JPH1085100A - Anti-clouding heat-insulated showcase - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-insulated showcase having anti-clouding transparent window panels that are excellent in visibility for food contained. SOLUTION: The inside surface of transparent window panels 12 of a heat- insulated showcase 10 is coated with a layer containing photocatalyst. When the photocatalyst is given photoexcitation, the surface of the photocatalyst layer becomes hydrophilic to have an angle of contact with water 10 deg. or less. As a result, water drops condensed on the inner surface of the transparent panels 12 spreads into a uniform water layer, and thus, visibility of displayed food is secured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulated showcase for displaying foods in an insulated state.

[0002]

2. Description of the Related Art A showcase for displaying food such as Chinese steamed bun which is desired to be kept warm is equipped with a heating device such as a steam generator so that the displayed food is kept warm. The heat-insulated showcase is provided with a transparent window panel made of glass, acrylic resin, or the like, so that the displayed food can be seen from the outside.

[0003]

The inside of the transparent window panel of the heat-insulated showcase becomes cloudy due to condensation of steam, so that it is difficult to clearly see the displayed food from the outside. When the condensation of the vapor further proceeds and fine condensed water droplets fuse with each other and grow into larger water droplets, the perspective image is distorted due to refraction of light at the interface between the water droplet and the window panel and at the interface between the water droplet and the air. Food inside is difficult to see.

[0004] It is an object of the present invention to provide an anti-fogging heat-insulating showcase which can prevent the transparent window from fogging and adhere to water droplets, and is excellent in the visibility of displayed food.

[0005]

Means for Solving the Problems The present inventors have discovered that the surface of a photocatalyst is highly hydrophilized by photoexcitation of the photocatalyst. The present invention is based on such a discovery, and the present invention is characterized in that, in a heat retaining showcase provided with a transparent window panel and a heating device, the inner surface of the transparent window panel is coated with a transparent layer containing a semiconductor photocatalyst. Is what you do. When the photocatalyst of the photocatalyst-containing layer is photoexcited, the surface of the photocatalyst-containing layer has a contact angle with water of 10 ° or less, more specifically 5 ° or less, particularly about 0 °.
It is highly hydrophilized to the degree of ゜. The condensed water attached to the superhydrophilized surface spreads quickly on the surface while forming a uniform water film, so that no fogging occurs on the transparent window panel. Even if the condensation of the vapor proceeds, the condensed water droplets become a uniform water film and flow down quickly. Therefore,
Good visibility of the displayed food is ensured.

It is preferable to use harmless and highly photoactive titania as the photocatalyst. Photocatalytic titania, such as anatase, can be photoexcited by ultraviolet light.
In order to optically excite titania, weak ultraviolet light contained in indoor lighting such as a fluorescent lamp is sufficient. Therefore, when the heat-insulated showcase is installed indoors, the photocatalytic titania can be photo-excited by the ultraviolet light from the room lighting that enters through the transparent window of the heat-insulated showcase. Alternatively, under conditions in which the heat retaining showcase is exposed to the sun, the titania can be photo-excited by the ultraviolet light contained in the sunlight. However, in a preferred embodiment, the insulated showcase is provided with an internal illuminator such as a fluorescent lamp that emits weak ultraviolet light together with visible light, and illuminates the displayed food with the illuminator and optically excites the photocatalyst. In this case, the ultraviolet illuminance of the illumination lamp is 0.1 mW / cm ²
It is preferable to make the above.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a heat-insulating showcase 10 includes, for example, four transparent window panels 12 made of glass or acrylic resin and a shelf frame 14 on which food is placed. ing. An internal illuminating lamp 16 such as a fluorescent lamp is arranged at an appropriate place of the showcase so as to illuminate the displayed food. Insulated showcase 1
A steam generator 18 is arranged at the lower part of 0 so as to steam the displayed food. The inner surface of the transparent window panel 12 is covered with a transparent layer 20 containing a semiconductor photocatalyst. The photocatalyst of the photocatalyst containing layer 20 is photoexcited by ultraviolet light contained in the light from the internal illumination lamp 16.

As a photocatalyst, titania (TiO ₂ ) is most preferable. Titania is harmless, chemically stable, and available at low cost. Both anatase titania and rutile titania can be used. An advantage of anatase titania is that a sol in which very fine particles are dispersed can be easily obtained on the market, and a very thin thin film can be easily formed. On the other hand, rutile-type titania can be sintered at a high temperature, and has an advantage that a film having excellent strength and wear resistance can be obtained. When the inner surface of the transparent window panel 12 is coated with the photocatalytic titania-containing layer 20 and the titania is photoexcited by ultraviolet light, water is chemically adsorbed on the surface in the form of hydroxyl groups (OH ⁻ ) by the photocatalysis, and as a result, the surface becomes super hydrophilic. It is considered to be sex. Other photocatalysts that can be used include Zn
There are metal oxides such as O, SnO ₂ , SrTiO ₃ , WO ₃ , Bi ₂ O ₃ , and Fe ₂ O ₃ . These metal oxides, like titania,
Since metal elements and oxygen exist on the surface, surface hydroxyl groups (OH
^- ) It is thought to adsorb. The photocatalyst-containing layer may be formed by mixing particles of photocatalytic titania with a metal oxide. In particular, when anatase titania is mixed with silica or tin oxide as described later, the surface can be highly hydrophilized.

The thickness of the photocatalyst-containing layer is preferably set to 0.2 μm or less. With such a film thickness, color formation due to light interference can be prevented. In addition, the thinner the photocatalyst-containing layer is, the more the transparency of the photocatalyst-containing layer can be secured and the more the wear resistance of the photocatalyst-containing layer is improved.

When the transparent window panel 12 is formed of a heat-resistant material such as glass, it contains a photocatalyst exhibiting super-hydrophilicity with a contact angle with water of 0 ° and excellent in abrasion resistance. One preferred way of forming the layer is to first coat the surface of the substrate with amorphous titania and then calcine the amorphous titania to remove crystalline titania (anatase or rutile).
Is to change the phase. Any of the following methods can be used for forming amorphous titania. (1) Hydrolysis and dehydration condensation polymerization of organic titanium compounds Alkoxides of titanium, for example, tetraethoxytitanium, tetraisopropoxytitanium, tetra-n-propoxytitanium, tetrabutoxytitanium, tetramethoxytitanium, and hydrochloride such as hydrochloric acid or ethylamine After adding a decomposition inhibitor and diluting with an alcohol such as ethanol or propanol, after partially or completely promoting hydrolysis, the mixture is spray-coated, flow-coated, spin-coated,
Apply to the substrate surface by dip coating, roll coating or other coating method
Dry at a temperature of 0 ° C. By drying, hydrolysis of the alkoxide of titanium is completed to produce titanium hydroxide, and a layer of amorphous titania is formed on the surface of the substrate by dehydration-condensation polymerization of titanium hydroxide. Instead of titanium alkoxides, other organic titanium compounds such as titanium chelates or titanium acetate may be used. (2) Formation of amorphous titania by inorganic titanium compound Spray coating, flow coating of an acidic aqueous solution of an inorganic titanium compound, for example, TiCl ₄ or Ti (SO ₄ ) ₂ ,
It is applied to the surface of a substrate by spin coating, dip coating, or roll coating. Next, the inorganic titanium compound is subjected to hydrolysis and dehydration-condensation polymerization by drying at a temperature of about 100 ° C to 200 ° C to form a layer of amorphous titania on the surface of the substrate. Alternatively, amorphous titania may be applied to the surface of the substrate by chemical vapor deposition of TiCl ₄ . (3) Formation of Amorphous Titania by Sputtering Amorphous titania is deposited on the surface of a substrate by irradiating an electron beam to a target of titanium metal in an oxidizing atmosphere. (4) Firing temperature The firing of amorphous titania is performed at least at a temperature higher than the crystallization temperature of anatase. If calcined at a temperature of 400 ° C. to 500 ° C. or higher, amorphous titania can be converted to anatase titania. By firing at a temperature of 600 ° C. to 700 ° C. or higher, amorphous titania can be converted to rutile type titania. (5) Formation of diffusion prevention layer When the base material is glass or glazed tile containing alkali network modifying ions such as sodium, an intermediate layer such as silica is previously formed between the base material and the amorphous titania layer. Good to keep. This prevents the alkali network modifying ions from diffusing from the substrate into the photocatalyst-containing layer during firing of the amorphous titania, and achieves a super-hydrophilic property such that the contact angle with water becomes 0 °. .

Another preferred method of forming a photocatalyst-containing layer exhibiting superhydrophilicity such that the contact angle with water is 0 ° and having excellent abrasion resistance is to form a photocatalyst-containing layer comprising a mixture of titania and silica. It is to form on the surface of the substrate. The ratio of silica to the total of titania and silica is 5 to 5.
It can be 90 mol%, preferably 10 to 70 mol%, more preferably 10 to 50 mol%. For forming the photocatalyst-containing layer made of silica-containing titania, any of the following methods can be employed. (1) A suspension containing particles of anatase type or rutile type titania and particles of silica is applied to the surface of a substrate, and sintered at a temperature equal to or lower than the softening point of the substrate. (2) precursors of amorphous silica (for example, tetraalkoxysilanes such as tetraethoxysilane, tetraisopropoxysilane, tetra-n-propoxysilane, tetrabutoxysilane, tetramethoxysilane, etc .; silanol which is a hydrolyzate thereof); Alternatively, a mixture of a polysiloxane having an average molecular weight of 3,000 or less) and crystalline titania sol is applied to the surface of the base material and, if necessary, hydrolyzed to form silanol, and then heated at a temperature of about 100 ° C. or higher to obtain silanol. Is subjected to dehydration-condensation polymerization to form a photocatalyst-containing layer in which titania is bound with amorphous silica. In particular, if the dehydration polycondensation of silanol is performed at a temperature of about 200 ° C. or more,
The polymerization degree of silanol can be increased, and the alkali resistance performance of the photocatalyst-containing layer can be improved. This approach can be applied to non-heat resistant substrates such as plastic. (3) Dispersing silica particles in a solution of amorphous titania precursor (organic titanium compound such as alkoxide, chelate or acetate of titanium, or inorganic titanium compound such as TiCl ₄ or Ti (SO ₄ ) ₂ ) The resulting suspension is applied to the surface of a substrate, and the titanium compound is subjected to hydrolysis and dehydration condensation polymerization at a temperature of from room temperature to 200 ° C. to form a thin film of amorphous titania in which silica particles are dispersed. . Next, the amorphous titania is changed into crystalline titania by heating to a temperature equal to or higher than the crystallization temperature of titania and equal to or lower than the softening point of the substrate. (4) Amorphous titania precursor (organic titanium compound such as alkoxide, chelate or acetate of titanium, or inorganic titanium compound such as TiCl ₄ or Ti (SO ₄ ) ₂ ) in a solution of a precursor of amorphous titania Body (eg, tetraethoxysilane, tetraisopropoxysilane, tetran
A mixture of tetraalkoxysilanes such as propoxysilane, tetrabutoxysilane, and tetramethoxysilane; silanol which is a hydrolyzate thereof; or polysiloxane having an average molecular weight of 3000 or less), and coating the mixture on the surface of the substrate. Next, these precursors are subjected to hydrolysis and dehydration condensation polymerization to form a thin film composed of a mixture of amorphous titania and amorphous silica. Next, the amorphous titania is changed into crystalline titania by heating to a temperature equal to or higher than the crystallization temperature of titania and equal to or lower than the softening point of the substrate.

Still another preferred method of forming a photocatalyst-containing layer exhibiting superhydrophilicity such that the contact angle with water is 0 ° and having excellent abrasion resistance is a photocatalyst containing a mixture of titania and tin oxide. Forming a layer on the surface of the substrate. The ratio of tin oxide to the total of titania and tin oxide can be 1 to 95% by weight, preferably 1 to 50% by weight. For forming the photocatalyst-containing layer made of tin oxide-containing titania, any of the following methods can be employed. (1) A suspension containing particles of anatase or rutile type titania and particles of tin oxide is applied to the surface of a substrate, and sintered at a temperature equal to or lower than the softening point of the substrate. (2) Tin oxide particles in a solution of amorphous titania precursor (organic titanium compound such as titanium alkoxide, chelate or acetate, or inorganic titanium compound such as TiCl ₄ or Ti (SO ₄ ) ₂ ) The suspension obtained by dispersing is applied to the surface of the base material, and the titanium compound is subjected to hydrolysis and dehydration condensation polymerization at a temperature of from room temperature to 200 ° C., thereby forming a thin film of amorphous titania in which tin oxide particles are dispersed. Form. Next, the amorphous titania is changed into crystalline titania by heating to a temperature equal to or higher than the crystallization temperature of titania and equal to or lower than the softening point of the substrate.

When the transparent panel 12 is formed of a non-heat-resistant material such as an acrylic resin, it is preferable to form a photocatalyst-containing layer exhibiting superhydrophilicity such that the contact angle with water becomes 0 °. The approach is to use a coating composition comprising photocatalyst particles dispersed in a film-forming element consisting of uncured or partially cured silicone or a silicone precursor. Transparent panel 1
When the photocatalyst is photo-excited after the coating on the inner surface of 2 and the film-forming element is cured, the organic groups bonded to the silicon atoms of the silicone molecules are replaced with hydroxyl groups by the photocatalysis of the photocatalyst, and the surface of the photocatalyst-containing layer becomes Super hydrophilic. Since the photocatalyst-containing silicone coating has a siloxane bond, it has sufficient resistance to the photooxidation action of the photocatalyst.

The coating film forming elements include methyltrichlorosilane, methyltribromosilane, methyltrimethoxysilane, methyltriethoxysilane, methyltriisopropoxysilane, methyltri-t-butoxysilane; ethyltrichlorosilane, ethyltribromosilane, Ethyltrimethoxysilane, ethyltriethoxysilane, ethyltriisopropoxysilane, ethyltri-t-butoxysilane; n-propyltrichlorosilane, n-propyltribromosilane, n-propyltrimethoxysilane,
n-propyltriethoxysilane, n-propyltriisopropoxysilane, n-propyltri-t-butoxysilane; n-hexyltrichlorosilane, n-hexyltribromosilane, n-hexyltrimethoxysilane, n
-Hexyltriethoxysilane, n-hexyltriisopropoxysilane, n-hexyltrit-butoxysilane; n-decyltrichlorosilane, n-decyltribromosilane, n-decyltrimethoxysilane, n-decyltriethoxysilane, n -Decyltriisopropoxysilane, n-decyltri-t-butoxysilane; n-octadecyltrichlorosilane, n-octadecyltribromosilane, n-octadecyltrimethoxysilane, n-octadecyltriethoxysilane, n-octadecyltriisopropoxysilane, n-octadecyltri-t-butoxysilane; phenyltrichlorosilane, phenyltribromosilane, phenyltrimethoxysilane, phenyltriethoxysilane, phenyltriisopropoxysilane, phenyltrisilane -Butoxysilane; tetrachlorosilane, tetrabromosilane, tetramethoxysilane, tetraethoxysilane, tetrabutoxysilane, dimethoxydiethoxysilane; dimethyldichlorosilane, dimethyldibromosilane, dimethyldimethoxysilane, dimethyldiethoxysilane; diphenyldisilane Chlorosilane, diphenyldibromosilane, diphenyldimethoxysilane,
Diphenyldiethoxysilane; phenylmethyldichlorosilane, phenylmethyldibromosilane, phenylmethyldimethoxysilane, phenylmethyldiethoxysilane; trichlorohydrosilane, tribromohydrosilane, trimethoxyhydrosilane, triethoxyhydrosilane, triisopropoxyhydrosilane, tri-t -Butoxyhydrosilane; vinyltrichlorosilane, vinyltribromosilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane,
Vinyl tri-t-butoxysilane; trifluoropropyltrichlorosilane, trifluoropropyltribromosilane, trifluoropropyltrimethoxysilane, trifluoropropyltriethoxysilane, trifluoropropyltriisopropoxysilane, trifluoropropyltri-t-butoxysilane; γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyltriisopropoxy Silane, γ-glycidoxypropyltri-t-butoxysilane; γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-metha Riloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-methacryloxypropyltriisopropoxysilane, γ-methacryloxypropyltri-t-butoxysilane; γ-aminopropylmethyldimethoxysilane, γ- Aminopropylmethyldiethoxysilane, γ
-Aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltriisopropoxysilane, γ-aminopropyltri-t-butoxysilane; γ-mercaptopropylmethyldimethoxysilane, γ-mercaptopropylmethyldiethoxysilane , Γ-mercaptopropyltrimethoxysilane, γ-
Mercaptopropyltriethoxysilane, γ-mercaptopropyltriisopropoxysilane, γ-mercaptopropyltri-t-butoxysilane; β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, β-
(3,4-Epoxycyclohexyl) ethyltriethoxysilane; and their partial hydrolysates; and mixtures thereof can be used.

When the transparent window panel 12 covered with the photocatalyst containing layer 20 is irradiated with ultraviolet rays, the photocatalyst is photoexcited and the surface of the photocatalyst containing layer is made superhydrophilic.

[0016]

EXAMPLE 1 86 parts by weight of ethanol solvent was mixed with tetraethoxysilane Si.
6 parts by weight of (OC ₂ H ₅ ) ₄ (Wako Pure Chemical), 6 parts by weight of pure water, and 2 parts by weight of 36% hydrochloric acid as a tetraethoxysilane hydrolysis inhibitor were added and mixed to prepare a silica coating solution. Since the solution generated heat by mixing, the mixture was left to cool for about 1 hour. This solution was applied to the surface of a 10 cm square soda lime glass plate by the flow coating method,
Dried at a temperature of ° C. With drying, tetraethoxysilane was hydrolyzed to silanol Si (OH) _{4 first} , and then a thin film of amorphous silica was formed on the surface of the glass plate by dehydration condensation polymerization of silanol. Next, 0.1 part by weight of 36% hydrochloric acid as a hydrolysis inhibitor was added to a mixture of 1 part by weight of tetraethoxytitanium Ti (OC ₂ H ₅ ) ₄ (Merck) and 9 parts by weight of ethanol to prepare a titania coating solution. It was prepared and this solution was applied to the surface of the glass plate by a flow coating method in dry air. The coating amount was 45 μg / cm ² in terms of titania. Since the rate of hydrolysis of tetraethoxytitanium is extremely fast, part of the tetraethoxytitanium is hydrolyzed at the coating stage, and titanium hydroxide Ti (O
H) ₄ began to form. Next, by maintaining the glass plate at a temperature of about 150 ° C. for 1 to 10 minutes, hydrolysis of tetraethoxytitanium is completed, and the generated titanium hydroxide is subjected to dehydration polycondensation to form amorphous titania. Generated. Thus, a glass plate in which amorphous titania was coated on amorphous silica was obtained. 500 ℃
The amorphous titania was converted to anatase titania to obtain # 1 sample. Amorphous silica coating is applied to the lower layer of the amorphous titania coating, so that the alkali network modifying ions such as sodium in the glass plate do not diffuse from the glass substrate into the titania coating during firing. it is conceivable that. # 1
After leaving the sample in a dark place for several days, the surface of the sample was irradiated with an ultraviolet illuminance of 0.5 mW / cm ² (band gap of anatase titania) using a 20 W black light blue (BLB) fluorescent lamp (Sankyo Denki, FL20BLB). Irradiance of ultraviolet light with energy higher than energy-ultraviolet light with a wavelength shorter than 387 nm)
Irradiated with ultraviolet light for an hour to obtain a # 2 sample. For comparison, a glass plate not coated with silica and titania was used as a # 3 sample. The contact angle between the # 2 sample and the # 3 sample with water was measured with a contact angle measurement device (model CA-X150, manufactured by Kyowa Interface Science Co., Ltd.). The lower angle side detection limit of this contact angle measuring instrument was 1 °. The contact angle was measured 30 seconds after a water drop was dropped on the sample surface from the micro syringe. The meter reading for water on the surface of the # 2 sample was 0 °, indicating superhydrophilicity. On the other hand, the contact angle of the # 3 sample with water was 30-40.
Was ゜. Next, the # 2 sample and the # 3 sample were evaluated for anti-fogging property and how the attached water droplets spread. The antifogging property was evaluated by placing 300 ml of hot water at about 80 ° C in a 500 ml beaker, then holding the sample on the beaker with the coating surface facing down for about 10 seconds, and immediately evaluating the presence or absence of fogging on the sample surface did. In the sample # 3, the surface was clouded by steam, but in the sample # 2, no clouding was observed. The spread state of the attached water droplets was evaluated by dropping a large number of water droplets from above on a surface of the sample inclined at 45 ° with a spoiler, and evaluating the attached state of the water droplets after the sample was once made vertical. In the sample # 3, unsightly and isolated water droplets adhered to the surface of the sample, and the refraction of light by the water droplets disturbed the perspective image, making it difficult to clearly observe the perspective image. On the other hand, in the sample # 2, the water droplets adhered to the surface of the sample spread on the surface without forming isolated water droplets and formed a uniform water film. Although a slight distortion was observed in the perspective image due to the presence of the water film, the perspective image could be sufficiently clearly recognized.

Example 2 Four kinds of coatings in which tetraethoxysilane (Wako Pure Chemical), anatase type titania sol (Nissan Chemical Co., TA-15), ethanol and pure water are mixed, and the mixing ratio of tetraethoxysilane and titania sol is different. A solution was prepared. The ratio of tetraethoxysilane to titania sol is 10 mol%, 30 mol%, 50 mol%, 70 mol in terms of the ratio of silica to the total of silica and titania after converting tetraethoxysilane to amorphous silica. %. These coating solutions are applied to the surface of a 10 cm square soda lime glass plate by a spray coating method, and maintained at a temperature of about 150 ° C. for about 20 minutes to subject tetraethoxysilane to hydrolysis and dehydration polycondensation, A coating in which anatase titania particles were bound with an amorphous silica binder was formed on the surface of the glass plate. After leaving these samples in a dark place for one week, they were irradiated with ultraviolet rays for about 1 hour at an illuminance of 0.3 mW / cm ² using a BLB fluorescent lamp. The contact angles of the surfaces of these samples with water after ultraviolet irradiation were measured with a contact angle measuring device (CA-X150), and the contact angles were all 0 °. Next, among these samples, the samples in which the proportion of silica was 30 mol% and 50 mol% were continuously irradiated with ultraviolet light at 0.004 mW / cm ² for 3 days using a white fluorescent lamp. The contact angle of the sample surface was maintained at less than 3 °.

Example 3 A 10 cm square aluminum substrate was used as a substrate.
In order to smooth the surface of the substrate, it was previously coated with a silicone layer. For this purpose, a liquid A (silica sol) and a liquid B (trimethoxymethylsilane) of Nippon Synthetic Rubber's coating composition “Glaska” are mixed so that the ratio of the weight of the silica sol to the weight of trimethoxymethylsilane becomes 3. The mixed solution was applied to an aluminum substrate and cured at a temperature of 150 ° C. to obtain an aluminum substrate (# 1 sample) coated with a 3 μm-thick silicone base coat. Next, the # 1 sample was coated with silicone containing a photocatalyst. For this reason,
Anatase-type titania sol (Nissan Chemical, TA-15) and the above-mentioned “Glaska” A solution (silica sol) are mixed, diluted with ethanol, and further added with the above “Glaska” B solution to obtain a titania-containing coating composition. Prepared. The composition of the coating composition was 33 parts by weight of silica sol, 11 parts by weight of trimethoxymethylsilane, and 56 parts by weight of titania sol. This coating composition was applied to the surface of a # 1 sample and cured at a temperature of 150 ° C. to form a top coat in which anatase-type titania particles were dispersed in a silicone coating, to obtain a # 2 sample. Next, 0.5 mW / cm ² was applied to the # 2 sample using a BLB fluorescent lamp.
The sample was irradiated with ultraviolet rays at an illuminance of 5 days to obtain a # 3 sample. The contact angle of the surface of this sample with water was measured using a contact angle measurement device (ERMA,
The contact angle reading was less than 3 ° when measured with the format GI-1000, low angle side detection limit 3 °). The contact angle of the # 2 sample before ultraviolet irradiation was measured and was found to be 70 °.
When the contact angle of the # 1 sample was measured, it was 90 °.
Further, the # 1 sample was irradiated with ultraviolet rays for 5 days under the same conditions as the # 2 sample, and the contact angle was measured. As a result, the contact angle was 85 °. From the above, it has been discovered that, despite the fact that silicone is inherently hydrophobic, when a photocatalyst is contained and the photocatalyst is excited by ultraviolet irradiation, it is highly hydrophilized. 22.8mW using a mercury lamp for # 2 sample
UV light was irradiated for 2 hours at a UV light intensity of / cm ² to obtain a # 4 sample. When the # 4 sample was subjected to Raman spectroscopy, there was no CH bond on the surface of this sample.
It was confirmed that an O—H bond was present. From this, the organic group bonded to the silicon atom of the silicone molecule is replaced with a hydroxyl group by the photocatalysis of the photocatalyst, and as a result,
It is considered that the surface of the silicone was made superhydrophilic.

Example 4 In the same manner as in Example 3, Liquid A and Liquid B of "Glaska" of Nippon Synthetic Rubber were mixed so that the ratio of the weight of silica sol to the weight of trimethoxymethylsilane was 3, A coating solution was prepared. This coating solution was applied to the surface of a 10 cm square acrylic resin plate and cured at a temperature of 100 ° C. to obtain a plurality of acrylic resin plates (# 1) coated with a 5 μm-thick silicone base coat. Next, anatase-type titania sol (Nissan Chemical Co., TA-15) and the above-mentioned “Glaska” solution A were mixed, diluted with ethanol, and further added with “Glaska” solution B to obtain four types of coating solutions having different compositions. Was prepared. The composition of these coating solutions, the ratio of the weight of titania to the sum of the weight of titania weight, silica weight and trimethoxymethylsilane weight, respectively,
It was adjusted to be 5%, 10%, 50%, and 80%.
Each coating solution is applied to the acrylic resin plate coated with a silicone layer, and cured at a temperature of 100 ° C. to form a top coat in which anatase type titania particles are dispersed in the silicone coating film. Five samples were obtained. # 1
Up to 200 to ~ # 5 samples BLB fluorescent lamp at an intensity of 0.5 mW / cm ²
Contact angle measuring device (ERMA) for measuring the contact angle of the surface of these samples with water at different time intervals while irradiating ultraviolet rays for hours
And the temporal change of the contact angle was observed. Fig. 3 shows the results.
Is shown in the graph. As can be seen from the graph of FIG. 3, in the # 1 sample having no titania-containing layer, almost no change was observed in the contact angle with water even when irradiated with ultraviolet rays. On the other hand, in the samples # 2 to # 5 provided with the titania-containing top coat, the contact angle with water was 10
It turns out that it becomes hydrophilic until it becomes less than ゜. In particular, in the samples # 3 to # 5 in which the ratio of titania is 10% by weight or more, the contact angle with water is 3 ° or less. Furthermore, the titania content is 50% by weight and 80% by weight, respectively.
It is noted that the contact angle with water becomes 3 ° or less for the 4 samples and the # 5 sample by short-time ultraviolet irradiation. Blowing on the # 4 sample did not result in fogging. # 4
After leaving the sample in a dark place for two weeks, a contact angle measuring instrument (CA-X15
When the contact angle with water was measured according to 0), the contact angle with water was 3 ° or less.

[0020]

According to the present invention, the condensed water adhering to the inner surface of the transparent panel of the heat retaining showcase is turned into a uniform water film, so that the transparent panel becomes cloudy and unsightly water droplets adhere to the transparent panel. And the visibility of the displayed food can be improved.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view of a heat retaining showcase of the present invention.

FIG. 2 is a schematic enlarged sectional view of a window panel of the heat retaining showcase shown in FIG.

FIG. 3 is a graph showing a temporal change of a contact angle with water due to ultraviolet irradiation in Example 4.

[Explanation of symbols]

 10: Insulated showcase 12: Transparent window panel 20: Photocatalyst containing layer

Claims (3)

[Claims] In a heat retaining showcase provided with a transparent window panel and a heating device, an inner surface of the transparent panel is covered with a transparent layer containing a photocatalyst, and the surface of the layer is hydrophilized by photoexcitation of the photocatalyst. Insulated showcase characterized by doing so. 2. The apparatus further comprises an internal light, wherein the photocatalyst is crystalline titania, the light is a light that emits light including both visible light and ultraviolet light, and the light is used for displaying items. The heat-insulated showcase according to claim 1, wherein the photocatalyst is light-excited while being illuminated. 3. The heat insulation showcase according to claim 2, wherein said illuminating light optically excites the photocatalyst with an ultraviolet illuminance of 0.1 mW / cm ² or more.