JP2822291B2 - Manufacturing method of magnetic recording medium - Google Patents

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 in which a magnetic layer is formed on a continuously running nonmagnetic support by using an extrusion type coating head.

[0002]

2. Description of the Related Art In recent years, the density of magnetic recording media has been increasing, and the magnetic layer applied on a non-magnetic support has conventionally been a single layer. Is being promoted. In the multi-layer coating of magnetic layers composed of a magnetic dispersion and the multi-layer coating with another organic solvent, a coating method in which both coated layers to be polymerized are in a wet state has been adopted in many cases. In this multi-layer coating, as one production method, a lower layer is first applied by a generally used gravure coating, roll coating, blade coating, extrusion coating device, or the like, and the lower layer is wet (hereinafter, referred to as a wet state). Using another coating apparatus, for example, in Japanese Patent Application Laid-Open No. 60-23817.
No. 9 or No. 63-20069, when the upper layer is coated by a coating apparatus, and
-88080, JP-A-2-17971, JP-A-2-179
As disclosed in Japanese Patent Publication No. 265672, there is a simultaneous multi-layer coating in which a coating liquid is simultaneously discharged from a plurality of slits and the upper and lower portions are coated almost simultaneously. Also, Japanese Patent Application Laid-Open No. 2-17 / 1990
As disclosed in Japanese Patent No. 4965, there is also a simultaneous multilayer coating method using an extrusion coating device with a backup roll.

In the case of the above-mentioned multi-layer coating, an organic solvent-based coating liquid used for a magnetic recording medium is a non-Newtonian fluid, and the viscosity of the same liquid varies depending on various conditions in which the liquid is placed. Therefore, it cannot be solved simply by approaching the viscosity like a coating solution for photographic light-sensitive materials, and the control is extremely difficult. It was an empirical area. Under such circumstances, it has been extremely difficult to obtain more stable quality and higher productivity than ever before.

[0004]

Under such circumstances, as a coating method capable of performing good coating at the time of multi-layer coating, a viscosity difference between coating liquids for forming a magnetic layer is set to 50 cp or less in a slit of a coating apparatus. A coating method is disclosed in JP-A-3-8471. According to this coating method, when the layers to be overlapped are the magnetic layers and when the layers are simultaneously overlapped by the same coating apparatus, the effect as disclosed in the disclosure can be obtained.

[0005] However, according to the earnest study of the present inventors, it has been found that in the multi-layer coating of the non-magnetic layer and the magnetic layer, good coating cannot be performed even by the above-mentioned coating method. In particular, in the sequential multi-layer coating instead of the simultaneous multi-layer coating, if the difference in the coating time increases, the meaning of the viscosity definition in the slit itself becomes less significant. Further, it was found that the above method could not be applied to a case where the magnetic layer forming the upper layer applied a thin coating having a dry film thickness of 1 μm or less on the non-magnetic layer.

An object of the present invention is to provide a method of manufacturing a magnetic recording medium having good magnetic recording characteristics without color unevenness or vertical stripes in various multilayer coating methods in order to solve the above-mentioned problems in the multilayer coating method. Is to provide. Therefore, the present inventors have conducted intensive research and development, and as a coating method of the magnetic layer and the non-magnetic layer in the above various multilayer coating methods,
It was found that the viscosity at the junction where the two layers collided had a large effect on the formation of a thin layer coating, rather than the viscosity regulation of the coating liquid in each slit or pool as in the past,
As a result of further study on this, the present invention has been achieved.

[0007]

That is, an object of the present invention is to form a magnetic layer having a dry film thickness of 1 μm or less on a continuously running nonmagnetic support using an extrusion type coating head. A method of manufacturing a magnetic recording medium, wherein the magnetic layer and the non-magnetic layer are simultaneously coated or the magnetic layer is sequentially coated on the non-magnetic layer in a wet state. This is achieved by a method for manufacturing a magnetic recording medium, wherein the viscosity difference between the two layers at the confluence with the magnetic layer is adjusted to 50 cp or less.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a coating apparatus to which the manufacturing method of the present invention is applied will be described below with reference to the drawings. FIG.
Is a coating apparatus using the coating apparatus disclosed in Japanese Patent Application Laid-Open No. 2-174965, and includes a backup roll 1 and a coating head 3 installed such that the head end faces the backup roll 1. Extrusion type coating device with backup roll.

The coating head 3 has a structure in which a doctor blade 4 is provided at the head end on the upstream side in the running direction of the flexible support 2 and a smoothing blade 5 is provided on the downstream side. The backup roll 1 supporting the back surface of the flexible support 2 coated with the first coating liquid, for example, the non-magnetic layer 8, and the doctor blade provided to face the backup roll 1 4 (strictly speaking, a gap h between the doctor blade 4 and the surface of the support 2) can be set freely. That is, the coating head 3 is fixed to, for example, a holding member 10, and the holding member 10 approaches or separates from the roll 1 along the normal line of the backup roll 1 (in the direction of the arrow B) (see arrow B). (In the direction of arrow C) It is possible to adjust with extremely high accuracy.

Further, the smoothing blade 5 has a slot side surface facing the downstream side surface of the doctor blade 4 and a coating surface facing the backup roll 1, and is formed by the downstream side surface and the slot side surface. The second liquid for forming the second coating layer 9 to be the upper layer of the first coating layer 8 is discharged from the slot 6 thus formed.

When the wet (undried) film thickness of the nonmagnetic layer formed on the support 2 is, for example, about 0.015 to 0.03 mm, the doctor blade 4 and the support 2 for forming the first layer are formed. Is 0.03 to 0.06, for example.
It can be set in the range of about mm. Further, the forward angle of the distal end of the doctor blade 4 may be formed substantially at a right angle as shown in the figure, but this range is desirably 70 to 110 degrees, and the clearance of the slot 6 is equal to that of the upper magnetic layer. It can be set appropriately in consideration of the coating thickness. Further, the upper end surface, which is the coating surface of the smoothing blade 5, is configured to retreat from the backup roll 1 more than the upper end surface of the doctor blade 4, and the retreat dimension is, for example, 0.005 to 0.05.
It can be set in the range of about 0mm.

In the coating apparatus configured as described above,
On the surface of the support 2, which has been run in a fixed direction (direction of arrow A) so as to be wound around the backup roll 1,
The backup roller 1 and the backup roller 1, which previously coated the first coating layer 8 (lower layer) with another coating device (not shown) and backed up the back side of the support 2.
The second coating layer 9 can be applied while the application amount of the first coating layer 8 is determined by setting the gap between the doctor blade 4 and the second coating layer 9.

That is, the surplus portion of the first liquid is scraped off by the front end portion of the doctor blade 4,
On the first coating layer 8 that only a predetermined amount has passed between the doctor blade 4 and the backup roll 1,
The second coating layer 9 which is supplied from the liquid supply system 11 to the liquid reservoir 7 and is discharged from the slot 6 is formed. The junction 4a where the two layers (coating liquid) join is formed by the doctor blade. 4 at the trailing edge. The difference between the viscosity of the first coating layer 8 and the second coating layer 9 at the junction 4a is set to 50 cp or less, whereby the junction 4a
Therefore, it is possible to prevent the flow state of the two layers from being disturbed due to the deviation in the flow direction of the two layers, and to prevent the generation of a vortex near the layer interface at the junction 4a. As a result, it can be estimated that both layers can maintain a stable layer state.

The setting of the viscosities of the coating layers (liquids) 8 and 9 can be easily measured by using a Rotovisco viscometer, and a unique viscosity curve of each coating liquid at an arbitrary shear rate can be obtained. it can. On the other hand, the average γ _s of the shear rate γ in the slit of the coating head 3 is given by the following formula: γ _s = 3Q /, where d is the slit clearance, W is the slit width, and Q is the flow rate (application amount) in the slit. With Wd ² , even a non-Newtonian fluid can be obtained approximately. However, in the present invention, since the two-layer merging section 4a is on the wall surface of the coating head 3 of the coating apparatus, the shear rate γ is the maximum value γ _SW , and the following equation γ _SW = 6Q / Wd ^2. -It can be approximated by (1). Also, the shear rate γ ₁ on the coating edge can be approximately determined by the following equation γ ₁ = v ² W / 2Q (2), assuming that the running speed of the support is v and the Couette flow is assumed. Can be done.

From the equations (1) and (2), it is possible to roughly estimate the clearance d of the slit 6 which can reduce the difference in viscosity of the coating liquid (coating layer) to be applied at the junction 4a. Therefore, when two types of coating liquids to be applied are drawn on the same graph, a region where the viscosity difference is small can be widened, and desired coating can be performed within a certain range of the viscosity difference.

Considering the above reasons further,
Conventionally, it has been clarified that a difference in the liquid properties at the time of coating is caused by a difference in the shearing histories of the coating solutions forming the adjacent layers, but this difference in shearing histories has a large effect on the behavior of the layer interface. It has been found that the influence is exerted when both layers are of similar composition, for example, a magnetic layer, and when there is little difference in time applied to the support after being subjected to various shears.

This is particularly true in the case where the first coating layer (lower layer) 8 is a non-magnetic layer and the second coating layer (upper layer) 9 is a magnetic layer, as described above. In the layer 8, since the second coating layer 9 is applied after a short time after application, the influence on stabilization of physical properties based on the difference in shear history between the two layers is reduced, and rather, The junction 4 where both layers come into contact (collide) in a wet state
It is believed that the liquid properties at a have very significant consequences.

Here, among the physical properties of the liquid, the difference in viscosity at the junction 4a of the two layers is a major factor as a coating condition because, in any case, the flow direction of the two layers at the junction 4a Because there is a gap between the two layers, the two layers are pressed against each other at the interface between the two layers. Therefore, when the viscosity difference between the two layers at the junction 4a increases, the balance tends to be lost. Therefore, the flow state of both layers is easily disturbed, and a vortex is generated in the vicinity of the layer interface. As a result, it is estimated that it is difficult to maintain a stable layer state of both layers. In particular, the second coating layer 9
If is a thin layer, not only the above-mentioned interface turbulence,
This has a great effect on the surface properties of the magnetic layer.

As a result of intensive studies, the viscosity difference is set to 50 cp or less at the junction 4a as described above, thereby stabilizing the behavior of the liquid at the interface between the coating liquids that are in contact with each other during coating. It is considered that good coating can be achieved. By clarifying the standard of the setting range that enables good coating as described above, a stable coating state can always be ensured.

The viscosity can be adjusted mainly by changing the liquid formulation. This method of changing the liquid formulation can produce, for example, a coating liquid exhibiting a viscosity characteristic as if the viscosity curve was moved substantially in parallel by changing the solvent amount of the coating liquid (magnetic dispersion liquid). When the amount is changed, a coating liquid exhibiting a viscosity curve with a different gradient characteristic can be obtained.

The method of changing the slit interval is as follows.
For example, the tip portion of the coating head, that is, the minimum tip portion directly involved when the coating solution adheres to the support is separated from the other head portions, and is detachably configured. By using ceramics or cemented carbides, it is possible to achieve good coating and to improve the workability of changing the slit interval at low cost.

An apparatus for carrying out the manufacturing method of the present invention is shown in FIG.
However, the present invention is not limited to the apparatuses shown in FIGS. 2A and 2B, and various coating apparatuses conventionally used, for example, as shown in FIGS. 2 to 4, can be used. FIG.
No. 69, in a state where the liquid is sealed by a first coating layer 8 which is an organic solvent previously applied to a coating surface of a support 2, and is upstream in a moving direction of the support. The front edge 24 is located on the downstream side with respect to the support moving direction, and the front end of the front edge 24 is retreated in the direction opposite to the support with a level difference from the front edge 24 so that the front end portion has an acute angle. A structure having an edge 25 and no backup roll. And
The junction 24a of the first coating layer 8 and the second coating layer 9 is a region of the rear edge of the front edge 24. still,
1 are the same as those shown in FIG.

The coating surface of the support 2 is first coated with an organic solvent by a coating means (not shown) using a generally used coating apparatus such as a gravure coater, roll coater, blade coater, or extrusion coater. This layer maintains a coating state in which entrained air from the upstream side of the front edge is prevented from entering the coating layer, thereby improving high-speed coating characteristics.

FIG. 3 shows a coating apparatus 30 disclosed in Japanese Patent Application Laid-Open No. 2-17971, in which an intermediate block 32 is arranged between blocks constituting an upstream edge 31 and a doctor edge 33. This is a simultaneous multi-layer type coating apparatus in which two slits 6a and 6b for discharging the first coating liquid 8 and the second coating liquid 9 are formed. In this apparatus, the leading end of the intermediate block 32 is inserted into the inside of the discharge port of the slit by an appropriate dimension (B). Then, the junction 32 a where the first coating layer 8 and the second coating layer 9 join together is the tip of the intermediate block 32. In this coating apparatus, the coating is performed while the second coating liquid 9 is pressed by the edge surface of the doctor edge 33 with a relatively high pressing force.

Referring to FIG.
In the coating apparatus 40 disclosed in Japanese Patent Application Laid-Open Publication No. H10-209, slits 6a and 6b are formed by an upstream edge 41, a first doctor edge 42, and a second doctor edge 43.
Each doctor edge surface 45, 46 has an appropriate curvature R _1, R _2, respectively. The first coating liquid 8 and the second coating liquid 9 are discharged from the slits 6a and 6b, and the two coating layers are almost simultaneously layered. In this device, the first coating layer 8 and the second coating layer 9
Merges with the first doctor edge 4
No. 2 at the rear end of the doctor edge surface. In this coating apparatus, the coating is performed while pressing the first coating liquid 8 by the edge surface of the doctor edge surface 45 and the second coating liquid 9 by the doctor edge surface 46 with a relatively high pressing force.

[0026]

As described above, the method of manufacturing a magnetic recording medium according to the present invention is characterized in that a magnetic layer and a non-magnetic layer are simultaneously coated on a running support or a thin layer is formed on the non-magnetic layer in a wet state. When sequentially coating the magnetic layers of the layers, the difference in viscosity between the two layers at the confluence of the nonmagnetic layer and the magnetic layer is reduced by 50%.
Since the coating was performed at cp or less, it was possible to effectively prevent the occurrence of turbulence in the flow state of both layers at the confluence, and the generation of eddy near the layer interface at the confluence was stable in both layers. The layer state can be maintained and good coating can be performed. As a result,
Even if the upper layer is an extremely thin layer without mixing between the coating liquid layers, it is possible to stably perform good coating without color unevenness and vertical stripes.

[0027]

EXAMPLES The effects of the present invention can be further clarified by the following examples. (Embodiment 1) Hereinafter, an embodiment of the present invention will be described in detail. With respect to the coating liquid, the following composition components were adjusted to prepare a coating liquid.

Composition of lower layer (non-magnetic layer), [Solution A] * 80 parts by weight of α-Fe ₂ O ₃ * 20 parts by weight of carbon black (average particle diameter 16 mμ) * vinyl chloride, vinyl acetate, vinyl alcohol copolymer 12 parts by weight * Polyester polyurethane resin neopentyl glycol / caprolactone polyol / MDI = 0.9-2.6 -1 (containing 1 × 10 ^-4 eq-g of SO ₃ Na group) 5 parts by weight * 1 part by weight of butyl stearate * Stearic acid 1 part by weight * Copper oleate 1 part by weight * Methyl ethyl ketone 200 parts by weight * Polyisocyanate "Coronate L" (manufactured by Nippon Polyurethane Co., Ltd.) 5 parts by weight * Butyl acetate 40 parts by weight

Composition of lower layer (non-magnetic layer), [B solution] * 80 parts by weight of α-Fe ₂ O ₃ * 20 parts by weight of carbon black (average particle size: 16 μm) * vinyl chloride, vinyl acetate, vinyl alcohol copolymer 12 parts by weight * Polyester polyurethane resin neopentyl glycol / caprolactone polyol / MDI = 0.9-2.6 -1 (containing 1 × 10 ^-4 eq-g of SO ₃ Na group) 5 parts by weight * 1 part by weight of butyl stearate * Stearic acid 1 part by weight * Copper oleate 1 part by weight * Methyl ethyl ketone 200 parts by weight * Polyisocyanate "Coronate L" (manufactured by Nippon Polyurethane Co., Ltd.) 5 parts by weight * Butyl acetate 350 parts by weight

Composition of upper layer (magnetic layer), [C solution] * 100 parts by weight of ferromagnetic metal fine powder [Fe / Zn / Ni = 92/4/4] (Hc1600Oe) * 12 parts by weight of vinyl chloride copolymer * Polyester polyurethane resin neopentyl glycol / caprolactone polyol / MDI = 0.9−2.6 −1 (containing 1 × 10 ⁻⁴ eq-g SO ₃ Na group) 3 parts by weight * α-alumina 2 parts by weight * Carbon black ( Average particle size 0.1 μm) 0.5 parts by weight * 1 part by weight of butyl stearate * 2 parts by weight of stearic acid * 200 parts by weight of methyl ethyl ketone * 6 parts by weight of polyisocyanate "Coronate L" (manufactured by Nippon Polyurethane Co., Ltd.) * 40 parts by weight of butyl acetate Department

Composition of upper layer (magnetic layer), [D solution] * 100 parts by weight of ferromagnetic metal fine powder [Fe / Zn / Ni = 92/4/4] (Hc1600Oe) * 12 parts by weight of vinyl chloride copolymer * Polyester polyurethane resin neopentyl glycol / caprolactone polyol / MDI = 0.9−2.6 −1 (containing 1 × 10 ⁻⁴ eq-g SO ₃ Na group) 3 parts by weight * α-alumina 2 parts by weight * Carbon black ( Average particle size 0.1 μm) 0.5 parts by weight * 1 part by weight of butyl stearate * 2 parts by weight of stearic acid * 200 parts by weight of methyl ethyl ketone * 6 parts by weight of polyisocyanate "Coronate L" (manufactured by Nippon Polyurethane Co., Ltd.) * 100 parts by weight of butyl acetate Department

The viscosities of the liquids A, B, C, and D are measured using a Rotovisco viscometer, and the viscosity of each of the coating liquids A, B, C, D, and the liquid showing the relationship between the shear rate and the viscosity is measured. Was prepared. The result is shown in FIG. Then, on a 10 μm-thick polyethylene terephthalate support,
Coating width 300mm, tension 5kg / 300mm, coating speed 600 / min,
The coating was performed as shown in Table 2 by combining the liquids A and B as the lower layer and the liquids C and D as the upper layer under the condition that the coating amount of the upper layer as the magnetic layer was 450 g / min (dry film thickness 0.5 μm). Table 2 shows the results. In addition, about the coating method and the coating device, coating is performed with the combination of the following devices, and the viscosity approximated to the confluence of each liquid in the combination of the coating devices is shown in Table 1 with four types of sample Nos. Specified as NO.4.

Coating Method and Coating Apparatus (1) 10 cc of the lower layer coating solution is applied by a coating apparatus shown in FIG. 1 of JP-A-2-265672 (a single-layer coating type apparatus of the apparatus shown in FIG. 4). / m ^2, and then an upper layer coating solution was applied by the apparatus shown in JP-A-63-20069 (coating apparatus 20 in FIG. 2).

At this time, the following two types of coating apparatuses were used for the slit clearance d ₀ . Slit clearance: d ₀ = 0.15 mm Slit clearance: d ₀ = 0.20 mm (2) The lower layer coating solution is applied at 10 cc / m ² by JP-A-2-17971 (coating device 30 shown in FIG. 3). And the upper layer was applied.

At this time, the following two types of coating apparatuses were used with slit clearances d ₁ (lower layer side) and d ₂ (upper layer side). Slit _{clearance: d 1 = 0.30mm, d 2} = 0.20
mm slit _{clearance: d 1 = 0.30mm, d 2} = 0.30
mm

[0036]

[Table 1]

[0037]

[Table 2]

As can be seen from Table 2 above, when the viscosity difference at the junction of the coating liquids was 50 cp or less, no unevenness was generated and good coating was possible.

[Brief description of the drawings]

FIG. 1 is a schematic view of a main part of an embodiment of a coating apparatus for performing a manufacturing method of the present invention.

FIG. 2 is a schematic view of a main part of another embodiment of a coating apparatus for performing the manufacturing method of the present invention.

FIG. 3 is a schematic view of a main part of another embodiment of a coating apparatus for performing the manufacturing method of the present invention.

FIG. 4 is a schematic view of a main part of another embodiment of a coating apparatus for performing the manufacturing method of the present invention.

FIG. 5 is a graph showing a viscosity characteristic curve of a coating solution used in an example of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 backup roll 2 support 3, 20, 30, 40 coating device 4 doctor blade or upstream edge 4 a junction 5 doctor edge 6, 6 a, 6 b slit 7 pocket 8 first coating layer 9 second coating layer 10 holding Member 11 Liquid supply system

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B05D 1/26 B05C 5/02 B05D 5/12 G11B 5/842-5/848

Claims (1)

(57) [Claims] 1. A dry film thickness of 1 μm on a continuously running nonmagnetic support using an extrusion type coating head.
m or less, wherein the magnetic layer and the non-magnetic layer are simultaneously multi-layer coated or the magnetic layer is sequentially multi-layer coated on the non-magnetic layer in a wet state. A method for producing a magnetic recording medium, wherein the difference in viscosity between the nonmagnetic layer and the magnetic layer at the junction is 50 cp or less.