Liquid coating device, liquid coating method, and method for manufacturing coated metal strip

Abstract

The present invention provides a liquid coating technology capable of suppressing coating defects caused by uneven film thickness. Provided is a liquid coating device having: a pair of rolls for applying a liquid to both surfaces of a metal strip continuously passed in a horizontal direction; and liquid ejection nozzles for ejecting the liquid into spaces sandwiched between the rolls and the metal strip on the inlet sides of the rolls. The central axes of the pair of rolls are arranged so as to be shifted in a transport direction of the metal strip, and the pair of rolls are arranged so as to push the metal strip. The present invention also pertains to a liquid coating method for applying a liquid, using a pair of rolls, to both surfaces of a metal strip continuously passed in a horizontal direction. The liquid coating method comprises: ejecting the liquid into spaces sandwiched between the rolls and the metal strip on the inlet sides of the rolls; arranging the central axes of the pair of rolls so as to be shifted in a transport direction of the metal strip; and applying the liquid to the metal strip while pushing the metal strip by using the pair of rolls.

Description

Liquid application device, liquid application method, and method for manufacturing coated metal strip

[0001] The present invention relates to a liquid application device that uses a roll coater to apply a liquid to a metal strip that is continuously passed horizontally, a liquid application method, and a method for manufacturing a coated metal strip.

[0002] Conventionally, coating liquids with various physical properties are applied to the surface of continuously passing metal strips, such as steel sheets, to form coating films, thereby imparting properties such as corrosion resistance, workability, aesthetics, and insulation to the metal strips. A roll coater is typically used as the liquid application device for this treatment. Liquid application methods using a roll coater can result in poor appearance due to uneven film thickness, depending on the properties of the coating liquid, the type of metal strip, and the surface condition of the metal strip. Examples of defects resulting from uneven film thickness include liquid shortages, such as smearing or no coating, due to insufficient paint supply, and overcoating due to overcoating, which is caused by an excessive supply of paint.

[0003] As a technique for solving this problem, for example, Patent Document 1 discloses a method for coating a strip in which a precoat nozzle is disposed immediately before the applicator roll of a roll coater. In Patent Document 1, the precoat nozzle is provided with a slit-shaped opening extending in the width direction of the strip, and the length of the slit-shaped opening is narrower than the width of the strip to supply the precoat liquid. As a result, even if the width of the strip varies, the precoat liquid can be supplied uniformly in the width direction, achieving a uniform wetting state.

[0004] Furthermore, Patent Document 2 discloses a metal strip coating method in which a precoat nozzle having a nozzle opening is used to spray paint onto a traveling metal strip to perform a preliminary coating, and then a roll is used to apply paint to the precoated metal strip to perform a main coating. In Patent Document 2, an edge mask that slides in the width direction of the metal strip and partially closes the nozzle opening is disposed near both ends of the nozzle opening. Then, the edge mask is slid based on the edge extension shape of the metal strip to adjust the position of the paint spray port 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, in which a surface treatment liquid is continuously supplied and applied to the front and back surfaces of a steel sheet traveling in a vertical direction before or after a plating process. In Patent Document 3, during application, 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 gas fluid from a direction perpendicular to the steel sheet surface.

[0006] JP 2005-246313 A JP 2012-217982 A JP 2002-126614 A

[0007] However, although the coating method of Patent Document 1 can prevent overcoating of the widthwise ends of the metal strip due to changes in the strip width, i.e., excessive coating, depending on the shape of the metal strip, poor appearance may occur.

[0008] Furthermore, the method of Patent Document 2 can improve film thickness defects caused by edge growth. However, according to research by the inventors, it was found that even when the coating device described in Patent Document 2 is used, defects such as excessive coating due to overcoating or liquid shortage due to no coating can occur on the metal strip, particularly on the widthwise end portions of the metal strip, due to pre-coating.

[0009] Furthermore, in the method of Patent Document 3, the surface treatment solution drips vertically downward, causing interference between the surface treatment solutions, which can result in defects such as excessive application of an overcoat to the metal strip or lack of solution due to no coating.

[0010] The present invention has been made in consideration of the problems of the prior art, and its object is to provide a liquid application device, application method, and method for manufacturing coated metal strip that can suppress coating defects due to uneven film thickness when applying liquid to a continuously passing metal strip using a roll coater.

[0011] The means for solving the above problems are as follows: [1] A liquid application device including a pair of rolls that apply liquid to both sides of a metal strip that is continuously passed horizontally, and a liquid ejection nozzle that ejects liquid into a space between the rolls and the metal strip on the entrance side of the rolls, the central axes of the pair of rolls being arranged to be offset in the transport direction of the metal strip, and the pair of rolls being arranged to push the metal strip. [2] A liquid application method that uses a pair of rolls to apply liquid to both sides of a metal strip that is continuously passed horizontally, the liquid being ejected into a space between the rolls and the metal strip on the entrance side of the rolls, the central axes of the pair of rolls being offset in the transport direction of the metal strip, and the liquid being applied to the metal strip while being pushed by the pair of rolls. [3] A method for producing a coated metal strip, including a step of applying liquid to the metal strip by the liquid application method described in [2] above.

[0012] By using the liquid application device and liquid application method according to the present invention, coating defects due to uneven liquid film thickness can be suppressed, and a coated metal strip with a good coating appearance can be produced.

[0013] 1 is a schematic diagram showing a liquid application apparatus according to an embodiment of the present invention;

[0014] Hereinafter, embodiments of the present invention will be described in detail. Note that the drawings are schematic and may differ from the actual embodiments. Furthermore, the following embodiments exemplify devices and methods for embodying the technical idea of ​​the present invention, and are not intended to limit the configuration to the following. In other words, the technical idea of ​​the present invention can be modified in various ways within the technical scope described in the claims.

[0015] The inventors conducted extensive research to solve the above-mentioned problems. As a result, they found that film thickness unevenness, such as overcoating (excessive application) or no-coating (lack of liquid) caused by applying a liquid to a metal strip, is caused by defects in the shape of the metal strip, such as edge elongation and C-warping. They then discovered that an effective way to prevent the above-mentioned film thickness unevenness is to displace the central axes of a pair of applicator rolls in the conveying direction of the metal strip, press the metal strip with the applicator rolls, and apply the liquid with a liquid ejection nozzle and the applicator roll while the metal strip is being wound around the applicator roll, leading to the development of the present invention. The present invention will be described below through embodiments of the present invention.

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

[0017] The liquid application device 10 according to this embodiment has an upper roll coater device 31 and a lower roll coater device 32. The upper roll coater device 31 is installed on the upper surface side of the metal strip 24, which is continuously passed through in the horizontal direction, and the lower roll coater device 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 "transport direction FD." The width direction of the metal strip also extends in a substantially horizontal direction.

[0018] The upper roll coater device 31 comprises 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 jet nozzle 41. The upper paint receiving pan 21 stores a coating liquid P. The upper pickup roll 312 draws up the coating liquid P from the upper paint receiving pan 21. The upper metering roll 313 adjusts the amount of 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 jet nozzle 41 is positioned so as to jet liquid 411 from the inlet upper surface of the metal strip 24 into the space between the metal strip 24 and the upper applicator roll 311.

[0019] The lower roll coater device 32 also includes a lower coating material 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 coating material receiving pan 22 stores coating liquid P. The lower pickup roll 322 draws up the coating liquid P from the lower coating material receiving pan 22. The lower metering roll 323 adjusts the amount of 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 positioned so as to eject liquid 422 from the inlet lower surface of the metal strip 24 into the space 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 or slit nozzles, and may have any structure as long as they are capable of supplying liquid. In this embodiment, a spray nozzle is used from the viewpoint of ease of supplying liquid.

[0021] The liquid ejection direction from the upper liquid ejection nozzle 41 is preferably set to a diagonally downward direction that is the same as the conveyance direction FD of the metal strip 24, 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 from the lower liquid ejection nozzle 42 is preferably set to a diagonally upward direction that is the same as the conveyance direction FD of the metal strip 24, 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 a 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 so as to achieve such an angle, the liquid ejection nozzles are spaced apart from the metal strip 24, making them less susceptible to vibrations when the metal strip 24 vibrates, and making it easier to eject liquid into the space between the rolls 311, 321 and the metal strip 24. It is more preferable that the angle θ between the liquid ejection direction of the liquid ejection nozzles 41, 42 and the coated surface of the metal strip 24 be within a range of 15° to 30°. Each liquid ejection nozzle 41, 42 is positioned so that the liquid ejection direction is set within a range of 10° to 45°, and the liquid ejected at that angle does not directly impinge on 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 positioned so that they impinge on the metal strip 24.

[0023] Furthermore, the distance L from the tip of the upper liquid jet nozzle 41 to the liquid collision point is preferably within a range of 10 mm to 200 mm. Similarly, the distance from the tip of the lower liquid jet nozzle 42 to the liquid collision point is preferably within the same range. By setting the distance L from each nozzle tip to the liquid collision point within a range of 10 mm to 200 mm, each liquid jet nozzle is spaced apart 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 jet liquid into the space between each roll and the metal strip 24. Note that the distance L from each nozzle tip to the liquid collision point is more preferably within a range of 20 mm to 100 mm. The distance L from the tip of the upper liquid jet nozzle 41 to the liquid collision point is the distance from the nozzle tip to the metal strip 24 in the liquid jet direction of each liquid jet nozzle 41, 42.

[0024] The upper pickup roll 312 and the lower pickup roll 322 are preferably made of metal, and particularly preferably made of 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, 322 against 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). 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 an appearance defect such as a streak-like pattern known as ribbing can be suppressed.

[0025] The upper paint receiving pan 21 is a tray that is open at the top, with the upper pickup roll 312 located directly above it. The height position 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 constantly supplied to the upper paint receiving pan 21, maintaining the liquid level of the coating liquid P constant. In addition, the bottom of the upper paint receiving pan 21 has a discharge port (not shown) for the coating liquid P, 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 a tray that is open at the top, with the lower pickup roll 322 located directly above it. The height position 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 constantly supplied to the lower paint receiving pan 22, maintaining the liquid level of the coating liquid P constant. The bottom of the lower paint receiving pan 22 has a discharge port (not shown) for the coating liquid P, 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 particularly preferably made of metal with a chrome-plated surface. The roll diameters of the upper metering roll 313 and the lower metering roll 323 are preferably 50 to 100 mm, and the upper metering roll 313 and the lower metering roll 323 are preferably located close to the upper pickup roll 312 and the lower pickup roll 322 with a predetermined gap therebetween. Furthermore, the rotation directions of the upper metering roll 313 and the lower metering roll 323 are preferably the same as the rotation directions of the upper pickup roll 312 and the lower pickup roll 322. By making the rotation directions of the upper metering roll 313 and the lower metering roll 323 the same as the rotation directions of the upper pickup roll 312 and the lower pickup roll 322, the amount of coating liquid P adhering to the surfaces 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 particularly preferably made of a rubber selected from urethane rubber, nitrile rubber, and hypalon rubber, which have excellent abrasion resistance. The roll diameters of the upper applicator roll 311 and the lower applicator roll 321 are preferably 100 to 300 mm. The nip pressure of each applicator roll 311, 312 against the metal strip 24 is preferably in the range of 9.8 to 98 N / cm (1 to 10 kgf / cm). Furthermore, the rotation direction of the upper applicator roll 311 and the lower applicator roll 321 is preferably opposite the conveyance 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 conveyance direction (FD) of the metal strip 24, the occurrence of a streak-like appearance defect known as ribbing can be suppressed.

[0029] The upper applicator roll 311 and the lower applicator roll 321 are preferably arranged with their central axes offset in the conveying direction FD of the metal strip 24. By arranging the central axes offset, the upper applicator roll 311 and the lower applicator roll 321 can push the metal strip 24 and apply liquid to the metal strip 24 while it is being wound around the upper applicator roll 311 and the lower applicator roll 321. As an example, the upper applicator roll 311 and the lower applicator roll 321 are preferably arranged with their respective central axes offset in the conveying direction FD by 40 mm to 150 mm. It is even more preferable to arrange the central axes of the rolls 311, 321 with an offset in the conveying direction FD by 80 mm to 100 mm. When the metal strip 24 is passed through in a straight line, the pushing amount 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 dashed dotted line in Figure 1 is used as the reference (0 mm).

[0030] Next, an example will be described. In Test No. 1, a coated metal strip was produced using the liquid application device 10 shown in FIG. 1 as an example of the invention. The specifications of the liquid application device used in the test were 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, which was opposite to the conveying direction FD of the metal strip 24. The upper applicator roll and the lower applicator roll were positioned with their respective central axes offset by 100 mm in the conveyance direction FD. The push-in amount Δt by each applicator roll was 5 mm, with the metal strip 24 running in a straight line being taken as the reference (0 mm). In contrast, as comparative examples, coated metal strips were produced in Tests Nos. 2 to 4 using the coating devices disclosed in Patent Documents 1, 2, and 3, respectively. In all tests, a cold-rolled steel strip was used as the metal strip 24, and an insulating coating liquid containing colloidal silica and phosphate as the main components was used as the coating liquid.

[0031] The failure rate due to coating defects under each coating condition is shown in Table 1. Coating defects were evaluated for overcoat (excessive application), no-coat (lack of coating), and the total. Test No. 1 had a lower failure rate than Test Nos. 2 to 4. This confirmed the effectiveness of the present invention.

[0032]

[0033] 10 Liquid application device 21 Upper paint receiving pan 22 Lower paint receiving pan 24 Metal strip 31 Upper roll coater device 311 Upper 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 jet nozzle 411 Liquid (jetted from upper liquid jet nozzle) 42 Lower liquid jet nozzle 422 Liquid (jetted from lower liquid jet nozzle) P Coating liquid FD Transport direction (of metal strip)

Claims

1. A liquid application device comprising: a pair of rolls that apply liquid to both sides of a metal strip that is continuously fed horizontally; and a liquid spray nozzle that sprays liquid into the space between the rolls and the metal strip on the entry side of the rolls, wherein the central axes of the pair of rolls are positioned so as to be offset in the transport direction of the metal strip, and the pair of rolls are positioned so as to push the metal strip.

2. A liquid application method using a pair of rolls to apply a liquid to both sides of a metal strip that is continuously fed horizontally, comprising the steps of: spraying liquid into a space between the roll and the metal strip on the entry side of the rolls; positioning the central axes of the pair of rolls so that they are offset in the transport direction of the metal strip; and applying the liquid to the metal strip while pressing the metal strip with the pair of rolls.

3. A method for producing a coated metal strip, comprising the step of applying a liquid to a metal strip by the liquid application method according to claim 2.

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