DE102005007933A1 - Preparation of heat conductive layer on ceramic, glass/ceramic or glass with preparation of slip from electrically conductive material and binder useful in cooking plate production involving, application of slip to selected substrate region - Google Patents

Abstract

Preparation of a heat conductive layer on a ceramic, glass/ceramic or glass by:substrate preparation, preparation of slip (sic) from electrically conductive material and binder, application of the slip to a selected substrate region, and drying and firing of the slip. An independent claim is included for a substate obtained from a slip as described above with firing preferably at 450-600[deg]C.

Description

The The invention relates to a method for producing a heat conductor layer on a substrate made of ceramic, glass ceramic or glass, as well as a cooking plate made with it.

at the development of cooktops with energy-saving direct heating are cooking systems in the foreground, where the heating element directly on the underside of the hob, where appropriate with intermediate layer an insulating layer can be applied. That way The losses avoided in conventional hobs so far connected to the heating by provided at a distance from the cooking plate radiators are where the energy transfer is done on the cooking plate essentially by radiation energy. The parboiling performance and the control behavior can thus be significantly improved.

Such directly heated hotplates and processes for their preparation are known (see. FR 2 744 116 A1 . DE 101 12 234 C1 . DE 101 12 235 C2 . DE 101 12 236 C1 . EP 0 967 838 A1 . US Pat. No. 6,762,396 B2 ).

in this connection is used as a carrier material usually a ceramic or a glass ceramic, in particular a lithium aluminosilicate glass ceramic (LAS glass-ceramic) used, the latter due to a thermal Expansion coefficients of near zero in the temperature range of interest up to about 550 ° C a high thermal shock resistance having.

On a substrate of LAS glass ceramic is according to the above mentioned documents first an electrical insulation layer, such as of alumina, Mullfit, zirconium silicate, cordierite or titanium oxide can exist.

On a heat conductor layer is applied, which according to the DE 100 59 990 A1 can be done in a common sintering step, when both the insulating layer and the Heizleiterschicht have a matched ceramic component.

Full-surface thin Heizleiterschichten are approximately from the EP 0 967 838 A1 or WO 00/18189. Conductive pastes with high metallic proportions are partially printed by screen printing (cf. EP 0 069 298 A1 ). Enamel layers, which may contain about palladium, are from the EP 0 861 014 A1 known. Layers with high silver contents are known from WO 01/02621 A1.

Heizleiterschichten produced in the sol-gel process are from US Pat. No. 6,736,997 B2 known.

From the DE 198 07 636 C1 is a method for producing a corrosion and oxidation resistant slip layer for the corrosion protection of turbine components known, which is not intended for the production of a heat conductor layer.

The in the prior art described approaches to improve the thermal stability the heating conductor on their substrates by mixing of metallic conductive Components with ceramic materials show in practical use in the direct heating of glass ceramic does not have the required long-term stability.

at a cyclic thermal cycling, as in normal Use arises, in many cases becomes steadily increasing electrical resistance observed. This is often due to one insufficient coordination of the different materials each other. So the differences in the thermal expansion coefficients, elastic moduli and the thermal conductivities usually too big. Furthermore, the oxidation resistance Of expansion-optimized layers often too low. This leads to, that the heat conductor layers gradually oxidize during operation, so that the electrical resistance increases.

The physical properties such as thermal expansion and the electric conductivity The heat conductor layers are sometimes very inhomogeneous. So can in a heating layer locally increased non-conductive components are present. This is comparable to a narrowing of the conductor cross-section and leads to overheating. A local agglomeration of electrically conductive particles with high thermal expansion leads, however for building up local mechanical stresses.

By the temperature cycles occurring in heating mode as well as by temperature inhomogeneities over the heated area the coating system will undergo varying mechanical stresses exposed. While the heating process, these are even compared to the continuous operation still significantly inflated.

This Over time, cracking can occur perpendicular to the layer plane and delamination of the heating conductor layer in the substrate or an insulation layer held on it. Furthermore, there are mussels in the area of the contact surface of the carrier material Cause for Failures. In a delamination of the layer system may be due to the different thermal expansion the materials the individual layers of the carrier system to be heated clearly lift off or flake off. When mussels burst complete Layer areas with adhesive carrier material. With progressive Cracking and thus cross-sectional constriction of the conductive layer areas of high resistance and thus high energy dissipation, what an additional local overheating can lead to the melting of the material.

One Another failure mechanism can be due to oxidation of conductive Layer components triggered become. In this case, locally non-conductive heating is produced Areas, which in turn reduces the line cross-section and overheating occurs. Since expansion coefficients are temperature-dependent, occur at a local overheating locally very high mechanical stresses, which then trigger a cracking could be. In the oxidation of particles found in the middle of the heat conductor locally a volume increase takes place, which can tear apart the heat conductor layer.

Of the Invention is therefore the object of a method for manufacturing a Heizleiterschicht on a substrate made of ceramic, glass ceramic or glass, leading to improved quality and in particular Long-term stability the produced Heizleiterschicht leads.

Further to specify a substrate with a long-term resistant Heizleiterschicht especially for a ceramic hob can be used.

• – Bereitstehen eines Substrates,
• – Herstellen eines Schlickers aus einem elektrisch leitfähigen Material und einem Bindemittel,
• – Auftragen des Schlickers auf ausgewählte Bereiche des Substrates,
• – Trocknen des Schlickers und
• – Einbrennen des Schlickers.

This object is achieved by a method for producing a heat conductor layer on a substrate made of ceramic, glass ceramic or glass with the following steps:

• - standing by a substrate,
• Preparing a slurry of an electrically conductive material and a binder,
• Applying the slip to selected areas of the substrate,
• - drying the slip and
• - Burning the slip.

The The object of the invention is further characterized by a substrate with a dissolved in a slurry produced Heizleiterschicht, the at temperatures between 350 ° C and 800 ° C, preferably between 450 and 750 ° C, more preferably between 450 ° C and 600 ° C baked is.

One leaves such substrate to use advantageous as a hotplate.

By the inventive method is a particularly gentle application of the heat conductor layer on the Substrate allows. This can be a better adaptation of the properties of the heating element be guaranteed to the underlying layer, so that thermal Tensions are reduced. At the same time the adhesion can be improved and the tendency for delaminations is reduced.

There the slip can be adjusted to withstand temperatures between 350 ° C and 800 ° C, preferably between 450 ° C and 750 ° C, more preferably between 450 ° C and 600 ° C is burned, results in a significantly reduced thermal cal Load compared to conventional Application method, such as thermal spraying.

When Substrate is preferably a lithium aluminosilicate glass-ceramic used.

On This way is a high thermal shock resistance in the interim area the operating temperature of up to 550 ° C guaranteed.

According to a further embodiment of the invention, the electrically conductive material contains a Me or a metal alloy, preferably Al, Cr, Fe, Ni, Co or MCrAlY, wherein M is selected from the group formed by Fe, Ni, Co and alloys based on Fe, Ni or Co.

On This way, good oxidation resistance can be ensured so that the heating conductor thus produced is durable.

According to one Another embodiment of the invention is the electrically conductive material added in powder form.

This is cheap for producing a suitable slip.

According to one Another embodiment of the invention is the slip at least an additive, preferably for mechanical reinforcement added.

in this connection it may be an additive in the form of powdered, fibrous or platy (flake-shaped) Particles is added.

As a material for this purpose come into consideration as additives, include glass, glass ceramic, ceramic or metal, in particular fibers or flakes from SiC, Al ₂ O _3, silicate glass, borosilicate glass, Inconel ^®, aluminum.

By such additives the mechanical resistance significantly improve the heating conductor thus produced. As far as the Additives are electrically conductive, they take a part the electric wire. In the case of non-conductors can be an adjustment of the resistance value to the target size easier reach (enlargement of Resistance).

in this connection can the added particles about a thickness or a diameter between 0.1 and 100 microns and a length between 5 microns and 5 millimeters, preferably between 0.5 and 2 microns, especially preferably about 1 micron.

By such a dimensioning leaves a very cheap structure to reach.

The Use of SiC in the form of fibers has the advantage that, then, if a crack propagates in the layer, the gap occurring through a fiber is stabilized. In this way, the mechanical Strength increased significantly. When using electrically conductive or semiconducting SiC fibers hold the pipe upright in the area of the crack through the fiber. When increasing the temperature drops electrical resistance of the semiconductive fiber. Thus wear supporting the fibers in addition, the risk of burnout of the leader in the event of occurrence to reduce cracks.

In an advantageous embodiment of the invention, the slurry for the production of the heat conductor layer as a binder CrPO ₄ , ie chromium phosphate, preferably in powder form added.

Of the Proportion of the binder in the slip is preferably from 2 to 40% by weight, particularly preferably 5 to 30 wt .-%.

On that way a cheap one structure achieve good adhesion.

Of the Order the slip on the underlying layer can through conventional Procedures, such as screen printing, spraying, dipping, brushing, doctoring or doctor blade method (Use of thin Foils which can be sintered in the wet state).

So far a screen printing application method is preferred, the slurry becomes an organic solvent added as screen printing oil.

According to a further embodiment of the invention, the heating conductor layer is made of a material containing a first component with a low resistivity (ρ about 0.015 to 1.2 Ω · mm ² / m), in particular of Al, Au, Pt, Pd, Mo, or mixtures or alloys thereof.

According to a further embodiment of the invention, the heating conductor layer is produced from a mixture which contains at least one first electrically conductive component and a second electrically insulating or semiconductive component, in particular Al ₂ O ₃ , ZrO ₂ , cordierite, mullite, SiO ₂ , glass, glass ceramic , ZrSiO ₄ , Si, SiC or TiO ₂ contains.

On that way the electrical resistance of the heat conductor layer produced on a desired Adjust the value. Furthermore the mechanical strength of the produced heat conductor is improved.

in this connection can the mixing ratio between the first and second components preferably between 100: 0 and 50:50 wt.%, Preferably between 99: 1 and 80:20 wt.% be set.

In a further preferred embodiment of the invention, the heat conductor layer is made of a material containing a component with high thermal conductivity (Λ between about 40 and 100 W / (m · K)), in particular AlN, Si ₃ N ₄ , TiB ₂ , ZrB ₂ contains.

On this way, the effects of thermal stresses are added Temperature cycling significantly reduced.

According to a further embodiment of the invention, the heating conductor layer is made of a material which contains a component with a low coefficient of thermal expansion (ie preferably ≦ 4.5 × 10 ^-6 / K and preferably ≥ 0.9 × 10 ^-6 / K), in particular SiC, B ₄ C, SiO ₂ , TiB ₂ , ZrB ₂ , WCCoCr, NiCrBSi, NiFe contains or contains a component with negative thermal expansion coefficients, in particular eucryptite contains.

Also by this measure the effects of thermal stresses are reduced, so that a better resistance the Heizleiterschicht is achieved.

Preferably will be on the substrate first produces an electrically insulating insulating layer on which the Heizleiterschicht is generated.

This Procedure is appropriate if substrate used is a lithium aluminosilicate glass ceramic, as these increased at Temperatures electrically conductive becomes.

The insulating layer may be formed of a material containing an electrically insulating ceramic, particularly containing Al ₂ O ₃ , ZrO ₂ , cordierite, mullite, TiO ₂ or the like.

Furthermore, the insulating layer may be formed of a material containing a high thermal conductivity component (Λ between about 40 and 100 W / (m · K)), particularly containing AlN, Si ₃ N ₄ or the like.

Further, the insulating layer may be formed of a material containing a component having a low coefficient of thermal expansion (ie, preferably ≦ 4.5 × 10 ^-6 / K, and preferably ≥ 0.9 × 10 ^-6 / K) or a coefficient of negative thermal expansion , in particular SiO ₂ , AlN or eucryptite.

Also through these measures the effects of thermal stresses are significantly reduced, so that improved durability is achieved.

According to one Another embodiment of the invention is the insulation layer made from a slip.

Here, for example, a SiO ₂ sol of nitric acid TEOS (tetraethyl orthosilicate) and ethanol may be added to the slurry as binder.

It It has been shown that in this way a favorable liability can be achieved can.

In alternative version According to the invention, the insulating layer can be formed by thermal spraying be applied to the substrate.

The heating conductor layer is preferably made in a meandering manner and preferably has an electrical resistivity of between 1.5 × 10 ^-8 and 1.5 × 10 ^-4 ohm · m, preferably between 3 × 10 ^-6 and 8 × 10 ^-6 Ohm · m is located.

The Width of the conductor tracks produced is preferably between 2 and 15, preferably about 10 millimeters. The thickness of the heating conductor may be between about 20 and 100 microns, preferably about 50 microns be.

For a ceramic hob more usual Size is the length of the meandering produced heating conductor approximately between 1.5 and 2.5 m, preferably about 1.8 m.

On that way Optimal adjustment of the heating power to the usual Ensure working area of a cooking plate.

It it is understood that the above and the following yet to be explained Features of the invention not only in the specified combination, but also usable in isolation or in other combinations are.

Further Features and advantages of the invention will become apparent from the following Description of preferred embodiments.

example 1

An insulating layer is applied by means of a slip method on LAS glass ceramic with the dimensions 500 × 500 × 4 mm. As components of the coating material 80 wt .-% Al ₂ O ₃ and 20 wt .-% AlN are used. The particle size distribution of the powder is 20 microns (50% percentile, d50). The binder used is a SiO ₂ sol of nitric acid, TEOS and ethanol. 250 g of powder and 80 g of binding sol are ground in a planetary ball mill for 3 hours to achieve homogenization.

Subsequently, will a coating performed by doctoring. There are four printing operations. Each printing process produces a wet film thickness of about 200 microns, after drying for 10 minutes at 150 ° C in a drying oven and 15 minutes Burn in oven at 550 ° C provides a layer thickness of 100 microns. This way will a layer thickness of about 400 microns produced.

In turn, a heat conductor layer is then applied to this insulation layer by means of a slurry process. The slurry can be applied, for example, by screen printing, rolling, spraying technology. Also, from the slurry by means of the Doctor Blade method, a film can be produced, which is rolled on. The coating material consists of aluminum powder (d50 <10 microns). The binder used is chromium phosphate powder CrPO ₄ with a mixing ratio of 85% by weight Al to 15% by weight CrPO ₄ ,

Of the Application to the insulation layer is carried out by screen printing. For this the powder mixture is first by means of an organic solvent (Screen printing oil) pasted. Subsequently the coating can be done by screen printing. As Siebtyp becomes a sieve of the type T 54N used, with two printing processes and one each intervening drying step at 150 ° C in a drying oven. The stratification takes place via a duration of 1 hour at 650 ° C.

Example 2

Under otherwise identical conditions as in Example 1, a mixture of Al and CrPO ₄ (75:25 wt .-%) of SiO ₂ fibers from Bayer ^® mixed with a share of 10 wt .-%. The fiber size is d50 = 31.3 microns in length. Otherwise, the procedure corresponds to Example 1.

Example 3

In a further modification of example 1, composite materials are admixed with the binder CrPO ₄ as the conductive component. For example, a mixture of Al and NiCrAlY with a ratio of 90:10 wt% is used.

Otherwise done the same procedure as in Example 1.

Example 4

In Modification to Examples 1 to 3, the insulating layer not by a slip process but by thermal spraying as in Example 1 applied to the substrate. The heating conductor is again applied by means of a slip method as in Example 2.

Example 5

According to one Process variant, the heat conductor layer is applied directly to the substrate applied. In this version the substrate is made of a material, preferably also at Operating temperatures is not electrically conductive.

Table 1 summarizes a series of experiments conducted to produce an insulating layer of Al ₂ O ₃ on a glass-ceramic substrate. These are each a slip application by doctoring as described in Example 1.

In Table 2 are different glasses summarized, according to the table 1 mixed in the form of powder, fibers or flakes of the insulating layer were.

The conductor tracks of the heating layer are usually designed meandering. The width of the conductor tracks is between 2 and 15, preferably about 10 mm. The thickness of the heating conductor is between 20 and 100 mm, preferably about 50 mm. The length of the Heizemeanders is dependent on the particular hob whose size and power usually between 1.5 and 2.5 m, preferably about 1.8 m. The resistivity of the printed conductors is generally between 1.5 × 10 ^-8 and 1.5 × 10 ^-4 ohm · m, preferably about 7 × 10 ^-6 ohm × m.

Tab. 1: Glass-ceramic substrate with insulating layer

Tab. 2: Composition of the glasses used

Claims (29)

Method for producing a heat conductor layer on a substrate made of ceramic, glass ceramic or glass with the following steps: - Provide a substrate, - Produce a slurry of an electrically conductive material and a binder, - Instruct of the slip on selected Areas of the substrate, - Dry of the slip and - burn in of the slip. The method of claim 1, wherein the slurry at temperatures between 350 ° C and 800 ° C, preferably between 450 ° C and 750 ° C, more preferably between 450 ° C and 600 ° C is burned. The method of claim 1 or 2, wherein as substrate a lithium aluminosilicate glass-ceramic is used. Method according to one of the preceding claims, in the electrically conductive Material contains a metal or a metal alloy, preferably Al, Cr, Fe, Ni, Co or MCrAlY, where M is selected from the group formed by Fe, Ni, Co and alloys based on Fe, Ni or Co. Method according to one of the preceding claims, in the electrically conductive Material is added in powder form. The method of claim 4 or 5, wherein the slurry at least one additive, preferably for mechanical reinforcement added becomes. The method of claim 6, wherein the additive in the form of powdered, fibrous or platelike (flake-shaped) Particles is added. The method of claim 6 or 7, wherein the additive contains glass, clad ceramic, ceramic or metal, in particular fibers or flakes of SiC, Al ₂ O ₃ , silicate glass, borosilicate glass, Inconel ^® , aluminum. The method of claim 7 or 8, wherein the added Particles have a thickness or diameter between 0.1 and 100 Micrometer and a length between 5 microns and 5 millimeters, preferably between 0.5 and 2 microns. Method according to one of the preceding claims, wherein CrPO ₄ , preferably in powder form, is added to the slurry for producing the heat conductor layer as binder. Method according to one of the preceding claims, in the proportion of the binder on the slip 2 to 40 wt .-%, preferably 5 to 30 wt .-% is. Method according to one of the preceding claims, in the silt by screen printing, spraying, dipping, brushing brushing or by a doctor blade method. Method according to one of the preceding claims, in an organic solvent is added to the slurry as screen printing oil becomes. Method according to one of the preceding claims, in the heat conductor layer is made of a material that a component with a high spec. electrical conductivity is made, in particular from Al, Au, Pt, Pd, Mo or mixtures or alloys thereof. Method according to one of the preceding claims, in which the heating conductor layer is produced from a mixture which contains at least one first electrically conductive component and a second electrically insulating or semiconducting component, in particular Al ₂ O ₃ , ZrO ₂ , cordierite, mullite, SiO ₂ , Glass, glass ceramic, ZrSiO ₄ , Si, SiC or TiO ₂ . A method according to claim 15, wherein a mixing ratio between the first and second components are used between 100: 0 and 50:50 wt .-%, preferably between 99: 1 and 80:20. Method according to one of the preceding claims, wherein the heating conductor layer is made of a material containing a component with high thermal conductivity, in particular AlN, Si ₃ N ₄ , TiB ₂ , ZrB ₂ . Method according to one of the preceding claims, wherein the Heizleiterschicht is made of a material containing a component with a low coefficient of thermal expansion, in particular SiC, B ₄ C, SiO ₂ , TiB ₂ , ZrB ₂ , WCCoCr, NiCrBSi, NiFe or with negative coefficient of thermal expansion, in particular eucryptite contains. Method according to one of the preceding claims, in on the substrate first an electrically insulating insulating layer is generated on the heat conductor layer is generated. The method of claim 19, wherein the insulating layer is formed of a material containing an electrically insulating ceramic, in particular Al ₂ O ₃ , ZrO ₂ , cordierite, mullite, TiO ₂ or the like. A method according to any one of claims 19 or 20, wherein the insulating layer is formed of a material containing a high thermal conductivity component (range specifying area), particularly AlN, Si ₃ N ₄ or the like. Method according to one of the preceding claims, wherein the insulating layer is made of a material containing a component with a low coefficient of thermal expansion or a negative coefficient of thermal expansion, in particular SiO ₂ , AlN, Eucryptite or the like. Method according to one of claims 19 to 22, wherein the insulating layer made from a slip. Process according to Claim 23, in which an SiO ₂ sol of nitric acid TEOS, and ethanol is added to the slurry as binder. A method according to claim 23 or 24, wherein the Slurry at temperatures between 350 ° C and 800 ° C, preferably between 450 ° C and 750 ° C, continue preferably between 450 ° C and 600 ° C is burned. A method according to any one of claims 19 to 22, wherein the Insulation layer is applied by thermal spraying. Method according to one of the preceding claims, in which the heating conductor layer is produced meander-shaped and has a specific electrical resistance between 1.5 × 10 ^-8 and 1.5 × 10 ^-4 ohm · m, preferably between 3 × 10 ^-6 and 8 × 10 ^-6 ohm.m. Substrate with one made from a slurry Heizleiterschicht, by burning the slurry at temperatures between 350 ° C and 800 ° C, preferably between 450 ° C and 750 ° C, more preferably between 450 ° C and 600 ° C is made. Use of the substrate according to claim 28 as a cooking plate.