JP2000218209A - Method and device for performing curtain coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve hanging connection between a fluid curtain and a horizontal guide and to contrive improving quality when guiding a falling curtain by feeding edge fluid having viscosity larger than that of a coating composition in a channel. SOLUTION: In a feeder 14 as a casting device for making a falling curtain 3 of a fluid coating composition, a curtain 3 consisting of a coating composition discharged from casting slots 25 is made to fall from a casting lip 23 for coating a carrier 2. The carrier 2 is guided by a casting roller 1 and continuously conveyed in the direction of the arrow 26. At this time, the falling curtain 3 is guided by side guides 5 at side edges, however at the same time, edge fluid 8 having viscosity larger than that of the coating composition is fed in a channel from an end piece 11 of a discharge means 7, thereby minimizing the effect of disturbance by an edge.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a fluid coating (fluid coating).
The curtain of the compound for coating) falls on the carrier (carrie
3. A method for curtain coating the carrier with at least one layer of the fluid coating composition while the carrier is being moved along a path through the coating area corresponding to r), and the preamb of claim 2.
le) according to the invention.

[0002]

BACKGROUND OF THE INVENTION Curtain coatings are used, for example, in the production of photographic materials for applying photographic silver-halide emulsions to a carrier such as a web. It is known that in this coating method, a falling curtain must be guided laterally to prevent the curtain from undergoing constriction due to surface tension. The so-called horizontal guide (la
teral guide) or curtain holder (curtain holde)
r) is used for this purpose. These are generally stationary parts of the coating device, made of solid material and having a contact surface with the curtain. The velocity of the fluid curtain at this interface is zero. The lateral guide exerts a deceleration effect on the edge of the fluid curtain. As a result, a speed profile is formed at the edge of the descending curtain. This velocity profile, viewed in the direction of the lateral guide, represents an increasingly slowing of the flow rate of the descending curtain, causing a weakening of the curtain in the edge region and a laminar flow in the central region of the curtain. It may interfere with the process. In the critical area of this coating process, the hanging connection between the curtain and the side guide breaks off. The unstable curtain disengages from the lateral guide and then, by convergence,
Coating of the carrier is no longer possible.

It is known to supply the descending curtain with additional fluid at the edge to prevent this slowing of the descending speed. The distribution of so-called auxiliary, edge or flushing fluid of low shear viscosity at the contact surface of the lateral guide reduces the deceleration effect of the solid lateral guide on the flow process of the descending curtain. This edge fluid can be distributed, for example, by a pump and an outlet opening in the lateral guide. For example, German Patent 1,928,025 discloses a hollow lateral guide having a long slot in the contact surface, from which the internal fluid associated with the curtain is pumped. .

[0004] For the stabilization of a freely descending fluid curtain, EP 0,115,621 uses a curtain holder from which a fluid of lower viscosity, as compared to the curtain, emerges in the direction of the curtain. In each case, the fluid forms a triangular, stabilizing fluid bridge between the curtain holder and the curtain.

In the case of the device known from EP 0,740,197, a lateral flow is also supplied to the curtain on both sides. Here, however, the flushing fluid is distributed on the curtain holder such that a parallel flow extending across the direction of the curtain is formed, and the curtain is in contact only with the flushing fluid but with the solid curtain. No contact with holder.

According to EP 0,414,721, flushing fluid is distributed on the lateral guide, said flushing fluid being sucked away around the position where the descending curtain hits the carrier.

In order to reduce the speed deceleration in the edge area,
EP 0,599,740 proposes a curtain holder consisting of a thin wire under which the flushing fluid flows, the flushing fluid being applied before the curtain hits the base at the edge of the curtain. Is sucked up again.

All methods known from the prior art are based on the principle that a flushing or lubricating effect is provided by the additional fluid at the edge. The flushing fluid is to reduce the deceleration effect of the solid curtain holder on the descending curtain. Thus, auxiliary fluids whose viscosity is lower than that of the coating formulation are exclusively used.

However, it has been found that the flow of these low-viscosity auxiliary fluids on the lateral guide is not steady. This non-steady, non-laminar flow is a source of disturbance for the free-fall curtain. This disturbing action leads to a detachment of the hanging connection between the curtain and the lateral guide and to a poor coating. Thin fluid curtains are particularly sensitive. This is a particular disadvantage when using a curtain coating method for photographic film production. In such cases, efforts have been made to uniformly apply a low flow rate, viscous coating formulation to the carrier with the highest possible curtain drop for economic reasons. Unsteady flow at the edge limits the processing speed during coating.

It is an object of the present invention to provide a method and apparatus for curtain coating in which the hanging connection between the fluid curtain and the lateral guide is improved and the edge of the fluid curtain drops with the least possible disturbance. To provide.

[0011]

This object is achieved by the features of claims 1 and 2.

According to the invention, it is proposed that on guiding the descending curtain, the edge fluid having a higher viscosity than that of the coating composition is distributed in the form of channels. This channel runs down the solid lateral guide such that the deceleration effect of the lateral guide is reduced without generating unsteady flow. This measure improves the hanging connection between the curtain and the side guide. Disturbances at the edge of the curtain, which occur with low viscosity edge fluids, are reduced.

[0013] Preferably, the edge fluid is embedded in the curtain. It may be distributed on the lateral guide so that it runs in a straight, laminar manner.
In other words, the free surface of the channel of auxiliary fluid is surrounded by the coating composition of the curtain over the entire height of the descent. The contact angle of the auxiliary fluid on the curtain holder is thus also surrounded by the curtain fluid.
This embedding ensures that the channel does not form meandering loops or bends. This is advantageous for the production of photographic materials, where usually a plurality of layers are laminated and applied simultaneously to the carrier. A separate one of these layers typically contains a wetting agent. These diffuse into the auxiliary fluid channels. If these channels are not filled, the wetting reagents will aid in the meandering and spiraling of the channels due to contact angle hysteresis. However, channels buried within the curtain and flowing down the lateral guide in a linear manner not only enhance the hanging connection between the curtain and the lateral guide, but also have a stabilizing effect against disturbances. I understood.

[0014] Advantageously, the edge fluid has a viscosity that is two to four times as great as the coating formulation.
If the curtain is composed of multiple layers with different flow characteristics, this measure can effectively prevent the curtain from damping and disturbing at the edge.

Conveniently, the channel is created by injecting the edge fluid into the coating formulation during the curtain formation. Thus, here the edge fluid is preferably supplied separately, whereby the distribution of the auxiliary fluid in the form of a channel can be effected in a technically simpler manner.

Preference is given to channels whose volume flow can be preset to less than 40 ml / min, preferably in the range of 10 to 35 ml / min. In this way, a narrow channel can be formed in which the curtain is buried along the entire descent height.

Photographic silver halide emulsion (photograph)
ic silver-halide emulsions) contain water and usually have a viscosity of less than 50 mPa · s, so the edge fluid is greater than 50 mPa · s, preferably 50 mPa · s-200 mPa · s.
It is also preferred that it be formed of a water-soluble fluid having a viscosity of s.

Here, the fluid is a water-soluble polymer compound having a viscosity of between 50 and 200 mPa · s.
It preferably comprises an r-soluble polymer compound).
This edge fluid is easy to make.

The edge fluid may be polyvinyl alcohol (polyvinyl alcohol), polyvinyl pyrrolidone (polyv
inyl-pyrrolidone, a copolymer of maleic acid-methylvinylether cop
olymer), butadiene maleic acid copolymer (butadien)
e maleic acid copolymer). These starting substances are commercially available and readily available. Also, for the edge fluid, an extremely cost-effective Newtonian fluid (Newtonian flui
d) It is possible to use glycerol.

In the design of the apparatus for curtain coating, the means for discharging includes means for creating a channel,
The means causes the edge fluid to flow down each lateral guide in the form of a channel, the viscosity of the edge fluid exceeding the viscosity of the coating formulation.

Structurally, when a sliding surface casting device is used to make the channel, the edge at the transverse end of the sliding surface of the sliding surface casting device. Nozzle-like end pieces (nozzles) for injecting fluid into the coating formulation
We recommend using a le-like end piece). This structural design for the supply of the edge fluid is also recommended in the case of an extrusion casting device. It is thus possible in a simple manner to create channels in which the lateral guides flow down linearly in known coating equipment.

Advantageously, the edge fluid is at a rate of 40 per minute.
It is added in each lateral guide in an adjustable manner with a volumetric flow of less than milliliters, preferably 10-35 milliliters per minute. In this way, in the case of curtain coating using a photographic cursing solution, the channel can be designed to fill the channel along the entire descent height.

Preferably, before the curtain hits the carrier, a deflecting device is provided to deflect the lateral edges of the curtain together with the edge fluid so that only the central part of the curtain coats the carrier. Good. This prevents edge fluid from reaching the carrier. A base such as a web can be coated up to the edge with a photosensitive cursing solution and no phenomenon of thickening at the edge is observed.

Table 1 shows the effect of various edge fluids of various flow characteristics on the experimental curtain casting apparatus of FIG. 1 in seven examples. In all the experimental examples, the curtain was formed with three layers of photographic silver halide emulsion, the drop height was 15 cm, and the volume flow of the edge fluid was 35 ml / min with each lateral guide. The quantity was supplied by jetting at the edge. The viscosity of the two lower layers positioned towards the carrier is 40 mPas, while that of the upper layer is 30 mPa
・ It is s.

The technical effect of the edge fluid supply according to the invention is evaluated by the so-called break-off limit. The separation limit is such that the minimum possible flow of the fluid curtain is such that the hanging connection between the curtain and the side guide is still maintained.
ssible volume flow of the fluid curtain).
As the fluid velocity further decreases, the curtain moves away from the lower end of the lateral guide. The curtain converges. Coating is no longer possible at that time. Thus, in the example of Table 1,
Starting from a stable curtain, the fluid velocity was reduced and the release limit, the limit of the coating process, was described for different edge fluids with different flow characteristics. The separation limit is shown in Table 1 as m ² / s. This value is the unit of the car width and time (castin
g width and time unit). here

[0026]

(Equation 1)

## EQU1 ##

The comparison between Examples 1 and 2 shows that the supply limit can be reduced by supplying a low-viscosity edge fluid, and thus a flushing fluid, as is known in the prior art. First shown.

Clearly good results can be achieved with the viscous edge fluid of the present invention, flowing in the form of channels, buried in the curtain. As illustrated in Examples 3 to 7, according to the present invention the separation limit is reduced by the prior art (Example 2).
Was substantially reduced by half. In other words, the standardized volume flow of the fluid curtain is increased by 1 until the hanging connection between the curtain and the lateral guide is separated.
50cm ³ / cm · s to the limit of 76cm ³ / cm · s
(Examples 4 to 7).

The present invention makes it possible to apply a very thin fluid film to the carrier.

As illustrated in Examples 4 and 7, the flow behavior of the edge fluid can also be made structurally viscous.
Without stress, the viscosity of these edge fluids exceeds 100 mPa · s.

[0032]

BRIEF DESCRIPTION OF THE DRAWINGS In the following, the invention will be described in detail in preferred exemplary embodiments with reference to the accompanying drawings.

A device for curtain coating according to the present invention is illustrated in FIG. 1 in overall perspective view. Here, the supply device 14 is shown as a sliding surface car-staining device for producing a falling curtain 3 with a fluid coating formulation. The curtain descends from the casting lip 23 of the sliding surface car staking device over a descent height 30 and coats the carrier 2. This carrier is guided by the car-staking roller 1 and is transported continuously through the coating area 31 in the direction of the path 28.
The descent curtain 3 is guided by lateral guides 5 at the side edges. These lateral guides are
The curtain extends from the upper edge 26 around the perimeter 3 beyond the total descent height 30 to the point where the curtain hits the carrier. The sliding surface 29
Each transverse end 12 is provided with means 10 for creating a channel 9 of the edge fluid 8. The edge fluid is supplied by discharge means 7 and the firing into the coating formulation is provided by an end piece 11 such as a nozzle. Each discharge means 7 is adjustable with respect to volumetric flow and is filled by the edge 6 of the curtain 3 and allows the edge fluid to exit the end piece 11 so as to flow down the lateral guide 5 in a laminar flow. . As illustrated in FIG. 1, this edge fluid is deflected at the lower end of the lateral guide 5 by a deflecting device 19 (not shown in detail). In the drawing, the width 21 of the coating 4 is shorter than the width 22 of the carrier 2. As illustrated in a partial cutaway view of the curtain 3, the coating formulation exits the car-staining slot 25 and forms a stacked layer 18 that flows down the sliding surface 29. As illustrated in detail in FIG.
The edge fluid is injected into the stack 18.

FIG. 2 is a sectional view of the curtain coating apparatus taken along line II-II of FIG. The end pieces 11, such as nozzles, are separated from the individual layers 15, 16, 1 as shown in this example.
The edge fluid is sprayed into a stack layer 18 of. The individual casting solution for these layers exits in each case from a casting slot 25 which is connected to a distributor channel 24 and to a conveyor (not shown). The casting solution coming out of each casting slot 25 is superimposed on the inclined sliding surface 29 of the feeder 14 to form a stacked layer 18. The edge fluid injected into the stack layer 18 at the transverse end forms a channel on the curtain holder, which channel has a laminar flow, a uniform cross section, from the upper end 26 to the lower end 27. . As illustrated in FIG. 2, the thickness of the curtain 3 decreases with increasing height of the descent. Here, the channel 9 of the edge fluid 8 whose volume flow can be preset in an adjustable manner is enclosed by the fluid of the descent curtain over the entire height of the descent. This filling of the channel 8 is illustrated in more detail in the following figures.

FIG. 3 is a detailed view of the lateral guide taken along line III-III of FIG. Here, the flat structure of a lateral guide with a channel 9 down it is shown,
The channel 9 is completely enclosed by the edge 6 of the curtain 3. As can be seen from the enlarged view, the contact angle of the channel is surrounded by the fluid coating composition of the curtain 3 over the entire height of the descent. On the one hand, burying the channel 9 in this way ensures that the deceleration effect of the solid curtain holder 5 is reduced. Convergence of the curtain in the edge region is thus prevented. On the other hand, the edge fluid 8 flows in a straight line and guides the fluid curtain consisting of the stacked layers 18. Here, the shearing viscosity of the edge fluid 8 is greater than that of the individual layers 15, 16 or 17 of the stacked layer 18. The edge fluid is deflectable by a deflecting device 19 at the lower end of the lateral guide. However, it is also possible with the edge fluid that the edge of the coating is sucked away only following the completion of the coating on the base. This is shown in FIG. 4, which illustrates the part of FIG. 1 in an enlarged view.

As can be seen from FIGS. 4 and 1, the edge fluid is supplied by discharge means 7, which is a means for making the channel 10 with a nozzle 11 forming a jet stream on the sliding surface. Of course, the nozzle 11 can also eject the edge fluid at a different position, for example, around the car stain grip 23. It is also possible to launch a high viscosity edge fluid from an outlet opening in the lateral guide (not shown). In this case, the lateral guide forms the discharge means. Thus, the lateral guide is structurally designed to facilitate the formation of channels on the curtain holder and so that the viscosity of the channel fluid is greater than the viscosity of the coating formulation.

The sliding surface cursting device illustrated in FIGS. 1, 2 and 4 is a preferred exemplary embodiment. Of course, the fluid curtain can also be formed by extrusion.

[0038]

[Table 1]

The features and aspects of the present invention are as follows.

1. A method for curtain coating a carrier with at least one layer of a fluid coating composition, the method comprising: moving the carrier along a path through a coating area; and a fluid extending across the path of the carrier. The process of forming the falling curtain of the coating composition and the edge fluid having a viscosity greater than the viscosity of the coating composition is distributed over in the form of a channel.
Guiding the descending curtain with a lateral guide. A method for curtain coating a carrier with at least one layer of a fluid coating formulation.

2. The method of claim 1, wherein the channels flow down each lateral guide in a straight, laminar flow manner buried within the curtain.

3. The method of claim 1 or 2, wherein the viscosity of the edge fluid is two to four times greater than the viscosity of the coating formulation.

4. The method of any of the preceding claims, wherein the channel is created by spraying the edge fluid into the coating formulation during formation of the curtain.

5. The method of any of claims 1 to 4, wherein the channel is adjustable to less than 40 milliliters per minute.
A method characterized by delivering an adjustable volume flow of preferably 10-35 milliliters per minute.

6 The method of any of the preceding claims, wherein the edge fluid is formed of a water-soluble fluid having a viscosity between 50 mPa · s and 200 mPa · s.

7. In the above method, the fluid may be a water-soluble polymer compound.
sound).

8. In the above methods 1 to 5, the edge fluid is polyvinyl alcohol (polyvinyl alcohol).
l), polyvinyl pyrrolidone
e), maleic acid-methyl-vinylether copolymer, butadiene maleic aci
d copolymer).

9. The method of any of the preceding claims, wherein the edge fluid is glycerol.

10. Passage through the coating area (2
A transport means for transporting the carrier along 8), a feeder (14) which is made of a fluid-coating formulation and which has a descent curtain (3) extending across the passage of the carrier and descending onto the carrier; A lateral guide (5) for guiding the descent curtain at an edge (6), and discharge means (7) for distributing edge fluid on the lateral guide, the carrier comprising at least one layer of the fluid-coating composition. In an apparatus for curtain coating (2), said discharge means (7) comprises means (10) for creating a channel, said means (10) being connected to said edge fluid by a channel (9). Flowing down each of the lateral guides in the form of: wherein the viscosity of the edge fluid (8) is greater than the viscosity of the coating formulation, wherein the carrier is carved with at least one layer of the fluid coating formulation. Apparatus for Nkoteingu.

11. The apparatus of claim 10, wherein the or each means (10) for creating a channel has the edge fluid buried in the curtain (3) (FIG. 3), in a straight line,
An apparatus characterized in that the lateral guide flows down in a laminar flow manner.

12. In the above eleventh apparatus, the supply device (14) is a sliding surface surfing device (sliding-surfing device).
an ace casting device and said means (10) for making said channel is an end piece, such as a nozzle, at the transverse end (12) of the sliding-surface (29) of said sliding surface car styling device. (Nozzle-like end piece)
An apparatus having (11).

13. In the above eleventh apparatus, the supply apparatus is an extrusion casting apparatus.
the means for making the channel and having an end piece, such as a nozzle, which injects the edge fluid into the coating formulation at the transverse end of the extrusion slot. An apparatus characterized in that:

14. In the above devices 11 to 13,
Said release means (7) is less than 40 milliliters per minute;
An apparatus characterized in that said edge fluid is discharged onto each lateral guide (5), preferably at an adjustable volume flow of 10 to 35 milliliters per minute.

15. In the above devices 10 to 14,
The width of the curtain (21) is equal to the width of the carrier (2).
2) a deflector (19) is arranged on each side guide before the curtain hits the carrier, the deflector (19) being smaller than the edge fluid (8); B) deflecting said lateral edges (6) of said curtain together with said curtain and only the central part of said curtain coats said carrier.

[Brief description of the drawings]

FIG. 1 is an overall perspective view of a curtain coating device according to the present invention.

FIG. 2 is a cross-sectional view of the curtain coating device taken along line II-II of FIG.

FIG. 3 is a detailed view of the lateral guide as a cross-sectional view along the line III-III in FIG. 1;

FIG. 4 is an enlarged view of a part of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Car stain roller 2 Carrier 3 Falling curtain 4 Coating layer 5 Lateral guide or solid curtain holder 6 Curtain edge 7 Discharge means 8 Edge fluid 9 Channel 10 Channel creation means 11 End piece like nozzle 12 Transverse end 14 Feeding device 15, 16, 17 Individual layers 18 Stacked layers 19 Deflectors 21 Coating width 22 Carrier width 23 Kerstain grips 24 Distributor channels 25 Kersting slots 26 Upper end 27 Lower end 28 Passage 29 Sliding surface 30 Drop height 31 Cursing range

Claims (2)

[Claims] 1. A method for curtain coating a carrier with at least one layer of a fluid-coating composition, the method comprising: moving the carrier along a path through a coating area; and a fluid extending across the path of the carrier. Forming a descending curtain of the coating composition; and guiding the descending curtain by a lateral guide over which an edge fluid having a viscosity greater than the viscosity of the coating composition is distributed in the form of a channel. A method for curtain-coating a carrier with at least one layer of a fluid-coating formulation, comprising: 2. A transportation means for transporting the carrier along a path through the coating area, and a supply device for forming a descent curtain extending across the path of the carrier and descending onto the carrier with a fluid coating composition. An apparatus for curtain coating the carrier with at least one layer of the fluid coating composition, comprising: a lateral guide for guiding the descent curtain at a lateral edge; and discharge means for distributing edge fluid to the lateral guide. Wherein the release means comprises means for creating a channel, the means causing the edge fluid to flow down each lateral guide in the form of a channel, the viscosity of the edge fluid being reduced by the coating formulation. An apparatus for curtain-coating a carrier with at least one layer of a fluid-coating composition, characterized by having a viscosity greater than the viscosity of the carrier.