JP4571909B2 - Multilayer coating method for metal plates - Google Patents

Description

  The present invention relates to a method for applying a multilayer film including a metal surface treatment agent coating film and a solvent-based paint film on the surface of a metal plate.

  A metal plate made of steel plate, galvanized steel plate, zinc alloy plated steel plate, aluminum plate, etc. forms a surface treatment film on its surface for the purpose of improving rust prevention or paintability, and if necessary further on it Various paints are overcoated.

  Conventionally, a chromate film has been used as a surface treatment film that has both improved rust prevention and improved paintability. In particular, the chromate film is suitable for preventing white rust of a galvanized steel sheet or a zinc alloy plated steel sheet. In addition, a phosphate film is excellent as a surface treatment film that improves paintability. These surface treatment films are also referred to as chemical conversion treatment films.

  In the background of increasing environmental problems, conventional chromate coatings have been gradually replaced by non-chromate coatings. As a non-chromate film having the same performance as a chromate film, Patent Document 1 describes a non-chromate film coated with a tannin or tannic acid, a silane coupling agent, and fine silica at the same time. Patent Document 2 discloses a non-chromate film containing a crosslinked resin matrix and an inorganic rust inhibitor, and the crosslinked resin matrix is formed by a reaction between an aqueous resin and a crosslinking agent.

  When forming a solvent-based paint film on the surface of a metal plate to obtain a coated metal plate, first, the chemical for forming the surface treatment film is applied and dried to form a surface treatment film. Is used as a base treatment layer, and a solvent-based paint is applied thereon, followed by drying and baking as necessary to obtain a coated metal plate.

  When applying a solvent-based paint on a surface-treated film, the surface-treated film is applied by a wiping method and then dried, and then a roll coating method is usually used as a method for applying a solvent-based paint thereafter. It is done. However, when the roll coating method is used, particularly when coating is performed on a hot-dip galvanized steel sheet, there is often a portion having a high roughness on the surface of the steel sheet, and wear of the roll is accelerated. In addition, when a roll is used, the roll is wrinkled at the end portion of the steel plate, so that it is necessary to use a schedule coating that changes from a wide width to a narrow width as a steel plate width schedule, which increases schedule constraints.

  As a method of forming a multilayer film on the surface of a plate without using a roll, a method is known in which a film of a coating solution is discharged from a plurality of slits and these films are applied onto a moving plate to form a multilayer film. It has been. For the multilayer coating method, a slide curtain coating apparatus can be used in which the coating liquid is allowed to flow down along the slide to form a curtain to form a multilayer film on the plate surface. Also, a slide bead device that does not form a curtain, or a die coater device that forms a multilayer film without using a slide by discharging paint from a plurality of adjacent slits can be used.

  As a multi-layer simultaneous coating apparatus that can apply a multi-layer coating film to a steel sheet surface at once, Patent Document 3 describes a slide curtain coating apparatus. The paint uses a polyester primer paint as the lower layer, a polymer polyester top coat paint as the middle layer, and a polymer polyester clear paint as the upper layer.

  When a slide curtain coating device is used, if the curtain width is equal to or smaller than the width of the plate at the coating position on the plate, the thickness of the film coated on the surface of the plate is the width direction. There is a tendency to be thick at the end, and the uniformity of the film thickness may not be maintained. On the other hand, if the width of the curtain is made wider than the width of the plate at the coating portion on the plate, the thickness of the film coated on the plate can be made uniform in the width direction.

  When the width of the curtain is made wider than the width of the plate, the curtain portion located outside the both ends of the width of the plate will fall below the plate. About this falling curtain part, if a curtain is a liquid film of a single layer, it can collect | recover and it can reuse as a curtain liquid film raw material. However, when coating a plurality of layers of liquid film as described in Patent Document 3, the curtain is a liquid film of a plurality of layers even in the curtain portion that falls outside the both ends of the width of the plate. Becomes a mixture of two or more different compositions and cannot be reused as a curtain liquid film raw material.

  In the invention described in Patent Document 4, one of the plurality of liquid films constituting the curtain is larger than the width of the web (plate), and the other layer has a width that does not overflow the web. . Thus, since the liquid film overflowing from the edge of the web is a single layer, the overflowing composition can be collected and recycled into the liquid feed of the same composition layer. Here, a layer that is larger than the width of the web and has a width equivalent to the curtain width is called a wide layer, and a layer that is equivalent to the web width or several tens of mm wider than the web width is called a narrow layer.

  Even when the above-mentioned multilayer coating method is used for coating, the surface treatment film as the undercoat layer is applied alone, and after the surface treatment film is dried, the coating is applied using the multilayer coating method. It has been broken.

JP 2005-206921 A JP 2005-281863 A JP-A-6-190323 Japanese Patent Publication No.62-47075

  As described above, when the surface treatment film and the paint film are formed on the surface of the metal plate, a method of separately applying the surface treatment film and the paint film as the base treatment layer is employed. Here, if a multi-layer simultaneous coating device can be used to coat the surface treatment film and the paint film at the same time, the coating line can be simplified, the manufacturing time of the coated metal plate can be shortened, and the manufacturing equipment cost can be reduced. It is possible and convenient.

  However, using a method of discharging a coating liquid film from a plurality of slits and applying these films onto a moving plate to form a multilayer film, the surface treatment film and the paint film are applied simultaneously. A phenomenon called “Waki” occurs in the coating film after baking or drying treatment after painting. Waki is a foam-like surface defect on the surface of the paint film, and the solvent remaining inside the paint film is rapidly evaporated by heating during baking and drying to form bubbles in the paint film. The film surface is deformed and appears as a bubble defect.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a multilayer film coating method for a metal plate, in which a surface treatment film and a paint film can be coated at the same time using a multilayer simultaneous coating apparatus without generating any cracks.

  The chemicals that form the non-chromate surface treatment film, the chromate surface treatment film, the phosphate film, and the like are all water-soluble, that is, an aqueous drug. On the other hand, solvent-based paints are often used as paints applied on the surface treatment film.

  When a multi-layer simultaneous coating device is used and a water-based surface treatment film and a solvent-based paint film are simultaneously coated on the surface of a metal plate, a water-based surface treatment film is formed on the side close to the metal plate, and the solvent-based side is in contact with the atmosphere. A paint film is formed. Since the formed surface treatment film contains a large amount of moisture, it is necessary to release this moisture into the atmosphere to form a dry film. However, a solvent-based paint film is formed between the surface treatment film and the air atmosphere. Moisture in the surface-treated film cannot be dissolved in the solvent-based paint, so that moisture cannot pass through the film and remains in the film. During the heating to dry and bake the paint, this moisture rapidly evaporates and bubbles are formed in the film, which deforms the already cured paint film and becomes a bubble defect. It has been found that this is the reason why when the surface treatment film and the paint film are applied at the same time, the coating film after baking or drying treatment is wrinkled.

  If a water-soluble solvent is used as the solvent for the solvent-based paint, the water in the aqueous surface treatment film can be dissolved in the paint, and can pass through the paint and escape to the atmosphere. . As a result, it is possible to simultaneously coat the surface treatment film and the paint film using a multi-layer simultaneous coating apparatus without generating any cracks.

This invention is made | formed based on the said knowledge, The place made into the summary is as follows.
(1) When a film of a coating solution is discharged from a plurality of slits and applied to a moving metal plate to form a multilayer film, the multilayer film is applied to the side closer to the metal plate. The coating liquid is an aqueous metal surface treatment agent, and one or more of the coating liquids coated on the side far from the metal plate is a solvent-based paint, and the solvent of the solvent-based paint contains a water-soluble solvent. A multilayer film coating method for a metal plate.
(2) The metal film multilayer film coating method according to the above (1), wherein the ratio of the water-soluble solvent in the solvent is 50% by mass or more.
(3) The above-mentioned aqueous metal surface treatment agent is composed of an organic or inorganic material not containing chromium, is water-soluble at room temperature, and becomes water-insoluble when heated to dryness (1) or (2) The multilayer film coating method of the metal plate described in 1.
(4) The method for coating a metal plate with a multilayer film according to any one of (1) to (3), wherein a slide curtain coating device is used when the coating solution is applied onto the metal plate.
(5) The method for coating a metal plate with a multilayer film according to the above (4), wherein the curtain width by the aqueous metal surface treatment agent is narrower than the curtain width by the solvent-based paint.
(6) About the coating film by the aqueous metal surface treatment agent, the wet film thickness is 2 to 10 μm, the dry film thickness is 0.5 to 3 μm, and the interface roughness between the metal surface treatment film and the solvent-based paint film is Ra. The metal film multilayer film coating method according to any one of (1) to (5) above, wherein the thickness is 0.2 μm or more.

  The present invention is a surface treatment using an aqueous metal surface treatment agent by using a water-soluble solvent as a solvent for a solvent-based paint when simultaneously applying a surface treatment film and a paint film using a multilayer simultaneous coating apparatus. Moisture in the film can be quickly moved to the outermost surface of the multilayer film, and the surface treatment film and the paint film can be applied simultaneously without generating any cracks.

  The present invention relates to a method for coating a multilayer coating film, wherein a coating film is discharged from a plurality of slits, and these films are applied onto a moving metal plate to form a multilayer film, followed by drying or baking. Any method and apparatus may be used as long as the apparatus has a coating apparatus and a multilayer coating film manufactured thereby.

  When coating a multilayer film, a slide curtain coating apparatus 1 as shown in FIG. 1 can be used. The slide curtain coating apparatus 1 has two or more slits 2. When the paint is discharged from each slit 2, the discharged paint becomes a liquid film and flows down along the slide. The liquid film that has become a multilayer film corresponding to the number of slits flows down along the slide 3, leaves the slide 3 at the slide end, and falls freely as a multilayer film curtain 6. Below the slide curtain coating apparatus, a metal plate 7 is running as an object to be curtain coated. The multilayer film curtain 6 that has fallen on the surface of the metal plate adheres to the surface of the metal plate while maintaining a multilayer state, and a plurality of layers of coating films are formed on the surface of the metal plate 7.

  As other multilayer coating methods, a slide bead device that does not form a curtain, a die coater device that forms a multilayer film without using a slide by discharging paint from a plurality of adjacent slits, etc. can be used. Is the same as a slide curtain coating device in that it can be formed simultaneously.

  Hereinafter, the case where the slide curtain coating apparatus of FIG. 1 is used will be described as an example.

  The slide curtain coating apparatus 1 has two or more slits 2. When the paint is discharged from each slit 2, the discharged paint becomes a liquid film and flows down along the slide. For example, in a slide curtain coating apparatus having three slits, the liquid film discharged from the first slit 2a flows down on the slide to the position of the second slit 2b and becomes a liquid film discharged from the second slit 2b. A two-layer liquid film is formed in contact, and the two-layer liquid film flows down to the third slit 2c and contacts the liquid film discharged from the third slit 2c to form a three-layer liquid film. The liquid film formed on the slide 3 includes a liquid film discharged from the first slit 2a in the uppermost layer, a liquid film discharged from the second slit 2b in the next layer, and a third slit in the lowermost layer. It is formed in layers in the order of the liquid film discharged from 2c. The width end of the liquid film on the slide 3 is guided by the edge guide 5. The three-layer liquid film flows down along the slide 3, leaves the slide 3 at the slide end, and freely falls as a three-layer multilayer film curtain 6. The width end portion of the curtain 6 is guided by the guide device 4. Below the slide curtain coating apparatus, a metal plate 7 is running as an object to be curtain coated. The multilayer curtain that has fallen on the surface of the metal plate adheres to the surface of the metal plate while maintaining a multilayer state, and a plurality of coating films are formed on the surface of the metal plate.

  When the metal plate travels in the direction of the metal plate traveling direction 8 shown in FIG. 1, the liquid film discharged from the third slit 2c forms the lowest layer closest to the metal plate 7, and is discharged from the first slit 2a. The liquid film thus formed forms the uppermost layer. If the traveling direction of the metal plate is opposite to the direction shown in FIG. 1, the stacking order of the liquid films on the metal plate 7 is reversed.

  In the example shown in FIG. 1, the aqueous metal surface treatment agent that forms the surface treatment film is discharged from the third slit 2c. When the coating material formed on the surface treatment film is one layer, the coating material is discharged from the second slit 2b, and the first slit 2a is not used. When the paint is two layers, each paint is discharged from the second slit 2b and the first slit 2a.

  In the present invention, at least one of the coating liquids applied to the side far from the metal plate is a solvent-based paint, and the solvent of the solvent-based paint is a water-soluble solvent. When a water-insoluble solvent that is usually used as a solvent for solvent-based paints is used, evaporation of moisture contained in the lowermost aqueous surface treatment agent is prevented, which causes cracking. In contrast, by using a water-soluble solvent as a solvent as in the present invention, moisture contained in the surface treatment layer can be removed from the system through the coating film, so that drying and baking after the multilayer coating is applied. Sometimes the moisture in the surface treatment layer is rapidly eliminated, and the occurrence of armpits can be suppressed.

  When the traveling direction of the metal plate is opposite to the direction shown in FIG. 1, the aqueous metal surface treatment agent that forms the surface treatment film is discharged from the uppermost slit, for example, the first slit 2a.

  As the water-soluble solvent used in the solvent-based paint of the present invention, one or two of dioxane and dimethyl sulfoxide can be employed. Since these solvents have physical properties of a melting point of 0 ° C. or higher and a boiling point of 50 ° C. or higher, they are liquid at room temperature, and the physical properties of the solvent do not change greatly even when contacted with an aqueous metal surface treatment agent. When a multilayer film composed of these solvents and an aqueous metal surface treatment agent is dried, the moisture of the metal surface treatment agent dissolves in the solvent and moisture evaporation occurs from the surface of the solvent. Both can be dried.

  As the water-insoluble solvent used together with the water-soluble solvent, a thinner-containing material containing cyclohexane, xylene and the like can be used. When both a water-soluble solvent and a water-insoluble solvent are used as the solvent, the water-soluble solvent ratio is preferably 50% by mass or more. This is because the moisture of the metal surface treatment agent can be dissolved in the solvent.

  In the multilayer coating method of the present invention, when two or more layers of paint are applied, a solvent-based paint and a water-based paint can be mixed. In that case, it is necessary to use the water-soluble solvent as a solvent for the solvent-based paint. Since the water-based paint is water-soluble in the first place, it is not necessary to use a water-soluble solvent again.

  In the present invention, as the coating liquid applied as a metal surface treatment film on the side close to the metal plate in the multilayer film, any aqueous metal surface treatment agent can be used.

  In the case of forming a non-chromate film as an aqueous metal surface-treated film, it is preferable to use a chemical that is composed of an organic or inorganic material that does not contain chromium, is water-soluble at room temperature, and becomes water-insoluble when dried by heating. For example, as described in Patent Document 1, a non-chromate agent containing tannin or tannic acid, a silane coupling agent, and fine silica simultaneously can be used. The non-chromate drug may contain 2 to 80 g / L tannin or tannic acid, 2 to 80 g / L silane coupling agent, and 1 to 40 g / L fine silica as solids. A polyester resin can be further contained in an amount of 1 to 60 g / L as a solid content. As the silane coupling agent in the non-chromate drug, one having a glycidyl ether group can be used.

  In the case of forming a chromate-based surface treatment film, for example, as disclosed in JP-A-3-131370, water is added to the olefin-α, β-ethylenically unsaturated carboxylic acid copolymer resin dispersion. A resin-based treatment agent containing a dispersible chromium compound and water-dispersible silica can be used.

  As the non-chromate treatment, a phosphate treatment such as zinc phosphate treatment may be used.

  In applying the coating liquid on the metal plate in the present invention, it is preferable to use a slide curtain coating apparatus as shown in FIG.

  As mentioned above, when using a slide curtain coating device, if the curtain width is wider than the width of the plate at the coating area on the plate, the thickness of the film coated on the plate must be uniform in the width direction. Can do.

  In this case, as shown in FIG. 2, one of the plural layers of liquid films constituting the curtain 6 is a wide layer 10 larger than the width of the web (plate), and the other layer has a web of several tens of mm. If the narrow layer 11 overflows only, the liquid film overflowing from the edge of the web is a single layer of the wide layer 10, so this overflowing composition is collected and recycled into the liquid feed of the same composition layer. Since it can be made to circulate, it is preferable. That is, there is an advantage that the portion of the wide layer 10 that overflows from the edge of the web can be recovered and reused.

  By the way, the liquid film by the metal surface treatment agent is usually applied in order to improve the coating adhesion, but the liquid film is much thinner than the solvent-based paint liquid film. When the wide layer 10 and the narrow layer 11 are provided when forming the multilayer film using the slide curtain coating apparatus as described above, if the liquid film of the metal surface treatment agent is the wide film 10, the slide curtain coating apparatus The curtain film flowing down from the film becomes a very thin film at the single-layer film portion at the width edge, which causes a problem that the curtain film cannot be formed. On the other hand, by setting the curtain width with the aqueous metal surface treatment agent to be narrower than the curtain width with the solvent-based paint, the solvent-based paint film becomes a wide film, and the film of the single-layer film portion at the width edge It is preferable because a sufficient thickness can be secured.

  That is, the liquid film made of the metal surface treatment agent is the narrow layer 11, and the liquid film made of the solvent-based paint is the wide layer 10. In the example shown in FIG. 2, the liquid discharged from the slit 2a is a metal surface treatment agent, and the liquid discharged from the slits 2b and 2c is a solvent-based paint. In this case, since the metal surface treatment film needs to be applied to the metal plate 7 side, the metal plate traveling direction 8 needs to be the direction shown in FIG.

  In this invention, about the coating film by an aqueous | water-based metal surface treating agent, it is preferable when a wet film thickness shall be 2-10 micrometers and a dry film thickness shall be 0.5-3 micrometers.

  The metal surface treatment film is applied to improve the adhesion between the metal surface and the paint and to improve the corrosion resistance. However, if the dry film thickness is 0.5 μm or more, the paint adhesion should be satisfied. Can do. Further, the corrosion resistance is improved to some extent when the thickness of the metal surface treatment film is increased, but the corrosion resistance is substantially constant even if the dry film thickness exceeds 3 μm. Then, it is preferable when the dry film thickness of a metal surface treatment film shall be 0.5-3 micrometers.

  Further, since the drying time increases as the wet film thickness increases, the upper limit is set to 10 μm. In order to make the dry film thickness 0.5 μm, which is the lower limit, when the solid content concentration of the wet film is 40%, the wet film thickness is 2 μm. When the solid content concentration exceeds 40%, the metal surface treatment agent becomes unstable, so the lower limit of the wet film thickness was set to 2 μm.

  When applying a metal surface treatment agent coating film and a solvent-based coating film on the surface of a steel sheet, the coating liquid film is discharged from a plurality of slits using a slide curtain coating device, and these films are moved onto the moving steel sheet. A method of forming a multilayer film by coating was adopted.

  As the metal surface treatment agent for forming the metal surface treatment agent coating film, an aqueous non-chromate metal surface treatment agent (treatment agent A, treatment agent B) was used.

  The treating agent A comprises an aqueous resin (acrylic resin) at 200 g / L, water containing 30 g / L of a thiocarbonyl group-containing compound (methylthiourea) and a vanadium compound (ammonium vanadate) at 10 g / L. An aqueous solution containing 100 g / L of L and water-dispersed silica.

  The treating agent B is an aqueous solution mainly composed of a titanium compound (titanium hydrofluoric acid) at 10 g / L and a zirconium compound (zirconium ammonium carbonate) at 10 g / L.

  For the solvent-based paint, thinner (containing cyclohexane and xylene) manufactured by Daishin Chemical was used as a water-insoluble solvent. Furthermore, dioxane or dimethyl sulfoxide was used as the water-soluble solvent. Table 1 shows the water-insoluble solvent ratio and the water-soluble solvent ratio in the solvent. The content of the coating material with respect to 100 parts by volume of the solvent was 50 parts by volume when the solvent was dioxane and 60 parts by volume when the solvent was dimethyl sulfoxide.

  The metal surface treatment agent and the paint were applied as a two-layer film to the steel sheet surface using a slide curtain coating apparatus, and then the steel sheet was heated and dried in a drying device. The heating rate during drying was 3 ° C./s. The surface of the steel sheet after drying was observed to confirm the presence or absence of cracks.

  Table 1 shows the coating conditions, drying conditions and results.

  No. in Table 1 For 1, 2, 6, and 7, the water-soluble solvent is contained in the solvent of the solvent-based paint in an amount of 50% by mass or more, and the wet film thickness of the metal surface treatment agent is 10 μm or less, which is a preferable range. There was no occurrence of cracks on the steel sheet surface after painting.

  In contrast, no. About 3-5, 8-10, although the water-soluble solvent was contained in the solvent of the solvent-based paint, the wet film thickness of the metal surface treatment agent is out of the preferred range, so the steel plate surface after painting is completed The occurrence of armpits was observed. No. For No. 11, since only a water-insoluble solvent was used as the solvent of the solvent-based paint, generation of cracks was observed on the steel sheet surface after the completion of coating.

  Table 2 shows examples when the water-soluble solvent ratio is changed. When the water-soluble solvent ratio exceeded 50% and became 45%, the occurrence of cracks was observed.

It is a perspective view which shows the multilayer film coating method of this invention. It is a figure which shows the multilayer film coating method of this invention using a slide curtain coating apparatus, (a) is a front view, (b) is AA arrow sectional drawing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Slide curtain coating apparatus 2 Slit 3 Slide 4 Guide apparatus 5 Edge guide 6 Curtain 7 Metal plate 8 Metal plate traveling direction 10 Wide layer 11 Narrow layer

Claims (7)

  When forming a multilayer film by discharging a film of coating liquid from a plurality of slits and applying these films onto a moving metal plate, the coating liquid applied to the side of the multilayer film close to the metal plate is A metal which is an aqueous metal surface treatment agent, wherein at least one of the coating liquids applied to the side far from the metal plate is a solvent-based paint, and the solvent of the solvent-based paint contains a water-soluble solvent. A multilayer coating method for a plate.   The metal film multilayer coating method according to claim 1, wherein a ratio of the water-soluble solvent in the solvent is 50% by mass or more.   The metal film multilayer coating method according to claim 1 or 2, wherein the water-soluble solvent is one or two of dioxane and dimethyl sulfoxide.   4. The water-based metal surface treatment agent is composed of an organic or inorganic material not containing chromium, is water-soluble at room temperature, and becomes water-insoluble when heated and dried. A multilayer film coating method for metal plates.   5. The method for coating a metal plate with a multilayer film according to claim 1, wherein a slide curtain coating device is used when the coating solution is applied onto the metal plate.   6. The method for coating a metal plate with a multilayer film according to claim 5, wherein the curtain width by the aqueous metal surface treatment agent is narrower than the curtain width by the solvent-based paint.   The metal film multi-layer according to any one of claims 1 to 6, wherein the coating film with the aqueous metal surface treatment agent has a wet film thickness of 2 to 10 µm and a dry film thickness of 0.5 to 3 µm. Film coating method.

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