JP2023068980A - Metal plate coating method, and precoated metal plate manufacturing method - Google Patents

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 The present disclosure relates to a method of coating a metal sheet and a method of manufacturing a precoated metal sheet.

Pre-coated metal sheets are widely used for home appliance housings and building materials. A precoated metal sheet is generally obtained by laminating a chemical conversion treatment layer, a primer layer and a top layer on the surface of a metal sheet. Each layer is laminated in order by coating and baking on a continuously threaded metal plate. A roll coater is often used for coating each layer. The top layer of the precoated metal sheet is a layer that ensures designability. If there is a coating defect in this top layer, the design is spoiled, and the commercial value is spoiled. In particular, uniformity is required for the top layer.

A precoated metal sheet is continuously manufactured, wound up in a coil shape in units of several kilometers to several tens of kilometers, and stored and transported. In order to increase the productivity of precoated metal sheets, it is necessary to increase the threading speed of the metal sheets.
In particular, when a precoated metal sheet is produced in a continuous galvanizing line (CGL), it is required to increase the threading speed of the metal sheet.

A roll coater coats a metal plate by contacting a roll with a negative gap. The film thickness follows the roll peripheral speed and plate threading speed. The higher the sheet threading speed, the faster the rolls need to be rotated. When the rotation speed of the roll is increased, air is entrained in the paint, rope-like paint defects (hereinafter referred to as roping) that occur during paint transfer, and paint scattering tend to occur. Therefore, high-speed sheet threading is difficult with a roll coater.

A curtain coater is known as a more uniform coating method than a roll coater. A curtain coater allows the paint to fall freely to form a curtain film. The 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 as in a roll coater are less likely to occur, making it easier to obtain a uniform paint appearance. However, it is difficult to coat a thin film with a curtain coater, and it is difficult to achieve a target film thickness for manufacturing a thin film type precoated metal sheet.

On the other hand, a slot coater is also known as a non-contact coating method similar to the curtain coater. A slot coater is a coating method that enables a thinner coating than a curtain coater.
However, the distance between the paint outlet of a general slot coater and the metal plate is about 0.01 to 0.5 mm. Therefore, the metal plate is easily brought into contact with the paint outlet of the slot coater made of metal depending on the shape or surface properties of the metal plate. Therefore, it is difficult to put it into practical use industrially.

Therefore, a method of supplying paint to a pick-up roll of a roll coater using a slot coater is being studied. Then, the multi-layer coating liquid is transferred from the intermediate roll to a rotating applicator roll, and then the applicator roll is brought into contact with a continuously running substrate to apply the multi-layer coating liquid to the substrate. When transferring, the intermediate roll rotates in the opposite direction to the applicator roll at the contact portion with the applicator roll, the applicator roll rotates in the opposite direction to the substrate at the contact portion with the substrate, and the slit die The multilayer coating liquid to be supplied has a wet film thickness h1 of the coating liquid forming the bottom layer, a wet film thickness h2 of the coating liquid forming the upper layer, and the gap between the slit die and the intermediate roll is G, 0.15≦h1/G≦0.70, 0.10≦h2/G≦0.60, and 0.60≦h1/G+h2/G≦0.90. ' is proposed.

A method of supplying the paint directly to the applicator roll has also been investigated. Specifically, for example, in Patent Document 2, "an applicator roll that contacts a metal strip to apply a coating liquid, a slit die that extrudes and supplies the coating liquid to the applicator roll in the form of a curtain, and an applicator roll. A coating device equipped with a scraping device that removes the remaining coating liquid from the talol that has not been transferred to the metal strip and a drying device that dries the coating liquid on the surface of the metal strip is used to coat the continuously running metal strip. A method of forming a film, wherein a coating liquid having a surface tension of 30 to 50 dyn/cm at room temperature obtained by diluting a water-based paint with a solvent having a lower surface tension than the paint is supplied from a slit die to an applicator roll. .” has been proposed.

Patent 5849780 specification Patent 5239457 specification

However, although the coating method of Patent Document 1 is said to make the appearance beautiful, it has not been put to practical use because roping occurs when the coating is transferred from the pickup roll to the applicator roll.

In addition, in the coating method of Patent Document 2, the gap between the applicator roll and the slit die is as small as 15 μm, and the impact energy generated when the paint drops onto the applicator roll is small. Therefore, air entrained in the paint when it is supplied to the applicator roll is difficult to be discharged to the outside of the paint, and air is entrained in the paint.

Therefore, an object of the present invention is to provide a method for coating a metal plate that suppresses the occurrence of air entrainment, roping, color loss, and paint scattering in the paint even if the metal plate threading speed is increased, and a precoated metal plate. It is to provide a manufacturing method.

Means for solving the above problems include the following aspects.
<1>
A paint is supplied to the rotating applicator roll from above the applicator roll by a paint supply unit whose paint supply port is arranged 1 to 10 mm away from the applicator roll, and the paint supplied by the applicator roll is passed through. A method of coating a metal plate in which the metal plate to be plated is transferred and coated.
<2>
A decompression unit arranged on the upstream side in the rotation direction of the applicator roll relative to the paint supply position of the applicator roll reduces the pressure of the applicator roll on the upstream side in the rotation direction of the applicator roll with respect to the paint supply position. The method of coating a metal plate according to <1>, wherein the coating material is supplied to the applicator roll by the coating material supply unit in a state where the air pressure on the downstream side in the rotation direction is low.
<3>
The absolute value of the pressure difference between the pressure upstream in the rotation direction of the applicator roll and the pressure downstream in the rotation direction of the applicator roll with respect to the paint supply position is 100 to 2000 Pa. The metal plate according to <2>. painting method.
<4>
The method of coating a metal plate according to any one of <1> to <3>, wherein the direction of rotation of the applicator roll is opposite to the direction of threading of the metal plate.
<5>
The method of coating a metal plate 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 paint contains a resin, a surfactant, and water, and has a dynamic surface tension of 30 to 60 mN/m at a bubble lifetime of 0.05 s, as measured by the maximum bubble pressure method. The method for coating a metal plate according to any one of <1> to <5>, which has a life time of 0.5 s and a life time of 20 to 50 mN/m.
<7>
The method of coating a metal plate according to any one of <1> to <6>, wherein the paint contains a solid content with a specific gravity of 1.2 to 10.0 g/cm ³ .
<8>
The method for coating a metal plate according to <7>, wherein the solid content has an average particle size of 0.5 to 5.0 μm.
<9>
A method for producing a precoated metal sheet using the method for coating a metal sheet according to any one of <1> to <8>.

According to the present disclosure, a metal plate coating method that suppresses entrainment of paint, roping, color loss, and paint scattering even if the metal plate threading speed is increased, and a method for manufacturing a precoated metal plate. can provide

1 is a schematic configuration diagram showing an example of a coating apparatus applied to a method of coating a metal plate according to the present disclosure; FIG. FIG. 2 is a partially enlarged schematic configuration diagram showing the surroundings of a coating material supply section in a coating apparatus applied to the metal plate coating method of the present disclosure; 1 is a schematic configuration diagram showing an example of a coating apparatus applied to a conventional metal plate coating method; FIG. FIG. 2 is a schematic configuration diagram showing another example of a coating apparatus applied to a conventional metal plate coating method;

An embodiment that is an example of the present disclosure will be described.
In this specification, the numerical range represented by using "to" is, if the numerical value described before and after "to" is not attached with "more" or "less than", these numerical values as lower and upper limits. In addition, a numerical range when "more than" or "less than" is attached to the numerical value described before and after "-" means a range that does not include these numerical values as the lower or upper limit.
In the numerical ranges described stepwise in this specification, the upper limit of a certain stepwise numerical range may be replaced with the upper limit of another stepwise numerical range. You may substitute the indicated values. In addition, the lower limit value of a certain stepwise numerical range may be replaced with the lower limit value of another stepwise stated numerical range, or may be replaced with the values shown in the examples.
In this specification, members having substantially the same functions are given the same reference numerals throughout the drawings, and duplicate descriptions may be omitted.

In the method of coating a metal plate of the present disclosure, a rotating applicator roll is supplied with a paint from above the applicator roll by a paint supply unit having a paint supply port disposed 1 to 10 mm away from the applicator roll, This is a method of coating a metal plate in which the coating material supplied by an applicator roll is transferred onto a passing metal plate for coating.
That is, in the method of coating a metal plate of the present disclosure, the distance between the coating supply port of the coating material supply unit and the applicator roll is 1 to 10 mm.

In the method of coating a metal plate of the present disclosure, the coating material is directly supplied to the applicator roll by the coating material supply unit without passing through a pickup roll or other intermediate rolls. Then, the supplied paint is transferred to the passing metal plate by the applicator roll. Therefore, roping that occurs when the paint is transferred is suppressed. As a result, even if the metal plate threading speed is increased, roping is less likely to occur.
In addition, since the pickup roll is not interposed, it is possible to suppress paint scattering due to the rotation of the pickup roll.

In addition, since the paint is supplied to the applicator roll downward in the direction of gravity from the paint supply port of the paint supply unit, which is sufficiently separated from the applicator roll by a distance of 1 mm, when the paint comes into contact with the applicator roll, the weight of the paint itself collision energy due to This promotes the discharge of entrained air to the outside of the paint. Therefore, air entrainment in the paint is less likely to occur even if the metal plate is fastened at a high threading speed.
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, the film of the paint discharged from the paint supply port of the paint supply unit, which is caused by the excessively wide gap, is divided. is suppressed. Therefore, the loss of color due to the division of the paint film is suppressed.

As described above, in the metal plate coating method of the present disclosure, air entrainment in the paint, roping, color loss, and paint scattering are suppressed even if the metal plate threading speed is increased.

In addition, conventionally, in a coating method in which the paint is supplied from a paint pan that stores paint to the applicator roll via a pickup roll or to the applicator roll via an intermediate roll, the solid content contained in the paint (especially the average particle size Solids such as pigments having a large diameter and a large specific gravity) tend to settle, resulting in poor coating.
However, in the method of coating 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 solids contained in the paint is unlikely to occur. In other words, even if a water-based paint with a relatively low viscosity is applied, the solid content contained in the paint does not settle, and good coating of the paint on the metal plate can be realized.

In addition, in the method of coating a metal plate of the present disclosure, the paint is applied to the metal plate with an applicator roll, so compared to the case of applying the paint to the metal plate with a curtain coater, it is difficult to apply a thin film. It is possible to achieve coating with a desired film thickness when manufacturing a metal plate.

By using the method of coating a metal sheet according to the present disclosure, it is possible to manufacture a precoated metal sheet while suppressing air entrainment in the paint and occurrence of roping.
Here, in general, in order to manufacture a precoated metal sheet in a continuous galvanizing line (CGL), application of a water-based paint and an increase in sheet threading speed are required.
However, even if the method for manufacturing a metal plate of the present disclosure is applied to a continuous hot-dip galvanizing line, sedimentation of solids contained in the paint is difficult to occur, and air entrainment and roping are suppressed, and a good paint film is obtained. It is possible to manufacture a precoated metal sheet having

Hereinafter, the method for coating a metal plate according to the present disclosure will be described in detail.

(Coating equipment)
First, a coating apparatus applied in the method of coating a metal plate according to the present disclosure will be described.
FIG. 1-1 is an example of a coating apparatus applied in the metal plate coating method of the present disclosure.

As shown in FIG. 1-1, a coating apparatus 100 is arranged opposite to an applicator roll 10 that applies coating to the surface of a metal plate M by transfer, with the metal plate M interposed therebetween, and supports the metal plate M to be passed. and a backup roll 12 .
Around the applicator roll 10, a paint supply unit 14 for supplying paint to the applicator roll 10, a scraping unit 16 for scraping off the paint remaining on the applicator roll 10 after the paint has been applied to the metal plate M by the applicator roll 10, It also includes a decompression unit 18 arranged on the upstream side in the rotation direction of the applicator roll 10 from the paint supply position of the applicator roll 10 .

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 plays a role of supporting the metal plate against the pushing pressure of the applicator roll 10 . For example, a well-known backup roll that rotates in synchronism with the threading speed of the metal plate, which is applied in a well-known roll coater, can be employed. It is also possible to omit the backup roll by applying tension to the metal plate.

The paint supply unit 14 is arranged above the applicator roll 10 and has a paint supply port 14A serving as a paint discharge port.
The gap 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. , until the paint reaches the outer peripheral surface of the applicator roll 10 (see FIG. 2).

A well-known coater such as a slot coater, curtain coater (roller curtain coater, slide curtain coater, etc.) can be used as the paint supply unit 14 .

The scraping section includes a scraping blade 16A that scrapes 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.

The scraping blade 16A is arranged downstream in the rotation direction of the applicator roll 10 from the paint coating P2 on the metal plate M by the applicator roll 10, and the tip is arranged in contact with the outer peripheral surface of the applicator roll 10 to scrape off the paint.

The scraping blade 16</b>A is a doctor-type blade that is arranged with its tip facing in the direction opposite to the direction of rotation of the applicator roll 10 . Adopting a doctor-type blade improves paint scraping performance.
However, it may be a wiper-type blade that is arranged with its tip directed toward the direction of rotation of the applicator roll 10 .

The scraping blade 16A is a blade made of plastic (a blade made of polyester, polyethylene, polyurethane, etc.), a blade made of ceramic (a blade made of zirconia, titania, etc.), etc., from the viewpoint of paint scraping properties. mentioned.

The decompression unit 18 is arranged upstream of the paint supply position P1 of the applicator roll 10 in the rotation direction of the applicator roll 10 and adjacent to the paint supply unit 14, and includes a hood 18A that covers the outer peripheral surface of the applicator roll 10, and a hood. It comprises a duct 18B connected with 18A.
In the decompression section 18, the duct 18B is connected to a suction pump (not shown). The atmospheric pressure on the upstream side in the direction of rotation of 10 is made negative.
Here, the atmospheric pressure can be measured with a pressure gauge provided on the inner surface of the hood 18A.

In addition to the above, the coating apparatus 100 can be equipped with various members that are provided in known coating apparatuses.

(Painting method)
An example of the method of coating a metal plate according to the present disclosure using the coating device 100 will be described.

In the method of coating a metal plate of the present disclosure, first, the applicator roll 10 is rotated, and the paint is discharged from the paint supply port 14A of the paint supply unit 14 arranged 1 to 10 mm away from the applicator roll 10, and onto the applicator roll 10. Supply paint.
After or at the same time as the start of supplying the coating material to the applicator roll 10, the threading of the metal plate M is started, and the coating material supplied by the applicator roll 10 is transferred to the passing metal plate M for coating.

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 transfer of the paint from the applicator roll 10 to the metal plate M is performed only once. Even if the sheet threading speed is increased, the occurrence of roping is suppressed.

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, the collision energy of the paint is small when the paint contacts the applicator roll 10, and the paint is supplied to the applicator roll 10. The air entrained in the paint is difficult to be discharged to the outside of the paint, and the air is entrained in the paint. In particular, when the metal plate M is passed at a high speed, entrainment of air in the paint tends to occur.
Therefore, the gap between the paint supply port 14A of the paint supply unit 14 and the applicator roll 10 is set to 1 mm or more.
From the viewpoint of suppressing entrainment of air into 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, the paint contains a color pigment, and if the metal plate M is passed faster, the film of the paint liquid is divided. may be When the paint film is divided, there are areas with paint on the applicator roll 10 and areas without paint. This is the starting point, and color loss of the coating film may occur. Therefore, the gap between the paint supply port 14A of the paint supply unit 14 and the applicator roll 10 is set to 10 mm or less.

The direction of rotation of the applicator roll 10 may be the same as the threading direction A of the metal plate M or the opposite direction to the threading direction A of the metal plate M. However, the direction of rotation of the applicator roll 10 is preferably opposite to the threading direction A of the metal plate M. When the direction of rotation of the applicator roll 10 is opposite to the threading direction A of the metal plate M, separation of the coating material is suppressed during transfer of the coating material, and occurrence of roping is suppressed.
In addition, the rotation direction of the applicator roll 10 means the direction at the position facing the metal plate M (that is, the paint application position P2).

The amount of paint supplied to the applicator roll 10 by the paint supply unit 14 is appropriately set according to the thickness of the coating film to be formed on the surface of the metal plate M. The rotation speed of the applicator roll 10 is also appropriately set according to the thickness of the coating film to be formed on the surface of the metal plate M.
The threading speed LS of the metal plate M is, for example, 20 to 200 m/min.

The paint is supplied to the applicator roll 10 by the paint supply unit 14 by reducing the air pressure on the upstream side in the rotation direction of the applicator roll with respect to the paint supply position P1 by the pressure reduction unit 18 to the air pressure on the downstream side in the rotation direction of the applicator roll 10. and implement. As a result, the pressure around the paint supply position P1 is reduced, and the air that is involved when the paint is supplied to the applicator roll 10 is easily discharged to the outside of the paint, thereby suppressing entrainment of air into the paint.

From the viewpoint of suppressing entrainment of air into the paint, the pressure difference between the air pressure on the upstream side in the rotation direction of the applicator roll 10 and the pressure on the downstream side in the rotation direction of the applicator roll 10 with respect to the paint supply position P1 of the applicator roll 10 is preferably 100 to 2000 Pa. , 200 to 800 Pa are more preferred.

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 measured by a pressure gauge (not shown) provided inside the decompression section 18 hood 18A. is regarded as the air pressure on the upstream side in the rotation direction of the applicator roll 10 with respect to the coating material supply position P1 of the applicator roll 10 .
On the other hand, the atmospheric pressure on the downstream side in the rotation direction of the applicator roll is atmospheric pressure.

Next, in the method of coating a metal plate of the present disclosure, after the supplied paint is transferred to the passing metal plate M by the applicator roll 10 and applied, the paint remaining on the applicator roll 10 is removed by the scraping unit 16. , is scraped off by the scraping blade 16A, and recovered by the paint recovery pan 16B. The recovered paint may be reused. In other words, the paint collected in the paint collection pan 16B may be circulated and discharged from the paint supply section 14 to be reused for painting.

The metal plate M to be painted includes galvanized steel plate, zinc-aluminum alloy plated steel plate, zinc-aluminum-magnesium alloy plated steel plate, aluminum plated steel plate, zinc-nickel alloy plated steel plate, zinc-iron alloy plated steel plate, Well-known metal plates such as copper plates, magnesium plates, aluminum plates, and stainless steel plates can be used.
Here, the metal plate M may be coated with a known chemical conversion treatment film or a known primer coating before coating with paint.

In the metal plate coating method of the present disclosure described above, air entrainment in the paint and roping can be suppressed even if the metal plate M is threaded at a high speed, as described above.

Then, after forming a coating film on the surface of the metal plate M by the method of coating a metal plate of the present disclosure, 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 for the coating film may be appropriately set according to the paint used.

(paint)
An example of the paint used in the method of coating a metal plate according to the present disclosure will be described below.

The paint can be 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 a water-based paint). .
Here, when forming a cured film as a coating film, the coating material may contain a curing agent together with the resin.

[resin]
The resin is not particularly limited, and includes well-known resins applied to paints, such as polyester resins, polyurethane resins, acrylic resins, fluorine resins, and epoxy resins. These resins may be used singly or in a blend of two or more.
Among these, in particular, the resin is preferably at least one selected from the group consisting of polyester resins, acrylic resins, and urethane resins, which are easy to achieve both workability and other performance, polyester resins, and At least one selected from the group consisting of urethane resins is more preferable.

Identification of the type of resin can be measured by a known method. For example, the type of resin is specified by measuring an infrared absorption spectrum (IR), pyrolysis gas chromatography, or the like on a sample obtained by drying the paint after centrifugation.

Although the number average molecular weight of the resin is not particularly limited, it is preferably 3,000 to 25,000. When resins having different number average molecular weights are used together, the number average molecular weight of the resin is the weighted average number average molecular weight.

A method for measuring the number average molecular weight of the resin is as follows.
After centrifuging the paint, weigh the paint supernatant to 20 mg as resin solids.
After dissolving the obtained sample in 10 ml of tetrahydrofuran (THF), using gel permeation chromatography (GPC, Tosoh Corporation HLC8220 GPC, column Shodex KF type), pump flow rate 0.6 ml / min, temperature 40 ° C. Measure in Then, the number average molecular weight of the resin is calculated from the chromatogram based on the molecular weight of standard polystyrene.

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

[Organic solvent]
An organic solvent is a solvent that dissolves the resin. In addition, the organic solvent must remain in a liquid state without reacting with a curing agent, coloring pigment, surfactant, or the like.
as an organic solvent. There are no particular restrictions, and known solvents can be used. Examples of organic solvents include ester organic solvents such as 3-methoxybutyl acetate, ethyl acetate, isopropyl acetate, and butyl acetate; ketone organic solvents such as methyl ethyl ketone, acetone, methyl isobutyl ketone, cyclohexanone, and isophorone; Solvesso 100 ( ExxonMobil), Solvesso 150 (ExxonMobil) and the like.
These organic solvents may be used singly or as a mixture of two or more at any ratio.

[water]
Examples of water include tap water, distilled water, and pure water.

[Surfactant]
Surfactants have the function of expelling the air caught in the paint and the function of stably forming a film of the discharged paint (that is, a curtain film).
Examples of surfactants include acrylic surfactants, silicone surfactants, fluorine-modified silicone surfactants, and the like.

Examples of acrylic surfactants include copolymers of acrylic monomers. Examples of acrylic monomers include acrylic acid alkyl esters, acrylic acid alkylene oxide esters, (meth)acrylic acid alkyl ether esters, acrylic acid amino Alkyl esters, acrylic acid amide compounds and the like can be mentioned.

Examples of silicone-based surfactants include polydimethylsiloxanes whose side chains or ends of main chains are modified with alkylene glycol (ethylene glycol, propylene glycol, etc.) or the like.
Examples of fluorine-modified silicone-based surfactants include those obtained by partially substituting the above silicone-based surfactants with perfluoroalkyl groups.

The surfactant concentration 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, the action of discharging the air entrained in the paint, and the action of stably forming a film of the discharged paint (that is, a curtain film). is easier to improve.

[Solid content]
The paint may contain solids with a specific gravity of 1.2 to 10.0. A solid content with a specific gravity of 1.2 to 10.0 tends to settle in the paint. In particular, solids having a specific gravity of 1.2 to 10.0 and an average particle size of 0.5 to 5.0 μm tend to settle in the paint.
However, even if the paint contains solids that tend to settle out, the metal plate coating method of the present disclosure supplies the paint directly from the paint supply unit to the applicator roll, thereby suppressing the sedimentation of the solids.
The specific gravity of the solid content is preferably 1.5-7.0. The average particle size of the solid content is preferably 1.0-5.0 μm.

The specific gravity of the solid content is measured as follows.
A paint to be measured is applied to the surface of a metal plate to form a paint film, and then the paint film is dried and/or cured to form a precoat layer.
A metal plate with a precoat layer is used as a sample, and the surface of the precoat layer (the surface facing in the thickness direction) is polished. Then, a cross section (here, a plane cross section) of the precoat layer formed by this polishing is analyzed with an electron probe microanalyzer (FE-EPMA: Electron Probe MicroAnalyser) to determine the ratio of elements constituting the solid content. In addition, the substances that make up the solid content are identified from the analysis results of microscopic Raman spectroscopy, microscopic infrared spectroscopy, and microscopic X-ray diffraction. Then, the specific gravity of the solid content is obtained from literature values.

The average particle size of the solid content is measured as follows.
As in the measurement of the specific gravity of the solid content, the metal plate with the precoat layer is used as a sample, and the cross section (flat cross section here) of the precoat layer formed by polishing is observed with an FE-SEM. The cross-sectional diameter of the solid content gradually increases each time polishing is repeated, and eventually reaches the maximum value. This maximum value corresponds to the particle size of the solid content. Further polishing reduces the cross-sectional diameter. Therefore, the cross-sectional diameter of the solid matter observed in a certain field of view is measured each time polishing is performed, and the maximum measured value is taken as the particle size of the solid matter. Then, the arithmetic average value of the particle sizes of a plurality of arbitrarily selected solids (for example, 20) is taken as the average particle size of the solids.
In addition, when the first observed cross-sectional diameter is the maximum value, the cross-sectional diameter may be smaller than the actual particle size, so it is excluded from the target when calculating the average value.

Here, the method for polishing the precoat layer is not particularly limited, and a known method can be adopted. For example, resin embedding polishing, microtome processing, or the like can be used. Cryo Scanning Electroscopy combined with Focused Ion Beam (FIB-SEM) is suitable as a polishing method when obtaining the average particle size of the beads 40 with particularly high accuracy. Since the sample temperature is about -100°C and the sample is processed with an ion beam, there is little damage to the coating due to the heat generated by the ion beam irradiation, and polishing in sub-nanometer units is possible. can also determine the particle size.

A typical component of the solid content is a pigment.

Examples of pigments include pigments that have one or both functions of coloring and imparting conductivity (that is, coloring pigments, conductive pigments, colored conductive pigments, etc.).
The pigment is not particularly limited, and known pigments can be used.
Specifically, as a pigment, 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) and the like.

Identification of the type of pigment can be measured by a known method. For example, the type of color pigment can be identified by elemental analysis by SEM-EDX or X-ray crystal diffraction measurement of the coating film or the sediment after centrifugation.

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

[Other additives]
Paints may also contain other known additives such as catalysts, waxes, UV absorbers, antioxidants, plasticizers, coupling agents, pigment dispersants, suspending agents, antimicrobial agents, and the like.

[Dynamic surface tension]
Among the paints, the dynamic surface tension of water-based paints measured by the maximum bubble pressure method is 30 to 60 mN / m at a bubble life time of 0.05 s, and 20 to 50 mN at a bubble life time of 0.5 s. /m is preferred.
When the dynamic surface tension is within these ranges, the action of discharging air entrained in the paint and the action of stably forming a film of the discharged paint (that is, a curtain film) are improved.
The dynamic surface tension can be adjusted by adjusting the type of resin and surfactant, and the concentration of the surfactant.

The dynamic surface tension of a water-based paint can be measured by the maximum bubble pressure method, for example, using Kyowa Interface Science DP-51. Specifically, it is as follows.
In order to stabilize the pressure at the start and end of the measurement, the dynamic surface tension was measured when the bubble lifetime was changed from 0.01 seconds to 5 seconds. Determine the dynamic surface tension in seconds.
A probe with a diameter of 1 mm is used, and the measurement is started with 100% air in the tank built into the device.
If the water-based paint has a high viscosity and cannot be measured, the paint temperature may be raised (the paint viscosity may be lowered) for measurement. Even if the temperature of the paint is raised and the viscosity is lowered, the dynamic surface tension does not change. The paint measurement temperature is preferably in the range of 10 to 60°C. If the temperature is too high, the organic solvent that is the solvent may volatilize and the dynamic surface tension may change.

[viscosity]
There are no particular restrictions on the viscosity of the paint. However, as the paint, a paint with a viscosity as low as 5 to 2000 mPa·s (preferably 10 to 500 mPa·s) can also be used. Even if a low-viscosity paint is used, even if the paint contains solids (in particular, solids such as pigments having a large average particle size and a high specific gravity), sedimentation of the solids is suppressed.
In addition, when a low-viscosity paint is used, when the applicator roll 10 transfers the paint to the metal plate M, separation of the paint is less likely to occur, and roping is suppressed.

The viscosity of the paint is the viscosity at normal temperature (25° C.) and is measured as follows. Known methods such as a Ford cup type viscometer, an Iwata cup type viscometer, a vibrating viscometer, and a rheometer can be used for paints whose viscosity does not change with shear rate. For paints whose viscosity varies depending on the shear rate, a rheometer is used to measure the viscosity in the range of 1000 to 10000 s ^-1 which is said to be the shear rate during roll coating.

EXAMPLES Hereinafter, the paint and the coating method thereof according to the present invention will be specifically described with reference to examples and comparative examples. The examples shown below are merely examples of the paint and the coating method according to the present invention, and the paint and the coating method according to the present invention are not limited to the following examples.

<Test Examples 1-1 to 5-6, 9-1 to 11-7>
Using the coating apparatus 100 shown in FIG. 1-1, metal plates were coated under the conditions shown in Table 1. In this test example, a slot coater was used as the paint supply unit 14 (indicated as "slot + APR" in the column of the coating method in the table).

The details of symbols, abbreviations, etc. in the table will be described below.
(Direction of roll rotation)
R: The direction of rotation of the applicator roll 10 is opposite to the threading direction A of the metal plate M.
·N: The direction of rotation of the applicator roll 10 is the same as the direction A of the metal plate M.

(scraping blade)
・Polyester: Polyester doctor blade ・Ceramic: Zirconia doctor blade

Air pressure difference (downstream side - upstream side): the absolute value of the air pressure difference between the air pressure on the upstream side in the rotation direction of the applicator roll 10 and the air pressure on the downstream side in the rotation direction of the applicator roll 10 with respect to the paint supply position P1.

Gap: the distance between the paint supply port 14A of the paint supply unit 14 and the applicator roll 10

・LS: Threading speed

(Column of resin/curing agent)
・A: Urethane/melamine (mass ratio = 100/20), urethane (manufactured, 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 Beccamin" ”=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 Beckamin" = 40% by mass)

(column of surfactant)
・a: Olfin WE-003 manufactured by Nissin Chemical Industry Co., Ltd.
・b: Polyflow No. manufactured by Kyoeisha Chemical Co., Ltd. 50E
・c: Floren AC-303 manufactured by Kyoeisha Chemical Co., Ltd.

(column of pigment)
・VB2: vanadium diboron ・Ag: silver ・Ni: nickel ・Al: aluminum

(column of solvent)
Solvent: A 1:1 mixture of Cyclohexanone/Shoei Chemical Industry Co., Ltd. and Solvesso 150/Exxon Mobil Co., Ltd. was used.

(column of dynamic surface tension)
・BLT 0.05 s: Dynamic surface tension (mN/m) at bubble lifetime 0.05 s
・BLT0.5s: Dynamic surface tension (mN/m) at bubble lifetime 0.5s

<Test Examples 6-1 to 6-6>
A metal plate was coated under the conditions shown in Table 1 using the coating apparatus 200 shown in FIG.
The coating apparatus 200 shown in FIG. 2 employs a configuration in which the slot coater 20 supplies paint to the intermediate roll 22 instead of the paint supply unit 14, and then the intermediate roll 22 supplies the paint to the applicator roll 10. Except for this, the coating apparatus has the same configuration as that of FIG.
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 the intermediate roll 22 has supplied the paint to the applicator roll 10 . On the other hand, the decompression unit 18 is not provided.

Here, "NR" and "NN" in the column of roll rotation direction in the table indicate the following items.
NR: The rotation direction of the intermediate roll 22 is the same as the threading direction A of the metal plate M, and the rotation direction of the applicator roll 10 is the opposite direction to the metal plate M threading direction A. NN: The rotation direction of the intermediate roll 22 is the same. The same direction as the threading direction A of the metal plate M, and the rotating direction of the applicator roll 10 is the same direction as the threading direction A of the metal plate M.

<Test Examples 7-1 to 8-6>
A metal plate was coated under the conditions shown in Table 1 using the coating apparatus 300 shown in FIG.
The coating apparatus 300 shown in FIG. 3 adopts a configuration in which the paint is picked up by the pickup roll 24 from a storage pan 26 that stores the paint, instead of the paint supply unit 14, and then the paint is supplied to the applicator roll 10. This coating apparatus has the same configuration as that shown in Fig. 1-1 (in the table, "Roll coater" is written in the coating method column).
The decompression unit 18 is not provided in the coating apparatus 300 shown in FIG.

Here, "NR" and "NN" in the column of roll rotation direction in the table indicate the following items.
NR: The rotation direction of the pickup roll 24 is the same as the threading direction A of the metal plate M, and the rotation direction of the applicator roll 10 is the opposite direction to the metal plate M threading direction A. NN: The rotation direction of the pickup roll 24 is the same. The same direction as the threading direction A of the metal plate M, and the rotating direction of the applicator roll 10 is the same direction as the threading direction A of the metal plate M.

<Evaluation>
The following evaluation was performed for each test example.

(entrained air)
Air entrainment was evaluated as follows.
The coated metal plate was dried and the surface was visually observed. Evaluation criteria are as follows. A score of 4 or more was regarded as passing.
・5: No appearance defects.
5-: No uncoated portion. The coating film has shading and cannot be seen when observed from a distance of 30 cm.
・4: No uncoated portion. The coating film has shading and cannot be observed from a distance of 50 cm.
3: No unpainted portion. The coating film has shading and cannot be seen when observed from a distance of 100 cm.
・2: There is an unpainted part. Observing an arbitrary place, the number of unpainted parts is 3 pieces/ ^1m2 or less.
・1: There is an unpainted part. Observation of any place, more ^than 3 unpainted parts/1m2.

(Roping)
Roping was evaluated as follows. The coated metal plate was dried and the surface was visually observed. Evaluation criteria are as follows. A score of 4 or more was regarded as passing.
・5: No appearance defects ・5-: With roping. It is invisible when observed from a distance of 30 cm.
・4 : With roping. Observed from a distance of 30 cm, it cannot be seen from the front. Slightly visible from an angle.
・3 : With roping. Observed from a distance of 30 cm, it cannot be seen from the front. visible from an angle.
・2 : With roping. It is visible from the front when observed from a distance of 30 cm. visible from an angle.
・1 : With roping. It is clearly visible from the front when observed from a distance of 30 cm. Clearly visible from an angle.

(color loss)
Color loss was evaluated as follows. The coated metal plate was dried and the surface was visually observed. Evaluation criteria are as follows. A score of 4 or more was regarded as passing.
・5: No color loss.
5-: No color loss. There is light and shade in the width direction. Observation from a distance of 30 cm makes it impossible to determine the density.
4: No color loss. There is light and shade in the width direction. Observation from a distance of 50 cm makes it impossible to determine the density.
・3: There is color omission. An arbitrary 1 m ² area was observed, and the area ratio of color loss was 1% or less. 2: Color loss was observed. An arbitrary 1 m ² area was observed, and the area ratio of color loss was 3% or less. 1: Color loss was observed. Observing an arbitrary 1 m ² , the color loss area rate is over 3%

(paint scattering)
Paint scattering was evaluated as follows. Paper was placed around the sprayer and the sprayer was run for 30 minutes under the specified conditions. It was investigated where the paint was scattered on the paper. Starting from the center of the coater, the maximum distance that the paint was scattered was investigated. Evaluation criteria are as follows. A score of 3 or more was considered as a pass.
5: No paint scattering.
4: The maximum paint scattering distance is 1 m or less.
3: The maximum paint scattering distance is more than 1 m and 2 m or less.
2: The maximum paint scattering distance is more than 2 m and 3 m or less.
1: The maximum paint scattering distance is over 3m.

(Conductivity)
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 measuring method specified in JIS C 2550, and the conductivity was evaluated according to the following criteria. Evaluation criteria are as follows. There are no specific eligibility criteria.
(Evaluation criteria)
6: Interlayer resistance is less than 1.0 Ω·cm ² 5: Interlayer resistance is 1.0 Ω·cm ² or more and less than 1.5 Ω·cm ² 4: Interlayer resistance is 1.5 Ω·cm ² or more. Less than 0 Ω·cm ² 3: Interlayer resistance is 2.0 Ω·cm ² or more and less than 2.5 Ω·cm ² 2: Interlayer resistance is 2.5 Ω·cm ^{2 or} more and less than 3.0 Ω·cm ² 1: Interlayer Resistance value is 3.0Ω・cm ² or more

From the above results, Test Examples 1-1 to 3-6, 9-1 to 9-2, 10-1 to 11-7 (Examples), Test Examples 4-1 to 8-6, 9-3 (Comparative It can be seen that air entrainment in the paint, roping, color loss, and paint scattering can be suppressed even if the metal plate threading speed is increased compared to Example).
Also, it can be seen that Test Examples 1-1 to 3-6, 9-1 to 9-2, and 10-1 to 11-7 (Examples) are also evaluated as good in conductivity.

10 Applicator roll 12 Backup roll 14 Paint supply part 14A Paint supply port 16 Scraping part 16A Scraping blade 16B Paint recovery pan 18 Decompression part 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 (9)

A paint is supplied to the rotating applicator roll from above the applicator roll by a paint supply unit whose paint supply port is arranged 1 to 10 mm away from the applicator roll, and the paint supplied by the applicator roll is passed through. A method of coating a metal plate in which the metal plate to be plated is transferred and coated. A decompression unit arranged on the upstream side in the rotation direction of the applicator roll relative to the paint supply position of the applicator roll reduces the pressure of the applicator roll on the upstream side in the rotation direction of the applicator roll with respect to the paint supply position. 2. The method of coating a metal plate according to claim 1, wherein the coating material is supplied to the applicator roll by the coating material supply part in a state in which the air pressure on the downstream side in the rotation direction is low. 3. The metal plate according to claim 2, wherein the absolute value of the pressure difference between the pressure upstream in the rotation direction of the applicator roll and the pressure downstream in the rotation direction of the applicator roll with respect to the paint supply position is 100 to 2000 Pa. painting method. The method of coating a metal plate according to any one of claims 1 to 3, wherein the direction of rotation of the applicator roll is opposite to the direction in which the metal plate is passed. The method of coating a metal plate according to any one of claims 1 to 4, wherein the paint is a paint containing a resin, a surfactant and an organic solvent. The paint contains a resin, a surfactant, and water, and has a dynamic surface tension of 30 to 60 mN/m at a bubble lifetime of 0.05 s, as measured by the maximum bubble pressure method. The method for coating a metal plate according to any one of claims 1 to 5, wherein the life time is 0.5 s and the life time is 20 to 50 mN/m. The method of coating a metal plate according to any one of claims 1 to 6, wherein the paint contains a solid content with a specific gravity of 1.2 to 10.0 g/cm ³ . 8. The method of coating a metal plate according to claim 7, wherein the solid content has an average particle size of 0.5 to 5.0 μm. A method for producing a precoated metal plate using the method for coating a metal plate according to any one of claims 1 to 8.

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