Coated object having a transparent clay coating and method for manufacturing the same
A transparent clay coating using saponite or hectorite with introduced metal ions addresses the swelling and color issues of smectite films, ensuring design integrity and antibacterial efficacy.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- TOKYO METROPOLITAN IND TECH RES INST
- Filing Date
- 2024-12-25
- Publication Date
- 2026-07-07
AI Technical Summary
Existing clay films formed from smectite with interlayer cations like sodium or lithium ions swell easily in water, leading to redispersion and reduced film-forming properties, and those replaced with heavy metals like silver, copper, or zinc result in reduced swelling and a grayish color, limiting their use in design and antibacterial applications.
A transparent clay coating is achieved by using saponite or hectorite with introduced silver, copper, or zinc ions between the layers, formed on a substrate, followed by an ion exchange process to maintain transparency and antibacterial properties.
The resulting transparent clay coating maintains substrate color and design aesthetics while providing antibacterial and antifungal protection, with visible light transmittance of 70% or more and effective mold prevention.
Smart Images
Figure 2026112669000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a coated article having a transparent clay film and a method for producing the coated article.
Background Art
[0002] Smectite, which is a group of clay minerals, is composed of a layered structure in which sheets made of oxides are stacked and cations between the layers. Smectite in which the cations between the layers are sodium ions or lithium ions is known to easily allow water to enter between the layers of the oxide sheets and swell in water to form a gel having thixotropic properties. It is known that a clay film can be obtained by applying and drying this gel or dispersion of clay due to its thixotropic properties (Non-Patent Document 1). However, since the obtained clay film is easily redispersed when it comes into contact with water, there is a problem in using it in an environment where it may come into contact with water.
[0003] Smectite has the ability to exchange cations between the layers. In Patent Document 1, an antibacterial silicate in which the interlayer cations of a synergistic silicate are replaced with silver, copper, and zinc has been proposed. Patent Document 1 describes that the antibacterial silicate can form a film, but the clay in which the interlayer cations are replaced with heavy metal ions has a reduced swelling property that it had when the interlayer cations were sodium or lithium, so the film-forming property is greatly reduced. Also, even if a film is obtained, the film is grayish white, which is the color of the clay, and it is difficult to say that it is excellent in design.
Prior Art Documents
Patent Documents
[0004]
Patent Document 1
Non-Patent Documents
[0005]
Non-Patent Document 1
[0006] The object of this invention is to provide a coated object having a transparent clay coating and a method for manufacturing the same. [Means for solving the problem]
[0007] The means for solving the problems of the present invention are as follows. 1. Having a transparent clay coating, The coating is characterized in that the transparent clay coating film comprises saponite or hectorite in which one or more metal ions selected from the group consisting of silver, copper, and zinc are introduced between the layers. 2. A step of forming a clay coating film by applying an aqueous coating agent containing saponite or hectorite with sodium or lithium ions as interlayer cations onto a substrate and drying it. An ion exchange step in which an aqueous solution containing one or more metal ions selected from the group consisting of silver, copper, and zinc is brought into contact with the clay coating film. A method for manufacturing a coated object having a transparent clay coating, characterized by comprising the following: [Effects of the Invention]
[0008] The present invention makes it possible to obtain coated articles having a transparent clay coating. Because the clay coating of the coated article of the present invention is transparent, it does not impair the color or pattern of the substrate and has excellent design properties. Because the coated article of the present invention has a transparent protective film (clay coating) on the substrate surface that has antibacterial and antifungal properties, it is possible to prevent mold from growing on the substrate. [Brief explanation of the drawing]
[0009] [Figure 1] X-ray diffraction patterns of the clay coating obtained in Example 1 and the coating made from saponite, its raw material. [Figure 2] X-ray diffraction patterns of the clay coating obtained in Example 5 and the coating made from hectorite, its raw material. [Figure 3] X-ray fluorescence spectra of the clay coating obtained in Example 1: (top row) overall view, (bottom left) magnified view of the area around the characteristic X-ray of sodium, (bottom right) magnified view of the area around the characteristic X-ray of copper. [Figure 4] X-ray fluorescence spectra of the clay coating obtained in Example 5: (top row) overall view, (bottom left) magnified view of the area around the characteristic X-ray of sodium, (bottom right) magnified view of the area around the characteristic X-ray of copper. [Figure 5] Transmission spectra of the clay coating (Cu, saponite) obtained in Example 1 and the substrate Tempax glass (1.1 mm). [Figure 6] Transmission spectra of the clay coating (Cu, hectorite) obtained in Example 1 and the substrate Tempax glass (1.1 mm). [Modes for carrying out the invention]
[0010] "Coated products" The coated material of the present invention has a transparent clay coating film, and this transparent clay coating film comprises saponite or hectorite in which one or more metal ions selected from the group consisting of silver, copper, and zinc are introduced between the layers. In this invention, the transparency of the clay coating means that the visible light transmittance of a laminate formed by creating a clay coating with a thickness of 5 μm to 10 μm on a Tempax glass substrate with a thickness of 1.1 mm is 70% or more from wavelength 380 nm to 780 nm. The definition of visible light transmittance is based on JIS R3126:2019. This visible light transmittance is preferably 74% or more, more preferably 78% or more, and even more preferably 82% or more.
[0011] The coated product of the present invention will be described below in accordance with its manufacturing method. "Method of manufacturing coated products" The coated article of the present invention is formed by applying an aqueous coating agent containing saponite or hectorite having sodium or lithium ions as interlayer cations onto a substrate and drying it to form a clay coating film. An ion exchange step of bringing an aqueous solution containing one or more metal ions selected from the group consisting of silver, copper, and zinc into contact with this clay coating film. It can be manufactured by a manufacturing method comprising the above steps.
[0012] ·Clay coating film formation step Saponite or hectorite having sodium or lithium ions as interlayer cations swells in water to form a transparent gel. This transparent gel exhibits thixotropy and its viscosity decreases to become liquid when shear stress is applied, so it can be applied as an aqueous coating agent. And the clay coating film obtained by coating and drying is transparent. The substrate to be coated with the aqueous coating agent is not particularly limited as long as it does not swell or dissolve in the aqueous solvent contained in the aqueous coating agent, and examples include wood, ceramic, metal, plastic, etc.
[0013] As saponite or hectorite, any of natural clay, purified natural clay, and synthetic clay can be used, but synthetic clay is preferred. Natural clay or purified natural clay tends to have lower transparency compared to when synthetic clay is used, perhaps because its purity is lower than that of synthetic clay. The cation exchange capacity (CEC) of saponite or hectorite used in the present invention is preferably 15 meq (milli-equivalent) / 100 g or more, more preferably 20 meq / 100 g or more, and even more preferably 25 meq / 100 g or more from the viewpoint of improving the swelling property during dispersion. The upper limit of the cation exchange capacity of saponite or hectorite is generally about 250 meq / 100 g or less.
[0014] The aqueous coating agent can contain additives such as dispersants, binder resins, crosslinking agents, curing agents, colorants, pigments, and ultraviolet absorbers that are used in coating agents containing clay within the range where a transparent clay coating film can be formed. However, it is preferable from the viewpoint of transparency after the ion exchange step that the aqueous coating agent of the present invention and the clay coating film before being coated, dried, and replaced with metal ions have as a main component saponite or hectorite having sodium or lithium ions as interlayer cations. Here, having as a main component means occupying 50% by weight or more of the solid content in terms of dry weight, and the ratio of saponite or hectorite having sodium or lithium ions as interlayer cations is more preferably 60% by weight or more, further preferably 70% by weight or more, still more preferably 80% by weight or more, still more preferably 90% by weight or more, still more preferably 95% by weight or more, still more preferably 98% by weight or more, and still more preferably 99% by weight or more.
[0015] · Ion exchange step Ion exchange is carried out by bringing an aqueous solution containing one or more metal ions selected from the group consisting of silver, copper, and zinc into contact with the clay coating film obtained in the above-described clay coating film forming step. Although the detailed mechanism is unknown, saponite or hectorite is not easily swollen even when brought into contact with water, and ion exchange can be carried out while maintaining the transparency without the clay coating film collapsing. The method of contact with the aqueous solution containing metal ions is not particularly limited as long as ion exchange is possible, but immersion is preferred because ion exchange can be carried out efficiently.
[0016] By the above-described method, that is, after obtaining a transparent clay coating film of saponite or hectorite having sodium or lithium ions as interlayer cations and then performing ion exchange with metal ions, an article to be coated having a transparent clay coating film provided with saponite or hectorite into which one or more metal ions selected from the group consisting of silver, copper, and zinc are introduced into the interlayer can be obtained, which is the present invention.
[0017] The transparent clay coating of the present invention mainly consists of saponite or hectorite in which one or more metal ions selected from the group consisting of silver, copper, and zinc are introduced between the layers. Because this clay coating mainly consists of metal ions and saponite or hectorite, the coated product of the present invention, when applied to a non-combustible substrate such as ceramic, can be fired. [Examples]
[0018] "Example 1" Synthetic saponite (Smecton SA, Kunimine Industries) was added at a concentration of 2 wt% to deionized water and mixed by shaking at 40°C for 4 hours to obtain a transparent gel. The obtained transparent gel was applied to a substrate (1.1 mm thick Tempax glass) using an applicator and dried at room temperature to obtain a transparent clay coating with a thickness of approximately 6 μm after drying. A glass substrate was immersed in a 5 mM copper sulfate aqueous solution, allowed to stand for 18 hours to perform ion exchange, washed by immersion in deionized water for 10 seconds, and then dried at room temperature to obtain a coated material having a transparent clay coating with copper ions introduced between the layers.
[0019] Example 2 A coated object having a transparent clay coating was obtained in the same manner as in Example 1, except that the film thickness after drying was adjusted to 3 micrometers and a 3 mM copper nitrate aqueous solution was used for ion exchange. The obtained clay coating had the same transparency as that of Example 1. "Example 3" A coated material having a transparent clay coating film with silver ions introduced between layers was obtained in the same manner as in Example 2, except that an aqueous silver nitrate solution was used. The obtained clay coating film had the same transparency as in Example 1.
[0020] "Example 4" A coated material having a transparent clay coating film with zinc ions introduced between layers was obtained in the same manner as in Example 2, except that an aqueous zinc nitrate solution was used. The obtained clay coating film had the same transparency as that of Example 1. Example 5 Except for using synthetic hectorite (Laponite RD, manufactured by BYK), a transparent clay coating with a drying thickness of approximately 6 μm and a coated product having a transparent clay coating with copper ions introduced between layers were obtained in the same manner as in Example 1.
[0021] "Comparative Example 1" The procedure was the same as in Example 1, except that synthetic stivunsite (Smecton SA, manufactured by Kunimine Industries Co., Ltd.) was used. Before substitution, a transparent clay coating was obtained, but when immersed in an aqueous copper sulfate solution, the clay coating disintegrated, and it was not possible to obtain a transparent clay coating substituted with copper ions. "Comparative Example 2" The procedure was the same as in Example 1, except that purified bentonite (Kunipia F, manufactured by Kunimine Industries Co., Ltd.) was used. The clay coating film retained its shape even when immersed in an aqueous copper sulfate solution, and a clay coating film with copper ions replaced was obtained. However, both before and after substitution, the coating film was cloudy, and a transparent clay coating film could not be obtained.
[0022] • Evaluation method (X-ray diffraction) The X-ray diffraction patterns of the clay coatings fabricated on Tempax glass substrates (1.1 mm) obtained in Examples 1 and 5 were measured using a Cu-based X-ray diffractometer (fully automated horizontal multi-purpose X-ray diffractometer SmartLab SE, Rigaku Corporation). Since the diffraction pattern of the clay coatings fluctuates with humidity, the measurement samples were dried at 105°C for more than 5 hours and then stored in a desiccator containing phosphorus pentoxide for one week. The X-ray output was 40 kV, 50 mA, and monochromatic X-rays were irradiated onto the samples. The diffraction patterns were acquired by one-dimensional scanning with a pixel detector, with a measurement range from 2° to 90°. The X-ray diffraction patterns are shown in Figures 1 and 2.
[0023] (Elemental analysis) The X-ray fluorescence spectrum of a clay coating film fabricated on a Tempax glass substrate (1.1 mm) was measured using an energy-dispersive X-ray fluorescence analyzer (XGT-9000, Horiba, Ltd.) with Rh as the radiation source. The measurement environment was vacuum, and the tube voltage was 50 kV. The fluorescence X-ray spectra are shown in Figures 3 and 4.
[0024] (transmittance) The transmittance from 380 to 780 nm was measured for the clay coating films prepared on Tempax glass substrates (1.1 mm) obtained in Examples 1 and 5 using a UV-Vis-Near-Infrared Spectrophotometer V-670 (JASCO). The visible light transmittance, as shown in JIS R3126:2019, was calculated from the obtained spectra. The visible transmission spectra are shown in Figures 5 and 6.
[0025] (Antifungal) A 1.1 mm thick Tempax glass substrate, washed with ethanol, was used. Three samples each of four types of transparent clay coatings were prepared: one without metal ions, one with copper ions introduced (obtained in Examples 2, 3, and 4), one with silver ions introduced, and one with zinc ions introduced. These samples were dried overnight at 70 degrees Celsius before being used for testing. The test conditions conformed to JIS Z 2911:2023 Mold Resistance Test Methods, Section 7, Testing of General Industrial Products (Measuring Instruments and Wood / Bamboo Products), and the products were evaluated according to the following criteria. The results are shown in Table 1. (Evaluation Criteria) 0: No mycelial growth was observed in the inoculated area of the sample or test piece. 1: The area of mycelial growth observed in the inoculated portion of the sample or test piece is: It does not exceed one-third of the total area. 2: The area of mycelial growth observed in the inoculated portion of the sample or test piece is: It accounts for more than one-third of the total area.
[0026] [Table 1]
[0027] ·result Figures 1-4 confirm that in saponite and hectorite, metal ions were substituted and copper ions were introduced into the interlayer. As shown in Figures 5 and 6, the transmittances of the clay coatings obtained in Examples 1 and 5 were 85% and 91%, respectively, indicating transparency. As shown in Table 1, the clay coatings obtained in Examples 2-4 exhibited antibacterial and antifungal properties.
Claims
1. Having a transparent clay coating, The coating is characterized in that the transparent clay coating film comprises saponite or hectorite in which one or more metal ions selected from the group consisting of silver, copper, and zinc are introduced between the layers.
2. A process of forming a clay coating film by applying an aqueous coating agent containing saponite or hectorite with sodium or lithium ions as interlayer cations onto a substrate and drying it, An ion exchange step in which an aqueous solution containing one or more metal ions selected from the group consisting of silver, copper, and zinc is brought into contact with the clay coating film. A method for manufacturing a coated object having a transparent clay coating, characterized by comprising the following: