Coating apparatus

Abstract

To provide a coating apparatus that can form a uniformly coated film.SOLUTION: A coating apparatus 1 according to one embodiment in the present invention comprises: a liquid tank 10 that stores coating liquid L; a gravure roll 20 that is immersed partially in the coating liquid L stored in the liquid tank 10 and is rotated to enable the coating liquid L to adhere to a surface of the roll; a doctor blade 30 that scrapes away excess of the coating liquid L on the surface of the gravure roll 20; and an auxiliary blade 40 that scrapes away portion of the coating liquid L on the surface of the gravure roll 20 so that a film thickness of the coating liquid L is reduced at an upstream side of the doctor blade 30. The auxiliary blade 40 has a plurality of reflux openings 41 through which the coating liquid L scraped away by the doctor blade 30 is refluxed to the liquid tank 10.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a coating device. [Background technology]

[0002] A coating device is widely used in which a coating liquid is applied to the outer peripheral surface of a rotating gravure roll and excess coating liquid is scraped off from the outer peripheral surface of the gravure roll with a doctor blade. When the viscosity of the coating liquid is high, a large amount of the coating liquid adheres to the outer peripheral surface of the gravure roll, and a single doctor blade alone cannot scrape off the excess coating liquid, which may result in unevenness or streaks in the coating film. Therefore, a technology has been proposed in which two doctor blades are provided to ensure the scraping off of excess coating liquid (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-109168 Summary of the Invention [Problem to be solved by the invention]

[0004] When two doctor blades are provided, the amount of coating liquid scraped off by the doctor blade downstream of the gravure roll in the direction of rotation is small. As a result, the scraped coating liquid remains at the tip of the doctor blade for a relatively long time, which can cause particles contained in the coating liquid to condense or the coating liquid to become concentrated due to solvent evaporation. If such condensation or concentration occurs, the condensate or concentrate can get between the gravure roll and the doctor blade, preventing the doctor blade from scraping off the coating liquid and causing unevenness or streaks in the coating film. Therefore, an object of the present invention is to provide a coating device capable of forming a uniform coating film. [Means for solving the problem]

[0005] (1) A coating device according to one aspect of the present invention includes a liquid tank for storing a coating liquid, a gravure roll that is partially immersed in the coating liquid stored in the liquid tank and rotates to deposit the coating liquid on its surface, a doctor blade that scrapes off excess coating liquid from the surface of the gravure roll, and an auxiliary blade that scrapes off part of the coating liquid from the surface of the gravure roll upstream of the doctor blade to reduce the film thickness of the coating liquid, and the auxiliary blade has a plurality of return openings that return the coating liquid scraped off by the doctor blade to the liquid tank.

[0006] (2) The coating device of (1) may have a guide structure that guides the coating liquid scraped off by the doctor blade to the reflux opening.

[0007] (3) In the coating device of (2), the guide structure may be a recessed portion formed in the upper surface of the auxiliary blade.

[0008] (4) In the coating device of (3), the recessed portion may be formed so as to be open over the entire length of the leading edge of the auxiliary blade.

[0009] (5) In the coating device according to any one of (1) to (4), the auxiliary blade may be made of fluororesin. [Effects of the Invention]

[0010] According to the present invention, a uniform coating film can be formed. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view showing a configuration of a coating apparatus according to a first embodiment of the present invention. [Figure 2] 2 is a partially enlarged perspective view of an auxiliary blade of the coating device of FIG. 1. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. For convenience, hatching and component reference numerals may be omitted. In such cases, reference should be made to other drawings. Furthermore, the dimensions of various components in the drawings have been adjusted for clarity.

[0013] First Embodiment Fig. 1 is a cross-sectional view showing the configuration of a coating device 1 according to a first embodiment of the present invention. The coating device 1 includes a liquid tank 10, a gravure roll 20, a doctor blade 30, and an auxiliary blade 40. The coating device 1 transfers a coating liquid L adhered to the surface of the gravure roll 20 onto an object to be coated S. In Fig. 1, the coating device 1 is arranged so that the gravure roll 20 faces a transport roll (backup roll) R that transports the web-like object to be coated S, but the object to be coated S and the method of transporting it are not particularly limited.

[0014] The liquid tank 10 stores the coating liquid L. There are no particular limitations on the coating liquid L, but the effects of the present invention become more pronounced when a liquid with a relatively high viscosity or a liquid containing a highly volatile solvent is used, specifically when the viscosity is 20 cp or more and the particle content is 1 mass % or more. The configuration of the liquid tank 10 can be the same as that of a liquid tank in a conventional gravure coating device.

[0015] The gravure roll 20 is partially immersed in the coating liquid L stored in the liquid tank 10, and rotates to apply the coating liquid L to its surface. The gravure roll 20 may have an uneven surface formed thereon to hold the coating liquid L. The configuration of the gravure roll 20 may be the same as that of a gravure roll in a conventional gravure coating device.

[0016] The doctor blade 30 scrapes off excess coating liquid L from the surface of the gravure roll 20. At least the tip of the doctor blade 30 is formed in a strip shape, and is held parallel to the rotation axis of the gravure roll 20 so that the tip contacts the surface of the gravure roll 20. The doctor blade 30 is held at an angle with respect to the surface of the gravure roll 20 so that the distance between the doctor blade 30 and the gravure roll 20 decreases toward the downstream side in the direction of rotation of the gravure roll 20 (the closer it is to the gravure roll). The doctor blade 30 is preferably positioned higher than the rotation axis of the gravure roll 20 and abuts at a position upstream of the apex in the direction of rotation. This allows the coating liquid L drawn by the doctor blade 30 to flow down along the surface of the gravure roll 20, making it easy to return it to the liquid tank 10. The detailed configuration of the doctor blade 30 can be similar to that of doctor blades in conventional gravure coating devices.

[0017] The auxiliary blade 40 scrapes off a portion of the coating liquid L from the surface of the gravure roll 20 upstream of the doctor blade 30 to reduce the coating liquid film thickness. For this reason, the auxiliary blade 40 is held with a gap between it and the gravure roll 20. The gap between the auxiliary blade 40 and the gravure roll 20 may be, for example, 1 μm or more and 2 mm or less, depending on the viscosity of the coating liquid L and other factors. If the gap between the auxiliary blade 40 and the gravure roll 20 is too small, the amount of coating liquid L supplied to the tip of the doctor blade 30 will be reduced, which may lead to particle aggregation or concentration of the coating liquid L. Furthermore, if the gap between the auxiliary blade 40 and the gravure roll 20 is too large, the doctor blade 30 will not be able to scrape off the excess coating liquid L, which may result in uneven coating.

[0018] As shown in detail in Fig. 2, the auxiliary blade 40 has a plurality of reflux openings 41 that serve as flow paths for returning the coating liquid L scraped off by the doctor blade 30 to the liquid tank 10. In addition, a recessed portion 42 is formed on the upper surface of the auxiliary blade 40 as a guide structure for guiding the coating liquid L scraped off by the doctor blade 30 to the reflux openings 41. The auxiliary blade 40 is preferably made of a material that has low wettability with the coating liquid L, such as a fluororesin such as PTFE, so that the coating liquid L can be quickly returned to the liquid tank 10 through the reflux openings 41. In addition, fluororesin has high resistance to organic solvents that the coating liquid L may contain.

[0019] The auxiliary blade 40 is disposed at an incline so that the position of the leading edge closest to the gravure roll 20 is higher. This allows the coating liquid L that has been scraped off by the doctor blade 30 and flowed down the gravure roll 20 to quickly flow into the reflux opening 41. The auxiliary blade 40 may be fixed to the edge of the liquid tank 10, for example.

[0020] The reflux openings 41 are preferably formed dispersedly at positions set back from the leading edge so as not to impair the strength of the leading edge close to the gravure roll 20. The reflux openings 41 are preferably formed in a row aligned in a direction parallel to the rotation axis of the gravure roll 20 so as to facilitate the arrival of the coating liquid L. The opening ratio of the reflux openings 41 on the center line of the row of reflux openings 41 can be set to 50% or more and 80% or less so as to ensure the strength of the auxiliary blade 40 and to facilitate the reflux of the coating liquid L. Furthermore, it is preferable that each reflux opening 41 has a sufficiently large width in the direction perpendicular to the center line of the row so as to facilitate the passage of the coating liquid L. A specific opening width of the reflux openings 41 can be, for example, 20 mm or more and 50 mm or less.

[0021] The sunken portion 42 is a recess that serves as a flow path for the coating liquid L scraped off by the doctor blade 30. To reliably guide the coating liquid L scraped off by the doctor blade 30 to the reflux opening 41, the sunken portion 42 preferably selectively opens to each of the reflux openings 41 at the base end of the auxiliary blade 40 and extends along the entire length of the distal end of the auxiliary blade 40. The depth of the sunken portion 42 is set to a depth that prevents the coating liquid L scraped off by the doctor blade 30 from overflowing, and may be, for example, 1 mm to 5 mm, depending on the viscosity of the coating liquid L, etc. Therefore, the thickness of the auxiliary blade 40 may be set to 3 mm to 10 mm. The distal end of the auxiliary blade 40 may have a tapered thickness that decreases toward the distal end.

[0022] In the coating device 1 having the above configuration, the auxiliary blade 40 first reduces the thickness of the coating liquid L on the surface of the gravure roll 20, preventing the supply of an amount of coating liquid L that exceeds the scraping capacity of the doctor blade 30. This reduces coating unevenness. Furthermore, in the coating device 1, the coating liquid L scraped off by the doctor blade 30 is returned to the liquid tank 10 through the return opening 41 of the auxiliary blade 40. This allows the gap between the auxiliary blade 40 and the gravure roll 20 to be increased so that a larger amount of coating liquid L is scraped off by the doctor blade 30, without exceeding the scraping capacity of the doctor blade 30. This allows the coating liquid L scraped off by the doctor blade 30 to be quickly returned to the liquid tank 10, shortening the residence time of the coating liquid L outside the liquid tank 10. This suppresses aggregation of particle components of the coating liquid L and concentration due to evaporation of the solvent of the coating liquid L, preventing coating unevenness caused by aggregates or concentrates being trapped at the tip of the doctor blade 30.

[0023] Although the present invention has been described above as an embodiment, it is not limited to the above embodiment and various modifications and variations are possible. For example, in the coating device according to the present invention, the guide structure that guides the coating liquid scraped by the doctor blade to the reflux opening may be formed by, for example, a wall-like or block-like member protruding from the plate forming the auxiliary blade. Alternatively, the guide structure may be omitted by forming reflux openings in another row on the auxiliary blade to prevent the coating liquid from passing through to the base end. Furthermore, depending on the inclination and wettability of the doctor blade, the coating liquid may flow down the underside of the doctor blade. Therefore, a protruding guide structure may be provided on the underside of the doctor blade to guide the coating liquid to the reflux opening, or a hopper-shaped guide structure, for example, may be provided between the doctor blade and the auxiliary blade to guide the coating liquid to the reflux opening. [Explanation of symbols]

[0024] 1 Coating device 10 Liquid tank 20 Gravure Roll 30 Doctor Blade 40 Auxiliary Blade 41 Reflux opening 42 Depression S Application target R transport roll

Claims

1. a liquid tank for storing a coating liquid; a gravure roll that is partially immersed in the coating liquid stored in the liquid tank and rotates to deposit the coating liquid on its surface; a doctor blade that scrapes off excess coating liquid from the surface of the gravure roll; an auxiliary blade that scrapes off a portion of the coating liquid on the surface of the gravure roll so as to reduce a film thickness of the coating liquid on the upstream side of the doctor blade; Equipped with The auxiliary blade has a plurality of return openings for returning the coating liquid scraped off by the doctor blade to the liquid tank.

2. The coating device according to claim 1 , further comprising a guide structure for guiding the coating liquid scraped off by the doctor blade to the return opening.

3. The coating device according to claim 2 , wherein the guide structure is a recessed portion formed on an upper surface of the auxiliary blade.

4. The coating device according to claim 3 , wherein the recessed portion is formed so as to be open over the entire length of the leading edge of the auxiliary blade.

5. The coating device according to claim 1 , wherein the auxiliary blade is made of a fluororesin.

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