JP7811241B2 - Coated metal sheet and method for manufacturing coated metal sheet - Google Patents

Description

The present invention relates to a coated metal sheet and a method for manufacturing a coated metal sheet.

Some painted metal sheets are used without further painting after being pressed or otherwise processed. Such painted metal sheets are stored in a coiled state or stacked. When stored in this manner, the appearance of one of the surfaces of the painted metal sheet may be damaged. One cause of this damage to the appearance is when a location on one of the coatings on the painted metal sheet is crushed. This location may be pressed against another location on the same painted metal sheet, or it may be against a location on another painted metal sheet. In the following explanation, the shape of the crushed location is referred to as a "pressure mark."

Coated metal sheets that are used without further painting after processing may have a coating containing a synthetic resin formed on one side. While such coatings have the advantage of making it easy to adhere objects to, they also have the disadvantage of being very hard. When a coating with high hardness comes into contact with a coating formed on another side during the storage process described above, pressure marks often form on the surface of the coating that comes into contact.

To solve this problem, a solution has been taken of blending soft synthetic resin beads into a hard coating. Patent Documents 1 and 2 disclose coated metal sheets that solve this problem.

The coated metal sheet disclosed in Patent Document 1 has a decorative coating film formed on one surface of a metal base, a non-cosmetic coating film formed on the other surface of the metal base, and beads formed of a polyurethane resin. The beads are contained in the non-cosmetic coating film. The non-cosmetic coating film has a primer coating film formed on the surface of the metal base and a topcoat coating film formed on the surface of the primer coating film. The topcoat coating film contains beads. The ratio of the bead protrusion amount to the primer coating film thickness is 2.0 or more and 8.0 or less. The bead protrusion amount in Patent Document 1 is the amount of beads protruding from the surface of the topcoat coating film. The bead protrusion amount in Patent Document 1 is expressed as the difference between the film thickness of the topcoat coating film and the average particle size of the beads. The base resin of the primer coating film and the topcoat coating film is a polyester resin or an epoxy resin. The bead-containing topcoat coating film is a cured product of a mixture containing beads and a paint containing a polyester resin or an epoxy resin. The average particle size of the beads is 10 to 30 micrometers. According to the invention disclosed in Patent Document 1, it is possible to prevent the occurrence of pressure marks while also preventing beads from falling off.

The coated metal sheet disclosed in Patent Document 2 has a decorative coating film formed on one surface of a metal base, a non-cosmetic coating film formed on the other surface of the metal base, and resin beads contained in the non-cosmetic coating film. The non-cosmetic coating film is formed on the surface of the metal base. The non-cosmetic coating film has a primer coating film containing beads and a coating film covering the surface of the beads and the primer coating film. The ratio of the bead protrusion amount to the coating film thickness is 3.0 or more and 9.0 or less. The bead protrusion amount is the amount of beads protruding from the surface of the primer coating film. The bead protrusion amount is expressed as the difference between the thickness of the primer coating film and the average particle size of the beads. The invention disclosed in Patent Document 2 can suppress the occurrence of pressure marks while also suppressing bead shedding.

Patent No. 7229756 Patent No. 7094864

However, the invention disclosed in Patent Document 1 has the problem of insufficient prevention of bead shedding. The invention disclosed in Patent Document 2 is able to further prevent bead shedding. However, the invention disclosed in Patent Document 2 has the problem that a coating film must be formed in addition to a primer coating film containing beads. In addition, the invention disclosed in Patent Document 2 has the problem that the coating film covers the beads, reducing the amount of protrusion of the beads from the surface of the coating film.

The present invention solves the above-mentioned problems. Its purpose is to provide a coated metal sheet that can suppress the occurrence of pressure marks and prevent beads from falling off even without the formation of a coating film.

The coated metal sheet and method for manufacturing the coated metal sheet of the present invention will be explained with reference to the drawings. Note that the use of reference numerals in the drawings in this section is intended to facilitate understanding of the invention and is not intended to limit the scope of the invention to that shown in the drawings.

In order to solve the above-mentioned problems, according to one aspect of the present invention, a painted metal sheet 30 includes a steel sheet 40 and a bead-containing coating film 46. The bead-containing coating film 46 is formed on one surface of the steel sheet 40. The bead-containing coating film 46 has a mother phase 70 and beads 72. The mother phase 70 contains an epoxy resin. Portions of the beads 72 protrude from the mother phase 70. Portions of the beads 72 that are embedded in the mother phase 70 float within the mother phase 70. Portions of the beads 72 that are embedded in the mother phase 70 are fused to the mother phase 70. The beads 72 contain a polyamide resin. The polyamide resin is nylon 12. The diameter of the beads 72 is greater than 15 micrometers and less than or equal to 40 micrometers. The protruding height of the beads 72 from the mother phase 70 is greater than or equal to 15 micrometers and less than or equal to 30 micrometers.

Because portions of the beads 72 protrude from the matrix 70, even when the bead-containing coating 46 overlaps a coating 44 different from the bead-containing coating 46, a large area of the bead-containing coating 46 is prevented from coming into contact with the coating 44. Additionally, nylon 12 polyamide resin exhibits excellent flexibility. This helps prevent crushing at the point where the beads 72 come into contact with the coating 44 different from the bead-containing coating 46, even when the bead-containing coating 46 overlaps the coating 44 different from the bead-containing coating 46. Because crushing is more easily prevented, the occurrence of pressure marks on the coating 44 different from the bead-containing coating 46 is reduced. Furthermore, because the portions of the beads 72 buried in the matrix 70 are fused to the matrix 70, bead detachment is prevented even when the beads 72 are not covered by a coating. Furthermore, nylon 12 has the lowest melting point among nylon 6, nylon 11, nylon 12, and nylon 66. This makes it the most likely for the polyamide resins to be thermally welded to the epoxy resin of the matrix 70 when forming the bead-containing coating film 46.

Furthermore, it is desirable that the bead content in the above-mentioned bead-containing coating film 46 be 10% by mass or more.

According to another aspect of the present invention, a method for manufacturing a coated metal sheet 30 includes a bead-containing paint application step S506 and a bead-containing paint drying step S508. In the bead-containing paint application step S506, paint is applied to the steel sheet 40. In the bead-containing paint drying step S508, the paint applied to the steel sheet 40 is dried to form a bead-containing coating film 46 having a matrix 70 and beads 72. The paint includes a solvent, an epoxy resin, an epoxy resin curing agent, and beads 72. The beads 72 include a polyamide resin. The polyamide resin is nylon 12. The beads 72 have a diameter of more than 15 micrometers and not more than 40 micrometers . After the bead-containing paint drying step S508, the portions of the beads 72 that are embedded in the matrix 70 float within the matrix 70. After the bead-containing paint drying step S508, the portions of the beads 72 that are embedded in the matrix 70 are fused to the matrix 70. The protrusion height of the beads 72 from the matrix 70 after the bead-containing paint drying step S508 is 15 micrometers or more and 30 micrometers or less. The drying temperature of the paint in the bead-containing paint drying step S508 is 473.15 Kelvin or more and 523.15 Kelvin or less.

The coated metal sheet and method for manufacturing coated metal sheet according to the present invention can suppress the occurrence of pressure marks and prevent beads from falling off even without forming a coating film.

1 is a cross-sectional view of a coated metal plate according to an embodiment of the present invention. 1 is a flowchart showing a method for manufacturing a coated metal plate according to an embodiment of the present invention.

Embodiments of the present invention will now be described with reference to the drawings. In the following description, identical components are designated by the same reference numerals. Their names and functions are also identical. Therefore, detailed descriptions of them will not be repeated.

<Configuration of painted metal sheet>
Fig. 1 is a cross-sectional view of a coated metal sheet 30 according to this embodiment. The configuration of the coated metal sheet 30 according to this embodiment will be described based on Fig. 1.

As is clear from FIG. 1 , the coated metal sheet 30 according to this embodiment comprises a steel sheet 40, a design surface base layer 42, a second surface base layer 43, a design surface forming coating film 44, and a bead-containing coating film 46.

The steel sheet 40 serves as a base for the coated metal sheet 30 according to this embodiment. The steel sheet 40 according to this embodiment is a well-known hot-dip zinc-aluminum alloy plated steel sheet having a well-known chemical conversion treatment applied to both the front and back surfaces.

The design surface base layer 42 is formed on one of the front and back surfaces of the steel plate 40. The design surface base layer 42 in this embodiment is formed by drying a well-known base paint. The other side base layer 43 is formed on the other of the front and back surfaces of the steel plate 40. The other side base layer 43 in this embodiment is formed by drying a well-known base paint. In this embodiment, the base paint used to form the other side base layer 43 is different from the base paint used to form the design surface base layer 42.

The design surface forming coating film 44 is formed on one of the front and back surfaces of the steel plate 40. The design surface forming coating film 44 according to this embodiment is formed so as to overlap the design surface base layer 42. The design surface forming coating film 44 according to this embodiment is formed by drying a well-known topcoat paint.

The bead-containing coating film 46 is formed on the other of the front and back surfaces of the steel sheet 40. The bead-containing coating film 46 according to this embodiment is formed so as to overlap the other-surface base layer 43. The bead-containing coating film 46 according to this embodiment has a matrix 70 and a plurality of beads 72.

The matrix 70 contains an epoxy resin. The matrix 70 according to this embodiment contains an epoxy resin to facilitate adhesion of an optional component to the bead-containing coating film 46. An example of such an optional component is a heat insulating material. Examples of heat insulating material include urethane and rock wool. The components of the matrix 70 according to this embodiment are not particularly limited, except that it contains an epoxy resin.

The beads 72 in this embodiment are particles made of the material described below. The material is a polyamide resin with an aliphatic skeleton, particularly nylon 12.

Polyamide resins with an aliphatic skeleton are highly elastic and soft. This reduces the risk of the coating being damaged when the beads 72 come into contact with another coating (the type of object on which the coating is formed is not particularly limited. For example, the coating may be the decorative surface forming coating 44 of the coated metal sheet 30 that has the beads 72, or a coating of another coated metal sheet 30).

The melting point of polyamide resins with an aliphatic skeleton (primarily 200°C ± 50°C, or primarily 473.15°C ± 50°C) is close to the temperature range described below. This temperature range is suitable for baking and drying paints containing epoxy resins (200°C to 250°C, or 473.15°C to 523.15°C). This facilitates melting of the surfaces of the beads 72 as the paint forming the matrix 70 bakes and dries. When the surfaces of the beads 72 melt, the portions of each bead 72 embedded in the matrix 70 tend to fuse strongly with the matrix 70. In addition, this prevents the beads 72 from melting completely and thereby failing to fuse with the matrix 70, and also prevents excessively melted beads 72 from protruding from the matrix 70. If the beads 72 do not melt completely and thus fail to fuse with the matrix 70, this can cause the beads 72 to fall off the bead-containing coating film 46.

Examples of polyamide resins having an aliphatic skeleton include nylon 6, nylon 11, nylon 12, and nylon 66. Among polyamide resins having an aliphatic skeleton, nylon 12 is particularly suitable as a component of the beads 72 according to this embodiment. Among nylon 6, nylon 11, nylon 12, and nylon 66, nylon 12 has the lowest melting point. This makes it the most likely of these polyamide resins to undergo thermal welding with the epoxy resin of the matrix 70 during the formation of the bead-containing coating film 46. Additionally, the melting point of nylon 12 (176°C, 449.15 Kelvin) is not too low compared to the temperature range in which epoxy resins polymerize (200°C to 250°C, i.e., 473.15 Kelvin to 523.15 Kelvin). This makes it easier to avoid excessive dissolution of the beads 72 during the formation of the matrix 70. Furthermore, nylon 12 has the lowest density among nylon 6, nylon 11, nylon 12, and nylon 66. Its low density means that it floats more easily when contained in a high-density liquid. Because they tend to float, the beads 72 tend to protrude more easily from the liquid that becomes the parent phase 70 when the film thickness of the bead-containing coating 46 is thick than when the beads 72 contain nylon 6, nylon 11, nylon 12, and nylon 66 other than nylon 12 .

A portion of each of the beads 72 protrudes from the mother phase 70. The portion of each of the beads 72 that is embedded in the mother phase 70 floats within the mother phase 70. The portion of each of the beads 72 that is embedded in the mother phase 70 is fused to the mother phase 70. In this embodiment, the protruding height of each of the beads 72 relative to the surface of the mother phase 70 is 15 micrometers or more and 30 micrometers or less.

In this embodiment, the diameter of the beads 72 is 15 micrometers or more and 40 micrometers or less. The diameter may also be 20 micrometers or more and 30 micrometers or less.

In this embodiment, the content of beads 72 in the bead-containing coating 46 is not particularly limited. For example, the content is 3% by mass or more. The content may also be 10% by mass or more.

<Manufacturing method of coated metal sheet>
2 is a flowchart showing a method for manufacturing the coated metal sheet 30 according to this embodiment. The method for manufacturing the coated metal sheet 30 according to this embodiment will be described with reference to FIG.

The manufacturing method for the coated metal sheet 30 according to this embodiment includes a primer coating process S500, a primer coating drying process S502, a design surface forming coating process S504, a bead-containing coating process S506, and a bead-containing coating drying process S508.

In the primer coating application step S500, a primer coating is applied to one of the front and back surfaces of the steel sheet 40. Another primer coating is applied to the other of the front and back surfaces of the steel sheet 40. The steel sheet 40 according to this embodiment is a hot-dip zinc-aluminum alloy plated steel sheet that has been subjected to a well-known chemical conversion treatment on both sides.

In the primer paint drying step S502, the primer paints applied to the front and back surfaces of the steel plate 40 are dried. The primer paints are dried together with the steel plate 40 in a drying device. When the primer paints are dried, a design surface primer layer 42 and an other surface primer layer 43 are formed on the front and back surfaces of the steel plate 40.

In the design surface forming paint application step S504, a topcoat paint is applied onto the design surface base layer 42 formed on one of the front and back surfaces of the steel plate 40.

In the bead-containing paint application step S506, paint is applied onto the other-side base layer 43 formed on the other side of the front or back surface of the steel plate 40. The paint contains a solvent, an epoxy resin dissolved in the solvent, a curing agent for the epoxy resin, and beads 72.

In the bead-containing paint drying step S508, the paint applied to the other of the front and back surfaces of the steel plate 40 is dried. This paint is the paint applied in the bead-containing paint application step S506. In the present embodiment, the top coat paint applied to one of the front and back surfaces of the steel plate 40 is also dried. In the present embodiment, the drying temperature of these paints is 200 degrees Celsius (473.15 Kelvin) or higher and 250 degrees Celsius (523.15 Kelvin) or lower. In the present embodiment, the drying time of these paints is 20 seconds or higher and 60 seconds or lower.

<How to use painted metal sheets>
The method of using the coated metal sheet 30 according to this embodiment is similar to that well known, and therefore, detailed description thereof will not be repeated.

[Effect description]
In the coated metal sheet 30 according to this embodiment, a portion of the beads 72 protrudes from the matrix 70. This prevents a large area of the bead-containing coating 46 from contacting the design surface-forming coating 44, even if the bead-containing coating 46 of another coated metal sheet 30 overlaps the design surface-forming coating 44 of this coated metal sheet 30. Additionally, polyamide resins with an aliphatic skeleton exhibit excellent flexibility. This helps prevent crushing at the contact points of the beads 72 of the design surface-forming coating 44, even if the bead-containing coating 46 overlaps the design surface-forming coating 44 of the former. This reduces the risk of crushing, thereby preventing pressure marks from appearing on the design surface-forming coating 44 of the former. Furthermore, because the portions of the beads 72 that are buried in the matrix 70 are fused to the matrix 70, the beads 72 are prevented from falling off even when the beads 72 are not covered by a coating film.

Furthermore, nylon 12 has the lowest melting point among nylon 6, nylon 11, nylon 12, and nylon 66. As a result, when forming the bead-containing coating film 46 on the coated metal sheet 30 according to this embodiment, nylon 12 is the most likely to thermally bond to the epoxy resin of the matrix 70 among nylon 6, nylon 11, nylon 12, and nylon 66. Furthermore, the beads 72 are more likely to protrude from the matrix 70 than when the beads 72 contain any of nylon 6, nylon 11, nylon 12, and nylon 66 other than nylon 12. This is because nylon 12 has the lowest density among nylon 6, nylon 11, nylon 12, and nylon 66.

[Description of Modifications]
The above-described coated metal sheet 30 is an example for embodying the technical concept of the present invention. The shape and structure of the metal base 40, the composition of the design surface primer layer 42, the composition of the other surface primer layer 43, the composition of the design surface forming coating film 44, and the composition of the bead-containing coating film 46 are not limited to those in the above-described embodiment. Various modifications can be made to these.

30... Coated metal plate 40... Metal base 42... Design surface primer layer 43... Other surface primer layer 44... Design surface forming coating film 46... Bead-containing coating film 70... Mother phase 72... Beads

Claims (3)

Steel plate and
a bead-containing coating film formed on any surface of the steel plate ,
The bead-containing coating film is
a matrix containing an epoxy resin;
A coated metal sheet having beads partially protruding from the matrix,
a portion of the beads that is embedded in the matrix is floating in the matrix,
a portion of the bead that is embedded in the matrix is fused to the matrix,
the beads comprise a polyamide resin;
the polyamide resin is nylon 12,
The diameter of the beads is greater than 15 micrometers and less than or equal to 40 micrometers;
A coated metal sheet characterized in that the protrusion height of the beads from the parent phase is 15 micrometers or more and 30 micrometers or less. The coated metal sheet according to claim 1, characterized in that the content of the beads in the bead-containing coating is 10% by mass or more. a bead-containing paint application step in which paint is applied to the steel plate ;
A method for producing a coated metal plate, comprising a bead-containing paint drying step in which the paint applied to the steel plate is dried to form a bead-containing paint film having a matrix and beads,
The paint is
A solvent,
Epoxy resin,
a curing agent for the epoxy resin;
beads;
the beads comprise a polyamide resin;
the polyamide resin is nylon 12,
The diameter of the beads is greater than 15 micrometers and less than or equal to 40 micrometers;
After the bead-containing paint drying step, the part of the beads that is embedded in the matrix floats in the matrix,
After the bead-containing paint drying step, the portions of the beads that are embedded in the matrix are fused to the matrix,
a protrusion height of the beads from the matrix after the bead-containing paint drying step is 15 micrometers or more and 30 micrometers or less;
A method for producing a coated metal sheet, wherein the drying temperature of the paint in the bead-containing paint drying step is 473.15 Kelvin or more and 523.15 Kelvin or less.