JPH09212861A - Production of magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure a coated state free from unevenness in multilayer coating for a thin film magnetic recording medium and to improve the electromagnetic transducing characteristics of the medium. SOLUTION: When plural coating films are simultaneously or successively formed by coating by means of an extrusion die 10 to produce a magnetic recording medium, the difference in shearing stress at 1,80Osec<-1> shear rate between a coating material for the thinnest coating film contg. ferromagnetic powder having >=32m<2> /g specific surface area and a coating material for a coating film adjacent to the thinnest coating film is regulated to <=800dyn/cm<2> and the thickness of each of upper and lower wet coating films is regulated to >=0.7μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a magnetic recording medium, and more particularly to a method for manufacturing a thin film magnetic recording medium having excellent electromagnetic conversion characteristics.

[0002]

2. Description of the Related Art Conventionally, as a method of manufacturing a magnetic recording medium,
There is a method in which a support is run and a plurality of coating layers are simultaneously or sequentially coated on the support by an extrusion die. Then, as the recording wavelength has become shorter due to the higher density of the magnetic recording medium, the surface layer of the recording layer required for the recording medium has advanced, and a thin magnetic layer having a high coercive force is formed on the upper layer. A low magnetic layer or a non-magnetic layer is formed on the other layers.

However, in Japanese Patent Laid-Open No. 4-325917, as a thin-film magnetic recording medium having excellent electromagnetic conversion characteristics, the lower layer dispersion liquid and the upper layer magnetic coating material have the same or similar thixotropic properties (for softening phenomenon of an object due to stress). Among them, those with recovery, those that cause softening by increasing the strain of the object) have been proposed.

Also, Japanese Patent Publication No. 60-10785 and Japanese Patent Laid-Open No. 60-1
Japanese Patent No. 43866 aims at improving coating conditions for coatings having poor thixotropy by applying mechanical shearing force to the coatings.

[0005]

However, Japanese Patent Laid-Open No.
Japanese Patent No. 325917 only proposes that the lower layer coating and the upper layer coating should have similar thixotropic properties in order to stabilize the lower layer and the upper layer in the thin film magnetic recording medium. . That is, it cannot be said that the specific disclosure of the thixotropic properties of the lower layer coating material and the upper layer coating material is sufficient. Although there is a description of thixotropy by the stress ratio of the shear rate in the claims, it cannot be said that the concrete description of the relationship between the lower layer coating material and the upper layer coating material is sufficient.

Further, the present invention is characterized in that it is limited to the manufacturing method, particularly the extrusion coating technique, and finds the optimum coating conditions.

It is an object of the present invention to secure a coating state with no coating unevenness during multi-layer coating of a thin film magnetic recording medium and improve the electromagnetic conversion characteristics of the magnetic recording medium.

[0008]

SUMMARY OF THE INVENTION The present invention provides a method for producing a magnetic recording medium in which a support is run and a plurality of coating layers are applied to the support simultaneously or sequentially by an extrusion die. There is a difference in shear stress at a shear rate of 1800 Sec ^-1 between the paint of the thinnest coating layer containing ferromagnetic magnetic powder of 32 m ² / g or more and the coating of the coating layer adjacent to the coating.
The thickness is 800 dyne / cm ² or less, and the upper wet coating film thickness and the lower wet coating film thickness are 0.7 μm or more.

[0009]

The magnetic paint is a non-Newtonian fluid, and in particular, the stress characteristic against shear has thixotropic property. The shear state of the paint in the extrusion type die receives a shear rate of about several hundred to a few thousand Sec ^-1 inside the slot, but the shear rate on the wall surface of the slot is almost the same.
Considered to be 0. The two paints that intersect each other at the confluence of the multi-layer paint to form adjacent coating layers are subjected to a shear rate of tens of thousands of Sec ^-1 or more from the state of shear rate 0 to the lip tip in a short time. . That is, in the multi-layer coating by the extrusion type die, it is necessary to collect a wide range of stress history information from the low shear rate region of the paint to the high shear rate region as the stabilization information of the coating interface adjacent to each other. In the invention, it is possible to predict the stress state in the high shear rate region only by investigating the stress state in the shear rate region of 1800 Sec ^-1 or less of the paint, and as a result, it is possible to determine a stable coating condition without uneven coating. I found it.

That is, the paint of the thinnest coating layer and the paint of the coating layer adjacent to the coating layer have thixotropic properties, and the difference in shear stress between the two coatings at a shear rate of 1800 Sec ^-1 or less. By setting the coating conditions for both coating layers to be 800 dyne / cm ² or less, it is possible to secure a coating state with no coating unevenness (good surface property) in the thinnest coating layer where uneven coating is most likely to occur. I found it.

[0011]

EXAMPLES FIG. 1 is a diagram showing the shear stress of coating A and coating B with respect to shear rate, FIG. 2 is a diagram showing the shear stress of coating A and coating B with respect to shear rate, and FIG. 3 is coating C and coating B. 4 is a diagram showing the shear stress with respect to the shear rate of the paint C, FIG. 4 is a diagram showing the shear stress with respect to the shear rate of the paint C and the paint B, FIG. 5 is a diagram showing the shear stress with respect to the shear rate of the paint A and the paint B,
FIG. 6 is a diagram showing the shear stress with respect to the shear rate of the paint D and the paint B, and FIG. 7 is a schematic diagram showing the extrusion type die.

As shown in FIG. 7, the extrusion die 10 for manufacturing a magnetic recording medium comprises a die head 11 having an upstream lip 12, a first downstream lip 13 and a second downstream lip 14, and the upstream lip 12 And the first downstream lip 1
The first slot portion 15 is formed between the first and second slots 13 and 3, and the first slot portion 15 is communicated with the liquid buffer portion 16, and the second slot portion 17 is provided between the first downstream lip 13 and the second downstream lip 14. The second slot portion 17 is communicated with the liquid buffer portion 18. The lower layer coating material supply system 19 supplies a lower layer coating material (for example, coating material B described later) to the first slot portion 15 via the liquid buffer portion 16. The upper layer paint supply system 20
Upper layer coating material (for example, coating materials A and C described later) is supplied to the second slot portion 17 via the liquid buffer portion 18. As a result, the lower-layer coating material extruded from the first slot portion 15 and the upper-layer coating material extruded from the second slot portion 17 are simultaneously applied to the surface of the non-magnetic support 1 by the wet-on-wet method. Will be applied when the lower layer paint is wet. Next, the lower layer coating material and the upper layer coating material are dried by a drying device to obtain a magnetic recording medium having the lower layer and the upper layer on the surface of the support 1.

In the magnetic recording medium of the present invention, in addition to the non-magnetic support, the upper layer and the lower layer, a back coat layer is further provided between the non-magnetic support and the lower or back coat layer. Other layers such as a primer layer and a magnetic layer provided for recording servo signals and the like corresponding to a hard system using a long wavelength signal may be provided.

As the non-magnetic support 1 used in the magnetic recording medium of the present invention, any known material can be used without any particular limitation. Specifically, it is made of a polymer resin and is flexible. Films and discs; Cu, Al,
Films, disks, cards, and the like made of non-magnetic metals such as Zn, ceramics such as glass, porcelain, and porcelain can be used.

As the polymer resin forming the flexible film or the disc, polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycyclohexylene dimethylene terephthalate, polyethylene bisphenoxycarboxylate, polyethylene, etc. , Polyolefins such as polypropylene, cellulose acetate butylate,
Cellulose derivatives such as cellulose acetate propionate, polyvinyl chloride, vinyl resins such as polyvinylidene chloride, or polyamide, polyimide, polycarbonate, polysulfone, polyetheretherketone, polyurethane, etc. Two or more can be used in combination.

In the magnetic recording medium of the present invention, the back coat layer, which is optionally provided on the back surface of the non-magnetic support, can be formed by using a known back coat paint without particular limitation.

In the magnetic recording medium of the present invention, the upper layer provided on the non-magnetic support is the uppermost layer of the magnetic recording medium, that is, the layer provided on the surface of the magnetic recording medium, and on the lower layer. It is formed by applying a magnetic paint to.

As the above-mentioned magnetic paint, a paint containing magnetic powder, a binder and a solvent as main components is preferably used.

Examples of the magnetic powder include a ferromagnetic metal powder mainly composed of iron or a hexagonal ferrite powder. Generally, the fineness of the powder progresses and the specific surface area of the magnetic powder tends to increase. However, from the viewpoint of manufacturing technology, the fineness of the powder causes the agglomeration of the coating material, which makes the coating property of the thin film difficult.

The present invention has found coating conditions such that good coating performance can be obtained even for fine particles having a specific surface area of magnetic powder of 32 g / m ² or more.

The coercive force of the ferromagnetic metal powder is 1600-25.
It is preferably 00 Oe, more preferably 1700 to 2400 Oe. The coercive force of the hexagonal ferrite powder is preferably 1600 to 2300 Oe. When the coercive force of the ferromagnetic metal powder and the hexagonal ferrite are each less than the lower limit, the short-wavelength RF output decreases because of easy demagnetization, and when the upper limit is exceeded,
Since the head magnetic field is insufficient and the writing ability is insufficient, and further the overwrite characteristics are deteriorated, it is preferable to set the value within the above range.

The saturation magnetization of the ferromagnetic metal powder is
100 to 180 emu / g, preferably 110 to 160 emu / g.
g, more preferably 140-160 emu / g. The saturation magnetization of the hexagonal ferrite powder is preferably 30 to 70 emu / g, 45 to 70 emu / g.
More preferably emu / g. When the saturation magnetization of the ferromagnetic metal powder and the hexagonal ferrite powder are each less than the lower limit, the filling rate of the magnetic powder is reduced, the output is reduced, and when the upper limit is exceeded. ,
It is necessary to reduce the binder, the interaction between the magnetic powders increases, and as a result, the magnetic powders are in an agglomerated state, and it is difficult to obtain a desired output. Is preferred.

The ferromagnetic metal powder has a metal content of 70
% Or more, and 80% by weight or more of the metal component is Fe. Specific examples of the ferromagnetic metal powder include, for example, Fe-Co, Fe-Ni, Fe
-Al, Fe-Ni-Al, Fe-Co-Ni, Fe-
Ni-Al-Zn, Fe-Al-Si and the like can be mentioned.
Further, the shape of the ferromagnetic metal powder is needle-like or spindle-like,
Its major axis length is preferably 0.05 to 0.25 μm, more preferably 0.05 to 0.2 μm, and the preferable acicular ratio is 3 to 20,
Preferably, the preferred X-ray particle size is between 130 and 250 Angstroms.

Further, as the hexagonal ferrite powder, barium ferrite and strontium ferrite in the form of fine plates, and a part of their Fe atoms are Ti, C
magnetic powders substituted with atoms such as o, Ni, Zn, V, and the like. The hexagonal ferrite powder preferably has a plate diameter of 0.02 to 0.09 μm and a plate ratio of 2 to 7.

In addition, the above magnetic powder may optionally contain
Rare earth elements and transition metal elements can be included.

In the present invention, the magnetic powder may be surface-treated in order to improve the dispersibility of the magnetic powder.

The above surface treatment is carried out according to "Characterization of
Powder Surfaces ": a method similar to the method described in the Academic Press and the like, for example, a method of coating the surface of the magnetic powder with an inorganic oxide. At this time, as the inorganic oxide that can be used, Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ ,
Examples include SnO ₂ , Sb ₂ O ₃ , and ZnO. When used, they can be used alone or as a mixture of two or more.

In addition to the above method, the surface treatment can be performed by an organic treatment such as a silane coupling treatment, a titanium coupling treatment and an alumina coupling treatment.

The binder may be a thermoplastic resin, a thermosetting resin, a reactive resin or the like, which may be used alone or as a mixture.

Specific examples of the binder include vinyl chloride resins, polyesters, polyurethanes, nitrocelluloses, epoxy resins, and the like, and in addition, JP-A-57-162128, page 2, upper right column 19 Row to page 2, lower right column
Resins and the like described in line 19 and the like can be mentioned. Further, the binder may contain a polar group for improving dispersibility and the like.

The amount of the above binder used is 10
The amount is preferably about 5 to 100 parts by weight, particularly preferably 5 to 70 parts by weight, based on 0 parts by weight.

Examples of the solvent include ketone solvents, ester solvents, ether solvents, aromatic hydrocarbon solvents, chlorinated hydrocarbon solvents, and the like. From page 17, lower right column, line 17 of Kaisho 57-162128
Solvents described on page 4, lower left column, line 10, etc. can be used.

The amount of the above solvent used is the above magnetic powder.
80 to 500 parts by weight, preferably 100 parts by weight,
~ 350 parts by weight are more preferred.

In addition, the above-mentioned magnetic coating material requires additives such as a dispersant, a lubricant, an abrasive, an antistatic agent, a rust preventive, a fungicide, and a curing agent, which are usually used in magnetic recording media. It can be added accordingly. As the above-mentioned additive, specifically, page 2, upper left column, line 6 of JP-A-57-162128
Page 2, upper right column, line 10 and Page 3, upper left column, line 6 to page 3 upper right column
Various additives described in line 18, etc. can be mentioned.

To prepare the above magnetic paint, for example, the above magnetic powder and the above binder together with a part of the solvent are put into a Nauta mixer or the like and premixed to obtain a mixture, and the obtained mixture is continuously pressurized. After kneading with a kneader or the like, then diluting with a part of the solvent, dispersing treatment using a sand mill or the like, mixing additives such as a lubricant, filtering, and further curing agents such as polyisocyanate and the remaining The method of mixing a solvent etc. can be mentioned.

In the magnetic recording medium of the present invention, the lower layer provided adjacent to the upper layer is formed by coating the non-magnetic support with a magnetic paint or a non-magnetic paint.

The concrete results of the present invention will be described below. (Examples 1 to 5) (Tables 1 to 6) Thickness as a support 6μ
A magnetic tape was manufactured using polyethylene terephthalate (PET) film of m and paints A to D having the formulations shown in Tables 1 to 4 as coating materials, and the coating state and output state were investigated. Tables 5 to 7 were obtained.

Magnetic coating A for upper layer (Table 1)

[Table 1]

Ferromagnetic metal powder Fe (Fe: Co: Ni: Al: Y = 100: 30: 30: 1: 5: 2) (specific surface area 33 m ² / g) 100 parts by weight Alumina (average particle size 0.3 μm) 12 parts by weight ・ Carbon black (average primary particle diameter 20 nm) 1 part by weight ・ "MR-110" 12 parts by weight [trade name, manufactured by Nippon Zeon Co., Ltd., sulfonic acid group-containing vinyl chloride polymer] ・ "UR- 8200] 8 parts by weight [trade name, manufactured by Toyobo Co., Ltd., sulfonic acid group-containing polyurethane resin] 1 part by weight of 2-ethylhexyl stearate 2 parts by weight of palmitic acid 3 parts by weight of "Coronate L" [trade name, Polyisocyanate compound manufactured by Nippon Polyurethane Industry Co., Ltd.]-Methyl ethyl ketone 120 parts by weight-Toluene 80 parts by weight-Cyclohexanone 40 parts by weight

Nonmagnetic coating B for the lower layer (Table 2)

[Table 2]

The same as in Table 1 (Paint A) except that the following ferromagnetic metal powder was used as the ferromagnetic metal powder. -Ferromagnetic metal powder {Fe: Co: Al: Y: Ca: Ni
= 100: 10: 4: 2: 0.5: 0.1 (weight ratio)}

Magnetic coating C for the upper layer (Table 3)

[Table 3]

Ferromagnetic metal powder Fe (Fe: Co: Ni: Al: Y = 100: 30: 30: 1: 5: 2) (specific surface area 45 m ² / g) 50 parts by weight Needle-like α-Fe ₂ O ₃ (average major axis length 0.11 μm, acicular ratio 10) 50 parts by weight Alumina (average particle size 0.3 μm) 6 parts by weight Carbon black (average primary particle size 20 nm) 3 parts by weight “MR-110” 9 parts by weight Part [trade name, manufactured by Nippon Zeon Co., Ltd., vinyl chloride polymer containing sulfonic acid group] 8 parts by weight [UR-8200] [trade name, manufactured by Toyobo Co., Ltd., polyurethane resin containing sulfonic acid group] 2-Ethylhexyl stearate 1 part by weight-Palmitic acid 2 parts by weight- "Coronate L" 3 parts by weight [trade name, manufactured by Nippon Polyurethane Industry Co., Ltd., polyisocyanate compound] -Methyl ethyl ketone 120 parts by weight-Toluene 80 parts by weight-Cyclohexanone 40 parts by weight

Magnetic coating D for upper layer (Table 4)

[Table 4]

Ferromagnetic metal powder Fe (Fe: Co: N
i: Al: Y = 100: 30: 1: 1: 5: 2) Same as Table 3 (Paint C) except for (specific surface area 28 m ² / g)

(Production of magnetic recording medium) The above-mentioned upper and lower magnetic coating materials were coated on the surface of a polyethylene terephthalate film having a thickness of 6 μm so that the wet thicknesses were the values shown in Tables 5 and 6, and the upper layer and A lower layer coating film was formed.
Next, the coating film was passed through a 5000 Oe solenoid while in a wet state to perform a magnetic field orientation treatment, dried at 80 ° C., and wound up. Then 85 ℃, 350kg /
After performing the calendar treatment under the condition of cm to form the upper and lower coating films, apply the back coat paint on the back surface of the above non-magnetic support to a dry thickness of 0.5 μm and dry at 90 ° C. And then rolled up. After that, at 50 ℃ or less, 16
After time aging, it was cut into a tape with a width of 8 mm to obtain a magnetic tape, and the obtained magnetic tape was loaded into an 8 mm cassette case to produce an 8 mm video cassette with a recording time of 120 minutes.

The coated state and C / N output characteristics (1 MHz, 9 MHz) of the obtained magnetic tape as a magnetic recording medium were evaluated.

Measurement method of C / N output characteristics (evaluation of 8 mm) Using a 8 mm video deck modified from a commercially available Hi 8 deck, a single wave of 1 MHz and 9 MHz was recorded, and the reproduction output (C) was observed with a spectrum analyzer. 8M noise level
C / N was expressed as Hz noise level (N).

A rheometer (RF ₁ S-2, manufactured by Rheometrics) was used for measuring the shear stress, but the measuring method is not particularly limited to this method.

(Results) (Tables 5 to 7) Example 1 shows the shear stress characteristics of the upper coating material A with respect to the lower coating material B, and the maximum stress difference at 1800 Sec ^-1 or less is 780 dyn.
It was e / cm ² . The electromagnetic characteristic data gave good results for the reference.

In Example 2, as in Example 1, the lower coating material B was used.
Is the shear stress property of the upper layer paint A against 1800 Sec
The maximum stress difference below ^-1 was 850 dyne / cm ² . The electromagnetic characteristics data did not give good results for the reference.

Example 3 shows the shear stress characteristics of the upper coating material C with respect to the lower coating material B, and the maximum stress difference at 1800 sec ^-1 or less was 880 dyne / cm ² . The electromagnetic characteristics were slightly inferior.

In Example 4, the coating used in Example 2 was mechanically dispersed by applying shearing force. As a result, 1800Sec ^-1
The maximum stress difference below decreased to 520 dyne / cm ² and good evaluation characteristics were obtained.

Examples 5 to 9 are the shear stress characteristics of the upper coating material A with respect to the lower coating material B, and the film thicknesses of the upper and lower layers were changed. As a result, when either of the upper and lower layers became 0.7 μm or less, the evaluation characteristics deteriorated even if the maximum stress difference at 1800 Sec ⁻¹ or less was 800 dyne / cm ² .

In Example 10, the influence of the specific surface area used for the magnetic powder was examined. When the specific surface area is large, the cohesive force of the coating is small, and the coating property is higher than when the specific surface area is small. Therefore, the maximum stress difference below 1800Sec ^-1 is 800dyn.
Good coating properties could be obtained even at e / cm ² or more. On the other hand, from comparison with Examples 1 and 2 (comparative example), it can be confirmed that the maximum stress difference at 1800 Sec ^-1 or less is effective when the specific surface area is 33 m ² / g or more.

[0056]

[Table 5]

[0057]

[Table 6]

[0058]

[Table 7]

[0059]

As described above, according to the present invention, in the multi-layer coating of a thin film magnetic recording medium, a coating state without uneven coating can be secured and the electromagnetic conversion characteristics of the magnetic recording medium can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing the shear stress with respect to the shear rate of paint A and paint B.

FIG. 2 is a diagram showing the shear stress with respect to the shear rate of paint A and paint B.

FIG. 3 is a diagram showing the shear stress with respect to the shear rate of paint C and paint B.

FIG. 4 is a diagram showing the shear stress with respect to the shear rate of paint C and paint B.

FIG. 5 is a diagram showing the shear stress with respect to the shear rate of paint A and paint B.

FIG. 6 is a diagram showing the shear stress with respect to the shear rate of paint D and paint B.

FIG. 7 is a schematic diagram showing an extrusion die.

[Explanation of symbols]

 1 Support 10 Extrusion Type Die

Claims (1)

[Claims] 1. A method for producing a magnetic recording medium, comprising: running a support and applying a plurality of coating layers to the support simultaneously or sequentially by means of an extrusion type die, wherein a ferromagnetic material having a specific surface area of 32 m ² / g or more is used. Shear rate 1800 Sec between the paint of the thinnest coating layer containing magnetic powder and the coating of the coating layer adjacent to the coating.
The difference in shear stress at ^-1 is 800 dyne / cm ² or less, and the upper wet coating film thickness and the lower wet coating film thickness are 0.7 μm or more, and a method for producing a magnetic recording medium.