JPH04341925A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To surely obtain the medium having a high capacity, high density and high output by using coating materials contg. magnetic powders and specifying the viscosities of the coating materials for 1st and 2nd coated layers. CONSTITUTION:The 1st coated layer (for example, a conductive layer contg. a carbon black) 2 and the 2nd coated layer (for example, a magnetic layer contg. Ba-ferrite magnetic powder) 4 on both surfaces of a nonmagnetic base 1 by laminating these layers in this order. The 2nd coated layer is applied before the 1st coated layer 2 is undried when this coated layer is applied. The coating materials for the 1st coated layer 2 and the 2nd coated layer 4 are otherwise applied simultaneously. The viscosities of the respective coating materials for the 1st coated layer 2 and the 2nd coated layer 4 are specified to 5 to 100 poises. The medium having the high capacity, the high density and the high output are surely obtd. in this way.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing magnetic recording media such as magnetic disks, magnetic tapes, and magnetic sheets.

0002

[Prior Art] In recent years, magnetic disks have become smaller, and with the trend towards higher densities due to increases in linear recording density and track density, magnetic particles with finer particles and higher magnetic force are being used. It's becoming more common.

Barium ferrite (hereinafter referred to as Ba-ferrite) magnetic powder is a hexagonal plate-shaped magnetic powder, and the axis of easy magnetization is perpendicular to the crystal plane, so it will be used as a future high-capacity magnetic recording material. It is seen as a promising technology, and many of its technologies have been made public.

However, Ba-ferrite has the disadvantage that it is difficult to output power, and when it is made into fine particles, the cohesive force between the particles is strong, so it is difficult to obtain a high degree of dispersibility in the magnetic layer or a sufficiently smooth surface of the magnetic layer. It is difficult to obtain sex.

[0005] Furthermore, since the magnetic layer in which Ba-ferrite magnetic powder is dispersed and bound with a binder does not have good electrical conductivity,
The disadvantage is that it has a high surface electrical resistance and is easily charged. As a result, noise may be generated when the charged charges are released, and dust may adhere, causing dropouts.

In order to lower the surface electrical resistance, conductive powders (carbon black, graphite, silver powder, nickel powder, etc.) and surfactants (natural, nonionic, anionic, cationic, etc.) are added to the magnetic layer containing metal magnetic powder. The technique of adding ampholytes) was disclosed in Japanese Patent Publications No. 46-22726 and No. 47-2.
No. 4881, No. 47-26882, No. 48-15
No. 440, No. 48-26761, U.S. Patent No. 22
No. 71623, No. 2240472, No. 22882
No. 26, No. 2676122, No. 2676924, No. 2676975, No. 2691566, No. 2
No. 727860, No. 2730498, No. 2742
No. 379, No. 2739891, No. 3068101
No. 3158484, No. 3201253,
No. 3210191, No. 3294540, No. 34
No. 15649, No. 3441413, No. 34426
No. 54, No. 3475174, No. 3545974
Disclosed in the issue etc.

However, in these conventional techniques, due to the special nature of magnetic disks used under severe conditions, a large amount of conductive powder is added to the magnetic layer (more than in the case of magnetic tape). On the contrary, the packing density and dispersibility of the metal magnetic powder decrease. For this reason, there is a drawback that the output is decreased and the noise is increased, and it is difficult to achieve both durability and low resistance. Moreover, the addition of a surfactant has a small effect on lowering the surface electrical resistance, and when the amount added is increased, the durability of the magnetic layer deteriorates due to plasticization of the coating film, which is a drawback.

[0008] Therefore, by forming a multilayer structure, forming a magnetic layer on the upper layer (second layer), making the lower layer (first layer) a conductive layer containing carbon black, and removing carbon black from the second layer, The output can be increased by increasing the volume ratio of magnetic powder in the paint. Increasing the output by separating the conductive layers into separate layers in this way is a known technique, and is being studied for media using Co-containing γ-Fe2 O3 and metal magnetic powder.

[0009] Even if such a multilayer structure is adopted, no coating technology has been proposed to date that reliably achieves the surface smoothness required for high-capacity, high-density media.

0010

OBJECTS OF THE INVENTION An object of the present invention is to provide a method that can reliably obtain high capacity, high density, and high output media.

[0011]

Structure of the Invention and Its Effects That is, the present invention provides a method for manufacturing a magnetic recording medium in which a first coating layer and a second coating layer are laminated in this order on a non-magnetic support. A paint containing magnetic powder is used as the paint for at least the second paint layer of the second paint layer, and when the paint for the first paint layer is applied (particularly extrusion coating), this paint layer remains undried. Either applying the paint for the second coating layer (particularly extrusion coating) or simultaneously applying each coating material for the first and second coating layers (particularly extrusion coating); The present invention relates to a method of manufacturing a magnetic recording medium, in which the viscosity of each coating material for the first and second coating layers is set to 5 poise to 100 poise.

[0012] As a result of various studies on the conventional techniques described above, the present inventor found that in order to create a medium with a high capacity, high density, and a smooth surface, the application of the coating layer should be wet-on.
wet method (i.e., when the paint for the lower first coating layer is extruded and applied, the paint for the upper second coating layer is extruded and applied while this coating layer is not dry; and It is extremely important to extrude each paint for the two coating layers at the same time, and at that time, it is important to select a specific viscosity range of 5 to 100 poise for each paint. found it to be essential. The features of the present invention will be specifically explained below.

A magnetic recording medium, for example a magnetic disk, obtained by the method of the present invention has a first coating layer (for example, a conductive layer containing carbon black) on both sides of a non-magnetic support 1, as shown in FIG. 2, a second coating layer (for example, a magnetic layer containing Ba-ferrite magnetic powder) 4, and, if necessary, an overcoat layer (not shown), which are laminated in this order.

Note that the magnetic recording medium shown in FIG.
An undercoat layer (not shown) may be provided between the substrate 1 and the support 1, or no undercoat layer may be provided. (Same below). The support may also be subjected to corona discharge treatment.

An example of a method for manufacturing the above-described medium according to the present invention will be explained with reference to FIG.

In this manufacturing apparatus, in manufacturing the medium shown in FIG. 1, first, the film-like support 1 fed out from the supply roll 32 is coated with the above-mentioned conductive layer 2, After applying each paint (not shown) for the magnetic layer 4 in multiple layers using a wet-on-wet method, it passes through a magnet for non-orientation or a magnet for vertical orientation 33, and is introduced into a dryer 34, where the upper and lower layers are It is dried by blowing hot air from a nozzle placed on it.

Next, the dried support 1 with each coated layer is
is led to a supercalender device 37 consisting of a combination of calender rolls 38, where it is calendered and then wound onto a winding roll 39.

These processes may be performed simultaneously in a series of steps or may be performed separately. For example, it may be dried, rolled up, and then calendered.

Thereafter, the conductive layer 2 and the magnetic layer 4 were coated on the other side of the support 1 in the same manner as described above, and dried.
Perform calendar processing (not shown). Furthermore, calender treatment and double-sided coating and drying may be performed. In that case, it is efficient to use a metal-metal roll calender.

The magnetic film thus obtained is punched out into a disk shape and placed in a cassette, for example, 3.5 mm.
manufactures inch floppy disks.

[0021] In the above method, each paint is extruded through an in-line mixer (not shown) and passed through a coater 10,
11. In addition, in the figure, arrow D indicates the conveyance direction of the nonmagnetic base film.

[0022] The extrusion coaters 10 and 11 are provided with liquid reservoirs 13 and 14, respectively, and the paint from each coater is layered in a wet-on-wet manner. That is, immediately after applying the conductive layer paint (in an undried state), the magnetic layer paint is applied in a multilayer manner.

The wet-on-wet multilayer coating method includes a method in which an extrusion coater for applying a conductive layer and an extrusion coater for applying a magnetic layer are used in parallel (FIG. 2 or 3), as well as the method shown in FIGS. An extrusion coater with an integrated paint outlet can also be used to apply two layers at the same time, as in No. 5. In addition, 2' in the figure is the paint for the conductive layer,
4' is a paint for the magnetic layer.

The shape of the head portion of the extrusion coater is as follows:
Those described in JP-A-2-251265 and JP-A-2-268862 are preferred, and have one or two slits and have a shape suitable for coating with two coater heads or one coater head. Preferably.

In addition, it is also possible to use a reverse roll and an extrusion coater, or a gravure roll and an extrusion coater. Furthermore, an air doctor coater, a blade coater, an air knife coater, a squeeze coat impregnation coater, a transfer roll coater, a kiss coater, a cast coater, a spray coater, etc. can be combined.

In multilayer coating using the wet-on-wet method described above, in order to coat the upper magnetic layer while the lower conductive layer is wet, the surface of the lower layer (that is,
The interface with the upper layer) is smooth, the surface properties of the upper layer are good, and the adhesion between the upper and lower layers is also sufficient.

As a result, it satisfies the performance requirements of a magnetic disk that requires high output and low noise, especially for high-density recording, and also meets the requirements for high durability performance. , film peeling is eliminated, film strength is improved, and durability is sufficient. In addition, the wet-on-wet multilayer coating method reduces dropouts and improves reliability.

[0028] In addition to cases in which there is substantially a clear boundary between the upper and lower layers formed by multilayer coating using the wet-on-wet method described above, there is a boundary in which components of both layers coexist at a constant thickness. Although there may be regions, the upper or lower layer excluding such boundary regions is referred to as the above-mentioned magnetic layer or conductive layer. Either case is within the scope of the present invention.

According to the present invention, furthermore, in the wet-on-wet multilayer coating described above, the viscosity of each coating material of the first coating layer and the second coating layer is set to a specific range of 5 to 100 poise. However, this is based on the special feature that the coating conditions in the above-mentioned multilayer coating are very strict, and the results are likely to be poor unless the viscosity is strictly specified.

That is, if the paint viscosity is less than 5 poise, the viscosity is too low and the paint is scraped off by the contact surface of the coater, resulting in poor adhesion (applicability) to the non-magnetic support. For paints for the second coating layer, the lower the viscosity, the better the controllability of the film thickness (especially for thin films of 1 μm or more), but convection is more likely to occur during drying and surface roughness occurs, so the lower limit of the viscosity is It should be 5 poise.

In this case, when the second coating layer is formed to a thickness of 1 μm or more, the coating speed (line speed)
can be made larger. In the multilayer coating of the present invention, coating is possible even when the paint viscosity is relatively low, such as 5 poise or more, which is a condition not found in conventional coating techniques.

For example, in the case of a reverse roll, if the viscosity is low, the paint will not adhere well to the roll, and the film thickness will easily change due to gap fluctuations during roll rotation. In the case of a gravure roll, it is the same as above, but although film thickness fluctuations are eliminated, gravure marks tend to remain, which is disadvantageous for high-capacity type media. On the other hand, in the multilayer coating of the present invention, multilayer coating can be performed at a high line speed even with the above-mentioned relatively low viscosity.

Furthermore, if the viscosity of the coating material exceeds 100 poise, the controllability of the film thickness becomes poor, especially the coating speed becomes low, and it becomes difficult to coat a thin film. In addition, residual stress remains,
Rowan-like roughness tends to occur on the surface, which deteriorates the surface properties.

[0034] The above viscosity range is preferably 5 to 50 poise, but it is better to make a certain difference between the first coating layer and the second coating layer, so that the viscosity of the former coating ≧ the coating viscosity of the latter coating. It is better to use viscosity. Specifically, the paint viscosity for the first coating layer is preferably 8 to 50 poise (especially 10 to 15 poise);
The viscosity of the paint for the second coating layer is 5 to 50 poise (especially 5 to 10 poise).
Poise) is good.

The viscosity of the above-mentioned paint is also related to the coating speed, and in the case of the present invention, the viscosity is 20 m/min to 500 m/min.
Application speeds in the range of m/min may be applied. As the coating speed increases, it is better to set the viscosity higher within the range of the present invention.

In manufacturing a magnetic recording medium according to the present invention, organic solvents are added to various materials, kneaded and dispersed to prepare a magnetic coating solution, and this is coated on the non-magnetic support, aligned, A medium can be created through the steps of drying and surface smoothing treatment.

Examples of the organic solvent include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, propanol, and butanol; methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, and ethylene glycol Esters such as acetate; ethers such as diethyl ether, glycol dimethyl ether, glycol monoethyl ether, dioxane, and tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene, and xylene;
One or a mixture of two or more of halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and dichlorobenzene can be used.

[0038] Further, during kneading and dispersion, each material is simultaneously or separately fed into a kneader and subjected to kneading and dispersion treatment.

After coating, it is preferable to carry out heat treatment and humidification treatment, and it is particularly preferable to carry out reprocessing at the same time. The temperature of this heating and humidification treatment is preferably in the range of 50°C to 85°C.

Further, in the magnetic recording medium according to the present invention, the dry film thickness of the second coating layer (for example, the magnetic layer) is 0.
1 to 4.0 μm, and 0.3 to 3.0 μm
It is preferably in the range of μm, and even more preferably in the range of 0.6 to 2.0 μm. Further, the dry film thickness of the first coating layer (for example, the conductive layer) is preferably 0.1 to 4.0 μm, and preferably 0.12 to 2.0 μm.
0 μm is even better.

In the present invention, at least the second coating layer is a magnetic powder-containing layer, that is, a magnetic layer. Usable magnetic powders include, in particular, hexagonal ferrite such as Ba-ferrite, Fe, Ni, Metals such as Co, Fe-Al series, Fe-Al-Ni series, Fe-Al-Co series, Fe-A
l-Zn system, Fe-Al-Ca system, Fe-Ni-Co system, Fe-Mn-Zn system, Fe-Ni system, Fe-Ni-A
l system, Fe-Ni-Zn system, Fe-Co-Ni-Cr system, Fe-Co-Ni-P system, Co-Ni system, Fe, Ni
, ferromagnetic powder such as metal magnetic powder containing Co as a main component. Iron nitride can also be used.

Furthermore, γ-Fe2 O3, Co-containing γ-Fe2 O3, Co-coated γ-Fe2 O3, F
e3 O4, Co-containing Fe3 O4, Co-coated Fe
Oxide magnetic powders such as 3O4 and CrO4 can also be used.

In particular, Ba-ferrite magnetic powder is BaO
・In addition to nFe2O3 (n≧1), the average grain size in which a part of Fe is replaced with at least Co and Zn (the average length of the diagonal of the plate surface of hexagonal ferrite for 100 grains) ) 400 to 900 Å, plate ratio (value obtained by dividing the length of the diagonal line of the plate surface of hexagonal ferrite by the plate thickness) 2.0 to 10.0, coercive force 350 to 200
Preferably, it is made of 0 Oe ferromagnetic Ba-ferrite.

In the Ba-ferrite magnetic powder that can be used in the present invention, coercive force is controlled to an appropriate value by partially replacing Fe with Co, and further by partially replacing Fe with Co, only Co can be replaced. It is possible to achieve high saturation magnetization that cannot be obtained with other methods, and to obtain magnetic disks and the like with excellent electromagnetic conversion characteristics and high reproduction output.

Furthermore, by substituting a part of Fe with Nb, a magnetic disk having higher reproduction output and excellent electromagnetic conversion characteristics can be obtained. In Ba-ferrite magnetic powder, a part of Fe is further composed of Ti, In, Mn, and Cu.
, Ge, Sn, and other transition metals may be substituted.

The Ba-ferrite constituting the magnetic powder used in the present invention is preferably represented by the following general formula (M is a substituted metal atom). BaO ・n(Fe1-mM m )2O3) Here, m may be set to 0, but n>0.36 (however, Co+Z
n=0.08~0.3, Co/Zn=0.5~10
) is better. Also, n≧1 may be used, but n=5.4 ~
6.0, and M is preferably a combination of two or more elements with an average valence of 3.

On the other hand, when using metal magnetic powder, Fe-based metal magnetic powder containing 80 atm % or more has excellent electrical properties, and is particularly suitable for Fe-Al, Fe-
Al-Ni, Fe-Al-Zn, Fe-Al-Co, F
Metal magnetic powders of e-Ni, Fe-Ni-Al, and Fe-Ni-Zn systems are preferred. Additives to these metal magnetic materials include Si, Cu, Zn, Al, P, Mn, and Cr.
These elements or compounds thereof may be included.

Next, the above-described first coating layer may also be formed as a magnetic layer containing the above-mentioned magnetic powder, but is preferably formed as a conductive layer containing carbon black.

If the first coating layer is such a conductive layer, there is no need to add an antistatic agent such as carbon black to the magnetic layer as the second coating layer. That is, if a conductive layer containing carbon black is provided between the magnetic layer and the nonmagnetic support, the surface electrical resistance of the magnetic layer can be sufficiently reduced by the conductive layer.

Furthermore, since the magnetic layer does not contain an antistatic agent, there is an advantage that the packing density and dispersibility of Ba-ferrite magnetic powder and the like in the magnetic layer are improved.

[0051] Carbon black is used for purposes other than antistatic.
For example, it may be added in small amounts to the second magnetic layer for the purpose of controlling surface roughness or imparting slipperiness.

Examples of carbon black used in such a conductive layer include Conductex 975 (specific surface area 250 m2/g, particle size 24 mμ) and Conductex 900 (specific surface area 125 m2/g) manufactured by Columbia Carbon Japan. g, particle size 27 mμ), Conductex 40-220 (particle size 2
0 mμ), Conductex SC (particle size 20 mμ), Cabot Vul
can) XC-72 (specific surface area 254 m2/g, particle size 30 mμ), Vulcan P (particle size 20 mμ), Raven 1
040, 420, Black Pearls 2000 (particle size 1
There are conductive carbon blacks such as #44 manufactured by Mitsubishi Kasei Corporation.

[0053] This carbon black has an oil absorption amount (DB
P) of 90 ml/100 g or more is desirable because a structured structure is easily formed and higher conductivity is exhibited.

[0054] This conductive layer may be made by fixing the carbon black described above with a binder resin described later, and may further include a lubricant described later.

[0055] The carbon black in this layer has an average particle size of 10
~50 mμ (and even 20 to 40 mμ) The amount added is 10 to 300 parts by weight per 100 parts by weight of binder resin (
Furthermore, 50 to 150 parts by weight) is preferable. The average particle size herein refers to the average particle size per 100 carbon black particles.

Note that when the first coating layer is a magnetic layer, the upper layer of the plurality of magnetic layers is used for high frequency recording such as video output, etc.
Each layer can be formed so as to have good playback characteristics, and to make the recording and playback characteristics of relatively low frequencies such as chroma and audio output good in the lower layer.

[0057] For this purpose, it is necessary that the retention force (Hc) of the upper layer (especially the top layer) is larger than that of the lower layer, and that the film thickness (or layer thickness) of the upper layer is thin, especially 0.6 μm. The following is desirable. The thickness of the lower layer adjacent to the upper layer is preferably 1.5 to 4.0 μm.

[0058] As the binder used for the first coating layer and the second coating layer in the present invention, conventionally used binders can be used, but from the viewpoint of dispersion of magnetic particles and other fillers, functional groups are or a resin modified by introducing a functional group that forms an inner salt, particularly a modified vinyl chloride resin, a modified polyurethane resin, or a modified polyester resin.

[0059] The functional group in the resins is, for example, any one of -SO3M, -OSO2M, aluminum, and sodium, and M1 and M2 are each a hydrogen atom, lithium, potassium, sodium, or an alkyl group. It is. Furthermore, M1 and M2 may be different from each other or may be the same. ), etc.

These functional groups are compatible with resins such as vinyl chloride resins, polyester resins, and polyurethane resins, for example, Cl-CH2 CH2 SO3 M, Cl-C
H2 CH2 M1 and M2 each have the same meaning as above. ), etc., by condensing with a compound containing a negative functional group and chlorine in the molecule through a dehydrochloric acid reaction.
can be introduced.

Among the resins thus obtained, preferred are vinyl chloride resins and polyurethane resins into which negative functional groups are introduced.

The binder may be a vinyl chloride resin or a polyurethane resin, but considering the high dispersibility and mechanical strength of the vinyl chloride resin and the abrasion resistance of the polyurethane resin, it is better to use these resins in combination. Good.

When used together, the ratio of vinyl chloride resin/polyurethane resin is preferably 30/7 in the magnetic layer.
0 to 90/10, 0/100 to 7 in the conductive layer
0/30, more preferably 30 in the magnetic layer.
/70~70/30, 10/90~ in the conductive layer
It is 70/30.

The magnetic layer preferably contains a certain amount of vinyl chloride resin in order to improve the dispersibility of the magnetic powder, and the conductive layer preferably contains a smaller amount of vinyl chloride resin than the magnetic layer. There is no problem even if
In short, the blending ratio of both resins can be determined depending on the required performance of each layer.

Examples of the vinyl chloride resin include vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl propionate-vinyl alcohol copolymer, and vinyl chloride-vinyl acetate-vinyl maleate-vinyl alcohol copolymer. Examples include vinyl chloride-vinyl propionate-vinyl maleate-vinyl alcohol copolymer.

In the present invention, in combination with the binder,
Alternatively, conventionally used unmodified vinyl chloride resins, polyurethane resins or polyester resins can be used as needed, and cellulose resins, phenoxy resins or specific usage methods can be used instead. Thermoplastic resins, thermosetting resins, reactive resins, electron beam curable resins, and the like may also be used.

The above-mentioned resin can be used as a binder for magnetic layers, conductive layers, etc. by selecting the optimum type and amount.

[0068] In order to improve the durability of the magnetic layer, conductive layer, etc., the paint for each layer can contain various curing agents, such as isocyanates.

Isocyanates that can be used as curing agents include, for example, aromatic isocyanates such as tolylene diisocyanate (TDI), and adducts of these isocyanates with active hydrogen compounds, and have an average molecular weight of 100 to 100. A value in the range of 3000 is preferred, and 200 to 2000 is more preferred.

Examples of aliphatic isocyanates include hexamethylene diisocyanate (HMDI) and adducts of these isocyanates with active hydrogen compounds, and those having an average molecular weight of 100 to 3,000 are preferable, but 200 to 3,000 are preferable. More preferably, the number is in the range of 2,000 to 2,000. Among fatty acid isocyanates, non-alicyclic isocyanates and adducts of these compounds with active hydrogen compounds are preferred.

[0071] A dispersant may be added to the coating material used to form the above magnetic layer or conductive layer, etc., if necessary, and additives such as lubricants and abrasives may also be contained, if necessary. Good too.

Usable dispersants include phosphoric acid esters, amine compounds, alkyl sulfates, fatty acid amides, higher alcohols, polyethylene oxides, sulfosuccinic acids, sulfosuccinic esters, known surfactants, and salts thereof. Yes, and also negative functional groups (e.g. -
It is also possible to use salts of polymeric dispersants with COOH). In addition, functional groups (SO3H, COOH, NH2
) can also be used. These dispersants may be used alone or in combination of two or more.

In addition, as lubricants, silicone oil, graphite, carbon black graphite polymer, molybdenum disulfide, tungsten disulfide, monobasic fatty acids having 12 to 20 carbon atoms (for example, myristic acid, stearic acid), fatty acid esters, etc. (eg, butyl stearate, oleyl oleate). These lubricants are preferably added in an amount of 0.2 to 20 parts by weight based on 100 parts by weight of the binder.

As the abrasive, commonly used materials such as alumina, silicon carbide, chromium oxide, corundum, artificial corundum, artificial diamond, garnet, and emery (
Main ingredients: corundum and magnetite) etc. are used. These abrasives may have an average particle size of 0.05 to 5 .mu.m, particularly preferably 0.1 to 2 .mu.m. These abrasives are preferably added in an amount of 1 to 20 parts by weight based on 100 parts by weight of the binder.

Examples of non-magnetic supports include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polyamide and polycarbonate. Examples include Cu, Al
, metals such as Zn, glass, ceramics such as boron nitride, silicon carbide, etc. can also be used.

[0076] The thickness of these supports is 6 μm to 200 μm.
It may be on the order of μm.

An intermediate layer for improving adhesion may be provided between the support and the magnetic layer, that is, between the magnetic layer and the conductive layer or between the conductive layer and the support. Such an intermediate layer may consist of an electrically conductive layer according to the invention.

The present invention is also applicable to magnetic tapes and the like.

[0079]

[Examples] Examples of the present invention will be described below along with comparative examples. Ingredients, proportions, order of operations, etc. may be varied without departing from the spirit of the invention. In addition, in the following examples, all "parts" are parts by weight.

Paint [A]: Carbon black (Conductex SC manufactured by Columbia Carbon) 100 parts VAGH (U
(PVC vinyl chloride resin manufactured by CC)
40 copies N-2
304 (polyurethane resin manufactured by Nippon Polyurethane Co., Ltd.)
40 parts phosphate ester (Gafac RP-710)
5 parts Coronate 3041 (polyisocyanate manufactured by Nippon Polyurethane Co., Ltd.) 15 parts Methyl ethyl ketone
400 parts toluene

400 copies

Paint [B]: Ba-ferrite (BET approx. 33 m2/g, H
c 550Oe) 10
0 parts Alumina oxide (AKP30 manufactured by Sumitomo Chemical Co., Ltd.
)
Part 10 VAGH (above)

10th part N-2
304 (above)

10 parts phosphate ester (Gafac RP-710)
Part 2 Fatty acid ester (oleyl oleate)
Part 5 Coronate 30
41 (above)
5 parts Methyl ethyl ketone

220 parts toluene


220 copies

Paint [C]: Co-γ-Fe2 O3 (BET35m2/
g, Hc 630Oe) 1
00 parts Alumina oxide (AKP3 manufactured by Sumitomo Chemical Co., Ltd.
0)
Part 10 VAGH (above)

Part 8 N-2
304 (above)

Part 8 Phosphate ester (Gafac R
P-710)
Part 2 Fatty acid ester (oleyl oleate)
Part 5 Coronate 304
1 (above)
5th part
Methyl ethyl ketone

220 parts toluene

2
20 copies

Paint [D]: Ferromagnetic metal powder (Fe99%, N: 1%)

100 copies (BE
T50m2/g, Hc1700Oe)
(σs130enu/g)
VAGH (above)

Part 14 N-2304 (above)

Part 6
Coronate 3041 (above)

Part 5 Phosphate ester (Gafac RP-710)
Part 2 Fatty acid ester (
oleyl oleate)
10 parts methyl ethyl ketone

220 parts toluene

220 copies

008
4] Paint [E]: Carbon black (Conductex SC manufactured by Columbia Carbon) 100 parts Vinyl chloride resin with functional group (MR110 manufactured by Nippon Zeon Co., Ltd.)
40 parts Polyurethane resin with functional groups (UR8700 manufactured by Toyobo Co., Ltd.)
40 copies Coronate 3041 (
Polyisocyanate manufactured by Nippon Polyurethane Co., Ltd.)
15 parts methyl ethyl ketone

400 parts toluene

400 copies

Paint [F]: Ba-ferrite (BET approx. 33 m2/g, H
c 550Oe) 10
0 parts Alumina oxide (AKP30 manufactured by Sumitomo Chemical Co., Ltd.
)
10 copies MR110 (above)

10th part U
R8700 (above)

10 parts fatty acid ester (oleyl oleate)
Part 5 Coronate 304
1 (above)
5th part
Methyl ethyl ketone

220 parts toluene

2
20 copies

Paint [G]: Co-γ-Fe2 O3 (BET35m2/
g, Hc 630Oe) 1
00 parts Alumina oxide (AKP3 manufactured by Sumitomo Chemical Co., Ltd.
0)
10 copies MR110 (above)

Part 8 U
R8700 (above)

8 parts Fatty acid ester (oleyl oleate)
Part 5 Coronate 3041
(the above)
5th part
Methyl ethyl ketone

220 parts toluene

22
0 copies

Paint [H]: Ferromagnetic metal powder (Fe99%, N: 1%)

100 copies (BE
T50m2/g, Hc1700Oe)
(σs130emu/g)
MR110 (above)

Part 14 UR8
700 (above)

Part 6 Coronate 3041 (above)

5 parts fatty acid ester (oleyl oleate)
10 copies
Methyl ethyl ketone

220 parts toluene

220
Department

A part of the composition of each of the above-mentioned paints is kneaded and dispersed using a kneader such as a kneader that applies high shear, and after dilution using a part of the remaining solvent, a sand grinder (200
A uniform dispersion was obtained by performing a dispersion treatment for about 3 hours at 0 rpm). Furthermore, the remaining materials are added and mixed uniformly using a dissolver, sand mill, etc. to form paints [A], [B], and [C].
, [D], [E], [F], [G], and [H] were created.

These paints were applied in various combinations and film thicknesses as shown in FIGS. 6 to 8. That is, width 300mm
It was coated on both sides of a polyethylene terephthalate film having a thickness of 75 μm so that the dry film thickness was as shown in FIGS. 6 to 8.

At this time, in accordance with the present invention, an extrusion type extrusion coater (as shown in FIGS. 3 to 5) is used.
Multilayer coating was performed using a wet-on-wet method.

[0091] Then, paints [A], [B], [C], [
D], [E], [F], [G], and [H] were further coated after adjusting the viscosity with a solvent of methyl ethyl ketone and toluene in a ratio of 1:1 to a predetermined viscosity. In addition, after drying, calender treatment was performed, and after that, each paint was similarly applied to the opposite side of the polyethylene terephthalate base film in a wet-on-wet manner after adding and mixing the polyisocyanate compound, and after drying. It was calendered and wound into a roll.

The resulting roll was unrolled and punched into a 3.5-inch floppy disk at room temperature and humidity (25° C., 50% RH) to obtain a magnetic disk.

Next, the obtained magnetic disk sample was
The sample was placed in a constant temperature and humidity chamber set at 0° C., 15% RH for 24 hours, and treated.

A method for measuring the performance of the magnetic disk manufactured above will be described below. The results are summarized in FIGS. 6 to 8. According to this, it can be seen that by applying the coating under the conditions of the present invention, each measurement result becomes better.

(1) RF output Record with a 500 KHz sine wave signal and measure the reproduced RF output.

(2) Coated surface condition The condition of the coating film surface was evaluated as follows. Good: smooth surface Slightly poor: There are streaks in some parts. Defective: Many streak failures

(3) Average surface roughness Ra Measured using a three-dimensional surface roughness meter (3FK) manufactured by Kosaka Institute (cutoff: 0.25 mm).

(4) Glossiness The glossiness of the coated sample film (without calender treatment) was measured at an incident angle of 60° perpendicular to the coating direction, and expressed as 100% for the standard plate.

(5) Paint viscosity A generally known B-type viscometer can be used for simplicity, but
This data was measured using a HAAKERV2 rotational viscometer.
It shows the viscosity when rotating at 2000 rpm.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an example of a magnetic disk according to the present invention.

FIG. 2 is a schematic diagram of a magnetic disk manufacturing apparatus according to the present invention.

FIG. 3 is a cross-sectional view showing an example of a wet-on-wet multilayer coating method.

FIG. 4 is a cross-sectional view showing another example of the wet-on-wet multilayer coating method.

FIG. 5 is a cross-sectional view showing still another example of the wet-on-wet multilayer coating method.

FIG. 6 is a diagram collectively illustrating media and their performance data according to each example.

FIG. 7 is a diagram collectively showing media and their performance data according to each example.

FIG. 8 is a diagram collectively showing media and their performance data according to each example.

[Explanation of symbols]

1 Non-magnetic support 2 Conductive layer 2' Paint for conductive layer 4 Magnetic layer 4' Paint for magnetic layer 10, 11 Extrusion coater

Claims (1)

[Claims] 1. When manufacturing a magnetic recording medium in which a first coating layer and a second coating layer are laminated in this order on a non-magnetic support, at least the second coating layer of the first coating layer and the second coating layer is laminated in this order on a non-magnetic support.
A paint containing magnetic powder is used as the paint for the coating layer,
Applying the paint for the second coating layer while the coating layer is not dry when the coating for the first coating layer is applied, and applying each coating for the first and second coating layers at the same time. A method for producing a magnetic recording medium, wherein the viscosity of each coating material for the first and second coating layers is set to 5 poise to 100 poise.