DE102013110564B4 - Glass ceramic items - Google Patents

Abstract

Glass ceramic article (1), in which at least one local elevation (20) is present in the surface, the smallest lateral dimension having a length of at least 0.05 mm, and wherein the local elevation has a height in the range from 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 under the elevation has a lower density than the material surrounding the elevation, wherein the coefficient of thermal expansion of the glass-ceramic material α20-600 is at most 2*10- 6K-1 lies.

Description

The invention relates to a glass ceramic with a local change in geometry in the form of an elevation on the surface.

Materials colored in the visible wavelength range (380 nm -780 nm) (and therefore usually also materials colored in the IR range) such as glasses and glass ceramics (green glass state or already ceramicized) should preferably be used. The change in geometry is caused by the local and time-limited effect of electromagnetic radiation, such as laser radiation from a diode laser with a wavelength of 1 μm
with CW mode and a not strongly focused laser beam, preferably with a beam diameter of greater than 400 μm.

State of the art

• Zum Einen kann durch das Anfügen eines zweiten Teils an das eigentliche Bauteil eine geometrische Vergrößerung erzeugt werden. Dabei können alle Fügeverfahren wie Löten, Schweißen und Kleben zum Einsatz kommen. Nachteilig ist dabei, dass zwei Bauteile benötigt werden. Zudem ist die Fügestelle meist optisch störend oder bildet eine Bruchausgangskante. Auch aufwändige Geometrieerhöhungen (Kreise, Abrundungen etc.) können nur schwer durch ein zusätzliches Bauteil angefügt werden.

According to the state of the art, a local change in the geometry of components made of glass ceramic takes place in three different variants:

• On the one hand, a geometric enlargement can be created by adding a second part to the actual component. All joining methods such as soldering, welding and gluing can be used. The disadvantage is that two components are required. In addition, the joint is usually visually disturbing or forms a fracture starting edge. Even complex geometric increases (circles, roundings, etc.) can only be added with difficulty using an additional component.

On the other hand, a local reduction in geometry can occur through (local) mechanical removal of material. Grinding and milling processes are used. The resulting damage to the surface can lead to a reduction in mechanical strength. Changing the surface in the removed area (grinding or polishing surface) can also have a visually disturbing effect. In addition, the production of locally raised structures is difficult to produce in this way, as a lot of surrounding material would have to be removed.

Third is in WO 2012/134 818 A1 describes a process according to which, using an ultra-short pulse laser in the UV range, locally very limited color centers are generated in a highly transparent glass, which then couple better and better to the UV radiation as a self-reinforcing effect and thus achieve a heating effect, which ultimately leads to a change in geometry of small, locally very limited elevations in the micrometer range.

The disadvantage here is the complex ultra-short pulse laser, which first has to create the prerequisite for the glass to connect at all. The self-reinforcing effect also leads to uncontrolled heating and uncontrollable control problems. Another disadvantage is that only glasses that are sufficiently transparent in the UV range can be used.
From the US 2007 / 0 201 797 A1 a glass-based micropositioning system is known. For this micropositioning system, microbumps are created in glass by locally heating part of the glass. This causes rapid local expansion of the glass.

From the US 6,287,663 B1 a glass-ceramic substrate is known which serves as a storage medium for magnetic information. The elevations described have a height in the range from 5 to 30 nm.

From the US 5,861,196 A A glass ceramic substrate is also known for use as a storage medium. The elevations described have a maximum height of 140 nm.

Teng et al. describe in the paper “Laser zone texture on alternative substrate disks”, IEEE Transactions on Magnetics, 1996 (32), No. 5, pages 3759-3761 , DOI: 10.1109/20.538827 the influence of increasing laser energy on glass ceramics with low coefficients of thermal expansion. Accordingly, a simple increase in laser energy does not lead to a multiple increase in elevations.

Task of the invention:

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

Additions or mechanical processing are then no longer required to create a haptic increase or depression.

This makes it possible to make geometric boundaries tangible on any type of glass ceramic component.

The disadvantages of a joint seam, namely the visual appearance and the presence
one or more additional component edges that could 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.

The invention makes it possible, in particular,

• - to change the geometry without damaging the surface,
• - an increase in volume without additional material, or
• - to achieve a reduction in volume without mechanical damage to the component.

Solution to the task

In order to achieve a change in the geometry of a glass ceramic, the temperature of the glass ceramic is increased, which is usually above the glass transition temperature T _g , and then a targeted, generally very rapid, cooling is carried out.

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

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

This means that energy is introduced not just on the surface, but over part or the entire thickness (in volume), resulting in a homogeneous effect that ideally has no influence on the geometry of the component outside of the local geometry change.

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

In particular, a method for producing a raised structure on a glass ceramic element is provided, in which the glass ceramic element is irradiated with electromagnetic radiation in a local area of the surface, the radiation penetrating the glass ceramic element and being at least partially absorbed, so that the glass ceramic element in the area of the irradiated electromagnetic radiation and is heated beyond the glass transition temperature of the residual glass phase, and the irradiation is ended after the heating, so that the heated area cools down again to the temperature of the surrounding glass ceramic material, and the heating causes a change in volume of the glass or the glass ceramic, which causes a local elevation of the surface, and this state is frozen when the heated area cools, so that after cooling a surface deformation in the form of an elevation 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 in a simple manner using the method. According to the invention, the coefficient of thermal expansion α _20-600 of such a glass ceramic is at most 2·10 ^-6 K ^-1 .

This method can be used to produce a glass ceramic article in which at least one local elevation is present in the surface, the smallest lateral dimension having a length of at least 0.05 mm, and the local elevation having a height in the range from 0.005 to 0.5 Millimeters, wherein the elevation and the surrounding glass ceramic material are monolithic and have the same composition, and wherein the glass ceramic material under the elevation has a lower density than the material surrounding the elevation. The process can be applied not only to glass ceramics, but also to glasses, thereby obtaining corresponding glass products.

Due to the choice of radiation source and the form in which the energy is introduced, the range of geometry changes can be from point-shaped to linear to flat.

Point-shaped irradiation allows many degrees of freedom in the design of the surveys. In this context, “punctiform” obviously means that the irradiated area still occupies a certain, small area. Areas in the range of up to 5 mm ² are particularly suitable. According to a further development of the method, the electromagnetic radiation is concentrated on an area with an area in the range of 0.05 mm ² to 5 mm ² . This area is preferably circular or elliptical.

If the energy is introduced at a point, the area of geometry change can take on any shape by moving the radiation source or moving the component. In this way, for example, letters, characters or even triangles, squares or any other geometric shapes can be produced in the form of elevations on the surface of the component. The dimensions of the geometry change can 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 a further development of the method, the point-shaped area into which the electromagnetic radiation is irradiated is moved over the surface of the glass ceramic element in order to produce an elevation with an area larger than the area of the point-shaped area.

UV radiation sources, IR emitters with tungsten filaments, laser sources such as diode lasers, fiber lasers or other radiation sources whose electromagnetic radiation can at least partially penetrate the glass ceramic material can be used as radiation sources.

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

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

Diode lasers with a wavelength in the near infrared range, for example in the range of 1 μm, are suitable for ceramized ceramic glass ceramics, or more generally lithium aluminosilicate glass ceramics. At this wavelength, the transmission of a 4mm thick glass ceramic plate is between 50% and 80%, so that enough radiation penetrates through 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, a temperature of greater than 700°C can be achieved at the point of energy input within a few seconds.

To create a local elevation, therefore
This also causes a local increase in temperature in the volume. This is done by electromagnetic radiation in a wavelength range in which the glass ceramic is partially transparent to the incident electromagnetic radiation. This means that energy is introduced not just on the surface 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 change in volume. If the product is too large, only the surface will be heated and therefore overheated and the effect in volume will not be large enough. If the product is too small, then it is heated too slowly and the effect either does not occur or can no longer be clearly localized, ie smeared. According to a further development of the invention, the radiation density or power density of the electromagnetic radiation and/or the absorption coefficient k of the glass ceramic material is selected such that the product P of the power density and the absorption coefficient k is at least P = 0.35 (W/mm ² )*( 1/mm). In order to avoid only superficial heating, according to another development of the invention, the absorption coefficient should be at most 2/d, where d denotes the thickness of the glass ceramic element.

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

In order to obtain elevations with steep flanks that can be easily detected haptically, it is advantageous if the heating takes place very quickly, so that a steep temperature gradient is generated in the direction perpendicular to the direction of irradiation in the glass ceramic material. This temperature gradient then causes a correspondingly sharp demarcation between the area of lower density beneath 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 the plate has cooled to room temperature, the volume at the point of energy application is larger than before the radiation treatment.

If necessary, a thermal post-treatment step can be provided after cooling. With such a post-treatment step, tensile stresses previously induced by heating can be reduced again. Individual fine-tuning of the transmission generated is also possible using a thermal post-treatment step.

• - 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 thermal aftertreatment are:

• - A second heating step using electromagnetic radiation, preferably using a laser, which heats the volume to a relaxation temperature and keeps it there.
• - A second heating step using electromagnetic radiation, preferably using a laser, which only heats the surface(s) and reduces tension there. This can be beneficial because stresses near the surface are much more critical than stresses in the volume. In order to achieve such more superficial heating, electromagnetic radiation which has different wavelengths than the electromagnetic radiation of the first heating step can be used for the second heating step.

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

In general, with glass ceramic plates, it is preferred to create a local elevation on the usable side in order to create structures that can be perceived haptically. For glass ceramic plates with knobs on one side, local elevations are therefore preferably applied to the smooth side.

The area of energy input can be achieved both by shaping the irradiation of the energy and by additionally masking the plate to be treated, so that parts of the glass ceramic that cannot be changed are effectively protected from the impact of radiation. Optics that enable 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 can also be used advantageously for the method according to the invention.

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

Three-dimensionally deformed components can also be treated. The process-based treatment of the component 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 process can be interesting for the following applications:

• -Cooking zone markings or delimitations of the controls on glass ceramic cooking surfaces, also for so-called “vulnerable people”, for example, in order to provide safety-relevant information on cooking surfaces using haptic structures,
• - Applying a 1D (bar) or 2D (dot matrix) barcode to the surface of the product (e.g. a vial/syringe) for permanent identification,
• -Application of a filling quantity scale or filling level marking on the glass wall of the product (e.g. vials, containers, tubes) or another marking,
• -Applying optical design elements to flat glass (e.g. architectural glazing) such as company logos or geometric objects (arrows as signposts, escape routes),
• - permanent, forgery-proof marking of products through a raised logo on the surface of the glass,
• - Applying pictograms, letters, geometric objects in touch applications for cell phone covers or other electronic devices,
• - Creation of tactile structures for visually impaired people, e.g. on a cooking surface
• -Reducing the contact area between the bottom of the pot and the glass ceramic cooking surface, thereby creating thermal insulation, especially with induction hobs,
• -Creation of haptic structures in recesses, especially in concave or recessed control elements.

The invention is explained in more detail below using exemplary embodiments and the drawings. In the drawings, like reference numerals designate like or corresponding elements.

• 1 eine Anordnung zur Durchführung des Verfahrens,
• 2 einen schematischen Querschnitt durch ein erfindungsgemäßes Glaskeramikelement,
• 3 ein Transmissionsprofil einer volumengefärbten Glaskeramikplatte entlang einer Positionskoordinate senkrecht zur Längsrichtung einer lokalen Erhebung,
• 4 Röntgenbeugungsspektren an einem aufgehellten und einem unveränderten Bereich einer volumengefärbten Glaskeramik,
• 5 den spektralen Transmissionsgrad eines behandelten und eines unbehandelten Bereichs einer Glaskeramik-Platte,
• 6 ein Höhenprofil einer Erhebung,
• 7 eine Weiterbildung der in 2 gezeigten Ausführungsform,
• 8 ein Glaskeramik-Kochfeld.

Show it:

• 1 an order to carry out the procedure,
• 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 on a brightened and an unchanged area of a volume-colored glass ceramic,
• 5 the spectral transmittance of a treated and an untreated area of a glass ceramic plate,
• 6 a height profile of an elevation,
• 7 further training in 2 embodiment shown,
• 8th a glass ceramic hob.

There is 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 the dimensions 50mm x 50mm and 4mm thick on a slip-cast silicon oxide ceramic base 7 with 100mm x 100mm and 30mm thick with one side 5 placed towards the silicon oxide ceramic base 7. Silicon oxide ceramic base 7 and glass ceramic plate are kept at room temperature. A laser scanner 13 with focusing optics 130, focal length 250 mm, is installed above this arrangement so that the laser beam 90 strikes the surface of the glass ceramic plate perpendicularly. In focus, the diameter of the laser beam is 1.5mm. The arrangement of quartz base 7 and glass ceramic plate was placed in the focal plane. The laser scanner 13 is exposed to laser radiation between 900 nm and 1100 nm wavelength via a fiber 11. The laser source 9 is a diode laser, for example from laserline, which delivers an adjustable power between 0 W and 3000 W.

The laser scanner is now programmed so that a circle with a diameter of 40mm is traversed 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. The laser 9 is then switched off and the glass ceramic plate is freely cooled in air. In the area of radiation, a raised circle on the glass ceramic plate can be clearly seen and felt. The rest of the plate remains geometrically unchanged. This affects both flatness and local thickness fluctuations.

Without limitation to the example explained above, rapid cooling
preferred. This is convenient to freeze the effect of the volume change. In a further development of the invention, it is therefore provided that the glass ceramic is cooled after heating at a cooling rate of at least 1 K per second, preferably at least 5 K per second, particularly preferably at least 10 K per second, at least within a temperature range from the maximum temperature to 100 K below Maximum temperature is cooled down.
2 shows a cross section through a glass ceramic element 1 according to the invention. Due to the rapid heating with the laser 9 or a radiation source comparable in terms of power and absorption in the glass ceramic material, a local elevation or elevation 20, or a raised structure, was created on one side 3. The change in volume that freezes during cooling causes an area 22 that extends into the glass ceramic material in the area of the elevation 20 and has a reduced density compared to the surrounding glass ceramic material. This area 22 can, as in the case in 2 Example shown extend to a side 5, which is opposite the side 3 with the elevation 20.

Elevations or local elevations 20 generated with the method have a characteristic profile with rounded edges.
In particular, as shown schematically in 2 shown, the edge of the elevation 20 has a concave curvature 24, which merges into a convex curvature 25 towards the center of the elevation.

With volume-colored glass ceramic elements 1, in addition to changing the surface, a surprising local color change can also be achieved. In particular, the light transmission can be increased locally in the area of the elevation 20. Such a color change in bulk-colored materials could be demonstrated on a glass ceramic colored with coloring metal ions, in particular with vanadium oxide.

Accordingly, in a further development of the invention, without limitation to the specific exemplary embodiments shown, it is provided that the glass ceramic of the glass ceramic article is volume-colored with coloring metal ions, whereby in the area of the local elevation the coloring of the glass ceramic differs from a second area next to the local elevation 20, so that the absorption coefficient in the area of the local elevation 20 is smaller than the absorption coefficient of the second area 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 to be a material in which the color centers or coloring ions are distributed throughout the material. Unlike pigments, these are not locally concentrated in the form of coloring crystallites. Corresponding to a dye, the coloring ions or color centers are dissolved in the glass or glass ceramic, while pigments are dispersed in the material. A volume coloring therefore influences the transmission, but not the scattering, whereas pigments themselves represent scattering particles. However, any additional pigments present are not excluded.

The process is very suitable for locally weakening the coloring of a glass ceramic article that has been volume-colored with vanadium oxide. Accordingly, in the local area, 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, a glass ceramic element volume-colored with vanadium oxide is therefore provided, in which in the area treated with the method, i.e. where the local increase is produced, the integral light transmission in the visible spectral range is increased compared to an adjacent second, untreated area.

In this way, for example, windows with higher transmission can be easily created in a glass ceramic hob that otherwise appears dark. A display can then be installed under such a window, which shines through the local elevation in a way that is clearly visible to the viewer. A window as a particularly preferred form of a brightened area produced using the method is understood to mean an area which is surrounded on 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 is at which
the increase in transmission occurs above the temperature at which the viscosity of the glass ceramic is 10 ¹⁴ dPas. If you do not heat up to the softening point, at which the viscosity has a value of 10 ^7.6 dPa*s, lightening can be achieved even without changes in shape. Accordingly, depending on the heating, local elevations and additionally only brightened areas can be produced.

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, percent by weight of vanadium oxide.

According to one embodiment of the invention, the glass ceramic is colored with coloring ions, preferably with vanadium oxide, such 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 a glass ceramic sample volume-colored with vanadium oxide, in which a local increase 20 in the form of a rib or bead was produced by the method according to the invention. The direction of the position coordinate is perpendicular to the longitudinal direction of the rib. The profile of the local elevation 20 is also visible in the discoloration caused by the heating of the glass ceramic and the associated increase in transmission compared to an adjacent second area next to the elevation. When viewed through, the area of the local elevation appears significantly brighter. It is also possible to only produce a discoloration or brightening without an increase 20 according to the invention if a flatter temperature ramp is selected for heating. If only a brightening is produced in an area without a change in volume, here, unlike what was explained above, the product P of the power density and the absorption coefficient k can be kept smaller. The product will have a value of at least P = 0.25 (W/mm ² ) * (1/mm).

With this method, a volume-colored, monolithic glass ceramic article is obtained, for example in the form of a cooking surface, which has a first area in which the coloring of the glass ceramic differs from a second, adjacent area, so that the absorption coefficient of the first area is smaller than that Absorption coefficient of a second, adjacent area 16 and thus the integral light transmission in the visible spectral range of the first area is higher than the integral light transmission of the second, adjacent area, the light scattering in the glass ceramic of the first area typically being at most absolute 20 percent, preferably at most is increased absolutely 10 percent, particularly preferably by at most absolutely 5%, particularly preferably by at most absolutely 1% compared to the light scattering in the glass ceramic of the second area. The light scattering in the glass ceramic of the first area is therefore essentially the same as the light scattering of the second, adjacent area with unchanged light transmission. The case where the light scattering in the first area is smaller than in the second area also falls under the upper limit of a maximum of 20 percent higher absolute light scattering. With the at most slightly increased light scattering, this does not appear as a visible effect. Light scattering is the proportion of the total intensity irradiated minus the directly transmitted light, the Fresnel reflection and absorption. The absolute increase in scattering, stated in percent, refers to the proportion of scattered light during the transmission of a light beam. If the proportion of the scattered light intensity in the second area is, for example, 3% of the total intensity, then an absolute increase of 5% in the first area then means a proportion of the scattered light intensity in the first area of 3% + 5% = 8%. The terms transmission, scattering, absorption and remission, as used in the context of the invention, correspond to the definitions according to DIN 5036-1 and can be determined using the measurement regulations according to ISO 15368 10. The first region mentioned additionally has the local elevation 20 according to the invention. It is possible to create one or more additional first areas without elevation. The effect of barely changed light scattering with the values given above can also be present in the area of local increase in a non-volume-colored glass ceramic or a glass ceramic in which no color change occurs as a result of the treatment.

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. Spectral light transmission is the light transmission at a specific wavelength. Unless spectral light transmission is mentioned, the term light transmission in the sense of this description is to be understood as integral light transmission.
The magnitude of the change in transmission can be 0.1% in absolute terms to more than 50% in absolute terms higher in addition to the original degree of transmission. Preferably, particularly in the case of dark-colored glass ceramics, the transmission in the visible 20 spectral range in the first area is increased by at least a factor of 2 compared to the second, adjacent area 16. At the in 3 In the example shown, the transmission in the area of the local increase increases by more than a factor of three compared to the non-brightened area 16 adjacent to the increase 20.

A further feature of this embodiment of the invention is the fact that the wavelength of the irradiation does not have to correspond to the wavelength of the effect achieved, i.e. the wavelength at which the change in transmission occurs. With the present invention it is therefore possible, for example, to irradiate in the infrared wavelength range at a wavelength of 1 μm because an absorption band is present in the glass ceramic in this wavelength range. But the resulting effect can for example, in the visible range between 380nm and 780nm and cause a change in transmission at one or more wavelengths in this range through physical-chemical 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, only minor structural changes occur in the changed or treated area.

2 shows X-ray diffraction spectra on a monolithic glass-ceramic element, as with the one based on 1 explained method is obtained. The glass ceramic examined is a volume-colored lithium aluminosilicate glass ceramic with vanadium oxide, as used for cooking surfaces. X-ray diffraction was used to compare the crystal phases, the crystal phase content and the crystallite size of an area 15 brightened by laser irradiation with neighboring, non-brightened areas 16. The relative intensities of different crystal phases are also marked with a diamond, a square or a circle. The squares are the X-ray diffraction peaks of high quartz mixed crystal (HQMK), the diamonds are the X-ray diffraction peaks of lithium aluminosilicate or keatite mixed crystal (KMK, 10 LiAlSi ₃ O ₈ ), and the circles are the zirconium titanate (ZrTiO ₄ ) detected in glass ceramics. Curve 150 is the X-ray diffraction spectrum of the brightened, i.e. treated area and curve 160
the X-ray diffraction spectrum of an adjacent, unchanged area 16. As can be seen, the curves are practically congruent, except for the offset, which is different for reasons of representation. A more precise evaluation of the intensities of the X-ray diffraction peaks reveals a very small increase in the content of the keatite mixed crystal phase. The results are summarized again 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 area 48 Not definable 55 67 1 1

The chemical composition of the glass ceramic and an assumed density of p=2.5g/cm ³ were used for the absorption corrections in the columns labeled “corrected”.

The phase content of the high quartz mixed crystal changes according to the table above 3 therefore not within the measurement error. Only the keatite mixed crystal content shows a change, which does not have a significant effect on the structure of the glass ceramic due to the small proportion of this crystal phase. Even if treated and untreated areas of a glass ceramic element do not have any significant structural differences, a treated area of an aluminosilicate glass ceramic, in particular a lithium aluminosilicate glass ceramic, can, according to a further development, have a higher content of keatite mixed crystal compared to an adjacent, untreated one Area can be detected.

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

The X-ray diffraction measurements were carried out on a sample in which only brightening was carried out without a change in volume. In the method with local deformation, due to the As warming increases, the keatite phase content increases significantly. For a sample in which a clearly prominent local elevation was created, a slight increase in scattering in the area of the elevation can also be visually observed. Since light scattering is generally caused by keatite mixed crystals, according to one embodiment of the invention, a higher proportion of keatite mixed crystals in the glass ceramic material in and below the elevation 20 in LAS glass ceramics is a feature of a glass ceramic article produced according to the invention. According to this development of the invention, a glass ceramic article made 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 content of keatite mixed crystal than a second one adjacent to the local elevation Area 16.

In the embodiment with glass ceramic volume-colored by vanadium oxide and an increase in transmission achieved at the same time as the local increase, a particularly advantageous effect also results in an increase in transmission reaching into the blue spectral range. This makes it possible to use the brightened area for blue-lighting optical displays that shine through the glass ceramic.

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

Remarkable in terms of the spectral transmittance 5 is also that the transmission in the blue and green spectral range increases relatively more than in the red range. The transmission at 500 nanometers increases from 0.0028 to 0.027, i.e. by a factor of more than nine. At 600 nanometers the factor is lower and is 4.7. This is particularly advantageous in order to improve the display capability for blue and/or green display elements or for color displays in volume-colored glass ceramics, in particular colored with vanadium oxide. According to a further development of the invention, the ratio of the spectral transmittance of the treated to the adjacent, untreated area is greater at a wavelength in the range of 400 to 500 nanometers 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 produced. Since the brightening occurs to the same or even greater extent when creating a raised structure or elevation through local exposure to electromagnetic radiation and heating above the glass temperature, the exemplary embodiment applies 5 also for a glass ceramic article according to the invention.

Below are the colors, measured on the treated and untreated areas 15, 16 in transillumination of the 4 mm thick glass ceramic plate for different color models (xyY, Lab, Luv) and different standard light sources: Standard illuminant A Area 16 Area 15 x 0.6307 0.5782 y 0.3480 0.3805 Y 1, 7 7.6 Standard illuminant D65 Area 16 Area 15 x 0.5550 0.4773 y 0.3540 0.3752 Y 1.2 6, 2 Ra -25.6 22.0 Standard illuminant C Area 16 Area 15 x 0.5545 0.4763 y 0.3495 0.3685 Y 1.2 6, 3 Yello wness I. 174.0120.8 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

In the color models Lab, xyY and Luv, the parameters L and Y respectively denote the brightness. When using the standard illuminant C or standard illuminant D65, the parameter Y in the xyY color model corresponds to the transmission τ _vis in the visible spectral range and the increase in transmission 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 also depends on the refractive index and the thickness of the illuminated glass ceramic cooking surface. In general, however, it can be said that, according to a further development of the invention, the transmission in the visible spectral range between 380 and 780 nanometers is increased by at least a factor of 2.5 based on a thickness of 4 millimeters.

The coloring by vanadium oxide, V ₂ O ₅ , as is also the case in the exemplary embodiments discussed above 3 and 5 was also from the DE 10 2008 050 263 B4 known. Accordingly, the coloring mechanism is a complex process. According to this publication, a redox process is required to convert the vanadium oxide into the coloring state. In the crystallizable starting glass, the V ₂ O ₅ still has a relatively weak color and results in a slightly greenish hue. During ceramization, the redox process takes place, the vanadium is reduced and the redox partner is oxidized.

The refining agent acts as the primary redox partner, which results from Mössbauer studies on Sb and Sn-refined compositions. During ceramization, part of the Sb ³⁺ or Sn ²⁺ in the original 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 in a reduced oxidation state as V ⁴⁺ or V ³⁺ and produces an intense color there through electron charge transfer reactions. As a further redox partner, TiO ₂ can also enhance the coloring caused by vanadium oxide. In addition to the type and amount of redox partners in the starting glass, the DE 10 2008 050 263 B4 The redox state that is set in the glass during melting also has an influence. A low oxygen partial pressure, i.e. a reducing melt, e.g. B. due to high melting temperatures, increases the color effect of the vanadium oxide.

However, it is also possible that the reduced V ⁴⁺ or V ³⁺ is not or not exclusively incorporated into the seed crystals, but possibly also into another structural environment, such as the high quartz mixed crystal or into clusters.

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

This can be associated with the influence on the color-producing charge transfer process. Since the hypothetical electron transfer between donor and acceptor centers is crucial for absorption during charge transfer, it can be assumed that a structural change occurs at the centers due to the high-energy radiation and heating. This structural change reduces the frequency/probability of electron transfer transitions and thus the absorption.

Because of the sensitivity with which the vanadium coloring reacts to oxygen partial pressure and redox processes during ceramization, competing changes in value can come into question. This means that the radiation combined with heating can potentially remove electrons from the donor or acceptor centers, thereby passivating them for the charge transfer process.

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

6 shows an optically measured height profile of elevation 20, on which the in 3 Transmission profile shown was measured. When depicting it, it should be noted that the scales on the abscissa and the ordinate were chosen very differently in order to clarify the form of the local increase. The graduation marks on the ordinate axis are approximately 16.5 µm apart. The concave curvature 24 at the edge of the elevation 20, which merges into a convex curvature 25 towards the middle, can also be clearly seen.

When comparing the 3 and 6 The result is that the half-width of the transmission profile is larger than the half-width of the increase 20. This is because the brightening or, more generally, the color change of the volume-colored glass ceramic already occurs at lower temperatures than the formation of the increase. As a result, brightening due to the temperature field during irradiation can occur even where there is no longer any change in volume. In further development of the invention, without limitation to the specific, in the 3 and 6 According to the exemplary embodiment shown, the half-width of the transmission profile of the integral light transmission in the area of the local elevation 20 is greater than the half-maximum width of the local elevation 20 itself.

The height of the local elevation 20 is still in the range of 0.025 to 0.3 millimeters. In particular, the height is at the in 6 example shown at about 100 micrometers. Elevations of this height can be easily perceived haptically, which is no longer the case if heights are too small. On the other hand, heights over 0.3 millimeters that are too high lead to tensions in the material due to the change in volume, which can negatively affect the strength of the glass ceramic article. A height of the elevation 20 in the range from 50 μm to 150 μm is particularly preferred.

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

8th shows, as an application of the invention, a glass ceramic hob 40 with a glass ceramic plate 1 which has at least one local elevation 20 produced using the method. According to one embodiment of the invention, advantage is taken of the fact that in the case of volume-colored glass ceramics, an increase in transmission can be achieved at the same time as the elevation 20 is introduced. This means that display elements, in particular self-illuminating display elements, can be made visible under the glass ceramic plate 1. Accordingly, in one embodiment of the invention it is provided that the glass ceramic plate 1 is volume-colored with coloring metal ions, whereby in the area of the local elevation 20 the coloring of the glass ceramic differs from a second area 16 next to the local elevation 20, so that the absorption coefficient in the area the local elevation 20 is 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 region 16. Below the first region 15 a preferably self-illuminating display device 23 is arranged, the light of which is visible through the first area 15.

Such a display can in particular also be provided with a control element according to 7 can be combined so that self-illuminating touch switches with haptically detectable local elevations 20 are created.

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

Reference symbol list

1

Glass ceramic element

3, 5

Page of 1

9

Laser source

11

fiber

13

Laser scanner

15

brightened area

16

to 15 adjacent, not brightened area

20

local survey

22

Area with reduced density.

24

concave curvature

25

convex curvature

30

deepening

33

sensor

34

Heating element

35

cooking zone

37

cooking vessel

38

air gap

40

Glass ceramic hob

90

laser beam

130

focusing optics

151

spectral transmittance of an area 15 treated with a laser of 1,

161

spectral transmittance of an adjacent, untreated area 16 of 1.

Claims (13)

Glass ceramic article (1), in which at least one local elevation (20) is present in the surface, the smallest lateral dimension having a length of at least 0.05 mm, and wherein the local elevation has a height in the range from 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 under the elevation has a lower density than the material surrounding the elevation, wherein the coefficient of thermal expansion of the glass ceramic material α _{is 20-600} at a maximum of 2 10 ^-6 K ^-1 lies. Glass ceramic articles according to Claim 1 , characterized in that the edge of the elevation has a concave curvature (24), which merges into a convex curvature (25) towards the elevation. Glass ceramic article according to one of Claims 1 or 2 , characterized in that the glass ceramic material has high quartz mixed crystal as the main crystal phase, the glass ceramic material having a higher proportion of keatite mixed crystal in the elevation compared to areas of the glass ceramic surrounding the elevation. Glass ceramic article according to one of Claims 1 until 3 , wherein the glass ceramic of the glass ceramic article is volume-colored with coloring metal ions, wherein in the area of the local elevation the coloring of the glass ceramic differs from a second area (16) next to the local elevation (20), so that the absorption coefficient in the area of the local elevation (20 ) is smaller than the absorption coefficient of the second region (16) and therefore the integral light transmission in the visible spectral range at the local elevation (20) is higher than the integral light transmission of the second region (16). Glass ceramic articles according to Claim 4 , characterized in that the glass ceramic contains at least 0.005, preferably at least 0.01 percent by weight of vanadium oxide. Glass ceramic article according to one of Claims 4 or 5 , characterized in that the integral light transmission of the glass ceramic in the visible spectral range of the second region (16) is at most 5%, preferably at most 2.5%. Glass ceramic article according to one Claims 4 until 6 , characterized in that the half-width of the transmission profile of the integral light transmission is greater than the half-width of the local elevation (20). Glass ceramic article according to one of Claims 1 until 7 , characterized in that the light scattering in the glass ceramic in the area of the local elevation is increased by a maximum of 20 percent absolute, preferably a maximum of 5 percent absolute, compared to the light scattering in the glass ceramic of a second area (16) next to the local elevation. Glass ceramic article according to one of Claims 1 until 8th , made of aluminosilicate glass ceramic, preferably made of lithium aluminosilicate glass ceramic, in which the glass ceramic material at the local elevation (20) has a higher content of keatite mixed crystal than a second area (16) adjacent to the local elevation. Glass ceramic article according to one of Claims 1 until 9 , characterized by a depression present in the surface, preferably an operating element designed as a depression, the at least one local elevation (20) being arranged in the depression. Glass ceramic hob (40) with a glass ceramic article according to one of Claims 1 until 10 in the form of a glass ceramic plate. Glass ceramic hob (40) according to the Claim 11 , wherein the glass ceramic plate (1) is volume-colored with coloring metal ions, wherein in the area of the local elevation the coloring of the glass ceramic differs from a second area (16) next to the local elevation (20), so that the absorption coefficient in the area of the local elevation ( 20) smaller than the absorption coefficient of the second region (16) and therefore the integral light transmission in the visible spectral range at the local elevation (20) is higher than the integral light transmission of the second region (16), and where below the first region (15) a preferably self-illuminating display device is arranged, the light of which is visible through the first area (15). Glass ceramic hob (40) according to one of the Claims 11 or 12 , characterized by a cooking zone (35) with local elevations (20), so that the contact surface of a cooking vessel (37) placed on the cooking zone is reduced by the local elevations (20) and between the bottom of the cooking vessel (37) and the surface of the glass ceramic plate (1) an air gap (38) is created.

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