TWI469866B - Precoated metal plate - Google Patents

Description

Pre-coated metal sheet Technical field

The present invention relates to pre-coated metal sheets having high thermal insulation properties, and electronic machines fabricated using at least a portion of the pre-coated metal sheets.

Background technique

In the past, metal plates such as steel plates and aluminum plates were used for boards other than electronic devices such as computers and digital home appliances. Such metal sheets are widely used as pre-coated metal sheets because of their design requirements.

In recent years, with the spread of computers and the electronicization of home electric appliances, etc., a large number of components such as motors or electronic components are used as heat sources in such computers or home electric appliances. Since the heat generated by these heat sources is constantly increasing, when the light touches the outer panel of the home appliance, it will feel hot and have a problem of being burnt.

Conventionally, in order to suppress an increase in the temperature of the outer panel of the home electric appliance, there is a method of providing an opening for heat dissipation or forcibly cooling by a fan. Further, methods such as using various heat dissipating materials or thermal insulating materials have also been carried out. However, such methods are still insufficient as a countermeasure, and since there is a need to attach a heat dissipating material or a thermal insulating material, there are problems such as hindrance in productivity and increase in cost.

Here, even if the temperature of the metal plate itself rises, as long as the heat of the metal plate is not transmitted to the skin that is in contact with it, heat is not felt and there is no concern about burns. Therefore, in order to convey the heat of the metal sheet to the skin to be contacted and to impart thermal insulation properties to the surface of the metal sheet, a technique of forming a coating layer containing bubbles having low thermal conductivity on the surface of the metal sheet has been disclosed. For example, Patent Document 1 or Patent Document 2 discloses a technique in which a foaming coating material is applied to foam when a coating is heat-cured, and bubbles are contained. Further, Patent Document 3 discloses a technique of containing bubbles by coating a coating material to which hollow fine particles or heat-expandable particles are added.

Here, the inventors of the present invention used the techniques of the above-mentioned Patent Documents 1 to 3 to confirm the coating film performance after forming a layer containing bubbles on a metal plate, and to check whether it is suitable for a precoated steel sheet. As a result, it has been found that the thermal insulating properties of the inventions of Patent Documents 1 and 2 are good, but the workability, particularly the stretch moldability, is not good. Further, although the invention of Patent Document 3 was found to be stretch-formed, the thermal insulating performance was not sufficient.

As described above, neither of the inventions satisfies both the thermal insulation performance and the processability, and the technical system of the pre-coated metal sheet which can simultaneously satisfy the thermal insulation performance and workability pursued by the outer panel of the home electric appliance has not been proposed.

Prior technical literature Patent literature

Patent Document 1: Japanese Patent Laid-Open Publication No. 2005-131830

Patent Document 2: Japanese Patent Laid-Open Publication No. 2005-219354

Patent Document 3: Japanese Patent Laid-Open Publication No. 2005-193533

The present invention has been made in view of the above circumstances, and it is an object of the invention to provide a precoated metal sheet and a coated metal molded article which have high thermal insulation properties and are excellent in workability.

In order to solve the above problems, the present inventors have made a review of the above-mentioned problems. As a result, as shown in Fig. 1, it has been found that a coating layer containing a large bubble is coated on one surface or both surfaces of a metal plate to obtain high thermal insulation performance. Further, as shown in Fig. 2, when the size of the bubble is too large as the thickness of the coating film, the processability or adhesion of the coating film is not good, as shown in Fig. 3, when the size of the bubble is too small, the thermal insulation property is shown. Not good. In addition, the inventors of the present invention have made a review, and as a result, as shown in Fig. 1, the coating layer containing a large bubble is thinned by the surface of the coating film and the upper portion of the bubble, so that it is processed or subjected to a square test or the like. In order to solve these problems, it is considered that the coating layer containing bubbles as the lower layer coating film (first coating layer) as shown in Fig. 4, and the upper layer is further provided thereon. The idea of the coating film (the second coating layer). In addition, it has been found that the thermal insulation property, the workability, and the adhesion of the precoated metal sheet which have been considered are both controlled by controlling the film thickness of the undercoat film and the bubble content rate within a certain relationship. Moreover, it has been found that by controlling the resin component of the coating layer (second coating layer) on the upper side and controlling the shape and number of bubbles contained in the coating layer (first coating layer) on the lower side, it is possible to achieve both Thermal insulation properties and processability and adhesion of the upper layer. The invention of the present application is based on the knowledge obtained from such observations.

In other words, the gist of the present invention is as follows.

(1) A precoated metal sheet having at least two coating layers on one surface or both sides of a metal sheet, wherein the first coating layer on the lower side of the at least two coating layers A bubble-containing layer containing bubbles, wherein when the bubble content of the bubble-containing layer is a volume concentration V (%) and the film thickness is t (μm), the following formula is satisfied: -0.1t+57.5≦V≦- 0.05t+92.5 and 50≦t≦350, the second coating layer on the upper side of the first coating layer contains a coating layer of a melamine-curable polyester resin or an isocyanate-curable polyester resin, and the polyester resin The number average molecular weight is 10,000 to 23,000, and the film thickness of the second coating layer is 3 to 30 μm.

(2) The precoated metal sheet according to (1), wherein the total film thickness of the first coating layer and the second coating layer is T (μm), and is relative to the surface of the coating film. When the diameter of the bubble measured in the vertical direction is Rv (μm), there are 20 or more bubbles satisfying Rv ≧ 0.8T in the width of 10 mm of the cross section of any coating film.

(3) The precoated metal sheet according to (1) or (2), wherein the first coating layer and the second coating layer each contain a pigment of the same color.

(4) The precoated metal sheet according to any one of (1) to (3), wherein a temperature of a surface opposite to a surface of the metal plate having the bubble containing layer is set at 80 ° C or more and 200 When the predetermined temperature is lower than °C, the total infrared ray emission rate in the region of the measured wave number 600 to 3000 cm ^-1 is 0.50 or less.

(5) An electronic device in which at least a part of the outer panel is a precoated metal sheet according to any one of (1) to (4), and the surface having the bubble containing layer is located outside the outer panel. side.

According to the present invention, it is possible to provide a precoated metal sheet and a coated metal formed article which have high heat insulating properties and are excellent in workability.

Simple illustration

Figure 1 is a cross-sectional view of a precoated metal sheet coated with a coating layer having a larger bubble.

Fig. 2 is a cross-sectional view of a precoated metal sheet coated with a coating layer with respect to a bubble having an excessively large film thickness.

Fig. 3 is a cross-sectional view of a precoated metal sheet coated with a coating layer with respect to a bubble having a too small film thickness.

Figure 4 is a cross-sectional view of a precoated metal sheet of the present invention.

Fig. 5 is a graph showing the relationship between the bubble content of the bubble-containing layer and the film thickness t (μm) in terms of volume concentration.

Fig. 6 is an explanatory view showing an outline of an experimental apparatus for measuring the rising temperature.

Fig. 7 is an explanatory view showing the structure of a casing used for the test of the contact time and the rising temperature.

Fig. 8 is a photograph of a cross section of a coating film portion of the precoated metal sheet of Example No. 4 observed by an optical microscope.

Form for implementing the invention

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The precoated metal sheet of the present invention has at least two coating layers on one side or both sides of a metal sheet as a substrate. The "lower" used when referring to the position of the coating layer of at least two layers of the precoated metal sheet refers to the side close to the metal sheet, and the "upper" means the side away from the metal sheet. Specifically, the coating layer includes at least a first coating layer containing bubbles (hereinafter referred to as "bubble-containing layer") and a polymer polyester resin having a surface layer side laminated on the first coating layer. The laminated structure of the second coating layer (hereinafter referred to as "upper coating").

The bubble-containing layer is characterized in that when the bubble content of the coating film is V (%) in terms of volume concentration and t (μm) in film thickness, -0.1t + 57.5 ≦V ≦ - 0.05 t + 92.5 is satisfied. And the relationship between 50≦t≦350. As a result of review by the inventors of the present invention, it has been found that the relationship between the bubble content ratio V (%) satisfying the bubble-containing layer and the film thickness t (μm) is -0.1 t + 57.5 ≦ V, and the relationship of t ≧ 50 is good. The thermal insulation performance, by satisfying V≦-0.05t+92.5, and t≦350, the coating film will have good processability as the metal plate is deformed.

Fig. 5 is a graph showing the relationship between the bubble content of the bubble-containing layer and V (%) and film thickness t (μm) in terms of volume concentration. As shown below, in the examples, the polyurethane (i) was used as the binder resin of the bubble-containing layer, and Cellmic CE was used as the bubble admixture type, carbon black as the pigment, and the top coat was set. In the case of 15 μm (Example No. 4, 13 to 31, 39 to 48), the bubble-containing layer film thickness: t (μm) and bubble content rate: V (%), and is classified into thermal insulation properties. The results of the evaluation and the workability and the results of the evaluation of the adhesion evaluation. The meaning of the evaluation mark in the figure is shown in the table below.

It can be seen from Fig. 5 that the area surrounded by the bubble content range (-0.1t+57.5≦V≦-0.05t+92.5) and the film thickness range (50≦t≦350) is in thermal insulation properties and processability. Good evaluation can be obtained on both aspects of adhesion.

Here, the film thickness t is obtained by cutting the coating film, filling the resin, and grinding the surface to make the cross section perpendicular to the surface of the coating film smooth, and then observing it by an optical microscope or an electron microscope, and observing 5 places in a range of 10 mm in width. The average of the ones sought. In addition, the bubble content rate V can be obtained by photographing the cross section of the coating film with an electron microscope or the like, and the transparent sheet used for the OHP is covered on the photograph, and the bubble portion is accurately drawn, and then the bubble portion and the other coating portion are cut out, and the mass is measured. , in terms of area ratio = volume ratio, V is obtained from the mass ratio. The bubble content rate V can also be obtained by observing the average value obtained by the range of 5 widths of 10 mm.

Further, the total film thickness of the bubble-containing layer of the pre-coated metal plate and the upper coating layer (as will be described later, when there is a layer below the bubble-containing layer, the thickness of the layer below it is not included). (μm), when the diameter of the bubble in the vertical direction of the surface of the coating film is Rv, when there are 20 or more bubbles satisfying ≧0.8T in the width of 10 mm of the cross section of any coating film, the surface is formed with moderate unevenness. Reducing the contact area of the skin with the pre-coated metal sheet when the pre-coated metal sheet is touched with a finger or the like can reduce the amount of heat transmitted to the skin. Further, the portion in contact with the skin is a field in which bubbles having a low thermal conductivity between the surface of the coating film and the steel sheet are not easily conveyed. Further, it is possible to obtain a thermal insulation effect by an air layer formed between the concave portion of the coating film and the skin. According to these multiplication effects, it is preferable to have 20 or more bubbles satisfying ≧0.8T in a width of 10 mm of any coating film cross section because of excellent thermal insulating properties. Further, the diameter and the number of the bubbles in the bubble-containing layer were observed by an optical microscope or an electron microscope, and the cross section perpendicular to the surface of the coating film was observed, and the average value obtained after 5 observations in the range of 10 mm in width was determined.

The binder used for the bubble-containing layer can be generally used, and for example, a polyester resin, an urethane resin, an acrylic resin, an epoxy resin, a melamine resin, a vinyl chloride resin, or the like can be used, and these resins are also used. It can be either a thermoformable or a thermosetting type. Among them, a urethane resin or a polyester resin which is excellent in ductility and which is excellent in adhesion to the polyester resin-based paint used for the top coat is preferable as the binder.

When an urethane resin or a polyester resin is used, the glass transition temperature (Tg) of the resins is preferably -10 to 70 °C. When the Tg of the urethane resin or the polyester resin is less than -10 ° C, there is a concern that the film is not sufficiently formed, and when it is more than 70 ° C, the film hardness is too high, so that there is a concern that the workability is lowered.

The method of containing the bubbles in the bubble-containing layer is not particularly limited, and for example, coating or burning of azomethoxamine or azobisisobutyronitrile is equivalent to an organic foaming agent which decomposes while generating gas while heating, or addition. The heat-expandable particles which are expanded by a solvent such as a microcapsule enclosed in a particle, or a coating material obtained by adding inorganic hollow particles or organic hollow particles may be used.

Further, in the bubble-containing layer of the present invention, when a part of the gas generated by the formation of the bubble is removed by the film, a hole is formed on the surface of the film, but since the upper layer is provided on the bubble-containing layer, It has a bad effect on performance and is not particularly problematic.

In the coating of the present invention, a melamine-curable polyester resin or an isocyanate-curing polyester resin is used as the base resin.

As described above, by controlling the bubble content, the film thickness, and the cell diameter of the bubble-containing layer, it is possible to ensure a certain degree of workability while maintaining the thermal insulation performance. However, the present inventors have found that by providing an overcoat layer on the upper layer of the bubble-containing layer, the desired processing property can be obtained by the bubble-containing layer alone and the processing property of the object of the present invention is not satisfied. As the base resin, a melamine-curable polyester resin having a number average molecular weight of 10,000 to 23,000 or an isocyanate-curing polyester resin having a number average molecular weight of 10,000 to 23,000 is used.

The reason why the main resin of the top coat is a polyester resin and the number average molecular weight is 10,000 to 23,000 is that the polyester resin having excellent ductility and adhesion is used as the top coat to ensure processability, and the polyester is defined. The reason why the resin is a melamine-curable polyester resin or an isocyanate-curable polyester resin is a coating film which is excellent in hardness and ductility. When the number average molecular weight of the top coat polyester resin is less than 10,000, workability is deteriorated. When the number average molecular weight of the top coat polyester resin is more than 23,000, workability is deteriorated. Further, when the number average molecular weight of the top coat polyester resin is more than 23,000, the surface of the coating film becomes too soft and the scratch resistance is deteriorated, so this is the upper limit.

In addition, the melamine-curable polyester resin or the isocyanate-curable polyester resin having 80% by mass or more of the above-mentioned number average molecular weight of 10,000 to 23,000 in the binder resin exhibits an effect of improving the workability.

The film thickness of the upper coating layer is preferably 3 to 30 μm. When the film thickness of the upper coating layer is less than 3 μm, it is not suitable because of poor workability. When the film thickness of the upper coating layer is more than 30 μm, foaming is likely to occur at the time of coating, and it is not suitable in terms of cost. Further, when the film thickness of the upper coating layer is more than 30 μm, there is a fear that the heat insulating effect by the unevenness of the surface of the coating film formed by controlling the shape of the bubble containing layer or the bubble content is not obtained.

The bubble-containing layer and the overcoat layer of the present invention may be added with a coloring pigment as needed. As the coloring pigment, generally known inorganic pigments, organic pigments, and metallic pigments can be used. For example, carbon black, titanium oxide, zinc oxide, naphthol red, bisazo yellow, bisazopyrazole orange, aluminum pigment, nickel pigment, and the like can be given.

The colored pigment added to the bubble-containing layer and the overcoat layer is preferably a homologous color. If the bubble-containing layer and the upper coating layer are of the same color, in addition to obtaining a stable color appearance, even if the upper coating layer is thinned or slightly cracked due to processing or the like, the appearance and the color tone can be suppressed, which is preferable. .

When the coloring pigment is added to the bubble-containing layer and the top coat layer of the present invention, it is preferably added in an amount of 130 parts by mass or less based on 100 parts by mass of the binder resin solid content. When the coloring pigment is more than 130 parts by mass, the amount of the coloring pigment is too large, the coating film becomes brittle, and there is a possibility that workability and adhesion are poor.

The bubble-containing layer and the overcoat layer of the present invention may be added together with an anti-rust pigment and a rust preventive agent as needed. For example, generally known chromium-based anticorrosive pigments such as strontium chromate or calcium chromate; or zinc phosphate, zinc strontium phosphate, aluminum phosphate, aluminum phosphite, molybdate, phosphomolybdate, vanadic acid/ Phosphoric acid mixed pigments, cerium oxide, and calcium citrate are commonly known as non-chromium rust-preventing pigments and rust inhibitors such as Ca-type cerium oxide. Among the rust preventive pigments and the rust preventive agent, a non-chromium rust preventive pigment and a rust preventive agent using chromic acid containing no environmentally-accepting substance are preferred.

When the rust-preventing pigment is added to the bubble-containing layer and the overcoat layer of the present invention, the amount of the binder resin is preferably 10 to 130 parts by mass based on 100 parts by mass of the binder resin. When the amount of the anti-rust pigment added is less than 10 parts by mass, there is a possibility that the corrosion resistance is not good. When the amount of the anti-rust pigment added is more than 130 parts by mass, the amount of the anti-rust pigment is excessive, the coating film becomes brittle, and the processing is performed. Possibility of poor sex and adhesion.

In addition, when both the coloring pigment and the rust preventive pigment are added to the bubble-containing layer and the overcoat layer of the present invention, the upper limit of the amount of the binder is 100 parts by mass of the binder resin to set the total amount of the pigments. 130 parts by mass or less is preferred. When the total amount of the pigment added is more than 130 parts by mass, the amount of the pigment is too large, the coating film becomes brittle, and there is a possibility that workability and adhesion are poor.

Further, in the bubble-containing layer and the overcoat layer of the present invention, a generally known leveling agent, a pigment dispersant or the like may be added as needed. The type or amount of the additives is not particularly specified, and may be appropriately selected as needed.

The bubble-containing layer and the overcoat layer of the present invention can be applied by, for example, a roll coater, a roll curtain coater, a water roll coater, a spray coating, or the like, using a generally well-known coating method, and thereafter, A commonly known coating baking furnace, for example, a hot air drying furnace, an induction heating furnace, an infrared heating furnace, or the like, is used in combination with such a furnace. Generally, when it is manufactured by a continuous pre-coated metal sheet manufacturing apparatus called CCL (Continuous Coating Lines), it is preferable to mass-produce it efficiently. When coating with CCL, the undercoat film is applied by a roll coater or a curtain coater, and the upper coat film is preferably applied by a curtain coater. The curtain coater is different from the roll coater and can be applied without contacting the substrate. Therefore, the undercoat film (the first coating layer) of the present invention comprising the bubble after the coating and drying and curing is foamed. When the upper coating film (second coating layer) is applied by a curtain coater, it is possible to apply the coating without damaging the bubbles in the lower coating film, and it is more preferable because the appearance of the coating is also beautiful. When the upper coating film is applied by a roll coater, the coating is applied while the bubbles in the lower coating film are damaged during coating, so that the thermal insulating property is impaired or the appearance of the upper coating film is poor. . When a multi-layer simultaneous coating apparatus called a slanted curtain curtain coater is used, and the undercoat film and the upper coating film before drying are laminated and curtain-coated, the drying and hardening step after coating is reduced to one step. It is preferable to dry and harden the multilayer at the same time, so that it is preferable from the viewpoint of energy reduction or production efficiency.

The precoated metal sheet of the present invention may optionally be coated with an undercoat film layer having an anticorrosive coating function under the bubble containing layer. When the undercoat film layer is applied, it is preferable because the corrosion resistance of the metal plate is improved. The undercoat film layer applied to the precoated metal sheet of the present invention is a well-known undercoat film for precoated metal sheets, and for example, a polyester primer, an epoxy primer, an amine can be used. Ethyl formate is used as a primer. The hardener for the undercoat film may be either melamine or isocyanate. A chromic acid-based, a phosphoric acid-based or a cerium oxide-based rust-preventing pigment which is added to the undercoating film is generally known, but it is preferable because the chromic acid-based one has a small burden on the environment.

The undercoat film applied to the precoated metal sheet of the present invention may be a generally well known coating method, for example, a roll coater, a roll curtain coater, a water roll coater, a spray coating, or the like. After coating, it is baked by a generally known coating baking furnace, for example, a hot air drying furnace, an induction heating furnace, an infrared heating furnace, or the like.

In the precoated metal sheet of the present invention, when the temperature of the surface opposite to the surface having the bubble containing layer is set to a predetermined temperature of 80 ° C or more and 200 ° C or less, the total infrared ray in the region of the wave number of 600 to 3000 cm ^{-1 is} measured. The emissivity is preferably 0.50 or less.

When the heat radiation is incident on the metal plate, the heat radiation is reflected or absorbed because there is no heat radiation. Here, when the heat radiation generated by the heat generating body inside the casing is incident on the inner surface of the outer casing, when the majority of the incident heat radiation is absorbed, the temperature of the outer casing rises. According to Kirchhoff's law on heat radiation, at a certain temperature, objects The absorption rate is the same as that of the emissivity (for example, "Mechanical Engineering Fundamental Lectures and Electrothermal Engineering" by Nishikawa and Fujita, p. 290, Issue: Institute of Science and Technology (1983)). Therefore, the inventors of the present invention have studied the emissivity of the opposite side of the surface containing the bubble in detail, and as a result, it has been found that the temperature of the outer surface of the outer casing can be lowered by lowering the emissivity of the inner side of the outer surface of the outer cover of the heat-generating body. In other words, the opposite surface of the surface having the bubble-containing layer is used as the inner side of the casing, and the total emissivity in the region of the wave number of 600 to 3000 cm ^-1 measured at a temperature of 80 ° C or more and 200 ° C or less is set. It is preferably 0.50 or less, preferably 0.40 or less, and it is found that the temperature of the outer panel of the casing can be greatly reduced.

The wave number region smaller than the wave number of 600 cm ^-1 or larger than 3000 cm ^-1 is extremely small because the heat applied to the outer surface of the casing is extremely small, so that the emissivity including the wavenumber regions is not good. By limiting the measured wave number to a region of 600 to 3000 cm ^-1 , the measurement can be performed with high precision and efficiency.

Further, when the temperature at which the emissivity is measured is less than 80 ° C, the amount of radiation energy emitted from the film is too small, so that when the emissivity is measured, a test error is likely to occur and it is not suitable. The measurement can be carried out with a temperature of 80 ° C or more and 200 ° C or less, and the measurement can be performed with high precision. Further, when the measurement temperature is more than 200 ° C, it is unsuitable for the thermal decomposition of the film depending on the type of the film.

In order to improve the heat reflectivity inside the casing, it is preferable to expose the metal base material to have high heat reflectivity. Further, it is more preferable to plate a metal having high heat reflectivity on the surface of the metal plate.

As the metal material having high heat reflectivity, generally known metal materials such as aluminum, nickel, stainless steel, and zinc, alloys thereof, and metal materials plated thereon can be used. When the film is peeled off without applying a film on the metal plate or the plating layer, the heat reflectance of the surface on the inner side of the casing is further improved. In the case of a steel sheet, a hot dip galvanized steel sheet, an electrogalvanized steel sheet, a galvanized-nickel alloy steel sheet, an alloyed hot dip galvanized steel sheet, an aluminized steel sheet, or an aluminized-zinc alloy steel sheet is preferred.

However, when the metal is peeled off, since it is easy to cause corrosion from the place, it is preferable to carry out chemical conversion treatment. However, with the type of chemical conversion treatment or the amount of adhesion, there is heat reflection. If you have low doubts, you should select the type or amount of adhesion as needed.

As the chemical conversion treatment, a general practitioner can be used. Specifically, for example, a zinc phosphate-based chemical conversion treatment, a non-chromic acid-based chemical conversion treatment, a coating type chromic acid treatment, an electrolytic chromic acid treatment, a reaction chromic acid treatment, or the like can be used. Among them, the coating type chromic acid treatment, the electrolytic chromic acid treatment, and the reaction chromic acid treatment are not preferable because they contain hexavalent chromium which is an environmentally burdening substance. Moreover, the zinc phosphate-based chemical conversion treatment also has doubts that the processing adhesion is poorer than other treatments. Therefore, the chemical conversion treatment of the metal material to be subjected to the present embodiment is preferably a non-chromic acid treatment.

The non-chromic acid-based chemical conversion treatment may be any one of those using an inorganic chemical conversion treatment agent and an organic chemical conversion treatment agent. Specifically, the non-chromic acid-based chemical conversion treatment is known, for example, by using an aqueous solution containing a decane coupling agent, a zirconium compound, a titanium compound, tannin or tannic acid, a resin, cerium oxide, or the like. Japanese Laid-Open Patent Publication No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. A well-known technique described in, for example, JP-A-2002-266081 and JP-A-2003-253464. Further, as the chemical conversion treatment, a commercially available chemical conversion treatment agent can be used, for example, a chromic acid treatment agent "ZM-1300AN" manufactured by Japan PARKERIZING Co., Ltd., and a non-chromic acid chemical conversion treatment agent "CT-E300N" manufactured by Japan PARKERIZING Co., Ltd. A three-valent chromium-based chemical conversion treatment agent "Surfcoat (registered trademark) NRC1000" manufactured by PAINT, Japan.

The metal plate of the present invention is preferably used as an outer plate of an electronic machine. By using the metal plate of the present invention on an outer plate such as an electronic device, the surface having the bubble-containing layer is formed on the outer surface side, and even when the skin directly contacts the outer surface of the electronic device, it is difficult to feel heat and prevent burns. It is better.

An electronic device that can use the metal plate of the present invention in at least a part of the outer panel may, for example, be a desktop PC (Personal Computer), a digital home appliance such as a thin television, a car navigation device, an automobile electronic device such as a car AV, or the like. Further, the metal plate of the present invention can be used as a part of the outer panel of the portable product such as a notebook PC or a mobile phone.

Example

Next, the present invention will be more specifically described by way of examples, but the constitution of the present invention is not limited to the following examples.

(Example 1)

First, the paint used in the present embodiment will be described in detail. In the present embodiment, the surface of the metal plate is formed by sequentially depositing a bubble containing layer (first coating film layer, hereinafter also referred to as "lower layer coating film") and an upper coating layer (second coating film layer) on the side of the metal plate. In the following, the two-layer structure of the "upper coating film" is also applied, and the inside of the steel sheet is not coated or formed with an inner coating film. Hereinafter, the coating composition to be used will be described in the order of the coating material for the bubble-containing layer (hereinafter referred to as "lower coating material"), the coating material for the top coating layer (hereinafter referred to as "upper layer coating material"), and the coating material.

First, the undercoat layer will be described in detail.

The closed isocyanate "Desmodur (registered trademark) BL1100 manufactured by Bayer Urethane Co., Ltd. was added to "DESMOPHEN (registered trademark) 1150", which is a polyol of Bayer Urethane Co., Ltd., to make the solid content ratio polyol: closed type. Isocyanate = 66:34, and a clear coating (hereinafter referred to as "ethyl urethane (i)") was prepared. In addition, isophorone was used as a solvent.

As the base resin, an amorphous polyester resin "VYLON (registered trademark) 600" manufactured by Toyobo Co., Ltd. (number average molecular weight: 16,000) was used. For the crosslinking agent, a butylated melamine resin "SUPER BECKAMINE (registered trademark) J830" manufactured by DIC Corporation (hereinafter referred to as butylated melamine) was used. (The table is marked as "polyester"). Further, the solvent was mixed with cyclohexanone: Solvesso 150 = 1:1.

As the other basic resin, the epoxy resin "EPICLON (registered trademark) P-439" manufactured by DIC Corporation was used. As the crosslinking agent, butylated melamine "SUPER BECKAMINE (registered trademark) J830" manufactured by DIC Corporation was used. (The table is marked as "epoxy"). Further, the solvent was mixed with cyclohexanone: Solvesso 150 = 1:1.

In addition, as the other basic resin, an acrylic resin "ACRYSET (registered trademark) AST-5531" manufactured by Nippon Shokubai Co., Ltd. was used. For the crosslinking agent, a butylated melamine resin "SUPER BECKAMINE (registered trademark) J830" manufactured by DIC Corporation (hereinafter referred to as butylated melamine) was used. (The table is labeled as "acrylic"). Further, the solvent was mixed with cyclohexanone: Solvesso 150 = 1:1.

Next, 100 parts by mass of phthalic anhydride, 57 parts by mass of neopentyl glycol, and 48 parts by mass of trishydroxyl were added to a one-liter four-necked flask equipped with a stirrer, a thermometer, a nitrogen-conducting tube, and a condenser. Methylpropane was subjected to a condensation reaction at 210 ° C while stirring under nitrogen, and water was distilled off. Thereafter, the mixture was cooled to 100 ° C, 531 parts by mass of ε-caprolactone was added, the temperature was raised to 150 ° C, and the mixture was kept for 3 hours, and then cooled to 100 ° C, and 78 parts by mass of cyclohexanone was added to synthesize a polyol.

The blocked isocyanate "Smodur (registered trademark) BL3175" manufactured by Bayer Urethane Co., Ltd. was added to the polyol, and the solid content ratio was changed to polyol: blocked isocyanate = 66:34, and a clear coating was produced. "Ethyl carbamate (ii)"). In addition, isophorone was used as a solvent. The solid content concentration in the paint can be appropriately adjusted in consideration of bubble content, paintability, and storage stability.

In the case of the bubble, the foaming agent "Cellmic (registered trademark) CE" manufactured by Sankyo Chemical Co., Ltd., and the hollow particle "Ganzpearl GMH-850" manufactured by GANZ Chemical Co., Ltd. were used.

In the case of the coloring pigment, the carbon black "TOKABLACK (registered trademark) #7350" manufactured by Tokai Carbon Co., Ltd. is used as the black pigment, and the titanium oxide "TIPAQUE WHITE (registered trademark) CR manufactured by Ishihara Sangyo Co., Ltd. is used for the white pigment. -95" and commercially available zinc oxide, commercially available cobalt aluminate and copper indigo for the blue pigment, and commercially available iron oxide and cinnabar for the red pigment.

Next, the top coat is explained in detail.

For the basic resin, the amorphous polyester resin "VYLON (registered trademark) 660" (number average molecular weight 8000), "VYLON (registered trademark) GK250" (quantitative average molecular weight 10000), and "VYLON (registered trademark)) manufactured by Toyobo Co., Ltd. are used. GK140" (number average molecular weight: 13,000), "VYLON (registered trademark) 240" (number average molecular weight: 15,000), "VYLON (registered trademark) 600" (number average molecular weight: 16,000), "VYLON (registered trademark) 280" (quantitative average) Molecular weight: 18,000), "VYLON (registered trademark) 245" (number average molecular weight: 19,000), "VYLON (registered trademark) 103" (number average molecular weight: 23,000), and "VYLON (registered trademark) 550" (number average molecular weight: 28,000). For the cross-linking agent, a butylated melamine resin (hereinafter referred to as butylated melamine) manufactured by DIC Corporation, "SUPER BECKAMINE (registered trademark) J830", and an isocyanate compound manufactured by Bayer Urethane Co., Ltd. "Desmodur BL3175 (trade name)" (The table is marked as HDI). The solvent was mixed using a mass ratio of cyclohexanone: Solvesso 150 = 1:1.

The coloring pigment is the same as the lower coating.

The inside paint was made of the gray color of the inner paint "FL100HQ" manufactured by Japan Fine Coatings Co., Ltd. (indicated as "inside-1" in the table) and "FL100HQ" (in the table, "inside-2").

Hereinafter, the precoated metal sheets used in the experiments of the examples will be described in detail.

Prepare galvanized steel sheets (denoted as "EG" in the table), hot-dip galvanized steel sheets (denoted as "GI" in the table), alloyed galvanized steel sheets (denoted as "GA" in the table), and stainless steel (denoted in the table) "SUS"), aluminum plate as the original board.

Then, the prepared raw plate was spray-degreased with an alkali degreasing liquid "FC-4336" manufactured by Japan PARKERIZING Co., Ltd. at a concentration of 2% by mass and 50 °C, washed with water, dried, and then coated with non-chromium manufactured by Japan PARKERIZING Co., Ltd. by a roll coater. The "CT-E300N" which was subjected to acid chemical conversion treatment was dried in a hot air oven. In the drying condition of the hot air oven, the arrival sheet temperature of the steel sheet was 60 °C. The adhesion amount of the non-chromic acid treatment was applied to adhere to 200 g/m ² in terms of total solid content.

Then, the undercoating agent is simultaneously applied to one side of the metal plate subjected to the chemical conversion treatment by a roll coater, the inner coating material is coated on the other side, and the induction heating furnace is blown into the induction heating furnace to the metal plate. It reached the plate temperature of 220 ° C and dried and hardened. Further, after drying and baking, water was sprayed onto the coated metal plate by a sprayer to perform water cooling.

Next, the upper coating layer was applied to the lower coating film by a roll curtain coater, and dried and hardened under the condition that the sheet temperature reached 230 ° C in the induction heating furnace in which the hot air was blown. Further, after drying and baking, water was sprayed onto the coated metal plate by a sprayer, and water-cooled to prepare a 2-layer precoated metal plate.

Hereinafter, the details of the evaluation method of the precoated metal sheet produced in the experiment will be described.

1. Thermal insulation performance 1.1 Determination of the contact time and rising temperature of the hot plate

The prepared precoated metal sheet was placed on the hot plate heated to 65 ° C for 120 seconds on the upper side, and then the load of 500 g was applied to the surface of the precoated metal sheet with the index finger, and the measurement was not felt. The hot contact time was evaluated on the basis of the following. In addition, the same test was carried out by five people, and the average time was evaluated. (The table is marked as "thermal insulation performance (i)".)

◎: 10 seconds or more ○: 5 seconds or more and less than 10 seconds △: 2 seconds or more and less than 5 seconds ×: less than 2 seconds

Further, Fig. 6 shows an outline of an experimental apparatus for measuring the rising temperature. The prepared precoated metal sheet was placed on the hot plate heated to 65 ° C for 120 seconds on the upper side, and then thermoelectrically held between the silicone rubber (thickness 3 mm, side length 10 mm square) The coupler was attached to the surface of the precoated metal sheet at 1 g/mm ² , and the temperature after 30 seconds was measured and evaluated on the basis of the following. (The table is labeled "Thermal insulation performance (ii)".) This is a test that uses helium oxide rubber as the skin to simulate the heat felt by the person.

◎: less than 35 ° C ○: 35 ° C or more and less than 37 ° C △: 37 ° C or more and less than 39 ° C ×: 39 ° C or more

1.2 Determination of the contact time and rising temperature of the use of the housing

A basket as shown in Fig. 7 was prepared and tested. The top of the basket system was opened, and the open surface was coated so that the inside of the prepared precoated metal sheet was inside. In this state, the heat of the heat source was set to 15 W and left for 120 seconds. In the same manner as in 1.1, a load of 500 g was applied to the surface of the precoated metal sheet with the index finger, and the contact time in which no heat was felt was measured, and the evaluation was performed based on the following criteria. In addition, the same test was carried out by five people, and the average time was evaluated. (In the table, it is marked as thermal insulation performance (iii).)

◎: 10 seconds or more ○: 5 seconds or more and less than 10 seconds △: 2 seconds or more and less than 5 seconds ×: less than 2 seconds

2. Processability

For the evaluation of the workability, the cylindrical drawing workability was investigated as follows. The punching was carried out under the conditions of a punch diameter of 50 mm, a punch shoulder R3 mm, a die shoulder R3 mm, a draw ratio of 2.0, and BHF1t, and the steel sheet was drawn from a mold and evaluated on the following basis.

◎: Visually observed that the processed part has no cracks or discoloration.

○: Visually observed that the processed portion has no cracks but is discolored.

△: Visually observing the slight cracking of the processed part

×: The case where the processing part has a large crack is visually observed.

3. Adhesion

The adhesion was measured by a checkered tape test. The checkered tape test was carried out in accordance with the method of JIS K 5600-5-6, and evaluated on the basis of the following criteria.

◎: There is no peeling at all.

○: It was found that there was some slight peeling at the edge of the square.

△: 80% of the square remains unpeeled

×: the case where the square which remains without being peeled is less than 80%

4. Pollution resistance

The evaluation of the stain resistance was investigated for the magic ink stain resistance as follows. The prepared precoated metal sheet was cut into a square having a side length of 50 mm, and three lines were drawn on a red magic ink (registered trademark) on the surface to be evaluated, and then placed in an ambient gas at 20 ° C for 24 hours. Wipe off the line with ethanol. The residual color of the ink was visually judged and evaluated based on the following criteria.

◎: The situation where the ink marks disappeared

○: A slight residual of ink traces

△: Remaining ink traces

×: The case where the ink trace has not disappeared

5. Scratch resistance

Scratch resistance was measured by pencil hardness. Based on the method of JIS K 5600-5-4, the scratch resistance of the coating film was investigated by breaking the coating film when the hardness of the pencil core was changed, and the highest hardness which was not found in the coating film was used as the pencil of the coating film. The hardness was evaluated on the basis of the following criteria.

◎: HB or more ○: B △: 2B ×: 3B or less

6. Determine the emissivity inside

Using the Fourier transform infrared spectrometer "VALOR-III" manufactured by JASCO Corporation, the infrared luminescence spectrum in the region of the wave number of 600 to 3000 cm ^-1 was measured when the temperature of the surface of the prepared surface-treated metal plate was set to 80 ° C. It is compared to the luminescence spectrum of a standard black body to determine the total emissivity of the surface treated metal sheet. In addition, the standard black system was used for the "THI-1B black body sprayer" sold by TACOS JAPAN Co., Ltd. (manufactured by OKITSUMO Co., Ltd.) having a film thickness of 30 ± 2 μm.

The compositions of the precoated metal sheets produced in this example and the evaluation results thereof are shown in Tables 3 and 4.

The details of the evaluation results are described below.

(1) Effect of molecular weight of the upper coating film

The influence of the molecular weight of the upper coating film is shown in Examples Nos. 1 to 12, and Comparative Examples are shown in Nos. 37 and 38.

The precoated metal sheet of the embodiment of the present invention has excellent thermal insulation properties, workability, adhesion, stain resistance, and scratch resistance.

The molecular weight of the upper coating film is 10000 (NO.1), and the molecular weight of the upper coating film is 23,000 (NO.7). The stain resistance and scratch resistance tend to be slightly lower, so the upper coating is applied. The molecular weight of the film is preferably from 13,000 to 19,000. Those having a molecular weight of less than 10,000 (NO. 37) are not suitable because of poor workability. The molecular weight of the upper coating film is more than 23,000 (NO. 38), which is not suitable due to poor stain resistance and scratch resistance.

(2) Relationship between the concentration of bubbles and the film thickness of the underlying coating film

The relationship between the concentration of the bubble and the film thickness of the undercoat film is shown in Examples Nos. 13 to 31, and Comparative Examples are shown in Nos. 39 to 48.

The precoated metal sheet of the embodiment of the present invention has excellent thermal insulation properties, workability, adhesion, stain resistance, and scratch resistance.

The bubble contains the concentration V volume (%) and the film thickness t (μm), V <-0.1t + 57.5 (NO. 39, 41, 43, 45) is the thermal insulation performance, and V>-0.05t+ 92.5 (NO. 40, 42, 44, 46) is not suitable because of poor workability and adhesion. Further, those having a film thickness of less than 50 μm (NO. 47) are thermally insulating properties, and those having a film thickness of more than 350 μm (NO. 48) are unsuitable because of poor workability and adhesion.

(3) Effect of film thickness of upper coating film

The influence of the film thickness of the upper coating film is shown in No. 32 to 36, and the comparative example is shown in No. 49 to 51.

The precoated metal sheet of the embodiment of the present invention has excellent thermal insulation properties, workability, adhesion, stain resistance, and scratch resistance.

When the film thickness of the upper coating film is 3 μm (NO. 32), the processability, adhesion, and scratch resistance tend to be slightly lower, while the film thickness of the upper coating film is 30 μm (NO. 36). The tendency to become high is such that the film thickness of the upper coating film is preferably 5 to 25 μm. In addition, those having no upper layer coating film (NO. 49) and the upper coating film having a film thickness of less than 3 μm (NO. 50) are inferior in workability, adhesion, and scratch resistance, and the film thickness of the upper coating film is larger than 30μm (NO.51) is not suitable because it is costly.

(4) Relationship between bubble diameter and total film thickness

The relationship between the bubble diameter and the total film thickness is shown in Examples of Nos. 52 to 56.

The relationship between the bubble diameter Rv (μm) measured in the vertical direction on the surface of the coating film and the total film thickness T (μm) of the lower coating film and the upper coating film is satisfied by the width of any coating film having a cross section of 10 mm. When the number of bubbles of Rv ≧ 0.8T is less than 20 (NO. 54, 56), the thermal insulation performance tends to be slightly lowered. Therefore, it is preferable that 20 or more bubbles satisfying Rv ≧ 0.8T in 10 mm of an arbitrary cross section.

(5) Effect of the pigmentation of the undercoat film and the upper coat film

The effect of the pigment of the undercoat film and the upper coat film is shown in Examples of Nos. 57 to 74. The coloring pigments of the lower coating film and the upper coating film are the same (NO. 57-60), the lower coating film and the upper coating film are not containing the coloring pigment (NO. 61), and the lower coating film and the upper coating film are colored pigments. Those with the same color (NO.62, 63, 68~71) have excellent processability. In contrast, the color of the underlying coating film and the upper coating film are not the same color (NO.64~67, 72~74). The micro-discoloration is visually observed in the processing section, and there is a concern that the workability is low. Therefore, the pigment of the lower layer coating film and the upper layer coating film is preferably the same color.

(5) The effect of emissivity inside

The effect of the emissivity in the inside is shown in the examples of NO. 58 to 68, and the comparative example is shown in No. 69.

The lower the emissivity in the inside, the higher the thermal insulation performance tends to be, and the emissivity of the inside is preferably 0.50 or less. Further, it is also known that even if the emissivity inside is low, the surface having the surface outside the scope of the invention (NO. 79) has poor thermal insulation properties.

(Example 2)

The precoated metal plate of Example No. 73 and Comparative Example No. 79 of Table 6 was used as a thin TV rear panel, and the inner side was made inside, and after 2 hours on the display screen, the back panel was touched with the index finger, and the measurement was performed. Contact time. In addition, the same test was carried out in 5 people. In addition, in the same manner, the galvanized steel sheet was processed into a shape of a rear panel, and the foamed polyethylene sheet "FOAMACE (registered trademark) SN-500" manufactured by Furukawa Electric Co., Ltd. was pressed.

Any tester can be exposed to NO. 73 for more than 1 minute, but at NO. 79, the contact time is less than 5 seconds. Further, those who have attached a foamed polyethylene sheet can be in contact for 1 minute or more, but it is difficult to attach the time and also impair the appearance.

(Example 3)

The pre-coated metal sheets of No. 4 in Table 3 were coated with a lower coat by a roll coater, dried and hardened by water-cooled induction heating furnace, and then coated with a roll curtain coater. The upper coating film may be obtained by drying and hardening the water in an induction heating furnace having a hot air, and may be formed in the same manner by a different coating method. The undercoat film was applied by a roll curtain coater and dried and cured, and then a precoated metal plate was formed by coating the upper coat film with a roll curtain coater as No. 87. No. 87 was prepared under the same conditions as No. 4 except for the coating method. In addition, at the same time, the lower layer coating film and the upper layer coating film are laminated by a multi-layer simultaneous coating device called a slanted curtain curtain coater, and the temperature of the sheet reaches a plate temperature of 230 ° C in an induction heating furnace in which hot air is blown. At the same time, the laminated film was dried and hardened and then water-cooled, and the precoated metal sheet thus produced was designated as No. 88. The precoated metal sheet of No. 88 was prepared under the same conditions as those of No. 4 except that the upper coating film and the lower coating film were applied by a slanted curtain curtain coater at the same time and baked at the same time. Further, a precoated metal sheet which was formed by coating a lower coating film with a roll curtain coater and drying and hardening, and then applying an upper coating film by a roll coater was designated as No. 89. No. 89 was prepared under the same conditions as No. 4 except for the coating method.

The thermal insulation performance, workability, adhesion, stain resistance, and scratch resistance described in (Example 1) were evaluated on the prepared precoated metal sheet. No. 87 and No. 88 were identical to the evaluation results of No. 4 described in Table 3, but the thermal insulation properties of No. 89 were obtained. versus The evaluation result was Δ, which was a slightly lower result than No. 4. When the upper film is applied by a roll coater, it is presumed that the air bubbles in the lower coat film are crushed by the coated roller, so that the thermal insulation performance is not good. Further, the coatings of No. 4, 87, and 88 were beautiful in appearance, but the coating film on the top of No. 89 was a mottled pattern. It is presumed that this is also because the coating of the lower coat film is applied to the roll coater while the lower coat film is applied by the coating roller, so that the base is uneven, and the step of completing the upper coat film becomes mottled. From the results, it is also known that the overcoat film of the invention of the present application is preferably coated by a curtain coater.

Further, in Fig. 8, a photograph of a cross section of the coating film portion of the precoated metal sheet of Example No. 4 was observed with an optical microscope.

The preferred embodiments of the present invention have been described above with reference to the accompanying drawings, but the invention is not limited by the examples. It is to be understood that various modifications and changes may be made without departing from the scope of the inventions of the inventions. By.

1. . . Hot plate

2. . . Pre-coated metal sheet

3. . . Oxygen rubber

4. . . Thermocouple

5. . . Heat source

6. . . Temperature Controller

Figure 1 is a cross-sectional view of a precoated metal sheet coated with a coating layer having a larger bubble.

Fig. 2 is a cross-sectional view of a precoated metal sheet coated with a coating layer with respect to a bubble having an excessively large film thickness.

Fig. 3 is a cross-sectional view of a precoated metal sheet coated with a coating layer with respect to a bubble having a too small film thickness.

Figure 4 is a cross-sectional view of a precoated metal sheet of the present invention.

Fig. 5 is a graph showing the relationship between the bubble content of the bubble-containing layer and the film thickness t (μm) in terms of volume concentration.

Fig. 6 is an explanatory view showing an outline of an experimental apparatus for measuring the rising temperature.

Fig. 7 is an explanatory view showing the structure of a casing used for the test of the contact time and the rising temperature.

Fig. 8 is a photograph of a cross section of a coating film portion of the precoated metal sheet of Example No. 4 observed by an optical microscope.

Claims (6)

A precoated metal sheet which is a coating layer having at least two layers on one surface or both sides of a metal sheet, wherein the first coating film on the lower side of the at least two coating layers The layer-based bubble-containing layer satisfies the following formula when the bubble content of the bubble-containing layer is a volume concentration V (%) and the film thickness is t (μm): -0.1t + 57.5 ≦ V ≦ - 0.05t +92.5, and 50≦t≦350, the second coating layer on the upper side of the first coating layer is a coating layer containing a melamine-curable polyester resin or an isocyanate-curable polyester resin, and the number of the above-mentioned polyester resin The average molecular weight is 10,000 to 23,000, and the film thickness of the second coating layer is 3 to 30 μm. The precoated metal sheet according to claim 1, wherein the total film thickness of the first coating layer and the second coating layer is T (μm), and is relative to the surface of the coating film. When the diameter of the bubble measured in the vertical direction is Rv (μm), there are 20 or more bubbles satisfying Rv ≧ 0.8T in the width of 10 mm of the cross section of any coating film. The precoated metal sheet according to claim 1 or 2, wherein the first coating layer and the second coating layer each contain a pigment of the same color. The precoated metal sheet according to claim 1 or 2, wherein a temperature on a surface opposite to a surface of the metal sheet having the bubble containing layer is set at a predetermined temperature of 80 ° C or more and 200 ° C or less, The total infrared ray emission rate in the region of the measured wave number 600 to 3000 cm ^-1 is 0.50 or less. The precoated metal sheet according to the third aspect of the invention, wherein the temperature of the surface opposite to the surface of the metal sheet having the bubble containing layer is set at a predetermined temperature of 80 ° C or more and 200 ° C or less, The total infrared ray emissivity in the region of the wave number 600 to 3000 cm ^-1 is 0.50 or less. An electronic device is a precoated metal sheet according to any one of the first to fifth aspects of the invention, wherein the surface of the bubble containing layer is located on an outer surface side of the outer panel.