JP2006346934A - Coated steel sheet and sizing material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coated steel sheet capable of reducing the cracking of a coating film at the time of emboss processing, capable of preventing the spreading of the crack of the coating film with the elapse of time and capable of holding the corrosion resistance of a processed part over a long period of time, and a sizing material. <P>SOLUTION: The coated steel sheet obtained by providing at least one coating film at least on one side of a steel sheet is characterized in that a thermosetting resin coating film, which contains a polyester resin as a main resin and of which the minimum value of the dynamic storage elastic modulus in its rubbery elastic region is 2×10<SP>7</SP>Pa or below and the gloss retention after a weatherability test due to a sunshine carbon arc lamp type weatherability tester is executed for 500 hr is 60% or above, is provided at least to the outermost surface layer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a coated steel sheet and a sizing material, and more particularly to a coated steel sheet having excellent corrosion resistance at an embossed portion even after embossing used for the sizing material.

  Painted steel sheets are widely used in the building materials field as roofing materials and sizing materials. When coated steel sheets are used as sizing materials, a method called embossing is applied, and a decorative pattern such as stucco, lysine, or wood grain patterns is given to the surface to improve the design. ing.

  In recent years, in the sizing material market where embossing has been performed, products that emphasize the shade and enhance the design by deeper embossing have become popular. However, when deep embossing is applied to a coated steel sheet that has been used in the past, there is a problem that the base plating is cracked or the coating film is cracked. In addition, even if cracking does not occur during processing, there is a problem that cracking or peeling occurs when used outdoors for a long time. These plating cracks and coating film cracks (coating peeling) could cause deterioration of the appearance of the sizing material and corrosion during long-term outdoor use.

  Against this background, embossed coated steel sheets have been improved from both the base-plated steel sheet and the coating film. For example, in patent document 1, the improvement from the surface of a base plating steel plate is proposed. This method improves the workability of the hot-dip Al-Zn alloy-plated layer by controlling the heat treatment during hot-dip plating or after plating in the hot-dip Al-Zn alloy-plated steel plate, which is known as a highly corrosion-resistant plated steel plate. In addition, it reduces plating cracks during processing, and further reduces coating film cracks caused by plating cracks.

  Certainly, this method can prevent the coating from cracking immediately after processing and maintain the initial corrosion resistance. However, when used outdoors for a long period of time, elastic strain energy remains applied to the processed part, and this strain energy may cause coating film cracking. There was a concern about the occurrence of corrosion at the part where film cracking occurred.

  In the method described in Patent Document 1, the glass transition temperature of the coating film is set to 30 to 90 ° C., and the workability is improved from the surface of the coating film. And when glass transition temperature exceeds 90 degreeC, the workability of a coating film will fall, and even if it uses a high workability base plating steel plate, it says that a coating-film crack will arise at the time of a process. Certainly, it is possible to prevent the initial coating film cracking to some extent by setting the glass transition temperature to about 30 to 90 ° C. However, the coating film cracking phenomenon over time cannot always be judged by the glass transition temperature.

  Considering sizing materials, since sizing materials are used outdoors, it is necessary to have deterioration resistance (weather resistance) against sunlight and wind and rain, but weather resistance cannot be judged by the glass transition temperature.

  In other words, even if the glass transition temperature of the coating film is controlled so that the coating film does not crack during processing, elastic strain energy remains in that part, so if it is used outdoors for a long period of time. , There is still a possibility of causing coating cracking and corrosion. Therefore, if excellent weather resistance was not given, the coating film deteriorated after long-term outdoor use, causing the possibility of choking, cracking, peeling, and corrosion.

  In this way, it is necessary to maintain the integrity of the coating film itself for a long time even when using a base-plated steel sheet with excellent workability.

  On the other hand, a fluororesin coating film is known as a coating film meeting such needs. Certainly, fluororesin coatings are effective for sizing materials that are deeply embossed because they have excellent processability and long-term stability. However, on the industrial side, there is a problem that the fluororesin coating is expensive.

  As described above, there is no embossed coated steel sheet that is inexpensive and can maintain the corrosion resistance of the machined part for a long period of time, and rapid development has been desired.

Japanese Patent No. 3507823

  Therefore, the present invention has been made in view of such problems, and its object is to provide a new and improved coated steel sheet and sizing material that can maintain the corrosion resistance of the embossed portion for a long period of time. It is to provide.

  In order to solve the above-mentioned problems, the present inventors embossed coated steel sheets prepared using various resins and plated steel sheets, and the physical properties of the coated steel sheets, coating film cracks during processing, and long The coating film cracking and corrosion behavior when left for a period were examined in detail. As a result, the present inventors controlled the physical properties of the coating film within a predetermined range, so that cracks and peeling did not occur in the processed part not only during embossing but also after standing for a long time, Or, even if it occurs, the present invention has been completed based on this finding, as a result of finding a coated steel plate that is light and corroded as a result.

The gist of the present invention is as follows.
(1) A coated steel sheet having one or more coating films on at least one side of the steel sheet, wherein the coating film of at least the outermost layer contains a polyester resin as a main resin and is dynamic in a rubber-like elastic region The minimum value of the storage elastic modulus is 2 × 10 ⁷ Pa or less, and the gloss retention after 60 hours of a weather resistance test (JIS B7753-1993) using a sunshine carbon arc lamp type weather resistance tester is 60%. A coated steel sheet, characterized by being a thermosetting resin coating film as described above.
(2) The coated steel sheet according to (1), wherein the outermost-layer coating film is a clear coating film.
(3) The coated steel sheet according to (1) or (2), wherein the outermost-layer coating film contains colored particles having an average particle diameter of 10 to 500 μm.
(4) The coated steel sheet according to any one of (1) to (3), wherein the steel sheet is a plated steel sheet containing at least Zn and Al.
(5) A sizing material obtained by embossing the coated steel sheet according to any one of (1) to (4).

  According to the present invention, not only during embossing, but also when used outdoors for a long period of time, a coated steel sheet capable of maintaining the corrosion resistance of the embossed part for a long period of time without causing cracks in the embossed part. A sizing material formed by embossing can be provided.

  Hereinafter, preferred embodiments of the present invention will be described in detail.

  In order to solve the above-mentioned problems, the present inventors embossed a coated steel sheet produced using various resins and plated steel sheets, and the physical properties of the coated steel sheet and coating film cracking (peeling) during molding, Furthermore, the coating film cracking and corrosion behavior when left for a long time were examined in detail. As a result, embossing is not a simple bending process that involves only tensile strain, but there is a drawing-like element that involves both compression and tensile strain, especially in deep embossing considering design. It turned out that the tendency was strong.

  As a result of further investigation, elastic strain energy is accumulated inside the coating film deformed during embossing, and a coating film with a large strain energy tends to buckle, and the coating film is easy to break and peel. In addition, even if it does not occur immediately after processing, it has been found that the coating film is likely to be destroyed or peeled off if left for a long period of time, and as a result, the underlying plated steel sheet is exposed to the surface and corrosion occurs. On the other hand, a coating film with low strain energy is difficult to buckle, and the coating film is difficult to break and peel for a long time. As a result, the plated steel sheet is not exposed to the surface, or even if it is exposed, it is slight. It was found that corrosion can be suppressed over a long period of time.

  As a result of research on a coating film in which the elastic strain energy accumulated inside the coating film is small, the present inventors have found that the elastic strain energy accumulated in the coating film after deformation constitutes the coating film. It was found that it depends on the molecular weight between the crosslinking points of the main resin. It is generally well known that the molecular weight between crosslink points of a resin has a correlation with the equilibrium elastic modulus of the rubbery elastic region of the resin.

  Here, details of the rubber-like elastic modulus of the resin will be described below.

Resin that is a viscoelastic body changes its elastic modulus depending on temperature and time (frequency in the case of dynamic storage elastic modulus). In the case of a cross-linked thermosetting resin, a high elastic modulus (generally this region is referred to as a glassy elastic region and is 10 ⁹ to ¹⁰ 10) in a low temperature or short time region (high frequency in the case of dynamic storage elastic modulus). Value in the vicinity of Pa). Then, as the temperature increases or the time increases (in the case of dynamic storage elastic modulus, the frequency decreases), a region where the elastic modulus decreases rapidly appears (generally called the transition region). Further, when the temperature becomes high or for a long time (low frequency in the case of dynamic storage modulus), the equilibrium elastic modulus becomes constant, and this equilibrium elastic region is called a rubber-like elastic region (generally a value in the vicinity of 10 ⁶ to 10 ⁸ Pa). Showing).

The present invention relates to a high temperature rubbery elastic region among dynamic storage elastic moduli measured in a region of constant frequency (angular frequency 6.28 rad / sec) and temperature of −50 to 200 ° C. with a dynamic viscoelasticity measuring device. The characteristic of the coating film is defined by the minimum value of the dynamic storage elastic modulus appearing at 1. The dynamic storage elastic modulus is generally represented by E ′ and is defined by E ′ = (σ ⁰ / γ ⁰ ) cos δ. Where σ ⁰ is the maximum stress amplitude, γ ⁰ is the maximum strain amplitude, and δ is the phase angle between the stress and strain.

  Since sizing materials with embossing are used outdoors, unlike the materials used only indoors, in addition to the dynamic storage modulus, the weather resistance of the coating film greatly affects the corrosion resistance of the processed parts. Turned out to give. That is, even if the coating film has the same embossing property, the coating film with higher weather resistance was superior in the corrosion resistance of the processed part after long-term outdoor use. This is because the coating film deteriorated in the natural environment such as sunlight, causing choking, cracking, and peeling, and the underlying plated steel sheet was exposed to cause corrosion. It was remarkable in the processed part.

The coated steel sheet of the present invention is a coated steel sheet having one or two or more coating films on at least one side of the steel sheet, and the outermost coating film includes a polyester-based resin as a main resin, and is in a rubber-like elastic region. Gloss retention after the minimum value of the dynamic storage elastic modulus is 2 × 10 ⁷ Pa or less and the weather resistance test by the sunshine carbon arc lamp type weather resistance tester described in JIS B7753-1993 is carried out for 500 hours It is a coated steel sheet characterized by being a thermosetting resin coating film having a rate of 60% or more.

In the coated steel sheet of the present invention, a thermosetting resin coating having a minimum dynamic storage elastic modulus of 2 × 10 ⁷ Pa or less in a rubber-like elastic region containing a polyester resin as a main resin is applied to at least one surface of the steel sheet. When the minimum value of the dynamic storage elastic modulus in the rubbery elastic region exceeds 2 × 10 ⁷ Pa, the molecular weight between the crosslinking points of the resin constituting the coating film becomes small and the film is coated. This is because the elastic strain energy accumulated inside the coating film increases. That is, even if the coating film looks healthy right after embossing, there is a high possibility that the coating film breaks or peels over time, which is inappropriate.

  Further, the gloss retention after the thermosetting resin coating film is subjected to a weather resistance test by a sunshine carbon arc lamp type weather resistance test machine described in JIS B7753-1993 is 60% or more. As a result of investigations by the present inventors, the treatment for 500 hours corresponds to about 1.5 years in Okinawa with strong sunshine, and the coating film showing a gloss retention of 60% or more under the conditions is outdoors. This is because, even after long-term use, the coating film deterioration (cracking / peeling) in the processed part is slight and corrosion is difficult. More preferably, the gloss retention is 70% or more.

In addition, when the coating film coated on at least one surface of the steel sheet has a multilayer structure, it is most preferable that the minimum value of the dynamic storage elastic modulus of all the layers in the coating film is 2 × 10 ⁷ Pa or less. When it is difficult to apply all the layers having dynamic storage elastic modulus within the range of the present invention in order to satisfy the performance other than embossability required for the coated steel sheet, at least the outermost layer is coated. If the film satisfies the dynamic storage elastic modulus and weather resistance in the range of the present invention, the embossability can be improved to a satisfactory level.

  Further, the coated steel sheet of the present invention may be a so-called top clear type coated steel sheet in which the outermost coating film is a clear coating film, and even in this case, excellent processed portion corrosion resistance can be obtained. Even at this time, if the gloss retention is 60% or more, it exhibits excellent processed portion corrosion resistance even when used outdoors, and more preferably 70% or more. Here, the reason why the outermost layer coating is a clear coating is to improve the design. When the outermost layer coating film contains colored particles, if the outermost layer coating film is a clear coating, the coloring effect of the colored particles can be emphasized. Here, the clear coating film refers to a film that does not contain a coloring pigment, or a film that does not inhibit the coloring effect of colored particles even if a coloring pigment is included.

  The coated steel sheet of the present invention may contain colored particles having an average particle diameter of 10 to 500 μm in the outermost coating film.

  If colored particles with a large particle size are included in a normal coating film, the coating film may crack (peel) at the interface between the colored particles and the coating film during embossing, and the same phenomenon may occur when used outdoors for a long time. Although there is a possibility, it has been found that it can be prevented by adding it to the outermost coating film of the present invention. This is thought to be because cracks at the interface between the colored particles and the coating are unlikely to occur because the elastic strain energy accumulated inside the coating after processing is small.

  The average particle size of the colored particles is set to 10 to 500 μm. If the particle size is less than 10 μm, the appearance effect of the colored particle particles is insufficient. On the other hand, if the particle size exceeds 500 μm, the paint is baked. This is because it is not preferable because the solvent is difficult to escape and a so-called phenomenon occurs. More preferably, it is 20-200 micrometers.

  The colored particles described here have the characteristic of imparting design properties not only by their colors but also by their external shapes, and are different from commonly used colored pigments and dyes having a particle size of 10 μm or less. There is no problem even if the coating film of the present invention contains a color pigment or dye having a particle size of 10 μm or less.

  The colored particles of the present invention are not particularly limited, and particles usually used as additives can be applied as they are. Examples thereof include resin-based particles such as polyacrylonitrile particles, polyester particles, and polyurethane particles, and inorganic particles such as mica, mica, aluminum powder, and glass beads. These may be used alone or in combination of two or more. For example, the white particles may be composed of a plurality of particles such as white acrylic particles and white mica, the white particles may be polyacrylonitrile particles, and the blue particles may be polyester particles. Further, the shape of the colored particles is not particularly limited, and examples thereof include a spherical shape, a scale shape, a disk shape, a fiber shape, and an indefinite shape.

  The color of the colored particles is not particularly limited because it is affected by the color of the base. However, when at least one of yellow particles, red particles, white particles, and black particles is added as a basic particle, it can be used for sizing purposes. Has a relatively suitable appearance.

  The resin used for the coating film of the present invention is a thermosetting type having a polyester resin as a main resin. The polyester resin is not particularly limited, and is generally a known ester compound of a polybasic acid and a polyhydric alcohol, and is synthesized by a known esterification reaction.

  Examples of the polybasic acid for obtaining the polyester-based resin include phthalic acid, isophthalic acid, terephthalic acid, phthalic anhydride, trimetic anhydride, maleic acid, adipic acid, fumaric acid and the like. These polybasic acids may be used alone or in combination of two or more.

  On the other hand, examples of the polyhydric alcohol for obtaining a polyester resin include ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, neopentylene glycol, 1,4-butanediol, 1,5. -Pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, polytetramethylene ether glycol, glycerin, trimethylolethane, trimethylolpropane, trimethylolbutane, hexanetriol, pentaerythritol, dipentaerythritol, etc. Can be mentioned. These polyhydric alcohols may be used alone or in combination of two or more.

  Moreover, when using a polyester-type resin as a main resin, you may mix | blend a hardening | curing agent. As this curing agent, any one or both of known polyisocyanate compounds and amino resins can be used.

  As a polyisocyanate compound used as a curing agent, for example, an isocyanate compound blocked with a blocking agent such as phenol, cresol, aromatic secondary amine, tertiary alcohol, lactam, or oxime is preferable. More preferred polyisocyanate compounds include HDI (hexamethylene diisocyanate) and its derivatives, TDI (tolylene diisocyanate) and its derivatives, MDI (diphenylmethane diisocyanate) and its derivatives, XDI (xylylene diisocyanate) and its derivatives, IPDI (isophorone) Diisocyanate) and derivatives thereof, TMDI (trimethylhexamethylene diisocyanate) and derivatives thereof, hydrogenated TDI and derivatives thereof, hydrogenated MDI and derivatives thereof, hydrogenated XDI and derivatives thereof, and the like.

  On the other hand, as an amino resin used as a curing agent, resins obtained by reacting urea, benzoguanamine, melamine, etc. with formaldehyde, and those obtained by alkylating these with alcohol can be used. Specific examples include methylated urea resins, n-butylated benzoguanamine resins, methylated melamine resins, n-butylated melamine resins, iso-butylated melamine resins, and the like.

  Resins widely used in the field of coated steel sheets are polyester / melamine resins having a polyester resin as a main resin and a melamine resin as a curing agent. The melamine-based resin referred to here indicates at least one of methylated melamine, n-butylated melamine, and iso-butylated melamine.

In this polyester / melamine resin, it is desirable that the number average molecular weight of the polyester resin is 8000 or more, and the addition amount of the melamine resin is 5 to 45 parts by mass with respect to 100 parts by mass of the polyester resin. When the number average molecular weight of the polyester resin is less than 8000 or the addition amount of the melamine resin exceeds 45 parts by mass, the molecular weight between the crosslinking points in the coating film becomes small, and the dynamic storage elasticity of the coating film after being thermally cured. The minimum value of the rate is likely to exceed 2 × 10 ⁷ Pa, and the coating may be destroyed or peeled off during embossing, or the coating may be destroyed or peeled off over time even when processing is good. May become unsuitable. Also, if the amount of melamine resin added is less than 5 parts by mass, a coating film is formed but the curing reaction tends to be insufficient, and coating performance other than embossability, such as coating film hardness, rubbing property, The possibility of inferior contamination and weather resistance increases, which may be inappropriate.

  On the other hand, the upper limit of the polyester-based resin is not particularly provided, but is preferably a number average molecular weight of 30000 or less. If it exceeds 30000, the viscosity becomes high, so that a large amount of dilution solvent is required, and there is a possibility that the coating workability is lowered and it is difficult to obtain an appropriate coating film.

  Moreover, it can add to a coating film of this invention without a problem, if it is the thing normally added to the coating film of the coated steel plate.

  For example, the coating film of the present invention may contain a gloss adjusting agent such as silica, and if necessary, a dye, pigment, surface smoothing agent, ultraviolet absorber, hindered amine light stabilizer, viscosity adjustment. An agent, a curing catalyst, a pigment dispersant, a pigment settling inhibitor, a color separation inhibitor, and the like may be included.

  The coating film of the present invention can be applied by any method. For example, the coating can be performed by a bar coater, spray coating, brush coating, roll coater, overflow curtain coater, slit curtain coater, roller curtain coater, T-die, multi-layer curtain coater, or the like.

  However, it is necessary to select an appropriate coating method in order to apply a paint containing large particles with a low film thickness. In the roll coater, particles cannot pass between the roll and the object to be coated and are excluded. Therefore, it is very difficult to apply a coating containing particles of 60 μm or more with a film thickness of about 20 μm. Also, with spray painting, it is difficult to reduce the coating thickness. However, a coating method such as an overflow curtain coater, a slit curtain coater, a roller curtain coater, or a multi-layer curtain coater is preferable because the above problems do not occur. Here, the curtain coater is a system in which the paint is dropped into a thin curtain shape, and the object under the coating such as a metal plate is passed through it. Since it is a non-contact coating method, even particles having a large particle size are not excluded, and the contents in the paint are surely applied directly onto the object to be coated. Also, thin film coating is easily possible by increasing the speed of passing the object to be coated. When applying a top clear coating film containing colored particles having a large particle size as described above, it is extremely useful to use these curtain coaters.

  In addition, the drying (curing) method of the coating film of the present invention is arbitrary, and a method suitable for the paint to be used, such as heat drying such as hot air heating, high frequency induction heating, natural drying, curing by irradiation with electron beam or ultraviolet ray, etc. Just choose.

  Although the base steel plate used for this invention is not specifically limited, A stainless steel plate and a plated steel plate are suitable. Examples of the stainless steel plate include a ferritic stainless steel plate, a martensitic stainless steel plate, and an austenitic stainless steel plate. Plated steel sheets include galvanized steel sheets, zinc-iron alloy plated steel sheets, zinc-nickel alloy plated steel sheets, zinc-chromium alloy plated steel sheets, zinc-aluminum alloy plated steel sheets, aluminum-plated steel sheets, zinc-aluminum-magnesium alloy-plated steel sheets, Zinc-aluminum-magnesium-silicon alloy plated steel sheet, aluminum-silicon alloy plated steel sheet, galvanized stainless steel sheet, aluminized stainless steel sheet and the like.

  Particularly suitable base steel plates are plated steel plates containing at least Zn and Al. For example, Zn-Al alloy plated steel plates, Zn-Al-Si alloy plated steel plates, Zn-Al-Mg alloy plated steel plates, Zn-Al- An Mg-Si alloy plated steel sheet can be mentioned. Since these plated steel sheets are excellent in corrosion resistance, they can be used outdoors for a long period of time, and even if cracks occur in the embossed part due to deterioration of the coating film, the progress of corrosion can be suppressed.

  As pre-coating treatments for steel sheets, there are water washing, hot water washing, pickling, alkali degreasing, grinding, polishing, etc., and these may be carried out alone or in combination as necessary. The conditions for the pretreatment for coating can be selected as appropriate.

  Moreover, you may perform a chemical conversion treatment on a steel plate as needed. The chemical conversion treatment is performed for the purpose of strengthening the adhesion between the coating film and the base steel sheet and improving the corrosion resistance. As the chemical conversion treatment, known techniques can be used. For example, zinc phosphate treatment, chromate treatment, silane coupling treatment, composite oxide film treatment, non-chromate treatment, tannic acid treatment, titania treatment, zirconia treatment, Ni surface An adjustment process, a Co surface adjustment process, a mixing process thereof, and the like can be given.

As a coating film of a coated steel plate having two or more coating film configurations, at least the outermost layer has a minimum value of dynamic storage elastic modulus in a rubber-like elastic region using the polyester resin of the present invention as a main resin, 2 × 10. ^Although it is necessary to use a thermosetting resin coating film of ⁷ Pa or less, as a coating film of the other layers, a commonly used known resin coating film can be used as it is. That is, high molecular polyester resin, polyester resin, acrylic resin, epoxy resin, urethane resin, fluorine resin, silicon polyester resin, vinyl chloride resin, polyolefin resin, butyral resin, polycarbonate resin, Resin components such as phenolic resins or these modified resins are cross-linked with n-butylated melamine, methylated melamine, iso-butyl melamine, methylbutyl mixed melamine, urea resin, isocyanate, or a crosslinker component of these mixed systems. Can be applied.

  In this case, the lower layer and the surface layer may be colored with a pigment as required, or a rust preventive pigment may be added for the purpose of improving the corrosion resistance. As the coloring pigment, known coloring pigments can be used, and for example, titanium oxide, zinc oxide, zirconium oxide, calcium carbonate, barium sulfate, alumina, iron oxide, phthalocyanine blue, carbon black and the like can be used. As the rust preventive pigment, known rust preventive pigments can be applied. For example, phosphate phosphate rust preventive pigments such as zinc phosphate, iron phosphate, aluminum phosphate, zinc phosphite, calcium molybdate, aluminum molybdate, molybdenum Molybdate anticorrosion pigments such as barium oxide, vanadium anticorrosion pigments such as vanadium oxide, silicate pigments such as calcium silicate, strontium chromate, zinc chromate, calcium chromate, potassium chromate, barium chromate and other chromate anticorrosion pigments Further, fine silica such as water-dispersed silica and fumed silica, ferroalloy such as ferrosilicon, and the like can be used. These may be used singly or in combination of two or more.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these at all.

(A) Base steel plate and pre-coating treatment As the base steel plate, hot dip galvanized steel plate (double-sided plating adhesion amount 180 g / m ² , plate thickness 0.27 mm), Zn-11% Al-3% Mg-0.2% Si Alloy-plated steel sheet (double-sided plating adhesion 120 g / m ² , sheet thickness 0.27 mm) and 55% Al-43.4% Zn-1.6% Si alloy-plated steel sheet (double-sided plating adhesion 150 g / m ² , sheet thickness 0.27 mm) was used. Each galvanized steel sheet was subjected to coating-type chromate treatment (ZM1300 manufactured by Nippon Parkerizing Co., Ltd., total Cr amount 50 mg / m ² ) as a chemical conversion treatment after degreasing.

(B) Coating preparation method and storage elastic modulus measurement method A commercially available linear polyester resin having various number average molecular weights was mixed with an organic solvent (Solvesso 150 (manufactured by Esso Petroleum Corporation)) and cyclohexanone in a mass ratio of 1: 1. In addition, methylated melamine (Mitsui Chemicals, Cymel 303) was added as a curing agent melamine resin at various compounding ratios, and p-toluenesulfone as a catalyst. An acid (Cytec Co., Ltd., Catalyst 6003B) was added and stirred to prepare various paints. The details of the polyester resin and melamine resin of the prepared paint are shown in Table 2.

  Furthermore, these paints are applied on the tin plate so that the dry film thickness is 20 μm, and after heat curing under the condition that the ultimate plate temperature is 230 ° C., the coating film is peeled off from the tin plate by the mercury amalgam method. A film free film was prepared. The dynamic storage elastic modulus was measured using a free film of this coating film. The dynamic storage elastic modulus was measured in a temperature range of −50 to 200 ° C. using a dynamic viscoelasticity test apparatus (Rheometrics, RSA-11). The measurement conditions were a strain of 0.01% and an angular frequency of 6.28 rad / sec. In this experiment, the minimum value of the storage modulus appearing in the rubbery elastic region was obtained from the relationship between temperature and dynamic storage modulus. FIG. 1 shows a typical example of the relationship between the temperature and dynamic storage elastic modulus (logarithmic display) obtained in this experiment. As can be seen from this graph, an elastic region on the glass having a high dynamic storage elastic modulus appears in a low temperature region (a temperature region of about 20 ° C. or less in FIG. 1), and a region having a higher temperature (about 20 to about in FIG. 1). In the region of 60 ° C., a transition region where the value of the dynamic storage elastic modulus rapidly decreases appears, and in a region where the temperature is higher (about 60 ° C. or more in FIG. 1), the dynamic storage elastic modulus becomes equilibrium at a low value. A rubbery elastic region appears. In the present invention, the minimum value of the storage elastic modulus appearing in the rubber-like elastic region is compared. In this example, the dynamic storage elastic modulus at 150 ° C. is usually shown as the temperature at which the coating film used for the coated steel sheet surely becomes a rubbery elastic region.

  The coating material which added 2 mass% of colored particles (red acrylic beads) of various particle diameters to the coating material according to the example of the present invention and the coating material according to the comparative example was also manufactured (see Table 6 below).

(C) Preparation method of coated steel plate The coating material of (B) was applied to the plated steel plate that had been subjected to the pretreatment before coating in (A) by the following method. That is, in the case of two-layer coating, the undercoat paint was applied with a roller curtain coater so that the dry film thickness was 5 μm, and cured and dried in a hot air heating furnace under a condition where the ultimate plate temperature was 210 ° C. Further thereon, a top coating was applied with a roller curtain coater so as to have a dry film thickness of 15 μm, and cured and dried in a hot air heating furnace at a final plate temperature of 230 ° C. On the other hand, in the case of single-layer coating, only top coating was applied.

  Moreover, the coating material to which the colored particles were added was applied only on the Zn-11% Al-3% Mg-0.2% Si alloy-plated steel sheet.

(D) Evaluation method of weather resistance For the coated steel sheet produced in (C), a sunshine carbon arc lamp type weather resistance tester (manufactured by Suga Test Instruments Co., Ltd., WEL-SUN-DC-B.EM type) is used. A weather resistance test (SWOM test) based on JIS B7753-1993 was conducted for 500 hours, and the gloss retention was calculated from the gloss values before and after the test. The weather resistance was evaluated in the state of a flat plate not subjected to embossing.

(E) Embossing and preparation of sizing material Embossing was performed on the coated steel sheet prepared in (C) using an embossing roll carved with a grain pattern. Furthermore, urethane foaming treatment was performed on the back surface, and a urethane layer was added to make a sizing material.

(F) Corrosion resistance evaluation method The sizing material was cut into a size of 150 mm x 70 mm, and an outdoor exposure test was conducted in Gushigami Village, Okinawa Prefecture. Considering the actual sizing material installation situation, the test piece was installed under the eaves. The outdoor exposure test was conducted for one year, and the corrosion occurrence state of the embossed part was visually evaluated in five stages as shown in Table 1 below.

  The results of the above tests are shown in Tables 3 to 6 below. Table 3 shows the case where the base plated steel sheet is a hot dip galvanized steel sheet (No. 1 to 10), and Table 4 shows that the base plated steel sheet is a Zn-11% Al-3% Mg-0.2% Si plated steel sheet. In the case (No. 11-20), Table 5 shows the case where the base plated steel plate is a 55% Al-Zn plated steel plate (No. 21-30), and Table 6 shows the case containing colored particles (No. 31-49). ) Examples.

  The test results are summarized below.

As shown in Tables 3 to 5, the minimum value of the dynamic storage elastic modulus in the rubber-like elastic region is 2 × 10 ⁷ Pa or less on the outermost layer, and the gloss retention of the weather resistance test is 60%. It was found that the coated steel sheet with the above-mentioned thermosetting organic resin coating film shows good corrosion resistance with little coating cracking at the embossed part. (See Examples Nos. 1, 2, 5-8, 11, 12, 15-18, 21, 22, 25-28 in Tables 3-5).

On the other hand, a coated steel sheet having a minimum value of storage elastic modulus in the rubber-like elastic region exceeding 2 × 10 ⁷ Pa is inferior in corrosion resistance even when the gloss retention is 60% or more (Comparative Examples Nos. 3 to 5 in Tables 3 to 5). 3, 9, 13, 19, 23, 29), and the coating film cracks in the embossed part after the outdoor exposure test were large, and there was also a lot of white rust, which was inappropriate.

Moreover, even if the minimum value of the storage elastic modulus in the rubber-like elastic region is 2 × 10 ⁷ Pa or less, if the gloss retention is less than 60%, the corrosion resistance is poor (Comparative Example No. 4 in Tables 3 to 5). , 10, 14, 20, 24, 30), the coating film cracks in the embossed part after the outdoor exposure test were large, and there was also a lot of white rust, which was inappropriate.

In addition, the minimum value of the dynamic storage elastic modulus in the rubber-like elastic region of both the undercoat and the topcoat is 2 × 10 ⁷ Pa or less, and the gloss retention of the topcoat is 60% or more, Conditions for the base plated steel sheet are Zn-11% Al-3% Mg-0.2% Si alloy plated steel sheet and 55% Al-43.4% Zn-1.6% Si alloy plated steel sheet (implementation of Tables 4 and 5) Example No. 15, 16, 25, 26) showed particularly excellent embossed part corrosion resistance.

Furthermore, as shown in Table 6, even under the condition where colored particles are added, the dynamic storage elastic modulus in the rubber-like elastic region is 2 × 10 ⁷ Pa or less, and the gloss retention in the weather resistance test is 60%. In the coated steel sheet having the above thermosetting organic resin coating film, the corrosion resistance of the embossed part was kept in a good state if the particle size of the colored particles was in the range of 10 to 500 μm.

  As mentioned above, although preferred embodiment of this invention was described, it cannot be overemphasized that this invention is not limited to this example. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

It is a graph which shows the representative example of the relationship between the temperature obtained by this experiment, and dynamic storage elastic modulus (logarithm display).

The present invention can be applied to a coated steel sheet and a sizing material, and in particular, can be applied to a coated steel sheet having excellent corrosion resistance at an embossed portion even after embossing used for the sizing material.

Claims (5)

A coated steel sheet having one or more layers on at least one side of the steel sheet:
At least the outermost coating layer contains a polyester resin as the main resin, the minimum value of the dynamic storage elastic modulus in the rubbery elastic region is 2 × 10 ⁷ Pa or less, and the sunshine carbon arc lamp type weather resistance test A coated steel sheet characterized by being a thermosetting resin coating film having a gloss retention of 60% or more after a weather resistance test by a machine for 500 hours.   The coated steel sheet according to claim 1, wherein the outermost-layer coating film is a clear coating film.   The coated steel sheet according to claim 1 or 2, wherein the outermost layer coating film contains colored particles having an average particle diameter of 10 to 500 µm.   The coated steel sheet according to any one of claims 1 to 3, wherein the steel sheet is a plated steel sheet containing at least Zn and Al. The sizing material formed by embossing the coated steel plate in any one of Claims 1-4.

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