JP2009023262A - Transparent material and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve various problems caused by a coating film formed on a transparent base material by paying attention to a difference in a refractive index between the base material and the coating film and eliminating the difference itself in the refractive index. <P>SOLUTION: The transparent material is characterized in that a functional thin film is made porous in such a manner that the apparent refractive index thereof is made substantially the same as that of the base material. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a transparent material formed by forming a thin film on a transparent substrate such as glass or plastics and a method for producing the same.

  Attempts to impart a photocatalytic function, a drip-proof function, and the like to the surface of a transparent substrate such as glass have been widely practiced, and some have been put into practical use. In such a case, it is most common to impart a desired function to the surface by forming a coating film made of a material that exhibits a desired function on the surface of a transparent substrate such as glass. In addition to sufficiently high photocatalytic activity, this coating film is also strongly required not to detract from the design of the transparent substrate, that is, the appearance. For example, when used for windows, transparency to visible light and its uniformity are essential. However, in many cases, the formation of the coating film significantly reduces the uniformity of visible light transmission. This is because there is a difference between the refractive index value of the transparent substrate and the refractive index value of the coating film, so that reflection of light occurs at the transparent substrate / coating film interface, and these light beams repeatedly interfere with each other. This is due to a phenomenon observed by unevenly rainbow-colored according to the film thickness distribution. This is because when the oil or the like is formed as a thin film in a puddle, water and oil are transparent to each other, but the refractive index with respect to visible light is different for each of water and oil. This is the same phenomenon as the oil that is generated and floats on the surface of the puddle is observed in a non-uniform rainbow color. Since this non-uniform coloration is caused by the distribution of the film thickness, it was necessary to make the film thickness uniform in order to reduce the non-uniformity. However, since the coating film is generally very thin as 100 to 1000 nanometers, it is extremely difficult to strictly control and manage the process to keep the film thickness strictly controlled. For this reason, it has been very troublesome and costly to ensure uniformity in various coating methods such as sputtering and sol-gel method (wet method).

  Even when the uniformity is ensured, light interference occurs depending on the thickness of the coating film, and as a result, the transparent substrate is observed as if colored. Often, even this coloring phenomenon itself is unfavorable in design, and the coating film formed on the surface of the transparent substrate is required to maintain a colorless and transparent appearance while maintaining a desired function at a high level. As an attempt to realize this, glass is prevented from being colored by driving the wavelength at which light interference occurs to the ultraviolet region by limiting the thickness of the coating film to 100 nanometers or less. However, the film thickness of 100 nanometers or less that can be adopted in this method is insufficient to maintain the desired function sufficiently high, so it is extremely difficult to fully express the essential functions and is widely adopted. It has not been done.

  In the present invention, instead of individually addressing each of the above-mentioned problems, it returns to the origin of all the problems, and the difference in refractive index between the substrate and the coating film that causes all the problems. By eliminating the difference in refractive index itself, the coating film created on a substrate such as glass and the like that does not cause all the above problems in principle, and its rational and excellent productivity It provides a creation method.

  The transparent material of the invention 1 is characterized in that it is porous so that the apparent refractive index of the functional thin film is substantially the same as the refractive index of the substrate.

  Invention 2 is characterized in that, in the transparent material of Invention 1, the functional thin film is made of a nanoporous material of an inorganic material.

  Invention 3 is the transparent material of Invention 2, wherein the functional thin film is made of a photocatalyst material.

  Invention 4 is characterized in that in the transparent material of Invention 3, the photocatalyst material contains titanium dioxide as a main component.

  Invention 5 is a method for producing a transparent material according to any one of Inventions 1 to 4, wherein the raw material containing the constituent elements of the functional thin film or a solution thereof and a solid or liquid at least at room temperature and combusted or more than the thin film constituent material A mixing step in which an auxiliary material having a low disappearance temperature due to vaporization is mixed and dispersed in a desired ratio, a coating step in which the mixed dispersion material is coated on the surface of the base material to form a precursor film, and the base material with the precursor film The thin film constituting material is heated to a temperature at which the auxiliary material disappears, and a functional thin film having a porous film shape is formed on the surface of the base material.

  The invention 6 is the method for producing a transparent material according to the invention 5, wherein the auxiliary material is an organic material or a solution thereof, and the thin film constituent material is a metal oxide crystal.

  Invention 7 is the method for producing a transparent material according to Invention 6, wherein the auxiliary material is a saccharide or an aqueous solution thereof.

  Invention 8 is the method for producing a transparent material according to any one of Inventions 5 to 7, wherein the thin film constituent material is a photocatalyst.

The present invention does not attempt to overcome the “coloring phenomenon” and “coloration non-uniformity” by making the coating film uniform and thin, but the refractive index between the transparent substrate and the coating film. By eliminating the difference itself, visible light interference itself does not occur in principle.
Usually, the value of the refractive index of a transparent substrate such as glass is often lower than the value of the refractive index of the functional coating film. By making the refractive index values of both the same, in order to create a situation in which no visible light interference occurs, increase the refractive index value of the substrate or decrease the refractive index value of the coating film. An approach is conceivable. However, industrially, there is little room for selection of the substrate. Although the refractive index of the coating film is a value specific to the material constituting the coating film, it is found that the apparent refractive index depends on the filling rate of the material, that is, the number of pores, the size of the pores, etc. Thus, the apparent refractive index is lower than that of a dense material. Therefore, if the coating film is made porous and the filling rate can be freely adjusted, the light at the interface between the two is obtained by apparently matching the refractive index value of the coating film with the refractive index value of the transparent substrate. In principle, the above-mentioned interference can be removed, and “coloring” and its non-uniformity do not occur.
Based on this principle, the present invention is carried out.

Further, in the method for producing a transparent material of the present invention, as shown in the invention 5, the pores are miniaturized as a method for realizing a porous coating film such as ceramics by using an element of a constituent material of the thin film. Dissolve / disperse the organic material or its solution as an auxiliary agent in the raw material or its solution, coat it on the transparent base material, and lose the auxiliary material as vapor etc. when heat-treating the transparent base material As a result, the portion of the auxiliary material that was present in the coating film remains as pores, and as a result, porous coating is possible.
As a further improvement, saccharides were used as shown in Invention 7 to facilitate the acquisition of auxiliary materials and the dispersion of thin film constituent materials.

  In the present invention, making the functional thin film porous has the effect of lowering the density (corresponding to the refractive index) of the functional thin film, that is, reducing the apparent refractive index with respect to visible light. When the apparent refractive index for visible light of this functional thin film reaches a value sufficiently close to the refractive index for visible light of the transparent substrate, the discontinuity of the refractive index disappears at the interface between the functional thin film and the transparent substrate, For this reason, there is an effect that the light interference itself due to the discontinuity of the refractive index is suppressed in principle. As a result, the coloring phenomenon and the non-uniformity of the transparent substrate, which have been observed with the formation of the normal functional thin film, lead to the effect that it does not occur in principle, and the problem of designability is solved in principle. .

  In the present invention 8, the functional thin film is made porous by a process with the intention of using saccharides, and there are various effects in the process using saccharides. First, saccharides are stably supplied as a food in a very large amount and at a low cost, and have a significant cost reduction effect when used as an additive to raw materials compared to other porosification processes. Saccharides are not “dispersed” in the raw material solution containing water as a main component but are “dissolved”, so they are aggregated and compared with a raw material solution in which micelles or the like that tend to aggregate cannot be obtained are dispersed. Therefore, it does not require a dispersing agent or the like, is inexpensive, and does not agglomerate. Therefore, the pore distribution of the produced porous membrane is extremely stable and the raw material solution management is extremely easy, so that it can be said that it is exhausted.

In addition, the range of saccharides soluble in water is extremely large, stable from a very dilute state of ppb to a very dense state with a volume ratio of about 1: 1 or more (can dissolve saccharides of 1 cubic centimeter or more in 1 cc of water). Can be controlled.
Moreover, a uniform solution can be easily obtained by simple stirring. That is, the process of forming a porous functional thin film by adding saccharides to a raw material solution is characterized by a wide refractive index control range.

In the present invention, if the refractive index of the functional thin film formed to a value close to the refractive index of the base material cannot be controlled, the coloring of the transparent base material due to light interference and the unevenness thereof cannot be overcome. Absent. Therefore, a sufficiently wide control range of the refractive index is extremely advantageous for the process.
In the present invention, an aqueous solution of saccharides can be used as a coating solution. This has the effect that the surface of the clean glass is hydrophilic, so that application is very easy. That is, since the aqueous solution is applied to the hydrophilic surface, the raw material aqueous solution used in the present invention is very well adapted to the surface of the clean glass, and the thin and uniform state is stable, that is, a thin and uniform coating is realized naturally, such as spin coating. There is an effect of omitting the forced uniformizing means. For this reason, even in a dip coating method in which only immersion is performed, uneven coating and uncoated areas are hardly generated, and a uniform coating film of nanometer order can be obtained very easily. The saccharide dissolved in the aqueous solution is contained in the nanometer order in the coating film before firing, and until the heating starts, it works like a skeleton that supports the coating film, maintaining the shape of the coating film and uniform fineness. There is an effect of maintaining the pore distribution and its size and shape. Furthermore, since it is automatically desorbed as vapor into the atmosphere near the crystallization completion temperature at the heating completion stage, removal treatment by acid treatment or the like is not necessary. It should also be noted that saccharides are mainly used for food, so they are harmless to humans, have no adverse effects on the human body or the environment even if released into the atmosphere as vapors, and do not emit harmful substances at all.

As the transparent substrate used in the present invention, various glass, polycarbonate, polyethylene, acrylic, polyimide-based, polylactic acid, olefin / maleimide copolymer, plate-like bodies made of transparent resin having heat resistance such as fluororesin are mainly used. The transparent material of the present invention may include vases and figurines made of glass or transparent resin blocks.
In addition, the material constituting the functional thin film is not particularly limited as long as it is a material that expresses a function that does not originally exist in the base material, but an inorganic material and a heat-resistant organic material that constitutes the base material. Powder can be used.
Inorganic materials such as titanium, zinc, indium, gallium, tantalum, zirconium, niobium, vanadium, iron, copper, nickel, tungsten, molybdenum, iron-derived nanoparticles, and fine crystals of the oxide A material porous body can be selected and used based on its function.
In the following examples, an example in which a nanocrystalline porous body of titanium oxide was used as a thin film constituent material was shown. As a raw material for producing this functional thin film material (hereinafter referred to as [(NH4) 4 [Ti2 (C6H4O7) 2 (O2) 2] · 4H2O] aqueous solution: trade name NEW TAS FINE 2% aqueous solution) in the examples) There is no particular limitation as long as it contains the constituent elements of the functional thin film to be considered, but the solution is easy to coat on the substrate and easily disperse / dissolve the auxiliary material used to realize the porous structure. Etc. are preferable in order to simplify the process. However, titanium oxide powder, titanium metal powder, titanium ions, or a solution containing these can be applied.
In addition, in the following examples, saccharides (granulated sugar) were used as auxiliary materials to be mixed with the raw material when creating the functional thin film material. However, auxiliary materials are not limited to saccharides, and are necessary for the functional manifestation of functional thin film materials that are easy to mix and disperse / dissolve with the raw materials for the production of functional thin film materials or their solutions. Any material that vaporizes or burns at a temperature lower than the heat treatment temperature and disappears and does not hinder the functional expression of the functional thin film material may be used.
For example, a non-heat-resistant polymer such as vinyl chloride, cellulose resin, resin such as styrene, resin-based materials such as the polymer, saccharides such as sugar, starches, etc., dissolved in a solvent applied to each, The liquid can be used.

Examples and comparative examples

  It is not appropriate to use expensive raw materials and materials that significantly increase the price of glass because of its application to window glass, etc., and it is necessary to carry out photocatalytic coating on architectural glass, which has recently been increasing in size. Therefore, it is impractical to employ a coating liquid (raw material) that requires spin coating, and it is necessary to keep in mind the formation of a coating film by dip coating. Focusing on the fact that the surface of the clean glass is hydrophilic, a coating liquid mainly composed of water that is easily compatible with the surface of the clean glass is employed so that the coating film is formed on the entire glass without being repelled.

Since titanium dioxide has the highest performance as a material exhibiting photocatalytic activity, water-soluble titanium raw material [(NH4) 4 [Ti2 (C6H4O7) 2 (O2) 2] · 4H2O] is removed from water in this embodiment. What was melt | dissolved in the solution which becomes this was employ | adopted as a coating liquid (brand name Furuuchi Chemical: NEW TAS FINE Ti2% aqueous solution).
Also, sugars (referring to all sugars such as sucrose, granulated sugar, glucose, etc.) that are familiar and inexpensive raw materials as auxiliary materials used to make the photocatalyst coating film porous, which can be said to be the main point of this example, especially commercially available granulated sugar Using.

  In general, when a ceramic or the like is made porous, a technique of dispersing polymer micelles or the like in a coating solution is often employed. Polymer micelles and the like in the coating raw material are decomposed and evaporated in the heat treatment process for crystallization of the photocatalytic ceramic thin film, and as a result, pores are formed in the photocatalytic ceramic thin film and become porous.

However, the method using sugars of this example is superior to the method using micelles as follows. First, sugar is not “dispersed” in water, but “dissolved” in a very stable and large amount. This indicates that there is no “aggregation” that is always a problem when polymer micelles are dispersed in a solution. The main component of the coating solution is water, and this is used to make it porous. Such a material provides a very stable and easy-to-handle raw material for making porous materials.
This agglomerated and stable raw material is an extremely easy-to-use raw material, i.e., the refractive index of the porous photocatalytic active film to be produced is determined mainly by the ratio of sugars and titanium raw material at the time of preparing the raw material solution. Not affected by the coating process at all. In addition, once this raw material solution is prepared, the performance as a raw material such as homogeneity can be easily maintained over a long period of time without requiring any special storage environment. It only goes through a very easy and controllable process of “dissolving” and the cost can be kept low. Furthermore, since sugar is dissolved in the water in the solution in this raw material solution, a finer and more uniform distribution of pores can be obtained than micelles or the like that are merely dispersed. Furthermore, because sugar can be dissolved in a very large amount of a solution containing water as a main component, the control range of the refractive index by making it porous is significantly wider than when using dispersion such as micelles. This is an important advantage.

In this example, a product obtained by dissolving granulated sugar at a rate of 3 grams (Experiment No. 2 and 3) in 2.5 cc of NEW TAS FINE Ti 2% aqueous solution + 2.5 cc of pure water (total 5 cc) is used as a raw material solution. A titanium dioxide thin film was used as a photocatalytic coating. Moreover, the case where NEW TAS FINE Ti2% aqueous solution (experiment No. 1) which does not add granulated sugar was used as a raw material solution was shown as a comparative example.

  The difference between the examples and the comparative examples is the difference in whether or not sugar is added to the NEW TAS FINE Ti 2% aqueous solution as the raw material solution, and other conditions are the same. In this embodiment, a NEW TAS FINE Ti 2% aqueous solution is used. However, the present invention can be applied to any water-soluble titanium raw material, and is not particularly limited to a NEW TAS FINE Ti aqueous solution.

  A glass plate (having a refractive index of about 1.7) was used as a base material for forming the coating, and the coating process was carried out using the simplest method of dip coating, that is, simply dipping the glass plate in a coating solution and then pulling it up. (Since glass coating for large areas cannot be applied with spin coating, etc., it is an important factor required for the coating raw material solution to satisfy the designability required for dip coating, that is, the presence or absence of coloring and its uniformity). . ) After coating, it was dried in the air for about 30 minutes, and then heat-treated at 450 ° C. for 3 hours in an electric furnace in the same air atmosphere.

  Formation of a coating film having photocatalytic activity was confirmed on each of the examples and comparative examples. Measurement of photocatalytic activity is a method of detecting a silver thin film formed on a coating film by photoreduction of silver ions by measuring transmittance (Japanese Patent Application No. 2005-020195: Photocatalytic activity evaluation and measurement method and apparatus therefor) Figure 1 shows the results.

  In FIG. 1, it is clearly observed that the transmittance of the sample decreases with time due to the deposition of the silver thin film by the photocatalytic effect of each of the example and the comparative example. It can be confirmed that it is formed on the surface. As described above, the photocatalytic activity of both the example and the comparative example shows the same excellent activity, but the optical characteristics of the respective samples are clearly observed.

  First, the purpose of the present invention is to remove the coloring effect due to the interference of light, but in the case of a comparative example in which sugar is not introduced into the raw material for porous formation, the coating is clearly green to blue, etc. Coloring is observed in a non-uniform pattern according to the film thickness distribution. This suggests that there is a distinct discontinuous interface of refractive index at the interface between the coating film and the glass, and this uneven coloring is fatal for high-design applications such as window glass. It becomes a serious drawback. However, in the case of the examples, coloring is not recognized, and the appearance is almost the same as that of a glass plate not coated. This means that the photocatalyst coating film is made porous by the effect of sugar introduced into the raw material, and as a result, the difference in refractive index between the photocatalyst coating film and glass is almost eliminated. In other words, the object of the present invention was achieved to eliminate the difference in refractive index between the photocatalyst coating film and the glass, which causes coloring and non-uniformity.

  The photocatalyst-coated glass of the example is extremely excellent because the design property when used as a window glass is the same as that of the glass not coated. As described above, it can be clearly seen that the application of the present invention clearly realizes coloring and non-uniformity removal by the application of the present invention. However, for more objective and quantitative evaluation, the light interference is reduced. The used film thickness and refractive index measurement (using F-20 by FILMETRICS) were performed on each sample of the comparative example and the example.

  Clear light interference was observed for the sample of the comparative example, and it was revealed by optical interference analysis that a photocatalyst coating film having an average film thickness of 83 nanometers and a refractive index of about 2.6 was formed on the glass substrate. became. The refractive index value 2.6 is in good agreement with the value of the rutile titanium dioxide material, indicating that a rutile titanium dioxide film having an average film thickness of 83 nanometers was formed on the glass substrate.

  However, in the examples, no light interference was observed, and therefore the average film thickness and refractive index could not be determined based on the light interference. This is because the photocatalytic titanium dioxide film in the example is made porous so that the apparent refractive index decreases from the original value 2.6 of the rutile-structured titanium dioxide material, and approaches the refractive index of glass around 1.7. I'm telling you. For this reason, the discontinuity of the refractive index at the coating film / glass interface necessary for light interference is reduced, indicating that there is no observable level of light interference. Corresponds well. In this way, the refractive index control of the coating film by making it porous is realized only by the process of mixing very simple and inexpensive sugar into the raw material aqueous solution, which can eliminate the coloring phenomenon of the coating film on the glass. It was.

The graph which shows the photocatalytic activity measurement result of the photocatalytic active film | membrane measured by the photoreduction of silver ion (1) Example (solid line) and (2) Comparative example (dotted line).

Claims (8)

  A transparent material in which a functional thin film expressing a desired function is provided on a transparent base material such as glass or plastics, and the apparent refractive index of the functional thin film is substantially equal to the refractive index of the base material. It is characterized by being made porous so as to be the same.   The transparent material according to claim 1, wherein the functional thin film is made of a nanoporous material of an inorganic material.   3. The transparent material according to claim 2, wherein the functional thin film is made of a photocatalytic material.   The transparent material according to claim 3, wherein the photocatalyst material contains titanium dioxide as a main component.   The method for producing a transparent material according to any one of claims 1 to 4, wherein the raw material containing the constituent elements of the functional thin film or a solution thereof and a solid or liquid at least at a normal temperature, are combusted or vaporized more than the thin film constituent material. A mixing step of mixing and dispersing the auxiliary material having a low disappearance temperature by a desired ratio (dispersion includes dissolution), and a coating step of coating the surface of the base material to form a precursor film. And heating the base material with the precursor film to a temperature at which the auxiliary material disappears without the thin film constituent material disappearing to form a porous functional thin film on the surface of the base material. A method for producing a transparent material.   6. The method for producing a transparent material according to claim 5, wherein the auxiliary material is an organic material or a solution thereof, and the thin film constituent material is a metal oxide crystal.   The method for producing a transparent material according to claim 6, wherein the auxiliary material is a saccharide or an aqueous solution thereof.   8. The method for producing a transparent material according to claim 5, wherein the thin film constituent material is a photocatalyst.