JPH07122359A - Window part of microwave oven - Google Patents

Abstract

PURPOSE:To improve heat efficiency by using a glass substrate having a transparent conductive film of specific sheet resistance value on the surface, for a window part. CONSTITUTION:An ITO solid film 1 is formed on a glass substrate 3, and a resist resin 2 is formed on the film 1 by screen printing method. A film part 1a which is not covered with the resin 2 is removed by etching and the resin 2 is then peeled off. The substrate 3 having this ITO pattern film 1b is used for the front window of an oven. The pattern of the film 1b is a complex body of island-shape small regions, and microwave is not easily absorbed in relation to wavelength, while the gap interval of the film 1b is made to be shorter than microwave length so as to prevent microwave from leaking to the outside of the microwave oven. Since excellent heat ray reflection characteristic and excellent transparency in visible region can be achieved and absorption of microwave is reduced at the time of cooking by the microwave oven, by using a glass substrate having a transparent conductive film of 100OMEGA/unit sq.-1000OMEGA/ unit sq. in sheet resistance, on the surface, for the front glass window, heat efficiency can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating for a window of a microwave oven (general term for microwave ovens and electric ovens).

[0002]

2. Description of the Related Art Conventionally, a heat ray reflective film is formed on the inner surface of a front glass window in order to improve the heat efficiency when cooking in a microwave oven or an electric oven. As a material for such a heat ray reflective film, tin oxide / antimony oxide (ATO) or indium oxide / tin oxide (ITO) is used.
Such metal oxides are known, and by forming these coatings on a glass substrate, a window glass having a transparent heat ray reflective film on its surface can be prepared. Since these heat ray reflective films have conductivity, they also have an effect of shielding microwaves. Therefore, it is very suitable as a window material for a microwave oven. As a method for forming these metal oxide films, a vacuum vapor deposition method, a sputtering method, a CVD method and a coating method are known.

[0003]

However, in each of the above-mentioned vacuum deposition method, sputtering method and CVD method, the apparatus is complicated and expensive, and there are problems in cost and mass productivity. Further, although the coating method has a possibility of solving the above-mentioned problems of the vacuum vapor deposition method, the sputtering method and the CVD method, it has been difficult to form a film that can be practically used.
For example, when an organic solution of an inorganic compound such as indium nitrate, indium chloride, or stannic chloride is used, white turbidity occurs in the formed film, or the mechanical strength of the obtained film is insufficient and scratches are easily caused. There are drawbacks such as sticking. In addition, in the method using an organic acid indium having a strong ionic bond such as indium octylate, the organic acid indium is easily hydrolyzed and chemically changes relatively easily, so that gelling of the coating liquid occurs. There are drawbacks. Furthermore, a method using an organic complex of indium or tin has been proposed, but in this method, during the thermal decomposition of the coating film applied on the substrate, the evaporation of the tin compound may hinder the uniformity of the film. Therefore, there is a drawback that a homogeneous film having a low resistance cannot be obtained. On the other hand, as the electric resistance of the film decreases, the microwaves during cooking are absorbed by the film in a microwave oven to a greater extent and heat is generated on the front window glass, which lowers the thermal efficiency of cooking and causes the window glass to experience thermal strain. There was an inconvenience that it was damaged due to. In particular, a film obtained by a vacuum process such as sputtering or vapor deposition has a low electric resistance due to its high crystallinity (individual resistance value of 1 × 10 ⁻⁴ to 1 × 10 ^4).
-5 [Ω · cm], sheet resistance value of 100 [Ω / □] or less (where Ω / □ represents the unit of sheet resistance by the four-point probe method), and such inconvenience is likely to occur. . Also,
Generally, the magnitude of the sheet resistance value of the film and the infrared reflectance are in inverse proportion to each other, and increasing the resistance value lowers the infrared reflectance. Thus, there is a problem in using the conventional sputtering film as it is in the window of the microwave oven.

The present invention is to solve the above problems and provides a transparent conductive film having a high visible light transmittance and a heat ray reflectance and a small microwave absorptivity in a window portion for a microwave oven. To aim.

[0005]

In order to achieve the above object, the present invention has a sheet resistance value of 100 [Ω / □] to 1
A glass substrate having a transparent conductive film of 000 [Ω / □] on its surface was used for the window of a microwave oven. Here, the transparent conductive film may have a pattern composed of an aggregate of individually separated small regions. The transparent conductive film is preferably a mixture of indium oxide and tin oxide or a complex oxide of indium and tin. The transparent conductive film is preferably obtained by coating and firing a thermally decomposable liquid containing an organic tin compound, an inorganic indium compound, an organic compound capable of coordinating with the compound, and a solvent.

[0006]

A sheet resistance value of 100 [Ω / □] to 1000 provided on the surface of the glass substrate of the window of a microwave oven or the like.
The transparent conductive film of [Ω / □] hardly absorbs microwaves during microwave oven cooking and has a high heat ray reflectance. Therefore, the thermal efficiency of the range is greatly increased. Moreover, since the heat generation is small due to the small absorption, the glass substrate is not damaged. In addition, the transparent conductive film having a pattern made up of a collection of individually separated small regions has a function of further hindering the absorption of microwaves.

[0007]

EXAMPLES Examples of the present invention will be described in detail below.
The composition for forming a transparent conductive film of the present invention is synthesized as follows. First, an inorganic indium compound is mixed with an organic compound capable of coordinating both indium and tin. Here, the inorganic indium compound may have an organic compound capable of coordinating with indium or tin and a ligand capable of substituting. Examples thereof include indium nitrate and indium chloride, and those having crystallization water are preferable. Further, an organic compound capable of coordinating both indium and tin is necessary for coordinating indium and tin in part, assisting formation of an intermediate compound thereof, and having solubility in an organic solvent. , Β-diketones, α- or β-ketone acids, esters of the above ketone acids, α- or β-amino alcohols. Next, an organic solvent and an organic tin compound are added to the solution, and the organic solution is heat-treated. Here, the organotin compound may be any one that is relatively stable in the air but is easily hydrolyzed by heat treatment. Examples thereof include tin carboxylate and tin dicarboxylate, and tin formate, tin acetate or tin oxalate having a small number of carbon atoms are preferable. Further, as the organic solvent, any solvent capable of dissolving the organic compound or the inorganic compound used in the present invention may be used. For example, aromatic hydrocarbons such as toluene and xylene, alcohols such as ethanol and isopropanol, acetic acid esters such as ethyl acetate and butyl acetate,
Examples thereof include ketones such as acetone and diethyl ketone, ethers such as methoxyethanol and ethoxyethanol, and tetrahydrofuran. Furthermore, the temperature of the heat treatment is preferably at or near the reflux temperature of the organic solution containing the inorganic indium compound, the organic tin compound, and the organic compound capable of coordinating with them.

Then, the organic solution after the heat treatment is cooled to around room temperature, polyhydric alcohols are added, and the mixed organic solution is made into a thermally decomposable composition. Here, the polyhydric alcohol provides the thickening effect of the organic solution and the stability of the coating film obtained by coating and drying the thermally decomposable composition on the glass substrate. Examples thereof include alcohols, and ethylene glycol and glycerin, which have a small number of carbon atoms and are less likely to remain carbon during thermal decomposition, are preferable. The heat-decomposable composition thus obtained is applied to a substrate, dried, and then fired to form a heat ray reflective film. Here, for the application of the thermally decomposable composition, a screen printing method,
A roll coating method, a dip coating method, a spin coating method or the like can be used, but the dip coating method and the spin coating method are preferable. The firing temperature may be higher than or equal to the temperature at which the thermally decomposable composition decomposes and lower than or equal to the deformation temperature of the glass substrate, preferably 400 to 700 ° C. Hereinafter, the present invention will be described with reference to more detailed examples, but it goes without saying that the present invention is not limited to these examples.

Example 1 45 g of indium nitrate (In (NO ₃ ) ₃ .3H ₂ O) was weighed in a 1-liter Erlenmeyer flask, 50 g of acetylacetone was added, and the mixture was mixed and dissolved at room temperature. Stannous oxalate (SnC ₂ O ₄ ) and acetone were added to the solution so that the Sn / (In + Sn) ratio was 35 wt%, and the mixture was refluxed. The solution after the reflux was cooled to around room temperature, 5 g of glycerin was added, and the mixture was stirred and mixed to synthesize a thermally decomposable composition. The thermally decomposable composition has a thickness of 5 m
m soda glass substrate was dip coated at a pulling rate of 60 cm / min. Leave the substrate at room temperature for 5 minutes and
After drying at 5 ° C for 5 minutes, it was baked at 500 ° C for 1 hour. The thickness of the film thus formed was 0.10 μm. In this way, an ITO glass in which an ITO film (hereinafter referred to as an ITO solid film) is applied to the entire surface of the glass substrate is completed. The resulting ITO glass is used for the front window of the microwave oven.

[Embodiment 2] FIG. 1 shows an ITO according to this embodiment.
It is sectional drawing which shows the structure of glass. In the figure, first, a glass substrate 3 having an ITO solid film 1 formed thereon by the method shown in Example 1 is prepared. Next, a resist resin 2 having a pattern as shown in FIG. 1, for example, is formed on the surface of the ITO solid film 1 by a screen printing method. Next, resist resin 2
The ITO film portion 1a not covered with is removed by etching, and then the resist resin 2 is peeled off. The glass substrate 3 having the ITO pattern film 1b thus obtained is used as a front window of a microwave oven. Here, the pattern of the ITO pattern film 1b is, for example, an aggregate of island-shaped (individually separated island-shaped) small regions. The formation of such a pattern makes it difficult for the microwave to be absorbed due to its relationship with the wavelength. The gap between the ITO pattern films 1b is shorter than the wavelength of the microwave in order to prevent the microwave from leaking to the outside of the microwave oven.

[Comparative Example 1] As a comparative example, an ITO film was formed on a soda glass substrate having a thickness of 3 mm by RF sputtering of an ITO target, and the ITO film was used as a front window of a microwave oven. Table 1 shows the comparison results of the infrared reflectance, visible light (wavelength 550 nm) transmittance, sheet resistance, degree of microwave absorption and thermal efficiency of Examples 1 and 2 and Comparative Example 1.

[0012]

[Table 1]

As is clear from Table 1, Example 1 is superior to Comparative Example 1 in thermal efficiency, and Example 2 is even more superior.

FIG. 2 is a plot of the microwave absorptivity and infrared reflectance of the ITO film of the present invention obtained by the dip pyrolysis method against the sheet resistance of the film. The sheet resistance can be adjusted by changing the film thickness or the (tin / indium) ratio. As is clear from the figure, the sheet resistance is 100 [Ω / □] and 1000 [Ω /
In □], a critical change is seen in the characteristics. That is,
The infrared reflectance (solid line) gradually decreases as the sheet resistance increases, but begins to decrease rapidly when the sheet resistance exceeds 1000 [Ω / □]. On the other hand, the microwave reflectivity (broken line) sharply decreases as the resistance value increases in the region where the sheet resistance is less than 100 [Ω / □], but decreases when the sheet resistance reaches 100 [Ω / □]. Very loose. Therefore, the sheet resistance is 100 to 1000 [Ω
In the range of [/ □], it can be seen that the microwave absorption is almost stable at a low level and the infrared reflectance is maintained at a relatively high level.

[Third Embodiment] FIG. 3 is a sectional view showing a third embodiment. This is a diagram showing a schematic structure of a microwave oven using the ITO glass according to the second embodiment. In the figure, first, the ITO film 12 is formed on the substantially hemispherical glass 13 by the same method as that described in the second embodiment. Finished almost hemispherical I
The TO glass 14 is used as the lid of the microwave oven. That is, the substantially hemispherical ITO glass 14 becomes the lid of the range and is placed on the plate part 15 of the main body, and the microwave emitted from the range main part 16 including the magnetron etc. passes through the plate part 15 and reaches the food 17. Is irradiated. Since the substantially hemispherical ITO glass 14 provided with the ITO film hardly absorbs microwaves and reflects infrared rays well, it is possible to provide a microwave oven having a novel appearance with good thermal efficiency.

In the first embodiment described above, the example in which the heat ray reflective films are formed on both surfaces of the glass substrate by the dip pyrolysis method has been described. It is of course possible to form a reflective film.

[0017]

Since the present invention is configured as described above, it has the following effects. Sheet resistance is 100 [Ω /
□] to 1000 [Ω / □] A glass substrate having a transparent conductive film on its surface is used for the front glass window, and thus has excellent heat ray reflection characteristics and transmittance in the visible region, and also absorbs microwaves during microwave cooking. Is smaller, so that the thermal efficiency is improved. Further, the window portion of the microwave oven configured by using the transparent conductive film also has the effect of reflecting microwaves, and the effect that the use of the front perforated metal plate that has been conventionally used for microwave shielding becomes unnecessary. There is. Further, the window portion of the microwave oven configured by the pattern of the aggregate of the small regions in which the transparent conductive film is separated is further difficult to absorb the microwave because of the relationship with the wavelength of the microwave, and thus the thermal efficiency is further improved. There is an effect.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a patterned ITO film of the present invention.

FIG. 2 is a diagram showing the relationship between the electric resistance of a film and both characteristics of infrared reflection and microwave absorption.

FIG. 3 is a cross-sectional view showing an example of a microwave oven using a transparent conductive film according to the present invention.

[Explanation of symbols]

 1 ITO solid film 1b ITO pattern film 3 Glass substrate

Claims (4)

[Claims] 1. The sheet resistance is 100 Ω / □ to 1000 Ω.
A window part of a microwave oven composed of a glass substrate having a transparent conductive film of / □ on its surface. 2. The window portion of a microwave oven according to claim 1, wherein the transparent conductive film has a pattern composed of an assembly of individually separated small regions. 3. The window part of a microwave oven according to claim 1, wherein the transparent conductive film is a mixture of an indium oxide and a tin oxide or a complex oxide of indium and tin. 4. The transparent conductive film is obtained by coating and firing a thermally decomposable liquid containing an organic tin compound, an inorganic indium compound, an organic compound capable of coordinating with the compound, and a solvent. The window of the microwave oven according to Item 1.