Top plate for heating cooker

Abstract

To provide a top plate for a cooker that uses crystallized glass showing high strength and low thermal expansion as a substrate, has high durability and exhibits white color.SOLUTION: A top plate for a cooker has: a crystallized glass substrate containing Li2O-Al2O3-SiO2 as a main component and containing a transition element; a substrate color improvement layer that is provided on the lower surface of the crystallized glass substrate, has having a refractive index smaller than that of the crystallized glass substrate or equal to or larger than (the refractive index of the crystallized glass substrate+0.1), and contain one or more lightness improvement layers including voids, and a blue pigment; and a strength improvement member.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a top plate for a cooking appliance. [Background technology]

[0002] Transparent heat-resistant glass is used as the base for the top plate of cooking appliances such as electromagnetic induction cooking appliances and electric cooking appliances that use infrared rays emitted from a heating element for heating. A light-shielding colored layer is provided on the underside of the heat-resistant glass substrate, i.e., the side opposite the cooking surface of the heat-resistant glass substrate, to realize cooking appliances with colors tailored to customer needs.

[0003] Conventionally, the heat-resistant glass substrate has been made of a quartz glass substrate, a borosilicate glass substrate, a crystallized glass substrate, etc. In recent years, a crystallized glass substrate, which has high strength and a reduced coefficient of thermal expansion, has been widely used.

[0004] As a top plate using the crystallized glass as a substrate, for example, a glass top plate for an induction cooker has been proposed, which has improved design without losing the inherent strength of the substrate glass. For example, Patent Document 1 discloses a glass top plate for an induction cooker, which comprises a transparent low-expansion glass substrate, a backside of which is laminated one or more layers of matte decorative glass made of a glass composition, and one or more glossy or light-shielding layers, the linear thermal expansion coefficients of the substrate glass and the matte decorative glass being specified. Patent Document 2 also discloses a glass top plate for a cooker, which comprises a transparent low-expansion glass substrate, a backside (opposite the cooking surface) of which is laminated a highly reflective film having a thickness of 20 to 300 nm and containing one or more of TiO2, CeO2, and ZrO2 as its main component, a pearlescent layer containing a pearlescent material, and a light-shielding layer on the pearlescent layer.

[0005] Furthermore, Patent Document 3 discloses a glass top plate for a cooker that combines texture and visibility of the display, in which a light-shielding portion and a light-transmitting display portion are provided on a substrate glass, and a display body is arranged below the display portion, the substrate glass has a cooking surface that is a smooth surface and a backside surface that is a roughened surface, the light-shielding portion is provided by laminating a light-shielding layer on the backside surface of the substrate glass, and the display portion is provided by bonding a light-transmitting plate to the backside surface of the substrate glass via a transparent intermediate layer, and further, at least the exposed surface of the light-transmitting plate that does not face the transparent intermediate layer is smooth.

[0006] Patent Document 4 also discloses a top plate for a cooker with excellent aesthetics, which comprises a transparent crystallized glass substrate containing titanium oxide, a reflective film formed on the back surface of the transparent crystallized glass substrate and reflecting light in at least a portion of the wavelength range in the visible wavelength range, and a color correction film between the transparent crystallized glass substrate and the reflective film, the light transmittance of which gradually decreases as the wavelength becomes longer in the visible wavelength range, and the reflective film and the color correction film are configured so that the average light reflectance at the interface between the color correction film and the transparent crystallized glass substrate in the visible wavelength range is lower than the average light reflectance at the interface between the color correction film and the reflective film.

[0007] Patent Document 5 discloses a cooker top plate used as a top plate for a cooker equipped with an electromagnetic induction heating device, the top plate being made of a low-expansion transparent crystallized glass plate, characterized in that a decorative layer made of a dense inorganic pigment layer is formed on part or all of the cooking surface side of the low-expansion transparent crystallized glass plate, and a light-shielding layer made of a porous inorganic pigment layer is formed on part or all of the heating device side. Patent Document 6 also discloses a light-shielding glass plate characterized in that a porous light-shielding layer made of 40 to 90 wt % inorganic pigment powder and 10 to 60 wt % glass flux is provided on the surface of a glass plate made of transparent low-expansion crystallized glass, and adjacent inorganic pigment powders or the inorganic pigment powder and the glass plate are bonded together with glass made by melting and solidifying the glass flux.

[0008] Patent document 7 discloses a method for producing a glass or glass-ceramic product with a decorative layer, which comprises mixing at least one decorative pigment with a sol-gel binder, and hardening the pigment mixed with the sol-gel binder on the glass or glass-ceramic substrate of the product by annealing to form a decorative layer with a porous ceramic-like structure.

[0009] Patent Document 8 proposes a glass ceramic plate or glass plate having reinforced mechanical strength, which comprises a glass ceramic or glass substrate in the form of a plate having two substantially parallel main surfaces, and at least one layer containing at least one high-temperature resistant (co)polymer or a porous silica-based inorganic matrix fixed to at least one of the two main surfaces, wherein the thickness of the glass ceramic or glass substrate is less than 4 mm. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-16318 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-215651 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-267633 [Patent Document 4] Japanese Patent Application Laid-Open No. 2011-208820 [Patent Document 5] Japanese Patent Application Laid-Open No. 2003-168548 [Patent Document 6] Japanese Patent Application Publication No. 10-273342 [Patent Document 7] Special Publication No. 2008-536791 [Patent Document 8] Special Publication No. 2007-530405 Summary of the Invention [Problem to be solved by the invention]

[0011] Although the glass-ceramics described above have excellent strength characteristics, the glass itself has a yellowish tint. This glass-ceramics is primarily composed of Li2O-Al2O3-SiO2, with transition elements such as Ti and Zr added for crystallization. These transition elements are believed to be the cause of the yellowish tint. If the colored layer provided on the underside of the glass-ceramics substrate is dark in color, a yellowish tint in the glass-ceramics substrate is not a problem. However, customers may need white top plates for cookware. When using conventional borosilicate glass for the substrate, a white colored layer provided on the underside of the substrate could be used to achieve a white top plate for cookware. However, when using glass-ceramics for the substrate, even if the colored layer is white, the color seen through the glass-ceramics substrate is yellowish, making it difficult to achieve a white top plate for cookware.

[0012] Patent Documents 1 to 3 and Patent Document 5 aim to enhance the texture of a matte finish or metallic luster as a design feature, but do not address the issue of realizing a white cookware top plate in particular. Patent Document 4 discloses a cookware top plate with excellent aesthetics, but does not address the issue of realizing a white cookware top plate, which is particularly difficult. Furthermore, Patent Documents 6 to 8 aim to enhance the mechanical strength of cookware top plates in particular, but do not address the issue of realizing a white cookware top plate in particular.

[0013] The present invention is intended to solve the above problems, and has an object to provide a white top plate for a cooker, which uses a crystallized glass that exhibits high strength and low thermal expansion as a substrate. [Means for solving the problem]

[0014] According to one aspect of the present invention, there is provided a top plate for a cooking appliance, comprising: a crystallized glass substrate containing Li2O-Al2O3-SiO2 as a main component and containing a transition element; a substrate color improvement layer containing a blue pigment; and a strength improvement member. The brightness improvement layer is provided on the underside of the crystallized glass substrate and has a refractive index that is smaller than that of the crystallized glass substrate or greater than the refractive index of the crystallized glass substrate +0.1, and contains one or more voids. [Effects of the Invention]

[0015] According to the present invention, a highly durable and white top plate for a cooker can be provided by using a ceramic glass that exhibits high strength and low thermal expansion as a substrate. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic cross-sectional view of a sample for a preliminary experiment. [Figure 2] FIG. 2 is a schematic cross-sectional view of a top plate for a cooking device according to one embodiment of the present invention. [Figure 3] FIG. 3 is a graph showing the results of another preliminary experiment. [Figure 4]FIG. 4 is a schematic cross-sectional view of another sample for a preliminary experiment. [Figure 5] FIG. 5 is a schematic cross-sectional view of a top plate for a cooking device according to another embodiment of the present invention. [Figure 6] FIG. 6 is a schematic cross-sectional view of a top plate for a cooking device according to another embodiment of the present invention. [Figure 7] FIG. 7 is a schematic cross-sectional view of a top plate for a cooking device according to another embodiment of the present invention. [Figure 8] FIG. 8 is a schematic cross-sectional view of a top plate for a cooking device according to another embodiment of the present invention. [Figure 9] FIG. 9 is a schematic cross-sectional view of a top plate for a cooking device according to another embodiment of the present invention. [Figure 10] FIG. 10 is a schematic cross-sectional view of a top plate for a cooking device according to another embodiment of the present invention. [Figure 11] FIG. 11 is a schematic cross-sectional view of a top plate for a cooking device according to another embodiment of the present invention. [Figure 12] FIG. 12 is a graph showing the results of a preliminary experiment. [Figure 13] FIG. 13 is a schematic cross-sectional view of a top plate for a cooking device according to another embodiment of the present invention. [Figure 14] FIG. 14 is a schematic cross-sectional view of a top plate for a cooking device according to another embodiment of the present invention. [Figure 15] FIG. 15 is a schematic cross-sectional view of a top plate for a cooking device according to another embodiment of the present invention. [Figure 16] FIG. 18 is a schematic cross-sectional view of a top plate for a cooking device according to another embodiment of the present invention. [Figure 17] FIG. 17 is a schematic cross-sectional view of a top plate for a cooking device according to another embodiment of the present invention. [Figure 18] FIG. 18 is a schematic cross-sectional view of a top plate for a cooking device according to another embodiment of the present invention. [Figure 19]FIG. 19 is a schematic cross-sectional view of a top plate for a cooking device according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present inventors conducted extensive research to develop a white top plate for a cooking appliance, which has a color similar to that of a conventional borosilicate glass substrate coated with a white paint, based on the premise that the substrate is made of a high-strength, low-thermal-expansion glass-ceramic substrate composed mainly of Li2O-Al2O3-SiO2 and containing a transition element. As a result, they discovered that a top plate for a cooking appliance can be made by using a Li2O-Al2O3-SiO2-ceramic glass substrate containing a transition element, and one or more void-containing brightness improving layers provided on the underside of the glass-ceramic glass substrate, the brightness improving layers having a refractive index lower than that of the glass-ceramic glass substrate or greater than the refractive index of the glass-ceramic glass substrate +0.1, the substrate color improving layer containing a blue pigment, and a strength improving member. This led to the invention.

[0018] Hereinafter, embodiments of the present invention will be described with reference to the drawings, including the background to the invention, but the present invention is not limited to these embodiments.

[0019] To study a method for correcting the color tone from yellow to white, the inventors first prepared a preliminary experimental sample in which a colored layer 9 containing 10% by volume of blue pigment, which is the complementary color of yellow, was provided on the lower surface (rear surface) of a crystallized glass substrate 2, as shown in Figure 1, and examined the color tone. In Figure 1, reflected light 10 represents light reflected at the interface between the crystallized glass substrate 2 and the colored layer 9. While the configuration in Figure 1 suppressed the yellow tone, the reflected light 10 was weak, resulting in a lower brightness and a gray appearance.

[0020] The inventors of the present invention have further investigated ways to improve the strength of the top plate for a cooking appliance while correcting the color tone from yellow to white. As a result, as described above, the inventors have found that the top plate for a cooking appliance has the following characteristics, as shown in FIG. A crystallized glass substrate 92 mainly composed of Li2O-Al2O3-SiO2 and containing a transition element; - provided on the lower surface of the crystallized glass substrate, a substrate color improvement layer including one or more brightness enhancement layers containing voids, the refractive index of which is smaller than that of the crystallized glass substrate or greater than (the refractive index of the crystallized glass substrate + 0.1), and the substrate color improvement layer including a blue pigment (FIG. 2 shows brightness enhancement layer 93 containing hollow glass 95); It was found that it is sufficient to have a strength improving member (in FIG. 2, an adhesion improving layer 97, which will be described later) in the top plate for a cooking device. Hereinafter, the substrate color improving layer, strength improving member, and crystallized glass substrate that constitute the top plate for a cooking device according to this embodiment will first be described.

[0021] [Substrate color improvement layer] The substrate color improvement layer is provided on the lower surface of the crystallized glass substrate, and has a refractive index smaller than that of the crystallized glass substrate or equal to or greater than the refractive index of the crystallized glass substrate +0.1. The substrate color improvement layer includes one or more brightness improvement layers containing voids and also includes a blue pigment. The brightness improvement layers and the blue pigment contained in the substrate color improvement layer will now be described.

[0022] (brightness improvement layer) The substrate color improvement layer includes a brightness improvement layer. To investigate the configuration of the brightness improvement layer, the following preliminary experiment was first conducted. The brightness of Kent paper and the brightness of a crystallized glass substrate (Neoceram N-0) placed on Kent paper were measured, and the difference was calculated. Additionally, a sample was prepared in which a white layer was formed by printing a white paint (Jujo Chemical (white)) on the underside (rear surface) of the crystallized glass substrate (Neoceram N-0), and a sample was prepared in which a blue-white layer was formed by printing a paint containing a blue pigment (Jujo Chemical (white 100: blue 2)) on the underside (rear surface) of the crystallized glass substrate (Neoceram N-0). The brightness of the underside (rear surface) and front surface of each sample was measured. The results are shown in Figure 3.

[0023] Figure 3 reveals the following. Specifically, when a crystallized glass substrate (Neoceram N-0) was placed on white paper (Kent paper), the brightness was 31.4 lower than the brightness of the Kent paper alone. In contrast, when white paint was directly printed on the underside of the crystallized glass substrate, the brightness was 44.9 lower than the brightness of the white paint alone. Furthermore, when blue-white paint was directly printed on the underside of the crystallized glass substrate, the brightness was also 43.5 lower than the brightness of the blue-white paint alone. These experimental results suggest that when the crystallized glass substrate (Neoceram N-0) is placed on Kent paper, an air gap exists between the Kent paper and the crystallized glass substrate (Neoceram N-0), and this air gap appears to result in a higher brightness than when paint is directly printed on the crystallized glass substrate. These results demonstrate the effectiveness of providing an air gap, or a layer that can improve brightness in a similar manner to this air gap, between the crystallized glass substrate and the color-adjusting layer.

[0024] Furthermore, when we investigated the difference in brightness depending on whether or not the air layer was present, as shown in Figure 4(a), when a white colored layer 11A was formed by directly printing paint on a crystallized glass substrate (Neoceram N-0) 2, the refractive index of the crystallized glass substrate 2 was 1.54, and the refractive index of the white colored layer 11A was approximately 1.5 to 1.6, so that the refractive indices of the two were almost the same or close to each other. In contrast, as shown in Figure 4(b), when a crystallized glass substrate (Neoceram N-0) 2 was placed on white paper (Kent paper) 11B, a thin air layer 12 existed between the white paper (Kent paper) 11B and the crystallized glass substrate 2, and the refractive index of this air layer 12 was 1.0, which was a larger difference from the refractive index of the crystallized glass substrate 2 than in the case of Figure 4(a). The inventors discovered that providing a difference in refractive index between the crystallized glass substrate 2 and the air layer 12 so as to approach the refractive index of the air layer 12, and that a large difference in refractive index between the crystallized glass substrate 2 and the air layer 12 contributes to improving brightness, and thus came to the conclusion that a brightness-improving layer with a controlled refractive index can be provided.

[0025] As described above, the refractive index of the brightness improving layer is smaller than that of the crystallized glass substrate or equal to or greater than (the refractive index of the crystallized glass substrate + 0.1). This allows the reflectance at the interface between the crystallized glass substrate 2 and the brightness improving layer 3 to be higher than that of the reflected light in the configuration shown in FIG. 1, thereby improving brightness. As a result, a white color can be achieved, i.e., a color tone closer to that of borosilicate glass coated with a white paint. The refractive index of the brightness improving layer can be, for example, equal to or greater than (the refractive index of the crystallized glass substrate + 0.3), even greater than (the refractive index of the crystallized glass substrate + 0.4), or even greater than (the refractive index of the crystallized glass substrate + 0.5). The refractive index of the brightness improving layer is preferably smaller than that of the crystallized glass substrate. The refractive index of the brightness improving layer is smaller than that of the crystallized glass substrate, preferably closer to the refractive index of the air layer (1.0), making it easier to extract blue light that enters the crystallized glass substrate and is difficult to extract due to total reflection within the crystallized glass substrate, and thus reducing the amount of blue light that is totally reflected within the crystallized glass substrate. As a result, it is believed that the brightness of the top plate for a cooking appliance can be further improved, and the yellowish color can be suppressed to increase the whiteness.

[0026] The difference between the refractive index of the brightness improving layer and the refractive index of the crystallized glass substrate is a value expressed as an absolute value, and includes both the case where "the refractive index of the brightness improving layer is greater than the refractive index of the crystallized glass substrate" and the case where "the refractive index of the brightness improving layer is less than the refractive index of the crystallized glass substrate."

[0027] If the difference in refractive index between the brightness improving layer and the crystallized glass substrate is too large, the amount of light transmitted through the brightness improving layer is likely to be reduced. For example, if a color tone adjustment layer is provided below the brightness improving layer, less light will reach the color tone adjustment layer, and the color correction effect of the color tone adjustment layer will likely be reduced. If the color of the color tone adjustment layer is made darker in order to enhance the color correction effect of the color tone adjustment layer, the brightness tends to decrease. From these perspectives, if the light reflectance at the interface between the brightness improving layer and the color tone adjustment layer is to be kept preferably at 20% or less, it is preferable that the difference in refractive index between the brightness improving layer and the crystallized glass substrate be 1.0 or less.

[0028] In this embodiment, as described above, the refractive index of the brightness improving layer is preferably smaller than that of the crystallized glass substrate. When the refractive index of the brightness improving layer is smaller than that of the crystallized glass substrate, it is more preferably 0.1 or more smaller than that of the crystallized glass substrate, and even more preferably 0.3 or more smaller than that of the crystallized glass substrate. The refractive index of the brightness improving layer is most preferably 1.0, the same as that of the air layer.

[0029] The refractive index of the brightness enhancing layer can be determined using an Abbe refractometer or a spectroscopic ellipsometer if the brightness enhancing layer is made of a uniform material. If the brightness enhancing layer has voids as described below, the refractive index of the brightness enhancing layer can be determined as follows. That is, the refractive index n2 of the brightness enhancing layer can be calculated using the following formula from the refractive index n1 of the bulk material, such as a hollow material for forming the voids, determined using an Abbe refractometer or a spectroscopic ellipsometer, and the porosity φ1 determined by observing a cross-section of the brightness enhancing layer containing voids using an electron microscope. n2=n1×(1-φ1)

[0030] The brightness improving layer only needs to satisfy the refractive index requirement. Materials for forming the brightness improving layer include inorganic coatings containing an inorganic material such as a glass component and a solvent as the main components, and organic coatings containing an organic resin and a solvent as the main components. Examples of organic resins contained in the organic coatings include silicone resins, modified silicone resins such as acrylic-modified silicone resins, and urethane-based resins, with silicone resins being preferred from the viewpoint of ensuring heat resistance. When the brightness improving layer contains a pigment such as a blue pigment, as described below, the inorganic coating or organic coating may contain an inorganic pigment such as a blue inorganic pigment.

[0031] To achieve the desired refractive index of the brightness enhancement layer, one or more brightness enhancement layers containing voids are provided. That is, the brightness enhancement layer is formed of or includes a void-containing layer. By including a void-containing layer in the brightness enhancement layer, the refractive index of the brightness enhancement layer can be made smaller than that of the crystallized glass substrate. The presence of voids can be confirmed, for example, by observing a cross section (e.g., a scanning electron microscope (SEM) image). The void ratio, in terms of volume ratio in the brightness enhancement layer, is preferably 10% or more, thereby easily achieving the desired refractive index. The ratio is more preferably 30% or more, even more preferably 50% or more, and even more preferably more than 60%. On the other hand, from the viewpoint of ensuring the strength of the top plate for a cooking appliance, the ratio can be preferably 90% or less. From the viewpoint of ensuring the above strength, the ratio is more preferably 60% or less.

[0032] The brightness improving layer is A void-containing layer containing one or more selected from the group consisting of hollow particles, porous materials, and structures having voids between particles, or The lower surface of the crystallized glass substrate may be provided with a void-containing layer having irregularities to ensure a void. When the substrate color improvement layer includes a color tone adjustment layer, the void-containing layer may be provided with spacers to ensure a void between the crystallized glass substrate and the color tone adjustment layer, or the upper surface of the color tone adjustment layer may be provided with irregularities to ensure a void.

[0033] The void-containing layer may contain a large number of hollow particles or particles made of a porous material (porous particles) as particles having voids. The structure having voids between particles is a structure having voids between particles formed when multiple solid / hollow particles overlap. Specifically, the structure having voids between particles can be formed, for example, by using a binder to bind the contact points of particles without filling the spaces between particles when forming a brightness enhancing layer using solid particles such as glass particles, ceramic particles, or silica particles. This structure allows for the formation of a voided structure without using hollow particles. In this case, the strength of the coating film can be increased because the particles are not hollow. The average particle diameter of the solid particles is, for example, 10 nm to 100 μm. The material of the glass particles is not particularly limited, and examples include crystallized glass particles, borosilicate glass particles, and soda glass particles.

[0034] Examples of the particles having a void include layers of hollow particles such as spheres and cylinders. The hollow particles may be sealed or non-sealed. If the particles are sealed, the pressure inside the void may be atmospheric pressure or close to vacuum. Examples of the hollow particles include hollow glass, glass beads, hollow ceramics such as hollow alumina and hollow silica, and hollow polymer particles. Examples of the hollow polymer include those made of, for example, silicone resin, which has excellent heat resistance. The hollow particles are preferably transparent, and may be colorless and transparent, or colored and transparent as long as the effects of this embodiment are not impaired. Examples of the particles having a void include those having an average particle diameter of, for example, a median diameter (d50) of 10 nm to 100 μm.

[0035] The ratio of the voided particles in the brightness improving layer is not particularly limited as long as it satisfies the above-mentioned ratio of voids in the brightness improving layer, and the ratio of the voided particles in the brightness improving layer can be, for example, 10 to 99% by volume.

[0036] The hollow particles are preferably hollow glass. Commercially available hollow glass products can be used. Examples of such commercial products include Glass Bubbles manufactured by 3M, Hollow Glass manufactured by Potters-Barotini Co., Ltd., CellSpheres manufactured by Taiheiyo Cement Co., Ltd., and Silinax (registered trademark) manufactured by Nittetsu Mining Co., Ltd.

[0037] Examples of the porous material include porous particles such as porous glass particles, porous ceramic particles, etc. Instead of using porous particles, a mixed material containing a glass material or ceramic material for forming pores and, for example, a polymer material that foams at high temperatures may be applied to a crystallized glass substrate, and the polymer material may be foamed by, for example, firing to form pores.

[0038] The porous material is not limited to the material having cavities, but may be, for example, a material in which voids are formed by an aggregation of fibers of glass, ceramic, etc. An example of an aggregate of glass fibers is cotton-like glass wool.

[0039] When particles such as hollow particles are used, the void-containing layer (brightness improving layer) may contain a binder such as a glass paste containing powdered glass or a transparent ink to bond the particles together. The binder content in the brightness improving layer may be, for example, 0.1% to 90% by volume of the brightness improving layer, and may even be 0.5% to 10% by volume. Examples of binders include glass paste manufactured by Nippon Electric Glass Co., Ltd., glass frit and glass paste manufactured by AGC Inc., and heat-resistant clear ink manufactured by Teikoku Ink Mfg. Co., Ltd.

[0040] An example of a brightness enhancement layer formed using the hollow particles is a top plate 71 for a cooking device, as shown in Fig. 5, which has a structure in which a crystallized glass substrate 72 and a layer containing a large number of hollow glass particles 75 and a blue pigment are laminated as a brightness enhancement layer 73. Although not shown in Fig. 5, a light-shielding layer or the like may be formed on the lower surface of the brightness enhancement layer 73. Note that Figs. 5 to 11 and 13 to 19 are intended to explain the configuration of the brightness enhancement layer and do not show strength enhancement members.

[0041] An example of a brightness enhancement layer formed using hollow particles includes a color tone adjustment layer (described later), such as a top plate 21 for a cooking appliance, which includes a crystallized glass substrate 22, a layer containing hollow glass particles 25 as a brightness enhancement layer 23, and a white pigment layer as a color tone adjustment layer 24, as shown in FIG. 6. Instead of the hollow glass-containing layer, the brightness enhancement layer 23 may include a layer containing one or more of the porous ceramic particles, glass wool, and glass fiber. Alternatively, a layer containing one or more of the porous ceramic particles, glass wool, and glass fiber may be formed in addition to the hollow glass. Although not shown in FIG. 6, a light-shielding layer (described later), for example, may be formed on the underside of the color tone adjustment layer 24.

[0042] When the void-containing layer includes a color-adjusting layer (described later), a spacer may be provided between the crystallized glass substrate and the color-adjusting layer to form a hollow layer. For example, as shown in FIG. 7 , a top plate 31 for a cooking appliance includes a crystallized glass substrate 32, a light blue glass paint layer as a color-adjusting layer 34, and a brightness-improving layer 33 with a hollow layer 36 formed therein by providing a spacer 35 between the crystallized glass substrate 32 and the color-adjusting layer 34. The size and arrangement of the spacer are not particularly limited as long as the above-mentioned void ratio is satisfied. Examples of materials for the spacer include glass and ceramic. Transparent spacers are preferred. Although not shown in FIG. 7 , a second glass substrate (described later) may be provided on the underside of the color-adjusting layer 34, for example, to further improve mechanical strength.

[0043] When the crystallized glass substrate has a color-adjusting layer (described later), the void-containing layer may be an uneven region provided on the lower surface of the crystallized glass substrate or on the upper surface of the color-adjusting layer. For example, from the viewpoint of enhancing brightness, it is possible to sufficiently roughen the lower surface of the crystallized glass substrate 2, and use the uneven region formed by the roughening as a brightness-improving layer (void-containing layer), with the color-adjusting layer provided on the roughened surface. For example, as shown in FIG. 8 , a top plate 41 for a cooking appliance may include a crystallized glass substrate 42, a light blue glass paint layer formed as a color-adjusting layer 44, and a brightness-improving layer 43 between the crystallized glass substrate 42 and the color-adjusting layer 44, which is formed by providing unevenness on the upper surface of the color-adjusting layer 44. Although not shown in FIG. 8 , a second glass substrate (described later) may be formed on the lower surface of the color-adjusting layer 44, for example, to further improve mechanical strength.

[0044] In another embodiment, when a color tone adjustment layer described later is included, for example, as shown in Fig. 9, a top plate 51 for a cooking appliance includes a crystallized glass substrate 52 having an uneven surface, a light blue glass paint layer as a color tone adjustment layer 54, and a brightness improvement layer 53 between the crystallized glass substrate 52 and the color tone adjustment layer 54. Although not shown in Fig. 9, a second glass substrate described later or the like may be formed on the lower surface of the color tone adjustment layer 54, for example, to further improve mechanical strength.

[0045] The degree of the unevenness is not particularly limited as long as voids are formed so as to preferably satisfy the void ratio, and there are no particular restrictions on the range of Ra.

[0046] When the brightness improving layer is a void-containing layer formed by providing irregularities on the surface of the crystallized glass substrate or the color tone adjusting layer, the area of ​​the brightness improving layer refers to the range of the maximum height (Rz), which is the sum of the maximum peak height (Rp) and the maximum valley depth (Rv), in the cross section of each of the crystallized glass substrate and the color tone adjusting layer provided with irregularities.

[0047] The brightness enhancement layer preferably exhibits low thermal expansion properties similar to those of the crystallized glass substrate to which it is in contact. From these viewpoints, the brightness enhancement layer is formed of an inorganic coating material containing an inorganic material such as a glass component and a solvent as its main components, and preferably contains the glass component as its main component. It is more preferable that the brightness enhancement layer has a composition similar to that of the crystallized glass substrate, for example, Li2O-Al2O3-SiO2 as its main component, and the composition of the brightness enhancement layer can be adjusted by changing the ratio of batch raw materials such as SiO2, Al2O3, Li2O, TiO2, ZrO2, PO2O5, BaO, Na2O+KO, and As2O3 in the glass composition of the crystallized glass substrate.

[0048] Furthermore, when the brightness enhancing layer contains a large amount of hollow particles, porous particles, glass particles, etc., the binder for binding them can be a material with thermal expansion similar to that of the particles. Examples of the binder include glass-based binders containing one or more batch raw materials selected from SiO2, Al2O3, BO3, ZnO, PO5, Li2O, Na2O+KO, Bi2O3, CaO, MgO, BaO, TiO2, ZrO2, and SnO2. The oxidation numbers of the compounds are not limited to these.

[0049] In this specification, for example, the phrase "mainly composed of Li2O-Al2O3-SiO2" means (a) The percentage of these oxides in the raw materials of the glass, or (b) The ratio of the total amount of oxides calculated by converting Li, Al, and Si in the glass to each individual oxide to the glass. At least one of the above is 50% by mass or more.

[0050] When the substrate color improving layer has a color tone adjusting layer, the brightness improving layer only needs to allow the color tone adjusting layer to be visible. From the viewpoint of visually recognizing the color tone adjusting layer, the brightness improving layer is preferably transparent or translucent. The term "semitransparent" means that the visible light transmittance is 20% or more and 80% or less. In other words, the "transparency" of the brightness improving layer means that the visible light transmittance is 20% or more.

[0051] In this embodiment, it is particularly preferable that the brightness enhancing layer is a void-containing layer, contains a glass component as a main component, and is transparent or translucent.

[0052] The difference in refractive index from the crystallized glass substrate may be controlled by adjusting the thickness of the brightness improving layer. The brightness improving layer is preferably 800 nm or more in order to further enhance the brightness improving effect. The brightness improving layer is more preferably 1 μm or more in thickness. The brightness improving layer may be, for example, 1 mm or less, for example, 500 μm or less, further, for example, 100 μm or less, or further, for example, 80 μm or less. For example, the brightness improving layer may be, for example, 50 μm or less in order to further suppress peeling and cracking of the brightness improving layer.

[0053] One example of a method for forming the brightness improving layer is to apply an inorganic coating material such as a paste containing a glass composition by screen printing or the like, dry it, and then bake it at a temperature in the range of 550 to 900° C., for example, in the range of 700 to 900° C. Another example of a method for forming the brightness improving layer is to apply an organic coating material, dry it, and then bake it at a temperature in the range of 250 to 400° C. Note that, for example, when the brightness improving layer and the color tone adjusting layer are formed from an inorganic material such as an inorganic coating material, the color tone adjusting layer is baked at a temperature of, for example, 700 to 900° C. when forming the brightness improving layer after forming the brightness improving layer, and therefore the baking step when forming the brightness improving layer can be omitted.

[0054] When a void-containing layer is formed as the brightness improving layer, the following methods can be used to form the void-containing layer: When particles such as hollow particles are used to form the void-containing layer, one example is to apply a paste containing the hollow particles and a binder by screen printing or the like, dry it, and then bake it at the above-mentioned temperature depending on the material used when forming the brightness improving layer or the color tone adjusting layer.

[0055] When a foaming material is used to form a porous layer, a mixed material containing a glass material, a ceramic material, and, for example, a polymer material that foams at high temperatures can be applied to a crystallized glass substrate by screen printing or the like, dried, and then baked at the temperature specified above depending on the material used when forming the brightness enhancement layer or the color tone adjustment layer, thereby foaming the polymer material and forming a porous brightness enhancement layer.

[0056] When spacers are used to form the void-containing layer, spacers may be arranged at desired intervals on a crystallized glass substrate via an adhesive, and a color tone adjusting layer may be further laminated via an adhesive to provide a hollow layer as the brightness improving layer.

[0057] When providing irregularities on the underside of the crystallized glass, the underside of the crystallized glass can be roughened. The purpose of providing irregularities on the underside of the crystallized glass can be to improve reflectivity, form a void-containing layer, etc. When the purpose is to improve the reflectivity, the roughening can be carried out, for example, so that the surface roughness Ra of the underside of the crystallized glass substrate is 0.1 μm or more. Note that the greater the surface roughness Ra, the better the brightness. However, from the viewpoint of increasing reflectivity, making Ra at a wavelength level, i.e., a submicron size, and maintaining the durability of the crystallized glass substrate against impact, it is preferable that the surface roughness Ra is small, for example, 10 μm or less. On the other hand, when the purpose is to form a void-containing layer, as mentioned above, it is preferable that voids are formed so as to satisfy the void ratio, and the range of Ra is not particularly limited.

[0058] The surface roughening treatment methods are divided into physical methods and chemical methods. Physical methods include sandblasting using abrasives such as silicon carbide (SiC), alumina (Al2O3), zirconia (ZrO2), and diamond (C), and free abrasive polishing using an abrasive. Chemical methods include immersion in an etching solution containing hydrofluoric acid.

[0059] When providing the unevenness on the upper surface of the color tone adjusting layer, the method for doing so is not particularly limited. For example, as described later, a second glass substrate is used to ensure mechanical strength, unevenness is provided on the second glass substrate, and the color tone adjusting layer is formed along the unevenness to form the color tone adjusting layer having unevenness.

[0060] The substrate color improving layer may be formed of the brightness improving layer, i.e., the substrate color improving layer may be formed of only the brightness improving layer without having a color tone adjusting layer (to be described later).

[0061] (Blue pigment contained in the substrate color improvement layer) The substrate color improving layer contains a blue pigment. The top plate for a cooking appliance of this embodiment is not limited to a specific embodiment as long as the substrate color improving layer has a brightness improving layer with a controlled refractive index as described above and contains a blue pigment. Therefore, the blue pigment may be contained in the brightness improving layer constituting the substrate color improving layer, or in a layer other than the brightness improving layer constituting the substrate color improving layer. When a color tone adjusting layer (described later) is included as a layer other than the brightness improving layer, the blue pigment may be contained only in the brightness improving layer, and the color tone adjusting layer may contain a pigment other than the blue pigment, such as a white pigment. Alternatively, the blue pigment may be contained only in the color tone adjusting layer, and the brightness improving layer may contain a pigment other than the blue pigment, such as a white pigment. Alternatively, the blue pigment may be contained in both the brightness improving layer and the color tone adjusting layer. When the blue pigment is contained in the brightness improving layer, the blue pigment may be contained within a range that maintains the transparency of the brightness improving layer. When the blue pigment is contained in the brightness improving layer, the substrate color improving layer may be formed solely by the brightness improving layer.

[0062] Examples of the blue pigment include blue inorganic pigments, such as Prussian blue (ferric ferrocyanide), ultramarine, cobalt-based inorganic pigments (Co-Al, Co-Al-Si, Co-Zn-Si), V-Zr-Si inorganic pigments (turquoise blue), and manganese-based inorganic pigments. Examples of the white pigment include white inorganic pigments such as titanium oxide, cerium oxide, zinc oxide, and barium sulfate. Commercially available blue and white pigments include Hicolor (manufactured by Mitsuboshi), XGL-HF Screen Ink (manufactured by Teikoku Ink Mfg. Co., Ltd.), and the Decorative Glass Color HZ Series (manufactured by Okuno Chemical Industries Co., Ltd.). Furthermore, to adjust the color tone, a red inorganic pigment such as iron oxide, iron hydroxide, or iron titanate may be included as a red pigment. Coloring pigments can be mixed in any ratio to obtain the desired color tone. The pigments are not limited to those listed here.

[0063] The layer not containing a blue pigment may contain, for example, a white pigment. In this case, the layer may contain only a white pigment, or may contain a white pigment and a pigment other than white.

[0064] [Strength improving member] The cooking appliance top plate according to this embodiment further includes a strength-enhancing member. The strength-enhancing member is a necessary member for enhancing the strength and durability of the cooking appliance top plate. Strength enhancement includes improving the adhesion between the crystallized glass substrate and the substrate color-improving layer, between adjacent layers, or improving the coating strength of the substrate color-improving layer, such as the brightness-improving layer. The provision of the strength-enhancing member enhances the strength of each layer constituting the cooking appliance top plate and the adhesion between each layer, thereby improving the overall strength and durability of the cooking appliance top plate. Furthermore, the improved strength of each layer and the improved adhesion between each layer make the cooking appliance top plate less likely to peel even when subjected to vibration or external impact. Even when there is a difference in the thermal expansion coefficient between the crystallized glass substrate and the brightness-improving layer, the high adhesion between each layer makes peeling less likely, resulting in improved durability and heat resistance of the cooking appliance top plate. Furthermore, when a thicker brightness enhancing layer is formed and heat is applied, thermal stress increases, which makes it more likely that the brightness enhancing layer will peel off from the crystallized glass substrate or other layers. However, by providing the strength enhancing member, such peeling is less likely to occur. Therefore, by forming a thicker brightness enhancing layer, the brightness of the top plate for a cooking appliance can be further improved, and the color tone can be more easily adjusted.

[0065] The strength-improving member may be any member capable of increasing the strength and durability of the top plate for a cooking appliance. Examples of such a member include providing an adhesion-improving layer between the crystallized glass substrate and the substrate color-improving layer constituting the top plate for a cooking appliance, or between adjacent layers, or including a filler in any of the layers constituting the top plate for a cooking appliance. Below, we will explain the embodiments in which an adhesion-improving layer is provided as the strength-improving member and the embodiments in which a filler is provided as the strength-improving member.

[0066] [Adhesion improving layer] An adhesion improving layer may be provided as the strength improving member between the crystallized glass substrate and the substrate color improving layer, and / or a plurality of the brightness improving layers may be provided, and an adhesion improving layer may be provided as the strength improving member between one brightness improving layer and another adjacent brightness improving layer.

[0067] The adhesion-improving layer is preferably one or more thin glass layers or a void-containing layer having a different porosity and / or material composition from the brightness-improving layer. Examples of materials constituting the adhesion-improving layer include glass materials whose main component is Li2O-Al2O3-SiO2. Alternatively, when the brightness-improving layer is formed of hollow glass, glass beads, or a porous material, the adhesion-improving layer can be made of a material with a thermal expansion coefficient close to that of the hollow glass or other material constituting the brightness-improving layer. Therefore, when the hollow glass contained in the brightness-improving layer is, for example, a borosilicate glass, the adhesion-improving layer may be made of a material with a thermal expansion coefficient greater than that of Li2O-Al2O3-SiO2. Filler materials may also be used. The thickness of the adhesion-improving layer is preferably equal to or thinner than that of the brightness-improving layer. The adhesion-improving layer may contain additives such as organic binders, such as silicone.

[0068] When forming a void-containing layer as an adhesion improving layer, the void ratio of the void-containing layer is preferably between the void ratio of one layer or substrate in contact with the adhesion improving layer and the void ratio of the other layer or substrate.For example, when forming a void-containing layer as an adhesion improving layer between a crystallized glass substrate and a void-containing brightness improving layer, by forming a void-containing layer with a void ratio smaller than the void ratio of the brightness improving layer, the change in void ratio can be alleviated, and the peeling between the substrate and the brightness improving layer due to the difference in thermal expansion coefficient can be reduced, and the film strength can be increased.On the other hand, when the thermal expansion difference between the crystallized glass substrate and the particles or binder used in the brightness improving layer is large, it is also possible to form a void-containing layer with a void ratio larger than that of the brightness improving layer as an adhesion improving layer to alleviate stress and increase strength.

[0069] Methods for forming the adhesion improving layer include applying a paste containing the above-mentioned glass or organic binder by screen printing or the like, drying it, and then baking it, or drying it and then baking it together with the materials that form the brightness improving layer or color tone adjusting layer when forming those layers.

[0070] Examples of a top plate for a cooking appliance having an adhesion improving layer include the top plate for a cooking appliance 91A shown in Fig. 2 and the top plate for a cooking appliance shown in Fig. 10. The adhesion improving layer 97 of the top plate for a cooking appliance shown in Fig. 2 is a filled layer of thin film glass or the like, whereas the adhesion improving layer 97B of the top plate for a cooking appliance 91B shown in Fig. 10 is a layer having hollow glass 5. As shown in Fig. 10, the inclusion of hollow glass in the adhesion improving layer is preferable because it improves the adhesion between the crystallized glass substrate and the lightness improving layer, increases the strength of the entire top plate for a cooking appliance, and makes it possible to easily achieve whitening of the top plate for a cooking appliance.

[0071] When a light-shielding layer (described later) is provided on the underside of the substrate color improving layer, an adhesion improving layer may be provided between the substrate color improving layer and the light-shielding layer as a strength improving member in order to ensure sufficient adhesion between the substrate color improving layer and the light-shielding layer.

[0072] [Filler] The substrate color improving layer may contain a filler as the strength improving member. The filler may be contained in one or more of the brightness improving layer constituting the substrate color improving layer and a layer other than the brightness improving layer, such as a color tone adjusting layer constituting the substrate color improving layer. It is preferable that the brightness improving layer contains a filler as the strength improving member.

[0073] The material, shape, size and content of the filler are not particularly limited and can be appropriately determined depending on the desired strength. The filler is preferably composed of one or more selected from the group consisting of metals, metal oxides, ceramics, metal salts, glass, silica, mica, talc, clay, zeolite, organic materials, composites thereof, and materials having at least one of coupling agents, active groups, reactive groups, organic materials and metal oxides bonded, adsorbed or vapor-deposited on the surface thereof. Examples of fillers that can be used include those made of: · Metals such as aluminum and titanium, Metal oxides such as alumina, titania, zirconia, and zinc oxide Ceramics containing the above metal oxides such as alumina Metal salts such as calcium carbonate and barium sulfate, Glass, silica, mica, talc, clay, zeolite, organic materials, and their composites, and Materials having at least one of coupling agents, active groups, reactive groups, organic substances, and metal oxides bonded, adsorbed, or deposited on their surfaces The number of particles may be one or more selected from the group consisting of: The same material may be used in combination with particles having different shapes and sizes such as particle diameters.

[0074] The shape of the filler may be particulate, angular, rod-like, branch-like, needle-like, thin plate-like, scale-like, fibrous, tetrapod-like, or porous. Hollow particles are also acceptable as long as strength can be ensured. The size of the filler is not particularly limited and may be determined appropriately taking into consideration the target layer strength. The average particle size of the filler may be, for example, 10 nm to 100 μm. More preferably, it may be in the range of 100 nm to 50 μm. When the length of the long side and the short side of a fibrous or other shape differ significantly, it is sufficient that the short side is of the above-mentioned size. The content of the filler in the substrate color improvement layer, particularly in the brightness improvement layer, may be in the range of 0 to 50% by volume, more preferably 0 to 30% by volume.

[0075] An example of a top plate for a cooking appliance containing a filler in the substrate color improving layer is shown in Figure 11. The top plate 101 for a cooking appliance in Figure 11 is an example in which a filler 108 is contained in a brightness improving layer 103, which is a substrate color improving layer. As shown in Figure 11, by containing a filler in the substrate color improving layer, the strength of the substrate color improving layer (brightness improving layer in the case of Figure 11) can be increased.

[0076] The filler may be contained in a color tone adjusting layer that can be provided as a substrate color improving layer, in addition to being contained in the brightness improving layer as shown in Figure 11. In this case, the filler may be contained in at least one of the color tone adjusting layer and the brightness improving layer.

[0077] The filler and the luster material and / or reflector described below may be contained together in one layer. The luster material and / or reflector may also serve as the filler. That is, the same material and shape may be used to adjust the color tone and to improve the strength of the layer.

[0078] (tone adjustment layer) The substrate color improving layer may include a color tone adjustment layer as a layer other than the brightness improving layer. When the brightness improving layer does not contain a blue pigment, the color tone adjustment layer may contain a blue pigment. When the brightness improving layer contains a blue pigment, the color tone adjustment layer may or may not contain a blue pigment, regardless of whether the color tone adjustment layer contains a blue pigment. That is, the substrate color improving layer may have a color tone adjustment layer containing a white pigment or a white pigment and the blue pigment, provided below the brightness improving layer. And / or the substrate color improving layer may have a color tone adjustment layer containing a white pigment or a white pigment and the blue pigment, provided between the crystallized glass substrate and the brightness improving layer.

[0079] The designer can freely select the type, amount, and color tone of the pigment. Methods for adjusting the color tone include selecting the type of blue pigment, as well as controlling the ratio of each pigment in a mixed pigment containing a blue pigment and a white pigment. For example, the following pigment-containing paints can be used. In addition to pigments, it is also possible to include hollow glass particles, void-containing particles such as porous materials, glass particles, silica particles, ceramic particles, etc.

[0080] Examples of the paint for forming the color tone adjusting layer include inorganic paints containing an inorganic material such as a glass component, a solvent, and the inorganic pigment as the main components, and organic paints containing an organic resin, a solvent, and the inorganic pigment as the main components. Examples of the organic resin contained in the organic paint include silicone resins, modified silicone resins such as acrylic-modified silicone resins, and urethane-based resins, and silicone resins are preferred from the viewpoint of ensuring heat resistance.

[0081] When the color-adjusting layer is formed using an inorganic paint, it may contain a glass component in addition to the pigment. The color-adjusting layer preferably exhibits low thermal expansion properties similar to those of a crystallized glass substrate. From this perspective, the color-adjusting layer is preferably formed from an inorganic paint containing an inorganic material, such as a glass component, and a solvent as its main components, and the glass component is preferred as its main component. It is more preferable that the color-adjusting layer have a composition similar to that of a crystallized glass substrate. For example, the composition of the color-adjusting layer can be adjusted by changing the ratio of batch raw materials, such as SiO2, Al2O3, Li2O, TiO2, ZrO2, PO5, BaO, Na2O+K2O, and As2O3, in the glass composition of the crystallized glass substrate. Alternatively, when the lightness-enhancing layer is formed from hollow glass, glass beads, or a porous material, the material constituting the color-adjusting layer can be one with a thermal expansion coefficient similar to that of the hollow glass or other material constituting the lightness-enhancing layer. Further, as a material constituting the color tone adjustment layer, it is also possible to use a glass-based binder containing one or more of, for example, SiO2, Al2O3, B2O3, ZnO, P2O5, Li2O, Na2O+K2O, Bi2O3, CaO, MgO, BaO, TiO2, ZrO2, Sn2O, etc.

[0082] The thickness of the color tone adjustment layer can be, for example, 0.1 μm or more to sufficiently eliminate the yellowish color of the crystallized glass substrate, and can be, for example, 100 μm or less, for example, 50 μm or less, and from the viewpoint of further suppressing peeling and cracking of the color tone adjustment layer, the thickness of the color tone adjustment layer can be, for example, 10 μm or less.

[0083] As an example of a method for forming the color tone adjustment layer, when an inorganic paint is used to form the color tone adjustment layer, the pigment, glass component, and a binder containing an ethyl cellulose resin or a nitrocellulose resin are mixed to form a paste, which is then applied by screen printing to the underside of the brightness improvement layer, i.e., the surface of the brightness improvement layer opposite the crystallized glass substrate side, dried, and then baked at 550 to 900°C. As another example of a method for forming the color tone adjustment layer, when an organic paint is applied, the paint can be dried and then baked at a temperature in the range of 250 to 400°C. When the color tone adjustment layer is formed together with the brightness improvement layer, a method can be used in which the brightness improvement layer is applied by screen printing or the like and dried, and then the color tone adjustment layer is applied by screen printing or the like and dried, and then baked at the above-mentioned temperature.

[0084] The present inventors conducted the following preliminary experiment with the aim of realizing the color tone obtained by applying white paint to a conventional borosilicate glass substrate by adjusting the color tone with the color tone adjustment layer when a color tone adjustment layer is provided.

[0085] To simulate the color-adjusting layer, white paper (Kent paper: Konayuki 210, manufactured by JITSUTA Corporation) and blue-white printed paper were prepared by printing the same white paper with a paint obtained by blending pigments in the ratios shown in Table 1. Then, a crystallized glass substrate (Neoceram N-0, manufactured by Nippon Electric Glass Co., Ltd.) was placed on each of the white paper and each of the blue-white printed papers, and the color of the front side of the crystallized glass substrate was measured. The color measurement was performed using a spectrophotometer (CM-2600d, manufactured by Konica Minolta) to measure the color tone of the obtained sample as a Lab color system value. The color difference between the target borosilicate glass substrate and a substrate with the underside printed with white ink (hereinafter referred to as a (borosilicate glass + white ink) substrate) was also measured. The results are shown in Table 1.

[0086] [Table 1]

[0087] Furthermore, based on the results in Table 1, Figure 12 shows a graph of the color difference with the (borosilicate glass + white ink) substrate. In Figure 12, lightness is represented in the direction perpendicular to the paper. The black squares in Figure 12 indicate the value for the (borosilicate glass + white ink) substrate, with the closer the value to this black square, the better. From the results shown in Figure 12, the color tone of the crystallized glass substrate + Kent paper (◆ in Figure 12) in Table 1 (No. 1) was significantly different from the target black square. In contrast, when blue-white printing paper was placed on the underside of the crystallized glass substrate (Neoceram N-0) as shown in Nos. 2 to 4 in Table 1, the result was sufficiently close to the target black square. These results demonstrate that a slightly bluer color scheme, i.e., a color scheme positioned downward in Figure 12, makes the image appear whiter.

[0088] In one embodiment of the present invention, a brightness improving layer having a refractive index lower than that of the crystallized glass substrate is preferably provided, thereby reducing the proportion of blue pigment in the color tone adjusting layer, for example, to 5% or less in terms of volume ratio in the color tone adjusting layer, thereby more easily realizing improvement in brightness and suppression of yellowness.

[0089] In another embodiment of the present invention, when realizing a highly reflective top plate for a cooking appliance, for example, when the reflectance at the interface between the crystallized glass substrate and the brightness improving layer is 70% or higher, the amount of light reaching the color-adjusting layer is as low as 30% or less of the incident light. In such a case, it is preferable to use a deep blue color for the color-adjusting layer in order to completely eliminate the yellowish color of the crystallized glass and achieve a color closer to white. For example, it is possible to select a blue color with a b value of less than -1 in the Lab value of the color-adjusting layer alone, or to reduce the proportion of white pigment mixed with the blue pigment.

[0090] 13, an embodiment having a color tone adjustment layer includes a top plate 61 for a cooking appliance having a laminated structure including a crystallized glass substrate 62, a layer containing hollow glass 65 and a blue pigment as a brightness improvement layer 63, and a white organic paint layer formed as a color tone adjustment layer 64. Although not shown in FIG. 13, a light-shielding layer, for example, may be formed on the lower surface of the color tone adjustment layer 64.

[0091] In addition to being formed below the brightness improving layer, the color tone adjusting layer may be provided between the crystallized glass substrate and the brightness improving layer as described above. In this case, the color tone adjusting layer may be provided in multiple locations, including between the crystallized glass substrate and the brightness improving layer and below the brightness improving layer.

[0092] The color tone adjustment layer can also function as an adhesion improving layer. For example, when a color tone adjustment layer is provided between a crystallized glass substrate and a brightness improving layer, the color tone adjustment layer can function as an adhesion improving layer between the crystallized glass substrate and the brightness improving layer. When a light-shielding layer is provided below the brightness improving layer and a color tone adjustment layer is provided between the lightness improving layer and the light-shielding layer, the color tone adjustment layer can function as an adhesion improving layer between the lightness improving layer and the light-shielding layer.

[0093] [Shining material / reflective material] One or more of the brightness improving layer (except when composed only of voids) and the adhesion improving layer serving as a strength improving member may contain one or more of a reflective material and a lustrous material. And / or, the substrate color improving layer may have a color tone adjusting layer, which may contain one or more of a reflective material and a lustrous material. FIG. 14 shows a case where the brightness improving layer 3 contains one or more of a reflective material and a lustrous material (also referred to as a "lustrous material and / or reflective material") 5. FIG. 15 is a schematic cross-sectional view of a top plate 111A for a cooking device in which a color tone adjusting layer 114 below the brightness improving layer 113 contains a lustrous material and / or a reflective material 5. FIG. 16 is a schematic cross-sectional view of a top plate 111B for a cooking device in which a color tone adjusting layer 114 located between the crystallized glass substrate 112 and the brightness improving layer 113 contains a lustrous material and / or a reflective material 5. These figures are intended to illustrate the location of the lustrous material and / or reflective material, and do not show the strength improving member. The glittering material and / or the reflecting material may also serve as a strength improving member.

[0094] The lustrous material and / or reflective material may be one or more selected from the group consisting of mica, silica (silicon dioxide), metal oxides such as alumina, titania, zirconia, and zinc oxide, aluminum, glass, their surfaces coated with metals or metal oxides, and polymer films on which metals or metal compounds have been vacuum-deposited and then powdered. Among these, one or more selected from the group consisting of mica, silica, the metal oxides, aluminum flakes, glass particles, glass flakes, glass flakes with a metal-deposited layer, and mica with a metal oxide layer are preferred. The glass particles may be, for example, self-reflective glass beads.

[0095] The shape of the luminous material and / or reflecting material 5 may be spherical, angular, rod-like, branch-like, or flake-like. The size of the luminous material and / or reflecting material 5 is not particularly limited and may be determined appropriately taking into consideration the target reflectance. The size of the luminous material and / or reflecting material 5 may be, for example, an average particle size of 0.1 μm to 100 μm. The proportion of the luminous material and / or reflecting material 5 in the brightness improving layer 3 is also not particularly limited and may be determined appropriately taking into consideration the target reflectance.

[0096] As the lustrous material and / or reflecting material 5, it is preferable to add a small amount of, for example, pearl mica, which is made by coating the surface of mica or the like with a metal or metal oxide, within a range that allows the transparency of the brightness enhancing layer 3 to be maintained, because this can enhance the reflective properties while also assisting in adjusting the color tone.

[0097] [Ceramic glass substrate] In the present invention, a crystallized glass substrate containing Li2O-Al2O3-SiO2 as the main component and a transition element is used. The glass constituting the substrate preferably contains one or more low-expansion crystals, such as β-quartz, β-spodumene, aluminum titanate, and cordierite. Furthermore, a glass containing β-quartz solid solution or β-spodumene solid solution as the main crystal is more preferable.

[0098] In the crystallized glass, the β-quartz solid solution crystals exhibiting negative expansion characteristics and the remaining glass layer exhibiting positive expansion characteristics cancel each other out, so that the thermal expansion coefficient of the entire crystallized glass can be kept low. Note that the low thermal expansion property is, for example, a value of the absolute value of the thermal expansion coefficient of 30 × 10 -7 / °C or less.

[0099] The crystallized glass substrate may have a thickness of, for example, 3 mm to 10 mm, and has a refractive index of, for example, about 1.4 to 2.0.

[0100] [Roughening the lower surface of the crystallized glass substrate] In one embodiment of the present invention, the underside of the crystallized glass substrate, i.e., the surface opposite the cooking side of the crystallized glass substrate, is roughened to cause diffuse reflection of light, thereby increasing reflectivity and, as a result, brightness.

[0101] When the purpose of the roughening is to increase the reflectivity, the roughening is carried out so that the surface roughness Ra of the lower surface of the crystallized glass substrate is 0.1 μm or more. Note that, although the brightness improves as the surface roughness Ra increases, from the viewpoint of maintaining the durability of the crystallized glass substrate against impact, it is preferable that the surface roughness Ra is small, for example, 10 μm or less.

[0102] The surface roughening treatment methods are divided into physical methods and chemical methods. Physical methods include sandblasting using abrasives such as silicon carbide (SiC), alumina (Al2O3), zirconia (ZrO2), and diamond (C), and free abrasive polishing using an abrasive. Chemical methods include immersion in an etching solution containing hydrofluoric acid.

[0103] Fig. 17 is a schematic cross-sectional view of a top plate for a cooking device according to one embodiment of the present invention. In Fig. 17, the interface between a crystallized glass substrate 2 and a brightness improving layer 3 is a roughened surface 6. In the top plate for a cooking device 1 of Fig. 17, the lower surface of the crystallized glass substrate 2 is roughened, and then a brightness improving layer 3 is formed on the roughened surface 6. In Fig. 17, the reflection at the interface between the crystallized glass substrate 2 and the brightness improving layer 3 is greater than in Fig. 2, thereby enabling a further increase in brightness.

[0104] Fig. 18 is a schematic cross-sectional view of a top plate for a cooking device according to one embodiment of the present invention. In the embodiment of Fig. 18, the interface between the crystallized glass substrate 2 and the brightness improving layer 3 is roughened, and a lustrous material and / or a reflective material 5 is dispersed in the brightness improving layer 3, as in the embodiment of Fig. 14. The top plate 1 for a cooking device shown in Fig. 18 is obtained by roughening the lower surface of the crystallized glass substrate 2, and then forming the brightness improving layer 3 containing the lustrous material and / or a reflective material 5 on the roughened surface 6. In Fig. 18, reflection at the interface between the crystallized glass substrate 2 and the brightness improving layer 3 and diffuse reflection of light by the lustrous material and / or a reflective material 5 in the brightness improving layer 3 result in even greater reflection than in Figs. 2, 14, and 17, thereby further increasing brightness.

[0105] (light shielding layer) In the top plate for a cooking appliance according to this embodiment, a light-shielding layer may be provided below the substrate color improvement layer, if necessary. Specifically, the substrate color improvement layer may include a light-shielding layer below the brightness improvement layer or color adjustment layer, if necessary. The light-shielding layer may be formed, for example, by applying a heat-resistant paint to the lower surface of the color adjustment layer. Examples of heat-resistant paint include a heat-resistant resin containing a silicone resin, a polyamide resin, a fluororesin, or a composite thereof, mixed with an inorganic coloring pigment. Alternatively, in consideration of heat resistance, a layer may be provided below the color adjustment layer, if necessary, coated with an ink containing a glassy component primarily composed of SiO2, Al2O3, Li2O, or the like, which is similar to that of a crystallized glass substrate, and a black inorganic pigment (such as a metal oxide pigment based on Fe2O3, MnO2, CuO, or Co2O3) as a light-shielding pigment.

[0106] As described above, when a light-shielding layer is provided on the underside of the substrate color improvement layer, the adhesion between the substrate color improvement layer and the light-shielding layer can be improved by providing an adhesion-improving layer as the strength-improving member between the substrate color improvement layer and the light-shielding layer.

[0107] (Second glass substrate) In the top plate for a cooking appliance of this embodiment, in addition to the crystallized glass substrate constituting the outermost surface of the top plate for a cooking appliance, a second glass substrate, such as a tempered glass substrate or a crystallized glass substrate, may be further formed on the underside of the substrate color improvement layer, more specifically, on the underside of the brightness improvement layer or the color tone adjustment layer, as needed.

[0108] The upper surface of the second glass substrate may be roughened by a method similar to that used for roughening the crystallized glass substrate. As described above, one method for providing irregularities on the upper surface of the color-adjusting layer is to roughen the upper surface of the second glass substrate to provide irregularities, and then form a color-adjusting layer (a light blue glass paint layer) along the irregularities to form a color-adjusting layer having irregularities on its upper surface. For example, as shown in FIG. 19, a top plate 81 for a cooking appliance can be formed in which a brightness-improving layer 83 is formed as a void-containing layer between a color-adjusting layer 84 having irregularities on its upper surface and a crystallized glass substrate 82, the color-adjusting layer 84 being provided on the upper surface of a second glass substrate 85 having irregularities. [Example]

[0109] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples, and can be practiced with appropriate modifications within the scope of the above-mentioned and below-mentioned aims, and all such modifications are included in the technical scope of the present invention.

[0110] [Sample Preparation] Example 1 To form the first layer, a paste containing a solvent and primarily composed of glass components: Li2O-Al2O3-SiO2 was screen-printed onto the surface of a crystallized glass substrate (Neoceram N-0, manufactured by Nippon Electric Glass Co., Ltd., 4 mm thick). The mesh used for screen printing was #325. After screen printing, the substrate was dried at 160°C for 10 minutes.

[0111] Next, to form the second layer, 1.1 g of hollow glass with a particle size of approximately 3 μm As a binder, 0.5 g of a paste containing a solvent and mainly composed of glass components: Li2O-Al2O3-SiO2, 0.1g of blue inorganic paint containing glass components, and Oil as needed A paste was prepared by kneading the above. The paste was screen-printed on the surface of the first layer before firing. The mesh used for screen printing was #100. After screen printing, the substrate was dried at 160°C for 10 minutes, and then fired at 600-700°C for 10 minutes, yielding a sample in which a first layer (approximately 20 μm) and a second layer (approximately 40 μm) were laminated in this order on the surface of the crystallized glass substrate.

[0112] Example 2 To form the first layer, Hollow glass with a particle size of approximately 3 μm: 0.4 g - As a binder, 0.5g of glass paste containing Li2O-Al2O3-SiO2 as the main component and a solvent, Blue inorganic paint: 0.1g, and Oil as needed The paste was prepared by kneading the above ingredients. The paste was screen-printed on the surface of a crystallized glass substrate (Neoceram N-0, manufactured by Nippon Electric Glass Co., Ltd., thickness 4 mm). The mesh used for screen printing was mesh number #325. After screen printing, the substrate was dried at 160°C for 10 minutes.

[0113] Next, to form the second layer, 1.1 g of hollow glass with a particle size of approximately 3 μm As a binder, 0.5 g of a paste containing a solvent and mainly composed of glass components: Li2O-Al2O3-SiO2, 0.1g of blue inorganic paint containing glass components, and Oil as needed A paste was prepared by kneading the above. The paste was screen printed on the upper surface of the first layer before firing. The mesh used for screen printing was #100. After screen printing, the substrate was dried at 160°C for 10 minutes, and then fired at 600-700°C for 10 minutes, yielding a sample in which a first layer (approximately 20 μm) and a second layer (approximately 40 μm) were laminated in this order on the surface of the crystallized glass substrate.

[0114] Example 3 To form the first layer, Hollow glass with a particle size of approximately 3 μm: 1.1 g - As a binder, paste containing glass components: SiO2-B2O3-ZnO as the main component and solvent: 0.5g Blue inorganic paint: 0.1g, and Oil as needed The above was kneaded to prepare a paste. The paste was screen-printed on the surface of a crystallized glass substrate (Neoceram N-0, manufactured by Nippon Electric Glass Co., Ltd., thickness 4 mm). The mesh used for screen printing was mesh number #100. After screen printing, the substrate was dried at 160°C for 10 minutes and then fired at 580 to 680°C for 10 minutes to obtain a brightness-enhancing layer as a first layer.

[0115] Next, to form the second layer, a paste was prepared by kneading an organic coating (silicone-based) with a titanium oxide-based material. The paste was screen-printed on the top surface of the first layer obtained by the above-mentioned firing. The mesh used for screen printing was #100. After screen printing, the substrate was dried at 160°C for 10 minutes, and then fired at 280°C for 1 hour, yielding a sample in which the first layer and the second layer were laminated in this order on the surface of the crystallized glass substrate.

[0116] Example 4 To form the first layer, Glass beads with a particle size of approximately 1 to 2 μm: 3 g - As a binder, paste containing glass components: SiO2-B2O3-ZnO as the main component and solvent: 0.5g, Blue inorganic paint: 0.1g, and Oil as needed The paste was prepared by kneading the above ingredients. The paste was screen-printed on the surface of a crystallized glass substrate (Neoceram N-0, manufactured by Nippon Electric Glass Co., Ltd., thickness 4 mm). The mesh used for screen printing was #100 mesh. After screen printing, the substrate was dried at 160°C for 10 minutes and then fired at 580-680°C for 10 minutes.

[0117] Next, to form the second layer, a paste was prepared by kneading an organic coating (silicone-based) with a titanium oxide-based material. The paste was screen-printed on the surface of the first layer obtained by the above-mentioned firing. The mesh used for screen printing was #180. After screen printing, the substrate was dried at 160°C for 10 minutes, and then fired at 280°C for 1 hour, yielding a sample in which the first and second layers were laminated in this order on the surface of the crystallized glass substrate.

[0118] (Example 5-1) For layer formation, Hollow glass with a particle size of approximately 3 μm: 1.1 g - As a binder, paste containing glass components: SiO2-B2O3-ZnO as the main component and solvent: 0.5g, ·Blue inorganic paint: 0.1g, - Thin plate-shaped material (pearl material) with titanium oxide coating around mica: 0.1g, and Oil as needed The paste was prepared by kneading the above ingredients. The paste was screen-printed on the surface of a crystallized glass substrate (Neoceram N-0, manufactured by Nippon Electric Glass Co., Ltd., thickness 4 mm). The mesh used for screen printing was mesh number #100. After screen printing, the substrate was dried at 160°C for 10 minutes and then fired at 580 to 780°C for 10 minutes, yielding a sample in which a brightness-enhancing layer containing a pearlescent material was formed on the surface of the crystallized glass substrate.

[0119] (Example 5-2) To form a second layer on the surface of the brightness enhancement layer of the sample of Example 5-1, a paste was prepared by kneading an organic coating (silicone-based) and a titanium oxide-based material. The paste was screen-printed on the surface of the first layer formed in the same manner as in Example 5-1. The mesh used for screen printing was #180. After screen printing, the sample was dried at 160°C for 10 minutes and then baked at 280°C for 1 hour, yielding a sample in which the first and second layers were laminated in this order on the surface of the crystallized glass substrate.

[0120] Example 6 For layer formation, Hollow glass with particle size of approximately 2 μm: 1.1 g Glass fiber: 0.5g, - 0.5g of paste containing silicone resin as the main component and solvent as the binder. Blue organic paint: 0.15g, and Oil as needed The paste was prepared by kneading the above. The paste was screen-printed on the surface of a crystallized glass substrate (Neoceram N-0, manufactured by Nippon Electric Glass Co., Ltd., thickness 4 mm). The mesh used for screen printing was mesh number #100. After screen printing, the substrate was dried at 160°C for 10 minutes and then baked at 280°C for 1 hour to obtain a sample in which the above layer was formed on the surface of the crystallized glass substrate.

[0121] Example 7 To form the first layer, Hollow glass with particle size of approximately 3 μm: 2 g Silica powder (primary particle diameter: several tens of nanometers): 0.3 g -As a binder, paste containing glass components: SiO2-B2O3-ZnO as the main component and solvent: 1g, Blue inorganic paint: 0.2g, and Oil as needed A paste was prepared by kneading the above. The paste was screen-printed on the surface of a crystallized glass substrate (Neoceram N-0, manufactured by Nippon Electric Glass Co., Ltd., thickness 4 mm). The mesh used for screen printing was mesh number #100. After screen printing, drying was carried out at 160°C for 10 minutes to obtain a first layer before firing. A second layer was formed on the surface of this first layer before firing in the same manner as the first layer, followed by drying at 160°C for 10 minutes and then firing at 580 to 680°C for 10 minutes to obtain a sample in which the first layer and second layer were laminated in this order on the surface of the crystallized glass substrate.

[0122] Example 8 To form the first layer, Hollow glass with a particle size of approximately 3 μm: 1.1 g - As a binder, paste containing glass components: SiO2-B2O3-ZnO as the main component and solvent: 0.5g Blue inorganic paint: 0.1g, and Oil as needed The paste was prepared by kneading the above ingredients. The paste was screen-printed on the surface of a crystallized glass substrate (Neoceram N-0, manufactured by Nippon Electric Glass Co., Ltd., thickness 4 mm). The mesh used for screen printing was #100 mesh. After screen printing, the substrate was dried at 160°C for 10 minutes to obtain a first layer before firing.

[0123] Next, to form the second layer, Hollow glass with particle size of approximately 3 μm: 0.8 g As a binder, 0.5 g of a paste containing a solvent and consisting mainly of glass components: SiO2-B2O3-ZnO, and Oil as needed A paste was prepared by kneading the above. The paste was used for screen printing on the surface of the first layer before firing. The mesh used for screen printing was #325. After screen printing, the product was dried at 160°C for 10 minutes, and then fired at 580 to 680°C for 10 minutes to obtain a laminate of the first and second layers.

[0124] Next, to form the third layer, a paste was prepared by kneading an organic coating (silicone-based) with a titanium oxide-based material. The paste was screen-printed on the surface of the second layer obtained by the above-mentioned firing. The mesh used for screen printing was #325. After screen printing, the substrate was dried at 160°C for 10 minutes, and then fired at 280°C for 1 hour, yielding a sample in which the first, second, and third layers were laminated in this order on the surface of the crystallized glass substrate.

[0125] Example 9 For layer formation, Glass beads with a particle size of approximately 35 μm and approximately 10 μm: 6 g As a binder, 0.5 g of a paste containing a solvent and consisting mainly of glass components: SiO2-B2O3-ZnO, and ·Blue inorganic paint: 0.1g The paste was prepared by kneading the above. The paste was screen-printed on the surface of a crystallized glass substrate (Neoceram N-0, manufactured by Nippon Electric Glass Co., Ltd., thickness 4 mm). The mesh used for screen printing was mesh number #100. After screen printing, the substrate was dried at 160°C for 10 minutes and then fired at 580-680°C for 10 minutes to obtain a sample.

[0126] (Comparative Example 1) To form the first layer, Hollow glass with a particle size of approximately 3 μm: 1.1 g - As a binder, paste containing glass components: SiO2-B2O3-ZnO as the main component and solvent: 0.5g, Blue inorganic paint: 0.1g, and Oil as needed The paste was prepared by kneading the above. The paste was screen-printed on the surface of a crystallized glass substrate (Neoceram N-0, manufactured by Nippon Electric Glass Co., Ltd., thickness 4 mm). The mesh used for screen printing was mesh number #100. After screen printing, the substrate was dried at 160°C for 10 minutes and then fired at 580-680°C for 10 minutes to obtain a sample.

[0127] (Comparative Example 2) To form the first layer, Hollow glass with a particle size of approximately 3 μm: 1.1 g - As a binder, paste containing glass components: SiO2-B2O3-ZnO as the main component and solvent: 0.5g, Blue inorganic paint: 0.1g, and Oil as needed A paste was prepared by kneading the above. The paste was screen-printed on the surface of a crystallized glass substrate (Neoceram N-0, manufactured by Nippon Electric Glass Co., Ltd., thickness 4 mm). The mesh used for screen printing was #100. After screen printing, the substrate was dried at 160°C for 10 minutes to obtain a first layer before firing. Next, to form a second layer, a paste was screen-printed on the surface of the first layer before firing in the same manner as for the first layer, and then dried at 160°C for 10 minutes. The substrate was then fired at 580 to 680°C for 10 minutes to obtain a sample in which the first and second layers were formed on the surface of the crystallized glass substrate.

[0128] 〔evaluation〕 The samples prepared above were evaluated as follows.

[0129] (Refractive index of brightness improving layer) The refractive index was determined using a spectroscopic ellipsometer according to the method described above. When the brightness enhancement layer was a void-containing layer, the refractive index was determined according to the proportion of voids, as described above. As a result, the refractive index of the crystallized glass substrate was 1.54, while in all examples the refractive index of the brightness enhancement layer was smaller than that of the crystallized glass substrate. These results show that by using a void-containing layer as the brightness enhancement layer, the refractive index becomes closer to the refractive index of 1.0 of the air layer, and as described above, the light extraction efficiency within the crystallized glass substrate is increased, making it possible to further improve brightness and suppress yellowing. In addition, when it is difficult to measure the refractive index of a film coated with a brightness enhancing layer, the film may be analyzed by, for example, energy dispersive X-ray analysis (EDX), wavelength dispersive X-ray analysis (WDX), fluorescent X-ray analysis, inductively coupled plasma (ICP) optical emission spectroscopy, NMR (nuclear magnetic resonance), X-ray photoelectron spectroscopy (XPS), or the like, and the refractive index of the brightness enhancing layer may be roughly calculated from the refractive index (which may be a literature value) of a material composition close to the material composition estimated from the analysis and the proportion of voids.

[0130] (Measurement of L value) The crystallized glass substrate of the sample obtained as described above was used as the outermost surface and color measurement was carried out. The color measurement was carried out using a color difference meter (Konica Minolta CR410) in the color space L * a * b * The results of the L value, which indicates the brightness, are shown in Table 2. These results show that by providing a substrate color improvement layer containing a layer having hollow glass as a brightness improvement layer on the underside of the crystallized glass substrate, the brightness can be increased more significantly than when a color adjustment layer made of an organic paint is directly formed on the underside of the crystallized glass substrate.

[0131] [Table 2]

[0132] (Adhesion evaluation (cross-cut evaluation)) Using a cutter, 100 grid-like cuts were made at 1 mm intervals, and then cellophane tape was applied. Cellophane tape was then applied and peeled off. This cellophane tape application and peeling process was repeated three times in total. If more of the grid-like coating film remained after the third cellophane tape peeling than in Comparative Example 1, the adhesion was evaluated as excellent. As a result, in all Examples, more of the grid-like coating film remained than in Comparative Example 1, resulting in excellent adhesion. Furthermore, in Example 5-2, more of the grid-like coating film remained than in Example 5-1, resulting in even better adhesion.

[0133] In Example 1, by providing a glass layer as an adhesion improving layer between the crystallized glass substrate and the brightness improving layer, the adhesion between the crystallized glass substrate and the brightness improving layer was improved, and the overall strength was improved. Example 2 is an example in which strength was improved by providing a first layer with a different filler (hollow glass) concentration between the crystallized glass substrate and the brightness improving layer (second layer). Furthermore, by incorporating hollow glass into the first layer, brightness was improved compared to Example 1. Example 3 is an example in which film strength was improved by including a filler (titanium oxide) in the color tone adjusting layer (second layer). It is also thought that adhesion was improved by partially penetrating the surface layer of the first layer with the second layer components (organic resin, titanium oxide). As an application example of Example 2, it is also thought that brightness can be further improved by forming two first layers.

[0134] Example 4 is an example in which the film strength is improved by including a filler (titanium oxide) in the color tone adjusting layer (second layer). Example 5-1 is an example in which the film strength is improved by adding a filler (thin plate-like material). Example 5-2 is an example in which the film strength is improved by including a filler (titanium oxide) in the color tone adjusting layer (second layer).

[0135] Example 6 is an example in which strength is improved by adding filler (glass fiber) to the brightness improving layer. Example 7 is an example in which strength is improved by adding particles of different particle sizes to fill gaps and provide a reinforcing effect. Example 8 is an example in which adhesion to the substrate color improving layer is further improved by providing a layer with a larger amount of binder between the brightness improving layer and the color tone adjusting layer (third layer). Example 9 is an example in which strength is improved by adding particles of different particle sizes to fill gaps and provide a reinforcing effect. [Industrial Applicability]

[0136] As described above, the present invention provides a white top plate for a cooking appliance using a substrate made of crystallized glass that exhibits high strength and low thermal expansion, thereby providing a white tabletop, freestanding, or built-in heating appliance for use on a dining table or countertop in an ordinary household, or in a commercial kitchen. [Explanation of symbols]

[0137] 1, 21, 31, 41, 51, 61, 71, 81, 91A, 91B, 101, 111A, 111B Top plate for heating cooker 2, 22, 32, 42, 52, 62, 72, 82, 92, 102, 112 Crystallized glass substrate 3, 23, 33, 43, 53, 63, 73, 83, 93, 103, 113 Brightness enhancement layer 4, 24, 34, 44, 54, 64, 74, 84, 114 tone adjustment layer 5. Shiny and / or reflective materials 6 Roughened surface 7 Light reflected at the interface between the crystallized glass substrate and the brightness enhancement layer 8 Light reflected at the interface between the brightness enhancement layer and the color adjustment layer 9. Colored layer of preliminary experiment sample (white + blue) 10 Light reflected at the interface between the crystallized glass substrate 2 and the colored layer 9 11A Preliminary experiment sample colored layer (white) 11B White paper in preliminary experiment sample 12 Air Layer 25, 65, 75, 95, 105, 115 hollow glass 35 spacer 36 Hollow layer 85 Second glass substrate 97, 97B Adhesion improving layer 108 Filler

Claims

1. Li 2 O-Al 2 O 3 -SiO 2 a crystallized glass substrate containing a transition element and a a substrate color improvement layer provided on the lower surface of the crystallized glass substrate, the substrate color improvement layer including one or more brightness improvement layers having a refractive index smaller than that of the crystallized glass substrate and containing voids, and the substrate color improvement layer including a blue pigment; A strength improving member is provided, A top plate for a cooking appliance, comprising an adhesion improving layer as the strength improving member between the crystallized glass substrate and the substrate color improving layer.

2. The top plate for a cooking appliance according to claim 1 , wherein the brightness improving layer contains the blue pigment.

3. 3. The top plate for a cooking appliance according to claim 1, wherein the top plate has a plurality of brightness improving layers, and an adhesion improving layer is provided as the strength improving member between one brightness improving layer and another brightness improving layer adjacent to the brightness improving layer.

4. 4. The top plate for a cooking appliance according to claim 1, wherein the adhesion improving layer is one or more layers of a thin glass film.

5. 4. The top plate for a cooking appliance according to claim 1, wherein the adhesion improving layer is a void-containing layer having a different porosity and / or material composition from the brightness improving layer.

6. The top plate for a heating cooker according to any one of claims 1 to 5, wherein one or more of the brightness improving layer and the adhesion improving layer as a strength improving member contain one or more of a reflective material and a lustrous material.

7. 7. The top plate for a cooking appliance according to claim 6, wherein at least one of the reflective material and the lustrous material is at least one selected from the group consisting of mica, silica, metal oxide, aluminum flake, glass particles, glass flake, glass flake having a metal vapor deposition layer, and mica having a metal oxide layer.

8. 8. The top plate for a cooking appliance according to claim 1, wherein the substrate color improving layer contains a filler as the strength improving member.

9. 9. The top plate for a cooking device according to claim 1, wherein the brightness improving layer contains a filler as the strength improving member.

10. 10. The top plate for a cooking appliance according to claim 8 or 9, wherein the filler is composed of one or more selected from the group consisting of metals, metal oxides, ceramics, metal salts, glass, silica, mica, talc, clay, zeolite, organic materials, composites thereof, and materials having at least one of a coupling agent, an active group, a reactive group, an organic material, and a metal oxide bonded to, adsorbed on, or vapor-deposited on the surface thereof.

11. 11. The top plate for a cooking appliance according to claim 1, wherein the substrate color improving layer is formed of a brightness improving layer containing the blue pigment.

12. The top plate for a cooking appliance according to any one of claims 1 to 10, wherein the substrate color improving layer has a color tone adjusting layer containing a white pigment or a white pigment and the blue pigment, the color tone adjusting layer being provided on the lower surface of the brightness improving layer.

13. The top plate for a cooking appliance according to any one of claims 1 to 10 and 12, wherein the substrate color improving layer has a color adjustment layer containing a white pigment or a white pigment and the blue pigment, the color adjustment layer being provided between the crystallized glass substrate and the brightness improving layer.

14. The top plate for a cooking appliance according to claim 13, wherein the color tone adjusting layer also serves as an adhesion improving layer.

15. The top plate for a cooking appliance according to claim 14, wherein the adhesion-improving layer is one or more thin glass layers.

16. 15. The top plate for a cooking appliance according to claim 14, wherein the adhesion improving layer is a void-containing layer having a porosity and / or material composition different from those of the brightness improving layer.

17. The brightness improving layer is a void-containing layer in which a spacer is provided between the crystallized glass substrate and the color tone adjusting layer so as to ensure a void; or The top plate for a cooking device according to claim 12, wherein the color tone adjusting layer has an upper surface that is a void-containing layer having irregularities formed thereon to ensure voids.

18. The top plate for a cooking appliance according to any one of claims 12 to 17, wherein the color-adjusting layer contains at least one of a reflective material and a glittering material.

19. 19. The top plate for a cooking appliance according to claim 18, wherein at least one of the reflective material and the lustrous material is at least one selected from the group consisting of mica, silica, metal oxide, aluminum flake, glass particles, glass flake, glass flake having a metal vapor deposition layer, and mica having a metal oxide layer.

20. 20. The top plate for a cooking appliance according to claim 1, further comprising a light-shielding layer on the underside of the substrate color improving layer.

21. 21. The top plate for a cooking appliance according to claim 20, further comprising an adhesion improving layer as the strength improving member between the substrate color improving layer and the light-shielding layer.

22. The brightness improving layer is a void-containing layer containing one or more selected from the group consisting of hollow particles, porous materials, and structures having voids between particles, or 22. The top plate for a cooking device according to claim 1, wherein the lower surface of the crystallized glass substrate is provided with a void-containing layer having irregularities formed thereon to ensure voids.

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