[DESCRIPTION]

[Invention Title]

PROCESS USING MAGNETIC FORCE FOR MANUFACTURING COLORED-

STEELSHEET AND MANUFACTURED COLORED-STEELSHEET

[Technical Field]

The present invention relates to a method of manufacturing a colored-steel sheet by

using a magnetic force and a colored-steel sheet manufactured using the method, and

more particularly, to a method of manufacturing a colored-steel sheet in which an

upper paint forming patterns by magnetic forces is coated and various patterns are

formed by applying magnetic force to the upper paint, and a colored-steel sheet

manufactured using the method.

[Background Art]

In general, a printed-steel sheet, which is printed using inks, is manufactured as

follows. A chromium coating layer 2, a lower coating layer 3, and a base coating

layer 4 are sequentially formed on a plate 1 as shown in FIG. 1. Then, after a printed

layer 5 corresponding to an ink 1 , a printed layer 6 corresponding to an ink 2, and a

printed layer 7 corresponding to an ink 3 are sequentially formed using natural drying-

type inks, a clear layer 8 for protecting the printed layers is formed.

The printing method using inks has problems in that a separate printing apparatus such

as a printer should be needed, printing should performed several times, and

weatherability deteriorates due to poor adherence of ink to the base coating layer 4.

A method of manufacturing a colored-steel sheet has been disclosed in Korea Patent

No. 10-0535910 in order to solve these problems. Since not ink but paints are used in

this method, it is possible to further improve corrosion resistance and durability and to

reduce the number of processes as compared to the printed-steel sheet. Further, a

transfer roll is used to transfer and coat patterns so as to obtain a surface property and a

feel of a material, which correspond to various patterns and are not obtained from the

printed-steel sheet.

[Disclosure]

[ Technical Problem ]

The present invention is made by improving a method of manufacturing a colored-steel

sheet in the related art that has been disclosed in Korean Patent No. 10-0535910, and it

is an object of the present invention to provide a method of manufacturing a colored-

steel sheet by using a magnetic force that can easily form three-dimensional various

patterns and a colored-steel sheet manufactured using the method.

[Technical Solution]

According to an embodiment of the present invention, a method of manufacturing a

colored-steel sheet by using a magnetic force includes performing alkaline degreasing

in order to remove foreign substances on a base plate 10 used in a general continuous

coating process, performing chromate coating, and forming a chromium coating layer

20; coating a lower paint on the chromium coating layer 20 and forming a lower

coating layer 30; and coating an upper paint, which includes iron materials to be

attracted by magnetic forces, on the lower coating layer, forming patterns on the upper

paint by applying magnetic forces to the upper paint, and forming an upper coating

layer 40 by heating and drying the upper paint at 210 to 250 ^° C

A magnet roll where various patters made of magnets are formed on a roll made of a

non-magnetic material may be used to apply the magnetic forces to the upper paint.

A paint that includes 30 to 35 % by weight of a linear polyester resin, 7 to 10 % by

weight of a melamine resin, 5 to 7 % by weight of a carbonyl iron pigment, 2 to 3 %

by weight of a silica pigment, 3 to 5 % by weight of an additive, 25 to 30 % by weight

of an aromatic hydrocarbon solvent, and 10 to 15 % by weight of an ester solvent may

be used as the upper paint.

A clear layer 50 may be formed on the upper coating layer 40 by coating a clear paint

on the upper coating layer, so as to make the upper coating layer glossy and protect the

upper coating layer.

[Advantageous Effects]

According to the method of manufacturing a colored-steel sheet by using a magnetic

force and a colored-steel sheet manufactured using the method, it is possible to easily

form three-dimensional and various patterns as compared to the method of

manufacturing a colored-steel sheet in the related art. Therefore, the present

invention can be wholly applied to a part of which shape is easily changed and variable,

that is, a colored-steel sheet for building exterior/interior materials and a fire door.

[Description of Drawings]

FIG. l is a cross-sectional view of a colored-steel sheet in the related art.

FIG. 2 is a cross-sectional view of an example of a colored-steel sheet manufactured

by the present invention.

FIG. 3 is a cross-sectional view of another example of a colored-steel sheet

manufactured by the present invention.

FIG. 4 is a view showing a roll coater and a magnet roll that are used to form an upper

coating layer of the present invention.

FIGS. 5A and 5B are views showing an upper coating layer of Example 1 of the

present invention before and after a laminated body passes through the magnet roll.

FIGS. 6 A and 6B are views showing an upper coating layer of Example 2 of the

present invention before and after a laminated body passes through the magnet roll.

FIGS. 7 A and 7B are views showing an upper coating layer of Example 3 of the

present invention before and after a laminated body passes through the magnet roll.

[Best Mode]

FIG. 1 is a cross-sectional view of an example of a colored-steel sheet manufactured

by the present invention. As shown in the drawing, a base plate 10, such as a

galvannealed steel sheet, a zinc-55% aluminum-plated steel sheet (super gallium steel

sheet), an electro-galvanized steel sheet, or a stainless steel sheet, which is used in a

general continuous coating process, is washed with an alkaline degreasing agent so that

foreign substances attached to the upper surface of the base plate 10 are removed.

Then, chromate coating is performed on the base plate, thereby forming a chromium

coating layer 20. The formation of the chromium coating layer 20 using the chromate

coating is performed by a known method.

Subsequently, a lower coating layer 30, which has a thickness of 3 to 7 μm, is formed

on the chromium coating layer 20 by coating a lower paint on the chromium coating

layer. A paint, which has excellent adherence to the steel sheet, excellent corrosion

resistance, and excellent adherence to an upper paint to be described below, should be

used as the lower paint. A paint that includes 20 to 30 % by weight of a linear

polyester resin, 3 to 5 % by weight of a melamine resin, 3 to 5 % by weight of an

epoxy resin, 15 to 20 % by weight of a known pigment, 2 to 4 % by weight of

additives such as a dispersant and a surfactant, 35 to 40 % by weight of an aromatic

hydrocarbon solvent, and 8 to 10 % by weight of an ester solvent is used as the lower

paint.

Then, the lower coating layer 30 is heated and dried at a temperature range of 200 to

220 ^° C that is higher than a general drying temperature of a polyester resin by a

temperature of 10 to 20 °C and is coated. After that, an upper paint, which contains

a carbonyl iron pigment to be attracted by a magnetic force, is coated. Subsequently,

magnetic forces are applied to form patterns on the upper paint, and the patterns are

then heated and dried at a temperature of 210 to 250 ^° C to form an upper coating layer

40 having a thickness of 10 to 20 μm. As a result, a colored-steel sheet shown in FIG.

2 is manufactured.

A paint, which has excellent workability and distinctness of image, should be used as

the upper paint. A paint that includes 30 to 35 % by weight of a linear polyester resin,

7 to 10 % by weight of a melamine resin, 5 to 7 % by weight of a carbonyl iron

pigment, 2 to 3 % by weight of a silica pigment, 3 to 5 % by weight of additives such

as a dispersant and a surfactant, 25 to 30 % by weight of an aromatic hydrocarbon

solvent, and 10 to 15 % by weight of an ester solvent is used as the upper paint. It is

preferable that the iron content of the carbonyl iron pigment be 3 to 50% of the weight

of the carbonyl iron pigment. The iron content of the carbonyl iron pigment is

adjusted depending on the shape of the patterns and the coating thickness.

The temperature range of 210 to 250 ^° C is a temperature range corresponding to a

resin drying condition where the resin or patterns of the upper paint are formed. The

lower limit (210 "C) of the temperature range is a lower limit of drying efficiency. If

the temperature exceeds the upper limit (250 ^° C ) thereof, the upper paint is excessively

dried. For this reason, defects that cracks are formed in the coating layer and

adherence deteriorates may be easily generated.

If the thickness of the upper coating layer 40 is 20 μm or more, there are problem in

that the patterns are not uniformly formed, adherence deteriorates, and a swell occurs.

FIG. 4 shows a three-roll coater and a magnet roll that are used to form the upper

coating layer. As shown in the drawing, the three-roll coater includes a pick-up roll P

that picks up the upper paint from a coating pan L serving a paint supply container, a

back-up roll B that transfers a coil strip S, and an application roll A that is provided

between the pick-up roll P and the back-up roll B. A two-roll coater without the

application roll A, a curtain flow roll (curtain flow coater), or the like may be used as

the roll coater.

After the upper paint is coated, a laminated body passes through the magnet roll M

while the upper paint is not dried (wet). In this case, patterns are formed. Then, the

upper paint is heated and dried at 210 to 250 ^° C(preferably, 220 to 232 ^° C ) for 30 to 60

seconds, so that three-dimensional patterns are formed.

The magnet roll M has a structure where various patters made of magnets are formed

on a roll made of a non-magnetic material (teflon or the like). Since magnetic forces

are applied to the iron materials included in the upper paint according to the patterns

formed on the magnet roll M, patterns are formed due to the magnetic attraction of iron.

Meanwhile, as shown in FIG. 3, a clear layer 50 may be formed on the upper coating

layer 40 by coating a clear paint on the upper coating layer at a thickness of 5 to 15 [M

and heating/drying the clear paint, so as to make the upper coating layer glossy and

protect the upper coating layer. A paint that includes 40 to 45 % by weight of a linear

polyester resin, 7 to 8 % by weight of a melamine resin, 1 to 2 % by weight of

additives such as a dispersant and a surfactant, 40 to 45 % by weight of an aromatic

hydrocarbon solvent, 6 to 10 % by weight of an ester solvent, and 5 to 10 % by weight

of an ether solvent is used as the clear paint. In addition, 2 to 3 % by weight of a

silica pigment or 1 to 2 % by weight of an acrylic pigment may be added to the paint to

make the layer glossy. The physical properties, such as weatherability, corrosion

resistance, and chemical resistance, of the colored-steel sheet including the clear layer

50 that is formed as described above are further improved.

The results of character tests for the colored-steel sheet, which is manufactured using

the present invention, will be described below by using examples of the present

invention.

[Mode for Invention]

[Example 1]

The colored-steel sheet having the laminated structure shown in FIG. 2 was

manufactured by performing alkaline degreasing on a galvannealed steel sheet

manufactured by a general hot-dip coating method in order to remove foreign

substances attached to the upper surface of the galvannealed steel sheet, performing

chromate coating, coating a lower paint at a thickness of 5 [M, heating and drying the

lower paint at 210 ^° C to form a lower coating layer, coating an upper paint including a

carbonyl iron pigment, allowing a laminated body to pass through a magnet roll (a

permanent magnet having a thickness of 5 mm) to form patterns corresponding to

magnetic fields (magnetic forces) while the upper paint is not dried (wet), and heating

and drying the upper paint at 230 ^° C to form an upper coating layer having a thickness

of 18 μm. A paint corresponding to middle values of the composition ranges was

used as the lower paint and the upper paint. FIG. 5A is a view showing the upper

coating layer after the upper paint is coated before the laminated body passes through

the magnet roll, and FIG. 5B is a view showing the upper coating layer on which

patterns are formed after the laminated body passes through the magnet roll.

[Example 2]

The colored-steel sheet having the laminated structure shown in FIG. 2 was

manufactured by performing alkaline degreasing on a galvannealed steel sheet

manufactured by a general hot-dip coating method in order to remove foreign

substances attached to the upper surface of the galvannealed steel sheet, performing

chromate coating, coating a lower paint at a thickness of 5 μm, coating an upper paint

including a carbonyl iron pigment, allowing a laminated body to pass through a

magnet roll (a permanent magnet having a thickness of 10 mm) to form patterns

corresponding to magnetic fields (magnetic forces) while the upper paint is not dried

(wet), and heating and drying the upper paint at 230 ^° C to form an upper coating layer

having a thickness of 18 μm. A paint corresponding to middle values of the

composition ranges was used as the lower paint and the upper paint. FIG. 6A is a

view showing the upper coating layer after the upper paint is coated before the

laminated body passes through the magnet roll, and FIG. 6B is a view showing the

upper coating layer on which patterns are formed after the laminated body passes

through the magnet roll.

[Example 3]

The colored-steel sheet having the laminated structure shown in FIG. 2 was

manufactured by performing alkaline degreasing on a galvannealed steel sheet

manufactured by a general hot-dip coating method in order to remove foreign

substances attached to the upper surface of the galvannealed steel sheet, performing

chromate coating, coating a lower paint at a thickness of 5 [M, coating an upper paint

including a carbonyl iron pigment, allowing a laminated body to pass through a

magnet roll (a permanent magnet that has a thickness of 10 mm and patterns in a width

direction of the roll) to form patterns corresponding to magnetic fields (magnetic

forces) while the upper paint is not dried (wet), and heating and drying the upper paint

at 230 ^" C to form an upper coating layer having a thickness of 18 μm. A paint

corresponding to middle values of the composition ranges was used as the lower paint

and the upper paint. FIG. 7A is a view showing the upper coating layer after the

upper paint is coated before the laminated body passes through the magnet roll, and

FIG. 7B is a view showing the upper coating layer on which patterns are formed after

the laminated body passes through the magnet roll.

[Example 4]

The colored-steel sheet having the laminated structure shown in FIG. 3 was

manufactured by performing alkaline degreasing on a galvannealed steel sheet

manufactured by a general hot-dip coating method in order to remove foreign

substances attached to the upper surface of the galvannealed steel sheet, performing

chromate coating, coating a lower paint at a thickness of 5 μm, coating an upper paint

including a carbonyl iron pigment, allowing a laminated body to pass through a

magnet roll (a permanent magnet having a thickness of 10 mm) to form patterns

corresponding to magnetic fields (magnetic forces) while the upper paint is not dried

(wet), heating and drying the upper paint at 230 ^° C to form an upper coating layer

having a thickness of 18 μm, coating a clear paint at a thickness of 5 μm, and heating

and hardening the clear paint. A paint corresponding to middle values of the

composition ranges was used as the lower paint, the upper paint, and the clear paint.

[Example 5]

The colored-steel sheet having the laminated structure shown in FIG. 3 was

manufactured by performing alkaline degreasing on a galvannealed steel sheet

manufactured by a general hot-dip coating method in order to remove foreign

substances attached to the upper surface of the galvannealed steel sheet, performing

chromate coating, coating a lower paint at a thickness of 5 μm, coating an upper paint

made of a high polymer polyester resin including a carbonyl iron pigment, allowing a

laminated body to pass through a magnet roll (a permanent magnet having a thickness

of 10 mm) to form patterns corresponding to magnetic fields (magnetic forces) while

the upper paint is not dried (wet), heating and drying the upper paint at 230 °C to form

an upper coating layer having a thickness of 15 [M, coating a clear paint at a thickness

of 5 [M, and heating and hardening the clear paint. A paint corresponding to middle

values of the composition ranges was used as the lower paint, the upper paint, and the

clear paint.

Table 1 showed the evaluation results of pencil hardness, adherence and workability,

corrosion resistance, weatherability, and chemical resistance that are obtained from the

colored-steel sheets manufactured as Examples 1 to 5. A linear high- weatherability

polyester resin (Examples 1 to 4) and a high-workability high polymer polyester resin

(Example 5) were employed as a typical resin used in the evaluation.

The pencil hardness is a result that is obtained from the manual test using 2kg of a

Mitsubishi Uni Pencil.

The adherence and the workability are obtained by measuring whether cracks are

generated after a T-Bending test is performed at a temperature of 25 ^° C , are obtained by

confirming the presence of exfoliation after boiling water after working and working

after boiling water are performed at 100 "C for 1 hour.

The corrosion resistance is obtained by confirming the presence of coating defects

such as plane NO Blister after the sheet is left in 5% of NaCl for 5 hours.

The weatherability is obtained by confirming gloss and chrominance after a test is

performed by using an accelerated weathering test (WOM) for 1500 hours.

The chemical resistance is obtained by confirming the presence of coating defects after

the sheet is left in 5% of HCl and 5% of NaOH for 24 hours.

[Table 1 ]

[Industrial Applicability]

According to the present invention, it is possible to easily form three-dimensional and

various patterns as compared to the method of manufacturing a colored-steel sheet in

the related art. Therefore, the present invention can be wholly applied to a part of

which shape is easily changed and variable, that is, a colored-steel sheet for building

exterior/interior materials and a fire door.