TW202419163A - Method for producing colored steel plate - Google Patents

Abstract

This invention provides a method for producing a colored steel plate including: a step of forming uncured coating film by Supplying a two-component urethane paint obtained by mixing a main agent containing a polyol component and a curing agent containing a polyisocyanate component using a two-liquid mixing device to a roll coater,and applying the two-component urethane paint to a steel plate using the roll coater, and a step of baking the uncured coating film to form a cured coating film.

Description

Manufacturing method of colored steel plate

The present invention relates to a method for manufacturing colored steel plates.

The so-called colored steel plate generally refers to a steel plate with a coating formed on the surface, and is sometimes also called a coated steel plate. In addition, the colored steel plate of the present invention also includes a steel plate with a coating formed on the surface that does not contain any pigment or dye.

In the industrial manufacturing line of colored steel plates, a roller coating machine is generally used to apply the coating to the steel plate to form an uncured coating film, and then the uncured coating film is baked in a heating furnace to form a hardened coating film to manufacture the colored steel plate. In this industrial manufacturing line, in order to form a hardened coating film, a single-liquid urethane coating (i.e., a coating containing a polyol component and a blocked polyisocyanate component) as described in Patent Document 1 has been gradually adopted in the past.

[Prior Art Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Publication No. 2002-179998

The reason why one-component urethane coatings were used in the industrial manufacturing lines of colored steel plates in the past is that they have a long shelf life. Although this one-component urethane coating has the advantage of a long shelf life, it still has the disadvantage of having to increase the baking temperature in order to form a hardened coating film with sufficient performance using the one-component urethane coating. In addition, in the embodiment of patent document 1 using a one-component urethane coating as the final coating, the baking is performed at 232°C × 60 seconds.

In recent years, due to the rising fuel costs and the pursuit of carbon neutrality, there is a demand for a hardened coating film with sufficient performance even at a low baking temperature. The present invention is developed with this in mind and provides a method for manufacturing a colored steel plate that can form a hardened coating film with sufficient performance even at a low baking temperature.

The present invention that can achieve the above-mentioned purpose is described as follows.

[1] A method for manufacturing a colored steel plate, comprising:

A process of supplying a two-component urethane coating obtained by mixing a main agent containing a polyol component and a hardener containing a polyisocyanate component using a two-component mixing device to a roller coater, and applying the two-component urethane coating to a steel plate using the roller coater to form an uncured coating film; and

The process of baking the aforementioned uncured coating to form a cured coating.

[2] The method for manufacturing a colored steel plate as described in [1] above, wherein the uncured coating is baked in a heating furnace, the ambient temperature of the heating furnace is 150 to 250°C, and the baking time is 20 to 80 seconds.

According to the manufacturing method of the colored steel plate of the present invention, a hardened coating film with sufficient performance can be formed even at a low baking temperature.

1: Measuring roller

2: Material roller

3: Coating roller

4: Back support roller

5: Supply port for two-component urethane coating

6:Steel plate

7: Scraper

8: Paint plate

FIG1 is a schematic cross-sectional view showing a roller coating machine that can be used in one embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view showing a roller coating machine that can be used in other aspects of the present invention.

FIG3 is a schematic cross-sectional view showing a roller coating machine that can be used in other aspects of the present invention.

FIG. 4 is a schematic cross-sectional view showing a roller coating machine that can be used in other aspects of the present invention.

One of the features of the present invention is that a two-component urethane coating is used to form a hardened coating film. The hardened coating film formed can be any one of a top coating, a primer layer, and an inner coating. That is, any one of a top coating, a primer layer, and an inner coating can be formed by the manufacturing method of the present invention.

The term "roof coating" in this manual refers to a coating with properties oriented toward building materials or home appliances. Here, building materials include roof materials, wall materials, etc. Home appliances include refrigerators, washing machines, etc.

The "primer layer" mentioned in this manual refers to the coating used to ensure the adhesion between the steel plate and the top coating or the performance of the colored steel plate (such as corrosion resistance, processability, etc.).

The term "inner coating" in this manual refers to the coating formed on the surface (inner surface) of the colored steel plate opposite to the surface (surface) on which the top coating is formed.

The so-called "two-component urethane coating" in this manual refers to a coating composed of a main agent containing a polyol component and a hardener containing a polyisocyanate component, which are mixed before coating. On the other hand, the so-called "one-component urethane coating" refers to a coating containing a polyol component and a blocked polyisocyanate component.

The "polyisocyanate" in this specification without the limitation of "blocking" means a polyisocyanate whose isocyanate group (also called "isocyanate group") is not blocked by a blocking agent. On the other hand, the so-called "blocked polyisocyanate" means a polyisocyanate whose isocyanate group is blocked by a blocking agent.

Compared with the one-component urethane coating containing a polyol component and a blocked polyisocyanate component, the two-component urethane coating composed of a main agent containing a polyol component and a hardener containing a polyisocyanate component has high reactivity and can form a coating film with sufficient performance even at a low baking temperature. However, the two-component urethane coating has a short pot life after mixing the main agent and hardener, so it has not been used in the industrial manufacturing line of colored steel plates in the past. In this regard, in the present invention, after using a two-component mixing device to mix the main agent and the hardener, the two-component urethane coating is immediately supplied to the roller coating machine, thereby allowing the two-component urethane coating to be immediately applied to the steel plate after mixing, thereby eliminating the problem of pot life.

The "two-component mixing device" mentioned in this manual refers to a device that can automatically measure and mix liquid A (such as the main agent of two-component urethane coating) and liquid B (such as the hardener of two-component urethane coating). The two-component mixing device can use commercial products. Examples of such commercial products include XP50 Plural-Component Sprayer (registered trademark) XP-h manufactured by Graco Inc.

In the present invention, the roller coating machine is preferably a device having a plurality of rollers. The roller coating machine that can be used in one embodiment of the present invention is described below using FIG. 1. In addition, FIG. 1 is a schematic cross-sectional view, and the ratio of the size between the rollers and the ratio of the size of each roller to the thickness of the steel plate are not consistent with the ratio of the actual device.

The arrows recorded in the metering roller 1, the strip roller 2, the coating roller 3 and the backing roller 4 in Figure 1 indicate the rotation direction of each roller, and the arrow recorded on the side of the steel plate 6 indicates the moving direction of the steel plate 6.

In one aspect of the present invention, as shown in FIG. 1 , a two-component urethane coating (i.e., a mixture of a main agent containing a polyol component and a hardener containing a polyisocyanate component obtained using a two-component mixing device) is supplied between a metering roller 1 and a belt roller 2 from a supply port 5 of the two-component urethane coating. In the roller coating machine shown in FIG1 , the back-up roll 4 is a roll used to support the steel plate 6, the application roll 3 is a roll used to apply the two-component urethane coating on the roll to the steel plate 6, the pick-up roll 2 is a roll used to transfer the two-component urethane coating on the roll to the application roll 3, and the metering roll 1 is a roll used to adjust the appearance or thickness of the coating film.

In FIG1 , the rollers are in contact. However, FIG1 is only a schematic cross-sectional view, and it can be easily understood by those with ordinary knowledge in the technical field to which the invention belongs that in an actual roller coating machine, for example, there will be a certain degree of spacing between the metering roller 1 and the belt roller 2 in order to adjust the coating thickness. In addition, for those with ordinary knowledge in the technical field to which the invention belongs, the spacing between the rollers and the number of revolutions of each roller can be appropriately set according to the required coating thickness or appearance.

In one aspect of the present invention, a roller coating machine having a roller and a supply port for a two-component urethane coating as shown in FIG. 1 can be used to apply the two-component urethane coating to a steel plate. Specifically, in one aspect of the present invention,

It has a metering roller 1, a material roller 2, a coating roller 3, a backing roller 4 and a supply port 5 for two-component urethane coating.

Measuring roller 1 is adjacent to belt roller 2, belt roller 2 is adjacent to coating roller 3, coating roller 3 is adjacent to back-up roller 4,

The supply port 5 of the two-component urethane coating is arranged between the metering roller 1 and the material roller 2, and

A roller coating machine is used in which a steel plate 6 moves between a coating roller 3 and a backing roller 4;

The two-component urethane coating is supplied from the supply port 5 of the two-component urethane coating to between the metering roller 1 and the belt roller 2.

Transfer the two-component urethane coating on the belt roller 2 to the coating roller 3, and

The two-component urethane coating on the coating roller 3 can be applied to the steel plate 6.

The supply port for supplying the two-component urethane coating to the roller of the roller coating machine (e.g., the supply port 5 of the two-component urethane coating in FIG. 1 ) preferably has a plurality of slits. By using the supply port having such a plurality of slits, the two-component urethane coating can be supplied, for example, in a curtain shape, and the coating can be uniformly supplied to the roller.

In the manufacturing method of the present invention, in order to form a more beautiful coating film, a roller coating machine equipped with a scraper can also be used. For example, a scraper can be set on the side of the metering roller 1 in the roller coating machine shown in Figure 1.

The following uses FIG. 2 to explain a roller coating machine with a scraper that can be used in one embodiment of the present invention. In addition, in FIG. 2, the same symbols as in FIG. 1 are used. In addition, the description of the arrows in FIG. 2 is the same as the description of the arrows in FIG. 1. In addition, FIG. 2 is a schematic cross-sectional view like FIG. 1, and the ratio of the size of each roller is not consistent with the ratio of the actual device.

In the roller coating machine shown in FIG2 , the scraper 7 is adjacent to the metering roller 1. By means of the scraper 7 , the appearance of the two-component urethane coating (i.e., the uncured coating film) supplied to the metering roller 1 is adjusted to be consistent. In addition, as shown in FIG2 , the two-component urethane coating can be supplied between the scraper 7 and the metering roller 1 from the supply port 5 of the two-component urethane coating. In detail, one aspect of the present invention can be as follows:

It has a metering roller 1, a material roller 2, a coating roller 3, a backing roller 4, a supply port 5 for two-component urethane coating, and a scraper 7.

The scraper 7 is adjacent to the metering roller 1, the metering roller 1 is adjacent to the belt roller 2, the belt roller 2 is adjacent to the coating roller 3, the coating roller 3 is adjacent to the backing roller 4,

The supply port 5 for the two-component urethane coating is arranged between the scraper 7 and the metering roller 1, and

A roller coating machine is used in which a steel plate 6 moves between a coating roller 3 and a backing roller 4;

The two-component urethane coating is supplied from the supply port 5 of the two-component urethane coating to between the scraper 7 and the metering roller 1.

Transfer the two-component urethane coating on the belt roller 2 to the coating roller 3, and

Apply the two-component urethane coating on the coating roller 3 to the steel plate 6.

In addition, in order to prevent the two-component urethane coating supplied to the scraper 7 and the metering roller 1 from overflowing from these lateral sides, shielding plates can also be installed on the sides of the scraper 7 and the metering roller 1.

In the manufacturing method of the present invention, a roller coating machine without a metering roller can also be used. The following uses Figures 3 and 4 to illustrate the roller coating machine without a metering roller used in one embodiment of the present invention. In addition, in Figures 3 and 4, the same symbols as Figures 1 and 2 are used. In addition, the description of the arrows in Figures 3 and 4 is the same as the description of the arrows in Figure 1. In addition, Figures 3 and 4 are schematic cross-sectional views like Figure 1, and the ratio of the size of each roller is not consistent with the ratio of the actual device.

In one aspect of the present invention, as shown in FIG3 , a roller coating machine having a coating plate 8 can be used. Specifically, in one aspect of the present invention, there is a belt roller 2, a coating roller 3, a backing roller 4, a supply port 5 for a two-component urethane coating, and a coating plate 8,

The material belt roller 2 is adjacent to the coating roller 3, and the coating roller 3 is adjacent to the backing roller 4.

The supply port 5 for the two-component urethane paint is arranged in a manner that the two-component urethane paint can be supplied to the paint pan 8, and

A roller coating machine is used in which a steel plate 6 moves between a coating roller 3 and a backing roller 4;

The two-component urethane paint is supplied to the paint pan 8 from the supply port 5 of the two-component urethane paint.

The two-component urethane coating supplied to the coating plate 8 is extracted onto the belt roller 2,

Transfer the two-component urethane coating on the belt roller 2 to the coating roller 3, and

The two-component urethane coating on the coating roller 3 can be applied to the steel plate 6.

In the manufacturing method of the present invention, in order to form a more beautiful coating film, a roller coating machine equipped with a scraper can also be used. For example, a scraper can be set on the lateral side of the belt roller 2 in the roller coating machine shown in Figure 3.

In one aspect of the present invention, as shown in FIG4 , a roller coating machine can be used in which a scraper 7 is arranged on the side of a belt roller 2 and a supply port 5 of a two-component urethane coating is arranged between the scraper 7 and the belt roller 2. Specifically, in one aspect of the present invention, the following can be used:

It has a material roller 2, a coating roller 3, a backing roller 4, a two-component urethane coating material supply port 5 and a scraper 7,

The scraper 7 is adjacent to the belt roller 2, the belt roller 2 is adjacent to the coating roller 3, the coating roller 3 is adjacent to the backing roller 4,

The supply port 5 of the two-component urethane coating is arranged between the scraper 7 and the belt roller 2, and

A roller coating machine is used in which a steel plate 6 moves between a coating roller 3 and a backing roller 4;

The two-component urethane coating is supplied from the supply port 5 of the two-component urethane coating to between the scraper 7 and the belt roller 2.

Transfer the two-component urethane coating on the belt roller 2 to the coating roller 3, and

Apply the two-component urethane coating on the coating roller 3 to the steel plate 6.

In addition, in order to prevent the two-component urethane coating supplied to the scraper 7 and the belt roller 2 from overflowing from these lateral sides, shielding plates can also be installed on the sides of the scraper 7 and the metering roller 1.

It is preferred to apply the two-component urethane coating to the steel plate in such a manner that the desired thickness of the hardened coating is obtained after drying (after baking). When the hardened coating formed by the manufacturing method of the present invention is a top coating, the thickness after drying (after baking) is preferably 5 to 30 μm, and more preferably 10 to 25 μm. When the hardened coating formed by the manufacturing method of the present invention is a primer layer, the thickness after drying (after baking) is preferably 2 to 25 μm, and more preferably 3 to 15 μm. When the hardened coating formed by the manufacturing method of the present invention is an inner coating, the thickness after drying (after baking) is preferably 2 to 15 μm, and more preferably 3 to 10 μm.

In the industrial manufacturing line of color steel plates, the baking of uncured coatings is usually carried out using a heating furnace. The ambient temperature of the heating furnace is preferably 150 to 250°C, preferably 160 to 230°C, and more preferably 170 to 220°C. The baking time of the uncured coating is preferably 20 to 80 seconds, preferably 20 to 70 seconds, and more preferably 30 to 60 seconds. Here, the so-called "baking time of the uncured coating" refers to the time that the uncured coating remains in the heating furnace.

The production line speed of the industrial manufacturing line of colored steel plates (i.e. the moving speed of the steel plates) is usually 30 to 150 m/min, preferably 50 to 120 m/min.

After the top coating is formed as a hardened coating film by baking, the obtained colored steel plate is preferably cooled, and water cooling is particularly preferred. Water cooling can be performed using, for example, water showering or mist.

Next, the two-component urethane coating that can be used in the present invention is described. In the following, the "two-component urethane coating for forming a top coating" is sometimes referred to as "top coating coating", the "two-component urethane coating for forming a primer layer" is sometimes referred to as "primer coating", and the "two-component urethane coating for forming an inner coating" is sometimes referred to as "inner coating coating". In addition, the following description of "two-component urethane coating, the main agent or hardener" without the limitation of "top coating, primer or inner coating" is a common description for top coating coating, primer coating and inner coating coating.

The main agent of two-component urethane coating contains a polyol component. Only one type of polyol component can be used or two or more types can be used in combination. Examples of polyol components include polyester polyol, polyether polyol, polysilicone-modified polyester polyol, fluorine-based polyol, etc. From the perspective of weather resistance or processability, the polyol component contained in the main agent of the top coating is preferably polyester polyol. From the perspective of adhesion, processability or corrosion resistance, the polyol component contained in the main agent of the primer coating is preferably polyester polyol or epoxy polyol. From the perspective of adhesion, processability or corrosion resistance, the polyol component contained in the main agent of the inner coating coating is preferably polyester polyol or epoxy polyol.

Carboxylic acids used to form polyester polyols include, for example, succinic acid, adipic acid, sebacic acid, dimer acid, maleic anhydride, phthalic anhydride, isophthalic acid, terephthalic acid, etc. To form polyester polyols, only one carboxylic acid may be used or two or more may be used in combination.

Alcohols used to form polyester polyols include, for example, ethylene glycol, propylene glycol, diethylene glycol, neopentyl glycol, trihydroxymethylpropane, glycerol, etc. To form polyester polyols, only one alcohol may be used or two or more alcohols may be used in combination.

Polyester polyols can also be used: polycaprolactone polyols obtained by ring-opening polymerization of ε-caprolactone using polyols.

From the perspective of coating viscosity or coating workability, the number average molecular weight of polyester polyol is preferably 2,500 to 7,000, and more preferably 3,000 to 5,000. This number average molecular weight can be determined by GPC (Gel permeation chromatography).

Polyester polyols are often added to the main agent of two-component urethane coatings in the form of solutions. From the perspective of reactivity or water resistance, the hydroxyl value of the polyester polyol solution is preferably 30 to 120 (mgKOH/g), and particularly preferably 50 to 100 (mgKOH/g).

The main agent of two-component urethane coating usually contains a solvent in addition to the polyol component. Examples of solvents include xylol, aromatic hydrocarbons, cyclohexanone, isophorone, etc. Solvents can be used alone or in combination of two or more.

From the perspective of the viscosity of the coating or the coating workability, the solid content of the main agent is preferably 30 to 80% by weight, and more preferably 40 to 70% by weight, relative to the entire main agent.

The main agent of two-component urethane coatings may also contain other components other than the polyol component and the solvent. Other components contained in the main agent of top coating coatings may include, for example, pigments, aggregates, matting materials, defoaming agents, surface conditioners, mar-proofing agents, hardening catalysts, and hardening inhibitors. Other components contained in the main agent of primer coatings may include, for example, rust-proof pigments, pigments, aggregates, matting materials, defoaming agents, mar-proofing agents, hardening catalysts, and hardening inhibitors. Other ingredients contained in the main agent of the interior coating can be listed as: anti-rust pigment, pigment, aggregate, matte material, defoaming agent, surface conditioner, anti-marring agent, hardening catalyst, hardening inhibitor, etc. For those with common knowledge in the technical field to which the invention belongs, the content of other ingredients in the main agent can be appropriately set according to the purpose of use of the ingredient.

In order to promote the urethanization reaction of the polyol component and the polyisocyanate component, the main agent of the two-component urethanization coating preferably contains a hardening catalyst. Hardening catalysts used for urethanization reactions are well known and sold on the market. Commercially available hardening catalysts include, for example, "K-KAT5218" manufactured by King Industries, Inc.

In order to extend the pot life after the main agent and hardener are mixed, the main agent of the two-component urethane coating may also contain a hardening inhibitor. Examples of hardening inhibitors include acetone, etc.

In order to promote the urethanization reaction and extend the pot life of the main agent and hardener after mixing, the main agent of the two-component urethane coating is preferably a combination of aluminum bis(ethyl acetylacetate) pyruvate (such as "K-KAT5218" manufactured by King Industries, Inc.) and acetylacetone.

The hardener of the two-component urethane coating contains a polyisocyanate component. The polyisocyanate component may be used alone or in combination of two or more. Examples of the polyisocyanate component include 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, xylene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 1,6-hexamethylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate, and 1,4-cyclohexane diisocyanate. Among these, 1,6-hexamethylene diisocyanate (HMDI) and isophorone diisocyanate (IPDI) are preferred from the perspective of weather resistance or heat yellowing resistance.

The polyisocyanate component may also use a modified product of the above-mentioned diisocyanate (e.g., alcohol-modified diisocyanate), a condensate of the above-mentioned diisocyanate (e.g., diuret (dimer), isocyanurate (trimer)), or a modified product of the condensate (e.g., alcohol-modified isocyanurate), or an adduct of the above-mentioned diisocyanate.

The hardener of two-component urethane coating usually contains a solvent in addition to the polyisocyanate component. Examples of the solvent include methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), ethyl acetate, butyl acetate, xylene, etc. The solvent may be used alone or in combination of two or more.

From the perspective of handling or coating workability, the solid content of the hardener is preferably 30 to 80% by weight, and more preferably 40 to 70% by weight, relative to the hardener as a whole. From the perspective of workability or economy, the NCO content of the hardener is preferably 5 to 30% by weight, and more preferably 10 to 20% by weight, relative to the hardener as a whole.

The main agent and hardener of the two-component urethane coating are preferably mixed in such a way that the molar ratio of the hydroxyl group in the main agent: the isocyanate group in the hardener is within the desired range. The molar ratio of the hydroxyl group in the main agent: the isocyanate group in the hardener is preferably 100:70 to 100:130, more preferably 100:80 to 100:120, and most preferably about 100:100.

Next, the steel plates that can be used in the present invention are described. Examples of the steel plates include: cold-rolled steel plates, molten zinc-plated steel plates, zinc electroplated steel plates, aluminum-zinc alloy-plated steel plates, aluminum-plated steel plates, stainless steel plates, copper-plated steel plates, tin-plated steel plates, etc. The thickness of the steel plate is preferably 0.1 to 2.0 mm, and more preferably 0.25 to 1.6 mm.

[Implementation example]

The following are reference examples to more specifically illustrate the present invention, but the present invention is not limited to the following reference examples. In addition, the "%" and "parts" mentioned below mean "weight %" and "weight parts" unless otherwise specified.

〈Compare Reference Example 1 and Reference Examples 1 to 4〉

Comparative reference example 1 using a single-component urethane coating (HD6000 U White (1PC)) and reference examples 1 to 4 using a two-component urethane coating (top coating coating) composed of a main agent (HD6000 U White (2PC)) and a hardener (HMDI hardener or IPDI hardener) were performed. In addition, the main agent and hardener of the two-component urethane coating (top coating coating) were not mixed using a two-component mixing device, but were mixed manually. In addition, the coating was applied to the steel plate using a rod coater instead of a roller coater.

The steel plate used was a commercially available hot-dip galvalume steel plate (aluminum-zinc alloy-coated steel plate, steel plate thickness: 0.35 mm, Al content in plating: 55%, Zn content in plating: 45%, plating adhesion on both sides: 150 g/m ² ).

"Precolor Primer HP32" manufactured by AkzoNobel Coatings Co., Ltd. was applied to the surface of the aforementioned steel plate and dried to form a primer layer (thickness of the primer layer after drying: 5μm).

In addition, "Precolor No. 7000" manufactured by AkzoNobel Coatings Co., Ltd. was applied to the inner surface of the aforementioned steel plate and dried to form an inner coating (the thickness of the inner coating after drying: 8μm).

A one-component urethane coating or a two-component urethane coating is applied to the surface of the aforementioned steel plate (the surface on which the primer layer is formed) and dried in the following manner to form a top coating.

Both the one-component urethane coating and the two-component urethane coating (top coating) use coatings made by AkzoNobel Coatings Co., Ltd. In addition, aggregates, matting materials, defoaming agents, anti-marring agents, hardening catalysts, and hardening inhibitors are added to these coatings. The amounts of components in the main agent (HD6000 U White (2PC)) of the one-component urethane coating (HD6000 U White (1PC)) and the two-component urethane coating (top coating) used are shown in Table 1. In addition, these components are described as follows

Pigment: Titanium oxide

Polyester polyol solution: polyester polyol solution manufactured by AkzoNobel Coatings Co., Ltd. (carboxylic acid components constituting esters: isophthalic acid, phthalic anhydride and adipic acid, alcohol components constituting esters: neopentyl glycol, trihydroxymethylpropane, neopentyletrol and 1,6-hexanediol, number average molecular weight of polyester polyol: 4,000, hydroxyl value of polyester polyol solution: 50 (mgKOH/g), solvent: cyclohexanone, xylene, aromatic hydrocarbons)

Blocked polyisocyanate: "Duranate TPA-B80E" manufactured by Asahi Kasei Co., Ltd. (HMDI isocyanurate type)

Aggregate: "Techpolymer MBX-30" from Sekisui Chemicals Co., Ltd.

Matt material: "SYLYSIA 310P" manufactured by Fuji Sylysia Chemical Co., Ltd.

Defoaming agent: "Miki Leveling MK Conch" manufactured by Kyoeisha Chemical Co., Ltd.

Anti-damage agent: "PTFE Wax KTL-8N" manufactured by Kitamura Co., Ltd.

Diluent (= solvent): cyclohexanone, xylene, aromatic hydrocarbons

Hardening catalyst: "K-KAT5218" manufactured by King Industries, Inc. (bis(ethyl acetate) pyruvate monoacetate aluminum)

Hardening inhibitor: acetylacetone

The 1,6-hexamethylene diisocyanate (HMDI) hardener or isophorone diisocyanate (IPDI) hardener used in the two-component urethane coating (top coating) was obtained from AkzoNobel Coatings Co., Ltd. The solid content and NCO content of these hardeners are shown in Table 2.

When using two-component urethane coating (top coating), the main agent and the hardener are mixed manually in the ratio shown in Table 3 in such a way that the molar ratio of hydroxyl group in the main agent: isocyanate group in the hardener becomes 100:100.

A single-component urethane coating or a two-component urethane coating (top coating coating) was applied to the steel plate using a rod coater so that the thickness of the hardened coating (top coating) after drying (after baking) became 18 μm, and a colored steel plate was manufactured by baking at the baking temperature shown in Table 3 for 55 seconds using an automatic discharge dryer manufactured by Toshang Thermal Co., Ltd. to form a hardened coating. The performance of the obtained colored steel plate was evaluated in the following manner. The evaluation results are shown in Table 3.

(1) Hardening

The abrasion test was performed using an abrasion tester (solvent: MEK, load: 1kg), and the hardening properties were evaluated using the following criteria.

(Benchmark)

○: After 100 back and forth movements, the primer layer was not exposed.

×: The primer layer is exposed when the number of reciprocating strokes is less than 100.

(2) Processability

The color steel plate obtained is tightly bent into a T-shape with the hardened coating facing upward. After being molded by a molding machine, a cellophane tape peeling test is performed on the bent portion, and the processability is evaluated according to the following criteria.

(Benchmark)

○: The hardened coating film is not peeled off at all

×: Hardened coating peeling off

(3) Agglomeration

Two colored steel plates were stacked so that their surfaces (i.e., the surface formed with the top coating) and the inner surface (i.e., the surface formed with the inner coating) were in contact, and then the obtained laminate was molded using a hot press at 40°C with a load of 40kg/ ^cm2 applied to the hardened coating. The pressurization was then stopped after maintaining the pressurization state for 24 hours. After the laminate was cooled to room temperature, the agglomeration was evaluated by the following criteria.

(Benchmark)

○: 2 colored steel plates peel off without any problems

×: The two colored steel plates are closely attached and difficult to peel off

[Table 1]

[Table 2]

[table 3]

From the results described in Table 3, it can be seen that in Comparative Reference Example 1 using a single-component urethane coating, when the ambient temperature is as low as 215°C, the performance of the hardened coating film (hardening, processability, and agglomeration) becomes insufficient. On the other hand, in Reference Examples 1 to 4 using a two-component urethane coating (top coating coating), even when the ambient temperature is as low as 155 to 215°C, a hardened coating film with excellent performance can be formed.

[Industrial applicability]

According to the manufacturing method of the color steel plate of the present invention, a hardened coating film (top coating, primer layer or inner coating) with sufficient performance can be formed even at a low baking temperature. The color steel plate obtained by the manufacturing method of the present invention is useful in various fields such as home appliances, construction materials, etc.

This application is based on Japanese Patent Application No. 2022-137205 filed in Japan, and the contents are fully covered by this specification.

Claims (2)

A method for manufacturing a colored steel plate includes: A process of supplying a two-component urethane coating obtained by mixing a main agent containing a polyol component and a hardener containing a polyisocyanate component using a two-component mixing device to a roller coater, and applying the two-component urethane coating to a steel plate using the roller coater to form an uncured coating film; and The process of baking the aforementioned uncured coating to form a cured coating. The method for manufacturing colored steel plates as described in claim 1 uses a heating furnace to bake the uncured coating film, the ambient temperature of the heating furnace is 150 to 250°C, and the baking time is 20 to 80 seconds.

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