JP3002416B2 - Manufacturing method of magnetic recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of manufacturing a magnetic recording medium, and more particularly to a method of manufacturing a magnetic recording medium having excellent electromagnetic conversion characteristics.

[0002]

2. Description of the Related Art With the recent increase in the density of magnetic recording media,
The film configuration of the coating type medium is changing from a single layer type to a multilayer type. As for the thickness of the magnetic layer, thinning of the magnetic layer for the purpose of reducing the demagnetizing field has progressed, and for the magnetic powder and magnetic composition, miniaturization and high packing for the purpose of high output characteristics have been required.

With the aim of achieving the above high performance, there have been some changes in the evolution of coating technology. JP-B-63-880 discloses a multi-layer forming method in which coating and drying are repeated one by one on a support as described in JP-B-54-43362 and JP-A-51-119204.
Coating techniques such as simultaneous multi-layer coating using an extrusion die coating machine as disclosed in Japanese Patent Application Laid-Open No. 80-179179 and Japanese Patent Application Laid-Open No. 2-17971 have been disclosed. The extrusion die can perform simultaneous multilayer coating because there is no roll nip at the time of coating as compared with a roll coating method such as a gravure or reverse coating method. Also, compared to the slide coating method, it is possible to handle a high-viscosity, high-solids paint. For example, Japanese Patent Application Laid-Open No. Hei 5-329433 discloses coating conditions for performing extrusion coating.

[0004]

The focus of these conventional coating conditions is on the viscosity, and these conditions cannot be said to be sufficient at present as media density is required to be further increased.

[0005] It is an object of the present invention to provide a magnetic recording medium in which a uniform coating state is ensured and the electromagnetic conversion characteristics of the magnetic recording medium are improved.

[0006]

According to a first aspect of the present invention, there is provided a method of manufacturing a magnetic recording medium in which a support is run and a coating material is applied to the support by an extrusion die. Before the paint is supplied to the paint, a shear force of 100 Sec ^-1 or more and a product of the shear rate and the shear application time of 30,000 or more are applied to the paint after the final dilution, and the paint is applied from the time the shear is applied until the application is performed. The average residence time is a change ratio of the storage elastic modulus G ′ (t + Δt) after a short time Δt from the storage elastic modulus G ′ (t) at a certain time t.

(Equation 3) Is within the time to reach 0.03 or more.

According to a second aspect of the present invention, in the method for manufacturing a magnetic recording medium according to the first aspect, the coating method is at least 100 sec. ^-1 or more, the product of the shear rate and the shear application time The shear force of 30,000 or more is applied, and the average residence time of the paint from the application of the shear to the application is determined by the storage elastic modulus G '(t ), The change ratio of the storage elastic modulus G ′ (t + Δt) after a short time Δt

(Equation 4) Is within the time to reach 0.03 or more.

[0008] As is generally known, magnetic paints have nonlinear viscoelastic properties. However, viscosity has only scalar information as a viscosity value. The actual paint contains the viscosity and elasticity values as vector information,
The present invention has paid particular attention to this point. That is, in the present invention, the application conditions for the simultaneous multi-layer application method using an extrusion die are found in terms of elastic characteristics. For example, elasticity represents the network state of the paint,
Knowing the elasticity value is important in knowing the dispersion state of the paint. Further, the discharge of the paint at the tip of the lip is a state in which the state changes from a low shear state to a high shear state in a short time, and the influence of the elasticity term is great.

In particular, according to the present invention, the optimum conditions in the extrusion coating method of paint can be efficiently reflected in the design.

It is well known that viscoelasticity of paints is known. Generally, attempts have been made to explain the viscoelastic state of a paint using a Voigt model, a Maxell model, a combination thereof, and the like. However, finding a complex combination of particle models has been very difficult.

In the present invention, attention has been paid to the time-dependent change rate of the storage elastic modulus G 'of the paint as a viscoelastic substance. That is, a shear rate of 100Sec- ¹ or more to the paint after the final dilution, a shear force of 30,000 or more of the product of the shear rate and the shear application time is applied, and the average residence time of the paint from application of the shear to application of the shear is a certain time. Change ratio of storage elastic modulus G '(t + Δt) after a short time Δt from storage elastic modulus G' (t) at t

(Equation 5) It has been found that, by setting the coating conditions to be within the time to reach 0.03 or more, a coating state without coating unevenness (good surface property) can be ensured.

The elastic modulus G of the viscoelastic substance is a complex number (G =
G ′ + iG ″), and the real part G ′ is the storage elastic modulus,
The imaginary part G ″ is defined as the loss modulus.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram summarizing the change with time of the storage elastic modulus G 'in Example 1 after changing the pre-shearing conditions of the coating material A (for the upper layer), and FIG. After changing the pre-shearing conditions of the paint B (for the lower layer), a diagram summarizing the change over time of the storage elastic modulus G ′. FIG. 3 shows Example 2, the pre-shearing conditions of the paint A (for the upper layer) were changed. FIG. 4 is a graph summarizing the change over time of the storage elastic modulus G ′, and FIG. 4 is a graph summarizing the change over time of the storage elastic modulus G ′ after changing the conditions of the preliminary shearing of the coating material A (for the upper layer) in Example 3. FIG. 5 is a diagram summarizing the change in storage elastic modulus G ′ with time after changing the pre-shearing conditions of Example 4, paint C (for a single layer), and FIG. 6 is a schematic diagram illustrating an extrusion die. FIG. 7 is a schematic diagram showing an inline distribution system, and FIG. 8 is a schematic diagram showing an offline distribution system.

Extrusion die 10 for single layer coating
6A, an upstream lip 12 and a downstream lip 13 are provided on a die head 11 as shown in FIG.
2 and a slot portion 14 are formed between the downstream lip 13 and
The slot 14 communicates with the liquid buffer 15. The paint supply system 16 includes a paint (for example, paint A or C described later).
Is supplied to the slot unit 14 via the liquid buffer unit 15.
Thereby, the slot portion 14 is formed on the surface of the non-magnetic support 1.
A coating material extruded from the substrate 1 is applied, and the coating material is dried by a drying device to produce a magnetic recording medium having a coating layer on the surface of the support 1.

As shown in FIG. 6B, the extrusion die 20 for simultaneous coating of two layers has an upstream lip 22, a first downstream lip 23, and a second downstream lip 24 on a die head 21. A first slot portion 25 is formed between the side lip 22 and the first downstream lip 23, the first slot portion 25 communicates with the liquid buffer portion 26, and the first downstream lip 23 and the second downstream lip 24 A second slot portion 27 is formed between the second slot portion 27 and the second slot portion 27 which communicates with the liquid buffer portion 28. The lower paint supply system 29 supplies a lower paint (for example, paint B described later) to the first slot 25 via the liquid buffer 26. Upper paint supply system 30
Supplies the upper layer paint (for example, paint A described later) to the second slot 27 via the liquid buffer 28. As a result, the lower coating material extruded from the first slot portion 25 and the upper coating material extruded from the second slot portion 27 are simultaneously applied to the surface of the nonmagnetic support 1 by a wet-on-wet method. Is applied when the lower layer paint is wet. Next, the lower layer paint and the upper layer paint are dried by a drying device to produce a magnetic recording medium having a lower layer and an 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 single layer, or the upper and lower layers, a back coat layer, a non-magnetic support and a lower or back coat layer Other layers, such as a primer layer provided between them and a magnetic layer provided for recording a servo signal or 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, a generally known non-magnetic support can be used without any particular limitation. Films and disks; 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.

Examples of the polymer resin for forming the flexible film and the disk include polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycyclohexylene dimethylene terephthalate, and polyethylene bisphenoxycarboxylate; , 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 backcoat layer provided on the back surface of the nonmagnetic support as necessary can be formed by using a known backcoat paint without any particular limitation.

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

As the above 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 and a hexagonal ferrite powder.

The coercive force of the ferromagnetic metal powder is 1600 to 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. Further, the saturation magnetization of the hexagonal ferrite powder is preferably 30 to 70 emu / g, and 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,
The major axis length is preferably 0.01 to 0.25 μm, more preferably 0.05 to 0.2 μm, and the preferred acicular ratio is 3 to 20,
Preferably, the preferred X-ray particle size is between 130 and 250 Angstroms.

As the hexagonal ferrite powder, barium ferrite and strontium ferrite in the form of fine flat plate, 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.

[0027] In addition, the above magnetic powder may, if necessary,
Rare earth elements and transition metal elements can be included.

In the present invention, the magnetic powder may be subjected to a surface treatment in order to improve the dispersibility and the like of the magnetic powder.

The above-mentioned surface treatment is performed by the
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.

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, in addition to the above-described methods.

Examples of the binder include a thermoplastic resin, a thermosetting resin, and a reactive resin. When used, they can be used alone or as a mixture.

Specific examples of the binder include vinyl chloride resins, polyesters, polyurethanes, nitrocellulose, epoxy resins and the like. In addition, JP-A-57-62128, page 2, upper right column 19 Line to lower right column on page 2 19
Resins and the like described in the rows and the like are included. Further, the binder may contain a polar group for improving dispersibility and the like.

The amount of the 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. No.57-62128, page 3, lower right column, line 17-
The solvents described on page 4, lower left column, line 10, etc. can be used.

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

In addition, the magnetic coating material needs additives usually used for magnetic recording media, such as dispersants, lubricants, abrasives, antistatic agents, rust inhibitors, fungicides, and curing agents. It can be added accordingly. As the additives, specifically, JP-A-57-62128, page 2, upper left column, line 6 to
Page 2, upper right column, line 10 and page 3, upper left column, line 6 to page 3, upper right column 18
Various additives described in the column and the like can be mentioned.

In order to prepare the magnetic paint, for example, the magnetic powder and the binder are put into a Nauta mixer or the like together with a part of the solvent and premixed to obtain a mixture. After kneading with a kneader or the like, then diluting with a part of the solvent, dispersing using a sand mill or the like, mixing additives such as a lubricant, filtering, further curing agent such as polyisocyanate and the remaining. Examples thereof include a method of mixing a solvent.

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

[0039]

Hereinafter, specific results of the present invention will be described. (Examples 1 to 4) (Tables 1, 2 and 3) A 6 μm-thick polyethylene terephthalate (PET) film was used as a support, and paints A having the formulations shown in Tables 1 to 3 were used as paints.
To C, a coating state and an output state were investigated, and FIGS. 1 to 5 and Tables 4 to 7 were obtained.

Magnetic paint A (Table 1)

[0041]

[Table 1]

Non-magnetic paint B (Table 2)

[0043]

[Table 2]

Magnetic paint C (Table 3)

[0045]

[Table 3]

(Manufacture of Magnetic Recording Medium) The above-mentioned single layer, or the upper and lower magnetic paints were coated on the surface of a 6 μm thick polyethylene terephthalate film by a shearing machine.
After changing the shearing conditions applied to the paint, it was applied to form a single layer, or an upper layer and a lower layer. 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, at 85 ° C, calendering is performed under the condition of 350 kg / cm.
A back coat paint was applied on the back surface of the nonmagnetic support so as to have a dry thickness of 0.5 μm, dried at 90 ° C., and wound up. Then, after aging treatment at 50 ° C or less for 16 hours, it was cut into an 8 mm wide tape shape, a magnetic tape was obtained, and the obtained magnetic tape was loaded into an 8 mm cassette case, and a 8 mm / 120 mm video cassette was recorded. Was prepared.

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).

As a method of applying shear to the final diluted paint by a paint disperser, there are an in-line dispersion method (1) and an offline dispersion method (2) below. (1) In-line dispersion method (FIG. 7) In the in-line dispersion method, as shown in FIG.
The paint in 1 is passed through a dispersing machine 102, and this is applied to a coating machine (large).
103. 104 is a pump, 105
Is a filter and 106 is a dryer.

(2) Offline distribution method (FIG. 8) In the offline distribution method, as shown in FIG.
1 is dispersed in a dispersing machine 202,
Get to 3. The paint in the tank 203 is transferred to a tank 204 and supplied to a coating machine (large) 205. 206
Denotes a pump, 207 denotes a filter, and 208 denotes a dryer.

In the first, third and fourth embodiments, an in-line distribution system is employed, and in the second embodiment, an off-line distribution system is employed.

The terms used in the description of the present invention will be described below. The average residence time of the coating material from the application of the shear to the application of the coating is defined as the volume V of the coating material and the volume v applied per unit time until immediately before the application from the shearing device (dispersing machine). The ratio, expressed as T = V / v, is the average time the paint has been in the line and the total volume of the application head.

The change ratio of the storage elastic modulus G 'is as follows:
^-1 or more, after having been subjected shear more product 30000 shear rate and shear application time, but the shear is removed storage modulus G 'increases with time, it refers to an increase ratio per unit time.

Let Gt be the storage modulus G 'at time t, and Δ
If it increases to Gt + Δt after t, the change ratio Δ becomes

(Equation 6) Is represented by

As is generally known, the product of the shear rate and the shear application time is used to represent the shear state applied to the paint. In which A product 10000 shear rate and shear application time, and when subjected 10Sec a shear rate of 1,000 sec ^-1, shearform according to paint in the case of over 100 sec shear rate 100 sec ^-1 is equivalent, to is there. For example, when a shearing force of 10 ⁴ Sec ⁻¹ is applied by a high shearing force applying device such as a tornado or the like, a shearing state similar to the present condition can be obtained by giving an application time of 3 seconds or more.

Example 1 (Table 4)

[Table 4]

(Confirmation of influence of lower layer coating. Confirmation of influence of shearing on multi-layer coating and single-layer coating.) FIG. 1 (upper layer, storage elastic modulus G ′) FIG. 2 (lower layer, storage elastic modulus G ′) Paint on upper layer A, simultaneous coating with an extrusion die was performed using paint B for the lower layer.

The final diluted upper layer paint and lower layer paint are sheared by the in-line paint disperser, and the average residence time of the paint from application of shear by the disperser to application is approximately 180.
Application was performed after a lapse of seconds. Shear by paint disperser is 5Sec ^-1
(Shear time 300 Sec), 500 Sec ^-1 (Shear time 300 S
ec) and 1800Sec ^-1 (shear addition time 300Sec).

Here, the average residence time of the paint from the application of the shear to the application is defined as the volume V stored in the paint until immediately before the application from the shearing applicator (dispersing machine), per unit time. When the applied volume is v, T = V /
The average time, expressed as v, that the paint has been in the line and the total volume of the application head.

As a result, irrespective of the state of the lower layer, the upper layer was sheared by 1800 Sec ^-1 (shear addition time: 300 Sec), 500 Sec.
^-1 (shearing time 300Sec) is in good condition, 5S
The coating condition at ec ^-1 (shear addition time 300 Sec) was not good.

The viscoelasticity of the paint was measured off-line (hereinafter referred to as Rheometrics RFS-2.
0sec applied, 30sec pause, 1% strain angular velocity 10rad / S
When the response was applied in ec and the torque applied to the probe was measured), the elastic rise time at which the change ratio of the storage elastic modulus G ′ of the upper coating material A reached 0.03 was 5 Sec ⁻¹ (shear addition time 300 Sec).
180Sec, 180 at 170Sec, 500Sec ^-1 (additional time 300Sec)
It was 800 Sec or more at 0 Sec ^-1 (shear addition time: 300 Sec).

The storage rise modulus G 'of the lower coating B (the elastic rise time at which the change ratio reaches 0.03 is 140 Sec at 5 Sec ^-1 (shear addition time of 300 Sec) and 1800 Sec ^-1 (shear addition time).
300Sec) and 300Sec.

Regardless of the elastic rise time of the lower layer paint, the elastic rise time at which the storage elastic modulus G 'change ratio of the upper layer paint reaches 0.03 is determined by the average residence time of the paint from the application of shear by the disperser to the application. It was confirmed that the coating state was good when the amount exceeded, and that the coating state was not good when the amount was lower.

Note that the calculation example of the change ratio ΔG ′ is described in the first embodiment.
FIG. 1 shows the case of the shearing condition of 500 Sec ^-1 . Assuming that the time of a certain storage elastic modulus Gt ′ is t and that it takes Δt for the storage elastic modulus to reach 10 times, in the case of this embodiment, Δt
= 310 seconds. Therefore, the change ratio of the storage modulus is

(Equation 7) Becomes Since this is nothing but the slope at (t, Gt ') of the graph, this slope may be obtained by another method.

Example 2 (Table 5)

[Table 5]

(Confirmation of Off-Line Dispersion Effect) Usage Diagram FIG. 3 (upper layer, storage elastic modulus G ′) Simultaneous multi-layer coating was performed by an extrusion die using paint A for the upper layer and paint B for the lower layer.

After the final diluted upper layer coating was sheared by the off-line coating disperser, the coating was immediately supplied to the die coating system, and the coating was performed between an average residence time of about 180 seconds and 600 seconds. The shearing by the paint disperser is 5 Sec ^-1 (shear addition time 300 Sec), 500 Sec ^-1 (shear addition time 300 Sec),
1800Sec ^-1 (shearing time 300Sec).

As a result, the application state of 500 sec ^-1 (shear addition time 300 sec) 1800 Sec ^-1 (shear addition time 300 Sec) was good on the upper layer, and the coating state of 5 Sec ^-1 (shear addition time 300 Sec) was not good. Was.

When the viscoelasticity of the paint was measured off-line, the change rate of the storage modulus G 'of the upper paint A reached 0.03, and the elastic rise time was 5 Sec ^-1 (shear addition time).
At 300 Sec) at 140 Sec, at 500 Sec ^-1 (shear addition time 300 Sec)
1100Sec at 460Sec, 1800Sec ^-1 (Shear time 300sec)
That was all.

As in Example 1, the storage elastic modulus G ′ of the upper coating material was
If the elastic rise time at which the change ratio reaches 0.03 exceeds the average residence time of the paint from the application of shear by the disperser to the application, the application state is good, and if it falls below, the application state is It was confirmed that it was not good.

Example 3 (Table 6)

[Table 6]

(Confirmation of Shearing Force that Gives Dispersion) Usage Diagram FIG. 4 (upper layer, storage elastic modulus G ′) Dispersing machine that uses paint A for the upper layer and paint B for the lower layer and affects the storage elastic modulus G ′ of the paint It was confirmed how much shear force was required.

The shears of the in-line disperser were reduced to 5, 10, 50,
The coating was changed to 100, 500, and 1800 Sec ⁻¹ (shear application time: 300 Sec), and the multilayer coating was performed. As a result, the shear conditions were 5, 1
In the case of ⁰ and 50 Sec- ^1, the coating condition was not good. But,
When the shearing conditions were 100, 500, and 1800 Sec- ^1, a good coating state was obtained.

When the viscoelasticity of the paint was measured off-line, the relationship between the shearing conditions and the shearing application time was as shown in FIG.

As a result, when a shearing time of 300 Sec was applied, and when the shearing conditions were 5, 10, and 50 Sec- ¹ , the average residence time of the coating material from application of the shearing force by the dispersing machine to application of the coating material (approximately 180 The change ratio of the storage elastic modulus G ′ within the second) was large, and the elastic state of the paint was not good. But the shear conditions are 1
In the cases of 00, 500, and 1800 Sec- ^1, the change ratio of the storage elastic modulus G 'was almost 0, and the paint state was very stable.

It was presumed that in the case of a shear of 50 Sec ^-1 or less, the dispersion of the paint did not progress even if the time for applying the shear was increased, but rather the agglomeration of the paint occurred. It was confirmed that a shearing effect of 100 Sec ^-1 or more produced an effect of dispersion.

Furthermore, it was confirmed that the shearing force of 1800 Sec ^-1 (application time of 300 Sec) in Example 1 was sufficient as a dispersing force applied to the coating material.

Example 4 (Table 7)

[Table 7]

(Confirmation of Single-Layer Application) Usage Diagram FIG. 5 (upper layer, storage elastic modulus G ′) Single-layer application was performed using paint C. The coating was sheared by an in-line coating disperser, and the coating was performed after an average residence time of about 200 seconds. As a result, although the coating surface quality was different, a coating tendency almost the same as the upper layer coating conditions (Example 1) in the multilayer coating was obtained.

[0080]

As described above, according to the present invention, when applying a magnetic recording medium, a coating state without coating unevenness is ensured,
The electromagnetic conversion characteristics of the magnetic recording medium can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram summarizing the change over time in storage modulus G ′ after changing the conditions of preliminary shearing of Example 1, paint A (for upper layer).

FIG. 2 is a diagram summarizing the change over time in storage modulus G ′ after changing the conditions of preliminary shearing of Example 1, paint B (for lower layer).

FIG. 3 is a diagram summarizing changes over time in storage elastic modulus G ′ after changing the conditions of preliminary shearing of Example 2, paint A (for upper layer).

FIG. 4 is a diagram summarizing the change over time in storage modulus G ′ after changing the conditions of preliminary shearing of Example 3, paint A (for upper layer).

FIG. 5 is a diagram summarizing the change over time in storage modulus G ′ after changing the pre-shearing conditions of Example 4, paint C (for single layer).

FIG. 6 is a schematic diagram showing an extrusion die.

FIG. 7 is a schematic diagram showing an inline dispersion method.

FIG. 8 is a schematic diagram showing an off-line distribution method.

[Explanation of symbols]

 1 support 10,20 extrusion die

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-9-106542 (JP, A) JP-A-4-129027 (JP, A) JP-A-1-224924 (JP, A) JP-A-1- 205727 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G11B 5/848

Claims (2)

(57) [Claims] 1. A method of manufacturing a magnetic recording medium, in which a support is run and a paint is applied to the support by an extrusion die, wherein the paint is diluted to a final dilution before the paint is supplied to a chamber in the die. A shear force of 100,000 sec ^-1 or more at a shear rate and a product of a shear rate and a shear application time of 30,000 or more is applied, and the average residence time of the paint from application of the shear to application of the shear is a certain time t.
Change ratio of the storage elastic modulus G '(t + Δt) after a short time Δt from the storage elastic modulus G' (t) at Is within the time required to reach 0.03 or more. 2. The method for producing a magnetic recording medium according to claim 1, wherein the coating method is an extrusion-type simultaneous multi-layer coating method.
^-1 or more, the product of the shear rate and the shear application time A shear force of 30,000 or more is applied, and the average residence time of the paint from application of the shear to application of the shear is the storage modulus G 'at a certain time t.
(T), the storage elastic modulus G '(t + Δ
change ratio of t) Is within the time required to reach 0.03 or more.