Liquid coating apparatus, liquid coating method, and method for manufacturing painted metal strip

Abstract

The present invention provides a liquid coating technology that can suppress coating defects caused by uneven film thickness. The liquid coating apparatus comprises a pair of rolls for coating both sides of a metal strip that is continuously passed horizontally, and a liquid ejection nozzle for ejecting liquid into the space between the rolls and the metal strip at the entry side of the rolls, wherein the central axes of each of the pair of rolls are offset in the direction of transport of the metal strip, and the pair of rolls are positioned to press the metal strip. The present invention also provides a liquid coating method for coating both sides of a metal strip that is continuously passed horizontally using a pair of rolls, wherein the liquid is ejected into the space between the rolls and the metal strip at the entry side of the rolls, the central axes of the pair of rolls are offset in the direction of transport of the metal strip, and the liquid is applied to the metal strip while the metal strip is pressed by the pair of rolls.

Description

Technical Field

[0001] The present invention relates to a liquid coating apparatus for applying a liquid to a metal strip continuously passed horizontally using a roll coater, a method for applying the liquid, and a method for manufacturing a coated metal strip.

Background Art

[0002] Conventionally, a treatment has been performed to form a coating film by applying a coating liquid having various physical properties to the surface of a metal strip such as a steel sheet continuously passed through, and to impart properties such as corrosion resistance, workability, aesthetics, and insulation to the metal strip. As a liquid coating apparatus for performing this treatment method, a roll coater is generally used. In the method for applying a liquid using a roll coater, depending on the properties of the coating liquid, the type of metal strip, and the surface state of the metal strip, appearance defects due to uneven film thickness may occur. Defects of uneven film thickness include liquid breakage such as streaks and no coating caused by insufficient supply of the paint, and overcoating due to over-supply of the paint, such as overcoating.

[0003] As a technique for solving this problem, for example, Patent Document 1 discloses a coating method for a strip-shaped body in which a precoat nozzle is disposed immediately before an applicator roll of a roll coater method. In Patent Document 1, the precoat nozzle is provided with a slit-shaped opening extending in the width direction of the strip-shaped body, and the length of the slit-shaped opening is made narrower than the width of the strip-shaped body to supply the precoat liquid. Thereby, even if there is a width fluctuation of the strip-shaped body, it is possible to supply the precoating liquid uniformly in the width direction and realize a uniform wet state.

[0004] Furthermore, Patent Document 2 discloses a method for painting a metal strip, in which paint is sprayed onto a moving metal strip using a pre-coat nozzle having a nozzle opening to perform pre-coating, and then paint is applied to the pre-coated metal strip by a roll to perform main coating. In Patent Document 2, an edge mask that slides in the width direction of the metal strip and partially covers the nozzle opening is positioned near both ends of the nozzle opening. Based on the edge shape of the metal strip, the edge mask is slid to adjust the position of the paint spray nozzle and the opening width in the width direction of the metal strip, which are determined by the nozzle opening and the edge mask.

[0005] Furthermore, Patent Document 3 discloses a method for uniformly applying a liquid to a steel sheet, which involves continuously supplying a surface treatment liquid to the front and back surfaces of a vertically moving steel sheet before or after a plating process. In Patent Document 3, during application, a coating is first performed to adjust the average application amount, and then the application amount is made uniform by using a leveling roll or by spraying a gaseous fluid perpendicular to the steel sheet surface. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2005-246313 [Patent Document 2] Japanese Patent Publication No. 2012-217982 [Patent Document 3] Japanese Patent Publication No. 2002-126614 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, while the coating method described in Patent Document 1 above can prevent overcoating, i.e., excessive coating, at the edges of the metal strip width due to changes in the strip width, it may result in appearance defects depending on the shape of the metal strip.

[0008] Furthermore, according to the method described in Patent Document 2, poor film thickness caused by edge stretching can be improved. However, the inventor's investigation revealed that even when using the coating apparatus described in Patent Document 2, defects such as excessive coating due to overcoating or liquid drying due to no coating can still occur in the metal strip, particularly at the edges of the metal strip's width, due to pre-coating.

[0009] Furthermore, it was found that in the method described in Patent Document 3, the surface treatment liquid drips vertically downward, causing interference between the surface treatment liquids, which can result in defects such as excessive coating due to overcoating or liquid shortage due to no coating on the metal strip.

[0010] This invention has been made in view of the problems of the prior art, and its purpose is to provide a liquid coating apparatus, a coating method, and a method for manufacturing a coated metal strip that can suppress coating defects due to uneven film thickness when applying a liquid to a continuously passing metal strip using a roll coater. [Means for solving the problem]

[0011] The means to solve the above problems are as follows: [1] A pair of rolls for applying liquid to both sides of a metal strip that is continuously passed horizontally, The device includes a liquid ejection nozzle that ejects liquid into the space between the roll and the metal strip at the entry side of the roll, The central axes of each of the pair of rolls are positioned offset in the direction of conveying the metal strip. The aforementioned pair of rolls are arranged to press the metal strip into the liquid coating device. [2] A method for applying liquid to both sides of a metal strip that is continuously passed horizontally, using a pair of rolls, A liquid is sprayed into the space between the roll and the metal strip at the entry side of the roll. The central axes of the pair of rolls are positioned offset from each other in the direction of conveying the metal strip, While pressing the metal strip with the pair of rolls, This is a method for applying a liquid to the metal strip. [3] A method for manufacturing a painted metal strip, comprising the step of applying a liquid to a metal strip by the liquid application method described in [2] above. [Effects of the Invention]

[0012] By using the liquid coating apparatus and liquid coating method according to the present invention, coating defects caused by uneven film thickness of the liquid can be suppressed, and a coated metal strip with a good coating appearance can be manufactured. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic diagram showing a liquid coating apparatus according to this embodiment. [Modes for carrying out the invention]

[0014] The embodiments of the present invention will be described in detail below. Note that the drawings are schematic and may differ from actual examples. Furthermore, the following embodiments are illustrative examples of devices and methods for realizing the technical concept of the present invention, and do not limit the configuration to those described below. In other words, the technical concept of the present invention can be modified in various ways within the technical scope described in the claims.

[0015] The inventor has intensively studied to solve the above problems. As a result, it has been found that uneven film thickness such as overcoat (excessive coating) and non-coating (liquid breakage) caused by the application of liquid to the metal strip is due to shape defects such as ear elongation and C warp of the metal strip. And in order to prevent the above uneven film thickness, it is effective to arrange the central axes of a pair of applicator rolls shifted in the conveying direction of the metal strip, push the metal strip by the applicator rolls, and apply the liquid by the liquid ejection nozzle and the applicator roll while winding the metal strip around the applicator roll. Based on this, the present invention has been developed. Hereinafter, the present invention will be described through embodiments of the present invention.

[0016] FIG. 1 is a schematic diagram showing a liquid coating apparatus 10 according to the present embodiment. The liquid coating apparatus 10 according to the present embodiment will be described with reference to FIG. 1.

[0017] The liquid coating apparatus 10 according to the present embodiment includes an upper roll coater apparatus 31 and a lower roll coater apparatus 32. The upper roll coater apparatus 31 is installed on the upper surface side of a metal strip 24 that is continuously passed through in the horizontal direction, and the lower roll coater apparatus 32 is installed on the lower surface side of the metal strip 24. Hereinafter, the passing direction of the metal strip 24 may be referred to as the "conveying direction FD". The metal strip also extends in the width direction substantially horizontally.

[0018] The upper roll coater device 31 includes an upper paint receiving pan 21, an upper pickup roll 312, an upper metering roll 313, an upper applicator roll 311, and an upper liquid ejection nozzle 41. The upper paint receiving pan 21 stores the coating liquid P. The upper pickup roll 312 pumps up the coating liquid P from the upper paint receiving pan 21. The upper metering roll 313 adjusts the amount of the coating liquid P adhering to the surface of the upper pickup roll 312. The upper applicator roll 311 receives the coating liquid P from the upper pickup roll 312 and transfers the coating liquid P to the surface of the metal strip 24. The upper liquid ejection nozzle 41 is arranged to eject the liquid 411 from the upper surface side of the inlet side of the metal strip 24 into the space sandwiched between the metal strip 24 and the upper applicator roll 311.

[0019] Also, the lower roll coater device 32 includes a lower paint receiving pan 22, a lower pickup roll 322, a lower metering roll 323, a lower applicator roll 321, and a lower liquid ejection nozzle 42. The lower paint receiving pan 22 stores the coating liquid P. The lower pickup roll 322 pumps up the coating liquid P from the lower paint receiving pan 22. The lower metering roll 323 adjusts the amount of the coating liquid P adhering to the surface of the lower pickup roll 322. The lower applicator roll 321 receives the coating liquid P from the lower pickup roll 322 and transfers the coating liquid P to the surface of the metal strip 24. The lower liquid ejection nozzle 42 is arranged to eject the liquid 422 from the lower surface side of the inlet side of the metal strip 24 into the space sandwiched between the metal strip 24 and the lower applicator roll 321.

[0020] The upper liquid ejection nozzle 41 and the lower liquid ejection nozzle 42 are not limited to nozzles such as spray nozzles and slit nozzles, and any structure may be used as long as it can supply liquid. In the present embodiment, a spray nozzle is used from the viewpoint of ease of supplying liquid.

[0021] The liquid ejection direction of the upper liquid ejection nozzle 41 is preferably the same direction as the conveying direction FD of the metal strip 24 and is diagonally downward, as shown in Figure 1. This makes it easier to eject the liquid 411 into the space between the upper applicator roll 311 and the metal strip 24. Similarly, the liquid ejection direction of the lower liquid ejection nozzle 42 is preferably the same direction as the conveying direction FD of the metal strip 24 and is diagonally upward, as shown in Figure 1. This makes it easier to eject the liquid 422 into the space between the lower applicator roll 321 and the metal strip 24.

[0022] The angle θ between the liquid ejection direction of the upper liquid ejection nozzle 41 and the coated surface of the metal strip 24 is preferably within the range of 10° to 45°. Similarly, the angle between the liquid ejection direction of the lower liquid ejection nozzle 42 and the coated surface of the metal strip 24 is preferably within the same range. By arranging the upper liquid ejection nozzle 41 and the lower liquid ejection nozzle 42 at such angles, each liquid ejection nozzle is separated from the metal strip 24, making it less susceptible to vibrations when the metal strip 24 vibrates, and making it easier to eject liquid into the space between each roll 311, 321 and the metal strip 24. It is more preferable that the angle θ between the liquid ejection direction of each liquid ejection nozzle 41, 42 and the coated surface of the metal strip 24 is within the range of 15° to 30°. Each liquid ejection nozzle 41, 42 is positioned such that the liquid ejection direction is set within a range of 10° to 45°, and the liquid ejected at that angle does not directly collide with the upper pickup roll 312 or the lower pickup roll 322. In other words, the liquids 411, 422 ejected from each nozzle 41, 42 are arranged to collide with the metal strip 24, respectively.

[0023] Furthermore, the distance L from the tip of the upper liquid ejection nozzle 41 to the point of impact of the liquid is preferably within the range of 10 mm to 200 mm. Similarly, the distance from the tip of the lower liquid ejection nozzle 42 to the point of impact of the liquid is preferably within the same range. By setting the distance L from the tip of each nozzle to the point of impact of the liquid to within the range of 10 mm to 200 mm, each liquid ejection nozzle is separated from the metal strip 24, making it less susceptible to the vibration of the metal strip 24. At the same time, it becomes easier to eject the liquid into the space sandwiched between each roll and the metal strip 24. It is more preferable that the distance L from the tip of each nozzle to the point of impact of the liquid is within the range of 20 mm to 100 mm. The distance L from the tip of the upper liquid ejection nozzle 41 to the point of impact of the liquid is the distance from the tip of the nozzle to the metal strip 24 in the liquid ejection direction for each liquid ejection nozzle 41, 42.

[0024] The upper pickup roll 312 and the lower pickup roll 322 are preferably made of metal, and more preferably metal with a chrome-plated surface. The roll diameters of the upper pickup roll 312 and the lower pickup roll 322 are preferably in the range of 100 to 300 mm. The nip pressure of each pickup roll 312 and 322 relative to the upper applicator roll 311 and the lower applicator roll 321 is preferably in the range of 9.8 to 98 N / cm (1 to 10 kgf / cm), respectively. Furthermore, the rotation direction of the upper pickup roll 312 and the lower pickup roll 322 is preferably the same as the rotation direction of the upper applicator roll 311 and the lower applicator roll 321. By making the rotation direction of the upper pickup roll 312 and the lower pickup roll 322 the same as the rotation direction of the upper applicator roll 311 and the lower applicator roll 321, the occurrence of streaky appearance defects called living patterns can be suppressed.

[0025] The upper paint receiving pan 21 is an open tray at the top, with the upper pickup roll 312 located directly above it. The height of the lower end of the upper pickup roll 312 is below the liquid level of the coating liquid P in the upper paint receiving pan 21. The upper paint receiving pan 21 is connected to a coating liquid tank (not shown) via a supply line (not shown), and a constant amount of coating liquid P is supplied to it at all times, maintaining a constant liquid level. The bottom of the upper paint receiving pan 21 has a coating liquid P outlet (not shown) which is connected to a return line (not shown) that returns the coating liquid P to the coating liquid tank.

[0026] The lower paint receiving pan 22 is an open tray at the top, with the lower pickup roll 322 located directly above it. The height of the lower end of the lower pickup roll 322 is below the liquid level of the coating liquid P in the lower paint receiving pan 22. The lower paint receiving pan 22 is connected to a coating liquid tank (not shown) via a supply line (not shown), and a constant amount of coating liquid P is supplied to it at all times, maintaining a constant liquid level. The bottom of the lower paint receiving pan 22 also has a coating liquid P outlet (not shown) which is connected to a return line (not shown) that returns the coating liquid P to the coating liquid tank.

[0027] The upper metering roll 313 and the lower metering roll 323 are preferably made of metal, and are particularly preferably made of metal with a chrome-plated surface. Furthermore, the roll diameters of the upper metering roll 313 and the lower metering roll 323 are preferably 50 to 100 mm, and they are preferably positioned close to the upper pickup roll 312 and the lower pickup roll 322 with a predetermined gap between them. In addition, the rotation direction of the upper metering roll 313 and the lower metering roll 323 is preferably the same as the rotation direction of the upper pickup roll 312 and the lower pickup roll 322. By making the rotation direction of the upper metering roll 313 and the lower metering roll 323 the same as the rotation direction of the upper pickup roll 312 and the lower pickup roll 322, the amount of coating liquid P adhering to the surface of the upper pickup roll 312 and the lower pickup roll 322 can be adjusted.

[0028] The upper applicator roll 311 and the lower applicator roll 321 are preferably made of rubber, and in particular, rubber selected from urethane rubber, nitrile rubber, and Hypalon rubber, which have excellent abrasion resistance, is preferred. The roll diameter of the upper applicator roll 311 and the lower applicator roll 321 is preferably 100 to 300 mm. The nip pressure of each applicator roll 311 and 312 on the metal strip 24 is preferably in the range of 9.8 to 98 N / cm (1 to 10 kgf / cm), respectively. Furthermore, the rotation direction of the upper applicator roll 311 and the lower applicator roll 321 is preferably in the opposite direction to the conveying direction FD of the metal strip 24. By rotating the upper applicator roll 311 and the lower applicator roll 321 in the opposite direction to the conveying direction FD of the metal strip 24, the occurrence of streak-like pattern defects called living can be suppressed.

[0029] It is preferable to position the upper applicator roll 311 and the lower applicator roll 321 with their central axes offset in the transport direction FD of the metal strip 24. By offsetting their central axes, the upper applicator roll 311 and the lower applicator roll 321 can press the metal strip 24 into them, allowing the liquid to be applied while the metal strip 24 is wrapped around the upper applicator roll 311 and the lower applicator roll 321. As an example, it is preferable to position the upper applicator roll 311 and the lower applicator roll 321 with their respective central axes offset in the transport direction FD by a range of 40 mm to 150 mm. It is even more preferable to position the central axes of each roll 311 and 321 offset in the transport direction FD by a range of 80 mm to 100 mm. The amount of indentation Δt by the upper applicator roll 311 and the lower applicator roll 321 is preferably in the range of 3 mm to 10 mm in the vertical direction, for example, when the metal strip 24 is passed through in a straight line, with the dashed line in Figure 1 as the reference (0 mm). [Examples]

[0030] Next, an example will be described. As an example of the invention, in Test No. 1, a coated metal strip was manufactured using the liquid coating apparatus 10 shown in Figure 1. The specifications of the liquid coating apparatus used in the test are as follows: The angle θ between the liquid ejection direction of the liquid ejection nozzle and the coated surface of the metal strip 24 was 20° in all cases. The distance L from the tip of the liquid ejection nozzle to the point of impact of the liquid was 50 mm in all cases. The roll diameter of the pickup roll was 100 mm in all cases. The nip pressure between the pickup roll and the applicator roll was 49 N / cm (5 kgf / cm) in all cases. The roll diameter of the metering roll was 80 mm in all cases. The roll diameter of the applicator roll was 200 mm in all cases. The nip pressure of the applicator roll on the metal strip 24 was 49 N / cm (5 kgf / cm) in all cases. The rotation direction of each roll was the same and was opposite to the conveying direction FD of the metal strip 24. The upper and lower applicator rolls were positioned with their respective central axes offset by 100 mm in the conveying direction FD. The indentation amount Δt by each applicator roll was 5 mm, with the case where the metal strip 24 was passed in a straight line being the baseline (0 mm). In contrast, as a comparative example, painted metal strips were manufactured in Tests No. 2 to 4 using the coating apparatus disclosed in Patent Documents 1, 2, and 3, respectively. In all tests, cold-rolled steel strip was used for the metal strip 24, and an insulating coating liquid mainly composed of colloidal silica and phosphate was used as the coating solution.

[0031] Table 1 shows the defect rates due to painting defects under each painting condition. Painting defects were evaluated for overcoat (excessive application), no-coat (lack of liquid), and overall. In Test No. 1, the defect rate was lower than in Tests No. 2-4. This confirmed the effectiveness of the present invention.

[0032] [Table 1] [Explanation of symbols]

[0033] 10 Liquid coating apparatus 21 Upper paint receiving pan 22 Lower paint receiving pan 24 Metal strip 31 Upper Roll Coater Device 311 Top Applicator Roll 312 Upper Pickup Roll 313 Upper metering roll 32 Lower Roll Coater Device 321 Lower Applicator Roll 322 Lower Pickup Roll 323 Lower Metering Roll 41 Upper liquid spray nozzle 411 (Liquid ejected from the upper liquid nozzle) 42 Lower liquid spray nozzle 422 (Liquid ejected from the lower liquid nozzle) P coating liquid FD (metal strip) transport direction

Claims

1. A pair of rolls for applying liquid to both sides of a metal strip that is continuously passed horizontally, The device includes a liquid ejection nozzle that ejects liquid into the space between the roll and the metal strip at the entry side of the roll, The rotation direction of at least the roll in contact with the metal strip among the pair of rolls is opposite to the direction of travel of the metal strip. The central axes of each of the pair of rolls are positioned offset in the direction of conveying the metal strip. A liquid coating apparatus in which the pair of rolls are arranged to press the metal strip.

2. A method for applying liquid to both sides of a metal strip that is continuously passed horizontally, using a pair of rolls, A liquid is sprayed into the space between the roll and the metal strip at the entry side of the roll. At least one of the pair of rolls that is in contact with the metal strip rotates in the opposite direction to the direction of travel of the metal strip. The central axes of the pair of rolls are positioned offset from each other in the direction of conveying the metal strip, While pressing the metal strip with the pair of rolls, A method for applying a liquid to a metal strip.

3. A method for manufacturing a painted metal strip, comprising the step of applying a liquid to the metal strip by the liquid application method described in claim 2.

Images