Sol-gel ink and method for producing same

Abstract

A method for producing a sol-gel ink, in particular from TEOS and MTEOS, is provided. The method includes adding inorganic particles as a filler and adding a high-boiling solvent.

Claims

1. A method for producing a sol-gel ink to be processed by screen printing, the method comprising: preparing a sol-gel precursor from inorganic irregularly shaped particles as a filler, a first hydrolyzable silane R.sub.nSiX.sub.(4-n), and a further hydrolyzable silane SiX.sub.4, wherein R is an aliphatic or aromatic radical and X is a hydrolytically cleavable group; removing volatile solvents that are generated during hydrolysis and condensation of the sol-gel precursor; mixing into a dispersion a solvent having a boiling point above 120 C. and the sol-gel precursor, to form a sol, adjusting the sol to a ROR value that is a molar ratio of water to hydrolyzable groups of less than 0.45; and adding pigments, wherein the inorganic irregularly shaped particles have a fractal dimension from 2.0 to 3.0.

2. The method for producing a sol-gel ink as claimed in claim 1, wherein the inorganic irregularly shaped particles comprise secondary particles formed from aggregated primary particles.

3. The method for producing a sol-gel ink as claimed in claim 2, wherein the primary particles have a mean particle size between 10 and 80 nm.

4. The method for producing a sol-gel ink as claimed in claim 2, wherein the secondary particles have a mean particle size along a direction of greatest dimension of more than 100 nm on average.

5. The method for producing a sol-gel ink as claimed in claim 1, further comprising a molar ratio of R.sub.nSiX.sub.(4-n) to SiX.sub.4 of between 2 and 6.

6. The method for producing a sol-gel ink as claimed in claim 1, wherein the first hydrolyzable silane is a quaternary silane RSiX.sub.3.

7. The method for producing a sol-gel ink as claimed in claim 1, wherein the inorganic irregularly shaped particles comprise aluminum oxide particles.

8. The method for producing a sol-gel ink as claimed in claim 1, further comprising adding an acidic catalyst.

9. The method of claim 8, further comprising adjusting the sol-gel precursor to a pH of less than 4.

10. The method for producing a sol-gel ink as claimed in claim 1, wherein the ROR value is below 0.4.

11. A sol-gel ink, obtained by the method of claim 1.

12. The sol-gel ink as claimed in claim 11, wherein the sol-gel ink comprises at least one feature selected from the group consisting of: a total degree of condensation of sol-gel binder between 70 and 95; a ratio of tertiary to quaternary silane from 2:1 to 6:1; a methyl- or phenyl-functionalized sol-gel binder with inorganic filler particles; a solvent having a boiling point above 120 C. and an volatility of greater than 10; and inorganic platelet-shaped or non-platelet-shaped pigments and graphite.

13. The sol-gel ink as claimed in claim 11, wherein, in its dried state, the ink contains dried agglomerates of the inorganic irregularly shaped particles, which agglomerates have a fractal dimension between 1.5 and 2.0.

14. The sol-gel ink as claimed in claim 11, wherein the ink includes less than 5% of polysiloxane resin.

15. The sol-gel ink as claimed in claim 11, further comprising a crosslinked sol-gel binder that has a degree of condensation of less than 90%, a viscosity from 10 to 100 mPa.Math.s, and that includes inorganic particles.

16. The sol-gel ink as claimed in claim 15, wherein, when stored at room temperature, a viscosity from 10 to 5000 mPa.Math.s is preserved for 10 weeks.

17. The sol-gel ink as claimed in claim 11, wherein the ink has a use selected from the group consisting of: printing on an object in a screen printing process, a coating on a bottom surface of a glass ceramic plate; and a coating on a bottom surface of a glass ceramic plate of a cooktop.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The patent or application file contains at least one photograph. Copies of this patent or patent application publication with the photograph(s) will be provided by the Office upon request and payment of the necessary fee.

(2) FIG. 1 shows a flow chart of one exemplary embodiment of a method for producing a sol-gel ink according to the invention.

(3) FIG. 2 shows the viscosity of a sol-gel binder according to the invention after one week.

(4) FIG. 3 shows the nitrogen sorption isotherms of a pigmented layer after baking.

(5) FIG. 4 shows the pore volume distribution of a pigmented layer after baking.

(6) FIG. 5 illustrates Al NMR measurements of the employed pure aluminum oxide particles dried at 60 C. and of the sol-gel binder as a function of the baking temperature.

(7) FIG. 6 illustrates the gelling times of the sol-gel binder as a function of the ROR value.

(8) FIG. 7 shows the result of a dynamic light scattering measurement of a 3.310.sup.5% dispersion in water of nanoscale Al.sub.2O.sub.3 produced by flame pyrolysis.

(9) FIG. 8 shows an SEM image of a diluted dispersion that was dropped on a support and then dried.

(10) FIG. 9 shows another SEM image in which some secondary particles are outlined in black.

(11) FIG. 10 is a schematic illustration in which the primary particles are indicated.

(12) FIG. 11 illustrates the fractal dimensions of three exemplary secondary particles.

DETAILED DESCRIPTION

(13) The subject matter of the invention will now be explained in more detail by way of schematically illustrated exemplary embodiments and with reference to the drawings.

(14) FIG. 1 shows a flow chart of one exemplary embodiment of a method for producing a sol-gel ink according to the invention.

(15) First, a mixture of MTEOS and TEOS is prepared.

(16) Then, the pH of the mixture is adjusted to less than 4 using an acidic catalyst.

(17) As filler particles, an aqueous dispersion of aluminum oxide particles is added. Now, a sol-gel network is being formed by hydrolysis and condensation of MTEOS and TEOS, with a degree of crosslinking that is controlled through the ROR value and the MTEOS/TEOS ratio.

(18) Once the desired degree of condensation has been reached, a high-boiling solvent is added.

(19) Low-boiling solvent generated during the sol-gel reaction may then be removed, so that a solvent exchange occurred.

(20) Then, pigments are added to the ink.

(21) The ink may then be used to print on a glass ceramic by screen printing.

(22) The printed glass ceramic may be tempered at more than 300 C., and the temperature may be increased such that organic components of the sol-gel ink are largely removed.

(23) Finally, a silicone sealing layer may be applied.

(24) In detail, a sol-gel ink may be produced and further processed according to the following exemplary embodiments:

Example 1

(25) For the synthesis of the sol-gel precursor, MTEOS and TEOS are provided in a molar ratio of 4:1, for example, and are adjusted to a pH of about 2 by addition of an acid, in particular para-toluenesulfonic acid.

(26) Then, a 30% aqueous dispersion of Al.sub.2O.sub.3 particles (30% solids content) (diameter of about 120 nm) is added under vigorous stirring. The ROR value is 0.425.

(27) For the synthesis of the matrix, the sol-gel precursor having a condensation degree of 85% and a T.sub.3/(T.sub.2+T.sub.1+T.sub.0) ratio of about 1.8 and a (Q.sub.4+Q.sub.3)/(Q.sub.2+Q.sub.1+Q.sub.0) ratio of about 3.0 is combined with a solvent mixture of terpineol and n-butyl acetate in a ratio of 4:1, for example.

(28) Here, the solvent content is 40%, for example. By removing the ethanol, the sol-gel binder is obtained with a content of T.sub.3 groups of about 55% and a content of Q.sub.4 groups of about 10%. The degree of condensation is about 905% over a period of six months when stored at 7 C.

(29) For the synthesis of the ink, the matrix (60-65%), DEGMEE (diethylene glycol monoethyl ether) (about 9%), mica pigments (about 24%), graphite (5%), and adjuvants or pasting agents (about 2%) are stirred together.

(30) Using a 77 mesh screen, a decorative layer is applied onto the substrate by screen printing and is then tempered at 450 C.

(31) Subsequently, the coating is sealed by a methyl/phenyl silicone sealing layer that is pigmented with mica and graphite, inter alia. The coating is dried at 400 C.

Example 2

(32) For the synthesis of the trisol, MTEOS and TEOS are provided in a molar ratio of 4:1, for example, and are adjusted to a pH of about 2 by adding para-toluenesulfonic acid. Then, a 30% aqueous dispersion of Al.sub.2O.sub.3 particles is added under vigorous stirring. The ROR value is 0.375.

(33) For the synthesis of the matrix, the sol-gel precursor having a condensation degree of 76% and a T.sub.3/(T.sub.2+T.sub.1+T.sub.0) ratio of about 1.0 and a (Q.sub.4+Q.sub.3)/(Q.sub.2+Q.sub.1+Q.sub.0) ratio of about 1.5 is combined with a solvent mixture of terpineol and n-butyl acetate in a ratio of 4:1, for example.

(34) Here, the solvent content is 40%, for example. By removing the ethanol, the sol-gel binder is obtained with a content of T.sub.3 groups of about 45% and a content of Q.sub.4 groups of about 5 to 7%. The degree of condensation is about 78%.

(35) The degree of condensation is preserved below 85% for six months when stored at 7 C.

(36) For the synthesis of the ink, the matrix (60-65%), DEGMEE (about 9%), mica pigments of a size of 15 m (about 20%), synthetic graphite of a size of 5 m (9%), and adjuvants or pasting agents (about 2%) are stirred together.

(37) Using a 77 mesh screen, a decorative layer is applied onto the substrate by screen printing and is then tempered at 450 C.

(38) Subsequently, the coating is sealed by a methyl/phenyl silicone sealing layer that is pigmented with mica and graphite, inter alia. The coating is dried at 400 C.

(39) FIG. 2 shows the viscosity of a sol-gel binder according to the invention after one week. The x-axis represents the shear rate in s.sup.1, the y-axis represents the viscosity in mPa.Math.s.

(40) It can be seen that the viscosity decreases with increasing rotational speed, that means the ink is pseudoplastic and is easily applied by screen printing.

(41) Due to the incorporation of solvent molecules in the free interstices of the sol-gel network, a weak thixotropic effect occurs at low shear rates (<20 s.sup.1).

(42) FIG. 3 shows the nitrogen sorption isotherms of a pigmented layer after baking at 450 C. The x-axis represents the relative pressure in p/p.sub.0, and the y-axis represents the adsorbed volume in cm.sup.3/g. The nitrogen sorption isotherms have a type I profile as classified according to IUPAC, which is a characteristic of micropores (d<2 nm). At the same time, the nitrogen sorption isotherms reveal indications of a type IV profile which is typical for mesopores (d>2 nm). Thus, there is a bimodal pore distribution existing in the layer system.

(43) By varying the ROR value, the specific surface area of the layers may be adjusted selectively.

(44) FIG. 4 shows the pore volume distribution of a pigmented layer after baking at 450 C., which depends on the ROR value of the sol-gel binder used for producing the ink.

(45) The x-axis represents the pore diameter in nanometers, and the y-axis represents the pore volume in cm.sup.3/g. The profile confirms a bimodal pore distribution. Approximately of the pore volume is attributable to micropores, about to mesopores.

(46) FIG. 5 illustrates Al NMR measurements of the employed pure aluminum oxide particles dried at 60 C. and of the sol-gel binder as a function of the baking temperature.

(47) It can be seen that the pure aluminum oxide particles substantially comprise tetragonally and predominantly hexagonally coordinated aluminum.

(48) At a baking temperature above 200 C., the sol-gel binder predominantly comprises hexagonally coordinated aluminum and a low fraction of tetragonally coordinated aluminum.

(49) FIG. 6 illustrates the gelling times of the sol-gel binder as a function of the ROR value. The x-axis represents the ROR value of the sol-gel binder, and the y-axis represents the corresponding gelling time in months. With the ROR value decreasing, the gelling time or pot life of the binder increases significantly.

(50) FIG. 7 shows the result of a dynamic light scattering measurement of a 3.310.sup.5% dispersion in water of nanoscale Al.sub.2O.sub.3 produced by flame pyrolysis.

(51) These particles may be added during the preparation of the sol-gel ink, for example.

(52) The measurement by dynamic light scattering reflects the diameter of the secondary particles.

(53) The x-axis represents the diameter in nanometers, and the y-axis represents the differential volume. It can be seen that the diameter is substantially distributed from about 50 nanometers to about 300 nanometers. D.sub.50 is 115 nanometers.

(54) FIG. 8 shows an SEM image of a diluted dispersion that was dropped on a support and then dried.

(55) The SEM image shows dried agglomerates in which the secondary particles are agglomerated.

(56) Such dried agglomerates may be redispersed, whereas the secondary particles are stable.

(57) FIG. 9 shows another SEM image in which some secondary particles are outlined in black.

(58) The diameter of the primary particles is about 10 to 80 nanometers. These primary particles are agglomerated into secondary particles with d.sub.50=150 nm. The dried agglomerates have a size of more than 200 nanometers.

(59) FIG. 10 is a schematic illustration in which the primary particles are indicated, which in this case have a diameter between 30 and 60 nanometers. Furthermore, secondary particles are measured along the direction of their largest dimension which is about 115 nanometers. The dried agglomerates are considerably larger, i.e. up to 600 nanometers.

(60) Referring to FIG. 11, the calculation of the fractal dimension according to Mandelbrot will be described in more detail. The fractal dimension is determined from SEM studies. Here, the secondary particles are considered in three dimensions. At least 10 randomly selected secondary particles are taken, and their fractal dimension is determined. From these measurements the average is calculated.

(61) The fractal dimension is calculated using the following formula:

(62) Fractal dimension D=ln N/ln(R/r), where N is the number of primary particles, r is the radius of the primary particles, and R is the radius of the secondary particle.

(63) FIG. 11 illustrates three exemplary secondary particles for which the fractal dimension has values of 1.78, 1.9, and 2.21, respectively.

(64) The invention relates to a sol-gel ink in which preferably one half of the secondary particles have a fractal dimension from 2.0 to 2.5.

(65) In the dried ink, dried agglomerates of a lower fractal dimension will form, in particular in a range from 1.7 to 2.0.