KR20110041921A - Steel plate for exterior material - Google Patents

Abstract

PURPOSE: A coated steel plate for an exterior material is provided to enhance processing performance and durability since a middle coated layer is formed, which has tight contact performance with priming and finishing coated layers. CONSTITUTION: A coated steel plate(100) for an exterior material comprises a base steel plate(110), a priming coated layer(120), a middle coated layer(130), and a finishing coated layer(140). The priming coated layer is formed on the base steel plate. The priming coated layer contains epoxy-modified or polyester-modified primer. The middle coated layer is formed on the priming coated layer. The middle coated layer contains two or more kinds of polyester resin as main resin, and melamin resin as cross-linking resin, and blocked isocyanate. The polyester resin has mean molecular weight of 5,000~20,000 and a glass transition temperature of 5~50°C. The finishing coated layer contains two or more kinds of oil-free polyester resin and melamin resin.

Description

Steel Plate for Exterior Material

The present invention relates to a coated steel sheet excellent in coating properties such as workability and durability while having a beautiful appearance for use in exterior materials such as roofing materials.

Conventional building roofing materials used natural asphalt single sheet with a beautiful appearance and rough texture, or a product sprayed with stone on hot-dip galvanized steel sheet pressed in the form of metal, but it was difficult to popularize due to its high price. Although the product lifespan is excellent and the metal sheet-type color coated steel sheet of economical price is widely used, it also causes the safety accidents such as fall and fall during roofing installation work due to the smoothness of the surface, Has been given away.

In addition, due to the characteristics of the roof material, the color of the deep color series is mostly applied, and thus the internal temperature of the building is increased due to the increase in the temperature of the roofing material itself due to the high infrared absorption rate of the solar light as compared to the pale color series.

Sunlight is composed of ultraviolet rays, visible rays, and infrared rays. Among them, long-wave infrared rays between 700 and 2500 nm have heat that is almost half of the solar energy, which is also called a hot ray. In addition, heat is emitted in the form of infrared rays in electronic products such as light bulbs. Therefore, in order to block external or internal heat, it is important to block near infrared rays and emit far infrared rays.

The choice of materials and the color of the surface of materials currently used for interior and exterior building materials has a significant impact on the internal temperature of buildings. The color of the exterior material may block or absorb external sunlight or heat. In addition, the metal roofing material has a higher heat transfer rate than natural roofing materials such as roof tiles or slits, so that the external heat is radiated as it is, thereby increasing the internal temperature of the room. Therefore, in building roofing, the choice of materials and colors is an important factor in blocking external heat.

In addition, expansion and contraction of the exterior material due to heat causes deformation of the coating film of the color steel sheet, discoloration, gloss reduction, coating film cracks on the processed portion, and the like. Therefore, it can be seen that the heat shielding of the exterior material has the effect of saving energy and extending the life cycle of the product since the external life can be used to further extend the life of the product.

In addition, the exterior material requires functionality such as weather resistance, corrosion resistance, UV resistance, scratch resistance, and workability. In addition, in the case of painted steel used as an exterior material such as a roofing material, the visual beauty, heat shielding function as well as long-term durability should be ensured. However, if the durability is improved, workability is lowered, and as a result, there is a fear that adverse effects such as rusting occur in the plated steel sheet itself.

Accordingly, the present invention is to provide a coating steel sheet for exterior materials having excellent durability while exhibiting visual properties, heat shielding function while minimizing the effects on basic physical properties and processability or exhibiting excellent physical properties.

According to one aspect, as a coated steel sheet used as an exterior material, it provides a coated steel sheet for the exterior material comprising the following layers.

a. Steel plate;

b. A coating layer formed on the base steel sheet and including an epoxy-modified or polyester-modified primer;

c. 2 or more types of polyester resins which are formed on the said undercoat layer, whose number average molecular weights are 5,000-20,000 as a main resin, a glass transition temperature (Tg) is 5-50 degreeC, and an OH value 0-30, and a crosslinking resin. A middle coating layer comprising a melamine resin and a blocked isocyanate; And

d. A top coat film layer comprising two or more oil-free polyester resins and a melamine resin.

The polyester resin which is the main resin in the intermediate coating layer is (i) a first polyester resin having a number average molecular weight of 6,000 to 12,000, an OH value of 25 to 50, and a glass transition temperature of 15 to 25, and (ii The second polyester resin having a number average molecular weight of 7,000 to 15,000, an OH value of 25 to 35, and a glass transition temperature of 5 to 10;

The melamine resin may be a methoxy type or methoxy butoxy mixed melamine resin having a number average molecular weight of 300 to 1000.

The blocked isocyanate may be an isocyanate blocked with a blocking agent having a dissociation temperature below the melting point of the main resin, polyester.

The blocking agent has a dissociation temperature of 80 to 200 ° C., a phenolic compound, an oxime compound, an alcohol compound, an alkylphenol compound, an active methylene compound, a mercaptan compound, an acid amide compound, an acid imide imidazole compound, and a urea. It may be selected from the group consisting of a compound, an oxime compound, an amine compound, an imide compound, a parasol compound, and an ester compound. In addition, the isocyanate may be selected from the group consisting of Toluenediisocyanate (TDI), Diphenylmethanediisocyanate (MDI), Isoporondiisocyanate (IPDI), Naphthalenendiisocyanate (NDI), and Hexamethylene diisocyanate (HDI).

Block isocyanate is included in an amount of 1 to 5% by weight, melamine resin is included in an amount of 1 to 10% by weight, and a total amount of crosslinked resin including melamine resin and block isocyanate is 3 to 10% by weight, based on the total weight of the intermediate coating layer. It may be included as.

The intermediate coating layer is 10 to 30% by weight of an organic solvent; Two or more oil-free polyester resins having a number average molecular weight of 5,000 to 20,000, a glass transition temperature (Tg) of 5 to 30 ° C, and an OH value of 0 to 30; Melamine resin 3-10 wt%; 2 to 5 weight percent of blocked isocyanates; And 0 to 40% by weight of one or more additives selected from the group consisting of organic pigments, inorganic pigments, extender pigments, deforming agents, leveling agents, curing accelerators, color separation agents, and antiblocking agents. Can be formed.

The total thickness of the undercoat layer and the intermediate coat layer may be 10 to 20 μm, and the thickness of the top coat layer may be 30 μm or less.

The top coat layer has a number average molecular weight of 6,000 to 15,000, a glass transition temperature (Tg) of 1 to 40 ° C, an OH value of 25 to 50, an oil-free polyester resin, and a modified oil-free poly-reacted melamine resin. Ester resins; And it may include an additive selected from inorganic pigments, ceramic pigments or wrinkle forming agents.

The coated steel sheet for the exterior material may be used as the color steel sheet for the roofing material, and in particular, may be applied to the color steel sheet for the roofing material having wrinkles or irregularities formed on the surface thereof.

Advantages and features of the present invention and methods of performing the same will be understood more readily by reference to the following detailed description of the embodiments and the accompanying drawings. However, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

FIG. 1 schematically illustrates a coated steel sheet according to an embodiment of the present invention. Hereinafter, each layer constituting the coated steel sheet according to the present example will be described in detail with reference to FIG. 1. For reference, the same or corresponding parts in the drawings are given the same identification number and redundant description is omitted. In addition, the dimension ratio of drawing is not limited to the ratio shown.

Referring to FIG. 1, the coated steel sheet 100 for an exterior material includes the following layers.

a. Holding plate 110;

b. It is formed on the base steel sheet, including an epoxy-modified or polyester-modified primer, the undercoat layer 120;

c. Two or more oil-free polyester resins formed on the undercoat layer, having a number average molecular weight of 5,000 to 20,000, a glass transition temperature (Tg) of 5 to 30 ° C, and an OH value of 0 to 30, and a melamine resin; A middle coating layer 130 including a crosslinked resin made of blocked isocyanate; And

d. A top coat layer 140 comprising two or more oil-free polyester resins and a melamine resin.

The coated steel sheet 100 according to the example of the present invention has a three-layer structure of the undercoat 120, the midway 130, and the top coat 140 as the three coating-3 baking system, not the two coating-2 baking system. That is, the midway 130 with excellent adhesiveness between the lower road 120 and the upper road 140 was introduced. As a result, adhesion can be maintained even for various processing of the end user, and excellent workability can be exhibited.

The thickness of each layer is not particularly limited and may be variously configured according to the demand of the demand and the use of the coated steel sheet.

In one example, the thickness of the top coat layer 140 is 30 μm or less, preferably 15 to 30 after the sum of the thicknesses of the bottom coat layer 120 and the middle coat layer 130 is 10-20 μm. When it is set to 탆, the workability is excellent. When the thickness of the top coat is 15 μm or less, fine surface wrinkles are formed, and at 30 μm or more, it is disadvantageous in terms of economic efficiency.

Since the coated steel sheet can exhibit excellent processability even in harsh processing, it can meet various demands when applied to color steel sheets having wrinkles, irregularities, etc., which exhibit excellent texture and appearance.

In the above-described coated steel sheet for the exterior material, each coating layer may be formed of a single layer or multiple layers, and various layers may be added as necessary.

According to another example, as shown schematically in FIG. 2, the coated steel sheet 101 for the exterior material may form a predetermined pretreatment layer 111 between the base steel plate and the undercoat layer 120. . The pretreatment layer 111 may be a chromate or non-chromate layer.

According to another example, as shown schematically in FIG. 3, the coated steel sheet 102 for the exterior material may additionally form a predetermined clear coating layer 141 on the top coat layer 140.

According to another example, as shown schematically in FIG. 4, the coated steel sheet 103 for the exterior material may further form a second undercoat layer 121 under the base steel plate 110, and is optional. Accordingly, various layers 150 may be added to the lower portion of the second undercoat layer 121.

Hereinafter, with reference to Figure 1 looks at each of the layers constituting the painted steel sheet according to the present example in detail.

One. Steel plate

As the base steel sheet, for example, a zinc-aluminum-silica alloy plated steel sheet or a plated steel sheet having a zinc or zinc alloy plated layer formed thereon, such as an electroplated / hot dip galvanized plated steel sheet, may be used. Alternatively, a copper plate, an aluminum plate, a stainless disc, or the like can also be used.

In one example, 0.4 to 0.5t of G / L, GI Al, and the like, but are not limited thereto.

If necessary, a pretreatment layer may be formed on the base steel sheet in order to increase corrosion resistance or improve adhesion to the undercoat layer 120. In the case of using non-chromate as a pretreatment layer, there is an advantage that it is environmentally friendly, while the corrosion resistance and processability are somewhat inferior to chromate. Therefore, chromate or trivalent chromium may be selected as a pretreatment layer in accordance with demand and use of the demand.

2. Undercoat

In addition to the general corrosion resistance, strengthening the adhesion between the top and embossed steel sheet, the undercoat layer 120 is provided with an elongation to provide a sufficient buffering action at the interface between the material and the top coat, so that the cracks of the material generated during processing to the top coat layer It does not develop and plays a role in being absorbed in the lower layer.

The material of the undercoat layer 120 may be, for example, polyester, undercoat, epoxy undercoat, acrylic undercoat, acrylic primer, or undercoat of modified type thereof, but is not limited thereto.

Commercially obtainable polyester-based roadways include FP 1800 series of Korea Chemical Co., Ltd., Y005 series of Samsung Precision Co., Ltd., HDP 600 of DCC Co., Ltd., and W003 of Samwha Paint Co., Ltd.

The undercoat layer 120 may optionally include a pigment. The pigments can be used for the corrosion resistance bar to prevent corrosion, organic and inorganic pigments used in PCM paints can be used without limitation.

Anti-rust pigments may optionally be used as toxic pigments or non-toxic anti-rust pigments free of lead or chromium. Existing rust preventive pigments include Red Leed, Zinc Potassium Chremate, Zinc Tetra Chromate and Strontium Chromate containing lead and chromium. Typical pigments include barium metaborate, barium metaborate, zinc molybdate, zinc zinc molybdate, zinc zinc phosphate and zinc phosphate. Phosphate (Aluminum Triphosphate), silicate based calcium borosilicate (Calcium Borosilicate), Phosphosilicate (Calcium Ion-exchanged Silicate), Magnesium Ion-exchanged Silicate (Calcium Ion-exchanged Silicate) ).

3. Middle coating layer

In view of the workability of the coated steel sheet, when the crosslinking density of the top coat layer 140 is high, the adhesion between the layers is lowered due to the rigidity, and defects such as cracks are likely to occur in the coating film during processing. However, when the degree of crosslinking is too low, it is difficult to exhibit sufficient durability.

Thus, the inventors of the present invention to the middle coat layer 130 and the top coat layer 120 and the top coat layer 140 having a relatively low crosslinking density compared to the top coat layer 140 to satisfy both processability and durability. Form between.

In order to lower the crosslinking density of the intermediate coating layer 130 relative to the upper coating layer 140, the present inventors first reduce the branch ratio in the backbone polyester resin and linear structure. Increase the ratio Thus, as the polyester resin, a resin having a number average molecular weight of 5,000 to 20,000, a glass transition temperature (Tg) of 5 to 50 ° C., and an OH value of 0 to 30 may be preferably applied. Such polyester-based resin may be 2 or more types.

Second, in addition to the melamine resin usually used as a crosslinking resin, a predetermined block isocyanate is added to increase the flexibility of the coating film.

 Through the coating design, the intermediate coating layer 130 plays a buffer role between the lower coating layer 120 and the upper coating layer 140, thereby manufacturing a coating steel sheet that satisfies both processability and durability. Hereinafter, each component constituting the intermediate coating layer 130 will be described in detail.

Main resin

In the intermediate coating layer 130 according to an exemplary embodiment of the present invention, a polyester resin having a relatively high linear ratio compared to the main resin used for the upper coating layer 140 may be used as the main resin.

Regular polyester resins for PCM paints, which are commonly used for building materials, have branched functional groups such as hydroxyl groups and carboxyl groups in the backbone. It is a crosslinking polyester resin. This has a network structure at the time of crosslinking with the melamine resin used as a crosslinking agent (curing agent), so that the elongation of the coating film after the coating film formation is extremely limited.

On the other hand, linear polyester resins having a linear structure of the main chain have excellent elongation of the coating film but are weak in weather resistance, ultraviolet resistance, and corrosion resistance.

As described later in Item 4, a branched polyester resin is used as the main resin for the top coat layer 140. Thus, the main resin of the intermediate coating layer 130 may have a lower crosslink density than the upper coating layer 140 by increasing the content of the linear polyester resin compared to the upper coating layer 140. As the content of the linear polyester increases, the glass transition temperature is lowered. In the example of the present invention, a relatively large amount of polyester resin having a low glass transition temperature is added to the middle coating layer 130.

In one example, the polyester resin as the main resin has a number average molecular weight of 6,000 to 12,000, an OH value of 25 to 50, and a glass transition temperature of 15 to 25 as shown in Table 1 below. A), and the number average molecular weight is 7,000 to 15,000, the OH value is 25 to 35, the second polyester resin (B) having a glass transition temperature of 5 to 10;

Molecular Weight OH value Tg A.V Main resin compound Resin A 6000-12000 25-50 15-25 10 ↓ Isophthalic Acid,
2-dimethyl-1 Resin B 7000 ~ 15000 25-35 5 to 10 10 ↓ Phthalic anhydride,
3-propane diol

TABLE 1

 When the two kinds of polyester resins are used as the main resin, not only the workability is excellent but also the interlayer adhesion between the top coat layer 140 and the bottom coat layer 120 may be increased.

Melamine resin

The melamine resin used as the crosslinking resin is not particularly limited and a known melamine resin can be used. In one example, the melamine resin may be a methoxy type or methoxy butoxy mixed type melamine resin having a number average molecular weight of 300 to 1000. When the butoxy melamine alone or a mixture of methoxy melamine and butoxy melamine is used, the compatibility with the polyester resin is drastically reduced, and the melamine is transferred to the upper portion of the paint, which may interfere with surface wrinkle formation or cause poor workability. Because it can.

Examples of commercially available melamine resins include RRESIMINE 755 (SOLUTIA company), RESIMINE 757 (SOLUTIA company), RESIMINE 751 (SOLUTIA company), CYMEL 1168 (CYTEL company), CYMEL 1170 (CYTEL company), CYMEL 325 (CYTEL company), CYMEL232 CYTEL company), CYMEL 303 (CYTEL company), and the like, but is not limited thereto. The content of the melamine resin may be 1 to 5% by weight.

Block isocyanate

Blocked isocyanate is a crosslinking reaction resin that does not react with other resins at room temperature but rises above the dissociation temperature and participates in the reaction and crosslinking.

Block isocyanate is formed by reacting a blocking agent with a compound having an isocyanate group as in Scheme 1 below, and the reactivity of the isocyanate group is limited.

Scheme 1

When the block isocyanate is added, it is maintained at a stable state without reacting with the hydroxyl group included in the polyester at room temperature, while when the blocking agent is heated above the dissociation temperature of the blocking agent, the blocking agent dissociates as shown in Scheme 2 below, and the isocyanate group and the hydroxyl group Can react rapidly and crosslink.

Scheme 2

By adding such blocked isocyanate to the intermediate coating layer, it is possible to enhance the interlayer adhesion between the top coating layer and the undercoat layer, and to act as a buffer against deep processing.

The block isocyanate may be blocked with a blocking agent having a dissociation temperature of less than or equal to the melting point of the main resin, polyester.

The isocyanate is a generic name for a compound having an NCO functional group in its molecular structure, and both aliphatic and aromatic isocyanates may be used.

Examples of such isocyanates include methylene phenyl diisocyanate (MDI), polymeric methylene diphenyl diisocyanate (polymeric MDI), tolylene diisocyanate (TDI), lysine diisocyanate (LDI), hydrogenated tolylene diisocyanate, hexamethylene di Isocyanate (HMDI), xylene diisocyanate (XDI), hydrogenated xylene diisocyanate, naphthalene diisocyanate (NDI), biphenylenedi isocyanide, 2,4,6, -triisopropylphenyl diisocyanate (TIDI), Diphenyl ether diisocyanate, tolidine diisocyanate (TODI), isophorone diisocyanate (IPDI), 4,4'-dicyclohexyl methane diisocyanate (HMDI), tetramethylxylene diisocyanate (TMXDI), 2, 2,4-trimethylhexamethylene diisocyanate (TMHDI), 1,12-diisocyanatododecane (DDI), norbornane diisocyanate (NBDI), 2,4-bis- (8-isocy Anatooctyl) -1,3-dioctylcyclobutane (OCDI), 2,2,4 (2,4,4,)-trimethylhexamethylene diisocyanate (TMDI), and the like. Or two or more types can be mixed and used.

The blocking agent may use various blocking agents known in the art and are not particularly limited as long as they do not easily react with hydroxyl groups at room temperature, but may be unblocked and react when heated.

In one preferred example, the blocking agent may have a dissociation temperature of less than the melting point of the polyester, which is a resin, and a specific example may be a dissociation temperature of 80 to 200 ° C.

Examples of blocking agents include various phenolic compounds, oxime compounds, alcohol compounds, alkylphenol compounds, active methylene compounds, mercaptan compounds, acid amide compounds, acid imide imidazole compounds, urea compounds, oxime compounds, amine compounds , Imide compounds, parasol compounds, ester compounds and the like. In specific examples, the blocking agent is phenol, 3-methoxyphenol, 4-methoxyphenol, nonylphenol, meta-cresol, paracresol, 4-chlorophenol, meta-hydrate Hydroxybenzaldehyde, ortho-hydroxybenzaldehyde, parahydroxybenzaldehyde, hydroquinone, 1-hydroxy-2-propanone, 3-hydroxyacetophenone, 4-hydroxyacetophenone, ethyl acetate, Caprolactam, imidazole, pyrazole, pyrazolinone, 1.2.4-triazole, diketopiperazine, malonate, oxime, cyclohexanone oxime, acetooxime, and the like.

In addition, the blocked isocyanate should minimize the release of volatile organic substances by the evaporation of the blocking agent dissociated during the heat drying process, it can be used that has no adverse effect on the coating film and low toxicity.

Examples of commercially available block isocyanates include Desmodur B1 3175, Desmodur B1 3272, Desmodur B1 3370, Desmodur B1 3475 and Desmodur B1 4265 available from Bayer, and Trixene BI 7982, Trixene 7983, Trixene BI 7984, Trixene BI 7984 from Baxsenden LLC. 7980, Trixene BI 7960, Trixene BI 7950, and the like, but are not limited thereto.

The higher the content of the block isocyanate, the higher the processability of the coating due to the soft film, but if the content is too high, the coating becomes too soft and the overall curing degree is lowered, thereby lowering the coating hardness.

Accordingly, the block isocyanate may be included in an amount of 1 to 5% by weight based on the weight of the entire intermediate coating layer 130, and the content of the melamine resin is preferably low.

In addition, the total amount of the crosslinked resin including the melamine resin and the block isocyanate is preferably 3 to 10 wt% based on the weight of the entire intermediate coating layer 130. If the total amount of the crosslinked resin exceeds 10% by weight, the wrinkled pattern becomes excessively dense, and if the total amount of the crosslinked resin is less than 3% by weight, the curing degree is lowered, which is not preferable.

additive

The intermediate coating layer 130 optionally further includes at least one additive selected from the group consisting of pigments such as organic pigments, inorganic pigments and extender pigments, deforming agents, leveling agents, curing accelerators, color separation inhibitors, and antiblocking agents. can do. However, since the heat shielding performance and the pattern forming ability is not necessary, the heat shielding pigment or pattern forming agent may not be included. Moreover, it is preferable not to contain the wax component which may lack interlayer adhesion. The additives are described in detail in section 5 below.

4. Top coat layer

The top coat layer 140 is not particularly limited, but a modified polyester obtained by reacting a polyester resin as a main resin and a melamine resin as a crosslinking resin can be used to maintain excellent processability, weather resistance, ultraviolet resistance, corrosion resistance, and scratch resistance. have.

In one example, the top coat layer 140 has a number average molecular weight of 6,000 to 15,000, two or more oil-free polyester resins having a glass transition temperature (Tg) of 1 to 40 ° C. and an OH value of 25 to 50. It may be made of a modified oil-free polyester resin reacted with the melamine resin. The polyester resin may be a third polyester resin (C) A and a fourth polyester resin (D) as shown in Table 2 below.

TABLE 2

Molecular Weight OH value Tg A.V Synthetic Resin Resin A 6,000-10,000 35-50 35-40 ㅀ 10 ↓ Iso Phthlic Acid,
2,2-Dimethyl-1,3-propanediol (2,2-Dimethyl-1,3-Propanediol) Resin B 7,000-15,000 25-35 1 ~ 5 ㅀ 10 ↓ 1,4-Dicarboxylic Acid, Phthalic Anhydride
2,2-Dimethyl-1,3-propanediol (2,2-Dimethyl-1,3-propanediol)

In addition, the wrinkle forming agent may be added to the composition for forming the top coat layer 140 so that irregularities or wrinkles may be formed on the surface of the coating film to impart surface feel or cause visual interest.

Pure amine may be used as the wrinkle forming agent. The pure amine may serve as a main component for controlling the size of wrinkle formation, and serves as an auxiliary curing accelerator for promoting crosslinking of the resin constituting the paint. Thus, during baking of the coating film, it floats to the surface at about 170 ~ 190 ℃ of PMT to make the surface curing speed of the coating film faster than the internal curing speed, and gradually forms the wrinkles by volume reduction due to the difference in the curing speed between the surface and the inside. will be. As the amines used as such co-promoter (wrinkle forming agent), both primary, secondary and tertiary amines can be used, and the secondary amine is preferable. This is because primary amines bring about a change in color such as yellowing in the coating film, and tertiary amines bring about strong shrinkage on the surface, but secondary amines have no yellowing and proper surface shrinkage. Of the secondary amines, triethylamine is preferred.

The amount of the amine used is preferably 0.5 to 1.0 parts by weight. If it is less than 0.5 parts by weight, the surface of the coating film and the inside of the curing at the same time difficult to form wrinkles, if it exceeds 1.0 parts by weight of the coating film hardly occurs so hard to show the soft texture of the coating film surface. Since the degree of formation of wrinkles varies depending on the adjustment amount, it is preferable to appropriately adjust the addition amount according to the purpose of use.

The top coat layer 140 may further include a heat shielding pigment for excellent heat shielding properties, and may optionally use organic or / and inorganic fillers to improve surface feel.

The wrinkles formed by the amine and the three-dimensional appearance of the wrinkles and irregularities on the surface of the coating film exhibited by the irregularities caused by the organic and inorganic fillers are relatively light scattering, resulting in the glossiness of the coating film. Effect. In general, an excessive amount of matting agent is used in the paint to about 7-10% (wt%). In this case, the PVC (Pigment Volume Content) value of the matting agent is high for the resin. On the other hand, the coating film of the color coated steel sheet of the present invention has a natural matting effect due to the natural matting effect due to wrinkle formation and / or oil absorption of heat shielding pigments. It is possible to further improve physical properties than the ultra matt coating film.

In one example, the top coat layer 140 may further include a CLEAR coating layer.

According to the demand of the customer, a CLEAR coating layer forming the top coating layer may be added. The clear coating layer is composed of a base coating composition of the top coat layer 140 excluding the pigment. In addition, in order to provide a rougher texture than the top coat layer 140 on the surface of the coating film, in addition to the adhesion with the top coat, high weather resistance, and workability, a pearl and / or metallic pigment may be partially added.

Also, on the surface of the top coat layer 140 (a clear coat layer when a clear coat layer is formed), a double-sided embossing roll having an uneven pattern such as a stucco is pressed on a steel sheet to form a three-dimensional pattern on the surface. It can also add designability further.

The top coat layer 140 optionally further includes one or more additives selected from the group consisting of pigments such as organic pigments, inorganic pigments and extender pigments, deforming agents, leveling agents, curing accelerators, color separation inhibitors, and antiblocking agents. can do. The additives are described in detail in section 5 below.

5. Manufacturing method of coated steel sheet

Method for manufacturing a coated steel sheet for an exterior material according to an embodiment of the present invention may include the following steps.

i. Providing a steel sheet;

ii. Applying a composition (hereinafter, also referred to as a 'composition for undercoat') in which a material constituting the undercoat layer is dissolved in an organic solvent on a base steel sheet, followed by drying to form a undercoat layer 120;

iii. Forming a middle coat layer 130 by applying a composition (hereinafter also referred to as a composition for middle coat ') in which a material constituting the middle coat layer is dissolved in an organic solvent on the undercoat layer 120;

iv. Forming a top coat layer 140 by applying a composition (hereinafter also referred to as a composition for a top coat ') in which a material constituting the top coat layer is dissolved in an organic solvent on the middle coat layer 130.

The steel sheet in the step i to form a zinc or zinc alloy plating layer electroplating or hot-dip treatment; And / or chromate or non-chromate treatment at a line speed of 50 to 120 mpm and drying at 60 to 140 ° C. to form the pretreatment layer 3. The pretreatment layer may be a chromate layer of 20-80 mg / m ² or a non-chromate layer of 100-250 mg / m ² .

The method of applying the respective compositions in the above steps ii to iv is not particularly limited, and a known roll coating method, bar coating method, floor coating method, or the like may be used. In addition, the drying may be performed to about 100 ~ 240 ℃ PMT.

Optionally, after forming the top coat layer 140 in step iv, a clear coat layer may be further formed. In addition, the method may include providing an embossed three-dimensional pattern by using the double-sided embossing roll on the top coat layer 140 or the clear coat layer.

The intermediate coating composition is, for example, 10 to 30% by weight of an organic solvent; Two or more oil-free polyester resins having a number average molecular weight of 5,000 to 20,000, a glass transition temperature (Tg) of 5 to 30 ° C, and an OH value of 0 to 30; Melamine resin 3-10 wt%; 2 to 5 weight percent of blocked isocyanates; And 0 to 40% by weight of one or more additives selected from the group consisting of pigments, deforming agents, leveling agents, curing accelerators, color separation inhibitors, and antiblocking agents.

In one preferred example, the intermediate coating composition may have a component and a content ratio as shown in Table 3 below, but is not limited thereto.

[Table 3]

division ingredient Content (weight ratio)%  Suzy Polyester resin A 25-45 Polyester resin B 5-15 Melamine resin 3 ~ 8 Block isocyanate 2 ~ 5 Fee Organic Pigments 0-3 Inorganic pigments 2-30 Sieving pigment 0-5 additive Deforming Agent 0.1-1.0 Leveling agent 0.3 ~ 1.0 Hardening accelerator 0.1-0.5 Color Separation Agent 0.1-1.0 Antiblocking Agent 0.1-1.0 Solvent Hydrocarbon 15-25 Ester (Ester system) 15-25 Acetate 15-25

(Content based on 100% (wt) of solid content per raw material)

In addition, the top coat composition, for example, 10 to 30% by weight of an organic solvent; Modified oil-free polyester compound obtained by reacting two oil-free polyester resins with melamine resin with number average molecular weight of 6,000 to 15,000, glass transition temperature (Tg) of 1 to 40 ° C and OH value of 25 to 50 weight%; Wrinkle forming agent 0.5 to 10% by weight; And 0 to 40 wt% of one or more additives selected from the group consisting of pigments, deforming agents, leveling agents, curing accelerators, color separation agents, and antiblocking agents.

In one preferred embodiment, the topcoat composition may have a component and content ratio as shown in Table 4 below, but is not limited thereto.

[Table 4]

division ingredient Content (weight ratio)%  Suzy Polyester resin A 20-40 Polyester resin B 10-30 Melamine resin 3-10 Fee Organic Pigments 2-5 Inorganic pigments 5-35 Heat shield pigment 25-35 filler Organic filler 0.5-3.0 Inorganic filler 0.3-1.0 additive Deforming Agent 0.1-1.0 Leveling agent 0.1-1.0 Hardening accelerator 0.04-0.1 Color Separation Agent 1.0-3.0 Antiblocking Agent 0.1-1.0 Solvent Hydrocarbon 15-25 Ester (Ester system) 15-25 Acetate 15-25 Wrinkle Forming Agent Secondary amine 0.5-1.0

(Content based on 100% (wt) of solid content per raw material)

Hereinafter, each component of the composition for intermediate or top coat films is explained in full detail.

Organic solvent

The solvent may be selected from hydrocarbon, ester, and acetate systems as much as possible for uniform surface wrinkle and roll mark prevention.

Pigment

Organic or inorganic pigments may be added to the middle coat layer 130 and the top coat layer 140. Even when the coat layer is peeled off or detached during processing and construction, the pigment of the coat layer 130 may be reinforced. And the pigment used in the top coat layer 140 may be used similar to the color.

In addition, in view of weather resistance, an inorganic or ceramic pigment may be used in order to avoid organic pigments and to increase weather resistance of the coating layer, unless it is a special deep color series.

In one example, a dedicated pigment having excellent infrared reflectance may be used to provide heat shielding to the top coat layer 140. In this case, it is an important factor to keep the room temperature constant by blocking heat by absorption, conduction and radiation of external infrared rays.

Such thermal barrier pigments are currently commercially available and include thermal barrier pigments from Ferro (USA), Shepherd (USA) and Isihara (Japan). Table 5 shows the pigment-specific solar energy reflectivity of the typical thermal barrier pigments of Ferro, USA.

TABLE 5

Kind of pigment (No of commercial pigment) Solar Ref Yellow (V-9415) 66.5% Golden (10415) 58.0% Brown (10364) 39.2% Green (V-9248) 30.0% Light blue (V-9250) 29.2% Red (V-13810) 39.0% Black (V-799) 25.1% Black (10203) 27.4%

The heat shield pigment reflects more than 60% of the infrared rays, the absorption is very low. The use of such thermal barrier pigments allows the internal temperature to be cooled. The heat shielding pigment is preferably 25 to 35 parts by weight in the case of a single pigment, relative to 100 parts by weight of the total pigment addition amount, and 15 to 30 parts by weight is appropriate for mixed use. If it is less than 25 parts by weight, the heat shielding function is insufficient and the concealment rate is lowered. If it exceeds 35 parts by weight, it is economically burdened and the oil absorption of the pigment is increased, resulting in poor paint production and paintability.

In addition, in addition to the heat shielding pigment, the top coat layer 140 may further use pearl particles or metallic particles in order to show a beautiful appearance. In the case of adding such pearl or metallic particles, the heat shielding function of the thermal barrier color pigment is added to the light reflection function inherent in the pearl or metallic particles, and thus synergistic effects can be improved to improve the overall thermal shielding performance.

In addition, the intermediate coating layer 120 may be added to the extender pigment in order to improve the adhesion between the interlaminar film and the coating properties, coating workability. The extender pigment does not have a color, but its own oil absorption increases the viscosity of the paint itself even at a small specific gravity, and it gives thixo property to improve the paintability of the roll coating work, so that a good appearance can be achieved. Examples of extender pigments include standard silica (Sio2) siloid (244). However, too much use of extender pigment may impair the processability of the final product, so it should be used at the level associated with minimum workability. The content of the pigment (P / B: pigment / binder) to the resin may vary depending on the color, but is preferably set to 1 or less, and it is preferable to design the lower value as the color becomes deeper.

filler

In each of the coating film forming compositions, organic or / and inorganic fillers may be used to improve the surface feel of the coated steel sheet.

The organic filler is a stable material and has excellent durability, chemical resistance, lubricity and high hardness to form the physical and chemical performance of the coating film. The usable organic filler may be selected from plastic fillers (called nylon (NYLON) fillers) such as polyacryl, polyamide, polypropylene and polyethylene, but is not limited thereto.

When the added organic filler reaches 100 ° C or more during the baking process, a slight melting process is performed on the surface of the solid organic filler, and fusion occurs on the surface of the resin and the organic filler. It will form the irregularities felt. In this case, when the colored organic filler is added as necessary, the visual sensitivity of the surface may be variously expressed according to the color of the selected organic filler. In addition, a transparent organic filler may be used if it is to simply give the characteristics of irregularities without affecting the color of the paint.

Therefore, transparent or colored organic fillers may be used alone or in combination for application purpose. For this reason, the degree of unevenness is also formed depending on the amount of addition of the organic filler and the selection of particle size. The range of 3.0% is appropriate, Preferably it is 1-2%. If the added organic filler is less than 0.5%, the effect of unevenness is insignificant, and if it exceeds 3.0%, the weather resistance becomes weak. Although the particle size is not particularly limited, it is preferable to select and use a transparent or colored spherical organic filler having a thickness of about 20 to 40 µm when the dry coating thickness is 10 to 30 µm.

Inorganic fillers generally use amorphous coating silica, known as a matting agent. In the present invention, the inorganic filler may be used to improve gloss stability and workability, in addition to providing surface feel, rather than matting purpose.

Such silica is 0.3 ~ 1.0% by weight is suitable, when used more than 1% wrinkles less bone gap, the bone gap becomes visually messy.

In the present invention, such organic and inorganic fillers may be optionally used alone or mixed as needed, and organic fillers may be selected and used as colored or / and colorless as described above. By the addition of such an organic inorganic filler, a coating film having a uniform three-dimensional appearance and a tactile effect such as a natural material can be further obtained on the entire surface of the coating film.

If necessary, a UV filler may be added to enhance UV resistance.

Hardening accelerator

The curing accelerator is to increase the density by promoting the crosslinking of the main resin polyester and the crosslinking resin. For example, p-toluene sulfonic acid, Dinonylnaphthalene Sulfonic Acid, dodecylbenzenesulfonic acid (DDBSA, Dodesyl Benzene Sulfonic Acid) or blocking as an acid masked by amine Non-dodecylbenzenesulfonic acids (DDBSA, Dodesyl Benzene Sulfonic Acid). In addition, epoxy masking sulfonic acid or epoxy resin masked sulfonic acid may be used. The amine is a material that can be dissociated by heat, and may form wrinkles on the surface of the coating film together with the pure amine, which is the aforementioned wrinkle-forming agent, when the top coat is baked. At this time, the usage amount of the curing accelerator is recommended 0.04 ~ 0.1 parts by weight. If it is less than 0.04%, it is difficult to secure the degree of curing, and if it exceeds 0.1%, the pattern becomes dense.

Other additives such as deforming agent, leveling agent, color separation inhibitor, antiblocking agent and the like can be used in the art and are not particularly limited.

<Examples>

Hereinafter, the present invention will be described in more detail with reference to Preparation Examples, Examples, Comparative Examples, Experimental Examples, and the like. However, the following Examples are for illustrative purposes only and the present invention is not limited to the following Examples. .

Example 1

The polyester-modified primer undercoat layer was bar-coated on a 0.4 ton non-chromate pretreated GI substrate, followed by drying to form a undercoat layer having a thickness of 5 μm.

Then, 35 parts by weight of an oil-modified polyester resin (5: 5) having a number average molecular weight of 12,000 and 15,000, respectively, 3 parts by weight of the melamine resins Cymel325 and Cymel 303 each as a curing agent, and a blocked tolylenediaocyanate 3 parts by weight of (TDI), 2.00 parts by weight of modified alkyl epoxy modified with a color separation agent, 0.42 parts by weight of an acrylic resin as an antifoaming agent, and unblocked dodesylbenzene sulfonic acid 0.06 as a curing accelerator. Parts by weight, 0.17 parts by weight of PTFE and PE wax polymers as antiblocking agents, 0.5 parts by weight of amorphous silica (SiO2) silod244 raw material, and intermediates comprising cellosolve acetate, xylene and acosolve DPM as solvents The coating composition was bar-coated on the undercoat layer and dried to form a middle coating layer having a thickness of 10 μm.

Finally, 42 parts by weight of oil-free polyester resin, 5.6 of melamine resin, 0.45 part by weight of matting agent, 2.00 parts by weight of modified alkyl epoxy modified with color separation agent, 0.42 part by weight of acrylic resin as antifoaming agent, as a curing accelerator. 0.06 parts by weight of unblocked dodesylbenzene sulfonic acid, 0.17 parts by weight of PTEE and PE wax polymer as antiblocking agent, 0.70 parts by weight of trimethylamine as a pattern forming agent, cellosolve acetate, xylene and acosolve as solvent A topcoat film composition comprising 18.8 parts by weight of DPM and black heat shielding pigment (Cr2O3 and Fe2O3 in a ratio of 1: 1), etc., is coated on a middle coat layer and dried to coat a top coat layer having a thickness of 20 μm. To form a coated steel sheet having a base steel sheet / coated film layer / middle coated layer / top coat layer laminated structure.

[Example 2]

Except that the thickness of the intermediate coating layer was formed to 15 ㎛ was prepared in the same manner as in Example 1 steel plate / coating film layer / coating film layer / top coating layer of a coated steel sheet was prepared.

Example 3

A coated steel sheet was prepared in the same manner as in Example 1 except that the intermediate coating layer was formed to have a thickness of 20 μm.

[Comparative Example 1]

Except that the intermediate coating layer was not formed, a coated steel sheet was prepared in the same manner as in Example 1 with the steel sheet / coating layer / top coating layer layered structure.

Comparative Example 2

A coated steel sheet was prepared in the same manner as in Comparative Example 1 except that the undercoat layer was formed to have a thickness of 10 μm.

Experimental Example 1

Physical property verification experiments were performed on the coated steel sheet samples according to Examples 1 to 3 and Comparative Examples 1 to 2. The experiment proceeded from the first lab test verification to the second pilot test, and the final physical property verification was the data based on the second experiment.

In the first lab experiment, paints were generally prepared, and final sample work was completed through the same coating method (bar coater) and the same dry curing method (automatic discharge type OVEN). . In other words, bar coating the composition for each coat, medium, and top coat on a GI material steel sheet to prepare a sample specimen and cut it to the same standard to perform a physical property test for each item. (All specimens were evaluated by the same experimenter at the same time after 1 day of manufacture)

Evaluation method of the coating film properties is as follows, and the results are shown in Table 6 below.

1. Workability: Means paint pick-up when making on-site roll coating, and visually evaluates the ease of roll coating work on paint in the second pilot test. Poor coating appearance or irregularities in surface irregularities

2. Surface wrinkles and irregularities: Means the surface wrinkles and irregularities of the dry coating film.

3. Solvent resistance: MEK Rubbing method, which measures the number of times until the undercoat is peeled off by performing reciprocating rubbing with a load of 1kg after MEK is wet with general medical gauze.

4. Pencil hardness: Measure the degree of traces left on the coating film by using the 'Uni Pencil', a Mitsubishi product manufactured by Japan and applying a 500kg load, scraping the surface of the coating film at a constant speed and then erasing it with an eraser (typically low hardness 2B B HB FH 2H 3H is high hardness)

5. Processability: The degree of cracking of the coating film after T bending at room temperature, and after the 2T bending at room temperature, it is attached with scotch tape to confirm the peeling of the coating film. (1 ~ 5 points evaluation: the level at which one point is peeled off, 5 Point not fully peeled off)

6. Adhesiveness: Cut the coating film with scotch tape by knife on the surface x 10mm width. Scotch tape peeling test after cross cut at 6mm interval

7. Impact resistance: 1/2 "x 1kg x 50cm free fall after film fall

8. Chemical resistance: Check the degree of swelling and discoloration of the film after immersion in the corresponding solution (acid resistance: 5% sulfuric acid, alkali resistant 5% sodium hydroxide) for 24 hours.

9. Corrosion resistance: SST (Salt spray test) 35'C 5% NaCl, after 500 hours of measurement, confirmed the degree of rust of the coating film

10. UV resistance: ΔE value measurement after 20W X 20cm X 500hrs

11. Weather resistance: Measure ΔE after 500 hours of Xenon arc lamp

TABLE 6

division Comparative Example 1 Comparative Example 2 Example 1 Example 2 Example 4 1. Workability ○ ○ ○ ○ ○ 2. Surface wrinkles and irregularities ○ ○ ○ ○ ○ 3. Solvent resistance ○ ○ ◎ ◎ ◎ 4. pencil hardness ◎ ◎ ◎ ◎ ◎ 5. Processability T-bending 6 ~ 7T 6T 5T 4T 3T S-cupping O O O ~ ◎ ◎ ◎ 6. Adhesiveness ◎ ◎ ◎ ◎ ◎ 7. Impact ◎ ◎ ◎ ◎ ◎ 8. Chemical resistance 5% NaOH ◎ ◎ ◎ ◎ ◎ 5% HCl ◎ ◎ ◎ ◎ ◎ 9. Corrosion resistance (500h) ○ ○ ◎ ◎ ◎ 10. UV resistance 500hr 0.68 0.77 0.62 0.64 0.58 11. Weather resistance 0.42 0.66 0.55 0.59 0.53

◎: very good, ○: good, △: normal, ㅧ: poor

Experimental Example 2

Surfaces of the coated steel sheet specimens according to Example 1 and Comparative Examples 1-2 were photographed using an optical microscope, and the results are shown in FIG. 5. In addition, tomographic pictures of the coated steel sheet specimens according to Comparative Example 1 and Example 1 were photographed using a scanning electron microscope (SEM) (350 magnification), and the results are shown in FIGS. 6 to 7.

As shown in FIGS. 5 to 7, in the case of the coated steel sheet according to the comparative examples, cracks or tears occur in the coating film (see A and B of FIG. 6), whereas the coated steel sheet according to the embodiment has a broken portion. You can see that it's connected seamlessly at all.

As described above, the exterior coated steel sheet of the present invention can exhibit not only durability but also excellent workability, so that defects of the coating film can be minimized even in a harsh processing environment. In addition, by forming wrinkles and / or irregularities on the surface, it exhibits excellent texture and beautiful aesthetics, and is excellent in heat shielding property as an exterior material for roofing materials, and thus it is possible to maintain a constant internal temperature without applying additional energy.

1 is a cross-sectional view of a coated steel sheet for an exterior material according to an embodiment of the present invention;

2 is a cross-sectional view of a coated steel sheet for an exterior material according to another embodiment of the present invention;

3 is a cross-sectional view of a coated steel sheet for an exterior material according to another embodiment of the present invention;

4 is a cross-sectional view of a coated steel sheet for an exterior material according to another embodiment of the present invention;

5 is a surface photographing image according to Example 2;

6 is a SEM photograph of the specimen of Comparative Example 1 according to Example 2;

7 is an SEM photograph of the specimen of Example 1 according to Example 2. FIG.

Claims (6)

A coated steel sheet used as an exterior material, the exterior coating steel sheet comprising the following layers: a. Steel plate; b. A coating layer formed on the base steel sheet and including an epoxy-modified or polyester-modified primer; c. 2 or more types of polyester resins which are formed on the said undercoat layer, whose number average molecular weights are 5,000-20,000 as a main resin, a glass transition temperature (Tg) is 5-50 degreeC, and an OH value 0-30, and a crosslinking resin. A middle coating layer comprising a melamine resin and a blocked isocyanate; And d. A top coat layer comprising two or more oil-free polyester resins and a melamine resin. The method of claim 1, The polyester resin which is the main resin in the intermediate coating layer is (i) a first polyester resin having a number average molecular weight of 6,000 to 12,000, an OH value of 25 to 50, and a glass transition temperature of 15 to 25, and (ii 2) The second polyester resin having a number average molecular weight of 7,000 to 15,000, an OH value of 25 to 35, and a glass transition temperature of 5 to 10; The method of claim 1, The melamine resin is a methoxy-type or methoxy butoxy mixed type melamine resin having a number average molecular weight of 300 ~ 1000, the coated steel sheet for exterior materials. The method of claim 1, The said block isocyanate is the coated steel sheet for exterior materials which is an isocyanate blocked with the blocking agent which has a dissociation temperature below melting | fusing point of polyester which is a main resin. The method of claim 1, Block isocyanate is included in an amount of 1 to 5% by weight, melamine resin is included in an amount of 1 to 10% by weight, and a total amount of crosslinked resin including melamine resin and block isocyanate is 3 to 10% by weight based on the total weight of the intermediate coating layer. Painted steel sheet for exterior materials, included as. The coated steel sheet for exterior materials according to claim 1, which is a color steel sheet for roofing material having wrinkles or irregularities.

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