Method for forming a multi-layer coating film for ceramic substrates, the multi-layer coating film, and a water-based paint for forming a first coating film for ceramic substrates.

Abstract

In a painting process where a multi-layer coating is formed on a ceramic substrate using a water-based paint, the drying process can be reduced, and a multi-layer coating with fewer occurrences of layer mixing or reversal can be provided. [Solution] A method for forming a multi-layer coating film for ceramic substrates, wherein the multi-layer coating film is formed using a two-coat, one-bake method, A method for forming a multilayer coating film, comprising the steps of: applying a first film-forming coating containing a water-dispersible resin and water; applying a second film-forming coating containing a water-dispersible resin and water on the first film-forming coating in a wet-on-wet manner; and drying the first and second film-forming coatings simultaneously, wherein the first film-forming coating has a storage modulus of 300 Pa or more after 90 seconds as measured under conditions (1) to (6). (1) Frequency: 10Hz (2) Distortion: 0.1% (3) Fixture: Parallel plate for drying evaluation (4) Jig diameter: 50mm (5) Distance (gap) between the sample stage and the jig: 0.5 mm (6) Sample stage temperature: 50℃

Description

Technical Field

[0001] The present invention relates to a method for forming a multilayer coating film for a ceramic substrate, a multilayer coating film for a ceramic substrate formed thereby, and an aqueous paint for forming a first coating film for a ceramic substrate. In particular, the present invention relates to a method for forming a multilayer coating film on a ceramic substrate by a 2-coat 1-bake method.

Background Art

[0002] Building materials used for the outer walls of buildings such as houses are pre-coated at a factory and then transferred to a construction site for prefabrication construction. For the outer walls of these houses, ceramic substrates are widely used. Such ceramic substrates are provided with a sealer layer on their surfaces during manufacturing for the purpose of improving water resistance, water permeability, etc., and then a multilayer coating film is often formed as a coating film for imparting a desired design and coloring. For example, a multilayer coating film having an enamel coating film and a clear coating film can be mentioned. When forming these multilayer coating films on a ceramic substrate, a step of heating and drying is generally performed for each coating of each layer. On the other hand, in automotive painting, reduction of environmental load and reduction of CO2 emissions by reducing or shortening the heating and drying process have been widely studied and put into practical use. In recent years, conversion to water-based paints has been widely studied in response to environmental concerns.

[0003] For example, Patent Document 1 is an invention related to a method for forming a topcoat film by a 2-coat 1-bake method mainly suitable for automotive painting applications. This Patent Document 1 shows that by each of the base coat composition and the clear coat composition forming a specific crosslinked structure, a coating film excellent in finish appearance, acid resistance, solvent resistance, slipperiness resistance, weather resistance, chipping resistance, and adhesion can be formed.

[0004] Furthermore, Patent Document 2 is an invention mainly relating to a 3-coat 1-bake coating for automobiles, and aims to form a multi-layer coating with good coating smoothness even when a second aqueous coating is formed without preheating after the first aqueous coating is formed. Patent Document 2 shows that a multi-layer coating with good coating smoothness can be formed when the first aqueous coating composition (A) of the first coat contains a water-dispersible polyurethane resin (a1) and a viscosity modifier (a2), the second aqueous coating composition (B) of the second coat contains a specific amount of a specific organic solvent, and the shear viscosity ηA of the uncured aqueous first coating is within a specific range when the second aqueous coating composition (B) is applied to the uncured aqueous first coating.

[0005] Furthermore, Patent Document 3 describes an invention for a method of forming a multi-layer coating for ceramic building materials, which includes a step of forming a clear coating by applying an aqueous clear coating composition wet-on-wet onto an aqueous base coating film. Patent Document 3 states that a coating film with a good coating appearance can be formed when the complex viscosity increase rate 10 minutes after the start of viscosity measurement of the aqueous base coating composition is 300 to 3,000%.

[0006] Furthermore, Patent Document 4 is an invention aimed at providing an exterior material having a clear coating film formed on its surface that is free from whitening and foaming, has a thin and uniform film thickness, and has excellent weather resistance, and relates to an exterior material having a conventional 3-coat 3-bake multilayer film.

[0007] In the aforementioned prior art patents 1 to 4, as described in patents 1 and 2, painting processes that reduce the drying step have been widely studied and put into practical use in automotive applications, resulting in reduced CO2 emissions in the painting line. However, it is difficult to directly apply automotive painting lines, which use steel plates as a base material and heat-curing paints, to ceramic substrates. Furthermore, when using paints that were conventionally painted in a 3-coat, 3-bake process as shown in patent 4 to a 2-coat, 1-bake process, or when reducing the drying step, problems arise such as deterioration of appearance due to interlayering, inversion, blistering, boiling between paint films, and deterioration of paint film performance due to poor curing. In addition, regarding the invention in patent 3, which describes a method for forming a multi-layer coating for ceramic substrates, the inventors' studies have confirmed that, because the complex viscosity increase rate 10 minutes after the start of viscosity measurement of the water-based paint composition is adjusted to a specific range, interlayering and poor film formation may occur in painting lines with short drying times between the base coating layer and the clear coating layer. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Special Publication No. 9-500819 [Patent Document 2] WO2020 / 241342 issue [Patent Document 3] Japanese Patent Publication No. 2012-240032 [Patent Document 4] Japanese Patent Publication No. 2008-246340 [Overview of the project] [Problems that the invention aims to solve]

[0009] In response to the aforementioned problems with the conventional technology, the inventors first investigated what kind of first coating (e.g., enamel coating) should be formed on a relatively thick and heavy ceramic substrate to prevent mixing with the upper coating (e.g., clear coating) and reduce the drying process. As a result, it was confirmed that forming the first coating using a paint with a high modulus of elasticity tends to reduce the likelihood of mixing even when the second coating is formed in a wet state. Next, the inventors used a rheometer to investigate the conditions under which a correlation can be obtained between the viscoelasticity of the paint for forming the first coating and the ease with which mixing occurs between layers. They found a correlation between the storage modulus of elasticity after 90 seconds of the paint for forming the first coating, such as enamel coating, and the formed first coating. They confirmed that for first coatings with a storage modulus that satisfies specific conditions, it is possible to prevent mixing between the formed first coating and the second coating-forming paint and its second coating applied on top, even when coating is formed using a so-called two-coat, one-bake method where the coating is applied wet-on-wet and then dried simultaneously.

[0010] Next, the inventors considered the conditions in the coating process of the ceramic substrate, which is the object to be coated, and conducted studies on the temperature of the rheometer's sample stage. As a result, they confirmed that, under specific conditions, particularly when the sample stage was set to 50°C, by ensuring that the storage modulus after 90 seconds of measurement was within a specific numerical range, it is possible to prevent the mixing of the first and second coatings even when coating is performed wet-on-wet, thus completing the present invention. The inventors speculate that the reason these measurement conditions are suitable is that the 50°C of the sample stage is close to the preferred surface temperature for forming the second coating, such as a clear coating, and that the storage modulus after 90 seconds is within a specific numerical range. This prevents the second coating, applied wet-on-wet on the first coating, from adhering to the surface of the first coating or the first coating even after the subsequent simultaneous drying process, thus preventing the second coating from penetrating into the first coating and preventing mixing or inversion.

[0011] Therefore, the object of the present invention is to provide a method for forming a multi-layer coating film using water-based paints on a ceramic substrate made of ceramic building materials, in a painting process such as a water-based paint factory, which reduces the drying process, reduces CO2 emissions, lowers costs and environmental burden, and reduces the occurrence of mixing or inversion in the formed multi-layer coating film.

[0012] Another object of the present invention is to provide a multilayer coating film formed by the method for forming a multilayer coating film described above, and further, to provide an aqueous paint suitable for forming a first coating film in the method for forming a multilayer coating film. [Means for solving the problem]

[0013] In other words, the gist of this invention is as follows: [1] A method for forming a multilayer coating film for a ceramic substrate, comprising forming a multilayer coating film having a first coating film and a second coating film on the upper layer of the first coating film using a two-coat, one-bake method, A process of applying a first film-forming coating containing a water-dispersible resin and water to a ceramic substrate. A step of applying a second film-forming coating containing a water-dispersible resin and water to the first film-forming coating applied in a wet-on-wet manner, and The process of simultaneously drying the first and second coating-forming paints that have been applied. Includes, A method for forming a multi-layer coating film for ceramic substrates, characterized in that the first coating-forming paint has a storage modulus of 300 Pa or more after 90 seconds, as measured using a rheometer under the following conditions (1) to (6). (1) Frequency: 10Hz (2) Distortion: 0.1% (3) Fixture: Parallel plate for drying evaluation (4) Jig diameter: 50mm (5) Distance (gap) between the sample stage and the jig: 0.5 mm (6) Sample stage temperature: 50℃ [2] The method for forming a multilayer coating film for a ceramic substrate according to [1], wherein the coating material for forming the first coating has a non-volatile content of 35% by mass or more and 60% by mass or less. [3] The method for forming a multilayer coating film for a ceramic substrate according to [1] or [2], wherein the coating material for forming the first coating has a thixotropy index [TI(23°C)] (6 rpm / 60 rpm) within the range of 3 to 7 at 23°C and a thixotropy index [TI(50°C)] (6 rpm / 60 rpm) within the range of 3 to 7 at 50°C. [4] The method for forming a multilayer coating film for a ceramic substrate according to [1] or [2], wherein the surface temperature of the ceramic substrate when the coating material for forming the first coating is applied is 40°C or higher. [5] The method for forming a multilayer coating film for a ceramic substrate according to [1] or [2], wherein the coating material for forming the second coating contains a crosslinking agent. [6] The method for forming a multilayer coating film for a ceramic substrate according to [1] or [2], including a step of forming an antifouling layer and / or a photocatalyst layer on the upper layer of the second coating. [7] A multilayer coating film for a ceramic substrate formed by a 2-coat 1-bake method on a ceramic substrate, having a first coating and a second coating on the upper layer of the first coating, wherein the first coating is a dried coating film of a coating material for forming the first coating containing a water-dispersible resin and water, the second coating is a dried coating film of a coating material for forming the second coating containing a water-dispersible resin and water and having a crosslinked structure, the coating material for forming the first coating has a non-volatile content of 35% by mass or more and 60% by mass or less, and the storage elastic modulus after 90 seconds measured under the following conditions (1) to (6) using a rheometer is 300 Pa or more. A multilayer coating film for a ceramic substrate. (1) Frequency: 10 Hz (2) Strain: 0.1% (3) Fixture: Parallel plate for dry evaluation (4) Fixture diameter: 50 mm (5) Distance (gap) between the sample stage and the fixture: 0.5 mm (6) Sample stage temperature: 50°C [8] An aqueous paint for forming a first coating on a ceramic substrate, having a multi-layer coating film with a first coating and a second coating on top of the first coating, formed by a 2-coat 1-bake method for the ceramic substrate. It contains a water-dispersible resin and water, the non-volatile content is 35% by mass or more and 60% by mass or less, and further, using a rheometer, the storage elastic modulus after 90 seconds measured under the following conditions (1) to (6) is 300 Pa or more. An aqueous paint for forming a first coating on a ceramic substrate, characterized in that. (1) Frequency: 10 Hz (2) Strain: 0.1% (3) Fixture: Parallel plate for drying evaluation (4) Fixture diameter: 50 mm (5) Distance (gap) between the sample stage and the fixture: 0.5 mm (6) Sample stage temperature: 50 °C

Advantages of the Invention

[0014] According to the present invention, in the painting for forming a multi-layer coating film on a ceramic substrate using a water-based paint with a ceramic building material as the substrate, the drying process can be reduced, the CO2 emission can be reduced, the cost and environmental load can be reduced, and a multi-layer coating film with less occurrence of mixed layers and inversions can be provided in the formed multi-layer coating film.

Brief Description of the Drawings

[0015] [Figure 1] Figure 1 is a diagram comparing a flowchart showing an embodiment of the method of the present invention (2C1B: 2-coat 1-bake) and a flowchart showing an embodiment of the method of the prior art (2C2B: 2-coat 2-bake). [Figure 2] Figure 2 is a schematic diagram of a measuring fixture, (a) is a top view, and (b) is a side view. [Figure 3] Figure 3 is a photograph showing a state where a measuring fixture and a sample are set on a rheometer.

Embodiments for Carrying Out the Invention

[0016] The following describes the details of embodiments of the present invention, but the scope of the present invention is not limited to the following embodiments, and various modifications and combinations are possible to the following embodiments without changing the gist of the present invention.

[0017] 1. Method for forming multi-layer coatings for ceramic substrates The present invention relates to a method for forming a multilayer coating film for ceramic substrates, which involves forming a multilayer coating film on a ceramic substrate using a two-coat, one-bake method, having a first coating film and a second coating film on top of the first coating film. The difference between the method of the present invention (2C1B: two coats, one bake) and the conventional method (2C2B: two coats, two bakes) is, for example, as shown in Figure 1. In the method of the present invention, the coating film is formed using a so-called two-coat, one-bake method, which does not include a step of drying only the first coating film.

[0018] The method of the present invention comprises the following steps: A process of applying a first film-forming coating containing a water-dispersible resin and water to a ceramic substrate. A step of applying a second film-forming coating containing a water-dispersible resin and water to the first film-forming coating applied in a wet-on-wet manner, and The process of simultaneously drying the first and second coating-forming paints that have been applied. This includes the above. Furthermore, the first coating paint in this case is characterized in that its storage modulus after 90 seconds, as measured using a rheometer under the following conditions (1) to (6), is 300 Pa or more. (1) Frequency: 10Hz (2) Distortion: 0.1% (3) Fixture: Parallel plate for drying evaluation (4) Jig diameter: 50mm (5) Distance (gap) between the sample stage and the jig: 0.5 mm (6) Sample stage temperature: 50℃

[0019] [Ceramic base materials] The ceramic base material (hereinafter sometimes simply referred to as "base material") is not particularly limited and can be appropriately selected and used from known materials. Examples include ceramic building materials such as gypsum, calcium silicate, cement, and wood chip cement, as well as ceramics such as pottery, glass, enamel, and fired tiles. In addition, examples include ceramic base materials and glass base materials described in JIS A 5422, JIS A 5430, etc., such as calcium silicate board, pulp cement board, slag gypsum board, magnesium carbonate board, asbestos perlite board, wood chip cement board, hard wood cement board, concrete board, and lightweight aerated concrete board.

[0020] There are no restrictions on the thickness of ceramic substrates, and typically 14mm to 80mm thick substrates are used. Unlike automotive steel sheets, which are usually around 1mm thick (at most about 2mm thick), these ceramic substrates are often relatively thick and heavy, and the painting specifications and painting lines also differ. Therefore, even when painting with the same two-coat, one-bake process, it is difficult to directly apply the painting specifications used for automotive steel sheets. On the other hand, because relatively thick and heavy ceramic substrates cool slowly once heated, this can be taken advantage of. For example, after applying a sealer, in the heating and drying process, the first film-forming paint can be applied directly to the heated substrate, and then the second film-forming paint can be applied to that, and then these can be heated and dried simultaneously to form a multi-layer coating. This has the advantage of reducing the total energy required for drying and CO2 emissions in the painting line.

[0021] Prior to the formation of the first coating described later, known pretreatments may be performed on the ceramic substrate. For example, pretreatments such as degreasing, chemical conversion, and polishing may be performed, or other post-drying coatings (such as ink decoration films) other than the first and second coatings may be formed in advance, or the substrate may be coated with a sealer to seal the pores, particularly to prevent absorption of paints containing pigments to be applied later, thereby forming a sealer layer. The sealer can be selected according to the type of substrate, and any sealer conventionally used for ceramic substrates can be used. For example, urethane-based sealers, epoxy-based sealers, and acrylic-based sealers can be used, but a water-based sealer is preferred in this embodiment because it reduces the environmental impact.

[0022] When a sealer is applied, the applied sealer can also be dried. The substrate temperature when applying the sealer is, for example, room temperature to 70°C, and the drying temperature of the sealer is, for example, room temperature to 130°C. These conditions can be appropriately changed depending on the type and composition of the sealer used. The dry film thickness of the sealer layer is preferably 5 to 100 μm. The film thickness of each coating was calculated from the solid content and application area of ​​each paint.

[0023] [Multi-layer coating] In the above method, the multilayer coating has a first coating formed on a ceramic substrate or the sealer layer, and a second coating formed on top of the first coating. The embodiment is not limited as long as it includes the steps described above or below, and thereby forms a multilayer coating on a ceramic substrate that minimizes mixing, inversion, and deterioration of coating performance, and can be implemented by appropriately changing the combination of the first coating and the second coating. For example, embodiments such as (I) to (IV) below can be given. (I) An embodiment having an enamel coating (first coating) and a clear coating (second coating) on ​​a substrate coated with a sealer. (II) An embodiment having a sealer (first coating) and an enamel coating (second coating) on ​​a substrate. (III) An embodiment having one or more coating films (coating films after drying), such as an enamel coating film and / or an ink decorative film, formed in advance on a substrate, and having a clear coating film 1 (first coating) and a clear coating film 2 (second coating) thereon. (IV) Embodiments having an enamel coating (first coating) and an enamel coating (second coating) on ​​a substrate coated with a sealer (including cases where the coating of the second coating is partial, such as a two-tone design).

[0024] Among the preferred embodiments described above, due to the purpose of use as a ceramic substrate and the fact that painting is often carried out continuously on the same line, a method can be cited as described in embodiment (I) above, in which enamel paint is applied to the substrate, followed by a clear paint, and these are dried simultaneously to form a multi-layer coating.

[0025] On the other hand, for applications and purposes such as when the sealing and enamel coating are applied on the same line, embodiment (II) above may be used from the viewpoint of reducing energy and CO2 emissions associated with drying. Similarly, for applications and purposes such as forming a first and second coating with a clear layer, such as a surface protection layer and a photocatalytic barrier layer, or laminating clear layers with different gloss and color, embodiment (III) above may be used from the viewpoint of reducing energy and CO2 emissions associated with drying by eliminating the drying process between layers. Furthermore, as described above, for applications and purposes such as forming a two-tone design, including partial coating of the second coating, using enamel paint, embodiment (IV) above may be used from the viewpoint of reducing energy and CO2 emissions associated with drying by eliminating the drying process between the enamel paint for forming the first coating and the enamel paint for forming the second coating.

[0026] Herein, in the present invention, the paint (coating film) of the above embodiment may be as commonly defined in the industry, as long as it has the features of the present invention. Enamel paint (coating film) may be a paint (coating film) that contains a coloring pigment and has opacity to cover the underlying color of the object to be coated. Clear paint (coating film) refers to a transparent paint and means a paint that does not conceal the underlying coating layer by coloring, but various extender pigments or resin beads may be appropriately added to adjust the gloss and / or design of the finished appearance. Furthermore, the ink-decorated film of embodiment (III) may be a coating film decorated with color, gloss, smoothness, pattern, and three-dimensionality by, for example, an inkjet printer.

[0027] [Paint for forming the first film] The first coating-forming paint for forming the first coating in the present invention can be appropriately changed according to the embodiment as described above, but as described above, the storage modulus after 90 seconds, measured using a rheometer under the following conditions (1) to (6), is 300 Pa or more. (1) Frequency: 10Hz (2) Distortion: 0.1% (3) Fixture: Parallel plate for drying evaluation (4) Jig diameter: 50mm (5) Distance (gap) between the sample stage and the jig: 0.5 mm (6) Sample stage temperature: 50℃

[0028] As mentioned above, our studies have shown a strong correlation between the storage modulus of a paint that forms the first film, such as enamel paint, after 90 seconds, and the formed first film. It has been found that even when a paint that forms the first film satisfying such a storage modulus is applied using a so-called two-coat, one-bake method, where the paint is applied wet-on-wet and then dried simultaneously, it is possible to prevent the formation of a mixed layer between the formed first film and the second film-forming paint applied on top of it and the second film.

[0029] The reason for measuring the storage modulus after 90 seconds is that, according to the inventors' research, this measurement timing more clearly reveals the difference in viscoelasticity between the mixed-layer paint and the unmixed-layer paint under conditions where the paint is not sufficiently dry. In other words, even if the second film is formed on top of the first film when it is more than touch-dry, it is difficult to determine the difference between paints suitable and unsuitable for the 2-coat 1-bake painting method. However, it was thought that the difference could be clearly determined when the setting time was slightly earlier than the general setting time and the paint was still wet and not yet touch-dry, so the inventors conducted their research. As a result, it was confirmed that under the measurement conditions (1) to (6) described above, a clear difference could be obtained in the storage modulus value after 90 seconds between the mixed-layer paint and the unmixed-layer paint.

[0030] The storage modulus is preferably 400 Pa or more, more preferably 500 Pa or more, even more preferably 600 Pa or more, and even more preferably 700 Pa or more. Setting the storage modulus to 300 Pa or more suppresses the formation of mixed layers when applying the second coating paint in a wet-on-wet manner. On the other hand, there is no particular upper limit to the storage modulus, but considering the ease of painting, it is, for example, 10,000 Pa or less.

[0031] A rheometer is used to measure the storage modulus. Any commercially available rheometer capable of measuring dynamic viscoelasticity is acceptable; there are no particular restrictions on the type of rheometer used.

[0032] Furthermore, the measurement conditions (1) to (6) above using a rheometer are primarily chosen because they allow for obtaining the storage modulus values ​​and ranges described above. As for the measurement fixture, a parallel plate for dry evaluation is used as shown in (3). The measurement fixtures do not need to be identical as long as they have the dimensions shown in (4) and (5) and the main shape is the same; the main shape and dimensions are as shown in Figure 2. The material of the fixture is not restricted, but it may be made of aluminum or an aluminum alloy, for example.

[0033] The measurement conditions, other than the type of jig and sample stage temperature, were derived from the results of investigating conditions that tend to cause differences in measurement values ​​between a first-coat forming paint suitable for 2-coat 1-bake painting and conventional paints that cause layer mixing or inversion under 2-coat 1-bake painting conditions.

[0034] To achieve this storage modulus, various adjustments to the formulation can be made, without limitation. These adjustments include adjusting the non-volatile content (NV) of the first coating paint, adjusting the type of pigment, its volume concentration (PVC), and its weight concentration (PWC) if pigments are included, and adjusting the components of the paint such as resins, film-forming aids, or viscosity modifiers. Of these, adjusting the non-volatile content (NV) is particularly preferable as it is an effective means of adjusting the storage modulus to the aforementioned range and also an effective means of preventing mixed layers during coating film formation using the two-coat, one-bake method. The preferred range for NV is 35% by mass or more and 60% by mass or less, more preferably 40% by mass or more and 60% by mass or less, and even more preferably over 42% by mass and 55% by mass or less. While adjusting the range of NV is one preferred means of adjusting the storage modulus, adjusting NV does not immediately achieve the storage modulus within the aforementioned range. Therefore, it is preferable in embodiments to adjust various formulations, including NV.

[0035] Here, the first coating paint contains a water-dispersible resin. Since water-dispersible resins readily form a continuous film through the fusion of resin particles after the volatilization of a medium such as water, designing the paint to increase the volatility of the medium and facilitate resin fusion is effective in achieving the objectives of the present invention. The water in this case may be contained in the water-dispersible resin, or it may be added separately as water alone or with other components. The water content can be determined, for example, by referring to the NV value mentioned above.

[0036] Such water-dispersible resins are resins that can be distributed in water and form a heterogeneous system (e.g., an emulsion or suspension). The water-dispersible resin preferably includes an emulsion resin. The emulsion resin is a water-dispersible resin that can have a high molecular weight and also exhibits excellent dispersion stability. In the first film-forming coating, the amount of water-dispersible resin in the film-forming component is preferably 30 to 95% by mass, more preferably 35 to 90% by mass, and even more preferably 40 to 80% by mass. The water-dispersible resin may be used alone or in combination of two or more types. In this invention, the term "film-forming component" refers to the components excluding volatile components such as water, organic solvents, and film-forming aids, and is the component that ultimately forms a coating film. In this invention, the components remaining after drying of the second film-forming paint (described later) are treated as the film-forming component and are synonymous with NV as described above. In the first film-forming paint, the amount of the film-forming component may be within the range of NV as described above.

[0037] The water-dispersible resin preferably includes a water-dispersible resin containing an acrylic component as a constituent (repeating unit, etc.). In this specification, "acrylic component" refers to acrylic acid, methacrylic acid and its derivatives (for example, compounds having a (meth)acryloyl group such as esters and amides of acrylic acid and methacrylic acid, nitrile acrylate, nitrile methacrylic acid, etc.). The acrylic component may be used alone or in combination of two or more types.

[0038] Water-dispersible resins containing acrylic components include not only acrylic resins but also various modified resins such as acrylicstyrene resins, acrylic silicone resins, fluorine-modified acrylic resins, fatty acid-modified acrylic resins, urethane-modified acrylic resins, and epoxy-modified acrylic resins.

[0039] The amount of acrylic component in the water-dispersible resin is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 45% by mass or more.

[0040] Furthermore, in addition to resins containing the aforementioned acrylic component or modified resins thereof, other water-dispersible resins such as water-dispersible fluororesins, water-dispersible polyester resins, and water-dispersible polyurethane resins can be used as water-dispersible resins.

[0041] Water-dispersible resins may contain non-acrylic components as constituent elements (repeating units, etc.). Non-acrylic components are components other than acrylic components and include, for example, carboxyl group-containing monomers such as styrene, fumaric acid, maleic acid, maleic anhydride, itaconic acid, crotonic acid, and vinyl versatic acid; aromatic monomers such as methylstyrene, chlorostyrene, methoxystyrene, and vinyltoluene; olefin monomers such as ethylene and propylene; vinyl monomers such as vinyl acetate and vinyl chloride; amide monomers such as maleic acid amide; alkoxysilyl group-containing monomers such as vinyltrimethoxysilane, vinyltriethoxysilane, vinylmethyldimethoxysilane, and vinylmethyldiethoxysilane; and dialkyl fumarates, allyl alcohols, vinylpyridine, and butadiene.

[0042] Furthermore, other means to achieve the objective in the first film-forming coating include adjusting the glass transition temperature (Tg) of the resin, using a water-dispersible resin having a different phase structure such as a core-shell structure, adjusting the type and amount of film-forming aids, and adjusting the type and amount of viscosity modifiers. The viscosity of the first film-forming coating is preferably 7 to 50 seconds in the Iwata Cup at 23°C, more preferably 15 to 40 seconds, and particularly preferably 25 to 35 seconds.

[0043] Of these, the film-forming aid is a temporary plasticizer that acts only during film formation, lowers the minimum film formation temperature, and is volatile after film formation is complete. Therefore, it is preferable to incorporate it as a first-layer coating. Making the volatile film-forming aid volatile during drying facilitates the fusion of the resin as described above, which improves film formation and contributes to adjusting the storage modulus. For this reason, considering the type and amount of the volatile film-forming aid is a preferred embodiment for adjusting the storage modulus.

[0044] The preferred amount of film-forming aid in the first coating is 0.01 to 10%, more preferably 0.1 to 8%, even more preferably 0.5 to 7%, and particularly preferably 1 to 5%. It is also preferable to include a film-forming aid with a relatively low boiling point, such as one with a boiling point of less than 200°C, to enhance the volatility of the film-forming aid and the initial film-forming properties of the resin, or to use two or more film-forming aids with different boiling points and SP values ​​in combination, or to use a water-soluble film-forming aid. As for the film-forming aid, any known one can be used without limitation based on the range of its boiling point, SP value, etc. Examples include propylene glycol, propylene glycol monomethyl ether (PGMME), propylene glycol monoethyl ether, propylene glycol monopropyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol monoiso-butyl ether, ethylene glycol monotert-butyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monoisopropyl ether, diethylene glycol mono-n-butyl ether, diethylene glycol monoiso-butyl ether, diethylene glycol monotert-butyl ether, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, diethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol monobutyl ether, and the like.

[0045] As mentioned above, the embodiments are not limited to the first coating, but it is preferable to use a sealer coating or an enamel coating, considering that it can adhere closely to the ceramic substrate and conceal the substrate surface, or that it can form a decorative layer. Pigments such as coloring pigments and extender pigments can be appropriately blended into the sealer coating or enamel coating. The preferred range for PWC is 5 to 70% by mass, and more preferably 10 to 60% by mass.

[0046] Furthermore, from the viewpoint of being able to coat substrates with uneven surfaces and increasing the storage modulus in the initial stages of film formation, it is preferable that the first film-forming paint has thixotropy. Thixotropy is preferably expressed in the thixotropy index (TI) shown below, where the TI value at 23°C [TI(23°C)] is in the range of 3 to 7, and more preferably in the range of 4 to 6. Also, the TI value at 50°C [TI(50°C)] is preferably in the range of 3 to 7, and more preferably in the range of 4 to 6. If the TI value is low, the paint is more likely to drip, which is thought to make mixing and inversion with the second film more likely. Generally, the fluidity of the paint increases and the TI tends to decrease at higher temperatures, but in water-based paints, due to the association state of the thickener and the cloud point of the surfactant, the TI(50°C) at higher temperatures may be higher than the TI(23°C). For this reason, in the present invention, it is preferable that the TI(50°C) is within the above range, but in a more preferred embodiment, it is preferable that both TI(23°C) and TI(50°C) are within the above range. By doing so, it becomes easier to set the storage modulus within the aforementioned range, and thus easier to achieve the objective of the present invention.

[0047] To measure the TI value, a BM-type viscometer (such as a Brookfield-type viscometer), known measurement methods, and apparatus can be used. The TI(23°C) is the value obtained by dividing the paint viscosity (mPa·s) at a temperature of 23°C and a rotor speed of 6 rpm by the paint viscosity (mPa·s) at a temperature of 23°C and a rotor speed of 60 rpm. In other words, TI(23°C) = (paint viscosity at 23°C and 6 rpm) / (paint viscosity at 23°C and 60 rpm). The TI(50°C) is defined similarly.

[0048] Any conventional coating method can be used for applying the first film-forming coating, including air spray coating, airless spray coating, curtain flow coater, and roll coater.

[0049] The amount of coating paint applied for the first film formation is, for example, preferably 2 to 300 μm, more preferably 5 to 200 μm, even more preferably 5 to 100 μm, and even more preferably 5 to 50 μm, resulting in a dry film thickness of the first film formed.

[0050] The surface temperature of the substrate when applying the first film-forming coating (hereinafter, including the surface temperature of the first film-forming coating after application in the case of applying the second film-forming coating, this may be referred to as the "pre-surface temperature") is preferably 40°C or higher, and more preferably 50°C or higher. There is no upper limit, but it is preferably 80°C or lower, and more preferably 70°C or lower. Setting the surface temperature of the substrate when applying the first film-forming coating to 40°C or higher improves the film-forming properties of the first film-forming coating and makes it easier to prevent mixing and inversion when applying the second film-forming coating. Furthermore, setting the surface temperature of the substrate when applying the first film-forming coating to 80°C or lower makes it less likely for coating abnormalities such as paint blotches and appearance defects that occur when applying water-based coatings to occur. In other words, by setting the surface temperature of the substrate within this range, the film-forming properties of the first coating are improved, and mixing with the second coating becomes less likely.

[0051] Furthermore, the first coating paint may contain various additives other than those mentioned above, as needed. These additives include dispersants, leveling agents, viscosity modifiers, defoamers, UV absorbers, light stabilizers, preservatives, and matting agents.

[0052] [Paint for forming second film] In the present invention, the second coating is also not limited, and examples include those shown in embodiments (I) to (IV) above. Of these, considering the uses and purposes of the multilayer coating of the present invention, it is preferable that the second coating be a clear coating, as it is preferable that the first coating be formed as a protective layer to protect the enamel coating, which is a preferred embodiment. Furthermore, the present invention is also preferable when forming a coating by layering different enamel layers, as in embodiment (IV). That is, it is preferable to use a clear coating or an enamel coating as the paint for forming the second coating.

[0053] The type of coating used for this second film formation is not particularly limited, but since it is a water-based coating, it contains a water-dispersible resin and water, similar to the first film formation coating. The water-dispersible resin can be the same as that used for the first film formation coating, and the addition of water and film-forming aids can also be the same.

[0054] Furthermore, while the NV value of the second coating-forming paint is not limited, it is preferably 10 to 60% by mass, and more preferably 20 to 50% by mass, from the viewpoint of excellent paintability, drying properties, and film thickness.

[0055] Furthermore, the TI value (TI(23°C) and / or TI(50°C)) of the second coating is preferably within the same range as that of the first coating, in order to prevent the coating from dripping and to prevent mixing and reversal with the first coating.

[0056] In this embodiment, it is preferable that the second film-forming coating contains a crosslinking agent. The inclusion of a crosslinking agent in the second film-forming coating improves the film strength of the second film itself, thereby improving its effectiveness as a protective layer and improving its adhesion and bonding with the first film. Furthermore, the inclusion of a crosslinking agent leads to improved film formation and also has a beneficial effect on other coating performance (water permeability resistance, freeze-thaw resistance, weather resistance, etc.) and blocking resistance.

[0057] Furthermore, the inclusion of a crosslinking agent in the second film-forming coating offers the following advantages. Specifically, since the method of the present invention employs a two-coat, one-bake system, there is no drying step after the application of the first film-forming coating. Therefore, the drying energy required for the application of the second film-forming coating is also consumed in drying the first film. Compared to the conventional two-coat, two-bake system, this is thought to make the film performance of the second film more susceptible to deterioration. For this reason, adding a crosslinking agent to the second film-forming coating improves the density of the film, thereby enhancing the coating performance (water permeability resistance, freeze-thaw resistance, weather resistance, etc.) and blocking resistance, and thus improving the performance as a multi-layer coating.

[0058] As crosslinking agents, those conventionally used in clear coatings and the like can be used without restriction. For example, silane coupling agents, melamine-based crosslinking agents, oxazoline-based crosslinking agents, acrylamide-based crosslinking agents, polyamide-based crosslinking agents, epoxy-based crosslinking agents, isocyanate-based crosslinking agents, aziridine-based crosslinking agents, titanate-based crosslinking agents, urea-based crosslinking agents, alkyl alcohol-derived urea-based crosslinking agents, hydrazide-based crosslinking agents, carbodiimide-based crosslinking agents, and polyvalent metal compounds such as zirconium compounds, zinc compounds, titanium compounds, and aluminum compounds can be used. Among these, silane coupling agents, oxazoline-based crosslinking agents, and carbodiimide-based crosslinking agents are preferred. The crosslinking-forming components may be used individually or in combination of two or more.

[0059] While there are no limitations on the silane coupling agent, epoxy group-containing silane coupling agents are preferred, for example.

[0060] Examples of oxazoline crosslinking agents include 2,2'-bis(2-oxazoline), 1,2-bis(2-oxazoline-2-yl)ethane, 1,4-bis(2-oxazoline-2-yl)butane, 1,8-bis(2-oxazoline-2-yl)butane, 1,4-bis(2-oxazoline-2-yl)cyclohexane, 1,2-bis(2-oxazoline-2-yl)benzene, 1,3-bis(2-oxazoline-2-yl)benzene, 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline.

[0061] Examples of carbodiimide-based crosslinking agents include carbodiimide compounds such as N,N'-dicyclohexylcarbodiimide, N,N'-diisopropylcarbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, N-[3-(dimethylamino)propyl]-N'-ethylcarbodiimide, N-[3-(dimethylamino)propyl]-N'-ethylcarbodiimidemethiozide, N-tert-butyl-N'-ethylcarbodiimide, N-cyclohexyl-N'-(2-morpholinoethyl)carbodiimide meso-p-toluenesulfonate, N,N'-di-tert-butylcarbodiimide, and N,N'-di-p-tolylcarbodiimide; carbodiimide compounds obtained by known condensation reactions of polyisocyanates in the presence of a carbodiimide catalyst; and carbodiimide compounds using polyisocyanates and polyalkylene oxides as raw materials.

[0062] In the coating for forming the second film, the amount of crosslinking agent added is preferably 0.1 to 15.0% by mass, and more preferably 0.5 to 10.0% by mass.

[0063] The second film-forming coating is applied wet-on-wet after the first film-forming coating has been applied. Here, the conditions for wet-on-wet application are not limited; any method that falls under the two-coat, one-bake system is acceptable. The intention is to avoid forced drying, including natural drying, but this does not exclude operations or states that can be considered as short-term natural drying before the application of the second film-forming coating. For example, this refers to a state in which a certain amount of volatile components, such as water and film-forming aids, remain in the first film-forming coating without volatilizing or drying. Specifically in this invention, if, for example, 5% by mass or more of these volatile components blended into the first film-forming coating remain without volatilizing or drying, the first film-forming coating and the second film-forming coating applied to it can be considered to be in a wet state.

[0064] The application method for the second coating is the same as for the first coating, and examples include air spray coating, airless spray coating, curtain flow coater, roll coater, etc.

[0065] The amount of coating paint applied for the second film formation is the same as that for the first film formation paint, and the dry film thickness of the formed second film is preferably in the range of 2 to 300 μm, more preferably 5 to 200 μm, even more preferably 5 to 100 μm, and even more preferably 5 to 50 μm.

[0066] When applying the second coating, the surface temperature (front plate temperature) of the applied first coating is preferably 30°C or higher, and more preferably 40°C or higher. There is no upper limit, but it is preferably 70°C or lower. Setting the front plate temperature within this range makes it easier to achieve good film formation and obtain a coated body with excellent coating performance.

[0067] Furthermore, various additives can be incorporated into the coating for forming the second film as needed. Examples of these additives include dispersants, leveling agents, viscosity modifiers, gloss modifiers, defoamers, UV absorbers, light stabilizers, preservatives, and anti-algal agents.

[0068] [Drying process] After the application of the first film-forming coating and the application of the second film-forming coating on top of it, these coated coatings are dried simultaneously. The drying conditions are not limited as long as they allow both coatings to dry and form a dried coating film, and can be set appropriately according to the composition of the coatings, the amount applied, the film thickness after drying, etc. For example, it can be done by heating at preferably 60 to 150°C, more preferably 80 to 130°C, for preferably 30 seconds to 20 minutes, more preferably 2 to 10 minutes.

[0069] Furthermore, by performing the painting and drying processes in this manner, in a ceramic substrate manufacturing line, even if the second coating is applied to the substrate in a wet-on-wet manner after the first coating is applied, without any special drying process, a multi-layer coating with a good coating appearance and performance can be formed without problems such as mixing or inversion.

[0070] [Functional Layer] In the present invention, after forming a multilayer coating having the first and second coatings as described above, a functional layer such as an antifouling layer or a photocatalytic layer can be further formed on the surface of the second coating. The antifouling layer can be an overcoat type hydrophilic layer or hydrophobic layer, or an anti-algal / anti-mold layer. These antifouling layers and photocatalytic layers can be conventionally known and used without limit.

[0071] Regarding such functional layers, if, for example, mixing or inversion occurs between the first and second coatings, or the coating performance deteriorates, in a manner that does not satisfy the objectives of the present invention, the effects of functional layers such as antifouling layers or photocatalytic layers may not be fully realized. For example, water may easily penetrate the formed multi-layer coating, or the protective layer (second coating) beneath the photocatalytic layer may become insufficient, leading to concerns about poor weather resistance. Therefore, by ensuring that the first and second coatings are configured in a manner that achieves the objectives of the present invention, the effects of any additionally added functional layers can be fully realized.

[0072] 2. Multi-layer coating film for ceramic substrates, water-based paint for forming the first coating for ceramic substrates The multilayer coating film for ceramic substrates according to the present invention is a multilayer coating film formed on a ceramic substrate by a two-coat, one-bake method, and comprises the first coating film and the second coating film, wherein the coating for forming the first coating film has a non-volatile content of 35% by mass or more and 60% by mass or less, and is characterized in that the storage modulus of elasticity after 90 seconds, measured using a rheometer under the aforementioned measurement conditions (1) to (6), is 300 Pa or more.

[0073] Furthermore, the aqueous coating for forming a first film on ceramic substrates according to the present invention is an aqueous coating for forming a first film for forming a multilayer coating film formed by such a two-coat, one-bake method, and is characterized by containing a water-dispersible resin and water, having a non-volatile content of 35% by mass or more and 60% by mass or less, and having a storage modulus of elasticity of 300 Pa or more after 90 seconds measured using a rheometer under the aforementioned measurement conditions (1) to (6).

[0074] Furthermore, these multilayer coatings and water-based paints for forming the first coating according to the present invention can all be implemented with reference to the embodiments described in "1. Method for forming multilayer coatings for ceramic substrates" above. [Examples]

[0075] The present invention will be described in detail below based on examples and comparative examples, but the present invention is not limited to these examples and comparative examples. In the examples and comparative examples, "parts" and "%" refer to mass unless otherwise specified.

[0076] Details of the substrates and paints used in the production of the painted object are shown below. <Ceramic base materials> Slate board [150mm x 70mm x 5mm, manufactured by TP Giken Co., Ltd.] <Sealer> Water-based Mighty Sealer Multi [Cationic water-based paint, product name manufactured by Dainippon Paint Co., Ltd.]

[0077] <First coating coating> • Paint 1: Water-based colored paint containing water-dispersible acrylic silicone resin, NV 52.0%, film-forming aid 0.5% by mass, thickener 1.4% by mass, viscosity 75 KU, PWC 50%, TI value 5.8 (23°C), minimum film-forming temperature (MFT) 5°C • Paint 2: Water-based colored paint containing water-dispersible acrylic silicone resin, NV 50.2%, film-forming agent 3.6% by mass, thickener 0.4% by mass, viscosity 72 KU, PWC 40%, TI value 4.7 (23°C), MFT 25°C • Paint 3: Water-based colored paint containing water-dispersible acrylic silicone resin, NV 45.2%, film-forming agent amount 4.0% by mass, thickener amount 0.8% by mass, viscosity 64 KU, PWC 42%, TI value 4.9 (23°C), MFT 12°C • Paint 4: Water-based colored paint containing water-dispersible acrylic resin, NV 44.3%, film-forming agent 5.0% by mass, thickener 0.8% by mass, viscosity 65 KU, PWC 40%, TI value 4.9 (23°C), MFT 12°C • Paint 5: Water-based colored paint containing water-dispersible acrylic silicone resin, NV 43.2%, film-forming agent 5.0% by mass, thickener 0.2% by mass, viscosity 64 KU, PWC 51%, TI value 4.7 (23°C), MFT 15°C • Paint 6: Water-based colored paint containing water-dispersible acrylic resin, NV 45.1%, film-forming agent 4.0% by mass, thickener 0.2% by mass, viscosity 64 KU, PWC 51%, TI value 2.5 (23°C), MFT 15°C

[0078] <Paint for forming second film> • Second film-forming coating A: Clear coating containing water-dispersible fluororesin, NV 37.0%, film-forming aid amount 7%, viscosity 65KU, TI value 5.4, MFT 2℃, carbodiimide-based crosslinking agent: 1% • Second film-forming coating B: Clear coating containing water-dispersible acrylic resin, NV 39.9%, film-forming aid amount 5.7%, viscosity 66 KU, TI value 3.2, MFT 26℃, alkoxysilane-based crosslinking agent: 1% • Second film-forming coating C: Clear coating containing water-dispersible acrylic silicone resin, NV 38.0%, film-forming aid amount 3.9%, viscosity 67KU, TI value 6.5, MFT 12℃, alkoxysilane-based crosslinking agent: 1% • Second film-forming coating D: Clear coating containing water-dispersible acrylic silicone resin, NV 37.0%, film-forming aid amount 3.9%, viscosity 67KU, TI value 6.5, MFT 12℃, no crosslinking agent (coated with the same formulation as coating C except for the absence of a crosslinking agent).

[0079] <Photocatalytic layer (photocatalytic coating agent)> Photocatalytic coating agent A: Teika Co., Ltd. TKC-304 Photocatalytic coating agent B: Purecoat, manufactured by Pialex Technologies Co., Ltd.

[0080] [Preparation of painted body] 1. Preparation of the sealing board Apply water-based Mighty Sealer Multi to the substrate at a rate of 100g / m². 2 The sealer board was created by painting it with an air spray and drying it at room temperature for two hours.

[0081] 2. Formation of the first coating The sealer board prepared in step 1 above was heated, and the first coating paints 1-6 described above were applied using a 6mil applicator. The board temperature before painting and the setting time are shown in Table 1.

[0082] 3. Formation of the second coating Apply the second coatings A to D described above to the first coating paint applied in step 2 above using an air spray, with a pre-painting board temperature of 40°C and a coating amount of 100g / m². 2 After painting, the first and second coatings were dried simultaneously at 120°C for 15 minutes, forming a multi-layer coating on the substrate. The paints used, their dilution ratios, coating NV, and viscosity are shown in Tables 1-3.

[0083] 4. Formation of the photocatalytic layer To the second film formed in step 3 above, the surface temperature of the second film is adjusted to 60°C, and photocatalytic coating agent A or B is applied by air spray at a rate of 20 g / m². 2 After coating the surface to a dry film thickness equivalent to 400 nm, the photocatalytic layer was formed by drying at 60°C for 3 minutes, thereby creating a coated body. In Tables 1-3, examples where "A" is written in the "Photocatalytic Coating Agent" column indicate that a photocatalytic layer was formed using photocatalytic coating agent A, while examples where "B" is written indicate that a photocatalytic layer was formed using photocatalytic coating agent B. In these examples, a photocatalytic layer is present on the outermost surface. On the other hand, in Tables 1-3, examples where "-" is written in the "Photocatalytic Coating Agent" column indicate that no photocatalytic layer was created. In these examples, the outermost layer is the second coating.

[0084] The front plate temperatures listed in Tables 1-3 were measured using an infrared non-contact thermometer (ISK-8700II, manufactured by AS ONE Corporation).

[0085] [Table 1]

[0086] [Table 2]

[0087] [Table 3]

[0088] 〔Evaluation of Paint〕 <Paint Property: Viscosity> For Paints 1 to 6 and Paints A to D, after preparation at 23°C, the viscosity was measured using an Iwata cup. The results are shown in Tables 1 to 3.

[0089] <Measurement of Storage Elastic Modulus> For the first coating-forming Paints 1 to 6, the storage elastic modulus was measured under the following conditions (1) to (6). The results are shown in Tables 1 to 3. Note that Figure 2 shows a schematic diagram and dimensions of the measurement jig, and Figure 3 shows the state where the measurement jig and the sample are set on the rheometer. For the first coating-forming Paints 1 to 6, dynamic viscoelasticity measurement was performed using a dynamic viscoelasticity apparatus MCR-301 (manufactured by Anton Paar). The sample was weighed 0.5 g and set in a disposable cup. Using a parallel plate for dry evaluation with a diameter of 50 mm for the upper measurement jig, after setting the first coating-forming paint so that the distance (gap) between the upper jig and the lower sample stage is 0.5 mm, with the measurement temperature set at 50°C, the sample was stirred at a shear rate of 1000 (1 / s) for 30 seconds at the start, and then measured at a measurement frequency of 10 Hz and a strain of 0.1% in the strain amount control mode at 10-second intervals for 30 points. The storage elastic modulus 90 seconds after the start is shown in Tables 1 to 3. (1) Frequency: 10 Hz (2) Strain: 0.1% [[ID=​​​​​​​​​​​​​In other words, TI(23°C) at a temperature of 23°C is the value obtained by dividing the paint viscosity (mPa·s) under the measurement conditions of 23°C and a rotor rotation speed of 6 rpm by the paint viscosity (mPa·s) under the measurement conditions of 23°C and a rotor rotation speed of 60 rpm, so TI(23°C) = (paint viscosity at 23°C and 6 rpm) / (paint viscosity at 23°C and 60 rpm). On the other hand, the same applies to TI(50°C) at 50°C, where TI(50°C) = (paint viscosity at 50°C and 6 rpm) / (paint viscosity at 50°C and 60 rpm).

[0091] [Evaluation of painted surfaces] The following evaluations were performed on the fabricated painted body. Furthermore, in Example 17, after forming the second film and drying it, clear paint A was diluted to a 10% dilution ratio, with a coating NV of 34% and a viscosity of 30 seconds. The paint was then applied by air spray at a pre-painting plate temperature of 40°C and a coating amount of 100 g / m². 2 After coating, the material was dried at 120°C for 15 minutes to form a third coating, after which the following evaluation tests were performed.

[0092] <Evaluation of layering properties: Surface observation> The fabricated coated surfaces were observed for their layering properties in the center and edges using a Keyence digital microscope and evaluated based on the following criteria. Edge observation was performed within 1 cm of the substrate edge. The results are shown in Tables 1-3. (Evaluation Criteria) ○: There are no mixed layers at all. △: There is a very slight presence of mixed layers. ×: Contains many mixed layers. ××: Mixed layers are present almost entirely.

[0093] <Assessment of layering: Cross-sectional observation> The fabricated coated body was cut from the center of its surface, polished, and the layered state of the cross-section was observed using a Keyence digital microscope. The number of layered locations per 2 cm was measured to evaluate the layering properties. The thickness of the first coating was also measured at this time. The results are shown in Tables 1-3. (Evaluation Criteria) ○: No mixed layers at all (0 locations of mixed layers in a 2cm area). △: There are very few mixed layers (1 to 10 mixed layer locations per 2 cm). ×: There are many mixed layers (11-40 mixed layer locations per 2cm). ××: Mixed layers are present across almost the entire surface (more than 40 mixed layer locations per 2cm).

[0094] <Appearance of the coating film> The fabricated coated bodies were visually inspected, and the appearance of the coating film on the surface of the coated bodies was evaluated according to the evaluation criteria below. The results are shown in Tables 1-3. (Evaluation Criteria) ○: Excellent appearance with no unevenness in gloss or color. △: There is a slight unevenness in the shine. ×: The entire surface has uneven gloss and color, resulting in a poor appearance.

[0095] <Water permeability> For the prepared coated surfaces, the amount of water passing through the coating over 24 hours was measured using a 75 mm funnel in accordance with JIS K 5400 8.16. These results were evaluated based on the following criteria. The results are shown in Tables 1-3. Smaller values ​​indicate better water permeability resistance. (Evaluation Criteria) ○: Water permeability < 0.5cc / day △:0.5cc / day ≦ Water permeability < 1.0cc / day ×:1.0cc / day ≦ Water permeability < 2.0cc / day

[0096] <Freeze resistance> The fabricated coated samples were placed in a freeze-thaw test machine, and a freeze-thaw test consisting of [freezing in air (-20°C) for 2 hours] - [thawing in water (+20°C) for 1 hour] was performed for 200 cycles. After removing the samples from the machine, the test plates were dried at 40°C for more than 10 hours. The appearance of the coating film and a secondary adhesion test using masking tape were then performed, and the freeze-thaw resistance was evaluated according to the following criteria. The results are shown in Tables 1-3. (Evaluation Criteria) ○: No abnormalities △: Slight cracks are visible, but no delamination was observed in the secondary adhesion test. ×: There are areas that peel off in the secondary adhesion test.

[0097] <Hot water resistance> To prevent water from entering from areas other than the painted surface, the sides and back of the test pieces were sealed with aluminum tape beforehand and then cured. Afterward, they were immersed in 50°C hot water for 60 days, and the changes in the appearance of the coating over time were visually observed and evaluated based on the following criteria. The results are shown in Tables 1-3. (Evaluation Criteria) ◎: No abnormalities for 30 days or more, up to 60 days. ○: No abnormalities such as whitening or swelling after immersion for 20 to 30 days. △: No abnormalities such as whitening or swelling after immersion for 10 to 20 days. ×: Abnormalities such as whitening or swelling occurred in less than 10 days.

[0098] <Weather resistance evaluation (SUV)> The fabricated painted body underwent a weather resistance test for 600 hours using Iwasaki Electric Co., Ltd.'s SUV-W261 under the following test conditions. (Test conditions) Irradiation wavelength range: 295-450nm, UV intensity on painted surface: 100mW / cm² 2 ±5% During illumination: Humidity 50%RH, Black panel temperature 63℃±2℃ Condensation: 95% RH or higher, Black panel temperature 40℃±2℃ Test conditions: Irradiation 6H / Condensation 2H In the weather resistance evaluation (SUV) of painted bodies after 600 hours, the gloss retention rate of the paint film surface was measured and evaluated based on the following criteria. The results are shown in Tables 1 to 3. Gloss retention rate (%) = (60° gloss value after testing) / (60° gloss value of the initial board) × 100 The gloss value was measured using a BYK micro-TRI-gloss device. (Evaluation Criteria) ○: The gloss retention rate after 600 hours is 80% or higher, and there is no unevenness in gloss on the surface of the coating. △: After 600 hours, the gloss retention rate is 50% or more but less than 80%, and there is uneven gloss on the surface of the coating. ×: The gloss retention rate after 600 hours is less than 50%, and there is uneven gloss on the surface of the coating.

[0099] <Hydrophilicity> The water contact angle of the coating surface was measured for the painted body after 600 hours of the aforementioned weather resistance evaluation (SUV), and evaluated based on the following criteria. The results are shown in Tables 1 to 3. (Evaluation Criteria) ◎: Below 20° 〇: 21°~30° △: 31°~40° ×: 41°~50°

Claims

1. A method for forming a multilayer coating film for a ceramic substrate, comprising forming a multilayer coating film having a first coating film and a second coating film on top of the first coating film using a two-coat, one-bake method, wherein the multilayer coating film is formed on the ceramic substrate using a two-coat, one-bake method, A process of applying a first film-forming coating containing a water-dispersible resin and water to a ceramic substrate. A step of applying a second film-forming coating containing a water-dispersible resin and water to the first film-forming coating applied in a wet-on-wet manner, and The process of simultaneously drying the first and second coating-forming paints that have been applied. Includes, A method for forming a multi-layer coating film for ceramic substrates, characterized in that the first coating-forming paint has a storage modulus of 300 Pa or more after 90 seconds, as measured using a rheometer under the following conditions (1) to (6). (1) Frequency: 10 Hz (2) Distortion: 0.1% (3) Fixture: Parallel plate for drying evaluation (4) Jig diameter: 50 mm (5) Distance (gap) between the sample stage and the jig: 0.5 mm (6) Sample stage temperature: 50°C

2. The method for forming a multi-layer coating film for a ceramic substrate according to claim 1, characterized in that the first coating-forming paint has a non-volatile content of 35% by mass or more and 60% by mass or less.

3. The method for forming a multilayer coating film for a ceramic substrate according to claim 1 or 2, characterized in that the first coating-forming paint has a thixotropy index [TI(23°C)] (6rpm / 60rpm) in the range of 3 to 7 at 23°C and a thixotropy index [TI(50°C)] (6rpm / 60rpm) in the range of 3 to 7 at 50°C.

4. The method for forming a multi-layer coating film for a ceramic substrate according to claim 1 or 2, characterized in that the surface temperature of the ceramic substrate when applying the first coating-forming paint is 40°C or higher.

5. The method for forming a multilayer coating film for a ceramic substrate according to claim 1 or 2, characterized in that the second coating-forming paint contains a crosslinking agent.

6. The method for forming a multi-layer coating film for ceramic substrates according to claim 1 or 2, characterized by including a step of forming an antifouling layer and / or a photocatalytic layer on the upper layer of the second coating film.

7. A multi-layer coating film for ceramic substrates, formed on a ceramic substrate using a two-coat, one-bake method, It has a first coating and a second coating on top of the first coating, The first coating is a dried coating film of a first coating-forming paint containing a water-dispersible resin and water. The aforementioned second coating is a dried coating film of a second coating-forming paint containing a water-dispersible resin and water, and has a cross-linked structure. The first coating for forming the coating is characterized in that it has a non-volatile content of 35% by mass or more and 60% by mass or less, and its storage modulus after 90 seconds, as measured using a rheometer under the following conditions (1) to (6), is 300 Pa or more, making it a multi-layer coating for ceramic substrates. (1) Frequency: 10 Hz (2) Distortion: 0.1% (3) Fixture: Parallel plate for drying evaluation (4) Jig diameter: 50 mm (5) Distance (gap) between the sample stage and the jig: 0.5 mm (6) Sample stage temperature: 50°C

8. This is a water-based paint for forming the first coating on a ceramic substrate, which forms a multi-layer coating on a ceramic substrate using a two-coat, one-bake method, having a first coating and a second coating on top of the first coating. A water-based coating for forming a first film on ceramic substrates, characterized by containing a water-dispersible resin and water, having a non-volatile content of 35% by mass or more and 60% by mass or less, and having a storage modulus of elasticity of 300 Pa or more after 90 seconds, as measured using a rheometer under the following conditions (1) to (6). (1) Frequency: 10 Hz (2) Distortion: 0.1% (3) Fixture: Parallel plate for drying evaluation (4) Jig diameter: 50 mm (5) Distance (gap) between the sample stage and the jig: 0.5 mm (6) Sample stage temperature: 50°C

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