Method for coating a metal plate and method for manufacturing a pre-coated metal plate

Abstract

To provide a metal plate coating method that suppresses occurrence of air entrainment and roping in a coating material even if increasing a threading speed of a metal plate, and a precoated metal plate manufacturing method.SOLUTION: Disclosed is a metal plate coating method according to which a coating material is supplied to a rotating applicator roll from an upper side of the applicator roll by a coating material supply part of which a coating material supply port is so located as to be separated from the applicator roll by 1 to 10 mm, and the coating material supplied by the applicator roll is transferred and coated onto a threading metal plate. Further, disclosed is a precoated metal plate manufacturing method with use of the same.SELECTED DRAWING: Figure 1-1

Description

Technical Field

[0001] The present disclosure relates to a method for coating a metal sheet and a method for manufacturing a pre-coated metal sheet.

Background Art

[0002] Pre-coated metal sheets are widely used in the housings of household appliances and building materials. A pre-coated metal sheet generally has a chemical conversion layer, a primer layer, and a top layer laminated on the surface of a metal sheet. Each layer is laminated by sequentially coating and baking on a continuously passing metal sheet. A roll coater is often used for coating each layer. The top layer of a pre-coated metal sheet is a layer that ensures designability. If there are coating defects in this top layer, the designability is impaired and the commercial value is damaged. In particular, uniformity is required for the top layer.

[0003] Pre-coated metal sheets are continuously manufactured and wound up, stored, and transported in coils in units of several km to several tens of km. To increase the productivity of pre-coated metal sheets, it is necessary to increase the passing speed of the metal sheet. In particular, when manufacturing a pre-coated metal sheet on a continuous hot-dip galvanizing line (CGL), an increase in the passing speed of the metal sheet is required.

[0004] A roll coater coats a metal sheet by bringing a roll into contact with the metal sheet with a negative gap. The film thickness follows the roll peripheral speed and the passing speed. The faster the passing speed, the more necessary it is to rotate the roll at a high speed. When the rotation speed of the roll is increased, air entrainment in the paint, stripe-like coating defects (hereinafter, roping) generated during paint transfer, and paint scattering are likely to occur. Therefore, it is difficult to pass the metal sheet at high speed with a roll coater.

[0005] As a coating method more uniform than a roll coater, a curtain coater is known. A curtain coater forms a curtain film by allowing paint to fall freely. A metal plate is coated by passing through the curtain film. Since the film thickness is adjusted by the paint flow rate, entrainment of air into the paint and roping, which are likely to occur in a roll coater, are less likely to occur, and a uniform coating appearance is easily obtained. However, with a curtain coater, it is difficult to apply a thin film coating, and it is difficult to apply a coating with the target film thickness when manufacturing a thin film type pre-coated metal plate.

[0006] On the other hand, as a non-contact coating method similar to a curtain coater, a slot coater is also known. A slot coater is a coating method capable of applying a thinner film than a curtain coater. However, the distance between the paint discharge port of a general slot coater and the metal plate is about 0.01 to 0.5 mm. Therefore, depending on the shape or surface properties of the metal plate, the paint discharge port of the metal slot coater easily comes into contact with the metal plate. Therefore, it is difficult to put it into industrial practical use.

[0007] Therefore, a method of supplying paint to the pickup roll of a roll coater by a slot coater has been studied. Specifically, for example, Patent Document 1 discloses that "a multilayer coating liquid is supplied to a rotating intermediate roll by a slit die, and then the multilayer coating liquid is transferred from the intermediate roll to a rotating applicator roll, and then the multilayer coating liquid is transferred to a substrate by bringing the applicator roll into contact with a continuously running substrate. In this case, the intermediate roll rotates in the direction opposite to the applicator roll at the contact portion with the applicator roll, the applicator roll rotates in the direction opposite to the substrate at the contact portion with the substrate, and the multilayer coating liquid supplied by the slit die has a wet film thickness h1 of the coating liquid forming the lowermost layer, a wet film thickness h2 of the coating liquid forming the upper layer, and a gap between the slit die and the intermediate roll of G. When 0.15 ≦ h1 / G ≦ 0.70, 0.10 ≦ h2 / G ≦ 0.60, and 0.60 ≦ h1 / G + h2 / G ≦ 0.90, a coating method for a substrate is proposed."

[0008] In addition, methods of directly supplying paint to the applicator roll are also being considered. Specifically, for example, Patent Document 2 proposes "a method of forming a coating film on a continuously running metal strip using a coating apparatus including an applicator roll that applies a coating liquid in contact with the metal strip, a slit die that extrudes and supplies the coating liquid to the applicator roll in a curtain shape, a scraping device that removes the coating liquid remaining without being transferred from the applicator roll to the metal strip, and a drying device that dries the coating liquid on the surface of the metal strip, wherein a coating liquid having a surface tension of 30 to 50 dyn / cm at room temperature, which is obtained by diluting an aqueous paint with a solvent having a lower surface tension than the paint, is supplied from the slit die to the applicator roll."

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0010] However, although the coating method of Patent Document 1 is said to be able to achieve a beautiful appearance, looping occurs during the transfer of paint from the pickup roll to the applicator roll, so it has not been put into practical use.

[0011] In addition, in the coating method of Patent Document 2, the distance between the applicator roll and the slit die is as small as 15 μm, and the collision energy generated when the paint falls onto the applicator roll is small. Therefore, it is difficult for the air entrained when the paint is supplied to the applicator roll to be discharged to the outside of the paint, resulting in air entrainment in the paint.

[0012] Therefore, an object of the present invention is to provide a method for coating a metal sheet that suppresses the generation of air entrainment, looping, color bleeding, and paint splashing in the paint even when the passing speed of the metal sheet is increased, and a method for manufacturing a pre-coated metal sheet.

Means for Solving the Problems

[0013] The means for solving the above problems include the following aspects. <1> A method for coating a metal sheet, wherein paint is supplied from above the applicator roll to a rotating applicator roll by a paint supply unit in which a paint supply port is arranged 1 to 10 mm away from the applicator roll, and the paint supplied by the applicator roll is transferred and coated onto a metal sheet passing therethrough. <2> By a decompression unit arranged on the upstream side in the rotation direction of the applicator roll from the paint supply position of the applicator roll, the air pressure on the upstream side in the rotation direction of the applicator roll with respect to the paint supply position is made lower than the air pressure on the downstream side in the rotation direction of the applicator roll, and the paint is supplied to the applicator roll by the paint supply unit in the state where the air pressure on the upstream side in the rotation direction of the applicator roll with respect to the paint supply position is lower than the air pressure on the downstream side in the rotation direction of the applicator roll. The method for coating a metal sheet according to <1>. Rather than The method for coating a metal sheet according to <2>, wherein the absolute value of the air pressure difference between the air pressure on the upstream side in the rotation direction of the applicator roll with respect to the paint supply position and the air pressure on the downstream side in the rotation direction of the applicator roll is 100 to 2000 Pa. <3> The method for coating a metal sheet according to any one of <1> to <3>, wherein the rotation direction of the applicator roll is opposite to the passing direction of the metal sheet. <4> The method for coating a metal sheet according to any one of <1> to <4>, wherein the paint is a paint containing a resin, a surfactant, and an organic solvent. <5> The method for coating a metal sheet according to any one of <1> to <4>, wherein the paint is a paint containing a resin, a surfactant, and an organic solvent. <6> The coating material is a coating material containing a resin, a surfactant, and water, and the dynamic surface tension measured by the maximum bubble pressure method of the coating material is 30 to 60 mN / m at a bubble lifetime of 0.05 s and 20 to 50 mN / m at a bubble lifetime of 0.5 s. The method for coating a metal plate according to any one of <1> to <5>. <7> The coating material contains a solid content with a specific gravity of 1.2 to 10.0 g / cm 3 The method for coating a metal plate according to any one of <1> to <6>. <8> The average particle diameter of the solid content is 0.5 to 5.0 μm. The method for coating a metal plate according to <7>. <9> A method for manufacturing a pre-coated metal plate using the method for coating a metal plate according to any one of <1> to <8>.

Advantages of the Invention

[0014] According to the present disclosure, even when the passing speed of the metal plate is increased, it is possible to provide a method for coating a metal plate that suppresses the occurrence of air entrainment, roping, color bleeding, and paint scattering in the coating material, and a method for manufacturing a pre-coated metal plate.

Brief Description of the Drawings

[0015]

Figure 1-1

Figure 1-2

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0016] An embodiment that is an example of the present disclosure will be described. In addition, in this specification, a numerical range represented by "~" means a range including these numerical values as the lower limit value and the upper limit value when no "more than" or "less than" is attached to the numerical values described before and after "~". Also, a numerical range when "more than" or "less than" is attached to the numerical values described before and after "~" means a range not including these numerical values as the lower limit value or the upper limit value. In the numerical ranges described step by step in this specification, the upper limit value of a certain stepwise numerical range may be replaced with the upper limit value of the numerical range described in other stepwise descriptions, or may be replaced with the value shown in the examples. Also, the lower limit value of a certain stepwise numerical range may be replaced with the lower limit value of the numerical range described in other stepwise descriptions, or may be replaced with the value shown in the examples. In this specification, members having substantially the same function may be given the same reference numerals throughout all the drawings, and duplicate explanations may be omitted.

[0017] The method for coating a metal plate of the present disclosure is a method for coating a metal plate in which paint is supplied from above the applicator roll to a rotating applicator roll by a paint supply unit in which a paint supply port is arranged 1 to 10 mm away from the applicator roll, and the paint supplied by the applicator roll is transferred and coated onto a metal plate passing through the plate. That is, in the method for coating a metal plate of the present disclosure, the distance between the paint supply port of the paint supply unit and the applicator roll is 1 to 10 mm.

[0018] In the method for coating a metal plate of the present disclosure, by the paint supply unit, the paint is directly supplied to the applicator roll without passing through a pickup roll or other intermediate rolls. Then, the supplied paint is transferred onto a metal plate passing through the plate by the applicator roll. Therefore, looping generated during the transfer of the paint is suppressed. As a result, even if the passing speed of the metal plate is increased, the occurrence of looping is less likely to occur. In addition, since the pickup roll is not interposed, paint scattering associated with the rotation of the pickup roll can also be suppressed.

[0019] In addition, since the paint is supplied from the paint supply port of the paint supply unit, which is sufficiently separated from the applicator roll by 1 mm, to the applicator roll downward in the gravitational direction, when the paint contacts the applicator roll, the impact energy due to the self-weight of the paint increases. As a result, the entrained air is promoted to be discharged outside the paint. Therefore, even if the passing speed of the metal plate is increased, it is difficult for air to be entrained in the paint. On the other hand, by setting the distance between the paint supply port of the paint supply unit and the applicator roll to 10 mm or less, it is possible to suppress the film of the paint discharged from the paint supply port of the paint supply unit from being segmented due to the overly wide distance. Therefore, color bleeding caused by the segmentation of the paint film is suppressed.

[0020] As described above, in the method for painting a metal plate according to the present disclosure, even if the passing speed of the metal plate is increased, the occurrence of air entrainment in the paint, looping, color bleeding, and paint scattering is suppressed.

[0021] Conventionally, in a painting method in which paint is supplied from a paint pan for storing paint to an applicator roll by a pickup roll or to an applicator roll via an intermediate roll, solid components contained in the paint (particularly, solid components such as pigments having a large average particle size and a large specific gravity) settle, and painting defects are likely to occur. However, in the method for painting a metal plate according to the present disclosure, since the paint is extruded from the paint supply port of the paint supply unit and directly supplied to the applicator roll, sedimentation of the solid components contained in the paint hardly occurs. That is, even when applying a water-based paint having a relatively low viscosity, sedimentation of the solid components contained in the paint does not occur, and good painting of the paint on the metal plate can be achieved.

[0022] In addition, in the method for painting a metal plate according to the present disclosure, since the paint is applied to the metal plate by an applicator roll, it is easier to apply a thin film compared to the case where the paint is applied to the metal plate by a curtain coater, and it is possible to achieve painting with a target film thickness when manufacturing a thin film type pre-coated metal plate.

[0023] Moreover, by using the method for coating a metal sheet of the present disclosure, it is possible to manufacture a pre-coated metal sheet while suppressing the generation of air entrainment and roping in the paint. Here, generally, in a continuous galvanizing line (CGL), in order to manufacture a pre-coated metal sheet, application of an aqueous paint and an increase in the sheet passing speed are required. However, even when the method for manufacturing a metal sheet of the present disclosure is applied in a continuous galvanizing line, sedimentation of the solid content contained in the paint hardly occurs, and it is possible to manufacture a pre-coated metal sheet having a good coating film while suppressing the generation of air entrainment and roping.

[0024] Hereinafter, the method for coating a metal sheet of the present disclosure will be described in detail.

[0025] (Coating apparatus) First, the coating apparatus applied in the method for coating a metal sheet of the present disclosure will be described. FIG. 1-1 shows an example of the coating apparatus applied in the method for coating a metal sheet of the present disclosure.

[0026] As shown in FIG. 1-1, the coating apparatus 100 includes an applicator roll 10 that coats a paint on the surface of the metal sheet M by transfer, and a backup roll 12 that is disposed opposite to the metal sheet M through the metal sheet M and supports the metal sheet M passing therethrough. Around the applicator roll 10, there are also provided a paint supply unit 14 that supplies paint to the applicator roll 10, a scraping unit 16 that scrapes off the paint remaining on the applicator roll 10 after the paint is coated on the metal sheet M by the applicator roll 10, and a decompression unit 18 that is disposed upstream of the paint supply position of the applicator roll 10 in the rotation direction of the applicator roll 10.

[0027] As the applicator roll 10, for example, a well-known applicator roll having a metal roll and a rubber coating layer provided on the outer peripheral surface of the metal roll, which is applied by a well-known roll coater, can be adopted. The backup roll 12 serves to support the metal plate against the pressing pressure of the applicator roll 10. For example, a well-known backup roll that rotates in synchronization with the passing speed of the metal plate, which is applied in a well-known roll coater, can be adopted. It is also possible to omit the backup roll by applying tension to the metal plate.

[0028] The paint supply unit 14 is disposed above the applicator roll 10 and has a paint supply port 14A that serves as a paint discharge port. And the distance between the paint supply port 14A of the paint supply unit 14 and the applicator roll 10 is set to 1 to 10 mm (preferably 2 to 9 mm, more preferably 3 to 7 mm). Specifically, the distance between the paint supply port 14A of the paint supply unit 14 and the applicator roll 10 is the shortest distance between the paint supply port 14A and the paint supply position P1 on the outer peripheral surface of the applicator roll 10, and is the distance until the paint reaches the outer peripheral surface of the applicator roll 10 from the paint supply port 14A (see Fig. 2).

[0029] As the paint supply unit 14, well-known coaters such as a slot coater, a curtain coater (roller curtain coater, slide curtain coater, etc.) can be adopted.

[0030] The scraping unit includes a scraping blade 16A that scrapes the paint remaining on the applicator roll 10 with its tip, and a paint collection pan 16B that collects the paint scraped by the tip of the scraping blade 16A.

[0031] The scraping blade 16A is arranged such that its tip contacts the outer peripheral surface of the applicator roll 10 on the downstream side in the rotation direction of the applicator roll 10 from the paint application P2 to the metal plate M by the applicator roll 10, and scrapes the paint.

[0032] The scraping blade 16A is a doctor-type blade arranged with its tip facing the reverse rotation direction side of the rotation direction of the applicator roll 10. When a doctor-type blade is adopted, the paint scraping performance is improved. However, it may also be a wiper-type blade arranged with its tip facing the rotational direction side of the applicator roll 10.

[0033] The scraping blade 16A may be a blade made of plastic (such as a blade made of polyester, polyethylene, polyurethane, etc.) or a blade made of ceramic (such as a blade made of zirconia, titania, etc.) from the viewpoint of the paint scraping property.

[0034] The decompression part 18 is arranged on the upstream side in the rotational direction of the applicator roll 10 from the paint supply position P1 of the applicator roll 10 and adjacent to the paint supply part 14, and includes a hood 18A covering the outer peripheral surface of the applicator roll 10 and a duct 18B connected to the hood 18A. In the decompression part 18, the duct 18B is connected to a suction pump (not shown). Then, in the decompression part 18, due to the suction by the suction pump, the air pressure on the upstream side in the rotational direction of the applicator roll 10 covered by the hood 18A and located upstream of the paint supply position P1 of the applicator roll 10 is made negative pressure. Here, the pressure of the air pressure can be measured by a pressure gauge provided on the inner surface of the hood 18A.

[0035] In addition to the above, the coating apparatus 100 can be provided with various members provided in a well-known coating apparatus.

[0036] (Coating method) An example of the coating method of the metal plate of the present disclosure using the coating apparatus 100 will be described.

[0037] In the coating method of the metal plate of the present disclosure, first, the applicator roll 10 is rotated, and paint is discharged from the paint supply port 14A of the paint supply part 14 arranged 1 to 10 mm away from the applicator roll 10 to supply the paint to the applicator roll 10. After starting the supply of the paint to the applicator roll 10 or simultaneously with the start, the continuous passing of the metal plate M is started, and the paint supplied by the applicator roll 10 is transferred and coated on the continuously passing metal plate M.

[0038] When the paint is discharged from the paint supply port 14A of the paint supply unit 14 and directly supplied to the applicator roll 10, the paint is transferred only once from the applicator roll 10 to the metal plate M. Therefore, even if the passing speed of the metal plate M is increased, the occurrence of roping is suppressed.

[0039]

[0039] If the distance between the paint supply port 14A of the paint supply unit 14 and the applicator roll 10 is less than 1 mm, when the paint contacts the applicator roll 10, the impact energy of the paint is small, and it is difficult for the air entrained when the paint is supplied to the applicator roll 10 to be discharged outside the paint, resulting in air entrainment in the paint. In particular, when the passing speed of the metal plate M is increased, air entrainment in the paint is likely to occur. Therefore, the distance between the paint supply port 14A of the paint supply unit 14 and the applicator roll 10 shall be 1 mm or more. From the viewpoint of suppressing air entrainment in the paint, the distance between the paint supply port of the paint supply unit and the applicator roll is preferably 3 mm or more. However, if the distance between the paint supply port 14A of the paint supply unit 14 and the applicator roll 10 exceeds 10 mm, when the paint contains a coloring pigment and the passing speed of the metal plate M is increased, the film of the paint liquid may be broken. When the film of the paint is broken, there will be areas with paint and areas without paint on the applicator roll 10. Starting from this, color bleeding of the paint film may occur. Therefore, the distance between the paint supply port 14A of the paint supply unit 14 and the applicator roll 10 shall be 10 mm or less.

[0040] The rotation direction of the applicator roll 10 may be the same as the passing direction A of the metal plate M or opposite to the passing direction A of the metal plate M. However, the rotation direction of the applicator roll 10 is preferably opposite to the passing direction A of the metal plate M. When the rotation direction of the applicator roll 10 is opposite to the passing direction A of the metal plate M, weeping separation of the paint during paint transfer is suppressed, and the occurrence of roping is suppressed. Note that the rotation direction of the applicator roll 10 means the direction at the position facing the metal plate M (i.e., the paint application position P2).

[0041] The paint supply amount from the paint supply unit 14 to the applicator roll 10 is appropriately set according to the film thickness of the paint film formed on the surface of the metal plate M. The rotation speed of the applicator roll 10 is also appropriately set according to the film thickness of the paint film formed on the surface of the metal plate M. Note that the passing speed LS of the metal plate M is, for example, 20 to 200 m / min.

[0042] The paint supply from the paint supply unit 14 to the applicator roll 10 is carried out in a state where the air pressure on the upstream side in the rotation direction of the applicator roll with respect to the paint supply position P1 is made lower than the air pressure on the downstream side in the rotation direction of the applicator roll 10 by the decompression unit 18. Thereby, the periphery of the paint supply position P1 is decompressed, and when the paint is supplied to the applicator roll 10, the air entrained is easily discharged to the outside of the paint, and the entrainment of air in the paint is suppressed. Rather than From the viewpoint of suppressing the entrainment of air in the paint, the air pressure difference between the air pressure on the upstream side in the rotation direction of the applicator roll 10 with respect to the paint supply position P1 of the applicator roll 10 and the air pressure on the downstream side in the rotation direction of the applicator roll is preferably 100 to 2000 Pa, and more preferably 200 to 800 Pa.

[0043] Note that the air pressure on the upstream side in the rotation direction of the applicator roll 10 with respect to the paint supply position P1 of the applicator roll 10 is regarded as the air pressure inside the decompression unit 18 hood 18A measured by a pressure gauge (not shown) provided inside the decompression unit 18 hood 18A.

[0044] On the other hand, the air pressure on the downstream side in the rotation direction of the applicator roll is set to the atmospheric pressure. On the other hand, the air pressure on the downstream side in the rotation direction of the applicator roll is the atmospheric pressure.

[0045] Next, in the method for coating a metal plate of the present disclosure, after the supplied paint is transferred and coated onto the metal plate M passing through the applicator roll 10 by the applicator roll 10, the paint remaining on the applicator roll 10 is scraped off by the scraping blade 16A in the scraping portion 16 and collected by the paint collection pan 16B. The collected paint may be reused. That is, the paint collected by the paint collection pan 16B may be circulated and discharged again from the paint supply unit 14 for reuse in coating.

[0046] Note that the metal plate M to be coated may be a well-known metal plate such as a galvanized steel plate, a zinc-aluminum alloy galvanized steel plate, a zinc-aluminum-magnesium alloy galvanized steel plate, an aluminum galvanized steel plate, a zinc-nickel alloy galvanized steel plate, a zinc-iron alloy galvanized steel plate, a copper plate, a magnesium plate, an aluminum plate, or a stainless steel plate. Here, before applying paint to the metal plate M, a known chemical conversion coating and a known primer coating film may be coated.

[0047] In the method for coating a metal plate of the present disclosure described above, as described above, even if the passing speed of the metal plate M is increased, the entrainment of air in the paint and the occurrence of looping can be suppressed.

[0048] Then, by the method for coating a metal plate of the present disclosure, after a coating film is formed on the surface of the metal plate M, the coating film is dried and / or cured to form a precoat layer, thereby obtaining a precoated metal plate. The drying conditions and curing conditions of the coating film may be appropriately set according to the paint used.

[0049] (Paint) Hereinafter, an example of the paint used in the method for coating a metal plate of the present disclosure will be described.

[0050] As the paint, either a paint containing a resin, a surfactant, and an organic solvent (hereinafter also referred to as a solvent-based paint), or a paint containing a resin, a surfactant, and water (hereinafter also referred to as an aqueous paint) can be adopted. Here, when forming a cured film as the coating film, the paint may contain a curing agent together with the resin.

[0051] [Resin] The resin is not particularly limited, and examples thereof include well-known resins applied to paints, such as polyester resins, polyurethane resins, acrylic resins, fluororesins, and epoxy resins. These resins may be used alone or in combination of two or more. Among these, in particular, as the resin, it is preferably at least one selected from the group consisting of polyester resins, acrylic resins, and urethane resins, which are easy to balance processability and other properties, and more preferably at least one selected from the group consisting of polyester resins and urethane resins.

[0052] The type of the resin can be determined by a known method. For example, for a sample obtained by drying the centrifuged paint, the type of the resin is determined by performing measurements such as infrared absorption spectrum (IR) and pyrolysis gas chromatography.

[0053] The number average molecular weight of the resin is not particularly limited, but is preferably 3000 to 25000. When resins having different number average molecular weights are used in combination, the number average molecular weight of the resin is the weighted average number average molecular weight.

[0054] The method for measuring the number average molecular weight of the resin is as follows. After centrifuging the paint, measure 20 mg of the paint supernatant as the resin solid content. After dissolving the obtained sample in 10 ml of tetrahydrofuran (THF), measure it at a pump flow rate of 0.6 ml / min and a temperature of 40 °C using gel permeation chromatography (GPC, Tosoh Corporation HLC8220 GPC, column Shodex KF type). Then, calculate the number average molecular weight of the resin based on the molecular weight of standard polystyrene from the chromatogram.

[0055] The concentration of the resin is preferably 5 to 50% by mass, more preferably 10 to 45% by mass, based on the paint. When the resin concentration is within the above range, the solid content concentration of the paint can be increased, and the cost related to painting can be reduced.

[0056] [Organic solvent] The organic solvent is a solvent that dissolves the resin. Also, the organic solvent should not react even when a curing agent, a coloring pigment, a surfactant, etc. are added and should remain in a liquid state. The organic solvent is not particularly limited, and known solvents can be mentioned. Examples of the organic solvent include ester-based organic solvents such as 3-methoxybutyl acetate, ethyl acetate, isopropyl acetate, butyl acetate; ketone-based organic solvents such as methyl ethyl ketone, acetone, methyl isobutyl ketone, cyclohexanone, isophorone; Solvesso 100 (ExxonMobil), Solvesso 150 (ExxonMobil), etc. These organic solvents may be used alone or in combination of two or more in any ratio.

[0057] [Water] Examples of water include tap water, distilled water, pure water, etc.

[0058] [Surfactant] The surfactant has both the function of discharging the air entrapped in the paint and the function of stably forming the film of the discharged paint (i.e., the curtain film). Examples of the surfactant include acrylic surfactants, silicone surfactants, fluorine-modified silicone surfactants, etc.

[0059] Examples of the acrylic surfactant include copolymers of acrylic monomers Examples of the acrylic monomer include alkyl acrylates, alkylene oxide acrylates, alkyl ether (meth)acrylates, aminoalkyl acrylates, acrylamide compounds, etc.

[0060] Examples of silicone surfactants include polydimethylsiloxanes whose side chains or the ends of the main chains are modified with alkylene glycols (such as ethylene glycol and propylene glycol). Examples of fluorine-modified silicone surfactants include those obtained by substituting a part of the above silicone surfactants with perfluoroalkyl groups.

[0061] The concentration of the surfactant is preferably 0.05 to 0.80% by mass, more preferably 0.10 to 0.50% by mass, based on the paint. When the concentration of the surfactant is within the above range, the dynamic surface tension of the paint is controlled, and the action of discharging the air entrained in the paint and the action of stably forming the film (i.e., the curtain film) of the discharged paint are likely to be improved.

[0062] [Solid content] The paint may contain a solid content having a specific gravity of 1.2 to 10.0. The solid content having a specific gravity of 1.2 to 10.0 is likely to settle in the paint. In particular, the solid content having a specific gravity of 1.2 to 10.0 and an average particle size of 0.5 to 5.0 μm is likely to settle in the paint. However, even if the paint contains a solid content that is likely to settle, in the method for coating a metal plate of the present disclosure, since the paint is directly supplied from the paint supply unit to the applicator roll, the settlement of the solid content is suppressed. The specific gravity of the solid content is preferably 1.5 to 7.0. The average particle size of the solid content is preferably 1.0 to 5.0 μm.

[0063] The specific gravity of the above solid content is measured as follows. The paint to be measured is applied to the surface of a metal plate, and after forming a coating film, the coating film is dried and / or cured to form a precoat layer. Use a metal plate with a precoat layer as a sample and polish the surface of the precoat layer (the surface facing the thickness direction). Then, analyze the cross-section (here, a flat cross-section) of the precoat layer formed by this polishing using an electron probe microanalyzer (FE-EPMA: Electron Probe MicroAnalyser) to determine the elemental ratio of the solid components. Also, identify the substances that make up the solid components from the analysis results such as microscopic Raman spectroscopy, microscopic infrared spectroscopy, and microscopic X-ray diffraction. And obtain the specific gravity of the said solid components from literature values.

[0064] The average particle size of the above solid components is measured as follows. Similar to the measurement of the specific gravity of the solid components, use the metal plate with the precoat layer as a sample and observe the cross-section (here, a flat cross-section) of the precoat layer formed by polishing with FE-SEM. The cross-sectional diameter of the solid components gradually increases each time polishing is repeated and eventually reaches a maximum value. This maximum value corresponds to the particle size of the solid components. If polishing is continued further, the cross-sectional diameter decreases. Therefore, measure the cross-sectional diameter of the solid components observed in a certain field of view each time polishing is performed, and take the maximum measured value as the particle size of the solid components. Then, take the arithmetic mean value of the particle sizes of a plurality of arbitrarily selected (for example, 20) solid components as the average particle size of the solid components. In addition, when the cross-sectional diameter observed first becomes the maximum value, since it may be smaller than the actual particle size, it is excluded from the objects when calculating the average value.

[0065] Here, the polishing method of the precoat layer is not particularly limited, and known methods can be adopted. For example, resin embedding polishing or microtome processing can be used. Particularly when obtaining the average particle size of the beads 40 with high accuracy, cryo FIB-SEM (Cryo Scanning Electronscopy combined with Focused Ion Beam) is suitable as the polishing method. Since the sample temperature is set to about -100°C and the sample is processed with an ion beam, there is less damage to the film due to heat generation associated with ion beam irradiation, and polishing in sub-nanometer units is possible, so the particle size can be obtained even for small solid components.

[0066] Typical components as the solid content include pigments.

[0067] Examples of pigments include pigments having one or both of the functions of coloring and imparting conductivity (i.e., coloring pigments, conductive pigments, colored conductive pigments, etc.). The pigments are not particularly limited, and known pigments can be used. Specifically, examples of pigments include, for example, Vanadium oxide compounds (vanadium carbide, vanadium monoboride, vanadium diboride, vanadium nitride, etc.), simple metals or alloys (aluminum, silver, nickel, stainless steel, ferrosilicon), oxides (titanium oxide, iron oxide, zinc oxide particles, magnesium oxide particles, calcium oxide particles, strontium oxide particles, carbon black (furnace black, ketjen black, acetylene black, channel black)), minerals (mica), etc.

[0068] The type of pigment can be determined by known methods. For example, the type of coloring pigment can be determined by elemental analysis using SEM-EDX or X-ray diffraction measurement on a coating film or a precipitate after centrifugation.

[0069] The concentration of the pigment is preferably 2 to 45% by mass, more preferably 10 to 40% by mass, based on the paint.

[0070] [Other Additives] The paint may contain other well-known additives such as catalysts, waxes, ultraviolet absorbers, antioxidants, plasticizers, coupling agents, pigment dispersants, anti-settling agents, antibacterial agents, etc.

[0071] [Dynamic Surface Tension] Among the paints, for water-based paints, the dynamic surface tension of the paint measured by the maximum bubble pressure method is preferably 30 to 60 mN / m at a bubble lifetime of 0.05 s and 20 to 50 mN / m at a bubble lifetime of 0.5 s. When the dynamic surface tension is within these ranges, the effect of discharging the air entrained in the paint and the effect of stably forming the film of the discharged paint (i.e., the curtain film) are improved. The dynamic surface tension can be adjusted by the types of resin and surfactant and the concentration of the surfactant.

[0072] The dynamic surface tension of the aqueous paint can be measured by the maximum bubble pressure method. For example, it can be measured using DP-51 manufactured by Kyowa Interface Science Co., Ltd. Specifically, it is as follows. In order to stabilize the pressure at the start and end of the measurement, the dynamic surface tension is measured when the bubble lifetime is changed from 0.01 second to 5 seconds, and the dynamic surface tensions at bubble lifetimes of 0.05 second and 0.5 second are obtained. A probe with a diameter of 1 mm is used, and the measurement is started with 100% air in the tank built into the apparatus. When the viscosity of the aqueous paint is too high to be measured, the paint temperature may be raised (the paint viscosity may be lowered) for measurement. Note that even if the paint temperature is raised and the viscosity is lowered, the dynamic surface tension does not fluctuate. The paint measurement temperature is preferably in the range of 10 to 60 °C. If the temperature is too high, the organic solvent as the solvent may volatilize, and the dynamic surface tension may change.

[0073] [Viscosity] The viscosity of the paint is not particularly limited. However, as the paint, low-viscosity paints of 5 to 2000 mPa·s (preferably 10 to 500 mPa·s) can also be adopted. Even when a low-viscosity paint is adopted, even if the paint contains solid components (especially solid components such as pigments with a large average particle size and a large specific gravity), the sedimentation of the solid components is suppressed. In addition, when a low-viscosity paint is adopted, when the paint is transferred to the metal plate M by the applicator roll 10, bleeding of the paint hardly occurs, and roping is suppressed.

[0074] The viscosity of the paint is the viscosity at normal temperature (25 °C) and is measured as follows. For paints whose viscosity does not change with the shear rate, known methods such as a Ford cup viscometer, an Iwata cup viscometer, a vibration viscometer, or a rheometer can be used. For paints whose viscosity varies with the shear rate, a rheometer is used to measure the viscosity in the range of 1000 - 10000 s -1 referred to as the shear rate during roll coating.

Examples

[0075] Hereinafter, the paint and the painting method according to the present invention will be specifically described while showing examples and comparative examples. Note that the examples shown below are merely examples of the paint and the painting method according to the present invention, and the paint and the painting method according to the present invention are not limited to the following examples.

[0076] <Test Examples 1 - 1 to 5 - 6, 9 - 1 to 11 - 7> Using the painting apparatus 100 shown in Fig. 1 - 1, the metal plate was painted under the conditions shown in Table 1. In this test example, a slot coater was employed as the paint supply unit 14 (in the table, it is denoted as "slot + APR" in the column of the painting method).

[0077] Hereinafter, the details of the symbols or abbreviations in the table will be described. (Rotation direction of the roll) · R: The rotation direction of the applicator roll 10 is opposite to the passing direction A of the metal plate M. · N; The rotation direction of the applicator roll 10 is the same as the passing direction A of the metal plate M.

[0078] (Doctor blade) · Polyester: A doctor blade made of polyester · Ceramic: A doctor blade made of zirconia

[0079] · Pressure difference (downstream - upstream side): The absolute value of the pressure difference between the pressure on the upstream side in the rotation direction of the applicator roll 10 with respect to the paint supply position P1 and the pressure on the downstream side in the rotation direction of the applicator roll 10.

[0080] · Gap: The distance between the paint supply port 14A of the paint supply unit 14 and the applicator roll 10

[0081] · LS: Web passing speed

[0082] (Resin / Hardener column) · A: Urethane / Melamine (mass ratio = 100 / 20), Urethane (self-made, number average molecular weight Mn = 17000), Melamine (Ornex Japan "Cymel 303LF" = 100% by mass) · B: Polyester / Melamine (mass ratio = 100 / 30), Polyester (Toyobo "Vylon 600", number average molecular weight Mn = 16000), Melamine (Ornex Japan "Cymel 303LF" = 60% by mass, DIC "Super Beckamine" = 40% by mass) · C: Polyester / Melamine (mass ratio = 100 / 30), Polyester: Toyobo "Vylon GK-810", number average molecular weight Mn = 6000), Melamine (Ornex Japan "Cymel 303LF" = 60% by mass, DIC "Super Beckamine" = 40% by mass)

[0083] (Surfactant column) · a: Orfin WE-003 manufactured by Nissin Chemical Industry Co., Ltd. · b: Polyflow No.50E manufactured by Kyoeisha Chemical Co., Ltd. · c: Floren AC-303 manufactured by Kyoeisha Chemical Co., Ltd.

[0084] (Pigment column) · VB2: Vanadium diboride · Ag: Silver · Ni: Nickel · Al: Aluminum

[0085] (Solvent column) · Solvent: A 1:1 mixture of cyclohexanone manufactured by Shoei Chemical Industry Co., Ltd. and Solvesso 150 manufactured by ExxonMobil was used.

[0086] (Dynamic surface tension column) ·BLT 0.05s: Dynamic surface tension (mN / m) at a bubble lifetime of 0.05 s ·BLT 0.5s: Dynamic surface tension (mN / m) at a bubble lifetime of 0.5 s

[0087] <Test Examples 6-1 to 6-6> Using the coating apparatus 200 shown in Fig. 2, the metal plate was coated under the conditions shown in Table 1. The coating apparatus 200 shown in Fig. 2 has the same configuration as that in Fig. 1-1, except that instead of the paint supply section 14, the paint is once supplied to the intermediate roll 22 by the slot coater 20 and then supplied to the applicator roll 10 by the intermediate roll 22 (in the table, it is denoted as "slot + PUR" in the column of the coating method). In the apparatus of Fig. 2, the intermediate roll 22 is also provided with a scraping blade 16A for scraping off the paint remaining on the intermediate roll 22 after supplying the paint to the applicator roll 10 by the intermediate roll 22. On the other hand, the decompression section 18 is not provided.

[0088] Here, in the column of the roll rotation direction in the table, "NR" and "NN" indicate the following matters. ·NR: The rotation direction of the intermediate roll 22 is the same as the passing direction A of the metal plate M, and the rotation direction of the applicator roll 10 is opposite to the passing direction A of the metal plate M ·NN: The rotation direction of the intermediate roll 22 is the same as the passing direction A of the metal plate M, and the rotation direction of the applicator roll 10 is the same as the passing direction A of the metal plate M

[0089] <Test Examples 7-1 to 8-6> Using the coating apparatus 300 shown in Fig. 3, the metal plate was coated under the conditions shown in Table 1. The coating apparatus 300 shown in Fig. 3 has the same configuration as that in Fig. 1-1, except that instead of the paint supply section 14, the paint is picked up by the pickup roll 24 from the storage pan 26 for storing the paint and then supplied to the applicator roll 10 (in the table, it is denoted as "roll coater" in the column of the coating method). The coating apparatus 300 shown in Fig. 3 is not provided with the decompression section 18.

[0090] Here, in the table, "NR" and "NN" in the column of the roll rotation direction indicate the following matters. ·NR: The rotation direction of the pickup roll 24 is the same as the passing direction A of the metal plate M, and the rotation direction of the applicator roll 10 is opposite to the passing direction A of the metal plate M. ·NN: The rotation direction of the pickup roll 24 is the same as the passing direction A of the metal plate M, and the rotation direction of the applicator roll 10 is the same as the passing direction A of the metal plate M.

[0091] <Evaluation> For each test example, the following evaluation was carried out.

[0092] (Air entrainment) Regarding air entrainment, the evaluation was carried out as follows. The painted metal plate was dried, and the surface was visually observed. The evaluation criteria are as follows. A score of 4 or more was considered passing. ·5: No appearance defects. ·5-: No unpainted parts. There are shades in the coating film, and it cannot be seen when observed from a distance of 30 cm. ·4: No unpainted parts. There are shades in the coating film, and it cannot be seen when observed from a distance of 50 cm. ·3: No unpainted parts. There are shades in the coating film, and it cannot be seen when observed from a distance of 100 cm. ·2: There are unpainted parts. Observe any location, and there are 3 unpainted parts per 1 m. 2 Below. ·1: There are unpainted parts. Observe any location, and there are more than 3 unpainted parts per 1 m. 2 Exceeding.

[0093] (Rooping) Regarding rooping, the evaluation was carried out as follows. The painted metal plate was dried, and the surface was visually observed. The evaluation criteria are as follows. A score of 4 or more was considered passing. ·5: No appearance defects ·5-: There is rooping. It cannot be seen when observed from a distance of 30 cm. ·4: There is rooping. It cannot be seen from the front when observed from a distance of 30 cm. It can be seen slightly from an oblique angle. ·3: Roping exists. When observed from a distance of 30 cm, it cannot be seen from the front. It can be seen obliquely. ·2: Roping exists. When observed from a distance of 30 cm, it can be seen from the front. It can be seen obliquely. ·1: Roping exists. When observed from a distance of 30 cm, it can be clearly seen from the front. It can be clearly seen obliquely.

[0094] (Color bleeding) Regarding color bleeding, the evaluation was carried out as follows. The painted metal plate was dried, and the surface was visually observed. The evaluation criteria are as follows. A score of 4 or more was considered passing. ·5: No color bleeding. ·5-: No color bleeding. There is shading in the width direction. When observed from a distance of 30 cm, the shading cannot be distinguished. ·4: No color bleeding. There is shading in the width direction. When observed from a distance of 50 cm, the shading cannot be distinguished. ·3: Color bleeding exists. Any 1 m 2 was observed, and the color bleeding area ratio was 1% or less ·2: Color bleeding exists. Any 1 m 2 was observed, and the color bleeding area ratio was 3% or less ·1: Color bleeding exists. Any 1 m 2 was observed, and the color bleeding area ratio exceeded 3%

[0095] (Paint splashing) Regarding paint splashing, the evaluation was carried out as follows. Paper was placed around the painting machine, and the painting machine was operated for 30 minutes under predetermined conditions. It was investigated where the paint splashed on the paper. Starting from the center of the coater, the maximum distance at which the paint splashed was investigated. The evaluation criteria are as follows. A score of 3 or more was considered passing. ·5: No paint splashing. ·4: The maximum paint splashing distance is 1 m or less. ·3: The maximum paint splashing distance is more than 1 m and 2 m or less. ·2: The maximum paint splashing distance is more than 2 m and 3 m or less. ·1: The maximum paint splashing distance exceeds 3 m.

[0096] (Conductivity) The conductivity was evaluated as follows. Using the metal plate obtained by painting and drying, the interlayer resistance value (Ω·cm 2 ) was measured by the measurement method specified in JIS C 2550, and the conductivity was evaluated according to the following criteria. The evaluation criteria are as follows. There is no specific pass / fail criterion. (Evaluation Criteria) 6: The interlayer resistance value is less than 1.0 Ω·cm 2 less than 5: The interlayer resistance value is 1.0 Ω·cm or more and less than 1.5 Ω·cm 2 and less than 2 1.5 Ω·cm 4: The interlayer resistance value is 1.5 Ω·cm or more and less than 2.0 Ω·cm 2 and less than 2 2.0 Ω·cm 3: The interlayer resistance value is 2.0 Ω·cm or more and less than 2.5 Ω·cm 2 and less than 2 2.5 Ω·cm 2: The interlayer resistance value is 2.5 Ω·cm or more and less than 3.0 Ω·cm 2 and less than 2 3.0 Ω·cm 1: The interlayer resistance value is 3.0 Ω·cm or more 2 or more

[0097] [Table 1-1]

[0098] [Table 1-2]

[0099] [Table 1-3]

[0100] From the above results, it can be seen that in Test Examples 1-1 to 3-6, 9-1 to 9-2, and 10-1 to 11-7 (Examples), even when the passing speed of the metal plate is increased, the generation of air entrainment, looping, color bleeding, and paint scattering in the paint can be suppressed compared to Test Examples 4-1 to 8-6 and 9-3 (Comparative Examples). Also, it can be seen that in Test Examples 1-1 to 3-6, 9-1 to 9-2, and 10-1 to 11-7 (Examples), the evaluation of conductivity is also good.

Explanation of Signs

[0101] 10 Applicator roll 12 Backup roll 14 Paint supply section 14A Paint supply port 16 Scraping section 16A Scraping blade 16B Paint recovery pan 18 Vacuum section 18A Hood 18B Duct 20 Slot coater 22 Intermediate roll 24 Pickup roll 26 Storage pan 100 Coating device 200 Coating device 300 Coating device

Claims

1. A method for coating a metal sheet, comprising supplying paint from above the rotatable applicator roll to the applicator roll by a paint supply unit in which a paint supply port is disposed 1 to 10 mm away from the applicator roll, and transferring and coating the paint supplied to the applicator roll onto a metal sheet passing through the paint.

2. The method for coating a metal sheet according to claim 1, wherein a reduced pressure portion disposed upstream of the paint supply position of the applicator roll in the rotation direction of the applicator roll reduces the air pressure upstream of the paint supply position of the applicator roll in the rotation direction of the applicator roll to be lower than the air pressure downstream of the applicator roll in the rotation direction of the applicator roll, and the paint supply unit supplies the paint to the applicator roll.

3. The method for coating a metal sheet according to claim 2, wherein the absolute value of the air pressure difference between the air pressure upstream of the paint supply position of the applicator roll in the rotation direction of the applicator roll and the air pressure downstream of the applicator roll in the rotation direction of the applicator roll is 100 to 2000 Pa.

4. The method for coating a metal sheet according to any one of claims 1 to 3, wherein the rotation direction of the applicator roll is opposite to the passing direction of the metal sheet.

5. The method for coating a metal sheet according to any one of claims 1 to 4, wherein the paint is a paint containing a resin, a surfactant, and an organic solvent.

6. The method for coating a metal sheet according to any one of claims 1 to 5, wherein the paint is a paint containing a resin, a surfactant, and water, and the dynamic surface tension measured by the maximum bubble pressure method of the paint is 30 to 60 mN / m at a bubble lifetime of 0.05 s and 20 to 50 mN / m at a bubble lifetime of 0.5 s.

7. The coating material has a specific gravity of 1.2 to 10.0 g / cm ３ The method for coating a metal plate according to any one of claims 1 to 6, which contains a solid content of.

8. The method for coating a metal sheet according to claim 7, wherein the average particle diameter of the solid content is 0.5 to 5.0 μm.

9. A method for manufacturing a pre-coated metal sheet using the method for coating a metal sheet according to any one of claims 1 to 8.

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