Coated substrate, paste and method for producing a paste

Abstract

The invention relates to a coated substrate made of glass or glass ceramic, the coating having pigment particles embedded in a glass matrix, the average layer thickness of the coating being 2 to 5 [mu] m, the transmittance of the coating being at most 2%, the average particle size d50 of the pigment particles being less than 1.0 [mu] m, and the thickness of the coating being at least 10 [mu] m. Wherein the polydispersity index (PI) of the particle size distribution of the pigment particles is at most 2.0.

Description

Technical Field

[0001] The present invention relates to a coated substrate made of glass or glass-ceramic, a paste for producing such a coated substrate, and a corresponding method for producing the paste. Background Technology

[0002] In the prior art, coated substrates made of glass or glass-ceramic, especially transparent substrates made of glass or glass-ceramic with a decorative coating, are known in various design schemes.

[0003] For example, this coated substrate, made of glass and glass ceramics, serves as a fireplace viewing window, thereby creating a separation between the fireplace combustion chamber and the surrounding environment. In this case, the coating, in the form of an opaque (blickdichten) decorative layer, is often applied to the edge areas of the substrate and to cover the transition area between the fireplace viewing window and the fireplace door on which it is mounted.

[0004] The use of fireplace viewing windows places high demands on both the decorative elements and the substrate. When the fireplace is running, the viewing window is sometimes subjected to temperatures significantly exceeding 100°C. This heating of the substrate and decorative elements typically causes substantial thermal expansion, which, at varying degrees, can lead to the decorative elements peeling off the substrate. Glass-ceramic substrates are frequently used as fireplace viewing windows, with a thermal expansion coefficient ranging from 0 to 2 × 10⁻⁶ within a temperature range of 20–700°C. -7 K -1 Within the range.

[0005] In another application, coated glass substrates are also used in vehicle manufacturing, for example, in the form of observation windows. Here, the glass substrate is also coated only in specific areas, where the coating is typically used to cover the mounting area of ​​the window, wiring extending within the window, or electronic components located behind the window. The substrates used in this application are typically made of borosilicate glass or soda-lime glass, and have a coefficient of thermal expansion of 10... -6 K -1 Up to 10 -5 K -1 Within the range.

[0006] Coated glass substrates are also used as observation windows for oven doors, in which case substrates made of borosilicate glass or soda-lime glass are often used.

[0007] As described above, in applications where decorative coatings are used to cover specific areas, there is a fundamental requirement that the decoration laminated onto that area must be completely opaque (opak), or blickdicht (opaque). To form such an opaque layer on a transparent substrate, enamel systems with high tinting strength and a layer thickness of at least 5 μm are often used. Enamel typically consists of molten glass frit and pigments. To produce enamel, a paste containing glass frit, pigments, and binders is applied to a substrate and then fired. During firing, the glass frit melts and forms a glass matrix bonded to the substrate, with the pigments embedded within the glass matrix.

[0008] At the common process temperatures of 600-950°C used to fire this decorative layer, a glass brine that melts well within this temperature range is required. Such a glass brine typically has a coefficient of thermal expansion (CTE) of at least 4 x 10⁻⁶. -6 K -1 Or even larger. Pigments stabilized in this firing process are typically oxides, especially non-ferrous metal spinels. The CTE of such spinels is approximately 10 x 10⁻⁶. -6 K -1 The final CTE of the obtained decorative layer is approximately 6 x 10⁻⁶. -6 K -1 Furthermore, when the thickness of the aforementioned layer is greater than 4 μm, stress is generated between the substrate and the decorative layer, which can lead to a reduction in the mechanical strength of the component. Summary of the Invention

[0009] On the one hand, the present invention is based on the task of providing a coated substrate and a paste for producing such a coated substrate, which overcomes the aforementioned disadvantages of the prior art, and thereby provides a decoration that is opaque and simultaneously resistant to thermal stress.

[0010] In a first aspect, the present invention relates to a coated substrate made of glass or glass-ceramic, wherein the coating has pigment particles embedded in a glass matrix, wherein the coating has an average layer thickness of 2 to 5 μm, preferably 2 to 4 μm, more preferably 2 to 3.5 μm, and wherein the transmittance τ of the coating is... vis The median particle size d of the pigment particles is at most 2%, preferably at most 1%, particularly preferably at most 0.5%, and very particularly preferably at most 0.3%. 50The particle size distribution (mittlere Partikelgröße d50) is less than 1.0 μm, preferably less than 0.8 μm, and particularly preferably less than 0.6 μm, wherein the polydispersity index (PI) of the particle size distribution of the pigment particles is a maximum of 2.0, preferably a maximum of 1.5, and particularly preferably a maximum of 1.

[0011] Due to the particle size d of the pigment particles 50 With a thickness of less than 1.0 μm, especially less than 0.8 μm, and even more especially less than 0.6 μm, combined with a polydispersity index of up to 2, exceptionally high opacity is achieved even at relatively small layer thicknesses. The small layer thickness correspondingly offers the advantage of reducing the risk of mechanical damage to the coating due to the different coefficients of thermal expansion between the coating and the substrate. The opacity of the coating should be understood as the reciprocal of its transmittance.

[0012] Therefore, particle size d 50 A particle size of less than 1.0 μm indicates that, when considering all pigment particles in the coating, 50% of the particles have a size smaller than 1.0 μm. Particle size is typically measured by laser diffraction, where the diameter determined in this way indicates that the diameter of a spherical pigment has the same scattering characteristics as measured for the pigment. Since particles are not typically perfectly spherical, for example, for a pigment particle with a measured diameter of 1.0 μm, the size of the pigment particle can deviate from this value in different spatial directions. In this case, it is also referred to as the volume equivalent spherical diameter.

[0013] In the context of this invention, the polydispersity index PI of the particle size distribution is understood as the d of the distribution. 90 Value and d 10 The decimal logarithm of the quotient, calculated according to the following formula: PI = log (d 90 / d 10 ) .

[0014] In this context, the polydispersity index (PI) provides information about the degree to which the particle size of the pigment particles fluctuates around the median value (Mittelwert). The closer the PI value is to 0, the more uniform the particle size distribution. A uniform particle size distribution also enables a more uniform distribution of pigment particles in the coating, thereby achieving a high pigment density in the coating with less pigment and therefore a smaller layer thickness. This correspondingly results in a high opacity of the coating. When the PI value of the pigment particle size distribution is at most 2.0, preferably at most 1.5, and particularly preferably at most 1, a particularly uniform and opaque layer is achieved.

[0015] Transmittance τ visThe specified value refers to light with a wavelength of 700 nm incident on the coating and can be measured, for example, by a clamp photometer (Zangenphotometer).

[0016] First, the substrate can be any form of glass or glass-ceramic. In particular, borosilicate glass can be used herein. Such borosilicate glass can, for example, have a composition having the following components, each explicitly given in weight percent based on oxides:

[0017] In addition, other components commonly used in glass production, such as clarifiers, may be included. Glass typically contains these components at a content of no more than 2% by weight.

[0018] Due to rounding errors in the analysis, the following compositions may deviate from 100% of the total weight.

[0019] An exemplary glass composition is provided herein, which is based on the following composition range of oxides by weight percent:

[0020] Exemplary compositions of glass within this compositional range based on oxides by weight percent are given herein:

[0021] Another exemplary glass composition is given herein, which is based on the following composition range of oxides by weight percent:

[0022] Another exemplary composition of glass within this compositional range based on oxides by weight percent is given here:

[0023] Glasses within the range of compositions described above, especially those having the specific exemplary compositions described above, are advantageous because they not only have a coefficient of thermal expansion (which, depending on the specific composition, can advantageously be between 2 and 10⁻⁶), but also possess a coefficient of thermal expansion that is advantageously between 2 and 10⁻⁶. -6 / K and 6*10 -6 (between / K), also because they can exhibit sufficient mechanical stability, for example, sufficient mechanical stability against surface loads.

[0024] However, the preferred substrate is a glass-ceramic, particularly a lithium-aluminate (LAS) glass-ceramic. Such glass-ceramics are known in the prior art in various designs and are characterized by very low thermal expansion, with the corresponding coefficient of thermal expansion for such LAS glass-ceramics typically ranging from 0 to 2 x 10⁻⁶. -7 K -1Within the specified range. The substrate can, in principle, be either a transparent substrate or a colored substrate. However, a transparent substrate is particularly preferred.

[0025] For example, such a substrate can have a composition comprising the following components, each of which is explicitly given in weight percent based on oxides:

[0026] For example, As2O3 or SnO can be used. 2， Clarification of green glass (Grünglases) is used to produce glass ceramics corresponding to the compositions described above. Accordingly, the exemplary substrate may further contain 0.5-1.5 wt% As2O3 or 0.05-0.5 wt% SnO2.

[0027] The substrate is preferably plate-shaped, with a thickness of 2 mm to 10 mm, preferably 2.5 mm to 6 mm, and particularly preferably 4 mm. Within the scope of this disclosure, a plate is generally understood to be a plate-shaped shaped body. A glass plate (which may be coated or uncoated) is a plate comprising or made of glass. A shaped body is plate-shaped when its spatial dimension in one spatial direction of a Cartesian coordinate system is at least one order of magnitude smaller than its spatial dimension in the other two spatial directions of the Cartesian coordinate system, in the spatial direction perpendicular to the first spatial direction. In other words, the thickness of the shaped body is at least one order of magnitude smaller than its length and width. Within the scope of this disclosure, the two main faces or main surfaces of a plate (i.e., whose dimensions are determined by its length and width) are also simply referred to as sides. In principle, the substrate may also be a curved plate.

[0028] The term "bent plate" refers to a plate that has been bent or bent in other ways. Furthermore, such a bent plate may have a constant radius of curvature or a profile with locally variable curvature. Therefore, a plate with one or more angled bending sections should also be understood as a "bent plate" in the sense described above.

[0029] The coating can be designed, in particular, to be decorative, rather than applied to the entire surface of the substrate, but only to a portion of the substrate surface. This decorative nature can consist of one or more coated areas. According to one embodiment, the coverage of the substrate with the coating can be at least 10% and at most 80%, preferably at least 15% and at most 65%, of the entire surface area of ​​the sides of the substrate to which the coating is applied.

[0030] Specifically, the coating can be a surrounding decoration in the edge area of ​​the substrate. Furthermore, the pattern can also be applied to the entire surface of the substrate. In this case, the entire decoration on the substrate is understood as a "coating." In principle, there is no restriction on which side of the substrate the coating is applied to. In particular, it is also possible, in principle, to apply the coating to both sides of the substrate separately, wherein the coating on the upper side of the substrate does not necessarily have to be the same as the coating on the lower side.

[0031] Within the scope of this disclosure, pigments are understood to be particulate colorants. Advantageously, the pigments according to this disclosure are temperature-stable, and therefore preferably ceramic colorants. Here, within the scope of this disclosure, colorants (or pigments) are generally understood to consist of particles (also referred to as pigment particles). Therefore, if a coating is indicated to include a pigment within the scope of this disclosure, it means that the coating comprises particles of a particular pigment or colorant, i.e., particles of a composition having a pigment or colorant.

[0032] According to another embodiment, pigment particles with a sphericity ψ of at least 0.6, preferably at least 0.7, and particularly preferably at least 0.8 contribute to their uniform distribution in decoration. The sphericity ψ of the particles is a parameter indicating the degree of sphericity of the particles. Preferably, the sphericity ψ of the particles is calculated as the ratio of the surface area of ​​equal volumes of spherical surfaces to the surface area of ​​the particles: Where V P This represents the volume of the particle, while A P This indicates its surface area.

[0033] For example, the sphericity value ψ for different particle types is: Ball: 1.0; Droplets, bubbles, and round particles (rundes Korn): 0.7-1.0; Angular particles: 0.45-0.6; Needle-like particles (Nadelförmiges Partikel): 0.2-0.45; Thin flake-like particles: 0.06-0.16; Particles with uneven surfaces (Partikel mit stark zerklüfteter Oberfläche): 10 -8 -10 -4 .

[0034] A high sphericity ψ, as defined in this invention, is achieved when the ψ value is at least 0.6. The closer the pigment particles in the coating are to a spherical shape, the greater the packing density of the pigment particles in the layer. This means that fewer pigment particles are used while maintaining high opacity.

[0035] In particular, the combination of a low polydispersity index of less than 2.0, preferably about 1.0, and a high sphericity of at least 0.6, preferably at least 0.8, is particularly advantageous for the opacity of coatings with small layer thicknesses. In this case, a very regular and dense arrangement of pigment particles in the coating can be achieved by combining the spherical, preferably polyhedral shape of the pigment particles with a uniform size distribution of the pigment particles. In this way, even very thin layers can provide opacity that meets the required limit values, while the small thickness of the layer improves the heat resistance of the coating.

[0036] In addition, the small diameter D of the pigment particles 50 The combination of low polydispersity index and high sphericity ψ of pigment particles results in a very large specific surface area of ​​pigment particles in the coating (35 to 55 m²). 2 / g), which also has a beneficial effect on layer scattering properties, and therefore has a favorable effect on opacity. As mentioned above, another effect of the high sphericity and low polydispersity index of the pigment particles is that the pigment particles form a very fine porous structure in the coating. In this way, it is particularly possible to compensate for the different CTEs of the coating and the substrate, because the stress generated in the coating due to different thermal expansion can be compensated at least partially by the fine pores of the coating. Accordingly, the design of the pigment particles also directly contributes to the mechanical strength and thermal stability of the coating.

[0037] According to another embodiment, the uniformity of pigment distribution in the coating is further manifested in the absence of pigment agglomerates in the coating, wherein the diameter of the pigment agglomerates is greater than 1.0 μm, preferably greater than 0.9 μm, particularly preferably greater than 0.8 μm, and very particularly preferably greater than 0.7 μm. Agglomerates are understood as aggregates of pigments in which the pigments are in direct contact, resulting in areas between the pigments that are free of binders. Here, the maximum diameter is understood as the maximum extension of the agglomerate in any spatial direction.

[0038] The characteristics of the pigment particles in the decorative layer, as described above, particularly the uniform distribution and high sphericity of the particles, are also reflected in other properties of the decorative layer, especially its surface. Therefore, according to another embodiment, a coating waviness Wt of less than 0.3 μm is also provided. The waviness Wt corresponds to the vertical distance from the lowest point of the coating surface relative to the substrate to the highest point of the coating surface relative to the substrate. The waviness provides direct information about the variation in layer thickness, which is correspondingly related to the uniformity of pigment distribution. The waviness of the coating surface can be determined according to DIN EN ISO 4287.

[0039] Furthermore, according to DIN EN ISO 4287, the uniform distribution of pigment particles in the decorative layer is also manifested in the very low roughness Ra of the decorative layer, which, according to another embodiment, is less than 0.4 μm, preferably less than 0.35 μm, and particularly preferably less than 0.3 μm.

[0040] The advantage of low waviness is that the optical impression of the coating, especially the transmission through the coating, is uniformly distributed. Furthermore, low surface waviness also has a positive impact on the coating's abrasion resistance or general mechanical durability.

[0041] According to another embodiment, a coating is also provided containing 7.5 to 50% by volume, preferably 15 to 40% by volume, and particularly preferably 25 to 38% by volume of pigment particles. Within this range, a particularly good trade-off is achieved between the mechanical hardness of the layer and low transmittance. The proportion of pigment particles in the coating can also depend on the substrate. Thus, for glass substrates, such as borosilicate glass substrates, a particularly preferred proportion of pigment particles in the coating is 20 to 26% by volume, while for glass-ceramic substrates, a particularly preferred proportion of pigment particles in the coating is 32 to 38% by volume.

[0042] High impact resistance of the coating can be achieved, especially when using a glass-ceramic substrate. When using a glass substrate, particularly a borosilicate glass substrate, a high flexural strength of up to 60 MPa can also be achieved, representing an improvement of over 50% compared to coatings known in the prior art for borosilicate glass. Preferably, the flexural strength is determined using the double-ring method according to DIN 1288-5. Preferably, the corresponding area of ​​the coating being measured is coated across the entire surface, so that uncoated areas of the substrate have virtually no influence on the measurement results.

[0043] According to another embodiment, additional coatings different from the stated coating are also provided on the substrate. These additional coatings may, in particular, be functional layers, such as layers with high reflectivity in the infrared spectral range. First, the order and arrangement of the coatings are not limited. Thus, it is permissible to provide additional coatings arranged on the same side of the substrate as the coating described above, or alternatively, on opposite sides. Furthermore, additional coatings may also be arranged on both sides of the substrate. It is also possible for additional coatings to completely or only partially overlap the stated coating. In principle, additional layers may also be arranged above and / or below the stated coating, thereby forming an arbitrary configuration of the coating stack.

[0044] In another aspect, the present invention relates to a paste for producing the coated substrate described above, comprising a glass-based binder, pigments, and a carrier medium, wherein the pigment particles have a particle size d. 50 The thickness is less than 1.0 μm, preferably less than 0.8 μm, and particularly preferably less than 0.6 μm. Within the scope of this disclosure, paste can be understood as, in particular, so-called decorative paste or coloring paste. To produce the coated substrate according to the invention, the paste can be applied to the printing area of ​​the substrate by a suitable printing method, especially screen printing, followed by firing. If the substrate of the final product is glass-ceramic, the firing of the paste can be carried out together with the ceramization of the substrate (i.e., the conversion of green glass into glass-ceramic) (also known as the primary firing), or subsequently, i.e., after the ceramization of the substrate (also known as the secondary firing).

[0045] The glass-based binder can be, in particular, a glass frit, i.e., finely ground glass powder with a particle size of up to 5 μm, preferably between 0.5 μm and 1.5 μm, which is melted onto a substrate during the firing of the paste, thereby forming a glass matrix in which pigment particles are embedded. A layer formed in this way is also known as enamel. An exemplary glass frit may contain the following components based on oxides by weight percent:

[0046] The specific design of the glass frit, and especially its chemical composition, should be coordinated with the substrate to be printed. Special attention should be paid to keeping the difference between the CTE of the glass frit and the CTE of the substrate as low as possible.

[0047] Typically, it is also feasible to include, in addition to the glass frit, another glass-based binder, such as a sol-gel binder, which is not composed of or derived from the glass frit. In this case, the binder of the coating is formed as a mixture of different binders.

[0048] Pigment particles can be, for example, metal oxides, such as spinel, especially non-ferrous metal spinel, or hematite. For example, pigments can contain cobalt oxide (CoO), chromium oxide (Cr2O3), manganese oxide (MnO), and iron oxide (Fe2O3), wherein the preferred composition is based on the following ranges of oxides by weight percent: The following compositions can be used as, for example, as black pigments:

[0049] The carrier or dispersion medium for the screen-printable coating solution is preferably a solvent with a vapor pressure of less than 10 bar, especially less than 5 bar, and very particularly less than 1 bar. These solvents can be, for example, combinations of water, n-butanol, diethylene glycol monoethyl ether, tripropylene glycol monomethyl ether, terpineol, and butyl acetate. Suitable organic and inorganic additives are used to adjust the desired viscosity. Organic additives can be, for example, hydroxyethyl cellulose, and / or hydroxypropyl cellulose, and / or xanthan gum, and / or polyvinyl alcohol, and / or polyethylene glycol, and / or polyethylene glycol, block copolymers, and / or triblock copolymers, and / or resins, and / or polyacrylates, and / or polymethacrylates. Commercially available screen printing media, such as those based on glycols or terpineol, or other screen printing media are also generally suitable.

[0050] According to another embodiment, a paste is also provided, which contains the following components by weight percent: This composition is particularly preferred when using a pseudoplastic carrier medium with a viscosity between 2 and 3.5 Pas at 50 rpm.

[0051] Alternatively, the ointment contains the following components by weight percent: This composition is particularly preferred when using Newtonian screen printing media with a viscosity of <1 Pas at speeds between 50 / s and 300 / s.

[0052] For pastes, the purpose of selecting the solid substances and carrier medium within the aforementioned ratio range is to adjust the paste viscosity to an optimal range of 2500-4000 mPas. Since the paste viscosity also depends on the characteristics of the carrier medium used, the weight ratio of this composition is preferably adjusted according to the carrier medium used.

[0053] In both cases, the solid material consists of 30-70% by weight of binder (glass frit) and 70-30% by weight of pigment, thus determining the composition of the final layer.

[0054] Similar to the description of the coated substrate above, according to a preferred embodiment, the polydispersity index (PI) of the pigment particle size distribution is specified to be a maximum of 2.0, preferably a maximum of 1.5, and particularly preferably a maximum of 1, for the paste.

[0055] Similar to the description of the coated substrate above, according to another embodiment, the sphericity ψ of the pigment particles is provided to be at least 0.6, preferably at least 0.7, and particularly preferably at least 0.8.

[0056] According to another embodiment, the process of applying a paste to the substrate used for producing the coated substrate described above is improved by the following: at a shear rate of 200 / s, the viscosity of the paste is 2000 to 8000 mPas, preferably 2500 to 6000 mPas, and particularly preferably 3000 to 4500 mPas. The viscosity of the paste can be determined, for example, using a plate viscometer. At this viscosity value, the paste is particularly suitable for large-scale application to substrates, especially glass plates, using common coating methods. The paste can be advantageously coated onto the substrate by printing methods, such as screen printing. Other printing methods, such as screen printing, pad printing, jet printing, or inkjet printing, can also be used here.

[0057] In another aspect, the present invention relates to a method for producing the ointment described above. The method includes the following steps: An initial powder is generated from a precursor solution, wherein the particle size of the particles contained in the initial powder is at most 20 nm. The initial powder is calcined to remove any possible volatile residues and to allow for microcrystal growth. Dry the initial powder after calcination. The dried powder is mixed with a binder and a carrier medium to produce the paste.

[0058] The precursor solution is preferably a solution containing a metal nitrate, sulfate, carbonate, or chloride, and preferably contains Mn, and / or Fe, and / or Co, and / or Ni, and / or Cu, and / or Cr. Therefore, the initial medium for pigment production is a salt of the metal type required for pigment production, dissolved in water, and the optical properties of the pigment can be influenced by selecting the metal type.

[0059] However, alternatively, the precursor solution can also be a solvent-based system, such as a sol-gel based system.

[0060] Different methods can be used to produce the initial powder. For example, (co)precipitation of the precursor solution can be used for this purpose, as well as other methods such as flame hydrolysis, thermal spray drying, gas concentration, laser ablation, plasma spraying (CVS), sol-gel method, hydrothermal method, combustion method, etc. The particles produced in this way are still in the very fine nanoscale range, with a particle size of approximately 2-20 nm.

[0061] In precipitation reactions, the particle shape and fraction of the initial powder are highly dependent on the precipitation conditions. A wide variety of initial powders can be prepared by choosing the precipitation medium (carbonate precipitation, hydroxide precipitation, oxalate precipitation), such as nitrate or chloride solutions. Powders with different qualities and initial properties (e.g., special surfaces) can also be obtained by different drying methods used to produce the filter cake from the precipitation (simple air drying, freeze-drying, azeotropic distillation). In precipitation, many other parameters (pH, stirrer speed, temperature, precipitation volume, etc.) also influence the produced initial powder and its physical and chemical properties. Ideally, the initial powder particles are connected to each other only through weak bridges in the form of sintered necks.

[0062] According to a preferred embodiment, the sphericity ψ of the dried powder particles is at least 0.6.

[0063] According to a particularly preferred embodiment, the initial powder is generated by a hot gas method, particularly by a pulse reactor. Using a pulse reactor to generate the initial powder has the advantage that the characteristics of the initial powder particles can be very precisely adjusted by appropriately selecting the process parameters of the pulse reactor. Simultaneously, the second method step of calcining the initial powder can also be carried out directly using a pulse reactor.

[0064] Calcination is used to remove volatile residues (carbonates, sulfates, etc.) that remain in the initial powder particles, for example, after precipitation of the precursor solution. Simultaneously, calcination is used to completely form the crystalline phase of the particles. Calcination can be carried out in a box furnace, rotary furnace, or roller furnace at temperatures between 800°C and 1400°C, especially 900°C to 1200°C, particularly preferably 900°C to 1100°C, especially 900°C to 1000°C, or 950°C to 1100°C, for 0.5 to 12 hours, preferably 0.5 to 10 hours, especially 2 hours to 8 hours, particularly preferably 3 hours to 6 hours. Furthermore, calcination can be carried out for a time period of 0.5 to 8 hours, particularly preferably 0.5 to 5 hours.

[0065] Depending on the method used, calcination causes powder particles to agglomerate, thus necessitating a subsequent de-agglomeration step, which can be performed, particularly by grinding. Dry or wet grinding can be performed, wherein, in the case of wet grinding, alcohol, liquid hydrocarbons (such as heptane), or water-based media can be used, for example. Grinding time can be up to 24 hours, but should be selected to allow for wear of the grinding media or grinding cylinder liner, as this can lead to particle contamination, for example, by Al2O3 or ZrO2, depending on the material of the grinding media / grinding cylinder. For dry grinding, resonant mixers, sieve mills, jet mills, taumler mills, or roller mills can be used, while wet grinding can be performed using annular gap mills, plate mills, grinders, rotary drum mills, or stirred cone mills.

[0066] The mixture can be dried in air at low temperatures. For example, the milled suspension can be dried by spray drying. Spray drying preferably produces soft agglomerates, which can be well pulverized in a three-roll mill during subsequent paste production. Alternatively, drying can be carried out by drying ovens, freeze dryers, or rotary evaporators. After drying, the median particle size d of the powder particles is... 50 Preferably, it is less than 1 μm.

[0067] In order to produce a paste for use in the production of coated substrates, dried powder is mixed with the paste's binder and carrier medium.

[0068] The paste is preferably designed such that the linear coefficient of thermal expansion of the glass frit contained in the paste is between 2 and 10⁻⁶. -6 / K and at most 10*10 -6 Between / K, preferably between at least 3*10 -6 / K and at most 6*10 -6 Between / K. In this way, when using a paste, it is possible to obtain a coating that gives the glass plate sufficient strength, especially in the case of an opaque (deckenden) coating. Particularly advantageous here is a coating between at least 3*10 -6 / K and at most 6*10 -6 The coefficient of thermal expansion is in the range between / K.

[0069] Screen printing is a preferred printing method for applying paste to a substrate. Screen thicknesses of 54-64, 54-70, 68-64, 68-70, 71-55, 77-48, 77-55, 100-40, 110-34W, 110-35Y, 120-35W, 130-34Y, 140-31, 140-31W, or 165-27Y are used to obtain the layer thicknesses described above. Particularly preferred screen thicknesses are 100-40, 110-34W, or 140-31. This corresponds to a theoretical ink volume of 10 to 30 cm³ for the screen used. 3 / m 2 .

[0070] After the paste is printed onto the substrate, the resulting layer is fired to produce a coating. During this process, the carrier medium essentially evaporates, and the composition of the layer is essentially determined by the proportion of solid matter in the paste used. Using the paste composition range described above, a coating is obtained containing 30-70% by weight of binder (i.e., molten glass frit) and 70-30% by weight of pigment. This is equivalent to a ratio of 85-50% by volume of binder and 15-50% by volume of pigment in the coating. The binder content in the coating is preferably 80-60% by volume, particularly preferably 75-60% by volume, which corresponds to a preferred proportion of 20-40% by volume of pigment in the coating, particularly preferably 25-40% by volume.

[0071] In this way, coatings can be obtained, especially those with sufficient opacity (Deckkraft) (or even opaque (Blickdichte)) for currently disclosed coating thicknesses, while also having sufficient scratch resistance and adhesion strength. Attached Figure Description

[0072] Preferred embodiments of the invention will now be described in detail with reference to the accompanying drawings. These drawings show: Figure 1 An enlarged image is shown comparing exemplary pigment particles used to generate a coating with pigment particles from the prior art. Figure 2 A cross-sectional view comparing an exemplary coated substrate with a prior art coated substrate is shown. Figure 3 A flowchart illustrating an exemplary method for producing a paste is shown. Figure 4 An enlarged image of an exemplary initial powder particle is shown. Figure 5 A magnified image of the particles after calcination at 800°C for 4 hours is shown, as well as Figure 6 A magnified image of the particles after calcination at 1000°C for 4 hours is shown.

[0073] In the following text, the same or similar features are indicated by the same reference numerals. Detailed Implementation

[0074] Figure 1 An enlarged image of an exemplary pigment particle 100 used to generate a coating is shown compared to pigments in the prior art. Figure 1 a) illustrates pigment particles according to the present invention for producing an exemplary coated substrate, while Figure 1 b) illustrates pigment particles 102 as used in a similar coated substrate according to the prior art. Obtained using a scanning electron microscope. Figure 1 The images in the image are at the same scale.

[0075] By comparison Figure 1 a) and Figure 1 b) It can be clearly seen that Figure 1 a) The exemplary geometry of the pigment particles and Figure 1 The geometry of the pigment particles used so far in b) is significantly different. Although the pigment particles 102 used so far have a highly irregular shape (with sharp edges) and each particle has a very different ratio of length, width and thickness; Figure 1 The exemplary pigment particles 100 in a) are significantly more uniform in shape and generally have a polyhedral shape that is largely similar to a sphere. Accordingly, the pigment particles 100 preferably have a sphericity, i.e., a mathematically determined "sphericity ψ" of at least 0.6. A sphericity ψ of 1 describes a perfect sphere. This particle shape is particularly beneficial to the scattering cross-section of the particles in the coating, and therefore to the opacity of the coating on the substrate.

[0076] In contrast, the pigment particles 102 according to the prior art have a significantly lower sphericity, typically less than 0.5. Overall, the particles 102 are fragmented in shape.

[0077] Figure 1 pigment particles 100 and in a) Figure 1 Another significant difference between pigment particles 102 in b) lies in the size distribution of pigment particles 100 and 102. Therefore, Figure 1 a) The size distribution of the pigment particles 100 is very uniform, with very few outliers, such as relatively large particles 104. Meanwhile, in the illustrated embodiment, the median particle size d of the pigment particles 100 is... 50 Approximately 0.3 μm. In comparison, Figure 1 The median particle size d of pigment particles 102 shown in b) 50The particle size is greater than 0.6 μm, where the size fluctuation between particles is large, and the particle size is difficult to measure due to particle aggregation.

[0078] like Figure 3 a) The pigment particles 100 shown can be, for example, by referring to the following text. Figure 2 Prepared by the described method.

[0079] Figure 2 a) An exemplary substrate 106 with coating 110 is shown. Figure 2 b) is a cross-sectional view comparing a substrate 108 with a coating 112 according to the prior art. Substrates 106 and 108 are made of the same material. Figure 2 a) and Figure 2 b) also has the same proportions, thus simplifying a direct comparison of the coatings. Figure 2 The thickness d of the coating 110 on the substrate 106 shown in a) is 3.5 μm in the illustrated embodiment.

[0080] pass Figure 2 a) and Figure 2 The comparison in b) clearly shows that Figure 2 a) The pigment particles in coating 110 are 100 times more than Figure 2 In coating 112 (b), the pigment particles 102 are significantly more evenly distributed. Figure 2 Compared to coating 112 in b), Figure 2 a) The uniformity of particle size distribution in coating 110 is also significantly better. Correspondingly, compared to coating 112, Figure 3 a) Coating 110 has significantly improved opacity at the same layer thickness.

[0081] Another effect can be seen by observing the trend of the corresponding surfaces 114 or 116 of coatings 110 and 112: Figure 2 a) Coating 110 exhibits a uniform particle size distribution and a uniform distribution of pigment particles. The surface 116 of coating 112 is strongly corrugated, while the surface 114 of coating 110 is significantly smoother. Figure 4 to Figure 6 As shown in b), the reason is that local agglomerates 118 of pigment particles 102 appear in coating 112, and relatively large pigment particles 102 are present in these agglomerates. At the same time, there is a region 120 in coating 112 where the density of pigment particles 102 is significantly lower compared to the rest of the coating.

[0082] Figure 4 An example of producing ointments is shown, such as for producing... Figure 4 a) A flowchart 200 of an exemplary method for coating a paste.

[0083] In the first method step 202, a precursor solution is first produced. Preferably, a salt of the initial substance required for pigment preparation is dissolved to form a precursor solution containing a metal nitrate, sulfate, carbonate, or chloride, wherein the precursor solution preferably contains Mn and / or Fe, and / or Co, and / or Ni, and / or Cu, and / or Cr. The choice of metal primarily affects the optical properties of the pigment, and thus the optical properties of the resulting coating. However, alternatively, the precursor solution can also be a solvent-based system, such as a sol-gel based system.

[0084] In subsequent method step 204, an initial powder is generated from the precursor solution. The precursor solution may be, in particular, a water-soluble salt solution in the form of nitrates, carbonates, and / or sulfates, and / or the precursor solution may be produced based on a solvent-based system, such as a sol-gel. For example, a pulse reactor known in the art can be used to produce pigment particles. The particle size can be controlled by appropriately selecting the reaction time in the pulse reactor.

[0085] The particles contained in the initial powder, for example obtained by a reactor process, and typically initially having a small number of fine microcrystals (with sizes in the low nanometer range (approximately 2-20 nm)), are subsequently calcined in method step 206. This calcination is preferably carried out at 800 to 1400 °C, particularly preferably at 900 to 1200 °C, very particularly preferably at 900 to 1100 °C, especially at 900 to 1000 °C, or at 950 to 1100 °C for a period of 1 to 12 hours, preferably 0.5 to 10 hours, particularly preferably 2 to 8 hours, and very particularly preferably 3 to 6 hours. Calcination can also be carried out for a period of 0.5 to 8 hours, particularly preferably 0.5 to 5 hours. Calcination is used to remove volatile residues (carbonates, sulfates, etc.) from the initial powder and to completely form the crystalline phase.

[0086] Following the calcination of the pigment particles, in step 208 of the method, deagglomeration of the pigment particles is performed. Deagglomeration is often necessary because the initial powder particles may agglomerate due to calcination, and therefore the particle size often does not meet the required specifications after calcination. A grinding process, particularly dry or wet grinding, can be used for deagglomeration.

[0087] Subsequently, in method step 210, the powder that has been deagglomerated after step 208 is dried. Different drying methods can be used for this purpose, such as spray drying or freeze drying. A drying oven or rotary evaporator can also be used.

[0088] Pigments produced in this manner can contain, for example, cobalt oxide (CoO), chromium oxide (Cr2O3), manganese oxide (MnO), and iron oxide (Fe2O3), wherein the preferred amounts are based on the following ranges by weight percent of oxides: In the final method step 212, the pigment, which is in the form of a dry powder, is mixed with a glass-based binder and a carrier medium (also known as a dispersion medium) to produce a paste.

[0089] Figure 4 Enlarged images of particles at different process stages during pigment production are shown. Each figure shows two images at different magnifications, with scale bars marked at the lower right edge of each image.

[0090] Figure 5 A magnified image of exemplary initial powder particles, which can be produced, for example, from a precipitation precursor solution, is shown. The particles are CoMnFeCr spinel. As can be clearly seen in the image shown, the different particles still aggregate into large clusters and do not yet show a recognizable crystal structure. Figure 5 In b), it is particularly noticeable that some particles have detached from the aggregate in the region of the aggregate shown in the right half of the image.

[0091] exist Figure 4 Some of the aggregates shown also contain volatile residues (carbonates, sulfates, etc.) derived from the precursor solution. These residues are removed during particle calcination. Additionally, calcination stimulates the growth of the pigment particle crystalline phase. Figure 4 and 6 Magnified images of the particles after calcination are shown, each corresponding to a different parameter in the calcination process.

[0092] exist Figure 4 In the example shown, the particles were calcined at approximately 800°C for 4 hours. Figure 6 In particular, the magnified image of b) clearly shows that the surface of the aggregates is... Figure 5 The image has changed in comparison; previously it appeared relatively smooth, but now the surface appears increasingly porous. Individual particles are now clearly visible on the surface of the aggregates, while... Figure 1 This situation does not exist in the aggregates of the particles shown.

[0093] exist ​ In the illustrated embodiment, the effect of calcination is more pronounced. Calcination is carried out at 1000°C for 4 hours, which results in... ​In comparison, the crystal structure of the pigment particles aggregated in the shown agglomerates is significantly more pronounced. The agglomerates obtained in this manner are then ground, followed by drying of the pigment particles obtained in this manner, which were initially formed in… ​ The pigment shown in a).

[0094] The optical properties of different layer compositions with different pigments on different substrates are given exemplarily below.

[0095] The following pigment composition (data by weight%) is used to produce the pigment: The pigment is obtained by precipitation reaction of nitro solution followed by calcination at a temperature between 900°C and 1100°C for 3 to 5 hours and then grinding.

[0096] For a layer composition having a weight ratio of 45% by weight of binder (i.e., glass frit) and 55% by weight of pigment, with a coating thickness of 4 mm on a transparent substrate (CERAN® Cleartrans) made of glass ceramic, and the coating being fired during the substrate ceramization process (so-called initial firing) at a temperature of approximately 920°C, the following properties were determined for different pigments: Pigment 1: Pigment 2: Pigment 3: Pigment 3: Pigment 4 Value L * a * and b * This indicates the CIELab color system. This ratio reflects the proportion of solid substances (pigments and binders) to the carrier medium in the paste used to produce the coating.

[0097] When using a glass substrate made of BOROFLOAT® 33 and a coating composition containing 65% by weight of binder and 35% by weight of pigment, the following parameters of the coating were measured after firing at 680°C: Optical density is represented by the decimal logarithm of opacity.

Claims

1. A coated substrate made of glass or glass-ceramic, wherein the coating has pigment particles embedded into a glass matrix, wherein the average layer thickness of the coating is 2 to 5 pm, wherein the transmittance τ of the coating is vis at most 2%, wherein the median particle size d50 of the pigment particles is less than 1.0 pm, 50 less than 1.0 pm, wherein the pigment particles have a polydispersity index PI of the particle size distribution of at most 2.

0.

2. The coated substrate of claim 1, wherein, the sphericity y of the pigment particles is at least 0.

6.

3. The coated substrate according to claim 1 or 2, characterized in that, the waviness Wt of the coating is less than 0.3 pm.

4. The coated substrate according to any of the preceding claims, characterized in that, the coating contains 7.5 to 50 vol% of pigment particles.

5. The coated substrate according to any of the preceding claims, characterized in that, the coating has no pigment agglomerates with a maximum diameter of more than 1.0 pm.

6. The coated substrate according to any of the preceding claims, characterized in that, arranging on the substrate a further coating different from the coating.

7. A paste for producing a coated substrate according to any of the preceding claims, comprising a glass-based binder, pigments and a carrier medium, wherein the particle size d of the pigment particles is less than 1.0 pm. 50 is less than 1.0 pm.

8. The paste of claim 7, wherein The paste contains the following components in wt%:

9. The paste of claim 7, wherein The paste contains the following components in wt%:

10. Paste according to any one of claims 7 to 9, characterized in that the sphericity y of the pigment particles is at least 0.

6.

11. Paste according to any one of claims 7 to 10, characterized in that the sphericity y of the pigment particles is at least 0.

6.

12. Paste according to any one of claims 7 to 11, characterized in that, the viscosity of the paste at a shear rate of 200 / s is 2000 to 8000 mPas.

13. A method for producing a paste according to any one of claims 7 to 12, having the following steps: generating an initial powder from a precursor solution, wherein the particles contained in the initial powder have a particle size of at most 20 nm, calcining the initial powder, drying the calcined initial powder, mixing the dried powder with a binder and a carrier medium to produce the paste.

14. The method according to claim 13, wherein the precursor solution is a solution of metal-containing nitrates, sulfates, carbonates or chlorides, wherein the precursor solution preferably contains Mn and / or Fe and / or Co and / or Ni and / or Cu and / or Cr.

15. The method according to claim 13 or 14, wherein the sphericity y of the particles of the dried powder is at least 0.

6.

16. The method according to any one of claims 13 to 15, wherein the initial powder is generated by means of a hot gas method, in particular by means of a pulse reactor.

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