above and below to dry. Next, the dried support 1 with each coating layer is guided to a calender 37 composed of a combination of calender rolls 38, where it is calendered, and then wound up by a take-up roll 29. Each paint may be supplied to the extrusion coater 10 through an in-line mixer (not shown). In the drawings, D indicates the transport direction of the non-magnetic base film.

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

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

<Preparation of Video Tape> First, the following paints were prepared.

<Magnetic paint A for upper layer> Co-γ-Fe ₂ O ₃ 100 parts (Hc = 900 Oe, average major axis length 0.2 μm) Potassium sulfonate-containing PVC resin 10 parts (MR110, manufactured by Zeon Corporation) Polyurethane resin 5 parts (XE-1, manufactured by Takeda Pharmaceutical Co., Ltd.) α-Al ₂ O ₃ (average particle size 0.2 μm) 5 parts Carbon black 1 part Myristic acid 1 part Stearic acid 1 part Butyl stearate 1 part Methyl ethyl ketone 100 parts 100 parts of cyclohexanone 100 parts of toluene After kneading and dispersing the above magnetic paint, 5 parts of Coronate L of Nippon Polyurethane Industry Co., Ltd. was added and prepared.

<Lower layer magnetic paint B> Co-γ-Fe ₂ O ₃ 100 parts (Hc = 700 Oe, average major axis length 0.25 μm) Potassium sulfonate-containing vinyl chloride resin 10 parts (MR110, manufactured by Zeon Corporation) Polyurethane resin 5 parts (XE-1, manufactured by Takeda Pharmaceutical Co., Ltd.) 1 part of myristic acid 1 part of stearic acid 1 part of butyl stearate 1 part of methyl ethyl ketone 100 parts of cyclohexanone 100 parts of toluene 100 parts After kneading and dispersing the above magnetic paint, Nippon Polyurethane Industry ( Was added and prepared.

<Coating for middle layer> Polyester resin containing sodium sulfonate 10 parts (Byron 530, manufactured by Toyobo Co., Ltd.) Methyl ethyl ketone 25 parts Toluene 25 parts <Coating for undercoat layer> Polyester resin 10 parts (Byron 200, Toyobo Co., Ltd. 25) Methyl ethyl ketone 25 parts Toluene 25 parts Then, the above-mentioned undercoat layer coating material, lower layer magnetic coating material B, intermediate layer coating material, and upper layer magnetic coating material A are successively formed on a 14.5 μm-thick polyethylene terephthalate base film. The following table
As shown in FIG. 1, various coatings, orientation, and drying were performed, followed by calendering.

Thereafter, a paint for a BC layer having the following composition was applied to the opposite surface of the magnetic layer and the like so as to have a dry thickness of 0.4 μm.

Carbon black (Raven1035) 40 parts Barium sulfate (average particle diameter 300 mμm) 10 parts Nitrocellulose 25 parts N-2301 (manufactured by Nippon Polyurethane) 25 parts Coronate L (〃) 10 parts Cyclohexanone 400 parts Methyl ethyl ketone 250 parts Toluene 250 parts To obtain a wide magnetic film, which was wound up. This film was cut to 1/2 inch width and
Each of the video tapes shown in FIG.

The following measurements were performed for each of these video tapes,
The results are shown in Table 2 below. The measuring method is as follows.

C / N: The reproduction output noise ratio was measured when recording was performed with a single frequency recording signal having a carrier-to-noise ratio of 4.5 MHz.

C-OUT: Color output The reproduction output level at 629 kHz when a 100% color signal was recorded was measured.

D / O: Dropout JVC dropout counter VD-
Using 5M, an output longer than 15 μsec and lowering the output of the RF envelope by 20 dB or more was regarded as one dropout, the entire length was measured, and the average value per minute was obtained.

As is clear from the results in Table 2 (Examples 1 to 4),
It can be seen that all of the tapes according to the present invention have large C / N and C-OUT, and very little dropout.
This is presumably because the former improved the surface properties due to the presence of the intermediate layer, and the latter reduced the powder drop due to the undercoat layer. On the other hand, in Comparative Example 1, since there is no undercoat layer, C / N and the like are good but dropout is remarkable, and in Comparative Example 2, since there is no intermediate layer, C / N and the like are poor. In Comparative Example 3, since both the undercoat layer and the intermediate layer were not present, all were poor.

[Brief description of the drawings]

 BRIEF DESCRIPTION OF THE DRAWINGS The drawings are intended to exemplify the present invention, and FIG. 1 is a sectional view of an example of a magnetic recording medium, FIG. 2 is a sectional view of an extrusion coater, and FIG. FIG. In addition, in the code | symbol shown in drawing, 1 ... Nonmagnetic support 2 ... Lower magnetic layer 3 ... Backcoat layer 4 ... Upper magnetic layer 5 ... Undercoat layer 6 ... Intermediate layer.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-164022 (JP, A) JP-A-61-139927 (JP, A) JP-A-56-108566 (JP, A) 146209 (JP, A)

Claims (3)

(57) [Claims] 1. A first non-magnetic layer, a first magnetic layer, a second non-magnetic layer, and a second magnetic layer are laminated on a non-magnetic support in this order. The thickness of the magnetic layer is 1.5 to 4.0 μm, the thickness of the second magnetic layer is 1.0 μm or less, and the second nonmagnetic layer sandwiched between the first magnetic layer and the second magnetic layer. _{layers, -SO 3 M, -COOM, -PO} (OM ') 2 ( where, M is hydrogen or an alkali metal, M' is hydrogen, an alkali metal or a hydrocarbon residue) hydrophilic member selected from the group consisting of A magnetic recording medium comprising a resin having a polar group. 2. A first non-magnetic layer, a first magnetic layer, a second non-magnetic layer, and a second magnetic layer are laminated on a non-magnetic support in this order. The second non-magnetic layer sandwiched between the magnetic layer and the second magnetic layer is -SO ₃ M, -COOM, -PO (OM ') ₂ (where M is hydrogen or an alkali metal, and M' is A method for producing a magnetic recording medium containing a resin having a hydrophilic polar group selected from the group consisting of hydrogen, an alkali metal and a hydrocarbon residue), wherein the first magnetic paint is formed on the first non-magnetic paint. A first laminated paint is formed by superimposition, and at the upstream position separated by a predetermined distance therefrom, the -SO ₃ M, -COO
M, -PO (OM ') ₂ (where M is hydrogen or an alkali metal,
M ′ is a hydrogen, an alkali metal or a hydrocarbon residue) and a second magnetic paint is superimposed on a second non-magnetic paint containing a resin having a hydrophilic polar group selected from the group consisting of Forming a paint, guiding the second laminated paint on the first laminated paint, and superimposing the paint on the first laminated paint, guiding the superimposed paint by a predetermined distance, and then on the non-magnetic support. A method for producing a magnetic recording medium, characterized in that the method is applied to a substrate. 3. A first non-magnetic layer, a first magnetic layer, a second non-magnetic layer, and a second magnetic layer are laminated on a non-magnetic support in this order. The second non-magnetic layer sandwiched between the magnetic layer and the second magnetic layer is -SO ₃ M, -COOM, -PO (OM ') ₂ (where M is hydrogen or an alkali metal, and M' is (Hydrogen, alkali metal or hydrocarbon residue) A manufacturing apparatus for a magnetic recording medium containing a resin having a hydrophilic polar group selected from the group consisting of: A downstream-side paint discharge unit that forms a first laminated paint by superimposition, and at the upstream position that is separated by a predetermined distance therefrom, the -SO ₃ M, -COO
M, -PO (OM ') ₂ (where M is hydrogen or an alkali metal,
M ′ is a hydrogen, an alkali metal or a hydrocarbon residue) and a second magnetic paint is superimposed on a second non-magnetic paint containing a resin having a hydrophilic polar group selected from the group consisting of An upstream-side paint discharging section for forming a paint; a guide section for guiding the second laminated paint on the first laminated paint to overlap on the first laminated paint; A guide part for applying the liquid on the non-magnetic support after being guided by a distance.