Light-transmitting substrate provided with a light-absorbing coating

Light-transmitting substrate equipped with light-absorbing coating

Technical field

The invention relates to a light-transmitting substrate at least partially equipped with a light-absorbing coating comprising silver and/or gold particles mixed in a sol-gel matrix. The present invention also relates to an electric lamp including a light-transmitting lamp tube containing a light source, wherein the lamp tube includes the above-mentioned light-transmitting substrate. In addition, the present invention also relates to the light-absorbing coating itself.

Background technique

A light-transmitting substrate equipped with a light-absorbing coating can be used as a colored layer on or in front of (incandescent) lamps for general lighting purposes. The substrate may include, for example, a colored filter made of a piece of (flat or non-flat) glass, which is designated to be placed in the trajectory of the light generated by the lamp. Such a device is usually used for outdoor lighting. Another example of a light-transmitting substrate is a lamp tube placed above the light source of an electric lamp. Such electric lights are mainly used as indicator lights in vehicles, such as red light sources in red tail lights and brake lights of vehicles. The electric light can also be used for traffic lights.

Compared with the use of ordinary (organic or inorganic) pigments, the main advantage of exclusively using metal particles such as silver or gold is that no thermochromic phenomenon occurs. In addition, since the size of the particles is very small, diffuse scattering is very small.

The color appearance of the coating material containing metal fine particles such as gold and silver can be adjusted because when metal particles are embedded in a dielectric with a higher refractive index, their optical absorption properties change toward longer wavelengths. For example, for gold particles, when they are mixed into a SiO2 matrix or a TiO2 matrix, respectively, the absorption peak is 520nm (green) or 620nm (red). Select the appropriate metal and matrix material to obtain a specific color.

For example, from US-A-5731091, it is known to include silver or gold coatings mixed in a sol-gel matrix.

However, an important disadvantage of the coating is that the gold and silver particles embedded in a suitable matrix material have strong absorption, especially in the yellow-green part of the spectrum. This results in the coating being transmissive to the blue and red parts of the spectrum. In order to sufficiently reduce the blue transmittance and obtain a red transmittance coating, a large amount of gold and silver particles are required. Clearly, this is a cost flaw. In addition, the reduction in the blue transmittance of the coating also reduces the red absorption, and therefore the effective light output of the lamp. For coatings including silver, the main defect is the low transmittance of the red coating, which is less than about 11%.

Summary of the invention

The present invention aims to provide a light-transmitting substrate according to the preamble, in which the above-mentioned drawbacks are avoided. In addition, the present invention aims to provide a coating that does not exhibit the above-mentioned defects.

To this end, the present invention provides a light-transmitting substrate according to the preamble, which is characterized in that a blue absorbing compound is added to the coating.

By adding a blue absorbing mixture to the coating, the light in the blue part of the spectrum is absorbed, thereby obtaining a red transmissive coating without requiring a very high number of gold or silver particles. Conversely, the amount of gold and silver can be greatly reduced. For example, in the case of gold, the amount can be reduced by 5 times. In the case of silver, an additional advantage is the ability to use a substrate with a higher refractive index, such as a substrate with a refractive index of about 2.3, thereby increasing the transmittance by 20%.

Such a blue absorption mixture absorbs light in the blue part of the spectrum. Therefore, in the case of a light-absorbing coating comprising silver and/or gold particles that strongly absorbs light in the yellow-green part of the spectrum, the addition of a blue-absorbing mixture results in absorption of both the yellow-green part of the spectrum and the light in the blue part. . Therefore, the red part of the spectrum maintains light transmission without requiring a very high number of silver or gold particles.

The blue absorption mixture can be an organic or inorganic mixture. Generally any yellow absorbing pigment can be used, as long as the absorption performance at wavelengths higher than 590nm is very low or negligible. The temperature to which the substrate-such as a glass tube-is subjected also determines the choice between organic and inorganic mixtures. In the case of high temperatures, inorganic mixtures are the preferred choice, while in the case of low temperatures, inorganic mixtures are advantageous.

A blue absorbing mixture can be added to the light absorbing coating. However, in a specific embodiment, the blue absorbing mixture is present in the additional layer.

Such an additional layer is preferably adjacent to the light-absorbing coating. Additional layers can be applied on top of the coating or between the coating and the substrate.

However, in another preferred embodiment of the present invention, the blue absorbing mixture is present in the substrate. For example, the blue absorbing mixture may be present in the glass of the lamp tube.

Preferable examples of the inorganic mixture include Fe2O3, a mixture given by the general formula Zn(1-x)Fe(2+x)O4 such as ZnFe2O4, and V2O5. However, other inorganic mixtures can also provide good results. For example, Ag can be added to the Au/MTMS coating to provide blue absorbency.

The aforementioned blue absorbing compounds or pigments are well known. For example, Fe2O3 is also used as the main pigment in the light-absorbing coating of electric lamp tubes. Iron oxide (Fe2O3) is an orange pigment, and phosphorus-doped Fe2O3 is an orange-red pigment. In this regard, reference may be made to WO01/20641 of the applicant. An important difference between WO01/20641 and the present invention is that in WO01/20641, inorganic pigments are used as the main pigments that absorb the visible light part, while in the present invention, gold and silver are the main light-absorbing components. In the present invention, inorganic pigments are specifically added to absorb light in the blue region, thus allowing a smaller amount of gold and silver.

The present invention also relates to an electric lamp including a light-transmitting lamp tube containing a light source, and the lamp tube includes a light-transmitting substrate according to the above.

As described above, the electric lamp can be advantageously used as an indicator light in a vehicle, for example, as a red light source in a red tail light and brake light of a vehicle.

In addition, the present invention also relates to a light-absorbing coating according to the above.

Description of the drawings

These and other aspects of the present invention will become apparent from the embodiments described hereinafter and will be explained with reference to such embodiments.

In the accompanying drawings: Figure 1 shows the color coordinate system of the light-transmitting substrate provided with a light-absorbing coating containing gold particles in the form of a partial CIE chromaticity diagram; Figure 2 shows the color coordinate system in the form of a partial CIE chromaticity diagram A color coordinate system of a light-transmitting substrate provided with a light-absorbing coating containing silver particles.

detailed description

The present invention will be illustrated with the following processing examples of coating preparation and application of the coating on the substrate.

Example 1-The sol-gel hydrolysis mixture of gold in MTMS/TEOS is obtained by mixing 4.3 g of ethanol, 40.0 g of methyltrimethoxy silane (MTMS), and 0.86 g of tetraethyl in 32.0 g of water. It is prepared by hydrolyzing the mixture with oxysilane (TEOS) and 0.14g 0.1M acetic acid for 48 hours.

The Fe2O3 dispersion was prepared by mixing 3g Fe2O3, 3g Dysperbyk-190, 7g water and 10g ethanol. The dispersion was added to the sol-gel hydrolysis mixture and methoxypropanol in a ratio of 1:2:0.2. Spin-coating the obtained solution on a glass plate or spraying it onto a rotating glass shell will result in a 2 micron thick coating containing about 20% by volume of Fe2O3.

Subsequently, 1 g of Au particle dispersion including 25% by weight of gold particles, 7% by weight of polymer, and 68% by weight of ethanol was mixed with the sol-gel hydrolysis mixture similar to the above in a ratio of 1:2. The polymer used to stabilize the metal particles is a polystyrene-polycarbonate block copolymer.

The coating liquid was then spin-coated onto the outer surface of the glass substrate covered with a Fe2O3 coating. The coating was cured at 350°C for 30 minutes, and as a result, a red coating was obtained. The thickness of this layer is approximately 2.8 microns.

The same result can be obtained when the Au dispersion is directly added to the mixture containing the sol-gel hydrolysis mixture and the dispersion containing Fe2O3. In this case the layer is applied in a single step.

Example 2-Silver in TEOTi was first coated with a 2 micron thick silicon oxide layer containing about 20 vol.% Fe2O3 as in Example 1.

The sol-gel hydrolysis mixture was prepared by mixing 20 g of ethanol, 3.3 g of tetraethoxy titanium (TEOTi), and 2.35 g of 0.1 M HCL (hydrochloric acid) and hydrolyzing the mixture for 48 hours.

Subsequently, 1g of Ag particle dispersion including 17wt% of silver particles, 13wt% of polymer and 70wt% of ethanol was added to 2g of ethanol and 2.5g of 10wt% of N-aminopropyltrimethoxysilane dissolved in ethanol. This solution was mixed with the TEOTi solution in a ratio of 1:2. The polymer used to stabilize the metal particles is a polystyrene-polycarbonate block copolymer.

The coating liquid is prepared by mixing the silver solution and the sol-gel hydrolysis mixture. Subsequently, the coating liquid was spin-coated on a glass substrate covered with a Fe2O3 coating and cured in air at a temperature of 350°C. The layer thickness of the coating is approximately 200 nm.

Figure 1 shows the color coordinate system of a light-transmitting substrate equipped with a light-absorbing coating containing gold particles in the form of a partial CIE chromaticity diagram, which is obtained by simulation. Red is designated by x=0.665 and y=0.335.

On the left side of Fig. 1, the colored dots represent a coating with 2 micron thick gold particles mixed into the matrix. The refractive index changes from 1.46 to 1.90, and the Au content changes from 0.5 to 3vol.%. Only at 3vol.% Au content, the transmitted light will fall within the red specification. Then the highest transmittance is obtained with a refractive index of about 1.5. Layers containing a smaller amount of Au will not be able to produce red because they have too much transmittance in the blue region.

The right-hand side of Figure 1 shows how the addition of Fe2O3 to the light-absorbing coating improves the red color transmittance. By using the coating according to the present invention-for example the coating according to Example 1: Au/sol-gel coating with about 20 vol.% Fe2O3 added-blue light transmission is effectively prevented. In this way, the layer containing only 0.5vol.% Au with a refractive index of 1.90 is within the red requirement range. If the refractive index of this layer is low (n=1.5), the amount of Au can be reduced to about 2 vol.%.

Figure 2 shows the color coordinate system of a light-transmitting substrate equipped with a light-absorbing coating containing silver particles in the form of a partial CIE chromaticity diagram, which is obtained by simulation.

It clearly shows that a coating that does not contain any Fe2O3 or a layer adjacent to it with any Fe2O3 will not produce a red color according to the color requirements.

However, adding a 2 micron thick silicon oxide layer containing about 20 vol.% Fe2O3 to the coating containing Ag-for example according to Example 2-will change the color point towards the red area. As shown in Figure 2, the color point and transmittance are not strongly dependent on the position of the Fe2O3 layer.

It should be clear that many variations can be made for those skilled in the art within the scope of the present invention. Many alternative preparation methods, namely wet chemical and physical deposition methods are feasible. In addition, other blue absorbing mixed compounds can also be used to produce the desired color point shift.

The scope of protection of the present invention is not limited to the examples given here. The present invention is embodied by each new feature and each feature combination.