DE102013110564A1 - Method for changing the geometry of glass ceramics and glass ceramic articles produced according to the method - Google Patents

Abstract

The invention is based on the object of locally generating a change in the geometry of a monolithic glass ceramic component. For this purpose, a method for producing a raised structure on a glass ceramic element (1) is provided, in which the glass ceramic element (1) is irradiated with electromagnetic radiation in a local area of the surface, wherein the radiation penetrates the glass ceramic element (1) and at least partially absorbs it is heated, so that the glass ceramic element (1) is heated in the region of the irradiated electromagnetic radiation and heated above the glass transition temperature, and wherein the irradiation is terminated after the heating, so that the heated area cools down again to the temperature of the surrounding glass ceramic material, and wherein the heating causes a change in volume of the glass-ceramic, which causes a local elevation of the surface, and wherein this state is frozen upon cooling of the heated area, so that after cooling, a surface deformation in the form of an increase (20) remains.

Description

The invention relates to a method for preferably locally changing the geometry of glass ceramics, as well as a glass ceramic with a local geometry change in the form of a survey on the surface.

In this case, preferably in the visible wavelength range (380 nm-780 nm) colored materials (and thus usually also in the IR range colored materials) such as glasses and glass ceramics (green glass state or already ceramized) to use. The change of geometry is effected by the local and temporary exposure to electromagnetic radiation, e.g. Laser radiation of a diode laser with 1 micron wavelength with CW mode and not strongly focused laser beam, preferably with a beam diameter of greater than 400 microns.

State of the art

A local change in the geometry of glass ceramic components is based on the prior art on three different variants:
On the one hand, by adding a second part to the actual component, a geometric enlargement can be generated. In this case, all joining methods such as soldering, welding and gluing can be used. The disadvantage here is that two components are needed. In addition, the joint is usually visually disturbing or forms a breakage exit edge. Even costly increases in geometry (circles, rounding, etc.) can be difficult to add by an additional component.

On the other hand, a local reduction of the geometry can be done by (local) mechanical removal of material. This involves grinding and milling processes. The occurring damage to the surface can lead to the reduction of mechanical strength. The change in the surface in the removed area (grinding or polishing surface) can also be visually disturbing. In addition, the production of locally raised structures in this way is difficult to produce, as this much much surrounding material would have to be removed.

The third one is in WO 2012/134818 describes a method according to which locally very limited color centers are produced with an ultra-short pulse laser in the UV range in a highly transparent glass, which then coupled as a self-reinforcing effect to the UV radiation always better and thus achieve a heating effect, which in the end to a change in geometry in shape leads from small locally very limited elevations in the micrometer range.

The disadvantage here is the elaborate ultrashort pulse laser, which must first create the condition that the glass ever couples. The self-reinforcing effect also leads to uncontrolled heating and an uncontrollable regulatory problem. Another disadvantage is that only glasses can be used that are sufficiently transparent in the UV range.

Object of the invention:

The invention is therefore based on the object locally to produce a change in the geometry of a monolithic glass ceramic component.

Attachments or mechanical operations are then no longer needed to create a haptic increase or decrease.

This makes it possible to make geometric demarcations on components of any kind made of glass ceramic felt.

The disadvantages of a joint seam, namely the visual appearance and the presence of one or more additional component edges, which can lead to breakage, are eliminated.

• – eine Veränderung der Geometrie ohne Schädigung der Oberfläche herzustellen,
• – eine Vergrößerung des Volumens ohne zusätzliches Material, oder
• – eine Verringerung des Volumens ohne mechanische Verletzung des Bauteils zu erreichen.

In particular, the invention makes it possible

• To make a change in the geometry without damaging the surface,
• An enlargement of the volume without additional material, or
• - To achieve a reduction of the volume without mechanical injury of the component.

Solution of the task

In order to achieve a geometry change of a glass ceramic, according to the invention a temperature increase of the glass ceramic, which is generally above the glass transition temperature T _g , followed by a targeted, generally very rapid, cooling carried out.

It heats not only the surface, but the volume of the material, to make the effect visible and not to overheat the surface. In order to achieve a local geometry change, therefore, a temperature increase is achieved locally in the volume.

This can be done by electromagnetic radiation in a wavelength range in which the glass or the glass ceramic has at least a partial transmission for the incident electromagnetic radiation.

Thus, not only superficially, but over part or all of the thickness (in volume) energy is introduced, so that there is a homogeneous effect that ideally has no influence on the geometry of the component outside the local geometry change.

If the product of radiation density and absorption is high enough, then there is a local shock-like increase in temperature and thus a change in the volume.

In particular, the invention thus provides a method for producing a raised structure on a glass ceramic element, in which the glass ceramic element is irradiated with electromagnetic radiation in a local area of the surface, wherein the radiation penetrates the glass ceramic element and thereby at least partially absorbed, so that the glass ceramic element is heated in the region of the irradiated electromagnetic radiation and is heated above the glass transition temperature of the residual glass phase, and wherein the irradiation is terminated after the heating, so that the heated area cools back to the temperature of the surrounding glass ceramic material, and wherein the heating causes a volume change of Glass or the glass ceramic, which causes a local elevation of the surface, and wherein this state is frozen when cooling the heated area, so that after cooling, a surface deformation in the form an increase remains. Surprisingly, such a volume change in a glass ceramic, which has a very low or even vanishing coefficient of _{thermal expansion} α _20-600 , can be brought about with the method in a simple manner. Typically, the coefficient of _{thermal expansion} α _20-600 of such a glass ceramic is at most 2 × 10 ^-6 K ^-1 .

With this method, a glass-ceramic article can be produced in which at least one local elevation is present in the surface, wherein the smallest lateral dimension has a length of at least 0.05 mm, and wherein the local elevation has a height in the range of 0.005 to 0.5 Millimeter, wherein the elevation and the surrounding glass-ceramic material are monolithic and have the same composition, and wherein the glass-ceramic material under the survey has a lower density than the material surrounding the survey. The method can be applied not only to glass ceramics, but also to glasses, whereby corresponding glass products are obtained.

By choosing the radiation source and the form of the introduction of the energy, the range of geometry change from point-like over linear to flat.

A punctiform irradiation allows many degrees of freedom in the design of the surveys. "Point-shaped" in this context means, of course, that the irradiated area still occupies a certain, small area. In particular, surfaces in the range up to 5 mm ² are suitable. According to a development of the method, therefore, the electromagnetic radiation is concentrated to a region having an area in the range of 0.05 mm ² to 5 mm ² . Preferably, this surface is circular or elliptical.

With a punctiform introduction of the energy, by movement of the radiation source or movement of the component, the region of the geometry change can take on any shape. In this way, for example, letters, characters or even triangles, squares or any other geometric shapes in the form of surveys on the surface of the component can be produced. The dimensions of the geometry change may vary from a diameter of 0.05 mm, preferably 0.1 mm, to an area of several square meters. The volume change can be from 0.1 mm ³ to several cubic millimeters.

According to one embodiment of the invention, therefore, the point-shaped region in which the electromagnetic radiation is irradiated, moved over the surface of the glass ceramic element to produce a survey with an area larger than the area of the point-shaped area.

As sources of radiation, UV radiation sources, IR radiators with tungsten filament, laser sources, e.g. Diode laser, fiber laser or other radiation sources whose electromagnetic radiation can penetrate into the glass-ceramic material at least partially, are used.

The choice of the correct radiation source depends on the absorption capacity of the glass-ceramic material to be treated in the range of the wavelength of the radiation source.

The heating is particularly preferably carried out with an infrared laser, preferably a diode laser, as the radiation source.

For ceramified ceran glass ceramics, or more generally lithium aluminosilicate glass ceramics, e.g. Diode laser with a wavelength in the near infrared range, for example in the range of 1 micron. At this wavelength, the transmission of a 4mm thick glass ceramic plate is between 50% and 80%, so that enough radiation penetrates the entire thickness of the plate to heat it homogeneously across the thickness of the plate at the point of energy input.

With a sufficiently high power, it is thus possible within a few seconds to achieve a temperature at the location of the energy input of greater than 700 ° C.

In order to generate a local survey, therefore, a temperature increase is also caused locally in the volume. This is done by electromagnetic radiation in a wavelength range in which the glass ceramic has a partial transmission for the incident electromagnetic radiation. This energy is introduced not only superficially but over the entire thickness or in a partial volume of the glass ceramic element. If the product of radiation density and absorption is high enough, there will be a (local) shock-like increase in temperature and thus a volume change. If the product is too large, only the surface will be heated and overheated, and the volume effect will not be large enough. If the product is too small, then heating is too slow and the effect either does not occur or is no longer clearly local to limit, ie smeared. According to a development of the invention, therefore, the radiation density or power density of the electromagnetic radiation and / or the absorption coefficient k of the glass ceramic material is selected so that the product P of the power density and the absorption coefficient k is at least P = 0.35 (W / mm ³ ) · ( 1 / mm). The absorption coefficient should be at most 2 / d to avoid only superficial heating according to another embodiment of the invention, where d denotes the thickness of the glass ceramic element.

Preferably, the electromagnetic radiation having an average power density of at least 2.5 W / mm ^{2 is} irradiated onto the region of the glass ceramic element to be heated in order to achieve a sufficiently rapid heating.

In order to obtain elevations with steep flanks, which are easy to detect haptically, it is favorable if the heating takes place very quickly, so that a steep temperature gradient is generated in the direction perpendicular to the irradiation direction in the glass-ceramic material. This temperature gradient then causes a correspondingly sharp demarcation between the area of lower density under the elevation and the surrounding material, which in turn leads to localized deformations. It is therefore preferred that the heating takes place with a temperature increase of at least 20 K per second.

After cooling the plate to room temperature, the volume at the point of energy input is greater than before the radiation treatment.

Optionally, a thermal post-treatment step after cooling may be provided. With such a post-treatment step, previously induced tensile stresses can be reduced again by the heating. An individual fine adjustment of the generated transmission by a thermal post-treatment step is also possible.

• – Ein zweiter Aufheizschritt mittels elektromagnetischer Strahlung, vorzugsweise mittels eines Lasers, der das Volumen auf eine Entspannungstemperatur aufheizt und dort hält.
• – Ein zweiter Aufheizschritt mittels elektromagnetischer Strahlung, vorzugsweise mittels eines Lasers, der nur die Oberfläche/n aufheizt und dort Spannungen abbaut. Dies kann günstig sein, da oberflächennahe Spannungen wesentlich kritischer sind als Spannungen im Volumen. Um eine solche mehr oberflächliche Erwärmung zu erzielen, kann für den zweiten Aufheizschritt elektromagnetische Strahlung verwendet werden, die andere Wellenlängen aufweist als die elektromagnetische Strahlung des ersten Aufheizschritts.

Possible variants of the thermal aftertreatment are:

• - A second heating step by means of electromagnetic radiation, preferably by means of a laser, which heats the volume to a relaxation temperature and holds there.
• - A second heating step by means of electromagnetic radiation, preferably by means of a laser, which heats only the surface / n and there dissipates voltages. This can be favorable since near-surface stresses are much more critical than stresses in the volume. In order to achieve such a more superficial heating, electromagnetic radiation having other wavelengths than the electromagnetic radiation of the first heating step may be used for the second heating step.

A thermal reheating and relaxation in a conventional oven, for example in a cooling oven.

In general, in the case of glass ceramic plates, the generation of the local increase on the useful side is preferred in order to produce haptically detectable structures. Therefore, in one-sided doubled glass ceramic plates, local elevations are preferably applied to the smooth side.

The area of the energy input can take place both via the shaping of the irradiation of the energy, as well as via an additional masking of the plate to be treated, so that parts of the glass ceramic which are not to be changed are effectively protected from the impact of radiation. Optics which allow beam shaping from a round beam spot into a rectangular or linear beam area and thus enable simultaneous irradiation of a delimited local geometric area are advantageously usable for the method according to the invention.

The advantage of this method over the prior art is the fact that you can make do with a monolithic component without any adjustments to the composition, joints or treatments. The process is very fast (in the seconds range), highly flexible and extremely well adaptable to a wide variety of geometries and applications.

Even three-dimensionally deformed components can be treated. The treatment of the component according to the method can be carried out both before and after the ceramization step in the case of a glass ceramic.

• – Kochzonenmarkierungen oder Abgrenzungen der Bedienelemente auf Glaskeramikkochflächen, auch beispielsweise für sogenannte „vulnerable people“, um mit haptischen Strukturen sicherheitsrelevante Informationen auf Kochflächen bereitzustellen,
• – Aufbringen eines 1D (Balken) oder 2D (Dot Matrix)-Barcodes auf die Oberfläche des Produktes (z.B. eines Vials / einer Spritze) zur dauerhaften Kennzeichnung,
• – Aufbringen einer Füllmengenskala oder Füllhöhenmarkierung auf die Glaswand des Produktes (z.B. Vials, Behälter, Rohre) oder einer anderen Markierung,
• – Aufbringen von optischen Designelementen auf Flachgläser (z.B. Architekturverglasung) wie Firmenlogos oder geometrische Objekte (Pfeile als Wegweiser, Fluchtweg),
• – dauerhafte fälschungssichere Markierung von Produkten durch ein erhabenes Logo auf der Oberfläche des Glases,
• – Aufbringen von Piktogrammen, Buchstaben, geometrischen Objekten in Touch-Anwendungen für Handy-Cover oder anderen elektronischen Geräten,
• – Erzeugung von Fühlstrukturen für sehbehinderte Menschen, z.B. auf einer Kochfläche
• – Verringerung der Kontaktfläche von Topfboden und Glaskeramik-Kochfläche, dadurch Schaffung einer Wärmeisolation, insbesondere bei Induktions-Kochfeldern,
• – Erzeugung von haptischen Strukturen in Vertiefungen, insbesondere in konkav geformten oder vertieften Bedienelementen.

The invention may be interesting for the following applications:

• Cooking zone markings or boundaries of the operating elements on glass ceramic cooking surfaces, also for example for so-called "vulnerable people", in order to provide security-relevant information on cooking surfaces with haptic structures,
• Applying a 1D (bar) or 2D (dot matrix) barcode to the surface of the product (eg a vial / syringe) for permanent labeling,
• Applying a fill scale or level mark to the glass wall of the product (eg vials, containers, tubes) or other marking,
• - application of optical design elements on flat glass (eg architectural glazing) such as company logos or geometric objects (arrows as signposts, escape route),
• - permanent counterfeit-proof marking of products by a raised logo on the surface of the glass,
• - applying pictograms, letters, geometric objects in touch applications for mobile phone covers or other electronic devices,
• - Creation of sensing structures for visually impaired people, eg on a cooking surface
• Reduction of the contact surface of the pot bottom and the glass ceramic cooking surface, thereby creating a heat insulation, in particular for induction hobs,
• - Creating haptic structures in wells, especially in concave-shaped or recessed controls.

The invention will be explained in more detail with reference to embodiments and the drawings. In the drawings, like reference characters designate like or corresponding elements.

Show it:

1 an arrangement for carrying out the method according to the invention,

2 a schematic cross section through a glass ceramic element according to the invention,

3 a transmission profile of a volume-colored glass ceramic plate along a position coordinate perpendicular to the longitudinal direction of a local elevation,

4 X-ray diffraction spectra at a brightened and an unaltered area of a volume-colored glass-ceramic,

5 the spectral transmittance of a treated and an untreated region of a glass-ceramic plate,

6 a height profile of a survey,

7 a further education in 2 shown embodiment,

8th a glass ceramic hob.

It becomes a glass ceramic element 1 , here in the form of a ceramized glass ceramic plate (a lithium aluminosilicate glass ceramic with high quartz mixed crystals as the main crystal phase) with dimensions of 50mm × 50mm and 4mm thickness on a silicon oxide ceramic substrate made in slip casting 7 with 100mm × 100mm and 30mm thickness with one side 5 to the silicon oxide ceramic substrate 7 placed there. Silica ceramic backing 7 and glass ceramic plate are kept at room temperature. Above this arrangement is a laser scanner 13 with a focusing optics 130 , Focal length 250mm, so installed that the laser beam 90 impinges perpendicular to the surface of the glass ceramic plate. In focus, the diameter of the laser beam is 1.5mm. The arrangement of Quarzalunterlage 7 and glass ceramic plate was placed in the focal plane. About a fiber 11 becomes the laser scanner 13 irradiated with a laser radiation between 900nm and 1100nm wavelength. As a laser source 9 serves a diode laser, for example, the company laserline, which provides a controllable power between 0 W and 3000 W.

The laser scanner is now programmed so that a circle of 40mm diameter is traveled at a speed of 1 m / s. After activation of the laser source 9 The glass ceramic plate is locally irradiated with a power of 1000W and a duration of 30s. After that, the laser becomes 9 switched off and the glass ceramic plate cooled in air. In the area of radiation, a raised circle on the glass ceramic plate is clearly visible and palpable. The rest of the plate remains geometrically unchanged. This affects both the flatness and local thickness variations.

Without being limited to the embodiment discussed above, rapid cooling is preferred. This is beneficial to freeze the effect of volume change. In a further development of the invention it is therefore provided that the glass ceramic after heating at a cooling rate of at least 1 K per second, preferably at least 5 K per second, more preferably at least 10 K per second at least within a temperature range of the maximum temperature to 100 K below the Maximum temperature is cooled.

2 shows a cross section through a glass ceramic element according to the invention 1 , Due to the fast heating with the laser 9 or a radiation source comparable in terms of performance and absorption in the glass-ceramic material became on one side 3 a local raise or survey 20 , or generates a raised structure. The volume change frozen on cooling causes one in the area of the elevation 20 in the glass ceramic material reaching into the area 22 with reduced relative to the surrounding glass ceramic material density. This area 22 can, as in the in 2 example shown up to one page 5 extend which of the page 3 with the survey 20 opposite.

Elevations generated by the method according to the invention, or local elevations 20 have a characteristic profile with rounded edges. In particular, as schematically shown in FIG 2 represented, the edge of the survey 20 a concave curvature 24 on, which towards the center of the elevation in a convex curvature 25 passes.

For volume-colored glass ceramic elements 1 In addition to changing the surface, a local color change can surprisingly also be achieved. In particular, the light transmission can be local in the area of the survey 20 increase. Such a color change on volume-dyed materials could be detected on a glass-ceramic stained with coloring metal ions, in particular with vanadium oxide.

Accordingly, it is provided in a further development of the invention, without limitation to the specific illustrated embodiments, that the glass ceramic of the glass ceramic article is volume-dyed with coloring metal ions, wherein in the region of the local survey, the coloring of the glass ceramic from a second area in addition to the local increase 20 differs, so the absorption coefficient in the area of local increase 20 smaller than the absorption coefficient of the second region and thus the integral light transmission in the visible spectral range at the local elevation 20 is higher than the integral light transmission of the second area.

For the purposes of the invention, a volume-colored glass ceramic is understood as meaning a material in which the color centers or coloring ions are distributed in the material. These are therefore not concentrated as in the case of pigments locally in the form of coloring crystallites. According to a dye, the coloring ions or color centers are thus dissolved in the glass or the glass ceramic, while pigments are dispersed in the material. Volume coloration accordingly influences the transmission, but not the scattering, whereas pigments themselves represent scattering particles. However, any additional pigments present are not excluded.

The method according to the invention is very well suited to locally attenuate the color of a vanadium oxide volume-colored glass-ceramic article. Accordingly, in the local region, the transmission in the visible spectral range between 380 nanometers and 780 nanometers is increased by the heating. According to one embodiment of the invention, therefore, a vanadium oxide volume-colored glass ceramic element is provided, in which, in the region treated according to the invention, ie where the local elevation is produced, the integral light transmission in the visible spectral range is raised relative to an adjacent second untreated region.

In this way, for example, windows with higher transmission can be generated in an otherwise dark-appearing glass ceramic hob in a simple manner. Under such a window, a display can then be attached, which shines for the viewer well visible through the local increase. A window as a particularly preferred form of a brightened area produced by the method according to the invention is understood to mean a region which is surrounded by at least three sides or at least 50% of its circumference by adjacent, non-brightened second areas. Preferably, the brightened first area is completely surrounded by second areas, or non-brightened glass ceramic material.

Typically, the temperature at which the increase in transmission occurs is above the temperature at which the viscosity of the glass-ceramic is 10 ¹⁴ dPas. Is not to the softening point, wherein the viscosity s has a value of 10 ^7.6 dPa ·, heated, a whitening can be achieved without changes in shape. Accordingly, local elevations and additionally only brightened areas can be produced depending on the heating.

In order to achieve a sufficiently dark color, it is preferred that the glass ceramic contains at least 0.005, preferably at least 0.01 weight percent vanadium oxide.

According to one embodiment of the invention, the glass ceramic is dyed with coloring ions, preferably with vanadium oxide, so that the integral light transmission of the glass ceramic in the visible spectral range of the second region is at most 5%, preferably at most 2.5%.

3 shows as an example a transmission profile of such vanadine oxide volume-stained glass-ceramic sample in which a local increase 20 was prepared in the form of a rib or bead by the inventive method. The direction of the position coordinate is perpendicular to the longitudinal direction of the rib. The profile of the local increase 20 is also visible on the discoloration caused by the heating of the glass-ceramic and the concomitant increase in transmission in relation to an adjacent second area next to the elevation. When looked at, the area of the local increase appears correspondingly brighter. It is also possible, only a discoloration, or lightening without an increase according to the invention 20 when a lower temperature ramp is selected during heating. If only a brightening without change in volume is generated in a region, it can be different from the above stated that the product P of the power density and the absorption coefficient k are kept smaller. For the product, a value of at least P = 0.25 (W / mm ³ ) · (1 / mm) is.

With this method, a volume-colored, monolithic glass-ceramic articles, for example in the form of a cooking surface, which has a first region in which the coloring of the Glass ceramic differs from a second, adjacent region, so that the absorption coefficient of the first region is smaller than the absorption coefficient of a second, adjacent region 16 and that the integral light transmission in the visible spectral range of the first region is higher than the integral light transmission of the second, adjacent region, wherein the light scattering in the glass ceramic of the first region is typically at most about 20 percent, preferably at most 10 percent, more preferably at most is increased by an absolute 5%, in particular preferably by at most 1% relative to the light scattering in the glass ceramic of the second region. The light scattering in the glass ceramic of the first region is thus substantially equal to the light scattering of the second, adjacent region with unchanged light transmission. The upper limit of light scattering, which is at most 20 percent higher, is also the case where the light scattering is smaller in the first region than in the second region. With the slight increase in light scattering, this does not appear as a visible effect. The light scattering is the proportion of the irradiated total intensity minus the directly transmitted light, the Fresnel reflection and absorption. The absolute percentage increase in scattering refers to the proportion of scattered light in the transmission of a light beam. For example, if the proportion of the scattered light intensity in the second region is 3% of the total intensity, then an increase of absolutely 5% in the first region means a proportion of the scattered light intensity in the first region of 3% + 5% = 8%. The terms of transmission, scattering, absorption and remission, as used in the context of the invention, correspond to the definitions according to DIN 5036-1 and can comply with the measurement requirements under ISO 15368 10 be determined. Said first area additionally has the local increase according to the invention 20 on. It is possible to create one or more further first areas without elevation. The effect of scarcely altered light scattering with the values given above can also be present in the region of the local increase in the case of a non-volume-colored glass ceramic or a glass ceramic in which no color change occurs due to the treatment according to the invention.

Integral light transmission is understood to mean the spectral light transmission averaged over a wavelength range, such as the visible spectral range between 380 and 780 nanometers wavelength. The spectral light transmission is the light transmission at a certain wavelength. Unless the term "spectral light transmission" is used, the term "light transmission" in the sense of this description is to be understood as an integral light transmission.

The amount of transmission change may be up to more than 50% higher than the original transmittance by an absolute 0.1%. Preferably, in particular in the case of dark-colored glass ceramics, the transmission in the visible region of the spectrum is in the first region in relation to the second, adjacent region 16 increased by at least a factor of 2. At the in 3 In the example shown, the transmission in the region of the local increase increases by more than a factor of three compared to the non-brightened, to increase 20 adjacent area 16 at.

A further feature of this embodiment of the invention is the fact that the wavelength of the radiation does not have to correspond to the wavelength of the effect achieved, that is to say the wavelength at which the transmission change occurs. In the present invention, it is thus possible to irradiate, for example, in the infrared wavelength range at 1 micron wavelength, because in the glass ceramic in this wavelength range, an absorption band is present. However, the resulting effect may, for example, be in the visible range between 380nm and 780nm and cause a change in transmission at one or more wavelengths in that region through physicochemical reactions of the elements and compounds present in the glass.

When introducing a local increase 20 and / or a brightening in the case of a volume-colored glass ceramic result in the changed or treated area only minor structural changes.

2 shows X-ray diffraction spectra on a monolithic glass ceramic element, as with the basis of 1 explained method is obtained. The glass ceramic investigated is a vanadium oxide volume-colored lithium aluminosilicate glass ceramic, as used for cooking surfaces. With the X-ray diffraction, the crystal phases, the crystal phase content and the crystallite size of a region lightened by the laser irradiation became 15 compared with adjacent, non-illuminated areas 16 , Additionally marked with a rhombus, a square or a circle are the relative intensities of different crystal phases. With the squares are X-ray diffraction peaks of high-quartz mixed crystal (HQMK), with diamonds the X-ray diffraction peaks of lithium aluminosilicate, or keatite mixed crystal (KMK, 10 LiAlSi ₃ O ₈ ) and circles the X-ray diffraction peaks of also in the glass-ceramic zirconium titanate (ZrTiO ₄ ). The curve 150 is in the X-ray diffraction spectrum on the brightened, so according to the invention treated area and the curve 160 the X-ray diffraction spectrum of an adjacent, unaltered area 16 , As can be seen, the curves are practically congruent, except for the different representation reasons for offset. Upon closer evaluation of the intensities of the X-ray diffraction peaks, the only result is a very small increase in the content of the keatite mixed crystal phase. The results are summarized in the table below: sample Crystallite size [nm] [+/- 5%] HQMK phase content [+/- 10%] KMK phase content [+/- 10%] HQMK KMK uncorrected corrected uncorrected corrected brightened area 49 Not definable 54 66 3 3 unchanged range 48 Not definable 55 67 1 1

For the absorption corrections in the columns marked "corrected", the chemical composition of the glass-ceramic and an assumed density of ρ = 2.5 g / cm ^{3 was} used.

The phase content of the high quartz mixed crystal changes according to the above table and 3 therefore not within the measurement error. Only the keatite mixed crystal content shows a change that does not significantly affect the structure of the glass ceramic due to the low proportion of this crystal phase. Even if treated and untreated areas of a glass ceramic element thus have no significant structural differences, an area treated according to the invention of an aluminosilicate glass ceramic, in particular a lithium aluminosilicate glass ceramic according to a development at a higher content of keatite mixed crystal compared to an adjacent, not treated area can be detected.

Changes in the crystal phases and / or their proportions can influence the light scattering. If the light scattering in the material changes, this also leads to a changed remission when illuminating the treated area. As demonstrated in the example above, treated and untreated areas are virtually identical in their morphology, especially with respect to the crystal phases present. Therefore, the remission in a product according to the invention between a treated and an untreated area does not change or only very slightly. In a further development of the invention, it is therefore provided without limitation to the embodiment described above that the remission of the first visible light range from the remission of the second range by at most absolute 20%, preferably at most absolute 10%, more preferably at most absolute 5 % differentiates. The light scattering increases in the first area, if at all, then at most slightly by less than 5% absolute.

The X-ray diffraction measurements were made on a sample in which only a brightening without volume change was made. In the method according to the invention with local deformation, a more pronounced increase in the keatite phase content is to be assumed due to the increased heating. In a sample in which a pronounced local increase was generated, a slight increase in scattering in the region of increase can also be observed visually. Since light scattering is generally caused by keatite mixed crystals, according to one embodiment of the invention, a higher proportion of keatite mixed crystal in the glass-ceramic material is in and below the increase 20 in the case of LAS glass ceramics, a feature of a glass ceramic article produced according to the invention. According to this embodiment of the invention, therefore, a glass ceramic article of aluminosilicate glass-ceramic, preferably made of lithium aluminosilicate glass-ceramic is provided in which the glass-ceramic material at the local elevation 20 has a higher keatite mixed crystal content than a second region adjacent to the local heightening 16 ,

In the embodiment with vanadium oxide volume-colored glass ceramic and a transmission increase achieved simultaneously with the local increase, a particularly advantageous effect also results in an increase in the transmission reaching into the blue spectral region. This makes it possible to use the brightened area for blue glowing, through the glass ceramic radiating optical displays.

5 shows the spectral transmittances of a treated according to the invention, with vanadium oxide volume-colored, 4 mm thick glass ceramic plate as a function of wavelength. The curve 151 in 5 denotes the spectral transmittance of a laser treated area, curve 161 the spectral transmittance of an adjacent, untreated area 16 , The two curves show that the spectral transmission in the entire spectral range between 420 nanometers and 780 nanometers in the treated area 15 is significantly increased. This is advantageous if less affects the color, but the transparency is to be improved, for example, to make specific areas of the glass ceramic hob for luminous or non-luminous display elements transparent or generally insert windows, especially viewing window. According to one embodiment of the invention and without being limited to the specific embodiment, therefore, in the first region, the spectral transmission within the entire spectral range between 420 nanometers and 780 nanometers is higher than in an adjacent second region.

Remarkable on the spectral transmittance according to 5 In addition, the transmission in the blue and green spectral range increases even more in relative terms than in the red range. The transmission at 500 nanometers increases from 0.0028 to 0.027, ie by a factor of more than nine. At 600 nanometers, the factor is lower and here is 4.7. This is especially favorable in order to improve the display capability for blue and / or green display elements or for color displays in the case of volume-colored glass ceramics, especially vanadium oxide-colored glass ceramics. According to a further development of the invention, therefore, the ratio of the spectral transmittances of treated to adjacent, untreated area at a wavelength in the range of 400 to 500 nanometers is greater than at a wavelength in the range of 600 to 800 nanometers. The spectral transmission was measured on a sample in which only a brightening, but no increase was generated. Since the brightening is carried out to the same or even greater extent in the inventive generation of a raised structure or increase by local action of electromagnetic radiation and heating over the glass transition temperature, the embodiment according to applies 5 also for a glass ceramic article according to the invention.

The following are the colors, measured on the treated and untreated areas 15 . 16 in fluoroscopy of the 4 mm thick glass ceramic plate for different color models (xyY, Lab, Luv) and various standard light sources listed: Standard illuminant A Area 16 Area 15 x .6307 .5782 y .3480 .3805 Y 1.7 7.6 Standard illuminant D65 Area 16 Area 15 x .5550 .4773 y .3540 .3752 Y 1.2 6.2 Ra -25.6 22.0 Standard illuminant C Area 16 Area 15 x .5545 0.4763 y .3495 .3685 Y 1.2 6.3 Yellowness I. 174.0 120.8 Standard illuminant A Area 16 Area 15 L * 13.6 33.2 a * 23.2 24.2 b * 19.1 27.7 C * 30.0 36.8 Standard illuminant D65 Area 16 Area 15 L * 10.6 30.0 a * 20.8 20.2 b * 13.8 22.9 C * 25.0 30.5 Standard illuminant C Area 16 Area 15 L * 10.8 30.2 a * 20.1 19.2 b * 14.1 23.2 C * 24.5 30.1 Standard illuminant A Area 16 Area 15 L * 13.6 33.2 u * 30.3 45.3 v * 0.9 4.3 Standard illuminant D65 Area 16 Area 15 L * 10.6 30.0 u * 22.6 36.6 v * 7.0 18.5 Standard illuminant C Area 16 Area 15 L * 10.8 30.2 u * 22.9 36.7 v * 7.8 20.3

For the color models Lab, xyY and Luv, the parameters L and Y respectively denote the brightness. The parameter Y in the xyY color model corresponds to the transmission τ _vis in the visible spectral range when using the standard illuminant C or standard illuminant D65, and the transmission increase can be determined from the comparison of the Y values. The values given above show that the transmission in the visible spectral range is increased by at least a factor of 2.5. In general, it should be noted that the transmission is also the refractive index and the thickness of the transilluminated Glass ceramic cooking surface depends. In general, however, it can be said that, according to a development of the invention, the transmission in the visible spectral range between 380 and 780 nanometers, based on a thickness of 4 millimeters, is increased by at least a factor of 2.5.

The coloring by vanadium oxide, V ₂ O ₅ , as in the above-discussed embodiments of the 3 and 5 is also out of the DE 10 2008 050 263 B4 known. Accordingly, the staining mechanism turns out to be a complex process. For the conversion of the vanadium oxide in the coloring state according to this document, a redox process is a prerequisite. In the crystallizable starting glass, the V ₂ O _{5 is} still relatively weak and leads to a slightly greenish hue. During the ceramization, the redox process takes place, the vanadium is reduced and the redox partner is oxidized.

The primary redox partner is the refining agent, which results from Mössbauer investigations on Sb- and Sn-purified compositions. During ceramification, part of the Sb ³⁺ or Sn ²⁺ in the starting glass is converted into the higher oxidation state Sb ⁵⁺ or Sn ⁴⁺ . It was assumed that the vanadium is incorporated into the seed crystal as V ⁴⁺ or V ³⁺ in a reduced oxidation state and stains intensely there by means of electron charge transfer reactions. As a further redox partner, TiO ₂ can also enhance the coloration by vanadium oxide. In addition to the type and amount of redox partner in the starting glass has after the DE 10 2008 050 263 B4 also the redox state, which is set in the glass at the melt an influence. A low oxygen partial pressure, that is, a reducing set melt, z. B. by high melting temperatures, enhances the color effect of vanadium oxide.

However, it is also possible that the reduced V ⁴⁺ or V ^{3+ is} not incorporated or not exclusively in the seed crystals, but possibly also in another structural environment, such as in the high-quartz solid solution or in clusters.

With the invention, this coloring is now changed locally by the irradiation of high-energy radiation and heating of the glass-ceramic.

This can be linked to the influence of the coloring charge transfer process. Since the hypothetical electron transfer between donor and acceptor centers during the charge transfer is decisive for the absorption, it can be assumed that the structural effect of the high-energy radiation and heating is a structural change at the centers. This structural change reduces the frequency / probability of electron transfer transitions and hence the absorption.

Because of the sensitivity with which the vanadium dyeing reacts to partial pressure of oxygen and redox processes during the ceramization, competing changes of valency can come into question. That is, the radiation associated with the heating may potentially remove electrons from the donor or acceptor centers and passivate them for the charge transfer process.

The observation that the reduced coloration can be reversed by thermal treatment supports the hypothesis. The thermodynamically more stable structural situation of the centers can be restored. This again increases the frequency of coloring batch transfer transitions.

6 shows an optically measured height profile of the increase 20 , in which also the in 3 measured transmission profile was measured. In the illustration, it should be noted that the scales on the abscissa and the ordinate have been chosen very differently in order to clarify the form of the local increase. The graduations on the ordinate axis are at a distance of about 16.5 μm. Clearly visible is the concave curvature 24 on the edge of the raise 20 towards the center into a convex curvature 25 passes.

When comparing the 3 and 6 shows that the half-width of the transmission profile is greater than the half-width of the increase 20 , This is because the lightening or, more generally, the color change of the volume-colored glass ceramic already takes place at lower temperatures than the formation of the increase. As a result, a brightening due to the temperature field in the irradiation also still occur where no volume change occurs. In a further development of the invention, without limitation to the specific, in the 3 and 6 Accordingly, the half-width of the transmission profile of the integral light transmission in the region of the local survey is accordingly shown 20 greater than the half width of the local survey 20 even.

The height of the local survey 20 is still in the range of 0.025 to 0.3 millimeters. In particular, the height is at the in 6 shown example at about 100 microns. Elevations of this height are haptically well detectable, which is no longer the case at too low altitudes. On the other hand, excessively high heights over 0.3 millimeters, due to the change in volume, create stresses in the material which can adversely affect the strength of the glass-ceramic article. Particularly preferred is a height of the survey 20 in the range of 50 μm to 150 μm.

7 shows a variant of in 2 illustrated embodiment. In this variant is in the surface on the side 3 a depression 30 introduced in the glass ceramic. In this depression, a local increase was then with the method according to the invention 20 generated. The recess can be produced, for example, before the ceramization by hot forming or by an abrasive process before or after the ceramization. A preferred application are operating elements, in particular on a glass ceramic hob, which through a depression 30 are marked. Such recessed or concave controls are used to make the control element, or its position haptically detectable. With the local increase, an additional haptic structure can be created. In particular, such a local increase can also replace an imprint which characterizes the function of the operating element. Here there is the advantage that the then introduced in particular in the form of a symbol local increase 20 more durable against abrasion compared to a print. Preferably, a touch switch is used for the operating element. For this purpose, under the depression, for example, a suitable sensor 33 be arranged, which detects a touch of the glass ceramic in the recess by inserting a finger. For example, a capacitive sensor is suitable. Also on the surface in the recess 30 For example, a suitable sensor could be arranged to provide a touch switch.

8th shows an application of the invention, a glass ceramic hob 40 with a glass ceramic plate 1 which at least one local increase produced according to the invention 20 having. According to one embodiment of the invention, use is made of volume-colored glass ceramics simultaneously with the introduction of the elevation 20 a transmission increase can be achieved. This allows display elements, in particular self-luminous display elements under the glass ceramic plate 1 be made visible. Accordingly, it is thus provided in one embodiment of the invention that the glass ceramic plate 1 is volume-dyed with coloring metal ions, being in the area of the local elevation 20 the staining of the glass ceramic from a second area 16 next to the local increase 20 differs, so the absorption coefficient in the area of local increase 20 smaller than the absorption coefficient of the second region 16 and thus the integral light transmission in the visible spectral range at the local elevation 20 is higher than the integral light transmission of the second area 16 , Under the first area 15 is a preferably self-luminous display device 23 arranged, whose light passes through the first area 15 is visible through.

Such a display can in particular also with a control according to 7 combined so that self-luminous touch switches with haptic detectable local elevations 20 be created.

The local raises 20 can also be used in a particularly advantageous manner, the heat conduction between a cooking vessel 37 and to reduce the surface of the glass-ceramic. This is favorable, for example, when used as a heating element 34 an induction heating element is used. In this case, the cooking vessel becomes hotter than the glass ceramic plate. Accordingly, it is provided in development of the invention that the glass ceramic hob 40 a cooking zone 35 with local elevations 20 so that by the local increases 20 the contact surface of a cooking vessel placed on the cooking zone 37 lowered and between the bottom of the cooking vessel 37 and the surface of the glass ceramic plate 1 an air gap 38 is created.

LIST OF REFERENCE NUMBERS

1

Ceramic element

3, 5

side of 1

9

laser source

11

fiber

13

Laser Scanner

15

brightened area

16

to 15 adjacent, non-illuminated area

20

local survey

22

 Low density area.

24

concave curvature

25

convex curvature

30

deepening

33

sensor

34

heating element

35

cooking zone

37

cooking pot

38

air gap

40

Ceramic glass hob

90

laser beam

130

 focusing optics

151

Spectral transmittance of a laser treated area 15 from 1 .

161

Spectral transmittance of an adjacent, untreated area 16 from 1 ,

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2012/134818 [0005]
• DE 102008050263 B4 [0079, 0080]

Cited non-patent literature

• DIN 5036-1 [0064]
• ISO 15368 10 [0064]

Claims (21)

Method for producing a raised structure on a glass ceramic element ( 1 ), in which the glass ceramic element ( 1 ) is irradiated with electromagnetic radiation in a local area of the surface, wherein the radiation is the glass ceramic element ( 1 ) penetrates and thereby at least partially absorbed, so that the glass ceramic element ( 1 ) is heated in the region of the irradiated electromagnetic radiation and is heated above the glass transition temperature, and wherein the irradiation is terminated after the heating, so that the heated area cools again to the temperature of the surrounding glass ceramic material, and wherein the heating causes a change in volume of the glass ceramic occurs, which causes a local elevation of the surface, and this state is frozen when cooling the heated area, so that after cooling, a surface deformation in the form of an increase ( 20 ) persists. The method according to the preceding claim, characterized in that the electromagnetic radiation onto a point-shaped region with a surface area in the range from 0.5 mm ² to 5 mm ² is concentrated. Method according to the preceding claim, characterized in that the punctiform region extends over the surface of the glass-ceramic element ( 1 ) is moved to produce a projection having an area larger than the area of the dot-shaped area. still entitled to flat lighting. Method according to one of the preceding claims, characterized in that the electromagnetic radiation having an average power density of at least 2.5 W / mm ² on the region of the glass ceramic element to be heated ( 1 ) is irradiated. Method according to one of the preceding claims, characterized in that the heating is carried out with an infrared laser as a radiation source. Method according to one of the preceding claims, characterized in that the heating takes place with a temperature rise of at least 20 K per second. Method according to one of the preceding claims, characterized in that the glass ceramic after heating at a cooling rate of at least 1 K per second, preferably at least 5 K per second, more preferably at least 10 K per second at least within a temperature range from the maximum temperature to 100 K. is cooled below the maximum temperature. Method according to one of the preceding claims, characterized in that a thermal post-treatment step after cooling is carried out, in particular to reduce tensile stresses, wherein the thermal post-treatment step preferably comprises at least one of the steps: - a second heating step by means of electromagnetic radiation - a thermal reheating and relaxation in an oven. Glass ceramic articles ( 1 ), in which at least one local survey ( 20 ), wherein the smallest lateral dimension has a length of at least 0.05 mm, and wherein the local elevation has a height in the range of 0.025 to 0.3 millimeters, wherein the elevation and the surrounding glass-ceramic material are monolithic and have the same composition and wherein the glass-ceramic material below the elevation has a lower density than the material surrounding the elevation. Glass-ceramic article according to the preceding claim, characterized in that the edge of the elevation has a concave curvature ( 24 ), which in the direction of the elevation in a convex curvature ( 25 ) passes over. Glass-ceramic article according to one of the preceding claims, characterized in that the glass-ceramic material comprises high-quartz mixed crystal as the main crystal phase, wherein the glass-ceramic material in the elevation has a higher proportion of keatite mixed crystal, compared to the elevation surrounding regions of the glass-ceramic. Glass-ceramic article according to one of the preceding claims, wherein the glass-ceramic of the glass-ceramic article is volume-dyed with coloring metal ions, wherein in the region of the local elevation the coloring of the glass-ceramic from a second region ( 16 ) next to the local increase ( 20 ), so that the absorption coefficient in the area of local increase ( 20 ) smaller than the absorption coefficient of the second region ( 16 ) and thus the integral light transmission in the visible spectral range at the local increase ( 20 ) is higher than the integral light transmission of the second area ( 16 ). Glass-ceramic article according to the preceding claim, characterized in that the glass-ceramic contains at least 0.005, preferably at least 0.01 percent by weight vanadium oxide. Glass-ceramic article according to one of the two preceding claims, characterized in that the integral light transmission of the glass-ceramic in the visible spectral region of the second region ( 16 ) is at most 5%, preferably at most 2.5%. Glass ceramic article according to one of the three preceding claims, characterized in that the half-width of the transmission profile of the integral light transmission is greater than the half-width of the local survey ( 20 ). Glass-ceramic article according to one of the preceding claims, characterized in that the light scattering in the glass-ceramic in the area of the local elevation is at most 20%, preferably at most 5%, above the light scattering in the glass-ceramic of a second region ( 16 ) is elevated next to the local survey. Glass-ceramic article according to one of the preceding claims, of aluminosilicate glass-ceramic, preferably of lithium-aluminosilicate glass-ceramic, in which the glass-ceramic material at the local heightening ( 20 ) has a higher content of keatite mixed crystal than a local area adjacent to the second region ( 16 ). Glass-ceramic article according to one of the preceding claims, characterized by a depression provided in the surface, preferably a control element designed as a depression, wherein the at least one local elevation ( 20 ) is arranged in the recess. Glass ceramic hob ( 40 ) with a glass ceramic article according to one of the preceding claims in the form of a glass ceramic plate. Glass ceramic hob ( 40 ) according to the preceding claim, wherein the glass-ceramic plate ( 1 ) is volume-dyed with coloring metal ions, wherein in the region of the local elevation the coloring of the glass-ceramic from a second region ( 16 ) next to the local increase ( 20 ), so that the absorption coefficient in the area of local increase ( 20 ) smaller than the absorption coefficient of the second region ( 16 ) and thus the integral light transmission in the visible spectral range at the local increase ( 20 ) is higher than the integral light transmission of the second area ( 16 ), and where below the first range ( 15 ) is arranged a preferably self-luminous display device whose light through the first area ( 15 ) is visible through. Glass ceramic hob ( 40 ) according to one of the preceding claims, characterized by a cooking zone ( 35 ) with local elevations ( 20 ), so that by the local increases ( 20 ) the contact surface of a cooking vessel erected on the cooking zone ( 37 ) and between the bottom of the cooking vessel ( 37 ) and the surface of the glass ceramic plate ( 1 ) an air gap ( 38 ) is created.

Images