WO1997021494A1

WO1997021494A1 - Coating device

Info

Publication number: WO1997021494A1
Application number: PCT/KR1996/000204
Authority: WO
Inventors: Young Gak Choi
Original assignee: Young Gak Choi
Priority date: 1995-12-08
Filing date: 1996-11-19
Publication date: 1997-06-19
Also published as: KR0156781B1; KR970033066A

Abstract

This invention provides the following coating device (10) wherein coating solution, continuously extruded through two slits (12) at constant intervals, as formed between two edges of the front end (14) consisting back edge (b) and front edge (f) in the moving direction of substrate, is adhered in such a manner to coat the ssurface of the moving substrate in a predetermined moving route, characterized in that each edge of said front end has a combination shape of flat surface or a protruded round-shape, the shortest distance (L1) between the vertical line passing through top point in back direction at front edge, and extended line of slit wall surface at front edge is 0.5 - 2 times of slit interval (d) and 0.5 times less than W1, the thickness of front edge, the distance (H) between horizontal lines passing through each top point of back edge and front edge is 0.5 - 2 times of slit interval (d), the shortest distance (L2) between vertical line passing through the top point at back edge and extended line of slit at back edge is 0.2 - 1.5 times of slit interval (d). By using a coating device according to this invention, good coating surface without coating defects, such as transverse step, stripe in the length direction, pin hole and overflow, may be obtained. In addition to that, the superior physical properties of final product may be obtained.

Description

TITLE OF INVENTION

COATING DEVICE

TECHNICAL FIELD

This invention relates to a device for applying a coating solution on the substrate and more particularly, to a coating device wherein the front end is comprised of back edge and front edge in the order of substrate moving direction; the shape of front edge is constructed suitable for smoothing the coating solution; and towards the surface of the moving substrate, a coating solution extruded continuously through two slits between two edges, is flowed into the front edge and simultaneously coated to the surface of a substrate in homogeneous thickness.

BACKGROUND ART

In case of the conventional coating device to apply the coating solution to a substrate, several devices (e.g., gravure roll coater, reverse roll coater, bar coater, knife coater, extrusion coater, slide coater and curtain coater) are recommended for use. Among these coating devices, the extrusion coating device has been recently widely used and it is more advantageous than the conventional roll-type coaters, which had been widely used in past. And also, it can be applied to the wide scope. In the above description, substrate is generally a plastic type film such as polyethyleneterephthalate, polyethylenenaphthalate, polycarbonate, polyamide, polyimide, polyamidimide, celluloseacetate, cellulosetriacetate, celluloseacetate- propionate, polyvinylchloride, polyvinylidenechloride etc. and its thickness is within the range of 5-100μm.

The coating property of a coating device is determined by the shape of the front end, homogeneity in discharging a coating solution and a coating process condition, with regard to the matter, a large number of patents have been suggested. For example, Japanese Patent Laid-open Nos. 1982-84771, 1983-104666 and 1985-238179, just shows the shape of the front end, and also, homogeneity in discharging a coating solution etc. is mentioned in Japanese Patent Laid-open Nos. 1987-95174, 1989-236968 and US Patent No. 4,465,707 and the condition of coating process in Japanese Patent No. 87-132566.

In said three patents showing the front end of a coating device, only the shape and dimension of each edge of the front end, especially the limited one part of the front edge (doctor edge) is mentioned but the relation between the dimensions of each specific portion is not mentioned. As described above, coating properties can not be determined with only the shape of a front end but be determined with mutual relation of each portion of a front end. From the point, above-mentioned patents have several deficiencies in their contents.

DISCLOSURE OF INVENTION

This invention used several tests and simulations to devise the structure of a coating device having good coating properties and as the result, it was confirmed that the coating properties was determined by the mutual relation among slit intervals, the dimension of a front edge and the shortest distances of each edge. Hence, it is experimentally ascertained that only the coating device satisfying these conditions could provide good coating properties without the coating defect like a scratch in the length direction, step in the transverse direction and bubble influx.

That is to select an optional coating system as simulation and calculate simultaneously material balance, momentum balance and momentum balance of substrate, in this system, by using finite element method , to get the pressure and current distribution at each portion. The simulations are performed by changing each dimension of the coating device in order to analyze the trends on each parameter and its successive experimental verification may result in obtaining a proper coating device.

This invention, therefore, is to provide a coating device wherein coating solution, continuously extruded through two slit(12) at constant intervals, as formed between two edges of the front end(14) consisting back edge(b) and front edge(f) in the moving direction of substrate, is adhered in such a such manner to coat the surface of the moving substrate in a predetermined moving route, characterized in that; each edge of said front end has a combination shape of flat surface or a protruded round-shape, the shortest distance (L.,) between the vertical line passing through top point in back direction at front edge and extended line of slit wall surface at front edge is 0.5 - 2 times of slit interval (d) and 0.5 times less than W₁ , the thickness of front edge, the distance (H) between horizontal lines passing through each top point of back edge and front edge is 0.5 - 2 times of slit interval (d) , the shortest distance (L₂) between vertical line passing through the top point at back edge and extended line of slit at back edge is 0.2 - 1.5 times of slit interval (d) .

The slit should be manufactured to have a proper scope of intervals and length for the homogeneity in the discharge pressure of coating solution and its width direction. Hence, the slit interval is preferably determined within 1mm by considering a proper discharge pressure. If the slit interval is more than 1mm, it is difficult to form good layer current, thus there may be turbulent or partial eddy flow. Therefore, it is preferable that the slit interval is less than 1mm. The longer the slit length becomes, the more advantageous the homogeneity of the discharge pressure becomes. However, the pressure requiring for discharging is increasing in such case that a proper level should be determined, preferably within around 100mm.

Said determination of the front end structure is obtained, while any part of each edge is not contacted with the moving substrate in coating, as the result of observing the tendency after changing the shortest distance(LJ between the vertical line passing through the top point at the front edge and the extended line of slit wall at the front edge, the thickness(W of the front edge, the distance(H) between the horizontal lines passing through each top point of the back and front edge, the shortest distance(L₂) between the vertical line passing through the top point at the back edge and the extended line of slit wall at the back edge direction, and the slit interval (d) .

In other words, when L₁ is 0.5 times less than the slit interval (d) , the entry of coating solution is difficult, which gives the step in the transverse direction as coating defect, on the contrary, when it is 2 times larger, smoothing defect or eddy flow is occurred, which gives coating defects. And L₁ should be 0.5 times less than the thickness (W.,) of the front edge because smoothing defects is appeared if it is out of this scope .

In case that H is 0.5 times less than slit interval (d) , successive coating is difficult, and if it is more 2.0 times, the coating bead is not formed so that the coating solution flows down the backward of the back edge. L₂ should be 0.2-1.5 times of slit interval not to cause the problem like the reduction of coating scope, the easy intermixing of a foreign substance in long time coating and the influx of bubble in high speed coating.

The front end is comprised of the front edge (f) and the back edge (b) , and its shape is preferably a combination of flat surface (as Fig. 3) or the protruded round shape (as Fig. 4) , and its material as used should be strong more than Rockwellhardness 80 like cemented carbides. If it is less than Rockwell¬ hardness 80, it is easily damaged by scratch to cause the coating defect.

Further, in the event that the surface processing of each edge at front end adjacent to the coating solution is poor, coating defects may occur. In this invention, the illumination intensity of surface adjacent to coating solution is preferably less than 5μm. If the mean illumination of intensity in center line of each edge surface is larger than 5μm, coating defect may occur.

This invention is described in more detail by referring to the attached drawings.

As illustrated in Fig. 1, a coating device (10) generally coats the substrate(30) between the driving roll (20) and the guide roll (40) with the coating solution extruded from the coating device(10) . The coating device (10) of this invention, as shown in Fig. 2, Fig. 3 and Fig. 4, is provided with the front end (13) comprising the back edge(b) and the front edge(f) constructed in order of the substrate moving direction; the shape of the front edge(f) is designed suitable for smoothing a coating solution; toward the moving substrate's surface, the coating solution continuously extruded from the slit (11) between two edges is inserted into the front edge (f) for coating the substrate's surface at constant thickness; the coating solution is poured from the inlet of coating solution (14) and saved in the cavity (11) , and the saved coating solution is coated on the substrate through the same process as above.

In the illustrated coating device (10), the structure of cavity (11) is designed for the discharge of the coating solution to give the homogeneity in the width direction at the front end, its shape should be constructed for the coating solution current not to make the turbulent flow or the stagnated field. Its shape and size are depended on the fluidity of coating solution. Fig. 2 shows a semicircular type as one example. The position of supplying a coating solution is at center, both ends or one end in the width direction. The method of supplying a coating solution is to coat the whole amount of supplied coating solution or to coat one part of supplied paint, while circulating the remaining amount. The cavity (in Fig. 2) illustrates the method coating the whole amount of coating solution supplied at the center position in the width direction.

The slit (12) with a proper scope in intervals and length can give the homogeneity in the width direction to the pressure discharging the coating solution. The intervals of slit portion, which is determined by considering a proper pressure of discharging, is good within around lmm. The longer the slit(12) length becomes, the more homogeneous the discharge pressure becomes. However, the pressure requiring for discharging is increasing in such case that a proper level should be determined, preferably within around 100mm.

The front end (13) is comprised of the front edge (f) and the back edge (b) , its shape is preferably a combination of flat surface (as Fig. 3) or the protruded round shape (as Fig. 4) , and its material as used should be strong more than Rockwellhardness 80 like cemented carbides.

The coating device of this invention as described above can be applied to a magnetic recording tape, photograph film, X-ray film, print paper, adhesive tape, light-baffling film and to the multi-layer coating in the manufacture of various functional films using coating process, especially, it is very suitable for manufacturing a magnetic recording tape.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a drawing of coating device according to this invention,

Fig. 2 is a drawing showing the structure of coating device of Fig. 1,

Fig. 3 is a drawing illustrating the front end with each edge, shown in Fig. 1 and Fig.2, designed in a combination shape of flat surface according to one example of this invention,

Fig. 4 is a similar drawing of Fig. 3, presenting the edge of front end designed in the protruded round shape according to other example of this invention, * Code description of main parts in the drawings

10: Coating device 20: Driving roll

30: Substrate 40: Guide roll 11, 11': Cavity 12: Slit

13: Front end 14: Inlet of coating solution b : Back edge f : Front edge d : Slit interval L₁ : The shortest distance between the vertical line passing through the top point at front edge and the extended line of slit wall at front edge. L₂ : The shortest distance between the vertical line passing through the top point of back edge and the extended line of slit at back edge. ₁ : The thickness of front edge W₂ : The thickness of back edge

H : The distance between the horizontal lines passing through each top point of back edge and front edge

BEST MODE FOR CARRYING OUT THE INVENTION

In the following examples, the coating device according to this invention is described more clearly but this invention is not limited to the examples.

[ EXAMPLE (E) and COMPARATIVE EXAMPLE (C) ]

ith the following composition, the first dispersed paint consisting of magnetic substance, carbon black or alumina etc. in powder form and vinyl binders resin solution was dispersed by kneading machine, agitator, mill dispersing machine and then, urethane resin solution, after that, fatty acid and fatty acid ester lubricant including solvent was added thereto. The resulting mixture was secondly dispersed by agitator and mill dispersing machine, and polyisocyanate, hardening agent, was added thereto and stirred prior to final filtration to manufacture the magnetic paint for magnetic recording media was.

(i) Mill Mix

Composition parts per weight

Denatured cobalt magnetic substance 100

(Coercive force: 650 Oe, specific surface 30 m²/g) Carbon black 5 α-alumina 2

Vinyl chloride-vinyl acetate-anhydrous maleate copolymer resin 8

Cyclohexanone 80 Methylethylketone 60

Toluene 50

(ii) Let Down

Composition parts per weight

Polyester polyurethane resin 12

Normal butylstearate 1.5

Myristic acid 1.5 Cyclohexanone 40

Methylethylketone 60

Toluene 50

Polyisocyanate 3

After filtration of the magnetic paint prepared, by using the apparatus shown in Fig. 3, with the condition as follows, the result paint is coated on the polyethlylene terephthalate film, the substrate in 14.5μm thickness. The paint's fluidity was measured at 25°C by Haake viscometer RV-20 (Germany) , as the result, when the shearing stress is 1000/sec, viscosity is 72.6 centipoise and in case of 5000/sec, it is 38.4 centipoise.

The coating conditions and the dimensions of each portion of a coating device

Coating speed 200 m/min Coating width 150 mm Coating thickness 15-20μm in a non-drying state

Substrate polyethylene terephthalate film, thickness 14.5μm Drying temperature 90°C (drying by heat gun) Transit tension 1.5Kg/150 mm

Edge's material Cemented carbide (Rockwellhardness 90) Slit length 70mm Slit interval d 0.2, 0.3, 0.4, 0.5mm ( adjusting slit interval by inserting spacer) Surface illumination intensity of edge (Ra) 4μm Thickness of front edge W₁ 3.5 mm Thickness of back edge ₂ 2.5 mm

Radius of cavity 8 mm (1) Slit interval d: when it is 0.2mm

E: Examples C: Comparative examples

Coating Properties X- bad coating state, O- good coating state (2) Slit interval d: when it is 0.3mm

(3) Slit interval d: when it is 0.4mm

(4) Slit interval d: when it is 0.5mm

As shown in the above Examples (E) and Comparative examples (C) , the application of coating device according to this invention may lead to obtainment of good coating surface without coating defects such as transverse step, stripe in the length direction, pin hole and overflow. In addition to that, the superior physical properties of final product may be obtained.

Claims

WHAT IS CLAIMED IS :

1. A coating device wherein coating solution, continuously extruded through two slit(12) at constant intervals, as formed between two edges of the front end(14) consisting back edge(b) and front edge(f) in the moving direction of substrate, is adhered in such a such manner to coat the surface of the moving substrate in a predetermined moving route, characterized in that; each edge of said front end has a combination shape of flat surface or a protruded round-shape, the shortest distance (L^ between the vertical line passing through top point in back direction at front edge and extended line of slit wall surface at front edge is 0.5 - 2 times of slit interval (d) and 0.5 times less than ₁ , the thickness of front edge, the distance (H) between horizontal lines passing through each top point of back edge and front edge is 0.5 - 2 times of slit interval (d) , the shortest distance (L₂) between vertical line passing through the top point at back edge and extended line of slit at back edge is 0.2 - 1.5 times of slit interval (d) .

2. A coating device according to claim 1 wherein the front end is manufactured with strong material, more than Rockwellhardness 80.

3. A coating device according to claim 1 wherein illumination intensity of surface adjacent to coating solution is less than 5μm as mean surface illumination intensity in center line.