Reversible light-sensitive coating and method for its production

Description

Technical area

[0001] The invention relates to a photosensitive coating based on nanotechnology having the property of changing colour in a reversible process, without thermal treatment, solely under the influence of light and of decolouring again without light.

[0002] The applications of the invention are, for example, in the field of ceramics, the design of surfaces, facades, interior and exterior spaces, swimming pools, in the field of the design of vehicles, objects as well as furniture, tableware and accessories. State of the art

[0003] Phototropic or photochromic glasses were described in the 1960s, among others, in US Pat. No. 3,208,860, and have been further developed since then. US Pat. No. 4,001,019 and US Pat. No. 5,019,538 describe technical improvements to reversible light-sensitive glasses with a high refractive index yet fast reaction times and high resistance to acids. Light-sensitive glasses are also known from EP 0 412 656 and EP 0 428 012 and DE 44 01 851. CH 693 774 A5 describes an improvement in mechanical strength, so that a light-sensitive layer can also be used for the production of wall, floor, or tabletops. Description of the invention

[0004] The object of the invention is to provide a light-sensitive coating which avoids the disadvantages of the known light-sensitive glaze and which in particular has an increased reaction speed and displays light images with higher contrast and better sharpness. Implementation of the invention

[0005] The coating according to the invention serves in particular to produce a coating which can be coloured under UV light and decoloured without UV light.

[0006] Surface. The coating comprises a base material, in particular a silicate or a silicate mixture. Furthermore, the coating contains at least one ingredient in the form of a water-soluble metal salt, which—optionally together with other ingredients—imparts light-sensitive properties when the coating is applied to a substrate as intended. For example, the ingredients commonly used for phototropic or photochromic glasses can be used. In the case of a coating formed as a glaze, proper application involves, for example, firing the glaze.

[0007] The ingredient is a water-soluble metal salt, especially a silver salt such as silver chromate, silver nitrate, or silver acetate. Organometallic silver compounds are also conceivable. Silver halides or ingredients that produce silver halides by reacting with other ingredients in the properly applied coating are particularly preferred. Titanium, chromium, copper, or lithium oxides in suitable combinations are also conceivable.

[0008] According to the invention, the base material, in particular the silicate or silicate mixture, consists at least partially of nanoparticles. A silicate mixture is understood to mean a silicate or a mixture of different silicates with one another or, if appropriate, with further additives. For the purposes of this invention, nanoparticles are understood to mean particles that typically have a size of less than 1 micrometer. Particularly preferably, at least 90% of the particles of the silicate mixture have a diameter of less than 0.8 µm. Further preferably, at least 50% of the particles of the silicate mixture have a diameter of less than 0.5 µm, and in particular at least 10% of the particles of the silicate mixture have a diameter of less than 0.1 µm. The nanoparticles can be obtained by finely grinding a coarser-grained starting material and / or by adding commercially available nanoparticles.Because the base material, particularly the silicate mixture, is at least partially in the form of nanoparticles, the speed of the reversible process—that is, the discoloration under the influence of UV light and the decolorization in the absence of light—is increased. The coating reacts to light with discoloration between 25 and 50 percent faster than previously known coatings. The discoloration becomes clearly visible within one minute. The improved optical properties significantly increase the design applications of the inventive coating.

[0009] Materials suitable for the coating according to the invention include, for example, ceramics (possibly already with a first glaze), metal, stone, and refractory concrete.

[0010] In principle, various applications are possible. The first application involves applying the photosensitive coating to the entire surface of the substrate. Exposure to light causes a darkening process; without light, a reversal process returns the coating to its original state.

[0011] Tiles that have been additionally coated with the above-described baked-on glaze layer on top of their conventional glaze, for example, darken under UV light. If a flat object is placed on these tiles and later removed or moved, it will soon leave a light shadow at its contact surface. If a three-dimensional object is placed on the tiles and then moved again, it will also leave a brightened area at the contact point. In addition, its shadow is reflected in a weaker, brightened area, and both together create a three-dimensional image of the object. Without light, these images disappear after a while, and the surface returns to its original state.

[0012] Instead of applying the light-sensitive glaze over the entire surface, a partial application of light-sensitive and light-insensitive glazes, as well as combinations with additional glaze layers, are possible. Positive or negative images are possible. Furthermore, a combination of the above-described applications with photoceramics produced using conventional methods and ceramic decals is possible. In addition, the photoceramics or ceramic decals can consist of the layer according to the invention. This allows a latent image to appear dark or light upon exposure to light and to return to its original state in a reversible process.

[0013] The production process using light-sensitive glaze for photoceramics and ceramic decals does not differ significantly from the usual production method for light-insensitive photoceramic images and decals.

[0014] Light-sensitive and light-insensitive coatings can be combined as described above. These light-sensitive and light-insensitive layers vary in color or are transparent. The light-insensitive layer serves, among other things, to temporarily enhance or neutralize the color effect of the light-sensitive layer. This makes a latently embedded image temporarily visible or invisible, depending on the lighting conditions.

[0015] The possibilities and combinations of layers mentioned above create new compositions with temporarily appearing and disappearing as well as fixed image elements.

[0016] The silicate mixture preferably consists at least partially of a commercially available glaze, which is finely ground until the desired particle size is achieved. Such a coating composition is preferably fired onto the substrate using a conventional, known ceramic process.

[0017] The coating particularly preferably contains a silver content of up to 25 wt.%.

[0018] Alternatively, it is also conceivable to add commercially available nanoparticles, e.g., hydrophilic fumed silicas such as Aerosil 300 or Aerosil MOX 80, to a coating composition instead of or in addition to fine grinding of a starting material. Such coating compositions containing additional nanoparticles can be applied as a glaze - optionally with a glass phase such as borax - or in a form other than a glaze, e.g., as an engobe.

[0019] It is also conceivable to add other substances such as pigments to the coating composition.

[0020] The method according to the invention serves to coat a surface with a light-sensitive coating. A coating composition as described above is applied to a surface and, in particular, subsequently baked.

[0021] The invention also relates to a product having an at least partially light-sensitive surface, in which at least a portion of the surface has been coated with a coating composition as described above.

[0022] Preferably, at least a portion of the surface is in a specific geometric shape, preferably in the form of a logo or lettering.

[0023] At least one further portion of the surface may be coated with a non-light-sensitive coating.

[0024] The product can be a ceramic or enamel plate, a piece of furniture, a piece of tableware, a vase, a statue, an art object, or a toy. The ceramic plate can be glazed or unglazed.

[0025] According to the invention, the coating composition can be used to produce a reversible light-sensitive glaze for coating wall, floor, facade, swimming pool, vehicle and / or furniture surfaces.

[0026] The invention is explained in more detail below using an exemplary embodiment: The commercially available glaze T23 (available from Lehmhuus AG, Basel) is used as the silicate mixture. Based on an 80% glaze by weight, 15% silver nitrate and 5% sodium chloride are used as ingredients that impart light-sensitive properties to the fired coating. In general, a commercially available barium-zinc frit can be used, for example.

[0027] The glaze originally contains particles approximately 40 µm in size. The glaze is finely ground in a ball mill for 100 hours using 3 mm zirconium oxide balls. The weight ratios of ball, glaze, and water are approximately 1:1:1. This results in a surface area of ​​10-15 m² / g in the glaze (compared to a surface area of ​​1-2 m² / g for the unmilled glaze). The surface area can be increased even further by adding additional nanoparticles such as fumed silica (e.g., Aerosil 300 or 380).

[0028] Then the salts are added. The product is sprayed onto the preheated surface and baked at 1000 to 1050 degrees Celsius.

Claims

1. A coating composition which can be cured as a glaze to produce a coating which can change colour under UV light and can revert to the initial colour in the absence of UV light, comprising - a base material, in particular a silicate or a silicate mixture - at least one component in the form of a water-soluble metal salt, in particular a silver salt, which is added to the base material and which changes the colour of the coating composition under UV light when applied as intended and which reverts the colour of the coating composition to the initial colour in the absence of UV light, characterised in that the base material, in particular the silicate or silicate mixture, consists at least partly of nanoparticles.

2. Coating composition according to claim 1, characterised in that the coating composition contains up to 25 wt. % of silver.

3. Coating composition according to claim 1, characterised in that the base material includes a silicate or silicate mixture which is a commercially available ground glaze or comprises enamel.

4. Coating composition according to claims 1 to 3, characterised in that at least 90% of the nanoparticles have a diameter of less than 0.8µm and in particular at least 50% of the particles of the silicate or silicate mixture have a diameter of less than 0.5µm and in particular at least 10% of the particles of the silicate or silicate mixture have a diameter of less than 0.1µm.

5. Coating composition according to any one of claims 1 to 4, characterised in that the component is selected from the group consisting of silver halides, silver nitrate, silver acetate, titanium oxides, chromium oxides, copper oxides, lithium oxides and organometallic silver compounds.

6. Coating composition according to any one of claims 1 to 5, characterised in that additional nanoparticles, in particular hydrophilic fumed silicas or mixed oxides, are added to the base material.

7. A process for coating a surface with a coating which can change colour under UV light and can revert to the initial colour in the absence of UV light, characterised in that a coating composition according to one of claims 1 to 6 is applied to a surface and then cured.

8. A product with a surface which at least partially changes colour under UV light and reverts to the initial colour in the absence of UV light, characterised in that at least a part of the surface has been coated with a coating composition according to one of claims 1 to 6 by a process according to claim 7.

9. The product according to claim 8, characterised in that at least part of the surface is in a specific geometric shape, preferably in the form of a logo or lettering.

10. The product according to one of claims 8 or 9, characterised in that at least one further part of the surface is coated with a coating that cannot change colour under UV light and revert to the initial colour in the absence of UV light.

11. The product according to any one of claims 8 to 10, characterised in that the product is a ceramic or enamel plate, a piece of furniture, a piece of tableware, a vase, a statue, an art object or a toy.

12. Use of a coating composition according to any one of claims 1 to 6 for producing a curable glaze which can reversibly change colour under UV light and revert to the initial colour in the absence of UV light for coating a wall, floor, facade, swimming pool, vehicle and / or furniture surfaces.