JPH1176898A - Coating apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating apparatus wherein sufficient smoothing effect on a sublayer membrane and effect for preventing a foreign particle from being trapped in a doctor lip are obtained by an easy and low cost apparatus and an excellent multi-layer coating membrane with less coating fault can be spread with an overlapping layer at the same time. SOLUTION: In the apparatus, an angle θ between a straight line L1 drawn (on a contact point G) so as to come into contact with a lip face 6a of a second doctor lip 6 from an edge D of a first doctor lip 5 and a tangent line L2 of a lip face 5a at the edge D of the first doctor lip 5 is formed into the range of 0 deg.<=θ<=10 deg. in a direction downward from the tangent line L2 . Relationship between a curvature radius R1 of the first doctor lip 5 and a curvature radius R2 of the second doctor lip 6 is formed into 0.2 R1<=R2 <0.8 R1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an extrusion type coating apparatus for continuously extruding a coating solution on the surface of a flexible support to form a coating film, and more particularly to simultaneous multilayer coating in the production of a magnetic recording medium. Related to the device.

[0002]

2. Description of the Related Art As a coating method of a coating type magnetic recording medium, a roll method such as a gravure roll method or a reverse roll method is used.
The coating method is generally used, but in recent years, an extrusion type coating method has been put to practical use in which the coating thickness is more uniform than these coating methods and a thin film coating is possible. Furthermore,
In this type of extrusion type coating method, a plurality of doctor lips formed on a front lip located on the most upstream side of a flexible support (base film of a medium) and a plurality of doctor lips located on a downstream side. Simultaneous multi-layer coating has also been put to practical use by applying a coating solution to the surface of a flexible support that has slots and discharges and runs a coating solution from each slot. (JP-B-6-77712, JP-A-2-251265, JP-A-3-258368, JP-A-5-104054, etc.)

In recent years, higher density and thinner magnetic recording media have been further promoted, and a high-viscosity magnetic coating material in which high-BET oxide magnetic powder or metal powder is dispersed is used under a condition of thin film and high-speed coating. It is required that the coating be performed in a good time. In the extrusion-type simultaneous multilayer coating method,
Various improvements have been made to solve the conventional problems. For example, in Japanese Patent Application Laid-Open No. Hei 5-104054, the positional relationship between the doctor lips is improved as shown in FIG. The intersection of a straight line drawn from the edge of the upstream doctor lip 30 so as to be in contact with the lip surface of the downstream doctor lip 31 and a perpendicular extending upward from the upstream end of the downstream doctor lip 31 is defined as the upstream end. The distance t is defined as 5 μm ≦ t ≦ 30 μm, where t is the distance between the two. If the distance t is smaller than this range, foreign substances in the coating solution are trapped at the upstream end of the doctor lip, and streaks frequently occur in the coating layer. The interface between the parts is disturbed and the coating amount is 10
It is disclosed that an upper layer of a thin film of cc / m ² or less cannot be applied.

[0004]

However, when the coating is performed using such a coating head, the coating properties (viscosity difference, mixing property, etc.) of the upper and lower layers and the coating head lip shape (radius of curvature, arc length, etc.) may vary. In some cases, coating streaks that are not caused by foreign matter traps may occur. this is,
The upper layer coating solution pushes up the lower layer near the discharge port of the slot, so that the lower layer coating does not contact the edge of the doctor lip on the upstream side, the smoothing effect of the lower layer coating is impaired, and streaks are generated on the lower layer surface. However, it is considered that the stripes on the surface of the lower film affect the surface of the upper film. Therefore, in order to obtain a good coating state using the coating head disclosed in Japanese Patent Application Laid-Open No. 5-104054, a coating head with extremely high processing accuracy is required. In order to minimize the fluctuation of the coating liquid, highly accurate and expensive coating liquid supply equipment and strict coating condition control are required. It is desirable that the coating equipment be inexpensive.
It is desirable that a good coating state can be obtained even if the above strict management is relaxed.

Accordingly, an object of the present invention is to provide a sufficient smoothing effect of the underlayer film and an effect of preventing foreign matter trapping in the doctor lip with easy and inexpensive equipment, and to reduce coating defects such as streaks and unevenness. It is an object of the present invention to provide a coating apparatus capable of simultaneously forming a good multi-layer coating film.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a front lip which is located on the most upstream side with respect to the moving direction of the flexible support and faces the flexible support. A front lip having a surface and an edge, a plurality of slots and a plurality of doctor lips located downstream with respect to the moving direction of the support, and a coating liquid is continuously supplied from each of the plurality of slot tips. In the extrusion type simultaneous multi-layer coating apparatus for simultaneously discharging and coating the coating liquid on the surface of the flexible support, the lip surfaces of the plurality of doctor lips for coating the coating layer including the lowermost layer are: An edge is provided at a downstream end of each lip surface of the plurality of doctor lips, while being formed in an arc-shaped cross section,
A straight line L1 drawn from the edge of the upstream doctor lip so as to be in contact with the lip surface of the downstream doctor lip, the relationship between one upstream doctor lip and the downstream doctor lip adjacent to the downstream doctor lip. And the angle θ between the tangent L2 at the edge of the upstream doctor lip and the tangent L2,
2 is set to be in the range of 0 ° ≦ θ ≦ 10 °, and the radius of curvature R1 of the lip surface of the upstream doctor lip and the radius of curvature R2 of the lip surface of the downstream doctor lip are set An application apparatus is provided, wherein 0.2R1 ≦ R2 <0.8R1.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A coating apparatus according to the present invention will be described below with reference to the drawings. Here, description will be made in detail sequentially according to an example of simultaneous coating of two layers. FIG. 1 is a perspective view of a coating head (extrusion type simultaneous multilayer coating head) according to an embodiment of the present invention. FIG. 2 is a sectional view of the coating head for explaining a coating state by the coating head of one embodiment, and FIG. 3 is a diagram showing a tip shape of the coating head of one embodiment.

As shown in FIG. 1, a coating head 1 comprises a first pocket 2 to which a lower layer coating solution 9 is supplied, and an upper layer coating solution 10
, A front lip 4 located on the most upstream side in the running direction of a flexible support (hereinafter referred to as a web), and a first doctor 3 located sequentially downstream thereof. It comprises a lip 5, a second doctor lip 6, a slot 7 communicating with the pocket 2, a slot 8 communicating with the pocket 3, and the like. The pockets 2 and 3 are through holes having a predetermined diameter. The opening lengths of the slots 7 and 8 are approximately equal to the coating width with a spacer (not shown) of an appropriate width sandwiched between both ends. Adjusted to equal length. Next, the application state is shown in FIG.
This will be described in detail with reference to FIG. In actual application, the lower layer coating liquid 9 is discharged from the slot 7 and the upper layer coating liquid 10 is simultaneously discharged from the slot 8, and is coated on the surface of the web W running in the direction of the arrow at the speed V. At this time, the lower coating film 9
a is smoothly smoothed by the edge D of the first doctor lip 5 shown in FIG. 3 and merges with the upper layer coating solution near the discharge port of the slot 8. The surface of the upper coating film 10a is formed smoothly by the smoothing effect of the edge F of the second doctor lip 6.

The front lip 4 is located at the most upstream position in the running direction of the web W, and has an upstream end A and an edge B
The lip surface 4a including the shape may have a circular arc shape or a hatched shape. The first doctor lip 5 is located on the downstream side of the front lip 4 with the slot 7 interposed therebetween, and its lip surface 5a is formed in a circular arc shape having a radius of curvature R1 including an upstream end C and an edge D. Similarly, the lip surface 6a of the second doctor lip 6 located on the downstream side of the first doctor lip 5 with the slot 8 interposed therebetween is also formed in a circular arc shape having a radius of curvature R2 including the upstream end E and the edge F. I have.

The positional relationship between the first doctor lip 5 and the second doctor lip 6 in the height direction is such that the lip surface 6 of the second doctor lip 6 extends from the edge D of the first doctor lip 5.
a and a tangent line L1 to the lip surface 5a at the edge D of the first doctor-lip 5
2 is 0 ° ≦ θ ≦ below the tangent line L2.
The relationship between the radius of curvature R1 of the first doctor lip 5 and the radius of curvature R2 of the second doctor lip 6 is 0.2R1 ≦ R2 <0.8R1.
It is configured so that Although the setting method of the angle θ is not shown, the height is adjusted by moving the second doctor lip up and down with an adjust bolt or by inserting a spacer having an appropriate thickness under the second doctor lip. Can be adjusted and set.

Next, an embodiment in which various parameters are changed will be described. In each of the following examples, in the production of a magnetic tape, a magnetic coating material was simultaneously applied in multiple layers, and the lower layer as the first layer was 30 cc / m ² (wet) or less and the upper layer as the second layer was 20 cc / m ² ( (wet) or less. In each of the examples, a coating liquid having the following composition was commonly used as the lower coating liquid 9, and a coating liquid having the following composition was commonly used as the upper coating liquid 10. Basic application conditions were also implemented as common elements.

[Lower layer coating liquid composition component] * Cobalt-coated γ-Fe ₂ O ₃ (magnetic powder) 100 parts by weight (BET value 28 m ² / g) * Vinyl chloride / acrylic copolymer 15 parts by weight * Polyurethane resin 15 parts by weight * ₃ parts by weight of granular Al ₂ O ₃ * 5 parts by weight of carbon black * 1 part by weight of myristic acid * 100 parts by weight of toluene * 100 parts by weight of methyl ethyl ketone * 100 parts by weight of methyl isobutyl ketone * 100 parts by weight of isocyanate-based curing agent 15 parts by weight * Viscosity (B-type viscometer No.3) 1500 cps

[Coating liquid composition components of upper layer] * Cobalt-coated Fe ₃ O ₄ (magnetic powder) 100 parts by weight (BET value 35 m ² / g) * Vinyl chloride / acrylic copolymer 15 parts by weight * Polyurethane resin 15 parts by weight Parts * 3 parts by weight of granular Al ₂ O ₃ * 5 parts by weight of carbon black * 1 part by weight of myristic acid * 100 parts by weight of toluene * 100 parts by weight of methyl ethyl ketone * 100 parts by weight of methyl isobutyl ketone * 15 parts by weight of isocyanate-based curing agent Part * Viscosity (B-type viscometer No.3) 2000cps

The other basic application conditions are as follows. Support (web): Polyester terephthalate film (width 320 mm, thickness 15.0 μm) Coating speed: 200 m / min Coating tension: Appropriately applicable (a value that can secure a predetermined coating thickness) Coating thickness: After drying Lower layer 2.5 μm ± 0.1 μm: After drying Upper layer 0.7 μm ± 0.05 μm Coating head conditions: ・ Front lip radius of curvature 5 mm (see FIG. 3) ・ Slot 7 gap (for lower layer) 0.15 mm ・ Slot 8 gap (for upper layer) ) 0.10mm

Visual observation of the applied state of the magnetic tape obtained by keeping the curvature radius R1 of the first doctor lip 5 shown in FIG. 3 constant and changing the curvature radius R2 and the angle θ of the second doctor lip as appropriate. did. FIG. 5 (R1 =
5 mm), FIG. 6 (R1 = 10 mm), FIG. 7 (R1 = 15
mm), FIG. 8 (R1 = 20 mm), FIG. 9 (R1 = 30 m
m).

In FIGS. 5 to 9, the coating state commonly observed will be described below. The mark “○” indicates that a good state of the coated surface without streaks, unevenness, dropout, etc. was obtained.
The marks ● indicate coating defects in which streaky thickness unevenness such as a record board groove is observed in the coating longitudinal direction on the surface of the multilayer coating film. This coating defect appears under the condition that the angle θ is formed above the tangent L2 at the edge D of the first doctor lip 5 (the angle θ is on the minus display side). The cause of this occurrence is that when the angle θ is on the minus side, the web travels without contacting the edge D of the first doctor lip 5 as the approximate travel position of the web. For this reason, in the formation of the lower layer film 9a, the lower layer paint 9 is placed on the first doctor before the edge D.
It is considered that the lip 5 is separated from the lip surface 5a, and that the lip 5 is not affected by the smoothing action at the edge D, so that streak-like thickness unevenness occurs at regular intervals, and this effect appears on the upper layer surface.

The black triangles indicate coating defects at which the multilayer coating film is scraped off at the lip surface 6a and the edge F of the second doctor lip 6. This phenomenon often occurs when the curvature radius R2 of the second doctor lip 6 is relatively small and the angle θ is small or on the minus side. The reason for this is that if the angle θ is small, a relatively large web tension (application tension) is required to obtain a predetermined lower layer thickness. Therefore, the radius of curvature R of the second doctor lip 6
When 2 is small, the load per unit area received from the tension applied to the lip surface 6a and the edge F of the second doctor lip 6 increases, and the gap between the web and the lip surface 6a and the edge F forms a predetermined multilayer coating thickness. Smaller than you can,
It is considered that the coating liquid was scraped off.

The symbol "■" indicates a coating defect in which coating loss has occurred in the upper layer film 10a. This coating defect was observed when the angle θ and the radius of curvature R2 of the second doctor lip 6 were relatively large. The reason is that when the angle θ is large, the web comes to strongly hit the edge D of the first doctor lip 5, so that the application is performed with relatively low tension in order to obtain a predetermined underlayer thickness. At this time, if the radius of curvature R2 of the second doctor lip 6 is relatively large, the load per unit area that the lip surface 6a and the edge F of the second doctor lip 6 receive from the web tension decreases, and the web and the lip surface 6a It is considered that the gap with the edge F becomes larger than the amount required for the predetermined multilayer coating film thickness. As a result, the gap becomes excessive with respect to the predetermined upper layer coating liquid supply amount, and it is considered that the coating loss occurs in the upper layer film 10a.

The crosses indicate coating defects that scrape off the lower coating liquid 9 discharged at the lip surface 5a and the edge D of the first doctor lip 5. Also, here, generation of streaks due to foreign matter traps was often observed. This coating defect is caused by the case where the angle θ is relatively large and the radius of curvature R2 of the second doctor lip 6.
This is especially true when is large. This is because the angle θ
Is large, the web W comes into strong contact with the lip surface 5a and the edge D of the first doctor lip 5, and the lower layer coating solution 9
Cannot pass through the edge D, and is scraped off. Further, when the radius of curvature of the second doctor lip 6 becomes large, the web tension must be applied with a relatively high web tension, whereby the contact of the web W at the edge D is promoted in a stronger direction, and the lower layer coating liquid is applied. It is likely to be scraped off.

Looking at the coating state shown in FIGS.
(A) A straight line L1 drawn from the edge D of the first doctor-lip 5 so as to be in contact with the lip surface 6a of the second doctor-lip 6 (contact point G), and the lip surface 5a at the edge D of the first doctor-lip 5 Of the tangent L2 with the tangent L2
In the range of 0 ° ≦ θ ≦ 10 ° below 2, and
(B) When the relationship between the radius of curvature R1 of the lip surface 5a of the first doctor lip 5 and the radius of curvature R2 of the lip surface 6a of the second doctor lip 6 is in the range of 0.2R1 ≦ R2 <0.8R1. It was found that a good coating state without coating defects such as streaks, unevenness, and scraping off of the coating liquid was obtained.

Although the above embodiment is an example of simultaneous coating of two layers, it is a matter of course that the number of slots and doctor lips may be increased to provide a coating apparatus capable of simultaneously coating multiple layers. In this case, the relationship between at least one pair of the upstream doctor lip and the downstream doctor lip adjacent to the downstream side is determined so that the edge of the upstream doctor lip contacts the lip surface of the downstream doctor lip. Straight line L1 drawn
And a tangent L at the edge of the upstream doctor lip
2 is 0 ° ≦ θ ≦ below the tangent line L2.
And the relationship between the radius of curvature R1 of the lip surface of the upstream doctor lip and the radius of curvature R2 of the lip surface of the downstream doctor lip is 0.2R.
It is set so that 1 ≦ R2 <0.8R1.

[0022]

As described above, according to the present invention, the coating condition range in which a good coating state free from streaks and unevenness can be obtained by simultaneous multi-layer coating is wide. And the coating liquid supply equipment can be manufactured relatively easily and inexpensively.

[Brief description of the drawings]

FIG. 1 is a perspective view of a coating head portion of one embodiment.

FIG. 2 is a schematic sectional view of a coating head according to one embodiment.

FIG. 3 is a diagram showing a tip shape of a coating head according to one embodiment.

FIG. 4 is a diagram showing a conventional example.

FIG. 5 is a diagram showing a result of a visual observation of an applied state of a magnetic tape.

FIG. 6 is a diagram showing the results of visual observation of the applied state of a magnetic tape.

FIG. 7 is a diagram showing the results of visual observation of the applied state of a magnetic tape.

FIG. 8 is a diagram showing the results of visual observation of the applied state of a magnetic tape.

FIG. 9 is a diagram showing a result of a visual observation of a coating state of a magnetic tape.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 coating head 2 first pocket 3 second pocket 4 front lip 5 first doctor lip 6 second doctor lip 7 first slot 8 second slot 9 first layer (lower layer) coating liquid 9a lower coating film 10 second Layer (upper layer) coating liquid 10a upper layer coating film W web

Claims (1)

[Claims] 1. A front lip, which is located on the most upstream side with respect to the direction of movement of a flexible support and has a front lip surface and an edge facing the flexible support, and a direction of movement of the support A plurality of slots and a plurality of doctor lips positioned downstream with respect to each other, and the coating liquid is continuously discharged from each of the plurality of slot tips to form a coating liquid on the surface of the flexible support. In the extrusion-type simultaneous multilayer coating apparatus for simultaneously coating the plurality of doctor lips, the lip surfaces of the plurality of doctor lips for coating the coating layer including the lowermost layer are formed in an arc-shaped cross section, and the plurality of doctor lips of the plurality of doctor lips are formed. An edge is provided at a downstream end of each lip surface, and a relationship between one upstream doctor lip and a downstream doctor lip adjacent to the downstream side is defined by an edge of the upstream doctor lip. The angle θ between the straight line L1 drawn so as to be in contact with the lip surface of the side doctor lip and the tangent L2 at the edge of the upstream doctor lip is 0 ° ≦ θ ≦ 10 ° below the tangent L2. And the radius of curvature R1 of the lip surface of the upstream doctor lip and the radius of curvature R2 of the lip surface of the downstream doctor lip are 0.2R1 ≦ R2 <0.8R1.
A coating apparatus characterized in that: