JP7540341B2 - Coating head, apparatus and method for producing coated web - Google Patents

Description

The present invention relates to a coating device and manufacturing method for simultaneously forming a coating film on both sides of a film, nonwoven fabric, paper, etc.

Conventionally, the double-sided simultaneous coating method, which simultaneously forms a coating film on both sides of a web, is widely known as a method in which coating heads such as bars, rolls, knives, and slit dies are arranged facing each other on the front and back of the web to form high-quality coating films on both sides.

As an example of such a coating head, Patent Document 1 discloses a coating head having a measuring section provided at a predetermined distance and a liquid storage section above the measuring section for storing coating liquid. It also discloses a method for producing a coated web in which the web is passed through the liquid storage section and measuring section of the coating head to simultaneously apply coating liquid to both sides of the web.

Major problems with this type of simultaneous double-sided coating method include poor coating caused by wrinkles in the web as it travels, uneven coating caused by uneven film thickness distribution, and coating streaks.

In response to these problems, Patent Document 2 discloses a coating head having a measuring section arranged at a predetermined distance from one another, as in Patent Document 1, and a liquid storage section for storing coating liquid above the measuring section, and discloses a method of reducing running wrinkles in the web by providing a groove across the width of the web midway along the measuring surface.

JP 2017-164682 A JP 2018-75531 A

However, even with the coating head disclosed in Patent Document 2, coating streaks may occur when the web running speed is increased or a coating liquid with low surface tension is used. It is known that many of these defects occur near the exit of the coating head, and during coating, the surface tension of the coating liquid near the exit of the coating head and the tensile force caused by the running web reduce the pressure of the coating liquid from the exit of the metering section to the inside, forming a negative pressure area at the exit of the metering section, which causes the coating liquid to be drawn into the metering section, causing coating streaks in the running direction of the web. This phenomenon occurs more significantly when the web running speed is increased or a coating liquid with low surface tension is used.

As a countermeasure, the degree of negative pressure formed at the metering section outlet can be reduced by slowing down the web running speed or using a coating fluid with high surface tension, thereby eliminating coating streaks. However, running the web at a slow speed reduces the production capacity of coated webs. In addition, using a coating fluid with high surface tension narrows the range of coating fluid formulation options, resulting in restrictions on the coating fluid properties.

In this way, in a coating head having a measuring section provided at a predetermined distance and a storage section for storing the coating liquid above the measuring section, when the negative pressure area at the outlet of the measuring section expands due to an increase in the web running speed to improve productivity or a change in the coating liquid due to a change in the production type, a coating head has not yet been found that can stably coat a wide range of coating liquids while maintaining production capacity and without causing coating streaks.

Therefore, the present invention provides a double-sided coating head that can simultaneously form a high-quality coating film on both sides of a web without causing coating streaks on the web.

The coating head of the present invention, which solves the above problems, is a coating head that simultaneously applies a coating liquid to both sides of a traveling web,
a liquid storage section for storing a coating liquid, the liquid storage section being formed by a pair of liquid storage members facing the web running surface;
a metering section for adjusting the coating film to a desired thickness, the metering section being formed by a pair of metering members disposed opposite each other with a gap therebetween, downstream of the liquid storage section in the web running direction, and sandwiching the web running surface;
The metering member is composed of a first metering surface, a groove, and a second metering surface extending in the web width direction, in this order from the upstream side to the downstream side in the web running direction,
The groove has a surface that extends from the bottom of the groove to the boundary between the groove and the second measurement surface and that approaches the web running surface toward the downstream side in the web running direction.

The coating web manufacturing apparatus of the present invention also includes the coating head of the present invention and a conveying device for conveying the web.

The method for producing a coated web of the present invention uses the coating head of the present invention to introduce and pass a web through the gap between the pair of measuring members, and in the liquid storage section, the coating liquid stored in the liquid storage section is applied to both sides of the web, and a coating film of the desired thickness is formed on both sides of the web by adjusting the gap between the pair of measuring members.

By using the coating head of the present invention, a high-quality coating film without coating streaks can be formed simultaneously on both sides of the web, even when the web running speed is increased.

1 is a schematic cross-sectional view of a dispensing head according to one embodiment of the present invention; FIG. 2 is an enlarged view of a metering portion of the application head of FIG. 1 . 1A and 1B are diagrams showing a metering section of a conventional coating head and pressure distribution of a coating liquid during coating. 2 is a diagram showing a metering portion of the coating head in FIG. 1 and pressure distribution of the coating liquid during coating. FIG. 1 is a schematic diagram showing an example of an apparatus for producing a coated web of the present invention.

A preferred embodiment of the present invention will be described with reference to the drawings. However, the present invention is not limited to the form shown in the drawings, and various modifications are possible as long as the object of the invention can be achieved and the gist of the invention is not deviated from.

Refer to Figure 1. Figure 1 is a schematic cross-sectional view of one embodiment of a coating head 100 of the present invention. When a web 1 passes through this coating head 100, a coating liquid 2 is applied to both sides of the web 1, resulting in a coated web 3. The interior of this coating head 100 consists of a liquid storage section X1 for storing the coating liquid and a metering section Y1 for adjusting the coating to a desired thickness.

This coating head 100 is composed of liquid storage members 101 and 101' and a pair of metering members 102 and 102', and the liquid storage members 101 and 101' form the inner wall surface of the liquid storage section X1 for storing the coating liquid 2. The metering members 102 and 102' are arranged opposite each other with a narrow gap t between them, downstream of the liquid storage members 101 and 101' in the running direction of the web 1, so as to sandwich the running surface of the web 1, and together with the liquid storage members 101 and 101' form the bottom surface of the liquid storage section X1.

Although not shown, in this coating head 100, side plates are provided at the front and back of the paper surface of FIG. 1 to sandwich the liquid storage members 101, 101' and the measuring members 102, 102' so as to prevent the coating liquid 2 from leaking from the liquid storage section X1 and the measuring section Y1.

Refer to FIG. 2. FIG. 2 is an enlarged view of the liquid contact portion of the metering section Y1 of the coating head in FIG. 1. The surface of the metering section Y1 that contacts the coating liquid 2 is composed of, from upstream to downstream in the running direction of the web 1, first metering surfaces 103 and 103', grooves 104 and 104', and second metering surfaces 105 and 105', all of which extend in the width direction of the web 1. The grooves 104 and 104' are formed so that the surfaces that connect from the bottoms of the grooves 104 and 104' to the boundaries between the second metering surfaces 105 and 105' approach the running surface of the web 1 as they move downstream in the running direction of the web 1.

As mentioned above, when a coating film is formed simultaneously on both sides of a web by passing the web through a metering section with a narrow gap t, coating streaks may occur in the running direction of the web. The mechanism by which coating streaks occur will be explained with reference to FIG. 3. FIG. 3 shows details of the metering section Y2 in a coating head 200 of a conventional shape and a graph of the pressure distribution of the coating liquid 2 present in the metering section Y2 during coating. The conventional coating head 200 does not have a groove or a second metering surface in the metering section, but has only the first metering surfaces 203, 203'. When coating a web at a low speed using this coating head 200, the pressure decreases from the outlet of the metering section Y2 located at the most downstream side of the coating head 200 to the inside of the metering section on the upstream side due to the surface tension of the coating liquid and the tensile force caused by the running of the web, and a negative pressure area is formed at the outlet of the metering section as shown by the dotted line in the right graph of FIG. 3. When the running speed of web 1 increases, the tensile force caused by the running web also increases, so the negative pressure area expands into the metering section as shown by the solid line in the graph on the right of Figure 3, and coating liquid 2 is drawn into the metering section. When the amount of drawing in exceeds a certain amount, coating streaks occur in the running direction of the web. The amount of drawing in that causes coating streaks varies depending on the coating liquid.

Next, the state of the coating liquid 2 in the liquid storage members 101, 101' and the metering members 102, 102' when a coating film is formed on both sides of a web using the coating head 100 of the present invention will be described in detail with reference to FIG. 4. FIG. 4 shows details of the metering section Y1 in the coating head 100 and a graph of the pressure distribution of the coating liquid 2 present in the metering section Y1 during coating.

Refer to FIG. 2 again. The coating head 100 of the present invention is provided with grooves 104, 104' extending in the web width direction in the middle of the metering section Y1. Furthermore, the surfaces 106, 106' of the grooves 104, 104', which are continuous from the bottom of the grooves 104, 104' to the boundary between the grooves 104, 104' and the second metering surfaces 105, 105', approach the running surface of the web 1 as they move downstream in the running direction of the web 1. As a result, the flow path of the coating liquid 2 that follows the running of the web 1 between the surfaces 106, 106' and the web 1 becomes narrower as it moves downstream in the running direction of the web 1, and a compression force is applied to the coating liquid 2 that tries to enter the gap between the second metering surfaces 105, 105', forming a high-pressure portion P as shown by the dotted line in the right graph of FIG. 4. Therefore, when the coating head of the present invention is used, even if the web running speed is increased, the negative pressure area formed at the outlet of the metering section Y1 does not expand into the inside of the metering section because of the high pressure section P, as shown by the solid line in the right graph of Figure 4. In other words, the drawing of the coating liquid into the metering section can be suppressed. In order to further suppress the expansion of the negative pressure area, it is sufficient to form the high pressure section P near the outlet of the metering section Y1, so it is preferable that the length of the second metering surface 105, 105' in the web running direction is short as long as the thickness of the coating film on the coated web 3 does not change.

In the embodiment of Figures 1 and 2, the surfaces 106, 106' are flat, but in the coating head of the present invention, the surfaces 106, 106' are not limited to flat surfaces and may be curved as long as they approach the web running surface as they move downstream in the web running direction. In addition, the depth and shape of the grooves 104, 104' can be changed in various ways without departing from the gist of the invention, but are preferably determined by the physical properties of the coating liquid 2 used. In addition, a shallow groove depth t1 is preferable in consideration of the ease of cleaning the coating head 100.

When surfaces 106, 106' are flat surfaces, the angle θ between surfaces 106, 106' and second metering surfaces 105, 105' is preferably 10° or more and 70° or less, and more preferably 10° or more and 45° or less in order to increase the pressure in the high pressure section P and suppress the expansion of the negative pressure area.

It is known that the thickness of the coating film when the coated web 3 is formed using the coating head 100 of the present invention is approximately half the minimum gap between the metering members 102, 102' and the surface of the web 1, and the gap t of the metering section Y1 is determined by the desired coating thickness and the thickness of the web 1. In other words, the installation positions of the metering members 102, 102' are determined. In addition, at this time, the first metering surfaces 103, 103' and the second metering surfaces 105, 105' are parallel to the running surface of the web 1, so that the liquid pressure on both sides of the web 1 is equal, which has the effect of making the thickness of the coating film uniform on both sides of the web 1.

As described above, since the thickness of the coating film depends on the installation position of the measuring members 102, 102', it is preferable that the coating head 100 is provided with a means (not shown) for moving the measuring members 102, 102' in the thickness direction. An example of such a means is a moving table on which the measuring members 102, 102' are mounted and which can move the measuring members 102, 102' in the thickness direction of the web 1. By providing such a moving means, the thickness of the coating film can be adjusted uniformly and easily with good reproducibility. As a result, the coating head 100 can be installed at the same gap t regardless of the operator. In addition, in order to continuously manufacture the coated web 3, when the seam where the new and old webs 1 are pasted with tape or the like passes through the measuring members 102, 102', the measuring members 102, 102' are moved in the direction in which the gap becomes wider. At that time, it is preferable that the gap between the web 1 and the measuring members 102, 102' moves at the same gap across the web 1.

The thickness of the coating does not depend on the running speed of the web 1, so coating can be done over a wide range of speeds, from low to high.

As described above, by using the coating head of the present invention, a coating film can be formed simultaneously on both sides of a web without causing coating streaks, even when the web running speed is increased. Therefore, a coating web manufacturing device using the coating head of the present invention can manufacture a high-quality coated web without coating streaks.

It is preferable that the application head 100 is composed of the liquid storage members 101, 101' and the measuring members 102, 102', but the liquid storage section 101 and the measuring section 102, and the liquid storage section 101' and the measuring section 102' may each be integral. Also, the liquid storage members 101, 101' and the measuring members 102, 102' may each be composed of multiple parts.

Next, a coated web manufacturing apparatus 4 using the coating head 100 of the present invention will be described with reference to FIG. 5. FIG. 5 is a schematic diagram showing a coated web manufacturing apparatus of the present invention. However, the present invention is not limited to the form shown in the drawing.

As shown in FIG. 5, the coated web manufacturing apparatus 4 using the coating head 100 of the present invention is composed of, in order from the upstream side in the web running direction, an unwinding section 5 that unwinds the web 1, the coating head 100, a post-processing device 7, and a winding section 6 that winds up the web 1, with a transport roller disposed between them. An example of the post-processing device 7 is a dryer for drying and solidifying the coating.

Next, a method for manufacturing a coated web 3 using the coating head 100 of the present invention will be described. The coated web 3 is manufactured by passing the web 1 through the gap between the metering members 102 and 102' after passing through the liquid storage section X of the coating head 100. At this time, the coating liquid 2 stored in the liquid storage section X decreases with application, so the amount of the coating liquid 2 stored is managed, and the coating liquid 2 is supplied to the liquid storage section X to maintain a certain amount or more of storage, thereby stably manufacturing the coated web 3. An example of a means for managing the amount of the coating liquid 2 stored is a method of detecting the liquid level of the coating liquid 2 in the liquid storage section X using a liquid level sensor or the like. An example of a means for supplying the coating liquid 2 is a method of receiving a signal from a liquid level sensor or the like and supplying the coating liquid 2 using a liquid supply pump or the like. However, any of the means is not limited to this method. Furthermore, the supply of the coating liquid 2 may be in the form of a constant supply based on a calculated amount of coating liquid consumed during coating, or in the form of an intermittent supply of a fixed amount of coating liquid 2 only when a liquid level sensor or the like detects that the liquid level has dropped to a predetermined height.

It is also preferable to provide a means for measuring the thickness of the coating film on the traveling web after the coating film is formed by the coating head 100. If the measured coating film thickness does not meet the standard, the gap t between the pair of measuring members 102, 102' can be adjusted to produce a coated web 3 of the desired thickness. Specifically, if the coating film is thicker than the desired thickness, the gap t is narrowed, and if it is thinner, the measuring members 102, 102' are moved in a direction that widens the gap t.

The present invention will be described in more detail below with reference to examples. A coating head 100 shown in Figures 1 and 2 was used to apply coating liquid 2 onto a web 1 having a thickness of 10 μm.

[Example 1]
The measuring member had a shape having a first measuring surface 103, 103', grooves 104, 104', and a second measuring surface 105, 105'. The gap t in the direction perpendicular to the web surface of the measuring section Y1 was 40 μm, and the lengths (L1, L3) of the first measuring surface 103, 103' and the second measuring surface 105, 105' in the web running direction were all 0.3 mm. The grooves 104, 104' had a depth t1 of 0.3 mm and a length L2 in the web running direction of 2 mm. Furthermore, the angle θ between the surfaces 106, 106' and the second measuring surfaces 105, 105' was 30°.

[Example 2]
The same coating head as in Example 1 was used, except that the angle θ between the surfaces 106, 106' and the second metering surfaces 105, 105' was set to 60°.

[Comparative Example 1]
The same coating head as in Example 1 was used, except that the angle θ between the surfaces 106, 106' and the second metering surfaces 105, 105' was set to 90°. That is, in the coating head of Comparative Example 1, the surfaces 106, 106' are not shaped to approach the running surface of the web 1 as they move downstream in the web running direction.

[Comparative Example 2]
The metering member had a shape having only the first metering surfaces 103, 103', without the grooves 104, 104' and the second metering surfaces 105, 105'. The gap t in the direction perpendicular to the web surface of the metering section Y1 was 40 μm, and the length of the first metering surfaces 103, 103' in the web running direction was 2.6 mm.

A coating test was carried out using a coating head having the above-mentioned shape to verify the speed at which coating streaks occur. In addition, fluid analysis was used to derive the pressure value of the high-pressure area P formed between the surface that connects the bottom of the grooves 104, 104' to the boundary with the second metering surface 105, 105' and the web 1. These results are shown in Table 1.

[Comparison between Example 1 and Comparative Example 2]
In Example 1, by forming a high pressure area between the surfaces 106, 106' and the web 1, the speed at which coating streaks occur increased four-fold to 140 m/min compared to 35 m/min in the absence of the grooves 104, 104'.

[Comparison between Example 1 and Comparative Example 1]
In Example 1, the surfaces 106, 106' are formed so as to approach the running surface of the web 1 as they move downstream in the web running direction. This makes the high pressure area between the surfaces 106, 106' and the web 1 about 1.4 times higher. As a result, the expansion of the negative pressure area can be suppressed, and the speed at which coating streaks occur increases from 90 m/min to 140 m/min, about 1.6 times higher.

[Comparison between Example 1 and Example 2]
In Example 1, the angle θ between the surfaces 106, 106' and the second metering surfaces 105, 105' is smaller than that in Example 2. Therefore, the high pressure area between the surfaces 106, 106' and the web 1 is approximately 1.3 times higher. As a result, the expansion of the negative pressure area can be suppressed, and the speed at which coating streaks occur increases from 100 m/min to 140 m/min, which is 1.4 times higher.

Comparing the examples and comparative examples, it was confirmed that by providing grooves 104, 104' in the web width direction in the middle of metering section Y1, and further forming surfaces 106, 106' so that they approach the running surface of web 1 as they move downstream in the running direction of the web, coating streaks can be suppressed and a high-quality coating film can be formed simultaneously on both sides of the web. It was also confirmed that the smaller the angle between surfaces 106, 106' and second metering surfaces 105, 106', the greater the effect of suppressing coating streaks.

The present invention can be applied to a coating head that simultaneously forms a coating film on both sides of a web such as paper, film, thin metal film, or cloth, and to a manufacturing device and manufacturing method for a coated web equipped with the coating head, but is not limited to this.

1 Web 2 Coating liquid 3 Coated web 4 Coated web manufacturing device 5 Unwinding section 6 Winding section 7 Post-processing device 100 Coating head 200 Coating head 101, 101' Liquid storage member 102, 102' Metering member 103, 103' First metering surface 104, 104' Groove 105, 105' Second metering surface 106, 106' Surface 203, 203' continuing from the bottom of the groove to the boundary between the groove and the second metering surface First metering surface X1 Liquid storage section Y1 Metering section Y2 Metering section P High pressure section t Gap t1 in a direction perpendicular to the web surface of the metering section Y Groove depth L1 Length of the first metering surface in the web running direction L2 Length of the groove in the web running direction L3 Length of the second metering surface in the web running direction

Claims (3)

A coating head that simultaneously applies a coating liquid to both sides of a traveling web,
a liquid storage section for storing a coating liquid, the liquid storage section being formed by a pair of liquid storage members facing the web running surface;
a metering section for adjusting the coating film to a desired thickness, the metering section being formed by a pair of metering members disposed opposite each other with a gap therebetween, downstream of the liquid storage section in the web running direction, and sandwiching the web running surface;
The metering member is composed of a first metering surface, a groove, and a second metering surface extending in the web width direction, in this order from the upstream side to the downstream side in the web running direction,
a surface of the groove extending from a bottom of the groove to a boundary between the groove and the second metering surface approaches the web running surface toward the downstream side in the web running direction. A coating web manufacturing device comprising the coating head of claim 1 and a conveying device for conveying the web. A method for producing a coated web, comprising the steps of: using the coating head of claim 1, introducing a web into the gap between the pair of measuring members, passing the web through the gap, depositing the coating liquid stored in the liquid storage section onto both sides of the web, and adjusting the gap between the pair of measuring members to form a coating film on both sides of the web.

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