Cooker top plate and manufacturing method for cooker top plate

Abstract

Provided are: a cooker top plate which is highly stain and scratch resistant and which achieves an appearance with a matte texture feeling; and a method for manufacturing the cooker top plate. This cooker top plate includes: a glass substrate having a cooking surface, on which a cooker is placed, and a rear surface opposite to the cooking surface; and a coating layer disposed on the cooking surface side of the glass substrate. The coating layer includes an inorganic layer, and the root mean square roughness Rq of a surface of the coating layer is 0.1 μm to 1 μm.

Description

Top plate for cooker and method for manufacturing the top plate for cooker

[0001] The present invention relates to a top plate for a cooker and a method for manufacturing a top plate for a cooker.

[0002] A cooker top plate is provided on the top of an induction cooker, a radiant heater cooker, a gas cooker, etc. Generally, the cooker top plate is provided with a transparent or opaque glass substrate having a cooking surface on which a cookware is placed and a back surface opposite the cooking surface. A coating layer may be provided on the cooking surface of the glass substrate to improve the design of the cooker top plate.

[0003] In recent years, growing interest in design has led to a demand for top plates for cookers with a matte appearance on the cooking surface. For example, Patent Document 1 below describes a cooker top plate in which a high-reflection film with a higher reflectivity than the glass substrate is laminated on the cooking surface of a glass substrate made of low-expansion crystallized glass, and a painted glass decorative layer is further laminated on the high-reflection film to achieve a matte appearance. Furthermore, Patent Document 2 below describes a cooker top plate in which a matte appearance can be achieved by laminating a reflective film with a lower reflectivity than the glass substrate on the glass substrate.

[0004] JP 2008-190846 JP 2008-290917

[0005] However, in Patent Document 1, the exposed painted glass decoration layer contains glass and a white pigment, which can inhibit the flow of glass during firing, resulting in a tendency for the arithmetic mean roughness Ra of the painted glass decoration layer to be large. As a result, when a cookware such as a pot is rubbed against the bottom of the pot, the pot's bottom is scraped, causing the paint or other coating to peel off and adhere to the painted glass decoration layer as stains, or the painted glass decoration layer is easily scraped and scratched. Patent Document 2 also describes that the painted glass decoration layer may be composed solely of a glass composition, or may contain an inorganic pigment or other coloring agent in addition to the glass composition. However, whether the layer is composed solely of a glass composition or contains an inorganic pigment, when a cookware such as a pot is rubbed against the bottom of the pot, the pot's bottom is scraped, causing the paint or other coating to peel off and adhere to the painted glass decoration layer as stains, or the painted glass decoration layer is easily scraped and scratched.

[0006] Therefore, it has been difficult to improve stain resistance and scratch resistance while achieving a matte appearance. Here, in the present invention, stain resistance refers to the resistance to the coating or the like of a cookware peeling off and becoming stains that adhere to the cookware top plate when a cookware such as a pot comes into contact with the cookware top plate, and scratch resistance refers to the resistance to the surface of the cookware top plate being scraped and scratched when a cookware such as a pot comes into contact with the cookware top plate.

[0007] In view of the above, an object of the present invention is to provide a top plate for a cooker that has a highly matte appearance while also having high stain resistance and scratch resistance, and a method for manufacturing such a top plate for a cooker.

[0008] As a result of extensive research, the present inventors have discovered that by controlling the surface shape of the coating layer provided on the cooking surface of a glass substrate, it is possible to provide a top plate for a cooker that has high stain resistance and scratch resistance while achieving a highly matte appearance, and a method for manufacturing such a top plate for a cooker.

[0009] A top plate for a cooker according to aspect 1 of the present invention comprises a glass substrate having a cooking surface on which a cookware is placed and a back surface opposite the cooking surface, and a coating layer disposed on the cooking surface side of the glass substrate, wherein the coating layer includes an inorganic layer, and the root-mean-square roughness Rq of the surface of the coating layer is 0.1 μm to 1 μm.

[0010] In a top plate for a cooker according to Aspect 2 of the present invention, in addition to Aspect 1, it is preferable that the inorganic layer contains inorganic beads.

[0011] In the top plate for a cooker according to Aspect 3 of the present invention, in Aspect 1 or 2, it is preferable that the arithmetic mean roughness Ra of the surface of the coating layer is 0.22 μm to 0.9 μm.

[0012] In the cooker top plate according to aspect 4 of the present invention, in aspect 2 or 3, it is preferable that the inorganic beads contain at least one type of inorganic beads selected from the group consisting of glass beads, alumina beads, silica beads, zirconia beads, quartz beads, feldspar beads, zeolite beads, corundum beads, and zircon beads.

[0013] In a cookware top plate according to Aspect 5 of the present invention, in any one of Aspects 2 to 4, it is preferable that the inorganic beads do not protrude from the surface of the coating layer.

[0014] In a top plate for a cookware according to Aspect 6 of the present invention, in any one of Aspects 2 to 5, it is preferable that the inorganic layer contains a glass matrix, and the difference in softening point between the inorganic beads and the glass matrix is ​​300°C or less.

[0015] In a cookware top plate according to Aspect 7 of the present invention, in any one of Aspects 1 to 6, it is preferable that the inorganic layer contains a glass matrix having a refractive index different from that of the inorganic beads.

[0016] In the top plate for a cookware according to Aspect 8 of the present invention, in any one of Aspects 1 to 7, it is preferable that the inorganic layer does not contain a color pigment.

[0017] In the top plate for a cooker according to Aspect 9 of the present invention, in any one of Aspects 1 to 8, it is preferable that the coating layer further comprises an anti-fouling layer and / or a protective layer on the inorganic layer.

[0018] In the top plate for a cookware according to Aspect 10 of the present invention, in any one of Aspects 1 to 9, it is preferable that the 20° gloss value of the surface of the coating layer is 38 or less.

[0019] In the top plate for a cookware according to Aspect 11 of the present invention, in any one of Aspects 1 to 10, it is preferable that the 60° gloss value of the surface of the coating layer is 70 or less.

[0020] A top plate for a cooker according to Aspect 12 of the present invention comprises a glass substrate having a cooking surface on which a cookware is placed and a back surface opposite to the cooking surface, wherein the root mean square roughness Rq of the cooking surface is 0.25 μm to 0.95 μm.

[0021] A manufacturing method of a top plate for a cooker according to Aspect 13 of the present invention is a manufacturing method of a top plate for a cooker configured according to any one of Aspects 1 to 11, characterized in that it comprises a step of applying an inorganic layer-forming paste containing inorganic beads to the surface of a glass substrate, and firing the paste to form a coating layer containing an inorganic layer on the surface of the glass substrate, and the root-mean-square roughness Rq of the surface of the coating layer is 0.1 μm to 1 μm.

[0022] According to the present invention, it is possible to provide a top plate for a cooker that has a highly matte appearance and is highly stain-resistant and scratch-resistant, and a method for manufacturing the top plate for a cooker.

[0023] Fig. 1 is a schematic cross-sectional view showing a top plate for a cooker according to an embodiment of the present invention. Fig. 2 is a scanning electron microscope (SEM) image (magnification: 5000x) of the cross section of the top plate for a cooker obtained in Example 2 of the present invention. Fig. 3 is a scanning electron microscope (SEM) image (magnification: 5000x) of the cross section of the top plate for a cooker obtained in Example 10 of the present invention.

[0024] Preferred embodiments will be described below. However, the following embodiments are merely examples, and the present invention is not limited to the following embodiments. In addition, in each drawing, components having substantially the same functions may be referred to by the same reference numerals.

[0025] In this specification, the term "top plate for a cooking appliance" may be abbreviated to "top plate."

[0026] The cooker top plate 1 shown in FIG. 1 includes a glass substrate 2. The glass substrate 2 has a cooking surface 2a and a back surface 2b. The cooking surface 2a and the back surface 2b are opposite each other. The cooking surface 2a is the surface on which a cookware such as a pot or frying pan is placed. The back surface 2b is the surface facing the light source and heating device inside the cooker. Therefore, the cooking surface 2a and the back surface 2b are in a front-back relationship. A coating layer 3 is disposed on the cooking surface 2a of the glass substrate 2. The coating layer 3 includes an inorganic layer 4. That is, the cooking surface 2a of the glass substrate 2 and the coating layer 3 are in contact, and the cooking surface 2a of the glass substrate 2 and the inorganic layer 4 are in contact.

[0027] The members and layers that make up the top plate 1 will be described in detail below.

[0028] The glass substrate 2 is not particularly limited. For example, the glass substrate 2 may be a white glass substrate or a transparent glass substrate. In this specification, the term "transparent" in reference to a glass substrate means that the light transmittance in the visible wavelength range of 450 nm to 700 nm is 70% or more.

[0029] The top plate 1 is repeatedly heated and cooled. Therefore, it is preferable that the glass substrate 2 has high thermal shock resistance and a low thermal expansion coefficient. Specifically, the softening temperature of the glass substrate 2 is preferably 700°C or higher, and more preferably 750°C or higher. The average linear thermal expansion coefficient of the glass substrate 2 at 30°C to 750°C is -10×10 －７ / ℃~+60×10 －７ / °C, and is preferably within the range of -10 × 10 －７ / ℃~+50×10 －７ / °C, and more preferably within the range of -10 × 10 －７ / ℃~+40×10 －７ / °C. Therefore, the glass substrate 2 is preferably made of glass or glass-ceramic that has a high glass transition temperature and low expansion. Specific examples of low-expansion glass-ceramic include LAS (Li ２ O-Al ２ O ３ -SiO ２ )-based crystallized glass, such as "N-11" and "N-0" manufactured by Nippon Electric Glass Co., Ltd. Note that the glass substrate 2 may also be a borosilicate glass substrate.

[0030] There is no particular limitation on the thickness of the glass substrate 2. The thickness of the glass substrate 2 can be appropriately set depending on the output temperature and structure of the cooking device. The thickness of the glass substrate 2 can be, for example, about 2 mm to 6 mm.

[0031] The arithmetic mean roughness Ra of the cooking surface 2a of the glass substrate 2 before the coating layer 3 is formed is preferably 1.5 μm or less, more preferably 1.0 μm or less, even more preferably 0.8 μm or less, and particularly preferably 0.5 μm or less. If it is greater than the above upper limit, the root mean square roughness Rq and arithmetic mean roughness Ra of the surface of the coating layer 3 tend to be large when the coating layer 3 is formed, which makes it easier for the cooking utensil to get caught on the surface irregularities of the coating layer 3, scraping off the metal or paint on the bottom of the cooking utensil and adhering to the coating layer 3 as dirt, or scraping off the convex parts of the surface of the coating layer 3, causing scratches on the coating layer 3, which is undesirable. The lower limit is not particularly limited.

[0032] The coating layer 3 is disposed on the cooking surface 2a of the glass substrate 2. The coating layer 3 includes an inorganic layer 4. That is, the coating layer 3 has a single-layer structure including one inorganic layer 4. Note that, as long as the matte appearance, stain resistance, and scratch resistance that are the objectives of the present invention are not impaired, the coating layer 3 may have a layer other than the inorganic layer 4 disposed on the inorganic layer 4, or may have a two-layer structure or a three-layer or more layer structure. In this case, the ratio of the constituent components of each layer may be different or the same. Details of the two-layer or more layer structure of the coating layer 3 will be described later. Note that, in the following description, the "surface of the coating layer 3" refers to the "surface of the inorganic layer 4" when the coating layer 3 is composed only of the inorganic layer 4, and refers to the "outermost surface of the layer other than the inorganic layer 4" when a layer other than the inorganic layer 4 is further formed on the inorganic layer 4.

[0033] The surface of the coating layer 3 has a root-mean-square roughness Rq of 0.1 μm to 1 μm. The root-mean-square roughness Rq of the surface of the coating layer 3 is more preferably 0.26 μm or more, even more preferably 0.32 μm or more, particularly preferably 0.38 μm or more, and is 1 μm or less, more preferably 0.75 μm or less, even more preferably 0.6 μm or less, and particularly preferably 0.5 μm or less. When the root-mean-square roughness Rq is equal to or less than the above upper limit and equal to or greater than the above lower limit, the contact area between the cooking utensil and the coating layer 3 when they rub against each other can be appropriately controlled, which makes it easier to reduce the frictional force generated between the cooking utensil and the coating layer 3, making it easier to improve stain resistance and scratch resistance, and to enhance the matte finish. If the root mean square roughness Rq of the surface of the coating layer 3 is smaller than the above lower limit, the contact area between the cooking utensil and the coating layer 3 becomes too large, the frictional force generated between the cooking utensil and the coating layer 3 increases, the stain resistance and scratch resistance decrease, and it becomes difficult to enhance the matte finish.

[0034] The surface of the coating layer 3 preferably has an arithmetic mean roughness Ra of 0.9 μm or less, more preferably 0.5 μm or less, even more preferably 0.4 μm or less, and particularly preferably 0.35 μm or less. The lower limit of the arithmetic mean roughness Ra is preferably 0.22 μm or more, preferably 0.25 μm or more, and even more preferably 0.29 μm or more. If the arithmetic mean roughness Ra is greater than the upper limit, when a cooking utensil such as a pot rubs against the coating layer 3, the cooking utensil is likely to get caught on the uneven surface of the coating layer 3, and the metal or paint on the bottom of the cooking utensil may be scraped off and adhere to the coating layer 3 as dirt, or the convex portions on the surface of the coating layer 3 may be scraped off, causing scratches on the coating layer 3, which is undesirable. If the arithmetic mean roughness Ra of the surface of the coating layer 3 is smaller than the above lower limit, when the cooking utensil rubs against the coating layer 3, the contact area between the cooking utensil and the coating layer 3 becomes too large, increasing the frictional force generated between the cooking utensil and the coating layer 3, reducing stain resistance and scratch resistance and making it difficult to enhance the matte finish, which is undesirable.

[0035] The arithmetic mean roughness Ra and the root mean square roughness Rq can be measured using a Mitutoyo SJ-210 in accordance with JIS B0601:2001 under the following conditions: Measurement speed: 0.5 mm / s Cutoff values ​​λc: 0.7 mm, λs: 2.5 mm Number of sections: 5 Gaussian filter

[0036] The light transmittance at a wavelength of 580 nm of the glass substrate 2 (top plate 1) provided with the coating layer 3 is preferably 75% or more, more preferably 80% or more, and even more preferably 81% or more. Note that the value of the light transmittance varies depending on the constituent components of the coating layer 3 when the transmittance of the glass substrate is high (for example, the light transmittance at a wavelength of 580 nm is approximately 86%). When the light transmittance of the glass substrate 2 provided with the coating layer 3 is equal to or greater than the lower limit, color differences are unlikely to occur between areas where the coating layer 3 is formed and areas where it is not formed. This makes it possible to achieve a highly matte appearance while improving the overall design of the top plate 1. The upper limit of the light transmittance of the glass substrate 2 provided with the coating layer 3 is not particularly limited, but is, for example, 90% or less. Note that the light transmittance is determined by the intensity (I ) of incident light emitted from a light source installed on the coating layer 3 side. ０) and the intensity (I) of light emitted from the glass substrate 2 side (rear surface 2b side).

[0037] The thickness of the inorganic layer 4 is preferably 0.1 to 20 μm, more preferably 1 to 10 μm, even more preferably 2 to 5 μm, and particularly preferably 3 to 4 μm. When the thickness is between the upper limit and the lower limit, the surface shape of the coating layer 3 can be easily adjusted to a desired level by the glass beads, which makes it easier to improve the stain resistance and scratch resistance while enhancing the matte finish.

[0038] The Mohs hardness of the surface of the coating layer 3 is preferably 4 to 7, and more preferably 5 to 6. If the Mohs hardness of the surface of the coating layer 3 is above the above upper limit, the surface of the coating layer 3 will be more likely to scrape the metal or paint on the bottom of the cookware, which means that stain resistance will be reduced. On the other hand, if it is below the above lower limit, the surface of the coating layer 3 will be more likely to be scratched by the cookware, which means that scratch resistance will be reduced. The Mohs hardness of the surface of the coating layer 3 can be measured using a known Mohs hardness scale; for example, a Mohs hardness scale (MH-10R) manufactured by Narica Co., Ltd. can be used.

[0039] Each component contained in the inorganic layer 4 will be described below.

[0040] The inorganic layer 4 includes a glass matrix as a matrix component. The glass matrix is ​​made of, for example, glass frit. Examples of glass compositions of the glass matrix (glass frit) include borosilicate glass, aluminoborosilicate glass, silicate glass containing at least one of an alkali metal component and an alkaline earth metal component, and phosphate glass containing zinc and aluminum. Examples of the glass frit that can be used include "Frit NPF," "Frit NPF10," and "Fine Frit NPF" manufactured by Nippon Electric Glass Co., Ltd. One type of glass frit may be used, or two or more types may be used in combination.

[0041] The content of the glass matrix in the inorganic layer 4 is preferably 55% by mass or more, preferably more than 55% by mass, more preferably 65% ​​by mass or more, even more preferably 70% by mass or more, and preferably 99% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less. When the content is equal to or greater than the above-mentioned lower limit and equal to or less than the above-mentioned upper limit, the arithmetic mean roughness Ra and root mean square roughness Rq of the surface of the coating layer 3 can be easily controlled within appropriate ranges, which makes it easier to improve the stain resistance and scratch resistance and to enhance the matte finish.

[0042] The inorganic layer 4 contains inorganic beads. That is, the coating layer 3 contains inorganic beads. As a result, approximately spherical inorganic beads are scattered throughout the inorganic layer 4, which facilitates scattering of light incident on the inorganic layer 4. Furthermore, the surface shape of the coating layer 3 can be easily adjusted to a desired level. As a result, the 20° gloss value and 60° gloss value of the surface of the coating layer 3 are likely to decrease, thereby achieving a highly matte appearance and improving stain resistance and scratch resistance. The inorganic beads preferably contain at least one selected from the group consisting of glass beads, alumina beads, silica beads, zirconia beads, quartz beads, feldspar beads, zeolite beads, corundum beads, and zircon beads, and among these, glass beads are particularly preferred. As a result, a highly matte appearance can be achieved and stain resistance and scratch resistance can be improved. Quartz beads, feldspar beads, zeolite beads, corundum beads, and zircon beads can be obtained by crushing their raw materials, natural minerals or artificial minerals such as quartz, feldspar, zeolite, corundum, and zircon.

[0043] Examples of the glass composition of the glass beads include borosilicate glass, aluminoborosilicate glass, silicate glass containing at least one of an alkali metal component and an alkaline earth metal component, and phosphate glass containing zinc and aluminum.

[0044] The presence of inorganic beads in the inorganic layer 4 can be confirmed using a scanning electron microscope or the like.

[0045] It is preferable that the inorganic beads do not protrude from the surface of the coating layer 3. If the inorganic beads protrude from the surface of the coating layer 3, the protruding inorganic beads may cause the paint on the bottom of the pot to peel off or the inorganic beads to be easily scraped, making it impossible to achieve the desired stain resistance and scratch resistance. In the present invention, "not protruding" means that the glass matrix and the inorganic beads are approximately flush with each other on the surface of the coating layer 3. However, there may be a small number of unintentionally and unavoidably protruding inorganic beads. In such cases, the area occupied by the inorganic beads protruding from the surface of the coating layer 3 relative to the surface area of ​​the coating layer 3 is 5% or less, 3% or less, or 1% or less. Whether the inorganic beads protrude can be confirmed using a scanning electron microscope.

[0046] The inorganic layer 4 preferably contains a glass matrix composed of glass beads and glass frit, and the glass beads and the matrix glass preferably have different softening points. Furthermore, the softening point relationship between the glass beads and the glass matrix is ​​preferably such that the softening point of the glass beads is greater than the softening point of the glass matrix. This facilitates partial softening of the inorganic beads near the surface of the coating layer 3 at the baking temperature of the inorganic layer 4. As a result, the inorganic beads are less likely to protrude from the surface of the coating layer 3, making it easier to control the surface shape of the coating layer 3 to a desired degree. This facilitates improved stain resistance and scratch resistance.

[0047] The difference in softening point between the inorganic beads and the glass matrix is ​​preferably 500°C or less, more preferably 200°C or less, and particularly preferably 100°C or less. In this way, the inorganic beads tend to soften partially near the surface of the coating layer 3 at the baking temperature of the inorganic layer 4. As a result, the inorganic beads are less likely to protrude from the surface of the coating layer 3, making it easier to control the surface shape of the coating layer 3 to a desired extent. This makes it easier to improve stain resistance and scratch resistance. In view of the above, it is preferable that the inorganic beads are made of aluminoborosilicate glass, and the matrix glass is made of borosilicate glass having a softening point lower than that of the glass constituting the inorganic beads.

[0048] The magnitude relationship between the softening point of the inorganic beads and the baking temperature of the inorganic layer 4 is preferably such that the softening point of the inorganic beads is greater than the baking temperature of the inorganic layer 4, and the difference between the softening point of the inorganic beads and the baking temperature of the inorganic layer 4 is preferably 200° C. or less, preferably 150° C. or less, and preferably 100° C. or less. In this way, the inorganic beads are less likely to protrude from the surface of the coating layer 3 at the baking temperature of the inorganic layer 4, making it easier to control the surface shape of the coating layer 3 to a desired degree. This makes it easier to improve stain resistance and scratch resistance.

[0049] The softening point of the inorganic beads is, for example, preferably 1500° C. or lower, more preferably 1000° C. or lower, even more preferably 950° C. or lower, and particularly preferably 900° C. or lower. In this way, the inorganic beads are less likely to protrude from the surface of the coating layer 3 at the baking temperature of the inorganic layer 4, making it easier to control the surface shape of the coating layer 3 to a desired degree. As a result, it is easier to improve the stain resistance and scratch resistance.

[0050] It is also preferable that the refractive index of the inorganic beads and the glass matrix are different, which makes it easier to scatter light incident on the coating layer 3 and to achieve a highly matte appearance.

[0051] The average particle size of the inorganic beads is preferably 1 μm to 9 μm, more preferably 2 to 8 μm, even more preferably 2.5 μm to 7 μm, and particularly preferably 3 to 6.5 μm. If the average particle size of the inorganic beads is equal to or less than the above upper limit and equal to or greater than the above lower limit, it becomes easier to adjust the surface shape of the coating layer 3 to a desired level, which makes it easier to improve stain resistance and scratch resistance while enhancing the matte finish.

[0052] The content of inorganic beads in the inorganic layer 4 is preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 11% by mass or more, particularly preferably 15% by mass or more, and is preferably less than 45% by mass, more preferably 40% by mass or less, even more preferably 35% by mass or less, and particularly preferably 30% by mass or less. If the content is equal to or more than the above lower limit and equal to or less than the above upper limit, the arithmetic mean roughness Ra and root mean square roughness Rq of the surface of the coating layer 3 can be easily controlled within appropriate ranges, making it easier to improve stain resistance and scratch resistance and to enhance the matte finish.

[0053] The content of glass beads in the inorganic layer 4 is preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 11% by mass or more, particularly preferably 15% by mass or more, and is preferably 60% by mass or less, preferably less than 45% by mass, more preferably 40% by mass or less, even more preferably 35% by mass or less, and particularly preferably 30% by mass or less. If the content is equal to or greater than the above lower limit and equal to or less than the above upper limit, the arithmetic mean roughness Ra and root mean square roughness Rq of the surface of the coating layer 3 can be easily controlled within appropriate ranges, making it easier to improve stain resistance and scratch resistance and to enhance the matte finish.

[0054] The mass ratio of the content of inorganic beads to the content of glass matrix in the inorganic layer 4 (content of inorganic beads / content of glass matrix) is preferably 0.01 or more, more preferably 0.05 or more, even more preferably 0.1 or more, particularly preferably 0.2 or more, and is preferably less than 0.81, more preferably 0.7 or less, even more preferably 0.6 or less, and particularly preferably 0.4 or less. If the mass ratio is equal to or greater than the above lower limit and equal to or less than the above upper limit, the arithmetic mean roughness Ra and root mean square roughness Rq of the surface of the coating layer 3 can be easily controlled within appropriate ranges, making it easier to improve stain resistance and scratch resistance and to enhance the matte finish.

[0055] The mass ratio of the glass bead content to the glass matrix content in the inorganic layer 4 (glass bead content / glass matrix content) is preferably 0.01 or more, more preferably 0.05 or more, even more preferably 0.1 or more, particularly preferably 0.2 or more, and is preferably less than 0.81, more preferably 0.7 or less, even more preferably 0.6 or less, and particularly preferably 0.4 or less. If the mass ratio is equal to or greater than the above lower limit and equal to or less than the above upper limit, the arithmetic mean roughness Ra and root mean square roughness Rq of the surface of the coating layer 3 can be easily controlled within appropriate ranges, making it easier to improve stain resistance and scratch resistance and to enhance the matte finish.

[0056] In addition to the inorganic beads, beads containing organic groups may be added to the inorganic layer 4. However, this is not preferred because the beads containing organic groups tend to protrude from the surface of the coating layer 3 at the baking temperature of the glass frit. Examples of beads containing organic groups include phenyl polysiloxane, methyl polysiloxane, methyl phenyl polysiloxane, and organic functionalized polysiloxane.

[0057] The inorganic layer 4 preferably does not contain a color pigment. The inorganic layer 4 preferably does not contain an extender pigment. This eliminates the presence of components in the inorganic layer 4 that do not soften at the firing temperature of glass and strongly inhibit the flow of glass, making it easier to control the surface shape of the coating layer 3 to a desired level and improve stain resistance and scratch resistance. Furthermore, color differences between the areas where the inorganic layer 4 is formed and the areas where it is not formed are less likely to occur, allowing for a highly matte appearance while improving the overall design of the top plate 1. Note that the inorganic layer 4 may contain a color pigment or an extender pigment, as long as the desired matte appearance, stain resistance, and scratch resistance are not impaired. In this case, the content of the color pigment and extender pigment in the inorganic layer 4 is preferably 5% by mass or less, more preferably 1% by mass or less.

[0058] The color pigment is not particularly limited as long as it is a colored inorganic substance. Examples of the color pigment include TiO ２ Powder, ZrO ２ Powder and ZrSiO ４Examples of the color pigment include white pigment powders such as powders, blue inorganic pigment powders containing Co, green inorganic pigment powders containing Co, Ti—Sb—Cr and Ti—Ni based yellow inorganic pigment powders, Co—Si based red inorganic pigment powders, brown inorganic pigment powders containing Fe, and black inorganic pigment powders containing Cu. Only one type of the color pigments may be used, or two or more types may be used in combination.

[0059] Examples of blue inorganic pigment powders containing Co include Co-Al-based and Co-Al-Ti-based inorganic pigment powders. ２ O ４ Examples of Co-Al-Ti based inorganic pigment powders include CoAl ２ O ４ -TiO ２ -Li ２ O powder and the like.

[0060] Examples of green inorganic pigment powders containing Co include Co-Al-Cr and Co-Ni-Ti-Zn inorganic pigment powders. Examples of Co-Al-Cr inorganic pigment powders include Co(Al,Cr) ２ O ４ Examples of Co-Ni-Ti-Zn based inorganic pigment powders include (Co, Ni, Zn) ２ TiO ４ Examples include powder.

[0061] Examples of brown inorganic pigment powders containing Fe include Fe-Zn-based inorganic pigment powders. Examples of Fe-Zn-based inorganic pigment powders include (Zn, Fe)Fe ２ O ４ Examples include powder.

[0062] Examples of black inorganic pigment powders containing Cu include Cu—Cr-based inorganic pigment powders and Cu—Fe-based inorganic pigment powders. Examples of Cu—Cr-based inorganic pigment powders include Cu(Cr,Mn) ２ O ４ Examples of Cu-Fe inorganic pigment powders include Cu-Fe-Mn powders and Cu-Cr-Mn powders.

[0063] Other color pigments include, for example, pearlescent pigments.

[0064] The extender pigment is an inorganic pigment powder different from color pigments and inorganic beads. The extender pigment is not particularly limited, but examples thereof include scaly, needle-like, and spherical inorganic pigment powders. Examples of the extender pigment include potassium carbonate, potassium titanate, kaolin, talc, and mica. Only one type of the extender pigment may be used, or two or more types may be used in combination.

[0065] The coating layer 3 may be two or more layers as long as the effects of the present invention can be exhibited.

[0066] From the viewpoint of improving the antifouling properties of the top plate 1 while exerting the effects of the present invention, it is preferable that an antifouling layer is further provided on the inorganic layer 4 in the coating layer 3. In this specification, the term "antifouling properties" refers to the ease of removing stains such as burnt-on stains.

[0067] The antifouling layer preferably contains, for example, a double oxide of silicon and zirconium, a double oxide of silicon and titanium, a double oxide of silicon and aluminum, silicon oxide, zirconium oxide, titanium oxide, aluminum oxide, a mixture of silicon oxide and zirconium oxide, silicon oxide and titanium oxide, a silicone resin, a modified silicone resin, or a fluororesin. From the viewpoint of further exerting the effects of the present invention, it is particularly preferable to use an antifouling layer containing silicon oxide.

[0068] Furthermore, for example, on a surface having a relatively high arithmetic mean roughness (Ra) and root-mean-square roughness (Rq), forming a protective layer made of the same material as the antifouling layer on the surface makes it possible to control the arithmetic mean roughness (Ra) and root-mean-square roughness (Rq) to the desired levels, thereby achieving the effects of the present invention. Even when forming a protective layer, it is particularly preferable for the protective layer to contain silicon oxide. Furthermore, in the coating layer 3, the arithmetic mean roughness (Ra) and root-mean-square roughness (Rq) may be controlled to the desired levels by forming an additional inorganic layer on the inorganic layer 4. In this case, it is preferable that the outermost inorganic layer does not contain inorganic beads. Furthermore, the arithmetic mean roughness (Ra) and root-mean-square roughness (Rq) may be controlled to the desired levels by polishing the surface of the coating layer 3. Methods for polishing the surface of the coating layer 3 include physical polishing and chemical polishing. Physical polishing methods include a method of polishing with a polishing machine using an abrasive slurry or the like for a certain period of time, followed by cleaning, a method of polishing with abrasive paste or the like for a certain period of time with a cloth or sponge, etc., and then cleaning, etc. Chemical polishing methods include a method of applying an aqueous solution containing hydrogen fluoride or the like to the surface of the inorganic layer 4 and leaving it for a certain period of time, followed by cleaning, a method of immersing the entire top plate 1 in an aqueous solution containing hydrogen fluoride or the like and leaving it for a certain period of time, then removing it and cleaning, and a method of spraying vapor of an aqueous solution containing hydrogen fluoride or the like onto the surface of the inorganic layer 4, leaving it for a certain period of time, and then cleaning, etc.

[0069] From the viewpoint of improving the design of the top plate 1, a decorative layer or the like may be further provided on the inorganic layer in the coating layer 3, but from the viewpoint of reducing the number of steps in the manufacturing process, neither layer may be provided.

[0070] The 20° gloss value of the surface of the coating layer 3 of the top plate 1 is preferably 38 or less, more preferably 30 or less, even more preferably 23 or less, and particularly preferably 15 or less. If it is equal to or less than the above upper limit, an appearance with a highly matte finish can be achieved. The lower limit is not particularly limited, but is, for example, 1 or more. Note that, from the viewpoint of realizing a luxurious appearance while enhancing the matte finish, 2 or more is preferred, and 5 or more is more preferred.

[0071] The 60° gloss value of the surface of the coating layer 3 of the top plate 1 is preferably 70 or less, more preferably 65 or less, even more preferably 60 or less, and particularly preferably 55 or less. If it is equal to or less than the above upper limit, an appearance with a highly matte finish can be achieved. The lower limit is not particularly limited, but is, for example, 20 or more. Note that, from the viewpoint of realizing a luxurious appearance while enhancing the matte finish, a value of 30 or more is preferred, and 40 or more is more preferred.

[0072] The top plate 1 for a cooker can be manufactured, for example, by the following manufacturing method.

[0073] First, a paste containing glass beads and glass frit is prepared for forming the inorganic layer 4. Next, the paste for forming the inorganic layer 4 is applied to the surface of the glass substrate 2 that will become the cooking surface 2a, and then dried and baked.

[0074] The inorganic layer 4 forming paste can be applied using known application methods such as screen printing, inkjet printing, and spraying. The drying temperature of the inorganic layer 4 forming paste can be, for example, 50°C or higher and 150°C or lower. The drying time of the inorganic layer 4 forming paste can be, for example, 5 seconds or higher and 50 hours or lower. The baking temperature of the inorganic layer 4 forming paste can be, for example, 600°C or higher and 950°C or lower. The baking time of the inorganic layer 4 forming paste can be, for example, 10 minutes or higher and 2 hours or lower. When the baking temperature and baking time of the inorganic layer 4 are equal to or higher than the above upper and lower limits, the surface shape of the coating layer 3 can be easily adjusted to the desired level, thereby enhancing the matte finish and improving the stain resistance and scratch resistance. In addition, when an additional layer (e.g., an anti-fouling layer, a protective layer, etc.) is formed on the inorganic layer 4 in the coating layer 3, the layer forming paste can be applied using known application methods such as screen printing, inkjet printing, and spraying. The baking temperature for the paste for forming the antifouling layer and the protective layer can be, for example, 400° C. or higher and 800° C. or lower, and the baking time can be, for example, 5 seconds or higher and 50 hours or lower. When the baking temperature and baking time for the antifouling layer and the protective layer are equal to or lower than the upper limit and equal to or higher than the lower limit, it becomes easier to adjust the surface shape of the coating layer 3 to a desired level, and it becomes easier to improve the stain resistance and scratch resistance while enhancing the matte finish.

[0075] In this manner, the top plate 1 for a cooker can be manufactured.

[0076] In the first embodiment described above, as shown in FIG. 1, the configuration of the cooker top plate is described as including a glass substrate and a covering layer disposed on the cooking surface of the glass substrate. However, in the cooker top plate of the present invention, a concealing layer may be disposed on the back surface of the glass substrate.

[0077] In the above-mentioned top plate for a cooker in which a coating layer is disposed on the cooking surface of a glass substrate, the coating layer may be disposed on the entire surface of the cooking surface of the glass substrate or on a portion of the surface of the cooking surface. Furthermore, the entire coating layer may have a single-layer structure or a multi-layer structure, or a portion of the coating layer may have a single-layer structure or a multi-layer structure.

[0078] Furthermore, even if a coating layer is not disposed on the cooking surface of the glass substrate, the effects of the present invention can be achieved as long as the root-mean-square roughness Rq and arithmetic mean roughness Ra of the cooking surface are strictly controlled. In this case, for example, the root-mean-square roughness Rq of the cooking surface is 0.25 to 0.95 μm. The arithmetic mean roughness Ra of the cooking surface is 0.3 to 0.8 μm. The method for controlling the surface condition of the cooking surface can be the above-mentioned method for polishing the surface of the coating layer.

[0079] The present invention will be described in more detail below with reference to examples. However, the following examples are merely illustrative and are not intended to limit the scope of the present invention.

[0080] The following glass substrate was prepared: a transparent crystallized glass plate (Nippon Electric Glass Co., Ltd., "N-0"; average linear thermal expansion coefficient at 30°C to 750°C: 0.5 × 10 －７ / °C, thickness: 4 mm) White crystallized glass plate (Nippon Electric Glass Co., Ltd. "N-11", average linear thermal expansion coefficient at 30°C to 750°C: 13 x 10 －７ / ℃, thickness: 4mm)

[0081] The following materials for the coating layer were prepared. <Glass matrix> Glass frit "Frit NPF" manufactured by Nippon Electric Glass Co., Ltd. (average particle size 3.5 μm, softening point 660° C., borosilicate glass) "Frit NPF10" manufactured by Nippon Electric Glass Co., Ltd. (average particle size 1 μm, softening point 660° C., borosilicate glass) "Fine Frit NPF" manufactured by Nippon Electric Glass Co., Ltd. (average particle size 1.5 μm, softening point 660° C., borosilicate glass) <Inorganic beads> Glass beads "UBS-0010E" manufactured by Unitika Ltd. (average particle size 6.1 μm, softening point 850° C., aluminoborosilicate glass) "UBS-K0005E" manufactured by Unitika Ltd. (average particle size 3.3 μm, softening point 850° C., aluminoborosilicate glass) Alumina beads "DAW-01" manufactured by Denka Company Limited (average particle size 1.9 μm, softening point (melting point) 1000°C or higher) Silica beads "FB-3SDC" manufactured by Denka Company Limited (average particle size 3.1 μm, softening point (melting point) 1650°C) <Resin binder> (Example 1) Glass frit ("Frit NPF" manufactured by Nippon Electric Glass Co., Ltd.), glass beads ("UBS-0010E" manufactured by Unitika Ltd.), and a resin binder were mixed in a mass ratio (glass frit:glass beads:resin binder) of 9:1:7.7 to prepare a paste for forming an inorganic layer. Next, the paste for forming an inorganic layer was screen-printed onto the cooking surface of a transparent crystallized glass plate ("N-0" manufactured by Nippon Electric Glass Co., Ltd.) so that the thickness after firing would be 3.5 μm. Next, the plate was dried by heating at 80°C for 1 minute, and then fired at 800°C for 30 minutes to form an inorganic layer (coating layer). The resin binder was completely volatilized by the heating and drying. Table 1 also lists the content of each component in the inorganic layer after drying and firing. Scanning electron microscope images of the cross section of the resulting cooker top plate are shown in Figures 2 and 3.

[0082] (Examples 2 to 7, 9 to 10 and Comparative Examples 1 and 2) A top plate for a cooker was obtained in the same manner as in Example 1, except that the ratio of each component in the inorganic layer was changed to be as shown in Table 1 below.

[0083] Example 8 The inorganic layer-forming paste used in Example 3 was screen-printed onto the cooking surface of a white crystallized glass plate ("N-11" manufactured by Nippon Electric Glass Co., Ltd.) so that the thickness after firing would be 3.5 μm. Next, the plate was heated and dried at 80°C for 1 minute, and then fired at 800°C for 30 minutes to form an inorganic layer. The resin binder was completely volatilized by heating and drying. Thereafter, an antifouling layer-forming paste having a mass ratio of silicon oxide to zirconium oxide of 1:9 was screen-printed onto the inorganic layer. Next, the plate was fired at 600°C for 20 minutes to form an antifouling layer. In this case, the thickness of the antifouling layer after firing was 0.03 to 0.15 μm.

[0084] Example 11 A top plate for a cooker was obtained in the same manner as in Example 8, except that the paste for forming an antifouling layer was changed to one containing 100% by mass of silicon oxide.

[0085] Example 12 A top plate for a cooker was obtained in the same manner as in Example 8, except that the paste for forming an antifouling layer was changed to one containing 100% by mass of silicone resin.

[0086] Examples 13 and 14 A top plate for a cooker was obtained in the same manner as in Example 8, except that the inorganic layer-forming paste was the same as in Comparative Example 2 and the protective layer-forming paste was changed to one containing 100 mass % silicon oxide. The thickness of the protective layer after firing in Example 13 was 4 to 6 μm, and the thickness of the protective layer after firing in Example 14 was 0.05 to 0.15 μm.

[0087] (Example 15) The inorganic layer-forming paste used in Example 10 was screen-printed onto the cooking surface of a white crystallized glass plate ("N-11" manufactured by Nippon Electric Glass Co., Ltd.) so that the thickness after firing would be 4.9 μm. Next, the plate was heated and dried at 80 ° C. for 1 minute, and then fired at 800 ° C. for 30 minutes to form an inorganic layer. The resin binder was completely volatilized by heating and drying. Then, a paste containing a mixture of glass frit ("Frit NPF" manufactured by Nippon Electric Glass Co., Ltd.) and a resin binder was further screen-printed onto the inorganic layer. Next, the plate was heated and dried at 80 ° C. for 1 minute, and then fired at 800 ° C. for 30 minutes to form a further inorganic layer on the inorganic layer. At this time, the total thickness of the first inorganic layer and the second inorganic layer after firing was 7.7 μm. When the total of the first and second inorganic layers was 100% by mass, the glass was 94% by mass and the silica beads were 6% by mass.

[0088] The following evaluations (1) to (3) and (5) were carried out on the top plates for cookers of Examples 1 to 15 and Comparative Examples 1 and 2. The following evaluation (4) was carried out on the top plates for cookers of Examples 8 and 11 to 12.

[0089] [Evaluation] (1) 20° Gloss Value and 60° Gloss Value of the Surface of the Coating Layer The 20° Gloss Value and 60° Gloss Value of the surface of the coating layer of the obtained cookware top plate were evaluated using a HORIBA IG-331 in accordance with JIS K5600-5-4 (1999). (2) Light Transmittance of the Cookware Top Plate (Coating Layer) The light transmittance of the obtained cookware top plate at a wavelength of 580 nm from the back side of the glass substrate was measured using a spectrophotometer (JASCO Corporation "V-770"). (3) Stain Resistance and Scratch Resistance of the Surface of the Coating Layer First, clay and sand were placed in a stainless steel pot with a bottom diameter of 200±10 mm, and the total weight was adjusted to 2.0 kg. Next, while the bottom of the stainless steel pot was in contact with the coating layer, the stainless steel pot was moved back and forth 100 times at a speed of approximately 1 m / s over a distance of 50 mm. The coating layer was then visually observed, and the degree of dirt adhering due to scraping of the pot bottom (stain resistance) and the degree of scratches on the coating layer due to friction with the pot bottom (scratch resistance) were evaluated according to the following criteria. In addition, the stainless steel pot was replaced with an enamel pot, and clay and sand were added to the enamel pot to adjust the total weight to 2.5 kg, and the same procedures and evaluations were performed. <Stain resistance> ◯: No visible pot stains were observed. △: Slightly visible pot stains were observed. ×: Pot stains that significantly impaired the design were observed. <Scratch resistance> ◯: No visible scratches were observed. △: Slightly visible scratches were observed. ×: Scratches that significantly impaired the design were observed. (4) Stain Resistance of the Stain-Resistant Layer For Example 8, the following stain resistance test 1 was performed, and for Examples 11 and 12, the following stain resistance test 2 was performed. (4-1) Antifouling Test 1 First, 1 g of commercially available yakiniku sauce was dropped onto the antifouling layer (the surface on the cooking side) of the obtained top plate for a cooker and spread thinly. Next, the top plate was heated in an electric furnace at 250°C for 30 minutes, then removed and allowed to cool naturally at room temperature, allowing the yakiniku sauce to scorch onto the surface of the antifouling layer. Next, the top plate was immersed in water at 20°C for 10 minutes, removed, and wiped dry with a cloth.Finally, the top plate was placed on a work surface covered with a non-slip mat, and the tip of a disposable chopstick was placed against the top plate at a 45-degree angle. A load of 750 g was applied while rubbing the burnt-on portion back and forth horizontally 10 times. The degree of removal of the burnt-on portion was evaluated according to the following criteria: ∘: Burnt-on portion was removed. ×: Burnt-on portion was not removed. (4-2) Antifouling Test 2 A top plate with scorched barbecue sauce on the surface of the antifouling layer was prepared using the same procedure as in Antifouling Test 1 above. The top plate was then immersed in water at 20°C for 10 minutes, removed, and wiped dry with a rag. Next, the top plate was fixed to the table of an abrasion tester, and plastic wrap coated with glass top cleaner (Nipro AD-KZ063) was pressed against the top plate surface. A load of 200 kg was applied from above while rubbing the burnt-on portion back and forth horizontally 50 times. The degree of removal of the burnt-on portion was evaluated according to the following criteria: ∘: Burnt-on portion was removed. ×: Burnt-on portion was not removed. (5) State of protrusion of inorganic beads Whether or not inorganic beads protruded from the surface of the coating layer of the obtained top plate for a cooker was confirmed using a scanning electron microscope. ◯: No protrusion x: Protrusion present.

[0090]

[0091]

[0092] As is clear from Tables 1 and 2, the top plates of Examples 1 to 15, in which the coating layer included an inorganic layer and the root-mean-square roughness Rq of the surface of the coating layer was 0.1 μm to 1 μm, had a high matte finish and excellent stain resistance and scratch resistance. Furthermore, the top plates of Examples 1 to 15 had an excellent matte finish and excellent stain resistance and scratch resistance compared to Comparative Examples 1 and 2, in which the root-mean-square roughness Rq of the surface of the coating layer was not 0.1 μm to 1 μm. In Examples 8, 11, and 12, in which an anti-fouling layer was further formed on the inorganic layer, the arithmetic mean roughness Ra and root-mean-square roughness Rq were able to be controlled to the desired levels, and the matte finish, stain resistance, and scratch resistance were excellent, with improved anti-fouling properties also being achieved. Furthermore, in Examples 13 and 14, in which a protective layer was further formed on an inorganic layer having a large arithmetic mean roughness Ra and root mean square roughness Rq, the arithmetic mean roughness Ra and root mean square roughness Rq could be controlled to the desired extent, and the matte finish, stain resistance, and scratch resistance could be improved.In Example 15, in which an inorganic layer made of glass frit was further formed on an inorganic layer made of glass frit and inorganic beads, the arithmetic mean roughness Ra and root mean square roughness Rq could be controlled to the desired extent, and the matte finish, stain resistance, and scratch resistance could be improved.

[0093] As is clear from Fig. 2, the glass beads (inorganic beads) were present in the coating layer as approximately spherical beads without protruding from the surface of the coating layer in the top plate of Example 2. Also, from Fig. 3, it was confirmed that the silica beads (inorganic beads) protruded from the surface of the coating layer in the top plate of Example 10.

[0094] DESCRIPTION OF SYMBOLS 1. Cooking appliance top plate 2. Glass substrate 2a. Cooking surface 2b. Back surface 3. Coating layer 4. Inorganic layer 5. Inorganic beads

Claims

1. A top plate for a cooker comprising: a glass substrate having a cooking surface on which a cookware is placed and a back surface opposite the cooking surface; and a coating layer disposed on the cooking surface side of the glass substrate, the coating layer including an inorganic layer, and the root mean square roughness Rq of the surface of the coating layer being 0.1 μm to 1 μm.

2. The top plate for a cookware according to claim 1, wherein the inorganic layer contains inorganic beads.

3. The top plate for a cooker according to claim 2, wherein the arithmetic mean roughness Ra of the surface of the coating layer is 0.22 μm to 0.9 μm.

4. A top plate for a cooker according to claim 2 or 3, wherein the inorganic beads contain at least one type of inorganic beads selected from the group consisting of glass beads, alumina beads, silica beads, zirconia beads, quartz beads, feldspar beads, zeolite beads, corundum beads, and zircon beads.

5. A top plate for a cooker according to claim 2 or 3, wherein the inorganic beads do not protrude from the surface of the coating layer.

6. A top plate for a cooker according to claim 2 or 3, wherein the inorganic layer contains a glass matrix, and the difference in softening point between the inorganic beads and the glass matrix is ​​300° C. or less.

7. A top plate for a cookware according to claim 2 or 3, wherein the inorganic layer comprises a glass matrix having a refractive index different from that of the inorganic beads.

8. The top plate for a cookware according to claim 2 or 3, wherein the inorganic layer does not contain a color pigment.

9. A top plate for a cooker according to claim 2 or 3, wherein the covering layer further comprises an anti-fouling layer and / or a protective layer on the inorganic layer.

10. A top plate for a cooker according to claim 1 or 2, wherein the 20° gloss value of the surface of the coating layer is 38 or less.

11. A top plate for a cooker according to claim 1 or 2, wherein the 60° gloss value of the surface of the coating layer is 70 or less.

12. A top plate for a cooker comprising a glass substrate having a cooking surface on which a cookware is placed and a back surface opposite to the cooking surface, the root mean square roughness Rq of the surface of the cooking surface being 0.25 μm to 0.95 μm.

13. A method for manufacturing a top plate for a cooker according to claim 1 or 2, comprising the steps of applying an inorganic layer-forming paste containing inorganic beads to a surface of a glass substrate, and firing the paste to form a coating layer containing an inorganic layer on the surface of the glass substrate, wherein the root-mean-square roughness Rq of the surface of the coating layer is 0.1 μm to 1 μm.

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