Claims
- 1. A low reflectance transparent material having antisoiling properties, which comprises a transparent substrate and a multi-layer coating formed on the substrate, said coating comprising at least one thin layer of a condensation product containing a metal oxide, and a thin layer of a condensation product of a fluorine-containing silicon compound having a perfluorocarbon chain containing from 3 to 20 carbon atoms, formed thereon.
- 2. The low reflectance transparent material according to claim 1, wherein the transparent substrate is made of glass.
- 3. The low reflectance transparent material according to claim 1, wherein the transparent substrate is made of a plastic.
- 4. The low reflectance transparent material according to claim 1, wherein the thin layer of a condensation product containing a metal oxide has a thickness of at most 0.3 .mu.m.
- 5. The low reflectance transparent material according to claim 1, wherein the condensation product containing a metal oxide is a co-condensation product containing a SiO.sub.2 compound and a TiO.sub.2 compound or a ZrO.sub.2 compound.
- 6. The low reflectance transparent material according to claim 1, wherein the thin layer of a condensation product of a fluorine-containing silicon compound having a perfluorocarbon chain has a thickness of at most 0.2 .mu.m.
- 7. The low reflectance transparent material according to claim 6, wherein the fluorine-containing silicon compound is a dialkoxy silane or trialkoxy silane compound having a perfluoroalkyl group containing from 3 to 20 carbon atoms.
- 8. The low reflectance transparent material according to claim 6, wherein the fluorine-containing silicon compound is a compound having a perfluoroalkylene group containing from 3 to 12 carbon atoms and a silyl group at each end.
- 9. The low reflectance transparent material according to claim 1, wherein the condensation product of a fluorine-containing silicon compound having a perfluorocarbon chain is a co-condensation product with a silane coupling agent.
Priority Claims (3)
| Number |
Date |
Country |
Kind |
| 59-129992 |
Jun 1984 |
JPX |
|
| 60-53317 |
Mar 1985 |
JPX |
|
| 60-82169 |
Apr 1985 |
JPX |
|
Parent Case Info
This application is a continuation of application Ser. No. 746,406, filed on June 19, 1985, now abandoned.
The present invention relates to a low reflectance transparent material with its surface having low reflecting properties. More particularly, it relates to a low reflectance transparent material having low reflecting properties and excellent antisoiling properties and durability, wherein a multi-layer coating is formed on a transparent substrate surface.
The transparency or see-through properties of transparent products such as windows of buildings, doors, show windows, show cases, windows of vehicles, optical lenses, eye glasses or the like, are likely to be impaired by a glare, glitering or a reflection of the scenery caused by the reflection of the sunlight or illumination light. Further, in the utilization of the sunlight, for instance, in order to improve the heat collecting efficiency of a solar heat warm-water generator, it is necessary to eliminate or reduce the reflection loss of a light-transmitting material such as glass or plastic used for the heat collecting element and thereby permit the passage of a great quantity of energy.
Heretofore, the prevention of the reflection on the surface of a transparent material such as glass or plastic has been studied and developed primarily for lenses as optical parts. It is known to form, by a vacuum vapour deposition method or a sputtering method, a single layer coating comprising MgF.sub.2 or cryolite for the prevention of the reflection of visible light on the surface of glass or plastic, or a single layer coating comprising SiO, CeO.sub.2 or ZnS, or a multilayer coating such as SiO-MgF.sub.2 or arsenic trisulfide glass-WO.sub.2 -cryolite for infrared rays, or a single layer coating comprising SiO.sub.2 or LiF for ultraviolet rays, and such coatings are practically used as antireflection coatings for optical lenses, lenses for eye glasses or filters.
On the other hand, there have been proposed a method and treating agent for forming an antireflection coating, whereby a treating agent for low reflectance comprising a polymeric substance is directly coated on the surface of glass or plastic, or the glass or plastic is immersed in the treating agent. As such a method and treating agent for forming an antireflection coating, there has been a disclosure of a process wherein for the purpose of improving the properties of the antireflection coating such as durability and abrasion resistance, a precoating layer is formed by treating a transparent material, particularly a plastic substrate, with a metal oxide-containing composition in a water-containing environment, and an antireflection coating comprising an organic silicon compound-containing composition is formed on the precoating layer (Japanese Unexamined Patent Publication No. 49960/1984).
For the formation of antireflection coatings, the vacuum vapour deposition method or sputtering method is rather restricted in its application to e.g. small size precision optical parts from the mechanical nature of the apparatus or from the aspect of costs. Further, such methods are not suitable for continuous mass production.
Further, in the case of an antireflection coating by a treating agent for low reflectance, the single layer coating for visible light exhibits antireflection effects only against a certain specific range of wavelength. Furthermore, antireflection coatings formed by the above-mentioned conventional treating agents for low reflectance are susceptible to stains, and the stains are hardly removed by a usual washing operation, and if wiped with a strong force, the coating is likely to be peeled.
Under these circumstances, there has been no low reflectance transparent material which fully satisfies the requirements for both antisoiling properties and high performance in the reduction of reflectance.
Accordingly, it is an object of the present invention to provide a low reflectance transparent material comprising a transparent substrate and a thin layer of an antireflection treating agent formed thereon, which can readily be formed by a conventional method such as coating, spraying or dipping without impairing the transparency or see-through properties, and which can be applied not only to small size precision optical parts but also to large transparent substrates.
Another object of the present invention is to provide a low reflectance transparent material having antisoiling properties, whereby the reflectance can be uniformly reduced over the entire region of visible light by the antireflection coating formed on the surface of the transparent substrate, and yet the coating has excellent antisoiling properties.
A further object of the present invention is to provide a low reflectance transparent material having excellent durability, whereby the antireflection coating formed on the surface of the transparent substrate maintains its properties for a long period of time.
The present invention provides a low reflectance transparent material having antisoiling properties, which comprises a transparent substrate and a multi-layer coating formed on the substrate, said coating comprising at least one thin layer of a condensation product containing a metal oxide, and a thin layer of a condensation product of a fluorine-containing silicon compound having a polyfluorinated carbon chain or a perfluorocarbon chain, formed thereon.
Now, the present invention will be described in detail with reference to preferred embodiments.
In the present invention, the transparent substrate is preferably made of glass or plastic. As the plastic, particularly transparent plastic, there may be mentioned, for instance, poly(diethyleneglycol bis-allylcarbonate), polymethyl methacrylate, polycarbonate, polystyrene or polyvinyl chloride. There is no particular restriction as to the shape or configuration of the substrate.
In the present invention, at least one thin layer formed on the surface of the transparent substrate, is advantageously a condensation product containing a metal oxide, which satisfies nd=.lambda./4-3.lambda./4 and which has excellent adhesion to an upper layer to be formed thereon. Such a metal oxide has excellent adhesion to a condensation product of a fluorine-containing silicon compound formed as an upper layer. By the formation of such a multi-layer coating, the reflection can be uniformly reduced over the entire region of visible light, and it is thereby possible to obtain a low reflectance transparent material having excellent antisoiling properties.
In the condensation product containing a metal oxide for the at least one thin layer, i.e. the under coating layer, formed on the surface of the transparent substrate, the metal oxide may suitably be a TiO.sub.2 compound, a SiO.sub.2 compound, a ZrO.sub.2 compound, a Ta.sub.2 O.sub.5 compound or a Al.sub.2 O.sub.3 compound. As the condensation product containing such a metal oxide, there may be mentioned, as a TiO.sub.2 compound, a titanium tetraalkoxides such as Ti(OCH.sub.3).sub.4, Ti(OC.sub.2 H.sub.5).sub.4, Ti(OC.sub.4 H.sub.7).sub.4 or Ti(OC.sub.4 H.sub.9).sub.4, or a low molecular weight polymer thereof, or a titanium chelate compound such as Ti(O-iC.sub.3 H.sub.7).sub.2 [OC(CH.sub.3)CHCOCH.sub.3 ].sub.2 or Ti(O-iC.sub.3 H.sub.7).sub.n [OCH.sub.2 CH(C.sub.2 H.sub.5)CH(OH)C.sub.3 H.sub.7 ].sub.4-n. As a SiO.sub.2 compound, there may be employed a tetraalkoxy silane such as Si(OCH.sub.3).sub.4, Si(OC.sub.2 H.sub.5).sub.4, Si(OC.sub.3 H.sub.7).sub.4 or Si(OC.sub.4 H.sub.9).sub.4, a trialkoxy silane such as HSi(OCH.sub.3).sub.3, HSi(OC.sub.2 H.sub.5).sub.3, HSi(OC.sub.4 H.sub.9).sub.3, CH.sub.3 Si(OCH.sub.3).sub.3, CH.sub.3 Si(OC.sub.2 H.sub.5).sub.3, CH.sub.3 Si(OC.sub.3 H.sub.7).sub.3 or CH.sub.3 Si(OC.sub.4 H.sub.9).sub.3, or a silane coupling agent such as ##STR1##
These metal oxides may be used alone. However, to adjust the refractive index, it is preferred to employ a co-condensation product of two components such as a TiO.sub.2 compound and a SiO.sub.2 compound, or a ZrO.sub.2 compound and a SiO.sub.2 compound, or of more components.
The refractive index of the condensation product containing metal oxides obtained by incorporating and reacting an additive to the above-mentioned TiO.sub.2 compound and the SiO.sub.2 compound, or the ZrO.sub.2 compound and the SiO.sub.2 compound, is within a range of 1.45 to 2.10.
Further, for the purpose of improving the adhesion and overcoming the brittleness of the thin layer composed of the condensation product of the metal oxide, other additives may be incorporated to form a co-condensation product. As other additives, there may be employed a polyhydric alcohol such polyethylene glycol or pentaerythritol, or a melamine resin or an epoxy resin. Such additives are useful for the improvement of the crack resistance and adhesion of the undercoating layer.
In the condensation product containing a metal oxide, the metal oxide is incorporated in the condensation product in an amount of at least 20% by weight, preferably at least 30% by weight. The condensation product containing a metal oxide is prepared in such a manner that after incorporating the metal oxide and, if necessary, the additives, the mixture is subjected to hydrolysis in a single or mixed solvent of alcohol-type such as ethanol or butanol. The hydrolysis is conducted at room temperature in the presence of acetic acid or hydrochloric acid as a catalyst.
The thin layer formed on the at least one thin layer of a condensation product containing a metal oxide, i.e. the top coating layer, is made of a condensation product of a fluorine-containing silicon compound having a polyfluorinated carbon chain or a perfluorocarbon chain. As the polyfluorinated carbon chain or the perfluorocarbon chain, there may be mentioned a perfluoroalkyl group or a perfluoroalkylene group. However, the perfluoroalkyl group is preferred in that it is thereby possible to advantageously improve the reduction of reflectance and the antisoiling properties.
The perfluoroalkyl group-containing compound has small polarizability of fluorine atoms, and accordingly the refractive index is low. For instance, the refractive index (at 25.degree. C.--the same applies hereinafter) of C.sub.8 F.sub.18 is 1.271, that of (C.sub.4 F.sub.9).sub.3 N is 1.290, and that of a polymer of (CF.sub.2 .dbd.CF.sub.2 /CF.sub.3 OCF.dbd.CF.sub.2) is 1.330. Such a perfluoroalkyl group-containing compound is suitable as a treating agent for low reflectance, but for the fabrication into a thin layer and chemical adhesion, the presence of --Si--OR, --Si--Cl or the like is preferred. Accordingly, the condensation product of a fluorine-containing silicon compound in the present invention is preferably composed of a dialkoxy silane or trialkoxy silane having a perfluoroalkyl group containing from 3 to 20 carbon atoms, or a co-condensation product of a silane coupling agent with at least one compound selected from the group consisting of a dichlorosilane and a trichlorosilane.
Further, as the condensation product of the fluorine-containing compound, there may be employed a compound having a perfluoroalkylene group containing from 2 to 12 carbon atoms, and a silyl group at each end.
In the above compound, if the perfluoroalkyl group contains less than 3 carbon atoms, it is impossible to adequately satisfy the requirements for both the antisoiling properties and the reduction of reflectance. On the other hand, a fluorine-containing compound having carbon atoms greater than the above range is hardly available, and is economically disadvantageous.
As the above-mentioned fluorine-containing compounds, various types may be mentioned. For instance, the following fluorine-containing silane compounds may be mentioned; ##STR2## These compounds are hydrolyzed and used in the form condensation products. Such condensation products have a refractive index within a range of from 1.33 to 1.44. The greater the fluorine content, the lower the refractive index. A desired refractive index can be obtained by properly selecting two or more fluorine-containing compounds among them.
As the silane coupling agent capable of forming the above-mentioned co-codensation product with the above fluorine-containing silane compound, there may be mentioned, for instance, ##STR3## Si(OCH.sub.3).sub.4, Si(OC.sub.2 H.sub.5).sub.4, SiCl.sub.4, HSiCl.sub.3 and CH.sub.3 SiCl.sub.3. Such a silane coupling agent is useful for a further improvement of the adhesion of the co-condensation product with the undercoating layer, and is usually incorporated in an amount of from 5 to 90% by weight, preferably from 10 to 75% by weight, relative to the fluorine-containing silane compound. Needless to say, the fluorine-containing silane compound can be practically useful even when it is not a co-condensation product with a silane coupling agent.
The condensation products or co-condensation products may be prepared by the hydrolysis in an alcohol solvent such as butanol, preferably tert-butanol, at room temperature in the presence of an acetic acid and an organic tin compound as catalysts.
For the formation of at least one thin layer of a condensation product containig a metal oxide on the surface of a transparent substrate, the thus prepared metal oxide-containing condensation product is applied to the surface of a transparent substrate by a conventional coating method such as brush coating, roll coating, spraying or dipping. After the application, the applied coating is dried at a temperature of from room temperature to 200.degree. C., and the formed thin layer is heated and cured at a temperature of from 200.degree. to 550.degree. C. In the case where the transparent substrate is made of a plastic, the applied coating is dried at a temperature of from room temperature to 150.degree. C. with no further treatment. The condensation product containing a metal oxide contains an alcohol solvent added during the preparation, and thus it has a proper fluidity and can readily be coated on the surface of the transparent substrate. Further, the cured thin layer is preferably subjected to activating treatment, e.g. by dipping it in a 2% hydrofluoric acid aqueous solution or in a 15% sodium hydroxide aqueous solution, followed by washing with water. By such a method, a thin layer of the condensation product containing a metal oxide, i.e. the undercoating layer, is formed on the surface of the transparent substrate.
A multi-layer undercoating may be formed by repeating the above method of forming the undercoating layer. However, a thin layer may be continuously formed to obtain a multi-layer coating. Such a method may be conducted by coating a metal oxide-containing condensation product on the surface of the transparent substrate, followed by drying as mentioned above to form a thin layer, and further coating the metal oxide-containing condensation product on the thin layer, followed by drying and then by heating and curing at a proper temperature.
When a multi-layer coating is formed, the respective thin layers are preferably different from one another in the metal oxide component or in the composition. However, the respective thin layers may be the same. The multi-layer construction, e.g. a double layer construction, of thin layers of a metal oxide-containing condensation product, brings about an improvement in the reduction of reflectance as compared with a single layer construction. However, it is useless to increase the number of layers unnecessarily. Further, such a multi-layer structure will be economically disadvantageous.
When the transparent substrate is made of a plastic, it is preferred to subject the plastic surface to activating treatment such as treatment with an alkaline solution, plasma treatment, glow discharge treatment or formation of a primer layer of a silane coupling agent or a functional group-containing acrylic resin, in order to improve the surface properties for the formation of the undercoating layer of the metal oxide-containing condensation product on the plastic surface.
Further, for the improvement of the properties of the undercoating layer and the top coating layer formed thereon and comprising the condensation product of a fluorine-containing silicon compound, it is preferred to subject the undercoating layer to activating treatment. As such activating treatment, there may be mentioned the dipping in a dilute hydrofluoric acid aqueous solution or in a sodium hydroxide aqueous solution, as mentioned above, followed by washing with water and drying.
Then, the top coating thin layer of the condensation product of a fluorine-containing silicon compound is formed on the at least one thin layer of the condensation product containing a metal oxide. There is no particular restriction to the method of coating the condensation product of a fluorine-containing silicon compound onto the above-mentioned thin layer. Namely, the top coating layer may be applied by brush coating, roll coating, spraying or dipping in the same manner as the above-mentioned coating method for the formation of the under-coating layer. After the application, the coated layer is heated at a temperature of from 120.degree. to 250.degree. C., or from 70.degree. to 150.degree. C. in the case where the transparent substrate is made of a plastic, and cured to form a thin layer. In the case of the plastic, it is preferred to conduct activating treatment such as mercury vapour lamp radiation.
In the present invention, the thickness of the undercoating layer of the condensation product containing a metal oxide, or the thickness of the top coating layer of condensation product of a fluorine-containing silicon compound formed on the undercoating layer, is determined by the above-mentioned equation of nd=.lambda./4-3.lambda./4. The thickness of the undercoating layer is usually at most 0.3 .mu.m, preferably from 0.03 to 0.2 .mu.m. The thickness of the top coating layer is usually at most 0.2 .mu.m, preferably from 0.05 to 0.1 .mu.m. Such a thickness can be controlled by adjusting the conditions for the coating method. For instance, in the dipping method, the thickness is determined by the concentration of the composition and the withdrawing speed.
The low reflectance glass of the present invention has an average reflectance of at most 1.6% in the visual light region, particularly at most 1.0% in the case where the undercoating layer is composed of a plurality of layers of a metal oxide-containing condensation product, and thus has substantially superior low reflecting properties as compared with the reflectance of 4.2% of ordinary soda lime glass. Yet, the formed thin layer has a pencil hardness of from H to 5H or higher. For instance, a thin layer composed solely of the condensation product of a fluorine-containing silicon compound is HB. Thus, the same layer of the present invention has substantially higher hardness. Further, the low reflectance material of the present invention shows excellent antisoiling properties, whereby the low reflecting properties will be maintained over a long period of time.
There is no particular restriction to the application of the low reflectance transparent material of the present invention. For instance, it may be employed for windows of buildings, transparent doors, show windows, show cases, windows of vehicles, optical lenses, lenses for eye glasses, filters, front non-glare plates for televisions, glass for watches or clocks or the like.
US Referenced Citations (3)
| Number |
Name |
Date |
Kind |
| 3986997 |
Clark |
Oct 1976 |
|
| 4211823 |
Suzuki et al. |
Jul 1980 |
|
| 4478873 |
Masso et al. |
Oct 1984 |
|
Foreign Referenced Citations (1)
| Number |
Date |
Country |
| 49960 |
Mar 1984 |
JPX |
Non-Patent Literature Citations (1)
| Entry |
| T. Wydeven and R. Kubacki, Applied Optics, vol. 15, No. 1, Jan. 1976, Antireflection Coating Prepared by Plasma Polymerization of Perfluorobutene-2. |
Continuations (1)
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Number |
Date |
Country |
| Parent |
746406 |
Jun 1985 |
|
Patent Grant
4687707
