KR102140600B1 - Pcm steel sheet havign excellent glossiness - Google Patents

Abstract

The present invention relates to a PCM (Pre Coated Metal) steel sheet manufactured by the 2C-2B method, a plated steel sheet; And a coating layer formed on at least one surface of the plated steel sheet, wherein the coating layer is sequentially composed of a transparent pretreatment layer, a transparent base clear paint layer, an ink paint layer and a top clear paint layer, and the transparent pretreatment layer comprises zirconium and titanium. Metal rust inhibitors; Silica; And at least one coupling agent selected from the group consisting of a titanium-based coupling agent, a zirconium-based coupling agent, and a silane-based coupling agent.

Description

PCM steel sheet made by 2-coat 2-baking that expresses the glossiness of the material{PCM STEEL SHEET HAVIGN EXCELLENT GLOSSINESS}

The present invention relates to a PCM (Pre Coated Metal) steel sheet, in particular, to a steel sheet manufactured by the 2C-2B method.

Existing Pre-Coated Metal (PCM) steel products include Cold Rolled Steel Sheet (CR), Electrolytic Galvanized Iron (EGI), and Hot-Dip Galvanized Steel. It is a steel sheet obtained by coating on materials such as Sheet, GI), and AL (Aluminium).

As shown in Fig. 1, the PCM steel sheet is subjected to a pretreatment (pretreatment layer) on the plated steel sheet, followed by primer coating (primer layer), and base clear coating (base coating layer), ink coating and top clear coating. It has a structure containing. This conventional PCM steel sheet is manufactured by a 3C-3B (3 coating 3 baking) method including performing primer coating, base clear coating, and top clear coating, and firing after each coating. In the PCM steel sheet according to the 3C-3B method, the manufacturing process of the PCM steel sheet is complicated, including many coating and firing processes.

On the other hand, PCM steel sheets generally cannot visually confirm the surface characteristics of the applied material after painting. That is, the primer coating applied to the PCB steel plate is in close contact with the steel plate by the pretreatment layer, and the primer coating layer provides adhesion to the upper base clear coating. In this case, the primer layer is included to provide corrosion resistance, and application of the primer layer is required to implement desired corrosion resistance.

On the other hand, in order to apply such a primer layer, solid adhesion to the steel sheet is required, and a pretreatment layer needs to be formed for such adhesion. Such a pretreatment layer usually uses a pigment. In this case, even if a primer layer, a base clear coating layer, an ink coating layer, etc. are formed transparently, the inherent glossiness of the material is prevented from being expressed to the outside. Accordingly, in order to impart a texture like a metal, it is necessary to include a metal component for imparting gloss in forming a subsequent layer such as a base clear coating layer.

In addition, these pigments not only perform the function of imparting color to the surface of the steel sheet as described above, but also play a role of improving adhesion and corrosion resistance to the PCM steel sheet. Therefore, when the pretreatment layer does not contain a pigment, it is required to use other fillers other than the pigment, for example, additives to supplement adhesion and corrosion resistance, and these additives lower the transparency of the pretreatment layer. Transparency cannot be secured, and due to this, the inherent glossiness of the steel sheet cannot be expressed externally.

In the case of utilizing the inherent glossiness of the material steel sheet, the aesthetics can be improved more than when a gloss agent is added to impart gloss, and the high quality of the steel sheet can be achieved.

Accordingly, improvement in the method of simplifying the process by manufacturing the PCM steel sheet by the 2C-2B process is required, but the PCM steel sheet and its manufacturing method that satisfy the corrosion resistance of the steel sheet and the adhesion between the steel sheet and the coating layer are introduced. It is not possible.

Furthermore, there is no disclosure of a PCM steel sheet in which properties such as glossiness of a steel sheet as a material can be checked with the naked eye even after painting.

In the PCM steel sheet, the present inventors have omitted the primer layer included in the PCM steel sheet manufactured by the conventional 3C-3B method, and have excellent adhesion to the material, thus preventing the problem of peeling of the paint, and also PCM having excellent corrosion resistance. I want to provide a grater.

In addition, as an embodiment of the present invention, it is intended to provide a steel plate capable of confirming the properties of a material applied to the manufacture of a PCM steel plate according to the 2C-2B method even after painting.

The present invention relates to a pre-coated steel sheet, wherein the pre-coated steel sheet is a plated steel sheet; And a coating layer formed on at least one surface of the plated steel sheet, wherein the coating layer is sequentially composed of a transparent pretreatment layer, a transparent base clear paint layer, an ink paint layer and a top clear paint layer, and the transparent pretreatment layer is formed from zirconium and titanium. Metal rust inhibitors including selected metals; Silica; At least one coupling agent selected from the group consisting of a titanium-based coupling agent, a zirconium-based coupling agent, and a silane-based coupling agent; And a resin selected from acrylic resins and silica-modified acrylic resins. The transparent pretreatment layer includes 0.5 to 1% by weight of a metal rust inhibitor, 10 to 15% by weight of silica, 0.5 to 3% by weight of a coupling agent, and the balance resin.

The transparent pretreatment layer has an adhesion amount of 40 to 80 mg/m 2.

The transparent base clear coating layer is a polyester resin, based on 100 parts by weight of the polyester resin, 0.1 to 0.5 parts by weight of a pickup improving agent, 1.0 to 2.5 parts by weight of a leveling agent, 1.0 to 3.0 parts by weight of an epoxy resin, 10 to 15 parts by weight of a curing agent It may include parts and 1 to 3 parts by weight of an acid catalyst.

The transparent base clear coating layer may have a thickness range of 12 to 18 μm.

The polyester resin preferably has a weight average molecular weight of 22,000 to 25,000, a glass transition temperature (Tg) of 50-55°C, and an OH equivalent number (OH value, OHv) of 5-10.

The ink coating layer may include a polyester resin having a weight average molecular weight of 1800 to 28,000, and 5 to 10 parts by weight of a pigment based on 100 parts by weight of the polyester resin, and may have a thickness of 1 to 10 μm.

According to the present invention, a PCM steel sheet can be manufactured by the 2C-2B process, and the manufacturing process can be simplified.

In addition, according to an embodiment of the present invention, since the primer layer is not included and the pigment is not used in the pretreatment layer, the glossiness of the steel sheet can be visually confirmed even after painting, thereby obtaining a more beautiful PCM steel sheet.

Further, it is possible to secure excellent adhesion between the material and the paint without including a primer layer, as well as to express corrosion resistance.

1 is a view schematically showing the structure of a PCM steel sheet manufactured by a conventional 3C-3B process.
2 is a view schematically showing the structure of the PCM steel sheet manufactured by the 2C-2B process of the present invention.
3 is a diagram conceptually showing a mechanism in which the pretreatment layer applied to the present invention acts between the material plated steel sheet and the base coating layer.
4 is a photograph taken of a surface of a specimen for testing the workability of a steel sheet having a pretreatment layer according to an embodiment.
5 is a photograph of the surface of a specimen for testing the chemical resistance of a steel sheet having a pretreatment layer according to an embodiment.
6 is a photograph taken of a surface of a specimen for testing the corrosion resistance of a steel sheet having a pretreatment layer according to Comparative Examples and Examples.

The present invention relates to a PCM (Pre Coated Metal) steel sheet, in particular, to a steel sheet manufactured by the 2C-2B method, wherein the PCM steel sheet of the present invention forms a pre-treatment layer on the surface of the plated steel sheet, and a primer on the pre-treatment layer. Without forming a layer, a resin coating layer is formed.

In general, in forming a resin coating layer on the surface of a steel plate, as shown in Fig. 1, a pretreatment layer and a primer layer are formed on the surface of the plated steel plate to improve adhesion between the steel plate and the coating layer, and a coating layer on the primer layer. To form. The pretreatment layer is to improve adhesion to the steel sheet, and the primer layer provides solid adhesion between the pretreatment layer formed on the steel sheet and the coating layer, and also provides corrosion resistance.

However, in the case of including a primer layer as described above, it contributes to improving the corrosion resistance, but the process is complicated, and for the formation of such a primer layer, a pigment may be added to improve adhesion to the pretreatment layer between the steel plate and the primer layer. There is a need. When the pigment is included in the pretreatment layer, the inherent glossiness of the steel sheet is prevented from being expressed to the outside, and thus, a separate layer to achieve high luminance by imparting gloss to the primer layer or the upper resin coating layer. It is necessary to add metal powder or mica.

On the other hand, if the primer is not included, the corrosion resistance is deteriorated, and for this reason, in the case of manufacturing a PCM steel sheet by the 2C 2B process, the 2C 2B process is usually applied twice to form a thick coating layer to secure corrosion resistance. The method is being applied.

On the other hand, when the pretreatment layer does not contain a pigment in order to express the glossiness of the material even after coating, there is a problem that the adhesion to the primer or resin coating is lowered, and the corrosion resistance is also lowered. Further, in order to prevent such decrease in adhesion and corrosion resistance, other additives must be added, but in this case, transparency is lowered due to the added additive, and thus it cannot be said to implement a transparent pretreatment layer.

As described above, in the case of including a primer, it is not easy to realize high transparency due to a chain action to express the gloss of the material even after painting. In addition, even when the pretreatment layer does not contain a pigment, it is difficult to achieve high transparency while securing adhesion and corrosion resistance, and thus it is difficult to use the gloss of the material.

Thus, the present invention is to provide a technique for manufacturing a PCM steel sheet by the 2C 2B method by not including the primer. Specifically, the PCM steel sheet as an embodiment of the present invention includes a pretreatment layer, a transparent base clear coating layer, a nano ink coating layer, and a top clear coating layer on the surface of a plated steel sheet material, as shown in FIG. 2.

The present invention is to provide a pretreatment layer capable of achieving high transparency because the pretreatment layer does not contain a pigment while the pretreatment layer expresses the function of improving adhesion and corrosion resistance provided by the conventional primer layer. The pretreatment layer according to the present invention is a chromium-free pretreatment layer containing a metal rust inhibitor, silica, a coupling agent, and a resin.

The pretreatment layer of the present invention comprises silica. The silica is located on the surface of the base plated steel sheet to form a film by covering the surface of the plated steel sheet and firmly adheres to the base steel sheet, thereby providing corrosion resistance and chemical resistance to the steel sheet.

The silica is preferably a powder having a nano-sized particle diameter. The particle size of the silica is not limited thereto, but, for example, having a size of 5 to 15 nm can minimize the space between the silica particles, and thus, it is preferable to prevent the occurrence of voids on the surface. .

The silica may be included in an amount of 10 to 15% by weight. If it contains less than 10% by weight, the film cannot be sufficiently formed on the surface of the steel sheet, so it is not sufficient to provide corrosion resistance and chemical resistance. If it exceeds 15% by weight, there is a problem that the improvement of physical properties is no longer improved. Bar, it is preferable to include in the above range.

The metal rust inhibitor is for providing corrosion resistance in the pretreatment layer, and a polyvalent metal ion compound is used. The polyvalent metal ions fill the voids between particles of silica powder located on the surface of the steel sheet, thereby providing a role of improving chemical resistance and corrosion resistance for the steel sheet. The polyvalent metal ion compound is preferably a titanium compound or a zirconium compound. The titanium compound and the zirconium compound may be mixed and used, and it is more preferable to improve physical properties such as workability and corrosion resistance when used in combination.

The polyvalent metal ion compound may be included in an amount of 0.5 to 1% by weight based on the solid content. If it is contained in an amount of less than 0.5% by weight, corrosion resistance cannot be secured, and if it exceeds 1% by weight, there is a problem of impairing solution stability, and it is preferable to include it in the above range.

In addition, the pretreatment layer of the present invention contains a coupling agent. The coupling agent cross-links between the silica and the base coating layer formed on the top of the pretreatment layer to provide adhesion between the steel plate and the base coating layer, thereby improving the durability and hardening of the base coating layer, thereby providing corrosion resistance to the steel sheet. to provide. As the coupling agent, a Ti-based crosslinking agent, a Si-based crosslinking agent, or a Si coupling agent may be used, and if it is commonly used, it may be suitably used in the present invention. The coupling agent may be included in an amount of 0.5 to 3% by weight.

The pretreatment layer of the present invention contains a resin in the balance as a main material. The resin is not particularly limited, but acrylic resin and silica-modified acrylic resin And the like. The resin provides adhesion to the material and functions as a binder for the composition component of the pretreatment layer.

The relationship between the pretreatment layer of the present invention and the plated steel sheet is conceptually shown in FIG. 3. As shown in FIG. 3, silica is in close contact with the surface of the plated steel sheet, and a film is formed in a form in which polyvalent metal ions are filled between the silica particles to provide a tight adhesion to the steel sheet while providing corrosion resistance. In addition, the crosslinking agent may crosslink between the silica particles and the base coating formed thereon to provide a strong adhesion between the steel plate and the coating layer.

The PCM steel sheet on which the pretreatment layer according to the present invention is formed can improve adhesion between the steel sheet and the base coating layer without including a primer layer, and provides excellent corrosion resistance and chemical resistance. In addition, since the pretreatment layer of the present invention does not contain a pigment inside, the glossiness of the plated steel sheet can be expressed to the outside, and the glossiness can be utilized. Therefore, it is not necessary to use a separate additive for imparting gloss to express high luminance.

The pretreatment layer may be formed by drying after applying a pretreatment composition having the composition of the pretreatment layer on the surface of the plated steel sheet. The application is not particularly limited, and may be applied by a method such as roll coating or spray coating.

The pretreatment composition includes a solid component having a composition of a pretreatment layer formed on the surface of the base plated steel sheet and a solvent, and the solvent may be isopropyl alcohol or ethanol.

The pretreatment layer may be formed by drying the steel sheet after applying the pretreatment composition to the surface of the plated steel sheet. The drying is not particularly limited, but may be performed using equipment such as an induction oven, a hot air oven, or a NIR oven, and may be dried in a temperature range of 80 to 100°C.

It is preferable that the pretreatment layer has an adhesion amount of 40 to 80 mg/m 2 after drying. If it is less than 40 mg/m 2, the corrosion resistance is not sufficient, and if it exceeds 80 mg/m 2, there is a problem that the workability is deteriorated. Therefore, it is preferable to have an adhesion amount within the above range.

The PCM steel sheet according to the present invention includes a transparent base clear coating layer on the pretreatment layer. The transparent base clear coating layer includes a polyester resin as a main resin, and includes a pickup improving agent, a leveling agent, an epoxy resin, a curing agent, and an acid catalyst.

The transparent base clear coating layer uses a linear polyester resin as the main resin. The present invention is to provide a two-coating coating system without a primer, and since the base paint is directly coated on the surface of the material, it is necessary to use a resin having excellent adhesion between the material and the base paint. Since the linear polyester resin can secure high adhesion to the material, it is preferable for use in the present invention.

The polyester resin has a weight average molecular weight in the range of 22000 to 25000, and it is preferable to use a resin having a glass transition temperature (Tg) of 50-55°C for the polyester resin. As described above, it is preferable to use a resin having a high molecular weight and a high glass transition temperature because excellent adhesion to the pretreatment layer can be realized without a primer. In addition, the polyester resin may be used having an OHv (OH value) of 5-10.

On the other hand, the transparent base clear coating layer of the present invention contains a pickup improving agent. The pickup improving agent is not particularly limited as long as it is generally used, as it can be suitably used in the present invention. For example, fumed silica (Aerosil), silica, or the like may be used.

The pickup improving agent may be included in the range of 0.1 to 0.5 parts by weight based on 100 parts by weight of the polyester resin. The pick-up improver is intended to improve the property of embedding the composition for forming the base coating layer on the pick-up roll, and the higher the content is, the better the pick-up property is improved, but if it is included in an excessive amount, excessive air bubbles are generated and the coating film is weakened. Defects can occur, such as intelligence. Therefore, it is preferable to be included in the content range as described above.

The transparent base clear paint layer of the present invention also contains a leveling agent. The leveling agent is not particularly limited as long as it is generally used, as it can be suitably used in the present invention. For example, an acrylic type additive can be used. The leveling agent may be included in the range of 1.0 to 2.5 parts by weight based on 100 parts by weight of the polyester resin. As the leveling agent is an acrylic type additive, the higher the content is, the lower the compatibility with the main resin may be, and there is a concern of defects such as occurrence of craters in the exterior or deterioration of pickup properties. On the other hand, when the content is small, problems such as generation of air bubbles and deterioration of appearance leveling may occur. Accordingly, it is preferable to add a leveling agent in the content range as described above.

The transparent base clear coating layer of the present invention contains an epoxy resin. The epoxy resin is intended to increase adhesion to the transparent base clear coating layer and improve chemical resistance, and may be included in the range of 1.0 to 3.0 parts by weight based on 100 parts by weight of the polyester resin. As the content of the epoxy resin increases, the processability tends to decrease, and it is preferable to include it in the above range.

The transparent base clear coating layer of the present invention contains an amine curing agent as a curing agent. Although it does not specifically limit as said amine hardening agent, Melamine is mentioned. The amine curing agent is preferably included in the range of 10 to 15 parts by weight based on 100 parts by weight of the polyester resin to implement the main resin and the optimum curing density.

The transparent base clear paint layer of the present invention also contains an acid catalyst. The acid catalyst acts as a catalyst for the crosslinking reaction during curing of the coating film and accelerates curing of the coating film. As the acid catalyst, sulfonic acid may be used. The amount of the acid catalyst added may be adjusted according to the content of the amine curing agent and is not particularly limited, but may be included in an amount of 1 to 3 parts by weight based on 100 parts by weight of the polyester resin.

The transparent base clear coating composition contains a solvent. The solvent can be applied to a generally used solvent, and for example, a ketone, hydrocarbon, or ester solvent may be used. The solvent may be used in an appropriate ratio in consideration of the appearance and popping of the coating film. Although not particularly limited, for example, the solid content and the solvent may be mixed in a weight ratio of 35 to 45:55 to 65.

The transparent base clear coating layer is not necessarily limited thereto, but the base coating composition may be coated on the surface of the steel sheet on which the pretreatment layer is formed by a method such as roll coating or spray coating.

After applying the transparent base clear coating composition, it can be formed by baking the steel sheet in an oven. At this time, the baking temperature may be slightly different depending on the boiling point of the solvent and the boiling point of the paint, but may be performed in the range of 210 to 216°C.

At this time, the base coating is preferably formed in a thickness range of 12 to 18㎛. When the thickness becomes thinner, the thickness of the barrier layer that can protect the material means that the barrier layer becomes thinner. Therefore, when the thickness of the base coating is less than 12 μm, properties obtainable from the coating film, for example, physical properties such as workability, chemical resistance, weather resistance, and durability, are weakened, which is not preferable.

On the other hand, the thicker the coating film, the better physical properties can be secured. However, if the coating film is too thick beyond 18㎛, the coating film popping phenomenon caused by solvents, etc. is likely to occur due to bubble generation and a difference in curing speed. For this reason, holes are easily generated on the surface of the coating film, which is not preferable.

It is preferable that the transparent base clear coating layer formed by the present invention is transparent. By forming the transparent coating layer, the pretreatment layer is made transparent, so that the glossiness of the material can be visually confirmed from the outside. Therefore, the glossiness of the material can be expressed as it is by forming the base coating layer as transparent.

The present invention includes an ink coating layer on the surface of the base coating layer. The ink coating layer contains a resin and a pigment.

At this time, the resin may be a polyester resin. The polyester resin may be used having a weight average molecular weight of 1800 or more, more preferably 1800 to 28,000.

The pigment contained in the ink is for imparting color to the surface of the steel sheet, and may be appropriately selected and used as necessary. However, it is preferable to use a nano-sized pigment as the pigment. For example, the pigment is preferably a powder having a particle size of 0.3 to 0.4㎛. By using such a nano-sized pigment, high saturation colors can be realized, chatter marks can be suppressed during mass production, and high gloss can be provided.

The pigment may contain an amount of 5 to 10 parts by weight based on 100 parts by weight of the resin, and if it is included in less than 5 parts by weight, color expression is not sufficient, and if it exceeds 10 parts by weight, the image quality is poor. There is.

Furthermore, the ink coating layer may further include a dispersant, a wetting agent, and an anti-settling agent, if necessary.

The ink coating layer of the present invention may be formed by printing on the surface of the base coating layer through a method such as inkjet printing. To this end, the ink composition for forming the ink coating layer as described above further includes a solvent in the above composition. As the solvent, high boiling point aromatic hydrocarbons such as cyclohexanone and Kocosol may be used.

The solvent may be included so that the solvent content is 50 to 70% by weight. When the solvent content is less than 50% by weight, there is a problem of workability, and when it exceeds 70% by weight, there is a problem of color expression.

The ink coating layer is preferably formed to a thickness of 1 to 10㎛. The ink coating layer includes a pigment, but since it is formed thin as described above, the glossiness of the material expressed externally due to the formation of the transparent pretreatment layer and the transparent base coating layer may still be expressed externally. Accordingly, the ink coating layer having a color has a high luminance while having a color.

At this time, the ink coating layer may form various patterns as necessary. At this time, the formed pattern can double the aesthetics of the steel sheet due to the high gloss characteristics of the material itself.

Next, the PCM steel sheet of the present invention may further include a transparent top clear coating layer. The top clear coating layer can protect the formed ink coating layer, and further, it is possible to adjust the texture, gloss, etc. of the PCM steel sheet. The top clear coating layer may include a polyester resin, a pickup improving agent, a leveling agent, a curing agent, and an acid catalyst.

Each composition, content, and method of forming the top clear coating layer applied to the top clear coating layer can be applied as it is applied to the transparent base clear coating layer, unless otherwise contradicted. Omitted for convenience.

Example

Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are examples of the present invention, and the present invention is not limited thereto.

Example 1

Based on the solid content, 0.8% by weight of a Ti compound of titanium tetraisopropyl oxide as a metal rust inhibitor, 12% by weight of silica having an average particle size of 12 nm, 2% by weight of vinyltrimethoxysilane as a silane coupling agent, and the balance acrylic resin as a solvent. It was added to ethanol and mixed (the weight ratio of the solid content and the solvent is 20:80), and a coating composition for forming a transparent pretreatment layer was prepared.

Polyester resin (Mw 23000, Tg 53°C, OHv 8), based on 100 parts by weight of polyester resin, 0.3 parts by weight of silica as a pickup improver, 2 parts by weight of a nonionic acrylic copolymer as a leveling agent, 2 parts by weight of an epoxy resin Part, 12 parts by weight of melamine as a curing agent and 1.5 parts by weight of sulfonic acid as an acid catalyst were mixed, and the mixture was mixed with an ester solvent to prepare a coating composition for forming a transparent base clear coating layer. The mixing ratio of the solid content and the solvent was taken as the weight ratio of the solid content 40 to the solvent 60.

A polyester resin (Mw 15000), based on 100 parts by weight of the polyester resin, 7 parts by weight of a pigment (particle diameter of 0.3-0.4 μm) was mixed and mixed with cyclohexanone as a solvent to prepare a coating composition for forming an ink coating layer. . As for the solvent, the mixing ratio of the solid content and the solvent was set as the weight ratio of the solid content 40 to the solvent 60.

Polyester resin (Mw 23000, Tg 53°C, OHv 8), based on 100 parts by weight of polyester resin, 0.3 parts by weight of silica as a pickup improver, 2 parts by weight of a nonionic acrylic copolymer as a leveling agent, melamine 12 as a curing agent A coating composition for forming a transparent base clear coating layer was prepared by mixing parts by weight and 1.5 parts by weight of sulfonic acid as an acid catalyst, and mixing this with an ester solvent. The mixing ratio of the solid content and the solvent was taken as the weight ratio of the solid content 40 to the solvent 60.

The coating composition for forming a transparent pretreatment layer was applied on the surface of a galvanized steel sheet (GI) by a roll coating method, and then dried with hot air at 85°C (approximately 60 mg/m 2 of adhesion amount after drying). Thereafter, the transparent base clear coating layer-forming coating composition was applied on the transparent pretreatment layer by a roll coating method (after drying, a coating film thickness of 16 μm) was applied, and then baked in an oven at 215°C to form a transparent pretreatment layer.

On the transparent pretreatment layer, the prepared coating composition for forming an ink coating layer was spray-coated to form an ink coating layer having a thickness of 5 μm after drying. Further, the ink coating layer was applied by a roll coating method (a film thickness of 16 μm after drying), and then baked in an oven at 215° C. to form a transparent pretreatment layer.

Quality evaluation

A 2C 2B coated steel sheet (invention material) was manufactured by the same method as described above. Processability, chemical resistance, corrosion resistance, and moisture resistance were evaluated for the manufactured 2C 2B coated steel sheet. For comparison, the same test was performed on the 3C3B coated steel sheet (comparative material) manufactured and sold by POSCO Steel Sheet.

1. Processability

For the invention material and the comparative material obtained in the examples, a workability test was performed according to EN 13523-7 bending test method. Specifically, it is as follows.

According to EN 23270;1991, EN standard 2T (domestic/ASTM-4T) and EN standard 4T (domestic/ASTM-) for specimens of 75×150 mm size at humidity (50±5)% and temperature (23±2)℃ Bending under the condition of 8T). Using Vice, do a 180 degree T-bend between 1 and 2 seconds. Using a transparent adhesive tape, a tape of approximately 75 mm in length is attached to the processing area, and then peeled off at an angle of 60 degrees at a uniform speed within 0.5 to 1 second (tape adhesive strength: 10 N per 25 mm in width). Check the occurrence of peeling and cracks with a 10x magnifying glass, and judge whether or not to pass.

The acceptance criteria

EN standard 2T (domestic/ASTM-4T): No peeling.

EN standard 4T (domestic/ASTM-8T): No crack.

As can be seen from FIG. 4, although the inventive material according to the present invention has a coating layer of 2C2B, it can be seen that it has an equivalent level of processing quality compared to the comparative material, which is a coating layer of 3C3B.

2. Chemical resistance

For a specimen having a size of 75×150 mm, the cut surface was completely sealed, and the specimen was immersed in a beaker containing a reagent (5% NaOH) under conditions of a temperature of 23±2°C and a humidity of 65±20%. After 24 hours after immersion, the specimen was taken out, washed with water, and dried.

The specimen was covered with the mouth of the glass cup containing 5% NaOH aqueous solution as a reagent, and the glass was turned over so that the reagent was in contact with the specimen. (A wax is applied to the edge of the entrance of the glass cup to prevent the solution from being discharged by contacting the specimen.) It was left in this state for 24 hours.

The surface of the specimen in contact with the reagent was visually observed, and appearance changes such as peeling, swelling, and the like were observed with the naked eye. The surface of the specimen was photographed and shown in FIG. 5.

As a result of observation, when there is no blistering of the coating film on the surface of the specimen and even if there is blistering, the blister size is No. Up to the 8F level is judged as a pass.

As can be seen from FIG. 5, no traces of blisters were found on the surface of the specimens of Examples and Comparative Examples, and it was confirmed that the chemical resistance was excellent. (The circular rim in the specimen is due to the wax used to adhere the specimen to the glass.)

3. Corrosion resistance

After cutting the coating layer on the surface of the steel plate in the shape of an X using a cutter knife on the surface of the 70cm×150cm specimen of the invention material and the comparative material, a spray salt solution test was performed. After 1000 hours of spraying with 5% NaCl brine, the surface of the steel plate was visually observed to determine whether rust or blister occurred. The specimen was photographed after 1000 hours of salt spray, and it is shown in FIG. 6.

As can be seen from FIG. 6, it can be seen that the invention material cannot observe a special blister generation with the naked eye, but the comparative material partially generates blisters at the cutting area.

Claims (9)

Plated steel sheet; And a coating layer formed on at least one surface of the plated steel sheet,
The coating layer is sequentially composed of a transparent pretreatment layer, a transparent base clear coating layer, an ink coating layer and a top clear coating layer,
The transparent pretreatment layer may include a metal rust inhibitor comprising a metal selected from zirconium and titanium; Silica; And at least one coupling agent selected from a titanium-based coupling agent, a zirconium-based coupling agent, and a silane-based coupling agent. A pre-coated steel sheet comprising at least one resin selected from acrylic resins and silica-modified acrylic resins, and being a chromium-free pretreatment layer having an adhesion amount of 40 to 80 mg/m 2. The precoated steel sheet according to claim 1, wherein the transparent pre-treatment layer comprises 0.5 to 1% by weight of a metal rust inhibitor, 10 to 15% by weight of silica, 0.5 to 3% by weight of a coupling agent, and the balance resin. delete The method of claim 1, wherein the transparent base clear coating layer is a polyester resin, 0.1 to 0.5 parts by weight of a pickup improving agent, 1.0 to 2.5 parts by weight of a leveling agent, 1.0 to 3.0 parts by weight of an epoxy resin, based on 100 parts by weight of the polyester resin, Pre-coated steel sheet containing 10 to 15 parts by weight of a curing agent and 1 to 3 parts by weight of an acid catalyst. The precoated steel sheet according to claim 1, wherein the transparent base clear coating layer has a thickness of 12 to 18 μm. The precoated steel sheet according to claim 1, wherein the ink coating layer comprises 5 to 10 parts by weight of a pigment of 0.3 to 0.4 μm particles based on 100 parts by weight of the resin and the resin. The precoated steel sheet according to claim 1, wherein the ink coating layer has a thickness of 1 to 10 μm. The method of claim 1, wherein the top clear coating layer is a polyester resin, 0.1 to 0.5 parts by weight of a pick-up improving agent, 1.0 to 2.5 parts by weight of a leveling agent, 10 to 15 parts by weight of a curing agent and an acid catalyst based on 100 parts by weight of the polyester resin. Pre-coated steel sheet containing to 3 parts by weight. The method of claim 4 or 8, wherein the polyester resin has a weight average molecular weight of 22,000-25,000, a glass transition temperature (Tg) of 50-55°C, and an OH equivalent number (OH value, OHv) of 5-10 Pre-coated steel sheet that is.

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