JP3707130B2 - Refrigerated showcase - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a cold display case for displaying foods that require cold storage such as vegetables and fruits.
[0002]
[Prior art]
The cold display case for displaying vegetables and fruits is provided with a transparent window made of glass or acrylic resin so that the displayed food can be seen from the outside.
[0003]
[Problems to be solved by the invention]
However, the transparent windows of the cold storage showcase are prone to cloudiness due to condensation of moisture, making it often difficult to see the displayed vegetables and fruits from the outside. When condensation of moisture progresses and fine condensed water droplets fuse together and grow into larger discrete water droplets, the perspective image is distorted by the refraction of light at the water droplet / window interface and water / air interface. After all, it is hard to see the vegetables and fruits inside.
In addition, the freshness of vegetables and fruits is rapidly reduced by ethylene and acetaldehyde that the vegetables and fruits themselves emit, and the commercial value is reduced.
[0004]
An object of the present invention is to provide a cold display case that is excellent in the visibility of displayed foods and that can preserve the freshness of foods for a long time.
[0005]
[Means for Solving the Problems]
The present inventor has discovered that the photocatalyst has an action of highly hydrophilizing the surface in addition to an action of decomposing a substance by a photooxidation-reduction action.
[0006]
The present invention is based on such a discovery, and the present invention is characterized in that, in a cold insulation showcase provided with a transparent window and an internal illumination lamp, the inner surface of the transparent window is coated with a transparent layer containing a semiconductor photocatalyst. Is.
The photocatalyst of the photocatalyst-containing layer is photoexcited by light from the internal illumination lamp, and the surface of the photocatalyst-containing layer is superhydrophilic so that the contact angle with water is 10 ° or less, more specifically 5 ° or less, especially about 0 °. Is done.
[0007]
Condensed water adhering to the superhydrophilic inner surface in this way spreads quickly on the inner surface of the window glass while forming a uniform water film, so that cloudiness does not occur. Even when the condensation of moisture proceeds, the condensed water droplets immediately become a water film and flow down along the inner surface. Therefore, good visibility of the displayed food is ensured.
Furthermore, electron-hole pairs are generated by photoexcitation of the photocatalyst, and the generated electrons reduce surface oxygen to generate superoxide ions (O ₂ ⁻ ), and the holes oxidize surface hydroxyl groups to generate hydroxyl radicals. (· OH) is generated, and gases such as ethylene and acetaldehyde in the showcase are decomposed by the oxidation-reduction reaction of these highly reactive active oxygen species (O ₂ ^- and · OH). Therefore, the freshness of vegetables and fruits is maintained longer.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 1, the cold showcase 10 includes a heat-insulating housing 12 and a transparent window 14 made of glass, acrylic resin, or the like, and an internal lamp 16 is disposed at an appropriate location. The inside of the cold storage showcase 10 is cooled by a refrigeration circuit (not shown). The inner surface of the transparent window 14 is covered with a transparent layer 18 containing a semiconductor photocatalyst.
[0009]
As the photocatalyst, titania (TiO ₂ ) is most preferable. Titania is harmless, chemically stable, and available at low cost. Furthermore, titania has a high band gap energy, and therefore requires ultraviolet light for photoexcitation and does not absorb visible light in the process of photoexcitation, so that color formation by complementary color components does not occur.
Either anatase-type titania or rutile-type titania can be used. The advantage of anatase type 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 has the advantage that it can be sintered at a high temperature and a film excellent in strength and abrasion resistance can be obtained.
When the inner surface of the transparent window 14 is covered with a photocatalytic titania-containing layer and the titania is photoexcited by the internal illumination lamp 16, water is chemisorbed on the surface in the form of hydroxyl groups (OH ⁻ ) by the photocatalytic action. It is thought to be hydrophilic.
Other photocatalysts which can be used include metal oxides such as _{ZnO, SnO 2, SrTiO 3,} WO 3, Bi 2 O 3, Fe 2 O 3. Since these metal oxides, like titania, contain metal elements and oxygen on the surface, it is thought that surface hydroxyl groups (OH ⁻ ) should be adsorbed.
You may form a photocatalyst content layer by mix | blending the particle of a photocatalytic titania with a metal oxide. In particular, when anatase titania is added to silica or tin oxide as described later, the surface can be highly hydrophilized.
[0010]
The film thickness of the photocatalyst containing layer is preferably 0.2 μm or less. With such a film thickness, color development due to light interference can be prevented. Moreover, the thinner the photocatalyst containing layer is, the more the transparency of the photocatalyst containing layer can be secured. Furthermore, if the film thickness is reduced, the wear resistance of the photocatalyst-containing layer is improved.
[0011]
When the transparent window 14 is formed of a heat-resistant material such as glass, a photocatalyst-containing layer excellent in abrasion resistance that exhibits super hydrophilicity with a contact angle with water of 0 ° is formed. One preferred way is to first coat the surface of the substrate with amorphous titania and then phase change the amorphous titania to crystalline titania (anatase or rutile) by firing. For the formation of amorphous titania, any of the following methods can be employed.
(1) Hydrolysis of organic titanium compound and dehydration condensation polymerization Titanium alkoxide, for example, tetraethoxy titanium, tetraisopropoxy titanium, tetra n-propoxy titanium, tetrabutoxy titanium, tetramethoxy titanium, and water such as hydrochloric acid or ethylamine After adding a decomposition inhibitor and diluting with an alcohol such as ethanol or propanol, the mixture can be spray coated, flow coated, spin coated, partially hydrolyzed or fully hydrolyzed, It is applied to the surface of the substrate by dip coating, roll coating, or other coating method, and dried at a temperature from room temperature to 200 ° C. By drying, the hydrolysis of titanium alkoxide is completed to produce titanium hydroxide, and an amorphous titania layer is formed on the surface of the substrate by dehydration condensation polymerization of titanium hydroxide.
Instead of the titanium alkoxide, other organic titanium compounds such as titanium chelate or titanium acetate may be used.
(2) Formation of amorphous titania with inorganic titanium compound Inorganic titanium compound, for example, acidic aqueous solution of TiCl ₄ or Ti (SO ₄ ) ₂ is spray coated, flow coated, spin coated, dip coated, roll coated, Apply to the surface. Next, the inorganic titanium compound is dried at a temperature of about 100 ° C. to 200 ° C. to be subjected to hydrolysis and dehydration condensation polymerization to form an amorphous titania layer on the surface of the substrate. Alternatively, amorphous titania may be formed on 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 the substrate by irradiating a target of titanium with an electron beam in an oxidizing atmosphere.
(4) Firing temperature The amorphous titania is calcined at a temperature at least equal to or higher than the crystallization temperature of anatase. Amorphous titania can be converted to anatase titania by baking at a temperature of 400 ° C to 500 ° C or higher. Amorphous titania can be converted into rutile titania by baking at a temperature of 600 ° C. to 700 ° C. or higher.
(5) Formation of anti-diffusion 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 formed in advance between the base material and the amorphous titania layer. It is good to keep. Then, during the firing of the amorphous titania, alkali network modification ions are prevented from diffusing from the base material into the photocatalyst containing layer, and super hydrophilicity is achieved so that the contact angle with water becomes 0 °. .
[0012]
Another preferred method of forming a photocatalyst-containing layer with excellent abrasion resistance that exhibits superhydrophilicity such that the contact angle with water is 0 ° is that a photocatalyst-containing layer composed of a mixture of titania and silica is used as a base material. It is to be formed on the surface. The ratio of silica to the total of titania and silica can be 5 to 90 mol%, preferably 10 to 70 mol%, more preferably 10 to 50 mol%. Any one of the following methods can be employed to form the photocatalyst-containing layer made of silica-containing titania.
(1) A suspension containing anatase-type or rutile-type titania particles and silica particles is applied to the surface of the substrate and sintered at a temperature below the softening point of the substrate.
(2) Amorphous silica precursors (for example, tetraalkoxysilanes such as tetraethoxysilane, tetraisopropoxysilane, tetra n-propoxysilane, tetrabutoxysilane, tetramethoxysilane; silanols that are hydrolysates thereof; Or a polysiloxane having an average molecular weight of 3000 or less) and a crystalline titania sol are coated on the surface of the substrate, and if necessary, hydrolyzed to form silanols, and then heated at a temperature of about 100 ° C. or higher to produce silanols. Is subjected to dehydration condensation polymerization to form a photocatalyst-containing layer in which titania is bound with amorphous silica. In particular, if dehydration condensation polymerization of silanol is carried out at a temperature of about 200 ° C. or higher, the degree of polymerization 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 plastics.
(3) Disperse silica 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 resulting suspension is applied to the surface of the substrate, and the titanium compound is subjected to hydrolysis and dehydration condensation polymerization at a temperature from room temperature to 200 ° C. to form an amorphous titania thin film in which silica particles are dispersed. . Next, amorphous titania is phase-changed to crystalline titania by heating to a temperature equal to or higher than the crystallization temperature of titania and to a temperature equal to or lower than the softening point of the substrate.
(4) Amorphous silica precursor 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 ). (E.g., tetraalkoxysilanes such as tetraethoxysilane, tetraisopropoxysilane, tetra n-propoxysilane, tetrabutoxysilane, tetramethoxysilane, etc .; hydrolyzed silanols thereof; or polysiloxanes having an average molecular weight of 3000 or less ) And apply to the surface of the substrate. Subsequently, these precursors are subjected to hydrolysis and dehydration condensation polymerization to form a thin film made of a mixture of amorphous titania and amorphous silica. Next, amorphous titania is phase-changed to crystalline titania by heating to a temperature equal to or higher than the crystallization temperature of titania and to a temperature equal to or lower than the softening point of the substrate.
[0013]
Still another preferred method for forming a photocatalyst-containing layer with excellent wear resistance that exhibits superhydrophilicity such that the contact angle with water is 0 ° is based on a photocatalyst-containing layer composed of a mixture of titania and tin oxide. It is to be formed on the surface of the material. 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. Any one of the following methods can be employed to form the photocatalyst-containing layer composed of tin oxide-containing titania.
(1) A suspension containing anatase-type or rutile-type titania particles and tin oxide particles is applied to the surface of the substrate and sintered at a temperature below 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 ) An amorphous titania thin film in which tin oxide particles are dispersed is obtained by applying the dispersed suspension to the surface of the base material and subjecting the titanium compound to hydrolysis and dehydration condensation polymerization at a temperature from room temperature to 200 ° C. Form. Next, amorphous titania is phase-changed to crystalline titania by heating to a temperature equal to or higher than the crystallization temperature of titania and to a temperature equal to or lower than the softening point of the substrate.
[0014]
When the substrate is formed of a non-heat-resistant material such as an acrylic resin, a preferable method for forming a photocatalyst-containing layer exhibiting super hydrophilicity with a contact angle with water of 0 ° is not yet available. It is to use a coating composition in which particles of photocatalyst are dispersed in a film-forming element made of cured or partially cured silicone or a precursor of silicone.
After coating the coating composition on the surface of the substrate and curing the coating film forming element, when the photocatalyst is photoexcited, the organic group bonded to the silicon atom of the silicone molecule is replaced with a hydroxyl group by the photocatalytic action of the photocatalyst, The surface of the photocatalyst containing layer is superhydrophilic.
Since the photocatalyst-containing silicone paint has a siloxane bond, it has sufficient resistance to the photooxidation action of the photocatalyst.
[0015]
Examples of the film-forming elements include methyltrichlorosilane, methyltribromosilane, methyltrimethoxysilane, methyltriethoxysilane, methyltriisopropoxysilane, methyltri-t-butoxysilane; ethyltrichlorosilane, ethyltribromosilane, ethyltrimethoxy Silane, ethyltriethoxysilane, ethyltriisopropoxysilane, ethyltri-t-butoxysilane; n-propyltrichlorosilane, n-propyltribromosilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, n-propyltri Isopropoxysilane, n-propyltri-t-butoxysilane; n-hexyltrichlorosilane, n-hexyltribromosilane, n-hexyltrimethoxysilane, n-hexyltriethoxysilane n-hexyltriisopropoxysilane, n-hexyltri-t-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, phenyltrit-butoxysilane; tetrac Silane, tetrabromosilane, tetramethoxysilane, tetraethoxysilane, tetrabutoxysilane, dimethoxydiethoxysilane; dimethyldichlorosilane, dimethyldibromosilane, dimethyldimethoxysilane, dimethyldiethoxysilane; diphenyldichlorosilane, diphenyldibromo Silane, diphenyldimethoxysilane, diphenyldiethoxysilane; phenylmethyldichlorosilane, phenylmethyldibromosilane, phenylmethyldimethoxysilane, phenylmethyldiethoxysilane; trichlorohydrosilane, tribromohydrosilane, trimethoxyhydrosilane, triethoxyhydrosilane, tri Isopropoxyhydrosilane, tri-t-butoxyhydrosilane; vinyltrichlorosilane, vinyltribromosilane, Vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane, vinyltri-t-butoxysilane; trifluoropropyltrichlorosilane, trifluoropropyltribromosilane, trifluoropropyltrimethoxysilane, trifluoropropyltriethoxysilane, tri Fluoropropyltriisopropoxysilane, trifluoropropyltri-t-butoxysilane; γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycyl Sidoxypropyltriethoxysilane, γ-glycidoxypropyltriisopropoxysilane, γ-glycidoxypropyltri-t-butoxysilane; γ-methacryloxypropyl Tildimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-methacryloxypropyltriisopropoxysilane, γ-methacrylic Roxypropyltri-t-butoxysilane; γ-aminopropylmethyldimethoxysilane, γ-aminopropylmethyldiethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltriisopropoxysilane, γ-aminopropyltri-t-butoxysilane; γ-mercaptopropylmethyldimethoxysilane, γ-mercaptopropylmethyldiethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropi Lutriethoxysilane, γ-mercaptopropyltriisopropoxysilane, γ-mercaptopropyltri-t-butoxysilane; β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, β- (3,4-epoxycyclohexyl) ethyltri Ethoxysilanes; and their partial hydrolysates; and mixtures thereof can be used.
[0016]
Thus, when the light of the internal illumination lamp 16 is irradiated to the transparent window 14 covered with the photocatalyst containing layer 18, the photocatalyst is photoexcited and the surface of the photocatalyst containing layer is made superhydrophilic. Furthermore, gases such as ethylene and acetaldehyde in the showcase are decomposed by the redox reaction of the photocatalyst.
As the internal illumination lamp 16, a white fluorescent lamp or an incandescent lamp can be used. White fluorescent lamps and incandescent lamps contain weak ultraviolet light in addition to visible light, and the photocatalyst can be sufficiently photoexcited by the weak ultraviolet light.
[0017]
【Example】
Example 1
86 parts by weight of ethanol, 6 parts by weight of tetraethoxysilane Si (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 hydrolysis inhibitor for tetraethoxysilane In addition, a silica coating solution was prepared by mixing. Since the solution generated heat by mixing, the mixture was allowed to cool for about 1 hour. This solution was applied to the surface of a 10 cm square soda lime glass plate by a flow coating method and dried at a temperature of 80 ° C. Along with drying, tetraethoxysilane was first hydrolyzed to become silanol Si (OH) ₄ , and then an amorphous silica thin film 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 obtain a titania coating solution. 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 hydrolysis rate of tetraethoxytitanium was extremely fast, a part of tetraethoxytitanium was hydrolyzed at the coating stage, and titanium hydroxide Ti (OH) ₄ began to be produced.
Next, the glass plate is kept at a temperature of about 150 ° C. for 1 to 10 minutes to complete the hydrolysis of tetraethoxytitanium, and the produced titanium hydroxide is subjected to dehydration condensation polymerization to form amorphous titania. Generated. Thus, a glass plate in which amorphous titania was coated on amorphous silica was obtained.
This sample was baked at a temperature of 500 ° C. to convert amorphous titania into anatase titania to obtain # 1 sample. Amorphous silica coating is applied to the lower layer of the amorphous titania coating so that 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 the dark for several days, using a 20W black light blue (BLB) fluorescent lamp (Sankyo Electric, FL20BLB), the surface of the sample was irradiated with UV light of 0.5 mW / cm ² (of anatase titania). No. 2 sample was obtained by irradiating ultraviolet rays for about 1 hour with ultraviolet rays having an energy higher than the band gap energy (ultraviolet rays having a wavelength shorter than 387 nm).
For comparison, a glass plate not coated with silica and titania was designated as # 3 sample.
The contact angle between the # 2 sample and the # 3 sample with water was measured with a contact angle measuring instrument (Kyowa Interface Science Co., Ltd., model CA-X150). The detection limit of the low angle side of this contact angle measuring device was 1 °. The contact angle was measured 30 seconds after a water droplet was dropped from the microsyringe onto the sample surface. The measuring instrument reading for water on the surface of # 2 sample was 0 °, indicating super hydrophilicity. In contrast, the contact angle of the # 3 sample with water was 30 to 40 °.
Next, the antifogging property and the spread of attached water droplets were evaluated for the # 2 sample and the # 3 sample. Evaluation of anti-fogging property is performed by putting 300 ml of hot water at about 80 ° C into a 500 ml beaker, then holding the sample for about 10 seconds with the coating surface facing down on the beaker, and evaluating the presence or absence of fog on the sample surface immediately after that. did.
In the sample # 3, the surface was clouded with steam, but in the sample # 2, no fogging was observed.
Evaluation of the spread state of the attached water droplets was made by evaluating the adhesion state of the water droplets after dropping a large number of water droplets from above with a dropper on the surface of the sample inclined at 45 ° and once verticalizing the sample.
In the # 3 sample, annoying isolated water droplets scattered on the surface of the sample adhered, and the fluoroscopic image was disturbed by the refraction of light by the water droplet, and it was difficult to clearly observe the fluoroscopic image. On the other hand, in the # 2 sample, water droplets adhering to the surface of the sample spread on the surface without forming isolated water droplets and formed a uniform water film. Although some distortion was observed in the fluoroscopic image due to the presence of the water film, the fluoroscopic image could be recognized sufficiently clearly.
[0018]
Example 2
Tetraethoxysilane (Wako Pure Chemical Industries), anatase type titania sol (Nissan Chemical, TA-15), ethanol and pure water were mixed to prepare four coating solutions having different mixing ratios of tetraethoxysilane and titania sol. 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 conversion of 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 the tetraethoxysilane to hydrolysis and dehydration condensation polymerization. A coating in which anatase-type titania particles were bound with an amorphous silica binder was formed on the surface of a glass plate.
These samples were left in the dark for one week, and then irradiated with ultraviolet rays at an illuminance of 0.3 mW / cm ² using a BLB fluorescent lamp for about 1 hour. When the contact angle between the surface of these samples after irradiation with ultraviolet light and water was measured with a contact angle measuring device (CA-X150), the contact angles were all 0 °.
Subsequently, among these samples, when the proportion of silica was 30 mol% and 50 mol%, the sample was continuously irradiated with ultraviolet rays for 3 days at an ultraviolet intensity of 0.004 mW / cm ² using a white fluorescent lamp. The contact angle of the sample surface was kept below 3 °.
[0019]
Example 3
A 10 cm square aluminum substrate was used as the substrate. In order to smooth the surface of the substrate, it was previously coated with a silicone layer. For this reason, the liquid A (silica sol) and the liquid B (trimethoxymethylsilane) of the Japanese synthetic rubber coating composition “Glaska” were mixed so that the weight ratio of silica sol to trimethoxymethylsilane was 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.
The # 1 sample was then coated with silicone containing photocatalyst. For this reason, anatase-type titania sol (Nissan Chemical, TA-15) and the above “Glaska” solution A (silica sol) are mixed, diluted with ethanol, and then added with “Glaska” solution B above for titania-containing paints A composition was 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 sample # 1 and cured at a temperature of 150 ° C. to form a topcoat in which anatase-type titania particles were dispersed in a silicone coating film, thereby obtaining sample # 2.
Next, the # 2 sample was irradiated with ultraviolet rays at an illuminance of 0.5 mW / cm ² for 5 days using a BLB fluorescent lamp to obtain a # 3 sample. When the contact angle between the surface of the sample and water was measured with a contact angle measuring device (ERMA, model GI-1000, low angle detection limit 3 °), the contact angle reading was less than 3 °.
The contact angle of sample # 2 before UV irradiation was measured and found to be 70 °. The contact angle of # 1 sample was measured and found to be 90 °. Furthermore, 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. The contact angle was 85 °.
From the above, it has been found that silicone is highly hydrophilic when it contains a photocatalyst and is excited by ultraviolet irradiation even though it is inherently hydrophobic.
A # 4 sample was obtained by irradiating the sample # ² with ultraviolet light at a UV intensity of 22.8 mW / cm ² for 2 hours using a mercury lamp. As a result of Raman spectroscopic analysis of the # 4 sample, it was confirmed that no C—H bond was present on the surface of this sample, and instead, an O—H bond was present. From this, it is considered that the organic group bonded to the silicon atom of the silicone molecule is substituted with a hydroxyl group by the photocatalytic action of the photocatalyst, and as a result, the surface of the silicone is superhydrophilic.
[0020]
Example 4
In the same manner as in Example 3, A solution and B solution of “Glaska” of Japanese synthetic rubber were mixed so that the ratio of the weight of silica sol to the weight of trimethoxymethylsilane was 3, to prepare a coating solution. 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, TA-15) and the “Glaska” solution A were mixed, diluted with ethanol, then “Glaska” solution B was added, and four coating solutions having different compositions were added. Was prepared. The compositions of these coating solutions were prepared so that the ratio of the titania weight to the sum of the titania weight, the silica weight, and the trimethoxymethylsilane weight was 5%, 10%, 50%, and 80%, respectively.
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 a silicone coating film. Five samples were obtained.
While irradiating the # 1 to # 5 samples with UV light at a illuminance of 0.5 mW / cm ² for up to 200 hours, the contact angles of the surface of these samples with water at different time intervals ( ERMA) and the change in contact angle over time was observed. The results are shown in the graph of FIG.
As can be seen from the graph of FIG. 2, in the # 1 sample without the titania-containing layer, the contact angle with water hardly changes even when irradiated with ultraviolet rays.
In contrast, in the samples # 2 to # 5 provided with the titania-containing topcoat, it can be seen that the sample is hydrophilized until the contact angle with water becomes less than 10 ° in accordance with the ultraviolet irradiation.
In particular, it is understood that the contact angle with water is 3 ° or less in the # 3 to # 5 samples having a titania ratio of 10% by weight or more.
In addition, it is noted that the contact angle with water in a # 4 sample and a # 5 sample having a titania ratio of 50% by weight and 80% by weight, respectively, is 3 ° or less by short-time ultraviolet irradiation.
When # 4 sample was blown, no haze occurred. After the # 4 sample was left in the dark for 2 weeks, the contact angle with water was measured with a contact angle measuring device (CA-X150). The contact angle with water was 3 ° or less.
[0021]
【The invention's effect】
According to the present invention, the condensed water adhering to the inner surface of the transparent window of the cold display case spreads while forming a uniform water film, so that the visibility of the displayed food can be improved. In addition, since gases such as ethylene and acetaldehyde in the showcase are decomposed by the oxidation-reduction reaction of the photocatalyst, the freshness of vegetables and fruits can be preserved for a longer time.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a cold showcase of the present invention.
2 is a graph showing temporal changes in contact angle with water accompanying ultraviolet irradiation in Example 4. FIG.
[Explanation of symbols]
10: Cold display case 14: Transparent window 18: Photocatalyst containing layer

Claims (4)

A transparent window and an internal illumination lamp are provided, the inner surface of the window is covered with a transparent layer containing a semiconductor photocatalyst, and the photocatalyst is photoexcited by irradiating the layer with light from the illumination lamp to thereby photoexcite the surface of the layer an antifogging cold showcase is characterized in that so as to decompose the gas in the showcase by the oxidation reduction action of the photocatalyst along with the contact angle with water is hydrophilized to 10 ° or less. The anti-fogging cold-retaining showcase according to claim 1, wherein the photocatalyst is crystalline titania, and the illuminating lamp is an illuminating lamp that emits light including both visible light and ultraviolet light. The anti-fogging cold storage showcase according to claim 1, wherein the layer further contains silica or tin oxide. The anti-fogging cold-holding showcase according to claim 1, wherein the illumination lamp is a white fluorescent lamp or an incandescent lamp.

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